Polymer immobilized tantalum(v)-amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

NJC

View Article Online

View Journal | View Issue

PAPER

Polymer immobilized tantalum(V)–amino acid

complexes as selective and recyclable

heterogeneous catalysts for oxidation of olefins

and sulfides with aqueous H O †

Cite this: New J. Chem., 2019,

43, 17251

2

Gangutri Saikia, Kabirun Ahmed, Chandrasee Rajkhowa, Mitu Sharma, Hiya Talukdar

and Nashreen S. Islam

*

Polymer supported heterogeneous peroxotantalum(V) catalysts were prepared by anchoring Ta(V)-diperoxo

species to chloromethylated poly(styrene–divinylbenzene) resin functionalized with amino acids asparagine

À

(

L-Asn) and arginine (L-Arg). The structurally well-defined catalysts, [Ta(O

2

)

2

(L)

2

] -MR, [L = asparagine

(catalyst 1) or arginine (catalyst 2) and MR = Merrifield resin], were comprehensively characterized by

elemental analysis (CHN, ICP-OES, energy dispersive X-ray spectroscopy), spectral studies (FT-IR, Raman,

13

C NMR, diffuse reflectance UV-vis and XPS), SEM, XRD, Brunauer–Emmett–Teller (BET) and thermo-

gravimetric analysis (TGA). The supported peroxotantalum (pTa) compounds displayed excellent catalytic

performance in epoxidation of alkenes with 30% H

2

O

2

, under solvent free reaction conditions. Styrene was

À1

epoxidized with 499% selectivity with the highest TOF of 1040 h obtained within 30 min reaction time,

À1

whereas the TOF for norbornene epoxidation was 2000 h within 1 h with 495% epoxide selectivity.

Furthermore, the immobilized catalysts facilitated chemoselective oxidation of a broad range of organic

Received 12th August 2019,

Accepted 13th October 2019

sulfides to the desired sulfoxides with H

2 2

O in methanol, under mild reaction conditions. The oxidations

proceeded with a high H efficiency percentage and are amenable to ready scalability. The hetero-

2

O

2

geneous catalysts could be easily recovered and reused for several consecutive catalytic cycles with

undiminished activity/selectivity profiles in all cases. The developed catalytic strategies are operationally

simple and, being free from halogenated solvent or any other toxic auxiliaries, environmentally clean.

DOI: 10.1039/c9nj04180j

rsc.li/njc

important organic transformation which holds immense interest

from both chemical and biological perspectives.

1

Introduction

2

The development of heterogeneous, selective oxidation catalysts

A large number of promising alkene epoxidation strategies

that support green and energy-eﬃcient oxidative transformations based on supported metal oxide catalysts have been developed

3

is of enormous contemporary importance, mainly owing to the over the years, many of which often relied upon expensive,

mounting environmental concerns in recent times. Epoxidation of non-aqueous organic oxidants such as tert-butyl hydroperoxide

olefins is one of the pivotal reactions in organic synthesis as (TBHP) and cumene hydroperoxide (CHP) along with chlori-

3

a,e–h,4

epoxides are valued precursors in the synthesis of a wide range of nated solvents to achieve high activity,

as the presence of

3

e,f,4a,5

fine chemicals including pharmaceuticals, food additives, paints water often leads to poisoning of such catalysts.

and epoxy resins. Selective oxidation of sulfides to sulfoxides oxidation catalysts, on the other hand, were reported to exhibit

or sulfone represents another fundamentally and industrially superior performance with hydrogen peroxide in comparison to

Ta-Based

1

4

a,6

organic peroxides.

Silica supported Ta catalysts in particular

have been documented to be inherently more selective than the

analogous titanium catalysts for epoxidations with aqueous

Dept. of Chemical Sciences, Tezpur University, Napaam, Tezpur-784028, Assam,

India. E-mail: nsi@tezu.ernet.in, nashreen.islam@rediﬀmail.com;

Fax: +91-3712-267006; Tel: +91-9435380222, +91-3712-267007

4

a,7

H

2

O

2

.

These findings are significant in view of the current

ecological concerns, which triggered an uninterrupted explora-

†

Electronic supplementary information (ESI) available: Analytical data of the

tion of alternative non-polluting oxidation protocols that utilize

complexes, N adsorption/desorption isotherms, FTIR spectra of catalyst 2, FTIR

2

3b,4a,8

aqueous H O as an oxidant,

an ideal waste preventing

13

2 2

and Raman data, DRUV-visible spectra, C NMR spectra of catalyst 2, C NMR

table and thermogravimetric data, sulfide oxidation optimization table, compar-

ison table of Ta based catalysts for sulfide oxidation, calculation of the eﬃciency

and cost effective terminal oxidant.

Catalysis by Ta compounds is a field of growing importance,

as evident from the literature showing the utility of such

2 2

of H O and characterization of sulfoxides. See DOI: 10.1039/c9nj04180j

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17251

View Article Online

Paper

NJC

systems in a number of organic transformations including arene divenylbenzene) support functionalized with amino acids

9

10

11

hydrogenation, polymerization, metathesis of alkanes, imines asparagine and arginine. With the ability to undergo facile

1

2

13

and olefins, and activation of C–N bonds. Significantly, Ta functionalization, in addition to its attractive attributes, viz., low

compounds have been considered ideal for ‘green chemistry’ cost, ready availability, and mechanical and chemical robust-

applications as such systems were reported to be inert to body ness, cross-linked poly(styrene–divenylbenzene) or Merrifield

fluid. Although the catalytic potential of Ta-based systems in resin still remains one of the most popular and versatile solid

organic oxidations is yet to be fully explored, there have been supports for catalytic applications.

1

4

1

8b,19a,22

An appropriate

several reports pertaining to efficient Ta-based heterogeneous choice of the ligand groups for functionalization of the resin

epoxidation catalysts supported on porous siliceous oxide or other is an important prerequisite for the formation of stable metal–

3b,4a,6c–f,7,15

metal oxide supports such as MCM-41 and SBA-15.

polymer linkages which would withstand repeated catalytic

Such supports are, however, known to be associated with cycles. Carboxylate containing ligands have been shown to be

1

6

20

limitations with respect to catalytic activity and selectivity

excellent co-ligands for stabilizing peroxotantalum species.

and often require the incorporation of hydrophobic organic Moreover, being relatively bulky with polar side chains, the

7

b,16a,17

groups onto the supports.

The Sharpless type silica chosen amino acid ligands offered the prospect of facilitating

supported chiral tantalum alkoxides coordinated with tartrate the formation of site isolated pTa grafted stable catalysts.

diolate systems developed by Meunier et al. are notable exam- Metal co-ordination through the side-chain amide group of

2

3

ples, which were shown to catalyze asymmetric epoxidation of asparagine or the guanidine moiety of arginine, which exists

6

d

allyl alcohol with TBHP. A calixarene–Ta(V) complex sup- normally in the protonated form in solution, has rarely been

2

4

ported on SiO has been reported to catalyze cyclohexene and observed. The bulky multidentate ligands were demonstrated

2

4

a

cyclooctene epoxidation with aqueous H O . Most of the to be ideal for creating stable surface species that ensure metal

2

tantalum based heterogeneous oxidation catalysts could not atom isolation during catalytic turnover in the case of supported

4

a

however retain their activity and selectivity in subsequent oxide based catalysts.

6

e,15b,16a

reaction cycles.

Moreover, some of these methodologies

We describe herein the preparation and characterization

suffer from drawbacks such as low to moderate TON and of heretofore unreported polymer supported pTa catalysts

selectivity, requirement of long reaction times and use of and their performance in epoxidation of olefins and selective

volatile organic solvents, due to which the important criterion oxidation of sulfides with 30% aqueous H O with respect to their

2 2

of ecological sustainability remains a challenging issue to selectivity, reusability, turn over number (TON) and environ-

address. Thus, realization of high conversion under mild con- mental compatibility.

ditions along with catalyst recyclability is an important objec-

tive in designing supported Ta-based catalysts.

In the recent past, we have reported the synthesis and 2 Results and discussion

catalytic and biochemical activities of a series of peroxo

complexes of d transition metals immobilized on various

2.1 Synthesis

0

As illustrated in Scheme 1, preparation of immobilized peroxo-

tantalum catalysts 1 and 2 involved a two-step synthetic protocol.

Functionalization of the resin with L-Asn or L-Arg was accom-

plished by reacting the polymer with the respective amino acid

polymeric supports ranging from water-soluble polymers

and biopolymers to insoluble cross-linked polymer resins.

1

8

Several of these systems demonstrated excellent stability, selec-

tivity and eﬃciency in a variety of organic oxidations under

1

8b,25

1

8b–d,g,h, j,k

in methanol using pyridine as a base.

were obtained in the subsequent step, by treating the function-

alized resin with the precursor complex Na [Ta(O ] in the

presence of 30% H . Maintenance of reaction parameters

The solid catalysts

environmentally benign conditions.

In this context,

it is somewhat surprising that, notwithstanding the well-

documented advantages associated with immobilization of

catalytically active transition metal species on polymer matrices

such as enhancement of catalyst stability, ease of work up of the

reaction mixture, and the facile regeneration and reusability of

3

2 4

)

2 2

O

such as near neutral pH, a contact time of 24 h and a reaction

temperature of ca. 4 1C was found to be crucial for the desired

synthesis. Chloromethylated polystyrene cross-linked with

3

a,19

such systems,

there appears to be no report available on

2% divinylbenzene was chosen as the polymer support due to

the preparation or activity of Ta-based oxidation catalysts

supported on organic polymers. Moreover, despite the avail-

ability of scores of well-defined pTa complexes in diverse ligand

its superior flexibility, which usually facilitates the anchoring of

1

8b,22c

metal atoms via the polymer grafted ligands.

It is impor-

2

0

tant to note that the catalysts are non-hygroscopic and remain

stable and active for a prolonged period.

environments, there still is a paucity of information regarding

the activity of discrete pTa complexes as oxidation catalysts,

although Ta mediated organic oxidations with H

2 2

O have been

2

.2 Characterization

shown to proceed via in situ formation of peroxo intermediate

2

6c,7b,15a,21

Ta(Z -O ).

Several characterization techniques including analytical and

2

In continuation of our quest for cleaner catalytic processes spectroscopic methods viz. CHN, ICP-OES, energy dispersive

to accomplish organic oxidations, in the present work, we directed X-ray spectroscopy, FT-IR, Raman, DRUV-visible spectroscopy,

13

our eﬀorts towards generating new heterogeneous catalysts

C NMR, powder XRD, XPS, BET and thermogravimetric analysis

by anchoring pTa species onto a cross-linked poly(styrene– were carried out to determine the structure of the catalysts.

1

7252 | New J. Chem., 2019, 43, 17251--17266

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online

NJC

Paper

Scheme 1 Synthesis of the chloromethylated poly(styrene–divinylbenzene) supported pTa complexes. (A) Possible structure of the polymer anchored

compounds. ‘‘ ’’ represents the polymer chain.

