Photogeneration of Very Active Homogeneous Catalysts Using Laser Light Excitation of Iron Carbonyl Precursors.

Abstract : To summarize our main findings, we conclude that photolysis of Fe(CO)5 or Fe3(CO)12 yeidls an exceedingly active catalyst. The active catalyst is likely not an excited state species since the excited lifetimes of Fe(CO)5 or Fe3(CO)12 are too short to effect catalysis. The active species is likely an unsaturated ground state species photoproduced by loss of CO from Fe(CO)5 or Fe-Fe bond cleavage in Fe3(CO)12. Very high turnover rates for alkene isomerization and hydrosilation have been found. Moreover, very high turnover numbers (moles of product per mole of Fe initially present) are achieved. For example, when a single flash yields approximately 50% conversion of neat 1-pentene using approximately .01 m Fe(CO)5 the turnover number exceeds 400. Subsequent flashes yield an even greater extent conversion to ultimately completely equilibrate the linear pentenes. High light intensity does not appear to alter the product distribution where a number of products are possible (alkene + HSiEt3). The data show that very high light intensity can be used to produce product at a high observed rate and with high quantum efficiency (much greater than 1). (Author)