Mechanism of Reactions of 1-Substituted Silatranes And

Article Mechanism of Reactions of 1-Substituted Silatranes and Germatranes, 2,2-Disubstituted Silocanes and Germocanes, 1,1,1-Trisubstituted Hyposilatranes and Hypogermatranes with Alcohols (Methanol, Ethanol): DFT Study

Denis Chachkov 1, Rezeda Ismagilova 2 and Yana Vereshchagina 2,* 1 Kazan Department of Joint Supercomputer Center of Russian Academy of Sciences–Branch of Federal State Institution “Scientiﬁc Research Institute for System Analysis of the RAS”, Lobachevskogo 2/31, 420111 Kazan, Russia; [email protected] 2 Department of Physical Chemistry, A.M. Butlerov Institute of Chemistry, Kazan Federal University, Kremlevskaya 18, 420008 Kazan, Russia; [email protected] * Correspondence: [email protected] or [email protected]

Academic Editor: Bagrat A. Shainyan Received: 20 May 2020; Accepted: 15 June 2020; Published: 17 June 2020 Abstract: The mechanism of reactions of silatranes and germatranes, and their bicyclic and monocyclic analogues with one molecule of methanol or ethanol, was studied at the Density Functional Theory (DFT) B3PW91/6-311++G(df,p) level of theory. Reactions of 1-substituted sil(germ)atranes, 2,2-disubstituted sil(germ)ocanes, and 1,1,1-trisubstituted hyposil(germ)atranes with alcohol (methanol, ethanol) proceed in one step through four-center transition states followed by the opening of a silicon or germanium skeleton and the formation of products. According to quantum chemical calculations, the activation energies and Gibbs energies of activation of reactions with methanol and ethanol are close, their values decrease in the series of atranes–ocanes–hypoatranes for interactions with both methanol and ethanol. The reactions of germanium-containing derivatives are characterized by lower activation energies in comparison with the reactions of corresponding silicon-containing compounds. The annular conﬁgurations of the product molecules with electronegative substituents are stabilized by the transannular N X (X = Si, Ge) bond and diﬀerent intramolecular hydrogen → contacts with the participation of heteroatoms of substituents at the silicon or germanium.

Keywords: atranes; ocanes; hypoatranes; conformational analysis; mechanism of reaction; alcohols; DFT calculations

1. Introduction Heterocyclic compounds of hypervalent atoms, primarily intra-complex compounds of triethanolamine–metallatranes, possess unique physical and chemical properties that are due to their unusual trigonal-bipyramidal structure with a transannular nitrogen–element bond and the presence of an axial fragment. Triethanolamine derivatives of silicon, germanium, tin, carbon, boron, phosphorus, and arsenic, as well as bismuth, titanium, vanadium, aluminum and iron are currently known [1,2]. The most studied compounds of the elements of group 14 are silatranes and germatranes, as well as their bicyclic analogues–ocanes and monocyclic–hypoatranes. The diverse biological activity of atrane systems depends on the nature of the substituents, and such compounds can be both eﬀective immunostimulants and adaptogens, and immunosuppressants, thus providing a stimulating or inhibiting eﬀect on the vital activity of micro- and macroorganisms [3–10]. In addition, atranes are used as important functional reagents [11–15], catalysts for the formation of polyurethanes [16,17].

Molecules 2020, 25, 2803; doi:10.3390/molecules25122803 www.mdpi.com/journal/molecules Molecules 2020, 25, x 2 of 18 can be both effective immunostimulants and adaptogens, and immunosuppressants, thus providing a stimulating or inhibiting effect on the vital activity of micro- and macroorganisms [3–10]. In Molecules 2020, 25, 2803 2 of 16 addition, atranes are used as important functional reagents [11–15], catalysts for the formation of polyurethanes [16,17]. Recent achievements, challengeschallenges andand prospects prospects for for using using atranes atranes are are given given in in the the reviews reviews [18 –[18–20]. 20].Atranes, Atranes, ocanes andocanes hypoatranes and hypoatranes contain an intramolecularcontain an coordinationintramolecular bond coordination nitrogen element. bond → nitrogenTheoretical→element. studies onTheoretical the structure studies and on hypervalent the structure intramolecular and hypervalent coordination intramolecular N X (Xcoordination= C, Si, Ge, → NB,→ P)X in (X some = C, atraneSi, Ge, systems B, P) in were some carried atrane out systems in [21 –were31]; information carried out onin the[21–31]; structure information of some ocaneson the structureis given in of [ 32some–39], ocanes and hypoatranes is given in [32–39], in [36,40 and–43]. hypoatranes in [36,40–43]. The length and strength of the intramolecularintramolecular transannular bond N →X is determined by the → number and naturenature ofof electronegativeelectronegative substituents substituents at at the the central central atom atom X: X: An an increase increase in in the the number number of ofhighly highly electronegative electronegative substituents substituents at the at siliconthe silicon or germanium or germanium atom atom signiﬁcantly significantly reduces reduces the length the lengthof the Nof theX bondN→X and, bond therefore, and, therefore, increases increases its strength its strength [33]. [33]. → Despite the long history of the chemistry of atrane systems, issues affecting aﬀecting their spatial and electronic structure,structure, as as well well as theas the reaction reaction mechanisms mechanisms of these of compounds,these compounds, do not losedo theirnot lose relevance, their relevance,and the development and the development of quantum of quantum chemistry chemis methodstry methods contributes contributes a lot to this.a lot Theseto this. new These results new resultsallow the allow available the available experimental experiment data toal data be substantiated. to be substantiated. Various Various aspects aspects of the reactivity of the reactivity of atranes of atranesare considered are considered in reviews in reviews [19,44], [1 the9,44], study the study of the of electron-donating the electron-donating ability ability of heteroatoms of heteroatoms of the of thesilatranyl silatranyl group group by calculation by calculation methods methods is described is described in [45–47 in]. [45–47]. There are There a few are publications a few publications concerned concernedwith reaction with mechanisms reaction mechanisms of metallatranes of metallatranes and their bicyclic and their and tricyclicbicyclic and analogs tricyclic with analogs nucleophiles. with nucleophiles.The results of The theoretical results of studies theoretical of the studies hydrolysis of the reactions hydrolysis of somereactions atrane, of some ocane atrane, and hypoatrane ocane and hypoatranesystems are systems described are in described [22,43,48– in52 ].[22,43,48–52]. In the present work, we performed a a theoretical st studyudy of the reactions of 1-substituted atranes, atranes, 2,2-disubstituted ocanes, an andd 1,1,1-trisubstituted hypo hypoatranesatranes with nucleophilic reagents—alcohols (methanol andand ethanol)—andethanol)—and comparedcompared thethe results results with with the the available available data data for for hydrolysis hydrolysis reactions reactions of ofthese these compounds. compounds.

