Synthesis, characterization and catalytic activity of dinuclear half-sandwich Ru(II), Rh(III) and Ir(III) complexes

The reaction in dichloromethane between the chloro-bridged complexes [(η6-p-iPrC6H4Me)2Ru2(μ-Cl)2Cl2], [(η5-C5Me5)2Rh2(μ-Cl)2Cl2] and [(η5-C5Me5)2Ir2(μ-Cl)2Cl2], and the ligand precursor, 3,3′-[(1E,1′E)-{(methylenebis(4,1-phenylene))bis(azanylylidene)}bis(ethan-1-yl-1-ylidene)]bis(4-hydroxy-6-methyl-2H-pyran-2-one) (LH2), has yielded the corresponding neutral dinuclear Ru(II), Rh(III) and Ir(III) complexes of the formula [{(η6-p-iPrC6H4Me)RuCl}2L] (1), [{(η5-C5Me5)RhCl}2L] (2) and [{(η5-C5Me5)IrCl}2L] (3). The complexes were characterized by elemental analysis, infrared, 1H NMR, 13C NMR, ESI mass spectrometry, and complexes 2 and 3 by single-crystal X-ray structure analysis. All complexes were used as catalysts under different reaction conditions for the formation of amides from aldehydes in the presence of NH2OH·HCl and NaHCO3. All complexes show good conversion with catalytic turnover numbers up to 500.