Highly active multidentate catalysts for efficient alkyne metathesis
The invention relates to highly active and selective catalysts for alkyne metathesis. In one aspect, the invention includes a multidentate organic ligand wherein one substrate-binding site of the metal center is blocked. In another aspect, the invention includes N-quaternized or silane-based multidentate organic ligands, capable of binding to metals. In yet another aspect, the invention includes N-quaternized or silane-based multidentate catalysts. The catalysts of the invention show high robustness, strong resistance to small alkyne polymerization and significantly enhanced catalytic activity compared to their corresponding non-quaternized or non-silane-based multidentate catalyst analogs.
1. 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;
R 1 is selected from the group consisting of N + R(A − ), B, CH, CR, SiR and a 1,3,5-trivalent phenyl moiety, wherein R is optionally substituted alkyl or aryl, and A − is an anion;
R 3 is selected from the group consisting of alkyl, alkyl(aryl) and aryl, all of which are optionally substituted;
R 4 is a single bond, heteroatom, or an optionally substituted C 1 -C 3 alkyl chain; and,
M is a metal.
2. The compound of claim 1 , wherein M is a transition metal.
3. The compound of claim 2 , wherein M is selected from the group consisting of Mo, W, Re and Ta.
4. The compound of claim 1 , wherein G is phenyl, naphthyl or anthracenyl.
5. The compound of claim 1 , wherein the compound of formula (III) is the compound of formula (IV) or a salt thereof:
wherein:
each occurrence of n is independently 0, 1, 2, 3, or 4;
R 1 is selected from the group consisting of N + R(A − ), B, CH, CR, SiR and a 1,3,5-trivalent phenyl moiety, wherein R is optionally substituted alkyl or aryl, and A − is an anion;
each occurrence of R 2 is independently selected from the group consisting of alkyl, alkoxy, halogen, nitro, cyano, trifluoromethyl, trichloromethyl, carboxy, formyl, lower alkanoyl, carboxyamido and aryl lower alkanoyl;
R 3 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.
6. The compound of claim 5 , wherein R 1 is N + (R)(A − ), R is optionally substituted alkyl or aryl, and A − is an anion.
7. The compound of claim 5 , wherein the compound of formula (III) is selected from the group consisting of:
8. A method of preparing a compound of formula (IV), comprising reacting a compound of formula (II) with a metal alkylidyne compound with exchangeable ligands:
wherein:
R 1 is selected from the group consisting of N + R(A − ), B, CH, CR, SiR and a 1,3,5-trivalent phenyl moiety, wherein R is optionally substituted alkyl or aryl, and A − is an anion;
each occurrence of n is independently 0, 1, 2, 3 or 4;
each occurrence of R 2 is independently alkyl, halogen or an electron-withdrawing group;
R 3 is alkyl, alkyl(aryl) or aryl, all of which are optionally substituted;
M is selected from the group consisting of Mo, W. Re and Ta.
9. A method of preparing an alkyne-containing metathesis product, 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;
R 1 is selected from the group consisting of N + R(A − ), B, CH, CR, SiR and a 1,3,5-trivalent phenyl moiety, wherein R is optionally substituted alkyl or aryl, and A − is an anion;
each occurrence of R 2 is independently selected from the group consisting of alkyl, halogen, nitro, cyano, trifluoromethyl, trichloromethyl, carboxy, formyl, lower alkanoyl, carboxyamido and aryl lower alkanoyl;
R 3 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.
10. The method of claim 9 , wherein the compound of formula (IV) is selected from the group consisting of: