Reactions of R₃PNNPR₃ Species with Boranes: Classical Adducts, FLPs, and Radical Cations

Although the nature of bis-phosphazine species is of much interest, there are few reports of their reactivity. Herein, we show that the bis-phosphazine species Ph₃PNNPPh₃ 1 react with Lewis acids to give the Lewis acid adducts Ph₃PNN(B(C₆F₅)₃)PPh₃ 3 and Ph₃PN(BF₃)N(BF₃)PPh₃ 4. Compound 1 also generates a frustrated Lewis pair (FLP) in the presence of BPh₃ and thermolysis of 1/BPh₃, or 3 at 80 °C released N₂ while 4 was stable at 80 °C. In contrast, the species Cy₃PNNPCy₃ 2 reacted with B(C₆F₅)₃ to effect single electron transfer affording a frustrated radical pair (FRP). Independent reactions of 1 and 2 with [Cp₂Fe][BF₄] gave the corresponding radical salts [R₃PNNPR₃]^•+[BF₄] (R = Cy 5b Ph 6). Structural and computational data show the N─N bond is strengthened in the bis-phosphazine radical cation.