摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1997, Pages 463–464 463 Crystal structure and synthesis of a novel tetranuclear iron(III) complex with a defective double-cubane core† Hui Li,a Zhuang Jin Zhong,*,a Wei Chen b and Xiao-Zeng You a a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, 210093, P. R. China b Department of Chemistry, University of Malaya, Lambah Pautai, 59100 Kuala, Malaysia A novel tetranuclear iron(III) complex [Fe4(OCH3)6(acac)4(N3)2] (acac = acetylacetonate) has been synthesized and shown by X-ray crystallography to contain an unusual defective doublecubane core connected by m-OCH3 and m3-OCH3 bridges; it also shows an antiferromagnetic interaction.One-dimensional magnetic compounds as important precursors of molecular magnets have aroused wide interest.1–3 The azide group is a versatile bridging ligand and useful for generating this kind of system. A series of one- and two-dimensional m-azide nickel(II) complexes has been synthesized and characterized.4–6 A few manganese(III) chain complexes have also been synthesized.7 However, no m-azide FeIII chain complexes have been reported until now.To obtain such a complex we have attempted the reaction of [Fe(acac)2NO3] with NaN3 in methanol. To our surprise, a methoxo-bridged tetranuclear iron(III) complex [Fe4(OCH3)6(acac)4(N3)2] (acac = acetylacetonate) was obtained instead in which the azide ion acts as a terminal ligand. There has been a growing interest in the synthesis of polynuclear iron complexes due to the discovery that the catalytic sites of a number of non-haem iron proteins contain oxo- or hydroxo-bridged diiron units and the relevance of large polyiron(II,III)–oxo aggregates to the ferritin core.8–10 And a large number of polynuclear oxo-, hydroxo- and alkoxobridged iron complexes have been synthesized and characterized so far.11–14 However, no tetranuclear [FeIII 4(OR)6]6+ complex has been reported.In this view, [Fe4(OCH3)6(acac)4(N3)2] is a novel example. In this communication, the synthesis, crystal structure and magnetic properties of this tetranuclear iron(III) complex are presented. The complex [Fe4(OCH3)6(acac)4(N3)2] was prepared by the reaction of equimolar amounts of [Fe(acac)2NO3] 15 (0.315 g, 1 mmol) and NaN3 (0.065 g, 1 mmol) in methanol and acetone (1 : 2; 30 cm3) with stirring for 0.5 h at room temperature.A red crystalline solid suitable for X-ray structure analysis was obtained after slow evaporation of this solution (Found: C, 34.90; H, 5.45; N, 9.75. Calc. for C26H46Fe4N6O14: C, 35.10; H, 5.20; N, 9.45%). The structure of the entire molecule is illustrated in Fig. 1.‡ The structure consists of a centrosymmetric tetranuclear FeIII complex. The four Fe atoms are located at four corners of a defective double cubane and bridged by four m-OCH3 and two m3-OCH3 groups. The intramolecular Fe ? ? ?Fe distances range from 3.193(6) [Fe(1) ? ? ?Fe(29)] to 5.514(5) Å [Fe(1) ? ? ?Fe(19)].The asymmetric unit consists of Fe2(acac)2N3(OCH3)3. Within the asymmetric unit, the geometrical environment of Fe(1) and † Non-SI unit employed: mB ª 9.274 × 10224 J T21. Fe(2) are roughly similar. Atom Fe(1) has a NO5 distorted octahedral ligand donor set in which the O-donor atoms are supplied by an acac ligand [O(1), O(2)], two m-OCH3 [O(6), O(79)] and a m3-OCH3 [O(5)].The N-donor atom comes from a terminal azide. However, Fe(2) has an O6 donor set in a distorted octahedron, where five of the oxygen-donor atoms are the same as those of Fe(1) and the remainder is supplied by another m3-OCH3 [O(59)]. The average Fe]m-OR bond length in [Fe4(OCH3)6(acac)4(N3)2] (1.99 Å) is close to those in other m-alkoxo iron(III) complexes [2.06 Å].12 The longest bond distance is Fe(1)]O(5) [2.196(5) Å], the m3-OCH3 ligand bridge being slightly asymmetric.The Fe(2)]O(5) bond distance [2.100(5) and 2.077(5) Å] is slightly shorter than Fe(1)]O(5) [2.196(5) Å] and the Fe(29)]O(5)]Fe(2) bond angle [100.6(2)8] is slightly larger than those of Fe(2)]O(5)]Fe(1) [96.8(2)8] and Fe(29)]O(5)]Fe(1) [96.7(2)8]. This is the first example of a structurally characterized tetranuclear iron(III) complex with a defective double cubane to our knowledge, although a pentanuclear one has been reported.18 The effective magnetic moment per iron ion in [Fe4(OCH3)6- (acac)4(N3)2] varies gradually from 4.26 mB at 300 K down to 2.75 mB at 80 K, indicative of an antiferromagnetic interaction between the metal ions.This behaviour is similar to another tetranuclear iron(III) complex, [Fe4O2(O2CCH3)7- (bipy)2][ClO4] (bipy = 2,29-bipyridine).13 Further investigation into the magnetic behaviour of [Fe4(OCH3)6(acac)4(N3)2] is in progress. Acknowledgements This work was supported by grants from the State Science and Technology Commission, the State Education Commission and the National Nature Science Foundation of China.‡ Crystal data. C26H46Fe4N6O14, red cubic crystal of dimension 0.25 × 0.14 × 0.05 mm, M = 890.08, monoclinic, space group P21/c, Z = 4, a = 11.500(1), b = 8.515(1), c = 20.385(2) Å, b = 99.26(1)8, U = 1970.1 Å3, Dc = 1.500 g cm23, T = 300(2) K, F(000) = 920, Mo-Ka radiation (l = 0.710 73 Å), m = 1.509 mm21. The structure was solved by the direct methods and refined by full-matrix least-squares methods using 3445 observed reflections.Absorption correction was not applied owing to the small size of the crystal. A total of 3617 unique data were measured on a four-circle Enraf-Nonius CAD4 diffractometer using w– 2q scans. The final R1 and wR2 values were 0.0697 and 0.1488 respectively for 226 parameters and [s2(Fo)]21 weights, goodness of fit = 0.871 on F 2 for all data. All non-H atoms were refined with anisotropic displacement parameters, whereas H atoms were located from the difference map.16,17 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 186/394.464 J. Chem. Soc., Dalton Trans., 1997, Pages 463–464 Fig. 1 Structure of [Fe4(OCH3)6(acac)4(N3)2]. Selected bond lengths (Å) and angles (8): Fe(1) ? ? ?Fe(19 ) 5.514(5), Fe(2) ? ? ?Fe(1) 3.212(5), Fe(1) ? ? ?Fe(29 ) 3.193(6), Fe(2) ? ? ?Fe(29 ) 3.214(5), Fe(1)]O(79 ) 1.974(5).Fe(1)]O(2) 1.986(5), Fe(1)]O(6) 1.993(5), Fe(1)]O(1) 1.997(6), Fe(1)]N(1) 1.986(8), Fe(1)]O(5) 2.196(5), Fe(2)]O(3) 1.949(6), Fe(2)]O(7) 1.973(5), Fe(2)]O(6) 1.968(5), Fe(2)]O(4) 1.980(5), Fe(2)]O(59 ) 2.077(5), Fe(2)]O(5) 2.100(5), O(5)]Fe(29 ) 2.077(5), O(7)]Fe(19 ) 1.974(5), N(1)]N(2) 1.175(1), N(2)]N(3) 1.116(1); O(79 )]Fe(1)]O(2) 89.6(2), O(79 )]Fe(1)]O(6) 92.1(2), O(2)]Fe(1)]O(6) 167.1(2), O(79 )]Fe(1)]O(1) 165.9(2), O(2)] Fe(1)]O(1) 86.2(2), O(6)]Fe(1)]O(1) 89.1(2), O(79 )]Fe(1)]N(1) 97.1(3), O(2)]Fe(1)]N(1) 97.0(3), O(6)]Fe(1)]N(1) 95.5(3), O(1)]Fe(1)]N(1) 96.8(3), O(79)]Fe(1)]O(5) 76.1(2), O(2)]Fe(1)]O(5) 92.0(2), O(6)] Fe(1)]N(5) 76.0(2), O(1)]Fe(1)]O(5) 90.5(2), N(1)]Fe(1)]O(5) 168.7(3), O(3)]Fe(2)]O(7) 93.5(2), O(3)]Fe(2)]O(6) 93.4(2), O(7)] Fe(2)]O(6) 169.6(2), O(3)]Fe(2)]O(4) 89.7(3), O(7)]Fe(2)]O(4) 94.5(2), O(6)]Fe(2)]O(4) 93.4(2), O(3)]Fe(2)]O(59 ) 170.9(2), O(7)] Fe(2)]O(59 ) 79.0(2), O(6)]Fe(2)]O(59 ) 93.4(2), O(4)]Fe(2)]O(59 ) 95.9(2), O(3)]Fe(2)]O(5) 96.0(2), O(7)]Fe(2)]O(5) 92.7, O(6)] Fe(2)]O(5) 78.8(2), O(4)]Fe(2)]O(5) 170.5(2), O(59 )]Fe(2)]O(5) 79.4(2), Fe(29 )]O(5)]Fe(2) 100.6(2), Fe(29 )]O(5)]Fe(1) 96.7(2), Fe(2)]O(5)]Fe(1) 96.8(2), Fe(2)]O(6)]Fe(1) 108.4(2), Fe(19 )]O(7)] Fe(2) 108.0(2) References 1 C.-T.Chen and K.S. Suslick, Coord. Chem. Rev., 1993, 128, 293. 2 E. Coronado, M. Drillon, A. Fuertes, D. Beltran, A. Mosset and J. Galy, J. Am. Chem. Soc., 1986, 108, 900. 3 R. Soules, F. Dahan and J.-P. Laurent J. Chem. Soc., Dalton Trans., 1988, 587. 4 R. Cortes, K. Urtiaga, L. Lezama, J. L. Pizarro, A. Goni, M. I. Arriortua and T. Rojo, Inorg. Chem., 1994, 33, 4009. 5 R. Vicente, A. Escuer, J. Ribas and X. Solans, Inorg. Chem., 1992, 31, 1726. 6 J. Ribas, M. Monfort, X. Solans and M. Drillon, Inorg. Chem., 1994, 33, 724. 7 B. J. Kennedy and K. S. Murray, Inorg. Chem., 1985, 24, 1552; A. Escuer, R. Vicente, M. A. S. Goher and F. A. Mautner, Inorg. Chem., 1995, 34, 5707 and refs. therein. 8 S. J. Lippard, Angew. Chem., Int. Ed. Engl., 1988, 27, 344. 9 W. Micklitz, V. McKee, R. L. Rardin, L. E. Pence, G. C. Papaefthymiou, S. G. Bott and S. J. Lippard, J. Am. Chem. Soc., 1994, 116, 8061. 10 W. Micklitz and S. J. Lippard, J. Am. Chem. Soc., 1989, 111, 6856. 11 S. Drudke, K. Wieghardt, B. Nuber, J. Weiss, E. L. Bominar, A. Sawaryn, H. Winkler and A. X. Trautwein, Inorg. Chem., 1989, 28, 4477. 12 A. Caneschi, A. Cornia, A. C. Fabretti, D. Gatteschi and W. Malavasi, Inorg. Chem., 1995, 34, 4660. 13 J. K. MaCusker, J. B. Vincent, E. A. Schmitt, M. L. Mino, K. Shin, D. K. Coggin, P. M. Hagen, J. C. Huffmen, G. Christou and D. N. Hendrickson, J. Am. Chem. Soc., 1991, 113, 3012 and refs. therein. 14 K. L. Taft, A. Caneschi, L. E. Pence, C. D. Delfs, G. C. Papaefthymiou and S. J. Lippard, J. Am. Chem. Soc., 1993, 115, 11 753 and refs. therein. 15 D. Laroque, I. Morgen Stern-Badarau, H. Winkler, E. Bill, A. X. Trautwein and M. Julve, Inorg. Chim. Acta, 1992, 192, 107. 16 G. M. Sheldrick, SHELXS 86, Acta Crystallogr., Sect. A, 1990, 46, 467. 17 G. M. Sheldrick, SHELXL 93, A Program for Crystal Structure Determination, University of Göttingen, 1993. 18 M. Mikuriya, Y. Hashimoto and S. Nakashima, Chem. Commun., 1996, 295. Received 18th November 1996; Communication 6/07790K

ISSN:1477-9226    

DOI:10.1039/a607790k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 465–468 465 Synthesis, crystal structure and biological activity of bis(acetone thiosemicarbazone-S)dichlorodiphenyltin(IV) Siang-Guan Teoh,*,a Show-Hing Ang,a Soon-Beng Teo,a Hoong-Kun Fun,b Khing-Ling Khewc and Chi-Wi Ong d a School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia b X-Ray Crystallographic Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia c School of Biological Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia d Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan 804, Republic of China The reaction between diphenyltin(IV) dichloride and thiosemicarbazide using acetone–ethanol as solvent resulted in the formation of bis(acetone thiosemicarbazone-S)dichlorodiphenyltin(IV), SnPh2Cl2(atsc)2.The crystal structure determination of the compound revealed it to be a monomeric six-co-ordinated organotin(IV) complex.Each of the two atsc functions as a monodentate ligand, co-ordinating to the tin atom through the sulfur atom and conferring a distorted-octahedral geometry upon the tin. The Sn]S bond length is 2.712(1) Å. The antifungal activity of the complex, atsc and SnPh2Cl2 against four plant pathogens has been evaluated. The complex displays marked fungitoxicity against these fungi and is more fungitoxic than free atsc and SnPh2Cl2. It has also shown significant cytotoxicity against human colon adenocarcinoma, breast adenocarcinoma, hepatocellular carcinoma and acute lymphoblastic leukaemia. Interest in the co-ordination chemistry of thiosemicarbazones has increased since their biological activity was shown to be related to their metal complexing ability.1 A large number of reports describing the transition-metal complexes of these compounds have appeared.2–5 However, little is known about the corresponding complexing behaviour of non-transition elements such as tin.2,6–8 In this paper we report the synthesis, crystal structure and antifungal and anticancer activities of bis(acetone thiosemicarbazone-S)dichlorodiphenyltin(IV), SnPh2Cl2 (atsc)2, obtained from the reaction between diphenyltin(IV) dichloride and acetone thiosemicarbazone (atsc) derived in situ from thiosemicarbazide and acetone.Experimental General and instrumental Thiosemicarbazide obtained from Fluka Chemie AG was used after purification from ethanol. Diphenyltin dichloride was used as obtained from Aldrich and the solvents used were reagent grade.Carbon, hydrogen and nitrogen analyses were carried out on a Control Equipment Corporation 240XA elemental analyser at the School of Chemical Sciences, Universiti Sains Malaysia, Penang, Malaysia. The tin analysis was performed using an Instrumental Laboratory aa/ee 357 atomic spectrophotometer. The IR spectrum was recorded using a Mattson 1000 FTIR spectrophotometer in the frequency range 4000–200 cm21 with the sample in a KBr disc, the 1H NMR spectrum on a Bruker 300 MHz AC-P spectrometer in (CD3)2SO solution.Synthesis of bis(acetone thiosemicarbazone-S)dichlorodiphenyltin( IV) A solution of SnPh2Cl2 (1 mmol) in ethanol (20 cm3) was added to a hot solution of thiosemicarbazide (2 mmol) in a mixture of acetone (10 cm3) and ethanol (10 cm3). The mixture was heated moderately (ª50 8C) and stirred for 45 min. The resulting solution was allowed to stand and slow evaporation at room temperature gave light yellow crystals which were stable in air.Yield 78%, m.p. 164–165 8C (Found: C, 39.4; H, 4.5; N, 12.9; Sn, 18.8. Calc. for C20H28Cl2N6S2Sn: C, 39.65; H, 4.65; N, 13.85; Sn, 19.6%). IR(KBr): 1595 (C]] N) and 770 cm21 (C]S), 1H NMR [(CD3)2SO]: d 9.89 (s, 1 H, NH), 7.92–7.26 (m, 5 H, C6H5), 7.97 (s, 1 H, NH2), 7.50 (s, 1 H, NH2) and 1.90 (d, 6 H, 2CH3). Crystallography A needle-shaped single crystal of dimensions 0.2 × 0.4 × 0.5 mm was mounted on a thin glass fibre on a Siemens P4 diffractometer equipped with graphite-monochromated Mo-Ka radiation, l = 0.710 73 Å, T = 298 K.The q–2q scan method was employed to measure a total of 3819 reflections in the 3.0 < 2q < 55.08 shell. Corrections were applied for Lorentzpolarization effects but not for absorption. There were 2988 independent reflections of which 2530 satisfied the F > 4.0s(F) criterion of observability and were used in the subsequent analysis.The structure was solved using direct methods and refined by a full-matrix least-squares procedure based on F using SHELXTL (PC version).9 All non-hydrogen atoms were refined using anisotropic thermal parameters and hydrogen atoms were placed in calculated positions (C]H 0.96, N]H 0.90 Å) and refined isotropically. A weighting scheme of the form w = [s2(F) + 0.0024F2]21 was used and the refinement continued to final R = 0.0258 and R9 = 0.0280. The final difference map had peaks between 20.87 and 0.54 e Å23.The crystal data and refinement parameters are given in Table 1, bond distances and angles in Table 2. 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 186/348.466 J.Chem. Soc., Dalton Trans., 1997, Pages 465–468 Antifungal test Fungitoxicity is usually measured in terms of the response of a treated culture relative to that of a control. In this assay, a 100 ppm stock of compound in PDA medium was prepared by dissolving the compound (0.01 g) in Me2SO (1 cm3), adjusting the volume to 100 cm3 with PDA (potatoes dextrose agar) medium. From the stock different concentrations (50, 10, 5 and 1 ppm) were prepared. The treated medium and control were then poured into five sterilized petri dishes respectively and allowed to set for 24 h before being inoculated with the fungus.As soon as the fungal colony covered the whole plate of the control medium the colony diameters of all the control and treated plates were measured. The areas of fungal growth were calculated by using the average diameters of the fungal colony. The fungal growth area was plotted against the compound concentration and the ED50 value was obtained as 50% of the largest fungal growth area at a certain compound concentration.The antifungal activities of the complex, the free thiosemicarbazone and the tin starting compound are summarized in Table 3. Table 1 Crystal data and refinement details for SnPh2Cl2(atsc)2 Formula M Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z Dc/Mg m23 m/mm21 F(000) h,k,l Ranges Reflections collected Independent reflections Observed reflections No. parameters refined RR 9 C20H28Cl2N6S2Sn 606.2 Monoclinic P21/c 9.3770(10) 13.7470(10) 10.8690(10) 111.640(10) 1302.3(2) 2 1.546 1.366 612 21 to 12, 21 to 17, 214 to 13 3819 2988 (Rint = 0.0211) 2530 [F > 4.0s(F)] 198 0.0258 0.0280 Table 2 Bond lengths (Å) and angles (8) with estimated standard deviations in parentheses for non-hydrogen atoms Sn]Cl(1) Sn]C(1) Sn]S(1A) S(1)]C(7) C(1)]C(6) C(3)]C(4) C(5)]C(6) C(7)]N(2) C(8)]C(10) N(2)]N(3) Cl(1)]Sn]S(1) S(1)]Sn]C(1) S(1)]Sn]Cl(1A) Cl(1)]Sn]S(1A) C(1)]Sn]S(1A) Cl(1)]Sn]C(1A) C(1)]Sn]C(1A) S(1A)]Sn]C(1A) Sn]C(1)]C(2) C(2)]C(1)]C(6) C(2)]C(3)]C(4) C(4)]C(5)]C(6) S(1)]C(7)]N(1) N(1)]C(7)]N(2) C(9)]C(8)]N(3) C(7)]N(2)]N(3) 2.589(1) 2.142(3) 2.712(1) 1.724(2) 1.396(3) 1.372(6) 1.398(6) 1.327(2) 1.503(5) 1.396(3) 88.8(1) 92.4(1) 91.2(1) 91.2(1) 87.6(1) 90.0(1) 180.0(1) 92.4(1) 120.2(2) 119.4(3) 120.1(4) 121.0(4) 120.7(2) 118.8(2) 126.8(3) 118.1(2) Sn]S(1) Sn]Cl(1A) Sn]C(1A) C(1)]C(2) C(2)]C(3) C(4)]C(5) C(7)]N(1) C(8)]C(9) C(8)]N(3) Cl(1)]Sn]C(1) Cl(1)]Sn]Cl(1A) C(1)]Sn]Cl(1A) S(1)]Sn]S(1A) Cl(1A)]Sn]S(1A) S(1)]Sn]C(1A) Cl(1A)]Sn]C(1A) Sn]S(1)]C(7) Sn]C(1)]C(6) C(1)]C(2)]C(3) C(3)]C(4)]C(5) C(1)]C(6)]C(5) S(1)]C(7)]N(2) C(9)]C(8)]C(10) C(10)]C(8)]N(3) C(8)]N(3)]N(2) 2.712(1) 2.589(1) 2.142(3) 1.386(4) 1.391(6) 1.377(7) 1.313(3) 1.491(4) 1.278(3) 90.0(1) 180.0(1) 90.0(1) 180.0(1) 88.8(1) 87.6(1) 90.0(1) 105.8(1) 120.3(2) 120.6(3) 119.8(6) 119.0(3) 120.5(2) 117.6(2) 115.6(3) 116.4(2) Cytotoxicity assay: MTT assay In principle, this assay is dependent on the cellular reduction of MTT [3-(4,5-dimethylthiazo-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] by the mitochondrial dehydrogenase of viable cells to give a blue formazan product.The viable cell number per well is directly proportional to the production of formazan, which following solubilization can be measured spectrophotometrically. Single-cell suspensions were obtained by mechanical disaggregation of the floating cell line for human acute lymphoblastic leukaemia (MOLT-4) and by trypsinization of the monolayer cultures for human colon adenocarcinoma (COLO-205), breast adenocarcinoma (SKBR-3) and hepatocellular carcinoma (HA22T/VGH) and counted by trypan blue exclusion.The cells were then planted on to 96 well plates (Nunc 67008) in a volume of 180 ml using a multichannel pipette (Gilson) and incubated for 24 h. The compound was dissolved in 10% Me2SO and 90% DPBS (Dulbecco’s phosphate-buffered saline) solution.The 20 ml solution was dispensed within appropriate wells (each treatment group and control, N = 3) to give final concentrations ranging from 100 to 0.01 mg/cm23 by a 10-fold dilutions. Peripheral wells for each plate (lacking cells) were utilized for drug blank and medium/tetrazolium reagent blank ‘background determinations’. The cells were then incubated for 72 h. A 20 ml volume of MTT (5 mg cm23) was added to each well and incubated for 4 h. Culture plates containing suspension lines or any detached cells were centrifuged at low speed (1000 revolutions min21) for 5 min.The 170 ml culture medium supernatant was removed from each well and replaced with 200 ml Me2SO per well using a multichannel pipette. Following thorough formazan solubilization (vibration on a plate shaker), the absorbance of each well was measured using an ELISA automatic plater (Molecular Devices Emax) at 545–690 nm interfaced with IBM computer Softmax software.Cell growth inhibition was calculated according to [1 2 (A upon compound treatment/A of control)] × 100%. The IC50 was obtained as the 50% growth inhibition at a certain compound concentration from a plot of the compound concentration vs. percentage growth inhibition. The values of IC50 of the complex and adriamycin (as a reference) are shown in Table 4. Results and Discussion As shown in Fig. 1 the structure of bis(acetone thio- Fig. 1 Molecular structure with atom labelling for SnPh2Cl2(atsc)2J. Chem.Soc., Dalton Trans., 1997, Pages 465–468 467 Table 3 Antifungal activity ED50/mg cm23 Compound Curvularia sp. Drechsiera sp. Rhizoctonia sp. Alternaria Bassicicola sp. SnPh2Cl2(atsc)2 atsc SnPh2Cl2 2.15 >100 10 0.50 >100 9 2.05 >100 >100 2.80 145 24 semicarbazone-S)dichlorodiphenyltin(IV) shows a distorted octahedron about the tin atom which is co-ordinated to two phenyl, two chloride and two acetone thiosemicarbazone (atsc) groups.Each of the atsc ligands co-ordinates to the tin atom in the trans configuration,10,11 and therefore it behaves as a monodentate ligand, bonding only through the sulfur atom. The deviation from octahedral symmetry is indicated by the bond angles subtended at the tin atom by adjacent donor atoms, ranging from 88.8(1)8 for Cl(1)]Sn]S(1) and Cl(1A)]Sn]S(1A) to 92.4(1)8 for S(1)]Sn]C(1) and S(1A)]Sn]C(1A). A comparison of bond distances with those of atsc,12 [W(CO)5(atsc)]1 and [Ni(atsc 2 H)2]13 can be made.The thiosemicarbazone acts as a monodentate ligand in [W(CO)5(atsc)], bonded through the sulfur atom, whereas in [Ni(atsc 2 H)2], both of the atsc ligands are bonded through S and hydrazine N atoms. The N(2)]N(3) [1.396(3) Å] bond distance in the present compound is close to N(1)]N(2) [1.398(6) Å] in free atsc and N(2)]N(3) [1.396(8) Å] in [W(CO)5(atsc)], but shorter than the average N]N bond length [1.425(7) Å] in [Ni- (atsc 2 H)2]. This indicates that co-ordination from N(3) to the tin atom does not occur in the present complex as in [W(CO)5(atsc)].The C(7)]S(1) [1.724(2) Å] bond length is shorter than the average C]S bond distance in [Ni(atsc 2 H)2]. This is because in the latter deprotonation of atsc has taken place before coordination through the sulfur anion and then formation of a C]S single bond. In the present complex, the atsc ligands coordinate to the tin atom without deprotonation but in the zwitterion resonance forms shown.14 Owing to resonance the C]S bond possesses partial double-bond character 15 and hence it is shorter.However, it is longer than the C]S distance in free atsc [1.690(5) Å], indicating that co-ordination causes an increase in the C]S single-bond character.16 The Sn]S [2.712(1) Å] bond length is longer than that observed for triphenyltin 1-amino-4-(2-hydroxyphenyl)-2,3- diazapenta-1,3-diene-1-thiolate 17 [2.440(2) Å]. This can be explained from the bond types.For the present compound the Sn]S bond exists as a weak dative bond while for the latter tin complex it is as a covalent bond. It is of interest that the 1H NMR spectrum of the complex exhibits two resonances for the NH2 protons (at d 7.50 and 7.97), indicating hindered rotation about the C(S)]NH2 bond NH C H2N S N C CH3 H3C N C H2N SH N C CH3 H3C +NH C H2N S– N C CH3 H3C NH C H2N+ S– N C CH3 H3C I (thione) II (thiol) III (zwitterion) IV Table 4 Cytotoxic activity IC50/mg cm23 Compound COLO-205 HA22T/VGH SKBR-3 MOLT-4 SnPh2Cl2(atsc)2 Adriamycin 4.62 0.470 3.76 0.300 1.44 0.053 0.50 <0.001 due to its partial double-bond character.18,19 The presence of the imine proton at d 9.89 shows that deprotonation does not take place during complexation.Results of the in vitro antifungal bioassay indicate that the metal complex is more fungitoxic than is free atsc and the parent organotin compound. It proved to have a very strong activity against the four fungi tested especially Drechsiera sp.where the minimum inhibitory concentration is only 0.50 mg cm23. On co-ordination the tin atom is firmly attached to the ligand and its positive charge is shared with the donor groups (S atoms). As a result the complex reduces the polarity of the metal ion and, in turn, increases its hydrophobic character and thus promotes its permeation through the lipoid layers of the fungus membranes.20 Thiosemicarbazones have been demonstrated to show biological activity against viruses, protozoas, pathogens and certain kinds of tumours.21 The fungicidal activity of thiosemicarbazones is due basically to their ability to chelate the necessary metals which the fungus requires in its metabolism.22 However, acetone thiosemicarbazone did not display any fungitoxicity against the fungi tested.One possible explanation is that there is no extensive delocalization involving the alkyl group CH3 and the thiosemicarbazide side chain.From the anticancer screening data presented in Table 4 it is obvious that the complex showed remarkable cytotoxicity as an IC50 value less than 4 mg cm23 normally is considered to represent activity. Interestingly the compound is most active against leukaemia where the IC50 value is only 0.5 mg cm23. Acknowledgements S.-G. T., S.-B. T. and H.-K. F. would like to thank the Malaysian Government and Universiti Sains Malaysia for R & D Grants Nos. 190/9609/3406 and 190/9609/2801.References 1 J. Valdes-Martinez, A. Sierra-Romero, C. Alvarez-Toledano, R. A. Toscano and H. Garcia-Tapia, J. Organomet. Chem., 1983, 352, 321. 2 Kiran, R. V. Singh and J. P. Tandon, Synth. React. Inorg. Metal-Org. Chem., 1986, 16, 1341. 3 M. Nath, N. Sharma and C. L. Sharma, Synth. React. Inorg. Metal- Org. Chem., 1989, 19, 339. 4 V. K. Arora, K. B. Pandeya and R. P. Singh, J. Indian Chem. Soc., 1979, 56, 656. 5 P. L. Maurya, B. V. Agarwala and A. K. Dey, J. Indian Chem.Soc., 1980, 57, 275. 6 A. K. Saxena, J. K. Koacher and J. P. Tandon, J. Inorg. Nucl. Chem., 1981, 43, 3091. 7 A. Saxena and J. P. Tandon, Polyhedron, 1984, 3, 681. 8 A. Varshney and J. P. Tandon, Polyhedron, 1986, 5, 739. 9 G. M. Sheldrick, SHELXTL PCTM, Release 4.1, Siemens Crystallographic Research Systems, Madison, WI, 1990. 10 M. J. M. Campbell, Coord. Chem. Rev., 1975, 15, 279. 11 S. Padhye and G. B. Kauffman, Coord. Chem. Rev., 1985, 63, 127. 12 G. J. Palenik, Acta Crystallogr., Sect. B, 1974, 30, 2390. 13 J. Valdes-Martinez, R. A. Toscano, M. Soriano-Garcia, M. Rubio, J. Gomez-Lara, M. A. Vazquez-M and S. Carranza, Polyhedron, 1989, 8, 727. 14 R. Restivo and G. J. Palenik, Acta Crystallogr., Sect. B, 1970, 26, 1397.468 J. Chem. Soc., Dalton Trans., 1997, Pages 465–468 15 M. K. Kokila, Puttaraja, M. V. Kulkarni and S. Thampi, Acta Crystallogr., Sect. C, 1995, 51, 330. 16 M. Mathew and G. J. Palenik, J. Am. Chem. Soc., 1969, 91, 6310. 17 S. W. Ng, V. G. Kumar Das, B. W. Skelton and A. H. White, J. Organomet. Chem., 1989, 377, 211. 18 C. Bellito, D. Gattegno, A. M. Giuliani and M. Bossa, J. Chem. Soc., Dalton Trans., 1976, 758. 19 P. Umpathy, A. P. Budhkar and C. S. Dorai, J. Indian Chem. Soc., 1986, 63, 714. 20 T. T. Bamgboye and O. A. Bamgboye, Inorg. Chim. Acta, 1987, 133, 247. 21 K. N. Thimmaiah, G. T. Chandrappa, Rangaswamy and Jayarama, Polyhedron, 1984, 3, 1237. 22 A. Albert and R. J. Goldere, Nature (London), 1948, 161, 95. Received 13th August 1996; Paper 6/05679B

