Tetrel Bonding along the Pathways of Transsilylation and Alkylation of

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A: Spectroscopy, Molecular Structure, and Quantum Chemistry

Tetrel Bonding along the Pathways of Transsilylation and Alkylation of N-Trimethylsilyl-N-methylacetamide with Bifunctional (Chloromethyl)fluorosilanes Nina N. Chipanina, Nataliya F. Lazareva, Larisa P. Oznobikhina, and Bagrat A. Shainyan J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.9b03876 • Publication Date (Web): 27 May 2019 Downloaded from http://pubs.acs.org on May 28, 2019

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The Journal of Physical Chemistry

1

Tetrel Bonding along the Pathways of Transsilylation and Alkylation

of

N-Trimethylsilyl-N-methylacetamide

with

Bifunctional (Chloromethyl)fluorosilanes Nina N. Chipanina, Nataliya F. Lazareva,* Larisa P. Oznobikhina, Bagrat A. Shainyan A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Sciences, 1 Favorsky Street, 664033 Irkutsk, Russian Federation; e-mail: [email protected]

Abstract Quantum chemical study has been carried out on the complexes formed in the first stage of the reaction of (chloromethyl)trifluorosilane with ambident nucleophile, N-trimethylsilyl-N-methylacetamide existing in the amide and the imidate tautomeric forms. The analysis of MESP maps of the electrophile molecule revealed the presence of two σ-holes belonging to the Si and C atoms. Each of the two tautomers of the nucleophile form complexes having the O∙∙∙Si, O∙∙∙C, N∙∙∙Si, N∙∙∙C bond of different character. The NBO (natural bond orbital) and QTAIM (quantum theory of atoms in molecules) analyses showed the presence of the O∙∙∙Si and O∙∙∙C tetrel bonds or of electrostatic interaction in the complexes with the amide tautomer, depending on orientation of the components. The imidate tautomer gives complex with covalent N–Si bond, whereas the N∙∙∙C bonding is very weak. The effect of the silicon atom arrangement on the structure of complexes between N-trimethylsilyl-N-methylacetamide and bifunctional silanes ClCH2SiXnF3-n (X = Me, OMe, Cl, n = 1,2) and the effect of σ-hole tetrel bonding interactions on the reaction pathways are discussed.

1. Introduction The chemistry of organosilicon hypervalent compounds was intensively developed during last several decades. The methods of synthesis were designed and the data on the structure and reactivity obtained for organosilicon compounds with intramolecular coordination bond DSi (D = O, N), which led to the use as synthons and catalysts in synthetic and medicinal chemistry as well as in the chemistry of materials.1–13 The nature of hypervalent DSi bonding has also been explored.11,

13–17

However, some problems still remain to be solved. Thus, for (O-Si)-

monochelate N-[(halogeno)silylmethyl]carboxamides and their analogs, which are classical representatives of pentacoordinate organosilicon compounds, the synthetic approaches, structure ACS Paragon Plus Environment

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2 and reactivity are well known,4,

6–12

but still there is no clear understanding of the process of

formation of these structures, that would allow to direct the reaction toward the selective formation of the desired products. Recently, we have studied the reaction of N-trimethylsilyl-Nmethylacetamide 1, as an ambident nucleophile existing as a tautomeric mixture of the amide 1a and imidate 1b forms, with bifunctional silane ClCH2SiF3 2, and showed the occurrence of two independent parallel processes – transsilylation and -alkylation (Schemes 1–3).18 The reaction of trans-silylation gives N-{[chloro(difluoro)silyl]methyl}-N-methylacetamide A, while alkylation leads to N-methyl-N-[(trifluorosilyl)methyl]acetamide B, both products belonging to (O-Si) chelate compounds with pentacoordinate silicon (Scheme 1). The alkylation reaction is preferable, judged from the ratio of products A/B, which was 1 : 2 in chloroform solution and reaches ~1 : 8.5 in acetonitrile solution. Scheme 1 Me Me

C N 1a

Me

C

O

SiMe3

O

Me

Me SiMe3

C

O Si

N

Me

F F Cl

A

C

O Si

+

Me

F

N

F F

B

Me N 1b

According to the quantum chemical studies, the first step of the reaction of transsilylation is the formation of intermolecular complexes between silane 2 and tautomer 1a or 1b, including the OSi or NSi bond, respectively (Scheme 2). Note, that silanes were shown to be weak Lewis acids towards neutral N- and O-Lewis bases.19 The formation of intermolecular complexes of silanes of N∙∙∙Si type with amines, imines, nitriles and of O∙∙∙Si type with the carbonyl group of aldehydes, ketones, esters and carboxamides was not only postulated when discussing the mechanism of some reactions but indications of their existence were obtained.1, 20–32 Therefore, the assumption on the formation of intermolecular complexes seems quite reasonable. For the reaction of alkylation, the formation of intermolecular pre-reaction complexes between the oxygen or nitrogen atoms of tautomers 1a, 1b and the carbon atom of the chloromethyl group in silane 2 can also be assumed (Scheme 3). (Chloromethyl)trifluorosilanes are good substrates for SN2 reaction at the carbon atom bearing large positive charge due to the presence of electron-withdrawing chlorine atom and trifluorosilyl group in the molecule.

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3 Scheme 2 ClCH2SiF3 + Me Me

C N

O

Me

SiMe3

Me N

1a

C

MeC MeN

O

MeC

Si F F F

Me

SiMe3

7a

MeC MeN

SiMe3 F

N Cl

Si F F

Cl

O

Si

MeC

F

MeN F2Si

Me

7b

Me Me

O

SiF2

Me

SiMe3

1b

Cl O

O

Si Me F Cl

Me

TS1b

TS1a -Me3SiF

MeC

O

SiF2

-Me3SiF TS2

MeC MeN

NMe CH2

O SiF2CH2Cl

Cl TS3

Me

Me

C

TS4

Cl

N

N

F

Si O

Me

F

O F Si F

A


Me

Cl


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4 Scheme 3 Me

Me3Si

MeC

NMe

O

CMe

O

N

SiMe3 1b

1a

ClCH2SiF3 Me

Me3Si

NMe

F O

Si

F

F

MeC

CMe

N

Si

O Cl

SiMe3

H

F

12b

H

O

C

O

SiMe3 SiF2 C Cl

MeC

Cl

SiF3

MeN

Me

SiMe3

N H

H TS5b

TS5a

SiF3 MeC C H H MeN Cl SiMe3 O

TS6a

MeC Me

F

Cl 12a

MeC

F

N

O

O

MeC

SiMe3 Cl N C SiF3 Me H H

- Me3SiCl

C

TS6b

H

Me

H Si F F

F

C N

TS7

Me

O

- Me3SiCl

F Si

F F

B

There is a recent growing interest in studying the SN2 type pre-reaction complexes by spectral and quantum chemical methods.33–38 However, still open is the question of the structure of intermolecular complexes formed in the first stage of the reaction of N-trimethylsilyl-Nmethylacetamide with (chloromethyl)fluorosilanes ClCH2SiMenF3-n (n = 0–2).18


