Unusual [3+1] cycloaddition of a stable silylene with a 2,3-diazabuta-l,3-diene versus [4+1] cycloaddition toward a buta-l,3-diene

Article abstract of DOI:10.1021/om901034w

Cycloaddition reactions of the thermally stable N-heterocyclic silylene LSi: 1 {L = CH[(C=CH₂)CMe][N(Ar)J₂], Ar = 2,6-{Pr ₂C₆H₃} with acetone azine (l, l, 4, 4-tetramethyl-2,3-diazabuta-l,3-diene) and buta-l,3-diene derivatives have been probed. Unexpectedly, acetone azine undergoes a unique [3+1] cycloaddition to give the 1-sila-2,3-diazacyclobutane 2 and its 1-sila-2,3-diazacyclobutane isomer 3. The latter rearranges further to decrease ring strain, affording the corresponding 1-sila-4, 5-diazacyclohex-3-ene 4. In contrast, reaction of 1 with isoelectronic 2,3-dimethylbuta-l,3-diene furnishes the expected [4+1] cycloaddition product silacyclopentane 5. The new compounds 2-5 were spectroscopically characterized, including single-crystal X-ray analyses of 2,4, and 5.

Full text of DOI:10.1021/om901034w

Organometallics 2010, 29, 987–990 987
DOI: 10.1021/om901034w
Unusual [3þ1] Cycloaddition of a Stable Silylene with a
2,3-Diazabuta-1,3-diene versus [4þ1] Cycloaddition toward a
Buta-1,3-diene
Yun Xiong, Shenglai Yao, and Matthias Driess*
€
Institute of Chemistry: Metalorganic and Inorganic Materials, Technische Universitat Berlin, Sekr. C2,
Strasse des 17. Juni 135, 10623 Berlin, Germany
Received December 1, 2009
Cycloaddition reactions of the thermally stable N-heterocyclic silylene LSi: 1 {L=CH[(CdCH2)-
CMe][N(Ar)]2], Ar=2,6-iPr2C6H3} with acetone azine (1,1,4,4-tetramethyl-2,3-diazabuta-1,3-diene)
and buta-1,3-diene derivatives have been probed. Unexpectedly, acetone azine undergoes a unique
[3þ1] cycloaddition to give the 1-sila-2,3-diazacyclobutane 2 and its 1-sila-2,3-diazacyclobutane
isomer 3. The latter rearranges further to decrease ring strain, affording the corresponding 1-sila-4,
5-diazacyclohex-3-ene 4. In contrast, reaction of 1 with isoelectronic 2,3-dimethylbuta-1,3-diene
furnishes the expected [4þ1] cycloaddition product silacyclopentane 5. The new compounds 2-5
were spectroscopically characterized, including single-crystal X-ray analyses of 2, 4, and 5.
Scheme 1. Silylene 1 and Several [nþ1] Cycloadducts Synthe-
Introduction
sized Thereof
Cycloaddition reactions involving unsaturated substrates
play an important role in organic and organometallic synth-
esis from fundamental as well as applied points of view.1
Carbenes, and their heavier homologues, are unsaturated
species that are indispensable building blocks in cycloaddi-
tion reactions. They can undergo [nþ1] cycloaddition reac-
tions (n =2, 3, 4) withn-oligoatomicπ-systems, among which
[2þ1] and [4þ1] cycloadditions are the most prevalent.2 In
contrast, [3þ1] cycloaddition reactions are scarce. The only
example involving a heavier group 14 element is the addition
of GeCl2 dioxane to the heterocumulene RNdSdC(CF3)2
3
(R=1-adamantyl).3
Recently we have described the synthesis and striking reacti-
vity of the stable ylide-like N-heterocyclic silylene LSi: 1 {L=
CH[(CdCH2)CMe][N(Ar)]2], Ar=2,6-iPr2C6H3} (Scheme 1).4
furnishes the initial dearomatized [4þ1] cycloaddition product
As expected for a carbene homologue, silylene 1 readily under-
goes [2þ1] cycloaddition with acetylene to give silacycloprop-2-
ene A5a and [4þ1] cycloaddition reactions with benzylidenea-
cetone affording the corresponding silaoxacyclopent-3-ene B
(Scheme 1).5b Interestingly, reaction of 1 with benzophenone
C at low temperature, which isomerizes to form the rear-
omatized species D at ambient temperature.5b Akin to C, the
dearomatized [4þ1] cycloaddition product E was reported
very recently from the reaction of 1 and diphenylhydrazone
(Scheme 1).6 The latter reactions prompted us to probe the
reactivity of 1 toward other π-conjugated compounds contain-
ing heteroatoms. Herein we report the remarkable [3þ1]
cycloaddition reaction of silylene 1 with acetone azine (1,1,4,
4-tetramethyl-2,3-diazabuta-1,3-diene), which does not pro-
ceed via the expected [4þ1] cycloaddition pathway.
