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.