Bonding, aromaticity, and planar tetracoordinated carbon in Si2CH2 and Ge2CH2

• Published in: Journal of molecular modeling Vol. 21; no. 8
• Main Authors: Vogt-Geisse, Stefan, Wu, Judy I-Chia, Schleyer, Paul v. R., Schaefer, Henry F.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.08.2015
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Computer Appl. in Life Sciences; Computer Applications in Chemistry; Molecular Medicine; Original Paper; Theoretical and Computational Chemistry; Nuclear-independent chemical shift; Planar tetracoordinated carbon; Main group chemistry; Aromaticity; 3–center 2–electron bond; Natural bond orbital; Electrostatic potential
• ISSN: 1610-2940; 0948-5023
• DOI: 10.1007/s00894-015-2736-8

Natural bond orbital (NBO) analyses and dissected nucleus-independent chemical shifts (NICS π z z ) were computed to evaluate the bonding (bond type, electron occupation, hybridization) and aromatic character of the three lowest-lying Si 2 CH 2 ( 1-Si , 2-Si , 3-Si ) and Ge 2 CH 2 ( 1-Ge , 2-Ge , 3-Ge ) isomers. While their carbon C 3 H 2 analogs favor classical alkene, allene, and alkyne type bonding, these Si and Ge derivatives are more polarizable and can favor “highly electron delocalized”? and “non-classical”? structures. The lowest energy Si 2 CH 2 and Ge 2 CH 2 isomers, 1-Si and 1-Ge , exhibit two sets of 3–center 2–electron (3c-2e) bonding; a π -3c-2e bond involving the heavy atoms (C–Si–Si and C–Ge–Ge), and a σ -3c-2e bond (Si–H–Si, Ge–H–Ge). Both 3-Si and 3-Ge exhibit π and σ -3c-2e bonding involving a planar tetracoordinated carbon (ptC) center. Despite their highly electron delocalized nature, all of the Si 2 CH 2 and Ge 2 CH 2 isomers considered display only modest two π electron aromatic character (NICS(0) π z z =--6.2 to –8.9 ppm, computed at the heavy atom ring center) compared to the cyclic-C 3 H 2 (–13.3 ppm). Graphical Abstract The three lowest Si2CH2 and Ge2CH2 isomers.