Oxidoperoxidotungsten(VI) Complexes with Secondary Hydroxamic Acids: Synthesis, Structure and Catalytic Uses in Highly Efficient, Selective and Ecologically Benign Oxidation of Olefins, Alcohols, Sulfides and Amines with H₂O₂ as a Terminal Oxidant

Abstract

Abstract The reaction of a solution of freshly precipitated WO 3 in H 2 O 2 separately with the secondary hydroxamic acids N ‐benzoyl‐ N ‐phenylhydroxamic acid (BPHAH), N ‐benzoyl‐ N ‐ ortho ‐tolylhydroxamic acid (B O THAH), N ‐benzoyl‐ N ‐ meta ‐tolylhydroxamic acid (B M THAH), N ‐benzoyl‐ N ‐ para ‐tolylhydroxamic acid (B P THAH) and N ‐cinnamyl‐ N ‐phenylhydroxamic acid (CPHAH) afforded [WO(O 2 )(BPHA) 2 ] ( 1 ), [WO(O 2 )(B O THA) 2 ] ( 2 ), [WO(O 2 )(B M THA) 2 ] ( 3 ), [WO(O 2 )(B P THA) 2 ] ( 4 ) and [WO(O 2 )(CPHA) 2 ] ( 5 ), respectively. Aqueous tungstate solution, on reaction with all these hydroxamic acids, produced [W(O) 2 (hydroxamato) 2 ] ( 6 ). The complexes show excellent catalytic functions in the oxidation of (a) olefins at room temperature in the presence of NaHCO 3 as promoter, (b) alcohols, sulfides and amines, at reflux, with H 2 O 2 as a terminal oxidant, yielding a high turnover number (TON), the highest being for olefin‐to‐epoxide conversion. An attempt to synthesize peroxide‐rich complexes of the type PPh 4 [WO(O 2 ) 2 (hydroxamato)] ( 7 ), for example PPh 4 [WO(O 2 ) 2 B M THA] ( 7C ), resulted in the isolation of PPh 4 [WO(O 2 ) 2 (C 6 H 5 COO)] ( 8 ), which was probably obtained by the hydrolysis of coordinated B M THA.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)