Unexpected Formation of Chiral Pincer CNN Nickel Complexes with β‑Diketiminato Type Ligands via C–H Activation: Synthesis, Properties, Structures, and Computational Studies

Reaction of lithiated chiral, unsymmetric β-diketimine type ligands HL2a–e containing oxazoline moiety (HL2a–e = 2-(2′-R1NH)-phenyl-4-R2-oxazoline) with trans-NiCl­(Ph)­(PPh3)2 afforded a series of new chiral CNN pincer type nickel complexes (3a–3e) via an unexpected cyclometalation at benzylic or aryl C–H positions. Single crystal X-ray diffraction analysis established the pincer coordination mode and the strained conformation. Chirality, and in one case, racemization of the target nickel complexes were confirmed by circular dichroism (CD) spectroscopy. Electronic structure and band assignments in experimental UV–vis and CD spectra were discussed on the basis of Density Functional Theory (DFT) and time-dependent (TD) DFT calculations.