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

Oxidative coupling reaction between Ph2P-CH=CH2 and a series of imines PI I C(R)=N(R') [where R = H, D; R' = H, Ph, p-Me(C6H4), p-Cl(C6H4), p-MeO(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 palladiu m template. The coupling reactions initially adopted a [2+2] cycloaddition mechanism followed by the ring-opening pathway to generate the acyclic liga nds. The rate of these coupling reactions was affected by the electronic pr operties of the R' group on the imines. No coupling reaction was observed b etween Ph2P-CH=CH2 and p-CF3(C6H4)N=CPh(H), which contains a strong electro nic withdrawing group at the p-position. In all the product complexes the n itrogen donors from the imine and from the naphthylamine chelates are coord inated regiospecifically in the cis positions. Similarly the R substituent and the PPh2 moiety are invariably located in the cis positions on the newl y generated C=C bonds. The imino-phosphine chelates are stable in strong su lfuric acid, while the naphthylamine moiety in the template complexes is re moved chemoselectively in the presence of this acid. Upon the removal of th e naphthylamine chelate, the imino-phosphines could be liberated from palla dium by the treatment with aqueous cyanide. Except far HN=C-C(=CPhH)PPh2, w hich decomposed readily in aqueous solution, all the other Liberated imino- phosphines were obtained as air-stable low-melting solids.