Structural Transformation of Porous Polyoxometalate Frameworks and

Aug 21, 2017 - However, low catalytic efficiency and easy auto-oxidative deactivation nature remain the problematic issues. To meet ... the catalytic ...
1 downloads 12 Views 1MB Size
Download PDF
Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Article

Structural Transformation of Porous Polyoxometalate Frameworks and Highly Efficient Biomimetic Aerobic Oxidation of Aliphatic Alcohols Min Zhao, Xian-Wei Zhang, and Chuan-De Wu ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b01985 • Publication Date (Web): 21 Aug 2017 Downloaded from http://pubs.acs.org on August 21, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 9

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Structural Transformation of Porous Polyoxometalate Frameworks and Highly Efficient Biomimetic Aerobic Oxidation of Aliphatic Alcohols Min Zhao, Xian-Wei Zhang and Chuan-De Wu* State Key Laboratory of Silicon Materials, Center for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, 310027, P. R. China ABSTRACT: Due to their inherent inert nature, it is difficult to oxidize unactivated aliphatic alcohols with molecular oxygen under mild conditions. Inspired by enzymatic catalysis, numerous biomimetic systems have been therefore established. However, low catalytic efficiency and easy auto-oxidative deactivation nature remain the problematic issues. To meet these challenges, we report herein a 2D porous polyoxometalate (POM) framework (CZJ-11), and a 3D porous POM framework Gd4(H2O)26[WZn{Cu(H2O)}2(ZnW9O34)2]·24H2O Gd4(H2O)24[WZn{Cu(H2O)}2(ZnW9O34)2]·11H2O (CZJ-12) transferred from CZJ-11 by partial dehydration, consisting of scaffolded redox active Cu(II) sites in the sandwich-type POM cluster [WZn{Cu(H2O)}2(ZnW9O34)2]12- (abbreviated as {Zn3Cu2W19}). To mimic the catalytic mechanism of enzymes, N-hydroxyphthalimide (NHPI) and tetramethylammonium bromide (TMAB) were introduced as co-catalysts, which performed as electron donor and electron transfer mediator, respectively. The coupled catalyst systems demonstrate analogue properties with oxygenase enzymes in the aerobic oxidation of aliphatic alcohols under mild conditions. Compared with molecular POM counterpart and metalloporphyrins, the catalytic efficiency of these POM frameworks is predominant in aerobic oxidation of unactivated aliphatic alcohols by imitating the active sites and the catalytic mechanism of enzymes. Compared with metal-organic coordination complexes, such as metalloporphyrins, the pure inorganic frameworks offer significant superiority of robustness to auto-oxidation and simple recovery for recycling with retained high catalytic efficiency.

INTRODUCTION Oxidation of aliphatic alcohols into carbonyl and carboxylic compounds is of considerable importance because they are the feed-stocks in the fine chemical and pharmaceutical industry.1 Due to their low reactivity, these chemical transformations are traditionally carried out using stoichiometric amounts of oxidants, such as CrO3, MnO2 and hypervalent iodine, which are expensive and environmental hazard.2 Even though many catalyst systems have been developed for the oxidation of unactivated aliphatic alcohols, however, sacrificial oxidants (e.g. hydrogen peroxide, alkyl hydroperoxides or iodosylbenzene), additives (e.g. bases, acids or aldehydes), or severe conditions (e.g. high pressure and temperature) have limited their practical applications.3 It is evident that the challenge is to design and cultivate effective, sustainable and environmentally friendly alcohol oxidation catalyst platforms with molecular oxygen as oxidant.4 Therefore, numerous endeavors have been inspired associating with this goal of molecular oxygen activation; however, only a handful of noble metals, such as Pd, Ru, Pt, Rh and Au, demonstrate high efficiency on the aerobic alcohol oxidation reaction.5 A limitation of these systems is the high catalyst loadings to result in low turnover numbers (TONs), which is not suitable for the production of less expensive and high volume fine chemicals.

It has been well known that aerobic oxidation of inert organic substrates is easily realized by enzymes under mild conditions, and copper site has been recognized as one of the important redox centers in many important biological processes.6 Numerous synthetic Cu complexes have been therefore established as biomimetic models of enzymes, which demonstrate high catalytic efficiency in a number of oxidation reactions.7 However, because copper-catalyzed oxidation involves the formation of metaloxide intermediates, Cu-organic catalysts are suffered from easy auto-oxidation and deactivation. In respect of susceptible to oxidative degradation, adoption of pure and stable inorganic-copper coordination complexes as catalysts represents one of the ideal pathways to overcome the easy auto-oxidation issue of copper-organic catalysts. Polyoxometalates (POMs), as a class of metaloxide nanoclusters with unmatched molecular structural diversity and versatile functions, exhibit high resistance toward hydrolysis and oxidative degradation, which offer great potential as stable inorganic scaffolds to immobilize copper sites for biomimetic catalysis.8 For examples, the sandwich-type POMs, [WM{M'(H2O)}2(MW9O34)2]n- (M, M' = MnII, CoII, CuII and ZnII, etc.; abbreviated as {M3M'2W19}), consist of two B-[α-MW9O34] truncated Keggin-type fragments linked by four coplanar close-packed transition metal atoms in the central rings, in which the ring belt metal sites are systematically tunable to modify

ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 9

the catalytic properties.9 It has been demonstrated that the redox active transition metal ions, such as FeIII, RuIII, MnII, RhIII, PdII and PtII, incorporated POMs exhibit analogue properties with oxygenase enzymes.10 Scaffolding redox Cu(II) sites in the ring belts of the sandwich-type POMs might result in stable and efficient catalysts for biomimetic aerobic oxidation of aliphatic alcohols under mild conditions. Moreover, incorporation of Cu-POMs into metal-oxide frameworks might facilitate synergistic effect to improve the catalytic efficiency by confining multiple redox active metal centers in the highly ordered pore surfaces, and improve the stability for long term recycling usage. The above considerations prompted us to use the sandwich-type POMs, {M3M'2W19}, as redox active inorganic linkers to connect with metal centers for the self-assembly of POM frameworks. Herein, we report a 2D porous POM framework, Gd4(H2O)26[WZn{Cu(H2O)}2(ZnW9O34)2]·24H2O (CZJ-11), building from Gd3+ metal nodes linking up [WZn{Cu(H2O)}2(ZnW9O34)2]12(abbreviated as {Zn3Cu2W19}) clusters consisting of redox active Cu(II) sites. CZJ-11 can be simply transformed into a stable 3D porous POM framework Gd4(H2O)24[WZn{Cu(H2O)}2(ZnW9O34)2]·11H2O (CZJ-12) by partial dehydration. Compared with molecular POM counterpart and metalloporphyrins, these POM frameworks demonstrate high catalytic efficiency on biomimetic activation of molecular dioxygen in aerobic oxidation of unactivated aliphatic alcohols. Compared with organic metalloporphyrins, the pure inorganic frameworks offer significant advantages of robustness to auto-oxidation and simple recovery for recycling.

RESULTS AND DISCUSSION Green needle crystals of the POM framework CZJ-11 were synthesized by heating a mixture of {Zn3Cu2W19}, copper nitrate and gadolinium chloride in acidified water solvent at 50 °C for one week. It should be noted that additional copper cations played vital roles for the formation of crystalline metal-oxide framework CZJ-11. Due to the highly oxophilic nature of Gd3+ ions, {Zn3Cu2W19} and Gd3+ ions would quickly combine together to form amorphous solid in the absence of Cu2+ ions. Buffered with Lewis acid copper ions, the reaction rate between {Zn3Cu2W19} anions and Gd3+ cations is significantly reduced due to the competed coordination between Cu2+ and Gd3+ cations to {Zn3Cu2W19} anions. The formula of as-synthesized CZJ-11 was calculated on the basis of single crystal structure, and characterized by thermogravimetric analysis (TGA) and FT-IR (Figures S1 and S2 in supporting information). The phase purity of the bulk material was confirmed by powder X-ray diffraction (PXRD). Single crystal X-ray diffraction analysis revealed that CZJ-11 crystallizes in the triclinic Pī space group, which consists of one {Zn3Cu2W19} polyanion and four ninecoordinated Gd3+ cations in the asymmetric unit (Figure 1). The copper(II) cation disubstituted polyoxoanion {Zn3Cu2W19} is of a dimer built from two tri-vacant

Figure 1. A) Ball-and-stick and polyhedral representations of 12the polyoxoanion [WZn{Cu(H2O)}2(ZnW9O34)2] and its coordination modes, and the coordination environments of 3+ Gd ions in CZJ-11. B) A view of the connections between 123+ [WZn{Cu(H2O)}2(ZnW9O34)2] polyanions and Gd ions in the 2D lamellar network of CZJ-11, in which one polyanion is highlighted in polyhedral model. C) Packing diagram of CZJ11 (the central lamellar network is highlighted as orange polyhedra). Color scheme: Cu, cyan; W, green and yellow green; Gd, purple; Zn, blue; O, red.

Keggin-type B-[α-ZnW9O34] fragments and a sandwiched ring belt consisting of one W, one Zn and two Cu sites. It is interesting to note that the chirality of {Zn3Cu2W19} cluster was firstly observed in the crystal structure of CZJ11. Even though it has been suggested that {M3M'2W19} clusters are chiral moieties in the literature, however, because the M and W atoms in the ring belt are statisti-