ISSN:1477-9226    

DOI:10.1039/a605679b

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 469–478 469 Chelate-ring-opened adducts of [Pt(en)(Me-Mal-O,O9)] (en = ethane-1,2-diamine, Me-Mal = 2-methylmalonate) with methionine derivatives: relevance to the biological activity of platinum anticancer agents ‡ Zijian Guo,a Trevor W. Hambley,a Piedad del Socorro Murdoch,a Peter J. Sadler *,†,a and Urban Frey b a Department of Chemistry, Birkbeck College, University of London, Gordon House and Christopher Ingold Laboratories, 29 Gordon Square, London WC1H 0PP, UK b Institute de Chimie Minérale et Analytique, University of Lausanne, BCH, CH-1015, Lausanne, Switzerland The anticancer drug carboplatin [Pt(cbdca-O,O9)(NH3)2] which contains the chelated dicarboxylate ligand cbdca, cyclobutane-1,1-dicarboxylate, may be activated in vivo by reaction with sulfur ligands.The reactions between the analogue [Pt(en)(Me-Mal-O,O9)] 1 (en = ethane-1,2-diamine, Me-Mal = 2-methylmalonate) and the methionine derivatives N-acetyl-L-methionine (Ac-Met), glycyl-L-methionine (Gly-Met) and L-methionylglycine (Met-Gly) have been studied at pH 7 and 4, 310 K, using 1H and two-dimensional [1H, 15N] heteronuclear single quantum coherence NMR spectroscopy and HPLC.The ring-opened species [Pt(en)(Me-Mal-O)(L-S)] (L = Ac-Met, Gly-Met or Met-Gly) containing monodentate malonate and S-bound monodentate methionine ligands were predominant in solution after 2 h. The second-order rate constant for the ring-opening reaction of 1 with Ac-Met at pH 6.56 was determined to be (1.48 ± 0.03) × 1021 s21 M21, and was similar for reactions with Gly-Met.Methylmalonate a-CH deuteriation rates were determined to be free Me-Met > ring-opened complex @ 1. Molecular-mechanics modelling suggested that hydrogen bonding between the free carboxylate group of monodentate Me-Mal and the co-ordinated amine groups, and between the two ring-opened ligands may contribute to the stability of the mixed-ligand adducts.However, in the case of Met-Gly, the ring-opening rate [(5.26 ± 0.10) × 1022 s21 M21] was nearly three times slower than that for the reaction of 1 with Ac-Met. In contrast, the ring-closure rate of [Pt(en)(Me-Mal-O)(Met-Gly-S)] [k1 = (1.37 ± 0.03) × 1024 s21] to give the S,N-chelated adduct was faster than that of [Pt(en)(Me-Mal-O)(Ac-Met-S)]2 2 [(2.27 ± 0.04) × 1025 s21]. The S,N-chelated adducts [Pt(en)(Ac-MetH21-S,N)] 3, [Pt(en)(Gly-MetH21-S,N)]+ and [Pt(en)(Met-GlyH21-S,N)]+ became the predominant products of the reactions after about 24 h.Ring-opened adducts of chelated dicarboxylate platinum anticancer complexes with methionine derivatives could play a significant role in their mechanism of action. Carboplatin [Pt(NH3)2(cbdca-O,O9)], where cbdca is cyclobutane- 1,1-dicarboxylate, is a widely used second generation anticancer drug.1,2 It is less toxic than cisplatin, and lacks significant neurotoxicity and nephrotoxicity. The activation mechanism of this drug is still under investigation.3–5 Some studies have concluded that the reaction of carboplatin with chloride ions is too slow to account for the reported half-life of the drug in blood plasma, and so it cannot be simply a pro-drug of cisplatin.3–5 Recent results obtained in our laboratory suggested that reactions of carboplatin with 59-GMP (guanosine 59-monophosphate) can occur by direct attack.5 In recent years, there has been an increasing interest in the interactions between the platinum drugs and sulfur-containing molecules.6,7 Although these interactions are generally considered to have negative (deactivation) effects on the drugs, some experiments have shown that S-bound thioethers can be substituted by guanine bases, the main DNA target for platinum, and potentially this provides a new route for DNA platination.8,9 The thioether-containing amino acid methionine plays an important role in the metabolism of platinum anticancer drugs.The complex [Pt(Met-S,N)2] has been isolated from the urine of patients treated with cisplatin,10 and its two geometrical isomers have been separated and characterised.11 † Present address: The Department of Chemistry, University of Edinburgh, King9s Buildings, West Mains Road, Edinburgh EH9 3JJ, UK. ‡ Non-SI unit employed: M = mol dm23. A remarkably stable ring-opened complex [Pt(cbdca-O)- (NH3)2(L-HMet-S)] has been detected during the reaction of carboplatin and L-HMet, and moreover, a similar species was found in the urine of animals treated with carboplatin.12 A recent in vivo study has shown that a mixture of cisplatin and methionine in a molar ratio of ca. 1:5 incubated over 24 h at 310 K is significantly cytotoxic, but lacks cisplatin-associated renal toxicity.13 Under the reported incubation conditions, the predominant platinum(II) species present are likely to be the bis- S,N-chelated adducts, [Pt(Met-S,N)2]. These data suggest that methionine adducts are not inert species devoid of cytotoxic activity.Our recent experiments have shown that under mildly acidic conditions S,N-chelated N-acetyl-L-methionine PtII complexes can be reactive towards the mononucleotide 59- GMP and the dinucleotide GpG [guanylyl(39-59)guanosine] to form mixed-ligand complexes [Pt(en)(Ac-Met-S)(GpG-N7)] (en = ethane-1,2-diamine),14 and it is of interest to investigate further interactions between methionine-containing ligands and platinum drugs.We report here reactions between methionine derivatives and the carboplatin analogue, [Pt(en)(Me-Mal-O,O9)] 1. Chelated en is less readily displaced from PtII than monodentate ammine ligands. Ammonia release induced by the high trans influence of S can severely complicate the interpretation of reactions of cisplatin and carboplatin.15 Our use of 2-methylmalonate (Me-Mal) in the place of cyclobutanedicarboxylate (cbdca) allows convenient monitoring of470 J.Chem. Soc., Dalton Trans., 1997, Pages 469–478 the biscarboxylate group via methyl peaks by 1H NMR and the Me-Mal complex is markedly more soluble than [Pt(en)- (cbdca)]. Malonate complexes of Pt–am(m)ine have been reported to exhibit substantial antitumour activity without the nephrotoxic effects of cisplatin.16 The L-methionine derivatives investigated were N-acetyl-L-methionine (Ac-Met), and the dipeptides glycyl-L-methionine (Gly-Met) and L-methionylglycine (Met-Gly).We show that stable ring-opened species are readily detectable by both 1H and two-dimensional [1H, 15N] HSQC† NMR spectroscopy.17,18 The ring-opening mechanism and the release of the dicarboxylate ligand are also discussed. Experimental Materials and methods The salts K2[PtCl4] and AgNO3 were purchased from Johnson Matthey Ltd, 2-methylmalonic acid (Me-H2Mal), N-acetyl-Lmethionine (Ac-Met), glycyl-L-methionine (Gly-Met) and Lmethionylglycine (Met-Gly) from Sigma, ethane-1,2-diamine, LiOH?H2O and other chemicals from Aldrich, and used as supplied.The complexes [Pt(en)Cl2] and [Pt([15N]en)Cl2] were prepared according to the reported method.19,20 Complex 1 [Pt(en)(Me-Mal-O,O9)] was prepared according to the literature method21 (Found: C, 19.55; H, 3.4; N, 7.5. Calc. for C6H12N2O4Pt: C, 19.4; H, 3.25; N, 7.55%). 13C NMR (pH 6.60): d 48.66 (CH2 of en), 181.11 (CO of Me-Mal), 51.53 (a-CH), 14.38 (CH3). The 1H NMR shifts of 1 are listed in Table 1.A 10 mM solution of [Pt([15N]en)(Me-Mal-O,O9)] 1n was prepared as follows. A stock solution of [Pt([15N]en)(H2O)2]2+ (10 mM, 1 cm3) in 90% water–10% D2O, prepared as reported,19 was incubated with one mol equivalent of Me-H2Mal (1.2 mg, 10 mmol) and 2 mol equivalents of LiOH?H2O (0.8 mg, 20 mmol) for 24 h in the dark at pH ca. 6.8. The two-dimensional [1H, 15N] HSQC NMR spectrum of the final solution contained a major cross-peak at d 5.38/243.24 which can be assigned to 1n and accounted for > 85% of the total Pt.A minor crosspeak at d 5.13/245.03 (NH2 trans to O) was also observed in the spectrum. The species giving rise to this peak was stable for hours in the presence of S-ligand (see below) and was therefore assigned to the hydroxy-bridged complex [{Pt- ([15N]en)}2(µ-OH)2]2+, which is significantly less reactive towards nucleophiles.22,23 NMR Spectroscopy The NMR spectra were recorded at 310 K, unless otherwise stated, on the following instruments: JEOL GSX270 (1H 270 MHz, 13C 67.5 MHz), JEOL GSX 500 (1H 500 MHz), Varian Unity 500 and 600 (1H 500 and 600 MHz; 15N 50.7 and 60.8 MHz) using 5 mm NMR tubes.The chemical shift references were as follows (all internal except 15N): 1H, dioxane (d 3.744); 13C, dioxane (d 67.3); 15N (external, 1 M 15NH4Cl in 1.5 M HCl). For 1H NMR, typical acquisition conditions for onedimensional spectra were as follows: 45–608 pulses, 16–32 K data points, 2–3 s relaxation delay, collection of 32–128 transi- O O C C O O Pt N H 2 N Ha CH3 H2 1 † HSQC: heteronuclear single quantum coherence; this involves inverse (1H detection) of 15N resonances and offers a sensitivity enhancement for 15N by a factor of up to 305.The pulse sequence is described in ref. 17, and some applications to platinum am(m)ines are reviewed in ref. 18. ents, final digital resolution of 0.2–1 Hz per point. When necessary, water suppression was achieved by presaturation. Spectra were processed using Varian VNMR software.24 The 13C-{1H} NMR spectra were typically the result of 12 h acquisitions using 32 K data points, 508 pulses, and relaxation delays of 3 s.Two dimensional, [1H, 15N] HSQC spectra were recorded as previously described 19,25 using standard sequences, optimised for 1J(NH) = 72 Hz, with 15N decoupling via the GARP procedure. Water suppression was achieved by pulsed-field gradients. HPLC The following equipment was used: Gilson 305 pumps, Gilson 806 manometric module, LKB 2141 variable wavelength monitor, and Rheodyne sample injector.Analytical separations were carried out on a PLRP-S column (250 × 4.6 mm, 100 Å, 5 mm, Polymer Labs) by injecting aliquots of the mixture at various time intervals with detection at 210 nm, using H2O as the eluent. The data were analysed using Dynamax Method Manager Software. pH Measurements Adjustments of pH were made using NaOD or DNO3. The measurements were carried out directly in NMR tubes, before recording spectra, using a Corning 240 pH meter equipped with an Aldrich micro combination electrode, calibrated with Aldrich buffer solutions at pH 4, 7 and 10. For D2O solutions, the value was read directly from the pH meter without correction for deuterium isotope effects and is designated as pH*.The reported pH values are those measured at the beginning of the reactions. No buffers were used in this study in order to avoid buffer co-ordination to platinum, e.g.of phosphate.5,26 S CH3 CH2 CH CO Ac-Met NH Met-Gly CH2 S CO NH CH3 CH2 CH2 CH COO– CH3 CH2 CH2 S CH COO– Gly-Met CH3 CH2 CH2 CO NH +NH3 COO– +NH3J. Chem. Soc., Dalton Trans., 1997, Pages 469–478 471 Table 1 Proton NMR chemical shifts for Me-Mal and its PtII complexes in D2O Me-Mal* Compound pH* SCH3 COCH3 (CH2) en CH CH3 Me-Mal 1 [Pt(en)(Me-Mal-O,O9)] 2 [Pt(en)(Me-Mal-O)(Ac-Met-S)]2 5 [Pt(en)(Me-Mal-O)(Gly-Met-S)] 9 [Pt(en)(Me-Mal-O)(Met-Gly-S)] 3.43 6.10 3.16 6.50 3.16 6.56 3.78 6.66 4.48 2.340 2.335 2.343 2.343 2.395 2.048 2.037 2.560 2.562 2.706 2.673 2.697 2.679 2.697 2.677 2.700 2.679 2.694 3.408 (7.3) 2.181 (7.5) 4.103 (7.3) 4.103 (7.0) 3.454 (7.3) 3.259 (7.2) 3.272 (6.5) 3.254 (6.5) 3.293 (6.9) 1.357 (7.1) 1.250 (7.4) 1.372 (7.2) 1.373 (7.2) 1.288 (7.1) 1.221 (7.2) 1.232 (7.0) 1.228 (7.0) 1.227 (7.3) * 3J(CH]CH3) coupling constants (Hz) in parentheses.Kinetics The kinetic data were obtained from 1H NMR spectra recorded at 310 K.The samples were also maintained at the same temperature whilst not in the probe. The relative concentrations were determined from peak integrals and the analysis of the data was performed using the program KALEIDAGRAPH.27 The rate constants, where applicable, were determined by a nonlinear optimisation procedure, using the appropriate equations and integrated numerically. Molecular-mechanics modelling Models of a number of conformers of [Pt(en)(Me-Mal-O)- (Ac-Met-S)]2 2 were generated using the HYPERCHEM program. 28 The energies of these structures were then minimised using MOMEC29 and a force field based on others described previously,30–32 extended using parameters from the AMBER force field 33 to enable the modelling of the N-acetylmethionine and methylmalonate ligands. Sample preparation The following reactions were investigated in NMR tubes; 1 (5 mM) + Ac-Met (5 mM) at pH* 6.56, 1 (5 mM) + Ac-Met (5 mM) at pH* 3.16, 1 (5 mM) + Gly-Met (5 mM) at pH* 6.66, 1 (5 mM) + Gly-Met (5 mM) at pH* 3.78, 1 (5 mM) + Met-Gly (5 mM) at pH* 4.48.Samples for the above reactions were prepared as follows. Complex 1 and Ac-Met, Gly-Met or Met-Gly were weighed and dissolved separately in 0.35 cm3 D2O. The pH* values of the solutions were adjusted to the desired region before mixing them in the NMR tube. The final pH* of the mixture was measured in the NMR tube after mixing. Samples for the reactions of 1n with Ac-Met, Gly-Met or Met-Gly were in 0.6 cm3 of 90% water–10% D2O (5 mM) and prepared by mixing aliquots of the stock solution of 1n (10 mM) with one mol equivalent of the methionine derivative as stated above.Results Deuterium exchange on methylmalonate The CH3 signal of Me-Mal appeared as a doublet due to coupling with the a-H, but with time this doublet decreased in intensity and became a singlet, overlapped with the low-field peak of the doublet, due to exchange of a-H with deuterium from D2O.By measuring the variation of peak integrals with time, firstorder rate constants for a-H–D exchange of Me-Mal were determined at pH 3.15 and 310 K to be (2.4 ± 0.4) × 1026 s21 (t2� 1 , 81 h) for complex 1, (2.03 ± 0.06) × 1025 s21 (t2� 1 , 9.5 h) for the ring-opened complex 2 (see below) and (6.11 ± 0.01) × 1025 s21 (t2� 1 , 3.2 h) for free malonate. Reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Ac-Met (1:1, pH* 6.56) On reaction of complex 1 with Ac-Met at 310 K for 20 min, the CH3 doublet for 1 (d 1.373) decreased in intensity, and a new doublet appeared at d 1.221.At the same time the SCH3 signal of free Ac-Met (d 2.110) decreased in intensity and a new peak at d 2.335 appeared and increased in intensity. After about 2 h, two new peaks at d 1.221 (CH3) and d 2.335 (SCH3) reached a maximum intensity (75% of the total integral of CH3 peaks for different Me-Mal species), followed by a slow decrease in intensity, as shown in Fig. 1. The latter two peaks varied in intensity in the same way during the reaction course, therefore they can be assigned to the same complex.The reaction was repeated with 1n and studied by two-dimensional [1H, 15N] HSQC spectroscopy. The cross-peak at d 5.38/243.24 for 1n decreased in intensity, and new cross-peaks appeared Fig. 1 The 500 MHz 1H NMR spectra of [Pt(en)(Me-Mal-O,O9)] 1 with Ac-Met (5 mM, 1 : 1 molar ratio) after reaction for various times at 310 K, pH* 6.56. Peak assignments: a CH3 and b CH2 (en) for 1; c SCH3 and d acetyl CH3 of free Ac-Met; e CH3, f acetyl CH3 and g SCH3 of [Pt(en)(Me-Mal-O)(Ac-Met-S]2 2; h CH3 for free Me-Mal; i SCH3 and j acetyl CH3 of [Pt(en)(Ac-Met-S,O)]+ 4; k, l, m, n SCH3 and acetyl CH3 of [Pt(en)(Ac-MetH21-S,N)] 3472 J.Chem. Soc., Dalton Trans., 1997, Pages 469–478 at d 5.54/239.94 and 5.46/210.96 and increased in intensity with time. The former can be assigned to the NH2 group trans to oxygen and the latter to NH2 trans to sulfur.Therefore, the data suggest the formation of the ring-opened species [Pt([15N]en)(Me-Mal-O)(Ac-Met-S)]2 2. These new two-dimensional peaks also reached a maximum intensity after 2 h incubation of the reaction mixture, so they can be correlated with the peaks at d 1.221 and 2.335 in the 1H NMR spectrum. A two-dimensional [1H, 15N] HSQC spectrum of the solution that was recorded after 2 h of reaction is shown in Fig. 2. The cross-peaks at d 5.54/239.94 and 5.46/210.96 assignable to complex 2 are the major peaks, together with peaks for unreacted 1.The two peaks for 2 are very broad in the 1H dimension. In addition to the cross-peaks for complexes 1 and 2, a series of cross-peaks is present in the region from d 5 to 5.5/225 toNH2 trans to N) and 28 to 211 (NH2 trans to S). These peaks appeared at the same time and had comparable intensities, suggesting assignment to [Pt(en)(Ac-MetH21-S,N)] 3. The complexity of the spectrum can be attributed to deprotonation of the amide nitrogen giving rise to cis and trans isomers, in addition to slow S inversion.15,34 Inversion at sulfur can lead to changes in conformation of the six-membered chelate ring.11,35,36 Correspondingly, in the 1H spectrum, new peaks at d 2.422, 2.401, 2.350 and 2.325 appeared and increased in intensity at a comparable rate to the two-dimensional crosspeaks.Hence these are also assigned to 3. The chemical shifts of all peaks are listed in Tables 1 and 2.After 24 h, all the Ac-Met had reacted since no peaks for free Ac-Met were observable in the 1H NMR spectrum. As shown in Fig. 2 A two-dimensional [1H, 15N] HSQC NMR spectrum of [Pt([15N]en)(Me-Mal-O,O9)] with Ac-Met (5 mM, pH* 6.56, 1 : 1 molar ratio) recorded at 310 K after 2 h incubation. Peaks assignments: A, NH2 (trans to O) and A9, NH2 (trans to S) of [Pt(en)(Me-Mal-O)(Ac- Met-S)]2 2; B, NH2 (trans to O) of [Pt([15N]en)(Me-Mal-O,O9)] 1; C, NH2 (trans to N) and C9, NH2 (trans to S) of [Pt(en)(Ac-MetH21-S,N)] 3.Peaks D and E for impurities {hydroxyl bridged [Pt(en)]2+ complexes and [Pt([15N]en)Cl2)]} contained in the stock solution of complex 1 Fig. 1, the peaks at d 1.221 and 2.335 assigned to complex 2 had nearly disappeared and peaks for complex 3 became dominant. Free Me-Mal accounted for 90% of the total Me-Mal species observed. The CH3 signal for free Me-Mal became a singlet due to deuterium exchange of the a-H signal with D2O.At this time, peaks at d 2.494, 2.486 and 1.960 were also observed in the spectrum. Consequently, in the two-dimensional [1H, 15N] HSQC spectrum recorded after a similar reaction time, crosspeaks at d 5.95, 5.81, 5.70, 5.60/243.0 (NH2 trans to O) and d 5.88, 5.42/26.2 (NH2 trans to S) had comparable intensity. These data are consistent with the formation of [Pt(en)(Ac-Met- S,O)]+ 4.14 The peaks assigned to complexes 3 and 4 accounted for 90% of the total Pt species.In the two-dimensional [1H, 15N] HSQC NMR spectrum, a minor cross-peak at d 6.01/25.39 (NH2 trans to S) was also present and can be assigned to the bis- (Ac-Met) complex [Pt(en)(Ac-Met-S)2] 5.14 Kinetic fits to the reaction profile in Scheme 1 are shown in Fig. 3, and the rate constants for each step are listed in Table 3. Reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Ac-Met (1:1, pH* 3.16) The reaction of 1 with Ac-Met at the lower pH* value of 3.16 was also followed by 1H NMR spectroscopy.After 20 min, the Table 2 Proton and 15N NMR Pt]NH2 chemical shifts for [Pt([15N]en)]2+ complexes Compound pH d(1H) d(15N) (trans to) 1 [Pt(en)(Me-Mal-O,O9)] 2 [Pt(en)(Me-Mal-O)- (Ac-Met-S)]2 3 [Pt(en)(Ac-Met- H21-N,S)] 4 [Pt(en)(Ac-Met-O,S)]+ 5 [Pt(en)(Ac-Met-S)2] 6 [Pt(en)(Me-Mal-O)- (Gly-Met-S)] 8 [Pt(en)(Gly- MetH21-N,S)]+* 7 [Pt(en)(Gly-Met-S)2]2+ 10 [Pt(en)(Met- GlyH21-N,S)]+ 6.60 6.56 6.56 6.56 6.56 6.66 6.66 7.40 4.48 5.38 5.54 5.46 5.47, 5.17 5.13 5.01, 4.93 5.33, 5.14, 5.05, 4.96 5.23, 4.86 5.01, 4.94 5.95, 5.81, 5.70, 5.60 5.88, 5.42 6.01 5.54 5.45 5.44, 5.29 5.34, 5.19 5.43, 5.07 5.25, 5.19 5.17, 4.94 5.12, 5.06, 5.02 6.04 5.51, 5.46 5.50, 5.47 5.56, 5.39 243.24 (O) 239.94 (O) 210.96 (S) 28.08 (S) 210.55 (S) 211.00 (S) 227.25 (N) 226.32 (N) 225.85 (N) 243 (O) 26.20 (S) 25.39 (S) 239.93 (O) 210.84 (S) 28.16 (S) 27.83 (S) 225.79 (N) 225.63 (N) 227.54 (N) 228.09 (N) 25.50 (S) 27.77 (S) 225.75 (N) 225.94 (N) * Tentative assignments.J. Chem.Soc., Dalton Trans., 1997, Pages 469–478 473 methyl doublet of 1 at d 1.372 (CH3) and the SCH3 signal for free Ac-Met at d 2.110 had decreased in intensity, whilst peaks at d 1.288 (doublet) and 2.340 appeared and increased in intensity. The latter peaks can again be assigned to the ringopened adduct [Pt(en)(Me-Mal-O)(Ac-Met-S)]2 2 (the charge on the Ac-Met carboxylate group is still assumed to be 21 although the pKa was not determined). In parallel with the reaction at pH 6.56, complex 2 became the dominant species after about 2 h (60% of the total Me-Mal).Then, the monodentate Me-Mal ligand was gradually displaced to give S,N or S,O chelation of Ac-Met with formation of complexes 3 and 4. After 22 h these became the dominant products, together