Dehydrogenation of LGeH by a lewis N-heterocyclic carbene borane pair under the formation of L'Ge and its reactions with B(C6F5) 3 and trimethylsilyl diazomethane: An unprecedented rearrangement of a diazocompound to an is

Article abstract of DOI:10.1021/ic900341r

Herein we report the dehydrogenation of LGeH (1) [L = CH{(CMe)(2,6-/Pr ₂C₆H₃N)}₂] by a frustrated Lewis NHC borane pair under the formation of an imidazolium borate salt (2) and the heterocyclic germylene L'Ge (

Full text of DOI:10.1021/ic900341r

Inorg. Chem. 2009, 48, 7645–7649 7645
DOI: 10.1021/ic900341r
Dehydrogenation of LGeH by a Lewis N-Heterocyclic Carbene Borane Pair under the
Formation of L0Ge and its Reactions with B(C6F5)3 and Trimethylsilyl Diazomethane:
An Unprecedented Rearrangement of a Diazocompound to an Isonitrile
Anukul Jana, Ina Objartel, Herbert W. Roesky,* and Dietmar Stalke
::
:: ::
::
Institut fur Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
Received February 19, 2009
Herein we report the dehydrogenation of LGeH (1) [L = CH{(CMe)(2,6-iPr2C6H3N)}2] by a frustrated Lewis NHC
borane pair under the formation of an imidazolium borate salt (2) and the heterocyclic germylene L0Ge (3) [L0 =
CH{(CdCH2)(CMe)(2,6-iPr2C6H3N)2}]. The reaction of 3 with B(C6F5)3 in toluene results in the formation of a
zwitterion containing a germylene moiety, [B(C6F5)3L00Ge] (4) [L00 = CH{(CCH2)(CMe)(2,6-iPr2C6H3N)2}].
Subsequent treatment of 4 with 1 equiv of 1,3-di-tert-butylimidazol-2-ylidene (NHC) gives B(C6F5)3L000Ge (5)
[L000 = CH{(CdCH2)(CCH2B(C6F5)3)(2,6-iPr2C6H3N)2}] under formation of the imidazolium cation. Moreover
compound 3 reacts with trimethylsilyl diazomethane (N2CHSiMe3) to form the diazogermylene LGeC(N2)SiMe3 (6)
under C-H bond cleavage. Compound 6 slowly rearranges to the isonitriletrimethylsilyl germanium(II) amide
LGeN(SiMe3)NC (6a). All compounds were characterized by microanalysis and multinuclear NMR spectroscopy.
Compounds 4, 6, and 6a were unequivocally identified by single crystal X-ray structure analysis.
Introduction
fluorophenyl)borane, B(C6F5)3)7 in combination with steri-
cally demanding phosphanes, amines, imines, and N-hetero-
cyclic carbenes (NHCs), respectively, are excellent non-
metallic systems for the activation of dihydrogen under mild
conditions. NHCs and B(C6F5)3 independently have also been
employed for proton and hydride abstraction reactions.8,9
Recently we reported on the synthesis of LGeCl,10 and
observed thatone hydrogenfrom the backbone ofone methyl
group can be eliminated.11 Therefore, it seemed possible that
LGeH (1)12 might be dehydrogenated with a Lewis NHC
borane pair because of a reversible reaction. In the literature
The Lewis acid-base concept is fundamental for under-
standing numerous chemical reactions.1 This principle is
essential for main group elements, as well as for transition
metals.2 In recent years, Stephan et al.,3 Rieger et al.,4 Erker
et al.,5 and Tamm et al.6 were able to demonstrate that
frustrated Lewis pairs of boranes (in particular tris(penta-
*To whom correspondence should be addressed. E-mail: hroesky@
gwdg.de. Fax: þ49-551-393373.
(1) Lewis, G. N. Valence and the Structure of Atoms and Molecules;
Chemical Catalogue: New York, 1923.
(2) Cotton, F. A.; Wilkinson, C. A.; Murillo, C. A.; Bochmann, M.
Advanced Inorganic Chemistry, 6th ed.; Wiley: New York, 1999.
(3) (a) Welch, G. C.; San Jun, R. R.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124–1126. (b) Welch, G. C.; Stephan, D. W. J. Am. Chem.
Soc. 2007, 129, 1880–1881. (c) Chase, P. A.; Stephan, D. W. Angew. Chem.
2008, 120, 7543–7547. Chase, P. A.; Stephan, D. W. Angew. Chem., Int. Ed.
2008, 47, 7433–7437. (d) Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Commun.
