Tridentate pincer ligand supported metal-alkylidyne and metallacycloalkylene complexes for alkyne polymerization
Tridentate pincer ligand supported metal complexes are formed where the complex is a trianionic pincer ligand supported metal-alkylidyne complex or a tetra-anionic pincer-ligand supported metallacycloalkylene complex formed by addition of an alkyne to the trianionic pincer ligand supported metal-alkylidyne complex. The tridentate pincer ligand supported metal complex that includes a group 5-7 transition metal and an OCO trianionic pincer ligand or an alkyne adduct thereof and methods of preparing the complexes are disclosed. The use of the tridentate pincer ligand supported metal complex for the polymerization of alkynes is disclosed, where high molecular weight poly(alkyne)s can be formed in high yield. The poly(alkyne) can be a macrocyclic polymer.
1. A tridentate pincer ligand supported metal complex, comprising the structure:
where: M is a group 5-7 transition metal; R is independently, H, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, or C 5 to C 20 alkyl: R′ is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl t-butyl, C 5 to C 20 alkyl, phenyl, naphthyl, or C 13 to C 22 aryl; X is independently O, N, S, P, or Se; n is independently 1 to 2, m is 1 to 2, and R″ is independently methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, C 5 to C 20 alkyl, phenyl, naphthyl, C 13 to C 18 aryl or two R″ are combined as a C 4 to C 6 alkylene, wherein XR″ 2 is a 5 to 7-membered ring; or
where: R is, independently, H, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl t-butyl, or larger alkyl; R′ is, independently, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, C 5 -C 22 alkyl, phenyl, naphthyl, C 13 -C 22 aryl, aryl substituted with one or more fluoro, C 1 -C 3 alkoxy, or trifluoromethyl, or trimethylsilyl; R′″ is H or methyl; X, independently, is O, N, S, P, or Se; R″, independently, is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, C 5 -C 22 , phenyl, naphthyl, C 13 -C 22 aryl, or two R″ are combined as a C 4 to C 6 alkylene; n is 1 to 3 depending on X; m is 1 to 2; and M is a group 5-7 transition metal.
2. The tridentate pincer ligand supported metal complex of claim 1 , wherein M is W.
3. The tridentate pincer ligand supported metal complex of claim 1 , wherein R is alkyl in the 3 and 3″ positions and H in all other positions.
4. The tridentate pincer ligand supported metal complex of claim 1 , wherein X is O.
5. The tridentate pincer ligand supported metal complex of claim 1 , wherein XR″ n is diethyl ether or tetrahydrofuran.
6. A trianionic pincer ligand supported metal-alkylidyne salt, comprising a tridentate pincer ligand supported metal complex anion and a cation derived from protonation of a base selected from tripheylphosphorane, methylithium, n-butyllithium, imidazole, pyrazole, pyridine, and 1,8diazabicyclo[5.4.0]undec-7-ene.
7. The trianionic pincer ligand supported metal-alkylidyne salt of claim 6 , having the structure:
8. The tridentate pincer ligand supported metal complex of claim 1 , having the structure:
9. The tridentate pincer ligand supported metal complex of claim 1 , having the structure:
10. The tridentate pincer ligand supported metal complex of claim 1 , having the structure:
11. The tridentate pincer ligand supported metal complex of claim 1 , having the structure:
12. The tridentate pincer ligand supported metal complex of claim 1 , having the structure:
13. A method for the preparation of the tridentate pincer ligand supported metal complex of claim 1 , comprising: combining a trialkoxy metal-alkylidyne with an OCO pincer ligand having a 1,1′:3′,1″ terphenyl-2,2″-diol structure:
wherein R is independently, H, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, or C 5 to C 20 alkyl, and wherein the metal of the trialkoxy metal-alkylidyne is a group 5-7 transition metal; and deprotonating the 2′-H of the OCO pincer ligand precursor by addition of a base, wherein the trianionic pincer ligand supported metal-alkylidyne complex of claim 1 is a salt, wherein the anion of the salt is a trianionic pincer ligand supported metal-alkylidyne complex.
14. The method of claim 13 , wherein the base is triphenylphosphorane, methyllithium, n-butyllithium, imidazole, pyrazole, pyridine, or 1,8-diazabicyclo[5.4.0]undec-7-ene.
15. The method of claim 13 , further comprising addition of an electrophile, wherein the salt is converted into a neutral trianionic pincer ligand supported metal-alkylidyne complex.
16. The method of claim 15 , wherein the electrophile is an alkyl-triflate or an alkyl-tetrafluoroborate.
17. The method of claim 15 , further comprising providing a second ligand and exchanging a first ligand of the neutral trianionic pincer ligand supported metal-alkylidyne complex to form a second neutral trianionic pincer ligand supported metal-alkylidyne complex.
18. The method of claim 17 , further comprising adding one to ten equivalents of an alkyne to the second neutral trianionic pincer ligand supported metal-alkylidyne complex to form a tetra-anionic pincer-ligand supported metallacycloalkylene complex.
19. A method of polymerizing an alkyne, comprising: providing a catalytic amount of a tridentate pincer ligand supported metal complex according to claim 1 ; and combining the trianionic pincer ligand supported metal-alkylidyne complex with a plurality of alkyne monomers to form a poly(alkyne).
20. The method of claim 19 , wherein the tridentate pincer ligand supported metal complex and alkyne monomers are provided in an aprotic solvent.
21. The method of claim 19 , further comprising providing an electrophile, wherein the tridentate pincer ligand supported metal complex is a salt.
22. The method of claim 19 , wherein the poly(alkyne) has a macrocyclic structure.
23. The method of claim 19 , wherein the alkyne monomer is phenylacetylene.