with the formation of complex 5 as a minor product. The time-course of Scheme 1 Fig. 3 Kinetic fits for the reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Ac-Met (5 mM, 1: 1 molar ratio) at 310 K and pH 6.56.The curves correspond to the rate constants listed in Table 3 the ring-opening reaction at this pH (data not shown) is quite similar to that observed at pH 6.56. However, the ring-opened adduct 2 was observed for a significantly longer time in solution at pH 3.16. Reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Gly-Met (1:1, pH* 6.66) In order to study the influence of methionine substituents on ring opening, the reaction of 1 with the dipeptide Gly-Met was followed by 1H and two-dimensional [1H, 15N] HSQC spectroscopy. When 1 was incubated with Gly-Met for about 30 min, the Me-Mal CH3 peak of 1 at d 1.372 and the SCH3 peak of free Gly-Met (d 2.103) decreased in intensity.New peaks at d 1.228 (doublet) and 2.343 appeared and increased in intensity with time (Fig. 4). These peaks attained maximum intensities after about 2 h (63% of the total integral of the CH3 signals for Me-Mal species), remained at the same intensity for another few hours and then began to decrease in intensity.At the corresponding times in the reaction of 1n with Gly-Met, the two-dimensional [1H, 15N] HSQC spectrum showed major cross-peaks at d 5.54/239.93 (NH2 trans to O) and 5.45/210.84 Fig. 4 The 500 MHz 1H NMR spectra of [Pt(en)(Me-Mal-O,O9)] 1 with Gly-Met (5 mM, 1: 1 molar ratio) at 310 K and pH 6.66. Peak assignments: a CH3 and b CH2 (en) for 1; c SCH3 of free Gly-Met; d CH3, e SCH3 and f CH2 (en) of [Pt(en)(Me-Mal-O)(Gly-Met-S)] 6; g CH3 of free Me-Mal; h SCH3 of [Pt(en)(Gly-Met-S)2]2+ 7 Table 3 Observed rate constants for the reactions of [Pt(en)(Me-Mal- O,O9)] 1 (5 mM) with Ac-Met (pH 6.56) and Met-Gly (pH 4.48) at 310 K.The rate constants of the reactions of carboplatin with L-HMet, 59- GMP and chloride are listed for comparison Nucleophile Ring-opening reaction (k/M21 s21) Displacement of Me-Mal or cbdca (k/s21) Reactions for 1 Ac-Met Met-Gly (1.48 ± 0.03) × 1021 (5.26 ± 0.10) × 1022 (2.27 ± 0.04) × 1025a (1.37 ±0.03) × 1024 Reactions for carboplatin L-HMet 59-GMP Chloride 27 × 1023 1.0 × 1024c 6.9 × 1026b (3.2 ± 0.5) × 1025d 7.7 × 1027d, 2.1 × 1027 e a The ring-opened adduct 2 (see Scheme 1) reacted with 2 mol equivalents of AC-Met to give [Pt(en)(Ac-Met-S)2] as product; the rate was (2.05 ± 0.35) × 1023 M21 s21.b Ref. 15. c Recalculated from the data of ref. 15. d Ref. 5. e Extrapolated to 310 K from values of ref. 4 at 298 K.474 J. Chem. Soc., Dalton Trans., 1997, Pages 469–478 (NH2 trans to S).Therefore, these data suggest the formation of the ring-opened adduct [Pt([15N]en)(Me-Mal-O)(Gly-Met-S)] 6. A two-dimensional [1H, 15N] HSQC spectrum recorded after 2.5 h of reaction at 310 K is shown in Fig. 5, and the ringopened species 6 can be seen to be the major product. After 17 h of reaction, complex 6 still accounted for about 40% of the total Me-Mal species present in solution, indicative of the high stability of this complex.A two-dimensional [1H, 15N] HSQC spectrum recorded after 17 h was rather complicated. In addition to cross-peaks assignable to 1 and 6, two series of cross-peaks distributed in the regions for NH2 trans to S and N were observed. A single cross-peak at d 6.04/25.50 (NH2 trans to S) was assignable to [Pt([15N]en)(Gly-Met-S)2]2+ 7 since it had very similar chemical shifts to those of [Pt([15N]en)(Ac-Met-S)2] 5, whereas, on the basis of their intensities and shifts, the four cross-peaks at d 5.44, 5.29, 5.34, 5.19/ 27.8 to 28.2 (NH2 trans to S) and nine cross-peaks at d 5.43, 5.07, 5.25, 5.19, 5.17, 4.94, 5.12, 5.06, 5.02/225.6 to 228.1 (NH2 trans to N) can be tentatively assigned to the S,N-chelated Gly-Met complex [Pt([15N]en)(Gly-MetH21-N,S)]+ 8, an analogue of 3.The complexity of the spectrum of 8 may be due to the presence of diastereoisomers arising from the presence of Fig. 5 A two-dimensional [1H, 15N] HSQC NMR spectrum of [Pt([15N]en)(Me-Mal-O,O9)] with Gly-Met (5 mM, pH 6.66, 1 : 1 molar ratio) recorded at 310 K after 2 h incubation.Peak assignments: A, NH2 (trans to O) and A9, NH2 (trans to S) of [Pt(en)(Me-Mal-O)(Gly- Met-S)] 6; B, NH2 (trans to O) of [Pt([15N]en)(Me-Mal-O,O9)] 1; peaks C and D are due to impurities {hydroxo bridged [Pt(en)]2+ complexes and [Pt([15N]en)Cl2)]} contained in the stock solution of complex 1 chiral co-ordinated S, as well as the cis- and trans-isomers arising from the peptide bond.14,34 There were still five cross-peaks remaining to be assigned at d 5.03, 4.97, 4.92/230.45 (NH2 trans to N) and 5.05, 4.93/ 245.29 (NH2 trans to O) (see Discussion).The time-course of the reaction is shown in Fig. 6, obtained by plotting the variation in intensity of the resonances for the different Me-Mal species. The reaction between [Pt(en)(Me-Mal-O,O9)] 1 and Gly-Met (1:1, 5 mM, pH 6.61, 303 K) was followed also by HPLC (Fig. 7). The dipeptide Gly-Met and 1 have retention times of 2.10 and 2.45 min, respectively.After 30 min of reaction, a new peak with a retention time of 1.65 min appeared in the chromatogram along with peaks for 1 and Gly-Met. Over the next few hours the new peak gradually increased in intensity while the peaks due to 1 and Gly-Met decreased in intensity. By comparing HPLC and NMR peak intensities with time, it is evident that the new HPLC peak can be assigned to the ring-opened complex [Pt(en)(Me-Mal-O)(Gly-Met-S)] 6.A very broad peak with retention time of 2.80 min also appeared in the chromatogram after about 4 h incubation. The time of appearance corresponded to the formation of [Pt(en)(Gly-MetH21-N,S)]+ 8 and [Pt([15N]en)(Gly-Met-S)2] 7. After 24 h of reaction, the mixture gave a chromatogram in which peaks for 1 and Gly-Met had nearly disappeared, and the broad peak due to 7 and 8 was dominant. However, the ring-opened species was still present. At the same time, another broad peak appeared with a retention time of 4.4 min.This peak may correspond to the unassigned cross-peaks in the two-dimensional NMR spectrum. Reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Gly-Met (1:1, pH* 3.78) This reaction was followed by 1H NMR spectroscopy. At this pH*, the Me-Mal CH3 and the Gly-Met SCH3 signals of the Fig. 6 Plot of relative percentages of Me-Mal species (based on the CH3 peak integrals) for the reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Gly-Met (5 mM, 1: 1 molar ratio) at 310 K and pH 6.66.The mixed ligand adduct [Pt(en)(Me-Mal-O)(Gly-Met-S)] 6 accounted for 40% of the Me-Mal adducts after 17 h. A kinetic fit to the data was not possible (see text)J. Chem. Soc., Dalton Trans., 1997, Pages 469–478 475 ring-opened complex 6 were observed at d 1.232 and 2.343, respectively. These peaks rose to maximum intensity (62% of the total integral of CH3 signals for Me-Mal species) after 2 h of reaction, followed by a gradual decrease in intensity.Peaks for free Me-Mal were observed after 40 min. After 20 h, complex 6 still accounted for over 20% of the total Me-Mal. The time-course of the reaction was similar to that at pH 6.66. Reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Met-Gly (1:1, pH* 4.48) This reaction was studied by 1H and two-dimensional [1H, 15N] HSQC NMR spectroscopy. The SCH3 signal of free Met-Gly was observed at d 2.120. After 30 min reaction of 1 with Met- Gly, new peaks appeared at d 1.227 (CH3) and 2.395 (SCH3).Since these peaks have very similar shifts to those previously assigned to ring-opened complex as 2 and 6, they can be assigned to the complex [Pt(en)(Me-Mal-O)(Met-Gly-S)] 9. In contrast to the reactions of 1 with Ac-Met and Gly-Met, the signal for free Me-Mal appeared concomitantly with that for the ring-opened species. After 1 h, peaks for complex 9 reached a maximum intensity (36% of the total integral of Me-Mal CH3 signals for different species); however, 20% of the total Me-Mal was present as free Me-Mal.After 12 h incubation, complex 9 had nearly disappeared, which suggested facile S,N-chelation of Met-Gly. A two-dimensional [1H, 15N] HSQC NMR spectrum was Fig. 7 The HPLC chromatograms of the reaction of [Pt(en)(Me-Mal- O,O9)] 1 with Gly-Met (5 mM, 1 : 1 molar ratio) at 303 K and pH 6.61. Peak assignments: a Gly-Met; b [Pt(en)(Me-Mal-O,O9)] 1; c [Pt(en)(Me-Mal-O)(Gly-Met-S)] 6; d free Me-Mal; e tentatively assigned to [Pt(en)(Gly-MetH21-N,S)]+ 8 and [Pt(en)(Gly-Met-S)2]2+ 7 (by comparison with the peaks in the two-dimensional [1H, 15N] HSQC NMR spectra at similar incubation time); f unassigned species recorded at 310 K after 24 h reaction and is shown in Fig. 8. A total of six cross-peaks are observed, among them four peaks at d 5.50, 5.47/225.75 and 5.56, 5.39/225.94 are assignable to the NH2 trans to nitrogen, and two peaks at d 5.51, 5.46/27.77 are assignable to the NH2 trans to sulfur. Therefore, the data suggest the formation of [Pt([15N]en)(Met-GlyH21-N,S)]+ 10.No other peaks were observed in the spectrum. The kinetic fits to the reaction course in Scheme 2 are shown in Fig. 9, and the rate constants for each step are shown in Table 3. Molecular modelling of [Pt(en)(Me-Mal-O)(Ac-Met-S)]2 2 Since the ring-opened mixed-ligand complexes were long-lived, e.g. the complex [Pt(en)(Me-Mal-O)(Ac-Met-S)]2 2 had a half life of 8.5 h at 310 K, we investigated the potential for hydrogen- bonding networks to contribute towards their stabilities in models of such intermediates.Monodentate co-ordination of both the N-acetyl-L-methionine and 2-methylmalonate ligands results in a complex with many degrees of conformational freedom, and very many sensible geometries can be envisaged. Therefore we chose to restrict our attention to those conformations that maximised the possibilities for intracomplex hydrogen- bond formation. Four of these were considered in detail, the two shown in Fig. 10, a third similar to that in Fig. 10(a) in which the hydrogen bond between the co-ordinated carboxylate group of the methylmalonate ligand and the ethane-1,2- diamine is missing, and a fourth in which there was a potential hydrogen bond between the free carboxylate groups of the two ligands. This latter model required protonation of the carboxylate groups but was found to result in severe distortion of the ligands and of the co-ordination geometry about the Pt. The other three models all had similar minimised strain energies, as might be expected given the flexibility of the ligands.The structure shown in Fig. 10(a) has hydrogen bonds between each of the free carboxylate groups, one from each ligand, and Fig. 8 A two-dimensional [1H, 15N] HSQC NMR spectrum of [Pt([15N]en)(Me-Mal-O,O9)] 1n with Gly-Met (5 mM, pH 4.48, 1: 1 molar ratio) recorded at 310 K after 24 h incubation. Peak assignments: A, NH2 (trans to N) and A9, NH2 (trans to S) of [Pt(en)(Met-GlyH21- N,S)]+ 10476 J.Chem. Soc., Dalton Trans., 1997, Pages 469–478 the two co-ordinated amine groups. That shown in Fig. 10(b) has a hydrogen bond between the free carboxylate group of the methylmalonate ligand and the peptide hydrogen atom. There are also close contacts between the co-ordinated carboxylate group and the two hydrogen atoms on the adjacent amine. Discussion The stable ring-opened complex [Pt(NH3)2(cbdca-O)(L-HMet- S)] has been detected during reactions of carboplatin with LHMet, and a similar species appears to be present as metabolite in the urine of animals treated with carboplatin.12 Therefore investigations of reactions between dicarboxylate PtII complexes and methionine derivatives may lead to a better understanding of activation mechanisms for this class of drug.However, reactions of complexes containing ammine ligands are complicated by the strong trans effect of sulfur which promotes the labilisation of the ammine ligands.15 Therefore the chelating ethane-1,2-diamine ligand was chosen in this work, and in addition the presence of the methyl group in the malonate ligand made it possible to follow the reactions easily by 1H NMR spectroscopy.Scheme 2 Fig. 9 Kinetic fits for reaction of [Pt(en)(Me-Mal-O,O9)] 1 with Met- Gly (5 mM, 1 : 1 molar ratio) at 310 K and pH 4.48. The curves correspond to the rate constants given in Table 3 Deuteriation of methylmalonate The exchange of the a-H of Me-Mal with deuterium has been reported to proceed via two steps with the enol form of the acid as an intermediate (Scheme 3).37,38 The enolisation rate constant has been previously determined by 1H NMR in 1 M D2SO4–D2O to be (5.7 ± 0.1) × 1025 s21 for Me-H2Mal itself at 298 K.37 This rate is accelerated by increasing the acidity of the medium.Considering the differences in the conditions (pH 3.15, 310 K), the rate constant determined in this work observed for Me-H2Mal [(6.11 ± 0.01) × 1025 s21] is remarkably similar to the reported value.The exchange rate for [Pt(en)- (Me-Mal-O)(Ac-Met-S)]2 2 is three times lower than for free Me-H2Mal, and for [Pt(en)(Me-Mal-O,O9)] 1 is ca. 25 times slower. Protonation of the carboxylate group would be expected to be less favourable for the platinated adducts compared to free Me-H2Mal and enol formation by the intermediate requires a change in the conformation of the six-membered chelate rings.Both of the factors may play a role in slowing down the rate. Chelate-ring opening Only a few kinetic data are available on ring-opening reactions of chelated dicarboxylate complexes: those obtained in the present work, and data for carboplatin.15 These are collected in Table 3. It can be seen that the rate of ring opening is dependent on the entering ligand suggesting differences in interactions within the expected five-co-ordinate intermediate. The second step, displacement of the dicarboxylate ligand is again faster for the Met-Gly adduct, [Pt(en)(Me-Mal-O)- (Met-Gly-S)] 9 than for that of Ac-Met.The dipeptide Met- Gly can more readily form a six-membered S,N-chelate than Ac-Met, although the two reactions were conducted at different pH values. The first step of the reaction of 1 with Gly-Met is similar to that with Ac-Met, i.e. the formation of the ring-opened species [Pt(en)(Me-Mal-O)(Gly-Met-S)] 6. However, the kinetic data (not shown) could not be fitted by the same reaction scheme (Scheme 1), presumably because of a back reaction involving re-closure of the dicarboxylate chelate ring.In the case of Gly- Met an S,N-ring cannot readily form unless the peptide NH is deprotonated. Indeed, the same situation was found for reactions of Ac-Met at pH 3.16, although the chelate of Ac-Met was favoured at high pH (6.56). Thus, it appears that the NH3 + group in Gly-Met hinders amide deprotonation and S,Nchelation.The ring-opened complex species [Pt(en)(Me-Mal- O)(Gly-Met-S)] 6 appeared to react further by several different pathways to give a mixture of products, perhaps involving polymeric species cross-linked via CO2 2 and/or NH2 groups of Gly-Met giving broad 1H NMR peaks (Fig. 4) and HPLC peaks (Fig. 7). Correspondingly, in the two-dimensional [1H, 15N] HSQC spectrum extra peaks that are assignable to a NH2 group trans to oxygen and trans to nitrogen were observed.No signals for free ethane-1,2-diamine were observed which rules out displacement of the diamine ligand. In general the number of resonances for the NH2 groups was consistent with rapid S inversion in ring-opened intermediates and slower inversion in S,N-chelates.14 The molecular-mechanics calculations show clearly that a number of intracomplex hydrogen bonds is feasible; these interactions would contribute to the stability of this ring- Scheme 3J. Chem. Soc., Dalton Trans., 1997, Pages 469–478 477 Fig. 10 Models showing the hydrogen bonding which may be involved in the stabilisation of the ring-opened complex [Pt(en)(Me-Mal-O)(Ac-Met- S)]2: C, cyan; H, white; N, blue; O, red; S, yellow; Pt, violet. Model (a) shows the hydrogen bonding between the two amine groups and the carboxylate group of Me-Mal, and model (b) shows the hydrogen bonding between the carboxylate group of Me-Mal and the amide group of Ac- Met opened complex. It is noteworthy in the context of the greater stability of the closely related complex [Pt(cbdca-O,O9)(HMet- S)(NH3)2] that similar hydrogen bonding arrangements are possible in the two complexes,15 but the relatively weak interligand hydrogen bond between the amide group and the free carboxylate as shown in Fig. 10(b) would be replaced by two stronger hydrogen bonds between a protonated NH3 + group and a free carboxylate group in the methionine complex. Conclusion The second generation drug carboplatin is relatively inert towards hydrolysis, and direct attack by DNA bases occurs only very slowly.5 Chelate-ring opening reactions provide a possible mechanism for in vivo activation of carboplatin, especially via reactions with methionine derivatives.We have studied chelatering- opening of the analogue [Pt(en)(Me-Mal-O,O9)] in the reactions with N-acetyl-L-methionine and dipeptides of Lmethionine. These serve as models of potential interactions of platinum drugs with proteins and the formation of DNA– protein cross-links.Platination of Me-Mal dramatically slowed down the rate of a-H exchange with deuterium. The ring-opened adducts were surprisingly stable and [Pt(en)(Me-Mal-O)(Ac-Met-S)]2 2, for example, had a half-life of 8.5 h at 310 K (body temperature). Intramolecular hydrogen bonding, as suggested by the molecular-mechanics modelling, may contribute to the stability of such ring-opened complexes. The least stable ring-opened intermediates contained poten-478 J.Chem. Soc., Dalton Trans., 1997, Pages 469–478 tially S,NH2-chelating ligands such as Met-Gly. Hence, methionine residues in the middle of peptide chains may give rise to relatively stable ring-opened adducts of bis(chelated) dicarboxylate PtII complexes, whereas reactions with N-terminal methionine residues may lead to stable S,N-chelated species. The latter species may undergo further activation or deactivation with amine release due to the high trans influence of sulfur.Acknowledgements We thank the Association for International Cancer Research, Biotechnology and Biological Sciences Research Council, and Engineering and Physical Sciences Research Council for their support for this work. We thank the Medical Research Council Biomedical NMR centre, Mill Hill and University of London Intercollegiate Research Service for the provision of NMR facilities and Dr. Kevin J. Barnham for discussion. 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Berners-Price, Inorg.Chem., 1993, 32, 2249. 12 K. J. Barnham, U. Frey, P. del. S. Murdoch, J. D. Ranford, P. J. Sadler and D. R. Newell, J. Am. Chem. Soc., 1994, 116, 11175. 13 P. M. Deegan, I. S. Pratt and M. P. Ryan, Toxicology, 1994, 89, 1. 14 K. J. Barnham, Z. Guo and P. J. Sadler, J. Chem. Soc., Dalton Trans., 1996, 2867. 15 K. J. Barnham, M. I. Djuran, P. del S. Murdoch, J. D. Ranford and P. J. Sadler, Inorg. Chem., 1996, 35, 1065. 16 M. J. Cleare, The Proceedings of the Third International Symposium on Platinum Coordination Complexes in Cancer Chemotherapy, Leland Fikes Foundation Press, Dallas, 1977, 1; J.M. Hill, E. Loeb, A. S. Pardue, A. Khan, N. O. Hill, J. J. King and R. W. Hill, The Proceedings of the Third International Symposium on Platinum Coordination Complexes in Cancer Chemotherapy, Leland Fikes Foundation Press, Dallas, 1977, 681. 17 J. Stonehouse, G. L. Shaw, J. Keeler and E. D. Laue, J. Magn. Reson., Ser. A, 1994, 107, 178. 18 S. J. Berners-Price and P. J. 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Hambley, Inorg. Chem., 1988, 30, 1073. 31 T. W. Hambley, Inorg. Chem., 1991, 30, 937. 32 E. C. L. Ling, G. W. Allen and T. W. Hambley, J. Chem. Soc., Dalton Trans., 1993, 3705. 33 S. J. Weiner, P. A. Kollman, D. A. Case, U. C. Singh, C. Ghio, G. Alagona, S. Profeta, jun. and P. Weiner, J. Am. Chem. Soc., 1984, 106, 765. 34 T. G. Appleton, P. D. Prenzler and R. A. Webb, 3th International Symposium on Applied Bioinorganic Chemistry, Fremantle, 1994, Abstract, p. A 11; 7th International Symposium on Platinum and other Metal Coordination Compounds in Cancer Chemotherapy, Amsterdam, 1995, Abstract, p. 105. 35 E. W. Abel, M. Booth and K. G. Orrell, J. Chem. Soc., Dalton Trans., 1980, 1582. 36 J. C. Barnes, G. Hunter and M. W. Lown, J. Chem. Soc., Dalton Trans., 1976, 1227. 37 E. W. Hansen and P. Ruoff, J. Phys. Chem., 1988, 92, 2641. 38 E. W. Hansen and P. Ruoff, J. Phys. Chem., 1989, 93, 2696. Received 17th June 1996; Paper 6/04210D

