Organometallics 2009, 28, 6639–6641 DOI: 10.1021/om9008873
6639
Iridium-Molybdenum Carbido Complex via C-Se Activation of a Selenocarbonyl Ligand: (μ-Se2)[Ir2{CtMo(CO)2(Tp*)}2(CO)2(PPh3)2] (Tp* = hydrotris(dimethylpyrazolyl)borate) Ian A. Cade, Anthony F. Hill,* and Caitlin M. A. McQueen Research School of Chemistry, Institute of Advanced Studies, The Australian National University, Canberra, ACT 0200, Australia Received October 12, 2009 Summary: The reaction of [Et4N][Mo(CSe)(CO)2(Tp*)}] (Tp* = hydrotris(dimethylpyrazolyl)borate) with [Ir(NCMe) (CO)(PPh3)2]BF4 results not in the anticipated isoselenocarbonyl complex [(Tp*)(CO)2Mo-CSe-Ir(CO)(PPh3)2] but rather in the tetranuclear bis(μ-carbido) complex (μ-Se2)[Ir2{CtMo(CO)2(Tp*)}2(CO)2(PPh3)2]. We have recently encountered the first examples of isoselenocarbonyl complexes1a that arise via the insertion of platinum into the alkynylselenoether C-Se bond of alkynylselenolatocarbyne complexes (Scheme 1a).1b Although this result was unexpected, we were aware of the potential lability of tC-Se linkages within a transition metal coordination sphere from our previous demonstration that alkynylselenoethers readily rearrange to provide selenolatovinylidene complexes (Scheme 1b).2 Once the viability of isoselenocarbonyl linkages had been established, a broader study by necessity required a more generally applicable synthetic strategy that was less dependent upon the propensity of a metal center to enter into oxidative addition of Se-C bonds, a reaction that remains comparatively rare.3 We have recently shown that Lalor’s bromocarbyne complex [Mo(tCBr)(CO)2(Tp*)] (1)4 (Tp* = hydrotris(dimethylpyrazolyl)borate) reacts with nBuLi to afford the lithiocarbyne complex [Mo(tCLi)(CO)2(Tp*)] (2). This in turn reacts with gray selenium to provide the selenocarbonyl complex Li[Mo (CSe)(CO)2(Tp*)] (Li[3]), which is more conveniently isolated as the salt [Et4N][3].5 Angelici and Stone have previously described the reactions of [Bu4N][W(CS)(CO)2{HB(pz)3}] (pz = pyrazolyl) with gold and molybde*To whom correspondence should be addressed. E-mail: a.hill@ anu.edu.au. (1) (a) Caldwell, L. M.; Hill, A. F.; Wagler, J.; Willis, A. C. Dalton Trans. 2008, 3538. (b) Caldwell, L. M.; Hill, A. F.; Rae, A. D.; Willis, A. C. Organometallics 2008, 27, 341. (2) Hill, A. F.; Hulkes, A. G.; White, A. J. P.; Williams, D. J. Organometallics 2000, 19, 371. (3) (a) Yoyofuku, M.; Fujiwara, S.-I.; Shin-ike, T.; Kuniyasu, H.; Kambe, N. J. Am. Chem. Soc. 2008, 130, 10504. (b) Kuniyasu, H.; Kato, T.; Inoue, M.; Terao, J.; Kambe, N. J. Organomet. Chem. 2006, 691, 1873. (c) Yu, K.; Li, H.; Watson, E. J.; Virkaitis, K. L.; Carpenter, G. B.; Sweigart, D. A. Organometallics 2001, 20, 3550. (d) Han, L.-B.; Choi, N.; Tanaka, M. J. Am. Chem. Soc. 1997, 119, 1795. (e) Yamamoto, T.; Akimoto, M.; Yamamoto, A. Chem. Lett. 1983, 1725. (4) (a) Lalor, F. J.; Desmond, T. J.; Cotter, G. M.; Shanahan, C. A.; Ferguson, G.; Parvez, M.; Ruhl, B. J. Chem. Soc., Dalton Trans. 1995, 1709. (b) For a review of poly(pyrazolyl)borate-ligated alkylidyne complexes see: Caldwell, L. M. Adv. Organomet. Chem. 2008, 57, 1. (5) Cordiner, R. L.; Hill, A. F.; Wagler, J. Organometallics 2008, 27, 5177. (6) (a) Doyle, R. A.; Daniels, L. M.; Angelici, R. J.; Stone, F. G. A. J. Am. Chem. Soc. 1989, 111, 4995. (b) Kim, H. P.; Kim, S.; Jacobson, R. A.; Angelici, R. J. J. Am. Chem. Soc. 1986, 108, 5154. r 2009 American Chemical Society
