The possibility of the transfer of the TH 3 group across a tetrel bond is considered by ab initio calculations. The TB is constructed by pairing PhTH 3 (Ph = phenyl; T = Si and Ge) with bases NH 3 , NHCH 2 , and the C 3 N 2 H 4 carbene. The TH 3 moves toward the base but only by a small amount in these dimers. However, when a Be 2+ or Mg 2+ dication is placed above the phenyl ring, the tetrel bond strength is greatly magnified reaching up to nearly 100 kcal mol −1 . This dication also induces a much higher degree of transfer which can be best categorized as half-transfer for the two N-bases and a near complete transfer for the carbene.
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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
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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- Award ID(s):
- 1954310
- NSF-PAR ID:
- 10419953
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 24
- Issue:
- 42
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 25895 to 25903
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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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Abstract Crystal structures document the ability of a TF3group (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. -
The π-hole above the plane of the X 2 T′Y molecule (T′ = Si, Ge, Sn; X = F, Cl, H; Y = O, S) was allowed to interact with the TH hydride of TH(CH 3 ) 3 (T = Si, Ge, Sn). The resulting TH⋯T′ tetrel bond is quite strong, with interaction energies exceeding 30 kcal mol −1 . F 2 T′O engages in the strongest such bonds, as compared to F 2 T′S, Cl 2 T′O, or Cl 2 T′S. The bond weakens as T′ grows larger as in Si > Ge > Sn, despite the opposite trend in the depth of the π-hole. The reverse pattern of stronger tetrel bond with larger T is observed for the Lewis base TH(CH 3 ) 3 , even though the minimum in the electrostatic potential around the H is nearly independent of T. The TH⋯T′ arrangement is nonlinear which can be understood on the basis of the positions of the extrema in the molecular electrostatic potentials of the monomers. The tetrel bond is weakened when H 2 O forms an O⋯T′ tetrel bond with the second π-hole of F 2 T′O, and strengthened if H 2 O participates in an OH⋯O H-bond.more » « less
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Coordination of the leucoverdazyl ligand 2,4-diisopropyl-6-(pyridin-2-yl)-1,4-dihydro-1,2,4,5-tetrazin-3(2H)-one VdH to Ru significantly weakens the ligand’s N-H bond. Electrochemical measurements show that the metalated leucoverdazyl Ru(VdH)(acetylacetonate)2 RuVdH has a lower pKa (-5 units), BDFE (-7 kcal/mol), and hydricity (-22 kcal/mol) than the free ligand. DFT calculations suggest that the increased acidity is in part attributable to the stabilization of the conjugate base Vd-. When free, Vd- distorts to avoid an 8πe- antiaromatic state, but it remains planar when bound to Ru. Proton-coupled electron transfer (PCET) behavior is observed for both the free and metalated leucoverdazyls. PCET equilibrium between Vd radical and TEMPOH affords a VdH BDFE that is in good agreement with that obtained from electrochemical methods. RuVd exhibits electrocatalytic PCET donor behavior. Under acidic conditions, it reduces the persistent trityl radical ·CAr3 (Ar = p-tert-butylphenyl) to the corresponding triarylmethane HCAr3 via net 1e-/1H+ transfer from RuVdH.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2CP04194D
