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

Buffered acetolyses and hydrolyses of 5,6,7,8-tetramethylidenbicyclo2.2.2]oct-2-yl methanesulfonate ( 17 ), of its ‘syn-endo’ ( 18 ), ‘syn-exo’ ( 19 ), ‘anti-endo’ ( 20 ), ‘anti-exo’ ( 21 ) tricarbonyliron complexes and of its ‘anti-exo,syn-endo’ ( 22 ) and ‘anti-endo,syn-exo’ ( 23 ) bis(tricarbonyliron) dinuclear complexes have been investigated (product analysis and kinetics). In contract with the solvolyses of the uncomplexed mesylate 17 , the solvolyses of the complexed esters can be highly chemo- and stereoselective. The nature of the products (non-rearranged bicyclo2.2.2]oct-2yl vs. rearranged bicyclo3.2.1]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)₃ groups, except in the cases where the diene moiety ‘anti’ with respect to the mesylate 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)₃ 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.