As seen from the analytical data presented in Table S1 (ESI†)

nearly 100% of the Cl of the –CH Cl groups of MR has been

2

substituted by asparagine to form MRAsn, whereas in the case

of MRArg ca. 86% of Cl was replaced by arginine. The elemental

analysis data confirmed the presence of two peroxo groups per

metal centre in each of the catalysts [Table S1 (ESI†)]. On the

basis of the metal content obtained from EDX and ICP-OES

analysis, the tantalum loading on the resin was found to be 0.37

and 0.32 mmol per gram of the polymer, for catalysts 1 and 2,

respectively. The magnetic susceptibility measurement revealed the

diamagnetic nature of the catalysts in accord with the occur-

rence of tantalum centres in their +5 oxidation state, which was

further confirmed from XPS analysis data.

2.2.1 SEM and energy dispersive X-ray (EDX) analysis.

Scanning electron micrographs were employed in order to

examine the morphological changes occurring on the surface

of the polymer resin after incorporation of amino acids and

subsequent anchoring of the pTa species. The micrographs

revealed that the smooth surface of MR turned considerably

coarse upon grafting of the amino acids. The attachment of the

peroxo-Ta moieties on the resin resulted in further roughening

Fig. 1 Scanning electron micrographs of (a) MR, (b) MRAsn, (c) catalyst 1,

d) MRArg and (e) catalyst 2.

(

of the surface with the appearance of randomly oriented catalysts 1 and 2 has thus been confirmed. Considering the

deposits on the external surface of the catalysts as has been intensity of the peaks for peroxotantalum species, it is also likely

clearly observed in the micrographs (Fig. 1).

that there are crystallites of pTa salt present in the resin in

The energy dispersive X-ray analysis of the compounds addition to the covalently anchored pTa compounds. This is also

carried out by focusing on multiple regions of the catalyst in accord with the roughening seen in the scanning electron

surface (Fig. 2) showed C, N, O, Na, and Ta as constituents of micrograph of the compounds.

the catalysts. The results depicted in Table S1 (ESI†) are the

2.2.3 X-ray photoelectron spectroscopy. The XPS spectra of

average data obtained from these regions. The composition of the pTa incorporated complexes 1 and 2 are presented in Fig. 4.

the compounds derived from energy dispersive X-ray spectro- XPS is an eﬀective tool for studying the electronic properties of the

scopy, which gave in situ analysis of the bulk, concurred well species formed on the surface. The complexes displayed typical

with the elemental analysis data.

.2.2 Powder X-ray diﬀraction studies. The X-ray diﬀracto-

4f5/2 and 4f7/2 peaks at binding energies of 27.8 and 26.2 eV.

2

grams of neat MR and pTa incorporated catalysts 1 and 2 are

presented in Fig. 3. The broad peak centered at a 2y value of

ca. 201 observed in the diﬀractogram of each of these species of

26

the complexes is characteristic of the PS–DVB resin. The

diffraction patterns of the polymeric catalysts displayed addi-

tional peaks at 2y values of 17.9, 19.6, 20.9, 29.2, and 30.11, which

are close to the peaks observed for the peroxotantalum species

(

PDF 25-0861) attributable to planes (002), (012), (301), (240) and

232), respectively. That the peroxotantalum complexes are

anchored onto the polymer matrix to afford the immobilized Fig. 2 EDX spectra of complexes (a) 1 and (b) 2.

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17253

View Article Online

Paper

NJC

Fig. 4 XPS spectra of Ta (4f5/2) and (4f7/2) peaks for (a) catalyst 1 and

(

b) catalyst 2.

Table 1 BET surface area, Vtot and pore radius of MR, amino acid linked

MR and polymer-bound catalysts 1 and 2

a

2

À1

b

À1

Compound

S

BET (m g

)

V

tot (cc g

)

Pore radius (Å)

MR

11.5

9.6

5.5

10.8

10.7

0.12

0.10

0.068

0.013

0.10

53.7

39.9

40.1

22.7

49.0

MRAsn

Catalyst 1

MRArg

Catalyst 2

a

b

BET surface area. Total pore volume.

2

.2.5 IR and Raman spectral analysis. A comparative evaluation

Fig. 3 X-ray diﬀraction (XRD) pattern of (a) MR, (b) catalyst 1, (c) catalyst 1

after the 5th cycle, (d) catalyst 2 and (e) catalyst 2 after the 5th cycle.

of FTIR and Raman spectral analysis data of the host MR, the amino

acid grafted resin and the immobilized catalysts demonstrated that

covalent anchoring of the amino acids to the polymer and

The values are in good agreement with the available literature subsequent anchoring of the pTa moieties to the functionalized

2

7

data for tantalum in the +5 oxidation state. The O1s peak at resin was successful. The FTIR and the complementary Raman

2

8

532.0 eV was attributed to the oxygen from metal peroxide.

spectra of each of these polymeric compounds are presented in

Thus, XPS analysis confirms the presence of peroxotantalum(V) Fig. 5, Fig. 6 and Fig. S2 (ESI†), and their significant features

species on the surface of the polymeric catalysts. The XPS results along with empirical assignments based on available relevant

1

8b,20a,25,33

are in accord with the diamagnetic nature of the complexes, as literature are outlined in Table S2 (ESI†).

indicated by the magnetic susceptibility measurements. Typical of the spectra of pristine polymer MR, the amino

.2.4 BET analysis. The surface areas of the functionalized acid functionalized polymers and metal-anchored catalysts are the

2

À1

resin and metal incorporated polymers were determined by using absorptions in the vicinity of ca. 3050, 2920, 1025 and 690 cm

BET analysis with the nitrogen adsorption method. The BJH due to the naromatic(CH), naliphatic(CH), daromatic in-plane(CH) and

model was used to determine the pore volume. The N

tion/desorption isotherms of the samples displayed typical type II ca. 1264 cm

,

29

3

0

18b,25,33a,c

2

adsorp-

d

aromatic out-of-plane(CH) vibrations.

An intense band at

À1

observed in the spectrum of MR has been

2

5,33a

2

adsorption of an IUPAC standard on particles with macropores or ascribed to the n(C–Cl) mode of the –CH Cl moiety.

31

nonpores showing poor adsorption. The result presented in Anchoring of a ligand group on Merrifield resin by replacement

Table 1 shows that after amino acid incorporation on the resin, of the Cl atom from the –CH Cl group can be monitored

the surface area of MR was decreased from 11.5 to 9.6 and conveniently by observing the change in intensity or disappear-

2

À1

25,33a

1

0.8 m g for the functionalized resins MRAsn and MRArg, ance of the intense n(C–Cl) mode of the –CH Cl moiety.

2

respectively. A further decrease in the catalyst surface area was In the spectrum of the functionalized polymers MRAsn and

observed after incorporation of pTa moieties, which is likely to be MRArg, the near disappearance of the n(C–Cl) band thus

due to the pore blockage resulting from the functionalization indicated replacement of Cl from the –CH

2

Cl group of MR with

1

8b,32

followed by attachment of peroxometal species to the resin.

the amino acid ligands. Further evidence regarding the grafting

1

7254 | New J. Chem., 2019, 43, 17251--17266

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online

NJC

Paper

Fig. 6 Raman spectra of (a) catalyst 1 and (b) catalyst 2.

with metal oxygen symmetric and asymmetric stretching vibra-

tions, appeared in both the IR and Raman spectra of catalysts 1

À1 20a,d

À1

and 2, in the expected 850–800 cm

region, respectively.

and 500–600 cm

2

0a,35

In contrast to the IR spectrum of the

starting sodium tetraperoxotantalate complex, which exhibited

À1

a single absorption at around 820 cm attributable to the

n(O–O) vibration, the IR as well as Raman spectra of both

the catalysts displayed two distinct peaks corresponding to

the n(O–O) mode in the 800–850 cm region. The observed

Fig. 5 IR spectra of (a) MRAsn, (b) catalyst 1 and (c) catalyst 1 after the 5th

cycle of reaction.

À1

spectral pattern is typical of diperoxotantalum species as has

2

0a,35a

been reported previously.

of the amino acid to the polymer could be derived from the

For the pTa complex 1, the n(CO) modes of the amino acid

À1

observance of additional bands in the spectra in the 1650 side chain remained unaltered at 1630 cm ruling out the

À1

to 1580 cm region, although the spectral patterns appeared possibility of involvement of the –CONH

2

group in metal com-

quite complex with a number of bands of the ligands occurring plexation. Participation of the carboxylate group in co-ordination

3

3d

in an overlapping region.

was indicated by a slight shift observed in the nasym(COO) mode

À1

The intense band observed at 1629 cm in the IR spectrum to a higher frequency of 1601 cm along with the appearance of

of MRAsn has been ascribed to the n(CQO) (amide I) band, as a medium intensity band at 1353 cm attributable to n_s_y_m(COO)

this absorption is the most prominent one in the asparagine shifted to lower frequency due to complexation. Thus, the

spectrum. The band due to d(NH

in the spectrum of free asparagine was absent in the spectrum stretching of the carboxylate group (Dn = 248 cm ) compared

of polymer bound MRAsn, indicating the participation of the to that of the free ligand (Dn = 176 cm ) indicated unidentate

group in bond formation with the polymer. In addition, the co-ordination of the carboxylate group to the Ta(V) centre of

appearance of a new band at 1085 cm for n(C–N) indicated immobilized catalyst 1.

À1

3

6

3

4

+

À1

3

) observed at ca. 1680 cm

increase in the difference between asymmetric and symmetric

À1

3

4a

À1

18b,37

the formation of a carbon–nitrogen bond by replacing the chloride

The IR spectrum of MRArg as well as its metal incorporated

1

8b,25,33a

group of the host resin.

The absorptions attributable to analogue catalyst 2 displayed bands at ca. 1627, 1599, 1421, and

À1

+

n_a_s_y_m(COO) and n_s_y_m(COO) bands of the amino acid occurred at 1089 cm , which were ascribed to n_s_y_m(CN H ), n_a_s_y_m(COO),

3

5

À1

34

1

598 and 1422 cm , respectively, in MRAsn.

nsym(COO), and nsym(C–N) vibrations on the basis of literature

3

8

+

Upon incorporation of peroxotantalum species onto the findings. The band due to the nsym(CN

3

5

H ) mode does

functionalized polymers, new well-resolved bands representing not shift significantly after metal complexation, suggesting the

2

the characteristic n(O–O) modes of the Z -peroxo group, along non-participation of the guanidine group in co-ordination.

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17255

View Article Online

Paper

NJC

An indication of co-ordination of the carboxylate group to the protonated aromatic and aliphatic methine carbons of pristine

4

0b

2

Ta(V) centre in a unidentate fashion was obtained from the MR. The absence of signal at ca. 46 ppm due to the –CH Cl

observance of a band attributable to n_s_y_m(COO) at a relatively group and appearance of a new signal at around 64 ppm

À1

lower frequency of 1352 cm , although the exact shifting of the attributable to amine bound methylene carbon evidenced

corresponding n_a_s_y_m(COO) mode could not be determined with the replacement of Cl from –CH Cl with the amino acid to

2

1

8b,41

13

certainty, due to overlapping of the region with the symmetric form C–N bonds.

