Synthesis and Characterization of (R)‐N‐1‐Cyclohexylethylamine Borane

(R)-N-1-cyclohexylethylamine borane C₆H₁₁CH(CH₃)NH₂BH₃ (CHEAB) is a new solid amine borane that forms as millimeter-sized translucent stick-like crystals (orthorhombic; s.g. P2₁2₁2₁) owing to the occurrence of intermolecular dihydrogen bonds between antiparallel NH₂BH₃ groups. Pure CHEAB decomposes under heating and is not suitable for hydrogen storage, but it may have potential as a precursor of polymers and/or carbon-doped boron nitride.

Abstract

A new solid amine borane is reported here. The reaction of (R)-(−)-1-cyclohexylethylamine (a liquid at room temperature) with borane dimethylsulfide yields crystals of pure (R)-N-1-cyclohexylethylamine borane C₆H₁₁CH(CH₃)NH₂BH₃ (CHEAB). The successful synthesis was confirmed by molecular analyses (FTIR, Raman and NMR). The crystals are in the form of millimeter-sized translucent sticks, which allowed determining that CHEAB crystallizes in the orthorhombic system, the space group being P2₁2₁2₁. All of the characterization results, together with DFT calculations, strongly suggest the occurrence of intermolecular dihydrogen bonds between antiparallel NH₂BH₃ groups that are in a trimeric configuration.

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