Metal ligand cooperativity is an essential strategy for both synthetic and biological systems that incorporate transition metals. Inspired by the oxidative reactivity of heme enzymes in biological systems and the wide range of cobalt-porphyrins used in synthetic oxidative chemistry, we have developed a cobalt complex that utilizes a similarly non-innocent ligand scaffold with pyrrole donors with the additional functionality of storing a full equivalent of dihydrogen. This cobalt compound with the redox-active ligand tBu,TolDHP (tBu,TolDHP = 2,5-bis((2-t-butylhydrazono)(p-tolyl)methyl)-pyrrole) has a cobalt(III) center coupled to a ligand-based radical (for a S= ½ compound) and displays a wide range of five electrochemically and synthetically accessible oxidation states.This cobalt compound has demonstrated potential as a catalyst for both reductive and oxidative reactivity. It enables the facile, high-yielding transfer of dihydrogen to olefin substrates under mild conditions and at room temperature, as well as being able to oxidatively couple amines with catalytic amounts of dioxygen. Preliminary studies indicate that both types of reactivity is enabled by reversible storage of hydrogen on the dihydrazonopyrrole ligand. This discovery demonstrates a new paradigm which could potentially enable synthesis to bypass the use of hazardous, pre-activated reagents and suggests that cooperativity between metals and ligands that can store hydrogen is a powerful strategy for any kind of catalysis that requires the addition or removal of hydrogen.

Reductive and oxidative reactivity via ligand-based non-innocence in a redox series of cobalt complexes

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.