Mechanisms and dynamics of the thermal deazetization of 2,3-diazabicyclo[2.2.1]hept-2-ene Komal Yadav and Upakarasamy Lourderaj School of Chemical Sciences, India The experimentally observed major double inversion of configuration in the thermal deazetization of 2,3-diazabicyclo[2.2.1]hept-2-ene ( dbh ) has been well studied both experimentally [1-3] and computationally [4-6]. The computational studies show that the potential energy surface for the deazetization was sensitive to the level of theory, and the stationary points along the asynchronous pathway could not be identified. It was thus proposed that the reaction follows synchronous pathway and the preference for the inversion of configuration in bicyclopentanewas attributed to dynamical effects [5]. In this study, the detailed potential energy profiles for the deazetization reaction of dbh were mapped by considering both the synchronous and asynchronous pathways using the CASSCF, CASPT2, and DFT methods. It was found that DFT methods were inadequate to describe the reaction pathways. The transition states and intermediates along the synchronous and asynchronous pathways were identified at the CASSCF(4,4) and CASSCF(12,12) levels. The energetics of the two pathways at the CASSCF levels were found to be comparable to the CASPT2(4,4) results. The barriers for the synchronous and asynchronous denitrogenation pathways were 36.1 and 37.2 kcal/mol respectively at the CASSCF(4,4)/6-31+G* level and strongly indicate that the reaction can follow both the synchronous and asynchronous pathways. To investigate the dynamical pathways followed during the reaction, the dynamics of the system was studied by using ab initio classical dynamics simulations at the CASSCF(4,4)/6-31+G* level of theory. Trajectories were initiated from the reactant, and the synchronous and asynchronous transition states. The simulations reveal the formation of products via both the synchronous and asynchronous denitrogenation pathways. A major double inversion of configuration was observed during the product formation for the trajectories integrated from all the three regions, consistent with the experiments. The five-membered cyclopentane diradical intermediate formed during the reaction was found to exhibit ring-puckering and pseudorotation before forming products. Several isomerization events between the bicyclopentane product with retention and double inversion of configuration were also observed during the reaction. References 1. R. J. Crawford, R. J. Dummel, and A. Mishra, J. Am. Chem. Soc., 1965 , 87 (13), 3023-3025. 2. W. R. Roth, and M. Martin, Justus Liebigs Ann. Chem., 1967 , 702 (1), 1-7. 3. C. J. S. M. Simpson, G. J. Wilson and W. Adam, J. Am. Chem. Soc., 1991 , 113 (13), 4728- 4732. 4. V. S. Safont, P. González-Navarrete, M. Oliva, and J. Andrés, Phys. Chem. Chem. Phys. , 2015 , 17 (48), 32358-32374.
5. M. B. Reyes, and B. K. Carpenter, J. Am. Chem. Soc. , 2000 , 122 (41), 10163-10176. 6. K. S. Khuong and K. N. Houk, J. Am. Chem. Soc. , 2003 , 125 (48), 14867-14883.
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