Organometallics 2010, 29, 473–477 DOI: 10.1021/om900891a
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Bimetallic Dihydrobis(methimazolyl)borate Coordination: Structure [Mo2{μ2-H2B(mt)2}(CO)7][Au2(μ2-H2B(mt)2}](PEt3)2] (mt = methimazolyl) Anthony F. Hill,* Matthew K. Smith, Never Tshabang, and Anthony C. Willis Research School of Chemistry, Institute of Advanced Studies, Australian National University, Canberra, ACT, Australia Received October 13, 2009
The reaction of Na[H2B(mt)2] (mt = methimazolyl) with [AuBr(PEt3)] provides [Au{H2B(mt)2}(PEt3)], which reacts with [Mo(CO)3(NCMe)3] or [Mo(CO)3(η6-C7H8)] to provide the bimetallic salt [Mo2{μ2H2B(mt)2}(CO)7][Au2{μ2-H2B(mt)2}](PEt3)2], featuring two distinct coordination modes for the H2B(mt)2 bridging ligands.
Introduction It has been suggested1 that the poly(methimazolyl)borate class of anionic ligands HxB(mt)4-x (x = 1, 2; methimazolyl, Chart 1) might have a role to play in bioinorganic chemistry as “tame thiolate” mimics. For most first-row biologically significant metals this would in general appear to be the case. Vahrenkamp,1 Reglinski,2 Parkin,3 and Rabinovich4 have each demonstrated that the curtailed propensity toward bridging by methimazolyl groups provides a useful design
feature for the study of small-molecule models of metalloenzymes involving sulfur-rich coordination environments. Nevertheless, a number of bi- and trimetallic complexes have now been isolated in which poly(methimazolyl)borate ligands adopt a bridging role.1e,f,2c,4a,4c,5 However, with the exception of molybdenum, the transition metals commonly explored from a bioinorganic perspective are not especially thiophilic (i.e., “soft”), such that bridging coordination modes have not generally been a feature of the biomimetic chemistry of poly(methimazolyl) chelates, to date. Thus, for example, binuclear complexes of the form [M2(μ-X)2{HB(mt)3}2] (MX = MnCl, FeCl, NiCl, NiBr) involve halide rather than sulfur bridges and appear to be prevalent,6 though it is implicit in their synthesis from [M{HB(mt)3}2] and MX2 that sulfur-bridged intermediates play a role in their formation.
*To whom correspondence should be addressed. E-mail: a.hill@anu. edu.au. (1) (a) Ibrahim, M. M.; Shu, M.; Vahrenkamp, H. Eur. J. Inorg. Chem. 2005, 1388. (b) Seebacher, J.; Shu, M.; Vahrenkamp, H. Chem. Commun. 2003, 2502. (c) Ji, M.; Benkmil, B.; Vahrenkamp, H. Inorg. Chem. 2005, 44, 3518. (d) Benkmil, B.; Ji, M.; Vahrenkamp, H. Inorg. Chem. 2004, 43, 8212. (e) Schneider, A.; Vahrenkamp, H. Z. Anorg. Allg. Chem. 2004, 630, 1059. (f ) Seebacher, J.; Vahrenkamp, H. J. Mol. Struct. 2003, 656, 177. (g) Shu, M.; Walz, R.; Wu, B.; Seebacher, J.; Vahrenkamp, H. Eur. J. Inorg. Chem. 2003, 2502. (h) Tesmer, M.; Shu, M.; Vahrenkamp, H. Inorg. Chem. 2001, 40, 4022. (2) (a) Garner, M.; Reglinski, J.; Cassidy, I.; Spicer, M. D.; Kennedy, A. R. Chem. Commun. 1996, 1975. (b) Reglinski, J.; Garner, M.; Cassidy, I. D.; Slavin, P. A.; Spicer, M. D.; Armstrong, D. R. Dalton Trans. 1999, 2119. (c) Dodds, C. A.; Garner, M.; Reglinski, J.; Spicer, M. D. Inorg. Chem. 2006, 45, 2733. (d) Garner, M.; Lehmann, M.-A.; Reglinski, J.; Spicer, M. D. Organometallics 2001, 20, 5233. (e) Wallace, D.; Gibson, L. T.; Reglinski, J.; Spicer, M. D. Inorg. Chem. 2007, 46, 3804. (f ) Cassidy, I.; Garner, M.; Kennedy, A. R.; Potts, G. B. S.; Reglinski, J.; Slavin, P. A.; Spicer, M. D. Eur. J. Inorg. Chem. 2002, 1235. (g) Dodds, C. A.; Lehmann, M.