Multiple spin-state scenarios in organometallic reactivity

This chapter gives an overview of the different spin-state crossing scenarios affecting the reactivity of organometallic compounds. It focuses on the effects of crossing spin states in a number of elementary reactions typically observed for organometallic compounds, such as ligand exchange, oxidative addition, reductive elimination, migration/insertion, β-hydride elimination, C-H bond activation and intramolecular electron transfer between a transition metal and a coordinated redox active ligand. These processes are highly relevant for catalysis. To address the influence of the spin-crossing on the reaction rate, Schroder et al. introduced the two-state reactivity (TSR) concept, which applies if the overall kinetics for product formation results from an interplay between the barriers for the spin-inversion and the barriers on the high- and low-spin surfaces. The chapter discusses examples of homogeneous first-row transition metal systems that catalyze (cyclo)oligomerization reactions of alkynes and alkenes, and which undergo a spin-crossing during the catalytic turnover.