Synthesis, Structures, and Stereodynamic Behavior of Novel

Article pubs.acs.org/Organometallics

Synthesis, Structures, and Stereodynamic Behavior of Novel Pentacoordinate Fluorosilanes: Fluorosilyl Derivatives of Proline Alexei A. Nikolin, Evgeniya P. Kramarova, Aleksander G. Shipov, Yuri I. Baukov, and Vadim V. Negrebetsky* Department of General and Bioorganic Chemistry, N. I. Pirogov Russian National Investigated Medical University, Ostrovityanov Street 1, Moscow 117997, Russian Federation

Alexander A. Korlyukov and Dmitry E. Arkhipov A. N. Nesmeyanov’s Institute of Organoelement Compounds, RAS, Vavilova Street 28, 119991 Moscow, Russian Federation

Allen Bowden, Sergey Yu. Bylikin, Alan R. Bassindale, and Peter G. Taylor Department of Chemistry, Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom S Supporting Information *

ABSTRACT: The (O→Si)-chelate N′-(dimethylfluorosilylmethyl))-N′-methyl-N-(organosulfonyl)prolinamides RSO2Pro-N(Me)CH2SiMe2F (2a−f, R = Me (a), Ph (b), 4MeC6H4 (c), 4-ClC6H4 (d), 4-BrC6H4 (e), 4-NO2C6H4 (f)) were synthesized from the corresponding disiloxanes 1a−f using Et2O·BF3. According to the NMR and IR data, the extent of dimerization of fluorosilanes 2a−f in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si−O bond length varies in a narrow range (2.22−2.24 Å) that is 0.02−0.11 Å longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the 19F signals in the 0−20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe2 signals in the 1H DNMR spectra was attributed to a permutational isomerization process involving a positional exchange of equatorial ligands. The narrow range of activational barriers of the process (23−24 kcal mol−1 and more) and high negative values of the entropy of activation are similar to those observed earlier for Si-substituted N-(dimethylsilylmethyl) and N-(methylphenylsilylmethyl) amides and lactams, which suggests similar permutational processes in all cases. Gas-phase quantum chemical studies demonstrate that the solvation of F− reduces the activation barrier.

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ompounds with nonclassical types of chemical bonds, in particular, the derivatives of silicon with an extended coordination sphere of the central atom due to additional intraor intermolecular coordination, have been studied extensively for many years. These studies included synthetic approaches and the structure, reactivity, biological activity, and stereodynamic behavior of these compounds in solution.1−3 In addition, the structures of pentacoordinate silicon derivatives with a XSiC3O coordination set were used as model intermediates in the SN2 reactions at tetracoordinate silicon.4−7 Depending on the nature of the monodentate ligand, pentacoordinate compounds of the group 14 elements can be

In the case of compounds with an XSiC3O (X = F, Cl, Br, I, OTf) coordination set, structures A and B make the largest contributions to fluorides, C to chlorides, D to bromides, and E to iodides and triflates. In addition, the weakening of the Si−X bond in hypervalent silicon compounds in comparison to their tetracoordinate analogues, together with further polarization of that bond due to more effective solvation at lower temperatures in some cases, can lead to increased electrostatic interaction between the molecules of silyl halides and the formation of dimers F.13,14

divided into several general types, A−E, reflecting the structure of their central coordination set (Scheme 1).8−12

Received: April 2, 2012

© XXXX American Chemical Society

A

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Scheme 1

The yields of all compounds were 80−90%. The structures of the final products were confirmed by X-ray date, elemental analysis and IR and 1H, 13C, 19F, and 29Si NMR spectroscopy. The synthetic details and analytical data of individual compounds are given in the Experimental Section. X-ray Study. The molecules 2a,c−f are constructed from three fragments: the O−Si chelate ring with exocyclic fluorine atoms bonded to the Si1 atom, the pyrrolidine ring, and the organosulfonyl moiety (Figures 1−5). As a result of the enhanced reactivity of the Si−Cl bond in pentacoordinate silicon compounds, chlorosilanes in solutions hydrolyze readily into the corresponding disiloxanes.15 In contrast, the Si−F bond is much more stable, which virtually excludes the possibility of hydrolysis of fluorosilanes in the common solvents (such as deuterochloroform) used in NMR experiments and makes these compounds very convenient for the study of equilibrium processes represented by Scheme 1.16 Additional information can be obtained from the 19F NMR spectra: while the chemical shifts of 19 F signals in tetracoordinate fluorosilanes are about −160 ppm,14 the signals of 19F in pentacoordinate N-(amidomethyl)fluorosilanes are typically shifted downfield to −110 to −120 ppm.17,18 A multinuclear (1H, 19F, and 29Si) DNMR study of (aroyloxymethyl)trifluorosilanes showed that the strength of the O→Si coordination decreases at higher temperatures.19 This effect was more pronounced for the compounds with longer O···Si distances. Among the various types of pentacoordinate fluorosilanes, C,O-chelates with an amino acid fragment at the amide carbon have not been reported in the literature. In the present paper, we report the synthesis, structure, and stereodynamic behavior of a series of pentacoordinate fluorosilanes RSO2-Pro-N(Me)CH2SiMe2F (2), derivatives of proline with different organosulfonyl groups at the α-nitrogen atom.

Figure 1. Molecular structure of 2a. Atoms are presented as ADP ellipsoids at the 50% probability level.

