Synthesis and evaluation of stable, efficient, and recyclable carbonylation catalysts: Polyether-substituted lmidazolium carbonyl cobalt lonic liquids
Graphical abstract
Polyether-substituted imidazolium ionic liquids, representing an affirmative case of stabilizing the highly air sensitive cobalt tetracarbonyl anion, have been successfully synthesized and used in hydroesterification of 4-isobutylstyrene by thermoregulated phase-separable catalysis (TPSC) system. The TPSC system exhibits good recycling efficiency and provides a potential route for an environmentally benign carbonylation reaction.
Introduction
In recent years, functionalized ionic liquids (FILs) have been paid increasing research attention because of their ability to be tailored for various chemical tasks [1], [2]. Many transition metal carbonyl species have been introduced into FILs, producing organometallic ionic liquids [3], [4], [5], which, while having comparable catalytic activity to conventional organometallic catalysts, show some improvements, such as lower viscosity, better stability, improved solubility, and excellent recovery [6], [7].
PEG-based ionic liquids are a new appealing group of solvents making the link between two distinct but very similar fluids: ionic liquids and poly(ethylene glycol)s. They find applications across a range of innumerable disciplines in science, technology, and engineering. In the last two years, the possibility to use these as alternative solvents for organic synthesis and catalysis has been increasingly explored [8].
The cobalt tetracarbonyl anion, [Co(CO)4]−, is one of the most important active catalytic species and has been widely used in a number of catalytic reactions [9], [10], [11], [12], [13], [14], [15], [16], [22]. Although some ionic liquid compounds containing [Co(CO)4]− have been successfully synthesized and employed in some reactions, most of them are homogeneous catalysts, which are difficult to recycle. In addition, because it is unstable and sensitive to air, the direct use of [Co(CO)4]− is limited [5].
The search for a way to combine the advantages of homogeneous catalysis, such as ease of modulation, and heterogeneous catalysis, such as ease of recycling, is one of the most exciting challenges in modern chemistry. Indeed, various efficient immobilization methods for homogeneous catalyst have been developed in recent years through the use of methods such as liquid–liquid organometallic biphasic catalysis and heterogenization of molecular catalysts on solid supports. However, the advantages of these methods come at the expense of catalytic activity [17].
For the purpose of the recycling of catalysts, functionalized ionic liquid methodology was tentatively applied to the ionic liquid/organic biphasic catalysis system [18]. For example, we have shown that [bmim] [Co(CO)4] (bmim = 1-butyl-3-methylimidazolium) is an efficient catalyst for the hydroesterification of ethylene oxide [14]. It was reported that introducing the polyether chain to the ligands or ionic liquids not only facilitates dispersion in the reaction system by reducing ionic liquid viscosity, but also allows catalysts to be thermoregulated [19].
In this paper, we report the convenient synthesis of a series of polyether-substituted imidazolium cobalt carbonyl ionic liquids, as well as their detailed characterization and catalytic performance in hydroesterification. Moreover, preliminary studies on the application of these functionalized ionic liquids in a thermoregulated phase-separation catalysis system (TPSC) have been performed by applying this system to the hydroesterification of 4-isobutyl styrene.
Section snippets
Synthesis of the polyether-substituted imidazolium carbonyl cobalt ionic liquids
The synthesis of [H(OCH2CH2)nbim][Co(CO)4)] 4 is shown in Scheme 1. NaCo(CO)4 was prepared by a method previously reported in the literature [20]. Firstly, ethylene oxide was reacted with imidazole to obtain 3-poly(ethylene glycol) imidazole 2 containing different numbers of polymerized ethylene oxide units (n = 8, 15, and 22). Then, 2 was reacted with n-butyl chloride to produce chloro-substituted 1-butyl-3-poly(ethylene glycol) imidazole 3, i.e., [H(OCH2CH2)nbim]Cl, 3. Finally, compounds 4 were
Conclusion
New polyether-substituted imidazolium ionic liquids (4a–c) have been successfully synthesized and characterized. Notably, compound [H(OCH2CH2)22bim] [Co(CO)4)] (4c) has good stability compared with formerly reported analogs, and may be regarded as a highly stabilized form of the highly air sensitive cobalt tetracarbonyl anion. We believe that the effective stabilization of the anion is brought about by interionic bonds and the structure of the polyether chain.
Due to its solubility in water and
Materials and analysis of product
All chemicals used in this work were purchased. The solvents were used after distillation and drying by standard procedures. The products of the reaction were analyzed by GC (SP6800A) equipped with a flame ionization detector, a capillary column (OV-17, 30 m × 0.25 μm × 0.25 mm). N2 was used as the carrier gas. GC–MS measurements were performed on a 7890A-G C/5975C-MSD instrument with a 19091S-433HP-5MS column (30 m × 250 μm × 0.25 μm). Helium was used as the carrier gas. IR spectra was measured from 4000 to
Competing interest
The authors declare no competing financial interest.
Acknowledgments
This work was supported by grants from the National Natural Science Foundation of China (NSFC21376128), Natural Research Foundation of Shan Dong Province (ZR2012BL02), and Research Project by education Department of Shan Dong Province (J10LB07).
References (43)
- et al.
J. Organomet. Chem.
(1969) - et al.
J. Organomet. Chem.
(1992) - et al.
J. Organomet. Chem
(2011) - et al.
Chem. Eng. Sci.
(2004) - et al.
J. Mol. Catal. A
(2000) - et al.
J. Electroanal. Chem.
(2004) - et al.
J. Catal.
(2012) - et al.
Angew. Chem. Int. Ed.
(2000) - et al.
Chem. Rev.
(2002) - et al.
Organometallics
(2005)
Dalton Trans.
Chem. Commun.
Chem. Eur. J.
Inorg. Chem.
ChemSusChem.
J. Org. Chem.
2004
Chem. Lett.
Pet Chem.
J. Am. Chem. Soc.
Oil Gas Sci. Technol.
Z. Naturforsch B
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