Coordination, Agostic Stabilization, and CâH Bond ... - ACS Publications

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Organometallics 2009, 28, 6676–6686 DOI: 10.1021/om9007532

Coordination, Agostic Stabilization, and C-H Bond Activation of N-Alkyl Heterocyclic Carbenes by Coordinatively Unsaturated Ruthenium Hydride Chloride Complexes Suzanne Burling, Elena Mas-Marza, Jose E. V. Valpuesta,§ Mary F. Mahon, and Michael K. Whittlesey* Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K. §Permanent address: University of Seville, Instituto de Investigaciones Quı´micas, Am erico Vespucio 49, Seville, Spain 41092. Received August 28, 2009

The products formed upon reaction of Ru(PPh3)3HCl and [Ru(PiPr3)2HCl]2 with the N-heterocyclic carbenes 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (IiPr2Me2, 1) and 1,3-diethyl-4,5-dimethylimidazol-2-ylidene (IEt2Me2, 2) proved to be dependent on the phosphine and the N-substituent of the carbene. Thus, Ru(PPh3)3HCl reacts with both 1 and 2 at room temperature in CH2Cl2 to give a mixture of products consisting of cis-/trans-PPh3 isomers of the agostic complexes Ru(NHC)(PPh3)2HCl (NHC = IiPr2Me2, 3a/3b; IEt2Me2, 8a/8b), the anagostic species Ru(NHC)(PPh3)2HCl (NHC = IiPr2Me2, 4; IEt2Me2, 9), and in the case of IiPr2Me2 the C-H activated complex Ru(IiPr2Me2)0 (PPh3)2Cl (5). Addition of 1 atm of C2H4 to the mixture of 3a/3b, 4, and 5 leads to complete conversion to 5. [Ru(PiPr3)2HCl]2 reacts with both 1 and 2 to yield only the anagostic complexes Ru(NHC)(PiPr3)2HCl (NHC = IiPr2Me2, 6; IEt2Me2, 10), which on the basis of NMR evidence react with C2H4 to give the doubly C-H activated alkenyl-NHC complexes Ru{η2-C(NiPr)CMeCMeN(CMedCH)}(PiPr3)2Cl (7) and Ru{η2-C(NEt)CMeCMeN(CHdCH)}(PiPr3)2Cl (11). Addition of 1 to Ru(PiPr3)2(CO)HCl affords the agostic stabilized monocarbene complex Ru(IiPr2Me2)(PiPr3)(CO)HCl (12) and the tris-carbene species Ru(IiPr2Me2)3(CO)HCl (13). Complexes 3a, 4, 5, 6, 8a, 10, 12, and 13 have been structurally characterized. Introduction Intramolecular C-H activation of N-aryl and -alkyl substituents in platinum group metal N-heterocyclic carbene *Corresponding author. E-mail: [email protected]. (1) For an overview of bond activation reactions in M-NHC complexes, see: Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248, 2247–2273. For specific examples, see: (a) Hitchcock, P. B.; Lappert, M. F.; Pye, P. L. J. Chem. Soc., Chem. Commun. 1977, 196–198. (b) Hitchcock, P. B.; Lappert, M. F.; Pye, P. L.; Thomas, S. J. Chem. Soc., Dalton Trans. 1979, 1929–1942. (c) Hitchcock, P. B.; Lappert, M. F.; Terreros, P. J. Organomet. Chem. 1982, 239, C26–C30. (d) Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics 2000, 19, 1194–1197. (e) Prinz, M.; Grosche, M.; Herdtweck, E.; Herrmann, W. A. Organometallics 2000, 19, 1692–1694. (f) Jazzar, R. F. R.; Macgregor, S. A.; Mahon, M. F.; Richards, S. P.; Whittlesey, M. K. J. Am. Chem. Soc. 2002, 124, 4944. (g) Danopoulos, A. A.; Winston, S.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 2002, 3090–3091. (h) Giunta, D.; H€olscher, M.; Lehmann, C. W.; Mynott, R.; Wirtz, C.; Leitner, W. Adv. Synth. Catal. 2003, 345, 1139–1145. (i) Chilvers, M. J.; Jazzar, R. F. R.; Mahon, M. F.; Whittlesey, M. K. Adv. Synth. Catal. 2003, 345, 1111–1114. (j) Trnka, T. M.; Morgan, J. P.; Sanford, M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T.-L.; Ding, S.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546–2558. (k) Caddick, S.; Cloke, F. G. N.; Hitchcock, P. B.; Lewis, A. K. D. Angew. Chem., Int. Ed. 2004, 43, 5824–5827. (l) Dorta, R.; Stevens, E. D.; Nolan, S. P. J. Am. Chem. Soc. 2004, 126, 5054–5055. (m) Cabeza, J. A.; del Río, I.; Miguel, D.; Sanchez-Vega, M. G. Chem. Commun. 2005, 3956–3958. (n) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 3516–3526. (o) Corberan, R.; Sanau, M.; Peris, E. J. Am. Chem. Soc. 2006, 128, 3974–3979. (p) Hong, S. Y.; Chlenov, A.; Day, M. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 2007, 46, 5148–5151. (q) Danopoulos, A. A.; Pugh, D.; Wright, J. A. Angew. Chem., Int. Ed. 2008, 47, 9765–9767. (r) Ohki, Y.; Hatanaka, T.; Tatsumi, K. J. Am. Chem. Soc. 2008, 130, 17174– 17186. (s) Steele, U. J.; Dechert, S.; Meyer, F. Chem.;Eur. J. 2008, 14, 5112– 5115. (t) Leitao, E. M.; Dubberley, S. R.; Piers, W. E.; Wu, Q.; McDonald, R. Chem.;Eur. J. 2008, 14, 11565–11572. (u) Torres, O.; Martín, M.; Sola, E. Organometallics 2009, 28, 863–870. (v) Zhang, C.; Zhao, Y.; Li, B.; Song, H.; Xu, S.; Wang, B. Dalton Trans. 2009, 5182–5189. (w) Vielle-Petit, L.; Luan, X.; Gatti, M.; Blumentritt, S.; Linden, A.; Clavier, H.; Nolan, S. P.; Dorta, R. Chem. Commun. 2009, 3783–3785. (x) Ledger, A. E. W.; Mahon, M. F.; Whittlesey, M. K.; Williams, J. M. J. Dalton Trans. 2009, 6941–6947. (y) Zhang, C.; Luo, F.; Cheng, B.; Li, B.; Song, H.; Xu, S.; Wang, B. Dalton Trans. 2009, 7230–7235. pubs.acs.org/Organometallics

Published on Web 10/21/2009

(NHC) complexes has been described for a number of different metal-ligand combinations,1-5 although the reaction product(s) that are formed are not always predictable in advance. Scheme 1 illustrates this in the case of the baseinduced C-H activation of Cp*Ir(NHC)Cl2 for different N-substituted NHC ligands. In the case of 1,3-diisopropyl4,5-dimethylimidazol-2-ylidene (IiPr2Me2, 1), the chloride complex A is formed, whereas the N-ethyl-substituted carbene 1,3-diethyl-4,5-dimethylimidazol-2-ylidene (IEt2Me2, 2) affords the hydride complex B.6 Moreover, whereas facile aliphatic C-H activation of an N-tBu substituent is found upon addition of base to Cp*Ir(1-benzyl-3-butylimidazol2-ylidene)Cl2, replacing the tBu group by an iPr group leads to the formation of the aromatic C-H activated compound C (Scheme 1).7 The different products were subsequently rationalized by considering the steric clash that occurs between the carbene substituents and the bulky Cp* ligand, (2) Abdur-Rashid, K.; Fedorkiw, T.; Lough, A. J.; Morris, R. H. Organometallics 2004, 23, 86–94. (3) Scott, N. M.; Pons, V.; Stevens, E. D.; Heinekey, D. M.; Nolan, S. P. Angew. Chem., Int. Ed. 2005, 44, 2512–2515. (4) For an example involving light-induced C-H activation, see: Ampt, K. A. M.; Burling, S.; Donald, S. M. A.; Douglas, S.; Duckett, S. B.; Macgregor, S. A.; Perutz, R. N.; Whittlesey, M. K. J. Am. Chem. Soc. 2006, 128, 7452–7453. (5) (a) Burling, S.; Paine, B. M.; Nama, D.; Brown, V. S.; Mahon, M. F.; Prior, T. J.; Pregosin, P. S.; Whittlesey, M. K.; Williams, J. M. J. J. Am. Chem. Soc. 2007, 129, 1987–1995. (b) H€aller, L. J. L.; Page, M. J.; Macgregor, S. A.; Mahon, M. F.; Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 4604–4605. (6) (a) Hanasaka, F.; Tanabe, Y.; Fujita, K.; Yamaguchi, R. Organometallics 2006, 25, 826–831. (b) Tanabe, Y.; Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2007, 26, 4618–4636. (7) Corberan, R.; Sana u, M.; Peris, E. Organometallics 2006, 25, 4002–4008. r 2009 American Chemical Society

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Organometallics, Vol. 28, No. 23, 2009 Scheme 1

Scheme 2

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the N-tert-butyl-substituted carbene ItBu (1,3-di-tert-butylimidazol-2-ylidene) to give an unstable species that behaves like “Ru(ItBu)(PPh3)2” and which can be trapped by H2 to give the isolable monocarbene complex Ru(ItBu)(PPh3)2H2. We have reported that treatment of Ru(PPh3)3HCl with ICy (1,3-dicyclohexylimidazol-2-ylidene) yields Ru(ICy)(PPh3)2HCl.11 Both of these formally 16-electron products are stabilized by agostic C-H interactions between the ruthenium and one of the carbene N-substituents. We now report that Ru(PPh3)3HCl reacts with IiPr2Me2 (1) to give a mixture of agostic and anagostic mono-IiPr2Me2 complexes, as well as the C-H activated product Ru(IiPr2Me2)0 (PPh3)2Cl. The reactivity of Ru(PPh3)3HCl has been contrasted with that of [Ru(PiPr3)2HCl]2, a source of the 14-electron moiety “Ru(PiPr3)2HCl”,12,13 which yields only the anagostic species Ru(IiPr2Me2)(PiPr3)2HCl. This reacts with alkene to afford a product that on the basis of NMR spectroscopy is assigned as a coordinated NHCalkenyl complex resulting from double C-H activation of the N-iPr arm. In addition, we have investigated the reactivity of Ru(PPh3)3HCl and [Ru(PiPr3)2HCl]2 with IEt2Me2 (2) to give some comparison to the chemistry of IiPr2Me2. Although similar agostic and anagostic products are formed, the results mirror our earlier findings in suggesting that IEt2Me2 is generally less susceptible to C-H activation. Studies to determine the influence of incoporating CO into the ruthenium precursor have been conducted with an exploratory investigation on the reactivity of IiPr2Me2 with Ru(PiPr3)2(CO)HCl.

