Organogermanium(II) Hydrides as a Source of Highly Soluble LiH

Article abstract of DOI:10.1002/chem.202000970

The reactions of monomeric C,N-chelated organogermanium(II) hydride L(H)Ge?BH₃ with organolithium salts RLi yielded lithium hydrogermanatoborates (Li(THF)₂{BH₃[L(H)GeR]})₂. Compound (Li(THF)₂{BH₃[L(H)GePh]})₂ was used as a source of LiH for the reduction of organic C=O or C=N bonds in nonpolar solvents accompanied by the elimination of a neutral complex L(Ph)Ge?BH₃. The interaction of (Li(THF)₂{BH₃[L(H)GePh]})₂ with the polar C=O bond was further investigated by computational studies revealing a plausible geometry of a pre-reactive intermediate. The experimental and theoretical studies suggest that, although the Li atom of (Li(THF)₂{BH₃[L(H)GePh]})₂ coordinates the C=O bond, the GeH fragment is the active species in the reduction reaction. Finally, benzaldehyde was reduced by a mixture of L(H)Ge?BH₃ with PhLi in nonpolar solvents.

Full text of DOI:10.1002/chem.202000970

A Journal of
Accepted Article
Title: Organogermanium(II) Hydrides as a Source of Highly Soluble LiH
Authors: Roman Jambor, Jakub Tremmel, Jiří Tydlitát, Libor Dostál,
Aleš Růžička, Xavier Deraet, and Jan Turek
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RESEARCH ARTICLE
Organogermanium(II) Hydrides as a Source of Highly Soluble LiH
Jakub Tremmel,[a] Jiří Tydlitát,[b] Libor Dostál,[a] Aleš Růžička,[a] Xavier Deraet,[c] Jan Turek,[c]* Roman
Jambor[a]*
[a]
Mr. J. Tremmel, Dr. L. Dostal, prof. A. Ruzicka, prof. R. Jambor, Department of General and Inorganic Chemistry, University of Pardubice, 532 10
Pardubice, Czech Republic, E-mail: roman.jambor@upce.cz,
[b]
[c]
Dr. J. Tydlitat, Institute of Organic Chemistry and Techology, University of Pardubice, 532 10 Pardubice, Czech Republic,
Mr. X. Deraet, Dr. J. Turek, Eenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium, E-mail: jan.turek@vub.be
Supporting information for this article is given via a link at the end of the document.
Abstract: The reactions of the monomeric C,N-chelated
organogermanium(II) hydride L(H)Ge·BH3 with organolithium salts
=
Ph, tBu, nBu). These reactions yielded lithium
hydrogermanatoborates {Li(THF)2{BH3[L(H)GeR]}}2 that were
used as a source of highly soluble LiH in nonpolar solvents.
RLi
yielded
lithium
hydrogermanatoborates
{Li(THF)2{BH3[L(H)GeR]}}2. Compound {Li(THF)2{BH3[L(H)GePh]}}2
was used as a source of LiH for the reduction of organic C=O or C=N
bonds in non-polar solvents accompanied by the elimination of a
Results and Discussion
neutral
complex
L(Ph)Ge·BH3.
The
interaction
of
{Li(THF)2{BH3[L(H)GePh]}}2 with the C=O polar bond was further
investigated by computational studies revealing a plausible geometry
of a pre-reactive intermediate. The experimental and theoretical
studies suggest that while the Li atom of {Li(THF)2{BH3[L(H)GePh]}}
coordinates the C=O bond, the GeH fragment is the active species in
the reduction reaction. Finally, benzaldehyde was reduced by the
mixture of L(H)Ge·BH3 with PhLi in non-polar solvents.
We have previously reported on the synthesis of monomeric
germanium
hydride
complexes
L(H)Ge·W(CO)5
and
L(H)Ge·Cr(CO)5.[9] Similarly, the reaction of L(Cl)Ge[10] with BH3
yielded complex L(Cl)Ge·BH3 (1) that was converted by the
subsequent reaction with Li[Et3BH] into the monomeric
germanium hydride L(H)Ge·BH3 (2) (Scheme 1). Complex 2 was
characterized by the help of NMR spectroscopy and X-ray
diffraction analysis. The most relevant NMR data are the 1H NMR
resonance at  6.59 ppm attributed to the GeH hydridic proton
and a signal of the BH3 group at  –38.3 ppm in the 11B{1H}
spectrum.
