ACTIVATION OF CO2 AT TRANSITION-METAL CENTERS - THE ROUTE OF THE CO2 REDUCTION AT NIKEL(0) MOIETIES

A competing reaction in the catalytic cyclooligomerization of hex-3-yne and CO2 at the (TMED)Ni(0)-fragment (TMED = N,N,N',N'-tetramethylethylendiamine) is the formation of carbon monoxide and (TMED)Ni(CO,). So it is possible to explain the generation of II (TMED)Ni(diethylmalicacidanhydride) and III (a nickel trimer with two (TMED)Ni(CO,) units). Both complexes are characterized by X-ray analysis. The reduction of CO2 to CO most likely proceeds via an intermediate in which two molecules of carbon dioxide are coupled head-to-tail to form a metallacycle. An ab initio scf geometry optimization supports the existence of such an intermediate.