Results and Discussion which either changes the reaction pathway available (i.e., A is proposed to form via β-hydrogen elimination from [Cp*Ir(IiPr2Me2)(OiPr)]Cl, whereas B originates upon reductive elimination of iPrOH from Cp*Ir(IEt2Me2)(OiPr)H followed by intramolecular C-H activation of the NHC ligand) or favors the approach and activation of one bond over another (aromatic versus aliphatic in C). The strongly electron-donating properties of NHCs are believed to aid intramolecular activation reactions such as those outlined above. In line with this, we have found in the case of ruthenium-induced carbene C-H activation that the strongly σ-donating IiPr2Me2 (1: pKa = 30.4)8 can be cleaved under far milder conditions than the less basic N-ethylsubstituted carbene IEt2Me2 (2).4,5,9 We have also shown that moderate changes to the nature of the ancillary ligands on the ruthenium center can dramatically alter the activation chemistry. Thus, addition of IiPr2Me2 to Ru(PPh3)3(CO)H2 results in C-H cleavage, whereas Ru(PPh3)3(CO)HCl reacts with the same NHC to give products that result from both C-H activation and C-N activation.10 In light of these differences that occur upon changing from a dihydride to a hydride chloride precursor, we were interested in probing further the reactivity of IiPr2Me2 with other ruthenium hydride chloride complexes. One obvious candidate is Ru(PPh3)3HCl, which Morris2 has shown reacts with (8) Magill, A. M.; Cavell, K. J.; Yates, B. F. J. Am. Chem. Soc. 2004, 126, 8717–8724. (9) Burling, S.; Mahon, M. F.; Paine, B. M.; Whittlesey, M. K.; Williams, J. M. J. Organometallics 2004, 23, 4537–4539. (10) Burling, S.; Mahon, M. F.; Powell, R. E.; Whittlesey, M. K.; Williams, J. M. J. J. Am. Chem. Soc. 2006, 128, 13702–13703.

Reactivity of Ru(PPh3)3HCl with IiPr2Me2. The roomtemperature addition of 2 equiv of IiPr2Me2 (1) to Ru(PPh3)3HCl in CH2Cl2 resulted in the discharge of the purple color of the starting material over a period of ca. 5 min and formation of a dark orange-red solution. Dichloromethane was employed to ensure a homogeneous solution of ruthenium precursor (the compound is barely soluble in benzene and gave the bis-carbene complex Ru(IiPr2Me2)2(PPh3)HCl as the major product in THF, paralleling the behavior described earlier for reaction of Ru(PPh3)3HCl with ICy11), although this also necessitated the use of excess carbene due to the side reaction with solvent that generates imidazolium chloride (identified through the appearance of a characteristic high-frequency singlet proton resonance at δ 10.8). Even with 2 equiv of 1, only monocarbene products were detected, although when g4 equiv of NHC were used, a purple color was observed due to the formation of [Ru(IiPr2Me2)4H]þ.14 A 1H NMR spectrum of the dichloromethane solution revealed the formation of two new hydride-containing species, which appeared as a well-defined triplet at δ -25.2 (11) Burling, S.; Kociok-K€ ohn, G.; Mahon, M. F.; Whittlesey, M. K.; Williams, J. M. J. Organometallics 2005, 24, 5868–5878. (12) Coalter, J. N.III; Huffman, J. C.; Streib, W. E.; Caulton, K. G. Inorg. Chem. 2000, 39, 3757–3764. (13) (a) Coalter, J. N. III; Ferrando, G.; Caulton, K. G. New J. Chem. 2000, 24, 835–836. (b) Coalter, J. N. III; Bollinger, J. C.; Huffman, J. C.; Werner-Zwanziger, U.; Caulton, K. G.; Davidson, E. R.; Gerard, H.; Clot, E.; Eisenstein, O. New J. Chem. 2000, 24, 9–26. (c) Coalter, J. N. III; Streib, W. E.; Caulton, K. G. Inorg. Chem. 2000, 39, 3749–3756. (14) (a) H€aller, L. J. L.; Mas-Marza, E.; Moreno, A.; Lowe, J. P.; Macgregor, S. A.; Mahon, M. F.; Pregosin, P. S.; Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 9618–9619. (b) Burling, S.; H€aller, L. J. L.; Mas-Marza, E.; Moreno, A.; Macgregor, S. A.; Mahon, M. F.; Pregosin, P. S.; Whittlesey, M. K. Chem.-Eur. J. 2009, 15, 10912-10923.

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(2JHP 23.1 Hz) and a broadened triplet at δ -25.7 (this resolved into a doublet of doublets with 2JPP = 27.5 and 26.5 Hz at ca. 280 K). The two signals were assigned to the trans- and cis-phosphine isomers (3a/3b) of the iPr-methyl agostic complex Ru(IiPr2Me2)(PPh3)2HCl (Scheme 2) because of the similarity of the spectroscopic data to that for the agostic species Ru(ICy)(PPh3)3HCl.11 Further evidence for the trans- and cis-structures of 3a and 3b was provided by 31P{1H} and 1H-31P correlation spectroscopy, which revealed a correlation between the hydride resonance of 3a at δ -25.2 and a singlet phosphorus peak at δ 47.2, and from the hydride resonance of 3b at δ -25.7 to two doublets at δ 73.7 and 49.1 in the phosphorus spectrum. Over a period of ca. 2 h, two additional species were detected spectroscopically: the hydride complex 4 and the non-hydride-containing species 5 (Scheme 2). Over time, the composition of the reaction mixture altered further, such that after 72 h only 3a, 3b, and 5 were observable. Complex 4 exhibited a triplet hydride resonance at δ -30.5 (2JHP 25.6 Hz), considerably lower in frequency than for either 3a or 3b. 1H-31P HMBC spectroscopy showed a correlation between this signal and singlet phosphorus resonance at δ 42.8, consistent with a trans-phosphine geometry. Further 1- and 2-D NMR experiments, along with X-ray crystallography (see below), proved that 4 has the same molecular formula as 3a/3b, namely, Ru(IiPr2Me2)(PPh3)2HCl, but contains no agostic interaction. Complex 5 was assigned as the C-H activated species Ru(IiPr2Me2)0 (PPh3)2Cl primarily on the basis of two 1 H NMR signals at δ 2.59 and 1.75 (which correlated by 13C-1H HMQC spectroscopy to a 13C resonance at δ 8.8) arising from the coordinated methylene group of an activated iPr arm. The 31 1 P{ H} NMR spectrum of 5 displayed two singlets separated by only 0.02 ppm, which most likely represent the observable inner two lines of an AB system. Characterization of the Agostic Complexes 3a and 3b: X-ray Crystallography and Solution NMR Behavior. Red crystals containing 50% of 3a (disordered with 50% of 4) were grown from benzene/hexane. The solid state structure of 3a is displayed in Figure 1 and shows quite clearly the agostic C-H interaction to an N-iPr methyl group, which affords a formally 18-electron Ru(II) species. Disorder was evident, as discussed later, but the model is unambiguous. The short Ru 3 3 3 H and Ru 3 3 3 C distances (Ru(1)-C(11), 2.904(5) A˚; Ru(1)-H(11A), 2.189(5) A˚) are more than 0.10 A˚ shorter than the next nearest ruthenium-iPr contact and consistent with a strong Ru 3 3 3 H-C interaction.15,16 (15) Baratta, W.; Mealli, C.; Herdtweck, E.; Ienco, A.; Mason, S. A.; Rigo, P. J. Am. Chem. Soc. 2004, 126, 5549–5562. (16) (a) Huang, D.; Streib, W. E.; Eisenstein, O.; Caulton, K. G. Angew. Chem., Int. Ed. Engl. 1997, 36, 2004–2006. (b) Huang, D.; Huffman, J. C.; Bollinger, J. C.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1997, 119, 7398–7399. (c) Huang, D.; Olivan, M.; Huffman, J. C.; Eisenstein, O.; Caulton, K. G. Organometallics 1998, 17, 4700–4706. (d) Takahashi, Y.; Hikichi, S.; Akita, M.; Moro-oka, Y. Organometallics 1999, 18, 2571–2573. (e) Huang, D.; Streib, W. E.; Bollinger, J. C.; Caulton, K. G.; Winter, R. F.; Scheiring, T. J. Am. Chem. Soc. 1999, 121, 8087–8097. (f) Hansen, S. M.; Rominger, F.; Metz, M.; Hofmann, P. Chem.;Eur. J. 1999, 5, 557–564. (g) Jimenez Tenorio, M.; Mereiter, K.; Puerta, M. C.; Valerga, P. J. Am. Chem. Soc. 2000, 122, 11230–11231. (h) Huang, D.; Bollinger, J. C.; Streib, W. E.; Folting, K.; Young, V. J.; Eisenstein, O.; Caulton, K. G. Organometallics 2000, 19, 2281–2290. (i) Amoroso, D.; Haaf, M.; Yap, G. P. A.; West, R.; Fogg, D. E. Organometallics 2002, 21, 534–540. (j) Aneetha, H.; Jimenez Tenorio, M.; Puerta, M. C.; Valerga, P.; Sapunov, V. N.; Schmid, R.; Kirchner, K.; Mereiter, K. Organometallics 2002, 21, 5334–5346. (k) Zhang, J.; Barakat, K. A.; Cundari, T. R.; Gunnoe, T. B.; Boyle, P. D.; Petersen, J. L.; Day, C. S. Inorg. Chem. 2005, 44, 8379–8390.

