Stable carbonium ions. Part II. The properties of 1-ferrocenyl-3-arylallyl cations

Abstract

Mixed hydride reduction of a series of substituted cinnamoylferrocenes affords the corresponding arylallylferrocenes together with dimeric products. The former undergo hydride abstraction with triphenylmethyl tetrafluoroborate providing a series of stable 1-ferrocenyl-3-arylallyl cations which have been characterised spectroscopically. By analysis of the mixture of products formed from these cations by reaction with methoxide, an estimate of the distribution of positive charge to the terminal allylic carbon atoms has been obtained. The position adjacent to the ferrocenyl group is the more electrophilic in all of the systems studied. Charge concentration at the benzylic position increases only slightly as the electron-releasing capacity of the aryl group is increased. The ¹H n.m.r. and electronic spectral characteristics of the cations are discussed.