Synthesis and properties of fluorous arenes and triaryl phosphorus compounds with branched fluoroalkyl moieties (“split pony tails”)
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Most compounds designed for immobilization in fluorous media feature linear pony tails of the formula (CH2) m(CF2)n-1CF3 [(CH2)mRfn]. This paper presents a first-generation approach to compounds with branched or "split" pony tails of the formula (CH2) lCH[(CH2)mRfn]2. Allyl tri(n-butyl)tin is reacted twice with perfluorooctyl iodide (Rf8I; first, photochemical, 78-81%; second, thermal with radical initiator, 71%; 13-18 g scales) to give the secondary alkyl iodide ICH(CH2Rf8)2 (3). A subsequent Ni(Cl)2(PPh3)2-catalyzed reaction with allyl tri(n-butyl)tin yields the branched alkene H2C=CHCH2CH(CH2Rf8) 2 (74%). A palladium-catalyzed Heck coupling with O=P(p-C6H4Br)3 gives the fluorous phosphine oxide O=P(p-C6H4CH=CHCH2 CH(CH2Rf8)2)3 (84%), and Pd/C-catalyzed hydrogenation affords O=P(p-C6H4 (CH2)3CH(CH2Rf8) 2)3 (>99%). Reduction with SiHCl3 gives P(p-C6H4(CH2)3 CH(CH2Rf8)2)3, which is protected as the air-stable borane adduct H3B·P(p-C6H4(CH2) 3CH(CH2Rf8)2)3 (9, 64%). The CF3C6F11/toluene partition coefficient of 9 is much higher than that of the analog with p-(CH2)3Rf8 groups (96.6:3.4 versus 37.3:62.7). The iodide 3 is unreactive towards PAr3 at 175-250 °C. However, a CuBr-catalyzed reaction with C6H5MgBr gives C6H5 CH(CH2Rf8)2, which also exhibits a high partition coefficient (97.9:2.1). © 2003 Elsevier B.V. All rights reserved.
author list (cited authors)
Wende, M., Seidel, F., & Gladysz, J. A.