Modelling nucleophilic substitution at silicon using hypervalent silicon compounds based on urea ligands

Article abstract of DOI:10.1016/S0022-328X(00)00562-3

The X-ray crystal structure of a pentacoordinate silicon compound, 3, with a urea ligand shows partial Si-O bond formation and Si-Cl cleavage. The solution NMR parameters for the related series of compounds with different leaving groups provides structura

Full text of DOI:10.1016/S0022-328X(00)00562-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 619 (2001) 132–140
Modelling nucleophilic substitution at silicon using hypervalent
silicon compounds based on urea ligands
Alan R. Bassindale a, Simon J. Glynn a, Peter G. Taylor a,*, Norbert Auner b,
Bernhard Herrschaft b
a The Chemistry Department, The Open Uni6ersity, Walton Hall, Milton Keynes, Buckinghamshire, MK7 6AA, UK
b Institut fu¨r Anorganische Chemie, Johann Wolfgang Goethe Uni6ersita¨t, Marie Curie Strasse 11, D-60439 Frankfurt am Main, Germany
Received 20 April 2000; accepted 3 August 2000
Abstract
The X-ray crystal structure of a pentacoordinate silicon compound, 3, with a urea ligand shows partial Si–O bond formation
and Si–Cl cleavage. The solution NMR parameters for the related series of compounds with different leaving groups provides
structural information and this can be used to model substitution at silicon. The corresponding thioureas exhibit N–Si bond
formation with the silicon remaining tetracoordinate. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Silicon; Pentacoordination; Urea; Crystal structure; Substitution
express the extent of pentacoordination and nucle-
ophile–silicon bond formation as a percentage.
1. Introduction
Our results suggest that irrespective of the nature of
the nucleophile, the position of the adduct on the
structural continuum between tetracoordinate silicon
and pentacoordinate silicon changes in a consistent
fashion with the degree of nucleophile–silicon bond
formation. In terms of the trajectory for substitution at
silicon, the nucleophile–silicon bond is formed at the
expense of the leaving group forming a genuine penta-
coordinate species followed by loss of the leaving
group. A similar conclusion has been reached using
X-ray crystallography [5–8]. It has been shown that in
the solid state the tetrahedral reactants are converted
into a trigonal bipyramidal structure with the non-par-
ticipating groups equatorial. This is followed by rever-
sion to a tetrahedral structure.
We were interested in examining the generality of our
solution technique by applying it to more simple amides
and ureas. In particular we have examined a series of
simple ureas where the % Si–O bond formation can be
calculated from the chemical shift of N-phenyl ring
carbons. In such compounds the 13C chemical shifts of
the ring carbons should depend upon the extent of
O–Si bond formation and, because of aromaticity, this
effect should be efficiently relayed to the more distant
We are interested in the use of NMR spectroscopy to
probe the structure of pentavalent silicon species and to
map the reaction coordinate for substitution at silicon
in solution [1–4]. This involves preparing a series of
structurally similar pentavalent silicon compounds that
provide snapshots of how the geometry around silicon
changes as the extent of formation of one bond to
silicon increases at the expense of another. The extent
of nucleophile–silicon bond formation is calculated
from the chemical shift of other atoms attached to the
nucleophilic atom. Our previous studies have focused
on substituted pyridones and thiopyridones and have
shown that the 13C chemical shifts of the aromatic
carbons change in a concerted fashion as the pyridone
oxygen, nitrogen or sulfur becomes progressively coor-
dinated to the silicon [3,4]. The extent of pentacoordi-
nation at silicon can be calculated from the 29Si
chemical shift. We have employed model compounds to
define the NMR characteristics of the limiting tetraco-
ordinate and pentacoordinate cases, enabling us to
* Corresponding author. Tel.: +44-1908-654859; fax: +44-1908-
655477.
E-mail address: p.g.taylor@open.ac.uk (P.G. Taylor).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00562-3

A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
133
carbons, less prone to other specific interactions at the
2. Results and discussion
reaction centre. However, we would expect smaller
changes in the chemical shifts than in the pyridone
system since the functional group is not part of the
aromatic system.
We have synthesised a number of pentacoordinated
silicon compounds starting from N,N-diethyl-N%-
phenyl-N%-trimethylsilyl urea (1). This was prepared by
reaction of N,N-diethyltrimethylsilylamine with
phenylisocyanate [10]. We found this to be a very
convenient route to N,N%,N%-trialkyl-N-trimethylsilyl
ureas with yields around 80%, and certainly more
straightforward than trimethylsilylation of the corre-
sponding N,N%,N%-trialkyl urea. Reaction of 1 with
chloro(chloromethyl)dimethylsilane or (bromomethyl)-
Voronkov and coworkers have prepared N-
(chlorodimethylsilylmethyl) ureas by reaction of the
N-trimethylsilylurea with chloro(chloromethyl)dime-
thylsilane [9]. They found that transilylation occurred
readily to give the N-chloromethyldimethylsilyl urea.
Unlike the corresponding amides they did not rapidly
rearrange to give the N-alkyl isomer. This was at-
tributed to intermolecular hydrogen bonding between
the NH proton of one urea and the carbonyl oxygen of
another. The N-silyl derivative did rearrange to the
desired N-chloromethyldimethylsilyl urea upon reflux-
ing for 6 h.
chlorodimethylsilane
methyl)-N%,N%-diethyl-N-phenyl urea (3), and N-(bro-
modimethylsilylmethyl)-N%,N%-diethyl-N-phenyl urea
gave
N-(chlorodimethylsilyl-
(4), respectively. The fluoro derivative, 2, and the trifl-
ato derivative, 5, were prepared from 3 using antimony
trifluoride and trimethylsilyltrifluoromethane sulfonate
respectively.
