Oxidative homo-coupling reactions of aryl boronic acids using a porous copper metal-organic framework as a highly efficient heterogeneous catalyst

Abstract

The disclosure provides methods for the use of open metal frameworks to catalyze coupling reactions.

Description

TECHNICAL FIELD

The disclosure provides methods for the use of open metal frameworks to catalyze coupling reactions.

SUMMARY

The disclosure provides methods and composition comprising open frameworks with accessible metal sites (open-metal-sites) for catalyzing coupling reactions. The disclosure includes all open framework materials that are constructed from organic links bridged by multidentate organic or inorganic cores. Including all classes of open framework materials: covalent organic frameworks (COFs), zeolitic imidozolate frameworks (ZIFs), metal organic polyhedral (MOP) and metal organic frameworks (MOFs) and all possible resulting net topologies as described within the reticular chemistry structure resource.

The disclosure provides a method of using noble metal-based metal organic framework (MOP) or metal organic polyhedral (MOP) such as Cu-based and Pd-based frameworks as the catalyst for homo-coupling synthesis of biaryls. Under un-optimized conditions MOF and/or MOP framework reactions show up to 95% conversion and 90% selectivity. The MOF and/or MOP catalyst is proved to be chemically stable and has the long-sought-after heterogeneous catalytic characteristics.

In one embodiment, a noble metal-based homocoupling of arylboronic acids to synthesize substituted biaryls is provided. Such methods replace traditional methods such as dimerization of aryl-diazonium salts in Gomberg-Bachman reactions and homocoupling of aryl-halides in Ullmann reactions.

The methods and compositions of the disclosure can be used in catalysis and developing new approach for drug precursor synthesis.

The disclosure provides a method for synthesizing biaryls comprising contacting a metal organic framework (MOF) or metal organic polyhedral (MOP) with an aryl boronic acid compound under conditions wherein the MOF or MOP catalyze the synthesis of the biaryl through a homo-coupling reaction. In some embodiment, the method further comprises cupric acetate and the MOF or MOP comprises the metal copper. In yet another embodiment, the aryl bornic acid has the general structure:

wherein R is selected from the group consisting of H, NO₂, CN, Cl, t-Bu, N(CH₃)₂ and substituted or unsubstituted napthyl. In one embodiment, the napthyl has the structure

In yet another embodiment, the MOF or MOP comprises a linking ligands selected from the group consisting of:

wherein R₁-R₁₅ may or may not be present and if present are independently selected from the group consisting of: —NH₂, —CN, —OH, ═O, ═S, —SH, —P, —Br, —Cl, —I, —F,

wherein X=1, 2, or 3. In yet another embodiment the linking moiety is

wherein R₁-R₃ may or may not be present and if present are independently selected from the group consisting of: —H, —NH₂, —CN, —OH, ═O, ═S, —SH, —P, —Br, —Cl, —I, —F,

wherein X=1, 2, or 3. In yet another embodiment, the MOF comprises copper. In a specific embodiment, the MOF comprises a Cu₃(BTC)₂ (where BTC is benzene-1,3,5-tricarboxylate). In other embodiments, the MOF comprises a metal selected from the group consisting of Cr(II), Pb(II), Mn(IV), Ti(II) and Ni(II).

The disclosure also provide a reaction mixture comprising a metal organic framework (MOF) or metal organic polyhedral (MOP) and an aryl boronic acid. In some embodiments, the mixture further comprises cupric acetate. In some embodiments, the aryl bornic acid has the general structure:

wherein R is selected from the group consisting of H, NO₂, CN, Cl, t-Bu, N(CH₃)₂ and substituted or unsubstituted napthyl. In one embodiment, the napthyl has the structure

In yet other embodiment, the MOF or MOP comprises a linking ligands selected from the group consisting of:

wherein R₁-R₁₅ may or may not be present and if present are independently selected from the group consisting of: —NH₂, —CN, —OH, ═O, ═S, —SH, —P, —Br, —Cl, —I, —F,

wherein X=1, 2, or 3. In one embodiment, the linking moiety is

wherein R₁-R₃ may or may not be present and if present are independently selected from the group consisting of: —H, —NH₂, —CN, —OH, ═O, ═S, —SH, —P, —Br, —Cl, —I, —F,

wherein X=1, 2, or 3. In one embodiment, the MOF comprises copper. In a specific embodiment, the MOF comprises a Cu₃(BTC)₂ (where BTC is benzene-1,3,5-tricarboxylate). In yet other embodiments, the MOF comprises a metal selected from the group consisting of Cr(II), Pb(II), Mn(IV), Ti(II) and Ni(II).

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A-D shows atomic connectivity and structure of crystalline Cu₃(BTC)₂. (A) Cu sites in as-synthesized (left) and activated Cu₃(BTC)₂ frameworks; (B) BTC link; (C) structure of as-synthesized Cu₃(BTC)₂; and (D) structure of activated Cu₃(BTC)₂. Cu, O and C are shown. All H atoms are omitted for clarity.

