Catalysis by metal-organic frameworks: Proline and gold functionalized MOFs for the aldol and three-component coupling reactions

RSC Advances

View Article Online

View Journal | View Issue

PAPER

Catalysis by metal–organic frameworks: proline

and gold functionalized MOFs for the aldol and

three-component coupling reactions†

Cite this: RSC Adv., 2014, 4, 13093

a

Liu Lili, Zhang Xin,* Rang Shumin, Yang Ying, Dai Xiaoping, Gao Jinsen,

a

b

Xu Chunming and He Jing

Translation of homogeneous catalysis into heterogeneous catalysis is a promising solution to green and

sustainable development in the chemical industry. Recent research has shown that metal–organic

frameworks (MOFs) could bridge the gap between homogeneous and heterogeneous catalysis. We

successfully prepared for the ﬁrst time a novel homochiral Zn-containing MOF referred to as CUP-1

based on the mixed linkers of 2-aminoterephthalic acid and L-lactic acid in a one-pot synthesis. The free

2

NH group in the homochiral framework of CUP-1, similar to the well known achiral IRMOF-3, is

potentially available for undergoing a variety of organic transformations, as demonstrated by choosing

the auxiliary chiral L-proline and nano gold to functionalize MOFs with postsynthetic modiﬁcation and

one-pot synthesis strategies. IRMOF-3, CUP-1 and their functionalized samples were in-depth

characterized by X-ray diﬀraction,

2

N adsorption–desorption, optical and transmission electron

microscopy, infrared spectroscopy, solid state nuclear magnetic resonance, thermogravimetric and

diﬀerential thermal analysis, and temperature-programmed reduction. L-Proline functionalized IRMOF-3

shows fair to excellent enantioselectivity (up to 98%) in asymmetrical aldol reactions of aldehydes and

acetone with higher turnover numbers and catalytic stabilities than the homogeneous counterpart. The

gold functionalized CUP-1 catalysts are found to be highly active, stable and reusable for the three-

component coupling reactions of aldehydes, alkynes and amines. This work provides general methods to

functionalize MOFs with the active ligand and metal nanoparticles for fabrication of highly eﬃcient MOF-

based heterogeneous catalysts.

Received 13th February 2014

Accepted 25th February 2014

DOI: 10.1039/c4ra01269k

www.rsc.org/advances

to their unique properties such as designable structures, high

catalytic activity and selectivity. However, homogeneous cata-

1

. Introduction

The challenge for green and sustainable development requires lysts are usually diﬃcult to separate from the reaction products

more eﬃcient chemical transformations with less emission. since the catalysts are in the same phase as the reactants and

With the development of catalytic transformations, chemists products. While catalyst recovery and process work-up are much

have found many eﬃcacious methods to promote both step and easier in the case of solid catalysts, it becomes more diﬃcult to

atom economies in chemical syntheses. Among the catalytic know the exact nature of the active sites. It is not then surprising

pathways, both homogeneous and heterogeneous catalysis that research eﬀorts are being made today to bridge the gap

1

show advantages as well as pitfalls. Obviously, homogeneous between homogeneous and heterogeneous catalysis.

catalysts are widely studied as powerful catalyst systems, owing

Metal–organic frameworks (MOFs) are crystalline mate-

rials generated using metal ions or metal ion clusters that act

as “nodes” combined with multidentate organic ligands to

a

2–6

State Key Laboratory of Heavy Oil Processing, China University of Petroleum,

serve as “rods”.

Unlike other materials (such as metal

Changping, Beijing 102249, China. E-mail: zhangxin@cup.edu.cn; Fax: +86 10 8973

oxides), the unique properties such as high porosities, large

surface areas, structural variety and considerable capacity to

accommodate guest molecules, may provide the fully exposed

active sites by anchoring them in proper position of the

4

979

b

State Key Laboratory of Chemical Resource Engineering, Beijing University of

Chemical Technology, Beijing 100029, China

†

Electronic supplementary information (ESI) available: Experimental section

(

reagents and chemicals and catalyst characterization), optical micrograph of MOFs. Recent researches have shown that MOFs could bridge

the CUP-1 crystals (Fig. S1), mesopore diameter distribution determined by BJH

desorption, TEM, GC-MS, selected bond lengths ( A˚ ) and crystal data for

the gap between homogeneous and heterogeneous catal-

7–9

ysis.

We noted that there are signicantly increasing

2

complexes Zn (atpt)(l-lac)(HCOO) (Tables S1–S3), HPLC traces and CUP-1.cif.

reports of chemical catalysis by MOFs in the past three

CCDC 909362. For ESI and crystallographic data in CIF or other electronic

format see DOI: 10.1039/c4ra01269k

7

–25

years,

however, only two dozens of chiral MOFs with

This journal is © The Royal Society of Chemistry 2014

RSC Adv., 2014, 4, 13093–13107 | 13093

View Article Online

RSC Advances

Paper

catalytically active sites for asymmetrical catalysis have been

reported to date.

2

. Experimental

5

,17–25

2.1. Catalyst preparation

Metals and organic struts can act as active species for

6

MOF-based asymmetrical catalysts. This work has focused

2.1.1 Preparation of IRMOF-3. IRMOF-3 was synthesized

3

3,34

on creating catalytically active sites by introduction of active and activated according to the procedure from literature

organic ligand (L-proline) and gold nanoparticles to fabricate slight modication. In a typical preparation, Zn(NO ) $6H O

with

3

2

solid MOF based catalysts. We have shown that the creation (24.9 mmol) and H atpt (8.3 mmol) were dissolved in 200 mL

2

of catalytic active sites can be facially achieved by post DMF and stirred for 0.5 h at room temperature in air. The

modication (PM) and one-pot (OP) synthetic methods. We solution was transferred and sealed in a 500 mL teon-lined

ꢀ

successfully synthesized a novel homochiral CUP-1 by the autoclave, and kept at 100 C for 18 h. The resulting brown solid

reaction of the mixed linkers of 2-aminoterephthalic (H atpt) was collected by centrifugation and washed thrice with DMF and

2

acid and L-lactic acid with zinc nitrate. The homochiral CUP- CHCl₃during three days, and the solid was nally dried in

ꢀ

1

entails free NH

coordination to the pentanuclear Zn that linked the struc-

ture. The free NH group in the homochiral framework of and L-lactic acid (0.5 mmol) were dissolved in 10 mL DMF and

CUP-1, similar to the well known achiral IRMOF-3 is poten- stirred 0.5 h at room temperature in air. Then Zn(NO ) $6H O

2

groups, which does not participate in vacuum at 50 C for 2 h.

2.1.2 Preparation of CUP-1. Typically, H atpt (0.5 mmol)

2

3

2

tially available for undergoing a variety of organic trans- (1 mmol) was added and continuingly stirred 0.5 h. The mixture

formations. It has been well documented that the post was transferred and sealed in a teon-lined stainless steel vessel

ꢀ

covalent modication of the NH₂group of IRMOF-3 with for a certain time (24–48 h) at various temperatures (70–110 C).

several linear alkyl anhydrides, salicylaldehyde to introduce The resulting brown solid was collected by centrifugation and

7

,26–29

more complex functionality within the lattice.

In recent washed thrice with DMF and ethylether during three days. The

ꢀ

studies, Zhang et al. demonstrated that IRMOF-3 containing solid was nally dried in vacuum at 50 C for 2 h.

the Au(III) Schiﬀ base complex can be lined the pore walls by

PM method. The extremely small (1.7 nm) gold nano- CUP-1 catalysts. A solution of L-proline (18.3 mg) in ethanol

2.1.3 Preparation of L-proline functionalized IRMOF-3 and

7

particles on the surface of IRMOF-3 has also been reported (0.5 mL) was added dropwise to IRMOF-3 (0.2 g), and stored

3

0

with the OP synthesis. We think that it is very interesting to overnight at room temperature. The samples were dried in

ꢀ

functionalize CUP-1 and IRMOF-3 with the catalytic chiral vacuum at 30 C to yield IRMOF-3–Pr(PM). IRMOF-3–Pr(OP) was

reagent. L-Proline was chosen to functionalize CUP-1 and prepared by a mixture of Zn(NO ) $6H O (1.0 mmol, 300 mg),

3

2

IRMOF-3 by PM and/or OP strategies, since L-proline and its H atpt (0.5 mmol, 93.0 mg), and L-proline (0.5 mmol, 57.5 mg)

2

derivatives are well-known asymmetrical organocatalysts dissolved in 20 mL DMF and 20 mL ethanol. The mixture was

ꢀ

accelerating a variety of enantioselective organic reactions heated in a teon-lined steel vessel for 24 h at 100 C. Then the

3

1,32

under homogeneous conditions.

The asymmetrical aldol yellow crystals were washed with DMF and CHCl during three

3

ꢀ

reaction of aldehyde and acetone and the three component days, and the product was dried in vacuum at 30 C. Specically,

coupling reaction of aldehyde, alkyne and amine (A ) IRMOF-3–Pr (OP) were synthesized by using 0.25 mmol

coupling reaction are chosen as the target reactions to L-proline and a same procedure with IRMOF-3–Pr(OP).

3

0

demonstrate the catalytic properties of the L-proline and gold

For the synthesis of CUP-1–Pr(OP) by OP synthesis, the

functionalized IRMOF-3 and CUP-1 catalysts. The interest of mixture of H atpt (0.5 mmol), L-lactic acid (0.5 mmol), and

2

these reactions lies on the versatility of their products as DMF (10 mL) was stirred for 0.5 h at room temperature.

synthetic intermediates in organic synthesis and as impor- Zn(NO ) $6H O (1.0 mmol) was added to the mixture and

3

2

3

0–32

tant therapeutic drug molecules.

