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Organometallics 2009, 28, 4394–4399 DOI: 10.1021/om900462p
A Bis-Carbyne (Ethanediylidyne) Complex via the Catalytic Demercuration of a Mercury Bis(carbido) Complex Annie L. Colebatch, Richard L. Cordiner, Anthony F. Hill,* Kelly T. H. D. Nguyen, Rong Shang, and Anthony C. Willis Research School of Chemistry, Institute of Advanced Studies, Australian National University, Canberra, Australian Capital Territory, Australia Received May 30, 2009
Successive treatment of [Mo(tCBr)(CO)2{HB(pzMe2)3}] (pz=pyrazol-1-yl) with nBuLi and mercuric chloride provides the bis(carbido)mercurial complex Hg[CtMo(CO)2{HB(pzMe2)3}]2, which is catalytically demercurated by [RhCl(CO)(PPh3)2] to provide the bis-carbyne (ethanediylidyne) compound (μ-C2)[Mo(CO)2{HB(pzMe2)3}]2. The vast majority of bimetallic complexes spanned by a two-carbon unit are best described in valence bond terms as dimetalated derivatives of ethyne1 (A, Chart 1). The alternative valence bond descriptions as either cumulenic (B) or bis-carbyne, (ethanediylidyne, C) are appropriate to a very small number of examples (Chart 2).2-7 For those examples based on 5d metals, the bonding description conforms to the bond localization that follows from the observed diamagnetism and simple electron-counting arguments, though more sophisticated theoretical treatments are available for (μ-C2)[Ta(OSitBu3)3]22b and (μ-C2)[W(OtBu)3]2.3c The situation is not as straightforward for 3d metals, where the orbital manifolds are more closely spaced, allowing access to triplet states; e.g., the manganese complex (μ-C2)[Mn(dmpe)(η-C5H4Me)]2 displays temperature-dependent 31 P NMR spectra suggestive of a singlet-triplet spin equilibrium.5 We report herein the synthesis of a dicarbido-bridged dimolybdenum complex, for which the bis-carbyne (ethane*To whom correspondence should be addressed. E-mail: a.hill@ anu.edu.au. (1) (a) Bruce, M. I.; Low, P. L. Adv. Organomet. Chem. 2004, 50, 179. (b) The terms bis-carbyne and ethanediylidyne, used here interchangeably, reflect the common usage of both “carbyne” and “alkylidyne” in the organometallic literature to refer to a complex involving a metal-carbon triple bond. The terms carbyne and carbene call to mind the free molecules “CR” and “CR2”, while the terms alkylidyne and alkylidene (recommended by IUPAC) denote covalent compounds of the CR and CR2 fragments. (2) (a) LaPointe, R. E.; Wolczanski, P. T.; Mitchell, J. F. J. Am. Chem. Soc. 1986, 108, 6382. (b) Neithamer, D. R.; LaPointe, R. E.; Wheeler, R. A.; Richeson, D. S.; Van Duyne, G. D.; Wolczanski, P. T. J. Am. Chem. Soc. 1989, 111, 9056. (3) (a) Listermann, M. L.; Schrock, R. R. Organometallics 1985, 4, 74. (b) Blau, R. J.; Chisholm, M. H.; Folting, K.; Wang, R. J. J. Am. Chem. Soc. 1987, 109, 4552. (c) Caulton, K. G.; Cayton, R. H.; Chisholm, M. H.; Huffman, J. C.; Lobkovsky, E. B.; Xue, Z. Organometallics 1992, 11, 321. (d) Gilbert, T. M.; Rogers, R. D. Acta Crystallogr. Sect. C 1993, 49, 677. (e) Gilbert, T. M.; Rogers, R. D. J. Organomet. Chem. 1991, 421, C1. (4) Binger, P.; Muller, P.; Phillipps, P.; Gabor, B.; Mynott, R.; Herrmann, A. T.; Langhauser, F.; Kruger, C. Chem. Ber. 1992, 115, 2209. (5) Kheradmandan, S.; Venkatesan, K.; Blacque, O.; Schmalle, H. W.; Berke, H. Chem. Eur. J. 2004, 10, 4872. (6) Woodworth, B. E.