FIG. 2 shows a comparison of the yields for three cycles of the homo-coupling of 4-cyanophenylboronic acid using recycled Cu₃(BTC)₂.

FIG. 3 shows the proposed mechanism for the Oxidative Homo-coupling catalyzed by Cu₃(BTC)₂.

FIG. 4 shows a comparison of the experimental PXRD patterns of fresh Cu₃(BTC)₂ (bottom) and Cu₃(BTC)₂ after homo-coupling of phenylboronic acid (top).

FIG. 5 shows a comparison of the experimental PXRD patterns of fresh Cu₃(BTC)₂ (bottom), and Cu₃(BTC)₂ after homo-coupling of 4-nitrophenylboronic acid (top).

FIG. 6 shows a comparison of the experimental PXRD patterns of fresh Cu₃(BTC)₂ (bottom), and Cu₃(BTC)₂ after homo-coupling of 4-cyanophenylboronic acid (top).

FIG. 7 shows a comparison of the experimental PXRD patterns of fresh Cu₃(BTC)₂ (bottom), and Cu₃(BTC)₂ after homo-coupling of 4-chlorophenylboronic acid (top).

FIG. 8 shows a comparison of the experimental PXRD patterns of fresh Cu₃(BTC)2 (bottom), and Cu3(BTC)₂ after homo-coupling of 4-tert-butylphenylboronic acid (top).

FIG. 9 shows a comparison of the experimental PXRD patterns of fresh Cu₃(BTC)₂ (bottom), and Cu₃(BTC)₂ after homo-coupling of 4-(dimethylamino)-phenylboronic acid (top).

FIG. 10 shows a comparison of the experimental PXRD patterns of fresh Cu₃(BTC)₂ (bottom), and Cu3(BTC)₂ after homo-coupling of 1-naphthylboronic acid (top).

FIG. 11 shows a comparison of the experimental PXRD patterns of Cu₃(BTC)₂ after first cycle homo-coupling of 4-cyanophenylboronic acid (bottom), Cu₃(BTC)₂ after second cycle (middle), and Cu₃(BTC)₂ after third cycle (top).

FIG. 12 shows FT-IR spectrum of fresh Cu₃(BTC)₂.

FIG. 13 shows FT-IR spectrum of benzene-1,3,5-tricarboxylic acid (BTC).

FIG. 14 shows FT-IR spectrum of recovered solid after the homo-coupling of phenylboronic acid.

FIG. 15 shows FT-IR spectrum of recovered liquid after the homo-coupling of phenylboronic acid.

DETAILED DESCRIPTION

As used herein and in the appended claims, the singular forms “a,” “and,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a framework” includes a plurality of such frameworks and reference to “the metal” includes reference to one or more metals and equivalents thereof known to those skilled in the art, and so forth.

Also, the use of “or” means “and/or” unless stated otherwise. Similarly, “comprise,” “comprises,” “comprising” “include,” “includes,” and “including” are interchangeable and not intended to be limiting.

It is to be further understood that where descriptions of various embodiments use the term “comprising,” those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language “consisting essentially of” or “consisting of.”

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although any methods and reagents similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods and materials are now described.

All publications mentioned herein are incorporated herein by reference in full for the purpose of describing and disclosing the methodologies, which are described in the publications, which might be used in connection with the description herein. The publications discussed above and throughout the text are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior disclosure.

The synthesis of functionalized biaryls is currently an area of great interest and importance, as these compounds account for some of the most critical structural units in natural products, drugs and functional materials. Homo-coupling of arylboronic acids using noble metal catalysts has proved to be a useful method for the synthesis of symmetrical biaryls. Although efficient, their cost and stability dramatically limit the viability of Pd-based catalysts in many applications. Another method employs Gomberg-Bachmann and Ullmann reactions which require high temperatures (ca. 200° C.) and thus severely limit their compatibility with many functional groups (—NO₂ and —CN).

The disclosure demonstrates that MOF and MOP structures serve as an outstanding alternative to precious metal dominated Suzuki homo-coupling reactions with comparable yield and selectivity. The methods and compositions of the disclosure also show great potential of MOF chemistry as it introduces desired complexity and functionality along with exceptional porosity. Specifically, such complexity offered by uniquely connected active centers behave in a favored pattern, which is unprecedented comparing to its molecular counter parts. The catalyst may also be modified in a way to allow the Chan-Lam Coupling, which is a side product of the desired homocoupling reaction and is equally valuable for synthesis.

The disclosure demonstrates the methods and compositions of the disclosure on a group of selected MOFs/MOPs—MOF-5, MOF-177, MIL-53, MOF-199 and MOP-OH (Cu-based). However, it will be apparent from the disclosure other MOF and MOP frameworks that can be utilized in methods of the disclosure.

