Macrocyclic Aryl–Nickel(II) Complexes: Synthesis, Structure, and Reactivity Studies

The synthesis, characterization, and reactivity of the monoaryl–Ni­(II) compound 2 and the diaryl–Ni­(II) compound 4 formed through the direct electrophilic metalation of two macrocyclic azacalix­[m]­arene­[n]­pyridine ligands are described. Compound 4 was much more stable in protic solvents and acids than the monoaryl–Ni­(II) compound 2. Moreover, 2 can react with a variety of nucleophiles, resulting in the formation of C–C, C–O, C–Br, and C–N bonds. In contrast, compound 4 exhibited very inert reactivity upon reaction with a large numberof nucleophiles. Interestingly, compound 2 was also capable of reacting with several less bulky alkyl halides to form new C–C bonds, while the same procedure is inapplicable to 4. The study reported in this work provides a thorough investigation on the reactivity of aryl–Ni­(II) species that should facilitate comprehension of the detailed mechanism of nickel-catalyzed C–H functionalization.