(7) (a) Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345–354. (b)
Piers, W. E. Adv. Organomet. Chem. 2004, 52, 1–75. (c) A. Y. Timoshkin, A. Y.;
Frenking, G. Organometallics 2008, 27, 371–380.
(8) Jancik, V.; Pineda, L. W.; Pinkas, J.; Roesky, H. W.; Neculai, D.;
Neculai, A. M.; Herbst-Irmer, R. Angew. Chem. 2004, 116, 2194–2197.
Jancik, V.; Pineda, L. W.; Pinkas, J.; Roesky, H. W.; Neculai, D.; Neculai, A. M.;
Herbst-Irmer, R. Angew. Chem., Int. Ed. 2004, 43, 2142–2145.
(9) (a) Masuda, J. D.; Walsh, D. M.; Wei, P.; Stephan, D. W. Organo-
metallics 2004, 23, 1819–1824. (b) Dureen, M. A.; Lough, A.; Gilbert, T. M.;
Stephan, D. W. Chem. Commun. 2008, 5966–5968. (c) Saverio, A. D.; Focante,
F.; Camurati, I.; Resconi, L.; Beringhelli, T.; D'Alfonso, G.; Donghi, D.;
Maggioni, D.; Mercandelli, P.; Sironi, A. Inorg. Chem. 2005, 44, 5030–5041.
(10) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Organo-
metallics 2001, 20, 1190–1194.
2008, 1701–1703.
::
(4) (a) Sumerin, V.; Schulz, F.; Nieger, M.; Leskela, M.; Repo, T.; Rieger,
B. Angew. Chem. 2008, 120, 6090–6092. Sumerin, V.; Schulz, F.; Nieger, M.;
::
Leskela, M.; Repo, T.; Rieger, B. Angew. Chem., Int. Ed. 2008, 47, 6001–6003.
::
(b) Sumerin, V.; Schulz, F.; Atsumi, M.; Wang, C.; Nieger, M.; Leskela, M.; Repo,
::
T.; Pyykko, P.; Rieger, B. J. Am. Chem. Soc. 2008, 130, 14117–14119.
::
(5) (a) Wang, H.; Frohlich, R.; Kehr, G.; Erker, G. Chem. Commun. 2008,
5966–5968. (b) Huber, D. P.; Kehr, G.; Bergander, K.; Frohlich, R.; Erker, G.;
::
Tanino, S.; Ohki, Y.; Tatsumi, K. Organometallics 2008, 27, 5279–5284. (c)
(11) Jana, A.; Objartel, I.; Roesky, H. W.; Stalke, D. Inorg. Chem. 2009,
48, 798–800.
::
Axenov, K. V.; Kehr, G.; Frohlich, R.; Erker, G. J. Am. Chem. Soc. 2009, 131,
(12) (a) Pineda, L. W.; Jancik, V.; Starke, K.; Oswald, R. B.; Roesky, H.
W. Angew. Chem. 2006, 118, 2664–2667. Pineda, L. W.; Jancik, V.; Starke, K.;
Oswald, R. B.; Roesky, H. W. Angew. Chem., Int. Ed. 2006, 45, 2602–2605. (b)
Jana, A.; Ghoshal, D.; Roesky, H. W.; Objartel, I.; Schwab, G.; Stalke, D. J. Am.
Chem. Soc. 2009, 131, 1288–1293.
3454–3455.
(6) Holschumacher, D.; Bannenberg, T.; Hrib, C. G.; Jones, P. G.; Tamm,
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7432.
r
2009 American Chemical Society
Published on Web 07/10/2009
pubs.acs.org/IC

7646 Inorganic Chemistry, Vol. 48, No. 16, 2009
Jana et al.
Table 1. Crystallographic Data for the Structural Analysis of 4, 6, and 6a
4
6
6a
empirical formula
CCDC No.
