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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 141–146 141 Synthesis and structural characterization of indium compounds with bidentate amide ligands Jungsook Kim, Simon G. Bott and David M. HoVman* Department of Chemistry, University of Houston, Houston, Texas 77204, USA Received 11 September 1998, Accepted 11th November 1998 Indium trichloride reacts with 1 equivalent of MeN(SiMe2NMeLi)2 to give the dimer [ClIn(NMeSiMe2)2NMe]2 and with 4 equivalents of HNMeSiMe2NMeLi to give [Li{In(HNMeSiMe2NMe)2(MeNSiMe2NMe)}]2.In the structure of [ClIn(NMeSiMe2)2NMe]2 a chloride and one amide group of a [MeN(SiMe2NMe)2]22 ligand are bonded to each In atom in terminal positions and the other amide group of the chelating ligand is shared between two In atoms. The terminal chlorides have an anti-ClIn ? ? ? InCl arrangement. The amine group of the [MeN(SiMe2NMe)2]22 ligand does not interact with In. Variable temperature NMR spectra show [ClNn(NMeSiMe2)2NMe]2 undergoes a fluxional process, and a mechanism involving bridge–terminal amide exchange is proposed to account for the data.The molecule [Li{In(HNMeSiMe2NMe)2(MeNSiMe2NMe)}]2 has a Li2In2Si2N4 adamantane-like core and overall virtual D2 symmetry. We recently reported the synthesis of new indium amide complexes including the neutral triamide compounds [In{N(Si- HMe2)(t-Bu)}3] and [In{NR(SiMe3)}3] where R = Ph or But.1 The compounds were prepared for possible use in combination with ammonia as chemical vapor deposition (CVD) precursors to indium nitride films,2 a process that would be analogous to one used to prepare GaN films at low temperature.3,4 Because we were interested in using the compounds for CVD studies, we restricted our synthetic work to simple amide ligands in the expectation that their complexes would have the necessary volatility to be good precursor candidates.The diYculties and successes we had while carrying out the syntheses, as well as the realization that there are only a few reported well-characterized indium complexes with multiple amide ligands,5–8 prompted us to take a more general approach and examine the synthesis of other types of indium amide compounds.Herein we report the syntheses and structures of two new indium complexes that contain the chelating amide ligands [MeN(SiMe2NMe)2]22 and [Me2Si(NMe)2]22. Results and discussion Syntheses A summary of our synthetic results is presented in Scheme 1.Indium trichloride reacts with 1 equivalent of the potentially tridentate ligand MeN(SiMe2NMeLi)2 to give the dimer [ClIn- (NMeSiMe2)2NMe]2 1. The reaction between InCl3 and 4 equivalents of HNMeSiMe2NMeLi gives [Li{In(HNMeSi- Scheme 1 (i) 2MeN(SiMe2NMeLi)2, diethyl ether, 24LiCl; (ii) 8HNMeSiMe2NMeLi, diethyl ether, 26LiCl, 22Me2Si(NMeH)2. In N In N Cl MeN Me2Si N Me SiMe2 NMe SiMe2 Me N Me2Si Cl Me Me In MeN In MeN MeN NMe SiMe2 N NMe SiMe2 N Me2Si N Me2Si N MeN Si N Li Li Me H H Me H Me H Me N Si Me2 Me2 2InCl3 Me Me 1 2 (i) (ii) Me2NMe)2(MeNSiMe2NMe)}]2 2 in 96% yield.In the latter case, if a stoichiometry consisting of an approximately 2: 1 mixture of HNMeSiMe2NMeLi and Me2Si(NMeLi)2 or only 3 equivalents of HNMeSiMe2NMeLi are used the product yield is ª70%. Interestingly, the related reaction of 2 equivalents of Me2Si[N(SiMe3)Li]2 with InCl3 has been reported to give a monomeric species, [Li{In{[N(SiMe3)]2SiMe2}2}].9 Compound 2 is partially soluble in hexane, benzene, toluene, diethyl ether, THF and CH2Cl2 while 1 is very soluble in the same solvents except for hexane, in which it is only partially soluble.X-ray crystallographic studies X-Ray crystal structure determinations of 1 (Fig. 1) and 2 (Fig. 2) were carried out. Selected bond distances and angles are presented in Tables 1 and 2. Compound 1 is situated about an inversion center and 2 lies on a two-fold axis. The amine hydrogens in 2 were located in a diVerence map and subsequently refined with distance constraints.Compound 1 is isomorphous with [ClAl(NMeSiMe2)2NMe]2.10 Three other closely related Fig. 1 View of [ClIn(NMeSiMe2)2NMe]2 1 showing the atomnumbering scheme (50% probability ellipsoids).142 J. Chem. Soc., Dalton Trans., 1999, 141–146 structures are [(py)Zn(NEtSiMe2)2NMe]2, [Be(NMeSiMe2)2- CH2]2 (see I), and [MeIn(NBut)2SiMe2]2.11–13 The In atom in 1 has a distorted tetrahedral geometry with the four coordination sites occupied by a Cl and three amide nitrogen atoms, one of which is terminal (N2 in Fig. 1) and the other two bridging (N1 and N19). The amine group of the [MeN(Me2SiNMe)2]22 ligand is not bonded to In. In the structure the indium atom is a member both of a four-membered In2N2 ring and a six-membered InN3Si2 ring. The molecule 2 has a Li2In2Si2N4 core with an adamantane structure II that incorporates the bridging [MeNSiMe2NMe]22 ligands. Exocyclic to the core are four six-membered rings that include the [HNMeSiMe2NMe]2 ligands.Overall, the molecule has virtual D2 symmetry, where, in addition to the crystallographic two-fold axis passing through Li1 and Li2, there are two virtual two-fold axes, one passing through the In atoms and the other through Si1 and Si19. Each indium atom is coordin- Fig. 2 View of [Li{In(HNMeSiMe2NMe)2(MeNSiMe2NMe)}]2 2 showing the atom-numbering scheme (40% probability ellipsoids). Zn N Zn N py EtN Me2Si N Me SiMe2 NEt SiMe2 Me N Me2Si py Et Et Be N Be N NMe SiMe2 CH2 Me2 Si MeN Me2Si H2C Si Me2 Me Me I Table 1 Selected bond distances (Å) and angles (8) for [ClIn- (NMeSiMe2)2NMe]2 1 In–Cl In–N1 In–N2 In–N19 Cl–In–N1 Cl–In–N2 Cl–In–N19 N1–In–N2 N1–In–N19 N2–In–N19 N1–Si1–N3 N2–Si2–N3 In–N1–Si1 In–N1–C1 2.350(3) 2.204(8) 2.036(7) 2.199(7) 110.1(2) 111.8(2) 116.3(2) 110.4(3) 89.5(3) 116.4(3) 107.5(4) 106.9(4) 107.7(3) 113.6(7) Si1–N1 Si1–N3 Si2–N2 Si2–N3 In–N1–In9 Si1–N1–C1 Si1–N1–In9 C1–N1–In9 In–N2–Si2 In–N2–C2 Si2–N2–C2 Si1–N3–Si2 Si1–N3–C3 Si2–N3–C3 1.768(6) 1.716(9) 1.708(8) 1.756(9) 90.5(1) 114.5(6) 120.1(3) 108.2(7) 121.9(4) 119.8(6) 118.3(6) 125.1(5) 118.4(8) 113.9(7) ated to the amide end of two [HNMeSiMe2NMe]2 ligands and also shares two bridging [MeNSiMe2NMe]22 ligands, resulting in an In atom surrounded by four amide groups (N1, N29, N3 and N5 in Fig. 2) in a tetrahedral arrangement.The amine ends of the [HNMeSiMe2NMe]2 ligands (N4 and N6) are coordinated to lithium, which also interacts with the bridging [MeNSi- Me2NMe]22 ligands.The cation has a distorted tetrahedral geometry with widely varying angles (101–1198). Charge separation in the complex can be described as [In(NRR9)4]2 and Li1. In 1 the angles around indium vary from 908 to 1168 with the smallest angle associated with the bridging amide groups, N1–- In–N19, but in 2 the N–In–N angles are in the narrow range 104–1128. The terminal amide nitrogens in both structures have essentially planar geometries. The angles about these nitrogens span a narrow range (118–1228) in 1 but vary more widely (112–- 1308) in 2 with the larger angles (129 and 1308) being associated with In–N–Si and the smaller with In–N–C (112 and 1138).In 2 the amine nitrogens, N4 and N6, and the amide nitrogens that interact with the Li1, N1 and N2, have distorted tetrahedral geometries. The terminal In–N amide distances, In–N3 [2.107(5) Å] and In–N5 [2.109(5) Å] in 2 and In–N2 [2.036(7) Å] in 1, are similar to those found in [In{Nt-Bu(SiHMe2)}3(p-Me2NC5H4N)] [average 2.125(3) Å], [In{NPh(SiMe3)}3(OEt2)] [average 2.095(2) Table 2 Selected bond distances (Å) and angles (8) for [Li{In(HNMeSiMe2NMe) 2(MeNSiMe2NMe)}]2 2 In–N(1) In–N(3) In–N(5) In–N(29) Si(1)–N(1) Si(1)–N(2) Si(2)–N(3) N(1)–In–N(3) N(1)–In–N(5) N(3)–In–N(5) N(1)–In–N(29) N(3)–In–N(29) N(5)–In–N(29) N(1)–Si(1)–N(2) N(3)–Si(2)–N(4) N(5)–Si(3)–N(6) In–N(1)–Si(1) In–N(1)–C(1) Si(1)–N(1)–C(1) In–N(1)–Li(1) Si(1)–N(1)–Li(1) C(1)–N(1)–Li(1) Si(1)–N(2)–C(4) Si(1)–N(2)–Li(2) C(4)–N(2)–Li(2) Si(1)–N(2)–In9 C(4)–N(2)–In9 Li(2)–N(2)–In9 In–N(3)–Si(2) In–N(3)–C(5) 2.165(5) 2.107(5) 2.109(5) 2.161(5) 1.719(5) 1.730(5) 1.697(6) 110.5(2) 111.9(2) 103.9(2) 111.7(2) 110.2(2) 108.4(2) 104.9(3) 106.9(3) 106.9(3) 112.5(2) 111.4(3) 112.9(4) 93.1(3) 124.5(3) 100.6(4) 113.3(4) 125.3(3) 100.0(4) 112.8(2) 110.4(4) 92.7(3) 128.8(3) 112.8(4) Si(2)–N(4) Si(3)–N(5) Si(3)–N(6) N(1)–Li(1) N(2)–Li(2) N(4)–Li(1) N(6)–Li(2) Si(2)–N(3)–C(5) Si(2)–N(4)–C(8) Si(2)–N(4)–Li(1) C(8)–N(4)–Li(1) In–N(5)–Si(3) In–N(5)–C(9) Si(3)–N(5)–C(9) Si(3)–N(6)–C(12) Si(3)–N(6)–Li(2) C(12)–N(6)–Li(2) N(1)–Li(1)–N(4) N(1)–Li(1)–N(19) N(4)–Li(1)–N(19) N(1)–Li(1)–N(49) N(4)–Li(1)–N(49) N(19)–Li(1)–N(49) N(2)–Li(2)–N(6) N(2)–Li(2)–N(29) N(6)–Li(2)–N(29) N(2)–Li(2)–N(69) N(6)–Li(2)–N(69) N(29)–Li(2)–N(69) 1.752(5) 1.696(6) 1.757(6) 2.073(8) 2.036(8) 2.232(8) 2.210(9) 118.3(5) 114.8(4) 125.4(4) 112.5(5) 130.3(3) 112.1(4) 117.4(5) 116.6(5) 122.7(3) 113.9(5) 110.4(2) 109.3(6) 103.8(2) 103.8(2) 119.0(6) 110.4(2) 100.7(2) 110.1(6) 114.5(2) 114.5(2) 116.9(6) 100.7(2)J.Chem. Soc., Dalton Trans., 1999, 141–146 143 Å], [In(NPh2)3(py)] [average 2.083(3) Å],1 [In{N(SiMe3)2}3] [2.049(1) Å], [(Me3C)2In{NSiPh3(2,6-i-Pr2Ph)}] [2.104(3) Å],6 [InL3] (HL = 2,2,6,6-tetramethylpiperidine)] [average 2.078(5) Å],8 [MeIn(Nt-Bu)2SiMe2]2 [2.107(3) Å] 13 and [Et2In(NC5H4)] [2.166(4) Å].14 The In–N1 and N19 distances in 1 [average 2.202(8) Å] are slightly shorter than the In–Nbridge distances in [MeIn(NBut)2SiMe2]2 [average 2.267(4)].13 In 2 the interaction of the amide nitrogens N1 and N29 with the lithium cations lengthens their In–N distances about 0.05 Å compared to In–- N3 and In–N5, and causes them to be almost as long as the In–- N1 [2.204(8) Å] and In–N19 [2.199(7) Å] bridging amide distances in 1. The Li–N1 and –N2 distances in 2, which involve the nitrogens associated with the long In–N distances, are significantly shorter than the Li–N distances involving the amine N4 and N6 atoms.Spectroscopic characterization In the 1H NMR spectrum of 2 there are five sharp singlets and a doublet, all with equal intensity, and a quartet with one-third relative intensity. The five singlets arise from three sets of four methyl groups attached to Si and two sets of four methyl groups attached to nitrogen, and the quartet (NH) and doublet (NMe) arise from the amine groups of the [HNMeSiMe2NMe]2 ligands.In the 13C-{1H} NMR spectrum there are six singlets. These data are consistent with the solid state structure (i.e., with the molecule having virtual D2 symmetry). A medium intensity band at 3310 cm21 is observed in the IR spectrum that can be assigned to the N–H stretch. At room temperature the 1H spectrum of 1 consists of three closely spaced singlets in the SiMe2 region in a 1:1:2 ratio and one sharp singlet and two slightly broad singlets in a 1:1:1 ratio in the NMe region (Fig. 3). The SiMe2 singlet of relative Fig. 3 The NMe (left) and SiMe (right) regions of the 1H NMR spectra for [ClIn(NMeSiMe2)2NMe]2 (toluene-d8) recorded at various temperatures. intensity 2 is composed of two accidently degenerate singlets of equal intensity. The 13C-{1H} spectrum has seven singlets, four in the SiMe2 region and three in the NMe region. These data are consistent with the solid state structure.Variable temperature NMR (Fig. 3) was used to determine why two of the NMe resonances in the room temperature spectrum of 1 are broad. As the temperature of the NMR sample is raised, the two broad NMe resonances broaden further, collapse into the baseline at ª60 8C (DG‡ = 16 kcal mol21 at 60 8C),15 and re-emerge at 70–80 8C as a broad hump. At 90 8C, the highest temperature examined, the coalesced resonances are beginning to sharpen back into a singlet. The sharp NMe resonance observed in the room temperature spectrum remains sharp in the entire temperature range examined.In the SiMe2 region, the two separated singlets merge into one peak as the temperature is raised while the accidentally degenerate peaks never separate and presumably merge, thereby resulting in two singlets being observed in the region at high temperatures. Conversely, as the NMR sample is cooled to below room temperature, the two broad NMe resonances sharpen and the resonances in the SiMe2 region sharpen and shift slightly; thus, at 210 8C there are three sharp singlets in the NMe region and four sharp equal intensity singlets in the SiMe2 region, as is consistent with the solid state structure.The variable temperature data indicate that the two amide methyl groups and, separately, two sets of two methyl groups attached to Si of the [MeN(SiMe2NMe)2]22 ligands are made equivalent by a dynamic process. Possible mechanisms to account for the NMR data include a concerted bridge–terminal amide exchange mechanism (Scheme 2, reading bottom to top) or, more likely, a mechanism involving In–N bond opening and rotation that passes through an intermediate with C2 symmetry (Scheme 2, reading top to bottom). A dimer–monomer equilibrium does not account for the data if the reasonable assumptions are made that the monomer would have a C2v trigonal planar ClInN2 core and the amine nitrogen undergoes rapid inversion in the temperature range examined.In contrast to the solution dynamic behavior of 1 the aluminium analog [ClAl(NMeSiMe2)2NMe]2 is reported to be Scheme 2 b a In N In N Cl N Si N Si N Si N Si Cl g' g a 'b b 'a d c' d' c e f e' 'f In N In N Cl N Si N Si N Si N Si Cl e' e c c' d d' b b' a' a g f g' f' In N In N Cl N Si N Si N Si N Si Cl e' e c d' d c' a' b' g f g' 'f In N In N Cl N Si N Si N Si N Si Cl g' e c b' d a' b c' d' a g f e' f' In N In N Cl N Si N Si N Si N Si Cl g' g a b' b a' d c' d' c e f e' f' B A a,a' b,b' e,e' f,f' A A B c',c d',d g',g f',f144 J. Chem.Soc., Dalton Trans., 1999, 141–146 stereochemically rigid on the NMR time scale near room temperature. 10 The related compounds [(py)Zn(NEtSiMe2)2NMe]2, [Be(NMeSiMe2)2CH2]2 (see I) and [MeIn(NBut)2SiMe2]2, however, all exhibit fluxional NMR behavior,11–13 which was attributed, respectively, to a monomer–dimer interconversion, an interconversion among oligomers, and an intramolecular dynamic process.In the room temperature 1H NMR spectrum of a CD2Cl2 solution of 1 there are in addition to the primary resonances discussed above four equal intensity sharp singlets in the SiMe2 region and three equal intensity sharp singlets in the NMe region. The relative intensities of these resonances are approximately 10% of the primary resonances. The resonances are present with about the same intensities in samples prepared from diVerent batches of crystals and from crystals grown from disparate solvent systems as well as when toluene-d8 or benzene-d6 is used as the NMR solvent instead of CD2Cl2, although there is more overlap of the resonances with the primary resonances in the hydrocarbon solvents, e.g., see Fig. 3. The intensities of the resonances do not change nor do the resonances change shape as a function of temperature (e.g., they do not broaden at high temperatures). From the observations it can not be determined whether the resonances are due to an isomer of 1 or a persistent impurity, but an isomer that would plausibly account for the data is III.A referee suggested that one might expect III to be fluxional, which is not observed. Conclusion Indium trichloride reacts with 1 equivalent of MeN(SiMe2NMeLi) 2 to give the dimer 1 and with 4 equivalents of HNMeSiMe2NMeLi to give 2. In the structure of 1, which is isomorphous with the known Al derivative, a chloride and one amide group of a [MeN(SiMe2NMe)2]22 ligand are bonded to each In atom in terminal positions and the other amide group of the chelating ligand is shared between two In atoms.The terminal chlorides have an anti-ClIn ? ? ? InCl arrangement. The amine group of the [MeN(SiMe2NMe)2]22 ligand does not interact with In. Variable temperature NMR spectra show 1 undergoes a fluxional process that makes the bridging and terminal amide groups and, separately, two sets of two methyl resonances of the [MeN(SiMe2NMe)2]22 ligand equivalent at high temperatures.A mechanism involving bridge–terminal amide exchange is proposed to account for the data. The molecule 2 has an adamantane-like Li2In2Si2N4 core with four InNSiNLiN rings fused to the core in such a way as to give the molecule virtual D2 symmetry. Experimental General techniques and reagents All manipulations were carried out in a glove box or by using Schlenk techniques. Solvents were purified by using standard techniques after which they were stored in the glove box over 4-Å molecular sieves until needed.H2NMe was purchased from Matheson and Me2SiCl2 from Aldrich. The former was used as received and the latter was degassed with an argon stream before it was used. The lithium salts of the amines were prepared by reacting the amines in hexanes with the appropriate amount of n-BuLi, washing the resulting solid with hexanes, and then In N In N MeN Me2Si N Me Si Me N Me2Si Cl Me MeN Si Cl Me Me2 Me2 III drying in vacuo.NMR spectra were collected on a 300 MHz instrument. Syntheses The amines MeN(SiMe2NHMe)2 and Me2Si(NHMe)2. These compounds were prepared by using a slight modification of the literature procedure.16 Methylamine was added via a syringe needle over the surface of a stirred solution of Me2SiCl2 (30 cm3, 0.25 mol) in cold (5–10 8C) diethyl ether (300 cm3). The amine addition continued for 4 h during which time a white solid formed. After the amine addition was stopped, the reaction mixture was refluxed for 1 h.The mixture was then cold-filtered (0 8C). The solvent was removed in vacuo from the filtrate, and the residue was fractionally distilled at atmospheric pressure, giving Me2Si(NHMe)2 as a colorless liquid (bp 107 8C at 760 mmHg). Yield, 12 g (40%). Low pressure distillation of the residue gave MeN(SiMe2NHMe)2 as a colorless liquid (bp 70 8C at 0.01 mmHg). Yield, 3.8 g (7.4%). 1H NMR (C6D6) for MeN(SiMe2NHMe)2: d 0.085 (s, 12, SiMe2), 0.28 (broad, 2, NH), 2.37 (slightly br s, 6, NMe), 2.43 (s, 3, NMe). 1H NMR (C6D6) for Me2Si(NHMe)2: d 20.056 (s, 6, SiMe2), 0.21 (broad, 2, NH), 2.39 (d, JHH = 6.6 Hz, 6, NMe). The dimer [ClIn(NMeSiMe2)2NMe]2. A diethyl ether solution (5 cm3) of MeN(SiMe2NMeLi)2 (0.22 g, 1.0 mmol) was added dropwise to a slurry of InCl3 (0.22 g, 1.0 mmol) in cold (278 8C) ether (25 cm3). The mixture was stirred for 24 h while the temperature was allowed slowly to warm to room temperature. A white precipitate formed.The ether was removed by vacuum distillation and the residue was extracted with hexane (3 × 10 cm3). The extracts were combined and filtered through Celite. The hexane was removed in vacuo and the residue, a white solid, was held in vacuo for 24 h. This material is pure product by 1H NMR. Yield, 0.20 g (57%). Colorless cubic crystals can be grown from ether at low temperature (235 8C). A satisfactory nitrogen analysis was not obtained (Found: C, 23.76; H, 6.13; N, 10.83.C14H42N6Cl2In2Si4 requires C, 23.76; H, 6.00; N, 11.88). See the text for complete details regarding the 1H NMR spectra of this compound. 1H NMR (C6D6): d 0.16 (s, 12, SiMe2), 0.20 (s, 6, SiMe2), 0.22 (s, 6, SiMe2), 2.60 (s, 6, NMe), 2.66 (s, 6, NMe), 2.91 (s, 6, NMe). 13C-{1H} NMR (C6D6): d 22.19 (SiMe2), 20.74 (SiMe2), 0.04 (SiMe2), 1.36 (SiMe2), 32.5 (NMe), 33.1 (NMe), 34.3 (NMe). IR (Nujol, CsI, cm21): 1307w, 1257s, 1219w, 1170m, 1151w, 1130w, 1076m, 1045m, 997w, 893m, 856m, 819w, 792m, 760w, 680w, 669w, 642w, 542w, 488w, 453w and 407w.The dimer [Li{In(HNMeSiMe2NMe)2(MeNSiMe2NMe)}]2. A diethyl ether solution (5 cm3) of HNMeSi(Me2)NMeLi (0.50 g, 4.0 mmol) was added dropwise to a slurry of InCl3 (0.22 g, 1.0 mmol) in ether (25 cm3) at room temperature. The mixture was stirred for 24 h and then the ether was removed by vacuum distillation. The residue was dried for 24 h after which it was extracted with hexane (10 × 10 cm3). The extracts were combined and filtered through Celite, and the hexane was removed in vacuo from the filtrate.The residue, a white solid, is pure product by 1H NMR. Yield, 0.45 g (96%). If the reaction is carried out by using a 2 : 1 mixture of HNMeSiMe2NMeLi and Me2Si(NMeLi)2 or only 3 equivalents of HNMeSiMe2NMeLi the yield is about 70%. Colorless crystals of the product can be formed by dissolving the solid in a hexane–ether mixture (1 : 9) and cooling (235 8C for 24 h) (Found: C, 30.03; H, 8.15; N, 17.52.C24H76N12In2Li2Si6 requires C, 30.50; H, 8.12; N, 17.79). 1H NMR (C6D6): d 0.22 (s, 12, SiMe2), 0.36 (s, 12, SiMe2), 0.46 (s, 12, SiMe2), 0.51 (q, J HH = 6.6, 4, NH), 2.21 (d, J HH = 6.6 Hz, 12, NMe), 2.79 (s, 12, NMe), 3.06 (s, 12, NMe). 13C-{1H} NMR (C6D6): d 21.91 (SiMe2), 21.07 (SiMe2), 0.48 (SiMe2), 30.1 (NMe), 34.0 (NMe), 34.6 (NMe). IR (Nujol, CsI, cm21): 3310m, 1246m, 1168m, 1062m, 1026m, 1003m, 854m, 823m, 763m, 690m, 671m, 511w, 474w and 443w.J.Chem. Soc., Dalton Trans., 1999, 141–146 145 Crystal structure determination of [ClIn(NMeSiMe2)2NMe]2 Crystal data. C14H42Cl2In2N6Si4, M = 707.42, triclinic, a = 8.313(2), b = 9.550(2), c = 10.244(2) Å, a = 102.06(2), b = 97.98(2), g = 110.03(2)8, U = 727.4 Å3, T = 23 8C, space group P1� , Mo-Ka (l = 0.71073 Å), Z = 1, Dc = 1.62 g cm23, F(000) = 356. Colorless rods. Crystal dimensions: 0.08 × 0.11 × 0.41 mm, m = 19.2 cm21. Data collection. The crystal was mounted in a capillary under an argon atmosphere. Enraf-Nonius CAD-4F (k geometry) diVractometer.q–2q scan mode with scan width Dq = 0.8 1 0.35tanq, scan speed range 0.67–88 min21, graphite-monochromated Mo-Ka radiation; 1766 reflections measured (38 £ 2q £ 448, h, ±k, ±l), 1766 unique, 1437 observed with F > 6s(F). Lorentz and polarization corrections were applied. A semi-empirical absorption correction was applied based on y scans of 5 reflections having c angles between 70 and 908.Three standard reflections were measured every 3600, and these showed no significant variation. Structure solution and refinement. The Laue symmetry was determined to be 1� , and the space group was shown to be P1 or P1� . P1� was assumed to be the correct setting, which was con- firmed subsequently by successful refinement. The structure was solved by using the MolEN Patterson interpretation program, which revealed the position of the In atom. The remaining non-hydrogen atoms were located in subsequent diVerence Fourier syntheses.The usual sequence of isotropic and anisotropic refinement was followed. Hydrogen atoms attached to carbon were then entered in ideal calculated positions and constrained to a riding motion such that U(H) = 1.3U(attached C). After all shift/esd ratios were less than 0.01, convergence was reached with R, R9 = 0.040, 0.048 (goodness-of-fit = 1.27). The weighting scheme was w = [0.04F2 1 (s(F))2]21. No unusually high correlations were noted between any of the variables in the last cycle of full-matrix least squares refinement, and the final diVerence map showed a maximum peak of about 0.62 e Å23 located near In.All calculations were made using the MolEN package of programs.17 Crystal structure determination of [Li{In(HNMeSiMe2NMe)2- (MeNSiMe2NMe)}]2 Crystal data. 2Li1?C24H76N12Si6In2 22, M = 945.18, monoc = 17.736(6), b = 12.778(4), c = 21.201(7) Å, b = 103.64(2)8, U = 4669 Å3, T = 250 8C, space group I2/a, Mo-Ka (l = 0.71073 Å), Z = 4, Dc = 1.34 g cm23, F(000) = 492.Crystal dimensions: 0.20 × 0.25 × 0.35 mm, m = 11.5 cm1. Data collection. The crystals were handled under mineral oil. The crystal chosen for analysis was transferred to a cold nitrogen stream for data collection on a Nicolet R3m/V diVractometer equipped with an LT-1 low-temperature device, w mode with scan width Dq = 1.30 1 (Ka2 2 Ka1)8, scan speed range 1.5–15.08 min21, graphite-monochromated Mo-Ka radiation; 3329 reflections measured (48 £ 2q £ 458, ±h, k, l), 2327 independent with I > 3s(I).Lorentz and polarization corrections were applied; however, no correction for absorption was made due to the small absorption coeYcient. Two standard reflections were measured every 2 h or after every 100 data points collected, and these showed no significant variation. Structure solution and refinement. The Laue symmetry was determined to be 2/m, and the space group was shown to be Ia or I2/a.Because the unitary structure factors displayed centric statistics, I2/a was assumed to be the correct setting from the outset, which was confirmed subsequently by successful refinement. The structure was solved by using the SHELXTL Patterson interpretation program, which revealed the position of the In atom in the asymmetric unit, consisting of one-half molecule situated about a two-fold axis. The remaining nonhydrogen atoms were located in subsequent diVerence Fourier syntheses.The usual sequence of isotropic and anisotropic refinement was followed. Hydrogen atoms attached to carbon were then entered in ideal calculated positions and constrained to a riding motion with a single variable isotropic thermal parameter for the SiMe3 hydrogens and a separate variable for the NMe hydrogens. The two amino hydrogens were located in difference maps and allowed to refine with distance constraints. All non-Li atoms occupy general positions, and both the Li atoms lie in special positions on a two-fold axis.The isotropic thermal parameters of both Li atoms refined to unreasonably small values (average 0.002 Å2); therefore, in the final least squares refinement the Li isotropic thermal parameters were fixed. The possibility that some other cationic species occupies the Li positions was considered because of the irregularity in the Li refinement. Based on the way in which the compound was synthesized the only other species that can reasonably be considered to occupy the Li positions is Na.Whether the atoms are Li or Na, charge balance requires the cation-to-In atom ratio be one (i.e., the positions cannot be half occupied). The possibility that the salt contains Na rather than Li was excluded for the following reasons: (1) a search of the Cambridge Crystallographic database for Li–N and Na–N distances where nitrogen is attached to at least two carbon atoms revealed that the distances are in the range 1.89–2.56 and 2.34–3.44 Å, respectively. In the present case, the Li–N distances range from 2.04 to 2.23 Å. This suggests that Li at 100% occupancy is the more reasonable choice.(2) The compound was synthesized in high yield using the Li salt HNMeSi(Me2)NMeLi. A high yield would not be expected if the Na came from a contamination source, such as the Li amide salt, Celite filter aid or glassware. (3) When Na was refined in the Li positions the isotropic thermal parameters became unreasonably large (average 0.14 Å2).After all shift/esd ratios were less than 0.2, convergence was reached with R, R9 = 0.034, 0.036. The weighting scheme was w = [s(F)]22. No unusually high correlations were noted between any of the variables in the last cycle of full-matrix least squares refinement, and the final diVerence map showed a maximum peak of about 0.7 e Å23 located 0.47 Å away from Li(1). There was also a peak of about 0.5 e Å23 located 0.7 Å away from Li(2).Calculations were made using Nicolet’s SHELXTL PLUS (1987) package of programs.18 CCDC reference number 186/1244. Acknowledgements Acknowledgement for support is made to the Robert A. Welch Foundation (S.G.B. and D.M.H.), The Energy Laboratory at UH (D.M.H.), and The Institute for Space Systems Operations (D.M.H.). We thank Dr. James Korp for his technical assistance with the crystal structure determination of [Li{In(HNMe- SiMe2NMe)2(MeNSiMe2NMe)}]2. References 1 J. Kim, S. G. Bott and D. M. HoVman, Inorg. Chem., 1998, 37, 3835. 2 S. Strite and H. Morkoç, J. Vac. Sci. Technol., B, 1992, 10, 1237; S. Strite, M. E. Lin and H. Morkoç, Thin Solid Films, 1993, 231, 197. 3 R. G. Gordon, D. M. HoVman and U. Riaz, Mater. Res. Soc. Symp. Proc., 1991, 204, 95. 4 R. G. Gordon, D. M. HoVman and U. Riaz, Mater. Res. Soc. Symp. Proc., 1992, 242, 445. 5 H. Bürger, J. Cichon, U. Goetze, U. Wannagat and H. J. Wismar, J. Organomet. Chem., 1971, 33, 1. 6 M. A. Petrie, K. Ruhlandt-Senge, H. Hope and P. P. Power, Bull. Soc. Chim. Fr., 1993, 130, 851. 7 G. Rossetto, N. Brianese, A. Camporese, M. Porchia, P. Zanella and R. Bertoncello, Main Group Met. Chem., 1991, 14, 113.146 J. Chem. Soc., Dalton Trans., 1999, 141–146 8 R. Frey, V. D. Gupta and G. Linti, Z. Anorg. Allg. Chem., 1996, 622, 1060. 9 M. Veith, M. Zimmer and S. Müller-Becker, Angew. Chem., Int. Ed. Engl., 1993, 32, 1731; Angew. Chem., 1993, 105, 1771. 10 U. Wannagat, T. Blumenthal, D. J. Brauer and H. Bürger, J. Organomet. Chem., 1983, 249, 33. 11 A. J. Elias, H.-G. Schmidt, M. Noltemeyer and H. W. Roesky, Organometallics, 1992, 11, 462. 12 D. J. Brauer, H. Bürger, H. H. Moretto, U. Wannagat and K. Wiegel, J. Organomet. Chem., 1979, 170, 161. 13 M. Veith, H. Lange, O. Recktenwald and W. Frank, J. Organomet. Chem., 1985, 294, 273. 14 M. Porchia, F. Benetollo, N. Brianese, G. Rossetto, P. Zanella and G. Bombieri, J. Organomet. Chem., 1992, 424, 1. 15 H. Günther, NMR Spectroscopy—An Introduction, Wiley, Chichester, 1980, ch. VIII. 16 L. W. Breed and R. L. Elliott, Inorg. Chem., 1964, 3, 1622. 17 MolEN, An Interactive Structure Solution Program, Enraf-Nonius, Delft, 1990. 18 G. M. Sheldrick, SHELXTL PLUS, Release 3.4 for the Nicolet R3m/v Crystallographic System, Nicolet Instrument Corp., Madison, WI, 1987. Paper 8/07041E

ISSN:1477-9226    

DOI:10.1039/a807041e

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

J. Chem. Soc., Dalton Trans., 1997, Pages 145–147 145 DALTON COMMUNICATION Synthesis and structural characterisation of two Á1-bonded N-phenylthioformamidate complexes of rhodium Patricia A. McEneaney,a Trevor R. Spalding *,a and George Ferguson *,b a Chemistry Department, University College, Cork, Ireland b Chemistry Department, University of Guelph, Guelph, Ontario N1G 2W1, Canada The complexes [3-{h1-SC(H)NPh}-3,3-(PMe2Ph)2-3,1,2-closo- RhC2B9H11] and [2-{h1-SC(H)NPh}-2,2-(PMe2Ph)2-2,1-closo- RhTeB10H10] have been structurally characterised using X-ray crystallography and are the first h1-bonded thioformamidate complexes to be isolated.Numerous metal complexes of ligands containing the S]C]N bond sequence have been characterised in the solid state. Reactions between isothiocyanates, RNCS, and metal hydrides usually lead to metal complexes with [h2-SC(H)NR]2 ligands which are bonded through both M]S and M]N bonds. A typical example is [ZrCl{h2-SC(H)NPh}(cp)2] (cp = h5-C5H5).1 Alternatively, more complex ligands derived from several SCNR molecules may be formed such as, [h2-S2C(H)NR]2 in [2-{h2- S2CN(H)Ph}-2-(PPh3)-2,1-closo-RhTeB10H10].2 Although there have been several reports of complexes containing monodentate ligands derived from pyridine-2-thiol and related compounds (see ref. 3 for a recent review), there has been no report to our knowledge of the structural characterisation of any complex with an h1-thioformamidato-to-metal functionality.Recently we proposed an [h1-SC(H)NPh]2 complex, [3-{h1- SC(H)NPh}-3,3-(PPh2Me)2-3,1,2-closo-RhC2B9H11] 1, as an intermediate in the synthesis of the rhodacarborane [3,3- (PPh2Me)2-3-Cl-3,1,2-closo-RhC2B9H11] 2, from [3-{h2-SC(H)- NPh}-3-(PPh3)-3,1,2-closo-RhC2B9H11] 3, Scheme 1.4 A study of the parallel reaction with PMe2Ph as the phosphine has afforded [3-{h1-SC(H)NPh}-3,3-(PMe2Ph)2-3,1,2-closo-RhC2- B9H11] 4, Fig. 1. This compound was isolated from the reaction between a ten-fold excess of PMe2Ph (0.109 g, 0.790 mmol) and a solution of 3 (0.050 g, 0.079 mmol) in CH2Cl2 (20 cm3) at room temperature (r.t.) for 30 min.After evaporating the solvent under reduced pressure, the residue was washed with hexane (3 × 5 cm3) to remove the excess phosphine. The single product was recrystallised from CH2Cl2–hexane solution affording orange crystals of [3-{h1-SC(H)NPh}-3,3-(PMe2Ph)2-3,1,2- closo-RhC2B9H11] 4?0.93CH2Cl2, in 83% yield (0.047 g).† An analogous reaction (r.t., 15 min) with the rhodatelluraborane complex which is formally isoelectronic with 3, i.e.[2-{h2- SC(H)NPh}-2-(PPh3)-closo-2,1-RhTeB10H10] 5, produced [2- {h1-SC(H)NPh}-2,2-(PMe2Ph)2-2,1-closo-RhTeB10H10] 6, Fig. 2. The rhodatelluraborane 6 was recrystallised from a CH2Cl2– hexane solution in a yield of 86%.‡ Satisfactory microanalytic data (C, H, N) were obtained for both 4 and 6. Both compounds 4 and 6 contain rhodium–sulfur bonded h1- † Crystal data for 4.C25H39B9NP2RhS?0.93CH2Cl2, orange platelet, 0.39 × 0.26 × 0.12 mm, M = 726.80, monoclinic, P21/c, a = 10.0955(12), b = 21.897(2), c = 15.960(2) Å, b = 96.599(9)8, U = 3504.6(6) Å3, Z = 4, Dc = 1.39 g cm–3, l(Mo-Ka) = 0.7107 Å, m(Mo-Ka) = 0.81 mm–1, F(000) = 1484, T = 294 K. Data for 8046 reflections were measured, of which 7625 reflections were unique (Rint = 0.009) and of these the 5575 with I > 2s(I ) were labelled ‘observed’. R(Fo) = 0.0348, R9(F2) = 0.0885 for all measured data where R(Fo) = S||Fo| 2 |Fc||/S|Fo|, R9(F2) = {S[w(Fo 2 2 Fc 2)2]/S(wFo 2)} � �� , and w = 1/[s2(Fo 2)].SC(H)NPh ligands. However, the orientation of these ligands with respect to the RhC2B3 or RhTeB4 moieties in each of the compounds is clearly different. The phenylthioformamidate group in compound 4 interacts solely with the rhodium atom of the RhC2B9 cage, Fig. 1, whereas in compound 6 there is also a Scheme 1 ‡ Crystal data for 6. C23H38B10NP2RhSTe, orange needle, 0.40 × 0.20 × 0.20 mm, M = 761.15, triclinic, P1� , a = 9.7040(13), b = 11.895(2), c = 14.4469(15) Å, a = 76.211(11), b = 80.557(11), g = 83.680(12)8, U = 1593.2(3) Å3, Z = 2, Dc = 1.587 g cm–3, l(Mo- Ka) = 0.7107 Å, m(Mo-Ka) = 1.616 mm–1, F(000) = 752, T = 294(1) K.Data for 5450 reflections were collected and of these the 4402 with I > 2s(I ) were labelled ‘observed’. R(Fo) = 0.0292, R9(F2) = 0.0800 for all measured data, R(Fo) and R9(F2) as for 4. Structure solution of 4 and 6.Data were collected using an Enraf- Nonius CAD4 diffractometer to a maximum q of 278 using graphitemonochromated Mo-Ka radiation. Data were corrected for Lorentz, polarisation and absorption effects (from y scans). The structures were solved by Patterson and Fourier methods and refined by full-matrix least-squares calculations initially using the NRCVAX system of programs5 and finally with SHELXL 93 6 using all F2 data. The H atoms were allowed for as riding atoms using the appropriate AFIX commands in SHELX 93.Diagrams were prepared with the aid of ORTEP7 and PLATON.8 Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/334.146 J. Chem. Soc., Dalton Trans., 1997, Pages 145.147 weak but significant intramolecular Te ? ? ? N contact, Fig. 2. The S(1)]C(3)]N(1)]C(41) plane in 4 is at an angle of 37.5(3)8 to the best-fit plane containing the C2B3 face, while the S(1)]C(2)]N(1)]C(31) plane in 6 is at an angle of 60.8(3)8 to the TeB4 face. The SC(H)NPh ligand in 6 is clearly positioned to facilitate the Te ? ? ? N interaction. Fig. 1 An ORTEP view of compound 4 with the atom numbering scheme. Displacement ellipsoids are at the 50% level except for H atoms which are drawn as small spheres of an arbitrary size.Selected interatomic distances (A) and angles (8): Rh(3)]S(1) 2.4010(8), Rh(3)]C(1) 2.246(3), Rh(3)]C(2) 2.212(3), Rh(3)]B(4) 2.280(4), Rh(3)]B(7) 2.216(3), Rh(3)]B(8) 2.274(3), Rh(3)]P(1) 2.3242(10), Rh(3)]P(2) 2.3346(8), C(1)]C(2) 1.613(4), S(1)]C(3) 1.724(3), C(3)]N(1) 1.254(4), N(1)]C(41) 1.424(4), C]B distances range from C(1)]B(6) 1.674(5) to C(2)]B(7) 1.753(4) and B]B distances from B(5)]B(6) 1.752(7) to B(4)]B(8) 1.818(5); C(3)]S(1)]Rh(3) 109.31(11), N(1)]C(3)]S(1) 126.7(2), C(41)]N(1)]C(3) 119.7(3), S(1)]Rh(3)]P(1) 82.11(3), S(1)]Rh(3)]P(2) 91.51(3), P(1)]Rh(3)]P(2) 95.83(3), S(1)]Rh(3)]C(1) 85.64(8), S(1)]Rh(3)]C(2) 103.55(8) Fig. 2 An ORTEP view of compound 6 with the atom numbering scheme. Displacement ellipsoids are at the 30% level except for H atoms which are drawn as small spheres of an arbitrary size. Selected interatomic distances (A) and angles (8): Rh(2)]S(1) 2.4147(10), Rh(2)]Te(1) 2.5788(4), Rh(2)]B(3) 2.336(4), Rh(2)]B(6) 2.362(4), Rh(2)]B(7) 2.241(4), Rh(2)]B(11) 2.253(4), Rh(2)]P(1) 2.3732(10), Rh(2)]P(2) 2.3601(10), S(1)]C(2) 1.712(4), C(2)]N(3) 1.256(5), N(3)]C(31) 1.423(5), Te(1) ? ? ? N(3) 2.737(3), Te]B distances range from Te(1)] B(4) 2.288(5) to Te(1)]B(3) 2.390(5) and B]B distances from B(10)] B(12) 1.745(7) to B(5)]B(6) 1.896(6); C(2)]S(1)]Rh(2) 114.83(14), N(3)]C(2)]S(1) 127.7(3), C(31)]N(3)]C(2) 120.1(3), S(1)]Rh(2)]P(1) 87.41(4), S(1)]Rh(2)]P(2) 81.74(4), P(1)]Rh(2)]P(2) 96.58(3), S(1)]Rh(2)]Te(1) 93.27(3) Within each SC(H)NPh ligand, the bond lengths and most of the bond angles are essentially the same.In both cases the S]C]N]C atoms are virtually coplanar with torsion angles of 177.5(3)8 in compound 4 and 178.3(3)8 in 6. The S(1)]C(3)]N(1) and C(3)]N(1)]C(41) angles in 4 are 126.7(2) and 119.7(3)8, while the corresponding angles in 6 are 127.7(3) and 120.1(3)8. The S]C distances of 1.724(3) and 1.712(4) A respectively in 4 and 6 are typical of delocalised sp2 hybridised carbon.sulfur bonds (1.720 A), i.e.longer than the typical S]] Csp2 distance of 1.681 A in thioureas and shorter than the typical S]Csp3 distance of 1.808 Als.5 The phenyl carbonto- nitrogen and the methine carbon-to-nitrogen distances are respectively 1.424(4) and 1.254(4) A in 4 and 1.423(5) and 1.256(5) A in 6, and are essentially identical. These bond lengths are respectively longer than typical N]Car bonds and shorter than typical N]] Csp2 bonds.9 The Te ? ? ? N interaction in compound 6 has implications for cluster electron counting.Although the Te ? ? ? N distance in 6 is long, 2.737(3) A compared with a typical Te]N distance (in covalent bonds 2.15 A), it is considerably shorter than the sum of the van der Waals¡� radii of Te and N, 3.61 A. Similar Te ? ? ? N distances of 2.702 and 2.752 A respectively have previously been reported in the compounds bis[2-(49- methoxyphenyl)iminomethinylphenyl]telluride 10 and 1,6-bis[(2- butyltelluro)phenyl]-2,5-diazahexa-1,5-diene.11 If the donation of electron density from the nitrogen lone pair to the tellurium in the RhTeB10 cage was strong it would imply an electronic character for 6 which is nido-type, but because the Te ? ? ?N interaction is weak, a nido structure for 6 is not observed and the closo structure of the system is maintained. It is noteworthy, however, that the Rh]S bond length in 6, 2.4147(10) A, is significantly longer than that in 4, 2.4010(8) A.In overall electron density terms, the relative weakening of the Rh]S bond in 6 may be considered to balance the Te ? ? ? N interaction. The rhodium.tellurium distance in 6, 2.5788(4) A, is well within the known range of 2.529(4) 12 to 2.6172(4) A13 for rhodatelluraboranes and is close to the distance found in [2-{h2-S2CN- (H)Ph}-2-(PPh3)-closo-2,1-RhTeB10H10] [2.5812(3) A].2 The dimensions of the RhC2B9H11 and RhTeB10H10 cages, Figs. 1 and 2 respectively, are typical of such structures and require no further comment.14 Finally, with respect to the previous suggestion that [3-{h1- SC(H)NPh}-3,3-(PPh2Me)2-3,1,2-closo-RhC2B9H11] 1 is an intermediate in the formation of [3,3-(PPh2Me)2-3-Cl-3,1,2- closo-RhC2B9H11] 2 from [3-{h2-SC(H)NPh}-3-(PPh3)-3,1,2- closo-RhC2B9H11] 3,4 Scheme 1, we wish to report that the rhodacarborane 1 has now been isolated from this reaction in 70% yield and characterised spectroscopically.The formation of the rhodium.chloride containing compounds [3-Cl-3,3- (PPh2Me)2-3,1,2-closo-RhC2B9H11] 2 (quantitative yield) or [3-Cl-3,3-(PMe2Ph)2-3,1,2-closo-RhC2B9H11] 7 (16% yield) is observed when the complexes 1 and 4 respectively are refluxed in CH2Cl2 solution for 48 h. Acknowledgements The generous loan of Rh salts by Johnson Matthey plc is gratefully acknowledged (T. R. S.). G. F. thanks the Natural Sciences and Engineering Research Council (Canada) for Grants in Aid of Research, P.McE. thanks Forbairt, Ireland for support. Thanks are due to Dr. B. S¢§ tibr and his colleagues in the Czech Republic for discussions. We wish to thank a referee for drawing our attention to ref. 3. References 1 W. Mei, L. Shiwei, B. Meizhi and G. Hefu, J. Organomet. Chem., 1993, 447, 227. 2 G. Ferguson, D. O¡�Connell and T. R. Spalding, Acta Crystallogr., Sect. C, 1994, 50, 1432.J. Chem. Soc., Dalton Trans., 1997, Pages 145–147 147 3 E.S. Raper, Coord. Chem. Rev., 1996, 153, 199. 4 G. Ferguson, J. Pollock, P. A. McEneaney, D. P. O’Connell, T. R. Spalding, J. F. Gallagher, R. Maciás and J. D. Kennedy, Chem. Commun., 1996, 679. 5 E. J. Gabe, Y. LePage, J. P. Charland, F. J. Lee and P. S. White, J. Appl. Crystallogr., 1989, 22, 384. 6 G. M. Sheldrick, SHELXL 93, A program for the refinement of crystal structures, University of Göttingen, 1993. 7 C. K. Johnson, ORTEPII, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 8 A. L. Spek, Molecular Graphics Program, University of Utrecht, 1994. 9 A. G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G. Watson and R. Taylor, in Structure Correlation, eds. H.-B. Burgi and J. D. Dunitz, VCH, Weinheim, 1994, vol. 2, Appendix. 10 V. I. Minkin, I. D. Sadekov, A. A. Maksimenko, O. E. Kompan and Yu. T. Struchkov, J. Organomet. Chem., 1991, 402, 331. 11 N. Al-Salim, T. A. Hamor and W. R. McWhinnie, J. Chem. Soc., Chem. Commun., 1986, 453. 12 Faridoon, M. McGrath, T. R. Spalding, X. L. R. Fontaine, J. D. Kennedy and M. Thornton-Pett, J. Chem. Soc., Dalton Trans., 1990, 1819. 13 Faridoon, O. Ni Dhubhghaill, T. R. Spalding, G. Ferguson, B. Kaitner, X. L. R. Fontaine, J. D. Kennedy and D. Reed, J. Chem. Soc., Dalton Trans., 1988, 2739. 14 See, for example, M. F. Hawthorne, J. Organomet. Chem., 1975, 100, 97 and refs. therein; R. N. Grimes, in Comprehensive Organometallic Chemistry, eds. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon, Oxford, 1982 and refs. therein. Received 11th September 1996; Communication 6/06

