Synthesis and Reactivity of Intramolecularly NHC-Stabilized Germylenes and Stannylenes

Article abstract of DOI:10.1021/acs.organomet.6b00925

The HOMO-LUMO energy gap of germylenes bearing C_NHC^∧N_amido chelate ligands has been calculated in order to find suitable candidates for the activation of small molecules. Identified as promising structures, intramolecularl

Full text of DOI:10.1021/acs.organomet.6b00925

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of Intramolecularly NHC-Stabilized
Germylenes and Stannylenes
Daniel Paul,† Frederik Heins,‡ Sergei Krupski,‡ Alexander Hepp,‡ Constantin G. Daniliuc,†
Kevin Klahr,†,§ Johannes Neugebauer,†,§ Frank Glorius,*,† and F. Ekkehardt Hahn*,‡
†Organisch-Chemisches Institut, Westfalische Wilhelms-Universitat Munster, Corrensstraße 40, 48149 Munster, Germany
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‡Institut fur Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstraße 28−30, 48149
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Munster, Germany
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§Center for Multiscale Theory and Computation, Westfalische Wilhelms-Universitat Munster, Corrensstraße 40, 48149 Munster,
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Germany
S
* Supporting Information
ABSTRACT: The HOMO−LUMO energy gap of germylenes
∧
bearing CNHC Namido chelate ligands has been calculated in order to
find suitable candidates for the activation of small mole-
cules. Identified as promising structures, intramolecularly NHC-
stabilized three-coordinate germylenes and stannylenes of type
∧
[E(CNHC Namido)Cl] (E = Ge and Sn) were synthesized and characterized by NMR spectroscopy and X-ray crystallography.
Chlorido substitution at the EII center for tert-butoxido or hexamethyl disilazide ligands was also performed. Chlorido abstraction
with NaBArF gave rise to cationic two-coordinate germylenes and stannylenes.
as 2007, Bertrand and co-workers showed that the substitution
of one nitrogen atom adjacent to the carbene carbon atom
in NHCs for another carbon atom leads to the cyclic(alkyl)
(amino)carbenes (CAACs). Due to the reduced stabilization of
the carbene center from the single nitrogen atom, the HOMO−
LUMO gap observed for CAACs is also reduced and both,
nucleophilicity and electrophilicity are increased. These effects
allowed the activation of elemental hydrogen (Scheme 1A).10
Sterically shielded diarylgermylenes and -stannylenes are also
able to activate dihydrogen and ammonia, as shown by Power
and co-workers (Scheme 1B).11 In 2014, Tobita et al. presented
the cationic germylene tungsten complex [Cp*(CO)3WGe-
INTRODUCTION
■
Tetrylenes are compounds of general formula R2E, where E
is an electron-deficient, divalent group 14 element with only
six electrons in the valence shell. The isolation of the first free
N-heterocyclic carbenes (NHCs) in 19911 triggered not only
intensive research on these compounds2 but also caused renewed
interest in the heavier NHC analogs, the N-heterocyclic silylenes
(NHSi), germylenes (NHGe), stannylenes (NHSn), and
plumbylenes (NHPb),3 generically named tetrylenes. Some of
the heavier tetrylenes have actually been known long before the
chemistry of stable carbenes developed.4 The first N-heterocyclic
stannylene (NHSn), for example, was reported by Veith in 1975,5
and the first isolable and stable acyclic diamido tetrylenes were
reported even earlier by the group of Lappert in 1974 and by
others.6
(IPr)](BArF ),12 and one year later, the same group demon-
4
strated the insertion of this complex into X−H bonds, where
X is H (Scheme 1C), B, or Si.13 The activation of the latter two
bonds was found to be reversible.
The nitrogen atoms of the cyclic (NHEs) and acyclic
diamido tetrylenes significantly contribute to the stability of the
molecules. They cause a positive mesomeric effect by electron
donation to the vacant pπ orbital of the divalent group 14 ele-
ment. At the same time the nitrogen atoms cause a negative
inductive effect by withdrawing electron density from the group
14 element.3 The heterocyclic NHEs are bent at the group 14
element and exclusively exist in the singlet ground state. In this
bent geometry, the σ-orbital of the divalent group 14 atom is
best described to contain two electrons, while its pπ orbital
remains vacant, leading to a characteristic ambiphilic reactivity
as nucleophiles and electrophiles. This situation has been
described early on for selected tetrylenes by others3b,c,7,8 and
later by us.3a,7,8
Density functional theory (DFT) calculations on the inser-
tion of different silylenes and germylenes into the H−H bond
showed that the energy difference between the HOMO and
LUMO of these tetrylenes determines the course of the reac-
tion. For NHGe, the activation energy for the insertion reaction
drops significantly at a HOMO−LUMO gap of 3.4−3.6 eV or
lower.14 These findings initiated various studies regarding the
activation of elemental hydrogen by tetrylenes including the
present one.
In an attempt to identify suitably substituted tetrylenes
for the insertion into the H−H bond, we have calculated the
HOMO−LUMO energy differences for a number of these
The ambiphilic reactivity of tetrylenes has already been used
Received: December 13, 2016
for the activation of small molecules (Scheme 1).9 As early
© XXXX American Chemical Society
A
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pπ orbital at the EII center. The calculated HOMO−LUMO
energy difference of 4.038 eV for simplified N,N′-dimethyl sub-
stituted NHGe C1 is too large for an insertion into the H−H
bond of elemental hydrogen (Table 1). Related HOMO−
LUMO energy gaps were found for NHGes featuring an
unsaturated imidazolin or a saturated imidazolidin skeleton.14,19
Substituting one NMe group of the heterocycle in C1 for a
CMe2 group leads to CAAC analogue C2. CAACs featuring a
CII atom have been successfully employed for the activation of
elemental hydrogen.10 The HOMO−LUMO energy gap of
3.808 eV calculated for the GeII CAAC derivative is smaller
than the value calculated for NHC analogue C1. The calculated
value for C2 is close to the threshold value of 3.4−3.6 eV previ-
ously calculated for dihydrogen activation by germylenes.14
Tobita et al. and our group also calculated the HOMO−LUMO
gap for compound C3: ref 13, 2.780 eV; this work, 2.715 eV.
