Hypercoordinate silicon complexes of (O,N,N′ vs. O,N,O') schiff base type N-(2-Carbamidophenyl)imines: Examples of exclusively O-Silylated carbamides

Article abstract of DOI:10.1002/ejic.200801176

Tridentate salphen-type O,N,N′ chelators, upon acylation of the NH₂ group, are capable of engaging an O,N,O' coordination mode in addition to their inherent O,N,N′ donor character. In six-coordinate silicon complexes of the type SiL₂

Full text of DOI:10.1002/ejic.200801176

FULL PAPER
DOI: 10.1002/ejic.200801176
Hypercoordinate Silicon Complexes of (O,N,NЈ vs. O,N,OЈ) Schiff Base Type
N-(2-Carbamidophenyl)imines: Examples of Exclusively O-Silylated
Carbamides
Alexander Kämpfe,[a] Edwin Kroke,[a] and Jörg Wagler*[a]
Keywords: Chelates / Coordination modes / Tridentate ligands / Silicon
Tridentate salphen-type O,N,NЈ chelators, upon acylation of
the NH2 group, are capable of engaging an O,N,OЈ coordina-
tion mode in addition to their inherent O,N,NЈ donor charac-
ter. In six-coordinate silicon complexes of the type SiL2 [L =
N-(2-carbamidophenyl)imine], these ligands were found to
exclusively form SiN2O4 coordination spheres by engaging
their tridentate O,N,OЈ donor capability. Selected ligands L
were also shown to preferably engage the O,N,OЈ coordina-
tion mode when incorporated in five- and four-coordinate
silicon compounds of the type LSiPhX (X = Cl, F) and LSiPh2,
respectively. The coordination modes of the herein presented
six-, five-, and four-coordinate silicon compounds represent
the first examples of X-ray structurally confirmed O-silylated
carbamides, which hence adopt structural features of C-sil-
oxyimines.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
Introduction
Results and Discussion
The class of hypercoordinate silicon complexes[1] com-
Tridentate salphen-type ligands such as 1a–c (Scheme 2)
prises a great variety of such bearing bi-, tri-, and tetra- are accessible from o-phenylenediamine and an o-hy-
dentate chelating ligands. Although a wide range of oligo- droxyphenyl ketone (or aldehyde) in a 1:1 molar ratio.[4]
dentate chelators with O, N, and C donor sites has already The anilino group of these ligands allows further modifica-
been explored,[2] the group of tridentate (O,N,N) donor li- tion, that is, acylation. Thus, three such ligands (1a–c) were
gands has apparently missed the entrance into silicon coor- synthesized and N-acylated to afford ligands 2a–f as a start-
dination chemistry, and thus they come into focus for our ing point for our study (Scheme 2). 1H and 13C NMR spec-
further investigations.[3] Surprisingly, in a preliminary study, tra revealed the existence of only one isomer (the o-iminom-
an N-acylated salphen-type ligand revealed extraordinary ethylphenol) in solution. Furthermore, single-crystal X-ray
behavior when attached to a diphenylsilicon moiety. The analyses of 2a, 2b, 2d, and 2e (Figure 1) confirm the exis-
initial O,N,N chelator underwent isomerization to yield a tence of the o-iminomethylphenol isomer in the solid state
benzimidazoline backbone of a now Si-bound bidentate also (well in accord with the molecular structure of a related
(O,N) chelator (Scheme 1).[3a] This finding tempted us to N-acetylated compound[3a]).
further explore silicon compounds of N-acylated Schiff base
type o-iminomethylphenols.
Scheme 1. Benzimidazoline formation upon silylation.
[a] Institut für Anorganische Chemie, Technische Universität
Bergakademie Freiberg,
09596 Freiberg, Germany
Fax: +49-3731-39-4058
E-mail: joerg.wagler@chemie.tu-freiberg.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 2. Syntheses of N-acylated salphen ligands.
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A. Kämpfe, E. Kroke, J. Wagler
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Figure 1. Molecular structures of 2d (left) and 2e (right). Thermal
ellipsoids with 50% probability, C-bound H-atoms omitted, se-
lected atoms labeled. Selected bond lengths [Å] for 2d: O1–C1
1.362(2), O2–C15 1.229(2), N1–C7 1.301(2), N2–C15 1.371(2); for
2e: O1–C1 1.355(1), O2–C14 1.223(1), N1–C7 1.286(1), N2–C14
1.366(1). The molecular structures of 2a and 2b (not depicted) exhi-
bit similar features of the iminomethylphenol and the carbamide
moieties.
Figure 2. Molecular structure of 3c in a crystal of 3c·(CHCl3)2.
Thermal ellipsoids with 50% probability, hydrogen atoms and chlo-
roform molecules omitted for clarity, selected atoms labeled.
Table 2. Selected bond lengths [Å] of compounds 3a, 3c, 3d, and
3f.
Reaction of ligands 2a–f with SiCl4 in a 2:1 molar ratio
(in the presence of triethylamine as supporting base) deliv-
ered hexacoordinate silicon complexes 3a–f (Scheme 3) as
pale-yellow solids, all of which exhibited poor solubility in
chloroform and dimethyl sulfoxide. In order to confirm the
hexacoordination of the Si atoms in each of these com-
plexes, 29Si CP/MAS NMR spectra were recorded (Table 1).
a
b
c
d
e
f
3a 1.734(2) 1.757(2) 1.908(3) 1.322(4) 1.328(4) 1.283(4)
1.736(2) 1.762(2) 1.915(3) 1.310(4) 1.330(4) 1.279(4)
3c 1.732(1) 1.748(1) 1.918(1) 1.309(1) 1.325(1) 1.287(1)
3d 1.734(2) 1.758(2) 1.925(2) 1.305(3) 1.326(3) 1.285(3)
3f 1.749(3) 1.752(3) 1.910(3) 1.302(4) 1.325(4) 1.294(4)
1.741(2) 1.761(2) 1.907(3) 1.300(4) 1.329(4) 1.294(4)
Scheme 3. Syntheses of hexacoordinate Si compounds 3a–f. The
same substitution pattern R,RЈ,RЈЈ applies to 2a–f and 3a–f.
To the best of our knowledge, these are the first struc-
tures of hexacoordinate silicon complexes with two triden-
tate O,N,OЈ ligands in a fac coordination mode.[5,6] Con-
cluding from the data in Table 2, one can find a number
of common features regarding the coordination of the N-
acylated salphen ligands with the silicon atom. In addition
to exclusively engaging the O,N,OЈ mode, the Si–O bond to
the phenoxy moiety is slightly shorter than the bond to the
O atom of the former carbonyl group, which is now part of
a C-siloxyimine. The formal dative Si–N bonds are in the
Table 1. 29Si NMR shifts δSi [ppm] of complexes 3a–f in the solid
state.