ISSN:1477-9226    

DOI:10.1039/a606276h

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 147–154 147 One-electron oxidation of paramagnetic chromium(II) alkyl complexes with alkyl halides: synthesis and structure of fivecoordinate chromium(III) complexes Michael D. Fryzuk,*a Daniel B. LeznoV,a (the late) Steven J. Rettig † and Victor G. Young, Jr.b a Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T 1Z1 b X-ray Crystallographic Center, Department of Chemistry, 160 Kolthoff Hall, University of Minnesota, Minneapolis, Minnesota 55455, USA Received 3rd August 1998, Accepted 6th November 1998 The reaction of square-planar, high-spin CrR[N(SiMe2CH2PPh2)2] (R = Me, CH2SiMe3) with alkyl halides (MeI, CF3CH2I, MeBr, PhCH2Cl) generates one-electron oxidation products Cr(R)X[N(SiMe2CH2PPh2)2], unusual examples of five-coordinate chromium(III) complexes.Cr(Me)Br[N(SiMe2CH2PPh2)2] and Cr(CH2SiMe3)Cl[N- (SiMe2CH2PPh2)2] have been structurally characterized.Alkylation of the latter complex with LiCH2SiMe3 gave a five-coordinate Cr(III) dialkyl complex Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2], which was structurally characterized as well. Attempts to isolate sterically unencumbered Cr(III) dialkyl (e.g., dimethyl) complexes resulted in decomposition. Addition of an excess of PhCH2Cl to {[(Ph2PCH2SiMe2)2N]Cr}2(m-Cl)2 resulted in halide-transfer to form CrCl2(THF)[N(SiMe2CH2PPh2)2] in low yield. Reaction of the low-spin CrCp[N(SiMe2CH2PPh2)2] complex with PhCH2Cl, however, gave both Cr(Cp)(CH2Ph)[N(SiMe2CH2PPh2)2] and Cr(Cp)Cl[N(SiMe2CH2PPh2)2]. The five-coordinate Cr(III) alkyl halide complexes do not polymerize ethylene at 60 8C and 1 atm; the dialkyl complex Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] does catalyze polyethylene formation but is quickly deactivated.A discussion comparing the structural distortions observed in these five-coordinate high-spin d3 Cr(III) complexes with those observed in the analogous low-spin d6 Ir(III) complexes is presented.Introduction Oxidative addition of a substrate to a metal complex is an important process in organometallic chemistry.1,2 The most commonly examined oxidative addition reactions involve formal two-electron redox processes in which the oxidation state of the metal centre is increased by two. One-electron processes, on the other hand, have been less studied in an organometallic context.1 For example, one very important group of substrates that undergoes oxidative addition reactions is alkyl halides.Studies on two-electron oxidative addition of substrates such as MeI to metal complexes LnMx to give LnMx 1 2(Me)(I) have been reported.1,2 Chromium(II) complexes, however, are more likely to undergo one-electron oxidative addition, and this is indeed observed for reactions with alkyl halides. For example, the reactions of [Cr(H2O)6]21 with alkyl halides and other radical sources to generate aqueous organometallic Cr(III) cations have been well studied.3–5 Although there are little structural data, mechanistic and kinetic data abound6–9 and all support a radical-based atom abstraction mechanism,10,11 shown in Scheme 1.More recently, 17-electron Cr(I) radical reactions with alkyl halides to give Cr(II) products have also been examined.12–15 In this case, the chromium starting material, commonly a metal– Scheme 1 † Professional OYcer: UBC Crystallographic Service. metal bonded dimer such as [CpCr(CO)3]2, reacts cleanly only in cases where the metal-centred radicals are stable with respect to dimerization.Detailed mechanistic studies utilizing other stable 17-electron radicals such as that produced from flash photolysis of [CpM(CO)3]2 (M = Mo, W)16 and Re(CO)4L17 have been reported. In every case studied, however, MLn has been a coordinatively saturated octahedral complex (n = 6), as have been the metal-containing products. There are also no examples of organometallic CrIILn reactants that undergo this reaction.A series of square-planar, high-spin chromium(II) alkyl complexes stabilized by a chelating amidodiphosphine ligand were previously prepared in our group; 18,19 in this study, we report their reactivity with alkyl halides to form unusual five-coordinate chromium(III) complexes. Results and discussion Reaction of CrMe[N(SiMe2CH2PPh2)2] 1 with methyl-iodide and -bromide A red-brown toluene solution of the Cr(II) methyl complex CrMe[N(SiMe2CH2PPh2)2] 1 18,19 reacts with MeX (X = Br, I) in a 2 : 1 stoichiometry to give a purple solution from which the chromium(III) alkyl halide complex Cr(Me)X[N(SiMe2CH2- PPh2)2] (X = Br 2, I 3) was isolated in ca. 40% yield [eqn. (1)].148 J. Chem. Soc., Dalton Trans., 1999, 147–154 These Cr(III) complexes are paramagnetic, with a solution magnetic moment of 3.8 mB (Evans’ method),20,21 consistent with a high-spin d3 complex.22 Note that this reactivity is diVerent from that observed for the square-planar, high-spin Cr(II) mesityl complex Cr(C6H2Me3)2(PMe3)2; in this case reaction with methyl iodide does not give one-electron oxidation chromium( III) products but rather a substitution with the Cr–R fragment to give organic products (C6H2Me4) and CrI2.23 The crystal structure of 2 is shown in Fig. 1, along with some pertinent bond lengths and angles in Tables 1 and 2. The structure reveals a distorted five-coordinate Cr(III) centre; the complex could be considered as a square-pyramid with the methyl C(31) in the apical position.The P(1)–Cr–P(2) angle of 170.88(7)8 and the Br(1)–Cr–N(1) angle of 141.0(1)8 define the distorted square base in this case. Alternatively, the phosphines can be considered the trans-axial ligands in a trigonalbipyramid, with the Br(1)–Cr–N, Br(1)–Cr–C(31) and N(1)– Cr–C(31) angles of 141.0(1)8, 99.6(2)8 and 119.4(2)8 defining the equatorial plane. Five-coordinate complexes of chromium( III) are extremely rare.The few structurally characterized examples of five-coordinate chromium(III) complexes are trigonal-bipyramidal CrCl3(NMe3)2,24,25 distorted trigonalbipyramidal Na2CrPh5?3Et2O?THF26 and Cr(Me)SPh[N(SiMe2- CH2PPh2)2],27 square-pyramidal Cr(tmtaa)Cl (H2tmtaa = 5,14-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine) 28 and two-legged piano-stool [h5-Me4- C5SiMe2-h1-NtBu]CrCH2SiMe3.29 The coordinative unsaturation of 2 and 3 can be compared with other complexes involving chromium(III) centres with alkyl and halide ligands; such complexes are invariably octahedral or dinuclear with bridging halides.Examples include (h3-L)Cr(CH2SiMe3)2Cl (L = 1,3,5-triazacyclohexane),30 Cr(nBu)2Cl[(Me2PCH2)3CMe],31 Cr- MeCl2(dippe)(THF) [dippe = 1,2-bis(diisopropylphosphino)- ethane] 32 and dinuclear [Cp9CrR]2(m-Cl)2 (Cp9 = Cp, R = Me;33 Cp9 = Cp*, R = Me,34 CH2Ph35) complexes. The CrIII–P bond lengths of 2.464(2) and 2.452(2) Å in 2 are typical of high-spin CrIII–P bonds.Other examples include Cr–P bonds ranging from 2.429(1) to 2.444(1) Å in [CrCl- {N(CH2CH2PMe2)2}2],36 and 2.414(2) Å in [CpCrCl2]2(dmpe)37 (dmpe = Me2PCH2CH2PMe2). The Cr–C bond length of 2.181(7) Å in 2 is slightly longer than some recently reported CrIII–C bond lengths; 38 it can be compared to CrIII–Me bond lengths of 2.09(2) and 2.14(2) Å in CrMe3[tBuSi(CH2PMe2)3],39 2.073(3) Å in [CpCrMe]2(m-Cl)2,33 2.087(2) Å in [Cp*CrMe]2- Fig. 1 Molecular structure (ORTEP)69 and numbering scheme for Cr(Me)Br[N(SiMe2CH2PPh2)2] 2, 33% ellipsoids. (m-Cl)2,34 and is much longer than the 2.054(5) Å found in the related five-coordinate Cr(Me)SPh[N(SiMe2CH2PPh2)2] complex. 27 The Cr–C bond length in 2 is also longer than the bond in the starting complex CrMe[N(SiMe2CH2PPh2)2] 1 [2.151(3) Å].19 On the other hand, the Cr–N bond length of 2.009(4) Å in 2 is significantly shorter than in 1 [2.117(3) Å]. This fact, coupled with the observed lengthening of the Si–N bonds in the product 2 [1.712(5), 1.725(4) Å vs. 1.697(3), 1.699(3) Å in 1] implies that the amide lone pair is substantially more involved with stabilizing the Cr(III) metal centre than was the case for Cr(II). Other examples of CrIII–N (amide) bond lengths include 1.996(2) and 2.017(2) Å in [CrCl{N(CH2CH2PMe2)2}2] 36 and a very short 1.87 Å in Cr(NiPr2)3.40 On the other hand, the Cr–Br bond length of 2.602(1) Å in 2 is long compared to other examples such as 2.478(2) Å in [CpCrBr]2(m-OCMe3)2,41 2.496(1) Å in cationic [CrBr2(L)]Br (L = 1,4,8,11-tetraazacyclotetradecane) 42 and 2.518(1) Å (average) in anionic [4-BrC6- Table 1 Selected bond lengths (Å) for the complexes Cr(Me)Br[N- (SiMe2CH2PPh2)2] 2, Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5 and Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] 6 Complex 2 Cr(1)–P(1) Cr(1)–N(1) Cr(1)–Br(1) P(1)–C(7) P(2)–C(2) P(2)–C(25) Si(1)–C(1) Si(1)–C(4) Si(2)–C(2) Si(2)–C(6) 2.464(2) 2.009(4) 2.602(1) 1.827(6) 1.803(6) 1.816(7) 1.884(6) 1.848(8) 1.890(7) 1.837(9) Cr(1)–P(2) Cr(1)–C(31) P(1)–C(1) P(1)–C(13) P(2)–C(19) Si(1)–N(1) Si(1)–C(3) Si(2)–N(1) Si(2)–C(5) 2.452(2) 2.181(7) 1.805(6) 1.809(6) 1.813(7) 1.712(5) 1.892(7) 1.725(4) 1.865(7) Complex 5 Cr(1)–P(1) Cr(1)–N(1) Cr(1)–Cl(1) P(1)–C(7) P(2)–C(18) P(2)–C(25) Si(1)–C(13) Si(1)–C(15) Si(2)–C(16) Si(2)–C(18) 2.525(2) 2.022(4) 2.315(2) 1.832(5) 1.805(5) 1.711(6) 1.895(6) 1.881(5) 1.876(6) 1.894(5) Cr(1)–P(2) Cr(1)–C(31) P(1)–C(1) P(1)–C(13) P(2)–C(19) Si(1)–N(1) Si(1)–C(14) Si(2)–N(1) Si(2)–C(17) 2.422(2) 2.110(6) 1.821(6) 1.804(5) 1.810(5) 1.731(4) 1.867(6) 1.715(5) 1.867(6) Complex 6 Cr(1)–P(1) Cr(1)–N(1) Cr(1)–C(35) P(1)–C(7) P(2)–C(6) P(2)–C(25) Si(1)–C(1) Si(1)–C(3) Si(2)–C(4) Si(2)–C(6) 2.563(2) 2.071(4) 2.090(5) 1.831(5) 1.808(5) 1.817(5) 1.892(5) 1.875(5) 1.868(5) 1.887(5) Cr(1)–P(2) Cr(1)–C(31) P(1)–C(1) P(1)–C(13) P(2)–C(19) Si(1)–N(1) Si(1)–C(2) Si(2)–N(1) Si(2)–C(5) 2.469(2) 2.112(5) 1.832(5) 1.836(5) 1.830(5) 1.714(4) 1.868(5) 1.722(4) 1.868(5) Table 2 Selected bond angles (8) for the complexes Cr(Me)Br[N- (SiMe2CH2PPh2)2] 2, Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5 and Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] 6 P(1)–Cr(1)–P(2) X–Cr(1)–P(1) X–Cr(1)–P(2) X–Cr(1)–N(1) X–Cr(1)–C(31) P(1)–Cr(1)–N(1) P(2)–Cr(1)–N(1) P(1)–Cr(1)–C(31) P(2)–Cr(1)–C(31) N(1)–Cr(1)–C(31) Si(1)–N(1)–Si(2) 2 X = Br(1) 170.88(7) 92.60(5) 95.40(5) 141.0(1) 99.6(2) 84.7(1) 86.3(1) 96.0(2) 87.0(2) 119.4(2) 122.7(3) 5 X = Cl(1) 148.95(6) 87.96(5) 92.10(6) 164.83(13) 93.5(2) 86.63(13) 85.32(13) 119.9(2) 91.1(2) 101.5(2) 118.4(2) 6 X = C(35) 164.87(5) 99.4(2) 89.0(2) 105.0(2) 101.5(2) 83.19(10) 82.48(10) 97.9(2) 92.6(2) 152.9(2) 119.1(2)J. Chem.Soc., Dalton Trans., 1999, 147–154 149 H4NH4]3[CrBr6].43 This long bond length in the methyl bromide complex 2 implies that there is little or no p-donation from the bromide to the metal in this complex; short Cr–Br bond lengths of 2.393(4) and 2.375(5) Å in Cp*CrOBr2 were interpreted as being due to extensive bromide to metal p-donation.44 Although the formation of the isolated product Cr(Me)X- [N(SiMe2CH2PPh2)2] (X = Br 2; X = I 3) is consistent with the mechanism outlined in Scheme 1, where 2 and 3 are the products of halide atom-abstraction from RX, the product of alkyl radical addition to CrMe[N(SiMe2CH2PPh2)2] 1, namely CrMe2[N(SiMe2CH2PPh2)2] should also have been formed; however, this product was not detected.Instead, a substantial amount of brown material was extracted from the reaction mixture. GC-MS head-space analysis failed to detect either MeH or MeMe (radical solvent abstraction or coupling products) and therefore attempts were made to synthesize the Cr(III) dimethyl compound by another route in order to test its stability. Addition of one equivalent of MeLi or MeMgBr to Cr(Me)Br[N(SiMe2CH2PPh2)2] 2 gave only brown intractable material from which no viable compounds could be isolated; this suggests that the desired chromium(III) dimethyl complex is unstable [eqn.(2)]. Under the assumption that bulky alkyl groups might enhance the stability of chromium(III) dialkyl complexes, the chromium( II) alkyl complex, Cr(CH2SiMe3)[N(SiMe2CH2PPh2)2] 4 19 was utilized as a starting material for the chromium(III) dialkyl complex. The reaction of trimethylsilylmethyl 4 with several mole equivalents of benzyl chloride resulted in a colour change from purple to orange-brown. After workup, the chloride abstraction product, Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5 was obtained in high yield [eqn.(3)]. Note that the use of several equivalents of benzyl chloride in this case allows for the high-yield synthesis of the chromium(III) alkyl halide complex. This result does not seem to imply that the benzyl radical does not combine with any chromium(II) starting material, as it is known that the halide abstraction step is slow while the radical coupling is fast.4,5,10 In particular, the lack of chromium(III) dialkyl or of decomposition products suggests that perhaps the reaction of the benzyl radical with 4 to form Cr(CH2- SiMe3)(CH2Ph)[N(SiMe2CH2PPh2)2] is slow due to the very bulky nature of the Cr(II) centre in the starting complex.The isolated trimethylsilylmethyl–chloride complex 5 is similar to the methyl–bromide complex 2 in that it is also a high-spin, spin-only chromium(III) complex, with a solution magnetic moment of 3.8 mB.The crystal structure of 5, shown in Fig. 2, reveals another distorted five-coordinate chromium(III) complex. Viewed as a distorted square pyramid, C(31) of the CH2SiMe3 unit is in the apical position and the trans-angles in the square base are 148.95(6)8 and 164.83(13)8 for P(1)–Cr–P(2) and N(1)–Cr–Cl(1) respectively (Table 2). Note that this orientation is the reverse of that observed in the methyl–bromide complex 2, where the trans-phosphine angle was easily the largest.If the geometry is to be considered as a distorted trigonal-bipyramid the equatorial plane is defined in this case by the two phosphines and the CH2SiMe3 group, with the amide and chloride being trans-axially oriented. The equatorial angles are 148.95(6)8, 119.9(2)8 and 91.1(2)8 for P(1)–Cr–P(2), C(31)–Cr–P(1) and C(31)–Cr–P(2) respectively. The much greater distortions in this complex compared to the methyl–bromide complex 2 could be due to the increase in steric interactions with the introduction of a trimethylsilylmethyl group.Distortions appear evident in the Cr–P bond lengths of 2.422(2) and 2.525(2) Å. Again, this is likely a reflection of increased steric congestion at the metal centre. The Cr–N bond length of 2.022(4) Å is also comparable to that observed in complex 2. The Cr–Cl and Cr–C bond lengths of 2.315(2) Å and 2.110(6) Å are unremarkable.38 Reaction of trimethylsilylmethyl–chloride 5 with MeLi, MeMgBr or KCH2Ph resulted in brown solutions from which no tractable products could be identified.However, metathesis with the bulky lithium reagent, LiCH2SiMe3, caused a change from orange-brown to dark green. Workup of the solution allowed for the isolation of a formally 13-electron, fivecoordinate chromium(III) dialkyl complex, Cr(CH2SiMe3)2- [N(SiMe2CH2PPh2)2] 6 in moderate yield [eqn. (4)]. The dialkyl complex 6 is very soluble in alkane solvents. X-Ray quality crystals could be grown from the slow evaporation of a hexamethyldisiloxane solution; the structure of this five-coordinate Cr(III) complex is shown in Fig. 3. It is Fig. 2 Molecular structure (ORTEP) and numbering scheme for Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5, 33% ellipsoids.150 J. Chem. Soc., Dalton Trans., 1999, 147–154 immediately apparent that there is a great deal of steric congestion around the metal and this manifests itself in the large distortions in this complex.The structure can be best described as a distorted square-based pyramid, with one trimethylsilylmethyl group [C(35)] in the apical position. The trans angles of the square base are defined by P(1)–Cr–P(2) [164.87(5)8] and N(1)–Cr–C(31) [152.9(2)8]. Alternatively, the complex could be considered as a very distorted trigonal-bipyramid, with the phosphines occupying the axial sites and the equatorial plane defined by the N(1)–Cr–C(31), N(1)–Cr–C(35) and C(31)–Cr– C(35) angles of 152.9(2)8, 105.0(2)8 and 101.5(2)8 respectively.As in the trimethylsilylmethyl chloride complex 5, severe distortions due to steric congestion are manifested in the diVerent Cr–P bond lengths of 2.563(2) and 2.469(2) Å. Although one of the Cr–P bond lengths is particularly long when compared to other systems, the origin of the extreme asymmetry is not known. The Cr–N bond length of 2.071(4) Å is slightly longer than the 2.009(4) and 2.022(4) Å observed in the methyl– bromide complex 2 or the trimethylsilylmethyl–chloride 5 respectively; again, this could easily be due to the steric interactions at the metal centre.The Cr–C bond lengths in bis- (trimethylsilylmethyl) 6 of 2.112(5) and 2.090(5) Å are fairly typical of high-spin chromium(III) systems.38 Chromium(III) dialkyl systems are relatively common; even b-hydrogen-containing n-butyl groups have been incorporated into a chromium(III) system. In almost every case, however, the alkyl complexes are octahedral.Structurally characterized examples of chromium(III) complexes containing more than one Cr–C s-bond include Cp*Cr(py)(CH2Ph)2 and LiCp*Cr- (CH2Ph)3,45 Cr(nBu)2Cl[(Me2PCH2)3CMe],31 (h3 -L)CrR2Y (L = 1,3,5-triazacyclohexane; R = CH2SiMe3, Y = Cl; 30 R = Y = CH2Ph),46 Cp*CrMe2(PMe3),47 CrR3[tBuSi(CH2PMe2)3] (R = Me, nBu)39 and anionic Li3CrMe6?3C4H8O2.48 Hence, there is no inherent diYculty in preparing chromium(III) alkyl complexes; the restrictions with our system could be due to the ligand system present, or due to the coordinative unsaturation at the metal centre.The crystal structure of Cr(CH2SiMe3)2[N(Si- Me2CH2PPh2)2] 6 illustrates the extreme steric protection around the metal centre which appears to be a factor in preparing dialkyl complexes stabilized by the amidodiphosphine ligand. Survey of alkyl halide reactivity with CrR[N(SiMe2CH2PPh2)2] complexes The complex CrMe[N(SiMe2CH2PPh2)2] 1 was shown to react with MeI and MeBr to yield the halide-transfer product Cr(Me)X[N(SiMe2CH2PPh2)2].The generality of this reaction with respect to other alkyl halides and other chromium(II) systems was examined. Benzyl chloride was found to be a Fig. 3 Molecular structure (ORTEP) and numbering scheme for Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] 6, 33% ellipsoids. suitable substrate for the formation of the chloride-transfer product Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5, as shown in the previous section. Similarly, the reaction of benzyl chloride with CrMe[N(SiMe2CH2PPh2)2] 1 produced the purple chloridetransfer product Cr(Me)Cl[N(SiMe2CH2PPh2)2] 7.In both cases, the benzyl-transfer product was not detected. Note that benzyl chloride does not react with [Cp*Cr(CO)3], a chromium(I) substrate that has been shown to undergo oneelectron oxidation reactions.15 The chromium(II) methyl complex 1 was also shown to react rapidly with CF3CH2I to form the purple iodide-transfer product 3. Attempts to isolate putative 13-electron Cr(III) dialkyl complexes that may have formed, prior to their decomposition, by conducting the redox reaction in the presence of suitable trapping agents such as PR3 or pyridine are foiled by the fact that RX reacts preferentially with the trapping agents.However, incorporation of alkyl groups capable of donating more than two electrons to form more stable 15- or 17-electron dialkyl complexes was considered a viable option. Hence, the use of the 16-electron complex Cr(h5-C5H5)[N(SiMe2CH2PPh2)2] 8 19 as a starting material allows for the formation of 15- or 17-electron chromium(III) products, although it should be noted that this is a low-spin complex and hence not directly comparable to the other reactions presented.Nevertheless, addition of 0.5 equivalent of benzyl chloride to a red solution of 8 gives a rapid colour change to green, from which pale green and dark green crystals (inseparable but distinctly observable) can be isolated.One set of crystals is likely CrCp(CH2Ph)[N(SiMe2CH2PPh2)2] 9, tentatively identified by mass spectral peaks only and the other set is Cr(Cp)Cl[N(SiMe2CH2PPh2)2] 10, identified by mass spectrometry. Fifteen- and 17-electron complexes containing h5-Cp and h3-allyl fragments are quite common in chromium(III) chemistry 49–51 so this stabilization is not particularly surprising; such ligands are useful for probing the oneelectron oxidation reactivity of our systems as both expected products become stable systems. The reactivity of the dinuclear five-coordinate chromium(II) chloride compound {[(Ph2PCH2SiMe2)2N]Cr}2(m-Cl)2 1118 with alkyl halides was also examined. Addition of benzyl chloride to 11 in THF resulted in the formation of the halide-transfer product CrCl2(THF)[N(SiMe2CH2PPh2)2] as an impure material; however, the corresponding alkyl-transfer product, Cr(CH2Ph)Cl[N(SiMe2CH2PPh2)2], could not be detected.Similar results were observed for 2-methylallyl chloride. Considering that in this situation the alkyl-transfer product should be stable, the fact that Cr(CH2Ph)Cl[N(SiMe2- CH2PPh2)2] was not observed is not easily rationalized.Reactivity of chromium(III) complexes with ethylene Chromium(III) complexes have been shown to be active catalysts for the production of polyethylene. In particular, a coordinatively and electronically unsaturated molecule (usually a 13-electron system is considered the active catalyst) that also contains a chromium–carbon bond is necessary in order for catalysis to occur.29,35,45,52 The charge on the system does not seem to be a vital component of the system.53 The fivecoordinate alkyl halide complexes Cr(R)X[N(SiMe2CH2PPh2)2] (R = Me, X = Br 2, I 3; R = CH2SiMe3, X = Cl 5) and the dialkyl complex Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] 6 all formally satisfy these requirements; they contain an open site for reactivity and a CrIII–C bond.However, addition of one atmosphere of ethylene at room temperature or 60 8C to a toluene solution of methyl–iodide complex 3 or the trimethylsilylmethyl–chloride complex 5 resulted in no production of polyethylene over one week.This lack of reactivity could be due to the fact that these complexes are not purely 13-electron systems but are closer to 15-electron systems by virtue of amide and/or halide p-donation. The added electron donation may eVectively negate the catalytic ability of the com-J.Chem. Soc., Dalton Trans., 1999, 147–154 151 plexes. In addition, although these are formally five-coordinate species, the steric congestion of the ligands around chromium may mitigate the ability of incoming olefins to interact with the metal centre. On the other hand, addition of ethylene to a solution of dialkyl 6 did result in the slow precipitation of a small amount of white solid, presumably polyethylene, but the solution turned brown over time and production quickly ceased.This catalyst deactivation is likely due to the same reaction that is responsible for the decomposition of sterically unencumbered chromium(III) dialkyl complexes; the colour of the final solution is reminiscent of such decompositions and may be due to some chromium(II) species. It appears then that simply the presence of an open site of reactivity on a chromium( III) centre is not suYcient to promote the polymerization of ethylene. Comparison of five-coordinate Cr(III) and Ir(III) complexes The crystal structures of the five-coordinate chromium(III) complexes presented here illustrate varying degrees of distortion from a regular trigonal-bipyramidal geometry. This distortion is electronic in origin; a perfect D3h structure for a high-spin d3 system is Jahn–Teller unstable due to the presence of one unpaired electron in the degenerate pair of orbitals dx2 2 y2 and dxy.Hence, trigonal-bipyramidal high-spin d3 complexes will distort to remove this degeneracy.The nature of the distortion depends on the ligand set present. In the literature there are three other examples of trigonal-bipyramidal Cr(III) systems, and all show distortions from ideal D3h symmetry. The distortions in the complex CrCl3(NMe3)2 are very small; the trans-N– Cr–N angle is 178.8(5)8 and the equatorial angles are 111.4(2)8, 124.3(1)8 and 124.3(1)8.25 Larger changes are observed in Na2- CrPh5?3Et2O?THF; the trans-angle is 1618 and the equatorial angles are 1048, 1118 and 1458; 26 the angles observed here are reminiscent of those observed in our systems.The recently reported Cr(Me)SPh[N(SiMe2CH2PPh2)2] complex has a trans- P–Cr–P angle of 166.30(6)8 and equatorial angles of 150.0(1)8, 92.8(2)8 and 117.2(2)8.27 Steric eVects are also important and must be taken into consideration. Of course, the incorporation of diVerent ligands into a complex reduces the symmetry, resulting in the degeneracy of the two d-orbitals in question being removed to a certain extent.A diamagnetic analogue of high-spin Cr(III) (d3) would be low-spin Rh(III) and Ir(III) (d6). Instead of three orbitals being half-filled, they are doubly occupied in the Rh(III) and Ir(III) systems. A substantial amount of work has been done using the amidodiphosphine ligand and these two diamagnetic metals.54 In fact, complexes with the exact ligand set as chromium(III) have been prepared.55–58 This provides an excellent opportunity to compare the geometries of two complexes which diVer only in metal centre.The iridium(III) complexes Ir(R)Y- [N(SiMe2CH2PPh2)2] (R = alkyl; Y = alkyl or halide) all show substantial distortions from trigonal-bipyramidal geometry and the nature of the distortion has been explained theoretically.59–62 Although the chromium(III) and iridium(III) crystal radii are diVerent (0.755 vs. 0.82 Å for octahedral geometry),63,64 it is not unreasonable to consider that the predictive theory for d6 iridium(III) distortions would apply to d3 chromium(III) systems as well.When the structure of Ir(Me)I[N(SiMe2CH2PPh2)2] is compared to Cr(Me)Br[N(SiMe2CH2PPh2)2] 2 it is clearly obvious the two structures are quite diVerent. The iridium complex is almost perfectly square-pyramidal, with the methyl in the apical position.55,57 The trans-angles in the square-base are 177.44(15)8 and 170.02(6)8. All other angles are within six degrees of 908.On the other hand, the chromium(III) complex could not be considered as a square-pyramid, with the two largest angles being 170.88(7)8 and 141.0(1)8. In the case of the trimethylsilylmethyl–chloride complex 5 as well the diVerence is obvious [trans-angles are 164.83(13)8 and 148.95(6)8] although perhaps a case for steric eVects could be made here. Not so in the methyl–bromide complex. In fact, the iridium methyl– bromide complex is more sterically hindered; the Ir–P bond lengths of 2.327(2) and 2.335(2) Å are much shorter than those found in the high-spin chromium(III) complexes [2.452(2) and 2.464(2) Å in 2] despite chromium(III) being a smaller metal centre.This implies that metal to phosphine electron-donation is increasingly more facile with diamagnetic iridium(III) than with paramagnetic chromium(III). Dialkyl complexes of iridium(III) were also prepared and a comparison of the structures of Ir(R)R9[N(SiMe2CH2PPh2)2] (R = R9 = CH2Ph; 58 R = CH2SiMe3, R9 = Me56) with Cr(CH2- SiMe3)2[N(SiMe2CH2PPh2)2] 6 reveals substantial diVerences.The iridium complexes were considered to be trigonalbipyramidal in nature (the so-called Y-shape), with two large and one very small angle (opposite the amide) in the equatorial plane. As an example, the equatorial angles in the iridium dibenzyl complex are 141.6(1)8, 140.8(1)8 and 77.6(1)8; the trans-phosphine angle is 170.2(5)8. In the chromium complex, the trans-phosphine angle is 164.87(5)8 but the equatorial angles are 152.9(2)8, 105.0(2)8 and 101.5(2)8, considerably diVerent and in fact much more square-pyramidal in nature.However, the extreme steric congestion in the chromium dialkyl makes it diYcult to ascribe the geometric diVerences purely to electronic eVects. The fact that complexes with exactly the same ligand sets yield diVerent structures with chromium(III) and iridium(III) implies that the calculations which predict geometric distortions for low-spin d6 iridium(III) complexes cannot be applied to high-spin d3 chromium(III) complexes.One explanation for the lack of applicability of the d6 iridium theoretical calculation to d3 chromium could be the inherent diVerence between first and third row transition metals: the energy splitting of 3d orbitals is much smaller than that of 5d orbitals. Distortions are expected to be exacerbated in first-row metal systems and that is in fact observed; the chromium(III) complexes prepared all show greater distortions than the analogous iridium(III) systems and the Cr(III) distortions are not necessarily in the fashion predicted for Ir(III).Calculations done on a chromium(III) centre in a similar manner to that for iridium(III) would likely be able to model the observed distortions. Conclusions Coordinatively and electronically unsaturated chromium(II) complexes that contain a metal–carbon bond have been shown to undergo facile one-electron oxidation reactions to chromium( III) products with a variety of alkyl halides.However, unless the alkyl groups on chromium are very bulky, stable dialkyl complexes could not be prepared and hence in many cases the details of the reactivity and product formation could not be discerned. The structures that were solved were all unusual examples of five-coordinate chromium(III) complexes. None of the chromium(III) alkyl complexes prepared was an eYcient ethylene polymerization catalyst despite the presence of an open coordination site.Experimental General procedures Unless otherwise stated all manipulations were performed under an atmosphere of dry, oxygen-free dinitrogen or argon by means of standard Schlenk or glovebox techniques. The glovebox used was a Vacuum Atmospheres HE-553-2 workstation equipped with a MO-40-2H purification system and a 240 8C freezer. 1H NMR spectroscopy was performed on a Bruker AC-200 instrument operating at 200 MHz and referenced to internal C6D5H (d 7.15). Magnetic moments were measured by a modification of Evans Method20,21 (C6D5H as a reference152 J.Chem. Soc., Dalton Trans., 1999, 147–154 peak) on the NMR spectrometer listed above. Mass spectra were measured using a Kratos MS-50 EI instrument operating at 70 eV. Microanalyses (C, H, N) were performed by Mr. P. Borda of this department. Materials The preparation of the lithium salt LiN(SiMe2CH2PPh2)2 65 and the chromium complexes {[(Ph2PCH2SiMe2)2N]Cr}2(m-Cl)2 18 and CrR[N(SiMe2CH2PPh2)2] 18,19 have been previously described.NaCp?DME was prepared by the reaction of Na with CpH in dry DME. KCH2Ph and LiCH2SiMe3 were prepared by literature procedures.66 Alkyl halides were either distilled under N2 or passed through a column of activated neutral alumina, and then degassed by 3 freeze–pump–thaw cycles. All other reagents were obtained from commercial sources and used as received. Hexanes, toluene and THF were heated to reflux over CaH2 prior to a final distillation from either sodium metal or sodium benzophenone under an Ar atmosphere.Deuteriated solvents were dried by distillation from sodium benzophenone under nitrogen; oxygen was removed by trap-to-trap distillation and 3 freeze–pump–thaw cycles. Synthesis and reactivity of complexes Synthesis of Cr(Me)Br[N(SiMe2CH2PPh2)2] 2. A 10 mL purple toluene solution of CrMe[N(SiMe2CH2PPh2)2] 1 (0.12 g, 0.19 mmol) in a bomb was frozen in liquid nitrogen.To this was added one-half equivalent of MeBr by quantitative vacuum transfer. Upon removal of the liquid nitrogen bath and melting of the toluene, a rapid reaction resulted in a dark purple solution. After being warmed to room temperature and being stirred for one hour, the solvent was removed in vacuo, the residue extracted with toluene, filtered through Celite and reduced to a minimum volume. Layering with hexanes (5 mL) yielded purple crystals of Cr(Me)Br[N(SiMe2CH2PPh2)2] 2 which were used for X-ray analysis. Yield: 0.050 g (39%) (Calc.for C31H39BrCrNP2Si2?0.5C7H8: C, 57.41; H, 6.00; N, 1.94. Found: C, 57.57; H, 6.20; N, 2.05%). 1H NMR (C6D6): d 11.2 (v br), 10.4 (br), 7.0 (br, sh), 6.2 (v br, overlap), 5.8 (v br, overlap), 4.2 (v br) and resonances for C7H8. MS: m/z 661 (M1 2 Me), 580 (M1 2 Me 2 Br). meff = 3.8 mB. Synthesis of Cr(Me)I[N(SiMe2CH2PPh2)2] 3. The reaction was performed as for 2, substituting one-half equivalent of MeI for MeBr.After workup, Cr(Me)I[N(SiMe2CH2PPh2)2] 3 was isolated as purple crystals. Yield: 0.060 g (43%) (Calc. for C37H44CrINP2Si2?0.5C7H8: C, 53.90; H, 5.64; N, 1.82; I, 16.51. Found: C, 54.17; H, 5.66; N, 1.60; I, 16.30%). 1H NMR (C6D6): d 11.2 (v br), 10.4 (br), 6.3 (v br, overlap), 5.9 (v br, overlap), 4.1 (v br) and resonances for C7H8. MS: m/z 722 (M1), 707 (M1 2 Me). meff = 3.8 mB. Synthesis of CrCl2(THF)[N(SiMe2CH2PPh2)2]. {[(Ph2PCH2- SiMe2)2N]Cr}2(m-Cl)2 11 (0.10 g, 0.08 mmol) was dissolved in 10 mL THF and cooled to 278 8C to give a blue solution.To this was added two drops of neat PhCH2Cl, causing an immediate change to dark brown. After being stirred overnight at room temperature, the solvent was then removed in vacuo, the residue extracted with minimum toluene (2 mL), filtered through Celite and hexanes added (2 mL). Purple crystals of CrCl2(THF)[N- (SiMe2CH2PPh2)2] precipitated from the solution overnight. Repeated elemental analysis had varying amounts of ligated THF remaining; extended drying in vacuo failed to remove all THF (Calc.for C30H36Cl2CrNP2Si2?C4H8O: C, 56.42; H, 6.13; N, 1.94. Calc. for C30H36Cl2CrNP2Si2?0.5THF: C, 55.89; H, 5.86; N, 2.04. Calc. for C30H36Cl2CrNP2Si2: C, 55.30; H, 5.57; N, 2.15. Found: C, 55.80; H, 6.15; N, 2.05%). 1H NMR (C6D6): d 12.5 (v br, 4 H), 3.5 (v br, 12 H) and resonances for THF. MS: m/z 650 (M1), 615 (M1 2 Cl). meff = 3.8 mB. Synthesis of Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5.To a 10 mL purple toluene solution of Cr(CH2SiMe3)[N(SiMe2- CH2PPh2)2] 4 (approximately 0.10 g, 0.15 mmol) was added 2 drops of neat benzyl chloride at 278 8C. No immediate reaction occurred but upon being warmed to room temperature the solution changed to golden orange-brown. After being stirred overnight, the solvent was removed in vacuo, the residue extracted with a minimum of toluene, filtered through Celite and hexanes added (1 : 1). Overnight, from the solution, dark orange crystals of Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5 suitable for X-ray analysis were deposited.Yield: 0.095 g (90%) (Calc. for C34H47ClCrNP2Si3: C, 58.06; H, 6.73; N, 1.99. Found: C, 58.43; H, 6.79; N, 1.92%). MS: m/z 701 (M1 2 H), 615 (M1 2 CH2SiMe3). meff = 3.8 mB. Synthesis of Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] 6. Crystals of Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5 (0.13 g, 0.18 mmol) were dissolved in 10 mL THF to give a dark orange solution, which was cooled to 278 8C.To this was added dropwise a 10 mL toluene solution of LiCH2SiMe3 (0.017 g, 0.18 mmol), which resulted in an instant colour change to dark green. Upon being warmed the solution turned a darker green and after 30 minutes of being stirred at room temperature the THF was removed in vacuo, the residue was extracted with 2 mL hexanes, filtered through Celite and then pumped to dryness again. This residue was dissolved in a minimum amount of hexamethyldisiloxane (1.5 mL) (and placed in a 240 8C freezer and allowed to slowly evaporate).Overnight, long green bars of Cr(CH2- SiMe3)2[N(SiMe2CH2PPh2)2] 6 suitable for X-ray analysis were isolated. Yield: 0.070 (51%) (Calc. for C38H58CrNP2- Si4?0.5(Me3Si)2O: C, 58.88; H, 8.07; N, 1.67. Found: C, 59.20; H, 7.61; N, 1.70%). MS: m/z 580 [M1 2 (CH2SiMe3)2]. Reaction of CrMe[N(SiMe2CH2PPh2)2] 1 with PhCH2Cl and CF3CH2I. Addition of two drops of neat PhCH2Cl or CF3CH2I to a toluene solution of CrMe[N(SiMe2CH2PPh2)2] 1 (0.05 g, 0.08 mmol) at room temperature resulted in a rapid colour change to dark purple.After being stirred for one hour, the solvent was removed in vacuo, the residue extracted with toluene, filtered through Celite and the solvent removed again. A mass spectrum of the crude products indicated the formation of Cr(Me)Cl[N(SiMe2CH2PPh2)2] 7 [m/z 630 (M1), 615 (M1 2 Me)] from the benzyl chloride reaction and Cr(Me)I[N- (SiMe2CH2PPh2)2] 3 [m/z 707 (M1 2 Me)] from the CF3CH2I reaction. Reaction of Cr(Á5-C5H5)[N(SiMe2CH2PPh2)2] 8 with PhCH2- Cl.To a deep red solution of Cr(h5-C5H5)[N(SiMe2CH2PPh2)2] 8 (0.09 g, 0.14 mmol) in 10 mL toluene at 278 8C was added PhCH2Cl (toluene stock solution, 0.07 mmol). No immediate reaction occurred but as the solution was warmed to room temperature, the solution turned dark green. After being stirred overnight, the dark green solution was reduced to a minimum (1 mL), hexanes added (2 mL). Dark green and light green crystals were deposited from the solution overnight.The two products were tentatively identified as Cr(Cp)Cl[N(SiMe2- CH2PPh2)2] 10 (MS as reported below) and CrCp(CH2Ph)- [N(SiMe2CH2PPh2)2] 9 [m/z 735 (M1 2 H), 670 (M1 2 Cp 2 H)]. The solids could not be separated suYciently to obtain elemental analysis. Conditions of attempted reaction of Cr(R)X[N(SiMe2- CH2PPh2)2] with ethylene. Addition of one atmosphere of ethylene to a bomb containing a 10 mL toluene solution of Cr(Me)I[N(SiMe2CH2PPh2)2] 3 (0.05 g, 0.07 mmol) or Cr(CH2- SiMe3)Cl[N(SiMe2CH2PPh2)2] 5 (0.05 g, 0.07 mmol) resulted in no apparent reaction over one week.No polyethylene was produced and no colour change occurred. Mild heating to 60 8C for three days also had no eVect.J. Chem. Soc., Dalton Trans., 1999, 147–154 153 Reaction of Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] 6 with ethylene. Addition of one atmosphere of ethylene to a bomb containing a 10 mL toluene solution of Cr(CH2SiMe3)2[N(Si- Me2CH2PPh2)2] 6 (0.05 g, 0.07 mmol) caused no immediate colour change but over twelve hours a small amount of white solid, presumably polyethylene, had been produced.After 24 hours, the solution had changed from green to dark brown-red and no further polymer formation was observed. X-Ray crystallographic analysis Cr(Me)Br[N(SiMe2CH2PPh2)2] 2. Crystal data. C31H39- BrCrNP2Si2, M = 675.67, triclinic, a = 10.217(3), b = 19.705(5), c = 9.353(3) Å, a = 101.94(2), b = 109.69(2), g = 95.21(2)8, U = 1707(1) Å3 (by least-squares refinement on the setting angles for 25 reflections with 128 < 2q < 188, l = 0.710 69 Å, T = 21 8C), space group P1� (no. 2), Z = 2, Dc = 1.314 g cm23, F(000) = 698. Brown irregular crystals. Crystal dimensions: 0.20 × 0.30 × 0.35 mm, m(Mo-Ka) = 16.92 cm21. Data collection and processing.67 Rigaku AFC6S diVractometer, w–2q scan mode, w scan width 1.37 1 0.35 tan q, w scan speed 16 min21 (up to 8 rescans), graphite-monochromated Mo-Ka radiation; 7846 unique reflections measured (1 £ q £ 27.58, h, ±k, ±l), 4106 having I > 3s(I).Absorption correction: azimuthal scans (relative transmission factors 0.88– 1.00). The intensities of three standard reflections, measured each 200 reflections, decayed linearly by 6.9% (correction applied). Structure analysis and refinement. Direct methods followed by Fourier synthesis. Full-matrix least-squares with all nonhydrogen atoms anisotropic and hydrogen atoms in calculated positions [C–H = 0.99 Å, Biso = 1.2B(parent atom)].Statistical weights = 4Fo/s2(F2).67 Final R = S |Fo| 2 |Fc| /S|Fo| = 0.067, Rw = (Sw(|Fo| 2 |Fc|)2/Sw|Fo|2)� �� = 0.030 for 4106 reflections with I > 3s(I). Computer programs and source of scattering factors are given in ref. 67. Selected bond lengths and bond angles appear in Tables 2 and 3. Cr(CH2SiMe3)Cl[N(SiMe2CH2PPh2)2] 5. Crystal data. C34H47ClCrNP2Si3, M = 703.39, triclinic, a = 11.0802(3), b = 11.2193(3), c = 17.9349(1) Å, a = 95.385(1), b = 100.353(1), g = 118.882(1)8, U = 1877.71(7) Å3, space group P1� (no. 2), Z = 2, Dc = 1.244 g cm23, F(000) = 742. Brown tals. Crystal dimensions: 0.35 × 0.20 × 0.12 mm, m(Mo-Ka) = 5.80 cm21. Data collection and processing. Siemens SMART CCD diVractometer, w–2q scan mode. Graphite-monochromated Mo-Ka radiation; 6320 unique reflections measured (1 £ q £ 258, h, ±k, ±l), 6318 having I > 2s(I). Absorption correction: SADABS.68 A crystal of 5, sealed in a glass capillary, was mounted on the Siemens SMART system for a data collection at 173(2) K.An initial set of cell constants was calculated from reflections harvested from three sets of 20 frames. These initial sets of frames are oriented such that orthogonal wedges of reciprocal space were surveyed. This produces orientation matrices determined from 80 reflections. Final cell constants are calculated from a set of 3459 strong reflections from the actual data collection.Final cell constants reported in this manner usually are about one order of magnitude better in precision than reported from four-circle diVractometers. The data technique used for this specimen is generally known as a hemisphere collection. Here, a randomly oriented region of reciprocal space is surveyed to the extent of 1.3 hemispheres to a resolution of 0.84 Å. Three major swaths of frames are collected with 0.308 steps in w. This collection strategy provides a high degree of redundancy.The redundant data provide good y input in the event an empirical absorption correction is applied. Structure analysis and refinement. The space group was determined based on systematic absences and intensity statistics. A successful direct-methods solution was calculated which provided most non-hydrogen atoms from the E-map. Several full-matrix least squares/diVerence Fourier cycles were performed which located the remainder of the non-hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were placed in ideal positions and refined as riding atoms with individual (or group if appropriate) isotropic displacement parameters. Function minimized Sw(|Fo| 2 |Fc|)2 where w21 = s2(Fo) 1 0.0010Fo 2, R = S|Fo 2 |Fc|/S|Fo| and Rw = S|(w� �� (Fo 2 Fc)|/S|(w)� �� Fo|.Final R = 0.072, Rw = 0.166 for 6318 reflections with I > 2s(I). The crystal was twinned; the twin was a minor component randomly oriented with respect to the major component. No integration of the minor component was necessary.Selected bond lengths and angles appear in Tables 2 and 3. Cr(CH2SiMe3)2[N(SiMe2CH2PPh2)2] 6. Crystal data. C38H58CrNP2Si4, M = 755.15, monoclinic, a = 12.9279(6), b = 19.5790(9), c = 17.1414(8) Å, b = 95.295(1)8, U = 4320.2(3) Å3, space group P21/c (no. 14), Z = 4, Dc = 1.161 g cm23, F(000) = 1612. Black needle crystals. Crystal dimensions: 0.48 × 0.16 × 0.10 mm, m(Mo-Ka) = 4.75 cm21.Data collection and processing. Siemens SMART CCD diVractometer, w–2q scan mode. Graphite-monochromated Mo-Ka radiation; 7471 unique reflections measured (1 £ q £ 25, h, ±k, ±l), 7469 having I > 2s(I). Absorption correction: SADABS.68 The data collection for 6 is analogous to that for 5 (above). Orientation matrices for initial cell constant calculations were determined from 24 reflections. Final cell constants were calculated from a set of 6991 strong reflections from the actual data collection.The sample diVracted poorly and was collected with 45 second frames. Structure analysis and refinement. The structure analysis and refinement for 6 is analogous to that for 5 (above). Function minimized S(|Fo| 2 |Fc|)2 where w21 = s2(Fo) 1 0.0010Fo 2, R = S|Fo 2 |Fc|/S|Fo| and Rw = S|(w� �� (Fo 2 Fc)|/S|(w)� �� Fo|. Final R = 0.073, Rw = 0.127 for 7469 reflections with I > 2s(I). Selected bond lengths and angles appear in Tables 2 and 3.CCDC reference number 186/1243. Acknowledgements Financial support was provided by NSERC of Canada in the form of a Research grant (to M. D. F.) and a 1967 Science and Engineering Research Scholarship (to D. B. L.). References 1 J. P. Collman, L. S. Hegedus, J. R. Norton and R. G. Finke, Principles and Applications of Organotransition Metal Chemistry, University Science Books, Mill Valley, CA, 1987. 2 R. H. Crabtree, The Organometallic Chemistry of the Transition Metals, John Wiley & Sons, New York, 1994. 3 J. K. Kochi and J. W. Powers, J. Am. Chem. Soc., 1970, 92, 137. 4 J. H. Espenson, Prog. Inorg. Chem., 1983, 30, 189. 5 J. H. Espenson, Acc. Chem. Res., 1992, 25, 222. 6 W. C. Kupferschmidt and R. B. Jordan, J. Am. Chem. Soc., 1984, 106, 991. 7 M. J. Sisley and R. B. Jordan, Inorg. Chem., 1988, 27, 1963. 8 Z. Zhang and R. B. Jordan, Inorg. Chem., 1993, 32, 5472. 9 A. Bakac, V. Butkovic, J. H. Espenson and M.Orhanovic, Inorg. Chem., 1993, 32, 5886. 10 M. C. Baird, Chem. Rev., 1988, 88, 1217. 11 D. R. Tyler, Prog. Inorg. Chem., 1988, 36, 125. 12 T. A. Huber, D. H. Macartney and M. C. Baird, Organometallics, 1993, 12, 4715. 13 T. A. Huber, D. H. Macartney and M. C. Baird, Organometallics, 1995, 14, 592. 14 C. A. Goulin, T. A. Huber, J. M. Nelson, D. H. Macartney and M. C. Baird, J. Chem. Soc., Chem. Commun., 1991, 798. 15 C. A. MacConnachie, J. M. Nelson and M. C. Baird, Organometallics, 1992, 11, 2521. 16 S. L. Scott, J. H. Espenson and Z. Zhu, J. Am. Chem. Soc., 1993, 115, 1789.154 J. Chem. Soc., Dalton Trans., 1999, 147–154 17 K.-W. Lee and T. L. Brown, J. Am. Chem. Soc., 1987, 109, 3269. 18 M. D. Fryzuk, D. B. LeznoV, S. J. Rettig and R. C. Thompson, Inorg. Chem., 1994, 33, 5528. 19 M. D. Fryzuk, D. B. LeznoV and S. J. Rettig, Organometallics, 1995, 14, 5193. 20 D. F. Evans, J. Chem. Soc., 1959, 2003. 21 S. K. Sur, J. Magn. Reson., 1989, 82, 169. 22 R. L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, 1986. 23 A. R. Hermes, R. J. Morris and G. S. Girolami, Organometallics, 1988, 7, 2372. 24 G. W. A. Fowles and P. T. Greene, Chem. Commun., 1966, 784. 25 P. T. Greene, B. J. Russ and J. S. Wood, J. Chem. Soc. A, 1971, 3636. 26 E. Müller, J. Krause and K. Schmiedeknecht, J. Organomet. Chem., 1972, 44, 127. 27 M. D. Fryzuk, D. B. LeznoV and S. J. Rettig, Organometallics, 1997, 16, 5116. 28 F. A. Cotton, J. Czuchajowska, L. R.Falvello and X. Feng, Inorg. Chim. Acta, 1990, 172, 135. 29 Y. Liang, G. P. A. Yap, A. L. Rheingold and K. H. Theopold, Organometallics, 1996, 15, 5284. 30 R. D. Köhn and G. Kocoik-Köhn, Angew. Chem., Int. Ed. Engl., 1994, 33, 1877. 31 E. G. Thaler, K. Folting, J. C. HuVman and K. G. Caulton, J. Organomet. Chem., 1989, 376, 343. 32 A. R. Hermes and G. S. Girolami, Inorg. Chem., 1990, 29, 313. 33 D. S. Richeson, S.-W. Hsu, N. H. Fredd, G. v. duyne and K. H. Theopold, J. Am. Chem.Soc., 1986, 108, 8273. 34 W. A. Herrmann, W. R. Thiel and E. Herdtweck, J. Organomet. Chem., 1988, 353, 323. 35 G. Bhandari, Y. Kim, J. M. McFarland, A. L. Rheingold and K. H. Theopold, Organometallics, 1995, 14, 738. 36 A. R. H. Al-Soudani, A. S. Batsanov, P. G. Edwards and J. A. K. Howard, J. Chem. Soc., Dalton Trans., 1994, 987. 37 J. C. Fettinger, S. P. Mattamana, R. Poli and R. D. Rogers, Organometallics, 1996, 15, 4211. 38 K. H. Theopold, Acc. Chem. Res., 1990, 23, 263. 39 T. G. Gardner and G. S. Girolami, J. Chem. Soc., Chem. Commun., 1987, 1758. 40 D. C. Bradley, M. B. Hursthouse and C. W. Newing, Chem. Commun., 1971, 411. 41 S. E. Nefedov, A. A. Pasynskii, I. L. Eremenko, B. Orazsakhatov, O. G. Ellert, V. M. Novotortsev, S. B. Katser, A. S. Antsyshkina and M. A. Porai-Koshits, J. Organomet. Chem., 1988, 345, 97. 42 J. N. Lisgarten, R. A. Palmer, A. M. Hemmings and D. M. Gazi, Acta Crystallogr., Sect. C, 1990, 46, 396. 43 D. M. Halepoto, L. F. Larkworthy, D. C. Povey, R. A. Siddiqui and G. W. Smith, Inorg. Chim. Acta, 1994, 227, 167. 44 D. B. Morse, T. B. Rauchfuss and S. R. Wilson, J. Am. Chem. Soc., 1988, 110, 8234. 45 G. Bhandari, A. L. Rheingold and K. H. Theopold, Chem. Eur. J., 1995, 1, 199. 46 R. D. Köhn, G. Kociok-Köhn and M. Haufe, J. Organomet. Chem., 1995,n, F. H. Köhler, G. Müller and H. Zeh, Chem. Ber., 1989, 122, 897. 48 J. Krausse and G. Marx, J. Organomet. Chem., 1974, 65, 215. 49 P. W. Jolly, Acc. Chem. Res., 1996, 29, 544. 50 R. Poli, Chem. Rev., 1996, 96, 2135. 51 R. P. A. Sneeden, Organochromium Compounds, Academic Press, New York, London, 1975. 52 B. J. Thomas, S. K. Noh, G. K. Schulte, S. C. Sendlinger and K. H. Theopold, J. Am. Chem. Soc., 1991, 113, 893. 53 K. H. Theopold, R. A. Heintz, S. K. Noh and B. J. Thomas, in Homogeneous Chromium Catalysts for Olefin Polymerization, ed. W. R. Moser and D. W. Slocum, American Chemical Society, Washington, DC, 1992. 54 M. D. Fryzuk, Can. J. Chem., 1992, 70, 2839. 55 M. D. Fryzuk, P. A. MacNeil and S. J. Rettig, J. Am. Chem. Soc., 1985, 107, 6708. 56 M. D. Fryzuk, P. A. MacNeil and R. G. Ball, J. Am. Chem. Soc., 1986, 108, 6414. 57 M. D. Fryzuk, P. A. MacNeil and S. J. Rettig, Organometallics, 1986, 5, 2469. 58 M. D. Fryzuk, P. A. MacNeil, R. L. Massey and R. G. Ball, J. Organomet. Chem., 1989, 368, 231. 59 D. L. Thorn and R. HoVmann, New J. Chem., 1979, 3, 39. 60 Y. Jean and O. Eisenstein, Polyhedron, 1988, 7, 405. 61 I. E.-I. Rachidi, O. Eisenstein and Y. Jean, New J. Chem., 1990, 14, 671. 62 J. F. Riehl, Y. Jean, O. Eisenstein and M. Pelissier, Organometallics, 1992, 11, 729. 63 R. D. Shannon and C. T. Prewit, Acta Crystallogr., Sect. B, 1969, 25, 925. 64 R. D. Shannon, Acta Crystallogr., Sect. B, 1976, 32, 751. 65 M. D. Fryzuk, P. A. MacNeil, S. J. Rettig, A. S. Secco and J. Trotter, Organometallics, 1982, 1, 918. 66 M. Schlosser and V. Ladenberger, J. Organomet. Chem., 1967, 8, 193. 67 M. D. Fryzuk, G. Giesbrecht and S. J. Rettig, Organometallics, 1996, 15, 3329. 68 G. M. Sheldrick, SADABS, University of Göttingen, 1997. 69 C. K. Johnson, ORTEP, report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. Paper 8/06099A