The disclosure provides a method for homo-coupling synthesis of biaryls using a metal-containing metal-organic frameworks (MOFs), e.g., Cu₃(BTC)₂ (where BTC is benzene-1,3,5-tricarboxylate), as the catalyst. Under un-optimized conditions, use of this MOF catalyst in the homo-couplings of arylboronic acids functionalized with, e.g., —H, —NO₂, —CN, —Cl, -t-Bu- and -Me₂N, and 1-naphthylboronic acid result in up to 92% yield. The MOF catalyst offers remarkably superior attributes as a heterogeneous catalyst that are endowed by its highly ordered and open structure; aspects that put its performance on par with the homogeneous catalysts. In addition the MOF catalyst has all the advantages associated with the variations that can be made on the MOF constituents. A description of some of these advantages and attributes are shown in Table 1.

TABLE 1
Comparison of Pd-based catalyst and MOF
catalyst
	Pd-based Catalyst	MOF Catalyst
Example	(SiPr)Pd(OAc)2(H2O)(4)	Cu3(BTC)2
Metal	Pd(II)	Cu(II)
Ligand
Oxidant		Air
Catalyst Type	Homogeneous	Heterogenous
Reusability	Low	High
Active Site	High	High
Accessibility
Diffusion Rate	High	High
Structural	Medium	High
Tunability

Other transition metals, such as Cr(II), Pb(II), Mn(IV), Ti(II) and Ni(II) have been used to accelerate this homo-coupling reaction, however other co-catalysts and environmentally harmful additives need to be added to facilitate efficient turnover. Cu-based compounds are known to catalyze some coupling reactions (e.g., Glaser Coupling and Chan-Lam Coupling) under homogeneous conditions and consequently high yields can be achieved. In order to maintain such performance in heterogeneous catalytic systems, materials with well-defined porous structures with mono-dispersed and fully accessible metal centers are needed. MOFs are a new class of porous crystals with exceptional porosity and record-breaking surface areas (up to 5,900 m² g⁻¹).

To illustrate embodiments of the disclosure, Cu₃(BTC)₂, a copper-based MOF, was used as the catalyst for various oxidative homo-coupling reactions. As shown in FIG. 1, the structure of this MOF is constructed from copper paddlewheel secondary building units (SBUs). The 12 carboxylate oxygen atoms from the two benzenetricarboxylic acid (BTC) groups bind to four coordination sites for each of the three Cu ions of the formula unit. Each metal completes its pseudooctahedral coordination sphere with an axial H₂O ligand along the Cu—Cu axis. Water molecules can be easily removed by heating under vacuum (FIG. 1A), which leads to open copper centers that are mono-dispersed throughout the pores (FIG. 1D). The copper centers have been shown to be Lewis acidic and they can be coordinated by various molecules. Such open metal centers in highly porous open framework may accelerate the initial coordination of amine and the following transmetallation.

FIG. 3 depicts a proposed mechanism of action of the MOF in the synthesis of biaryls. The copper paddlewheel in the framework is coordinated by the base, followed by being oxidized by O₂ to form the catalytic copper (III) species I. Transmetallation of I with aryl boronic acid gives rise to complex II. The subsequent reductive elimination at the copper center leads to the Chan-Lam coupling product R—NHR′ and the copper (I) species IV. On the other hand, a second transmetallation of complex II with aryl boronic acid produces III, which subsequently forms species IV and the homo-coupling product R—R by a reductive elimination reaction. Hydrolysis of species IV forms intermediate V and borate anion (evidenced by an ¹¹B NMR shift of 3.69 ppm).^[13] The catalytic cycle was fulfilled by an oxidation reaction of V to regenerate the catalytic active species I.

As noted the Cu(II) core is linked using a linking ligand or moiety. The linking ligand or moiety can be any number of different compounds as described below. In the specific examples provided herein, the linking ligand/moiety is a BTC compound. Furthermore, it will be recognized that the linking ligand/moiety may be further functionalized as described below.

As used herein, a “core” refers to a repeating unit or units found in a framework. Such a framework can comprise a homogenous repeating core or a heterogeneous repeating core structure. A core comprises a metal or cluster of metals and a linking moiety. A plurality of cores linked together defines a framework.

The term “cluster” refers to identifiable associations of 2 or more atoms. Such associations are typically established by some type of bond—ionic, covalent, Van der Waal, and the like.

A “linking cluster” refers to a one or more reactive species capable of condensation comprising an atom capable of forming a bond between a linking moiety substructure and a metal group or between a linking moiety substructure and another linking moiety substructure. Examples of such species are selected from the group consisting of a boron, oxygen, carbon, nitrogen, and phosphorous atom. In some embodiments, the linking cluster may comprise one or more different reactive species capable of forming a link with a bridging oxygen atom. For example, a linking cluster can comprise CO₂H, CS₂H, NO₂, SO₃H, Si(OH)₃, Ge(OH)₃, Sn(OH)₃, Si(SH)₄, Ge(SH)₄, Sn(SH)₄, PO_SH, AsO₃H, AsO₄H, P(SH)₃, As(SH)₃, CH(RSH)₂, C(RSH)₃, CH(RNH₂)₂, C(RNH₂)₃, CH(ROH)₂, C(ROH)₃, CH(RCN)₂, C(RCN)₃, CH(SH)₂, C(SH)₃, CH(NH₂)₂, C(NH₂)₃, CH(OH)₂, C(OH)₃, CH(CN)₂, and C(CN)₃, wherein R is an alkyl group having from 1 to 5 carbon atoms, or an aryl group comprising 1 to 2 phenyl rings.

