Synthesis of the first carbon dioxide coordinated palladium(0) complex, Pd(η²-CO₂)(PMePh₂)₂

A new palladium(0) complex, (η²-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 ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR and IR spectroscopy and the chemical reactions. Spectroscopic evidence indicates that complex 3 has a side-on (η²) 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 H₂ and CO₂ into formic acid was found to be promoted by PdCl₂L₂ (L = PMe₃, PMePh₂, PPh₃).