Bis(methimazolyl)silyl Complexes of Ruthenium - American Chemical

Jan 28, 2010 - (Hmt) and phenyldichlorosilane, reacts with [Ru(η4-C8H12)(η6-C8H10)] in refluxing tetrahydrofuran to provide the cis and trans isomer...
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Organometallics 2010, 29, 1026–1031 DOI: 10.1021/om901067t

Bis(methimazolyl)silyl Complexes of Ruthenium Anthony F. Hill,*,† Horst Neumann,† and J€ org Wagler*,†,‡ †

Research School of Chemistry, Institute of Advanced Studies, The Australian National University, Canberra, ACT 0200, Australia, and ‡Institut f€ ur Anorganische Chemie, Technische Universit€ at Bergakademie Freiberg, D-09596 Freiberg, Germany Received December 12, 2009

The new bis(methimazolyl)silane PhSiH(mt)2 (mt = methimazolyl), obtained from methimazole (Hmt) and phenyldichlorosilane, reacts with [Ru(η4-C8H12)(η6-C8H10)] in refluxing tetrahydrofuran to provide the cis and trans isomers of [Ru{κ3Si,S,S0 -SiPh(mt)2}]. The structurally characterized trans isomer crystallizes directly from THF but on dissolution in CH2Cl2 converts exclusively to the cis isomer.

The dihydrobis(methimazolyl)borate ligand, [H2B(mt)2]-, coordinates to a diverse variety of metal centers and in doing so displays a geometrically derived proclivity toward tridentate coordination through two sulfur donors and one threecenter, two-electron B-H-metal interaction (Chart 1; A, κ3H,S,S0 ).1,2 This behavior is of particular relevance to the *To whom correspondence should be addressed. E-mail: a.hill@ anu.edu.au (A.F.H.); [email protected] (J.W.). (1) (a) Crossley, I. R.; Hill, A. F.; Humphrey, E. R.; Smith, M. K. Organometallics 2006, 25, 2242. (b) Hill, A. F.; Smith, M. K. Dalton Trans. 2005, 28. (c) Hill, A. F.; Smith, M. K. Dalton Trans. 2007, 3363. (d) Hill, A. F.; Smith, M. K. Organometallics 2007, 26, 3900. (e) Hill, A. F.; Smith, M. K. Chem. Commun. 2005, 1920. (f) Hill, A. F.; Smith, M. K.; Wagler, J. Organometallics 2008, 27, 2137. (g) Abernethy, R. J.; Foreman, M. R. St.-J.; Hill, A. F.; Tshabang, N.; Willis, A. C.; Young, R. D. Organometallics 2008, 27, 4455. (h) Foreman, M. R. St.-J.; Hill, A. F.; Smith, M. K.; Tshabang, N. Organometallics 2005, 24, 5224. (i) Abernethy, R. J.; Hill, A. F.; Neumann, H.; Willis, A. C. Inorg. Chim. Acta 2005, 358, 1605. (j) Abernethy, R. J.; Foreman, M. R. St.-J.; Hill, A. F.; Tshabang, N.; Willis, A. C.; Young, R. D. Organometallics 2008, 27, 4455. (k) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2005, 24, 4889. (2) (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) Kimblin, C.; Bridgewater, B. M.; Hascall, T.; Parkin, G. Dalton Trans. 2000, 1267. (d) Kimblin, C.; Bridgewater, B. M.; Churchill, D. G.; Hascall, T.; Parkin, G. Inorg. Chem. 2000, 39, 4240. (e) 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. (f) Alvarez, H. M.; Gillespie, P. A.; Gause, C. D.; Rheingold, A. L.; Golen, J. A.; Rabinovich, D. Polyhedron 2004, 23, 617. (g) Alvarez, H. M.; Tanski, J. M.; Rabinovich, D. Polyhedron 2004, 23, 395. (h) Philson, L. A.; Alyounes, D. M.; Zakharov, L. N.; Rheingold, A. L.; Rabinovich, D. Polyhedron 2003, 22, 3461. (i) White, J. L.; Tanski, J. M.; Churchill, D. G.; Rheingold, A. L.; Rabinovich, D. J. Chem. Crystallogr. 2003, 33, 437. (j) Alvarez, H. M.; Tran, T. B.; Richter, M. A.; Alyounes, D. M.; Rabinovich, D.; Tanski, J. M.; Krawiec, M. Inorg. Chem. 2003, 42, 2149. (k) Mohamed, A. A.; Rabinovich, D.; Fackler, J. P. Acta Crystallogr., Sect. E 2002, E58, m726. (l) Alvarez, H. M.; Krawiec, M.; DonovanMerkert, B. T.; Houzi, M.; Rabinovich, D. Inorg. Chem. 2001, 40, 5736. (m) Maria, L.; Paulo, A.; Santos, I. C.; Santos, I.; Kurz, P.; Spingler, B.; Alberto, R. J. Am. Chem. Soc. 2006, 128, 14590. (n) Paulo, A.; Correia, J. D. G.; Campello, M. P. C.; Santos, I. Polyhedron 2004, 23, 331. (o) Garcia, R.; Xing, Y.-H.; Paulo, A.; Domingos, A.; Santos, I. Dalton Trans. 2002, 4236. (p) Garcia, R.; Domingos, A.; Paulo, A.; Santos, I.; Alberto, R. Inorg. Chem. 2002, 41, 2422. (q) Garcia, R.; Paulo, A.; Domingos, A.; Santos, I. J. Organomet. Chem. 2001, 632, 41. (r) Garcia, R.; Paulo, A.; Domingos, A.; Santos, I.; Ortner, K.; Alberto, R. J. Am. Chem. Soc. 2000, 122, 11240. (s) Kuan, S.; Ling, L.; Weng, K.; Goh, L. Y.; Webster, R. D. J. Organomet. Chem. 2006, 691, 907. pubs.acs.org/Organometallics