The difference is probably due to slightly different structures/
computational settings, which has been demonstrated to acti-
vate elemental hydrogen.
Scheme 1. Activation of Dihydrogen with Tetrylenes
Based on these calculations, we concluded that a C- and
N-substituted germylene similar to C2 might be suitable for the
activation of elemental hydrogen. Considering the reactivity of
germylene C3, it was decided that the carbon substituent for
the desired germylene should be an NHC. An R,R′,N-amido
group, as is found in germylenes C1 and C2, was selected as the
second substituent for the gemanium(II) center. These consi-
∧
derations led us to compound C4 bearing a CNHC Namido
chelate ligand, which we envisaged to be a suitable germylene
for the activation of dihydrogen. We calculated a HOMO−
LUMO energy gap of 3.214 eV for C4, which is lower than the
equivalent value calculated for germylene C2. While some
examples of donor-stabilized tetrylenes have been described,20
no intramolecularly NHC-stabilized cationic germylens are
known, which makes the synthesis of compounds of type C4
also an interesting synthetic target.
derivatives and compared these to the known tetrylene C3
(Table 1) which is known to insert into the H−H bond. Based
The compound 1-mesityl-3-[2-(mesitylamino)ethyl]-1H-imi-
dazol-3-ium chloride (Scheme 2) was prepared utilizing a
Table 1. Calculated HOMO−LUMO Energy Gaps for
a
Different NHGe Structures
Scheme 2. Synthesis of Imidazolium Salt 2
b
compound
HOMO−LUMO energy gap
C1
C2
C3
C4
4.038
3.808
2.780
modified version of a described procedure21a to give imidazolium
salt 2 in moderate yield. This compound has been prepared
previously by Fryzuk et al.21b and was used as ligand precursor
for transition metal NHC complexes.21c Compound 2 was
characterized by NMR spectroscopy and mass spectrometry.
3.214
a
b
Cp* = η5-C5M5, Mes = 2,4,6-trimethylphenyl. Values are given
in eV.
1
The H NMR spectrum features the characteristic resonances
on these results, we designed and prepared a novel intra-
molecularly stabilized cationic tetrylene featuring an amido
and an NHC donor and studied its reaction with elemental
hydrogen. Few related heavier tetrylenes stabilized by C- and
N-donors have previously been described.15−17
for the C2 and NH protons at δ 10.50 and 4.12 ppm,
respectively. The resonance for the C2 carbon atom was found
at δ 139.7 ppm in the 13C{1H} NMR spectrum.
The reaction of compound 2 with equimolar amounts of
E[N(SiMe3)2]2 (E = Ge and Sn) in toluene afforded tetrylenes 3a
and 3b in good yields (Scheme 3). No external base was needed
for the deprotonation of the C2 carbon atom of the imidazolium
group or the secondary amine function. Compounds 3a and 3b are
stable under argon over weeks both as solids and in THF solution.
RESULTS AND DISCUSSION
■
In our initial studies we have focused on Arduengo-type
NHGes and NHSns.7c,e,18 Unfortunately, these tetrylenes
appear not suitable for the actvation of small molecules by
simultaneous action of the nucleophilic sp2 and the electrophilic
1
The H NMR spectra of 3a and 3b no longer feature any
resonances for C2 and NH protons, and we take the absence of
B
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are rather similar to the exception of the inner-ring N8−E−C2
angle in 3b (83.37(10)°) which is in accord with the longer
E−N8 and E−C2 bond distances in this tetrylene being smaller
than those in 3a (88.27(9)°).
Scheme 3. Synthesis of Tetrylenes 3a and 3b
Next, we studied the substitution of the chlorido ligand of the
tetrylenes for other monodentate anionic ligands (Scheme 4).
Scheme 4. Ligand Substitution and Ligand Abstraction at
Tetrylenes 3a and 3b
these resonances as an indication for the double deprotona-
tion of 2 and the coordination of the resulting C∧N chelate
ligand. This conclusion is corroborated by the observation of
diastereotopic protons at the ethylene bridge in accord with
previous observations for complexes bearing donor-function-
alized NHCs with an ethylene linker.22 Based on these obser-
vations, we assumed that compounds 3a and 3b did form accor-
ding to Scheme 3. The 13C{1H} NMR resonances for the CNHC
carbon atoms were detected at δ 171.4 (3a) and δ 178.6 ppm
(3b). A signal at δ −149 ppm in the 119Sn NMR spectrum
confirms the formation of electron-rich tin(II) compound 3b.
X-ray diffraction analyses with crystals of compositions
3a·0.5THF and 3b·0.5THF confirmed that the EII atoms in
tetrylenes 3a and 3b are surrounded by the neutral NHC donor
and one anionic amido and a chlorido ligand (Figure 1).
The reaction products were completely characterized by NMR
spectroscopy. Treatment of tetrylenes 3a or 3b with potassium
tert-butoxide in benzene resulted in the exchange of the
chlorido ligand for a tert-butoxido ligand. The 13C{1H} NMR
spectrum of germylene 4a features the resonance for the C2
carbon atom at δ 173.7 ppm only slightly downfield shifted
(Δδ 2.3 ppm) compared to the resonance for the C2 carbon
atom in 3a (δ 171.4 ppm). A slightly different behavior was
found for stannylene 4b. The C2 carbon atom resonance for
the chlorido stannylene 3b was observed at δ 178.6 ppm. Upon
substitution of the chloride ligand to give stannylene 4b, this
resonance is shifted downfield to δ 207.5 ppm (Δδ 28.9 ppm).
The reasons for this strong downfield shift are not completely
clear at this time. The chemical shift for the CNHC atom in 4b
falls in the range observed for free imidazolin-2-ylidenes
(δ 211−220 ppm),2b but dissociation of the NHC as part of a
chelate ligand from the metal center is not very likely. We are
currently investigating reasons for the observed downfield shift
such as fluxionality of the Sn−CNHC bond.
Germylene 4a was crystallized from the C6D6 solution
used for NMR spectroscopy to give crystals of composition
4a·0.5C6D6. The X-ray diffraction analysis with these crystals
revealed the expected molecular structure for germylene 4a
composed of a germanium atom surrounded by the NHC
donor and anionic amido and t-butoxido ligands (Figure 2).
The Ge−O bond, as previously observed for the Ge−Cl bond
in 3a, is oriented almost perpendicular to the C2−Ge−N8
plane, and the germanium containing heterocycle is not planar.
Comparable metric parameters in chlorido germylene 3a and
t-butoxido germylene 4a are rather similar, confirming an
essentially identical influence of the anionic ligands on the
molecular structures. The Ge−O bond length in 4a compares
well to the Ge−OH bond length observed for a related three-
coordinate GeII hydroxide (Ge−O 1.8249(18) Å)20f but is
significantly longer than the GeO bond in a four-coordinate
germanones (about 1.67 Å).20d
Figure 1. Molecular structure of one molecule of 3a in 3a·0.5THF
(top) and 3b in 3b·0.5THF (bottom). Only one of the two essentially
identical molecules in the asymmetric unit for both compounds is
depicted (50% probability displacement ellipsoids; hydrogen atoms
have been omitted for clarity). Selected bond lengths (Å) and angles
(deg) for 3a [3b]: EA−ClA 2.03708(8) [2.5069(10)], EA−N8A
1.891(2) [2.088(2)], EA−C2A 2.062(2) [2.249(3)], N1A−C2A
1.343(3) [1.350(4)], N3A−C2A 1.350(3) [1.348(4)]; ClA−EA−N8A
99.07(7) [96.51(8)], ClA−EA−C2A 90.82(7) [89.66(8)], N8A−EA−
C2A 88.27(9) [83.37(10)], N1A−C2A−N3A 105.4(2) [105.3(2)].
The E−Cl bonds are oriented almost perpendicular relative to
the C2−E−N8, which constitutes a typical geometric situation
for chlorido-substituted germylenes.20g,i The plane of the ring
incorporating the EII atom deviates significantly from planarity
in accord with previous observations.20g This arrangement of
bonds would indicate an sp2-hybridized EII atom featuring an
empty p-orbital for interaction with the chlorido ligand. The
metric parameters in the two tetrylenes vary with the atomic
radius of the EII atom. Consequently, the E−Cl, E−N8, and
E−C2 distances in germylene 3a are significantly shorter than
those in stannylene 3b. The bond angles in the two tetrylenes
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chlorido ligand in these tetrylenes can be substituted for
monodentate anionic t-butoxido or bis(trimethylsilyl)amido
ligands. Removal of the chlorido ligand leads to cationic
tetrylenes 6a/6b bearing only the bidentate NHC∧amido
chelate ligand. DFT calculations indicated that germylene 6a
features a HOMO−LUMO energy gap which might make
germylenes of this type potentially suitable for the activation of
elemental hydrogen. However, no such hydrogen activation was
observed so far.
Figure 2. Molecular structure of 4a in 4a·0.5C6H6 (50% probability
displacement ellipsoids, hydrogen atoms have been omitted for
clarity). Selected bond lengths (Å) and angles (deg): Ge−O
1.8832(10), Ge−N8 1.9123(11), Ge−C2 2.0673(13), N1−C2
1.348(2), N3−C2 1.352(2); O−Ge−N8 100.25(5), O−Ge−C2
87.71(5), N8−Ge−C2 87.30(5), N1−C2−N3 105.22(11).
EXPERIMENTAL SECTION
■
All reactions were carried out under an inert argon atmosphere using
standard Schlenk techniques or in a glovebox if not stated otherwise.
Solvents were dried and freshly distilled by standard procedures prior
to use. NMR spectra were recorded at ambient temperature (unless
stated otherwise) using Bruker AVANCE I 400, Bruker AVANCE III
400, Varian 500 MHz INOVA or Varian 600 unity plus spectrometers.
Chemical shifts (δ) are expressed in ppm downfield from tetra-
methylsilane using the residual protonated solvent (1H NMR) or
Me4Sn (119Sn NMR) as an internal standard. EI mass spectra were
recorded on a MicroTof spectrometer (Bruker Daltronics, Bremen)
with loop injection, using the nanospray technique and sodium
formate cluster for calibration. Di[bis(trimethylsilyl)amido]tin(II) and
di[bis(trimethylsilyl)amido]germanium(II) were prepared by pub-
lished procedures.6a
Next, the reactivity of 3a/3b toward potassium bis(tri-
methylsilyl)amide was investigated (Scheme 4). In contrast
to tert-butoxido tetrylenes 4a and 4b, HMDS tetrylenes 5a
(E = Ge) and 5b (E = Sn) do not show significant differ-
ences of the CNHC resonances in the 13C{1H} NMR spectra
(δ 174.3 ppm for 5a, δ 178.5 ppm for 5b). The CNHC
resonances observed for 5a and 5b are also very similar to
those observed for chloride tetrylenes 3a and 3b.
Synthesis of 2-Chloro-N-mesitylacetamid 1.
