UC San Diego

Herein we report the synthesis and characterization of transition metal complexes with modified 2,2'-bipyridines. Bipyridines with different substitutions at the 4,4' and 6, 6' position were synthesized and their complexes with several transition metals were investigated to elucidate the electronics and steric requirements for the electrochemical reduction of CO₂ to CO. The synthesis of tripbipy (6,6'-(2,4,6-triisopropylphenyl)-2,2'-bipyridine), a new substituted bipyridine ligand, and the syntheses, structures, and magnetic properties of the first coordination compounds based on this ligand are described. Reported here are the tripbipy complexes of five late first row transition metal chlorides (MCl₂; M = Fe, Co, Ni , Cu, Zn). All MCl₂tripbipy complexes are four coordinate and contain a distorted tetrahedral metal center. The synthesis and X-ray crystallographic characterization of several reduced complexes from the chemical reduction of Re(tripbipy)(CO)₃Cl are reported. The one-electron reduction of this complex results in the loss of the halide to form the neutral 5-coordinate complex. The two- electron reduction of the starting material with KC₈ results in the loss of the halide, and reduction of the bipyridine ligand. Bond alternation can be seen in the XRD as well as the DFT calculations using ADF 2007.1. We report a series of complexes synthesized from the chemical reduction of the fac-tricarbonyl complex Re(bpy)(CO)₃Cl. Reduction of the parent complex with one equivalent of KC₈ results in the formation of the dimer [Re(bpy)(CO)₃]₂. The one-electron reduction of this dimer does not result in cleavage of the metal-metal bond, but leads to the formation of the anionic dimer [Re(bpy)(CO₃]₂⁻. The reduction of the parent compound with 2.1 equivalents of KC₈ results in the formation of the anionic species Re(bpy)(CO)₃⁻, which has long been postulated as the active species that reacts with carbon dioxide in the electrochemical reduction of CO₂ to CO. Modification of the 6,6' position of 2,2'-bipyridine for the addition of proton relays to the electrocatalyst Re(bipy)(CO)₃Cl is reported. Synthesis and electrochemistry of Re(bipy- CH₂OH)(CO)₃Cl and Re(6,6'-dmb)(CO₃Cl (6,6'-dmb = 6,6'- dimethyl-2,2'-bipyridine) are reported. Addition of substituents at the 6,6' position inhibits catalysis when compared to the complexes with the functional groups at the 4,4' position