Published on Web 01/28/2010

mechanism by which such complexes of the platinum group metals may evolve, via B-H activation, into dibuttressed metallaboratranes which feature a dative MfB bond (B, κ3B,S,S0 ).3,4 It has also been noted that rhodium complexes of the bis(methimazolyl)methane ligand adopt geometries that bring one C-H bond of the bridgehead methylene into close (“pregostic”) proximity with the rhodium center,1a while bis(imidazolyl)triselenane, when coordinated to ruthenium, does so via one bridgehead selenoether and two nitrogen donors.5 In addition to facilitating the formation of MfB interactions, methimazolyl bridges have also been found to support bimetallic assemblies,1b including recent examples of dative PdfSn, PdfSi, and PtfSi bonds in the complexes [PdSn(μ-mt)4Cl2](PdfSn) and [MSi(μ-mt)4Cl2](MfSi) (M = Pd, Pt).6 It has even been observed that in some cases the tris(methimazolyl)borate ligand adopts the κ3H,S,S0 coordination mode in preference to the more common κ3S,S0 ,S00 (3) (a) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2006, 25, 289. (b) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2007, 26, 3891. (c) Crossley, I. R.; Hill, A. F.; Humphrey, E. R.; Willis, A. C. Organometallics 2005, 24, 4083. (d) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2005, 24, 1062. (e) Crossley, I. R.; Foreman, M. R. St.-J.; Hill, A. F.; White, A. J. P.; Williams, D. J. Chem. Commun. 2005, 221. (f) Crossley, I. R.; Hill, A. F. Organometallics 2004, 23, 5656. (g) Foreman, M. R. St.-J.; Hill, A. F.; White, A. J. P.; Williams, D. J. Organometallics 2004, 23, 913. (h) Hill, A. F.; Owen, G. R.; White, A. J. P.; Williams, D. J. Angew. Chem., Int. Ed. 1999, 38, 2759. (i) Crossley, I. R.; Hill, A. F. Dalton Trans. 2008, 201. (j) Crossley, I. R.; Hill, A. F. Dalton Trans. 2008, 231. (k) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2008, 27, 312. (l) Crossley, I. R.; Foreman, M. R. St. J.; Hill, A. F.; Owen, G. R.; White, A. J. P.; Williams, D. J.; Willis, A. C. Organometallics 2008, 27, 381. (4) (a) Pang, K.; Quan, S. M.; Parkin, G. Chem. Commun. 2006, 5015. (b) Figueroa, J. S.; Melnick, J. G.; Parkin, G. Inorg. Chem. 2006, 45, 7056. (c) Landry, V. K.; Melnick, J. G.; Buccella, D.; Pang, K.; Ulichny, J. C.; Parkin, G. Inorg. Chem. 2006, 45, 2588. (d) Pang, K.; Tanski, J. M.; Parkin, G. Chem. Commun. 2008, 1008. (e) 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. (f) Blagg, R. J.; Charmant, J. P. H.; Connelly, N. G.; Haddow, M. F.; Orpen, A. G. Chem. Commun. 2006, 2350. (g) Senda, S.; Ohki, Y.; Yasuhiro, H.; Tomoko, T.; Toda, D.; Chen, J.-L.; Matsumoto, T.; Kawaguchi, H.; Tatsumi, K. Inorg. Chem. 2006, 45, 9914. (5) Dewhurst, R. D.; Hansen, A. R.; Hill, A. F.; Smith, M. K. Organometallics 2006, 25, 5843. (6) (a) Wagler, J.; Hill, A. F.; Heine, T. Eur. J. Inorg. Chem. 2008, 4225. (b) Wagler, J.; Brendler, E. Angew. Chem., Int. Ed. 2010, 49, 624. r 2010 American Chemical Society

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Chart 1. Coordination Modes for (A) Bis(methimazolyl)borate, (B) Bis(methimazolyl)borane, (C) Bis(methimazolyl)silane, and (D) Bis(methimazolyl)silyl Ligands

Figure 1. Molecular structure of HSiPh(mt)2 (1) in the crystal form (200 K, 50% displacement ellipsoids, C-bound hydrogen atoms omitted for clarity, carbon atoms in gray). Selected bond lengths (A˚) and angles (deg): Si1-N3 = 1.759(1), Si1-N1 = 1.776(1), Si1-C9 = 1.8514(12), Si1-H1 = 1.372(16), S1-C1 = 1.6734(13), S2-C5 = 1.6864(12); N3-Si1-N1 = 105.31(5), N3Si1-C9 = 109.68(5), N1-Si1-C9 = 105.98(5), N3-Si1-H1 = 114.1(7), N1-Si1-H1 = 105.7(7), C9-Si1-H1 = 115.2(7). Scheme 2. Reaction of 2 with Ph2PC6H4CH2SiMe2H (3; COD = η4-1,4-Cyclooctadiene, COT = η6-1,3,5-Cyclooctatriene)10 Scheme 1. Synthesis of HSiPh(mt)2 (1)

scorpionate type of coordination.7 Thus, it would appear that the methimazolyl moiety is well-disposed geometrically to orchestrate or sustain unusual bonding situations. Given the diagonal relationship between boron and silicon, we therefore considered whether ligands based on poly(methimazolyl)silanes might show novel features that parallel those already demonstrated for the poly(methimazolyl)borates: i.e., agostic Si-H-metal coordination (C) leading to Si-H bond activation (D). Herein we report the synthesis of bis(methimazolyl)phenylsilane and its reactions with the complexes [Ru(η4-C8H12)(η6-C8H10)] and [Ru(CO)2(PPh3)3], which do indeed proceed via Si-H activation.