Tobita et al. demonstrated that cationic germylenes such as
C3 (Table 1)13 obtained by chlorido abstraction from a three-
coordinate germylene leads to cationic derivatives which are
capable of activating elemental hydrogen. Based on our cal-
culation of the HOMO−LUMO energy gap for compound
C4 (Table 1), we decided to prepare cationic tetrylenes by
chlorido abstraction from 3a/3b. Reaction of 3a and 3b with
NaBArF (BArF = tetrakis[3,5-bis(trifluoromethyl)phenyl]-borate,
Scheme 4) gave tetrylenes 6a (E = Ge) and 6b (E = Sn).
Evidence for the formation of the cationic tetrylenes comes from
the NMR spectra of the compounds. Upon removal of the
chlorido ligand from 3a to give 6a, the CNHC resonace shifts from
δ 171.4 to 166.0 ppm. The upfield shift of the H4 and H5
protons of the NHC-ring backbone is also significant, shifting
from δ 7.25 and 7.52 ppm for 3a to δ 5.84 and 5.97 ppm for 6a.
Similar observations were made for stannylene 3b and its cationic
derivative, 6b. Formation of cationic stannylene 6b is most
clearly demonstrated by the chemical shift difference observed
in the 119Sn NMR spectra for 3b (δ −149 ppm) and 6b (δ −
60 ppm). Related cationic two-coordinate germylenes of type
[(β-diketiminate)Ge]+ have been obtained from the three-coordinate
chloride compounds by chloride removal with B(C6F5)3.23
Compound 1 was prepared following a procedure described by
Grubbs et al.21a Mesitylamine (2.71 g, 2.82 mL, 20.0 mmol) and
K2CO3 (5.53 g, 40.0 mmol) were suspended in acetonitrile (50 mL).
Chloroacetyl chloride (2.27 g, 1.60 mL, 20.0 mmol) was added drop-
wise, and the reaction mixture was stirred at ambient temperature for
48 h. Subsequently, the mixture was filtered through a pad of silica,
and hexane was added to the concentrated MeCN solution leading to
the formation of crystalline 1. The colorless crystals were isolated
by filtration and washed with cold hexane (10 mL). Yield: 3.45 g
(16.3 mmol, 82%). RF (pentane/EtOAc 8:2): 0.08. 1H NMR (300 MHz,
CDCl3, δ) 7.83 (s, 1H, NH), 6.92 (s, 2H, Mes−H), 4.26 (s, 2H, CH2Cl),
2.28 (s, 3H, Mes−CH3), 2.19 (s, 6H, Mes−CH3). 13C{1H} NMR
(75 MHz, CDCl3, δ) 164.9 (CO), 137.7, 135.0, 129.9, 129.1 (Mes−C),
42.7 (CH2Cl), 21.0, 18.2 (Mes−CH3). HRMS (ESI, positive ions): m/z =
234.0656 (calcd for [1 − Na]+, [C11H14ClNONa]+ 234.0661).
Synthesis of 1-Mesityl-3-(2-(mesitylamino)ethyl)-1H-imida-
zol-3-ium Chloride 2.
The cationic germylenes and stannylenes were tested in the
activation of elemental hydrogen. For these studies, a sample of
the tetrylene was dissolved in toluene, and this solution was
submitted to a hydrogen pressure of 1 bar under vigorous stir-
ring. Analysis of the reaction products was performed by
1H NMR spectroscopy. The results were, however, not conclusive.
For the compounds of types 3−5, no reaction or decomposi-
tion of the tetrylene was observed. Even the cationic tetrylenes
of type 6 did not react with elemental hydrogen. Apparently,
the calculated HOMO−LUMO gap of 3.214 eV is still to large
for the hydrogen activation to proceed.
A sample of 2-chloro-N-mesitylacetamid 1 (4.23 g, 20.0 mmol) was
dissolved in dry THF (50 mL), and the solution was cooled to 0 °C.
At this temperature, borane dimethylsulfide complex (5.36 mL, 4.29 g,
56.6 mmol) was added slowly. After stirring at ambient temperature
for 24 h, the reaction mixture was quenched with MeOH until gas
evolution ceased. Subsequently, brine (50 mL) was added, and the
mixture was extracted with pentane (50 mL). The solvent from the
pentane solution was removed in vacuo to give a light yellow oil which
was used for the next reaction. Under neat conditions, the obtained
chloroamine was mixed with mesitylimidazole (3.70 g, 20.0 mmol),
and the mixture was stirred at 140 °C for 15 h. A white solid was
obtained which was purified by column chromatography (SiO2,
CH2Cl2/MeOH 9:1) to give 2 as a colorless solid. Yield: 2.367 g
CONCLUSIONS
■
We succeeded in preparing several novel intramolecularly
stabilized three-coordinate germylenes and stannylenes of
type 3 bearing NHC∧amido chelate and chlorido ligands. The
D
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(6.165 mmol, 31%). RF (CH2Cl2/MeOH 9:1): 0.21. 1H NMR
(400 MHz, CDCl3, δ) 10.50 (s, 1H, H2), 8.03 (s, 1H, H5), 7.09 (s br,
1H, H4), 6.93 (s, 2H, H20 and H22), 6.70 (s, 2H, H11 and H13), 5.06
(t, 2H, J = 5.4 Hz, H6), 4.12 (br, 1H, NH), 3.24 (t, 2H, J = 5.4 Hz,
H7), 2.30 (s, 3H, H25), 2.15 (s, 3H, H16), 2.09 (s, 6H, H15 and
H17), 2.01 (s, 6H, H24 and H26). 13C{1H} NMR (100 MHz,
CDCl3, δ) 142.1 (C9), 141.2 (C21), 139.7 (C2), 134.3 (C19 and
C23), 132.4 (C12), 131.4 (C10 and C14), 130.9 (C18), 129.9 (C20
and C22), 129.3 (C11 and C13), 123.6 (C5), 122.4 (C4), 49.9 (C6),
47.6 (C7), 21.1 (C25), 20.6 (C16), 18.3 (C15 and C17), 17.6 (C24
and C26). HRMS (ESI, positive ions): m/z = 348.2436 (calcd for
[2 − Cl]+, [C23H30N3]+ 248.2434.
