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

Although the nature of bis-phosphazine species are of much interest, there are few reports of their reactivity. Herein, we show that the bis-phosphazine species Ph3PNNPPh31 react with Lewis acids to give the Lewis acid adducts Ph3PNN(B(C6F5)3)PPh33 and Ph3PN(BF3)N(BF3)PPh34. 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 Cy3PNNPCy32 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.