Results and Discussion The reaction of phenyldichlorosilane with methimazole (Hmt, 1-methyl-2-mercaptoimidazole) in the presence of triethylamine results in the formation of bis(methimazolyl)phenylsilane, HSiPh(mt)2 (1), in high yield (Scheme 1). Although 1 is the first example of a hydride-substituted methimazolyl silane, it is but one of a diverse range of methimazolylsilanes which we have now prepared via similar protocols and on which we will report in detail subsequently. The formulation of 1 rests on both spectroscopic and crystallographic data (Figure 1). The spectroscopic data call for little comment, other than to note that the retention of the Si-H functional group is indicated directly by the (7) (a) Abernethy, R. J.; Hill, A. F.; Tshabang, N.; Willis, A. C.; Young, R. D. Organometallics 2009, 28, 488. (b) Foreman, M. R. St.-J.; Hill, A. F.; Owen, G. R.; White, A. J. P.; Williams, D. J. Organometallics 2003, 22, 4446.

observation of a Si-H resonance at 6.38 ppm in the 1H NMR spectrum and indirectly by the coupling displayed (1JSiH = 290 Hz) by the doublet resonance observed at 33.8 ppm in the 29Si NMR spectrum. Although the compound is very prone to hydrolysis, satisfactory mass spectra (low and high resolution) were obtained which confirmed the gross composition, as do elemental microanalytical data. Despite the remarkable versatility of the zerovalent ruthenium complex [Ru(η4-C8H12)(η6-C8H10)] (2)8 and the early report that 2 catalyzes the hydrosilylation of alkenes,9 it is only recently that stoichiometric reactions between 2 and silanes have been explored by Sabo-Etienne and co-workers as part of a wider study of σ-complex formation.10 Specifically, the reaction of 2 with the γ-phosphinosilane Ph2PC6H4CH2SiMe2H (3) results in the formation of a bischelate complex derived from benzylic C-H (cf. Si-H) activation and featuring two agostic Si-H-Ru interactions (4; Scheme 2). Agostic Si-H-Ru interactions are also present in the products of the reactions of 2 with chelating (8) (a) Fischer, E. O.; M€ uller, J. Chem. Ber. 1963, 96, 3217. (b) Pertici, P.; Vitulli, G.; Porri, L. J. Chem. Soc., Chem. Commun. 1975, 846. (c) Pertici, P.; Vitulli, G.; Paci, M.; Porri, L. J. Chem. Soc., Dalton Trans. 1980, 1961. (d) Itoh, K.; Nagashima, H.; Ohshima, T.; Ohshima, N.; Nishiyama, J. J. Organomet. Chem. 1984, 272, 179. (e) Frosin, K.-M.; Dahlenburg, L. Inorg. Chim. Acta 1990, 167. (9) Hori, Y.; Mitsudo, T.; Watanabe, Y. Bull. Chem. Soc. Jpn. 1988, 61, 3011. (10) Montiel-Palma, V.; Mu~ noz-Hernandez, M. A.; Ayed, T.; Barthelat, J.-C.; Grellier, M.; Vendier, L.; Sabo-Etienne, S. Chem. Commun. 2007, 3963.

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Hill et al.

Scheme 3. Reaction of 2 with HSiPh(mt)2 (1)

disilanes in the presence of additional phosphines (PR3) under hydrogen pressure, though perhaps under such conditions intermediates of the form [RuH2(H2)2(PR3)2] quite possibly play a role.11 We therefore envisaged that 2 would serve as a suitable substrate for investigating the possibility of 1 entering into agostic Si-H-Ru interactions. Heating a solution of 1 (2 equiv) and 2 in tetrahydrofuran under reflux for 1 h results in the formation of an orange precipitate and a dark brown supernatant. The orange precipitate is the single compound 5 3 THF, and 5 is also present in the supernatant in addition to a second compound, 6. Over a period of 5 h in CD2Cl2 solution at room temperature, preisolated 5 was found to slowly but completely convert to yellow 6 and both 5 and 6 were found to have the same composition by mass spectrometry. These two compounds are therefore formulated as the isomers trans-[Ru{κ3-SiPh(mt)2}2] (5; Scheme 3), which precipitates as a monosolvate from THF, and the more soluble cis-[Ru{κ3-SiPh(mt)2}2] (6; Scheme 3), which is the preferred geometry in the more polar solvent CH2Cl2. The isomer cis-6 is also unstable for prolonged periods in CD2Cl2, eventually decomposing completely over 24 h to unidentified products possibly arising from chloromethylation of the electron-rich thione group(s). Crystals of trans-5 3 THF were obtained from THF, allowing the formulation to be confirmed by a crystallographic study (vide infra, Figure 2). The yellow isomer cis-6, having C2 symmetry, gives rise to two methyl and four NCHCHN resonances in the 1H NMR spectrum. Similarly, two distinct methimazolyl environments are observed in the 13C{1H} NMR spectra, while a single silicon environment is indicated by the 29Si{1H} NMR spectrum (δSi 58.80, cf. δ -34.70 for 1). By way of contrast, the isomer trans-5 displays only one methimazolyl environment in each spectrum. Due to the poor solubility of trans-5 in most solvents, the 29Si resonance was not identified with confidence. A weak signal was observed in CD2Cl2 at δSi (11) (a) Delpech, F.; Sabo-Etienne, S.; Daran, J.-C.; Chaudret, B.; Hussein, K.; Marsden, C. J.; Barthelat, J.-C. J. Am. Chem. Soc. 1999, 121, 6668. (b) Lachaize, S.; Sabo-Etienne, S. Eur. J. Inorg. Chem. 2006, 2105.