General Procedure for the Preparation of Germylene 3a
and Stannylene 3b. Di[bis(trimethylsilyl)amido]germanium(II)
Ge[N(SiMe3)2]2 (393 mg, 1.0 mmol) or di[bis(trimethylsilyl)amido]-
tin(II) Sn[N(SiMe3)2]2 (439 mg, 1.0 mmol) and 2 (384 mg, 1.0 mmol)
were suspended in toluene (15 mL) in a Schlenk flask. After stirring of
the reaction mixture at 110 °C for 48 h, the solvent and volatile
HN(SiMe3)2 were removed in vacuo. The solid residue was washed
with hexane (3 × 5 mL) to give the germylene (as a yellow solid) and
the stannylene (as an orange solid), respectively. The tetrylenes were
further recrystallized from THF to give single crystals of composition
3a·0.5THF and 3b·0.5THF, respectively.
Germylene 4a.
In the glovebox, a sample of germylene 3a (20 mg, 0.044 mmol) was
suspended in C6D6 (0.6 mL), and solid KOtBu (5 mg, 0.045 mmol)
was added. The resulting solution was characterized using NMR
spectroscopy. Single crystals of 4a·0.5C6D6 were obtained from a C6D6
1
solution. H NMR (500 MHz, C6D6, δ) 7.04 (s, 1H, H13), 6.99 (s,
1H, H11), 6.78 (s, 1H, H20), 6.68 (s, 1H, H22), 5.97 (s, 1H, H5),
5.87 (s, 1H, H4), 4.66−4.54 (m, 1H, H7a), 3.55−3.48 (m, 1H, H6a),
3.23 (d, 1H, J = 13.1 Hz, H6b), 2.99 (d, 1H, J = 13.1 Hz, H7b), 2.72
(s, 3H, H17), 2.58 (s, 3H, H15), 2.27 (s, 3H, H16), 2.15 (s, 3H, H25),
2.06 (s, 3H, H24), 2.03 (s, 3H, H26), 1.30 (s, 9H, H28). 13C{1H}
NMR (126 MHz, C6D6, δ) 173.7 (C2), 152.2 (C9), 139.5 (C19),
136.5 (C21), 134.9 (C23), 134.2 (C18), 130.3 (C10 and C14), 130.3
(C12 and C13), 129.4 (C22), 129.2 (C11 and C20), 121.7 (C5),
120.1 (C4), 69.4 (C27), 52.5 (C6), 48.6 (C7), 33.6 (C28), 21.5
(C15), 21.0 (C16 or C24), 21.0 (C16 or C24), 20.8 (C17), 18.6
(C25), 17.9 (C26).
Germylene 3a.
Stannylene 4b.
1
Yield: 391 mg (0.86 mmol, 86%). H NMR (400 MHz, THF-d8, δ)
7.52 (d, 3J = 1.8 Hz, 1H, H5), 7.25 (d, 3J = 1.8 Hz, 1H, H4), 6.99 (s br,
1H, H22), 6.97 (s br, 1H, H20), 6.75 (s br, 1H, H11), 6.72 (s br, 1H,
H13), 4.48−4.44 (m, 1H, H6a), 4.32−4.22 (m, 2H, H6b, H7a), 3.22−
3.18 (m, 1H, H7b), 2.35 (s br, 3H, H15 or H17), 2.30 (s, 3H, H25),
2.21 (s br, 3H, H17 or H15), 2.16 (s br, 3H, H24), 2.15 (s, 3H, H16),
2.04 (s br, 3H, H26). 13C{1H} NMR (100 MHz, THF-d8, δ) 171.4
(C2), 151.0 (C9), 140.4 (C21), 137.4 (C19 or C23), 136.9 (C23 or
C19), 135.4 (C10 or C14), 135.2 (C14 or C10), 134.2 (C18), 132.3
(C12), 130.3 (C22), 129.6 (C20), 128.8 (C13), 123.8 (C5), 122.3
(C4), 52.7 (C6), 50.5 (C7), 21.1 (C25), 20.9 (C16), 20.5 (C15 or
C17), 20.3 (C17 or C15), 18.5 (C24), 17.8 (C26). MS (EI): m/z (%)
In the glovebox, a sample of stannylene 3b (20 mg, 0.04 mmol) was
suspended in C6D6 (0.6 mL), and solid KOtBu (10 mg, 0.09 mmol)
was added. The resulting solution was characterized using NMR
1
spectroscopy. H NMR (500 MHz, C6D6, δ) 7.03 (s, 2H, H11 and
H13), 6.75 (s, 2H, H20 and H22), 6.02 (s, 1H, H4), 5.97 (s, 1H, H5),
4.31−4.21 (m, 2H, H6), 3.91−3.83 (m, 2H, H7), 2.69 (s, 6H, H15
and H17), 2.26 (s, 3H, H16), 2.08 (s, 3H, H25), 1.85 (s, 6H, H24 and
H26), 1.36 (s, 9H, H28). 13C{1H} NMR (126 MHz, C6D6, δ) 207.5
(C2), 153.2 (C9), 139.2 (C18), 137.8 (C19, C23 and C21), 136.8
(C10 and C14), 130.0 (C12), 129.5 (C11 and C13), 128.9 (C20 and
C22), 120.3 (C5), 119.2 (C4), 69.8 (C27), 56.3 (C7), 55.7 (C6), 35.7
(C28), 21.4 (C15 and C17), 21.1 (C16), 20.9 (C25), 17.8 (C24 and
C26). 119Sn NMR (224 MHz, C6D6, δ) −148.
