Mono and dinuclear rhodium, iridium and ruthenium complexes containing chelating 2,2′-bipyrimidine ligands: Synthesis, molecular structure, electrochemistry and catalytic properties

Abstract

The mononuclear cations [(η 5-C 5Me 5)RhCl(bpym)] + ( 1), [(η 5-C 5Me 5)IrCl(bpym)] + ( 2), [(η 6- p-Pr i C 6H 4Me)RuCl(bpym)] + ( 3) and [(η 6-C 6Me 6)RuCl(bpym)] + ( 4) as well as the dinuclear dications [{(η 5-C 5Me 5)RhCl} 2(bpym)] 2+ ( 5), [{(η 5-C 5Me 5)IrCl} 2(bpym)] 2+ ( 6), [{(η 6- p-Pr i C 6H 4Me)RuCl} 2(bpym)] 2+ ( 7) and [{(η 6-C 6Me 6)RuCl} 2(bpym)] 2+ ( 8) have been synthesised from 2,2′-bipyrimidine (bpym) and the corresponding chloro complexes [(η 5-C 5Me 5)RhCl 2] 2, [(η 5-C 5Me 5)IrCl 2] 2, [(η 6-Pr i C 6H 4Me)RuCl 2] 2 and [(η 6-C 6Me 6)RuCl 2] 2, respectively. The X-ray crystal structure analyses of [ 3][PF 6], [ 5][PF 6] 2, [ 6][CF 3SO 3] 2 and [ 7][PF 6] 2 reveal a typical piano-stool geometry around the metal centres; in the dinuclear complexes the chloro ligands attached to the two metal centres are found to be, with respect to each other, cis oriented for 5 and 6 but trans for 7. The electrochemical behaviour of 1– 8 has been studied by voltammetric methods. In addition, the catalytic potential of 1– 8 for transfer hydrogenation reactions in aqueous solution has been evaluated: All complexes catalyse the reaction of acetophenone with formic acid to give phenylethanol and carbon dioxide. For both the mononuclear and dinuclear series the best results were obtained (50 °C, pH 4) with rhodium complexes, giving turnover frequencies of 10.5 h −1 for 1 and 19 h −1 for 5.