Burling et al.

Figure 1. Molecular structure of 3a. Thermal ellipsoids are represented at 30% probability. Solvent, disorder, and all hydrogen atoms (except the agostic methyl and Ru-H) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 1.9943(19), Ru(1)-P(1) 2.3310(5), Ru(1)-P(2) 2.3300(5), Ru(1)-Cl(1) 2.4781(4), P(1)-Ru(1)-P(2) 169.208(17), C(1)-Ru(1)-Cl(1) 169.27(6), C(1)-Ru(1)-P(1) 93.35(5), P(1)-Ru(1)-Cl(1) 86.792(15), C(1)-Ru(1)-P(2) 93.84(5), P(2)-Ru(1)-Cl(1) 87.642(16).

Figure 2. Molecular structure of 4. Thermal ellipsoids are represented at 30% probability. Solvent, minor disordered component, and all hydrogen atoms (except the isopropyl methine and Ru-H) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 1.998(2), Ru(1)-P(1) 2.3401(5), Ru(1)-P(2) 2.3227(5), Ru(1)-Cl(1) 2.4626(5), P(1)-Ru(1)-P(2) 176.78(2), C(1)-Ru(1)-Cl(1) 167.87(7), C(1)-Ru(1)-P(1) 91.49(6), P(1)-Ru(1)-Cl(1) 89.199(18), C(1)-Ru(1)-P(2) 91.45(6), P(2)-Ru(1)-Cl(1) 88.210(18).

Although the minor isomer 3b could not be crystallized, we assume, again by comparison to Ru(ItBu)(PPh3)2H2 and Ru(ICy)(PPh3)2HCl, that it is also agostically stabilized.

Article

The 1H NMR spectrum of a mixture of 3a and 3b showed a lowfrequency, doublet methyl resonance for each compound (3a, δ 0.00; 3b, δ 0.43), which we believe provides evidence for the Ru 3 3 3 H3C interactions being maintained in solution. The ratio of 3a:3b proved to be very solvent dependent (1:0.6 in CD2Cl2, 298 K; 1:1.3 in C6D6, 298 K) and, to a lesser extent, temperature dependent (1:0.4 in CD2Cl2, 260 K). EXSY spectroscopy confirmed the interconversion of 3a and 3b in C6D6 solution at room temperature, although no exchange was found with the nonagostic complex 4. Characterization of 4. As noted above, 4 was only ever formed as a minor species during the reaction of 1 with Ru(PPh3)3HCl, and we were unable to find any reaction conditions under which it was present for longer or at higher concentration. Somewhat fortuitously, crystals of 4 suitable for an X-ray crystal structure determination were isolated and revealed the absence of any agostic interaction in the five-coordinate square-pyramidal structure (Figure 2). One of the N-iPr groups is oriented such that the methine C-H bond is directed toward the metal center. While the long Ru(1) 3 3 3 C(4) and Ru(1) 3 3 3 H(4) distances (3.288(2), 2.57(2) A˚) preclude any form of γ-Ru 3 3 3 H-C agostic bond, both the Ru 3 3 3 H distance and Ru 3 3 3 H-C angle (ca. 129°) meet the criteria for an anagostic interaction, a term that implies a M 3 3 3 H-C interaction that is not three-center-two-electron in nature.17a A comparison of other metrical data in 3a and 4 reveals that the Ru-CNHC distance is the same in the two species (3a, 1.9943(19) A˚; 4, 1.998(2) A˚), but that the P-Ru-P angle is considerably wider in the anagostic complex (3a, 169.208(17)°; 4, 176.78(2)°). On the basis of the X-ray structure of 4, the hydride chemical shift of -30.5 ppm can be rationalized by the position of the hydride trans to the anagostic interaction.18 The appearance of two sets of isopropyl methine and methyl resonances in the room-temperature proton spectrum indicates restricted rotation about the Ru-CNHC bond, as also reported by Caulton and co-workers for the related species Ru(IMe)(PiPr3)2HCl, where IMe = 1,3-dimethylimidazol-2-ylidene.19 Characterization of the C-H Activated Complex Ru(IiPr2Me2)0 (PPh3)2Cl (5). Exposure of a benzene solution containing a mixture of 3a, 3b, 4, and 5 to 1 atm of ethene resulted in complete conversion to just the C-H activated compound 5, which was structurally characterized as shown in Figure 3. The activated arm lies in the apical position of a square-pyramidal structure and leads to a strained five(17) (a) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 6908-6914. See also: (b) Yao, W.; Eisenstein, O.; Crabtree, R. H. Inorg. Chim. Acta 1997, 254, 105–111. (c) Brammer, L. Dalton Trans. 2003, 3145–3157. (d) Montag, M.; Efremenko, I.; Cohen, R.; Leitus, G.; Shimon, L. J. W.; Diskin-Posner, Y.; Ben-David, Y.; Martin, J. M. L.; Milstein, D. Chem.;Eur. J. 2008, 14, 8183–8194. (e) Huynh, H. V.; Wong, L. R.; Ng, P. S. Organometallics 2008, 27, 2231–2237. (f) € Taubmann, C.; Ofele, K.; Herdtweck, E; Herrmann, W. A. Organometallics 2009, 28, 4254–4257. (18) (a) Buil, M. L.; Elipe, S.; Esteruelas, M. A.; O~ nate, E.; Peinado, E.; Ruiz, N. Organometallics 1997, 16, 5748–5755. (b) Winter, R. F.; Hornung, F. M. Inorg. Chem. 1997, 36, 6197–6204. (c) Gusev, D.; Dolgushin, F. M.; Antipin, M. Y. Organometallics 2000, 19, 3429–3434. (d) Lee, H. M.; Smith, D. C. Jr.; He, Z.; Stevens, E. D.; Yi, C. S.; Nolan, S. P. Organometallics 2001, 20, 794–797. (e) Ferrando-Miguel, G.; Coalter, J. N.III; Gerard, H.; Huffman, J. C.; Eisenstein, O.; Caulton, K. G. New J. Chem. 2002, 26, 687–700. (f) Gusev, D.; Lough, A. J. Organometallics 2002, 21, 2601–2603. (g) Kuznetsov, V. F.; Abdur-Rashid, K.; Lough, A. J.; Gusev, D. J. Am. Chem. Soc. 2006, 128, 14388–14396. (h) Salem, H.; Shimon, L. J. W.; Diskin-Posner, Y.; Leitus, G.; Ben-David, Y.; Mistein, D. Organometallics 2009, 28, 4791–4806. (19) Ho, V. M.; Watson, L. A.; Huffman, J. C.; Caulton, K. G. New J. Chem. 2003, 27, 1446–1450.


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Figure 3. Molecular structure of 5. Thermal ellipsoids are shown at 30% probability. Solvent, second disordered positions for C(4) and C(6), and all hydrogen atoms (except the methine and methylene groups) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 1.9695(17), Ru(1)-C(5) 2.116(2), Ru(1)-Cl(1) 2.4535(4), Ru(1)-P(1) 2.3326(4), Ru(1)-P(2) 2.3290(4), P(1)-Ru(1)-P(2) 177.264(15), C(1)Ru(1)-Cl(1) 159.34(6), C(5)-Ru(1)-C(1) 76.61(8), P(1)-Ru(1)-Cl(1) 89.321(15).

membered metallacycle ring containing C(5), judging by the C(5)-Ru(1)-C(1) angle of 76.61(8)o, which is considerably smaller than the ideal value of 90°. However, although trans to a vacant site, the Ru-CH2 distance (Ru-C(5) 2.116(2) A˚) is the same as that in the coordinatively saturated C-H activated complex Ru(IiPr2Me2)0 (PPh3)2(CO)H (2.2100(16) A˚ for the cis-phosphine isomer,5a 2.230(3) A˚ for the trans-phosphine isomer5b). The two phosphine ligands in 5 are essentially eclipsed and are approximately staggered with respect to the Ru-CNHC, Ru-CH2, and Ru-Cl bonds. In the presence of 1 atm of H2, a toluene solution of 5 slowly converted back to a mixture of 3a and 3b (no 4 was observed) over a period of 2 h at room temperature. Over a further 12 h, 3a and 3b converted to a new species, which exhibited a broad singlet hydride resonance at δ -7.1, but no IiPr2Me2 signals. When the reaction with H2 was run in CH2Cl2, a mixture of 3a, 3b, Ru(PPh3)3HCl, and the imidazolium salt [IiPr2Me2H]Cl was formed within minutes. Over time, a new species was generated that exhibited a broad room-temperature hydride resonance at δ -13.2, which separated into three signals at δ -9.0, -12.4, and -18.2 upon cooling. While we have not attempted to characterize the products from the reaction with ethene in toluene or CH2Cl2 any further, the number of signals and their chemical shifts seen in CH2Cl2 bear similarities to the hydride-bridged

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dimers that form from ruthenium phosphine hydride complexes.20 Synthesis and Reactivity of the Anagostic Species Ru(IiPr2Me2)(PiPr3)2HCl. In contrast to Ru(PPh3)3HCl, the tri-isopropyl phosphine precursor [Ru(PiPr3)2HCl]2 reacted with IiPr2Me2 in benzene at room temperature to form only a single species, which has been characterized as the anagostic complex Ru(IiPr2Me2)(PiPr3)2HCl (6, Scheme 3). Fortuitously, this precipitated directly from the reaction mixture as small red-brown, highly air-sensitive crystals, although in quite low yield (39%). The molecular structure (Figure 4) revealed that the closest Ru 3 3 3 C and Ru 3 3 3 H methine distances are 3.108(1) and 2.54(1) A˚. On the basis of this Ru 3 3 3 H distance and the corresponding Ru 3 3 3 H-C angle (ca. 131°), 6 is best interpreted as being an anagostic complex directly comparable to 4. The bulk of the iPr substituents present on both the carbene and phosphines most likely account for both the lengthening of the Ru-CNHC distance and the widening of the P-Ru-P angle in 6 (2.0009(16) A˚, 157.390(16)°) compared to Ru(IMe)(PiPr3)2HCl (1.967(5) A˚, 163.28(8)°).19 The proton NMR spectrum of 6 showed similar properties to that of 4, with a low-frequency hydride resonance (δ -29.4) and two sets of methine septet and methyl doublet resonances from the N-iPr groups due to restricted rotation about the Ru-CNHC bond. In contrast to 4 however, reaction with ethene failed to yield any analogue of 5, with only ethane and PiPr3 apparent as major species in 1H and 31 P{1H} NMR spectra recorded at early times.21 Over several hours at room temperature, the formation of a single new ruthenium-containing product became apparent (>95% yield by NMR), assigned as the bidentate propenyl-NHC species Ru{η2-C(NiPr)CMeCMeN(CMedCH)}(PiPr3)2Cl (7) formed as a result of double C-H activation of an iPr arm of the carbene (Scheme 3).22 Although neither structural characterization nor elemental analysis of 7 proved possible due to a combination of the very high solubility of the product in alkane solvent and extreme sensitivity to air, 1- and 2-D multinuclear NMR spectra were consistent with the proposed structure. In the 1H NMR spectrum, there was only a single iPr group, but most pertinent were two resonances, a multiplet of integral 1 at δ 7.79 for the R-CH of the (20) (a) Arliguie, T.; Chaudret, B.; Morris, R. H.; Sella, A. Inorg. Chem. 1988, 27, 598–599. (b) Van Der Sluys, L. S.; Kubas, G. J.; Caulton, K. G. Organometallics 1991, 10, 1033–1038. (c) Burrow, T.; Sabo-Etienne, S.; Chaudret, B. Inorg. Chem. 1995, 4, 1722–1726. (d) Sabo-Etienne, S.; Chaudret, B. Coord. Chem. Rev. 1998, 180, 381–407. (21) No mono-C-H activated complex analogous to 5 could be observed even upon adding C2H4 to 6 in d8-toluene. (22) Dehydrogenation of an iPr group in the N-aryl carbene IPr (1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene) has been reported in reactions with Ni (Dible, B. J.; Sigman, M. S.; Arif, A. M. Inorg. Chem. 2005, 44, 3774-3776) and Ir precursors (Tang, C. Y.; Smith, W.; Vidovic, D.; Thompson, A. L.; Chaplin, A. B.; Aldridge, S. Organometallics 2009, 28, 3059-3066). In the latter, the resulting bidentate carbene-alkene ligand chelates to the Ir center.

Figure 4. Molecular structure of 6 with thermal ellipsoids shown at 30% probability. Solvent and all hydrogen atoms (except Ru-H) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 2.0009(16), Ru(1)-Cl(1) 2.4733(4), Ru(1)-P(1) 2.3551(3), P(1)-Ru(1)-P(1)0 157.390(16), C(1)-Ru(1)-Cl(1) 151.61(5), C(1)-Ru(1)-P(1) 97.047(11), P(1)-Ru(1)-Cl(1) 87.982(8). P(1)0 generated by the x, y, 1/2 - z symmetry operation.

alkenyl arm, which correlated to a triplet (2JCP 12.0 Hz) 13C signal at δ 150.3, and a multiplet of integral 3 at δ 2.32 assigned to the β-CMe group on the grounds of a 1H-13C HSQC cross-peak to a quaternary 13C signal at δ 132.1. These data are best compared with those from Dixneuf and co-workers, who have described the formation of a similar ruthenium alkenyl-NHC complex with similar 1H and 13C signals for Ru-R-CH (at δ 8.65 and 154.7, respectively), formed upon deprotonation of an imidazolium salt with an NCH2CH2X (X = OMe, Cl) arm in the presence of [(pcymene)RuCl2]2.23 In contrast to the relatively slow reaction observed between 5 and H2 in aromatic solvents, the introduction of 1 atm of H2 to a C6D6 solution of 7 resulted in complete reformation of 6 within minutes at room temperature, although continued exposure to H2 ultimately afforded a new unknown non-carbene-containing hydride complex over hours. Reaction of IEt2Me2 with Ru(PPh3)3HCl or [Ru(PiPr3)2HCl]2. To provide a comparison to the reactions of IiPr2Me2 (1), brief studies were carried out on the reactivity of the N-ethyl-substituted carbene IEt2Me2 (2) toward the (23) Cariou, R.; Fischmeister, C.; Toupet, L.; Dixneuf, P. H. Organometallics 2006, 25, 2126–2128.

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Scheme 4

Scheme 5

same two ruthenium hydride chloride precursors. The coordinating abilities of 2 prove to be very similar to those of 1. Thus, addition of 3 equiv of 2 to Ru(PPh3)3HCl in CH2Cl2 at ambient temperature resulted in the rapid formation of a mixture of four products, which by comparison to the above and the reactivity of Ru(PPh3)3HCl with ICy11 were assigned as cis- and trans-phosphine isomers of the agostic stabilized complex Ru(IEt2Me2)(PPh3)2HCl (8a/8b), anagostic Ru(IEt2Me2)(PPh3)2HCl (9),24 and the bis-carbene complex Ru(IEt2Me2)2(PPh3)HCl (Scheme 4).25,26 No resonances for an analogue of 5 arising from C-H activation of the carbene were detected. When IEt2Me2 was reacted with [Ru(PiPr3)2HCl]2 in benzene (Scheme 5), only the anagostic complex Ru(IEt2Me2)(PiPr3)2HCl (10) was formed. The X-ray crystal structures of 8a and 10 are shown in Figures 5 and 6, respectively. The former clearly exhibits a clear agostic interaction involving the CH3 group of the N-ethyl arm. The Ru 3 3 3 C and Ru 3 3 3 H distances of 2.823(4) and 2.083(4) A˚ are somewhat shorter than the corresponding interactions in 3a (Ru 3 3 3 C, 2.904(5) A˚; Ru 3 3 3 H, 2.189(5) A˚), suggestive of a stronger agostic interaction. In contrast, the Ru 3 3 3 C(4) and Ru 3 3 3 H(4b) distances (3.228(2) and 2.57(2) A˚) in 10 are too long for the complex to be considered as agostic, although comparison of the Ru 3 3 3 H distance with that in 6 (2.54(1) A˚) again suggests an anagostic interaction. Addition of an atmosphere of C2H4 to a mixture of 8a, 8b, and 9 in warm CH2Cl2 failed to give any clean C-H activation reaction and resulted mostly in decomposition to imidazolium salts. An NMR scale experiment suggested that 10 reacted with ethene in C6D6 to give the alkenylNHC product 11 (Scheme 5), which displayed two multiplet proton resonances at δ 8.67 and 6.60 assigned to the R- and β-CH resonances of the alkenyl ligand (cf. 7). Harsher conditions (3 days at 323 K) are required for the formation of 11 compared to 7. (24) The nonagostic nature of 9 was assumed due to the appearance of the Ru-H signal at the very low frequency chemical shift of δ -30.02 (cf. 4). No other characteriszation of 9 was attempted as the compound was always made as a mixture with 8a, 8b, and Ru(IEt2Me2)2(PPh3)HCl. (25) Assignment was based on the similarity of the hydride chemical shift to that of Ru(ICy)2(PPh3)HCl (δ -33.31, 2JHP = 26.2 Hz).11 For the same reasons as in ref 24, Ru(IEt2Me2)2(PPh3)HCl could not be fully characterized. (26) The use of >4 equiv of IEt2Me2 led to the formation of [Ru(IEt2Me2)4H]þ.14b

Figure 5. Molecular structure of 8a with thermal ellipsoids shown at 30% probability. Solvent and hydrogen atoms (except Ru-H and agostic methyl) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 2.007(3), Ru(1)-P(1) 2.3446(7), Ru(1)-P(2) 2.3046(7), Ru(1)-Cl(1) 2.4858(7), P(1)-Ru(1)-P(2) 168.06(2), C(1)-Ru(1)-Cl(1) 173.13(8), C(1)-Ru(1)-P(1) 95.60(7), P(1)-Ru(1)-Cl(1) 85.69(2), C(1)Ru(1)-P(2) 91.03(7), P(2)-Ru(1)-Cl(1) 88.91(2).

