Labile N-Heterocyclic Carbene Complexes of Iridium - ACS Publications

Jan 9, 2009 - The complex [IrH2(η6-C6H6)(IMes)]PF6 provides easy access to other iridium dihydrides and derivatives with cyclometalated IMes ligands ...
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Organometallics 2009, 28, 863–870

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Labile N-Heterocyclic Carbene Complexes of Iridium Olga Torres, Marta Martı´n, and Eduardo Sola* Departamento de Quı´mica de Coordinacio´n y Cata´lisis Homoge´nea, Instituto de Ciencia de Materiales de Arago´n, UniVersidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain ReceiVed October 8, 2008

The arene complex [IrH2(η6-C6H6)(IMes)]PF6 (3) has been prepared in a one-pot synthesis from conventional starting materials. The facile substitution of its benzene ligand can be exploited in the preparation of many other NHC Ir(III) dihydrides, for which the solvent complexes [IrH2(L)3(IMes)]PF6 (L ) acetone-d6, 4; NCMe, 5), the NHC-phosphine compound [IrH2(NCMe)2(IMes)(PiPr3)]BF4 (6), and the water-soluble analogue [IrH2(NCMe)2(IMes)(TPPTS)]BF4 (7) constitute representative examples. The reactions of dihydrides 5 and 6 with hydrogen acceptors such as ethylene, propylene, and diphenylacetylene have been examined. Depending on the dihydride and the acceptor, they have led to different Ir(III) complexes with a cyclometalated IMes moiety and hydride, alkyl, or alkenyl ligands: [Ir(R)(IMes′)(NCMe)2(L)]PF6 {R ) H, L ) NCMe (8), PiPr3 (9); L ) NCMe, R ) Et (10); nPr (11); Z-C(Ph)dCHPh (12)}. Because of their six-membered rings, such cyclometalated compounds have been found to adopt two possible conformations in equilibrium. The rates of exchange between conformers are of the same order as the NMR time scale, and the equilibrium position is governed by steric factors. By reaction with phenylacetylene, compounds 6 and 9 have afforded a common hydride alkynyl complex [IrH(CtCPh)(NCMe)2(IMes)(PiPr3)]PF6 (14). Its selective formation as a deuteride isotopomer from the reaction between 9 and PhCtCD has proven that Ir(I) species, although nonobserved, are accessible. Introduction Following their success as alternatives to phosphine ligands in catalytic reactions such as olefin metathesis,1 the research of N-heterocyclic carbenes (NHCs), their coordination complexes, and their applications has experienced a spectacular expansion.2 The reasons behind this boom are the strength and high donor ability of NHCs as ligands,3 their ease of preparation,4 and, especially, their stereoelectronic5 and topologic6 versatility. For iridium in particular, dozens of new complexes with a variety of NHC ligands have been described in an interval of few years, although, from the standpoint of the coordination around the metal, all these compounds look very similar. In fact, the vast majority of NHC iridium complexes reported so far are Ir(I)

* Corresponding author. E-mail: [email protected]. (1) (a) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18–29. (b) Furstner, A.; Ackermann, L.; Gabor, B.; Goddard, R.; Lehmann, C. W.; Mynott, R.; Stelzer, F.; Thiel, O. R. Chem.;Eur. J. 2001, 7, 3236–3253. (2) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290–1309. (b) N-Heterocyclic Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley-VCH: Weinheim, Germany, 2006. (c) Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. G. Angew. Chem., Int. Ed. 2007, 46, 2768–2813. (3) Bourissou, D.; Guerret, O.; Gabbaı¨, F. P.; Bertrand, G. Chem. ReV. 2000, 100, 39–91. (4) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122– 3172. (5) (a) Dı´ez-Gonza´lez, S.; Nolan, S. P. Coord. Chem. ReV. 2007, 251, 874–883. (b) Cavallo, L.; Correa, A.; Costabile, C.; Jacobsen, H. J. Organomet. Chem. 2005, 690, 5407–5413. (c) Crabtree, R. H. J. Organomet. Chem. 2005, 690, 5451–5457. (6) (a) Arnold, P. L.; Pearson, S. Coord. Chem. ReV. 2007, 251, 596– 609. (b) Mata, J. A.; Poyatos, M.; Peris, E. Coord. Chem. ReV. 2007, 251, 841–859. (c) Pugh, D.; Danopoulos, A. A. Coord. Chem. ReV. 2007, 251, 610–641. (d) Ku¨hl, O. Chem. Soc. ReV. 2007, 36, 592–607. (e) Liddle, S. T.; Edworthy, I. S.; Arnold, P. L. Chem. Soc. ReV. 2007, 36, 1732–1744. (f) Cesar, V.; Bellemin-Laponnaz, S.; Gade, L. H. Chem. Soc. ReV. 2004, 33, 619–636. (g) Sommer, W. J.; Weck, M. Coord. Chem. ReV. 2007, 251, 860–873.

species with 1,5-cyclooctadiene (COD) or CO ligands,7-9 and derivatives of the [CpIr(III)] fragment.10 As an alternative to overcome this structural monotony and increase the arsenal of possible catalyst designs, we describe here a new and versatile (7) Recent examples: (a) Appelhans, L. N.; Incarvito, C. D.; Crabtree, R. H. J. Organomet. Chem. 2008, 693, 2761–2766. (b) Hintermair, U.; Gutel, T.; Slawin, A. M. Z.; Cole-Hamilton, D. J.; Santini, C. C.; Chauvin, Y. J. Organomet. Chem. 2008, 693, 2407–2414. (c) Zanardi, A.; Peris, E.; Mata, J. New J. Chem. 2008, 32, 120–126. (d) Chen, T.; Liu, X. G.; Shi, M. Tetrahedron 2007, 63, 4874–4880. (e) Green, S. P.; Jones, D. P.; Stasch, A. Organometallics 2007, 26, 3424–3430. (f) Frey, G. D.; Rentzsch, C. F.; von Preysing, D.; Scherg, T.; Muhlhofer, M.; Herdtweck, E.; Herrmann, W. A. J. Organomet. Chem. 2006, 691, 5725–5738. (g) Nanchen, S.; Pfaltz, A. HelV. Chim. Acta 2006, 89, 1559–1573. (h) Prinz, M.; Veiros, L. F.; Calhorda, M. J.; Romao, C. C; Herdtweck, E.; Kuhn, F. E.; Herrmann, W. A. J. Organomet. Chem. 2006, 691, 4446–4458. (i) Viciano, M.; MasMarza´, E.; Sanau´, M.; Peris, E. Organometallics 2006, 25, 3063–3069. (j) Messerle, B. A.; Page, M. J.; Turner, P. Dalton Trans. 2006, 3927–3933. (k) Herrmann, W. A.; Baskakov, D.; Herdtweck, E.; Hoffmann, S. D.; Bunlaksananusorn, T.; Rampf, F.; Rodefeld, L. Organometallics 2006, 25, 2449–2456. (l) Burling, S.; Mahon, M. F.; Reade, S. P.; Whittlesey, M. K. Organometallics 2006, 25, 3761–3767. (8) (a) Vazquez-Serrano, L. D.; Owens, B. T.; Buriak, J. M. Chem. Commun. 2002, 2518–2519. (b) Leutha¨uβer, S.; Schwarz, D.; Plenio, H. Chem.;Eur. J. 2007, 13, 7195–7203. (c) Kownacki, I.; Kubicki, M.; Szubert, K.; Marciniec, B. J. Organomet. Chem. 2008, 693, 321–328. (d) Kelly III, R. A.; Clavier, H.; Giudice, S.; Scott, N. M.; Stevens, E. D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.; Cavallo, L.; Nolan, S. P. Organometallics 2008, 27, 202–210. (9) (a) Hahn, F. E.; Holtgrewe, C.; Pape, T.; Martı´n, M.; Sola, E.; Oro, L. A. Organometallics 2005, 24, 2203–2209. (b) Hahn, F. E.; Heidrich, B.; Pape, T.; Hepp, A.; Martı´n, M.; Sola, E.; Oro, L. A. Inorg. Chim. Acta 2006, 359, 4840–4846. (10) Recent examples:(a) Wang, X.; Liu, S.; Weng, L. H.; Jin, G. X. Chem.;Eur. J. 2007, 13, 188–195. (b) Corbera´n, R.; Sanau´, M.; Peris, E. Organometallics 2007, 26, 3492–3498. (c) Corbera´n, R.; Sanau´, M.; Peris, E. Organometallics 2006, 25, 4002–4008. (d) Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2006, 25, 4643–4647. (e) Corbera´n, R.; Lillo, V.; Mata, J. A.; Fernandez, E.; Peris, E. Organometallics 2007, 26, 4350–4353. (f) Corbera´n, R.; Sanau´, M.; Peris, E. J. Am. Chem. Soc. 2006, 128, 3974–3979. (g) Tanabe, Y.; Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2006, 25, 4618–4626. (h) Hanasaka, F.; Tanabe, Y.; Fujita, K.; Yamaguchi, R. Organometallics 2006, 25, 826–831.

