Formation of a unsymmetrical ring system via C-H bond activation of diazobenzene by stable N-heterocyclic chlorosilylene (PhC(N t Bu) 2SiCl)

Article abstract of DOI:10.1021/om200207v

The reaction of N-heterocyclic chlorosilylene (1; LSiCl, L = PhC(NtBu) ₂) with diazobenzene is described, which afforded the unsymmetrical polycyclic product 2 via chloro-silylene mediated aromatic C-H bond activation. The reaction proceeds without the cleavage of the N-N bond of diazobenzene. Polycycle 2 was fully characterized by single-crystal X-ray diffraction analysis, multinuclear NMR spectroscopy, EI-MS spectrometry, and elemental analysis.

Full text of DOI:10.1021/om200207v

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pubs.acs.org/Organometallics
Formation of a Unsymmetrical Ring System via CꢀH Bond Activation
of Diazobenzene by Stable N-Heterocyclic Chlorosilylene
(PhC(NtBu)2SiCl)
Shabana Khan, Sakya S. Sen, Reent Michel, Daniel Kratzert, Herbert W. Roesky,* and Dietmar Stalke
Institut f€ur Anorganische Chemie der Universit€at G€ottingen, Tammannstrasse 4, 37077 G€ottingen, Germany
S Supporting Information
b
ABSTRACT: The reaction of N-heterocyclic chlorosilylene (1;
LSiCl, L = PhC(NtBu)2) with diazobenzene is described, which
afforded the unsymmetrical polycyclic product 2 via chloro-
silylene mediated aromatic CꢀH bond activation. The reaction
proceeds without the cleavage of the NꢀN bond of diazoben-
zene. Polycycle 2 was fully characterized by single-crystal X-ray
diffraction analysis, multinuclear NMR spectroscopy, EI-MS
spectrometry, and elemental analysis.
ince the isolation of stable silylenes,1 it has been frequently
experienced that addition of stable silylenes to homo- and
double bond. CꢀH bonds of the phenyl ring are considered to be
unreactive, although we recently showed selective CꢀH bond
activation with silylene.8 Moreover, direct activation of the CꢀH
bond to form a SiꢀC bond under mild conditions is rare, and in
this respect the formation of CꢀH activation products obtained
from the reactions between silylene and alkane or diethyl ether is
particularly noteworthy.9 Given the growing importance of
silylene in synthetic chemistry, we presume that treatment of 1
with diazobenzene may also activate the CꢀH bond of the
phenyl group and lead to a unusual addition and rearrangement
product or furnish a siladiaziridine derivative.
Addition of a toluene solution of diazobenzene to a colorless
toluene solution of 1 in a 1:3 molar ratio at ambient temperature
resulted in a greenish yellow solution after stirring for 12 h
(Scheme 1).10 Single block-shaped yellow crystals of 2 suitable for
X-ray diffraction analysis were grown from a saturated toluene solution
(Figure 1).11 Selected bond lengths and bond angles of 2 are given in
the legend of Figure 1. Compound 2 crystallizes in the triclinic space
group P1 and has a crystallographic inversion center in the middle of
the NꢀN bond.11 The molecular structure of 2 displays a unsymme-
trical polycycle of six (four-, five-, and six-membered) rings. The silicon
atom Si1 is 5-fold coordinated and exhibits a distorted-trigonal-
bipyramidal geometry. It is coordinated by two nitrogen atoms (N1
and N2) from the backbone of the chelating ligand, one carbon atom
(C16) of the diazobenzene phenyl ring, and one bridging nitrogen
atom (N3). The fifth position in the coordination sphere of Si1 shows
Cl/H disorder. Hydrogen (H1) and chlorine (Cl1) atoms were found
on similar positions, each with 50% occupancy. There are two possible
reasons for this disorder: (i) alternating orientation of the SiꢀH
