When using weak-field supporting ligands, organometallic complexes of first-row 'base' transition metals may be high-spin and paramagnetic. Paramagnetic species in organometallic chemistry are often viewed as ill-behaved because of broadened and shifted ?1?H NMR resonances, and because of the conventional wisdom that radical reactions will degrade selectivity and/or lifetime of catalysts. However, recent successes in organometallic chemistry using iron and cobalt precatalysts suggest that high-spin species can indeed mediate effective catalytic reactions. This presentation describes our studies on high-spin organometallic complexes of iron and cobalt, which have elucidated the structures, thermodynamics, and kinetics of key organometallic transformations. Quantum chemical calculations show how formally spin-forbidden reactions of high-spin complexes can occur, and the results give insight into the important roles of spin-state energetics and metal geometry. These in turn are closely tied to ligand design. Examples of catalytic reactions show that attention to these principles can give unprecedented selectivity.

Challenges and opportunities in high-spin organometallic complexes of iron and cobalt

246th National Meeting (2013)

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