Synthesis, structures and stereodynamic behavior of novel pentacoordinate (O→Si)-Chelate Difluoro(methyl)silylmethyl derivatives of amides and imides

Article abstract of DOI:10.1016/j.jorganchem.2018.07.027

The structures and stereodynamic behavior of (O→Si)-chelate methyldifluorosilanes in solutions were studied by multinuclear (¹H, ¹³C, ¹⁹F, ²⁹Si) and 2D (COSY, HETCOR ¹H, ¹³C) NMR spectrosco

Full text of DOI:10.1016/j.jorganchem.2018.07.027

Accepted Manuscript
Synthesis, structures and stereodynamic behavior of novel pentacoordinate (O→Si)-
Chelate Difluoro(methyl)silylmethyl derivatives of amides and imides
Vadim V. Negrebetsky, Eugeniya P. Kramarova, Aleksander G. Shipov, Yuri I.
Baukov, Alexander A. Korlyukov, Dmitry E. Arkhipov, Alan R. Bassindale, Peter G.
Taylor, Sergey Yu Bylikin
PII:
S0022-328X(18)30297-3
10.1016/j.jorganchem.2018.07.027
JOM 20514
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 1 May 2018
Revised Date: 16 July 2018
Accepted Date: 23 July 2018
Please cite this article as: V.V. Negrebetsky, E.P. Kramarova, A.G. Shipov, Y.I. Baukov, A.A. Korlyukov,
D.E. Arkhipov, A.R. Bassindale, P.G. Taylor, S.Y. Bylikin, Synthesis, structures and stereodynamic
behavior of novel pentacoordinate (O→Si)-Chelate Difluoro(methyl)silylmethyl derivatives of amides and
imides, Journal of Organometallic Chemistry (2018), doi: 10.1016/j.jorganchem.2018.07.027.
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ACCEPTED MANUSCRIPT
F2
Me
Me
F1
N
N
Si
F1
N
O
O
F1
Si
N
Si
Me
F2
F1
O
O
Me
F2
Si
F2

ACCEPTED MANUSCRIPT
Synthesis, Structures and Stereodynamic Behavior of Novel Pentacoordinate
(O→Si)-Chelate Difluoro(methyl)silylmethyl Derivatives of Amides and Imides
ꢀ
Vadim V. Negrebetsky , Eugeniya P. Kramarova, Aleksander G. Shipov, Yuri I. Baukov
Department of Chemistry, N. I. Pirogov Russian National Research Medical University, Ostrovityanov
St. 1, Moscow 117997, Russian Federation; e-mail: negrebetsky1@rsmu.ru
Alexander A. Korlyukov, Dmitry E. Arkhipov
A. N. Nesmeyanov Institute of Organoelement Compounds, RAS, Vavilova St. 28, 11991 Moscow,
Russian Federation
Alan R. Bassindale, Peter G. Taylor, Sergey Yu. Bylikin
Department of Chemistry, Open University, Walton Hall, Milton Keynes, MK7 6AA,
United Kingdom
ABSTRACT
The structures and stereodynamic behavior of (O→Si)-chelate methyldifluorosilanes in solutions were
1
13
19
29
1
13
studied by multinuclear ( H, C, F, Si) and 2D (COSY, HETCOR H, C) NMR spectroscopy.
The range of studied complexes included amides RC(O)N(R')CH SiMeF [R = Ph, R' = H (1a); R = R'
2
2
=
Me (1b); R = Me, R' = CHMePh (1c)], lactams LCH SiMeF (L = 2-oxoazepan-1-yl (2a), 2,2-
2 2
dimethyl-4-oxo-2H-benzo[1,3]oxazin-3-yl (2b) or 4-methyl-2-oxoquinolin-1-yl (2c)] and the six-
6
membered imide Im CH [2,6-dioxopiperidin-1-yl (3)]. The pentacoordination of silicon atoms in all
2
studied compounds was confirmed by NMR study in solutions and single-crystal X-ray studies of
1
9
complexes 1c, 2a, 2c and 3. The temperature dependency observed for F NMR signals in solution
was explained by the ligand exchange in the coordination environment of silicon atoms (permutational
1
9
isomerization) and used for determining the activation parameters of this process by F DNMR.
Quantum-chemical calculations for various isomers of complexes 1c, 2a, 2c and 3 suggested the
"turnstile rotation" as the most likely mechanism for the observed stereodynamic processes.
Key words: pentacoordinated difluorosilanes, synthesis, X-ray, dynamic NMR, permutational
isomerization, quantum-chemical calculations.
Introduction
Compounds of hypercoordinate silicon continue to attract attention due to their unusual
1
–
structural features, increased reactivity, biological activity and stereochemical nonrigidity in solution.
8
9,10
Neutral fluorides of pentacoordinate silicon
are generally more stable and less susceptible to
hydrolysis, so they are commonly used as model compounds in various applications. However, certain

