Annulation with and without co-insertion: striking a balance in reactivity of chromium carbene complexes with chalcogen-stabilized iron cluster appendage

Two new sets of products [(CO)6Fe2EE'{μ-indanone}] (2a: E, E'=Se; 2b: E=S, E'=Se) and [(CO)6Fe2EE'{μ-(2-ethoxy, a-naphthol)}] (3a: E, E'=Se; 3b: E=S, E'=Se; 3c: E=S, E'=Te) have been isolated from the thermolysis of the cluster-bound Fischer carbene complex, [(CO)6Fe2EE'{μ-C(Ph)=C-C(OEt)=Cr(CO)5}], 1a-c (1a: E, E'=Se; 1b: E=S, E'=Se; 1c: E=S, E'=Te) in THF. The products are formed by annulation pathway with and without the intermediacy of CO insertion step, from the same substrate. They have been characterized by IR and 1H, 13C, 77Se and 125Te NMR spectroscopy and the structural types were unequivocally established by crystallographic analysis of compounds 2a and 3c