The reactions of the tri-µ-hydroxo-bis[η6-p-cymeneosmium(II)] cation with aldehydes and acids and the homogeneously catalysed oxidation of acetaldehyde and propionaldehyde with water. X-Ray structure of [(p-MeC6H4CHMe2)2Os2(µ-HCO2)(µ-OH)(µ-H)][PF6]

Abstract

Reaction of [(p-MeC₆H₄CHMe₂)₂Os₂Cl₄] with sodium hydroxide in water gave the tri-µ-hydroxo cation [(p-MeC₆H₄CHMe₂)₂Os₂(µ-OH)₃]⁺, isolated as PF₆(1a) or BPh₄(1b) salts. Complex (1a) reacted with formaldehyde, acetaldehyde, or propionaldehyde to give the complexes [(p-MeC₆H₄CHMe₂)₂Os₂(µ-RCO₂)(µ-OH)(µ-H)][PF₆][R = H (2a), Me (2b), Et (2c)], and with cinnamaldehyde, benzaldehyde, or pivaldehyde to give the complexes [(p-MeC₆H₄CHMe₂)₂Os₂(µ-RCO₂)(µ-OH)₂][PF₆][R =trans-PhCHCH (3a), Ph (3b), Bu^t(3c)]. Reaction of (1a) with carboxylic acids gave (3; R =trans-PhCHCH, Ph, Me, or H). Complex (1a) catalysed the oxidation of acetaldehyde and propionaldehyde by water to the corresponding carboxylic acids; hydrogen was also produced. This reaction was slower but more selective than the previously reported ruthenium-catalysed reaction. The complexes have been characterised by microanalysis and i.r. and ¹H n.m.r. spectra. A single-crystal X-ray diffraction study on complex (2a) confirmed the proposed structure.