These products are continuingly stirred for 0.5 h. Then a solution of L-proline (0.5

conventionally synthesized by using homogenous organo- mmol) in ethanol (10 mL) was dropwise added. The mixture was

metallic or purely organic catalysts with stoichiometric transferred into a teon-lined stainless steel vessel and heated

ꢀ

amounts under strictly controlled reaction conditions.

for 48 h at 100 C. The resulting yellow solid was collected by

By immobilization of L-proline and gold nanoparticles centrifugation and washed thrice with DMF and CHCl during

3

into MOFs, we have developed green and sustainable three days.

heterogeneous catalysis for synthesis of b-hydroxy carbonyl

2.1.4 Preparation of gold functionalized CUP-1 catalysts.

compounds and propargylamines. L-Proline functionalized For the synthesis of gold functionalized CUP-1 by PM method, a

IRMOF-3 catalysts show fair to excellent enantioselectivity solution of NaAuCl $2H O (0.045 g) in 0.3 mL MeCN was

4

2

(

up to 98%) in asymmetrical aldol reactions of aldehydes and dropwise added to the CUP-1 (0.438 g) at room temperature and

ꢀ

acetone with higher turnover numbers and catalytic stabili- stored overnight. Then the sample was dried in vacuum at 30 C

ties than the homogeneous counterpart. The gold func- for 2 h. The sample was referred to as Au/CUP-1(PM).

tionalized CUP-1 catalysts are found to be highly active,

A typical procedure for preparing Au/CUP-1(OP) by OP

3

1

stable and reusable for the three-component coupling reac- method was following. A mixture of H atpt (0.5 mmol, 0.092 g), L-

2

tions of aldehyde, alkyne and amine. This work provides lactic acid (0.5 mmol, 0.045 g), and DMF (10 mL) were stirred for

general methods to functionalize MOFs with the active ligand 0.5 h at room temperature. Zn(NO ) $6H O (1.0 mmol, 0.300 g)

3

2

and metal nanoparticles for fabrication of highly eﬃcient was added to the mixture and continuingly stirred for 0.5 h.

MOF-based catalysts.

13094 | RSC Adv., 2014, 4, 13093–13107

This journal is © The Royal Society of Chemistry 2014

View Article Online

Paper

RSC Advances

ꢀ

Then a solution of AuCl (0.005 g) in DMF (1 mL) was dropwise starting components and hydrothermal heating at 100 C for

added. The mixture was transferred into a teon-lined stainless 48 h, a novel homochiral MOF referred to as CUP-1 was

ꢀ

steel vessel and heated for 24 h at 110 C. The resulting green obtained (Scheme 1b). The introduction of auxiliary chiral L-

solid was collected by centrifugation and washed thrice with proline unit inside preassembled framework of IRMOF-3 with

ꢀ

DMF and CHCl

for 2 h.

3

. Then the sample was dried in vacuum at 30 C PM method aﬀorded IRMOF-3–Pr(PM) (Scheme 1c). In an

alternative approach, L-proline was introduced with the starting

components composed of IRMOF-3 or CUP-1 in a one-pot

reaction to give IRMOF-3–Pr(OP) (Scheme 1e) or CUP-1–Pr(OP)

2

.2. Catalytic performance

(Scheme 1f). Specically, gold functionalized CUP-1 with PM

2.2.1 Asymmetrical aldol reaction of aldehyde with

and OP methods aﬀorded Au/CUP-1(PM) (Scheme 1d) and Au/

CUP-1(OP) (Scheme 1g), respectively. Clearly the synthesis

component for preparing IRMOF-3 is the same with CUP-1,

except for the latter containing an additional chiral L-lactic acid.

CUP-1 and IRMOF-3 and their functionalized catalysts have a

close relationship in preparation procedures. According to the

elemental analysis of the samples, 5.8, 3.2 and 7.4 wt% of

acetone. The mixture of benzaldehyde (0.3 mmol, 31.8 mg),

acetone (3.0 mmol, 174.4 mg), DMSO (6.4 mmol, 0.5 g), and

catalyst (20 mg) was put into a closed glass reactor (2 mL,

SUPELCO) and extensively stirred (ca. 500 rpm) at a desired time

and temperature. The amounts of active sites (i.e., proline

species) referred to benzaldehyde are 3.8, 9.2, and 14.6 mol%

over IRMOF-3–Pr(OP), IRMOF-3–Pr(PM), and CUP-1–Pr(OP),

respectively. Aer the reaction, the catalyst was removed from

the solution by centrifugation at 6000 rpm for 10 minutes. The

conversion of benzaldehyde and the yield of b-hydroxy carbonyl

and a,b-unsaturated carbonyl compounds were determined by

GC analysis (SP6890, Capillary Column, HP-5). And n-nonane

was used as an internal standard. The product of b-hydroxy

0

L-proline was introduced in IRMOF-3–Pr(OP), IRMOF-3–Pr (OP),

and CUP-1–Pr(OP) samples, respectively. And 15.8 wt% of

L-proline was introduced in IRMOF-3–Pr(PM). ICP-OES shows

that the gold contents are 4.52 and 0.10 wt% on Au/CUP-1(PM)

and Au/CUP-1(OP), respectively.

carbonyl compound was separated and puried by column 3.2. Optical micrographs and transmission electron

chromatography on silica gel (EtOAc–hexane ¼ 1/4 as the microscope (TEM)

eluent). The ee values were determined by HPLC with a Chir-

alpak ID column, using hexane–2-propanol–diethylamine (80/

Fig. 1A gives the optical micrographs of IRMOF-3, IRMOF-3–

0

Pr(OP), IRMOF-3–Pr (OP), IRMOF-3–Pr(PM), CUP-1, and CUP-1–

ꢁ

1

2

0/0.1) as a mobile phase at a ow rate of 1.0 mL min and a

33,34

Pr(OP) samples. The IRMOF-3 structure

4

is made of Zn O

ꢀ

column temperature of 35 C.

tetranuclear clusters connected by rigid dicarboxylic linkers

3

2

.2.2 The A coupling reaction. Typical procedure for the A

coupling reaction: a mixture of catalyst (0.070 g), benzaldehyde

0.250 mmol, 0.027 g), piperidine (0.300 mmol, 0.026 g), phe-

H atpt to generate a cubic framework as illustrated in Scheme

2

1

a. IRMOF-3 exhibits a light brown cubic shape with sizes of 90–

10 mm as illustrated in Fig. 1Aa. Using the auxiliary chiral

(

nylacetylene (0.325 mmol, 0.034 g), and dioxane (1.000 g) was

put into a closed glass reactor (2 mL, SUPELCO) and extensively

stirred (ca. 500 rpm) at the desired time and temperature. The

mole ratio of gold to benzaldehyde is 6.42 mol% and 0.14 mol%

on Au/CUP-1(PM) and Au/CUP-1(OP), respectively. Aer the

reaction, the catalyst was removed from the solution by centri-

fugation at 6000 rpm for 10 minutes. The product was analysed

by GC (SP6890, Capillary Column, SE-30) and GC-MS. And

n-nonane was used as an internal standard to calibrate the

reaction products. The recovered catalyst was thoroughly

washed with 1,4-dioxane and used for the next run. The ee

values were determined by HPLC with a Chiralcel OD column,

using hexane–ethanol (95/5) as a mobile phase at a ow rate of

L-proline to modify IRMOF-3 with OP method doesn't signi-

cantly aﬀect the cubic crystal morphology for IRMOF-3–Pr(OP)

(Fig. 1Ab), however, the size (30–80 mm) of cubic phase sharply

decreased and very small cubic phase with ca. 10 mm was

0

observed on IRMOF-3–Pr (OP) (Fig. 1Ac). The modication of

IRMOF-3 with L-proline by PM method resulted the fuzzy edge

of IRMOF-3–Pr(PM) in despite of the discernable cubic

morphology (Fig. 1Ad). CUP-1 with yellow plate crystals can be

synthesized from the mixture of Zn(NO ) $6H O, H atpt, l-lac,

3 2 2 2

DMF in a mole ratio of 2 : 1 : 1 : 258 as illustrated in Scheme 1b.

We have studied the eﬀect of crystallization temperature (70–

ꢀ

1

10 C) for CUP-1. It was found that heated at 70–100 C for 24 h

in a teon-lined stainless-steel autoclave under autogeneous

pressure there were no yellow plate products immerging, but

amorphous substance (Fig. S1†). Extending the crystallization

ꢁ1

0

.5 mL min . Before ee analysis, the product was puried with

ash column chromatography on silica gel using the mixture of

hexane and ethyl acetate (ethyl acetate ¼ 15 vol%) as the eluent.



ꢀ

time from 24 to 48 h at 100 C or increasing the reaction

ꢀ

temperature to 110 C for 24 h both achieved high quality plate

crystals (Fig. 1Ae). It seems that crystallization temperature

ranged from 100 to 110 C has no signicant eﬀect on the

crystal morphology of CUP-1 (Fig. S1†). Notably, the modica-

3

. Results

ꢀ

3.1. Strategies for functionalization of IRMOF-3 and CUP-1

Scheme 1 illustrates our synthetic strategy to prepare the chiral tion of CUP-1 with L-proline by OP method aﬀects a spherical

MOF. The starting components are composed of H atpt, morphology (Fig. 1Af), which is sharply diﬀerent from the plate

2

Zn(NO ) $6H O and DMF. The hydrothermal reaction of these crystal of CUP-1.

3

2

ꢀ

components in the mole ratio of 1 : 3 : 311 at 100 C for 18 h

The representative TEM images of Au/CUP-1(PM) and

aﬀorded IRMOF-3 (Scheme 1a). By adding L-lactic acid to the Au/CUP-1(OP) samples are shown in Fig. 1B. Gold nanoparticles

This journal is © The Royal Society of Chemistry 2014

RSC Adv., 2014, 4, 13093–13107 | 13095

View Article Online

RSC Advances

Paper

Scheme 1 The strategies and accordingly models for functionalizing IRMOF-3 and CUP-1 catalysts by postsynthetic modiﬁcation (PM) and one-

pot synthesis (OP).

ꢀ

are close to spherical morphology with size distributions of 13.9 2q ¼ 6.8 disappears, indicating that the crystalline structure of

ꢂ 4.7 and 2.1 ꢂ 0.7 nm over Au/CUP-1(PM) and Au/CUP-1(OP), IRMOF-3–Pr(PM) slightly changes. The result is in accordance

3

respectively. Aer four successive cycles of the A coupling with the observation of optical micrographs.

reaction, both gold nanoparticles containing samples exhibited Fig. 2B shows the powder XRD patterns of CUP-1 and gold

signicant agglomeration. In the case of the recycled Au/CUP- or L-proline functionalized CUP-1 samples. The theoretical

1

(OP) catalyst, the size distributions of gold particles range from simulated framework of CUP-1 from the structure solved by

0 to 60 nm (Fig. S2†).

single-crystal XRD is also included. Clearly, the powder XRD

patterns of CUP-1 give the high crystallinity and match very

well with the theoretical patterns. Notably CUP-1 displays a

3

.3. Powder X-ray diﬀraction (XRD)

2

similar XRD pattern with a homochiral MOF Zn (bdc)(l-

5

Fig. 2A shows the powder XRD patterns of IRMOF-3 and its lac)(dmf)$(DMF) (1$DMF). The gold functionalized CUP-1

modied samples. XRD patterns of IRMOF-3–Pr(OP), IRMOF-3– catalysts by PM and OP methods retain the crystalline

0

ꢀ

Pr (OP), and IRMOF-3 samples are nearly identical. The similar structure. Notably, three additional peaks at 2q ¼ 38.2 ,

ꢀ

XRD patterns with IRMOF-3 indicate that IRMOF-3–Pr(OP) and 44.4 , and 64.5 are observed for Au/CUP-1(PM), which are

0

IRMOF-3–Pr (OP) samples keep the crystalline integrity. indexed to the (111), (200), and (220) reections of face

Although the peak intensities decreased on IRMOF-3–Pr(OP) centered cubic crystalline Au, respectively. The average

ꢀ

aer being used the aldol reaction at 60 C for 72 h, the main diameter of gold crystal was 12.5 nm calculated by Scherrer

diﬀraction peaks were retained. The XRD patterns of IRMOF-3– formula, which coincided with the observations from the

Pr(PM) show a diﬀerence with IRMOF-3, i.e., the peak located at TEM images. Similar to IRMOF-3–Pr(OP), the crystallinity of

13096 | RSC Adv., 2014, 4, 13093–13107

This journal is © The Royal Society of Chemistry 2014

View Article Online

Paper

RSC Advances

Fig. 2 (A) Powder XRD patterns of IRMOF-3 (a), IRMOF-3–Pr(OP) (b),

0

IRMOF-3–Pr (OP) (c), and IRMOF-3–Pr(PM) (d); (B) the simulated

framework for CUP-1 (a), experiment measured CUP-1 (b), Au/CUP-

1

(PM) (c), Au/CUP-1(OP) (d), and CUP-1–Pr(OP) (e) samples.

3.4. Single-crystal XRD

Single-crystal XRD was carried out to determine exact crystalline

structure of CUP-1 (see Tables S1–S3† of the ESI). X-ray crys-

tallographic analysis reveals that CUP-1 crystallizes in the

orthorhombic system, chiral space group P2(1)2(1)2(1) with the

2

formula of Zn (atpt)(l-lac)(HCOO). Fig. 3 illustrates the section

of the X-ray crystal structure of CUP-1. There are two unique zinc

centers (Zn(1) and Zn(2)) in the polymeric structure, and both of

them have a coordination number ve and an uncommon

trigonal-bipyramidal coordination environment as depicted in

2

+

Fig. 3. The rst Zn ion is coordinated with a deprotonated

Fig. 1 (A) The optical microscope photograph of IRMOF-3 (a), IRMOF-

0

3

-Pr(OP) (b), IRMOF-3-Pr (OP) (c), IRMOF-3–Pr(PM) (d), CUP-1 (e), and

CUP-1–Pr(OP) (f); (B) TEM images and gold size distributions of Au/

CUP-1(PM) (a) and Au/CUP-1(OP) (b) samples.

3

ꢀ

Au/CUP-1(PM) aer the A coupling reaction at 120 C for 12

h sharply decreased despite of retaining the main diﬀraction

peaks. No signicant diﬀractions of gold crystal on Au/CUP-

1

(OP) are found due to the small gold size and low gold

content (0.1%). The introduction of auxiliary chiral L-proline

into the components of CUP-1 by OP method results in a

Fig. 3 Section of the X-ray crystal structure of CUP-1, showing the

coordination environments of the Zn ions and their connectivity with

lactate anions. Thermal ellipsoids are set at 50% probability. The chiral

C atom of the lactic ligand is marked by an asterisk.

sharp decrease of crystallinity, and only a weak peak at 2q ¼

2+

ꢀ

6

.8 is observed, indicating that the crystalline structure

partially collapsed.

This journal is © The Royal Society of Chemistry 2014

RSC Adv., 2014, 4, 13093–13107 | 13097

View Article Online

RSC Advances

Paper

hydroxy group of a lactate ligand, a carboxylate oxygen atom of shows a view of the 1D chiral chains (A), projection in the (110)

-amino-1,4-benzenedicarboxylate ligand, and the oxygen atom plane (B), and perspective view along a axis (C) in the structure

2

+

of a formic ligand (the formic acids are generated by decom- of CUP-1. It can be seen that the Zn ions and lactate ligands

position of DMF ) rather than DMF in the structure of 1$DMF.

The second Zn ion is chelated by one carboxylic oxygen atom as secondary building units (SBUs), which are further inter-

of lactate ligand, and coordinated to a carboxylic oxygen atom of connected by the benzene rings of 2-amino-1,4-benzenedi-

3

5

form 1D chiral chains running along the a axis. These chains act

2

+

2

-amino-1,4-benzenedicarboxylate ligand. The chiral C atom carboxylate in the other two directions to generate a 3D network

˚

(C(10)) of the lactic ligand is marked by an asterisk as shown in with quadrangular channel dimensions of ca. 12 A ꢃ 20 A

2+

Fig. 3. In addition, the two Zn ions are linked to each other by (measured between opposite atoms) viewed along the a axis.

bridging carboxylate of H atpt ligand and one lactate ligand. The chiral centers of the L-lactate moieties are exposed within

2

+

And each lactate dianion connects four Zn ions. In this the pores. In a word, the pores in CUP-1 have a homochiral

˚

structure, the Zn–Zn distance and Zn–O–Zn angles are 3.421 A environment.

ꢀ

for Zn(1)–Zn(2), and 106.36 for Zn(2)–O(2)–Zn(1), respectively.

˚

The Zn–O bond lengths vary from 1.932 to 2.145 A, and O–Zn–O

angles vary from 79.34 to 171.5 (Tables S1 and S2†). Fig. 4

ꢀ

2

3.5. N adsorption and desorption

Table 1 summarizes the data of surface area, pore size, and pore

ꢀ

volume from N

3

2

adsorption–desorption at ꢁ196 C for IRMOF-

0

, IRMOF-3–Pr(OP), IRMOF-3–Pr (OP), and CUP-1 samples. In

the present study, IRMOF-3 was synthesized by solvothermal

with H atpt and Zn(NO $6H O in DMF without N protection.

The surface area determined by BET and Langmuir equation is

2

3

)

2

ꢁ1

1

6

212 and 1468 m g , respectively. This BET surface area is

2

ꢁ1

2% higher than that (750 m

g ) prepared by the “direct

7

2

ꢁ1

mixing” synthesis, but it is still much lower than 2446 m g

36

when using DEF as solvent. We notice that diﬀerent surface

7,10,33,34,36,37

areas of IRMOF-3 have been reported.

should be due to the diﬀerent preparation conditions (e.g., with/

without N protection, the diﬀerent solvent employed). It was

reported that higher BET surface area was obtained by using

DEF rather than DMF as solvent. The moisture adsorbed by

MOFs upon exposure to ambient air and water residue in the

reagent also aﬀected the structure. By introducing the auxil-

iary chiral L-proline into the components of IRMOF-3 with OP

method, the surface area of IRMOF-3–Pr(OP) sharply decreased

in comparison with IRMOF-3 (Table 1). The BET surface areas of

The diﬀerence

2

10

34

0

2

ꢁ1

IRMOF-3–Pr(OP) and IRMOF-3–Pr (OP) are 140 and 166 m g

,

respectively, which are ca. one eighth of IRMOF-3. It seems that

the higher concentration of L-proline results in lower BET

surface area. The BET and Langmuir surface area of CUP-1 is

2

ꢁ1

7

8 and 104 m g , respectively, which is only ca. one-tenth of

IRMOF-3.

Fig. 5A shows the N

2

adsorption–desorption isotherms of

0

IRMOF-3, IRMOF-3–Pr(OP), IRMOF-3–Pr (OP) and CUP-1

samples. At rst sight it seems that all samples feature the type

IV isotherm with a hysteresis loop and thus possess mesopore,

however, the adsorption isotherms exhibit a distinctive plateau

so that adsorption volume approaches a limiting value as p/p₀

increasing from 0.009 to 0.90 for IRMOF-3, IRMOF-3–Pr(OP),

and CUP-1 samples, which is a prominent feature of type I with

microporous material. We also noted that the physisorption

0

hysteresis in Fig. 5A includes type H2 for IRMOF-3–Pr (OP) and

type H1 for other samples. The pore diameters determined by

BJH desorption method are 4.27, 3.75, 3.81, and 1.41 nm for

IRMOF-3, IRMOF-3–Pr(OP), IRMOF-3–Pr (OP) and CUP-1

samples, respectively (Table 1, Fig. S3†). The Saito–Foley (SF)

method based on cylindrical pore geometry has been adopted to

derive the microporous size distribution from physisorption

Fig. 4 A view of the 1D chiral chains (as both ball-and-stick/polyhedra

and wire models; polyhedra represent the Zn coordination environ-

ments) in the structure of CUP-1 (A); projection of the structure of

CUP-1 in the (110) plane (B); perspective view of the structure of CUP-1

along a axis (C). Note: the purple, red, blue, gray, and white represent

Zn, O, N, C, and H atoms, respectively.

0

13098 | RSC Adv., 2014, 4, 13093–13107

This journal is © The Royal Society of Chemistry 2014

View Article Online

Paper

Table 1 Texture properties of IRMOF-3, IRMOF-3–Pr(OP), IRMOF-3–Pr (OP), and CUP-1 samples

RSC Advances

0

2

ꢁ1

3

ꢁ1

Surface area data (m g

)

Pore size data (nm)

Pore volume data (cm g )

a

b

c

d

e

Sample

BET

Langmuir

Average

Micro-

Meso-

Total

Micro-

Meso-

IRMOF-3

IRMOF-3–Pr(OP)

IRMOF-3–Pr (OP)

CUP-1

1212

140

166

78

1468

188

242

104

2.56

2.86

5.31

3.08

0.97

0.69

0.73

0.66

4.27

3.75

3.81

1.41

0.77

0.10

0.22

0.06

0.51

0.07

0.08

0.04

0.40

0.05

0.24

0.03

0

a

b

c

d

e

Saito–Foley (SF) method pore diameter. BJH method desorption pore diameter. Total pore volume. SF method cumulative pore volume. BJH

interpolated cumulative pore volume.

Fig. 6 (A) TG-DTA curves on IRMOF-3 (a), IRMOF-3–Pr(OP) (b),

IRMOF-3–Pr(PM) (c); (B) TG-DTA curves on CUP-1 (a), CUP-1–Pr(OP)

Fig. 5

2

N adsorption–desorption isotherms (A) and pore diameter

(b), and Au/CUP-1(OP) (c) samples.

distribution determined by SF method (B) of IRMOF-3 (a), IRMOF-3–

Pr(OP) (b), IRMOF-3–Pr (OP) (c), and CUP-1 (d) samples.

0

IRMOF-3–Pr(OP), respectively, was due to the release of physi-

cally adsorbed solvent molecules (e.g. CHCl and DMF) and

3

isotherms as depicted in Fig. 5B. Clearly, the narrow micropo-

rous size distributions were found on IRMOF-3, IRMOF-3–

Pr(OP), and CUP-1 samples, while a wider size distribution was

unreacted ligands (e.g. 2-aminoterephthalic), which was

ꢀ

accompanied with an endothermic peak centered at ca. 100 C

0

in the DTA curve. The second stage ranged from 384 to 550 C

observed on IRMOF-3–Pr (OP). The microporous size diameters

was due to the organic decomposition, which was accompanied

are 0.97, 0.69, 0.73, and 0.66 nm on IRMOF-3, IRMOF-3–Pr(OP),

ꢀ

0

with a broad exothermic peak centered at ca. 510 C in the DTA

IRMOF-3–Pr (OP), and CUP-1 samples, respectively.

curve. Notably, IRMOF-3–Pr(PM) started to decompose aer ca.

ꢀ

3

14 C. Clearly the thermal stability of IRMOF-3 and IRMOF-3–

3.6. Thermogravimetric and diﬀerential thermal analysis

Pr(OP) samples was superior to that of IRMOF-3–Pr(PM). No

plateau of weight loss was possibly due to too much physical

(

TG-DTA)

TG-DTA experiment has been carried out to investigate the adsorbed solvent remained on all the samples.

thermal stabilities of the IRMOF-3, CUP-1, and their modied

Fig. 6B shows the TG-DTA curves of CUP-1, CUP-1–Pr(OP)

samples. Fig. 6A shows the TG-DTA curves of IRMOF-3, IRMOF- and Au/CUP-1(OP) samples. The weight loss of CUP-1 and Au/

3

–Pr(OP) and IRMOF-3–Pr(PM) samples. The TG curves of all CUP-1(OP) samples could be divided into three stages with 40–

ꢀ

samples show two steps of weight loss stages in the temperature 264, 264–371, and 371–510 C, corresponding to the desorption

range from 25 to 700 C. The rst stage ranged from 40 to 384 C of physically adsorbed solvent molecules, further desorption of

ꢀ

corresponding to 29% and 22% of weight loss on IRMOF-3 and solvent and/or unreacted ligands within pores or on the surface

This journal is © The Royal Society of Chemistry 2014

RSC Adv., 2014, 4, 13093–13107 | 13099

View Article Online

RSC Advances

Paper

of the material, and the decomposition of the crystal structure,

respectively. On the other hand the continuous loss of the

weight was found on CUP-1–Pr(OP) until it was completely

ꢀ

decomposed at 510 C. It is evident that the thermal stability of

CUP-1 and Au/CUP-1(OP) samples is much higher than that of

CUP-1–Pr(OP).

3.7. Infrared spectrum (IR)

Fig. 7 shows IR spectra of IRMOF-3, IRMOF-3–Pr(OP), and

IRMOF-3–Pr(PM) samples. The IR spectra of CUP-1, CUP-1–

Pr(OP), Au/CUP-1(OP) and Au/CUP-1(PM) samples are given

in Fig. 8. The IR spectra of IRMOF-3 show two peaks centered

ꢁ1

38

at 3473 and 3356 cm due to the existence of the amino.

Whereas, these peaks become notably weak for IRMOF-3–

Pr(PM), indicating the formation of amide by reaction of the

NH

2 2

group of the H atpt ligand with carboxyl group of

L-proline. However, it seems that the N–H stretches on

IRMOF-3–Pr(OP) feature the same mode with IRMOF-3. This

result could mean that NH group of IRMOF-3–Pr(OP) is not

2

transformed and the free L-proline should be encapsulated

on the surface or pore. Notably the N–H stretches of CUP-1

ꢁ

1

red shi to 3458 and 3341 cm

IRMOF-3, and these bands on CUP-1–Pr(OP) become weak,

indicating that NH group reacts with L-proline and trans-

in comparison with

2

Fig. 8 Infrared spectra of CUP-1 (a), and CUP-1–Pr(OP) (b), Au/CUP-

forms into amide. This result is in sharp contrast with 1(OP) (c), and Au/CUP-1(PM) (d) samples.

L-proline functionalized IRMOF-3 by OP method. The N–H

stretches were also observed on gold functionalized CUP-1

samples, the weak intensity could be due to nano gold

particles deposited on their surface. The bands at 2926 cm

on all samples could be due to the stretching vibrations of the

aromatic C–H. Specically, the bands at 2973 and 2926 cm

ꢁ1

on CUP-1 and its modied samples can be assigned to the

vibrations of C–H originated from aromatic and/or formic

ligand. The formic could be generated by decomposition of

3

5

DMF. For all samples, the two sharp bands at 1574 and

ꢁ1

1

382 cm

correspond to asymmetric (nas(C–O)) and

symmetric (n

s

(C–O)) vibrations of carboxyl groups, respec-

3

9

ꢁ1

tively. And the peaks centered at 1660, 1501, and 1432 cm

are ascribed to C]C stretching vibration of the aromatic. The

ꢁ1

1

253 cm frequency can be assigned to C–N vibrations for all

samples.

13

Fig. 7 Infrared spectra of IRMOF-3 (a), IRMOF-3–Pr(OP) (b), and Fig. 9 Solid C-NMR of IRMOF-3 (a) and IRMOF-3–Pr(PM) (b). The

IRMOF-3–Pr(PM) (c) samples. asterisks correspond to rotation bands.

13100 | RSC Adv., 2014, 4, 13093–13107

This journal is © The Royal Society of Chemistry 2014

View Article Online

Paper

RSC Advances

IRMOF-3 are assigned to the resonance signals of C]O of

amide and N–CH, respectively (Fig. 9b). Spectral assignments of

1

3

the aromatic C resonances of IRMOF-3 are based on previous

7,40,41

works.

3.9. Temperature-programmed reduction (TPR)

TPR technique is usually used to quantitatively measure the

reduction of oxidized gold species and thereby calculate the

distribution of diﬀerent gold oxidation states in supported Au

30,42

catalysts.

2

Fig. 10 shows H -TPR proles of CUP-1, Au/CUP-

1

(OP) and Au/CUP-1(PM) samples. The Au/CUP-1(PM) aer one

3

Fig. 10 TPR proﬁles of CUP-1 (a), Au/CUP-1(PM) (b), Au/CUP-1(PM) successive cycle of the A coupling reaction is also included. The

after reaction (c), and Au/CUP-1(OP) (d).

pristine CUP-1 and Au/CUP-1(OP) feature no hydrogen

consumption in the range of 50–350 C, indicating the gold

ꢀ

species in Au/CUP-1(OP) should be metallic. However, one

1

3

.8. Solid state C magic angle spinning nuclear magnetic

ꢀ

reduction peak centered at 196 C was found on Au/CUP-1(PM),

resonance (MAS NMR)

3

the reduction peak disappeared aer the A coupling reaction.

1

3

Fig. 9 represents the solid state C MAS NMR spectra of IRMOF- The attempt to characterize the gold oxidation states of Au/CUP-

and IRMOF-3–Pr(PM). The C resonance peaks at 174.8, 149.8 1(PM) by X-ray photoelectron spectroscopy was failed due to the

1

3

and 137.2–117.0 ppm of IRMOF-3 are assigned to O–C]O, overlap of binding energies between Au 4f and Zn 3p. Zhang

7

phenylene C–NH

2

, and the aromatic region, respectively. The et al. have previously observed two reduction peaks over

post functionalization of L-proline for NH

signicant eﬀect upon the C spectra. Of particular note is the and proposed that the reduction peak at ca. 239 C was due to

decreased intensity of the resonance of the ring carbon with the the reduction of Au . We earlier prepared Au/IRMOF-3 using

attached amino group at 149.8 ppm. And the two carboxyl the similar method with Au/CUP-1(PM) and ascribed the peak

resonances are partially resolved. The additional resonances at ranged from 190 to 270 C to the reduction of Au . Similar to

2

–Ph in IRMOF-3 has a IRMOF-3 immobilized gold catalyst prepared by PM method,

1

3

ꢀ

3

+

ꢀ

3+ 30

7,30

181.3 and 66.7 ppm on IRMOF-3–Pr(PM) compared with the earlier works, we presume that the low temperature peak

a

Table 2 Aldol reaction catalyzed by L-proline functionalized IRMOF-3 and CUP-1 catalysts

ꢀ

b

c

d

e

Entry

1

Catalyst

Aldehyde

T ( C)

t (h)

Conv. (%)

S

1

(%)

S

2

(%)

Y

1

(ee) (%)

TON

L-Proline

IRMOF-3

R ¼ H

40

r.t.

60

r.t.

40

60

r.t.

40

12

24

4

72

20

5

96

72

30

120

96

180

96

66

—

22

1

49

15

47

58

41

50

66

36

34

57

31

—

54

66

4

55

48

44

28

23

33

63

35

31

69

—

46

34

96

45

53

56

72

77

67

38

65

69

20 (12)

62 (60)

68 (76)

12 (0)

<1 (n.d.)

2 (n.d.)

8 (98)

23 (73)

26 (10)

11 (89)

11 (88)

22 (28)

23 (52)

12 (93)

18 (33)

3

2

—

3

f

2

3

R ¼ H

f

R ¼ 4-NO

2

4

5

6

7

8

9

R ¼ H

CUP-1

R ¼ H

CUP-1–Pr(OP)

IRMOF-3–Pr(OP)

IRMOF-3–Pr(PM)

R ¼ H

4

R ¼ H

12

15

11

13

17

9

R ¼ H

10

11

12

13

14

15

R ¼ 4-NO

2

R ¼ 3-Cl

n-Octaldehyde

Cyclohexane-carboxaldehyde

R ¼ H

6

10

R ¼ H

a

Reaction condition: IRMOF-3, IRMOF-3–Pr(OP) and IRMOF-3–Pr(PM): 20 mg; CUP-1–Pr(PM) and CUP-1–Pr(OP) 60 mg; L-proline 7.0 mg (0.06

mmol); benzaldehyde: 0.3 mmol. The molar ratio of benzaldehyde : acetone was 1 : 10, solvent: DMSO 0.5 g (6.4 mmol). The selectivity of

b-hydroxy carbonyl compound (1). The selectivity of b-unsaturated carbonyl compound (2). The yield of b-hydroxy carbonyl compound (1),

b

c

d

the data in the parentheses are ee values which were determined by HPLC analyses (Chiralpack ID) with hexane/isopropanol as the eluent. The

e

f

absolute conguration was not determined, n.d., not determined. Calculated on the basis of L-proline. Data from the ref. 31, the reaction

conditions: 30% mmol proline, 0.1 mmol aldehyde, acetone–DMSO ¼ 1/4 (v/v), acetone 0.2 mL.

This journal is © The Royal Society of Chemistry 2014

RSC Adv., 2014, 4, 13093–13107 | 13101

View Article Online

RSC Advances

is due to the reduction of Au ions into Au atoms, and the ratio

Paper

3

+

0

3

+

0

of Au /Au in Au/CUP-1(PM) is 2.0.

3.10. Catalytic performance test

3.10.1 Asymmetric aldol reaction of aldehyde and acetone.

Table 2 summarizes the catalytic performance of L-proline

functionalized IRMOF-3 and CUP-1 catalysts for the aldol reac-

tion. Reacting aldehyde with acetone on L-proline functionalized

IRMOF-3 and CUP-1 catalysts aﬀords the aldol products

including b-hydroxy carbonyl compound (1) and a,b-unsaturated

carbonyl compound (2). The product 2 is obtained by the

dehydration of product 1, and the two products are demon-

Fig. 11 Improve catalytic performance of IRMOF-3–Pr(OP) for the

strated by GC-MS analysis (Fig. S4†). The experiments of aldol reaction by optimizing the reaction condition.

screening solvents (neat, DMF and DMSO) using the represen-

tative model reaction consisting of benzaldehyde and acetone

showed that DMSO was a suitable solvent (Table S4†). Reacting

One prominent advantage of the heterogeneous functional-

benzaldehyde with acetone on the reference homogeneous ized IRMOF-3 catalysts is their easy separation and recyclability.

ꢀ

L-proline at 40 C addresses products 1 and 2 with selectivity of Aer the second successive cycles with intermediate extensive

3

1% and 69%, respectively, under the present reaction condi- washing with DMSO, the catalytical activity of IRMOF-3–Pr(OP)

31

tions. The yield of 1 is 20% with 12% ee (entry 1). List et al.

and IRMOF-3–Pr(PM) decreases by around 30%. The further

obtained the yield of 62%, 68% with 60% and 76% ee, respec- recycling however featured much less decrease (<10%) in

tively, in the case of benzaldehyde and 4-nitrobenzaldehyde as activity.

3

the substrate (entries 2 and 3). The reaction catalyzed by IRMOF-

3.10.2 The A coupling reaction. The development of

3

produces the products 1 and 2 with the selectivity of 54%, 46%, heterogeneous catalysts for preparing propargylamines by the

3

27,42,43

respectively, at 22% of benzaldehyde conversion (entry 4), while

A coupling reaction remains an active research area.

3

a control experiment with unmodied CUP-1 fails to give Table 3 summarizes the A coupling reaction catalyzed by gold

signicant conversion (entry 5). Notably, the reaction catalyzed functionalized CUP-1 catalysts. Gold functionalized CUP-1

by CUP-1–Pr(OP) gives a signicant conversion (49%) and high catalysts feature 100% selectivity to the product of propargyl-

selectivity (96%) to 2 (entry 6). By introducing L-proline on amine for the reaction. Eﬀect of reaction temperature on the

IRMOF-3 by OP method, the benzaldehyde conversion of yield of propargylamine over Au/CUP-1(PM) was explored (Table

IRMOF-3–Pr(OP) decreases a little compared with L-proline; 3, entries 1–5). No higher than 17% yield of propargylamine was

ꢀ

however, the benzaldehyde conversion is signicantly enhanced found at the reaction temperature less than 80 C. A moderate

ꢀ

compared with IRMOF-3 (entry 9 vs. 4). We note that a moderate yield (51%) is obtained at 100 C, and a good yield (89%) can be

ꢀ

conversion (58%) at 60 C and 26% yield for 1 on IRMOF-3– obtained at 120 C. We have analyzed the enantioselectivity for

Pr(OP), however, the ee is only 10% (entry 9). By decreasing the the propargylamine. The ee values are 6% and 4% with benz-

ꢀ

reaction temperature, the ee is sharply increased. Specically, aldehyde at 100 and 120 C, respectively (entries 4 and 5). The

ꢀ

3

9

8% ee with 8% yield can be obtained on IRMOF-3–Pr(OP) at high reaction temperature (>100 C) of the A coupling reaction

room temperature (entry 7). The aryl aldehydes possessing on Au/CUP-1(PM) catalyst oﬀers no advantage for the ee.

electron withdrawing groups aﬀord 1 with an enhanced ee Aromatic aldehydes including those bearing functional groups

ꢀ

(

entries 10 and 11) over IRMOF-3–Pr(OP) catalyst at 60

C

such as alkyl and chloro are able to undergo the corresponding

ꢀ

compared with benzaldehyde. The reaction with aliphatic alde- three-component-coupling at 120 C, and aﬀord good to excel-

hyde like cyclohexanecarboxaldehyde also displays a moderate lent yields (entries 6 and 7). Aliphatic aldehydes such as n-

enantioselectivity, while the reaction with n-octaldehyde shows octaldehyde and cyclohexanecarboxaldehyde also display good

3

low ee on IRMOF-3–Pr(OP) catalyst (entries 12, and 13). Notably, to excellent yields (entries 8 and 9). The A coupling reaction

reacting benzaldehyde with acetone on IRMOF-3–Pr(PM) at with alicyclic amines such as piperidine, pyrrolidine, and

room temperature aﬀords an excellent enantioselectivity (93%) morpholine proceeds smoothly to aﬀord the corresponding

with 12% yield of 1 (entry 14). The yield increases to 18%, propargylamines (entries 5, 10 and 11). Au/CUP-1(OP) with

ꢀ

whereas, the ee sharply decreases to 33% at 40 C (entry 15).

0.1 wt% gold aﬀords 5% yield at 120 C, however, the turnover

By changing the reaction conditions, the catalytic perfor- number (TON) calculated based on the gold weight is up to 35

mance of IRMOF-3–Pr(OP) for the aldol reaction can be signif- (entry 12). The yield (79%) and TON (556) over Au/CUP-1(OP)

icantly enhanced. As evidenced in Fig. 11, by increasing the can be remarkably enhanced by increasing the reaction

ꢀ

amounts of catalyst (60 mg) and DMSO (1.0 g), the mole ratio of temperature from 120 to 150 C (entry 13).

acetone/benzaldehyde (20), and by shortening the reaction time

Fig. 12 shows the reusability of Au/CUP-1(PM) and Au/CUP-

3

ꢀ

(24 h), the benzaldehyde conversion and the selectivity to 1 1(OP) catalysts for the A coupling reaction at 120 and 150 C,

increased from 47% to 90%. The 1 yield was sharply enhanced respectively. The benzaldehyde conversion is 90% within 4 h at

ꢀ

from 23% to 78% while retaining the ee value of 73%.

120 C over the fresh Au/CUP-1(PM) catalyst. Aer three

13102 | RSC Adv., 2014, 4, 13093–13107

This journal is © The Royal Society of Chemistry 2014

View Article Online

Paper

RSC Advances

a

Table 3 Coupling of aldehyde, alkyne, and amine catalyzed by gold functionalized CUP-1 catalysts

1

2

3

b

ꢀ

c

Entry

Catalyst

R

R R NH

T (h)

T ( C)

Yield (ee) (%)

TON

1

2

3

4

5

6

7

8

9

1

Au/CUP-1(PM)

Au/CUP-1(OP)

Ph

4-CH

3-ClC

Heptyl

Piperidine

Pyrrolidine

Morpholine

Piperidine

6

5

4

12

4

12

4

40

60

80

2

4

—

3

17

51 (6)

89 (4)

91

89

79

97

81

84

5

100

120

150

8

14

12

15

13

35

556

3

C

H

6 4

6

H

4

Cyclohexyl

0

1

2

3

Ph

21

79

a

Reaction conditions: aldehyde (0.250 mmol), amine (0.300 mmol), alkyne (0.325 mmol), catalyst (0.07 g, Au/CUP-1(PM): 6.42 mol%, Au/CUP-1(OP):

.14 mol%). The reaction time was not optimized. The data in the parentheses are ee values determined by HPLC with a Chiralcel OD column,

b

c

0

using hexane–ethanol (95/5) as a mobile phase.

fresh Au/CUP-1(OP) exhibits an induction period for ca. 20 h.

ꢀ

The maximum conversion (79%) is found at 150 C within 21 h.

The conversions are 75%, 82%, and 72% at the reaction time of

5, 13, and 13 h, respectively for the three successive runs.

Clearly, no signicant deactivation is found on Au/CUP-1(OP)

catalyst.