2. Results Results and and Discussion Discussion

2.1. Methodology Methodology A theoretical theoretical study study of of the the reacti reactionsons of of1-substituted 1-substituted silatranes silatranes 1a–g1a and–g and germatranes germatranes 2a–g2a, 2,2-–g, disubstituted2,2-disubstituted silocanes silocanes 3a–3ag –andg and germocanes germocanes 4a4a–g–,g ,1,1,1-trisubstituted 1,1,1-trisubstituted hyposilatranes hyposilatranes 5a5a––gg and hypogermatranes 6a–g (Scheme 11)) withwith nucleophilicnucleophilic reagentsreagents methanolmethanol andand ethanolethanol waswas carriedcarried outout by quantum chemical calculations.

Scheme 1. StructuresStructures of atranes, ocanes, and hypoatranes.

The Density FunctionalFunctional Theory Theory (DFT) (DFT) with with B3PW91 B3PW91 hybrid hybrid functional functional [53,54 [53,54]] and 6-311and 6-311++G(df,p)++G(df,p) [55] [55]extended extended basis setbasis (calculations set (calculations of the molecules of the mo inlecules vacuum) in usingvacuum) GAUSSIAN using GAUSSIAN 09 software package09 software [56] packagewere earlier [56] successfully were earlier used successfully to study hydrolysis used reactionsto study of hydrolysis atrane, ocane reactions and hypoatrane of atrane,systems ocane [43 and,52]. hypoatraneThe choice of systems the B3PW91 [43,52]. method The choice was also of basedthe B3PW91 on the datamethod [57]. was In all also cases, based the on geometric the data parameters [57]. In all cases,of the moleculesthe geometric were fullyparameters optimized. of the The molecules critical points were on fully the potential optimized. energy The surfaces critical werepoints identified on the as energy minima by the absence of imaginary frequencies in the corresponding Hessian matrices and as transition states by the presence of one imaginary frequency therein. Transition states were assigned to reaction paths by descent toward starting molecule and reaction product. Hessian was generated Molecules 2020, 25, 2803 3 of 16 analytically in all cases, when searching for minimum energy it was calculated once to confirm that a minimum energy has been entered. In the case of a search for transition state, the Hessian was analytically calculated at each iteration. The parameter GRID = UltraFine was used. The solvent has not been taken into account. Reactions of 1-substituted silabicyclo[3.3.3]undecanes 1a–g and 1-germabicyclo[3.3.3]undecanes 2a–g, 2,2-disubstituted 1,3,6,2-dioxazasilocanes 3a–g and 1,3,6,2-dioxazagermocanes 4a–g, hyposilatranes 5a–g and hypogermatranes 6a–g with one methanol molecule or one ethanol molecule were simulated. First, we carried out theoretical conformational analysis of all starting compounds 1–6. Namely, the conformational analysis of all reaction participants is a necessary step in studying their reactivity and establishing the reaction mechanisms. We found energetically preferred conformers for each of compounds 1–6. These structures were used as the starting reagents in the simulation of the mechanism of their reactions with alcohol (methanol or ethanol). The energy difference between the conformers was 5–15 kJ/mol. The barrier of the transition between the conformers was noticeably higher: 18–46 kJ/mol. The reactions studied can proceed not only for the most favorable conformer of the starting reagent, but also for those which are not advantageous. The reaction barrier for unfavorable conformers was 5–25 kJ/mol higher than for the most favorable conformation of the reagent. According to our previous quantum chemical calculations [52], 1-substituted compounds 1a–g, 2a–g are classical atrane systems where the silicon or germanium atom has a flattened tetrahedral configuration, and the nitrogen moiety is also flattened; the substituent R at the X atom occupies the axial position. Eight-membered silicon-nitrogen-oxygen-containing cycles in them have crown conformations (chair–chair or chair–bath), the molecules have a transannular N X bond (X = Si, Ge). → The most preferred conformation of bicyclic analogues of atranes–2,2-disubstituted ocanes, 3a–g, 4a–g, is symmetrical crown (chair–chair) where the silicon (germanium) and nitrogen atoms are close, the transannular interaction N X (X = Si, Ge) is observed [52]. The silicon and germanium atoms are → tetrahedra with one axial and one equatorial substituent. In the preferred conformers of monocyclic hypoatranes 5a–g, 6a–g [43], the silicon (germanium) and nitrogen atoms are flattened tetrahedra where oxygen atom and two substituents at the Si (Ge) are in equatorial positions, and third substituent is axial. In hypoatranes with perchlorate (5e, 6e), nitrate (5f, 6f), and thiocyanate (5g, 6g) substituents, intramolecular contacts between one of the hydrogen atoms of the amino group and the heteroatom (O or N) of one of the functional groups at the Si and/or Ge, in halogen derivatives (5b–d, 6b–d), contacts between the hydrogen atoms of the amino group and the halogen atoms are possible. The Endo-configuration of the molecules 5a–g, 6a–g is determined by the transannular interaction N Si or N Ge as well as for atranes 1a–g, 2g and → → ocanes 3a–g, 4a–g.

2.2. Reactions of 1-Substituted Atranes with Methanol The mechanism of reactions of atranes 1a–g, 2a–g with one methanol molecule according to quantum chemical calculations is shown in Scheme2. The obtained energy characteristics of the reactions and some geometric parameters of the reaction participants are given in Table1 and Table S1. As an example, the reaction schemes for some atranes according to theoretical studies are presented in Figure1. The interaction of atranes 1a–g, 2a–g with methanol proceeds in one step. Initially, prereaction complexes are formed between the molecules of atrane and methanol, in which the N Si (N Ge) → → bond length decreases, a contact arises between the proton of the hydroxyl group of methanol and the O1 atom of the atrane skeleton (Table S1). The prereaction complexes are transformed into transition states in which the N Si (N Ge) distance is further reduced, the Si(Ge)-O1 and O4-H1 bonds are → → stretched in methanol, and the H1 ... O1 contact is reduced (Scheme2, Table S1). The third stage of interaction is the opening of one of the half rings of the atrane skeleton, as a result, the Si(Ge)-O1 bond is cleaved, and the Si(Ge)-O4 and O1-H1 bonds are formed. The products of methanol addition to atranes are substituted ocanes—2-R-6-(2-hydroxyethyl)-1,3,2,6-dioxazasil(germ)ocane-2-ols 7a–g, 8a–g. Molecules 2020, 25, 2803 4 of 16 Molecules 2020, 25, x 4 of 18

Scheme 2. Mechanism of reactions of atranes with methanol.

