KINETICS OF NUCLEOPHILIC ATTACK ON COORDINATED ORGANIC MOIETIES. XX. NOVEL ANCHIMERIC ASSISTANCE IN THE ADDITION OF ARYL PHOSPHINES TO +

Article abstract of DOI:10.1016/S0022-328X(00)87441-0

Kinetic studies in acetone solvent of the addition of triarylphosphines, (XC6H4)3P, to the dienyl ring of ⁺ (I) reveal the following rate variation with X: 2-MeO > 4-MeO > 4-Me > H >> 2-Me (relative rates 90/9/4/1/10^-3).The unexpectedly rapid reaction with (2-MeOC6H4)3P is rationalised in terms of stabilization of the transition state via an anchimeric effect involving overlap between the filled 2p orbital of the 2-MeO oxygen and the empty phosphorus 3d orbital.This anchimeric effect, quantified by the k(2-MeO)/k(H) ratio of 91, is considerably larger than that previously observed for addition of arylphosphines to benzyl chloride, suggesting a greater degree of phosphorus-carbon bond formation in the transition state for attack on (I).