Competition between Inter and Intramolecular Tetrel Bonds: Theoretical Studies Complemented by CSD Survey

Abstract

Crystal structures document the ability of a TF3 group (T=Si, Ge, Sn, Pb) situated on a naphthalene system to engage in an intramolecular tetrel bond (TB) with an amino group on the adjoining ring. Ab initio calculations evaluate the strength of this bond and evaluate whether it can influence the ability of the T atom to engage in a second, intermolecular TB with another nucleophile. A very strong CN− anionic base can approach the T either along the extension of a T−C or T−F bond and form a strong TB with an interaction energy approaching 100 kcal/mol, although this bond is weakened a bit by the presence of the internal T⋅⋅⋅N bond. The much less potent NCH base engages in a correspondingly longer and weaker TB, less than 10 kcal/mol. Such an intermolecular TB is weakened by the presence of the internal TB, to the point that it only occurs for the two heavier tetrel atoms Sn and Pb.

Competition between Intra and Intermolecular Pnicogen Bonds: Complexes between Naphthalene Derivatives and Neutral or Anionic Bases

“…The systems studied show important similarities to previously described complexes containing triel [20] and tetrel [21] atoms with respect to their potential ability to form both internal and external noncovalent bonds. In all cases there is a negative anti‐cooperative effect in that the two bonds tend to weaken each other.…”

“…The strength of the tetrel bond depends on the choice of interacting monomers [21] . Tetrel atoms can interact with both anionic (CN − ) and neutral molecules (HCN) to form strong and weak complexes, respectively.…”

“…The strength of the tetrel bond depends on the choice of interacting monomers. [21] Tetrel atoms can interact with both anionic (CN À ) and neutral molecules (HCN) to form strong and weak complexes, respectively. E int exceeds À 70 kcal/mol for the former, while the weak complexes with HCN do not exceed À 10 kcal/mol.…”

“…In fact, a survey of the CSD (Cambridge Structural Database) [19] provides several examples of crystal structures with tricoordinated pnicogen atoms attached to naphthalene as discussed here, in the context of both triel [20] and tetrel [21] bonding situations. As one example of a pnicogen‐containing system, the RECBUW [22] system is presented in Figure 1 where the AsCl 2 and NMe 2 groups are properly disposed on the adjacent rings of a naphthalene scaffold for the desired As⋅⋅⋅N PnB.…”

Unique Dispersion-Induced Tetrel Bond with Co-operative σ-hole-Induced Pnicogen Bond in the POCl3-Acetone Heterodimer: Experimental Confirmation at Low Temperatures

“…The electron density over carbonyl carbon forms a π-hole, which was thought to drive this tetrel bond, initially. However, the ESP map of acetone revealed the absence of any critical points over carbonyl carbon, which does not fit with the hitherto notion of the tetrel bond being an electrostatic phenomenon, primarily. − Also, the tetrel bond has been revealed to be primarily of dispersive origins, which is a cause of intrigue on its own. The results from this study inspire a fundamental question regarding the tetrel bonds: is the presence of a σ-/π-hole necessary for their existence?…”