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

Reactions of [(eta(4)-COD)M(mu-Cl)](2) (M = Rh, Ir) with the potassium pentadienides (KPdl*) derived from (1R)-(-)-myrtenal allowed the corresponding enantiomerically pure Rh-I and Ir-I compounds [(eta(4)-COD)M(eta(5)-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 eta(5)-U coordination with a fully delocalized negative charge within the Pdl* moiety was achieved in the Ir-I derivatives, the structures for the Rh-I analogues are best described by a eta(3):eta(2)-U coordination in which the metal slips into an allyl-ene structure. Furthermore, while only one species was observed for the Ir-I compounds in solution consistent with their molecular structures established in solid state, the solution behavior of the Rh-I 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 eta(3)-S coordinated Pdl* ligand. Exposure of [(eta(4)-COD)Ir(eta(5)-Pdl*)] to H-2 rapidly forms Ir (nano)particles, resulting from the initial hydrogenation of the Pdl* moiety. Intermediates with a partially hydrogenated Pdl*-ligand were successfully isolated.