Hard to Handle: Extremely Labile Hydrido Nickel(II) Complexes of Cyclometalated (CNN)-N-& BOTTOM;-N-& BOTTOM; and (NCN)-C-& BOTTOM;-N-& BOTTOM; Ligands

Fromthe two organonickel(II) scaffolds [Ni(Phbpy)](+) and [Ni(PyPhPy)](+) (HPhbpy = 6-phenyl-2,2 & PRIME;-bipyridine V(HCNN)-N-& BOTTOM;-N-& BOTTOM; and Py(HPh)Py = 2,6-di-2-pyridyl-benzene VN-& BOTTOM;(HC)N-& BOTTOM;) the hydrido complexes [Ni((CNN)-N-& BOTTOM;-N-& BOTTOM;)H] and [Ni((NCN)-C-& BOTTOM;-N-& BOTTOM;)H] were studied in a combined experimental/theoreticalapproach. The hydrido complexes were prepared via the reaction ofthe halido derivatives [Ni((CNN)-N-& BOTTOM;-N-& BOTTOM;)X] and [Ni((NCN)-C-& BOTTOM;-N-& BOTTOM;)X] (X = Cl,Br) with Li(Et3BH) (superhydride). The (CNN)-N-& BOTTOM;-N-& BOTTOM; 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 H-1 nuclear magnetic resonance (NMR) spectroscopy allowed detectionof a signal at & delta; = -2.86 ppm assignable to the hydridoligand. The different stabilities can be directly correlated to the cis (Phbpy) and trans (PyPhPy) orientationsof the carbanionic phen-2-ide group with the hydrido ligand, and rapidRE occurs from the cis position which is also supportedby the density functional theory (DFT) calculations which are presented.A further TD-DFT/UV-vis absorption study is also reported torationalize and confirm the fleeting existence of the Ni-Hmoiety, and proposals are made on the route of its decomposition.