Ag NMR 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

[Structure: see formula]. As demonstrated by 1H, 13C, and 109Ag 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-sp2 cross-coupling reactions. This finding allows for a rationale of the mechanisms of these reactions.