Theoretical study of carbon dioxide coordination in palladium complexes

Abstract

Activation of the relatively inert CO 2 molecule to form higher organic molecules has been a focus of research for many years. Therefore, the coordination of CO 2 to transition metal fragments is of considerable interest. The coordination of CO 2 to transition metals may involve η 1 -O, η 1 -C, or η 2 -C,O bonding. The η 1 -C, or η 2 -C,O coordination with both early and late transition metal complexes are known. The ancillary ligands on the metal can play a significant role in effecting coordination of CO 2 to the metal center. Here we report a theoretical study of coordination modes of carbon dioxide to palladium complexes. The theoretical geometry and energies of a series of phosphine-substituted palladium carbon dioxide complexes, (PR 3 ) 2 Pd(CO 2 ), were investigated. The phosphine ligands included PH 3 , PMe 3 , PCy 3 , PMe 2 Ph, PMePh 2 , PPh 3 , P(OCH 3 ) 3 , P (CH=CH 2 ) 3 , PF 3 , PCl 3 , and PBr 3 . The electron-rich (PR 3 ) 2 Pd fragments can act as Lewis bases towards the CO 2 molecule. We have examined the phosphine ligand influence on the electron density of the palladium center. In all cases the η 2 -C,O bonding mode was lowest in energy. The interaction between metal fragment and CO 2 frontier orbitals will be presented in order to provide an understanding of Pd-CO 2 bonding.