Phase‐Transfer Catalysis with Ionene Polymers

Abstract

Ionene polymers were found to be versatile phase-transfer catalysts for a variety of different reactions like a-alkylation reactions or Michael addition reactions. Reasonably low catalyst loadings allowed us to obtain the target products under operationally simple biphasic conditions at ambient temperature and the ionenes can be recovered and reused by simple filtration.Ionene polymers constitute an important class of polyelectrolytes [1] in which quaternary ammonium groups form part of the polymer backbone. [2] These polymers are typically prepared either by chain or step polymerization of suitable monomers (e. g., self-polyaddition of aminoalkylhalides, Menshutkin reaction between bis-tertiary amines and activated dihalides) or by cationic functionalization of reactive precursor polymers. [3] The first ionene was synthesized by Marvel and co-workers in 1930, [4] and since then ionenes have been widely studied for a number of applications in chemistry, biology, physics, medicine and materials science. [2] Some of us have recently described the synthesis of new ionene polymers containing DABCO and N,N'-(x-phenylene)dibenzamide (x = ortho-/meta-/para-) and their intriguing self-assembly properties in aqueous medium (Scheme 1). [5] On the other hand, the use of quaternary ammonium salts as phase-transfer catalysts (PTCs) has emerged as one of the fundamental principles in catalysis, which found widespread applications on laboratory scale and for industrial processes [6] by using either achiral or chiral ammonium salt catalysts. [7] Based on our interests in the design and development of new (asymmetric) PTCs [8] and the above-mentioned functional ionenes, [5] we report here the first evidences of the catalytic potential of some ammonium ionene polymers for different fundamental reactions under phase-transfer conditions.We put our main focus on the alkylation of glycine Schiff base 1 under biphasic conditions. This transformation, which gives access to a variety of natural and non-natural amino acids in either a racemic [9] or an enantioenriched manner, [10] turned out to be one of the benchmark reactions for novel PTCs in the past. Scheme 2 shows a simplified mechanistic illustration for the possible function of ionene polymers A as phase-transfer catalysts for this transformation (as these polymers show a rather limited solubility in organic solvents and aqueous solutions an interfacial mechanism seems to be most likely but it must be pointed out that presently no further experimental proof therefore is available). Table 1 gives an overview of the most significant results obtained in a thorough screening of the alkylation of 1 with benzylbromide (2) by using the three regioisomeric ionenes A under different biphasic conditions. The reactions proceeded [a] M.

Isomeric cationic ionenes as n-dopant agents of poly(3,4-ethylenedioxythiophene) for in situ gelation

“…Cationic polyelectrolytes bearing quaternary ammonium in the backbone constitute an important group of highly charged polymers, named ionenes, with potential uses in the biomedical [1][2][3] and catalytic applications. [4][5][6][7] The synthesis of new ionene polymers (Scheme 1) containing 1,4-diazabicyclo[2.2.2]octane (DABCO) and N,N'-(xphenylene)dibenzamide (x= ortho-/ meta-/ para-) was described and their gelation capacity in aqueous media was reported by some of us. 8,9 It was found that the topology of this polymers plays a fundamental role in their self-assembly properties in pure water 8 and in aqueous solutions with different acidic pH and ionic strength.…”

Cationic Polymers Bearing Quaternary Ammonium Groups-Catalyzed CO2 Fixation with Epoxides

“…These salts were prepared by carrying out a chloride to iodide exchange of the initially used salts (see the supporting information for details). Very interestingly, this lead to a significant improvement in case of the A and B series (entries [17][18][19][20], which performed rather slow with chlorides only. On the other hand, those polymers that performed well for the chloride salts already (i.e.…”

“…To investigate the influence of the counter anion we next tested the corresponding iodide-based polymers (entries [17][18][19][20][21][22][23][24]. These salts were prepared by carrying out a chloride to iodide exchange of the initially used salts (see the supporting information for details).…”

“…ortho-, meta-, para-) in some of these polymers was found to play a key role on the hydrogelation [15], dye uptake [16] and antimicrobial properties [17]. In addition, our groups and others have shown that these versatile polymers can also serve as easily recoverable and reusable phase-transfer catalysts for a variety of different transformations [18][19][20].…”

“…Some rather recent reports describing the use of functionalized polymers to catalyze the CO 2 fixation with epoxides caught our interest [45][46][47]. Considering the previously described potential of ionenes as catalysts [18], we thus now started a program with the focusing on investigating a variety of structurally different polycations bearing ammonium groups A-F for their potential to catalyze the CO 2 incorporation into epoxides 1 under an atmospheric pressure of CO 2 (Scheme 1).…”