By analogy with the C spectrum of free

stretching frequency of the guanidine moiety. asparagine, two closely spaced peaks observed at 181 and 179 ppm

À1

Both the complexes showed bands near 1710 cm depicting in the case of MRAsn have been assigned to free carboxylate and

the presence of free –COOH groups in the compound. Broad amide C atoms, respectively. The spectrum of MRArg also displayed

À1

and strong n(OH) bands displayed at 3400–3500 cm showed a resonance due to the carboxylate C atom at 181 ppm.

the presence of lattice water in the complex. Due to the over-

lapping of n(N–H) vibrations with n(OH) modes of lattice water, resins, the intensity of the carboxylate carbon resonance at

these bands could not be assigned with certainty. ca. 181 ppm was observed to decrease in the spectra of both

.2.6 Electronic spectral studies. The diﬀuse reflectance the catalysts and an additional peak appeared at considerably

After anchoring of the metal complex to the functionalized

2

UV-visible spectra of complexes 1 and 2 showed two distinct peaks lower field of 219 ppm. The new resonance is characteristic

in the region 270–380 nm [Fig. S3 and S4 (ESI†)]. The peak at of a complexed carboxylate carbon, indicative of the metal

2

79 nm was attributed to the p - p* transition in the polymeric incorporation through the carboxylate group. The significant

39

resin, while a new peak was observed in both the complexes at downfield shift of nearly 39 ppm (Dd = dcomplex À dfree carboxylate

)

around 380 nm. This characteristic absorption of peroxotantalum relative to the free carboxylate peak reflected strong metal

species was ascribed to the peroxo to metal charge transfer band ligand interactions, as has also been observed previously in

2

8

(LMCT) on the basis of the available literature.

the case of peroxo-Mo anchored valine and alanine function-

1

3

13

18b

13

2.2.7

C NMR analysis. The C NMR spectra of catalysts 1 alized MR.

In fact, previous reports showed that C NMR

and 2 recorded in the solid state are presented in Fig. 7 and chemical shifts induced by co-ordination have been widely used

Fig. S5 (ESI†), respectively. The corresponding resonances as a tool to interpret the mode of bonding of the co-ligands in

4

2

along with those of free MR as well as functionalized resins peroxometal compounds. The nearly unaltered position of

MRAsn and MRArg are provided in Table S3 (ESI†) for compar- the guanidyl carbon resonance in the spectrum of catalyst 2

ison. The assignments have been made based on reported at ca. 167 ppm negated the possibility of participation of the

1

8b,40

43

data although

there may be slight variations in the exact guanidyl group of arginine in metal co-ordination.

resonance positions depending on the NMR technique used viz.,

2.2.8 Thermogravimetric analysis. Thermograms of the pTa

solid or liquid state analysis. The resin after functionalization loaded catalysts 1 and 2 revealed a close analogy with the

displayed typical resonances corresponding to the respective decomposition pattern of the respective functionalized polymers

amino acid along with peaks due to quaternary aromatic, MRAsn and MRArg. The compounds undergo multistage degra-

dation upon heating up to a temperature of 700 1C (Fig. 8). As

seen in Table S4 (ESI†) in the case of MRAsn and MRArg, the

degradation step occurring between room temperature and

ca. 100 1C, due to the loss of water of crystallization, was

followed by a weight loss of 12.5% and 9.4% in the temperature

range of 148–257 1C and 155–239 1C, respectively. This degra-

dation has been attributed to the release of amino acids from

the polymer, based on available reports on the thermal

13

Fig. 7 Solid state C NMR spectra of (a) MRAsn and (b) catalyst 1.

Fig. 8 TG plot of (a) catalyst 1 and (b) catalyst 2.

1

7256 | New J. Chem., 2019, 43, 17251--17266

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online

NJC

Paper

4

decomposition characteristics of amino acids. The decompo-

sition observed in the temperature range of 284–700 1C was due

4

5

to the degradation of the base polymer.

In the thermograms of catalysts 1 and 2, a degradation

subsequent to the initial dehydration step, occurring in the range

of 104–146 1C and 104–145 1C, respectively, has been ascribed to

2 2

the loss of peroxo groups from the [Ta(O ) ] moieties anchored to

the polymer. The degradation corresponding to release of amino

acids from compounds 1 and 2 occurred in the temperature range

of 147–299 1C and 150–291 1C, respectively. The remaining resin

degraded in the temperature range of 300–700 1C with a weight

loss of 59.9% and 61.6%, respectively, from complexes 1 and 2.

The black residue obtained after complete degradation of the

complexes was analyzed with IR spectral analysis and was

devoid of any significant bands of the peroxo group, the amino

acid and the polymer matrix. Thus it has been confirmed

Fig. 9 Eﬀect of solvent on styrene conversion. Reaction conditions:

styrene (5 mmol), catalyst 1 (0.005 mmol of Ta, 13.5 mg), 30% H

10 mmol, 1.13 mL), 60 1C, solvent (5 mL), 2 h.

2

O

2

(

that the residue remaining after degradation of the catalysts Table 3 Eﬀect of temperature on styrene oxidation with 30% H O

2

consisted of the oxotantalum compound along with the char catalyzed by complex 1

residue of the polymer.

Entry Temperature Conversion (%) Epoxide selectivity (%) TON

2

.3 Catalytic activities of the supported complexes 1 and 2

1

2

3

4

RT

40

60

80

5

20

83

91

100

Z99

50

200

830

915

2.3.1 Alkene epoxidation. The catalytic performance of the

pTa complexes in alkene epoxidation was examined by con-

ducting exploratory experiments using styrene epoxidation as a

probe reaction in a variety of solvents as well as without solvent.

With an aim to optimize the reaction conditions for maximum

alkene conversion, the influence of reaction parameters such

as catalyst amount, oxidant concentration, solvent nature,

temperature and time was investigated using complex 1 as a

representative catalyst. The results presented in Table 2 and

Fig. 9 illustrate that the epoxidation reaction conducted under

solvent free conditions, maintaining a Ta : styrene molar ratio

in epoxidation without addition of any solvent for the subsequent

reactions.

Next, we have examined the influence of temperature on the

reaction rate by conducting the reaction under four diﬀerent

temperature conditions keeping the other variables constant

(Table 3 and Fig. 10). While there was only 5% conversion

at room temperature [Fig. 10 and Table 3 (entry 1)], a significant

leap in the rate of styrene conversion was observed at a

moderately elevated temperature of 60 1C [Fig. 10 and Table 3

2 2

of 1 : 1000 with 30% H O as a terminal oxidant (2 equivalents),

proceeded smoothly to provide good styrene conversion with

Z99% epoxide selectivity within 2 h [Fig. 9 and Table 2 (entry 5)].

To investigate the solvent eﬀect, apart from water, we have chosen

relatively safe organic solvents, omitting the use of perilous

chlorinated solvents. Interestingly, the epoxide was obtained as

the sole reaction product in each of the tested solvents under

similar reaction conditions, despite the relatively lower conver-

sions obtained in the presence of solvent. The likely cause of

the greater eﬃciency of the solvent free procedure appears to be

the reduced mobility experienced by the reactants in the

absence of solvent in the reaction mixture. Based on these

results, we have opted to study the activity of the catalysts

(

entry 3)]. On increasing the temperature further to 80 1C, 91%

conversion of styrene could be attained within 2 h [Fig. 10

and Table 3 (entry 4)]. Thus in order to obtain the highest TON

and TOF, without aﬀecting the epoxide selectivity, the reaction

temperature of 80 1C appeared to be optimal.

Table 2 Eﬀect of solvent on styrene oxidation with 30% H

by complex 1

2

O

2

catalyzed

a

Entry

Solvent

Conversion (%) Epoxide selectivity (%)

TON

1

2

3

4

5

H

2

O

27

8

6

83

Z99

100

Z99

270

80

60

830

3

CH OH

C

2

H

5

CN

OH

CH

—

3

Fig. 10 Eﬀect of temperature on styrene conversion. Reaction condi-

2 2

tions: styrene (5 mmol), catalyst 1 (0.005 mmol of Ta, 13.5 mg), 30% H O

(10 mmol, 1.13 mL), 2 h.

a

TON (turn over number) = mmol of product per mmol of catalyst.

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17257

View Article Online

Paper

NJC

Table 4 Eﬀect of H

complex 1

2

O

2

concentration on styrene oxidation catalyzed by

Table 5 Eﬀect of catalyst amount on styrene oxidation with 30% H

catalyzed by complex 1

2 2

O

Entry

2 2

H O (equiv.) Conversion (%) Epoxide selectivity (%) TON Entry Molar ratio (Ta : Sty) Conversion (%) Epoxide selectivity (%) TON

1

2

3

4

5

6

7

1

2

3

4

5

6

8

84

91

90

88

79

65

50

Z99

Z98

844

915

898

880

790

652

500

1

2

3

4

5

6

1 : 500

1 : 1000

1 : 1500

1 : 2000

—

95

91

80

69

11

24

Z98

Z99

477

915

1201

1384

—

a

b

1 : 2000

480

a

b

Blank experiment without any catalyst. Using Na

3

2

[Ta(O )

4

]ÁH

2

O as

the catalyst (1.0 mg, 0.0025 mmol Ta).

2 2

Fig. 11 Eﬀect of H O concentration on styrene conversion. Reaction condi-

Fig. 12 Eﬀect of catalyst amount (catalyst 1) on styrene conversion.

Reaction conditions: styrene (5 mmol), 30% H (10 mmol, 1.13 mL),

0 1C, 2 h.

tions: styrene (5 mmol), catalyst 1 (0.005 mmol of Ta, 13.5 mg), 80 1C, 2 h.

2 2

O

8

A systematic screening of the eﬀect of oxidant concentration

was subsequently performed using seven diﬀerent equivalents of a blank reaction conducted under catalyst free conditions

of 30% H ranging from 1–8 with respect to the substrate provided just 11% conversion of styrene within the stipulated

2 2

O

under otherwise identical reaction conditions. As can be seen reaction time [Fig. 12 and Table 5 (entry 5)]. Moreover, signifi-

from Table 4 and Fig. 11, an interesting trend with respect cantly lower conversion was obtained using free unsupported

3 2 4

to the % conversion of styrene versus oxidant concentration pTa complex Na [Ta(O ) ] as the catalyst [Fig. 12 and Table 5

emerged, although the epoxide selectivity remained close to (entry 6)]. That the enhanced activity displayed by the solid

9

9% irrespective of the amount of H O used. An increase in catalysts 1 and 2 is a consequence of immobilization of the pTa

2 2

the H

2

O

2

concentration from 1 to 2 equivalents led to a rise in species on a polymer support is evident from these observations.

