Tungsten oxo alkylidene complexes for

1. A compound of formula I-c:

wherein:

each of R 1 and R 2 is independently R, —OR, —SR, —N(R) 2 , —OC(O)R, —SOR, —SO 2 R, —SO 2 N(R) 2 , —C(O)N(R) 2 , —NRC(O)R, or —NRSO 2 R;

R 3′ is R 3 or —OSi(R) 3 ;

R 3 is R, —N(R) 2 , —NRC(O)R, —NRC(O)OR, —NRC(O)N(R) 2 , —NRSO 2 R, —NRSO 2 N(R) 2 , —NROR, NR 3 , —OR, O(R) 2 , or an optionally substituted group selected from a 5-6 membered monocyclic heteroaryl ring having at least one nitrogen and 0-3 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-2 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur;

R 4 is halogen, R, —N(R) 2 , —NRC(O)R, —NRC(O)OR, —NRC(O)N(R) 2 , —NRSO 2 R, —NRSO 2 N(R) 2 , —NROR, NR 3 , —OR, O(R) 2 , a phosphorus-containing ligand, or an optionally substituted group selected from a 5-6 membered monocyclic heteroaryl ring having at least one nitrogen and 0-3 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-2 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur;

each R is independently hydrogen or an optionally substituted group selected from C 1-20 aliphatic, C 1-20 heteroaliphatic having 1-3 heteroatoms independently selected from nitrogen, oxygen, or sulfur, phenyl, ferrocene, a 3-7 membered saturated or partially unsaturated carbocyclic ring, an 8-10 membered bicyclic saturated, partially unsaturated or aryl ring, a 5-6 membered monocyclic heteroaryl ring having 1-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having 1-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having 1-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or:

two or three R groups on the same nitrogen atom are taken together with the nitrogen to form an optionally substituted 3-12 membered saturated, partially unsaturated, or aryl ring having 0-5 additional heteroatoms not including the same nitrogen atom independently selected from nitrogen, oxygen, or sulfur; or:

two R groups on the same oxygen atom are taken together with the oxygen to form an optionally substituted 3-12 membered saturated, partially unsaturated, or aryl ring having 0-5 additional heteroatoms not including the same oxygen atom independently selected from nitrogen, oxygen, or sulfur;

n is 0, 1, or 2;

each R 5 is independently a monodentate ligand, or two R 5 are taken together with their intervening atoms to form an optionally substituted bidentate group; and

two or more of R 1 , R 2 , R 3 , R 4 and R 5 may be taken together with their intervening atoms to form an optionally substituted polydentate ligand; and

wherein the compound is other than WO(CH-t-Bu)(O-2,6-Ph 2 C 6 H 3 ) 2 (R 5 ) n , WO(CH-t-Bu)(O-t-Bu) 2 (R 5 ) n , W(O)(CHCMe 3 )(Me 2 Pyr) 2 (PMe 2 Ph) n , and

WO(CH—CH═C(Ph) 2 )(OC(CH 3 )(CF 3 ) 2 ) 2 (R 5 ), wherein Me 2 Pyr is 2,5-dimethylpyrrolyl.

2. The compound of claim 1 , wherein:

R 3′ is —OR or —OSi(R) 3 ;

R 4 is halogen.

3. The compound of claim 1 , wherein:

R 3′ is —OR or —OSi(R) 3 ;

R 4 is —N(R) 2 , or an optionally substituted group selected from a 5-6 membered monocyclic heteroaryl ring having at least one nitrogen and 0-3 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-2 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur.

4. The compound of claim 3 , wherein the compound promotes Z-selective olefin metathesis reactions.

5. A compound of formula IX:

wherein R 1′ and R 2′ are taken together with W to form an optionally substituted 3-8 membered saturated or partially unsaturated ring having, in addition to the intervening metal atom, 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, wherein both R 1′ and R 2′ are directly bonded to W through carbon atoms;

R 3′ is R 3 or —OSi(R) 3 ;

each of R 3 and R 4 is independently halogen, R, —N(R) 2 , —NRC(O)R, —NRC(O)OR, —NRC(O)N(R) 2 , —NRSO 2 R, —NRSO 2 N(R) 2 , —NROR, NR 3 , —OR, O(R) 2 , a phosphorus-containing ligand, or an optionally substituted group selected from a 5-6 membered monocyclic heteroaryl ring having at least one nitrogen and 0-3 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-2 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur;

each R is independently hydrogen or an optionally substituted group selected from C 1-20 aliphatic, C 1-20 heteroaliphatic having 1-3 heteroatoms independently selected from nitrogen, oxygen, or sulfur, phenyl, ferrocene, a 3-7 membered saturated or partially unsaturated carbocyclic ring, an 8-10 membered bicyclic saturated, partially unsaturated or aryl ring, a 5-6 membered monocyclic heteroaryl ring having 1-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having 1-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having 1-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or:

two or three R groups on the same nitrogen atom are taken together with the nitrogen to form an optionally substituted 3-12 membered saturated, partially unsaturated, or aryl ring having 0-5 additional heteroatoms not including the same nitrogen atom independently selected from nitrogen, oxygen, or sulfur; or:

two R groups on the same oxygen atom are taken together with the oxygen to form an optionally substituted 3-12 membered saturated, partially unsaturated, or aryl ring having 0-5 additional heteroatoms not including the same oxygen atom independently selected from nitrogen, oxygen, or sulfur;

n is 0, 1, or 2;

each R 5 is independently a monodentate ligand, or two R 5 are taken together with their intervening atoms to form an optionally substituted bidentate group; and

two or more of R 1′ , R 2′ , R 3 , R 4 and R 5 may be taken together with their intervening atoms to form an optionally substituted polydentate ligand; and

wherein the compound is other than

wherein —ORf 6 is OC(CH 3 )(CF 3 ) 2 .