*To whom correspondence should be addressed. Phone: þ49(0)30-
314-22265. Fax: þ49(0)30-314-29732. E-mail: matthias.driess@
tu-berlin.de. Web site: http://www.driess.tu-berlin.de.
(1) (a) Huisgen, R. Angew. Chem., Int. Ed. 1968, 7, 321. (b) Xu, Y.-J.;
Zhang, Y.-F.; Li, J.-Q. J. Phys. Chem. B 2006, 110, 13931.
(2) See for examples: (a) Takeda, N.; Tokitoh, N. Synlett 2007, 16,
2483. (b) Gehrhus, B.; Hitchcock, P.; B. J. Organomet. Chem. 2004, 689,
1350. (c) Clendenning, S. B.; Gehrhus, B.; Hitchcock, P. B.; Moser, D. F.;
Nixon, J. F.; West, R. Dalton Trans. 2002, 4, 484.
Results and Discussion
Treatment of an equimolar amount of 1 with acetone azine
in n-hexane at 0 °C leads to the unusual zwitterionic [3þ1]
cycloaddition product 2 (Scheme 2). This is in contrast to the
(3) May, A.; Roesky, H. W.; Irmer, R. H.; Freitag, S.; Sheldrick, G. M.
Organometallics 1992, 11, 15.
(4) Driess, M.; Yao, S.; Brym, M.; van Wullen, C.; Lenz, D. J. Am.
€
Chem. Soc. 2006, 128, 9628.
€
(5) (a) Yao, S.; van Wullen, C.; Sun, X.-Y.; Driess, M. Angew. Chem.,
Int. Ed. 2008, 47, 3250. (b) Xiong, Y.; Yao, S.; Driess, M. Chem.;Eur. J.
2009, 15, 5545.
(6) Jana, A.; Roesky, H. W.; Schulzke, C.; Samuel, P. P. Organometallics
2009, 28, 6574.
r
2010 American Chemical Society
Published on Web 01/19/2010
pubs.acs.org/Organometallics

988 Organometallics, Vol. 29, No. 4, 2010
Xiong et al.
Scheme 2. Conversion of 1 with Acetone Azine to Give 2, 3, and 4
common reactivity of acetone azine, which generally occurs
by 1,2-addition,7a 1,4-addition,7b or intramolecular coupled
1,3 and 2,4 crisscross cycloaddition.7c,d To date, all known
[3þ1] cycloaddition reactions involve cumulenes or related
unsaturated species,3,8 and most reaction products were
either only postulated as intermediates or merely character-
ized by 1H NMR and/or IR spectroscopy; only two products
could be characterized structurally by X-ray diffraction
analysis.3,8j To the best of our knowledge, there has been
no report of a [3þ1] cycloaddition reaction involving a
silylene and a heteroatom π-conjugated substrate.
Although the mechanism for the formation of the striking
product 2 is unknown, we propose that its formation occurs
first by nucleophilic attack of a nitrogen atom in the acetone
azine on the empty 3p orbital of the divalent Si atom in 1. The
latter donor-acceptor intermediate resembles the isolable
silylene-carbene adducts that have been described recently.9
Because of steric congestion, the intermediate subsequently
converts into the ylide-like [3þ1] cycloaddition product 2
instead of forming the hypothetical [4þ1] cycloadduct
(Scheme 2). Owing to the tendency to undergo isomerization
in solution, compound 2 could be isolated only in low yield in
the form of single crystals suitable for X-ray diffraction
analysis. The isomerization of 2 gives the 1-sila-2,3-diazacy-
clobutane 3, involving a C-H activation. Because of the ring
strain in the four-membered SiN2C ring in 3, the latter
compound is also labile and after two days at room tem-
perature isomerizes to generate solely the 1-sila-4,5-diazacy-
clohex-3-ene 4 as the final product (Scheme 2). Because of its
lability, 3 could not be separated from 4, but its constitution
can be unequivocally deduced from NMR spectroscopic
data (see Experimental Section). However, compound 4 is
Figure 1. Molecular structure of 2. Thermal ellipsoids are drawn
at the 50% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths (A) and angles (deg): Si1-N1
1.719(3), Si1-N2 1.797(4), Si1-C19 1.883(5), N2-C16 1.308(6),
N3-C19 1.514(6), N2-N3 1.379(5), N1-Si1-N2 114.1(1),
N2-Si1-C19 75.5(2), N1-Si1-N10 104.0(2),N1(N10)-Si1-C19
123.2(1).
