A Catalyst with Two‐Coordinate Nickel: Theoretical and Catalytic Studies

The bisadduct (cAAC) 2 Ni II Cl 2 [ 1 ; cAAC = cyclic (alkyl)(amino)carbene] was directly synthesized by treating cAAC with NiCl 2 . Compound 1 was reduced to (cAAC) 2 Ni 0 ( 2 ) by using lithium diisopropylamide or KC 8 . Crystals of 2 were stable under an inert gas for several months and decomposed upon heating above 165 °C. On the basis of the calculated natural bond orbital charge values of the nickel atom in 2 , the oxidation state of nickel was determined to be between Ni I and Ni 0 (+0.34). Theoretical calculations suggested a closed‐shell singlet electronic configuration of 2 with little biradical character. Ab initio multiconfigurational C(R)ASSCF/CASPT2 calculations predicted a closed‐shell singlet electronic configuration (Ni 0 ), whereas excited spin states possessed Ni I character with unpaired electrons on neighboring carbon atoms. The catalytic activity of complex 2 was investigated for the homocoupling of various unactivated aryl chlorides/fluorides. The biaryls were obtained in good yields at moderate temperature. Theoretical studies showed that an intermediate containing Ni III was more favored than one with Ni IV .