Reaction of IiPr2Me2 with Ru(PiPr3)2(CO)HCl. 1H and P{1H} NMR spectra recorded shortly after the addition of 1.8 equiv of IiPr2Me2 to the carbonyl hydride chloride precursor Ru(PiPr3)2(CO)HCl in benzene solution revealed the presence of unreacted starting material along with two new hydride-containing products: the mono- and triscarbene species Ru(IiPr2Me2)(PiPr3)(CO)HCl (12) and Ru(IiPr2Me2)3(CO)HCl (13). When the reaction was rerun using just 1 equiv of IiPr2Me2, only 12 was formed, while the use of 3 equiv of carbene generated 13 in quantitative yield (Scheme 6).27 At no stage in any of the reactions were we able to find spectroscopic evidence for the bis-carbene complex Ru(IiPr2Me2)2(PiPr3)(CO)HCl. This behavior is 31

(27) Treatment of isolated 12 with a further 2 equiv of 1 resulted in the formation of 13, although addition of >2 equiv afforded signals in the NMR spectrum consistent with the tetrakiscarbene species [Ru(IiPr2Me2)4H]þ.14

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Figure 7. Molecular structure of 12 with thermal ellipsoids shown at 30% probability. All hydrogen atoms (except Ru-H and the agostic methyl) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 1.849(3), Ru(1)-C(2) 2.100(2), Ru(1)-P(1) 2.3683(5), Ru(1)-Cl(1) 2.4517(6), C(2)-Ru(1)-P(1) 177.51(5), C(1)-Ru(1)-Cl(1) 177.47(6), C(1)-Ru(1)-P(1) 90.18(6), P(1)-Ru(1)-Cl(1) 92.35(2). Scheme 6 Figure 6. Molecular structure of 10 with thermal ellipsoids shown at 30% probability. All hydrogen atoms (except Ru-H and those attached to C(4)) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 1.9847(14), Ru(1)-P(1) 2.3457(4), Ru(1)-P(2) 2.3525(4), Ru(1)-Cl(1) 2.4733(4), P(1)-Ru(1)-P(2) 161.988(15), C(1)-Ru(1)-Cl(1) 153.96(4), C(1)-Ru(1)-P(1) 94.59(4), P(1)-Ru(1)-Cl(1) 88.994(14), C(1)-Ru(1)-P(2) 95.18(4), P(2)-Ru(1)-Cl(1) 88.944(14).

similar to that reported by Puerta, Caulton, and co-workers, who found that the tris-phosphine species Ru(PiPr2Me)3(CO)HCl was always formed in preference to the bis-phosphine product Ru(PiPr2Me)2(CO)HCl.28 The X-ray crystal structure of 12 is shown in Figure 7. The complex exhibits a Ru 3 3 3 iPr-Me agostic interaction trans to the hydride ligand, although the Ru 3 3 3 C and Ru 3 3 3 H distances (2.849(3) and 2.21(2) A˚) are suggestive of a weaker interaction than exists in either 3a or 8a. The iPr group on the phosphine is too far removed from the metal (ca. 3.9 A˚, similar to the distance in the nonagostic precursor Ru(PiPr3)2(CO)HCl)16e for any agostic interaction. The shift of the hydride resonance from -24 ppm in Ru(PiPr3)2(CO)HCl to -19 ppm in 12 suggests that the sixth coordination site is not vacant in solution and that the agostic interaction is retained.29,30 Addition of 1 atm of ethene to a C6D6 solution of 12 followed by heating to 343 K for 1 h gave no evidence for C-H activation of the carbene ligand. (28) Marchenko, A. V.; Huffmann, J. C.; Valerga, P.; Jimenez Tenorio, M.; Puerta, M. C.; Caulton, K. G. Inorg. Chem. 2001, 40, 6444–6450. (29) Esteruelas, M. A.; Werner, H. J. Organomet. Chem. 1986, 303, 221–231. (30) Hydride chemical shifts of ca. δ -24 have been reported for the N-aryl NHC complexes Ru(IMes)(PR3)(CO)HCl and Ru(SIMes)(PR3)(CO)HCl (R = Cy, Ph), none of which display any agostic interactions between metal and carbene. (a) Dinger, M. B.; Mol, J. C. Eur. J. Inorg. Chem. 2003, 2827–2833. (b) Dharmasena, U. L.; Foucault, H. M.; dos Santos, E. N.; Fogg, D. E.; Nolan, S. P. Organometallics 2005, 24, 1056– 1058. (c) Beach, N. J.; Dharmasena, U. L.; Drouin, S. D.; Fogg, D. E. Adv. Synth. Catal. 2008, 350, 773–777.

The molecular structure of the 18-electron tris-carbene complex 13 is shown in Figure 8. In contrast to 12, in which the πdonor chloride and π-acceptor CO ligands are trans, the structure of 13 displayed trans arrangements of chloride and hydride, and CO and carbene, implying that 13 is not formed by the simply replacing the phosphine and agostic interaction in 12 by two IiPr2Me2 ligands.31 All three Ru-CNHC bond lengths are longer than in 12, with Ru(1)-C(2) (trans to CO) significantly longer (2.189(2) A˚) than the mutually trans Ru(1)-C(13) (2.151(2) A˚) and Ru(1)-C(24) (2.132(2) A˚). Notwithstanding the 80:20 trans disorder evident for the chloride, the Ru(1)-Clpartial distances are long in 13. In particular, the major chloride component is located 2.6577(7) A˚ from the ruthenium, some 0.2 A˚ longer than the Ru-Cl distances in 4, 5, 6, and 10. Closer examination of the structure revealed that this lengthening may be accounted for, in part, by sterics. Distances between the methine hydrogens and Cl(1) range from 2.29 to 2.55 A˚, which is considerably shorter than the sum of the van der Waals radii of both atoms (1.75 and 1.09 A˚), forcing the chloride to be “squeezed” further away from the metal center, as illustrated in the space-filling diagram shown in Figure 8. The appearance of 12 separate iPr methyl resonances in the 1 H NMR spectrum further emphasizes the congestion apparent in the crystal structure that results from the presence of three mer-carbene ligands. (31) This contrasts with the trans-Cl-Ru-CO geometry found in the spectroscopically characterized trisphosphine complexes Rut (P Bu2Me)2(PMe3)(CO)HCl, Ru(PiPr3)2(PMe3)(CO)HCl, and Ru(PiPr2Me)3(CO)HCl. (a) Poulton, J. T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1994, 33, 1476–1485. (b) Ref 28.

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Figure 8. (Left) Molecular structure of 13 with thermal ellipsoids shown at 30% probability. Solvent, the minor disordered chlorine component, and all hydrogen atoms (except Ru-H) are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Ru(1)-C(1) 1.833(2), Ru(1)-C(2) 2.189(2), Ru(1)-C(13) 2.151(2), Ru(1)-C(24) 2.132(2), Ru(1)-Cl(1) 2.6577(7), C(1)-Ru(1)-C(2) 178.77(9), C(1)-Ru(1)-C(13) 90.06(8), C(1)-Ru(1)-C(24) 90.73(9), C(13)-Ru(1)-C(24) 175.68(8), C(2)-Ru(1)-C(13) 91.17(8), C(2)-Ru(1)-C(24) 88.04(7), C(2)-Ru(1)-Cl(1) 95.54(5). (Right) Space-filling diagram of 13 illustrating the lengthening of the Ru-Cl bond.

Concluding Remarks

Experimental Section

The reactivity of the two N-alkyl-substituted N-heterocyclic carbenes IiPr2Me2 1 and IEt2Me2 2 with the ruthenium hydride halide precursors Ru(PPh3)3HCl, [Ru(PiPr3)2HCl]2, and Ru(PiPr3)2(CO)HCl has been investigated. Treatment of Ru(PPh3)3HCl with either 1 or 2 affords a mixture of agostic and anagostic products, which, in the case of the former, can be be fully converted to the C-H activated complex Ru(IiPr2Me2)0 (PPh3)2Cl upon reaction with ethene. Alkene also induces C-H activation in both of the PiPr3 complexes Ru(IiPr2Me2)(PiPr3)2HCl and Ru(IEt2Me2)(PiPr3)2HCl as well, but to give alkenyl products as a result of doubleactivation reactions. The formation of these more reduced products is consistent with the strong π-basic character of [Ru(PiPr3)2HCl]2.13a,18e Although high solubility and sensitivity to air have prevented these alkenyl compounds from being isolated, the conditions required for their formation reinforce our general preception that C-H activation of an N-Et group is harder than N-iPr activation. The formation of anagostic Ru(IiPr2Me2)(PiPr3)2HCl compared to agostic Ru(IiPr2Me2)(PiPr3)(CO)HCl upon reacting IiPr2Me2 with [Ru(PiPr3)2HCl]2 and Ru(PiPr3)2(CO)HCl, respectively, shows how the presence of a π-acid ligand changes the nature of the reaction products. Moreover, Ru(IiPr2Me2)(PiPr3)(CO)HCl shows no willingness to undergo C-H activation of the NHC, although the significant lengthening of the Ru-Cl bond in the tris-carbene complex Ru(IiPr2Me2)3(CO)HCl makes this molecule worthy of further study for C-H activation upon abstraction of halide. This line of investigation is actively being pursued in efforts to shed additional light on intramolecular bond activation reactions of NHCs.

