Hydrosilylation and Hydrogermylation of CO2 and CS2 by Al and Ga Functionalized Silanes and Germanes – Cooperative Reactivity with Formation of Silyl Formates and Disilylacetals

Article abstract of DOI:10.1002/ejic.202000723

Hydrometallation of the alkynylelement hydrides iPr₂E(H)–C≡C-tBu (1; E = Si, Ge) with R₂M–H [M = Al, Ga; R = tBu, CH(SiMe₃)₂] afforded in moderate yields the Al and Ga functionalized alkenylsilanes and -germanes

Full text of DOI:10.1002/ejic.202000723

European Journal of Inorganic Chemistry
Accepted Article
Title: Hydrosilylation and –germylation of CO2 and CS2 by Al and Ga
functionalized silanes and germanes – cooperative reactivity with
formation of silyl formates and disilylacetals
Authors: Michael Tolzmann, Lina Schürmann, Alexander Hepp,
Werner Uhl, and Marcus Layh
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000723
Link to VoR: https://doi.org/10.1002/ejic.202000723
01/2020

10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
Hydrosilylation and –germylation of CO2 and CS2 by Al and Ga
functionalized silanes and germanes – cooperative reactivity with
formation of silyl formates and disilylacetals
Michael Tolzmann,[a] Lina Schürmann,[a] Alexander Hepp,[a] Werner Uhl,[a] Marcus Layh*[a]
[a]
Dr. Michael Tolzmann, Lina Schürmann, Dr. Alexander Hepp, Prof. Dr. Werner Uhl, Dr. Marcus Layh
Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstraße 30, 48149 Münster, Germany
E-mail: layhm@uni-muenster.de
Supporting information for this article is given via a link at the end of the document.
i
Abstract: Hydrometallation of the alkynylelement hydrides Pr2E(H)-
CC-tBu (1; E = Si, Ge) with R2M-H [M = Al, Ga; R = tBu, CH(SiMe3)2]
afforded in moderate yields the Al and Ga functionalized
BPh3 was shown to catalyse hydrosilylation of CO2 with R3SiH in
the presence of [NnBu4]+[HCO2]-.[11,12]
Recently, we reported on Al or Ga functionalized vinylsilanes or
–germanes, R2E(X)C(MtBu2)=C(H)-tBu (E = Si, Ge; X = NEt2, Cl,
alkynyl; M = Al, Ga) (Scheme 1), which had Lewis bases X
attached to their central Si or Ge atoms. Interactions of the donors
with the Lewis acidic Al or Ga atoms resulted in formation of four-
membered CMXE heterocycles with lengthened E-X bonds and
an increased cationic character of the Si and Ge atoms.[13] These
compounds reacted readily with various heterocumulenes by
insertion into their E-X bonds as a result of cooperative activation
by the Lewis acid.[13] Silanes and germanes with Si-H or Ge-H
bonds may also be prone to an activation by the geminally
arranged Lewis acids, but the direct interaction between the
weakly donating H atoms and the Lewis acids is expected to be
energetically less favorable. Such interactions have been termed
charge inverted hydrogen bonds.[14] B compounds with a Si-H···B
bridge showed a downfield shift of the H(Si) resonance, a
alkenylsilanes and -germanes Pr2E(H)C(MR2)=CH-tBu (2). The air
i
and moisture sensitive Al compounds reacted with CO2 under mild
conditions (room temperature,
1 bar) to yield the formates
[iPr2EC(AlR2)=C(H)-tBu]O2CH (3) by C=O insertion into the E-H bond
and coordination of the second O atom to aluminum. The acetal
MeAl[C(SiiPr2)=CH-tBu]2O2CH2 (4a) was obtained as a unique side-
product. The less Lewis acidic Ga compound 2c did not react with
CO2 even at higher temperature and pressure. Reaction with CS2
yielded the dithioacetals [iPr2EC(MtBu2)=CH-tBuS]2CH2 (6) by
reduction of both C=S bonds. Compounds 6 have two ECMS
heterocycles bridged by a CH2 group. The reaction of the Ga
compound 2c required elevated temperature (40 °C). At 70 ºC the
formal elimination of H2C=CMe2 and “CH4” afforded the unusual
gallium sulfide {iPr2SiC[Ga(tBu)(µ-S)]=CH-tBu}2 (7c) which crystallised
as a dimer with a central Ga2S2 heterocycle that is joined via its Ga-S
edges to two four-membered GaSCSi heterocycles.
1
decrease of the JSiH coupling constant, a red shift of the Si-H
stretching vibration and comparatively short B···H distances.[15]
Recent studies into a series of vinylgermanes (E = Ge, X = H, M
= Al) demonstrated similar, albeit smaller effects for Ge-H···Al
interactions. These compounds showed a surprising reactivity
that allowed hydrogermylation reactions of an alkyne and various
polar double bonds under mild conditions.[16] The increased
reactivity may be the result of the activation of the substrates by
the Lewis acid. CO2 is relatively inert, but the specific functionality
of such silanes and germanes with Lewis acids and reductive E-
H bonds in single molecules may contribute to its activation and
may help to support its chemical transformation. In this article we
report on the reactivity of Al or Ga functionalized vinylsilanes and
-germanes (E = Si, Ge; X = H; M = Al, Ga) towards CO2 and CS2.
The influence of the polarity of the E-H bonds, the different Lewis
acidity of the Al and Ga atoms and the specific character of the
C=O and C=S bonds was of particular interest.
Introduction
The transformation of CO2 to valuable C1 building blocks is a
highly important aspect of current research.[1] Promising lines are
directed towards electrochemical reduction[2] or catalytic
transformation. The latter is essentially based on heterogeneous
and homogenous transition metal catalysts, on organocatalysts
such as N-heterocyclic carbenes (NHCs) or on frustrated Lewis
pairs (FLPs).[3] FLPs based on main group elements[4] found
enormous interest since the discovery that the B/P FLP Mes2P-
C6F4-B(C6F5)2 was able to reversibly bind H2.[5] Several FLP
systems were found to capture CO2 irreversibly and to form stable
stoichiometric adducts. Less frequently, CO2 was bound in a
reversible manner and could be expelled from the adducts at
elevated temperatures.[6] Only a very limited number of systems
was found that in a catalytic fashion reduced CO2 to HCO2H or
H3COH in the presence of hydrogen sources such as H2, boranes
or silanes.[3e,7] In other cases combinations of Et3SiH with
tetramethylpiperidine/B(C6F5)3,[8] Al(C6F5)3/B(C6F5)3
or (2,6-
[9]
Mes2C6H3O)2Al]+[CHB11Cl11]-[10] converted CO2 to methane by
hydrogen transfer from the silane. The relatively weak Lewis acid
Scheme 1. Hydrometallated alkynylsilanes and -germanes and donor-acceptor
interactions.
1
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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
Results and Discussion
reported, aluminum functionalized germanes showed similar
structural motifs with the Ge-H groups either pointing towards the
Lewis acidic Al atom or in opposite direction.[16] Quantum
chemical calculations based on the open-closed method[14,16,20]
suggested low Ge⸱⸱⸱H interaction energies of less than 8
kcal/mol and only a small stabilization of the isomer with E-H···M
interaction.
t
n
In situ deprotonation of Bu-CC-H with BuLi and reactions of
i
i
the intermediate lithium alkynide with Pr2Si(Cl)H or Pr2GeCl2
afforded the starting alkynylsilanes and -germanes (Scheme 2).
The Si-H compound (1a) was generated directly, while for Ge a
dichloride was isolated, which was converted to the Ge-H
compound 1b upon treatment with HAliBu2 in THF. Reactions of
t
t
compounds 1 with R2Al-H [R = Bu, CH(SiMe3)2] or Bu2Ga-H in
non-coordinating solvents afforded the hydrometallation products
2 (Scheme 2), which are low melting, air- and moisture sensitive
materials. The sterically most encumbered compound 2b [R =
CH(SiMe3)2] was formed in high selectivity and isolated in a
crystalline form. It melted at 31 ºC and was characterized by X-
ray crystallography. Sterically less shielded systems afforded two
products, which could not be separated. But the integration ratio
of the 1H NMR resonances allowed the unambiguous assignment
of their constitution. 2a, 2c and 2d are similar to 2b and have
dialkylelement units bound to
a vinyl group. The minor
components 2a’, 2c’ and 2d’ in contrast have two vinyl groups
attached to a central M-R moiety (Scheme 2). They may be
formed by condensation and release of trialkylelement derivatives.
Such reactions have been observed by our group previously.
They require substituent exchange and were observed for
relatively small alkyl groups.[17] AltBu3 was identified in the mass
spectra of 2a and 2d. An NMR experiment with 1a and HAltBu2 in
a sealed NMR tube showed apart from the usually observed
1
t
resonances a very broad H NMR signal in the Bu region which
may indicate the formation of AltBu3 as the second product of
dismutation. The NMR spectra remained almost unchanged with
increasing temperature. For secondary reactions the mixtures
were prepared in situ and used directly. They allowed the isolation
of interesting secondary products in high purity.
Compounds 2a-c showed signals in the 1H NMR spectra at
about  = 4.3 for the H atoms bound to the Group 14 elements. IR
absorptions were observed at about 2100 cm–1 for the stretching
vibrations of the Si-H groups. Both observations suggest very
weak Si-H···M interactions as evident from a comparison with the
corresponding values of 1a ( = 4.01, ν(SiH) = 2119 cm–1). The
resonances of the vinylic protons are found at  = 6.48 to 7.21.
3JSiH coupling constants of about 22 Hz and the molecular
structure of 2b (Fig. 1) confirm trans-positions of Si and vinylic H
atoms as expected for the kinetically controlled cis-
hydrometallation.[18] The 29Si NMR spectra showed only one
resonance at  = -3.3 for 2b, while two signals in the range of  =
-5 and -3 were expectedly observed for the mixtures 2a/2a’ and
2c/2c’. The mass spectra of the mixtures (2a, 2c) showed the
Scheme 2. Hydrometallation of alkynylsilanes and –germanes [Bis
CH(SiMe3)2].
=
t
molecular ion peaks minus a Bu group of the mono- and divinyl
compounds and confirm the interpretation of the NMR spectra.