The progress of the reaction monitored within a time span

the conversion of styrene from 84 to 91%, providing a reason-

ably good TON of 915 [Fig. 11 and Table 4 (entry 2)]. However, of 0.5 to 6 h showed a gradual increase in styrene conversion till

on a further increase of the oxidant a gradual decline in the the completion of the reaction occurring at 6 h [Table 6 and

overall styrene conversion was noted. Thus, styrene : H O = 1 : 2 Fig. 13]. The observation clearly indicated that the catalyst

2 2

was regarded as the optimal ratio for styrene conversion. retained its high activity and epoxide selectivity at an elevated

Dilution of the reacting species occurring due to the increasing temperature of 80 1C even on prolonging the reaction up to 6 h.

volumes of H O added to the reaction mixture beyond the

2

optimum requirement is likely to be responsible for the afore-

mentioned observation. Previous reports, including our own

past experiences with organic oxidations, reveal that such a

dilution effect is not unusual in the case of metal catalyzed

Table 6 Eﬀect of reaction time on styrene oxidation with 30% H

catalyzed by complex 1

2 2

O

a

Time

(h)

Conversion

(%)

Epoxide

selectivity (%)

TOF

(h )

4

6

À1

H

2

O

2

induced organic oxidations.

Entry

TON

The reaction was further optimized with respect to the catalyst

1

2

3

4

5

6

0.5

1

2

3

4

26

27

69

71

87

Z99

520

553

1384

1386

1738

2000

1040

553

692

462

434

333

amount and the results are shown in Table 5 and Fig. 12. The

conversion increased to nearly 100% as the catalyst loading

increased while maintaining high selectivity. A catalyst : substrate

ratio of 1 : 2000 was considered as ideal for achieving high TON

along with complete epoxide selectivity in the presence of

6

100

a

TOF (turn over frequency) = mmol of product per mmol of catalyst per

2

2 2

equivalents of H O [Fig. 12 and Table 5 (entry 4)]. The result hour.

1

7258 | New J. Chem., 2019, 43, 17251--17266

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online

NJC

Paper

faster rate compared to styrene epoxidation. It is generally

assumed that oxidation of terminal alkenes is diﬃcult owing

4

9

to the presence of electron deficient double bonds. As shown

in Table 7, norbornene, a relatively bulky cyclic olefin, was

epoxidized with 95% selectivity under the reaction conditions

optimized for styrene epoxidation. Epoxidation of norbornene

has been receiving a great deal of interest owing to the utility of

its epoxide as pharmaceutical intermediates and in polymer

5

0

synthesis. No report appears to exist on norbornene epoxida-

tion mediated by Ta-based catalysts. In the case of cyclohexene,

100% conversion was achieved within 1 h, however the selec-

tivity towards the epoxide was observed to be moderate with

formation of diol as a secondary product.

Fig. 13 Eﬀect of reaction time on styrene conversion. Reaction condi-

tions: styrene (5 mmol), catalyst amount (0.0025 mmol of Ta, 6.8 mg), 30%

2.3.2 Sulfide oxidation. The encouraging results achieved

in the case of alkene epoxidation under solvent-less conditions

prompted us to explore the catalytic performance of com-

pounds 1 and 2 in sulfide oxidation in the absence of solvent.

2 2

H O (10 mmol, 1.13 mL), 80 1C.

Significantly, at 0.0025 mmol of catalyst the initial TOF of Accordingly, an initial reaction was carried out with thioanisole as

À1

approximately 1040 h was obtained within 30 min of starting the model substrate by maintaining a catalyst : substrate molar

the reaction [Fig. 13 and Table 6 (entry 1)].

ratio of 1 : 1000 and substrate : oxidant molar ratio of 1 : 2 under

Determination of the utilization eﬃciency of hydrogen per- solvent free conditions at room temperature. Under these condi-

À1

oxide or the eﬀective use of H

2

O

2

in the oxidation process is of tions, the oxidation proceeded rapidly (a TOF of 601 h

)

great interest as many transition metal catalysts are known (Table S5, entry 1, ESI†), hence the reaction aﬀorded a mixture

1

5a,47

to decompose H

eﬃciency percentage (defined as: 100 Â moles of H

sumed in the formation of the oxidized product/moles of H

2

O

2

at elevated temperatures.

The H

con- the reaction in the presence of diﬀerent solvents and examined

the eﬀect of various reaction parameters on the rate of the

2

O

2

of the sulfoxide and sulfone. We have subsequently screened

2 2

O

2 2

O

4

8

converted) [Text S1 (ESI†)] for epoxidation of styrene in the reaction in Table S5 (ESI†). MeOH emerged to be the best

present study was found to be 88%, which is reasonably high solvent for attaining complete oxidation of MPS with 100%

considering that the reaction was conducted at 80 1C and required sulfoxide selectivity within 40 min reaction time using 4 equivalents

6

2 2

h for completion. It is also notable that we have ascertained the of H O . Although a high TON of 1920 could be obtained

potential of the catalytic methodologies developed for alkene with a substantially low catalyst loading (Ta : S = 1 : 2000), a

epoxidation for relatively larger scale synthetic applications by catalyst : substrate molar ratio of 1 : 1000 was found to be

conducting the styrene epoxidation reaction at ten-fold scale optimal to obtain a high TOF without compromising the

f

under the optimized conditions (Table 7, entry 1 ).

sulfoxide selectivity (Table S5, entry 8, ESI†). The oxidation

Subsequent to optimization of the reaction conditions for reaction conducted in the absence of the catalyst in a control

epoxidation of styrene, a conjugated olefin, we proceeded to explore experiment provided a very low yield (14%) with poor selectivity

the potential of the catalytic procedure for wider applications (Table S5, entry 12, ESI†), whereas in the presence of the

and the results are summarized in Table 7. Both the pTa neat unsupported pTa complex Na

catalysts were found to be highly eﬀective in the epoxidation was 38% (Table S5, entry 13, ESI†). It is also notable that,

3

[Ta(O

2

)

4

]ÁH

2

O, the yield

of cyclohexene and norbornene, which occurred at a much despite the considerable rate enhancement of the reaction

a

Table 7 Selective oxidation of alkenes to epoxides with 30% H

2

O

2

catalyzed by catalysts 1 and 2

Catalyst 2

Catalyst 1

Selectivity

b

c

À1

b

c

À1

Entry Substrate Time (h) Conversion (%) Epoxide Others TON TOF (h ) Time (h) Conversion (%) Epoxide Others TON TOF (h

)

d

6

100_e

99

100

99

1

2000

1980

2000

333

330

333

6

84

97

95

97

3

5

3

1680

1640

1680

280

273

280

e

1

2

82_f

f

84

g

h

1

100

68

32

2000 2000

2

100

66

34

2000 1000

i

3

1

100

95

5

2000 2000

1.5

94

6

2000 1333

a

b

2 2

Reactions were carried out with 5 mmol of substrate and 10 mmol of 30% H O without solvent at 80 1C. Catalyst (0.0025 mmol of Ta). TON

c

(

turn over number) = mmol of product per mmol of catalyst. TOF (turn over frequency) = mmol of product per mmol of catalyst per hour.

d

e

f

g

Benzaldehyde. % conversion for the 5th reaction cycle. Scale-up reaction (5.7 g). 2-Cyclohexen-1-ol = 1.7%, 2-cyclohexen-1-one = 3.7%,

h

i

cyclohexane-1,2-diol = 26.6%. 2-Cyclohexen-1-ol = 1.9%, 2-cyclohexen-1-one = 3.2%, cyclohexane-1,2-diol = 28.9%. Norbornanone.

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17259

View Article Online

Paper

NJC

a

Table 8 Selective oxidation of sulfides to sulfoxides with 30% H

2

O

2

catalyzed by catalysts 1 and 2 at room temperature

Catalyst 1

Catalyst 2

b

c

À1

b

c

À1

Entry

1

Substrates

Time (min)

Isolated yield (%)

97

TON

TOF (h

)

Time (min)

Isolated yield (%)

95

TON

TOF (h

)

40

970

960

1447

1432

70

950

970

960

812

829

820

d

40

96

97

e

40

96

2

3

25

40

98

94

980

940

2333

1402

40

70

97

96

970

960

1448

820

4

5

6

7

45

40

96

97

94

95

53

960

970

940

950

530

1280

1448

289

271

88

80

70

95

97

94

98

51

950

970

940

980

510

714

829

256

245

85

195

210

360

220

240

360

8

a

All the reactions were carried out with 5 mmol of substrate and 20 mmol of 30% H

2

O

2

in 5 mL of solvent at RT. Catalyst (0.005 mmol of Ta).

b

d

c

TON (turn over number) = mmol of product per mmol of catalyst. TOF (turn over frequency) = mmol of product per mmol of catalyst per hour.

e

%

conversion for the 5th reaction cycle. Scale-up data (7.5 g of MPS).

conducted at 60 1C, the selectivity of the reaction system was the rates of oxidation displays the expected trend, which is also

1

8b–d,g,h, j,k

found to diminish with the formation of both the sulfoxide and in accord with previous literature.

sulfone (Table S5, entry 14, ESI†). Thus ambient temperature The catalysts displayed excellent chemoselectivity, as exem-

was found to be more favorable for the sulfoxidation reaction, plified by oxidation of allylic and alcoholic sulfides (Table 8,

in contrast to the epoxidation reaction, where the best results entries 6 and 7) to aﬀord the corresponding sulfoxide as the

were obtained at a relatively elevated temperature.

sole product without eﬀecting other oxidation prone functional

A broad range of structurally diverse sulfides were subjected groups, such as the CQC bond or –OH group. Moreover, the

to the standardized catalytic methodology in the presence of each H O efficiency percentage was observed to be consistently high

2

of the catalysts 1 and 2 under optimized conditions. The data (94–97%) in the presence of both catalysts 1 and 2 for the

presented in Table 8 demonstrate that all the tested substrates sulfoxidation reactions. The milder reaction conditions employed

were eﬀectively oxidized to form the respective sulfoxide as the for oxidation of sulfides (viz., room temperature and a relatively

exclusive product in excellent yield and TOF. Catalyst 1 showed shorter reaction time) are likely to be responsible for the relatively

2 2

relatively superior performance compared to catalyst 2, as has higher H O efficiency observed in sulfoxidation comparison to

been observed in the case of the epoxidation reaction. The lower styrene oxidation. The developed sulfoxidation procedure was also

e

activity of catalyst 2 may be attributed to the presence of relatively found to be amenable to ready scalability (Table 8, entry 1 ), as

bulky guanidine groups of arginine side chains, due to which the has been found in the case of the epoxidation reaction.

Ta bound peroxo groups are probably less readily accessible to the

2.3.3 Test for heterogeneity of the reactions. The hetero-

approaching substrate, compared to catalyst 1.

geneous nature of the catalytic processes was confirmed by

Our findings also revealed several attractive features of the conducting independent experiments using MPS or styrene as

developed environment friendly catalytic protocol. Importantly, the substrate representing each type of transformation. After

no overoxidation of the sulfoxide to the sulfone occurred for completion of the reaction and separating the solid catalyst, the

any of the tested substrates under these conditions even on filtrate obtained was treated with a fresh batch of reagents.

prolonging the reaction. It is further evident that dialkyl- The reactions were allowed to run for a further 2 h without the

sulfides (Table 8, entries 2 and 3) were more readily oxidized catalyst. That none of the catalytic reactions proceeds after

compared to less nucleophilic conjugated systems such as removal of the catalyst from the reaction mixture was evident,

aromatic and allylic sulfides. As thioether oxidation by H

2

O

2

as the conversions were found to be o18% in the case of

has been known to generally proceed via electrophilic addition styrene epoxidation, whereas for MPS oxidation it was o15%.