6. The compound of claim 1 , wherein R is —OR, wherein R is optionally substituted phenyl.

7. The compound of claim 6 , wherein R 3′ is

8. The compound of claim 3 , wherein R 4 is —N(R) 2 , wherein the two R groups are taken together with the nitrogen to form an optionally substituted 3-8 membered saturated, partially unsaturated, or aryl ring having 0-3 additional heteroatoms not including the N atom from —N(R) 2 independently selected from nitrogen, oxygen, or sulfur.

9. The compound of claim 8 , wherein R 4 is

10. The compound of claim 3 , wherein the compound is selected from:

W(O)(CH-t-Bu)(Ph 2 Pyr)(OHMT), W(O)(CH-t-Bu)(Ph 2 Pyr)(OHIPT), W(O)(CH-t-Bu)[N(C 6 F 5 ) 2 (OHMT)(PPhMe 2 ), W(O)(CH-t-Bu)N—(C 6 F 5 ) 2 (OHMT), W(O)(CH-t-Bu)(Me 2 Pyr)(DFTO)(PPhMe 2 ), W(O)(CH-t-Bu)(Me 2 Pyr)(DFTO), W(O)(CHCMe 2 Ph)(Me 2 Pyr)(DFTO)(PPhMe 2 ), W(O)(CHCMe 2 Ph)(Me 2 Pyr)(DFTO), and W(O)(CH-t-Bu)[N—(C 6 F 5 ) 2 ](DFTO).

11. The compound of claim 1 , wherein:

R 3′ is —OR; and

R 4 is —OR.

12. The compound of claim 1 , wherein:

R 3′ is —OSi(R) 3 ; and

R 4 is —OR.

13. The compound of claim 1 , wherein the compound is W(O)(CH-t-Bu)(OHMT) 2 , W(O)(CH-t-Bu)(OHIPT) 2 , W(O)(CH-t-Bu)(DFTO) 2 , or WO(CH-t-Bu)[OSi(t-Bu) 3 ](OHMT).

14. The compound of claim 1 , wherein n is 0.

15. The compound of claim 1 , wherein R 1 is optionally substituted C 1-20 aliphatic, and R 2 is hydrogen.

16. A compound or compound complex comprising the compound of claim 1 and a Lewis acid.

17. The compound or compound complex of claim 16 , wherein the Lewis acid comprises a boron atom.

18. The compound or compound complex of claim 17 , wherein the Lewis acid is B(C 6 F 5 ) 3 .

19. The compound or compound complex of claim 16 , wherein the compound or compound complex is W[OB(C 6 F 5 ) 3 ](CH-t-Bu)(Me 2 Pyr)(OHMT).

20. The compound of claim 1 , wherein:

R 3′ is R 3 ;

R 3 is —OR; and

R 4 is —N(R) 2 .

21. The compound of claim 20 , wherein:

R 3 is an optionally substituted group selected from:

R 4 is —N(R) 2 , wherein the two R groups are taken together with the nitrogen to form an optionally substituted 3-8 membered saturated, partially unsaturated, or aryl ring having 0-3 additional heteroatoms not including the N atom from —N(R) 2 independently selected from nitrogen, oxygen, or sulfur.

22. The compound of claim 21 , wherein R 4 is optionally substituted pyrrolyl.

23. The compound of claim 20 , wherein each of R 3 and R 4 is independently substituted

24. The compound of claim 5 , wherein R 1′ and R 2 are taken together with W to form an optionally substituted 4-membered metallacyclobutane.

25. The compound of claim 1 , wherein:

R 3 is —R, —N(R) 2 , —NRC(O)R, —NRC(O)OR, —NRC(O)N(R) 2 , —NRSO 2 R, —NRSO 2 N(R) 2 , —NROR, —OR, or an optionally substituted group selected from a 5-6 membered monocyclic heteroaryl ring having at least one nitrogen and 0-3 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-2 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur; and

R 4 is halogen, —R, —N(R) 2 , —NRC(O)R, —NRC(O)OR, —NRC(O)N(R) 2 , —NRSO 2 R, —NRSO 2 N(R) 2 , —NROR, —OR, or an optionally substituted group selected from a 5-6 membered monocyclic heteroaryl ring having at least one nitrogen and 0-3 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 4-7 membered saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-2 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, a 7-10 membered bicyclic saturated or partially unsaturated heterocyclic ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur, or an 8-10 membered bicyclic heteroaryl ring having at least one nitrogen and 0-4 additional heteroatoms independently selected from nitrogen, oxygen, or sulfur.

26. The compound of claim 25 , wherein R 3 and R 4 are different.