Ab initio dynamics trajectory study of the heterolytic cleavage of H-2 by a Lewis acid [B(C6F5)(3)] and a Lewis base [P(tBu)(3)]

作者：Pu Maoping^*; Privalov Timofei

来源：Journal of Chemical Physics, 2013, 138(15): 154305.

DOI：10.1063/1.4799932

Activation of H-2 by a "frustrated Lewis pair" (FLP) composed of B(C6F5)(3) and P(tBu)(3) species has been explored with high level direct ab initio molecular dynamics (AIMD) simulations at finite temperature (T = 300 K) in gas phase. The initial geometrical conditions for the AIMD trajectory calculations, i.e., the near attack conformations of FLP + H-2, were devised using the host-guest model in which suitable FLP conformations were obtained from the dynamics of the B(C6F5)(3)/P(tBu)(3) pair in gas phase. AIMD trajectory calculations yielded microscopic insight into effects which originate from nuclear motion in the reacting complex, e. g., the alternating compression/elongation of the boron-phosphorous distance and the change of the pyramidality of boron in B(C6F5)(3). The ensemble averaged trajectory analysis has been compared with the minimum energy path (MEP) description of the reaction. Similar to MEP, AIMD shows that an attack of the acid/base pair on the H-H bond gives rise to the polarization of the H-2 molecule and as a consequence generates a large dipole moment of the reacting complex. The MEP and AIMD portrayals of the reaction are fundamentally different in terms of the magnitude of the motion of nuclei in B(C6F5)(3) and P(tBu)(3) during the H-2 cleavage. In the AIMD trajectory simulations, geometries of B(C6F5)(3) and P(tBu)(3) appear as nearly "frozen" on the short time scale of the H-2 cleavage. This is contrary to the MEP picture. Several of the concepts which arise from this work, e. g., separation of time scales of nuclear motion and the time-dependence of the donor-acceptor interactions in the reacting complex, are important for the understanding of chemical reactivity and catalysis.

• 出版日期2013-4-21