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5 A new impetus was given to investigation of noncovalent interactions and development of the notions about the nature of chemical bond when new term ‘tetrel bonding’ was coined by A. Frontera.39, 40 The term describes noncovalent interaction between neutral or negatively charged Lewis bases with the covalently bonded ‘tetrels’ – heavier elements of the 14 group of the Periodic Table (Si, Ge, Sn, Pb). This interaction can be described using the concept of ‘σ-holes’ – that is, the positively charged region localized at the backside along the extension of the covalently bond formed by the atom.41 The σ-holes are responsible for the interaction of a Lewis base with the tetrel atom.42–45 The concept of tetrel bonds, having, as was specially noticed,39 comparable strength to hydrogen bonds and other σ-hole-based interactions, is actively developing and successfully used in studying silicon complexes22,25,27,30,43,46–51 as well as the mechanism of bimolecular nucleophilic substitution.22,52,53 The question whether carbon can form similar bonds as silicon does, was also studied,26,33,43,46,54–57 but still remains actual. Recently, stable intermolecular complexes of triarylmethyl cations with bidentate ligands 1,2bis(pyridin-2-ylethynyl)benzenes were synthesized and shown to be structurally similar to the SN2 transition state having 3c–4e tetrel bond N∙∙∙C∙∙∙N with central pentacoordinate carbon.33 This was an experimental proof of the formation of tetrel bonds with participation of carbon Lewis acid. Still, the tetrel bonds with carbon atom are much weaker than those with its heavier cousins (Si, Ge, Sn, Pb),58 as follows, e.g., from the comparison of the corresponding binding energies, or the absence of bond critical points (BCP) on the N∙∙∙C bond path, unlike in the corresponding Si or Ge analogs.53 Very recently, small tetrel-bonded complexes of carbon dioxide with N2, CO, H2O and NH3 were analyzed theoretically, including their adsorption on graphene.59 Strong electron-withdrawing effect of three fluorine atoms facilitates the attack of Lewis bases on the σ*C–F lobe inside the CF3 umbrella in perfluorotoluene leading to the σ-hole tetrel bonding, which was asserted to be important in biological systems.26 Tetrel-bonded intermolecular complexes of fluorosilanes with a large series of N-bases were studied using the NBO and QTAIM methodologies.60 The NBO binding energy and the electron density at BCPs were found to exponentially depend on the Si∙∙∙N distance. Remarkably, the equatorial C–F bonds, if present, strongly affect the charge transfer from the N-base to the silane. The equatorial F atoms at silicon may cause deviation from linearity of the Si∙∙∙N electron density bond path trajectory. Moreover, in some cases, BCPs were found not on the direct intermolecular bond path Si∙∙∙N but on the curved bond paths Feq∙∙∙N or Heq∙∙N, while no BCP could be found on the direct bond path Si∙∙∙N. In strong complexes with lSi∙∙∙N < 2.8 Å the total electron density (HBCP) is negative, indicating that the Si–N bond has a partial covalent character. The goal of this work was to theoretically investigate intermolecular complexes formed by tautomeric N-trimethylsilyl-N-methylacetamide 1a and О-trimethylsilyl-N-methylacetimidate 1b ACS Paragon Plus Environment


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6 and (chloromethyl)trifluorosilane ClCH2SiF3 2, to compare the geometry and energy parameters, as well as electron density distribution in order to find σ-holes on the silicon and carbon atoms and σ-hole tetrel bonds with their participation. The effect of the silyl group structure on the structure and energy of intermolecular complexes with tautomers 1a, 1b was investigated on the example of (chloromethyl)fluorosilanes ClCH2SiRR'F [R = F, R' = Cl, (3); R = F, R' = OMe (4); R = F, R' = Me (5); R = R' = Me (6)] (Scheme 4). Scheme 4 Me3Si Cl

R

O

Me

NMe CMe

Si

MeC

Si

O

R'

SiMe3

R'

F

Cl

R

N

F

7b-11b

7a-11a

ClCH2SiFRR'

Me3Si O

Me NMe

MeC

N

O

CMe

SiMe3 1b

1a

ClCH2SiFRR' Me3Si R F

O

Si R'

Me NMe

MeC

CMe

R

N

Si

O SiMe3

Cl

F

R'

Cl 12a

12b

7a, 7b, 12a, 12b (R = R' = F); 8a, 8b (R = F, R' = Cl); 9a, 9b (R = F, R' = OMe); 10a, 10b (R = F, R' = Me); 11a, 11b (R = R' = Me).

σ-Holes at the 14th group elements are characterized by the region of positive molecular electrostatic potential (MESP).39 Orientation of molecules in complexes often depends on the contacts between the MESP regions of the opposite sign.53 Correlations between the values of MESP and the energies of interaction in complexes have been found.44, 61–63 Note, however, that the MESP value over the center of the benzene ring in the same molecule (π-hole) is twice as large as that at the σ-hole, making the interaction of the former site with Lewis bases much stronger. To determine the sites of maximum positive MESP for electrophiles 2–6 and of maximum negative MESP for nucleophiles 1a and 1b, the MESP maps were obtained and visualized as electron density isosurfaces. The effect of the substituents in the equatorial plane of the silicon bipyramid on the strength of the tetrel bond was estimated from topological QTAIM analysis of the electron density at the BCPs by comparing with the length of this bond. The NBO method ACS Paragon Plus Environment

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7 was used for quantitative estimation of the charge transfer from the Lewis base to Lewis acid and of the energy of orbital interaction of the nitrogen or oxygen lone pair (LP) and the σ*-orbital of the axial Si–Xax bond. The geometry parameters of the tetrel bond and redistribution of the electron density in the complexes were compared to the parameters of the first transition state for the reactions of transsilylation and alkylation in order to clarify their interplay, to confirm the role of the σ-hole tetrel bonds in these reactions and to elucidate the correctness of considering the formation of these complexes as a preliminary stage of the processes.