Introduction
Low valent group 14 hydrides belong to an important class of
organometallic compounds due to their reactivity towards various
organic substrates.[1] It is well known that unsaturated organic
bonds may interact with these compounds without any catalyst
and that the substrate inserts into the E–H bond during the first
step of a hydroelementation catalytic cycle.[2] However, the main
disadvantage of this catalytic cycle is the recovering of the low-
valent group 14 hydrides through metathesis reactions, which do
not take place so prominently despite the progress made by
groups of Power,[3] Aldridge,[4] Roesky,[5] Rivard[6] or Jones.[7]
Besides these stoichiometric reductions, the recent studies of
Jones demonstrated that the two-coordinate (amido)(hydrido)-
tetrylenes [(L*)(H)E:] (E = Ge, Sn, L* = [N(Ar)(SiMe3)], Ar =
[C6H2Me{C(H)Ph2}2-2,4,6]) may be used as efficient catalysts in
the hydroboration of aldehydes or ketones RR1C=O by the pinacol
borane (HBpin).[8] It was reported that the [(L*)(H)E:] catalyst
reacts with aldehydes or ketones RR1C=O resulting in the
formation of (amido)(alkoxy)tetrylene [(L*)(RR1CHO)E:] in the first
step.[8] The regeneration of the [(L*)(H)E:] catalyst was achieved
through the reaction of [(L*)(RR1CHO)E:] with HBpin along with
the elimination of RR1CHOBpin.[8] Moreover, the kinetic studies
also suggested that the metathesis reaction is the rate
determining step of this particular hydroboration.
NEt2
NEt2
NEt2
.
BH3 SMe2
Li[BHEt3]
BH3
BH3
tBu
Ge
Cl
tBu
Ge
Cl
tBu
Ge
H
- LiCl, BEt3
tBu
L(Cl)Ge
tBu
tBu
L(Cl)Ge . BH3 (1)
L(H)Ge . BH3 (2)
Scheme 1. Synthesis of the monomeric L(H)Ge·BH3 (2)
The molecular structure of the germanium(II) hydride 2 showed
that it retains its monomeric form in the solid state as well (Figure
1, Left). The selected bond lengths and angles are given in the
caption of Figure 1, while the M06/cc-pVDZ(-PP) optimized
geometry of 2 along with relevant bonding distances is shown in
the right part of Figure 1.
As such, the studies of the reactions between the low valent group
14 compounds and various inorganic substrates may provide the
last key aspect of the full catalytic cycle, which is essential for their
application as catalysts in various organic transformations. Here
we present our results of the reactivity studies of the borane
adduct of the N→Ge coordinated germanium hydride L(H)Ge·BH3
with organolithium salts RLi (L = [2-(CH2NEt2)-4,6-tBu2-C6H2]- , R
Figure 1. (Left) ORTEP presentation of the molecular structure of 2. Selected
bonding distances (in Å): Ge(1)-C(1) 1.9674(18); Ge(1)-N(1) 2.0686(16); Ge(1)-
H(1) 1.54(2); Ge(1)-B(1) 2.050(2). (Right) M06/cc-pVDZ(-PP) optimized
geometry of 2 along with relevant distances (in Å).
1
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10.1002/chem.202000970
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RESEARCH ARTICLE
in the dimeric structures of 3 – 5 are involved in the Li–H–B
contacts (the Li–B distances range from 2.434(10) to 2.523(7) Å)
resulting in a formation of the ten-membered Li2B2H6 cluster
(Figure 2). The Li and B atoms are placed at antipodal positions
with the Li–Li distances ranging from 3.087(12) to 3.244(11) Å and
the B–B distances in the range of 3.777(7) – 3.844(6) Å,
structurally resembling the arrangement of the inorganic complex
{TMEDA·LiBH4}2,[23] but deviating from the monomeric structure of
alkyltrihydroborate [(THF)3Li(-H)3BC(SiMe2Ph)3][24] or dimeric
structure of [{[(Me3Si)2N]AlH3Li·2OEt2}2] with eight-membered
Li2Al2H4 ring.[25]
The Ge(1) atom is four coordinate by the C(1) and N(1) atom of
the ligand L and by the B(1) and H(1) atoms. The Ge(1)-H(1) bond
distance of 1.54 Å and the Ge(1)-B(1) bond length of 2.050(2) Å,
which is close to the sum of the covalent radii of the parent atoms
(covGe,B = 2.06 Å),[11] are similar to those found in related BH3
complexes
of
the
germanium(II)
hydrides
[2,6-
(Me2N)2C6H3]2Ge·BH3[12], IPr·GeH2·BH3,[13] IPr·GeH2·W(CO)5,[14]
IPr·GeH(BH3)NHDipp,[15]
Ph3PCMe2·GeH2·BH3,[17] and IPr·GeH(OSiMe3)·BH3
IPrCH2·H2Ge−GeH2·W(CO)5,[16]
[18]
(IPr =
[(HCNDipp)2C:]; Dipp = 2,6-iPr2C6H3) with the Ge-B and Ge-H
distances in the range of 2.032(3) - 2.0786(17) and 1.42(3) -
1.60(4) Å, respectively. It should also be noted that compound 2
is air and moisture stable.
The reaction of 2 with organolithium salts RLi (R = Ph, nBu, tBu)
provided
lithium
hydrogermanatoborates
{Li(THF)2{BH3[L(H)GeR]}}2 (R = Ph(3), nBu(4), tBu(5)) as the
addition products (Scheme 2). Compounds 3 - 5, characterised
by the help of NMR spectroscopy and X-ray diffraction analysis,
are highly soluble in non-polar solvents such as hexane or toluene.
THF
THF
Li+
Et2
N
tBu
H
R
H
NEt2
Ge-
H
H
B
+ RLi, THF
tBu
Ge-
BH3
tBu
H
B
Li+
H
tBu
Ge
H
Figure 2. General motif of Li2B2H6 core found in the molecular structures of 3 –
H
R
H
tBu
5
NEt2
THF
THF
tBu
2
{Li(THF)2{BH3[L(H)GeR]}}2
R = Ph(3), nBu(4), tBu(5)
The Ge atom is four-coordinate by two carbon atoms of the L and
R groups, and by the hydrogen and boron atom. As suggested by
the NMR data, the R group influences the GeH moiety. In 3 (R =
Ph), the GeH atom has the longest Ge(1)-H(1) (1.50(3) Å) and
B(1)-H(1) (2.94(4) Å) bond distances, while shorter Ge(1)-H(1)
and B(1)-H(1) distances were found in 4 (R = nBu; 1.46(4) and
2.85(4) Å, respectively) and 5 (R = tBu; 1.41(4) and 2.86(5) Å).
The BH3 protons have the B–H distances in the range of 1.09(4)
– 1.15(5) Å, while the Ge–C bond lenghts are ranging from
1.972(3) to 2.028(4) Å (values typical for a covalent bond).[11] The
Ge–B bond distances of 2.058(5) - 2.069(4) Å indicate the
presence of a strong Ge→B donation in 3 – 5 (covGe,B = 2.06
Å).[11] Since the similar value was found in starting 2 (2.050(2) Å),
one can propose that the Ge→B donation is not affected by the
addition of RLi. This strongly contrasts with the N→Ge donation,
that is present in 2 (2.069(2) Å), but is missing in 3 – 5 (distances
up to 4 Å). Consequently, the addition of the R group is
accompanied by the decoordination of the NEt2 group from the
Ge coordination sphere emphasizing the importance of the
flexibility of the ligand L.
Scheme 2. Synthesis of hydrogermanatoborates {Li(THF)2{BH3[L(H)GeR]}}2 (R
= Ph(3), nBu(4), tBu(5)) as the addition products of RLi to 2.
1
The H NMR spectra of C6D6 solutions of 3 – 5 showed that the
GeH hydridic proton resonates at  5.65 (3), 5.03 (4) and 4.93 (5)
ppm, respectively, as a consequence of different R group in 3 – 5.
All signals are shifted upfield as compared with the neutral
complex 2 ( 6.59). The 1H NMR also showed the presence of a
quartet of the BH3 protons at  0.34 (3), 0.12 (4), 0.19 (5) ppm
with 1J(11B, 1H) ~ 80 Hz. The 11B NMR spectra of 3 – 5 proved the
presence of the BH3 group by showing quartets at  -41.4 (3),  -
40.7 (4),  -41.5 (5), shifted upfield in comparison with 2. These
data indicate the higher electron density on the BH3 moiety. For
comparison, the BH protons in the neutral borane adduct 2-
B5H8GeHMe2 resonate at  ~ 7 ppm.[19] The only analogue,
monomeric
complex
[{HC(C(CH2)NAr)CMeNAr}Ge(H)BH3]Li(OEt2)3
(Ar
=
2,6-
1
iPr2C6H3), showed similar resonances for the BH3 group ( H
ranging from -0.65 to -1.15 ppm,  11B at -43.68 ppm),[20] but the
GeH proton resonated downfield at  6.70 ppm in comparison to
3 – 5. Finally, the 7Li{1H} NMR spectrum showed the signals at 
-0.03 (3), - 0.16 (4), -0.14 (5), shifted downfield in comparison with
the monomeric [{HC(C(CH2)NAr)CMeNAr}Ge(H)BH3]Li(OEt2)3 (
-1.41).[20]
Single crystalline material suitable for XRD analysis was grown
from the hexane/toluene solutions of 3 – 5 at -20°C (Figures 2, 3
and Figures S1, S2 in SI); selected bond lengths are summarized
in Table 1. The Li atom is six-coordinate by two oxygen atoms
from the THF and by hydrogen atoms of two 2-BH3 groups. The
range of the Li–H distances in 3 - 5 (1.97 (5) – 2.12(4) Å is
comparable with those found in the hexane-soluble LiH
[21]
complexes
[{(DippNPPh2)Li}4(LiH)4]·C6H6
[22]
[{[(Me3Si)2N]2AlH}3(LiH)4][22] and [[{(Me3Si)2N}2AlH2]Li]n
(a
Figure 3. ORTEP presentation of the molecular structure of 3
range of 1.81(4) – 2.26(2) Å). The hydrogen atoms of BH3 groups
2
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RESEARCH ARTICLE
substituents. Since the only structurally related compound was
shown to be monomeric,[20,25] we have also optimized a plausible
monomeric compound 3-mon. As shown in Figure 4, the bonding
pattern in the monomeric compound is almost identical as in the
dimer, apart from the obvious shortening of the B···Li contact of
ca. 0.1 Å. Interestingly, the 2-coordination of the BH3 group
resulting in the bending of the Ge→B···Li angle (130.9) is also
preserved in 3-mon in contrasts to the angle of 161.0 found for
[{HC(C(CH2)NAr)CMeNAr}Ge(H)BH3]Li(OEt2)3.[20] Moreover, the
relative Gibbs free energy of 3 was found to be 2.6 kcal mol-1
lower in energy than that of 3-mon, which confirms the formation
of the dimeric compounds both in solution and solid state.
