Protic N-Heterocyclic Germylenes and Stannylenes: Synthesis and Reactivity

Article abstract of DOI:10.1021/om5012616

The monoalkylated or monoarylated o-phenylenediamines 1a-d (1a, R = t-Bu; 1b, R = adamantyl; 1c, R = phenyl; 1d, R = mesityl) react via transamination with Ge[N(SiMe₃)₂]₂ or Sn[N(SiMe₃)₂]₂ to give the protic benzimidazolin-2-germylenes 2a-d or the benzimidazolin-2-stannylenes 3a,b. Germylenes 2a,b can be deprotonated to give the salts Na-4a and Na-4b, each containing an anionic N-deprotonated N-heterocyclic germylene. The protic stannylenes 3a,b react with NaH presumably via reduction of the tin(II) center by the deprotonated electron-rich o-phenylenediamine ligand and release of elemental tin. To prevent this reduction, the electron-poor N-H,N′-H-5,6-dibromobenzimidazolin-2-stannylene (5) was prepared and successfully N-deprotonated to give an anionic stannylene in Na-6. The molecular structures of 2a, 3a, and Na-4a were established by X-ray diffraction studies. (Chemical Presented).

Full text of DOI:10.1021/om5012616

Article
pubs.acs.org/Organometallics
Protic N‑Heterocyclic Germylenes and Stannylenes: Synthesis and
Reactivity
Sergei Krupski, Christian Schulte to Brinke, Hannah Koppetz, Alexander Hepp, and F. Ekkehardt Hahn*
Institut fur Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstraße 30, D-48149 Munster, Germany
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* Supporting Information
ABSTRACT: The monoalkylated or monoarylated o-phenyl-
enediamines 1a−d (1a, R = t-Bu; 1b, R = adamantyl; 1c,
R = phenyl; 1d, R = mesityl) react via transamination with
Ge[N(SiMe3)2]2 or Sn[N(SiMe3)2]2 to give the protic
benzimidazolin-2-germylenes 2a−d or the benzimidazolin-2-
stannylenes 3a,b. Germylenes 2a,b can be deprotonated to
give the salts Na-4a and Na-4b, each containing an anionic N-deprotonated N-heterocyclic germylene. The protic stannylenes
3a,b react with NaH presumably via reduction of the tin(II) center by the deprotonated electron-rich o-phenylenediamine ligand
and release of elemental tin. To prevent this reduction, the electron-poor N-H,N′-H-5,6-dibromobenzimidazolin-2-stannylene
(5) was prepared and successfully N-deprotonated to give an anionic stannylene in Na-6. The molecular structures of 2a, 3a, and
Na-4a were established by X-ray diffraction studies.
INTRODUCTION
■
The heavier group 14 analogues of carbenes (R2C:), the
silylenes, germylenes, stannylenes, and plumbylenes of the
general formula R2E: (generically named tetrylenes) feature an
electron-deficient group 14 element (E:) with only six electrons
in the valence shell. The first examples for stable stannylenes
and plumbylenes of type M[CH(SiMe3)2]2 were described by
Lappert more than 40 years ago.1 Subsequently, a large number
of tetrylenes bearing different substituents R at the R2E: center
have been reported.2 In contrast to the subvalent carbon deriv-
atives R2C:, where depending on the substituents both the
singlet and triplet ground states can be observed,3 the heavier
tetrylenes occur exclusively in the diamagnetic singlet ground
state with two nonbonding paired electrons.2,4 Normally,
tetrylenes feature a bent geometry. The electronic situation is
best described by sp2 hybridization at the E atom with the
electron pair residing in one of the sp2 orbitals and the p orbital
remaining empty. However, excitation to the triplet state can
occur, and this is thought to play a role in the activation of
dihydrogen by selected diarylstannylenes.5
Early on it was noted that the electronic situation in
tetrylenes can lead to amphiphilic behavior with the free elec-
tron pair acting as a Lewis base and the empty p orbital func-
tioning as a Lewis acid.2 Consequently, different germylenes
and stannylenes have been shown to form adducts with both
Lewis bases and Lewis acids.2 These interesting properties have
led to a resurgence of interest in tetrylenes and their potential
for the activation of unreactive substrates.5
Figure 1. Benzannulated N-heterocyclic carbenes A and tetrylenes B−E.
NHC. The corresponding benzannulated N-heterocyclic silylene
B has been prepared by Gehrhus and Lappert.2c Various
benzannulated N-heterocyclic germylenes C,7 stannylenes D,8
and plumbylenes E9 (Figure 1), including chiral germylenes
and stannylenes,7f have been prepared and characterized.
N-heterocyclic germylenes and stannylenes C and D have
been used as Lewis base ligands for the synthesis of transition-
metal complexes.7c,e,8f−h In addition, compounds of types C−E
form adducts with Lewis bases which interact with the empty p
orbital7c,d,h,8c−h,9,9c (Figure 1, F).