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RESULTS AND DISCUSSION Synthesis. The (O→Si)-chelate N′-(dimethylfluorosilylmethyl)-N′-methyl-N-(organosulfonyl)prolinamides (2a−f) discussed in the present paper were prepared by the reaction of the corresponding disiloxanes 1a−f with BF3·Et2O (Scheme 2).

Figure 2. Molecular structure of 2c. Atoms are presented as ADP ellipsoids at the 50% probability level.

Scheme 2

The low rotation barrier of the C4−C6 bond could be the main reason for the changes in mutual orientation of the aforementioned molecular fragments described by the pseudotorsion angle N1−C4−N2−S1 (Table 1). The organosulfonyl moiety and the O−Si chelate ring in 2a,f adopt a conformation intermediate between synclinal and anticlinal, while in 2c−e the conformation is intermediate between synperiplanar and synclinal. The O−Si chelate ring and the C6H4NO2 group demonstrate unusual head-to-tail orientation that implies their maximal proximity. In 2c−e, the separation between the substituted Ph groups and O−Si chelate ring is more pronounced. Most likely, the conformation with B

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maximum separation of the substituted Ph groups and the O− Si chelate ring is more favorable than the head-to-tail conformation due to steric restraints. The head-to-tail orientation in 2f could be stabilized by a weak intermolecular stacking interaction of the C6H4NO2 groups in the crystal lattice (Figure 6). The coordination Si1−O1 bond in 2a,c−f varies in the range 2.13−2.22 Å. Taking into account the weakness of the Si1−O1 coordination bond, this fact can be explained by the conformational flexibility of 2a,c−f described in the previous paragraph. Indeed, the Si1−O1 bond is shorter in 2c−e in comparison with those in 2a,f. Therefore, the elongation of the Si1−O1 bond can be related to the steric repulsion between the R substituent and the O−Si chelate ring. Solvation Effects and Concentration Studies. The 29Si NMR data for fluorosilanes 2a−f in the solid state (CP/MAS) and in solution are summarized in Table 2. The pentacoordinate state of the silicon atom in solution is confirmed by the upfield shift of signals in the 29Si NMR spectra (by −40 to −50 ppm, see Table 2) as compared to that of the model Me3SiF compound of tetracoordinate silicon (31 ppm).20 The dissolution of fluorosilanes is accompanied by downfield shifts (Δδ) of the 29Si signals, which are the greatest (up to 18 ppm) in CDCl3. At the same time, the Δδ values in solvents with higher electron-donor capacity, such as (CD3)2CO, are significantly lower (Table 2). This indicates that, in the liquid phase, the O→Si coordination in fluorosilanes 2a−f is weaker than that in the solid state. The above conclusion is further supported by the IR spectroscopic data for these compounds (Table 3). In the solid state, the absorptions of the NCO fragment are observed within a range typical for pentacoordinate compounds (1611−1615 cm−1),21 while in solution these absorption bands shift toward higher wavenumbers by approximately 10 cm−1, which is more common for compounds with weaker O→Si coordination. At the same time, we found that the concentration of the solution in CDCl3 had almost no effect on the position of the NCO absorption bands in fluorosilanes 2a−f. This fact suggests that at room temperature and within the range of concentrations studied (0.01−0.5 mol L−1) the degree of dimerization of these compounds in CDCl3 is insignificant. In CDCl3, the 19F NMR signals of most of the compounds 2a−f are registered at room temperature as broad singlets. In the stronger electron donor (CD3)2CO, these signals split into multiplets, which is probably a result of the more significant contribution of form C (Scheme 1) in this solvent. Therefore, the observed weakening of the O→Si coordination in solutions of fluorosilanes 2a−f can be attributed to the solvent effects, i.e., to more effective solvation of forms A and B (Scheme 1) in comparison to other possible structures of these compounds. Analysis of chemical shifts 29Si in the crystalline state and in solution (Tables 1 and 2) reveals that values of δ(29Si) correlate to the Si1−O1 bond length (Figure 7). Hence, the molecules 2a,c−f in solution possess the same conformation as in the crystalline state. Using this correlation, it is possible to evaluate the Si···O interatomic distance in solution. The range of δ(29Si) in (CD3)2O in 2a,c−f is close to that in the crystalline state, but the Si1−O1 bonds are a bit longer (mean value 2.22 Å). In turn, in CDCl3 the mean length of the Si−O bond slightly exceeds that in (CD3)2O (2.24 Å).

Figure 3. Molecular structure of 2d. Atoms are presented as ADP ellipsoids at the 50% probability level.

Figure 4. Molecular structure of 2e. Atoms are presented as ADP ellipsoids at the 50% probability level.

Figure 5. Molecular structure of 2f. Atoms are presented as ADP ellipsoids at the 50% probability level.

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Table 1. Selected Bond Lengths (Å) and Angles (deg) in Compounds 2a,c−f Si1−F1 Si1−C1 Si1−C2 Si1−C3 Si1−O1 O1−C4 F1−Si1−O1 N1−C4−N2−S1

2a

2c

2d

2e

2f

1.6558(14) 1.858(3) 1.866(2) 1.885(2) 2.2005(14) 1.251(2) 172.31(7) 96.5

1.664(2) 1.853(4) 1.849(3) 1.880(3) 2.140(2) 1.251(3) 172.20(11) 24.8

1.6713(9) 1.8607(15) 1.8618(15) 1.8891(13) 2.1313(10) 1.2509(15) 171.41(5) 26.9

1.651(6) 1.842(9) 1.857(8) 1.860(8) 2.161(7) 1.255(9) 171.9(3) 24.1

1.658(3) 1.844(7) 1.850(6) 1.881(6) 2.220(6) 1.253(6) 171.6(2) 84.1

Table 3. FT-IR Data for Fluorosilanes RSO2-ProN(Me)CH2SiMe2F (2a−f)

