Antiaromaticity-Promoted Activation of Dihydrogen with Borole Fused Cyclooctatetraene Frustrated Lewis Pairs: A Density Functional Theory Study

Aromaticity and frustrated Lewis
pairs (FLP), two important concepts
in chemistry, have attracted considerable attention from theoretical
and experimental chemists. However, combining these two concepts together
for H2 activation is less developed. Herein, we report
a density functional theory study on antiaromaticity-promoted H2 splitting. The antiaromatic borole (as Lewis acid) and aromatic
pyridine (as Lewis base) were introduced into the cyclooctetraene
skeleton. Due to the geometric constraints, such systems can be classified
as FLPs. In the process of hydrogenation, breaking the antiaromatic
boron-containing ring can decrease the reaction barrier, whereas breaking
an aromatic boron-containing heterocycle makes dihydrogen activation
both kinetically and thermodynamically unfavorable. Further investigation
reveals that smaller deformation as well as stronger interaction between
distorted reactants in those FLPs with antiaromatic rings lead to
lower activation barriers in comparison with FLPs with nonaromatic
five-membered rings or aromatic six-membered rings. These findings
could be helpful to design novel FLPs toward H2 activation.