An efficient route for the synthesis of a Tin(II) substituted carbodiimide from a diazo compound

Article abstract of DOI:10.1021/ic100031d

The reaction of β-diketiminate substituted tin(II) chloride, LSnCl (1 ; L = HC{(CMe)(2,6-/Pr₂C₆H₃N)}₂), with the lithium salt of trimethylsilyl diazomethane (LiC(N₂) SiMe₃) is described. In the course of the reaction, the exclusive formation of tin(II) substituted carbodiimide LSnNCNSiMe₃ (2) Is observed In good yield. This reaction occurs at room temperature without any side products. Furthermore, we reacted diiron nonacarbonyl, Fe ₂(CO)₉, with compound 2 to confirm the carbodiimide skeleton (N=C=N) without rearrangement. The latter reaction leads to the tin(II) coordinate iron carbonyl complex LSnNCNSiMe₃Fe(CO)₄ (3). Compounds 2 and 3 were investigated by microanalysis and multinuclear NMR spectroscopy and were further characterized by X-ray structural analysis.

Full text of DOI:10.1021/ic100031d

Inorg. Chem. 2010, 49, 3461–3464 3461
DOI: 10.1021/ic100031d
An Efficient Route for the Synthesis of a Tin(II) Substituted Carbodiimide from a
Diazo Compound
Anukul Jana,† Herbert W. Roesky,*,† Carola Schulzke,‡ and Prinson P. Samuel†
†
€
€
€
Institut fu€r Anorganische Chemie der Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany,
and ‡School of Chemistry, Trinity College Dublin, Dublin 2, Ireland
Received January 6, 2010
The reaction of β-diketiminate substituted tin(II) chloride, LSnCl (1; L = HC{(CMe)(2,6-iPr2C6H3N)}2), with the lithium
salt of trimethylsilyl diazomethane (LiC(N2)SiMe3) is described. In the course of the reaction, the exclusive formation of
tin(II) substituted carbodiimide LSnNCNSiMe3 (2) is observed in good yield. This reaction occurs at room temperature
without any side products. Furthermore, we reacted diiron nonacarbonyl, Fe2(CO)9, with compound 2 to confirm the
carbodiimide skeleton (NdCdN) without rearrangement. The latter reaction leads to the tin(II) coordinate iron
carbonyl complex LSnNCNSiMe3Fe(CO)4 (3). Compounds 2 and 3 were investigated by microanalysis and
multinuclear NMR spectroscopy and were further characterized by X-ray structural analysis.
Introduction
LSnCl.6 The reaction of lithiated trimethylsilyl diazomethane
with LSnCl leads to carbodiimide that reacts further with
diiron nonacarbonyl to form the tin(II) coordinate iron
carbonyl complex, without rearrangement. Recently, we
reported on the unprecedented end-on nitrogen insertion of
a diazo compound into a germanium(II) hydrogen bond,7
and furthermore we showed the C-H bond cleavage of
trimethylsilyl diazomethane, when this was reacted with a
N-heterocyclic germylene.8
The chemistry of transition metals with diazoalkanes is
well documented,1 although the corresponding chemistry
with main group elements has not been extensively studied.2
Trialkylsilyl diazomethane derivatives are established for the
synthesis of chemical building blocks,3 and they also possess
six known or suspected structural isomers including nitrili-
mine and carbodiimide. In synthetic organic chemistry
compounds containing the carbodiimide functionality are
used as dehydration agents, and to activate carboxylic acids
toward amide or ester formation. For this purpose especially,
dicyclohexylcarbodiimide (DCC) with additives, such as
N-hydroxybenzotriazole, is applied for peptide synthesis in
biochemistry.4 In the literature there are reports on the
synthesis of carbodiimides from diazo compounds at very
high temperatures or in the presence of a metal catalyst.5
Herein, we report our efforts to explore diazoalkane main
group chemistry with β-diketiminate substituted tin(II) chloride,
Results and Discussion
The reaction of LSnCl (1; L = HC{(CMe)(2,6-iPr2C6H3-
N)}2), with lithiated trimethylsilyl diazomethane, obtained
from nBuLi and Me3SiCHN2 in THF, resulted in the forma-
tion of LSnNCNSiMe3 (2; Scheme 1). The reaction proceeds
at ambient temperature without using any additional catalyst.