ISSN:1477-9226    

DOI:10.1039/a604210d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 479–483 479 Carbon-13 nuclear magnetic resonance of transition-metal carbonyl clusters through intermolecular cross-polarisation transfer in the solid state Taro Eguchi,*,a Rachel A. Harding,a,b Brian T. Heaton,*,b Giuliano Longoni,c Kei Miyagi,a Jens Nähring,b Nobuo Nakamura,a Hirokazu Nakayamaa and Anthony K. Smith b a Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560 Japan b Department of Chemistry, University of Liverpool, Liverpool L69 3BX, UK c Dipartimento di Chimica Fisica ed Inorganica, Viale del Risorgimento 4, 40136, Bologna, Italy The 13C cross polarisation magic angle spinning NMR spectra of [Ni6(CO)12]22 at natural 13C abundance have been recorded with four different cations, [NMe4]+, [NEt4]+, [AsPh4]+ and [N(PPh3)2]+ and the crystal structure of the previously unreported [AsPh4]+ salt of [Ni6(CO)12]22 has been determined. Carbonyl resonances of the anion at natural 13CO abundance with excellent signal-to-noise ratio (ca. 1 : 1 for a single scan) are only observed for [NMe4]2[Ni6(CO)12] and the possible reasons for this are discussed. In the course of our continuing work to understand the dynamic behaviour of transition-metal carbonyl clusters in the solid state,1–3 13CO resonances with good signal-to-noise ratio (ca. 0.14 : 1 for a single scan) have been observed for [NMe4]2- [Ni12(CO)21H2] at natural 13CO abundance.4 It is very surprising to observe 13CO signals for transition-metal carbonyl clusters with such good signal-to-noise ratio without 13CO enrichment.In order to investigate this further, 13C cross polarisation magic angle spinning (CP MAS) spectra of a series of [Ni6(CO)12]22 clusters have now been recorded for four different cations, [NMe4]+, [NEt4]+, [AsPh4]+ and [N(PPh3)2]+. The values of the proton relaxation times T1 and T1r have been measured to determine the origin of the cross polarisation and line broadening due to molecular motion.The crystal structures of the [NMe4]+ and [N(PPh3)2]+ salts have been reported previously 5,6 and, in order to compare interatomic H ? ? ? CO distances, we now report the structure of the [AsPh4]+ salt of [Ni6(CO)12]22. The structure of the anion in all these salts is similar and consists of a distorted Ni6 trigonal antiprism with one terminal CO on each Ni and each of the six triangular nickel edges is bridged by one CO. Crystallographic data for all of these salts are summarised in Table 1.Unfortunately, it was not possible to obtain X-ray-quality crystals of [NEt4]2[Ni6(CO)12]. Consistent with the solid-state structure, there are two equally intense 13CO NMR resonances in solution at d ca. 237 and 197 due to bridge and terminal CO, respectively.7 The crystallographic data show that the site symmetry of [Ni6(CO)12]22 is S6 for the [NMe4]+ salt and Ci for both the [AsPh4]+ and [N(PPh3)2]+ salts. Thus, for the [NMe4]+ salt there should be only one 13CO resonance in the solid state for each of the terminal and bridging CO whereas there could be up to three resonances for each of the terminal and bridging CO for the other two salts.Results and Discussion The 13CO CP MAS NMR spectra of [Ni6(CO)12]22 at the natural 13C abundance level are shown in Figs. 1–3 for four different cations, [NMe4]+, [NEt4]+, [AsPh4]+ and [N(PPh3)2]+. For the [NMe4]+ salt two intense, sharp 13CO resonances are detected at d 239.0 and 200.6; they can be observed quickly (480 scans) and have chemical shifts similar to those found in solution for the bridging and terminal carbonyls respectively [Fig. 2(a)].For the [NEt4]+ salt [Fig. 2(b)] the signal-to-noise ratio of the two 13CO resonances at d 238 and 198 is much worse despite much longer collection times (see legend for Fig. 1). In the case of the [AsPh4]+ salt [Fig. 2(c)] we were not able to detect the carbonyl Fig. 1 The 13C CP MAS NMR spectra of (a) [NMe4]2[Ni6(CO)12] (480 scans) with MAS rate = 3.5 kHz, (b) [NEt4]2[Ni6(CO)12] (6640 scans) with MAS rate = 4.0 kHz, (c) [AsPh4]2[Ni6(CO)12] (2400 scans) with MAS rate = 3.5 kHz, and (d) [N(PPh3)2]2[Ni6(CO)12] (13 000 scans) with MAS rate = 2.5 kHz, at room temperature; * represents the spinning side band480 J. Chem. Soc., Dalton Trans., 1997, Pages 479–483 resonances, even on changing the spinning rate from 2 to 4 kHz to eliminate the interference due to the spinning side bands.On the contrary, for the largest cation, [N(PPh3)2]+ [Figs. 2(d) and 3], very weak but sharp bridging carbonyl resonances were found at d 239.5, 238.0, and 235.4, and terminal resonances at d 200.0, 199.3 and 198.5, respectively; the occurrence of three resonances in each of the bridging and terminal regions is consistent with the site symmetry of the anion as described above. These and other presently unpublished results 4 show that the signal-to-noise ratio of 13CO resonances in CP MAS measurements of anionic carbonyl clusters appear to be much higher when [NMe4]+ salts are used.We thus examine below some of Fig. 2 Expanded plots of Fig. 1 in the carbonyl resonance region Table 1 Crystallographic data for [Ni6(CO)12]22 with different cations Cation [NMe4]+ 5 [AsPh4]+ [N(PPh3)2]+ 6 Crystal form Trigonal Triclinic Triclinic Space group P3� P1� P1� a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Dc/g cm23 ZT a/K d(Ni]Ni)b d(Ni]Ni)c 11.003(1) 11.003(1) 7.045(1) 90.00(0) 90.00(0) 120.00(0) 738.7 1.88 1 298 2.38 2.77 11.760(5) 12.648(5) 11.266(6) 103.15(4) 117.42(3) 95.72(4) 1407(1) 1.717 1 153 2.379(2) 2.745(5) 2.847(3) 13.299(4) 13.343(4) 13.051(5) 106.24(3) 119.04(2) 81.41(3) 1943(1) 1.508 1 296 2.392(5) 2.789(4) 2.761(5) a Temperature used to collect X-ray data.b Within the Ni3(CO)3(m-CO)3 plane. c Between the Ni3(CO)3(m-CO)3 planes. the factors which could be responsible for this enhancement. Many factors are known to influence the signal-to-noise ratio of 13C resonances in CP MAS measurements.8–12 The structure of the anion [Ni6(CO)12]22 in the [NMe4]+,5 [AsPh4]+ and [N(PPh3)2]+ 6 salts is quite similar and consists of two planar Ni3(CO)3(m-CO)3 groups in a trigonal-antiprismatic arrangement; for the [NMe4]+ salt all six values of d(Ni]Ni) between the two Ni3(CO)3(m-CO)3 planes are similar whereas in the [AsPh4]+ and [N(PPh3)2]+ salts the trigonal antiprism is slightly distorted resulting in two shorter and four longer Ni]Ni distances between these two planes (see Table 1) and this static distorted structure is retained on the NMR time-scale (see above).In all cases the value of d(Ni]Ni) is significantly shorter within the Ni3(CO)3(m-CO)3 plane than between these planes. The different packing arrangements induced on changing the cation {[NMe4]+, [AsPh4]+, [N(PPh3)2]+} are represented schematically in Fig. 4(a)–4(c), respectively. These variations are difficult to predict and rationalise but it is of interest that for [NMe4]2[Ni6(CO)12] the Ni6 units stack with adjacent staggered Ni3(CO)3(m-CO)3 planes [Fig. 4(a)] whereas phenyl rings from both [AsPh4]+ and [N(PPh3)2]+ separate these Ni3(CO)3(m-CO)3 planes between adjacent Ni6 units [Fig. 4(b), 4(c)]. Fig. 4 also shows the minimum interatomic H ? ? ? CO contacts for both terminal and bridging carbonyls. These distances, which are based on the calculated H atom positions, have been calculated using the ORFFE program13 and are summarised in Table 2.With increasing bulk of the cation the density of the [Ni6(CO)12]22 salts decreases and the calculated densities of the [NMe4]+, [AsPh4]+ and [N(PPh3)2]+ salts are 1.88, 1.717 and 1.508 g cm23 respectively but this can only have a minor effect on the variation of the signal-to-noise ratio for these different salts. As outlined in the introduction, the anion site symmetry in the unit cell is S6 for the [NMe4]+ and Ci for the [AsPh4]+ and [N(PPh3)2]+ salts.If all other factors are equal then this could lead to a maximum signal-to-noise ratio reduction by a factor of 3 on changing the cation from [NMe4]+ to [AsPh4]+ or [N(PPh3)2]+. It is, therefore, obvious that the anion site symmetry Fig. 3 Carbonyl resonance region in 13C CP MAS NMR spectra of [N(PPh3)2]2[Ni6(CO)12] with MAS rate = (a) 3.8 (12 700 3.5 (2540), and (c) 2.5 kHz (13 000 scans). Shaded peaks represent the real carbonyl resonances.The linewidths of the bridging CO (near d 240) become slightly broad on increasing the MAS rateJ. Chem. Soc., Dalton Trans., 1997, Pages 479–483 481 Fig. 4 Packing diagrams of different salts of [Ni6(CO)12]22: (a) [NMe4]+, (b) [AsPh4]+ and (c) [N(PPh3)2]+. Hydrogen atoms white, carbon grey, oxygen red, nitrogen blue, arsenic yellow, phosphorus cyan, nickel magenta, green solid lines shortest H ? ? ?CObridge and green dotted lines shortest H? ? ?COterminal plays an important role.However, the observed reduction is greater (see Fig. 2) and other factors must also be taken into account. Even if the Hartmann–Hahn condition, gCH1 C = gHH1 H, is ful- filled in the cross-polarisation experiment, the signal intensity is determined by the kinetics of magnetisation transfer. It depends on the contact time or cross-polarisation time tm according to equations (1) and (2).8–10 These equations show M(tm) = M0l21F1 2 expS2 ltm TCH DGexpF2 tm T1r(1H)G (1) l = 1 + TCH T1r(13C) 2 TCH T1r(1H) (2) that the magnetisation M increases with a time constant l21TCH during the short contact time tm of the 13C nuclei with the 1H nuclei, if the cross-relaxation time, TCH, is sufficiently short compared with T1r(13C) and T1r(1H).Subsequently, a reduction in the magnetisation occurs due to the relaxation of the protons in the rotating frame with a time constant T1r. In order to get reasonable 13CO CP MAS spectra, T1r(1H) must be longer than TCH, and T1 must be short enough to allow effective accumulation of the free induction decay.In order to assess the above conditions, proton relaxation times T1 and T1r have been measured for [Ni6(CO)12]22 with four different cations and the results obtained are shown in Table 3. All four compounds have short T1 values which allow a recycle delay of 2 s to be used. The T1r values are long enough to have a contact time, tm, of 1–2 ms, which is the time used to482 J.Chem. Soc., Dalton Trans., 1997, Pages 479–483 measure 13C signals for hydrocarbons, although the T1r values for the [NMe4]+ and [N(PPh3)2]+ salts are one order of magnitude longer than those for the [NEt4]+ and [AsPh4]+ salts. Consequently, if TCH is less than 1 ms it should be relatively easy to obtain 13CO CP MAS spectra for all four compounds. Magnetisation transfer occurs through dipole–dipole interactions between 13C and 1H, and these interactions are proportional to r26 where r denotes the C]H distance.In the case of hydrocarbons, the direct C]H contact r is about 1 Å, and TCH is less than 1 ms. For this intramolecular cross-polarisation it has also been shown that the efficiency of cross-polarisation decreases dramatically with the onset of molecular motion.12 In metal carbonyl clusters, however, the distances between the carbons of the CO groups and the hydrogens of the cation are considerably longer than 1 Å (see Table 2).In fact, for [NMe4]2[Ni6(CO)12]5 the shortest interatomic H ? ? ? CO distance is 3.16 Å and, as a result TCH will be longer than 1 ms and becomes comparable with the value of T1r(1H) for the salts of [Ni6(CO)12]22. These data suggest that it should be difficult to observe 13C CP MAS CO spectra for transition-metal carbonyl clusters, irrespective of molecular motion. However, in spite of these considerations, well resolved spectra are observed when using the [NMe4]+ cation.Other factors which have been found to affect the signal-tonoise ratio in CP MAS measurements are line broadening caused by various dynamic effects. Thus, the variation in linewidth can result from (i) chemical intraexchange as is often observed in solution, (ii) dynamic molecular reorientations which occur with a similar frequency to the radiofrequency decoupling field, and (iii) coupling between the MAS rate and chemical shift anisotropy. In the case of (i) peak coalescence of the terminal and bridging CO groups may be triggered by slow intraexchange (tc = 1023–1024 s: Dd = 40 ppm); such fluxional processes are often observed in solution NMR studies but not for [Ni6(CO)12]22.In contrast to the Cotton mechanism 11 for terminal–bridge carbonyl exchange which is well established in solution, there is some evidence for restricted reorientation of the metal skeleton within the carbonyl cage for [Co4(CO)12]1,2 and [Fe2Os(CO)12].14 However, it appears to us unlikely that this reorientation of the metal skeleton within the carbonyl framework can be markedly affected by the variation in packing effects caused by different cations and is an unlikely explanation for the variation in signal-to-noise ratio observed in Fig. 1. For (ii) Rothwell and Waugh15 have found relationship (3) 1 T2 = gH 2gC 2"2 5r6 S tc 1 + w1 2tc 2D (3) for CP MAS NMR linewidths from temperature-dependent studies, where the protons are subjected to a radiofrequency decoupling of intensity w1.According to equation (3) the linewidth becomes a maximum when w1tc = 1. This mechanism of line broadening has been clearly observed in the 13CO spectra of [M(h6-C6H5Me)(CO)3] (M = Cr or Mo)16 and [Cr(h6- C6H6)(CO)3].17 In all cases, the correlation time (tc) for the C3 Table 2 Minimum H ? ? ? CO contacts for [Ni6(CO)12]22 with different cations d(H ? ? ? CO)/Å Cation Terminal CO Bridging CO [NMe4]+ 5 [AsPh4]+ [N(PPh3)2]+ 6 3.173 2.952 2.916 3.160 2.853 3.204 rotation of the M(CO)3 group satisfies the condition w1tc = 1 as a result of tC being 1024–1025 s.This condition also holds at the temperature at which the T1r minimum appears. In the case of [NMe4]+ it has been shown that both reorientation of the CH3 group about a C3 axis and overall reorientation of the whole cation at room temperature occurs in the region of w1tc ! 1 (tc ! 1025 s, short correlation limit) in many kinds of solids, e.g. NMe4X (X = Cl, Br or I),18 NMe4ClO3 19 and [NMe4]2[MCl6] (M = Pb, Sn or Te).20 These results are consistent with our T1r measurements on [NMe4]2[Ni6(CO)12] and must be one of the reasons why it is possible to observe such intense, sharp carbonyl resonances for [NMe4]2[Ni6(CO)12].It is also worth noting that the rapid isotropic motion of the cation results in a very small chemical shift anisotropy of the methyl carbon so that it is possible to detect the carbonyl resonances separately as shown in Fig. 1(a). When the cation becomes intermediate in size, e.g. [NEt4]+ or Fig. 5 Molecular structure of the cluster anion of [AsPh4]2[Ni6(CO)12] Table 3 Proton relaxation times T1 and T1r of A2[Ni6(CO)12] at room temperature A T1/ms T1r/ms [NMe4]+ [NEt4]+ [AsPh4]+ [N(PPh3)2]+ 220 87 243 380 124 17 12 216 Table 4 Selected bond lengths (Å) and angles (8) for [AsPh4]2- [Ni6(CO)12] Ni(1)]Ni(2) Ni(1)]Ni(2*) Ni(1)]Ni(3) Ni(1)]Ni(3*) Ni(2)]Ni(3) Ni(2)]Ni(3*) Ni(1)]C(1) Ni(1)]C(2) Ni(2)]Ni(1)]Ni(3) Ni(1)]Ni(2)]Ni(3) Ni(1)]Ni(3)]Ni(2) Ni(2)]Ni(1)]Ni(2*) Ni(2)]Ni(1)]Ni(3*) Ni(3)]Ni(1)]Ni(3*) Ni(2*)]Ni(1)]Ni(3*) 2.386(2) 2.847(3) 2.377(2) 2.749(2) 2.375(2) 2.740(2) 1.90(1) 1.89(1) 59.84(6) 59.90(7) 60.26(7) 89.75(7) 64.03(6) 87.15(7) 62.49(7) Ni(1)]C(4) Ni(2)]C(1) Ni(2)]C(3) Ni(2)]C(5) Ni(3)]C(2) Ni(3)]C(3) Ni(3)]C(6) C(1) ? ? ? H(16) Ni(3)]Ni(2)]Ni(3*) Ni(1)]Ni(2)]Ni(3*) Ni(2)]Ni(3)]Ni(2*) Ni(3)]Ni(2)]Ni(1*) Ni(2)]Ni(3)]Ni(1*) Ni(1)]Ni(3)]Ni(1*) Ni(1)]Ni(3)]Ni(2*) 1.77(1) 1.88(1) 1.90(1) 1.74(1) 1.87(1) 1.87(1) 1.76(1) 2.853 87.40(7) 64.44(6) 92.60(7) 62.75(6) 67.20(7) 92.85(7) 67.05(7)J.Chem. Soc., Dalton Trans., 1997, Pages 479–483 483 [AsPh4]+, the overall reorientation of the whole cation or the substituents must be slower and then T1r approaches a minimum value (w1tc = 1). The carbonyl resonances, therefore, start to broaden [see Fig. 2(b)] or are completely lost [Fig. 2(c)]. For the largest cation, [N(PPh3)2]+, we again observe very sharp resonances (Fig. 3). In this case, the molecular motion of the relatively rigid cation is expected to be in the region of w1tc @ 1 (tc @ 1023 s, long correlation limit) in the solid state. This is consistent with the T1r value in Table 2 and from equation (3) a very narrow linewidth is to be expected. The observed linewidth at 333 K is the same as that observed at room temperature, suggesting that the molecular motion is still in the slow limit even at 333 K.Recently Barrie et al.21 have pointed out that mechanism (iii) can cause line broadening in solid [Cr(h6-C6Me5H)(CO)3] when the rate of chemical exchange becomes comparable with the magnitude of the chemical shift anisotropy (Ds = 32.9 kHz). For the different salts of [Ni6(CO)12]22 there is only a very weak MAS rate dependence on the lineshape for the [N(PPh3)2]+ salt (see Fig. 3). However, the time-scale (tc = 1024–1025 s) responsible for this mechanism is almost identical to that in case (ii).It is, therefore, difficult to distinguish between these two mechanisms. Finally, another mechanism resulting from high-speed sample spinning can sometimes prolong TCH and reduce the intensity of the 13C CP MAS resonance.22,23 However, this cannot occur for A2[Ni6(CO)12] {A = [NMe4]+, [NEt4]+, [AsPh4]+ or [N(PPh3)2]+} because the spectral intensity has negligible spinning-rate dependence between 2.5 and 4 kHz. In conclusion, 13CO CP MAS spectra with good signal-tonoise ratio (ca. 1 : 1) at natural 13CO abundance are observed for carbonyl anions when a small, proton-containing, spherical cation, as exemplified by [NMe4]+, is used.This must mainly result from the combined effects of very rapid cation motion and the site symmetry of the anion, and should prove useful for the study of other anionic carbonyl clusters. Experimental The compound [NMe4]2[Ni6(CO)12] was prepared as described previously 5,7 and salts containing other cations were prepared by metathetical exchange with the appropriate cation.Solidstate NMR measurements were carried out on a Bruker MSL200WB spectrometer using a 7 mm rotor and T1r values were obtained using standard procedures from CP MAS measurements. Crystallography A dark red crystal of [AsPh4]2[Ni6(CO)12] of dimensions 0.35 × 0.15 × 0.25 mm was mounted on a glass fibre. Using a Rigaku AFC6S diffractometer and Mo-Ka radiation (l = 0.710 73 Å), cell dimensions were determined from angular settings of 25 reflections with 2q between 20.48 and 31.578.Crystal data. C60H40As2Ni6O12, M = 1455, triclinic, space group P1� , a = 11.760(5), b = 12.648(5), c = 11.266(6) Å, a = 103.15(4), b = 117.42(3), g = 95.72(4)8, U = 1407(1) Å3, Z = 1, Dc = 1.717 g cm23, F(000) = 730, m = 32.02 cm21. Data collection and processing. Scan mode w–2q with w scan width = (1.37 + 0.30tan q)8. 4928 Unique reflections recorded (qmax = 258, 0 < h < 12, 214 < k < 14, 213 < l < 11) of which 3128 with I > 3s(I) were used in refinement.Temperature 153 K. Empirical absorption correction based on azimuthal scans applied. Three standard reflections showed no significant variation during data collection. Structure analysis and refinement. The structure was solved by direct methods using the TEXSAN package.13 All nonhydrogen atoms were refined anisotropically (based on F 2). The hydrogen atoms were placed in calculated positions and not refined.Final unweighted and weighted agreement factors {R = S(|Fo| 2 |Fc|)/S|Fo|, R9 = [Sw(|Fo| 2 |Fc|)2/Sw(Fo)2]� �� } were 0.054 and 0.067 respectively. A weighting scheme [w = 1/s2(Fo)] including a factor (p = 0.03) to downweight intense reflections was used. The final electron-density difference map showed no peaks >1.27 or <20.75 e Å23. Selected bond lengths and angles are given in Table 4 and the structure of [Ni6(CO)12]22 in Fig. 5. 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 186/343. Acknowledgements We thank the Japan Society for the Promotion of Science, the Royal Society, the British Council and the EC (contract No. CHRX-CT93-0277) for financial support.We also thank Mr. J. V. Barkley for help with the X-ray data collection. References 1 B. T. Heaton, J. Sabounchei, S. Kernaghan, H. Nakayama, T. Eguchi, S. Takeda, N. Nakamura and H. Chihara, Bull. Chem. Soc. Jpn., 1990, 63, 3019. 2 T. Eguchi, H. Nakayama, H. Ohki, S. Takeda, N. Nakamura, S. Kernaghan and B. T. Heaton, J. Organomet. Chem., 1992, 428, 207. 3 T. Eguchi, B. T. Heaton, R. Harding, K. Miyagi, G. Longoni, J. Nähring, N. Nakamura, H. Nakayama, T. A. Pakkanen, J.Pursiainen and A. K. Smith, J. Chem. Soc., Dalton Trans., 1996, 625. 4 T. Eguchi, R. Harding, B. T. Heaton, G. Longoni, K. Miyagi, J. Nahring, N. Nakamura, H. Nakayama and A. K. Smith, unpublished work. 5 J. C. Calabrese, L. F. Dahl, P. Chini, G. Longoni and S. Martinengo, J. Am. Chem. Soc., 1974, 96, 2616. 6 R. E. Bachmann and K. H. Whitmire, Acta Crystallogr., 1993, 49, 1121. 7 G. Longoni, B. T. Heaton and P. Chini, J. Chem. Soc., Dalton Trans., 1980, 1537. 8 E. O. Stejskal, J. Schaefer and T. R. Steger, Faraday Symp. Chem. Soc., 1979, 13, 56. 9 M. Mehring, Principals of High Resolution NMR in Solids, Springer, Berlin, 1983. 10 R. Voelkel, Angew. Chem., Int. Ed. Engl., 1988, 27, 1468. 11 F. A. Cotton and B. E. Hanson, Rearrangements in Ground and Excited States, ed. P. de Mayo, Academic Press, New York, 1980, p. 379. 12 D. Schulze, H. Ernst, D. Fenzke, W. Meiler and H. Pfeifer, J. Phys. Chem., 1990, 94, 3499. 13 TEXSAN-TEXRAY, Structure Analysis Package, Molecular Structure Corporation, Houston, TX, 1985. 14 D. Braga, L. J. Farrugia, F. Grepioni and A. Senior, J. Chem. Soc., Chem. Commun., 1995, 1219; L. J. Farrugia, A. M. Senior, D. Braga, F. Grepioni, A. G. Orpen and J. G. Crossley, J. Chem. Soc., Dalton Trans., 1996, 631. 15 W. P. Rothwell and J. S. Waugh, J. Chem. Phys., 1981, 74, 2721. 16 G. W. Wagner and B. E. Hanson, Inorg. Chem., 1987, 26, 2019. 17 A. E. Aliev, K. D. M. Harris, F. Guillaume and P. J. Barrie, J. Chem. Soc., Dalton Trans., 1994, 3193. 18 S. Albert, H. S. Gutowsky and J. A. Ripmeester, J. Chem. Phys., 1972, 56, 3672. 19 T. Tsuneyoshi, N. Nakamura and H. Chihara, J. Magn. Reson., 1977, 27, 191. 20 Y. Furukawa, Y. Baba, S. Gima, M. Kaga, T. Asaji, R. Ikeda and D. Nakamura, Z. Naturforsch., Teil A, 1991, 46, 809. 21 P. J. Barrie, C. A. Mitsopoulou and E. W. Randall, J. Chem. Soc., Dalton Trans., 1995, 2125. 22 J. R. Long, B. Q. Sun, A. Bowen and R. G. Griffin, J. Am. Chem. Soc., 1994, 116, 11950. 23 S. Hedinger, B. H. Meier and R. R. Ernst, J. Chem. Phys., 1995, 102, 4000. Received 10th June 1996; Paper

ISSN:1477-9226    

DOI:10.1039/a604078k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 497–500 497 The gadolinium(III) chelate of 1-oxa-4,7,10-triazacyclododecane- 4,7,10-triacetic acid. Formation of polymeric chains in the solid state and relaxivity properties Marie-Rose Spirlet,a Jean Rebizant,b Xiangyun Wang,c Tianzhu Jin,c Dominique Gilsoul,c Vinciane Comblin,c Frédérique Maton,d Robert N. Muller d and Jean F. Desreux *,†,c a Laboratories of Experimental Physics, University of Liège, Sart Tilman (B6), B4000 Liège, Belgium b European Commission, Joint Research Centre, Institute for Transuranium Elements, Postfach 2340, D-76125 Karlsruhe, Germany c Coordination and Radiochemistry, University of Liège, Sart Tilman (B6), B4000 Liège, Belgium d NMR Laboratory, Department of Organic Chemistry, University of Mons-Hainaut, B-7000 Mons, Belgium The crystal structure of the gadolinium(III) chelate of the macrocyclic ligand odotra (1-oxa-4,7,10- triazacyclododecane-4,7,10-triacetate) was determined by X-ray single-crystal analysis: [Gd(odotra)(H2O)5] crystallizes in the orthorhombic space group Pbca, with a = 12.84(8), b = 21.53(4), c = 15.30(7) Å and Z = 8.The metal ion is at the centre of a square antiprism capped with one water molecule. The chelate units are linked by bridging carboxylic groups and form linear polymeric chains. The macrocycle adopts its preferred square [3333] conformation. Nuclear magnetic resonance dispersion studies indicate that [Gd(odotra)] and its analogue [Gd(dotra)] (dotra = 1,4,7,10-tetraazacyclododecane-4,7,10-triacetate) exhibit the same relaxivity behaviour but are not as effective magnetic resonance imaging contrast agents as expected presumably because of their low symmetry.Several gadolinium(III) polyaminopolycarboxylic chelates are currently used as contrast agents because these paramagnetic compounds can highlight lesions that might otherwise be missed on magnetic resonance images. The chelates must be thermodynamically highly stable and kinetically inert to ensure complete excretion from the body within a few hours.This goal has been achieved with twelve-membered macrocyclic polyaza polycarboxylic ligands which impart their steric constraints on lanthanide complexes. The preferred square [3333] conformation of cyclododecane is adopted in the solid state 1 and in solution 2 by the chelates formed by its 1,4,7,10-tetraazasubstituted derivatives such as 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid, (H4dota).This [3333] arrangement favours the formation of a highly rigid nine-co-ordinated capped square-antiprismatic geometry with four nitrogen atoms defining one square face, four carboxylic oxygen atoms delimiting the other square face and one water molecule on the C4 axis. It will be shown here that this conformational preference is maintained in the solid-state structure of the gadolinium( III) chelate of H3odotra (1-oxa-4,7,10-triazacyclododecane- 1,4,7-triacetic acid) although this features an oxatriaza cycle and only three carboxylic groups.A second objective of the present study is an analysis of the relaxivity properties of this chelate and of its fully nitrogenated analogue H3dotra (1,4,7,10-triazacyclododecane-1,4,7-triacetic acid). Experimental The compounds H3dotra 3 and H3odotra 4,5 and their gadolinium(III) chelates 1 were synthesized according to previously outlined procedures. The purity of the chelates was checked by HPLC according to the method of Kumar et al.6 Proton-relaxation dispersion profiles (NMRD curves) were † E-Mail: jf.desreux@ulg.ac.be recorded as reported earlier 7 on an IBM research field-cycling relaxometer over the field range 2 × 1024 to 1.2 T (corresponding proton Larmor frequencies ranging from 0.01 to 50 MHz).The NMRD curves of at least two different samples of [Gd- (odotra)] and [Gd(dotra)] originating from different syntheses were recorded at 25 ± 0.1 and 37 ± 0.1 8C and the gadolinium content of the solutions used for the measurements was measured by inductively coupled plasma (ICP) atomic emission on a Bausch and Lomb 3510 spectrometer. Crystallography Crystals (white, prismatic) suitable for X-ray analysis were obtained after dissolving the hydrated [Gd(odotra)] complex in the minimum volume of methanol, adding a layer of acetone and allowing the two solutions to mix slowly by diffusion.A selected specimen (0.25 × 0.20 × 0.25 mm) was mounted on a glass fibre.X-Ray diffraction data were obtained with an Enraf- Nonius CAD-4 four-circle computer-controlled diffractometer (using graphite-monochromated Mo-Ka radiation, l = 0.710 73 Å) at 293 K. The unit-cell parameters and standard deviations were calculated for the setting angles of 25 reflections with 5 < 2q < 30o. The space group was established from systematic absences. N N N N N R N N HO O O OH HO O HO O O OH HO O O OH H4dota H3odotra R = O H3dotra R = NH498 J.Chem. Soc., Dalton Trans., 1997, Pages 497–500 Crystal data and data-collection parameters. C14H32GdN3O12, Mr = 591.67, orthorhombic, space group Pbca, a = 12.84(8), b = 21.53(4), c = 15.30(7) Å, U = 4231(6) Å3, Z = 8, Dc = 1.858 Mg m23, m(Mo-Ka) = 3.2129 mm21, F(000) = 2376. The intensities of 4507 [I > s(I)] reflections were measured by the w–2q scan technique in the range 4 < 2q < 45o (index ranges: 16 < h < 0, 218 < k < 0,225 < l < 25).They corresponded to 2304 independent reflections (Rint = 0.025). Three standard reflections were monitored at 30 min intervals to check crystal stability. No significant decrease in intensity during data collection was observed. Data were corrected for Lorentz-polarization and absorption effects, the latter by a semiempirical method.8 The transmission factors ranged from 0.79 to 1.00. Structure solution and refinement. The structure was solved by direct methods and Fourier techniques and refined by fullmatrix least squares minimizing Sw(|Fo| 2 |Fc|)2.A weighting scheme based on counting statistics was used: w = 1/[s(Fo)]2. Refinement was carried out on 1925 reflections (based on Fo) with F > 3s(F). The non-hydrogen atoms were treated anisotropically. Hydrogen atoms placed in calculated positions (C]H 0.95 Å) were included in the final structure-factor calculation with Biso = 1.30Biso of the attached C atom.A secondary extinction coefficient was refined to a value of g = 3.83 × 1028 {Fc = Fc/[1 + g(Fc)2Lp]}. The final agreement factors for the observed data were R = 0.037 and R9 = 0.058 {R = S|Fo| 2 |Fc|/ S|Fo|; R9 = [Sw(|Fo| 2 |Fc|)2/Sw|Fo|2]� �� }. Number of parameters refined 272, goodness of fit S = 1.53, data-to-parameter ratio 7.08 : 1, maximum shift/e.s.d. in final cycle 0.02. The highest peak in the final Fourier-difference map, 1.45 e Å23, was located near the Gd atom.Calculations were performed with the SDPplus package.9 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 186/356. Results The molecular structure of the [Gd(odotra)] complex together with the atomic numbering scheme is shown in Fig. 1.Selected bond distances and angles are summarized in the legend. The Fig. 1 Molecular structure of [Gd(odotra)]. Selected bond distances (Å) and angles (8): Gd]N(1) 2.674(9), Gd]N(4) 2.644(9), Gd]N(7) 2.674(9), Gd]O(10) 2.574(7), Gd]O(19) 2.327(7), Gd]O(49) 2.351(7), Gd]O(79) 2.357(7), Gd]O(w1) 2.559(7) and Gd]O(40*) 2.328(6); N(1)]Gd]N(4) 66.3(3), N(1)]Gd]N(7) 102.7(3), N(1)]Gd]O(10) 64.1(3), N(1)]Gd]O(49) 78.3(3), N(1)]Gd]O(79) 148.6(3), N(1)] Gd]O(40*) 127.0(3), N(1)]Gd]O(19) 63.5(3) and N(1)]Gd]O(w1) 127.0(2) gadolinium(III) ion lies in a slightly distorted monocapped square-antiprismatic environment of nitrogen and oxygen atoms provided by the four heteroatoms of the twebered ring (N3O face), by four acetate oxygen atoms (O4 face) and by one water molecule. This co-ordination geometry is achieved by sharing carboxylic groups between adjacent chelates in infinite polymeric chains as shown in Fig. 2. The two square faces of the chelate are quasi-parallel (angle 3.438) and the heteroatoms form exact planar arrays (average displacements of 0.03 and 0.01 Å for the N3O and O4 faces respectively).The metal ion lies 0.720 Å above the O4 face and 1.633 Å below the N3O face. The Gd]Owater bond is nearly at right angles with the O4 face (angle 80.18) and the water molecule is located at a distance of 2.559(7) Å from the metal ion {corresponding value 10 in the case of [Gd(dota)]2 is 2.447 Å}.The average Gd]N distance in [Gd(odotra)] [2.654(9) Å] is very similar to the value 10 for [Gd(dota)]2 (2.663 Å) and is slightly longer than the Gd]Oring distance as indicated in the legend of Fig. 1. All the distances between the gadolinium ion and the acetate oxygen atoms [mean 2.345(7) Å] are very similar to the values reported 10 for [Gd(dota)]2 (mean 2.364 Å). The oxygen atom O(40*) which completes the square-antiprismatic co-ordination sphere of each [Gd(odotra)] unit belongs to a carboxylic group from an adjacent molecule in the polymeric chain.The Gd]O(40*) distance is identical to the other Gd]O distances and the formation of a polymer has no influence on the geometry of the chelate. The interatomic distances in the ligand fall within the range documented for similar bonds2,10 and the macrocycle is in the expected square [3333] conformation with torsion angles close to the usual g±g±a or + - 60, + - 80, ±1658 sequence 11 previously found in [Gd(dota)] 210 and [Eu(dota)] 22 {mean torsion angles in [Gd(odotra)]: 258(1), 280(1) and Fig. 2 The polymeric structure of [Gd(odotra)]. The non-carbon atoms are cross-hatched and hydrogen atoms are omitted for clarityJ. Chem. Soc., Dalton Trans., 1997, Pages 497–500 499 160(1)8}. Despite their structural differences, the ligands odotra and dota thus form nearly identical co-ordination spheres around the gadolinium ion. One difference between the two chelates should however be pointed out: the macrocycle in [Gd(odotra)] and [Gd(dota)]2 adopts the same conformation but the acetate substituents are arranged around the central metal ion with opposite chiralities in a propeller-like manner that is counterclockwise for the former chelate and clockwise for the latter.Moreover, the angles between two vectors defined respectively by N atom–centroid of the N3O face and O atom– centroid of the O4 face in the same NCH2CO2 2 group are somewhat smaller in [Gd(odotra)] (30.3 and 31.28) than in [Gd(dota)]2 (37.6 and 39.68).Therefore, [Gd(odotra)] is a slightly more distorted square antiprism (ideal angle 458) and is slightly more elongated than [Gd(dota)]2 (distance between the two square faces: 2.488 and 2.353 Å respectively). The presence of diastereoisomers in crystals of various derivatives of the lanthanide dota chelates featuring asymmetric centres has been reported 12–14 and seems to be a general rule for these complexes. The [Gd(odotra)] polymeric chain itself is made up of alternating enantiomers, i.e.the conformations of both the macrocyclic ring and the acetate arms are inverted along the chain. The mean N4 planes of two successive chelates make an angle of ±99.98 and the stacking of the crystals results from a three-dimensional network of hydrogen bonds involving the carboxylate oxygens and five water oxygen atoms. To our knowledge this is the first example of a polymeric chain formed by a chelate of the dota family.However, the structure of smaller aggregates has been described. A dimeric structure with a bridging carboxyl group between the two metal ions has been reported for the gadolinium(III) complex of (1R,4R,7R)-a,a9,a0-trimethyl-1,4,7,10-tetraazacyclododecane- 1,4,7-triacetic acid 13 and [Gd(dotra)] is known14,15 to form a trimer with a bridging carbonate ion when it crystallizes in the presence of Na2CO3. The stereochemical preferences of the twelve-membered tetraaza macrocycles are so pronounced that a square-antiprismatic geometry with a [3333] arrangement is formed even if the chelate ring contains different heteroatoms, features only three substituting arms and is part of a di-, tri- or poly-meric structure.The proton-relaxation dispersion profiles of [Gd(odotra)] and [Gd(dotra)] at 25 and 37 8C are reproduced in Fig. 3. The NMRD curves of at least two samples of each chelate prepared Fig. 3 Proton-relaxation dispersion curves of [Gd(odotra)] ((, e × ) and [Gd(dotra)] (), _) at 25 (upper curves) and 37 8C (lower curves). These data are compared with the corresponding curves calculated for [Gd(dota)]2 16 with a hydration number of two at 25 (—·—· —) and 37 8C (·····) from Gd2O3 or Gd(OH)3 with macrocycles obtained from different syntheses were found to be identical within the experimental errors.The relaxivity curves of [Gd(odotra)] and [Gd(dotra)] are nearly identical at all frequencies and can be interpreted by a best-fit approach based on the Solomon– Bloembergen–Morgan equation.17 The complex [Gd(ttha)]32 was used for estimating the outer-sphere contribution to the relaxivity since ttha completely encapsulates the Gd3+ ion and prevents its co-ordination to a water molecule 18 {H6ttha = [CH2N(CH2CO2H)CH2CH2N(CH2CO2H)2]2}. Moreover, the exchange lifetime tm of a hydration water molecule in the first co-ordination sphere of [Gd(odotra)] and [Gd(dotra)] was fixed at 10 ns.This parameter has little or no influence on the relaxivity properties provided it is much smaller than the longitudinal relaxation time of the water protons as shown earlier for [Gd(dota)]2.19 It was assumed that the Gd3+ ion is co-ordinated to two water molecules and the water proton–Gd3+ distance was fixed at 3.13 Å, a mean value found in the present crystallographic study and in earlier investigations.2,10 A good agreement between the experimental and calculated relaxivities of [Gd- (odotra)] and [Gd(dotra)] was obtained with the following mean parameters (in ps): ts0 (electronic relaxation time at zero field) = 120 ± 15, tv (correlation time of the modulation of the zero-field splitting) = 55 ± 14, tr (rotational correlation time) = 81 ± 13 at 25 8C and ts0 = 134 ± 10, tv = 16 ± 2, tr = 45 ± 3 at 37 8C.The errors are standard deviations on the mean of the parameters calculated for each chelate. The tv and tr values are in the ranges found17 for other small rapidly rotating chelates. These correlation times and the absence of a maximum in relaxivity around 20 MHz clearly indicate that, as expected, [Gd(odotra)] loses its polymeric structure on dissolution in water.The ts0 correlation time is significantly shorter than the values reported for [Gd(dota)]2 (460 ps at 25 8C20 and 650 ps or higher at 37 8C21). This difference can be assigned to the lower symmetry and/or the reduced rigidity of the triacetic ligands which causes a larger zero-field splitting and thus a reduction in ts0.22 Symmetry effects have already been noted for dota derivatives with identical substituents in different arrangements20 and for a triacetic monoamide dota derivative, 23 although unusually small t0 values have been reported in the case of highly symmetric unhydrated polyphosphinate macrocyclic chelates.24 Surprisingly, replacing an oxygen atom in the tetraaza ring by a NH group does not seem to modify signifi- cantly ts0.This insensitivity to ligand-field effects could arise because [Gd(odotra)] and [Gd(dotra)] have the same symmetry and similar rigidity, but it cannot be ruled out that a compensation of the effect of the Gd? ? ?Hwater distance, of the hydration number and of the various correlation times of these two chelates was not revealed by the best-fit computations. On the more practical side, [Gd(odotra)] is not expected to be a useful magnetic resonance imaging contrast agent because of its probable low stability.However, our measurements confirm that designing contrast agents with a higher number of exchangeable water molecules does not necessarily lead to the expected increase in relaxivity at low and medium fields presumably because of the lower symmetry and rigidity of the ligands. Should [Gd(dota)]2 contain two hydration water molecules instead of one, one would expect 16 a relaxivity at 0.1 MHz close to 17.9 and 14.1 dm3 mmol21 s21 at 25 and 37 8C respectively, i.e.significantly higher than the values obtained for [Gd(odotra)] and [Gd(dotra)] as shown in Fig. 3. Acknowledgements We gratefully acknowledge the financial support of the Fonds National de la Recherche Scientifique, the Institut Interuniversitaire des Sciences Nucléaires and the European Cooperation in the Field of Scientific and Technical Research COST D1. The Liège group is also indebted to Bracco Research USA for financial support.500 J.Chem. Soc., Dalton Trans., 1997, Pages 497–500 References 1 J. F. Desreux, Inorg. Chem., 1980, 19, 1319. 2 M.-R. Spirlet, J. Rebizant, J. F. Desreux and M. F. Loncin, Inorg. Chem., 1984, 23, 359. 3 M. F. Tweedle, G. T. Gaughan and J. J. Hagan, Eur. Pat., 292 689, 1988. 4 W. Rasshofer, W. Wehner and F. Vögtle, Liebigs Ann. Chem., 1976, 916. 5 M. T. S. Amorim, R. Delgado, J. J. R. Frausto da Silva, C. T. A. Vaz and M. F. Vilhena, Talanta, 1988, 35, 741. 6 K. Kumar, K. V. Sukumaran and M. F. Tweedle, Anal. Chem., 1994, 66, 295. 7 W. D. Kim, G. E. Kiefer, F. Maton, K. McMillan, R. N. Muller and A. D. Sherry, Inorg. Chem., 1995, 34, 2233. 8 A. C. T. North, D. C. Philips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. 9 SDP, Structure Determination Package, version 18, Enraf-Nonius, Delft, 1981. 10 J. P. Dubost, J. M. Leger, M. H. Langlois, D. Meyer and M. Schaefer, C. R. Acad. Sci., Ser. II. Mec. Phys., 1991, 312, 349. 11 J. Dale, Isr. J. Chem., 1980, 20, 3. 12 K. O. A. Chin, J. R. Morrow, C. H. Lake and M. R. Churchill, Inorg. Chem., 1994, 33, 656. 13 S. I. Kang, R. S. Ranganathan, J. E. Emswiler, K. Kumar, J. Z. Gougoutas, M. F. Malley and M. F. Tweedle, Inorg. Chem., 1993, 32, 2912. 14 K. Kumar, C. A. Chang, L. C. Francesconi, D. D. Dischino, M. F. Malley, J. Z. Gougoutas and M. F. Tweedle, Inorg. Chem., 1994, 33, 3567. 15 C. A. Chang, L. C. Francesconi, M. F. Malley, K. Kumar, J. Z. Gougoutas and M. F. Tweedle, Inorg. Chem., 1993, 32, 3501. 16 F. Maton, Ph.D. Thesis, Université de Mons-Hainaut, 1993. 17 L. Banci, I. Bertini and C. Luchinat, Nuclear and electron relaxation, VCH, Weinheim, 1991, pp. 1–208. 18 T. Kimura and Y. Kato, J. Alloy Compd., 1995, 225, 284. 19 D. Pubanz, G. Gonzalez, D. H. Powell and A. E. Merbach, Inorg. Chem., 1995, 34, 4447. 20 S. Aime, M. Botta, G. Ermondi, F. Fedeli and F. Uggeri, Inorg. Chem., 1992, 31, 1100. 21 C. F. G. C. Geraldes, A. D. Sherry, I. Lazar, A. Miseta, P. Bogner, E. Berenyi, B. Sumegi, G. E. Kiefer, K. McMillan, F. Maton and R. N. Muller, Magn. Reson. Med., 1993, 30, 696. 22 S. H. Koenig, Magn. Reson. Med., 1991, 22, 183. 23 A. D. Sherry, R. D. Brown, III, C. F. G. C. Geraldes, S. H. Koenig, K.-T. Kuan and M. Spiller, Inorg. Chem., 1989, 28, 620. 24 S. Aime, A. S. Batsanov, M. Botta, J. A. K. Howard, D. Parker, K. Senanayake and G. Williams, Inorg. Chem., 1994, 33, 4696. Received 14th August 1996; Paper 6/05697K

