Homogeneously catalysed disproportionation of acetaldehyde into ethanol and acetic acid

The complexes [Rh2(C5Me5)2(OH)3]+(1), [M2(C5Me5)2Cl4], M = Rh or Ir, [Ru2(p-cymene)2Cl4], and [Ru2(C6Me6)2(OH)3]+ all catalyse the disproportionation of acetaldehyde to acetic acid and ethanol in water in the absence of base, and other aldehydes react similarly; rhodium hydride complexes can be isolated from the reactions involving (1).