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entry into the chemistry of iridium NHC complexes, via the labile cationic complex [IrH2(η6-C6H6)(IMes)]PF6. This work has made use of a single NHC ligand, the 1,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene (IMes), whose large size and proclivity to undergo cyclometalation via C-H activation have certainly influenced the characteristics of the new compounds obtained.

Results and Discussion Dihydride Complexes. We have recently described that reaction of the dimer [Ir(µ-OMe)(COD)]2 with two equivalents of imidazolium salt constitutes a straightforward method for the synthesis of [IrX(COD)(NHC)] complexes.9 The application of this procedure to 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride (IMes · HCl) produces the known complex [IrCl(COD)(IMes)] (1).8 Removal of the chloride ligand with silver hexafluorofosfate followed by COD ligand hydrogenation in the presence of benzene leads to the dihydride arene complex [IrH2(η6-C6H6)(IMes)]PF6 (3) (eq 1). This sequence of reactions can be stopped at any of the intermediates in eq 1, but leads to better yield in 3 when carried out in a one-pot procedure in acetone as solvent. A similar synthesis using phosphonium salts instead of imidazolium chloride was reported to afford analogues of 3 with PiPr3 or PCy3.11

The structure of the cation of 3 determined by X-ray diffraction (Figure 1) shows a geometry around the iridium very similar to those found in the closely related phosphine complexes [IrH2(η6-mesitylene)(PiPr3)]BF411a and [IrH2{η5-(C6H5)NHCH2Ph}(PiPr3)]BF4.12 The NMR spectra of the compound in CD2Cl2 are consistent with this structure and indicate that no part of the molecule is affected by rotation restrictions. In agreement with data previously reported,13 the 13C NMR chemical shift of the NHC carbenic carbon significantly moves toward higher field upon formal oxidation of the iridium, going from δ 173.72 in 2 to δ 144.95 in 3. The benzene ligand of 3 can be replaced by coordinating solvents such as acetone or acetonitrile to form tris-solvent compounds: [IrH2(L)3(IMes)]PF6 (L ) OC(CD3)2, 4; NCMe, 5; eq 2). Complex 4 has been characterized only in solution, since its formation from 3 is not quantitative even in acetone(11) (a) Torres, F.; Sola, E.; Martı´n, M.; Lo´pez, J. A.; Lahoz, F. J.; Oro, L. A. J. Am. Chem. Soc. 1999, 121, 10632–10633. (b) Torres, F.; Sola, E.; Martı´n, M.; Ochs, C.; Picazo, G.; Lo´pez, J. A.; Lahoz, F. J.; Oro, L. A. Organometallics 2001, 20, 2716–2724. (12) Martín, M.; Sola, E.; Tejero, S.; Andre´s, J. L.; Oro, L. A. Chem.;Eur. J. 2006, 12, 4043–4056. (13) For example: (a) Viciano, M.; Poyatos, M.; Sanau´, M.; Peris, E.; Rossin, A.; Ujaque, G.; Lledo´s, A Organometallics 2006, 25, 1120–1134. (b) Mas-Marza´, E.; Sanau´, M.; Peris, E. Inorg. Chem. 2005, 44, 9961– 9967.

Figure 1. Molecular structure of the cation of 3. Selected bond distances (Å) and angles (deg): Ir-C(1), 1.997(4); Ir-C(22) to Ir-C(27), 2.308(4), 2.304(4), 2.326(4), 2.185(4), 2.242(4), and 2.247(4), respectively; Ir-H(1A), 1.540(18); Ir-H(1B), 1.497(18); C(1)-Ir-H(1A), 75.4(14); C(1)-Ir-H(1B), 80.3(16); H(1A)Ir-H(1B), 82.4(8).

d6. At room temperature, the equilibrium between 3 and 4 is slow in the NMR time scale, and therefore its position can be estimated by integration of the separate signals of each compound. The equilibrium constant in the sense of solvent coordination (K ) [4][C6H6]/[3]) is 3.5 M in solutions 3.6 × 10-3 M at 297 K. Interestingly, under the same conditions, the triisopropylphosphine analogue [IrH2(η6-C6H6)(PiPr3)]BF4 shows an equilibrium constant 1 order of magnitude lower (0.35 M).11a

In contrast to acetone, only the stoichiometric amount of acetonitrile (3 equiv) is required to displace the benzene ligand of 3 and form the isolable acetonitrile complex 5. Yet, the acetonitrile ligands of 5 remain labile and can be further replaced. As an example, eq 2 shows the formation of the two phosphine derivatives 6 and 7, with PiPr3 and TPPTS (tris(3sulfonatophenyl)phosphine, P(C6H4-m-SO3Na)3), respectively. The latter complex is water-soluble and much more resistant to hydrolysis when isolated as tetrafluoroborate instead of hexafluorophosphate salt. The structures of the cations of 5 and 6 are shown in the Figure 2, and their important structural parameters are collected in Table 1. The nearly perfect octahedral structure of 5 features two very long Ir-N distances trans to hydride, that should correspond to readily dissociable acetonitriles.14 In spite of that, the bulky incoming phosphine ligands replace the more strongly bonded acetonitrile trans to IMes, showing that substitutions in 5 are thermodynamically controlled to minimize steric repulsion, (14) Sola, E.; Navarro, J.; Lo´pez, J. A.; Lahoz, F. J.; Oro, L. A.; Werner, H. Organometallics 1999, 18, 3534–3546.

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respectively, and splits into a doublet as a result of a phosphorus coupling constant of about 110 Hz. Hydrogenation Reactions and Cyclometalated Complexes. Hydrogen acceptors such as olefins or internal alkynes are readily hydrogenated by dihydrides 5 and 6. As a result, instead of the expected Ir(I) derivatives, the hydrogenations afford Ir(III) complexes with cyclometalated IMes ligands (κ2 - C, denoted as IMes′). Equation 3 summarizes the course of various reactions using ethylene, propylene, or diphenylacetylene as hydrogen acceptors. The reactions of complex 5 with excess of the acceptor have led to alkyl or alkenyl compounds of general formula [Ir(R)(IMes′)(NCMe)3]PF6 (R ) Et, 10; nPr, 11; Z-C(Ph)d CHPh, 12), most probably via a hydrogenation/C-H activation/ insertion reaction sequence. The insertion products 10-12 display rather different stabilities in solution, depending on the nature of R. Thus, while the β-elimination of hydrogen from 12 to form 8 has not been observed,16 this elementary reaction is very facile in the propyl derivative 11, which, in fact, could not be isolated analytically pure as a result of this circumstance. Actually, the bubbling and subsequent removal of propylene constitutes the simplest alternative to prepare the intermediate hydride [IrH(IMes′)(NCMe)3]PF6 (8) from solutions of 5. The stability toward β-elimination of the ethyl complex 10 is enough to allow for its isolation, although the persistent removal of dissolved ethylene under reduced pressure can eventually reverse the insertion reaction. Figure 2. Molecular structures of the cations of 5 (above) and 6 (below). Table 1. Bond Distances (Å) and Angles (°) for Complexes 5 and 6 5 Ir-P Ir-H(1A) Ir-H(1B) Ir-C(1) Ir-N(3) Ir-N(4) Ir-N(5) P-Ir-C(1) P-Ir-N(3) P-Ir-N(4) C(1)-Ir-N(3) C(1)-Ir-N(4) C(1)-Ir-N(5) N(3)-Ir-N(4) N(3)-Ir-N(5)

1.505(19) 1.57(5) 1.966(6) 2.098(5) 2.126(5) 2.042(5)

99.2(2) 95.7(2) 173.7(2) 86.15(18) 85.87(17)

6 2.3123(17) 1.545(19) 1.486(19) 2.029(6) 2.116(5) 2.117(5) 164.56(15) 95.72(13) 91.16(13) 99.03(19) 94.28(19) 86.40(18)

as already described for the PiPr3 analogous complex.14 The structure of the bis-triisopropylphosphine analogue of 6 is known and, once again, shows close similarities.15 These include the Ir-P distances, barely altered by the replacement of PiPr3 by IMes (2.3251(26) and 2.3263(27) Å vs 2.3123(17) Å). This indicates that, despite their different basicity,5,8d these two ligands are not too different from the viewpoint of structural trans effects. As for 3, the 1H and 13C{1H} NMR spectra of 5-7 indicate four equivalent IMes aromatic CHs, the result of fast Ir-C and N-Mes bond rotations in the NMR time scale. The NHC carbenic carbon, at δ 149.37 in the 13C{1H} NMR spectrum of 5, shifts back to lower field upon coordination of a good donor ligand in trans position, to δ 165.23 and 162.19 in 6 and 7, (15) He, X. D.; Ferna´ndez-Baeza, J.; Chaudret, B.; Folting, K.; Caulton, K. G. Inorg. Chem. 1990, 29, 5000–5002.

In contrast to the behavior of 5, the reactions of the phosphine complex 6 stop at the hydride [IrH(IMes′)(NCMe)2(PiPr3)]PF6 (9), irrespective of the acceptor. The inability of 9 to form insertion products could be tentatively attributed to thermodynamic reasons, since the steric congestion should further destabilize them. Alternative kinetic explanations would point to the importance of the coordination vacancy trans to the IMes carbenic carbon, although, given that the lack of such a vacancy does not impede hydrogenation in complex 6, it seems unlikely that that could hinder insertion in 9. All cyclometalated derivatives in eq 3 revert to their respective precursor, 5 or 6, by reaction with dihydrogen. This indicates that any of these compounds can be used as a catalyst precursor in hydrogenation reactions, at least versus the acceptors of eq 3. Nevertheless, such applications have not yet been investigated in detail. (16) The β-elimination of H from an iridium alkenyl is known, although very unusual: (a) Ghosh, R.; Zhang, X.; Achord, P.; Emge, T. J.; KroghJespersen, K.; Goldman, A. S. J. Am. Chem. Soc. 2007, 129, 853–866.

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There are various precedents for the cyclometalation of NHC ligands at iridium complexes,10e-h,17 while for the IMes ligand such intramolecular C-H activations are known in compounds of Rh, Ru, and Os.18 None of these precedents reports on the observation of different conformers for the resulting metalacycle, a fact that complicates the characterization of some derivatives in eq 3. Because of their six-membered metalacycle, these compounds can adopt two possible conformations, which result in two different orientations of the methylene group relative to the hydride (or the R ligand in the insertion products). This can be visualized with the help of the molecular structures of cations 8-10 in Figure 3 and the included schematic representations of their equatorial planes. Thus, hydride and methylene are mutually syn in the structures of 8 and 9, while the orientation of this latter group relative to ethyl in complex 10 is anti. Each conformation has different steric constraints, as illustrated again by the schematic representations of Figure 3. In the anti structures, the intact mesityl substituent of IMes’ shares a region of space occupied by the two equatorial acetonitriles, while in the syn conformers it is located between one of the acetonitriles and the hydride (or R) ligand. The latter suggests that the relative stability of the syn conformers could depend on the size of R and, in fact, the steric repulsion between R and the mesityl ring seems to govern the adoption of one or another structure in solution. Thus, the 1H nuclear Overhauser effect spectroscopy (NOESY) NMR spectra indicate that hydrides 8 and 9 only exist as syn isomers, whereas 12 is exclusively anti, most probably forced by its bulky alkenyl ligand. In the intermediate cases, the alkyls 10 and 11, both conformers coexist in equilibrium. The rates of interconversion between conformers are of the same order than the NMR time scale, producing broad spectra at room temperature. The exchange can be slow down to produce narrow spectra below 240 K, permitting the identification of each conformer and the evaluation of the equilibrium position (Figure 4). Despite of the anti structure found in the X-ray determination of 10, the syn conformers remain the most stable for the alkyl complexes 10 and 11 (syn:anti approximately 5:2 in both cases). In the same context of steric restrictions, the 13C{1H} APT NMR spectrum of 11 at 233 K indicates that propylene insertion selectively produces n-propyl complexes. Apart from the above-mentioned aspects relative to conformations of the six-membered rings, the structures of 8-10 in Figure 3 display rather regular octahedral structures that do not deserve further comment (Table 2). All Ir-N distances are long and suggest easily replaceable acetonitrile ligands, thus guaranteeing the possible continuation of this chemistry via any of the compounds. The various structures in this work also allow for straight comparisons among structural parameters of Ir-IMes, Ir-IMes′ and Ir-CH2 moieties, showing that distortions associated with the cyclometalation of this NHC ligand to iridium are minimum. As a result, and taking into account that, in many cases, the neighboring ligand environment is likely to restrict (17) (a) Scott, N. M.; Pons, V.; Stevens, E. D.; Heinekey, D. M.; Nolan, S. P. Angew. Chem., Int. Ed. 2005, 44, 2512–2515. (b) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 3516–3526. (18) (a) Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics 2000, 19, 1194–1197. (b) Jazzar, R. F. R.; Macgregor, S. A.; Mahon, M. F.; Richards, S. P.; Whittlesey, M. K. J. Am. Chem. Soc. 2002, 124, 4944– 4945. (c) Abdur-Rashid, K.; Fedorkiw, T.; Lough, A. J.; Morris, R. H. Organometallics 2004, 23, 86–94. (d) Cooke, C. E.; Jennings, M. C.; Pomeroy, R. K.; Clyburne, J. A. C. Organometallics 2007, 26, 6059–6062, See also. (e) Diggle, R. A.; Kennedy, A. A.; Macgregor, S. A.; Whittlesey, M. K. Organometallics 2008, 27, 938–944.

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Figure 3. Molecular structures of the cations of 8 (above), 9 (center), and 10 (below). The schematic representation next to each structure corresponds to the top view, once the ligand trans to the IMes carbenic carbon has been eliminated for clarity.

the mobility of coordinated IMes anyway, this ligand is not expected to oppose a strong thermodynamic resistance to cyclometalation. Terminal alkynes such as phenylacetylene can also work as hydrogen acceptors against dihydrides 5 and 6, although, given that they are good oxidative addition reactants too, their reactions afford products very different from those in eq 3. Unfortunately, the intricate evolution of the more reactive complex 5 in the presence of phenylacetylene has not yet been understood, although its complexity is by itself suggestive of similarities with the triisopropylphosphine analogue of 5, the reactivity of which against 1-alkynes has been found to be particularly rich.19 On the contrary, the reaction of 6 with an excess of phenylacetylene has been observed to selectively produce styrene and the hydride alkynyl complex [IrH(CtCPh)(NCMe)2(IMes)(PiPr3)]PF6 (14). Monitoring of this reaction by NMR using alkyne defect has made possible detection of a hydride alkenyl (19) Navarro, J.; Sa´gi, M.; Sola, E.; Lahoz, F. J.; Dobrinovitch, I. T.; Katho´, E.; Joo´, F.; Oro, L. A. AdV. Synth. Catal. 2003, 345, 280–288.

