Cationic iridium complexes of the Xantphos ligand. Flexible coordination modes and the isolation of the hydride insertion product with an alkene

Reaction of the Ir(I)-Xantphos complex [Ir(kappa(2)-Xantphos)(COD)][BAr4F] (Xantphos - 4,5-bis(diphenyl-phosphino)-9,9-dimethylxanthene, Ar-F = C6H3(CF3)(2)) with H-2 in acetone or CH2Cl2/ MeCN affords the Ir(III)-hydrido complexes [Ir(kappa(3)-Xantphos)(H)(2)(L)][BAr4F], L = acetone or MeCN, whereas in non-coordinating CH2Cl2 solvent dimeric [Ir(kappa(3)-Xantphos)(H)(mu-H)](2)[BAr4F](2) is formed. A common intermediate in these reactions that invokes a (sigma, eta(2)-C8H13) ligand is reported. Addition of excess tert-butylethene (tbe) to [Ir(kappa(3)-Xantphos)(H)(2)(MeCN)][BAr4F] results in insertion of a hydride into the alkene to form [Ir(kappa(3)-Xantphos)(MeCN)(CH2CH2C(CH3)(3))(H)][BAr4F], an Ir(III) alkyl-hydrido-Xantphos complex. This reaction is reversible, and heating (80 degrees C) results in the reformation of [Ir(kappa(3)-Xantphos)(H)(2)(MeCN)][BAr4F] and tbe. These complexes have been characterised by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. They show variable coordination modes of the Xantphos ligand: cis-kappa(2)-P,P, fac-kappa(3)-P,O,P and mer-kappa(3)-P,O,P with the later coordination mode like that found in related PNP-pincer complexes. (C) 2011 Elsevier B.V. All rights reserved.