Amphiphilic Polycarbonate Micellar Rhenium Catalysts for Efficient Photocatalytic CO₂ Reduction in Aqueous Media

Abstract

A triblock amphiphilic polymer derived from the copolymerization of CO2 and epoxides containing a bipyridine rhenium complex in its backbone is shown to effectively catalyze the visible‐light‐driven reduction of CO2 to CO. This polymer provides uniformly spherical micelles in aqueous solution, where the metal catalyst is sequestered in the hydrophobic portion of the nanostructured micelle. CO2 to CO reduction occurs in an efficient visible‐light‐driven process in aqueous media with turnover numbers up to 110 (>99 % selectivity) in the absence of a photosensitizer, which is a 37‐fold enhancement over the corresponding molecular rhenium catalyst in organic solvent. Notably, the amphiphilic polycarbonate micelle rhenium catalyst suppresses H2 generation, presumably by preventing deactivation of the active catalytic center by water.

Photocatalytic CO2 Conversion Using Metal-Containing Coordination Polymers and Networks: Recent Developments in Material Design and Mechanistic Details

“…The authors used triblock amphiphilic micelles which are able to self-assemble in water. The polycarbonate-based triblock polymeric micelles contained a rhenium complex in the backbone, namely Re(dcbpy) (dcbpy = 2,2′-bipyridine-5,5′-dicarboxylic acid), as a photocatalyst [ 42 ]. The material was synthesized by the copolymerization of CO 2 and epoxide, followed by subsequent thiol-ene click reactions according to a previous publication [ 43 ].…”

“…Only CO and H 2 were detected as products. CO selectivity was higher than 99% and the TON could be boosted to be 110, which is 37 times higher compared to the molecular Re catalyst in the organic solvent [ 42 ].…”

A Dicationic fac-Re(bpy)(CO)3Cl for CO2 Electroreduction at a Reduced Overpotential

“…Rhenium and manganese tricarbonyl catalysts with one bidentate ligand are useful platforms for probing new catalyst strategies or additives and for testing secondary coordination sphere effects. − Fundamental mechanisms of these species are well established, and the carbonyl ligands offer intense infrared spectroscopic features, which are sensitive to the environment and oxidation state, for probing reactivity. − Results are frequently challenging to predict, and a variety of outcomes have been observed by modifying the coordination sphere of [ fac -Re/Mn­(bpy)­(CO) 3 Cl/Br] with Brønsted acid/base sites, charged moieties, and sterically hindered environments. For example, Mn catalysts with pendent amine bases that work as proton relays produce formate with striking turnover rates, but Re catalysts of the same ligand are much slower and largely selective for CO .…”

Hydrophobic pockets built in polymer micelles enhance the reactivity of Cu2+ions

“…A hydrophobic pocket that envelops a hydrated substrate has been hypothesized to be a key characteristic of primeval enzymes. 34–37 Therefore, polymer micelles can improve the compatibility and solubility of apolar substrates to enhance reactivity and improve the selectivity of some reactions, such as Heck coupling in water. 38…”

“…A hydrophobic pocket that envelops a hydrated substrate has been hypothesized to be a key characteristic of primeval enzymes. [34][35][36][37] Therefore, polymer micelles can improve the compatibility and solubility of apolar substrates to enhance reactivity and improve the selectivity of some reactions, such as Heck coupling in water. 38 The core-shell structure of micelles is similar to the biological membranes that mediate the reaction equilibria and reactivity by confining active sites in the hydrophobic microenvironment.…”