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(κ²-Xantphos)(COD)]BAr^F₄] (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Ar^F = C₆H₃(CF₃)₂) with H₂ in acetone or CH₂Cl₂/MeCN affords the Ir(III)-hydrido complexes Ir(κ³-Xantphos)(H)₂(L)]BAr^F₄], L = acetone or MeCN, whereas in non-coordinating CH₂Cl₂ solvent dimeric Ir(κ³-Xantphos)(H)(μ-H)]₂BAr^F₄]₂ is formed. A common intermediate in these reactions that invokes a (σ, η²-C₈H₁₃) ligand is reported. Addition of excess tert-butylethene (tbe) to Ir(κ³-Xantphos)(H)₂(MeCN)]BAr^F₄] results in insertion of a hydride into the alkene to form Ir(κ³-Xantphos)(MeCN)(CH₂CH₂C(CH₃)₃)(H)]BAr^F₄], an Ir(III) alkyl-hydrido-Xantphos complex. This reaction is reversible, and heating (80 °C) results in the reformation of Ir(κ³-Xantphos)(H)₂(MeCN)]BAr^F₄] 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-κ²-P,P, fac-κ³-P,O,P and mer-κ³-P,O,P with the later coordination mode like that found in related PNP-pincer complexes.