Mechanistic Evaluation of the Ni(IPr)2-Catalyzed Cycloaddition of Alkynes and Nitriles to Afford Pyridines: Evidence for the Formation of a Key ?1-Ni(IPr)2(RCN) Intermediate.

ABSTRACT: A detailed mechanistic evaluation of the Ni(IPr)2-catalyzed [2+2+2]-cycloaddition of diynes and nitriles was 2 conducted. Through kinetic analysis of these reactions, observed regioselectivities of the products, and stoichiometric reactions, Ni(IPr)2-catalyzed cycloadditions of diynes and nitriles appear to proceed by a heterooxidative coupling mechanism, contrary to other common cycloaddition catalysts. Reaction profiles demonstrated strong dependence in nitrile, resulting in variable nitrile-dependent resting states. Strong coordination and considerable steric bulk of the carbene ligands facilitate selective initial binding of nitrile thereby forcing a heterocoupling pathway. In situ IR data suggests the initial binding of the nitrile resides in a rare, ?1-bound conformation. Following nitrile coordination are a rate-determining hapticity shift of the nitrile and subsequent loss of carbene. Alkyne coordination then leads to heterooxidative coupling, insertion of the pendant alkyne, and reductive elimination to afford pyridine products.

SUBMITTER: Stolley RM 

PROVIDER: S-EPMC4159214 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature