Search for: All records

ABSTRACT: We review in this Viewpoint recent progress on the development of a new class of sustainable electrocatalytic systems for water-splitting and molecular hydrogen generation using diiron disulfide ([2Fe-2S]) active site methacrylate metallopolymers. To date, noble metal catalysts (e.g, platinum) remain the best electrocatalysts for molecular hydrogen generation using water as the chemical feedstock and proton donor. However, there remains a need for the synthesis of efficient electrocatalytic systems using low cost, earth abundant materials for sustainable H2 generation. We focus on our recent work in this area using well-defined single site [2Fe-2S]-metallopolymer catalysts. Thus far, these systems have demonstrated rates of hydrogen production >25 times faster than [FeFe]-hydrogenase enzymes and match the current densities of platinum with only 0.2 V higher potential when operating in water at neutral pH with tris(hydroxymethyl)aminoethane (TRIS) buffer (Faradaic yields 100±3%). The molecular design and synthesis of [2Fe-2S]-metallopolymers are reviewed along with mechanistic studies unraveling the causality of efficient H2 production from this catalytic system. The overall current output and overpotential are improved by (a) the reversible electrostatic adsorption of the metallopolymer on the carbon electrode surface that enhances the proton and electron transfer rates and (b) the use of protic buffer electrolytes (PBEs) that enhance the availability of protons. The schemes summarized here to improve the performance of [2Fe-2S] catalysts by incorporation into metallopolymers may be used to enhance the performance of other molecular electrocatalysts at the electrode surface. 

ABSTRACT: The diverse functionalization of the polymeric support phase of diiron disulfide[2Fe–2S] metallopolymer elec-trocatalysts offers a route to enhanced generation of molecular hydrogen production via water-splitting. Click chemistry has been shown to be a useful tool in post-polymerization functionalization for a wide range of polymeric materials under mild conditions which is a requirement for [2Fe-2S] metallopolymers due to the presence of iron carbonyl (Fe-CO) bonds in the active site. In this study, we developed a new synthetic methodology to functionalize [2Fe–2S] metallopolymers using atom transfer radical polymerization (ATRP) and post-polymerization functionalization using azide-alkyne “click” cycloaddition. Azide functional [2Fe–2S] metallopolymers were prepared by the ATRP of 3-azidopropyl methacrylate (AzPMA) with either methyl methacrylate (MMA), or 2-(dimethylamino)ethyl methacrylate (DMAEMA), followed by copper-catalyzed “click” cycloaddition with functional terminal alkynes. Both families of PMMA and PDMAEMA functional [2Fe–2S] metallo-co-polymers were found to be retain Fe-CO bonds from the catalyst active site after the click chemistry reactions, and more importantly, exhibited high electrocatalytic activity for electrochemical water-splitting under pH neutral aqueous conditions.Not Available 

Organocatalyzed ring-opening polymerization is a powerful tool for the synthesis of a variety of functional readily degradable polyesters and polycarbonates. We report the use of (thio)ureas in combination with cyclopropenimine bases as unique catalyst for the polymerization of cyclic esters and carbonates with a large span of reactivities. Methodologies of exceptionally effective and selective cocatalyst combinations were devised to produce polyesters and polycarbonates with narrow dispersity (Đ = 1.01 – 1.10). Correlations of the pKa of the various ureas and cyclopropenimine bases revealed the critical importance of matching the pKa of the two cocatalysts to achieve the most efficient polymerization conditions. It was found that promoting strong H-bonding interactions with a noncompetitive organic solvent, such as CH2Cl2, enabled greatly accelerated polymerization rates. The stereoselective polymerization of rac-lactide afforded stereoblock poly(lactides) that crystallize as stereocomplexes, as confirmed by wide-angle x-ray scattering.