A “linking moiety” refers to a mono-dentate or polydentate compound that, through a linking cluster, bind a metal or a plurality of metals, respectively. Generally a linking moiety comprises a substructure having an alkyl or cycloalkyl group, comprising 1 to 20 carbon atoms, an aryl group comprising 1 to 5 phenyl rings, or an alkyl or aryl amine comprising alkyl or cycloalkyl groups having from 1 to 20 carbon atoms or aryl groups comprising 1 to 5 phenyl rings, and in which a linking cluster is covalently bound to the substructure. A cycloalkyl or aryl substructure may comprise 1 to 5 rings that comprise either of all carbon or a mixture of carbon with nitrogen, oxygen, sulfur, boron, phosphorus, silicon and/or aluminum atoms making up the ring. Typically the linking moiety will comprise a substructure having one or more carboxylic acid linking clusters covalently attached.

As used herein, a line in a chemical formula with an atom on one end and nothing on the other end means that the formula refers to a chemical fragment that is bonded to another entity on the end without an atom attached. Sometimes for emphasis, a wavy line will intersect the line.

In one embodiment, the linking moiety substructure is selected from any of the following:

wherein R₁-R₁₅ may or may not be present and if present are independently selected from the group consisting of: —NH₂, —CN, —OH, ═O, ═S, —SH, —P, —Br, —Cl, —I, —F,

wherein X=1, 2, or 3.

In some embodiments, the framework used in the catalysis has a zeolitic structure. In such embodiments, the organic link typically comprises at least one 5-membered ring with a nitrogen in the one position and three position of the 5-membered ring, which forms the linking moiety or bridge between two metal ions. The imidazole ring can be further functionalized to form benzimidazoles, triazole, bensotriazole, tetrazole, guanine, xanthine and hypoxanthine derivatives. For example, the following linking moieties can be used in the formation of catalytic frameworks of the disclosure:

wherein R-R₄ is —H, —NH₂, —COOH, —CN, —NO₂, —F, —Cl, —Br, —S, —O, —SH, —SO₃H, —PO₃H₂, —OH, —CHO, —CS₂H, —SO₃H, —Si(OH)₃, —Ge(OH)₃, —Sn(OH)₃, —Si(SH)₄, —Ge(SH)₄, —Sn(SH)₄, —PO₃H, —AsO₃H, —AsO₄H, —P(SH)₃, —As(SH)₃, —CH(RSH)₂, C(RSH)₃, —CH(RNH₂)₂, —C(RNH₂)₃, —CH(ROH)₂, —C(ROH)₃, CH(RCN)₂, —C(RCN)₃

In yet another embodiment, the substructure can comprise substituted or unsubstituted aromatic rings, substituted of unsubstituted heteroacromatic rings, substituted or unsubstituted nonaromatic rings, substituted or unsubstituted nonaromatic heterocyclic rings, or saturated or unsaturated, substituted or unsubstituted, hydrocarbon groups. The saturated or unsaturated hydrocarbon groups may include one or more heteroatoms. For example a linking moiety can comprise the following structures:

wherein A₁, A₂, A₃, A₄, A₅, and A₆ are each independently absent or any atom or group capable of forming a sable ring structure and R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, and R₁₆ are each independently H, alkyl, aryl, OH, alkoxy, alkenes, alkynes, phenyl and substitutions of the foregoing, sulfur-containing groups (e.g., thioalkoxy), silicon-containing groups, nitrogen-containing groups (e.g., amides), oxygen-containing groups (e.g., ketones, and aldehydes), halogen, nitro, amino, cyano, boron-containing groups, phosphorus-containing groups, carboxylic acids, or esters. In one embodiment, R₁, R₂, R₃, R₄ are each independently selected from the group consisting of NH₂, CN, OH, ═O, ═S, SH, P, Br, CL, I, F,

wherein X=1, 2, or 3.

All of the foregoing linking moieties that possess appropriate reactive groups can be chemically transformed by a suitable reactant post framework synthesis to further functionalize the framework. By modifying the organic links within the framework post-synthesis, access to function groups there were previously inaccessible or accessible only through great difficulty and/or cost is possible and facile. Post framework reactants include all known organic transformations and their respective reactants; rings of 1-20 carbons with functional groups including atoms such as N, S, O. All metals that may chelate to and add functional groups; or a combination of previously existing and newly added functional groups. All reactions that result in tethering an organometallic complex to the framework for use, for example, as a heterogenous catalyst.

A post framework reactant refers to any organic reactant. Rings of 1-20 carbons with functional groups comprising atoms such as N, S, O, and P are useful. In addition, metal and metal containing compounds that may chelate to and add functional groups or a combination of previously existing and newly added functional groups are also useful. Reactions that result in the tethering of organometallic complexes to the framework for use as, for example, a heterogeneous catalyst can be used. For example, converting a reactive side group in a linking agent to an alcohol followed by reacting the group with an alkali earth metal to generate a metal alkoxide is provided.

