Oxidation of Olefins Using Rhenium Supported by Imidazole-Functionalized Amphiphilic Copolymers
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Oxidation of Olefins Using Rhenium Supported by Imidazole-Functionalized Amphiphilic Copolymers Sheng-Hsuan Wei Æ Shiuh-Tzung Liu
Received: 12 August 2008 / Accepted: 10 September 2008 / Published online: 7 October 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Well-defined amphiphilic EO45-b-MAm block copolymers modified with aminopropyl-imidazole groups are used as a support for methyltrioxorhenium. This material appears to be a good catalyst for the oxidation of olefins into the corresponding diols and can be recycle-used. Keywords Oxidation of olefin Amphiphilic block copolymer Recycle catalyst Rhenium
intended to use EOn-b-MAm for preparation of a core-shelltype nano-reactor where the hydrophobic core provides a favorable environment for the metal complex and the reactant, while the hydrophilic shell allows these reactors to be water soluble. Here we describe the preparation of welldefined amphiphilic copolymers (EOn-b-MAm) with imidazole units covalently attached to the polymer. The rhenium complexes with this copolymer are studied for the aqueous two-phase oxidation of alkenes.
1 Introduction
2 Experimental
The use of micelle systems, which are capable of dissolving organic molecules in water, in obtaining product formation has received much attention and provokes chemist to examine the potential micelles as reaction media [1, 2]. In this context, it has been demonstrated that polymer supports undergo self-assemble in water to form micellar aggregates with a hydrophobic environment providing reactivity better than conventional micelles based on small molecule surfactant [1, 2]. Soluble polymeric supports involve polystyrene, poly(ethylene glycol), and dendritic/hyperbranched polymers [3–7]. In our previous work, we have found that polymers of poly (ethylene glycol)-b-(methyl acrylate) [denoted as EOnb-MAm] are excellent agents to form uniformly micellar aggregates in water with a hydrophobic core and watersoluble shell, thus templating the synthesis of mesoporous silicas [8–10]. Inspired by polymer-support catalysis, we
All reaction steps for polymerization were performed under a dry nitrogen atmosphere. Dichoromethane was dried with CaH2 and distilled under nitrogen. [CH3(OCH2CH2)45 NH2], N[CH2CH2N(CH3)2]3 (Metren), and macro-initiator MI were prepared according to the method reported in literature [10]. Nuclear magnetic resonance spectra were recorded on a Bruker AVANCE 400 spectrometer. Infrared spectra were measured on a Nicolet Magna-IR 550 spectrometer (Series-II) as KBr pallets. Gel permeation chromatography (GPC) data were obtained from a Waters Model 590 liquid chromatograph installed with a Lab Allience RI 2000 detector using THF as eluant (at the rate 1 mL/min) at 40 °C and polystyrene calibration curve for analyses. 2.1 Synthesis and Characterization (Scheme 1) 2.1.1 Diblock Copolymer (EO45-b-MAm)
S.-H. Wei S.-T. Liu (&) Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, ROC e-mail: [email protected]
A mixture of MI (5.0 g, 2.3 mmol) and CuBr (85 mg,
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