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intermediate of tentative formula: [IrH(E-CHdCHPh)(NCMe)2(IMes)(PiPr3)]PF6 (13, eq 4). The intermediate just forms in very minor amounts within a mixture of 6 and 14, but its very characteristic NMR signals can be readily identified in the spectra. These include two vinylic signals in the 1H NMR spectrum, at δ 5.95 and 7.79 with a JHH mutual coupling constant of 17.7 Hz, and a hydride resonance at δ -21.14 coupled to phosphorus with a constant of 15.0 Hz. On the other hand, the most characteristic NMR signals of the main reaction product 14 are those due to the alkynyl ligand in the 13C{1H} spectrum: a doublet at δ 77.04 (JCP ) 13.4 Hz) and a singlet at δ 100.85, which correspond to the R and β carbons, respectively.

Complex 14 can also be readily obtained from reaction of the metalated hydride 9 with 1 equiv of the 1-alkyne (eq 4). Notably, the reaction with the deuterium-labeled reactant PhCtCD selectively affords the isotopomer of 14 deuterated at the hydride position, 14-d, which does not undergo subsequent processes of deuterium redistribution to other parts of the molecule. The lack of H/D scrambling during and after the formation of 14-d suggests that hydride and deuteride never come together at the metal center, thus discarding both Ir(V) reaction intermediates and C-H activations via σ-bond metathesis. Therefore, the experiment supports the only remaining mechanistic alternative: the intermediacy of Ir(I) species, formed via C-H reductive elimination, that cleave C-H bonds by oxidative addition. This latter experiment indicates that, even though we have not been able to observe them, IMes iridium(I) cationic species are accessible from the more stable Ir(III) cyclometalated hydrides. This contributes to further broaden the scope of possible synthetic and catalytic uses within the reach of these labile NHC complexes, which has only been very briefly presented along this work.

Experimental Section Equipment. C, H, N, and S analyses were carried out in a PerkinElmer 2400 CHNS/O analyzer. Matrix-assisted laser desorption/ ionization time of flight mass spectra (MALDI-TOF MS) were obtained in a Bruker Microflex mass spectrometer using 1,1dicyano-4-terbuthylphenyl-3-methylbutadiene (DCTB) as the matrix. Infrared spectra were recorded in KBr using a FT-IR PerkinElmer Spectrum One spectrometer. NMR spectra were recorded

Figure 4. Region of the 1H NOESY NMR spectrum of 10 at 233 K. The NOE part (positive, above) and the exchange part + diagonal (negative, below) have been separated for clarity. NOE signals corresponding to the major conformer (syn) and spin saturation transfer peaks evidencing the syn to anti exchange are highlighted. on Bruker Avance 400 or 300 MHz spectrometers. 1H (400.13 or 300.13 MHz) and 13C (100.6 or 75.5 MHz) NMR chemical shifts were measured relative to partially deuterated solvent peaks, but are reported in ppm relative to tetramethylsilane. 31P (162.0 or 121.5 MHz) chemical shifts were measured relative to H3PO4 (85%). Coupling constants, J, are given in hertz. In general, NMR spectral assignments were achieved through 1H COSY, 1H NOESY, 13C APT and 1H/13C-HSQC experiments. Synthesis. All manipulations were carried out under argon by standard Schlenk techniques. Solvents were obtained from an Innovative Technology Solvent Purification System. Deuterated solvents were carefully dried by known procedures and stored under argon prior to use. The starting complex [Ir(µ-OMe)(COD)]2,20 and the imidazolium salt IMes · HCl21 were prepared following reported methods. All commercial reagents were used as received without further purification. Preparation of [IrCl(COD)(IMes)] (1). A suspension of [Ir(µ-OMe)(COD)]2 (529 mg, 0.80 mmol) in acetone (20 mL) was (20) Uso´n, R.; Oro, L. A.; Cabeza, J. Inorg. Synth. 1985, 23, 126–130. (21) Arduengo, A. J., III. U.S. Patent 5077414, 1991.

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Table 2. Bond Distances (Å) and angles (o) for the Complexes 8-10 8 Ir-P Ir-H(1) Ir-C(1) Ir-C(12) Ir-C(28) Ir-N(3) Ir-N(4) Ir-N(5) P-Ir-C(1) P-Ir-C(12) P-Ir-N(3) P-Ir-N(4) C(1)-Ir-C(12) C(1)-Ir-C(28) C(1)-Ir-N(3) C(1)-Ir-N(4) C(1)-Ir-N(5) C(12)-Ir-C(28) C(12)-Ir-N(3)

1.37(5) 1.925(6) 2.077(5) 2.135(5) 2.069(5) 2.043(5)

81.9(2) 94.00(19) 98.29(19) 173.8(2)

9 2.3367(17) 1.521(19) 1.973(7) 2.087(6) 2.100(5) 2.068(5) 166.96(18) 95.16(17) 100.95(14) 90.52(15) 79.8(2) 91.3(2) 95.5(2)

10

1.986(5) 2.097(5) 2.098(5) 2.127(5) 2.106(5) 2.072(4)

82.69(19) 92.91(18) 91.95(17) 99.13(17) 171.90(18) 92.8(2) 86.2(2)

treated with IMes · HCl (544 mg, 1.60 mmol) and stirred at room temperature (RT) for 30 min. The resulting solution was concentrated to ca. 2 mL, and the orange solid formed was separated by decantation. The solid was washed two times with methanol (2 mL portions) and dried in vacuo. The complex was further purified by column chromatography, using SiO2 and dichloromethane:acetone (8:1) as eluent. Yield: 875 mg (86%). 1H NMR (CDCl3, 293 K) δ 1.25, 1.62 (both m, 4H each, CH2), 2.10 (s, 6H, CH3), 2.29 (s, 12H, CH3), 2.91, 4.09 (both m, 2H each, CH), 6.97 (s, 2H, CH), 7.00, 7.02 (both s, 2H each, CH). 13C{1H} NMR (CDCl3, 293 K) δ (all s) 18.07, 19.51, 20.97 (CH3), 28.78, 33.35 (CH2), 51.30, 82.37, 123.16, 128.00, 129.37 (CH), 134.29, 135.95, 137.19, 138.49, 180.65 (C). Anal. Calcd for C29H36ClIrN2: C, 54.40; H, 5.67; N, 4.38. Found: C, 54.31; H, 5.88; N, 4.11. MS: 640 [M+], 605 [M+Cl]. Preparation of [Ir(COD){OC(CH3)2}(IMes)]PF6 (2). A solution of 1 (592 mg, 0.93 mmol) in acetone (10 mL) was treated with 1 equiv of AgPF6 (235 mg, 0.93 mmol) and stirred for 30 min in the dark at RT. The resulting suspension was filtered through Celite and concentrated to ca. 0.5 mL. Addition of diethyl ether produced an orange solid, which was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 649 mg (86%). IR (cm-1): 1650 ν(CdO). 1H NMR (CD2Cl2, 253 K) δ 1.42, 1.77 (both m, 4H each, CH2), 2.17 (s, 12H, CH3), 2.22 (br, 6H, CH3), 2.44 (s, 6H, CH3), 3.41, 3.72 (both m, 2H each, CH), 7.15 (s, 2H, CH), 7.16 (br, 4H, CH). 13C{1H} NMR (CD2Cl2, 253 K) δ (all s) 18.14, 20.91 (CH3), 27.89 (CH2), 32.85 (COCH3), 33.22 (CH2), 55.07, 83.11, 124.68, 129.53 (CH), 135.09, 135.17, 140.00, 173.72 (C), 207.47 (COCH3). Anal. Calcd for C32H42N2F6IrOP: C, 47.58; H, 5.24; N, 3.47. Found: C, 47.89; H, 5.30; N, 3.37. MS: 605 [M+OC3H6]. Preparation of [IrH2(η6-C6H6)(IMes)]PF6 (3). A solution of 2 (358 mg, 0.44 mmol) in acetone (10 mL) was treated with benzene (0.5 mL) and stirred under dihydrogen atmosphere (1 bar) for 10 min. The resulting pale yellow solution was filtered through Celite and concentrated to ca. 0.5 mL. Addition of diethyl ether produced a white solid, which was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 194 mg (61%). IR (cm-1): 2240, 2213 ν(Ir-H). 1H NMR (CD2Cl2, 293 K) δ (all s) -15.78 (2H, IrH), 2.03 (12H, CH3), 2.45 (6H, CH3), 5.93 (6H, C6H6), 7.12 (2H, CH), 7.16 (4H, CH). 13C{1H} NMR (CD2Cl2, 293 K) δ (all s) 18.06, 21.09 (CH3), 96.36 (C6H6), 122.91, 129.89 (CH), 135.51, 136.72, 140.81, 144.95 (C). Anal. Calcd for C27H32N2F6IrP: C, 44.93; H, 4.47; N, 3.88. Found: C, 44.64; H, 4.44; N, 3.90. MS: 577 [M+]. [IrH2{OC(CD3)2}3(IMes)]PF6 (4). The NMR spectra recorded from solutions of 3 (13.1 mg, 0.018 mmol) in acetone-d6 (0.5 mL) at 293 K indicated that part of the precursor complex was