Figure 2. Molecular structure of trans-5 in a crystal of 5 3 THF (200 K, 50% displacement ellipsoids, solvent and hydrogen atoms omitted for clarity, atoms in gray generated by the crystallographic inversion center at Ru1 = 1/2, 1/2, 0). Selected bond lengths (A˚) and angles (deg): Ru1-Si1 = 2.349(1), Ru1-S1 = 2.3895(9), Ru1-S2 = 2.3990(9), Si1-N1 = 1.820(3), Si1-N3 = 1.837(3), Si1-C9 = 1.888(4), S1-C5 = 1.703(4), S2-C1 = 1.711(4); Si1-Ru1-S1* = 94.81(3), Si1-Ru1-S1 = 85.19(3), Si1-Ru1-S2* = 95.01(3), Si1-Ru1-S2 = 84.99(3), S1-Ru1-S2* = 92.71(3), S1-Ru1-S2 = 87.29(3), N1-Si1N3 = 99.43(15), N1-Si1-C9 = 102.49(16), N3-Si1-C9 = 100.57(16), N1-Si1-Ru1 = 106.5(1), N3-Si1-Ru1 = 105.24(10), C9-Si1-Ru1 = 136.91(13), C5-S1-Ru1 = 105.19(13), C1S2-Ru1 = 105.04(13) (asterisks denote symmetry-generated atoms).

63.17 which is tentatively assigned to trans-5, with the caveat that in this solvent during the requisite data acquisition period, significant conversion to cis-6 had clearly occurred. Although the RuS4Si2 donor set is without precedent, there nevertheless exist copious structural data for silyl complexes of divalent ruthenium,12 against which to assess the metrical parameters displayed by trans-5. Selected representative examples are collated in Table 1, which presents Ru-Si bond lengths for mononuclear octahedral (or pseudo-octahedral) ruthenium bound to nonchelated four-coordinate silicon LnRu-SiR3, in addition to the sum of the angles between the substituents “R” (Σ). From Table 1 it appears that replacing hydrocarbon silicon substituents with halides generally results in a contraction of the Ru-Si bond lengths, which span almost 0.2 A˚. The values of Ru-Si and Σ for trans-5 are, however, very close to the mean values for this series, and so it might be concluded that the constraints of chelation are not manifested in any untoward distortion of the SiCN2 geometry. Interligand angles are all close to 90°, although notably those between donors of the same chelate are acute while those between donors on adjacent chelates are obtuse. The Ru-S separations of 2.3895(9) and 2.3990(9) A˚ are somewhat shorter than those for poly(methimazolyl)borate and -borane complexes of ruthenium, e.g., [RuH(CO)(PPh3){HB(mt)3}] (2.4448(11), 2.470(2) A˚)7b and [Ru(CO)(PPh3){B(mt)3}] (2.4857(11), 2.4066(14), 2.4112(14) A˚),3h presumably reflecting the more compact nature of the cage due to the formal Ru-Si covalent bonds. The one geometric parameter that is anomalous is the Ru1-Si1-C9 angle, which at 136.91(13)° clearly indicates a departure from ideal tetrahedral silicon (12) Conquest; Cambridge Crystallographic Data Centre, Cambridge, U.K., February 2009 release.

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Table 1. Selected Structural Data for Silyl Complexes of Ruthenium(II)12-20 Ru-Sia (A˚)

complex LnRu-SiR3 þ

[Cp*(Me3P)2Ru(SiMe2CH2Ph3)] (η6-C6H4tBu2)(CO)2Ru(SiCl3)2 Cp(PMe2Ph)2Ru(SiCl3) Cp(PMe3)2Ru(SiCl2Me) Cp(PMe3)2Ru(SiCl2Ph) (CO)3(PPh3)HRu(SiPh3) [Cl3(CO)2Ru(SiClPh2)]2(η-C6H6)(PPh3)Ru(SiMe3)2 (η-C6H6)(PPh3)Ru(SiCl3)2 Cl(CO)(S2CNMe2)(PPh3)2Ru(SiClPh2) (PMe3)4HRu(SiMe3) mean trans-5 a

2.381 2.339 2.282 2.294 2.302 2.446 2.362 2.436 2.325 2.409 2.463 2.37 2.349

P

(deg)

30413 30614 29415 29615 29815 31416 30817 30318 29918 30119 29820 302 303

Mean distances for complexes with two silyl ligands.

