Preparation and structures of a series of phosphorus‐free Nickel(II) diamine complexes and their applications in hydrogenation of acetophenone

To develop economical and phosphorus‐free catalysts for hydrogenation of ketones, three new complexes, [Ni(1R,2R‐dpen)₂(H₂O)Cl]₂Cl₂· 2Et₂O (1), [Ni(1R,2R‐dpen)(phen)(CH₃OH)₂]Cl₂·2CH₃OH (2) and [Ni(1,8‐dan)₂(DMF)Cl]₂Cl₂· 3H₂O (3), and three reported compounds, [Ni(opda)(phen)Cl₂]·CH₃OH (4), [Ni(opda)₂Cl₂] (5) and [Ni(1,2‐dach)₂]Cl₂ (6), were prepared and the structures of new compounds were determined by single crystal X‐ray diffraction analysis, in which 1R,2R‐dpen, phen, 1,8‐dan, opda and 1,2‐dach denote 1R,2R‐1,2‐diphenylethylenediamine, 1,10‐phenanthroline, 1,8‐diaminonaphthalene, o‐phenylenediamine and 1,2‐diaminocyclohexane, respectively. The catalytic effects for hydrogenation of acetophenone of these compounds were tested. This revealed very poor or no catalytic effects of these complexes in transfer hydrogenation of acetophenone using isopropanol or HCOOH? NEt₃ as hydrogen source. However, they presented much better catalytic effects in ionic hydrogenation of acetophenone using H₂ gas as hydrogen source with a dependence of the catalytic effects on the base used in the hydrogenation reactions. The complexes represent a kind of green hydrogenation catalyst, although the conversion in the hydrogenation reactions is not as high as expected. Copyright © 2010 John Wiley & Sons, Ltd.