Mechanistic investigations of the Ni-catalyzed asymmetric reductive alkenylation of N-hydroxyphthalimide (NHP) esters and benzylic chlorides are reported. Investigations of the redox properties of the Ni-bis(oxazoline) catalyst, the reaction kinetics, and mode of electrophile activation show divergent mechanisms for these two related transformations. Notably, the mechanism of C(sp 3 ) activation changes from a Nimediated process when benzyl chlorides and Mn 0 are used to a reductant-mediated process that is gated by a Lewis acid when NHP esters and tetrakis(dimethylamino)ethylene is used. Kinetic experiments show that changing the identity of the Lewis acid can be used to tune the rate of NHP ester reduction. Spectroscopic studies support a Ni II −alkenyl oxidative addition complex as the catalyst resting state. DFT calculations suggest an enantiodetermining radical capture step and elucidate the origin of enantioinduction for this Ni-BOX catalyst.
A Ni-catalyzed reductive cross-coupling of heteroaryl imines with C(sp 3 ) electrophiles for the preparation of heterobenzylic amines is reported. This umpolung-type alkylation proceeds under mild conditions, avoids the pre-generation of organometallic reagents, and exhibits good functional group tolerance. Mechanistic studies are consistent with the imine substrate acting as a redox-active ligand upon coordination to a low-valent nickel center. The resulting Ni-bis(2-imino)heterocycle complexes can engage in alkylation reactions with a variety of C(sp 3 ) electrophiles, giving the heterobenzylic amine products in good yields.
Ni II (IB) dihalide [IB = (3aR,3a′R,8aS,8a′S)-2,2′-(cyclopropane-1,1-diyl)bis(3a,8a-dihydro-8H-indeno[1,2-d]-oxazole)] complexes are representative of a growing class of first-row transition-metal catalysts for the enantioselective reductive cross-coupling of C(sp 2 ) and C(sp 3 ) electrophiles. Recent mechanistic studies highlight the complexity of these ground-state cross-couplings but also illuminate new reactivity pathways stemming from one-electron redox and their significant sensitivities to reaction conditions. For the first time, a diverse array of spectroscopic methods coupled to electrochemistry have been applied to Ni II -based precatalysts to evaluate specific ligand field effects governing key Ni-based redox potentials. We also experimentally demonstrate DMA solvent coordination to catalytically relevant Ni complexes. Coordination is shown to favorably influence key redox-based reaction steps and prevent other deleterious Ni-based equilibria. Combined with electronic structure calculations, we further provide a direct correlation between reaction intermediate frontier molecular orbital energies and cross-coupling yields. Considerations developed herein demonstrate the use of synergic spectroscopic and electrochemical methods to provide concepts for catalyst ligand design and rationalization of reaction condition optimization.
A Ni-catalyzed reductive cross-coupling of heteroaryl imines with C(sp 3 ) electrophiles for the preparation of heterobenzylic amines is reported. This umpolung-type alkylation proceeds under mild conditions, avoids the pre-generation of organometallic reagents, and exhibits good functional group tolerance. Mechanistic studies are consistent with the imine substrate acting as a redox-active ligand upon coordination to a low-valent nickel center. The resulting Ni-bis(2-imino)heterocycle complexes can engage in alkylation reactions with a variety of C(sp 3 ) electrophiles, giving the heterobenzylic amine products in good yields.
A Ni-catalyzed reductive cross-coupling of heteroaryl imines with C(sp3) electrophiles for the preparation of heterobenzylic amines is reported. This umpolung-type alkylation proceeds under mild conditions, avoids the pre-generation of organometallic reagents, and ex-hibits good functional group tolerance. Mechanistic studies are consistent with the imine substrate acting as a redox-active ligand upon coordination to a low-valent nickel center. The resulting Ni-bis(2-imino)heterocycle complexes can engage in alkylation reactions with a variety of C(sp3) electrophiles, giving the heterobenzylic amine products in good yields.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.