3,5‐Bis(n‐perfluorooctyl)benzyltriethylammonium Bromide (F‐TEBA): An Efficient, Easily Recoverable Fluorous Catalyst for Solid‐Liquid PTC Reactions

Abstract

A readily available 3,5-bis(perfluorooctyl)benzyl bromide and triethylamine were reacted under mild conditions to give 3,5-bis(n-perfluorooctyl)benzyltriethylammonium bromide (F-TEBA), an analogue of the versatile phase-transfer catalyst, benzyltriethylammonium chloride (TEBA), containing two fluorous ponytails. This perfluoroalkylated quaternary ammonium salt was successfully employed as a catalyst in a variety of reactions run under solid-liquid phase-transfer catalysis (SL-PTC) conditions. Thus, being both hydrophobic and lipophobic, F-TEBA could be quickly recovered in quantitative yields, and reused without loss of activity over several reaction cycles.

Di(1H,1H,2H,2H-perfluorooctyl)-dibenzo-18-crown-6: A “light fluorous” recyclable phase transfer catalyst

“…4 and Table 3 demonstrate clearly that by adding perfluoroalkyl sidearms to the dibenzo-18-crown-6 structure in compounds (14) and (15), the phase transfer catalytic activity is increased significantly, but when alkyl sidearms are attached in compound (11), the catalytic activity only increases moderately compared to dibenzo-18-crown-6 (9). The results also showed that compounds (14) and (15) have essentially the same catalytic activity and so, the length of the perfluoroalkyl group does not affect the catalytic activity in benzotrifluoride. On the other hand, the cis-4,4 0 -dialkylamino crown ether (18) showed extremely poor catalytic activity under the same reaction conditions, whilst the cis-4,4 0 -di(1H,1H-perfluoroalkylamino)-derivatised crown ether (19) had a very similar rate profile to dibenzo-18-crown-6 after 5 h. Presumably, the polarity and solubility of (18) had an important effect on the reaction equilibria constants in benzotrifluoride and (18) may be a more efficient PTC catalyst in an alternative non-fluorinated organic solvent.…”

“…Initially, when the reaction was carried out with the supported catalyst (14) in benzotrifluoride at 110 8C, the conversion was only 30% after 5 h. In comparison to the homogeneous reaction, which was complete after 3 h, this result demonstrated the reduced activity of the supported catalyst (14). The iodide displacement reaction was then carried out in ethyl acetate and THF in order to evaluate the effect of a different solvent environment on the reactivity of the supported catalyst.…”

“…The fluorous ponytails were introduced by an efficient, palladiumcatalysed Heck reaction [18] between dibromo-dibenzo-18-crown-6 and the appropriate 1H,1H,2H-perfluoroalkene to give the desired intermediates, (12) and (13), as a mixture of cis-4,4 0 -and trans-4,5 0 -isomers. The di(1H,1H,2H,2H-perfluoroalkyl)-dibenzo-18-crown-6 ether derivatives, (14) and (15), were then obtained in excellent yields by the subsequent reduction of the alkenes by a rhodium-catalysed hydrogenation. Significantly, these new dibenzo-18-crown-6 ether derivatives are soluble in most common organic solvents.…”

“…First, supported fluorous phase catalysis (SFPC) [29][30][31] was investigated for recycling the perfluoroalkylated dibenzo-18-crown-6 ether (14), which was immobilized on fluorous reverse phase silica gel (FRPSG) by simply refluxing in dichloromethane for 2 h. After cooling to room temperature, the solvent was removed under reduced pressure giving the FRPSG-supported crown ether (14) as an air-stable, free-flowing powder.…”

“…This is a relatively underexplored area of fluorous PTC with just two reports in the literature. In 2007 we reported the synthesis of a perfluoroalkylated 4,13-diaza-18-crown-6 ether (6) that is an effective phase transfer catalyst under solid-liquid conditions in aliphatic and aromatic nucleophilic substitutions [13], whilst Pozzi [14] reported in 2009 that 3,5-bis(perfluorooctyl)benzyl-triethyl ammonium bromide (7) is an efficient solid-liquid phase transfer catalyst in epoxide ring opening and N-alkylations. Both of these PTCs can be reused without loss of activity over several reaction cycles.…”