Rate and selectivity of reduction of alkylcyclohexanones with 2-propanol in presence of triphenylphosphine complexes of ruthenium, rhodium, and iridium

Abstract

1. The rate and selectivity of the reduction of the 2-, 3-, and 4-alkylcyclohexanones with 2-propanol in the presence of Ru, Rh, and Ir complexes depends on the nature of the central atom, the coupling of the ligands (PPh3, Cl−, CO, OH−, NO−, Me2SO), and the position of the alkyl substituent. A substituent in the 2 position lowers the rate of hydrogen transfer. 2. The complexes RhCl(PPh3)3 and Rh(NO)Cl2(PPh3)2 catalyze the reduction of the 3- and 4-alkylcyclohexanones with 2-propanol to give predominantly the thermodynamically less stable alkylcyclohexanol, while RuCl2(PPh3)3, HRu(CO)Cl(PPh3)3, Ir(CO)(PPh3)2, Rh(CO)Cl(PPh3)2, Rh(Me2SO)Cl(PPh3)2, and Rh(OH) (CO)(PPh3)2 direct the process toward the formation of the thermodynamically more stable alkylcyclohexanol. 3. The reduction of the 2-alkylcyclohexanones in the presence of the investigated complexes of Ru, Ir, and also Rh, devoid of the CO group, proceeds with the predominant formation of the thermodynamically less stable cis-2-alkylcyclohexanol.