Scheiner Steve
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, United States.
Inorg Chem. 2023 Aug 14;62(32):13030-13037. doi: 10.1021/acs.inorgchem.3c01837. Epub 2023 Aug 3.
While a good deal of information has accumulated concerning the manner in which an intramolecular noncovalent bond can affect the relative energies of various conformers, less is known about how such bonds might affect the dynamics of interconversion between them. A series of molecules are constructed in which symmetrically equivalent conformers containing a noncovalent bond can be interconverted by a bond rotation, the energy barrier to which is computed by quantum chemical methods. The rotation of a CF group attached to a phenyl ring is speeded up if a Se··F chalcogen bond can be formed with a SeH or SeF group placed in an ortho position, a bond that is present in and stabilizes the rotational transition state. The analogous SnF group can, on the other hand, engage in a Sn··Se tetrel bond in its global minimum. The energetic cost of breakage of this bond is not fully compensated by the appearance of a Se··F chalcogen bond in the rotational transition state. Other systems were designed by placing two phenyl rings on opposite ends of an octahedrally disposed SeF group. A high barrier inhibits their rotation with bulky Br atoms in ortho positions, but this barrier is lowered if Br is replaced by groups that can engage in either chalcogen (SeH or SeF) or pnicogen (AsH) bonds with the F atoms in the rotational transition state. The barrier reduction is closely related to the strength of these noncovalent bonds.
尽管已经积累了大量关于分子内非共价键如何影响各种构象异构体相对能量的信息，但对于此类键如何影响它们之间相互转化的动力学却知之甚少。构建了一系列分子，其中含有非共价键的对称等效构象异构体可通过键旋转相互转化，其能垒通过量子化学方法计算。如果与处于邻位的SeH或SeF基团形成Se··F硫族元素键，连接在苯环上的CF基团的旋转会加快，该键存在于旋转过渡态并使其稳定。另一方面，类似的SnF基团在其全局最小值中可形成Sn··Se 主族元素键。该键断裂的能量成本并未因旋转过渡态中出现Se··F硫族元素键而得到完全补偿。通过将两个苯环置于八面体排列的SeF基团的相对两端设计了其他体系。在邻位带有大体积Br原子时，高势垒会抑制它们的旋转，但如果将Br替换为能在旋转过渡态与F原子形成硫族元素（SeH或SeF）或氮族元素（AsH）键的基团，该势垒会降低。势垒降低与这些非共价键的强度密切相关。