S
heteronuclear multiple bonds is a convenient method for the
synthesis of novel ring compounds containing silicon atoms.2
Recently we have reported the synthesis of 1,2-disilacyclobutene3
by treating benzamidinatochlorosilylene (1; LSiCl, L = PhC-
(NtBu)2) with diphenylalkyne. In sharp contrast to that, the
reaction of 1 with adamantylphosphaalkyne leads to the forma-
tion of a Si2CP four-membered ring system, which shows a
zwitterionic configuration.4 The structural and chemical aspects
of these ring compounds are of interest because they contribute
new insight into the bonding properties. In this respect diazo-
benzene is particularly interesting as a precursor, since it contains
three reactive sites: a NdN π-bond and a lone pair of electrons
on each nitrogen atom. The unique reactions of diazobenzene
with lanthanide(II),5a Mg(I),5b Ge(I),5c,d and Sn(I)5c have
already been described. Despite such evident interest, until
now there have been very limited examples of silylene addition
to diazobenzene6,7 and the results show dissimilar behavior of
diazobenzene toward different silylenes. Ando et al. reported on
the photolysis of hexamesitylcyclotrisilane and tetramesityldisi-
lene on exposure to light in the presence of diazobenzene, which
afforded 1,2-disiladiazacyclobutane.6a Formation of a similar
product was also observed by So et al. very recently from
the reaction between silylsilylene [{PhC(NtBu)2}SiSi(Cl)-
{N(tBu)2C(H)Ph}] and diazobenzene.6b In marked contrast,
Weidenbruch and co-workers described the reactions of the
sterically encumbered silylenes R2Si: (R = 2,4,6-Me3C6H2, 2,4,6-
iPr3C6H2) generated in situ with diazobenzene, furnishing 1,3-
diaza-2-silaindan or 1-aza-2-silaindan derivatives.7 The most
intriguing feature of this reaction is the activation of the o-
CꢀH bond of diazobenzene and an entire cleavage of the NdN
Received: March 7, 2011
Published: April 18, 2011
r
2011 American Chemical Society
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the presence of only one SiꢀH proton in the polycycle 2. The
29Si NMR spectrum exhibits a doublet resonance (δ ꢀ94.28
1
ppm) with a coupling constant of J(SiꢀH) = 280.42 Hz.14
Another silicon center attached to a chlorine atom shows a
resonance at δ ꢀ86.7 ppm. In the 13C NMR spectrum two sets of
resonances were observed; they confirm the presence of two
chemically different silicon atoms in 2. The IR spectrum displays a
characteristic absorption band at 2086 cmꢀ1 for the SiꢀH bond.14
The molecular ion was observed in the EI-MS spectrum as the most
abundant peak with the highest relative intensity at m/z 734 [Mþ].
A molecular ion with a high relative intensity is an additional proof
for the presence of SiꢀH and SiꢀCl units in 2. The formation of
LSiHCl2 as a byproduct was observed during the reaction, and it was
confirmed by a 29Si NMR investigation (δ ꢀ96.8 ppm).3
Figure 1. Crystal structure of 2 (toluene). Hydrogen atoms, except
3
those freely refined at Si1, and disordered toluene are not shown for
clarity. Atoms labeled with the letter A are symmetry-generated by
inversion. Cl1 and H1 are disordered in a 1:1 ratio, but Cl1A and H1 are
omitted for clarity. Anisotropic displacement parameters are depicted at
the 50% probability level. Selected bond distances (Å) and bond angles
(deg): N1ꢀSi1 = 1.980(2), N2ꢀSi1 = 1.822(2), Si1ꢀN3 = 1.811(2),
C16ꢀSi1 = 1.855(3), Cl1ꢀSi1 = 2.1507(15), H1AꢀSi1A = 1.44(7),
N3ꢀN3A = 1.426(4), C19ꢀN3 = 1.372(3); N1ꢀSi1ꢀN2 = 69.06(9),
The CꢀH bond activation, a phenomenon known mainly for s-
and d-block elements, is not common for silicon compounds.7ꢀ9 In