+
455 (100) [3a]+, 419 (87), [3a − HCl] . Anal. Calcd for (C23H28-
ClGeN3)·0.5THF: C, 61.20; H, 6.58; N, 8.57. Found: C, 61.15; H,
6.44; N, 8.58.
Stannylene 3b.
Germylene 5a.
In the glovebox, germylene 3a (20 mg, 0.044 mmol) was suspended in
C6D6 (0.6 mL), and KN(SiMe3)2 (9 mg, 0.045 mmol) was added. The
resulting solution was characterized using NMR spectroscopy. 1H
NMR (500 MHz, C6D6, δ) 7.02 (s, 1H, H11), 6.98 (s, 1H, H13), 6.75
(s, 1H, H20), 6.67 (s, 1H, H22), 5.97 (d, 1H, J = 1.8 Hz, H5), 5.87
(d, 1H, J = 1.8 Hz, H4), 4.38 (ddd, 1H, J = 14.3, 12.5, 3.1 Hz, H7a),
3.52 (m, 1H, H6a), 3.21 (ddd, 1H, J = 12.5, 3.1, 1.9 Hz, H6b), 3.01
(ddd, 1H, J = 14.3, 4.5, 1.9 Hz, H7b), 2.65 (s, 3H, H15), 2.48 (s, 3H,
H17), 2.24 (s, 3H, H16), 2.14 (s, 3H, H24), 2.08 (s, 3H, H25), 1.92
(s, 3H, H26), 0.23 (s, 18H, H27). 13C{1H} NMR (126 MHz, C6D6, δ)
174.3 (C2), 152.6 (C9), 139.6 (C21), 136.6 (C10), 135.9 (C23),
135.0 (C14), 134.7 (C19), 133.9 (C18), 131.1 (C12), 130.0 (C11),
129.8 (C22), 129.4 (C20), 128.9 (C13), 122.2 (C5), 121.5 (C4), 52.7
(C6), 48.8 (C7), 21.6 (C17), 21.2 (C15), 21.1 (C16), 20.9 (C25),
1
Yield: 451 mg (0.90 mmol, 90%). H NMR (400 MHz, THF-d8, δ)
7.53 (d, 3J = 1.7 Hz, 1H, H5), 7.29 (d, 3J = 1.7 Hz, 1H, H4), 7.03 (s br,
1H, H20), 7.01 (s br, 1H, H22), 6.76 (s br, 1H, H11), 6.72 (s br, 1H,
H13), 4.72−4.66 (m, 1H, H6a), 4.31−4.18 (m, 2H, H6b and H7a),
3.46−3.38 (m, 1H, H7b), 2.36 (s, 3H, H15), 2.32 (s, 3H, H25), 2.21
(s, 3H, H17), 2.14 (s br, 6H, H16, H26), 2.04 (s, 3H, H24). 13C{1H}
NMR (101 MHz, THF-d8, δ) 178.6 (C2), 152.7 (C9), 140.6 (C21),
137.4, 136.9, 135.1, 135.0 (C10, C14, C19 and C23), 134.8 (C18),
131.5 (C12), 130.4 (C20), 130.3 (C11), 129.8 (C22), 128.9 (C13),
124.5 (C5), 122.3 (C4), 54.5(C6), 53.2 (C7), 21.2 (C25), 20.9 (C16),
20.4 (C15 or C17), 20.3 (C17 or C15), 18.3 (C26), 17.8 (C24).
119Sn NMR (149 MHz, THF-d8, δ) −149. MS (EI): m/z (%) 501
(46) [3b]+.
E
DOI: 10.1021/acs.organomet.6b00925
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
19.4 (C24), 18.4 (C26), 6.6 (C27). 29Si NMR (99 MHz, C6D6, δ)
−2.83 ppm.
Stannylene 5b.
H16), 2.14 (s, 6H, H15 and H17), 2.02 (s, 3H, H25), 1.60 (s, 6H, H24
and H26). 13C{1H} NMR (151 MHz, C6D6, δ) 162.7 (q, J = 49.9 Hz,
C27), 149.3 (C9), 141.0 (C21), 135.5 (C28), 134.3 (C12, together
with C10, C14, C19, and C23), 132.7 (C18), 129.9 (s, C11, C13, C20,
and C22), 129.0 (m, C29) 125.3 (q, J = 272.6 Hz, C31), 123.2 (C4 or
C5), 122.1 (C4 or C5), 118.1 (p, J = 4.3 Hz, C30), 53.6 (C6 or C7),
53.6 (C6 or C7), 20.8 (C16), 20.8 (C25), 19.8 (C15 and C17), 17.1
(C24 and C26). The resonance for the C2 carbon atom was not
detected. 11B NMR (192 MHz, C6D6, δ) −5.97. 19F NMR (564 MHz,
C6D6, δ) −62.21. 119Sn NMR (149 MHz, THF-d8, δ) −60.
Computational Details. All calculations were carried out using
the Gaussian09 program.24 Structural optimizations were carried out
with the B3LYP25 hybrid exchange-correlation functional, a 6-31G(d,p)26
basis set for all atoms except W, and a LanL2DZ27 effective core
potential/basis set for W atoms. HOMO−LUMO gaps were calculated
with the same method for the optimized structures. The threshold
values in ref 14 were calculated with the larger 6-311+G** basis. Test
calculations carried out here for compounds C1 and C2 indicate that
this leads to slightly lower (∼0.1 eV) HOMO−LUMO gaps compared
to the 6-31G(d,p) data.
X-ray Diffraction Studies. X-ray diffraction data for compounds
3a·0.5THF, 3b·0.5THF, and 4a·0.5C6D6 were recorded with graphite
monochromated Mo Kα radiation (λ = 0.71073 Å) at T = 100(2) K
for 4a·0.5C6D6 and at T = 153(2) for 3a·0.5THF and 3b·0.5THF.
