Approach for Catalyst-Product Separation Using Recyclable Liquid

Aug 18, 2010 - The concept involves the use of liquid phase catalyst that is soluble in organic ... Shoeb R. Khan , Mayur V. Khedkar , Ziyauddin S. Qu...
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Ind. Eng. Chem. Res. 2010, 49, 8360–8364

Approach for Catalyst-Product Separation Using Recyclable Liquid Phase Catalysis Anil G. Panda, Yogesh P. Patil, Pawan J. Tambade, and Bhalchandra M. Bhanage* Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai 400 019, India

A novel recyclable liquid phase catalyst system consisting of polyether metal diphosphinite complex anchored in polyethylene glycol was developed. The concept involves the use of liquid phase catalyst that is soluble in organic solvents like toluene and was tested for a variety of reactions like hydroformylation, hydrogenation, carbon dioxide fixation, and C-C coupling reactions in a homogeneous manner. The catalyst, in liquid form, can be quantitatively separated from the reactants/products with the help of addition of antisolvent and thus can be easily recycled. 1. Introduction Homogeneous catalysis using soluble transition metal complexes has a wide range of potential applications. These catalysts operate at mild reaction conditions and show high activity and selectivity performance as compared to heterogeneous catalysts. However, it has a major limitation of catalyst product separation and their recycle. Tedious procedures are required for the catalyst-product separation, which quite often leads to the deactivation of sensitive metal complex catalysts. The recycling of precious metal catalyst is also another important task. To counteract these limitations, several novel approaches have been designed. The catalysis using aqueous-organic biphasic systems is one such example.1 In this case, the catalyst is in the aqueous phase and reactants/products are present in the organic phase and the catalyst-product can be separated using simple phase separation and can be recycled. Several other elegant approaches including fluorous biphasic catalysis,2,3 reactions in supercritical CO2,4-6 ionic liquids,7 catalyst immobilization on solid support material,8 and a thermoregulated PEG biphasic system composed of PEG, toluene, and n-heptane together with Rh-polyether phosphite9 have been reported over the past decades. The complex procedures for the preparation of catalyst, catalyst leaching, low reaction rate due to poor mass transfer, oxidation of ligands, etc. are some of the major limitations of these systems. Hence, an effort to develop a new, active, and selective metal complex catalyst with an industrially feasible separation strategy is one of the most desirable tasks. In this work, a novel concept of using homogeneous catalysis coupled with biphasic separation strategy with liquid phase metal diphosphinite complex catalyst anchored in polyethylene glycol was developed. The concept involves use of liquid phase catalysts that are soluble in organic solvent and applied for homogeneous hydroformylation of olefins retaining the merits of homogeneous systems. After the reaction, the catalyst was quantitatively separated in liquid form from the reactants/ products with the help of addition of a volatile antisolvent (which forms two phases), and thus the liquid phase catalyst can be subsequently recycled. We have recently described highly active rhodium polyether phosphinite catalysts [RhPEGD] for homogeneous hydroformylation reaction of styrenes.10 Selecting polyethylene glycol as a scaffold and solvent has several advantages, including commercial availability at low cost, environmentally tested benignity, * Corresponding author. E-mail address: bhalchandra_bhanage@ yahoo.com; [email protected].

and good mechanical and chemical stability. In addition, polyethylene glycol has only two free terminal hydroxyl groups per polymer strand. The polyethylene glycol based diphosphinite ligands were obtained by substituting the hydrogen or the hydroxy substituents at the ends (R,ω-positions) of the polyethylene glycol with diphenylphosphine groups. Coordinating the two ends to the transition metal atom constitutes a supramolecular catalytic system.11,12 Our approach involves the use of polyethylene glycol with an average molecular weight of 600 Da as a solvent as well as a scaffold to anchor organometallic complexes. Polyethylene glycol-600 is completely miscible in toluene at ambient conditions but highly immiscible in nonpolar aliphatic solvents such as n-hexane even at its boiling temperature. On the basis of the concept of “like dissolves like”, polyethylene glycol was utilized and we decided to use it as a scaffold and solvent for carrying out hydroformylation of olefins under homogeneous conditions wherein recyclability of catalyst was a major challenge. The catalytic system consists of a novel polyether metal (Rh) phosphinite complex dissolved in a homogeneous mixture of toluene and PEG-600 (3:1) solvent. Thus the methodology is somewhat similar to reactions conducted in fluorous solvents and ionic liquids wherein the catalysts are modified by introducing suitable groups or tags such as a perfluorinated alkyl chain for fluorous solvents and an imidazolium cation or ionic sulfonate group for ionic liquids. However, it is different from fluorous biphasic catalysis and a thermoregulated PEG biphasic system in terms of operation where the reaction has to be carried out at higher temperature to make the reaction mixture homogeneous. 2. Experimental Section 2.1. General Details. All chemicals like olefins, iodobenzene, styrene, and phenylacetylene were used as received (SigmaAldrich, Acros Organics, Alfa Aesar). PEG-600 was supplied by S. D. Fine Chemicals. All other reagents used were of analytical grade and were used without further purification. Synthesis gas (H2 and CO, 1:1), hydrogen gas, and CO2 gas with a purity of 99.9% were obtained from Alchemie Gases Ltd. R,ω-Bis(diphenylphosphino)poly(ethylene glycol-600 [DPPPEG-600] and Rh(I) carbonyl phosphinite complex (RhPEGD-600) were prepared by reported procedures.12 31P NMR analysis of the diphosphinite ligand (DPPPEG-600) and polyether metal (Rh, Ru and Pd) complexes were carried out using a Varian 300 MHz instrument. Thermogravimetric

10.1021/ie101244m  2010 American Chemical Society Published on Web 08/18/2010

Ind. Eng. Chem. Res., Vol. 49, No. 18, 2010

analysis of metal complexes were done using an SDT-Q600 instrument. Reaction product analysis was performed on a Chemito GC-1000 gas chromatograph equipped with a BP10 capillary column (30 m × 0.32 mm × 0.25 µm) and a flame ionization detector using an external standard method. The products were identified using GC-MS (Shimadzu, GCMSQP2010) equipped with Rtx wax capillary column (30 m length and 0.25 mm diameter) and NMR technique. 2.2. Synthesis of r,ω-Bis(diphenylphosphino)poly(ethylene glycol) [DPPPEG-600] Ligand. Chlorodiphenylphosphine (2.3 g, 10.0 mmol) in THF (2.0 mL) was added into a stirred solution of polyethylene glycol-600 (PEG-600) (5.0 mmol) and pyridine (Py) (0.8 g, 10.0 mmol) in THF (20 mL) at room temperature in an inert atmosphere. The reaction mixture was stirred for 3 h at room temperature. Precipitated Py · HCl was filtered, and the THF solution was passed through a silica gel column to remove the dissolved Py · HCl. R,ω-Bis(diphenylphosphino)polyethylene glycol-600 ligand was obtained in 80% (4.0 g) yield after the solvent, THF was evaporated. 31P NMR (400 MHz, DMSO): δ 19.98 (s). 2.3. Synthesis of Polyether Phosphinite Rh(I) Complex. A solution of RhCl3 · H2O (1 g, 3.8 mmol) in ethanol (30 mL) was added to a refluxing solution of polyether diphosphinite (11.4 mmol) in ethanol (150 mL). After 30 min, 40% aqueous formaldehyde (5 mL) was added dropwise, and the solution turned pale yellow. Addition of sodium borohydride (1 g) in ethanol to this hot mixture yielded the greenish yellow product as 4.21 g (70% yield). 31P NMR (400 MHz, DMSO): δ 73.88 (d, J(Rh,P) ) 144 Hz). 2.4. Synthesis of Wilkinson’s Catalyst Type Polyether Phosphinite Rh(I) Complex (ClRhPEGD-600). A solution of RhCl3. H2O (1 g, 3.8 mmol) in ethanol (35 mL) was added to a refluxing solution of R,ω-bis(diphenylphosphino)poly(ethylene glycol) ligand [DPPPEG-600] (11.4 mmol) in ethanol (150 mL) under a nitrogen atmosphere. The solution was refluxed for 2 h and cooled to room temperature. Water (10 mL) was added to the reaction mixture to precipitate the product. The pale yellow product obtained was filtered and washed with small portions of ethyl alcohol to give 4.12 g (68% yield) of ClRhPEGD-600 catalyst. 31P NMR (400 MHz, DMSO): δ 81.085 (d, J(Rh,P) ) 135 Hz). 2.5. Synthesis of Cl2RuPEGD-600 Catalyst. RuCl3 · H2O (1 g, 3.8 mmol) was dissolved in 35 mL of ethanol, and the solution was added to a refluxing solution of R,ω-bis(diphenylphosphino)poly(ethylene glycol) [DPPPEG-600] ligand (11.4 mmol) in ethanol (150 mL) under a nitrogen atmosphere. The solution was refluxed under nitrogen gas for 3 h. Addition of water (10 mL) to this solution yielded the dark green product. The product obtained was filtered and washed with small portions of ethyl alcohol to give 4.32 g (70% yield) of Cl2RuPEGD-600 catalyst. 2.6. Synthesis of Cl2PdPEGD-600 Catalyst. A mixture of palladium chloride (0.354 g, 2 mmol), NaCl (0.1 g), and methanol (25 mL) was stirred at room temperature for 3 h under nitrogen. Once a clear solution was obtained, sodium carbonate (2 mmol) and DPPPEG-600 ligand (5 mmol) were added and stirred overnight at room temperature. Ten milliliters water was added to this solution, and the pale yellow product obtained was filtered off and washed with small portions of ethyl alcohol to give 1.56 g (68% yield) of the product. 31P NMR (400 MHz, DMSO): δ 80.95 (d, J(Pd,P) ) 202.9 Hz). 2.7. Typical Hydroformylation Procedure. In a typical hydroformylation reaction, to a high pressure reactor of 100 mL capacity were added polymeric Rh-diphosphinite complex

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[RhPEGD-600] (5 µmol) (7.9 mg), 10 mmol of olefin, 15 mL of toluene, and 5 mL PEG-600. The reactor was flushed with nitrogen followed by synthesis gas (1:1 mixture of H2 and CO gas) at room temperature. The reactor was heated to the desired temperature and then pressurized to 5 MPa of synthesis gas. The stirring speed was maintained at 1000 rpm. The reaction mixture was sampled at different time intervals to monitor the progress of the reaction. After completion of the reaction, the reactor was cooled to room temperature and remaining syn gas was carefully vented. Twenty milliliters of n-hexane was added to separate the lower catalyst-philic PEG phase from the upper product phase. The product phase was quantitatively analyzed by gas chromatography and products were characterized by GC-MS. The catalyst-philic PEG phase containing polyether Rh(I) catalyst was subjected to reuse by charging with the same amount of the olefin (10 mmol) and toluene without losing its efficiency. 2.8. Typical Hydrogenation Procedure. In a typical hydrogenation reaction, to a high pressure reactor of 100 mL capacity were added polymeric Rh-diphosphinite complex [ClRhPEGD-600] (5 µmol) (7.9 mg), 10 mmol of olefin, 15 mL of toluene, and 5 mL PEG-600. The reactor was flushed with nitrogen followed by hydrogen gas at room temperature. The reactor was heated to the desired temperature and then pressurized to 2 MPa of hydrogen gas. The stirring speed was maintained at 1000 rpm. The reaction mixture was sampled at different time intervals to monitor the progress of the reaction. After completion of the reaction, the reactor was cooled to room temperature and the remaining hydrogen gas was carefully vented. Twenty milliliters of n-hexane was added to separate the lower catalyst-philic PEG phase from the upper product phase. The product phase was quantitatively analyzed by gas chromatography, and products were characterized by GC-MS. The catalyst-philic PEG phase containing Wilkinson’s catalyst type polyether Rh(I) catalyst was subjected to reuse by charging with the same amount of the substrate (10 mmol) and toluene. 2.9. Typical Procedure for Heck and Sonogashira Reaction. In a typical reaction, iodobenzene (1.0 mmol) and styrene (Heck, 2.0 mmol) or phenylacetylene (Sonogashira, 2.0 mmol) were reacted in a homogeneous mixture of toluene and PEG-600 (20 mL, 3:1) in the presence of 3 mol % of Cl2PdPEGD-600 catalyst and cesium carbonate (2.0 mmol) (34.4 mg), under a nitrogen atmosphere at 80 °C for the desired time until complete consumption of iodobenzene. The reaction progress was monitored by TLC and GC analyses. The mixture was cooled to room temperature, and 20 mL of n-hexane was added to separate the lower catalyst-philic PEG phase from the upper product phase. The product was isolated by decantation and evaporation of solvents under vacuum. The catalyst-philic PEG phase containing polyether Pd(II) catalyst was subjected to reuse by charging with the same amount of the substrates [iodobenzene (1.0 mmol) and styrene (2.0 mmol, Heck) or phenylacetylene (2.0 mmol, Sonogashira)], toluene, and base, Cs2CO3 (2.0 mmol). 2.10. Typical Carbon Dioxide Fixation Procedure. In a typical reaction phenylacetylene (10 mmol), diethylamine (20 mmol), Cl2RuPEGD-600 (0.2 mmol) (325.4 mg), toluene (15 mL), and PEG 600 (5 mL) were added to a 100 mL stainless steel autoclave. The autoclave was then flushed with carbon dioxide and pressurized with 5 MPa of carbon dioxide. The reaction mixture was stirred at 100 °C for 24 h. After the completion of reaction, the autoclave was cooled to room temperature and remaining carbon dioxide gas was vented. Twenty milliliters of n-hexane was added to separate the lower

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Scheme 1. Hydroformylation of Olefins Using Polyether Rh Diphosphinite Complex (RhPEGD-600)

catalyst-philic PEG phase from the upper product phase. The catalyst-philic PEG phase containing polyether Ru(II) catalyst was subjected to reuse by charging with the same amount of the substrates. The product phase was quantitatively analyzed by gas chromatography. Isolated products were characterized by GC-MS and 1H NMR. 3. Results and Discussion Initially, we chose the hydroformylation of styrene as a model reaction to test this concept (Scheme 1). The catalytic system composed of PEG, toluene, and polyether rhodium phosphinite catalyst was used for preliminary optimization of reaction conditions such as styrene to rhodium mole ratio, reaction temperature, CO/H2 pressure, phosphorus to rhodium ratio, and solvent. The optimum reaction conditions using RhPEGD-600 catalyst for hydroformylation are 80 °C, 5 MPa syn gas pressure, P/Rh-10, substrate/Rh-2000. To determine the scope of hydroformylation reaction using RhPEGD-600 catalyst, we performed the reaction with other substrates, like substituted styrenes with electron donating/ withdrawing groups and simple aliphatic higher olefins such as 1-octene and 1-dodecene (Table 1, entries 1-7). These substrates are water immiscible, and hence, the applications of conventional catalyst product recycle techniques like SAPC13 and aqueous-organic biphasic catalysis1 are not possible. For most of the substituted styrenes, the rate of reaction

Figure 1. Photograph of catalytic hydroformylation using polyether Rh diphosphinite complex (RhPEGD-600): (A) homogeneous reaction mixture before reaction; (B) homogeneous reaction mixture after reaction; (C) phase separation after adding n-hexane.

and the selectivity was almost the same as that of styrene. The selectivity observed in all the cases was 95-98% with a negligible amount of ethylbenzene as the only hydrogenation byproduct at milder reaction conditions using the present catalyst system. A main objective of the present study using polyethylene glycol as a scaffold and solvent was to study the reusability of the catalyst. With this objective in mind, we studied the reusability of the catalyst by adding 20 mL of n-hexane as an antisolvent to the reaction mixture after completion of reaction. The upper organic phase was then separated from the lower

Table 1. Hydroformylation of Olefins Using RhPEGD-600 Catalysta

Reaction conditions: olefin ) 10 mmol, RhPEGD-600 ) 5 µmol (7.9 mg), P/Rh ) 10, toluene/PEG 600 ) 15:5 mL, 80 °C, 5 MPa of CO/H2 (1:1), 6 h. b Aldehyde selectivity. c Branched to linear aldehyde ratio. d 8% isomerization product. e 7% isomerization product. a

Ind. Eng. Chem. Res., Vol. 49, No. 18, 2010 Table 2. Hydroformylation of Styrene Using RhPEGD-600: Catalyst Recyclabilitya

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Table 4. Cl2PdPEGD-600 Catalyzed Heck Reaction: Catalyst Recyclabilitya

run

conversion, %

selectivity, %

b/nb

TOF/h

run

yield

selectivity (trans/cis)

TOF/h

1 2 3

100 100 98

96 98 96

1.44 1.44 1.38

800 860 820

1 2 3

94 94 93

92:8 92:8 91:9

10.6 10 10

a Reaction conditions (for hydroformylation): styrene )10 mmol, toluene/PEG-600 ) 15/5 (ml), RhPEGD-600 ) 5 µmol, P/Rh ) 10, temp ) 80 °C, 5 MPa syngas pressure, 6 h. b b/n ) ratio of branched aldehyde to linear aldehyde.

Scheme 2. Transition Metal Catalyzed Reactions Using Metal Diphosphinite Catalysts in Homogeneous Toluene-PEG Mixture: (A) Hydrogenation Reaction; (B) Heck Reaction; (C) Sonogashira Reaction; (D) Carbon Dioxide Fixation Reaction

a Reaction conditions (for Heck reaction): iodobenzene ) 1 mmol, styrene ) 2 mmol, toluene/PEG-600 ) 15/5 mL, Cl2PdPEGD-600 ) 3 mol %, Cs2CO3 ) 2 mmol, P/Pd ) 10, temp ) 80 °C, 6 h.

Table 5. Cl2PdPEGD-600 Catalyzed Sonogashira Reaction: Catalyst Recyclabilitya run

yield

TOF/h

1 2 3

90 92 89

23 23 22

a Reaction conditions (for Sonogashira reaction): iodobenzene ) 1 mmol, phenylacetylene ) 2 mmol, toluene/PEG-600 ) 15/5 mL, Cl2PdPEGD-600 ) 3 mol %, Cs2CO3 ) 2 mmol, P/Pd ) 10, temp ) 80 °C, 3 h.

Table 6. Cl2RuPEGD-600 Catalyzed Vinyl Carbamate Synthesis: Catalyst Recyclabilitya run

yield

E/Z

TOF/h

1 2 3

60 58 55

78:22 78:22 77:22

4 4 4

a Reaction conditions (for CO2 fixation reaction): phenylacetylene ) 10 mmol, diethylamine ) 20 mmol, Cl2RuPEGD-600 ) 2 mol %, toluene/PEG-600 ) 15/5 mL, 100 °C, 24 h.

Table 3. Hydrogenation of Styrene Using ClRhPEGD-600: Catalyst Recyclabilitya run

conversion, %

selectivity, %

TOF/h

1 2 3

100 100 100

100 100 100

140 160 150

a Reaction conditions (for hydrogenation): styrene ) 10 mmol, ClRhPEGD-600 ) 5 µmol, toluene/PEG-600 ) 15/5 (ml), 60 °C, 3 h.

catalyst-philic polyethylene glycol phase containing rhodium catalyst (Figure 1) by phase separation. Then, when fresh toluene and substrate were added, the catalyst was recycled directly like a homogeneous catalyst. Under the optimized reaction conditions the polyether rhodium phosphinite (RhPEGD-600) catalyst was tested up to three recycles without loss of catalyst performance in terms of reaction rate, selectivity, and activity. The organometallic complex prepared by the use of PEG supported diphosphinite ligand is extremely soluble in the PEG phase and ICP-AES analysis of the separated product phase showed only trace amounts (0.01 ppm) of Rh metal at room temperature. The initial rates of reaction for all the consecutive cycles were found to be the same (Table 2). The hydroformylation reaction of styrene was also conducted using n-hexane as solvent in place of toluene at the optimized reaction conditions, which worked in a biphasic mode, giving a low conversion of 32% due to complete immiscibility of n-hexane with the catalyst containing the PEG phase. To demonstrate the superiority of the toluene + PEG-600 (3:1) solvent mixture, the hydroformylation reaction was carried out in PEG-600 as the only solvent and it was observed that only

