Syntheses and reactivities of disubstituted and trisubstituted fluorous pyridines with high fluorous phase affinities: Solid state, liquid crystal, and ionic liquid-phase properties

Reactions of 2,6-dibromo-, 3,5-dibromo-, and 2,4,6-tribromopyridine with IZnCH2CH2Rf8 (R-f8 = (CF2)(7)CF3) in THF at 65 degreesC in the presence of trans-Cl2Pd(PPh3)(2) (5 mol %) gave the fluorous pyridines 2,6- and 3,5-NC5H3(CH2CH2Rf8)(2) (1 and 2; 85%, 31%) and 2,4,6-NC5H2(CH2CH2Rf8)(3) (3, 61%). Reaction of 2,6-pyridinedicarboxaldehyde with [Ph3PCH2CH2Rf8]I-+(-)/K2CO3 (p-dioxane/H2O, 95 degreesC) gave 2,6-NC5H3(CH = CHCH2Rf8)(2) (95%; 70:30 ZZ/ZE), which was treated with H-2 (1 atm, 12 h) and 10% Pd/C to yield 2,6-NC5H3(CH2CH2CH2Rf8)(2) (5, 95%), a higher homologue of 1. Longer reaction times afforded piperidine cis-2,6-HNC5H8(CH2CH2CH2Rf8)(2) (6, 98%). The stereochemistry was established by NMR analysis of the N-benzylpiperidine. Pyridines 1-3 and 5 are low-melting white solids with CF3C6F11/toluene partition coefficients (24 degreesC) of 93.8:6.2, 93.9:6.1, > 99.7:< 0.3, and 90.4:9.6, respectively (6, 93.6:6.4). Reaction of 1 and CF3SO3H gave a pyridinium salt, and Cl2Pd(NCCH3)(2) (0.5 equiv) yielded trans-Cl2Pd(1)(2). The crystal structure of the former, which also exhibited liquid crystalline and ionic liquid phases, was determined.