Diffraction data were collected over the full sphere and were corrected
for absorption. Structure solutions were found with the SHELXS28
package using direct methods and were refined with SHELXL28
against |F2| using first isotropic and later anisotropic thermal param-
eters for all non-hydrogen atoms. Hydrogen atoms were added to the
structure models on calculated positions and refined as riding atoms.
If not noted otherwise, then no hydrogen positions were calculated for
disordered atoms (see the individual refinement details).
In the glovebox, a sample of stannylene 3b (20 mg, 0.04 mmol)
was suspended in toluene-d8 (0.6 mL), and KN(SiMe3)2 (8 mg,
0.04 mmol) was added. The resulting solution was characterized using
1
NMR spectroscopy. H NMR (500 MHz, toluene-d8, 253 K, δ) 7.02
(s, 1H, H13), 6.92 (s, 1H, H11), 6.68 (s, 1H, H22), 6.56 (s, 1H, H20),
5.85 (s, 1H, H4 or H5), 5.73 (s, 1H, H4 or H5), 4.70 (t, 1H, J =
12.6 Hz, H7a), 3.41−3.29 (m, 2H, H6a and H7b), 3.24 (d, 1H, J =
12.6 Hz, H6b), 2.66 (s, 3H, H17), 2.37 (s, 3H, H15), 2.28 (s, 3H, H16),
2.04 (s, 3H, H24), 2.01 (s, 3H, H25), 1.93 (s, 3H, H26), 0.11 (s, 18H,
H27). 13C{1H} NMR (126 MHz, toluene-d8, 253 K, δ) 178.5 (C2),
152.8 (C9), 139.5 (C21), 135.1 (C23), 134.9 (C14), 134.8 (C19), 134.3
(C18), 133.6 (C10), 130.4 (C13), 129.9 (C20), 129.5 (C22), 129.3
(C12), 129.0 (C11), 123.0 (C4 or C5), 121.8 (C4 or C5), 52.9 (C6),
49.3 (C7), 21.8 (C15), 21.1 (C17), 20.9 (C16), 20.8 (C25), 18.8 (C26),
18.7 (C24), 2.5 (C27). 29Si NMR (99 MHz, toluene-d8, 253 K, δ) −3.53.
119Sn NMR (186 MHz, toluene-d8, 253 K, δ) −124.3.
Germylene 6a.
Crystal Data and Structure Refinement Details for
3a·0.5THF. C23H28N3ClGe·0.5C4H8O, Mr = 490.58 g·mol−1, colorless
block, 0.42 × 0.25 × 0.25 mm3, monoclinic, space group P21/n, Z = 8,
a = 8.21160(10) Å, b = 12.2330(2) Å, c = 48.3211(6) Å, β =
94.3080(10)°, V = 4840.36(12) Å3, ρcalcd = 1.346 g·cm−3, μ = 1.395 mm−1,
ω- and φ-scans, 64 438 measured intensities (1.7° ≤ 2θ ≤ 59.1°),
semiempirical absorption correction (0.645 ≤ T ≤ 0.746), 13 573
independent (Rint = 0.0368) and 11 367 observed intensities (I ≥ 2σ(I)),
refinement of 562 parameters against |F2| of all measured intensities with
hydrogen atoms on calculated positions. R = 0.0481, wR = 0.1134,
Rall = 0.0616, wRall = 0.1193. The asymmetric unit contains two
formula units of 3a and one THF molecule. The THF molecule is
disordered over two positions (SOF = 0.62/0.28). The positional
parameters of the THF molecule were refined with isotropic thermal
parameters, and no hydrogen positions were calculated for the THF
molecule.
Crystal Data and Structure Refinement Details for
3b·0.5THF. C23H28N3Cl2OSn, Mr = 536.68 g·mol−1, colorless block,
0.16 × 0.15 × 0.12 mm3, monoclinic, space group P21/n, Z = 8,
a = 8.2740(4) Å, b = 12.2320(6) Å, c = 49.393(2) Å, β = 94.8040(10)°,
V = 4981.4(4) Å3, ρcalcd = 1.431 g·cm−3, μ = 1.152 mm−1, ω- and
φ-scans, 143 770 measured intensities (4.2° ≤ 2θ ≤ 61.1°), semi-
empirical absorption correction (0.746 ≤ T ≤ 0.677), 15 264
independent (Rint = 0.0630) and 11 310 observed intensities (I ≥
2σ(I)), refinement of 557 parameters against |F2| of all measured
intensities with hydrogen atoms on calculated positions. R = 0.0485,
wR = 0.1022, Rall = 0.0771, wRall = 0.1113. The asymmetric unit contains
two formula units of 3b and one THF molecule. The THF molecule is
disordered.
In the glovebox, a sample of germylene 3a (20 mg, 0.044 mmol) was
suspended in C6D6 (0.6 mL), and NaBArF (9 mg, 0.045 mmol) was
added. The resulting solution was characterized using NMR spectro-
scopy. 1H NMR (600 MHz, C6D6, δ) 8.35 (s, 8H, H28), 7.65 (s, 4H,
H30), 6.72 (s, 2H, H11 and H13), 6.57 (s, 2H, H20 and H22), 5.97
(s, 1H, H5), 5.84 (s, 1H, H4), 3.16 (t, 2H, J = 5.5 Hz, H6), 2.75−2.68
(m, 2H, H7), 2.08 (s, 3H, H16), 1.98 (s, 3H, H25), 1.80 (s, 6H, H15
and H17), 1.49 (s, 6H, H24 and 26). 13C{1H} NMR (151 MHz, C6D6, δ)
166.0 (C2), 163.3−162.0 (q, J = 49.8 Hz, C27), 144.6 (C9), 142.1
(C21), 137.7 (C12), 135.4 (C28), 133.8 (C19 and C23), 133.2 (C10
and C14), 130.2 (C11, C13, C20 and C22), 129.0 (m, C29) 125.2
(q, J = 272.6 Hz, C31), 123.4 (C4), 122.5 (C5), 118.1 (C30), 52.2
(C7), 50.3 (C6), 20.8 (C25), 20.7 (C16), 18.4 (C15 and C17), 16.7
(C24 and C26). 11B NMR (192 MHz, C6D6, δ) −6.03. 19F NMR
(564 MHz, C6D6, δ) −62.23.
