Trimethylsilylacetylene

Trimethylsilylacetylene is an acetylene molecule protected on one end by the trimethylsilyl group. It is popularly used in alkynylations, e.g. the Sonogashira reaction. After desilylation (e.g. with TBAF), the ethynyl group is introduced. Using a protected alkyne, as opposed to acetylene gas, prevents further (undesired) coupling reactions and also has the benefit of being a liquid.