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.