Carbon dioxide reacts with 2,3-dimethylbutadiene and bis-cyclooctadiene(1,5)-nickel(O) in the presence of N,N′-tetramethyl-ethylendiamine (tmeda) to form [(3,4,5-η3)-3,4-dimethyl-3-pentenylato](N,N′-tetramethyl-ethylendiamine)-nickel(II) as the product of the oxidative coupling of CO2 and the diene. The deep red complex crystallizes in the rhombic space group Pbca. The structure was determined by an X-ray analysis. The monodendate carboxylate group, the π-allyl system and a N-atom of tmeda form a planar coordination sphere around the central atom. The distance between Ni and the second N-atom of tmeda is very long (2.314 Å). Reaction of the complex with R−X (R: H, CH3) yield 3-unsaturated carboxylic acids; tmeda can be substituted by 2,2′-bipyridine.