ACCEPTED MANUSCRIPT
types of these compounds, in particular monochelate difluorosilanes, have not been studied
thoroughly.
In the present paper we discuss the synthesis, structures and stereodynamic behaviour in solution
of pentacoordinate mono-(O→Si)-chelate (methyldifluorosilyl)methyl derivatives of amides, lactams
1
13
19
29
and imides. The reported compounds were studies by multinuclear ( H, C, F, Si) and 2D (COSY,
1
13
HETCOR H, C) NMR spectroscopy, quantum-chemical calculations and single-crystal X-ray
crystallography.
Results and discussion
Synthesis of pentacoordinate complexes of difluorosilanes
Pentacoordinate mono-(O→Si)-chelate (methyldifluorosilyl)methyl derivatives of amides
RC(O)N(R')CH SiMeF (1a–c) were synthesized according to Scheme 1. The difluoroderivatives of
2
2
6
lactams LCH SiMeF (2a–c) and imide Im CH SiMeF (3) (Chart 1) were synthesized by similar
2
2
2
2
procedures. In all cases, the intermediate pentacoordinate methyldichlorosilanes A were synthesized
1
1,12
either by the reactions of N-trimethylsilyl amides, lactams or imides with ClCH Si(Me)Cl (a)
or
2
2
by the reactions of respective NH-compounds with a mixture of (Me Si) NH and ClCH Si(Me)Cl
3
2
2
2
1
3,14
(b)
.
Scheme 1
R'
R
R
C
2 2
ClCH SiMeCl
a) RC(O)NSiMe3
C
O
R'
R'
H O
Et O BF
2
O
N
2
3
N
Me
Cl
Me
F
NaHCO3
CH2 Si
CH2 Si
F
1a
(
3 2
Me Si) NH
b) RC(O)NHR'
ClCH SiMeCl2
Cl
2
A
–c
R = Ph, R' = H (1a); R = R' = Me (1b); R = Me, R' = CH(Ph)Me (1c)
Chart 1
Me
O
O
N
O
O
N
O
Si
F
N
O
Si
F
N
Me
Me
Me
Me
Me
Me
Si
F
Si
F
F
F
F
F

ACCEPTED MANUSCRIPT
2
a
2b
2c
3
1
5
Method (a) was used for silanes 1a, 2b , 2c and 3 while all other silanes were prepared by
method (b). The hydrolysis of intermediate products A was followed by in situ reaction of the resulting
oligosiloxanes with BF ꢀEt O, producing target difluorides 1–3 in low to moderate yields (6–68%).
3
2
The structures and composition of target compounds was confirmed by elemental analysis, IR
and NMR spectroscopy, and single-crystal X-ray diffraction study of complexes 1c, 2a, 2c and 3. The
1
6
15
X-ray structures of difluorides 1b and 2b were published earlier.
Single crystal X-ray studies
A single crystal X-ray study of compounds 1c, 2a, 2c and 3 confirm that they are difluorosilanes
with a five-membered (O→Si)-chelate ring (Figures 1–4).
Figure 1. Molecular structure of 1c in ADP ellipsoids at 50% probability.
Figure 2. Molecular structure of 2a in ADP ellipsoids at 50% probability.

ACCEPTED MANUSCRIPT
Figure 3. Molecular structure of 2c in ADP ellipsoids at 50% probability.
Figure 4. Molecular structure of 3 in ADP ellipsoids at 50% probability.
Only a few crystal structures of similar difluorides have been published to date. Owing to the
presence of an equatorial fluorine atom, the Si1–O1 coordination bond in such compounds was
expected to be somewhat shorter than that in similar chelates with the Me SiF moiety. However, the
2
Si1–O1 distances in (O→Si)-chelate difluorides vary in a wide range from 2.217 Å in
1
8
methyl(benzoyloxymethyl)difluorosilane to 1.971 Å in N-methyl-N-(methyldifluorosilylmethyl)
1
6
acetamide. Thus, the geometry of the MeFOSiF coordination centre is very sensitive to the nature of

ACCEPTED MANUSCRIPT
the five membered chelate ring and its substituents. The strength of the electron withdrawing effect of
the O1 atom depends on substituents at the N1 and C3 positions. Compounds 1c, 2a, 2c, and 3 contain
several types of aromatic and alkyl moieties bonded to the N1 and C3 atoms and so the Si1–O1
distances in these difluorosilanes varies in the range of 1.95–2.16 Å (Table 1).
Table 1. Selected bond length (Å) and angles (°) in complexes 1c, 2a, 2c and 3.
1
c
2a
2c
3
Si1—F1
Si1—F2
Si1—O1
Si1—C1
Si1—C2
O1—C3
F1–Si1–O1
1.6607(12)
1.6094(11)
2.0072(13)
1.841(2)
1.6566(13) 1.6571 (11) 1.6380(12)
1.6149(11) 1.6056 (10) 1.5972(12)
2.0004(14) 1.9507 (11) 2.1599(16)
1.852(2)
1.891(2)
1.271(3)
173.65(8)
1.8918 (15)
1.831(2)
1.8844(19)
1.269(2)
1.8428 (16) 1.8769(19)
1.2764 (16) 1.2367 (19)
172.41(6)
171.48(5)
171.97(5)
The presence of a piperidine-2,6-dione ring in 3 reduces the ability of the O1 atom to donate
electrons, which causes the elongation of the Si1–O1 bond to 2.1599(16) Å. In contrast, the aromatic
4-methylquinoline fragment in 2c increases the electron-donating ability of the O1 atom and, as a
consequence, leads to a considerable shortening of the Si1–O1 bond. It should be noted that the Si1–
1
6
O1 distance in 2c is even shorter than in N-methyl-N-(methyldifluorosilylmethyl)acetamide.
The lengths of apical Si1–F1 and equatorial Si1–F2 bonds differ by 0.04–0.05 Å. The longest
Si1–F1 bond, 1.6607(12) Å, was found in 1c while the Si1–F1 distances in 2c and 2a were only
slightly shorter. The electron-withdrawing effect of the piperidine-2,6-dione ring in 3 caused a more
noticeable shortening of the Si1–F1 bond, down to 1.6380(12) Å.
1
9
Variable-temperature NMR F studies
19
At ambient temperature, the F signals in NMR spectra of difluorosilanes 1 and 2 appear as
singlets at –120 to –130 ppm due to a fast (on NMR time scale) positional exchange of the equatorial
(
F ) and apical (F ) fluorine atoms. At temperatures below –40 °C, this exchange slows down
e a
1
9
19
significantly, producing two separate F and F signals of equal intensity at approximately –100 and
a
e
–145 ppm, respectively (Fig. 5). The DNMR spectra of complex 3 are complicated by continuous re-
coordination of the silicon atom between the two carbonyl groups.

