Hydroalumination of Oligoalkynylgermanes and -digermanes – Reactions with Heterocumulenes by Al–C or Ge–C Bond Activation and Formation of a Hexazenedialuminum Complex

Article abstract of DOI:10.1002/zaac.201800159

Hydroalumination of the dialkynylgermane Ph₂Ge(C≡CtBu)₂ (1) and the digermanes Ph_n(tBuC≡C)_3–nGe–Ge(C≡CtBu)_3–nPh_n (2a: n = 2; 2b: n = 1) with two equivalents of H–AltBu₂ or H–AlEt₂ yielded the mixed Al/Ge compounds Ph₂Ge[C(AltBu₂)=CH-tBu]₂ (3), [Ph₂GeC(AltBu₂)=CH-tBu]₂ (4a), and [Ph₂GeC(AlEt₂)=CH-tBu]₂ (4b). Reactions of 2b with both aluminum hydrides afforded inseparable mixtures of products. 3 reacted with heterocumulenes by retrohydroalumination. Phenyl isocyanate gave insertion of the C=N group into the resulting Ge–C(≡C–tBu) bond (5), whereas the NCS and NCN groups of phenyl isothiocyanate and a carbodiimide inserted into Al–C_vinyl bonds (6 and 7) with unaffected terminal Ge–C≡C–tBu moieties. The generation of 5 represents the first example of the insertion of a heterocumulene into a Ge–C bond, which may be favored by the activation of the isocyanate group by the Lewis acidic Al atom and the increased polarity of the N=C=O fragment as determined by NBO calculations. The reactions of the digermanes 4 with heterocumulenes were unselective and afforded inseparable mixtures. Treatment of 4a with the azide (4-tBu)C₆H₄CH₂–N₃ led interestingly to reductive coupling of two azide molecules, and the hexazene complex (tBuC₆H₄CH₂N₃–N₃C₆H₄tBu)(AltBu₂)₂ (8) was isolated in moderate yield. Six nitrogen atoms form a dianionic chain, which coordinated two AltBu₂ fragments by formation of two joint AlN₄ heterocycles.

Full text of DOI:10.1002/zaac.201800159

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201800159
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Hydroalumination of Oligoalkynylgermanes and -digermanes –
Reactions with Heterocumulenes by Al–C or Ge–C Bond
Activation and Formation of a Hexazenedialuminum Complex
Werner Uhl,*[a] Christian Honacker,[a] Neil Lawrence,[a] Alexander Hepp,[a] Lina Schürmann,[a] and
Marcus Layh[a]
Dedicated to Prof. Alexander Filippou on the Occasion of his 60th Birthday
Abstract.
Hydroalumination
of
the
dialkynylgermane first example of the insertion of a heterocumulene into a Ge–C bond,
Ph2Ge(CϵCtBu)2 (1) and the digermanes Phn(tBuCϵC)3–nGe– which may be favored by the activation of the isocyanate group by the
Ge(CϵCtBu)3–nPhn (2a: n = 2; 2b: n = 1) with two equivalents of
H–AltBu2 or H–AlEt2 yielded the mixed Al/Ge compounds
Ph2Ge[C(AltBu2)=CH-tBu]2 (3), [Ph2GeC(AltBu2)=CH-tBu]2 (4a),
and [Ph2GeC(AlEt2)=CH-tBu]2 (4b). Reactions of 2b with both alumi-
Lewis acidic Al atom and the increased polarity of the N=C=O frag-
ment as determined by NBO calculations. The reactions of the diger-
manes 4 with heterocumulenes were unselective and afforded insepa-
rable mixtures. Treatment of 4a with the azide (4-tBu)C6H4CH2–N3
num hydrides afforded inseparable mixtures of products. 3 reacted with led interestingly to reductive coupling of two azide molecules, and
heterocumulenes by retrohydroalumination. Phenyl isocyanate gave in-
sertion of the C=N group into the resulting Ge–C(ϵC–tBu) bond (5),
whereas the NCS and NCN groups of phenyl isothiocyanate and a
the hexazene complex (tBuC6H4CH2N3–N3C6H4tBu)(AltBu2)2 (8) was
isolated in moderate yield. Six nitrogen atoms form a dianionic chain,
which coordinated two AltBu2 fragments by formation of two joint
carbodiimide inserted into Al–Cvinyl bonds (6 and 7) with unaffected AlN4 heterocycles.
terminal Ge–CϵC–tBu moieties. The generation of 5 represents the
alkene, which was found to be crucial for the rearrangement
of the kinetically favored cis isomer to the thermodynamically
stable trans form.[15]
Hydrometallation of alkynylsilanes or -germanes afforded
compounds with new and interesting structural motifs, which
showed an exceptional reactivity. Treatment of dialkynyl de-
rivatives with one equivalent of an aluminum or gallium hy-
dride yielded mixed alkenyl-alkynyl compounds (A,
Scheme 1), in which the Lewis acidic metal atoms have a close
Introduction
Functionalized alkynylsilanes and -germanes are facile start-
ing materials for the generation of various unprecedented sec-
ondary products. They are available on simple routes and can
be modified by various donors such as additional alkynyl
groups,[1–6] halide atoms,[7–9] and amino substituents.[9–12]
Their highly selective reactions with dialkylaluminum or -gal-
lium hydrides afforded functionalized alkenes in which vinylic
C atoms are bound in a 1,1-fashion to Al or Ga and Si or
Ge atoms.[1–14] The observed regioselectivity depends on the
electronegativity difference between Si or Ge and sp-hy-
bridized alkynyl C atoms, which results in a relatively high
partial negative charge at the Cα atom of the alkyne and the
exclusive attack of the metal atom at this position. The con-
certed addition of Al–H groups to alkynes causes a high stereo-
selectivity and the cis arrangement of Al and H atoms at the
resulting alkenyl groups.[1–13] cis/trans-Isomerization was ob-
served only in rare cases and is often suppressed by steric
shielding of the metal atoms or their coordinative saturation
by electron donating functional groups.[5] Both effects prevent
the approach of an Lewis acidic center to the Cα atom of the
* Prof. Dr. W. Uhl
Fax: +49-251-8336660
E-Mail: uhlw@uni-muenster.de
[a] Institut für Anorganische und Analytische Chemie
Universität Münster
Scheme 1. Schematic drawings of the functionalized alkenylgermanes
A to C.
Corrensstraße 30
48149 Münster, Germany
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contact to the Cα atoms of the remaining alkynyl
groups.[1–6,8–13,16] This interaction resulted in an activation of
the E–C(ϵC–R) bond (E = Si, Ge) and favored thermal re-
arrangement (1,1-carbometallation) to yield sila- or germacy-
clobutenes, which showed interesting fluorescence proper-
ties.[17,18] Halogen atoms attached to Si or Ge resulted in
strong intramolecular Al–X or Ga–X interactions (B) and a sig-
nificant lengthening and activation of E–X bonds (X = Cl,
Br),[7–9] which resulted in rearrangement and exchange of
halogen atoms and Al bound tert-butyl groups.[8,9] Similar
structural motifs with N atoms in the bridging positions
(Si/Ge–N–Al/Ga) are formed by hydrometallation of amino
substituted silanes and germanes.[10–12,16] An activated dieth-
ylamino germane (C) reacted by the unprecedented elimination
of an imine under mild conditions.[10] As suggested by quan-
tum chemical calculations rearrangement and imine elimi-
nation proceeded via highly reactive silyl or germyl cations.
Furthermore, the intramolecular activation of Si–X and Ge–X
bonds resulted in an unusual reactivity, e.g. toward hetero-
cumulenes.[7,19]
Scheme 2. Synthesis of 2a.
Twofold hydrometallation of dialkynylsilanes or -germanes
opened facile access to chelating Lewis acids with two coordi-
natively unsaturated metal atoms,[1,6,10,13] which effectively
coordinated halide anions in a chelating fashion.[1,10,13] Two
Lewis acidic centers in a single molecule may help to activate
substrates by the chelating coordination of functional groups
and may result in new reactivity patterns. This manuscript de-
scribes the synthesis of a dialkynylgermane and two alkynyl-
digermanes containing Ge–Ge bonds, their hydroalumination
reactions and the unexpected reactivity of the resulting dialu-
minum compounds towards various heterocumulenes and an
azide.