Examples of post framework reactants include, but are not limited to, heterocyclic compounds. In one embodiment, the post framework reactant can be a saturated or unsaturated heterocycle. The term “heterocycle” used alone or as a suffix or prefix, refers to a ring-containing structure or molecule having one or more multivalent heteroatoms, independently selected from N, O and S, as a part of the ring structure and including at least 3 and up to about 20 atoms in the ring(s). Heterocycle may be saturated or unsaturated, containing one or more double bonds, and heterocycle may contain more than one ring. When a heterocycle contains more than one ring, the rings may be fused or unfused. Fused rings generally refer to at least two rings share two atoms there between. Heterocycle may have aromatic character or may not have aromatic character. The terms “heterocyclic group”, “heterocyclic moiety”, “heterocyclic”, or “heterocyclo” used alone or as a suffix or prefix, refers to a radical derived from a heterocycle by removing one or more hydrogens there from. The term “heterocyclyl” used alone or as a suffix or prefix, refers a monovalent radical derived from a heterocycle by removing one hydrogen there from. The term “heteroaryl” used alone or as a suffix or prefix, refers to a heterocyclyl having aromatic character. Heterocycle includes, for example, monocyclic heterocycles such as: aziridine, oxirane, thiirane, azetidine, oxetane, thietane, pyrrolidine, pyrroline, imidazolidine, pyrazolidine, pyrazoline, dioxolane, sulfolane 2,3-dihydrofuran, 2,5-dihydrofuran tetrahydrofuran, thiophane, piperidine, 1,2,3,6-tetrahydro-pyridine, piperazine, morpholine, thiomorpholine, pyran, thiopyran, 2,3-dihydropyran, tetrahydropyran, 1,4-dihydropyridine, 1,4-dioxane, 1,3-dioxane, dioxane, homopiperidine, 2,3,4,7-tetrahydro-1H-azepine homopiperazine, 1,3-dioxepane, 4,7-dihydro-1,3-dioxepin, and hexamethylene oxide. For example, heterocycles useful in the methods of the disclosure include:

In addition, heterocycle includes aromatic heterocycles (heteroaryl groups), for example, pyridine, pyrazine, pyrimidine, pyridazine, thiophene, furan, furazan, pyrrole, imidazole, thiazole, oxazole, pyrazole, isothiazole, isoxazole, 1,2,3-triazole, tetrazole, 1,2,3-thiadiazole, 1,2,3-oxadiazole, 1,2,4-triazole, 1,2,4-thiadiazole, 1,2,4-oxadiazole, 1,3,4-triazole, 1,3,4-thiadiazole, and 1,3,4-oxadiazole.

A framework can undergo post synthetic modification by reacting the framework with a reactive species. For example, if a side group on a linking moiety comprises, for example, NH₂ reaction with an aziridine containing compound results in opening of the reactive species ring depicted generally by:

Using such methods variations and functionalized frameworks can be generated. As shown above, the reaction of the linking moiety with aziridine results in the addition of a side group to the linking moiety. In such a framework the reactive side group can extend into the pores of the framework thereby modifying their size or charge.

The preparation of the frameworks of the disclosure can be carried out in either an aqueous or non-aqueous system. The solvent may be polar or non-polar as the case may be. The solvent can comprise the templating agent or the optional ligand containing a monodentate functional group. Examples of non-aqueous solvents include n-alkanes, such as pentane, hexane, benzene, toluene, xylene, chlorobenzene, nitrobenzene, cyanobenzene, aniline, naphthalene, naphthas, n-alcohols such as methanol, ethanol, n-propanol, isopropanol, acetone, 1,3,-dichloroethane, methylene chloride, chloroform, carbon tetrachloride, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, N-methylpyrolidone, dimethylacetamide, diethylformamide, thiophene, pyridine, ethanolamine, triethylamine, ethlenediamine, and the like. Those skilled in the art will be readily able to determine an appropriate solvent based on the starting reactants and the choice of solvent is not believed to be crucial in obtaining the materials of the disclosure.

Templating agents can be used in the methods of the disclosure. Templating agents employed in the disclosure are added to the reaction mixture for the purpose of occupying the pores in the resulting crystalline base frameworks. In some variations of the disclosure, space-filling agents, adsorbed chemical species and guest species increase the surface area of the metal-organic framework. Suitable space-filling agents include, for example, a component selected from the group consisting of: (i) alkyl amines and their corresponding alkyl ammonium salts, containing linear, branched, or cyclic aliphatic groups, having from 1 to 20 carbon atoms; (ii) aryl amines and their corresponding aryl ammonium salts having from 1 to 5 phenyl rings; (iii) alkyl phosphonium salts, containing linear, branched, or cyclic aliphatic groups, having from 1 to 20 carbon atoms; (iv) aryl phosphonium salts, having from 1 to 5 phenyl rings; (v) alkyl organic acids and their corresponding salts, containing linear, branched, or cyclic aliphatic groups, having from 1 to 20 carbon atoms; (vi) aryl organic acids and their corresponding salts, having from 1 to 5 phenyl rings; (vii) aliphatic alcohols, containing linear, branched, or cyclic aliphatic groups, having from 1 to 20 carbon atoms; or (viii) aryl alcohols having from 1 to 5 phenyl rings.