ACCEPTED MANUSCRIPT
1
9
Figure 5. DNMR F spectra of difluoride 1с (Jeol JNM-EX400, CD Cl + CDCl ).
2
2
3
1
9
19
The additional splitting of F and F signals observed in low-temperature NMR spectra of
a
e
difluorides 1c and 2a is caused by the presence of chiral carbon centers in their chelate ligands. Below
75 °C, the NMR spectra of these compounds in equimolar mixtures of CDCl and CD Cl show two
–
3
2
2
2
pairs of doublets with integral ratios of 1 : 1 ( J
~ 23 Hz), which correspond to two diastereomers.
e
F –F
a
1
9
In the case of 1с, these signals appear at δ( F) = –99.18, –99.91, –143.48 and –143.75 ppm (Fig. 5).
The activation parameters of the permutational isomerization in difluorides 1 and 2 were
1
9
19
calculated from DNMR F data (Table 2).
Table 2. Activation parameters of the permutational isomerization of difluorides RC(O)N(R')CH SiMeF2
2
(
1a–c) and LCH SiMeF (2a–c) in CDCl + CD Cl .
2
2
3
2
2
#
#
#
ꢁG
298,
ꢁH ,
ꢁS ,
Compound
T, K
–
1
–1
–1
–1
kcal mol
kcal mol
cal mol K
1
1
a
9.6 ± 0.2
9.7 ± 0.3
9.6 ± 0.2
9.7 ± 0.2
9.9 ± 0.2
9.7 ± 0.2
11.3 ± 0.2
11.1 ± 0.1
10.8 ± 0.2
11.2 ± 0.2
13.3 ± 0.2
10.9 ± 0.2
7 ± 2
6 ± 3
4 ± 3
7 ± 2
14 ± 3
5 ± 2
245
234
239
241
244
240
b
1
c
2
2
a
b
2
c

ACCEPTED MANUSCRIPT
The positional exchange of fluorine atoms in difluorides 1 and 2 is characterized by a relatively
–
1
–1 –1
low activation barrier (9.6–9.9 kcal mol ) and a positive entropy of activation (4–14 cal mol K ,
#
2
#
Table 2). These parameters differ significantly from the ꢁG
and ꢁS values observed for
98
–1
–1 –1
monofluorides LCH SiMe(R)F (R = Me, Ph) (ca. 24 kcal mol
and –20 cal mol K ,
2
1
0,20
respectively)
, which suggests that stereodynamic processes in these complexes proceed via
different mechanisms. Within the studied concentration range (0.02–0.30 M), the activation parameters
for difluorides remain virtually unchanged, which is typical for intramolecular processes.
Earlier we found that the permutational isomerization in (O→Si)-chelate monofluorides of
pentacoordinate silicon involved an "open" intermediate produced via reversible cleavage of the O→Si
9
,10
coordination bond.
According to X-ray data, the O→Si distance in the difluoride
MeC(O)N(CHMePh)CH SiMeF (1c) is 2.007 Å, which is significantly shorter than that in the
2
2
2
1
structurally similar monofluoride MeC(O)N(CHMePh)CH SiMe F (2.149 Å). The cleavage of this
2
2
–
1
bond in 1c would have an activation barrier of over 24 kcal mol , which contradicts the experimental
data (Table 2). Therefore, the positional exchange of fluoride ligands in difluorides 1 and 2 is unlikely
to involve the cleavage of the O→Si coordination.
Quantum chemical calculations of permutational isomerization in difluorides
The available X-ray and DNMR data are insufficient for elucidating the exact pathway of the
permutational isomerization in complexes 1 and 2. Additional information can be obtained from
quantum-chemical calculations that allow the characterization of all possible stationary points
(supporting materials, Table 1s) on the potential energy surface (PES) and then the determination of
the lowest energy pathways between these points.
The stationary points on the PES of 1c, 2a, 2c and 3 include the structures with intramolecular
O→Si bonds (c), acyclic forms without such bonds (a) and the structures where methyl groups are in
an apical position (mea). Our calculations suggest that the molecular geometries of the complexes with
intramolecular O→Si bonds in CDCl are very similar to those in crystal. The acyclic forms of all
3
studied complexes are less stable, as the elongation of the O→Si bond increases the total energy by
–
1
4
–11 kcal mol , both in the gas phase and in CDCl solution (Fig. 6).
3

