Reactions of Ferrocenyldiphenylphosphine. Effects of the Ferrocenyl Group at Phosphorus on the Course of Decomposition of Phosphonium Betaines and Vinylphosphonium Salts

The reaction of ferrocenyldiphenylphosphine with styrene oxide in ethanol gives, as the major product, ferrocenyl(phenyl)(l,2-diphenylethyl)phosphine oxide (5, R = Ph), the result of a rearrangement involving phenyl migration from phosphorus to adjacent carbon in the decomposition of a vinylphosphonium ion arising from protonation and subsequent elimination of water from the initially-formed phosphonium betaine. A related phenyl migration occurs in the reaction of the phosphine with ethyl propiolate in wet THF. The presence of a ferrocenyl group at phosphorus in Wittig reactions of semistabilised ylides causes the expected decrease in the cis-trans ratio of the resulting alkenes, consistent with its behaviour as an electron-donating substituent.