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)][BArF4] (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, ArF = C6H3(CF3)2) with H2 in acetone or CH2Cl2/MeCN affords the Ir(III)–hydrido complexes [Ir(κ3–Xantphos)(H)2(L)][BArF4], L = acetone or MeCN, whereas in non-coordinating CH2Cl2 solvent dimeric [Ir(κ3–Xantphos)(H)(μ-H)]2[BArF4]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)][BArF4] results in insertion of a hydride into the alkene to form [Ir(κ3–Xantphos)(MeCN)(CH2CH2C(CH3)3)(H)][BArF4], 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)][BArF4] 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.

Xantphos is an analogue to a PNP–pincer ligand in Ir(III)–complexes, but can also show a variety of coordination modes.Figure optionsDownload as PowerPoint slideHighlights
► Ir(III)–hydrido complexes [Ir(κ3–Xantphos)(H)2(L)][BArF4], L = acetone or MeCN, are direct analogues of Ir–PNP pincer complexes.
► Dimeric [Ir(κ3–Xantphos)(H)(μ-H)]2[BArF4]2 shows a, different, cis-binding mode of Xantphos.
► Addition of excess tert-butylethene (tbe) to [Ir(κ3–Xantphos)(H)2(MeCN)][BArF4] results in insertion of the hydride into the alkene to form [Ir(κ3–Xantphos)(MeCN)(CH2CH2C(CH3)3)(H)][BArF4], this reaction being reversible.
► These complexes show variable coordination modes of the Xantphos ligand: cis-κ2–P,P, fac–κ3–P,O,P and mer-κ3–P,O,P.