Crystallization can be carried out by leaving the solution at room temperature or in isothermal oven for up to 300° C.; adding a diluted base to the solution to initiate the crystallization; diffusing a diluted base into the solution to initiate the crystallization; and/or transferring the solution to a closed vessel and heating to a predetermined temperature.

The frameworks of the disclosure can be used in various devices and systems to perform the catalysis described and depicted in FIG. 3. The MOF and/or MOP compositions can be added to a reaction vessel comprising a reagents to be coupled (e.g., homocoupled). For example, a MOF-199 can be added to a reaction mixture comprising an arylboronic acid to be coupled and the reaction allowed to proceed. In some embodiments, the reaction mixture can be passed through a column comprising a MOF and/or MOP that catalyzes the homo-coupling of the reagents. In another embodiment, the reaction vessel can be agitated or mixed. As described elsewhere herein the MOF and/or MOP can be reused. In some embodiments, the reaction is carried out at room temperature. In another embodiment, the reaction is carried out with stirring at room temperature. After filtration and washing with fresh dichloromethane, the MOF can be fully recovered and re-used without any significant loss of activity.

The following examples are intended to illustrate but not limit the disclosure. While they are typical of those that might be used, other procedures known to those skilled in the art may alternatively be used.

EXAMPLES

Materials: MOF-199 (Basolite C300, Aldrich), cyclohexylamine, triethylamine, phenylbornic acid, 4-nitrophenylboronic acid, 4-cyanophenylbornic acid, 4-chlorophenylboronic acid, 4-ter-burlyphenylboronic acid, 4-(dimethylamino)-phenylboronic acid, naphthalene-1-bonronic acid and 1,3,5-trimethyoxybenzene were purchased form Aldrich Chemical Co. Dichloromethane was purchased from Fisher Scientific International Inc. All starting materials were used without further purification. All experimental operations, unless otherwise noted, were performed in air.

General Homo-coupling Reaction Procedure:

A mixture of arylboronic acid, (3.01 mmol), cyclohexylamine (0.248 g, 286 μL, 2.51 mmol) and triethylamine (0.253 g, 348 μL, 2.49 mmol) were premixed and dissolved in 20 mL dichloromethane in a 50 mL round-bottom flask. MOF (0.100 g, 0.165 mmol, 0.495 mmol Cu(II)) or cupric acetate monohydrate (Cu(OAc)₂.H2O, 0.100 g, 0.501 mmol) was then added to the solution. The mixture was stirred at room temperature for 5 h, followed by filtration and washing with fresh dichloromethane. The excess dichloromethane in the filtrate was subsequently removed by rotovap. 1,3,5-trimethoxybenzene (0.168 g, 1.00 mmol) was added to the filtrate as internal standard for ¹H NMR. Chemical shifts of all products in ¹H NMR agree well with literature data.

Biphenyl: 47% yield of biphenyl (based on phenylboronic acid) was afforded when MOF was used; no biphenyl product was formed in the case of cupric acetate monohydrate. GC-MS, m/z+154.1; 4,4′-dinitrobiphenyl: 87% and 18% yields of 4,4′-dinitrobiphenyl (based on 4-nitrophenylboronic acid) were afforded when MOF and cupric acetate monohydrate were used, respectively. GC-MS, m/z+244.2; Biphenyl-4,4′-dicarbonitrile: 92% and 19% yields of biphenyl-4,4′-dicarbonitrile (based on 4-cyanophenylboronic acid) were afforded in the presence of MOF and cupric acetate monohydrate, respectively. 1.34 mmol (yield: 90%) and 1.35 mmol (yield: 92%) biphenyl-4,4′-dicarbonitrile were observed in the second and third cycles, respectively. GC-MS, m/z+204.1; 4,4′-dichlorobiphenyl: 81% and 8% yields of 4,4′-dichlorobiphenyl (based on 4-chlorophenylboronic acid) were afforded in the presence of MOF and cupric acetate monohydrate, respectively. GC-MS, m/z+223.1; 4,4′-di-tert-butylbiphenyl: 25% yield of 4,4′-di-tert-butylbiphenyl (based on 4-tert-butylphenylboronic acid) was afforded when MOF was used, but none was formed in the case of cupric acetate monohydrate. GC-MS, m/z+266.1; N,N,N′,N′-tetramethyldiphenyl-4,4′-diamine: 43% and 5% yields of N,N,N′,N′-tetramethyldiphenyl-4,4′-diamine (based on 4-(dimethylamino)-phenylboronic acid) for MOF and cupric acetate monohydrate, respectively. GC-MS, m/z+240.1; 1,1′-binaphthyl: 90% and 6% yields of 1,1′-binaphthyl (based on naphthalyl-1-boronic acid) were afforded for MOF and cupric acetate monohydrate, respectively. GC-MS, m/z+254.2.

