Chiral ligand-based metal-organic frameworks for broad-scope asymmetric catalysis
Metal-organic framework (MOFs) compositions based on chiral phosphine-, chiral oxazoline-, chiral pyridine-, and chiral diene-derived organic bridging ligands were synthesized and then post-synthetically metalated with metal precursors such as Ru and Rh complexes. The metal complexes could also be directly incorporated into the MOFs. The MOFs provide a versatile family of recyclable and reusable single-site solid catalysts for catalyzing a variety of asymmetric organic transformations, including the addition of arylboronic acids to α,β-unsaturated ketones and alkimines, the hydrogenation of substituted alkene and carbonyl compounds, and cyclization reactions. The solid catalysts can also be integrated into a flow reactor or a supercritical fluid reactor.
1. An asymmetric heterogeneous catalyst comprising a crystalline and porous metal-organic framework (MOF), wherein said crystalline and porous MOF comprises periodic repeats of a coordination complex comprising (a) a metal-based secondary building unit (SBU), wherein said metal-based SBU comprises a first metal, and (b) a chiral bridging ligand, wherein said chiral bridging ligand is coordinatively bonded to more than one SBU, wherein said chiral bridging ligand is further complexed to a second metal to provide a catalytic moiety, and wherein said chiral bridging ligand is a dicarboxylate-substituted chiral bisphosphine or a dicarboxylate-substituted chiral bicyclo[2.2.2]octane-2,5-diene.
2. The catalyst of claim 1 , wherein said catalyst is prepared by providing the chiral bridging ligand, contacting the chiral bridging ligand with a first metal source to obtain a MOF, and further comprising contacting the MOF with a second metal source to metalate the organic bridging ligand.
3. The catalyst of claim 1 , further comprising a non-chiral bridging ligand, optionally wherein the non-chiral bridging ligand is 4,4′((2-nitro-[1,1′-biphenyl]-4,4′-diyl)bis(ethyne-2,1-diyl))dibenzoic acid or 4,4′-(2-nitro[1,1′-biphenyl])bisbenzoic acid.
4. The catalyst of claim 1 , wherein the SBU is a Zr-oxo cluster.
5. The catalyst of claim 1 , wherein the second metal is Ru or Rh.
6. A method for preparing the asymmetric heterogeneous catalyst of claim 1 , said method comprising providing the chiral bridging ligand; contacting the chiral bridging ligand with a first metal source to obtain the crystalline and porous MOF; and contacting the crystalline and porous MOF with a second metal source to metalate the chiral bridging ligand.
7. The method of claim 6 , wherein the first metal source is ZrCl 4 .
8. The method of claim 6 , wherein the second metal source is Ru(cyclooctadiene)(2-Me-allyl) 2 , Rh(norbornadiene) 2 BF 4 , [RhCl(C 2 H 2 ) 2 ] 2 , or Rh(acetylacetonate)(C 2 H 4 ) 2 .
9. The method of claim 6 , wherein the chiral bridging ligand and the first metal source are contacted in a solvent or mixture of solvents selected based on solvent molecule size, such that the sizes and/or shapes of internal pores, cavities, and/or open channels in the crystalline and porous MOF can be tailored to enhance catalytic activity and selectivity.
10. The method of claim 9 , wherein the solvent comprises dimethylformamide (DMF).
11. A method for preparing an asymmetric compound comprising contacting a substrate capable of forming an asymmetric product by an asymmetric reaction with an asymmetric heterogeneous catalyst of claim 1 .
12. The method of claim 11 , wherein the asymmetric reaction is selected from the group consisting of hydrogenation; isomerization, optionally the isomerization of an allylamine, an allyl alcohol, or an α,β-unsaturated ketone; allylic substitution; a coupling reaction, optionally wherein the coupling reaction is a Buchwald-Hartwig amination, an intramolecular Heck reaction, or an intermolecular Heck reaction; conjugate addition, optionally wherein the conjugate addition is a Michael addition or an azo-Michael addition; an aldol reaction; a Mannich-type reaction; nucleophilic addition, optionally wherein the nucleophilic addition is to a carbonyl or imine group and/or wherein the nucleophilic addition is a cyanation, a propargylation, an allylation, a dienylation, an arylation, an alkenylation, or an alkylation; hydroformylation; hydroacylation; hydroboration; hydroamination; intra- or intermolecular hydrosilylation; an α-substitution reaction, optionally wherein the α-substitution reaction is a protonation, a fluorination, an amination, an arylation, or an orthoester alkylation; an ene reaction; a Diels-Alder reaction; a Pauson-Khand reaction; an Alder-Ene reaction, an enyne intramolecular cyclization; a [2+2+2] cycloaddition; a [3+2] cycloaddition; and a ring-opening reaction.
13. The method of claim 11 , wherein the asymmetric reaction is performed in the presence or absence of a solvent, optionally wherein a solvent is present, further optionally wherein the solvent is supercritical carbon dioxide.
14. The method of claim 11 , wherein the asymmetric reaction is performed in a flow reactor.
15. The method of claim 11 , wherein the asymmetric reaction is selected from the group consisting of 1,4-addition of an arylboronic acid to an α,β-unsaturated ketone; 1,2-addition of trimethylaluminum to an α,β-unsaturated ketone, 1,2-addition of an arylboronic acid to an aldimine, hydrogenation of a β-keto ester, hydrogenation of a substituted alkene, reductive cyclization of a 1,6-enyne, an Alder-Ene reaction, and a Pauson-Khand reaction.
16. The method of claim 11 , wherein the contacting is performed by contacting the substrate with about 3 mole percentage or less of the catalyst as compared to the substrate.
17. A method of preparing a compound, wherein the method comprises using a catalyst of claim 1 to catalyze a multi-step reaction or to catalyze sequential reactions.
18. A method of preparing a compound, wherein the method comprises using a plurality of catalysts of claim 1 to catalyze sequential reactions or to catalyze a multi-step reaction.