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(PhC=CH2)(CF3CO2)

The zerovalent complexes Pd(Ph(2)Ppy)(3) 1 and Pd(Ph(2)Ppy)(2)(dba) 2, where Ph(2)Ppy 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(Ph(2)Ppy)(2)(eta(2)-DMAD) 3, where DMAD is dimethyl acetylenedicarboxylate, isolated and structurally characterised. The complexes trans-Pd(Ph(2)Ppy)(2)(PhC=CH2)X, X=CF3CO2- 4 or Cl- 5, and trans-Pd(Ph(2)Ppy)(2){CO(CH3)C=CH2}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 alpha 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 pi-allyl complex [Pd(Ph(2)Ppy)(2){eta(3)-C3H4C(Ph)=CH2}][CF3CO2] 7. The complex Pd(Ph(2)Ppy)(3) is found to catalyse the vinylation of Ph(2)Ppy to the corresponding 2-propenylphosphonium trifluoromethanesulfonate.