transformed into the new compound 4, which, under these conditions, was the major species. Data for 4: 1H NMR (acetone-d6, 293 K): (all s) -30.45 (2H, IrH), 2.12 (12H, CH3), 2.36 (6H, CH3), 7.06 (4H, CH), 7.19 (2H, CH). 13C{1H} NMR (acetone-d6, 293 K) δ (all s) 18.04, 21.00 (CH3), 123.16, 129.10 (CH), 137.16, 137.87, 139.49, 141.37 (C). Preparation of [IrH2(NCMe)3(IMes)]PF6 (5). A solution of 2 (453 mg, 0.56 mmol) in acetone (10 mL) was reacted with acetonitrile (ca. 0.5 mL) and stirred under dihydrogen atmosphere (P ) 1 bar) for 30 min. The resulting pale yellow solution was filtered through Celite, concentrated to ca. 0.5 mL, and treated with diethyl ether to afford a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 290 mg (68%). IR (cm-1): 2256, 2163 ν(Ir-H). 1H NMR (CDCl3, 293 K) δ (all s) -22.48 (2H, IrH), 2.08 (12H, CH3), 2.11 (br, 6H, NCCH3), 2.25 (3H, NCCH3), 2.37 (6H, CH3), 6.87 (2H, CH), 7.01 (4H, CH). 13C{1H} NMR (CDCl3, 293 K) δ (all s) 2.83, 3.39 (NCCH3), 17.93, 21.12 (CH3), 117.04, 118.32 (NCCH3), 121.88, 128.84 (CH), 135.85, 137.44, 138.76, 149.37 (C). Anal. Calcd for C27H35N5F6IrP: C, 42.29; H, 4.60; N, 9.14. Found: C, 42.02; H, 4.90; N, 8.98. MS: 538 [M+-2 NCMe]. Preparation of [IrH2(NCMe)2(IMes)(PiPr3)]PF6 (6). A solution of 5 (145 mg, 0.19 mmol) in CH2Cl2 (8 mL) was treated with triisopropylphosphine (0.19 mmol, 38 µL) and allowed to react at RT for 10 min. The resulting solution was concentrated to ca. 0.5 mL and treated with diethyl ether to afford a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 120 mg (72%). IR (cm-1): 2181 ν(Ir-H). 1H NMR (CDCl3, 293 K) δ -22.42 (d, JHP ) 17.5, 2H, IrH), 0.91 (dd, JHP ) 13.0, JHH ) 7.0, 18H, PCHCH3), 1.89 (m, 3H, PCHCH3), 2.10 (s, 12H, CH3), 2.12 (s, 6H, NCCH3), 2.35 (s, 6H, CH3), 6.99 (s, 2H, CH), 7.00 (s, 4H, CH). 31P{1H} NMR (CDCl3, 293 K) δ 27.32 (s), -145.33 (m, JPF ) 715.6, PF6). 13C{1H} NMR (CDCl3, 293 K) δ 3.19 (s, NCCH3), 17.90 (s, CH3), 19.21 (s, PCHCH3), 21.05 (s, CH3), 23.99 (d, JCP ) 26.4, PCHCH3), 118.68 (s, NCCH3), 122.14, 128.65 (both s, CH), 135.90, 137.72, 138.65 (all s, C), 165.23 (d, JCP ) 108.2, C). Anal. Calcd for C34H53N4F6IrP2: C, 46.09; H, 6.03; N, 6.33. Found: C, 46.57; H, 6.15; N, 6.17. MS: 657 [M+-2NCMe-2H]. Preparation of [IrH2(NCMe)2(IMes)(TPPTS)]BF4 (7). The starting complex used in this synthesis was an analogue of 5 with BF4- as anion, prepared as described for 5 but using AgBF4 instead of AgPF6. A solution of this analogue of 5 (373 mg, 0.55 mmol) in acetone (8 mL) was treated with 2 mL of an aqueous solution of P(m-C6H4SO3Na)3 (TPPTS, 310 mg, 0.55 mmol), and the resulting mixture was allowed to react at RT for 10 min. The resulting solution was concentrated to ca. 0.5 mL and treated with diethyl ether to afford a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 512 mg (75%). IR (cm-1): 2226, 2182 ν(Ir-H). 1H NMR (D2O, 293 K) δ -21.63 (d, JHP ) 16.5, 2H, IrH), 1.49 (s, 6H, NCCH3), 1.82 (s, 12H, CH3), 1.97 (s, 6H, CH3), 6.66 (s, 2H, CH), 6.72 (s, 4H, CH), 7.11, 7.62 (both m, 6H each, CH). 31P{1H} NMR (D2O, 293 K) δ 19.79 (s). 13C{1H} NMR (D2O, 293 K) δ 1.60 (s, NCCH3), 17.53, 20.44 (both s, CH3), 119.03 (s, NCCH3), 122.73, 127.68, 128.78 (all s, CH), 129.01 (d, JCP ) 10.0, CH), 129.97 (d, JCP ) 11.1, CH), 133.04 (d, JCP ) 48.9, C), 135.73 (s, C), 136.31 (d, JCP ) 12.3, CH), 137.19, 139.49 (both s, C), 143.50 (d, JCP ) 9.5, C), 162.19 (d, JCP ) 117.4, C). Anal. Calcd for C43H44N4BF4IrNa3O9PS3: C, 41.78; H, 3.59; N, 4.53; S, 7.78. Found: C, 41.26; H, 3.90; N, 4.46; S, 7.46. Preparation of [IrH(IMes′)(NCMe)3]PF6 (8). Propylene was slowly bubbled through a solution of 5 (194 mg, 0.25 mmol) in CH2Cl2 (15 mL) for 5 min. The resulting solution was concentrated to ca. 0.5 mL, and diethyl ether was added to give a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 136 mg (70%). 1H (CD2Cl2, 253 K) RMN