In view of the possible problems associated with
hydrogen bonding we chose to prepare and study the
chelates arising from N,N%,N%-trialkyl-N-trimethylsilyl
ureas.
Monitoring the reaction of 1 with chloro(chloro-
methyl)dimethylsilane or (bromomethyl)chlorodime-
thylsilane using NMR revealed that the reaction was
complete in a matter of minutes with no sign of the
corresponding transilylated or O–CH2 intermediates.
This suggests that N,N%,N%trialkyl-N-trimethylsilyl
ureas are as reactive as amides and lactams, confirming
Voronkov’s conclusion that it is the presence of an
N–H in the urea that leads to a reduced reactivity.
The structure of the N-(chlorodimethylsilylmethyl)-
N%,N%-diethyl-N-phenyl urea was confirmed by X-ray
crystallography. Fig. 1 shows an ORTEP image of one of
the two crystallographically independant molecules 3
and Table 1 gives selected bond lengths and angles. In
the subsequent discussion, values for the second
molecule are in parentheses.
The geometry at the silicon is close to trigonal
bipyramidal with the oxygen and the chlorine in the
apical positions. The equatorial bond angles are be-
tween 117.52(14) and 123.16(12)° (119.38(12) and
120.24(13)°) and the sum of the equatorial angles is
359.70° (359.72°). The axial bond angles range between
83.31(9) and 83.66(9)°, the C2–Si1–O5 bond angle
being limited by the five-membered ring. The Si–O
Fig. 1. Molecular structure of 3. The thermal ellipsoids are drawn at
50% probability. Hydrogen atoms are omitted for clarity.
Table 1
,
Selected bond lengths (A) and angles (°) from the crystal structure of
3 a
,
bond lengths (1.923(2) and 1.937(2) A) clearly show a
high degree of bonding (standard Si–O covalent bond,
Si1–Cl1
Si11–Cl11
Si1–O5
Si11–O3
O5–C4
O15–C14
C4–N3
C14–N13
N3–C2
2.3163(11)
2.3278(10)
1.923(2)
1.937(2)
1.282(3)
1.273(3)
1.338(3)
1.331(3)
1.346(3)
1.362(3)
1.885(3)
1.892(3)
C6–Si1–C7
C16–Si2–C17
C6–Si1–C2
C16–Si2–C12
C7–Si1–C2
C17–Si2–C12
O5–Si1–Cl1
O15–Si2–Cl11
C2–Si1–O5
117.52(14)
120.24(13)
123.16(12)
120.10(12)
119.02(13)
119.38(12)
170.42(6)
171.12(6)
83.66(9)
,
1.68 A [6]). Similarly, the Si–Cl bond lengths
(2.3163(11) and 2.3278(10) A) show some bond break-
ing (standard Si–Cl covalent bond, 2.03 A). The X-ray
crystal structures of a variety of N-(halodimethylsilyl)
ureas, amides and lactams have been published and
Table 2 gives key bond length and bond angle data
[6,11–17]. In this series of structurally similar pentaco-
ordinate species, as the Si–O bond becomes stronger so
the Si–Cl bond becomes weaker. Of the amides, the
acyclic compound 6 has the smallest Si–O bond dis-
,
,
N13–C12
C2–Si1
C12–Si2
C12–Si2–O15
C2–Si1–Cl1
C12–Si2–Cl11
83.31(9)
86.96(8)
87.80(8)
a The data in italics belong to the second molecule in the lattice

134
A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
Table 2
,
Selected bond lengths (A) and angles (°) from the crystal structure of 6–12
,
,
Compound Si–O bond length (A) Si–Cl bond length (A) O–Si–Cl bond angle (°) Reference
29Si chemical shift
Reference
[3]
6
1.918
1.923
1.939
1.950
1.954
1.975
2.050
2.077
2.348
2.316
2.321
2.315
2.307
2.306
2.284
2.229
[11]
−39.9
−42.5
−38.4
−35
−38.5
−38.1
−5.7
3
170.42
171.24
171.70
171.16
170.8
12
11
10
8
[12]
[13]
[14]
[15]
[16]
[17]
[12]
[20]
[20]
[15]
[20]
[21]
9
8
−24.2
Table 3
% Pentacoordination and % Si–O bond formation together with selected chemical shift data for compounds 2, 3, 4 and 5
Compound
29Si
% Pent
13C-iC
13C-oC
13C-mC
13C-pC
% Si–O
13
2
3
4
5
148.6
146.1
143.7
142.2
141.7
141.4
124.5
124.6
125.0
125.2
125.5
125.9
129.2
129.6
130.0
130.2
130.5
130.7
124.3
125.8
127.2
128.0
128.9
129.4
0
29
55
71
87
−19.5
−42.5
−19.5
+16
70
103
73
26
14
100
tance. Inclusion of the amide in a lactam leads to
slightly longer bond length depending upon the size of
the ring [18,19]. Ureas and amides have similar basicity
and, since chelate formation also involves coordination
at the amide or urea oxygen, it is not surprising that the
Si–O and Si–Cl bond lengths are very similar in the
acyclic urea 3 and amide 6. The O–Si–Cl bond angle
has a value of around 171°, which varies little with the
extent of bond formation/breaking. The 29Si chemical
shifts of the chelates are also given in Table 2. The
pentacoordinate amides and ureas all have values
around −40 ppm confirming that in this series of
compounds amides and ureas have a similar nucle-
ophilicity towards silicon.