2. Computational details All calculations including NBO analysis64,65 were performed by the M06-2X/6-311G(d,p) method with full geometry optimization as implemented in the Gaussian09 program package.66 Belonging of stationary points on the potential energy surface to minima was proved by positive eigenvalues of the corresponding Hessian matrices. The complex formation energies were calculated as the difference between the energy of the complex and the sum of the energies of monomers in their minimum geometries. The inherent basis set superposition error (BSSE) has been taken into account using the full counterpoise method.67 Solvate complexes in solutions were calculated within the framework of Polarizable Continuum Model using the integral equation formalism (IEFPCM). The MESPs were computed on the 0.001 au contour of the electronic density at the MP2/aug-cc-pVDZ level and analyzed with the Multiwfn 3.3.5 program.68 The charge transfer from Lewis base to Lewis acid ∆Q was calculated from the NBO atomic charges. The QTAIM analysis69 was performed by the use of the AIM2000 program (version 2.0)70 with the wave function taken from MP2/6-311++G(d,p) single-point calculations on the DFT pre-optimized structures.

3. Results and discussion 3.1. Electron densities, geometries and energies The MESP maps for Lewis acids 2–6 are presented in Figure 1. The largest positive (Vmax) and largest negative MESPs (Vmin) are given in Table 1. For silanes 2–4, two σ-holes were found on the maps, which have very close values of Vmax. For 2 and 3 they are located at the ends of the CH2–Si bond and for 4 also in the region of carbon and silicon atoms. This suggests the possibility of formation of σ-hole tetrel bond by the base 1a or 1b not only with the silicon but also with the carbon atom of the chloromethyl group. This is in agreement with the ability of silane 2 to react via both pathways – the transsilylation and alkylation, and allows predicting the ability of silanes 3 and 4 having σ-holes at both ends of the CH2–Si bond to react in the same ACS Paragon Plus Environment


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8 manner. Silanes 5 and 6 have one σ-hole at the CH2–SiF bond, that also provides the formation of tetrel bonds of two types with the molecules of bases. The maximum values of Vmax 53.72 and 53.54 kcal/mol were obtained for the σ-holes of trifluoromethylsilane 2, whereas the lowest one of 35.32 kcal/mol – for dimethyldifluoromethylsilane 6. For silanes 3–5, the values of Vmax decrease in the order 3 > 5 > 4 suggesting that the overall effect of the chlorine atom on the σhole at silicon is electron withdrawal (electronegativity outweighs n-donation), while in the case of methoxy group it is electron release (n-donation outweighs electronegativity). 53.72

39.09

●

F

47.70

Si

F

F

F Cl

●F

C

Cl

●

Cl

53.54

2

39.36

●

C F

Cl

46.05

4

3 F

Si

●

Si C

●

F

F

42.40

●

Si

C

Si

C

F

Cl

●

Cl

35.32

5

6

Fig. 1. MESP maps of silanes 2–6. Blue color corresponds to the maximum and red color to the minimum MESP. Black dots indicate the location of σ-holes, their values are given in kcal/mol. The region of negative MESP is around the fluorine and chlorine atoms in silane 2, and around fluorine atoms in silanes 3–6. Their minimum values Vmin on the MESP maps increase from –15.93 to –30.42 kcal/mol with simultaneous decrease of the Vmax values. On the MESP maps of the bases 1a and 1b this region appears at the oxygen and nitrogen atoms, respectively, and the larger value Vmin of –46.02 kcal/mol was obtained for amide 1a, whereas in imidate 1b it is much lower, –26.83 kcal/mol. By contrast, the proton affinity of oxygen in 1a and nitrogen in 1b calculated as the difference of formation energies of the protonated and neutral molecules, is 227.12 kcal/mol in 1a and notably higher (241.10 kcal/mol) in 1b. We believe that much lower absolute value of Vmin at nitrogen in imidate 1b is due to extension of positive potential from the N-methyl group to the nitrogen atomic basin, thus lowering its negative potential. ACS Paragon Plus Environment

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9 Table 1 Most positive (Vmax, kcal/mol), relative positive [Vmax = Vmax(molecule) – Vmax(complex), kcal/mol], and most negative electrostatic potentials (Vmin, kcal/mol) on the MESP maps of silanes 2–6 and complexes 7a–12a and 7b–12ba Vmin

Complex Vmax

Vmax Vmin

Complex Vmax

Vmax Vmin

Molecule

Vmax

2

53.72 –15.93 53.54 –15.93

7a

21.06 32.66

–41.62

7b

18.60 35.12

–41.80

3

47.70 –16.99 46.05

8a

14.30 33.40

–41.15

8b

19.17 28.53

–41.17

4

39.36 –22.38 39.09

9a

6.56

32.80

–41.12

9b

15.33 24.03

–39.36

5

42.40 –23.06

10a

18.52 23.88

–32.04

10b

20.78 21.62

–41.94

6

35.32 –30.42

11a

15.77 19.55

–37.12

11b

15.42 15.00

–35.20

2

53.72 –15.93 53.54 –15.93

12a

47.58 6.15

–28.87

12b

42.38 11.34

–21.76

The minimum electrostatic potentials for 1a and 1b are located on O (–46.02 kcal/mol) and N (–26.83 kcal/mol) atoms, respectively. a

Due to the presence of σ-holes in silanes 2–6 with Vmax varying within 35–54 kcal/mol, they form with tautomers 1a and 1b complexes with O∙∙∙Si 7a–11a and N∙∙∙Si bonds 7b–11b along the pathway of transsilylation, and with O∙∙∙C 12a and N∙∙∙C bonds 12b along the pathway of alkylation (Figure 2). These complexes correspond to minima on the potential energy surface differing in geometric and energetic characteristics (Table 2). The apical (axial) positions of the silicon bipyramid in complexes 7a–11a and 7b–11b contain the atoms of oxygen or nitrogen of 1a or 1b and the fluorine atom (Fax). The O∙∙∙Si and N∙∙∙Si distances depend on the substituents in the equatorial plane (Feq, Cleq, OMeeq and Meeq) and are shorter in complexes 7a–9a (2.028–2.035 Å) and 7b–9b (1.992–2.008 Å), in which the equatorial positions are occupied by electronegative fluorine, chlorine or oxygen atoms. These distances are substantially longer in complexes 10a, 11a (2.690, 3.094 Å) and 10b, 11b (2.091, 3.243 Å) due to electron-donating effect of the methyl groups, as well as steric hindrances from the methyl groups of the bases and the silanes. Complexes 12a and 12b are formed along the pathway of alkylation and are included in consideration, although the O∙∙∙C (2.826 Å) and N∙∙∙C (3.323 Å) distances in these complexes, even being the shortest in the complexes of this type, are too large to possess characteristics of a tetrel bond, as indicated by the results of the NBO and AIM analysis (see below).