˚
stable and can be easily isolated as colorless crystals in
71% yield.
1
Compounds 2, 3, and 4 have been identified by H, 13C,
and 29Si NMR spectroscopy. Each 1H NMR spectrum
exhibits three characteristic singlets for the γ-CH proton
and the two chemically inequivalent exocyclic methylene H
atoms of the C3N2 backbone of the silylene moiety, similar to
the features of 1.4 Moreover, compounds 3 and 4 exhibit
additional singlets in the range of 3 to 6 ppm (three singlets
for NH, NCMe(dCH2) in 3 and one singlet for NH in 4).
Accordingly, in the 13C{H} NMR spectra each compound
displays two characteristic resonances in the range of δ = 80
to 110 ppm for the exocyclic methylene and γ-13C nuclei
of the silylene moiety. Compound 3 shows an additional
signal at δ = 82.2 ppm, resulting from the NC(dCH2)Me
group in the former acetone azine moiety. The compounds
2, 3, and 4 give slightly different 29Si NMR resonances at
δ = -35, -44, and -25 ppm, respectively.
The spectroscopically deduced structures of 2 and 4 have
been confirmed by single-crystal X-ray diffraction analyses.
Compound 2 crystallizes in the orthorhombic space group
Pnma (Figure 1). It consists of a spirobicyclic skeleton with
the two SiN2C3 and SiN2C rings perpendicular to each other.
Thus the Si atom is bonded to one carbon and three nitrogen
atoms in a distorted tetrahedral fashion. The short N2-C16
€
(7) (a) Uhl, W.; Molter, J.; Neumuller, B.; Schmock, F. Z. Anorg.
Allg. Chem. 2001, 627, 909. (b) Talma, A. G.; Goorhuis, J. G.; Kollogg,
R. M. J. Org. Chem. 1980, 45, 2544. (c) Schantl, J. G.; Gstach, H.; Hebeisen,
P.; Lanznaster, N. Tetrahedron 1985, 41, 5525. (d) Bailey, J. R.; McPherson,
A. T. J. Am. Chem. Soc. 1917, 39, 1322.
(8) (a) Thompson, Q. E. J. Am. Chem. Soc. 1961, 83, 845. (b) Deyrup,
J. A. Tetrahedron Lett. 1971, 24, 2191. (c) Burger, K.; Fehn, J. Angew.
Chem., Int. Ed. Engl. 1972, 11, 47. (d) Burger, K.; Fehn, J.; Mueller, E.
Chem. Ber. 1973, 106, 1. (e) Burger, K.; Manz, F.; Braun, A. Synthesis 1975,
250. (f) Deyrup, J. A.; Kuta, G. S. Chem. Commun. 1975, 34. (g) Moderhack,
˚
bond distance of 1.308(6) A is consistent with a double bond,
˚
whereas the longer distance of 1.514(6) A for the N3-C19
bond clearly indicates a single bond. The length of the new
˚
Si1-C19 bond (1.883(5) A) falls in the range of typical values
for Si-C single bonds. However, the Si1-N2 bond distance
of 1.797(4) A is slightly longer than those in the precursor 1
˚
˚
(1.734(2) and 1.735(2) A).
ꢀ
D.; Lorke, M. Chem. Commun. 1977, 831. (h) Riviere, P.; Satge, J.; Castel,
A.; Cazes, A. J. Organomet. Chem. 1979, 177, 171. (i) Burger, K.;
Marschke, G.; Manz, F. J. Heterocycl. Chem. 1982, 19, 1315. (j) Schwarz,
D. E.; Rauchfuss, T. B. Chem. Commun. 2000, 1123. (k) Choudary, B. M.;
Reddy, C. R.V.; Prakash, B. V.; Kantam, M. L.; Sreedhar, B. Chem.