Compound
δSi
Compound
δSi
3a
3b
3c
–178.0
–178.2
–182.5
3d
3e
3f
–178.6
–181.1
–176.3,–177.3
Although the 29Si NMR shifts indicate hexacoordination expected range for hexacoordinate silicon complexes with a
of the silicon atoms, the coordination mode of the triden- SiN2O4 skeleton. Substituent R (Scheme 3) did not reveal
tate chelating ligand cannot be assigned by this method. any significant influence on the Si–N coordination behavior
Hence, the solid-state structures of 3a, 3c, 3d, and 3f were within this class of complexes. As regards selected bonds
determined by single-crystal X-ray structural analyses (Fig- within the ligand molecules, the former carbonyl group of
ure 2, Table 2). All of these complexes exhibit similar coor- the N-acylated salphen ligand now exhibits features that
dination spheres about their silicon atoms. In most of these can be described as a C–O and a C=N bond, and this C=N
structures (except 3a) the silicon atom is situated on a crys- bond is even shorter than the C=N bond to the Si-coordi-
tallographically imposed center of inversion. Despite this nated Schiff base imine N atom. These features are similar
missing center of symmetry in 3a, the bonding parameters for the benzoyl- and pivaloyl-substituted ligands. It is note-
of the Si coordination sphere are very similar to those of worthy that the molecular structures of 3a–f are in contrast
3c, 3d, and 3f.
to our initial expectations for the following reasons: (i) In
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Examples of Exclusively O-Silylated Carbamides
the above compounds, the silicon atom favors a situation
within a seven-membered chelate ring rather than forming
a five-membered ring system. (ii) The bonding character
within the carbamide moiety (bonding situation C–N and
C=O) was converted into a C-siloxyimine group (bonding
situation C–O and C=N). Although it can be regarded as a
general principle that Si–O bonds appear favorable, up to
now X-ray diffraction analyses revealed the predominance
of N-silylated carbamides.[7] Examples for such C-siloxy-
imine tautomeric forms bearing a two-coordinate siloxy-
imine N atom were not encountered so far.
In order to rule out that this coordination mode mainly
depends on the rather bulky acyl groups at the ligand back-
bones, complex 3g (Scheme 3; R = Ph, RЈ = OMe, RЈЈ =
Me) was synthesized in a similar manner and analyzed by
X-ray diffraction analysis. The structural features of 3g
were found to be very similar to those of the above com-
plexes and thus are not further discussed here.
Figure 3. Molecular structure of 5b in the solid state. Thermal ellip-
soids with 30% probability, hydrogen atoms and chloroform mole-
cule omitted for clarity, selected atoms labeled.
Table 3. Selected bond lengths [Å] and angles [°] of 4b (X = Cl)
and 5b (X = F).
To elucidate the coordination behavior of N-acylated
salphen ligands further, compounds 2a and 2b were treated
with phenyltrichlorosilane to afford 4a and 4b, respectively
(Scheme 4, top). 29Si NMR spectroscopic analysis of the
product solutions revealed the near-exclusive formation of a
product comprising a pentacoordinate silicon atom in both
cases. Although all attempts to isolate 4a and 4b in good
yields as solids failed so far, one single crystal of 4b suitable
for X-ray analysis formed from a residual drop of chloro-
form solution left in a Schlenk tube. Cl versus F exchange
4b
5b
4b
5b
Si1–O1 1.656(2)
Si1–O3 1.662(2)
Si1–N1 1.980(2)
Si1–C28 1.863(3)
2.204(1)
N1–C7 1.307(3)
1.663(1)
1.669(1)
2.026(1)
1.866(1)
1.649(1)
1.305(2)
N2–C21
O1–Si1–O3
1.272(3)
119.4(1)
O1–Si1–C28 116.1(1)
O3–Si1–C28 124.5(1)
1.279(2)
119.8(1)
116.6(1)
123.3(1)
175.4(1)
Si1–X
N1–Si1–X
174.2(1)
In general, the tridentate ligand exhibits two similarities
(Scheme 4, bottom) of 4b, however, afforded complex 5b, to the above-mentioned hexacoordinate silicon complexes,
which was isolated as a crystalline solid in moderate yield. as both O,N,OЈ coordination modes of this chelator are ob-
The solid-state structure of 5b was also determined by sin- served with only slightly shorter Si–O bonds to the phenoxy
gle-crystal X-ray diffraction analysis. As a result of its iso- oxygen O1 than to the original carbonyl oxygen atom O3.
structural relationship with 4b, only the molecular structure These Si–O bonds are, due to their equatorial position, no-
of 5b is depicted in Figure 3.
ticeably shorter than the Si–O bonds in the hexacoordinate
complexes. The Si–N bonds are noticeably longer than in
hexacoordinate silicon complexes 3, and one can find a sig-
nificant Si–N bond lengthening upon replacing the Si-
bound chlorine atom for a fluorine atom. This effect was
also observed for other Si–Cl/Si–F pairs of N-donor-substi-
tuted hypercoordinated silicon complexes and is not limited
to such compounds bearing trans-disposed N–Si–X
bonds.[8]
Surprisingly, the 29Si NMR spectrum of the crude prod-
uct solution of 4a exhibited a small signal at δ =
–172.5 ppm, indicative of the presence of a hexacoordinate
silicon compound. During our attempts to crystallize 4a
from this solution, some crystals formed that, upon X-ray
diffraction analysis, provided an answer as to which ad-
ditional hypercoordinate silicon complex had formed in this
reaction (Scheme 5, Figure 4).
Scheme 4. Syntheses of pentacoordinate silicon complexes from N-
acylated salphen ligands (a: R = tBu, b: R = Ph).
A slight excess of the ligand led to the addition of a sec-
The silicon atom of 5b, as for 4b, is housed within a tri- ond equivalent of 2a to complex 4a to yield ionic com-
gonal-bipyramidal coordination sphere with the imine ni- pound 6a comprising a hexacoordinate siliconium cation.
trogen atom N1 in an axial position trans to the halide. This The o-iminomethylphenolate O,N braces are situated in one
arrangement has also been found for a SiMeCl-substituted plane with their N and O atoms trans to one another, an
silicon complex bearing a tridentate O,N,OЈ ligand.[1r]
A
arrangement also found for other hexacoordinate silicon
comparison of selected bond lengths and angles of 4b and complexes of bidentate Schiff base ligands.[8,9] The position
5b is given in Table 3.
trans to the Si-bound phenyl group is occupied by a carb-
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cedure the presence of two species bearing tetracoordinate
silicon atoms became apparent from 29Si NMR signals at δ
= –25.9 and –36.2 ppm, the first originating from the major
component. The signal at δ = –25.9 ppm was attributed to
the presence of benzimidazoline 7bЈ (which was supported
by a 13C NMR signal at δ = 90.0 ppm originating from
the benzimidazoline quaternary carbon atom, as reported
previously[3a]), and the signal at δ = –36.2 ppm was assigned
to compound 7b. The molecular structures of 7a and 7b
were confirmed by X-ray crystallographic analyses of single
crystals obtained from product solutions (Scheme 6, Fig-
ure 5). In spite of only a small difference at the ligand back-
Scheme 5.
Figure 4. Molecular structure of 6a in the solid state. Thermal ellip-
soids with 20% probability, hydrogen atoms, chloride anion, and
chloroform molecules omitted for clarity, selected atoms labeled.
