Intermolecular propargyl/allenyl group transfer from Pd(II) to Pt(0) and Pt(II) to Pd(0). Key reaction in metal-catalyzed isomerization between propargyl and allenyl metal complexes

Isomerization of phenyl-substituted propargylplatinum(II) complex, trans-Pt(CH2CCPh)(Cl)(PPh3)2 (1) to allenyl complex, trans-Pt(CPhCCH2)(Cl)(PPh3)2 (2) was found to be catalyzed by zerovalent complex Pd(PPh3)4. The reaction was proposed to proceed through the transfer of the propargyl/allenyl ligand both from Pt(II) to Pd(0) and Pd(II) to Pt(0). The former transfer, which seemingly has a thermodynamic disadvantage, has unambiguously been confirmed to take place; treatment of 1 with Pd(PPh3)4 or a mixture of Pd2(dba)3 and PPh3 resulted in the formation of Pd(I) complex, Pd2(μ-PhCCCH2)(μ-Cl)(PPh3)2 which lies in equilibrium with a mixture of propargyl/allenylpalladium(II) and Pd(0) complexes.