Transition metal catalyzed hydrogenation or reduction in water

This paper summarizes recent reports on (i) hydrogenation (including transfer hydrogenation by HCO2Na) of olefins or aldehydes in water, and (ii) reduction of aromatic nitro compounds with carbon monoxide and water by homogeneous transition metal catalysts. The discussion will be focused on the hydrogenation of alpha,beta-unsaturated aldehydes by ruthenium-sulfonated phosphine complexes that show remarkable chemoselectivity toward C=O bonds. The author also introduces selective reduction of aromatic nitro-groups by ruthenium or rhodium catalysts under CO/H2O conditions. These catalytic reactions are very important from both synthetic and industrial viewpoints, not only because the after-treatment of by-products can be simplified from the conventional methods, but also because the reaction also proceeds with high selectivity affording the desired products. (C) 1998 Elsevier Science B.V.