Stannylene 6b.
Crystal Data and Structure Refinement Details for
4a·0.5C6D6. C30H37D3N3GeO, Mr = 534.26 g·mol−1, colorless prism,
0.26 × 0.18 × 0.09 mm3, monoclinic, space group P21/c, Z = 4, a =
13.0226(4) Å, b = 15.0573(5) Å, c = 14.4071(5) Å, β = 96.067(1)°,
V = 2809.2(2) Å3, ρcalcd = 1.263 g·cm−3, μ = 1.117 mm−1, ω- and
φ-scans, 65 178 measured intensities (4.8° ≤ 2θ ≤ 55.1°), semi-
empirical absorption correction (0.86 ≤ T ≤ 0.90), 6460 independent
(Rint = 0.0457) and 5712 observed intensities (I ≥ 2σ(I)), refinement
of 325 parameters against |F2| of all measured intensities with
In the glovebox, stannylene 3b (20 mg, 0.04 mmol) was suspended in
C6D6 (0.6 mL), and NaBArF (9 mg, 0.045 mmol) was added. The
resulting solution was characterized using NMR spectroscopy. 1H
NMR (600 MHz, C6D6, δ) 8.39 (s, 8H, J = 2.1 Hz, H28), 7.67 (s, 4H,
H30), 6.89 (s, 2H, H11 and H13), 6.45 (s br, 2H, H20 and H22), 6.01
(d, 1H, J = 1.6 Hz, H4 or H5), 5.86 (d, 1H, J = 1.6 Hz, H4 or H5),
3.43 (m br, 2H, H6 or H7), 3.28 (m br, 2H, H6 or H7), 2.22 (s, 3H,
F
DOI: 10.1021/acs.organomet.6b00925
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
hydrogen atoms on calculated positions. R = 0.0247, wR = 0.0563,
Rall = 0.0311, wRall = 0.0592. The asymmetric unit contains one
formula unit 4a·0.5C6D6.
(10) Frey, D. D.; Lavallo, V.; Donnadieu, B.; Schoeller, W. W.;
Bertrand, G. Science 2007, 316, 439−441.
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ASSOCIATED CONTENT
* Supporting Information
■
S
(13) Inomata, K.; Watanabe, T.; Miyazaki, Y.; Tobita, H. J. Am.
Chem. Soc. 2015, 137, 11935−11937.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00925.
(14) Wang, Y.; Ma, J. J. Organomet. Chem. 2009, 694, 2567−2575.
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Schoeller, W. W.; Jutzi, P. Organometallics 1998, 17, 2149−2151.
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Schley, N. D.; Zhu, Z.; Pu, L.; Fettinger, J. C.; Teat, S. T.; Nowik, I.;
Herber, R. H.; Takagi, N.; Nagase, S.; Power, P. P. J. Am. Chem. Soc.
2007, 129, 16197−16208.
NMR spectra for all compounds (PDF)
X-ray crystallographic data for 3a·0.5THF, 3b·0.5THF,
and 4a·0.5C6D6 (CIF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: glorius@uni-muenster.de.
*E-mail: fehahn@uni-muenster.de.
(17) Su, B.; Ganguly, R.; Li, Y.; Kinjo, R. Chem. Commun. 2016, 52,
613−616.
(18) (a) Piel, I.; Dickschat, J. V.; Pape, T.; Hahn, F. E.; Glorius, F.
■
Dalton Trans. 2012, 41, 13788−13790. (b) Krupski, S.; Pottgen, R.;
̈
Schellenberg, I.; Hahn, F. E. Dalton Trans. 2014, 43, 173−181.
(19) Wang, L.; Lim, Y. S.; Li, Y.; Ganguly, R.; Kinjo, R. Molecules
2016, 21, 990−1000.
ORCID
Alexander Hepp: 0000-0003-1288-925X
Frank Glorius: 0000-0002-0648-956X
F. Ekkehardt Hahn: 0000-0002-2807-7232
(20) (a) Akkari, A.; Byrne, J. B.; Saur, I.; Rima, G.; Gornitzka, H.;
Barrau, J. J. Organomet. Chem. 2001, 622, 190−198. (b) Leung, W.-P.;
So, C.-W.; Chong, K.-H.; Kan, K.-W.; Chan, H.-S.; Mak, T. C. W.
Organometallics 2006, 25, 2851−2858. (c) Rupar, P. A.; Jennings, M.
C.; Ragogna, P. J.; Baines, K. M. Organometallics 2007, 26, 4109−4111.
(d) Yao, S.; Xiong, Y.; Driess, M. Chem. Commun. 2009, 6466−6468.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from the Deutsche
Forschungsgemeinschaft (SFB 858 and IRTG 2027).
́
(e) Katir, N.; Matioszek, D.; Ladeira, S.; Escudie, J.; Castel, A. Angew.
■
Chem., Int. Ed. 2011, 50, 5352−5355. (f) Wang, W.; Inoue, S.; Yao, S.;
Driess, M. Organometallics 2011, 30, 6490−6494. (g) Siwatch, R. K.;
Kundu, S.; Kumar, D.; Nagendran, S. Organometallics 2011, 30, 1998−
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