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10 2.551 2.365

F

2.397

F

O

Si

F F

N

2.035

O

Si

N

F Si

2.711

Si

2.739 Cl

Cl

Si

2.488

Cl

F

Si 2.826

N

O

2.381

Si

2.404

F

Si

3.094

O

F

F

2.580

N

Cl F

2.409

Si

2.899

Si

O

Cl

9a

F O 2.690

2.028

2.582

8a 2.263

Si

N

F

Si

2.489

7a

N

F

O 2.034

Cl

Cl

10a

11a

Cl

N O

Si

O

Cl 2.008

F

Si

2.349

2.435

Si

2.006

2.412

O

2.008 2.737 F 2.433

10b

9b

N Cl

O

Si

Si

F

F

8b

N

Si

2.347

2.434

F

Cl

F

Si

Si

O

O

Cl

F

2.364

7b

2.342

N

N

F

1.992

Si

12a

N O

3.243

2.270 Cl

F

2.433

F

11b

Fig. 2. M062X/6-311G** molecular structure of 7a–12a and 7b–12b complexes.


3.323

2.679 Si Si F

Si

2.883

F

F 2.618

12b

Cl

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11 Table 2. M06-2X/6-311G(d,p) lengths (l, Å) of O…Si, N…Si and O∙∙∙C (italic) bonds, complex formation (ΔEf) and BSSE corrected complex formation energies (∆Ef+BSSE), free energies (ΔG0), kcal/mol; and entropies (ΔS0, eu) of complexes 7a–12a, 7a'–11a' and 7b–12b. Complex

l

–∆Ef

–∆Ef+BSSE

∆G0

–∆S0

O…Si 7a

2.035

14.65

8.79

0.44

44.97

8a

2.034

12.86

7.72

3.41

50.51

9a

2.028

13.88

8.24

2.38

50.39

10a

2.690

13.10

9.92

0.49

42.81

11a

3.094

9.15

7.05

2.92

35.42

12a

2.826

10.46

7.06

1.48

35.85

7a'

2.620 2.728

9.46

5.54

4.52

44.88

8a'

2.772 2.785

8.00

4.61

3.99

35.82

9a'

2.803 2.898

10.45

6.88

4.57

48.03

10a'

2.912 3.070

9.89

6.54

4.07

49.04

11a’

3.122

9.86

7.91

2.70

36.95

N…Si 7b

1.992

15.36

7.67

2.45

53.40

8b

2.008

11.46

4.69

6.55

54.06

9b

2.006

12.01

6.48

6.59

55.55

10b

2.091

7.49

1.59

10.77

54.70

11b

3.243

4.52

2.02

11.36

50.60

12b

3.323

10.71

6.99

3.40

43.18

In the series of complexes 7a–11a the energies of their formation –Ef+BSSE decrease from 10 to 7 kcal/mol, although it is not directly dependent on the increase of the O∙∙∙Si distance. This can be explained by the presence of intermolecular hydrogen bonds between the methyl group protons of amide 1a and the fluorine or chlorine atoms of the silanes, as well as between the protons of the chloromethyl and methyl groups in silanes and the carbonyl oxygen (Figure 2). The surprisingly high formation energy of complex 10a of –Ef+BSSE = –9.92 kcal/mol for the ACS Paragon Plus Environment


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12 O∙∙∙Si distance of 2.690 Å is due to the value of Vmax at the σ-hole of silane 5 equal to 42.40 kcal/mol, which is larger than that in silane 4 (39.36 kcal/mol) and can be explained by polarization interaction responsible for stabilization of the tetrel-bonded complexes.29 In the series of imidate complexes 7b–11b, the –Ef+BSSE values decrease from 8 to 2 kcal/mol. This is in a better agreement with the increased N∙∙∙Si distance; note, that the energies of formation of the imidate complexes are lower than those of the amide complexes 7a–11a in agreement with the lower MESP in imidate 1b with respect to amide 1a. Highly negative entropy of formation of complexes 7a–11a and 7b–11b (from –35 to –55 e.u.) outweighs the gain in energy, so that the values of G0 become positive (Table 2). This is typical for complexes of moderate stability; only the silane complexes with the very strong Lewis base F– have negative free energy of formation.19 Apparently, the observed formation of complexes 7–11 in spite of being thermodynamically unfavorable in the gas phase is due to decrease of entropy loss as a result of desolvation of the reagents when performing the reaction in solution. In complexes of bases 1a and 1b with silanes 2–6 having σ-holes, the O∙∙∙Si and N∙∙∙Si distances fall in the range 1.992–3.243 Å, which is less than the sum of the van der Waals radii (vdW) of the silicon and oxygen (3.62 Å) or silicon and nitrogen atoms (3.65 Å).71 Hence, one can assume that the complexes are formed by the σ-hole tetrel bonding, provided that the electron distribution characteristics are appropriate for such bonding (see next Section). The O∙∙∙C distance of 2.826 Å in complex 12a formed (2.826 Å) along the pathway of the reaction of alkylation amide 1a with silane 2 is also less than the sum of the vdW radii of the carbon and oxygen atoms (3.22 Å).71 The chlorine atom in 12a is in the apical position of the trigonal bipyramid of carbon, the energy of formation Ef+BSSE of –7.06 kcal/mol is outweighed by the entropy loss S0 = –35.85 e.u. resulting in a positive free energy G0 = 1.48 kcal/mol. In complex 12b, formed in the reaction of alkylation of 1b by silane 2, the N∙∙∙C distance of 3.323 Å is larger than the sum of vdW radii of the nitrogen and carbon atoms (3.25 Å),71 although the values of thermodynamic parameters are close to those of complex 12a (–Ef+BSSE = 6.99 kcal/mol, S0 = –43.18 e.u., G0 = 3.40 kcal/mol). 3.2 NBO analysis In the intermolecular tetrel bonding the charge is normally transferred from the LP of nitrogen or oxygen to the σ*(Si–Xax) orbital. The NBO second order perturbation energies E(2) of the nO → σ*Si–Fax interaction between the LP of the carbonyl oxygen and the Si–Fax group in complexes 7a–11a are summarized in Table 3. The values of E(2) fall in the range 34.07–1.14 kcal/mol and decrease with the increase of the O∙∙∙Si distance from 2.03 to 3.09 Å. ACS Paragon Plus Environment