ACS Paragon Plus Environment

Page 3 of 9

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

cally occupying two diagonal positions, the chirality of {M3M'2W19} has never been clearly defined by crystallography.11 As observed in the crystal structure of CZJ-11, the specific positions of Zn and W atoms in the ring belt are specifically defined, and thus to differentiate clearly the enantiomers of {Zn3Cu2W19}. Without the interference of distortion, the actual coordination environments of copper(II) ions in the polyanions are also clearly defined for comprehensively understanding the structure-function relationship. In CZJ-11, each copper atom in the ring belt is coordinating to one μ3-OZnWCu (Cu-O = 2.003-2.004 Å), one μ3-OWWCu (Cu-O = 2.389-2.417 Å), one μ4-OWZnZnCu (Cu-O = 2.001-2.014 Å), two μt-OW (Cu-O = 1.982-1.982 and 2.223-2.224 Å), and one water (Cu-O = 1.976-2.021 Å). It is obvious that the copper atom comprises of highly disordered octahedral coordination environment, which consists of four strong Cu-O coordination bonds (1.982-2.021) and two weak Cu-O bonds (2.223-2.417 Å). The Zn atom in the central ring is also highly deviated the ideal octahedral coordination environment with four equatorial Zn-O distances of Zn-O = 1.919-2.015 Å and two axial Zn-O distances of 2.322-2.349 Å, which is rarely observed in metalorganic coordination complexes. The unusual coordination spheres of these transition metal atoms in {Zn3Cu2W19} suggest that the {CuO6} octahedra are flexibly combined with two B-[α-ZnW9O34] fragments, which are beneficial for molecular oxygen activation and subsequent substrate oxidation. In the crystal structure of CZJ-11, the {Zn3Cu2W19} cluster acts as a nine-dentate ligand to coordinate with nine GdIII cations through nine terminal oxygen atoms of nine {WO6} octahedra (Figure 1a). According to the coordination environments, there are three kinds of ninecoordinated GdIII cations. The first one (Gd1) terminates on the {Zn3Cu2W19} cluster (Gd-O = 2.476 Å) and further coordinates with eight aqua ligands (Gd-O = 2.375-2.503 Å). The second one (Gd3) bridges two {Zn3Cu2W19} moieties by coordinating to two oxygen atoms of two {WO6} octahedra (Gd-O = 2.368-2.467 Å) and seven water molecules (Gd-O = 2.407-2.603 Å). The remaining two GdIII ions (Gd2 and Gd4) serve as three-connecting nodes to combine with three {Zn3Cu2W19} moieties (Gd-O = 2.4062.577 Å) and terminated by six water molecules (Gd-O = 2.385-2.511 Å) for each Gd ion. The connections between {Zn3Cu2W19} clusters and GdIII ions result in a 2D lamellar network with micropore dimensions of about 7.8 × 10.4 Å2 (Figure 1b). Two neighboring redox active copper(II) sites are located on the pore surfaces with average Cu…Cu distance of 7.85 Å. The layered networks are further connected by extensive hydrogen bondings to form a 3D supramolecular network (Figure 1c). TGA showed that a weight loss of 13.9% occurred between 30 and 420 oC, corresponding to the loss of water ligands and guests (expected 14.5%; Figure S2). PLATON calculations indicate that CZJ-11 consists of 27.5% (40.4%) void space to accommodate water guests (water guests and ligands).12

Figure 2. PXRD patterns for calculated CZJ-11 based on single crystal structure, as-synthesized CZJ-11, acetone-exchanged o CZJ-11, evaporated CZJ-11 by heating at 65 C under vacuum for 12 h, transformed CZJ-12 from CZJ-11, and calculated CZJ12 based on single crystal structure, indicating the structural transformation from 2D lamellar network of CZJ-11 to 3D porous framework of CZJ-12.

As shown in Figure 2, the PXRD pattern of assynthesized CZJ-11 is basically identical to that of the calculated one based on single crystal structure. Because lattice water molecules in CZJ-11 are easily evaporated during data collection, it is inevitable to result in partial loss of its crystallinity with broadened diffraction peaks. After CZJ-11 was guest-exchanged with dry acetone for 24 h (referred as acetone-exchanged CZJ-11) and further heated at 65 oC under vacuum for 12 h (referred as evaporated CZJ-11), PXRD patterns of the acetone-exchanged and evaporated samples are different from that of the assynthesized CZJ-11. Moreover, the sharp diffraction peaks cannot be restored to the original positions by immersing the evaporated sample in water for 24 h (referred as transformed CZJ-12). These results suggest that structural transformations might occur upon the exchange and removal of water guests and ligands. Single crystal X-ray diffraction analysis revealed that the new crystalline phase is a 3D porous metal-oxide framework CZJ-12, formed from dehydration and rehydration of CZJ-11. CZJ12 crystallizes in the triclinic Pī space group, which consists of one half {Zn3Cu2W19} polyanion and two Gd3+ cations in the asymmetric unit (Figure 3). Due to structural distortion, the Zn and W atoms in the ring belt of {Zn3Cu2W19} are statistically occupying two diagonal positions. Consequently, the chirality of {Zn3Cu2W19} cannot be directly observed in the crystal structure of CZJ-12, which is same to the literature structures.11 As a result, the actual coordination environments of copper(II) and zinc(II) ions in the ring belt of the polyanion cannot be unambiguously defined in CZJ-12. The statistic Cu-O distances are ranging from 1.970-2.225 Å with statistic Zn-O distances of 1.850-2.164 Å, which are significantly different to those in CZJ-11. In the crystal structure of CZJ-12, the {Zn3Cu2W19} cluster acts as a ten-dentate ligand to

ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

coordinate with ten GdIII cations (Figure 3a). According to the coordination environments, there are two kinds of nine-coordinated GdIII cations. The first one (Gd1) serves as a three-connecting node to coordinate with three {Zn3Cu2W19} moieties (Gd-O = 2.475-2.535 Å) and terminate by six water molecules (Gd-O = 2.363-2.518 Å). Compared with the crystal structure of CZJ-11, Gd1 in CZJ-12 is corresponding to Gd2 and Gd4 in CZJ-11 with almost unchanged coordination environment (Figure 4). The second one (Gd2) bridges two {Zn3Cu2W19} moieties by coordinating to three oxygen

Figure 3. A) Ball-and-stick and polyhedral representations of 12the polyoxoanion [WZn{Cu(H2O)}2(ZnW9O34)2] and its coordination modes, and the coordination environments of 3+ Gd ions in CZJ-12. B) A view of the connections between 123+ [WZn{Cu(H2O)}2(ZnW9O34)2] polyanions and Gd ions in the 3D framework of CZJ-12, in which one polyanion is highlighted in polyhedral model. C) The 3D porous structure of CZJ-12. Color scheme: Cu, cyan balls; W, green balls and polyhedra; ZnW, purple polyhedra and yellow green balls; Gd, blue balls and polyhedra; Zn, orange; O, red.