In the solid state the molecules of 2b are disordered over two
positions in a ratio of 0.64 to 0.36, and both forms reflect the
borderline cases usually observed for related compounds. In both
molecules the Si-H and Al-Cvinyl bonds are almost in a plane. In
one molecule the Si bound H atom (H1 on ideal position)
approaches the Al atom (torsion angle Al1C1Si1H1 -5.7°;
Al⸱⸱⸱H distance close to the sum of van der Waals radii of 345
pm[19]), while the second one has the inverted configuration at Si
with a torsion angle Al1C1Si1(A)H1(A) of -179.9°. The first isomer
is the main component and shown in Figure 1. Its constitution may
be supported by the bulk of the substituents at the Si atom with
i
the vinyl group bisecting the angle Pr-Si-iPr. As previously
2
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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
Figure 1. Molecular structure and numbering scheme of 2b. Displacement
ellipsoids are drawn at the 40% level. H atoms (except H1 at Si1, H2, H4 and
H5 at the corresponding C atoms, CHMe2) are omitted; only the structure of the
main component of two disordered molecules is shown (see text). Selected
bond lengths (pm) and angles (º): Al1-C1 196.7(2), Al1-CSi2 196.8(av.), C1-C2
134.7(2) Si1-H1 150, Al-H(Si) 315; Al1-C1-Si1 117.1(2).
compared
to
related
insertion
products
such
as
HCO2[Al(DIPP)(Me)]2B(C6F5)4,[23] HCO2[Al(C6F5)3]2(HPtBu3),[6b]
HCO2[B(C6F5)3]2(TMPH),[7]
[Mg(thf)4][HCO2BPh3]2,[25]
HCO2(NiL3)[B(C6F5)3][27]
HCO2(Zn/MgSiR3)[B(C6F5)3],[24]
HCO2(ScCp*2)[B(C6F5)3],[26]
and
the
silylformate
HCO2(SiEt3)[Al(C6F5)3].[28] They show similar 13C NMR shifts for
the carboxylato groups, but the signals of the formate H atoms
are usually observed at a lower field ( > 8). The NMR spectra of
4a are similar to those of 3. The main difference is a 29Si NMR
signal at a higher field ( = 24.0) and two signals for the H atoms
of the acetal group (1H:  = 5.09/5.18, 2JHH = 4.4 Hz; 13C:  = 87.6)
that may be compared with H2C(OBRR’)2 (1H:  = 5.72; 13C:  =
90.9)[27] or H2C(OSiMe3)2 (1H:  = 5.06; 13C:  = 84.5).[29] The
molecular structure of 4a (see Figure 3) reveals two different
siloxy groups, of which one is coordinated to the Al atom via an
Al-O bond. At room temperature only one set of NMR signals was
observed for the vinyl groups which confirms equivalent molecular
The divinylaluminum or –gallium compounds 2’ are highly
interesting starting materials for secondary reactions, but we were
not able to increase the concentration of 2’ by heating samples of
2 in vacuum up to 100 °C in order to remove volatile AltBu3 and to
shift the equilibrium towards the divinyl compounds (see below).
Above 75 ºC decomposition was observed.
Addition of HNEt2 to the mixture of 2a and 2a’ resulted in the
quantitative formation of the monovinyl compound [2a(HNEt2)],
which was isolated in 78% yield after crystallization from the
concentrated reaction mixture (Scheme 2). 2a(HNEt2) resembles
an HNEt2 adduct of a germane, which was characterized by X-ray
crystallography and had a dihydrogen bond.[16] 2a(HNEt2) showed
i
halves and a dynamic behavior in solution. The Pr groups and
CH2 protons show diasterotopic splitting of their resonances,
which indicates retention of the coordination number of four at Al.
Low temperature NMR studies in d8-toluene showed that the
signals of the vinylic H atoms, the adjacent tBu groups and the iPr
groups broadened on cooling and disappeared at about 220 K in
the baseline. These observations indicate an approach to
coalescence. Lower temperatures were not accessible due to the
increasing viscosity of the solution and instrumental limitations.
t
single sets of NMR signals for the Al bound and the vinylic Bu
groups. The CH3 groups of the iPr substituents are diastereotopic,
and two resonances were observed each in the 1H and 13C NMR
spectra. The resonances of the Si-H and N-H protons (δ = 3.61
and 2.66) were shifted to higher and lower field compared to the
starting material 2a and to an HNEt2 complex with AltBu3 (δ = 4.41
and 1.40).[21] The IR absorptions of the Si-H and N-H bonds (2035
and 3197 cm-1) are red-shifted compared to the starting
compounds and to AltBu3ꞏHNEt2 (for N-H).[21] All observations
are characteristic of dihydrogen bonds.[22] The results of a
preliminary crystal structure determination of compound
2a(HNEt2) verified the constitution given in Scheme 2 and
confirms, that the equilibrium between mono- and divinyl
compounds is shifted to the monovinyl product upon addition of a
donor.
We further treated the silanes and germanes 2 with CO2 (room
temperature, 1 bar CO2, Scheme 3). All compounds except the
Ga derivative 2c reacted smoothly, and the cyclic monoinsertion
products 3 were obtained as colorless crystals in yields of 70%
(3a) to 92% (3b,d). CO2 inserted into the Si-H or Ge-H bonds of
the starting hydrides to yield selectively the corresponding
formates. The Ga compound 2c in contrast did not react even at
elevated temperature (80 ºC) and pressure (8 bar CO2). It
decomposed under these conditions to unidentified products. The
lower reactivity of 2c may be attributed to the presence of a softer,
less polarizing Lewis acidic Ga atom which is less capable of
activating hard substrates by adduct formation. In case of 2a, the
disilicon compound 4a was reproducibly isolated as a minor by-
product in 24% yield. It is formally formed by the reaction of CO2
with the disilicon compound 2a’ and dual hydrosilylation of the
substrate to yield a disilylacetal.
Scheme 3. Reduction of CO2 by 2, formation of formates and a disilylacetal [Bis
= CH(SiMe3)2].
The molecular structure of 3a (Figure 2) features an almost
planar backbone consisting of the atoms of the vinyl group and
the six-membered CAlOCOSi heterocycle (largest deviation for
Al1, 6 pm). The Al-C/O and Si-C bond lengths are typical of four-
coordinate Al and Si atoms. The C-O distances are with 126.7(3)
and 128.3(3) pm significantly longer than standard values of C=O
bonds (121 pm) which is consistent with an increased
coordination number of two at O and π-electron delocalization in
the formate group. 3d is similar but deviates slightly more from
planarity (largest deviation from plane for O and Ge, 11 pm) while
compound 3b adopts an envelope conformation with the Si atom
in the apical position [62(av) pm above the plane]. The Si and
1
Compounds 3 showed in the H NMR spectra signals for the
vinylic H atoms at about  = 7.1, that are in the same range as
those of the starting materials. The 3JSiH coupling constants of 3a
and 3b are with 27 Hz slightly larger than those of 2 and indicate
the trans arrangement of H and Si at the C=C bonds. The low field
shifts in the 29Si NMR spectra indicate with  = 33 a deshielding
compared to 2, which may be caused by the replacement of H by
O. The formate groups show signals at  = 6.9 to 7.4 in the 1H and
at about  = 170 in the 13C NMR spectra. The compounds may be
3
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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
Figure 3. Molecular structure and atomic numbering scheme of 4a.
Displacement ellipsoids are drawn at the 40% level. H atoms (except H2, H8,
CH2 and CHMe2) are omitted. Selected bond lengths (pm): Al1-C1 199.7(1),
Al1-C6 200.6(1), Al1-C7 198.3(1), Al1-O1 193.54(9), Si1-C1 184.2(1), Si1-O1
175.64(8), Si2-C7 184.6(1), Si2-O2 169.39(9), C12-O1 144.2(1), C12-O2
138.0(1).
vinylic H atoms adopt trans-positions as predicted by the NMR
data. The Si-O and Ge-O bond lengths are with 177 and 195 pm
on average relatively long if compared to values of simple ethers
or esters[30] but in the same range as found in the formic acid ester
HCO2(SiEt3)[Al(C6F5)3][9] [177.2(2) pm)].
Compounds 2a to 2d showed remarkable differences in their
reactions towards CO2. 2a, 2c and 2d consist of mono- and divinyl
compounds. 2c did not react at all, which is in accordance with
the low polarization capability of Ga atoms and the insufficient
activation of CO2. The Si compound 2a afforded two products,
which are derived from the mono- and divinyl constituents, while
the Ge compound 2d afforded only a single product derived from
the monovinyl germane. The addition of a donor (CO2) to the
starting mixture may initiate commutation similar to the reaction of
2a with HNEt2.[16] Hydrosilylation reactions are very fast and may
proceed
before
commutation
is
significant,
while
hydrogermylation is slower and may occur after the equilibration
is achieved. The sterically most shielded silane 2b is a single, well
defined species and afforded the CO2 adduct 3b in a highly
selective reaction.
Figure 2. Molecular structure and numbering scheme of 3a. 3b and 3d are
similar. Displacement ellipsoids are drawn at the 40% level. H atoms (except
H2, H8, CHMe2) are omitted. Selected bond lengths (pm) and angles (º): 3a:
Al1-C1 200.4(2), Al1-O2 190.5(2), Si1-O1 176.7(2), C1-Si1 183.1(2), C8-O1
126.7(3), C8-O2 128.3(3); Al1-C1-Si1 119.6(1), O1-C8-O2 127.7(2). 3b
(average of two independent molecules): Al1-C1 201.5, Al1-O2 192.8, Si1-O1
176.8, C1-Si1 184.0, C8-O1 127.6, C8-O2 124.0; Al1-C1-Si1 114.9, O1-C8-O2
126.7. 3d (average of two independent molecules): Al1-C1 200.0, Al1-O2 188.7,
Ge-O1 194.7, C1-Ge 192.0, C8-O1 126.0, C8-O2 123.8; Al1-C1-Ge 119.5, O1-
C8-O2 128.0.
Since condensation reactions with elimination of volatile AlR3
compounds[17] are favored for small alkyl groups (R = Me, Et) we
treated the alkynes tBu-CC-E(H)R2 (E = Si, Ge; R = iPr, Ph) with
H-AlMe2 and H-AlEt2 in n-pentane, removed the solvent and
stirred the crude products in a dynamic vacuum at room
temperature (5a, 5b) or 100 °C (5c) for 12 h. The trialkylalanes
were removed quantitatively and identified by NMR spectroscopy.
The condensation products 5 were isolated in 60 to 80% yield as
colorless solids or as a highly viscous liquid (5b; Scheme 4). The
isopropyl compounds 5a and 5b decomposed slowly at room
temperature and were highly sensitive towards air and moisture.
In contrast to the phenylsilyl compound 5c, their handling and
characterization proved to be difficult. The Ge compound 5b could
not be purified at all. Interestingly, not the kinetically favored cis-
addition products, but the thermodynamically stable products (H
trans to Al; 5a and 5c)[18] were isolated, as established by
Compound 4a has a unique molecular structure (Figure 3). It
contains two Si atoms, represents a disilylacetal and results from
the reduction of both C=O bonds of CO2. It features a planar, four-
membered AlCSiO ring annulated to a six-membered AlOCOSiC
heterocycle in a chair conformation with O2 and Al1 in the apical
positions (52 and 61 pm above and below the average plane).
The angle between both planes is 46º. The vinylic H and Si atoms
are in trans positions. The Si-O distances differ, Si1-O1 is with
175.64(8) pm similar to those of compounds 3, but the Si2-O2
distance is with 168.39(9) pm close to values observed for simple
silylesters. The different C-O bond lengths [144.2(1) (C12-O1)
and 138.0(1) pm (C12-O2)] reflect the different coordination
numbers of O1 (CN = 3) and O2 (CN = 2).