Table 2. 29Si NMR Data for Fluorosilanes RSO2-ProN(Me)CH2SiMe2F (2a−f) 2a

a

2b

2c

2d

2e

c, mol L−1

ν, cm−1 (solvent)

2a 2b 2c 2d

1615 1614 1612 1613

0.5 0.3

1624 (CHCl3) 1623 (CHCl3)

0.2 0.2 0.1

1623 (CH3CN) 1624 (CHCl3) 1625 (C6H6)

2e 2f

1614 1611

1625 (C6H6)

Variable-Temperature 1H and 19F NMR Studies. Additional information on the equilibrium between different forms of fluorosilanes 2a−f in solution (Scheme 1) was obtained from a study of temperature effects on the chemical shifts. The study of temperature effects on the 1H and 19F NMR spectra of fluorosilanes 2a−f provided important information on the contributions of the various forms of these compounds in solution. The presence of a fluorine atom on the silicon and a chiral carbon atom in the proline fragment resulted in a complex splitting of the SiMe2 protons in the 1H NMR spectra. At room temperature, these signals appeared as two doublets of equal intensity. A decrease in temperature (down to −60 °C in CDCl3) led to gradual sharpening of the signals, while the 3JHF value stayed within a narrow range of 7−8 Hz. An increase in temperature to +50 °C resulted in noticeable broadening of all components of the multiplet. In addition, the 1H NMR signal of the SiMe2 group drifts downfield (by 0.03 ppm) in the

2f

−21.4

−20.4

−29.4

−29.6

−28.5

−16.6

−10.3 (d) 258

−13.5 (d) 256 −19.9 (d)

−13.7 (d) 256 −20.0 (d)

−11.5 (d) 257 −17.6 (d)

−11.2 (d) 257 −18.0 (d)

−7.0 (d) 258 −16.2 (d)

258

257

261

259

266

6.9

15.7

18.1

17.3

9.6

0.5

9.4

12.0

10.5

0.4

11.1

ν, cm−1 (solid)

Figure 7. Correlation between interatomic distance Si···O (x) and δ(29Si) (y).

Figure 6. Stacking interactions in the crystal structure of 2f.

δ(29Si), CP/ MAS, ppm δ(29Si), CDCl3, ppm 1 JSiF, CDCl3, Hz δ(29Si), (CD3)2CO, ppm 1 JSiF, (CD3)2CO, Hz Δδa in CDCl3, ppm Δδa in (CD3)2CO, ppm

compd

Δδ = [δ(29Si), solvent] − [δ(29Si), CP/MAS].

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Figure 8. Signals of the SiMe2 protons in the 1H DNMR spectra of fluorosilane 2d (JEOL JNM-EX400 spectrometer, CDCl3).

temperature interval from −60 to +50 °C (Figure 8); the greatest change (by 0.02 ppm) in the chemical shift is observed between −60 and −20 °C. This fact suggests that the increase in temperature weakens the O→Si coordination (Scheme 1).3 All observed changes were reversible, and the original spectrum was obtained upon cooling the sample to room temperature (Figure 8).

The variable-temperature studies also revealed some interesting structural changes. Figure 9 shows how the 19F chemical shift of 2c changes as a function of temperature. A tetrahedral fluorosilane exhibits a fluorine chemical shift of about −160 ppm; thus, complexes that involve little silicon− oxygen coordination have fluorine chemical shifts in the range −150 to −160 ppm.3,22 E

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A similar temperature dependence of the 19F NMR signals was observed by us earlier for pentacoordinate fluorosilanes 3 and 4.14 Similar to the case for complexes 3 and 4, the 29Si NMR signal of 2c in CDCl3 shifts upfield (−15.5 ppm, d, 1JSiF = 254 Hz) when the temperature is decreased to −50 °C. Together with the observed temperature dependence in 19F spectra, this also indicates a strengthening of the O→Si coordination at lower temperatures. In the case of compounds 2b,e in CDCl3 solutions, the temperature affected not only the chemical shift but also the multiplicity of the 19F signal, which appeared as a multiplet between 20 and −10 °C (Figure 10). The appearance of a fine splitting pattern for the 19F signal indicated an increased contribution of form B to the equilibria (Scheme 1) in that temperature range. The loss of spin−spin coupling at lower temperatures could be a result of increasing the degree of pentacoordination. In this case, an increased polarization of the Si−F bond and longer distance between silicon and fluorine would favor the fluorine exchange as a result of intermolecular association 2 B ⇄ F and the formation of dimers with two bridging fluorine atoms (see above).14 At high temperatures, the change in multiplicity of the 19F signals (Figure 10) and the broadening of the SiMe2 signals in the 1H NMR spectra (Figure 8) were probably caused by fluorine exchange via a dissociative mechanism. The dissociation of fluorosilanes in CDCl3 can be facilitated by trace amounts of acids produced by partial hydrolysis of the compounds 2a−f by atmospheric moisture.14 Protonation of fluorine substituents increases their leaving ability and thus catalyzes the fluoride exchange. At the same time, electrondonor solvents such as (CD3)2CO can bind protons more effectively and significantly decrease the rate of the above process. Indeed, the signals of 19F nuclei in NMR spectra of fluorides 2c,e,f appear as broad singlets in CDCl3 and as multiplets in (CD3)2CO. The solvent influence is less

Figure 9. Plot of the 19F NMR chemical shift against temperatures for complex 2c (CDCl3).