1998 Weidenbruch et al. reported the formation of a bicyclic system by
the reaction of dimesitylsilylene with diazobenzene, and they explained
the formation of the final product as the result of the cleavage of the
NꢀNbondandCꢀH bond activation altogether.7 It is noteworthy to
mentionthatinourcaseweisolatedthefinal product without cleavage
of the NꢀN bond. Although the mechanism of this reaction is still
unknown, it can be proposed that the first step of the reaction is the
formation of the five-membered ring intermediate via a [1 þ 4]
cycloaddition reaction between the silicon(II) center and the PhNꢀ
moiety of diazobenzene, followed by rearomatization, which in situ
gives rise to the formation of the unsymmetrical polycycle 2 (see the
Supporting Information for the tentative mechanism). This is the first
example, to the best of our knowledge, where stable silylene reacts with
diazobenzene to form the dimeric unsymmetrical polycycle 2 via
CꢀH bond activation as well as SiꢀC bond formation without
cleavage of the NꢀN bond. Here it is noteworthy that there was no
reaction observed between tBuꢀNdNꢀtBu and 1. Therefore, it is
obvious that the activation of the aromatic o-CꢀH bond of diazo-
benzene is the key step for the reaction along with rearomatization.
In summary we have shown a unique reactivity of chlorosily-
lene 1 with diazobenzene featuring aromatic o-CꢀH bond
activation without the cleavage of the NꢀN bond to form the
unsymmetrical polycycle 2. This is the first example of six rings
(four-, five-, and six-membered) being arranged together by
[1 þ 4] cycloaddition of diazobenzene with LSiCl.
N1ꢀSi1ꢀN3
N3ꢀSi1ꢀC16
=
=
174.55(10), N2ꢀSi1ꢀN3
86.10(10), N2ꢀSi1ꢀC16
=
=
105.96(10),
117.48(11),
N2ꢀSi1ꢀCl1 = 114.27(8), N3ꢀSi1ꢀCl1 = 90.17(8), N3AꢀN3ꢀSi1 =
115.5(2), C19AꢀC16ꢀSi1 = 111.38(17).
Scheme 1. Preparation of 2
and SiꢀCl fragments in the crystal packing and (ii) a 1:1 ratio of
the dihydro and dichloro derivatives of 2 in the crystal. However,
a detailed spectrochemical analysis of the data gives strong
evidence for compound 2 (Figure 1).
’ ASSOCIATED CONTENT
The Si1ꢀN3 bond length is 1.811(2) Å, in accordance with
the SiꢀN single bonds reported in the literature.12a,b The NꢀN
bond length is 1.426(4) Å, which is consistent with a single
bond.5d,12c,12d The coordination of the nitrogen atoms is almost
planar in 2, with an angular sum of 349.5°. The N3ꢀN3A bond is
arranged in such a manner that it provides the bridging platform
for the formation of a unsymmetrical polycycle via fusion of two
different units so that it ultimately forms the fused ring system in
Figure 1. The most noticeable feature is the formation of a new
SiꢀC bond via o-CꢀH bond activation of the phenyl group of
diazobenzene. The new SiꢀC bond length is 1.855(3) Å, which
is consistent with a SiꢀC single-bond distance.13 Another
interesting feature is the C19ꢀN3 bond distance (1.372(3) Å),
which is shorter compared to that of diazobenzene (1.43 Å).
The crystal structure was further supported by the spectro-
scopic data. The 1H NMR spectrum exhibits resonances for two
sets of tBu protons (δ 0.94 and 1.46 ppm) and each set
corresponds to 18 protons. The resonance for one SiꢀH proton
appears at δ 6.34 ppm as a doublet, and the integration confirms
S
Supporting Information. A figure giving the tentative
b
mechanism for the formation of 2 and a CIF file giving crystal-
lographic data for 2. This material is available free of charge via
the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: þ49551393001. Fax: þ49551393373. E-mail: hroesky@
gwdg.de.
