Copper(I) Complexes Containing PCP Ligand Catalyzed Hydrogenation of Carbon Dioxide to Formate under Ambient Conditions.

The five new copper(I) complexes [Cu(μ-Cl)(κ-PCP)] (), [Cu(μ-Br)(κ-PCP)] (), [Cu(μ-I)(κ-PCP)] (), [Cu(μ-CN)(κ-PCP)] (), and [Cu(μ-SCN)(κ-PCP)]·CHCl () bearing a 1,3-bis[(di--butylphosphino)methyl]benzene ligand were synthesized and characterized spectroscopically, and the molecular structures of , , and were determined by single-crystal X-ray diffraction techniques. Structural studies for and revealed their binuclear structures with Cu···Cu separations of 2.609(3) and 2.6359(19) Å, respectively. However, has a tetranuclear cubane structure with an 18-electron configuration at each copper without any metal-metal bonds. The two copper centers in and are bonded to one bridging PCP ligand in a κ-manner and two bridging (pseudo)halido ligands in a μ-bonding mode to generate a nonplanar Cu(μ-X) framework. The four copper centers in are at the vertices of a tetrahedron. Each copper center has pseudo-tetrahedral coordination provided by two bridging PCP ligands in a κ-manner and the four bridging thiocyanate groups in a μ-manner. These complexes were used as catalysts for the hydrogenation of CO to formate in the presence of DBU as a base to produce valuable energy-rich chemicals, and therefore it is a promising, safe, and simple strategy to conduct reactions under ambient pressure at room temperature. Among all of the five copper(I) complex based catalysts, displayed the best catalytic performance with turnover number (TON) values of 38-8700 in 12-48 h of reaction at 25-80 °C. The outstanding catalytic performance of [Cu(μ-I)(κ-PCP)] () makes it a potential candidate for realizing the large-scale production of formate by CO hydrogenation.