-A.; Ojo, J. F.; Reglinski, J.; Spicer, M. D. Inorg. Chem. 2004, 43, 4927. (h) Schwalbe, M.; Andrikopoulos, P. C.; Armstrong, D. R.; Reglinski, J.; Spicer, M. D. Eur. J. Inorg. Chem. 2007, 1351. (i) Spicer, M. D.; Reglinski, J. Eur. J. Inorg. Chem. 2009, 1553. (3) (a) Kimblin, C.; Hascall, T.; Parkin, G. Inorg. Chem. 1997, 36, 5680. (b) Kimblin, C.; Bridgewater, B. M.; Hascall, T.; Parkin, G. Dalton Trans. 2000, 891. (c) Melnick, J. G.; Docrat, A.; Parkin, G. Chem. Commun. 2004, 2870. (d) Morlok, M. M.; Docrat, A.; Janak, K. E.; Tanski, J. M.; Parkin, G. Dalton Trans. 2004, 3448. (e) Docrat, A.; Morlok, M. M.; Bridgewater, B. M.; Churchill, D. G.; Parkin, G. Polyhedron 2004, 23, 481. (f ) Bridgewater, B. M.; Fillebeen, T.; Friesner, R. A.; Parkin, G. Dalton Trans. 2000, 4494. (g) Kimblin, C.; Bridgewater, B. M.; Churchill, D. G.; Hascall, T.; Parkin, G. Inorg. Chem. 2000, 39, 4240. (h) Parkin, G. Chem. Rev. 2004, 104, 699. (i) Minoura, M.; Landry, V. K.; Melnick, J. G.; Pang, K.; Marchio, L.; Parkin, G. Chem. Commun. 2006, 3990. ( j) Figueroa, J. S.; Melnick, J. G.; Parkin., G. Inorg. Chem. 2006, 45, 7056. (k) Kimblin, C.; Churchill, D. G.; Bridgewater, B. M.; Girard, J. N.; Quarless, D. A.; Parkin, G. Polyhedron 2001, 20, 1891.
(4) (a) Mihalcik, D. J.; White, J. L.; Tanski, J. M.; Zakharov, L. N.; Yap, G. P. A.; Incarvito, C. D.; Rheingold, A. L.; Rabinovich, D. Dalton Trans. 2004, 1626. (b) Graham, L. A.; Fout, A. R.; Kuehne, K. R.; White, J. L.; Mookherji, B.; Marks, F. M.; Yap, G. P. A.; Zakharov, L. N.; Rheingold, A. L.; Rabinovich, D. Dalton Trans. 2005, 171. (c) Patel, D. V.; Mihalcik, D. J.; Kreisel, K. A.; Yap, G. P. A.; Zakharov, L. N.; Kassel, W. S.; Rheingold, A. L.; Rabinovich, D. Dalton Trans. 2005, 2410. (d) Alvarez, H. M.; Tanski, J. M.; Rabinovich, D. Polyhedron 2004, 23, 395. (e) Philson, L. A.; Alyounes, D. M.; Zakharov, L. N.; Rheingold, A. L.; Rabinovich, D. Polyhedron 2003, 22, 3461. (f ) White, J. L.; Tanski, J. M.; Rabinovich, D. Dalton Trans. 2002, 2987. (g) Bakbak, S.; Incarvito, C. D.; Rheingold, A. L.; Rabinovich, D. Inorg. Chem. 2002, 41, 998. (h) Bakbak, S.; Bhatia, V. K.; Incarvito, C. D.; Rheingold, A. L.; Rabinovich, D. Polyhedron 2001, 20, 3343. (i) Alvarez, H. M.; Krawiec, M.; Donovan-Merkert, B. T.; Fouzi, M.; Rabinovich, D. Inorg. Chem. 2001, 40, 5736. ( j) Patel, D. V.; Kreisel, K. A.; Yap, G. P. A.; Rabinovich, D. Inorg. Chem. Commun. 2006, 9, 748. (k) Maffett, L. S.; Gunter, K. L.; Kreisel, K. A.; Yap, G. P. A.; Rabinovich, D. Polyhedron 2007, 26, 4758. (5) (a) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2005, 24, 4889. (b) Crossley, I. R.; Hill, A. F.; Humphrey, E. R.; Willis, A. C. Organometallics 2005, 24, 4083. (c) Cade, I. A.; Hill, A. F.; Tshabang, N.; Smith, M. K. Organometallics 2009, 28, 1143. (d) Foreman, M. R. St.-J.; Hill, A. F.; Smith, M. K.; Tshabang, N. Organometallics 2005, 24, 5224. (e) Effendy; Lobbia, G. G.; Pettinari, C.; Santini, C.; Skelton, B. W.; White, A. H. Inorg. Chim. Acta 2000, 308, 65. (f ) Cetin, A.; Ziegler, C. J. Dalton Trans. 2006, 1006. (6) Senda, S.; Ohki, Y.; Hirayama, T.; Toda, D.; Chen, J.-L.; Matsumoto, T.; Kawaguchi, H.; Tatsumi, K. Inorg. Chem. 2006, 45, 9914.