ISSN:1477-9226    

DOI:10.1039/a806099a

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1997, Pages 149.151 149 EVects of metal-centre orbital control on cluster character and electron distribution between borane and hydrocarbon ligands; significance of the structures of [I-9,10-(SMe)-8,8-(PPh3)2-nido-8,7- IrSB9H9] and [I-9,10-(SMe)-8-(A4-C5Me5H)-nido-8,7-RhSB9H9] Ramon Macias,a Josef Holub,a,b John D. Kennedy,a Bohumil S¢§ tibr,b Mark Thornton-Pett a and William Clegg c a School of Chemistry of the University of Leeds, Leeds LS2 9JT, UK b Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic, 25068 R¢§ ez¢§ u Prahy, The Czech Republic c Department of Chemistry of the University of Newcastle, Newcastle upon Tyne NE1 7RU, UK In [m-9,10-(SMe)-8-(h4-C5Me5H)-nido-8,7-RhSB9H9] the nonborane ligand has been found to prefer {h4-C5Me5H} rather than {h5-C5Me5} character, demonstrating factors behind (a) metallaborane core cluster control of exopolyhedral ligand-tometal co-ordination modes, and (b) the stability of sixteenelectron transition-element centres that engender stable formally ¡®low¡� cluster-electron counts.There is current interest in polyhedral boron-containing cluster compounds that deviate 1 from the dictates of the classical 2,3 Williams.Wade cluster geometry.electron-counting formalism or which exhibit other unusual cluster behaviour. In this general context there have recently been reports of (a) the unusual incidence of a tetrahapto h4-C5Me5H ligand in [1-(h5-C5Me5)-2- (h4-C5Me5H)-nido-1,2-Co2B3H8], which is suggested to be sterically driven to form this bidentate h4 type of co-ordination rather than the h5-C5Me5 ligand generally found in metallaborane chemistry,4 and (b) unusual hydrogen-to-metal agostic interactions in [8-(h2-Ph2PCH2CH2Ph2)-nido-8,7-RhSB9H10] which are proposed5 in order to convert what can be regarded as a formal Wadian closo electron count into a nido one that would be perhaps interpretable as more consistent with the conventional eleven-vertex nido cluster structure.We now report preliminary results from two compounds that together generate additional significant perspective on these two interesting behavioural modes. Reaction of essentially equimolar amounts (reaction scale 80 mmol] of m-(MeS)SB9H10 6 1 (schematic structure I) with [IrCl(PPh3)3] and N,N,N9,N9-tetramethylnaphthalene-1,8- diamine (tmnda) in CH2Cl2 at room temperature for 30 min, followed by chromatographic separation (TLC, silica gel G, CH2Cl2.C6H14 1 : 1), resulted in the isolation of red air-stable [m-9,10-(SMe)-8,8-(PPh3)2-nido-8,7-IrSB9H9] 2 (Rf 0.34; 58%; schematic structure II), characterised by single-crystal X-ray diffraction analysis¢Ó (Fig. 1, upper) and NMR spectroscopy.¢Ô The compound has a nido-shaped eleven-vertex {IrSB9} cluster, but has associated with it 5 a formally closo Wadian 3 elevenvertex electron count if the metal centre is regarded as formally square-planar iridium(I).An essentially equivalent procedure (reaction scale 250 mmol), but using [{Rh(h5-C5Me5)Cl2}2] with 1 and tmnda, resulted in the isolation of yellow air-stable [m-9,10-(SMe)-8-(h4-C5Me5H)- nido-8,7-RhSB9H9] 3 (Rf 0.59; 21%; schematic structure III), also characterised by single-crystal X-ray diffraction analysis ¢Ó (Fig. 1, lower) and NMR spectroscopy.¢Ô This has a tetrahapto bidentate pentamethylcyclopentadiene ligand, h4-C5Me5H, ¢Ó Crystals of compounds 2 and 3 were both grown by diffusion of hexane into solutions of them in CH2Cl2.Data for 2 were collected at 200 K on a Stoe STADI4 diffractometer operating in the w.q scan mode, those for 3 at 160 K on a Siemens SMART CCD area-detector diffractometer with narrow w-rotation frames. In both cases Mo-Ka radiation (l = 0.710 73 A) was used. The structures were solved by heavy-atom methods using SHELXS 86 7 and refined by full-matrix least squares (against all the unique F2 data) using SHELXL 93.8 Non-hydrogen atoms were refined with anisotropic displacement parameters.Restraints were applied to the phenyl rings of 2 such that they remained flat with overall C2v symmetry. In both cases the hydrogen atoms associated with the ligands were constrained to idealised positions, whereas those associated with the cluster [including that with the mixed-atom site B/S(4) in 3 (see below)] were located on Fourier-difference maps and freely refined.Compound 2, C37H42B9IrP2S2, Mr = 902.26, crystal dimensions 0.38 ¡¿ 0.28 ¡¿ 0.14 mm, triclinic, space group P1. , a = 9.7888(11), b = 11.1211(12), c = 18.455(3) A, a = 85.471(3), b = 77.651(8), g = 79.813(8)8, Z = 2, U = 1929.9(4) A3, Dc = 1.553 g cm.3; 8345 reflections were collected to q = 25.08; 6793 unique reflections (Rint = 0.0505) were used in calculations after Lorentzpolarisation and absorption corrections (m = 3.679 mm.1; azimuthal y scans, transmission factors 0.356.0.744). Final wR2 = [Sw(Fo 2 2 Fc 2)2/ S(Fo 2)2] .©ö©÷ = 0.0779, conventional R = 0.0318 for F values of 5624 reflections with Fo 2 > 2s(Fo 2); w = 1/[s2(Fo 2) + 0.0504P2] where P = (Fo 2 + 2Fo 2)/3, goodness of fit = 1.020 for all F2 values and 493 parameters. Maximum and minimum residual electron density 1.10 and 21.86 e A.3 respectively. Compound 3, C11H28B9RhS2, Mr = 424.71, crystal dimensions 0.42 ¡¿ 0.40 ¡¿ 0.08 mm, monoclinic, space group P21/c, a = 14.4790(2), b = 10.1752(2), c = 14.9360(2) A, b = 114.936(1)8, Z = 4, U = 1868.24(5) A3, Dc = 1.51 g cm.3; 11 398 reflections were collected to q = 28.518 of which 4280 (Rint = 0.0356) were used in calculations after Lorentz-polarisation and absorption corrections (m = 1.020 mm.1; based on repeated and equivalent data, transmission factors 0.741.0.794).The cluster was disordered across two positions related by a pseudomirror plane passing through atoms Rh(8), C(1) and C(6), and the midpoint of the C(3)]C(4) bond vector of the pentamethylcyclopentadiene ligand.It is disordered in a 9 : 1 ratio over two positions for which there are three types of atom: (i) Rh(8), B(3), B(10) and B(6) (labelling refers to highest-occupancy molecule) lie on the plane and are common to both molecules, (ii) B(1), B(4) and B(5) are related to B(2), S(7), B(11) respectively and interchange when going from the major- to minor-occupancy molecule and (iii) B(9) and S(91) which are unique to the major-occupancy molecule and are related to B(99 ) and S(919 ) of the minor-occupancy molecule.Atoms B(4) and S(7) were refined as mixed-occupancy atoms (9 : 1 B: S for the former and 9 : 1 S: B for the latter) and ¡®soft¡� rigid-bond and similarity restraints were applied to the displacement parameters of B(9), B(99), S(91) and S(919). Final wR2 = 0.0694, conventional R = 0.0268 for F values of 3765 reflections with Fo 2 > 2 s(Fo 2); w = 1/[s2(Fo 2) + 0.0321P2 + 1.205P], with P as for 2, goodness of fit = 1.098 for all F2 values and 269 parameters.Maximum and minimum residual electron density 0.48 and 20.81 e A.3 respectively. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/328.150 J.Chem. Soc., Dalton Trans., 1997, Pages 149–151 which would complete a sixteen-electron square-planar rhodium( I) bonding sphere in the same manner as the two monodentate PPh3 ligands would complete a formal iridium(I) bonding sphere in compound 2. Hydrogen is incorporated into the {RhC5Me5} unit with the generation of an approximation of rhodium(I) square-planar character, and a concomitant generation of arachno, rather than pyramidal nido, six-vertex cluster character for the {RhC5} unit.This contrasts to the several previously characterised nido-structured {MSB9} cluster compounds of general formulation [8-(arene)-nido-8,7-MSB9H11] [{(arene)M} = {(h6-C6H5Me)Fe} 4a, {(h5-C5Me5)Co} 4b, {(h5- C5Me5)Rh} 4c or {(h5-C5Me5)Ir} 4d; schem cluster configuration IV],10–12 which retain pyramidal nido character in the {(arene)M} unit and formally octahedral metal character. Significantly, the generation of the {h4-C5Me5H} unit in 3 effectively occurs in preference to an incorporation of hydrogen that would engender unambiguous rhodium(III) octahedral character and generate a formal nido electron count for the {RhSB9} unit that would then be consistent with its nido eleven-vertex cluster shape.That the {Rh(h4-C5Me5H)} unit also occurs in preference to the retention of the stable nido six-vertex {Rh(h5- C5Me5)} pyramidal unit is also noteworthy. The origins of this different behaviour of 3 compared to the set of compounds 4a– 4d presumably derive from the lack of mobility of the bridging SMe group in 3 compared to a relative lability of the bridging hydrogen system in 4a–4d.This interesting preference for {h4-C5Me5H} bidentate behaviour has two general connotations. (a) In [1-(h5-C5Me5)-2- (h4-C5Me5H)-nido-1,2-Co2B3H8] an arachno six-vertex {Co(h4- C5Me5H)} subcluster is similarly adopted in preference to an arachno five-vertex {Co2B3H9} one. Here, it has been suggested that the h4-{C5Me5H} mode may be sterically enforced by the proximity of the two bulky {Co(C5Me5)}-based units, rather than by the electronic requirements of the cluster core.4 By contrast, the h4 mode observed here for compound 3, in which ‡ Cluster BH NMR data (CDCl3, 294–297 K), ordered as d(11B) (relative to BF3?OEt2) [d(1H) of directly attached hydrogen atom]: for 2, +11.8 [+5.12], +6.2 [+3.39], +6.0 [+1.89], +3.6 [+2.93], 21.6 [+2.77], 25.8 [+2.97], 210.9 [+2.48], 220.2 [+2.03] and 231.2 [+1.32]; also d(1H) +2.41 (SMe) and d(31P) +20.8 and +11.2 [2J(31P]31P) 26.3 Hz]; for 3, +16.5 [+2.53], +12.2 [+3.82], +10.4 [+2.88], +4.2 [+3.70], 22.3 [+2.06], 25.6 [+2.75], ca. 213.7 [+2.10], ca. 213.7 [+2.43] and 229.5 [+0.90]; also d(1H) +2.54 (3 H, SMe), +3.09 (1 H, br), +2.20 [3 H, d, 3J(1H]1H) 1.6 Hz], +1.97 (3 H), +1.71 (3 H) and +1.31 (6 H) (accidental coincidence of two sets of C5Me5H methyl-proton resonances). there is no steric conflict, demonstrates that control by the electronic dictates of the metallaborane cluster core is also feasible. (b) For [8-(h2-Ph2PCH2CH2PPh2)-nido-8,7-RhSB9H10], long-range interactions involving PPh hydrogen atoms and the otherwise sixteen-electron transition-element centre are invoked to propose an eighteen-electron centre and thence a ‘correct’ 26-electron nido eleven-vertex cluster-electron count.5 In 3, by contrast, the nido-shaped eleven-vertex {RhSB9} cluster effectively rejects the hydride moiety that would enable it to gain a ‘correct’ 26-electron nido count. There is no real evidence for any significant interaction between the rhodium centre and the hydrogen atoms of the {h4-C5Me5H} ligand, the two closest Fig. 1 The ORTEP-type diagrams9 for the crystallographically determined molecular structures of compounds 2 (upper) and the major component (see footnote †) of 3 (lower).Ellipsoids are drawn at the 40% probability level with hydrogen atoms as circles of a small arbitrary radius.For 2 all phenyl atoms other than the ipso-carbons have been omitted for clairty. Selected interatomic distances (Å): for 2, Ir(8)]P(1) 2.2916(13), Ir(8)]P(2) 2.3895(12), Ir(8)]S(7) 2.3902(14), Ir(8) ? ? ? S(9,10) 2.6367(14), Ir(8)]B(2) 2.260(5), Ir(8)]B(3) 2.282(5), Ir(8)]B(9) 2.248(6), S(9,10)]B(9) 2.005(7), S(9,10)]B(10) 1.997(6), S(7)]B(2) 2.064(6), S(7)]B(6) 1.981(6), S(7)]B(11) 1.912(6), B(9)]B(10) 1.968(9) and B(10)]B(11) 1.912(9): for 3, Rh(8) ? ? ? C(1) 2.736(2), Rh(8)]C(2) 2.186(2), Rh(8)]C(3) 2.142(2), Rh(8)]C(4) 2.166(2), Rh(8)]C(5) 2.260(2), Rh(8)]B(3) 2.298(3), Rh(8)]B(4) 2.337(2), Rh(8)]S(7) 2.4107(6), Rh(8)]B(9) 2.254(3), Rh(8) ? ? ? S(9,10) 2.4852(6), B(9)]S(9,10) 1.999(3), B(10)]S(9,10) 2.002(3), B(9)]B(10) 1.978(5) and B(10)]B(11) 1.940(4).For each of 2 and 3 there is little difference among the various metal-to-boron distances, emphasising the ambiguities of bonding interpretation and, in particular, the limitations of bonding models that involve or otherwise imply simplistic square-planar or octahedral models for transition-element centresJ.Chem. Soc., Dalton Trans., 1997, Pages 149.151 151 contacts being ca. 3.1 and ca. 3.4 A, somewhat longer than distances to the closest borane-cluster hydrogen atoms on B(9), B(10) and B(11) which are in the range 2.90(3).2.93(3) A. There is, however, an increasingly closer approach of the methylated sulfur atom to the metal centre when 2 and 3 are compared [2.6367(14) and 2.4852(6) A respectively] indicating an incipient twelve- rather than eleven-vertex nido cluster character.Acknowledgements Paper no. 59 from the R¢§ ez¢§-Leeds Anglo-Czech Polyhedral Collaboration (ACPC). We thank the Government of the Basque Country, the EPSRC (UK), the Academy of Sciences of the Czech Republic, the Czech Grant Agency and the Royal Society (London) for support, and Professor Pascual Roman of the University of the Basque Country, Bilbao, for his good offices. References 1 See, for example, J. D. Kennedy and B. S¢§ tibr, in Current Topics in the Chemistry of Boron, ed. G. W. Kabalka, Royal Society of Chemistry, Cambridge, 1994, pp. 285.292 and refs. therein. 2 R. E. Williams, Inorg. Chem., 1971, 10, 210; Adv. Inorg. Chem. Radiochem., 1976, 18, 67. 3 K. Wade, Chem. Commun., 1971, 792; Adv. Inorg. Chem. Radiochem., 1976, 18, 1. 4 Y. Nishihara, K. J. Deck, M. Shang and T. P. Fehlner, J. Am. Chem. Soc., 1993, 115, 12224. 5 K. J. Adams, T. D. McGrath and A. J. Welch, Acta Crystallogr., Sect. C, 1995, 51, 401. 6 J. Holub, A. E. Wille, B. S¢§ tibr, P. J. Carroll and L. G. Sneddon, Inorg. Chem., 1994, 33, 4920. 7 G. M. Sheldrick, Acta Crystallogr., Sect A., 1990, 46, 467. 8 G. M. Sheldrick, SHELXL 93, Program for refinement of crystal structures, University of Gottingen, 1993. 9 P. McArdle, J. Appl. Crystallogr., 1995, 28, 65. 10 S.-O. Kang, P. J. Carroll and L. G. Sneddon, Organometallics, 1988, 7, 772. 11 S.-O. Kang, P. J. Carroll and L. G. Sneddon, Inorg. Chem., 1989, 28, 96. 12 K. Nestor, X. L. R. Fontaine, N. N. Greenwood, J. D. Kennedy and M. Thornton-Pett, J. Chem. Soc., Dalton Trans., 1991, 2657. Received 28th October 1996; Communication 6/07342E

