Bidentate Ru(ii)-NC complexes as catalysts for the dehydrogenative reaction from primary alcohols to carboxylic acids

Abstract

Four Ru(II)-NC complexes were synthesized by one-step processes from the corresponding NC ligands with RuHCl(CO)(PPh₃)₃. These complexes were tested as catalysts for alcohol dehydrogenative reactions, and complex {(C₅H₄N)-(C₆H₄)}RuCl(CO)(PPh₃)₂ (1) showed the highest activity. With KOH as the nucleophile and 0.5 mol% catalyst loading, a series of carboxylic acids were synthesized in toluene without any oxidant. Catalyst 1 could be transformed to complex {(C₅H₄N)-(C₆H₄)}RuH(CO)(PPh₃)₂ (6) when treated with KOH and benzyl alcohol. Complex 6 further reacted with PhCHO and H₂O to generate product {(C₅H₄N)-(C₆H₄)}Ru(OCOPh)(CO)(PPh₃)₂ (7). Complexes 6 and 7 exhibited similar efficiency to complex 1, suggesting that they can be regarded as the catalytic intermediates of 1.