Selected bond lengths [Å] and angles [°]: Si1–O1 1.725(2), Si1–O3
1.938(2), Si1–O4 1.727(2), Si1–N1 1.943(3), Si1–N3 1.948(2), Si1–
C51 1.912(3), N1–C7 1.312(4), N3–C32 1.308(4), O3–C21 1.256(4),
N2–C21 1.329(4), O6–C46 1.224(4), N4–C46 1.355(4), O1–Si1–O4
170.4(1), N1–Si1–N3 168.0(1), O3–Si1–C51 178.3(1).
Scheme 6.
amide carbonyl O atom, which renders this compound a
further example of a hexacoordinate Si complex with a fac-
coordinated O,N,OЈ ligand. In sharp contrast to the pre-
viously presented hexacoordinate silicon complexes, this
Si1–O3 bond is remarkably longer, which thus gives rise to
its interpretation as a formal dative bond. This altered
bonding pattern, together with the now N-bound hydrogen
atom at N2, is accompanied by typical carbamide bonding
features, that is, a short C=O bond and a significantly
longer C–N bond. Although representing an unexpected
side product, 6a complements a wide range of silicon coor-
dination compounds bearing carbamide carbonyl oxygen
donor atoms in their coordination sphere.[10]
In contrast to the pentacoordination of the silicon atoms
in 4a, 4b, and 5b, the products obtained from the reactions
of ligands 2a and 2b with diphenyldichlorosilane did not
give any indication of the presence of hypercoordinate sili-
con compounds, neither in solution nor in the solid state.
Ligand 2a, upon reaction with Ph2SiCl2 in the presence of
triethylamine, afforded a product mixture, which as solution
in CDCl3, produced one predominant signal in the 29Si
NMR spectrum at δ = –43.2 ppm (7a). The absence of a
signal at δSi ≈ –25 ppm in solutions of 7a indicates hin-
drance of benzimidazoline formation, most likely due to the
sterically more-demanding tBu substituent. In the product
Figure 5. Molecular structures of 7a (top) and 7b (bottom). Ther-
mal ellipsoids with 50% probability, hydrogen atoms omitted for
clarity, selected atoms labeled. Selected bond lengths [Å] and angles
[°] for 7a: Si1–O1 1.637(2), Si1–O3 1.647(1), O3–C21 1.367(2), N1–
C7 1.276(3), N2–C21 1.261(3); O1–Si1–O3 112.8(1); Si1–O1–C1
137.3(1), Si1–O3–C21 139.9(1); for 7b: Si1–O1 1.626(3), Si1–O3
1.653(3), O3–C21 1.369(5), N1–C7 1.304(6), N2–C21 1.259(5); O1–
solution obtained from ligand 2b in an analogous pro- Si1–O3 105.1(2); Si1–O1–C1 143.2(3), Si1–O3–C21 142.8(3).
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Examples of Exclusively O-Silylated Carbamides
The orange solid product was separated from the still-cold solution
by vacuum filtration, washed with isobutyl alcohol (20 mL) and
dried in air. Yield: 33.2 g (147 mmol, 79%). M.p. 108 °C.
C14H14N2O (226.28): calcd. C 74.31, H 6.24, N 12.38; found C
bone (pivaloyl vs. benzoyl substituent), the bonding features
in closer proximity of the silicon atoms in compounds 7a
and 7b in the solid state differ significantly from each other.
Although both compounds exhibit slightly distorted tetra-
hedral coordination spheres about the silicon atom, the O1–
Si1–O3 angle is larger than the tetrahedral angle for 7a,
whereas it is noticeably smaller in 7b. In addition, the Si–
O–C angles in 7b are significantly wider than their ana-
logues in 7a. As common features of 7a and 7b, the slightly
shorter Si–O bonds to the phenoxy O atoms and the pro-
nounced C=N double bond character within the C-siloxy-
imine moiety (N2=C21) are to be mentioned. The latter
clearly distinguishes 7a and 7b from the above hexa- and
1
74.30, H 6.19, N 12.31. H NMR (400.13 MHz, CDCl3, 25 °C): δ
= 2.37 (s, 3 H, CH3), 3.63 (s br., 2 H, NH2), 6.70–7.05 (mm, 6 H),
7.37 (m, 1 H), 7.64 (dd, J = 8.0 Hz, 1 H, 1.2 Hz), 14.76 (s, 1 H,
OH) ppm. 13C NMR (100.62 MHz, CDCl3, 25 °C): δ = 17.2 (CH3),
115.7, 118.2, 118.3, 118.5, 119.7, 121.5, 126.2, 129.0, 133.2, 133.3,
138.2, 162.1, 173.7 ppm.
2a: To a solution of compound 1a (6.00 g, 18.8 mmol) and triethyl-
amine (5.00 g, 49.5 mmol) in thf (80 mL) was added chlorotrimeth-
ylsilane (2.10 g, 19.3 mmol) dropwise, whereupon [Et3NH]Cl pre-
cipitated. The resulting mixture was stirred at ambient temperature
pentacoordinate silicon compounds, the C-siloxyimine for 10 min, whereafter pivaloic chloride (2.50 g, 20.7 mmol) was
added, and the mixture was stirred for a further 10 min. [Et3NH]-
Cl was then removed by filtration, washed with thf (20 mL), and
discarded. From the combined filtrate and washings the solvent
was removed under reduced pressure. The residue was dissolved in
methanol (20 mL) under gentle heating to yield a clear yellow solu-
tion, wherefrom crystallization of 2a commenced within a few min-
utes. After 1 d the supernatant was decanted from the yellow crys-
talline product, which was washed with small portions of methanol
(5 mL) and dried in air. Yield: 5.44 g (13.5 mmol, 72%). M.p.
144 °C. C25H26N2O3 (402.48): calcd. C 74.61, H 6.51, N 6.96;
found C 74.98, H 6.60, N 6.75. 1H NMR (400.13 MHz, CDCl3,
25 °C): δ = 1.31 [s, 9 H, C(CH3)3], 3.85 (s, 3 H, OCH3), 6.30–7.30
(mm, 11 H), 7.98 (s, 1 H, NH), 8.29 (d, J = 8.0 Hz, 1 H), 14.32 (s,
1 H, OH) ppm. 13C NMR (100.62 MHz, CDCl3, 25 °C): δ = 27.7
[C(CH3)3], 40.1 [C(CH3)3], 55.5 (OCH3), 101.4, 106.7, 113.4, 119.9,
C=N bonds of which range between 1.272(3) and
1.294(4) Å.
Conclusions
In addition to the previously reported benzimidazoline
formation upon silylation of an NЈ-acetylated tridentate
O,N,NЈ salphen-type ligand, this isomerization was now
shown to also proceed with N-bound acyl groups other
than acetyl. Increasing steric bulk, however, may prevent
benzimidazoline formation, that is, for ligands carrying a
tBu-substituted acyl group. In these cases, and upon forma-
tion of hypercoordinate silicon complexes (five- and six-co-
ordinate) NЈ-acylated salphen-type ligands were shown to 122.0, 123.2, 125.5, 128.4, 128.5, 129.4, 131.4, 134.0 (2ϫ), 136.5,
164.3, 164.8, 175.5, 176.6 ppm. A single crystal of dimensions
0.70ϫ0.50ϫ0.40 mm obtained by slow evaporation of a solution
in ethanol was chosen for data collection. Selected crystallographic
data for 2a: C25H26N2O3, Mr = 402.48, T = 90(2) K, triclinic, space
swap from the inherent O,N,NЈ to the tautomeric O,N,OЈ
coordination mode. The herein presented examples of
hexa-, penta-, and tetracoordinate silicon compounds,
which were characterized by single-crystal X-ray diffraction
analyses, represent the first such evidence for solely
O-silylated carbamides comprising a two-coordinate nitro-
gen atom, and hence exhibiting C-siloxyimine structural
features. Additionally, some of the herein reported com-
plexes are the first to exhibit tridentate (O,N,OЈ) chelators
¯
group P1, a = 9.4917(3) Å, b = 9.8900(3) Å, c = 12.6894(3) Å, α =
111.162(1)°, β = 104.971(1)°, γ = 96.357(2)°, V = 1045.28(5) Å3, Z
= 2, ρcalcd. = 1.279 Mgm–3, µ(Mo–Kα) = 0.084 mm–1, F(000) = 428,
2θmax = 70.0°, 36473 collected reflections, 9127 unique reflections
(Rint = 0.0219), 283 parameters, S = 1.076, R1 = 0.0406 [IϾ2σ(I)],
wR2(all data)
= 0.1260, max./min. residual electron density
in a fac coordination mode in the coordination sphere of +0.552/–0.257 eÅ–3.
hexacoordinate silicon atoms.
2b: The same procedure as for 2a applies. Starting materials used:
1a (6.00 g, 18.8 mmol), triethylamine (5.00 g, 49.5 mmol), Me3SiCl
(2.10 g, 19.3 mmol), PhCOCl (2.70 g, 19.2 mmol) in thf (80 mL).
After removal of the solvent and upon treatment of the crude prod-
uct with methanol (30 mL) 2b precipitated immediately. The yellow
solid obtained was filtered off with suction and dried in air. Yield:
6.12 g (14.5 mmol, 77%). M.p. 180 °C. C27H22N2O3 (422.47): calcd.
Experimental Section
General Methods: All syntheses were carried out under an inert
atmosphere of dry argon in dry solvents by using Schlenk tech-
niques. 1H, 13C, and 29Si NMR spectra (solution) were recorded
with a Bruker DPX 400 instrument by using SiMe4 as an internal
standard. Solid-state NMR spectra (29Si CP/MAS) were recorded
with a Bruker AVANCE 400WB instrument. Single-crystal X-ray
diffraction data were collected with a Bruker-Nonius X8 APEXII
CCD instrument by using Mo-Kα radiation. The structures were
solved with direct methods (SHELXS97) and refined with full-ma-
trix least-squares methods on F2 (SHELXL97).[11] The syntheses
of compounds 1a[3a] and 1c[4] were described in the literature.
1
C 76.76, H 5.25, N 6.63; found C 76.73, H 5.23, N 6.63. H NMR
(400.13 MHz, CDCl3, 25 °C): δ = 3.84 (s, 3 H, OCH3), 6.30–8.50
(mm, 18 H), 14.40 (s, 1 H, OH) ppm. 13C NMR (100.62 MHz,
CDCl3, 25 °C): δ = 55.5 (OCH3), 101.5, 106.7, 113.7, 120.2, 122.3,
123.6, 125.6, 127.1, 128.4, 128.6, 128.9, 129.4, 131.5, 131.8, 134.1
(2ϫ), 135.0, 136.8, 164.4, 164.9, 165.2, 175.7 ppm. A single crystal
of dimensions 0.65ϫ0.55ϫ0.40 mm obtained by slow evaporation
of a solution in methanol and tetrahydrofuran was chosen for data
collection. Selected crystallographic data for 2b: C27H22N2O3, Mr
= 442.47, T = 90(2) K, monoclinic, space group P21/c, a =
10.1615(3) Å, b = 14.5152(4) Å, c = 15.5414(4) Å, β = 108.589(1)°,
V = 2172.71(10) Å3, Z = 4, ρcalcd. = 1.292 Mgm–3, µ(Mo–Kα) =
0.085 mm–1, F(000) = 888, 2θmax = 70.0°, 41321 collected reflec-
tions, 9573 unique reflections (Rint = 0.0277), 297 parameters, S =
1b: O-Phenylenediamine (20.0 g, 185 mmol), o-hydroxyacetophen-
one (25.2 g, 185 mmol), and piperidine (15.7 g, 185 mmol) were
dissolved in isobutyl alcohol (120 mL) and stirred under reflux for
14 h. The resulting orange-red solution was cooled to room tem-
perature before stored at 8 °C overnight, whereupon 1b crystallized.
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A. Kämpfe, E. Kroke, J. Wagler
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1.080, R1 = 0.0432 [IϾ2σ(I)], wR2(all data) = 0.1324, max./min.
residual electron density +0.561/–0.464 eÅ–3.
data)
=
0.1160, max./min. residual electron density +0.381/
–0.251 eÅ–3.
2f: The same procedure as for 2a applies. Starting materials used:
1c (3.00 g, 14.1 mmol), triethylamine (4.00 g, 39.6 mmol), Me3SiCl
(1.55 g, 14.3 mmol), PhCOCl (2.16 g, 15.4 mmol) in thf (70 mL).
After removal of the solvent and upon treatment of the crude prod-
uct with methanol (20 mL) 2e precipitated. The yellow solid ob-
tained was filtered off with suction, washed with methanol (5 mL)
and dried in air. Yield: 3.41 g (10.8 mmol, 77%). M.p. 160 °C.
C20H16N2O2 (316.36): calcd. C 75.93, H 5.10, N 8.85; found C
2c: The same procedure as for 2a applies. Starting materials used:
1b (3.00 g, 13.3 mmol), triethylamine (4.00 g, 39.6 mmol), Me3SiCl
(1.44 g, 13.3 mmol), tBuCOCl (1.75 g, 14.5 mmol) in thf (40 mL).
After removal of the solvent and upon treatment of the crude prod-
uct with methanol (25 mL) all our attempts to crystallize 2c failed.
Thus, the yellow oil obtained (yield: 3.53 g, 11.4 mmol, 85.7%) was
used for further reactions as a thf solution (50%). 1H NMR
(400.13 MHz, CDCl3, 25 °C): δ = 1.18 [s, 9 H, C(CH3)3], 2.35 (s, 3
H, N=CCH3), 6.75–8.25 (mm, 9 H), 13.8 (s br., 1 H, OH) ppm.
13C NMR (100.62 MHz, CDCl3, 25 °C): δ = 17.1 (N=CCH3), 27.0
[C(CH3)3], 39.3 [C(CH3)3], 117.8, 118.1, 119.0, 120.8, 121.5, 123.8,
125.5, 128.9, 129.6, 133.2, 136.9, 161.4, 174.1, 176.1 ppm.
