Cyclic Group 15 Radical Cations

Abstract

Singlet cyclo-1,3-dipnicta-2,4-diazane-1,3-diyls of the type [E(μ-NTer)2 E] (2, E=P, As, Ter=2,6-dimesitylphenyl) can undergo a one-electron-oxidation utilizing silver salts of weakly coordinating anions such as [AgLn][B(C6F5)4 ] (L=donor solvents) to afford the novel cyclic radical cations, [E(μ-NTer)2E](+·) (3(+·)). When smaller and more basic anions were employed in the reaction, the anions were found to form covalent bonds to the radical centers yielding dipnictadiazanes, [FP(μ-NTer)2PF] (5) and [(CF3CO2)P(μ-NTer)2P(CF3CO2)] (6). A two-electron oxidation process, resulting in the formation of dications of the type [E(μ-NTer)2E](2+), could not be observed. Computational and EPR data revealed that the spin density is almost completely localized at the two heavier pnictogen centers E of the former 1,3-dipnictadiazane-1,3-diyls. The bonding situation in the radical cations features a rare example of a transannular one-electron π bond without having a σ bond.

Keywords: arsenic; group 15 elements; oxidation; phosphorus; radical.