In analogy to stable N-heterocyclic carbenes, N-heterocyclic
tetrylenes have been prepared, with selected compounds of
this type being known even before the NHC analogues were
described. After the preparation of the first benzannulated
N-heterocyclic carbene A6 (Figure 1), we and others became
interested in the germanium, tin, and lead analogues of this
Special Issue: Mike Lappert Memorial Issue
Received: December 9, 2014
© XXXX American Chemical Society
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We have unsuccessfully tried to utilize the amphiphilic prop-
erties of the heavier tetrylenes for the cooperative activation of
less reactive substrates such as dihydrogen. Such activation was,
however, performed with diarylstannylenes5 and with selected
cyclic alkylaminocarbenes (CAACs).10 We therefore decided to
generate nucleophilic and electrophilic reaction sites at different
positions of the tetrylenes. For metal complexes of protic
NHCs G, a similar separation can be achieved by N deprotona-
tion of the NHC ligand, generating a highly nucleophilic ring
nitrogen atom in H.11 Alternatively, complexes with N-
deprotonated NHC ligands of type H can be obtained by the
procedures.14 A subsequent transamination reaction of 1a−d
with M[N(SiMe3)2]2 (M = Ge, Sn)15 in dry toluene at room
temperature led to the protic benzimidazolin-2-germylenes 2a−d
and stannylenes 3a,b (Scheme 2). The protic tetrylenes have been
isolated as orange or yellow solids or brown oils in good yields.
In analogy to the N,N′-dialkylated derivatives C−E (Figure 1),
the monoprotic N-heterocyclic germylenes and stannylenes are
sensitive toward air and moisture. Germylenes 2a−d exhibit a
solubility in organic solvents which depends on the N,N′-
substitution pattern. For example, 2a dissolves rather well in
nonpolar solvents such as n-hexane, while germylene 2b shows
a poor solubility in this nonpolar solvent but dissolves well in
ethers or aromatic hydrocarbons. The protic N-adamantyl-
substituted stannylene 3b shows poor solubility even in a polar
solvent such as THF.
oxidative addition of 2-halogeno-N-alkylbenzimidazoles12
I
or 2-halogenobenzimidazoles13 to selected transition-metal
complexes (Scheme 1, top). Similarly to the lighter NHC
Formation of the germylenes 2a−d and the stannylenes 3a,b
was monitored by 1H NMR spectroscopy. For all tetrylenes, the
NH resonance was detected with a relative intensity of 1 and
this resonance was shifted downfield in comparison to the cor-
responding o-phenylenediamine starting material. For example,
the resonance δ(NH2 and NHtBu) 3.03 ppm for 1a shifted
upon formation of the germylene 2a to δ(NH) = 7.40 ppm
(both measured in C6D6). NMR spectra for the germylene 2b
and the stannylene 3a were measured both in C6D6 and in
THF-d8. In the 1H NMR spectra, the chemical shift for the NH
resonances depended strongly on the solvent used. The N−H
signal for the protic germylene 2b in C6D6 (δ 7.48 ppm)
appears at Δδ ≈ 2 ppm shifted to higher field in comparison
to the N−H resonance detected in the polar solvent THF-d8
(δ 9.47 ppm). A similar observation was made for stannylene 3a
(δ 5.44 ppm in C6D6 and δ 7.40 ppm in THF-d8). A likely
reason for these observations is the formation of hydrogen bonds
(N−H···O) between the N−H groups of the tetrylenes and the
oxygen atoms of THF molecules. Such hydrogen bonds cannot
form in C6D6.
Scheme 1. Deprotonation of Coordinated Protic NHCs and
of Free Protic Tetrylenes
In addition, the 119Sn{1H} NMR spectra also reveal a strong
solvent dependence of the resonance for the stannylene tin
atoms. The 119Sn{1H} NMR signal for 3a in C6D6 (δ 223 ppm)
is shifted downfield (Δδ ≈ 46 ppm) in comparison to the
resonance observed in THF-d8 (δ 177 ppm). This difference in
chemical shift can be explained by THF coordination to the tin
center with a concurrent increase of electron density at the
metal, causing the observed high-field shift of the 119Sn{1H}
resonance in THF-d8. This observation is consistent with
previous 119Sn{1H} NMR studies on N,N′-dialkylbenzimidazo-
lin-2-stannylenes, where also a high-field shift of the 119Sn{1H}
resonance in ether solvents in comparison to hydrocarbon
solvents was observed.8d In addition to the NMR studies, all
new tetrylenes were analyzed by mass spectrometry. All
germylenes 2a−d and stannylenes 3a,b exhibit strong peaks
for the molecular ions and for typical fragmentation products
[M − (Ge or Sn)]+ with the correct isotope distribution.
Single crystals suitable for an X-ray diffraction study were
obtained by cooling of a saturated n-hexane solution of compound
2a to −30 °C. Germylene 2a crystallizes as transparent yellow
prisms. The asymmetric unit contains eight essentially identical
molecules of 2a. One molecule of 2a is depicted in Figure 2.
In the solid state, germylene 2a exists as monomers which do
not maintain any intermolecular interactions. This behavior
differs from that of various other benzannulated N-heterocyclic
germylenes, which have been shown to form higher oligomers
in the solid state by interaction of the ring nitrogen atoms with
neighboring Lewis acidic germanium(II) centers.7c,d,h The Ge1−N1
homologues, it should also be possible to deprotonate the heavier
protic tetrylenes (Ge, Sn). Here we describe the preparation of
novel monoprotic (J) and diprotic (K) N-heterocyclic germylenes
and stannylenes and their deprotonation to give the sodium salts L
and M, respectively (Scheme 1, bottom).