T [K]
crystal system
space group
a [pm]
C47H40BF15GeN2
720891
100(2)
triclinic
P1
1216.90(13)
1371.36(15)
1504.04(16)
109.9890(10)
91.1810(10)
108.7890(10)
2.2088(4)
2
C33H50GeN4Si
734212
100(2)
triclinic
P1
1074.32(4)
1200.91(5)
1450.66(6)
106.9280(10)
94.2460(10)
109.4780(10)
1.65736(12)
2
C33H50GeN4Si
728257
100(2)
triclinic
P1
1077.8(3)
1204.0(4)
1444.5 (4)
107.113(3)
94.231(4)
109.254(3)
1.6607(8)
2
b [pm]
ꢀ
˚
c [A]
R [deg]
β [deg]
γ [deg]
V [nm3]
Z
Dcalcd [Mg m-3
]
1.505
0.794
1016
1.209
0.987
644
1.207
0.985
644
μ [mm-1
F(000)
]
θ range [deg]
1.69-25.39
43135
8111
8111/0/604
0.0385, 0.0953
0.0527, 0.0998
1.085
1.91-26.74
40967
7047
7047/0/365
0.0258, 0.0677
0.0273, 0.0685
1.053
1.50-25.35
24779
6039
6039/0/365
0.0311, 0.0869
0.0331, 0.0880
1.063
reflections collected
independent reflections
data/restraints/parameters
R1, wR2 [I > 2σ(I)]a
R1, wR2 (all data) a
GoF
-3
˚
Residual density max./min. [e A
]
0.391/-0.656
1.378/-0.287
0.900/-0.221
P
Scheme 1. Preparation of 2 and 3
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|. wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]0.5
.
Scheme 2. Preparation of 4
dehydrogenation of alkanes is reported using transition
metal catalyst.13 Herein we report on the dehydrogenation
of LGeH by a frustrated Lewis NHC borane pair and the
reaction of resulting heterocyclic germylene L0Ge (3) with
B(C6F5)3 and trimethylsilyl diazomethane.
We have shown that the heterocyclic germylene 3 cleaves
one N-H bond of ammonia at room temperature upon
formation of LGeNH2.11 Moreover, Driess et al. had inde-
pendently demonstrated that 3 has a dipolar character.15
Consequently we reacted 3 with B(C6F5)3 at room tempera-
ture to afford the zwitterionic compound [B(C6F5)3L00Ge]
(4), containing a germylene moiety (Scheme 2). Only two
reports on the synthesis of germanium(II) cations are in the
current literature, one was reported by Power and co-workers
where they also used a β-diketiminate ligand.16,17
Compound 4 was isolatedasair and moisture sensitive pale
yellow crystals in 78% yield, which are insoluble in common
hydrocarbon solvents but highly soluble in THF (Figure 1).
In this solvent there is no equilibrium between 3 and 4
observed in contrast to the isoelectronic silicon analogue of
4.18 4 crystallizes in the triclinic space group P1 (Table 1) and
consists of a planar six-membered C3N2Ge ring with an
exocyclic B(C6F5)3 group attached to C13. The β-diketimi-
nate N-C and C-C ring bond lengths have average values
Results and Discussion
In this paper we show the dehydrogenation of LGeH (1)
with a frustrated Lewis NHC borane pair. A toluene solution
of equimolar amounts of 1 and of B(C6F5)3 under stirring
changed the color from red to colorless after a few minutes.
To this reaction mixture we added an equivalent of 1,3-di-
tert-butylimidazol-2-ylidene,14 and the reaction mixture im-
mediately turned to brown-red with the formation of an
insoluble white precipitate (Scheme 1). The latter was identi-
fied as [(CHNtBu)2CH][HB(C6F5)3] (2) and was recovered
by filtration and dissolved in dichloromethane. The 1H NMR
spectrum of 2 indicates the formation of an imidazolium
cation. The 11B NMR resonance of 2 at -25.3 ppm is
identical with a previously reported imidazolium borate
salt.3c,6 The soluble part of the reaction mixture was char-
acterized to contain the heterocyclic germylene L0Ge (3).
::
(15) (a) Driess, M.; Yao, S.; Brym, M.; van Wullen, C. Angew. Chem.
::
2006, 118, 4455–4458. Driess, M.; Yao, S.; Brym, M.; van Wullen, C. Angew.
::
(13) Selected references: (a) Goldman, A. S.; Roy, A. H.; Huang, Z.;
Ahuja, R.; Schinski, W.; Brookhart, M. Science 2006, 312, 257–261. (b) Fekl,
U.; Kaminsky, W.; Goldberg, K. I. J. Am. Chem. Soc. 2003, 125, 15286–15287.
(c) Jensen, C. M. Chem. Commun. 1999, 2443–2449.
(14) (a) Arduengo, A. J.; Bock, H.; Chen, C.; Denk, M.; Dixon, D. A.;
Green, J. C.; Herrmann, W. A.; Jones, N. L.; Wagner, M.; West, R. J. Am.
Chem. Soc. 1994, 116, 6641–6649. (b) Scott, N. M.; Dorta, R.; Stevens, E. D.;
Correa, A.; Cavallo, L.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 3516–3526.
Chem., Int. Ed. 2006, 45, 4349–4352. (b) Yao, S.; van Wullen, C.; Driess, M.
Chem. Commun. 2008, 5393–5395.
(16) Stender, M.; Phillips, A. D.; Power, P. P. Inorg. Chem. 2001, 40,
5314–5315.
(17) Dias, H. V. R.; Wang, Z. J. Am. Chem. Soc. 1997, 119, 4650–4655.
::
(18) Driess, M.; Yao, S.; Brym, M.; van Wullen, C. Angew. Chem. 2006,
::
118, 6882–6885. Driess, M.; Yao, S.; Brym, M.; van Wullen, C. Angew. Chem.,
Int. Ed. 2006, 45, 6730–6733.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7647
Scheme 3. Reaction of LAl with B(C6F5)3
Scheme 4. Preparation of 5
Figure 1. Molecularstructure of4;anisotropicdisplacementparameters
are depicted at the 50% probability level, and all restrained refined
hydrogen atoms and isopropyl groups are omitted for clarity.
species is one proton. This is demonstrated in the reactivity
of 3 and LAl, respectively, with B(C6F5)3 (Scheme 3). 3
assembled as a zwitterionic germanium(II) species 4 and
the LAl forms a compound with a boron-aluminum bond.20
Preliminary studies of 4 with 1,3-di-tert-butylimidazol-2-
ylidene (NHC) show the deprotonation of the second methyl
group from the backbone with formation of compound
B(C6F5)3L000Ge (5) under complete conversion (Scheme 4).
The 1,3-di-tert-butylimidazol-2-ylidene reacts (Schemes 1
and 3) under formation of the imidazolium cation. However,
the counteranion is different. The neutral compound 3 is
formed to give the anion [HB(C6F5)3]-, whereas in 5 we
assume that the borate anion forms a stable ion pair with the
imidazolium cation.
The anion of 5 gives rise to the expected resonance with
the γ-CH proton at 5.87 ppm, which is comparable with
that of 3. The deprotonation of the second methyl group
leads to the exocyclic carbon-carbon double bond. The
two vinylic protons exhibit two non-equivalent singlets
(δ 3.63, 2.96 ppm), indicating that the germanium(II) atom
is neutral in 5. This is the first time we have shown that the
double C-H bond activation of the two methyl groups at the
ligand backbone has occurred by NHC. So far there is only
one C-H bond activation of the methyl group at the ligand
backbone reported.21 Unfortunately we were not able to
prove this result by an X-ray crystal structural analysis of 5
because of the lack of single crystals.
˚
Table 2. Selected Bond Distances [A] and Angles [deg] of 4, 6, and 6a
Compound 4
Ge(1)-N(1)
Ge(1)-N(2)
N(1)-C(14)
N(2)-C(16)
B(1)-C(1)
1.881(2)
1.873(2)
1.361(3)
1.361(3)
1.661(4)
B(1)-C(13)
F(1)-C(2)
C(13)-C(14)
C(16)-C(17)
1.657(4)
1.363(3)
1.506(4)
1.499(3)
N(1)-Ge(1)-N(2)
93.91(9)
N(1)-C(14)-C(13)
119.3(2)
119.7(2)
Ge(1)-N(1)-C(14) 128.52(17) B(1)-C(13)-C(14)
Ge(1)-N(2)-C(16) 127.40(17)
Compound 6
Ge(1)-N(1)
Ge(1)-N(2)
N(1)-C(26)
N(2)-C(29)
2.0111(12) Ge(1)-C(25)
1.9974(12) C(25)-Si(1)
1.3293(19) C(25)-N(3)
1.3295(18) N(3)-N(4)
1.9969(14)
1.8345(15)
1.3037(19)
1.1458(19)
N(1)-Ge(1)-N(2)
90.34(5)
N(1)-Ge(1)-C(25) 98.14(5)
Ge(1)-N(1)-C(26) 127.12(10) Ge(1)-C(25)-Si(1) 118.37(7)
Ge(1)-N(2)-C(29) 127.69(10) C(25)-N(3)-N(4)
175.74(15)
Compound 6a
Ge(1)-N(1)
Ge(1)-N(2)
N(1)-C(2)
N(2)-C(4)
1.9994(16) Ge(1)-N(3)
1.9862(16) N(3)-Si(2)
1.9491(16)
1.7699(17)
1.350(2)
1.330(3)
1.336(2)
N(3)-N(4)
N(4)-C(1)
1.154(3)
N(1)-Ge(1)-N(2)
Ge(1)-N(1)-C(2)
Ge(1)-N(2)-C(4)
90.84(7)
N(1)-Ge(1)-N(3)
97.61(6)
119.19(9)
174.91(19)
126.74(13) Ge(1)-N(3)-Si(2)
127.74(13) N(3)-N(4)-C(1)
Recently we reported on the cleavage of N-H11 and
O-H22 bonds using the heterocyclic germylene L0Ge (3).
