Wrapping an Organic Reducing Reagent in a Cationic Boron Complex and Its Use in the Synthesis of Polyhalide Monoanionic Networks

The reaction between BF 3 ⋅ OEt 2 and one of two guanidines, 1,8‐bis(tetramethylguanidinyl)naphthalene (btmgn) and 1,2,4,5‐tetrakis(tetramethylguanidinyl)naphthalene (ttmgn), yields the salts [(btmgn)(BF 2 )]BF 4 and [(ttmgn)(BF 2 ) 2 ](BF 4 ) 2 . NMR spectroscopic data show that the boron atoms in the cation and anion exchange in the case of [(ttmgn)(BF 2 ) 2 ](BF 4 ) 2 , but not in the case of [(btmgn)(BF 2 )]BF 4 . The rate constant for this exchange was estimated to be 4 s −1 at 80 °C for solutions in CH 3 CN. These salts were subsequently used for the reduction of dihalides Br 2 or I 2 to give polyhalide salts. We report the synthesis and first complete characterization (including structural analysis) of salts that contain pentabromide monoanions. In these salts, the Br 5 − anions interact to give dimeric units or polymeric chains. Our results are compared to previous quantum chemical calculations on the gas‐phase structure of the Br 5 − anion. The possible pathways that lead to the polyhalides are evaluated. In the case of [(ttmgn)(BF 2 ) 2 ](BF 4 ) 2 , reduction is accompanied by ttmgn oxidation, whereas in the case of [(btmgn)(BF 2 )]BF 4 reduction is initiated by aromatic substitution.