Unfortunately we were unable to obtain crystal struc-
tures of the other urea derivatives 2, 4 and 5, and we
thus used our solution mapping technique to examine
the structures of these pentacoordinate species. Table 3
gives the relevant 29Si and 13C chemical shift data. As
observed in other series the 29Si chemical shift first
becomes more negative on going from the fluoride to
the chloride then more positive on going to the bromide
and then the triflate. Our interpretation is that as the
leaving group ability increases the silicon first becomes
more pentacoordinate then reverts to a tetrahedral ge-
ometry. Very similar 29Si chemical shifts are observed in
the urea and amide series. For example, the corre-
sponding piperidone compounds [20] have chemical
shifts of −19.6 (F), −38.5 (Cl) and −22.6 (Br) and
the pyridone series has chemical shifts of −22.3 (F),
−41.1 (Cl), −18.4 (Br) and 32.3 (TfO). This again
highlights the similarity between the amides and the
ureas.
The % Si–O bond formation can be calculated by
monitoring the chemical shift of atoms adjacent to the
nucleophile and using model compounds to anchor the
scale to 0 and 100% Si–O bond formation. The nuclei
chosen need to have chemical shifts that are susceptible
to the extent of coordination at oxygen, but not af-
fected by other changes at the reaction centre. The 13C
chemical shifts of the aromatic ring carbons in 2–5
reveal a regular variation on going from fluoro to
chloro to bromo to triflato and were thus used to
determine the % Si–O bond formation. The model
compound used to define 0% Si–O bond formation was
the disiloxane, 13, formed by hydrolysis of the chloro
derivative. Titration of 13 with trimethylsilyl trifl-
uoromethanesulfonate showed a regular variation of
the 13C chemical shift of the aromatic ring carbons,
until 2 mol equivalent had been added. This led to the
formation of the O-silylated adduct, 14, which was used
as the model for 100% Si–O formation. The 13C chem-
ical shift of the aromatic ring carbons of 13 and 14 are
shown in Table 3. The % Si–O bond formation was
calculated using the equation:
Percentage SiꢀO bond formation
(l13C)cmpd−(l13C)
=
0%×100
(l13C)100%−(l13C)0%
Where (l13C)cmpd is the chemical shift of the particu-
lar ring carbon in the compound under study,
(l13C)100% is the chemical shift of the particular ring
carbon in the model compound for 100% Si–O bond
formation, 14, and (l13C)0% is the chemical shift of the

A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
135
approaches the silicon there is first formation of a
pentavalent species followed by loss of the leaving
group and reversion to the tetrahedral compound. Data
for the pyridone series are also included in Fig. 1[3]
and, within experimental error, the two sets of data
overlap, suggesting that irrespective of the nature of the
nucleophilic species, the extent of bond formation is the
primary factor in determining the degree to which the
adduct resembles a fully pentacoordinate silicon.
We also prepared N-(chlorodimethylsilylmethyl)-
N%,N%-dimethyl-N-phenylurea. This had a 29Si chemical
shift of −39.6 ppm corresponding to 99% pentacoordi-
nation. This suggests that changing the alkyl group on
the nitrogen from ethyl to methyl has little effect on the
extent of coordination. This is confirmed by the 13C
chemical shifts of the aromatic ring carbons (C1 143.7
ppm; C2 124.8 ppm; C3 130.2 ppm and C4 127.1 ppm)
which correspond to 53% Si–O bond formation, ex-
tremely close to that of 3.
To extend the series of nucleophiles examined we
tried to synthesise the corresponding thiourea deriva-
tives. The parent N,N-diethyl-N%-methyl-N%-trimethyl-
silyl thiourea was prepared by the reaction of
N,N-diethyltrimethylsilylamine with methyl isothio-
cyanate, however, in this case heating was required.
NMR spectroscopy shows that the N-trimethylsilylated
species predominates although a small amount of the
S-trimethylsilylated species may be present. Unlike the
corresponding urea derivative, the reaction of
chloro(chloromethyl)dimethylsilane with N,N-diethyl-
N%-methyl-N%-trimethylsilyl thiourea required heating at
50°C for 2 days. The spectra of the product revealed a
S–CH2 linkage, corresponding to structure 15. The 29Si
chemical shift was at 41 ppm suggesting a completely
tetrahedral silicon with little if any Si–Cl interaction.
This was confirmed by reaction of the thiourea with
particular ring carbon in the model compound for 0%
Si–O bond formation, 13. For each compound this
gave four values for the % Si–O bond formation (one
for each carbon environment), thus, the values were
averaged to give the values shown in Table 3. As
expected the % Si–O bond formation increased with
leaving group ability and had very similar values to the
pentacoordinate silicon complexes formed with pyri-
done (30% (F), 50% (Cl), 70% (Br) and 90% (OTf)).
This method gives an approximate bond order of 0.55
for the Si–O bond in 4, which compares well with the
Pauling Si–O bond order of 0.56 derived from the
crystal structure [6,22].