ISSN:1477-9226    

DOI:10.1039/a605697k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 501–508 501 Main-group and transition-metal complexes of 1-thia-4,7-diazacyclononane, [9]aneN2S. Crystal structures of [VOCl2([9]aneN2S)]? MeCN, [Fe([9]aneN2S)2][ClO4]2, [Zn([9]aneN2S)2][PF6]2, [Ru(cym)([9]aneN2S)][BPh4]Cl2?MeCN (cym = p-cymene), [RhCl3([9]aneN2S)]?H2O and [Tl([9]aneN2S)][ClO4] Ulrich Heinzel, Andreas Henke and Rainer Mattes * Anorganisch-Chemisches Institut der Westfälischen Wilhelms-Universität, Wilhelm-Klemm-Strasse 8, 48149 Münster, Germany A series of half-sandwich and sandwich complexes of the nine-membered mixed donor macrocyclic 1-thia-4,7-diazacyclononane ([9]aneN2S) with metals in different oxidation states has been synthesized and characterized.In each case, the ligand provides tridentate face-capping co-ordination to the metal ion.X-Ray crystallographic structure determinations have been performed for most complexes; [Fe([9]aneN2S)2]2+ and [Zn([9]aneN2S)2]2+ display trans-octahedral N4S2 co-ordination. The metal–nitrogen and metal–sulfur bond distances are greater than the respective lengths in the homoleptic complexes [M([9]aneN3)2]2+ and [M([9]aneS3)2]2+ (M = Fe or Zn, [9]aneN3 = 1,4,7-triazacyclononane, [9]aneS3 = 1,4,7-trithiacyclononane).In the complexes of metal ions with larger radii, e.g. RhIII and TlI, the metal–sulfur distances are equal to or smaller than those in the complexes of [9]aneS3. The difference between the metal–nitrogen and the metal–sulfur bond lengths varies from 0.21 Å to 0.40 Å in the complexes studied. Both ÎÎÎ and ΉΠconformations of the three chelate rings formed were observed.The chemistry of 1,4,7-triazacyclononane ([9]aneN3) and 1,4,7- trithiacyclononane ([9]aneS3) has been extensively developed over the last decade.1 Far less is known about the co-ordination compounds of the mixed N,S-donor nine-membered macrocycles 1-thia-4,7-diazacyclononane ([9]aneN2S)2–4 and 1,4-dithia- 7-azacyclononane ([9]aneNS2),5 mainly due to the difficulties encountered during their synthesis.The four macrocycles mentioned ideally co-ordinate to triangular faces of tetrahedra, octahedra or trigonal prisms. The macrocycle [9]aneN2S features different binding sites in close proximity and has the potential to co-ordinate to both harder and softer ions or molecules. The loss of three-fold symmetry introduces interesting stereochemical consequences.No half-sandwich complexes of [9]aneN2S have been reported so far, in contrast to [9]aneN3 and [9]aneS3. In a more extended study we are presently exploring the co-ordination chemistry of mixed N,S-macrocycles with various ring sizes.6 In this paper we report the synthesis and characterization of several halfsandwich and sandwich complexes of [9]aneN2S with metals in different oxidation states.Results and Discussion [VOCl2([9]aneN2S)]?MeCN The reaction of VCl3 with 1 mol equivalent of [9]aneN2S in MeCN affords the vanadium(IV) compound [VOCl2([9]aneN2- S)]?MeCN. Vanadium(III) is oxidized to vanadium(IV) by traces of oxygen during the slow crystallization process. The presence of the VO group and the ligand was confirmed by IR and UV/ VIS spectroscopy.The IR spectrum shows sharp n(NH) absorptions at 3240 and 3200 cm21, and n(VO) at 985 cm21. In the UV/ VIS spectrum all three expected vanadyl(IV) d–d transitions are observed, giving a value for Dq of 19 800 cm21. The value is slightly larger than usually found in oxovanadium(IV) complexes with N-, O- or S-donor ligands.The high ligand field exerted by [9]aneN2S is confirmed by the EPR parameters at ambient and low temperatures. The 51V hyperfine coupling constants of Aiso = 91.2 × 1024 cm21 at g = 1.986 and of A|| = 161.1 × 1024 cm21 at g|| = 1.965 were established. (The signals of the inner octet, displaying A^ and g^, were poorly resolved, so these parameters could not be determined.) Vanadium is octahedrally co-ordinated in [VOCl2([9]ane- N2S)]? MeCN according to the structure determination.A view of the molecule is shown in Fig. 1. Selected bond lengths and angles are given in Table 1. The sulfur atom of [9]aneN2S and the terminal oxygen atom are co-ordinated in mutual trans positions. The V]O bond is short at 1.632(2) Å and has a strong trans influence upon the V]S bond.Its length is 2.689(1) Å. A shorter bond length of 2.634 Å has been observed in [VOCl2([9]aneS3)].7 Corresponding to the weak bonding of the sulfur atom the VO vibration frequency is shifted to rather high wavenumbers at 985 cm21. Sulfur co-ordination at the site with the largest metal-to-metal ligand distance is favoured also by the asymmetric structure of [9]aneN2S. The nitrogen atoms of [9]aneN2S are strongly co-ordinated in the equatorial plane.The V]N bond lengths of 2.153(2) and 2.150(2) Å are similar to those reported for oxovanadium(IV) complexes of [9]aneN3,8 whereas the V]Cl bond lengths of 2.346(1) and 2.337(1) Å are slightly larger than in the closely related compound [VOCl2([9]aneS3)].7 The vanadium atom is situated 0.32 Å above the mean plane containing the equatorial ligands Cl(1), Cl(2), N(1) and N(2). The molecules are interconnected in the solid state by weak O ? ? ? N hydrogen bonds.[Mn([9]aneN2S)2][ClO4]2 This compound has been prepared very recently in an independent study,9 and the crystal structure has also been reported. The metal ion of the complex cation is situated on a site of 2/m symmetry with Mn]N and Mn]S bond lengths of 2.242(7) and 2.625(3) Å, respectively.All ligand atoms show502 J. Chem. Soc., Dalton Trans., 1997, Pages 501–508 rather high thermal parameters due to disorder. There is no doubt that the compound prepared by us is identical with the complex described. [Fe([9]aneN2S)2][ClO4]2 The green iron(II) complex was obtained in high yield under an inert atmosphere. The analogous [Fe([9]aneN2S)2]Br2 was also prepared.From an ethanolic solution of this compound the dark brown iron(III) complex [Fe([9]aneN2S)Br]Br2 could be synthesized by slow crystallization in an open vessel. Its structure is not known, but the iron(III) ion is probably tetrahedrally co-ordinated by Br and the ligand [9]aneN2S. The complex [Fe([9]aneN2S)2][ClO4]2 consists of [Fe([9]aneN2S)2]2+ cations situated on crystallographic inversion centres.The cation is depicted in Fig. 2. Selected bond lengths and angles are given in Table 2. The metal centre is trans-N4S2 co-ordinated. The isolation of both cis and trans geometric isomers has been achieved so far only for cobalt(III).4 The Fe]N(1) and Fe]S bond lengths are 2.072(6) and 2.337(2) Å, respectively.Both values are greater than the respective bond distances in the homoleptic complexes [Fe([9]aneN3)2]2+ and [Fe([9]aneS3)2]2+ where the following bond distances have been found: Fe]N 2.02(1) and Fe]S 2.250(1) Å.3,10 Obviously the capability of [9]aneN2S to form Fig. 1 Structure of [VOCl2([9]aneN2S)] Fig. 2 Structure of the [Fe([9]aneN2S)2]2+ ion strong bonds to iron(II) is lower than that of both related, more symmetrical ligands.Iron(II) is in the low-spin state in the complexes of all three nine-membered macrocycles. The apparent symmetry of the cation [Fe([9]aneN2S)2]2+ in the crystal lattice is close to 2/m. This symmetry is incompatible with any of the possible configurations of the three chelate rings. A close inspection of the vibrational ellipsoids showed, however, that the carbon atoms in the N]C]C]N moiety are disordered.The disorder could be resolved by introducing split positions and is caused by the presence of l- and d-configured N,N-chelate rings at a single crystal site. Of the two remaining N,S-chelate rings one displays a d configuration, the other l. An independent determination of the structure of [Fe([9]ane- N2S)2][ClO4]2 has been reported recently.* [Zn([9]aneN2S)2][PF6]2 The reaction of Zn(acac)2 (acac = acetylacetonate) with [9]aneN2S in the ratio 1 : 2 yields the bis-complex [Zn([9]ane- N2S)2]2+, which could be crystallized as its PF6 2 salt.Experiments failed to prepare the mono-complex [ZnCl([9]aneN2S)]+, with four-fold co-ordination of the metal, by reaction of ZnCl2 with [9]aneN2S in the ratio 2 : 1.Instead the compound [Zn([9]- aneN2S)2][ZnCl4] was obtained in high yield. The structures of both the PF6 2 and the [ZnCl4]22 salts have been determined. Fig. 3 shows the cations and Table 3 contains selected bond Table 1 Selected bond lengths (Å) and angles (8) for [VOCl2([9]- aneN2S)]?MeCN V]O V]N(1) V]N(2) Cl(1)]V]Cl(2) N(1)]V]S Cl(1)]V]N(2) N(1)]V]N(2) N(2)]V]S Cl(2)]V]N(1) 1.632(2) 2.153(2) 2.150(2) 95.1(1) 78.6(1) 159.8(1) 78.5(1) 77.6(1) 163.4(1) V]S V]Cl(1) V]Cl(2) O]V]N(1) O]V]N(2) O]V]Cl(1) O]V]Cl(2) O]V]S 2.689(1) 2.337(1) 2.346(1) 95.2(1) 95.9(1) 101.2(1) 99.7(1) 171.7(1) Table 2 Selected bond lengths (Å) and angles (8) for [Fe([9]ane- N2S)2][ClO4]2 and [RhCl3([9]aneN2S)]?H2O [Fe([9]aneN2S)2][ClO4]2 Fe]S Fe]N(1) S]Fe]N(1) S]Fe]N(2) N(1)]Fe]N(2) 2.337(2) 2.072(7) 84.9(2) 84.6(2) 82.5(3) Fe]N(2) S]Fe]N(1a) S]Fe]N(2a) N(1)]Fe]N(2a) 2.063(7) 95.1(2) 95.4(2) 97.5(3) [RhCl3([9]aneN2S)]?H2O Rh]S Rh]N(1) Rh]N(2) S]Rh]Cl(1) S]Rh]Cl(2) Cl(1)]Rh]Cl(2) S]Rh]Cl(3) Cl(2)]Rh]N(1) S]Rh]N(2) Cl(2)]Rh]N(2) N(1)]Rh]N(2) 2.246(1) 2.036(3) 2.040(3) 177.8(1) 89.6(1) 91.3(1) 90.7(1) 93.0(1) 87.6(1) 175.4(1) 83.2(1) Rh]Cl(1) Rh]Cl(2) Rh]Cl(3) Cl(1)]Rh]Cl(3) Cl(2)]Rh]Cl(3) S]Rh]N(1) Cl(1)]Rh]N(1) Cl(3)]Rh]N(1) Cl(1)]Rh]N(2) Cl(3)]Rh]N(2) 2.396(1) 2.368(1) 2.358(1) 91.3(1) 92.8(1) 87.2(1) 90.7(1) 173.8(1) 91.4(1) 90.9(1) * The observed symmetry of [Fe([9]aneN2S)2][ClO4]2 is clearly monoclinic; [Fe([9]aneN2S)2][ClO4]2 and [Mn([9]aneN2S)2][ClO4]2 are isostructural.The assignment of orthorhombic symmetry to the structure of [Mn([9]aneN2S)2][ClO4]2 9 is the reason that the structure seems to be extensively disordered in the anionic and cationic moieties, and that the disorder could not be resolved.J.Chem. Soc., Dalton Trans., 1997, Pages 501–508 503 Fig. 3 Structure of [Zn([9]aneN2S)2]2+ in the [PF6]2 salt (a) and the [ZnCl4]22 salt (b) lengths and angles of both compounds.The Zn]S bond lengths of 2.548(2), 2.550(3) and 2.555(3) Å are very similar in these compounds, but the Zn]N bond lengths seem to be slightly different in the PF6 2 and the ZnCl4 22 salts. The mean values are 2.144 and 2.170 Å, respectively. The effect is probably caused by strong hydrogen bonds between the N]H and Zn]Cl bonds, which connect anions and cations to a three-dimensional net.In the complexes of fourteen-membered azamacrocycles the Zn]N distances vary from 2.03 to 2.19 Å with a mean value of 2.11 Å.11 The bond lengths in the present complexes are close to the upper limit of the specified range. In the [Zn([9]aneS3)2]2+ ion the mean Zn]S bond length is 2.494 Å.12 As in the case of the iron(II) complexes the bond length in the mixed-donor complex is greater than respective bond distance in the homoleptic complex.The structure of the [Zn([9]aneN3)2]2+ ion is so far unknown. In the PF6 2 salt the carbon atoms within the N]C]C]N moiety are disordered. This situation has been discussed above for [Fe([9]aneN2S)2][ClO4]2. The unit cell contains lld and dld configurational isomers at a single site.In the ZnCl4 22 salt the two crystallographically independent complex ions clearly display symmetrical lll or ddd configuration of the chelate rings. Fig. 4 Structure of [RhCl3([9]aneN2S)] [RhCl3([9]aneN2S)]?H2O The compound RhCl3?H2O reacts smoothly with [9]aneN2S to form [RhCl3([9]aneN2S)]?H2O in good yields. The presence of water of crystallization gives rise to rather sharp absorptions at 3510 and 3460 cm21 in its IR spectrum.The NH vibrations are observed at 3210 and 3180 cm21. In the neutral half-sandwich complex [RhCl3([9]aneN2S)], which is displayed in Fig. 4, rhodium( III) is octahedrally co-ordinated by [9]aneN2S and three Cl atoms in a facial arrangement. The three five-membered chelate rings have lll (or ddd) conformation. The Rh]S bond of 2.246(1) Å (see Table 2) is considerably shorter than in the homoleptic rigorously octahedral [Rh([9]aneS3)2]3+,13,14 where bond lengths in the range 2.331(2)– 2.348(2) Å have been observed.Probably a closer approach of the ligand is inhibited in the latter by a large number of nonbonding S ? ? ? S contacts of 3.26 and 3.33 Å. In [RhCl3([9]ane- N2S)]?H2O only two non-bonding S ? ? ? Cl contacts [3.251(1) and 3.276(1) Å] are present. The short Rh]S bond implies some RhÆS back donation.The Rh]S bond also exerts a slight structural trans influence on the Rh]Cl bond which is in the position trans to it. The Rh]Cl(1) bond is longer by 0.033 Å than the average Rh]Cl (cis) distance and this effect may well be caused by the participation of Cl(1) in two hydrogen bonds.The Rh]N bond lengths are 2.036(3) and 2.040(3) Å. For comparison Rh]N bond lengths in the range 2.08 to 2.28 Å have been found in [Rh2H2(m-H)2L2][PF6]2 (L = 1,4,7-trimethyl-1,4,7- triazacyclonane, Me3[9]aneN3).15 In the solid state water of crystallization and complex molecules are interconnected by N]H? ? ? Cl and O]H? ? ? Cl hydrogen bonds. Table 3 Selected bond lengths (Å) and angles (8) for [Zn([9]ane- N2S)2][PF6]2 and [Zn([9]aneN2S)2][ZnCl4] [Zn([9]aneN2S)2][PF6]2 [Zn([9]aneN2S)2][ZnCl4] Zn]S(1) Zn]N(1) Zn]N(2) S(1)]Zn]N(1) S(1)]Zn]N(2) S(1)]Zn]N(1a) S(1)]Zn]N(2a) N(1)]Zn]N(2) N(1)]Zn]N(2a) 2.548(2) 2.160(5) 2.149(5) 82.7(1) 82.6(1) 97.3(1) 97.4(1) 81.6(2) 98.4(2) 2.550(3) 2.206(6) 2.162(6) 82.4(2) 84.2(2) 97.6(2) 95.8(2) 79.7(2) 100.3(2) 2.555(3) 2.159(8) 2.153(7) 83.5(2) 83.6(2) 96.5(2) 96.4(2) 81.0(3) 99.0(3)504 J.Chem. Soc., Dalton Trans., 1997, Pages 501–508 [Ru(cym)([9]aneN2S)][BPh4]Cl2?MeCN (cym = p-cymene) Homoleptic ruthenium complexes of [9]aneN3,16,17 Me3[9]aneN3 18,19 and [9]aneS3 20–22 have been known for a long time. More recently half-sandwich complexes with these ligands, e.g. [Ru(cym)([9]aneN3)]2+ have been studied.23–25 Apart from structural interests some of the complexes show intriguing reactivities.The mixed-sandwich complex [Ru(cym)([9]- aneN2S)][BPh4]Cl2?MeCN was obtained by reaction of [{RuCl2(cym)}2] with [9]aneN2S in methanol. Ruthenium(II) was converted to ruthenium(III) during this reaction by aerial oxidation. The structure of [Ru(cym)([9]aneN2S)]3+ is shown in Fig. 5; Table 4 contains selected bond lengths and angles.The Ru]S and Ru]N bond lengths are 2.324(2), 2.120(7) and 2.105(7) Å, respectively. The observed RuIII]S bond length is slightly shorter than in [Ru([9]aneS3)2]2+.20–22 In the half-sandwich complexes [Ru([9]aneS3)L3]n+ (L = MeCN, Cl, PPh3, PMe2Ph, PEtPh2 or CO) and others, significantly shorter Ru]S distances were found.24,25 Missing S ? ? ? S non-bonding interactions as well as the nature of the coligands may account for this.As a consequence of the smaller radius of ruthenium(III) compared to ruthenium(II) the Ru]N bond lengths in [Ru(cym)([9]- aneN2S)]3+ and [Ru(cym)([9]aneN3)]2+ differ slightly. The macrocycle [9]aneN2S displays a lll (or ddd) configuration in the former. As in the starting compound p-cymene is h6 coordinated to the metal centre.The Ru]C bond lengths vary in the small range 2.196(7)–2.233(8) Å, with a mean distance of 2.214 Å. The complex cation displays approximately mirror Fig. 5 Structure of [Ru(cym)([9]aneN2S)][BPh4]Cl2?MeCN symmetry. Three of the carbon atoms of the phenyl ring and the three macrocyclic donor atoms are eclipsed looking down the pseudo-three-fold axes of the complex.[ReO3([9]aneN2S)][ReO4] It has been shown26–28 that [9]aneN3 and [9]aneS3 were able to form complexes with metals in very high oxidation sates. We prepared the rhenium(VII) half-sandwich complex of [9]aneN2S by reaction of dirhenium heptaoxide with the unco-ordinated macrocycle in tetrahydrofuran (thf) as described by Herrmann et al.27 The compound was obtained in good yield, but attempts to grow single crystals failed.Its identity was proven by elemental analysis, IR and Raman spectroscopy, which gave the most valuable information. The two strong, well resolved bands 972 and 964 cm21 in the Raman spectrum have equal intensity and are assigned to the symmetric stretching vibration of the ReO3 + and the ReO4 2 groups, respectively.The IR spectrum shows a broad and intense absorption at 910 cm21 with a shoulder at approximately 930 cm21. We assign these bands to the asymmetric stretching vibrations of the ReO4 2 and the ReO3 + moieties. In [ReO3([9]aneN3)][ReO4] and [ReO3([9]aneS3)][ReO4] the relevant vibrations (IR spectra only) have been observed at 935 and 909, 921 and 912 cm21, respectively.Recrystallization of [ReO3([9]aneN2S)][ReO4] from water yields the salts [H2([9]- aneN2S)][ReO4]2 and [H([9]aneN2S)][ReO4], depending on the pH. Their crystal structures have been determined.29 Table 4 Selected bond lengths (Å) and angles (8) for [Ru(cym)([9]ane- N2S)][BPh4]Cl2?MeCN and [Tl([9]aneN2S)][ClO4] [Ru(cym)([9]aneN2S)][BPh4]Cl2?MeCN Ru]N(1) Ru]N(2) Ru]C(9) Ru]C(11) Ru]C(12) 2.120(7) 2.105(7) 2.196(7) 2.205(7) 2.213(8) Ru]C(7) Ru]C(10) Ru]C(8) Ru]S 2.216(8) 2.222(7) 2.233(8) 2.324(2) N(2)]Ru]N(1) N(2)]Ru]S N(1)]Ru]S C(9)]Ru]S C(11)]Ru]S 79.4(3) 83.2(2) 82.8(2) 138.5(3) 137.2(2) C(12)]Ru]S C(7)]Ru]S C(10)]Ru]S C(8)]Ru]S 104.3(2) 90.1(2) 170.3(2) 104.7(2) [Tl([9]aneN2S)][ClO4] Tl(1)]N(1) Tl(1)]N(2) Tl(1)]S(1) 2.68(2) 2.66(2) 2.920(8) Tl(2)]N(3) Tl(2)]N(4) Tl(2)]S(2) 2.60(2) 2.26(2) 2.955(7) N(2)]Tl(1)]N(1) N(2)]Tl(1)]S(1) N(1)]Tl(1)]S(1) 65.8(7) 68.7(5) 68.5(6) N(3)]Tl(2)]S(2) N(4)]Tl(2)]S(2) N(3)]Tl(2)]N(4) 68.3(4) 68.6(4) 67.2(6) Fig. 6 Structure of [Tl([9]aneN2S)][ClO4]J. Chem. Soc., Dalton Trans., 1997, Pages 501–508 505 [Tl([9]aneN2S)][ClO4] So far mainly transition-metal complexes of [9]aneN2S have been described, whereas from the related nine-membered ligands a number of complexes with p block metal ions have been reported, e.g.[Pb([9]aneN3)]X2 (X = ClO4 or NO3),30 [Tl(Me3[9]aneN3)][PF6] 31 and [Tl([9]aneS3)][PF6].32 The structure of the latter is dominated by secondary Tl ? ? ? S interactions. The complex [Tl([9]aneN2S)][ClO4] was prepared from thallium(I) carbonate in methanol and recrystallized from water.In order to establish the connectivity and stereochemistry a structure determination was performed. The structure is composed of two slightly different ion pairs [Ti([9]aneN2S)]+ and ClO4 2 in the asymmetric unit. Their structure is shown in Fig. 6 and selected bond lengths and angles are given in Table 4. The macrocycle [9]aneN2S is bound facially to the metal centres, with Tl(1)]S(1) 2.920(8) and Tl(2)]S(2) 2.955(7) Å.The Tl]S bond lengths are less than the sum of the ionic radii of 3.34 Å and significantly less than the values of 3.092(3)–3.114(3) Å, found in [Tl([9]aneS3)]PF6,32 thus suggesting substantial covalency. In addition to the primary co-ordination, there is a weak secondary interaction via exodentate co-ordination between S(1) and Tl(2), Tl(2)]S(1a) 3.761(3) Å.The Tl]N bond lengths at Tl(1) and Tl(2) differ slightly. The mean value exceeds the Tl]N bond lengths in [Tl(Me3[9]aneN3)][PF6] by 0.04 to 0.08 Å. The X]Tl]Y angles (X,Y = N,S) are substantially narrower than those observed in the transition-metal complexes and reflect the large size of the Tl+ cation. The atom Tl(1) is five-co-ordinate, if one includes intermolecular contacts at 3.179 and 3.347 Å to two oxygen atoms of the perchlorate ion, whereas Tl(2) is six-co-ordinate including contacts to oxygen atoms of the second perchlorate ion at 3.310 and 3.406 Å, and the exodentate interaction mentioned above.Atom Tl(1) is pseudo-octahedrally co-ordinated and Tl(2) is situated in a pseudo-pentagonal bipyramidal environment.At both metal centres the lone pair has a very distinct stereochemical influence. In both polyhedra all five, respectively six donor atoms are situated at the same side with respect to the Fig. 7 Co-ordination around Tl(1) and Tl(2) in [Tl([9]aneN2S)][ClO4] metal centres (see Fig. 7). The shortest Tl(1) ? ? ? T1(2) distance is 4.22 Å and [9]aneN2S displays a lll (or ddd) configuration in both cations. Conclusion The macrocycle [9]aneN2S forms stable 1 : 1 and 1 : 2 complexes with a variety of main-group and transition metals in oxidation states I to VII. In the bis-complexes of 3d elements the metal– nitrogen and metal–sulfur bond lengths generally exceed the bond lengths in the corresponding homoleptic complexes of [9]aneN3 and [9]aneS3.Obviously the more symmetrical structure of these ligands, with equal distances between the donor atoms, allows a closer approach of these atoms towards the metal centre.For metal ions with larger radii, e.g. TlI, we observed a different situation. Here the metal–sulfur distance in the complexes of [9]aneN2S is equal to or even smaller than that in the complexes of [9]aneS3. The conformational strain exerted upon [9]aneN2S upon co-ordination increases with decreasing radii of the metal ions.This is evident in the C]N]C angles and the X]C]C]X torsion angles. In this respect it is also interesting to compare the difference between the metal–nitrogen and the metal–sulfur bond lengths D(M]S, M]N) in the complexes studied. This value changes from 0.21 Å in [RhCl3([9]aneN2S)]? H2O and [Ru(cym)([9]aneN2S)][BPh4]Cl2?MeCN to 0.39–0.40 Å in [Mn([9]aneN2S)2][ClO4]2 and [Zn([9]aneN2S)2][PF6]2.We observed both lll and ldl (the two rings coupled by the S atom have opposite chiralities) conformations of the three chelate rings formed. The conformational behaviour is independent of the metal-to-donor-atom bond lengths, D(M]S or of M]N). The conformation actually adopted seems to depend upon external forces.4 Experimental CAUTION: Perchlorate salts are potentially explosive and should be handled with care.All chemicals used for the preparative work were of standard reagent grade quality and were used without further purification. Preparations 1-Thia-4,7-diazacyclononane ([9]aneN2S). The macrocycle was prepared as described earlier2 and stored as [9]aneN2S?2HBr.[VOCl2([9]aneN2S)]?MeCN. A solution of [9]aneN2S (146 mg, 1 mmol) in acetonitrile (20 cm3) was added to a boiling solution of VCl3 (157 mg, 1 mmol) in acetonitrile (30 cm3). The reaction mixture was refluxed for 30 min under N2, then filtered and cooled to 215 8C. Within a week light blue crystals of [VOCl2([9]aneN2S)]?MeCN (120 mg, 42%) separated, which loose solvent in air (Found: C, 24.7; H, 4.9; N, 9.9.Solventfree C6H14Cl2N2OSV requires C, 25.4; H, 4.95; N, 9.85%). n& max/ cm21 (KBr disc): 3240s, 3200s (NH), 1020s, 985vs (VO), 946s, 791m, 354m, 275s (VCl). lmax/nm (e/dm3 mol21 cm21) (EtOH): 362 (67), 505 (21) and 670 (63). [Mn([9]aneN2S)2][ClO4]2. To a solution of [9]aneN2S (293 mg, 2 mmol) in methanol (50 cm3) was added a solution of manganese perchlorate (300 mg, 2 mmol) in methanol (20 cm3).The combined solutions were stirred for a further 30 min under N2. The compound crystallized upon standing at 220 8C as tiny air-sensitive needles (340 mg, 60%) (Found: C, 26.30; H, 5.25; N, 10.00. C12H28Cl2MnN4O8S2 requires C, 26.40; H, 5.15; N, 10.25%). n& max/cm21 (KBr disc): 3280s, 3130vs (br) (NH), 1090vs (vbr) (ClO), 800m, 635s, 625vs (ClO).[Fe([9]aneN2S)2][ClO4]2. Under Ar a solution of [9]aneN2S (150 mg, 1 mmol) in CHCl3 was added to a solution of iron(II)506 J. Chem. Soc., Dalton Trans., 1997, Pages 501–508 Table 5 Crystallographic data for the VIV, FeII, ZnII, RhIII, RuIIIand TlI complexes Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 m/mm21 F(000) Crystal size/mm 2q range/8 Data collected Unique data Data with Fo > 4s(Fo) Absorption correction Parameters refined g in weighting scheme RR 9 Dr(max.)/e Å23 C6H14Cl2N2OSV 325.1 Monoclinic P21/c 12.429(2) 7.270(1) 15.555(3) — 102.86(3) — 1370.3 4 1.576 1.226 668 0.1 × 0.12 × 0.18 4–54 3404 3012 2138 y scan 213 0.0002 0.029 0.029 0.84 C12H28Cl2FeN4O8S2 547.3 Monoclinic P21/c 8.079(2) 8.636(2) 14.960(4) — 90.01(2) — 1043.8 2 1.74 1.218 568 0.1 × 0.2 × 0.13 4–54 2291 1933 1139 — 169 0.0004 0.0613 0.0686 0.65 C12H28F12N4S2P2Zn 647.8 Monoclinic P21/c 7.315(1) 16.899(3) 9.469(2) — 95.78(3) — 1164.6 2 1.85 1.490 656 0.1 × 0.15 × 0.18 4–54 2704 2512 1791 y scan 151 0.0004 0.059 0.073 0.63 C12H28Cl4N4S2Zn2 1130.0 Monoclinic P21/c 17.647(4) 8.116(2) 16.790(3) — 117.06(8) — 2141.5 4 1.753 2.994 1152 0.2 × 0.1 × 0.08 4–54 3677 3559 2257 y scan 220 0.0003 0.050 0.047 0.84 C6H16Cl3N2ORhS 373.5 Triclinic P1� 7.304(1) 7.919(2) 10.475(2) 86.55(3) 89.44(3) 88.11(3) 604.4 2 2.05 2.200 372 0.1 × 0.15 × 0.15 4–54 2453 2270 2139 y scan 191 0.0002 0.023 0.029 0.66 C42H51BCl2N3RuS 812.7 Triclinic P1� 9.711(2) 11.006(2) 19.414(4) 74.14(3) 87.54(3) 89.72(3) 1994.1 2 1.289 0.608 806 0.05 × 0.06 × 0.17 4–54 9208 8688 4597 — 213 — 0.075(R1) 0.226(wR2) 1.07 C12H28Cl2N4O8S2Tl 900.1 Monoclinic P21/c 13.520(3) 7.577(2) 23.353(5) — 91.73(3) — 2448 4 2.44 13.58 1680 0.2 × 0.11 × 0.12 4–54 4656 4534 2231 — 220 — 0.099(R1) 0.27(wR2) 3.86 R = S |Fo| 2 |Fc| /S|Fo|, R9 = S|[w(Fo 2 Fc)]� �� |/S[w|Fo|]� �� , R1 = S |Fo| 2 |Fc| /S|Fo|, wR2 = S[w(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� .J.Chem. Soc., Dalton Trans., 1997, Pages 501–508 507 perchlorate (360 mg, 1 mmol) in ethanol (30 cm3). The resulting green precipitate of [Fe([9]aneN2S)2][ClO4]2 (250 mg, 92%) was filtered off (Found: C, 27.25; H, 5.50; N, 9.70. C12H28Cl2FeN4O8S2 requires C, 26.35; H, 5.15; N, 10.25%). n& max/ cm21 (KBr disc): 3268s, 3104s (NH), 1090vs (br) (ClO), 625s (ClO). Single crystals of X-ray quality were obtained by slow diffusion of concentrated solutions of iron(II) perchlorate and the macrocycle.[Zn([9]aneN2S)2][PF6]2. To a solution of zinc acetylacetonate (400 mg, 15 mmol) in methanol (30 cm3) was added a solution of [9]aneN2S (450 mg, 3 mmol) in methanol (10 cm3). The clear solution was stirred for 1 h.Then NaPF6 (1 g) was added to precipitate [Zn([9]aneN2S)2][PF6]2 as a white solid (330 mg, 58%) (Found: C, 22.20; H, 4.15; N, 8.70. C12H28F12N4S2P2Zn requires C, 22.20; H, 4.30; N, 8.65%). n& max/cm21 (KBr disc): 3310vs, 3110m (NH), 830vs (br) (PF), 550s (PF). [Ru(cym)([9]aneN2S)][BPh4]Cl2?MeCN. A methanolic (10 cm3) solution of [9]aneN2S (292 mg, 2 mmol) was added to a solution of [{RuCl2(cym)}2] (306 mg, 0.5 mmol) in methanol (30 cm3).During this procedure the colour changed from redorange to dark green. The reaction was stirred for a further 0.5 h and then a concentrated solution of potassium tetraphenylborate (680 mg, 2 mmol) in methanol was added. The light green precipitate which formed was filtered off and recrystallized from acetonitrile to yield (620 mg, 80%) colourless crystals (Found: C, 61.65; H, 5.90; N, 4.90.C42H51BCl2N3RuS requires C, 62.05; H, 6.30; N, 5.15%). n& max/cm21 (KBr disc): 3241m (NH), 3053s (CHaryl), 735s, 710s (CHaryl). [ReO3([9]aneN2S)][ReO4]. To a solution of dirhenium heptaoxide (242.2 mg, 0.5 mmol) in tetrahydrofuran (10 cm3) was added a solution of [9]aneN2S (73.1 mg, 0.5 mmol) in the same amount of tetrahydrofuran to afford a white solid.This was filtered off and dried in vacuo (280 mg, 80%) (Found: C,11.45; H, 2.30; N, 4.40. C6H12N2O7Re2S requires C, 11.45; H, 2.25; N, 4.45%). n& max/cm21 (KBr disc): 2980–2700m (CH), 1440m, 1420m (CH), 930vs (sh), 910vs (br) (ReO), 360m, 350m (ReO). Raman spectrum: 972vs [nsym(ReO3)], 964vs cm21 [nsym(ReO4)]. [RhCl3([9]aneN2S)]?H2O. Combined solutions of [9]aneN2S (300 mg, 1.6 mmol) in ethanol (10 cm3) and rhodium trichloride hydrate (130 mg, 0.57 mmol) in ethanol (20 cm3) were refluxed for 0.5 h.Upon cooling a light brown solid precipitated from the clear solution. It was recrystallized from water to give yellow-orange crystals of [RhCl3([9]aneN2S)]?H2O (380 mg, 70%) (Found: C, 19.25; H, 4.30; N, 7.60.C6H16Cl3N2ORhS requires C, 19.30; H, 4.30; N, 7.50%). n& max/cm21 (KBr disc): 3510m, 3460m (OH), 3210vs, 3180vs (NH), ca. 900, ca. 300 (RhCl). [Tl([9]aneN2S)][ClO4]. To a solution of thallium(I) carbonate (500 mg, 1 mmol) in water (50 cm3) was added a solution of [9]aneN2S (750 mg, 5 mmol) in methanol (40 cm3) and solid NaClO4 (10 mg, 8.2 mmol). The solution was concentrated slightly. White crystals of [Tl([9]aneN2S)][ClO4] (250 mg, 55%) appeared within a few hours (Found: C, 16.0; H, 3.15; N, 6.05.C6H14ClN2O4STl requires C, 16.0; H, 3.15; N, 6.20%). n& max/cm21 (KBr disc): 3310m (br), 3220s (NH), 1160vs (br), 625s (ClO). Single-crystal structure determinations Details of the crystal data, data collection and processing, and structure analysis are given in Table 5.The data for [VOCl2([9]- aneN2S)]?MeCN and [Ru(cym)([9]aneN2S)][BPh4]Cl2 were collected at 80 K using a Siemens R3m/V diffractometer, the data for the remaining compounds at ambient temperature by using an Enraf-Nonius CAD4 diffractometer, both equipped with graphite-monochromated Mo-Ka radiation (l = 0.710 73 Å). Lattice parameters were determined by least-squares fits to the setting parameters of 15–25 reflections.The structures were solved by Patterson methods (SHELXTL PLUS33 program packages) and developed by iterative cycles of full-matrix leastsquares anisotropic refinement for all non-hydrogen atoms and Fourier-difference syntheses. Except for the complexes of RuIII and Tl, the quantity minimized was Sw(Fo 2 Fc)2 with the weighting scheme w21 = s2(Fo) + gFo 2 (for g values see Table 5).The structures of [Ru(cym)([9]aneN2S)][BPh4]Cl2 and [Tl([9]- aneN2S)][ClO4] were refined on F 2 using the program SHELXL.34 In the structure of the former three of the four phenyl substituents of the [BPh4]2 ion and the solvent molecule MeCN are disordered over two positions in the ratio 1 : 1. The disorder in the structure of [Fe([9]aneN2S)2][ClO4]2 could be resolved by introducing split positions for two carbon atoms (see above) and for two oxygen atoms of the ClO4 2 ion.Hydrogen atoms were localized in difference syntheses for [VOCl2([9]- aneN2S)]?MeCN and [RhCl3([9]ane- N2S)]?H2O and were placed for the remaining compounds in idealized positions with isotropic thermal parameters fixed at 0.08 Å2.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 186/340. Physical measurements Infrared spectra were measured on a Perkin-Elmer PE 683 instrument, Raman spectra on a Bruker IFS FT-Raman Module FRA 66 and EPR spectra on a Bruker ESP 300 X-band spectrometer.The UV/VIS spectra were recorded on solutions using a Shimadzu UV-3100 spectrometer. Microanalyses were performed by the Institute of Organic Chemistry of the Westfälische Wilhelms-University. Acknowledgements We thank the Fonds der Chemischen Industrie for financial support. References 1 P.Chaudhuri and K. Wieghardt, Prog. Inorg. Chem., 1987, 35, 329; S. R. Cooper and S. C. Rawle, Struct. Bonding (Berlin), 1990, 72, 1; A. J. Blake and M. Schröder, Adv. Inorg. Chem., 1990, 35, 1. 2 P. Hoffmann, A. Steinhoff and R. Mattes, Z. Naturforsch., Teil B, 1987, 42, 867; P. Hoffmann and R. Mattes, Z. Naturforsch., Teil B, 1988, 43, 261; P.Hoffmann, F.-J. Hermes and R. Mattes, Z. Naturforsch., Teil B, 1988, 43, 567; P. Hoffmann and R. Mattes, Inorg. Chem., 1989, 28, 2092; K. Wasielewski and R. Mattes, Acta Crystallogr., Sect. C, 1990, 46, 1826; U. Heinzel and R. Mattes, Polyhedron, 1991, 10, 19; U. Heinzel and R. Mattes, Polyhedron, 1992, 11, 597; U. Heinzel and R. Mattes, Inorg.Chim. Acta, 1992, 194, 157. 3 S. M. Hart, J. C. A. Boeyens, J. P. Michael and R. D. Hancock, J. Chem. Soc., Dalton Trans., 1983, 1601; M. Nonoyama and T. Ishida, Transition Met. Chem., 1984, 9, 367; L. Fabbrizzi and D. M. Proserpio, J. Chem. Soc., Dalton Trans., 1989, 229; J. C. A. Boeyens, S. M. Dobson and R. D. Hancock, Inorg. Chem., 1985, 24, 3073; R. D. Hancock, S. M. Dobson and J.C. A. Boeyens, Inorg. Chim. Acta, 1987, 133, 221; D. M. Wambeke, W. Lippens, G. G. Hermann, A. M. Goeminne and G. P. van der Kelen, Po89. 4 L. R. Gahan, T. W. Hambley, G. H. Searle, M. J. Bjerrum and E. Larsen, Inorg. Chim. Acta, 1988, 147, 17; T. W. Hambley, L. R. Gahan and G. H. Searle, Acta Crystallogr., Sect. C, 1989, 45, 864. 5 A. McAuley and S. Subramanian, Inorg.Chem., 1990, 29, 2830; A. J. Blake, R. D. Crofts, B. de Groot and M. Schröder, J. Chem. Soc., Dalton Trans., 1993, 485; I. A. Kahwa, D. Miller, M. Mitchel and F. R. Fronczek, Acta Crystallogr., Sect. C, 1993, 49, 320. 6 R. Bentfeld, N. Ehlers and R. Mattes, Chem. Ber., 1995, 128, 1199. 7 G. R. Willey, M. T. Lakin and N. W. Alcock, J. Chem. Soc., Chem. Commun., 1991, 1414.508 J.Chem. Soc., Dalton Trans., 1997, Pages 501–508 8 K. Wieghardt, U. Bossek, K. Volckmar, W. Swiridoff and J. Weiss, Inorg. Chem., 1984, 23, 1387. 9 L. R. Gahan, V. A. Grillo, T. W. Hambley, G. R. Hanson, C. J. Hawkins, E. M. Proudfoot, B. Moubaraki, K. S. Murray and D. Wang, Inorg. Chem., 1996, 35, 1039. 10 H.-J. Küppers, K. Wieghardt, Y.-H. Tsay, C. Krüger, B.Nuber and J. Weiss, Angew. Chem., 1987, 99, 583; Angew. Chem., Int. Ed. Engl., 1987, 26, 575. 11 R. Feldhaus, J. Köppe and R. Mattes, Z. Naturforsch., Teil B, 1996, 51, 869. 12 H.-J. Küppers and K. Wieghardt, Z. Anorg. Allg. Chem., 1989, 577, 155. 13 S. C. Rawle, R. Yagbasan, K. Prout and S. R. Cooper, J. Am. Chem. Soc., 1987, 109, 6181. 14 A. J. Blake, R. O. Gould, A. J. Holder, T.I. Hyde and M. Schröder, J. Chem. Soc., Dalton Trans., 1988, 1861. 15 D. Hanke, K. Wieghardt, B. Nuber, R.-S. Lu, R. K. McMullan, T. F. Koetzle and R. Bau, Inorg. Chem., 1993, 32, 4300. 16 K. Wieghardt, W. Herrmann, M. Köppen, I. Jibril and G. Huttner, Z. Naturforsch., Teil B, 1984, 39, 1335. 17 P. Bernhard and A. M. Sargeson, Inorg. Chem., 1988, 27, 2582. 18 P. Neubold, K. Wieghardt, B.Nuber and J. Weiss, Angew. Chem., 1988, 100, 990; Angew. Chem., Int. Ed. Engl., 1988, 27, 933. 19 P. Neubold, K. Wieghardt, B. Nuber and J. Weiss, Inorg. Chem., 1989, 28, 459. 20 S. C. Rawle and S. R. Cooper, J. Chem. Soc., Chem. Commun., 1987, 308. 21 S. C. Rawle, T. J. Sewell and S. R. Cooper, Inorg. Chem., 1987, 26, 3769. 22 M. N. Bell, A. J. Blake, A. J. Holder, T. I. Hyde and M. Schröder, J. Chem. Soc., Dalton Trans., 1990, 3841. 23 S.-M. Yang, W.-C. Cheng, S.-M. Peng, K.-K. Cheung and C.-M. Che, J. Chem. Soc., Dalton Trans., 1995, 2955 and refs. therein. 24 S. R. Cooper, Acc. Chem. Res., 1988, 21, 141. 25 A. J. Blake, R. M. Christie, Y. V. Roberts, M. J. Sullivan, M. Schröder and L. J. Yellowlees, J. Chem. Soc., Chem. Commun., 1992, 848; A. F. Hill, N. W. Alcock, J. C. Cannadine and G. R. Clark, J. Organomet. Chem., 1992, 426, C40; N. W. Alcock, J. C. Cannadine, G. R. Clark and A. F. Hill, J. Chem. Soc., Dalton Trans., 1993, 1131; J. C. Cannadine, A. Hector and A. F. Hill, Organometallics, 1992, 11, 2323; C. Landgrafe and W. S. Sheldrick, J. Chem. Soc., Dalton Trans., 1994, 1885. 26 H.-J. Küppers, B. Nuber, J. Weiss and S. R. Cooper, J. Chem. Soc., Chem. Commun., 1990, 979. 27 W. A. Herrmann, P. W. Roesky, F. E. Kühn, W. Scherer and M. Kleine, Angew. Chem., 1993, 105, 1768; Angew. Chem., Int. Ed. Engl., 1993, 32, 1714. 28 K. Wieghardt, C. Pomp, B. Nuber and J. Weiss, Inorg. Chem., 1986, 25, 1659. 29 A. Henke, Ph.D. Dissertation, University of Münster, 1994. 30 K. Wieghardt, M. Kleine-Boymann, B. Nuber, J. Weiss, L. Zsolnai and G. Huttner, Inorg. Chem., 1986, 25, 1647. 31 K. Wieghardt, M. Kleine-Boymann, B. Nuber and J. Weiss, Inorg. Chem., 1985, 25, 1664. 32 A. J. Blake, J. A. Greig and M. Schröder, J. Chem. Soc., Dalton Trans., 1991, 529. 33 G. M. Sheldrick, SHELXTL PLUS, Program package for structure solution and refinement, Version 4.2, Siemens Analytical Instruments Inc., Madison, W1, 1990. 34 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993. Received 30th August 1996; Paper 6/05999F

