A mechanistic study of a topochemical dihydrogen to covalent bonding transformation

Solid-state decomposition of the dihydrogen-bonded complex LiBH4·TEA (TEA: triethanolamine) into a covalent material was probed via 11B MAS NMR and FT-IR spectroscopies, as well as single-crystal and powder X-ray diffraction and optical microscopy. Based on variable-temperature kinetic analysis and H/D exchange experiments, H2 loss appears to occur via rate-limiting proton transfer from the TEA’s OH groups to the BH4– anions at the reactant/product interface. The activation parameters ΔH‡=84±10 kJ/mol and ΔS‡=−70±26 J/(mol K) are comparable to those found for neutral aqueous hydrolysis of BH4−, suggesting similar mechanisms for the solid and solution decompositions.