Hard to Handle: Extremely Labile Hydrido Nickel(II) Complexes of Cyclometalated C^∧N^∧N and N^∧C^∧N Ligands

Abstract

From the two organonickel(II) scaffolds [Ni(Phbpy)]+ and [Ni(PyPhPy)]+ (HPhbpy = 6-phenyl-2,2′-bipyridineHC∧N∧N and Py(HPh)Py = 2,6-di-2-pyridyl-benzeneN∧(HC)∧N) the hydrido complexes [Ni(C∧N∧N)H] and [Ni(N∧C∧N)H] were studied in a combined experimental/theoretical approach. The hydrido complexes were prepared via the reaction of the halido derivatives [Ni(C∧N∧N)X] and [Ni(N∧C∧N)X] (X = Cl, Br) with Li(Et3BH) (superhydride). The C∧N∧N complex undergoes rapid reductive elimination (RE) yielding HPhbpy and Ni particles even at the lowest temperatures, while the PyPhPy derivative is more stable. Low-temperature 1H nuclear magnetic resonance (NMR) spectroscopy allowed detection of a signal at δ = −2.86 ppm assignable to the hydrido ligand. The different stabilities can be directly correlated to the cis (Phbpy) and trans (PyPhPy) orientations of the carbanionic phen-2-ide group with the hydrido ligand, and rapid RE occurs from the cis position which is also supported by the density functional theory (DFT) calculations which are presented. A further TD-DFT/UV–vis absorption study is also reported to rationalize and confirm the fleeting existence of the Ni–H moiety, and proposals are made on the route of its decomposition.

Carbon Dioxide Electroreduction and Formic Acid Oxidation by Formal Nickel(I) Complexes of Di‐isopropylphenyl Bis‐iminoacenaphthene

“…[12,13] Rich redox properties combined with varying coordination geometries of the nickel center, as well as the rational design of the ligand environment for the metal coordination, confer specific catalytic properties to the nickel-based materials. [14][15][16][17] Furthermore, nickel is one of the few metals capable of efficiently catalyzing the reduction of CO 2 to hydrocarbons (C 1 -C 3 ), including methane. [18][19][20] The uniqueness of Ni-based catalysts can be attributed to the optimal combination between COand H 2 -producing catalysts, facilitating the activation of CO 2 and the subsequent hydrogenation of CO, that is, a crucial step in hydrocarbon formation.…”

“…Nickel is considered a suitable replacement for precious metals in developing catalysts for the electroreduction of CO 2 due to its wide valence range spanning from 0 to +4 [12,13] . Rich redox properties combined with varying coordination geometries of the nickel center, as well as the rational design of the ligand environment for the metal coordination, confer specific catalytic properties to the nickel–based materials [14–17] . Furthermore, nickel is one of the few metals capable of efficiently catalyzing the reduction of CO 2 to hydrocarbons (C 1 –C 3 ), including methane [18–20] .…”

Nickel(II) Analogues of Phosphorescent Platinum(II) Complexes with Picosecond Excited‐State Decay

“…Here, we explore how this change in coordination environment affects the photophysical behavior of the isostructural Ni II complexes in Scheme 1b. A recent study reported that such changes of the coordination environments provided by different tridentate chelate ligands can greatly affect the stability and reactivity of the resulting Ni II complexes, but the influence on the excited state structure and the photophysics remains underexplored [34] . Here, we investigate how the Ni II complexes dissipate their excitation energy and how long‐lived luminescent 3 LC or 3 MLCT excited states similar to those encountered in many Pt II and Au III complexes can potentially be obtained in square‐planar Ni II compounds.…”