General Comments. All manipulations were carried out using standard Schlenk, high-vacuum, and glovebox techniques. Solvents were purified using an MBraun SPS solvent system, under a nitrogen atmosphere from sodium benzophenone ketyl or, in the case of ethanol, from Mg/I2. Deuterated solvents (Aldrich) were vacuum transferred from potassium (C6D6, THF-d8) or calcium hydride (CD2Cl2). Hydrogen (BOC, 99.99%) and ethene (Aldrich, 99.5%) were used as received. Ru(PPh3)3HCl,32 [Ru(PiPr3)2HCl]2,12 Ru(PiPr3)2(CO)HCl,29 IiPr2Me2, and IEt2Me233 were prepared according to the literature. NMR spectra were recorded on Bruker Avance 400 and 500 MHz spectrometers at 298 K unless otherwise specified, with 1H and 13C{1H} spectra referenced as follows: δ 5.32 and 53.7 (CD2Cl2); δ 7.15 and 128.0 (C6D6); δ 3.58 and 67.2 (THFd8). 31P chemical shifts were referenced externally to 85% H3PO4 (δ 0.0). IR spectra were recorded on a Nicolet Nexus FTIR spectrometer. Mass spectra were recorded using a microTOF electrospray time-of-flight (ESI-TOF) mass spectrometer (Bruker Daltonik GmbH) coupled to an Agilent 1200 LC sytem (Agilent Technologies). Elemental analyses were performed by Elemental Microanalysis Ltd., Okehampton, Devon, UK. Formation of Ru(IiPr2Me2)(PPh3)2HCl (3a/3b/4). A solution of IiPr2Me2 1 (60 mg, 0.33 mmol) and Ru(PPh3)3HCl (155 mg, 0.17 mmol) in CH2Cl2 (5 mL) was stirred under argon at room temperature for 1 h. The volatiles were removed in vacuo and the residue washed with hexane (2 5 mL) and filtered. The resulting brown solid was dissolved in ethanol and stirred for 18 h at room temperature. The resulting yellow precipitate was isolated by filtration and washed with ethanol, affording Ru(IiPr2Me2)(PPh3)2HCl as a mixture of isomers. Yield: (32) Schunn, R. A.; Wonchoba, E. R.; Wilkinson, G. Inorg. Synth. 1971, 13, 131–134. (33) K€ uhn, N.; Kratz, T. Synthesis 1993, 561–563.

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90 mg (63%). Further recrystallization was carried out from CH2Cl2/hexane. Anal. Found (calcd) for C47H51N2P2ClRu 3 CH2Cl2: C, 62.13 (62.17); H, 5.74 (5.76); N, 2.98 (3.02). NMR data for 3a: 1H (CD2Cl2, 500 MHz): δ 7.41-7.36 (m, 12H, PPh3), 7.29 (m, 6H, PPh3), 7.25-7.22 (m, 12H, PPh3), 5.18 (sept, 3 JHH = 7.0 Hz, 1H, CH), 3.87 (sept, 3JHH = 6.9 Hz, 1H, CH), 2.16 (s, 3H, im-CH3), 1.87 (s, 3H, im-CH3), 0.86 (d, 3JHH = 7.0 Hz, 6H, CH3), 0.00 (d, 3JHH = 6.9 Hz, 6H, CH3), -25.16 (t, 2 JHP = 23.1 Hz, 1H, Ru-H). 31P{1H} (202 MHz): δ 47.2 (s). 13 C{1H} (126 MHz): δ 189.3 (t, 2JCP = 12.6 Hz, Ru-CNHC), 138.6 (vt, J = 16.4 Hz, PPh3), 134.8 (vt, J = 6.3 Hz, PPh3), 128.9 (s, PPh3), 127.8 (vt, J = 3.7 Hz, PPh3), 124.6 (s, im-C), 124.1 (s, im-C), 53.0 (s, CH), 50.7 (s, CH), 20.1 (s, CH3), 17.6 (s, CH3), 10.8 (s, im-CH3), 9.8 (s, im-CH3). Selected NMR data for 3b: 1H (CD2Cl2, 500 MHz, 260K): δ 5.75 (sept, 3JHH = 7.5 Hz, 1H, CH), 4.83 (sept, 3JHH = 6.5 Hz, 1H, CH), 2.32 (s, 3H, im-CH3), 1.98 (s, 3H, im-CH3), 1.43 (d, 3JHH = 7.0 Hz, 3H, CH3), 1.06 (d, 3 JHH = 7.0 Hz, 3H, CH3), 0.80 (d, 3JHH = 6.5 Hz, 3H, CH3), 0.43 (d, 3JHH = 7.0 Hz, 3H, CH3), -25.64 (m, 1H, Ru-H)* (* = Ru-H signal best observed at room temperature). 31P{1H} (202 MHz): δ 73.7 (m), 49.1 (m). Selected NMR data for 4: 1H (CD2Cl2, 400 MHz): δ 4.85 (sept, 3JHH = 7.3 Hz, 1H, CH), 2.93 (sept, 3JHH = 7.3 Hz, 1H, CH), 2.25 (s, 3H, im-CH3), 2.06 (s, 3H, im-CH3), 0.88 (d, 3JHH = 7.3 Hz, 6H, CH3), 0.23 (d, 3JHH = 7.3 Hz, 6H, CH3), -30.47 (t, 2J = 25.6 Hz, 1H, Ru-H). 31P{1H} (162 MHz): δ 42.8 (s). Ru(IiPr2Me2)0 (PPh3)2Cl (5). Ru(IiPr2Me2)(PPh3)2HCl (30 mg, 36 μmol) was dissolved in benzene (2 mL) and degassed by three freeze-pump-thaw cycles. Ethene (1 atm) was introduced and the mixture stirred at room temperature. Within 20 min, a pink-purple solid precipitated. After further stirring for 16 h, the solid was isolated by filtration and washed with hexane. Recrystallization from CH2Cl2/pentane afforded 5 as red crystals. Yield: 23 mg (77%). Anal. Found (calcd) for C47H49N2P2ClRu 3 CH2Cl2: C, 61.91 (62.31); H, 5.55 (5.56); N, 3.02 (3.03). NMR data: 1H (CD2Cl2, 400 MHz)†: δ 4.92 (sept, 3 JHH = 6.7 Hz, 1H, CH), 2.59 (m, 1H, CH), 2.13 (s, 3H, imCH3), 1.75 (m, 1H, CH2), 1.56 (s, 3H, im-CH3), 1.47 (m, 1H, CH), 0.54 (d, 3JHH = 6.7 Hz, 6H, CH3), -0.16 (d, 3JHH = 6.1 Hz, 3H, CH3). 31P{1H} (162 MHz): δ 43.74 (“s”), 43.72 (“s”). Selected 13C{1H} (100 MHz)†: δ 184.1 (t, 2JCP = 13.8 Hz, RuCNHC), 126.0 (s, im-C), 122.9 (s, im-C), 57.7 (s, CH), 52.8 (s, CH), 21.3 (s, CH3), 20.6 (s, CH3), 20.5 (s, CH3), 10.5 (s, im-CH3), 9.8 (s, im-CH3), 8.8-8.7 (m, CH2) († = aromatic resonances could not be assigned as a result of significant overlap resulting from the slight inequivalence of the two phosphine ligands). Ru(IiPr2Me2)(PiPr3)2HCl (6). Benzene (10 mL) was added to i I Pr2Me2 (47 mg, 0.26 mmol) and [Ru(PiPr3)2HCl]2 (110 mg, 0.12 mmol) in an ampule under argon. The mixture was stirred at room temperature for 1 h, then left to stand overnight. The resulting crystalline precipitate was isolated by filtration and washed with hexane (2 5 mL) to give Ru(IiPr2Me2)(PiPr3)2HCl (6) as small red-brown crystals. Yield: 60 mg (39%). NMR data: 1H (C6D6, 400 MHz): δ 5.53 (sept, 3JHH = 6.7 Hz, 1H, CH), 5.22 (sept, 3JHH = 6.6 Hz, 1H, CH), 2.60 (br s, 6H, PiPr3), 1.75 (s, 3H, im-CH3) 1.73 (s, 3H, im-CH3), 1.46 (d, 3JHH = 6.6 Hz, 6H, CH3), 1.40 (vq, J = 6.5 Hz, 18H, PiPr3), 1.18 (vq, J = 6.5 Hz, 18H, PiPr3), 1.10 (d, 3JHH = 6.7 Hz, 6H, CH3), -29.35 (t, 2JHP = 23.7 Hz, 1H, Ru-H). 31P{1H} (C6D6, 162 MHz): δ 51.5 (s). 13C{1H} (THF-d8, 100 MHz): δ 191.3 (t, 2 JCP = 10.2 Hz, Ru-CNHC), 125.3 (s, im C), 123.4 (s, im C), 51.8 (s, CH), 50.0 (s, CH), 26.0 (vt, J = 7.3 Hz, PiPr3), 23.7 (s, CH3), 23.0 (s, CH3), 20.9 (s, CH3, PiPr3), 20.0 (s, CH3, PiPr3), 10.6 (s, im CH3), 10.6 (s, im CH3). Repeated attempts to record microanalytical data always yielded unacceptably low values for %C. Ru{η2-C(NiPr)CMeCMeN(CMedCH)}(PiPr3)2Cl (7). Ethene (1 atm) was introduced to a degassed sample of complex 6 (ca. 10 mg) in C6D6 in an NMR tube fitted with a resealable J. Youngs PTFE tap. Monitoring by 1H and 31P{1H} NMR spectroscopy indicated the reaction was complete after 16 h at room temperature,

