From hypervalent xenon difluoride and aryliodine(III) difluorides to onium salts: Scope and limitation of acidic fluoroorganic reagents in the synthesis of fluoroorgano xenon(II) and iodine(III) onium salts

Abstract

Fluorinated organodifluoroboranes R fBF 2 are in general suitable reagents to transform XeF 2 and RIF 2 into the corresponding onium tetrafluoroborate salts [R fXe][BF 4] and [R(R f)I][BF 4], respectively. (4-C 5F 4N)BF 2 and trans-CF 3CF CFBF 2 which represent boranes of high acidity form no Xe–C onium salts in reactions with XeF 2 but give the desired iodonium salts with RIF 2 (R = C 6F 5, o-, m-, p-C 6FH 4). The reaction of (4-C 5F 4N)BF 2 with XeF 2 ends with a XeF 2–borane adduct. C 6F 5Xe(4-C 5F 4N), the first Xe-(4-C 5F 4N) compound, was obtained when C 6F 5XeF was reacted with Cd(4-C 5F 4N) 2. We describe the synthesis of (4-C 5F 4N)IF 2 and reactions of (4-C 5F 4N)IF 2 and C 6F 5IF 2 with (4-C 5F 4N)BF 2. Analogous to [(4-C 5F 4N) 2I][BF 4] and [C 6F 5(4-C 5F 4N)I][BF 4] aryl(perfluoroalkenyl)iodonium salts [R(R′)I][BF 4] were obtained from RIF 2 (R = C 6F 5, o-, m-, p-C 6FH 4) and R′BF 2 (R′ = trans-CF 3CF CF, CF 2 CF). The gas phase fluoride affinities pF − of selected fluoroorganodifluoroboranes R fBF 2 and their hydrocarbon analogs are calculated (B3LYP/6-31+G *) and discussed with respect to their potential to introduce R f-groups into hypervalent EF 2 bonds. Four aspects which influence the transformation of hypervalent EF 2 bonds (E = Xe, R′I) under the action of Lewis acidic reagents RAF n−1 (A = B, P; n = 3, 5) into the corresponding [RE][AF n+1 ] salts are presented and the important role of the acidity is emphasized. Fluoride affinities may help to plan the introduction of organo groups into EF 2 moieties and to expand the types of acidic reagents. Thus C 6H 5PF 4 with a pF − value comparable to that of R fBF 2 compounds is able to introduce the C 6H 5 group into RIF 2 (R = C 6F 5, p-C 6FH 4).