摘要:

J. CHEM. SOC. DALTON TRANS. 1985L1533( 1 1 ) R = Ph or C6H4Me-4Rhenium Nitrosyl Complexes with Simple and with Sterically DemandingAromatic Thiolate Ligands: X-Ray Crystal Structures of [PPh,] [ Re,(SC,H,-Me-4),( NO),]*CH,CI, and [ Re(SC,H,Pri,-2,6),( NO)]tPhilip J. Blower and Jonathan I?. Dilworth"A. F. R. C. Unit of Nitrogen Fixation, University of Sussex, Brighton BNl9RQJohn P. Hutchinson and Jon A. ZubietaChemistry Department, The University at Albany, Albany, New York 7 2222, U.S.A.Reaction of [ReCI,(OMe) (NO) (PPh,),] with a range of thiophenols under basic conditions givesone of two classes of products depending on the steric requirements of the thiols. A representativemember of each class has been characterised by an X-ray crystal structure determination.Thio-phenols with methyl or isopropyl groups in their ortho positions give the mononuclear complexes[Re( SR),( NO)] (SR = SC,H,Pr',-2,4,6, SC6H3Pr',-2,6, SC6H2Pr',-2,6-4- Br, or SC6H,Me3-2,4,6)which are trigonal bipyramidal with an axial NO group. Thiophenols without ortho-substituentsgive the dinuclear anions [Re,(SR),(N0)2] - (SR = SPh or SC&i,Me-4) which contain a triplethiolate bridge between two equivalent rhenium atoms. These anions show a fluxionality involvingintramolecular exchange of six thiolato-ligands.The binding and activation of small molecules at transitionmetals (in particular molybdenum) ligated primarily by sulphuris of interest because of its relevance to the functioning of theenzyme nitrogenase, the active site of which is believed to be aMo-Fe-S cluster.As part of our studies of the binding of smallmolecules to such sites we have prepared a series ofnitrosylrhenium complexes with aromatic thiolato-co-ligands.The nitrosonium ion NO+ is formally isoelectronic with N,and co-ordinated NO is analogous to the diazenido-ligand-NNH, the proposed primary intermediate in the biologicalreduction of N,.A large number of nitrosyl complexes of rhenium-(I), -(XI), and-(XII) is known. The majority of these contain some tertiaryphosphines or other neutral donors, e.g. [ReCl,(NO)(PPh,), J1and [ReF(CO)(NO)(PPh,),] +., Rhenium nitrosyl com-plexes with no neutral ligands include [ReXs(N0)I2- (X = C1or Br 4). There are no previously reported rhenium nitrosylcomplexes with thiolato-ligands.However, there are a fewrhenium thiolato-complexes of other types, including the oxo-complexes [ReO(SCH,CH,S),] - and [ReO(SPh),] -,6 theneutral complex [Re(SPh),(MeCN)(PPh3)l7 and the tetra-meric, cubane-like [(Re(SMe)(CO),},], the X-ray crystalstructure of which has been determined.8Results and DiscussionPreparation and Characterisation of the Complexes.-Wehave examined the reaction of [ReCl,(OMe)(NO)(PPh3),1$with thiophenol, 4-methylthiophenol, and a series of moret Tetraphenylphosphonium tri-y4-methylthiophenolato-bis[di(4-methylthiophenolato)nitrosylrhenate]~ichloromethane (1 /1) andtetrakis(2,6-di-isopropylthiophenolato)nitrosylrhenium.$ This compound was originally prepared by Adams et af.' andformulated as [ReCl,(NO)(PPh,),], but recently Cameron et aL2presented a convincing case for its reformulation as [ReCI,-Supplementary data available (No.SUP 56230, 25 pp.): thermalparameters, H-atom co-ordinates, complete bond lengths and angles.See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1985, Issue 1,pp. xvii-xix. Structure factors are available from the editorial office.Non-S.I. unit employed: mmHg x 133 Pa.(OMe)(NO)(PPhd,l.NO NONO NO NOSR OMe C IS' S' S' S'L = P r i o P r i P r i o P r i M e o M e P r i o P r i\ \ \ \Pri Me BrScheme 1. Preparation of complexes. (i) HSPh or HSC,H,Me-4; (ii)NEt,-MeOH; (iii) MeOH; (iv) HCIsterically demending aromatic thiols, 2,4,6-tri-isopropylthio-phenol, 2,6-di-isopropylthiophenol, 2,4,6-trimethylthiophenol,and 4-bromo-2,6-di-isopropylthiophenol, in the presence oftriethylamine. The major NO-containing products fall into twocategories depending on the steric properties of the thiolemployed, i.e.whether it bears ortho-substituents. In addition,small amounts of side products are formed containing co-ordinated triphenylphosphine. These have not yet been fullycharacterised.The reaction scheme is summarised in Scheme 1. Thereactions with thiophenol and 4-methylthiophenol give theanionic, formally rhenium(r1) complexes [Re,(SPh),(NO),] -(1) and [Re,(SC6H,Me-4),(NO),] - (2a), (2b), isolated as atetraphenylphosphonium salt [(I), (2a)] or as a triethyl-ammonium salt [(2b)]. The empirical formulations for (I), (2a),and (2b) were based on microanalysis and integration of 'Hn.m.r.spectra. In addition, the diamagnetism of the complexes,as inferred from the sharp, unperturbed n.m.r. spectra, isconsistent with their being dinuclear. The broadness of the N1534 J. CHEM. SOC. DALTON TRANS. 1985Table 1. Vibrational and electronic spectra'+( NO)/cm- ' ~ln,x./nm &/dm3 mot' cm-'1 738s, 1 718s 480 4600(1 718s) 336 sh(2a) ~PPh4~~Re2(SC6H4Me~4)7(No~2~ 1 720s, 1 690m 473.5 4 290(1 720s) 340 sh(3) [ Re(SC,H, Pri3-2,4,6),(NO)] 1760s 516 4 450355 28 90028 1 23 700(1 760s) 390 sh(4) [ Re(SC,H Pri,-2,6),(N0)][ Re(SC,H, Pri,-2,6-Br-4),(N0)]1758s 523 n.d.