Synthesis, structures, and stereodynamic behavior of novel pentacoordinate fluorosilanes: Fluorosilyl derivatives of proline

Article abstract of DOI:10.1021/om3002697

The (O→Si)-chelate N′-(dimethylfluorosilylmethyl))-N′- methyl-N-(organosulfonyl)prolinamides RSO₂-Pro-N(Me)CH ₂SiMe₂F (2a-f, R = Me (a), Ph (b), 4-MeC₆H ₄ (c), 4-ClC₆H₄ (d), 4-BrC₆H ₄ (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 A) that is 0.02-0.11 A 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 SiMe ₂ 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.

Full text of DOI:10.1021/om3002697

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′-(dimethylfluorosilyl-
methyl))-N′-methyl-N-(organosulfonyl)prolinamides RSO2-
Pro-N(Me)CH2SiMe2F (2a−f, R = Me (a), Ph (b), 4-
MeC6H4 (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
1
in these complexes. The temperature dependence of the SiMe2 signals in the H 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.
ompounds with nonclassical types of chemical bonds, in
particular, the derivatives of silicon with an extended
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
C
coordination sphere of the central atom due to additional intra-
or intermolecular coordination, have been studied extensively
for many years. These studies included synthetic approaches
and the structure, reactivity, biological activity, and stereo-
dynamic 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
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
1
analysis and IR and H, 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 19F 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.
Figure 1. Molecular structure of 2a. Atoms are presented as ADP
ellipsoids at the 50% probability level.
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 organo-
sulfonyl groups at the α-nitrogen atom.
RESULTS AND DISCUSSION
■
Synthesis. The (O→Si)-chelate N′-(dimethylfluorosilyl-
methyl)-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
Figure 3. Molecular structure of 2d. Atoms are presented as ADP
ellipsoids at the 50% probability level.
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.
Figure 4. Molecular structure of 2e. Atoms are presented as ADP
ellipsoids at the 50% probability level.
Therefore, the observed weakening of the O→Si coordina-
tion 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 5. Molecular structure of 2f. Atoms are presented as ADP
ellipsoids at the 50% probability level.
C
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Table 1. Selected Bond Lengths (Å) and Angles (deg) in Compounds 2a,c−f
2a
2c
2d
2e
2f
Si1−F1
Si1−C1
Si1−C2
Si1−C3
Si1−O1
O1−C4
F1−Si1−O1
N1−C4−N2−S1
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-Pro-
N(Me)CH2SiMe2F (2a−f)
compd
ν, cm−1 (solid)
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)
Figure 7. Correlation between interatomic distance Si···O (x) and
δ(29Si) (y).
Figure 6. Stacking interactions in the crystal structure of 2f.
Table 2. 29Si NMR Data for Fluorosilanes RSO2-Pro-
N(Me)CH2SiMe2F (2a−f)
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.
2a
2b
2c
2d
2e
2f
δ(29Si), CP/
−21.4
−20.4
−29.4
−29.6
−28.5
−16.6
MAS, ppm
δ(29Si), CDCl3,
−10.3
−13.5
−13.7
−11.5
−11.2
−7.0
1
The study of temperature effects on the H and 19F NMR
ppm
(d)
(d)
(d)
(d)
(d)
(d)
1JSiF, CDCl3, Hz 258
256
256
257
257
258
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
δ(29Si),
(CD3)2CO,
ppm
−19.9
−20.0
−17.6
−18.0
−16.2
(d)
(d)
(d)
(d)
(d)
1JSiF, (CD3)2CO,
258
6.9
0.5
257
15.7
9.4
261
18.1
12.0
259
17.3
10.5
266
9.6
0.4
Hz
a
Δδ in CDCl3,
11.1
ppm
a
Δδ in
(CD3)2CO,
ppm
a
Δδ = [δ(29Si), solvent] − [δ(29Si), CP/MAS].
1
components of the multiplet. In addition, the H NMR signal
of the SiMe2 group drifts downfield (by 0.03 ppm) in the
D
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1
Figure 8. Signals of the SiMe2 protons in the H 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
1
signal of 2c in CDCl3 shifts upfield (−15.5 ppm, d, JSiF = 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 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
1
(Figure 10) and the broadening of the SiMe2 signals in the H
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, electron-
donor 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
At high temperature complex 2c has a fluorine chemical shift
of −126 ppm, suggesting a reasonable amount of pentacoordi-
nation. 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.
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-(1-
phenylethyl)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):
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
1
SiMe2 signals in the H 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-depend-
ent 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
1
calculated by a H 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 intra-
molecular 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 rate-
limiting 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
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
Table 4. 13C NMR Spectra of Compounds 2a−f in CDCl3
δ(13C), ppm
−
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.
signal
SiMe2
2a
1.10
2b
1.17
2c
1.11,
1.14
2d
2e
2f
0.90,
1.10
1.11
0.74,
1.02
SiCH2
40.9 (d, 41.02 (d, 41.02
41.00
41.12
41.09
2JCF
2JCF
CONCLUSIONS
■
30.96
Hz)
38.14
Hz)
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.
NMe
C-2
C-3
C-4
C-5
C-1′
37.25
37.47
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
37.56
56.93
30.75
24.86
48.19
57.11
30.65
24.80
47.50
56.10
30.59
24.94
48.22
138.81
127.36
138.07 145.13
127.39 128.72
C-2′ + C-
6′
C-3 ′ + C-
5′
129.02
132.85
129.63
129.20
139.30
129.0
124.13
C-4′
143.70
21.44
127.85 150.09
SMe/
CMe
39.33
a
CO
172.60
172.52
172.52
172.40
172.33 172.05
a
δ in ppm in (CD3)2CO at room temperature for 2b−f, respectively:
174.00, 173.10, 173.83, 173.88, 173.65.
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
Disiloxanes 1a−f were synthesized according to published
procedures.34
1
APR element, respectively. H, 13C, and 19F NMR spectra in CDCl3
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.
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
1
The H, 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-EX-
400 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 subse-
quent calculation of Hessian matrix.
(O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methyl-
N-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
3
(CDCl3, δ, ppm): 0.12, 0.23 (two d, 6H, SiMe2, JHF 7.7 Hz), 1.81,
2.32 (two m, 2H, C3H2), 2.04 (quintet, 2H, C4H2, 2JHH 6.6 Hz), 2.43,
2
2.58 (dd, 2H, CH2Si, JHH 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′-methyl-
N-phenylsulfonyl-(S)-prolinamide (2b). Yield: 85%. Mp: 107−
25
108 °C (heptane/benzene, 4/1). [α]D = −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,
3
2.55 (dd, 2H, CH2Si, JHH 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
3
3
1
(t, 1H, JHH 8.1 Hz, Ar), 7.9 (d, 2H, JHH 8.1 Hz, Ar). H NMR
3
((CD3)2CO, δ, ppm): 0.12, 0.19 (two d, 6H, SiMe2, JHF 7.7 Hz),
1.73−2.15 (m, 4H, C3H2 and C4H2), 2.43, 2.51 (dd, 2H, CH2Si, JHH
3
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
3
(d, 2H, JHH 8.0 Hz, Ar).
(O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methyl-
N-tosyl-(S)-prolinamide (2c). Yield: 80%. Mp: 127−129 °C
25
(heptane/benzene, 2/1). [α]D = −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
dx.doi.org/10.1021/om3002697 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Table 5. Variable-Temperature 19F NMR Spectra of Compounds 2a−f in CDCl3
δ(19F), ppm
T, °C
2a
2b
2c
2d
2e
2f
−60
−50
−40
−30
−20
−10
0
−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
−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
−121.6
−122.4
−123.2
−124.0
−124.7
−125.6
−126.4
−122.1 (3JHF 7.6)
−122.8
10
−124.44 (3JHF 7.6)
−125.2
20
−126.4
−127.1
−127.9
−128.7
−129.5
−123.7
−124.2
−125.0
−125.7
−123.3
−124.1
−124.7
−125.4
−126.2
−127.9
−128.7
−129.5
−130.4
−131.3
30
−126.0
−126.7
−127.5
−128.3
40
50
60
−126.4
a
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
2c
2d
2e
2f
chem formula
C10H21FN2O3SSi
296.44
C16H25FN2O3SSi
372.53
C15H22ClFN2O3SSi
392.95
C15H22BrFN2O3SSi
437.41
C15H22FN3O5SSi
403.51
formula wt
cryst syst, space group
monoclinic, P21/n orthorhombic,
P212121
orthorhombic,
P212121
orthorhombic,
P212121
orthorhombic,
Pca21
temp (K)
a (Å)
b (Å)
c (Å)
120
120
100
120
100
6.8344(10)
29.411(4)
7.8777(11)
110.176(2)
1486.3(4)
4
6.2309(11),
15.816(3)
19.111(3)
6.2703(4)
16.3805(10)
17.9546(11)
6.299(2)
16.398(6)
18.228(7)
18.5530 (16)
7.4458(6)
26.979(2)
β (deg)
V (Å3)
Z
1883.3(6)
1844.1(2)
1882.7(12)
3727.0(5)
4
4
4
8
μ (mm−1
)
0.31
0.26
0.41
2.38
0.28
cryst size (mm)
0.29 × 0.24 × 0.20 0.27 × 0.26 × 0.12
Bruker Smart 1000 Bruker Smart 1000
0.30 × 0.22 × 0.21
Bruker APEX II
0.887, 0.919
24 335, 5615, 5269
0.02 × 0.02 × 0.11
Bruker Smart 1000
0.780, 0.954
18 650, 4318, 1750
0.19 × 0.19 × 0.17
Bruker APEX II
0.949, 0.954
20 433, 9269, 7003
diffractometer
Tmin, Tmax
0.915, 0.940
0.933, 0.969
nos. of measd, indep, and obsd [I > 2σ(I)]
rflns
16 835, 4299, 3266 21 597, 5453, 3165
Rint
0.026
0.049
0.032
0.071
0.0000
R(F2 > 2σ(F2)), Rw(F2), GOF
0.048, 0.099, 1.00
167
0.054, 0.116, 0.95
221
0.028, 0.062, 1.01
220
0.0734, 0.1894, 0.822 0.065, 0.138, 1.08
no. of params
Δρmax, Δρmin (e Å−3
Flack param
220
476
)
0.48, −0.34
0.37, −0.27
−0.10(10)
0.36, −0.25
0.00(4)
0.87, −1.22
0.01(2)
1.14, −0.38
−0.01(12)
C5H2), 4.74 (m, 2H, C2H), 7.30 (d, 2H, 3JHH 8.0 Hz, Ar), 7.75 (d, 2H,
(O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methyl-
N-(4-bromophenylsulfonyl)-(S)-prolinamide (2e). Yield: 90%.