A knowledge of the % Si–O bond formation enables
the percentage pentacoordination to be determined,
that is the relative position of the adduct on the struc-
tural continuum between a tetracoordinate tetrahedral
silicon (0%) and a fully pentacoordinate trigonal
bipyramidal silicon (100%). As with the pyridone series,
if the compound exhibits a % Si–O bond formation
between 0 and 50%, the extent of pentacoordination
was calculated using 29Si chemical shifts of +28 and
−40 ppm for 0% and 100% pentacoordination respec-
tively. The value of +28 ppm corresponds to that of a
trimethylhalosilane (92 ppm) and the value of −40
ppm reflects that observed in many fully pentacoordi-
nate silicon species [3]. For compounds that exhibited a
% Si–O bond formation between 50 and 100%, the
extent of pentacoordination was calculated using 29Si
chemical shifts of −40 and +36 ppm for 100% and
0% pentacoordination respectively. In this case, the
value of +36 reflects that of a O-trimethylsilylated
N-alkyl-2-hydroxypyridine [3]. The percentage pentaco-
ordinations of compounds 2–5 are given in Table 3 and
plotted against the % Si–O bond formation in Fig. 2.
The data cover the full range of nucleophile–silicon
bond formation and exhibit the same pattern as ob-
served previously. As a model for the pathway for
substitution at silicon it confirms that as the nucleophile
bromo(bromomethyl)dimethylsilane which gave
a
product with almost identical spectra to that of 15. An
unusually high 29Si chemical shift of 44 ppm was again
obtained suggesting an essentially ionic structure.
The change in regiochemistry from O–Si to N–Si is
not unexpected, the reaction of chloro(chloromethyl)-
dimethylsilane with thiolactams leads to structures of
the type 16 rather than the N-alkyl species [23,24].
Similarly, in the thiopyridone series we have observed
that reaction of the thiopyridone with chloro(chloro-
methyl)dimethylsilane leads to compounds of the type
17 [4]. However, when a 6-methyl substituent is present
in the thiopyridine, N-alkylation with S–Si coordina-
tion is observed as a result of steric factors. The 29Si
chemical shifts of 16 (n=1) and 17 are −38.1 ppm and
−19.4 ppm respectively, demonstrating substantial
pentacoordination [23]. Extensive pentacoordination is
also demonstrated in the X-ray crystal structure of 16
which shows it to be a distorted trigonal bipyramid
where the Si–N and Si–Cl bond lengths are
Fig. 2. Plot of % pentacoordination versus % Si–O bond formation.

136
A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
,
1.95 and 2.42 A respectively [24]. This suggests that the
nitrogen in the thiourea is much more nucleophilic than
that in the thiolactams and thiopyridones, since no
Si–Cl coordination is observed in 15. This is borne out
by the extent of N–Si bond formation which appears to
be 100% in 15 but only only 36% in 17.
and Si–Cl bond lengths in compound 18 are 1.90 and
,
2.60 A respectively, whereas the Si–O and Si–Cl bond
lengths in the 2-quinolinone analogue, 12, are 1.94 and
,
2.32 A respectively [25]. However, in all these cases
pentacoordination is still observed with sp2 nitrogens,
unlike compound 15. Kummer has reported the crystal
structure of the aminopyridine derivative 21, which
involves coordination of an sp2 nitrogen to a silicon.
This is essentially ionic and has a 29Si chemical shift of
19.0 ppm [28]. However, the crystal structure and vari-
able temperature NMR studies suggest that hydrogen
bonding between the chloride ions and the NH group
play an important part in stabilising the ionic structure.
No such stabilisation by hydrogen bonding is possible
in 15.
The crystal structures have been reported of a num-
ber of pentavalent alkylchlorosilicon compounds in-
volving an sp2 nitrogen as the donor atom in a five
membered ring, 18 [25], 19 [26] and 20 [27]. Examina-
tion of the silicon–nitrogen bond lengths and the sili-
con–chlorine bond lengths suggests that an sp2
nitrogen has a similar, if not greater, nucleophilicity
than that of an sp2 oxygen. For example, The Si–N

A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
137
One possible explanation of this behaviour is that the
3. Conclusions
donor nitrogen in 15 can easily convert from sp2 to sp3
hybridisation with concomitant formation of a full
covalent Si–N bond and rotation of the alkyl group
out of the plane of the urea, thus relieving steric strain
between the methyl group and the adjacent ethyl group.
The resulting charge is then largely delocalised between
the sulfur and uncoordinated nitrogen. Such a conver-
sion from sp2 to sp3 does not occur for the coordinating
nitrogen in 18 since this would involve localisation of
the charge onto only one electronegative centre. In 19
such a change would lead to loss of aromaticity. A
conversion from sp2 to sp3 hybridisation is possible
with 20 with delocalisation of the charge onto the
adjacent two nitrogens, however, relief of steric strain is
not so great with ring systems and the positive charge
may not be stabilised as well by two nitrogens as by a
sulfur and a nitrogen. Conversion of the oxygen to an
sp3 species in the series 2–5 is not favoured because the
oxygen would no longer be available for delocalisation
of the charge and there is no steric relief, the alkyl
groups remaining in the plane of the urea.
Our results suggest that trisubstituted ureas readily
form pentacoordinate silicon compounds involving Si–
O coordination. The variation of structure with leaving
group is similar to that obtained with the amide series,
providing a consistent model for substitution at silicon.
However, the thiourea derivatives involve N–Si bond
formation with no pentacoordination at silicon. This is
probably due to the donor nitrogen changing its coordi-
nation from sp2 to sp3 hybridisation.
