Application of silica-supported Shvo's catalysts for transfer hydrogenation of levulinic acid with formic acid

Accepted Manuscript Application of silica-supported Shvo's catalysts for transfer hydrogenation of levulinic acid with formic acid Dongmei He, István T. Horváth PII:

S0022-328X(17)30336-4

DOI:

10.1016/j.jorganchem.2017.05.039

Reference:

JOM 19965

To appear in:

Journal of Organometallic Chemistry

Received Date: 7 March 2017 Revised Date:

17 May 2017

Accepted Date: 18 May 2017

Please cite this article as: D. He, Istvá.T. Horváth, Application of silica-supported Shvo's catalysts for transfer hydrogenation of levulinic acid with formic acid, Journal of Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2017.05.039. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Application of Silica-Supported Shvo’s Catalysts for Transfer Hydrogenation of Levulinic Acid with Formic Acid Dongmei He and István T. Horváth* Department of Biology and Chemistry City University of Hong Kong, Kowloon, Hong Kong Email address of the corresponding author: [email protected]

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Highlights

• Triethoxysilylpropyl-functionalized Shvo’s catalyst precursors were prepared, characterized, and immobilized on silica by covalent anchoring and sol-gel methods. • The immobilized Shvo’s catalyst precursors were used for the transfer hydrogenation of levulinic acid with formic acid. • Hot filtration tests showed no leaching of the immobilized Shvo’s catalysts.

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Dedicated to Professor John A. Gladysz on the occasion of his 65th birthday.

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Abstract

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Two triethoxysilylpropyl-functionalized Shvo’s catalyst precursors were synthesized and

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characterized by IR, NMR and HRMS. Both covalent anchoring and sol-gel methods

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were used for their immobilization. The homogeneous and immobilized catalysts were

20

used for the transfer hydrogenation of levulinic acid with formic acid to form

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hydroxyvaleric acid, which was readily dehydrated to yield gamma-valerolactone. The

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immobilized catalysts prepared by the sol-gel method showed higher activity than the

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covalently grafted catalysts. Hot filtration tests showed no leaching of the immobilized

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Shvo’s catalysts, opening the door to facile catalyst recycling.

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Graphical abstract

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Keywords

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Transfer hydrogenation, Shvo’s catalyst, immobilization, levulinic acid, formic acid, gamma-valerolactone.

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1.

Introduction

2 The overarching goal of the immobilization of homogeneous catalytic systems is

4

the combination of high product yield with facile catalyst separation [1]. This can be

5

achieved by “breaking” the uniformity among the molecules of the catalyst and the

6

product(s) by rendering them in separable phases to allow their separation [2]. The

7

most frequently used variations involve two liquid phases with no, limited, or

8

temperature-regulated miscibility of the two phases [3] or a solid phase and a liquid

9

phase with no, limited, or temperature regulated solubility of the constituent(s) of the

10

solid phase in the liquid phase [1]. The attachment of ligands of homogeneous catalysts

11

to the surface of inorganic or organic solid supports via covalent bonds is a typical

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method to prepare immobilized catalysts [2, 4, 5], which could be used in continuous

13

and batch reactors. In the latter case, simple filtration of the reaction mixture is enough

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for separation and catalyst recycling.

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Homogeneous transfer hydrogenations are catalyzed by transition metal

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catalysts [6, 7]. The Ru-catalyst precursor, {[2,3,4,5-Ph4(η5-C4CO)]2H}Ru2(CO)4(µ-H) (1)

18

(Scheme 1), was discovered by Shvo in 1984 [8-13]. Each ruthenium atom is ligated by

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R

O H R

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R'

R

R'

O

H

R

Ru

AC C

R' OC

O

R

H

CO

Ru

CO

R' OC

R

H

Ru

R R'

CO (2) - H2

R'

O H2

R' Ru

R' CO R

(1)

O

R

CO OC CO CO - CO (4)

R

R' Ru

R' OC

CO (3)

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Scheme 1. Shvo’s catalytic systems (1a, 2a, 3a, 4a: R=R’=Ph; 1b, 2b, 3b, 4b: R=Ph and R’=p-MeOPh).

21

two carbonyl and a functionalized cyclopentadienyl ligands, which are bridged with a

22

hydride ligand between the two ruthenium atoms and with a proton shared by two

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oxygen atoms attached to the cyclopentadienyl ligands. The combination of these

2

peculiar structural features provides remarkable stability even under air at ambient

3

conditions and a mechanism for reversible dissociation at higher temperatures leading

4

to the Shvo’s catalyst [1-OH,2,3,4,5-Ph4(η5-C5)]2RuH(CO)2 (2) and the 16-electron

5

species [2,3,4,5-Ph4(η4-C4C=O)]Ru(CO)2 (3) [14-18]. Although the latter has not been

6

observed yet, it could form readily from [2,3,4,5-Ph4(η4-C4C=O)]Ru(CO)3 (4) by CO

7

dissociation and could react with hydrogen or a broad range of hydrogen donors such

8

as secondary-alcohols or formic acid to generate 2 during transfer hydrogenation

9

reactions.