Now we reacted 3 with trimethylsilyl diazomethane under
formation of the diazogermylene LGeC(N2)SiMe3 (6) by a
C-H bond cleavage (Scheme 5). Here it is also noted that the
trimethylsilyl diazomethane reacts with LGeH (1) with an
unprecedented end-on nitrogen insertion of diazo nitrogen
into the Ge-H bond under formation of germanium(II)-
˚
(1.36 and 1.39 A) and are shorter than those of 3, indicative
for the delocalization of the π-electrons. The Ge-N bond
˚
lengths (1.873(2) and 1.881(2) A) (Table 2) are comparable
with those of the cation [LGe]þ.16 The H NMR spectrum
1
exhibits a signal for the γ-CH proton at 6.50 ppm, which
differs from that of germylene 3 (5.43 ppm). The 11B NMR
spectrum shows a singlet resonance at -14.82 ppm, and the
19F NMR spectrum displays three resonances (-131.6,
-167.2, and-163.40 ppm) for the ortho, para, and meta
fluorine atoms, respectively.
(20) Yang, Z.; Ma, X.; Oswald, R. B.; Roesky, H. W.; Zhu, H.; Schulzke,
C.; Starke, K.; Baldus, M.; Schmidt, H.-G.; Noltemeyer, M. Angew. Chem.
2005, 117, 7234–7236. Yang, Z.; Ma, X.; Oswald, R. B.; Roesky, H. W.; Zhu, H.;
Schulzke, C.; Starke, K.; Baldus, M.; Schmidt, H.-G.; Noltemeyer, M. Angew.
Chem., Int. Ed. 2005, 44, 7072–7074.
(21) (a) Ding, Y.; Ma, Q.; Roesky, H. W.; Herbst-Irmer, R.; Noltemeyer,
M.; Schmidt, H.-G. Organometallics 2002, 21, 5216–5220. (b) Qian, B.; Baek,
S. W.; Smith, M. R. Polyhedron 1999, 18, 2405–2414. (c) Harder, S. Angew.
Chem. 2003, 115, 3553–3556. Harder, S. Angew. Chem., Int. Ed. 2003, 42,
3430–3434.
Compound 3 might be compared with the monomeric
aluminum(I), LAl,19 although the difference of the two
(19) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.; Hao, H.;
Cimpoesu, F. Angew. Chem. 2000, 112, 4444–4446. Cui, C.; Roesky, H. W.;
Schmidt, H.-G.; Noltemeyer, M.; Hao, H.; Cimpoesu, F. Angew. Chem., Int. Ed.
2000, 39, 4274–4276.
(22) Jana, A.; Nekoueishahraki, B.; Roesky, H. W.; Schulzke, C. Orga-
nometallics 2009, 28; DOI: 10.1021/om900149k.

7648 Inorganic Chemistry, Vol. 48, No. 16, 2009
Jana et al.
Figure 3. Molecular structure of 6a; anisotropic displacement para-
meters are depicted at the 50% probability level, and all restrained refined
hydrogen atoms are omitted for clarity.
Figure 2. Molecularstructure of6;anisotropicdisplacementparameters
are depicted at the 50% probability level, and all restrained refined
hydrogen atoms are omitted for clarity.
Scheme 6. Equilibrium between 6 and 6a
Scheme 5. Preparation of 6
The above-described silyl group and germanium substitu-
ent migration has been confirmed by X-ray structure analysis
of 6a. Compounds 6 and 6a are isostructural (Figure 3). The
germanium atom in 6a is coordinate to three nitrogen atoms
substituted hydrazone.23 6 is readily soluble in hydrocarbon
and ether solvents and has been fully characterized.