38% of the styrene was hydroformylated at the optimum reaction condition in 6 h. The low reactivity observed might be due to the highly viscous nature of PEG-600. Thus, the role of toluene is to decrease the viscosity of PEG-600 and facilitate the reaction at a faster rate. To illustrate the applicability of this catalysis concept to a set of diverse reactions using homogeneous catalysis, a few set of examples, such as hydrogenation of styrene, Sonogashira coupling reaction, Heck coupling reaction, and CO2 fixation, were studied (Scheme 2). 3.1. Hydrogenation. Hydrogenation of olefins to corresponding saturated hydrocarbons is a simple and fast reaction known to be easily carried out using classical Wilkinson’s catalyst [ClRh(PPh3)3].14,15 Wilkinson’s type polyether rhodium phosphinite complex [ClRhPEGD-600] was used as a catalyst for the hydrogenation of styrene to ethylbenzene. Hydrogenation of styrene to ethylbenzene is technologically important and was chosen as a test reaction to demonstrate the feasibility of the approach (Scheme 2A). The reaction was studied using 0.5 mol % of Wilkinson’s catalyst type polyether Rh diphosphinite complex [ClRhPEGD-600]. Under the optimized reaction conditions (60 °C, 2 MPa H2 gas) complete conversion of styrene to ethylbenzene was observed within 3 h of reaction time. The catalyst shows good activity and can be recycled up to three consecutive cycles without loss in its catalytic activity (Table 3). 3.2. Heck Reaction. For the Heck coupling reaction, iodobenzene and styrene were chosen as coupling partners in the present catalyst system using the novel polymeric Cl2PdPEGD600 (3 mol %) catalyst and Cs2CO3 (2 equivalent) as the base (Scheme 2B). The coupling reaction between iodobenzene and styrene led to a product yield of 94% at 80 °C for 6 h with a trans/cis ratio of 11.5:1. 3.3. Copper and Amine Free Sonogashira Reaction. Coupling between phenylacetylene and iodobenzene in a copper and

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amine free Sonogashira procedure was investigated with very high efficiency (Scheme 2C). Diphenylacetylene was obtained in 92% yield using 3 mol % of Cl2PdPEGD-600 catalyst and 2 equiv of Cs2CO3 as the base at 80 °C for 3 h. 3.4. Carbon Dioxide Fixation. The synthesis of carbon dioxide based industrially important chemicals has gained considerable attention in recent years. Vinyl carbamates, or enol carbamates, are useful intermediates for agricultural chemicals, pesticides, pharmaceutical products, monomers for transparent polymers, and varnishes.16-18 We herein report the synthesis of vinyl carbamates from carbon dioxide, amines, and alkynes catalyzed by Cl2RuPEGD-600 (Scheme 2D). This is the first homogeneous recyclable catalyst for the title reaction. 4. Conclusions In summary, polyethylene glycol is suitable both as a scaffold to anchor an active metal (Rh, Ru, and Pd) catalyst and as a solvent to conduct hydroformylation of higher olefins, hydrogenation, CO2 fixation, and C-C coupling reactions. In addition, the catalyst can be easily separated from the product by phase separation and efficiently reused with no decrease in effectiveness. Thus the concept is more general and can be applicable to a wide range of transition metal catalyzed reactions where absence of water is desirable. Acknowledgment We are thankful for financial support for this work from the Council of Scientific and Industrial Research (CSIR), India though Grant no. 01(2127)/07/EMR-II. Literature Cited (1) Chaudhari, R. V.; Bhanage, B. M.; Deshpande, R. M.; Delmas, H. Enhancement of interfacial catalysis in a biphasic system using catalystbinding ligands. Nature 1995, 373, 501. (2) Horwath, I. T.; Rabai, J. Facile Catalyst separation without water: fluorous biphase hydroformylation of olefins. Science 1994, 266, 72. (3) Adams, D. J.; Bennett, J. A.; Cole-Hamilton, D. J.; Hope, E. G.; Hopewell, J.; Kight, J.; Pogorzelec, P.; Stuart, A. M. Rhodium catalysed hydroformylation of alkenes using highly fluorophilic phosphines. Dalton Trans. 2005, 3862. (4) Jessop, P. G.; Ikariya, T.; Noyori, R. Homogeneous catalysis in supercritical fluids. Science 1995, 1065.

