Lewis Base\nand Metal Cation-Assisted Isomerization\nof Disilyne

We computationally explored the influence of two Lewis\nbases (<i>N</i>-heterocyclic carbene (NHC) and trimethylphosphine\n(PMe<sub>3</sub>) and four metal cations (Li<sup>+</sup>, Na<sup>+</sup>,\nK<sup>+</sup>, and Mg<sup>2+</sup>) used in experiments on the isomerizations\nof disilyne Si<sub>2</sub>Ph<sub>2</sub> (Ph = C<sub>6</sub>H<sub>5</sub>) and Si<sub>2</sub>Tip<sub>2</sub> (Tip = 2,4,6-<i>i</i>Pr<sub>3</sub>C<sub>6</sub>H<sub>2</sub>) in this work. Computations\ndemonstrated that kinetically, both NHC and PMe<sub>3</sub> increase\nthe energy barriers and thus stabilize disilavinylidene. Thermodynamically,\nhowever, NHC can reduce the energy gap between disilyne and disilavinylidene,\nwhile PMe<sub>3</sub> stabilizes disilavinylidene or slightly influences\nthe relative stability. Further analyses showed that it is polarization\nthat governs the energy barriers and gaps. When metal cations are\nfurther introduced, they tend to adopt the end-on bonding mode and\ncooperate with Lewis bases via a push–pull effect. The electrostatic\ninteraction between Mg<sup>2+</sup> and NHC-stabilized disilyne can\neven improve the relative stability of disilyne. Therefore, the synergy\nbetween NHC and Mg<sup>2+</sup> can help the preparation of disilyne\nif the energy barrier from Lewis base-stabilized disilavinylidene\nto disilyne is overcome, but to obtain disilavinylidene, it might\nbe better to use phosphine alone without metal cations.