Stabilization of active metal catalysts at metal-organic framework nodes for highly efficient organic transformations
Metal-organic framework (MOFs) compositions based on post¬synthetic metalation of secondary building unit (SBU) terminal or bridging OH or OH 2 groups with metal precursors or other post-synthetic manipulations are described. The MOFs provide a versatile family of recyclable and reusable single-site solid catalysts for catalyzing a variety of asymmetric organic transformations, including the regioselective boryiation and siiylation of benzyiic C—H bonds, the hydrogenation of aikenes, imines, carbonyls, nitroarenes, and heterocycles, hydroboration, hydrophosphination, and cyclization reactions. The solid catalysts can also be integrated into a flow reactor or a supercritical fluid reactor.
1. A method for preparing a catalyst, said method comprising:
providing a parent metal-organic framework (MOF), wherein the parent MOF comprises (i) a secondary building unit (SBU) comprising a metal oxo cluster comprising a terminal or bridging OH or OH 2 group and (ii) an organic bridging ligand; and
reacting the parent MOF with a catalyst precursor, wherein the catalyst precursor is a compound of the formula ML n X, wherein X is a halide, H, alkyl or aryl group, M is a catalytically active metal, n is an integer from 0 to 5, and each L is independently selected from the group consisting of H, a halide, an alkyl group, an aralkyl group, an aryl group, a heteroaryl group, an alkoxy group, and an amine, thereby forming a MOF catalyst comprising a SBU comprising a metal oxo cluster further comprising a —OML n group or a —(OH)ML n group.
2. The method of claim 1 , wherein the SBU of the parent MOF is selected from the group consisting of Zr-oxo clusters, Hf-oxo clusters, Zn-oxo clusters, Ti-oxo clusters, Al-oxo clusters, Cu-carboxylate paddlewheels, and Ce-oxo clusters.
3. The method of claim 1 , wherein the organic bridging ligand is substituted with one or more carboxylate, pyridine, and/or phosphonate moieties, optionally wherein the organic bridging ligand is a dicarboxylate, a tricarboxylate, or a tetracarboxylate.
4. The method of claim 3 , wherein the organic bridging ligand comprises one or more aryl or arylene groups, optionally wherein the organic bridging ligand is selected from the group consisting of 1,4-bis(4-carboxyphenyl)benzene, p,p′-terphenyldicarboxylic acid (TPDC), methane tetrakis(p-biphenylcarboxylate) (MTBC), trimesic acid (BTC), 4,4′-bis(carboxyphenyl)-2-nitro-1,1′-biphenyl (TPHN), and 1,1′-biphenyl-4,4′-dicarboxylate.
5. The method of claim 1 , wherein M is selected from the group consisting of Mg, Zr, Hf, V, Fe, Co, Cr, Mn, Ni, and Cu.
6. The method of claim 5 , wherein the catalyst precursor is selected from CoCl 2 , Me 2 Mg, Zr(CH 2 Ph) 4 , and FeBr 2 .
7. A method for preparing a catalyst, said method comprising:
providing a parent metal-organic framework (MOF), wherein the parent MOF comprises (i) a secondary building unit (SBU) comprising a metal oxo cluster comprising a terminal or bridging OH or OH 2 group and (ii) an organic bridging ligand; and
reacting the parent MOF with a catalyst precursor, wherein the catalyst precursor is a compound of the formula ML n X, wherein X is a halide, H, alkyl or aryl group, M is a catalytically active metal, n is an integer from 0 to 5, and each L is independently selected from the group consisting of H, a halide, an alkyl group, an aralkyl group, an aryl group, a heteroaryl group, an alkoxy group, and an amine, thereby forming a MOF catalyst comprising a SBU comprising a —OML n group or a —(OH)ML n group,
wherein the parent MOF is reacted with a base prior to reaction with the catalyst precursor to form a deprotonated SBU, optionally wherein the base is a salt of a Group 1 element and a carbanion, amide or hydride, further optionally wherein the base is n-butyl lithium (n-BuLi) or trimethylsilylmethyllithium (LiCH 2 SiMe 3 ).
8. A catalyst prepared according to the method of claim 1 .
9. The method of claim 7 , wherein the deprotonated SBU is reacted with a reducing agent, optionally wherein the reducing agent is a borane, further optionally wherein the reducing agent is pinacolborane.
10. The method of claim 9 , wherein the SBU of the parent MOF comprises a Ce-oxo cluster, optionally wherein the parent MOF further comprises a trimesic acid organic bridging ligand.
11. A metal-organic framework (MOF) comprising (i) a secondary building unit (SBU), wherein the SBU comprises a metal oxo cluster comprising a first metal and further comprising one or more —OM′L x and/or —(OH)M′L x groups, wherein M′ is a second metal, wherein said second metal is different than the first metal, x is an integer between 0 and 5, and each L is independently selected from the group consisting of H, a halide, an alkyl group, an aralkyl group, an aryl group, a heteroaryl group, an alkoxy group, and an amine, optionally wherein the 0 or OH of the —OM′L x or —(OH)M′L x group is a metalated terminal oxo group, a metalated oxygen from a deprotonated μ-OH group, a metalated terminal OH group, or a metalated bound water group; and (ii) an organic bridging ligand.
12. The MOF of claim 11 , wherein the second metal is free of decomposition due to disproportionation.
13. The MOF of claim 11 , wherein M′ is selected from Li, Mg, Fe, Co, Cr, Mn, Ni, and Cu, optionally wherein M′ is a catalytically active metal selected from Co, Fe, Cu and Mg.
14. The MOF of claim 11 , wherein the SBU is derived from a Zr-oxo cluster, a Hf-oxo cluster, a Zn-oxo cluster, a Ti-oxo cluster, an Al-oxo cluster, a Cu-carboxylate paddlewheel, or a Ce-oxo cluster, optionally wherein the SBU is derived from a cubic or octahedral metal oxo cluster, further optionally wherein the cubic or octahedral metal oxo cluster is of the formula Zr 8 (μ 2 -O) 8 (μ 2 -OH) 4 or Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 .
15. The MOF of claim 11 , wherein the MOF comprises a plurality of SBUs comprising one or more —OM′L x and/or —(OH)M′L x groups, optionally wherein each SBU comprises between 1 and 4 —OM′L x and/or —(OH)M′L x groups.
16. The MOF of claim 11 , wherein the MOF has the formula Zr 6 O 4 (OH 4-n )(OM′L) n (O 2 CR) 12 , wherein n is an integer between 1 and 4, M′ is Co, Fe, Cu or Mg, L is H or a halide, and R is an arylene group.
17. The MOF of claim 11 , wherein the SBU has the formula Ce III 6 (μ 3 -O) 4 (μ 3 -OLi) 4 (H) 6 (THF) 6 .
18. A method for preparing a compound comprising contacting a substrate capable of forming a product by catalytic transformation with a heterogeneous catalyst of claim 8 , wherein the catalytic transformation is selected from the group consisting of ethylene oligomerization, alkyne coupling, hydromethylation, alkane dehydrosilation, alkane metathesis, dehydrogenative alkyl C—H phosphination, pyridine functionalization, dehydrocoupling, hydrosilation of olefins, ketones and aldehydes, oxidation of primary alcohols, hydroamination, hydroformylation, C—H borylation, hydrogenation of alkenes, imines, carbonyls, nitroarenes, and heterocycles, hydroboration, hydrophosphination, and C—H amination.
19. The method of claim 18 , wherein the catalytic transformation is conducted in a batch reactor, a flow reactor, or in a supercritical fluid reactor.
20. A catalyst prepared according to the method of claim 7 .