RESULTS AND DISCUSSION
The monosubstituted o-phenylendiamine derivatives 1a−d
(Scheme 2) have been prepared following published
■
Scheme 2. Synthesis of the Germylenes 2a−d and the
Stannylenes 3a,b
B
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intramolecular Sn−N distances (Sn1−N1 2.1510(11) Å, Sn1−N2
2.1194(11) Å, Sn2−N3 2.1838(10) Å, Sn2−N4 2.1464(10) Å)
fall in the range normally observed for N,N′-dialkylated
benzimidazolin-2-stannylenes8 and are only about 0.2 Å shorter
than the intermolecular Sn−N separations (Sn1−N3 2.3266(11) Å,
Sn2−N1 2.3471(11) Å). We take this as an indication of the
presence of strong intermolecular interactions between the
stannylenes. While the nonaggregated germylene 2a features a
short N(H)−Ge and a longer N(tBu)−Ge bond, the opposite
situation was found for the dimerized stannylene 3a (long
N(H)−Sn and short N(tBu)−Sn bonds). Intermolecular
coordination of the N(H) ring nitrogen atoms apparently
leads to a lengthening of the intramolecular Sn−N bond
lengths. In addition, a pyramidalization is observed for those
ring nitrogen atoms, which coordinate to two SnII centers.
Similar structural features have been observed for dimers
formed from two N,N′-dialkylated benzimidazolin-2-stannyle-
nes.8d Some additional intermolecular interactions between the
dimer (3a)2 with the aromatic π system of a neighboring dimer
(Sn···centroid distances of the phenyl group of a neighboring
dimer 3.492−3.583 Å) have also been noted, in accord with
previous observations for benzimidazolin-2-stannylenes.8b
Next the deprotonation of protic benzimidazolin-2-germylenes
and stannylenes was attempted. Germylenes 2a,b and
stannylenes 3a,b were selected for the deprotonation reaction,
since they could be prepared in high yields. Germylenes
2a,b react with NaH as a base in THF at 65 °C to give the
germylenes Na-4a and Na-4b as gray-yellow salts, each
featuring an N-deprotonated germylenide anion (Scheme 3).
Figure 2. Molecular structure of one molecule of germylene 2a in the
asymmetric unit (50% displacement ellipsoids, hydrogen atoms, except
for the N−H hydrogen atom, omitted for clarity). Selected bond
lengths (Å) and angles (deg): Ge1−N1 1.878(2), Ge1−N2 1.836(3),
N1−C6 1.397(4), N1−C7 1.488(4), N2−C1 1.380(4); N1−Ge1−N2
84.39(11), Ge1−N1−C6 114.0(2), Ge1−N2−C1 114.5(2).
distance involving the alkylated ring nitrogen atom measures
1.878(2) Å and falls in the range observed for equivalent bonds
in N,N′-dialkylbenzimidazolin-2-germylenes.7 The bond dis-
tance Ge1−N2 involving the protonated ring nitrogen atom is
slightly shorter (1.836(3) Å). The N1−Ge1−N2 angle (84.39(11)°)
also falls in the range observed previously for N,N′-
dialkylbezimidazolin-2-germylenes,7 confirming that the sub-
stitution of one N-alkyl substituent for a hydrogen atom does
not change the overall geometry of the germylene significantly.
Both ring nitrogen atoms are surrounded in a trigonal-planar
fashion.
Scheme 3. Deprotonation of Protic Benzimidazolin-2-
germylenes and -stannylenes
Next we determined the molecular structure of stannylene 3a
(Figure 3). Single crystals of 3a were obtained from a saturated
However, the same reaction performed with stannylenes 3a,b
(at slightly lower temperature to prevent decomposition of the
temperature-sensitive stannylenes) did not yield the anionic
stannylenes but led to decomposition of the starting materials
3a,b with release of elemental tin. We have noticed previously
that otherwise identical GeII and SnII compounds react differently
under reducing conditions, as observed in the reaction of
M[N(SiMe3)2]2 (M = GeII, SnII) with electron-rich 1,2,4,5-
tetrakis(alkylamine)benzenes. In this reaction, the GeII precursor
yielded the expected benzobis(germylene), while the SnII pre-
Figure 3. Molecular structure of the dimer (3a)2 in (3a)2·THF (50%
displacement ellipsoids, hydrogen atoms, except for the N−H
hydrogen atom, omitted for clarity). Selected bond lengths (Å) and
angles (deg): Sn1−N1 2.1510(11), Sn1−N2 2.1194(11), Sn1−N3
2.3266(11), Sn2−N3 2.1838(10), Sn2−N4 2.1464(10), Sn2−N1
2.3471(11), N1−C1 1.432(2), N2−C2 1.387(2), N2−C7 1.479(2),
N3−C11 1.421(2), N4−C12 1.390(2), N4−C17 1.477(2); N1−Sn1−
N2 79.13(4), N1−Sn1−N3 88.59(4), N3−Sn2−N4 79.13(4), N3−
Sn2−N1 88.59(4), Sn1−N1−C1 111.49(8), Sn1−N2−C2 114.68(8),
Sn2−N3−C11 110.53(8), Sn2−N4−C12 113.34(7).
cursor reacted with oxidation of the electron-rich ligand.7g
A
similar oxidation of the deprotonated o-phenylenediamine ligand
might also be responsible for the instability of the deprotonated
stannylenes.
THF solution of the compound by cooling to −30 °C. In
contrast to the identical NH-NtBu-substituted germylene 2a,
stannylene 3a forms a dimer in the solid state, which co-
crystallizes with one molecule of THF. Dimerization of two
molecules of 3a is achieved by two intermolecular Sn···N
interactions involving the protonated ring nitrogen atoms. The
1
The H NMR spectra of the protic germylene 2b (in red)
and the product of deprotonation Na-4b (in green), both mea-
sured in THF-d8, are depicted in Figure 4 for comparison. The
NH resonance at δ 9.47 ppm is clearly visible in the spectrum
C
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1
Figure 4. H NMR spectra of 2b (in red) and Na-4b (in green) measured in THF-d8.
of 2b, but no resonance in this region can be detected in the
spectrum of Na-4b, confirming the successful deprotonation. In
addition, the aromatic signals are shifted to high field upon
deprotonation, obviously a consequence of the increased elec-
tron density in the ligand scaffold. In addition, the 13C{1H}
NMR spectrum of compound Na-4b shows a noteworthy
downfield shift of both ipso carbon signals (δ 158.8, 145.6 ppm
in THF-d8) in comparison to the signals for 2b (δ 145.4,
139.9 ppm in THF-d8).
