PI-OLEFIN-IRIDIUM COMPLEXES .20. CRYSTAL- STRUCTURE OF BIS-(ETA(4)-CYCLOHEXA-1,3-DIENE) (2-FURYL)IRIDIUM AND REACTIVITY OF BIS-(ETA(4)-CYCLOHEXA-1,3-DIENE)IRIDIUMHETEROARYL COMPLEXES

The X-ray diffraction analysis of (eta4-chd)2Ir-2-furyl (chd=cyclohexa -1,3-diene) proves its square-pyramidal geometry and supine-supine ori entation of the diene ligands. A model computation for the correspondi ng 2-N-methylpyrrolyl complex shows the N-methyl group to be responsib le for hindered rotation of the sigma-bonded ligand. Protonation of th e heteroaryl complexes eta4-chd)2IrR (R=2-furyl, 2-thienyl, 2-N-methyl pyrrolyl) by CF3CO2H yields the novel compounds [(eta4-chd)2Ir(CCH= CH CH2X)]+CF3CO2- (X = O, S, N-CH3) which can best be described as ylides . In the furyl case, the reaction is shown to be reversible. With exce ss PMe3, the neutral species undergo ligand substitution to form (eta4 -chd)(PMe3)2Ir(C4H3X) (X = O, S), while attempts to isolate the corres ponding derivative with X = N-CH3 failed.