Ruthenium Arene Derivatives of Chiral Ferrocene-Based P,N or P,O Ligands. Transformation of Chloro–Alcohol into Hydrido–Carbonyl Complexes

Several ferrocene-based chiral nonracemic aminophosphine and racemic hydroxyphosphine ligands have been used in the synthesis of RuII(arene) derivatives (arene = p-cymene, benzene). The reaction of suitable ruthenium complexes with the aminophosphine (P,N) ligands and NaBPh4 led to chelate complexes [RuCl(arene)(P,N)]BPh4 in which the ferrocenyl ligand is coordinated in a bidentate fashion. When these reactions were carried out with the hydroxyphosphine (P,O) ligands the alcohol functionality was oxidized, and hydrido–ketone (or hydrido–aldehyde) derivatives of the type [RuH(arene)(PCO)]BPh4 were obtained. The structures of two derivatives containing either an aminophosphine or a ketophosphine ligand were determined by X-ray diffraction. The reaction of the hydroxyphosphine ligands with the ruthenium precursors was studied in detail. Derivatives with coordinated hydroxyphosphine ligands were isolated and, in the case of a p-cymene hydroxyphosphine derivative, the rate constants and also the thermal and thermodynamic activation parameters were calculated for the hydride formation. The effects of certain parameters on the hydride generation, such as the type of solvent, the counterion, pH, and solvent deuteration, were also analyzed. In addition, a new ruthenium ether derivative was obtained. This compound was formed by reaction of the alcohol group with methanol-d4 in the presence of the acid that is released in the hydride generation step. A mechanism for the transformation of the hydroxyphosphine complex into the hydride or ether derivatives is proposed. Furthermore, a number of ruthenium complexes with P,N ligands were tested in the catalytic transfer hydrogenation of acetophenone.