3
relatively small JSiH coupling constants across the C=C bonds
(<15 Hz; Si cis to H) and crystal structure determination of 5a
(Figure 4). A vinylsilyl group showed a disorder (0.93:0.07) similar
to that of 2b with one Si-H bond pointing towards Al1, while the
second Si-H bond of the minor component pointed towards the
opposite direction. The structure of the main component is shown
in Figure 4. The positions of the Si bound H atoms were refined
with isotropic displacement parameters (with exception of the
minor component of the disordered group). The conformation
across the Si-Cvinyl bonds is similar to that in 2b with torsion angles
AlCSiH of 29.7 and 21.5° (-179.9° for the minor component) and
results in Al⸱⸱⸱H distances close to the sum of the van der
Waals radii. The structure of 5c is similar, but the quality of the X-
ray data did not allow a satisfactory refinement. The configuration
of the Ge compound 5b could not be assigned. It was, therefore,
not applied in secondary reactions. When compounds 5a and 5c
were treated with CO2 at pressures of up to 8 bar no reaction was
observed at room temperature while temperatures of 40 ºC led to
unselective decomposition. NMR signals of compounds similar to
4a were not detected. This behavior may be influenced by the
different configuration of the vinyl groups in the starting
t
compounds. In compounds 5, the vinylic Bu groups and the Al
atoms adopt cis-positions and the steric shielding of the metal
atoms seems to be more efficient than in compounds with a cis-
4
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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
arrangement of Al and H atoms. The approach of the CO2
molecules to the Al atoms and their activation may be hindered
by steric repulsion.
over a period of 12 h at room temperature to yield the thioacetals
6, the reaction of the Ga compound 2c required a temperature of
40 ºC. The relatively soft Ga atoms were evidently unable to
activate CO2 (see above), but they allowed reactions with CS2.[32]
In all cases CS2 reacted with two equivalents of the hydrides by
reduction of both C=S bonds and formation of a methylene-
bridged disulfur compound.
Scheme 4. Synthesis of the condensation products 5.
Scheme 5. Reactions with CS2 [Bis = CH(SiMe3)2].
Figure 4. Molecular structure and numbering Scheme of 5a. Displacement
ellipsoids are drawn at the 40% level. H atoms (except H2, H7, SiH, CHMe2)
are omitted. Selected bond lengths (pm) and angles (º): Al1-C1 196.6(2), Al1-
C6 195.3(2), Al1-C(Me) 195.9(2), C1-C2 134.6(2), C6-C7 134.9(2), Si1-H1
138(2), Si2-H2 140(2); C1-Al1-C6 116.61(8).
In an attempt to reduce the reaction time a mixture of 2c and
CS2 was heated for 12 h to 70 ºC. An unexpected dimeric Ga-S
compound 7c was formed, while 6c, 1a and H2C=CMe2 were
identified as by-products by NMR spectroscopy. 7c was isolated
in 77% yield after recrystallization from CH2Cl2. The constitution
of the product suggests a reaction course via (i) hydrosilylation of
CS2 by two equivalents of 2c to yield the dithioacetal, (ii) -hydride
elimination with formation of isobutene and Ga-H and (iii)
transformation of the dithioacetal to CH4 and 7c. While isobutene
was unambiguously identified in an NMR experiment ( = 4.74,
1.58),[33] a signal consistent with CH4 ( = 0.16) was not detected.
In an attempt to obtain an Al analogue of compound 7c a solution
of 2a and CS2 was heated to 60 ºC. Only an increased reaction
rate resulted with complete conversion to 6a after approximately
30 min. Higher temperatures led to unselective decomposition.
Attempts to stop the reaction of 2a on the thioformic acid state by
using CS2 as a solvent yielded only compound 6a. 2b with the
bulky CH(SiMe3)2 substituents did not react with CS2 at lower
temperatures, while at 75 ºC retro-hydroalumination to 1a and
[(Me3Si)2HC]2Al-H was observed. The latter reacted with CS2 to
We hoped to release the formate ligands from compounds 3, to
recover the starting materials 2 and to conduct the reduction of
CO2 in a catalytic fashion. The adducts 3a and 3d were therefore
treated with hydride sources such as H-SiEt3, H-B(O2C4Me4) and
H3B(SMe2) in d6-benzene in a sealed NMR tube. No reaction was
observed up to temperatures of 75 ºC. The reaction of 3a with
iBu2Al-H or LiAlH4 under the same conditions led to unselective
decomposition. The related adduct HCO2(SiEt3)[Al(C6F5)3] was
converted into CH4 and O(SiEt3)2 in the presence of HSiEt3 as a
hydride source and catalytic amounts of B(C6F5)3.[9] 3a and 3d
reacted with HSiEt3 in the presence of B(C6F5)3 but the reaction
was unselective and led to the formation of isobutene and
numerous unknown products. Compound 3a afforded a small
quantity of 1a which was presumably formed by retro-
hydroalumination.
compound
8
which for comparison was independently
CS2 showed a different behavior, which may be caused by the
larger atomic radius and softness of S atoms and the lower
polarity of C=S bonds. Insertion of CS2 into a Si-H bond has
previously only been observed for a silatrane with a five-
coordinate Si atom and afforded an intermediate siladithioformic
acid ester which reacted further to yield a monomeric N stabilized
silathioketone.[31] The Al functionalized vinylsilanes 2 were
synthesized in situ and treated in n-hexane or n-pentane with CS2
(Scheme 5). While the Al derivatives 2a and 2d reacted smoothly
synthesized from [(Me3Si)2HC]2Al-H and CS2.
The NMR spectra of compounds 6 are similar to those of 3. The
vinylic H atoms show chemical shifts between  = 6.68 and 7.01,
and 3JSiH coupling constants (6a, 6b) of about 27 Hz indicate the
trans arrangement of Si and H atoms. The signals in the 29Si NMR
spectra are with  = 41.5 (6a) and  = 36.2 (6c) comparable to
those of 3 and significantly downfield compared to those of the
starting compounds 2. The methylene bridge shows signals in the
5
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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
1H and 13C NMR spectra at about  = 4.5 and 27.9, respectively.
They are similar to values of simple dithioacetals H2C(SR)2[34] or
metal complexes with dithioacetals as ligands.[34a,34b,35] The
relevant NMR data of the dimeric gallium sulfide 7c (1H:  = 6.78,
3JSiH = 23.5 Hz, C=CH; 29Si:  = 34.3) are similar to those of 6 but
lack the characteristic signals for the dithioacetal group. The mass
spectra of all compounds show m/z values corresponding to the
molecular ion peaks minus H2C=CMe2 or tBu and indicate in case
of 7c the retention of the dimeric structure in the gas phase.
within the range of values reported for organometallic gallium
sulfides (R2GaSR)2.[38] The Si-S bonds are with 220.0 pm on
average shorter than in compounds 6, but longer than in simple
dithioacetals (see above).
The molecular structures of compounds 6 (Figure 5) feature
two almost planar four-membered SMCE heterocycles (M = Al,
Ga; E = Si, Ge; largest deviation from plane for C, ~12 pm) that
are bridged by a CH2 group (S-CH2-S ~111º). The angles between
the normals of the rings indicate with 74 to 81º an almost
perpendicular arrangement. The C-S bonds of 6 are with 182 pm
[34]
in the typical range of those in dithioacetals H2C(SR)2
metal complexes[35] such as H2C[S(Ph)(AuCl)]2
or in
or
[35c]
H2C[S(Me)Mn(CO)3(µ-Br)]2.[35b] The coordination to the metal
atom and the formation of the heterocycles cause a lengthening
of the S-Si bond from less than 216 pm in silylthioethers such as
R’3Si-SR (R, R’ = Me, Ar)[36] to about 226 pm in 6a and 6c. The
Al-S distances are with about 247 pm in the typical range of
adducts such as Me3Al←SMe2 (246 pm)[37a] or [14]aneS4(AlMe3)4
(252 pm).[37b] The Ga-S bond lengths in 6c are with 258.0(av.) pm
significantly longer.
Figure 6. Molecular structure and numbering scheme of 7c. Displacement
ellipsoids are drawn at the 40% level. H atoms (except H2 and H8 at C2 and
C8) have been omitted. Selected bond lengths (pm): Ga1-C1 198.6(2), Ga1-S1
245.37(6), Ga1-S2 236.23(6), Ga1-tBu 199.0(2), Si1-S1 220.14(8), Si1-C1
187.2(2), Ga2-S1 237.08(6), Ga2-S2 246.29(6), Ga2-C7 198.5(2), Si2-S2
219.94(8), Si2-C7 187.4(2), C1-C2 133.7(3), C7-C8 134.2(3).
Conclusion
The transformation of CO2 to valuable C1 building blocks is an
important field in current research. Hydrosilylation of activated
molecules was identified as an efficient method and has been
applied in various processes. The combination of E-H bonds (E =
Si, Ge) and Lewis acidic Al or Ga atoms in single molecules
seems to be an interesting aspect for the activation of CO2. Such
functional compounds (2) are accessible on a simple route by
hydroalumination or hydrogallation of alkynylsilanes and
–
germanes containing E-H bonds. The activation of CO2 molecules
may proceed by the approach of an O atom to the metal atom
which in the next step should facilitate the insertion of a C=O into
an E-H bond. Such reactions occurred with 2 at mild conditions
and afforded formates in highly selective reactions. In one case,
the formation of an acetal was observed by double hydrosilylation
of CO2. The softer CS2 molecule reacted directly with two
equivalents of the hydrides to yield dithioacetals in moderate to
good yields. These reactions confirm that these silanes and
germanes are promising starting materials for the cooperative
reduction of CO2 or related molecules. The specific arrangement
of functional groups may serve as a model for the generation of
similar compounds incorporating various elements. The E-O bond
energies and the substitution patterns influence the reactivity of
the CO2 adducts as was shown by exchange of the relatively hard
Si and Al atoms by less polarizing Ge and Ga atoms. These
results will stimulate investigations into the further modulation of
these systems for an optimization of their chemical properties and,
finally, the development of catalytic processes.
Figure 5. Molecular structure and numbering scheme of 6d. 6a and 6c are
similar. Displacement ellipsoids are drawn at the 40% level. H atoms (except
H2, H10, CH2 group) have been omitted. Selected bond lengths (pm) and
angles (º); average values for both molecular halves: 6a: Al-Cvinyl 200.8, Al-S
248.2, Si-Cvinyl 184.2, Si-S 227.4, H2C-S 182.4; S-CH2-S 110.8(1). 6c
(disordered GaCSiS ring, data of the main component): Ga-Cvinyl 201.8, Ga-S
258.0, Si-Cvinyl 185.4, Si-S 224.5, H2C-S 182.1; S-CH2-S 110.9(2); 6d (average
values for both molecular halves and two independent molecules): Al-Cvinyl
199.5, Al-S 247.6, Ge-Cvinyl 195.5, Ge-S 236.8, H2C-S 181.7; S-CH2-S 111.5.