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The Shvo’s catalyst 2a was one of the first examples of a bifunctional ligand-

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metal catalyst. In the case of hydrogenation of ketones with 2, a concerted transfer of

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the hydride from the metal center to the carbon atom and a proton transfer from the

14

hydroxycyclopentadienyl ligand to the oxygen atom was proposed [14]. We have used

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Shvo’s catalysts 2a for the transfer hydrogenation of levulinic acid (LA) to 4-

16

hydroxyvaleric acid (4-HVA), which readily undergoes dehydration to form gamma-

17

valerolactone (GVL) (Scheme 2.) [19]. It should be noted, that the equimolar mixture of

18

LA and FA is the co-products of the acid catalyzed hydration of 5-(hydroxymethyl)-2-

19

furaldehyde, which can be prepared by acid catalyzed dehydration of carbohydrates

20

[19].

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Scheme 2. Transfer hydrogenation of LA with FA to 4-HVA in the presence of Shvo’s catalyst 2a followed

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by the dehydration of 4-HVA to GVL.

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Although the Shvo’s catalyst 2a could be separated from GVL by vacuum

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distillation [18], the required energy could be a limiting factor for large scale

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applications.

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separation or use in continuous processes [20-21], we report the synthesis and

Since the immobilization of Shvo’s catalysts could enable its facile

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characterization of triethoxysilylpropoxy-functionalized Shvo’s catalysts, which were

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immobilized to silica and used for the conversion of LA and FA to GVL.

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2.

Results and Discussions

4 The multistep synthesis of the catalyst precursors of the Shvo’s catalyst was

6

achieved by a combination of known and new methods (Scheme 3). The reaction of

7

4,4’-dimethoxybenzil with 1,3-diphenylacetone resulted in 3,4-dimethoxyphenyl-2,5-

8

diphenyl-2,4-cyclopentadien-1-one (5) in 90% yield. 5 was converted to 3,4-

9

dihydroxyphenyl-2,5-diphenyl-2,4-cyclopentadien-1-one (6) in 88% yield by the addition

10

of three equivalents of BBr3 followed by hydrolysis at 0 °C [22]. The preparation of 3,4-

11

triethoxysilylpropoxyphenyl-2,5-diphenyl-2,4-cyclopentdien-1-one (7) was achieved in

12

43% yield by the coupling reaction of 6 and (3-iodopropyl)triethoxysilane (IPTES) in

13

acetonitrile in the presence of Cs2CO3 catalyst at 80 °C and 6 hours [23]. IPTES was

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obtained from commercial available (3-chloropropyl)triethoxysilane (CPTES) in 95%

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yield [24]. Refluxing 7 and 1/3 equivalent of Ru3(CO)12 in toluene for 32 hours resulted

16

in the mono-nuclear ruthenium complex 8, which was converted to the dinuclear

17

ruthenium complex 9 by stirring the solution of 8 in refluxing iso propanol for 40 hours.

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Compounds 5-9 were purified by column chromatography and structurally characterized

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by IR (Figures S1-S5), 1H- and

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S19).

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5

MeO

O

Ph

HO Ph

Ph

O Ph

AC C

MeO

(EtO)3Si

1. 3 eq BBr3, CH2Cl2, 0 C, 1 h O

2. H2O, 0 oC, 1 h 88%

Ph HO

5

2 eq I

6

Si(OEt)3

Cs2CO3, CH3CN, 80 oC, 6 h 43% (EtO)3Si

Si(OEt)3

O

Ph

O H O

O

Ph

Ph Ph H Ru Ru OC CO O

(EtO)3Si

Ph

O

(EtO)3Si

O O

Isopropanol

OC CO O

reflux for 40 h 43%

Ph 1/3 eq Ru3(CO)12

Ph (EtO)3Si

O

Ru OC CO

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Ph

o

NaOH, Ethanol, reflux for 6 h 90%

O

MeO

C-NMR (Figures S6-S15), and HRMS (Figures S16-

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OMe

O

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O Toluene, reflux for 32 h 55%

CO

Ph O

Si(OEt)3

9

7

8 (EtO)3Si

Scheme 3. Synthesis of triethoxysilylpropoxy-group functionalized Shvo’s catalysts.

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1 Initially, we tried to attach ligand 7 to the surface of silica gel by stirring a

3

solution of 7 in toluene with a certain amount of silica gel at room temperature until the

4

red color of the ligand in toluene almost disappeared. After washing and filtration, we

5

isolated a red powder. Then, a solution of Ru3(CO)12 in toluene was added and the

6

reaction mixture was refluxed for 24 hours. After filtration and drying, the final solid was

7

immediately tested as a catalyst for the conversion of LA and FA to GVL. Since the

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catalytic activity was too low, we then tried the covalent anchoring of preformed

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complexes 8 and 9 as well as their immobilization by the sol-gel method [25-26].

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In the case of covalent anchoring, the silica gel was sintered at 500 °C for 8

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hours under nitrogen. Complex 8 was dissolved in d8-toluene to give a yellow solution

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and its concentration was measured by 1H NMR. A known amount of sintered silica gel

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was added and the slurry was stirred at room temperature for 72 hours resulting in the

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silica supported catalyst 10a, which was isolated by filtration (Scheme 4).