ACCEPTED MANUSCRIPT
(a)
(b)
(
Figure 6. Relaxed energy scan using the O→Si coordination bond as the coordinate for 1c (a), 2a (b),
c (c), and 3 (d).
c)
(d)
2
The acyclic form of 1c could be detected neither in the gas phase nor in solution. In contrast, the
acyclic forms of other complexes could exist in CDCl but not in isolated molecules. In all cases, the
3
structures with the O→Si coordination and the equatorial methyl group were the most stable while the
–
1
acyclic forms were up to 11 kcal mol less favorable (Fig. 7).
–
1
Figure 7. The energies (kcal mol ) of stationary points and transition states found on the PES of
molecules 1c, 2a, 2c and 3 in the gas phase (left) and in CDCl solution (right). All values are relative
3
to the most stable cyclic isomer.

ACCEPTED MANUSCRIPT
In CDCl , the acyclic forms of 2a and 2c are even less stable than the structures with apical
3
methyl groups. According to our calculations, the formation of mea structures is not possible without
the cleavage of the O→Si coordination bond. The most obvious way to produce a mea structure would
involve the formation of an acyclic form with subsequent rotation around the Si1–C2 bond.
The search for transition states (TS) produced structures that were intermediate between square
pyramid and trigonal bipyramid. The only exception was isolated molecule 3, where the TS was on the
pathway between O1→Si1 and O2→Si1 coordination and had a rather low potential barrier of
–
1
3
.8 kcal mol . However, the use of the PCM model led to a different structure that resembled the TS
of other compounds. In both isolated molecules and CDCl solutions, the imaginary frequencies of all
3
–
1
TS were between 30 and 70 cm . The potential barriers determined by the IRC model for the
interconversion between TS and the structures with O→Si coordination were in the range 11.9–
–
1
–
1
5.8 kcal mol , which is close to the barriers for structurally similar trifluorides (10.2–10.8 kcal mol
1
17
#
–1
)
and the experimental ꢁG 2 values for complexes 1 and 2 (9.6–9.9 kcal mol , Table 2).
98
Therefore, the permutational isomerization in complexes 1 and 2 probably proceeds in a fashion
22,23
similarly to a turnstile rotation
and involves the positional exchange of fluorine atoms with the
retention of the O→Si coordination (Scheme 2).
Scheme 2
F2
N
Si
F1
F
1
Me
O
N
N
F1
Si
Si
Me
TBP(Stationary point)
Me
O
O
F2
Me
F2
N
TBP(Stationary point)
SP (TS)
Si
F1
O
F2
TBP(Stationary point)
Conclusions
New mono-(O→Si)-chelate methyldifluorosilyl derivatives of amides (1), lactams (2) and imide
3) were synthesized and studied by NMR, IR and X-ray methods. All complexes contain a
(
pentacoordinate silicon atom with one apical and one equatorial fluorine atoms (F and F ,
a
e
respectively). According to X-ray data, the Si–F distances in compounds 1c, 2a, 2c and 3 are 0.04–
a
0
.05 Å longer than the Si–F distances.
e
1
9
The temperature dependency observed for NMR F signals of complexes 1 and 2 in solutions is
a result of a permutational isomerization in the coordination environment of silicon. Quantum

ACCEPTED MANUSCRIPT
сhemical сalculations suggest that the most likely mechanism of this isomerization is the positional
exchange of F and F atoms with the retention of the O→Si coordination, which is similar to the
a
e
turnstile rotation mechanism.
Experimental section
IR spectra of compounds in solution and in the solid state were recorded on a Bruker Tensor-27
1
13
19
spectrometer using KBr cells and an APR element, respectively. H, C and F NMR spectra in
1
13
19
CDCl were recorded on a Bruker Avance II 300 ( H, 300 MHz; C, 75.6 MHz; F, 282.2 MHz) and
3
1
13
19
Jeol JNM-EX400 ( H, 400 MHz; C, 100.6 MHz; F, 376.3 MHz) instruments using standard pulse
sequences.
1
13
29
The H, C, Si chemical shifts were measured using Me Si as external reference. Negative
4
values are to high field.
The temperature calibration of the NMR spectrometers was performed by measuring the
differences in chemical shifts between non-equivalent protons in methanol (–90…+30 °C) and
2
4
ethyleneglycol (+30…+85 °C).
The activation parameters of the permutational isomerization were calculated using DNMR-SIM
2
5
19
software and a modified Eyring equation . In each case, at least twelve temperature points were
obtained to achieve a correlation coefficient of 0.997–0.999.
Single crystals suitable for X-ray diffraction analysis were obtained from the following solvents
or mixtures: octane–benzene, 5:2 (1c); octane–benzene, 2:1 (2a); benzene (2c); hexane (3). The details
of crystallographic data and experimental conditions are given in Table 3.