The formation of the diazo compound LSnC(N2)SiMe3 (2a)
or nitrilimine compound LSnNNCSiMe3 (2b) was not ob-
served on the basis of analytical and structural data. In this
context it is worth mentioning that the synthesis of diazo
germylene and stannylene compounds was previously reported
using ArGeCl (Ar = 2,6-(CH2NR2)2C6H3, R = Et, iPr) and
Ar1SnCl (Ar1 = 2,6-Tip2C6H3, Tip = 2,4,6-iPr3C6H2).9,10
*To whom correspondence should be addressed. Fax: þ49-551-393373.
E-mail: hroesky@gwdg.de.
(1) (a) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18–29.
(b) Schrock, R. R. Angew. Chem. 2006, 118, 3832–3844. Angew. Chem., Int.
Ed. 2006, 45, 3748-3759. (c) Grubbs, R. H. Angew. Chem. 2006, 118, 3845–
3850. Angew. Chem., Int. Ed. 2006, 45, 3760-3765.
(2) Barnier, J.-P.; Blanco, L. J. Organomet. Chem. 1996, 514, 67–71.
(3) Bertrand, G. Organosilicon Chemistry III: From Molecules to Materi-
als; Wiley-VCH: New York, 1998; pp 223-236.
(7) Jana, A.; Sen, S. S.; Roesky, H. W.; Schulzke, C.; Dutta, S.; Pati, S. K.
Angew. Chem. 2009, 121, 4310–4312. Angew. Chem., Int. Ed. 2009, 48,
4246-4248.
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r
2010 American Chemical Society
Published on Web 03/03/2010
pubs.acs.org/IC

3462 Inorganic Chemistry, Vol. 49, No. 7, 2010
Scheme 1. Preparation of 2
Jana et al.
Scheme 2. Proposed Pathway for the Formation of 2
Figure 1. Molecular structureof2. Thermal ellipsoidsare shown at50%
probability. H atoms are omitted for clarity reasons. Selected bond
˚
lengths [A] and angles [deg]: Sn1-N1 2.121(7), N1-C1 1.124(10),
C1-N2 1.239(11), N2-Si1 1.718(7), Sn1-N3 2.169(3); Sn1-N1-C1
152.5(8), N1-C1-N2 178.6(10), C1-N2-Si1 136.2(7), N1-Sn1-N3
90.35(18), N3-Sn1-N3A 86.5(2).
constant of 58.3 Hz. This is an indication that the SiMe3
group binds to the N atom and not anymore to carbon.
Moreover, the 29Si NMR spectrum shows the resonances
which are attributed to the 15N satellite with a coupling
constant of 16.8 Hz from the nitrogen atom of the carbodii-
mide backbone. The ratio of the two satellite lines matches
well with their abundances. The 119Sn NMR resonance of 2
arises at δ -321.4 ppm as a triplet (J(119Sn-14N) = 250 Hz),
which is upfield shifted when compared with that of the
starting material LSnCl (1; δ -224 ppm). In the 14N NMR
spectrum, the signal at δ -329 ppm corresponds to the N
atom bound to the silyl group, which was proven by the
15N-1H correlation experiment. The resonance of the NCN
carbon is found in the 13C NMR spectrum at δ 129.7 ppm (δ
131.0 ppm; iPr3SiNCNSnMe3).5 In the EI mass spectrum, the
molecular ion is observed at m/z 649 as the base peak for 2.