Scheme 3. Synthesis of 2b.
The NMR spectra of compounds 2 are similar to those of 1
with a characteristic large difference of about Δδ = 44 between
the 13C NMR shifts of the Cα [δ = 76.7 (2a), 74.7 (2b)] and
Cβ atoms [δ = 120.7 (2a), 118.6 (2b)] of the alkyne. The differ-
ence between the shifts of both alkynyl carbon atoms is a mea-
sure of the polarization of the triple bond.[23] The charge on
Cα is influenced by the substituents on the alkyne with tBu
leading to a higher negative partial charge than Ph (e.g. NBO
calculations on dimesitylphosphines).[24] The slightly larger Δδ
value in compounds 2 as compared to 1 (41.6) may result from
the Ge–Ge bond and the lower oxidation state of germanium
(GeIII).
The molecular structure of compound 2a is shown in Fig-
ure 1. 2a crystallizes with a center of symmetry between the
two Ge atoms resulting in an ideal staggered conformation
with the alkyne substituents on opposite sides of the molecule.
The arrangement is similar in 2b, which crystallizes with two
independent molecules that both adopt a staggered conforma-
tion. Bond lengths and angles are in the expected ranges with
CϵC bond lengths of around 120 pm and Ge–Ge bond lengths
of 241.8(1) and 240.1(av) pm, respectively.
Results and Discussion
Following a previously described procedure, the air-stable
dialkynylgermane Ph2Ge(CϵC–tBu)2 (1) was conveniently
obtained in high yield from commercially available Ph2GeCl2
and two equivalents of Li–CϵC–tBu, which was in situ gener-
ated from H–CϵC–tBu and nBuLi.[3] The syntheses of
the digermanes 2 is less straight forward. According to a
literature procedure[20] Ph3Ge–GePh3 was treated with
Cl3CCO2H to yield the corresponding carboxylic acid ester
Ph4Ge2(O2CCCl3)2 (Scheme 2), which was converted to
[21]
Ph4Ge2Cl2
by reaction with aqueous HCl. Reaction of the
dichloride with two equivalents of Li–CϵC–tBu afforded by
salt elimination the dialkynyldigermane 2a in 70% yield
(Scheme 2). The tetraalkynyldigermane 2b was obtained via
treatment of PhGeCl3 with two equivalents of Li–CϵC–Ph
Hydroalumination of 1 and 2a with two equivalents of H–
AltBu2 yielded the respective hydroalumination products 3 and
4a in 59 and 65% yield (Scheme 4 and Scheme 5). The analo-
gous reaction with sterically less demanding H–AlEt2 was only
successful with 2a yielding 4b in 82% yield, while in case of 1
a mixture of unknown and inseparable products was obtained.
Attempts to isolate a hydroalumination product from the reac-
tion of compound 2b with these aluminum hydrides failed, and
[8]
(Scheme 3). Intermediately formed PhGeCl(CϵC–tBu)2
yielded the digermane by reductive coupling in high yield
(77%). Unselective reactions were observed with strong reduc-
ing agents such as Na or K, and only the SmI2 mediated re-
duction with magnesium[22] afforded 2b.
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ppm (Cα) and 163.1 to 169.9 ppm (Cβ) in the 13C NMR spectra
result from vinylic C atoms. The latter may be compared to
similar values found in related mono-hydroalumination prod-
ucts.[3] The signals of the quaternary C atoms of the alkyne
bound tert-butyl groups are with values of δ = 39 ppm con-
siderably shifted to lower field compared to the starting materi-
als (about δ = 29 ppm). The NMR spectra of compound 4a
show broad lines at ambient temperature, which prevented the
unambiguous assignment of signals in the phenyl region and
indicates a dynamic behavior in solution. Despite the broad-
ness of signals two different AltBu2 groups (1H, δ = 1.35/0.69)
are resolved, while the tBu substituents at aluminum are equiv-
alent in compounds 3 and 4b. Different tert-butyl groups were
recognized in the solid-state structure of 4a (Figure 3) with
one group (C41) showing a close Me3C···HC contact (293 pm)
to one of the phenyl substituents at Ge. While similar contacts
(see discussion below) are also observed for 3 and 4b the
bulkiness of the tBu groups and the presence of a second ger-
myl fragment in 4a may increase the rotational barrier about
the Cvinyl–Al and all Ge–C bonds, prevent free rotation around
these bonds and result in the observed broadening of signals.
The strongly differing chemical shifts of the tBu groups may
indicate that they are in different regions of the anisotropy
cone of the phenyl substituent.[25] C41 is closer to the deshield-
ing area, C51 closer to the shielding area. The average value
of the tBu shifts of 4a (δ = 1.02 ppm) is close to that found
for compound 3 (δ = 0.99 ppm). A low temperature NMR
spectrum (200 K) led to a reduction in line width but complete
assignment of the signals was still not possible. The major
difference being the splitting of the broad signal at δ = 8.15
Figure 1. Molecular structure of compound 2a. The structure of com-
pound 2b is similar. Displacement ellipsoids are drawn at the 40%
level. Hydrogen atoms are omitted for clarity; equivalent atoms were
generated by –x + 2, –y + 1, –z + 1. Selected bond lengths /pm and
angles /° (data of compound 2b in square brackets, average values
from two independent molecules): Ge1–Ge1’ 241.81(3) [240.14],
Ge1–C11 194.6(1) [193.9], Ge1–C21 195.0(1), Ge1–C31 190.7(2)
[189.7], C31–C32 120.5(2) [119.3]; Ge1–C31–C32 176.2(1) [171.0].
NMR spectra of the reaction mixtures gave no evidence for
the formation of the expected products.
into two doublets at 8.42 (2JHH = 7.3 Hz) and 7.96 (2JHH
=
7.4 Hz). The new signals may tentatively be assigned to the o-
H atoms of the phenyl substituents, of which one shows a weak
interaction to the Al atom and C41 (Figure 3). Hindered rota-
tion about the Ge–Cipso bond may result in two distinct H sig-
nals. Similar interactions between metal atoms such as Li, Ru
or Ir and H were previously shown to cause such a hindered
rotation and a high field shift of the involved o-H atoms.[26]
The molecular structures of compounds 3, 4a, and 4b are
shown in Figure 2, Figure 3, and Figure 4. Compound 3 fea-
tures an approximate twofold rotation axis, which passes
through the Ge atom and bisects the C11–Ge1–C21 and C31–
Ge1–C41 angles. The molecule of 4a resides on a crystallo-
graphic twofold rotation axis that passes through the center of
the Ge–Ge bond, and 4b has an inversion center located on
the Ge–Ge bond. Molecular symmetry is consistent with the
magnetic equivalence of the phenyl, vinyl, and AltBu2 substit-
uents in solution. Weak intramolecular contacts between the
Al atoms and an o-C atom in 3 and 4a [258 (4a) and 263 or
267 pm (3)] result in a deviation from planarity for the Al
atoms [Al 29 (4a) to 32 (3) pm above the plane of the three
directly bonded C atoms] and may help to explain the magnetic
inequivalence of the two tBu substituents of an AltBu2 group
in 4a.
Scheme 4. Hydroalumination of dialkynylgermane 1.
Scheme 5. Hydroalumination of dialkynyldigermane 2a.