4. Discussion

4.1. Prominent features of CUP-1 and IRMOF-3

Novel chiral MOFs could be synthesized by using a chiral ligand

during the hydrothermal process or switching a preassembled

3,5,25

achiral framework by PM with chiral catalytic units.

In this

work we have successfully prepared a homochiral MOF denoted

CUP-1 by using a mixture of chiral L-lactic acid and achiral

H

2

atpt ligands with conventional hydrothermal synthesis. The

structure of CUP-1 is similar to that of 1$DMF which was

obtained by hydrothermal reaction of a mixture of Zn(NO

L-lactic acid, and 1,4-benzenedicarboxylic acid (H bdc) in a

3 2

) ,

2

ꢀ

5

mole ratio of 2 : 1 : 1 at 110 C for 2 days. The prominent

advantage of CUP-1 over 1$DMF is that the 2-amino group of the

H atpt acid does not participate in coordination to the penta-

2

ꢀ

nuclear Zn nodes that link the structure together, and is

potentially available for undergoing a variety of organic trans-

Fig. 12 The reusability of Au/CUP-1(PM) at 120 C (A) and Au/CUP-

ꢀ

3

1

(OP) at 150 C (B) for the A coupling reaction.

7,26–29

formations as already demonstrated by IRMOF-3.

As mentioned earlier, the IRMOF-3 containing NH

2

–BDC as a

successive cycles with intermediate extensive washing with 1,4- building block was recently shown to undergo chemical modi-

dioxane, the conversions were 59%, 61%, and 57% at the cation with a diverse series of anhydrides, isocyanates and sali-

7,26–29

reaction time of 7, 9, and 10 h, respectively. Au/CUP-1(PM) cylaldehyde by PM strategy.

The PM strategy potentially

features a signicant deactivation by around 33% for the rst provides a simple, eﬃcient, and versatile route to synthesize

run, while further recycling leads to very slight deactivation. The numerous catalytically active chiral MOFs from a robust achiral

RSC Adv., 2014, 4, 13093–13107 | 13103

View Article Online

RSC Advances

Paper

MOF for a variety of asymmetrical transformations, however, as IRMOF-3–Pr(PM). Considering that the decrease of N–H

6

ꢁ1

commented by Yoon et al. in a recent review that no example by stretches at 3473 and 3356 cm associated with the amine of

introducing of organocatalytic units on the organic strut of the H atpt ligand for FTIR of IRMOF-3–Pr(PM) could be due to

2

preassembled framework with the PM strategy in asymmetrical the low-resolution spectrum or more water adsorbed, the solid

1

3

transformations has been reported yet. By virtue of free NH

2

C MAS NMR was employed to characterize the amide bond.

group in the frameworks of CUP-1 and IRMOF-3, we have The decrease of resonance at 149.8 ppm is informative revealing

explored L-proline functionalized IRMOF-3 and CUP-1 catalysts that post-functionalization of the amine-pending groups of

1

3

by PM and OP strategies for asymmetrical catalyzing aldol reac- IRMOF-3. The new C NMR band at 181.3 ppm attributed to the

tion of aldehyde with acetone. Considering creating metal ions/ resonance signals of C]O of amide is in strong support of

1

3

nanoparticles in MOFs representing another important class of formation of amide (Fig. 9). It should be pointed out that the

C

MOF catalyst, we used the OP and PM strategies to introduce spectral signals of our IRMOF-3 agree well with the previous

7,40

catalytic active sites of gold nanoparticles in the CUP-1.

works,

while the resonance signals of C]O of amide in

IRMOF-3–Pr(PM) changed down-eld (shied to le) compared

48,49

13

with that earlier reported.

Oh et al. have assigned C NMR

4

.2. Physicochemical properties of proline and gold

band at 176.0 ppm to the amide bond of poly(2-cyano-1,4-phe-

functionalized CUP-1 and IRMOF-3 catalysts

48

nyleneterephthalamide). Serrano et al. reported the signal of

49

The L-proline functionalized IRMOF-3 samples by OP method C]O of poly(ester amide)s was centered at ca. 168.0 ppm. The

retain the crystalline integrity from the XRD analysis, while the diﬀerence should result from the C]O of amide in diﬀerent

IRMOF-3–Pr(PM) sample by PM method features some struc- molecular structures.

ture change of crystal (Fig. 2A). The diﬀerences in peak ratios at

2

The thermodynamically stable amide bond is, in principle,

ꢀ

q ¼ 6.8, 9.6 between IRMOF-3–Pr(OP) and IRMOF-3 would formed when a carboxylic acid reacts with an amine with the

mean that some unreacted linker/solvent was still present in the release of water. The energy threshold of the ammonium

pores of IRMOF-3–Pr(OP), leading to the block, deviation or carboxylate salt formation must, however, be overcome, and the

shrinkage of the pore in crystalline structure. We noted that activating reagents such as carbodiimides imidazolium and

IRMOF-3 modied with anhydrides by PM method also aﬀected phosphonium salts are employed. Direct amidation of carbox-

the intensity ratio for the typical two peaks (see Fig. 4 in ref. 27 ylic acids and amines occurs spontaneously under solvothermal

ꢀ

50

and Fig. 3 in ref. 29). This assumption could be supported by the conditions at high temperatures (>160 C). Therefore it seems

sharp decrease of the BET and Langmuir surface area for diﬃcult for the reaction between proline and the amine-

0

IRMOF-3–Pr(OP) and IRMOF-3–Pr (OP) samples (Table 1).

pending group of IRMOF-3. The possibility of the amide

It is well known that IRMOF-3 is microporous material, formation in the IRMOF-3–Pr(PM) should be considered. Costa

however, a well-dened type IV with a hysteresis, which is a et al. have reported that the reaction of carboxylic acids (e.g.,

prominent feature for mesoporous materials, is found on acetic acid) with the amine-pending groups of MOF-LIC-1

ꢀ

IRMOF-3, as well as CUP-1 (Fig. 5A). The mesoporosity should without any activating reagents at 120 C for 1 h led to forma-

51

be attributed to the secondary particle piled pore, which comes tion of amide. It was also reported that metallic Lewis acids,

from the aggregation of nanocrystals. This has been previously including heterogeneous Lewis acidic materials, and early

reported for materials synthesized in DMF under microwave transition metal complexes, like titanium(IV) species, have been

44

irradiation, the so-called metal–organic gels. The aggregation employed as mediators or catalysts for the amidation reac-

51,52

of nanocrystals was observed on IRMOF-3, CUP-1, and their tion.

We presume that transition metal-containing MOFs

modied samples by optical microscope photograph (Fig. 1A). (e.g. MOF-LIC-1 and IRMOF-3) may act as the catalysts for the

The IR results are commonly employed to distinguish the amidation reaction. IRMOF-3 and aminofunctionalized MIL-53

coordination modes of the carboxylate groups. A correlation of are reported the stable solid basic catalysts in the Knoevenagel

the carboxylate coordination mode to metal ions is usually condensation of ethyl cyanoacetate and ethyl acetoacetate with

10

made by examining the diﬀerence Dn(COO) ¼ nas(COO) ꢁ benzaldehyde. It is possible that a small amount of proline

4

5

n

s

(COO) of the compound. Clearly, the asymmetric (nas(COO)) functionalized with IRMOF-3 by the PM method.

and symmetric (n (COO)) vibrations of carboxylate groups on all

A surprising discovery made by Kim and coworkers has

samples appeared at 1574 and 1382 cm , respectively (Fig. 7 recently disclosed that ligand exchange can even occur with the

s

ꢁ

1

ꢁ

53

and 8). The value of Dn(COO) is 192 cm which is less than 200 inert Zr(IV)-based UiO-66 MOFs at room temperature. The

ꢁ

1

cm , indicating the bis-chelation of the carboxylic groups to ligands including NH

the metal ion. These results are in accordance with the single- (Br-BDC), 2-azido-1,4-benzenedicarboxylate (N

crystal X-ray analysis of IRMOF-3 and CUP-1. The absence of IR hydroxy-1,4-benzenedicarboxylate (OH-BDC) and 2,5-dihydroxy-

which is ascribed to a stretching of 1,4-benzenedicarboxylate (2,5-(OH) -BDC) can occur between

2

protonated carboxylic group, can be further in support that all UiO-66 MOFs as monitored by aerosol time-of-ight mass

2

-BDC, 2-bromo-1,4-benzenedicarboxylate

3

-BDC), 2-

ꢁ

1

spectra at 1730 cm

46

the carboxylate groups of the H

deprotonated on all samples.

2

atpt ligand are completely spectrometry (ATOFMS). The detail of linker exchange could

only be uncovered by a single-particle analysis method, i.e.,

The new stretches of amide I (1695–1610 cm ) and amide II ATOFMS. We are not sure if there is linker exchange during the

ꢁ

1

ꢁ

1

47

(1552–1520 cm

)

could be overlapped by the stretches of post-synthetic modication of IRMOF-3 with proline, due to no

ꢁ

1

ꢁ1

aromatic (1625–1575 cm , 1525–1475 cm ) for the FTIR of availability of the ATOFMS at present.