Page 4 of 9

atoms of three {WO6} octahedra (Gd-O = 2.504-2.511 Å) and six water molecules (Gd-O = 2.361-2.528 Å). Gd2 in CZJ-12 is corresponding to Gd1 and Gd3 in CZJ-11. Comparing the coordination environments of Gd ions in CZJ-11 and CZJ-12, one aqua ligand of Gd3 in CZJ-11 was replaced by a μ3-OWWCu atom for Gd2 in CZJ-12. One aqua ligand of the terminated Gd ion (Gd1) in CZJ-11 is substituted by an oxygen atom from neighboring {Zn3Cu2W19} cluster for Gd2 in CZJ-12. Substitution of water ligands with oxygen atoms on {Zn3Cu2W19} for Gd ions resulted in an expanded 3D porous framework structure of CZJ-12, consisting of almost unchanged micropore sizes of about 7.7 × 10.4 Å2 in dimensions (Figure 3). TGA showed that a weight loss of 13.3% occurred between 30 and 410 oC, corresponding to the loss of water ligands and guests (expected 13.6%; Figure S3). PLATON calculations indicate that the void space in CZJ-12 is slightly shrunk to 15.9% (31.8%) for water guest molecules (water guests and ligands).12

Figure 4. Comparison of the connections between 123+ [WZn{Cu(H2O)}2(ZnW9O34)2] and Gd ions in CZJ-11 (A) and CZJ-12 (B), in which the highlighted Gd ions (deep green and deep purple balls) represent the ones with changed coordination environments. Color scheme: Cu, cyan; W, green and yellow green; Gd, purple; Zn, orange; O, red; ZnW, blue polyhedra.

The permanent porosity of CZJ-11 and CZJ-12 has been examined by CO2 adsorption experiments at 273 K (Figures S4 and S5). When the solid samples of CZJ-11 and CZJ-12 were activated by heating at 65 oC under vacuum

ACS Paragon Plus Environment

Page 5 of 9

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

for 6 h, the activated solid samples take up 8.81 and 8.83 cm3 g-1 CO2 at 273 K and 1 bar, respectively. Compared with those of traditional porous materials, these values are relatively low, which should be ascribed to the very large formula weights (6240-6470) and high densities (4.181-4.653 g·cm−3) of these pure inorganic metal-oxide frameworks. To check whether the inside pores are accessible to small organic molecules, we studied the sorption ability of activated CZJ-11 and CZJ-12. When the activated samples of CZJ-11 and CZJ-12 were immersed in acetonitrile, ethanol and n-butanol for 12 h at room temperature, GC-MS analysis suggests that their inside pores are accessible to these small molecules. The uptakes of acetonitrile, ethanol and n-butanol are of 8.9, 9.6 and 5.5 wt% for CZJ11, and 7.5, 5.2 and 1.9 wt% for CZJ-12, respectively. The above results clearly indicate that the immobilized redox active Cu(II) sites in the pore surfaces of CZJ-11 and CZJ-12 are readily accessible to small reactant molecules to prompt their catalytic chemical transformations. Direct oxidation of aliphatic alcohols into highly valuable carboxylic acids with molecular oxygen represents one of the most elegant and environmentally friendly pathways.13 To realize highly efficient catalysis on this chemical transformation, we established a biomimetic catalyst platform to mimic the catalytic mechanism of enzymes, in which the immobilized copper(II) sites inside the pore surfaces of inorganic framework CZJ-11 or CZJ-12 were used to mimic the roles of redox active sites in enzymes, and N-hydroxyphthalimide (NHPI) and tetramethylammonium bromide (TMAB) as co-catalysts to mimic the roles of co-enzymes.14 The catalytic properties of the biomimetic catalyst platform were evaluated by aerobic oxidation of aliphatic alcohols in acetonitrile at 50 °C under 1 atm O2 atmosphere. As shown in Table 1 (entry 1), the coupled catalyst system efficiently prompts aerobic oxidation of n-butanol with 96% n-butyric acid yield and high selectivity (>99%). When CZJ-12 was used as a catalyst under the otherwise identical conditions, the yield of n-butyric acid is of 85% (entry 2). Compared with that of CZJ-11, the slightly decreased catalytic efficiency of CZJ-12 should be ascribed to the slight shrinkage of the pore space which would reduce the diffusion rate of reactant and product molecules. The catalytic efficiency of the combined catalyst platform is significantly higher than that of the single individuals such as CZJ-11, NHPI and TMAB, and their simply combined mixtures (entries 3-8). The superior aerobic oxidation efficiency of the combined catalyst platform indicates that every constituent played vital roles on the biomimetic catalysis. It has been known that enzymatic oxidation of organic substrates involves in a multiple active site system of molecular oxygen complexation with redox active metal sites and oxygen reduction with co-enzyme centers.1,13 Compared with biocatalyst system, the copper ions in CZJ-11 and CZJ-12 perform as redox active sites for O2 complexation, NHPI acts as an electron donor to mimic the roles of reductases, and Brmight act as an electron transfer mediator to improve the electron transfer efficiency (Scheme 1).15 Additionally, electron donation from NHPI results an intermediate of

phthalimido-N-oxyl radical (PINO), which would abstract a hydrogen atom from organic substrate to initiate the aerobic oxidation of alcohols in a radical propagation mechanism.14 Therefore, the synergistic work between these moieties in the coupled catalyst system is very similar to that of enzymes, which significantly improved the catalytic efficiency in aerobic oxidation of aliphatic alcohols under mild conditions. Table 1. Aerobic oxidation of n-butanol for the formation of n-butyric acida

Entry Catalyst

Yield b Entry Catalyst (%)

Yield b (%)

