Carbon–Carbon Bond Formation in a Weak Ligand Field: Leveraging Open-Shell First-Row Transition-Metal Catalysts

Unique features of earth-abundant transition-metal catalysts are reviewed in the context of catalytic carbon–carbon bond-forming reactions. Aryl-substituted bis(imino)pyridine iron and cobalt dihalide compounds, when activated with alkyl aluminum reagents, form highly active catalysts for the polymerization of ethylene. Open-shell iron and cobalt alkyl complexes have been synthesized that serve as single-component olefin polymerization catalysts. Reduced bis(imino)pyridine iron and cobalt dinitrogen compounds have also been discovered that promote the unique [2+2] cycloaddition of unactivated terminal alkenes. Studies of the electronic structure support open-shell intermediates, a deviation from traditional strong-field organometallic compounds that promote catalytic C−C bond formation.