Calibration dependencies for aluminum organic compounds and mechanism of their thermal decomposition

In the present work the calibration dependencies for the values of ∆raHo(Xn) of atomization of aluminum organic compounds (AOC), as well as the values of RMSEAli and σAli, are determined using the 5 DFT (M062X, B3LYP, wB97XD, M08HX, and MN15 at 6-311++G(d,p) level of theory) and two composite (CBSQB3 and G3B3) approaches. The best consistencies, as well as the lowest values of RMSEAli and σAli, are observed for the M062X, CBS-QB3, and G3B3 approaches. These dependencies are found to be most consistent with those reported previously for the hydrocarbons. The determined calibration dependencies are used for the calculation of the values of ∆fHo(Xn)rec of the AOC and analysis of the thermochemistry of their reactions of association and decomposition. The results indicate the importance of dimers of AOC for the mechanism of their thermal decomposition. The most thermochemically favorable pathways of decomposition of considered AOC are the reactions of formation of hydride bond and unsaturated hydrocarbons (R27-R30). The values of activation energy for these reactions are estimated 120-130 kJ/mol. At the same time, this mechanism cannot be applied for the decomposition of Al(CH3)3 and its dimer (Al2(CH3)6). In this case, the formation of C2H6 (reaction R28) is considered more appropriate.