Reactions of Amine–Boranes with Oxalic Acid: Substitution on the N or B Atom Leads to Different Spiroborate Compounds

• Published in: European journal of inorganic chemistry 2018-06, Vol.2018 (23), p.2659-2665
• Main Authors: Zhao, Qianyi, Li, Jiaxuan, Ma, Na‐Na, Wei, Chang‐Geng, Xu, Ting, Li, Bao, Zhang, Jie, Chen, Xuenian
• Format: Article
• Language: English
• Subjects: Amine–borane; Ammonia; Boranes; Boron; Dehydrogenation; Dihydrogen bond; Divergence; Inorganic chemistry; NMR spectroscopy; Oxalic acid; Spiro compounds; Substitution reactions
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201800258

A mild and convenient reaction of amine–boranes and oxalic acid to bi‐ or tricyclic spiroborate compounds is presented. The substitution position (on the N or B atom) of amine–boranes plays an important role on the divergence of reaction pathways: ammonia–borane (NH3·BH3, AB) or N‐substituted amine–boranes NHnMe3–n·BH3 (n = 0, 1, 2) give bicyclic spiroborate compounds 1a–d, whereas B‐substituted amine–borane NH3·BH2Me leads to tricyclic spiroborate compound 3. Fortunately, acyloxyboranes were detected as important intermediates by NMR spectroscopy in the reaction of ammonia–borane and oxalic acid, uncovering a stepwise dehydrogenation pathway. Reactions of N‐ or B‐methyl‐substituted amine–boranes and oxalic acid led to bicyclic or tricyclic spiroborate compounds, indicating that the substitution position influences the reactivity of boranes and the reaction pathway. The synthesized bicyclic bis(oxalato)borates show excellent electrochemical stability and have potential use as electrolyte salts in many electrochemical systems.