Commun. 2003, 754.
(9) (a) Xiong, Y.; Yao, S.; Driess, M. J. Am. Chem. Soc. 2009, 131,
7562. (b) Yao, S.; Xiong, Y.; Driess, M. Chem.-Eur. J. 2010, in press; DOI:
10.1002/chem.2000902467.
Compound 4 crystallizes in the triclinic space group P1
(Figure 2). Both six-membered SiN2C3 rings in 4 are strongly
puckered, and the silicon atom possesses a tetrahedral
coordination environment with bond angles from 101.2(1)°
to 116.2(1)°. The short C31-N3 distance of 1.289(3) A
versus that of C16-N2 at 1.308(6) A in 2 is consistent with
˚
˚

Article
Organometallics, Vol. 29, No. 4, 2010 989
Figure 3. Molecularstructure of 5. Thermal ellipsoids are drawn
at the 50% probability level. Hydrogen atoms (except for those
˚
at C1) are omitted for clarity. Selected bond lengths (A) and
angles (deg): Si1-N1 1.738(2), Si1-N2 1.743(2), Si1-C33
1.868(3), Si1-C30 1.871(3), C31-C32 1.334(3), C30-C31
1.506(3), C32-C33 1.519(3), N1-Si1-N2 104.1(1), N1-Si1-
C33 116.2(1), N2-Si1-C33 112.3(1), N1-Si1-C30 115.0(1),
N2-Si1-C30 114.8(1), C33-Si1-C30 94.9(1).
Figure 2. Molecular structure of 4. Thermal ellipsoids are drawn
at the 50% probability level. Hydrogen atoms (except for those
˚
at C1 and N4) are omitted for clarity. Selected bond lengths (A)
and angles (deg): Si1-N1 1.752(2), Si1-N2 1.749(2), Si1-C30
1.912(3), Si1-C33 1.892(2), N3-N4 1.415(3), N3-C31 1.289(3),
N4-C33 1.498(3), N1-Si1-N2 104.1(1), C30-Si1-C33 101.2(1),
N1-Si1-C30 110.4(1), N2-Si1-C33 115.7(1), N2-Si1-C30
109.3(1), N1-Si1-C33 116.2(1).
CdC double bond, whereas the relatively long C32-C33
˚
˚
(1.519(3) A) and C30-C31 (1.506(3) A) distances represent
C-C single bonds. The XSiY bond angles (X, Y = N1, N2,
C30, andC33) of the SiC2N2 core are from 94.9° to 116.2° and
thus significantly distorted from a regular tetrahedron.
Scheme 3. Reactivity of 1 toward 2,3-Dimethylbuta-1,3-diene
and 1,1,4,4-Tetramethylbuta-1,3-diene
Conclusions
In summary, the reaction of the stable N-heterocyclic
silylene 1 with the heteroatom π-conjugated acetone azine
initially affords the unusual [3þ1] cycloadduct 2, the first
zwitterionic 1-sila-2,3-diazacyclobutane, which subsequently
undergoes isomerization in solution to give the 1-sila-2,3-
diazacyclobutane 3. The latter isomerizes further in solu-
tion at room temperature by ring expansion and release of
strain energy of the four-membered SiCN2 ring in 3, yielding
the 1-sila-4,5-diazacyclohex-3-ene 4. In contrast, the isoelec-
tronic 1,1,4,4-tetramethylbuta-1,3-diene does not react with 1
even at 50 °C. However, employing the less bulky 2,3-
dimethylbuta-1,3-diene furnishes the expected [4þ1] cycload-
duct 5, which can be isolated in 90% yield.
a CdN double bond, whereas the N4-C33 distance of
˚
1.498(3) A is indicative of a C-N single bond. The new
˚
˚
Si1-C30 (1.912(3) A) and Si1-C33 bonds (1.892(2) A) are
˚
slightly longer than the Si1-C19 distance in 2 (1.883(5) A).
Interestingly, 1,1,4,4-tetramethylbuta-1,3-diene which is
isoelectronic with the acetone azine, does not react with 1
even at 50 °C after several days (Scheme 3). However, 1 reacts
with the less hindered 2,3-dimethylbuta-1,3-diene in hexane
even below room temperature, yielding the expected [4þ1]
cycloadduct 5.
