Development and Mechanistic Studies of (E)-Selective Isomerization/Tandem Hydroarylation Reactions of Alkenes with a Nickel(0)/Phosphine Catalyst

A stereoselective alkene isomerization and sequential hydroarylation with arylboronic acid using a nickel(0) catalyst has been developed. The bulky monophosphine PAd(2)(n-Bu) is an effective ligand in these reactions to furnish both various stereo-defined internal alkenes and hydroarylation products (isomerization: up to 98%, E/Z = 98:2; tandem hydroarylation: up to 82%). Mechanistic studies based on experiments and computational calculations suggested that the isomerization proceeds via an intra- or intermolecular hydrogen shift. Furthermore, a concerted multibond recombination with boronic acid-assisted oxidative protometallation of the alkene was found to be a reasonable mechanism for the formation of the alkylnickel(II) species from the alkene, nickel(0), alcohol, and boronic acid in the hydroarylation.