Generation of Tris(dialkylamino)cyclopropenyl Radical Dications by Pulse Radiolysis and Redox Potential Determination for the C3(NEt2)3•2+/C3(NEt2)3+ and C3(NC5H10)3•2+/C3(NC5H10)3+ Couples

Abstract

Pulse radiolysis experiments were carried out with neutral aqueous solutions of cyclopropenyl cations C3(NR2)3+, (R2 = Et2, C5H10) also containing bromide, iodide, or azide, to study possible one-electron transfer rates and equilibria involving C3(NR2)3•2+/C3(NR2)3+ couples. Br2•- oxidized C3(NR2)3+ completely to the corresponding radical dication with rate constants of 2.1 × 108 (R2 = Et2) and 7.4 × 108 L mol-1 s-1 (R2 = C5H10), whereas no reaction was detected between Br- and C3(NR2)3•2+. In contrast, the C3(NR2)3•2+ radical was found to oxidize I-, although no reaction was observed between I2•- and C3(NR2)3+. With azide, however, the system reached equilibrium, N3• + C3(NR2)3+ ⇄ N3- + C3(NR2)3•2+. From the equilibrium constants K = 90 (R2 = Et2) and K = 280 (R2 = C5H10) and the known redox potential E(N3•/N3-) = 1.35 V, we calculate E(C3(NR2)3•2+/C3(NR2)3+) = 1.23 ± 0.04 (R2 = Et2) and 1.20 ± 0.03 V (R2 = C5H10) versus NHE.