Formation of imino-phosphine bidentate chelates by an unprecedented organopalladium complex promoted oxidative coupling reaction between diphenylvinylphosphine and imines

Abstract

Oxidative coupling reaction between Ph2P-CH=CH2 and a series of imines PhC(R)=N(R′) [where R = H, D; R′ = H, Ph, p-Me(C6H4), p-Cl(C6H4), p-Cl(C6H4)] in the presence of (S)-ortho-palladated[1-(dimethylamino)ethyl]naphthylene as the reaction template produced the unexpected imino-phosphine ligands (R′)N=C-C(=CPhR)PPh2 where the P,N-bidentate chelates to the chiral palladium template. The coupling reactions initially adopted a [2+2] cycloaddition mechanism followed by the ring-opening pathway to generate the acyclic ligands. The rate of these coupling reactions was affected by the electronic properties of the R' group on the imines. No coupling reaction was observed between Ph2P-CH=CH2 and p-CF3(C6H4)N=CPh(H), which contains a strong electronic withdrawing group at the p-position. In all the product complexes the nitrogen donors from the imine and from the naphthylamine chelates are coordinated regiospecifically in the cis positions. Similarly the R substituent and the PPh2 moiety are invariably located in the cis positions on the newly generated C=C bonds. The imino-phosphine chelates are stable in strong sulfuric acid, while the naphthylamine moiety in the template complexes is removed chemoselectively in the presence of this acid. Upon the removal of the naphthylamine chelate, the imino-phosphines could be liberated from palladium by the treatment with aqueous cyanide. Except for HN=C-C(=CPhH)PPh2, which decomposed readily in aqueous solution, all the other liberated imino-phosphines were obtained as air-stable low-melting solids. © 2000 American Chemical Society.