(5) Heldebrandt, D. J.; Jessop, P. G. Liquid Poly (ethylene glycol) and supercritical carbon dioxide: A benign biphasic solvent system for use and recycling of homogeneous catalysts. J. Am. Chem. Soc. 2003, 125, 5600. (6) Chemical Synthesis Using Supercritical Fluids; Jessop, P. G., Leitner, W., Eds.; Wiley-VCH: Weinheim, 1999. (7) Haumann, M.; Riisager, A. Hydroformylation in room temperature ionic liquids (RTILs): catalyst and process developments. Chem. ReV. 2008, 108, 1474. (8) Reek, J. N. H.; van Leeuwen, P. W. N. M.; vander Ham, A. G. J.; de Haan, A. B. In catalyst separation, recoVery and recycling chemistry and process design; Cole-Hamilton, D. J., Tooze, R. P., Eds.; Springer: Dordrecht, The Netherlands, 2006. (9) Feng, C.; Wang, Y.; Jiang, J.; Yang, Y.; Jin, Z. Rh/TMPGP complex catalyzed hydroformylation of p-isobutylstyrene in thermoregulated PEG biphase system. J. Mol. Catal. A: Chem. 2007, 268, 201. (10) Panda, A. G.; Bhor, M. D.; Ekbote, S. S.; Bhanage, B. M. Regioselectivity in hydroformylation of aryl olefins using novel rhodium polyether phosphinite catalysts. Catal. Lett. 2009, 131, 649. (11) Hong, L.; Ruckenstein, E. Immobilization of alkoxylated phosphine ligands and their Rh complexes to a silica surface coated with an organic mono- or multilayer. J. Mol. Catal. 1994, 90, 303. (12) Hong, L.; Ruckenstein, E. Liquid polymer catalyst immobilized on polymer-coated silica: application to hydroformylation. J. Chem. Soc. Chem. Comm. 1993, 1486. (13) Arhancet, J. P.; Davis, M. E.; Merola, J. S.; Hanson, B. E. Hydroformylation by supported aqueous-phase catalysis: a new class of heterogeneous catalysts. Nature 1989, 339, 454. (14) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. The preparation and properties of tris(triphenylphosphine)halogenorhodium(I) and some reactions there of including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives. J. Chem. Soc. A 1966, 1711. (15) da Rosa, R. G.; Martinelli, L.; da Silva, L. H. M.; Loh, W. Easy and efficient processes for catalyst recycling and product recovery in organic biphase systems tested in the hydrogenation of hex-1-ene. Chem. Commun. 2000, 33. (16) Mahe, R.; Sasaki, Y.; Bruneau, C.; Dixneuf, P. H. Catalytic synthesis of vinyl carbamates from carbon dioxide and alkynes with ruthenium complexes. J. Org. Chem. 1989, 54, 1518. (17) Bruneau, C.; Dixneuf, P. H. Catalytic incorporation of CO2 into organic substrates: Synthesis of unsaturated carbamates, carbonates and ureas. J. Mol. Catal. 1992, 74, 97. (18) Patil, Y. P.; Tambade, P. J.; Nandurkar, N. S.; Bhanage, B. M. Ruthenium tris(2,2,6,6-tetramethyl-3,5-heptanedionate) catalyzed synthesis of vinyl carbamates using carbon dioxide, amines and alkynes. Catal. Commun. 2008, 9, 2068.

ReceiVed for reView June 8, 2010 ReVised manuscript receiVed July 26, 2010 Accepted August 4, 2010 IE101244M