AgNMR as a tool for mechanistic studies of Ag-catalyzed reactions:: Evidence for in situ formation of alkyn-1-yl silver from alkynes and silver salts

As demonstrated by H-1, C-13, and Ag-109 NMR, a pi-alkyne-Ag complex and then an alkynyl silver are in situ formed from alkyne and silver salt in conditions related to those used for Ag-catalyzed alkynylation or for Ag/Pd-catalyzed sp-sp(2) cross-coupling reactions. This finding allows for a rationale of the mechanisms of these reactions.