Figure 1.1.Mechanism Mechanism of reactionsof reactions of germatranes of germatranes2a, 2b ,2a2e, with2b, methanol2e with methanol according toaccording DFT calculations. to DFT calculations. According to the quantum chemical calculations, the possible intramolecular hydrogen bonds O4 ...TheH1O1 interaction as well as of the atranes transannular 1a–g, 2a–g interactions with methanol N Si orproceeds N Ge (Schemein one step.2, Table Initially, S1, and prereaction Figure1) The interaction of atranes 1a–g, 2a–g with methanol→ proceeds→ in one step. Initially, prereaction stabilizecomplexes the are structure formed between of molecules the molecules7a–g, 8a–g of. atrane The ocane and methanol, fragments in of which product the molecules N→Si (N→ haveGe) crownbond lengthconformation—a decreases, chair–boata contact forarises silocane between7a and the germocanesproton of the8a hydroxyl–g, and symmetrical group of methanolboat–boat andfor silocanesthe O1 atom7b– gof. The the siliconatrane (germanium) skeleton (Table atom S1). is ﬂattenedThe prereaction tetrahedron, complexes and the are nitrogen-containing transformed into fragmenttransition isstates also ﬂattened.in which the The N N→SiSi (N (N→Ge)Ge) distance bond in theis further molecules reduced, of products the Si(Ge)7a–‒gO1, 8a –andg is O4 longer‒H1 transition states in which the N→→Si (N→→Ge) distance is further reduced, the Si(Ge)‒O1 and O4‒H1 (Tablebonds S1)are thanstretched in the in molecules methanol, of and the startingthe H1...O1 atranes, contact which is reduced is generally (Scheme consistent 2, Table with S1). the The change third instage the of N interactionSi (N Ge) is the bond opening length of in one similar of the atranes half rings and of their the hydrolysisatrane skeleton, products as a result, [52]. In the the Si(Ge) series‒ stage of →interaction→ is the opening of one of the half rings of the atrane skeleton, as a result, the Si(Ge)‒ ofO1 halogen-substituted bond is cleaved, and products the Si(Ge)7b–‒dO4and and8b –O1d,‒ theH1 distancebonds are N formed.Si (N TheGe) increasesproducts fromof methanol F to Br. O1 bond is cleaved, and the Si(Ge)‒O4 and O1‒H1 bonds are →formed.→ The products of methanol Theaddition smallest to atranes distance are is substituted observed for ocanes—2-R-6 perchlorate derivatives-(2-hydroxyethyl)-1,3,2,6-dioxazasil(germ)ocane-2-7e and 8e. The intramolecular hydrogen ... bondsols 7a–g O4, 8a–gH1O1. in molecules 7a–g, 8a–g are quite strong, as evidenced by their lengths (Table S1); According to the quantum chemical calculations, the possible intramolecular hydrogen bonds O4…H1O1 as well as the transannular interactions N→Si or N→Ge (Scheme 2, Table S1, and Figure 1) stabilize the structure of molecules 7a–g, 8a–g. The ocane fragments of product molecules have

Molecules 2020, 25, 2803 5 of 16 the strongest ones are in hydroxyl 8a and fluorine 8b derivatives, moreover the angle O4H1O1 is 161◦–176◦. The analysis of Table1 shows that the reactions of compounds 1a–g, 2a–g with methanol are controlled by thermodynamic factors; the contribution of the enthalpy component is most significant, since the activation enthalpy and the Gibbs activation energy change symbiotically. This conclusion is valid not only for activation parameters, but also for the enthalpy of the reaction (thermal effect) and for the Gibbs energy of the reaction.

Table 1. Activation energies, Gibbs activation energies (kJ/mol), and imaginary vibration frequencies 1 # (cm− ) of transition states of reactions of atranes 1a–g, 2a–g with methanol.

# # 1 ∆E ∆G ν1, cm− 1a 91.3 149.4 877i 1b 69.3 128.1 910i 1c 72.4 131.9 951i 1d 73.2 132.8 966i 1e 62.4 120.4 992i 1f 71.9 129.1 969i 1g 78.8 135.8 972i 2a 56.4 113.2 821i 2b 61.5 115.6 803i 2c 67.3 121.4 815i 2d 68.7 122.7 819i 2e 56.1 110.9 891i 2f 66.3 119.4 851i 2g 72.4 124.8 822i

In the series of halogenated silatranes and germatranes (F, Cl, Br), the activation energy increases (Table1) naturally with a decrease in the electronegativity of the substituents [ 33,58]. The reactions of germatranes 2a–g proceed with slightly lower activation energies compared with reactions of silatranes 1a–g. In transition states, the smallest distance N-X (X = Si, Ge) and the lowest activation energy (Table1, Table S1) are observed for perchlorate-substituted atranes 1e and 2e.

2.3. Reactions of 2,2-Disubstituted Ocanes with Methanol According to DFT calculations, the mechanism of reactions of ocanes 3a–g, 4a–g with one methanol molecule is presented in Scheme3. The obtained energy characteristics of the reactions and some geometric parameters of the reaction participants are given in Table2 and Table S2. As an example, theMolecules reaction 2020, schemes25, x for some ocanes according to theoretical studies are presented in Figure2. 6 of 18

Scheme 3. Mechanism of reactions of ocanes with methanol.

Figure 2. Mechanism of reactions of silocanes 3a, 3c, 3f with methanol according to DFT calculations.

The interaction of ocanes 3a–g, 4a–g with methanol also proceeds in one step. Initially, prereaction complexes are formed between the molecules of ocanes and methanol, in which the N‒ Si (N‒Ge) bond length decreases, a contact arises between the proton of the hydroxyl group of methanol and the O1 atom. Prereaction complexes are transformed into transition states, in which N‒Si (N‒Ge) distance is further reduced, while the Si‒O1 (Ge‒O1) bond is extended (Table S2), the silicon(germanium)- and nitrogen-containing fragments are flattened, which leads to distortion of crown conformation. The O3‒H2 bond is stretched, and the O1‒H2 contact arises. The nucleophilic attack of a methanol molecule leads to the cleavage of the Si‒O1 (Ge‒O1) bond in the molecules of ocanes 3a–g, 4a–g and the appearance of a new Si‒O3 (Ge‒O3) bond. The annular configuration of product molecules 9a–g, 10a–g is stabilized due to the dative interaction N→Si (N→Ge) and the intramolecular hydrogen bond O2...H3 (Table S2). The possibility of a transannular interaction N→Si (N→Ge) is evidenced by both the spatial factor (the distance N‒Si (N‒Ge) is less than the sum of the van der Waals radii of these elements) and the presence of electronegative substituents at the acceptor silicon or germanium atom. In addition, short contacts between the

Molecules 2020, 25, x 6 of 18

Molecules 2020, 25, 2803 6 of 16 Scheme 3. Mechanism of reactions of ocanes with methanol.