1
75.61, H 5.10, N 8.81. H NMR (400.13 MHz, CDCl3, 25 °C): δ =
6.97 (t, J = 7.4 Hz, 1 H), 7.05 (d, J = 8.0 Hz, 1 H), 7.10–7.55 (mm,
8 H), 7.91 (d, J = 2 H, 8.0 Hz), 8.58–8.65 (m, 3 H, NH, ar, N=CH),
12.47 (s, 1 H, OH) ppm. 13C NMR (100.62 MHz, CDCl3, 25 °C):
δ = 117.4, 118.1, 119.3, 119.6, 120.7, 124.6, 127.0, 128.1, 128.9,
131.9 ppm. 132.2, 132.9, 133.9, 134.6, 138.3, 160.9, 164.5,
165.1 ppm.
2d: The same procedure as for 2a applies. Starting materials used:
1b (3.00 g, 13.3 mmol), triethylamine (4.00 g, 39.6 mmol), Me3SiCl
(1.44 g, 13.3 mmol), PhCOCl (2.10 g, 14.9 mmol) in thf (40 mL).
After removal of the solvent and upon treatment of the crude prod-
uct with methanol (10 mL) 2d precipitated as a yellow fine crystal-
line powder. The yellow solid obtained was filtered off with suction,
washed with methanol (5 mL) and dried in air. Yield: 3.34 g
(10.1 mmol, 76%). M.p. 152 °C. C21H18N2O2 (330.37): calcd. C
76.34, H 5.50, N 8.48; found C 76.10, H 5.48, N 8.49. 1H NMR
(400.13 MHz, CDCl3, 25 °C): δ = 2.43 (s, 3 H, CH3), 6.87 (d, J =
7.6 Hz, 1 H), 6.93 (t, J = 7.4 Hz, 1 H), 7.07 (d, J = 8.0 Hz, 1 H),
7.18 (t, J = 7.4 Hz, 1 H), 7.20–7.50 (mm, 5 H), 7.67 (d, J = 8.0 Hz,
1 H), 7.82 (d, J = 2 H, 7.2 Hz), 8.02 (s, 1 H, NH), 8.53 (d, J =
8.0 Hz, 1 H), 14.24 (s, 1 H, OH) ppm. 13C NMR (100.62 MHz,
CDCl3, 25 °C): δ = 17.8 (CH3), 118.5, 118.7, 119.6, 121.3 (2ϫ),
124.3, 126.3, 127.0, 128.9, 129.3, 130.2, 131.9, 133.8, 134.6, 136.6,
Compounds 3 were almost insoluble in solvents such as CDCl3 and
DMSO. Hence, they were characterized in the solid state only.
3a: To a solution of ligand 2a (0.90 g, 2.24 mmol) dissolved in chlo-
roform (9 mL) was added triethylamine (0.67 g, 6.6 mmol) followed
by the rapid addition of SiCl4 (0.19 g, 1.12 mmol) whilst stirring.
Immediately a clear solution resulted, and stirring was stopped 10 s
after the addition of SiCl4 was complete. Within a few minutes
precipitation of 3a (as chloroform solvate) commenced. After
1 week the fine precipitate was filtered off, washed with chloroform
(2 mL), and briefly dried in a vacuum. Yield: 1.15 g. This product
comprises an undefined fraction of solvent of crystallization. Upon
storage in a 20-mL Schlenk tube for 2 weeks large amounts of this
solvent must have escaped from the crystals, as microanalysis re-
vealed a composition matching the C/H/N contents for the solvent-
free compound. C50H48N4O6Si (829.06): calcd. C 72.44, H 5.84, N
6.76; found C 72.48, H 6.16, N 6.99. 29Si CP/MAS NMR
(79.51 MHz, 25 °C): δ = –178.0 ppm. In order to obtain single crys-
tals of 3a suitable for X-ray diffraction analysis, ligand 2a (0.38 g,
0.95 mmol), triethylamine (0.15 g, 1.5 mmol), and the (compared
with SiCl4) less-reactive (Et2N)2SiCl2 (0.11 g, 0.56 mmol) were dis-
solved in chloroform (9 mL), stored at room temperature for 1 d
and then stored at 8 °C for 1 week, whereupon a precipitate of
small crystals of 3a·(CHCl3)3 had formed. A single crystal of di-
mensions 0.23ϫ0.18ϫ0.03 mm was chosen for data collection. Se-
lected crystallographic data for 3a·(CHCl3)3: C53H51Cl9N4O6Si, Mr
= 1187.12, T = 90(2) K, monoclinic, space group P21/c, a =
10.6909(3) Å, b = 18.0804(5) Å, c = 28.2333(8) Å, β = 91.019(1)°,
V = 5456.5(3) Å3, Z = 4, ρcalcd. = 1.445 Mgm–3, µ(Mo–Kα) =
0.537 mm–1, F(000) = 2448, 2θmax = 50.0°, 50406 collected reflec-
tions, 9605 unique reflections (Rint = 0.0681), 666 parameters, S =
1.040, R1 = 0.0535 [IϾ2σ(I)], wR2(all data) = 0.1289, max./min.
residual electron density +0.354/–0.635 eÅ–3.
161.9, 165.2, 175.0 ppm.
A single crystal of dimensions
0.55ϫ0.18ϫ0.14 mm obtained by slow evaporation of a solution
in methanol was chosen for data collection. Selected crystallo-
graphic data for 2d: C21H18N2O2, Mr = 330.37, T = 90(2) K, ortho-
rhombic, space group Pbca, a = 19.7096(13) Å, b = 7.8678(4) Å, c
= 21.9221(14) Å, V = 3399.5(4) Å3, Z = 8, ρcalcd. = 1.291 Mgm–3,
µ(Mo–Kα) = 0.084 mm–1, F(000) = 1392, 2θmax = 50.0°, 18293 col-
lected reflections, 2995 unique reflections (Rint = 0.0803), 233 pa-
rameters, S = 1.010, R1 = 0.0378 [IϾ2σ(I)], wR2(all data) = 0.0914,
max./min. residual electron density +0.200/–0.225 eÅ–3.
2e: The same procedure as for 2a applies. Starting materials used:
1c (3.00 g, 14.1 mmol), triethylamine (4.00 g, 39.6 mmol), Me3SiCl
(1.55 g, 14.3 mmol), tBuCOCl (1.85 g, 15.4 mmol) in thf (70 mL).
After removal of the solvent and upon treatment of the crude prod-
uct with methanol (20 mL) crystallization of 2e commenced. The
supernatant was decanted, the crystals were washed with methanol
(5 mL) and dried in air. Yield: 2.48 g (8.38 mmol, 59%). M.p.
