1‐Silacyclopent‐2‐enes and 1‐silacyclohex‐2‐enes bearing functionally substituted silyl groups in 2‐positions. Novel electron‐deficient SiHB bridges

Strength of Si–H ⋯ B charge-inverted hydrogen bonds in 1-silacyclopent-2-enes and 1-silacyclohex-2-enes

“…More importantly for the present article, based on the NMR spectra obtained for two members (1 and 2 in Fig. 1) of 1-silacyclopent-2-enes, Wrackmeyer et al [4] have concluded that Si-H-B bridges in these molecules are either absent or extremely weak. This was to be in opposition to their 1-silacyclohex-2-ene counterparts (3 and 4 in Fig.…”

“…This was to be in opposition to their 1-silacyclohex-2-ene counterparts (3 and 4 in Fig. 1), where existences of Si-H-B bridges have been confirmed by similar spectroscopic data [4]. This difference in Si-H-B bonding effect was attributed to stronger repulsion between silyl groups in both 1-silacyclohex-2-enes forcing the exocyclic relevant silyl group to approach closer to the 9-borabicyclo[3.3.1]nonane group (9-BBN) and, as a consequence, considerably reducing the H· · · B distance.…”

“…Wrackmeyer is most likely the first who paid attention to the presence and the bonding character of a Si-H-B bridge Mirosław Jabłoński teojab@chem.uni.torun.pl 1 Department of Quantum Chemistry, Faculty of Chemistry, Nicolaus Copernicus University in Toruń, 7-Gagarina St., 87-100 Toruń, Poland in organoboron compounds [1][2][3][4]. The role of this bridge in the formation of heterocyclic systems containing both silicon and boron atoms was discussed on the basis of both NMR and IR spectroscopic data [1].…”

“…For example, in case of Y being a transition metal, this interaction is called an agostic bond [10][11][12][13] or a σ interaction [12][13][14][15][16][17] depending on a specific situation, whereas if Y is an electron-deficient element (as, for example, boron), this type of interaction was called a "charge-inverted hydrogen bond" (CIHB) [11][12][13][18][19][20][21][22][23][24][25]. Therefore, the electron-deficient Si-H-B bridge (this term was being used by Wrackmeyer et al [1][2][3][4]) in investigated systems in fact represents one of the examples of intramolecular charge-inverted hydrogen bonds (IMCIHB).…”

“…Although this energetical parameter is not accessible to experimental Fig. 1 Structural formulas of 1-silacyclopent-2-enes and 1-silacyclohex-2-enes investigated by Wrackmeyer et al [4] measurements, it is relatively easily accessible to theoretical methods of molecular modeling. As widely believed, the interaction energy directly describes the strength of a (local) intramolecular interaction.…”