’ ACKNOWLEDGMENT
We are thankful to the Deutsche Forschungsgemeinschaft for
supporting this work. S.K. is grateful to the Deutscher Akademischer
Austausch Dienst for a research fellowship. D. S. thanks the DNRF
funded Center for Materials Crystallography (CMC) for support and
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COMMUNICATION
the Land Niedersachsen for providing a fellowship in the Catalysis of
Sustainable Synthesis (CaSuS) Ph.D. program.
f€ur Anorganische Chemie, Universit€at G€ottingen. The melting point was
measured in a sealed glass tube on a B€uchi B-540 melting point
apparatus. To a solution of 1 (0.293 g, 1 mmol) in toluene (30 mL)
was added a solution of PhNNPh (0.06 g, 0.33 mmol) in toluene
(20 mL) slowly at room temperature. The mixture was stirred for 12 h
and the resulting greenish yellow solution was concentrated in vacuo to
5 mL and stored at room temperature to yield block-shaped yellow
crystals of 2 (0.14 g, 20%). Mp: 168 °C. 1H NMR (500 MHz, THF-d8,
25 °C): δ 0.94 (s, 18H, tBu), 1.46 (s, 18H , tBu), 6.30 (s, 1H, Si-H),
6.67ꢀ6.77 (m, 2H, Ph), 7.16ꢀ7.66 (m, 14H, Ph), 7.92ꢀ7.97 (m, 2H,
Ph) ppm. 13C{1H} NMR (125.75 MHz, THF-d8, 25 °C): δ 31.21-
(CMe3), 32.13(CMe3), 54.69 (CMe3), 55.61(CMe3), 115.43, 116.43,
128.30, 128.91, 130.06, 130.71, 131.03, 131.12, 135.41, 136.29, 153.78,
153.98 (Ph), 172.11, 172.87 (NCN) ppm. 29Si{1H} NMR (99.36 MHz,
THF-d8, 25 °C): δ ꢀ94.28 (d, 1J(SiꢀH) = 280.42 Hz), ꢀ86.7 ppm. EI-
’ REFERENCES
(1) For recent reviews see: (a) Gehrhus, B.; Lappert, M. Polyhedron
1998, 17, 999–1000. (b) Haaf, M.; Schmedake, T. A.; West, R. Acc.
Chem. Res. 2000, 33, 704–714. (c) Weidenbruch, M. Organometallics
2003, 22, 4348–4360. (d) Kira, M. J. Organomet. Chem. 2004,
689, 4475–4488. (e) Ottosson, H.; Steel, P. G. Chem. Eur. J. 2006,
12, 1576–1585. (f) Nagendran, S.; Roesky, H. W. Organometallics 2008,
27, 457–492. (g) Mizuhata, Y.; Sasamori, T.; Tokitoh, N. Chem. Rev.
2009, 109, 3479–3511. (h) Wang, Y.; Robinson, G. H. Chem. Commun.
2009, 5201–5213. (i) Kira, M. Chem. Commun. 2010, 46, 2893–2903.
(j) Mandal, S. K.; Roesky, H. W. Chem. Commun. 2010, 46, 6016–6041.
(k) Asay, M.; Jones, C.; Driess, M. Chem. Rev. 2011, 111, 354–396.
(2) For recent papers see: (a) Yao, S.; van W€ullen, C.; Sun, X.-Y.;
Driess, M. Angew. Chem. 2008, 120, 3294–3297; Angew. Chem., Int. Ed.
2008, 47, 3250–3253. (b) Sen, S. S.; Roesky, H. W.; Stern, D.; Meindl,
K.; Henn, J.; St€uckl, A. C.; Stalke, D. Chem. Commun. 2010,
46, 5873–5875. (c) Gao, Y.; Zhang, J.; Hu, H.; Cui, C. Organometallics
2010, 29, 3063–3065. (d) Khan, S.; Sen, S. S.; Roesky, H. W.; Kratzert,
D.; Michel, R.; Stalke, D. Inorg. Chem. 2010, 49, 9689–9693. (e) Yasuda,
H.; Lee, V. Y.; Sekiguchi, A. J. Am. Chem. Soc. 2009, 131, 6352–6353.
