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.