It is evident that the reaction of 2 with RLi salts is of a general
character. The RLi salt attacks compound 2 and the nucleophilic
addition of the R group to the Ge(II) atom takes place. This
converts the neutral L(H)Ge(II) moiety into the organogermanato
[L(H)Ge(II)R]- anion. As the latter moiety contains the Ge(II) atom,
it may coordinate to the BH3 group to provide hydrogermanato-
borates {BH3[L(H)GeR]}- compensated by the Li+ cation.
Table 1. Selected bond lengths of 3 – 5 (in Å)
Compound/
Bond length
3
4
5
Ge(1)-B(1)
Li(1)-B(1)
2.069(4)
2.481(9)
2.523(7)
2.007(3)
1.973(3)
1.50(3)
2.058(5)
2.482(9)
2.497(9)
2.023(4)
1.988(5)
1.46(4)
2.068(5)
2.460(9)
2.434(10)
2.028(4)
2.022(4)
1.41(6)
Li(1)-B(1A)
Ge(1)-C(1)
Ge(1)-C(20)
Ge(1)-H(1)
B(1)-H(1)
Figure 4. Optimized geometries of 3 and 3-mon along with the selected
distances (in Å) and relative Gibbs free energies (in kcal mol-1; calculated in THF
at the M06/cc-pVTZ(-PP) level)
2.94(4)
2.85(4)
2.86(5)
B(1)-H(1A-1C)
1.15(5) –
1.09(4) –
1.10(6) –
1.14(4)
1.10(5)
1.14(6)
The natural bond orbital (NBO) analysis[28] of the starting
compounds 1 and 2 (Figure S4 in SI) revealed a strong
intramolecular nN→p*Ge donor-acceptor interaction that provides
a stabilization energy of 56.6 and 79.8 kcal mol-1 for 1 and 2,
respectively. The strength and a high degree of covalent
character of the Ge→B interaction is supported by the computed
Wiberg bond index (WBI)[29] showing WBIGe-B values higher than
0.9 (Table S2 in SI). This also results in the increase of the
positive natural population analysis (NPA)[28] charge on the
germanium centre in comparison to L(Cl)Ge. The NBO analysis
of 3 – 5 showed an additional (Ge–CR) NBO, which is highly
polarized with the electron density mainly localized on the carbon
atom (ca. 70 %) (Figure S4 in SI). The formation of the new Ge–
CR covalent bond in 3 – 5 instead of the N→Ge interaction in 1
and 2 leads to the higher energies of (Ge–H) and (Ge→B)
NBOs. However, in agreement with the geometrical data, the
WBIGe-B (0.97) and WBIGe-H (0.90) values of 3 – 5 are equal to
those found for 2. The negative NPA charge on the boron atom
(ca. -0.8 e), as a result of a strong Ge→B interaction, is
compensated by the positive NPA charge on the lithium atom (ca.
0.9 e), which suggest an ionic interaction between the BH3 group
and the lithium atom in 3 – 5 (This is further confirmed by a
molecular electrostatic potential map of the simplified complex 3’;
Figure S5 in SI).
Li(1)-H(1A)a
Li(1)-H(1B)a
Li(1)-H(1C)
B(1)-B(1a)
Li(1)-Li(1a)
1.98(5)
2.05(6)
2.10(4)
3.844(6)
3.203(8)
1.99(6)
1.98(4)
2.04(5)
2.04(5)
2.12(4)
2.02(5)
3.777(7)
3.244(11)
3.797(7)
3.087(12)
This strongly contrasts with the reaction of tBuLi and
[{HC(CMeNAr)2}GeH(BH3)] (Ar = 2,6-iPr2C6H3) that provided
[{HC(C(CH2)NAr)CMeNAr}Ge(H)BH3]Li(OEt2)3 along with the
elimination of tBuH, without any evidence of tBu addition to the
Ge(II)
[Ge{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}Cl] with an excess of
PhC≡CLi afforded the lithium germinate
centre.[20]
Similarly,
the
reaction
of
[{(PhC≡C)3Ge}3GeLi(Et2O)3] as the side product of the elimination
of the amido ligand.[26] These rare examples demonstrate the
stability of 2 that can be easily transformed by nucleophilic
addition of RLi to 3 – 5, without any side reactions.