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successful immobilization was indicated by the disappearance of the yellow color of the

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d8-toluene solution and the disappearance of the 1H NMR peaks for 8. Complex 9 was

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immobilized similarly to yield 11a.

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characteristic bands for the terminal carbonyl ligands on the ruthenium.

The

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FT-IR of 10a and 11a showed the expected

Scheme 4. Immobilization of triethoxysilylpropoxy-group functionalized Shvo’s catalyst 8 to silica.

The immobilization of 8 and 9 was also performed by the in situ sol-gel method

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resulting in 10b and 11b, respectively. Complex 8 was dissolved in ethanol to give a

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yellow solution and then the appropriate amounts of NH4OH and tetraethyl orthosilicate

26

(TEOS) were added successively (Scheme 5). The resulting mixture was stirred at

27

room temperature for 48 hours to form a yellow precipitate, which was isolated as a

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yellow powder of catalyst 10b. The same sol-gel procedure was used to incorporate

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complex 9 into the silica framework resulting in catalyst 11b. FT-IR of 10b and 11b

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confirmed the presence of the terminal carbonyl ligands on the ruthenium.

Scheme 5. Immobilization of triethoxysilylpropoxy-group functionalized Shvo’s catalyst 8 by the sol-gel method.

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The surface area and the porous nature of silica before and after sintering, and

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catalysts 10a, 10b, 11a, and 11b were established by nitrogen adsorption-desorption experiments (Table 1. and Figures S20-S22).

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Table 1. Physical properties of silica supports and silica supported catalysts 10a, 10b, 11a, and 11b with their catalyst loading. Pore volume DBJH SBET 2 3 (m /g) (cm /g) (nm) Silicaa 482.62 0.59 4.09 b Silica 135.89 0.31 7.91 10a 115.35 0.25 7.33 11a 126.43 0.25 7.42 10b 7.60 0.02 14.14 11b 8.08 0.02 16.47 a Silica before sintering. bSilica after sintering.

Catalyst loading (mmol/g) N/A N/A 0.10 0.09 0.11 0.11

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Both, the surface area and pore volume of silica were reduced after sintering at high

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temperature, as expected [27], and further reduced after the immobilization of the

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ruthenium complexes to form catalysts 10a and 11a. The surface area and the pore

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volume of catalysts 10b and 11b, prepared by the sol-gel method, were significantly

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lower. In contrary, their pore diameter was two times greater than catalysts 10a and

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11a.

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Compounds 1b and 4b and the two triethoxysilylpropyl-functionalized ruthenium

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complexes 8 and 9 were used as homogeneous catalysts for the conversion of LA to

3

GVL (Table 2). The observed selectivity of LA to GVL was 99.90%, as expected [19]. Table 2. Transfer hydrogenation of levulinic acid with formic acid in the presence of homogeneous and heterogenized Shvo’s catalysts at 90 °C under nitrogen. -1 Catalyst t (h) n(FA)/n(LA) n(LA)/n(catalyst) Yield of GVL (%) TON TOF (h )

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a 1b 12* 2.2 371 90.93 ± 0.39 334 28 a 4b 24** 2.2 371 88.74 ± 0.28 326 14 a 8 24** 2.2 371 11.16 ± 0.28 41 2 b 9 24** 2.5 573 20.06 ± 0.45 115 5 b 10a 24** 2.5 573 23.03 ± 0.18 132 6 b 10b 24* 2.5 573 87.91 ± 0.30 504 21 b 11a 30** 2.5 573 31.04 ± 0.27 178 6 b 11b 24* 2.5 573 66.98 ± 0.44 384 16 *The experiments were done in duplicate. **The experiments were done in triplicate. a 1.28 g of LA (11.02 mmol) and 1.14 g of FA (24.77 mmol) were added in 4 mL of 1,4b dioxane. 2 g of LA (17.2 mmol) and 2 g of FA (43.4 mmol) were added without solvent.

10 11

1b showed the highest activity, which was about two times of that of 4b indicating that

12

the dissociation of carbon monoxide from 4b requires higher activation than the

13

disproportionation of 1b. In the latter case, one of the products is the active species 2b

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and the other is ready to activate FA to form 2b.

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triethoxysilylpropyl groups to two phenyl rings in the para-position has significantly

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lowered the catalytic activity of 8 and 9.

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The attachment of the

The covalently grafted triethoxysilylpropyl-functionalized ruthenium catalysts 10a and

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11a displayed somewhat higher activities than 8 and 9. The sol-gel catalysts 10b and

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11b were even more active, the conversion of LA and FA to GVL after 24 hours was

21

88% and 67% yield, respectively (Figure 3.). A typical 1H-NMR of the reaction mixture

22

after heating 17.2 mmol LA and 43.4 mmol FA in the presence of 10b at 90 oC for 36

23

hours is shown on Figure S23.

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100

60 11b 10b 11a 10a

40

20

0 0

20

40

60

80

Time (h)

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GVL yield (%)

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100

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Figure 3 Conversion of LA and FA to GVL with catalysts 10a, 10b, 11a and 11b.