Scheme 1. Synthesis of (a) Isoselenocarbonyl1 and (b) Selenolatovinylidene2 Complexes
num halides, which led to the first examples of semibridging and σ-π four-electron bridging thiocarbonyl ligands (Chart 1).6 Accordingly, the anionic complex [3]- appeared to be a promising substrate for the synthesis of heterobimetallic selenocarbonyl complexes via simple salt elimination reactions with various transition metal halides. Herein, we report the first such investigation that while not ultimately affording an isoselenocarbonyl complex, does provide a most unusual bis(μ-carbido) complex, the formation of which may be rationalized as proceeding via the desired isoselenocarbonyl. The reaction of Vaska’s complex [IrCl(CO)PPh3)2] with the lithium alkynylselenolate LiSeCtCC6H4Me-4 afforded the first example of an alkynylselenolato complex, [Ir(SeCt CC6H4Me-4)(CO)(PPh3)2] (4),7 with further examples following in the interim.8 We therefore explored the reaction of [IrCl(CO)(PPh3)2] with [Et4N][3] but found that, in contrast (7) Bedford, R. B.; Dyson, P. J.; Hill, A. F.; Hulkes, A. G.; Yates, C. J. Organometallics 1998, 17, 4117. (8) (a) Sunada, Y.; Hayashi, Y.; Kawaguchi, H.; Tatsumi, K. Inorg. Chem. 2001, 40, 7072. (b) Sugiyama, H.; Hayashi, Y.; Kawaguchi, H.; Tatsumi, K. Inorg. Chem. 1998, 37, 6773. (c) Schaefer, S.; Moser, C.; Tirree, J. J.; Nieger, M.; Pietschnig, R. Inorg. Chem. 2005, 44, 2798. Published on Web 11/10/2009
pubs.acs.org/Organometallics
6640
Organometallics, Vol. 28, No. 23, 2009
Cade et al.
Chart 1. Coordination Modes for Carbon Monochalcogenide (CA: A = S, Se): (a) Terminal; (b) Bridging; (c) Semibridging; (d) σ-π-Bridging; (e) Isochalcocarbonyl
Scheme 2. Proposed Mechanism for the Formation of the Tetrametallic μ-Carbido Complex 5
Figure 1. Molecular structure of 5 in a crystal (hydrogen atoms and phenyl groups omitted). Selected bond lengths (A˚) and angles (deg): Ir1-Ir2 2.7555(3), Ir1-Se5 2.5575(6), Ir1Se6 2.5118(5), Ir1-C1 1.976(5), Ir2-Se5 2.5143(5), Ir2Se6 2.5561(6), Ir2-C2 1.969(5), Mo1-C1 1.840(5), Mo2C2 1.846(5), Se5-Se6 2.3628(7), Ir1-C1-Mo1 171.3(3), Ir2-C2-Mo2 168.2(3), Ir2-Ir1-C1 105.12(14), Ir1-Ir2-C2 104.94(14).
to the synthesis of 4, no reaction ensued at room temperature. However, employing the more labile salt [Ir(NCMe)(CO)(PPh3)2]BF49 resulted in a slow reaction over 3 days.10 Chromatographic purification afforded the orange product 5, the spectroscopic data for which were not, however, consistent with the anticipated product [Ir{SeCtMo(CO)2(Tp*)}(CO)(PPh3)2] (A, Scheme 2). Specifically, integration of the 1H NMR spectrum suggests a 1:1 ratio of Tp* and PPh3 ligands. The possibility that phosphine dissociation had occurred, followed by the formation of a seleniumbridged dimer (D, Scheme 2), seemed plausible and consis(9) Reed, C. A.; Roper, W. R. J. Chem. Soc., Dalton Trans. 1973, 1365. (10) 5: A mixture of [Ir(NCMe)(CO)(PPh3)2][BF4]9 (0.260 g, 0.298 mmol) and Et4N[3]5 (0.200 g, 0.298 mmol) in THF was stirred for 72 h. The orange supernatant was separated from unreacted Et4N[3] via a filter cannula, and the solvent removed under reduced pressure. The residue was redissolved in CH2Cl2 and chromatographed (silica gel, 1:4 CH2Cl2/hexane) to provide an orange band. The solvent was removed under reduced pressure, and the product crystallized from a mixture of CH2Cl2 and ethanol. Yield: 0.070 g (23%). IR (νCO, cm-1), KBr: 1981, 1953, 1901; THF: 1989, 1960, 1909. NMR (C6D6, 298 K). 