Effect of Fluoride Ion on the Activation of Molecular Hydrogen by Silver(I)

Abstract

ACCORDING to Halpern¹ the effect of complex forming ligands on the activation of molecular hydrogen by metal ions can be explained by the following scheme: Thus the heterolytic splitting of hydrogen is the consequence of the concerted action of the central metal ion and the ligand bond. Great activation effect can be expected from the ligands which, although weak acids, form unstable complexes with the metal ion, that is, which do not screen the positive charge partly responsible for the heterolytic splitting. These requirements are contradictory in general, being a parallelism between the proton affinity and the complex forming tendency of the ligands. In the case of silver(I), the reduction of which by hydrogen was thoroughly investigated by Halpern et al.^2–5, the fluoride ion fulfils the requirements mentioned: although hydrogen fluoride is a rather weak acid (pK = 3.4), the fluoride ion forms an unstable monofluorosilver(I) complex^6,7.