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13 Table 3. M06-2X/6-311G(d,p) angle α (OSiC), NBO second order perturbation energy E(2), kcal/mol of nO → σ*Si–Fax, nO → σ*C–Clax and nO → σ*Si–Yeq (Y = F, Cl, OMe, C) interactions in complexes 7a–12a and 7a'–11a'; coefficients of polarization Polmon, Polcom (%) corresponding to F atom in Si-Fax in the isolated Lewis acid unit and in the complex, respectively; electron charge transfer from the Lewis acids to Lewis bases ∆Q (e). Complex

E(2)

α

Polmon

Polcom

–∆Q

nO → σ*Si–Fax

nO → σ*Si–Yeq 20.80 F(1)eq 17.95 F(2)eq 24.28 Feq 13.31 Cleq

87.1

88.0

0.136

87.0

87.9

0.147

7a

82.8

30.45

8a

82.6

34.07

9a

84.0

31.51

19.41 Feq 15.53 OMeeq

87.2

90.1

0.142

10a

73.6

3.64

87.1

87.8

0.019

11a

73.0

1.14

2.59 Feq 0.97 C(1)eq 0.94 C(2)eq 0.19 C(1)eq 0.28 C(2)eq 0.27 C(3)eq

86.9

87.3

0.009

12a

69.2

1.23a

46.1b

54.7b

0.001

7a'

72.8

2.23 2.17

1.84 F(1)eq 1.51 F(2)eq

87.1 46.1

87.6 54.5

0.020

8a'

70.8

1.63 1.41

2.35 F(1)eq 1.63 F(2)eq 0.40 Ceq

87.0 53.9

87.4 54.4

0.018

9a'

73.8

1.59 0.34

1.20 Feq 0.81 OMeeq

87.2 54.3

87.7 55.2

0.009

10a'

76.4

1.04 0.07

0.87 Feq 0.25 Ceq

87.1 45.7

87.6 55.5

0.009

11a’

72.4

0.85

0.19 C(1)eq 0.19 C(2)eq 0.20 C(3)eq

86.9

87.3

0.010

a

italic – nO → σ*C–Clax interaction. b italic – polarization of C–Cl bond

The value of E(2) is a quantitative characteristic of the tetrel bond and for complexes 7a– 10a vary within 34.07–3.64 kcal/mol. Charge transfer from the base to other orbitals, including those lying in the equatorial plane of the central atom of the Lewis acid, also contribute to the tetrel bond.72 Thus, in complexes 7a–9a, along with nO → σ*Si–Fax interaction with the axial orbital σ*Si–Fax of 31.5–34 kcal/mol, the interactions with equatorial orbitals of the carbonyl oxygen LP with the equatorial σ* orbitals of the Si–Feq, Si–Cleq and Si–OMeeq bonds exist, ACS Paragon Plus Environment


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14 which, when summarized, exceed the axial–axial interaction (Table 3). These values drop to 2.6 kcal/mol for the Si–Feq bond in complex 10a and to 1.0–0.2 kcal/mol for interaction with the σ*(Si–Ceq) orbitals in complexes 10a and 11a. The values of charge transfer Q from the Lewis base to the Lewis acid in complexes 7a– 11a are in full agreement with E(2) values of the nO → σ*Si–Fax interaction. The values of Q = 0.147–0.019e in 7a–10a, as the corresponding E(2) values, quantitatively characterize the formed tetrel bonds. The charge transfer in complexes 7a–9a Q = 0.14e corresponds to larger values of Polcom (88–90%, Table 3) as compared to those of 87% in the starting silanes, and, along with large values of E(2), indicates the formation of strong tetrel bond. In complex 10a, it is weaker, in agreement with much lower E(2) value (Table 3). The covalent nature of the N∙∙∙Si bond was determined by the NBO analysis of complexes 7b–10b (Table S1), which showed a high degree of polarization of 91% and substantial charge transfer Q = 0.2 e. Thus, the species may be treated not as a complex but as a single molecule or ion [53]. Negligible E(2) values of ~1 kcal/mol and Q of ~0.01 and 0.001 e for nN → σ*Si–Fax interaction in complexes 11a and 11b, or nN(O) → σ*C–Clax interaction in complexes 12a, 12b indicate the absence of tetrel bonds in these complexes. An additional characteristic of a tetrel bond is the angle α between the O∙∙∙Si or N∙∙∙Si axis and equatorial Si–X bonds, which is used for estimation of the progress of the SN2 reactions and which is equal to 90 for fully symmetrical transition state and to 70.5 in the absence of the reaction.57 In the complexes of silanes 2–6 with tautomers 1a and 1b the angle α corresponds to OSiC or NSiC angles reflecting the initial stage of transsilylation. For complexes 7b–10b with covalent N–Si bond they are equal to 90–92, for complexes 7a–9a with the tetrel bond – 82.8–84.0, and for complexes 11a and 11b having no tetrel bond –73.0 and 73.1, respectively. In complex 10a with α = 73.6 a weak tetrel bond can be assumed to be formed and characterized by low NBO parameters such as E(2) and Q. Charge transfer from the Lewis base 1a to the Lewis acids 2–6 results in a decrease of the maximum positive values Vmax at the silicon atom on the MESP maps of complexes 7a–11a. In complexes 7a–9a these values are almost the same, Vmax ~33 kcal/mol (Table 1). With this, the lowest value of Vmax = 6.56 kcal/mol was found for complex 9a, that corresponds to the shortest O∙∙∙Si distance (2.028 Å), the largest angle α (84.0) and the degree of polarization of 90.1%. In complexes 10a and 11a, in agreement with lowering the charge transfer, the value of Vmax decreases to 23.88 and 19.55 kcal/mol, respectively. The lowest value of Vmax was found in complex 12a (6.15 kcal/mol), in which the charge transfer is almost negligible (0.001 e). By contrast, negative MESP values Vmin in complexes 7a–12a increase due to charge transfer by 10–30 kcal/mol. On the MESP maps they appear at the axial fluorine atoms and have larger ACS Paragon Plus Environment

