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

• The synthesis of dinuclear half-sandwich catalysts is presented.
• The dinuclear complexes are active catalysts for the formation of amides from aldehydes.
• An imine intermediate has been observed and identified.
• A mechanism for the catalytic rearrangement of aldoximes to amides was proposed.

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.

Dinuclear Ru(II), Rh(III) and Ir(III) half-sandwich complexes have been synthesized by reacting a bis-bidentate ligand with the respective metal precursors. The catalytic activity of the complexes for the conversion of aldehyde to amide has been investigated in the presence of NH2OH·HCl and NaHCO3.Figure optionsDownload as PowerPoint slide