1
The situation is different for compound 4b, in which the Al
NMR spectra of 3 and 4 confirm hydroalumination. The H
NMR spectra show characteristic signals at δ = 6.89 to 7.14 atom is coordinated by three C atoms (C31, C41, C43) in an
ppm for the vinylic H atoms, and signals at δ = 142.5 to 146.4 essentially planar fashion (distance Al to the plane 0.3 pm) and
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Figure 2. Molecular structure of compound 3. Displacement ellipsoids
are drawn at the 40% level. A disordered solvent molecule (1,2-difluo-
robenzene) and hydrogen atoms (except H32, H42; arbitrary radius)
are omitted. Selected bond lengths /pm and angles /° Ge1–C31(vinyl)
195.0(2), Ge1–C41(vinyl) 195.5(2), Ge1–C11(Ph) 197.2(2), Ge1–C21
197.5(2), C31–C32 134.4(2), C41–C42 134.7(2), Al–C(tBu)
199.6(av.), Al–Cvinyl 198.0(av.), Al1···C26 262.7(2), Al2··C16
266.9(2), C11–Ge1–C21 103.08(7), C31–Ge1–C41 134.93(7).
Figure 4. Molecular structure of compound 4b. Displacement ellip-
soids are drawn at the 40% level. Hydrogen atoms (except H32;
arbitrary radius) are omitted; equivalent atoms were generated by –x
+ 2, –y + 1, –z + 1. Selected bond lengths /pm and angles /° Ge1–Ge1’
242.49(4), Ge1–C11 197.1(2), Ge1–C21 195.7(2), Ge1–C31 195.7(2),
C31–C32 134.2(2), Al–C(Et) 196.6(av.), Al1–C31 197.5(2), Al1···C12
301, Al1···C35 284, Ge1’–Ge1–C31 116.19(5), C11–Ge1–C21
105.52(6).
The Ge–C bond lengths to those phenyl rings that show close
contacts to Al are slightly longer (ca. 1.5 pm) than the other
Ge–C(Ph) distances.
We studied the reactivity of the hydroalumination products
3 and 4 toward the heterocumulenes PhNCO, PhNCS, and (4-
Me)H4C6N=C=NC6H4(4-Me). While treatment of compound 3
with two equivalents of the heterocumulenes at room tempera-
ture yielded the insertion products 5 to 7 (44 to 65% yield;
Scheme 6), the corresponding reactions of 4a and 4b at room
Figure 3. Molecular structure of compound 4a. Displacement ellip-
soids are drawn at the 40% level. Hydrogen atoms (except H32;
arbitrary radius) are omitted; equivalent atoms were generated by –x,
y, –z + 1/2. Selected bond lengths /pm and angles /° Ge1–Ge1’
246.48(3), Ge1–C11 195.6(2), Ge1–C21 197.1(1), Ge1–C31 195.7(2),
C31–C32 134.2(2), Al1–C(tBu) 200.3(av.), Al1–C31(vinyl) 199.0(2),
Al1···C26 258.0(2), Ge1’–Ge1–C31 118.79(4), C11–Ge1–C21
102.97(6).
shows two long distances to an o-C atom (301 pm) and a tBu
group (284 pm) hereby completing the coordination environ-
ment of the Al atom to a distorted trigonal bipyramid. The
unusual coordination in 4b may be correlated to the surprising
trans-arrangement of Al and vinylic H atoms, while in 3 and
4a the Al and vinylic H atoms adopt the expected cis-positions.
The isomerization of the kinetically favored cis product to the
trans isomer for compound 4b may be favored by the low
steric bulk of ethyl as compared to tBu groups, which allows
a four-coordinate Al atom as key intermediate in the isomeriza-
tion process.[15] The Al–C distances are similar to related hy-
droalumination products[3,4,8,13,17,19] with the Al–Cvinyl slightly
shorter than Al–Calkyl bonds. The Ge–Ge bond lengths are 4.7
(4a) and 1.9 pm (4b) longer than in the starting material 2a. Scheme 6. Reactions of 3 with heterocumulenes (Tol = 4-MeC6H4).
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temperature or at 50 °C led to complex mixtures of unknown tached tBu group [δ(1H) = 0.54; 1.2 for 6 and 7], which reflects
compounds as determined by NMR spectroscopy. Isolation or the different bonding environment of the alkynyl group in 5
enrichment of one of the components by recrystallization from (O=C–CϵC–tBu) as compared to 1, 6 or 7 (Ge–CϵC–tBu).
different solvents was not successful. 5 to 7 are formed by In the IR spectrum of 5 the stretching vibration ν(CϵC) is
insertion of the respective heterocumulene into the shifted to higher wave numbers as compared to 1, 6, or 7. The
Ge–Cvinyl (PhNCO) or the Al–Cvinyl bonds [PhNCS, C atoms in the heterocycles of compounds 6 and 7 show the
(4-Me)-H4C6N=C=NC6H4(4-Me). Retrohydroalumination oc- characteristic downfield signals in the 13C NMR spectra [NCS:
curred which may be favored by an interaction of the Lewis δ = 204.2 (6); NCN: δ = 176.2 (7)].
acidic metal atoms with the nucleophilic O, S, or N
Compound
5
(Figure 5) features
a
six-membered
atoms.[10,27] Reaction of released H–AltBu2 with one molecule AlCGeNCO heterocycle with the atoms Al1C31Ge1N1 in a
of the heterocumulene probably afforded different hydroalumi- plane (largest deviation from plane 3 pm for C31) and C41 and
nation products. One of these was unambiguously identified as O1 significantly below that plane (C41: 41 pm; O1: 70 pm).
PhNC(H)S–AltBu2. Its characteristic signals [CH: δ(1H) = The C41–O1 and C41–N1 bond lengths in the heterocycle are
8.58; δ(13C) = 185.4] were observed in NMR spectra of the with 127.1(2) and 132.0(2) pm between the typical values of
crude product by comparison with spectra of a pure sample of single and double bonds and confirm delocalization of π elec-
PhNC(H)S–AltBu2, which was independently synthesized tron density. Short distances to a m-H atom (GePh) of one
from H–AltBu2 and PhN=C=S. Signals of the corresponding molecule and the O and Cα atoms of the alkynyl substituent
formamide side-product (synthesis of 5; see Experimental Sec- (O···H–C: 269 pm; CϵC···H–C: 284 pm) of a second molecule
tion) were detected only with low intensity in the complicated result in the formation of weakly bound dimers.[29]
NMR spectra of the reaction mixture. Both by-products could
not be isolated in a solid and pure form by recrystallization. A
mass spectrum of the S compound showed the mass of the
dimer minus a Ph–N–C(H)–S group and a H atom and may
confirm the existence of dimeric units in the solid state.
The formation of 5 is unexpected as it is the first example
for the insertion of an electrophile into a Ge–C bond of a hy-
drometallated alkynylgermane. Amino- and aluminum-func-
tionalized germanes showed a comparable reactivity with an
insertion into activated Ge–N bonds.[12] The different reactiv-
ity of PhNCO and PhNCS may be related to charge distribu-
tion in the NCX groups. NBO calculations (TPSS/def2TZVP
+
GD3BJ)[28] on the adducts PhNCOǞAlMe3 and
PhNCSǞAlMe3 as models for the likely first intermediate (ad-
duct between 3 and the heterocumulene) showed a signifi-
cantly larger charge separation for the NCO complex
(PhNCOǞAlMe3: N: –0.409, C: +0.826, O: –0.542;
PhNCSǞAlMe3: N: –0.338, C: +0.229; S: +0.034), which in-
dicates a higher polarity in the PhNCO adduct and a much
larger positive charge on the central C atom. The polarity of a
Ge–C bond on the other hand is significantly lower than that
of an Al–C bond due to the higher electronegativity of Ge in
comparison to Al. It seems likely that the larger partial charge
in case of the PhNCO adduct initiates insertion into the
Ge–Calkynyl bond. The same reaction is energetically less fa-
vored in case of the less polarized heterocumulenes PhNCS
and (4-Me)C6H4N=C=NC6H4(4-Me).