Figure 2. Mechanism of reactions of silocanes 3a, 3c, 3f with methanol according to DFT calculations. Figure 2. Mechanism of reactions of silocanes 3a, 3c, 3f with methanol according to DFT calculations. The interaction of ocanes 3a–g, 4a–g with methanol also proceeds in one step. Initially, The interaction of ocanes 3a–g, 4a–g with methanol also proceeds in one step. Initially, prereaction prereaction complexes are formed between the molecules of ocanes and methanol, in which the N‒ complexes are formed between the molecules of ocanes and methanol, in which the N-Si (N-Ge) bond Si (N‒Ge) bond length decreases, a contact arises between the proton of the hydroxyl group of length decreases, a contact arises between the proton of the hydroxyl group of methanol and the O1 methanol and the O1 atom. Prereaction complexes are transformed into transition states, in which atom. Prereaction complexes are transformed into transition states, in which N-Si (N-Ge) distance N‒Si (N‒Ge) distance is further reduced, while the Si‒O1 (Ge‒O1) bond is extended (Table S2), the is further reduced, while the Si-O1 (Ge-O1) bond is extended (Table S2), the silicon(germanium)- silicon(germanium)- and nitrogen-containing fragments are flattened, which leads to distortion of and nitrogen-containing fragments are flattened, which leads to distortion of crown conformation. crown conformation. The O3‒H2 bond is stretched, and the O1‒H2 contact arises. The O3-H2 bond is stretched, and the O1-H2 contact arises. The nucleophilic attack of a methanol molecule leads to the cleavage of the Si‒O1 (Ge‒O1) bond The nucleophilic attack of a methanol molecule leads to the cleavage of the Si-O1 (Ge-O1) bond in in the molecules of ocanes 3a–g, 4a–g and the appearance of a new Si‒O3 (Ge‒O3) bond. The annular the molecules of ocanes 3a–g, 4a–g and the appearance of a new Si-O3 (Ge-O3) bond. The annular configuration of product molecules 9a–g, 10a–g is stabilized due to the dative interaction N→Si configuration of product molecules 9a–g, 10a–g is stabilized due to the dative interaction N Si (N Ge) (N→Ge) and the intramolecular hydrogen bond O2...H3 (Table S2). The possibility of a transannular→ → and the intramolecular hydrogen bond O2 ... H3 (Table S2). The possibility of a transannular interaction interaction N→Si (N→Ge) is evidenced by both the spatial factor (the distance N‒Si (N‒Ge) is less N Si (N Ge) is evidenced by both the spatial factor (the distance N-Si (N-Ge) is less than the sum than →the sum→ of the van der Waals radii of these elements) and the presence of electronegative of the van der Waals radii of these elements) and the presence of electronegative substituents at the substituents at the acceptor silicon or germanium atom. In addition, short contacts between the acceptor silicon or germanium atom. In addition, short contacts between the hydrogen (N-H) and the heteroatom of the axial substituent at the Si (Ge) atom contribute to the stabilization of the crown-like 10-membered configuration of molecules: oxygen in hydroxyl substituted 9a and 10a, perchlorate 9e and 10e, nitro 9f and 10f, halogen in 9b–d and 10b–d, nitrogen of the thiocyanate group in 9g and 10g. The silicon, germanium and nitrogen atoms in the molecules 9a–g, 10a–g are flattened tetrahedra. The N–Si (N-Ge) distance in the molecules of the products 9a–g, 10a–g is less than in the reagents, as well as in the hydrolysis reactions of these compounds [52], with the exception of dichloro- and dibromo-substituted germocanes 10c and 10d (Table S2). Silocanes are characterized by a regular decrease in the N–X distance as the electronegativity of the exocyclic halogen substituent increases in a series—F, Cl, Br; however, the opposite regularity is observed for germocanes (Table S2). Molecules 2020, 25, 2803 7 of 16

The reactions of ocanes 3a–g, 4a–g are controlled by thermodynamic factors. The activation energy in a series of halogen-substituted ocanes 9b–d and 10b–d (F, Cl, Br) increases naturally with a decrease in the electronegativity of the substituents (Table2). In the case of reactions of germocanes 4a–g, the activation energies and Gibbs activation energies are lower than those of silocanes 3a–g. The smallest N–Si (N-Ge) distances and the smallest values of the activation energy (Gibbs activation energy) are observed for the diperchlorate derivatives 9e and 10e (Table2, Table S2). The same regularity was revealed for hydrolysis reactions of similar ocanes [52].

Table 2. Activation energies, Gibbs activation energies (kJ/mol), and imaginary vibration frequencies 1 # (cm− ) of transition states of reactions of ocanes 3a–g, 4a–g with methanol.

# # 1 ∆E ∆G ν1, cm− 3a 67.7 125.6 835i 3b 48.1 106.0 942i 3c 55.1 114.0 990i 3d 55.8 113.4 1020i 3e 33.7 93.3 1041i 3f 48.6 104.6 1000i 3g 49.9 107.6 1035i 4a 42.1 97.3 802i 4b 24.4 79.8 922i 4c 38.0 93.9 917i 4d 41.5 97.3 928i 4e 14.2 70.8 1010i 4f 37.6 92.6 950i 4g 38.5 95.3 952i

2.4. Reactions of 1,1,1-Trisubstituted Hypoatranes with Methanol The mechanism of reactions of 1,1,1-substituted hyposilatranes 5a–g and hypogermatranes 6a–g with one methanol molecule according to quantum chemical calculations is shown in Scheme4. The obtained energy characteristics of the reactions and some geometric parameters of the reaction participants are given in Table3 and Table S3. As an example, the reaction schemes for some ocanes according to theoretical studies are presented in Figure3. Molecules 2020, 25, x 8 of 18

Scheme 4. MechanismMechanism of reactions of hypoatranes with methanol.

Table 3. Activation energies, Gibbs activation energies (kJ/mol), and imaginary vibration frequencies (cm−1) of transition states # of reactions of hypoatranes 5a–g, 6a–g with methanol.

# # ΔE ΔG ν1, cm−1 5a 79.9 136.0 963i 5b 30.8 −95.1 1020i 5c 35.5 92.9 1049i 5d 39.3 96.3 1064i 5e −4.7 56.0 1145i 5f 13.9 72.6 1074i 5g 28.4 83.9 1103i 6a 56.9 110.7 925i 6b 13.4 68.3 1000i 6c 27.7 84.2 995i 6d 33.4 89.9 994i 6e −15.1 44.8 1120i 6f 3.6 61.2 1037i 6g 21.7 79.2 1034i

Molecules 2020, 25, 2803 8 of 16

Table 3. Activation energies, Gibbs activation energies (kJ/mol), and imaginary vibration frequencies 1 # (cm− ) of transition states of reactions of hypoatranes 5a–g, 6a–g with methanol.

