Unexpected Formation of Chiral Pincer CNN Nickel Complexes with 尾-Diketiminato Type Ligands via C鈥揌 Activation: Synthesis, Properties, Structures, and Computational Studies
文摘
Reaction of lithiated chiral, unsymmetric 尾-diketimine type ligands HL2a鈥?b>e containing oxazoline moiety (HL2a鈥?b>e = 2-(2鈥?R1NH)-phenyl-4-R2-oxazoline) with trans-NiCl(Ph)(PPh3)2 afforded a series of new chiral CNN pincer type nickel complexes (3a鈥?b>3e) via an unexpected cyclometalation at benzylic or aryl C鈥揌 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鈥搗is and CD spectra were discussed on the basis of Density Functional Theory (DFT) and time-dependent (TD) DFT calculations.