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Enhancement of tetrel bond involving tetrazole-TtR ₃ (Tt = C, Si; R = H, F). Promotion of SiR ₃ transfer by a triel bond

https://doi.org/10.1039/D2CP04194D

Wu, Qiaozhuo; Xie, Xiaoying; Li, Qingzhong; Scheiner, Steve (November 2022, Physical Chemistry Chemical Physics)

When attached to a tetrazole, a TtR 3 group (Tt = C, Si; R = H, F) engages in a Tt⋯N tetrel bond (TtB) with the Lewis base NCM (M = Li, Na). MP2/aug-cc-pVTZ calculations find that the Si⋯N TtB is rather strong, more than 20 kcal mol −1 for SiH 3 , and between 46 and 53 kcal mol −1 for SiF 3 . The C⋯N TtBs are relatively weaker, less than 8 kcal mol −1 . All of these bonds are intensified when a BH 3 or BF 3 molecule forms a triel bond to a N atom of the tetrazole ring, particularly for the C⋯N TtB, up to 11 kcal mol −1 . In these triads, the SiR 3 group displaces far enough along the line toward the base that it may be thought of as half transferred.
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Resonance-assisted intramolecular triel bonds

https://doi.org/10.1039/D2CP01244H

Liu, Na; Li, Qingzhong; Scheiner, Steve; Xie, Xiaoying (June 2022, Physical Chemistry Chemical Physics)

The possibility that the intramolecular Tr⋯S triel bond is strengthened by resonance is examined by quantum chemical calculations within the planar five-membered ring of TrH 2 –CRCR–CRS (Tr = Al, Ga, In; R = NO 2 , CH 3 ). This internal bond is found to be rather short (2.4–2.7 Å) with a large bond energy between 12 and 21 kcal mol −1 . The pattern of bond length alternation and atomic charges within the ring is consistent with resonance involving the conjugated double bonds. This resonance enhances the triel bond strength by some 25%. The electron-withdrawing NO 2 group weakens the bond, but it is strengthened by the electron-donating CH 3 substituent. NICS analysis suggests the presence of a certain degree of aromaticity within the ring.
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Enhancement of the Tetrel Bond by the Effects of Substituents, Cooperativity, and Electric Field: Transition from Noncovalent to Covalent Bond

https://doi.org/10.1002/cphc.202100612

Liu, Na; Xie, Xiaoying; Li, Qingzhong; Scheiner, Steve (September 2021, ChemPhysChem)

Abstract The T⋅⋅⋅N tetrel bond (TB) formed between TX₃OH (T=C, Si, Ge; X=H, F) and the Lewis base N≡CM (M=H, Li, Na) is studied by ab initio calculations at the MP2/aug‐cc‐pVTZ level. Complexes involving TH₃OH contain a conventional TB with interaction energy less than 10 kcal/mol. This bond is substantially strengthened, approaching 35 kcal/mol and covalent character, when fluorosubstituted TF₃OH is combined with NCLi or NCNa. Along with this enhanced binding comes a near equalization of the TB T⋅⋅⋅N and the internal T−O bond lengths, and the associated structure acquires a trigonal bipyramidal shape, despite a high internal deformation energy. This structural transformation becomes more complete, and the TB is further strengthened upon adding an electron acceptor BeCl₂to the Lewis acid and a base to the NCM unit. This same TB strengthening can be accomplished also by imposition of an external electric field.
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