# # 1 ∆E ∆G ν1, cm− 5a 79.9 136.0 963i 5b 30.8 95.1 1020i − 5c 35.5 92.9 1049i 5d 39.3 96.3 1064i 5e 4.7 56.0 1145i − 5f 13.9 72.6 1074i 5g 28.4 83.9 1103i 6a 56.9 110.7 925i 6b 13.4 68.3 1000i 6c 27.7 84.2 995i 6d 33.4 89.9 994i 6e 15.1 44.8 1120i − 6f 3.6 61.2 1037i 6g 21.7 79.2 1034i Molecules 2020, 25, x 9 of 18

FigureFigure 3. Mechanism3. Mechanism ofof reactionsreactions of of hypogermatranes hypogermatranes 6a, 6d6a,, 6g6d with, 6g methanolwith methanol according according to DFT to calculations. DFT calculations. The interaction of hypoatranes 5a–g, 6a–g with methanol proceeds in several stages, as in the The interaction of hypoatranes 5a–g, 6a–g with methanol proceeds in several stages, as in the case case of atranes 1a–g, 2a–g and ocanes 3a–g, 4a–g. At the first stage, prereaction complexes are formed of atranes 1a–g, 2a–g and ocanes 3a–g, 4a–g. At the ﬁrst stage, prereaction complexes are formed in in which the reagent molecules come together, the distance N‒X (X = Si, Ge) is reduced (Scheme 4, whichTable the reagentS3). Then, molecules the prereaction come together, complexes the are distance transformed N-X (Xinto= Si,transition Ge) is reducedstates, the (Scheme distances4, TableN‒X S3). Then,(X the = Si, prereaction Ge) and O1 complexes...H3 are shortened, are transformed and the X‒ intoO1 bond transition is stretched, states, a new the distancescontact arises N-X between (X = Si, Ge) and O1the... siliconH3 are (germanium) shortened, atom and and the X-O1the oxygen bond atom is stretched, of methanol a new (Scheme contact 4, arisesTable S3). between At the the final silicon (germanium)stage, the atom Si‒O1 and (Ge the‒O1) oxygen bond breaks atom ofand methanol a new Si (Scheme‒O2 (Ge‒4O2), Table bond S3). arises, At theresulting ﬁnal stage, in reaction the Si-O1 (Ge-O1)products–complexes bond breaks and aof new 2-aminoethanol Si-O2 (Ge-O2) bondwith arises,trisubstituted resulting methoxysilanes in reaction products–complexes 11a–g and of 2-aminoethanolmethoxygermanes with 12a trisubstituted–g, in which the methoxysilanes N–Si or N‒Ge distance11a–g isand shorter methoxygermanes than in the reagent12a molecules–g, in which the N–Si(Table or S3). N-Ge distance is shorter than in the reagent molecules (Table S3). The configuration of molecules 11a–g, 12a–g is due to the transannular bond N→Si or N→Ge, the dative interaction O→Si or O→Ge (11b–g, 12b–g), and the bonding between the oxygen of methoxyl substituent at the Si (Ge) and a hydrogen of the hydroxyl group of 2-aminoethanol (with the exception of trinitroderivative 12f) (Scheme 4, Table S3). In addition, as in the starting molecules 5b–g and 6b–g, in complexes 11b–g and 12b–g hydrogen contacts between the hydrogen atoms of the amino group and heteroatoms (halogen, oxygen of perchlorate or nitro groups, and nitrogen of thiocyanate groups) of substituents at the Si or Ge are possible. In complexes 11a–g and 12a–g, the silicon or germanium polyhedron expands: the tetravalent Si or Ge atom is six-coordinated and has the structure of a distorted tetragonal bipyramid. Two substituents at the silicon (germanium) and oxygen atoms lie in the equatorial plane of this bipyramid, and the nitrogen and third substituent at the Si (Ge) occupy axial positions (Scheme 4, Figure 3). Apparently, the preferred configurations of the complexes 11a–g, 12a–g are stabilized precisely due to the dative interactions and intramolecular hydrogen bonds arising because of the favorable orientation of the substituents at the silicon or germanium. The reactions of hypoatranes 5a–g, 6a–g with methanol, as in the case of ocanes 3a–g, 4a–g and atranes 1a–g, 2a–g, are controlled by thermodynamic factors. In series of halogen-substituted (F, Cl,

Molecules 2020, 25, 2803 9 of 16

The configuration of molecules 11a–g, 12a–g is due to the transannular bond N Si or N Ge, → → the dative interaction O Si or O Ge (11b–g, 12b–g), and the bonding between the oxygen of methoxyl → → substituent at the Si (Ge) and a hydrogen of the hydroxyl group of 2-aminoethanol (with the exception of trinitroderivative 12f) (Scheme4, Table S3). In addition, as in the starting molecules 5b–g and 6b–g, Moleculesin complexes 2020, 25,11b x –g and 12b–g hydrogen contacts between the hydrogen atoms of the amino10 group of 18 and heteroatoms (halogen, oxygen of perchlorate or nitro groups, and nitrogen of thiocyanate groups) Br)of substituentshyposilatranes at theand Si hypogermatranes, or Ge are possible. the In activation complexes energy11a–g increasesand 12a– (Tableg, the silicon3), which or is germanium naturally associatedpolyhedron with expands: a decrease The in tetravalent the electronegativity Si or Ge atom of the is substituents six-coordinated and is and consistent has the with structure the data of a fordistorted the corresponding tetragonal bipyramid. atranes and Two ocanes. substituents For the reactions at the silicon of hypogermatranes (germanium) and 6a oxygen–g, the atoms activation lie in energiesthe equatorial are lower plane in comparison of this bipyramid, with the and reactions the nitrogen of hyposilatranes and third substituent 5a–g (Table at 3). the The Si smallest (Ge) occupy N‒ Xaxial (X = positions Si, Ge) distance (Scheme in4, the Figure transition3). Apparently, states and the the preferred lowest configurationsactivation energy of theare complexes observed for11a the–g, reactions12a–g are of stabilized triperchlorate precisely derivatives due to the 5e dative and 6e interactions (Tables 5, S3). and intramolecular hydrogen bonds arising becauseThe ofenergy the favorable diagrams orientation of the reactions of the of substituents hydroxy-, atfluoro-, the silicon and perchlorate-substituted or germanium. atranes, ocanes,The and reactions hypoatranes of hypoatranes are shown5a in–g, Figure 6a–g with4. To methanol, estimate the as inthermal the case effect of ocanes of the3a reactions,–g, 4a–g andfor zeroatranes we 1achose–g, 2athe–g ,energies are controlled of the bystarting thermodynamic reagent and factors. methanol In series molecules of halogen-substituted infinitely distant from (F, Cl, eachBr) hyposilatranes other. and hypogermatranes, the activation energy increases (Table3), which is naturally associatedA comparison with a decrease of the results in the electronegativityobtained for 1-subs of thetituted substituents atranes, and2,2-di issubstituted consistent with ocanes the and data 1,1,1-trisubstitutedfor the corresponding hypoatranes atranes and (Tables ocanes. 1, 2, For 3) sh theows reactions that the of values hypogermatranes of activation6a energy–g, the and activation Gibbs activationenergies areenergy lower decrease in comparison in the series with of the atra reactionsnes—ocanes—hypoatranes. of hyposilatranes 5a A–g decrease(Table3). in The the smallestnumber ofN-X cycles (X = inSi, the Ge) molecule distance inin the this transition series and states an andincrease the lowest in the activation number energyof highly are observedelectronegative for the substituentsreactions of (having triperchlorate negative derivatives mesomeric5e and inductive6e (Table3 ,effects) Table S3).at the silicon or germanium atom led to a decreaseThe energy in the diagrams N‒Si or of N the‒Ge reactions bond length of hydroxy-, (Tables S1, fluoro-, S2, S3) and and, perchlorate-substituted consequently, an increase atranes, in itsocanes, strength. and hypoatranesProbably, this are fact, shown along in Figure with 4the. To presence estimate theof dative thermal and e ff ectintramolecular of the reactions, hydrogen for zero interactions,we chose the explains energies ofthe the high starting stability reagent of andtris methanolubstituted molecules hypoatranes infinitely obtained distant in from an aqueous– each other. alcoholic medium at elevated temperatures [36,40–42].