(f) Tavꢀcar, G.; Sen, S. S.; Roesky, H. W.; Hey, J.; Kratzert, D.; Stalke, D.
Organometallics 2010, 29, 3930–3935. (g) Atwell, W. H. Organometallics
2008, 28, 3573–3586. (h) Sen, S. S.; Khan, S.; Kratzert, D.; Roesky,
H. W.; Stalke, D. Eur. J. Inorg. Chem. 2011, 1370–1373. (i) Khan, S.; Sen,
S. S.; Kratzert, D.; Tavꢀcar, G.; Roesky, H. W.; Stalke, D. Chem. Eur. J.
2011, 17, 4283–4290.
MS: m/z: 734 [Mþ] (100%). IR (Nujol, cmꢀ1): ν 2086 (SiꢀH). For
h
elemental analysis 2 (toluene) was treated under vacuum overnight to
3
remove the toluene molecule. Anal. Calcd for C42H55ClN6Si2 (734.37):
C, 68.58; H, 7.54; N, 11.43. Found: C, 68.17; H, 7.23; N, 10.77.
(11) X-ray investigation of 2: the data sets were collected from oil
coated shock-cooled crystals ((a) Stalke, D. Chem. Soc. Rev. 1998,
27, 171–178. (b) Kottke, T.; Lagow, R. J.; Stalke, D. J. Appl. Crystallogr.
1996, 29, 465–468. (c) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993,
26, 615–619. ) on a Bruker SMART-APEX diffractometer with a D8
goniometer (Mo KR radiation, λ = 0.710 73 Å) equipped with an
Incoatec microfocus source (Schulz, T.; Meindl, K.; Leusser, D.; Stern,
D.; Graf, J.; Michaelsen, C.; Ruf, M.; Sheldrick, G. M.; Stalke, D. J. Appl.
Crystallogr. 2009, 42, 885–891. ) and a low-temperature device in ω-scan
mode at 100(2) K. The data were integrated with SAINT (SAINT
v7.68A; Bruker, Madison, WI, 2009) and an empirical absorption
correction was applied with SADABS ( Sheldrick, G. M. SADABS
2008/1; Universit€at G€ottingen, G€ottingen, Germany, 2008). The struc-
tures were solved by direct methods (SHELXS-97) and refined by full-
matrix least-squares methods against F2 (SHELXL-97, Sheldrick, G. M.
Acta Crystallogr., Sect. A 2008, 64, 112–122. ). CCDC no 819818
contains the supplementary crystallographic data for this paper. Crystal
(3) Sen, S. S.; Roesky, H. W.; Stern, D.; Henn, J.; Stalke, D. J. Am.
Chem. Soc. 2010, 132, 1123–1126.
(4) (a) Sen, S. S.; Khan, S.; Roesky, H. W.; Kratzert, D.; Meindl, K.;
Henn, J.; Stalke, D.; Demers, J.-P.; Lange, A. Angew. Chem. 2011,
123, 2370–2373; Angew. Chem., Int. Ed. 2011, 50, 2322–2325.
(5) (a) Evans, W. J.; Drummond, D. K.; Chamberlain, L. R.;
Doedens, R. J.; Bott, S. G.; Zhang, H.; Atwood, J. L. J. Am. Chem. Soc.
1988, 110, 4983–4994; (b) Bonyhady, S. J.; Green, S. P.; Jones, C.;
Nembenna, S.; Stasch, A. Angew. Chem. 2009, 121, 3017–3021; Angew.
Chem., Int. Ed. 2009, 48, 2973–2977. (c) Cui, C.; Olmstead, M. M.;
Fettinger, J. C.; Spikes, G. H.; Power, P. P. J. Am. Chem. Soc. 2005,
127, 17530–17541. (d) Sen, S. S.; Kratzert, D.; Stern, D.; Roesky, H. W.;
Stalke, D. Inorg. Chem. 2010, 49, 5786–5788.