1
3JHH 8.0 Hz, Ar). H NMR ((CD3)2CO, δ, ppm): 0.11, 0.21 (two d,
25
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,
3JHH 7.8 Hz, Ar).
Mp: 138−140 °C (ethanol). [α]D = −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,
3
0.27 (two d, 6H, SiMe2, JHF 7.7 Hz), 1.87−1.95 and 2.07−2.23 (m,
(O→Si)-Chelate N′-(Dimethylfluorosilylmethyl)-N′-methyl-
3
4H, C3H2 and C4H2), 2.43 and 2.58 (dd, 2H, CH2Si, JHH 15.8 Hz),
N-(4-chlorophenylsulfonyl)-(S)-prolinamide (2d). Yield: 80%.
3.20 (s, 3H, MeN), 3.34−3.51 (m, 2H, C5H2), 4.83 (m, 2H, C2H),
25
Mp: 138−139 °C (heptane/benzene, 1/2). [α]D = −28.7° (c 1.33,
7.67 (d, 2H, 3JHH 8.5 Hz, Ar), 7.78 (d, 2H, 3JHH 8.5 Hz, Ar). 1H NMR
CHCl3). Anal. Found: C, 46.15; H, 5.57; N, 7.09. Calcd for
3
C15H22ClFN2O3SSi: C, 45.85; H, 5.64; N, 7.13. IR (ν, cm−1): 1613
((CD3)2CO, δ, ppm): 0.21, 0.27 (two d, 6H, SiMe2, JHF 5.8 Hz),
s, 1520 w (NCO→Si), 1585 w (Ar), 1345 m, 1156 s (SO2). H
1.81−2.20 (m, 4H, C3H2 and C4H2), 2.41 and 2.52 (dd, 2H, CH2Si,
3JHH 15.2 Hz), 3.29 (s, 3H, MeN), 3.41−3.50 (m, 2H, C5H2), 4.89 (m,
1
3
NMR (CDCl3, δ, ppm): 0.20, 0.26 (two d, 6H, SiMe2, JHF 7.6 Hz),
1.85−1.95 and 2.08−2.20 (m, 4H, C3H2 and C4H2), 2.49 (m, 2H,
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′-methyl-
N-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
3
CH2Si, JHF 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,
1
Ar). H NMR ((CD3)2CO, δ, ppm): 0.13, 0.18 (two d, 6H, SiMe2,
3JHF 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,
3JHH 8.3 Hz, Ar).
3
(CDCl3, δ, ppm): 0.10, 0.19 (two d, 6H, SiMe2, JHF 7.8 Hz), 1.88−
2.29 (m, 4 H, C3H2 and C4H2), 2.46, 2.62 (dd, 2H, CH2Si, 2JHH 15.6),
I
dx.doi.org/10.1021/om3002697 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3.19 (s, 3H, MeN), 3.36, 3.53 (two m, 2H, C5H2), 4.91 (m, 2H, C2H),
(16) Negrebetsky, Vad. V. A Thesis for the degree of Doctor of
Chemistry, The Institute of Organic Chemistry, Russian Academy of
Science, Moscow, 2006.
8.10 (d, 4H, 3JHH 8.3 Hz, Ar), 8.34 (d, 4H, 3JHH 8.3 Hz, Ar). 1H NMR
3
((CD3)2CO, δ, ppm): 0.15, 0.20 (two d, 6H, SiMe2, JHF 7.7 Hz),
1.83−2.25 (m, 4 H, C3H2 and C4H2), 2.44, 2.53 (dd, 2H, CH2Si, 2JHH
(17) Bassindale, A. R.; Borbaruah, M.; Glynn, S. J.; Parker, D. J.;
Taylor, P. G. J. Chem. Soc., Perkin Trans. 2 1999, 2099−2109.
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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.
15.8), 3.30 (s, 3H, MeN), 3.52 (m, 2H, C5H2), 5.00 (m, 2H, C2H),
3
3
8.21 (d, 4H, JHH 8.1 Hz, Ar), 8.48 (d, 4H, JHH 8.1 Hz, Ar).
ASSOCIATED CONTENT
* Supporting Information
■
S
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.
(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.
AUTHOR INFORMATION
Corresponding Author
*E-mail: negrebetsky1@rsmu.ru.
■
Notes
The authors declare no competing financial interest.
(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.
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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Academic Press: New York, 1988.
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dx.doi.org/10.1021/om3002697 | Organometallics XXXX, XXX, XXX−XXX