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1998, 120, 9028. (7) De Angelis, S.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Angew. Chem., Int. Ed. 1995, 34, 1092. N.B.: discussions on the C-C bond order in this “ate” complex are limited by the close association of two lithium atoms, though the Ti-C bonds (1.809(9), 1.757(7) A˚) are noticeably shorter than in simple titanocene acetylides or Binger's dititanacumulene [(μ-C2) Ti2(PMe3)2(η-C5H5)4] (2.051(2) A˚).4 pubs.acs.org/Organometallics
Published on Web 07/16/2009
diylidyne) valence description (C) is appropriate, via a novel synthetic strategy involving the catalytic demercuration of a bis(carbido)mercurial, which is itself the first of its kind. Chart 1. Valence-Bond Descriptions for Bimetallic Complexes Spanned by C2
Results and Discussion The majority of alkylidyne complexes8 are accessed via Fischer- or Schrock-type protocols that are not appropriate for the construction of examples bearing electron-withdrawing (“EWG”) carbyne substituents. Thus, a typical Fischer type strategy involves introduction of the substituent via nucleophilic attack on coordinated carbon monoxide, imposing limitations on the range of sufficiently potent nucleophiles.9 Schrock type strategies typically involve R-metal-hydride elimination or abstraction from intermediate kinetically stabilized alkyls, LnM-CH2R (R = H, tBu, SiMe3, CMe2Ph, etc.).10 While a recent series of papers by Sundermeyer has demonstrated that such processes also afford access to phosphoniocarbynes,11 in general elaborate non-hydrocarbyl substituents are not suitable for R-elimination strategies. The possibility of introducing (8) For reviews on alkylidyne complexes see: (a) Caldwell, L. M. Adv. Organomet. Chem. 2008, 56, 1. (b) Kim, H.-S.; Angelici, R. J. Adv. Organomet. Chem. 1987, 27, 51. (c) Mayr, A.; Hoffmeister, H. Adv. Organomet. Chem. 1991, 32, 227. (d) Mayr, A; Ahn, S. Adv. Transition Met. Coord. Chem. 1996, 1, 1. (e) Transition Metal Carbyne Complexes; Kreissl, F. R., Ed.; Kluwer: Dordrecht, The Netherlands, 1992; NATO ASI Series 392. (f) Gallop, M. A.; Roper, W. R. Adv. Organomet. Chem. 1986, 25, 121. (9) Fischer, E. O.; Kreis, G.; Kreiter, C. G.; M€ uller, J.; Huttner, G.; Lorenz, H. Angew. Chem., Int. Ed. 1973, 12, 564. (10) Schrock, R. R. Chem. Commun. 2005, 2773. (b) Schrock, R. R. Chem. Rev. 2002, 102, 145. (11) (a) Li, X.; Wang, A.; Sun, H.; Wang, L.; Schmidt, S.; Harms, K.; Sundermeyer, J. Organometallics 2007, 26, 3456. (b) Li, X.; Wang, A.; Wang, L.; Sun, H.; Harms, H.; Sundermeyer, J. Organometallics 2007, 26, 1411. (c) Li, X.; Schopf, M.; Stephan, J.; Kipke, J.; Harms, K.; Sundermeyer, J. Organometallics 2006, 25, 528. (d) Li, X.; Stephan, J.; Harms, K.; Sundermeyer, J. Organometallics 2004, 23, 3359. r 2009 American Chemical Society