The germanium complex 6 crystallizes in the triclinic space
group P1 with one molecule in the asymmetric unit
(Figure 2). The germanium atom is coordinated to two
nitrogen atoms of the ligand (N1, N2) and to the carbon
atom (C25) of the diazolyl group. The Ge1-C25 (1.9969(14)
ꢀ
˚
whereas the bond length of Ge1-N3 (1.9491(16) A) is
marginally shorter than the average Ge-N bond lengths of
ꢀ
˚
the bidentate ligand (Ge1-N1 (1.9994(16) A, Ge1-N2
ꢀ
ꢀ
˚
˚
(1.9862(16) A). The N3-Si2 (1.7699(17) A) bond length is
ꢀ
˚
in the range of a standard N-Si bond (1.74 A). The N4-C1
ꢀ
˚
bond length (1.154(3) A) correlates with a normal N-C triple
˚
˚
A) and Si1-C25 (1.8345(15) A) bond lengths are close to the
ꢀ
˚
ꢀ
˚
bond (NtC 1.156 A) while theN3-N4bond(1.350(2) A) lies
˚
normal values for σ bonds of 1.99 and 1.87 A, respectively.
˚
between a N-N single and double bond (N-N 1.45 A, NdN
˚
Also the C25-N3 bond length with 1.3037(19) A is in the
1.25 A). The 29Si NMR spectrum of 6a exhibits a singlet
˚
˚
range of a carbon-nitrogen double bond (1.29 A); the N3-
(δ 12.50 ppm).
˚
N4 bond length (1.1458(19) A) lies between a nitrogen-
˚
˚
nitrogendouble and triplebond(NdN 1.25 A, NtN 1.10 A).
The Ge1-C25-Si1 angle of 118.37(7)° is consistent with an
sp2 hybridized carbon atom (C25). These values are closely
related to those of a reported diazogermylene compound.24
Compound 6 has one SiMe3 group and displays a singlet in
the 29Si NMR spectrum (δ -2.43 ppm).
Conclusion
In summary we have shown the synthesis of the N-hetero-
cyclic germylene L0Ge (3) from dehydrogenation of germy-
lene hydride, LGeH (1) by using a frustrated Lewis
N-heterocyclic carbene borane pair. The sequential cleavage
of C-H and Ge-H bonds without a catalyst is shown herein.
Germylene 3 reacts with B(C6F5)3 at room temperature
under C-B bond formation to the zwitterionic germanium-
(II) compound 4. The reaction of 1,3-di-tert-butylimidazol-2-
ylidene (NHC) with 4 results in a C-H bond cleavage of the
backbone methyl group and the formation of an exocyclic
carbon carbon double bond. Moreover compound 3 reacts
with N2CHSiMe3 to form the diazogermylene compound 6
by cleavage of a C-H bond, and after about 3 months it
rearranges to the isonitriletrimethylsilyl germanium(II)
amide LGeN(SiMe3)NC (6a).
When a supernatant solution of 6 is stored for a longer
period of time (about 3 months) at room temperature, a silyl
group, as well as germanium moiety, shift from the diazo
carbon atom to the end-on nitrogen atom of the diazoger-
mylene has been observed (Scheme 6). Thus, the diazo group
is converted into an isonitrile species. A comparable migra-
tion of a silyl group of azides and the lithium salt of
trimethylsilyl diazomethane is known for organolantha-
nides.25
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K. Angew. Chem. 2009, 121, 4310–4312. Jana, A.; Sen, S. S.; Roesky, H. W.;
Schulzke, C.; Dutta, S.; Pati, S. K. Angew. Chem., Int. Ed. 2009, 48, 4246–4248.
Experimental Section
ꢁ
(24) Bibal, C.; Mazieres, S.; Gornitzka, H.; Couret, C. Angew. Chem.
All manipulations were performed under a dry and oxygen
free atmosphere (N2) using standard Schlenk techniques or a
MBraun MB 150-GI glovebox. All solvents were dried by
MBraun solvent purifying system prior to use. The starting
material 1 was prepared using literature procedures.12b Other
ꢁ
2001, 113, 978–980. Bibal, C.; Mazieres, S.; Gornitzka, H.; Couret, C. Angew.
Chem., Int. Ed. 2001, 40, 952–954.
(25) (a) Johnson, A. W. Ylides and Imines of Phosphorus; Wiley: New York,
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Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7649
chemicals were purchased and used as received. 1H, 11B, 13C,
and 29Si 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. 11B and
Synthesis of 6 and 6a. A solution of N2CHSiMe3 (0.7 mL, 2 M,
in n-hexane) was added to a solution of 3 (0.49 g, 1.0 mmol) in n-
hexane (10 mL) at room temperature. Then the flask was kept at
room temperature for 3 days and after that yellow crystals of 6
were obtained, which are suitable for X-ray structural analysis.