7c has a unique molecular structure, is dimeric in the solid state
and features an eight-membered tricycle in a boat conformation
consisting of two four-membered CSiSGa heterocycles that are
connected via Ga-S bonds to form the central Ga2S2 ring (Figure
6). The three four-membered heterocycles are essentially planar
(largest deviation from average plane 5 pm) with interplanar
angles to the Ga2S2 plane of about 62º. The endocyclic angles of
the CSiSGa rings are smallest for Si-S-Ga [78.2(av.)º] and largest
for Ga-C-Si [99.4(av.)º]. The Ga-S distances of the CGaSiS
heterocycles are with 245.8 pm on average significantly longer
than those between these rings (236.7 pm), but both values are
6
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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
temperature and added dropwise to a cooled (-78 ºC) solution of iPr2GeCl2
(3.33 g, 14.5 mmol) in Et2O (30 mL). The mixture was warmed to room
temperature overnight, cooled to 0 ºC and treated with a saturated solution
of NH4Cl in H2O (20 mL). The organic phase was separated, the aqueous
phase extracted with Et2O (3 x 10 mL). The combined organic phases were
dried with MgSO4. Filtration, removal of the volatiles in vacuo and
distillation of the residue (70 ºC, 10-3 Torr) yielded Me3C-CC-Ge(Cl)iPr2
as a colorless oil (2.96 g, 74%). [C12H23ClGe] calcd. C 52.34, H 8.42; found
Experimental Section
General Considerations. All procedures were carried out under an
atmosphere of purified argon in dried solvents (n-hexane and n-pentane
with LiAlH4; Et2O, THF and toluene with Na/benzophenone; CH2Cl2 and
t
pentafluorobenzene with molecular sieves). Commercially available Bu-
CCH and iPr2Si(H)Cl were dried over molecular sieves; iPrMgCl in THF,
i
n-BuLi in n-hexane, CS2, CO2, Bu2Al-H and Et2Al-H were used without
1
C 51.96, H 8.52. H NMR (C6D6, 300K): δ = 1.12 (s, 9H, CMe3), 1.17 (d
further purification. tBu2Al-H,[39] tBu2Ga-H,[39] [(Me3Si)2CH]2Al-H,[39] Me2Al-
H[40] and Ph2Si(H)-CC-tBu[41] were synthesised according to literature
procedures. An optimized procedure for the synthesis of iPr2GeCl2 is given
below. Elemental analyses were determined by the microanalytic
laboratory of the Westfälische Wilhelms Universität Münster. NMR spectra
were recorded in CDCl3 or C6D6 at ambient probe temperature using the
following Bruker instruments: Avance I (1H, 400.13; 13C, 100.60 MHz; 29Si
79.49 MHz), Avance III (1H, 400.03; 13C, 100.59; 29Si 79.47 MHz,15N 40.55
MHz), Avance Neo 500SB (1H 500.23 MHz, 13C 125.80 MHz). The signals
were referenced internally to residual solvent resonances or to liquid NH3
in case of 15N (chemical shift data in δ). 13C NMR spectra were all proton-
decoupled. The assignment of NMR spectra is based on HMBC, HSQC
and DEPT135 data. IR spectra were recorded as KBr pellets or with the
neat material between CsI plates on a Shimadzu Prestige 21 spectrometer,
electron impact mass spectra on a Finnigan MAT95 mass spectrometer.
Only the most intensive masses are given, the isotopic patterns were in
agreement with the calculated ones.
3
3
overlap, 6H, JHH = 7.4 Hz, CHMe), 1.19 (d overlap, 6H, JHH = 7.7 Hz,
CHMe), 1.43 (pseudo-sept, 2H, 3JHH = 7.4 Hz, CHMe). 13C{1H} NMR (C6D6,
300K): δ = 18.1 and 18.2 (CHMe), 21.0 (CHMe), 28.5 (CMe3), 30.8 (CMe3),
75.8 (CC-CMe3), 119.3 (CC-CMe3). IR (cm–1, KBr pellet): 2967 vs, 2949
vs, 2928 vs, 2894 vs, 2866 vs ν(CH); 2183 s, 2149 s ν(CC); 1464 vs,
1387 w, 1366 s, 1254 vs δ(CH3); 1227 m, 1204 m, 1164 vw, 1084 w, 1005
m, 922 m, 878 m, 751 s ν(CC); 687 vw, 577 m, 556 m, 486 m ν(GeC),
(CC). MS (20 eV, 298K): m/z (%): 276 (5) [M]+, 233 (100) [M – CHMe2]+.
t
i
Synthesis of Bu-CC-Ge(H)iPr2 (1b): Bu2Al-H (1.80 mL, 1.42 g, 10.0
mmol) was added at room temperature to a solution of tBu-CC-Ge(Cl)iPr2
(1.73 g, 6.28 mmol) in THF (30 mL). The mixture was stirred for 3 h, treated
with Et2O (20 mL), cooled to 0 °C and treated with water (15 mL). The
precipitate was dissolved by addition of HCl (a few drops, 6%). The
aqueous phase was separated and extracted with Et2O (3 x 10 mL). The
combined organic phases were dried over MgSO4, and the solvent was
removed in vacuo to yield 1b as a colourless oil (1.35 g, 89%). It was
directly used for further reactions. Attempts of purification by column
chromatography failed; substituent exchange was initiated with the
formation of diisopropyl-dialkynylgermane. 1H NMR (C6D6, 300K): δ = 1.16
(d, 6H, 3JHH = 6.8 Hz, CHMe), 1.21 (s, 9H, CMe3), 1.23 (d overlap, 6H, 3JHH
Synthesis of iPr2GeCl2: iPr2GeCl2 was synthesised according to a
literature procedure,[42] but work-up by vacuum distillation instead of
preparative HPLC improved the yield from 19 to 73%. PrMgCl (40.0 mL,
i
80.0 mmol, 2 M in THF) was added dropwise over a period of 2 h to a
solution of GeCl4 (4.55 mL, 8.65 g, 40.3 mmol) in THF (100 mL) at -78 ºC.
The mixture was warmed to room temperature overnight and treated with
a saturated solution of NH4Cl in H2O (20 mL) at 0 ºC. The organic phase
was separated and the aqueous phase extracted with Et2O (3 x 20 mL).
The combined organic phases were washed with a saturated NaCl solution
and dried with Na2SO4. The organic phase was separated, the solvent
removed in vacuo and the residue distilled at 2.2 10-3 mbar and room
3
= 6.7 Hz, CHMe), 1.29 (m, 2H, CHMe), 4.30 (t, 1H, JHH ≈ 2 Hz, GeH).
13C{1H} NMR (C6D6, 300K): δ = 15.1 (CHMe), 20.0 and 20.3 (CHMe), 28.6
(CMe3), 31.3 (CMe3), 75.4 (CC-CMe3), 118.1 (CC-CMe3). IR (cm–1, KBr
pellet,): 2957 vs, 2942 vs, 2923 vs, 2888 vs, 2865 vs ν(C-H); 2184 m, 2151
s ν(CC); 2028 vs ν(GeH); 1600 vw, 1465 s, 1385 w, 1364 s, 1297 vw,
1254 vs δ(CH3); 1225 m, 1204 m, 1162 vw, 1085 w, 1006 m, 921 w, 880
m, 724 vs ν(CC); 556 m, 483 m ν(GeC), (CC).
i
temperature into a cooled (0 °C) vessel to yield Pr2GeCl2 as a colorless
Synthesis of tBu-CC-Si(H)Ph2 (1c):[41] Compound 1c was synthesised
according to the procedure described for 1a from tBu-CCH (1.13 mL, 0.75
g, 9.15 mmol), n-BuLi (5.7 mL, 9.14 mmol, 1.6 M in n-hexane) and
Ph2Si(H)Cl (1.79 mL, 2.00 g, 9.16 mmol) in Et2O (40 mL). After addition of
the lithium alkynide to the silane solution the mixture was warmed to room
temperature and heated under reflux overnight. Addition of water (0 ºC, 20
mL), extraction of the aqueous phase with pentane (3 x 20 mL) and
purification by column chromatography afforded 1c as a colorless solid
(2.08 g, 86%). The NMR spectra were in agreement with those published
in the literature.[41]
1
3
liquid (6.76 g, 74%). H NMR (CDCl3, 300K): δ = 1.29 (d, 6H, JHH = 7.3
Hz, CHMe), 1.94 (sept, 1H, 3JHH = 7.3 Hz, CHMe).
Synthesis of tBu-CC-Si(H)iPr2 (1a): n-BuLi (12.4 mL, 19.8 mmol, 1.6 M
in n-hexane) was added to a solution of tBu-CCH (2.48 mL, 1.64 g, 20.0
mmol) in Et2O (20 mL) at -78 ºC. The mixture was warmed to room
temperature and stirred for 30 min. It was added dropwise to a cooled (-78
ºC) solution of iPr2Si(H)Cl (2.62 mL, 2.31 g, 15.3 mmol) in Et2O (20 mL).
The mixture was warmed to room temperature, cooled to 0 °C and treated
with water (20 mL). The organic phase was separated, the aqueous phase
was extracted with n-pentane (3 x 10 mL), and the combined organic
phases were dried with MgSO4. Filtration and removal of the volatiles in
vacuo yielded an oil which was purified by column chromatography (Silica,
n-pentane) to afford compound 1a as a colorless oil (2.38 g, 79%).
[C12H24Si] calcd. C 73.38, H 12.32; found C 72.91, H 12.76. 1H NMR (C6D6,
300K): δ = 0.98 (m, 2H, CHMe), 1.11 (d, 6H, 3JHH = 7.2 Hz, CHMe), 1.15
(s, 9H, CMe3), 1.16 (d overlap, 6H, 3JHH = 7.2 Hz, CHMe), 4.01 (t, 1H, 3JHH
i
t
Synthesis of Pr2(H)SiC[AltBu2]=C(H)-tBu (2a): A solution of Bu2Al-H
(0.22 g, 1.55 mmol) in n-pentane (15 mL) was added to a cooled (-78 ºC)
solution of tBu-CC-Si(H)iPr2 (1a, 0.30 g, 1.53 mmol) in n-pentane (15 mL).
The mixture was warmed to room temperature and stirred for 2 h. The
solvent was removed in vacuo to yield a colorless oil (0.48 g, 93% related
on 2a). NMR spectroscopy revealed two sets of resonances, which result
from the monovinyl (2a) and the divinyl silane (2a’). The molar ratio of both
compounds is about 4:1. Attempts to crystallize one component from
various non-coordinating solvents failed. The mixture was synthesised in
situ and used without further purification. 2a: 1H NMR (C6D6, 300K): δ =
1.12 (m overlap, 2H, CHMe), 1.12 (m overlap, 6H, CHMe), 1.12 (s, 9H,
CMe3), 1.14 (m overlap, 6H, CHMe), 1.17 (s, 18H, AlCMe3), 4.41 (s, 1H,
1
= 2.6 Hz, JSiH = 193.6 Hz, SiH). 13C{1H} NMR (C6D6, 300K): δ = 11.3
(CHMe), 18.5 and 18.8 (CHMe), 28.5 (CMe3), 31.0 (CMe3), 75.9 (CC-
CMe3), 119.3 (CC-CMe3). 29Si{1H} NMR (C6D6, 300K): δ = -16.2. IR (cm–
1, KBr pellet,): 2946 vs, 2929 vs, 2896 vs, 2865 vs ν(CH); 2198 m, 2155 vs
ν(CC); 2119 vs ν(SiH); 1463 s, 1384 w, 1365 s, 1255 vs δ(CH3); 1204 w,
1164 vw, 1071 w, 1002 s, 938 s, 921 w, 882 s, 803 vs, 790 vs, 767 m
ν(CC); 662 m, 624 w ν(SiC); 597 vw, 539 w, 458 w, 414 vw, 381 vw (CC).