ACCEPTED MANUSCRIPT
Table 3. Crystallographic data for compounds 1c, 2a, 2c, and 3.
1
c
2a
2c
3
Brutto formula
Formula weight
T, K
C H F NOSi
C H F NOSi
C H F NOSi
C H F NO Si
12
17
2
8
15
2
12 13
2
7
11
2
2
257.35
120
207.30
120
253.32
200
207.26
173
Bruker Smart
000
Diffractometer
Bruker APEX II Bruker APEX II
Syntex P21
1
Space group
P2 2 2
Pca21
4
P–1
2
P2 /c
1
1
1
1
Z
4
4
a, Å
b, Å
c, Å
α, °
β, °
γ, °
10.3448(4)
10.9723(5)
11.3822(5)
90
8.9150(6)
18.4947(12)
12.1393(8)
90
5.2373(17)
8.867(3)
12.867(4)
80.33(3)
86.07(3)
82.73(3)
583.6(3)
1.442
12.704(9)
7.435(4)
9.793(6)
90.00
90
90
92.68(5)
90.00
90
90
3
V, Å
1291.95(10)
1.323
2001.5(2)
1.376
2.26
923.9(10)
1.490
–
3
d , g cm
calc
–
1
ꢀ
, cm
F(000)
θmax, °
1.90
2.09
2.53
544
880
264
432
2
63.48
60.66
22206
6170
50
54
Reflections collected
Independent reflections
Independent reflections
18645
4381
3093
2135
2798
2014
4
020
6380
2321
1828
[
I > 2σ(I)]
Parameters
157
237
156
119
R1 [I > 2σ(I)]
0.0336
0.0882
1.029
0.0318
0.0801
1.028
0.0361
0.1126
1.064
0.0335
0.0988
1.064
wR2
GOF
Residual electron density,
0
.332/–0.273
0.279/–0.202
0.437/–0.288
0.447/–0.289
–
3
e⋅Å (ρ /ρmax)
min
2
6
The structures were solved by the direct method using XS software and refined using a full-
2
matrix least-squares technique against F in the anisotropic-isotropic approximation using SHELXL
2
7
software. The hydrogen atoms were placed in geometrically calculated positions and refined using a
rigid body model [U (H) = 1.2U (CH, CH ), U (H) = 1.5U (CH )]. Preparation of graphic
iso
eq
2
iso
eq
3
2
8
materials was performed using OLEX2 software. Crystallographic data for the structural analysis of
c, 2a, 2c and 3 have been deposited with the Cambridge Crystallographic Data Centre (CCDC Nos.
1

ACCEPTED MANUSCRIPT
1834453 – 1834456).
Quantum-chemical calculations of 1c, 2a, 2c and 3 were carried out using Gaussian 03W
2
9
software.
Hybrid PBE0 functional and 6-311G(d,p) basis sets were used for structure optimization,
hessian calculations, relaxed potential energy scans and transition state search. To account for the
effect of nonspecific solvation, the PCM model was applied (using the value of the dielectric constant
for chloroform). All calculations were carried out with tight optimization criteria (Opt=tight) and
precise grid for computation of two-electron integrals (Int(Grid=Ultrafine)). Molecular plots was
3
0
drawn with ChemCraft software.
Optical rotations of compounds were measured in 10 cm cuvettes using a Perkin Elmer 341
instrument.
The starting materials (hexamethyldisilazane, dichloro(chloromethyl)(methyl)silane, boron
trifluoride–diethyl ether complex and 4-methylquinolin-2-one) and solvents were obtained from Acros
and Sigma-Aldrich. The synthesis of (O→Si)-chelate 1-(methyldifluorosilylmethyl)hexahydroazepin-
1
3
16
15
2
-one (2a) and the X-ray structures of difluorides 1b and 2b were published earlier.
6.1. N-Trimethylsilyl (TMS) derivatives
N-TMS-amides and N-TMS-glutarimide were prepared by the reactions of respective NH-
3
1
compounds with chlorotrimethylsilane in the presence of triethylamine or hexamethyldisilazane.
6.1.1. N-TMS-benzamide
3
1
Yield 67%, m. p. 103–106 °C (benzene).
6.1.2. 4-Methyl-N-TMS-quinolin-2-one
Yield 91%, b. p. 152–153 °C (10 mm Hg). Found, %: C 67.60, H 7.40, N 5.89. C H NOSi.
1
3
17
–1
Calculated, %: C 67.49, H 7.41, N 6.05. IR spectrum (CHCl , ν, cm ): 1670 s, 1615 s, 1510 m (C=O).
3
1
NMR H spectrum (acetone-d , δ, ppm): 0.1 s (9H, Si(Me) ), 2.08 s (3H, CH ), 6.42 m (H, CH=), 7.0–
6
3
3
8.1 m (4H, Ar).
6.1.3. N-TMS-glutarimide
2
0
Yield 72%, b. p. 80–82 °C (0.5 mm Hg), nD 1.4728. Found, %: C 51.70; H 8.10; Si 15.00.
–1
C H O NSi. Calculated, %: C 51.85; H 8.15; Si 15.15. IR spectrum (CHCl , ν, cm ): 1670 s, 1720 s
8
15
2
3
1
29
(
C=O). NMR H (CCl , δ, ppm): 0.28 s (Me), 1.85 m (CCH C) 2.42 s (NCH ). NMR Si (CCl , δ,
4 2 2 4
ppm): 13.8.