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Organometallics, Vol. 29, No. 2, 2010
Chart 1. Dihydrobis(methimazolyl)borate Coordination: (a) K3H,S,S0 ; (b) K2-S,S0 ; (c) K1-S
We have recently suggested on the basis of spectroscopic data that the anionic complex [Mo2{μ-H2B(mt)2}(CO)7]- is a plausible intermediate in the synthesis of [Mo2Au{μ:κ3, κ2-H2B(mt)2}(CO)7(PPh3)] from the sequential treatment of Na[H2B(mt)2)] with [Mo(CO)4(pip)2] (pip=piperidine), [Mo(CO)3(η6-C7H8)] (or [Mo(CO)3(NCMe)3]), and [AuCl(PPh3)].5c The same complex arises from the reaction of preformed [Au{H2B(mt)2}(PPh3)]7 with [Mo(CO)4(pip)2] (Scheme 1). In an attempt to illuminate the concourse of this trimetallic species, we have investigated the reaction of the (new) complex [Au{H2B(mt)2}(PEt3)] with [Mo(CO)3(NCMe)3], which in contrast does not afford a molybdenum-gold bonded species but rather the salt [Mo2{μ-H2B(mt)2}(CO)7][Au2(μ-H2B(mt)2}(PPh3)2], which features two distinct bridging modes for the H2B(mt)2 ligands.
Hill et al. Scheme 1. Synthesis of Bi- and Trimetallic H2B(mt)2 Complexes:5c (i) [Mo(pip)2(CO)4], (ii) [Mo(CO)3(η6-C7H8)] or [M(CO)3(NCMe)3] (M = Mo, W), (iii) [AuCl(PPh3)]
Scheme 2a
Results and Discussion Rabinovich has described the structural characterization of the complex [Au(PPh3){H2B(mt)2}] (1),7 in which the gold center is coordinated by the phosphine and both sulfur donors of the H2B(mt)2 ligand. Furthermore, a close approach between the B-H group and the gold center (B-H 3 3 3 Au = 2.557 A˚) might be taken to indicate a secondary interaction. The related complex [Au(PPh3){HB(mttBu)3}] has even shorter B-H 3 3 3 Au separations (2.450-2.489 A˚).4c Complex 1 results from the reaction of Na[H2B(mt)2]8 and either [Au(NO3)(PPh3)]7 or [AuCl(PPh3)].5c In contrast, Reglinski and Spicer have reported that the reaction of Li[PhB(mt)3] with [AuCl(PEt3)] affords [Au(PEt3){PhB(mt)3}] (2), in which the potential chelate coordinates to gold through a single sulfur donor.2c We find that a similar reaction occurs between [AuBr(PEt3)]9 and Na[H2B(mt)2] to afford the complex [Au(PEt3){H2B(mt)2}] (3) in high yield (Scheme 2). The formulation of 3 rests on spectroscopic and elemental microanalytical data and a crystallographic study, the results of which are summarized in Figure 1. The 1H NMR spectrum of 2 indicates a single methimazolyl environment, and it might therefore be supposed that a similar structure is adopted by 2 to that observed in the solid state for 1. However, this appears to not be the case in that while fluxionality may equilibrate the two methimazolyl groups on the NMR time scale (as observed for 22c), the solid-state structure of 3 is distinct from that of 1 and more akin to that of 2. (7) Mohamed, A. A.; Rabinovich, D.; Fackler, J. P. Acta Crystallogr., Sect. E: Struct. Rep. Online 2002, 58, m726. (8) Foreman, M. R. St.-J.; Hill, A. F.; Tshabang, N.; White, A. J. P.; Williams, D. J. Organometallics 2003, 22, 5593. (9) (a) Coates, G. E.; Kowala, C.; Swan, J. M. Aust. J. Chem. 1966, 19, 539. (b) Gibson, C. S.; Johnson, J. D. A. J. Chem. Soc. 1929, 1229.
a Reagents: (i) [AuBr(PEt3)]. (ii) [Mo(CO)3(NCMe)3] or [Mo(CO)3(η6-C7H8)].
