From Neutral Diarsenes to Diarsene Radical Ions and Diarsene Dications

Stable main-group element-centered radicals have attracted tremendous attention. We report here the synthesis and molecular structures of both an arsenic-centered radical anion and a radical cation. In addition, the synthesis of base-coordinated and base-free diarsene dications is presented.

Abstract

Diarsene [L(MeO)GaAs]₂ (L=HC[C(Me)N(Ar)]₂, Ar=2,6- ⁱ Pr₂C₆H₃, 4) reacts with MeOTf and ^MeNHC (^MeNHC=1,3,4,5-tetra-methylimidazol-2-ylidene) to the diarsene [L(TfO)GaAs]₂ (5) and the carbene-coordinated diarsene [L(MeO)GaAsAs(^MeNHC)Ga(OMe)L] (6). The NHC-coordination results in an inversion of the redox properties of the diarsene 4, which shows only a reversible reduction event at E _1/2=−2.06 V vs Fc^0/+1, whereas the carbene-coordinated diarsene 6 shows a reversible oxidation event at E _1/2=−1.31 V vs Fc^0/+1. Single electron transfer reactions of 4 and 6 yielded [K[2.2.2.]cryp][L(MeO)GaAs]₂ (8) and [L(MeO)GaAsAs(^MeNHC)-Ga(OMe)L][B(C₆F₅)₄] (9) containing the radical anion [L(MeO)GaAs]₂⋅⁻ (8⋅⁻) and the NHC-coordinated radical cation [L(MeO)GaAsAs(^MeNHC)Ga(OMe)L]⋅⁺ (9⋅⁺), respectively, while the salt-elimination reaction of the triflate-coordinated diarsene 5 with Na[B(C₆F₅)₄] gave [LGaAs]₂[B(C₆F₅)₄]₂ (11) containing the dication [LGaAs]₂ ²⁺ (11²⁺ ). Compounds 1–11 were characterized by ¹H and ¹³C NMR, EPR (8, 9), IR, and UV-Vis spectroscopy and by single crystal X-ray diffraction (sc-XRD). DFT calculations provided a detailed understanding of the electronic nature of the diarsenes (4, 6) and the radical ions (8⋅⁻, 9⋅⁺), respectively.

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