ISSN:1477-9226    

DOI:10.1039/a605999f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON PERSPECTIVE J. Chem. Soc., Dalton Trans., 1999, 509–516 509 The figure-of-eight twist to macrocycles: preorganization, self-organization and dynamics Peter Comba,* Andreas Kühner and Alexander Peters Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany. Fax: 149 (6221) 54 66 17. E-mail: comba@akcomba.oci.uni-heidelberg.de Received 3rd August 1998, Accepted 30th October 1998 Large macrocyclic rings (30- to 36-membered) with two dithiadiimine donor sets and two para- or meta-phenylene spacer groups undergo copper(I) induced folding with � stacking of the two benzene spacer groups.The type of folding (twisted to a helical or squeezed to an achiral macrocyclic shape) and the stability of the dicopper(I) compounds are analysed as a function of the ligand structure, the solid state structures, solution equilibria and dynamics and the comparison of the observed data with computed structures and conformational equilibria.Preliminary preparative studies suggest that derivatives with the observed structural motifs may be used to build heterometallic oligonuclear arrays. 1 Introduction The metal ion-induced assembly of ligand molecules to give distinct structures is known as complex formation; Alfred Werners co-ordination theory 1 was the basis for a development that has led us to an understanding of the directionality of the interactions involving transition metal centers and of ways to design ligands that may be used to construct arrays of transition metal ions and ligand molecules with distinct topological features.Thus, self-assembly and self-organization processes that involve transition metal ions are often simple complex formation reactions, and the orientation of relatively rigid ligands around metal ions has been used extensively to produce co-ordination compounds with specific structural features.2 Polytopic ligands have been designed to produce oligonuclear arrays with regular and aesthetically satisfying structures.Polypyridine-based ligands have been of particular importance, due to the photophysical properties of some of the corresponding transition metal complexes [specifically those of ruthenium(II)],3,4 due to their increasing availability and to their Peter Comba (born in 1953) obtained a diploma in chemistry and in chemical education from the ETH Zürich and a PhD from the Université de Neuchâtel [base hydrolysis of cobalt(III) pentaamines, Werner Marty].He made preparative, structural and spectroscopic studies on transition metal hexaamine cage compounds with Alan Sargeson in Canberra and NMR studies on titanyl and decavanadate with André Merbach in Lausanne before setting up his own research group in Basel and later in Heidelberg. Two sabbaticals were used to start projects on single crystal spectroscopy and angular overlap model (AOM) calculations (with Michael Hitchman in Hobart) and on blue copper proteins (with Gerard Canters in Leiden). Peter’s research is based on classical co-ordination chemistry with projects that range from bioinorganic chemistry (metalloproteins and model compounds) to structural, spectroscopic, electrochemical and mechanistic studies, and that also include applications such as metal ion selectivity and catalysis. New approaches to molecular modeling of inorganic compounds have been developed, and these are used extensively for the design of new compounds and for the determination of structures in solution.Andreas Kühner (born in 1968) obtained his diploma and PhD from Heidelberg University. Currently, he has a position with Merck (Darmstadt). Andreas’ main preparative achievements in Heidelberg were the development of a new method for the synthesis of tetrathiamacrocyclic ligands and the preparation of a series of new ligands with ferrocenyl end groups. He also developed a new molecular mechanics based approach for the quantification of the preorganization of macrocyclic ligands.Andreas’ main scientific activity for his PhD in Peter’s research group was the study of the solution structure and dynamics of the helical dicopper(I) compounds by NMR spectroscopy and molecular modeling. Alexander Peters (born in 1969) obtained his diploma from Heidelberg Universtity and is now doing research work for his PhD thesis in Peter’s group. Alex has done a beautiful mechanistic study on the ring contraction of tetrathiamacrocyclic ligands.He was involved in the synthesis of the ligands with the ferrocenyl end groups and also in structural studies on dicopper(II) compounds that included solid state structures, solution structures based on EPR spectra and molecular modeling. His main area of interest now is metal–metal interactions, and he develops ligand systems that bind RuII/III as well as CuI/II. Peter Comba Andreas Kühner Alexander Peters510 J. Chem.Soc., Dalton Trans., 1999, 509–516 rigidity and the emerging structural and molecular properties. 2,5,6 There is an increasing literature on molecular devices based on self-assembled ladders, grids, wires, metallacycles, polyhedra and helicates.2,5–10 Metal ion-induced helicity, in particular, has attracted much attention because helicity is an important structural element in biological systems. The large majority of reported helicates is based on polypyridine derivatives,11–22 and there are relatively few systems where the solution structural properties and the dynamic behavior have been studied in detail.15 Exceptions include recent reports on helical titanium(IV) catecholate compounds23 and on six-coordinated cobalt(II), nickel(II) and zinc(II) compounds of a macrocyclic SchiV base ligand.24 In both of these examples solution NMR studies have been used to confirm the conservation of the observed solid state structural features, and temperature-dependent NMR studies have been used to analyse dynamic processes in solution.Recently, a new type of macrocyclic SchiV base compound with (N2S2)2 (bis-dithiadiimine) donor sets has been reported which, upon co-ordination to two copper(I) ions, leads to double helical figure-of-eight shaped folding (see Chart 1).25–29 The solid state structural properties of these dicopper(I) compounds have been studied as a function of the chelate ring sizes and the substitution pattern of the phenylene spacer groups (see Table 1).28 A preorganized ligand, based on a tetrasubstituted paracyclophane anchor group, has also been prepared and studied for comparison (Table 1).27 The solution structures and dynamics have been investigated with high-field and variable temperature 1H NMR spectroscopy, respectively.28 The experimentally determined isomer and conformer equilibria have been compared to the computed ratios based on force field calculations.29 The mechanisms for the isomerization and racemization processes are discussed on the basis of the observed and the computed data, and these have some implication on the understanding of the redox stability of these compounds and on the stereochemistry and dynamics of other compounds in the areas of supramolecular and biological systems.Folded macrocyclic structures are also observed in some cyclic peptides (e.g. Cyclosporin A, Ascidiacylamide, Patellamide D) and their metal complexes.30–34 The unique properties of these macrocycles and their metal complexes, occurring in bacteria, fungi, plants and marine organisms, have been related to the folding of the macrocyclic rings, and the results of our figure-of-eight-twisted system might have some implication in that area.Chart 1 2 Solid state structures The structure of the molecular cation of the dicopper(I) compound of the helically preorganized ligand with the paracyclophane anchor group (phane-222, see Table 1), based on X-ray crystallography, is shown in Fig. 1.27 The copper(I)–donor distances and the valence angles around the metal centers and the donor groups (see Table 2 for the relevant structural data) are as expected for this type of co-ordination compound, that is the observed geometry is relatively unstrained and, therefore, the paracyclophane anchor gro might not be required for the folding to a figure-of-eight shaped geometry of this type of ligand.Indeed, the geometry of the dicopper(I) product of the large macrocyclic ligand para-222 (32-membered macrocycle), whose experimental structure is also given in Fig. 1,26 is very similar: the main and expected diVerences are a decrease in the distance between the aromatic rings for the paracyclophane derivative, due to the ethylene bridges, and a concomitant small increase in the copper(I)–copper(I) distance (see Table 2). Thus, a preorganization with the synthetically demanding paracyclophane anchor group is not required for the helical figure-ofeight shaped folding.An interesting feature is that copper(I) induced folding of the isomer of para-222 with meta- instead of para-phenylene spacer groups, meta-222 (30- instead of 32-membered macrocycle), leads to a similar shape of the ligand backbone [the experimental structure of the dicopper(I) compound of meta-222 is also presented in Fig. 1].26 The copper(I) co-ordination geometries, the copper(I)–copper(I) distances and the relative orientation of the two aromatic rings are very similar (see also Table 2) but the [Cu2(meta-222)]21 structure is achiral (“squeezed” instead of “twisted” macrocyclic ring, see Chart 2).All other Table 1 Nomenclature of the ligands Name para-222 para-222-Me para-222-OMe para-phane-222 para-Ph2Ph para-232 para-242 para-323 para-333 meta-222 ma,b (CH2)2 (CH2)2 (CH2)2 (CH2)2 5 (CH2)2 (CH2)2 (CH2)3 (CH2)3 (CH2)2 n a (CH2)2 (CH2)2 (CH2)2 (CH2)2 (CH2)2 (CH2)3 (CH2)4 (CH2)2 (CH2)3 (CH2)2 spacer b 1236111114 a See Chart 1.b Spacer groups (1)–(6) are shown below. Table 2 Structural parameters (bond lengths in Å, angles in 8) of the chromophores of the dicopper(I) compounds of Fig. 1 Cu–S Cu–N Cu ? ? ? Cu S–Cu–S S–Cu–N S–Cu–Nbite N–Cu–N para-222 2.38(2) 2.01(8) 7.83 91.0(4) 115.1(37) 90.8(18) 144.1(42) meta-222 2.43(1) 1.99(1) 8.15 88.2 113.3(24) 89.7(6) 148.5 phane-222 2.38(2) 1.96(1) 8.22 91.51(2) 117.4(14) 90.2(6) 141.2(1)J.Chem. Soc., Dalton Trans., 1999, 509–516 511 ligand modifications lead to species that show copper(I) induced helicity [note that increasing thiaether–imine chelate ring sizes lead to instability of the dicopper(I) products, see below]. The structures of all helicates, based on macrocyclic ligands, that have been determined experimentally are assembled in Fig. 2 and the relevant structural data are summarized in Table 3. The only significant structural variations are those of the valence angles that involve the metal centers, and these are due to the changes in the chelate ring sizes.For the helicates there are three sources of chirality: the helicity, based on the backbone of the co-ordinated macrocycle Fig. 1 Plots of the experimentally determined (X-ray) structures of the molecular cations of (a) [Cu2(phane-222)]21,27 (b) [Cu2(para- 222)]2126 and (c) [Cu2(meta-222)]21.26 (L or D), the configuration of the co-ordinated thioether donors (S* or R*) and the conformation of the chelate rings (l or d for five-membered chelate rings).Since the assignment of the configuration of the co-ordinated thioether-S donor groups depends on the ligand structure (chelate ring sizes), we use a generalized nomenclature (S9* or R9*) which is based on the ligand with ethylene bridges between all donor groups of each co-ordination site (para-222), that is the priorities [Cahn– Ingold–Prelog (CIP) rules] are Cu1 > Cthiaether > Cimine > lone pair.All structurally characterized helicates crystallize in racemic point groups, and all structures have the same configuration, that is DR9*R9*R9*R9* or LS9*S9*S9*S9* (for species with five-membered chelate rings the corresponding conformations are d and l for the thioether-S configurations R9* and S9*, respectively; e.g. DR9*R9*R9*R9*dddddd). The exclusive observation of a single isomer out of 350 non-degenerate diastereomeric possibilities in the solid state indicates that this might be considerably more stable than all the others.Support for this assumption emerges from force field calculations 29 and from the investigation of the solution structures and dynamics (see below). From the fact that only one isomer is observed, that is that all stereocenters are strongly coupled, it follows that the structure of the co-ordinated ligand is rather rigid. Thus, the folded structures might be retained in solution and dynamic processes might be slower than anticipated and possibly detectable by NMR spectroscopy (the rate of interconversion of fivemembered chelate rings is generally of the order of 108 s21 35,36 and water exchange at copper(I) is of the order of 1010 s21 37).It also follows that the figure-of-eight shaped structures are probably due to the tetrahedral co-ordination geometry, enforced by Fig. 2 Plots of the experimentally determined (X-ray) structures of the molecular cations of (a) [Cu2(para-222)]21,26 (b) [Cu2(para-222- OMe)]21,28 (c) [Cu2(para-222-Me)]21,28 (d) [Cu2(para-Ph2Ph)]21,25 (e) [Cu2(para-232)]2128 and (f) [Cu2(para-242)]21.28 Chart 2512 J.Chem. Soc., Dalton Trans., 1999, 509–516 Table 3 Average distances (Å) and angles (8) of all figure-of-eight-shaped dicopper(II) compounds with (N2S2)2 donor sets Cu–S Cu–N Cu ? ? ? Cu Cbenz ? ? ?Cbenz benz ? ? ? benz S–Cu–S S–Cu–N S–Cu–Nbite N–Cu–N Cimine–Cbenz a q b fc para-222 2.38(2) 2.01(8) 7.83 3.43 3.59 91.0(4) 115.1(37) 90.8(18) 144.1(42) 31 73 16 para-222-Me 2.40(6) 1.98(1) 7.70 3.57 3.55 90.2 114.1(25) 89.4(6) 147.2 29 72 14 para-222-OMe 2.40(2) 1.98(2) 7.86 3.53 3.56 90.3(6) 114.8(57) 89.7(12) 145.4(3) 33 73 13 para-Ph2Ph 2.34(4) 2.00(2) 7.77 3.42 3.45 93.1(2) 113.2(22) 88.0(2) 149.8(4) 23 72 17 para-232 2.35(3) 2.02(3) 7.95 3.42 3.49 102.6(34) 116.4(66) 90.2(2) 138.1(17) 25 73 19 para-242 2.41(2) 2.02(2) 8.14 3.45 3.57 103.6(9) 118.8(80) 88.5(12) 136.1(8) 28 72 13 meta-222 2.43(1) 1.99(1) 8.15 3.26; 3.43 3.39 88.2 113.3(24) 89.7(6) 148.5 27 73 — phane-222 2.38(2) 1.96(1) 8.22 — 3.09 91.51(2) 117.4(14) 90.2(6) 141.2(1) 32 71 — a Torsional angle around the imine bond.b Tetrahedral twist angle (S–Cu–S; N–Cu–N planes; tetrahedral: 908). c Torsional angle about the centroids of the benzene spacer groups. the copper(I) centers. Although the aromatic spacer groups are ideally p-stacked, the resulting stabilization is probably not decisive for the enforcing of the figure-of-eight geometry.28 From the rigidity of the co-ordinated ligand it follows also that co-ordination to copper(I) is entropically an unfavorable process.That is, the gain in complex stability by the preorganization of the ligand (phane-222) should be appreciable. 3 Structures in solution Proton NMR spectroscopy indicates that the metal-free ligands are not preorganized (that is they have a flexible, macrocyclic structure) and that the figure-of-eight shaped folding of the dicopper(I) complexes is retained in solution when an inert solvent (e.g.nitromethane) is used.25–28 In the simplest example for 1H NMR spectroscopy, that of para-Ph2Ph, which has only one type of methylene proton, there is one sharp singlet for these protons in the metal-free ligand. In the helical dicopper(I) compound these become diastereotopic and give rise to a four line AX system at 200 MHz, with a geminal coupling of 10.5 Hz and a chemical shift diVerence of Dd = 1.5 ppm (the vicinal coupling that would give rise to an AA9XX9 pattern is not observed).25 The observation that the metal-free ligands are unfolded supports the assumption that the p-stacking interaction is not strong and is not the main driving force for the figure-of-eight shapes (see above).For three of the double helical dinuclear compounds [the dicopper(I) compounds of para-222, para-242 and para-222-OMe] the solution structures have been determined by high resolution 1H NMR spectroscopy in nitromethane.28 The spectrum of [Cu2(para-222)]21 (aliphatic region) is shown in Fig. 3 and the nomenclature of the protons is given in Chart 3. The assignment of the signals is based on two dimensional homonuclear (1H–1H)- and hetero- Chart 3 nuclear (1H–13C)-correlated spectra, and the coupling patterns (see Fig. 3) are based on a first-order analysis. In the region of aromatic protons there should be two doublets for the structurally diVerent protons of the para-phenylene spacer groups (see Chart 3).The fact that only one singlet was observed indicates that a dynamic process is involved which interconverts the two sites.28 A helix inversion with full retention of the co-ordinative bonds corresponds to an epimerization, that is to an equilibrium between two diastereomers, e.g. LS9*S9*S9*S9* DS9*S9*S9*S9* (see sections on conformational analysis and on dynamics, below; the rigidity of the co-ordinated ligands, discussed above, implies that both diastereoisomers have distinct and possibly diVerent sets of five-membered chelate ring conformations).For the achiral dicopper(I) compound of meta-222 the expectation is that in the low field region of the 1H NMR spectrum there is a singlet for the imine proton (double intensity), and a singlet, a doublet (double intensity) and a triplet for the three distinct aromatic protons (see Chart 3). The observed spectrum (Fig. 4) indicates that two isomers in a ratio of approximately 1 : 3 are present.29 While one of them probably is that observed in the solid (see Fig. 1; tail-to-tail isomer), the other may correspond to one of the other two structures that result from a rotation of the phenylene spacer groups around the Caromat–Cimine–bonds (Chart 4). Note that the tail-to-tail and head-to-head isomers both have C2h symmetry while that of the head-to-tail isomer is Cs. That is, the head-to-tail isomer should have two sets of signals for protons 1, 2 and 3, and a possible conclusion is that the two isomers present in solution are tailto- tail and head-to-head.Fig. 3 Proton NMR spectrum (500 MHz) of [Cu2(para-222)]21 (high field region).28J. Chem. Soc., Dalton Trans., 1999, 509–516 513 4 Conformational analysis Empirical force field calculations have been used extensively for predictions of conformational equilibria.38–40 The MOMEC force field is mainly based on structural experimental data but there are good reasons to believe that the steepness of the potentials is approximately realistic, that is the isomer ratios are well represented by the relative strain energies 41–43 and this has been tested extensively.40–45 The two isomers [Cu2(para-222)]21 and [Cu2(meta-222)]21 (ethylene bridges between all donor atoms) were analysed in detail.29 For the isomer with parasubstituted spacer groups the geometry observed in the solid, that is L-S9*S9*S9*S9*-llllll-[Cu2(para-222)]21, is the most stable structure (0 kJ mol21).The destabilization due to an inversion of a five-membered chelate ring is approximately 5 kJ mol21; that due to an inversion of a thioether-S donor is approximately 16 kJ mol21. Obviously, these eVects are not additive (that is for each configuration there is a preferred set of conformations). The next lowest energy structure (fivemembered ring inversions alone excluded; inversion barriers Fig. 4 Proton NMR spectrum (200 MHz) of [Cu2(meta-222)]21 (low field region).29 Chart 4 of five-membered chelate rings are approximately 25 kJ mol21,35,36 that is their interconversion will not be frozen, even at low temperature) is that of the helix inversion product, D-S9*S9*S9*S9*-llllll-[Cu2(para-222)]21, with a strain energy of 6 kJ mol21 (Fig. 5). Only two of the three putative isomers of [Cu2(meta-222)]21 from Chart 4 converge to a stable structure. The lowest energy structure is tail-to-tail-R9*R9*S9*S9*-dddlll-[Cu2(meta- 222)]21 (12 kJ mol21), that is the geometry observed in the crystal.26 Inversion of thioether-S donors and five-membered chelate rings leads to destabilizations of the same order of magnitude as for the isomers with the para-phenylene spacer groups.The lowest energy conformer of the head-to-tail rotamer, R9*R9*S9*S9*-ldldll-[Cu2(meta-222)]21, is approximately 7 kJ mol21 less stable than the lowest energy tail-to-tail isomer.29 No energy minimum could be detected for the headto- head rotamer.There are two interesting features emerging from the strain energy minimized head-to-tail rotamer (see Fig. 6). (i) The two meta-phenylene rings are tilted with respect to each other. (ii) There is a shallow energy surface with at least three minima with similar energies and energy barriers of less than approximately 25 kJ mol21, that is there is a wagging mode of the two spacer groups. Both observations are consistent with the observed 1H NMR spectrum (Fig. 4): the observed ratio of isomers of approximately 3 : 1 is in agreement with a strain energy diVerence of ca. 7 kJ mol21. The fast dynamics in the head-to-tail isomer that involves three orientations of each of the meta-phenylene spacer groups is consistent with the observation of single sets of singlets, doublets and triplets for the aromatic protons. The chemical shift diVerences between the metal-free meta-222 ligand and the major isomer (tail-to-tail) and those between the major and the minor species in the 1H NMR spectrum of Fig. 4 (tail-to-tail and head-to-tail) were interpreted with a tilt of the two aromatic rings, and that is in agreement with the computed structures (Fig. 6).28,29 5 Dynamics For the helical dicopper(I) compounds there are two dynamic processes: (i) a low temperature (coalescence at approximately 220 K) solvent independent process assigned to helix inversion Fig. 5 Computed structures 29 of the helix inversion products of [Cu2(para-222)]21 with conserved thioether-S configurations (DR9* R9*R9*R9*-dddddd L-R9*R9*R9*R9*-dddddd).Fig. 6 Computed structures 29 of the tail-to-tail (head-to-tail) conversion products of [Cu2(meta-222)]21 showing the three low-energy structures of the head-to-tail rotamer.514 J. Chem. Soc., Dalton Trans., 1999, 509–516 with retention of the thioether-S configurations, that is epimerization that involves L-S9*S9*S9*S9*- and D-S9*S9*S9*S9*- [Cu2(para-222)]21; (ii) a high temperature (coalescence at approximately 300 K) process in acetonitrile attributed to full racemization (helix inversion and scrambling at all thioether-S donors).28 The former process is observed in the low field region of the 1H NMR spectrum.Each of the two diastereoisomers (ratio of approximately 92 : 8, based on the strain energy diVerence of 6 kJ mol21) is expected to have a singlet for the imine protons and two doublets for the aromatic protons (exception: species with substituted para-phenylene spacer groups, see below).The ambient temperature 1H NMR spectra of all helicates have two singlets (ratio 1 : 2) in the low field