N-Heterocyclic Carbene Iridium Complexes δ -22.75 (s, 1H, IrH), 1.78 (s, 3H, NCCH3), 2.00 (d, JHH ) 11.4, 1H, IrCH2), 2.05 (s, 3H, CH3), 2.06 (s, 3H, NCCH3), 2.13, 2.31 (both s, 3H each, CH3), 2.38 (s, 6H, CH3), 2.42 (s, 3H, NCCH3), 3.17 (d, JHH ) 11.4, 1H, IrCH2), 6.85 (s, 1H, CH) 6.94 (d, JHH ) 2.0, 1H, CH), 6.98 (s, 2H, CH), 7.09 (s, 1H, CH), 7.49 (d, JHH ) 2.0, 1H, CH). 13C{1H} RMN (CD2Cl2, 253 K) δ (all s) -12.48 (IrCH2), 1.86, 3.18, 3.59 (NCCH3), 17.50, 17.72, 19.58, 20.58, 20.93 (CH3), 116.17, 116.55, 117.67 (NCCH3), 120.64, 121.32, 125.66, 127.64 (CH), 129.05 (C), 129.32 (CH), 135.73, 135.84, 135.97, 136.04, 136.43, 139.15, 147.33, 152.34 (C). Anal. Calcd for C27H33N5F6IrP: C, 42.40; H, 4.35; N, 9.16. Found: C, 42.51; H, 4.54; N, 9.08. MS: 748 [M+-3NCMe+DCTB]. Preparation of [IrH(IMes′)(NCMe)2(PiPr3)]PF6 (9). Ethylene was slowly bubbled through a solution of 6 (204 mg, 0.23 mmol) in CH2Cl2 (15 mL) during 30 min. The resulting solution was taken to dryness, and the residue was treated with diethyl ether to give a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 167 mg (82%). 1H RMN (CDCl3, 293 K) δ -22.46 (d, JHP ) 18.6, 1H, IrH), 1.09, 1.13 (both dd, JHP ) 10.9, JHH ) 7.2, 9H, PCHCH3), 1.61 (dd, JHH ) 11.3, JHP ) 10.9, 1H, IrCH2), 1.84, 2.08 (both s, 3H each, NCCH3), 2.13, 2.19 (both s, 3H each, CH3), 2.23 (m, 3H, PCHCH3), 2.28, 2.34, 2.42 (all s, 3H each, CH3), 2.80 (d, JHH ) 11.3, 1H, IrCH2), 6.81, 6.82, 6.96 (all br, 1H each, CH), 6.98 (d, JHH ) 1.6, 1H, CH), 7.00 (br, 1H, CH), 7.49 (d, JHH ) 1.6, 1H, CH). 31P{1H} RMN (CDCl3, 293 K) δ 15.44 (s), -145.33 (m, JPF ) 715.6, PF6). 13 C{1H} RMN (CDCl3, 293 K) δ -14.60 (d, JCP ) 4.9, IrCH2), 1.80, 3.12 (both s, NCCH3), 17.68, 17.79 (both s, CH3), 18.37 (s, PCHCH3), 19.37, 20.81, 21.01 (all s, CH3), 22.88 (d, JCP ) 24.9, PCHCH3), 117.75, 118.78 (both s, NCCH3), 120.56, 122.00 (both d, JCP ) 3.3, CH), 125.74, 127.36, 127.85, 129.04 (all s, CH), 134.15, 135.72, 135.79, 136.00, 136.08, 136.49, 138.94, 148.07 (all s, C), 166.69 (d, JCP ) 114.0, C). Anal. Calcd for C34H51N4F6IrP2: C, 46.19; H, 5.81; N, 6.34. Found: C, 45.91; H, 5.99; N, 6.27. Preparation of [Ir(Et)(IMes′)(NCMe)3]PF6 (10). A solution of 5 (230 mg, 0.30 mmol) in CH2Cl2 (5 mL) was stirred under ethylene atmosphere (1 bar) for 30 min. The resulting solution was concentrated to ca. 0.5 mL, and diethyl ether was added to give a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 206 mg (87%). Anal. Calcd for C29H37N5F6IrP: C, 43.93; H, 4.70; N, 8.84. Found: C, 43.75; H, 5.10; N, 8.37. MS: 538.1 [M+-2NCMe-C2H4]. The NMR spectra of the compound at RT were broad, but at 233 K showed the presence of two compounds in relative proportion 5:2. Data for 10-syn: 1H RMN (CD2Cl2, 233 K) δ 0.42 (t, JHH ) 7.3, 3H, IrCH2CH3), 0.86, 1.21 (both m, 1H each, IrCH2CH3), 1.72 (s, 3H, NCCH3), 1.85 (s, 3H, CH3), 2.02 (s, 3H, NCCH3), 2.08 (d, JHH ) 11.2, 1H, IrCH2), 2.28 (s, 6H, CH3), 2.32, 2.34 (both s, 3H each, CH3), 2.43 (s, 3H, NCCH3), 2.48 (d, JHH ) 11.2, 1H, IrCH2), 6.82 (s, 1H, CH), 6.85 (d, JHH ) 2.0, 1H, CH), 6.90, 6.96, 7.05 (all s, 1H each, CH), 7.48 (d, JHH ) 2.0, 1H, CH). 13C{1H} RMN (CD2Cl2, 233 K) δ (all s) -12.35 (IrCH2CH3), -0.75 (IrCH2), 2.09, 3.73, 3.96 (NCCH3), 17.02 (IrCH2CH3), 18.08, 18.16, 20.18, 20.73, 21.03 (CH3), 115.34, 115.75, 115.77 (NCCH3), 121.02, 122.35, 125.31, 127.51, 127.64, 129.30 (CH), 128.70, 135.40, 136.08, 137.96, 138.72, 147.14, 155.21 (C). Data for 10-anti: 1H RMN (CD2Cl2, 233 K) δ 0.52 (m, 1H, IrCH2CH3), 0.54 (t, JHH ) 7.1, 3H, IrCH2CH3), 0.74 (both m, 1H each, IrCH2CH3), 1.97 (s, 3H, CH3), 2.02 (s, 3H, NCCH3), 2.03, 2.17 (both s, 3H each, CH3), 2.20 (d, JHH ) 11.4, 1H, IrCH2), 2.27 (s, 3H, NCCH3), 2.34, 2.37 (both s, 3H each, CH3), 2.45 (s, 3H, NCCH3), 3.30 (d, JHH ) 11.4, 1H, IrCH2), 6.85 (d, JHH ) 2.0, 1H, CH), 6.85, 6.93, 6.96, 7.06 (all s, 1H each, CH), 7.52 (d, JHH ) 2.0, 1H, CH). 13C{1H} RMN (CD2Cl2, 233 K) δ (all s) -14.61 (IrCH2CH3), -5.65 (IrCH2), 2.09, 3.73, 3.95 (NCCH3), 17.81 (IrCH2CH3), 17.94, 18.07, 18.15, 18.49, 20.80 (CH3), 114.96, 115.58, 115.59 (NCCH3), 121.40, 121.57, 126.93,

