Acrylonitrile codimerization

These codimerization reactions are mainly limited by the degree of n-bond strength of the electron deficient alkenes to Pd(0). Strongly bonded ligands may prevent any interaction of the metal with the methylenecyclopropane. Typical examples of too strongly bonded alkenes are maleic anhydride, acrolein and acrylonitrile. On the other hand, too weak interactions may result in cyclodimerization of the methylenecyclopropane rather than codimerization. 

Most remarkably, no codimerization involving the unsaturated ester molecule is observed, even though nickel compounds such as the acrylonitrile complex are efficient catalysts for such codimerization reactions vide infra). An additional homodimer, l,3-bis(methylene)cy-clohexane (6), is formed as a minor product with phosphane-modified nickel catalysts. Only trace amounts of product 6 are obtained with maleic anhydride as cocatalyst. 

Thus reaction occurs at both the electron-deficient and nonactivated olefin moieties of the norbornadiene diester32. Noteworthy also is the much higher exo selectivity compared with the chemoselective TMM-Pd process24. When the olefin is too electron-deficient, as in maleic anhydride, acrolein or acrylonitrile, bonding to the palladium center is so strong that no codimerization occurs. Conversely, if the initial /[-interaction is too weak, then a common side reaction becomes apparent, cyclodimerization of the methylenecyclopropane. 

The codimerization of acrylonitrile and methyl acrylate is catalyzed by ruthenium complexes under an atmosphere of hydrogen. Besides the hydrodimerization products of each monomer, up to 50% of the head-to-head codimerization products are formed [65] (Equation 47). 

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