Water-medium Barbier Reactions over the Mesoporous Pd(II) Organometal Catalyst with Crystal-like...

http://www.paper.edu.cn

- 1 -

中国科技论文在线

Water-medium Barbier Reactions over the Mesoporous Pd(II) Organometal Catalyst with Crystal-like Pore Walls

and High Stability He Wenhan, Zhang Fang, Li Hexing, Huang Jianlin

(Department of Chemistry, Shanghai Normal University, ShangHai 200234)

Foundations: 教育部（博士点基金）（No.20070270001) Brief author introduction:何文翰（1984-），男，环境催化 Correspondance author: 李和兴（1963-），男，教授，环境催化. E-mail: [email protected]

Abstract: A new approach was developed to prepare an immobilized Pd(II) organometallic catalyst with mesoporous structure by surfactant-directed co-condensation between biphenyl-bridged organosilane and Pd(II) organometallicsilane. Both the Pd(II) organometallic complex and the biphenyl groups were embedded in the pore wall, which could diminish the blockage of mesoporous channels. As a result, such catalyst exhibited high activity and selectivity in water-medium Barbier reactions owing to the high surface area, large pore size and strong surface hydrophobicity resulting from biphenyl functionaliztion, which facilitated the diffusion and adsorption of organic reactant molecules on the active sites. Meanwhile, the as-prepared catalyst also displayed long durability owing to the crystal-like mesoporous wall resulting from the π-π stacking of biphenyl groups, which could protect the mesoporous structure from collapsing in aqueous Barbier reactions. Keywords:Environmentalcatalysis;biphenylene-bridgedPMOmaterials;crystal-likeporewalls;mesoporous Pd(II) organometallic catalyst;water-medium Barbier reactions

0 Introduction Environmental concerns associated with chemical processes have encouraged the

development more environmentally friendly (greener) organic reactions. In recent years, reactions that take place in the environmentally clean, safe and cheap solvent water have received considerable interest[1]. However, formidable challenges remain to be addressed as results of the solubility and diffusion limits of organic substances in aqueous solution.

Homogenous catalytic processes, which in general occur in high yield and under mild reaction conditions, are dominant strategies in chemical catalysis. Nevertheless, the industrial use of homogeneous catalysts is relatively limited because of difficulties in separation and reuse that eventually adds cost and cause environmental pollution from heavy metallic ions[2]. A great number of attempts have been made to prepare immobilized heterogeneous catalysts which show in some cases superiority in separation and repetitive uses[3]. However, such heterogeneous catalysts cannot match in activity and selectivity with their corresponding homogeneous counterparts due to the low dispersion degree of active sites. Mesoporous materials with large surface area, ordered pore channels, and highly dispersed active sites afford powerful supports for anchoring homogeneous catalysts. Previously, we reported the preparation of metal and organometallic catalysts anchored on the SBA-15 and FDU-12 supports and their applications in water-medium organic reactions[4]. We found that functionalization of silica supports with organic groups could greatly promote the adsorption of organic reactant molecules on the catalysts owing to the enhanced surface hydrophobicity, leading to high activity and selectivity. However, the traditional immobilization of homogeneous catalysts by coordinating the metallic ions with organic ligands incorporated into the silica support usually blocks the pore entrance and pore channels. Furthermore, functionalization of silica support with organic groups inevitably blocks the pore channels and causes damage to pore structure. Accordingly, the catalytic efficiency


- 2 -


decreases dramatically due to the diffusion limit. Recently, we incorporated a Pd(II) organometallic catalyst into the periodic mesoporous organosilicas (PMO) [5], which effectively diminishes the blockage of pore channels since the organic groups are uniformly embedded into the silica wall. More recently, we have developed a new approach to prepare immobilized Ru(II) catalyst with mesoporous structure via co-condensation of Ru(II) organometallicsilane with TEOS in the presence of a surfactant self-assembly[6]. Although these materials possessed high activity and selectivity, owing to poor hydrothermal stability these catalysts usually exhibited short durability in water-medium organic reactions.

It has been demonstrated that the PMO materials with crystal-like walls exhibit stronger hydrothermal stability than those with amorphous silica walls[7]. Up to now, nearly all PMO materials with crystalline mesoporous walls are prepared under basic condition[7, 8]. This is unfavorable for preparing immobilized organometallic catalysts via co-condensation due to the decomposition of organometallicsilane under basic conditions. In this paper, we wish to disclose a new Pd(II) organometallic catalyst immobilized in a biphenylene-bridged PMO support prepared by co-condensation under acidic conditions. This catalyst exhibited mesoporous structure with crystal-like walls, having both the high activity and the strong durability during water-medium Barbier reactions.

1 Experimental

1.1 Catalyst preparation Firstly, a Pd(II) organometallicsilane was synthesized in dry and oxygen-free argon

atmosphere using Schlenk techniques. In a typical run of synthesis, 2.7 g PPh2CH2CH2Si(OEt)3 was added slowly into 25 ml anhydrous toluene containing 1.0 g PdCl2(COD). After being stirred for 24 h at 25 oC, the toluene was evaporated to about 5.0 ml. A yellow solid product was then obtained by adding hexane. According to ICP analysis and 1H NMR (CD2Cl2) analysis: 7.2-7.5, 7.6-7.8 (3 m, 20 H, ArH), 3.7 (m, 12 H, OCH2), 2.5 (m, 4H, CH2P), 1.1 (m, 18 H, CH3), 0.79 (m, 4 H, SiCH2) the composition of the Pd(II) organometallicsilane was determined as PdCl2[PPh2(CH2)2Si(EtO)3]2.

Then, the immobilized Pd(II) organometallic catalyst was synthesized through surfactant-directed co-condensation between the 4, 4’-bis(triethoxysilyl)-biphenyl (BTESBP) and the as-prepared PdCl2[PPh2(CH2)2Si(EtO)3]2 under acidic solution. Briefly, certain mount of BTESBP was added dropwise into 20 ml aqueous solution containing 0.50 g P123 (EO20PO70EO20) and 0.20 M HCl. After pre-hydrolysis for 2.5 h at 40oC, 4.0 ml THF solution containing required amount of PdCl2[PPh2(CH2)2Si(EtO)3]2 was added into the mixture. The initial molar ratio in this system is fixed at Si : P123: HCl : H2O = 1 : 0.017 : 0.80 : 218, where Si refers to the total silica source including both the BTESBP and the PdCl2[PPh2(CH2)2Si(EtO)3]2. The mixture was stirred for 24 h at 40oC and transferred to a sealed autoclave. After hydrothermal treatment at 100oC for another 24 h, the yellow precipitate was filtrated and washed thoroughly with water, following by vacuum drying at 80oC overnight. The surfactant, together with both the Pd(II) species and organic residues physisorbed on the solid were then removed by refluxing in 0.5mol/L HCl/ethanol at 80oC for 24 h. The as-prepared sample was denoted as Pd-PPh2-PMO(Ph-Ph)-X, where X refers to the different Pd loadings which could be adjusted by changing the amount of PdCl2[PPh2(CH2)2Si(EtO)3]2 in the mother mixture. As a reference, Pd-PPh2-SBA-15(Ph) was synthesized in the same way except for the replacement of BTESBP by the mixture of TEOS and phenyltrimethoxysilane (PTMS) which was co-condensed with palladium saline in the acid


- 3 -


condition, meanwhile with the same procedure in mind, the Pd-PPh2-PMO(Et) was synthesized by using bis(triethoxysilyl)ethane (BTESE) to replace the BTESBP as the precursor in the acid condition.

1.2 Characterization The Pd(II) loadings were determined by an inductively coupled plasma optical emission

spectrometer (ICP, Varian VISTA-MPX). Solid state nuclear magnetic resonnce (NMR) spectra were recorded on a Bruker AV-400 spectrometer at 79.5, 100.6 and 169.3 MHz, respectively. The X-ray powder diffraction (XRD) patterns were obtained on a Rigaku D/Max-RB diffractometer with CuKα radiation. Transmission electron microscopy (TEM) morphologies were observed on a JEOL JEM2010. N2 adsorption–desorption isotherms were measured at -196oC on a Quantachrome NOVA 4000e analyzer after being degassed at 100oC overnight. Based on adsorption-branches, the specific surface area (SBET), pore size distribution, pore volume (VP) and average pore diameter (DP) were calculated by using the multiple-point Brunauer–Emmett–Teller (BET) and the Barrett–Joyner–Halenda (BJH) models, respectively. The X-ray Photoelectron Spectra (XPS) were analyzed on the PHI 5000 VersaProbe. All the binding energy values were calibrated by using C1S = 284.8 eV as a reference.

1.3 Activity test The water-medium Barbier reaction (see Scheme 1) was carried out at 50oC in a 10 ml flask

containing 25 ul benzaldehyde, 150 ul allyl bromide, 0.45 g SnCl2 and 5.0 ml H2O, and a catalyst with 0.065mmol Pd(II). The organic substances were protected from evaporation by refluxing. After reaction under vigorous stirring for 12 h, the reaction mixture was extracted by toluene and dried by anhydro-magnesium sulfate. The liquid products were quantitatively analyzed on a gas chromatograph (GC, Agilent 1790) equipped with a FID and a JWDB-5 95% dimethyl 1-(5%)-diphenylpolysiloxane column at 373 K in N2 flow, from which both the conversion, selectivity and yield to target product were determined by using internal standards. The conversion was calculated based on benzaldehyde since allyl bromide was greatly excess. The reproducibility was checked by repeating each result at least three times and was found to be within acceptable limits (±5%).

In order to determine the catalyst durability, the target catalyst was allowed to settle down after each run of reactions and the clear supernatant liquid was decanted slowly. After being washed with water, acetone and ethyl ether for three times each, followed by vacuum drying at 80oC overnight, the catalyst was re-used with fresh charge of solvent and reactant for subsequent reaction under the same conditions. The content of Pd species both in the solution and on the solid support were determined by ICP analysis to show the leach of Pd(II) active sites during each run of reactions.

Sch. 1 The formula of Barbier reaction equation

2 Result and Discussion The Pd(II) loadings in different catalytic reactions were determined by ICP analysis and


- 4 -


listed in Table 1. The XPS spectra further confirmed the presence of Pd(II) in the heterogeneous catalytic reactions which coordinated with the PPh2-CH2-CH2-ligand. As shown Figure 1, all the Pd species in Pd-PPh2-PMO(Ph-Ph)-2 sample were present in the divalent oxidation state, which corresponds to the binding energies (BE) of 343.0 and 337.8 eV in Pd 3d5/2 and 3d3/2 levels[9], respectively. In comparison with the BE of the Pd(II) in Pd(PPh3)2Cl2, the BE of the Pd(II) in Pd-PPh2-PMO(Ph-Ph)-2 shifted negatively, showing a decrease of electron density on the Pd atom owing to stronger electron-donation ability of the PPh2-CH2-CH2-ligand to the Pd(II) than that of the PPh3-ligand. This could be easily understood by considering the conjugation system 　

between P and Ph, which could dilute the electron density on the P atom. Obviously, the P in the PPh3-ligand exhibited lower electron density than that in the PPh2-CH2-CH2-ligand due to the larger conjugation system, indicating the poor electron　 -donating ability to the Pd atom in the coordination bonds[9].

330 336 342 348

(b)

Pd3d

343.0 eV

343.3 eV

337.8 eV

338.0 eV

Inte

nsity

(a.u

.)

Binding Energy (eV)

(a)

Fig. 1 The XPS spectra of (a) Pd(PPh3)2Cl2 and (b) Pd-PPh2-PMO(Ph-Ph)-2 samples

Figure 2 shows the solid state NMR spectra of the Pd-PPh2-PMO(Ph-Ph)-2 sample. The 29Si

MAS spectrum displayed three resonance peaks up-field corresponding to T3 (δ = -80 ppm), T2 (δ = - 72 ppm) and T1 (δ = - 63 ppm), where Tm = RSi(OSi)m-(OH)3-m, m = 1 ~ 3. No Qn peaks are observed, where Qn = Si(OSi)n-(OH)4-n, n = 2 ~ 4, suggesting that all the Si species were covalently bonded with carbon atoms[8d]. The 13C CPMAS NMR spectrum revealed that the Pd-PPh2-PMO(Ph-Ph)-2 sample exhibited two peaks at 16 and 30 ppm due to the two C atoms in the -CH2-CH2- group bound with the PPh2 group. An additional triplet peak was observed around 130 ppm and could be assigned to the C atoms from the benzene ring[9]. The peak at 58 ppm was assigned to the C atoms in the C2H5O- ngroup connecting with Si due to incomplete hydrolysis[9]. Other peaks denoted by asterisks were attributed to rotational sidebands[10]. No significant resonance peaks in the range of 67~77 ppm were observed, implying the complete removal of P123 surfactant in the Pd-PPh2-PMO-Ph sample[11]. From the 31P CP MAS NMR spectrum, an intensive peak could be seen near 20 ppm which is characteristic of the P atom coordinating with Pd(II) [12]. The above results from 29Si MAS, 13C CPMAS NMR and 31P CP MAS NMR spectra confirmed the successful incorporation of PdCl2[PPh2(CH2)2Si(EtO)3]2 into the PMO(Ph-Ph) support. The 31P CP MAS NMR spectrum showed only the peaks from the rotational side bands and the peak near 20 ppm pointing out the P atom, indicating only one type of Pd-PPh2 complexes


- 5 -


present in the Pd-PPh2-PMO(Ph-Ph) catalyst[10]. Ideally the Pd atom and two PPh2 should be arrayed linearly, therefore it was most probable that the Pd-PPh2 complex was embedded into the pore walls of the PMO(Ph-Ph) support.

100 50 0 -50 -100 -150 -200

T3T 1

T 2

Chem ical Shift (ppm )

29Si CP M A S NM R

300 200 100 0 -100 -200

* *

P-Pd

Chemical Shift (ppm)

31P CP MAS NMR

3 0 0 2 5 0 2 0 0 1 5 0 1 0 0 5 0 0 - 5

S i - O - E t*

*

C2

C 1

CP h -

C h e m i c a l S h i f t ( p p m )

1 3 C C P M A S N M R

Fig. 2 The solid state NMR spectra of the Pd-PPh2-PMO(Ph-Ph)-2 sample

Figure 3 demonstrated that similar to both the Pd-PPh2-PMO(Et) and the

Pd-PPh2-SBA-15(Ph) with equivalent Pd loadings, the Pd-PPh2-PMO(Ph-Ph)-2 displayed type IV N2 adsorption-desorption isotherms with the H1 hysteresis loop characteristic of mesoporous structure[13]. The increase of the Pd loading caused deformation of the N2 adsorption-desorption isotherm. The low-angle XRD patterns in Figure 4 showed that the Pd-PPh2-PMO(Ph-Ph) samples with low Pd loading displayed a resolved peak around 2θ = 0.8 -1.0 o indicative of (100) diffraction[14], which further confirmed the presence of mesoporous structure. The weak peak intensity and the absence of additional peaks denoting the (111) and (200) diffraction patterns implies a poor degree of ordering of the mesoporous structure. No significant XRD peaks were observed in the Pd-PPh2-PMO(Ph-Ph)-3 with high Pd loading, suggesting that mesoporous structure is completely disordered.

0.0 0.2 0.4 0.6 0.8 1.0

Vol

ume A

dsor

bed

(cm

3 /g)

Relative Pressure (P/Po)

Pd-PPh2-PMO(Ph-Ph)-2

Pd-PPh2-SBA-15(Ph)

Pd-PPh2-PMO(Et)

Fig. 3 Nitrogen adsorption-desorption isotherms of different catalysts


- 6 -


1 2 3 4 5

Pd-PPh2-PMO(Ph-Ph)-3 Pd-PPh2-PMO(Ph-Ph)-2

Inte

nsity

Two-Theta (degree)


Fig. 4 Low-angle XRD patterns of different catalysts

This could be further confirmed by the TEM image. As revealed in Figure 5, only worm-like

mesoporous structure was observed in the Pd-PPh2-PMO(Ph-Ph)-2. The increase of Pd loading reduced the ordered array of mesoporous channels, which could be attributed to the disturbance of the surfactant-directed self-assembly during co-condensation between 4,4’-bis(triethoxysilyl)-biphenyl and PdCl2[PPh2(CH2)2Si(EtO)3]2. Table 1 further demonstrated that the increase of Pd loading caused rapid decrease in SBET and VP, due to the damage of ordering mesoporous structure.

Fig. 5 TME image of the Pd-PPh2-PMO(Ph-Ph)-2 sample

The wide angle XRD patterns (Figure 6) revealed that the Pd-PPh2-PMO(Et) displayed only a

broad peak at 2θ ranging from 10 to 30 o, suggesting that the mesoporous wall was present in a typical amorphous state. However, the Pd-PPh2-PMO(Ph-Ph)-2 displayed a diffraction peaks around 2θ = 7.3 and 15.0 o indicative of the crystal-like mesoporous wall resulting from the π-π stacking of biphenyl groups[8c]. According to Bragg equation, the d-spacing corresponding to the


- 7 -


peak at 2θ = 7.3o was determined as 11.5 Å, suggesting that the biphenyl groups embedded in the silica walls were arranged in a head-to-tail manner to form a lamellar structure in the molecular crystal[8c].

10 20 30 40 50

Pd-PPh2-PMO(Et)

200

100

Inte

nsity

(Arb

. Uni

ts)

2 Theta (degree)


Fig. 6 Wide-angle XRD patterns of different catalysts

Table 1 summarized the catalytic parameters obtained from various Pd(II)-based catalysts

and the effect of reaction temperature in the water-medium Barbier reaction. In each run of the catalytic reaction, the Pd(II) content in the system was fixed at 0.065 mmol by adjusting the amount of catalyst with different Pd loading. The GC-MS analysis demonstrated that, besides the target product (1-phenyl-3-buten-1-ol), the major side product was 1, 5-hexadiene formed through the self-coupling reaction of allylic bromide. From entries 1, 2 and 5 of Table 1, it is apparent the activity (i.e., the reaction conversion) of the Pd-PPh2-PMO(Ph-Ph) first increased and then decreased with additional Pd(II) loading, while the selectivity to 1-phenyl-3-buten-1-ol remained almost unchanged. At very low Pd(II) loading, the Pd(II) active sites located separately, leading to low activity since the Barbier reaction needs two neighboring active sites for adsorbing both the benzaldehyde and allyl bromide molecules. However, very high Pd loading was also harmful to activity owning to the severe damage of the mesoporous structure in the Pd-PPh2-PMO(Ph-Ph), corresponding to the abrupt decrease in both the SBET and the VP. Thus, the optimum catalyst was determined as Pd-PPh2-PMO(Ph-Ph)-2. Entries 2, 3 and 4 of Table 1 demonstrated that activity of Pd-PPh2-PMO(Ph-Ph)-2 increased abruptly with the variation in reaction temperature increasing from 30 to 50 ºC, while the selectivity remained almost constant. However further increase of temperature from 50 to 70 ºC caused an abrupt decrease in selectivity as a result of the increase of side reactions, leading to the low yield to 1-phenyl-3-buten-1-ol. The Pd-PPh2-SBA-15(Ph) (entry 7) displayed much lower activity and selectivity than either the Pd-PPh2-PMO(Ph-Ph)-2 (entry 2) or the Pd-PPh2-PMO(Et) (entry 6) with the similar Pd(II) loading, due to the different ways for functionalizing the silica support with organic groups. In Pd-PPh2-PMO(Ph-Ph) and Pd-PPh2-PMO(Et) samples, the organic groups were embedded in the silica walls. However, in Pd-PPh2-SBA-15(Ph), the organic groups were anchored on the pore surface, corresponding to abrupt decrease in SBET and VP (see Table 1), which was unfavorable for the diffusion and adsorption of reactant molecules on the active sites, leading to the lower activity. Meanwhile, the Pd-PPh2-PMO(Ph-Ph)-2 exhibited slightly higher activity and selectivity than the Pd-PPh2-PMO(Et) since the biphenyl fragments embedded in silica walls resulted in stronger surface hydrophobicity than the ethyl fragments.


- 8 -


Tab. 1 Structural parameters and catalytic performances of the as-prepared samples Samples Pd%

(mg/g)SBET

(m2/g)Dp

(nm)Vp

(cm3/g)T

(oC) Conv. (%)

Sel. (%)

Yield (%)

Pd-PPh2-PMO(Ph-Ph)-1 29.7 487 3.4 0.27 50 71.2 91.3 65.0 Pd-PPh2-PMO(Ph-Ph)-2 39.2 444 3.3 0.23 30 73.3 94.0 68.9 Pd-PPh2-PMO(Ph-Ph)-2 39.2 444 3.3 0.23 50 92.1 94.5 87.0 Pd-PPh2-PMO(Ph-Ph)-2 39.2 444 3.3 0.23 70 93.1 80.2 74.5 Pd-PPh2-PMO(Ph-Ph)-3 45.6 85 3.1 0.050 50 72.8 90.1 65.7

Pd-PPh2-PMO(Et) 39.8 523 4.2 0.53 50 88.0 93.0 82.0 Pd-PPh2-SBA-15(Ph) 40.3 158 3.3 0.16 50 76.8 81.4 62.5

Pd(PPh3)2Cl2 / / / / 50 94.9 95.9 91.1 Used Pd-PPh2-PMO(Ph-Ph)-2b 39.0 327 3.2 0.20 50 87.6 94.6 82.9

a Reaction conditions: 0.065 mmol Pd, 25 ul benzaldehyde, 150 ul allyl bromide, 0.45 g SnCl2 and 5.0 ml H2O, reaction time = 12 h; bThe Pd-PPh2-PMO(Ph-Ph)-2 catalyst after being used repetitively for 8 times.

The Pd-PPh2-PMO(Ph-Ph)-2 exhibited high activity and selectivity, which matched with the corresponding Pd(PPh3)2Cl2 homogeneous catalyst (entries 2 and 8, Table 1). This was also observed by using p-chlorobenzaldehdye and p-methylbenzaldehyde instead of benzaldehyde as the reactants in theBarbier reaction (Table 2). To make sure whether the heterogeneous or the dissolved homogeneous Pd(II) species were the real catalyst responsible for the Barbier reaction, the following procedure according to Sheldon et al[15] was carried. After for 6 h of reaction time and the conversion exceeding 30%, the solid catalyst was filtered and the mother liquor was allowed to react for another 12 h under the same conditions. No significant change in either the benzaldehyde conversion or the product yield was detected, indicating that the reaction completely stopped. It is concluded that the active phase was not the dissolved Pd(II) species leached from the supports. Therefore, the present catalysis was really heterogeneous in nature.

Tab. 2 The homolog catalytic performances of the as-prepared samples

Samples R Conversion (%) Selectivity (%) Yield (%) Pd-PPh2-PMO(Ph-Ph)-2 Cl 90.7 94.0 85.3

Pd(PPh3)2Cl2 Cl 95.0 95.0 90.2 Pd-PPh2-PMO(Ph-Ph)-2 CH3 89.1 92.1 82.1

Pd(PPh3)2Cl2 CH3 94.1 93.1 87.4 Reaction conditions: 0.065 mmol Pd, 0.025mmol aldehyde, 150 ul allyl bromide, 0.45 g SnCl2 and 5.0 0 ml H2O, reaction time = 12 h, temperature = 50 oC

Fig. 8 demonstrated that the Pd-PPh2-PMO(Ph-Ph)-2 could be used repetitively for 8 times without significant decrease in catalytic efficiency, showing its strong durability which was superior over the corresponding Pd(PPh3)2Cl2 homogeneous catalyst in reducing cost and diminishing environmental pollution from heavy metallic ions. On one hand, the excellent durability of the Pd-PPh2-PMO(Ph-Ph)-2 could be ascribed to the effective inhibition of the Pd(II) leaching. According to ICP analysis, only less than 5 ppm Pd(II) species were detected in the solution after the catalyst was used repetitively for 8 times, which could be easily understood since the Pd(II) organometallic complexes embedded in the silica pore walls could effectively inhibit the leach of Pd(II) species from the support. On the other hand, the the excellent durability of the Pd-PPh2-PMO(Ph-Ph)-2 could also be attributed to its strong stability during water-medium reactions. As shown in Fig. 9, the N2 adsorption-desorption isotherm, the TEM image, the low-angle XRD pattern demonstrated that the mesoporous structure of the Pd-PPh2-PMO(Ph-Ph)-2 was well preserved after recycling test for 8 times, corresponding to the similar SBET and VP values (see Entry 9 in Table 1). Furthermore, the wide-angle XRD pattern (Fig. 10) also displayed diffractional peaks indicative of the crystal-like mesoporous wall as observed in the fresh Pd-PPh2-PMO(Ph-Ph)-2 sample, indicating the preservation of π-π stacking of biphenyl groups in the silica wall. On contrast to the Pd-PPh2-PMO(Ph-Ph)-2, the


- 9 -


Pd-PPh2-PMO(Et) exhibited very poor durability and could be used repetitively only for 6 times. Since no significant leaching of Pd(II) active species were detected by ICP analysis, the deactivation could be mainly ascribed to the damage of mesoporous structure. Taking into account that the Pd-PPh2-PMO(Et) was comprised of the amorphous mesoporous walls, it was reasonable to conclude that the crystal-like mesoporous walls in the Pd-PPh2-PMO(Ph-Ph)-2 was responsible for its strong stability [7], leading to its stronger durability during water-medium Barbier reaction.