Compounds 5 to 7 show a downfield shift of the AltBu2
resonances in the 1H NMR spectra from δ = 0.99 in 3 to about
1.2 (6, 7) or 1.63 (5) as a result of the increased coordination
number of Al. The tBu groups are equivalent in 5 (pseudo-
mirror plane through Al and the six-membered heterocycle,
Figure 5) but magnetically inequivalent in 6 (extremely broad
signals; ν1/2 Ͼ 50 Hz) and 7 (δ = 1.32, 1.08) which is likely a
result of hindered rotation around the GeC–CNS (GeC–CN2)
bond (Figure 6). Compound 5 is further characterized by high-
Figure 5. Molecular structure of compound 5. Displacement ellipsoids
are drawn at the 40% level. Hydrogen atoms are omitted (except H32,
arbitrary radius). Selected bond lengths /pm and angles /° Ge1–C(Ph)
194.7(av.), Ge1–C31 192.0(2), Ge1–N1 198.4(1), C31–C32 134.9(2),
C42–C43 118.9(2), C41–N1 132.0(2), C41–O1 127.1(2), Al1–O1
186.0(1), All–C31 199.4(2), Al1–C(tBu) 200.1(av), C31–Ge1–N1
104.55(6), Ge1–N1–C41 126.7(1), N1–C41–O1 124.3(1), C41–O1–
Al1 131.1(1), O1–Al1–C31 101.45(6), Al1–C31–Ge1 116.66(8).
The molecular structures of compounds 6 and 7 (Figure 6)
are similar. The Al atoms are coordinated in a chelating man-
ner by NCS or NCN ligands to form planar four-membered
NCSAl or NCNAl heterocycles [largest deviation from plane
for C51 (6: 4 pm, 7: 3 pm)]. The vinyl group is perpendicular
to that plane and on the same side as one of the tBu(Al)
groups, the second tBu group is neighboring the
GePh2(CϵCtBu) moiety. This structure is consistent with their
magnetic inequivalence as observed in the NMR spectra of 7,
if rotation about the bond C41–C51 is slow on the NMR time
field shifts of the alkynyl C signals [δ(13C) = 74.3, 108.6; 6 scale in solution (see discussion above). The angles in the
and 7: ca. 80 and 119] and of the Me resonances of the at- four-membered heterocycles differ considerably and are
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smaller than 90° at Al [72.63(8)° (6); 68.41(5)° (7)] and S RMg–H, or FeII [34] or recently by transmetallation with a Zn-
[74.49(9)°] and larger than 90° for the atoms C51 [113.8(2)° hexazene complex as a precursor.[34,35] Purely organic hexa-
6; 108.2(1)° (7)] and N1/N2 [98.7(2)° 6; 91.6(av.)° (7)]. The aza-1,5-dienes were obtained by coupling of triazenyl radicals
π-electron density in the CNS or CN2 groups is delocalized which were in situ formed from diazoaminobenzene[36] or
as evident from the bond lengths [C51–S1 173.7(4), C51–N1 from diacylhydrazine and suitable diazonium salts.[37] For-
131.9(4) (6); C51–N1 134.4(2), C51–N2 134.1(2) pm (7)] that mally, a germaallene is eliminated in our reaction, but such a
are between those of standard C–N or C–S single and double compound or any secondary product was not identified in the
bonds[30] and similar to those found in DippN=CH–NDip- NMR spectra of the reaction mixture. Germallenes are highly
p(AlMe2).[31] In related adducts with five- or six-coordinate reactive and must be kinetically protected by bulky substitu-
metal atoms[32] bond lengths are shorter (C–N Յ ca. 131; ents.[38] The NMR spectra of 8 are unexceptional, the EI-MS
C–S ca. 170 pm). The neutral ligands may formally be gener- spectrum shows the molecular ion peak minus one tBu group.
ated by protolytic cleavage of the Al–X bonds and have signifi-
cantly shorter C–S distances (165–169 pm), but longer C–N
bond lengths (133–135 pm) for the thio compounds and
strongly differing C–N distances (ca. 128 and 137 pm) in the
carbodiimide derivatives. These observations may indicate a
more localized bonding situation.[33] The ligand–metal dis-
tances in these compounds are about 250 pm for Al–S and
about 200 pm for Al–N bonds and longer than those in 6
[Al1–S1 234.91(1) pm; Al1–N1 195.7(3) pm], 7 [Al1–N
193.4(av.) pm] and DippN=CH–NDipp(AlMe2) [Al–N
195.9(2) pm].[31]
Scheme 7. Reaction of 4a with 4-tBuH4C6N3.
The structure of compound 8 (Figure 7) features a molecular
plane that incorporates two five-membered N4Al heterocycles.
The rings are fused by a common edge (N1–N1’) to afford an
unsaturated chain of six N atoms. The central N–N bond is
located on a center of symmetry. The aromatic rings adopt a
trans arrangement relative to the molecular plane. The endo-
cyclic angles are 78.17(4)° at the Al and 114.14(9) to
117.61(7)° at the N atoms. The Al–N and Al–C bond lengths
Figure 6. Molecular structure of compound 6. Compound 7 is similar.
Displacement ellipsoids are drawn at the 40% level. Hydrogen atoms
are omitted (except H42; arbitrary radius). Selected bond lengths /pm
(data of 7 in square brackets): Ge1–C(Ph) 194.2(av.) [194.1(av.)],
Ge1–C31 190.2(3) [190.0(1)], Ge1–C41 197.5(3) [197.2(1)], C41–C42
133.3(4) [134.2(2)], C31–C32 119.0(5) [119.9(2)], C51–N1 131.9(4)
[134.4(2), 134.1(2)], C51–S1 173.7(4), Al1–N1 195.7(3) [193.6(1),
193.4(1)], Al1–S1 234.9(1), Al1–C(tBu) 198.5(av.) [198.6(av.)].
Since reactions with heterocumulenes were not successful,
4a was treated at 65 °C in n-hexane with the azide 4-
tBuH4C6CH2–N3, which yielded via reductive coupling the co-
Figure 7. Molecular structure of compound 8. Displacement ellipsoids
ordinatively stabilized hexazene derivative 8 (Scheme 7). Ge–
are drawn at the 40% level. Hydrogen atoms are omitted; equivalent
Ge bonds acting as reducing agents were unexpected, pre-
atoms were generated by –x + 1, –y, –z + 1. Selected bond lengths /
pm: Al1–C(tBu) 198.3(av.), Al1–N1 193.2(1), Al1–N3’ 195.0(1), N1–
either by using strong reducing agents such as ZnI, MgI, N2 130.1(1), N2–N3 129.7(1), N1–N1’ 141.1(2).
viously reported hexazene complexes have been obtained
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at ambient probe temperature using the following instruments, Bruker
are with 194.1 and 198.3 pm on average in the typical ranges
Avance I (1H, 400.13; 13C, 100.62; 15N 40.55 MHz), BrukerAvance III
(1H, 400.03; 13C, 100.59), and referenced internally to residual solvent
resonances (1H, 13C). 13C NMR spectra were all proton decoupled.
The assignment of NMR spectra is based on HSQC, HMBC,
DEPT135, HN-HMBC, and H,H-ROESY data. Elemental analyses
were determined by the microanalytic laboratory of the Westfälische
Wilhelms Universität Münster. IR spectra were recorded as KBr pellets
with a Shimadzu Prestige 21 spectrometer, electron impact mass spec-
tra with a Finnigan MAT 95 mass spectrometer. Commercial PhNCO
of four-coordinate Al atoms. The N–N bond lengths in the
hexazene backbone differ significantly and correspond to a sin-
gle bond for N1–N1’ [141.1(2) pm] and a delocalized π-bond
for N1–N2 [130.1(1) pm] and N2–N3 [129.7(1) pm]. The
hexazene ligand is formally dianionic and formed from two
triazaallyl N3 fragments, an interpretation that has been con-
firmed by quantum chemical calculations.[34b] Previously re-
ported and structurally authenticated hexazene complexes are
–
similar to compound 8 and show the same planar backbone. and PhNCS were distilled in vacuo and stored in an argon atmosphere.
H–AlEt2, (4-tBu)C6H4N=C=NC6H4(4-tBu), Ph2GeCl2 were used as
purchased. H–AltBu2,[39] (Ph2GeCl)2,[12] PhGe(Cl)(CϵCtBu)2,[8] and
Ph2Ge(CϵCtBu)2 (1)[3] were synthesized according to literature pro-
cedures.