(1 758s) 388 sh347 n.d.28 1 n.d.1757s 498 4600346 27 600275 20 900(1 763s) 365 sh1755s( 1 768s)515 4 500388 sh3 56 31 500282 25 500(7) [Re(SC,H,Me3-2,4,6)3(OMe)(NO)] I 747s n.d.n.d.(8) [ Re(SC, H Pri3-2,4,6) 3( OMe)( NO)] 1 745s n.d. n.d.(9) [Re(SC,H3Pri2-2,6)3(o€3)(NO)] 1 746s n.d.n.d.n.d.n.d.(10) [ Re(SC6Hz Pri3-2,4,6) 3Cl(NO)] 1 780s n.d. n.d.a Nujol mulls; values in parentheses are for CH,Cl, solutions. ' Tetrahydrofuran (tho solutions, range 250-600 nm; n.d. = not determined. v(C0)1 086s cm-'. v(C0) 1 087s cm-'. v(C0) 1 Om, 6(OCH,) 920 cm-'.stretching absorptions in the i.r. spectra, both in the solid stateand in solution, is suggestive of weak vibrational couplingbetween two nitrosyl groups in a dinuclear complex. Theformulation is confirmed in the case of (2a) by an X-ray crystalstructure determination.With thiols bearing ortho-substituents the products were thefourteen-electron, neutral, mononuclear rhenium(II1) complexes[Re(SC6H2Pri3-2,4,6),(N0)] (3), [Re(SC6H3Pri2-2,6),(N0)](4), [Re(SC,H2Me3-2,4,6),(N0)J (5), and [Re(SC6H2Pri2-2,6-Br-4),(NO)] (6).Molecular-weight determinations on (3) and(5) are consistent with mononuclearity, as are the very narrowv(N0) absorptions in their i.r. spectra. A conductivitymeasurement on a tetrahydrofuran solution of complex (5)showed no appreciable ionisation. The steric bulk of the thiolsprohibits them from bridging between two metals, thus allowingformation of mononuclear species. Although the product type ismarkedly dependent on the ortho-substituents of the thiols, wedo not rule out the possibility that the compounds [Re(SR),-(NO)] (R = aryl) when the thiol carries no large ortho-substituents can be formed oia another synthetic route.Theelectrochemical behaviour (see below) of complexes (1) and (2a)suggests that [Re(SPh),(NO)] and [Re(SC6H,Me-4),(NO)]may be reasonably stable. It would appear that, under thereaction conditions employed, the anions [Re(SR),(NO)] - areunstable and their formation is avoided by formation of thebridged anions (1) and (2a), or where this is not possible becauseof the bulky ortho-substituents, by undergoing a one-electronoxidation to give ultimately [Re(SR),(NO)]. The fate of theelectron in this oxidation is unknown. The isolated yields of themononuclear compounds are low because of solubilityproblems imposed by the lipophilic substituents.All of thesemononuclear compounds are highly soluble in hydrocarbons.One of the thiolates, presumably that trans to NO, in each ofthe compounds (3)-(6) is labile, being slowly substituted byalkoxide (OR') in an alcoholic solution in the absence of excessof thiol to give compounds of the type [Re(OR')(SR),(NO)],e.g. (7)--(9). The alkoxide ligands in these compounds can bemetathesised with chloride using HCl, to give, for example, (10).Compounds (7)--(10) have not been fully investigated and mustbe regarded as incompletely characterised.1.r. data for all the complexes are given in Table 1. The NOstretching frequencies of (1) and (2a) are comparable to those ofother formally rhenium(@ nitrosyl complexes, CReCl,(NO)] 2-(1 720 cm-') and [ReBrs(N0)l2- (1 715 ~ m - ' ) , ~ even though thelatter two complexes carry a double negative charge per metalatom whereas (1) and (2a) carry only half a negative charge permetal atom.This probably reflects the strongly electron-releasing nature of the thiolato-ligands, and a certain degree ofthiolate-to-metal R donation. It thus appears that the thiolato-ligands create a site of high 'electron-richness' available fordonation to NO R* orbitals. The v(N0) values for themononuclear complexes (3)+10) are ca. 100 cm-' higher thanthose of the isoelectronic [Mo(SPh),(NO)] - anion (1 675ern-'),'' consistent with the negative charge of the latteJ. CHEM. soc. DALTON TRANS. 1985 1535Table 2. Electrochemical data'Compound Primary reduction potential (V)b AEp/V Comments- 1.25- 1.44-0.83 0.09 C- 0.67 0.08 C- 0.64 0.08 C- 0.44 0.09 cReverse scan shows reversiblewave at -0.65 VReverse scan shows reversiblewave at -0.52 V' c u .1 mmol dm-3 solution in thf containing 0.2 mol dm-3 NBu4BF4 as supporting electrolyte, platinum-wire electrode, with[Mo(Ph,PCH,CH,PPh,),(N,),] (-0.16 V us. s.c.e. under these conditions) as internal reference, scan rates (u) 0.01-1.0 V s-l. Quoted us. s.c.e.Compounds (3)--(6) show no oxidation in the range 0 to + 1.8 V us. s.c.e.; EFd is quoted for irreversible processes, E, for reversible processes.ipox/ipfed x I, iprcd/vf = constant.