4. Kartik Chandra Mondal, Prinson P. Samuel, Yan Li, Herbert W. Roesky, Sudipta Roy, Lutz Ackermann, Navdeep S. Sidhu, George M. Sheldrick, Elena Carl, Serhiy Demeshko, Susmita De, Pattiyil Parameswaran, Liviu Ungur, Liviu F. Chibotaru, Diego M. Andrada. A Catalyst with Two Coordinate Nickel: Theoretical and Catalytic Studies.
The bis adduct (cAAC)2NiIICl2 (1) was directly synthesized reacting cAAC: with NiCl2. Compound 1 was reduced to (cAAC)2Ni0 (2) by LDA or KC8. Crystals of 2 are stable under an inert atmosphere for several months and decompose when heated above 165 °C. Based on the calculated NBO charge values of the nickel atom for 2 the oxidation state of nickel is an intermediate between NiI and Ni0 in 2 (+0.34). Theoretical calculations suggest a closed-shell singlet electronic configuration of 2 with little biradical character. Ab initio multiconfigurational C(R)ASSCF/CASPT2 calculations predict a closed-shell singlet electronic configuration (Ni0), while the excited spin states possess a NiI character with unpaired electrons on neighboring carbon atoms. The catalytic activity of the complex 2 was investigated for the homo-coupling reaction of various unactivated aryl chlorides/fluorides. The biaryls were obtained in good yields at moderate temperature. Theoretical studies show that intermediate containing Ni(III) is more favorable over with that of Ni(IV).