4. Experimental
Melting points were determined on a Buchi 510
melting point apparatus and are uncorrected. Infrared
spectra were obtained as Nujol mulls or thin films using
sodium chloride plates or as KBr discs on a Pye
Unicam SP1050 or a Nicolet 205 FT-IR spectrometer.
NMR spectra were recorded as solutions in deuteri-

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A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
ochloroform with tetramethylsilane as internal standard
on a Jeol FX 90Q or a JEOL EX 400 NMR spectrom-
eter (J values are given in Hz). Mass spectra were
obtained using a Cresta MS 30 instrument or a VG20-
250 quadrupole instrument.
40 mA, tube power 2.00 kW, temperature 120 K,
detector distance 80 mm, resolution 3.8°BqB56.3°,
„-rotation angle 220.8°, „-rotation increment 2.3°,
frames 96, exposure 2.5 min/frame, duration 11 h,
recorded reflections 23410/5243 (independent 5173,
Rmerge 0.1340). The raw intensity data were corrected
for Lorentz and polarization effects, no attempts were
made to correct for absorption. Structure solutions
were searched and refined by direct methods [30]
4.1. N,N-Diethyl-N%-phenyl-N%-trimethylsilyl urea (1)
N,N-Diethyl trimethylsilylamine (2.9 g, 3.8 ml, 20
mmol) was cooled in an ice bath. Phenyl isocyanate (2.4
g, 2.2 ml, 20 mmol) was then added slowly over 5 min
with vigorous stirring. The mixture was allowed to
warm to room temperature and then stirred for 3 h.
The yellow crude product was purified by distillation
under reduced pressure to give 4.2 g (79%) of N,N-di-
ethyl-N%-phenyl-N%-trimethylsilyl urea, as a colourless
liquid; b.p. 100°C/0.1 mm Hg; wmax (cm−1) 2970, 1632,
1592, 1251 and 847; lH (400 MHz, CDCl3, Me4Si) 0.17
(
SHELXS 97-2) and difference Fourier analyses (SHELXL
97-2) [30], respectivly based on F2. Atom form factors
for neutral atoms were taken from the literature [31].
Second and third row elements were allowed to refine
anisotropically; hydrogen atoms were assumed in ideal-
ized positions riding on their pivot atoms.
4.4. Structure analysis of 3
3
(9H, s, Si(CH3)3), 0.83 (6H, t, J 7.1, CH3), 3.10 (4H, q,
Mf=365.4, crystal dimensions 0.80×0.60×0.60
mm3, space group P(21/n) (no.14), a=18.890(3), b=
3J 7.1, NCH2) and 6.85–7.45 (5H, m, arom); lC (100
MHz, CDCl3, Me4Si) 0.4 (Si(CH3)3), 12.5 (CH3), 42.0
(NCH2), 124.5 (Ph), 127.3 (Ph), 128.8 (Ph), 144.2 (Ph)
and 161.1 (CꢁO); lSi (17.8 MHz, CDCl3, Me4Si) 9.5.
,
9.753(2), c=19.306(3) A, h=114.296(12)°, V=
3
3242.0(9) A , zcalc=1.225 g cm−3, Z=8, F000=1280,
,
v=0.261 mm−1, 5243 reflections (Rint=0.000), 344
parameter, ratio 15.24, R1=0.0530, wR2=0.1492 (I\
4.2. N-(Chlorodimethylsilylmethyl)-N%,N%-diethyl
-N-phenyl urea (3)
2|I), R1=0.0590, wR2=0.1588 (all data), GoF=
−3
,
1.139; residual electron density 0.514 e A
(max.).
N,N-Diethyl-N%-phenyl-N%-trimethylsilyl urea (1.0 g,
3.8 mmol) was placed in a dry flask under nitrogen.
Dry ether (5 ml) was then added, followed by
(chloromethyl)dimethylsilane (0.54 g, 3.8 mmol) and
the flask was agitated to mix the reactants. After 2 h,
the ether was removed gradually by placing the flask
under vacuum until the product was observed to crys-
tallise. The remaining ether was then removed via a
syringe. The product was dried under vacuum and
transferred to a dry box for storage; wmax (cm−1) 2975,
1570. 1510, 1255, 1229 and 848; lH (400 MHz, CDCl3,
4.5. N-(Bromodimethylsilylmethyl)-N%,N%-diethyl-
N-phenyl urea (4)
N,N-Diethyl-N%-phenyl-N%-trimethylsilyl urea (1.0
g,3.8 mmol) was placed in a flask under nitrogen and
dry ether (5 ml) was added. (Bromomethyl)dimethyl-
chlorosilane (0.71 g, 3.8 mmol) was then added and the
flask agitated briefly. After 2 h, a precipitate had
formed. The ether was removed and the precipitate
washed with further dry ether and then dried under
vacuum. The N-(bromodimethylsilylmethyl)-N%,N%-di-
ethyl-N-phenyl urea was then transferred to a dry box
for storage; wmax (cm−1) 2975, 1576, 1506, 1255, 1228,
910 and.850; lH (400 MHz, CDCl3, Me4Si) 0.83 (6H, s,
3
Me4Si) 0.67 (6H, s, Si(CH3)2), 0.95 (6H, t, J 7.0, CH3),
3
3.07 (4H, q, J 7.0, NCH2), 3.26 (2H, s, NCH2Si) and
6.8–7.5 (5H, m, arom); lC (100 MHz, CDCl3, Me4Si),
7.4 (Si(CH3)2), 12.8 (CH3), 43.6 (NCH2), 50.2
(NCH2Si), 125.0 (Ph), 127.2 (Ph), 130.0 (Ph), 143.7 (Ph)
and 161.5 (CꢁO); lSi (17.8 MHz, CDCl3, Me4Si)
−42.1; m/z (EI) 298 (M+), 283 (M+−Me), 269 (M+
−Et) and 263 (M+−Cl). Anal. Found: C 55.97, H
7.70, N 9.29. C14H23N2OSiCl requires: C 56.26, H 7.76,
N 9.37%.