-0.5 -1.0 -1.5EIV vs. s.c.e.Figure 1. Cyclic voltammogram of [PPh4][Re2(SPh),(NO),1 (condi-tions as in Table 2), scan rate 0.3 V s-', held at negative switchingpotential for 10 s before reverse scancomplex, and comparable to that of [ReCl,(NO)(PMe,Ph),](1 750 cm-').IThe 90-MHz 'H n.m.r.spectra of complexes (2a) and (2b) areconsistent with their formulations as judged from the relativeintegrated intensities of the p-methyl and counter-ionresonances. In addition they show a temperature dependencewhich demonstrates a fluxional behaviour of the thiolato-ligands. This is discussed in detail below. The correspondingspectra of the mononuclear compounds (3)--(6) are complex,but in the 360-MHz n.m.r. spectra of (4) and (6) (in which theisopropyl splitting patterns are identical) at least sevenmagnetically distinct environments for the CH, groups areresolved.The methine protons in (4) and (6) give rise to two wellseparated heptets of integrated ratio 3: 1. The 90-MHz spectrumof [Re(SC,H2Me,-2,4,6),(N0)] shows several methyl peakswhich do not correspond to integral numbers of methyl groups.This may be the result of a conformational equilibrium insolution involving variation of the orientation of the aromaticgroups, although solution i.r. studies give no support to thissuggestion.The electronic spectra of complexes (1) and (2a) are similar, asare those of ( 3 H 6 ) (see Table 1); all are dominated by intensecharge-transfer bands. Detailed assignments are not made sincefor the dinuclear species insufficient data are available and forthe mononuclear series there are no significant variationsin vmx.with the electron-releasing ability of the thiols.Corresponding absorptions are at similar wavelengths for all ofthe mononuclear tetrathiolato-complexes [even the stronglyelectron-withdrawing Br atoms in (6) have little effect] exceptTable 3. Selected atomic co-ordinates ( x lo4) for [PPh4][Re2(SC,H,-M~-~),(No),I (wX9 144(1)9 491(1)7 980(4)8 463(4)10 700(4)7 634(4)9 671(5)10 448(4)8 719(4)9 932(13)10 078(16)10 577( 12)7 979(15)9 130(17)11 876(15)6 415(16)11 073(17)11 834( 15)9 641(12)8 659(19) -Y2 745(1)1 003(1)1 713(4)1555(3)2 065(3)3 623(4)3 878(4)- lOl(3)- 253(4)3 306(11)3 688(13)91 l(11)93 1 ( 1 3)1 SOS(l5)1681(13)2 412(12)3 013( 15)4 063(12)196(12)- 1 280(18)z7 639(1)7 716(1)7 852(3)6 516(3)7 232(4)7 056(4)7 253(3)7 324(4)8 521(11)9 132(9)8 579( 16)9 280( 10)9 779(11)5 890(11)8 389(13)6 837( 14)7 355(13)7 593(10)7 570( 17)7 579(3)(5), suggesting that the differences between (5) and the othermononuclear complexes are steric in origin, arising from thedifferent distortions imposed by ortho-methyl and -isopropylgroups.The electrochemistry of complexes (1)-(6) has been brieflystudied using cyclic voltammetry (see Table 2).The mono-nuclear compounds (3)+6) are reduced in a reversible one-electron process at potentials between -0.44 and -0.83 V us.saturated calomel electrode (s.c.e.), at scan rates from 0.01 to 1.0V s-'. The reversible potentials show a qualitative correlationwith the expected electron-withdrawing and -donating proper-ties of the ring substituents, thus the electron-withdrawingnature of the bromine atoms in (6) enhances the relative stabilityof the reduced species. The reversible nature of the processessuggests that the fifteen-electron anions formed in the reduction,[Re(SR),(NO)] -, are formed without any substantial structuralchange.Complexes (1) and (2a) are reduced irreversibly at morenegative potentials. However on the reverse sweep (see Figure 1)secondary reversible waves appear at -0.65 and -0.52 V (us.s.c.e.) for (1) and (24 respectively. The similarity of thesepotentials with those of the reversible processes for (3)-(6)suggests that among the products of decomposition of thereduced species [Re(SR),(N0)J2- are [Re(SR),(NO)] - (SR =SPh or SC,H,Me-4) which are subsequently oxidised to[Re(SR),(NO)] on the return sweep. The reversibility of thesecondary wave suggests that [Re(SPh),(NO)] and [Re(SC,1536 J.CHEM. SOC. DALTON TRANS. 1985Table 4. Selected bond lengths (A) and angles (") for [PPh4][Re2(SC,H4Me-4),(NO)2] (2a)2.783( 1)2.383( 1)2.553( 5 )2.408(5)2.455(6)2.441(7)2.721( 18)2.421 (6)2.575( 5 )2.388(5)2.439(6)2.445(2)1.638(27)1.807(24)1.777(26)1.825( 18)1.741(21)1.778(23)1.777( 19)1.81 l(29)1.191(25)1.305(32)71.5(2)109.3( 2)75.2(2)87.8(2)9 5.0( 2)98.1(2)86.5(2)7 2.6( 2)107.3( 6)96.9( 7)99.7(6)95.2(6)96.3( 7)70.6(2)108.7(2)75.1(2)87.2(2)80.5(2)88.0(2)79.0(2)108.2( 6)97.4(9)100.3(8)94.8(8)100.2(7)70.8(2)116.3(7)11 1.8(7)65.7( 1)110.9(6)118.1(7)70.9(2)113.5(8)115.2(8)1 13.0(7)176.q 18)1734 17)(61NO NOFigure 2.(a) Structure of [Re2(SC,H4Me-4),(N0)J -, showing theatom labelling scheme; (b) diagram to show geometrical parametersdiscussed in the textH4Me-4),(NO)] are stable on the time-scale used even thoughthe thiolates are not bulky enough to prevent thiolato-bridgeformation.Structure of Complex (2a).