Powder X-ray diffraction (PXRD) data were collected using a Bruker D8-Discover θ-2θ diffractometer in reflectance Bragg-Brentano geometry. Cu Kα radiation (λ=1.5406 Å; 1,600 W, 40 kV, 40 mA) was focused using a planer Gobel Mirror riding the Kα line. A 0.6 mm divergence slit was used for all measurements. Diffracted radiation was detected using a Vantec line detector (Bruker AXS) (6° 2θ sampling width) equipped with a Ni monochrometer. All samples were ground to ensure mono dispersity in the bulk, and then mounted onto a glass slide fixed on a sample holder by dropping powders and then leveling the sample surface with a wide-blade spatula. The best counting statistics were achieved by using a 0.02° 2θ step scan from 1-50° with an exposure time of 0.4 s per step. The diffraction patterns collected for Cu₃(BTC)₂ both before and after homo-couplings are shown in FIGS. 4-10. Powder patterns of Cu3(BTC)₂ after three cycles also illustrated in FIG. 11.

FT-IR spectra of benzyltricarboxylic acid (BTC) and Cu₃(BTC)₂ (fresh and after coupling reaction) were obtained as KBr pellets using Nicolet 400 Impact spectrometer. FT-IR of recovered liquid after coupling reaction was performed on two clear KBr crystal plates. As shown in FIGS. 12 and 13, the C═O stretch of carboxylates in Cu₃(BTC)₂ absorbs at 1653 cm⁻¹, whereas the C═O stretch of free carboxylic acid in BTC absorbs at 1734 cm⁻¹, which is a strong characteristic peak for presence of any non-coordinated carboxylic groups. Recovered Cu₃(BTC)₂ solid, as shown in FIG. 14, clearly indicated that no free carboxylic acid from decomposition was trapped in Cu₃(BTC)₂ framework. Furthermore, FIG. 15 shows that no BTC leached out into the solution. This discussion pertaining to the IR spectral relationships between these compounds is offered as support for the intactness of MOFs throughout the coupling reactions.

¹H and ¹¹B NMR spectra were recorded at 295K on Bruke ARX 400 and ARX 500 instruments, respectively (¹H, 400 MHz; 11B, 160 MHz). ¹H chemical shift values are reported in parts per million (ppm) relative to SiMe4 (δ 0 ppm). ¹¹B chemical shift value are reported in ppm relative to BF3.Et₂O (δ 0 ppm). Monitor reaction by ¹¹B NMR: The reaction of boronic acid was monitored by ¹¹B NMR to track in detail of the boron source.

The ¹¹B NMR shift of the suspension of boronic acid in CH₂Cl₂ is δ 30.49 ppm, which corresponding the trimerized product boroxine (PhBO)₃; after 2 equivalent of cyclohexyl amine added to the solution, the solution became clear and the ¹¹B chemical shift showed two signals: a weak peak at δ 29.45 ppm and a strong signal of δ 19.97 ppm (we assign this to intermediate II based on the chemical shift which corresponding to a three-coordinated boron center). 5 mol % of MOF199 was added and the mixture was stirred for 1 h, followed by 11B NMR for the aliquitor. In addition to the previous two signals, a third peak at δ 3.69 ppm was observed. Although the product was not isolate this ¹¹B chemical shift falls into a four-coordinated boron species region; hence this was tentatively assigned to a borate anion.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

The activity of copper MOFs were tested in the homo-coupling reactions of several representative arylboronic acids with various functional groups (see Table 2A and 2B). 5.5 mol percent of MOF catalyst was added in air to a solution of dry dichloromethane containing the arylboronic acids, triethylamine and cyclohexylamine. For comparison, a nonporous cupric acetate monohydrate having the same Cu paddlewheel unit and a molecular structure was employed under identical reaction conditions. The reactions were run for 5 hours at room temperature under stirring. The homo-coupling of phenylboronic acid and tert-butyl phenylboronic acid on the MOF resulted in up to 47% yield of biaryl. In contrast, cupric acetate failed to show any observable activity. In the homo-couplings of nitro-, cyano-, chloro-, or dimethylamino-phenylboronic acids and 2-naphthylboronic acid, use of MOF catalyst gave up to 92% yield. Cupric acetate, in contrast, did catalyze these reactions with poor yields (5%-19%). The presence of MOF in catalytic quantities clearly resulted in up to 15 times higher yield.

TABLE 2A
Synthesis of biaryls with MOF catalyst and copper acetate.
	Cu3(BTC)2		Cu(OAc)2·H2O
R3	Yield %2	Biaryl Product1	Yield %
—H	47		0
—NO2	87		18
—CN	92		19
—Cl	81		8
-t-Bu	25		0
	43		5
	90		6
Based on GC-MS and 1H NMR.
Yield of the biaryls was calculated based on recovered boronic acid. In every reaction, arylated cyclohexylamine from the Chan-Lam coupling was the only by-product.
Naphthyl-1-boronic acid was used for the last reaction.

