ROTATIONAL-ISOMERISM IN OCTAHEDRAL D6-IRIDIUM(III) COMPLEXES TRANS,MER-[IRCL2(PME3)3L]+ WHERE L = PME3, PME2PH OR PMEPH2 - X-RAY CRYSTAL-STRUCTURE OF [IRCL2(PME3)3(PME2PH)]CLO4.CH2CL2

The cationic d6-complexes [IrCl2(PMe3)3L]+ where L = PMe3, PMe2Ph or PMePh2 have been synthesized and the single-crystal X-ray structure of trans,mer-[IrCl2 (PMe3)3(PMe2Ph)]ClO4.CH2Cl2 determined; the cation is chiral because of the conformation adopted about the Ir-PMe2Ph bond. The low-temperature P-31{H-1} NMR spectrum (- 75-degrees-C, CD3COCD3) of this salt shows a major ABCD component (95%), consistent with the chiral conformer found in the crystal, and a minor AB2C component (5%) corresponding to a symmetrical achiral isomer. These isomers interconvert by rotation about the Ir-PMe2Ph bond and at 45-degrees-C a sharp coalesced AB2C spectrum is obtained. In the low-temperature H-1 NMR spectrum, the major chiral isomer shows non-equivalent orthoprotons, whereas the minor achiral isomer gives a single resonance for these protons. Related rotamers are observed for the PMePh2 complex but we could not obtain frozen-out spectra for [IrCl2(PMe3)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.