pubs.acs.org/Organometallics Published on Web 08/04/2010 r 2010 American Chemical Society Organometallics 2010, 29, 5535–5543 5535 DOI: 10.1021/om100496x Evidence for C-H 333 X-Ir (X = Cl or I) Hydrogen Bonding between Imidazolium Salts and Iridium-Bound Halides and Formation of Ir(I) NHC Complexes † Weiwei Zuo and Pierre Braunstein* Laboratoire de Chimie de Coordination, Institut de Chimie, UMR 7177 CNRS, Universit e de Strasbourg, 4 Rue Blaise Pascal, F-67081 Strasbourg Cedex, France Received May 20, 2010 Reactions between an N,N 0 -adamantyl-substituted bis(imidazolium) diiodide (CH imid CHCH imid )I 2 (1) and the dinuclear iridium(I) complex ([Ir( μ-X)(cod)] 2 [X = Cl, I (prepared in situ)] in the absence of a base yielded the hydrogen-bonded complexes [(CH imid CHCH imid )I] þ [IrCl(I)(cod)] - (2) and [(CH imid CHCH imid )I] þ [IrI 2 (cod)] - (2 0 ). The charge-assisted intermolecular C-H 333 X-M hydro- gen-bonding interactions between the [(CH imid CHCH imid )I] þ cations and the [IrX(I)(cod)] - (X=Cl or I) anions involve two (C2-)H atoms of the imidazolium salt precursors and a halogen atom terminally bound to iridium. These hydrogen-bonded compounds can be converted to the mono- metalated iridium(I) N-heterocyclic carbene (NHC) complexes [IrCl(cod)(CH imid CHC NHC )]I (3) and [IrI(cod)(CH imid CHC NHC )]I (3 0 ) by strong or weak bases. On the basis of our experimental results, we suggest an explanation for the influence of the imidazolium counteranions on the metalation reactions. The reaction between the bis(imidazolium) diiodide and [Ir( μ-Cl)(cod)] 2 in the presence of excess Cs 2 CO 3 in refluxing acetonitrile directly afforded the monometalated iridium(I) NHC complex 3. The crystal structures of 2 0 3 MeCN and 3/3 0 3 MeCN have been determined by X-ray diffraction. Introduction The importance of C-H 333 X-M (X = halide, M = transition metal) interactions is now well established and has found broad applications in supramolecular chemistry, biochemistry, and organometallic chemistry. 1-9 The prob- ability for C-H 333 X-M hydrogen bonds to occur in a given crystal and the strength of such interactions are influenced by three main factors: (a) the availability of suitable proton donors; (b) the existence of suitable proton acceptors, and, in many cases, (c) crystal packing forces. 1 Due to the low acidity of unactivated C-H groups, they are usually thought to be poor proton donors, 4,8,10,11 although theoretical calcula- tions and experimental investigations have already confirmed the possibility of forming hydrogen bonds with such C-H groups. 4,9,12-15 It is clear that (C-)H atoms that have adja- cent electron-withdrawing groups are more likely to form C-H 333 X hydrogen bonds. 1 The C2-bound hydrogen of imidazolium salts is usually acidic and thus is expected to be a hydrogen bond donor. 16,17 It is very common that, in the solid state, imidazolium halides display C-H 333 X hydrogen- bonding interactions. 18,19 Although the C-X (X = halogen) moieties are relatively poor hydrogen-bond acceptors, the M-X (M = transition metal) groups have higher potential to interact with hydrogen-bond donors, owing to the larger negative charge on the halides involved in these partially ionic M-X bonds. 2-4,20-22 It is well known that the presence of weak bases, e.g., NEt 3 , Cs 2 CO 3 , or NaOAc, facilitates the transformation of the † Part of the Dietmar Seyferth Festschrift. Dedicated to Prof. Dietmar Seyferth, with our warmest wishes, for his outstanding career dedicated to all aspects of organometallic chemistry: research, teaching, and publishing. *To whom correpondence should be addressed. E-mail: braunstein@ unistra.fr. (1) Taylor, R.; Kennard, O. J. Am. Chem. Soc. 1982, 104, 5063. (2) Aullon, G.; Bellamy, D.; Brammer, L.; Bruton, E. A.; Orpen, A. G. Chem. Commun. 1998, 653. (3) Brammer, L.; Bruton, E. A.; Sherwood, P. New J. Chem. 1999, 23, 965. (4) Neve, F.; Crispini, A. Cryst. Growth Des. 2001, 1, 387. (5) Brammer, L.; Bruton, E. A.; Sherwood, P. Cryst. Growth Des. 2001, 1, 277. (6) Balamurugan, V.; Hundal, M. S.; Mukherjee, R. Chem.;Eur. J. 2004, 10, 1683. (7) Kovacs, A.; Varga, Z. Coord. Chem. Rev. 2006, 250, 710. (8) Hay, B. P.; Bryantsev, V. S. Chem. Commun. 2008, 2417. (9) Pedzisa, L.; Hay, B. P. J. Org. Chem. 2009, 74, 2554. (10) Bryantsev, V. S.; Hay, B. P. J. Am. Chem. Soc. 2005, 127, 8282. (11) Bryantsev, V. S.; Hay, B. P. Org. 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