The most notable feature of 3 is that, in contrast to 1, the normally strongly chelating H2B(mt)2 ligand adopts a monodentate mode of coordination, leaving one methimazolyl donor pendant. The geometry at gold is essentially linear (174.99(9)°) with no statistically significant ( 2σ([I]), 2θ e 55°), 220 parameters, three restraints, CCDC 750505. Synthesis of [Mo2{H2B(mt)2}(CO)7][Au2(μ-H2B(mt)2}(PEt3)2] (4). A mixture of [Mo(CO)3(NCMe)3]20 (0.14 g, 0.45 mmol) and [Au{H2B(mt)2}(PEt3)] (1: 0.25 g, 0.45 mmol) was stirred in tetrahydrofuran (20 mL) for 12 h at room temperature. The reaction was monitored by infrared spectroscopy to ensure that the starting molybdenum complex had been consumed (only a slight color change occurs during the reaction). The THF was removed under vacuum, the product was extracted with CH2Cl2 (2 10 mL), the total solvent volume of the combined and filtered extracts was reduced to a minimum, and air-free ethanol (20 mL) was added. The total volume was reduced slowly under dynamic vacuum to provide a yellow crystalline product. The product was washed with diethyl ether (2 15 mL) and dried under vacuum. The crude product was recrystallized once from CH2Cl2 and ethanol. Yield = 0.21 g (53%). IR (CH2Cl2): νBH = 2417 cm-1, νBHMo = 2280 cm-1, νCO = 2015, 1916, 1902, 1866, 1800 cm-1. IR (Nujol): νBH = 2409 cm-1, νBHMo = 2282 cm-1, νCO = 2013, 1917, 1990, 1873, 1794 cm-1. 1H NMR (25 °C, CD2Cl2): δH -4.18 (m br, 1 H BHMo), 1.23 (m, 9 H,
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CCH3), 1.72 (m, 6 H, PCH2), 3.69 (s, 6 H, NCH3), 3.73 (s, 6 H, NCH3), 7.09, 7.00, 6.92, 6.89 (d 4, 3JHH = 2 Hz, 2 H 4, NHCdCHN) ppm. 13C{1H} NMR (25 °C, CD2Cl2): δC 221.5, 214.7, 206.4 (MoCO), 160.6, 164.2 (NCdS), 126.7, 124.9, 119.8, 118.6, (NHCdCHN), 35.4, 35.2 (NCH3), 18.4 (d, 1JPC = 34.0 Hz, PCH2), 8.93 (CCH3) ppm. 31P{1H} NMR (25 °C, CD2Cl2): δP 36.4 ppm. FAB-MS(þve): m/z 869.2(100) [M]þ, 743.6(30) [M-PEt3]þ]. ESI-MS(-ve): m/z 438.9(10) [M - 7CO]-. Anal. Found C, 27.61; H, 3.61; N, 7.53. Calcd for C17H27AuBN4O3PS2Mo: C, 27.81; H, 3.71; N, 7.63. A sample of 4 3 CH2Cl2 for crystallographic analysis was obtained by layering hexane on a saturated solution of 4 in CH2Cl2. Crystal data: [C20H42Au2BN4P2S2][C15H12BMo2N4O7S2] 3 CH2Cl2; Mr = 1581.44; triclinic; P1(No 2); a = 14.9617(2) A˚; b = 15.0139(2) A˚; c = 15.7497(2) A˚; a = 70.5816(9)°; β = 64.4391(8)°; γ = 62.1557(8)°; V = 2783.84(7) A˚3 ; Z = 2; Dc = 1.887 Mg m-3; μ(Mo KR) = 6.046 mm-1; T = 200(2) K, yellow plate, 0.20 0.15 0.12 mm; 67 579 independent measured reflections, F refinement, R1=0.0294, wR2=0.0317; 8071 independent observed absorption corrected reflections [I ] > 3σ([I ]), 2θmax e 54°], 603 parameters, CCDC 750506.
Acknowledgment. We thank the Australian Research Council (ARC) for financial support (Grant No. DP0556236) and the University of Botswana for a studentship (to N.T.). Supporting Information Available: Full details of the crystal structure determinations of 3 (CCDC 750505) and 4 3 CH2Cl2 (CCDC 750506) in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.