Experimental Section
General Considerations. All experiments and manipulations
were carried out under dry oxygen-free nitrogen using standard
Schlenk techniques or in an MBraun inert atmosphere drybox
containing an atmosphere of purified nitrogen. Solvents were
dried by standard methods and freshly distilled prior to use. The
starting material silylene 1 was prepared according to a litera-
ture procedure.4 The NMR spectra were recorded with Bruker
spectrometers ARX200 and AV400 and with residual solvent
signals as internal reference (1H and 13C{H}) or with an external
reference (SiMe4 for 29Si). Abbreviations: s = singlet; d =
doublet; t =triplet; sept=septet; m =multiplet; br =broad.
Single-Crystal X-ray Structure Determination. Crystals were
each mounted on a glass capillary in perfluorinated oil and
measured in a cold N2 flow. The data of 2, 4, and 5 were collected
on an Oxford Diffraction Xcalibur S Sapphire at 150 K (Mo KR
Compound 5 was fully characterized by elemental analy-
sis, EI-MS, and 1H, 13C, and 29Si NMR spectroscopy. Its 29Si
NMR spectrum exhibits a resonance signal at δ = 0.90 ppm,
which is deshielded compared with those observed for 2, 3,
and 4 (-35, -44, and -25 ppm). An X-ray single-crystal
diffraction analysis revealed that 5 consists of a spirobicyclic
core with a central silicon atom coordinated to two nitrogen
and two carbon atoms (Figure 3).
˚
The Si-N bond distances (1.738(2) and 1.743(2) A) in 5 are
almost identical to those in its precursor 1 (1.734(2) and
˚
˚
1.735(2) A), and the Si-C distances (1.868(3) and 1.871(3) A)
are in the common range for Si-C single bonds. The
˚
short C32-C31 distance of 1.334(3) A is indicative of a

990 Organometallics, Vol. 29, No. 4, 2010
Xiong et al.
˚
radiation, λ=0.71073 A). The structures were solved by direct
SiCMe2), 0.63 (s, 3 H; SiCMe2), 1.21-1.47 (m, 24 H; CHMe2),
1.51 (s, 3 H; SiNCMe), 1.68, 1.97 (AB system, 2 H, SiCH2), 1.91
(s, 3 H, N-NdCMe), 3.27 (m, 2 H; CHMe2), 3.31 (s, 1 H;
NCCH2), 3.66 (m, 1 H; CHMe2), 3.87 (m, 1 H; CHMe2), 3.98 (s,
1 H; NCCH2), 4.13 (s, br, NH), 5.42 (s, 1 H; γ-H), 6.98-7.22
ppm (m, br, 6 H; 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz,
[D6]benzene, 25 °C): δ 20.7, 22.7, 23.2, 23.6, 24.4, 24.5, 24.8,
25.5, 25.9, 26.4, 26.6, 26.7 (NCMe, CHMe2), 28.7, 28.8, 28.9,
29.1 (CHMe2), 43.5 (SiCMe2), 87.5 (NCCH2), 107.7 (γ-C),
124.1, 124.4, 124.8, 125.6, 138.6, 139.5, 142.7, 147.7, 147.8,
148.4, 148.6, 148.8, 149.4 ppm (NCMe, NCCH2, 2,6-iPr2C6H3,
NdCMe2). 29Si{1H} NMR (79.49 MHz, [D6]benzene, 25 °C):
δ -25.1 ppm (s). EI-MS (70 eV, m/z): 556 (10) [Mþ], 541 (100)
[Mþ - Me], 513(45) [Mþ - iPr]. Anal.Calcd(%) forC35H52N4Si:
C 75.49, H 9.41, N 10.06. Found: C 75.45, H 9.37, N 9.88. The
spectroscopic data for 3 can be assigned from NMR data of
reaction mixtures of 3 and 4 after subtraction of the NMR
signals for 4. Spectroscopic data for 3: 1H NMR (200.13 MHz,
[D6]benzene, 25 °C): δ 0.52 (s, 3 H; SiCMe2), 0.54 (s, 3 H;
SiCMe2), 1.13-1.52 (m, 24 H; CHMe2), 1.39 (s, 3 H; NCMe),
2.16 (s, 3 H, NdCMe), 3.05 (s, 1 H; dCH2), 3.24 (s, 1 H; dCH2),
3.60 (m, 4 H; CHMe2), 3.88 (s, 1 H; dCH2), 3.93 (s, 1 H; dCH2),
3.94 (s, br, 1 H; NH), 5.25 (s, 1 H; γ-H), 6.98-7.22 ppm (m, br, 6
H; 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, [D6]benzene,
25 °C): δ 20.1, 21.8, 23.0, 23.4, 24.2, 24.5, 24.9, 25.0, 26.0, 26.3,
26.9, 27.2 (NCMe, CHMe2), 28.5, 28.6, 29.4, 29.5 (CHMe2),
57.6 (SiCMe2), 82.2 (NC(dCH2)Me), 86.8 (NCCH2), 104.2
(γ-C), 124.1, 124.5, 125.2, 125.4, 137.5, 137.8, 141.2, 141.7,
142.3, 142.7, 147.6, 148.5, 148.9, 149.1 ppm (NCMe, NCCH2,
2,6-iPr2C6H3, NdCMe2). 29Si{1H} NMR (79.49 MHz,
[D6]benzene, 25 °C): δ -44.3 ppm (s).