Given the unique structural motif of 3 – 5, a DFT computational
study was performed to gain a better understanding of their
molecular structure and bonding. The geometries of all studied
complexes were fully optimized at the M06/cc-pVDZ(-PP)[27] level
of theory, which was chosen on the basis of our previous studies
of the transition metal complexes of the type L(H)Ge·TM(CO)5.[9]
The agreement between the experimental X-ray diffraction data
and the calculated structural parameters is very good (Figures 1
and 5, Figure S3 in SI). The structure of all compounds is very
similar, showing a four-coordinate Ge centre with a distorted
tetrahedral geometry. In line with the experimental data, a minor
elongation of the Ge–CR bond was observed going from 3 to 5,
while the Ge→B interaction was not affected by the different R
As the compounds 3 – 5 contain either B-H or Ge-H bonds, the
ability of 3 to reduce C=O and C=N bonds in nonpolar solvents
(hexane or toluene) was assessed in the stoichiometric reaction
of 3 with benzaldehyde or iminopyridine (Scheme 3, for
experimental details see SI). Interestingly, a new complex
L(Ph)Ge·BH3 (6) was isolated from this reaction (for experimental
detail see SI), while the GC-MS analysis of the hydrolysed mixture
proved complete reduction of the starting material (Scheme 3,
Figures S6 and S7 in SI).
3
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RESEARCH ARTICLE
THF
THF
Et2
N
H
NEt2
YM
tBu
Ph
H
Y
Li+
B
H
H
hexane
0.5 h
Ge-
H
H
B
tBu
+
H
tBu
Ge
Ph
X
X
tBu
Ge-
+
H
B
Li+
H
H
Ph
tBu
tBu
H
NEt2
THF THF
Y = O, N(Dipp)
X = C, N
L(Ph)GeBH3 (6)
3
M
=
Li or
H
(after hydrolysis)
Figure 6. Optimized geometries of a pre-reactive intermediate 3INT and its
monomeric analogue 3INT-mon along with the selected distances (in Å) and
relative Gibbs free energies (in kcal mol-1; calculated in hexane at the M06/cc-
pVTZ(-PP) level)
Since we have also found out that complex 3 can be recovered
by the reaction of 6 with LiAlH4 (for experimental details see SI),
a plausible reaction mechanism of the reduction can be described
according to Scheme 4, based on experimental and theoretical
studies.
Scheme 3. Reduction ability of 3 towards C=Y polar bonds along with the GC-
MS analysis of the reduced materials obtained from the reaction mixture.
Complex 6 was fully characterised by NMR spectroscopy, XRD
analysis (Figure 5, Left) and DFT calculations (Figure 5, Right).
The Ge atom in 6 is four-coordinate, proving again the importance
of the flexibility of the pendant NEt2 group (for the NBO analysis
of 6 see Figure S4 and Table S2 in SI).
THF
Y
Et2
N
tBu
Ph
Ge-
H
Li+
H
H
H
B
tBu
tBu
Ge-
H
B
Li+
H
H
Ph
tBu
H
Y
NEt2
THF
+
Y
THF
THF
Li+
Et2
N
tBu
Ph
YLi
H
YH
H
Ge-
H
H
B
tBu
tBu
Ge-
H
B
Li+
NEt2
H
H
H
+ H2O
Ph
tBu
H
H
B
NEt2
+ LiAlH4
THF THF
tBu
Ge
Ph
H
3
tBu
6
Scheme 4. Suggested mechanism of the reduction of C=Y bonds by 3
Compounds 3 – 5 represent a good hydrocarbon-soluble LiH
source, which can be used for the reduction of C=Y polar bonds
in non-polar solvents, similarly to systems reported by Stach[21] or
Mulvey[30], who used either [{(DippNPPh2)Li}4(LiH)4]·C6H6[21] or 1-
Figure 5A. (Left) ORTEP presentation of the molecular structure of 6. Selected
bonding distances (in Å): Ge(1)-C(1) 1.976(2); Ge(1)-N(1) 2.0844(17); Ge(1)-
C(1) 1.966(2); Ge(1)-B(1) 2.047(3). (Right) M06/cc-pVDZ(-PP) optimized
geometry of 6 along with relevant distances (in Å).
lithio-2-alkyl-1,2-dihydropyridine
2-tBuC5H5NLi·Me6TREN
(Me6TREN is tris(N,N-dimethyl-2-aminoethyl)amine)[30] for the
reduction of benzophenone in the non-polar solvents.
The isolation of 6 from the reaction mixture suggests that LiH
eliminates from
3 during the reaction and therefore the
Finally, to prove the simplicity of the reduction process, the PhLi
was mixed with complex 2 to generate complex 3 in situ, and the
benzaldehyde was added. The organic fraction was examined by
GC-MS analysis after 30 minutes (Scheme 5, Entry 2) and the
peak of the benzyl alcohol (Rt ~ 5.7 min, [M]+ = 108 Da) was
determined in ~ 90% (Figure S8 in SI). For comparison, the
reduction of benzaldehyde with 9-borabicyclo(3.3.1)nonane (9-
BBN) was performed under the same conditions and the GC-MS
analysis provided the evidence of benzyl alcohol (Rt ~ 5.7 min,
[M]+ = 108 Da, ~ 10%) and its boronic ester (Rt ~ 13.5 min, [M-
2H]+ = 226 Da, ~ 88%) (Figure S9 in SI) due to the insufficient
hydrolysis of the B-O bond (Scheme 5, Entry 3). The reduction of
benzaldehyde by HBpin is much slower and with a conversion of
95% after 8 hours.[31]
unsaturated C=Y bonds are reduced by LiH. According to the DFT
calculations, the reduction of the C=O polar bond of
benzaldehyde by 3 might proceed via a pre-reactive intermediate
where one of the THF molecules is replaced by the benzaldehyde
(Figure 6 and Table S2 in SI). Analogous to 3, the intermediate
3INT is suggested to retain its dimeric structure with the related
monomer 3INT-mon being higher in energy by 6.7 kcal mol-1. The
structure of 3INT closely resembles that of 3 with elongated B-Li
distances, which is most probably caused by a stronger
interaction of the benzaldehyde with the Li atom in comparison to
the THF. Furthermore, the orientation of the carbonyl function
towards the GeH hydridic proton (Ge-H···CHO distance of 2.75
Å) is in line with the formation of 6.
