NEW CATALYSTS IN THE PHOTOOXIDATION OF WATER

Of the 20 dithiolene complexes investigated, only three were effective in the photo-oxidation of water to O-2 in the visible region and at t he same time sufficiently stable: l)-2-phenyl-1,2-ethylenodithiolenic- S,S']tungsten, ethoxy-phenyl)-2-phenyl-1,2-ethylenodithiolenic-S, S']t ungsten and hoxyphenyl)-1,2-ethylenodithiolenic-S,S']tungsten. Four mo re produced oxygen, but were not sufficiently stable for the reaction to be truly catalytic. The three successful catalysts are non-symmetri cal and have phenyl rings with para electron-donating substituents. Th e metals used were W, Mo, Re and Ni. The dithiolene complexes of the f irst three are trigonal prismatic and of nickel are square planar. The best results in terms of yield and stability were obtained with tungs ten, and specifically with l)-2-phenyl-1,2-ethylenodithiolenic-S,S']tu ngsten; the light storage efficiency for this catalyst was estimated t o be better than 9%. As indicated by the oxidation potentials, the exc ited states of the dithiolenes used were powerful oxidizing agents, su fficient to oxidize water. (C) 1997 Elsevier Science S.A.