136 °C. C18H20N2O2 (296.36): calcd. C 72.94, H 6.81, N 9.45;
found C 72.86, H 6.70, N 9.46. 1H NMR (400.13 MHz, CDCl3,
25 °C): δ = 1.33 (s, 9 H, CH3), 6.90–7.50 (mm, 7 H), 8.16 (s, 1 H,
NH), 8.45 (d, J = 8.0 Hz, 1 H), 8.63 (s, 1 H, N=CH), 12.43 (s, 1
H, OH) ppm. 13C NMR (100.62 MHz, CDCl3, 25 °C): δ = 27.6
[C(CH3)3], 40.1 [C(CH3)3], 117.3, 117.9, 119.2, 119.6, 120.6, 124.2,
128.0, 132.3, 132.8, 133.9, 138.2, 160.8, 164.2, 176.6 ppm. single
crystal of dimensions 0.40ϫ0.28ϫ0.22 mm obtained directly from
the above synthesis was chosen for data collection. Selected crystal-
lographic data for 2e: C18H20N2O2, Mr = 296.36, T = 90(2) K, mo-
noclinic, space group P21/c, a = 13.8500(6) Å, b = 9.2073(3) Å, c
= 12.3970(4) Å, β = 99.952(2)°, V = 1557.09(10) Å3, Z = 4, ρcalcd.
In general, for the syntheses of compounds 3b–f the same pro-
cedure applies as for the synthesis of 3a (hence starting from SiCl4,
triethylamine and ligand 2b–3f, respectively).
3b: Starting materials used: 2b (0.900 g, 2.13 mmol), triethylamine
(0.640 g, 6.32 mmol), SiCl4 (0.180 g, 1.06 mmol), chloroform
(9 mL). Yield: 0.90 g. Whereas solid-state 29Si NMR spectroscopy
revealed the formation of a hexacoordinate silicon compound (δ =
–178.2 ppm), C/H/N analysis was not conclusive: C54H40N4O6Si:
calcd. C 74.63, H 4.69, N 6.45; found C 71.95, H 6.00, N 6.50.
= 1.264 Mgm–3, µ(Mo–Kα) = 0.083 mm–1, F(000) = 632, 2θmax
60.0°, 17698 collected reflections, 4499 unique reflections (Rint
=
=
3c: Starting materials used: 2c (0.750 g, 2.42 mmol, as 1.50 g of
a 50% solution in thf), triethylamine (0.730 g, 7.21 mmol), SiCl4
(0.200 g, 1.18 mmol), chloroform (9 mL). Crystals of 3c·(CHCl3)2
0.0335), 209 parameters, S = 1.063, R1 = 0.0407 [IϾ2σ(I)], wR2(all
1032
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1027–1035

Examples of Exclusively O-Silylated Carbamides
formed within some hours. Yield: 0.75 g (0.83 mmol, 70%).
C40H42Cl6N4O4Si (883.57): calcd. C 54.37, H 4.79, N 6.34; found
compound of the composition 3g·(CHCl3). Yield: 0.10 g
(0.12 mmol, 12%). C45H37Cl3N4O6Si (864.24): calcd. C 62.54, H
C 55.47, H 5.06, N 6.64. 29Si CP/MAS NMR (79.51 MHz, 4.32, N 6.48; found C 62.33, H 4.51, N 6.56. A single crystal of
25 °C):
δ
=
–182.5 ppm.
A
single crystal of dimensions
dimensions 0.29ϫ0.08ϫ0.03 mm was chosen for data collection
from the crude crystalline product in chloroform. Selected crystal-
lographic data for 3g·(CHCl3)3: C47H39Cl9N4O6Si, Mr = 1102.96,
T = 90(2) K, monoclinic, space group P21/c, a = 24.7743(8) Å, b =
8.9571(2) Å, c = 22.8209(8) Å, β = 101.522(1)°, V = 4962.0(3) Å3,
Z = 4, ρcalcd. = 1.476 Mgm–3, µ(Mo–Kα) = 0.584 mm–1, F(000) =
2256, 2θmax = 52.0°, 39100 collected reflections, 9738 unique reflec-
tions (Rint = 0.0694), 647 parameters, S = 0.949, R1 = 0.0430
0.60ϫ0.45ϫ0.35 mm was chosen for data collection. Crystals of
this compound turned out to be systematically twinned. Determi-
nation of the twin law was carried out with CELL-NOW,[12] data
integration was performed with SAINTPLUS.[13] Refinement of
twin contributions resulted in populations of 54 and 46%. Selected
crystallographic data for 3c·(CHCl3)2: C40H42Cl6N4O4Si, Mr
883.57, T = 150(2) K, monoclinic, space group P21/c, a =
=
10.8547(5) Å, b = 16.3569(7) Å, c = 12.0130(5) Å, β = 100.647(2)°, [IϾ2σ(I)], wR2(all data) = 0.0986, max./min. residual electron den-
V = 2096.18(16) Å3, Z = 2, ρcalcd. = 1.400 Mgm–3, µ(Mo–Kα) =
0.484 mm–1, F(000) = 916, 2θmax = 64.0°, 40120 collected reflec-
tions, 7273 unique reflections (Rint = 0.0246), 268 parameters, S =
1.059, R1 = 0.0381 [IϾ2σ(I)], wR2(all data) = 0.1044, max./min.
residual electron density +0.558/–0.604 eÅ–3.
sity +0.318/–0.388 eÅ–3.
4a and 6a: To a solution of ligand 2a (0.700 g, 1.74 mmol) and
triethylamine (0.500 g, 4.94 mmol) dissolved in thf (10 mL) at
–10 °C was added phenyltrichlorosilane (0.370 g, 1.75 mmol),
whereupon triethylamine hydrochloride precipitated. This precipi-
tate was filtered off and from the filtrate the solvent was removed
under reduced pressure. The crude product was dissolved in chloro-
form and a 29Si NMR spectrum was recorded: δ = –104.3 ppm (4a)
and δ = –172.5 ppm (6a), ratio 9:1. Whereas our attempts to isolate
4a failed so far, crystals of 6a·(CHCl3)5 formed when the crude
solution in chloroform (5 mL) and diethyl ether (5 mL) was placed
in a freezer (–22 °C) for 3 d. These crystals were separated by de-
cantation and briefly dried in a vacuum. Yield of (the composition
3d: Starting materials used: 2d (0.600 g, 1.82 mmol), triethylamine
(0.550 g, 5.43 mmol), SiCl4 (0.160 g, 0.91 mmol), chloroform
(7.5 mL). Yield: 0.97 g (0.83 mmol, 92%) of 3d·(CHCl3)4.
C46H36Cl12N4O4Si (1162.28): calcd. C 47.53, H 3.12, N 4.82; found
C 50.18, H 4.42, N 5.90. 29Si CP/MAS NMR (79.51 MHz, 25 °C):
δ = –178.6 ppm. From the reaction product a single crystal of di-
mensions 0.28ϫ0.06ϫ0.06 mm was chosen for data collection. Se-
lected crystallographic data for 3d·(CHCl3)4: C46H36Cl12N4O4Si,
Mr = 1162.28, T = 90(2) K, monoclinic, space group P21/n, a =
9.1276(2) Å, b = 19.0043(6) Å, c = 13.9283(4) Å, β = 92.125(1)°,
V = 2414.39(12) Å3, Z = 2, ρcalcd. = 1.599 Mgm–3, µ(Mo–Kα) =
0.763 mm–1, F(000) = 1180, 2θmax = 54.0°, 20991 collected reflec-
tions, 5264 unique reflections (Rint = 0.0378), 318 parameters, S =
1.071, R1 = 0.0398 [IϾ2σ(I)], wR2(all data) = 0.1074, max./min.
