The substituent effect of the phosphaalkenyl group

Article abstract of DOI:10.1002/ejoc.200200618

Several novel phosphaalkenes (E)-Mes*P=CHC₆H₄X (6; X = Me₃Si, Me₃Sn, CHO, COOH, CN) were prepared and, together with other known members of this series, subjected to an analysis of linear free-energy relationships based on the values of pK_a and values of δ(¹³C_para) of substituted benzoic acids and on the values of δ(¹³C_para) of substituted bromobenzenes. These analyses indicate that the (E)-es*P=CH group is a weak electron donor with a predominantly inductive effect (δp = -0.1) on a neighboring benzene ring; resonance interactions are of minor importance. This result shows that the P=C bond is surprisingly analogous to the C=C bond, and thus confirms the well-known diagonal relationship in the Periodic System between carbon and phosphorus atoms. The relationship between X and the values of δ(³¹P) of 6 is quite pronounced. It confirms the dominance of inductive interactions on the value of δ(³¹P); only with strongly electron-donating substituents may a certain degree of resonance interaction be involved. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.