Synthesis, Characterization, and Reactivity of PCN Pincer Nickel Complexes

New diamagnetic nickel(II) complexes based on an unsymmetrical (1-(3-((ditert-butylphosphino)methyl)phenyl)-N,N-dimethyl-methanamine) (PCN) pincer ligand were synthesized and characterized by ¹H, ³¹P{¹H}, and ¹³C{¹H} NMR spectroscopy. Their molecular structures were confirmed by X-ray diffraction. Oxidation to high-valent paramagnetic Ni(III) dihalide complexes was achieved through straightforward reaction of the corresponding diamagnetic halide complexes with anhydrous CuX₂ (X = Cl, Br). In agreement with this, the complexes are active in Kharasch addition of CCl₄ to olefins. The reaction of the hydroxo complex (8) and the amido complex (11) with CO₂ produced the hydrogen carbonate and carbamate complexes, respectively. The hydrogen carbonate complex was converted to the dinuclear nickel carbonate complex (10). The methyl (13), phenyl (14), and p-tolylacetylide (15) complexes are also described in the current study providing the first example of the hydrocarbyl nickel complexes based on an unsymmetric aromatic pincer ligand. Furthermore, the reactivity of the methyl complex toward different electrophiles has been investigated, showing that C-C bond formation is possible with aryl halides, whereas the reaction with CO₂ is sluggish.