A Series of 4- and 5-Coordinate Ni(II) Complexes: Synthesis, Characterization, Spectroscopic, and DFT Studies

Abstract

A series of four- and five-coordinate Ni(II) complexes Cz (Pyr)NiX (1-3 and 1·THF-3·THF), where X = Cl, Br, and I, were synthesized and fully characterized by NMR and UV-vis spectroscopy, X-ray crystallography, cyclic voltammetry, and density functional theory calculations. The solid-state structures of 1-3 reveal rare examples of seesaw Ni(II) complexes. In solution, 1-3 bind reversibly to a THF molecule to form five-coordinate adducts. The electronic transitions in the visible region (630-680 nm), attributed to LMCT bands, for 1 → 3 exhibit a bathochromic shift. The thermochromic tendency of the five-coordinate complexes implies the loss of THF coordination at elevated temperatures. Finally, the electronic properties of all Ni(II) complexes were studied by time-dependent density functional theory calculations to characterize the nature of the excited states.

Nickel(ii)-methyl complexes adopting unusual seesaw geometries

“…[7][8][9][10][11] Despite this, catalytically active Ni(II)-alkyl species may likely exhibit or transition through different coordination geometries. [12][13][14] For example, other synthetic Ni(II) complexes can be found in tetrahedral geometries in addition to the more common square planar geometries. While a square planar geometry is favored due to electronic stabilization of the d 8 Ni(II) ion, a tetrahedral geometry may be favored with suitably bulky or chelating ligands.…”

“…In fact, only a handful of examples of Ni(II) complexes in this geometry have been reported. 13,[16][17][18] In these cases, steric bulk is used to enforce the desired geometry. For example, the first of these reported by Bröring and co-workers utilized a tripyrranato ligand which positions methyl substituents within the square plane, forcing halide ligands above this plane.…”

“…14,22 Another recent example of a seesaw geometry at a Ni(II) center involves a diisopropylpyrazole-substituted carbazole ligand to enforce steric crowding of the square plane. 13 Finally, an example of a ligand-constrained geometry around a Ni(II) center can be seen in a complex bound to a triphosphacyclododecane ligand. 23 This ligand binds in a facial manner with strongly donating trialkylphosphines which are proposed to enforce a low-spin state at nickel.…”

Rational design of pincer‐nickel complexes for catalytic cyanomethylation of benzaldehyde: A systematic DFT study

“…First, the calculation level was selected based on a previous report on Ni complexes. 24 The first combination BS1, consist of B3LYP functional 25 in conjunction with 6-31G(d,p) BS, 26 the second combination BS2, consist of B3LYP functional 25 in conjunction with 6-311G(d) BS 26 for the nonmetal elements, while for Ni we used an effective core Stuttgart/Dresden (SDD) pseudopotential and the associated BS with a polarization function. 22 In our previous reports 27 the Perdew-Burke-Ernzerhof (PBEPBE) functionals and LANL2DZ BS for similar complexes gave better results.…”

“…The geometries were optimized (Table S1‐S55) using four sets of functionals and basis sets (BS). First, the calculation level was selected based on a previous report on Ni complexes 24 . The first combination BS1, consist of B3LYP functional 25 in conjunction with 6‐31G(d,p) BS, 26 the second combination BS2, consist of B3LYP functional 25 in conjunction with 6‐311G(d) BS 26 for the nonmetal elements, while for Ni we used an effective core Stuttgart/Dresden (SDD) pseudopotential and the associated BS with a polarization function 22 .…”