geometry. This perhaps reflects a mutual destabilization of the trans-Si-Ru-Si assembly based on the potent transdirecting silyl groups surrounded by a collar of π-dative sulfur donors. Most likely, however, this deformation also represents a response to the cage ring strain. Similar, though less pronounced, openings of the Ru-Si-Ph angles of a range of monotethered silyl complexes have been noted.19 This would account for the downfield 29Si chemical shifts of both 5 and 6 relative to those for more conventional nonchelated ruthenium silyl complexes (ca. -10 to þ20 ppm).11b While the silyl substituents will contribute to the chemical shift, we note that the tripyrrolylsilyl complex [Ru{Si(pyr)3}H3(PPh3)3] (pyr = 1-pyrrolyl)21 with N-heterocyclic Si substituents has δSi 8.6 while the dichloromethylsilyl analogue [Ru(SiMeCl2}H3(PPh3)3]22 has δSi 36.4. It should however also be noted that both these complexes involve three secondary RuIV-H 3 3 3 Si interactions, thereby compromising direct comparison. The mechanism by which 5 and 6 form could proceed in one of two ways. The first is simple substitution of the cyclic polyolefins by two 1 ligands, followed by Si-H activation and elimination of hydrogen. Alternatively, under the conditions employed (THF reflux), rearrangement to the symmetric [Ru(η5-C8H11)2] could occur8 followed by sequential transfer of hydrogen from 1 to generate cyclooctadiene. We have no evidence in support of either possibility but have, with only modest success, investigated the reaction of 1 with [Ru(CO)2(PPh3)3] (7, δP 51.1),23 a zerovalent ruthenium substrate that is devoid of ligands which could act as hydrogen acceptors. Although a reaction ensued, with complete consumption of 7, attempts to isolate a pure complex met with failure, due to the formation of two inseparable side products (vide infra). The major product was the desired complex [RuH(CO)(PPh3){κ3-SiPh(mt)2}] (8); however, this (13) Grumbine, S. K.; Mitchell, G. P.; Straus, D. A.; Tilley, T. D.; Rheingold, A. L. Organometallics 1998, 17, 5607. (14) Einstein, F. W. B.; Jones, T. Inorg. Chem. 1982, 21, 987. (15) Freeman, S. T. N.; Petersen, J. L.; Lemke, F. R. Organometallics 2004, 23, 1153. (16) Brinkley, C. G.; Dewan, J. C.; Wrighton, M. S. Inorg. Chim. Acta 1986, 121, 119. (17) Berenbaum, A.; Lough, A. J.; Manners, I. Acta Crystallogr., Sect. E: Struct. Rep. Online 2002, 58, m679. (18) Burgio, J.; Yardy, N. M.; Petersen, J. L.; Lemke, F. R. Organometallics 2003, 22, 4928. (19) Kwok, W.-H.; Lu, G.-L.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J. J. Organomet. Chem. 2004, 689, 2979. (20) Dioumaev, V. K.; Procopio, L. J.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 2003, 125, 8043.

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forms slowly in contrast to the rapid reaction of 7 with CO liberated by the formation of 8 to provide [Ru(CO)3(PPh3)2] (9) (δP 57.423b) and triphenylphosphine (δP -4.0). The identification of complex 9 included a crystallographic study of a previously unknown but otherwise unremarkable trigonal modification (Experimental Section). The second side product (ca. 15%) was identified as the dihydrido complex cct-RuH2(CO)2(PPh3)2] (δH -12.5, t, 2JPH = 19.4 Hz), which has previously been noted as the sole product of the reaction of 7 with more conventional silanes.24 Nevertheless, sufficient salient spectroscopic data could be extracted from spectra of the three-component product mixture to confidently arrive at the formulation of 8. The 29Si NMR spectrum comprises a doublet (δSi 48.0) showing coupling to phosphorus (2JPSi = 139 Hz), the magnitude of which is consistent with the mutually trans disposition of phosphorus and silicon. Once again, this falls outside the typical chemical shift range for nonchelated ruthenium silyls and may emerge as a recurrent feature of this ligand cage. The 1H NMR spectrum includes a doublet resonance (δH -5.90), showing coupling (2JPH = 12 Hz) consistent with the hydride ligand coordinating cis to the phosphine in addition to revealing two methimazolyl environments. These data taken together point to the geometry depicted in Scheme 4. The complex is thus somewhat reminiscent of the previously reported borate complexes [RuH(CO)(PPh3){κ3H,S,S0 -HxB(mt)4-x] (x = 1, 2).7b Interestingly, and in contrast to 7, the osmium analogue [Os(CO)2(PPh3)3] does react with simple silanes via Si-H oxidative addition,24 while 7 has been shown to react with tripyrrolylsilane to provide [RuH{Si(pyr)3}(CO)2(PPh3)2] (pyr = 1-pyrrolyl).25 Thus, although our working hypothesis, on the basis of boron chemistry, is that the initial chelation through sulfur geometrically predisposes the Si-H bond for oxidative addition, we should not discount the possibility that the first step actually involves coordination through silicon followed by cage closure as a phosphine and carbonyl ligand depart. Concluding Remarks. Initial results indicate that, at least in terms of geometrical factors and diagonal relationships, the parallels indicated in Chart 1 between boron and silicon derivatives of methimazole can be demonstrated. Thus, the coordination and organometallic chemistry of poly(methimazolyl)silanes would appear to be a viable and potentially fertile area of study. However, there is a subtle difference that may have significant ramifications. The boron-based chemistry begins with the salts Na[HxB(mt)4-x] (x = 1, 2), which with the exception of group 6 binary carbonyls have been exclusively combined with metal substrates where the metal is in a positive oxidation state, proceeding via salt elimination. Neutral poly(methimazolyl)silanes in combination with low-valent metal substrates in principle offer an alternative reaction pathway via initial Si-H activation followed by cage closure.

