Lewis Base and Metal Cation-Assisted Isomerization of Disilyne

We computationally explored the influence of two Lewis
bases (N-heterocyclic carbene (NHC) and trimethylphosphine
(PMe3) and four metal cations (Li+, Na+,
K+, and Mg2+) used in experiments on the isomerizations
of disilyne Si2Ph2 (Ph = C6H5) and Si2Tip2 (Tip = 2,4,6-iPr3C6H2) in this work. Computations
demonstrated that kinetically, both NHC and PMe3 increase
the energy barriers and thus stabilize disilavinylidene. Thermodynamically,
however, NHC can reduce the energy gap between disilyne and disilavinylidene,
while PMe3 stabilizes disilavinylidene or slightly influences
the relative stability. Further analyses showed that it is polarization
that governs the energy barriers and gaps. When metal cations are
further introduced, they tend to adopt the end-on bonding mode and
cooperate with Lewis bases via a push–pull effect. The electrostatic
interaction between Mg2+ and NHC-stabilized disilyne can
even improve the relative stability of disilyne. Therefore, the synergy
between NHC and Mg2+ can help the preparation of disilyne
if the energy barrier from Lewis base-stabilized disilavinylidene
to disilyne is overcome, but to obtain disilavinylidene, it might
be better to use phosphine alone without metal cations.