ISSN:1477-9226    

DOI:10.1039/a607342e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 153–159 153 Synthesis and properties of mononuclear tris(heteroleptic) osmium(II) complexes containing bidentate polypyridyl ligands † Erik Z. Jandrasics and F. Richard Keene * Department of Chemistry and Chemical Engineering, School of Molecular Sciences, James Cook University of North Queensland, Townsville, Queensland 4811, Australia A general synthetic methodology has been elaborated for tris(bidentate ligand)osmium(II) complexes containing three different polypyridyl ligands.The tris(heteroleptic) complexes were characterized by NMR techniques, and the ligand dependence of their electrochemistry and electronic spectroscopy examined. We recently published details of a general synthetic methodology for tris(heteroleptic)ruthenium(II) complexes of the type [Ru(pp)(pp9)(pp0)]2+ (where pp, etc. are bidentate polypridyl ligands) based on the sequential addition of the pro-ligands to the oligomeric precursor [{Ru(CO)2Cl2}n].1,2 The consequent ability to deliberately control the ligand environment has been exploited in spectral,3 photophysical 2,4 and electrochemical 2 characteristics of the ruthenium(II) species.Furthermore, the methodology has also been utilized in the synthesis of ligandbridged dinuclear 5,6 and higher nucleate 7 complexes, and stereochemical aspects of the scheme have been investigated.6,8 The osmium(II) centre is of fundamental importance in the study of d6 polypyridyl complexes, and while earlier studies using bis(heteroleptic) species have dealt with the influence of the ligand environment on the characteristics of the metal centre,9–14 the wider variations provided by tris(heteroleptic) complexes have not been available. The present work details a general procedure for such species, which has close analogies with that used for the ruthenium counterparts,1,2 and provides access to an extensive array of osmium complexes, [Os(pp)(pp9)(pp0)]2+.Preliminary studies of the physical characteristics of such species are reported. Results and Discussion Synthesis In developing a synthetic methodology for the tris(heteroleptic) osmium(II) complexes a number of strategies were investigated, all necessarily involving an intermediate species of type [Os(pp)(pp9)X2]n+. For example, the possibility of forming the precursor [Os(pp)(pp9)Cl2] by reaction of [Os(pp)Cl4] 15 with a second diimine (pp9) was attempted: however, under forcing conditions (microwave oven using high-boiling solvents such as ethylene glycol or N-methylpyrrolidone) 16 the major products were bis(heteroleptic) species, e.g.[Os(pp)(pp9)2]2+. As an alternative approach, [Os(pp)(CO)2Cl2] was sought as a possible precursor for the synthesis of [Os(pp)(pp9)(CO)2]2+, which in turn could be transformed into the tris(heteroleptic) species. Schemes involving the carbonylation of [Os(bipy)Cl4] (bipy = 2,29-bipyridine) in 2-methoxyethanol under an elevated CO pressure (60 psig) at 80 8C,15 an attempted carbonylation of the same substrate by formic acid–formaldehyde (40 : 3 v/v) and the reaction of OsCl3?xH2O with a 2.3-fold excess of bipy in 2- methoxyethanol solution under a CO atmosphere (60 psig) 17 all realised the target compound [Os(bipy)(CO)2Cl2] in a very low yield (<10%).In addition, Johannsen et al.18 had reported the synthesis of cis-[Os(CO)2Cl4]22 (as the NEt4 + salt) from the † Non-SI unit employed: psi ª 6895 Pa.reaction of hexahalogenoosmate(IV) complexes with unsaturated alcohols such as propen-2-ol (allyl alcohol). While this may have provided a pathway to [Os(pp)(CO)2Cl2], the yield was unsatisfactory and the method suffers the disadvantages of a long reaction time (7 d) and the toxicity of the alcohol. Since none of these alternatives proved entirely satisfactory, we pursued a strategy similar to that for the ruthenium(II) species. 2 The first intermediate in that scheme was [Ru(pp)- (CO)2Cl2], formed by reaction of pp with the oligomer [{Ru(CO)2Cl2}n]: however, an alternative path was required in the present case as there appears no analogue of the ruthenium oligomer in osmium chemistry.Formic acid was treated under reflux with K2[OsCl6], and a polymeric compound of as yet uncertain composition isolated which reacted in the next step readily with a bidentate compound (pp) to produce [Os(pp)(CO)2Cl2]. It is assumed that K2[OsCl6] reacts (like RuCl3 2) as a decarbonylating reagent of formic acid: the formation of the polymer is favoured by the presence of formaldehyde in the reaction mixture.Over the course of the reaction (2.5 d) a change from red to green to orange and (finally) light yellow was observed. A solid material (1) was isolated in high yield: its IR spectrum exhibited CO stretching frequencies at 2114, 2053, 2015, 1968 and 1927 cm21, the number of absorptions being an indication of the presence of a polymeric structure although not the same as the ruthenium equivalent, [{Ru(CO)2Cl2}n].The exact formulation of this polymer is not known although microanalysis revealed near parity in the Cl :C atom ratio (ca. 6 : 5). Characterization was not rigorously pursued as the material proved satisfactory as a precursor for the subsequent reactions. The synthetic strategy applied for the synthesis of tris(heteroleptic) osmium(II) complexes containing diimine ligands is summarized in Scheme 1.The polymer 1 reacted readily with a bidentate polypyridyl ligand [pp = bipy or 4,49-dimethyl-2,29- bipyridine (dmbipy)] to form a complex [Os(pp)(CO)2Cl2] 2, with slight modifications in the procedure described for the ruthenium analogue.2 As osmium(II) is in general more inert than ruthenium(II), ethanol was used as a solvent rather than methanol to reach higher reaction temperatures, in conjunction with microwave heating techniques to introduce some overheating effects to accelerate the reaction.16 Complex 2 was isolated in good yield (typically around 70%), and absence of free proligand was checked by thin-layer chromatography.The reaction showed no dependence on the choice of the pp. In the IR spectrum the CO stretching frequencies (n& CO) of [Os(pp)- (CO)2Cl2] did not seem to show a predictable dependence on the nature of the ligand pp (n& CO = 2037 and 1933 cm21 for dmbipy, and 2021 and 1942 cm21 for bipy).The 1H NMR data for two complexes [Os(pp)(CO)2Cl2] (pp = bipy or dmbipy) are given in the Experimental section: the spectra indicate the equivalence154 J. Chem. Soc., Dalton Trans., 1997, Pages 153–159 of the two heterocyclic rings of the symmetrical ligand pp in the complex, consistent with either of two geometries: viz. trans- (Cl),cis(CO) or cis(Cl),trans(CO). As previously reported for the ruthenium(II) analogue,2 the carbonyl ligands would be expected to adopt a cis relationship due to competition for p back bonding from the metal d orbitals, so the stereochemistry trans(Cl),cis(CO) is assumed.The addition of the second bidentate compound pp9 to the complex [Os(pp)(CO)2Cl2] was achieved after the conversion of 2 into the bis(trifluoromethanesulfonato) species [Os(pp)- (CO)2(CF3SO3)2] 3. Compound 2 and trifluoromethaneslfonic acid were allowed to react in 1,2-dichlorobenzene at 120 8C,19 and 3 was obtained in yields of 78 (pp = bipy) and 94% (pp = dmbipy) after purification.The grey solid material showed two CO stretching bands (2076 and 1986 cm21 for pp = bipy and 2071 and 1993 cm21 for pp = dmbipy) in the IR spectrum. Infrared characteristics of co-ordinated trifluoromethanesulfonate were also observed: 20,21 n& SO at 1346 and 1163 cm21 (pp = bipy) and 1330 and 1170 cm21 (pp = dmbipy) as well as n& CF at 1236 and 1200 cm21 (pp = bipy) and 1237 and 1208 cm21 (pp = dmbipy). According to the 1H NMR spectra, [Os(pp)(CO)2(CF3SO3)2] possesses a cis(CO),cis(CF3SO3) geometry, based on the inequivalence of the two pyridyl rings in the pp ligand.The reaction of compound 3 with a second bidentate compound pp9 in 2-methoxyethanol (120 8C) led to [Os(pp)- (pp9)(CO)2]2+ 4 in yields of 40–60%. The purity was checked K2[OsIVCl6] æÆ (i) osmium carbonyl polymer 1 | (ii) |Ø [Os(pp)(CO)2(CF3SO3)2] 3 �æ (iii) [Os(pp)(COCl2] 2 | (iv) |Ø [Os(pp)(pp9)(CO)2]2+ 4 æÆ (v) [Os(pp)(pp9)(pp0)]2+ 5 Scheme 1 Synthetic strategy for tris(heteroleptic) complexes.pp = bipy, dmbipy; pp9 = bipy, dmbipy, tmbipy, phen, dmphen; pp0 = bipy, dmphen, phen, bdebipy, bpm. (i) Formic acid-formaldehyde, 2–3 d; (ii) pp, ethanol, microwave oven, 30 min; (iii) CF3SO3H, 1,2- dichlorobenzene, 3 h; (iv) pp9, 2-methoxyethanol, 3 h; (v) pp0, Et3NO, 2- methoxyethanol primarily by 1H NMR spectroscopy, and from a combination of NMR and IR spectroscopic studies there was no suggestion of the formation of the trans(CO) isomer: for example, in the case of [Os(bipy)(dmbipy)(CO)2]2+, the 1H NMR spectrum showed two magnetically non-equivalent singlet methyl resonances, with an additional 14 distinct signals in the aromatic region.The decarbonylation of compound 4 with trimethylamine N-oxide in the presence of a third bidentate compound pp0 produced tris(heteroleptic)osmium(II) complexes 5. Purification was achieved by cation-exchange chromatography (SP Sephadex C25 absorbent; 0.2 mol dm23 sodium chloride or 0.125 mol dm23 sodium toluene-p-sulfonate solution as eluent), and [Os(pp)(pp9)(pp0)]2+ species 5 were isolated in variable yields depending on the ligand pp and pp9. The yields obtained for the osmium(II) complexes (10–40%) were generally lower than those obtained for the ruthenium(II) analogues.2 The microanalyses of representative examples of the intermediate species, and of the tris(heteroleptic) target compounds, are provided in the Experimental section.The tris(heteroleptic) complexes were examined and characterized by several physical methods. Electrospray mass spectroscopy The ESMS measurements were undertaken on representative examples of the dicarbonyl (4) and tris(heteroleptic) species (5) to verify the characterization. For each of the complexes [Os- (dmbipy)(bipy)(CO)2][PF6]2 4a, [Os(dmbipy)(dmphen)(CO)2]- [PF6]2 4c and [Os(dmbipy)(bipy)(dmphen)][PF6]2 5a, a m/z peak corresponding to the loss of one PF6 2 anion was obtained. For the complex 4a two signals at m/z = 433 and 405 were also observed, corresponding to the ions [Os(dmbipy)(CO)2H]+ and [Os(bipy)(CO)2H]+, respectively. NMR spectroscopy Owing to the low symmetry (C1) of the tris(heteroleptic) complexes, the 1H NMR spectra can be relatively complicated.2 However, in the cases where the three ligands are derivatives of the same basic ligand structure (e.g.bipy), the ‘pseudosymmetry’ provided by the three parent bipy rings leads to a simplified spectrum because of the overlap of resonances,2 whereas if pp9 or pp0 differ from a bipy-derived structure the spectrum shows a more complex pattern.The complex [Os(dm-J. Chem. Soc., Dalton Trans., 1997, Pages 153–159 155 Fig. 1 Chemical shifts and coupling constants of the ligands in the tris(heteroleptic) complex [Os(dmbipy)(bipy)(tmbipy)][PF6]2 5c bipy)(bipy)(tmbipy)][PF6]2 5c is taken as an example for discussion: while in principle there are 18 different environments for the aromatic protons, only 9 signals are observed because in each ligand the two constituent rings are similar and their resonances overlap.The aromatic protons associated with the dmbipy and tmbipy ligands are shifted to high field compared with those of 2,29-bipyridine, as a consequence of a combination of inductive and anisotropic effects.8 The assignments were achieved by decoupling and correlation spectroscopy (COSY) experiments.Fig. 1 shows the three ligands with their respective chemical shifts and coupling constants for the complex 5c. The separation of the magnetically non-equivalent methyl resonances for the tris(heteroleptic) complexes 5 is significantly smaller (Dd < 0.02 ppm) than that observed for the bis(heteroleptic) dicarbonyl compounds 4. For the latter series, well separated singlet resonances are observed in the aliphatic region of the spectrum (Dd < 0.37 ppm). Such phenomena are based on differences in the p-acceptor characteristics and anisotropic effects of the CO and pp0 ligands, and have also been observed for the analogous ruthenium(II) complexes.2,8 Table 1 Electrochemical properties of the tris(heteroleptic)osmium(II) complexes E��� b/V vs.SSCE Complex a Oxidation Reduction DE��� c [Os(bipy)3]2+ 5a [Os(dmbipy)(bipy)(dmphen)]2+ 5b [Os(dmbipy)(bipy)(phen)]2+ 5c [Os(dmbipy)(bipy)(tmbipy)]2+ 5d [Os(dmbipy)(bipy)(bpm)]2+ 5e [Os(dmbipy)(bipy)(bdebipy)]2+ +0.81 +0.74 +0.79 +0.70 +0.92 +0.46 21.29 21.46 21.79 21.33 21.55 21.84 21.29 21.51 21.82 21.34 21.59 21.93 20.99 21.42 21.70 21.40 21.67 2.10 2.08 2.08 2.05 1.91 1.87 a As PF6 2 salts.b Acetonitrile–0.1 mol dm23 NBun 4PF6 solution; platinum-button working electrode; 298 K; scan rate 100 mV s21; Ag– Ag+ reference electrode (quoted vs. SSCE as reference, which is 0.310 V cathodic of Ag–Ag+). c DE��� = E��� (OsIII/II) 2 E��� (first ligand reduced). Electrochemical studies Cyclic voltamograms of the tris(heteroleptic)osmium(II) complexes clearly show the metal-based oxidation and a series of reductions associated with the ligands.The ligand-based reductions occur in a stepwise manner to each ligand p* system, with the order of the reduction correlating with the ease of reduction of the unco-ordinated pro-ligands. The respective E��� values for all tris(heteroleptic) complexes synthesized in this work are given in Table 1: in all cases, DEp were in the range 70–90 mV, so that the couples are essentially reversible.In the case of [Os(dmbipy)(bipy)(bdebipy)]2+ 5e only two of the three reductions were observed, presumably because the p* energy level of (bdebipy) is raised so that reduction is too cathodic to be accessible under the experimental conditions. For the same complex it is also noted that the OsIV–OsIII couple can be observed at E��� ª 1.24 V, although the couple is only quasireversible (DEp ª 120 mV).There have been a number of recent proposals for the use of a ‘ligand electrochemical series’ in prediction of the oxidation and reduction potentials of metal complexes.12,22 In the approach by Lever and co-workers 12 the fundamental electrochemical parameter [EL(L)] for each ligand L is defined as onesixth the potential for the RuIII–RuII couple for RuL6 in acetonitrile solution. The metal-based couple of any complex is postulated 12a to obey the relationship (1) where SM and IM are Eobs = SMoEL(L) + IM (1) constants for a particular metal.For the first ligand-based reduction process, there is a similar relationship 12b (2). An Ered = SLoEL(L) + IL (2) implication of the use of the parameter EL(L) in this way is that all ligands behave in the same way when attached to different metal centres, and also to the same metal centre in circumstances where the other ligands may be widely varied in terms of their s-donor and p-donor/acceptor characteristics.While some studies have been done using osmium complexes, the availability of tris(heteroleptic) species makes possible a much broader testing of the hypothesis. For the metal-based OsIII–OsII couples the values of SM and IM [equation (1)] have been reported as 1.01 and 20.40, respectively, in organic solvents such as acetonitrile.12a For the present series of complexes a plot of Eobs vs. o EL(L) is a straight line (R = 0.99) with SM = 1.03 and IM = 20.50 (Fig. 2). The discrep-156 J. Chem. Soc., Dalton Trans., 1997, Pages 153–159 ancy between this value of IM and that previously reported is interesting as the present value actually leads to an improved predictive use of equation (1) for calculating values of the redox potential for OsIII–OsII couples for many of the species listed in the original work.12a The contributions of the ligands to the overall potential appears to be additive, with no significant synergism between them. For the ligand-based reduction processes, the values of SL and IL [equation (2)] of Os(pp) may be deduced from electrochemical data following the assumption of the assignment of the most reducible ligand.In previous studies the values for Os(bipy) (SL = 0.27; IL = 21.38) 12b have been repod can be assumed as the site of reduction for the complexes [Os(bipy)3]2+ and [Os(dmbipy)- (bipy)L]2+ (L = dmphen, tmbipy or bdebipy) and the plot is a straight line (R = 0.994) with SL = 0.29 and IL = 21.33.Again, these values lead to an improved use of equation (2) for calculating values of the redox potential for the first reduction of many of the osmium complexes listed in the original work.12b Electronic spectroscopy The archetype of tris(bidentate ligand)osmium(II) complexes of the present type is [Os(bipy)3]2+. A broad and weak absorption band around 580 nm is assigned to arise from a spin-forbidden 3m.l.c.t. (metal-to-ligand charge-transfer) transition; 1m.l.c.t.(dp æÆ p1*) absorptions are located in the domain between 370 and 480 nm as well as in the UV range (dp æÆ p2*) and further absorptions in the UV range are associated with ligandcentred p æÆ p* transitions.23–26 The UV/VIS data for the tris(heteroleptic) species synthesized in this work are presented in the Experimental section, and representative spectra are shown in Fig. 3 for the series of complexes [Os(dmbipy)- (bipy)L]2+ (where L = bpm, tmbipy or bdebipy).In earlier studies from our laboratory it was reported that the variation of the ligand environment in analogous ruthenium complexes allowed systematic control of the spectral and electrochemical characteristics of the complexes because of the ability to ‘tune’ the dp and p* energy levels.3 The two approaches taken to the problem of shifting absorption to the red end of the spectrum were either to add electronwithdrawing groups to a polypyridyl ligand to lower p*,12,19,27,28 or to stabilize the ‘hole’ at RuIII in the m.l.c.t.state by introducing electron-donating ligands.29,30 This strategy was useful in designing potential photosensitizers with broad-band absorption (‘black absorbers’), complexes with desired redox characteristics, 3 and complexes with controllable photophysical properties, particularly with regard to lifetimes and photoinertness. In Fig. 3 it can be observed that as the p* level of the ligand L in the series of complexes [Os(dmbipy)(bipy)L]2+ is raised (i.e.Fig. 2 Plot of Eobs (redox potential for OsIII–OsII couple) as a function of o (EL) (the sum of the ‘electrochemical ligand parameters’). Complexes: 1, 5e; 2, 5c; 3, 5a; 4, 5b; 5, [Os(bipy)3]2+; 6, 5d bpm < tmbipy < bdebipy) there is a bathochromic shift in the m.l.c.t. absorptions. This is in fact opposite to the trend observed for similar series of ruthenium complexes.2,3 The contrast is interesting. For both metal centres it is observed that as the ligand L becomes more readily reducible the p* level and the dp level are lowered.This is seen in electrochemical studies of the respective trends in the reduction and oxidation potentials of their complexes. Furthermore, the trend in reduction potentials is closely similar for the same ligands, regardless of the identity of the metal centre. The correlation between the OsIII–OsII potential and the energy of the lowest spin-allowed m.l.c.t.transition is shown in Fig. 4. In a manner consistent with previous observations,11 we observe a shift of the lowestlying 1m.l.c.t. bands towards higher energies as the OsIII–OsII couple is shifted to higher potentials, which is not consistent with the results for analogous ruthenium species. Since the directional trends of the dependence of the p* and dp energy levels on the identity of ligands correspond for the two metal centres, it would appear that the ligands have a more significant effect on the dp levels in the case of Os, leading to the observed reversal of the energy of the dp æÆ p* transition as the p* level varies.Accordingly, from the present data the dp levels appear to determine the absorption in the visible domain of the spectra. Such a result is consistent with the notion that the osmium centre has greater orbital extension, but a wider range of the tris(heteroleptic) complexes would need to be investigated to confirm these observations.Fig. 3 The UV/VIS absorption spectra of [Os(dmbipy)(bipy)- (bpm)][PF6]2 (– – –), [Os(dmbipy)(bipy)(bdebipy)][PF6]2 (——) and [Os(dmbipy)(bipy)(tmbipy)][PF6]2 (······) in acetonitrile solution Fig. 4 Charge-transfer band energies for the lowest-energy 1m.l.c.t. transition as a function of E��� for the OsIII–OsII couple. Data are taken from Tables 2 and 3. Complexes as in Fig. 2J. Chem. Soc., Dalton Trans., 1997, Pages 153–159 157 Experimental The UV/VIS spectra were recorded on a Cary 5E UV-visible- NIR spectrophotometer, NMR spectra on a Bruker AM3000 spectrometer, and infrared spectra on a Perkin-Elmer Series 1600 FTIR spectrometer.Electrochemical measurements were made in a dry-box (Ar) using a Bioanalytical Systems (BAS) 100A Electrochemical Analyzer. Unless otherwise indicated, cyclic voltammetry was carried out by using platinum working electrodes, and all potentials were measured relative to an Ag– AgNO3 (0.01 mol dm23 in acetonitrile) reference electrode.Potentials are quoted relative to a saturated sodium chloride calomel electrode (SSCE, which is 310 mV cathodic of Ag– Ag+), unless otherwise specified. Electrospray mass spectra were recorded using methods previously described.31 Materials The salt K2[OsCl6] (Strem), formic acid (BDH: AnalaR, 90%), FeCl2?4H2O (AJAX Chemicals) and 1,2-dimethoxyethanol (Fluka, puriss) were used without further purification. Trifluoromethanesulfonic acid (3 M) was distilled under vacuum before use.Trimethylamine N-oxide was obtained by vacuum sublimation of the hydrate (Fluka, purum) at 120 8C. The proligands were used as supplied, or obtained from reported synthetic routes. Reagent solvents were used without further purifi- cation. For UV/VIS spectroscopy, HPLC-grade acetonitrile (Sigma-Aldrich) was used. The compound bdebipy was kindly donated by P. Besler (Université de Fribourg Suisse). Syntheses [{Os(CO)xCly}n] 1. Formaldehyde (5 cm3) and K2[OsCl6] (1 g, 2.08 mmol) were added to a N2-sparged solution of formic acid (90%, 50 cm3).The solution was refluxed for 3 d: it changed from red-orange to brown-green within 1 h, to light green after 3 h, and ultimately to light yellow. It was allowed to cool to room temperature, then stored at 4 8C overnight. The solution was evaporated to dryness using an oil-bath (105 8C), the residue triturated with hexane and diethyl ether, and then dissolved in acetone to remove KCl.After filtration, the filtrate was evaporated to dryness, and the solid dried in vacuo. Yield: 840 mg; IR (Nujol): n& CO = 2114, 2053, 2015, 1968 and 1927 cm21 (Found: C, 6.2; Cl, 21.9%). trans(Cl)-[Os(pp)(CO)2Cl2] 2. In a typical synthesis, [{Os(CO)xCly}n] (200 mg) and dmbipy (115 mg, 0.620 mmol) were dissolved in 95% ethanol (40 cm3), and the reaction mixture heated for 3 × 10 min intervals in a microwave oven (Sharp Carousel, medium power level). The volume of the solution was reduced to half, and the precipitated yellow solid was filtered off and washed with cold methanol.The procedure of volume reduction of the filtrate was repeated, with separation of further fractions. The excess of free pro-ligand was removed by adding a saturated methanolic solution of FeCl2?4H2O to the filtrate until no further red colouration was observed, followed by column chromatography (Sephadex LH20, methanol eluent). The combined light yellow, TLC-pure solid material was dried in vacuo.The absence of the ligand was confirmed by 1H NMR spectroscopy and TLC [silica gel absorbent, ethanol–water–sodium chloride (1 : 1 : 0.1 mol dm23) eluent]. [Os(dmbipy)(CO)2Cl2] 2a: yield 70% (Found: C, 33.2; H, 2.2; N, 5.3. C14H12Cl2N2O2Os requires C, 33.5; H, 2.4; N, 5.6%); IR(Nujol) n& CO = 2037 and 1933 cm21; 1H NMR (CDCl3): d 8.90 [d, 2 H, H6, J(H5H6) = 5.5], 8.00 (s, 2 H, H3), 7.42 [d, 2 H, H5, J(H5H6) = 5.5 Hz] and 2.70 (s, 6 H, CH3).[Os(bipy)(CO)2Cl2] 2b: yield 60%; IR(Nujol) n& CO = 2021 and 1942 cm21; 1H NMR (CD3CN): d 9.08 [d, 2 H,(H5H6) = 5.6], 8.48 [d, 2 H, H3, J(H3H4) = 8.1], 8.27 [dd, 2 H, H4, J(H3H4) = 8.1, J(H4H5) = 7.7, J(H4H6) = 1.2] and 7.76 [dd, 2 H, H5, J(H5H6) = 5.6, J(H4H5) = 7.7, J(H3H5) = 1.2 Hz] [Os(phen)(CO)2Cl2] 2c: yield 70%; IR(Nujol) n& CO = 2035 and 1978 cm21; 1H NMR (CDCl3): d 9.44 [d, 2 H, H2, H9, J(H2H3) = J(H9H10) = 5.5], 8.60 [d, 2 H, H4, H7, J(H3H4) = J(H7H8) = 8.3], 8.00 (s, 2 H, H11, H12) and 7.97 [dd, 2 H, H3, H8, J(H2H3) = J(H8H9) = 5.5, J(H7H8) = J(H3H4) = 8.3 Hz].cis,cis-[Os(pp)(CO)2(CF3SO3)2] 3. In a typical experiment, [Os(dmbipy)(CO)2Cl2] (100 mg, 0.199 mmol) was dissolved in 1,2-dichlorobenzene (50 cm3), the solution sparged for 40 min with N2, trifluoromethanesulfonic acid (0.5 cm3) added, and the solution then heated for 3 h at 120 8C. After cooling to room temperature, the solution was stirred for 1 h at 0 8C.The complex was precipitated by addition of diethyl ether, the mixture being stored overnight in a freezer before filtration. The solid product was washed with cold water and diethyl ether, and dried at room temperature in vacuo. [Os(dmbipy)(CO)2(CF3SO3)2] 3a: yield 94%; IR(Nujol) 2071 and 1993 cm21 (n& CO), 1330 and 1170 (n& SO), 1237 and 1208 cm21 (n& CF); 1H NMR (CD3CN): d 8.79 [d, 1 H, H6, J(H5H6) = 6.0], 8.65 [d, 1 H, H69, J(H59H69) = 6.0], 8.38 (s, 1 H, H39), 8.32 (s, 1 H, H3), 7.77 [d, 1 H, H59, J(H59H69) = 6.0], 7.45 [d, 1 H, H5, J(H5H6) = 6.0 Hz], 2.64 (s, 3 H, CH3) and 2.62 (s, 3 H, CH3).[Os(bipy)(CO)2(CF3SO3)2] 3b: yield 78%; IR(Nujol) 2076 and 1986 (n& CO), 1346 and 1163 (n& SO), 1236 and 1200 cm21 (n& CF); 1H NMR (CD3CN): d 9.00 [d, 1 H, H6, J(H5H6) = 6.0], 8.85 [d, 1 H, H69, J(H59H69) = 6.0], 8.55 [d, 1 H, H39, J(H39H49) = 8.2], 8.46 [d, 1 H, H3, J(H3H4) = 8.2], 8.42 [dd, 1 H, H49, J(H39H49) = 8.2, J(H49H59) = 7.7, J(H49H69) = 1.6], 8.26 [dd, 1 H, H4, J(H3H4) = 8.2, J(H4H5) = 7.7, J(H4H6) = 1.6], 7.98 [dd, 1 H, H59, J(H49H59) = 7.7, J(H59H69) = 5.0, J(H39H59) = 1.6], and 7.62 [dd, 1 H, H5, J(H4H5) = 7.7, J(H5H6) = 6.0, J(H3H5) = 1.6 Hz].[Os(phen)(CO)2(CF3SO3)2] 3c: yield 73%; IR(Nujol) 2067 and 1998 (n& CO), 1336 and 1169 (n& SO), 1240 and 1208 cm21 (n& CF); 1H NMR (CD3CN): d 9.36 [d, 1 H, H2, J(H2H3) = 5.5], 9.20 [d, 1 H, H9, J(H8H9) = 4.9], 8.97 [d, 1 H, H7, J(H7H8) = 8.2], 8.83 [d, 1 H, H4, J(H3H4) = 8.3], 8.33–8.20 (2s, dd, 3 H, H5, H6, H8) and 7.95 [dd, 1 H, H3, J(H3H4) = 8.3, J(H2H3) = 5.5 Hz]. [Os(pp)(pp9)(CO)2][PF6]2 4.In a typical synthesis, [Os(dmbipy)( CO)2(CF3SO3)2] (50 mg, 0.068 mmol) and bipy (21.4 mg, 0.136 mmol) were dissolved in 2-methoxyethanol (20 cm3) and the solution heated under reflux for 3 h. After evaporation to dryness, the brownish residue was dissolved in boiling water and the mixture filtered to remove the excess of pro-ligand.The complex was precipitated as the PF6 2 salt by adding a saturated solution of KPF6 to the filtrate. The light yellow solid was filtered off and washed with water and diethyl ether. The crude product was purified by column chromatography (Sephadex LH20 absorbent, methanol eluent). Recrystallization from acetonitrile–diethyl ether led to light yellow, feathery crystals. [Os(dmbipy)(bipy)(CO)2][PF6]2 4a: yield 58% (Found: C, 33.0; H, 2.25; N, 6.2.C24H20F12N4O2OsP2 requires C, 32.9; H, 2.30; N, 6.4%); IR(Nujol) n& CO = 2078 and 2009 cm21; 1H NMR (CD3CN): d 9.26 [d, 1 H, H60, J(H50H60) = 5.6, J(H40H60) = 1.2], 9.06 [d, 1 H, H69, J(H59H69) = 5.6], 8.61 [d, 1 H, H30, J(H30H40) = 8.1], 8.52–8.43 [dd, d, s, 3 H, H40, H39, H3-], 8.33 (s, 1 H, H3), 8.23 [dd, 1 H, H4-, J(H3-H4-) = 8.1, J(H4-H5-) = 7.6, J(H4-H6-) = 1.6], 7.90 [dd, 1 H, H50, J(H40H50) = 7.6, J(H50H60) = 5.6], 7.54 [dd, 1 H, H5-, J(H4-H5-) = 7.6, J(H5-H6-) = 6.0, J(H3-H5-) = 1.6], 7.38 [d, 1 H, H6-, J(H5-H6-) = 5.6], 7.34 [d, 1 H, H5, J(H5H6) = 6.0], 7.22 [d, 1 H, H6, J(H5H6) = 6.0 Hz], 2.75 (s, 3 H, CH39) and 2.50 (s, 3 H, CH3).[Os(dmbipy)(dmbipy)(CO)2]- [PF6]2 4b: yield 67% (Found: C, 37.1; H, 2.90; N, 5.8%. C28- H28F12N4O2OsP2 requires C, 36.1; H, 3.05; N, 6.0%); IR(Nujol) n& CO = 2070 and 2005 cm21; 1H NMR (CD3CN): d 9.04 [d, 1 H, H69, J(H59H69) = 5.5], 8.77 (s, 1 H, H6-), 8.43 (s, 1 H, H39), 8.31158 J. Chem. Soc., Dalton Trans., 1997, Pages 153–159 (2s, 2 H, H3, H3-), 8.22 (s, 1 H, H30), 7.70 [d, 1 H, H59, J(H59H69) = 5.5], 7.32 [d, 1 H, H5, J(H5H6) = 6.0 Hz], 7.27 [d, 1 H, H6, J(H5H6) = 6.0 Hz], 6.95 (s, 1 H, H60), 2.73 [s, 3 H, CH3(49)], 2.60 [s, 3 H, CH3(4-)], 2.50 [s, 3 H, CH3(4)] 2.47 [s, 3 H, CH3(5-)], 2.41 [s, 3 H, CH3(40)] and 2.04 [s, 3 H, CH3(50)].[Os(dmbipy)(dmphen)(CO)2][PF6]2 4c: yield 43%; IR(Nujol) n& CO = 2083 and 2015 cm21; 1H NMR (CD3CN): d 9.45 [d, 1 H, H90, J(H80H90) = 6.0], 9.15 [d, 1 H, H6, J(H5H6) = 6.0], 8.47 (s, 2 H, H39), 8.45 (s, 1 H, H12), 8.39 (s, 1 H, H11), 8.31 (s, 1 H, H3), 8.04 [d, 1 H, H80, J(H80H90) = 6.0], 7.75 [d, 1 H, H59, J(H59H69) = 6.0], 7.65 [d, 1 H, H30, J(H20H30) = 5.5], 7.58 [d, 1 H, H20, J(H20H30) = 5.5], 7.12 [d, 1 H, H5, J(H5H6) = 6.0], 7.02 [d, 1 H, H6, J(H5H6) = 6.0 Hz], 3.11 [s, 3 H, CH3(70)], 2.90 [s, 3 H, CH3(49)], 2.75 [s, 3 H, CH3(40)] and 2.41 [s, 3 H, CH3(4)].[Os- (dmbipy)(phen)(CO)2][PF6]2 4d: yield 63% (Found: C, 34.8; H, 2.15; N, 6.1.C26H20F12N4O2OsP2 requires C, 34.7; H, 2.35; N, 6.2%); IR(Nujol) n& CO = 2076 and 2008 cm21; 1H NMR (CD3CN): d 9.62 [d, 1 H, H90, J(H80H90) = 5.2], 9.15 [d, 1 H, H6, J(H5H6) = 5.5], 9.03 [d, 1 H, H70, J(H70H80) = 8.2], 8.79 [d, 1 H, H40, J(H30H40) = 8.2], 8.49 (s, 1 H, H3), 8.40 (3s, d, dd, 5 H, H5, H50, H60, H39, H80), 7.83 [dd, 1 H, H30, 3J(H30H40) = 8.2, J(H20H30) = 5.0], 7.75 [2d, 2 H, H20, H5, J(H20H30) = 5.0, J(H5H6) = 5.5], 7.11 [d, 1 H, H59, J(H59H69) = 5.1], 7.05 [d, 1 H, H69, J(H59H69) = 5.1 Hz], 2.75 (s, 3 H, CH3) and 2.41 (s, 3 H, CH3).[Os(pp)(pp9)(pp0)][PF6]2 5. The compound [Os(dmbipy)- (dmphen)(CO)2][PF6]2 (20 mg, 0.022 mmol) and bipy (10.1 mg, 0.066 mmol) were dissolved in dry 2-methoxyethanol (6 cm3), and a six-fold excess of trimethylamine N-oxide (9.9 mg, 0.132 mmol) was added. The almost colourless solution turned dark green within 10 min. It was heated at reflux for 3 h. After evaporation to dryness the residue was dissolved in hot water, and the solution filtered to eliminate the excess of pro-ligand. The filtrate was applied to a column of SP-Sephadex C25 cation exchanger, eluted with 0.2 mol dm23 NaCl, and the product precipitated by addition of a saturated aqueous solution of KPF6 to the eluent containing the major band.The solid was collected on a low-porosity frit, and then washed with water (5 cm3) and diethyl ether. Recrystallization of the green complex was achieved from acetonitrile–diethyl ether.Yield: 40%. [Os(dmbipy)(bipy)(dmphen)][PF6]2 5a: yield 40% (Found: C, 41.0; H, 3.3; N, 7.6. C36H32F12N6OsP2 requires C, 41.3; H, 3.1; N, 8.1%); 1H NMR (CD3CN): d 8.45 (dd, 2 H), 8.37–8.27 (m, 4 H), 7.88–7.65 (m, 5 H), 7.75–7.38 (m, 4 H), 7.30 (dd, 1 H), 7.22 (d, 1 H), 7.15 (d, 1 H), 7.06 (dd, 1 H), 6.94 (d, 1 H), 2.98 (s, 3 H, CH3), 2.96 (s, 3 H, CH3), 2.70 (s, 3 H, CH3) and 2.45 (s, 3 H, CH3); UV/VIS [acetonitrile, l/nm (e/dm3 mol21 cm21)] 206 (71 700), 232 (37 400), 266 (57 700), 290 (63 400), 370 (8780), 408 (12 300), 438 (15 900), 484 (15 500) and 546 (4900).[Os(dmbipy)(bipy)(phen)][PF6]2 5b: yield 26%; 1H NMR (CD3CN): d 8.48 (d, 1 H), 8.43 (d, 1 H), 8.40–8.28 (m, 4 H), 8.21 (s, 2 H), 7.98 (d, 2 H), 7.82 (dd, 1 H), 7.74 (dd, 2 H), 7.64 (m, 2 H), 7.54 (d, 1 H), 7.40 (d, 1 H), 7.33 (dd, 1 H), 7.20 (2d, 2 H), 7.07 (dd, 1 H), 6.95 (d, 1 H), 2.62 (s, 3 H, CH3) and 2.52 (s, 3 H, CH3); UV/VIS [acetonitrile, l/nm (e/dm3 mol21 cm21)] 202 (57 500), 268 (45 800), 290 (54 100), 364 (6780), 394 (8300), 434 (12 200), 484 (12 500) and 564 (3490).[Os(dmbipy)- (bipy)(tmbipy)][PF6]2?H2O 5c: yield 32% (Found: C, 41.0; H, 3.3; N, 7.6. C36H38F12N6OsP2 requires C, 41.1; H, 3.45; N, 8.0%); 1H NMR (CD3CN): d 8.42 [d, 1 H, H3, J(H3H4) = 8.2], 8.41 [d, 1 H, H3I, J(H3IH4I) = 8.2], 8.29 (s, 1 H, H3II), 8.27 (s, 1 H, H3III), 8.19 (s, 1 H, H3IV), 8.18 (s, 1 H, H3V), 7.78 [2dd, 2 H, H4, H49, J(H3H4) = J(H3IH4I) = 8.2], 7.60 [d, 2 H, H6, H6I, J(H5H6) = J(H5IH6I) = 5.5], 7.38 [d, 2 H, H6II, H6III, J(H5IIH6II) = J(H5IIIH6III) = 5.5], 7.27–7.19 [2d, 2s, H5, H59, H6IV, H6V, J(H5H6) = J(H5IH6I) = 5.5], 7.11 [2d, 2 H, H5II, H5III, J(H5IIH6II) = J(H5IIIH6III) = 5.5 Hz], 2.59 [s, 3 H, CH3(4II)], 2.57 [s, 3 H, CH3(4III)], 2.49 [s, 3 H, CH3(4IV)], 2.48 [s, 3 H, CH3(4V)], 2.07 [s, 3 H, CH3(5IV)] and 2.05 [s, 3 H, CH3(5V)]; UV/VIS [acetonitrile, l/nm (e/dm3 mol21 cm21)] 206 (59 800), 252 (26 100), 256 (26 800), 292 (88 600), 332 (10 900), 374 (11 700), 424 (10 800), 448 (13 300), 484 (13 600) and 600 (4430). [Os- (dmbipy)(bipy)(bpm)][PF6]2?2Et2O 5d: yield 10% (Found: C, 40.1; H, 3.45; N, 9.5.C38H46F12N8O2OsP2 requires C, 40.5; H, 3.2; N, 9.9%); 1H NMR (CD3CN): d 8.98 (2d, 2 H), 8.81 (2d, 2 H), 8.67 (s, 2 H), 8.42 (2dd, 2 H), 8.,19 (d, 1 H), 8.10–7.92 (m, 5 H), 7.73 (d, 1 H), 7.64–7.46 (m, 4 H), 7.37 (d, 2 H) and 2.62 (s, 6 H, 2CH3); UV/VIS [acetonitrile, l/nm (e/dm3 mol21 cm21)] 200 (52 700), 244 (27 200), 288 (45 100), 364 (9380), 438 (10 100) and 574 (3000). [Os(dmbipy)(bipy)(bdebipy)][PF6]2 5e: yield 33%; 1H NMR (CD3CN): d 8.38 (2d, 2 H), 8.30 (s, 1 H), 8.25 (s, 1 H), 7.85 (d, 1 H), 7.72–7.56 (m, 4 H), 7.39 (d, 1 H), 7.35–7.23 (m, 3 H), 7.18 (d, 1 H), 7.14 (dd, 1 H), 7.00 (d, 1 H), 6.83 (2d, 2 H), 6.45 (m, 2 H), 3.50 (4q, 8 H, CH2 of Et2N), 2.63 (s, 3 H, CH3), 2.52 (s, 3 H, CH3) and 1.15 (4t, 12 H, CH3 of Et2N); UV/VIS [acetonitrile, l/nm (e/dm3 mol21 cm21)]: 206 (57 000), 262 (56 300), 286 (58 500), 294 (63 500), 336 (20 100), 394 (12 400), 468 (11 600), 512 (11 200) and 620 (2920).Acknowledgements This research was supported by the Australian Research Council. We thank Dr Ray Colton (La Trobe University) for the ESMS measurements. E. Z. J. acknowledges financial support from the Swiss National Science Foundation in the form of a Postdoctoral Fellowship for his sojourn at James Cook University.We are grateful to Mr Laurie Kelso and Mr Todd Rutherford for valuable discussions, Mr Mick Henderson for his experimental contribution, and Dr Bruce Bowden and Mr David Reitsma for assistance with the COSY experiments. References 1 G. F. Strouse, P. A. Anderson, J. R. Schoonover, T. J. Meyer and F. R. Keene, Inorg. Chem., 1992, 31, 3004. 2 P. A. Anderson, G. B. Deacon, K. H. Haarmann, F. R. Keene, T. J. Meyer, D. A. Reitsma, B. W. Skelton, G. F. Strouse, N.C. Thomas, J. A. Treadway and A. H. White, Inorg. Chem., 1995, 34, 6145. 3 P. A. Anderson, G. F. Strouse, J. A. Treadway, F. R. Keene and T. J. Meyer, Inorg. Chem., 1994, 33, 3863. 4 J. A. Treadway, B. Loeb, R. Lopez, P. A. Anderson, F. R. Keene and T. J. Meyer, Inorg. Chem., 1996, 35, 2242. 5 D. A. Reitsma and F. R. Keene, J. Chem. Soc., Dalton Trans., 1993, 2859. 6 T. J. Rutherford, M. G. Quagliotto and F. R. Keene, Inorg. Chem., 1995, 34, 3857. 7 T. J. Rutherford and F.R. Keene, unpublished work. 8 T. J. Rutherford, D. A. Reitsma and F. R. Keene, J. Chem. Soc., Dalton Trans., 1994, 3659. 9 J. V. Casper, B. P. Sullivan, E. M. Kober and T. J. Meyer, Chem. Phys. Lett., 1982, 91, 91. 10 E. M. Kober, J. C. Marshall, W. J. Dressick, B. P. Sullivan, J. V. Casper and T. J. Meyer, Inorg. Chem., 1985, 24, 2755. 11 E. M. Kober, J. V. Casper, B. P. Sullivan and T. J. Meyer, Inorg. Chem., 1988, 27, 4587. 12 (a) A. B. P. Lever, Inorg. Chem., 1990, 29, 1271; (b) E. S. Dodsworth, A. A. Vlcek and A. B. P. Lever, Inorg. Chem., 1994, 33, 1045. 13 A. A. Vlcek, E. S. Dodsworth, W. J. Pietro and A. B. P. Lever, Inorg. Chem., 1995, 34, 1906. 14 S. S. Fielder, M. C. Osborne, A. B. P. Lever and W. J. Pietro, J. Am. Chem. Soc., 1995, 117, 6990. 15 D. A. Buckingham, F. P. Dwyer, H. A. Goodwin and A. M. Sargeson, Aust. J. Chem., 1964, 17, 315. 16 D. M. P. Mingos and D. R. D. Baghurst, Chem. Soc. Rev., 1991, 20, 1. 17 J. P. Collins and W. R. Roper, J. Am. Chem. Soc., 1966, 88, 3504. 18 F. H. Johannsen, W. Preetz and A. Scheffler, J. Organomet. Chem., 1975, 102, 527. 19 B. P. Sullivan, J. V. Caspar, S. R. Johnson and T. J. Meyer, Organometallics, 1984, 3, 1241. 20 D. S. Black, G. B. Deacon and N. C. Thomas, Polyhedron, 1983, 2, 409.J. Chem. Soc., Dalton Trans., 1997, Pages 153–159 159 21 D. S. Black, G. B. Deacon and N. C. Thomas, Aust. J. Chem., 1982, 35, 2445. 22 E. C. Constable, A. M. W. Cargill Thompson, D. A. Tocher and M. A. M. Daniels, New J. Chem., 1992, 16, 855. 23 J. V. Caspar, T. D. Westmoreland, G. H. Allen, P. G. Bradley, T. J. Meyer and W. H. Woodruff, J. Am. Chem. Soc., 1984, 106, 3492. 24 S. Decurtins, F. Felix, J. Ferguson, H.-U. Güdel and A. Ludi, J. Am. Chem. Soc., 1980, 102, 4102. 25 F. Felix, J. Ferguson, H.-U. Güdel and A. Ludi, Chem. Phys. Lett., 1979, 62, 153. 26 F. Felix, J. Ferguson, H.-U. Güdel and A. Ludi, J. Am. Chem. Soc., 1980, 102, 4096. 27 J. C. Curtis, B. P. Sullivan and T. J. Meyer, Inorg. Chem., 1983, 22, 224. 28 Y. Ohsawa, K. W. Hanck and M. K. De Armond, J. Electroanal. Chem. Interfacial Electrochem., 1984, 175, 229. 29 D. P. Rillema and K. B. Mack, Inorg. Chem., 1982, 21, 3849. 30 D. P. Rillema, C. B. Blanton, R. J. Shaver, D. C. Jackman, M. Boldaji, S. Bundy, L. A. Worl and T. J. Meyer, Inorg. Chem., 1992, 31, 1600. 31 R. Colton and J. C. Traeger, Inorg. Chim. Acta, 1992, 201, 153. Received 23rd July1996; Paper 6/05161H

ISSN:1477-9226    

DOI:10.1039/a605161h

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 155–159 155 Synthesis, structure and redox behaviour of facial [ReIIIL(PPh3)Cl3] and its stereoretentive conversion to [ReIVL9(PPh3)Cl3] via metal promoted aldimine æÆ amide oxidation (L 5 pyridine-2-aldimine; L9 5 pyridine-2-carboxamide) Sibaprasad Bhattacharyya, Sangeeta Banerjee, Bimal Kumar Dirghangi, Mahua Menon and Animesh Chakravorty * Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India Received 11th August 1998, Accepted 29th October 1998 The reaction of mer-[ReIIIL(OPPh3)Cl3] 2 with PPh3 in benzene has aVorded bluish violet fac-[ReIIIL(PPh3)Cl3] 1, where L is the SchiV base of pyridine-2-carbaldehyde and the substituted aniline p-XC6H4NH2 (X = H, Me, OMe or Cl).Geometrical preferences are rationalized in terms of the electronic nature of the ligands OPPh3 (s- and p-donor), PPh3 (s-donor and p-acceptor) and L (s-donor and p-acceptor).The cyclic voltammetric E1/2 values of 1 lie near 0.6 V (ReIV–ReIII) and 20.6 V (ReIII–ReII). Electrooxidation of 1 at 1.0 V vs. SCE in wet acetonitrile aVords yellow fac-[ReIVL9(PPh3)Cl3] 3 which is also obtainable via oxidation by dilute nitric acid (L9 is a monoanionic pyridine-2- carboxamide). Complex 3 displays ReIV–ReIII and ReV–ReIV couples near 20.2 V and 1.4 V respectively reflecting superior stabilization of the rhenium(IV) state by the amide ligand. The X-ray structures of two representative complexes of type 1 and 3 have revealed the presence of severely distorted and facially configured RePN2Cl3 coordination spheres.The average Re–Cl distance is lower by 0.06 Å in 3 due to contraction of the metal radius upon oxidation. The Re–P length is however larger by 0.1 Å in 3 signifying a weakening of Re–P back-bonding. The rhenium chemistry of SchiV bases of pyridine-2- carbaldehyde is under scrutiny in this laboratory. Facile oxygen-atom-transfer, metal-mediated ligand oxidation and stabilization of unusual rhenium moieties are among the notable features that have so far been documented.1–6 In this work we disclose a spontaneous geometrical transformation associated with ligand substitution. The reaction has aVorded a family of pyridine-2-aldimine chelates of trivalent rhenium incorporating phosphine coordination.The species are redox active and undergo facile aldimineæÆ amide oxidation. The structure and properties of the present complexes and their oxidized derivatives are described.Results and discussion Synthesis of fac-[ReL(PPh3)Cl3] 1 Four pyridine-2-aldimine ligands (L1–L4; general abbreviation is L), diVering in the X substituent have been utilized. The complexes have facial geometry (see below) and are formed upon reacting the meridional phosphine oxide complexes of type [ReL(OPPh3)Cl3] 2,1–3 with PPh3, in boiling benzene, N N H Re X Cl Cl Cl PPh3 N N H Re X Cl Cl OPPh3 Cl 1d [ReL4(PPh3)Cl3] (X = Cl) 1c [ReL3(PPh3)Cl3] (X = OMe) 1b [ReL2(PPh3)Cl3] (X = Me) 1a [ReL1(PPh3)Cl3] (X = H) 2 [ReL(OPPh3)Cl3] III III equation (1). The reaction of mer-[ReOCl3(PPh3)2] with L also furnishes 1, equation (2), but in poorer yield.mer-[ReL(OPPh3)Cl3] 1 PPh3 æÆ fac-[ReL(PPh3)Cl3] 1 OPPh3 (1) mer-[ReOCl3(PPh3)2] 1 L æÆ fac-[ReL(PPh3)Cl3] 1 OPPh3 (2) Selected spectral and magnetic characterization data for the complexes are listed in Tables 1 and 2. The magnetic moments (ª2 mB, Table 1) are lower than the spin-only value for the t2g 4 (assuming idealised octahedral geometry) configuration which is not unusual for trivalent rhenium.7 The paramagnetically shifted 1H NMR signals of 1 have been assigned (Table 2) on the basis of signal intensity, spin–spin structure and previous work.8–10 A selected portion of the 1H NMR spectrum of 1b is displayed in Fig. 1. Structure The X-ray structure of fac-[ReL1(PPh3)Cl3] 1a has been determined. A molecular view is shown in Fig. 2 and selected bond parameters are listed in Table 3. The aldimine and phosphine ligands are facially disposed and so are the chloride ligands, forming a severely distorted octahedral RePN2Cl3 coordination sphere. The chelate ring along with the pyridine ring and Cl(2), Cl(3) atoms constitute a good plane (mean deviation 0.05 Å) to which the pendent phenyl ring makes a dihedral angle of 50.18. The X-ray structures of a few ReIII–PPh3 complexes are known.8,11,12 Only one of these has the ReCl3 moiety but in a meridional configuration.8 To the best of our knowledge 1a is the first structurally characterized PPh3 complex having facial ReCl3 disposition.The Re–P distance, 2.463(2) Å in 1a is normal.8,12156 J. Chem. Soc., Dalton Trans., 1999, 155–159 Table 1 Electronic spectral,a IR b and magnetic moment data at 298 K Compound 1a [ReL1(PPh3)Cl3] UV/VIS lmax/nm (e/dm23 mol21 cm21) 1575(260), 665(2085), 525(3250), 405(2985), 300 c(10230) IR n/cm21 320, 335, 510, 700, 1600 meff /mB 2.02 1b [ReL2(PPh3)Cl3] 1575(205), 665(2345), 525(4320), 400(2840), 300 c(10865) 315, 335, 510, 700, 1590 2.10 1c [ReL3(PPh3)Cl3] 1560(370), 670(2530), 525(3820), 400(2910), 300 c(10430) 330, 510, 710, 1595 2.15 1d [ReL4(PPh3)Cl3] 1565(350), 670(2460), 525(3360), 410(2890), 310 c(10000) 320, 500, 700, 1585 2.05 3a [ReL19(PPh3)Cl3] 430(3775), 300(7350) 320, 330, 500, 710, 1600, 1640 3.32 3b [ReL29(PPh3)Cl3] 440(2900), 300(7310) 315, 330, 510, 700, 1610, 1640 3.41 3c [ReL39(PPh3)Cl3] 440(2860), 295(6940) 335, 510, 700, 1605, 1630 3.45 3d [ReL49(PPh3)Cl3] 440(3010), 295(7185) 320, 330, 500, 700, 1610, 1630 3.38 a In dichloromethane.b In KBr disc; n(R–Cl) 310–335, n(C]] N) 1590–1600, n(PPh3) 510, 700, n(C]] O) 1600–1640 cm21. c Shoulder. Geometrical preference The striking geometrical diVerence between 1 and 2 is believed to be of electronic origin. In 1, PPh3 is a p-accepting ligand, the acceptor orbital being a mixture of 3dp and P–C s* components. 13 The L ligand is also p-accepting due to the a-diimine Fig. 1 A part of the proton NMR spectrum of fac-[ReL2(PPh3)Cl3] 1b in CDCl3 solution; o-H, m-H and p-H refer respectively to ortho, meta and para protons of PPh3. Table 2 1H NMR data in CDCl3 d o-H(d) m-H(t) p-H(t) 1-H(d) 2-H(t) 3-H(t) 4-H(d) 6-H(s) 8,12-H(d) 9,11-H(d) 10-H(t) CH3(s) 1a 13.80 8.96 8.73 25.70 211.40 5.23 5.00 246.00 21.35 11.85(t) 7.70 — 1b 13.70 8.96 8.74 24.80 211.00 5.27 4.60 247.60 20.9 11.44 — 3.64 1d 13.50 8.90 8.76 26.70 211.90 5.29 4.70 243.60 21.00 11.62 —— Tetramethylsilane was used as internal standard; s = singlet, d = doublet, t = triplet. function (–N]] C–C]] N–).2,14 Trivalent rhenium is prone to backbonding. 15 Assuming idealised octahedral geometry this bonding has t2g(Re) æÆ p(P) and t2g(Re) æÆ p*(L) components in 1. Back-bonding is maximized when the acceptor ligands are facially disposed so that competition between ligands for identical metal orbitals is minimal.Fig. 2 A view of [ReL1(PPh3)Cl3] 1a; the atoms are represented by their 30% thermal probability ellipsoids. Table 3 Selected bond lengths (Å) and angles (8) for complexes 1a and 3d Re–N(1) Re–N(2) Re–Cl(1) Re–Cl(2) Re–Cl(3) Re–P N(1)–C(5) N(2)–C(6) C(5)–C(6) O(1)–C(6) N(2)–Re–N(1) N(2)–Re–Cl(2) N(1)–Re–Cl(2) N(2)–Re–Cl(1) N(2)–Re–Cl(3) N(1)–Re–Cl(1) N(1)–Re–Cl(3) Cl(2)–Re–Cl(3) Cl(2)–Re–Cl(1) Cl(3)–Re–Cl(1) N(2)–Re–P N(1)–Re–P Cl(2)–Re–P Cl(1)–Re–P Cl(3)–Re–P C(5)–N(1)–Re C(6)–N(2)–Re N(1)–C(5)–C(6) O(1)–C(6)–N(2) 1a 2.103(5) 2.083(5) 2.407(2) 2.350(2) 2.379(2) 2.463(2) 1.371(8) 1.309(8) 1.408(9) — 75.9(2) 99.5(2) 174.1(2) 87.0(2) 167.0(2) 86.3(2) 91.3(2) 93.18(7) 89.74(7) 90.46(8) 93.7(2) 97.0(2) 86.97(7) 176.70(6) 89.55(7) 115.8(4) 116.6(5) 113.5(6) — 3d 2.123(7) 2.061(7) 2.331(3) 2.300(3) 2.345(3) 2.549(3) 1.336(12) 1.349(12) 1.524(13) 1.217(11) 78.2(3) 95.1(2) 173.2(2) 90.2(2) 170.1(2) 86.0(2) 92.0(2) 94.77(11) 94.42(11) 90.53(11) 93.7(2) 90.7(2) 89.37(10) 174.29(9) 84.89(10) 114.5(6) 118.2(6) 116.3(8) 127.1(9)J.Chem. Soc., Dalton Trans., 1999, 155–159 157 The meridional geometry is expected to be favoured by steric as well as electrostatic factors. In the case of 1 these advantages are more than oVset by the superior back-bonding of the facial configuration. This does not apply to [ReL(OPPh3)Cl3] since OPPh3 is purely a donor in both s and p senses. Hence its geometry is logically meridional.It is instructive to compare the metal–ligand bond distances of 1a with those of mer- [ReL2(OPPh3)Cl3].2 The average Re–Cl length of two complexes are nearly equal (2.37–2.38 Å). However the Re–N lengths in 1a are ca. 0.06 Å longer than those in the phosphine oxide complex where L2 alone is available for back-bonding [t2g(Re) æÆ p*(L2)]. The geometrical selectivity in 1 and 2 is strong and exclusive. In no case have isomers been observed. It is noteworthy that [ReL(O)Cl3] 3 and [ReL(NAr)Cl3] 5,6 are meridional, the O and NAr ligands being pure donors like OPPh3.Upon reacting 1 with aromatic amines (ArNH2) in benzene solution in air, facile and quantitative transformation to mer-[ReL(NAr)Cl3] occurs. This reaction ( fac æÆ mer) represents a reversal of the geometrical change (mer æÆ fac) characterizing the reaction of equation (1). Metal redox: formation of [ReL9(PPh3)Cl3] 3 The fac-[ReL(PPh3)Cl3] complexes are electroactive in dichloromethane solution displaying two quasi-reversible one-electron responses in the range 20.5 to 0.7 V vs.SCE. Reduction potential data are listed in Table 4. The responses are assigned to the ReIV–ReIII (E1/2 ª 0.6 V) and ReIII–ReII (E1/2 ª 20.6 V) couples. In 2 the ReIV–ReIII couple occurs at ca. 0.3 V.3 Thus the trivalent state of rhenium is more diYcult to oxidize in 1 than in 2. This is consistent with the presence of phosphine back-bonding in 1. The red oxidized complex [ReIVL(PPh3)Cl3]1 11 can be generated in solution by coulometric oxidation of 1 in dry acetonitrile at 1.0 V.It reacts spontaneously with added water aVording the amide complex fac-[ReIVL9(PPh3)Cl3] 3, equation (3). The facial geometry is conserved in the conversion of 3 [ReIVL(PPh3)Cl3]1 1 H2O æÆ fac-[ReIVL9(PPh3)Cl3] 1 2 fac-[ReIIIL(PPh3)Cl3] 1 3H1 (3) 1 æÆ 3, vide infra. When coulometry is performed in moist acetonitrile the regenerated fac-[ReIIIL(PPh3)Cl3] complex, equation (3), is reoxidized and in this manner the whole of 1 is finally converted to 3.The total coulomb count at full conversion corresponds to the transfer of three electrons. From the electrolytic solution 3 can be isolated in excellent yields. These findings encouraged us to explore the chemical oxidation of 1 to 3. Aqueous nitric acid and hydrogen peroxide were indeed found to be very eVective. The most convenient synthesis of 3 is based on aqueous nitric acid oxidation of 1 in acetonitrile solution.Aldimine æÆ amide conversion in oxidizing aqueous environments has previously been observed 2 in the cases of 2 Table 4 Cyclic voltammetric formal potential a at 298 K Compound 1a 1b 1c 1d 3a 3b 3c 3d E2� 1 /V (DEp/mV) 20.60(100), 0.65(80) 20.61(100), 0.62(80) 20.64(100), 0.58(80) 20.59(100), 0.68(80) 20.10(80), 1.28(80) 20.15(80), 1.19(80) 20.18(80), 1.10(80) 20.06(80), 1.35(80) a Solvent, dichloromethane; scan rate, 50 mV s21; E2� 1 = 1/2 (Epa 1 Epc) where Epa and Epc are anodic and cathodic peak potentials respectively; DEp = Epc 2 Epa.Reference electrode, SCE. The concerned couples are 1–12 (ReIII–ReII), 11–1 (ReIV–ReIII), 3–32 (ReIV–ReIII), 31–3 (ReV–ReIV). and mer-[ReL(NAr)Cl3].5,6 Rate studies on 23 and on a ruthenium system 16 have demonstrated that the reaction proceeds by the addition of a molecule of water to the aldimine function polarized by metal oxidation. In the present case the oxidized metal is rhenium(IV) as in 11.Rapid oxidation of the corresponding water adduct 4 via induced transfer to two electrons 17 associated with proton dissociation, can aVord 3. Spectral and magnetic data for fac-[ReIVL9(PPh3)Cl3] 3 are listed in Table 1. The magnetic moments are lower 3 than the t2g 3 (assuming idealised octahedral geometry) spin-only value. Two strong amide stretches occur in the range 1600–1640 cm21. In dichloromethane solution 3 displays two quasi-reversible cyclic voltammetric responses in the range of 20.2 to 1.4 V corresponding to the couples ReIV–ReIII (E1/2 ª 20.2 V) and ReV– ReIV (E1/2 ª 1.4 V) (Table 4).Thus the ReIV–ReIII couple moves to lower potential by ~700 mV in going from 1 to 3 reflecting the ease of ReIII–ReIV oxidation upon amide binding. The facial geometry of 3 has been proven by structure determination of [ReL49(PPh3)Cl3] 3d (Fig. 3, Table 3). As in 1a the chelate ring, the pyridine ring and Cl(2), Cl(3) atoms are coplanar (mean deviation 0.02 Å).The pendant aryl ring makes a dihedral angle of 68.98 (50.18 in 1a) to the plane. The amide group C(5)C(6)O(1)N(2) is nearly perfectly planar. Contraction of the metal radius upon oxidation causes a ca. 0.06 Å decrease in average Re–Cl distances between 1a and 3d. For comparison we note that between a similar phosphine Fig. 3 A view of [ReL49(PPh3)Cl3] 3d; the atoms are represented by their 30% thermal probability ellipsoids. N N Re X Cl Cl Cl PPh3 O 3d [ReL4'(PPh3)Cl3] (X = Cl) 3c [ReL3'(PPh3)Cl3] (X = OMe) 3b [ReL2'(PPh3)Cl3] (X = Me) 3a [ReL1'(PPh3)Cl3] (X = H) IV N N Re X Cl Cl Cl PPh3 HO H H 4 + IV158 J.Chem. Soc., Dalton Trans., 1999, 155–159 oxide pair both the Re–Cl and Re–OPPh3 (no back-bonding) bonds contract.2 In contrast the Re–P length increases by 0.1 Å between 1a and 3d. This is primarily attributed to the weakening of Re–P back-bonding upon metal oxidation. The residual interaction is, however suYcient to sustain facial geometry in 3 which fails to isomerise even on prolonged boiling in toluene.Conclusion The fac-[ReIIIL(PPh3)Cl3] 1 family having a facially configured RePN2Cl3 coordination sphere has been synthesized via ligand displacement from mer-[ReIIIL(OPPh3)Cl3] 2. The facial geometry of 1 is a result of the optimization of Re–PPh3 and Re–L back-bonding. The electrochemical and chemical oxidation of 1 is stereoretentive and has furnished fac-[ReIVL9(PPh3)Cl3] 3 in which the rhenium(IV) state is stabilized by amide bonding.The Re–P back-bonding and bond length orders are respectively 1 > 3 and 1 < 3. Experimental Materials [ReL(OPPh3)Cl3],3 [ReOCl3(PPh3)2] 18 and pyridine-2-aldimine 19 were prepared by reported methods. The purification and drying of dichloromethane and acetonitrile for synthesis as well as for electrochemical work were done as described.20 Toluene and benzene were distilled over sodium before use.All other chemicals and solvents were of reagent grade and used as received. Physical measurements Spectra were recorded with the following equipment: electronic spectra, Hitachi 330 spectrophotometer; infrared spectra (KBr disc, 4000–300 cm21), Perkin-Elmer 783 spectrophotometer, proton NMR spectra were recorded on a Bruker FT 300 MHz spectrometer. Electrochemical measurements were done by using a PAR model 370-4 electrochemistry system as described.13b All experiments were performed at a platinum working electrode under a dinitrogen atmosphere, the supporting electrolyte being tetraethylammonium perchlorate.The potentials are referenced to the saturated calomel electrode (SCE) and are uncorrected for the junction contribution. Magnetic susceptibilities were measured on a PAR-155 vibrating sample magnetometer. Microanalyses were done by using a Perkin-Elmer 240C elemental analyser. Syntheses fac-[ReIIIL(PPh3)Cl3] 1. The complexes were prepared by the same general methods. Details are given for 1b (L = L2).To a pink solution of mer-[ReL2(OPPh3)C(100 mg, 0.14 mmol) in dry benzene (15 cm3), PPh3 (200 mg, 0.75 mmol) was added and the mixture was heated to reflux under pure nitrogen for 1 h aVording a violet solution which yielded crystalline fac- [ReL2(PPh3)Cl3] (20 mg) upon cooling to room temperature. The complex was collected by filtration and the filtrate was stripped of solvent. The residue was dissolved in a small volume of CH2Cl2 and subjected to chromatography on a silica gel column prepared in benzene.Upon elution with benzene– acetonitrile (25 : 1, 15 : 1 and 10 : 1) mer-[ReL2(OPPh3)Cl3] (18 mg), mer-[ReL2(NC6H4Me)Cl3] (7 mg) and fac-[ReL2(PPh3)Cl3] (28 mg) were successively isolated. The total yield of bluish violet fac-[ReL2(PPh3)Cl3] is 48 mg, 50%. The complex was also synthesized starting from a solution of [ReOCl3(PPh3)2] (100 mg, 0.12 mmol) in dry benzene (15 cm3) containing L2 (29 mg, 0.15 mmol).The mixture was heated to reflux under pure nitrogen for 1 h. The violet solution was stripped of solvent and the residue subjected to chromatography as described above. The yield of fac-[ReL2(PPh3)Cl3] was 37 mg, 40% (Found: C, 48.95; H, 3.25; N, 3.70. Calc. for C30H25Cl3N2PRe 1a: C, 48.87; H, 3.39; N, 3.80. Found: C, 48.68; H, 3.51; N, 3.61. Calc. for C31H27Cl3N2PRe 1b: C, 49.56; H, 3.60; N, 3.73. Found: C, 48.40; H, 3.35; N, 3.50. Calc. for C31H27Cl3N2OPRe 1c: C, 48.52; H, 3.52; N, 3.65.Found: C, 47.00; H, 3.25; N, 3.50. Calc. for C30H24Cl4N2PRe 1d: C, 46.69; H, 3.11; N, 3.63%). fac-[ReIVL9(PPh3)Cl3] 3. The same general methods were used for all the complexes. The case of 3b (L9 = L29) is detailed below. A solution of fac-[ReIIIL2(PPh3)Cl3] (20 mg, 0.027 mmol) in wet acetonitrile (20 cm3) containing tetraethylammonium perchlorate (25 mg, 0.11 mmol) was electrolyzed exhaustively under nitrogen at 1.0 V vs. SCE.The bluish violet solution changed to red and finally to yellow. The coulomb count corresponded to the transfer of three electrons, equation (4) fac-[ReIIIL(PPh3)Cl3] æÆ fac-[ReIVL9(PPh3)Cl3] 1 3H1 1 3e2 (4) (observed count, 7.25; calculated count for one electron, 2.45). The electrolyzed solution was stripped of the solvent and the residue was washed thoroughly with hot water and then dried over P4O10, yielding pure yellow fac-[ReL29(PPh3)Cl3]. The yield was 14 mg, 72%. Chemical synthesis of the complex was achieved by oxidation of fac-[ReL2(PPh3)Cl3] (50 mg, 0.067 mmol) in acetonitrile (20 cm3) by aqueous HNO3 (0.5 M, 0.5 cm3).The mixture was stirred for 1 h at room temperature aVording a yellow solution [hydrogen peroxide (0.5 cm3, 30%) requires 12 h stirring in an ice bath]. The solvent was removed and the residue washed and dried as above, yielding fac-[ReL29(PPh3)Cl3]. The yield was 40 mg, 80% (Found: C, 47.80; H, 3.25; N, 3.60. Calc. for C30H24Cl3N2OPRe 3a: C, 47.89; H, 3.19; N, 3.73.Found: C, 48.80; H, 3.25; N, 3.50. Calc. for C31H25Cl3N2OPRe 3b: C, 48.58; H, 3.40; N, 3.66. Found: C, 47.50; H, 3.42; N, 3.45. Calc. for C31H26Cl3N2O2PRe 3c: C, 47.59; H, 3.33; N, 3.58. Found: C, 46.00; H, 2.80; N, 3.65. Calc. for C30H23Cl4N2OPRe 3d: C, 45.79; H, 2.93; N, 3.56%). Conversion of fac-[ReIIIL2(PPh3)Cl3] to mer-[ReVL2(NC6H4Me)- Cl3] A solution of fac-[ReL2(PPh3)Cl3] (50 mg, 0.067 mmol) in toluene (10 cm3) was heated to reflux for 1 h in the presence of p-toluidine (35 mg, 0.33 mmol).The violet solution was stripped of solvent and the residue was subjected to chromatography on a silica gel column using benzene–acetonitrile (15 : 1) as the eluent. The complex mer-[ReL2(NC6H4Me)Cl3] was isolated (yield 35 mg, 88%) by removing the solvent. Crystallography Dark prismatic crystals of 1a and orange prismatic crystals of 3d were grown by slow diVusion of hexane into dichloromethane solutions of the respective complexes.Cell parameters were determined by a least-squares fit of 30 machine-centered reflections (2q = 15–308). Data were collected by the w-scan technique in the range 3 < 2q < 458 for 1a and 3 < 2q < 478 for 3d on a Siemens R3m/V four-circle diVractometer with graphite-monochromated Mo-Ka radiation (l = 0.71073 Å). Two check reflections after every 198 showed no intensity reduction. All data were corrected for Lorentzpolarization and absorption.21 The metal atoms were located from Patterson maps, and the rest of the non-hydrogen atoms emerged from successive Fourier syntheses.The structures were then refined by a full-matrix least-squares procedure on F 2. All non-hydrogen atoms [except O(2) for 3d] were refined anisotropically. All hydrogen atoms were included in calculatedJ. Chem. Soc., Dalton Trans., 1999, 155–159 159 Table 5 Crystal data for [ReIII L1(PPh3)Cl3] 1a and [ReIVL49(PPh3)Cl3] 3d Complex Formula M Crystal size/mm Crystal system Space group (no.) a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 m(Mo-Ka)/cm21 F(000) Transmission coeYcient Total reflections Number unique reflections (Rint) Number observed reflections [I > 2s(I)] Data/restraints/parameters R1,a wR2b [I > 2s(I)] R1, wR2 (all data) Goodness of fit on F2 Maximum and mean D/s Maximum, minimum diVerence peaks/e Å23 1a C30H25Cl3N2PRe 737.04 0.5 × 0.2 × 0.15 Monoclinic P21/n (14) 11.505(6) 13.545(5) 18.720(11) — 97.66(4) — 2891(3) 4 1.693 45.58 1440 0.56/1.00 4105 3801 (0.03) 3065 3797/0/334 0.0316, 0.0680 0.0485, 0.0851 1.040 0.002/0.000 0.672, 20.849 3d C30H23Cl4N2OPRe?H2O 804.49 0.42 × 0.32 × 0.2 Triclinic P1� (2) 9.994(6) 11.617(6) 15.135(9) 76.26(4) 88.11(5) 67.40(4) 1573(2) 2 1.699 42.85 786 0.53/1.00 4733 4663 (0.051) 4054 4652/0/357 0.0506, 0.1319 0.062, 0.1554 1.153 0.002/0.000 3.087, 21.727 a R1 = S Fo| 2 |Fc /S|Fo|.b wR2 = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� . positions. The programs of SHELXTL‘ V 5.03 (Bruker Analytical X-ray Systems: Part Number 269-015900) were utilized.Significant crystal data are listed in Table 5. The relatively large residual maxima in the case of 3d occurred very close (<1 Å) to the metal/chloride sites and are assigned to ghosts caused by series-termination eVects. CCDC reference number 186/1224. See http://www.rsc.org/suppdata/dt/1999/155/ for crystallographic files in .cif format. Acknowledgements We thank the Department of Science and Technology, Indian National Science Academy and the Council of Scientific and Industrial Research, New Delhi for financial support.AYliation with the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore is acknowledged. References 1 M. Menon, S. Choudhury, A. Pramanik, A. K. Deb, S. K. Chandra, N. Bag, S. Goswami and A. Chakravorty, J. Chem. Soc., Chem. Commun., 1994, 57. 2 M. Menon, A. Pramanik, N. Bag and A. Chakravorty, Inorg. Chem., 1994, 33, 402. 3 B. K. Dirghangi, M. Menon, A. Pramanik and A. Chakravorty, Inorg. Chem., 1997, 36, 1095. 4 B. K. Dirghangi, S. Banerjee, M. Menon and A. Chakravorty, Indian J. Chem., Sect. A, 1997, 36, 249. 5 S. Banerjee, B. K. Dirghangi, M. Menon, A. Pramanik and A. Chakravorty, J. Chem. Soc., Dalton Trans., 1997, 2149. 6 B. K. Dirghangi, M. Menon, S. Banerjee and A. Chakravorty, Inorg. Chem., 1997, 36, 3595. 7 H. P. Gunz and G. J. Leigh, J. Chem. Soc. A, 1971, 2229. 8 F. Tisato, F.Refosco, C. Bolzati, A. Cagnolini, S. Gatto and G. Bandoli, J. Chem. Soc., Dalton Trans., 1997, 1421. 9 J. C. Bryan, R. E. Stenkamp, T. H. Tulip and J. M. Mayer, Inorg. Chem., 1987, 26, 2283. 10 G. Rouschias and G. Wilkinson, J. Chem. Soc. A, 1967, 993; J. V. Caspar, B. P. Sullivan and T. J. Mayer, Inorg. Chem., 1984, 23, 2104; B. K. Dirghangi, Ph.D. Thesis, Jadavpur University, 1998. 11 A. S. M. Al-Shihri, J. R. Dilworth, S. D. Howe, J. Silver and R. M. Thompson, Polyhedron, 1993, 12, 2297; X. L. R. Fontaine, E. H. Fowles, T. P. Lyzell, B. L. Shaw and M. Thornton-pett, J. Chem. Soc., Dalton Trans., 1991, 1519; R. Rossi, A. Duatti and L. Magon, J. Chem. Soc., Dalton Trans., 1982, 1949. 12 M. Hirsch-Kuchma, T. Nicholson, A. Davison, W. M. Davis and A. G. Jones, J. Chem. Soc., Dalton Trans., 1997, 3185; M. Luaphon, P. E. Fanwick and R. A. Walton, Inorg. Chem., 1990, 29, 4348. 13 (a) F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemohn Wiley & Sons, New York, 5th edn., 1988, p. 64; (b) A. Pramanik, N. Bag, D. Ray, G. K. Lahiri and A. Chakravorty, Inorg. Chem., 1991, 30, 410. 14 H. Brunner and W. A. Herrmann, Chem. Ber., 1972, 105, 770; M. N. Ackermann, C. R. Barton, C. J. Deodence, E. M. Specht, S. C. Keill, W. E. Schreiber and H. Kim, Inorg. Chem., 1989, 28, 397. 15 P. Ghosh, A. Pramanik, N. Bag and A. Chakravorty, J. Chem. Soc., Dalton Trans., 1992, 1883. 16 M. Menon, A. Pramanik and A. Chakravorty, Inorg. Chem., 1995, 34, 3310. 17 H. Taube, Electron Transfer Reactions of Complex ions in Solution, Academic Press, New York, 1973, p. 73. 18 J. Chatt and G. A. Rowe, J. Chem. Soc., 1962, 4019. 19 G. Bähr and H. Z. Thamlitz, Z. Anorg. Allg. Chem., 1955, 282, 3. 20 P. Basu, S. Bhanja Choudhury and A. Chakravorty, Inorg. Chem., 1989, 28, 2680. 21 A. C. T. North, D. C. Philips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. Paper 8/06346J

