Redox-Controlled Reactivity at Boron: Parallels to Frustrated Lewis/Radical Pair Chemistry.

We report the synthesis of new Lewis-acidic boranes tethered to redox-active vanadium centers, (Ph2N)3V(μ-N)B(C6F5)2 (1a) and (N(CH2CH2N(C6F5))3)V(μ-N)B(C6F5)2 (1b). Redox control of the VIV/V couple resulted in switchable borane versus "hidden" boron radical reactivity, mimicking frustrated Lewis versus frustrated radical pair (FLP/FRP) chemistry, respectively. Whereas heterolytic FLP-type addition reactions were observed with the VV complex (1b) in the presence of a bulky phosphine, homolytic peroxide, or Sn-hydride bond cleavage reactions were observed with the VIV complex, [CoCp2*][(N(CH2CH2N(C6F5))3)V(μ-N)B(C6F5)2] (3b), indicative of boron radical anion character. The extent of radical character was probed by spectroscopic and computational means. Together, these results demonstrate that control of the VIV/V oxidation states allows these compounds to access reactivity observed in both FLP and FRP chemistry.