Yield: 0.53 g (88%). Mp 244 °C. 1H NMR (500 MHz, C6D6): δ
7.09-7.17 (m, 6H, Ar-H), 4.51 (s, 1H, γ-CH), 3.63 (sept, 2H,
CH(CH3)2), 3.60 (sept, 2H, CH(CH3)2), 1.62 (s, 6H, CH3), 1.58
(d, 6H, CH(CH3)2), 1.43 (d, 6H, CH(CH3)2), 1.25 (d, 6H,
CH(CH3)2), 1.13 (d, 6H, CH(CH3)2), -0.07 (Si(CH3)3) ppm.
13C{1H} NMR (125.77 MHz, C6D6): δ 166.43 (CN), 146.92,
143.76, 139.99, 127.56, 124.98, 124.76 (Ar-C), 95.35 (γ-C),
31.91 (CN2), 29.60 (CH(CH3)2), 27.39 (CH(CH3)2), 25.34
(CH(CH3)2), 25.32 (CH(CH3)2), 24.68 (CH(CH3)2), 23.68
(CH(CH3)2), 0.03 (Si(CH3)3) ppm. 29Si{1H} NMR (99.35 Hz,
C6D6): δ -2.43 (Si(CH3)3) ppm EI-MS (70 eV): m/z (%): 561
(100) [M-iPr)]þ. Anal. Calcd for C33H50GeN4Si (603.50): C,
65.68; H, 8.35; N, 9.28. Found: C, 64.96; H, 8.62; N, 8.87. For
6a: After keeping the supernatant solution of 6 for about 3
months at room temperature we observed the conversion of 6 to
6a. Mp 210 °C. 1H NMR (500 MHz, C6D6): δ 7.06-7.18 (m, 6H,
Ar-H), 4.75 (s, 1H, γ-CH), 3.89 (sept, 2H, CH(CH3)2), 3.39
(sept, 2H, CH(CH3)2), 1.66 (s, 6H, CH3), 1.57 (d, 6H, CH-
(CH3)2), 1.37 (d, 6H, CH(CH3)2), 1.26 (d, 6H, CH(CH3)2), 1.07
(d, 6H, CH(CH3)2), -0.04 (Si(CH3)3) ppm. 13C{1H} NMR
(125.77 MHz, C6D6): δ 167.04 (CN), 147.39, 143.37, 139.81,
127.80, 125.34, 124.53 (Ar-C), 97.23 (γ-C), 29.76 (CH(CH3)2),
28.59 (NC), 27.35 (CH(CH3)2), 25.85 (CH(CH3)2), 25.22
(CH(CH3)2), 24.44 (CH(CH3)2), 23.93 (CH(CH3)2), 0.03
(Si(CH3)3) ppm. 29Si{1H} NMR (99.35 Hz, C6D6): δ 12.50
(Si(CH3)3) ppm EI-MS (70 eV): m/z (%): 604 (100) [M]þ.
Crystallographic Details for Compounds 4, 6, and 6a. The data
sets of 4, 6, and 6a were collected on a Bruker TXS-Mo rotating
anode equipped with INCOATEC Helios mirror optics (Mo KR
29Si NMR spectra were referenced to BF3 Et2O and SiMe4,
3
respectively. Elemental analyses were performed by the Ana-
lytisches Labor des Instituts fur Anorganische Chemie der
::
:: ::
Universitat Gottingen. 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 and are not corrected.
Synthesis of 2 and 3. A solution of B(C6F5)3 (0.51 g, 1.0 mmol)
in toluene (10 mL) was added drop by drop to a stirred solution
of 1 (0.49 g, 1.0 mmol) in toluene (10 mL) at room temperature.
Immediately the red color of the reaction mixture changed to
colorless. The reaction mixture was stirred for additional
10 min. After that a solution of 1,3-di-tert-butylimidazol-2-
ylidene (0.18 g, 1.0 mmol) in toluene (10 mL) was added drop
by drop to the reaction mixture. During this time the reaction
mixture turned to brown-red with the formation of a white
precipitate. After another 10 min the solvent was removed in
vacuum, and the residue was extracted with n-hexane (15 mL).