3
3
Si(CH3)2), 0.99 (6H, t, J 7.1, CH3), 3.13 (4H, q, J 7.1,
NCH2), 3.52 (2H, s, NCH2Si) and 7.0–7.5 (5H, m,
arom); lC (100 MHz, CDCl3, Me4Si) 6.7 (Si(CH3)2),
12.8 (CH3), 44.1 (NCH2), 51.4 (NCH2 Si), 125.2 (Ph),
128.0 (Ph), 130.2 (Ph), 142.2 (Ph) and 160.8 (CꢁO); lSi
(17.8 MHz, CDCl3, Me4Si) −19.5; m/z (EI) 344 (M+),
315 (M+−Et), 263 (M+−Br). Anal. Found: C 49.32,
H 6.89, N 8.13. C14H23N2OSiBr requires: C 48.98, H
6.75, N 8.16%.
4.3. X-ray crystallographic study
Compound 3 was measured on a one-circle diffrac-
tometer equipped with an imaging plate system as
detector (IPDS 2.75) [29]. Graphite monochromated
4.6. N,N-Diethyl-N%-phenyl-N%-(trifluoromethylsul-
fonatodimethysilylmethyl) urea (5)
,
Mo–Ka radiation (u=0.71073 A) was used. The data
collection was performed in a „-rotation mode (50 kV,
To a solution of N,N-diethyl-N%-phenyl-N%-trimethyl-
silyl urea (0.5 g, 1.67 mmol) in dry ether (3 ml) was

A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
139
added trimethylsilyltrifluoromethylsulfonate (0.37 g,
1.67 mmol). A precipitate formed almost immediately.
The solvent was removed and the precipitate washed
with further dry ether, after which it was dried under
vacuum and tranferred to a dry box; wmax (cm−1) 2975,
1577, 1509, 1235, 1030 and 845; lH (400 MHz, CDCl3,
2971, 1634 1597, 1253, 1053 and 842; lH (400 MHz,
CDCl3, Me4Si) 0.15 (6H, s, Si(CH3)2), 0.89 (6H, t, J
3
7.1, CH3), 3.07 (4H, q, 3J 7.1, NCH2), 3.07 (2H, s,
NCH2Si) and 6.9–7.3 (5H, m, arom); lC (100 MHz,
CDCl3, Me4Si) 0.9 (Si(CH3)2), 12.8 (CH3), 42.0
(NCH2), 46.1 (NCH2Si), 124.3 (Ph), 124.5 (Ph), 129.2
(Ph) and 148.6 (Ph); lSi (17.8 MHz, CDCl3, Me4Si) 4.5;
m/z (EI) 527 (M+−Me), 337 (M+−Et2NCON-
PhCH2) and 263 (M+−Et2NCONPhCH2SiMe2O).
Anal. Found: C 61.55, H 8.55, N 10.37. C28H46N4O3Si2
requires: C 61.95, H 8.54, N 10.32%.
3
Me4Si) 0.60 (6H, s, Si(CH3)2), 0.95 (6H, t, J 7.1, CH3),
3
3.11 (4H, q, J 7.1, NCH2), 3.38 (2H, s, NCH2Si) and
7.0–7.5 (5H, m, arom); lC (100 MHz, CDCl3, Me4Si)
0.0 (Si(CH3)2), 12.6 (CH3), 44.6 (NCH2), 47.9
(NCH2Si), 120.5 (q, 1JC–F 319.2, CF3), 125.5 (Ph), 128.9
(Ph), 130.5 (Ph), 141.7 (Ph) and 160.3 (CꢁO); lF (90
MHz, CDCl3, Me4Si) −80.1; lSi (17.8 MHz, CDCl3,
Me4Si) 16.5; m/z (EI) 412 (M+), 397 (M+−Me), 383
(M+−Et), 263 (M+−OSO2CF3). Anal. Found: C
43.20, H 5.49, N 6.78. C15H23N2O4SSiF3 requires: C
43.67, H 5.62, N 6.79%.
4.9. N-(Chlorodimethylsilylmethyl)-N%,N%-
dimethyl-N-phenyl urea
N,N-Dimethyl-N%-phenyl urea (4.1 g, 25 mmol) and
hexamethyldisilazane (1.6 g, 10 mmol) were dissolved in
dry
benzene
(35
ml).
Chloro(chloromethyl)-
4.7. N,N-Diethyl-N-( fluorodimethylsilylmethyl)-
N%-phenyl urea (2)
dimethylsilane (3.5 g, 25 mmol) was then added with
stirring, and the reaction mixture was refluxed for 2 h.
