Water photolysis. Part 2. An investigation of the relative advantages of various components of the sensitiser–electron relay–metal colloid system for the photoproduction of hydrogen from water, and the use of these systems in the photohydrogenation of unsaturated organic substrates

The photoredox systems metal complex sensitiser–electron relay–metal colloid have been investigated for the photoproduction of hydrogen from water. Metal colloids studied were Ru, Ir, Au, Pt, Rh, Pd, and Ag, and under the conditions employed the advantages are Pt > Rh Pd. The systems metal colloid–[Ru(bipy)3]2+–H2dmbipy2+–Na2(H2edta)(bipy = 2,2′-bipyridyl, H2dmbipy = 1,1′-dimethyl-4,4′-bipyridinium, edta = ethylenediaminetetra-acetate) have been used to generate hydrogen to photohydrogenate a number of unsaturated organic substrates, viz. styrene, cyclohexene, cyclohex-2-en-1-one, acrylonitrile, benzyl chloride, prop-2-en-1-ol, cyclohexa-1,3-diene, hex-3-yne, butanol, carbon monoxide, and 1,1-diphenylethene. Some general features have emerged: both alkene and alkynes are readily reduced, while carbonyl and nitrile groups are not affected; the reduction of alkynes and dienes does not selectively give monoalkenes, since both alkenes and alkanes are produced; photohydrogenation of carbon monoxide under very mild conditions gave trace amounts of methanol and formaldehyde.