Finally, hot filtration tests were used to study possible catalyst leaching to the

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solution. We examined the conversion of LA and FA to GVL at 90 °C and 120 °C in the

5

presence of silica supported catalysts 10a and 10b. After 12 hours half of each reaction

6

mixture was filtered at the reaction temperature, and the conversion of GVL was

7

measured by quantitative 1H NMR. Both, the filtered portion and the other portion with

8

the catalyst were heated at reaction temperature for an additional 12 hours. The GVL

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yield in the reaction mixture with the catalyst increased, as expected, while the filtered portion showed no change of the GVL yield (Table 3).

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Table 3. Hot filtration test of 10a and 10b.

Catalyst

Temperature (°C)

Conversion to GVL a after hot filtration (%)

Conversion to GVL after additional 12 hours heating (%)

Remaining portion 27 Filtered portion 16 10a Remaining portion 45 120 24 Filtered portion 24 Remaining portion 84 90 41 Filtered portion 41 10b Remaining portion 95 120 55 Filtered portion 55 a 1.28 g of LA (11.02 mmol) and1.14 g of FA (24.77 mmol) in 2 mL of d6-DMSO. The molar ratio of catalyst to substrate was 1:367 16

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3.

Conclusions

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Triethoxysilylpropyl-functionalized

ruthenium

complexes

were

synthesized

and

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immobilized on two types of silica support. The homogeneous and immobilized catalysts

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were tested for the conversion of LA and FA to GVL. The catalytic activity of the

2

triethoxysilylpropyl-functionalized ruthenium complexes was lower than the conventional

3

Shvo’s catalyst precursors. The immobilized catalysts prepared by the sol-gel method

4

showed higher TONs, TOFs and yield of GVL as compared with covalently grafted

5

catalysts. Hot filtration tests confirmed that the catalytic activity is due to the supported

6

Shvo’s catalyst and not from some active species leached from the solid support to the

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solution under the reaction conditions, opening the opportunity to facile catalyst

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recycling.

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4.

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Experimental

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4.1 General Procedures.

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Unless stated otherwise, all reactions were carried out under nitrogen using standard

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Schlenk techniques. All solvents used for the synthesis were purified and dried by

16

standard methods.

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boron tribromide (BBr3), 1,3-diphenylacetone, ruthenium (III) chloride hydrate, Cs2(CO)3,

18

NaI, NaOH, NH4OH, HNO3, Si(OCH2CH3)4 (tetraethyl orthosilicate or TEOS), levulinic

19

acid, HCOOH, (CH3)2SO2 (dimethyl sulfone), CD2Cl2, CDCl3, d8-toluene and d6-DMSO

20

were purchased from commercial sources (Sigma-Aldrich, Acros and Merck) and used

21

as received.

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methoxyphenyl)-2,5-diphenylcyclopentadien-3-one [27], Shvo’s catalyst precursors

23

{[3,4-(p-MeOPh)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(µ-H) (1b) [13] and [3,4-(p-MeOPh)2-

24

2,5-Ph2(η4-C4CO)]Ru(CO)3 (4b) [14], Ru3(CO)12 [29], and ICH2CH2CH2Si(OCH2CH3)3

25

(3-iodopropyl)triethoxysilane or IPTES) [24]. All reactions were monitored by thin-layer

26

chromatography (TLC) using Merck aluminum sheets silica gel 60 F254 and visualized

27

with UV light.

28

chromatography. The silica gel used for covalent grafting was purchased from Sigma-

29

Aldrich with high-purity grade.

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4,4’-Dimethoxybenzil, (3-chloropropyl)triethoxysilain (CPTES),

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Modified literature methods were used for the synthesis of 3,4-bis(4-

E. Merck silica gel 60 (230−400 mesh) was used for column

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H and

1

13

C NMR spectra were recorded on a 400 or a 600 MHz Bruker

2

instrument at room temperature. The concentrations of LA and GVL were measured by

3

using

4

methylsulfonylmethane or biphenyl as internal standard. All chemical shifts were

5

recorded in ppm relative to residual CH2Cl2, CHCl3, toluene or DMSO on the δ scale.

6

MS and HRMS were measured on a Thermo-Finnigan MAT 95 KL or Bruker 9.4 Tesla

7

Fourier Transform Ion Cyclotron Resonance Mass spectrometer. IR spectra of samples

8

in KBr pellets or Nujol films were recorded in the range of 400−4000 cm−1 using an

9

AVATAR 360 FT-IR spectrometer. BET surface area analysis and BJH pore size and

10

volume analysis were conducted by Micromeritics Tri Star 3000 Surface Area and

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Porosity Analyzer. Ruthenium analysis was done by a Perkin Elmer Elan 6100 DRC

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ICP-MS.

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H-NMR of the reaction mixture in the presence of known amount of

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4.2

Synthesis and Characterization

4.2.1.

3-Iodopropyl-triethoxysilane (IPTES)

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To a stirred solution of NaI (6.00 g, 40 mmol) in anhydrous acetone (40 mL) in a

19

250 mL three-neck round bottom flask equipped with a condenser and a pressure-

20

equalizing dropping funnel, 3(chloropropyl)triethoxysilane (CPTES) (4.82 g, 20 mmol)

21

was added dropwise. The reaction mixture was stirred at 60 °C for 60 hours under N2

22

and then cooled to room temperature.

