Catalytically Competent Nickel(I)-Isocyanide Compounds

Nickel-catalyzed cross-coupling reactions have emerged as a powerful strategy to construct complex molecules. A salient feature of Ni catalysts is their ability to engage in one-electron chemistry involving paramagnetic Ni(I) and Ni(III) intermediates, which has led to development of cross-coupling reactions involving alkyl substrates; however, such reactions generally employ Ni(II) or Ni(0) complexes as pre-catalysts. Although highly desirable, well-defined and catalytically competent Ni(I) sources with exchangeable ancillary ligands are lacking. Here we report the synthesis, characterization, and catalytic activity of a family of thermally stable dinuclear Ni(I) complexes supported by commercially available isocyanides as a general solution to this problem. Two classes of Ni(I) isocyanide complexes showing high thermal and solid-state stability have been developed – coordinatively saturated homoleptic compounds and coordinatively unsaturated Ni(I)-halide compounds. The Ni(I) compounds exhibit rapid ligand substitution and are efficient catalysts in Kumada, Suzuki-Miyaura, and Buchwald-Hartwig cross-coupling reactions, suggesting their potential use as either Ni(I) catalysts or pre-catalysts. In addition, bromide-selective functionalization of polyhalogenated arenes with Grignard reagents was achieved for the first time under nickel catalysis. Finally, spectroscopic and mechanistic studies were performed to establish the general use of simple isocyanide ligands as spectator ligands for cross-coupling reactions, representing an untapped chemical space for new reaction discovery.