ACCEPTED MANUSCRIPT
6
.2. (O→Si)-chelate N-methyldifluorosilylmethyl amides
6.2.1. N-(methyldifluorosilylmethyl)benzamide (1a)
A mixture of N-TMS-benzamide (5.0 g, 20 mmol) and dichloro(chloromethyl)(methyl)silane
(
4.24 g, 26 mmol) was heated at 120–140 °C until all chlorotrimethylsilane was distilled off. The
remaining mixture was dissolved in 25 mL of chloroform and stirred with a solution of NaHCO3
4.37 g, 52 mmol) in 50 mL of water for 1 h. The organic layer was separated, the volatiles were
removed in vacuum, and the residue was heated with BF · Et O (2.46 g, 17 mmol) at 100–120 °C for
(
3
2
30 min. The residue was recrystallized from a mixture of o-xylene and octane (3:1) to afford 3.8 g
(
68%) of difluoride 1a with m. p. 98–99 °C. Found, %: C 50.18; H 5.16; Si 12.96. C H F NOSi.
9
11 2
–1
Calculated, %: C 50.21; H 5.15; Si 13.05. IR spectrum (neat solid, ν, cm ): 1580 s, 1603 s (NCO).
1
3
NMR H (CDCl , δ, ppm,): 0.51 br.t (3H, MeSi, J 5.1 Hz), 2.73 m (2H, NCH Si), 7.2 br.s (1H,
3
HF
2
1
3
2
NH), 7.5–7.9 m (5H, C H ). NMR C (CDCl , δ, ppm): 0.42 br.t (MeSi, J 21.8 Hz), 28.54 t (NCH ,
6
5
3
CF
2
2
meta
para
orto
ipso
JCF 30.2 Hz), 127.54 s (C ), 128.61 s (C ), 129.03 s (C ), 133.51 s (C ), 170.45 s (C=O).
1
9
29
1
NMR F (CDCl , δ, ppm): –125.40. NMR Si (CDCl , δ, ppm): –43.54 t ( J 256.9 Hz).
3
3
SiF
6.2.2. N-(methyldifluorosilylmethyl)-N-methylacetamide (1b)
A solution of N-methylacetamide (14.6 g, 0.20 mol), hexamethyldisilazane (12.8 g, 80 mmol)
and dichloro(chloromethyl)(methyl)silane (32.6 g, 0.20 mol) in 100 mL of benzene was refluxed for
h, then cooled down and stirred with a solution of NaHCO (50 g, 0.59 mol) in 200 mL of water
1
3
overnight. The organic layer was separated, dried over anhydrous MgSO and evaporated in vacuum to
4
dryness. The residue was heated with BF · Et O (19.8 g, 0.14 mol) at 100–120 °C for 30 min, then
3
2
distilled in vacuum to afford 9.6 g (29%) of difluoride 1b with b. p. 135–137 °C (4 mm Hg). Found,
: C 35.96; H 6.60; N 8.26. C H F NOSi. Calculated, %: C 35.90; H 6.63; N 8.37. IR spectrum
%
5
11 2
–
1
1
3
(
CHCl , ν, cm ): 1510 s, 1600 s (NCO). NMR H (CDCl , δ, ppm): 0.33 t (3H, MeSi, J 5.1 Hz),
3 3 HF
1
3
2
.17 s (3H, CMe), 3.11 s (3H, NMe), 2.50 br.s (2H, NCH ). NMR C (CDCl , δ, ppm): 0.34 br.t
2 3
2
2
(
MeSi, J Hz), 17.19 s (CMe), 37.36 s (NMe), 37.97 t (NCH , J 29.2 Hz), 173.27 s (C=O). NMR
CF
2
CF
1
9
29
1
F (CDCl , δ, ppm): –124.12. NMR Si (CDCl , δ, pm): –54.71 t ( J 258.1 Hz).
3
3
SiF
6.2.3. N-(methyldifluorosilylmethyl)-N-(1-phenylethyl)acetamide (1c)
2
0
A solution of N-(1-phenylethyl)acetamide (16.3 g, 0.10 mol) {[α]D –124° (c 0.019, CH Cl )},
2
2
hexamethyldisilazane (6.4 g, 40 mmol) and dichloro(chloromethyl)(methyl)silane (16.3 g, 0.10 mol) in
0 mL of benzene was refluxed for 1 h, then cooled down and stirred with a solution of NaHCO3
25 g, 0.29 mol) in 150 mL of water for 1 h. The organic layer was separated, evaporated in vacuum to
dryness and heated with BF · Et O (9.9 g, 70 mmol) at 100–120 °C for 15 min. The residue was
5
(
3
2