However, pentacoordinate fluorosilanes, which involve substantial silicon oxygen coordination, for example 3 and 4, have fluorine chemical shifts in the range −110 to −120 ppm.13,14

At high temperature complex 2c has a fluorine chemical shift of −126 ppm, suggesting a reasonable amount of pentacoordination. The results in Figure 9 suggest that, as the temperature is lowered, complex 2c becomes more pentacoordinate.

Figure 10. 19F DNMR spectrum of 2b (JEOL JNM-EX400 spectrometer, CDCl3). F

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Scheme 3

pronounced for compounds 2b,d: their 19F NMR signals are registered as broad singlets in both solvents. External Nucleophile. The stereodynamic behavior of compounds 2d,e in the presence of an external nucleophile Nu, such as F−, was studied by 1H, 19F, and 29Si NMR spectroscopy. Addition of 10 mol % of Bu4NF to the solutions of these fluorosilanes in CDCl3 led to significant broadening of the SiMe2 signals in the 1H NMR spectra, while the signals of all other protons remained virtually unaffected. For compound 2e, the addition of Bu4NF resulted in the loss of H−F spin−spin coupling and the transformation of the 19F signal from a multiplet to a broad singlet. At the same time, the presence of Bu4NF had no effect on the 29Si spectra of fluorosilanes 2d,e, which indicated the retention of the coordination number of silicon in these complexes. Permutational Isomerization. The temperature-dependent changes of the SiMe2 signals (Figure 8) observed in the 1H NMR spectra of fluorosilanes 2a,c,d,f were caused by positional exchange of equatorial ligands in the course of permutational isomerization processes at the central coordination sets of these compounds. The activation parameters of the permutation were calculated by a 1H DNMR method using a full line-shape analysis of the signals. For all studied compounds, the stereodynamic processes in CDCl3 were characterized by a narrow range of activation energies (23−24 kcal mol−1 and more) and high negative values of the entropies of activation (ca. −20 cal mol−1 K−1). These values were very similar to the activation parameters of N-(dimethylfluorosilylmethyl) and N[fluoro(methyl)(phenyl)silylmethyl] amides and lactams.3,23 It should be noted that the estimated values of the activation energies in the electron donor (CD3)2CO are significantly higher (by 5−7 kcal mol−1). According to earlier studies,24,25 the energy of the intramolecular coordination bond calculated by the DFT method with the B3LYP/6-311G** basis set for model compounds, (O→Si)-chelate dimethyl(N-acetylacetamidomethyl)silanes, is relatively low in the gas phase (3.7 kcal mol−1)24 but increases to 7.7−10.5 kcal mol−1 in solution.25 Therefore, the much higher permutational barriers (23−24 kcal mol−1 and more) observed for fluorides 2a−f suggest that, in our case, the ratelimiting step of the process was most likely to be the dissociation of the Si−F bond. At the same time, the high negative ΔS⧧values for the dynamic processes could be a result

of effective solvation of the intermediates, as has been shown earlier for the ionization of hexacoordinate silicon compounds.3 It should be noted that the activational parameters of complexes 2a−f are very close to those calculated by us earlier for pentacoordinate N-(dimethylfluorosilyl)methyl-N-(1phenylethyl)acetamide.14 This indicates that the mechanisms of permutational processes in both cases are also similar and involve a series of penta- and tetracoordinate intermediates (Scheme 3). At higher temperatures, the equilibrium B ⇄ A (Schemes 1 and 3) shifts toward the tetracoordinate topomer A. Nucleophilic attack at the Si atom by the nucleophile (F*−) produces the pentacoordinate difluoride G, which subsequently loses the F− anion (bottom fluoride in Scheme 3) and forms tetracoordinate intermediate H. The rotation around the Si− CH2 bond produces topomer A′ and finally complex B′ with inverted orientation of the methyl groups at silicon. At lower temperatures, the initial step of the stereodynamic process can also involve the formation of the dimer F (see above), where one molecule of the fluorosilane acts a donor of the fluoride anion. Quantum Chemical Calculations. To reduce the computational effort, quantum chemical calculations were carried out for molecule 2a. The results of the computational study demonstrate the ease of the Si−O bond dissociation in solution. The difference in total energy between the A and B forms is 4.3 kcal mol−1. In solution, the tetracoordinate Si atom in the acyclic topomer A can form coordination bonds with several nucleophiles (Nu):

In the present paper, the complexes of the A topomer with H2O, F−, and HF2− are discussed. The dissociation energy calculated for the complex (De) with H2O is 0.8 kcal mol−1, which indicated the absence of coordination. At the same time, the complex with F− is much more stable (De = −90.8 kcal mol−1). Although the latter De value apparently disagrees with the experimental values of permutational isomerization (23−24 G

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kcal mol−1), the specific solvation of the F− ion (due to hydrogen bonding) is responsible for the reduction of De. The simplest model for this case is the complex with HF2−, where the value of De is nearly 2 times lower (−50.4 kcal mol−1). Further reduction of De can be achieved by the increase of the solvation sphere of the F− ion.