After cooling the resulting precipitate was removed by
filtration, and removal of the solvent under vacuum
gave N-(chlorodimethylsilyl) N%,N%-diethyl-N-phenyl
urea in a yield of 5.5 g (81%), wmax (cm−1) 2986, 1600,
1518, 1415, 1257, 837, 720 and 697; lH (400 MHz,
CDCl3, Me4Si) 0.60 (6H, s, Si(CH3)2), 2.63 (6H, s,
NCH3), 3.25 (2H, s, NCH2) and 6.9–7.4 (5H, m, arom);
lC (100 MHz, CDCl3, Me4Si) 7.8 (Si(CH3)2), 39.7
(NCH3), 50.1 (NCH2), 124.8 (Ph), 127.1 (Ph), 128.7
(Ph), 130.2 (Ph), 143.7 (Ph) and 161.9 (CꢁO); lSi (17.8
MHz, CDCl3, Me4Si) −39.6; m/z (EI) 270 (M+), 255
(M+−Me), 235 (M+−Cl) and 198 (M+−Me2N–
CꢁO). Anal. Found: C 53.49, H 6.92, N 10.49.
C12H19N2OSiCl requires: C 53.22, H 7.07, N 10.34%.
N - (Chlorodimethylsilylmethyl) - N%,N% - diethyl - N-
phenyl urea (0.5 g, 1.67 mmol) was dissolved in dry
benzene (5 ml). Antimony trifluoride (0. 10g, 0.56
mmol) was then added and the mixture stirred for 3 h,
during which time it became warm. Water (30 ml) was
then added and the solution extracted with chloroform
(3×50 ml). The combined organic extracts were dried
over magnesium sulfate, filtered and the solvent re-
moved to give the N,N-diethyl-N%-(fluorodimethylsilyl-
methyl)-N%-phenyl urea as a yellow liquid in a yield of
0.4 g (84%); wmax (cm−1) 2976, 1592, 1496, 1254, 1233
3
and 835; lH (400 MHz, CDCl3, Me4Si) 0.23 (6H, d, J
3
7.8, Si(CH3)2), 0.82 (6H, t, J 7.0, CH3), 2.80 (2H, s,
3
NCH2Si), 2.93 (4H, q, J 7.0, NCH2) and 6.9, 7.3 (5H,
2
m, arom); lC (100 MHz, CDCl3, Me4Si) 1.7 (d, JC–Si–F
4.10. N,N-Diethyl-N%-methyl-N%-trimethylsilyl
thiourea
4
24.8, Si(CH3)2), 12.8 (CH3), 43.0 (NCH2), 45.3 (d, J
44.3, NCH2Si), 124.6 (Ph), 125.8 (Ph), 129.6 (Ph), 146.1
(Ph) and 161.9 (CꢁO); lF (90 MHz, CDCl3, Me4Si)
Methyl isothiocyanate (0.73 g 10 mmol) was added to
N,N-diethyltrimethylsilylamine (1.45 g, 10 mmol) and
the mixture stirred at 100°C for 4 h. Vacuum distilla-
tion of the crude product gave N,N-diethyl-N%-methyl-
N%-trimethylsilyl urea as a pale yellow liquid (1.95 g,
85.5%), b.p. 95°C/0 05 mm Hg; wmax (cm−1) 2971, 1482,
1408, 1315, 1258, 1126 and 847; lH (400 MHz, CDCl3,
3
−120.5 (septet, J 7.8); lSi (17.8 MHz, CDCl3, Me4Si)
1
−19.5 (d, JSi–F 258.8); m/z (EI) 282 (M+), 267 (M+
−Me), 263 (M+−F), 253 (M+−Et). Anal. Found: C
59.21, H 8.01, N 9.98. C14H23N2OSiF requires: C 59.54,
H 8.21, N 9.91%.
3
4.8. 1,3-Bis(2,4-diaza-4,4-diethyl-3-oxo-2-
phenylbutyl)-1,1,3,3-tetramethyldisiloxane (13)
Me4Si) 0.32 (9H, s, Si(CH3)3), 1.20 (6H, t, J 6.6, CH3),
3
2.92 (3H, s, NCH3) and 3.78 (4H, q, J 6.6, NCH2); lC
(100 MHz, CDCl3, Me4Si) −0.4 (Si(CH3)3), 12.3
(CH3), 37.9 (NCH3), 46.1 (NCH2) and 196.0 (CꢁS); lSi
(17.8 MHz, CDCl3, Me4Si) 11.6.
N - (Chlorodimethylsilylmethyl) - N%,N% - diethyl - N-
phenyl urea (0.5 g, 1.67 mmol) was dissolved in chloro-
form (5 ml). Water (5 ml) was then added and the
mixture stirred overnight. The organic layer was sepa-
rated and the aqueous layer extracted with further
chloroform (3×10 ml). The chloroform extracts were
combined, dried over magnesium sulfate, filtered and
4.11. S-(Chlorodimethylsilylmethyl)-N,N-diethyl-N%-
methyl isothiourea (15)
N,N-Diethyl-N%-methyl-N%-trimethylsilyl
thiourea
the solvent removed to give the disiloxane; wmax (cm−1
)
(0.50 g, 2.3 mmol) was dissolved in deuterated chloro-

140
A.R. Bassindale et al. / Journal of Organometallic Chemistry 619 (2001) 132–140
Trans. 1 (2000) 1059.
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form (2 ml) in a 10 mm NMR tube. Chloro(chloro-
methyl)dimethylsilane (0.33 g. 2.3 mmol) was added
and the mixture kept at 50°C. Monitoring using 29Si-
NMR revealed that after 2 days reaction was complete.