ISSN:1477-9226    

DOI:10.1039/a806346j

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 161–165 161 Synthesis, characterisation and reactivity of the molybdenum(VI) dimethyl complex [Mo(NR)2Me2] (R 5 2,6-Pri 2C6H3) Vernon C. Gibson,*a Carl Redshaw,a Gary L. P. Walker,a Judith A. K. Howard,b Vanessa J. Hoy,b Jacqueline M. Cole,b Lyudmila G. Kuzmina b and Dinali S. De Silva b a Department of Chemistry, Imperial College, London, UK SW7 2AY b Department of Chemistry, University Science Laboratories, South Road, Durham, UK DH1 3LE Received 5th August 1998, Accepted 12th November 1998 The reaction of [Mo(NR)2Cl2(dme)] (R = 2,6-Pri 2C6H3, dme = 1,2-dimethoxyethane) with 2 equivalents of methylmagnesium bromide in diethyl ether aVorded [Mo(NR)2Me2] 2 as a red crystalline solid in good yield.Treatment of 2 with the donor molecules tetrahydrofuran (thf), pyridine, PMe3, and PMe2Ph gave the five-coordinate adducts [Mo(NR)2Me2(L)] (L = PMe3 3, PMe2Ph 4, thf 5 or pyridine 6). Exposure of solutions of 2 to atmospheric dioxygen aVorded the orange methoxide-bridged complex [{Mo(NR)2Me(m-OMe)}2] 7.[{Mo(NBut)2- Me(m-OMe)}n], 8 (n = 1 or 2) was obtained from the reaction of [{Mo(NBut)2Me2}2] 1 with dioxygen. The crystal structures of 2, 4 and 7 have been determined. In 1980, Nugent and Harlow1 described the first molybdenum imido alkyl complex, [Mo(NBut)2Me2] 1, which they showed exists as an imido-bridged dimer. They also noted that the violet solutions of 1 are readily discharged upon introduction of donor molecules such as phosphines or pyridine, or upon exposure to dioxygen.The precise nature of the products was not established. We have been investigating the chemistry of the bis(2,6- diisopropylphenylimido)molybdenum system2 and describe herein the synthesis and X-ray structural characterisation of [Mo(NR)2Me2] 2 (R = 2,6-Pri 2C6H3), a mononuclear analogue of 1. The reactivity of 2 towards a similar range of donor molecules and dioxygen has been examined with a view to gaining insight into the intriguing reactivity noted earlier by Nugent and Harlow.Results and discussion Synthesis and characterisation of [Mo(NR)2Me2] 2 Treatment of [Mo(NR)2Cl2(dme)] 3 (R = 2,6-Pri 2C6H3, dme = 1,2-dimethoxyethane) with 2 equivalents of MgMeBr in diethyl ether, followed by work-up and recrystallisation from a concentrated pentane solution, gives [Mo(NR)2Me2] 2 as deep red, highly air and moisture sensitive crystals in 75% isolated yield (Scheme 1).The 1H NMR spectrum of 2 is consistent with a C2v symmetric species, the Mo–CH3 groups resonating at d 1.39. This is to higher frequency than the corresponding methyl resonance of 1 (d 1.13 1) consistent with the greater electronwithdrawing eVect of the arylimido ligand. Analogously, the 13C NMR spectrum of 2 reveals a quartet resonance at d 37.74 due to the metal-bonded carbons, cf. d 28.30 for 1. Crystals of complex 2 were grown from a saturated pentane solution at 235 8C.The molecular structure is shown in Fig. 1; selected bond lengths and angles are collected in Table 1. The geometry about the metal centre is best described as distorted tetrahedral, with interligand angles in the range 107.5–113.68. The aromatic rings of the imido ligands lie ‘face to face’. The distances of 1.749(4) Å for the Mo–N bonds and 1.389(6) Å for the N–C(ipso) bonds, combined with angles of 159.6(3)8 for the Mo–N–C connection, are consistent with a linear arylimido ligand.4 The Mo–C bond distance, at 2.109(5) Å, is relatively short when compared to those of other terminal methyl ligands (2.254 Å mean, 2.189 Å lower quartile 5).A subsequent neutron structure determination 6 on 2 has revealed possible multiple a-agostic interactions between the molybdenum centre and the hydrogens of the methyl ligands. Attempts to prepare the mixed bis(imido)molybdenum Scheme 1 (i) PR3, 2MgMeBr, Et2O; (ii) thf or py, room temperature (r.t.); (iii) ��� [Mo(NBut)2Me2], benzene, r.t.; (iv) O2, toluene, r.t.; (v) 2MgMeBr, Et2O. 2 [Mo(NR)(NBut)Me2] 2 O O Cl Cl (i) (ii) (iii) (iv) (v) N N Mo N N Mo Me Me L L = PMe3 3 PMe2Ph 4 thf 5 py 6 N N Mo Me Me N N Mo Me N Mo Me O O Me Me N 7162 J. Chem. Soc., Dalton Trans., 1999, 161–165 complex, [Mo(NR)(NBut)Me2], a hybrid of 1 and 2, were unsuccessful. Treatment of [Mo(NR)(NBut)Cl2(dme)] 7 with 2 equivalents of methylmagnesium bromide aVorded [{Mo- (NBut)2Me2}2] 1 as the only isolable product in ca. 30% yield.It seemed likely that the mixed imido species was generated but that 1 was subsequently formed by exchange of imido ligands between molybdenum centres.8 In order to establish whether or not imido ligand exchange was occurring, the reaction between 1 and 2 was investigated by NMR spectroscopy. The complex [{Mo(NBut)2Me2}2] 1 was mixed with 2 equivalents of [Mo- (NR)2Me2] 2 in an NMR tube, dissolved in d8-toluene (400 ml), and the 1H and 13C NMR spectra recorded.The 1H NMR spectrum revealed a new doublet signal at d 1.26 (12 H) with an associated singlet resonance at d 1.15 (9 H) due to the methyl hydrogens of the isopropyl and tert-butyl groups of [{Mo- (NR)(NBut)Me2}n] (n = 1 or 2). The isopropyl-methine and metal-bound methyl groups appeared as a septet at d 3.62 (4 H) and a singlet at d 1.13 (6 H) respectively. The 13C NMR spectrum gave a metal-bound methyl carbon resonance at d 32.46, a value intermediate to those found for 1 (d 28.30) and 2 (d 37.74).An equilibrium in favour of [{Mo(NR)(NBut)Me2}n] [for n = 1, Keq (298 K) = 24] was attained after 24 h at room temperature [eqn. (1)]. The diYculties in crystallising this product are most [Mo(NR)2Me2] 1 ��� [{Mo(NBut)2Me2}2] 2 [Mo(NR)(NBut)Me2] (1) likely due to the lower solubility of dimeric 1 which precipitates from solution thereby driving the equilibrium back towards 1 and 2. These solubility characteristics provide an indication that [Mo(NR)(NBut)Me2] is likely to be monomeric, since the less solubilising characteristics of the arylimido ligand would be expected to lead to preferential precipitation of the mixedimido product if it were a dimer.Base adducts of [Mo(NR)2Me2] 2 Treatment of [Mo(NR)2Cl2(dme)] with 2 equivalents of methylmagnesium bromide, in the presence of an excess of the phosphine PMe3 or PMe2Ph, aVorded the monophosphine adducts [Mo(NR)2Me2(PMe3)] 3 and Mo(NR)2Me2(PMe2- Ph)] 4 as orange crystalline materials in 70 and 76% yield respectively.In accordance with the observations of Nugent and Harlow on the tert-butylimido system,1 the 1H and 13C NMR spectra of complexes 3 and 4 reveal upfield shifts for the methyl resonances relative to the phosphine-free complex 2 [1H NMR: d 0.99 (3) and 1.05 (4) cf. 1.39 for 2; 13C NMR: d 14.87 (3) and 16.06 (4), cf. 37.74 for 2]. The larger shifts are observed for the more Fig. 1 Molecular structure of complex 2, without H atoms and with key atoms labelled. electron donating PMe3 derivative.An analogous shift to higher field is also seen for the phosphorus nucleus of 3 compared with 4 [d 217.3 (3) and 24.0 (4)]. The thf complex [Mo(NR)2Me2(thf)] 5 is generated in high yield upon recrystallisation of 2 from thf solution, and its pyridine analogue, [Mo(NR)2Me2(py)] 6, was accessed by treatment of a pentane solution of 2 with 1 equivalent of pyridine. The pyridine adduct has more pronounced upfield 1H and 13C NMR shifts [1H NMR: d 0.99, cf. 1.39 for 2; 13C NMR: d 27.39, cf. 37.74 for 2]. For 5, the 1H NMR shift of the methyl resonance is approximately the same as for base-free 2, which is also true of the 13C NMR shift [d 36.70, cf. 37.74 for 2] in line with thf being the weakest of these donor ligands. In contrast to the stable adducts 3–6, treatment of 2 with an excess of acetonitrile (4 equivalents) in d6-benzene gave a product that was unstable to vacuum. The 1H NMR spectrum indicated that an adduct had formed, evidenced by the upfield shift (d 1.31) of the metal methyl resonance, but on removal of the volatile components and re-recording of the spectrum in fresh d6-benzene 2 only was observed.The molecular structure of complex 4 has been determined and is shown in Fig. 2; selected bond lengths and angles are collected in Table 2. The gt the metal centre in 4 is best described as distorted trigonal bipyramidal, with an imido ligand and phosphine molecule occupying the axial sites.There is a large disparity between the bend angles of the two imido ligands. The axial imido ligand is essentially linear (176.08), whilst the equatorial imido ligand is borderline between ‘bent’ Fig. 2 Molecular structure of complex 4, without H atoms and with key atoms labelled. Table 1 Selected bond lengths (Å) and angles (8) for compound 2 Mo(1)–N(1) Mo(1)–C(13) N(1)–Mo–N(1a) N(1)–Mo–C(13) 1.749(4) 2.109(5) 112.6(2) 107.8(2) N(1)–C(2) C(13)–Mo–C(13a) C(2)–N(1)–Mo(1) 1.389(6) 113.6(3) 159.6(3) Table 2 Selected bond lengths (Å) and angles (8) for compound 4 Mo–N(1) Mo–N(2) Mo–C(1) Mo–C(2) N(1)–Mo–N(2) N(2)–Mo–C(2) N(1)–Mo–C(2) N(2)–Mo–C(1) N(1)–Mo–C(1) C(1)–Mo–C(2) 1.759(3) 1.759(3) 2.299(3) 2.205(4) 111.61(13) 107.86(14) 95.04(13) 107.90(12) 93.17(12) 137.10(13) Mo–P N(1)–C(11) N(2)–C(21) Mo–N(1)–C(11) Mo–N(2)–C(21) N(1)–Mo–P N(2)–Mo–P C(1)–Mo–P C(2)–Mo–P 2.6793(10) 1.394(4) 1.409(4) 175.9(3) 151.9(2) 153.19(10) 95.20(9) 78.23(8) 75.69(10)J.Chem. Soc., Dalton Trans., 1999, 161–165 163 and ‘linear’ (152.08). A similar significant bending at the nitrogen of the equatorial imido ligand in trigonal bipyramidal bis(imido)molybdenum compounds has been reported and good evidence has been presented for the five co-ordinate trigonal bipyramidal system that this is more likely to be due to an electronic eVect rather than crystal packing.9 Reactivity towards dioxygen Exposure of a pentane solution of [Mo(NR)2Me2] 2 to dry dioxygen gas, followed by recrystallisation, aVords a bright orange crystalline product (7) in good yield (86%).The 1H NMR spectrum of 7 reveals a singlet resonance at d 1.45 due to the hydrogens of one metal-bound methyl group and a resonance, at d 4.35, also integrating for three hydrogens of a methyl unit. The 13C NMR spectrum gave corresponding resonances at d 25.68 and 67.71 respectively for these methyl carbons.The identity of 7 could not be established with certainty from these NMR data, though the shifts of the new methyl group would be appropriate for a methoxide unit. A crystal structure determination on 7 was therefore undertaken. Crystals suitable for an X-ray crystallographic study were obtained from within a sealed NMR sample tube that contained a saturated d6-benzene solution of complex 7, stored for several days at room temperature. The molecular structure is shown in Fig. 3; selected bond lengths and angles are presented in Table 3.Complex 7 is binuclear, the molybdenum centres being asymmetrically bridged by two methoxide ligands. The Mo–O distances are consistent with one ‘normal’ covalent bond [2.048(2) Å] and one dative covalent bond [2.207(2) Å] to each molybdenum atom. The five-co-ordinate geometry about each metal centre is best described as distorted trigonal Fig. 3 Molecular structure of complex 7, without H atoms and with key atoms labelled.Table 3 Selected bond lengths (Å) and angles (8) for complex 7 Mo(1)–(1) N(1)–C(1) Mo(1)–C(25) Mo(1)–O(1a) Mo(1)–N(1)–C(1) O(1)–Mo(1)–O(1a) Mo(1)–O(1)–C(26) O(1)–Mo(1)–C(25) N(2)–Mo(1)–C(25) N(1)–Mo(1)–O(1) O(1a)–Mo(1)–C(25) O(1a)–Mo(1)–N(2) 1.764(2) 1.397(3) 2.161(3) 2.207(2) 173.2(2) 68.42(7) 123.6(2) 131.34(9) 103.5(1) 97.27(8) 83.91(8) 94.99(8) Mo(1)–N(2) N(2)–C(13) Mo(1)–O(1) O(1)–C(26) Mo(1)–N(2)–C(13) Mo(1)–O(1)–Mo(1a) Mo(1a)–O(1)–C(26) O(1)–Mo(1)–N(2) N(1)–Mo(1)–C(25) N(1)–Mo(1)–N(2) O(1a)–Mo(1)–O(1) 1.754(2) 1.401(3) 2.048(2) 1.430(3) 156.3(2) 111.58(7) 123.2(2) 117.65(9) 93.6(1) 107.82(9) 68.42(7) bipyramidal, each molybdenum atom possessing a local geometry not dissimilar to that established for the phosphine adducts 3 and 4.The axial sites are occupied by an arylimido ligand and a methoxide group bonded through a dative covalent interaction, the equatorial sites by a terminal methyl ligand, the second methoxide group, this time with the short Mo–O contact, and the second arylimido unit.The local geometry around the molybdenum centres is shown in Fig. 4. The Mo–N–C angles for the axial [173.2(2)8] and equatorial [156.3(2)8] imido ligands are comparable in terms of size and orientation to those seen for 4 [175.9(3) and 151.9(2)8], wherein the equatorial imido unit is bent towards the adjacent axial linear imido group. A Mo–C distance of 2.161(3) Å for the terminal methyl ligands in 7 is intermediate between those of [Mo(NR)2Me2] [2.109(5) Å] and 4 [ 2.252(4) Å (average)].Selective oxygen insertion into transition-metal methyl bonds has been seen in Group 4 chemistry by Lubben and Wolczanski, 10 the reaction of [Ti(tritox)Me3] [tritox = (Me3C)3CO] with O2 aVording the methoxide-bridged product [{Ti(tritox)- Me2}2(m-OMe)2]. This selective insertion into just one of the metal–carbon bonds bears close similarity to the reaction described here. Treatment of [M(tritox)2Me2] (M = Ti, Zr or Hf) with dioxygen does not stop at the first insertion product, instead proceeding to aVord exclusively the bis(methoxide) product [M(tritox)2(OMe)2].10 Contrastingly, 7 is unreactive towards further oxygen insertion to give [Mo(NR)2(OMe)2] even though the latter is accessible and stable.11 Finally, in order to provide clarification of Nugent and Harlow’s observations 1 on the tert-butylimido system, we then treated a pentane solution of 1 with an atmosphere of dry dioxygen gas.This led to discharging of the violet solution to pale yellow in accordance with their report. Upon removal of the solvent, a sensitive free-flowing golden-yellow oil 8 was obtained. Its 1H NMR spectrum (d8-toluene) revealed resonances at d 0.88 (3 H) and 4.00 (3 H) attributable to metal-bound methyl and methoxy groups respectively. The corresponding 13C NMR resonances occur at d 16.0 and 66.7, values comparable to those observed for the bis(arylimido)molybdenum methoxide species 7.Conclusion This study has shown that the 2,6-diisopropylphenylimido ligand stabilises a mononuclear molybdenum(VI) dimethyl species in contrast to the tert-butylimido ligand which aVords an imido-bridged dimer. A subsequent study of the reactions of [Mo(NR)2Me2] towards donor molecules and dioxygen, and the characterisation of the products by NMR spectroscopy and X-ray crystallography, have allowed the origin of the earlier observations of Nugent and Harlow on the tert-butylimido system to be rationalised. The selective insertion of oxygen into just one of the molybdenum-bonded methyl groups to give a methoxy-bridged dimer is particularly noteworthy.Experimental General All manipulations were carried out under an atmosphere of nitrogen using standard Schlenk and cannula techniques or in a conventional nitrogen-filled glove-box. Solvents were refluxed Fig. 4 The local geometry around the molybdenum centres of complex 7.N(1) Mo N(2) O(1) C(25) O(1a)164 J. Chem. Soc., Dalton Trans., 1999, 161–165 over an appropriate drying agent, and distilled and degassed prior to use. Elemental analyses were performed by the microanalytical services of the Department of Chemistry at Durham, Medac Ltd and at Imperial College. The NMR spectra were recorded on a Varian VXR 400 S spectrometer at 400.0 (1H), 100.6 (13C) and 100.0 MHz (31P) with chemical shifts referenced to the residual protio impurity of the deuteriated solvent, IR spectra (Nujol mulls, KBr or CsI windows) on Perkin-Elmer 577 and 457 grating spectrophotometers. The complex [Mo- (NR)2Cl2(dme)] was prepared by the previously reported method.2 Trimethylphosphine was prepared by the method of Wolfsberger and Schmidbaur.12 All other chemicals were obtained commercially and used as received unless stated otherwise.Preparations [Mo(NR)2Me2] 2. To a solution of [Mo(NR)2Cl2(dme)] (5.0 g, 8.23 mmol) in diethyl ether (100 cm3) at 278 8C was slowly added (over about 20 min) MgMeBr (5.5 cm3, 3.0 M solution, 16.46 mmol) in diethyl ether (10 cm3).After slowly warming to ambient temperature and stirring for 12 h the orange suspension was filtered. The remaining solid was further extracted with diethyl ether (2 × 50 cm3) and pentane (50 cm3). The volatiles were removed from the combined extracts to aVord a red solid. Extraction into pentane (60 cm3) and cooling to 278 8C gave complex 2 as orange-red crystals. Yield 2.94 g, 75% (Found: C, 65.63; H, 8.39; N, 5.84.Calc. for C26H40MoN2: C, 65.53; H, 8.46; N, 5.88%). IR: 3057s, 1916w, 1570w, 1324vs, 1272vs, 1225m, 1177w, 1149m, 1114m, 1058m, 1046m, 985s, 933m, 896w, 794s, 752vs, 612w, 581w, 562w, 536w, 516s and 457m cm21. 1H NMR (d6-benzene, 298 K): d 6.10–6.97 (m, 6 H, m- and p-H of C6H3Pri 2-2,6), 3.64 (sept, 4 H, 3JHH 6.8, CHMe2), 1.39 (s, 6 H, CH3) and 1.13 (d, 24 H, 3JHH 6.8 Hz, CHMe2). 13C NMR (d6-benzene, 298 K): d 153.09 (s, ipso-C of C6H3Pri 2-2,6), 142.44 (s, o-C of C6H3Pri 2-2,6), 126.21 (d, 1JCH 159.8, p-C of C6H3Pri 2-2,6), 122.75 (d, 1JCH 158.7, m-C of C6H3Pri 2-2,6), 37.74 (q, 1JCH 125.8, CH3), 28.86 (d, 1JCH 128.1, CHMe2) and 23.27 (q, 1JCH 125.9, CHMe2).[Mo(NR)2Me2(PMe3)] 3. Onto a frozen mixture of [Mo- (NR)2Cl2(dme)] (2.19 g, 3.6 mmol) and diethyl ether (100 cm3) at 2198 8C was vacuum transferred PMe3 (0.76 g, 10 mmol). On slowly warming to 278 8C MgMeBr (2.4 cm3, 3.0 M solution, 7.2 mmol) was added and the mixture stirred at ambient temperature for 12 h.The volatile components were then removed in vacuo and the residue was extracted into pentane to give, upon cooling to 240 8C, orange crystals of complex 3. Yield 1.4 g, 70% (Found: C, 63.30; H, 9.14; N, 5.07. Calc. for C29H49MoN2P: C, 63.03; H, 8.04; N, 5.07%). IR: 1620w, 1583w, 1421m, 1359s, 1331m, 1273s, 1224w, 1175w, 1156w, 1112w, 1097w, 1056w, 1045w, 1024m, 978s, 957w, 934m, 849m, 829m, 801m, 793m, 762vs, 752vs, 674w, 543m, 532m and 508m cm21. 1H NMR (d6-benzene, 298 K): d 7.09–6.99 (m, 6 H, m- and p-C of C6H3Pri 2-2,6), 3.91 (sept, 4 H, 3JHH 6.8, CHMe2), 1.20 (d, 24 H, 3JHH 6.8, CHMe2), 0.99 (s, 6 H, CH3) and 0.88 (d, 9 H, 2JPH 6.8 Hz, PMe3). 13C NMR (d6-benzene, 298 K): d 153.30 (s, ipso- C of C6H3Pri 2-2,6), 144.03 (s, o-C of C6H3Pri 2-2,6), 125.23 (d, 1JCH 159.2, p-C of C6H3Pri 2-2,6), 122.60 (d, 1JCH 156.9, m-C of C6H3Pri 2-2,6), 28.49 (d, 1JCH 129.1 Hz, CHMe2), 23.84 (qd, 1JCH 125.8, 2JCH 5.4, CHMe2), 14.87 (q, 1JCH 126.0, CH3) and 13.35 [dq, 1JCH 130.0, 1JCP 15.2 Hz, P(CH3)3]. 31P NMR (C6D6, 298 K): d 217.27 (s, PMe3). [Mo(NR)2Me2(PMe2Ph)] 4. The same procedure was adopted as described for complex 3, but using PMe2Ph. Orange 5 was obtained in 76% yield (Found: C, 66.49; H, 8.46; N, 4.41. Calc. for C34H51MoN2P: C, 66.43; H, 8.36; N, 4.56%). IR: 3046w, 1421m, 1358w, 1336w, 1323w, 1271m, 1223w, 1176w, 1153w, 1112w, 1099w, 1059w, 1047w, 1027w, 998w, 977s, 944s, 935m, 914m, 904vs, 865w, 837w, 800m, 756vs, 743s, 694m, 675w, 613w and 491w cm21.Mass spectrum (CI, NH4 1, m/z): 600, [M 2 CH3]1; 585, [M 2 2CH3]1 and 478, [M 2 PMe2Ph 1 H]1. 1H NMR (d6-benzene, 298 K): d 7.40 (td, 2 H, 3JHH 8.5, 3JPH = 1.8, PPh), 6.40–7.10 (m, 9 H, aryl H), 3.91 (sept, 4 H, 3JHH 6.8, CHMe2), 1.28 (d, 6 H, 2JPH 6.4, PMe2Ph), 1.22 (d, 24 H, 3JHH 6.8 Hz, CHMe2) and 1.05 (s, 6 H, CH3). 13C NMR (d6- benzene, 298 K): d 153.31 (ipso-C of C6H3Pri 2-2,6), 144.19 (o-C of C6H3Pri 2-2,6), 135.70 (d, 1JCP 26.2, ipso-C of PMe2Ph), 130.98 (dm, 2JCP 11.0, o-C of PMe2Ph), 129.70 (d, 4JCP 1.5, p-C of PMe2Ph), 128.74 (dm, 3JCP 8.7, m-C of PMe2Ph), 125.36 (d, 1JCH 158.2, p-C of C6H3Pri 2-2,6), 122.67 (ddd, 1JCH 154.5, 2JCH 7.2, 3JCH 4.9, m-C of C6H3Pri 2-2,6), 28.49 (dq, 1JCH 128.5, 2JCH 3.7, CHMe2), 23.88 (qm, 1JCH 125.1, CHMe2), 16.06 (q, 1JCH 125.2, CH3) and 12.44 (qd, 1JCH 129.7, 2JCP 15.5 Hz, PMe2Ph). 31P NMR (C6D6): d 24.0 (s, PMe2Ph).[Mo(NR)2Me2(thf)] 5. To solid complex 2 (0.375 g, 0.79 mmol) was added thf (20 cm3). After stirring for 5–10 min at room temperature the volatile components were removed under reduced pressure to aVord 5 as an orange solid. Yield 0.4 g, 92% (Found: C, 65.5; H, 8.7; N, 5.5. Calc. for C30H48MoN2O: C, 65.7; H, 8.8; N, 5.1%). IR: 3058m, 1571w, 1378s, 1326s, 1278s, 1226w, 1197m, 1179m, 1148m, 1101w, 1059w, 985m, 935w, 894w, 795m, 775s and 752s cm21. Mass spectrum (EI, m/z): 478, [M 2 thf]1. 1H NMR (d6-benzene, 298 K): d 6.92–7.00 (m, 6 H, m- and p-C of C6H3Pri 2-2,6), 3.66 (sept, 4 H, 3JHH 6.9, CHMe2), 3.59 (br t, 4 H, thf), 1.39 (br t, 4 H, thf), 1.36 (s, 6 H, CH3) and 1.14 (d, 24 H, 3JHH 6.9 Hz, CHMe2). 13C NMR (d6-benzene, 298 K): d 153.13 (s, ipso-C of C6H3Pri 2-2,6), 142.54 (s, o-C of C6H3Pri 2-2,6), 126.12 (d, 1JCH 159.7, p-C of C6H3Pri 2-2,6), 122.75 (dt†, 1JCH 156.7, m-C of C6H3Pri 2-2,6), 68.13 (t, 37.74 1JCH 145.3, thf), 36.70 (q, 1JCH 132.5, CHMe2), 25.73 (t, 1JCH 132.5 Hz, thf) and 23.24 (q, 1JCH = 125.8 Hz, CHMe2).[Mo(NR)2Me2(py)] 6. To complex 2 (0.524 g, 1.1 mmol) in pentane (20 cm3) was added pyridine (0.087 g, 1.1 mmol) in pentane (10 cm3). After stirring for 30 min the yellow solution was filtered from the suspension. The remaining residue was washed with pentane (20 cm3), and the combined extracts were reduced to half-volume and cooled to 0 8C for 12 h to aVord 6 as orange cubes. Yield 0.52 g, 82% (Found: C, 67.08; H, 8.44; N, 7.56.Calc. for C31H45MoN3: C, 67.01; H, 8.16; N, 7.56%). IR: 1620w, 1601w, 1584w, 1418w, 1377m, 1357w, 1289w, 1215w, 1176w, 1147w, 1096w, 1039w, 1011w, 972m, 933w, 844s, 799s, 755s, 709s, 627w and 408w cm21. 1H NMR (d8-toluene, 298 K): d 8.53 (dd, 2 H, 3JHH 6.3, 4JHH 1.6, py), 6.90–7.04 (m, 6 H, m- and p-C of C6H3Pri 2-2,6), 6.75 (tt, 1 H, 3JHH 7.6, 4JHH 1.6, py), 6.46 (m, 2 H, py), 3.93 (sept, 4 H, 3JHH 6.9, CHMe2), 1.19 (d, 24 H, 3JHH 6.8 Hz, CHMe2) and 0.99 (s, 6 H, CH3). 13C NMR (d8-toluene, 298 K): d 153.42 (s, ipso-C of C6H3), 150.16 (d, 1JCH 181.6, py Co), 143.81 (s, o-C of C6H3), 129.54 (d, py Cp), 128.61 (d, py Cm), 125.14 (dt, 1JCH 165.9, 2JCH 6.8, p-C of C6H3), 124.63 (ddd, 1JCH 155.6, m-C of C6H3), 28.53 (dq, 1JCH 129.2, 2JCH 3.8, CHMe2), 27.39 (q, 1JCH 125.1, CH3) and 23.97 (qm, 1JCH 125.5 Hz, CHMe2). [{Mo(NR)2Me(Ï-OMe)}2] 7. Dry oxygen gas was passed through a solution of complex 1 (1.0 g, 1.65 mmol) in toluene (40 cm3).After 5 min, the volatile components were removed in vacuo, and the residue was extracted with diethyl ether (3 × 40 cm3). Cooling to 278 8C aVorded orange 7. Yield 1.4 g, 86% (Found: C, 63.43; H, 7.87; N, 6.04. Calc. for C52H80Mo2- N4O2: C, 63.40; H, 8.19; N, 5.69%). IR: 2721w, 1584w, 1410w, 1350m, 1320m, 1269s, 1223w, 1160w, 1094w, 1054w, 1021m, 975m, 933m, 895w, 795m, 755s, 687w, 573w, 546w and 496w cm21. Mass spectrum (EI, m/z): 939 [M 2 CH3 2 OCH3]1; 492, [��� M]1; and 477, [��� M 2 CH3]1. 1H NMR (d6-benzene, 298 K): † Resolution insuYcient to determine 3JHH.J. Chem. Soc., Dalton Trans., 1999, 161–165 165 d 7.10–6.90 (m, 12 H, m- and p-C of C6H3Pri 2-2,6), 4.35 (s, 6 H, OCH3), 3.83 (sept, 8 H, 3JHH 6.9, CHMe2), 1.45 (s, 6 H, CH3), 1.25 (d, 24 H, 3JHH 6.9 Hz, CHMe2) and 1.18 (d, 24 H, 3JHH 6.9, CHMe2). 13C NMR (d6-benzene, 298 K): d 152.59 (s, ipso-C of C6H3Pri 2-2,6), 144.23 (s, o-C of C6H3Pri 2-2,6), 126.70 (d, 1JCH 159.5, p-C of C6H3Pri 2-2,6), 122.68 (d, 1JCH 156.5, m-C of C6H3Pri 2-2,6), 67.71 (q, 1JCH 143.0 ,OCH3), 28.76 (dq, 1JCH 128.5, 2JCH 3.5, CHMe2), 25.68 (q, 1JCH 128.0, CH3), 24.21 (qm, 1JCH 126.0, CHMe2) and 23.64 (qm, 1JCH 125.8Hz, CHMe2).[{Mo(NBut)2Me(Ï-OMe)}n] 8 (n 5 1 or 2). As for complex 7, but using [Mo(NBut)2Me2]. Yield 82% (Found: C, 39.1; H, 7.6; N, 9.0. Calc. for C20H48Mo2N4O2: C, 42.2; H, 8.5; N, 9.9%). Satisfactory microanalytical data could not be obtained due to the air sensitivity of this oil.IR: 2969s, 2922s, 2894s, 2861m, 2820m, 1471w, 1452m, 1383w, 1355s, 1256s, 1219s, 1152w, 1121m, 1064m, 1034s, 804m, 686m, 593m, 568m, 525m, 495m, 467w and 442w cm21. Mass spectrum (CI271, [��� M 2 CH3]1. 1H NMR (d8-toluene, 298 K): d 4.0 (s, 6 H, OCH3), 1.30 [s, 36 H, (CH3)3C] and 0.88 (s, 6 H, CH3). 13C NMR (d8-toluene, 298 K): d 137.80 (s, NCMe3), 66.69 (q, 1JCH 141.5, OCH3), 31.89 (q, 1JCH 126.1, NCMe3) and 16.00 (q, 1JCH 126.6 Hz, CH3).Crystallography The air sensitive samples were mounted on glass fibres using a perfluoropolyether oil.13 Crystal data were collected at 150 K, using a Siemens SMART CCD (4 and 7) or a Siemens P4 diffractometer (2). Graphite monochromated Mo-Ka radiation (l = 0.71073 Å) was used throughout. In the case of data collections performed with the Siemens SMART, cell parameters were refined using 512 reflections from all regions of reciprocal space and data were reduced using the SAINT program.14 In the case of data collections performed with the Siemens P4, cell parameters were determined from 20 reflections located using a hemispherical search and data were reduced using XSCANS.15 The structures were solved by direct methods (2, 4 and 7) using the SHELXS 86 program16 and refined by full matrix least squares methods on F2 using SHELXL 93.17 Atomic scattering factors were taken from ref. 18. Positional and anisotropic atomic dispacement parameters were refined for all non-hydrogen atoms, except those of the disordered pentane solvent in complex 4 (see below).Hydrogen atoms were placed geometrically and positional parameters were refined using a riding model (including free rotation about C–C bonds for methyl groups). Isotropic atomic displacement parameters were constrained to be 1.2 (1.5 for methyl groups) times the equivalent isotropic atomic displacement parameter of the adjacent heavy atom. Complex 4 contains a pentane solvent molecule disordered over two symmetry related sites, each with occupancy 0.5.Positional and isotropic atomic displacement parameters were refined for the pentane carbon atoms. The pentane hydrogen atoms were not included in the final model. Crystal data. For 2: C26H40MoN2, M = 476.54, monoclinic, space group C2/c, a = 20.240(4), b = 6.5500(10), c = 19.910(4) Å, b = 103.99(3)8, U = 2561.2(8) Å3, Z = 4, m(Mo-Ka) = 0.53 mm21, 2936 reflections measured, 2253 unique (Rint = 0.0356) which were used in all calculations.The final wR(F2) was 0.1191, R1 = 0.0466. For 4: C34H51MoN2P?C5H12, M = 686.82, monoclinic, space group P21/c, a = 9.8278(7), b = 14.6163(10), c = 25.183(2) Å, b = 94.6660(10)8, U = 3605.4(4) Å3, Z = 4, m(Mo-Ka) = 0.44 mm21, 15240 reflections measured, 6306 unique (Rint = 0.0459). The final wR(F2) was 0.1124, R1 = 0.0475. For 7: C52H80Mo2N4O2?2C6D6, M = 1147.30, triclinic, space group P1� , a = 10.0757(6), b = 11.3939(7), c = 14.3761(9) Å, a = 93.136(1), b = 99.548(1), g = 111.915(1)8, U = 1497.6(3) Å3, Z = 1, m(Mo-Ka) = 0.46 mm21, 6468 reflections measured, 4795 unique (Rint = 0.0206).The final wR(F2) was 0.0806, R1 = 0.0288. CCDC reference number 186/1248. Acknowledgements The EPSRC is thanked for support of this work. References 1 W. A. Nugent and R. L. Harlow, J. Am. Chem. Soc., 1980, 102, 1759. 2 P. W. Dyer, V. C. Gibson and W. Clegg, J. Chem. Soc., Dalton Trans., 1995, 3313. 3 H. H. Fox, K. B. Yap, J. Robbins, S. Cai and R. R. Schrock, Inorg. Chem., 1992, 31, 2287. 4 D. E. Wigley, Prog. Inorg. Chem., 1994, 42, 239; W. A. Nugent and J. M. Mayer, Metal–Ligand Multiple Bonds, Wiley-Interscience, New York, 1988; A. Bell, W. Clegg, P. W. Dyer, M. R. J. Elsegood, V. C. Gibson and E. L. Marshall, J. Chem. Soc., Chem. Commun., 1994, 2247. 5 F. H. Allen, L. Brammer, O. Kennard, A. G. Orpen, R. Taylor and D. G. Watson, J. Chem. Soc., Dalton Trans., 1989, S14. 6 J. M. Cole, V. C. Gibson, J. A. K. Howard, G. J. McIntyre and G. L. P. Walker, Chem. Commun., 1998, 1829. 7 R. C. B. Copley, P. W. Dyer, V. C. Gibson, J. A. K. Howard, E. L. Marshall, W. Wang and B. Whittle, Polyhedron, 1996, 15, 3001. 8 M. Jolly, J. P. Mitchell and V. C. Gibson, J. Chem. Soc., Dalton Trans., 1992, 1331. 9 V. C. Gibson, E. L. Marshall, C. Redshaw, W. Clegg and M. R. J. Elsegood, J. Chem. Soc., Dalton Trans., 1996, 4197. 10 T. V. Lubben and P. T. Wolczanski, J. Am. Chem. Soc., 1987, 109, 424. 11 P. A. Cameron and V. C. Gibson, unpublished work. 12 W. Wolfsberger and H. Schmidbaur, Synth. React. Inorg. Metal- Org. Chem., 1974, 4, 149. 13 D. S. Stalke and T. Kottke, J. Appl. Crystallogr., 1993, 26, 615. 14 SAINT, Version 4.050, Siemens Analytical X-ray Instruments Inc., Madison, WI, 1995. 15 XSCANS, X-ray Single Crystals Analysis System, Version 2.1, Siemens Analytical X-ray Instruments Inc., Madison, WI, 1994. 16 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. 17 G. M. Sheldrick, SHELXL 93, Program for the refinement of crystal structures using single crystal diVraction data, University of Göttingen, 1993. 18 International Tables for Crystallography, ed. A. J. C. Wilson, Kluwer, Dordrecht, 1992, vol. C, Tables 4.2.6.8 and 6.1.1.4. Paper