With one exception the metal atoms are four-coordinate with
a distorted tetrahedral coordination sphere.[34,36]
Conclusions
Synthesis of [Ph2GeCϵCtBu]2 (2a): nBuLi (9.7 mL, 15.5 mmol,
1.6 m in n-hexane) was added at 0 °C to a solution of tBu–CϵC–H
(1.9 mL, 1.27 g, 15.5 mmol) in diethyl ether (25 mL). The mixture was
stirred for 1 h at room temperature. (Ph2GeCl)2 (3.65 g, 6.97 mmol)
was added at 0 °C, and the mixture was stirred for 16 h at room tem-
perature. After aqueous workup (20 mL of H2O, separation of the or-
ganic phase, further extraction of the aqueous phase with 20 mL of
Et2O), the combined organic phases were dried over MgSO4. The sus-
pension was filtered, the solvent removed in vacuo and the residue
dissolved in hot n-hexane (5 mL). The solution was cooled to –20 °C
to yield compound 2a as a colorless, amorphous solid (3.01 g, 70%).
M.p. 145 °C (dec.). C36H38Ge2 (615.9): C 70.2 (calcd. 70.2); H 6.2
Hydroalumination of alkynyl germanes is a facile method
for the generation of mixed aluminum-germanium compounds.
Their specific reactivity depends on the activation of substrates
by the Lewis-acidic Al atoms. Dual hydroalumination of mo-
nonuclear dialkynylgermanes or dinuclear dialkynyldiger-
manes possessing a Ge–Ge bond afforded dialuminum com-
pounds, in which the Lewis-acids showed a weak interaction
with aryl groups attached to germanium. While usually the
kinetically favored cis-addition products were isolated, sponta-
neous cis/trans isomerization afforded the trans arrangement
of Al and H atoms in the alkenyl groups for the sterically less
shielded AlEt2 compound 4b. These dialuminum species are
promising candidates for an application in the chelating coordi-
nation of suitable Lewis bases and may help to activate sub-
strates by an interaction to both metal atoms. Furthermore, the
Ge–Ge bond was expected to contribute to the reactivity of
these compounds. Heterocumulenes such as PhNCO, PhNCS,
or R–N=C=N–R were indeed activated by the coordinatively
unsaturated Al atoms probably via an increased polarity of the
functional groups. However, these reactions proceeded surpris-
ingly by retrohydroalumination, elimination of a dialkylalumi-
num hydride molecule and reformation of one alkynyl group
per formula unit. With PhNCO the activated heterocumulene
was unexpectedly inserted into the Ge–C(alkynyl) bond,
whereas in other cases insertion into the more polar Al–C(vi-
nyl) bond resulted. These heterocumulenes afforded compli-
cated reaction mixtures with the digermanium derivatives. The
Ge–Ge bond was, however, involved in the remarkable re-
duction of an azide to a dianionic hexazene derivative via N–
N bond formation. The unsaturated N6 chain in the product
was stabilized by coordination to two dialkylaluminum groups.
This reaction confirms unusual reaction behavior of these new
Al functionalized digermanium compounds and will stimulate
further systematic investigations into their chemical properties
in particular with respect to the influence of the Ge–Ge bond.
1
(6.2)%. H NMR (400 MHz, C6D6, 300 K): δ = 7.93 (m, 8 H, o-H),
7.14 (m, 8 H, m-H), 7.08 (m, 4 H, p-H), 1.20 (s, 18 H, CϵCCMe3).
13C NMR (101 MHz, C6D6, 300 K): δ = 136.8 (ipso-C), 135.1 (o-C),
129.3 (p-C), 128.6 (m-C), 120.7 (CϵCCMe3), 76.7 (CϵCCMe3), 31.1
(CϵCCMe3), 28.8 (CϵCCMe3). IR (KBr): ν˜ = 3067 s, 3046 s, 3017
m, 2972 vs, 2965 vs, 2924 vs, 2897 s, 2864 s ν(CH); 2172 vs, 2139
vs ν(CϵC); 1981 w, 1960 w, 1904 w, 1884 w, 1823 w, 1767 w, 1653
w, 1584 w, 1568 w, 1551 w (phenyl); 1481 s, 1454 vs, 1429 vw, 1385
m, 1360 s, 1335 w, 1306 m, 1246 vs, 1240 vs δ(CH); 1204 s, 1188 s,
1159 w, 1088 vs, 1063 m, 1026 m, 995 m, 972 vw, 914 m, 852 w, 745
vs, 735 vs, 727 vs ν(CC); 694 vs, 689 vs, 671 vs (phenyl); 619 w, 548
vw, 482 vs, 451 vs, 397 vs, 368 w ν(GeC), δ(CC) cm–1. MS (EI, 20 eV,
383 K): m/z (%): 616 (27) [M]+, 560 (5) [M – H2C=CMe2]+, 535 (6)
[M – CϵCCMe3]+, 454 (74) [M – 2 CϵCCMe3]+.
Synthesis of [PhGe(CϵCtBu)2]2 (2b): THF (25 mL) was added to
solid Mg filings (1.22 g, 50.2 mmol) and Ph(Cl)Ge(CϵCtBu)2 (1.27 g,
3.66 mmol). The mixture was treated with a solution of SmI2
(2.5 mmol, 25 mL, 0.1 m in THF) and stirred for 16 h at room tempera-
ture. After aqueous work-up (20 mL of H2O, separation of the organic
phase, further extraction of the aqueous phase with 20 mL of Et2O),
the combined organic phases were dried over MgSO4. Filtration, re-
moval of the solvents in vacuo and recrystallization of the residue from
n-hexane yielded compound 2b as a colorless amorphous solid (1.76 g,
77%). M.p. 155 °C (dec.). C36H46Ge2 (624.0): C 69.3 (calcd. 69.3); H
1
3
7.4 (7.4)%. H NMR (400 MHz, C6D6, 300 K): δ = 8.10 (d, JHH
=
3
7.7 Hz, 4 H, o-H), 7.25 (pseudo-t, JHH = 7.7 Hz, 4 H, m-H), 7.15 (m
overlap, 2 H, p-H), 1.14 (s, 36 H, CϵCCMe3). 13C NMR (101 MHz,
C6D6, 300 K): δ = 135.7 (ipso-C), 134.4 (o-C), 129.6 (p-C), 128.5
(m-C), 118.6 (CϵCCMe3), 74.7 (CϵCCMe3), 30.9 (CϵCCMe3), 28.6
(CϵCCMe3). IR (KBr): ν˜ = 3069 s, 3049 vs, 3024 m, 2978 vs, 2961
Experimental Section
General: All procedures were carried out in an atmosphere of purified vs, 2928 vs, 2899 vs, 2866 vs ν(CH); 2183 vs, 2144 vs ν(CϵC); 1950
argon in dried solvents (n-pentane, n-hexane over LiAlH4; Et2O and
THF over Na/benzophenone, pentafluorobenzene over molecular si-
eves). NMR spectra (chemical shift data in δ) were recorded in C6D6
w, 1877 w, 1813 w, 1759 w, 1645 w, 1584 m, 1545 w (phenyl); 1474
vs, 1454 vs, 1433 vs, 1391 w, 1362 vs, 1333 vw, 1304 vw, 1252 vs
δ(CH3); 1202 s, 1186 m, 1090 vs, 1065 w, 1026 m, 997 w, 920 s, 849
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vw, 750 vs, 745 vs, 733 vs ν(CC); 694 vs, 673 s, 494 vs, 482 vs, 451
(p-C), 129.1 (m-C), 38.7 (C=CCMe3), 28.7 (C=CCMe3), 9.4
vs, 370 vs ν(GeC), δ(CC) cm–1. MS (EI, 20 eV, 373 K): m/z (%): 624 (AlCH2Me), 3.7 (AlCH2). IR (KBr): ν˜ = 3065 s, 3049 s, 3019 m, 2992
(32) [M]+, 609 (15) [M – Me]+, 567 (23) [M – CMe3]+.
m, 2949 vs, 2899 vs, 2862 vs, 2781 m, 2725 w ν(CH); 1956 w, 1884
w, 1821 w, 1775 w, 1701 vw, 1651 vw,1599 m, 1582 m, 1558 vs, 1512
w ν(C=C), phenyl; 1479 vs, 1460 s, 1427 vs, 1400 m, 1375 m, 1354
s, 1331 w, 1304 w, 1250 s δ(CH3), δ(CH2); 1227 m, 1188 s, 1157 w,
1082 vs, 1063 w, 1024 m, 955 vs, 949 m, 935 m, 916 m, 905 s, 893
s, 856 w, 796 vs, 733 vs, 700 vs ν(CC); 642 vs, 617 vs (phenyl); 596
vs, 521 m, 461 vs, 399 s ν(GeC), ν(AlC), δ(CC) cm–1. MS (EI, 25 eV,
298 K): m/z (%): 674 (32) [M – 2 CMe3]+, 645 (21) [M – 2 CMe3
– Et], 617 (24) [M – AlEt2 – CMe3 – Et]+.
