Mingxia Zhang’s research while affiliated with Northeast Normal University and other places

External electric field (EEF), as a metal-free catalyst, catalyzing the Markovnikov hydrosilylation of styrene was studied for the first time. Compared to the field-free situation, the barrier height was almost halved upon application of an EEF with a field strength of 180 ×10-4 au in the direction perpendicular to the “bond axis”. Therefore, the use of EEF not only resolved the questions of separation of homogeneous catalysts from the reaction mixture, but also facilitated the reaction by decreasing its barriers. Furthermore, we found that the lower the energy of transition state (TSX) and the higher the energy of HOMO of reactant (R1’), the lower the barrier height of the hydrosilylation. Hopefully, this study could provide a guide for the experiment of external electric field.

Generally, the hydroboration of benzonitrile produces BN containing compound. However, an unprecedented BC bond may be formed in the presence of suitable external electric field (EEF). In reactions of benzonitrile with borane, when EEF is oriented to parallel the positive direction (N→C) of N≡C bond, the barriers of path M are decreased gradually, meaning the pathway of generating BC bond is easier and easier. Accordingly, EEF could influence hydroboration and control selectivity by changing its magnitude and directions.

Employing the oriented external electric field as the catalyst or inhibitor, the model reactions of hydroboration of terminal olefins with the simplest borane were studied for the first time. The used electric fields in this work are oriented in the direction of parallel and perpendicular to the C=C bond in olefins to explore its influences on regioselectivity and barrier height. Excitedly, the first hydroboration of ethylene in electric field along the parallel direction perfectly proved that the relationship between the positively polarized carbon atom on C=C bond and regioselectivity of this reaction. A much significant finding is the dominant inverse hydroboration of propene occurred when the external electric field along the flipping direction, that is, the Markovnikov hydroboration. And the kinetic calculations showed that this extent of inverse hydroboration would give an obvious advantage as the rising of fields, because the ratio of kA:kM had decreased to 0.36 when the field is up to -70 (×10-4) a.u.. Additionally, all of the hydroboration of olefins (whether for ethylene or propene) with borane just changed their barrier heights instead of regioselectivity when the external electric filed are oriented in the direction of perpendicular to the C=C bond. This model reaction in this work is meaningful for exploring more complicated hydroboration reactions of olefins in experiment.