-The X-ray crystal structures of arepresentative of each class of compound have been determined.Tables 3 and 4 give atomic co-ordinates and selected bondlengths and angles for (2a) and the structure is shown in Figure2.Comparisons of Re-N and N-O bond lengths in (2a) withthose in other structurally characterised rhenium nitrosylcomplexes ([ReCl,(NO)(PMePh,),], N-0 1.182(14), Re-N1.775(10) A;' [ReF(CO)(NO)(PPh,),] +, N-O 1.20(3), Re-N1.76(2) A2] show that in (2a) the Re-N distances arecomparatively short and the N-0 distances rather long,reinforcing the suggestion that x donation to NO is particularlystrong.The asymmetric structure of the triple thiolato-bridge impliesthe existence of a metal-metal bond. Evidence for this comesfirst from the short [2.783( 1) A] Re-Re distance and, further,from the observed diamagnetism of the complex, since a Re-Rebond would provide a suitable spin-pairing mechanism. Aformal electron count reveals that each metal atom can attainan eighteen-electron configuration by formation of a Re-Rebond, all of the valence electrons occupying bonding orbitalsaccording to the following scheme.If each NO contributes threeelectrons, each terminal thiolate one, each bridging thiolatethree, and each rhenium seven, the overall uninegative chargebrings the total electron count to 34. If a 0 bond is allocated toeach terminal ligand, two G bonds to each bridging thiolate, andtwo x bonds to each Re-N group, there are 16 metal-ligandbonding orbitals occupied by 32 electrons, and a Re-Rebonding orbital occupied by two electrons. Considered inisolation, each Re had a singly occupied non-binding orbital ofcorrect symmetry for mutual overlap.The six thiolates cis to NO are bent away from the NO groupso that N-Re-S angles are all greater than 90", resulting indistortion of the bridge structure to Czv symmetry.Thebridge structure is also influenced by metal-metal bonding.Distortions of confacial bioctahedra due to metal-metalinteractions have been quantified by Cotton and Ucko." Of thegeometric parameters they define, only (p - 70.53') (where p =M-L-M angle for the bridging ligand) is meaningful in complex(2a) because of the lack of D,, symmetry. The 'ideal' value forthis parameter is 0". In the absence of attractive M-Minteractions this angle should deviate from the ideal so as toincrease the M-M distance, because of strain at the ligand atomand an underlying repulsion between the metal atoms. A valueclose to 0" therefore suggests significant attraction between themetal atoms.The values for (2a), (p - 70.53") = + 0.3, - 4.8,and +0.4" for S(1), S(2), and S(3) respectively, are thusindicative of a Re-Re bond. The only other structurallycharacterised example of a triple thiolato-bridge is the double1537 J. CHEM. SOC. DALTON TRANS. 1985(0 18.0 7.0 6.0 5.0 4.0 3.0 2.0 1.06lp.p.m.Figure 3. Proton n.m.r. spectra of [NHEt,][Re2(SC,H4Me-4)7(NO)2]at 23.0 (a) and -6.5 "C (b) in CD2CI2. Solvent and triethylammoniumpeaks are labelled (*)cubane [{(EtS)3MoFeS4),(p-SEt)3]3 - reported by Holm andco-workers.12 Here the Mo-Mo distance is 3.67 A and theCotton-Ucko criteria deviate from the 'ideal' in such a way as tosuggest a lack of Mo-Mo bonding.The observation of the nearly planar Re( l)-S(l)-Re(2)-S(3)unit (the dihedral angle y = 178.1", see Figure 2) suggests thatthere may be a special stability of this arrangement sufficient tocontribute to the distortion of the bridging system away fromD,, symmetry.Metal-ligand distances for a given ligand areusually significantly longer for bridging than for terminalligands. In complex (2a) this is true for the trans bridgingthiolate but not for the cis bridging thiolates, for which thedistances are smaller rather than larger than the terminal Re-Sdistances, although the difference of 0.04 A (average) is smallbut significant.Fluxional Behaviour of Complex (2b).-For the 'H n.m.r.studies of the fluxional behaviour the triethylammonium salt(2b) was used to avoid complicating counter-ion peaks.Thespectra in the fast- and slow-exchange limits are shown in Figure3. The important features of the high-temperature spectrum arethe signals due to thep-methyl groups and the o- and m-protonsof the thiolates. The methyl signals consist of a sharp 3 H singlet(6 = 2.34)* and a broad 18 H singlet (6 2.18). Since theapproximately C2" symmetry of the anion permits only oneunique methyl group, i.e. that of the bridging thiolate trans toNO, the 3 H singlet is unequivocally assigned to this ligand. The* For [NHEt,][SC,H,Me-pJ under these conditions G(p-Me) = 2.25.NO NOScheme 2.Figure 4. Structure of [Re(SC,H3Pri2-2,6),(NO)], showing the atomlabelling schemearomatic signals consist of a sharp 4 H 'AB system (6 7.42, J 8.2and 60 Hz), similarly assigned to the trans bridging thiolate, andother very broad bands.Below 1 1 "C the broad signals split intoa pattern of sharp lines. The 18 H methyl peak becomes a pair ofsharp singlets (12 H, 6 2.36 and 6 H, 6 2.09) while the 3 H, 6 2.36signal is unaffected. The 4 H AB quartet is also unchanged onlowering the temperature, while the broad aromatic signals splitinto a complex pattern. The entire low-temperature aromaticpattern is simulated as five overiapping AB quartets ofintegrated ratios 4 H : 8 H : 8 H : 4 H : 4 H, implying that, below1 1 "C at least, rotation of aromatic rings about C-S or S-Rebonds is slow on the n.m.r. time-scale. The observedtemperature dependence of the spectrum implies that the six'equatorial' thiolates are interchanged by a fluxional mechanism,T, = 1 1 "C, in which the trans thiolate is not involved.The combined n.m.r. data suggest that above 11 "C the sixequatorial ligands exchange rapidly about a rigid Re( 1)-S(2)-Re(2) core.A plausible mechanism involving partial bridgecleavage is suggested in Scheme 2. A precedent for fluxionalexchange of thiolato-ligands between bridging and terminalpositions is the behaviour of the complex [MoTl(SC,F,),(q-C,H,)]13 as observed by 19F n.m.r. spectroscopy.Structure of Complex (4).