In order to stabilize a deprotonated benzimidazolin-2-
stannylene, electron-withdrawing bromide substituents were
introduced to the aromatic ring. The compound 5,6-
dibromobenzimidazolin-2-stannylene (5) was synthesized
from the known 4,5-dibromo-o-phenylenediamine16 by a
transamination reaction with Sn[N(SiMe3)2]2 (Scheme 4).
the two nitrogen atoms on the NMR time scale. The resonance
for the NH proton was observed upfield at δ 3.59 ppm in
comparison to the NH resonance for 5 (δ 4.20 ppm). The
deprotonation of 5 leads to a drastic change in the 119Sn{1H}
NMR spectrum. Upon deprotonation, the resonance for the tin
atom shifts from δ 57 ppm in 5 to δ −326 ppm in Na-6. This
drastic shift clearly illustrates the electron-rich nature of the
anion 6− and a delocalization of the negative charge over the
N−Sn−N moiety.
Crystals of (Na-4a)2·4THF were obtained for a concentrated
THF solution of Na-4a at ambient temperature. The molecular
structure (Figure 5) shows a centrosymmetric dimer linked by a
Scheme 4. Synthesis of Stannylene 5 and Deprotonation
of 5 To Give Na-6
Figure 5. Molecular structure of (Na-4a)2·4THF (50% displacement
ellipsoids, hydrogen atoms omitted for clarity). Selected bond lengths
(Å) and angles (deg): Ge−N1 1.905(2), Ge−N2 1.810(2), N2−Na
2.450(2), N2−Na* 2.337(2), N1−C6 1.387(3), N1−C7 1.479(3),
N2−C1 1.374(3); N1−Ge−N2 88.80(8), Ge−N1−C6 110.46(14),
Ge−N1−C7 126.66(14), Ge−N2−C1 110.74(14), Na−N2−Na*
82.86(7).
Stannylene 5 was obtained as a yellow solid which is insoluble
in n-hexane and toluene and only sparingly soluble in THF.
In contrast to the decomposition observed during the
deprotonation of 3a,b with NaH, the reaction of 5 with NaH in
THF gave the monodeprotonated stannylene Na-6·THF as an
extremely air sensitive gray powder in 61% yield. As intended,
the introduction of the electron-withdrawing bromide sub-
stituents stabilized the deprotonated stannylene. The salt Na-6
was completely characterized by NMR spectroscopy and micro-
four-membered N2Na2 ring. The sodium atoms of the central
four-membered ring are coordinated in a tetrahedral fashion by
the deprotonated nitrogen atoms of two germylenes and by the
oxygen atoms of two THF molecules. After N-deprotonation
the Ge−N2 bond becomes significantly shorter (1.810(2) Å)
than the Ge−N1 bond (1.905(2) Å), in spite of the fact that
1
analytical data. In the H NMR spectrum of Na-6 only one
signal for the aromatic protons was observed. This would
indicate a fast exchange of the remaining NH proton between
D
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moisture. A complete set of NMR spectra is provided in the
Supporting Information instead.
Synthesis of N-(tert-Butyl)-1,2-diaminobenzene (1a).
N1 binds to four partners while N2 only maintains three bonds.
Electrostatic interactions between the deprotonated ring
nitrogen atom and the GeII center appear responsible for this
bond shortening. Ring nitrogen atom N1 adopts a trigonal-
planar geometry. The N1−Ge−N2 angle is 88.80(8)° and is
slightly larger than that in the protonated N-heterocyclic
germylene 2a (N1−Ge1−N2 84.39(11)°). Upon deprotona-
tion, the intra-ring Ge−N−C angle at the deprotonated ring
nitrogen atom (Ge−N2−C1 110.74(14)°) does not signifi-
cantly differ from the intra-ring Ge−N−C angle at the alkylated
ring nitrogen atom (Ge−N1−C6 110.46(14)°).
The preparation of compound 1a has been described in the litera-
ture,14a,b but no NMR spectroscopic data are available. Therefore, we
report here the 1H NMR spectrum of 1a. 1H NMR (400 MHz, C6D6):
δ 6.91−6.83 (m, 2H, Ar-H), 6.80−6.75 (m, 1H, Ar-H), 6.53−6.50 (m,
1H, Ar-H), 3.03 (s br, 3H, NH), 1.10 ppm (s, 9H, CH3)).
Given the presence of a basic deprotonated ring nitrogen
atom and a Lewis acidic GeII center in Na-4a, it appeared
attractive to utilize deprotonated N-heterocyclic tetrylenes as
frustrated Lewis pairs. This would, however, require the
liberation of the basic nitrogen center by removal of the
sodium cation. All attempts to prepare a free anionic
N-heterocyclic germylene by the reaction of Na-4a with crown
ethers or cryptands have so far led to decomposition of the
compound. Preliminary DFT calculations (B3LYP/6-31G(d)
level) on the anion 4a− (without an Na atom) have shown that
an anionic tetrylene of type 4a− would feature negatively
charged ring nitrogen atoms. The LUMO in compounds of
type 4a− is the electrophilic empty p orbital at the GeII center,
which is still available in spite of the increased electron density
in the heterocycle due to N-deprotonation.