Burling et al. with Ru{η2-C(NiPr)CMeCMeN(CMedCH)}(PiPr3)2Cl (7) identified as the major product (>95%). NMR data: 1H (C6D6, 400 MHz): δ 7.79 (br s, 1H, Ru-CH), 5.66 (sept, 3JHH = 7.0 Hz, 1H, CH), 2.49 (m, 6H, PiPr3), 2.32 (m, 3H, CH3), 2.00 (s, 3H, imCH3) 1.85 (s, 3H, im-CH3), 1.38 (d, 3JHH = 7.0 Hz, 6H, CH3), 1.23 (vq, J = 7.0 Hz, 18H, PiPr3), 1.14 (vq, J = 7.0 Hz, 18H, PiPr3). 31 1 P{ H} (162 MHz): δ 42.5 (s). 13C{1H} (100 MHz): δ 192.3 (t, 2 JCP = 11.0 Hz, Ru-CNHC), 150.3 (t, 2JCP = 12.0 Hz, Ru-CH), 132.1 (s, Ru-CdC), 122.3 (s, im-C), 120.5 (s, im-C), 50.6 (s, CH), 25.0 (vt, J = 7.6 Hz, CH, PiPr3), 23.3 (s, CH3), 20.7 (s, CH3, PiPr3), 20.6 (s, CH3, PiPr3), 19.7 (s, CH3), 10.6, (s, CH3), 9.6 (s, CH3). Ru(IEt2Me2)(PPh3)2HCl (8a/8b). Ru(PPh3)3HCl (84 mg, 90 μmol) and IEt2Me2 (55 mg, 0.36 mmol) were dissolved in CH2Cl2 (4 mL), and the solution was stirred at room temperature for 2 h. Removal of the solvent gave a red-brown residue, which was washed with hexane (2 5 mL). The residue was extracted with THF (5 mL), filtered, and evaporated to dryness. The resulting solid was recrystallized from benzene/hexane to give a small amount of a mixture of 8a/8b as orange-red crystals. NMR data for 8a: 1H NMR (CD2Cl2, 400 MHz): δ 7.48-7.42 (m, 12H, PPh3), 7.30 (m, 6H, PPh3), 7.26-7.21 (m, 12H, PPh3), 3.32 (q, 3JHH = 7.2 Hz, 2H, CH2), 2.58 (q, 3JHH = 7.2 Hz, 2H, CH2), 2.00 (s, 3H, im-CH3), 1.64 (s, 3H, im-CH3), 0.42 (t, 3 JHH = 7.2 Hz, 3H, CH3), -0.11 (t, 3JHH = 7.2 Hz, 3H, CH3), -26.50 (t, 2JHP = 23.2 Hz, 1H, Ru-H). 31P{1H} (162 MHz): δ 48.1 (s, PPh3). 13C{1H} (126 MHz): δ 188.3 (t, 2JCP = 13.1 Hz, Ru-CNHC), 138.2 (vt, J = 17.6 Hz, PPh3), 134.7 (vt, J = 5.0 Hz, PPh3), 128.8 (s), 127.7 (vt, J = 3.8 Hz, PPh3), 123.7 (s, im-C), 123.4 (s, im-C), 42.0 (s, CH2), 41.9 (s, CH2), 12.7 (m, CH3), 12.6 (s, CH3), 9.6 (s, im-CH3), 9.4 (s, im-CH3). Ru(IEt2Me2)(PiPr3)2HCl (10). Benzene (5 mL) was added to IEt2Me2 (14 mg, 92 μmol) and [Ru(PiPr3)2HCl]2 (42 mg, 46 μmol) in an ampule under argon. The mixture was stirred at room temperature for 1 h, then left to stand overnight. The mixture was filtered, the volatiles were removed from the filtrate, and pentane was added to the residue. The pentanesoluble fraction was filtered into an ampule and refrigerated. Red-orange crystals were produced (yield 22 mg, 39%). Anal. Found (calcd) for C27H59N2P2ClRu: C, 53.25 (53.14); H, 10.07 (9.75); N, 4.66 (4.59). NMR data: 1H (C6D6, 500 MHz): δ 4.22 (q, 3JHH = 7.5 Hz, 2H, CH2), 3.93 (q, 3JHH = 7.5 Hz, 2H, CH2), 2.48 (br s, 6H, PiPr3), 1.61 (s, 3H, im-CH3), 1.60 (s, 3H, im-CH3), 1.39 (vq, J = 6.5 Hz, 18H, PiPr3), 1.25 (t, 3JHH = 7.5 Hz, 3H, CH3), 1.17 (vq, J = 6.5 Hz, 18H, PiPr3), 0.95 (t, JHH = 7.5 Hz, 3H, CH3), -29.54 (t, 2JHP = 23.0 Hz, 1H, Ru-H). 31P{1H} (202 MHz): δ 51.2 (s). 13C{1H} (126 MHz): δ 191.4 (t, 2JCP = 11.3 Hz, Ru-CNHC), 123.3 (s, im-C), 121.7 (s, im-C), 43.3 (s, CH2), 41.6 (s, CH2), 25.5 (vt, J = 7.5 Hz, PiPr3), 20.7 (s, CH3, PiPr3), 19.4 (s, CH3, PiPr3), 15.0 (s, CH3), 14.9 (s, CH3), 9.5 (s, im-CH3), 9.2 (s, im-CH3). Ru{η2-C(NEt)CMeCMeN(CHdCH)}(PiPr3)2Cl (11). Ethene (1 atm) was introduced to a degassed sample of complex 10 (ca. 10 mg) in C6D6 in a NMR tube fitted with a resealable Teflon tap. The sample was heated at 323 K over 3 days, with regular monitoring by 1H and 31P{1H} NMR spectroscopy. The doubly C-H activated species Ru{η2-C(NEt)CMeCMeN(CHdCH)}(PiPr3)2Cl (11) was identified spectroscopically as the major product present in solution. NMR data: 1H (C6D6, 400 MHz): δ 8.67 (m, 1H, Ru-CH), 6.60 (m, 1H, Ru-CHdCH), 4.39 (q, 3JHH = 7.6 Hz, 2H, CH2), 2.55 (m, 6H, PiPr3), 1.82 (s, 3H, im-CH3), 1.74 (s, 3H, im-CH3), 1.24 (t, 3 JHH = 7.6 Hz, 3H, CH3), 1.17-1.09 (m, 36H, PiPr3). 31P{1H} (162 MHz): δ 41.4 (s, PiPr3). 13C{1H} (100 MHz): δ 186.9 (Ru-CNHC)*, 157.2 (t, 2JCP = 11.4 Hz, Ru-CH), 121.6 (t, 3JCP = 2.7 Hz, Ru-CHdCH), 120.5 (s, im-C), 120.1 (s, im-C), 42.8 (s, CH2), 24.8 (vt, J = 8.3 Hz, PiPr3), 20.1 (s, CH3, PiPr3), 20.0 (s, CH3, PiPr3), 15.3 (s, CH3), 9.4 (s, im-CH3), 8.9 (s, im-CH3) (* = chemical shift identified by 1H-13C HMBC spectroscopy). Ru(IiPr2Me2)(PiPr3)(CO)HCl (12). Ru(PiPr3)2(CO)HCl (100 mg, 0.21 mmol) and IiPr2Me2 (37 mg, 0.21 mmol) were dissolved in C6H6 (5 mL), and the solution was stirred at room

reflns collected indep reflns, Rint reflns obsd (>2σ) absorp corr max., min. transmn data/restraints/params goodness-of-fit on F2 final R1, wR2 [I > 2σ(I)] final R1, wR2 (all data) largest diff peak, hole/e A˚-3 absolute struct param

empirical formula fw T/K cryst syst space group a/A˚ b/A˚ c/A˚ R/deg β/deg γ/deg U/A˚3 Z Dc/g cm-3 μ/mm-1 F(000) cryst size/mm θ min., max. for data collection index ranges C48H52.6Cl3N2P2Ru 926.88 150(2) triclinic P1 12.5800(1) 14.2480(2) 14.6440(2) 103.998(1) 106.055(1) 110.100(1) 2197.50(5) 2 1.401 0.648 959 0.50 0.40 0.20 3.59, 27.52 -16 e h e 16; -18 e k e 18; -18 e l e 19 38 527 10 052, 0.0311 8461 multiscan 0.88, 0.74 10 052/1/537 1.028 0.0325, 0.0764 0.0439, 0.0817 0.868, -1.061

-14 e h e 14; -17 e k e 17; -25 e l e 25 38 543 12 120, 0.0346 10 257 multiscan 0.902, 0.956 12 120/37/874 1.047 0.0326, 0.0715

0.0442, 0.0768 0.995, -0.809

4

C62H66ClN2P2Ru 1037.63 150(2) triclinic P1 11.2020(1) 13.4210(2) 19.8430(3) 80.383(1) 74.956(1) 67.616(1) 2656.13(6) 2 1.297 0.447 1086 0.25 0.15 0.10 3.52, 27.46

3a

0.0431, 0.0944 1.084, -1.305

-17 e h e 17; -19 e k e 18; -20 e l e 20 41 239 12 694, 0.0273 11 078 multiscan 0.86, 0.82 12 694/2/536 1.029 0.0356, 0.0899

C48H51Cl3N2P2Ru 925.27 150(2) triclinic P1 12.5900(1) 14.1530(1) 14.6440(1) 105.247(1) 106.279(1) 108.457(1) 2191.48(3) 2 1.402 0.650 956 0.25 0.25 0.20 3.72, 30.06

5

0.0308, 0.0647 0.640, -0.849

5710/2/215 1.065 0.0259, 0.0627

-15 e h e 15; -25 e k e 25; -26 e l e 26 74 899 5710, 0.0426 5248 none

C35H69ClN2P2Ru 716.38 150(2) orthorhombic Pbnm 10.9400(1) 18.2770(1) 19.0420(1) 90 90 90 3807.46(5) 4 1.250 0.591 1536 0.20 0.20 0.15 3.71, 30.04

6

0.0395, 0.0657 0.757, -0.832

-15 e h e 15; -15 e k e 15; -21 e l e 22 34 825 9512, 0.0416 8105 multiscan 0.82, 0.77 9512/3/327 1.026 0.0287, 0.0618

-14 e h e 14; -17 e k e 17; -23 e l e 23 42 274 10 987, 0.0541 9015 multiscan 0.96, 0.89 10 987/1/573 1.068 0.0455, 0.0807 0.0635, 0.0865 0.679, -0.721


10


8a

Table 1. Crystal Structure Details for Compounds 3a, 4, 5, 6, 8a, 10, 12, and 13

0.0437, 0.0735 0.954, -0.750


C21H42ClN2OPRu 506.06 150(2) monoclinic I21/n 14.9410(2) 9.6240(1) 17.5520(3) 90 92.026(1) 90 2522.26(6) 4 1.333 0.804 1064 0.50 0.30 0.30 3.52, 27.48

12

0.0308, 0.0635 0.510, -0.527 -0.022(19)


