Syntheses, structures, and stabilities of aliphatic and aromatic fluorous iodine(I) and iodine(III) compounds: the role of iodine Lewis basicity.
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abstract
The title molecules are sought in connection with various synthetic applications. The aliphatic fluorous alcohols Rfn CH2OH (Rfn = CF3(CF2) n-1; n = 11, 13, 15) are converted to the triflates Rfn CH2OTf (Tf2O, pyridine; 22-61%) and then to Rfn CH2I (NaI, acetone; 58-69%). Subsequent reactions with NaOCl/HCl give iodine(III) dichlorides Rfn CH2ICl2 (n = 11, 13; 33-81%), which slowly evolve Cl2. The ethereal fluorous alcohols CF3CF2CF2O(CF(CF3)CF2O) x CF(CF3)CH2OH (x = 2-5) are similarly converted to triflates and then to iodides, but efforts to generate the corresponding dichlorides fail. Substrates lacking a methylene group, Rfn I, are also inert, but additions of TMSCl to bis(trifluoroacetates) Rfn I(OCOCF3)2 appear to generate Rfn ICl2, which rapidly evolve Cl2. The aromatic fluorous iodides 1,3-Rf6C6H4I, 1,4-Rf6C6H4I, and 1,3-Rf10C6H4I are prepared from the corresponding diiodides, copper, and Rfn I (110-130 C, 50-60%), and afford quite stable Rfn C6H4ICl2 species upon reaction with NaOCl/HCl (80-89%). Iodinations of 1,3-(Rf6)2C6H4 and 1,3-(Rf8CH2CH2)2C6H4 (NIS or I2/H5IO6) give 1,3,5-(Rf6)2C6H3I and 1,2,4-(Rf8CH2CH2)2C6H3I (77-93%). The former, the crystal structure of which is determined, reacts with Cl2 to give a 75:25 ArICl2/ArI mixture, but partial Cl2 evolution occurs upon work-up. The latter gives the easily isolated dichloride 1,2,4-(Rf8CH2CH2)2C6H3ICl2 (89%). The relative thermodynamic ease of dichlorination of these and other iodine(I) compounds is probed by DFT calculations.