ISSN:1477-9226    

DOI:10.1039/a806171h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 167–173 167 Synthesis and structural characteristics of metal–acyclovir (ACV) complexes: [Ni(or Co)(ACV)2(H2O)4]Cl2?2ACV, [Zn(ACV)- Cl2(H2O)], [Cd(ACV)Cl2]?H2O and [{Hg(ACV)Cl2}x]. Recognition of acyclovir by Ni–ACV Ángel García-Raso,*a Juan J. Fiol,a Ferran Bádenas,a Rosa Cons,a Ángel Terrón a and Miguel Quirós b a Departament de Química, Universitat de les Illes Balears, 07071 Palma de Mallorca, Spain. E-Mail: dquagr0@ps.iub.es b Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain Received 6th October 1998, Accepted 10th November 1998 The monomeric [M(ACV)2(H2O)4]Cl2?2ACV (M = NiII 1 or CoII 2), [Zn(ACV)Cl2(H2O)] 3 and the polymeric [Cd(ACV)Cl2]?H2O 4 [ACV = acyclovir = 9-(2-hydroxymethoxymethyl)guanine] complex have been prepared and characterised by X-ray diVraction and IR data; 1H and 13C NMR have been used to interpret the structural characteristics of the complexes in solution.Compounds 1 and 2 exist as octahedral complexes with four H2O ligands in the basal plane [Ni–OW 2.053(2) and 2.057(7) Å] and two axial ACV molecules linked to Ni through N(7) [Ni–N(7) 2.160(2) Å]. Two additional ACV molecules are included in the outer sphere of the complex, interacting by means of hydrogen bonds with the co-ordinated ACVs. This reveals the unprecedented recognition of free acyclovir molecules by Ni(or Co)-ACV (1 and 2). The monomeric zinc(II) complex 3 exhibits a distorted-tetrahedral geometry, involving two chlorides, the N(7) of the ACV ligand [Zn–N(7) 2.009(2) Å] and a water molecule.The hydrogen bonding of two guanine bases via NH2 and N(3) (unit 1) with N(3) and NH2 (unit 2) represents a novel type of interaction between nucleobases. In the case of the cadmium(II) complex 4 the structure is built by polymeric (CdCl2)n chains which are held together by ACV ligands. The cadmium cation is octahedrically coordinated by four chlorides, the N(7) from an ACV molecule and the hydroxylic oxygen from another ACV molecule, the latter two atoms being placed in cis disposition. On the other hand, the complex [{Hg(ACV)Cl2}x] 5 can be tentatively assigned as a polymer by comparison with analogous guanosine systems and spectroscopic and conductometric data.Acyclovir (ACV), 9-[(2-hydroxyethoxy)methyl]guanine, an analogue of 29-deoxyguanosine is an eYcient topically active acyclic nucleoside with inhibitory activity towards several herpes viruses, especially HSV-1 and HSV-2.1 Several studies have shown that the antiviral action of acyclovir involves its enzymatic conversion into the triphosphate of acycloguanosine {9-[(2-hydroxyethoxy)methyl]guanine}.2 It is converted into the monophosphate in herpes-infected cells (yet only to a very limited extent in uninfected cells) by viral-induced thymidine kinase.It is further phosphorylated by the host cell guanosine monophosphate kinase to acyclovir diphosphate, which in turn is phosphorylated to the triphosphate by unidentified cellular enzymes.The triphosphate of acycloguanosine is more inhibitory to the viral DNA polymerase than to the a-DNA polymerase of the cell.3 As a result, acyclovir is much more toxic to herpes viruses in an HSV-infected cell than to the cell itself. Metals can play an important role in both the mechanism of action and toxic side eVects of organic drugs and their metabolites.4 Although several acyclovir complexes and derivatives have been described 5–8 very little structural information is available.8–10 Thus in the present work studies of several metal(II) complexes with acyclovir have been carried out.Experimental Reagents were used as received from Roig Farma (acyclovir) and Aldrich (metallic salts). Syntheses [M(ACV)2(H2O)4]Cl2?2ACV (M 5 NiII 1 or CoII 2). To an aqueous solution (20 ml of water at 70 8C) of 12 mmol of MCl2?6H2O (M = Ni or Co), 6 mmol of acyclovir were added.The resulting solution was stirred for 2–3 h. After several days crystals were obtained. Complex 1 exhibits a mass decrease (Found: 28.5. Calc.: 29.0%) between 30 and 335 8C corresponding to the loss of 4 H2O 1 4 CH2OH–CH2OH per formula unit (Found: C, 34.78; H, 4.84; N, 25.19. Calc. for C32H52Cl2N20NiO16: C, 34.83; H, 4.72; N, 25.37%). Selected IR bands (cm21): 1123s, 1182m, 1403m, 1462m, 1490s, 1537m, 1574s, 1637vs, 1670vs and 1682 (sh).UV/VIS (DMSO): l 786 (e 5.4), 720 (sh), 425 (13) and 259 nm (7.2 × 104 dm3 mol21 cm21). The complex undergoes solvation in solution and Ni(DMSO)6 21 seems to be formed. LM/W21 cm2 mol21 (1023 mol dm23 in DMSO, 25 8C) = 63.7. Complex 2 exhibits a first mass decrease (Found: 3.4. Calc.: 3.3%) between 40 and ca. 150 8C corresponding to the loss of two water molecules per formula unit and a second mass decrease (Found: 25.0. Calc.: 25.9%) between 150 and 330 8C corresponding to the loss of 2 H2O 1 4 CH2OH–CH2OH per formula unit (Found: C, 34.76; H, 4.80; N, 25.19.Calc. for C32H52Cl2CoN20O16: C, 34.84; H, 4.72; N, 25.41%). Selected IR bands (cm21): 1122s, 1186m, 1404m, 1460m, 1488s, 1539m, 1574s, 1635vs, 1669vs and 1683 (sh). UV/VIS (DMSO): l 678 (e 90), 610 (sh) and 259 nm (8.2 × 104 dm3 mol21 cm21). The complex undergoes solvation in solution and Co(DMSO)6 21 seems to be formed. LM/W21 cm2 mol21 (1023 mol dm23 in DMSO, 25 8C) = 47.7.[Zn(ACV)Cl2(H2O)] 3, [Cd(ACV)Cl2]?H2O 4 and [{Hg(ACV)- Cl2}x] 5. To an aqueous solution (20 ml of water at 70 8C) of 12 mmol of MCl2 (M = Zn or Hg) or CdCl2?2.5 H2O, 6 mmol of168 J. Chem. Soc., Dalton Trans., 1999, 167–173 acyclovir were added. The resulting solution was stirred for 2–3 h. The complex precipitated during the reaction and was filtered oV, washed with water and air dried. Crystals of 3 and 4 were obtained by slow evaporation of mother-liquors. Complex 3 exhibits a mass decrease (Found: 4.9.Calc.: 4.7%) between 30 and 190 8C corresponding to the loss of the water molecule per formula unit (Found: C, 24.99; H, 3.42; N, 18.29. Calc. for C8H13Cl2N5O4Zn: C, 25.30; H, 3.42; N, 18.44%). Selected IR bands (cm21): 1130s, 1188m, 1403m, 1461w, 1494m, 1548m, 1587vs, 1651vs and 1690vs. UV (DMSO): l 259 nm (e 1.4 × 104 dm3 mol21 cm21). 1H NMR (DMSO-d6): d 10.86 [s, 1 H, H(1)], 8.04 [s, 1 H, H(8)], 6.68 (s, 2 H, NH2), 5.48 [s, 2 H, C(10)H], 4.79 (br t, 1 H, OH, J = 3.6 Hz) and 3.56 [s, 4 H, C(11)H and C(12)H]. 13C NMR (DMSO-d6): d 160.5 [C(6)], 158.0 [C(2)], 155.3 [C(4)], 142.4 [C(8)], 119.7 [C(5)], 76.2 [C(10)], 74.5 [C(12)] and 63.9 [C(11)]. LM/W21 cm2 mol21 (1023 mol dm23 in DMSO, 25 8C) = 6.8. Complex 4 exhibits a mass decrease (Found: 16.7. Calc.: 16.7%) between 40 and 280 8C corresponding to the loss of two chlorine atoms per formula unit (Found: C, 22.45; H, 3.07; N, 16.20. Calc. for C8H13CdCl2N5O4: C, 22.50; H, 3.05; N, 16.41%).Selected IR bands (cm21): 1118m, 1190m, 1398w, 1456 (sh), 1471m, 1539m, 1571 (sh), 1635vs and 1676s. UV (DMSO): l 259 nm (e 1.4 × 104 dm3 mol21 cm21). 1H NMR (DMSO-d6): d 10.75 [s, 1 H, H(1)], 7.93 [s, 1 H, H(8)], 6.62 (s, 2 H, NH2), 5.45 [s, 2 H, C(10)H], 4.78 (br t, 1 H, OH, J = 2.4 Hz) and 3.56 [s, 4 H, C(11)H and C(12)H]. 13C NMR (DMSO-d6): d 160.5 [C(6)], 158.1 [C(2)], 155.2 [C(4)], 142.1 [C(8)], 119.4 [C(5)], 76.4 [C(10)], 74.6 [C(12)] and 64.0 [C(11)].LM/W21 cm2 mol21 (1023 mol dm23 in DMSO, 25 8C) = 17.3. Complex 5 is thermally stable until 230 8C (Found: C, 19.22; H, 2.16; N, 13.83. Calc. for C8H11Cl2HgN5O3: C, 19.33; H, 2.22; N, 14.10%). Selected IR bands (cm21): 1112s, 1183m, 1396 (sh), 1463 (sh), 1485m, 1539m, 1585s, 1624s, 1666 (sh) and 1694vs. UV (DMSO): l 260 nm (e 1.6 × 104 dm3 mol21 cm21). 1H NMR (DMSO-d6): d 10.85 [s, 1 H, H(1)], 8.01 [s, 1 H, H(8)], 6.67 (s, 2 H, NH2), 5.48 [s, 2 H, C(10)H], 4.78 (br s, 1 H, OH) and 3.58 [s, 4 H, C(11)H and C(12)H]. 13C NMR (DMSO-d6): d 160.6 [C(6)], 158.3 [C(2)], 155.1 [C(4)], 142.9 [C(8)], 119.4 [C(5)], 76.7 [C(10)], 74.7 [C(12)] and 64.0 [C(11)]. LM/W21 cm2 mol21 (1023 mol dm23 in DMSO, 25 8C) = 2.6. Physical measurements Elemental analyses were carried out using a Carlo Erba model 1106 microanalyser. The infrared spectra in the solid state (KBr pellets) were recorded on a PE 683 spectrometer with a PE 1600 infrared data station and electronic spectra on a PE 552 spectrophotometer.The 1H and 13C NMR spectra were recorded on a Bruker AMX 300 spectrometer. Proton and carbon chemical shifts in DMSO-d6 were referenced to DMSOd6 [1H, d(DMSO) 2.60; 13C, d(DMSO) 43.5]. The 1H NMR temperature studies were referenced to tetramethylsilane [d(DMSO) 2.50 relative to TMS]. Thermogravimetric data in the range from 30 to 900 8C were obtained in air (heating rate 10 8C min21) on a PE TGA-2 thermobalance. Crystallography Crystal of compounds 1, 3 and 4 were mounted in a Siemens P4 diVractometer equipped with Mo-Ka radiation.The unit cell was determined in each case from 40 random reflections in the range 4 < q < 258. The number of independent reflections measured and the ranges of q, h, k and l are indicated together with other procedural data in Table 1. Three standards reflections were measured every 100, showing slight decomposition of samples 1 and 3 (around 5%). Data were corrected for Lorentz-polarisation eVects and empirically (y scans) for absorption in compounds 3 and 4 (not for 1); the transmission ranges were 0.333–0.503 and 0.462–0.516 respectively.The structures were solved by the heavy atom method and refined by full-matrix least squares on F 2. Extinction was corrected for compound 4 by means of the method implemented in SHELXTL-V5,11 the corresponding parameter reaching the value c = 0.0482(13). Hydrogen atoms were introduced in their ideal positions, except those of water molecules and the hydroxyl group of the ligand that were found in DF maps and refined with fixed (0.86 Å) O–H distances; thermal parameters 1.2 times those of their parent atoms were applied to all H atoms.Final residuals as well as crystal data are in Table 1. The program package SHELXTL-V5 was used for structure solution and refinement and for the drawings. CCDC reference number 186/1242. Powder X-ray diVraction diagrams were collected on a Siemens D5000 diVractometer with secondary graphitemonochromated Cu-Ka radiation (l = 1.54056 Å).Reflections were placed in the range 2 < 2q < 60. Results and discussion Crystal structures Nickel(II) and cobalt(II) complexes (1 and 2). The structure of complex 1 consists of elongated centrosymmetric octahedral molecules with H2O ligands in the basal plane [Ni–OW 2.053(2) and 2.057(7) Å] and two ACV molecules bound to Ni through N(7) [Ni–N(7) 2.160(2) Å] (Table 2). In order to complete the structural unit, two other ACV molecules are included in the outer sphere of the complex, interacting by means of hydrogen bonds with the co-ordinated ACVs [N(1A) ? ? ? O(12B) 2.803(3); N(2A) ? ? ? O(12B) 3.001(3); O(12A) ? ? ? N(1B) 2.776(3); O(12A) ? ? ? N(2B) 2.885(3) Å; O(1W) ? ? ? O(6A) 2.634(2); O(2W) ? ? ? O(6B) 2.696(2) Å] (Fig. 1). The oxygen atom of the carbonyl group of both co-ordinated and secondary ACV are involved in hydrogen bonds to the co-ordinated water molecules [O(1W) ? ? ? O(6A) 2.634(2); O(2W) ? ? ? O(6B) 2.696(2) Å] as observed in several Cu–ACV complexes.8,9 Values of Ni–OW and Ni–N(7) are similar to those in other structurally related complexes such as [Ni(IMP)(H2O)5],12 [Ni(en)(IMP)2(H2O)2],13 [Ni(GMP)(H2O)5],14 [Ni(GMP)2(H2O)4]22,15 [Ni(en)0.7 (dGMP)2- (H2O)0.6(H2O)2]2215 and [Ni(dGMP)(H2O)5].16 The guanine moiety, of all ACV molecules presented in complex 1, is essentially planar.The bond lengths and angles of guanine conform well to those found in the three molecules of the asymmetric unit of crystalline ACV?2 3 – H2O17 and those corresponding to [Cu(ACV)2Cl2(H2O)2],9 [Cu(ACV)2(H2O)x]21 (x = 2 10a or 310b), [Cu(ACVP)2(H2O)2] 8 (ACVP = acyclovir monophosphate) and [Pt(ACVA)Cl2(h2-C2H4)] 7 (ACVA = acyclovir monoacetate).In previously described complexes the C(10) is coplanar to the plane of guanine however in 1 a noticeable distortion {t[N(7)–C(8)–N(9)–C(10)] = 171.048 (8.98 up to plane)} appears.The Ni bonded to N(7) is placed 11.28 below the plane of guanine {t[N(9)–C(8)–N(7)–Ni] = 168.788}. This Fig. 1 Molecular structure of [Ni(ACV)2(H2O)4]Cl2?2ACV 1.J. Chem. Soc., Dalton Trans., 1999, 167–173 169 Table 1 Crystal data and structure refinement for [Ni(ACV)2(H2O)4]Cl2?2ACV 1, [Zn(ACV)Cl2(H2O)] 3 and [Cd(ACV)Cl2]?H2O 4 Empirical formula M Crystal system Space group Crystal dimensions/mm a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Dc/g cm23 Z m(Mo-Ka)/cm21 T/K q Range/8 hkl Ranges No.reflections collected No. independent reflections (Rint) F(000) Data/restraints/parameters Goodness of fit on F 2 Final R1, wR2 [I > 2s(I)] (all data) Largest diVerence peak, hole/e Å23 1 C32H52Cl2N20NiO16 1102.55 Monoclinic P21/n 0.45 × 0.3 × 0.25 12.6672(8) 15.1340(12) 12.8273(11) 111.077(5) 2294.5(3) 1.596 2 6.31 293(2) 1.94–25.00 21 to 15, 21 to 17, 215 to 14 4999 4035 (0.0241) 1148 4035/6/340 1.027 0.0383, 0.0973 0.0443, 0.1019 1.051, 20.374 3 C8H13Cl2N5O4Zn 379.50 Triclinic P1� 0.5 × 0.4 × 0.2 7.7878(7) 8.6616(6) 10.9133(10) 97.841(7) 106.910(7) 94.220(6) 692.74(10) 1.819 2 21.78 293(2) 1.98–30.0 21 to 10, 212 to 12, 215 to 15 4815 4001 (0.0171) 384 3999/3/190 1.087 0.0327, 0.0873 0.0385, 0.0928 0.455, 20.940 4 C8H13CdCl2N5O4 426.53 Triclinic P1� 0.2 × 0.3 × 0.4 7.2653(5) 7.9452(6) 12.5441(10) 84.702(6) 75.186(6) 78.932(5) 686.30 2.064 2 20.00 293(2) 1.68–30.00 21 to 10, 211 to 11, 217 to 17 4879 4008 (0.0175) 420 4008/3/191 1.141 0.0220, 0.0580 0.0225, 0.0584 0.514, 20.562 value is higher than those of the corresponding Pt 7 (8.28) and Cu9 (5.28) complexes.The acyclic chains of the two diVerent ACVs present in the structural unit of 1 are folded, with C(11)– C(12) bonds in gauche conformation, but a syn conformation between N(7) and O(12) appears † which permits five hydrogen bonds to stabilise the non-co-ordinated ACVs in the complex structure. On the other hand, stacking between co-ordinated and non-co-ordinated ACVs is present (average distance between the two rings = 3.4 Å; this distance is essentially the same as that found between adjacent base pairs in DNA17).These subtle changes in the lateral chains could be responsible for the recognition of non-co-ordinated ACV by Ni–ACV. The powder X-ray diVraction diagrams of the nickel 1 and cobalt 2 complexes clearly demonstrate that the compounds are isostructural, diVraction peaks changing only slightly in position and intensity from one diagram to the other.Zinc(II) complex 3. The co-ordination geometry about the ZnII in complex 3 is approximately tetrahedral with an ACV molecule [Zn–N(7) 2.009(2) Å], two chlorine atoms [Zn–Cl(1) 2.2544(6) and Zn-Cl(2)=2.1976(6) Å] and a water molecule [Zn– OW 1.996(2) Å] [Table 2 and Fig. 2(a)]. The crystal structure is formed by three types of hydrogen bonds between ACVs [N(2)H2(unit 1) ? ? ? N(3)(unit 2) 3.041(2) Å], between acyclovir and the chlorine atom [N(1)(unit 1) ? ? ? Cl(1)(unit 3) 3.255(2) and N(2)H2(unit 1) ? ? ? Cl(1)(unit 3) 3.473(2) Å] and between the hydroxyl group of the lateral chain of ACV and the water molecule [O(12)(unit 2) ? ? ?OW(unit 3) 2.690(2)].The hydrogen bond scheme of two guanine bases via NH2 and N(3) (unit 1) with N(3) and NH2 (unit 2) could represent a novel type of interaction between nucleobases as described by Lippert and co-workers.18 The value of Zn–N(7) is similar to that of polymeric Zn(59-IMP)19 [Zn–N(7)(distorted tetrahedral coordination) 1.99 Å] but lower than those corresponding of [Zn(H2O)4(Me-59-IMP)] and [Zn(H2O)4(Me-59-GMP)] 20 [Zn– N(7)(octahedral co-ordination) 2.158 and 2.143 Å] [Fig. 2(b)]. † A similar C(11)–C(12) gauche conformation but an anti conformation between N(7) and C(12) is present in units A and B of free ACV (see ref. 16). Like in the other complexes, the guanine moiety of ACV in 3 is essentially planar and bond lengths angles are similar.7–10,17 Nevertheless, this complex presents an important noncoplanarity of C(10) {t[N(7)–C(8)–N(9)–C(10)] = 190.908} and Zn{t[N(9)–C(8)–N(7)–Zn] = 164.178} with these two atoms placed on the same side of the plane of guanine [C(10) 10.98 and Zn 15.88].As in 1, the acyclic chain of ACV in 3 is folded Fig. 2 (a) Molecular structure of [Zn(ACV)Cl2(H2O)] 2. (b) Packing of three complex units showing the hydrogen bonds and the novel type of interaction between two guanine nucleobases [NH2 and N(3) (unit 1) with N(3) and NH2 (unit 2)].170 J.Chem. Soc., Dalton Trans., 1999, 167–173 Table 2 Bond lengths (Å) and angles (8) Nickel complex 1 Ni–O(1W) N(1A)–C(2A) N(1A)–C(6A) C(2A)–N(3A) C(2A)–N(2A) N(3A)–C(4A) C(4A)–N(9A) C(4A)–C(5A) C(5A)–N(7A) C(5A)–C(6A) 2.053(2) 1.369(3) 1.389(3) 1.324(3) 1.331(3) 1.349(3) 1.372(3) 1.382(3) 1.400(3) 1.422(3) Ni–O(2W) N(1B)–C(2B) N(1B)–C(6B) C(2B)–N(3B) C(2B)–N(2B) N(3B)–C(4B) C(4B)–N(9B) C(4B)–C(5B) C(5B)–N(7B) C(5B)–C(6B) 2.057(7) 1.371(3) 1.387(3) 1.319(3) 1.333(3) 1.356(3) 1.371(3) 1.384(3) 1.383(3) 1.416(3) Ni–N(7A) C(6A)–O(6A) N(7A)–C(8A) C(8A)–N(9A) N(9A)–C(10A) C(10A)–O(10A) O(10A)–C(11A) C(11A)–C(12A) C(12A)–O(12A) 2.160(2) 1.237(3) 1.313(3) 1.369(3) 1.471(3) 1.387(3) 1.428(3) 1.498(4) 1.418(3) C(6B)–O(6B) N(7B)–C(8B) C(8B)–N(9B) N(9B)–C(10B) C(10B)–O(10B) O(10B)–C(11B) C(11B)–C(12B) C(12B)–O(12B) 1.238(3) 1.304(4) 1.375(4) 1.464(3) 1.390(3) 1.386(4) 1.482(5) 1.398(3) Hydrogen bonds present in the molecular unit N(1A) ? ? ? O(12B) O(1W)–Ni–N(7A) O(1W)–Ni–O(2W) C(2A)–N(1A)–C(6A) N(3A)–C(2A)–N(2A) N(3A)–C(2A)–N(1A) N(2A)–C(2A)–N(1A) C(2A)–N(3A)–C(4A) N(3A)–C(4A)–N(9A) N(3A)–C(4A)–C(5A) N(9A)–C(4A)–C(5A) C(4A)–C(5A)–N(7A) C(4A)–C(5A)–C(6A) N(7A)–C(5A)–C(6A) O(6A)–C(6A)–N(1A) 2.803(3) 87.23(7) 91.51(8) 126.2(2) 120.7(2) 122.7(2) 116.6(2) 112.4(2) 124.7(2) 129.2(2) 106.0(2) 109.9(2) 117.6(2) 132.2(2) 119.1(2) N(1B) ? ? ? O(12A) O(2W)–Ni–N(7A) C(2B)–N(1B)–C(6B) N(3B)–C(2B)–N(2B) N(3B)–C(2B)–N(1B) N(2B)–C(2B)–N(1B) C(2B)–N(3B)–C(4B) N(3B)–C(4B)–N(9B) N(3B)–C(4B)–C(5B) N(9B)–C(4B)–C(5B) C(4B)–C(5B)–N(7B) C(4B)–C(5B)–N(7B) N(7B)–C(5B)–C(6B) O(6B)–C(6B)–N(1B) 2.776(3) 90.76(7) 125.7(2) 120.9(2) 123.6(2) 115.6(2) 112.1(2) 125.9(2) 128.3(2) 105.7(2) 110.7(2) 118.8(2) 130.5(2) 118.8(2) N(2A) ? ? ? O(12B) C(8A)–N(7A)–Ni O(6A)–C(6A)–C(5A) C(5A)–C(6A)–N(1A) C(8A)–N(7A)–C(5A) N(7A)–C(8A)–N(9A) C(8A)–N(9A)–C(4A) C(8A)–N(9A)–C(10A) C(4A)–N(9A)–C(10A) O(10A)–C(10A)–N(9A) C(10A)–O(10A)–C(11A) O(10A)–C(11A)–C(12A) O(12A)–C(12A)–C(11A) 3.001(3) 121.0(2) 129.2(2) 111.7(2) 104.4(2) 113.1(2) 106.6(2) 127.6(2) 125.3(2) 113.0(2) 114.4(2) 108.6(2) 109.4(2) N(2B)–O(12A) C(5A)–N(7A)–Ni O(6B)–C(6B)–C(5B) C(5B)–C(6B)–N(1B) C(8B)–N(7B)–C(5B) N(7B)–C(8B)–N(9B) C(8B)–N(9B)–C(4B) C(8B)–N(9B)–C(10B) C(4B)–N(9B)–C(10B) O(10B)–C(10B)–N(9B) C(10B)–O(10B)–C(11B) O(10B)–C(11B)–C(12B) O(12B)–C(12B)–C(11B) 2.885(3) 133.38(14) 129.7(2) 111.5(2) 104.1(2) 113.8(2) 105.7(2) 128.4(2) 125.9(2) 112.9(2) 115.7(3) 110.9(3) 110.6(3) Zinc complex 3 Zn–O(1W) N(1)–C(2) N(1)–C(6) C(2)–N(2) C(2)–N(3) N(3)–C(4) O(1W)–Zn–Cl(1) N(7)–Zn–Cl(1) Zn–N(7)–C(8) O(1W)–Zn–N(7) C(2)–N(1)–C(6) N(3)–C(2)–N(2) N(2)–C(2)–N(1) N(3)–C(2)–N(1) 1.996(2) 1.379(2) 1.389(2) 1.329(2) 1.331(2) 1.350(2) 108.49(7) 110.92(5) 123.08(12) 104.53(7) 125.42(14) 120.0(2) 116.7(2) 123.3(2) Zn–N(7) C(4)–N(9) C(4)–C(5) C(5)–N(7) C(5)–C(6) O(1W)–Zn–Cl(2) N(7)–Zn–Cl(2) Zn–N(7)–C(5) O(6)–C(6)–C(5) C(5)–C(6)–N(1) C(8)–N(7)–C(5) N(7)–C(8)–N(9) 2.009(2) 1.378(2) 1.382(2) 1.385(2) 1.416(2) 111.58(6) 106.96(5) 129.50(12) 127.6(2) 111.38(14) 105.16(14) 112.4(2) Zn–Cl(1) C(6)–O(6) N(7)–C(8) C(8)–N(9) N(9)–C(10) C(2)–N(3)–C(4) N(3)–C(4)–N(9) N(3)–C(4)–C(5) N(9)–C(4)–C(5) C(4)–C(5)–N(7) C(4)–C(5)–C(6) N(7)–C(5)–C(6) O(6)–C(6)–N(1) 2.2544(6) 1.236(2) 1.316(2) 1.364(2) 1.470(2) 112.37(14) 126.36(14) 128.01(14) 105.62(14) 109.99(14) 119.5(2) 130.4(2) 121.0(2) Zn–Cl(2) C(10)–O(10) O(10)–C(11) C(11)–C(12) C(12)–O(12) C(8)–N(9)–C(4) C(8)–N(9)–C(10) C(4)–N(9)–C(10) O(10)–C(10)–N(9) C(10)–O(10)–C(11) O(10)–C(11)–C(12) O(12)–C(12)–C(11) 2.1976(6) 1.389(2) 1.426(2) 1.501(3) 1.421(3) 106.84(13) 125.09(14) 127.06(14) 113.0(2) 113.2(2) 108.6(2) 112.9(2) Cadmium complex 4 Cd–Cl(1) Cd–Cl(2) N(1)–C(2) N(1)–C(6) C(2)–N(2) C(2)–N(3) N(3)–C(4) O(12*)–Cd–N(7) O(12*)–Cd–Cl(2) O(12*)–Cd–Cl(1)2 O(12*)–Cd–Cl(1) O(12*)–Cd–Cl(2)3 C(2)–N(1)–C(6) N(3)–C(2)–N(2) N(2)–C(2)–N(1) N(3)–C(2)–N(1) C(2)–N(3)–C(4) N(3)–C(4)–N(9) N(3)–C(4)–C(5) 2.6631(5) 2.5654(5) 1.374(2) 1.386(2) 1.351(2) 1.323(2) 1.344(2) 83.11(5) 163.99(4) 89.87(3) 88.45(4) 81.25(4) 125.2(2) 119.5(2) 117.1(2) 123.4(2) 112.4(2) 125.4(2) 128.9(2) Cd–Cl(19) Cd–Cl(20) C(4)–N(9) C(4)–C(5) C(5)–N(7) C(5)–C(6) Cd–Cl(2)–Cd3 Cd–Cl(1)–Cd2 Cd–N(7)–C(8) Cd–N(7)–C(5) N(9)–C(4)–C(5) C(4)–C(5)–N(7) C(4)–C(5)–C(6) N(7)–C(5)–C(6) O(6)–C(6)–N(1) Cd4–O(12)–O(6)4 2.5993(5) 2.6884(5) 1.374(2) 1.385(2) 1.393(2) 1.419(2) 94.66(2) 96.82(2) 115.94(12) 138.97(11) 105.66(14) 110.2(2) 118.0(2) 131.8(2) 119.4(2) 108.76(6) Cd–N(7) C(6)–O(6) N(7)–C(8) C(8)–N(9) N(9)–C(10) N(7)–Cd–Cl(2) N(7)–Cd–Cl(1)2 N(7)–Cd–Cl(1) N(7)–Cd–Cl(2)3 Cl(1)–Cd–Cl(2)3 O(6)–C(6)–C(5) C(5)–C(6)–N(1) C(8)–N(7)–C(5) N(7)–C(8)–N(9) C(8)–N(9)–C(4) C(8)–N(9)–C(10) C(4)–N(9)–C(10) 2.402(2) 1.243(2) 1.313(2) 1.369(2) 1.458(2) 88.52(4) 165.91(4) 84.43(4) 91.29(4) 169.26(2) 128.4(2) 112.15(14) 104.45(14) 113.0(2) 106.64(14) 125.8(2) 127.2(2) Cd–O(12*) C(10)–O(10) O(10)–C(11) C(11)–C(12) C(12)–O(12) Cl(1)–Cd–Cl(1)2 Cl(2)–Cd–Cl(1)2 Cl(2)–Cd–Cl(2)3 Cl(1)2–Cd–Cl(2)3 O(10)–C(10)–N(9) C(10)–O(10)–C(11) O(10)–C(11)–C(12) O(12)–C(12)–C(11) C(12)–O(12)–O(6)4 C(12)–O(12)–Cd4 2.3050(13) 1.405(2) 1.443(2) 1.496(2) 1.433(2) 83.18(2) 101.02(2) 85.34(2) 99.73(2) 111.70(14) 113.58(14) 107.56(14) 109.27(14) 107.24(11) 123.22(10) a Superscripts represent other diVerent monomeric units.J.Chem.Soc., Dalton Trans., 1999, 167–173 171 with C(11)–C(12) bonds in gauche conformation and syn conformation between N(7) and O(12). Cadmium(II) complex 4. The CdII in the polymeric complex 4 presents a distorted octahedral co-ordination with four chlorine atoms, N(7) from an ACV molecule and O(12) from another ACV molecule [Cd–Cl between 2.5654(5) and 2.6884(5), Cd– N(7) 2.402(2), Cd–O(12) 2.3050(13) Å] (Table 2). These two ACVs are placed in cis disposition [Fig. 3(a)]. The value of the distance Cd–N(7) is slightly higher than that of the octahedral monomeric structure of Cd(59-GMP)21 [Cd–N(7) 2.37 Å]. The guanine moiety of ACV in 4 is also essentially planar. As in 3, C(10) and Cd atoms of the complex are placed on the same side of the plane of guanine [C(10) 6.88 and Cd 7.78] and although the acyclic chain of ACV is folded with C(11)–C(12) bonds in gauche conformation a trans conformation between N(7) and O(12) can be observed.To our knowledge, this is the first example where the hydroxyl group of the lateral chain of ACV interacts directly with the metal. The structure is built by polymeric (CdCl2)n chains linked by ACV ligands [Fig. 3(b)]. The chains run along the a axis and cadmium atoms alternate in them with pairs of bridging chlorine ligands. Four-membered Cd2Cl2 centrosymmetric rings are generated in this way, which considerably deviate from a perfect square-planar geometry as far as the angles are concerned.Consecutive Cd2Cl2 rings are almost perpendicular (average dihedral angle = 81.528) and therefore the polymeric chain is twisted.22 The chains are linked to each other by the acyclovir ligands which are co-ordinated via N(7) to a cadmium atom of one chain and via the terminal hydroxyl group O(12) to a cadmium atom of another chain. This latter bond is reinforced by a hydrogen bond formed with the carbonyl oxygen atom O(6) of the ACV molecule co-ordinated via N(7) [O(12) ? ? ? O(6) 2.636(2) Å], yielding a two-dimensional polymer perpendicular to the c axis. An interstitial water molecule completes the asymmetric unit, being strongly attached to the structure via Fig. 3 (a) Molecular structure of [Cd(ACV)Cl2]?H2O 3. (b) Drawing of the polymeric chain (CdCl2)n. hydrogen bonds [N(1) ? ? ?OW 2.801(2), O(6) ? ? ?OW 2.893(2) and O(10) ? ? ?OW 2.841(2) Å]. The Ni–ACV 1, Zn–ACV 3, Cd–ACV 4, Cu–ACV8–10 and Pt–ACV7 complexes present a lateral chain with a global conformation type: gauche [N(9)–C(10)], gauche [C(10)–O(10)], trans [O(10)–C(11)] and gauche [C(11)–C(12)] which is equivalent to those observed in the A and B molecules of free acyclovir 17 (Table 3).The gauche conformation of the glycosidic bond N(9)–C(10) is consistent with the observed distances [from 1.459(2) to 1.471(3) Å] which are longer than those usually found in the opposite trans conformation [1.441(5) Å].7 Infrared spectra The IR spectra of the obtained complexes were compared with that of acyclovir.23,24 The more relevant features are: (a) shift to lower frequencies of the strong band at 1718 cm21 (1682, 1670 for 1; 1683, 1669 for 2; 1690 for 3; 1676 for 4 and 1694, 1666 cm21 for 5) which is assigned to the vibration n[C(6)]] O(6)] in free ACV. This is consistent with the C]] O group involved in hydrogen bonds.In some Cu–ACV complexes 8,9 it has been observed that short hydrogen bonds involving O(6) significantly diminish the carbonyl stretching frequency in the IR spectra. The 1634 cm21 band related to d(NH2) is not appreciably shifted for 1, 2, 4 and 5, although for 3 it is shifted to 1651 cm21, possibly due to the double interaction of the NH2 group present [N(3) ? ? ?H2N, Cl ? ? ?H2N].(b) Splitting of the 1487 cm21 band23 (1490, 1462 for 1; 1488, 1460 for 2; 1494, 1461 for 3; 1471, 1456 for 4 and 1485, 1463 for 5) assigned to d[C(8)– H] 1 n[C(8)–N(7)] and these variations, related to the fivemembered ring, have been observed in the spectra of several structurally known N(7)-metallated complexes.23,25 The far-IR spectra of the complexes show a new band at 312 1 and 313 cm21 2 assigned as essentially n(M–N).26 The low frequency band at 332 cm21, found for compound 3, may be attributed to the Zn–Cl stretching mode of the terminal chlorides.27 NMR spectra Unequivocal assignments of 1H and 13C NMR spectra of compounds 3, 4 and 5 are shown in Table 4.As can be appreciated, the spectra of the compounds of ZnII, CdII and HgII show small diVerences with regards to the ACV ligand, but are similar to those of other equivalent guanosine complexes,28 which can be explained by the practically no modification of the structural features of the guanine ring and the lateral chain (see X-ray section). Thus, at room temperature, in the 1H NMR only slight modifications (Zn 10.12, Cd 10.01 and Hg 10.09 ppm) of H(8) of the guanine ring can be observed.On the other hand, the 13C NMR of these complexes show a slight general upfield shift of C(5) (Zn 20.7, Cd 21.0 and Hg 21.0 ppm) and down- field shift of C(8) (Zn 10.7, Cd 1 0.4 and Hg 11.2 ppm), which can be explained by the formation of the metal(II)–N(7) bond. Although we cannot discard the substitution of the remaining ligands by DMSO molecules, the existence in solution of ACV–metal interaction has been studied between 20 and 60 8C (internal reference: tetramethylsilane). In the Zn–ACV 3 and Hg–ACV 5 complexes the resonance of the aromatic H(8) proton shows an upfield shift when the temperature is increased (ca. 0.04 ppm per 10 8C) compared with free ACV which remains practically unaltered. A possible explanation is the reversible labilisation of the N(7)–M bond which diminishes the non-shielding eVect of the metal over H(8). The H(8) of the Cd–ACV complex 4 shows similar behaviour to that of ACV and we cannot conclude whether in solution the N(7)–M bond remains unaltered.Conclusion The compound ACV presents a general N(7)–M interaction172 J. Chem. Soc., Dalton Trans., 1999, 167–173 Table 3 Dihedral angles (8) corresponding to the lateral chain in ACV and ACV complexes ACV Molecule Dihedral angle C(4)–N(9)–C(10)–O(10) N(9)–C(10)–O(10)–C(11) C(10)–O(10)–C(11)–C(12) O(10)–C(11)–C(12)–O(12) A 276.5 276.9 173.2 60.6 B 274.4 266.3 2176.2 73.5 C 290.5 2173.3 2171.9 2174.4 Ni–ACV 273.8 282.8 2179.5 266.6 (272.7) a (2103.2) (172.5) (260.8) Zn–ACV 74.6 73.2 178.8 59.3 Cd–ACV 282.7 271.2 2170.8 63.2 Cu–ACV 92.5 288.7 2178.2 269.1 Pt–ACV 74.2 77.0 2178.4 265.9 a Non-co-ordinated ACV.Table 4 Proton and 13C NMR (selected peaks, at 294 K) of ACV and complexes 3–5 Dd H(1) H(8) NH2 C(6) C(2) C(4) C(8) C(5) C(10) C(12) C(11) ACV 10.77 7.92 6.62 160.8 157.8 155.4 141.7 120.4 76.0 74.4 63.9 3 10.86(10.09) 8.04(10.12) 6.68 160.5(20.3) 158.0(10.2) 155.3(20.1) 142.4(10.7) 119.7(20.7) 76.2(10.2) 74.5(10.1) 63.9(0.0) 4 10.75(20.02) 7.93(10.01) 6.62 160.5(20.3) 158.1(10.3) 155.2(20.2) 142.1(10.4) 119.4(21.0) 76.4(10.4) 74.6(10.2) 64.0(10.1) 5 10.85(10.08) 8.01(10.09) 6.67 160.6(20.2) 158.3(10.5) 155.1(20.3) 142.9(11.2) 119.4(21.0) 76.7(10.7) 74.7(10.3) 64.0(10.1) [Hg(Guo)Cl2] (10.21) (10.08) (20.4) (10.1) (20.3) (0.0) (20.6) [Hg(Guo)Br2] (10.06) (10.11) (20.4) (10.1) (20.6) (10.3) (0.0) [Hg(Guo)(SCN)2] (10.21) (10.21) (20.5) (10.3) (20.7) (10.8) (20.4) which is accompanied by hydrogen bonds, stabilising a monomeric unit and/or the crystal structure.Although all heteroatoms of the ligand constitute potential sites to form hydrogen bonds in metal chloride complexes of Co, Ni, Cu, Zn, Cd and Hg with ACV, there is a preference of the guanidine moiety of the guanine ring [N(1), N(2) and N(3)] for ACV? ? ?ACV interactions, whereas oxygens [O(6), O(10) and O(12)] are normally involved in ACV? ? ?H2O interactions. On the other hand, Ni (and Co)–ACV constitute examples of recognition of ACV for Ni(or Co)–ACV.The Cd–ACV complex is the first example where an oxygenated group [O(12)H] of the lateral chain of ACV interacts directly with the metal. In the Zn–ACV complex the hydrogen bonding of two guanine bases via NH2 and N(3) (unit 1) with N(3) and NH2 (unit 2) represents a novel type of interaction between nucleobases. Based on X-ray and spectral data we can conclude that Co–, Ni–, Cu–9 and Zn–ACV are monomeric complexes and Cd– ACV is a polymeric structure (Figs. 1–3). The complex Hg– ACV could be tentatively assigned as a [{Hg(ACV)Cl2}x] polymer based on spectral data which show direct N(7)–Hg interaction, conductometric measurements (no electrolyte) and comparison with other similar structures [{Hg(Guo)X2}x] (X = Cl, Br or SCN).28 Acknowledgements We are grateful to Dirección General de Investigación Científica y Técnica, Ref. PB94-0922-C02-02, for financial support. References 1 H.J. SchaeVer, L. Beauchamp, P. de Miranda, G. B. Elion, D. J. Bauer and P. Collins, Nature, 1978, 272, 583. 2 J. A. Fyfe, P. M. Keller, P. A. Furman, R. L. Miller and G. B. Elion, J. Biol. Chem., 1978, 253, 8721; G. B. Elion, J. Antimicrob. Chemother., 1983, 12, Suppl. B, 9. 3 R. B. Silverman, in The Organic Chemistry of Drug Design and Drug Action, Academic Press, New York, 1992, p. 392; C. J. Coulson, in Molecular Mechanisms of Drug Action, 2nd edn., Taylor & Francis, London, 1994, p. 30. 4 P. J. Sadler, Adv. Inorg. Chem., 1991, 36, 1. 5 S. Grabner and N. Bukovec, 4th FGIPS Meeting in Inorganic Chemistry, European Mediterranean Conference in Inorganic Chemistry, Corfu, October 1997, Abstract PA32. 6 Z. Balcarova, J. Kasparkova, G. Natile and V. Brabec, 4th FGIPS Meeting in Inorganic Chemistry, European Mediterranean Conference in Inorganic Chemistry, Corfu, October 1997, Abstract ORA 20. 7 L. Cavallo, R. Cini, J. Kobe, L. G. Marzilli and G. Natile, J.Chem. Soc., Dalton Trans., 1991, 1867. 8 I. Turel, I. Leban and K. Gruber, J. Inorg. Biochem., 1996, 63, 41. 9 B. Blazic, I. Turel, N. Bukovec, P. Bukovek and F. Lazarini, J. Inorg. Biochem., 1993, 51, 737. 10 (a) B. Andersen, T. I. Sjastad, I. Turel, A. Emwas, E. Sletten, C. A. Blindauer and H. Sigel, COST D8 — Chemical Properties of Platinum and Other Metal Ion Complexes with Nucleobases and Antiviral Nucleotide Analogues. Dortmund, September 1998; (b) I. Turel, N. Bukovec, M.Goodgame and D. J. Williams, Polyhedron, 1997, 16, 1701. 11 G. M. Sheldrick, SHELXTL Version 5 for PC, Siemens Analytical X-ray Instruments, Inc., Madison, WI, 1994. 12 K. Aoki, Bull. Chem. Soc. Jpn., 1975, 48, 1260; G. R. Clark and J. D. Orbell, J. Chem. Soc., Chem. Commun., 1974, 139. 13 J. J. Fiol, A. Terrón, A. M. Calafat, V. Moreno, M. Aguiló and X. Solans, J. Inorg. Biochem., 1989, 35, 191. 14 P. de Meester, D. M. L. Goodgame, A. C. Skapski and B. T. Smith. Biochem.Biophys. Acta, 1974, 340, 113. 15 N. S. Begum, M. D. Poojary and H. Manohar, J. Chem. Soc., Dalton Trans., 1988, 1303. 16 R. W. Gellert, J. K. Shiba and R. Bau, Biochem. Biophys. Res. Commun., 1979, 88, 1449. 17 G. I. Birnbaum, M. Cygler and D. Shugar, Can. J. Chem., 1984, 62, 2646. 18 R. K. O. Sigel, E. Freisinger and B. Lippert, Chem. Commun., 1998, 219; R. K. O. Sigel, E. Freisinger, S.M. Thompson and B. Lippert, COST D8 — Chemical Properties of Platinum and Other Metal Ion Complexes with Nucleobases and Antiviral Nucleotide Analogues, Dortmund, September 1998. 19 P. de Meester, D. M. L. Goodgame, T. J. Jones and A. C. Skapski, Biochem. Biophys. Acta, 1974, 353, 392. 20 S. K. Miller, D. G. VanDerveer and L. G. Marzilli, J. Am. Chem. Soc., 1985, 107, 1048. 21 K. Aoki, Acta Crystallogr., Sect. B, 1976, 32, 1454. 22 (a) A. Bonamartini, M. R. Cramarossa and M. Saladini, Inorg. Chim. Acta, 1997, 257, 19; (b) E. A. H. GriYth, N. G. Charles and E. L. Amma, Acta Crystallogr., Sect. B, 1982, 38, 942. 23 H. A. Tajmir-Riahi and T. Theophanides, Can. J. Chem., 1984, 62, 1429.J. Chem. Soc., Dalton Trans., 1999, 167–173 173 24 M. Tsuboi, S. Takahoshi and I. Harada, in Physicochemical Properties of Nucleic Acids, ed. J. Duchesne, Academic Press, New York, 1973, vol. 2, p. 91; H. A. Tajmir-Riahi and T. Theophanides, Inorg. Chim. Acta, 1983, 80, 223; D. U. Young, P. Tollin and H. R. Wilson, Acta Crystallogr., Sect. B, 1974, 30, 2012; T. Theophanides and H. A. Tajmir-Riahi, in Spectroscopy of Biological Molecules, eds. C. Sandorfy and T. Theophanides, D. Reidel, Dordrecht, 1982, p. 137; S. Shirotake and T. Sakaguchi, Chem. Pharm. Bull., 1978, 26, 2941. 25 H. A. Tajmir-Riahi and T. Theophanides, Can. J. Chem., 1985, 63, 2065. 26 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York, 1978. 27 N. B. Behrens and D. M. L. Goodgame, Inorg. Chim. Acta, 1980, 46, 15. 28 M. Quirós, J. M. Salas-Peregrín, M. P. Sánchez-Sánchez and R. Fauré, An. Quim., 1990, 86, 518. Paper 8/07787H

