Crystal Structures and Spectroscopic and Theoretical Properties of Pentacoordinate Nickel(II) Complexes Containing Tris(pyrazolyl)borate and Quinolinate Ligands

Abstract

A series of quinolinate nickel-tris(pyrazolyl)borate complexes [Ni(Tp*)(N,O-2,5,7-R 1 ,R 2 ,R 3 -8-hq)] {Tp* = hydrotris-(3,5-dimethylpyrazolyl)borate, 8-hq = 8-hydroxyquinoline} were synthesized and characterized by spectroscopic methods. Single-crystal X-ray studies indicate that these complexes exhibit a pentacoordinate arrangement with chelating quinolinate and hydrotris(3,5-dimethylpyrazolyl)borate ligands. The substituents on the quinolinate generate variations in the absorption and emission wavelengths. Substituents in the 5,7-positions and a 2-CN substituent in the quinolinate induce a bathochromic shift with respect to the unsubstituted derivative; however, 2-Me and 2-NH 2 substituents cause a blueshift. The UV/Vis spectra were investigated by time-dependent (TD)-DFT on the basis of the optimized [a]

A Single Nickel Catalyst for the Acceptorless Dehydrogenation of Alcohols and Hydrogenation of Carbonyl Compounds

“…In stark contrast, when [Tp′Ni­(μ-OH)] 2 and 2-hydroxyquinoline were mixed in a 1:2 ratio and the catalytic dehydrogenation of 1-phenylethanol was carried out in refluxing toluene, 86% of acetophenone was formed after 24 h. This clearly demonstrates the participation of the ancillary 2-hydroxyquinoline ligand in catalysis. Furthermore, having the −OH group at the ortho position of the quinoline moiety was found to be critical, as Tp′Ni­(8-OH-quinoline) did not catalyze the dehydrogenation reaction. On the basis of these observations, we propose a reaction pathway that highlights the importance of the 2-hydroxyquinoline moiety in the catalyst (Scheme ).…”