Organometallics, Vol. 28, No. 3, 2009 869 127.79, 128.04 (CH), 128.17 (C), 128.64 (CH), 135.13, 135.29, 135.47, 135.57, 137.73, 139.22, 144.72, 152.21 (C). [Ir(nPr)(IMes′)(NCMe)3]PF6 (11). Propylene was slowly bubbled for 2 min through a solution of 5 (25 mg, 0.30 mmol) in CD2Cl2 (0.5 mL) contained in a NMR tube. The tube was sealed and allowed to react in the presence of propylene for 30 additional minutes. The NMR spectra at 233 K showed the presence of two compounds in relative proportion 5:2. Data for 11-syn: 1H RMN (CD2Cl2, 233 K) δ 0.65 (m, 1H, IrCH2CH2CH3), 0.77 (m, 5H, IrCH2CH2CH3, IrCH2CH2CH3 y IrCH2CH2CH3), 1.22 (m, 1H, IrCH2CH2CH3), 1.71 (s, 3H, NCCH3), 1.87 (s, 3H, CH3), 2.05, (s, 3H, NCCH3), 2.07 (d, JHH ) 11.4, 1H, IrCH2), 2.29 (s, 6H, CH3), 2.33, 2.35 (both s, 3H each, CH3), 2.43 (s, 3H, NCCH3), 2.49 (d, JHH ) 11.4, 1H, IrCH2), 6.82 (s, 1H, CH), 6.85 (d, JHH ) 2.2, 1H, CH), 6.90, 6.96, 7.05 (all s, 1H each, CH), 7.48 (d, JHH ) 2.2, 1H, CH). 13C{1H} RMN (CD2Cl2, 233 K) δ (all s) -1.27 (IrCH2CH2CH3), -081 (IrCH2), 2.30, 4.02, 4.28 (NCCH3), 17.75 (IrCH2CH2CH3), 18.29, 18.56, 20.33, 20.81, 21.13 (CH3), 25.83 (IrCH2CH2CH3), 115.36, 115.70, 115.92 (NCCH3), 121.01, 122.31, 125.32, 127.42, 127.60 (CH), 128.75 (C), 129.18 (CH), 135.07, 135.43, 135.56, 136.05, 137.85, 138.73, 147.16, 154.91 (C). Data for 11-anti: 1H RMN (CD2Cl2, 233 K) δ 0.41 (t, JHH ) 6.8, 3H, IrCH2CH2CH3), 0.45, 0.65 (both m, 1H each, IrCH2CH2CH3), 1.49 (m, 1H, IrCH2CH2CH3), 1.99 (s, 3H, CH3), 2.01 (m, 1H, IrCH2CH2CH3), 2.03, 2.05 (both s, 3H each, NCCH3), 2.15 (s, 6H, CH3), 2.18 (d, JHH ) 11.6, 1H, IrCH2), 2.26 (s, 3H, NCCH3), 2.28, 2.37 (both s, 3H each, CH3), 3.28 (d, JHH ) 11.6, 1H, IrCH2), 6.85 (br, 2H, CH), 6.93, 6.96, 7.05 (all s, 1H each, CH), 7.51 (d, JHH ) 2.0, 1H, CH). 13C{1H} RMN (CD2Cl2, 233 K) δ (all s) -5.69 (IrCH2), -2.98 (IrCH2CH2CH3), 2.63, 4.02, 4.11 (NCCH3), 17.64 (IrCH2CH2CH3), 18.20, 18.65, 20.58, 20.90, 21.17 (CH3), 26.81 (IrCH2CH2CH3), 114.96, 115.65, 115.98 (NCCH3), 121.38, 121.56, 126.78, 127.71, 127.94 (CH), 128.32 (s, C), 128.50 (CH), 135.17, 135.31, 135.34, 135.71, 137.65, 139.31, 145.04, 152.06 (C). Preparation of [Ir{Z-C(Ph))CHPh}(IMes′)(NCMe)3]PF6 (12). A solution of 5 (146 mg, 0.19 mmol) in CH2Cl2 (8 mL) was treated with diphenylacetylene (86.7 mg, 0.48 mmol) and stirred at RT for 14 h. The resulting solution was concentrated to ca. 0.5 mL, and diethyl ether was added to afford a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 85 mg (47%). 1H RMN (CD2Cl2, 293 K) δ 1.96, 2.12 (both s, 3H each, CH3), 2.14 (s, 3H, NCCH3), 2.25, 2.31 (both br, 3H each, NCCH3), 2.32, 2.35, 2.42 (all s, 3H each, CH3), 2.70, 3.37 (both d, 1H each, JHH ) 11.8, IrCH2), 5.74 (s, 1H, IrC(Ph)dCHPh), 6.35 (d, 2H, JHH ) 7.2, CH), 6.54 (br, 2H, CH), 6.79 (m, 1H, CH), 6.81 (br, 1H, CH), 6.86 (m, 2H, CH), 6.93 (d, 1H, JHH ) 2.0, CH), 6.98 (br, 1H, CH), 7.00 (m, 1H, CH), 7.03 (br, 1H, CH), 7.09 (m, 2H, CH), 7.16 (br, 1H, CH), 7.63 (d, 1H, JHH ) 2.0, CH). 13C{1H} RMN (CD2Cl2, 293 K) δ (all s) -3.31 (IrCH2), 2.45 (NCCH3), 2.91 (br, NCCH3), 18.21, 18.39, 20.35, 20.38, 20.74 (CH3), 115.88 (NCCH3), 121.74, 122.36, 123.82, 124.13, 127.07, 127.25, 127.70, 128.13 (CH), 128.45 (C), 128.57, 128.65, 128.98 (CH), 132.86 (C), 133.71 (IrC(Ph))CHPh), 135.33, 136.09, 136.17, 136.32, 137.34, 139.67, 140.86, 144.54, 149.60, 152.74 (C). Anal. Calcd for C41H43N5F6IrP: C, 52.22; H, 4.60; N, 7.43. Found: C, 52.15; H, 4.79; N 7.50. MS: 675 [M+-3NCMe]. Preparation of [IrH(CtCPh)(NCMe)2(IMes)(PiPr3)]PF6 (14). Method A: A solution of 6 (179 mg, 0.20 mmol) in CH2Cl2 (8 mL) was treated with phenylacetylene (45 µL, 0.40 mmol) and stirred at RT for 20 min. The resulting solution was concentrated to ca. 0.5 mL, and diethyl ether was added to afford a white solid. The solid was separated by decantation, washed with diethyl ether, and dried in vacuo: yield 126 mg (63%). Method B: The same procedure described above but starting from 8 (188 mg, 0.21mmol) and phenylacetylene (24 µL, 0.21 mmol): yield 140 mg (67%). IR (cm-1): 2115 ν(Ir-H), 2118 ν(CtC). 1H RMN (CD2Cl2, 293 K) δ -21.46 (d, JHP ) 15.6, 1H, IrH), 1.04 (dd, JHP ) 13.4, JHH ) 7.2,

870 Organometallics, Vol. 28, No. 3, 2009

Torres et al.

