Infrared observation of the chemical consequences of cobalt catalyst produced in mixed solutions of Al(Et)3 and Co(acac)2

Abstract

Cobalt catalysts obtained from the reduction of Co(acac)₂ with Al(Et)₃ have been studied by infrared spectroscopy (in the selective hydrogenation of multifunctional compounds). These solids prepared in situ were in suspension in a liquid mixture containing solvent and reagent. In order to obtain information on the preparation and the composition of the catalyst we carried out an FT-IR characterization using a special device warranting sample manipulation in air-free atmosphere. At room temperature there were instantaneous and reductive ligand-exchange between Al(Et)₃ and Co(acac)₂ and formation of Co⁰ particles, Co⁰ soluble complexes and Al(Et)₂(acac). The multistep process may be initiated through the formation of a donor-acceptor complex ((acac)Co(acac)→Al(Et)₃). The presence of CO in the gas phase (H₂) when heating the reaction mixture up to 180°C enhances the reduction of cobalt and probes Co⁰ in different coordination symmetries. Some of the Co⁰ species could be surrounded with cobalt alkoxide species and aluminium acetylacetonate.