Experimental Section General Considerations. All manipulations were carried out under a dry and oxygen-free nitrogen atmosphere using standard Schlenk, vacuum line, and inert atmosphere (argon) drybox techniques, with dried and degassed solvents which were distilled from either calcium hydride (CH2Cl2) or sodiumpotassium alloy and benzophenone (ethers and paraffins). NMR spectra were obtained at 25 °C on Varian Gemini 300BB (1H at 299.9 MHz and 13C at 75.43 MHz, referenced to

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Organometallics, Vol. 29, No. 4, 2010 Scheme 4. Reaction of 1 with [Ru(CO)2(PPh3)3] (7)

residual protio solvent peaks; 31P at 121.4 MHz, referenced to external 85% D3PO4; 29Si at 59.59 MHz) or Bruker Avance 600 (1H at 600.0 MHz and 13C at 150.9 MHz) spectrometers. Elemental microanalysis was performed by the microanalytical service of the Australian National University. Electrospray (ESI) and EI mass spectrometry was performed by the Research School of Chemistry mass spectrometry service. Data for X-ray crystallography were collected with a Nonius Kappa CCD diffractometer. The compounds [Ru(η4-C8H12)(η6-C8H10)] (2)8 and [Ru(CO)2(PPh3)3] (7)23b were prepared according to the indicated published procedures. Other reagents were used as received from commercial suppliers. Synthesis of HSiPh(mt)2 (1). A solution of methimazole (1.20 g, 10.5 mmol) and triethylamine (1.4 g, 13.9 mmol) in THF (30 mL) was added dropwise to a cooled (-5 °C) solution of phenyldichlorosilane (0.94 g, 5.3 mmol) in THF (10 mL). Immediately a precipitate of triethylammonium chloride formed. The mixture was stored at 4 °C for 2 h and then filtered. The residue was washed with THF (15 mL) and the solvent removed under reduced pressure from the combined filtrate and washings to provide a colorless foam, which was recrystallized from toluene (15 mL) to yield colorless crystals of 1. The supernatant was decanted and the crystals dried under vacuum. Yield: 1.51 g (4.54 mmol, 86%). N.B.: exposure to air results in complete hydrolysis to provide Hmt. Anal. Found: C, 50.41; H, 5.12; N, 16.65. Calcd. for C14H16N4S2Si: C, 50.57; H, 4.85; N, 16.85. 1H NMR (CDCl3, 600.0 MHz): δH 3.56 (s, 6 H, CH3), 6.38 (s, 1 H, Si-H), 6.52 (d, 2 H, 3JHH 2.5 Hz, C3N2H2), 6.73 (d, 2, 3JHH 2.5 Hz, C3N2H2), 7.47 [m, 3 H, H3-5(C6H5)), 7.71 (d, 2 H, 3 JHH 8.0 Hz). 1H NMR (CD2Cl2, 299.9 MHz): δH 3.52 (s, 6 H, CH3), 6.35 (s, 1 H, Si-H), 6.41 (d, 2 H, 3JHH 2.1 Hz, C3N2H2), 6.78 (d, 2, 3JHH 2.4 Hz, C3N2H2), 7.45-7.55 (m, 3 H, H3-5(C6H5)), 7.77 (dd, 2 H, 3JHH 8.0 Hz, 4JHH 1.5 Hz, H2,6(C6H5)). 13 C{1H} NMR (CDCl3, 150.9 MHz): δC 34.4 (CH3), 119.3, 120.7 (NCHCHN),127.0 (C1(C6H5)), 128.5, 134.9 (C2,3,5,6(C6H5)), 131.7 (C4(C6H5)), 168.2 (CdS). 29Si NMR (CDCl3, 99.32 MHz): δSi -33.8 (d, 1JSiH 290 Hz). 29Si NMR (CD2Cl2, 59.59 MHz): δSi -34.70. EI-MS (positive ion, CH2Cl2): m/z 333.0 [HM]þ. Crystals of 1 suitable for diffractometry were obtained from a cooled concentrated solution of 1 in toluene. Crystal data: C14H16N4S2Si; Mr = 332.52; triclinic; P1 (No. 2); a = 7.1934(1) A˚; b = 8.7353(2) A˚; c = 13.6170(2) A˚; R = 105.738(1)°; β = 95.836(1)°; γ = 96.114(1)°; V = 811.23(3) A˚3; Z = 2; colorless plate, 0.64  0.45  0.22 mm; Dc = 1.361 Mg m-3; μ(Mo KR) = 0.40 mm-1; T = 200(2) K. A total of 42 980 absorption-corrected reflections provided 7124 independent reflections, 5135 of which were observed (|I| > 2σ(|I|), 2θ e 70°). F2 refinement gave R1 = 0.0437 and wR2 = 0.1172 for 5135 independent, observed, absorption-corrected

