Electron Deficient Bridges Involving Silylenes:  A Theoretical Study

Abstract

Ab initio and density functional studies show that silylenes can form complexes with BH(3) and the resultant complexes possess 3c-2e bridges. The complexation energy for the formation of the these H-bridged structures is in the range of 18-46 kcal/mol. The characteristics of the electron deficient bridges depend on the substituents attached to the silylenes. With an increase in the pi-donating capacity of the substituents, the exothermicity of complex formation gets reduced but the kinetic stability of the H-bridged structures increase. The natural bond orbital analysis shows that all the H-bridged structures are associated with sigma(B-H)-->ppi(Si) second-order delocalization, which is responsible for the origin of the 3c-2e bonds. The complexation energies of the silylene-BH(3) complexes have been shown to have a correlation to the singlet-triplet energy gaps of silylenes.

Reactions of Stable N-Heterocyclic Silylenes with Ketones and 3,5-Di-tert-butyl-o-benzoquinone

“…The reactivity pattern of NHSis is quite comparable with that of the N-heterocyclic carbenes (NHCs), where the latter led to many applications in chemistry. , Silylenes have two nonbonding electrons in the HOMO which possess nucleophilic character, and an empty 3p-orbital as the LUMO which causes electrophilic properties. They possess both nucleophilic and electrophilic reactive sites at the same silicon atom, therefore they are ambiphilic and behave as Lewis acids as well as Lewis bases . Owing to this, there is an extensive research activity going on in the chemistry of NHSis, which is very challenging (insertion: C–H, N–H, O–H, S–H, P–P, N–Si, C–F, C–X (Cl, Br, I), Si–Cl, P–H, As–H, addition, ,,, metal complexes, Lewis acids).…”

Experimental and theoretical investigation on binary semiconductor clusters of B/Si and Al/Si

“…studied the reactions of SiH 4 and B 2 H 6 , and the interactions of SiH 4 and BH 3 . Bharatam et al 22. studied H‐bridging bonds in SiBH 5 compounds.…”

Silylenes: A Unified Picture of Their Stability, Acid−Base and Spin Properties, Nucleophilicity, and Electrophilicity via Computational and Conceptual Density Functional Theory

“…In these structures one of the H atoms of BH 3 is in bridging position between silicon and boron, 22 and the structure is stabilized by the σ B-H f Si 3p z delocalization. 37 This interaction is only favorable when the Si 3p z orbital is not filled with electrons.…”

“…The effect on nucleophilicity is exerted via the possible donation of the B-H electron density into the empty Si 3p z orbital and when this interaction is not favorable the nucleophilic character of the silylenes will emerge. 37 In Table S3, we collected the orbital energies of the MOs corresponding to the silicon lone pair for the 12 compounds studied in this work. The results show that the σ-donor/acceptor property of the substituent influences the lone pair energy level considerably, e.g., in the case of the strong electron-withdrawing CF 3 group the orbital energy (-0.30 a.u.)…”