Compound 2 crystallizes from a saturated n-hexane solu-
tion at -30 °C after two days in the monoclinic space group
C2/m, with one monomer in the asymmetric unit. The
coordination around the tin atom features a distorted tetra-
hedral geometry with one lone pair (Figure 1). Crystallo-
graphic studies on 2 also indicate that the N-bound silyl
group structure LSn-NdCdN-SiMe3 was formed. All the
bond lengths and bond angles are as expected. It is worth
mentioning that in the solid state of 2 weak Sn-Sn interac-
Furthermore, N-bound silyl products, [(MeC5H4)TiCl(μ-
NSiMe3)]2,11 and [(C5Me5)2Ln{μ-N(SiMe3)NC}]2 (Ln =
Sm, La)12 have been previously observed in the reaction of
Li[Me3SiCN2] with (MeC5H4)TiCl3 and [(C5Me5)2Ln][(μ-
Ph)2BPh2] (Ln = Sm, La), respectively, with migration of
the silyl group. However, compound 2 represents the first
structurally characterized carbodiimide of heavier group 14
elements containing the Sn(II) motif.
It is well-known that the reaction of lithium salts of
substituted diazomethane with different electrophiles gener-
ates diazo or nitrilimine compounds.13 Therefore, the present
observation of a carbodiimide formation requires an unpre-
cedented rearrangement. Wentrup and co-workers reported
the evidence for nitrilimine to carbodiimide rearrangement
through an isodiazirine and imidoylnitrene intermediate,
based on the nature of the products obtained in the pyrolysis
of different nitrilimine precursors at 500 to 960 °C.14 Subse-
quently, Bertrand and co-workers mentioned the direct
evidence for the nitrilimine to imidoylnitrene rearrangement
by the isolation of a unusual nitrene complex.15 Considering
all the facts, we propose the following pathway for the
formation of 2 (Scheme 2).
Compound 2 was characterized by multinuclear NMR
spectroscopy, EI mass spectrometry, elemental analysis, and
X-ray structural analysis (Figure 1). The 1H NMR spectrum
of 2 exhibits a singlet (δ 4.96 ppm) corresponding to the CH
proton of the backbone of the C3N2Sn ring. Compound 2 has
one SiMe3 group and displays a singlet in the 29Si NMR
spectrum (δ -6.0 ppm) and shows only one type of 13C
satellite line due to the methyl groups with a coupling
˚
tions (3.708 A) are observed which are below the sum of van
16
˚
der Waals radii of 4.40 A for two tin atoms (Figure 2).
From the multinuclear NMR and X-ray data, we formu-
lated compound 2 as a carbodiimide derivative. To verify this
skeleton, we reacted 2 with Fe2(CO)9 to show whether the
lone pair on tin is still prone to complexation with Fe(CO)4
(Scheme 3). In the course of the reaction, the tin(II) coordi-
nate iron carbonyl complex LSnNCNSiMe3Fe(CO)4 (3) is
formed with the same carbodiimde functionality.
Compound 3 was characterized by multinuclear NMR, EI
mass spectrometry, and X-ray structural analysis. In the 29Si
NMR spectrum, 3 exhibits a singlet at δ -3.2 ppm with a 13C
(11) Bai, G.; Roesky, H. W.; Hao, H.; Noltemeyer, M.; Schmidt, H.-G.
Inorg. Chem. 2001, 40, 2424–2426.
(12) Evans, W. J.; Montalvo, E.; Champagne, T. M.; Ziller, J. W.;
DiPasquale, A. G.; Rheingold, A. L. J. Am. Chem. Soc. 2008, 130, 16–17.
ꢀ
(13) Reau, R.; Veneziani, G.; Bertrand, G. J. Am. Chem. Soc. 1992, 114,
6059–6063.
(14) Fischer, S.; Wentrup, C. J. Chem. Soc., Chem. Comm. 1980, 502–503.
€
(15) Granier, M.; Baceiredo, A.; Grutzmacher, H.; Pritzkow, H.;
(16) Allan, R. E.; Beswick, M. A.; Edwards, A. J.; Paver, M. A.; Rennie,
M.-A.; Raithby, P. R.; Wright, D. S. J. Chem. Soc., Dalton Trans. 1995,
1991–1994.
Bertrand, G. Angew. Chem. 1990, 102, 671–672. Angew. Chem., Int. Ed.
1990, 29, 659-661.

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3463
˚
Figure 2. Unit cell of2, showing the weak Sn-Sn interactions (3.708 A).
Scheme 3. Preparation of 3
Figure 3. Molecular structureof3. Thermal ellipsoidsare shown at50%
probability. H atoms and isopropyl groups are omittedfor clarity reasons.
Selected bond lengths [A] and angles [deg]: Sn1-N1 2.081(6), N1-C1
˚
1.136(9), C1-N2 1.198(9), N2-Si1 1.649(7), Sn1-N3 2.122(3), Sn1-Fe1
2.4777(9); Sn1-N1-C1 141.2(7), N1-C1-N2 172.9(10), N1-Sn1-N3
95.87(15), N3-Sn1-N3A 88.93(16).
material 1 was prepared using literature procedures.6 Other che-
1
micals were purchased and used as received. H, 13C, 29Si, and
satellite (2J(29Si-13C) = 59.0 Hz). In the 119Sn NMR
spectrum, 3displays a resonance at δ11.45 ppm, which is down-
field shifted when compared with that of 2 (δ -321.4 ppm).
Moreover, in the 13C NMR spectrum, the resonance arises at δ
212.9 ppm for the CO group, a value comparable to those of
LGe(OH)Fe(CO)4 (δ 214.8 ppm)17 and LSn(OH)Fe(CO)4 (δ
213.1),18 and also matches with the other reported Sn(II)-Fe
carbonyl complexes.19
Compound 3 crystallizes in the orthorhombic space group
Pnma with one molecule in the asymmetric unit from a
saturated toluene solution (Figure 3). The coordination
polyhedron around the tin atom features a distorted tetra-
hedral geometry.
119Sn NMR spectra were recorded on a Bruker Avance DRX
500 MHz instrument and referenced to the deuterated solvent in
the case of the 1H and 13C NMR spectra and SiMe4 and SnMe4 for
the 29Si and 119Sn NMR spectra, respectively. Elemental analyses
€
were performed by the Analytisches Labor des Instituts fur
€
€
Anorganische Chemie der Universitat Gottingen. Infrared spectral
data were recorded on a Perkin-Elmer PE-1430 instrument. EI-MS
were measured on a Finnigan Mat 8230 or a Varian MAT CH5
instrument. Melting points were measured in sealed glass tubes
€
with a Buchi melting point B 540 instrument.
Synthesis of LSnNCNSiMe3 (L = HC{(CMe)(2,6-iPr2C6H3-
N)}2) (2). A solution of lithium trimethylsilyldiazomethane
(4.0 mmol) prepared from a solution of trimethylsilyldiazo-
methane (2.0 mL, 2 M in n-hexane) and nBuLi (2.5 mL, 1.6 M
in n-hexane) in THF (15 mL) was added drop by drop to the
solution of 1 (2.20 g, 4.0 mmol) in THF (35 mL) at -78 °C. The
resulting solution was allowed to warm slowly to room tem-
perature and was stirred for another 30 min. Solvents were
removed in a vacuum, and the residue was dissolved in n-hexane
(80 mL). The solution was filtered, the solvent was partially
removed, and 2 was obtained as a yellow crystalline solid after
being stored for two days at -30 °C in a freezer. The crystals
were suitable for X-ray structural analysis. Yield (1.76 g, 68%).
Summary and Conclusion
In this manuscript, we describe the facile synthesis of a
carbodiimide with a tin(II) moiety. This reaction proceeds
probably via a unique diazo-nitrilimine-isodiazirine-imidoyl-
nitrene-carbodiimde rearrangement at ambient temperature.
The high yield synthesis of a stable Sn(II) carbodiimide
creates a potential precursor to generate a variety of com-
pounds containing low valent group 14 elements.
1
Mp 177 °C. H NMR (500 MHz, C6D6): δ 7.02-7.15 (m, 6H,
Ar-H), 4.96 (s, 1H, CH), 3.82 (sept, 2H, CH(CH3)2), 3.14 (sept,
2H, CH(CH3)2), 1.61 (s, 6H, CH3), 1.51 (d, 6H, CH(CH3)2), 1.32
(d, 12H, CH(CH3)2), 1.18 (d, 6H, CH(CH3)2), 1.07 (d, 6H,
CH(CH3)2), 0.27 (s, 9H, Si(CH3)3) ppm. 13C NMR (75.46
MHz, C6D6, 25 °C): δ 165.4 (CN), 145.7, 142.8, 141.8, 125.3,
125.1, 124.0 (ArC), 129.7 (NCN), 99.9 (CH), 29.2 (CH(CH3)2),
28.2 (CH(CH3)2), 27.1 (CH3), 24.7 (CH(CH3)2), 24.4 (CH-
(CH3)2), 24.2 (CH(CH3)2), 24.8 (CH(CH3)2), 2.0 (Si(CH3)3)
ppm. 14N{1H} NMR (50.68 Hz, C6D6): δ -184 (NSn), -291
(NC), -329 (NSi) ppm. 29Si{1H} NMR (125.77 Hz, C6D6): δ
-6.0 (Si(CH3)3) ppm. 119Sn{1H} NMR (186.46 MHz, C6D6): δ
-321.4 ppm. EI-MS (70 eV): m/z (%): 649 (100) [M]þ. Anal.
Calcd for C33H50N4SiSn (649.55): C, 61.02; H, 7.76; N, 8.63.
Found: C, 61.42; H, 8.04; N, 8.42.
Experimental Section
General Considerations. All manipulations were performed
under a dry and oxygen free atmosphere (N2) using standard
Schlenk techniques or inside an MBraun MB 150-GI glovebox
maintained at or below 1 ppm of O2 and H2O. Solvents were
purified with the MBraun solvent drying system. The starting
(17) Pineda, L. W.; Jancik, V.; Colunga-Valladares, J. F.; Roesky, H. W.;
Hofmeister, A.; Magull, J. Organometallics 2006, 25, 2381–2383.
(18) Jana, A.; Sarish, S. P.; Roesky, H. W.; Schulzke, C.; Samuel, P. P.
Chem. Commun. 2010, 46, 707–709.
€
€
(19) (a) Mehring, M.; Low, C.; Schurmann, M.; Uhlig, F.; Jurkschat, K.
€
Organometallics 2000, 19, 4613–4623. (b) Schneider, J. J.; Czap, N.; Blaser, D.;
Synthesis of LSnNCNSiMe3Fe(CO)4 (L = HC{(CMe)(2,6-
iPr2C6H3N)}2) (3). Aflaskwas chargedwith2 (0.650 g, 1.00 mmol)
and Fe2(CO)9 (0.370 g, 1.00 mmol) in THF (140 mL). The solution
Boese, R.; Ensling, J.; G€utlich, P.; Janiak, C. Chem.;Eur. J. 2000, 6, 468–474.
(c) Cardin, C. J.; Cardin, D. J.; Convery, M. A.; Dovereux, M. M.; Twamley, B.;
Silver, J. J. Chem. Soc., Dalton Trans. 1996, 1145–1151.

3464 Inorganic Chemistry, Vol. 49, No. 7, 2010
Jana et al.