Synthesis of Ph2Ge[C(AltBu2)=CHtBu]2 (3): H-AltBu2 (1.33 g,
9.35 mmol) was suspended in n-hexane (20 mL) at –78 °C.
Ph2Ge(CϵCtBu)2 (1.82 g, 4.68 mmol) was added, the cooling bath re-
moved and the mixture stirred for 3 h at room temperature. The ob-
tained solution was concentrated and stored at –20 °C to yield colorless
crystals of compound 3 (1.85 g, 59%). Microanalysis of the product
failed although NMR spectroscopic characterization showed only a
small quantity of unknown impurities (Ͻ5%). Further purification of
the product by recrystallization was not successful. M.p. 131 °C (dec.).
1H NMR (400 MHz, C6D6, 300 K): δ = 7.74 (m, 4 H, o-H), 7.26 (t,
Synthesis of Ph2Ge[C(AltBu2)=CHtBu][N(Ph)C(O)CϵCtBu] (5):
PhNCO (100 μL, 0.11 g, 0.92 mmol) was added at room temperature
to a solution of compound 3 (0.30 g, 0.45 mmol) in n-hexane (10 mL).
The solution was stirred for 16 h, concentrated and stored at –45 °C
to yield colorless crystals of compound 5 (0.13 g, 44%). M.p. 186 °C
(dec.). C39H52AlGeNO (650.5): C 71.9 (calcd. 72.0); H 8.1 (8.1); N
3
4
3JHH = 7.5 Hz, 4 H, m-H), 7.02 (tt, JHH = 7.5, JHH = 1.4 Hz, 2 H, p-
H), 6.89 (s, 2 H, C=CH), 1.25 (s, 18 H, C=CCMe3), 0.99 (s, 36 H,
AlCMe3). 13C NMR (101 MHz, C6D6, 300 K): δ = 163.1 (GeC=C),
152.0 (ipso-C), 146.4 (GeC=C), 132.4 (m-C), 131.7 (o-C), 129.8 (p-
C), 39.3 (C=C–CMe3), 30.9 (AlCMe3), 29.7 (C=C-CMe3), 20.2 (s br.,
AlCMe3). IR (KBr): ν˜ = 3070 m, 3051 m, 2947 vs, 2924 vs, 2864 vs,
2828 vs, 2762 m, 2729 w, 2700 m ν(CH); 2148 vw, 2095 m; 1965 w,
1883 vw, 1830 vw, 1769 vw, 1703 vw, 1651 vw, 1601 m, 1558 vs
ν(C=C), phenyl; 1462 vs, 1431 s, 1385 m, 1360 s, 1306 w, 1246 s
δ(CH3); 1198 s, 1159 sh w, 1086 s, 1051 m, 1026 m, 999 s, 935 m,
918 w, 893 w, 876 w, 810 vs, 735 vs, 718 vs ν(CC); 698 vs, 667 w,
637 m (phenyl); 583 vs, 538 w, 503 m, 459 s, 415 s, 388 vw ν(GeC),
ν(AlC), δ(CC) cm–1.
1
2.5 (calcd. 2.2)%. H NMR (400 MHz, C6D6, 300 K): δ = 7.66 [m, 4
H, o-H(GePh)], 7.51 (s, 1 H, GeC=CH), 7.07 [m overlap, 2 H, p-
3
H(GePh)], 7.06 [m overlap, 4 H, m-H(GePh)], 6.72 [tt, JHH = 7.4,
3
4JHH = 1.1 Hz, 1 H, p-H(NPh)], 6.60 [pseudo-t, JHH = 7.7 Hz, 2 H,
m-H(NPh)], 6.41 [m, 2 H, o-H(NPh)], 1.63 (s, 18 H, AlCMe3), 0.92
(s, 9 H, C=CCMe3), 0.56 (s, 9 H, CϵCCMe3). 13C NMR (101 MHz,
C6D6, 300 K): δ = 169.4 (GeC=C), 163.2 (NCO), 142.8 [ipso-C(NPh)],
137.9 [ipso-C(GePh)], 137.5 (s br., GeC=CH), 135.2 [o-C(GePh)],
130.1 [p-C(GePh)], 128.6 [m-C(GePh) and o-C(NPh)], 128.4 [m-
C(NPh)], 127.2 [p-C(NPh)], 108.6 (CϵCCMe3), 74.3 (CϵCCMe3),
39.8 (C=CCMe3), 32.0 (AlCMe3), 29.7 (C=CCMe3), 29.1 (CϵCCMe3)
27.5 (CϵCCMe3), 17.1 (br., AlCMe3). IR (KBr): ν˜ = 3071 s, 3053 s,
3028 m, 2972 vs, 2938 vs, 2922 vs, 2905 vs, 2864 vs, 2818 vs, 2750
s, 2718 m, 2689 s ν(CH); 2278 w; 2218 vs ν(CϵC); 1969 w, 1954 w,
1896 vw, 1884 vw, 1830 vw, 1717 sh, 1668 m, 1651 m, 1593 vs, 1553
vs, 1528 vs ν(C=N), phenyl, ν(C=C); 1487 vs, 1460 vs, 1420 vs, 1414
vs, 1408 vs, 1381 vs, 1360 vs, 1308 s, 1287 m, 1258 vs, 1248 sh
δ(CH); 1223 vs, 1198 vs, 1088 vs, 1072 w, 1020 m, 999 s, 928 s, 899
s, 887 m, 810 vs, 769 s, 733 vs, 719 s ν(CC), ν(CN); 694 vs, 679 sh
(phenyl); 598 vs, 586 sh, 540 s, 513 s, 474 vs, 428 s, 413 vs ν(GeN),
ν(GeC), ν(AlO), ν(AlC), δ(CC) cm–1. MS (EI, 20 eV, 298 K): m/z (%):
594 (100) [M – CMe3]+, 538 (4) [M – CMe3 – butene]+.
Synthesis of [Ph2GeC(AltBu2)=CHtBu]2 (4a): H-AltBu2 (0.41 g,
2.90 mmol) was suspended in n-hexane (15 mL) at –78 °C.