1H: δH 2.02 (s, 3 H, pzCH3), 2.13 (s, 6 H, pzCH3), 2.44 (s, 3 H, pzCH3), 2.69 (s, 6 H, pzCH3), 5.38 (s, 1 H, pzH), 5.58 (s, 2 H, pzH). 13C{1H}: δC 286.1 (d, MotC, 2JPC = 28 Hz), 222.8 (MoCO), 181.1 (d, IrCO. 2JPC = 11 Hz), 151.9, 151.3, 145.2, 144.3 [1:2:1:2, C3,5(pz)], 135.8 [d, C1(C6H5), 1JPC = 54 Hz], 134.3 [d, C2,6(C6H5), 2JPC = 12 Hz], 130.2 [d, C3,5(C6H5), 3JPC = 3 Hz], 128.2 [C4(C6H5), assignment equivocal due to C6D6 overlap], 107.5, 107.3 [1:2, C4(pz)], 17.5, 15.1, 12.8, 12.6 (2:1:1:2, pzCH3). 31P{1H}: δP 28.0. ESI-MS (þve ion, MeOH): m/z 2045.2 [M]þ, 1024.21 [M]2þ. Anal. Found: C, 43.90; H, 3.86; N, 7.76. Calcd for C74H74B2Ir2Mo2N12O6P2Se2: C, 43.46; H, 3.65; N, 8.22. (11) The spectroscopic data alone do not allow for a distinction between the isomeric possibilities 5 and D given that the ranges observed so far for selencarbonyl, carbyne, and carbido ligand 13C resonances overlap considerably.12
tent with all the available spectroscopic data.11 A crystallographic study (Figure 1),13 however, revealed that this was not the case and that a tetranuclear complex (5) had formed involving two bridging carbido ligands tangential to a diiridadiselenatetrahedrane, Ir2(μ^-Se2), core. The molecular structure of 5, which has approximate, though not crystallographic, C2 symmetry, reveals a number of points of interest. The geometric parameters associated with the “Tp* (CO)2Mo” fragments conform to the copious precedent for carbyne complexes of this moiety, which have been recently surveyed.4b The iridium centers are coordinatively saturated (18 electron), and within the Ir2Se2 tetrahedrane the angles at iridum and selenium span the narrow ranges 55.56(1)-57.84(1) and 61.24(1)-65.87(1), i.e., not far from the ideal value (60). Dimetalladiselenatetrahedranes are known for earlier transition metals (V, Nb, Yb, Ta, Mo, W, Mn and Fe),14 the most widely (12) Colebatch, A. L.; Cordiner, R. L.; Hill, A. F.; Nguyen, K. T. H. D.; Shang, R.; Willis, A. C. Organometallics 2009, 28, 4394. (13) Crystal data for C74H74B2Ir2Mo2N12O6P2Se2: Mr = 2045.29, triclinic, P1 (No. 2), a = 14.5985(3) A˚, b = 16.2000(3) A˚, c = 21.0841(4) ˚A, R = 110.657(1), β = 95.278(1), γ = 99.185(1), V = 4546.2(2) A˚3, Z = 2, Dc =1.494 Mg m-3, μ(Mo KR) = 4.073 mm-1, T = 200(2) K, orange plate, 0.19 0.09 0.07 mm, 16 046 independent reflections, F2 refinement, R = 0.0308, wR = 0.0713 for 15 989 reflections (I > 2σ(I), 2θmax = 50), 919 parameters (CCDC 750110). (14) (a) Campana, C. F.; Lo, F.; Dahl, L. F. Inorg. Chem. 1979, 18, 3060. (b) Seyferth, D.; Henderson, R. S. J. Organomet. Chem. 1980, 204, 333. (c) Kwak, J. E.; Hahn, S. I.; Yun, H. Acta Crystallogr., Sect. E 2007, E63, i27. (d) Kornienko, A. Y.; Emge, T. J.; Brennan, J. G. J. Am. Chem. Soc. 2001, 123, 11933. (e) Sokolov, M.; Imoto, H.; Saito, T.; Fedorov, V. Polyhedron 1998, 17, 3735. (f) Guo, G.-C.; Mak, T. C. W. J. Chem. Soc., Dalton Trans. 1997, 709. (g) Liao, J.-H.; Li, J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 2658. (h) Chau, C. N.; Wardle, R. W. M.; Ibers, J. A. Inorg. Chem. 1987, 26, 2740. (i) Belletti, D.; Graiff, C.; Pattacini, R.; Predieri, G.; Tiripicchio, A. Eur. J. Inorg. Chem. 2004, 3564. (j) Adams, R. D.; Kwon, O.-S. Inorg. Chem. 2003, 42, 6175. (k) Fedin, V. P.; Sokolov, M. N.; Geras0 ko, O. A.; Virovets, A. V.; Podberezskaya, N. V.; Fedorov, V. Y. Polyhedron 1992, 11, 3159.