MS (20 eV, 298K): m/z (%): 196 (12) [M]+, 153 (70) [M – CHMe2]+, 139 (28)
[M – CMe3]+, 125 (100) [M – CH2=CMe2 – Me]+.
3
1JSiH = 178 Hz, SiH), 6.76 (s, 1H, JSiH = 22.0 Hz, C=CH). 13C{1H} NMR
(C6D6, 300 K): δ = 12.6 (CHMe), 18.9 (br., AlCMe3), 19.7 and 20.2 (CHMe),
30.4 (C=CH-CMe3), 30.9 (AlCMe3), 40.2 (C=CH-CMe3), 142.5 (C=CH),
163.9 (C=CH). 29Si NMR (C6D6, 300K): δ = -5.6. 2a’: 1H NMR (C6D6, 300K):
δ = 1.14 (s, 18H, CMe3), 1.18 (m overlap, 2H, CHMe), 1.18 (m overlap,
Synthesis of tBu-CC-Ge(Cl)iPr2: n-BuLi (9.05 mL, 14.5 mmol, 1.6 M in
n-hexane) was added to a cooled (0 ºC) solution of Bu-CCH (1.80 mL,
24H, CHMe), 1.27 (s, 9H, AlCMe3), 4.32 (s, 2H, SiH), 7.16 (s, 2H, 3JSiH
22.0 Hz, C=CH). 13C{1H} NMR (C6D6, 300K): δ = 13.7 (CHMe), 18.1 (br.,
=
t
1.19 g, 14.5 mmol) in Et2O (30 mL). The mixture was stirred for 1 h at room
7
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
AlCMe3), 19.9 and 20.8 (CHMe), 30.2 (C=CH-CMe3), 31.4 (AlCMe3), 39.2
(C=CH-CMe3), 140.4 (C=CH), 169.0 (C=CH). 29Si{1H} NMR (C6D6, 300K):
δ = -2.8. IR (cm–1, KBr pellet): 3175 w, 2965 vs, 2853 vs, 2767 s, 2732 m,
2705 s, 2616 w, 2562 w ν(CH); 2107 vs, 2099 vs ν(SiH); 1654 w, 1596 s,
1553 vs, 1546 sh ν(C=C); 1457 vs, 1385 vs, 1362 vs, 1299 vw, 1243 s
δ(CH3); 1202 vs, 1181 m, 1071 s, 1029 s, 1000 vs, 967 m, 936 vs, 855 vs
br., 789 vs br., 720 vs ν(CC); 658 vs, 637 vs ν(SiC); 583 vs, 546 s, 529 w,
487 m ν(AlC), (CC). MS (20 eV, 298K): m/z (%): 421 (2) [M(2a’) – tBu]+,
281 (20) [M(2a) – tBu]+.
result from the monovinyl (2d) and the divinyl silane (2d’). The molar ratio
of both compounds is about 1:0.9. Attempts to crystallize one component
from various non-coordinating solvents failed. The mixture was
synthesised in situ and used without further purification. 2d: 1H NMR (C6D6,
300K): δ = 1.11 (s, 9H, C=C-CMe3), 1.19 (s, 18H, AlCMe3), 1.22 (m overlap,
6H, CHMe), 1.28 (m overlap, 6H, CHMe), 1.46 (m overlap, 2H, CHMe),
4.16 (s, 1H, GeH), 7.21 (s, 1H, C=CH). 13C{1H} NMR (C6D6, 300K): δ =
18.8 (overlap, CHMe), 18.8 (overlap, AlCMe3), 21.8 and 22.3 (CHMe), 29.8
(C=CH-CMe3), 30.7 (AlCMe3), 38.4 (C=CH-CMe3), 138.6 (C=CH), 166.6
(C=CH). 2d’: 1H NMR (C6D6, 300K): δ = 1.09 (s, 18H, C=C-CMe3), 1.19 (s,
9H, Al-CMe3), 1.20 and 1.22 (m overlap, 12H, CHMe), 1.38 (s, 4H, CHMe),
4.32 (s, 2H, GeH), 6.86 (s, 2H, C=CH). 13C{1H} NMR (C6D6, 300 K): δ =
17.2 (CHMe), 18.8 (br., AlCMe3), 21.4 and 21.9 (CHMe), 30.1 (C=CH-
CMe3), 30.7 (Al-CMe3), 39.2 (C=CH-CMe3), 140.9 (br., C=CH), 163.5
(C=CH).
i
Synthesis of Pr2(H)SiC{Al[CH(SiMe3)2]2}=C(H)-tBu (2b): A solution of
[(Me3Si)2CH]2Al-H (0.53 g, 1.53 mmol) in n-hexane (20 mL) was added at
t
-78 ºC to a solution of Bu-CC-Si(H)iPr2 (1a, 0.30 g, 1.53 mmol) in n-
hexane (15 mL). The mixture was warmed to room temperature and stirred
at 55 ºC overnight. The solvent was removed in vacuo and the residue
recrystallized from CH2Cl2 at -30 ºC to yield colorless crystals of 2b (0.44
g, 50%); the solid encapsulated small quantities of CH2Cl2 (0.13 to 0.33
equivalents). M.p. 31 ºC. [C26H63AlSi5·(CH2Cl2)1/3] calcd. C 55.33, H 11.22;
found C 55.21, H 11.34. 1H NMR (C6D6, 300K): δ = -0.17 (s, 2H, CHSi2),
0.30 (s, 36H, SiMe3), 1.15 (s, 9H, CMe3), 1.19 (m overlap, 6H, CHMe),
1.20 (m overlap, 2H, CHMe), 1.21 (m overlap, 6H, CHMe), 4.21 (s, 1H,
Synthesis of iPr2(H)SiC(AltBu2)=C(H)-tBu·HNEt2 [2a(HNEt2)]: A solution
of tBu2Al-H (0.18 g, 1.27 mmol) in n-hexane (10 mL) was added to a cooled
(-78 °C) solution of tBu-CC-Si(H)iPr2 (1a) (0.25 g, 1.27 mmol) in n-hexane
(15 mL). The mixture was warmed to room temperature and stirred
overnight. It was cooled to -80 ºC, treated with HNEt2 (0.09 g, 0.13 mL,
3
1JSiH = 173 Hz, SiH), 7.19 (s, 1H, JSiH = 22.0 Hz, C=CH). 13C{1H} NMR
1.27 mmol), warmed to room temperature and stirred for 1 h.
(C6D6, 300K): δ = 5.0 (s, 1JSiC = 50 Hz, SiMe3), 9.8 (CHSi2), 14.7 (CHMe),
20.7 and 21.7 (CHMe), 29.7 (CMe3), 39.0 (CMe3), 143.6 (C=CH), 172.5
(C=CH). 29Si{1H} NMR (C6D6, 300 K): δ = -3.3 (CHSi2), 0.5 (SiH). IR (cm–
1, KBr pellet,): 2956 vs, 2898 vs, 2865 vs, 2755 w, 2724 w ν(CH); 2105 s
ν(SiH); 1927 vw, 1879 vw, 1600 m, 1549 s ν(C=C); 1465 s, 1428 m, 1399
m, 1385 m, 1362 m, 1249 vs δ(CH3); 1200 m, 1160 vw, 1069 m, 1054 m
ν(CC); 1009 vs δ(CHSi2); 938 s, 853 vs, 828 vs, 784 vs, 753 s, 720 w
ρ(CH3Si); 674 s, 612 w ν(SiC); 556 vw, 521 s, 500 m ν(AlC), (CC). MS
(20 eV, 353K): m/z (%): 485 (56) [M – CMe3]+, 345 (39) [Al[CH(SiMe3)2]2]+.
Concentrating the reaction mixture and cooling to -30 ºC yielded colorless
crystals of 2a(HNEt2) (0.41 g, 78%). M.p. 135 ºC (dec.). [C24H54AlNSi]
1
calcd. C 70.00, H 13.22, N 3.40; found C 69.71, H 12.90, 3.29. H NMR
(C6D6, 300K): δ = 0.78 (t, 3JHH = 7.2 Hz, 6H, NCH2Me), 1.17 (s, 9H, C=C-
CMe3), 1.21 (m overlap, 6H, CHMe2), 1.22 (m overlap, 2H, CHMe), 1.22
(m overlap, 6H, CHMe), 1.28 (s, 18H, AlCMe3), 2.23 (dq, 2JHH = 14.3 Hz,
3JHH = 6.9 Hz, 2H, NCH2), 2.66 (m, 1H, NH), 3.10 (dq, 2JHH = 15.5 Hz, 3JHH
= 7.2 Hz, 2H, NCH2), 3.61 (t, 1JSiH = 158 Hz, 3JHH = 3.2 Hz, 1H, SiH), 7.14
3
(s, JSiH = 24.7 Hz, 1H, C=CH). 13C{1H} NMR (C6D6, 300K): δ = 15.6
(CHMe), 16.0 (NCH2Me), 16.7 (AlCMe3), 21.57 and 21.61 (CHMe), 29.6
(C=CH-CMe3), 32.9 (AlCMe3), 39.1 (C=CH-CMe3), 44.7 (NCH2), 135.8 (br.
C=CH), 169.9 (C=CH). 29Si{1H} NMR (C6D6, 300 K): δ = 3.9. 15N{1H} (C6D6,
300K): δ = 48.0. IR (cm–1, KBr pellet): 3197 m ν(NH), 3079 w, 2952 vs,
2927 sh, 2865 vs, 2826 vs, 2759 m, 2726 w, 2695 m ν(CH); 2124 m, 2035
s ν(SiH); 1855 vw, 1785 vw, 1688 w, 1656 w, 1598 m, 1546 s ν(C=C),
δ(NH); 1465 vs, 1420 m, 1384 s, 1358 s, 1316 vw, 1247 m δ(CH3); 1222
vs, 1198 s, 1154 m, 1123 m, 1063 s, 1031 s, 1004 vs, 969 w, 938 s, 882
s, 811 vs, 795 vs, 776 sh, 757 w, 705 s ν(CC), ν(CN); 660 vs, 624 s, 608
s ν(SiC); 587 m, 564 m, 535 w, 518 vw, 479 m ν(AlC), (CC), ν(AlN). MS
(20 eV, 373K): m/z (%): 281 (14) [2a - tBu]+.