area of the spectrum (see Fig. 7). At the lowest possible temperature, the signal for the aromatic protons of [Cu2(para-242)]21 splits into two doublets. The signals of the aromatic protons of the less abundant isomer could not be resolved. However, a small signal (see 39 in Fig. 7; this signal was reproduced in various samples) may be attributed to the resonance of the imine protons of the less abundant diastereoisomer.28 The high-field shift is consistent with the expected change of the torsion around the imine bond.28,29 The high temperature dynamics process (high field region of the 1H NMR spectrum, see Fig. 8), attributed to full racemization, is only observed in acetonitrile which has a high aYnity for copper(I). This and the fact that the activation barrier for this process is significantly higher suggest that some bond breaking might be involved.That is, there are intermediates where acetonitrile is co-ordinated to the copper(I) centers. Crystals of such a putative intermediate could be isolated and structurally characterized (Fig. 9).28 Fig. 7 Temperature dependent 500 MHz 1H NMR spectra of [Cu2- (para-242)]21 (low field region).28 The coalescence temperature of the two compounds with substituted para-phenylene bridges is approximately 50 K higher than for all the other helicates (approximately 320 vs.approximately 270 K).28 A possible explanation is that acetonitrile exchange is activated along the helix inversion reaction coordinate, a process that is disfavoured by the paraphenylene substitution (see Chart 5). This is supported by strain energy minimized structures along the helix inversion coordinate (constrained pseudo-torsional angle that involves the two para-phenylene centroids) that indicate that the paraphenylene –para-phenylene distance increases from approximately 3.3 to approximately 4.9 Å at the transition state of the inversion reaction.29 The distortions along the helix inversion reaction coordinate also indicate that there is a low energy rotation of the para-phenylene rings along this mode, and this is consistent with the 1H NMR data.The computed activation barrier of approximately 50 kJ mol21 is qualitatively in agreement with the barrier emerging from the 1H NMR experiments.29 The dynamics of the “squeezed ring” isomer [Cu2(meta- Fig. 8 Temperature dependent 200 MHz 1H NMR spectra of [Cu2- (para-232)]21 (high field region).28 Fig. 9 Plot of the experimentally determined (X-ray) structure of the molecular cation of [Cu2(para-323)(CH3CN)2]21.28J. Chem. Soc., Dalton Trans., 1999, 509–516 515 Chart 5 222)]21 is strikingly diVerent: (i) only one process has been observed, and, based on 1H NMR spectroscopy, it is attributed to full scrambling, that is it involves copper–donor bond breaking; (ii) this process is solvent dependent but it also occurs in nitromethane (coalescence temperature: in acetonitrile, 250 K; in nitromethane, 330 K).29 This is interpreted to be due to a more dissociative character of the scrambling process than for the helicates, and this interpretation is supported by force field calculations and the general observation that the “squeezed ring” isomer is considerably less stable than the “twisted ring” compounds (activation of the oxygenation reaction along the intramolecular dynamic process).29 6 Extensions The preparative concepts used for the ligands that lead to helical and “squeezed ring” figure-of-eight shaped dicopper(I) compounds have been extended to include a variety of aldehydes and amines (Chart 6).The combination of the di- or tetra-aldehydes 1–3 with dithiadiamines 6 leads to SchiV-base ligands that form figure-of-eight shaped dicopper(I) compounds. 25–29 Similar ligands may be isolated in good yields when dialdehydes of the type 4 are used (nomenclature of the resulting ligands: 222-S4, 222-S6, 222-S8, for n = 0, 1, 2, respectively). The structures of the corresponding tricopper(I) compounds [Cu3(222-S4)]31, [Cu3(222-S6)]31 and [Cu3(222-S8)]31 were characterized by elemental analysis, 1H NMR, ESI-MS and IR spectroscopy. Proton NMR spectroscopy was used to analyse the binding mode of the copper(I) ion that is co-ordinated to the central S4, S6 or S8 donor group.In acetonitrile and in nitromethane there is formation of C2v-symmetric complex cations. The resonances attributed to the two peripheral dithiadiimine donor sets are similar to those of the dicopper(I) helicates. Thus the corresponding two copper(I) ions are tetrahedrally co-ordinated but, based on the 1H NMR chemical shift data of the para-phenylene groups, there is no p stacking of the Chart 6516 J. Chem. Soc., Dalton Trans., 1999, 509–516 aromatic spacer groups.28 The downfield shifts of the ethylene bridges in the central S4, S6 or S8 binding sites upon coordination to copper(I) are in the range that usually is observed for co-ordinated thioether macrocyclic ligands.46 These chemical shifts indicate that the third copper(I) center is co-ordinated in the central cavity.For [Cu3(222-S6)]31 there is a fast dynamic process that leads to an average co-ordination mode that makes all six thioether donors identical.In [Cu3(222-S8)]31 the coordination of the central copper(I) ion involves only the four central thioether donors. The [2 1 1] condensation of 1,19-bis(formyl)ferrocene 5 with the tetrathiatetraamines 7–9 leads to ligands with two ferrocenyl end-groups and two sites for metal ion co-ordination. The structure of the bis(ferrocenyl) “free” ligand and the corresponding dicopper(I) compound, based on 7, have been determined by X-ray crystallography and 1H NMR spectroscopy, respectively.For 7 and 8 there are two isomers, and both were observed by 1H NMR spectroscopy of the copper(I)-free ligands. The isomer that crystallized (Fig. 10) does not lead to stable dicopper(I) compounds, and this also emerged from 1H NMR spectroscopy. The metal–metal interactions in the dicopper(I) compounds have been studied by electrochemistry, IR and Mössbauer spectroscopy.47 Of particular interest is the bifunctional diamine building block 10 which recently has been isolated and characterized. This allows the combination of the chemistry of the helicates discussed here with ruthenium–phenanthroline type coordination chemistry.Together with the ferrocenyl and the tris- (phenanthroline) ruthenium end-groups, based on 5 and 10, there is now the possibility to assemble helicates and arrays of helicates with photochemically and/or electrochemically active sites. 7 Acknowledgements Generous financial support by the Deutsche Forschungsgemeinschaft (DFG) and the Fond der Chemischen Industrie (FCI) is gratefully acknowledged. 8 References 1 A.Werner, Z. Anorg. Allg. Chem., 1893, 3, 271. 2 J.-M. Lehn, Supramolecular chemistry concepts and perspectives, VCH, Weinheim, 1995. 3 A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser and A. von Zelewsky, Coord. Chem. Rev., 1988, 84, 85. 4 F. Scandola, M. T. Indelli, C. Chiorboli and C. A. Bigmozzi, Top. Curr. Chem., 1990, 158, 73. 5 E. C. Constable, Adv. Inorg.Chem. Radiochem., 1987, 30, 69. 6 V. Balzani and F. Scandola, Supramolecular Photochemistry, Ellis Horwood, Chichester, 1991. 7 S. Mann, G. Huttner, L. Zsolnai and K. Heinze, Angew. Chem., 1996, 108, 2983. Fig. 10 Plot of the experimentally determined (X-ray) structure of the ligand based on two ferrocenyl end groups and the tetraamine 7.47 8 B. Hasenknopf, J. M. Lehn, B. O. Kneisel, G. Baum and D. Fenske, Angew. Chem., 1996, 108, 1987. 9 P. N. W. Baxter, G. S. Hanan and J.M. Lehn, Chem. Commun., 1996, 2019. 10 A. Harriman and R. Ziessel, Chem. Commun., 1996, 1707. 11 E. C. Constable, Nature (London), 1990, 346, 314. 12 J.-P. Sauvage, Acc. Chem. Res., 1990, 23, 319. 13 J.-M. Lehn, Angew. Chem., 1990, 102, 1347. 14 E. C. Constable, Chem. Ind., 1994, 56. 15 C. Piguet, G. Bernardinelli and G. Hopfgartner, Chem. Rev., 1997, 97, 2005. 16 U. Koert, M. M. Harding and J.-M. Lehn, Nature (London), 1990, 346, 339. 17 W. Zarges, J. Hall and J.-M.Lehn, Helv. Chim. Acta, 1991, 74, 1843. 18 J. K. Judice, S. J. Keipert and D. J. Cram, J. Chem. Soc., Chem. Commun., 1993, 1323. 19 K. T. Potts, M. Keshavarz, F. S. Tham, H. D. Abruna and C. Arana, Inorg. Chem., 1993, 32, 4436. 20 R. Krämer, J.-M. Lehn and A. DeCian, Angew. Chem., 1993, 105, 764. 21 E. C. Constable, A. J. Edwards, P. R. Raithby and J. V. Walker, Angew. Chem., 1993, 105, 1486. 22 A. Bilyk and M. M. Harding, J. Chem. Soc., Dalton Trans., 1994, 77. 23 M. Albrecht, Chem.Eur. J., 1997, 3, 1466. 24 D. E. Fenton, R. W. Matthews, M. McPartlin, B. P. Murphy, I. J. Scowen and P. A. Tasker, J. Chem. Soc., Chem. Commun., 1994, 1391. 25 P. Comba, A. Fath, T. W. Hambley and D. T. Richens, Angew. Chem., 1995, 107, 2047. 26 P. Comba, A. Fath, T. W. Hambley and A. Vielfort, J. Chem. Soc., Dalton Trans., 1997, 1691. 27 P. Comba, A. Fath, G. Huttner and L. Zsolnai, Chem. Commun., 1996, 1885. 28 P. Comba, A. Fath, T. W. Hambley, A. Kühner, D. T. Richens and A. Vielfort, Inorg. Chem., 1998, 37, 4389. 29 P. Comba and A. Kühner, Eur. J. Inorg. Chem., 1998, accepted. 30 J. P. Michael and G. Pattenden, Angew. Chem., 1993, 105, 1. 31 J. R. Lewis, Nat. Prod. Rep., 1989, 6, 503. 32 H. C. Krebs, Fortschr. Chem. Org. Naturst., 1986, 49, 151. 33 D. P. Fairlie, G. Abbenante and D. M. March, Curr. Med. Chem., 1995, 2, 672. 34 P. Comba, R. Cusack, D. P. Fairlie, L. R. Gahan, G. R. Hanson, U. Kazmaier and A. Ramlow, Inorg. Chem., 1998, in the press. 35 T. W. Hambley, J. Comput. Chem., 1987, 8, 651. 36 Y. Kuroda, N. Tanaka, M. Goto and T. Sakai, Inorg. Chem., 1989, 28, 997. 37 Y. Ducommun and A. E. Merbach, Inorganic High Pressure Chemistry, Kinetics and Mechanisms, ed. R. van Eldik, Elsevier, Amsterdam, 1986. 38 G. R. Brubaker and D. W. Johnson, Coord. Chem. Rev., 1984, 53, 1. 39 R. D. Hancock, Prog. Inorg. Chem., 1989, 37, 187. 40 P. Comba, Coord. Chem. Rev., 1993, 123, 1. 41 P. Comba and T. W. Hambley, Molecular Modeling of Inorganic Compounds, VCH, Weinheim, 1995. 42 P. Comba, in Implications of Molecular and Materials Structure for New Technologies, eds. J. K. A. Howard and F. H. Allen, Kluwer, Dordrecht, in the press. 43 P. Comba, Coord. Chem. Rev., 1998, in the press. 44 P. Comba, in Molecular Modeling and Dynamics of Bioinorganic Compounds, eds. L. Banci and P. Comba, Kluwer, Dordrecht, Boston, 1997, p. 21. 45 J. E. Bol, C. Buning, P. Comba, J. Reedijk and M. Ströhle, J. Comput. Chem., 1998, 19, 512. 46 P. Comba, A. Fath, A. Kühner and B. Nuber, J. Chem. Soc., Dalton Trans., 1997, 1889. 47 P. Comba, A. Kühner and A. Peters, submitted for publication. Paper 8/06075D

ISSN:1477-9226    

DOI:10.1039/a806075d

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Pages 511–512 511 Dioxygen activation by a novel manganese(II) thiolate complex with hydrotris(3,5-diisopropylpyrazol-1-yl)borate ligand Hidehito Komatsuzaki,a,b Yuichi Nagasu,a Kantaro Suzuki,a Takao Shibasaki,a Minoru Satoh,a Fujio Ebina,a Shiro Hikichi,*,b Munetaka Akita b and Yoshihiko Moro-oka *,b a Department of Chemistry and Material Engineering, Ibaraki National College of Technology, 866 Nakane, Hitachinaka 312, Japan b Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan Reaction of a MnII thiolate complex bearing hydrotris(3,5- diisopropylpyrazol-1-yl)borate with O2 resulted in O]O bond activation to give a dinuclear MnIII bis(m-oxo) complex and a ligand-oxygenated dinuclear MnIII m-oxo complex, or the dinuclear MnIII,IV m-acetato-bis(m-oxo) complex in the presence of a MnII acetate complex. Dioxygen activation on transition-metal ions is one of the attractive topics from the standpoints of bioinorganic and synthetic chemistry.Manganese–oxygen (O2 2, O2 22, O22, etc.) species are suggested to take part in the physiological dioxygen metabolism and catalytic oxidation of organic compounds.1 By using the hindered tris(pyrazolyl)borate ligand, hydrotris(3,5- diisopropylpyrazol-1-yl)borate (L), we have investigated the chemistry of Mn complexes with dioxygen and its derivatives, for example, synthesis and characterization of the mononuclear MnIII peroxo complex,2 aliphatic C]H bond oxygenation in the dimanganese complex with O2,3 and superoxide anion dismutation by the MnII–carboxylate complexes.4 It is notable that the co-ordinatively unsaturated carboxylate complex, MnIIL(O2CPh),4,5 cannot activate O2, although the FeII derivative shows reversible O2 binding ability to give the corresponding dinuclear FeIII–m-peroxo complex.6 In order to realize O2 activation on a MnL complex, we adopted a thiolate ligand, which is known to be a highly electrondonating soft base compared to such ligands as carboxylate, so as to increase the electron density at metal centers.In this communication, we report the dioxygen activation by a coordinatively unsaturated MnIIL–thiolate complex, and the intermediacy of a Mn–O2 adduct has been confirmed by a trapping experiment. Synthesis of the thiolate complex and its oxygenation reactions are summarized in Scheme 1. The MnII thiolate complex MnIIL(SC6H4NO2-p) 1 † was prepared by reaction of a dinuclear MnII bis(m-hydroxo) complex, LMn(m-OH)2MnL 2,7 with pnitrobenzenethiol under Ar.Formulation of complex 1 is based † Spectroscopic data for complex 1 (Found: C, 59.13; H, 7.40; N, 14.45. Calc. for C33H50BMnN7O2: C, 58.75; H, 7.47; N, 14.53%). IR (KBr pellet, n& /cm21): 2550m (BH), 1586, 1571s (PhC]] C and NO2). Field desorption MS: m/z 675 (M1). The two co-ordinating MeCN molecules are dissociated from the metal center in a non-co-ordinating solvent such as toluene or CH2Cl2, evidenced by the reversible color change from yellow (in toluene) to reddish orange (in MeCN).UV/VIS data: [toluene solution, 23 8C, nm (e/M21 cm21)] 322 (9860); [MeCN solution, 23 8C, nm (e/M21 cm21)] 318 (7580), 487 (9740). In the present study, oxygenation reactions were carried out in toluene to avoid the co-ordination of solvent. The monomeric structure of 1 has been confirmed by X-ray crystallography.Single crystals suitable for analysis have been obtained from MeCN solution. The MnII center is co-ordinated by an N5S donor set including two MeCN molecules. Crystal data for MnL(SC6H4NO2)(MeCN)2?3.5MeCN: C44H68BMnN12.5O2S, M = 901.9, monoclinic, space group C2/c (no. 15), a = 42.99(6), b = 12.475(4), c = 19.686(6) Å, b = 94.85(6)8, U = 10 519(5) Å3, Z = 8, T = 260 8C, Dc = 1.14 g cm21, m(Mo-Ka) = 3.36 cm21, R (R9) = 10.01 (10.98)% for 3728 reflections with 484 parameters.CCDC reference number 186/859. on its IR spectrum, with sharp absorptions around 1590–1570 cm21 arising from the p-nitrophenyl group, and its field desorption MS spectrum [m/z = 675 (M1)]. The Mn center of 1 is assumed to have a co-ordinatively unsaturated geometry as found in the analogous PhO- and RS-LFeII complexes.8 As expected, the thiolate complex 1 readily reacted with dioxygen in a manner similar to the dinuclear MnII bis- (m-hydroxo) complex 2.3 When a toluene solution of 1 was stirred under O2 atmosphere for 1 d, the solution changed from yellow to dark brown.From this dark brown solution, three products were isolated: the dinuclear MnIII bis(m-oxo) complex, LMn(m-O)2MnL 3,7 the ligand-oxygenated dinuclear MnIII complex 4,3 and the corresponding disulfide (O2NC6H4S]SC6- H4NO2).‡ The thiolate complex 1 was not hydrolyzed by treatment with an excess amount of H2O [equation (1)]. We can conclude that the present oxidation reactions proceed via degradation of Mn–O2 species which are formed by reaction of O2 and 1 (not 2) as will be discussed below.LMnII SR + H2O 2 + RSH (1) 1 Scheme 1 H O LMnII MnIIL OH 2 2xRSH 2xH2O LMnII SR 1 O LMnIII MnIIIL O O LMnII O 5 NO2 R = O2 N N N N N B N H L = O LMnIII MnIVL O O O 6 3 + + RS SR N N O N N O O H H N N N N 4 + RS SR B N B N MnIII N MnIII N ‡ The disulfide product was obtained almost quantitatively. The yield (based on complex 1) was determined by GC analysis.Yield of RS]SR in the reaction of 1 with O2 in the absence of 5 88.2%, in the presence of 5 87.4%.512 J. Chem. Soc., Dalton Trans., 1998, Pages 511–512 Although no Mn–O2 species was detected, its participation was supported by the following trapping experiment. Reaction of 1 with dioxygen in the presence of a MnII acetate complex, MnL(OAc) 5,§ resulted in the predominant formation of the MnIII,IV m-acetato-bis(m-oxo) complex, LMn(m-OAc)(m-O)2- MnL 6 ¶ (59% isolated yield based on 1),9 and the disulfide.‡ It is worth noting that the acetate complex 5 is sluggish toward oxidation under similar reaction conditions.When a toluene solution of 5 was stirred under O2, the solution turned from pale yellow to pale brown, but the reaction was very slow (over a week), and neither the Mn–O2 adducts nor the MnIII,IV complex 6 were detected. In addition, reactions of the bis(m-oxo) complex 3 and the acetate complex 5 or aqueous NaOAc or acetic acid under O2 did not yield 6 [equation (2)].Therefore, it is concluded that the dinuclear MnIII,IV complex 6 is formed via a trapping process of the Mn–O2 adduct by 5. Plausible mechanisms for the present O2 activation reactions are summarized in Scheme 2. Reaction of complex 1 with O2 may form a MnIII–superoxo complex 7, which further reacts with another molecule of the MnII complex 1 or 5 to give the corresponding dinuclear MnIII m-peroxo intermediate 8. Metal– superoxo species are known to work as nucleophiles, therefore, the nucleophilic attack of anionic 7 at the positive MnII center of 5 is more favorable than that of 1 and therefore the trapping experiment is successful.Subsequent homolysis of the O]O and Mn]S bonds || results in the formation of 3, 4 and/or 6.10 During the formation of the m-acetato-bis(m-oxo) complex 6, the acetate ligand in 5 bridges the two metal centers (so- Scheme 2 1 O2 – LMnIII SR 7 LMnII X 1: X = SR 5: X = OAc SR LMnIII O O MnIIIL X 8 X = SR X = OAc RS SR RS SR 3 + 4 6 O2 3 + HOAc 5 or or NaOAc(aq) 6 (2) O2 § The acetate complex 5 was obtained by treating Mn(OAc)2?4H2O with KL.Spectroscopic data for 5 (Found: C, 59.84; H, 8.65; N, 14.61. Calc. for C29H49- BMnN6O2: C, 60.11; H, 8.52; N, 14.50%). IR (KBr pellet, n& /cm21): 2545m (BH), 1561s [CO2(asym)]. Field desorption MS: m/z 579 (M1). The acetate ligand is assumed to bind to the MnII center in a bidentate fashion on the basis of the similarity of the n[CO2(asym)] of the benzoate analogue MnL(O2CPh) (1568 cm21), which has a five-co-ordinated distorted trigonal bipyramid MnII center with the bidentate carboxylate ligand established by crystallography (see refs. 4 and 5). The n[CO2(asym)] of 5 is indistinguishable from other peaks arising from the MnL moiety, whereas the unidentate acetatozinc complex with the same ligand gives n[CO2(asym)] and n[CO2(asym)] at 1601 and 1331 cm21, respectively. ¶ The dinuclear MnIII,IV m-acetato-bis(m-oxo) complex 6 was identified by comparison with the data (EPR, field desorption MS, IR and X-ray crystallography) of an authentic sample (see ref. 9). || The O]O bond homolysis of a dinuclear m-peroxo core [Mn1(m-O2 22)Mn1] gives the corresponding two-electron oxidized bis(m-oxo) core [M(n11)1(m-O22)2M(n11)1] and metal]sulfur bond homolysis of a Mn1(SR) core yields a one-electron reduced metal [M(n21)1] center. called ‘carboxylate shift’) as observed in the formation of the dinuclear FeIII m-peroxo complex containing L.11 It is known that reduction of dioxygen to superoxide in a one-electron transfer step has a more negative electrochemical potential than that of the two-electron reduction (O2 to O2 22).12 The O2 activation ability of the co-ordinatively unsaturated thiolate complex 1 may arise from the high electron density at the MnII center as we anticipated.Thiolate complexes with redoxactive metal ions are known to cause homolytic metal–sulfur bond cleavage to give the corresponding disulfides and reduced metal ions, in fact, the thiolate ligand of 1 works as a good leaving group as well as a reductant toward the Mn center.In the case of our previous O2 activation studies by the hydroxo complex 2,3 the dinuclear structure constructed by two fiveco- ordinated MnII centers is advantageous for the two-electron reduction of O2 giving the m-peroxo intermediates, and the hydroxide ligands are proposed to be eliminated as H2O during further O]O bond activation.3 Therefore, it is concluded that a requisite of the O2-activating MnII complex is the presence of co-ordinatively unsaturated metal centers with O2 reducing potential, and good leaving ligands to induce further O]O bond activation.In conclusion, O2 activation has been achieved by a MnII– thiolate complex and the resulting superoxo intermediate reacts with an acetate complex to give a m-peroxo intermediate 8, which is converted into the m-acetato-bis(m-oxo) complex 6 after O]O and Mn]S bond rupture.Further investigations including detection of the O2 adducts and oxidation reactions of external substrates will be performed. Acknowledgements We are grateful to the Ministry of Education, Science, Sports and Culture of the Japanese government for financial support of the research (Grant-in-Aid for Specially Promoted Scientific Research: No. 08102006). References 1 Manganese Redox Enzymes, ed.V. L. Pecoraro, VCH, New York, 1992; K. Wieghardt, Angew. Chem., Int. Ed. Engl., 1989, 28, 1153; V. L. Pecoraro, M. J. Baldwin and A. Gelasco, Chem. Rev., 1994, 94, 807; T. Mukaiyama and T. Yamada, Bull. Chem. Soc. Jpn., 1995, 68, 17. 2 N. Kitajima, H. Komatsuzaki, S. Hikichi, M. Osawa and Y. Morooka, J. Am. Chem. Soc., 1994, 116, 11 596. 3 N. Kitajima, M. Osawa, M. Tanaka and Y. Moro-oka, J. Am. Chem. Soc., 1991, 113, 8952. 4 N. Kitajima, M. Osawa, N. Tamura, Y. Moro-oka, T. Hirano, M. Hirobe and T. Nagano, Inorg. Chem., 1993, 32, 1879. 5 M. Osawa, Y. Moro-oka and N. Kitajima, Yuki Gosei Kagaku Kyokaishi, 1993, 51, 921. 6 N. Kitajima, H. Fukui, Y. Moro-oka, Y. Mizutani and T. Kitagawa, J. Am. Chem. Soc., 1990, 112, 6402; N. Kitajima, N. Tamura, H. Amagai, H. Fukui, Y. Moro-oka, Y. Mizutani, T. Kitagawa, R. Mathur, K. Heerwegh, C. A. Reed, C. R. Randall, L. Que, jun. and K. Tatsumi, J. Am. Chem. Soc., 1994, 116, 9071. 7 N. Kitajima, U. P. Singh, H. Amagai, M. Osawa and Y. Moro-oka, J. Am. Chem. Soc., 1991, 113, 7757. 8 M. Ito, H. Amagai, H. Fukui, N. Kitajima and Y. Moro-oka, Bull. Chem. Soc. Jpn., 1996, 69, 1937. 9 M. Osawa, K. Fujisawa, N. Kitajima and Y. Moro-oka, Chem. Lett., 1997, 919. 10 Oxygen–oxygen bond activation via a dinuclear MnIII–m-peroxo intermediate has been reported recently. Z. Shirin, V. G. Young, jun. and A. S. Borovik, Chem. Commun., 1997, 1967. 11 K. Kim and S. J. Lippard, J. Am. Chem. Soc., 1996, 118, 4914. 12 D. T. Sawyer, in Oxygen Complexes and Oxygen Activation by Transition Metals, eds. A. E. Martell and D. T. Sawyer, Plenum, New York, 1988, p. 131. Received 14th November 1997; Communication 7/08210J