-Tables 5 and 6 give atomic co-ordinates and selected bond lengths and angles for (4). Th1538 J. CHEM. SOC. DALTON TRANS. 1985Table 5. Selected atomic co-ordinates ( x lo4) for [Re(SC,H,Pr',-2,6),(NOll (4)Atom X Y zRe 4 852(1)S(l) 6094(4)S(2) 6 138(4)S(3) 4637(5)S(4) 4049(4)0(1) 3 256(14)N 3 889(12)C(11) 5 632(18)C(21) 6 179(17)C(31) 5404(17)C(41) 2 886(16)6 967( 1)6 197(3)7 676(3)7 741(3)7 082(3)6 098(9)6 463(8)5 453( 1 1)7 595(11)8 508( 1 1)6 642( 1 1)1 388(1)1 498(1)1 123(1)1831(1)8 W 1)1 691(4)1588(4)1736(6)648(5)1 786(5)833(5)Table 6.Selected bond lengths (A) and angles (") for [Re(SC,H,Pr',-2,6)4(NO)I (4)Re-S( 1 ) 2.266(5) S( 1 )-C( 1 1) 1.820(23)Re-S(2) 2.413(5) S(2)-C(2 1) 1.8 18(2 1)Re-S(3) 2.286(5) S(3)-C(31) 1.8 17(22)Re-S(4) 2.272(5) S(4)-C(41) 1.765(22)Re-N 1.781(16) 0-N 1.167( 24)S( 1 )-Re-S(2)S(l)-Re-S(3)S(2)-Re-S(3)S( 1 )-Re-S(4)S(2)-Re-S(4)S(3)-Re-S(4)S( 1 )-Re-NS(2)-Re-N87.0(2) S(3)-Re-N 87.7(5)1 13.1(2) S(4)-Re-N 95.6(5)90.9(2) Re-S(l)-C(ll) 112.3(8)124.6(2) Re-S(2w(21) 112.8(7)84.6(2) Re-S(3w(31) 114.0(7)121.8(2) Re-S(4)-C(41) 114.7(7)94.1 (5) Re-N-0 173.6( 14)17835)structure is shown in Figure 4.The molecule possesses a slightlydistorted trigonal-bipyramidal structure similar to that of theisoelectronic [M(SC,H2Pri,-2,4,6),(MeCN)] (M = Ru orOs)I4 and it would appear since the recent preparation andcharacterisation of several different 14-electron complexes ofthe trigonal-bipyramidal geometry, with one or two n-acceptorligands, that such structures have a particular stability withthiolate and alkoxide ligands. In such cases the x-acid ligands(CO," MeCN,', or PR,7) are always in axial sites.Inthe complex [Mo(SPh),(NO)] - the equatorial thiolates orienttheir aromatic groups towards the NO, forming a pocket whichthe NO occupies.'* This arrangement may be adopted tominimise repulsion between the lone pairs of the equatorialsulphur atoms and the Mo-N-O x electrons. A similararrangement occurs in the complexes [Re(SPh),(MeCN)-(PPh,)17 and [W(OPr'),(NO)(py)] (py = pyridine).' Incontrast, two of the equatorial aromatic groups in complex (4)are directed towards (endo) the NO and one away (em);presumably the steric interaction of the bulky substituentsoutweighs the effect of the sulphur-MNO repulsion. Thisarrangement is seen in other complexes of sterically hinderedthiols, [MoL,(CO),]- '' and [RuL,(MeCN)] (L =SC,H,Pr',-2,4,6).'4 The axial aromatic group in (4) is orientedso as to occupy the space left between the equatorial aromaticgroups.The Re-N-0 group is slightly bent away from the endo-thiolates.Consistent with the calculations of Rossi and Hoffmann,'the axial Re-S bond is longer (2.41 A) than the average of theequatorial bond lengths (2.27 A). Their calculation ignores theeffect of n bonding in the equatorial bonds, but they furtherpredict that weak n-donor ligands in d4 systems will occupyequatorial positions and orient themselves so as to maximise xoverlap in the xy plane (defining the Re-N bond as the z axis).. - - I - IldXY I dxzFigure 5. (a) Interaction of metal-based orbitals with NO x* orbitals inan idealised trigonal bipyramid '"; (6) diagram showing interaction ofthe metal with the equatorial sulphur p orbital in I (left) and 11 (right)planesThis is indeed the case in complex (4).x Donation by equatorialsulphurs (see Figure 5 ) would be weaker in a 11 plane (i.e. onecontaining the z axis) since of the vacant orbitals available for xinteraction with equatorial ligands the e" (which interacts in the11 plane) has much higher energy than the e' (which wouldinteract in the I plane). Hence the S-C bonds of the equato;ialthiolates are directed so as to maximise the weak S-to-Re xdonation. Similarly there are no suitable metal orbitalsavailable to accept n-electron density from the axial sulphur.Thus, n donation, although weak, probably accounts for theshort equatorial Re-S bonds and explains why the equatorialthiolates do not adopt a 'propeller' arrangement with the S-Cbonds in the xy plane, a situation which sterically would bemore favourable particularly for [Mo( SC,H Pri,-2,4,6) 3-(CO)2]-, where there are no bulky axial ligands.ExperimentalCrystal parameters and experimental details for the X-raydiffraction studies are given in Table 7.1.r. spectra weredetermined for Nujol mulls or CH2C12 solutions using a Pye-Unicam SP2000 spectrophotometer. Electronic spectra weredetermined for tetrahydrofuran solutions using a Perkin-ElmerLambda 5 u.v.