Synthesis of Pr2(H)SiC(GatBu2)=C(H)-tBu (2c): A solution of Bu2Ga-H
(0.20 g, 1.08 mmol) in n-hexane (15 mL) was added to a cooled (-78 °C)
solution of tBu-CC-Si(H)iPr2 (1a, 0.21 g, 1.07 mmol) in n-pentane (15 mL).
The mixture was warmed to room temperature and stirred for 2 h. The
solvent was removed in vacuo to yield a colorless, highly air- and moisture-
sensitive oil (0.32 g, 78% related on 2c). NMR spectroscopy revealed two
sets of resonances, which result from the monovinyl (2c) and the divinyl
silane (2c’). The molar ratio of both compounds is about 2:1. Attempts to
crystallize one component from various non-coordinating solvents failed.
The mixture was synthesised in situ and used without further purification.
2c: 1H NMR (C6D6, 300K): δ = 1.11 (m overlap, 6H, CHMe), 1.12 (m
overlap, 2H, CHMe), 1.13 (m overlap, 6H, CHMe), 1.16 (s, 9H, C=CH-
CMe3), 1.25 (s, 18H, GaCMe3), 4.40 (s, 1H, SiH), 6.48 (s, 1H, 3JSiH = 21.0
Hz, C=CH). 13C{1H} NMR (C6D6, 300K): δ = 12.9 (CHMe), 19.8 and 20.3
(CHMe), 29.6 (GaCMe3), 30.8 (C=CH-CMe3), 31.0 (GaCMe3), 39.1
(C=CH-CMe3), 144.0 (s br., C=CH), 162.8 (C=CH); GaCMe3 not observed.
29Si{1H} NMR (C6D6, 300 K): δ = -4.6. 2c’: 1H NMR (C6D6, 300K): δ = 1.17
(s, 18H, C=CH-CMe3), 1.18 (m overlap, 4H, CHMe), 1.18 (m overlap, 12H,
CHMe), 1.19 (m overlap, 12H, CHMe), 1.34 (s, 9H, GaCMe3), 4.30 (s, 2H,
SiH), 6.84 (s, 2H, 3JSiH = 20.7 Hz, C=CH). 13C{1H} NMR (C6D6, 300K): δ =
13.6 (CHMe), 20.0 and 20.9 (CHMe), 29.2 (GaCMe3), 30.6 (C=CH-CMe3),
31.3 (GaCMe3), 38.7 (C=CH-CMe3), 143.6 (C=CH), 166.6 (C=CH).
29Si{1H} NMR (C6D6, 300K): δ = -3.3. IR (cm–1, KBr pellet): 2963 vs, 2867
vs, 2767 m, 2736 w, 2709 m ν(CH); 2196 w, 2155 m, 2107 vs, 2035 sh
ν(SiH); 1848 vw, 1798 vw, 1775 vw, 1735 vw, 1717 vw, 1702 w, 1586 m,
1551 vs ν(C=C); 1465 vs, 1385 s, 1362 vs, 1252 s δ(CH3); 1202 s, 1177
m, 1071 m, 1002 vs, 971 vw, 938 s, 915 s, 880 vs, 845 vs, 793 vs, 708 vs
ν(CC); 660 vs ν(SiC); 593 w, 537 w, 469 vw ν(GaC), (CC). MS (20 eV,
298K): m/z (%): 463 (2) [M(2c’) – tBu]+, 323 (100) [M(2c) – CMe3]+.
i
t
Synthesis
of
[iPr2SiC(AltBu2)=C(H)-tBu]O2CH
(3a)
and
tBuAl[C(SiiPr2)=CH-tBu]2O2CH2 (4a): 2a was synthesised in situ as
t
described above from a solution of Bu2Al-H (0.18 g, 1.27 mmol) in n-
pentane (15 mL) and a solution of Bu-CC-Si(H)iPr2 (1a) (0.25 g, 1.27
t
mmol) in n-pentane (10 mL). CO2 was bubbled through the mixture for 5
min at room temperature, and stirring was continued for 1 h. An NMR
spectrum showed the presence of 3a and 4a in an approximate ratio of 5:1.
3a was isolated as colorless crystals (0.34 g, 70%) by cooling the
concentrated mixture to -30 ºC. Separation of the mother liquor, removal
of all volatiles in vacuo and repeated recrystallization of the residue from
pentafluorobenzene yielded 4a (0.08 g, 24%, based on the alkyne) in a
purity of 90%. 3a: M.p. 64 ºC. [C21H43AlO2Si] calcd. C 65.91, H 11.33;
found C 65.40, H 10.78. 1H NMR (C6D6, 300 K): δ = 0.98 (s overlap, 9H,
C=C-CMe3), 0.99 (m overlap, 2H, CHMe), 0.99 (d overl, 12H, CHMe), 1.28
(s, 18H, AlCMe3), 7.02 (s, 1H, CHO), 7.12 (s, 1H, 3JSiH = 27.0 Hz, C=CH).
13C{1H} NMR (C6D6, 300K): δ = 16.2 (HMBC, AlCMe3), 16.5 (CHMe), 18.6
and 19.1 (CHMe), 29.1 (C=CH-CMe3), 31.6 (AlCMe3), 38.9 (C=CH-CMe3),
136.0 (s br., C=CH), 170.2 (1JCH = 230 Hz, CHO), 170.7 (C=CH). 29Si{1H}
NMR (C6D6, 300K): δ = 33.6. MS (20 eV, 298K): m/z (%): 325 (100) [M –
CMe3]+, 283 (17) [M – butene – CHMe2]+. IR (cm–1, KBr pellet): 3027 w,
2944 vs, 2867 s, 2822 vs, 2753 w, 2722 vw, 2691 w ν(CH); 1704 vw, 1615
vs ν(C=O); 1563 s ν(C=C); 1463 s, 1401 m, 1384 m, 1362 vs, 1247 m
δ(CH3); 1198 w, 1179 w, 1075 w, 996 m, 936 w, 923 w, 884 m, 805 s, 772
w, 718 s ν(CC); 678 s, 651 m, 612 m ν(SiC), ν(SiO); 587 m, 543 m, 531 m
i
t
Synthesis of Pr2(H)GeC(AltBu2)=C(H)-tBu (2d): A solution of Bu2Al-H
(0.19 g, 1.34 mmol) in n-hexane (15 mL) was added to a cooled (-78 °C)
solution of Bu-CC-Ge(H)iPr2 (1b) (0.33 g, 1.37 mmol) in n-hexane (15
mL). The mixture was warmed to room temperature and stirred for 2 h. The
solvent was removed in vacuo to yield a colorless oil (0.45 g, 1.17 mmol
related on 2d). NMR spectroscopy revealed two sets of resonances, which
t
1
ν(AlC), ν(AlO), (CC). 4a: M.p. 129 ºC (dec.). H NMR (C6D6, 300K): δ =
1.03 (s, 18H, C=C-CMe3), 1.08 (m overlap, 6H, CHMe), 1.14 (d, 6H, 3JHH
8
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
= 6.8 Hz, CHMe), 1.20 (m overlap, 4H, CHMe and 12H, CHMe), 1.31 (s,
9H, AlCMe3), 5.09 and 5.18 (d, 1H, JHH = 4.4 Hz, CH2O2), 7.07 (s, 2H,
1H NMR (C6D6, 300K): δ = 0.00 (s, 3H, AlMe), 1.14 (s overlap, 18H, CMe3),
1.15 (d overlap, 24H, CHMe), 1.16 (m overlap, 4H, CHMe), 4.11 (s, 2H,
2
3JSiH = 24.4 Hz, C=CH). 13C{1H} NMR (C6D6, 300K): δ = 13.9 and 15.2
(CHMe), 16.4 (s br., AlCMe3), 18.3, 19.11, 19.06 and 19.5 (CHMe), 28.9
(C=CH-CMe3), 31.5 (AlCMe3), 38.0 (C=CH-CMe3), 87.6 (CH2O2), 141.6
(C=CH), 167.4 (C=CH). 29Si{1H} NMR (C6D6, 300 K): δ = 24.0 (HMBC). MS
(20 eV, 315K): m/z (%): 465 (100) [M – CMe3]+. IR (KBr pellet, cm–1): 2950
vs, 2867 vs, 2824 vs, 2759 w, 2722 w, 2699 w ν(CH); 1684 w, 1615 vs,
1565 m, 1538 vw, 1511 vw ν(C=C); 1465 s, 1416 vw, 1384 w, 1358 s, 1308
vw, 1243 s δ(CH3); 1200 m, 1162 m, 1125 m, 1071 w, 1044 w, 996 m, 953
w, 921 vw, 882 m, 813 m, 799 m, 778 m, 718 m ν(CC), ν(CO); 703 s, 668
s, 639 sh, 612 vw ν(SiC), ν(SiO); 587 vw, 570 vw, 525 vw, 504 w ν(AlC),
ν(AlO), (CC).
3JSiH = 172 Hz, SiH), 6.96 (s, 2H, JSiH = 12.8 Hz, C=CH). 13C{1H} NMR
3
(C6D6, 300K): δ = -1.5 (AlMe), 12.1 (CHMe), 19.5 (CHMe), 29.7 (C=CH-
CMe3), 38.4 (C=CH-CMe3), 136.0 (s br., C=CH), 171.8 (C=CH). 29Si{1H}
NMR (C6D6, 300K): δ = 0.7. MS (20 eV, 303 K): m/z (%): 436 (4) [M]+, 421
(8) [M – Me]+, 393 (14) [M – iPr]+, 379 (16) [M – tBu]+. IR (cm–1, neat, CsI
plates): 2974 vs, 2926 vs, 2885 vs, 2856 vs, 2754 vw, 2720 w ν(CH); 2097
vs ν(SiH); 1610 vw, 1545 m ν(C=C); 1456 vs, 1383 s, 1362 vs, 1238 s
(CH3); 1200 s, 1155 vw, 1065 m, 1053 m, 999 s, 939 w, 914 s, 878 s, 830
m br., 808 s, 789 s, 775 s, 746 s, 721 w ν(CC); 698 m, 683 m, 673 w, 652
s, 644 m, 633 w, 610 vw ν(SiC); 586 w, 505 w, 444 vw ν(AlC), (CC).
Synthesis of [tBu(H)C=C(GeHiPr2)]2AlMe (5b): A solution of Me2Al-H
(0.11 g, 1.90 mmol) in n-pentane (10 mL) was added to a cooled (-78 ºC)
Synthesis of {iPr2SiC[Al(CH(SiMe3)2)2]=C(H)-tBu}O2CH (3b): 2b was
generated in situ as described above from a solution of [(Me3Si)2CH]2Al-H
(0.53 g, 1.53 mmol) in n-hexane (20 mL) and a solution of Bu-CC-
t
solution of Bu-CC-Ge(H)iPr2 (1b) (0.46 g, 1.91 mmol) in n-pentane (20
t
mL). The mixture was warmed to room temperature and stirred for 12 h.
The solvent was removed in vacuo and the residue kept in a dynamic
vacuum (10–3 Torr) for 12 h to complete condensation by removal of AlMe3.
Attempts to crystallise the colorless oil (5b) from a various solvents at
temperatures between 25 and -70 ºC failed. 1H NMR (C6D6, 300K): δ
Si(H)iPr2 (1a) (0.30 g, 1.53 mmol) in n-pentane (15 mL). The mixture was
warmed to 55 ºC overnight. CO2 was bubbled through the mixture for 5
min at room temperature, and stirring was continued for 1 h. The solvent
was removed in vacuo and the residue recrystallized from CH2Cl2 at -45
ºC to yield compound 3b as colourless crystals (0.83 g, 92%). M.p. 129 ºC.
[C27H63AlO2Si5 calcd. C 55.23, H 10.81; found C 54.72, H 10.87. 1H NMR
(C6D6, 300K): δ = -0.97 (s, 2H, 2JSiH = 10.6 Hz, CHSi2), 0.29 and 0.37 (s,
18H, 2JSiH = 6.2 Hz, SiMe3), 1.03 and 1.05 (d, 6H, 3JHH = 7.4 Hz, CHMe),
1.08 (s, 9H, CMe3), 1.29 (sept overlap, 2H, 3JHH = 7.4 Hz, CHMe), 6.90 s,
= -0.02 (s, 3H, AlMe), 1.14 (s, 18H, CMe3), 1.23 and 1.27 (d, 12H, 3JHH
=
3
7.3 Hz, CHMe), 1.47 (m overlap, 4H, CHMe), 4.25 (t, 2H, JHH = 3.2 Hz,
GeH), 6.83 (s, 2H, C=CH). 13C{1H} NMR (C6D6, 300 K): δ = -2.8 (AlMe),
15.8 (CHMe), 21.0 and 21.1 (CHMe), 29.9 (C=CH-CMe3), 38.1 (C=CH-
CMe3), 138.2 (s br., C=CH), 168.5 (C=CH).
3
3
1H, JSiH = 4.8 Hz, CHO), 7.20 (s, 1H, JSiH = 27.0 Hz, C=CH). 13C{1H}
1
Synthesis of [tBu(H)C=C(SiHPh2)]2AlEt (5c): A solution of Et2Al-H (0.25
mL, 0.20 g, 2.33 mmol) in n-hexane (20 mL) was added to a cooled (-78
ºC) solution of tBu-CC-Si(H)Ph2 (1c) (0.60 g, 2.27 mmol) in n-hexane (20
mL). The mixture was stirred for 30 min, warmed to room temperature and
stirred for 1 h. The volatiles were removed in vacuo and the residue heated
in vacuum (10–3 Torr) to 100 ºC overnight. The solid residue was
recrystallized from n-hexane at -45 ºC to yield colorless crystals of
compound 5c (1.09 g, 82%). M.p. 89 ºC (dec.). [C38H47AlSi2] calcd. C 77.75,
H 8.07; found C 77.38, H 7.84. 1H NMR (C6D6, 300K) δ = 0.50 (q, 2H, 3JHH
= 8.1 Hz, AlCH2), 0.89 (s, 18H, CMe3), 1.27 (t, 3H, 3JHH = 8.1 Hz, AlCH2Me),
5.63 (s, 2H, 1JSiH = 188 Hz, SiH), 7.01 (s, 2H, 3JSiH = 14.8 Hz, C=CH), 7.20
(m overlap, 4H, p-H), 7.22 (m overlap, 8H, m-H), 7.67 (dd, 8H, 3JHH = 7.7
NMR (C6D6, 300K): δ = 3.1 (s br., CHSi2), 5.3 and 5.7 (s, JSiC = 50 Hz,
SiMe3), 16.2 (CHMe), 18.2 and 19.0 (CHMe), 29.7 (C=CH-CMe3), 38.7
(C=CH-CMe3), 140.5 (s br., C=CH), 169.8 (CHO), 172.9 (C=CH). 29Si{1H}
NMR (C6D6, 300K): δ = 32.9 (SiO), -1.8 and -2.2 (SiMe3). MS (20 eV,
313K): m/z (%): 586 (12) [M]+, 529 (13) [M – CMe3]+, 427 (59) [M –
CH(SiMe3)2]+. IR (cm–1, KBr pellet,): 2953 vs, 2897 vs, 2872 vs, 2806 m
ν(CH); 1620 vs ν(C=O); 1557 s ν(C=C); 1464 s, 1398 s, 1360 vs, 1244 vs
(CH3); 1198 w, 1065 w, 1003 vs, 924 vs, 912 s, 843 vs, 795 vs, 779 vs,
750 vs, 712 vs ν(CC), ρ(CH3Si); 675 vs, 602 vs ν(SiC), ν(SiO); 534 s, 517
s, 467 m, 440 m ν(AlC), ν(AlO), (CC).
Synthesis of [iPr2GeC(AltBu2)=C(H)-tBu]O2CH (3d): 2d was generated
in situ as described above from a solution of tBu2Al-H (0.20 g, 1.41 mmol)
4
Hz, JHH = 1.7 Hz, o-H). 13C{1H} NMR (C6D6, 300K): δ = 8.3 (br., AlCH2),
t
in n-pentane (10 mL) and a solution of Bu-CC-Ge(H)iPr2 (1b) (0.33 g,
9.6 (AlCH2Me), 29.0 (C=CH-CMe3), 38.3 (C=CH-CMe3), 128.2 (m-C),
129.7 (p-C), 133.8 (C=CH), 135.7 (ipso-C), 136.4 (o-C), 175.2 (C=CH).
29Si{1H} NMR (C6D6, 300K): δ = -16.4. MS (20 eV, 313 K): m/z (%): 557 (3)
[M – Et]+. IR (cm–1, KBr pellet): 3133 w, 3067 s, 3050 s, 3017 s, 3000 s,
2957 vs, 2902 vs, 2863 vs, 2732 w, 2697 w ν(CH); 2117 s, 2093 s ν(SiH);
1956 w, 1887 w, 1819 w, 1773 w, 1723 vw, 1673 w, 1652 w, 1611 m, 1590
m, 1546 s ν(C=C), phenyl; 1478 m, 1461 s, 1428 vs, 1360 s, 1330 w, 1304
w, 1256 m, 1237 m (CH3); 1202 m, 1158 w, 1114 vs, 1065 w, 1025 w,
996 m, 940 w, 913 s, 849 vs, 816 vs, 789 vs, 730 vs ν(CC); 699 vs, 631 s,
614 s ν(SiC), phenyl; 508 m, 489 s, 465 s ν(AlC), (CC).
1.37 mmol) in n-pentane (15 mL). CO2 was bubbled through the mixture
for 5 min at room temperature, and stirring was continued for 1 h. The
solvent was removed in vacuo and the residue recrystallized from
pentafluorobenzene at -45 ºC to yield colorless crystals of 3d (0.54 g, 92%).
M.p. 53 ºC. [C21H43AlGeO2] calcd. C 59.04, H 10.15; found C 59.36, H 9.87.
1H NMR (C6D6, 300K): δ = 0.90 (s, 9H, C=C-CMe3), 1.06 and 1.07 (d, 6H,
3JHH = 7.4 Hz, CHMe), 1.32 (s, 18H, AlCMe3), 1.38 (m overlap, 2H, 3JHH
=
7.4 Hz, CHMe), 7.12 (s, 1H, C=CH), 7.40 (s, 1H, CHO). 13C{1H} NMR (C6D6,
300K): δ = 16.2 (HMBC, AlCMe3), 19.2 and 19.6 (CHMe), 24.1 (CHMe),
29.0 (C=CH-CMe3), 31.6 (AlCMe3), 37.7 (C=CH-CMe3), 138.1 (HMBC,
C=CH), 167.2 (C=CH), 171.5 (CHO). MS (20 eV, 303 K): m/z (%): 371
(100) [M – CMe3]+. IR (cm–1, KBr pellet): 2942 vs, 2921 vs, 2865 vs, 2821
vs, 2753 m, 2720 w, 2689 m ν(CH); 1598 vs ν(C=O); 1559 m ν(C=C); 1463
s, 1391 s, 1372 vs, 1233 w (CH3); 1198 w, 1181 w, 1162 vw, 1087 vw,
1004 m, 936 w, 878 m, 813 s, 799 m, 766 w, 716 m ν(CC); 591 s, 546 w,
527 vw, 514 vw, 475 m ν(AlC), ν(AlO), ν(GeC), ν(GeO), (CC).
Synthesis of [iPr2SiC(AltBu2)=C(H)-tBu]2S2CH2 (6a): 2a was
synthesised in situ as described above from a solution of tBu2Al-H (0.15 g,
t
1.06 mmol) in n-hexane (10 mL) and a solution of Bu-CC-Si(H)iPr2 (1a)
(0.21 g, 1.07 mmol) in n-hexane (15 mL). CS2 (0.06 ml, 0.08 g, 1.05 mmol)
was added at -78 ºC. The mixture was warmed to room temperature
overnight. Concentration of the solution and cooling to -30 ºC yielded
yellow crystals of 6a (0.29 g, 73%). M.p. 176 ºC (dec.). [C41H86Al2S2Si2]
calcd. C 65.36, H 11.51; found C 64.95, H 11.34. 1H NMR (C6D6, 300K): δ
= 0.94 (s, 18H, C=CH-CMe3), 1.16 (d, 12H, 3JHH = 7.5 Hz, CHMe), 1.26 (d,
12H, 3JHH = 7.3 Hz, CHMe), 1.33 (s, 36H, AlCMe3), 1.47 (m, 4H, CHMe),
Synthesis of [tBu(H)C=C(SiHiPr2)]2AlMe (5a): A solution of Me2Al-H
(0.13 g, 2.24 mmol) in n-pentane (10 mL) was added to a cooled (-78 ºC)
t
solution of Bu-CC-Si(H)iPr2 (1a) (0.45 g, 2.29 mmol) in n-pentane (20
3
mL). The mixture was warmed to room temperature and stirred for 12 h.
The solvent was removed in vacuo and the residue kept in a dynamic
vacuum (10–3 Torr) for 12 h to complete condensation by removal of AlMe3.
5a remained as a colourless oil which was crystallized from CH2Cl2 at -45
ºC to yield colorless crystals of 5a (0.29 g, 59%) which melted below room
temperature. The highly viscous liquid is difficult to handle. 5a decomposes
slowly at room temperature and is highly sensitive toward the atmosphere.
