Highly active multidentate catalysts for efficient alkyne metathesis

A compound of formula (III) or a salt thereof:

• wherein:
• each G is independently alkyl, aryl or heteroaryl, wherein the alkyl, aryl or heteroaryl is optionally and independently substituted with alkyl, halogen or electron-withdrawing substituents;
• R1 is selected from the group consisting of N, N+(A−), and P, and A− is an anion;
• R3 is selected from the group consisting of alkyl, alkyl(aryl) and aryl, all of which are optionally substituted;
• R4 is a single bond, heteroatom, or an optionally substituted C1-C3 alkyl chain;
• and,
• M is a metal.

A method of preparing an alkyne-containing metathesis product, the method comprising contacting a first alkyne-containing substrate with a second alkyne-containing substrate in the presence of a compound of formula (IV) or a salt thereof, whereby the metathesis product of the first and second alkyne-containing substrates is formed:

• wherein:
• each occurrence of n is independently 0, 1, 2, 3, or 4;
• R1 is selected from the group consisting of N, N+H(A−), and P, C and A− is an anion;
• each occurrence of R2 is independently selected from the group consisting of alkyl, halogen, nitro, cyano, trifluoromethyl, trichloromethyl, carboxy, formyl, lower alkanoyl, carboxyamido and aryl lower alkanoyl;
• R3 is alkyl, alkyl(aryl) or aryl, all of which are optionally substituted;
• and
• M is selected from the group consisting of Mo, W. Re and Ta,
• with the proviso that, if R1 is selected from the group consisting of N and P, at least one occurrence of n is not zero.