C40H67ClN6ORu 784.52 150(2) orthorhombic P212121 9.8460(1) 17.3210(1) 24.2240(2) 90 90 90 4131.22(6) 4 1.261 0.481 1672 0.30 0.20 0.20 3.56, 27.47

13

Article Organometallics, Vol. 28, No. 23, 2009 6685

6686


temperature for 1 h. Removal of the solvent gave a yellow residue, which was extracted with hexane (2 3 mL) and concentrated. Upon standing for 24 h at room temperature, yellow crystals of 12 precipitated. In a number of separate experiments, the maximum yield of 12 that was isolated was 38% (40 mg) due to the high solubility of the compound in hexane, which makes separation from the free PiPr3 difficult to achieve. 1H NMR (C6D6, 500 MHz): δ 6.29 (br s, 1H, CH), 3.68 (br m, 1H, CH), 2.58 (m, 3H, PiPr3), 1.72 (s, 3H, im-CH3), 1.47 (s, 6H, im-CH3 þ CH3), 1.39 (dd, 3J = 12.7 Hz, 3J = 7.3 Hz, 9H, PiPr3), 1.31 (dd, 3J = 12.7 Hz, 3J = 7.3 Hz, 9H, PiPr3) 1.25 (br m, 3H, CH3), 1.18 (d, 3JHH = 6.5 Hz, 3H, CH3), 0.88 (d, 3JHH = 6.5 Hz, 3H, CH3), -19.15 (d, 2JHP = 25.5 Hz, 1H, Ru-H). 31 P{1H} (162 MHz): δ 60.3 (s, PiPr3). 13C{1H} (125 MHz): δ 201.6 (d, 2JCP = 12.5 Hz, CO), 185.8 (d, 2JCP = 95.6 Hz, RuCNHC), 124.5 (s, im-C), 123.3 (s, im-C), 55.1 (br s, CH), 50.2 (s, CH), 24.4 (d, 1JCP = 18.2 Hz, PCH), 23.9 (s, CH3), 22.2 (s, CH3), 20.6 (s, CH3), 20.2 (s, PCCH3), 19.8 (s, PCCH3), 10.6 (s, CH3), 8.8 (s, CH3). IR (KBr, cm-1): 2099 (νRuH), 1900 (νCO). Repeated attempts to record microanalytical data always yielded consistently erroneous values for %C probably due to small amounts of contamination by phosphine. Ru(IiPr2Me2)3(CO)HCl (13). Ru(PiPr3)2(CO)HCl (100 mg, 0.21 mmol) and IiPr2Me2 (111 mg, 0.62 mmol) were dissolved in C6H6 (10 mL), and the solution was stirred at room temperature for 1 h (with longer periods of time, precipitation of [Ru(IiPr2Me2)4H]þ is observed).14 Removal of the solvent gave a red residue, which was washed with hexane (2 5 mL). Redissolution in a minimal amount of benzne and layering with hexane afforded 13 as a pale pink, microcrystalline solid in 37% yield (55 mg). NMR data: 1H (C6D6, 500 MHz): δ 8.21 (sept, 3 JHH = 7.1 Hz, 1H, CH), 6.94 (br m, 2H, CH), 6.58 (sept, 3 JHH = 7.1 Hz, 1H, CH), 6.28 (sept, 3JHH = 7.1 Hz, 1H, CH), 5.85 (sept, 3JHH = 7.1 Hz, 1H, CH), 1.97 (s, 3H, im-CH3), 1.93 (s, 3H, im-CH3), 1.89 (s, 3H, im-CH3), 1.83 (s, 9H, im-CH3), 1.81 (d, 3JHH = 7.1 Hz, 3H, CH3), 1.74 (d, 3JHH = 7.1 Hz, 3H, CH3), 1.59 (d, 3JHH = 7.1 Hz, 3H, CH3), 1.53 (d, 3JHH = 7.1 Hz, 3H, CH3), 1.27 (d, 3JHH = 7.1 Hz, 3H, CH3), 1.21 (d, 3JHH = 7.1 Hz, 3H, CH3), 1.16 (d, 3JHH = 7.1 Hz, 3H, CH3), 0.77 (d, 3JHH = 7.1 Hz, 3H, CH3), 0.67 (br m, 9H, CH3), 0.64 (d, 3JHH = 7.1 Hz, 3H, CH3), -18.11 (s, 1H, Ru-H). 13C{1H} (125 MHz): δ 207.8 (s, CO), 194.9 (s, Ru-CNHC), 190.9 (s, Ru-CNHC), 189.0 (s, RuCNHC), 125.7 (s, im-C), 125.2 (s, im-C), 125.0 (s, im-C), 124.2 (s, im-C), 124.1 (s, im-C), 123.6 (s, im-C), 52.4 (s, CH), 52.2 (s, CH), 52.1 (s, CH), 51.7 (s, CH), 51.6 (s, CH), 25.9 (s, CH3), 24.3 (s, CH3), 23.9 (s, CH3), 22.4 (s, CH3), 22.3 (s, CH3), 21.1 (s, CH3), 20.6 (s, CH3), 20.4 (s, CH3), 20.2 (s, CH3), 20.1 (s, CH3), 19.9 (s, CH3), 19.3 (s, CH3), 10.9 (s, im-CH3), 10.5 (s, im-CH3), 10.4 (s, im-CH3), 10.2 (s, im-CH3), 9.9 (s, im-CH3). IR (KBr, cm-1): 1987 (νRuH), 1886 (νCO). ESI-TOF MS: [M - Cl]þ m/z = 671.4024 (theoretical 671.3954). X-ray Crystallography. Single crystals of compounds 3a, 4, 5, 6, 8a, 10, 12, and 13 were analyzed using a Nonius Kappa CCD diffractometer. Details of the data collections, solutions, and refinements are given in Table 1. The structures were solved using SHELXS-9734 and refined using full-matrix least-squares in SHELXL-97.34 Refinements were uneventful with the following exceptions and points of note. In 3a, the asymmetric unit was seen to contain one molecule of the ruthenium complex and 2.5 molecules of benzene. The halfmolecule of solvent is located proximate to an inversion center, which serves to generate the remainder. All solvent entities exhibited 1:1 disorder over 2 sites. Disorder was also prevalent in the metal complex. In particular, the carbene moiety position is averaged over two sites, one relating to agostic bonding between the metal and a methyl hydrogen attached to the (34) Sheldrick, G. M. Acta Crystallogr. 1990, 467-473, A46. Sheldrick, G. M. SHELXL-97, a computer program for crystal structure refinement; University of G€ ottingen, 1997.

Burling et al. terminal isopropyl carbon C11, the other involving an interaction between Ru1 and the hydrogen attached to the central (imidazole-bound) isopropyl carbon. Because of the disorder, all carbene hydrogens were included at calculated positions. Notwithstanding this, there was evidence for the hydrogens attached to C9 and C11 in the penultimate difference Fourier map, which largely coincide with the finalized calculated positions. The hydride attached to Ru1 was readily located and refined at 1.6 A˚ from the central metal. The data for 4 were of excellent quality, and consequently, H1, H4, and H9 were all prominent in the penultimate difference Fourier map and refined freely. The structural model was refined subject to accounting for some localized disorder. In particular, the isopropyl unit based on C9 is disordered in an 80:20 ratio with the comparative component based on C9A. The major fragment has an accompanying hydride ligand (H1) also at 80% occupancy. The minor component represents a fraction of an activated complex present in the lattice, which displaces the hydride ligand. It should be noted that the 20% hydrogens included in this moiety are at calculated positions and that derived parameters involving the same should be treated with a generous peppering of scepticism. C4 and C6 were seen to be disordered in 1:1 ratio with C4 and C6A, within the asymmetric unit of 5. The hydrogen atoms attached to C5 in this structure were located and refined at a distance of 0.89 A˚ from the parent carbon atom. The asymmetric unit in 6 was seen to comprise half of a molecule of benzene (proximate to an inversion center) and half of one complex molecule (with the central metal, chloride and hydride ligands, carbene heterocycle ring atoms, alpha isopropyl carbons, and associated hydrogen atoms located on a crystallographic mirror plane). H4 and H1 were located and refined at distances of 0.89 and 1.60 A˚ from the relevant parent atoms. In addition to one molecule of the complex, the structure of 8a was also noted to contain two benzene molecules in the motif. H1 was located and refined at a distance of 1.6 A˚ from the central metal. A noteworthy structural feature is the deviation by some 8° of the C32-C33-C28-P2 torsion angle from the ideal value of 180°. For 10, the positions of the hydride ligand and the hydrogen atoms attached to C4 were indentified, and these atoms were refined at distances of 1.6 and 0.99 A˚ from Ru1 and C4, respectively. In 12, the hydrides (H1 and H10) and the hydrogens attached to C12 were similarly treated to those in 10. Finally, in 13, the asymmetric unit was seen to contain one molecule of the tris-carbene complex plus one molecule of benzene. The chloride ligand exhibited disorder in an 80:20 ratio with the trans hydride. The 80% component of the latter was located and refined as for other hydrides above. Restraining the Ru-Clpartial distances to being similar did not assist refinement and, if anything, resulted in adverse lengthening of the Ru-Cl80% bond distance. Hence, both fractional moieties were refined freely. Crystallographic data for compounds 3a, 4, 5, 6, 8a, 10, 12, and 13 have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC 730645-730652. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: (þ44) 1223 336033, e-mail: deposit@ccdc. cam.ac.uk].

Acknowledgment. We thank the EPSRC (S.B.) and Spanish Ministerio de Ciencia e Innovaci on (E.M.M.) for financial support. Johnson Matthey plc is acknowledged for the kind loan of hydrated ruthenium trichloride. Supporting Information Available: CIF files giving X-ray crystallographic data for 3a, 4, 5, 6, 8a, 10, 12, and 13. This material is available free of charge via the Internet at http:// pubs.acs.org.

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