Syntheses, oxidations, and palladium complexes of fluorous dialkyl sulfides: new precursors to highly active catalysts for the Suzuki coupling
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Reactions of Rf8(CH2)nI (Rf8=CF3(CF2)7) with Li2S give the fluorous dialkyl sulfides (Rf8(CH2)n)2S (n=2, 1, 71%; 3, 2, 67%) as low melting white solids that are soluble in most fluorous and organic solvents. Reactions of 1 and 2 with CH3CO3H yield the corresponding sulfoxides (Rf8(CH2)n)2S=O (85; 80%), which are soluble in CF3C6F5 at room temperature, but insoluble in most other solvents. At higher temperatures, solubilities can become appreciable. Reactions of 1 and 2 with Na2PdCl4 (ca. 0.5equiv.) give palladium complexes [(Rf8(CH2)n)2S]2PdCl 2 (5, 94%; 6, 95%), which are soluble in only a limited range of fluorinated solvents at room temperature. The CF3C6F11/toluene partition coefficients of 1 and 2 are 98.7:1.3 and 96.6:3.4 (24C). The Suzuki coupling of aryl bromides and PhB(OH)2 to biaryls is catalyzed by 5 and 6 (0.02mol%) in CF3C6F11/DMF/H2O in the presence of K3PO4, generally at room temperature. Turnover numbers of 4500-5000 are easily achieved. However, activities decrease under fluorous biphase recycling conditions, and implications for the nature of the catalytically active species are discussed. 2002 Elsevier Science Ltd. All rights reserved.