ISSN:1477-9226    

DOI:10.1039/a708210j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Pages 513–514 513 Synthesis and structural characterisation of tetraruthenium Ï4-nitrene clusters containing tolylacetylene (HC2Tol). Molecular structures of [Ru4(CO)9(Ï-CO)2(Ï4-NH)(Ï4-Á2-HC2Tol)] and [Ru4(CO)9- (Ï-CO)2{Ï4-NC(O)OMe}(Ï4-Á2-HC2Tol)] Emmie Ngai-Man Ho and Wing-Tak Wong *,† Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China Two structurally characterized tetraruthenium carbonyl clusters, [Ru4(CO)9(m-CO)2(m4-NH)(m4-h2-HC2Tol)] 1 and [Ru4(CO)9(m-CO)2{m4-NC(O)OMe}(m4-h2-HC2Tol)] 2, have been isolated from the reaction between [Ru3(CO)9(m3-CO)- (m3-NOMe)] and tolylacetylene (HC2Tol) in refluxing n-octane.The chemistry of transition-metal clusters containing a m4- nitrene ligand, in particular m4-NH, has not been well developed. In contrast, a large number of m3-nitrene clusters are known and they are found to be a key intermediate for the catalytic nitroarene carbonylation reactions.1,2 Blohm and Gladfelter 3 have shown that protonation of the tetraruthenium nitrido cluster anion [Ru4(CO)12(m4-N)]2 in the presence of diphenylacetylene produced the m4-NH containing species [Ru4(CO)9- (m-CO)2(m4-NH)(m4-h2-PhC2Ph)].3 Reactions of triruthenium nitrene clusters [Ru3(CO)9(m-H)2(m3-NPh)] with diphenylacetylene were found to produce the m4-nitrene cluster [Ru4(CO)9- (m-CO)2(m4-NPh)(m4-h2-PhC2Ph)].4 It appears that the alkynes are important auxiliary ligands that favour the formation and isolation of m4-nitrene species.Recently we reported a series of penta- and hexa-nuclear ruthenium m4-nitrene carbonyl clusters prepared from the thermolysis or pyrolysis of [Ru3(CO)9- (m3-CO)(m3-NOMe)].5 However, preparative methods for m4- nitrene species reported so far are not very specific and lead to low yields of the products, hence their reactivity studies are hindered. Herein, we report the reactivity of tolylacetylene (HC2Tol) towards the triruthenium carbonyl cluster [Ru3(CO)9 (m3-CO)(m3-NOMe)], which resulted in the isolation of two tetraruthenium clusters containing m4-nitrene ligands in more accessible yields.Heating of [Ru3(CO)9(m3-CO)(m3-NOMe)] with excess tolylacetylene in refluxing n-octane for 5 h afforded a brown reaction mixture. Two new yellow clusters [Ru4(CO)9(m-CO)2(m4- NH)(m4-h2-HC2Tol)] 1 and [Ru4(CO)9(m-CO)2{m4-NC(O)OMe}- (m4-h2-HC2Tol)] 2 were isolated in 35% yield each by preparative TLC on silica, see Scheme 1.Owing to the similarity in the chromatographic behaviour of clusters 1 and 2, they could not be separated. Indeed the compounds could only be obtained in the form of solvated co-crystals containing equimolar amounts of 1 and 2 which were then characterized by spectroscopy ‡ and chemical and structural analysis.§ † E-Mail: wtwong@hkucc.hku.hk ‡ Spectroscopic data for the mixture of clusters 1 and 2. IR: [n(CO), nhexane, cm21] 2089w, 2059vs, 2049s, 2037vs, 2026m, 2008m, 1987m, 1904w, 1856m; [n(NH), KBr disc, cm21] 3347w (Found: C, 30.0; H, 1.4; N, 1.7.Calc. for C90H54N4O48Ru16: C, 30.23; H, 1.52; N, 1.57%). Cluster 1. 1H NMR (CDCl3): 6.79 (m, 2 H), 6.20 (m, 2 H), 3.86 (s, 1 H), 2.17 (s, 3 H) and 1.96 (t, 1 H, JNH = 49.3 Hz). FAB mass spectrum: m/z 843 (calc. 843), M1. Cluster 2. 1H NMR (CDCl3): 6.79 (m, 2 H), 6.20 (m, 2 H), 3.94 (s, 1 H), 2.94 (s, 3 H) and 2.17 (s, 3 H). FAB mass spectrum: m/z 901 (calc. 901), M1. X-Ray analysis showed that the asymmetric unit contains two identical molecules of cluster 1, two isomeric molecules of cluster 2 and a n-hexane solvate molecule. Intermolecular hydrogen bonds are found between the m4-NH of 1 and the carbonyl oxygen atom in the m4-NC(O)OMe group of 2, see Fig. 1. The molecular geometries of clusters 1 and 2 are similar in that, the four ruthenium atoms form a slightly twisted square-base arrangement with a quadruply bridging TolC2H ligand.Both 1 and 2 have two CO-bridged Ru]Ru bonds [ave 2.691(1) Å] and two unbridged Ru]Ru bonds [ave 2.747(1) Å]. The square tetraruthenium planes Ru(1)]Ru(2)]Ru(3)]Ru(4) and Ru(9)]Ru(10)]Ru(11)]Ru(12) are coplanar with a mean deviation from the least squares planes of less than 0.19 and 0.20 Å respectively. The nitrene N atom symmetrically caps the square base with average Ru]N distances of 2.150(9) Å for 1 and 2.183(8) Å for 2 and it lies 0.99 and 1.05 Å above the basal plane for 1 and 2 respectively. In cluster 1, the hydrogen atom was located by Fourier-difference synthesis using low angle data at 0.84 Å from the m4-nitrene nitrogen atom.The 1H NMR spectrum of 1 showed a triplet, at d 1.96 (JNH = 49.3 Hz), which is similar to that of [Ru4(CO)11(m4-NH)(m4-h2-PhC2Ph)].3 The two molecules of cluster 2 in the asymmetric unit differ in the alkyne orientation and are presented as 2a and 2b in Scheme 1. Scheme 1 (i) Tolylacetylene, n-octane, 120 8C Ru Tol CO OC H Ru N Ru H Tol CO OC C Ru C N MeO O Ru C Ru C H C Ru Ru 1 2a Ru OC Tol C Ru N C H C Ru Ru 2b O OMe C O C Ru Ru N Ru O O CH3 + ( i ) § Crystal data for co-crystal of [1?2]2?C6H14, C90H54N4O48Ru16 = 2(C20H9NO11Ru4)?2(C22H11NO13Ru4)?C6H14, M = 3576.53, triclinic, space group P1� (no. 2), a = 17.763(1), b = 18.481(1), c = 19.185(1) Å, a = 112.21(2), b = 100.68(2), g = 92.53(2)8, U = 5684(1) Å3, Z = 2, Dc = 2.089 g cm23, F(000) = 3420. Mo-Ka radiation, T = 298 K, l = 0.710 73 Å, m(Mo-Ka) = 21.45 cm21, yellow block 0.19 × 0.28 × 0.31 mm, 19 366 unique data measured on a MAR research image-plate scanner, 11 156 observed reflections [I > 3s(I)].An approximation of absorption by inter-image scaling was applied. R = 0.048 and R9 = 0.065, w = [s2(Fo)]21. CCDC reference number 186/857.514 J. Chem. Soc., Dalton Trans., 1998, Pages 513–514 Fig. 1 Molecular structure of clusters 1 and 2 in the asymmetric unit with selected bond distances (Å) and angles (8): Ru(1)]Ru(2) 2.670(1), Ru(1)]Ru(4) 2.692(1), Ru(2)]Ru(3) 2.717(1), Ru(3)]Ru(4) 2.783(1), Ru(1)]N(1) 2.157(9), Ru(2)]N(1) 2.136(9), Ru(3)]N(1) 2.146(9), Ru(4)]N(1) 2.172(8), N(1)]H 0.82, Ru(9)]Ru(10) 2.684(1), Ru(9)]Ru(12) 2.706(1), Ru(10)]Ru(11) 2.727(1), Ru(11)]Ru(12) 2.778(1), Ru(9)]N(3) 2.192(8), Ru(10)]N(3) 2.162(7), Ru(11)]N(3) 2.174(8), Ru(12)]N(3) 2.217(8), C(72)]O(45) 1.21(1); Ru(2)]Ru(1)]Ru(4) 84.23(4), Ru(1)]Ru(2)]Ru(3) 95.74(4), Ru(2)]Ru(3)]Ru(4) 81.64(4), Ru(1)]Ru(4)]Ru(3) 93.74(4), Ru(10)]Ru(9)]Ru(12) 83.64(4), Ru(9)]Ru(10)]Ru(11) 95.84(4), Ru(10)]Ru(11)]Ru(12) 81.50(4), Ru(9)]Ru(12)]Ru(11) 94.17(4) However, we believe that they exist in one form in solution as indicated by 1H NMR studies.Unfortunately low-temperature 1H NMR experiments could not reveal the signals due to the individual isomers at 220 K. The NC(O)OMe moiety in 2 can be regarded as a carbamate derivative which is essentially coplanar (maximum deviation 0.004 Å in 2a and 0.0008 Å in 2b).It is mutually perpendicular to the metal plane as is evident from the dihedral angle of 91.48 between the planes N(3)]C(72)] O(45)]O(46) and Ru(9)]Ru(10)]Ru(11)]Ru(12). Although the exact mechanism is not known, clusters 1 and 2 are products of a reaction involving the Ru-assisted cleavage of the bound methoxynitrido moiety. This moiety is implicated as a metal– surface-bound intermediate in a number of chemical processes such as nitrogen oxide reduction.6 Further work on the study of the intermediates which might be involved is underway. Acknowledgements We gratefully acknowledge financial support from the Hong Kong Research Grants Council and the University of Hong Kong. E. N.-M. H. acknowledges the receipt of a postgraduate studentship administered by the University of Hong Kong. References 1 M. Pizzotti, S. Cenini, C. Crotti and F. Demartin, J. Organomet. Chem., 1989, 375, 123. 2 S.-H. Han, G. L. Geoffroy and A. L. Rheingold, Organometallics, 1986, 5, 2561; 1987, 6, 2380. 3 M. L. Blohm and W. L. Gladfelter, Organometallics, 1986, 5, 1049. 4 J.-S. Song, S.-H. Han, S. T. Hguyen, G. L. Geoffroy and A. L. Rheingold, Organometallics, 1990, 9, 2386. 5 K. K.-H. Lee and W. T. Wong, J. Chem. Soc., Dalton Tns., 1996, 1707; Inorg. Chem., 1996, 35, 5393. 6 W. L. Gladfelter, Adv. Organomet. Chem., 1985, 24, 41. Received 13th November 1997; Communication 7/08168E

ISSN:1477-9226    

DOI:10.1039/a708168e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Pages 515–516 515 Saturated and unsaturated triruthenium clusters containing three sterically demanding phosphine ligands: synthesis and structure of [Ru3(CO)9(PCy3)3] and [Ru3H2(CO)6(PCy3)3] Georg Süss-Fink,* Isabelle Godefroy, Vincent Ferrand, Antonia Neels and Helen Stoeckli-Evans Institut de Chimie, Université de Neuchâtel, Avenue de Bellevaux 51, CH-2000 Neuchâtel, Switzerland The reaction of Na[Ru3H(CO)11] with an excess of tricyclohexylphosphine in methanol afforded, depending on the reaction conditions, the tri-substituted clusters [Ru3(CO)9- (PCy3)3] (48e) and [Ru3H2(CO)6(PCy3)3] (44e), inaccessible hitherto.Ligand substitution reactions of dodecacarbonyltriruthenium with tertiary phosphines have been studied in great detail.1 The thermal reaction of Ru3(CO)12 with PR3 (R = Ph, Et, Bun, OPh) in general leads to the mono-, di- and tri-substituted derivatives [Ru3(CO)11(PR3)], [Ru3(CO)10(PR3)2] and [Ru3(CO)9(PR3)3].2 For the directed synthesis of these substitution products, the trimethylamine oxide-induced carbonyl substitution,3 the radical ion-initiated ligand substitution,4 and the bis(triphenylphosphine) iminium salt-catalysed carbonyl substitution 5 have been developed.However, with sterically demanding phosphine ligands, the synthesis of the tri-substituted derivatives failed. Even a six-fold excess of tricyclohexylphosphine with [Ru3(CO)12] in the presence of Na[Ph2CO] gave only the mono- and the di-substituted complexes, but no [Ru3(CO)9(PCy3)3].4b On the other hand, bulky phosphines containing cyclohexyl or tert-butyl substituents are known to allow unusual structures and unsaturated configurations for steric reasons.6 Thus the electron-deficient triruthenium cluster [Ru3H2(CO)5(PBut 2)2- (Ph2PCH2PPh2)] with an electron count of 46 was synthesized by Böttcher et al. in 1996.6b Apart from this complex and its adamantyl derivative,6b the only electron-deficient Ru3 clusters reported so far are [Ru3H(CO)9(NSOMePh)],7 and (very recently) [Ru3H2(CO)10] as well as its phosphine derivative [Ru3H2(CO)9(PPh3)];8 all of which have an electron count of 46.Interestingly, no unsaturated triruthenium cluster is mentioned in Deeming’s review of 1995.1 In this paper we describe the synthesis and structure of the tris(tricyclohexylphosphine)-substituted derivative [Ru3(CO)9- (PCy3)3] 1 and the highly electron-deficient (44e) triruthenium cluster [Ru3H2(CO)6(PCy3)3] 2, both accessible from Na[Ru3H- (CO)11] and PCy3.The reaction of Na[Ru3H(CO)11], easily accessible from [Ru3(CO)12] and Na[BH4],9 with tricyclohexylphosphine (1 : 5) in methanol leads, upon heating for 1 h at 80 8C in a closed reactor (pressure Schlenk tube), to the tri-substituted derivative [Ru3(CO)9(PCy3)3] 1, which precipitates from the reaction solution as a purple microcrystalline solid in 55% yield. Cluster 1 can be recrystallised from dichloromethane–methanol to give Ru Ru Ru OC PCy3 OC CO PCy3 OC C O C O OC OC Cy3P C O Ru H OC OC Ru Ru H Cy3P OC PCy3 CO CO PCy3 CO 1 2 dark red, air-stable, cube-like crystals which contain two water molecules of crystallisation (source: methanol).† The single crystal X-ray structure analysis ‡ of 1 (Fig. 1) reveals a triruthenium framework with the three phosphine ligands occupying equatorial positions at the three ruthenium atoms. The molecule has a perfect C3 symmetry.The nine carbonyl ligands are all terminal, six occupying the two axial positions of the Ru atoms, while the other three are alternating with the phosphine ligands in one of the two equatorial positions of each ruthenium atom. The Ru]CO(eq) distances of 1.876(7) Å are distinctly shorter than the Ru]CO(ax) distances [1.924(7) and 1.931(7) Å]. This is in keeping with the findings in the known cluster [Ru3(CO)9(PMe3)3],10 the Ru]P distances, however, are considerably longer in 1 [2.414(2) Å] than in the methyl derivative [2.330 Å (average)],10 reflecting the bulkiness of the cyclohexyl substituents.The Ru]Ru bonds in 1 [2.9396(8) Å] are also elongated with respect to those in [Ru3(CO)9(PMe3)3] [2.860(1), 2.862(1), 2.854(1) Å] 10 and in [Ru3(CO)12] [2.852(1), 2.851(1), Fig. 1 Molecular structure of [Ru3(CO)9(PCy3)3] 1 showing the atom numbering scheme; H atoms have been omitted for clarity. Selected bond lengths (Å) and angles (8): Ru(1)]Ru(2) 2.9396(8), Ru(1)]Ru(3) 2.9396(8), Ru(2)]Ru(3) 2.9396(8), Ru(1)]P(1) 2.414(2), Ru(1)]C(2) 1.876(7), Ru(1)]C(1) 1.924(7), Ru(1)]C(3) 1.931(7); Ru(3)]Ru(1)]P(1) 111.21(5), P(1)]Ru(1)]C(2) 98.3(2), P(1)]Ru(1)]C(1) 92.1(2), P(1)] Ru(1)]C(3) 90.3(2), Ru(1)]Ru(2)]Ru(3) 60.0, C(4)]P(1)]C(10) 101.4(3), C(10)]P(1)]C(16) 102.5(3) † Spectroscopic data for cluster 1.IR(CH2Cl2): n(CO) 1959vs, 1949vs cm21; 1H NMR (CDCl3): d 1.29–2.04 (m, C6H11); 31P NMR (CDCl3): d 47.3 (s, PCy3); FAB-MS: m/z 1397 (1395 related to 101Ru) (Found: C, 52.64; H, 7.0.Calc. for C63H99O9P3Ru3?2H2O: C, 52.82; H, 7.25%). ‡ Crystal data for cluster 1. C63H99O9P3Ru3?2H2O, M 1474.52, cubic space group Pa3� , a = 24.1347(12) Å, U = 14 058.1(12) Å3, T = 223(2) K, Z = 8, m(Mo-Ka) = 0.802 mm21. 4156 Reflections collected. Disordered molecules of dichloromethane and water were found in the crystal structure. Refinement converged at R1 = 0.0577 and wR2 = 0.1346 for 3224 data with I > 2s(I), and R1 = 0.0837 and wR2 = 0.1536 for all 4156 unique data.516 J. Chem.Soc., Dalton Trans., 1998, Pages 515–516 2.860(1) Å].11 The molecule 1 has almost D3h symmetry, the three phosphorus atoms being almost in the plane of the three ruthenium atoms (maximum distance between P and the Ru3 plane 0.20 Å) and the torsion angles C(axial)]Ru]Ru]C(axial) being less than 108. If Na[Ru3H(CO)11] is reacted with PCy3 (1 : 5) in methanol in an open reactor for 1 h under reflux (80 8C bath temperature), the reaction yields (instead of 1) the dihydro cluster [Ru3H2- (CO)6(PCy3)3] 2.The product precipitates directly from the reaction solution as a purple powder (60% yield). It can be recrystallised from dichloromethane–methanol to give dark red, block-shaped crystals which, in contrast to 1, are airsensitive. The 1H NMR spectrum of 2 shows two signals in the region of m3-hydrides, both showing a homo-spin coupling with the other hydride ligand and two hetero-spin couplings with the two types of phosphorus atoms (two trans and one cis, or one trans and two cis).§ The single-crystal X-ray structure analysis ¶ of 2 (Fig. 2) shows Fig. 2 Molecular structure of [Ru3H2(CO)6(PCy3)3] 2 showing the atom numbering scheme; H atoms on carbon have been omitted for clarity. Selected bond lengths (Å): Ru(1)]Ru(2) 2.6702(6), Ru(1)]Ru(3) 2.7180(7), Ru(2)]Ru(3) 2.6931(7), Ru(1)]P(1) 2.332(2), Ru(2)]P(3) 2.336(2), Ru(3)]P(2) 2.344(2), Ru(1)]H(1) 1.94, Ru(1)]H(2) 1.61, Ru(2)]H(1) 2.04, Ru(2)]H(2) 1.94, Ru(3)]H(1) 1.93, Ru(3)]H(2) 1.85, Ru(1)]C(4) 1.834(7), Ru(2)]C(6) 1.834(7), Ru(3)]C(5) 1.825(8), Ru(1)]C(1) 2.134(7), Ru(1)]C(3) 2.154(6), Ru(2)]C(3) 2.129(6), Ru(2)]C(2) 2.107(7), Ru(3)]C(2) 2.147(5), Ru(3)]C(1) 2.161(6) § Spectroscopic data for cluster 2.IR(CH2Cl2): n(CO) 2027vw, 1949m, 1917vs, 1871w, 1855w, 1819vs, 1757w cm21; 1H NMR (CDCl3): d 1.27– 2.30 (99 H, m, C6H11), 219.46 [1 H, dtd, J (H2]P3) = 28.3, J(H2]P1,P2) = 5.3, J(H1]H2) = 2.2, m3-H2], 221.02 [1 H, tdd, J(H1]P1,P2) = 26.4, J(H1]P3) = 5.4, J(H1]H2) = 2.1 Hz, m3-H1]; 31P-{1H} NMR (CDCl3): d 74.8 (s, 1 P), 71.3 (s, 2 P), no coupling observed; FABMS: m/z 1313 (based on 101Ru) (Found: C, 53.63; H, 7.45. Calc.for C60H101O6P3Ru3?2H2O: C, 53.36; H, 7.84%). ¶ Crystal data for cluster 2. C60H101O6P3Ru3?2H2O, M 1314.53, monoclinic, space group P21/n, a = 10.561(1), b = 36.649(2), c = 15.957(1) Å, b = 96.32(1)8, U = 6138.4(8) Å3, T = 223(2) K, Z = 4, m(Mo-Ka) = 0.854 mm21. 38 984 Reflections were collected. The cyclohexyl ring C(31)]C(36) was found to be disordered. Two positions for atoms C(33) and C(36) (the head and the foot of the chair conformation) were refined with occupancy 0.5 each. Refinement converged at R1 0.049 and wR2 = 0.090 for 6231 data with I > 2s(I ), and R1 = 0.104 and wR2 = 0.103 for all 11 651 unique data. CCDC reference number 186/ 846. See http://www.rsc.org/suppdata/dt/1998/515/ for crystallographic files in .cif format.a Ru3 skeleton bearing two m3-hydrido caps, one on either side of the triangle. The three Ru]Ru bonds are bridged by three m2-carbonyl ligands, being almost in the plane of the metal triangle. The three terminal carbonyl ligands as well as the three phosphine ligands are co-ordinated to the three Ru atoms, above and below the metal plane. Complex 2 is, to our knowledge, the only Ru3 cluster known presenting an electron count of 44.Trinuclear clusters with 44e have been reporting so far only for d8 metals: [Pd3(SO2)2(ButNC)5],12 [Pt3(CO)3(PCy3)3] 13 and [FePt2(CO)5{P(OPh)3}3].14 In accordance with this high electron deficiency, the Ru]Ru bonds in 2 are found to be rather short [2.6702(6), 2.6931(7) and 2.7180(7) Å] with respect to the typical Ru]Ru single bonds [2.9396(8) Å] in 1. In addition, the Ru]P bonds in 2 [2.332(2), 2.336(2) and 2.344(2) Å] are also shorter than in 1 [2.414(2) Å]. The two capping hydride ligands are slightly unsymmetrically co-ordinated, H(2) is also closer to the Ru3 triangle than H(1), reflecting the different environments [one PCy3 and two CO ligands surrounding H(2), two PCy3 and one CO ligands surrounding H(1)].Owing to the high degree of unsaturation (4e with respect to the EAN rule) cluster 2 is expected to be a highly reactive species. A study on the reactivity of 2 towards CO and other simple molecules is in progress. References 1 A. J. Deeming, in Comprehensive Organometallic Chemistry II, eds.E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995, vol. 7, ch. 12. 2 M. I. Bruce, G. Shaw and F. G. A. Stone, J. Chem. Soc., Dalton Trans., 1972, 2094. 3 B. F. G. Johnson, J. Lewis and D. Pippard, J. Organomet. Chem., 1978, 160, 263; J. Chem. Soc., Dalton Trans., 1981, 407. 4 (a) M. I. Bruce, D. C. Kehoe, J. G. Matisons, B. K. Nicholson, P. H. Riegger and M. L. Williams, J. Chem. Soc., Chem. Commun., 1982, 442; (b) M.I. Bruce, J. G. Matisons and B. K. Nicholson, J. Organomet. Chem., 1983, 247, 321. 5 C. E. Kampe, N. M. Boag, C. B. Knobler and H. D. Kaesz, Inorg. Chem., 1984, 23, 1390; G. Lavigne and H. D. Kaesz, J. Am. Chem. Soc., 1984, 106, 4647. 6 (a) H. C. Böttcher, G. Rheinwald, H. Stoeckli-Evans and G. Süss- Fink, J. Organomet. Chem., 1994, 469, 163; (b) H. C. Böttcher, H. Thönnessen, P. G. Jones and R. Schmutzler, J. Organomet. Chem., 1996, 520, 15. 7 G. Süss-Fink, G. Rheinwald and H. Stoeckli-Evans, Inorg. Chem., 1996, 35, 3081. 8 N. E. Leadbeater, J. Lewis and P. R. Raithby, J. Organomet. Chem., 1997, 543, 251. 9 B. F. G. Johnson, J. Lewis, P. R. Raithby and G. Süss-Fink, J. Chem. Soc., Dalton Trans., 1979, 1356; G. Süss-Fink, Inorg. Synth., 1986, 24, 168. 10 M. I. Bruce, M. J. Liddell, O. bin Shawkataly, C. A. Hughes, B. W. Skelton and A. H. White, J. Organomet. Chem., 1988, 347, 207. 11 M. R. Churchill, F. J. Hollander and J. P. Hutchinson, Inorg. Chem., 1977, 16, 2655. 12 R. J. Haines, N. D. C. T. Steen and R. B. English, J. Organomet. Chem., 1981, 209, C34; J. Chem. Soc., Dalton Trans., 1984, 515. 13 S. Otsuka, Y. Tatsuno, M. Miki, T. Aoki, M. Matsumoto, H. Yoshioka and K. Nakatsu, J. Chem. Soc., Chem. Commun., 1973, 445. 14 A. Albinati, G. Cartuan and A. Musco, Inorg. Chim. Acta, 1977, 22, L31. Received 7th November 1997; Communication 7/08037I

ISSN:1477-9226    

DOI:10.1039/a708037i

出版商:RSC    

年代:1998

数据来源: RSC