Table 4. 13C NMR Spectra of Compounds 2a−f in CDCl3 δ(13C), ppm signal

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CONCLUSIONS The new pentacoordinate fluorosilanes RSO2-Pro-N(Me)CH2SiMe2F were synthesized and studied by spectroscopic methods. According to IR and NMR data, the O→Si coordination in solutions of these compounds was weaker than in the solid state, due to effective solvation of the Si−F bond. At room temperature, all studied complexes existed in solution predominantly as monomers. At lower temperatures, an increased polarization of the Si−F bond could favor the formation of associates with bridging fluorine atoms, while higher temperatures favored O→Si bond dissociation and increased the contribution of tetracoordinate species. The observed effects of temperature and concentration on the spectra of the compounds studied were explained by a dynamic process at silicon, initiated by a dissociation of the O→Si coordination bond.

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2a

2b

2c

2d

2e

2f

1.11, 1.14 41.02

0.90, 1.10 41.00

1.11 41.12

0.74, 1.02 41.09

37.45 56.06 30.53 24.86 48.22 135.67 127.39

37.50 56.30 30.60 24.90 48.10 137.60 128.90

37.48 56.29 30.65 24.97 48.10 138.07 127.39

37.56 56.93 30.75 24.86 48.19 145.13 128.72

129.02

129.63

129.20

129.0

124.13

132.85

143.70 21.44

139.30

127.85

150.09

172.52

172.52

172.40

172.33

172.05

SiMe2

1.10

1.17

SiCH2

40.9 (d, 2 JCF 30.96 Hz) 37.25 57.11 30.65 24.80 47.50

41.02 (d, 2 JCF 38.14 Hz) 37.47 56.10 30.59 24.94 48.22 138.81 127.36

NMe C-2 C-3 C-4 C-5 C-1′ C-2′ + C6′ C-3 ′ + C5′ C-4′ SMe/ CMe COa

39.33 172.60

δ in ppm in (CD3)2CO at room temperature for 2b−f, respectively: 174.00, 173.10, 173.83, 173.88, 173.65.

a

EXPERIMENTAL SECTION

IR spectra of compounds in solution and in the solid state were recorded on a Bruker Tensor-27 spectrometer using KBr cells and an APR element, respectively. 1H, 13C, and 19F NMR spectra in CDCl3 and (CD3)2CO were recorded on a Bruker Avance II 300 (1H, 300 MHz; 13C, 75.6 MHz; 19F, 282.2 MHz), JEOL JNM-EX400 (1H, 400 MHz; 13C, 100.6 MHz; 19F, 376.3 MHz) using standard pulse sequences. 29Si NMR spectra were recorded using the 1H−29Si HSQC pulse sequence supplied with the Bruker Avance II 600 instrument.26 The 1H, 13C, and 29Si chemical shifts were measured using Me4Si as internal reference for 0.5 M solutions in deuteriochloroform and deuterioacetone. The 19F chemical shifts were measured using BF3 as external reference. Negative values are to high field. 29Si NMR CP/ MAS spectra in the solid phase were recorded on a JEOL JNM-EX400 instrument using 5 mm zirconia rotors and a Doty probe. The temperature calibration of the NMR spectrometers was performed by measuring the differences in chemical shifts between nonequivalent protons in methanol (−90 to +30 °C) and ethylene glycol (+30 to +85 °C).27 The activational parameters of the permutational isomerization were calculated using DNMR-SIM software28 and a modified Eyring equation.29 In each case, at least 12 temperature points were obtained to achieve a correlation coefficient of 0.997−0.999. The 13C NMR spectra at room temperature and temperature-dependent 19F NMR spectra of the final products are summarized in Tables 4 and 5, respectively. The chemical shifts of the 29Si nuclei in fluorides 2a−f have been given earlier (see Table 1). X-ray experiments were carried out with Mo Kα radiation. Absorption correction was made with the SADABS program based on the multiscan method of Blessing.30 The structures 2a−f were solved by direct methods and refined in an anisotropic approximation for non-hydrogen atoms. Coordinates of the hydrogen atoms were calculated to match the hybridization of the carbon atoms that is established from the information about the bond lengths and angles. The C−H bonds and isotropic displacement parameters were constrained. The refinement was carried out using the SHELXTL program package.31 Principal bond lengths and angles are presented in Table 5. The experimental details are summarized in Table 6. Molecular graphics were prepared using the Olex2 program.32 Computational studies were carried out using the Gaussian03 program.33 The structures described in respective section were optimized using PBE0/6-311G(d,p) method/basis set with subsequent calculation of Hessian matrix.