Hill et al. reflections and 194 parameters, with residual electron density between -0.54 and þ 0.58 e A˚ -3. CCDC 705043. Synthesis of [Ru(η4-COD)(η6-COT)](2). Various modifications8d,e of the Vitulli procedure8b,c,26 for preparing this complex have been described, including the observation that complex mixtures are often obtained.8d Our attempts to scale up this method from the original 1.3 mmol procedure resulted in a reduction in yield relative to the 50% originally claimed, though this may be related in part to the variable composition of “RuCl3 3 xH2O” and the activity of the zinc dust used. Commercial cyclooctadiene was passed through a column of neutral alumina under an atmosphere of argon to remove peroxides (unidentified yellow orange material remained bound to the alumina). Zinc dust was degassed in vacuo overnight. To a solution of “RuCl3 3 xH2O” (1.02 g ≈ 3.9 mmol) in degassed ethanol (20 mL) was added peroxide-free 1,5-cyclooctadiene (30.0 mL, 24.3 mmol) followed by degassed zinc dust (9.00 g, 138 mmol, excess). The brown mixture was heated to 80 °C for 3 h, resulting in a black-green suspension. Upon cooling, the mixture was filtered through a plug of degassed diatomaceous earth which was rinsed through with benzene (3  20 mL). The combined filtrates were freed of volatiles in vacuo at 30 °C. The residue was extracted with pentane, and the combined extracts were filtered through a column (5 cm3) of alumina (degassed, activity III) and concentrated to ca. 20 mL. Cooling to -20 °C overnight afforded a small amount of black deposit that was removed by filtration though diatomaceous earth. The filtrate was concentrated to ca. 5 mL and cooled (-20 °C) to afford yellow crystals that were isolated by decantation, washed with cold pentane, and dried in vacuo. Yield: 0.390 g (30%). The same procedure using RuCl3 3 xH2O (1.30 g), EtOH (25 mL), COD (40 mL), and Zn (9.0 g) afforded a comparable yield of 0.430 g (27%). Synthesis of trans-[Ru{K3Si,S,S0 -SiPh(mt)2}2](THF) (5 3 THF). A mixture of [Ru(COD)(COT)] (2; 0.090 g, 0.29 mmol) and PhSiH(mt)2 (1; 0.190 g, 0.57 mmol) in THF (16 mL) was heated under reflux for 1 h, during which time a bright orange precipitate formed. The suspension was cooled slowly to room temperature without stirring and then cooled further in an ice bath. The supernatant was removed by cannula and the residue washed with THF (2  1 mL) and then dried in vacuo. Yield of 5 3 THF: 0.100 g (0.131 mmol, 45%). The volatiles were removed from the supernatant, and this was then dissolved in CD2Cl2 and the 1H NMR spectrum measured immediately to reveal an approximate 1:1 mixture of 5 and 6. N.B.: both 5 and 6 are immediately decomposed upon exposure of their solutions to air. Data for 5 are as follows. IR (KBr, cm-1): 1455 s, 1379 vs, 1295 m, 1280 m, 1170s, 1131 m, 1098 m, 1065 m, 912 w, 957 w. No peaks were observed in regions typical of Ru-H, Si-H, or Si-H-Ru modes (1600-2500 cm-1). Anal. Found: C, 45.82; H, 4.54; N, 13.11. Calcd for C32H38N8RuS4Si2O (5 3 THF): C, 45.96; H, 4.58; N, 13.40. ESI-MS (positive ion, CH2Cl2/MeOH): m/z (%) 882.9 (28) [M þ Na þ 3MeOH]þ, 764.0 (100) [M]þ. Acc mass: m/z found 764.0093, calcd for C28H30N8102RuS4Si2 764.0091. 1H NMR: δH 1.81 (m, 4 H, C2H4), 3.41 (s, 6 H, NCH3), 3.68 (m, 4 H, OCH2), 6.67, 6.77 (d  2, 4 H  2, 3JHH = 1.8 Hz, NCHCHN), 7.45, 7.76 (m  2, (21) H€ ubler, K.; H€ ubler, U.; Roper, W. R.; Schwerdtfeger, P.; Wright, L J. Chem. Eur. J. 1997, 3, 1608. (22) Yardy, N. M.; Lemke, F. R.; Brammer, L. Organometallics 2001, 20, 5670. (23) (a) Cavit, B. E.; Grundy, K. R; Roper, W. R. Chem. Commun. 1972, 60. (b) Hill, A. F.; Tocher, D. A.; White, A. J. P.; Williams, D. J.; Wilton-Ely, J. D. E. T. Organometallics 2005, 24, 5342. (24) Clark, G. R.; Flower, K. R.; Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright, L. J. J. Organomet. Chem. 1993, 462, 331. (25) H€ ubler, K.; Roper, W. R.; Wright, L. J. Organometallics 1997, 16, 2730. (26) Pertici, P.; Vitulli, G.; Spink, W. C.; Rausch, M. D. Inorg. Synth. 1983, 22, 176.