5

1

of an oxygen atom to the substrate, the observed variation in These values are quite close to the ones obtained for the respective

17260 | New J. Chem., 2019, 43, 17251--17266 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online

NJC

Paper

It is worthy of note that, keeping in view the environmental

aspect, we have strategically refrained from using any additional

acid or other hazardous additives in our oxidation procedures, as

far as possible. Thus, both types of transformations viz., olefin

epoxidation and sulfide oxidation, were carried out at the natural

pH of the reaction medium.

The merits of the developed catalytic epoxidation methodology

with respect to conversion, selectivity and the reaction conditions

employed, in comparison with several other reported hetero-

geneous catalyst systems for styrene epoxidation, are high-

lighted in Table 9. However, a precise comparison of the TON

or TOF obtained is not possible in the absence of suﬃcient

reported kinetic data. It is significant to note that, except for a

5

2

few reports, most of the metal catalyzed heterogeneous solvent-

Fig. 14 Recyclability of catalyst 1 for selective oxidation of sulfides and

styrene.

4

6b,49,53

free epoxidation processes utilized TBHP as an oxidant.

No report however appears to exist related to styrene epoxidation

catalyzed by a Ta based catalyst under solventless conditions.

blank experiments. Furthermore, the possibility of metal leaching As shown in Table 9, we have come across two reports on Ta

out of the support could be ruled out as the ICP-OES analysis of the catalyzed heterogeneous epoxidation of styrene using MeCN as

3

b,15b

filtrate showed no sign of metal presence.

.3.4 Recyclability of the catalysts. The immobilized cata- the performance of catalysts 1 and 2 in selective sufoxidation

lysts enabled easy and eﬃcient recovery from the spent reaction is superior to the activities of other Ta(V) catalysts reported

a solvent.

It is further evident from Table S6 (ESI†) that

2

6

b,14a,54

mixture by simple filtration or centrifugation. The recovered so far.

catalyst, after washing with acetone and drying under a vacuum, 2.3.5 Proposed catalytic cycle. It has already been established

was recharged in the subsequent reaction run without further by work from several laboratories that epoxidation reactions

0

conditioning. The catalyst recyclability in olefin epoxidation and catalyzed by d transition metal peroxo systems usually follow a

oxidation of thioether was probed independently using styrene common reaction pathway which involves the direct electrophilic

or MPS under the respective optimized reaction conditions, up transfer of the oxygen atom of the peroxo group to the alkene

5

to five consecutive cycles of oxidation in each case.

through a spiro-like transition state in a concerted step. Although

e

d

6c,7b,15a,56

The results given in Table 7 (entry 1 ) and Table 8 (entry 1 ) Ta(V) peroxo systems still remain relatively unexplored,

2

and Fig. 14 illustrate that the activity and selectivity of the involvement of a catalytically active Ta(Z -O

2

) intermediate species

catalysts even after several cycles of oxidation did not show any in olefin epoxidation with related supported Ta catalysts has

6c,7a,b,15a

significant alteration. The used catalysts were further character- been proposed previously.

ized by FTIR, XRD and EDX spectral studies. The IR (Fig. 5 and Taking into account the aforementioned observations and on the

Fig. S2, ESI†) and XRD patterns (Fig. 3) of the recovered catalysts basis of the findings of the present study, we have proposed a

displayed close resemblance with those of the fresh catalysts. credible catalytic cycle for the selective styrene epoxidation mediated

Furthermore, the elemental analysis and EDX spectral data of by pTa catalysts 1 and 2. As shown in Fig. 15, in the first step the

the recovered catalysts showed no significant loss in peroxide transfer of electrophillic oxygen from the diperoxotantalate complex

content and metal loading compared with the fresh ones. These of the catalyst to the substrate occurs to form the corresponding

findings clearly demonstrated that the catalysts are structurally epoxide, with concomitant formation of oxoperoxotantalate

robust and are capable of retaining their activity even after reuse intermediate II (reaction (a)). The resulting monoperoxotantalate

in repeated reaction cycles, notwithstanding the relatively higher intermediate after the formation of the epoxide combines with the

temperature employed in the case of alkene oxidation.

peroxide of H O to regenerate the starting complex (I) leading to

2 2

Table 9 The comparison of the activity of pTa catalysts 1 and 2 with various heterogeneous catalysts in the epoxidation of styrene

Conditions

[time, temperature, oxidant, solvent]

Conversion (%)/epoxide

selectivity (%)

Entry

Catalyst

Catalyst amount

Ref.

À

1

2

3

4

5

6

7

8

9

[Ta(O

Ta–SiO

2

)

2

(Asn)

2

] -MR

0.002 mmol

0.01 mmol

0.015 mmol

0.02 mmol

6 h, 80 1C, 30% H

6 h, 65 1C, 30% H

24 h, 70 1C, TBHP, CH

5 h, 80 1C, TBHP, solvent free

2

O

2

, solvent free

100/99

84/97

37/36

73/34

28.8/10.8

95/80

58/56

85/10.6

90/38

This work

3b

15b

46b

49

52a

53a

53b

À

2

(Arg)

2

] -MR

, CH

CN

3

CN

DET-Ta-MCM650

3

a-ZrPÁFe(III)

À3

MP-MoOO

2

1.25 Â 10 mmol

30 min, 95 1C, TBHP, solvent free

(PW11

SBA15-NH

MoO(O (phox)/Fe

[MoO(O (phox)]/SBA-15

)

2

/Al

2

O

3

25 mg

4 h, 80 1C, O

2

, solvent free

2

-DAMO-Ni

50 mg

0.0005 mmol

24 h, 60 1C, TBHP, solvent free

60 min, 95 1C, TBHP, solvent free

2

)

2

3

O

4

1

0

2

)

2

87/30

53c

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17261

View Article Online

Paper

NJC

Fig. 15 The proposed mechanism.

a catalytic cycle (reaction (b)). Formation of such an oxoperoxo- L-arginine (1.08 g, 6.25 mmol) in 20 mL water was added and

tantalate intermediate during oxygen transfer from a pTa species the resulting mixture was refluxed for 24 h at 90 1C in the

56

to a substrate has been documented in the literature.

presence of pyridine (0.50 mL, 6.25 mmol). The overall molar

In the catalytic cycle proposed for sulfide oxidation (Fig. 15), the ratio of Cl : amino acid : pyridine on the basis of the percent

facile transfer of the peroxo oxygen from the diperxotantalum(V) replaceable chlorine on the polymer was maintained at approxi-

complex of the catalyst to the organic sulfide to yield the sulfoxide mately 1 : 1.25 : 1.25. The reaction mixture was subsequently

(reaction (c)) is accompanied by simultaneous formation of mono- cooled and allowed to stand for one week with occasional

peroxotantalate intermediate II. The original catalyst is regenerated stirring. The incorporation of the amino acid was indicated

subsequently (reaction (b)) when the monoperoxotantalate complex by a change of colour of the polymer beads from off white to

reacts with hydrogen peroxide. The above catalytic cycle is in yellow. The amino acid functionalized polymer beads were

line with the mechanisms proposed for several other reported then filtered and washed repeatedly with hot water until no

1

8b–d,g,h, j,k,51d,57

peroxometal catalyzed sulfide oxidation reactions.

precipitate of AgCl was observed in the filtrate on treating with

AgNO . This was followed by washing with ethanol and the

3

beads of MRArg or MRAsn obtained were finally dried under a

vacuum at 90 1C for 8 h.

3

Experimental

3.1 Materials

3

.3 Preparation of sodium tetraperoxotantalate

Acetone, methanol, acetonitrile, ethylacetate, hydrogen peroxide,

diethyl ether, sodium hydroxide, potassium dichromate,

Na [Ta(O ) ]ÁH O (pTa)

3

2 4

2

sulfuric acid (E. Merck, India), sodium thiosulphate petroleum The Na

3

[Ta(O

2

)

4

]ÁH

2

O complex was prepared by adopting a

2

0a,d,58

ether (boiling range 60–80 1C) (RANKEM), boric acid, sodium reported procedure with slight modifications.

bicarbonate, potassium iodide, silica gel (60–120 mesh) (SRL), crucible, 1 g of tantalum oxide (Ta ) and 1.6 g of NaOH were

fused together at 700 1C. The product obtained was cooled and

dissolved in 70 mL of 1 M 30% H O with continuous stirring

In a nickel

2 5

O

L-asparagine (Asn), L-arginine (TCI Chemicals (India) Pvt. Ltd),

À1

chloromethylated poly(styrene–divinylbenzene) (2.5 mmol g

2 2

to get a clear solution. The solution was then filtered and

Cl loading, 2% DVB) (MR), pyridine, tantalum pentoxide,

methyl phenyl sulfide (MPS), methyl p-tolylsulfide (MpTS), ethyl the filtrate was allowed to settle in an ice-bath for 12 h. The

phenyl sulfide (EPS), dimethyl sulfide (DMS), dibutylsulfide tetraperoxotantalate was isolated as a white crystalline solid,

(

DBS), 2-(phenylthio)ethanol (PTE), diphenylsulfide (DPS) and which was then dried at room temperature.

allyl phenyl sulfide (APS) were obtained from the Sigma-Aldrich

Chemical Company, Milwaukee, USA. Before functionalization,

the resin was pre-treated with aqueous dioxane (50 : 50 (v/v))

followed by washing with methanol and dried under a vacuum

at 90 1C for 8 h. Distilled and deionized water was used for

solution preparation.

3

.4 Synthesis of supported diperoxotantalum compounds

À

[

(

Ta(O

2

)

2

(L)

catalyst 2)]

2

] -MR, [L = asparagine (catalyst 1) or arginine

Sodium tetraperoxotantalate Na ]ÁH

3

[Ta(O

2

)

4

2

O (pTa) (1.0 g,

2.5 mmol) was dissolved in 30% H O (10 mL, 88.49 mmol)

2 2

at ambient temperature. The pH of the reaction solution was

observed to be ca. 6. Keeping the temperature below 4 1C, 1 g of

3.2 Preparation of amino acid grafted polymers

The functionalization of chloromethylated poly(styrene–divinyl- MRAsn or MRArg was added to the solution, which was pre-

benzene) (MR) with amino acids L-asparagine or L-arginine was swelled in 5 mL ethanol for 1 h. The mixture was constantly

18b,25

done by following reported methods with some modifications.

stirred for 24 h in an ice bath. After decanting the supernatant

Pre-washed MR beads (2 g, 5 mmol of Cl) were kept for swelling liquid, the resulting residue was repeatedly washed with acetone.

in 6 mL methanol for 1 h. To the swollen polymer in methanol, The products were separated by centrifugation and dried

an aqueous solution of L-asparagine (0.83 g, 6.25 mmol) or in vacuo over concentrated sulfuric acid.