-visible spectrophotometer. N.m.r. spectra wererecorded for CD2C12 solutions using JEOL FX-90Q (90 MHz)or Bruker WH360 (360 MHz) instruments.Cyclic voltammetricmeasurements were made using a Chemical-Electronics typeRB1 waveform generator and type TR70/2A potentiostat and aBryans 24000 A4 XY chart recorder. Molecular weights weremeasured cryoscopically in benzene solution. Carbon, H, and Nanalyses were performed by Mrs. G. Olney, University ofSussex, chlorine analyses by Butterworth Laboratories Ltd.,Teddington, Middlesex.All reactions were carried out in dry, deoxygenated solventsunder a dinitrogen atmosphere unless indicated. The complex[ReC12(OMe)(NO)(PPh,)2] was prepared according to ref. 1.Thiophenol and 4-methylthiophenol were used as purchased.2,4,6-Tri-isopropylthiophenol and 2,4,6-trimethylthiophenoJ. CHEM. SOC. DALTON TRANS. 1985 1539TabJe 7.Experimental details for X-ray diffraction study of [PPh4][Re2(SC,H,Me-4),(N0),] (2a) and [Re(SC,H,Pri,-2,6),(NO)] (4)(a) Crystal parameters at 23 "C" (2a)-CH,CI, (4)alAblAC I Aa/"PI"rl"u/A3Space groupZDJg ~ m - ~D,/g ~ m - ~(6) Measurement of intensity dataCrystal dimensions (mm)Scan rate/" min-IScan range/"Background measurementNo. of reflections collectedNo. of independent reflections used13.465(3)15.574(4)19.630(5)98.00(2)109.80(2)91.85(2)3 821.6(16)PT21.491.45-1.47*0.10, 0.27, 0.33 (mounted in capillary)Variable: 6-303 < 20 < 45Stationary crystal and counter, at thebeginning and end of each 20 scan, eachfor one half the time taken for the 28 scan8 3416371 for F, > 3alF0113.218(6)19.534(9)38.115(1)90.0090.0090.009 84 1.30(6)Pbca81.351.33(2)0.20, 0.29, 0.24Variable: 10-300 < 20 < 45Stationary crystal and counter, at thebeginning and end of each 28 scan,each for the time taken for the 28 scan7 2403 047 for F, > 3olF0((c) Reduction of intensity data and summary of structure solution and refinementAbsorption coefficientlcm-IAbsorption correctionFinal discrepancy factors RRGoodness of fit35.8 28.00.0792 0.06430.0807 0.06341.14 1.936None (intensity ratio Tm,JTrnin.= 1.13) None (Tm.JTmin. = 1.07)Details common to both complexes: diffractometer, Nicolet R3m; radiation, Mo-K, (x = 0.710 69 A); scan mode, coupled 8(crystal)--20(counter);scan length, [28(Mo-KaI) - 1.0) to [28(Mo-K,,) + 1.01"; standards, 3 measured every 197 reflections, no significant deviations; neutral atomicscattering factors; anomalous dispersion correction applied to all non-hydrogen atoms ('International Tables for X-Ray Crystallography,' KynochPress, Birmingham, 1962, vol.3).Structure solution: Re atoms located by Patterson synthesis; all other non-hydrogen atoms located on subsequent difference Fourier maps. All non-hydrogen and non-carbon atoms were refined anisotropically. Hydrogen atoms were included as fixed contributors in the final cycle of refinement.Three highly disordered CH,Cl, molecules of crystallisation were located on the Fourier maps of (2a), each showing a population of ca. 0.33. Nosystematic attempt was made to resolve the disorder as this region of the structure was not of chemical interest.a From a least-squares fitting of the setting angle of 25 reflections.* Observed density varied with time as a consequence of the slow loss of CH,CI, ofcrystallisation.Over a period of a week crystals of (2a) became opaque and analysis revealed loss of CH,CI,. All calculations were performed on aData General Nova 3 computer with 32K of 16-bit words using local versions of the Nicolet SHELXTL interactive crystallographic software packageas described by G. M. Sheldrick, Nicolet SHELTX Operations Manual, Nicolet XRD Corp., Cupertino, 1979. Data corrected for backgroundattenuators, Lorentz and polarisation effects in the usual manner. R = XIIFoI - lFc~/XIFol]; R = [Cw(lF,I - IFcI)2/Xw(Fo12]f; w = [02(Fo) +g(F0)']-'; g = 0.001 for (4), 0.005 for (2a).[ ~ w ( ( F o ~ - ( F c ~ ) 2 / ( N , - NJJf, where No is the number of observations and N, the number of variables.were prepared from 2,4,6-tri-isopropylbenzenesulphonyl chlor-ide and 2,4,6-trimethylbenzenesulphonyl chloride (each used aspurchased from Aldrich Chemicals Ltd.) respectively. 2,6-Di-isopropylthiophenol and 4-bromo-2,6-di-isopropylthiophenolwere prepared from 2,6-di-isopropylphenol (used in 90% purityas purchased from Aldrich Chemicals Ltd.) by an adaptation ofthe Newman-Kwart rearrangement.2,4,6- Tri-isopropyZthiophenoL-Lit hium aluminium hydride(27 g, 0.71 mol) was suspended in diethyl ether (200 cm3) in aflask equipped with an efficient condenser and cooled to 0 "C inan ice-bath.While this suspension was magnetically stirred, asolution of 2,4,6-tri-isopropylbenzenesulphonyl chloride (100 g,0.33 mol) in diethyl ether (300 cm3) was added dropwise. Whenthis addition was complete and the initial vigorous reaction hadsubsided, a further 13 g (0.34 mol) of lithium aluminium hydridepowder was added and the solution refluxed for 5 h. The largeexcess of hydride was destroyed by dropwise addition of excessof methanol under N,. The solution was then poured into 1 1 oficed water. Finally this mixture was acidified with 2 mol dm-3H2S04 and extracted with diethyl ether (3 x 200 cm3). Thecombined ether extracts were dried over MgSO,, and thesolvent stripped on a rotary evaporator. The liquid residue wasdistilled (b.p.117-120 "C, 0.3 mmHg) to yield 67.4 g (87%) of2,4,6-tri-isopropylthiophenol as a colourless liquid.2,4,6- Trimethyfthiophenof was prepared exactly analogouslyfrom 2,4,6-trimethylbenzenesulphonyl chloride, using similarmolar ratios of LiAlH,, in similar yield (b.p. 69-72 "C, 0.3mmHg).2,6-Di-isopropylthiophenof.