Synthesis of N-(1-Adamantyl)-1,2-diaminobenzene (1b).
A suspension of 1-fluoro-2-nitrobenzene (1.5 g, 10.6 mmol), KF
(0.7 g, 12.0 mmol), and 1-adamantylamine (1.6 g, 10.6 mmol) in dry
DMF (3 mL) was sealed in a Young tube under argon and heated to
170 °C for 12 h. Subsequently, the orange reaction mixture was
poured into a saturated aqueous NH4Cl solution (40 mL) and
extracted with ethyl acetate (3 × 40 mL). The organic layer was
washed twice with H2O and then dried over MgSO4. Evaporation of
the solvent gave orange crystals of N-(1-adamantyl)-2-nitroaniline
(2.73g, 10.0 mmol, 94%). The spectroscopic data were identical with
those reported in the literature.14c
A sample of N-(1-adamantyl)-2-nitroaniline (1.1 g, 4.04 mmol) and
hydrazine hydrate (1.0 mL, 16.1 mmol) were dissolved in dry
methanol (20 mL) under argon at 0 °C. Then a catalytic amount of
Raney Ni was added (100 mg). At this point a vigorous dihydrogen
evaluation was observed. The reaction mixture was slowly brought to
room temperature, and the stirring was continued for 24 h. Then all
solids were removed by filtration. Removal of the solvent in vacuo gave
analytically pure 1b. Yield: 0.96 g (3.96 mmol, 98%) of colorless
crystals. 1H NMR (400 MHz, C6D6): δ 6.93 (td, 3JHH = 7.6, 4JHH = 1.4
Hz, 1H, Ar-H5), 6.88 (dd, 3JHH = 7.6, 4JHH = 1.4 Hz, 1H, Ar-H6), 6.76
CONCLUSIONS
■
We have prepared the protic N-heterocyclic germylenes 2a−d
and stannylenes 3a,b. The deprotonation of protic germylenes
with NaH leads to compounds containing new anionic
germylenes in the salts Na-4a and Na-4b. While a similar
N-deprotonation with the protic stannylenes 3a,b gave only
decomposition products and elemental tin, the use of electron-
poor 5,6-dibromo-substituted benzannulated N-heterocyclic
stannylenes such as 5 allowed the N-deprotonation and yielded
the salt Na-6. Deprotonated N-heterocyclic germylenes and
stannylenes might lead to new FLPs with a Lewis basic site
located at the one of the ring nitrogen atoms and a Lewis acidic
site at the EII atom, provided that the anionic tetrylene can be
separated from the cation present. Corresponding investiga-
tions are in progress.
(td, 3JHH = 7.6, 4JHH = 1.4 Hz, 1H, Ar-H4), 6.55 (dd, 3JHH = 7.6, 4JHH
=
1.4 Hz, 1H, Ar-H3), 3.14 (s br, 3H, NH-Ad and NH2), 1.94−1.88 (m,
3H, Ad-H), 1.72−1.68 (m, 6H, Ad-H), 1.54−1.42 ppm (m, 6H,
Ad-H). 13C{1H} NMR (101 MHz, C6D6): δ 143.27, 131.72 (Ar-Cipso),
126.27, 123.75, 118.19, 115.99 (Ar-C), 53.11 (Ad-Cq), 43.40, 36.55,
29.91 ppm (Ad-C). MS (EI): m/z (%) 242 (100) [1b]+.
General Procedure for the Preparation of the Germylenes
2a−d and Stannylenes 3a,b. A sample of bis[bis(trimethylsilyl)amido]-
germanium(II) (Ge[N(SiMe3)2]2; 0.393 g, 1.0 mmol), or bis[bis-
(trimethylsilyl)amido]tin(II) (Sn[N(SiMe3)2]2; 0.439 g, 1.0 mmol)
was added to a solution of one of the N-aryl- or N-alkyldiamines
1a−d (1.0 mmol) in dry toluene (10 mL). The reaction mixture was
stirred for 48 h at ambient temperature. Subsequently, the solvent and
the volatile HN(SiMe3)2 were removed in vacuo. For compounds 2b,d
and 3a,b, solids were obtained which were each washed three times
with n-hexane (2 mL) and recrystallized from toluene (2b,d) or THF
(3a,b). Compounds 2a,c were isolated as brown oils, and 2a was
recrystallized from n-hexane at −30 °C.
EXPERIMENTAL SECTION
■
General Procedures. If not noted otherwise, all reactions were
carried out under an argon atmosphere using conventional Schlenk
techniques or in a glovebox. Solvents were dried and freshly distilled
by standard procedures prior to use. NMR spectra were recorded at
ambient temperature with Bruker AC 200, Bruker AVANCE I 400,
and Bruker AVANCE III 400 spectrometers. Chemical shifts (δ) are
expressed in ppm downfield from tetramethylsilane using the residual
protonated solvent (1H NMR) or Me4Sn (119Sn NMR) as an internal
standard. EI mass spectra were obtained with a Finnigan MAT 95
spectrometer. Bis[bis(trimethylsilyl)amido]tin(II),15 bis[bis(trimethylsilyl)-
amido]germanium(II),15 and 5,6-dibromo-o-phenylenediamine16 were
prepared by published procedures. Compounds 1a,14a,b 1c,14d,e and
1d14f,g were prepared by the reaction of 1-fluoro-2-nitrobenzene with
the suitable primary amine and subsequent reduction of the nitro
group with Raney Ni14a and hydrazine in methanol. Compound 1b
was prepared from N-(1-adamantyl)-2-nitroaniline, followed by
reduction with hydrazine and Raney Ni in dry methanol. The
preparation and spectroscopic data for the precursor compound N-(1-
adamantyl)-2-nitroaniline have been previously reported.14c Satisfac-
tory elemental analyses of compounds 2b,d, 3a,b, and 5 were difficult
to obtain due to the sensitivity of the compounds toward oxygen and
Synthesis of N-H,N′-tert-Butylbenzimidazolin-2-germylene (2a).
