Synthesis and chemistry of diphenyl-2-pyridylphosphine complexes of palladium(0). X-Ray characterisation of Pd(Ph2Ppy)2(η2-DMAD) and trans-Pd(Ph2Ppy)2(PhCCH2)(CF3CO2)

Abstract

The zerovalent complexes Pd(Ph₂Ppy)₃1 and Pd(Ph₂Ppy)₂(dba) 2, where Ph₂Ppy is diphenyl-2-pyridylphosphine and dba = trans,trans-dibenzylideneacetone, have been synthesized and characterised. Reactions of 1 with alkynes have been studied and the dimethyl acetylenedicarboxylate complex Pd(Ph₂Ppy)₂(η²-DMAD) 3, where DMAD is dimethyl acetylenedicarboxylate, isolated and structurally characterised. The complexes trans-Pd(Ph₂Ppy)₂(PhCCH₂)X, X = CF₃CO₂⁻4 or Cl⁻5, and trans-Pd(Ph₂Ppy)₂{CO(CH₃)CCH₂}Cl 6 result from oxidative addition of phenylacetylene/CF₃CO₂H, phenylacetylene/Et₃NHCl and methacryloyl chloride respectively to 1, and the crystal structure of 4 is presented. The alkenyl ligand is bound to palladium through the α carbon in 4. Insertions into the M–C bond of the vinyl complexes have been studied. No isolable insertion product is obtained with carbon monoxide although the complex is active for the catalytic alkoxycarbonylation of phenylacetylene to 2-phenylpropenoate. Propadiene inserts into the Pd–C bond in 4 to give the cationic π-allyl complex [Pd(Ph₂Ppy)₂{η³-C₃H₄C(Ph)CH₂}][CF₃CO₂] 7. The complex Pd(Ph₂Ppy)₃ is found to catalyse the vinylation of Ph₂Ppy to the corresponding 2-propenylphosphonium trifluoromethanesulfonate.