--Crude 2,6-di-isopropylphenol(100 g, containing 0.51 mol) was dissolved in N,N-dimethyl-formamide. To the magnetically stirred solution, sodiumhydride (15.3 g of an 80% dispersion in mineral oil, 0.15 mol)was added slowly. When gas evolution was complete, dimethyl-thiocarbamoyl chloride2 (63 g, 0.5 1 mol) was added slowly. Oncompletion of the addition the stirred solution was heated at100 "C for 16 h, then cooled to room temperature and pouredinto 1.5 I of 2% aqueous KOH.The resulting precipitate wascollected and recrystallised from hot ethanol, to give off-white 0-2,6-di-isopropyZphenyl N,N-dimethylthiocarbamate, 50g (34%). This material was heated at 230 "C for 48 h unde1540 J. CHEM. SOC. DALTON TRANS. 1985dinitrogen; on melting it was continuously stirred. On coolingto room temperature, the solid product (crude S-2,6-di-iso-propylphenyl N,N-dimethylthiocarbamate) was used withoutpurification for the next step. The crude material (50 g, 0.19 mol)was dissolved in 1,2-dimethoxyethane (200 cm3) and thesolution added dropwise to a stirred suspension of lithiumaluminium hydride (22 g, 0.58 mol) in 1,2-dimethoxyethane (150cm3) cooled in an ice-bath. When the initial reaction hadsubsided the solution was refluxed for 6 h.The excess of hydridewas destroyed as described above. Acidification, etherextraction, drying, and solvent removal were carried out as forHSC6H,Pr',-2,4,6. The final yellow liquid residue was distilled(b.p. 82-88 "C, 0.3 mmHg) to yield 2,6-di-isopropylthiophenolas a colourless liquid, 20 g (20% based on 2,6-di-isopropyl-phenol).4-Bromo-2,6-di-isopropylthiophenol.-Crude 2,6-di-isopro-pylphenol(100 g, containing 0.51 mol) was dissolved in glacialacetic acid (200 cm3). Dibromine (81.6 g, 0.51 mol) was addeddropwise to the stirred solution. On completion of the additionthe mixture was poured into water (500 cm3), forming aseparable brown oil, which was washed repeatedly with waterand dried over MgSO,, to give crude 4-bromo-2,6-di-isopropylphenol, 1 18 g (9 1%).This material, without purificationand assuming 100% purity, was used to make 4-bromo-2,6-di-isopropylthiophenol in a manner exactly analogous to that forHSC6H3Pr',-2,6 and in overall yield based on 2,6-di-isopropylphenol of 15% (b.p. 140-141 "C, 0.3 mmHg).Tetraphenylphosphonium Tri-p-thiophenolato-bisCnitrosyldi-(thiophenolato)rhenate], [PPh,] [Re,(SPh),(NO),] (l).-To asuspension of [ReCl,(0Me)(NO)(PPh3),] (0.3 g, 0.36 mmol) inmethanol (30 cm3) were added thiophenol(O.24 cm3, 2.2 mmol)and triethylamine (0.21 cm3, 1.5 mmol). The system was heatedunder reflux for 1 h. The cooled orange-brown solution wasfiltered to remove insoluble side products, and treated withtetraphenylphosphonium bromide (0.3 g) yielding micro-crystalline (1).After washing with Pr'OH and diethyl ether, theproduct was recrystallised from dichloromethanediethyl etheras orange-brown needles, 49% (Found: C, 51.4; H, 3.75; N, 1.90.Tetraphenylphosphonium Tri-p-4-methylthiophenolato-bis[di-(4-methylthiophenolato)nitrosylrhenate], [PPh,][Re2(SC6H,-Me-4),(NO),] (2a), was prepared analogously to (1) using 4-methylthiophenol, yield 59% of orange prisms (Found: C, 53.7;H, 4.45; N, 1.75. C73H69N202PRe2S7 requires C, 53.6; H, 4.25,N, 1.70%). Crystals suitable for X-ray crystallography weregrown by diffusion of diethyl ether into a dichloromethanesolution of (2a).C66HssN202PRe2S7 requires c, 51.6; H, 3.60, N, 1.80%).Triethylammonium Tri-p-4-methylthiophenolato-bis[di(4-methylphenolato)nitrosylrhenate], [NHEt3][Re2(SC,H,-Me-4),(NO),] (2b).-The reaction was carried out as forcomplex (2a) but instead of adding tetraphenylphosphoniumbromide the filtered reaction solution was evaporated underreduced pressure to ca.10 cm3, yielding an orange,microcrystalline precipitate which was washed with Pr'OH anddiethyl ether to give pure (2b) (Found: C, 47.35, H, 4.90; N, 2.95.C5,H6,N30,Re2S7 requires C, 47.3; H, 4.65; N, 3.00%).Nitrosyltetrakis(2,4,6-tri- isopropylthiophenolato)rhenium,[Re(SC6H2Pr',-2,4,6),(NO)] @).-To a stirred suspension of[ReCl,(OMe)(NO)(PPh3)2] (1.0 g, 1.2 mmol) in methanol (30cm3) were added HSC6H,Pri3-2,4,6 (1.87 cm3, 7.13 mmol) andtriethylamine (0.82 cm3, 5.93 mmol).The system was heatedunder reflux for 0.5 h then the solution was filtered quickly whilehot. On cooling the filtrate, brown microcrystals formed whichwere collected and washed with methanol, yielding 0.61 g (44%)of dark brown, hydrocarbon-soluble (3) (Found: C, 62.15; H,7.70; N, 1.20. C6,H,,NOReS, requires C, 62.25; H, 7.95; N,1.20%).Tetrakis( 2,6-di-isopropylthiophenolato)nitrosylrhenium,[Re(SC6H,Pri,-2,6),(NO)] (4).