Experimental charge density study of a silylone

Area of Science:

• Organosilicon Chemistry
• Quantum Chemistry
• Crystallography

Background:

• The electronic structure and bonding in silicon compounds are crucial for understanding their reactivity and properties.
• Silylones, silicon analogues of carbenes, are of interest due to their unique bonding characteristics.
• The interpretation of (cAAC)2Si as a silylone requires detailed investigation of its charge density distribution.

Purpose of the Study:

• To experimentally and theoretically confirm the silylone nature of (cAAC)2Si.
• To investigate the charge density distribution and its implications for bonding.
• To explore the influence of intermolecular interactions and substituents on the electronic structure.

Main Methods:

• Experimental charge density study using X-ray diffraction.
• Theoretical calculations of charge density distribution.
• Analysis of bond lengths, ellipticities, and valence shell charge concentration (VSCC).
• Computational modeling with varying spheres of surrounding point charges.

Main Results:

• Confirmation of (cAAC)2Si as a silylone with two lone pairs on the central silicon atom.
• Experimental observation of variations in Si-C bond lengths and ellipticities, particularly in the cyclohexyl derivative.
• Successful recovery of charge density distribution changes caused by intermolecular interactions using computational methods.
• Evidence for significant double-bond character in the nitrogen-carbene-carbon bond, suggesting a singlet carbene state.

Conclusions:

• The interpretation of (cAAC)2Si as a silylone is experimentally and theoretically validated.
• The electronic structure, including lone pairs and bonding character, is well-described by charge density analysis.
• Intermolecular interactions and substituents play a role in modulating the electronic properties.
• The sum of bond angles at nitrogen atoms can serve as an indicator for the singlet/triplet state of cyclic (alkenyl) carbenes (cAACs).