Synthesis, characterization, and study of n-heterocyclic ligands for single and mixed metal coordination and photolysis.

摘要

The splitting of water may provide a long-term solution to our world's energy and CO2 issues. However, this requires an efficient photochemical oxidation/reduction of water to O2 and H2. Previous work on fac-Re(bpy)(CO)3H has indicated rhenium hydrides form H 2 gas and rhenium dimers when exposed to light. New 4,4'-substituted-fac-Re(bpy)(CO) 3H were synthesized and characterized via a two-step synthesis. Time resolved spectroscopy was employed to determine excited state lifetimes and to better understand the excited state dynamics of the rhenium complexes. These new complexes exhibited strong photo-induced absorption in the excited state and the excited state of the rhenium hydrides experienced quenching from triplet oxygen. Additionally, new photolysis experiments were performed to determine the role of triplet oxygen and water in the production of H 2 and a new mechanism for H2 production was proposed. Since the formation of the first stable carbene in 1991, Arduengo-type carbenes have been studied extensively as ligands for new metal complexes. Carbene complexes, such as N-heterocyclic metal carbenes, exhibit a range of interesting properties including catalytic transformations. Our work involves the synthesis and characterization of a fused phenanthroline-imidazole ring system allowing for not only coordination to the carbene site but also at the N,N' phenanthroline position. Time resolved spectroscopy revealed that the excited state features are dominated by the metal coordinated to the N,N' phenanthroline position.