Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane:Ab initio, density functional, and molecular mechanics (MM3) studies

NH bond activation of ammonia and amines by ditetrelenes: key insights into the stereochemistry of nucleophilic addition

The NH bond activation of ammonia, primary and secondary amines by tetramesityldisilene and -digermene was investigated. In each case, a disilyl- or digermylamine was formed as the only product of amine addition. The mechanism of the addition of ammonia to tetramesityldisilene was computed and revealed a three-step reaction pathway: formation of the anti-ammonia-disilene adduct, inversion at the β-silicon, and syn-transfer of the proton to give the syn-product, where each step follows a distinct stereochemical course. Examination of the reaction landscape also revealed several additional insights: (a) that, in the initial step, the formation of the anti-oriented zwitterionic intermediate is kinetically more preferable than formation of the syn-oriented zwitterionic intermediate, (b) that intermolecular transfer of a proton is not energetically feasible in non-polar solvents, and (c) that the bulk of the substituents can have a profound effect on the stereochemical course of the reaction. With this detailed understanding, nucleophilic additions to ditetrelenes can be exploited in the future.

Modelling the non-local thermodynamic equilibrium spectra of silylene (SiH2)

This paper sets out a robust methodology for modelling spectra of polyatomic molecules produced in reactive or dissociative environments, with vibrational populations outside local thermal equilibrium (LTE). The methodology is based on accurate, extensive ro-vibrational line lists containing transitions with high vibrational excitations and relies on the detailed ro-vibrational assignments. The developed methodology is applied to model non-LTE IR and visible spectra of silylene (SiH2) produced in a decomposition of disilane (Si2H6), a reaction of technological importance. Two approaches for non-LTE vibrational populations of the product SiH2 are introduced: a simplistic 1D approach based on the Harmonic approximation and a full 3D model incorporating accurate vibrational wavefunctions of SiH2 computed variationally with the TROVE (Theoretical ROVibrational Energy) program. We show how their non-LTE spectral signatures can be used to trace different reaction channels of molecular dissociations.