TABLE 2B
Synthesis of biaryls with MOF catalyst and copper acetate.
Product yield and selectivity.
	MOF-199		Cu(OAc)2·H2O
R	Yield %2	Selectivity %3	Product1	Yield %	Selectivity %
—H	47	65		0	0
—NO2	87	95		18	20
—CN	92	98		19	24
—Cl	81	85		8	10
-t-Bu	25	74		0	0
	43	63		5	8
	90	99		6	24
—H4	65	75		0	0
1Based on GC-MS and 1H-NMR.
2Yeild of the biaryls was calculated based on boronic acid.
3MOP-OH was used as the catalyst.

After filtration and washing with fresh dichloromethane, the MOF can be fully recovered and re-used without any significant loss of activity. The PXRD pattern of MOF after each homo-coupling was measured and compared to the original. No apparent changes or shifts were observed. Furthermore, three continuous reactions were carried out for the homo-coupling of 4-cyanophenylboronic acid using MOF. FIG. 2 and FIG. 11 clearly show that the biaryl yield was maintained throughout all cycles. It is note-worthy that no further re-activation is needed between cycles, which offer great potential in industrial scale continuous production. In order to further determine whether the reactions take place under completely heterogeneous conditions, control experiments and several leaching tests were conducted. First, control experiments were performed in the absence of MOF under identical conditions, and no conversion, as monitored by GC-MS and 1H NMR, was observed for any homo-coupling. Second, no further conversion was observed when the filtrate from each reaction catalyzed by MOF was recovered and used with fresh reactants. Third, the FT-IR spectra of both recovered solids and liquids after the homo-coupling of phenylboronic acid were measured. As expected, no carbonyl stretch from free carboxylic acid was observed (FIGS. 12 and 15), which indicates that the MOF network remains intact throughout the reactions. The coupling reactions were also monitored using ¹¹B NMR. Based on the boron species presented in the catalytic cycle and the Homo-coupling reaction mechanism.

The data demonstrate that a copper-containing MOF can serve as an alternative catalyst for precious metal-dominated oxidative homo-coupling reactions of aryl boronic acids with comparable yield. More importantly, in the search for versatile and efficient catalysts for the systematic synthesis of substituted biaryls, the heterogeneous nature of MOFs may open up new possibilities for the C—C coupling of boronic acids. This discovery also shows the great potential of MOF chemistry as it introduces complexity and functionality along with exceptional porosity. Specifically, such complexity, offered by uniquely connected active centers, can lead to behavior that is unprecedented in its molecular counterparts.

Claims

1. A method to connect aryls by homocoupling comprising contacting a porous metal organic framework (MOF) or a porous metal organic polyhedral (MOP) with boronic acid substituted aryls wherein the MOF or MOP catalyze the synthesis of a biaryl through a homo-coupling reaction, wherein the MOF or MOP comprises a plurality of linking moieties that have a substructure selected from the group consisting of (C1-C20)alkyl, (C3C20)cycloalky, aryl, (C1-C20)alkylamine, arylamine, and heterocycle; and wherein the substructure has one or more covalently attached CO2H linking clusters that undergo condensation with a copper metal and wherein the MOF or the MOP comprise open copper centers that are mono-dispersed throughout the pores.

2. The method of claim 1, wherein the method further comprises cupric acetate.

3. The method of claim 1, wherein the method further comprises a solvent.

4. The method of claim 1, wherein the method further comprises a base.

5. The method of claim 4, wherein the copper center of the MOF or the MOP forms a coordinate bond with the base.

6. The method of claim 1, wherein the method further comprises an oxidant.

7. The method of claim 6, wherein the one or more oxidant is air.

8. The method of claim 1, wherein the method is performed at room temperature.

9. The method of claim 1, wherein the boronic acid substituted aryls are phenylboronic acids that can be optionally substituted at the para position.

10. The method of claim 9, wherein the boronic acid substituted aryls comprise the general structure of:

11. The method of claim 1, wherein the boronic acid substituted aryls is boronic acid substituted naphthalene that may or may not be further substituted.

12. The method of claim 11, wherein the boronic acid substituted naphthalene is 1-naphthylboronic acid.

13. The method of claim 1, wherein the MOF or MOP comprises one or more linking moieties comprising:

14. The method of claim 13, wherein the MOF or MOP comprises one or more linking moieties comprising:

15. The method of claim 14, wherein the MOF or MOP comprises one or more linking moieties comprising:

16. The method of claim 1, wherein the MOF or MOP contains a transition metal.

17. The method of claim 16, wherein the MOF or MOP contains Cu.

18. A method to connect aryls by homocoupling comprising contacting a metal organic framework (MOF) with boronic acid substituted aryls, wherein the MOF catalyzes the synthesis of a biaryl through a homo-coupling reaction, and wherein the MOF comprises Cu3(BTC)2 (where BTC is benzene-1,3,5-tricarboxylate).

19. The method of claim 1, wherein the method can be repeated for one or more cycles with the same MOF or MOP.