The mechanism of the Pauson–Khand reaction has attracted significant interest due to the unusual dinuclear nature of the Co₂(CO)_x active site. Experimental and computational data have indicated that the intermediates following the initial Co₂(CO)₆(alkyne) complex are thermodynamically unstable and do not build up in appreciable concentrations during the course of the reaction. As a consequence, the key steps that control the scope of viable substrates and various aspects of selectivity have remained largely uncharacterized. Herein, a direct experimental investigation of the dinuclear metallacycle-forming step of the Pauson–Khand reaction is reported. These studies capitalize on well-defined d⁹–d⁹ dinickel complexes supported by a naphthyridine–diimine (NDI) pincer ligand as functional surrogates of Co₂(CO)₈.

Dinuclear Ni complexes supported by naphthyridine-diimine (NDI) ligands catalyze the reductive cyclopropanation of alkenes with CH₂Cl₂ as the methylene source. The use of mild terminal reductants (Zn or Et₂Zn) confers significant functional-group tolerance, and the catalyst accommodates structurally and electronically diverse alkenes. Mononickel catalysts bearing related N chelates afford comparatively low cyclopropane yields (≤20 %). These results constitute an entry into catalytic carbene transformations from oxidized methylene precursors.

The mechanism of the Pauson–Khand reaction has attracted significant interest due to the unusual dinuclear nature of the Co₂(CO)_x active site. Experimental and computational data have indicated that the intermediates following the initial Co₂(CO)₆(alkyne) complex are thermodynamically unstable and do not build up in appreciable concentrations during the course of the reaction. As a consequence, the key steps that control the scope of viable substrates and various aspects of selectivity have remained largely uncharacterized. Herein, a direct experimental investigation of the dinuclear metallacycle-forming step of the Pauson–Khand reaction is reported. These studies capitalize on well-defined d⁹–d⁹ dinickel complexes supported by a naphthyridine–diimine (NDI) pincer ligand as functional surrogates of Co₂(CO)₈.

Dinuclear Ni complexes supported by naphthyridine-diimine (NDI) ligands catalyze the reductive cyclopropanation of alkenes with CH₂Cl₂ as the methylene source. The use of mild terminal reductants (Zn or Et₂Zn) confers significant functional-group tolerance, and the catalyst accommodates structurally and electronically diverse alkenes. Mononickel catalysts bearing related N chelates afford comparatively low cyclopropane yields (≤20 %). These results constitute an entry into catalytic carbene transformations from oxidized methylene precursors.