23

pressure and the solid residue was washed with diethyl ether three times.

24

combined filtrate was concentrated under reduced pressure. The crude product was

25

purified by column chromatography using hexane-ethyl acetate (10:1) as the eluent to

26

afford the pure 3-iodopropyl-triethoxysilane (IPTES) as a colorless oil (6.31 g, 95%). 1H

27

NMR (400 MHz, d6-DMSO): δ 0.64−0.68 (m, 2H, CH2Si), 1.15 (t, 9H, J = 6.0 Hz, CH3),

28

1.75−1.83 (m, 2H, CH2), 3.28 (t, 2H, J = 6.0 Hz, ICH2), 3.75 (q, 6H, J = 8.0 Hz, OCH2).

29

13

30

(OCH2), 57.8 (SiOCH2).

The solvent was removed under reduced The

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C{1H} NMR (100 MHz, d6-DMSO): δ 11.6 (CH2Si), 12.4 (CH2), 18.2 (CH3), 27.3

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4.2.2.

3,4-(p-MeOPh)2-2,5-Ph2(C4CO) (5)

2 4,4’-Dimethoxybenzil (2.90 g, 10.36 mmol) and 1,3-diphenylacetone (2.26 g, 10.36

4

mmol) were dissolved in 30 mL ethanol in a 100 mL two-neck round bottom flask

5

equipped with a condenser. The reaction mixture was warmed up nearly to the boiling

6

point of ethanol, followed by the slow addition of a solution of 0.36 g NaOH in 3 mL

7

ethanol. When the addition was finished, the reaction mixture was refluxed for 6 hours

8

followed by cooling to 0 °C. The crude product was then filtered and washed several

9

times with deionized water and ethanol, and dried under vacuum overnight at room

10

temperature to afford 5 (4.15 g, 90%) as a dark purple solid. IR (KBr) in cm−1: 1707 (s,

11

νC=O).

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H NMR (400 MHz, CD2Cl2): δ 3.77 (s, 6H, OCH3), 6.72 (d, 4H, J = 8.0 Hz,

12

aromatic H), 6.86 (d, 4H, J = 8.0 Hz, aromatic H), 7.20−7.29 (m, 10H, aromatic H).

13

13

14

aromatic), 125.2 (C2,5 of cyclopentadienone or Cp-dienone), 154.7 (C3,4 of Cp-dienone),

15

200.6 (C1 of Cp-dienone). MS (ESI) m/z (relative intensity) [M+H]+: 445.

C{1H} NMR (100 MHz, CD2Cl2): δ 55.6 (OCH3), 113.7−160.3 (8 resonances,

16 4.2.3

3,4-(p-HOPh)2-2,5-Ph2(C4CO) (6)

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To an ice-cold solution of 5 (0.44 g, 1 mmol) in dry CH2Cl2 (9 mL) in a 50 mL

20

three-neck round bottom flask equipped with a condenser and a pressure-equalizing

21

dropping funnel, BBr3 (3.5 mL, 1 M in DCM) was added dropwise at 0 °C under N2 in 1

22

hour. After the addition of all BBr3, the reaction mixture was stirred at 0 °C for an

23

additional hour, and then quenched with ice-water (10 mL) at 0 °C.

24

mixture was diluted with ethyl acetate (20 mL), washed with saturated NaHCO3 (3 x 10

25

mL) and saturated NaCl (3 x 10 mL). The organic layer was dried over anhydrous

26

MgSO4.

27

purified by column chromatography using hexane-acetone (2:1) as the eluent to afford 6

28

(0.37 g, 88%) as a black powder. IR (KBr) in cm−1: 3416 (s, νO–H), 1687 (s, νC=O).

29

NMR (400 MHz, d6-DMSO): δ 6.60 (d, 4H, J = 8.0 Hz, aromatic H), 6.72 (d, 4H, J = 8.0

30

Hz, aromatic H), 7.27−7.15 (m, 10H, aromatic H), 9.77 (s, 2H, OH).

31

MHz, d6-DMSO): δ 115.0−158.0 (8 resonances, aromatic), 123.1 (C2,5 of Cp-dienone),

The reaction

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The solvent was removed under reduced pressure and the residue was 1

H

13

C{1H} NMR (100

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154.8 (C3,4 of Cp-dienone), 199.8 (C1 of Cp-dienone). MS (ESI) m/z (relative intensity)

2

[M+H]+ 417, HRMS (ESI) calcd for C29H20O3 [M+H]+: 417.1485, found: 417.1481.

3 4

4.2.4

3,4-[p-(EtO)3Si(CH2)3OPh]2-2,5-Ph2(C4CO) (7)

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Compound 6 (0.88 g, 2.12 mmol) and cesium carbonate (1.38 g, 4.24 mmol)

7

were dissolved in dry CH3CN (200 mL) in a 500 mL two-neck round bottom flask

8

equipped with a condenser. IPTES (1.41 g, 4.24 mmol) was added dropwise by using a

9

micro-syringe. The reaction mixture was stirred at 80 °C for 6 hours under N2 and then

10

cooled to room temperature. The solvent was removed under reduced pressure. The

11

crude residue was re-dissolved in 10 mL of hexane and filtered. The solid was washed

12

with an additional 10 mL of hexane and then the filtrates were concentrated under

13

reduced pressure. The crude product was purified by column chromatography using

14

hexane - ethyl acetate (8:1) as the eluent to afford 7 (0.75 g, 43%) as a red sticky solid.

15

IR (thin film) in cm−1: 1705 (s, νC=O). 1H NMR (400 MHz, d6-DMSO): δ 0.63−0.67 (m, 4H,

16

CH2Si), 1.12 (t, 18H, J = 6.0Hz, CH3), 1.68−1.75 (m, 4H, CH2), 3.74 (q, 12H, J = 8.0 Hz,

17

SiOCH2), 3.88 (t, 4H, J = 6.0 Hz, OCH2), 6.76 (4H, d, J = 8.0 Hz, aromatic H), 6.83 (4H,

18

d, J = 8.0 Hz, aromatic H), 7.13−7.29 (10H, m, aromatic H).

19

DMSO): δ 6.0 (CH2Si), 18.2 (CH3), 22.3 (CH2), 57.8 (SiOCH2), 69.1 (OCH2),

20

114.0−158.9 (8 resonances, aromatic), 124.2 (C2,5 of Cp-dienone), 154.4 (C3,4 of Cp-

21

dienone), 199.6 (C1 of Cp-dienone). MS (ESI) m/z (relative intensity) [M+Na]+ 847,

22

HRMS (ESI) calcd for C47H60O9Si2 [M+Na]+: 847.3668, found: 847.3666.

25 26

C{1H} NMR (100 MHz, d6-

4.2.5.

[3,4-(p-MeOPh)2-2,5-Ph2(η4-C4CO)]Ru(CO)3 (4b)

AC C

23 24

13

EP

TE D

M AN U

SC

6

Ru3(CO)12 (60 mg, 0.09 mmol) and 5 (125.2 mg, 0.28 mmol) were suspended in

27

anhydrous toluene (20 mL) in a 50 mL two-neck round bottom flask equipped with a

28

condenser. The reaction mixture was stirred at 110 °C under N2 for 48 hours until the

29

color of reaction mixture changed from dark red to light red, then cooled to room

30

temperature. The toluene was removed under reduced pressure. The crude residue

31

was purified by column chromatography using hexane:ethyl acetate (2:1) as the eluent

12

ACCEPTED MANUSCRIPT

1

to afford 4b (147.2 mg, 83%) as a yellow solid. IR (KBr) in cm−1: 2079 (vs, νC≡O), 2020

2

(vs, νC≡O), 2008 (vs, νC≡O), 1642 (s, νC=O).

3

OCH3), 6.64 (d, 4H, J = 6.0 Hz, aromatic H), 6.96 (d, 4H, J = 6.0 Hz, aromatic H),

4

7.21−7.26 (m, 6H, aromatic H), 7.47 (d, 4H, J = 6.0 Hz, aromatic H).

5

MHz, CDCl3): δ 55.1 (OCH3), 82.4 (C2,5 of Cp-dienone), 107.3 (C3,4 of Cp-dienone),

6

113.5−159.6 (8 resonances, aromatic), 174.1 (C1 of Cp-dienone), 194.7 (terminal

7

carbonyls on Ru). MS (ESI) m/z (relative intensity) [M+H]+ 631, HRMS (ESI) calcd for

8

C34H24O6 Ru [M+H]+: 631.0695, found: 631.0693.

1

10

4.2.6.

C{1H} NMR (151

RI PT

13

SC

9

H NMR (600 MHz, CDCl3): δ 3.74 (s, 6H,

{3,4-[p-(EtO)3Si(CH2)3OPh]2-2,5-Ph2(η4-C4CO)}Ru(CO)3 (8)

M AN U

11

Ru3(CO)12 (25.8 mg, 0.04 mmol) and 7 (100 mg, 0.12 mmol) were suspended in

13

anhydrous toluene (10 mL) in a 50 mL two-neck round bottom flask equipped with a

14

condenser. The reaction mixture was stirred at 95 °C under N2 for 32 hours and then

15

cooled to room temperature. The toluene was removed under reduced pressure. The

16

crude residue was purified by column chromatography using hexane:ethyl acetate (4:1)

17

as the eluent to afford 8 (66.7 mg, 55%) as a yellow sticky solid. IR (thin film) in cm−1:

18

2081 (vs, νC≡O), 2022 (vs, νC≡O), 1970 (w, νC≡O), 1649 (s, νC=O).

19

CDCl3): δ 0.72−0.74 (m, 4H, CH2Si), 1.21 (t, 18H, J = 6.0Hz, CH3), 1.83−1.88 (m, 4H,

20

CH2), 3.82 (q, 12H, J = 8.0 Hz, OCH2), 3.86 (t, 4H, J = 8.0 Hz, OCH2), 6.62 (d, 4H, J =

21

8.0 Hz, aromatic H), 6.93 (d, 4H, J = 8.0 Hz, aromatic H), 7.21−7.26 (m, 6H, aromatic

22

H), 7.45−7.47 (m, 4H, aromatic H).

