The complexes [OsCl2(azole)2(dmso)2] and [OsCl2(azole)(dmso)3]:: Synthesis, structure, spectroscopic properties and catalytic hydration of chloronitriles

Two families of mixed-ligand osmium(II) complexes, namely trans, cis, cis-[(OsCl2)-Cl-II (azole)(2)(dmso)(2)] [azole = indazole (1), pyrazole (2), benzimidazole (3) and imidazole (4)] and cis,fac-[(OsCl2)-Cl-II(azole)(dmso)(3)] [azole = indazole (5), pyrazole (6), benzimidazole (7) and imidazole (8)] have been prepared by taking advantage of the destabilising trans effect of the S-bonded dmso ligands. These complexes have been characterised by microanalysis, IR, UV/Vis, H-1 and C-13 NMR spectroscopy, electrospray mass spectrometry, cyclic voltammetry and X-ray crystallography. They have been found to catalyse the hydration of trichloroacetonitrile to trichloroacetamide and dichloroacetonitrile to dichloroacetamide with high selectivity. The catalyst efficiency depends strongly on the nature of the complex and the azole ligand present. The highest turnover (TON of 412 for trichloroacetamide and 578 for dichloroacetairlide) and product yield (82.7% for trichloroacetamide and 75.3% for dichloroacetamide) have been achieved with complex 7. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)