Rotational isomerism in octahedral d6-iridium(III) complexes trans,mer-[IrCl 2(PMe 3) 3L] + where L = PMe 3, PMe 2Ph or PMePh 2; X-ray crystal structure of [IrCl 2(PMe 3) 3(PMe 2Ph)]ClO 4·CH 2Cl 2

Abstract

The cationic d 6-complexes [IrCl 2(PMe 3) 3L] + where L = PMe 3, PMe 2Ph or PMePh 2 have been synthesized and the single-crystal X-ray structure of trans,mer-[IrCl 2(PMe 3) 3(PMe 2Ph)]ClO 4·CH 2Cl 2 determined; the cation is chiral because of the conformation adopted about the IrPMe 2Ph bond. The low-temperature 31P{ 1H} NMR spectrum (−75°C, CD 3COCD 3)of this salt shows a major ABCD component (95%), consistent with the chiral conformer found in the crystal, and a minor AB 2C component (5%) corresponding to a symmetrical achiral isomer. These isomers interconvert by rotation about the IrPMe 2Ph bond and at 45°C a sharp coalesced AB 2C spectrum is obtained. In the low-temperature 1H NMR spectrum, the major chiral isomer shows non-equivalent ortho-protons, whereas the minor achiral isomer gives a single resonance for these protons. Related rotamers are observed for the PMePh 2 complex but we could not obtain frozen-out spectra for [IrCl 2(PMe 3) 4] +. We conclude that, even for these small tertiary phosphines, it is possible to have rotamers that interconvert slowly enough for line-shape effects to be observed in NMR spectra at ambient temperatures provided that there are four phosphines in each complex. Chiral rotamers may be dominant in rotameric equilibria.