Synthesis, Structures, and Reactivities of BCN-Heterocyclic B–N Chains

The BCN-heterocyclic B–N chain compounds, the sodium and potassium salts of 3 and 4 anions (Na3, Na4, and K4), were synthesized by reactions of ethane 1,2-diamineborane (BH3NH2CH2CH2NH2BH3, 1) and propane 1,2-diamineborane (BH3NH2CH2CH2CH2NH2BH3, 2) with MH (M = Na and K). Then, the neutral B–N chain compounds 5 and 6 were prepared with dehydrogenation of [NH4]3 and [NH4]4, formed by metathesis reactions of Na3 and Na4 with NH4Cl or NH4SCN, respectively. Compounds 7 and 8, analog 5, were also prepared using pyridine and 4-methoxypyridine instead of NH3 in 5. These synthesized compounds were characterized spectroscopically, and the singe-crystal structures of the Na3·18-crown-6 and K4·18-crown-6 adducts were determined. Furthermore, the reactions of Na3 and Na4 with cationic B–N chain compounds, [NH3BH2NH3]Cl and [NH3BH2NH2BH2NH3]Cl, could not form longer BCN-heterocyclic B–N chain. The solubility of metal hydrides, the ability for proton abstracting, the basicity of Lewis bases, and the chelate effect may influence these reactions even though the reaction mechanism is not fully understood.