A study of stereochemical and electronic factors in the nickel promoted dimerization of norbornadiene [pt.I] : electro-organometallic catalysts [pt.II]

TLDR: Pillbury et al. as mentioned in this paper studied the nickel-promoted dimerization of norbornadiene (NBD) from three aspects; stereochemical and electronic factors in the substrate and the influence of ligands bound to the nickel which are not directly involved in the reaction.

Abstract: To gain a better understanding of metal promoted cycloaddition reactions, the nickel promoted dimerization of norbornadiene (NBD) was examined from three aspects; stereochemical and electronic factors in the substrate and the influence of ligands bound to the nickel which are not directly involved in the reaction. As an example of stereochemical perturbation, the 7-methyl derivative of NBD was dimerized using bis(tri-phenylphosphine)dicarbonylnickel, Ni(CO)2(P03)2 , as a promoter with both thermal and photochemical activation. It was found by an analysis of the nuclear magnetic resonance'spectra of the dimers that both 2+2 and 2+2+2 cyclodimerization products were produced. The major dimers had the same skeletal stereochemical configurations as the dimers produced from the corresponding thermal and photochemical reactions of NBD and to investigate substrate electronic factors, norbornene, pentacyclbtetradeca-5,11-diene (exo-trans-exo isomer) and [2,2,2]bicycloocta-2,5-diene were subjected, without success, to conditions found to produce dimers with NBD. A proposal describing the requisite electronic factors for active olefinic substrates was made. The influence of indirectly involved ligands was examined through a study of kinetics parameters in the thermal reaction of Ni(CO)2(P03)2 with NBD. The reaction was found to be very temperature sensitive, to be strongly inhibited by carbon monoxide and triphenylphosphine, and to exhibit an induction period followed by the major reaction period in which the rate of production of the two 2+2 dimers (both known) was constant. The kinetics results were viewed as the initial establishment of equilibrium between a number of competing reactions to produce very low steady state concentrations of active catalytic species. The substrate modification data and kinetics data were coordinated with the work of other investigators to give a unified picture of the nickel promoted cyclodimerization reaction. The use of electrochemical regeneration of active organometallic coupling reagents was also studied. It was found benzyl halides, bromo-benzene, benzoyl chloride, phenacyl bromide and n-hexyl bromide could be coupled with electro chemically produced metal species. The reactions were run in single compartment cells using N,N-dimethylformamide as solvent, a catalytic amount of a metal ion and stabilizing ligands such as triphenylphosphine to prevent zero valent metal from plating out. Carbonyl insertion and a unique formylation reaction were also studied. (Formula not captured by OCR) (Formula not captured by OCR) PART I: A STUDY OF STEREOCHEMICAL AND ELECTRONIC FACTORS IN THE NICKEL PROMOTED DIMERIZATION OF NORBORNADIENE PART II: ELECTRO-ORGANOMETALLIC CATALYSTS ■ by DALE GRANT PILLSBURY A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY