Supporting Information Layered Materials with

Supporting Information Layered Materials with Coexisting Acidic and Basic Sites for Catalytic One-Pot Reaction Sequences Ken Motokura, Mizuki Tada, and Yasuhiro Iwasawa* Department of Chemistry, Graduate School of Science, The University of Tokyo

General: 1H- and 13C-NMR spectra were measured on a JNM-AL400 spectrometer at 400 MHz in CDCl3 with TMS as an internal standard. Solid state 13C and 29Si MAS NMR spectra were recorded with a Chemagnetics CMX-300 spectrometer operating at 75.5 and 59.7 MHz, respectively.

13

C

MAS NMR spectra with cross polarization (CP) were acquired at a contact time of 0.1 ms and a delay time of 4 s in single-pulse detection method. In

29

Si NMR analysis the pulse duration and

delay time were 1.5 µs and 20 s, respectively. The rotor spin rate was 4 kHz. Hexamethylbenzene (13C: 17.17 and 176.46 ppm) and TMS (29Si: 0 ppm) were used as external standards for the calibration of chemical shifts. The accumulation number was fixed at about 10000. Infrared spectra were obtained with a JASCO FTIR-410. Powder X-ray diffraction patterns were recorded using Rigaku MultiFlex with Cu Kα radiation. Analytical GLC and GLC-Mass were performed by Shimadzu GC-2010 with a flame ionization detector equipped with silicon SE-30 column. Unless otherwise noted, materials were purchased from Wako Pure Chemicals, Tokyo Kasei Co., and Aldrich Inc. and they were used after appropriate purification. Sodium-exchanged montmorillonite (Na+-mont) was obtained from Kunimine

Industry Co. as Kunipia F

(Na0.66(OH)4Si8(Al3.34Mg0.66Fe0.19)O20; Na 2.69, Al 11.8, Fe 1.46, Mg 1.97%). Silica (Aerosil® 300, 300 m2/g), alumina (γ-Al2O3, SOEKAWA CHMICALS), and H-USY (Tosoh Co., HSZ-330HUA, Si/Al=3.17, 626 m2/g) were used. The identities of products were confirmed by comparison with reported mass and NMR data.

Preparation of H-mont-NH2: Proton-exchanged montmorillonite (H-mont) was prepared from Na+-mont in an aqueous solution of hydrogen chloride by a reported procedure.[1] The H-mont (0.5 g) was added to 15 mL of a solution of 3-aminoropyltrimethoxysilane (0.82 mmol) and stirred at room temperature for 2 h. Then the solvent was removed by filtration and the functionalized H-mont was washed with the same solvent, followed by drying under vacuum. The elemental analysis results are listed in Table 1S. Other solid-supported primary amines (Support-NH2) were also synthesized by the similar procedure.

Table 1S. Elemental analysis results and interlayer distances of supported amine catalysts. catalyst

N content (wt%)

C content (wt%)

interlayer distance (Å)a

H-mont-NH2 [heptane]

1.16

6.36

7.7

H-mont-NH2 [THF]

0.78

9.43

7.9

H-mont-NH2 [toluene]

1.21

9.20

9.6

H-mont-NH2 [DMSO]

0.59

8.41

8.4

H-mont-NH2 [acetonitrile]

1.05

5.03

5.4

H-mont-NH2 [water]

1.48

5.15

7.3

H-mont

-

-

2.6

SO2-NH2 [heptane]

1.26

4.76

-

Al2O3-NH2 [heptane]

0.82

3.50

-

H-USY-NH2 [heptane]

1.05

5.83

-

a

Determined by subtracting the c dimension of the silicate sheet (9.6 Å) from the observed d001

values in the XRD spectrum,[2] shown in Figure 1S. The large carbon content of H-mont-NH2 [THF], H-mont-NH2 [toluene], and H-mont-NH2 [DMSO] indicates remaining solvents, resulting large interlayer spaces. The larger interlayer space of H-mont-NH2 [water] than H-mont-NH2 [acetonitrile] is derived from higher amine loading.

XRD

Figure

1S.

XRD

spectra

for

(A)

H-mont,

(B)

H-mont-NH2[heptane],

and

(C)

H-mont-NH2[acetonitrile].

Tandem deacetalization-Konevenagel condensation with H-mont-NH2 [heptane]: Into a pyrex glass reactor were placed the H-mont-NH2[heptane] (3.0×10-2 g, 2.5×10-2 mmol), acetonitrile (1 mL), benzaldheyde diemethylacetal (0.5 mmol), and ethyl cyanoacetate (0.6 mmol). The resulting mixture was vigorously stirred at 333 K. After 1 h, the catalyst was separated by filtration

and

the

1

H

NMR

analysis

of

the

filtrate

showed

95%

yield

of

2-cyano-3-phenyl-2-propenoic acid ethyl ester.

Tandem deacetalization-nitro-aldol reaction with H-mont-NH2 [heptane]: Into a pyrex glass reactor were placed the H-mont-NH2[heptane] (3.0×10-2 g, 2.5×10-2 mmol), nitromethane (1 mL), and benzaldheyde diemethylacetal (0.5 mmol). The resulting mixture was vigorously stirred at 373 K under N2. After 1 h, the catalyst was separated by filtration and the 1H NMR analysis of the

filtrate showed >99 yield of β-nitrostyrene.

Nitro-aldol reaction with H-mont-NH2 [heptane]: Into a pyrex glass reactor were placed the H-mont-NH2[heptane] (1.0×10-2 g, 8.3×10-3 mmol), nitromethane (1 mL), and benzaldheyde (0.5 mmol). The resulting mixture was vigorously stirred at 373 K under N2. The initial formation rate of β-nitrostyrene was determined by 1H NMR analysis at low conversion of benzaldehyde.

The activity of sole H-mont for deacetalization reaction (Table 1, entry 11): Formation of aldehyde from acetal is hydrolysis reaction, but the acid-base tandem reaction shown in Table 1 was performed without addition of water. The formation of water molecule by Knoevenagel condensation (2nd reaction) accelerates the acid-catalyzed deacetalization reaction step (1st reaction). This is the reason for the higher conversion on the H-mont-NH2 [heptane] catalyst (Table 1, entry 1) than that for the H-mont (entry 11). The originally adsorbed water molecules on the fresh H-mont or H-mont-NH2 are consumed in the initial step of the reaction. The sole H-mont shows higher performance for the deacetalization reaction than the H-mont-NH2[heptane] and H-mont + n-hexylamine in the presence of enough amount of water. This result seems to support interaction between amine and H-mont acid site (Scheme 1D). NC

CO2Et 2

Ph

1

base site

acid site

O O

-2MeOH

Ph 4 H 2O

O

CO2Et

Ph 3

CN

Solid-state 29Si MAS NMR spectra: Figure 2S shows

29

Si MAS NMR spectra for

H-mont-NH2 around T sites (-80~-30 ppm) with peak deconvolution These spectra clearly show the downfield shift by 5 ppm between the samples grafted in acetonitrile (B) versus heptane (A). Both -55 (main) and -60 ppm signals were detected in the sample grafted in water (C). The reason might be the higher amine loading in H-mont-NH2[water] (1.06 mmol/g) than those of H-mont-NH2[heptane](0.83) and [acetonitrile](0.75).

Figure 2S. 29Si MAS NMR spectra for (A) H-mont-NH2[heptane], (B) H-mont-NH2[acetonitrile], (C) H-mont-NH2[water], and (D) H-mont.

Proposed amine immobilization and catalytic reaction mechanisms: Acid Sites on H-mont Motokura et al. reported NH3-TPD (temperature programmed desorption) analysis of the H-mont (Ref. 1, supporting information). The spectra shows two NH3 desorption peaks (around 600 (h-peak) and 800 K (h+-peak)) indicates the presence of two types of acid sites. In addition, weak silanol group also exists on the H-mont.

silanol OHOH SiOH Si Si

strong H+ O- OH Si

weak H+ OHOH Si SiOH OSi

H-mont

Amine Immobilization Mechanism In heptane solvent, amine groups in 3-aminopropyltriethoxysilane (APS) readily interact with strong acid sites, then, silane-coupling reaction proceeds with neighboring silanol groups. The formation of covalent Si-O-Si(surface) bonds may tend to increase the distance between the amine group and the acid site geometrically, which induces a decrease in the acid-base interaction. We have already reported that the undesired acid-amine neutralization is suppressed by the silane-coupling immobilization of amines in non-polar solvents.[3] It seems that the strongest acid site still connects with the nitrogen atom, while weak acid site leaves from the amine group, resulting

the

formation

of

both

protonated

and

unprotonated

primary

amines

in

H-mont-NH2[heptane] (13C NMR, Figure 1). Highly active for base reaction

Scheme 1S.

Active for acid reaction

Active for acid reaction Si(OEt)3

silanol OHOH SiOH Si Si

strong

H-mont

+

HO OH Si

weak H O-

+

OHOH Si SiOH Si

(EtO)3Si (APS)

NH2

NH2 + OHOH HSiOH Si O SiOH Si

H2N H O-

H2N H + N H H

(EtO)3Si +

OHOH Si SiOH Si

+ Si H O O OSiOSi O SiOH Si

Si O O SiOSi Si

heptane

H-mont-NH2 [heptane]

Ethoxysilane groups [Si(OEt)3] react with acid sites on H-mont to form Si-O-Si(Surface) covalent bonds, where both [Si(OEt)3] groups and surface acid sites may be affected by polar solvents like acetonitrile. A part of cationic charge (δ+) remains on the Si atom of APS as indicated by 29Si MAS NMR spectra (Figure 2S). To keep the charge balance, a neighboring Si-O(H)-Si group becomes weak H+ site, and then, the new acid sites interact with all NH2 group to generate NH3+ (by 13