Communication
studied being [Fe2(μ^-Se2)(CO)6],14a,b which may be considered isoelectronic with 5 (FeL3 = IrXL2).15 However the M2(μ^-Se2) core appears unprecedented for later transition metals of group 9 and beyond. Seyferth has demonstrated a variety of reactions of the Se-Se bond (2.293(2) A˚14a) of [Fe2(μ^-Se2)(CO)6] that topologically parallel those of conventional organic diselenides, e.g., insertion of metal fragments and cleavage by Li[Et3BH] or organolithium reagents.14b It is therefore perhaps noteworthy that the Se1-Se2 bond length in 5 (2.3628(7) A˚) is significantly longer than those of all other previously reported M2(μ^-Se2) structures, which span the range 2.214-2.333 A˚. The Mo-C-Ir linkages are close to linear (171.3(3), 168.2(3)), though significant deviations from linearity are not uncommon.1,4b The metal carbon bond lengths for the Mo-C-Ir linkages are as expected for MotC (1.840(5), 1.846(5) A˚) and Ir-C (1.976(5), 1.969(5) A˚) triple and single bonds, respectively, such that the bonding in 5 is most akin to that observed by Templeton for the heteronuclear carbido complex [Fe{CtMo(CO)2(Tp*)}(CO)2(η-C5H5)].16 Although 5 is the first structurally characterized bis(carbido) complex, we have recently reported the formation of the bis(carbido) mercurial [Hg{CtMo(CO)2(Tp*)}2] and shown that it may be catalytically demercurated by [RhCl(CO)(PPh3)2] to afford an ethandiylidyne complex, [(Tp*)(CO)2MotC-CtMo(CO)2(Tp*)].12 Given that rhodium carbido complexes [LnRh{CtMo(CO)2(Tp*)}2] were suggested as intermediates in this process, the isolation of an iridium carbido complex, 5, assumes some significance. Mechanistic conjecture for the formation of 5 is presented in Scheme 2. The two considered routes begin with the common, targeted isoselenocarbonyl intermediate A, by analogy with the complex [Ir(SeCtCC6H4Me-4)(CO) (15) (a) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711. (b) Green, M. L. H. J. Organomet. Chem. 1995, 500, 127. (16) Etienne, M.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1991, 113, 2324.
Organometallics, Vol. 28, No. 23, 2009
6641
(PPh3)2] (6)7 and our recent isolation of isoselenocarbonyls bound to platinum.1 The routes vary depending on whether C-Se scission precedes or follows the formation of a bimolecular species. Precedent for the binuclear intermediate D is provided by the complex [Ir2(μ-StBu)2(CO)2{P(OMe)3}2],17 while support, albeit circumstantial, for an intermediate of the form B is provided by Werner’s demonstration that mononuclear η2-C,Se-CSSe complexes of platinum react with [Pt(η2-C2H4)(PPh3)2] to afford binuclear derivatives in which the initially π-bound CdSe bond is cleaved to afford thiocarbonyl and μ-selenide ligands.18 To conclude, the origin of interstitial carbido atoms in clusters is often traced to the cleavage of CO; however this typically requires forcing conditions.19 Recently Johnson has demonstrated the synthesis of carbido complexes of ruthenium and osmium via sulfur abstraction from thiocarbonyl ligands by early transition metal siloxides or amides.20 The remarkably facile cleavage of a selenocarbonyl ligand into carbide and selenide constituents in 5 under ambient conditions is therefore noteworthy and provides a further example of the fragility of C-Se bonds within metal coordination spheres.
Acknowledgment. This work was supported by the Australian Research Council (DP0556236). (17) Bonnet, J. J.; Thorez, A.; Maisonnat, A.; Galy, J.; Poilblanc, R. J. Am. Chem. Soc. 1979, 101, 5940. (18) Werner, H.; Ebner, M.; Otto, H. J. Organomet. Chem. 1988, 350, 257. (b) Ebner, M.; Otto, H.; Werner, H. Angew. Chem., Int. Ed. Engl. 1985, 24, 518. (19) Bradley, J. S. Adv. Organomet. Chem. 1983, 22, 1. (b) Johnson, B. F. G.; Lewis, J.; Nelson, W. J. H.; Nicholls, N.; Vargas, M. D. J. Organomet. Chem. 1983, 249, 255. (20) (a) Caskey, S. R.; Stewart, M. H.; Kivela, J. E.; Sootsman, J. R.; Johnson, M. J. A.; Kampf, J. W. J. Am. Chem. Soc. 2005, 127, 16750. (b) Stewart, M. H.; Johnson, M. J. A.; Kampf, J. W. Organometallics 2007, 26, 5102.