4
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O
OH
OR
[2]
[3]
T. J. Hadlington, M. Driess, C. Jones, Chem. Soc. Rev. 2018, 47, 4176 -
4197.
0.5 h, toluene
+ reducing agent
+
R = Li, BBN, Bpin
a) G. H. Spikes, J. C. Fettinger, P. P. Power, J. Am. Chem. Soc. 2005,
127, 12232–12233; b) Y. Peng, M. Brynda, B. D. Ellis, J. C. Fettinger, E.
Rivard, P. P. Power, Chem. Commun. 2008, 6042–6044; c) P. P. Power,
Nature 2010, 463, 171–177; d) Y. Peng, B. D. Ellis, X. Wang, P. P.
Power, J. Am. Chem. Soc. 2008, 130, 12268–12269; e) Y. Peng, J.-D.
Guo, B. D. Ellis, Z. Zhu, J. C. Fettinger, S. Nagase, P. P. Power, J. Am.
Chem. Soc. 2009, 131, 16272–16282; f) B. E. Eichler, P. P. Power, J.
Am. Chem. Soc. 2000, 122, 8785–8786. g) F. Lips, J. C. Fettinger, A.
Mansikkamaki, H. M. Tuononen, P. P. Power, J. Am. Chem. Soc. 2014,
136, 634–637; h) E. Rivard, P. P. Power, Dalton Trans. 2008, 4336–
4343; i) O. T. Summerscales, C. A. Caputo, C. E. Knapp, J. C. Fettinger,
P. P. Power, J. Am. Chem. Soc. 2012, 134, 14595–14603; j) L. Pu, B.
Twamley, P. P. Power, J. Am. Chem. Soc. 2000, 122, 3524–3525.
A. V. Protchenko, K. H. Birjkumar, D. Dange, A. D. Schwarz, D. Vidovic,
C. Jones, N. Kaltsoyannis, P.Mountford, S. Aldridge, J. Am. Chem. Soc.
2012, 134, 6500–6503; b) A. V. Protchenko, J. I. Bates, L. M. A. Saleh,
M. P. Blake, A. D. Schwarz, E. L. Kolychev, A. L. Thompson, C. Jones,
P. Mountford, S. Aldridge, J. Am. Chem. Soc. 2016, 138, 4555–4564; c)
J. A. B. Abdalla, I. M. Riddlestone, R. Tirfoin, S. Aldridge, Angew. Chem.,
Int. Ed. 2015, 54, 5098–5102.
+ H2O
A
B
Entry
Reducing
agent
Time (h)
% conversion
(ratio of A:B)
1
3
0.5
0.5
0.5
8
>99 (100:0)
>90 (100:0)
>90 (10:90)
95 (0:100)
2
2/PhLi
9-BBN
HBpin
3
4[31]
[4]
[5]
benzaldehyde (1 mmol) and reducing agent (1.1 mmol); % conversions and ratios were obtained by GC MS
Scheme 5. Reduction ability of system 2/PhLi towards C=O polar bond.
Thus, the complex 3 is a very strong reducing agent in non-polar
solvent and its key advantage is that it can be easily prepared by
mixing of 2 with PhLi in hexane.
a) R. S. Ghadwal, H. W. Roesky, S. Merkel, J. Henn, D. Stalke, Angew.
Chem., Int. Ed. 2009, 121, 5793–5796; b) R. S. Ghadwal, R. Azhakar, H.
W. Roesky, Acc. Chem. Res. 2013, 46, 444–456; d) A. Jana, D. Leusser,
I. Objartel, H. W. Roesky, D. Stalke, Dalton Trans. 2011, 40, 5458–5463;
e) L. W. Pineda, V. Jancik, K. Starke, R. B. Oswald, H. W. Roesky,
Angew. Chem., Int. Ed. 2006, 45, 2602–2605; f) A. Jana, D. Ghoshal, H.
W. Roesky, I. Objartel, G. Schwab, D. Stalke, J. Am. Chem. Soc. 2009,
131, 1288–1293; g) A. Jana, G. Tavcar, H. W. Roesky, M. John, Dalton
Trans. 2010, 39, 9487–9489; h) A. Jana, H. W. Roesky, C. Schulzke, A.