The crude reaction product was recrystallized from n-hexane (3 mL)
at −30 °C. Yield: 0.214 g (0.91 mmol, 91%) of orange-yellow crystals.
1H NMR (400 MHz, C6D6): δ 7.40 (s br, 1H, NH), 7.31−7.27 (m,
1H, Ar-H), 7.02−6.93 (m, 2H, Ar-H), 6.84−6.80 (m, 1H, Ar-H),
1.54 ppm (s, 9H, CH3). 13C{1H} NMR (101 MHz, C6D6): δ 144.3,
139.9 (Ar-Cipso), 118.1, 117.9, 114.3, 113.8 (Ar-C), 56.2 (C(CH3)3),
E
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32.3 ppm (C(CH3)3). MS (EI): m/z (%) 236 (83) [2a]+, 221 (65)
[2a − CH3]+, 180 (28) [2a − tBu + H]+, 164 (100) [2a − Ge + 2H]+.
Anal. Calcd for 2a (C10H14N2Ge): C, 51.14; H, 6.01; N, 11.93. Found:
C, 50.94; H, 6.03; N 11.87.
32.2 ppm (C(CH3)3). 119Sn{1H} NMR (149 MHz, C6D6): δ 223 ppm.
119Sn{1H} NMR (149 MHz, THF-d8): δ 177 ppm. MS (EI): m/z (%)
282 (100) [3a]+, 267 (34) [3a − CH3]+, 226 (10) [3a + H − tBu]+.
164 (59) (100) [3a + 2H − Sn]+.
Synthesis of N-H,N′-Adamantylbenzimidazolin-2-germylene (2b).
Synthesis of N-H,N′-Adamantylbenzimidazolin-2-stannylene (3b).
1
1
Yield: 0.260 g (0.83 mmol, 83%) of orange crystals. H NMR (400
Yield: 352 mg (0.98 mmol, 98%) of a yellow solid. H NMR (400
MHz, C6D6): δ 7.54−7.51 (m, 1H, Ar-H), 7.48 (s br, 1H, NH), 7.03−
MHz, THF-d8): δ 7.96 (s br, 1H, NH), 7.16−7.13 (m, 1H, Ar-H),
6.74−6.68 (m, 1H, Ar-H), 6.48−6.35 (m, 2H, Ar-H), 2.40−2.36 (m,
6H, Ad-H), 2.21 (s br, 3H, Ad-H), 1.86−1.75 ppm (m, 6H, Ad-H).
13C{1H} NMR (101 MHz, THF-d8): δ 116.2, 115.8, 115.7, 115.2
(Ar-C), 57.9 (Ad-Cq), 47.2, 37.9, 31.7 ppm (Ad-C). Due to the poor
solubility of 3b, the two Ar-Cipso signals could not be detected.
119Sn{1H} NMR (149 MHz, THF-d8): δ 183 ppm. MS (EI): m/z (%)
6.95 (m, 2H, Ar-H), 6.87−6.83 (m, 1H, Ar-H), 2.32−2.29 (m, 6H, Ad-
1
H), 1.98 (s br, 3H, Ad-H), 1.57−1.54 ppm (m, 6H, Ad-H). H NMR
(400 MHz, THF-d8): δ 9.47 (s br, 1H, NH), 7.43−7.41 (m, 1H, Ar-
H), 6.97−6.95 (m, 1H, Ar-H), 6.72−6.68 (m, 2H, Ar-H), 2.44 (m, 6H,
Ad-H), 2.22 (s br, 3H, Ad-H), 1.89−1.78 ppm (m, 6H, Ad-H).
13C{1H} NMR (101 MHz, C6D6): δ 144.4, 139.3 (Ar-Cipso), 118.0,
117.8, 114.8, 114.1 (Ar-C), 57.8 (Ad-Cq), 45.7, 36.9, 30.5 ppm
(Ad-C). 13C{1H} NMR (101 MHz, THF-d8): δ 145.4, 139.9 (Ar-
Cipso), 117.9, 117.6, 114.8, 114.1 (Ar-C), 58.2 (Ad-Cq), 46.4, 37.6, 31.5
ppm (Ad-C). MS (EI): m/z (%) 314 (100) [2b]+.
360 (100) [3b]+.
Synthesis of Sodium N,N′-(tert-Butyl)benzimidazolin-2-ger-
mylenide (Na-4a).
Synthesis of N-H,N′-Phenylbenzimidazolin-2-germylene (2c).
A Schlenk flask was flame-dried and then charged under argon with
germylene 2a (100 mg, 0.426 mmol) and an excess of NaH (0.031 g,
1.292 mmol). Subsequently dry THF (5 mL) was added and the
resulting orange-yellow suspension was stirred at 65 °C for 24 h. Over
that period the suspension turned to brown-black. The solvent was
then removed in vacuo, and the resulting brown residue was washed
with n-hexane (2 mL) and was then taken up in toluene (4 mL) and
a small amount of THF (0.5 mL). Unreacted NaH was removed
by filtration over Celite, leaving a clear dark-brown solution. Removal
of solvents gave Na-4a·0.5THF as a yellow solid. This solid was
recrystallized by slow evaporation of the solvent from a saturated THF
solution at ambient temperature over 2 weeks to give (Na-4a)2·4THF,
which was subsequently characterized by an X-ray diffraction study.
