Photohydrogenation of acetylenes in water-oil two-phase systems: application of novel metal colloids and mechanistic aspects of the process.

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Photohydrogenation of phenylacetylene and methylphenylacetylene was accomplished in a H2O-cyclohexane system, using tris(bipyridine)ruthenium Ru(bpy)32+ (bpy = 2,2'- bipyridine) as a photosensitizer, N,N'-dialkyl-4,4'-bipyridinium (viologen), CnV2+, as a charge relay, Na2EDTA as a sacrificial electron donor, and a Pt or Pd colloid stabilized in the org. phase as a hydrogenation catalyst. The photogenerated bipyridinium radical cations undergo induced disproportionation in the water-oil two-phase system, and the 2-electron charge relay CnV: is the active photoproduct that charges the metal colloid and generates metal-bound H atoms that are active in the hydrogenation of the substrate. The Pt and Pd colloids differ in their effectiveness in the generation of metal-bound H atoms. While Pt is a superior catalyst in this function, Pd is superior to Pt in the activation of the substrate toward hydrogenation. Use of a mixt. of Pt and Pd colloids in a water-oil 2-phase system shows a synergetic catalytic activity in the photohydrogenation of the acetylenic substrates. [on SciFinder(R)]


CAPLUS AN 1987:415340(Journal)