17262 | New J. Chem., 2019, 43, 17251--17266

View Article Online

NJC

Paper

3

.5 Elemental analysis

Magnetic susceptibilities of the complex were determined by

the Gouy method with Hg[Co(NCS)] as the calibrant. The

melting points of the products were determined on a B u¨ chi

Melting Point B-540. GC analysis was carried out using an

Agilent 7890A gas chromatograph (GC/GC-MS) with an FID

and a 240 ion trap mass detector.

A PerkinElmer 2400 series II elemental analyzer was used to

determine the C, H, and N amounts of the synthesized com-

pounds. The sodium and tantalum content were estimated

by inductively coupled plasma-optical emission spectroscopy

(ICP-OES). EDX analysis was also used to determine the compo-

sition of the compounds. The peroxide amount in the com-

pounds was measured volumetrically by the iodometric method

where a weighed amount of the compound was added to a cold

solution of 1.5% boric acid (w/v) in 0.7 M sulfuric acid (100 mL)

3

.7 General procedure for epoxidation of alkenes

The catalytic protocol of epoxidation was as follows: to the reaction

mixture of the catalyst (containing 0.0025 mmol of Ta) [catalyst 1

(6.8 mg) or catalyst 2 (7.8 mg)] and styrene (5.0 mmol), 30% H O₂

5

9

2

and titrated with standard sodium thiosulfate solution.

(1.13 mL, 10 mmol) was added to initiate the reaction at 80 1C under

continuous stirring. The molar ratio of Ta : substrate : oxidant was

maintained at 1 : 2000 : 4000. The progress of the reaction was

3.6 Physical and spectroscopic measurements

The IR spectra of the samples were recorded as KBr pellets monitored by HPLC. At 80 1C, the distinct phase separation between

using a PerkinElmer spectrum 100 FTIR spectrophotometer. the organic and aqueous phases of the reaction mixture nearly

The Raman spectra of the compounds were measured using disappeared as the organic substrate became partially miscible with

2 2

a EZRaman-N (Enwaveoptronics) that was equipped with a aqueous H O and the reaction mixture turned cloudy. To monitor

diode laser with an excitation wavelength of 785 nm and a the progress of the reaction, aliquots of the reaction mixture were

laser maximum output power of 350 mW. The measurement withdrawn periodically after stopping stirring, which caused the

parameters were 10 s exposure time, 5 accumulation, laser solid catalyst to settle at the bottom of the round-bottomed flask.

power 10% of output power and a 100Â objective and the The product and unreacted substrates in the samples were extracted

À1

pixel resolution was set to 1.44 cm per pixel. The diﬀuse with ethyl acetate. The extracted samples were analyzed with HPLC

reflectance electron absorption spectra of the compounds were to monitor the progress of the reaction. After completion of the

recorded using a Hitachi U-3400 spectrophotometer equipped reaction, the solid catalyst was separated by filtration and washed

with a diﬀuse reflectance accessory with an integrating sphere with acetone for further use.

of 60 mm inner diameter and BaSO was used as the standard.

The quantitative analysis of styrene and its oxidized products was

4

The powder X-ray diﬀraction (XRD) patterns were recorded on a performed on a Thermo-Scientific Dionex Ultimate 3000 HPLC

Rigaku X-ray diﬀractometer (Miniflax, UK) at a scanning rate system equipped with a UV detector. The products were detected

À1

of 10 1C min in the 2y range 10–701 with the use of Cu Ka at a wavelength of 254 nm and well separated by the use of a

(

k = 0.154 nm) radiation. XPS measurements were performed on reversed phase C18 column (250 Â 4.6 mm). The mobile phase was

a Thermo Fisher Scientific X-ray photo spectrometer with an composed of acetonitrile, methanol and water in a volume ratio of

Al Ka (monochromatic) X-ray source. The source was operated 2:3:5 with a flow rate of 1 mL min and an injection volume of

À1

À9

at 12 kV and 2 Â 10 mbar is the maintained base pressure in 20 mL. The substrate and products were identified by using authentic

the analysis chamber. The charging of the samples was rectified samples. The content of the compounds in the sample was deter-

by setting the binding energy of adventitious carbon (C 1s) at mined directly from interpolation of the calibration curves.

2

84.6 eV. Thermogravimetric analysis (TGA) was done on a

3

.8 General procedure for oxidation of sulfide to sulfoxides

SHIMADZU TGA-50 system under a N

rate of 10 1C min

2

atmosphere at a heating

À1

by using an aluminium pan. A JEOL In a typical reaction, the catalyst (0.005 mmol of Ta) [catalyst 1

JSM-6390LV scanning electron microscope with an attached (13.5 mg) or catalyst 2 (15.6 mg)] and 5 mL of solvent were

2 2

energy-dispersive X-ray detector was used to carry out scanning taken in a 50 mL two-necked round-bottomed flask. 30% H O

electron microscopy (SEM) and energy-dispersive X-ray analysis (2.26 mL, 20 mmol) was added to the reaction mixture with

of the compound. Scanning was carried out in the 1–20 mM constant magnetic stirring at room temperature. This was followed

range, and the images were taken at a magnification of 15–20 kV. by the subsequent addition of the substrate (MPS) (5 mmol) to the

Data were obtained using INCA software. Standardization of the mixture. The progress of the reaction was monitored by thin layer

data analysis is an essential part of the SEM-EDX instrument. chromatography (TLC) and GC. After completion of the reaction,

1

3

The C NMR spectra of the compounds were recorded using a the catalyst was separated out from the reaction mixture by

JEOL JNM-ECX400II spectrometer at a carbon frequency of filtration and washed with acetone. The reaction products as

1

5

00.5 MHz using 1024 X-resolution points, number of scans well as the unreacted organic substrates were then extracted

44, 3.5 ms acquisition time and 5 s relaxation delay. The surface with diethyl ether and dried over anhydrous Na SO followed by

2

4

areas were determined by nitrogen adsorption/desorption distillation under reduced pressure to eliminate the excess

measurements based on the Brunauer–Emmett–Teller (BET) diethyl ether. The products were then purified by column

method at 77.3 K on a standard module NOVA 1000E, Quanta- chromatography using ethyl acetate–hexane (1 : 9) as the sol-

chrome Instruments. The pore size and pore volumes were vent system. The obtained products were characterized by using

measured by the use of the Barrett–Joyner–Halenda (BJH) IR and NMR spectral analysis and melting point determination

model using a NOVA 1000E, Quantachrome Instruments. for solid products [Text S2, ESI†].

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17263

View Article Online

Paper

.9 Procedure for regeneration of the catalyst

NJC

3

acknowledged. The authors are thankful to Mr D. Shriniwas,

National Chemical Laboratory (NCL), Pune, India for XPS

analysis.

The recyclability of the catalysts was examined using styrene as

the substrate for epoxidation. After completion of the reaction

as mentioned under Section 3.7, the heterogeneous catalyst was

separated by filtration, washed with acetone and dried in vacuo.

For the next cycle, the recovered solid catalyst was added to a fresh References

reaction mixture of styrene (5 mmol) and 30% H O (10 mmol)

to repeat the experiment under the optimized conditions. The

progress of the reaction was monitored by HPLC.

In the case of oxidation of MPS to sulfoxide, the solid

catalyst was similarly recovered and was placed in a fresh

reaction mixture comprising MeOH (5 mL), MPS (5 mmol)

2

1

(a) S. M. Roberts and J. Whittall, Regio- and Stereo-Controlled

Oxidations and Reductions, Wiley-Interscience, New York,

2

007, vol. 5; (b) F. Cavani and J. H. Teles, ChemSusChem,

009, 2, 508; (c) K. Bauer, D. Garbe and H. Surburg, Common

fragrance and flavor materials: preparation, properties and uses,

John Wiley & Sons, New York, 2008; (d) S. Caron, R. W. Dugger,

S. G. Ruggeri, J. A. Ragan and D. H. B. Ripin, Chem. Rev., 2006,

and 30% H

cycle under the standardized conditions for sulfide oxidation

Section 3.8). The oxidation reactions were repeated up to five

reaction cycles in each case.

2 2

O (20 mmol) to carry forward the subsequent

106, 2943.

(

2

(a) T. Toru and C. Bolm, Organosulfur chemistry in asymmetric

synthesis, John Wiley & Sons, New York, 2008; (b) H. Cotton,

T. Elebring, M. Larsson, L. Li, H. S ¨o rensen and S. von Unge,

Tetrahedron: Asymmetry, 2000, 11, 3819; (c) M. C. Carre n˜ o,

G. Hern ´a ndez-Torres, M. Ribagorda and A. Urbano, Chem.

Commun., 2009, 6129.

4

Conclusions

In summary, we have developed new heterogeneous catalysts

comprising peroxotantalum(V) complexes immobilized on

asparagine and arginine grafted cross-linked chloromethylated

poly(styrene–divinylbenzene) resin which satisfactorily cata-

lyzed the epoxidation of olefins with excellent TON and TOF

under solvent free condition. To our knowledge, this report is

the first to demonstrate the use of peroxotantalate based

heterogeneous catalysts for solvent free olefin epoxidation.

The versatility of the catalysts is further evident from their

ability to facilitate the chemoselective oxidation of a broad

range of structurally diverse thioethers to the desired sulfoxides

in impressive yield and TOF in methanol at ambient tempera-

ture. The catalysts are sufficiently robust to afford easy

and successful regeneration with reusability at least up to a

minimum of five reaction cycles in all cases without any

3 (a) D. C. Sherrington, Catal. Today, 2000, 57, 87; (b) N. E.

Thornburg, A. B. Thompson and J. M. Notestein, ACS Catal.,

2015, 5, 5077; (c) M. G. Clerici and O. A. Kholdeeva, Liquid

Phase Oxidation via Heterogeneous Catalysis: Organic Synthesis

and Industrial Applications, Wiley, Hoboken, NJ, 2013;

(d) J. M. Thomas and W. J. Thomas, Principles and Practice

of Heterogeneous Catalysis, Wiley VCH, New York, NY, 2005;

(e) A. Corma, Chem. Rev., 1997, 97, 2373; ( f ) R. A. Sheldon,

J. Mol. Catal., 1980, 7, 107; (g) J. M. Thomas, R. Raja and D. W.

Lewis, Angew. Chem., Int. Ed., 2005, 44, 6456; (h) J. Liang,

Z. Liang, R. Zou and Y. Zhao, Adv. Mater., 2017, 29, 1701139.

4 (a) N. Morlan ´e s and J. M. Notestein, J. Catal., 2010, 275, 191;

(b) M. Dusi, T. Mallat and A. Baiker, Chem. Rev., 2000, 42, 213.