23

(CH3), 22.9 (CH2), 58.5 (SiOCH2), 69.9 (OCH2), 82.4 (C2,5 of Cp-dienone), 107.5 (C3,4 of

24

Cp-dienone), 114.0−159.2 (8 resonances, aromatic), 174.2 (C1 of Cp-dienone), 194.7

25

(terminal CO on Ru). MS (ESI) m/z (relative intensity) [M+H]+: 1011, HRMS (ESI) calcd

26

for C50H60O12RuSi2 [M+H]+: 1011.2753, found: 1011.2755.

27 28

1

H NMR (600 MHz,

13

C{1H} NMR (151 MHz, CDCl3): δ 6.7 (CH2Si), 18.4

AC C

EP

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12

4.2.7.

{[3,4-(p-MeOPh)2-2,5-Ph2(η5-C4CO)]2H}Ru2(CO)4(µ-H) (1b)

29 30

Compound 5 (400 mg, 0.90 mmol) and Ru3(CO)12 (192 mg, 0.30 mmol) were

31

added in methanol (50 mL) in a 250 mL two-neck round bottom flask equipped with a

13

ACCEPTED MANUSCRIPT

1

condenser and heated at reflux for 48 hours. A bright yellow precipitate was formed

2

and the reaction mixture was cooled to room temperature. The methanol was removed

3

by filtration and the crude residue was washed with methanol to afford 1b (374.2 mg,

4

69%) as a yellow powder. IR (CH2Cl2) in cm−1: 2037 (vs, νC≡O), 2006 (m, νC≡O), 1978 (s,

5

νC≡O).

6

6.54−6.58 (m, 8H, aromatic H), 6.91−6.95 (m, 8H, aromatic H), 7.01−7.08 (m, 16H,

7

aromatic H), 7.12−7.17 (m, 4H, aromatic H).

8

(OCH3), 88.4 (C2,5 of Cp), 103.5 (C3,4 of Cp), 113.2−154.8 (8 resonances, aromatic),

9

159.5 (C1 of Cp), 201.6 (terminal CO on Ru). MS (ESI) m/z (relative intensity) [M+H]+:

C{1H} NMR (100 MHz, CD2Cl2): δ 55.4

1207, HRMS (ESI) calcd for C66H50O10Ru2 [M+H]+: 1207.1569, found: 1207.1567. 4.2.8.

M AN U

11 12

13

RI PT

H NMR (400 MHz, CD2Cl2): δ -18.47 (s, 1H, RuHRu), 3.67 (s, 12H, OCH3),

SC

10

1

{{3,4-[p-(EtO)3Si(CH2)3OPh]2-2,5-Ph2(η5-C4CO)}2H}Ru2(CO)4(µ-H) (9):

13 14

Compound 8 (200 mg, 0.20 mmol) was dissolved in isopropanol (20 mL) in a

15

100 mL two-neck round bottom flask equipped with a condenser, and heated at reflux

16

for 40 hours.

17

isopropanol was removed under reduced pressure. The crude residue was purified by

18

column chromatography using hexane/diethyl ether (1:1) as the eluent to afford 9 (167.4

19

mg, 43%) as a yellow sticky solid. IR (thin film) in cm−1: 2031 (vs, νC≡O), 2001 (m, νC≡O),

20

1972 (str, νC≡O).

21

8H, CH2Si), 1.19 (t, 36H, J = 6.0 Hz, CH3), 1.76−1.86 (m, 8H, CH2), 3.80 (q, 24H, J =

22

8.0 Hz, OCH2), 3.79 (t, 8H, J = 8.0 Hz, OCH2), 6.52 (d, 8H, J = 12.0 Hz, aromatic H),

23

6.88 (d, 8H, J = 12.0 Hz, aromatic H), 6.97−7.02 (m, 8H, aromatic H), 7.08−7.13 (m,

24

12H, aromatic H).

25

(CH2), 58.5 (SiOCH2), 69.8 (OCH2), 88.0 (C2,5 of Cp), 103.0 (C3,4 of Cp), 113.5−154.1

26

(8 resonances, aromatic), 158.6 (C1 of Cp), 201.2 (terminal CO on Ru). MS (ESI) m/z

27

(relative intensity) [M+H]+ 1968, HRMS (ESI) calcd for C98H122O22Ru2Si4 [M+H]+

28

1967.5705, found 1967.5707.

H NMR (600 MHz, CDCl3): δ -18.50 (s, 1H, RuHRu), 0.67−0.72 (m,

AC C

EP

1

TE D

The reaction mixture was cooled to room temperature and then the

13

C{1H} NMR (151 MHz, CDCl3): δ 6.6 (CH2Si), 18.4 (CH3), 22.9

29 30

4.2.9.

