EXAFS investigation of nickel and cobalt precursors of homogeneous ziegler-type hydrogenation catalysts

Abstract

A preliminary EXAFS study is reported of precursors of homogeneous hydrogenation catalysts obtained by addition of AlEt3 to nickel or cobalt octoate solutions in benzene. For a given nickel octoate solution studied before reduction, monodentate coordination of the nickel cations to at least four carboxylic anions was established and accurate Ni...O1, Ni...C1 distances (i.e. 2.06±0.01 Å, 3.01±0.02 Å) were determined. The spectra of the reduced solutions are however clearly dominated by intense Ni*...Ni or Co*...Co signals at distances comparable to the relevant distances of the bulk metal, and thus suggest the presence of rather disordered, amorphous-like metal clusters. Strong evidence is also produced in favour of additional metal...carbon bonds which were often assumed to play an important role in the catalytic activity of these or related solutions.