Carbon dioxide pressure induced heterogeneous and homogeneous Heck and Sonogashira coupling reactions using fluorinated palladium complex catalysts

Abstract

The Heck reaction of iodobenzene and methyl acrylate was investigated with CO 2 -philic Pd complex catalysts having fluorous ponytails and the organic base triethylamine (Et 3 N) in the presence of CO 2 under solventless conditions at 80 C. The catalysts are not soluble in the organic phase in the absence of CO 2 and the reaction occurs in a solid-liquid biphasic system. When the organic liquid mixture is pressurized by CO 2 , CO 2 is dissolved into the organic phase and this promotes the dissolution of the Pd complex catalysts. As a result, the Heck reaction occurs homogeneously in the organic phase, which enhances the rate of reaction. This positive effect of CO 2 pressurization competes with the negative effect that the reacting species are diluted by an increasing amount of CO 2 molecules dissolved. Thus, the maximum conversion appears at a CO 2 pressure of around 4 MPa under the present reaction conditions. The catalysts are separated in the solid granules by depressurization and are recyclable without loss of activity after washing with n-hexane and/or water. When the washing is made with hexane alone, the catalytic activity tends to increase on the repeated Heck reactions, probably due to the accumulation of such a base adduct as Et 3 NHI on the catalysts. When the washing is further made with water, however, the base adduct is taken off from the catalysts and they show similar activity levels in the repeated runs. The potential of CO 2 pressure tunable heterogeneous/homogeneous reaction system has also been investigated for Sonogashira reactions of iodobenzene and phenylacetylene under similar conditions.

ScCO2/Green Solvents: Biphasic Promising Systems for Cleaner Chemicals Manufacturing

“…In these cases, CO 2 acts as a solubility switch. 54 This interesting feature of CO 2 and its utilization for reactions such as hydrogenations and epoxidations have been reviewed in a paper published by Eckert et al 55 In order to promote green solvents such as glycerol as an alternative solvent to water when this last one cannot be used, sugar-based surfactants have been designed in order to stabilize several catalysts and are used in the ring opening of several epoxides with carboxylic acids. The surfactants thus used were aminopolysaccharides obtained by the oxidation of hydroxyethylcellulose with sodium periodate, followed by a catalytic amination over Pd/C.…”

Selective photoreduction of CO2 to CO in CO2-dissolved expanded liquid phase with heterogeneous CO2-philic Pd complex catalysts

“…R f = n-C 11 F 23 , was reported elsewhere [29,30], which will be abbreviated as Pd-F 21 and Pd-F 23 , respectively, in the following. A fluorinated silica support, silica gel 60 C 8 -reversed phase perfluorinated (synonym: perfluorinated silica gel 60), was purchased from Fluka.…”

Synthesis of new CO2-soluble ruthenium(II) and cobalt(II) polypyridine complexes bearing fluorinated alkyl chains and their application to photoreduction of liq. CO2

“…Four new ligands, F84OPh, F44OPh, F62Ph, and F62O, were prepared from appropriate 2,2 0 -bipyridine derivatives and fluoroalkyl chains, as shown in Scheme 1, according to the literature [5][6][7][8][9][10][11][12][13][14][15]: F84OPh and F44OPh were obtained by coupling between 4,4 0 -bis(p-hydroxyphenyl)-2,2 0 -bipyridine and the corresponding 4-(perfluoroalkyl)butyl tosylates [5][6][7][8][9][11][12][13]15]. F62Ph was prepared by the Suzuki coupling reaction between 4,4 0 -dibromo-2,2 0 -bipyridine and p-(2-(perfluorohexyl)ethyl)phenylboronic acid [8][9][10][11][12]16,17].…”

“…CO 2 is expected to be enhanced by incorporating ''CO 2 -philic'' ligands, an enhancement that can be achieved by the introduction of fluoroalkyl chains into the parent ligands to enhance their lipophilicity [2][3][4][5][6][7]. In this paper, we present a preliminary report on the first preparation of CO 2 -soluble Ru(II) and Co(II) polypyridine complexes bearing fluorinated alkyl chains and their application to the photoreduction of liq.…”