(Ph2GeCϵCtBu)2 (2a) (0.80 g, 1.30 mmol) was added, the cooling
bath removed, and the reaction mixture stirred for 16 h at room tem-
perature. The solution was concentrated and stored at –20 °C to yield
colorless crystals of compound 4a (0.76 g, 65%). The signals in the
phenyl region of the NMR spectra were comparatively broad, which
prevented a complete assignment of the resonances. M.p. 156 °C
1
(dec.). C52H76Al2Ge2 (900.4): C 69.8 (calcd. 69.4); H 8.8 (8.5)%. H
NMR (400 MHz, C6D6, 300 K): δ = 8.15 (s br., ca. 4 H, Ph), 7.32 (s
br., ca. 4 H, Ph), 7.14 (s, 2 H, C=CH), 6.83 (s br., ca. 12 H, Ph), 1.35
(s br., 18 H, AlCMe3), 1.07 (s, 18 H, C=CHCMe3), 0.69 (s br., 18 H,
AlCMe3). 13C NMR (101 MHz, C6D6, 300 K): δ = 167.2 (GeC=C),
142.5 (GeC=C), ca. 137 (Ph), ca. 128 (Ph), 39.7 (C=CCMe3), 31.7 and
30.6 (AlCMe3), 28.9 (C=CCMe3), 20.0 (s br., AlCMe3). IR (KBr): ν˜
= 3067 s, 3049 s, 2953 vs, 2926 vs, 2907 vs, 2864 vs, 2830 vs ν(CH);
1954 w, 1896 vw, 1877 vw, 1823 w, 1773 w, 1651 vw, 1593 m, 1554
s ν(C=C), phenyl; 1462 vs, 1429 vs, 1385 m, 1358 s, 1307 m, 1246 s
δ(CH3); 1200 s, 1157 m, 1084 s, 1065 w, 1024 m, 999 s, 966 w, 934
w, 910 w, 891 w, 874 w, 810 s, 733 vs, 700 vs ν(CC); 667 w, 640 w,
625 w (phenyl), 577 s, 501 w, 465 s ν(GeC), ν(AlC), δ(CC) cm–1. MS
(EI, 20 eV, 413 K): m/z (%): 701 (2) [M – CMe3 – HAl(CMe3)2]+, 618
(4) [M – 2 Al(CMe3)2]+.
Synthesis of Ph2Ge[CϵCtBu][C(=CHtBu)(C(=S)N(Ph)AltBu2)] (6):
PhNCS (133 μL, 0.15 g, 1.11 mmol) was added at room temperature
to a solution of compound 3 (0.37 g, 5.50 mmol) in n-hexane (15 mL).
The mixture was stirred for 16 h. Concentration in vacuo and storage
of the solution at -45 °C yielded colorless crystals of compound 6
(0.24 g, 65%). The product was contaminated with small quantities of
impurities (Ͻ5%) which could not be removed by recrystallization
and led to unsatisfactory results for microanalysis. M.p. 104 °C (dec.).
1H NMR (400 MHz, C6D6, 300 K): δ = 7.93 [s br., 4 H, o-H(GePh)],
7.32 [m, 2 H, o-H(NPh)], 7.19 [m overlap, 2 H, m-H(NPh)], 7.16 [s
br., 4 H, m-H(GePh)], 7.10 [m overlap, 2 H, p-H(GePh)], 6.95 [tt, 3JHH
Synthesis of [Ph2GeC(AlEt2)=CHtBu]2 (4b): (Ph2GeCϵCtBu)2 (2a)
(1.00 g, 1.62 mmol) was suspended in n-pentane (30 mL), and H–
AlEt2 (350 μL, 0.28 g, 3.26 mmol) was added at –78 °C. The cooling
bath was removed and the mixture stirred for 3 h at room temperature. 13C NMR (101 MHz, C6D6, 300 K): δ = 204.2 (NCS), 159.4 (GeC=C),
4
= 7.4, JHH = 1 Hz, 1 H, p-H(NPh)], 6.54 (s, 1 H, C=CH), 1.22 (s, 9
H, CϵCCMe3), 1.17 (s br., 18 H, AlCMe3), 0.99 (s, 9 H, C=CCMe3).
The solution was concentrated in vacuo and stored at –45 °C to yield
144.0 [ipso-C(NPh)], 136.8 [br., ipso-C(GePh)], 135.7 (br., GeC=CH),
compound 4b as colorless crystals (1.06 g, 82%). M.p. 140 °C (dec.). 135.3 [o-C(GePh)], 129.8 [p-C(GePh)], 129.3 [m-C(NPh)], 128.6 [m-
1
C44H60Al2Ge2 (788.2): C 66.7 (calcd. 67.1); H 7.6 (7.7)%. H NMR
C(GePh)], 126.0 [p-C(NPh)], 124.5 [o-C(NPh)], 119.4 (CϵCCMe3),
(400 MHz, C6D6, 300 K): δ = 7.76 (m, 8 H, o-H), 7.16 (m overlap, 8 78.9 (CϵCCMe3), 36.2 (C=CCMe3), 30.8 (CϵCCMe3), 30.3
3
H, m-H), 7.10 (t, JHH = 7.2 Hz, 4 H, p-H), 7.03 (s, 2 H, C=CH), 1.05 (AlCMe3), 29.8 (C=CCMe3), 28.7 (CϵCCMe3), 16.9 (br., AlCMe3).
3
(t, JHH = 8.1 Hz, 12 H, AlCH2Me), 1.02 (s, 18 H, C=CCMe3), 0.00
(q, 3JHH = 8.1, 8 H, AlCH2). 13C NMR (101 MHz, C6D6, 300 K): δ =
169.9 (GeC=C), 142.7 (GeC=C), 141.0 (ipso-C), 135.5 (o-C), 129.3
IR (KBr): ν˜ = 3069 s, 3049 m, 3026 m, 2961 vs, 2938 vs, 2920 vs,
2907 vs, 2866 vs, 2830 vs, 2760 m, 2729 w, 2700 m ν(CH); 2178 m,
2145 s ν(CϵC); 2112 sh, 2066 w; 1967 vw, 1952 w, 1933 vw, 1896
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vw, 1879 w, 1856 vw, 1815 w, 1776 w, 1763 vw, 1721 vw, 1686 vw,
1651 w, 1584 s ν(C=N), phenyl, ν(C=C); 1493 vs, 1462 vs, 1447 sh
H), 7.01 (m, 2 H, m-H), 6.95 (m, 1 H, p-H), 1.13 (s, 18 H, AlCMe3).
13C NMR (101 MHz, C6D6, 300 K): δ = 170.2 (1JCH = 196.7 Hz,
vs, 1433 vs, 1385 w, 1362 vs, 1331 w, 1308 w, 1252 vs δ(CH); 1233 NCO), 142.6 (ipso-C), 125.5 (o-C), 127.4 (p-C), 129.7 (m-C), 30.8
s, 1204 s, 1173 w, 1155 w, 1119 s, 1090 s, 1028 w, 999 m, 934 m, (AlCMe3), 15.3 (s br., AlCMe3). 15N NMR (41 MHz, C6D6, 300 K):
918 m, 874 m, 839 m, 810 vs, 750 vs, 735 vs ν(CC); 694 vs, 673 s,
638 s phenyl; 596 s, 546 m, 492 m, 467 s, 417 s, 387 vw ν(GeC),
ν(AlO), ν(AlS), ν(AlC), δ(CC) cm–1. MS (EI, 20 eV, 413 K): m/z (%):
610 (5) [M – CMe3]+, 526 (9) [M – AltBu2]+, 470 (37) [M – AltBu2 –
butene]+.
δ = 195.
Synthesis of PhNC(H)S(AltBu2): PhNCS (0.53 g, 3.93 mmol) was
added at 0 °C by a syringe to a solution of H-AltBu2 (0.51 g,
3.59 mmol) in n-hexane (20 mL). The mixture was stirred at room
temperature overnight, the solvent was removed in vacuo and the resi-
due recrystallized from n-pentane (10 mL) to yield colorless crystals
of PhNC(H)S(AltBu2) (0.69 g, 69%). 1H NMR (400 MHz, C6D6,
300 K): δ = 8.58 (s, 1 H, CHS), 6.91 (m, 2 H, m-H), 6.85 (m, 1 H, p-
Synthesis of Ph2Ge[CϵCtBu][C(=CHtBu){C(NC6H4Me)2(AltBu2)}]
(7): [4-MeC6H4N=]2C (0.20 g, 0.90 mmol) was added at room tem-
perature to a solution of compound 3 (0.60 g, 0.89 mmol) in n-hexane
(10 mL). The mixture was stirred for 16 h and heated for further 16 h
to 65 °C. The solvent was removed in vacuo, and the residue recrys-
tallized from pentafluorobenzene (6 mL) at –45 °C to yield colorless
crystals of compound 7 (0.35 g, 52%). The product was contaminated
with small quantities of impurities (Ͻ5%) which could not be removed
by recrystallization and led to unsatisfactory results for microanalysis.
