Chemistry of palladium phosphinite (PPh2(OR)) and phosphonite (P(OPh)2(OH)) complexes: catalytic activity in methoxycarbonylation and Heck coupling reactions

Abstract

The new phosphinite and phosphonite complexes (1–8) are very efficient catalysts for the methoxycarbonylation of iodobenzene and Heck cross-coupling of bromobenzene with butyl acrylate. High catalytic activity of these complexes can be explained by their in situ transformations during the reaction, stimulated by the presence of water, acid (HCl) or base (NEt₃). Hydrolysis of phosphinite palladium complexes of the form trans-PdCl₂[PPh₂(OR)]₂ (R = C₆F₅2, ^tBu 3, or O-menthyl 4) results in the formation of the dimeric complex [μ-ClPd(PPh₂OH)(PPh₂O)]₂5, which is deprotonated by NEt₃, producing a polymeric complex of formula [Pd(P(O)PPh₂)₂]_n8. The reverse reaction, protonolysis of 8 with HCl, leads back to 5 and the monomeric complex 5a. The phosphinite complex PdCl₂[PPh₂(OBu)]₂1 with a more lipophilic ligand, PPh₂(OBu), does not undergo hydrolysis under the same conditions. In the reaction of PdCl₂(cod) with P(OPh)₂(OH), the new dimer [μ-ClPd(P(OPh)₂OH)(P(OPh)₂O)]₂6 was obtained, whereas reaction of Pd(OAc)₂ with P(OPh)₂(OH) leads to the polymeric complex [Pd[P(O)(OPh)₂]₂]_n7. Protonolysis of 7 with HCl results in the formation of 6.