5 (a) J. M. Notestein, E. Iglesia and A. Katz, J. Am. Chem. Soc.,

2004, 126, 16478; (b) F. Bonino, A. Damin, G. Ricchiardi,

M. Ricci, G. Spano, R. D’Aloisio, A. Zecchina, C. Lamberti,

C. Prestipino and S. Bordiga, J. Phys. Chem. B, 2004, 108, 3573.

6 (a) V. Cimpeanu, V. Parvulescu, V. I. Parvulescu, M. Capron,

P. Grange, J. M. Thompson and C. Hardacre, J. Catal., 2005,

235, 184; (b) M. Fadhli, I. Khedher and J. M. Fraile, J. Mol.

Catal. A: Chem., 2015, 410, 140; (c) D. A. Ruddy and T. D.

Tilley, J. Am. Chem. Soc., 2008, 130, 11088; (d) D. Meunier,

A. de Mallmann and J. M. Basset, Top. Catal., 2003, 23, 183;

(e) P. Guillo, M. I. Lipschutz, M. E. Fasulo and T. D. Tilley,

ACS Catal., 2017, 7, 2303; ( f ) R. L. Brutchey, C. G. Lugmair,

L. O. Schebaum and T. D. Tilley, J. Catal., 2005, 229, 72.

2 2

significant loss in activity or selectivity. A high H O efficiency

percentage and ready scalability are additional salient features

of the catalytic strategies. Most importantly, being absolutely

free from halogenated solvent, co-solvent or co-catalysts or any

other hazardous auxiliaries, the presented reaction protocols are

clean and eco-compatible. Ease of preparation of the catalysts,

commercially available starting materials, and simplicity in the

work-up procedure are other synthetically valuable attributes of

the catalytic systems, making them potentially attractive for

practical applications.

Conflicts of interest

7

(a) D. A. Ruddy, R. L. Brutchey and T. D. Tilley, Top. Catal.,

008, 48, 99; (b) D. A. Ruddy and T. D. Tilley, Chem.

2

There are no conflicts to declare.

Commun., 2007, 3350.

8

(a) R. Noyori, M. Aoki and K. Sato, Chem. Commun., 2003,

1

977; (b) C. W. Jones, Applications of Hydrogen Peroxide and

Acknowledgements

Derivatives, Royal Society of Chemistry, Cambridge, 1999;

(c) B. S. Lane and K. Burgess, Chem. Rev., 2003, 103, 2457;

(d) H. Srour, P. Le Maux, S. Chevance and G. Simonneaux,

Coord. Chem. Rev., 2013, 257, 3030.

Financial support from Science and Engineering Research

Board, Department of Science and Technology, New Delhi,

India under Grant No. EMR/2016/003158 is gratefully

17264 | New J. Chem., 2019, 43, 17251--17266 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online

NJC

Paper

9

D. R. Mulford, J. R. Clark, S. W. Schweiger, P. E. Fanwick

and I. P. Rothwell, Organometallics, 1999, 18, 4448.

Rev., 2008, 109, 515; (e) X. S. Zhao, X. Y. Bao, W. Guo and

F. Y. Lee, Mater. Today, 2006, 9, 32.

10 Y. Matsuo, K. Mashima and K. Tani, Angew. Chem., Int. Ed., 20 (a) D. Bayot and M. Devillers, Coord. Chem. Rev., 2006,

2

001, 40, 960.

250, 2610; (b) D. Bayot, B. Tinant and M. Devillers, Inorg.

Chem., 2004, 43, 5999; (c) C. Djordjevic and N. Vuletic, Inorg.

Chem., 1968, 7, 1864; (d) A. C. Dengel and W. P. Griﬃth,

Polyhedron, 1989, 8, 1371; (e) V. Petrykin, M. Kakihana,

K. Yoshioka, S. Sasaki, Y. Ueda, K. Tomita, Y. Nakamura,

M. Shiro and A. Kudo, Inorg. Chem., 2006, 45, 9251.

21 D. T. Bregante, N. E. Thornburg, J. M. Notestein and

D. W. Flaherty, ACS Catal., 2018, 8, 2995.

1

1 (a) E. Le Roux, M. Chabanas, A. Baudouin, A. de Mallmann,

C. Cop ´e ret, E. A. Quadrelli, J. Thivolle-Cazat, J. M. Basset,

W. Lukens, A. Lesage and L. Emsley, J. Am. Chem. Soc., 2004,

1

26, 13391; (b) Y. Chen, E. Abou-Hamad, A. Hamieh,

B. Hamzaoui, L. Emsley and J. M. Basset, J. Am. Chem.

Soc., 2015, 137, 588.

2 M. C. Burland, T. W. Pontz and T. Y. Meyer, Organometallics,

1

2

002, 21, 1933.

22 (a) R. B. Merrifield, J. Am. Chem. Soc., 1963, 85, 2149; (b) S. B.

Roscoe, C. Gong, J. M. Fr ´e chetand and J. F. Walzer, J. Polym.

Sci., Part A: Polym. Chem., 2000, 38, 2979; (c) S. Gil,

R. Gonzalez, R. Mestres, V. Sanz and A. Zapater, React. Funct.

Polym., 1999, 42, 65.

1

3 (a) K. J. Weller, P. A. Fox, S. D. Grayand and D. E. Wigley,

Polyhedron, 1997, 16, 3139; (b) L. L. Anderson, J. Arnoldand

and R. G. Bergman, Org. Lett., 2004, 6, 2519.

1

4 (a) M. Kirihara, J. Yamamoto, T. Noguchi, A. Itou, S. Naito

and Y. Hirai, Tetrahedron, 2009, 65, 10477; (b) J. Black, Clin. 23 (a) A. Gergely, I. Nagypal and E. Farkas, J. Inorg. Nucl. Chem.,

Mater., 1994, 16, 167.

1975, 37, 551; (b) L. Lomozik and A. Wojciechowska,

´

5 (a) P. J. Cordeiro and T. D. Tilley, Langmuir, 2011, 27, 6295;

Polyhedron, 1989, 8, 1; (c) A. David, E. T. Hartman, N. Lihi,

I. S o´ v ´a g o´ and K. V ´a rnagy, New J. Chem., 2018, 42, 8131;

(d) M. C. Lim, J. Chem. Soc., Dalton Trans., 1977, 1398;

(e) I. S o´ v ´a g ´o , C. K ´a llay and K. V ´a rnagy, Coord. Chem. Rev.,

2012, 256, 2225.

(b) M. Fadhli, I. Khedher and J. M. Fraile, C. R. Chim, 2017,

20, 827.

6 (a) M. L. Lin, K. Hara, Y. Okubo, M. Yanagi, H. Nambu and

A. Fukuoka, Catal. Commun., 2011, 12, 1228; (b) I. Nowak,

A. Feliczak, I. Nekoksov ´a and J. Cejka, Appl. Catal., A, 2007, 24 (a) H. Eljajouli, M. Laabd, M. Elamine and A. Albourine, J. Mater.

ˇ

3

21, 40.

Eng. Struct., 2017, 8, 2421; (b) Y. Shimazaki, M. Takani and

O. Yamauchi, Dalton Trans., 2009, 7854; (c) E. R. Clarke and

A. E. Martell, J. Inorg. Nucl. Chem., 1970, 32, 911.

1

7 (a) R. L. Brutchey, D. A. Ruddy, L. K. Andersen and T. D.

Tilley, Langmuir, 2005, 21, 9576; (b) K. Lin, P. P. Pescarmona,

K. Houthoofd, D. Liang, G. Van Tendelooand and A. Jacobs, 25 V. B. Valodkar, G. L. Tembe, M. Ravindranathan, R. N. Ram

J. Catal., 2009, 263, 75; (c) R. Ballesteros, Y. P ´e rez, M. Fajardo,

and H. S. Rama, J. Mol. Catal. A: Chem., 2003, 202, 47.

I. Sierraand and I. del Hierro, Microporous Mesoporous Mater., 26 (a) L. Sen, W. Kuan, C. K.-C. Alan, Z. Ming, W. Jing, C. Y. Gang,

2

008, 116, 452.

B. YuHua, W. TaiMing and Z. ZhiRen, Sci. China: Chem., 2012,

55, 1134; (b) J. W. Kim, K. J. Kim, S. Y. Park, K. U. Jeong and

M. H. Lee, Bull. Korean Chem. Soc., 2012, 33, 2966.

1

8 (a) J. J. Boruah, D. Kalita, S. P. Das, S. Paul and N. S. Islam,

Inorg. Chem., 2011, 50, 8046; (b) J. J. Boruah, S. P. Das,

S. R. Ankireddy, S. R. Gogoi and N. S. Islam, Green Chem., 27 (a) R. V. Gonçalves, R. Wojcieszak, P. M. Uberman, S. R. Teixeira

2

013, 15, 2944; (c) J. J. Boruah, S. P. Das, R. Borah,

S. R. Gogoi and N. S. Islam, Polyhedron, 2013, 52, 246;

d) S. P. Das, J. J. Boruah, N. Sharma and N. S. Islam,

J. Mol. Catal. A: Chem., 2012, 356, 36; (e) S. P. Das,

and L. M. Rossi, Phys. Chem. Chem. Phys., 2014, 16, 5755;

(b) I. Perez, V. Sosa, F. G. Perera, J. T. E. Galindo, J. L. E.

Carrejo, P. G. M. Gonzalez and C. I. R. Rodriguez, 2018,

arXiv:1804.02067.

(

S. R. Ankireddy, J. J. Boruah and N. S. Islam, RSC Adv., 28 S. Q. Shi, Y. G. Chen, J. Gong, Z. M. Dai and L. Y. Qu,

012, 2, 7248; ( f ) D. Kalita, S. Sarmah, S. P. Das, D. Baishya, Transition Met. Chem., 2005, 30, 136.

A. Patowary, S. Baruah and N. S. Islam, React. Funct. Polym., 29 S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc.,

2

008, 68, 876; (g) N. S. Islam and J. J. Boruah, J. Chem. Sci.,

015, 127, 777; (h) J. J. Boruah, K. Ahmed, S. Das, 30 E. P. Barrett, L. G. Joyner and P. P. Halenda, J. Am. Chem.

Soc., 1951, 73, 373–380.

Catal. A: Chem., 2016, 425, 21; (i) G. Saikia, S. R. Gogoi, 31 (a) K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou,

1938, 60, 309–319.

S. R. Gogoi, G. Saikia, M. Sharma and N. S. Islam, J. Mol.

J. J. Boruah, B. M. Ram, P. Begum, K. Ahmed, M. Sharma,

G. Ramakrishna, T. Ramasarma and N. S. Islam, Chemistry-

Select, 2017, 21, 5838; ( j) G. Saikia, K. Ahmed, S. R. Gogoi,

M. Sharma, H. Talukdar and N. S. Islam, Polyhedron, 2019,

R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure Appl.

Chem., 1985, 57, 603; (b) S. J. Gregg and K. S. W. Sing,

Adsorption, Surface Area and Porosity, Academic Press,

London, 1982; (c) M. Thommes, K. Kaneko, A. V. Neimark,

J. P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol and

K. S. Sing, Pure Appl. Chem., 2015, 87, 1051; (d) S.-J. Park,

D.-I. Seo and C. Nah, J. Colloid Interface Sci., 2002, 251,

225–229.