Yield: 57 mg of Na-4a·0.5THF (0.195 mmol, 46%) of yellow needles.
1H NMR (400 MHz, THF-d8): δ 7.15−7.03 (m, 2H, Ar-H), 6.56−
Yield: 0.155 g (0.63 mmol, 61%) of a viscous red-brown oil. 1H NMR
(400 MHz, C6D6): δ 7.32 (s br, 1H, NH), 7.20−7.11 (m, 5H, Ph-H),
7.05−6.99 (m, 1H, Ar-H), 6.97−6.91 (m, 1H, Ar-H), 6.90−6.84 (m,
1H, Ar-H), 6.80−6.74 ppm (m, 1H, Ar-H). 13C{1H} NMR (101 MHz,
C6D6): δ 142.2, 140.9 (Ar-Cipso), 129.6, 126.3, 125.7, 119.2, 119.1,
113.4, 111.1 ppm (Ar-C and Ph-C). The resonance for the N-phenyl-
Cipso carbon atom was not observed. MS (EI): m/z (%) 256 (100) [2c]+.
Synthesis of N-H,N′-Mesitylbenzimidazolin-2-germylene (2d).
6.44 (m, 2H, Ar-H), 1.76 ppm (s, 9H, CH3). 13C{1H} NMR (101
MHz, THF-d8): δ 158.8, 146.3 (Ar-Cipso), 117.1, 114.9, 114.0, 112.3
(Ar-C), 55.8 (C(CH3)3), 33.0 ppm (C(CH3)3). Anal. Calcd for Na-4a·
0.5THF (C12H17N2GeNaO0.5): C, 49.21; H, 5.85; N, 9.56. Found: C,
50.32; H, 5.97, N, 9.19.
1
Yield: 0.193 mg (0.65 mmol, 65%) of orange needles. H NMR (400
MHz, C6D6): δ 7.65 (s br, 1H, NH), 6.99−6.94 (m, 1H, Ar-H), 6.88
(s, 2H, Mes-H), 6.87−6.82 (m, 2H, Ar-H), 6.58−6.53 (m, 1H, Ar-H),
2.20 (s, 3H, CH3), 1.93 ppm (s, 6H, CH3). 13C{1H} NMR (101 MHz,
C6D6): δ 141.5, 140.9 (Ar-Cipso), 135.8, 135.3 (Mes-C-CH3), 129.6,
119.4, 119.0, 113.0, 110.5 (Ar-C and Mes-C), 21.0, 18.1 ppm (CH3).
The resonance for the N-mesityl-Cipso carbon atom was not observed.
MS (EI): m/z (%) 298 (100) [2d]+.
Synthesis of Sodium N,N′-Adamantylbenzimidazolin-2-ger-
mylenide (Na-4b).
Synthesis of N-H,N′-tert-Butylbenzimidazolin-2-stannylene (3a).
Compound Na-4b was prepared as described for Na-4a from 2b
(80 mg, 0.256 mmol) and NaH (0.018 g, 0.768 mmol) in THF
(5 mL). After filtration over Celite and removal of the solvents, Na-4b
was obtained as a brown powder. This powder could also contain
varying amounts of THF, depending on the lengths of drying in vacuo.
1
The crude reaction product was recrystallized from a saturated THF
Yield: 67 mg (0.200 mmol, 78% of the solvent-free compound). H
1
solution to give orange crystals. Yield: 239 mg (0.85 mmol, 85%). H
NMR (400 MHz, C6D6): δ 7.62−7.51 (m, 1H, Ar-H), 7.35−7.14 (m,
NMR (400 MHz, C6D6): δ 7.12−7.04 (m, 1H, Ar-H), 6.95−6.87 (m,
1H, Ar-H), 7.00−6.83 (m, 2H, Ar-H), 2.68 (s, 6H, Ad-H), 2.17 (s br,
1
1H, Ar-H), 6.79−6.72 (m, 1H, Ar-H), 6.68−6.62 (m, 1H, Ar-H), 5.44
3H, Ad-H), 1.86−1.65 ppm (m, 6H, Ad-H). H NMR (400 MHz,
1
(s, br, 1H, NH) 1.45 ppm (s, 9H, CH3). H NMR (400 MHz, THF-
THF-d8): δ 7.31−7.27 (m, 1H, Ar-H), 7.16−7.12 (m, 1H, Ar-H),
6.57−6.44 (m, 2H, Ar-H), 2.50 (m, 6H, Ad-H), 2.21 (s br, 3H, Ad-H),
1.91−1.79 ppm (m, 6H, Ad-H). 13C{1H} NMR (101 MHz, C6D6): δ
156.8, 145.0 (Ar-Cipso), 116.2, 115.1, 115.0, 113.2 (Ar-C), 57.0 (Ad-Cq),
45.8, 37.5, 31.0 ppm (Ad-C). 13C{1H} NMR (101 MHz, THF-d8): δ
d8): δ 7.40 (s, br, 1H, NH), 7.00−6.96 (m, 1H, Ar-H), 6.73−6.68 (m,
1H, Ar-H), 6.57−6.51 (m, 1H, Ar-H), 6.44−6.38 (m, 1H, Ar-H), 1.72
ppm (s, 9H, CH3). 13C{1H} NMR (101 MHz, THF-d8): δ 146.9,
144.1 (Ar-Cipso), 116.2, 115.0, 114.4, 113.7 (Ar-C), 55.4 (C(CH3)3),
F
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Article
158.8, 145.6 (Ar-Cipso), 117.4, 115.0, 113.9, 112.8 (Ar-C), 57.1 (Ad-Cq),
46.7, 38.2, 31.7 ppm (Ad-C). MS (EI): m/z (%) 314 (62) [4b + H]+,
242 (100) [4b + H − Ge]+.
atoms on calculated positions. R = 0.0146, Rw = 0.0377, Rall = 0.0155,
Rw,all = 0.0383. The asymmetric unit contains two molecules of 3a
forming a dimer and one THF molecule.
