SYNTHESIS OF THE 1ST CARBON-DIOXIDE COORDINATED PALLADIUM(0) COMPLEX, PD(ETA-2-CO2)(PMEPH2)2

A new palladium(0) complex, (eta2-carbon dioxide)bis(methyldiphenylphosphine)palladium(0) (Pd-(CO2)(PMePh2)2., 3), has been prepared by the reaction of PdEt2(PMePh2)2 (1) with methyl acrylate followed by treatment with CO2. The complex was characterized by means of H-1, C-13{H-1}, and P-31{H-1} NMR and IR spectroscopy and the chemical reactions. Spectroscopic evidence indicates that complex 3 has a side-on (eta2) coordination mode. Thermal decomposition of the solution of complex 3 caused cleavage of the Pd-coordinated CO2 to give CO and O=PMePh2, together with CO2. Hydrogenation of 3 yielded HCO2H. Catalytic conversion of H-2 and CO2 into formic acid was found to be promoted by PdCl2L2 (L = PMe3, PMePh2, PPh3).