Diversity in Complexation of [RhI(cod)]+ and [IrI(cod)]+ by Pyridine-Amine-Pyrrole Ligands

Abstract

Complexation of [RhI(cod)]+ and [IrI(cod)]+ by the new pyridine-amine-pyrrole ligands Py–CH2–N(R)–CH2–Pyr–H (HLR; R = H, Bzl, Bu) and the corresponding pyridine-amine-pyrrolate ligands [Py–CH2–N(R)–CH2–Pyr]− (LR−; R = H, Bzl, Bu, CH2Py) has been investigated. The neutral ligands HLR (R = H, Bu, Bzl) give [(HLR)MI(cod)]+ (M = Rh, Ir) in which HLR acts as a didentate ligand via the pyridine nitrogen (NPy) and the amine nitrogen (NRamine). The crystal structures of [(HLH)MI(cod)]PF6 (M = Rh: [1]PF6 and M = Ir: [2]PF6) have been determined. Deprotonation of [(HLR)MI(cod)]+ (M = Rh, Ir; R = H, Bzl, Bu) results in the neutral complexes [(LR)MI(cod)] (M = Rh, Ir) of the mono-anionic ligands LR− (R = H, Bzl, Bu). In square-planar [(LH)MI(cod)] (M = Rh: 3, M = Ir: 4), LH− is didentate via NHamine and the pyrrolate nitrogen (NPyr). The X-ray structures of 3 and 4 reveal that in both cases the uncoordinated NPy accepts a hydrogen bond from NHamine. The X-ray structures of [(LBzl)MI(cod)] (M = Rh: 5, M = Ir: 6), show that LBzl− is didentate via Namine and NPyr for M = Rh and tridentate for M = Ir. In solution LBzl− is tridentate for both M = Rh and M = Ir. The neutral complexes [{Py–CH2–N(R)–CH2–Pyr}MI(cod)] (M = Rh, Ir) cannot be oxidised selectively with H2O2. This is in marked contrast to the previously observed selective oxidation of the corresponding cationic complexes [{Py–CH2–N(R)–CH2–Py}RhI(cod)]+. Rhodium complex 5 is an active catalyst for the stereoregular polymerisation of phenylacetylene, whereas iridium complex 6 is inactive.