9H, PCHCH3), 1.08 (dd, JHP ) 13.2, JHH ) 7.3, 9H, PCHCH3), 1.91 (br, 3H, NCCH3), 2.27 (s, 12H, CH3), 2.38 (s, 6H, CH3), 2.41 (s, 3H, NCCH3), 2.42 (m, 3H, PCHCH3), 6.99 (d, JHH ) 7.1, 2H, CH), 7.05 (s, 2H, CH), 7.06 (m, 1H, CH), 7.08 (s, 2H, CH), 7.14 (m, 2H, CH), 7.17 (s, 2H, CH). 31P{1H} RMN (CD2Cl2, 293 K) δ 8.17 (s), -144.36 (m, JPF ) 710.7, PF6). 13C{1H} RMN (CD2Cl2, 263 K) δ 3.30, 3.59 (both s, NCCH3), 17.91 (s, CH3), 18.12, 18.21 (both s, PCHCH3), 20.89 (s, CH3), 23.23 (d, JCP ) 26.8, PCHCH3), 77.04 (d, JCP ) 13.4, IrC′C), 100.85 (s, IrC′C), 118.62, 118.98 (both s, NCCH3), 123.45, 123.49 (both s, CH), 124.31, 127.83, 128.78, 129.03 (all s, CH), 129.40, 129.42 (both s, C), 130.58, 130.59 (both s, CH), 136.35, 139.03 (both s, C), 159.07 (d, JCP ) 115.5, C). Anal. Calcd for C42H57N4F6IrP2: C, 51.15; H, 5.83; N, 5.68. Found: C, 51.60; H, 5.36; N, 5.26. MS: 760 [M+-2NCMe]. [IrH(E-CHdCHPh)(NCMe)2(IMes)(PiPr3)]PF6 (13). The reaction leading to 14 via method A was carried out in a NMR tube, in CD2Cl2 (0.5 mL) as solvent, and using only 1 equiv of phenylacetylene per Ir. After ca. 30 min of reaction, the NMR spectra of the reaction showed a mixture of compounds 5 and 14, together with a new minor product 13. Partial data for 13: 1H RMN (CDCl3, 293 K) δ -21.14 (d, JHP ) 15.0, IrH), 5.95 (d, JHH ) 17.7, IrCH)CHPh), 7.79 (d, JHH ) 17.7, IrCH ) CHPh). 31P{1H} RMN (CDCl3, 293 K) δ 6.51 (s), -144.36 (m, JPF ) 710.7, PF6). Structural Analysis of Complexes 3, 5, 6, 8, 9, and 10. X-ray data were collected for all complexes at low temperature on a Bruker SMART APEX CCD diffractometer equipped with a normal focus 2.4 kW sealed tube source (molybdenum radiation, λ ) 0.71073 Å), operating at 50 kV and 30 (3 and 6) or 40 (5, 8, 9 and 10) mA. Data were collected over the complete sphere by a combination of four sets (5, 6, 8, 9, and 10) or three sets (3). Each frame exposure time was 10 (5, 6 and 9), 20 (3 and 8), or 30 (10) s covering 0.3° in ω. Data were corrected for absorption by using a multiscan method applied with the SADABS program.22 The structures were solved by Patterson method and refined by fullmatrix least-squares on F2 using the Bruker SHELXTL program package,23 including isotropic and subsequently anisotropic displacement parameters. Weighted R factors (Rw) and goodness of fit (S) are based on F2, and conventional R factors are based on F. Hydride ligands were located, although most of them did not refine appropriately. In such cases (3, 5, 6, and 9), some restrains were applied to thermal parameters, and the Ir-H distance was fixed to 1.59(1) Å (average value found in the Cambridge Structural Database). The other hydrogen atoms were calculated using a restricted riding model on their respective carbon atoms with the thermal parameter related to the bonded atom. All the highest electronic residuals were observed in close proximity of the Ir centers and make no chemical sense. Crystal Data for 3. C27H32F6IrN2P, M ) 721.73; colorless prism, crystal size 0.22 × 0.06 × 0.06 mm3; monoclinic, P21/c; a ) 16.0740(10) Å, b ) 10.9790(6) Å, c ) 16.1079(10) Å, β ) 111.0650(10); Z ) 4; V ) 2652.7(3) Å3; Dc ) 1.807 g/cm3; µ ) 5.155 mm-1, minimum and maximum transmission factors 0.534 and 0.734; 2θmax ) 57.88; temperature 100.0(2) K; 23428 reflections collected, 6534 unique [R(int) ) 0.0483]; number of data/restraints/ parameters 6534/3/352; final GoF 0.843, R1 ) 0.0326 [4875 reflections I > 2σ(I)], wR2 ) 0.0530 for all data; largest difference peak and hole 1.533, -1.440 eÅ-3.

Crystal Data for 5. C27H35F6IrN5P · 0.88CH2Cl2, M ) 841.52; colorless prism, crystal size, 0.36 × 0.06 × 0.02 mm3; triclinic, P-1; a ) 8.3869(6) Å, b ) 13.1155(10) Å, c ) 15.6637(12) Å, R ) 98.8920(10), β ) 100.7010(10), γ ) 97.5110(10); Z ) 2; V ) 1650.0(2) Å3; Dc ) 1.694 g/cm3; µ ) 4.297 mm-1, minimum and maximum transmission factors 0.714 y 0.918; 2θmax ) 57.8; temperature 100.0(2) K; 20703 reflections collected, 7905 unique [R(int) ) 0.0583]; number of data/restraints/parameters 7905/7/ 412; final GoF 0.863, R1 ) 0.0782 [6053 reflections I > 2σ(I)], wR2 ) 0.0811 for all data; largest difference peak and hole 2.272, -1.120 eÅ-3. Crystal Data for 6. C34H53F6IrN4P2 · CH2Cl2, M ) 970.89; colorless irregular block, crystal size 0.11 × 0.06 × 0.06 mm3; triclinic, P-1; a ) 8.4651(13) Å, b ) 13.452(2) Å, c ) 18.884(3) Å, R ) 86.411(3), β ) 80.230(3), γ ) 81.115(3); Z ) 2; V ) 2092.3(5) Å3; Dc ) 1.541 g/cm3; µ ) 3.451 mm-1, minimum and maximum transmission factors 0.7027 y 0.8197; 2θmax ) 57.92; temperature 173.0(2) K; 26600 reflections collected, 10117 unique [R(int) ) 0.0613]; number of data/restraints/parameters 10117/6/ 492; final GoF 0.809, R1 ) 0.0497 [6622 reflections I > 2σ(I)], wR2 ) 0.0876 for all data; largest difference peak and hole 1.827, -0.878 eÅ-3. Crystal Data for 8. C27H33F6IrN5P · 2CH2Cl2, M ) 934.62; colorless irregular block, crystal size, 0.10 × 0.08 × 0.06 mm3; triclinic, P-1; a ) 8.1151(6) Å, b ) 12.2121(9) Å, c ) 18.4128(14) Å, R ) 93.213(2), β ) 92.829(2), γ ) 91.661(2); Z ) 2; V ) 1818.7(2) Å3; Dc ) 1.707 g/cm3; µ ) 4.067 mm-1, minimum and maximum transmission factors 0.652 y 0.787; 2θmax ) 58; temperature 105.0(2) K; 21902 reflections collected, 8707 unique [R(int) ) 0.0587]; number of data/restraints/parameters 8707/0/426; final GoF 0.760, R1 ) 0.0420 [6234 reflections I > 2σ(I)], wR2 ) 0.0701 for all data; largest difference peak and hole 1.484, -1.087 eÅ-3. Crystal Data for 9. C34H51F6IrN4P2, M ) 883.95; colorless irregular block, crystal size, 0.08 × 0.04 × 0.04 mm3; triclinic, P-1; a ) 10.1040(9) Å, b ) 12.7983(11) Å, c ) 15.5380(13) Å, R ) 87.028(2), β ) 74.630(2), γ ) 72.895(2); Z ) 2; V ) 1851.0(3) Å3; Dc ) 1.586 g/cm3; µ ) 3.753 mm-1, minimum and maximum transmission factors 0.7534 y 0.8644; 2θmax ) 57.84; temperature 105.0(2) K; 22434 reflections collected, 8866 unique [R(int) ) 0.0823]; number of data/restraints/parameters 8866/1/439; final GoF 0.699, R1 ) 0.0494 [5896 reflections I > 2σ(I)], wR2 ) 0.0800 for all data; largest difference peak and hole 1.142, -1.108 eÅ-3. Crystal Data for 10. C29H37F6IrN5P, M ) 792.81; colorless irregular block, crystal size, 0.12 × 0.06 × 0.04 mm3; orthorrombic, Pbca; a ) 11.6306(10) Å, b ) 20.3394(18) Å, c ) 26.673(2) Å; Z ) 8; V ) 6309.8(9) Å3; Dc ) 1.669 g/cm3; µ ) 4.345 mm-1, minimum and maximum transmission factors 0.643 y 0.840; 2θmax ) 58.08; temperature 100.0(2) K; 75128 reflections collected, 8063 unique [R(int) ) 0.0843]; number of data/restraints/parameters 8063/2/396; final GoF 0.803, R1 ) 0.0361 [4140 reflections I > 2σ(I)], wR2 ) 0.0748 for all data; largest difference peak and hole 1.714, -0.800 eÅ-3.

(22) Blessing, R. H. Acta Crystallogr. 1995, A51, 33–38. (a) SADABS: Siemens Area-Detector Absorption Correction; Bruker-AXS: Madison, WI, 1996. (23) SHELXTL Package, v. 6.10; Bruker-AXS: Madison, WI, 2000. (a) Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of Go¨ttingen: Go¨ttingen, Germany, 1997.

Supporting Information Available: X-ray crystallographic file for the complexes 3, 5, 6, 8, 9, and 10 in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgment. This work was supported by the Spanish MEC/FEDER (Grant CTQ2006-01629/BQU and Consolider Ingenio 2010, Grant INTECAT CSD2006-0003).

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