Rhenium complex photochemical oxidation

Rhenium is an element known for its abundance of metal hydride complexes spanning a variety of oxidation states, for example, from Re(I), Re(CO)sH to Re(VII), ReH92 . However, despite the recent interest in light-driven H2 formation from different substrates (such as water) there are few recent photochemical studies of Re hydride complexes. 

Attention turned to the dinuclear carbonyls Mn2(CO)io, Re2(CO)io, and Co2(CO)g. Regarding mechanistic information, the study of Re2(CO)io has been the most fruitful. Here two distinct oxocarbonyl species, which appear to contain only one rhenium atom each, are formed. The final product of the reaction is the O-bridged oxide Re207. In a similar vein, Mn2(CO)io yields Mu207 upon matrix photooxidation, although there is no hint of any intermediate in this process, no matter what steps are taken to produce such species. The photooxidation of C02 (CO)g is likely to follow a pathway even more complex than that of Mn2(CO)io or Re2(CO)io- In this case not only is there competition between M-C and M-M bond ruptme as the primary photochemical step, but there is also the complication of photoisomerism of the molecule. 

Complexes of osmium, platinum, rhenium, copper, iron, and iridium able to be used as sensitizers have been reported [33, 34]. The osmium complex (Fig. 38.3a) [26, 27] was synthesized and characterized and it was found that its IPCE values were lower than those of the Ru complexes [26]. Osmium complexes (Fig. 38.2a) used as sensitizers were found to be 50% less efficient than Ru complexes. However, osmium complexes have greater photochemical stability compared to the black dye [27, 34]. The osmium complex in CH3OH showed a reversible Os Os oxidation process that extended the spectral response of Ti02 photoanodes [26, 27, 34]. 

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