Palladium complexes with a tridentate PNO ligand. Synthesis of eta(1)-allyl complexes and cross-coupling reactions promoted by boron compounds

The iminophosphine 2-(2-Ph2P)C6H4N=CHC6H4OH (P-N-OH) reacts with [Pd(mu-Cl)(eta(3)-C3H5)](2) yielding [PdCl(P-N-O)] and propene. In the presence of NEt3, the reaction of P-N-OH with [Pd(mu-Cl)(eta(3)-1-R-1,3-(RC3H3)-C-2)](2) (R-1 = R-2 = H, Ph; R-1 = H, R-2 = Ph) affords the eta(1)-allyl derivatives [Pd(eta(1)-1-R-1,3-(RC3H3)-C-2)](P-N-O)] (R-1 = R-2 = H: 1; R-1 = H, R-2 = Ph: 2; R-1 = R-2 = Ph: 3). In solution, the complexes 1 and 3 undergo a slow dynamic process which interconverts the bonding site of the allyl ligand. The X-ray structural analysis of 1 indicates a square-planar coordination geometry around the palladium centre with a P, N, O,-tridentate ligand and a sigma bonded allyl group. The complexes [PdR(P-N-O)] (R = C6H4Me-4, C CPh) react slowly with p-bromoanisole in the presence of p-tolylboronic acid to give [PdBr(P-N-O)] and the coupling product RC6H4OMe-4. The latter reactions also proceed at a low rate under catalytic conditions. The coupling of allyl bromide with p-tolylboronic acid is catalyzed by [PdCl(P-N-O)]/K2CO3 to give 4-allyltoluene.