-To a stirred suspension of[ReCl,(OMe)(NO)(PPh,),] (0.2 g, 0.24 mmol) in methanol (30cm3) were added HSC6H3Pri2-2,6 (0.23 cm3, 1.18 mmol) andtriethylamine (0.16 cm3, 1.16 mmol). The system was heatedunder reflux for 0.5 h then the solution was filtered while hot.On cooling, brown crystals of (4) were formed in the filtrate.Extraction of the insoluble residue with diethyl ether gave abrown solution which was filtered and evaporated to dryness.The residue was recrystallised from hot methanol to give afurther crop of complex (4).The total yield was 0.16 g (66%)C, 58.3; H, 6.90; N, 1.40%). Crystals suitable for X-rayanalysis were obtained by recrystallising from dichloromethane-methanol.[Re(SC,H2Me3-2,4,6),(NO)] (5), was prepared in an exactlyanalogous manner to (4), using HSC6H,Me3-2,4,6 (0.17 cm3,1.18 mmol) in place of HSC6H3Pri,-2,6 to yield brown crystalsof (5), 0.11 g (55%) (Found: C, 52.5; H, 5.40 N, 1.70.C3,H,,NOReS4 requires C, 52.4; H, 5.50; N, 1.65%).(Found: c, 58.45; H, 7.15; N, 1.35. C48H,8NOReS4 requiresNitrosyltetrakis(2,4,6- trimethylthiophenolato)rhenium,Tetrakis(4-bromo-2,6-di-isopropylthiophenolato)nitrosyl-rhenium, [Re(SC6H2Pri,-2,6-Br-4),(N0)1 (6).-To a stirredsuspension of [ReCl,(0Me)(NO)(PPh3),] (0.3 1 g, 0.37 mmol)in methanol (30 cm3) were added HSC6H,Pri,-2,6-Br-4 (0.38cm3, 1.81 mmol) and triethylamine (0.21 cm3, 1.52 mmol). Thesystem was heated under reflux for 0.75 h, giving a brownsuspension.The solid was collected by filtration while hot andwashed with methanol, yielding a crude sample of (6). Thefiltered reaction solution, on cooling to room temperature, gavea second crop of complex (6). The combined crops wererecrystallised from hot hexane, yield 0.31 g (65%) (Found: C,N, 1.05%).Methoxonitrosyltris(2,4,6- trimethylthiophenolato)rhenium,[Re( SC6H 2Me3-2,4,6)3( OMe)(NO)] (7), was obtained asbrown crystals by partial evaporation of a CH,Cl,-MeOHsolution of (5) which had been standing at room temperature forseveral days (Found: C, 47.5; H, 5.25; N, 1.95.C2,H3,NO2ReS3requires C, 48.0; H, 5.15; N, 2.00%).Methoxonitrosyltris( 2,4,6-tri-isopropylthiophenolato)rhenium,[Re(SC6H,Pr',-2,4,6)3(OMe)(NO)I (8), was obtained as red-brown crystals in a similar manner to (7). No microanalyticaldata available; the formulation was on the basis of similarity ofthe i.r. spectrum with that of complex (7).Tris( 2,6-di-isopropylthiophenolato)ethoxonitrosylrhenium,[Re(SC6H3Pr'2-2,6)3(OEt)(NO)] (9), was obtained as browncrystals by partial evaporation of an ethanolic solution of (4)which had been standing for several days (Found: C, 54.2; H,1.65%).44.65; H, 5.20 N, 1.10.C48H64NOReS4 requires C, 44.5; H, 4.90;6.30; N, 1.65; C ~ ~ H S ~ N O ~ R ~ S ~ requires C, 54.25; H, 6.65; N,Chloronitrosyltris( 2,4,6-tri-isopropylthiophenolato)rhenium,(lo).-To a solution of complex (8) in dichloromethane-methanol (50: 50) was added excess of chlorotrimethylsilane.The solution turned green immediately but on standing theorange-brown colour returned. Partial evaporation underreduced pressure yielded orange-brown crystals of (lo), whichwere collected and washed with methanol (Found: C, 56.5; H,7.30; Cl, 3.35; N, 1.40. C4,H6,C1NOReS3 requires C, 56.45; H,7.20 C1, 3.70; N, 1.45%)J. CHEM. SOC. DALTON TRANS. 1985 1541References1 R. W. Adams, J. Chatt, N. E. Hooper, and G. J. Leigh, J. Chem. SOC.,2 T. S. Cameron, K. R. Grundy, and K. N. Robertson, Znorg. Chem.,3 B. K. Sen, P. Bandyopadhyay, and P. B. Sarkar, J. Indian Chem. SOC.,4 S. Rakshit and P. Bandyopadhyay, J. Indian Chem. SOC., 1970,447,5 A. Davidson, C. Orvig, H. S. Trop, M. Sohn, B. V. DePamphilis, and6 A. C. McDonell, T. W. Hambley, M. R. Snow, and A. G. Wedd, Aust.7 J. R. Dilworth, B. D. Neaves, J. P. Hutchinson, and J. A. Zubieta,8 E. W. Abel, W. Harrison, R. A. N. McLean, W. C. Marsh, and J.9 D. Giusto and G. Cova, Gazz. Chim. Ital., 1972, 102, 265.Dalton Trans., 1974, 1075.1982,21,4149.1967,44,227.1205.A. G. Jones, Znorg. Chem., 1980, 19, 1988.J. Chem., 1983,36,253.Znorg. Chim. Ada, 1982, 65, L223.Trotter, Chem. Commun., 1970, 1531.10 J. R. Dilworth, P. T. Bishop, and J. A. Zubieta, unpublished work.1 1 F. A. Cotton and D. A. Ucko, Znorg. Chim. Acta, 1972, 6, 161.12 T. W. Wolff, J. M. Berg, K. 0. Hodgson, R. B. Frankel, and R. H.13 J. L. Davidson, K. Davidson, and W. E. Lindsell, J. Chem. SOC.,14 S. A. Koch and M. Miller, J. Am. Chem. SOC., 1983, 105, 3362.15 J. R. Dilworth, J. Hutchinson, and J. A. Zubieta, J. Chem. SOC., Chem.16 P. J. Blower, unpublished work.17 M. H. Chisholm, F. A. Cotton, M. W. Extine, and R. L. Kelly, Znorg.18 J. A. Zubieta, personal communication.19 A. R. Rossi and R. Hoffmann, Znorg. Chem., 1975, 14, 365.20 M. S. Newman and H. A. Kames, J. Org. Chem., 1966,31, 3980.21 M. S. Newman and F. W. Hetzel, Org. Synth., 1971, 51, 139.Holm, J. Am. Chem. Soc., 1979, 101,4140.Chem. Commun., 1983,452.Commun., 1983, 1034.Chem., 1979, 18, 116.Received 27th April 1984; Paper 4/69

ISSN:1477-9226    

DOI:10.1039/DT9850001533

出版商:RSC    

年代:1985

数据来源: RSC