ACCEPTED MANUSCRIPT
cooled down and triturated with 50 mL of diethyl ether. The powder formed was recrystallized from
1
5
5
50 mL of benzene to afford 12.4 g (48%) of difluoride 1c with m. p. 128–130 °C (octane–benzene,
2
0
:2), [α]D –26.3° (c 0.021, CH Cl ). Found, %: C 55.87; H 6.65. C H F NOSi. Calculated, %: C
2
2
12 17
2
–
1
1
6.00; H 6.66. IR spectrum (CH Cl , ν, cm ): 1578 s, 1510 m (NCO). NMR H (CDCl , δ, ppm): 0.34
2
2
3
3
3
t (3H, SiMe, J 5.3 Hz), 1.69 d (3H, *C–CH , J 6.7 Hz), 2.33 s (3H, CH CO), 2.14, 2.46 dd (2H,
HF
3
HH
3
2
3
13
NCH , J 17.2 Hz), 5.09 q (1H, *C–CH, J 6.7 Hz), 7.2–7.4 m (5H, C H ). NMR C (CDCl , δ,
2
HH
HH
6
5
3
2
2
ppm): 0.57 t (SiMe, J 23.3 Hz), 17.68 s (CH CH), 17.79 s (CH C(O)), 28.66 t (NCH , J
CF
3
3
2
CF
meta
para
orto
ipso
3
0.5 Hz), 56.13 s (CH), 126.37 s (C ), 128.44 s (C ), 129.18 s (C ), 138.17 s (C ), 172.81 s
1
9
29
(
C=O). NMR F (room temperature, CDCl , δ, ppm): –123.41 br.s. NMR Si (CDCl , δ, ppm): –
3
3
1
5
5.47 t ( J 258 Hz).
SiF
6.2.4. N-(methyldifluorosilylmethyl)-4-methylquinolin-2-one (2c)
Dichloro(chloromethyl)(methyl)silane (4.9 g, 30 mmol) was added dropwise to an ice-cold
solution of 4-methyl-N-TMS-quinolin-2-one (7.0 g, 30 mmol) in 20 mL of CHCl . The reaction
3
mixture was stirred overnight, then diluted with 50 mL of CHCl and stirred with a solution of
3
NaHCO (6.0 g, 70 mmol) in 100 mL of water for 24 h. The organic layer was separated, evaporated in
3
vacuum to dryness and heated with BF · Et O (4.26 g, 30 mmol) at 100–120 °C for 30 min. The
3
2
residue was recrystallised from 100 mL of benzene to afford 3.0 g (39%) of difluoride 2c with m. p.
187–189 °C (benzene). Found, %: C 56.37, H 5.04, N, 5.39. C H F NOSi. Calculated, %: C 56.99, H
12 13 2
–
1
1
5
.17, N 5.53. IR spectrum (CHCl , ν, cm ): 1637 s, 1577 m (NCO). NMR H (CDCl , δ, ppm): 0.46 t
3
3
3
3
6 3
(
3H, MeSi, J 5.35 Hz), 2.66 s (3H, Me), 3.24 s (2H, NCH Si), 6.86 s (1H, H ), 7.92 d (1H, H , J
HF 2 HH
7
3
8
3
9 3
7
.9 Hz), 7.79 t (1H, H , J 7.9 Hz), 7.51 t (1H, H , J 7.9 Hz), 7.68 d (1H, H , J 7.9 Hz). NMR
HH HH HH
1
3
2
2
C (CDCl , δ, ppm): 0.80 t (MeSi, J 23.9 Hz), 19.58 s (Me), 32.01 t (NCH , J 33.2 Hz), 114.34 s
3
CF
2
CF
3
9
4
8
7
6
5
(
C ), 115.42 s (C ), 122.29 s (C ), 124.45 s (C ), 125.77 s (C ), 132.26 s (C ), 137.87 s (C ), 151.96 s
1
0
19
29
(
C ), 162.52 s (C=O). NMR F (room temperature, CDCl , δ, ppm): –121.65 br.s. NMR Si (CDCl ,
3
3
1
δ, ppm): –58.96 t ( J 254.3 Hz).
SiF
6
.3. N-(methyldifluorosilylmethyl)glutarimide (3)
A mixture of N-TMS-glutarimide (7.4 g, 40 mmol) and dichloro(chloromethyl)(methyl)silane
6.25 g, 40 mmol) was heated at 120–140 °C until all chlorotrimethylsilane was distilled off. The
residue was cooled down and stirred with a mixture of 40 mL of chloroform and a solution of NaHCO3
8.0 g, 0.10 mol) in 60 mL of water for 1 h. The organic layer was separated, evaporated in vacuum to
dryness and heated with BF · Et O (3.7 g, 26 mmol) at 100–120 °C for 30 min. The residue was
(
(
3
2
recrystallised from 50 mL of hexane to afford 0.5 g (6%) of difluoride 3 with m. p. 73–75 °C (hexane).

