PHOTOCATALYTIC HYDROGEN FORMATION FROM TH IOLES IN THE PRESENCE OF VITAMIN-B12 MODEL COMPLEXES WITH AZIDE AS PHOTOCHEMICAL SACRIFICIAL LIGAND

The photolysis of [N3Co(chelat)B] complexes (1-3) (chelat = dimethylgl yoxime, dmg; N,N'-o-phenylene bis(salicylidenimine), salphen; N,N'-eth ylene-bis(salicylidenimine), salen; 13 = pyridine) leads by homolytic cleavage of the Co-N-3 bond to both coordinatively unsaturated cobalt( II) chelates [Co(chelat)B] and N-3(.) ligand radicals that undergo fas t decay to dinitrogen. The photolysis of the cobalt(III) complexes 1-3 in the presence of thiophenole and other thioles proceeds catalytical ly and yields the corresponding disulphides and dihydrogen. The mechan ism of this photocatalytic generation of dihydrogen is due to the cata lytic activity of the coordinatively unsaturated cobalt(II) species fo rmed photochemically. A photocatalytic cycle is proposed describing th e generation of hydrogen. Possible photochemical and thermal steps of that cycle are discussed.