Scope of Anion Addition to (η⁴ -1,3-Cyciohexadiene)tricarbonyliron(0)

Reactive carbanions add to (η4-l,3-cyclohexadiene)tricarbonyliron(0) to produce intermediates that can be protonated to give 2- or 3-substituted cyclohexenes as the major products. Alkyllithium reagents react inefficiently, primarily by addition to a coordinated carbon monoxide to produce simple aldehydes along with ketones from addition to the diene ligand. Trapping of the intermediates with other electrophiles generally fails, with regeneration of the starting complex being the preferred pathway. However, benzoyl chloride was observed to react with the intermediate from trityl anion and (η4-l,3-cyclohexadiene)tricarbonyliron(O) to give a 1,4-disubstituted 2-cyclohexene. The regioselectivity of addition is not clear from the additions to the 1,3-cyclohexadiene ligand, but preliminary results concerning the addition of 2-lithio-2-methylpropionitrile to (η4-l,3-butadiene)tricarbonyliron(0) require that addition is preferred at C-2 of the 1,3-diene ligand.