residual electron density +0.839/–0.488 eÅ–3.
found by elemental microanalysis corresponds to) 6a·(CHCl3)2.8
:
0.14 g (0.30 mmol, 15%). C58.8H57.8Cl9.4N4O6Si (1277.87): calcd. C
55.27, H 4.56, N 4.38; found C 55.41, H 4.62, N 4.40. From the
crystalline product obtained in the freezer a single crystal of
6a·(CHCl3)5 of dimensions 0.70ϫ0.60ϫ0.30 mm was chosen for
data collection. Selected crystallographic data for 6a·(CHCl3)5:
C61H60Cl16N4O6Si, Mr = 1540.42, T = 200(2) K, monoclinic, space
group P21/c, a = 22.3508(6) Å, b = 18.8348(5) Å, c = 17.7535(5) Å,
β = 101.932(1)°, V = 7312.3(3) Å3, Z = 4, ρcalcd. = 1.399 Mgm–3,
µ(Mo–Kα) = 0.666 mm–1, F(000) = 3152, 2θmax = 50.0°, 57101 col-
lected reflections, 12675 unique reflections (Rint = 0.0335), 939 pa-
rameters, S = 1.121, R1 = 0.0596 [IϾ2σ(I)], wR2(all data) = 0.1931,
max./min. residual electron density +0.692/–0.548 eÅ–3.
3e: Starting materials used: 2e (0.750 g, 2.53 mmol), triethylamine
(0.760 g, 7.51 mmol), SiCl4 (0.220 g, 1.29 mmol), chloroform
(9 mL). Yield: 0.66 g (1.07 mmol, 85%). C36H36N4O4Si (616.81):
calcd. C 70.10, H 5.89, N 9.08; found C 69.83, H 6.19, N 9.25. 29Si
CP/MAS NMR (79.51 MHz, 25 °C): δ = –181.1 ppm.
3f: Starting materials used: 2f (0.750 g, 2.37 mmol), triethylamine
(0.720 g, 7.11 mmol), SiCl4 (0.200 g, 1.18 mmol), chloroform
(9 mL). Within some hours a crystalline precipitate of 3f·(CHCl3)
had formed. Yield: 0.74 g (0.95 mmol, 81%). C41H29Cl3N4O4Si
(776.12): calcd. C 63.45, H 3.77, N 7.22; found C 62.01, H 4.05, N
7.17. 29Si CP/MAS NMR (79.51 MHz, 25 °C): δ = –177.3 ppm.
4b: The same procedure applies as described for 4a. Starting mate-
rials used: 2b (0.700 g, 1.66 mmol), triethylamine (0.500 g,
4.94 mmol), PhSiCl3 (0.350 g, 1.66 mmol), thf (10 mL). In analogy
to 4a the crude product was dissolved in chloroform and a 29Si
NMR spectrum was recorded (δ = –103.3 ppm). So far, our
attempts to isolate 4b as a crystalline solid in reasonable amounts
failed. However, from a residual drop of a chloroform solution of
4b in a Schlenk tube a crystal of 4b·(CHCl3) of dimensions
0.45ϫ0.37ϫ0.08 mm had formed and was chosen for data collec-
From this product
a
single crystal of dimensions
0.45ϫ0.04ϫ0.03 mm was chosen for data collection. Selected
crystallographic data for 3f·(CHCl3): C41H29Cl3N4O4Si, Mr
=
¯
776.12, T = 90(2) K, triclinic, space group P1, a = 11.8304(11) Å,
b = 12.6157(12) Å, c = 14.285(2) Å, α = 108.473(5)°, β =
tion.
Selected
crystallographic
data
for
4b·(CHCl3):
111.797(6)°, γ = 100.134(4)°, V = 1770.2(4) Å3, Z = 2, ρcalcd.
1.456 Mgm–3, µ(Mo–Kα) = 0.344 mm–1, F(000) = 800, 2θmax
50.0°, 15054 collected reflections, 6214 unique reflections (Rint
=
=
=
C34H26Cl4N2O3Si, Mr = 680.46, T = 150(2) K, triclinic, space
¯
group P1, a = 9.5302(4) Å, b = 12.9429(7) Å, c = 13.2766(7) Å, α
= 99.397(2)°, β = 94.445(2)°, γ = 90.515(2)°, V = 1610.42(14) Å3,
Z = 2, ρcalcd. = 1.403 Mgm–3, µ(Mo–Kα) = 0.443 mm–1, F(000) =
700, 2θmax = 52.0°, 21617 collected reflections, 6201 unique reflec-
tions (Rint = 0.0341), 422 parameters, S = 1.100, R1 = 0.0472
[IϾ2σ(I)], wR2(all data) = 0.1452, max./min. residual electron den-
sity +0.456/–0.572 eÅ–3.
0.1013), 523 parameters, S = 0.858, R1 = 0.0584 [IϾ2σ(I)], wR2(all
data)
= 0.1136, max./min. residual electron density +0.318/
–0.355 eÅ–3.
3g: Starting materials used: The NЈ-acetylated derivative of 1a com-
pound 2g[3a] (0.700 g, 1.94 mmol), triethylamine (0.550 g,
5.43 mmol), SiCl4 (0.165 g, 0.97 mmol), thf (10 mL). In contrast to
previous syntheses, the initial precipitate was filtered off, the sol-
vent was removed from the filtrate under reduced pressure, and the
residue was then dissolved in chloroform (2 mL), whereupon crys-
tals of 3g·(CHCl3)3 formed within some hours. Upon drying the
crystalline product lost some of its chloroform content to yield a
5b: Starting from 2b (1.00 g, 2.37 mmol), triethylamine (0.700 g,
6.92 mmol), and PhSiCl3 (0.500 g, 2.37 mmol) the synthesis of 4b
was repeated. After removal of the triethylamine hydrochloride by
filtration ZnF2 (0.25 g, 2.4 mmol) was added to the filtrate, and the
mixture was stirred at ambient temperature for 80 h. The solvent
was then removed under reduced pressure, and the residue was dis-
Eur. J. Inorg. Chem. 2009, 1027–1035
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1033

A. Kämpfe, E. Kroke, J. Wagler
FULL PAPER
solved in chloroform (5 mL) and filtered. Upon storage at room
temperature for 1 week crystals of 5b·(CHCl3) had formed, which
were separated by decantation and briefly dried in a vacuum. Yield:
0.71 g (1.07 mmol, 45%). C34H26Cl3FN2O3Si (664.01): calcd. C
dissolution in CDCl3 exhibited the same 29Si NMR behavior as
the crude product. From the solid product a tiny single crystal of
dimensions 0.16ϫ0.04ϫ0.03 mm was chosen for data collection.
Selected crystallographic data for 7b: C39H30N2O3Si, Mr = 602.74,
61.50, H 3.95, N 4.22; found C 59.20, H 4.13, N 4.29. 1H NMR T = 90(2) K, orthorhombic, space group Pna21, a = 18.518(5) Å,
(400.13 MHz, CDCl3, 25 °C): δ = 3.84 (s, 3 H, OCH3), 5.44 (d, J
= 8.0 Hz, 1 H), 6.28 (t, J = 7.2 Hz, 1 H), 6.42 (d, J = 8.8 Hz, 1 H),
b = 19.693(6) Å, c = 8.389(3) Å, V = 3059.4(16) Å3, Z = 4, ρcalcd.