The solution was transferred to a flask and the solvent
removed to give the product. wmax (cm−1) 2977,
1572,1360, 1261,929, 839 and 724; lH (400 MHz,
[6] A.A. Macharashvili, V.E. Shklover, Yu.T. Struchkov, G.I.
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Soc. Chem. Commun. (1988) 683.
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Shipov, Yu.I. Baukov, J. Struct. Chem. 35 (1994) 91.
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V.A. Pestunovich, Bull. Acad. Sci. USSR Div. Chem. Sci. 12
(1989) 2604.
[10] G. Oertel, M. Motz, H. Holtschmidt, Ber. 97 (1964) 891.
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Chem. Soc. Chem. Commun. (1978) 209.
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Herrschaft, in press.
[13] A.A. Macharashvili, V.E. Shklover, Yu.T. Struchkov, V.A. Pes-
tunovich, Yu.I. Baukov, E.P. Kramarova, G.I. Oleneva, Zh.
Strukt. Khim. 29 (1988) 121.
[14] A.A. Macharashvili, Yu.I. Baukov, E.P. Kramarova, G.I.
Oleneva, V.A. Pestunovich, Yu.T. Struchkov, V.E. Shklover, J.
Struct. Chem. 28 (1986) 730.
[15] Yu.I. Baukov, Yu.E. Ovchinnikov, A.G. Shipov, E.P. Kra-
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Chem. 536 (1997) 399.
[16] O.B. Artamkina, E.P. Kramarova, A.G. Shipov, Yu.I. Baukov,
A.A. Macharashvili, Yu.E. Ovchinnikov, Y.T. Struchkov, Zh.
Obshch. Khim. 64 (1994) 263.
3
CDCl3, Me4Si) 0.75 (6H, s, Si(CH3)2), 1.38 (6H, t, J
6.5, CH3), 2.65 (2H, s, SCH2), 3.38 (3H, s, NCH3) and
3.79 (4H, q, 3J 6.5, NCH2); lC (100 MHz, CDCl3,
Me4Si) −0.8 (Si(CH3)2), 11.6 (CH3), 13.6 (SCH2), 35.9
(NCH3), 48.7 (NCH2) and 77.0 (CꢁS); lSi (17.8 MHz,
CDCl3, Me4Si) 41.4; m/z (EI) 255, 253 (MH+) and 217
(M+−Cl). Anal. Found: C 42.52, H 8.20, N 10.79.
C9H21N2SSi requires: C 42.78, H 8.38, N 11.08%.
4.12. S-(Bromodimethylsilylmethyl)-N,N-diethyl-
N%-methyl isothiourea
N,N-Diethyl-N%-methyl-N%-trimethylsilyl
thiourea
(0.50 g, 2.3 mmol) was dissolved in deuterated chloro-
form (2 ml) in a 10 mm NMR tube. (bromomethyl)-
chlorodimethylsilane (0.33 g. 2.3 mmol) was added and
the mixture kept at 50°C. Monitoring using 29Si-NMR
revealed that after 3 h reaction was complete: wmax
(cm−1) 2978, 2176, 1570, 1357, 1261, 924, 829 and 728;
lH (400 MHz, CDCl3, Me4Si) 0.76 (3H, s, Si(CH3)2),
[17] A.A. Macharashvili, V.E. Shklover, Yu.T. Struchkov, M.G.
Voronkov, B.A. Gostevskii, I.D. Kalikhman, O.B. Bannikova,
V.A. Pestunovich, Metalloorg. Khim. 1 (1988) 1131.
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M.Y. Antipin, Y.T. Struchkov, Metalloorg. Khim. 5 (1992) 666.
[19] D. Kost, I. Kalikhman, in: Z. Rappoport, Y. Apeloig (Eds.),
The Chemistry of Organosilicon compounds, vol. 2, Wiley, New
York, 1998, Chapter 23, pp. 1339–1445.
3
1.39 (6H, t, J 7.1, CH3), 2.67 (3H, s, SCH2), 3.39 (311,
s, NCH3) and 3.81 (4H, q, 3J 7.1, NCH2); lC (100
MHz, CDCl3, Me4Si) −1.0 (Si(CH3)2), 11.5 (CH3),
13.6 (SCH2), 36.4 (NCH3), 48.9 (NCH2) and 177.3
(CꢁS); lSi (17.8 MHz, CDCl3, Me4Si) 44.4; m/z (EI)
299, 297 (MH+) and 217 (M+−Me).
[20] M.G. Voronkov, V.A. Pestunovich, Yu.I. Baukov, Metallorgan.
Khim. 4 (1991) 1210.
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Zh. Obsch. Khim. 58 (1988) 407.
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Khim. 1 (1988) 127.
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Sergeev, S.V. Pestunovich, Yu.I. Baukov, Russ. Chem. Bull. 42
(1993) 173.
[25] D. Kummer, S.C. Chaudhry, J. Seifart, B. Deppisch, G. Mat-
tern, J. Organomet. Chem. 382 (1990) 345.
5. Supplementary material
The crystal structure of 3 has been deposited with the
Cambridge Crystallographic Data Centre, CCDC no.
140097. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-
336033; e-mail: deposit@ccdc.cam.ac.uk or www: http:
//www.ccdc.cam.ac.uk).
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(1985) 1.
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[28] D. Kummer, S.H. Abdel Halim, W. Kuhs, G. Mattern, Z.
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