Dring, Angew. Chem., Int. Ed. 2009, 48, 1106–1109.
Conclusion
In conclusion, we have reported on the synthesis of complexes
{Li(THF)2{BH3[L(H)GeR]}}2 that are easily formed by the reaction
of L(H)Ge·BH3 with RLi. The polarity of their Ge-H bonds depends
on the R group, based on NMR and XRD analysis. These
compounds represent a non-polar solvent-soluble LiH source that
can be further used for the reduction of organic C=O or C=N
bonds together with the elimination of a neutral complex
L(Ph)Ge·BH3. As the complexes {Li(THF)2{BH3[L(H)GeR]}}2 may
be easily prepared, the system of 2/PhLi was successfully tested
in the reduction of the benzaldehyde as well. Reactions of 2 with
nucleophiles of different alkali metals to obtain soluble Group 1
metal hydrides are of our current interest.
[6]
a) Y. Peng, M. Brynda, B. D. Ellis, J. C. Fettinger, E. Rivard, P. P. Power,
Chem. Commun. 2008, 6042–6044; b) K. C. Thimer, S. M. I. Al-Rafia, M.
J. Ferguson, R. McDonald, E. Rivard, Chem. Commun. 2009, 7119–
7121; c) d); e) S. M. I. Al-Rafia, A. C. Malcolm, S. K. Liew, M. J. Ferguson,
R. McDonald, E. Rivard, Chem. Commun. 2011, 47, 6987–6989; f) E.
Rivard, P. P. Power, Dalton Trans., 2008, 4336–4343; g) S. M. I. Al-
Rafia, A. C. Malcolm, R. McDonald, M. J. Ferguson, E. Rivard, Angew.
Chem., Int. Ed. 2011, 50, 8354–8357; h) i) E. Rivard, R. C. Fischer, R.
Wolf, Y. Peng, W. A. Merrill, N. D. Schley, Z. Zhu, L. Pu, J. C. Fettinger,
S. J. Teat, I. Nowik, R. H. Herber, N. Takagi, S. Nagase, P. P. Power, J.
Am. Chem. Soc. 2007, 129, 16197–16208; j) S. M. I. Al-Rafia, O.
Shynkaruk, S. M. McDonald, S. K. Liew, M. J. Ferguson, R. McDonald,
R. H. Herber, E. Rivard, Inorg. Chem. 2013, 52, 5581–5589.
[7]
a) J. Li, C. Schenk, C. Goedecke, G. Frenking, C. Jones, J. Am. Chem.
Soc. 2011, 133, 18622–18625; b) T. J. Hadlington, C. Jones, Chem.
Commun. 2014, 50, 2321–2323; c) T. J. Hadlington, M. Hermann, G.
Frenking, C. Jones, Chem. Sci. 2015, 6, 7249–7257; d) T. J. Hadlington,
M. Hermann, G. Frenking, C. Jones, J. Am. Chem. Soc. 2014, 136,
3028–3031; e) L. Zhao, M. Hermann, C. Jones, G. Frenking, Chem. Eur.
J. 2016, 22, 11728–11735; f) T. J. Hadlington, M. Hermann, J. Li, G.
Frenking, C. Jones, Angew. Chem., Int. Ed. 2013, 52, 10199–10203; g)
T. J. Hadlington, B. Schwarze, E. I. Izgorodina, C. Jones, Chem.
Commun. 2015, 51, 6854–6857
Acknowledgements
R.J would like to acknowledge the Czech Science foundation
(project 20-10417S) for financial support. J.T. would like to
acknowledge the financial support of the Research Foundation–
Flanders (FWO; Project No. 12Y7718N) and the computational
resources and services provided by the Shared ICT Services
Centre funded by the Vrije Universiteit Brussel, the Flemish
Supercomputer Centre (VSC) and FWO. X.D. wishes to
acknowledge the Vrije Universiteit Brussel for the Strategic
Research Program.
[8]
[9]
T. J. Hadlington, M. Hermann, G. Frenking, C. Jones, J. Am. Chem. Soc.
2014, 136, 3028–3031.
J. Tremmel, M. Erben, L. Dostal, Z. Ruzickova, J. Turek, R. Jambor, Eur.
J. Inorg. Chem. 2019, 14, 1884–1894.
[10] J. Tremmel, L. Dostál, M. Erben, Z. Růžičková, J. Turek, F. De Proft, R.
Jambor, Eur. J. Inorg. Chem. 2017, 2017, 3100-3104.
[11] a) P. Pyykkö, M. Atsumi, Chem. Eur. J. 2009, 15, 186-197; b) P. Pyykkö,
M. Atsumi, Chem. Eur. J. 2009, 15, 12770-12779.
Keywords: hydride • solubility • reduction • DFT calculation •
NMR spectroscopy
[12] Ch. Drost, P. B. Hitchcock, M. F. Lappert, Organometallics 1998, 17,
3838 – 3840.
[1]
a) E. Rivard, Chem. Soc. Rev. 2016, 45, 989–1003; b) S. K. Mandal, H.