1

CZJ-11/NHPI /TMAB

96

9

CZJ-11/NHPI /TMAB

91

2

CZJ-12/NHPI /TMAB

85

10

CZJ-12/NHPI /TMAB

84

3

CZJ-11

trace 11

{Zn3Cu2W19}/ NHPI/TMAB

92

4

NHPI

trace 12

Cu(ClO4)2/ NHPI/TMAB

61

5

TMAB

trace 13

Cu-TPP/ NHPI/TMAB

69

6

CZJ-11/NHPI

50

14

FeCl-TPP/ NHPI/TMAB

trace

7

CZJ-11/TMAB

14

15

{Zn3Cu2W19}/ NHPI/TMAB

25

8

NHPI/TMAB

trace 16

Cu-TPP/ NHPI/TMAB

5

c

c

d

e

a

n-butanol (0.25 mmol), catalyst (0.001 mmol), NHPI (0.025 mmol) and TMAB (0.013 mmol) in acetonitrile (2 mL) were o stirred under an O2 atmosphere (balloon) at 50 C for 24 h. The usage amounts of control catalysts are identical to those b of corresponding agents based on the effective centers. Yield% was determined by GC-MS on a SE-54 column (Figures c d e S8-S17). The sixth cycle. The fourth cycle. The second cycle.

Scheme 1. Proposed catalytic cycles for the aerobic oxidation of aliphatic alcohols by Cu-POM and NHPI

CZJ-11 and CZJ-12 are very stable, which can be easily recovered by centrifugation, and reused in the successive runs for six cycles with almost retained high catalytic efficiency (Table 1, entries 9 and 10; Figures S6 and S7). A PXRD pattern of the recovered solid after catalysis (re-

ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ferred as recovered CZJ-11) indicates that the catalytic reaction induces a serious loss of crystallinity in the sample of CZJ-11 because participation of the redox active Cu sites in catalysis would significantly affect their local coordination environments and partially lose the lattice water guests in CZJ-11 (Figure 5). However, the structure of CZJ-11 can be easily regenerated (referred as regenerated CZJ-11) when the recovered solid sample was immersed in water for 24 h. Different to that of the 2D lamellar solid CZJ-11, the structural integrity of CZJ-12 was maintained after catalysis (referred as recovered CZJ-12) attributed to the rigid 3D framework structure. After CZJ-11 or CZJ-12, NHPI and TMAB in acetonitrile were stirred under an O2 atmosphere at 50 oC for 24 h, the mixture was filtered. nButanol was added to the filtrate, which was reacted for another 24 h under the otherwise identical conditions. GC analysis showed that the conversion of n-butanol is identical to that of the background reaction catalyzed by NHPI/TMAB (Table 1, entry 8). These results proved the heterogeneous catalytic nature of CZJ-11 and CZJ-12. Moreover, after the reaction proceeded for 12 h, the catalytic reaction was interrupted, and the solid catalyst was collected by centrifugation. GC-MS analysis showed that the desorbed n-butanol and n-butyric acid from the reacted solids are of 8 and 23 mol for CZJ-11, and 5 and 8 mol for CZJ-12 per formula unit, respectively. These results proved that the catalytic aerobic oxidation did mainly occur inside the pore space of CZJ-11 and CZJ-12. To make comparisons, we studied the catalytic properties of molecular [WZn{Cu(H2O)}2(ZnW9O34)2]12-, copper(II) perchlorate, and traditional biomimetic molecular catalysts, metalloporphyrins, CuII-TPP and FeIIICl-TPP (TPP = tetraphenylporphyrin).16 As shown in Table 1 (entries 1114), the catalytic properties of these molecular catalysts are inferior to those of CZJ-11 and CZJ-12. Compared to the organic metalloporphyrin analogues, the superiority of inorganic metal-oxide frameworks and molecular [WZn{Cu(H2O)}2(ZnW9O34)2]12- is predominant in terms of stability and sustainability (entries 9, 10, 15 and 16). We also studied the kinetic behavior of solid catalyst CZJ-11 by using large scale of substrate. As shown in Figure 6, when enlarging the amount of the substrate, the ratio of mol of substrate converted to mol catalyst is about 20750 after 58 h. Interestingly, the kinetic curve exhibits lag phase in a sigmoidal behavior. The presence of a short induction period should be ascribed to activation of the catalyst CZJ-11 by NHPI and diffusion of the reactant molecules into the pore space at the first step. After the induction time, the catalytic reaction is therefore self-accelerated. The subsequent decrease of the reaction rate is because the substrate is almost exhausted. These results indicate that the catalyst platform has the ability to self-accelerate the catalytic reaction after a short induction period. When CZJ-11 was replaced by Cu(ClO4)2 under the identical conditions, the ratio of mol of substrate converted to mol catalyst is quickly reached to 3275 after 13 h. However, the reaction rate is quickly slowdown after 13 h, which indicates that its catalytic properties are much inferior to those of CZJ-11.

Page 6 of 9

Figure 5. PXRD patterns for as-synthesized CZJ-11, recovered CZJ-11 after catalysis, regenerated CZJ-11 by immersing in water for 24 h, as-synthesized CZJ-12 and recovered CZJ-12 after catalysis.

Figure 6. Aerobic oxidation of n-butanol catalyzed by the combined use of CZJ-11/Cu(ClO4)2, NHPI and TMAB catalyst system. Conditions: n-Butanol (125 mmol), CZJ-11/Cu(ClO4)2 (0.005 mmol), NHPI (12.5 mmol) and TMAB (1.33 mmol) in o acetonitrile (150 mL) were stirred at 50 C under an atmosphere of oxygen (balloon).

