ja508909u_si_002.xlsx (10.57 kB)
Dimer Involvement and Origin of Crossover in Nickel-Catalyzed Aldehyde–Alkyne Reductive Couplings
dataset
posted on 2015-12-17, 06:25 authored by M. Taylor Haynes, Peng Liu, Ryan D. Baxter, Alex J. Nett, K. N. Houk, John MontgomeryThe
mechanism of nickel(0)-catalyzed reductive coupling of aldehydes
and alkynes has been studied. Extensive double-labeling crossover
studies have been conducted. While previous studies illustrated that
phosphine- and N-heterocyclic carbene-derived catalysts
exhibited differing behavior, the origin of these effects has now
been evaluated in detail. Many variables, including ligand class,
sterics of the ligand and alkyne, temperature, and ring size being
formed in intramolecular versions, all influence the extent of crossover
observed. A computational evaluation of these effects suggests that
dimerization of a key metallacyclic intermediate provides the origin
of crossover. Protocols that proceed with crossover are typically
less efficient than those without crossover given the thermodynamic
stability and low reactivity of the dimeric metallacycles involved
in crossover pathways.