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15 values when the equatorial positions at silicon in complexes 7a–9a are occupied by fluorine, chlorine, or methoxy group. In complexes 7b–12b, the decrease of Vmax is in good agreement with the increase of the N∙∙∙Si distance. A relatively small decrease of Vmax and increase of Vmin in complexes 12a and 12b, as well as small charge transfer in these complexes are indicative of electrostatic nature of interaction of the complex components. 3.3 QTAIM analysis. The role of tetrel bonding in transsilylation and alkylation The nature of intermolecular bonds O∙∙∙Si, N∙∙∙Si, O∙∙∙C and N∙∙∙C in complexes 7a12a and 7b12b was analyzed by QTAIM approach.73 For 7a10a and 7b10b, BCPs were found (Figure S1) and their topological properties determined (Table 4): the electron density ρ(rc), the Laplacian of electron density 2ρ(rc) and the total energy density H(rc). The binding energies (E) were calculated by equations74 E = 1/2Vc;

Vc = 1/42ρ(rc)  2Gc

where Gc is the local kinetic electron energy density. The topological properties of the BCPs between the oxygen and silicon atoms in complexes 7a10a, such as ρ(rc)  0.05 au, positive values of 2ρ(rc) and negative values of H(rc) are characteristic of closed shell interactions with partially covalent character. Note, that the tetrel bond in the complex of 4-iodopyridine with PhSiF3 also was shown to be partially covalent.29 The O∙∙∙Si bond energy in 7a9a with close interatomic distances O∙∙∙Si is rather large and practically constant, E = 24.5 and 24.4 kcal/mol. This value is reduced to 3.9 kcal/mol in 10a, in which the O∙∙∙Si bond is strongly elongated. In complexes 7b10b, the electron densities ρ(rc) > 0.05 au, positive values of 2ρ(rc) and negative values of H(rc) are indicative of more covalent character of the N∙∙∙Si tetrel bond than that of O∙∙∙Si. This results in the increase of the N∙∙∙Si bond energy to 3537 kcal/mol in 7b9b and to 26.2 kcal/mol in 10b. The QTAIM and electron density analyses allow to conclude on the formation of the O∙∙∙Si tetrel bonds in complexes 7a10a. No BCPs were found in complexes 11a, 12a and 11b, 12b, which suggests the electrostatic nature of bonding between the corresponding Lewis acids and bases with a certain contribution to the stabilization of the complexes from the energy of intermolecular hydrogen bonds CH···O, CH···F and CH···Cl. The energy profiles of the reactions of transsilylation and alkylation of tautomers 1a and 1b with silanes 2, 5 and 6, including the transition states between the reagents, intermediates and the final products were calculated (Schemes 2, 3).18 According to calculations, the reactions are exothermic; complexes 7a, 10a and 11a precede the first transition states TS1 having the energies of activation of 17.4, 19.8 and 21.7 kcal/mol, respectively, at the M06-2X/6-311G(d,p) level. The relationship between the complexes of amide 1a with silanes 25 and the ACS Paragon Plus Environment


Page 16 of 29

16 corresponding transition states of the reactions of transsilylation TS1 and alkylation TS1' must cause similar changes of energetic, geometric and topological parameters as the charge is transferred along the reaction coordinate, as is the case when the tetrel-bonded complexes participate in SN2 reactions at silicon.22,53 Since the orientation of amide 1a and silanes in complexes 7a10a is the same, the analyzed parameters are given in Figure 3 on the example of the reaction of 1a with (chloromethyl)trifluorosilane 2. The first thing which becomes evident when comparing the geometric parameters of complex 7a and transition state TS1 is that the orientation of the SiF3 group in the silane with respect to the SiMe3 group to which the fluorine atom is moved in the course of the reaction is different. This difference is characterized by the angle Me3SiNSiF equal to 144 in complex 7a and 36 in TS1. The structure with orientation of these fragments corresponding to TS1 with dihedral angle Me3SiNSiF of 56 is achieved in complex 7a', which is formed from 7a via barrierless transition (E‡ = 0.72 kcal/mol) by rotation of the silane and amide about the O∙∙∙Si bond (Figure 3). Rotation of one of components of the complex during SN2 reaction was considered when studying the dynamics of anion-molecular nucleophilic substitution52 and determining the role of the σ-hole tetrel bond in the SN2 reaction of CH3Br with pseudohalide anion (N3–).22 tetrel bond

Q = -0.101  = 90.7 (O...Si)=0.104

O

N

Si

Si 1.897 1.857

TS2–TS4 Scheme 2

Cl

F

N

-Me3SiF

F

1.825

O Si

2.035

F

Si

A, E = –22.6

tetrel bond

tetrel bond F

1.256

Si Cl

TS1a, E = 17.4

N

F 1.971

1.724

F

F

O

1.315

1.806

Cl

2.728

O

Cl

2.620

Si

Si

F F

7a, E = –12.8

Q = -0.020  = 72.8 (O...C)=0.018

1.229

N F

F

7a', E = –8.7

Q = -0.136  = 82.8 (O...Si)=0.053

tetrel bond

O

TS6a, TS7 Scheme 3

N

Q = -0.230  = 87.12 (O...C)=0.070

1.256

1.821

Si

O

F

F

1.935

-Me3SiCl

F F

1.988

N

Si

Si Cl 2.286

tetrel bond

F

TS5a, E = 19.1

Fig. 3. Reaction scheme for interaction of amide 1a with silane 2.