1 2

3 4

Figure 4. Cont.

Molecules 2020, 25, 2803 10 of 16 Molecules 2020, 25, x 11 of 18

5 6

FigureFigure 4. 4.EnergyEnergy diagrams diagrams for for reactions reactions of of1a1a,b,be;, e2a; 2a,b,,be;, e3a; 3a,b,,be;, e4a; 4a,b,,be;, e5a; 5a,b,,be,;e 6a; 6a,b,,be, ewithwith methanol methanol (Δ(E∆,E kJ/mol)., kJ/mol).

2.5. ReactionsA comparison of Atranes, of Ocan the resultses, and Hypoatranes obtained for with 1-substituted Ethanol atranes, 2,2-disubstituted ocanes and 1,1,1-trisubstituted hypoatranes (Tables1–3) shows that the values of activation energy and Gibbs activationWe studied energy the decrease reactions in the of seriessubstituted of atranes—ocanes—hypoatranes. atranes and their analogues A decreasewith ethanol in the using number the of reactionscycles in of the hydroxy molecule derivatives in this series 1a, and 2a, an3a, increase4a, 5a, 6a in and the numberhalogen of derivatives highly electronegative 1b–d, 2b–d, substituents3b–d, 4b– d, 5b–d, 6b–d to compare the interactions with methanol. The mechanism of reactions of 1- (having negative mesomeric and inductive effects) at the silicon or germanium atom led to a decrease substitutedin the N-Si orsilatranes N-Ge bond and length germ (Tablesatranes, S1–S3) 2,2-disubstituted and, consequently, silocanes an increase and in germocanes, its strength. Probably,1,1,1- trisubstitutedthis fact, along hyposilatranes with the presence and hypogermatranes of dative and intramolecular with one ethanol hydrogen molecule interactions, according to explains quantum the chemicalhigh stability calculations of trisubstituted is shown in hypoatranes Scheme 5. The obtained calculated in an data aqueous–alcoholic are given in Tables medium 4, S4, S5, at S6. elevated As in the case of interaction with methanol, the reactions with ethanol proceed in one step: temperatures [36,40–42]. initially, prereaction complexes are formed that transform into transition states, as a result of the cleavage2.5. Reactions of one of Si Atranes,‒O (Ge‒ Ocanes,O) bond and and Hypoatranes the arising with of a Ethanol new Si‒O(CH2CH3) or Ge‒O(CH2CH3) bond, the reaction products are formed. We studied the reactions of substituted atranes and their analogues with ethanol using the reactions of hydroxy derivatives 1a, 2a, 3a, 4a, 5a, 6a and halogen derivatives 1b–d, 2b–d, 3b–d, 4b–d, 5b–d, 6b–d to compare the interactions with methanol. The mechanism of reactions of 1-substituted silatranes and germatranes, 2,2-disubstituted silocanes and germocanes, 1,1,1-trisubstituted hyposilatranes and hypogermatranes with one ethanol molecule according to quantum chemical calculations is shown in Scheme5. The calculated data are given in Table4, Tables S4–S6. As in the case of interaction with methanol, the reactions with ethanol proceed in one step: Initially, prereaction complexes are formed that transform into transition states, as a result of the cleavage of one Si-O (Ge-O) bond and the arising of a new Si-O(CH2CH3) or Ge-O(CH2CH3) bond, the reaction products are formed. The transition states are characterized by a decrease in the N-Si (N-Ge) distance, the Si(Ge)-O1 and O-H bonds are stretched, and the H1 ... O1 contact is reduced (Scheme5, Tables S4–S6). Molecules of the products of ethanol addition reactions have a configuration similar to the configuration of the corresponding product molecules formed upon interaction with methanol. The products of reactions of atranes are substituted silocanes 13a–d and germocanes 14a–d. According to the quantum chemical calculations, the ocane fragments of product molecules have crown conformation—symmetrical boat–boat for silocanes and chair–boat for germocanes. The silicon (germanium) and nitrogen-containing fragments are flattened. The transannular interaction N Si or → N Ge and the possible intramolecular hydrogen bonds O4 ... H1O1 stabilize these structures (Table S4, → Scheme5). The N Si (N Ge) bond in the molecules of products 13a–d and 14a–d is longer than in → → the molecules of the starting atranes (Table S4).

