Discrete Complexes of 3d Metals with Monodentate Bulky Alkoxide Ligands and Their Reactivity in Bond Activation and Bond Formation Reactions

Abstract

This review focuses on the design, synthesis, and reactivity of low-coordinate base transition metal complexes supported by bulky alkoxide ligands. The unique electronic features of alkoxide ligands result in strongly electrophilic character at the metal centers, which enhances reactivity of metal-bound substrates and facilitates their transformation. However, insufficiently bulky alkoxide ligands tend to form oligomeric and polymeric aggregates, thus circumventing well-defined reactivity at isolated metal centers. This review examines first the requirements for the attainment of mononuclear complexes in alkoxide ligand environments. Coordination chemistry of the most prominent alkoxide ligands [OCR3] is discussed, with particular emphasis on the impact of the R group on the nuclearity of the resulting complex and the number of alkoxide ligands bound to it. Next, the behavior of such complexes in group transfer chemistry and ensuing reactivity is examined. While several previously synthesized alkoxide ligands are discussed, the major focus of this review is on the recent chemistry of the “asymmetric” alkoxide ligands [OCtBu2Me] and [OCtBu2Ph] with the middle and late 3d metals.