Dienophile cycloaddition to cycloheptatriene and related complexes of tricarbonyliron. X-Ray crystal structures of [Fe(CO)3(η4-C7H7CN)]·C2(CN)4 and [ Fe(CO)3(η4-C7H7–C7H7)]

Abstract

The rate of tetracyanoethene (tcne) addition to tricarbonyliron complexes of some substituted azepines and 1-cyanocycloheptatriene have been measured. Experimental support for a concerted mechanism for the cycloaddition of tcne to tricarbonyl(η⁴-cycloheptatriene) iron is provided by the high dienophile dependence of the observed reaction rate on chaning from tcne to tricyanoethene. Frontier orbital theory successfully predicts that 1,3-addition is the reaction mode favoured for cycladdition of tcne to a range of cyclic triene complexes of tricarbonyliron.