159, 192; (k) S. R. Gogoi, K. Ahmed, G. Saikia and N. S. Islam,

J. Ind. Chem. Soc., 2018, 95, 801.

9 (a) K. C. Gupta, A. K. Sutar and C. C. Lin, Coord. Chem. Rev.,

1

2009, 253, 1926; (b) M. Boudart, Catalysis by supported

metals, Academic Press, Advances in catalysis, 1969; 32 D. T. Gokak and R. N. Ram, J. Mol. Catal., 1989, 49, 285.

c) C. A. McNamara, M. J. Dixon and M. Bradley, Chem. 33 (a) V. B. Valodkar, G. L. Tembe, M. Ravindranathan and

Rev., 2002, 102, 3275; (d) P. Barbaro and F. Liguori, Chem. H. S. Rama, React. Funct. Polym., 2003, 56, 1; (b) B. Altava,

(

This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17251--17266 | 17265

View Article Online

Paper

M. I. Burguete, E. Garcıa-Verdugo, S. V. Luis and M. J. Vicent,

NJC

R. Chokhare, P. Shrivastava and J. S. Kirar, Indian J. Chem.,

2015, 54, 1032; (c) M. R. Maurya and S. Sikarwar, J. Mol. Catal. A:

Chem., 2007, 263, 175; (d) K. N. Bhagya and V. Gayathri,

J. Porous Mater., 2013, 20, 257.

Tetrahedron, 2001, 57, 8675; (c) K. Nakamoto, Infrared and

Raman Spectra of Inorganic and Co-ordination Compounds, Part

B, Wiley and Sons, New York, 1997; (d) B. Korb ´e ly, J. T. Kiss,

K. Hern ´a di and I. P ´a link o´ , J. Mol. Struct., 2007, 834, 345.

4 (a) J. Casado, J. T. Lopez Navarrete and F. J. Ramirez,

47 I. A. Salem, M. El-Maazawi and A. B. Zaki, Int. J. Chem.

Kinet., 2000, 32, 643.

3

J. Raman Spectrosc., 1995, 26, 1003; (b) S. Masilamani, 48 V. Hulea, A. L. Maciuca, F. Fajula and E. Dumitriu, Appl.

P. Ilayabarathi, P. Maadeswaran, J. Chandrasekaran and Catal., A, 2006, 313, 200.

K. Tamilarasan, Optik, 2012, 123, 1304; (c) S. Y. Venyaminov 49 B. Babaei, A. Bezaatpour, M. Amiri, S. Szunerits and

and N. N. Kalnin, Biopolymers, 1990, 30, 1243. R. Boukherroub, ChemistrySelect, 2018, 3, 2877.

5 (a) D. Bayot, M. Devillers and D. Peeters, Eur. J. Inorg. Chem., 50 (a) N. K. Raj, A. V. Ramaswamy and P. Manikandan, J. Mol.

3

2

005, 4118; (b) G. Haxhillazi and H. Haeuseler, J. Solid State

Catal. A: Chem., 2005, 227, 37; (b) Y. Bai, P. Chiniwalla,

E. Elce, R. A. Shick, J. Sperk, S. A. B. Allen and P. A. Kohl,

J. Appl. Polym. Sci., 2004, 91, 3023.

Chem., 2004, 177, 3045.

6 (a) S. Sarmah, D. Kalita, P. Hazarika, R. Borah and

N. S. Islam, Polyhedron, 2004, 23, 1097; (b) V. Ravinder 51 (a) M. Bonchio, V. Conte, M. A. De Conciliis, F. Di Furia,

and A. V. Prasad, Transition Met. Chem., 2007, 32, 23.

7 (a) K. Nakamoto, Infrared and Raman Spectra of Inorganic

and Co-ordination Compounds, Part B, Wiley and Sons,

New York, 5th edn, 1997, p. 60; (b) G. B. Deacon and

R. J. Phillips, Coord. Chem. Rev., 1980, 33, 227.

F. P. Ballistreri, G. A. Tomaselli and R. M. Toscano, J. Org.

Chem., 1995, 60, 4475; (b) A. L. Maciuca, C. E. Ciocan,

E. Dumitriu, F. Fajula and V. Hulea, Catal. Today, 2008,

138, 33; (c) V. Conte and B. Floris, Inorg. Chim. Acta, 2010,

363, 1935; (d) V. Conte and O. Bortolini, The Chemistry of

Peroxides – Transition Metal Peroxides. Synthesis and Role in

Oxidation Reactions, Wiley Interscience, 2006, and refer-

ences cited therein.

3

8 (a) J. Herrklotz, Doctoral dissertation, University of Vienna,

2012; (b) A. Barth, Biochim. Biophys. Acta, Bioenerg., 2007,

1767, 1073; (c) S. Kumar and S. B. Rai, Indian J. Pure

Appl. Phys., 2010, 48, 251; (d) S. Mukerji and T. Kar, Mater. 52 (a) P. A. Shringarpure and A. Patel, Ind. Eng. Chem. Res., 2011,

Res. Bull., 1998, 33, 619; (e) A. Wojciechowska, A. G ˛a gor,

W. Zierkiewicz, A. Jarz ˛a b, A. Dylong and M. Duczmal, RSC

Adv., 2015, 5, 36295.

50, 9069; (b) O. Rogers, S. Pattisson, J. Macginley, R. Engel,

K. Whiston, S. Taylor and G. Hutchings, Catalysts, 2018, 8, 311;

(c) K. M. Parida, M. Sahoo and S. Singha, J. Catal., 2010, 276, 161.

39 (a) L. Gao, K. Deng, J. Zheng, B. Liu and Z. Zhang, Chem. 53 (a) L. Paul, B. Banerjee, A. Bhaumik and M. Ali, J. Solid State

Eng. J., 2015, 270, 444; (b) M. L. Kantam, T. Ramani,

L. Chakrapani and B. M. Choudary, J. Mol. Catal. A: Chem.,

Chem., 2016, 237, 105; (b) M. Zare and Z. Moradi-Shoeili, Appl.

Organomet. Chem., 2017, 31, 3611; (c) M. Zare, Z. Moradi-Shoeili,

¨

2007, 274, 11; (c) R. M. Silverstein, G. C. Bassler and T. C.

P. Esmailpour, S. Akbayrak and S. Ozkar, Microporous

Morrill, Spectrometric Identification of Organic Compounds,

John Wiley and Sons, New York, 1991, p. 294.

0 (a) F. Lorg ´e , A. Wagner and C. Mioskowski, J. Comb. Chem.,

Mesoporous Mater., 2017, 251, 173–180.

54 M. Kirihara, A. Itou, T. Noguchi and J. Yamamoto, Synlett,

2010, 1557.

4

1

2

999, 1, 25; (b) S. Mohanraj and W. T. Ford, Macromolecules, 55 (a) K. B. Sharpless, J. M. Townsend and D. R. Williams,

985, 18, 351; (c) K. Kawamoto and Y. Tsujimoto, J. Endod.,

004, 30, 45.

J. Am. Chem. Soc., 1972, 94, 295; (b) N. R o¨ sch, P. Gisdakis,

I. V. Yudanov and C. Di Valentin, in Peroxide Chemistry:

Mechanistic and Preparative Aspects of Oxygen Transfer,

ed. W. Adam, Wiley, 2000, pp. 601–619; (c) I. V. Yudanov,

J. Struct. Chem., 2007, 48, S111; (d) D. V. Deubel, G. Frenking,

P. Gisdakis, W. A. Herrmann, N. R ¨o sch and J. Sundermeyer,

Acc. Chem. Res., 2004, 37, 645; (e) P. Gisdakis, I. V. Yudanov

and N. R ¨o sch, Inorg. Chem., 2001, 40, 3755.

4

1 (a) M. Kassaee, S. Sayyed-Alangi and H. Sajjadi-Ghotbabadi,

Molecules, 2004, 9, 825; (b) A. LeTiran, J. P. Stables and

H. Kohn, Bioorg. Med. Chem., 2001, 9, 2693.

2 (a) A. C. Dengel, W. P. Griﬃth, R. D. Powell and A. C. Skapski,

J. Chem. Soc., Dalton Trans., 1987, 991; (b) S. E. Jacobson, R. Tang

and F. Mares, Inorg. Chem., 1978, 17, 3055; (c) L. Pettersson,

I. Andersson and A. Gorzs ´a s, Coord. Chem. Rev., 2003, 237, 77.

3 (a) S. R. Gogoi, J. J. Boruah, G. Sengupta, G. Saikia, K. Ahmed,

K. K. Bania and N. S. Islam, Catal. Sci. Technol., 2015, 5, 595;

56 (a) W. Ma, C. Chen, K. Kong, Q. Dong, K. Li, M. Yuan, D. Li

and Z. Hou, Chem. – Eur. J., 2017, 23, 7287; (b) W. Ma,

Y. Qiao, N. Theyssen, Q. Zhou, D. Li, B. Ding, D. Wang and

Z. Hou, Catal. Sci. Technol., 2019, 9, 1621.

4

(b) M. Assunta Girasolo, S. Rubino, P. Portanova, G. Calvaruso,

G. Ruisi and G. Stocco, J. Organomet. Chem., 2010, 695, 609; 57 (a) M. H. Dickman and M. T. Pope, Chem. Rev., 1994, 94, 569;

(

c) M. Nath, R. Yadav, G. Eng and P. Musingarimi, Appl.

(b) V. Conte, A. Coletti, B. Floris, G. Licini and C. Zonta, Coord.

Chem. Rev., 2011, 255, 2165; (c) B. M. Choudary, B. Reddy,

C. V. Bharathi and M. L. Kantam, J. Chem. Soc., Perkin Trans. 1,

2002, 2069.

Organomet. Chem., 1999, 13, 29.

4

4 (a) F. Rodante, G. Marrosu and G. Catalani, Thermochim.

Acta, 1992, 194, 197; (b) I. M. Weiss, C. Muth, R. Drumm and

H. O. Kirchner, BMC Biophys., 2018, 11, 2.

58 (a) C. W. Balke, J. Am. Chem. Soc., 1905, 27, 1140; (b) A. Sieverts

and E. L. M u¨ ller, Z. Anorg. Allg. Chem., 1928, 173, 297.

4

5 A. Mukherjee and M. Biswas, J. Appl. Polym. Sci., 1993, 50, 1485.

46 (a) M. Sharma, G. Saikia, K. Ahmed, S. R. Gogoi, V. G. Puranik 59 M. K. Chaudhuri, S. K. Ghosh and N. S. Islam, Inorg. Chem.,

and N. S. Islam, New J. Chem., 2018, 42, 5142; (b) S. Khare, 1985, 24, 2706.

17266 | New J. Chem., 2019, 43, 17251--17266 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

Article Doi

Polymer immobilized tantalum(v)-amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

DOI: 10.1039/c9nj04180j

Source and publish data:

Authors:

Article abstract of DOI:10.1039/c9nj04180j

Full text of DOI:10.1039/c9nj04180j

Products guided by the article

R&D Labs maybe for 104113-36-2

Relevant to this article

Hot Product