Preparation and Characterization of 10a, 10b, 11a and 11b

31

14

ACCEPTED MANUSCRIPT

1

(a) In the glove box, a sample of about 0.1 mmol of 8 or 9 and 1.0 g silica gel

2

(sintered at 500 °C for 8 h under N2) were weighed into a 25 mL round bottom flask

3

containing a magnetic stir bar, then 6.0 mL of d8-toluene was added. At this point,

4

quantitative 1H NMR (t = 0 h) of a small sample was carried out. The resulting mixture

5

was stirred at ambient temperature for 72 hours.

6

separated by filtration, washed with CH2Cl2 several times, and dried under vacuum at

7

room temperature overnight to yield catalysts 10a and 11a. The d8-toluene phase was

8

analyzed by quantitative 1H NMR (t = 72 h) to determine the catalyst loading. The

9

catalyst loading was confirmed by digestion of samples of 10a and 11a followed by ICP-

RI PT

SC

10

The formed yellow solid was

MS analysis.

M AN U

11

(b) A sample of about 0.1 mmol 8 or 9 and 3 mL of TEOS were dissolved in 4

13

mL ethanol in a 25 mL two-neck round bottom flask equipped with a condenser and a

14

magnetic stir bar under N2. 2 mL of ammonium hydroxide solution (25% NH3) was

15

added dropwise. The mixture was stirred at room temperature under N2 for 48 hours.

16

The produced light yellow powder was separated by filtration, washed with ethanol three

17

times, and dried under vacuum at room temperature overnight to yield catalysts 10b

18

and 11b. The liquid phase was concentrated and analyzed by quantitative 1H NMR to

19

determine the catalyst loading. The catalyst loading was confirmed by digestion of

20

samples of 10b and 11b followed by ICP-MS analysis.

23 24

EP

22

4.2.10. Determination of ruthenium concentration immobilized Shvo’s catalysts

AC C

21

TE D

12

A sample of 35 mg of 10a, 10b, 11a or 11b was digested in 3 mL of

25

concentrated nitric acid at 80 °C for 24 hours. Corresponding blank samples were

26

prepared in the same way. Each solution was then diluted to 25 mL deionized water and

27

then ICP-MS analysis was conducted.

28 29

4.2.11. Transfer hydrogenation of levulinic acid with formic acid without solvent

30

15

ACCEPTED MANUSCRIPT

A mixture of levulinic acid (2 g, 17.2 mmol) and formic acid (2 g, 43.4 mmol)

2

was placed in a 25 mL two-neck round bottom flask equipped with a condenser. About

3

0.03 mmol of 9 or a known amount of silica-supported Shvo’s catalyst (10a, 10b, 11a or

4

11b) was added and the resulting solution was stirred at 90 °C for specified times. The

5

concentration of GVL at different times was determined by quantitative 1H NMR.

RI PT

1

6 7

4.2.12. Transfer hydrogenation of levulinic acid with formic acid in dioxane

8

A mixture of levulinic acid (1.28 g, 11.02 mmol), formic acid (1.14 g, 24.77

10

mmol) and 1,4-dioxane (4 mL) was placed in a 25 mL two-neck round bottom flask

11

equipped with a condenser.

12

reaction mixture was stirred at 90 °C for specified times. The concentration of GVL at

13

different times was determined by quantitative 1H NMR.

M AN U

About 0.03 mmol of 1b, 4b or 8 was added and the

14 15

SC

9

4.2.13. Hot filtration test of heterogenized Shvo’s catalysts

16

To a solution of 1 mL levulinic acid (1.28 g, 11.02 mmol) and 1 mL formic acid

18

(1.14 g, 24.77 mmol) in 2 mL of d6-DMSO in a 25 mL two-neck round bottom flask

19

equipped with a condenser and a magnetical stirrer, a certain amount of 10a or 10b was

20

added. The resulting suspension was stirred at 90 °C or 120 °C for 12 hours. 2 mL of

21

the reaction solution was separated from the catalyst via a Pasteur pipette and put in a

22

syringe equipped with a 45 µm PTFE syringe filter. The filtered portion was then added

23

to a septum capped NMR tube for 1H NMR test. At this point, the conversion to GVL

24

was recorded for t = 12 h. Both the remaining portion of the solution with catalyst and

25

the filtered portion without catalyst were heated to 90 °C for another 12 hours. Then 1H

26

NMR spectra of both portions were recorded to obtain the conversions to GVL at t = 24

27

h.

AC C

EP

TE D

17

28 29

Acknowledgements

30

16

ACCEPTED MANUSCRIPT

This work was funded by the City University of Hong Kong and the Innovation

2

and Technology Support Programme of the Innovation and Technology Fund of the

3

Government of the Hong Kong SAR (ITS/079/13). Any opinions, findings, conclusions or

4

recommendations expressed in this material/event (or by members of the project team)

5

do not reflect the views of the Government of the Hong Kong Special Administrative

6

Region, the Innovation and Technology Commission or the Panel of Assessors for the

7

Innovation and Technology Support Programme of the Innovation and Technology

8

Fund. We also thank the Environment and Conservation Fund (ECF/31/2014) for partial

9

financial support.

10

SC

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1

Appendix A. Supplementary data

12

Supplementary data related to this article can be found at ….

13

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18