complex 7 , which is analogous to 6, but rather 2, R=mesityl."' Compound 7, however, is formed as a by-product in the reaction of 1-BF,, R=mesityl, with diethyl ether and Br0/CH2Cl2 .[l"l Compound 7 can be generated cyclovoltammetrically by reversible reduction of the cation 1, R = mesityl ( E , = + 0.66 V versus sat. Ag@/AgCI, -30 "C, 0.3 M NBu,BF, in CH2CI2). At room temperature, 7 reacts rapidly (in less than one minute) with Br2 to give 2, R=mesityl; yield ca. 40% for 7:Br2= 1:l. In contrast, 7 reacts with Br' only very slowly upon prolonged standing of the solution at room temperature.
The reaction sequence summarized in Scheme 1 is thus an impressive example for SET (single-electron-transfer) reactivity:l"] the species I-Br and 5-Br, formed by removal of AIBr3 undergo an intramolecular SET reaction to form a radical pair, presumably on account of the very positive redox potentials of the cations and the easy oxidation of bromide in CH,C12; both cage products"" ( 2 in the case of the tungsten complex) and primary (6, 7) and secondary (3) escape products are detectable. We are currently investigating the fate of the Bra species. To the best of our knowledge, 6 and 7 are the first complexes in which an isocyanide radical functions as complex ligand.1121