ISSN:1477-9226    

DOI:10.1039/a807787h

出版商:RSC    

年代:1999

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DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 173 Lanthanoid complexes of a tripodal acetal ligand: synthesis, structural characterisation and reactivity with 3d metals Stephen J. Archibald, Alexander J. Blake,*,† Simon Parsons, Martin Schröder *,† and Richard E. P. Winpenny * Department of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK A novel tripodal ligand (H3L1) has been prepared by condensation of tris(2-aminoethyl)amine with 2,6- diformyl-4-methylphenol in MeOH.The compound has three equivalent side-arms, each containing four possible donor groups, an imine N atom, a phenol O atom and two O-donors from an acetal group. The crystal structure showed the arms to be arranged such that a non-crystallographic three-fold axis passes through the bridgehead N atom. Reaction of H3L1 with lanthanoid perchlorate salts resulted in the isolation of two series of complexes. With early lanthanoids compounds of stoichiometry [Ln(H3L1)(H2O)][ClO4]3 were obtained and the compounds with Ln = La and Pr have been structurally characterised.The lanthanoid site in these complexes is ten co-ordinate, with a geometry which can be related to an icosahedron. For later lanthanoids, complexes of stoichiometry [Ln(H3L1)][ClO4]3 are found in which the lanthanoid site is nine-co-cordinate, with a tricapped trigonalprismatic geometry. The complex with Ln = Y has been characterised by diffraction techniques.Mass spectroscopic studies indicated that the acetal functions within H3L1 are stabilised by co-ordination to the lanthanoid metals. Reaction of the complex [La(H3L1)(H2O)][ClO4]3 with nickel(II) perchlorate led to a novel heterobimetallic complex in which both La and Ni are encapsulated within the tripodal ligand. Compartmental ligands derived from Schiff-base condensation of 2,6-diformyl- and 2,6-diacetyl-4-methylphenol have received much attention.1 These types of compound provide a framework from which polymetallic, and especially binuclear, metal complexes can be generated with considerable control of the topology and composition of the resulting complex.1,2 In particular where heterobimetallic compounds are the desired product, design of a suitable polydentate ligand is a more elegant approach than use of simpler, less specific chelates.For example, Okawa and co-workers 3 have shown how ring expansion of one compartment of a Schiff-base macrocycle can allow complexation of both 3d and 6p elements by the same ligand.Recent work by Costes et al.4 has shown that binuclear 3d/4f complexes can be made utilising such a route, whereas previous synthetic methods have always led to larger oligomers when such metals have been mixed.5–9 A second approach to the preparation of mixed-metal complexes is via the use of tripodal ligands where metals can be encapsulated by the three arms of a suitably designed ligand. In particular, Orvig and co-workers 10 have demonstrated that such ligands provide suitable hosts for lanthanoid metals, and the resulting complexes may be of use as contrast agents for magnetic resonance imaging (MRI).Related macrocyclic species have potential use in RNA and DNA cleavage,11 and because of their photophysical properties.12 McCleverty and co-workers 13 have also reported an interesting podand with chelating sidearms which appears ideal for co-ordinating to 4f elements.We report herein the synthesis and structures of a free tripodal compartmental ligand and of its complexes with lanthanum, praseodymium and yttrium.14 Additionally we demonstrate that its lanthanoid complexes can be deprotonated and a second metal incorporated within the tripodal host. Experimental Preparation of compounds 2,6-Diformyl-4-methylphenol was prepared by a literature pro- Present address: Department of Chemistry, The University of Nottingham, University Park, Nottingham, UK NG7 2RD.cedure.15 Tris(2-aminoethyl)amine (tren), lanthanoid salts and solvents were used as obtained. CAUTION: perchlorate salts are potentially explosive and should be handled with great care and in small quantities. Proton NMR spectra in CDCl3 (for H3L1) or CD3NO2 (for metal complexes) were recorded on a Bruker AM-360 MHz spectrometer referenced to SiMe4, mass spectra by fast-atom bombardment (FAB) of samples in a 3-nitrobenzyl alcohol matrix on a Kratos MS50 spectrometer, and infrared spectra on a Perkin-Elmer Paragon 1000 FT-IR spectrometer as Nujol mulls.Analytical data were obtained on a Perkin-Elmer 2400 Elemental Analyser by the University of Edinburgh Microanalytical Service. H3L1. 2,6-Diformyl-4-methylphenol (1.0 g, 6 mmol) was dissolved in MeOH (40 cm3) and tren (2 mmol) dissolved in MeOH (10 cm3) was added dropwise with stirring. The resulting yellow solution was stirred at 40 8C for 30 min then concentrated to 20 cm3 under reduced pressure. Dimethyl sulfoxide (3 cm3) was added with stirring and left to evaporate at room temperature.After 24 h brown-yellow crystals had formed which were filtered off and washed with Et2O. Further crystals could be obtained by addition of MeOH and Me2SO to the filtrate and continued evaporation at room temperature. Yield: 74% (Found: C, 65.5; H, 7.6; N, 7.7. Calc. for C39H54N4O9: C, 64.8; H, 7.5; N, 7.8%). IR (Nujol mull), cm21: 1636s, 1601s, 1273m, 1252m, 1104s, 1074s, 986m, 936m and 657w. 1H NMR: d 2.08 (s, 9 H), 2.81 (t, 9 H), 3.37 (s, 18 H), 3.47 (t, 6 H), 5.69 (s, 3 H), 5.89 (d, 3 H), 7.35 (d, 3 H), 7.76 (s, 3 H) and 14.2 (s, 3 H). FAB mass spectrum (significant peaks, possible assignments): m/z 691, [H3L1 2 OMe]+; 659, [H3L1 2 2OMe]+; and 627, [H3L1 2 3OMe]+. [La(H3L1)(H2O)][ClO4]3 1. The compound H3L1 (0.14 g, 0.19 mmol) was dissolved in methanol (30 cm3) at 40 8C and the solution filtered. Hydrated lanthanum perchlorate (0.11 g, 0.2 mmol) dissolved in MeOH (10 cm3) was added dropwise; there was no immediate colour change but on stirring for 5 min a yellow precipitate was observed. The temperature was maintained and the solution stirred for 1 h.The yellow precipitate174 J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 was then filtered off and dried in vacuo. Yield: 84% (Found; C, 39.3; H, 5.2; N, 4.5. Calc. for C39H56Cl3LaN4O22?CH3OH: C, 39.1; H, 5.1; N, 4.6%). FAB mass spectrum: m/z 879, [La(H3L1)(H2O)]+, 849, [La(H3L1)(H2O) 2 OMe]+ and 719, [H3L1]+. A single crystal suitable for X-ray analysis was obtained by diffusion of diethyl ether vapour into a nitromethane solution of complex 1 at 258 K.[Pr(H3L1)(H2O)][ClO4]3 2. This complex was synthesized in an identical manner to that described for 1 but with Pr(ClO4)3?xH2O in place of lanthanum perchlorate. Yield: 80% (Found: C, 39.3; H, 5.4; N, 4.5. Calc. for C39H56Cl3N4O22Pr? CH3OH: C, 39.0; H, 5.0; N, 4.6%). FAB mass spectrum: m/z 881, [Pr(H3L1)(H2O)]+; 851, [Pr(H3L1)(H2O) 2 OMe]+; and 719, [H3L1]+.A single crystal suitable for X-ray analysis was obtained by diffusion of diethyl ether vapour into a nitromethane solution of 2 at 258 K. [Y(H3L1)][ClO4]3 3. This complex was synthesized in an identical manner to that described for 1, but with Y(ClO4)3?xH2O in place of lanthanum perchlorate. Yield: 79% (Found: C, 40.1; H, 5.6; N, 4.9. Calc. for C39H54Cl3N4O21Y?CH3OH: C, 40.8; H, 5.3; N, 4.8%).FAB mass spectrum: m/z 810, [Y(H3L1)]+. A single crystal suitable for X-ray analysis was obtained by diffusion of diethyl ether vapour into an acetonitrile solution of 3 at 258 K. [LaNiL1(H2O)][ClO4]2 4. Compound H3L1 (255 mg, 0.2 mmol) was dissolved in MeCN (20 cm3) and hydrated nickel perchlorate (80 mg, 0.2 mmol) in MeCN (10 cm3) was added dropwise causing a change to light green. Ethyldiisopropylamine (0.12 cm3) was added with rapid stirring which was continued for 30 min.The solution was then concentrated to 5– 10 cm3. Slow addition of Et2O gave a green solid which was filtered off. Yield: 6% (Found: C, 40.1; H, 4.6; N, 4.8. Calc. for C39H53Cl2LaN4NiO18: C, 40.8; H, 4.7; N, 4.9%). FAB mass spectrum: m/z 1033, [LaNiL1(H2O)(ClO4)]+; and 1015, [LaNi- L1(ClO4)]+. A single crystal suitable for X-ray analysis was produced by diffusion of Et2O vapour into an MeOH solution of complex 4 over a period of 3 d. [Gd(H3L2)(H2O)2][ClO4]2.83Cl0.17 6. The complex [Gd(H3L1)- (H2O)][ClO4]3 5 was synthesized in an identical manner to that described for 1, but with Gd(ClO4)3?xH2O in place of lanthanum perchlorate.It (150 mg, 0.12 mmol) was dissolved in MeCN (50 cm3), then hydrated copper(II) perchlorate (44 mg, 0.12 mmol) in MeCN (10 cm3) was added dropwise to give a light green solution. Ethyldiisopropylamine (3.2 cm3 of a 0.1148 mol dm23 solution in MeCN, 0.36 mmol) was added immediately and the solution stirred for 1 h at room temperature before being filtered and concentrated to half its original volume.Addition of diethyl ether produced a yellow-green precipitate in low yield which was filtered off. Yield: ca. 5% (Found: C, 35.1; H, 4.0; N, 5.4. Calc. for C33H40Cl3GdN4O19.32: C, 37.2; H, 3.8; N, 5.3%). FAB mass spectrum: m/z 783, [Gd(H3L2)(H2O)2]+; and 763, [Gd(H3L2)(H2O)]+. A single crystal suitable for X-ray analysis was produced by diffusion of Et2O vapour into an MeCN solution of complex 6 over a period of 3 weeks.Crystallography Crystal data and data collection and refinement parameters for compounds H3L1, 1–4 and 6 are given in Table 1; selected bond lengths in Tables 2 and 3. Data collection and processing. Data were collected on a Stoë Stadi-4 four-circle diffractometer equipped with an Oxford Cryosystems low-temperature device,16 using graphitemonochromated Mo-Ka radiation (l 0.710 73 Å) w–2q scans and on-line profile fitting.17 Data were corrected for Lorentz polarisation effects.Semiempirical absorption corrections based on azimuthal measurements 18 were applied for all compounds. Structure analysis and refinement. Structure H3L1 was solved by Patterson search techniques: a phenol fragment was located using the ORIENT and TRACOR routines of the DIRDIF suite.19 All other structures were solved by direct methods using SHELXS 86 20 and completed by iterative cycles of DF syntheses and full-matrix least-squares refinement. For H3L1 all non-H atoms were refined anisotropically with a similarity restraint applied to the three side-arms. In 1–4 the perchlorate anions and solvate molecules displayed considerable disorder which was modelled with partial site occupancies of several sites for oxygen atoms, and two orientations for the solvate molecules in 1 and 2.For 1–3 all non-H atoms within cations and the Cl atoms of the anions were refined anisotropically. For 4 only metal atoms were refined anisotropically.For all structures H atoms were included in idealised positions, allowed to ride on their parent C atoms (C–H 1.08 Å), and assigned isotropic thermal parameters [U(H) = 1.2Ueq(C) for aromatic H atoms; U(H) = 1.5 Ueq(C) for methyl H atoms]. Structures H3L1 and 1–4 were refined against F2 using SHELXL 93.21 The crystal structure of complex 6 was refined by full-matrix least squares against F using CRYSTALS.22 The long c axis and broad profiles of the diffraction peaks led to substantial peak overlap, while refinement was complicated by disorder in two of the three anion sites.One of these was modelled as a single perchlorate anion disordered over two orientations, while the other was modelled as being occupied by 0.83 ClO4 2, disordered over two orientations, and 0.17 chloride, again disordered over two positions; the sum of the occupancies was restricted to unity. The perchlorate anions were treated initially as rigid groups and subsequently with similarity restraints on all Cl]O distances and O]Cl]O angles. Deviations in the angles in the minor components from 1098 attests to the presence of further unresolved disorder.The geometries of the three equivalent side-arms of H3L2 were also restrained to be similar, and full-weight H atoms were placed in calculated positions and iteratively reidealised during refinement. Only the Gd and ordered ClO4 2 atoms were refined with anisotropic displacement parameters. Restrained anisotropic refinement of the ligand atoms, while possible, did not lead to any significant improvement, and so these atoms, together with atoms in the disordered anions and solvent molecules, were refined isotropically.The Uiso for the disordered O atoms in the anions was restrained to a common value. The two molecules of MeCN were made subject to explicit geometric restraints. The modelling of the electron density in the region of the mixed ClO4 2/Cl2 site led to difficulties in full-matrix refinement, which diverged with symptoms associated with ill conditioning of the normal matrix.This was alleviated by the use of a combination of eigenvalue filtering and the application of shift-limiting restraints on the positional, thermal and occupancy factors of the part-occupancy Cl sites. Atomic coordinates, thermal parameters and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J.Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/302. Results and Discussion Synthesis and characterisation of H3L1 The compound H3L1 results from a reaction sequence which we had envisaged would produce the cryptand H3L3. Reaction of tren with 2,6-diformyl-4-methylphenol in MeOH leads to the expected Schiff-base condensation reaction of one formyl group with tren, but formation of a dimethyl acetal at theJ.Chem. Soc., Dalton Trans., 1997, Pages 173–179 175 second group. It is worth noting that H3L1 is produced in very good yield, and that variation of the ratios of the reactants does not produce the cyclised H3L3 in this solvent, merely producing poorer yields of H3L1 and unreacted tren. The cryptand H3L3 has been made by Gagné and co-workers 23 by a two-step condensation of tren with 2,6-diformyl-4-methylphenol, and this synthetic strategy has been used by Nelson and co-workers 24 to produce related cryptands. The intermediate tripodal proligand isolated contained aldehyde functions, not acetals as in H3L1.Spectroscopic characterisation of H3L1 does not decisively indicate its nature. The FAB mass spectrum does not show the molecular ion, only peaks at m/z 691, 659 and 627 due to loss of one, two and three methoxy groups respectively. Infrared spectroscopy confirms the disappearance of the carbonyl groups of the reactants, while NMR spectroscopy confirms a strong resonance due to the OMe groups of the acetal.Definitive proof of structure came from a crystallographic determination. The compound crystallises with a non-crystallographic three-fold axis running through the bridgehead N atom (Fig. 1). This N atom is pyramidal and the lone pair is pointing towards the cavity formed by the arms of the compound. The orientation of the phenol rings within the three side-arms is such that the planes of these rings are at approximately 1208 to each other and the potential donor groups within the arms, one N- and three O-donors in each, are pointing away from the central cavity.Although the H atoms were not located, all hydrogen bonding appears to be confined within each sidearm, with strong interactions likely between the imine N and the phenol O atom (average N? ? ? O 2.547 ± 0.020 Å): no significant interactions were found between molecules.Crystallisation of H3L1 could only be achieved by addition of Me2SO to a MeOH solution yet no molecules of either solvent are found in the crystal lattice. Fig. 1 Structure of H3L1 in the crystal showing the numbering scheme Synthesis and characterisation of lanthanoid complexes of H3L1 Reaction of a hydrated rare-earth-metal perchlorate salt with H3L1 in MeOH produces a yellow precipitate which analyses as [Ln(H3L1)(H2O)][ClO4]3 for the larger, early lanthanoids, and as [Ln(H3L1)][ClO4]3 for the later lanthanoids. As representative examples of the early lanthanoids we have crystallised complexes where Ln = La and Pr (1 and 2 respectively), and for the latter lanthanoids we have crystallised the yttrium complex 3.Yttrium, although a 4d rather than a 4f element, forms compounds which are normally isostructural with those of the heavier rare earths. Spectroscopic characterisation is again useful but not conclusive. The NMR spectra of 1 and 3 differ little from that of free H3L1, with a small shift to higher frequency observed for all resonances. Assignment of the various methyl resonances is complicated due to residual nitromethane in all samples.One intriguing change is that the resonance at d 8.53, assigned to the CH proton of the imine function, appears as a doublet rather than as a singlet in the spectrum of H3L1 (d 7.76). Irradiation of the resonance at d 12.9 causes this splitting to collapse, indicating that the CH proton of the imine group is coupled to the proton involved in the hydrogen bond between the imine N and the phenol O atom of each side-arm.As this coupling is resolved for 1 and 3, but not for H3L1, it seems likely that this H atom is more firmly located on the N atom in the complex, consistent with co-ordination of the phenol O atom to a metal centre. For 2 all resonances are broadened and shifted due to the paramagnetism of the Pr. The FAB mass spectra of all three complexes show a peak for the molecular ion, and fragment peaks for loss of one MeO Fig. 2 Structure of complex 1 in the crystal showing the numbering scheme. The latter is common to 2 Fig. 3 The lanthanum co-ordination geometry in complex 1176 J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 group. By comparison with the spectrum of free H3L1, where the only peaks observed were for products where methoxy groups had been lost, these results suggest that co-ordination of the acetal side-arms to the metal has occurred thus stabilising the acetal functions.Single-crystal X-ray diffraction studies show that compounds 1 and 2 are isostructural. In each the 4f metal is ten-coordinate, bound exclusively to oxygen donors. These are derived from all three side-arms, with two acetal and one phenolic oxygen attached from each leg of the tripod, and the final oxygen donated by a water molecule (Fig. 2). There is a noncrystallographic three-fold axis running through the metal site, the bridgehead N atom and the bound water molecule.The Ln]O bond lengths depend on the type of oxygen atom, with bonds to phenol oxygens (for H3L1, average 2.47 Å) signifi- cantly shorter than bonds to acetal oxygens (for H3L1, average 2.65 Å) or to the water (for H3L1, 2.63 Å). There is also a predictable general shortening of these bonds moving from La to Pr due to the lanthanoid contraction. The co-ordination geometry around the Ln can be related to an icosahedron (Fig. 3) where the three phenolic oxygens [O(1), O(4) and O(7)] form a triangular face, the six acetal oxygens [O(2), O(3), O(5), O(6), O(8) and O(9)] form a puckered six-membered ring above this face and the final oxygen atom [O(10)] is at the centre of what would be the final triangular face. The geometry therefore corresponds closely to a trirhombohedron. For complex 3 the co-ordination number of the metal has fallen to nine, with loss of the water molecule found in 1 and 2 (Fig. 4). Again the molecule has a non-crystallographic C3 axis running through the metal and the bridgehead nitrogen. The Y]O distances show the same dependence on the character of the O atom, with shorter bonds to the O-donors from the phenol groups. The co-ordination geometry about the yttrium centre is now based on a tricapped trigonal prism (Fig. 5), and Fig. 4 Structure of complex 3 in the crystal showing the numbering scheme Fig. 5 The yttrium co-ordination geometry in complex 3 is comparatively regular.For example, the upper and lower triangular faces of the prism are essentially equilateral (angle range 59.0–61.78), and the angles at the corners of the square faces are almost right angles (range 83.8–95.58). It is interesting that the change in co-ordination number from ten in 1 and 2 to nine in 3 is achieved with retention of the three-fold axis through the metal centre. No significant intermolecular hydrogen-bonding interactions are found in any of these structures, although strong intramolecular hydrogen-bonds between the imine N atom and the phenolic O atom in each side-arm are present.The second cavity of the compartmental ligand is therefore occupied by three protons in each of these complexes. Co-ordination of metal ions to chelate acetal ligands is relatively rare. Binding of RbI 25 and AgI 26 to chelate acetalcontaining antibiotics has been reported, while other nonchelate examples include binding of hard metal ions, usually main-group ions, to cyclic 27 and non-cyclic 28 acetals.However, no previous structural reports of lanthanide metal ions to acetals have been reported. Reactions of lanthanoid complexes of H3L1 Given the structures of complexes 1–3 we argued that deprotonation of [H3L1] to [L1]32 would facilitate insertion of a second metal into the vacant octahedral cavity formed by the three imine N- and the three phenolic O-donors. This methodology proves moderately successful for a range of lanthanoids when Fig. 6 Structure of complex 4 in the crystal showing the numbering scheme Fig. 7 The co-ordination geometries of La and Ni in complex 4J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 177 Table 1 Experimental data for the X-ray diffraction studies of compounds H3L1, 1–4 and 6 H3L1 1 2 3 4 6 Formula C39H54N4O9 C39H56Cl3LaN4O22?3CH3NO2 C39H56Cl3N4O22Pr?3CH3NO2 C39H54Cl3N4O21Y?3CH3CN C39H53Cl2LaN4NiO18?CH3OH C33H39GdN4O8?2.83ClO4?0.17 Cl?2CH3CN M 722.8 1361.3 1363.3 1233.3 1157.3 1152.3 Crystal system Monoclinic Monoclinic Monoclinic Monoclinic Trigonal Monoclinic Space group P21/n P21/n P21/n P21/c R3 P21/c a/Å 16.088(9) 13.013(3) 12.998(2) 17.381(13) 34.204(13) 10.845(10) b/Å 13.353(10) 25.275(17) 25.265(8) 17.070(12) a 11.641(11) c/Å 18.798(23) 17.869(8) 17.771(3) 19.385(14) 24.59(3) 40.77(2) b/8 93.92(5) 92.27(5) 92.282(12) 94.74 93.21(7) U/Å3 4029 5873 5831 5864 24914 5139 T/K 293 150.0(2) 150.0(2) 220.0(2) 150.0(3) 150.0(2) Z 4 4 4 4 18 4 Dc/ g cm23 1.192 1.510 1.553 1.397 1.388 1.490 Crystal size/mm 0.1 × 0.1 × 0.1 0.2 × 0.2 × 0.2 0.70 × 0.43 × 0.27 0.4 × 0.4 × 0.1 0.55 × 0.15 × 0.08 0.61 × 0.33 × 0.15 m/mm21 0.085 0.937 1.064 1.208 1.265 1.533 Unique data 6113 7604 10 080 7628 4960 4883 Observed data 1810 5583 8917 4411 2032 2675 Parameters 477 719 760 632 300 576 Maximum D/s ratio 21.99 0.118 20.75 20.27 0.047 0.087 — R1, wR2a 0.0938, 0.3862 0.0500, 0.1439 0.0372, 0.1609 0.0553, 0.1830 0.1236, 0.5184 — R, R9 b — — — — — 0.1088, 0.1175 Weighting scheme,c w21 s2(Fo 2) + (0.1776P)2 s2(Fo 2) + (0.0515P)2 + 40.70P s2(Fo 2) + (0.0418P) + 22.17P s2(Fo 2) + (0.0835P)2 + 20.71P s2(Fo 2) + (0.013P)2 Chebychev three-term polynomial Goodness of fit 1.068 1.034 1.040 0.987 1.201 1.100 Largest residuals/e Å23 0.54, 20.33 1.07, 20.76 0.75, 20.56 0.72, 20.54 2.00, 21.56 +1.94, 21.50 Common feature: all compounds crystallise as yellow tablets.a SHELXL93:21 R1 based on observed data, wR2 on all unique data.b CRYSTALS:22 R and R9 based on observed data. c P = ��� [max(Fo 2, 0) + 2Rc].178 J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 treated with nickel(II) salts, but markedly less successful with copper(II) salts. Addition of 3 molar equivalents of dipropylamine to a 1 : 1 molar solution of complex 1 and Ni(ClO4)2?6H2O in MeCN gives a green solution from which a green precipitate of a mixed La–Ni complex can be precipitated by addition of diethyl ether.Structural analysis reveals the binuclear complex [LaNiL1- (H2O)][ClO4]2 4 (Fig. 6). As expected the ligand [L1]32 uses all twelve potential donor atoms to encapsulate a six-co-ordinate NiII and a ten-co-ordinate LaIII. The trigonal axis, present in all the other structures involving H3L1, is also present in 4. The NiII is six-co-ordinate, bound to the three imine Ndonors and three phenolic O-donors (Fig. 7). Significantly, the bond angles between the N atoms are markedly different from those of an ideal octahedron and all trans-N]Ni]O angles are reduced to ca. 1618 by a trigonal compression imposed by the ligand. The strain within this cavity is perhaps most poly illustrated by considering the angles at the bridgehead sp3-N atom [N(1)], which are close to 1208. The three phenolic O atoms are shared with the LaIII, which has a co-ordination geometry very similar to that in complex 1. Therefore a face is shared by the 3d and 4f metals leading to a Ni ? ? ? La contact of 3.355(5) Å.It is interesting that the geometry at La is closely maintained between 1 and 4, with La]O bond lengths statistically unchanged (Fig. 7). It is the d-block metal ion which has a considerable distortion imposed on its geometry by the requirements of [L1]32. Similar products can be obtained for other 4f metals investigated (Ln = GdIII, ErIII or PrIII) when treated with Ni(ClO4)2?6H2O. The FAB mass spectra of the products always Fig. 8 Structure of complex 6 in the crystal showing the numbering scheme Fig. 9 The co-ordination geometry of Gd in complex 6. The full lines show the O? ? ? O contacts within the mutually perpendicular trapezia of the dodecahedral oxygen array confirmed the formation of binuclear [LnNiL1][ClO4] complexes, e.g. for 4 at m/z 1015. Elemental analytical data were less reassuring, and in most cases indicated the presence of some impurity beyond additional solvate molecules.This is reflected in low values for C, H and N. This suggests that encapsulation of two metals by H3L1 is difficult, presumably due to the trigonal strain imposed at the 3d-metal site. The problems associated with addition of nickel to lanthanoid complexes of H3L1 become much more serious when copper(II) salts are utilised. The second trigonally compressed octahedral cavity is clearly incompatible with the requirements of the d9 metal ion. All reactions produced compounds which do not contain both metals, and there is no indication from mass spectrometry that heterobimetallic complexes are formed.For example, reaction of [Gd(H3L1)(H2O)][ClO4]3 5 with Cu(ClO4)2 appears promising, but crystallisation gives crystals of a mononuclear gadolinium complex 6. These crystals diffracted poorly, however the structure demonstrates that incorporation of a second metal has failed and that the ligand has been modified, with the acetal groups hydrolysed (Fig. 8), which reduces the number of available oxygen-donor atoms to six; three phenolic oxygens and three O-donors from aldehydes. Therefore in order to reach a satisfactory coordination number at gadolinium two water molecules are also present. The Gd]O distances show a similar variation to that found for complexes 1–3; bonds to phenolic O atoms are shorter (ca. 2.32 Å) than those to other O-donors (2.37–2.44 Å). The geometry of the eight-co-ordinated Gd can be related to a dodecahedron (Fig. 9), with the two intersecting mutually perpendicular trapezia required by this geometry described by O(1), O(8), O(4), O(6) and O(7), O(2), O(5) and O(3). It is also noticeable that the three-fold symmetry evident in the structures featuring H3L1 has disappeared, which suggests it is the steric requirements of the six OMe groups of the acetal functions which were causing the trigonal arrangement of the ligand. Table 2 Selected bond lengths (Å) for compounds 1–3 and 6 1 2 3 6 Ln = La Pr Y Gd Ln]O(1) 2.543(5) 2.396(3) 2.240(5) 2.31(1) Ln]O(2) 2.650(5) 2.567(3) 2.432(5) 2.42(1) Ln]O(3) 2.663(5) 2.613(3) 2.526(5) 2.31(1) Ln]O(4) 2.462(5) 2.409(3) 2.230(5) 2.41(1) Ln]O(5) 2.697(5) 2.658(3) 2.542(5) 2.32(1) Ln]O(6) 2.631(5) 2.560(3) 2.400(5) 2.37(1) Ln]O(7) 2.490(5) 2.438(3) 2.243(5) 2.40(2) Ln]O(8) 2.587(5) 2.531(3) 2.526(5) 2.44(2) Ln]O(9) 2.674(5) 2.654(3) 2.412(5) Ln]O(10) 2.626(5) 2.588(3) Table 3 Selected bond lengths (Å) and angles (8) for compound 4 Ln]O(1) 2.44(2) Ln]O(9) 2.62(2) Ln]O(2) 2.72(3) Ln]O(10) 2.60(3) Ln]O(3) 2.57(2) Ni]O(1) 2.07(2) Ln]O(4) 2.45(2) Ni]O(4) 2.07(2) Ln]O(5) 2.58(2) Ni]O(7) 2.05(2) Ln]O(6) 2.67(2) Ni]N(2) 2.07(3) Ln]O(7) 2.43(2) Ni]N(3) 2.08(3) Ln]O(8) 2.64(2) Ni]N(4) 2.09(3) O(7)]Ni]N(2) 161.5(10) O(1)]Ni]N(3) 160.9(10) O(7)]Ni]O(1) 77.4(8) O(4)]Ni]N(3) 84.3(11) N(2)]Ni]O(1) 84.5(9) O(7)]Ni]N(4) 84.3(10) O(7)]Ni]O(4) 78.1(9) N(2)]Ni]N(4) 96.3(10) N(2)]Ni]O(4) 101.9(10) O(1)]Ni]N(4) 103.4(10) O(1)]Ni]O(4) 77.1(9) O(4)]Ni]N(4) 161.8(10) O(7)]Ni]N(3) 103.1(10) N(2)]Ni]N(4) 95.6(11) N(2)]Ni]N(3) 95.3(11)J.Chem. Soc., Dalton Trans., 1997, Pages 173–179 179 Conclusion Although the reaction to give H3L1 and related Ln–Ni complexes works, the strain at the bridgehead N atom in [L1]32 incorporating ethylene linkages leads to some loss of the 3d metal from the inner co-ordination site during recrystallisation. This is further exacerbated by potential instability of the ligand where both the imine linkage and acetal groups are susceptible to further reaction. Current work is aimed at synthesizing derivatives of [L1]32, especially with longer chain lengths between the bridgehead N atom and the imine donor atoms, and with saturated amine chains in place of the imine linkers.It is envisaged that these larger and/or more flexible ligands will lead to more stable binuclear complexes. Such complexes might also allow us to examine any correlation 9 between Ln ? ? ?M distance and magnetic exchange interactions.Acknowledgements We are grateful to the EPSRC for funding a diffractometer and for a postdoctoral fellowship (to S. P.), and to the University of Edinburgh for a studentship (to S. J. A.). References 1 N. H. Pilkington and R. Robson, Aust. J. Chem., 1970, 23, 2225; V. McKee, Adv. Inorg. Chem., 1993, 40, 323; D. E. Fenton and H. Okawa, in Perspectives in Coordination Chemistry, eds. A. F. Williams, C.Floriani and A. E. Merbach, VCH, Weinheim, 1992, p. 203; K. K. Nanda, L. K. Thompson, J. N. Brisdon and K. Nag, J. Chem. Soc., Chem. Commun., 1994, 1337; K. K. Nanda, R. Das, L. K. Thompson, K. Vewnkatsubrammanian, P. Paul and K. Nag, Inorg. Chem., 1994, 33, 1188; A. J. Atkins, D. Black, A. J. Blake, A. Marin-Becerra, S. Parsons, L. Ruiz-Ramirez and M. Schröder, Chem. Commun., 1996, 457. 2 For example, see B. F. Hoskins and G. A. Williams, Aust. J. Chem., 1975, 28, 2593, 2607; R.R. Gagné, L. M. Henling and T. J. Kistenmacher, Inorg. Chem., 1980, 19, 1226; R. R. Gagné, C. L. Siro, T. J. Smith, C. A. Hamann, W. R. Thies and A. K. Shiemke, J. Am. Chem. Soc., 1981, 103, 4073; R. C. Long and D. N. Hendrickson, J. Am. Chem. Soc., 1983, 105, 1513; S. K. Mandal, L. K. Thompson, K. Nag, J.-P. Charland and E. Gabe, Inorg. Chem., 1987, 26, 1391; D. Luneau, J.-M. Savariault, P. Cassoux and J.-P. Tuchagues, J. Chem. Soc., Danton Trans., 1988, 1225; V.McKee and S. S. Tandon, J. Chem. Soc., Chem Commun., 1988, 385; M. Tadokoro, H. Sakiyama, N. Matsumoto, H. Okawa and S. Kida, Bull. Chem. Soc. Jpn., 1990, 63, 3337; M. Tdokoro, H. Okawa, N. Matsumoto, M. Koikawa and S. Kida, J. Chem. Soc., Dalton Trans., 1991, 1657; M. Tadokoro, H. Sakiyama, N. Matsumoto, M. Kodera, H. Okawa and S. Kida, J. Chem. Soc., Dalton Trans., 1992, 313; R. Gagné, C. L. Spiro, T. J. Smith, C. A. Hamann, W. R. Thies and A. K. Shiemke, J. Am. Chem. Soc., 1981, 103, 4073; H.-R.Chang, S. K. Larsen, P. D. W. Boyd, C. G. Pierpont and D. N. Hendrickson, J. Am. Chem. Soc., 1988, 110, 4565; D. G. McCollum, L. Hall, C. White, R. Ostrander, A. L. Rheingold, J. Whelan and B. Bosnich, Inorg. Chem., 1994, 33, 924; J. Nishio, H. Okawa, S.-I. Ohtsuka and M. Tomono, Inorg. Chim. Acta,1994, 218, 27; C. Fraser, R. Ostrander, A. L. Rheingold, C. White and B. Bosnich, Inorg. Chem., 1994, 33, 324. 3 H. Okawa and S. Kida, Bull. Chem. Soc. Jpn., 1972, 45, 1759; T.Aono, H. Wada, Y. Aratake, N. Matsumoto, H. Okawa and Y. Matsuda, J. Chem. Soc., Dalton Trans., 1996, 25; M. Sakamoto, Y. Nishida, K. Ohhara, Y. Sadaoka, A. Matsumoto and H. Okawa, Polyhedron, 1995, 14, 2505; Sh Ohtsuka, M. Kodera, K. Motoda, M. Ohba and H. Okawa, J. Chem. Soc., Dalton Trans., 1995, 2599. 4 J.-P. Costes, F. Dahan, A. Dupuis and J.-P. Laurent, Inorg. Chem., 1996, 35, 2400. 5 A. Bencini, C. Benelli, A. Caneschi, R. L. Carlin, A. Dei and D. Gatteschi, J.Am. Chem. Soc., 1985, 107, 8128; A. Bencini, C. Benelli, A. Caneschi, A. Dei and D. Gatteschi, Inorg. Chem., 1986, 25, 572; C. Benelli, A. Caneschi, D. Gatteschi, O. Giullou and L. Pardi, Inorg. Chem., 1990, 29, 1751. 6 A. J. Blake, P. E. Y. Milne, P. Thornton and R. E. P. Winpenny, Angew. Chem., Int. Ed. Engl., 1991, 31, 1139; A. J. Blake, P. E. Y. Milne and R. E. P. Winpenny, J. Chem. Soc., Dalton Trans., 1993, 3727; A. J. Blake, V. A. Cherepanov, A. A. Dunlop, C.M. Grant, P. E. Y. Milne, J. M. Rawson and R. E. P. Winpenny, J. Chem. Soc., Dalton Trans., 1994, 2719. 7 M. Andruh, I. Ramade, E. Codjovi, O. Giullou, O. Kahn and J. C. Trombe, J. Am. Chem. Soc., 1993, 115, 1822. 8 S. Wang, S. J. Trepanier and M. J. Wagner, Inorg. Chem., 1993, 32, 833. 9 A. J. Blake, C. Benelli, P. E. Y. Milne, J. M. Rawson and R. E. P. Winpenny, Chem. Eur. J., 1995, 1, 614. 10 S. Liu, L.-W. Yang, S. J. Rettig and C. Orvig, Inorg. Chem., 1993, 32, 2773. 11 K. A. O. Chin, J. R. Morrow, C. H. Lake and M. R. Churchill, Inorg. Chem., 1994, 33, 656. 12 N. Sabbatini, M. Guardigli and J.-M. Lehn, Coord. Chem. Rev., 1993, 123, 201 and refs. therein. 13 A. J. Amoroso, A. M. Cargill Thompson, J. C. Jeffery, P. L. Jones, J. A. McCleverty and M. D. Ward, J. Chem. Soc., Chem. Commun., 1994, 2571. 14 S. J. Archibald, A. J. Blake, M. Schröder and R. E. P. Winpenny, J. Chem. Soc., Chem. Commun., 1994, 1669. 15 R. R. Gagné, C. L. Spiro, T. J. Smith, C.A. Hamann, W. R. Thies and A. K. Shiemke, J. Am. Chem. Soc., 1981, 103, 4073. 16 J. Cosier and A. M. Glazer, J. Appl. Crystallogr., 1986, 19, 105. 17 W. Clegg, Acta Crystallogr., Sect. A, 1981, 37, 22. 18 A. C. T. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. 19 P. T. Buerskens, W. P. Bosman, H. M. Doesburg, R. O. Gould, Th. E. M. Van den Hark, P. A. J. Prick, J. H. Noordik, G. Buerskens, V. Parathasarathi, H. J. Bruins-Slot, R. C. Haltiwanger, M.K. Strumpel and J. M. M. Smits, Crystallographic Computing 3, eds. G. M. Sheldrick, C. Krüger and R. Goddard, Clarenden Press, Oxford, 1985, pp. 216–226. 20 G. M. Sheldrick, SHELXS 86, University of Göttingen, 1986. 21 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993. 22 D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W. Betteridge, CRYSTALS, Issue 10, Chemical Crystallography Laboratory, University of Oxford, 1996. 23 M. D. Timken, W. A. Marritt, D. N. Hendrickson, R. A. Gagné and E. Sinn, Inorg. Chem., 1985, 24, 4202. 24 O. W. Howarth, Q. Lu, J. F. Malone, D. J. Marrs, N. Martin, V. McKee and J. Nelson, J. Chem. Soc., Dalton Trans., 1995, 1739 and refs. therein. 25 For example, see J. R. Oscarson, J. Bordner, W. D. Celmer, W. P. Cullen, L. H. Huang, H. Maeder, P. M. Moshier, S. Nishiyama, L. Presseau, R. Shibakawa and J. Tone, J. Antibiot., 1989, 42, 37; J. P. Dirlam, L. Presseau-Linabury and D. A. Koss, J. Antibiot., 1990, 43, 727; Y. Takahashi, H. Nakamura, R. Ogata, N. Matsuda, M. Hamada, H. Naganawa, T. Takita, Y. Iitaka, K. Sato and T. Takeuchi, J. Antibot., 1990, 43, 441. 26 For example, see M. Pinkerton and L. K. Steinrauf, J. Mol. Biol., 1970, 49, 533; J. F. Blount, R. H. Evans, jun., C.-M. Liu, T. Hermann and J. W. Westley, J. Chem. Soc., Chem. Commun., 1975, 853; H. Koyama and K. Utsumi-Oda, J. Chem. Soc., Perkin Trans. 2., 1977, 1531. 27 J. J. Daly, F. Sanz, R. P. A. Sneeden and H. H. Zeiss, Helv. Chim. Acta, 1974, 57, 1863; H. W. Roesky, E. Peymann, J. Schimkowiak, M. Noltmeyer, W. Pinkert and G. M. Sheldrick, J. Chem. Soc., Chem. Commun., 1983, 981; P. G. Jones, H. W. Roesky, J. Liebermann and G. M. Sheldrick, Z. Noturforsch., Teil. B, 1984, 39, 1729; G. R. Newkome, H. C. R. Taylor, F. R. Fronczek and V. K. Gupta, J. Org. Chem., 1986, 51, 970; Inorg. Chem., 1986, 25, 1149; E. Lindner, J. Dettinger, H. A. Mayer, H. Kuhbauch, R. Fawzi and M. Steimann, Chem. Ber., 1993, 126, 1317; E. Lindner, J. Dettinger, R. Fawzi and M. Steimann, Chem. Ber., 1993, 126, 1347. 28 P. D. Brotherton, D. Wege, A. H. White and E. N. Maslen, J. Chem. Soc., Dalton Trans., 1974, 1876; Y. Barbay, J. Loset, R. Roulet and G. Chapuis, Helv. Chim. Acta, 1986, 69, 195; D. M. Walba, M. Hermsmeier, R. C. Haltiwanger and J. H. Noordik, J. Org. Chem., 1986, 51, 245; S. J. Angyal, D. C. Craig, J. Defaye and A. Gadelle, Can. J. Chem., 1990, 68, 1140; Y. Takai, Y. Okumura, T. Tanaka, M. Sawada, S. Takahashi, M. Shiro, M. Kawamura and T. Uchiyama, J. Org. Chem., 1994, 59, 2967. Received 23rd July 1996; Paper 6/05154E

