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Cyclometalated Ni(II) Complexes [Ni(N∧C∧N)X] of the Tridentate 2,6-di(2-pyridyl)phen-ide Ligand
journal contribution
posted on 2020-07-23, 17:48 authored by Lukas Kletsch, Gerald Hörner, Axel KleinA series of cyclometalated Ni(II)
complexes [Ni(PyPhPy)X] containing
anionic N∧C∧N– tridentate ligand Py(Ph–)Py 2,6-di(2-pyridyl)benzene-1-ide,
(Py(HPh)Py = 1,3-di(2-pyridyl)benzene) and X = Cl, Br, or I as coligands,
were studied. All three complexes were obtained through direct C–H
base-assisted nickelation from NiX2 and Py(HPh)Py using
KOAc/K2CO3 in nonpolar high-boiling point solvents.
While the overall molecular structures are quite similar to those
of the previously studied [Ni(C∧N∧N)X] complexes with the anionic C∧N∧N tridentate –Phbpy (HPhbpy = 6-(phenyl)-2,2′-bipyridine)
ligand, bond lengths in the molecular structures are slightly different.
Large differences between these N∧C∧N and C∧N∧N Ni complexes which
can be traced to the different orientation of the X coligand to the
carbanionic phen-ide group, trans or cis, and the different ligand pattern, Py–Ph–Py versus
Ph–Py–Py, were found for the UV–vis absorption
spectra and the electrochemical reductions, while the oxidation potentials
are very similar. Extended DFT calculations with the TPSSh functional
associate the indifference of oxidation potentials with conserved
energies of metal-borne HOMOs. By contrast, the diminished π-acceptor
qualities of the N∧C∧N ligand
translate into a destabilization of the LUMO by ca. 400 mV and a blue-shift
of the leading visible transition by 80 nm in very good agreement
with the experimental data.