Disiloxanes 1a−f were synthesized according to published procedures.34 Fluorosilanes 2a−f were prepared as follows. A solution of disiloxane 1a−f (1 mmol) in acetonitrile (5 mL) was refluxed with Et2O·BF3 (0.11 g, 0.8 mmol) for 2 h and cooled, and the volatiles were removed in vacuo. The residue was extracted with hot benzene (15 mL) and cooled, the solvent was removed in vacuo, and the remaining oil was crystallized under ethanol (1 mL) and dried in the open air. The solvents used for recrystallization of compounds for melting point measurements are given in parentheses after the values. (O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methylN-mesyl-(R,S)-prolinamide (2a). Yield: 87%. Mp: 103−105 °C (heptane/benzene, 5/2). Anal. Found: C, 40.61; H, 7.10; N, 9.56. Calcd for C10H21FN2O3SSi: C, 40.52; H, 7.14; N, 9.45. IR (ν, cm−1): 1615 s, 1519 w (NCO→Si), 1315 s, 1150 s (SO2). 1H NMR (CDCl3, δ, ppm): 0.12, 0.23 (two d, 6H, SiMe2, 3JHF 7.7 Hz), 1.81, 2.32 (two m, 2H, C3H2), 2.04 (quintet, 2H, C4H2, 2JHH 6.6 Hz), 2.43, 2.58 (dd, 2H, CH2Si, 2JHH 15.6 Hz), 2.96 (s, 3H, Me), 3.10 (s, 3H, MeN), 3.41, 3.60 (two m, 2H, C5H2), 4.80 (m, 2H, C2H). (O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methylN-phenylsulfonyl-(S)-prolinamide (2b). Yield: 85%. Mp: 107− 108 °C (heptane/benzene, 4/1). [α]D25 = −44.7° (c 1.76, CHCl3). Anal. Found: C, 50.04; H, 6.42; N, 7.59. Calcd for C15H23FN2O3SSi: C, 50.25; H, 6.47; N, 7.83. IR (ν, cm−1): 1614 s, 1516 w (NCO→ Si), 1320 m, 1153 s (SO2). 1H NMR (CDCl3, δ, ppm): 0.21, 0.26 (two d, 6H, SiMe2, 3JHF 7.6 Hz), 1.82−2.15 (m, 4H, C3H2 and C4H2), 2.45, 2.55 (dd, 2H, CH2Si, 3JHH 15.4 Hz), 3.22 (s, 3H, MeN), 3.39−3.51 (m, 2H, C5H2), 4.78 (m, 2H, C2H), 7.53 (t, 2H, 3JHH 8.1 Hz, Ar), 7.61 (t, 1H, 3JHH 8.1 Hz, Ar), 7.9 (d, 2H, 3JHH 8.1 Hz, Ar). 1H NMR ((CD3)2CO, δ, ppm): 0.12, 0.19 (two d, 6H, SiMe2, 3JHF 7.7 Hz), 1.73−2.15 (m, 4H, C3H2 and C4H2), 2.43, 2.51 (dd, 2H, CH2Si, 3JHH 15.8 Hz), 3.30 (s, 3H, MeN), 3.41−3.48 (m, 2H, C5H2), 4.77 (m, 2H, C2H), 7.62 (t, 2H, 3JHH 8.0 Hz, Ar), 7.72 (t, 1H, 3JHH 8.0 Hz, Ar), 7.95 (d, 2H, 3JHH 8.0 Hz, Ar). (O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methylN-tosyl-(S)-prolinamide (2c). Yield: 80%. Mp: 127−129 °C (heptane/benzene, 2/1). [α]D25 = −53.7° (c 1.4, CHCl3). Anal. Found: C, 51.61; H, 6.83; N, 7.58. Calcd for C16H25FN2O3SSi: C, 51.59; H, 6.76; N, 7.52. IR (ν, cm−1): 1612 s, 1520 w (NCO→Si), 1345 m, 1156 s (SO2). 1H NMR (CDCl3, δ, ppm): 0.11, 0.21 (two d, 6H, SiMe2, 3JHF 7.6 Hz), 1.85−2.07 (m, 4H, C3H2 and C4H2), 2.43 (s, 3H, CH3), 2.49 (m, 2H, CH2Si), 3.20 (s, 3H, MeN), 3.40 (m, 2H, H

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Table 5. Variable-Temperature 19F NMR Spectra of Compounds 2a−f in CDCl3a δ(19F), ppm

a

T, °C

2a

2b

2c

2d

2e

2f

−60 −50 −40 −30 −20 −10 0 10 20 30 40 50 60

−120.2 −121.0 −121.7 −122.4 −123.2 −124.0 −124.7

−118.5 −119.0 −119.6 −120.2 −120.8 −121.5 −122.1 (3JHF 7.6) −122.8 −123.7 −124.2 −125.0 −125.7 −126.4

−118.4 −119.0 −119.5 −120.0 −120.7 −121.3 −122.0

−119.7 −120.3 −120.9 −121.6 −122.3 −123.0 −123.8 −124.5 −125.3 −126.1 −126.8 −127.6 −128.3

−119.6 −120.2 −120.9 −121.6 −122.3 −123.0 −123.7 −124.44 (3JHF 7.6) −125.2 −126.0 −126.7 −127.5 −128.3

−121.6 −122.4 −123.2 −124.0 −124.7 −125.6 −126.4

−126.4 −127.1 −127.9 −128.7 −129.5

−123.3 −124.1 −124.7 −125.4 −126.2

−127.9 −128.7 −129.5 −130.4 −131.3

δ, ppm (3JFH, Hz) in (CD3)2CO at room temperature for 2b−f, respectively: −118.9 (br s), −118.7 (m), −119.8 (br s), −119.9 (m), −121.30 (m).

Table 6. Experimental Details of Single-Crystal X-ray Studies 2a chem formula formula wt cryst syst, space group

C10H21FN2O3SSi 296.44 monoclinic, P21/n

temp (K) a (Å) b (Å) c (Å) β (deg) V (Å3) Z μ (mm−1) cryst size (mm) diffractometer Tmin, Tmax nos. of measd, indep, and obsd [I > 2σ(I)] rflns Rint R(F2 > 2σ(F2)), Rw(F2), GOF no. of params Δρmax, Δρmin (e Å−3) Flack param

120 6.8344(10) 29.411(4) 7.8777(11) 110.176(2) 1486.3(4) 4 0.31 0.29 × 0.24 × 0.20 Bruker Smart 1000 0.915, 0.940 16 835, 4299, 3266 0.026 0.048, 0.099, 1.00 167 0.48, −0.34

2c

2d

2e

2f

C16H25FN2O3SSi 372.53 orthorhombic, P212121 120 6.2309(11), 15.816(3) 19.111(3)