Molecules 2020, 25, 2803 11 of 16 Molecules 2020, 25, x 12 of 18

# 1 N O N N CH3CH2OH 1 X 2 1 H 2 1 O O 4 X 1 X 2 4 O O O H 3 O O O R O 3 O 3 R R H3CH2C CH2CH3 1, 2 13, 14

1 1 H 1 H H # N N N CH3CH2OH 2 1 2 O 1 12 X O X 2 O O X O 2 O H 3 R 43 R H 3 R R R O 3 O R 4 3, 4 15, 16 CH2CH3 CH2CH3

1 # 1 H H 1 2 2 H H H 2 N N H N O 1 CH3CH2OH R 1 X R R O 3 2 X 1 X R H 32 O O R R R H O R R CH2CH3 5, 6 CH2CH3 17, 18

X=Si1, 3, 5, 13, 15, 17;Ge2, 4, 6, 14, 16, 18; R=OHa,Fb,Clc,Brd SchemeScheme 5. Mechanism 5. Mechanism of of reactions reactions ofof atranes,atranes, oc ocanes,anes, and and hypoatranes hypoatranes with with ethanol. ethanol.

TheThe annular transition configuration states are characterized of product moleculesby a decrease15a in– thed and N‒Si16a (N–‒dGe)is distance, also stabilized the Si(Ge) due‒O1 to the ... dativeand interaction O‒H bonds N areSi (Nstretched,Ge) and and the the intramolecular H1 O1 contact hydrogen is reduced bond (Scheme O2 ... 5,H3 Tables (Table S4, S5, S5, Scheme S6). 5). → → In addition,Molecules short of the contacts products between of ethanol the hydrogen addition reactions atom at thehave nitrogen a configuration and the similar heteroatom to the of the configuration of the corresponding product molecules formed upon interaction with methanol. axial substituent at the silicon (germanium) atom contribute to the stabilization of the crown-like The products of reactions of atranes are substituted silocanes 13a–d and germocanes 14a–d. 10-memberedAccording configuration to the quantum of moleculeschemical calculations,15a–d and the16a –ocaned: oxygen fragments in the of hydroxy-substituted product molecules have15a and 16a orcrown halogen conformation—symmetrical in 15b–d and 16b–d. Theboat–boat N-Si for (N-Ge) silocanes distance and chair–boat in the molecules for germocanes. of products The silicon15a–d and 16a–d(germanium)is shorter than and innitrogen-containing the molecules of fragments the starting are ocanes,flattened. as The in thetransannular case of reactions interaction with N→ methanol,Si or and thisN→ distanceGe and the increases possible inintramolecular15b and 16d hydrogen(Table S5). bonds O4…H1O1 stabilize these structures (Table TheS4, Scheme configuration 5). The N of→ theSi (N molecules→Ge) bond17a in –thed and molecules18a–d ofis products due to the 13a transannular–d and 14a–d is interaction longer than N Si → or Nin Gethe andmolecules hydrogen of the bondingstarting atranes O2 ... (TableH3 between S4). oxygen atom of the ethoxyl substituent at the → silicon (germanium)The annular andconfiguration hydrogen of atom product of the molecules hydroxy 15a group–d and of 16a 2-aminoethanol–d is also stabilized (Scheme due5 ,to Table the S6). dative interaction N→Si (N→Ge) and the intramolecular hydrogen bond O2...H3 (Table S5, Scheme In addition, as in the starting molecules 5a–d and 6a–d, hydrogen contacts between the hydrogen 5). In addition, short contacts between the hydrogen atom at the nitrogen and the heteroatom of the atoms of the amino group and the heteroatoms (oxygen or halogen) of the substituents at the silicon or axial substituent at the silicon (germanium) atom contribute to the stabilization of the crown-like 10- germaniummembered are configuration possible in products of molecules17a –15ad and–d and18a 16a–d–.d In: oxygen complexes in the17a hydroxy-substituted–d and 18a–d, the 15a tetravalent and six-coordinated16a or halogen silicon in 15b or– germaniumd and 16b–d atom. The N has‒Si the (N‒ structureGe) distance of a in distorted the molecules tetragonal of products bipyramid, 15a–d in the equatorialand 16a plane–d is ofshorter which than there in the are molecules two substituents of the starti at theng ocanes, silicon oras in germanium the case of andreactions oxygen with atoms, and themethanol, nitrogen and and this the distance third increases substituent in 15b at theand Si16d (Ge) (Table occupy S5). the axial positions. The transannularThe configuration interaction of the molecules N Si 17a (N –dGe) andin 18a the–d productis due to the molecules transannular is due interaction to both N the→Si spatial → → factoror and N→ theGe and presence hydrogen of electronegative bonding O2...H3 substituentsbetween oxygen at theatom acceptor of the ethoxyl silicon substituent or germanium at the atom. In allsilicon product (germanium) molecules, and su hydrogenfficiently atom strong of the hydrogen hydroxy bonds group areof 2-aminoethanol formed between (Scheme the oxygen 5, Table atom S6). In addition, as in the starting molecules 5a–d and 6a–d, hydrogen contacts between the hydrogen of the ethoxyl substituent at the silicon (germanium) and the hydrogen atom of the hydroxy group atoms of the amino group and the heteroatoms (oxygen or halogen) of the substituents at the silicon (Scheme5, Tables S4–S6). The analysis of obtained data shows that the reactions with ethanol are controlled by thermodynamic factors (Table4, Figure5). The value of activation energy naturally increases in the series of halogen- substituted (F, Cl, Br) compounds 1b–d, 2b–d, 3b–d, 4b–d, 5b–d, and 6b–d by a decrease in the Molecules 2020, 25, 2803 12 of 16 electronegativity of the substituents [33,58]. Reactions of germanium-containing derivatives proceed with slightly lower activation energies as compared with reactions of silicon-containing derivatives. In addition, the activation energy decreases in the series of atranes–ocanes–hypoatranes (Table4, Figure5). The same regularities were revealed for hydrolysis reactions of similar atranes, ocanes [ 52], and hypoatranes [43].

Table 4. Activation energies, Gibbs activation energies (kJ/mol), and imaginary vibration frequencies 1 # (cm− ) of transition states of reactions of 1a–d—6a–d with ethanol.

# # 1 ∆E ∆G ν1, cm− 1a 76.4 137.4 893i 1b 71.4 130.5 917i 1c 74.8 134.5 956i 1d 75.7 134.7 973i 2a 58.3 115.5 833i 2b 63.3 117.9 814i 2c 69.5 124.1 820i 2d 71.1 125.6 828i 3a 74.1 130.9 857i 3b 50.0 108.1 951i 3c 57.1 116.1 998i 3d 57.9 116.5 1028i 4a 53.4 107.9 905i 4b 33.4 88.3 976i 4c 43.4 99.1 968i 4d 47.6 103.1 965i 5a 78.4 131.9 914i 5b 32.1 88.8 1030i 5c 36.8 93.6 1056i 5d 40.6 97.4 1072i 6a 54.8 106.6 883i 6b 14.6 69.7 1012i 6c 29.3 86.1 1003i 6d 35.2 91.9 1001i Molecules 2020, 25, x 14 of 18

13 14

15 16 Figure 5. Cont.