Article 10 H, C6H5). 13C{1H} NMR (150.88 MHz, 25 °C, CD2Cl2): 25.94 (C2H4), 34.82 (NCH3), 68.12 (OCH2), 116.4, 117.5 (NCHCHN), 127.2, 128.4, 134.6 (C6H5); CdS resonances not unequivocally identified. 29Si{1H} NMR (59.59 MHz, 25 °C, CD2Cl2): δSi 63.17 (tentative, see text). The complex cis-6 was not isolated as such, due to the preferred crystallization of the less soluble form trans-5. Solutions of cis-6 were obtained by allowing trans-5 to stand in dichloromethane for 5 h, by which time NMR assay indicated complete isomerization had occurred. ESI-mass spectrometry of these solutions provided data identical with those for the isomer trans-5. Data for cis-6 are as follows. NMR (CD2Cl2, 25 °C): 1H (299.9 MHz) δ 3.38, 3.63 (s  2, 3 H  2, NCH3), 6.26, 6.35, 6.55, 6.70 (d  4, 2 H  4, 3JHH = 1.8 Hz), 7.10, 7.22 (m  2, 10 H, C6H5); 13C{1H} (75.42 MHz) δC 33.89, 34.71 (NCH3), 117.4, 117.5, 122.6, 122.7 (NCHCHN), 127.1, 134.5 (4C  2, C2,3,5,6(C6H5)), 128.5 (C4(C6H5)), 139.0 (C1(C6H5)), 171.8, 173.1 (CS); 29Si{1H} (59.59 MHz) δSi 58.80. Acc. mass: m/z found 764.0063, calcd for C28H30N8102RuS4Si2 764.0091. Crystals of trans-5 3 THF suitable for diffractometry were obtained from a cooled concentrated solution of trans-5 in tetrahydrofuran. Crystal data: C28H30N8RuS4Si2C4H8O; Mr = 836.19; monoclinic; P21/n; a = 14.4461(3) A˚; b = 13.1482(2) A˚; c = 19.7672(4) A˚; β = 92.121(1)°; V = 3752.01(12) A˚3; Z = 4; orange plate, 0.12  0.10  0.05 mm; Dc = 1.480 Mg m-3; μ(Mo KR) = 0.743 mm-1; T = 200(2) K. A total of 44 750 absorption-corrected reflections provided 7339 independent reflections, 5503 of which were observed (|I| > 2σ(|I|), 2θ e 52°). F2 refinement gave R1 = 0.0453 and wR2 = 0.1248 for 5503 independent, observed, absorption-corrected reflections and 466 parameters and 54 restraints, with residual electron density between -1.13 and þ 0.92 e A˚ -3. CCDC 705044. Reaction of [Ru(CO)2(PPh3)3] (7) with PhSiH(mt)2 (1). A mixture of [Ru(CO)2(PPh3)3]23b (7; 0.390 g, 0.414 mmol) and PhSiH(mt)2 (1; 0.140 g, 0.422 mmol) in tetrahydrofuran (2 mL) was stirred at 60 °C for 30 min and then freed of volatiles. The crude mixture thus obtained comprised (31P NMR, CDCl3/ THF) [Ru(CO)3(PPh3)2] (9; δP 57.1, integral 108 for 2 PPh3), [RuH{PhSi(mt)2}(CO)(PPh3)] (8; δP 39.4, integral 54 for 1 PPh3), and PPh3 (δP -4.2, integral 89) in addition to unreacted [Ru(CO)2(PPh3)3] (7; δ 50.5, integral 46 for 3 PPh3) and traces of [RuH2(CO)2(PPh3)2] (δP 58.6, integral 12 for 2 PPh3), corresponding the overall reaction stoichiometry 1 þ 7 þ 7 f 8 þ 9 þ 2

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PPh3. N.B.: no definitive information is available regarding possible side products devoid of phosphorus due to poor signal/noise in the 29Si{1H} NMR spectrum and the generally uninformative nature of the 1H NMR spectrum. The plausible products of silane decomposition and methimazole captured tby 7 or 8, i.e. [RuH(mt)(CO)(PPh3)2] and [Ru(mt)2(PPh3)2],5 were conclusively absent, however (31P{1H} NMR). NMR (CDCl3/ THF, 25 °C): 29Si{1H} (59.59 MHz) δSi = 48.00 (d, 2JPSi = 139 Hz); 1H (299.9 MHz) δH -5.90 (d, 2JPH = 12.6 Hz). Attempts to obtain pure 8 from the above 7/8/9 mixture by fractional crystallization afforded instead crystals of 9. Crystal data for [Ru(CO)3(PPh3)2] (9): C39H30O3P2Ru; Mr = 709.64; trigonal; P3c1; a = b = 15.6749(1) A˚; c = 23.0971(3) A˚; V = 4914.71(8) A˚3 ; Z = 6; yellow needle, 0.49  0.27  0.11 mm; Dc = 1.439 Mg m-3; μ(Mo KR) = 0.613 mm-1; T = 100(2) K. A total of 107 567 absorption-corrected reflections provided 8918 independent reflections, 6235 of which were observed (|I| > 2σ(|I|), 2θ e 76°). F2 refinement gave R1 = 0.0328, wR2 = 0.0845 for 6235 independent, observed, absorption corrected reflections and 205 parameters without restraints, with residual electron density between -0.63 and þ 0.81 e A˚-3. CCDC 705045. The crystals structures of 9 3 C4H8O27 and 9 3 CH2Cl228 have been reported previously, while the solvate free modification presented here is isomorphous with the corresponding osmium analogue described by Ibers.29

Acknowledgment. We thank the Australian Research Council (ARC) for financial support (Grant Nos. DP0771497 and DP0881692) and the Deutscher Akademischer Austauschdienst for a postdoctoral fellowship (to J.W.). Supporting Information Available: CIF files giving full details of the crystal structure determinations of 1 (CCDC 705043), trans-5 3 THF (CCDC 705044), and 9 (CCDC 705045). This material is available free of charge via the Internet at http:// pubs.acs.org. (27) Dahan, F.; Sabo, S.; Chaudret, B. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1984, 40, 786. (28) Ng, S. Y.; Goh, L. Y.; Koh, L. L.; Leong, W. K.; Tan, G. K.; Ye, S.; Zhu, Y. Eur. J. Inorg. Chem. 2006, 663. (29) Stalick, J. A.; Ibers, J. A. Inorg. Chem. 1969, 8, 419.