Thermolytic Decomposition of Ethane 1,2-Diamineborane Investigated by Thermoanalytical Methods and in Situ Vibrational Spectroscopy

Ethane 1,2-diamineborane (BH3NH2CH2CH2NH2BH3, EDAB hereafter) samples have been synthesized by reacting ethylenediamine dihydrochloride with sodium borohydride in tetrahydrofuran solution. Structural and bonding properties of EDAB have been characterized by liquid-state nuclear magnetic resonance, X-ray powder diffraction, and vibrational spectroscopy (infrared and Raman). The thermolytic decomposition of EDAB has been investigated by means of combined thermogravimetry, differential thermal analysis, and mass spectrometry measurements, both under vacuum and inert gas flow conditions. These experiments allow the determination of the enthalpies and activation energies of two hydrogen desorption stages below 520 K as well as the yields and purity of the released gases. These results show that EDAB presents a thermal stability, both under vacuum and under inert gas flow, higher than that of its parent counterparts methylamine borane (BH3NH2CH3) and ammonia borane (BH3NH3). Contrary to those compounds, EDAB releases pure hydrogen when heated under inert flow. In contrast, moderate fractions of diborane, residual tetrahydrofuran, and volatile B–N–C–H species are released when conducting the experiments under dynamic vacuum. In situ temperature-programmed infrared spectroscopy measurements using synchrotron radiation and operando Raman-mass spectrometry experiments provide insight into the EDAB thermolysis reaction mechanism.