4.57 (s, 2H, CH2S2), 7.01 (s, 2H, JSiH = 28.0 Hz, C=CH). 13C{1H} NMR
(C6D6, 300K): δ = 16.1 (CHMe), 18.6 (br., AlCMe3), 19.5 and 19.7 (CHMe),
28.3 (CS2), 28.6 (C=CH-CMe3), 31.8 (AlCMe3), 38.0 (C=CH-CMe3), 139.5
(br., C=CH), 170.7 (C=CH). 29Si{1H} NMR (C6D6, 300K): δ = 41.5. MS (20
eV, 373 K): m/z (%): 696 (15) [M – butene]+, 553 (48) [M – HAl(CMe3)2 –
CMe3] – H+]. IR (cm–1, KBr pellet): 2952 vs, 2921 vs, 2913 vs, 2865 vs,
2824 vs, 2759 m, 2726 m, 2695 m ν(CH); 1683 w, 1584 vs, 1555 vs
9
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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
ν(C=C); 1463 vs, 1384 s, 1360 vs, 1326 vw, 1285 vw, 1249 s δ(CH3); 1195
vs, 1129 vw, 1067 m, 1004 vs, 932 m, 886 vs, 811 vs, 784 vs, 710 vs
ν(CC); 678 vs, 649 vs ν(SiC); 581 s, 564 s, 533 m, 512 m, 477 vs ν(AlC),
(CC).
vs, 1561 s, 1548 w ν(C=C); 1461 vs, 1384 m, 1360 s, 1287 vw, 1252 m
δ(CH3); 1198 m, 1173 w, 1069 w, 1009 m, 986 w, 940 w, 921 w, 882 s,
809 m, 786 m ν(CC); 705 s, 658 vs ν(SiC); 589 w, 572 s, 527 vw, 498 vw,
475 s ν(GaC), ν(GaS), (CC).
Synthesis of [iPr2SiC(GatBu2)=C(H)-tBu]2S2CH2 (6c): 2c was
synthesised in situ as described above from a solution of tBu2Ga-H (0.30
g, 1.62 mmol) in n-hexane (10 mL) and a solution of tBu-CC-Si(H)iPr2 (1a)
(0.32 g, 1.63 mmol) in n-hexane (15 mL). CS2 (0.10 ml, 0.12 g, 1.58 mmol)
was added at -78 ºC. The mixture was warmed to room temperature and
warmed to 40 ºC overnight. The solvent was removed in vacuo and the
residue recrystallized from CH2Cl2 at -45 ºC to yield yellow crystals of 6c
(0.40 g, 59%). M.p. 76 ºC (dec.). Elemental analysis gave the correct H
content, but the C content was too low by about 2% in several
determinations. 1H NMR (C6D6, 300K): δ = 0.98 (s, 18H, C=CH-CMe3),
1.19 and 1.29 (12H, d, 3JHH = 7.3 Hz, CHMe), 1.40 (s, 36H, GaCMe3), 1.47
(m, 4H, CHMe), 4.47 (s, 2H, CH2S2), 6.68 (s, 2H, 3JSiH = 26.3 Hz, C=CH).
13C{1H} NMR (C6D6, 300K): δ = 16.1 (CHMe), 19.6 and 19.8 (CHMe), 27.2
(GaCMe3), 28.2 (CS2), 29.0 (C=CH-CMe3), 32.1 (GaCMe3), 37.8 (C=CH-
CMe3), 142.4 (br., C=CH), 167.1 (C=CH). 29Si{1H} NMR (C6D6, 300K): δ =
36.2 (HMBC). MS (20 eV, 353 K): m/z (%): 781 (18) [M – CMe3]+, 595 (32)
[M – HGa(CMe3)2 – CMe3]+. IR (cm–1, KBr pellet): 2965 m, 2942 m, 2898
m, 2867 m, 2838 m ν(CH); 1656 w, 1623 w, 1563 w, 1546 vw ν(C=C);
1474 m, 1443 w, 1370 s, 1281 vs, 1243 m δ(CH3); 1177 vs, 1137 vs, 1007
w, 986 vw, 930 w, 899 m, 867 vw, 847 w, 818 m, 762 vw, 722 w, 703 w
ν(CC); 685 m, 668 w, 637 w, 602 w ν(SiC); 579 w, 510 w, 462 w ν(GaC),
(CC).
Synthesis of HCS2Al[CH(SiMe3)2]2 (8): A solution of [(Me3Si)2CH]2Al-H
(0.20 g, 0.58 mmol) in toluene (15 mL) was added at -78 ºC to a solution
of CS2 (0.035 mL, 0.044 g, 0.58 mmol) in toluene (10 mL). The mixture
was heated to 80 ºC overnight. The volatiles were removed in vacuo, and
the residue was recrystallized from CH2Cl2 at -45 ºC to yield 8 as a yellow
1
solid (0.18 g, 73%). M.p. 202 ºC (dec.). H NMR (C6D6, 300K): δ = -0.72
(s, 2H, CHSi2), 0.22 (s, 36H, SiMe3), 10.08 (s, 1H, HCS2). 13C{1H} NMR
(C6D6, 300K): δ = 1.4 (CHSi2), 4.2 (SiMe3), 239.7 (CS2). 29Si{1H} NMR
(C6D6, 300K): δ = -1.4. MS (20 eV, 298K): m/z (%): 422 (3) [M]+, 407 (10)
[M – Me]+, 263 (100) [M – CH(SiMe3)2]+. IR (cm–1, KBr pellet): 2952 s, 2898
w, 2853 vw, 2817 vw ν(CH); 1424 vw, 1247 vs δ(CH3); 1156 w, 1054 vw;
1004 m δ(CHSi2); 967 m, 926 m, 842 vs, 778 m, 751 w ρ(CH3Si); 672 m,
631 w ν(SiC); 556 w, 518 m ν(AlC), ν(AlS).
X-Ray crystallography. Crystals suitable for X-ray crystallography were
obtained from n-pentane (-30 °C; 3a, 6a, 6d), n-hexane (-30 ºC; 2b),
CH2Cl2 (-45 ºC; 3b, 5a, 6c) or pentafluorobenzene (-45 ºC; 3d, 4a, 7c).
Intensity data was collected on Bruker D8-Venture (2b, 3a, 3b, 3d, 4a, 5a,
6a, 6d, 7c) or Apex II Quazar (6c) diffractometers with monochromated
MoK radiation. The collection method involved  scans. Data reduction
was carried out using the program SAINT+.[43] The crystal structures were
solved by Direct Methods using SHELXTL.[44,45] Non-hydrogen atoms were
first refined isotropically followed by anisotropic refinement by full matrix
least-squares calculation based on F2 using SHELXTL.[44,45] H atoms were
positioned geometrically and allowed to ride on their respective parent
atoms. Compounds 3b, 3d and 6d have each two independent molecules
in the asymmetric unit. The SiHiPr2 and a tBu group of 2b were disordered;
Synthesis of [iPr2GeC(AltBu2)=C(H)-tBu]2S2CH2 (6d): 2d was
synthesised in situ as described above from a solution of tBu2Al-H (0.15 g,
1.06 mmol) in n-pentane (10 mL) and a solution of tBu-CC-Ge(H)iPr2 (1b)
(0.25 g, 1.04 mmol) in n-pentane (15 mL). CS2 (0.06 ml, 0.08 g, 1.05 mmol)
was added at -78 ºC. The solution was warmed to room temperature and
stirred overnight. Concentration and cooling of the solution to -30 ºC
yielded yellow crystals of 6d (0.36 g, 82%). M.p. 193 ºC (dec.).
[C41H86Al2Ge2S2] calcd. C 58.45, H 10.29; found C 57.98, H 10.17.1H NMR
(C6D6, 300K): δ = 0.91 (s, 18H, C=CH-CMe3), 1.23 (d, 12H, 3JHH = 7.4 Hz,
CHMe), 1.34 (s, 36H, AlCMe3), 1.37 (d, 12H, 3JHH = 7.3 Hz, CHMe), 1.83
(sept, 4H, 3JHH = 7.4 Hz, CHMe), 4.54 (s, 2H, CH2S2), 6.98 (s, 2H, C=CH).
13C{1H} NMR (C6D6, 300K): δ = 18.5 (br., AlCMe3), 20.3 and 20.7 (CHMe),
22.7 (CHMe), 27.1 (CH2S2), 28.8 (C=CH-CMe3), 31.7 (AlCMe3), 37.0
(C=CH-CMe3), 142.9 (C=CH), 166.0 (C=CH). MS (20 eV, 393K): m/z (%):
785 (4) [M – CMe3]+, 643 (5) [M – HAl(CMe3)2 – CMe3]+. IR (cm–1, KBr
pellet): 2948 vs, 2919 vs, 2865 vs, 2825 vs, 2755 w, 2726 w, 2694 w ν(CH);
1685 vw, 1654 vw, 1588 s, 1558 s ν(C=C); 1463 vs, 1384 m, 1359 m, 1340
vw, 1311 w, 1247 s δ(CH3); 1228 s, 1191 s, 1158 m, 1093 vw, 1004 s, 933
w, 879 m, 811 s, 786 m, 718 s ν(CC); 684 w, 643 vw, 574 s, 543 m, 504 w
ν(AlC), ν(GeC), (CC).
t
the atoms were refined on split positions (0.64:0.36; 0.60:0.40). A Bu
group of 3b was disordered (0.78:0.22). One of the iPr2Si(H)-C=C(H)-tBu
fragments of 5a was disordered (0.93:0.07). A complete molecular half and
i
an Pr group of 6a and 6c were disordered (0.81:0.19 and 0.55:0.45;
0.82:0.18 and 0.58:0.42). CCDC 2015895 (2b), 2015896 (3a), 2015897
(3b), 2015898 (3d), 2015899 (4a), 2015900 (5a), 2015901 (6a), 2015902
(6c), 2015903 (6d), 2015904 (7c) contain the supplementary
crystallographic data for this paper. This data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information (see footnote on the first page of this article):
NMR spectra.
Keywords: Carbon dioxide activation ⸱ silanes ⸱ aluminium ⸱
formates ⸱ thioacetals
Synthesis of [iPr2SiC(GatBu)(µ-S)]=C(H)-tBu]2 (7c): 2c was synthesised
in situ as described above from a solution of tBu2Ga-H (0.25 g, 1.35 mmol)
in n-hexane (10 mL) and a solution of tBu-CC-Si(H)iPr2 (1a) (0.27 g, 1.37
mmol) in n-hexane (15 mL). CS2 (0.09 ml, 0.11 g, 1.44 mmol) was added
at -78 ºC, the mixture was warmed to room temperature and stirred at 70
ºC overnight. The solvent was removed in vacuo and the residue
recrystallized from CH2Cl2 at -45 ºC to yield colourless crystals of
compound 7c (0.37 g, 77%). M.p. 149 ºC (dec.). [C32H66Ga2S2Si2] calcd.
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C 54.09, H 9.36; found C 53.61, H 9.33. H NMR (C6D6, 300K): δ = 1.02
(s, 18H, C=CH-CMe3), 1.19 (m overlap, 6H, CHMe), 1.21 (m overlap, 12H,
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2865 vs, 2840 vs, 2765 w, 2705 w ν(CH); 1684 w, 1669 vw, 1654 w, 1590
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This article is protected by copyright. All rights reserved.

10.1002/ejic.202000723
European Journal of Inorganic Chemistry
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This article is protected by copyright. All rights reserved.

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10.1002/ejic.202000723
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents
Key topic: CO2 activation
Cooperation between Lewis acidic Al or Ga atoms and Si-H or Ge-H bonds of functionalized silanes and germanes facilitates the
reduction of carbon dioxide or carbon disulfide to formates, acetals and dithioacetals under mild conditions. The starting compounds
are easily accessible by hydroalumination of alkynylsilanes and –germanes.
13
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