The molybdenum nitride complex [(Ph(3)SiO)(3)Mo[triple bond]N] (10), which can be conveniently prepared in situ from readily available [(Me(3)SiO)(2)((Me(3)Si)(2)N)Mo[triple bond]N] (9) and Ph(3)SiOH, and the pyridine adduct of 10, [(pyridine)(Ph(3)SiO)(3)Mo[triple bond]N] (11), exhibit excellent catalytic activity in alkyne metathesis reactions of all kinds. Adduct 11 is sufficiently stable to be weighed in air and is therefore much easier to use than any of the established, structurally defined alkyne metathesis precatalysts known to date. This new system is compatible with a host of functional groups, including esters, amides, alkenes, carbamates, ethers, silyl ethers, sulfonates, thioethers, THP acetals, glycosides, ketones, enoates, thiophenes, pyridines, thiazoles, and nitro groups, and even accepts protected propargyl alcohols as substrates. It has been used for the preparation of key intermediates for bioactive natural products, such as gallicynoic acid I, homoepilachnene, epothilone A, cruentaren A, and a fully synthetic latrunculin analogue. However, 9 and 11 react with aldehydes and acid chlorides to give the corresponding nitrile derivatives.