5: 2,3-Dimethylbuta-1,3-diene (0.14 mL, d = 0.73 g/mL, 1.24
mmol) was added to a solution of silylene 1 (0.55 g, 1.24 mmol)
in hexane (10 mL) at -30 °C. The reaction mixture was allowed
to warm to room temperature. After 4 h stirring at that
temperature the solution was concentrated to about 5 mL and
cooled to -20 °C. Compound 5 was obtained as colorless
crystals. Yield: 0.59 g (1.12 mmol, 90%). Mp: 163 °C (dec). 1H
NMR (200.13 MHz, [D6]benzene, 25 °C): δ 1.22 (d, 3J(H,H) =
7.0 Hz, 6 H; CHMe2), 1.23 (d, 3J (H,H) = 7.0 Hz, 6 H; CHMe2),
1.31 (s, 6 H; Me), 1.32 (d, 3J(H,H) = 7.0 Hz, 6 H; CHMe2), 1.42
(d, 3J(H,H) = 7.0 Hz, 6 H; CHMe2), 1.51 (s, 3 H; NCMe), 3.32
(s, 1 H; NCCH2), 3.58 (m, 4 H; CHMe2), 3.97 (s, 1 H; NCCH2),
5.43 (s, 1 H; γ-H), 7.02-7.16 ppm (m, br, 6 H; 2,6-iPr2C6H3).
13C{1H} NMR (100.61 MHz, [D6]benzene, 25 °C): δ 18.6, 22.2,
22.5, 24.0, 24.3, 24.8, 25.1, 26.4, 28.6, 28.7 (CHMe2, NCMe, -
MeCdCMe-), 86.2 (NCCH2), 106.5 (γ-C), 112.9, 124.3, 124.9,
130.4, 136.7, 138.1, 141.9, 148.4, 148.5, 148.8 ppm (NCMe,
NCCH2, 2,6-iPr2C6H3, -MeCdCMe-). 29Si{1H} NMR (79.49
MHz, [D6]benzene, 25 °C): δ 0.90 ppm (s). EI-MS (70 eV, m/z):
526 (42) [Mþ], 511 (100) [Mþ - Me], 483 (60) [Mþ - iPr]. Anal.
Calcd (%) for C35H50N2Si: C 79.79, H 9.56, N 5.32. Found: C
79.65, H 9.59, N 5.22.
methods and refined on F2 with the SHELX-9710 software
package. The positions of the H atoms (except that on N4
in 4) were calculated and considered isotropically according to
a riding model. The 2,6-iPr2C6H3 group in 2 is distorted over
two orientations in a population ratio of 0.47:0.53 and was
refined with distance restraints and restraints for the anisotropic
displacement parameters.
˚
2: orthorhombic, space group Pnma, a=16.8960(9) A, b=
˚
3
˚
˚
20.2468(10) A, c=9.5609(4) A, V=3270.7(3) A , Z=4, Fcalc
=
1.133 Mg/m3, μ(Mo KR) = 0.101 mm-1, 14 604 collected reflec-
tions, 2967 crystallographically independent reflections [Rint=
0.1133], 1659 reflections with I > 2σ(I), θmax = 25°, R(Fo) =
0.0769 (I > 2σ(I)), wR(Fo2) = 0.1654 (all data), 305 refined
parameters.