13104 | RSC Adv., 2014, 4, 13093–13107

View Article Online

Paper

RSC Advances

31

Combined the synthetic strategies with the characterization asymmetric aldol reaction. They obtained 68% yield and 76%

results, we suggest that IRMOF-3, CUP-1, and their modied ee in the reaction of acetone with 4-nitrobenzaldehyde, and 62%

samples could be well understood on the basis of models as yield and 60% ee by using 30–40 mol% proline in the case of

depicted in Scheme 1. The free NH group of the H atpt ligand benzaldehyde (entries 2 and 3, Table 2). The much higher yield

2

in both CUP-1 and IRMOF-3 provides the possibility for modi- and ee than ours (20% yield and 12% ee, entry 1, Table 2) should



cation with catalytical active sites. By functionalizing CUP-1 be due to the larger amount of L-proline (30–40 mol%), acetone

ꢁ

1

and IRMOF-3 with auxiliary chiral L-proline with OP method, (acetone–aldehyde, mol mol

diﬀerent scenarios can be devised based on the results of N

adsorption desorption, XRD, IR, and NMR characterizations. acetone–aldehyde ¼ 10, DMSO–aldehyde ¼ 21). The higher

Our powder XRD measurements show that the crystalline amount of proline and acetone can certainly improve the

structure of IRMOF-3–Pr(OP) is the same with IRMOF-3 conversion of aldehyde and the yield. The higher amounts of

¼ 27), and DMSO solvent

2

(DMSO–aldehyde ¼ 113) compared with ours (20 mol%,

(Fig. 2A). The NH₂group also keeps intact on the sample acetone and DMSO also signicantly suppressed the side prod-

demonstrated by IR analysis (Fig. 7). These results show clearly ucts. It should be pointed out that the signicant side product of

that the chiral L-proline is solely encapsulated in the surface a,b-unsaturated carbonyl compound was found under the

and/or pore of IRMOF-3–Pr(OP) (Scheme 1e). On the other present reaction conditions. It is well known that the a,b-

hand, the crystalline structure was partly broken and the hydroxy carbonyl compound is not stable and can be facially

stretching vibrations of N–H of CUP-1–Pr(OP) were sharply condensed. The only signicant side product (unsaturated

31

weakened compared with CUP-1 (Fig. 2B, and 8). These results ketone) was earlier observed by List et al. As demonstrated by

25,31

mean that NH group has reacted with L-proline into amide as the earlier works,

L-proline and its derivatives are essentially

shown in Scheme 1f. Notably, by postsynthetic modication of the active sites for the asymmetric aldol reaction. Due to the low

IRMOF-3 with auxiliary chiral L-proline, the NH group of amounts of active sites in IRMOF-3–Pr(OP) (3.8 mol%) and

2

IRMOF-3–Pr(PM) has also transformed with L-proline into IRMOF-3–Pr(PM) (9.2 mol%) catalysts under the present condi-

amide as indicated by XRD, IR, and NMR analysis (Scheme 1c). tions, the yields are thus generally low. Notably the TON (4–17)

For Au/CUP-1(PM) prepared by PM method, the catalyst calculated on the basis of L-proline on IRMOF-3–Pr(OP) and

3

+

contains both metallic gold nanoparticles and cationic Au

IRMOF-3–Pr(PM) are signicantly higher than that of the

homogeneous L-proline (2–3). Furthermore, the catalyst recovery

3

+

species as indicated by H -TPR analysis. The cationic Au

2

species could be stabilized by O, N and Cl atoms (Scheme 1d). In and process work-up for the homogeneous L-proline are much

the case of Au/CUP-1(OP) prepared by OP method, only metallic diﬃcult and the ee values in some cases are low. It is not then

gold nanoparticles were veried by the H

2

-TPR (Scheme 1g).

surprising that research eﬀorts are being made today to bridge

the gap between homogeneous and heterogeneous catalysis.

The low yields of b-hydroxy carbonyl compounds can be

greatly enhanced by optimizing the reaction conditions. As

4.3. Proline functionalized MOFs for the aldol reaction

Aldol reaction is a useful method for preparing b-hydroxy shown in Fig. 11, by using thrice amount of IRMOF-3–Pr(OP)

carbonyl compounds and has attracted a great deal of attention and suppressing the side-product with increasing the amounts

31,33,41,42

from synthetic organic chemists.

The catalytic asym- of acetone and DMSO, and shortening the reaction time, the

metric aldol reaction as a fundamental C–C bond forming reac- yield of 1 is increased signicantly from 23% to 78%. And

31

25

tion in chemistry and biology is a hot topic. We observed that the TON number is 8. Banerjee and coworkers introduced

aryl aldehydes possessing electron withdrawing groups feature a L-proline derivatives into the metal nodes of MIL-101 with PM

much higher ee than benzaldehyde (entries 9–11, Table 2). This method which contained very high concentration of active

was in accordance with the earlier report by using homogenous groups. The high yield (up to 91%) of b-hydroxy carbonyl

31

L-proline for the aldol reaction. At room temperature, both compound was reported, however, the TON calculated on the

18

IRMOF-3–Pr(OP) and IRMOF-3–Pr(PM) show an excellent ee basis of the active L-proline derivatives was only ca. 5. Lun et al.

value ($93%) (entries 7 and 14). IRMOF-3–Pr(OP) catalyst incorporated proline protected by Boc groups into MOFs by

ꢀ

exhibits a much higher ee than IRMOF-3–Pr(PM) at 40 C, presynthesis. And then the Boc groups were unveiled by a

however, both catalysts show much higher ee than the homo- simple postsynthetic heating step. The resulted IRMOF-Pro

geneous L-proline under the present reaction conditions (entries was evaluated for asymmetrical aldol reaction of 4-nitro-

1, 8 and 15). The better ee in the heterogeneous L-proline func- benzaldehyde with acetone. Although the complete consump-

tionalized IRMOF-3 catalysts than the homogeneous counterpart tion of 4-nitrobenzaldehyde was deduced by TLC within 24 h,

may originate from the restricted movement of the substrates in the ee of aldol product was determined to be 29% by chiral

the well conned microporous system in combination with HPLC analysis. Wu et al. explored the aldol reaction between

5,25

multiple chiral inductions. And the well dened framework of aldehydes and cyclohexanone on pyrrolidine based ligands

crystalline structure of IRMOF-3–Pr(OP) than that of IRMOF-3– (BCIP) incorporated MOFs. Moderate ee values (ca. 60%) were

54

Pr(PM) could result a higher ee for the reaction.

observed.

Considering in the synthesis of IRMOF-3–Pr(PM) catalyst,

Despite the good to excellent enantioselectivity on L-proline

functionalized IRMOF-3 catalysts in most cases, the yield of there was no wash step for removing un-reacted L-proline. The

b-hydroxy carbonyl compounds was below 30% (Table 2). List leach of un-reacted and un-bounded L-proline should be

et al. rst discovered that proline can eﬃciently catalyze responsible for the deactivation of the rst recycled IRMOF-3–

RSC Adv., 2014, 4, 13093–13107 | 13105

View Article Online

RSC Advances

Paper

Pr(PM) and IRMOF-3–Pr(OP) catalysts during the aldol reaction. that there is a slight leaching of gold (ca. 10%) over Au/CUP-

The leach of proline was however sharply decreased evidenced 1(PM) aer each recycle, however, much lower amount (<5%) of

by GC analysis during the further recycling.

gold leaching is found on Au/CUP-1(OP), which is in accordance

with our earlier nding that the catalyst prepared with OP

strategy has much higher stability than that prepared with PM

3

4.4. Catalytic performance of MOFs catalysts for the A

30

strategy.

coupling reaction

The marriage between catalytically active metal ions/clusters

and MOFs could bridge the gap between homogeneous and

5

. Conclusion

4,7–9,55

56

heterogeneous catalysts.

Wei and Li have initially repor- In summary, a novel homochiral Zn-containing MOF referred to

ted that the A coupling reaction catalyzed by homogeneous as CUP-1 was successfully prepared based on the reaction of the

gold catalysts (e.g. AuBr

). The silver, copper, and mercury salts mixed linkers of H atpt and L-lactic acids in a OP synthesis.

were also found to be able to catalyze the reaction. The homo- CUP-1 crystallizes in the orthorhombic system, chiral space

geneous gold salts were reported to endow the highest catalytic group P2(1)2(1)2(1) with the formula of Zn (atpt)(l-lac)(HCOO).

group in the frameworks of CUP-1 and

3

2

57–59

activity.

However, the limitations and the deactivation for By virtue of free NH

2

homogenous gold salts make it impossible for sustainable IRMOF-3, the catalytically active chiral L-proline or gold was

catalytic process. Our Au/CUP-1(PM) catalyst showed good to chosen to modify the CUP-1 and/or IRMOF-3 catalysts by OP

3

excellent yields of propargylamine for the A coupling reaction and PM strategies. The L-proline functionalized IRMOF-3 cata-

ꢀ

at 120 C. And the catalyst can be applied to various aldehydes lysts showed fair to excellent enantioselectivity (up to 98%) in

(

including aromatic and aliphatic aldehydes), as well as amines asymmetrical aldol reactions with a higher TON and catalytic

piperidine, pyrrolidine and morpholine). The good yield can be stabilities than the homogeneous counterpart of L-proline. By

also achieved with the highest TON (556) on Au/CUP-1(OP) increasing the amounts of catalyst, acetone and DMSO, and

ꢀ

catalyst at 150 C (Table 3). Since the size of gold nanoparticles shorten the reaction time, the yield of desired b-hydroxy

on Au/CUP-1(PM) and Au/CUP-1(OP) catalysts is clearly much carbonyl compound can be signicantly enhanced while the by-

larger than that of the average pore size of CUP-1, the gold product a,b-unsaturated carbonyl compound can be greatly

nanoparticles should be deposited on the surface of CUP-1. suppressed. The gold functionalized CUP-1 by PM method

3

0

3+

Therefore the A coupling reactions occur on the surface of contain a mixture of Au and Au , while the catalyst prepared

CUP-1. Compared with the other heterogeneous catalysts for the with OP method contained ultrane metallic gold nanoparticles

3

A coupling reaction, our gold functionalized CUP-1 catalysts with averaged size of ca. 2.1 nm. The gold functionalized CUP-1

showed higher TON numbers than that of unsupported gold catalysts showed high activity, selectivity (100% for propargyl-

6

0

3

nanoparticles (TON: ca. 9), and comparable activity with the amines), and reusability (3 recycles) for the A coupling reac-

30

earlier reported Au/IRMOF-3 catalysts. Specically, the TON tion, despite the signicant aggregation of the gold

numbers on Au/CUP-1(OP) catalyst at 150 C is much higher nanoparticles during the recycle runs. This work provides

than that of gold on layered double hydroxide (ca. 30) and gold general methods to functionalize MOFs with the active ligand

supported on commercial nano active magnesium oxide (ca. and metal nanoparticles for fabrication of highly eﬃcient MOF-

ꢀ

61

62

4

07). In particular, the gold functionalized CUP-1 catalysts based heterogeneous catalysts.

show a good stability and can be reused at least 4 times. The

excellent performances for catalyst reuse shed the advantage of

Acknowledgements

using MOFs as stabilizers.

3

The high catalytic performance for the A coupling reaction We thank the National Natural Science Foundation of China

should be due to CUP-1 immobilized gold nanoparticles. The (no. 20903119, 21173269, and 91127040) and National Key

2

relatively high surface area and the free NH groups of the Technology R & D Program (grant: 2011BAK15B05) of China.

