Enantiomerically Pure Pentadienyl Rhodium(I) and Iridium(I) Complexes – Their Synthesis and Reactivity

Abstract

Reactions of [(η4‐COD)M(µ‐Cl)]2 (M = Rh, Ir) with the potassium pentadienides (KPdl*) derived from (1R)‐(–)‐myrtenal allowed the corresponding enantiomerically pure RhI and IrI compounds [(η4‐COD)M(η5‐Pdl*)] to be isolated. Full characterization of these species was accomplished by NMR spectroscopy, elemental analysis and X‐ray diffraction studies. Notably, the coordination modes of the Pdl* ligands vary in the solid‐state structure of the Ir and Rh compounds. While η5‐U coordination with a fully delocalized negative charge within the Pdl* moiety was achieved in the IrI derivatives, the structures for the RhI analogues are best described by a η3:η2‐U coordination in which the metal slips into an allyl–ene structure. Furthermore, while only one species was observed for the IrI compounds in solution consistent with their molecular structures established in solid state, the solution behavior of the RhI derivatives is more complex. In these cases a mixture of isomers, which are in chemical equilibrium with each other, are observed. The major isomer exhibits NMR signatures that are in line with the solid‐state structures of these molecules. The minor component, however, is derived from a rotation of the myrtenal moiety to yield a η3‐S coordinated Pdl* ligand. Exposure of [(η4‐COD)Ir(η5‐Pdl*)] to H2 rapidly forms Ir (nano)particles, resulting from the initial hydrogenation of the Pdl* moiety. Intermediates with a partially hydrogenated Pdl*‐ligand were successfully isolated.