Isolation of Redox Active Disilyl-Dithiolene Compound: Chemical Bonding by EDA-NOCV Analyses

The reaction of an C≡C containing conjugated bis-chlorodisilene, [(L)SiCl(Ph₂C₄)SiCl(L)] (L = PhC(N^tBu)₂) (1) with lithium dithiolene radical anions [SS-NHC = E^•-, NHC = N-hetero cyclic carbene] affords unprecedented C₄-cumulene-bridged disilicon compounds, [(L)(SS-NHC = E)Si-(Ph₂C₄)-Si(SS-NHC = E)(L)]; 2 (E = S) and 3 (E = Se) featuring chelating dithiolene coordination at silicon atoms. This transformation provides a direct route to cumulene-based bis-silyl architectures in which the redox-active dithiolene ligand binds through two sulfur donors to the silicon centers. Both the compounds were structurally characterized by single-crystal x-ray diffraction and spectroscopically by IR, Raman, UV-vis, NMR measurements. The redox property has been investigated by cyclic voltammetry studies. The stability, bonding, and distribution of electron densities of 2' and 3' were studied by NBO, QTAIM, and EDA-NOCV analyses. Interestingly, the latter analyses showed that both the Si─C bonds of [(L^Me)(SS-NHC = E^Me)Si-(Me₂C₄)-Si(SS-NHC = E^Me)(L^Me)], where E = S (2') and E = Se (3') prefer to be electron sharing in nature by 42.9 kcal/mol while previously reported tetrachlorine analogue [(L)(Cl)₂Si-(Ph₂C₄)-Si(Cl)₂(L)] (D) of 2 and 3 possesses a covalent dative and an electron sharing Si─C σ-bond which is favored by 13.3 kcal/mol.