ISSN:1477-9226    

DOI:10.1039/a605154e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 175–182 175 Crystal structures of a protonated form of trans-[Pt(NH3)2(mura)2] and of a derivative containing three diVerent metal ions, Pt21, Ag1, and Na1 (mura 5 1-methyluracilate). Major diVerence in packing between heteronuclear pyrimidine nucleobase complexes of cis- and trans-(NH3)2PtII Felix Zamora,a,b Holger Witkowski,a Eva Freisinger,a Jens Müller,a Birgit Thormann,a Alberto Albinati *c and Bernhard Lippert *a a Fachbereich Chemie, Universität Dortmund, D-44221 Dortmund, Germany b Universidad Autonoma de Madrid, Departamento de Quimica Inorganica, Cantoblanco, E-28049 Madrid, Spain c Istituto Chimico Farmaceutico della Università di Milano, I-20131 Milano, Italy Received 24th June 1998, Accepted 16th November 1998 The complex trans-[Pt(NH3)2(mura)2] 1 (mura = 1-methyluracilate), a compound of very low water solubility, is markedly solubilised in the presence of acid or suitable metal salts due to protonation and metal binding to the exocyclic oxygen atoms, respectively.The perchlorate salt trans-[Pt(NH3)2(Hmura)2][ClO4]2?2H2O 2 has been characterised by X-ray analysis. With Ag1, 1 formed heteronuclear species of varying stoichiometries, e.g. Pt2Ag3 3, the composition of which can be further varied by the presence of alkali metal salts. The complex trans-[{Pt(NH3)2- (mura)2}2AgNa(H2O)4][ClO4]2?6.5H2O 4 appears to be the first structurally characterised example of a nucleobase complex containing three diVerent metal ions.Tetranuclear cations of 4 are arranged in the crystal in such a way as to permit both intermolecular hydrogen bonding between NH3 ligands and O2 sites of mura nucleobases and p stacking between adjacent trans-[Pt(NH3)2(mura)2] entities. This feature is radically diVerent from that observed in related diand tri-nuclear complexes derived from cis-(am)2PtII. With mercury(II) salts initially binding to exocyclic oxygen atoms of the mura ligand takes place, followed by metal binding to the C5 atoms of both uracil ligands of 1.Metal binding properties of cis-[Pt(am)2L2] [am = NH3 or (am)2 = diamine, L = mura = 1-methyluracilate or mthy = 1- methylthyminate] have been studied by us in detail,1 as has protonation, 2 which produces metal-stabilised forms of the rare pyrimidine nucleobase tautomers. The extremely low solubility of trans-[Pt(NH3)2(mura)2] 1 in any common solvent thus far has prevented a similar detailed study.Only with a large excess of Ag1, a solubilisation of this compound in water has been achieved as well as the isolation and crystal structure determination of a polymeric complex of PtAg2 stoichiometry.3 In contrast, with the structurally related complex trans-[Pt(am)2- (Hmcyt)2]21 (Hmcyt = 1-methylcytosine) a rich chemistry has been developed.4 It has been realised that as a consequence of diVerent metal orbitals interacting in dinuclear complexes of the two systems cis- and trans-(am)2PtII the types of metal– metal bonds utilised are also diVerent.5 This fact has pronounced consequences for Pt–M distances.For example, while PtII–PdII separations in the cis-(am)2PtII system are typically in the 2.8–2.9 Å range, they are around 2.5 Å in the case of compounds derived from trans-(am)2PtII. Here we report the crystal structure determinations of a protonated form of complex 1, trans-[Pt(NH3)2(Hmura)2][ClO4]2 2, as well as of a heteronuclear derivative of 1, trans-[{Pt(NH3)2- (mura)2}2AgNa(H2O)4][ClO4]2?6.5H2O which contains three different metal ions in a nucleobase complex and which represents the first example of its kind.In addition, limited solution studies with other metal ions leading to a solubilisation of 1 have been carried out. Experimental Preparation of compounds trans-[Pt(NH3)2(mura)2] 1. This complex was prepared by reaction of trans-[Pt(NH3)2Cl2] 6 (2 mmol in 20 cm3 water) with AgNO3 (3.98 mmol), filtration of AgCl, and addition of Hmura 7 (4 mmol) and NaOH (20 cm3, 0.2 mol dm23), and stirring the mixture for 2 h at 60 8C and for 3 d at 40 8C.The white precipitate formed was filtered oV, washed with water and dried. The solid (940 mg) was subsequently stirred in MeOH (500 cm3) for 1 d to dissolve unchanged Hmura, filtered oV, washed with more MeOH and dried at 100 8C. The yield of 1 was 94% (Found: C, 24.5; H, 3.5; N, 17.4. Calc. for C10H16- N6O4Pt : C, 25.05; H, 3.37; N, 17.53%).IR: 3349s (sp), 3204s, 3138s, 1640vs, 1620 (sh), 1580vs, 1550s, 1475m, 1450s, 1420m, 1365s, 1340s, 1305s, 1230m, 1200w, 1150s, 955w, 885w, 845m, 830w, 810w, 775s, 725s, 645m, 595m, 490s, 445s, 370w and 310w cm21. Partially (>50%) deuteriated complex 1 was obtained by keeping a sample of 1 (0.25 mmol) in D2O–NaOD (10 cm3, pD 9.9) for 24 h at 95 8C, filtering oV the precipitate and drying the sample for 2 h at 50 8C. Deuteriation of the ammine ligands was evident from the IR spectrum, which revealed characteristic shifts of the n(ND) modes (2495s, 2406s, 2297s cm21).trans-[Pt(NH3)2(Hmura)2][ClO4]2?2H2O 2. Complex 1 (0.2 mmol) was dissolved in aqueous HClO4 (8 cm3, 1 mol dm23), the solution filtered and kept for 1 week at 4 8C. Colourless crystals were filtered oV, washed with a small amount of ice– water and dried in air. The yield was 48% (Found: C, 16.5; H, 2.9; N, 11.8. Calc. for C10H22Cl2N6O14Pt: C, 16.77; H, 3.10; N, 11.73%).IR: 1639s, 1562s, 1481m, 1447s, 1371s, 1331s, 1094s, 806s, 775s, 625s, 482s, 443s and 365w cm21. trans-[{Pt(NH3)2(mura)2}2Ag3][ClO4]3 3. To a suspension of complex 1 (0.23 mmol) in water (10 cm3) was added NaClO4?H2O (1 mmol) and subsequently an aqueous solution176 J. Chem. Soc., Dalton Trans., 1999, 175–182 of AgNO3 (1023 mol dm23) until all solid had dissolved (0.69 mmol). After heating to 60 8C and filtration from a very little unidentified gray precipitate, the resulting solution was brought to room temperature and then allowed to evaporate at 4 8C.Microcrystalline 3 was isolated in 22% yield. Electron probe X-ray microanalysis (EPXMA) gave a Pt:Ag ratio of 2 : 3 (Found: C, 14.9; H, 2.0; N, 10.6. Calc. for C20H32Ag3Cl3- N12O20Pt2: C, 15.23; H, 2.05; N, 10.66%). Alternatively: to a suspension of 1 (0.21 mmol) in water (15 cm3) was added AgClO4 (0.69 mmol), the mixture warmed to 60 8C to prevent immediate formation of a precipitate, filtered, and the solution (pH 5.3) allowed to stand at 4 8C for a day.Microcrystalline 3 was then filtered oV (48% yield). IR: 3448vs (br), 3300 (sh), 3200 (sh), 1638vs, 1569s, 1525s, 1476m, 1447s, 1370s, 1329s, 1148s, 1120–1091vs, 810m, 774m, 723w, 627m, 493w and 451w cm21. trans-[{Pt(NH3)2(mura)2}2AgNa(H2O)4][ClO4]2?6.5H2O 4. This compound was obtained accidentally in the course of work concerned with the mixed mura/gly (gly = glycine anion) complex trans-[Pt(NH3)2(mura-N3)(gly-N)].A sample of the crude product, obtained from trans-[Pt(NH3)2(mura)Cl], AgNO3 and Hgly,8 had been kept at 60 8C for 6 h in the presence of an excess of NaClO4 and HClO4 at pH 3. Following filtration of some unidentified grayish precipitate, and slow evaporation at 4 8C, single crystals of 4 were obtained in low yield (<5%) besides other products. Compound 4 was characterised by X-ray analysis only. Its formation was rationalised by means of 1H NMR spectroscopy (see below).trans-[{Pt(NH3)2(mura 2 H)2}Hg3(CF3CO2)4]?2H2O 5. To a suspension of complex 1 (0.2 mmol) in water (1 cm3) was added solid Hg(CF3CO2)2 (0.8 mmol). Within a few minutes a clear, yellow solution formed, which was stirred at room temperature for 24 h. Then a colourless precipate of 5 was filtered oV, washed with water and dried in air. The yield was 88% (Found: C, 13.6; H, 1.2; N, 5.2. Calc. for C18H18F12Hg3N6O14Pt: C, 13.79; H, 1.16; N, 5.36%); EPXMA confirmed a Pt : Hg ratio of 3 : 1.Complex 5 is sparingly soluble in D2O, giving a strongly acidic reaction (pD 1.9). Only resonances due to H6 singlets are observed, at d 7.58, 7.39 and 7.34 (ca. 1 : 4 : 3), and four CH3 resonances (d 3.47, 3.42, 3.37, 3.30, ca. 1 : 15:2:4), showing that both uracil ligands are mercurated at C5. IR: 1663s, 1617s, 1558s, 1539s, 1209s, 1138s and 692m cm21. Spectroscopic studies The IR spectra (KBr pellets) were recorded on a Perkin-Elmer 580B and a Bruker IFS 28 spectrometer, 1H, 195Pt, and 199Hg NMR spectra (200.13, 42.95, 35.79 MHz) on a Bruker AC200 instrument.Chemical shifts are given in ppm and referenced to internal (Me3Si)CH2CH2CH2SO3Na (TSP) (D2O), tetramethylammonium tetrafluoroborate (D2O, d 3.1776 relative to TSP), external Na2PtCl6 (195Pt), and external HgCl2 in D2O (199Hg; to recalculate data referred to HgMe2 add 11228 ppm), respectively. For the 1H NMR spectra taken during the reaction of complex 1 with 5 equivalents HgII, a Gaussian window function (line broadening parameter = 24.5, Gaussian broadening parameter = 0.25) was applied prior to the Fourier transformation.The pD values (in D2O) were obtained by adding 0.4 to the pH meter reading. Crystallography The crystal structure of complex 2 was determined on a CAD4 diVractometer at 190 K. Unit cell dimensions were obtained by a least-squares fit of the 2q values of 25 high order reflections (9.5 £ q £ 16.78). Data were measured with variable scan speed to ensure constant statistical precision on the collected intensities.Three standard reflections were used to check the stability of the crystals and of the experimental conditions, and measured every hour. The collected intensities were corrected for Lorentz-polarisation factors 9 and empirically for absorption 10 by using the azimuthal (y) scans of 2 “high-c” (c > 878) reflections. The standard deviations on intensities were calculated in terms of statistics alone.The structures were solved by a combination of Patterson and Fourier methods and refined by full matrix least squares 9 (the function minimised being S[w(Fo 2 k21Fc 21)2]), using anisotropic displacement parameters for all atoms except for those of a counter ion (see below). No extinction correction was deemed necessary. The scattering factors used, corrected for the real and imaginary parts of the anomalous dispersion, were taken from the literature.11 The oxygen atoms of the two water molecules were refined anisotropically, however, it was not possible to locate the positions of the hydrogen atoms bonded to them.One of the two perchlorate counter ions is strongly disordered, even at low temperature. Therefore a model was constructed using the strongest peaks of a Fourier diVerence map. During the refinement, the positional parameters of the oxygen atoms were kept fixed and only their isotropic displacement parameters were allowed to vary, while the chlorine was refined anisotropically without constraints.The hydrogen atom bonded to atom O4 was located on a Fourier diVerence map, while the remaining hydrogen atoms were put in calculated positions, [C–H 0.95 Å, B(H) = 1.3B (Cbonded) Å2]; their contribution was taken into account but not refined. Upon convergence no significant features were found in the final Fourier diVerence map. All calculations were carried out using the Enraf-Nonius MOLEN package.9 Intensity data for complex 4 were collected on an Enraf- Nonius-KappaCCD diVractometer 12 with graphitemonochromated Mo-Ka radiation (l = 0.71069 Å) at room temperature.It covered the whole sphere of reciprocal space by measurement of 360 frames rotating about w in steps of 18 with 45 s scan time per frame. Preliminary orientation matrices and unit cell parameters were obtained from the peaks of the first ten frames and refined using the whole data set. Frames were integrated and corrected for Lorentz-polarisation eVects using DENZO.13 The scaling as well as the global refinement of crystal parameters was performed by SCALEPACK.13 Reflections, which were partly measured on previous and following frames, were used to scale these frames on each other.This empirical procedure in part eliminates absorption eVects and also considers a crystal decay if present. The structure was solved by standard Patterson methods 14 and refined by full matrix least squares based on F 2 using the SHELXTL-PLUS15 and SHELXL 93 programs.16a The scattering factors for the atoms were those given in the SHELXTLPLUS program.Transmission factors were calculated with SHELXL 97.16b Hydrogen atoms were placed in geometrical calculated positions and refined with a common isotropic thermal parameter, except for the ammine hydrogens and those of the methyl group C1 [U(H) = 1.5U(Nbonded)/U(Cbonded) Å2]. A part of the mura non-hydrogen ring atoms were only refined isotropically in order to save parameters as well as the partly disordered perchlorate anions and water molecules (except O1w) and the Na1.Thermal parameters for O atoms of ClO4 2 were applied to H2O molecules bound to Na1 and gave the occupation scheme. Crystal data and data collection parameters are summarised in Table 1. CCDC reference number 186/1251. See http://www.rsc.org/suppdata/dt/1999/175/ for crystallographic files in .cif format. Results and discussion Starting compound 1 and protonated form 2 Unlike cis-[Pt(NH3)2(mura)2]?2H2O,17 which is well soluble in water, trans-[Pt(NH3)2(mura)2] 1 represents an extremely poorlyJ.Chem. Soc., Dalton Trans., 1999, 175–182 177 soluble microcrystalline material. The IR spectrum of 1 in the 3000–3500 cm21 range is, unlike that of the cis isomer, very characteristic, however, with three prominent and sharp absorptions at 3349, 3204, and 3138 cm21. Upon deuteriation, these bands are shifted to 2495, 2406, and 2297 cm21, respectively, identifying them as n(NH) modes.The isotope shifts are 1.342, 1.332, and 1.366. Taken together, these values suggest involvement of the NH3 protons in weak hydrogen bonding.18 With trans-[Pt(NH3)2Cl2], the n(NH) modes occur at 3300 and 3220 cm21, the n(ND) modes at 2465 and 2341cm21, with wavenumber shifts of 1.339 and 1.375.19 We note that in the heteronuclear derivatives 3 and 4 this characteristic pattern of NH3 modes is lost and rather ill structured bands occur between 3500 and 3200 cm21.The 1H NMR resonances of complex 1 in D2O, pD 7.4 occur at d 7.46 (d, 3J 7.4 Hz) for H6, 5.72 (d) for H5, and 3.38 (s) for CH3. These resonances are downfield relative to those of the cis isomer (d 7.30; 5.52; 3.26), and reflect the situation that no intracomplex nucleobase stacking is possible in the case of the trans compound. Addition of acid to a suspension of 1 in D2O leads to formation of a clear solution, with 1H NMR resonances of the uracil ligands downfield from those of 1, e.g.at d 7.89 (H6), 6.15 (H5), and 3.52 (CH3) at pD 0 (1 mol dm23 DNO3). The 195Pt NMR shift (22458 ppm) is consistent with a PtN4 environment. As with neutral uracil and thymine ligands bound to cis-(am)2PtII,2 the Hmura ligands of 2 are susceptible to Pt–N3 bond cleavage, leading to complex decomposition and release of Hmura. The half-life of 2 at pD ª 0, 22 8C is approximately 25 h.Cation structure of complex 2 and packing pattern The cation structure of complex 2 is given in Fig. 1. Platinum is bound to the N3 positions of the two 1-methyluracil nucleobases, which are oriented head-head and are close to coplanar [dihedral angle 8(2)8]. Selected interatomic distances and angles of compound 2 are reported in Table 2. The two uracil rings in 2 do not display any significant diVerences in bond lengths and internal ring angles. Comparison of C–O bond lengths shows a lengthening of C4–O4 [1.326(16) Å] as compared to C2–O2 [1.237(18) Å] in the same base, which corresponds to 3.7 s [with e.s.d.calculated according to s = (s1 2 1 s2 2)� �� and s1 and s2 being the standard deviations of the two bonds] and suggests that O4 is protonated. In the second uracil ligand this diVerence [1.331(22) vs. 1.258(17) Å] corresponds to 2.6s only. Both O4 and O49 are involved in short hydrogen bonds to water molecules, distances being 2.56(2) Å for O4 ? ? ?Ow1 and 2.48(2) Å for O49 ? ? ?Ow2. This feature does not permit an unambiguous diVerentiation between the three possible forms [Pt(NH3)2- (Hmura)2][ClO4]2?2H2O, [H3O][Pt(NH3)2(Hmura)(mura)]- [ClO4]2?H2O, and [H3O]2[Pt(NH3)2(mura)2][ClO4]2, as discussed in similar cases,3a but we tentatively favor the first possibility, hence the pe of the rare 4-hydroxo, 2-oxo tautomeric form for the following reason: the IR spectrum of 2 gives no hint for the presence of two diVerent uracil ligands (Hmura, mura), but displays a pronounced shift of the intense 1580 cm21 Fig. 1 View of trans-[Pt(NH3)2(Hmura)2][ClO4]2 2 with atom numbering scheme. band of 1 to 1562 cm21 for 2, consistent with a loss in doublebond character of one of the CO groups. Moreover, the 1H NMR spectrum of 2 clearly indicates protonation of the mura ligands in solution. A section of the packing of the cation of complex 2 and the water molecules is presented in Fig. 2. As can be seen cations are arranged in pairs with stacking (ca. 3.5 Å) between the four bases and four hydrogen bonds involving the O2 oxygen atoms of the two bases and the N12 ammine groups. Distances and angles are included in Table 2. As a consequence of this packing, N11–Pt–N12 vectors are parallel, forming a 588 angle with the mean plane of the two uracil bases. The Pt ? ? ? Pt separation within the stacked pair is 4.046(1) Å. Pairs of stacked cations are interconnected by longer hydrogen bonds between N11 and O2.In addition there is hydrogen bonding between water molecules and the O4 sites, as mentioned above. The extent of base stacking between cations of complex 2 deserves some comment. As seen in a view perpendicular to the planes of the uracil ligands (Fig. 3), stacking is quite substantial and, as mentioned above, the stacking distance is only slightly longer than in unperturbed DNA (3.4 Å). With regard to crosslinking adducts of trans-(NH3)2PtII with two complementary bases in double-stranded DNA,20 this implies that the NH3 groups of a trans-(NH3)2PtII entity within the center of a DNA helix do not automatically disrupt base stacking by increasing the separation between the platinated base pair and the adjacent pairs.If the NH3 groups are not perpendicular to the mean plane of the two bases but held through hydrogen bonds in a position similar to that seen in 2, base stacking is expected strongly to depend on the flanking sequences.A model of a DNA dodecamer duplex containing a central guanine, cytosine Fig. 2 Detail of stacking pattern of cations of complex 2 with hydrogen bonds indicated. Fig. 3 Detail of stacking pattern of complex 2 with view perpendicular to the uracil rings to demonstrate the base overlap.178 J. Chem. Soc., Dalton Trans., 1999, 175–182 Table 1 Crystallographic data for compounds 2 and 4 Chemical formula M Crystal system Space group a/Å b/Å c/Å b/8 V/Å3 T/K Z m(Mo-Ka)/mm21 2q Range/8 No.reflections collected No. independent reflections [Fo 2 > 4s(F2)] Tmax/Tmin Rint R/R1 (obs. data) R9/wR2 (obs. data) 2 C10H22Cl2N6O14Pt 716.31 Monoclinic P21/c 8.210(2) 17.582(5) 15.511(5) 98.88(2) 2212(1) 190 4 6.728 5–50 3886 2873 1.097/0.7535 0.052 b 0.075 b 4 C10H26.5Ag0.5ClN6Na0.5O13.25Pt 738.84 Monoclinic C2/c 17.379(3) 20.590(4) 14.925(3) 108.52(3) 5064.1(17) 293(2) 8 6.085 6.3–46.4 55374 a 1760 0.700/0.115 0.085 0.0440 c 0.0922 c a Number of reflections after merging of the redundant data: 6765.b R = S Fo| 2 (1/k)|Fc /S|Fo|, R9 = [Sw(|Fo| 2 k21|Fc|)2/Sw|Fo|2]� �� . c R1 = S Fo| 2 |Fc /S|Fo|, wR2 = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� . cross-link and two diVerent pairs at either side and obtained by molecular mechanics, gives a mixed result, namely retention of base stacking on one side and a rise of base residues to 5 Å on the other.21 The packing pattern found in 2 is very similar to that of 4 (see below) and analogous to that in trans- [Pt(NH3)2(Hmcyt-N3)(dmgua-N1)]21 (Hmcyt = 1-methylcytosine, dmgua = 7,9-dimethylguanine),22 although in the latter case the base overlap is more reduced.Solubilisation of complex 1 by metal ions Heterometal ion (Ag1, Hg21, Cu21, Zn21, Tl1) binding to complex 1 in aqueous solution is immediately evident from the fact that 1 dissolves in part or fully and, with diamagnetic ions, leads to a significant improvement of the signal : noise ratio of the mura resonances in the 1H NMR spectra.With increasing amounts of the metal salt added, slight downfield shifts of the aromatic protons of the mura ligands of 1 are observed, with no indication of the formation of kinetically inert heterometallic species with Ag1, Zn21 and Tl1, however. Considering the rather modest eVects in the 1H NMR spectra, low formation constants seem likely. For example, with an excess of Ag1 (>5 equivalents) downfield shifts of H5 and H6 are ca. 0.05 ppm only (cPt ª 0.075 mol dm23, D2O).Likewise, the 195Pt NMR resonance (d 22405 of 3) is hardly aVected by an excess of Ag1. Mixed-metal complexes Pt2Ag3 3 and Pt2AgNa 4 The isolation and crystal structure analysis of a polymeric Table 2 Selected distances (Å) and angles (8) for trans-[Pt(NH3)2- (Hmura)2][ClO4]2?2H2O 2 a Pt–N(11) Pt–N(12) Pt–N(3) Pt–N(39) N(11)–Pt–N(12) N(11)–Pt–N(3) N(11)–Pt–N(39) O(4)–Ow(11) O(49)–Ow(2) N(11)–O(23) 2.06(1) 2.06(1) 2.05(1) 2.07(1) 177.7(5) 89.6(5) 91.2(5) 2.56(2) 2.48(2) 3.20(1) C(4)–O(4) C(2)–O(2) C(49)–O(49) C(29)–O(29) N(12)–Pt–N(3) N(12)–Pt–N(39) N(3)–Pt–N(39) N(12)–O(22) N(12)–O(292) 1.33(2) 1.24(2) 1.33(2) 1.26(2) 90.4(4) 88.8(5) 179.2(5) 2.90(2) 2.92(2) a Symmetry operations: 1 1 1 x, 0.5 2 y, 0.5 1 z; 2 2 x, 2 y, 1 2 z; 3 1 2 x, 2 y, 1 2 z.mixed PtAg2 complex of composition trans-[Pt(NH3)2(mura)2- Ag2(NO3)2(H2O)]?H2O has previously been reported by us.3 Applying only a slight modification, viz. addition of an excess of NaClO4 to a mixture of 1 and AgNO3, gave a compound of diVerent stoichiometry, [{Pt(NH3)2(mura)2}2Ag3][ClO4]3 3.It appears to be a member of a similar group of compounds of general composition PtxAgy(mura)z previously reported for the cis-Pt(NH3)2(mura)2/Ag1 system.23 As in the former system, and by no means restricted to Ag,17 it is not possible to predict complex stoichiometry in a rational way. Considering the large structural variety of mixed platinum–silver complexes found in the cis-[Pt(NH3)2L2] system (L = mura or mthy),24–28 it is not possible to assign a specific structure to 3.We had hoped that addition of NaClO4 to a mixture of complex 1 and AgNO3, rather than producing 3, would give in higher yield and in a rational way trans-[{Pt(NH3)2(mura)2}- AgNa(H2O)4][ClO4]2?6.5H2O 4, a compound which we had accidentally obtained in crystalline form but low yield in a rather diVerent way (cf. Experimental section). As we have clarified by 1H NMR spectroscopy,8 upon addition of HClO4 to trans-[Pt(NH3)2(mura-N3)(gly-N)] (and in the absence of Ag1 and Na1) a complicated rearrangement takes place, following initial protonation of the glycinate and the mura ligand.This situation parallels that seen for cis-[Pt(NH3)2(mura)(gly)].29 As a consequence, both Hgly and Hmura are partially displaced, but within 30 h at 40 8C, pH 3, there is clear evidence for formation of 1, both from 1H NMR spectroscopy and precipitation of 1.Considering the relatively low pH, formation of 1 from the mono(nucleobase) complex and free Hmura is remarkable. The tetranuclear cation of trans-[{Pt(NH3)2(mura)2}2AgNa- (H2O)4][ClO4]2?6.5H2O 4 (Fig. 4, Table 3) consists of two Pt21, a Ag1, and a Na1 ion, arranged in the form of a Y, with an angle of 146.9(1)8 between the two Pt–Ag bars. The Pt–Ag distances are 2.847(1) Å, in the normal range for mixed platinum–silver complexes of uracil and thymine, regardless if derived from cisor trans-(am)2PtII,3,24–28 or diVerent systems.30,31 The Ag1 and Na1 are 3.57(1) Å apart.All four mura nucleobases are arranged head-head and use their O4 oxygen atoms as heterometal (Ag, Na) binding sites. The cation has a C2 symmetry axis which passes through Ag and Na. Ignoring Pt21 and Na1 ions, Ag1 is bound to four oxygen atoms of four mura ligands, which form a distorted tetrahedron (Table 3). Distances to the bridging O49 oxygen a9) Å] are slightly longer than those to the O4 oxygen atoms [2.411(9) Å], which bind in a monodentate fashion, yet are in the normal range.3,32 The Ag1 is markedly out of theJ.Chem. Soc., Dalton Trans., 1999, 175–182 179 Fig. 4 View of the cation of trans-[{Pt(NH3)2(mura)2}2AgNa(H2O)4][ClO4]2?6.5H2O 4 with atom numbering scheme. plane of the chelating mura pairs (see below) because the two oxygens bridging Ag1 and Na1 are pulled together by Na1 [O49 ? ? ?O49a 3.20(1) Å]. In trans-[(NH2Me)2Pt(dmcyt)2Ag2]- [NO3]2 (dmcyt = 1,5-dimethylcytosinate), which represents a good structural model of a hypothetical trans-[(NH3)2- Pt(mura)2Ag]1 cation, the two Ag1 ions are essentially coplanar with the two bases.4f The Na1 ion is surrounded by two oxygens (O49) of the mura ligands and by four water molecules (O4w, O6wa) (Table 3). The Na–O distances are somewhat variable but not unusual.33 The quadrilateral formed by Na, Ag, and the two oxygen atoms O49 and O49a can be considered a mix of two similar quadrilaterals seen in the solid state structures of trans-[Pt(NH3)2(mura)2- Ag2(NO3)2(H2O)]?H2O3 (Ag2,O2) and cis-[Pd(en)(mthy)2Na2]- [NO3]2?H2O34 (Na2,O2), respectively.In all three cases the motif is identical, viz. exocyclic oxygen atoms of the pyrimidine bases function as bridges between the metal ions. The two mura bases within one half of the cation are close to planar [dihedral angle 4.9(8)8] and inclined by 638 (average) with respect to the PtN4 plane.As compared to other bis- (nucleobase) complexes of trans-(am)2PtII, where frequently almost perpendicular orientations are observed,22,35 this value is relatively low. It is the consequence of both intra- and intermolecular hydrogen bonding (see below). The Ag1 is markedly out of the planes of the mura ligands, by 1.05(2) Å from the ring containing N3, and by 1.38(2) Å from the ring containing N39. Packing pattern of complex 4. Cations of complex 4 form infinite zigzag arrays with repetitive Pt–Ag–Pt ? ? ? Pt–Ag–Pt units (Fig. 5) and intercationic Pt ? ? ? Pt separations of 4.271(2) Å.A detail of the packing is shown in Fig. 6. It demonstrates that adjacent cations interact both through stacking (3.5 Å) of four mura ligands and intermolecular hydrogen bonding between NH3 ligands and O2 oxygen atoms of the mura rings very much as in 2: N10 ? ? ?O2a 2.87(1); N10 ? ? ?O29a 2.95(1) Å; Pt1–N10–O2a 117.6(5); Pt1–N10–O2a9 116.8(5)8.This situation is reminiscent of that realised in related mixed nucleobase complexes (“metal-modified base pairs”) of trans-(am)2PtII.22,36 The packing pattern seen in complex 4 is completely diVerent from those of dinuclear Pt2 or multinuclear mixed PtxMy complexes of mura or mthy with cis-(am)2PtII.37 While in both systems strings of metal ions form, with intermolecular hydrogen bonding between the am(m)ine ligands of Pt and carbonyl oxygen atoms of the pyrimidine nucleobases, only in the trans- (am)2PtII complex 4 there is p stacking between the nucleobases.If intermolecular p stacking is observed in cis-(am)2PtII com- Fig. 5 Packing pattern of cations of complex 4.180 J. Chem. Soc., Dalton Trans., 1999, 175–182 plexes, it either involves aromatic amine ligands of the PtII, e.g. 2,29-bipyridine, yet not nucleobases,38 or it is intramolecular as a consequence of a stereoactive electron lone pair at a heterometal ion (TlI) bound to cis-(NH3)2Pt(mthy)2.39 As far as intercationic Pt ? ? ? Pt separations are concerned, they are rather variable with cis-(am)2PtII compounds, depending on relative nucleobase orientation (head-head or head-tail) and packing of the cationic units.37b They may be as low as 3.25 Å 25 and as long as 5.66 Å.37b The intermolecular distance seen in 4 [4.271(2) Å] is in between these two extremes and considerably shorter than in mononuclear complexes of trans-(am)2PtII displaying a similar stacking pattern.22,36 Reactions of complex 1 with HgX2 (X 5 NO3 or CF3CO2) Reactions of complex 1 with Hg(NO3)2 and Hg(CF3CO2)2 were Fig. 6 Detail of packing pattern of cations of complex 4, demonstrating hydrogen bonding and p-stacking interactions of platinum entities of adjacent cations. carried out in D2O and followed by 1H NMR spectroscopy. Addition of either salt to a suspension of 1 in D2O (1 £ pD £ 2) instantaneously leads to solubilisation of 1 and gives rise to new sets of resonances of mura, all of which are downfield with respect to those of 1.For example, at a 1 : 1 ratio r of HgII and 1, two sets of resonances of relative intensities of 3 : 1 are observed, viz. at d 7.57, 5.83, 3.45 (major species, A) and at 7.55, 5.88, 3.39 (minor species, B). Within hours, a new H6 singlet of low intensity at ca. d 7.45 grows in (C). The latter resonance forms more quickly and in higher yield as the ratio r is increased. With r = 5 (Fig. 7) this resonance represents the only one in the aromatic region after 2–3 h (pD 1, 22 8C).Application of a Gaussian window function to the FID of the spectra clearly Table 3 Selected bond lengths (Å) and angles (8) for the cation of complex 4 a Pt(1)–N(3) Pt(1)–N(39) Pt(1)–N(10) Pt(1)–N(109) Na(1)–O(49) Na(1)–O(4w2,3) N(3)–Pt(1)–N(39) N(3)–Pt(1)–N(10) N(3)–Pt(1)–N(109) N(39)–Pt(1)–N(10) N(39)–Pt(1)–N(109) N(10)–Pt(1)–N(109) O(49)–Na(1)–O(491) O(49)–Na(1)–O(6wa2) O(4)–Ag(1)–O(41) O(4)–Ag(1)–O(491) 2.049(9) 1.998(10) 2.044(9) 2.037(9) 2.318(13) 2.61(2) 179.1(4) 89.6(4) 90.9(4) 89.8(4) 89.7(4) 179.4(4) 86.6(6) 167.0(10) 130.9(5) 99.4(3) Pt(1)–Ag(1) Ag(1)–O(4) Ag(1)–O(49) Ag(1) ? ? ? Na(1) Na(1)–O(6wa2,3) O(49)–Na(1)–O(6wa3) O(49)–Na(1)–O(4w2) O(49)–Na(1)–O(4w3) O(6wa2)–Na(1)–O(6wa3) O(6wa2)–Na(1)–O(4w2) O(6wa2)–Na(1)–O(4w3) O(4w2)–Na(1)–O(4w3) O(4)–Ag(1)–O(49) O(49)–Ag(1)–O(491) 2.8474(11) 2.411(9) 2.462(9) 3.568(12) 2.44(4) 93.4(9) 82.9(6) 77.1(6) 90(2) 109.7(12) 90.0(11) 152.5(11) 118.1(3) 80.4(4) a Symmetry operations: 1 2x 1 1, y, 2z 1 1.5; 2 x 1 0.5, 2y 1 0.5, z 1 0.5; 3 2x 1 0.5, 2y 1 0.5, 2z 1 1.Fig. 7 Proton NMR spectra (H6, H5 and NCH3 protons) of mixtures of Hg(CF3CO2)2 and complex 1 (r = 5) at diVerent reaction times, recorded in D2O (pD 1–2).J. Chem. Soc., Dalton Trans., 1999, 175–182 181 Fig. 8 Possible di- and tri-nuclear, mixed Pt, Hgx (x = 1 or 2) complexes derived from head-head (hh) and head-tail (ht) rotamers of 1. The expected number ns of H5 and H6 doublets is given.reveals that the apparent singlet C consists of two components (C1, C2), as does the NCH3 resonance. In the initial state of the reaction, three H6 and H5 doublets of uneven intensities (A, B1, B2) are observed, unlike with r = 1 (two doublets). We propose that the species formed in the early stage of the reaction (A, B) represent heteronuclear PtHgx (x = 1 or 2) species with HgII binding to exocyclic oxygen atoms (O4, O2) of the mura ligands.Chemical shifts of the H6 and H5 doublets are neither consistent with protonated 1 nor with free Hmura. We are unable to assign these species, considering the multiplicity of products feasible, depending on the relative orientations of the two bases (Fig. 8). All we can tell is that the species formed are not in fast exchange and apparently depend on r. Species C and C1, C2, respectively, represent C5-mercurated species, since the disappearance of the H5 doublets of mura during the reaction is not due to an isotope exchange (2D vs. 1H) as clearly seen from the behaviour of the H6 doublets. The chemical shift of the H6 singlet is in the range expected for this kind of species.40–43 However, unlike in similar cases, we do not observe coupling between the 199Hg isotope and H6. Values of 3J of 100–170 Hz could have been expected.43 Likewise, a 199Hg NMR resonance is not detected. The 195Pt NMR resonance of the sample r = 5 containing only species C1 and C2 consists of an unusually broad (half width ca. 200 ppm) signal at an unexpected chemical shift (d 21808). This value compares with d 22830 for a complex of Hmura with a (dien)PtII entity at N3 and a HgII at Fig. 9 Chemical shifts of 195Pt NMR resonances for mixed Pt, Hgx species (a,b) and proposed structure of the compound formed at r = 5 (HgII : 1). C5,40 and d 22195 for a cyclic complex of 1-methylcytosine containing PtII at N3 and HgII both bound to N4 and C5 [Fig. 9(a), 9(b)].4b It suggests that in the present case PtII might be surrounded by two HgII, as schematically pointed out in Fig. 9(c). It is neither possible at present to assign a rotational state (head-head or head-tail) of the two uracil rings nor to determine the degree and kind of condensation (dimeric, polymeric, cyclic) via C5–Hg–C5 bonds. Attempts further to characterise complex 5, which was obtained in a preparative scale with r = 4, were unsuccessful. However, mercuration of both uracil ligands at C5 was clearly evident.Conclusion As shown in this work, trans-[Pt(NH3)2(mura-N3)2] 1 behaves as a ligand toward other metal ions (Ag1, Na1, Hg21). In this respect, 1 is very similar to the corresponding cis isomer, cis- [Pt(NH3)2(mura-N3)2].1 What is diVerent in the two systems, is essentially the relative orientations of the metal ions (Fig. 10) as well as the intercationic interactions. Thus, in dinuclear complexes derived from cis-[Pt(NH3)2(mura-N3)2], Pt and the second metal in general are facing each other [Fig. 10(a)], unless severe bulk of other ligands prevents it.44 If the second metal ion is likewise PtII in a cis geometry, this feature permits removal of electrons from the dz2 orbitals directed toward each other, hence oxidation. In 4, PtII and AgI are not at the closest possible distance [Fig. 10(b)], which they would be if AgI were linearly co-ordinated by two O4 oxygen atoms and coplanar with the two uracil rings [Fig. 10(c)]. As to the diVerences in intermolecular interactions between cations of 4, and likewise of 2, from those seen in related compounds of cis geometry, nucleobase stacking in the trans compounds appears to be a recurring motif 22 as opposed to mainly hydrogen bonding in cis complexes, with the latter sometimes reinforced by metal–metal bond formation.45 Fig. 10 Schematic representations of dinuclear Pt, M complexes derived from (a) cis-[Pt(NH3)2(mura-N3)2], (b) trans-[Pt(NH3)2(mura- N3)2] as observed in 4 and (c) trans-[Pt(NH3)2(mura-N3)2] with M coplanar with Pt and the two nucleobases.182 J.Chem. Soc., Dalton Trans., 1999, 175–182 Acknowledgements Support by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie and the European HCM project is gratefully acknowledged. References 1 B. Lippert, Prog. Inorg. Chem., 1989, 37, 1; E. Zangrando, F. Pichierri, L. Randaccio and B. Lippert, Coord. Chem. Rev., 1996, 156, 275 and refs.therein. 2 H. Schöllhorn, U. Thewalt and B. Lippert, J. Am. Chem. Soc., 1989, 111, 7213; B. Lippert, Inorg. Chim. Acta, 1981, 55, 5; O. Renn, B. Lippert and A. Albinati, Inorg. Chim. Acta, 1991, 190, 285. 3 (a) H. Schöllhorn, U. Thewalt and B. Lippert, J. Chem. Soc., Chem. Commun., 1984, 769; (b) I. Dieter, B. Lippert, H. Schöllhorn and U. Thewalt, Z. Naturforsch., Teil B, 1990, 45, 731. 4 (a) B. Lippert, Met. Ions Biol. Syst., 1996, 33, 105 and refs. therein; (b) H. Rauter, I.Mutikainen, M. Blomberg, C. J. L. Lock, P. Amo-Ochoa, E. Freisinger, L. Randaccio, E. Zangrando, E. Chiarparin and B. Lippert, Angew. Chem., Int. Ed. Engl., 1997, 36, 1296; (c) G. Fusch, E. C. Fusch, A. Erxleben, J. Hüttermann, H.-J. Scholl and B. Lippert, Inorg. Chim. Acta, 1996, 252, 167; (d ) D. Holthenrich, I. Sóvágó, G. Fusch, A. Erxleben, E. C. Fusch, I. Rombeck and B. Lippert, Z. Naturforsch., Teil B, 1995, 50, 1767; (e) I. Sóvágó, A. Kiss and B. Lippert, J. Chem. Soc., Dalton Trans., 1995, 489; ( f ) D.Holthenrich, M. Krumm, E. Zangrando, F. Pichierri, L. Randaccio and B. Lippert, J. Chem. Soc., Dalton Trans., 1995, 3275; ( g) M. Krumm, E. Zangrando, L. Randaccio, S. Menzer, A. Danzmann, D. Holthenrich and B. Lippert, Inorg. Chem., 1993, 32, 2183; (h) M. Krumm, E. Zangrando, L. Randaccio, S. Menzer and B. Lippert, Inorg. Chem., 1993, 32, 700; (i) M. Krumm, B. Lippert, L. Randaccio and E. Zangrando, J. Am. Chem. Soc., 1991, 113, 5129. 5 C. Mealli, F. Pichierri, L. Randaccio, E. Zangrando, M. Krumm, D. Holthenrich and B. Lippert, Inorg. Chem., 1995, 34, 3418; F. Pichierri, E. Chiarparin, E. Zangrando, L. Randaccio, D. Holthenrich and B. Lippert, Inorg. Chim. Acta, 1997, 264, 109. 6 G. B. KauVman and D. O. Cowan, Inorg. Synth., 1963, 7, 239. 7 T. T. Sakai, A. L. Pogolotti and D. V. Santi, J. Heterocycl. Chem., 1968, 5, 849; W. Micklitz, B. Lippert, H. Schöllhorn and U. Thewalt, J. Heterocycl. Chem., 1989, 26, 1499. 8 H. Witkowski and B. Lippert, unpublished work. 9 MOLEN, Molecular Structure Solution Procedure, Enraf-Nonius, Delft, 1990. 10 A. C. T. North, D. C. Philips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. 11 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. IV. 12 KappaCCD package, Nonius, Delft, 1997. 13 Z. Otwinowsky and W. Minor, DENZO and SCALEPACK, Methods Enzymol., 1997, 276, 307. 14 G. M. Sheldrick, Acta Crystallogr., Sect.A, 1990, 46, 467. 15 G. M. Sheldrick, SHELXTL-PLUS (VMS), Siemens Analytical X-Ray Instruments, Inc., Madison, WI, 1990. 16 G. M. Sheldrick, (a) SHELXL 93, Program for crystal structure refinement, University of Göttingen, 1993; (b) SHELXL 97, Program for the Refinement of Crystal Structures, University of Göttingen, 1997. 17 B. Lippert and C. Neugebauer, J. Am. Chem. Soc., 1982, 104, 6596. 18 J. Emsley, Chem. Soc. Rev., 1980, 9, 91. 19 K. Nakamoto, P. J. McCarthy, J. Fujita, R.A. Condrate and G. T. Behnke, Inorg. Chem., 1965, 4, 36. 20 V. Brabec and M. Leng, Proc. Natl. Acad. Sci. USA, 1993, 90, 5345. 21 V. Brabec, M. Sip and M. Leng, Biochemistry, 1993, 32, 11676. 22 S. Metzger, A. Erxleben and B. Lippert, J. Biol. Inorg. Chem., 1997, 2, 256 and refs. therein. 23 D. M. L. Goodgame, R. W. Rollins and B. Lippert, Polyhedron, 1985, 4, 829 and refs. therein. 24 B. Lippert and D. Neugebauer, Inorg. Chim. Acta, 1980, 46, 171. 25 B. Lippert and D.Neugebauer, Inorg. Chem., 1982, 21, 451. 26 U. Thewalt, D. Neugebauer and B. Lippert, Inorg. Chem., 1984, 23, 1713. 27 H. Schöllhorn, U. Thewalt and B. Lippert, Inorg. Chim. Acta, 1987, 135, 155. 28 B. Lippert, H. Schöllhorn and U. Thewalt, Inorg. Chem., 1987, 26, 1736. 29 S. Höhmann, A. Erxleben, T. Wienkötter and B. Lippert, Inorg. Chim. Acta, 1996, 247, 79. 30 A. Erxleben and B. Lippert, J. Chem. Soc., Dalton Trans., 1996, 2329. 31 R. Uson, J. Fornies, M. Tomas, I. Ara and J. M. Casas, Inorg. Chem., 1989, 28, 2388; R. Uson, J. Fornies, M. Tomas and I. Ara, Inorg. Chem., 1994, 33, 4023; R. Uson, J. Fornies, B. Menjon, F. A. Cotton, L. R. Falvello and M. Tomas, Inorg. Chem., 1985, 24, 4651. 32 F. Guay and A. L. Beauchamp, J. Am. Chem. Soc., 1979, 101, 6260; K. Aoki and W. Saenger, Acta Crystallogr., Sect. C, 1984, 40, 775. 33 N. S. Poonia and A. V. Bajaj, Chem. Rev., 1979, 79, 389; B. Fischer, H. Preut, B. Lippert, H. Schöllhorn and U. Thewalt, Polyhedron, 1990, 9, 2199. 34 W. Micklitz, B. Lippert, F. Lianza and A. Albinati, Inorg. Chim. Acta, 1994, 227, 5. 35 A. Schreiber, M. S. Lüth, A. Erxleben, E. C. Fusch and B. Lippert, J. Am. Chem. Soc., 1996, 118, 4124 and refs. therein. 36 S. Metzger, J. F. Britten, A. Erxleben, C. J. L. Lock, A. Albinati and B. Lippert, submitted. 37 (a) W. Micklitz, J. Riede, B. Huber, G. Müller and B. Lippert, Inorg. Chem., 1988, 27, 1979; (b) H. Schöllhorn, U. Thewalt and B. Lippert, Inorg. Chim. Acta, 1984, 93, 19 and refs. therein; (c) B. Lippert, D. Neugebauer and G. Raudaschl, Inorg. Chim. Acta, 1983, 78, 161; (d ) D. Neugebauer and B. Lippert, Inorg. Chim. Acta, 1982, 67, 151. 38 G. Trötscher, W. Micklitz, H. Schöllhorn, U. Thewalt and B. Lippert, Inorg. Chem., 1990, 29, 2541. 39 O. Renn, B. Lippert and I. Mutikainen, Inorg. Chim. Acta, 1993, 208, 219. 40 M. Höpp, A. Erxleben, I. Rombeck and B. Lippert, Inorg. Chem., 1996, 35, 397. 41 F. Zamora, M. Kunsman, M. Sabat and B. Lippert, Inorg. Chem., 1997, 36, 1583. 42 F. Zamora, M. Sabat, M. Janik, C. SiethoV and B. Lippert, Chem. Commun., 1997, 485. 43 F. Zamora, M. Sabat and B. Lippert, Inorg. Chem., 1996, 35, 4858. 44 G. Frommer, F. Lianza, A. Albinati and B. Lippert, Inorg. Chem., 1992, 31, 2434. 45 M. Peilert, A. Erxleben and B. Lippert, Z. Anorg. Allg. Chem., 1996, 622, 267; M. Peilert, S. Weißbach, E. Freisinger, V. I. Korsunsky and B. Lippert, Inorg. Chim. Acta, 1997, 265, 187 and refs. therein. Paper 8/04813D

ISSN:1477-9226    

DOI:10.1039/a804813d

出版商:RSC    

年代:1999

数据来源: RSC