31 Homogeneous Catalytic Activation of Molecular Hydrogen by Metal Ions

Abstract

Recent work on the homogeneous catalytic activation of molecular hydrogen by metal ions in aqueous solution is reviewed, and some new results in this field are presented. Among the ions which have been found to exhibit catalytic activity are Cu++, Ag+, Hg++, Hg2++, and MnO4−. In perchlorate medium the rate of activation of H2 is given by rate = kM[H2][M]n, where n = 1 for M = Cu++, Hg++, Hg2++, MnO4− and n = 2 for M = Ag+. The catalytic activity of Cu++ is enhanced by complexing with negative ions such as Cl−, SO4−-, and CH3COO−, but lowered by chelate formation, particularly with nitrogen-containing reagents. The catalytic mechanism in these systems is discussed and the possible roles of electron- and atom-transfer between H2 and the catalyst, in the activation process, are examined. Some conclusions are drawn concerning the action of other hydrogenation catalysts.