Article Chart 2. Cumulenylidene (B) and Bis-Carbyne (Ethanediylidyne, C) Bridged Bimetallic Compoundsa 2-7
Organometallics, Vol. 28, No. 15, 2009
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Scheme 1. Generation of Nucleophilic Anionic Carbido Complexesa
Abbreviations: R = OSitBu3, Cp = η-C5H5, MeCp = η-C5H4Me, Tp* = κ3-HB(pzMe2)3. a
alkylidyne substituents in electrophilic form has, however, been demonstrated by Templeton12 and by Cummins,13 via the intermediacy of anionic carbido complexes (Scheme 1). Recently we have developed an expedient route to the anionic carbido complexes [M(tC)(CO)2{HB(pzMe2)3}]Li (M = Mo (1a), W (1b); pz = pyrazol-1-yl)14 via the simple low-temperature lithium/halogen exchange reaction between n BuLi and the bromocarbyne complexes [M(tCBr)(CO)2{HB(pzMe2)3}] (M = Mo (2a), W (2b)).15 Although we have not yet successfully isolated these species, they may be readily generated and used in situ in reactions with a range of electrophiles. We had encountered a similar situation previously wherein the tricarbido complexes [W(tCCtC)(CO)2(L)]- (L=HB(pz)3, HB(pzMe2)3) could be generated via fluoride-mediated desilylation of silylpropargylidynes [W(tCCtCSiMe3)(CO)2(L)] but could not be isolated.16 In that instance we found that the corresponding mercury derivatives Hg[CtCCtW (CO)2(L)]2 could, however, be isolated17 and that these served (12) (a) Enriquez, A. J.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 2001, 123, 4992. (b) Jamison, G. M.; White, P. S.; Harris, D. L.; Templeton, J. L. In Transition Metal Carbyne Complexes; Kreissl, F. R., Ed.; Kluwer Academic: Dordrecht, The Netherlands, 1992; Proceedings of the NATO Advanced Research Workshop on Transition Metal Carbyne Complexes, Wildbad Kreuth, Germany, p 201. (c) Jamison, G. M.; Bruce, A. E.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1991, 113, 5057. (13) (a) Peters, J. C.; Odom, A. L.; Cummins, C. C. Chem. Commun. 1997, 1995. (b) Greco, J. C.; Peters, J. C.; Baker, T. A.; Davis, W. M.; Cummins, C. C.; Wu, G. J. Am. Chem. Soc. 2001, 123, 5003. (c) Agapie, T.; Diaconescu, P. L.; Cummins, C. J. Am. Chem. Soc. 2002, 124, 2412. (14) Cordiner, R. L.; Hill, A. F.; Wagler, J. Organometallics 2008, 27, 5177. (15) (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) Desmond, T.; Lalor, F. J. J. Chem. Soc., Chem. Commun. 1983, 457. (16) (a) Dewhurst, R. D.; Hill, A. F.; Smith, M. K. Angew. Chem., Int. Ed. 2004, 43, 476. (b) Dewhurst, R. D.; Hill, A. F.; Willis, A. C. Organometallics 2004, 23, 1646. (c) Dewhurst, R. D.; Hill, A. F.; Willis, A. C. Organometallics 2004, 23, 5903. (17) Dewhurst, R. D.; Hill, A. F.; Willis, A. C. Chem. Commun. 2004, 2826. (18) Dewhurst, R. D.; Hill, A. F.; Rae, A. D.; Willis, A. C. Organometallics 2005, 24, 4703.
