Electron deficient bridges involving silylenes: a theoretical study

Area of Science:

• Computational Chemistry
• Inorganic Chemistry
• Quantum Chemistry

Background:

• Silylenes are reactive silicon species with a divalent silicon atom.
• Borane (BH3) is a Lewis acid known to form adducts with Lewis bases.

Purpose of the Study:

• To investigate the complexation of silylenes with borane (BH3).
• To characterize the electronic structure and stability of the resulting silylene-BH3 complexes.
• To understand the role of substituents on silylenes in modulating complex properties.

Main Methods:

• Ab initio calculations
• Density Functional Theory (DFT)
• Natural Bond Orbital (NBO) analysis

Main Results:

• Silylenes form stable complexes with BH3 featuring three-center, two-electron (3c-2e) H-bridged structures.
• Complexation energies range from 18-46 kcal/mol.
• Increased pi-donating capacity of substituents on silylenes reduces exothermicity but enhances kinetic stability.
• Second-order delocalization (sigma(B-H)-->ppi(Si)) is identified as the origin of the 3c-2e bonds.
• A correlation exists between complexation energies and the singlet-triplet energy gaps of silylenes.

Conclusions:

• Silylenes can effectively complex with BH3, forming robust H-bridged structures.
• Substituent effects play a crucial role in tuning the stability and reactivity of these complexes.
• The bonding in these complexes is well-described by sigma-pi delocalization, confirming the 3c-2e nature.