Table 1. Crystallographic Data for the Structural Analyses of Compounds 2
and 3
product was attained from a saturated toluene solution of 3 and
storing it at -30 °C in a freezer. Compound 3 deposited as light
brown crystals. Yield: 0.60 g (73%). Mp 197 °C. 1H NMR (500.13
MHz, C6D6, 25 °C): δ 7.04-7.15 (m, 6H, ArH), 5.00 (s, 1H;
CH), 3.71 (sept, 2H, CH(CH3)2), 3.06 (sept, 2H, CH(CH3)2), 1.56
(d, 6H, CH (CH3)2), 1.52 (s, 6H; CH3), 1.32 (d, 6H, CH(CH3)2),
1.26 (d, 6H, CH(CH3)2), 1.02 (d, 6H, CH(CH3)2), 0.23 (s, 9H,
Si(CH3)3) ppm. 13C NMR (125.75 MHz, C6D6, 25 °C): δ 212.9
(CO), 169.9 (CN), 145.3, 143.2, 139.9, 128.8, 125.4, 124.8 (ArC),
129.1 (NCN), 101.6 (CH), 29.4 (CH(CH3)2), 28.6 (CH(CH3)2),
25.7 (CH3), 24.5 (CH(CH3)2), 24.5 (CH(CH3)2), 24.3 (CH(CH3)2),
24.0 (CH(CH3)2), 1.5 (Si(CH3)3) ppm. 29Si{1H} NMR (125.77 Hz,
C6D6): δ -3.2 (Si(CH3)3) ppm. 119Sn NMR (111.92 MHz, C6D6,
25 °C): δ11.4 ppm. EI-MS (70 eV; m/z(%)): 734 (15) [M- 3CO]þ,
706 (100) [M - 4CO]þ.
2
3
empirical formula
CCDC no.
T [K]
C
33H50N4SiSn
745456
C37H50FeN4O4SiSn
749249
133(2) K
monoclinic
C2/m
133(2) K
orthorhombic
Pnma
cryst syst
space group
˚
˚
17.018(3) A
a [A]
23.764(5)
16.231(3)
10.373(2)
90
˚
b [A]
˚
c [A]
19.998(4)
12.539(3) A
˚
R [deg]
β [deg]
γ [deg]
V [A ]
Z
calcd [g cm-3
μ [mm-1
F(000)
90
126.27(3)
90
90
90
3
˚
3440.5(12)
4
1.254
4001.3(14)
4
1.357
Crystallographic Details for Compounds 2 and 3. Suitable
crystals of 2 and 3 were mounted on a glass fiber, and data were
collected on an IPDS II Stoe image-plate diffractometer (graphite
D
]
]
0.803
1360
1.057
1688
˚
monochromated Mo KR radiation, λ = 0.71073 A) at 133(2) K
(Table 1). The data were integrated with X-Area. The structures
were solved by direct methods (SHELXS-97)20 and refined by full-
matrix least-squares methods against F2 (SHELXL-97).20 All non-
hydrogen atoms were refined with anisotropic displacement para-
meters. The hydrogen atoms were refined isotropically on calcu-
lated positions using a riding model.
θ range [°]
data/restraints/params
reflns collected/unique
1.94 to 25.86
3415/0/168
13525/3415
(Rint = 0.0419)
0.0468, 0.1206
0.0506, 0.1228
1.026
1.71 to 25.82
3837/3/237
14172/3837
(Rint = 0.0288)
0.0472, 0.1220
0.0554, 0.1269
1.021
R1, wR2 [I > 2σ(I)]a
R1, wR2 (all data)a
GoF
-3
˚
ΔF(max), ΔF(min) [e A
]
2.553, -1.638
2.739, -2.985
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft.
P
P
P
P
aR1 =
Fo| - |Fc
/
|Fo|. wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]0.5
.
Supporting Information Available: X-ray data for 2 and 3
(CIF). This material is available free of charge via the Internet at
http://pubs.acs.org.
was stirred for 24 h at ambient temperature. The byproduct was
removed by filtration of the solution over Celite, resulting in a clear
pale brown filtrate. From the resulting solution, the volatiles were
removed, giving a pale brown solid. Crystallization of the crude
(20) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.