Cationic Chains of Parent Arsanylboranes and Substituted Phosphanylboranes

The substituted monomeric phosphanylboranes Ph₂P−BH₂⋅NMe₃ (1) and tBuHP−BH₂⋅NMe₃ (2) have been used for the synthesis of cationic chain compounds built up by R₂P−BH₂ units. With a simple synthesis route, the highly stable cations [Me₃N⋅H₂B−PR₁R₂−BH₂⋅NMe₃]⁺ (1 a, 2 a) and [Me₃N⋅H₂B−PR₁R₂−BH₂−PR₁R₂−BH₂⋅NMe₃]⁺ (1 b, 2 b) (R₁=R₂=Ph; R₁=H, R₂=tBu) are obtained as iodide (I⁻) salts. The reaction of H₂As−BH₂⋅NMe₃ (3) with IBH₂⋅SMe₂ leads to [Me₃N⋅H₂B−AsH₂−BH₂−AsH₂−BH₂⋅NMe₃][I] (3 a), the longest so far known arsanylborane chain. Compound 3 a reacts with acetonitrile through a formal hydroarsination reaction to form [cyclo-{As(BH₂⋅NMe₃)(CMe=NH)₂(BH₂)}][I] (4). The reported synthetic strategy has proved to be a powerful tool for the formation of small, cationic oligomeric units. All products were comprehensively characterized by X-ray structure analysis, NMR, IR spectroscopy, and mass spectrometry in cooperation with DFT calculations.