Multinuclear Assemblies. We are targeting poly-metallic systems to mediate the multielectron activation of small molecules. Nature’s poly-metallic enzymes for multielectron catalysis inspire this approach. The targeted systems can directly impact energy concerns by unveiling more efficient small molecule activation catalysts (e.g., N₂ fixation). The catalytic activation and conversion of CO₂, CO, and NO_x could potentially convert these small molecule substrates from harmful greenhouse gases into viable C, N and O sources for synthesis. We will target poly-metallic molecules that utilize readily synthesized ligand architectures designed for pre-organized, poly-metallic reaction sites. The impetus for the design and preparation of these trimetallic systems lies in their potential to cooperatively bind small molecule substrates and mediate multielectron redox processes in a predictable manner.

Organometallics. Work by the Bergman and Wolczanski groups demonstrated that electrophilic Zr(IV) imido complexes could stoichiometrically activate C—H bonds. To develop this stoichiometric reaction into a catalytic process requires a catalyst that features a reactive metal imido/oxo fragment capable of C—H bond activation, while exhibiting the 2-electron redox reactivity typical of late transition metal systems. We are developing sterically encumbered multi-anionic ligand frameworks to facilitate isolation of reactive metal-ligand multiply bonded species in uncommonly low-coordination environments. The target high-valent, late transition metal complexes feature imido/oxo functionalities bound to highly electrophilic, coordinatively unsaturated metal centers. The hard-ligand/soft-metal mismatch may produce the same type of polarization and, ultimately, activation effect on C—H bonds exhibited by the early transition metal analogues. If C—H bond activation is realized, the system is well poised to reductively eliminate functionalized product and reform the reactive metal precursor.

Aerobic Oxidation. We are synthesizing binucleating ligands for the development of bio-inspired, aerobic alkane hydroxylase catalysis. The target diiron systems are based upon mononuclear iron complexes shown to be competent in binding and activating dioxygen. Upon dioxygen activation, the diiron core is architecturally predisposed to promote diamond core formation (pictured left), yielding diiron cores reminiscent of the reactive intermediates nature employs to oxidize methane to methanol (i.e., soluble methane monooxygenase). Ultimately, the proposed complexes will be canvassed for their efficacy for hydroxylation chemistry of C—H bonds using a variety of oxidants and alkane substrates.