Development of Catalytic Carbon–Carbon Bond Formations Based on Composite Metal Catalysts

Transition-metal-catalyzed C–C bond(s) formations are one of the most fundamental organic transformations, where the design of transition metal catalysts is the key of success. To activate two coupling partners simultaneously, we focused on the combination of a transition metal anion and a typical metal cation. The anionic transition metal center itself or own ligands are nucleophilically activated by the anionic charge, and the Lewis acidic typical metal cation activates the electrophilic counterpart. The synergy of these two metal centers located closely by electrostatic interaction enables cross-coupling and multicomponent coupling reactions. For instance, Co–Mg–Li system catalyzed cross-coupling reaction of alkyl halides with tertiary alkyl Grignard reagents to construct quaternary carbon center. The cross-coupling reaction of alkenyl ethers with aryl Grignard reagents via C– O bond cleavage could be achieved with Rh-Mg and Rh-Li combinations. The key catalytic active species containing Rh anion and Li cation was successfully isolated and characterized by X-ray crystallography to clarify a unique structure and reactivity of the Rh-Li complex. In addition, we successfully connected dimerizative transformation of 1,3-dienes promoted by a neutral Ni complex and a C–C bond formation with carbon electrophiles promoted by an anionic Ni complex in one catalytic cycle. The isolation of and structural insight into the anionic Ni complexes clarified the reaction mechanism and the origin of selectivity between multicomponent coupling reaction and competing cross-coupling reaction.