Visible-light promoted bimetallic catalysis

Visible-light promoted molecular transformations catalyzed by bimetallic species containing a [Ru(bipy)(3)](2+) (TB)-like fragment as the photosensitizing unit are reviewed. Catalytic reactions are classified according to the following two criteria: (1) electron transfer (A)/energy transfer (B) from TB and (2) intra- (I) and inter-molecular catalyst systems (II). Reactions promoted by electron transfer (A) involve reductive processes such as W-reduction giving H-2 and CO2-reduction giving CO, which have been extensively studied also by using mononuclear catalysts. The catalytic H+- and CO2-reductions have been considerably improved by the use of II-A- and I-A-type bimetallic catalysts, respectively. Furthermore, as recently reported by our research group, photocatalysis is extended to organic transformations, which have been much less explored compared to transformations of small inorganic molecules mentioned above. While Sonogashira coupling is mediated by II-A-type catalysts, up-hill trans-to-cis isomerization of cyanostilbene and dimerization of alpha-methylstyrene follow the energy transfer processes (B). Thus new aspects of the photochemical bimetallic catalysis have been unveiled as mentioned above but catalyst design is still in its infancy. Continued accumulation of reaction data and mechanism analysis will lead to development of practical bimetallic photocatalysts, which promote unique reactions including up-hill reactions. (C) 2009 Elsevier B.V. All rights reserved.