Research Synopsis

Research in the Rohde Group involves the synthesis and investigation of reactive transition metal complexes that can be used for the activation of small and inert molecules, electron transfer, and atom/group transfer. These research efforts may contribute to the development of new synthetic methods that use energy and raw materials (e.g., hydrocarbons) more efficiently or utilize abundant and environmentally benign reagents (e.g., O₂, N₂O). Our ongoing projects are aimed at i) the stabilization and reactivity of late transition metals in high oxidation states, ii) the synthesis, structure and reactivity of redox-active ligand complexes, and iii) the activation of small molecules by metal-alkene complexes.

High-Oxidation State Complexes of Late Transition Metals. Complexes of late transition metals in high oxidation states are attractive synthetic targets, because they often are proposed as intermediates in C-H bond activation, oxygen atom transfer, and water oxidation chemistry. In our research, the use of strongly donating guanidinato ligands has led to the discovery of a new class of Ir^IV complexes. These complexes are sufficiently stable to be characterized by spectroscopic and crystallographic methods. Our current efforts are focused on the stabilization of other transition metals in high oxidation states as well as the reactivity of these complexes toward organic substrates. Also of interest is the reactivity of oxoiron(IV) complexes supported by multidentate nitrogen-donor ligands.

Complexes of Redox-Active Ligands. Due to their capacity to participate in the multielectron redox chemistry of a coordinated metal center, redox-active ligands can facilitate bond-forming and bond-breaking processes. Our research in this area is focused on the synthesis of ligand-radical complexes of Co and Ni, the elucidation of their molecular and electronic structure through spectroscopic and crystallographic studies, and their reactivity toward small molecules such as O₂.

Activation of Small Molecules by Metal-Alkene Complexes. One strategy for the use of small molecules, such as O₂ and S₈, for the functionalization of substrates involves their activation by complexes of low-valent transition metals. For example, Ir^I(alkene) complexes supported by monoanionic guanidinato or amidinato ligands react with O₂ to oxygenate the coordinated alkene substrate via (alkene)peroxoiridium(III) intermediates. We investigate the mechanisms of such reactions and the properties of intermediates with the goal of developing stoichiometric and catalytic cycles of small-molecule activation and atom transfer.