PHOTOLYTIC BEHAVIOR OF RICARBONYL[(1,2,5,6-ETA))-CYCLOOCTA-1,5-DIENELIRON IN SOLUTION AND LOW-TEMPERATURE MATRICES

The photo-induced isomerization of Fe(CO)(3)[(1,2,5,6-eta)-1,5-COD] (1 ) yields Fe(CO)(3)[(1,2,3,4-eta)-1,3-COD] (2) with a quantum yield of phi 0.04 +/- 0.005 (lambda(exc) 405 nm). Photolysis of 1 in low-temper ature matrices generates the fragment Fe(CO)(2)[(1,2,5,6-eta)-1,5-COD] (3) as the only primary photoproduct observed by conventional IR spec troscopy. The species 3 is also produced upon laser-flash photolysis ( lambda(exc) 308 nm) of 1 in solution at ambient temperature, as detect ed by time-resolved IR spectroscopy. Accordingly, (CO)-C-12/(CO)-C-13 exchange occurs upon photolysis of 1 in the presence of (CO)-C-13. How ever, the isomerized complex 2 is initially formed without (CO)-C-13 i ncorporation, thus discounting the possible involvement of the dicarbo nyl fragment 3 in this process. It is concluded that photolytic genera tion of the de-chelated species Fe(CO)(3)[(1,2-eta)-1,5-COD] (4) is th e initial step in the photo-induced isomerization of 1 to 2.