B, E = –25.4

F

Page 17 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17 In going from complex 7a to complex 7a', which is by 4.15 kcal/mol less stable, the O∙∙∙Si distance is increased to 2.620 Å and then reduced to 1.724 Å in TS1a, approaching to a covalent OSi bond in the intermediate product 13 (Scheme 2).18 With this, the interatomic distances in complex 7a' and in the transition state TS1a vary in a similar manner with respect to the starting amide 1a and silane 2. Thus, the C∙∙∙O distance increases to 1.229 Å in 7a' and to 1.315 Å in TS1a as compared to 1.219 Å for the C=O bond in amide 1a, and the N∙∙∙Si distance increases to 1.806 Å in 7a' and to 2.058 Å in TS1a as compared to the NSi bond of 1.793 Å in 1a. The length of the SiF bond in silane 2 is 1.583 Å, while the Si∙∙∙F distance is 1.595 Å in 7a' and 1.857 Å in TS1a. While complexes 7a'10a' are 24 kcal/mol less stable than 7a10a, the O∙∙∙Si distances in them are larger by 0.30.8 Å (Table 2), but are still less than the sum of the vdW radii of the O and Si atoms. The QTAIM analysis showed no BCP between the oxygen and silicon atoms in complexes 7a'10a'. In complexes 7a' and 8a', BCPs were found on the O∙∙∙C bonds (Table 4, Figure 4). Table 4 M06-2X/6-311G(d,p) bond lengths (l, Å), topological electron density properties at BCPs [ρ(rc), 2ρ(rc), and H(rc); au], energies (E, kcal/mol) of intermolecular bonds O∙∙∙Si, N∙∙∙Si and O∙∙∙C in complexes 7a10a, 7b10b, and 7a', 8a'. Complex

l

ρ(rc)

2ρ(rc)

H(rc)

E

O∙∙∙Si 7a

2.035

0.053

0.170

0.0179

24.5

8a

2.034

0.054

0.166

0.0183

24.5

9a

2.028

0.053

0.175

0.0170

24.4

10a

2.690

0.017

0.046

0.0005

3.9

O∙∙∙C 7a'

2.728

0.018

0.054

0.0001

4.2

8a'

2.785

0.015

0.060

0.0017

3.6

0.015

0.050

0.0010

3.3

N∙∙∙Si 7b

1.992

0.074

0.222

0.0316

37.3

8b

2.008

0.072

0.199

0.0317

35.5

9b

2.006

0.070

0.210

0.0294

35.0

10b

2.091

0.059

0.140

0.0243

26.2



Page 18 of 29

18

7a'

8a'

Fig. 4. Molecular graphs of complexes 7a' and 8a'. Their topological parameters and energies (3.34.2 kcal/mol) are close to those in 10a, characterizing the O∙∙∙Si bond in this complex as a weak tetrel bond. There is a common exponential dependence between the lengths of the O∙∙∙Si, N∙∙∙Si, O∙∙∙C bonds and the values of E in all three types of complexes (Figure S2), which is indicative of the similar character of bonding. A similar dependence we observed earlier for different coordination and hydrogen bonds.75 This allows to consider not only the O∙∙∙C, but also O∙∙∙Si in 7a' and 8a' as tetrel bonds. More short distances O∙∙∙Si than O∙∙∙C (Figure 3), slightly larger E(2) values of nO → σ*Si–Fax interaction as compared to nO → σ*C–Clax (Table 3) and the form of molecular graphs44 in 7a' and 8a' allow to consider the O∙∙∙Si bond in these complexes as a weak tetrel bond, in spite of the absence of BCP in the QTAIM analysis. Such a conclusion is supported also by the exponential dependence between the O∙∙∙Si, O∙∙∙C distances and the energies of nO → σ*Si–Fax, nO → σ*C–Clax interactions (Figure S3). The dependence includes the E(2) values for complexes 7a10a and 7a' and 8a' for both types of interaction. The absence of BCP on the bond path between the O and Si atoms can be counterbalanced by the presence of BCPs on the curved bond paths to the equatorial substituents at silicon. Such a situation was observed in complex FSiMe3···NH3, where no BCP was found between N and Si; however, the NBO analysis revealed the presence of weak Si∙∙∙N tetrel bonds.76 Tetrel bonding in 7a' and 8a' is also confirmed by redistribution of charges, small Q = 0.02 e, yet enough to be noticeable22,53 and the increase of polarization of the C∙∙∙Clax and Si∙∙∙Fax bonds (Table 3). This nicely correspond to the presence of high Vmax values of MESP at the carbon and silicon ends of the SiC bonds in silanes 2 and 3. Lower Vmax values in silanes 4 and 5 at much longer O∙∙∙C and O∙∙∙Si distances in complexes 9a' and 10a' prevent the formation of tetrel bonds these complexes. The interaction of the components in this case is mainly electrostatic, and BCPs were found only on the intermolecular hydrogen bonds. ACS Paragon Plus Environment

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19 The effect of solvent polarity and specific solvation on the formation of the tetrel bond was studied by calculating complex 7a' and solvate 1:1 complexes of 7a' with chloroform, in which the solvent molecule forms hydrogen bond with the axial fluorine (SiFax) or chlorine atom (CClax), as well as 1:2 complexes in which two molecules of the solvent are bound to both halogens, in chloroform solution (Figure S4). The choice of the solvent was determined by the fact that it was used for carrying out and IR monitoring the reaction.18 QTAIM analysis showed the presence of BCPs on the O∙∙∙Si bonds of the complex, which in all cases are tetrel bonds, whereas no BCPs were found between the CH2Cl carbon and the carbonyl oxygen atoms (Figure S5). Topological characteristics of the O∙∙∙Si bonds and the values of their energies prove that these bonds are substantially stronger than those in 7a' in the gas phase (Tables 4, 5). The values of ρ(rc) > 0.05 au, positive values of 2ρ(rc) and negative values of H(rc) are characteristic of closed shell interactions with high covalent character. This is most evident in 1:1 and 1:2 solvate complexes with SiFax∙∙∙HCCl3 bond. Note, that the hydrogen atom of the chloroform molecule in 1:2 complex forms the intermolecular hydrogen bond not only with the fluorine atom, but also with the chlorine atom of the CH2Cl group, resulting in a bifurcate hydrogen bond (Figure S4). The CClax bond in 7a' is much less polarized than the SiFax bond (Table 3), so, the effect of both specific and nonspecific solvation on the shortening of the O∙∙∙C bond is much less pronounced than that on the O∙∙∙Si bond. Note, that the O∙∙∙C distance in the solvate complexes of 2.5602.587 Å are shorter than in the isolated molecule 7a' (2.728 Å), and the absence of BCPs in the complexes is, apparently, connected with a high covalent character of the O∙∙∙Si bond, resulting from competition for charge transfer from the Lewis base 1a onto the Lewis acid 2. The formation of solvate complexes 7a' having the tetrel bond O∙∙∙Si is the second stage of transsilylation reaction. The same complexes, having the O∙∙∙C bond of electrostatic character are formed in the second stage of alkylation reaction. Complex 12a with the C∙∙∙O bond of electrostatic character (2.826 Å) (vide supra) is formed by the reaction of amide 1a with silane 2 in the initial stage of alkylation. The O∙∙∙Si distance in this case is 3.372 Å. In chloroform solution, similar to complex 7a', it has the O∙∙∙Si tetrel bond (1.942 Å), whereas the C∙∙∙O (2.545 Å) retains its electrostatic character. The structure of the first transition state TS5a in the reaction of alkylation of amide 1a with silane 2, as well as TS1a, is similar to the structure of complex 7a' (Figure 3). The C∙∙∙O and N∙∙∙Si distances in TS5a increase to 1.256 and 1.821 Å, respectively, and the C∙∙∙Cl distance – to 2.286 Å as compared to 1.794 Å in silane 2. Both transition states TS5a and TS1a are characterized by high values of topological parameters (O∙∙∙C) 0.070 a.u. and (O∙∙∙Si) 0.104 a.u., angles α 87.1 and 90.7, and charge transfer Q = 0.230 and 0.101 e, respectively.