0.0 0.2 0.4 0.6 0.8 1.00

20

40

60

80

100

120

140

160

180

200

220

240

a

1 2 3 4 5

Inte

nsity

T wo-theta (degree)

Vol

ume

Ads

orbe

d (c

m3 /g

)

Relative Pressure (P/Po)

Fig. 9 The N2 adsorption-desorption isotherm (a) and the TEM image (b) of the Pd-PPh2-PMO(Ph-Ph)-2 catalyst

after being used repetitively for 8 times. The attached is the low-angle XRD pattern.

10 20 30 40 50

002

001

Inte

nsity

Two-theta (degree)

Fig. 10 The wide-angle XRD patterns of the Pd-PPh2-PMO(Ph-Ph)-2 catalyst after being used repetitively for 8

times

3 Conclusion This investigation results in a new approach for preparing immobilized Pd(II) organometallic

catalyst by self-assembly assisted co-condensation between Pd(II) organometallicsilane and 4, 4’-bis(triethoxysilyl)-biphenylene. This mesoporous catalyst structure features high surface area and large pore size since both the Pd(II) organometallic complexes and organic groups are embedded in the silica wall, which diminishes the blockage of pore channel, thus facilitating the diffusion of reactant molecules. Furthermore, the biphenyl functionalization greatly enhances the surface hydrophobicity, which promotes adsorption of organic molecules on the catalyst, especially in aqueous solution. As a result, the as-prepared catalyst exhibits high activity and selectivity in water-medium Barbier reactions, nearly the same as the Pd(PPh3)2Cl2 homogeneous

b


- 10 -


catalyst. The catalyst also displays long durability owing to the inhibition of Pd(II) leaching and strong hydrothermal stability since the crystal-like mesoporous wall can protect the mesoporous structure from collapsing in liquid phase reaction. The general strategy can be applied for the preparation of other mesoporous organometallic catalysts, thus significant expanding the scope in developing environmentally friendly chemical technologies for practicing organic synthesis.

References

[1] Hayashi Y. In Water or in the Presence of Water?[J]. Angew. Chem. Int. Ed., 2006, 45 (48): 8103~8104. (b) Lindstrom U M. Stereoselective Organic Reactions in Water[J]. Chem. Rev., 2002, 102 (8): 2751~2772. (c) Kobayashi S, Manabe K. Development of Novel Lewis Acid Catalysts for Selective Organic Reactions in Aqueous Media[J]. Acc. Chem. Res., 2002, 35 (4): 209~217.

[2] Li C J. Organic reactions in aqueous media - with a focus on carbon-carbon bond formation[J]. Chem. Rev., 1993, 93 (6): 2023~2035.

[3] Corma A. From Microporous to Mesoporous Molecular Sieve Materials and Their Use in Catalysis[J]. Chem. Rev., 1997, 97 (6): 2373~2420. (b) Stein A, Melde B J, Schroden R C. Hybrid Inorganic-Organic Mesoporous Silicates - Nanoscopic Reactors Coming of Age[J]. Adv. Mater., 2000, 12 (19): 1403~1419. (c) Horvath I T, Anastas P T. Innovations and Green Chemistry[J]. Chem. Rev., 2007, 107 (6): 2169~2173. (d) Ruddy D A, Tilley T D. Kinetics and Mechanism of Olefin Epoxidation with Aqueous H2O2 and a Highly Selective Surface-Modified TaSBA-15 Heterogeneous Catalyst[J]. J. Am. Chem. Soc., 2008, 130 (33): 11088~11096.

[4] Li H X, Zhang F, Lu Y F. Homoallylic Alcohol Isomerization in Water over an Immobilized Ru(II) Organometallic Catalyst with Mesoporous Structure[J]. J. Phys. Chem. B, 2006, 110 (45): 22942~22946. (b) Li H X, Chai W, Zhang F. Water-medium Ullmann reaction over a highly active and selective Pd/Ph-SBA-15 catalyst[J]. Green Chem., 2007, 9: 1223~1228. (c) Li H X, Zhang F, Lu Y F. Water-medium isomerization of homoallylic alcohol over a Ru(II) organometallic complex immobilized on FDU-12 support[J]. Green Chem., 2007, 9: 500~505. (d) Li H X, Chen J, Lu Y F. Aqueous medium Ullmann reaction over a novel Pd/Ph-Al-MCM-41 as a new route of clean organic synthesis[J]. Green Chem., 2007, 9: 273~280.

[5] Li H X, Xiong M W, Zhang F. Water-Medium Barbier Reaction over a Mesoporous Pd(II) Organometallic Catalyst Immobilized on the Ethyl-Bridged PMOs[J]. J. Phys. Chem. C, 2008, 112 (16): 6366~6371.

