PI-OLEFIN IRIDIUM COMPLEXES .19. SYNTHESI S, STRUCTURE AND REACTIVITYOF BIS(DIENE)IRIDIUM-BENZYL, IRIDIUM-CYCLOPROPYL, IRIDIUM-VINYL AND IRIDIUM-CYCLOPENTADIENYL COMPLEXES

The square-pyramid complexes (eta3-diene)2IrR [R = CH2C6H5, cyclo-C3H5 , diene = 2,3-dimethylbuta-1,3-diene (dmb), cyclohexa-1,3-diene (chd); R = C2 H 3, diene = chd] are obtained by treatment of (eta4-diene)2 I rCl with RM (M = MgX, Li). For diene = chd and RM = NaCp, (eta2-chd)2I r(eta5-Cp) was formed as the first compound with eta2 -bonded cyclohex adiene ligands, and was characterized by X-ray crystal analysis. With an excess of PMe3, (chd)2IrCH2C6H5 undergoes ligand substitution to fo rm (chd)(PMe3)2IrCH2C6H5, whereas the dmb compound does not react. The heterobimetallic complexes (dmb)2IrCH2C6H5Cr(CO)3, as well as (dmb)2I rC6H5M(CO)3 (M = Cr, Mo), have been prepared, whilst attempts to synth esize the corresponding (chd)2IrRM(CO)3 species failed. A general mech anism for the formation of pentacoordinated (eta4-diene)2IrR by treatm ent of the corresponding halides with carbanions is proposed.