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

Abstract

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.