Remote Tricarbonyl(diene)iron Substituent Effect on Ester Heterolysis. The Solvolyses of 5,6,7,8‐Tetramethylidenebicyclo[2.2.2]oct‐2‐yl Methanesulfonate and of its Tricarbonyliron Mono‐ and Dinuclear Complexes

Abstract

Buffered acetolyses and hydrolyses of 5,6,7,8-tetramethylidenebicyclo[2.2.2]oct-2-yl methanesulfonate (17), of its 'syn-endo' (18), 'syn-exo' (19), hnti-endo' (20), 'anti-exo' (21) tricarbonyhon complexes and of its hntiexo, syn-endo' (22) and 'anti-endo, syn-exo' (23) bis(tricarbony1iron) dinuclear complexes have been investigated (product analysis and kinetics). In contrast with the solvolyses of the uncomplcxed mesylate 17, the solvolyses of the complexed esters can be highly chemo-and stereoselective. The nature of the products (non-rearranged bicyclo[2.2.2]oct-2-yl us. rearranged bicyclo[3.2.l]oct-2-yl derivatives) depends on the relative configuration of the tricarbonyl(diene)iron moieties and on the medium. The rates of solvolyses of 17 are only slightly affected by complexation of one or both s-cis-butadiene units with Fe(CO), groups, except in the cases where the diene moiety 'anti' with respect to the mcsylate is complexed onto its 'endo' face (20,23). In these cases, significant rate-retardation effects are observed, consistent with the inductive effect of the Fe(CO), substituent. Such retardation effects are overwhelmed by competing accelerating homoallylic participation by uncoordinated 'anti'-diene moieties (18, 19) or. as in the case of the 'anti-exo'-Fe(CO)3 complexes 21 and 22, by possible direct metal participation to the ionization process.