˚
˚
4: triclinic, space group P1, a = 8.9196(4) A, b = 12.2620(5) A,
˚
c=15.7788(7) A, R=79.254(4)°, β=77.307(4)°, γ=85.832(4)°,
V=1653.16(12) A , Z=2, Fcalc =1.119 Mg/m3, μ(Mo KR)=
3
˚
0.100 mm-1, 12 823 collected reflections, 5816 crystallographi-
cally independent reflections [Rint=0.0344], 4150 reflections with
2
I>2σ(I), θmax=25°, R(Fo)=0.0578 (I > 2σ(I)), wR(Fo )=0.1426
(all data), 377 refined parameters.
˚
5: monoclinic, space group P21/c, a = 8.9102(6) A, b =
3
˚
˚
˚
20.5824(10) A, c=17.2568(9) A, β=90.286(5)°, V=3164.7(3) A ,
Z = 4, Fcalc = 1.106 Mg/m3, μ(Mo KR) = 0.099 mm-1, 28018
collected reflections, 5544 crystallographically independent reflec-
tions [Rint = 0.1189], 2759 reflections with I>2σ(I), θmax =25°,
2
R(Fo)=0.0542 (I>2σ(I)), wR(Fo )=0.0977 (all data), 254 refined
parameters.
Syntheses. 2: Acetone azine (0.16 mL, d= 0.84 g/mL, 1.19 mmol)
was added to a solution of silylene 1 (0.53 g, 1.19 mmol) in hexane
(10 mL) at 0 °C. The reaction mixture was then stored at 4 °C. After
24 h about 40% of 1has been converted into 2according to 1HNMR
spectroscopy. At this stage, compound 2 could be obtained only
in very low yield (ca. 10% of its amount in reaction solutions;
1H NMR) as colorless crystals from concentrated reaction solu-
1
tions at -20 °C. H NMR (200.13 MHz, [D6]benzene, 25 °C):
δ 0.64-1.58 (m, 27 H; CHMe2), 1.20(s, 3 H, CMe2), 1.23 (s, 3 H,
CMe2), 1.38 (s, 3 H; NCMe), 1.96 (m, 3 H; NCMe2), 2.11 (m, 3 H;
NCMe2),3.23(m,1H;CHMe2),3.34(s,1H;NCCH2), 3.63 (m, 3 H;
CHMe2), 3.93 (s, 1 H; NCCH2), 5.27 (s, 1 H; γ-H), 7.01-7.20
ppm (m, br, 6 H; 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz,
[D6]benzene, 25 °C): δ 20.0-30.1 (NCMe, CHMe2, CMe2,
NC(CH2)Me), 63.5 (CMe2), 88.5 (NCCH2), 104.4 (γ-C),
124.0-147.8 ppm (NCMe, NCCH2, 2,6-iPr2C6H3, NdCMe2).
29Si{1H} NMR (79.49 MHz, [D6]benzene, 25 °C): δ -35.5 ppm
(s). EI-MS (70 eV, m/z): 556 (10) [Mþ], 541 (100) [Mþ - Me]. Anal.
Calcd (%) for C35H52N4Si: C 75.49, H 9.41, N 10.06. Found:
C 75.40, H 9.38, N 9.98.
3 and 4: Acetone azine (0.26 mL, d = 0.84 g/mL, 1.93 mmol)
was added to a solution of silylene 1 (0.86 g, 1.93 mmol) in
hexane (15 mL) at 0 °C. The reaction mixture was allowed to
warm to room temperature slowly. The complete conversion of
1 can be reached within 4 days at room temperature, affording a
mixture of 3 and 4 in a molar ratio of 1:5. Complete conversion
of 3 to 4 can be achieved after standing of the solution for one
additional day. Compound 4 can be isolated by fractional
crystallization of the reaction solution at 0 °C as colorless
crystals. Yield: 0.76 g (1.37 mmol, 71%). Mp: 145 °C (dec). 1H
NMR (200.13 MHz, [D6]benzene, 25 °C): δ 0.36 (s, 3 H;
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft and Fonds der Che-
mischen Industrie. We thank Dr. Matt Asay for critical
reading of the manuscript.
Supporting Information Available: CIF files giving crystal-
lographic data for 2, 4, and 5. This material is available free of
charge via the Internet at http://pubs.acs.org.
(10) Sheldrick, G. M. SHELX-97 Program for Crystal Structure
€
€
Determination; Universitat Gottingen: Germany, 1997.