(6) (a) Sakakibara, A.; Kabe, Y.; Shimizu, T.; Ando, W. J. Chem. Soc.,
Chem. Commun. 1991, 43–44. (b) Zhang, S.-H.; Yeong, H.-X; So, C.-W.
Chem. Eur. J. 2011, 17, 3490–3494.
(7) Weidenbruch, M.; Olthoff, S.; Saak, W.; Marsmann, H. Eur. J.
Inorg. Chem. 1998, 1755–1758.
data for 2 (toluene): C49H63N6Si2Cl, Mr = 827.68, triclinic, space group
3
P1, a = 9.3427(11) Å, b = 10.7563(13) Å, c = 12.2182(15) Å, R =
94.310(2)°, β = 97.304(2)°, γ = 108.196(2)°, V = 1148.4(2) Å3, Z = 1,
Fcalcd = 1.197 Mg/m3, μ = 0.176 mmꢀ1, 27 534 reflections measured,
4737 independent reflections, R1(I > 2σ(I)) = 0.0611, wR2(I > 2σ(I)) =
0.1343. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
(12) (a) Mitzel, N. W. Z. Naturforsch., B 2003, 58, 369–375. (b)
Hemme, I.; Klingebiel, U. Adv. Organomet. Chem. 1996, 39, 159–192. (c)
Glidewell, C.; Rankin, D. W. H.; Robiette, A. G.; Sheldrick, G. M. J.
Chem. Soc. A 1970, 318–320. (d) Veith, M.; Rammo, A. Z. Anorg. Allg.
Chem. 2001, 627, 662–668.
(13) (a) Sen, S. S.; Tavꢀcar, G.; Roesky, H. W.; Kratzert, D.; Hey, J.;
Stalke, D. Organometallics 2010, 29, 2343–2347. (b) Kaftory, M.; Kapon,
M.; Botoshansky, M. In The Chemistry of Organic Silicon Compounds;
Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, U.K., 1998; Vol. 2,
Chapter 5.
(14) (a) Jana, A.; Schulzke, C.; Roesky, H. W. J. Am. Chem. Soc. 2009,
131, 4600–4601. (b) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2005,
127, 643–656. (c) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2002,
124, 6814–6815.
(8) Jana, A.; Samuel, P. P.; Roesky, H. W.; Schulzke, C. J. Am. Chem.
Soc. 2010, 132, 10164–10170.
(9) (a) Walker, R. H.; Miller, K. A.; Scott, S. L.; Cygan, Z. T.;
Bartolin, J. M.; Kampf, J. W.; Holl, M. M. B. Organometallics 2009,
28, 2744–2755. (b) Hartmann, M.; Haji-Abdi, A.; Abersfelder, K.;
Haycock, P. R.; White, A. J. P.; Scheschkewitz, D. Dalton Trans. 2010,
39, 9288–9295. (c) Nguyen, T.-I.; Scheschkewitz, D. J. Am. Chem. Soc.
2005, 127, 10174–10175. (d) Abersfelder, K.; Scheschkewitz, D. J. Am.
Chem. Soc. 2008, 130, 4114–4121.
(10) All manipulations were carried out under an inert atmosphere
of dinitrogen using standard Schlenk techniques and in a dinitrogen-
filled glovebox. Solvents were purified with the MBRAUN solvent
purification system MB SPS-800. Compound 1 was prepared according
to the literature method,3 and diazobenzene purchased from Aldrich was
used without further purification. 1H, 13C, and 29Si NMR spectra were
recorded in THF-d8 with Bruker Avance DRX 500 spectrometer. The
chemical shifts δ are given relative to SiMe4. The EI-MS spectrum was
obtained using a Finnigan MAT 8230 instrument. The IR spectrum was
recorded on a Bio-Rad Digilab FTS7 spectrometer in the range
4000ꢀ350 cmꢀ1. Elemental analyses were performed by the Institut
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