Reactions of co-ordinated ligands. Part 15. The cycloaddition of electronegatively substituted unsaturated systems to tricarbonyl(η-N-methoxycarbonyl-1H-azepine)-iron and -ruthenium and tricarbonyl(η-cyclohepta-2,4,6-trien-1-one)iron

Hexafluoroacetone, tetracyanoethylene, and 1,1 dicyano-2,2-bis(trifluoromethyl)ethyiene form exo-1,3 adducts with tricarbonyl(η-cyclohepta-2,4,6-trien-1-one)iron and tricarbonyl(η-N-methoxycarbonyl-1H-azepine)-iron and -ruthenium. A 1,6 adduct is also obtained with the azepineiron system. Deuteriation experiments show that the unco-ordinated double bond is the initial site of electrophilic attack. The 1,3-tetracyanoethylene adduct of the cycloheptatrienoneiron complex readily isomerises to a 1,5 adduct in solution. The generally accepted dipolar mechanism for these cycloaddition reactions is critically assessed and an alternative concerted reaction path is presented.