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

Abstract

Reaction of the Ir(I)–Xantphos complex [Ir(κ 2–Xantphos)(COD)][BAr F 4] (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Ar F = C 6H 3(CF 3) 2) with H 2 in acetone or CH 2Cl 2/MeCN affords the Ir(III)–hydrido complexes [Ir(κ 3–Xantphos)(H) 2(L)][BAr F 4], L = acetone or MeCN, whereas in non-coordinating CH 2Cl 2 solvent dimeric [Ir(κ 3–Xantphos)(H)(μ-H)] 2[BAr F 4] 2 is formed. A common intermediate in these reactions that invokes a (σ, η 2-C 8H 13) ligand is reported. Addition of excess tert-butylethene (tbe) to [Ir(κ 3–Xantphos)(H) 2(MeCN)][BAr F 4] results in insertion of a hydride into the alkene to form [Ir(κ 3–Xantphos)(MeCN)(CH 2CH 2C(CH 3) 3)(H)][BAr F 4], an Ir(III) alkyl–hydrido-Xantphos complex. This reaction is reversible, and heating (80 °C) results in the reformation of [Ir(κ 3–Xantphos)(H) 2(MeCN)][BAr F 4] 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-κ 2– P, P, fac–κ 3– P, O, P and mer-κ 3– P, O, P with the later coordination mode like that found in related PNP–pincer complexes.