C CP/MAS NMR, Figure 1). The new acid sites are generated on the neighboring position of the Si

atom of APS, hence, the immobilized propylamine shows a bent structure. We think this is the reason for the smaller interlayer space of the H-mont-NH2[acetonitrile] (5.4 Å) than that for the H-mont-NH2[heptane] (7.7 Å) regardless of the similar amine loadings. Scheme 2S. Active for base reaction

:solvent H2 N

silanol

strong

OHOH SiOH Si Si

H-mont

H+ O OH Si

+

OHOH Si SiOH Si

NH2

Si(OEt)3 (EtO)3Si

weak H O-

:solvent

(EtO)3Si (APS)

NH2

acetonitrile

+ OHOH HSiOH Si O SiOH Si

δ+

H+ OHOH Si SiOH OSi -EtOH -EtOH

Si O O SiOH Si Si

H N+ H H H + N H δ+ O O Si Si H O O Si O O Si Si

Formation of new weak acid sites on neighboring positions H-mont-NH2 [acetonitrile]

Christopher Jones group at Georgia Institute of Technology reported that the amine groups aggregate in nonpolar solvent (C. W. Jones et al. Chem. Mater. 2006, 18, 5022). It is suggested that nonuniformly immobilization occurred in nonpolar solvent (Scheme 3S(A)). On the other hand, the amines are uniformly dispersed and immobilized on surface (Scheme 3S(B)). During the uniformly immobilization, all strong acid sites might be deactivated by amine groups. We think it is also the reason for the coexistence of acid and base sites by the immobilization in non-polar solvent.

Scheme 3S. (EtO)3Si Si(OEt)3 H2N NH2 H2 N Si(OEt) 3 H H +H N H+ Si OSi Si

H2N H+ O-

H+ O-

H+ O

non-polar solvent

H+ O-

H2 N

H-mont

H+ O-

(A)

H-mont-NH2[non-polar solvent] NH2

NH2

Si(OEt)3

Si(OEt) 3

NH2

Si(OEt)3 H+ O-

+

H O-

N+ HH H

polar solvent

H+ O

H-mont

OEt Si OEt OH

N+ H H

OEt Si OEt N+ O OEt H H H Si OEt O

(B)

H-mont-NH2[polar solvent]

n-Hexylamine adsorbs on the acid sites of H-mont (Scheme 4S). The NH3+ group from strongest acid site still remains a catalytic activity for deacetalization (Table 1, entry 10). Scheme 4S Active for acid reaction

silanol OHOH SiOH Si Si

strong H+ O- OH Si

weak +

H O-

OHOH Si SiOH Si

H-mont

NH2

H H H N+ HN H OHOH +HO OH O SiOH Si Si Si

OHOH Si SiOH Si

H-mont + n-C6H13NH2

Proposed Catalytic Reaction Mechanism A proposed reaction mechanism by the H-mont-NH2[heptane] catalyst is shown in Scheme 4S. (i) An acetal is activated by NH3+ group from strongest acid site, then reacts with water to form an aldehyde and methanol. (ii) The aldehyde is activated by surface acid sites and reacts with the primary amine, affording surface imine species and water [4]. (iii) Finally, donor substrates (nitrile of nitro compounds) attacks to the imine intermediate to form the corresponding alkene produsts. Surface weak acid site was also considered as a catalytic acid site for deacetalization.

The formation of water molecule from aldehyde and amine accelerates the acid-catalyzed deacetalization reaction step. This is the reason for the higher conversion on the H-mont-NH2 [heptane] catalyst (Table 1, entry 1) than that for the H-mont (entry 11). The H-mont shows higher performance for the deacetalization reaction than the H-mont-NH2[heptane] in the presence of enough amount of water. The originally adsorbed water molecules on the H-mont-NH2[heptane] is consumed in the initial step of the reaction. H2O OMe

Scheme 4S

OMe H2N H2N H N+ H H

OMe OMe Si O O SiOSi Si

+ Si H O O OSiOSi O SiOH Si

H N+ H H Si O O SiOSi O SiOH Si

+

Si O O SiOSi Si

H O-

H2O

H-mont-NH2 [heptane]

2MeOH

R EWG EWG R

H H N+ H

N +

Si O O SiOSi O SiOH Si

H H N+ H

H2O

H O-

H

H2N

O Si O O SiOSi Si R

EWG

Si O O SiOSi O SiOH Si

H+ O-

Si O O SiOSi Si

References (1) Motokura, K.; Fujita, N.; Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Angew. Chem. Int. Ed. 2006, 45, 2605. (2) McBride, M. B.; Pinnavaia, T. J.; Mortland, M. M. J. Phys. Chem. 1975, 79, 2430. (3) (a) Motokura, K.; Tada, M.; Iwasawa, Y. J. Am. Chem. Soc. 2007, 129, 9540; (e) Motokura, K.; Tomita, M.; Tada, M.; Iwasawa, Y. Chem. Eur. J. 2008, 14, 4017. (4) Bass, J. D.; Solovyov, A.; Pascall, A. J.; Katz, A. J. Am. Chem. Soc. 2006, 128, 3737.