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

By Ashley J. Pontiggia, Adrian B. Chaplin and Andrew S. Weller


Reaction of the Ir(I)-Xantphos complex [Ir(kappa(2)-Xantphos)(COD)][BAr(4)(F)] (Xantphos - 4,5-bis(diphenyl-phosphino)-9,9-dimethylxanthene, Ar(F) = C(6)H(3)(CF(3))(2)) with H(2) in acetone or CH(2)Cl(2)/ MeCN affords the Ir(III)-hydrido complexes [Ir(kappa(3)-Xantphos)(H)(2)(L)][BAr(4)(F)], L = acetone or MeCN, whereas in non-coordinating CH(2)Cl(2) solvent dimeric [Ir(kappa(3)-Xantphos)(H)(mu-H)](2)[BAr(4)(F)](2) is formed. A common intermediate in these reactions that invokes a (sigma, eta(2)-C(8)H(13)) ligand is reported. Addition of excess tert-butylethene (tbe) to [Ir(kappa(3)-Xantphos)(H)(2)(MeCN)][BAr(4)(F)] results in insertion of a hydride into the alkene to form [Ir(kappa(3)-Xantphos)(MeCN)(CH(2)CH(2)C(CH(3))(3))(H)][BAr(4)(F)], 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)][BAr(4)(F)] 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

Topics: QD
Publisher: Elsevier Science SA
Year: 2011
DOI identifier: 10.1016/j.jorganchem.2011.01.036
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