17 18

Figure 5. Energy diagrams of formation of products 13a,b; 14a,b; 15a,b; 16a,b; 17a,b; 18a,b.

A comparison of the results for reactions of atranes, ocanes and hypoatranes with ethanol and the corresponding data for reactions with methanol allowed us to conclude that the activation energies are close; moreover, in the case of ocanes they are slightly higher in reactions with ethanol.

3. Conclusions Thus, we have studied the mechanism of reactions of 1-sustituted sil(germ)atranes, 2,2- disustituted sil(germ)ocanes, and 1,1,1-trisubstituted hyposil(germ)atranes with one molecule of methanol or ethanol at the DFT B3PW91/6-311++G(df,p) level of theory. These reactions with alcohol (methanol, ethanol), as well as with water [43,52], proceed in one step through four-center prereaction complexes and transition states followed by the opening of heteroatom (silicon or germanium) skeleton and the formation of products. According to DFT calculations, the activation energies and Gibbs energies of activation of reactions with methanol and ethanol are close, their values decrease in the series of atranes-ocanes- hypoatranes for reactions with both methanol and ethanol. Reactions of germanium-containing derivatives are characterized by lower activation energies in comparison with silicon-containing compounds. The results of theoretical conformational analysis show that the annular configurations of the product molecules with electronegative substituents are stabilized by the transannular N→X (X = Si,

Molecules 2020, 25, x 14 of 18

13 14

Molecules 2020, 25, 2803 13 of 16

15 16

17 18

Figure 5.FigureEnergy 5. Energy diagrams diagrams of formation of formation of of products 13a13a,b; ,14ab; ,14ab; 15a,b,;b15a; 16a,,bb; 17a16a,b,b; 18a; 17a,b. ,b; 18a,b.

A comparison of the results for reactions of atranes, ocanes and hypoatranes with ethanol and A comparisonthe corresponding of the resultsdata for forreactions reactions with ofmethanol atranes, allowed ocanes us and to conclude hypoatranes that the with activation ethanol and the correspondingenergies data are forclose; reactions moreover, with in the methanol case of ocanes allowed they are us slightly to conclude higher in that reactions the activation with ethanol. energies are close; moreover, in the case of ocanes they are slightly higher in reactions with ethanol. 3. Conclusions 3. ConclusionsThus, we have studied the mechanism of reactions of 1-sustituted sil(germ)atranes, 2,2- disustituted sil(germ)ocanes, and 1,1,1-trisubstituted hyposil(germ)atranes with one molecule of Thus,methanol we have or studied ethanol at the the mechanism DFT B3PW91/6-311++G(df,p of reactions of) level 1-sustituted of theory. These sil(germ)atranes, reactions with alcohol 2,2-disustituted sil(germ)ocanes,(methanol, and ethanol), 1,1,1-trisubstituted as well as with water hyposil(germ)atranes [43,52], proceed in one with step through one molecule four-center of methanolprereaction or ethanol at the DFTcomplexes B3PW91 and/6-311 transition++G(df,p) states levelfollowed of theory.by the opening These reactionsof heteroatom with (silicon alcohol or germanium) (methanol, ethanol), as well asskeleton with water and the [ formation43,52], proceed of products. in one step through four-center prereaction complexes and According to DFT calculations, the activation energies and Gibbs energies of activation of transitionreactions states followedwith methanol by and the ethanol opening are close, of heteroatom their values decrease (silicon in or the germanium) series of atranes-ocanes- skeleton and the formationhypoatranes of products. for reactions with both methanol and ethanol. Reactions of germanium-containing Accordingderivatives to DFT are calculations,characterized by the lower activation activation energies energies and in comparison Gibbs energies with silicon-containing of activation of reactions with methanolcompounds. and ethanol are close, their values decrease in the series of atranes-ocanes-hypoatranes The results of theoretical conformational analysis show that the annular configurations of the for reactionsproduct with molecules both methanol with electronegative and ethanol. substituents Reactions are stabilized of germanium-containing by the transannular N→X (X derivatives = Si, are characterized by lower activation energies in comparison with silicon-containing compounds. The results of theoretical conformational analysis show that the annular conﬁgurations of the product molecules with electronegative substituents are stabilized by the transannular N X (X = Si, → Ge) interaction and diﬀerent intramolecular hydrogen contacts with the participation of heteroatoms of substituents at the silicon or germanium.

Supplementary Materials: The following are available online, Table S1: Selected interatomic distances (Å) in the reagents, prereaction complexes, transition states, and products of the reactions of atranes 1a–g, 2a–g (a OH, b F, c Cl, d Br, e OClO3, f ONO2, g SCN) with methanol. For X-N distances the Mayer bond order in the NAO basis are given in parentheses, Table S2: Selected interatomic distances (Å) in the reagents, prereaction complexes, transition states, and products of the reactions of ocanes 3a–g, 4a–g (a OH, b F, c Cl, d Br, e OClO3, f ONO2, g SCN) with methanol. For X-N distances the Mayer bond order in the NAO basis are given in parentheses, Table S3: Selected interatomic distances (Å) in the reagents, prereaction complexes, transition states, and products of the reactions of hypoatranes 5a–g, 6a–g (a OH, b F, c Cl, d Br, e OClO3, f ONO2, g SCN) with methanol. For X-N distances the Mayer bond order in the NAO basis are given in parentheses, Table S4: Selected interatomic distances (Å) in the reagents, prereaction complexes, transition states, and products of the reactions of atranes 1a–d, 2a–d (a OH, b F, c Cl, d Br) with ethanol, Table S5: Selected interatomic distances (Å) in the reagents, prereaction complexes, transition states, and products of the reactions of ocanes 3a–d, 4a–d (a OH, b F, c Cl, d Br) with ethanol, Table S6: Selected interatomic distances (Å) in the reagents, prereaction complexes, transition states, and products of the reactions of hypoatranes 5a–d, 6a–d (a OH, b F, c Cl, d Br) with ethanol. Author Contributions: Conceptualization, D.C. and Y.V.; investigation, D.C., R.I., and Y.V.; methodology, Y.V.; software, D.V.; project administration, Y.V.; supervision, Y.V.; visualization, R.I. and Y.V.; writing—original draft, D.C., R.I., and Y.V.; writing—review & editing, D.C. and Y.V. All authors have read and agreed to the published version of the manuscript. Funding: This study was partly performed under financial support by the state subsidy allocated to Kazan (Volga Region) Federal University to increase its competitiveness among world leading scientific educational centers. Conflicts of Interest: The authors declare no conflict of interest. Molecules 2020, 25, 2803 14 of 16

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Sample Availability: Samples of the compounds are not available from the authors.

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