The biomimetic platform is also highly efficient and selective for the aerobic oxidation of a range of alcohols under the above-mentioned mild conditions (Table 2, entries 1-14). The conversion of alcohol substrate decreases slightly when the size of the substrate increases, which might be attributed to their difficult access to the active Cu(II) sites inside the pore space of CZJ-11 or CZJ-12. The remarkable catalytic properties of the combined catalyst system further encouraged us to study the universality of CZJ-11 and CZJ-12 for the aerobic oxidation of different kinds of organic substrates. As shown in Table 2 (entries 15-20), the coupled catalyst system demonstrates high efficiency in aerobic oxidation of benzyl alcohol, ethylbenzene and isochroman into the corresponding oxygenated products with very high conversion and selec-

ACS Paragon Plus Environment

Page 7 of 9

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

tivity. It is interesting to note that isochroman was almost full oxidized within 1 h under the identical mild conditions, which might be attributed to its special electronic effect. There have been many reported homogeneous and heterogeneous catalysts based on Pt, Ru, Rh, Pd, Ir, Ag and Au noble metals for the aerobic oxidation of aliphatic alcohols into carboxylic acids.17 Compared with these noble metal catalysts, CZJ-11 and CZJ-12 present superior features of high efficiency, sustainability and turnover numbers, and environmental friend in the aerobic oxidation of aliphatic alcohols. Table 2. Aerobic oxidation of different organic substratesa Entry Substrate

Catalyst

1

CZJ-11

2

CZJ-12

3

CZJ-11

4

CZJ-12

5

CZJ-11

6

CZJ-12

7

CZJ-11

8

CZJ-12

9

CZJ-11

10

CZJ-12

11

CZJ-11

12

CZJ-12

13

CZJ-11

14

CZJ-12

15

CZJ-11

16

CZJ-12

17

CZJ-11

18

CZJ-12

19

CZJ-11

20

CZJ-12

Time Product (h) 21

24

Yield b (%) >99.9 93 96 85 98

44

44

44

44

39

24

24

91 91

ASSOCIATED CONTENT Supporting Information. Experimental details, additional figures, crystal data, and CIF files. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

79

Corresponding Author

87

*[email protected]

87

Author Contributions

80

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

82

The authors declare no competing financial interest.

79

ACKNOWLEDGMENT

83

83

We are grateful for the financial support of the National Natural Science Foundation of China (grant nos. 21373180 and 21525312), and the Fundamental Research Funds for the Central Universities (grant nos. 2017XZZX001-03A and 2017FZA3007).

83

REFERENCES

84

52

95 1

bridging ligand to connect with highly oxophilic Gd3+ ions, we successfully synthesized a 2D inorganic porous POM framework material CZJ-11, consisting of redox copper(II) sites inside the pore space. CZJ-11 was simply transformed into a stable 3D porous POM framework CZJ-12 by partial dehydration. To realize highly efficient biomimetic activation of molecular oxygen for aerobic oxidation of aliphatic alcohols, NHPI and TMAB were introduced as cocatalysts to form a combined catalyst system. The coupled catalyst platform exhibits enzyme-like features in aerobic oxidation of aliphatic alcohol under mild conditions with very high efficiency, selectivity and sustainability. This work demonstrates that the use of pure porous inorganic frameworks instead of metal-organic coordination complexes would significantly improve the sustainability in oxidation reaction. Moreover, the use of combined catalyst system, consisting of multiple active sites to mimic different functional sites of enzymes for synergistic catalysis, represents one of the most feasible pathways to realize highly efficient biomimetic catalysis under mild conditions.

92

a

Substrate (0.25 mmol), catalyst (0.001 mmol), NHPI (0.025 mmol) and TMAB (0.013 mmol) in acetonitrile (2 mL) were o b stirred under an O2 atmosphere (balloon) at 50 C. Yield% was determined by GC on a SE-54 column.

CONCLUSIONS In summary, to make use of the sandwich-type POM {Zn3Cu2W19} cluster as inorganic redox active moiety and

Notes

(1) (a) Mallat, T.; Baiker, A. Chem. Rev. 2004, 104, 3037-3058. (b) Tojo, G.; Fernández, M. Oxidation of Primary Alcohols to Carboxylic Acids: A Guide to Current Common Practice, Springer, New York, 2007. (c) Backvall, J. E. Modern Oxidation Methods, Wiley-VCH, Weinheim, Germany, 2nd edn, 2010. (2) Sheldon, R. A.; Arends, I.; Hanefeld, U. Green Chemistry and Catalysis, Wiley-VCH, Weinheim, 2007. (3) Karimi, B.; Naderi, Z.; Khorasani, M.; Mirzaei, H. M.; Vali, H. ChemCatChem 2016, 8, 906-910. (4) (a) Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D. Nat. Chem. 2013, 5, 122-125. (b) Rodr.guez-Lugo, R. E.; Trincado, M.; Vogt, M.; Tewes, F.; Santiso-Quinones, G.; Grützmacher, H. Nat. Chem. 2013, 5, 342-347. (c) Nielsen, M.; Alberico, E.; Baumann, W.; Drexler, H.-J.; Junge, H.; Gladiali, S.; Beller, M. Nature 2013, 495, 85-89. (d) Guo, Z.; Liu, B.; Zhang, Q.; Deng, W.; Wang, Y.; Yang, Y. Chem. Soc. Rev. 2014, 43, 3480-3524. (e) Sankar, M.;

ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Nowicka, E.; Carter, E.; Murphy, D. M.; Knight, D. W.; Bethell, D.; Hutchings, G. J. Nat. Commun. 2014, 5, 3332. (f) Lagerblom, K.; Wrigstedt, P.; Keskiv-li, J.; Parviainen, A.; Repo, T. ChemPlusChem 2016, 81, 1160-1165. (g) Gianetti, T. L.; Annen, S. P.; Santiso-Quinones, G.; Reiher, M.; Driess, M.; Grützmacher, H. Angew. Chem., Int. Ed. 2016, 55, 1854-1858. (5) (a) ten Brink, G-J.; Arends, I. W. C. E.; Sheldon, R. A. Science 2000, 287, 1636-1640. (b) Annen, S.; Zweifel, T.; Ricatto, F.; Gretzmacher, H. ChemCatChem 2010, 2, 1286-1295. (c) Wang, F.; Ueda, W.; Xu, J. Angew. Chem., Int. Ed. 2012, 51, 3883-3887. (d) Karimi, B.; Gholinejad, M.; Khorasani, M. Chem. Commun. 2012, 48, 8961-8963. (e) Karimi, B.; Elhamifar, D.; Yari, O.; Khorasani, M.; Vali, H.; Clark, J. H.; Hunt, A. J. Chem. - Eur. J. 2012, 18, 13520-13530. (f) Tang, L.; Guo, X.; Li, Y.; Zhang, S.; Zha, Z.; Wang, Z. Chem. Commun. 2013, 49, 5213-5215. (g) Huang, X.; Zhang, X.; Zhang, D.; Yang, S.; Feng, X.; Li, J.; Lin, Z.; Cao, J.; Pan, R.; Chi, Y.; Wang, B.; Hu, C. Chem. - Eur. J. 2014, 20, 2557-2564. (h) Dornan, L. M.; Muldoon M. J. Catal. Sci. Technol. 2015, 5, 1428-1432. (i) Karimi, B.; Khorasani, M.; Bakhshandeh Rostami, F.; Elhamifar, D.; Vali, H. ChemPlusChem 2015, 80, 990-999. (j) Karimi, B.; Khorasani, M.; Vali, H.; Vargas, C.; Luque, R. ACS Catal. 2015, 5, 4189-4200. (6) (a) Holm, R. H.; Kennepohl, P.; Solomon, E. I. Chem. Rev. 1996, 96, 2239-2314. (b) Koval, I. A.; Gamez, P.; Belle, C.; Selmeczi, K.; Reedijk, J. Chem. Soc. Rev. 2006, 35, 814-840. (c) Holzwarth, M. S.; Plietker, B. ChemCatChem 2013, 5, 1650-1679. (d) Faber, K. Biotransformations in Organic Chemistry, SpringerVerlag, Berlin, 5th edn, 2004. (7) (a) Marko, I. E.; Giles, P. R.; Tsukazaki, M.; Brown, S. M.; Urch, C. J. Science 1996, 274, 2044-2045. (b) Steves, J. E.; Stahl, S. S. J. Am. Chem. Soc. 2013, 135, 15742-15745. (c) Paria, S.; Reiser, O. ChemCatChem 2014, 6, 2477-2483. (d) Ryland, B. L.; Stahl, S. S. Angew. Chem., Int. Ed. 2014, 53, 8824-8838. (e) Shi, D.; He, C.; Qi, B.; Chen, C.; Niu, J.; Duan, C. Chem. Sci. 2015, 6, 1035-1042. (f) Castro, K. A. D. F.; Rodrigues, J. M. M.; Mendes, R. F.; Neves, M. d. G. P. M. S.; Simões, M. M. Q.; Cavaleiro, J. A. S.; Almeida Paz, F. A.; Tomé, J. P. C.; Nakagaki, S. J. Catal. 2016, 344, 303-312. (8) (a) Dolbecq, A.; Dumas, E.; Mayer, C. R.; Mialane, P. Chem. Rev. 2010, 110, 6009-6048. (b) Sun, M.; Zhang, J.; Puta, P.; Caps, V.; Lefebvre, F. D. R.; Pelletier, J.; Basset, J.-M. Chem. Rev. 2014, 114, 981-1019. (c) Du, D.-Y.; Qin, J.-S.; Li, S.-L.; Su, Z.-M.; Lan, Y.Q. Chem. Soc. Rev. 2014, 43, 4615-4632. (d) Mitchell, S. G.; Streb, C.; Miras, H. N.; Boyd, T.; Long, D.-L.; Cronin, L. Nat. Chem. 2010, 2, 308-312. (e) Kuang, X.; Wu, X.; Yu, R.; Donahue, J. P.; Huang, J.; Lu, C.-Z. Nat. Chem. 2010, 2, 461-465. (f) Yin, Q.; Tan, J. M.; Besson, C.; Geletii, Y. V.; Musaev, D. G.; Kuznetsov, A. E.; Luo, Z.; Hardcastle, K. I.; Hill, C. L. Science 2010, 328, 342-345. (g) Kamata, K.; Yonehara, K.; Nakagawa, Y.; Uehara, K.; Mizuno, N. Nat. Chem. 2010, 2, 478-483. (h) Song, J.; Luo, Z.; Britt, D. K.; Furukawa, H.; Yaghi, O. M.; Hardcastle, K. I.; Hill, C. L. J. Am. Chem. Soc. 2011, 133, 16839-16846. (i) Ma, F.-J.; Liu, S.-X.; Sun, C.Y.; Liang, D.-D.; Ren, G.-J.; Wei, F.; Chen, Y.-G.; Su, Z.-M. J. Am. Chem. Soc. 2011, 133, 4178-4181. (j) Izarova, N. V.; Pope, M. T.; Kortz, U. Angew. Chem., Int. Ed. 2012, 51, 9492-9510. (k) Kamata, K.; Yamaura, T.; Mizuno, N. Angew. Chem., Int. Ed. 2012, 51, 72757279. (l) Zou, C.; Zhang, Z.; Xu, X.; Gong, Q.; Li, J.; Wu, C.-D. J. Am. Chem. Soc. 2012, 134, 87-90. (m) Li, S.; Liu, S.; Liu, Y.; Tang, Q.; Shi, Z.; Ouyang, S.; Ye, J. J. Am. Chem. Soc. 2012, 134, 1971619721. (n) Han, Q.; He, C.; Zhao, M.; Qi, B.; Niu, J.; Duan, C. J. Am. Chem. Soc. 2013, 135, 10186-10189. (o) Rausch, B.; Symes, M. D.; Chisholm, G.; Cronin, L. Science 2014, 345, 1326-1330. (p) Hao, X.-L.; Ma, Y.-Y.; Zang, H.-Y.; Wang, Y.-H.; Li, Y.-G.; Wang, E.-B. Chem. - Eur. J. 2015, 21, 3778-3784. (q) Zhang, Z.-M.; Zhang, T.; Wang, C.; Lin, Z.; Long, L.-S.; Lin, W. J. Am. Chem. Soc. 2015, 137, 3197-3200. (r) Qin, J.-S.; Du, D.-Y.; Guan, W.; Bo, X.-J.; Li, Y.-F.; Guo, L.-P.; Su, Z.-M.; Wang, Y.-Y.; Lan, Y.-Q.; Zhou, H.-C. J. Am. Chem. Soc. 2015, 137, 7169-7177. (s) Liu, Y.; Liu, S.; He, D.; Li, N.;