ACCEPTED MANUSCRIPT
Found, %: C 40.51, H 5.26, N 6.74. C H F NO Si. Calculated, %: C 40.56, H 5.35, N 6.75. IR
7
11
2
2
−
1
1
spectrum (CHCl , ν, cm ): 1730 m, 1660 s, 1520 w (NCO). NMR H (CDCl , δ, ppm): 0.45 t (3H,
3
3
3
3,5
4
13
MeSi, J 5.1 Hz), 2.75 br.m (4H, H ), 2.03 m (2H, H ), 2.83 br.s (2H, NCH Si). NMR C (CDCl ,
HF
2
3
2
3,5
4
2
δ, ppm): 0.82 t (MeSi, J 21.6 Hz), 31.19 s (C ), 16.65 s (C ), 27.52 t (NCH , J 26.8 Hz), 173.82
CF
2
CF
1
9
29
1
s (C=O). NMR F (CDCl , δ, ppm): –130.45. NMR Si (CDCl , δ, ppm): –30.22 t ( J 253.4 Hz).
3
3
SiF
Acknowledgment
This work supported by the Russian Foundation for Basic Research (grants Nos 16-03-00957 and
6-03-00984).
1
References
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ACCEPTED MANUSCRIPT
M.A. Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W.
Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03, C.01.
0. G.A. Zhurko, D.A. Zhurko, 2011, Chemcraft Program, Academic version 1.7
1. A.E. Pierce. Silylation of Organic Compounds: A Technique for Gasphase Analysis. Pierce
Chemical Co., Rockford III, Illinois. 1968, 487 pp.
3
3

ACCEPTED MANUSCRIPT
Supporting materials
Table 1s. Principal bond length and angles in isomers of compounds 1c, 2a, 2b and 3 calculated by
PBE0/6-311G(d,p) method/basis combinations
Si1–F1
1.652/1.671 1.622/1.636
n.a. n.a.
Si1–F2
Si1–O1
2.146/2.049
n.a.
Si1–C1
1.858/1.860 172.17/172.69
n.a. n.a.
F1–Si1–O1
1
1
1
2
2
2
2
2
2
3
3
3
c-c
c-a
c-mea
a-c
1.625/1.634 1.621/1.634
1.653/1.672 1.621/1.635
1.619/1.623 1.616/1.620
1.622/1.635 1.622/1.635
1.656/1.674 1.622/1.635
2.192/2.114
2.138/2.044
3.538/3.652
2.179/2.096
2.089/2.012
n.a./3.598
2.116/2.047
1.876/1.881 178.97/179.90
1.858/1.861 172.11/172.80
1.840/1.839 117.59/129.47
1.878/1.883 179.27/179.97
1.858/1.860 171.44/172.26
a-a
a-mea
c-c
c-a
n.a./1.622
n.a./1.615
n.a./1.838
n.a./149.00
c-mea
-c
1.623/1.636 1.623/1.636
1.880/1.884 178.68/179.64
1.637/ 1.653 1.615/ 1.627 2.340/ 2.207 1.851/ 1.853 171.93/ 172.4
-a
n.a./1.615
n.a./1.619
n.a./1.617
n.a./1.620
n.a./3.093
n.a./2.439
n.a./1.842
n.a./1.859
n.a./172.67
n.a./179.21
-mea
a – acyclic isomer
c – cyclic isomer (most stable)
mea – isomer with a methyl group in apical position
n.a. – not available

ACCEPTED MANUSCRIPT
Scheme 1
R'
R
R
C
ClCH SiMeCl2
2
a) RC(O)NSiMe3
C
R'
R'
O
H
2
O
Et
2
O BF
3
O
N
N
Me
Cl
Me
F
NaHCO
3
CH2 Si
CH2 Si
F
(
Me Si) NH
3
2
b) RC(O)NHR'
ClCH
2
SiMeCl
2
Cl
A
1a–c
R = Ph, R' = H (1a); R = R' = Me (1b); R = Me, R' = CH(Ph)Me (1c)
Chart 1
Me
O
O
N
O
Si
O
N
N
O
Si
F
O
Si
F
N
Me
Me
Me
Me
Me
Me
Si
F
F
F
F
F
F
2
a
2b
2c
3
Figure 1. Molecular structure of 1c in ADP ellipsoids at 50% probability.

ACCEPTED MANUSCRIPT
Figure 2. Molecular structure of 2a in ADP ellipsoids at 50% probability.
Figure 3. Molecular structure of 2c in ADP ellipsoids at 50% probability.

ACCEPTED MANUSCRIPT
Figure 4. Molecular structure of 3 in ADP ellipsoids at 50% probability.
1
9
Figure 5. DNMR F spectra of difluoride 1с (Jeol JNM-EX400, CD Cl + CDCl ).
2
2
3
(a)
(b)

ACCEPTED MANUSCRIPT
(
c)
Figure 6. Relaxed energy scan using the O→Si coordination bond as the coordinate for 1c (a),
a (b), 2c (c), and 3 (d).
(d)
2
–
1
Figure 7. The energies (kcal mol ) of stationary points and transition states found on the PES of
molecules 1c, 2a, 2c and 3 in the gas phase (left) and in CDCl solution (right). All values are
3
relative to the most stable cyclic isomer.
Scheme 2
F2
N
Si
F1
F
1
Me
O
N
N
F1
Si
Si
Me
TBP(Stationary point)
Me
O
O
F2
Me
F2
N
TBP(Stationary point)
SP (TS)
Si
F1
O
F2
TBP(Stationary point)