C15H22ClFN2O3SSi 392.95 orthorhombic, P212121 100 6.2703(4) 16.3805(10) 17.9546(11)

C15H22BrFN2O3SSi 437.41 orthorhombic, P212121 120 6.299(2) 16.398(6) 18.228(7)

C15H22FN3O5SSi 403.51 orthorhombic, Pca21 100 18.5530 (16) 7.4458(6) 26.979(2)

1883.3(6) 4 0.26 0.27 × 0.26 × 0.12 Bruker Smart 1000 0.933, 0.969 21 597, 5453, 3165

1844.1(2) 4 0.41 0.30 × 0.22 × 0.21 Bruker APEX II 0.887, 0.919 24 335, 5615, 5269

1882.7(12) 4 2.38 0.02 × 0.02 × 0.11 Bruker Smart 1000 0.780, 0.954 18 650, 4318, 1750

3727.0(5) 8 0.28 0.19 × 0.19 × 0.17 Bruker APEX II 0.949, 0.954 20 433, 9269, 7003

0.049 0.054, 0.116, 0.95 221 0.37, −0.27 −0.10(10)

0.032 0.028, 0.062, 1.01 220 0.36, −0.25 0.00(4)

0.071 0.0734, 0.1894, 0.822 220 0.87, −1.22 0.01(2)

0.0000 0.065, 0.138, 1.08 476 1.14, −0.38 −0.01(12)

(O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methylN-(4-bromophenylsulfonyl)-(S)-prolinamide (2e). Yield: 90%. Mp: 138−140 °C (ethanol). [α]D25 = −21.3° (c 0.74, CHCl3). Anal. Found: C, 41.39; H, 5.19; N, 6.26. Calcd for C15H22BrFN2O3SSi: C, 41.19; H, 5.07; N, 6.40. IR (ν, cm−1): 1614 s, 1519 w (NCO→Si), 1573 w (Ar), 1347 m, 1157 s (SO2). 1H NMR (CDCl3, δ, ppm): 0.21, 0.27 (two d, 6H, SiMe2, 3JHF 7.7 Hz), 1.87−1.95 and 2.07−2.23 (m, 4H, C3H2 and C4H2), 2.43 and 2.58 (dd, 2H, CH2Si, 3JHH 15.8 Hz), 3.20 (s, 3H, MeN), 3.34−3.51 (m, 2H, C5H2), 4.83 (m, 2H, C2H), 7.67 (d, 2H, 3JHH 8.5 Hz, Ar), 7.78 (d, 2H, 3JHH 8.5 Hz, Ar). 1H NMR ((CD3)2CO, δ, ppm): 0.21, 0.27 (two d, 6H, SiMe2, 3JHF 5.8 Hz), 1.81−2.20 (m, 4H, C3H2 and C4H2), 2.41 and 2.52 (dd, 2H, CH2Si, 3 JHH 15.2 Hz), 3.29 (s, 3H, MeN), 3.41−3.50 (m, 2H, C5H2), 4.89 (m, 2H, C2H), 7.81 (d, 2H, 3JHH 8.1 Hz, Ar), 7.89 (d, 2H, 3JHH 8.1 Hz, Ar). (O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methylN-nosyl-(R,S)-prolinamide (2f). Yield: 90% Mp: 157−158 °C (benzene). Anal. Found: C, 44.57; H, 5.31; N, 10.33. Calcd for C15H22FN3O5SSi: C, 44.65; H, 5.50; N, 10.41. IR (ν, cm−1): 1612 s (NCO→Si), 1528 s, 1347 s (NO2), 1105 s (SO2). 1H NMR (CDCl3, δ, ppm): 0.10, 0.19 (two d, 6H, SiMe2, 3JHF 7.8 Hz), 1.88− 2.29 (m, 4 H, C3H2 and C4H2), 2.46, 2.62 (dd, 2H, CH2Si, 2JHH 15.6),

C5H2), 4.74 (m, 2H, C2H), 7.30 (d, 2H, 3JHH 8.0 Hz, Ar), 7.75 (d, 2H, 3 JHH 8.0 Hz, Ar). 1H NMR ((CD3)2CO, δ, ppm): 0.11, 0.21 (two d, 6H, SiMe2, 3JHF 5.2 Hz), 1.72−2.12 (m, 4H, C3H2 and C4H2), 2.45 (s, 3H, CH3), 2.50 (m, 2H, CH2Si), 3.30 (s, 3H, MeN), 3.41 (m, 2H, C5H2), 4.72 (m, 2H, C2H), 7.45 (d, 2H, 3JHH 7.8 Hz, Ar), 7.82 (d, 2H, 3 JHH 7.8 Hz, Ar). (O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methylN-(4-chlorophenylsulfonyl)-(S)-prolinamide (2d). Yield: 80%. Mp: 138−139 °C (heptane/benzene, 1/2). [α]D25 = −28.7° (c 1.33, CHCl3). Anal. Found: C, 46.15; H, 5.57; N, 7.09. Calcd for C15H22ClFN2O3SSi: C, 45.85; H, 5.64; N, 7.13. IR (ν, cm−1): 1613 s, 1520 w (NCO→Si), 1585 w (Ar), 1345 m, 1156 s (SO2). 1H NMR (CDCl3, δ, ppm): 0.20, 0.26 (two d, 6H, SiMe2, 3JHF 7.6 Hz), 1.85−1.95 and 2.08−2.20 (m, 4H, C3H2 and C4H2), 2.49 (m, 2H, CH2Si, 3JHF 15.75 Hz), 3.20 (s, 3H, MeN), 3.40 (m, 2H, C5H2), 4.82 (m, 2H, C2H), 7.50 (d, 2H, 3JHH 8.5 Hz, Ar), 7.85 (d, 4H, 3JHH 8.5 Hz, Ar). 1H NMR ((CD3)2CO, δ, ppm): 0.13, 0.18 (two d, 6H, SiMe2, 3 JHF 7.7 Hz), 1.81−1.93 and 2.05−2.20 (m, 4H, C3H2 and C4H2), 2.41, 2.52 (dd, 2H, CH2Si, 3JHH 15.7 Hz), 3.29 (s, 3H, MeN), 3.44 (m, 2H, C5H2), 4.89 (m, 2H, C2H), 7.67 (d, 2H, 3JHH 8.3 Hz, Ar), 7.95 (d, 4H, 3 JHH 8.3 Hz, Ar). I