W. Roesky, Acc. Chem. Res. 2012, 45 , 298 —307; c) S. S. Sen , S. Khan , P.
P. Samuel, H. W. Roesky, Chem. Sci. 2012, 3 , 659 —682; d) R. C. Fischer,
P. P. Power, Chem. Rev. 2010, 110, 3877–3923; e) S. Aldridge, A. J.
Downs , Chem. Rev. 2001, 101, 3305 —3365.
[13] K. C. Thimer, S. M. I. Al-Rafia, M. J. Ferguson, R. McDonald, E. Rivard,
Chem. Commun. 2009, 7119–7121.
[14] S. M. I. Al-Rafia, A. C. Malcolm, S. K. Liew, M. J. Ferguson, E. Rivard, J.
Am. Chem. Soc. 2011, 133, 777–779.
5
This article is protected by copyright. All rights reserved.

10.1002/chem.202000970
Chemistry - A European Journal
RESEARCH ARTICLE
[15] S. M. I. Al-Rafia, R. McDonald, M. J. Ferguson, E. Rivard,Chem. Eur. J.
2012, 18, 13810 – 13820.
[16] S. M. I. Al-Rafia, M. R. Momeni, M. J. Ferguson, R. McDonald, A. Brown,
E. Rivard, Organometallics 2013, 32, 6658–6665;
[17] A. K. Swarnakar, S. M. McDonald, K. C. Deutsch, P. Choi, M. J.
Ferguson, R. McDonald, E. Rivard, Inorg. Chem. 2014, 53, 8662–8671
[18] M. M. D. Roy, S. Fujimori, M. J. Ferguson, R. McDonald, N. Tokitoh, E.
Rivard, Chem. Eur. J. 2018, 24, 14392 – 14399
[19] D. F. Gaines, J. Ulman, Inorganic Chemistry, 1974, 13, 2792 – 2796.
[20] Y. Ding, H. Hao, H. W. Roesky, M. Noltemeyer, H.-G. Schmidt,
Organometallics 2001, 20, 4806-4811.
[21] A. Stasch, Angew. Chem. Int. Ed. 2012, 51, 1930 –1933.
[22] M. Veith, P. König, A. Rammo, V. Huch, Angew. Chem. Int. Ed. 2005, 44,
5968 – 5971.
[23] D. R. Armstrong, W. Clegg, H. M. Colquhoun, J. A. Daniels, R. E. Mulvey,
I. R. Stephenson, K. Wade, Chem. Soc., Chem. Commun. 1987, 630 -
632.
[24] C. Eaborn, M. N. A. El-Kheli, P. B. Hitchcock, J. D. Smith, J. Chem. Soc.,
Chem. Commun. 1984, 1673 – 1674.
[25] A. Heine, D. Stalke, Angew. Chem., Int. Ed. 1992, 31, 941 – 942.
[26] W.-P. Leung, Ch.-W. So, K.-H. Chong, K.-W. Kan, H.-S. Chan, T. C. W.
Mak, Organometallics 2006, 25, 2851-2858.
[27] a) T. H. Dunning, Jr. J. Chem. Phys. 1989, 90, 1007–1023; b) B. Metz,
H. Stoll, M. Dolg, J. Chem. Phys. 2000, 113, 2563–2569; c) K. A.
Peterson, J. Chem. Phys. 2003, 119, 11099–11112; d) Y. Zhao, D. G.
Truhlar, Theor. Chem. Acc. 2008, 120, 215–241; e) B. P. Prascher, D. E.
Woon, K. A. Peterson, T. H. Dunning, Jr., A. K. Theor. Chem. Acc. 2011,
128, 69–82.
[28] a) J.P. Foster and F. Weinhold, J. Am. Chem. Soc., 1980, 102, 7211-
7218; b) F. Weinhold, J. Comput. Chem., 2012, 33, 2363-2379 and
references therein. c) C.R. Landis and F. Weinhold, F. The NBO View of
Chemical Bonding, in “The Chemical Bond: Fundamental Aspects of
Chemical Bonding” (eds G. Frenking and S. Shaik), Wiley-VCH Verlag
GmbH & Co. KGaA, Weinheim, Germany, 2014.
[29] K.B. Wiberg, Tetrahedron 1968, 24, 1083-1096.
[30] S. D. Robertson, A. R. Kennedy, J. J. Liggat, R. E. Mulvey, Chem.
Commun. 2015, 51, 5452 – 5455.
[31] S. Sinhababu, D. Singh, M. K. Sharma, R. K. Siwatch, P. Mahawar, S.
Nagendran, Dalton Trans. 2019, 48,4094 – 4100.
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Entry for the Table of Contents
The reduction of C=Y polar bonds by RLi in the presence of monomeric germanium hydride is possible. The combination of PhLi with
L(H)Ge·BH3 yielded {Li(THF)2{BH3[L(H)GePh]}} (3), a source of LiH for the reduction of benzaldehyde in non-polar solvents. The
reaction proceeds via intermediate 3INT accompanied by the elimination of a neutral complex L(Ph)Ge·BH3 (6).
7
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