a Abbreviations: L = HB(pzMe2)3; NRAr = NtBuC6H3Me2-3,5). Reagents: (i) Li[Et3BH]; (ii) [nBu4N]F (moist); (iii) LiNiPr2;12 (iv) Na (Hg), tBuCOCl; (v) Na, MeCN; (vi) KCH2Ph, Kryptofix 222.13
as heat- and air-stable reagents for the transfer of “CtCCtW (CO)2(L)” groups to other metals.18 Furthermore, they could also be catalytically demercurated to provide the first examples of dimetallaoctatetraynes, [(L)(CO)2WtCCtCCtCCtW (CO)2(L)]19 (Scheme 2). We find that a similar strategy proves successful in extending the chemistry of the monocarbido complex 1a to the synthesis of the bis(carbido)mercurial Hg[CtMo(CO)2{HB(pzMe2)3}]2 (3), followed by its catalytic demercuration by [RhCl(CO)(PPh3)2] (4) to provide the bimetallic bis-carbyne complex (μ-C2)[tMo(CO)2{HB(pzMe2)3}]2 (5; Chart 2). Treating 2a with 1 equiv of nBuLi in tetrahydrofuran at low temperature (dry ice/propanone) followed by addition of mercuric chloride and slow warming to room temperature affords, following chromatographic purification, a peach-colored compound formulated as the trimetallic bis(carbido)mercurial Hg[CtMo(CO)2{HB(pzMe2)3}]2 (3; Scheme 3, 75% yield). Spectroscopic data associated with the “Mo(CO)2{HB(pzMe2)3}” fragment are unremarkable and conform to copious precedent for alkylidyne derivatives of this fragment.8a The carbonyl ligands on each molybdenum center should in principle be too remote for the oscillators to couple significantly, and accordingly only two νCO absorptions might be expected in the infrared spectrum. However, the symmetric stretch is split (CH2Cl2: 1999, 1993 cm-1) and is somewhat weaker in relative intensity (cf. the antisymmetric stretch at 1911 cm-1) than would be expected for an inter-carbonyl angle close to 90°. Thus, it would appear that the two distal (19) (a) Dewhurst, R. D.; Hill, A. F.; Willis, A. C. Organometallics 2005, 24, 3043. (b) Dewhurst, R. D.; Hill, A. F.; Willis, A. C. Dalton Trans. 2009, 3384.
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Scheme 2. Synthesis and Catalytic Demercuration of Bis(tricarbido)mercurialsa
Colebatch et al. Table 1. Chemical Shifts for Binuclear Carbido Complexesa LnM
M0 Ln
δC, ppm
D: LnMdCdM0 Ln (Silox)2(O)W (Silox)2(NMes)W (TPP)Fe Cl4(Cym)(Cy3P)Ru
WCl2(Silox)2 WCl2(Silox)2 Re2(CO)9 RuCl4(PCy3)(Cym)
379.125 406.325 211.724 430.526
E: LnMtC-M0 Ln (tBuO)3W Tp*(CO)2Mo (σ-IMes)Cl2Ru Tp*(CO)2Mo
Ru(CO)2Cp Fe(CO)2Cp RuH(η6-IMes) 1 /2Hg (3)
237.327 38120 414.028 373.0
F: LnMtCfM0 Ln Cl2(Cy3P)2Ru Cl2(Cy3P)2Ru
Mo(CO)5 PdCl2(SMe2)
446.329 381.229
a Abbreviations: Silox = OSitBu3, Tp* = HB(pzMe2)3, Cp = ηC5H5, IMes = C{N(C6H2Me3-2,4,6)CH2}2, TPP = tetraphenylporphyrinato, Mes = C6H2Me3-2,4,6, Cym = iPrC6H4Me-4.
a Abbreviations: L = HB(pz)3, HB(pzMe2)3. Reagents: (i) [nBu4N]F; (ii) HgCl2;17 (iii) [RhCl(CO)(PPh3)2] (4; 5 mol %).19
Scheme 3. Synthesis of Carbido and Dicarbido Complexesa
a Abbreviation: L = HB(pzMe2)3. Reagents: (i) nBuLi; (ii) HgCl2; (iii) [RhCl(CO)(PPh3)2] (4; 5-10 mol %).
Mo(CO)2 oscillators are indeed coupled, though only weakly, given the small splitting (6 cm-1) that is observed. The 1 H NMR spectrum of 3 is as expected; however, the 13C{1H} spectrum includes one notable feature, that being the comparatively low field chemical shift of the carbyne (carbido) resonance at 373.0 ppm (Table 1). With the exception of Templeton’s μ-carbido complex [MoFe(μ-C)(CO)4(η-C5H5){HB(pzMe2)3}] (δC 381)20 and the silyl carbyne complex [Mo(CSiMe2Ph) (CO)2{HB(pzMe2)3}] (δC 360.4)12b the vast majority of alkylidyne complexes of the form [M(tCR)(CO)2(L)] (L=η-C5H5, (20) Etienne, M.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1991, 113, 2324.
η-C5Me5, HB(pz)3, HB(pzMe2)3) have 240
