New Rh(III) complexes of 5‐methyl‐5‐(pyridyl)‐2,4‐imidazolidenedione: Synthesis, X‐ray structure, electrochemical study and catalytic behaviour for hydrogenation of ketones

Abstract

We describe the reaction of anion [RhCl6]3− with a series of hydantoin ligands (HL1, HL2 and HL3 = 5‐methyl‐5‐(2‐, 3‐ and 4‐pyridyl)‐2,4‐imidazolidenedione, respectively). Based on spectroscopic, cyclic voltammetric, elemental and MS analyses, the complexes have the general formula K[RhCl2(L1)2] (1), cis‐ and trans‐K[RhCl4(HL2)2] (2a and 2b) and cis‐ and trans‐K[RhCl4(HL3)2] (3a and 3b). Complexes 2a, 2b, 3a and 3b were characterized successfully using infrared, 1H NMR and 13C NMR spectral analyses. Dissolution of complex 1 in dimethylsulfoxide (DMSO) led to elimination of one KL1 ligand and coordination of two DMSO molecules as ligands and transformation of this complex to cis‐ and trans‐[RhCl2L1(DMSO)2] (1a and 1b). Recrystallization led to separation and isolation of crystals of 1a from the initial mixture. X‐ray analysis results showed that this complex was crystallized as solvated complex cis‐[RhCl2L1(DMSO)2]DMSO. The catalytic activity of these complexes was then evaluated for the hydrogenation of various ketones.