Organomanganese compounds in organic synthesis

Abstract

This thesis describes the preparation and reactions of some cyclomanganated chalcones, dienones and aryl ketones. Investigation has previously been undertaken into the reaction of cyclomanganated chalcones and dienones with alkynes to give both pyranyl and cycloheptadienyl Mn(CO)₃ complexes. In the current study, the reaction was further investigated with a cyclomanganated dienone derived from a cyclic ketone which gave only the (pyranyl)Mn(CO)₃ complex (2-6) and not the cycloheptadienyl product as consistent with a mechanism previously proposed. Also extended in the current study was previous work involving the methylmanganese pentacarbonyl-mediated transformation of enynes to cyclopropanated bicyclic compounds and cyclopentanes bearing an exocyclic double bond. In the current study, benzylmanganese pentacarbonyl was used instead of methylmanganese pentacarbonyl under similar conditions. In the current study however, the type of product that formed in diethyl ether (3-4) was the one dominant in acetonitrile in the MeMn(CO)₅ study, and that formed in acetonitrile (3-5) was the dominant product type in diethyl ether (3-4). There was no apparent explanation for this reverse reactivity. Ferrocenyl pyrylium salts of the type 5-5 have been prepared using a new route to ferrocenyl pyrylium from cyclomanganated chalcones and ferrocenylethyne. UV-visible and electrochemical properties of the pyrylium salts have been investigated. The ferrocenyl pyrylium salt (5-5) was obtained by the oxidation of [2-ferrocenyl-4,6-diphenyl-ɳ₅]-pyranyltricarbonylmanganese (5-6). The crystal structure of 5-6 was also determined.