UC Santa Barbara

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 V^IV/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 V^V complex (1b) in the presence of a bulky phosphine, homolytic peroxide, or Sn-hydride bond cleavage reactions were observed with the V^IV 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 V^IV/V oxidation states allows these compounds to access reactivity observed in both FLP and FRP chemistry.