CUP-1 can stabilize the gold nanoparticles. The alkyne was

activated by the CUP-1 immobilized gold nanoparticles and

transformed into the alkenyl–Au intermediate, which then

reacted with the iminium ion generated in situ from the alde-

hydes and secondary amines to give the corresponding prop-

References

1 A. Corma, Catal. Rev.: Sci. Eng., 2004, 46, 369.

2 J. R. Long and O. M. Yaghi, Chem. Soc. Rev., 2009, 38, 1213.

3 Z. Wang, G. Chen and K. L. Ding, Chem. Rev., 2009, 109, 322.

4 L. Q. Ma, C. Abney and W. B. Lin, Chem. Soc. Rev., 2009, 38,

1248.

30,43,57

argylamines.

species showed higher catalytic activity than that of metallic

As it was well established that cationic gold

3

43,56

gold counterpart for the A coupling reaction,

we presume

that the deactivation of Au/CUP-1(PM) in the rst recycle could

5 D. N. Dybtsev, A. L. Nuzhdin, H. Chun, K. P. Bryliakov,

E. P. Talsi, V. P. Fedin and K. Kim, Angew. Chem., Int. Ed.,

2006, 45, 916.

6 M. Yoon, R. Srirambalaji and K. Kim, Chem. Rev., 2012, 112,

1196.

3

+

be due to the reduction of Au into metallic atoms as demon-

strated by the TPR analysis (Fig. 10). Moreover, we didn't wash

the catalyst in the synthesis of Au/CUP-1(PM). It is possible that

un-reacted gold precursor remained in the Au/CUP-1(PM). The

leach of gold precursor could be another reason for the deac-

7 X. Zhang, F. X. L. I. Xamena and A. Corma, J. Catal., 2009,

265, 155.

3

tivation in the A coupling reaction. It should be pointed out

13106 | RSC Adv., 2014, 4, 13093–13107

View Article Online

Paper

RSC Advances

8

9

I. Luz, F. X. L. I. Xamena and A. Corma, J. Catal., 2010, 276, 134. 35 J. H. He, Y. T. Zhang, Q. H. Pan, J. H. Yu, H. Ding and

I. Luz, F. X. L. I. Xamena and A. Corma, J. Catal., 2012, 285,

85.

R. R. Xu, Microporous Mesoporous Mater., 2006, 90,

145.

2

10 J. Gascon, U. Aktay, M. D. Hernandez-Alonso, G. P. M. Klink 36 J. L. C. Rowsell and O. M. Yaghi, J. Am. Chem. Soc., 2006, 128,

and F. Kapteijn, J. Catal., 2009, 261, 75. 1304.

11 J. Juan-Alcaniz, E. V. Ramos-Fernandez, U. Lafont, J. Gascon 37 S. J. Wang, X. X. He, L. X. Song and Z. Y. Wang, Synlett, 2009,

and F. Kapteijn, J. Catal., 2010, 269, 229. 447.

12 P. Serra-Crespo, E. V. Ramos-Fernandez, J. Gascon and 38 S. J. Garibay, Z. Q. Wang and S. M. Cohen, Inorg. Chem.,

F. Kapteijn, Chem. Mater., 2011, 23, 2565. 2010, 49, 8086.

13 E. V. Ramos-Fernandez, C. Pieters, B. Linden, J. Juan- 39 J. H. He, Y. T. Zhang, J. H. Yu, Q. H. Pan and R. R. Xu, Mater.

Alca n˜ iz, P. Serra-Crespo, M. W. G. M. Verhoeven,

Res. Bull., 2006, 41, 925.

H. Niemantsverdriet, J. Gascon and F. Kapteijn, J. Catal., 40 W. Morris, R. E. Taylor, C. Dybowski, O. M. Yaghi and

2

012, 289, 42.

M. A. Garcia-Garibay, J. Mol. Struct., 2011, 1004, 94.

41 S. Antonijevic and N. Halpern-Manners, Solid State Nucl.

Magn. Reson., 2008, 33, 82.

42 X. Zhang, Y. C. Guo, Z. Z. Zhang, J. S. Gao and C. M. Xu,

J. Catal., 2012, 292, 213.

43 X. Zhang and A. Corma, Angew. Chem., Int. Ed., 2008, 47,

4358.

44 S. K. Nune, P. K. Thallapally and B. P. McGrail, J. Mater.

Chem., 2010, 20, 7623.

1

4 S. Marx, W. Kleist and A. Baiker, J. Catal., 2011, 281, 76.

5 D. Jiang, T. Mallat, D. M. Meier, A. Urakawa and A. Baiker,

J. Catal., 2010, 270, 26.

6 A. M. Shultz, O. K. Farha, D. Adhikari, A. A. Sarjeant,

J. T. Hupp and S. T. Nguyen, Inorg. Chem., 2011, 50, 3174.

7 J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon and

K. Kim, Nature, 2000, 404, 982.

8 D. J. Lun, G. I. N. Waterhouse and S. G. Telfer, J. Am. Chem.

Soc., 2011, 133, 5806.

9 R. K. Deshpande, J. L. Minnaar and S. G. Telfer, Angew.

Chem., Int. Ed., 2010, 49, 4598.

1

2

45 K. Nakamoto, Infrared and Raman Spectra of Inorganic and

Coordination Compounds, John Wiley and Sons, New York,

1997.

0 M. J. Ingleson, J. Bacsa and M. J. Rosseinsky, Chem. 46 Z. L. Xie, M. L. Feng, J. R. Li and X. Y. Huang, Inorg. Chem.

Commun., 2007, 3036. Commun., 2008, 1143.

1 C. D. Wu, A. Hu, L. Zhang and W. Lin, J. Am. Chem. Soc., 47 T. Miyazawa and E. R. Blout, J. Am. Chem. Soc., 1961, 83, 712.

2

005, 127, 8940.

48 T.-J. Oh, J.-H. Nam and Y. M. Jung, Vib. Spectrosc., 2009,

51, 15.

2

2 C. Wu and W. Lin, Angew. Chem., Int. Ed., 2007, 46, 1075.

3 R. Vaidhyanathan, D. Bradshaw, J. N. Rebilly, J. P. Barrio, 49 P. J. M. Serrano, J. P. M. van Duynhoven, R. J. Gaymans and

J. A. Gould, N. G. Berry and M. J. Rosseinsky, Angew.

Chem., Int. Ed., 2006, 45, 6495.

4 M. J. Ingleson, J. P. Barrio, J. Bacsa, C. Dickinson, H. Park

and M. J. Rosseinsky, Chem. Commun., 2008, 1287.

5 M. Banerjee, S. Das, M. Yoon, H. J. Choi, M. H. Hyun,

R. Hulst, Macromolecules, 2002, 35, 8013.

50 H. Lundberg, F. Tinnis and H. Adolfsson, Chem.–Eur. J.,

2012, 18, 3822.

51 J. S. Costa, P. Gamez, C. A. Black, O. Roubeau, S. J. Teat and

J. Reedijk, Eur. J. Inorg. Chem., 2008, 1551.

2

S. M. Park, G. Seo and K. Kim, J. Am. Chem. Soc., 2009, 52 M. Hosseini-Sarvari, E. Sodagar and M. M. Doroodmand,

131, 7524.

J. Org. Chem., 2011, 76, 2853.

2

6 S. M. Cohen, Chem. Rev., 2012, 112, 970.

7 K. K. Tanabe, Z. Wang and S. M. Cohen, J. Am. Chem. Soc.,

53 M. Kim, J. F. Cahill, Y. Su, K. A. Prather and S. M. Cohen,

Chem. Sci., 2012, 3, 126.

2

008, 130, 8508.

54 P. Wu, C. He, Z. Xie and C. Duan, J. Am. Chem. Soc., 2010,

132, 14321.

2

3

8 M. J. Ingleson, J. P. Barrio, J. B. Guilbaud, Y. Z. Khimyak and

M. J. Rosseinsky, Chem. Commun., 2008, 2680.

9 Z. Wang and S. M. Cohen, J. Am. Chem. Soc., 2007, 129,

55 O. K. Farha, A. M. Shultz, A. A. Sarjeant, S. T. Nguyen and

J. T. Hupp, J. Am. Chem. Soc., 2011, 133, 5652.

56 C. Wei and C. J. Li, J. Am. Chem. Soc., 2003, 125, 9584.

12368.

0 L. L. Liu, X. Zhang, J. S. Gao and C. M. Xu, Green Chem., 2012, 57 C. Wei, Z. Li and C. J. Li, Org. Lett., 2003, 5, 4473.

1

4, 1710.

1 B. List, R. A. Lerner and C. F. Barbas III, J. Am. Chem. Soc.,

000, 122, 2395.

58 L. Shi, Y. Q. Tu, M. Wang, F. M. Zhang and C. A. Fan, Org.

Lett., 2004, 6, 1001.

59 L. P. Hua and W. Lei, Chin. J. Chem., 2005, 23, 1076.

2

2 N. Wolfgang, T. Fujie and C. F. Barbas III, Acc. Chem. Res., 60 M. Kidwai, V. Bansal, A. Kumar and S. Mozumdar, Green

004, 37, 580. Chem., 2007, 9, 742.

3 M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, 61 M. L. Kantam, B. V. Prakash, C. R. V. Reddy and B. Sreedhar,

M. O'Keeﬀe and O. M. Yaghi, Science, 2002, 295, 469. Synlett, 2005, 2329.

4 J. G. Nguyen and S. M. Cohen, J. Am. Chem. Soc., 2010, 132, 62 K. Layek, R. Chakravarti, M. L. Kantam, H. Maheswaran and

560. A. Vinu, Green Chem., 2011, 13, 2878.

2

4

RSC Adv., 2014, 4, 13093–13107 | 13107

Article Doi

Catalysis by metal-organic frameworks: Proline and gold functionalized MOFs for the aldol and three-component coupling reactions

DOI: 10.1039/c4ra01269k

Source and publish data:

Authors:

Article abstract of DOI:10.1039/c4ra01269k

Full text of DOI:10.1039/c4ra01269k

Products guided by the article

R&D Labs maybe for 10519-33-2

Relevant to this article

Hot Product