Page 20 of 29

20 Table 5 PCM//M06-2X/6-311G(d,p) bond lengths (l, Å), topological electron density properties at BCP [ρ(rc), 2ρ(rc), and H(rc); au], energies (E, kcal/mol) of intermolecular bonds O∙∙∙Si and O∙∙∙C in solvate complexes of 7a' with CHCl3 as a solvent: 7a' and its 1:1 and 1:2 complexes with CHCl3. Solvate complex

lO∙∙∙Si lO∙∙∙C

ρ(rc)

2ρ(rc)

H(rc)

E

7a'

1.950 2.560a

0.059

0.240

0.0173

29.7

7a'∙CHCl3 (SiFax∙∙∙HCCl3)b

1.921 2.575

0.063

0.275

0.0181

32.9

7a'∙CHCl3 (CH2Cl∙∙∙HCCl3)

1.946 2.558

0.061

0.243

0.0174

30.02

7a'∙2CHCl3 (SiFax∙∙∙HCCl3) (CH2Cl∙∙∙HCCl3)

1.917 2.587

0.064

0.281

0.0172

32.9

lO∙∙∙C distance in italics; b bonds formed by CHCl3 with 7a' in solvate complexes 1:1 and 1:2, are given in parentheses. a

Therefore, the formation of the σ-hole tetrel bond O∙∙∙Si in complexes 7a10a is the first stage on the reaction pathways of transsilylation and alkylation of amide 1a with silanes 25, whereas for complexes 7a' and 8a' the tetrel bonding O∙∙∙C is the second stage, which, according to QTAIM analysis, may lead to predominant alkylation of amide 1a with silanes 2 or 3. Besides, the first stage of the reaction of transalkylation is the formation of complex 12a from amide 1a and silanes 2, and similar complexes with silanes 36, with the O∙∙∙C bond having electrostatic nature. In polar medium, the O∙∙∙Si bond in complex 7a' is strengthened to tetrel bond and becomes the second stage in the reaction of transsilylation. The resemblance of geometric, energetic and topological parameters and electron redistribution in complexes 7b10b and transition state TS1b (Table S1, 4, Figure S6) suggests that the first stage on the pathway of the reaction of transsilylation of imidate 1b is the formation of these complexes with covalent N∙∙∙Si bond.

4. Conclusions Using the methods of quantum chemistry, the complexes of ambident N,О-donor, Ntrimethylsilyl-N-methylacetamide 1a and its tautomer, O-trimethylsilyl-N-methylacetimidate 1b with bifunctional silane ClCH2SiF3 2 were studied and their energetic, geometric and electron density characteristics determined. The analysis of MESP contours revealed two σ-holes ACS Paragon Plus Environment

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21 localized at the carbon and silicon ends of the silane molecule ClCH2SiF3. Their close values of Vmax 53.72 and 53.54 kcal/mol indicate the possibility of formation of tetrel bonds with participation of both the silicon atom and the carbon atom of the chloromethyl group with the oxygen atom of amide 1a or the nitrogen atom of imidate 1b. This allows to explain the interplay of dual reactivity and the formation of both the transsilylation and alkylation products in the reaction of silane 2 with tautomers 1a and 1b.18 Two types of complexes are initially formed in the reaction of amide 1a and silane 2. For the complex of the first type, the results of NBO and QTAIM analyses suggest the formation of the O∙∙∙Si tetrel bond between the silicon atom and the oxygen atom of the amide tautomer. However, orientation of the molecules of the components in it does not correspond to the structure of the first transition state of the reaction of transsilylation. To become a precursor of this transition state, the two components must rotate around the incipient O∙∙∙Si bond to form a rotamer in which the O∙∙∙C bond is a tetrel bond while the O∙∙∙Si bond has electrostatic character. The IEF-PCM calculations of the solvate complexes with chloroform of 1:1 and 1:2 composition in chloroform solution showed that the O∙∙∙Si bond is strengthened and becomes a tetrel bond, and the O∙∙∙C bond acquires electrostatic character. The reaction of tautomer 1b with silane 2 results in the formation of complex with covalent bond N– Si. A challenging question, which has no definite answer, is whether the reaction is favored by the formation of pre-reaction complex of electrostatic or covalent nature. It cannot be ruled out that the formation of covalently bonded complexes (O–Si) or (N–Si) chelates, due to highly electropositive nature of silicon, makes them stable and hampers further reaction. This could explain, at least, partly, the predominance of alkylation versus transsilylation in the reaction of tautomers 1a and 1b with silane 2.

ASSOCIATED CONTENT Supporting Information The Supporting Information to this article n is available free of charge on the ACS Publications website at DOI: Detailed results of QC calculations, mol.files, molecular graphs, reaction scheme for interaction of amide 1b with silane 2, plots of QTAIM energy vs. О∙∙∙Si, N∙∙∙Si, O∙∙∙C bond lengths and of NBO energy vs. О∙∙∙Si, O∙∙∙C bond lengths.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ACS Paragon Plus Environment


Page 22 of 29

22 ORCID Nataliya F. Lazareva: 0000-0003-0877-9656 Bagrat A. Shainyan: 0000-0002-4296-7899 Notes The authors declare no competing financial interest.

Acknowledgements The main results were obtained using the equipment of Baikal Analytical Center of Collective Using of the SB RAS.

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Graphic abstract


Tetrel Bonding along the Pathways of Transsilylation and Alkylation of

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