Palladium complexes with a tridentate PNO ligand. Synthesis of η1-allyl complexes and cross-coupling reactions promoted by boron compounds.

The iminophosphine 2-(2-Ph2P)C6H4N=CHC6H4OH (P-N-OH) reacts with [Pd(m-Cl)(h3 -C3H5)]2 yielding [PdCl(P-N-O)] and propene. In the presence of NEt3, the reaction of P-N-OH with [Pd(m-Cl)(h3-1-R1,3-R2C3H3)]2 (R1 = R2 = H, Ph; R1 = H, R2 = Ph) affords the h1-allyl derivatives [Pd(h1-1-R1,3-R2C3H3)](P-N-O)] (R1 = R2 = H: 1; R1 = H, R2 = Ph: 2; R1 = R2 = 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 s 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.