Page 8 of 9

Ji, Y.; Zheng, Z.; Luo, F.; Liu, S.; Shi, Z.; Hu, C. J. Am. Chem. Soc. 2015, 137, 12697-12703. (9) (a) Neumann, R. Modern Oxidation Methods, Wiley-VCH, Weinheim, 2004. (b) Mizuno, N.; Yamaguchi, K.; Kamata, K. Coord. Chem. Rev. 2005, 249, 1944-1956. (c) Simões, M. M. Q.; Santos, I. C. M. S.; Neves, M. G. P. M. S.; Cavaleiro, A. M. V.; Cavaleiro, J. A. S. Advances in Organometallic Chemistry and Catalysis: The Silver/Gold Jubilee International Conference on Organometallic Chemistry Celebratory Book, John Wiley & Sons Hoboken, USA, 2014. (10) (a) Wang, S.-S.; Yang, G.-Y. Chem. Rev. 2015, 115, 48934962. (b) Ye, J.-J.; Wu, C.-D. Dalton Trans. 2016, 45, 10101-10112. (11) Tourné, C. M.; Tourné, G. F.; Zonnevijlle, F. J. Chem. Soc., Dalton Trans. 1991, 1, 143-155. (12) Spek, A. L. PLATON, a multipurpose crystallographic tool, Utrecht University, Utrecht, The Netherlands, 2008. (13) Arends, I. W. C. E.; Sheldon, R. A. Modern Oxidation Methods, Wiley-VCH Verlag Gmb & Co, Weinheim, 2004. (14) (a) Ishii, Y.; Sakaguchi, S.; Iwahama, T. Adv. Synth. Catal. 2001, 343, 393-427. (b) Recupero, F. C.; Punta, F. Chem. Rev. 2007, 107, 3800-3842. (c) Iwahama, T.; Yoshino, Y.; Keitoku, T.; Sakaguchi, S.; Ishii, Y. J. Org. Chem. 2000, 65, 6502-6507. (15) Keown1, W.; Gary1, J. B.; Stack1 T. D. P. J. Biol. Inorg. Chem. 2017, 22, 289-305. (16) Zhao, M.; Ou, S.; Wu, C.-D. Acc. Chem. Res. 2014, 47, 11991207. (17) (a) Hou, Z.; Theyssen, N.; Brinkmann, A.; Leitner, W. Angew. Chem., Int. Ed. 2005, 44, 1346-1349. (b) Hou, W.; Dehm, N. A.; Scott, R. W. J. J. Catal. 2008, 253, 22–27. (c) Han, J.; Liu, Y.; Guo, R. Adv. Funct. Mater. 2009, 19, 1112–1117. (d) Wang, L.; Meng, X.; Wang, B.; Chi, W.; Xiao, F.-S. Chem. Commun. 2010, 46, 5003-5005. (e) Wang, M.; Wang, F.; Ma, J.; Chen, C.; Shi, S.; Xu, J. Chem. Commun. 2013, 49, 6623-6625. (f) Lu, T.; Du, Z.; Liu, J.; Ma, H.; Xu, J. Green Chem. 2013, 15, 2215-2221. (g) Gandarias, I.; Nowicka, E.; May, B. J.; Alghareed, S.; Armstrong, R. D.; Miedziak, P. J.; Taylor, S. H. Catal. Sci. Technol. 2016, 6, 4201-4209. (h) Huang, D. L.; Vinyard, D. J.; Blakemore, J. D.; Hashmi, S. M.; Crabtree, R. H. Organometallics 2017, 36, 199-206.

ACS Paragon Plus Environment

Page 9 of 9

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

TOC Figure

ACS Paragon Plus Environment