Crystal data and structure refinement details for (Na-4a)2·4THF:
C36H58N4O4Ge2Na2O4, Mr = 802.02, yellow crystal, 0.20 × 0.20 ×
0.20 mm3, monoclinic, space group P21/m, Z = 2, a = 8.6146(3) Å, b =
12.5729(4) Å, c = 18.9466(5) Å, β = 93.006(2)°, V = 2049.29(11) Å3,
ρcalcd = 1.300 g cm−3, μ = 1.527 mm−1, ω and φ scans, 35465 measured
intensities (3.9° ≤ 2θ ≤ 62.1°), semiempirical absorption correction
(0.750 ≤ T ≤ 0.743), 6497 independent (Rint = 0.0409) and 4621
observed intensities (I ≥ 2σ(I)), refinement of 269 parameters against
|F2| of all measured intensities with hydrogen atoms on calculated
positions. R = 0.0413, Rw = 0.1173, Rall = 0.0710, Rw,all = 0.1429. The
asymmetric unit contains two molecules of Na-4a forming a dimer and
four THF molecules coordinating to the sodium cations.
Synthesis of N-H,N′-H-5,6-Dibromobenzimidazolin-2-stan-
nylene (5).
Compound 5 was prepared in analogy to the synthesis of 3a,b from
Sn[N(SiMe3)2]2 (0.220 g, 0.5 mmol) and 4,5-dibromo-o-phenylenedi-
amine (0.133 g, 0.5 mmol) in THF (3 mL). The reaction was
completed after 36 h. Yield: 182 mg (0.476 mmol, 95%) of yellow
powder. 1H NMR (400 MHz, THF-d8): δ 6.78 (s, 2H, Ar-H),
4.20 ppm (s br, 2H, NH). 13C{1H} NMR (101 MHz, THF-d8): δ
137.5 (Ar-Cipso), 119.3 (Ar-C), 111.4 ppm (Ar-C−Br). 119Sn{1H}
NMR (149 MHz, THF-d8): δ 57 ppm. MS (EI): m/z (%) 382 (100)
[5]+, 266 (29) [5 − Sn + 2H]+.
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis of Sodium N-H,N′-5,6-Dibromobenzimidazolin-2-
Figures giving NMR spectra of all new compounds and CIF
files containg the X-ray crystallographic data for 2a, (3a)2·THF,
and (Na-4a)2·4THF. This material is available free of charge via
the Internet at http://pubs.acs.org.
stannylenide (Na-6).
AUTHOR INFORMATION
Corresponding Author
*E-mail for F.E.H.: fehahn@uni-muenster.de.
Notes
A sample of stannylene 5 (0.100 g, 0.261 mmol) and an excess of NaH
(0.019 g, 0.792 mmol) were mixed together in THF (5 mL) and
stirred at ambient temperature under an atmosphere of argon. After a
few minutes gas evolution was observed and the yellow suspension
became dark. The reaction mixture was stirred for 12 h to complete
the reaction. Subsequently, toluene (5 mL) was added. After filtration
and removal of the solvent compound Na-6·THF was isolated as a
■
The authors declare no competing financial interest.
1
ACKNOWLEDGMENTS
gray solid. Yield: 76 mg (0.160 mmol, 61%). H NMR (400 MHz,
■
THF-d8): δ 6.39 (s, 2H, Ar-H), 3.59 ppm (s br, 1H, NH). 13C{1H}
NMR (101 MHz, THF-d8): δ 145.6 (2 × Ar-Cipso), 114.5 (2 × Ar-C),
105.9 ppm (2 × Ar-C-Br). 119Sn{1H} NMR (149 MHz, THF-d8):
δ −326 ppm. MS (EI): m/z (%) 266 (100) [6 + 2H − Sn]+. Anal.
Calcd for Na-6·THF (C10H11N2Br2NaOSn): C, 25.19; H, 2.33; N,
5.88. Found: C, 24.84; H, 2.22; N, 6.02.
X-ray Crystallography. X-ray diffraction data for 2a, (3a)2·THF,
and (Na-4a)2·4THF were collected at T = 153(2) K with a Bruker
APEX-II CCD diffractometer equipped with a rotating anode using
monochromated Mo Kα radiation (λ = 0.71073 Å). Diffraction data
were collected over the full sphere and were corrected for absorption.
Structure solutions were found with the SHELXS-9717 package using
direct methods and were refined with SHELXL-9717 against |F2| using
first isotropic and later anisotropic thermal parameters for all non-
hydrogen atoms. Hydrogen atoms were added to the structure models
on calculated positions.
The authors thank the Deutsche Forschungsgemeinschaft (SFB
858) for financial support. In memoriam Professor Michael F.
Lappert.
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DOI: 10.1021/om5012616
Organometallics XXXX, XXX, XXX−XXX