[6] Li H X, Yin H, Zhang F. Water-Medium Clean Organic Reactions over an Active Mesoporous Ru(II) Organometallic Catalyst[J]. Environ. Sci. Technol., 2009, 43 (1): 188~194.

[7] Inagaki S, Guan Y, Ohsuna T. An ordered mesoporous organosilica bybrid material with a crystal-like wall structure[J]. Nature, 2002, 416: 304~306.

[8] Cornelius M, Hoffmann F, Froba M. Periodic Mesoporous Organosilicas with a Bifunctional Conjugated Organic Unit and Crystal-like Pore Walls[J]. Chem. Mater., 2005, 17 (26): 6674~6678. (b) Sayari A, Wang W H. Molecularly Ordered Nanoporous Organosilicates Prepared with and without Surfactants[J]. J. Am. Chem. Soc., 2005, 127 (35): 12194~12195. (c) Kapoor M P, Yang Q H, Inagaki S. Self-Assembly of Biphenylene-Bridged Hybrid Mesoporous Solid with Molecular-Scale Periodicity in the Pore Walls[J]. J. Am. Chem. Soc., 2002, 124 (51): 15176~15177. (d) Yang Y, Sayari A. Molecularly Ordered Biphenyl-Bridged Mesoporous Organosilica Prepared under Acidic Conditions[J]. Chem. Mater., 2007, 19 (17): 4117~4119.

[9] Zhang F, Li H X, Lu Y F. Mesoporous Silica with Multiple Catalytic Functionalities[J]. Adv. Funct. Mater. 2008, 18 (22): 3590~3597.

[10] Posset T, Blumel J. New Mechanistic Insights Regarding Pd/Cu Catalysts for the Sonogashira Reaction: HRMAS NMR Studies of Silica-Immobilized Systems[J]. J. Am. Chem. Soc., 2005, 128 (26): 8394~8395.

[11] Margolese D, Melero J A, Stucky G D. Direct Syntheses of Ordered SBA-15 Mesoporous Silica Containing Sulfonic Acid Groups[J]. Chem. Mater., 2000, 12 (8): 2448~2459.

[12] Krcher O, Kppel R A, Baiker A. Silica Hybrid Gel Catalysts Containing Group(VIII) Transition Metal Complexes: Preparation, Structural, and Catalytic Properties in the Synthesis of N,N-Dimethylformamide and Methyl Formate from Supercritical Carbon Dioxide[J]. J. Catal., 1998, 178 (1): 284~298.

[13] Zhao D Y, Huo Q, Stucky G D. Nonionic Triblock and Star Diblock Copolymer and Oligomeric Surfactant Syntheses of Highly Ordered, Hydrothermally Stable, Mesoporous Silica Structures[J]. J. Am. Chem. Soc., 1998, 120 (24): 6024~6036.

[14] Chong A S M, Zhao X S. Functionalization of SBA-15 with APTES and Characterization of Functionalized Materials[J]. J. Phys. Chem. B, 2003, 107 (46): 12650~12657.

[15] Sheldon R A, Wallau M I, Schuchardt U. Heterogeneous Catalysts for Liquid-Phase Oxidations: Philosophers' Stones or Trojan Horses?[J]. Acc. Chem. Res., 1998, 31 (8): 485~493.


- 11 -


高稳定类结晶壁介孔 Pd(II)有机金属催化

水介质 Barbier 反应的研究何文翰，张昉，李和兴，黄建林

（上海师范大学化学系，上海 200234）

摘要：采用表面活性剂自组装合成联苯基和 Pd(II)有机金属的 PMO 类型催化剂。该催化剂

具有大比表面积、介孔结构以及强的表面疏水性，在水介质 Barbier 反应显示高活性和选择

性。同时，由于联苯基的 π-π 堆积形成的类结晶孔壁大大提高了催化剂的稳定性，使其

能重复使用多次后结构仍保持基本不变。关键词：环境催化；联苯基桥联 PMO 材料；类结晶孔壁；介孔 Pd(II)有机金属催化剂；水

介质 Barbier 反应中图分类号：O643.36+1

Water-medium Barbier Reactions over the Mesoporous Pd(II) Organometal Catalyst with Crystal-like...

Documents

Transcript of Water-medium Barbier Reactions over the Mesoporous Pd(II) Organometal Catalyst with Crystal-like...