= 1.309 Mgm–3, µ(Mo–Kα) = 0.119 mm–1, F(000) = 1264, 2θmax
6.8–6.9 (m, 4 H), 7.05 (d, J = 7.6 Hz, 1 H), 7.15–7.25 (m, 7 H), = 50.1°, 8878 collected reflections, 4490 unique reflections (Rint
=
7.34 (d, J = 2 H, 6.8 Hz), 7.45–7.50 (m, 3 H), 8.36, 8.37 (2s, 2 H)
ppm. 13C NMR (100.62 MHz, CDCl3, 25 °C): δ = 55.9 (OCH3),
105.1, 110.0, 112.4, 123.3, 124.1, 126.4, 126.6, 127.0, 127.2, 128.0,
128.3, 128.7, 128.9, 129.3, 131.2, 133.4, 134.6, 134.9, 135.8, 138.6,
139.1, 141.1, 153.8, 159.8, 166.4, 173.9 ppm. 29Si NMR (79.5 MHz,
0.0780), 407 parameters, S = 0.915, R1 = 0.0578 [IϾ2σ(I)], wR2(all
data)
= 0.1059, max./min. residual electron density +0.250/
–0.276 eÅ–3.
CCDC-710471 (for 2a), -710472 (for 2b), -710475 (for 2d), -710467
(for 2e), -710469 [for 3a·(CHCl3)3], -710470 [for 3c·(CHCl3)2],
-710466 [for 3d·(CHCl3)4], -710468 [for 3f·(CHCl3)], -710478 [for
3g·(CHCl3)3], -710476 [for 6a·(CHCl3)5], -710477 [for
4b·(CHCl3)], -710479 [for 5b·(CHCl3)], -710473 (for 7a), -710474
(for 7b) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
1
CDCl3, 25 °C): δ = –113.8 (t, JSi,F = 220 Hz) ppm. A single
crystal of dimensions 0.55ϫ0.45ϫ0.18 mm was chosen for data
collection. Selected crystallographic data for 5b·(CHCl3):
C34H26Cl3FN2O3Si, Mr = 664.01, T = 130(2) K, triclinic, space
¯
group P1, a = 9.3768(3) Å, b = 12.9632(4) Å, c = 13.0210(5) Å, α
= 97.397(1)°, β = 92.310(1)°, γ = 91.869(1)°, V = 1567.16(9) Å3, Z
= 2, ρcalcd. = 1.407 Mgm–3, µ(Mo–Kα) = 0.375 mm–1, F(000) = 684,
2θmax = 64.0°, 30198 collected reflections, 10714 unique reflections
(Rint = 0.0204), 431 parameters, S = 1.117, R1 = 0.0473 [IϾ2σ(I)],
Supporting Information (see footnote on the first page of this arti-
cle): ORTEP diagrams of the molecular structures of 2a, 2b, 3a,
3d, 3f, 3g, and 4b with selected bond lengths and angles.
wR2(all data)
= 0.1564, max./min. residual electron density
+0.633/–0.676 eÅ–3.
7a: To a solution of 2a (0.700 g, 1.74 mmol) and triethylamine
(0.530 g, 5.25 mmol) in thf (10 mL) at 0 °C was added diphenyl-
dichlorosilane (0.440 g, 1.74 mmol) dropwise. The reaction mixture
was then stirred at 40 °C for 1 h, cooled to room temperature, and
triethylamine hydrochloride was removed by filtration. From the
filtrate the solvent was removed under reduced pressure. The yellow
residue was dissolved in chloroform (3 mL) and diethyl ether
(2 mL) and stored at 8 °C overnight, whereupon crystals of 7a had
formed, which were separated from the solution by decantation,
washed with diethyl ether (1 mL) and dried in a vacuum. Yield:
0.29 g (0.50 mmol, 29%). M.p. 207 °C. C37H34N2O3Si (582.75):
Acknowledgments
The authors wish to thank Dr. Erica Brendler, Institut für Analy-
tische Chemie, TU Bergakademie Freiberg, for recording the solid-
state 29Si NMR spectra.
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1
calcd. C 76.25, H 4.81, N 5.88; found C 75.90, H 4.78, N 5.60. H
NMR (400.13 MHz, CDCl3, 25 °C): δ = 1.05 [s, 9 H, C(CH3)3],
3.61 (s, 3 H, OCH3), 6.06 (s, 1 H), 6.2–7.8 (mm, 21 H) ppm. 13C
NMR (100.62 MHz, CDCl3, 25 °C): δ = 28.2 [C(CH3)3], 38.8
[C(CH3)3], 55.2 (OCH3), 106.4, 108.2, 118.1, 118.7, 123.0, 124.1,
127.6, 127.9, 129.5, 130.0, 130.9, 132.7, 134.6, 135.0, 139.2, 140.7,
142.7, 151.8, 160.5, 161.4, 163.4, 176.4 ppm. 29Si NMR (79.5 MHz,
CDCl3, 25 °C): δ = –44.1 ppm. A single crystal of dimensions
0.18ϫ0.14ϫ0.10 mm was chosen for data collection. Selected
crystallographic data for 7a: C37H34N2O3Si, Mr = 582.75, T = 90(2)
K, monoclinic, space group P21/c, a = 9.426(1), b = 17.749(2), c
= 18.476(2) Å, β = 96.864(4)°, V = 3068.9(6) Å3, Z = 4, ρcalcd.
1.261 Mgm–3, µ(Mo–Kα) = 0.116 mm–1, F(000) = 1232, 2θmax
50.0°, 18061 collected reflections, 5398 unique reflections (Rint
=
=
=
0.0629), 392 parameters, S = 0.982, R1 = 0.0447 [IϾ2σ(I)], wR2(all
data)
= 0.1118, max./min. residual electron density +0.420/
–0.404 eÅ–3.
7b: The same procedure applies as described for 7a. Starting mate-
rials used: 2b (0.700 g, 1.66 mmol), triethylamine (0.530 g,
5.25 mmol), diphenyldichlorosilane (0.420 g, 1.66 mmol), thf
(10 mL). 29Si NMR spectroscopy of the crude product solution re-
vealed two predominant signals (δ = –36.2 and –25.9 ppm) in a
ratio of 1:3, which can be attributed to 7b and its benzimidazoline
isomer, respectively. In addition to the 29Si shift of δ = –25.9 ppm,
the presence of the latter compound was indicated by a 13C reso-
nance signal at δ = 90.0 ppm. Upon storing a solution of the crude
product in chloroform (1 mL) and diethyl ether (2 mL) at 8 °C for
1 week a crystalline precipitate formed (Yield: 0.35 g), which upon
1034
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1027–1035

Examples of Exclusively O-Silylated Carbamides
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Received: December 4, 2008
Published Online: February 3, 2009
Eur. J. Inorg. Chem. 2009, 1027–1035
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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