[2+2]-Cyclodimerization of norbornadiene to pentacyclic products with exo-trans(cis)-exo structure in the presence of model catalytically active η4-norbornadiene nickel hydride complex was simulated at the DFT/PBE level of theory. According to the calculations, the rate-determining step in the cyclodimerization process is reductive elimination of the metallacycle whose decomposition yields norbornadiene dimer. The formation of cis-dimer is unfavorable for both kinetic and thermodynamic reasons.

Quantum-chemical study on the mechanism of catalytic dimerization of norbornadiene in the presence of hydride nickel(I) complex

Nickel(I) compounds whose concentration was 10−4–10−6 of the total concentration of nickel added to the system were identified by EPR in the reaction of 2,5-norbornadiene with nickel homoligand allyl complexes Niall2 (all is C3H5, 1-CH3C3H4, or 2-CH3C3H4). The Ni(I) complexes were stable at room temperature under oxygen-free conditions. It was shown that the paramagnetic complexes were in equilibrium with diamagnetic forms. The temperature dependence of the concentration of the paramagnetic species was determined. The structure of the paramagnetic nickel(I) complexes and the possible routes of their formation are discussed on the basis of the obtained data.

Paramagnetic complexes of nickel(I) stabilized by norbornadiene

In a joint investigation of the kinetic laws of the catalytic cyclodimerization of norbornadiene in the presence of bis-η3-allyl complexes of nickel by gas chromatography and ESR, a definite correspondance in the change in the concentrations of norbornadiene, its dimers, and the paramagnetic nickel(I) complex was detected The absence of an ESR signal in model systems, as well as the substantial differences in the relative amounts of Ni(I) when bis-η3 -allyl nickel complexes of different structure were used, suggests that paramagnetic Ni(I) does not participate as one of the intermediates in the catalytic process

L. M. Grundel

Papers

Paramagnetic complexes of nickel(I) stabilized by norbornadiene

Role of the paramagnetic nickel(I) complex in the catalytic dimerization of norbornadiene