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3.19 (s, 3H, MeN), 3.36, 3.53 (two m, 2H, C5H2), 4.91 (m, 2H, C2H), 8.10 (d, 4H, 3JHH 8.3 Hz, Ar), 8.34 (d, 4H, 3JHH 8.3 Hz, Ar). 1H NMR ((CD3)2CO, δ, ppm): 0.15, 0.20 (two d, 6H, SiMe2, 3JHF 7.7 Hz), 1.83−2.25 (m, 4 H, C3H2 and C4H2), 2.44, 2.53 (dd, 2H, CH2Si, 2JHH 15.8), 3.30 (s, 3H, MeN), 3.52 (m, 2H, C5H2), 5.00 (m, 2H, C2H), 8.21 (d, 4H, 3JHH 8.1 Hz, Ar), 8.48 (d, 4H, 3JHH 8.1 Hz, Ar).

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(16) Negrebetsky, Vad. V. A Thesis for the degree of Doctor of Chemistry, The Institute of Organic Chemistry, Russian Academy of Science, Moscow, 2006. (17) Bassindale, A. R.; Borbaruah, M.; Glynn, S. J.; Parker, D. J.; Taylor, P. G. J. Chem. Soc., Perkin Trans. 2 1999, 2099−2109. (18) Bassindale, A. R.; Borbaruah, M.; Glynn, S. J.; Parker, D. J.; Taylor, P. G. J. Organomet. Chem. 2000, 606, 125−131. (19) Albanov, A. I. A Thesis for the degree of Candidate of Chemical Sciences, The Institute of Organic Chemistry, Russian Academy of Science, Irkutsk, 1984, 147 p. (20) Marsmann, H. 29Si-NMR Spectroscopic Results. NMR-17 Basic Princ. Prog. 1981, 17, 64−235. (21) (a) Voronkov, M. G.; Pestunovich, V. A.; Baukov, Yu. I. Metalloorg. Khim. 1991, 4, 1210−1227. (b) Negrebetsky, V. V.; Baukov, Yu. I. Russ. Chem. Bull. 1997, 46, 1807−1831. (22) Bassindale, A. R.; Borbaruah, M.; Glynn, S. J.; Parker, D. J.; Taylor, P. G. J. Chem. Soc., Perkin Trans. 2 1999, 10, 2099−2109. (23) Negrebetsky, Vad. V.; Shipov, A. G.; Kramarova, E. P.; Negrebetsky, V. V.; Baukov, Yu. I. J. Organomet. Chem. 1997, 530, 1− 12. (24) Chipanina, N. N.; Aksamentova, T. N.; Voronkov, M. G.; Turchaninov, V. K. J. Struct. Chem. 2006, 46, 1066−1070. (25) Bannikova, O. B. A Thesis for the degree of Candidate of Chemical Sciences, The Institute of Organic Chemistry, Russian Academy of Science, Irkutsk, 1986, 20 p. (26) Pulse methods in 1D and 2D liquid-phase NMR; Brey, W. S., Ed.; Academic Press: New York, 1988. (27) van Geet, A. L. Anal. Chem. 1970, 42, 679−680. (28) Haegele, G.; Fuhler, R.; Lenzen, Th. Comput. Chem. 1995, 19, 277−282. (29) Binsch, G. In Dynamic Nuclear Magnetic Resonance Spectroscopy; Jackman, L. M., Cotton, F. A., Eds.; Academic Press: New York, 1975; p 45. (30) Blessing, R. H. Acta Crystallogr. 1995, A51, 33−38. (31) Sheldrick, G. M. Acta Crystallogr. 2007, A64, 112−122. (32) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341. (33) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, C.01; Gaussian Inc., Wallingford, CT. (34) Nikolin, A. A.; Arkhipov, D. E.; Shipov, A. G.; Kramarova, E. P.; Kovalchuk, N. A.; Korlukov, A. A.; Negrebetskiy, V. V.; Baukov, Yu. I.; Bassindale, A. R.; Taylor, P. G.; Bowden, A.; Bylikin, S. Yu. Chem. Heterocycl. Compd. 2011, 534, 1869−1890.

ASSOCIATED CONTENT

S Supporting Information *

Tables and a figure giving details of the calculations and CIF files giving crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was carried out as a part of the research activities of the Science and Education Centre for the Synthesis and Investigation of Biologically Active Compounds at the N. I. Pirogov Russian National Research Medical University and supported by the Russian Foundation for Basic Research (Grant No. 10-03-000824).

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REFERENCES

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