Base-Free Photoredox/Nickel Dual-Catalytic Cross-Coupling of Ammonium Alkylsilicates

Single-electron transmetalation is recognized as an enabling technology for the mild transfer of alkyl groups to transition metal catalysts in cross-coupling reactions. Hyper­coordinate silicates represent a new and improved class of radical precursors because of their low oxidation potentials and the innocuous byproducts generated upon oxidation. Herein, we report the cross-coupling of secondary and primary ammonium alkyl­silicates with (hetero)­aryl bromides in good to excellent yields. The base-free conditions have exceptional protic group tolerance on both partners, permitting the cross-coupling of unprotected primary and secondary amines

Nickel/Photoredox-Catalyzed Amidation via Alkylsilicates and Isocyanates

A nickel/photoredox, dual-catalyzed amidation reaction between alkylsilicate reagents and alkyl/aryl isocyanates is reported. In contrast to the previously reported reductive coupling process, this protocol is characterized by mild reaction conditions and the absence of a stoichiometric reductant. A mechanistic hypothesis involving a nickel-isocyanate adduct is proposed based on literature precedent and further validation by experimental results

Nickel-Catalyzed Cross-Coupling of Photoredox-Generated Radicals: Uncovering a General Manifold for Stereoconvergence in Nickel-Catalyzed Cross-Couplings

The cross-coupling of sp³-hybridized organo­boron reagents via photoredox/​nickel dual catalysis represents a new paradigm of reactivity for engaging alkyl­metallic reagents in transition-metal-catalyzed processes. Reported here is an investigation into the mechanistic details of this important transformation using density functional theory. Calculations bring to light a new reaction pathway involving an alkyl­nickel­(I) complex generated by addition of an alkyl radical to Ni(0) that is likely to operate simultaneously with the previously proposed mechanism. Analysis of the enantio­selective variant of the transformation reveals an unexpected manifold for stereo­induction involving dynamic kinetic resolution (DKR) of a Ni­(III) intermediate wherein the stereo­determining step is <i>reductive elimination</i>. Furthermore, calculations suggest that the DKR-based stereo­induction manifold may be responsible for stereo­selectivity observed in numerous other stereo­convergent Ni-catalyzed cross-couplings and reductive couplings