H), 6.66 (d, JHH = 7.7 Hz, 2 H, o-H), 1.24 (s, 18 H, AlCMe3). 13C
2
NMR (101 MHz, C6D6, 300 K): δ = 185.4 (1JCH = 181.0 Hz, CHS),
143.2 (ipso-C), 129.9 (m-C), 127.1 (p-C), 119.6 (o-C), 29.8 (AlCMe3),
16.8 (s br., AlCMe3). MS (EI, 20 eV, 353 K): m/z = 417 (21)
[M(dimer) – Ph-N-C(H)-S – H]+, 137 (100) [Ph-N-C(H)-SH]+, 136
(75) [Ph-NC(H)-S]+.
1
M.p. 217 °C (dec.). H NMR (400 MHz, C6D6, 300 K): δ = 7.36 [m,
3
4 H, o-H(GePh)], 7.29 [d, JHH = 8.3 Hz, 4 H, o-H(NTol)], 7.09 [m
X-ray Crystallography: Crystals suitable for X-ray crystallography
were obtained by recrystallization from n-hexane at room temperature
(2a, 2b) or –45 °C (5, 6, 8), 1,2-difluorobenzene (–30 °C, 3) or penta-
fluorobenzene (–20 °C: 4a; –45 °C: 4b and 7). Intensity data was col-
lected with Bruker Venture or Bruker Quazar (6) diffractometers with
multilayer optics and Mo-Kα radiation. Data reduction was carried out
using the program SAINT+.[40] The crystal structures were solved by
direct methods using SHELXTL.[41] Non-hydrogen atoms were first
refined isotropically followed by anisotropic refinement by full-matrix
least-squares calculation based on F2 using SHELXTL.[41] The
hydrogen atoms were positioned geometrically and allowed to ride on
their respective parent atoms. The molecule of 2a was located on an
inversion center. Compound 2b crystallized with two molecules in the
asymmetric unit, two tBu groups (molecule 1) and a central Ge–Ge
unit (molecule 2) were disordered and refined on split positions
[0.67:0.33 (C43); 0.73:0.27 (C63); 0.95:0.05 (Ge3–Ge4)]. Compound
3 crystallized with half a molecule of 1,2-difluorobenzene per formula
unit, which was disordered over an inversion center. The structure of
4b contained a disordered Ge–Ge bond (0.94:0.06). The tBu groups of
the vinyl and alkynyl substituents of compound 6 were rotationally
disordered and refined on split positions [0.83:0.17 (C33); 0.71:0.29
(C43)]. The molecules of 8 reside on a center of symmetry.
overlap, 4 H, m-H(NTol)], 7.07 [m overlap, 4 H, m-H(GePh)], 7.06 [m
overlap, 2 H, p-H(GePh)], 6.80 (s, 1 H, C=CH), 2.21 (s, 6 H, CH3),
1.32 (s, 9 H, AlCMe3), 1.24 (s, 9 H, CϵCCMe3), 1.08 (s, 9 H,
AlCMe3), 1.05 (s, 9 H, C=CCMe3). 13C NMR (101 MHz, C6D6,
300 K): δ = 176.2 (NCN), 164.4 (GeC=C), 141.1 [ipso-C(NTol)],
136.8 [ipso-C(GePh)], 135.0 [o-C(GePh)], 133.0 [p-C(NTol)], 129.8
[m-C(NTol)], 129.6 [p-C(GePh), 128.4 [m-C(GePh)], 125.8 [o-
C(NTol)], 126.0 (GeC=C), 118.7 (CϵCCMe3), 80.0 (CϵCCMe3), 37.2
(C=CCMe3), 30.9 (CϵCCMe3), 30.8 and 30.5 (AlCMe3), 29.6
(C=CCMe3), 28.7 (CϵCCMe3), 20.9 (Me), 16.8 and 15.7 (s br.,
AlCMe3). 15N NMR (41 MHz, C6D6, 300 K): δ = 163 (C=N). IR
(KBr): ν˜ = 3069 m, 3053 s, 3017 m, 2967 vs, 2938 vs, 2918 vs, 2905
vs, 2862 vs, 2824 vs, 2758 w, 2727 w, 2696 w ν(CH); 2187 m, 2153
m ν(CϵC); 1960 vw, 1886 w, 1827 vw, 1773 vw, 1651 sh, 1634 m,
1591 vs, 1574 m, 1506 vs ν(C=N), phenyl, ν(C=C); 1462 vs, 1412 vs,
1379 sh, 1360 vs, 1319 vs, 1300 s, 1252 vs δ(CH); 1202 s, 1155 w,
1123 w, 1109 w, 1090 s, 1069 vw, 1024 w, 1001 m, 986 w, 937 w,
916 s, 903 m, 847 w, 814 vs, 787 w, 768 w, 737 vs ν(CC), ν(CN); 698
vs, 673 m, 646 w, 610 s (phenyl); 598 sh, 548 m, 513 m, 498 s, 473
s, 459 s, 442 s ν(GeC), ν(AlN), ν(AlC), δ(CC) cm–1. MS (EI,
20 eV, 413 K): m/z (%): 697 (100) [M – CMe3]+, 613 (15) [M –
Al(CMe3)2]+, 557 (91) [M – Al(CMe3)2 – butene]+.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-1836910 (2a), CCDC-1836911 (2b), CCDC-1836912
(3), CCDC-1836913 (4a), CCDC-1836914 (4b), CCDC-1836915 (5),
CCDC-1836916 (6), CCDC-1836917 (7), and CCDC-1836918 (8)
(Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://
www.ccdc.cam.ac.uk)
Synthesis of [tBuC6H4CH2N3(AltBu2)-]2 (8): A solution of com-
pound 4a (0.26 g, 0.29 mmol) in n-hexane (10 mL) was treated at room
temperature with solid 4-tBuC6H4CH2N3 (0.11 g, 0.58 mmol). The
mixture was heated to 65 °C and stirred for 16 h. The solution was
concentrated in vacuo and stored at -15 °C to afford colorless crystals
of compound 8 (0.13 g, 68%). Many unknown by-products were
formed, which could not be removed completely (Ͻ5%) be removed
by repeated recrystallization. Excess azide was identified as one impu-
rity by IR spectroscopy. Microanalysis gave, therefore, insufficient re-
sults, and we do not present the data of the IR spectrum. M.p. 95 °C
(dec.). 1H NMR (400 MHz, C6D6, 300 K): δ = 7.21 (s, 4 H, o-H), 7.20
(s, 4 H, m-H), 4.68 (s, 4 H, NCH2), 1.16 (s, 18 H, 4-CMe3), 1.05 (s,
36 H, AlCMe3).13C NMR (101 MHz, C6D6, 300 K): δ = 152.0 (p-C),
133.0 (ipso-C), 129.5 (o-C), 126.2 (m-C), 59.7 (NCH2), 34.6 (4-
CMe3), 31.3 (4-CMe3), 29.7 (AlCMe3), 15.5 (s br., AlCMe3). MS (EI,
20 eV, 413 K): m/z (%): 603 (100) [M – CMe3]+.
Acknowledgements
We are grateful to the Deutsche Forschungsgemeinschaft for generous
financial support.
Keywords: Alkynylgermanes; Digermane; Germanium;
Hydroalumination; Heterocumulene; Hexazene; σ-Bond acti-
vation
Synthesis of PhNC(H)O(AltBu2): In an NMR experiment PhNCO
and H-AltBu2 were combined in a molar ratio of 1:1. 1H NMR
(400 MHz, C6D6, 300 K): δ = 7.68 (s, 1 H, HCO), 7.09 (m, 2 H, o-
Z. Anorg. Allg. Chem. 0000, 0–0
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Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
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Received: April 20, 2018
Published online: ᭿
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Journal of Inorganic and General Chemistry
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W. Uhl,* C. Honacker, N. Lawrence, A. Hepp, L. Schürmann,
M. Layh ........................................................................... 1–12
Hydroalumination of Oligoalkynylgermanes and -diger-
manes – Reactions with Heterocumulenes by Al–C or Ge–C
Bond Activation and Formation of a Hexazenedialuminum
Complex
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