The results of nanosecond laser flash photolysis (XeCl excimer irradiation at 308 nm) of the Fischer carbene complex [(CO) 5 WdC(OMe)Ph] (C Z ) in di-n-butyl ether and n-hexane are reported. Spectrokinetical detection of the intermediates was based on transient absorptions simulaneously recorded in the UV/vis and the IR spectral regions. The primary photoproducts are the unstable isomer C E produced with a quantum yield of about 30% and a tetracarbonyl complex I-S, probably of structure [(CO) 4 (S)WdC(OMe)Ph], where S is a solvent molecule. The quantum yield of CO photoelimination was estimated as 1.7%. The C E isomer was found to return to the stable C Z isomer within a few microseconds, confirming previous results of McGarvey and co-workers. The tetracarbonyl species reacts with cosolutes present in the solution such as N 2 , H 2 O, acetonitrile, and methyl trans-crotonate to form secondary complexes of cis-tetracarbonyl complex structure [(CO) 4 (L)WdC(OMe)Ph] (I-L). The tetracarbonyl complexes react readily with CO. For I-N 2 in n-hexane the rate constant is 3.5 × 10 8 M -1 s -1 . The rate constants of the corresponding reactions with acetonitrile (MeCN) and the olefin are larger by a factor of 2. In the presence of CO the complexes I-MeCN and I-olefin revert to C Z in a dissociative reaction mechanism. The rate constants for the elimination of MeCN or olefin are 5 and 10 5 s -1 , respectively. The I-olefin complex irreversibly decomposes with a rate constant of 8 × 10 3 s -1 .

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