Spin Crossover and Its Application in Organometallic Catalysis: Concepts and Recent Progress.

Spin crossover is one of the most important properties of open-shell metal complexes. In organometallic catalytic reactions, catalysts can alter reaction kinetics by spin crossover, i. e., accelerating or hindering the reaction progression, as well as altering reaction pathways, modulating the reaction selectivity or promoting new reactions. This personal account outlines the introduction and development of important concepts such as "two-state reactivity" involving spin crossover, and proposes a new concept, "spin-responsive catalysis" to summarize the catalytic processes in which spin effects are present. Finally, the electronic mechanism of spin crossover accelerating the reaction and the role of spin crossover in changing the reaction path and regulating the reaction selectivity are introduced by taking two recent typical iron-catalyzed reactions recently reported by our group as examples.