The extracted brown-red solution contained compound 2. The
insoluble part was collected and identified as imidazolium
borate salt 3. Both are formed almost quantitatively, and the
NMR data matches with the previously reported samples.3c,9
Synthesis of 4. A solution of B(C6F5)3 (0.51 g, 1.0 mmol) in
toluene (10 mL) was added to a solution of 3 (0.49 g, 1.0 mmol)
in toluene (10 mL) at room temperature. The brown-red color of
the solution of 3 vanished slowly, and pale yellow crystals of 4
were formed after 2 days at room temperature. Yield: 0.78 g
(78%). Mp 265 °C. 1H NMR (500 MHz, THF-D8): δ 7.37-7.44
(m, 6H, Ar-H), 6.50 (s, 1H, γ-CH), 2.73 (sept, 2H, CH(CH3)2),
2.61 (sept, 2H, CH(CH3)2), 2.47 (s, 2H, CH2), 1.84 (s, 3H, CH3),
1.39 (d, 6H, CH(CH3)2), 1.25 (d, 6H, CH(CH3)2), 1.19 (d, 6H,
CH(CH3)2), 1.15 (d, 6H, CH(CH3)2) ppm. 13C{1H} NMR
(125.77 MHz, THF-D8): δ 180.93, 166.74 (CN), 145.62,
137.35, 130.25, 129.65, 128.89, 126.02 (Ar-C), 149.13, 139.52,
137.41 (C6F5), 108.96 (γ-C), 29.42 (CH(CH3)2), 29.32
(CH(CH3)2), 27.50 (CH(CH3)2), 25.85 (CH(CH3)2), 25.62
(CH(CH3)2), 25.46 (CH(CH3)2), 25.30 (CH3) ppm. 11B{1H}
NMR (96.29 MHz, THF-D8): δ -14.82. 19F{1H} NMR
(188.31 MHz, THF-D8): δ -131.60 (d, 6F, o-F), -163.40 (t,
6F, m-F), -167.28 (t, 3F, p-F). EI-MS (70 eV): m/z (%): 475
(100) [M-(B(C6F5)3, Me)] þ. Anal. Calcd for C47H40BF15GeN2
(1001.26): C, 56.38; H, 4.03; N, 2.80. Found: C, 56.27; H, 3.82;
N, 2.68.
˚
λ = 0.71073 A). The crystal was mounted in a shock-cooled oil
drop at the tip of a fiber.26 The data was integrated with
SAINT V7.46A (4, 6a) and SAINTV7.60A (6),27 and an em-
pirical absorption correction (SADABS-2008/2) was applied.28
The structure was solved by direct methods (SHELXS)29 and
refined on F2 using the full-matrix least-squares methods of
SHELXL.30 All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. All hydrogen atoms bonded to
sp2 (sp3) carbon atoms were assigned ideal positions and refined
using a riding model with Uiso constrained to 1.2 (1.5) times the
U
eq value of the parent carbon atom.
Acknowledgment. This work was supported by the Deutsche
Forschungsgemeinschaft.
Synthesis of 5. A solution of 1,3-di-tert-butylimidazol-2-yli-
dene (0.18 g, 1.0 mmol) in toluene (10 mL) was added to a
solution of 4 (0.49 g, 1.0 mmol) in toluene (10 mL) at room
temperature. Immediately the reaction mixture turns to red in
color. After 10 min the solvent was removed in vacuum, and the
product was isolated as a red oil. 1H NMR (500 MHz, C6D6): δ
7.32 (s, 1H, NCH), 6.99-7.20 (m, 6H, Ar-H), 6.33 (s, 2H, NCH),
5.87 (s, 1H, γ-CH), 3.86 (sept, 2H, CH(CH3)2), 3.63(s, 1H, CH),
3.60 (sept, 2H, CH(CH3)2), 2.96 (s, 1H, CH), 2.45 (s, 2H, CH2),
1.70 (d, 6H, CH(CH3)2), 1.35 (d, 12H, CH(CH3)2), 1.32 (d, 6H,
CH(CH3)2), 0.75 (s, 18H, C(CH3)3) ppm. 11B{1H} NMR (96.29
MHz, C6D6): δ -13.66. 19F{1H} NMR (188.31 MHz, C6D6):
δ -130.65 (br, 6F, o-F), -163.77 (t, 6F, m-F), -167.32 (br, 3F,
p-F). From the analytical data we do not obtain satisfactory results.
Supporting Information Available: X-ray data for 4, 6, and 6a
(CIF). This material is available free of charge via the Internet at
http://pubs.acs.org.
(26) (a) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615–619. (b)
Kottke, T.; Lagow, R. J.; Stalke, D. J. Appl. Crystallogr. 1996, 29, 465–468.
(27) SAINT v7.46A/v7.60A in Bruker APEX v2.2-0; Bruker AXS Inst.
Inc.: Madison, WI, 2005.
::
::
(28) Sheldrick, G. M. SADABS 2008/2; University of Gottingen: Gottingen,
Germany, 2008.
(29) Sheldrick, G. M. SHELXS in SHELXTL v6.10; Bruker AXS Inst. Inc.:
Madison, WI, 2000.
(30) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.