03 September 2020

Discovery of NHC‐ethynyl coupling process

The product of a revealed transformation — NHC-ethynyl coupling — was observed as a catalyst transformation pathway in the Sonogashira cross-coupling, catalyzed by Pd/NHC complexes. The 2-ethynylated azolium salt was isolated in individual from and fully characterized, including the X-ray analysis. A number of possible intermediates of this transformation with common formulae (NHC) xPd(C2Ph) (x = 1,2) were observed and subjected to collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) experiments studies to elucidate their structure. Measured bond dissociation energies (BDEs) and IRMPD spectra were in an excellent agreement with quantum calculations for coupling product pi-complexes with Pd(0). Molecular dynamics simulations confirmed multiple observed CID fragmentation pathways. Performed study of catalyst evolution suggests the reported transformation to be considered in the development of new catalytic systems for alkyne functionalization reactions.

Reference: Chem. Eur. J., 2020, ASAP

DOI: 10.1002/chem.202003533