Reactions of pentaborane(11) with ethers

Article abstract of DOI:10.1021/ic50151a044

Reactions of pentaborane(11) (B₅H₁₁) with ethers were studied at low temperatures by means of ¹¹B NMR spectroscopy. The reactions of B₅H₁₁ with dimethyl and diethyl thioethers give the symmetrical cleavage products R₂S·BH₃ and R₂S·B₄H₈. Species that are produced in the reaction system of B₅H₁₁ and oxoethers are very dependent upon the base strength of the ether. Strongly basic tetrahydrofuran can effect the unsymmetrical cleavage of B₅H₁₁ to produce H₂B(THF)₂⁺B₄H₉ ^-. Evidence for the formation of this cleavage product is based on the NMR spectral evidence and on the observed reaction products produced in the reaction of HCl with the B₅H₁₁-THF system. A second species is observable in the THF-B₅H₁₁ system which is more predominant at higher temperatures. This species is assigned as the simple adduct B₅H₁₁·THF. Moderately basic ethers like dimethyl and diethyl ethers produce only one observable species which is considered to be B₅H₁₁·OR₂. Weakly basic diisopropyl ether does not react with B₅H₁₁. No direct evidence for the symmetrical cleavage of B₅H₁₁ by oxoethers has been observed. The similarities and differences between these reactions and analogous B₄H₁₀ reactions are discussed.