Synthesis and characterization of neutral and cationic organopalladium complexes containing an imidazolylphosphine P,N-ligand and their carbonylation reactions

Abstract

Several new neutral and cationic organopalladium complexes containing a P–N chelating ligand, 2-(diisopropylphosphinomethyl)-1-methylimidazole, have been synthesized and characterized. The neutral complexes [PdPh(I)(P–N)] 1 and [PdMe(I)(P–N)] 2 have been synthesized by oxidative addition of PhI and MeI, respectively to Pd(dba)₂ (dba = dibenzylideneacetone) in the presence of the P–N ligand. The cationic complexes [PdPh(PPh₃)(P–N)]BF₄ 3 and [PdMe(PPh₃)(P–N)]BF₄ 4 were obtained by adding an acetone solution of AgBF₄/PPh₃ to the corresponding neutral precursors 1 and 2, respectively. A cationic allyl complex, [Pd(η³-C₃H₅)(P–N)]Br 5, has also been prepared by oxidative addition of 3-bromopropene to Pd(dba)₂ in presence of the P–N ligand. Single crystal structure determinations have been carried out for 1, 4 and 5. Carbonylation of the metal–carbon bond in these new complexes was also studied. The neutral complexes 1 and 2 react smoothly with CO to give carbonylated products [Pd(C(O)Ph)I(P–N)] 6 and [Pd(C(O)Me)I(P–N)] 7, respectively. The methyl complex 2 reacted much faster than the phenyl complex 1. The cationic complexes 3 and 4 are inert and do not give any carbonylated product. However, in the case of the reaction of 3, evidence has been obtained for the formation of a CO-coordinated complex [PdPh(PPh₃)(CO)(P–N)]BF₄ 8 in which the P–N ligand temporarily acts as a monodentate phosphorus-bonded ligand. On the other hand, a cationic complex containing a weakly coordinating acetone molecule, [PdMe{(CD₃)₂CO}(P–N)]BF₄ 9, showed an enhanced reactivity toward CO and gave [Pd{MeC(O)}(CO)(P–N)]BF₄ 10.