Aryl Oligogermanes as Ligands for Transition Metal Complexes

Article abstract of DOI:10.1002/ejic.201801095

The ligand properties of a series of aryl oligogermanes R₃Ge-GeAr₃, 3–7 [Me₃Ge-GePh₃ (3), Me₃Ge-Ge(pTol)₃ (4), Ph₃Ge-GePh₃ (5), (C₆F₅)₃Ge-GePh₃ (6), Ph₃Ge-GeMe₂GePh₃ (7)] for the synthesis of transition metal carbonyl complexes such as R₃Ge-GeAr₂(R′C₆H₄-η⁶)M(CO)₃ (M = Cr, 3a–7a; M = Mo, 3b; M = W, 3c) were investigated. The target complexes were obtained in moderate yields using several different synthetic approaches. The physicochemical properties of these new derivatives were investigated by IR, UV/Vis, NMR spectroscopy, electrochemistry, and DFT calculations. The molecular structures of 3c, 4a, and 5a were studied by single-crystal X-ray diffraction analysis. A comparative analysis of donor and acceptor properties of aryl oligogermanes as ligands for transition metal carbonyl complexes is reported.

Full text of DOI:10.1002/ejic.201801095

A Journal of
Accepted Article
Title: Aryl Oligogermanes as Ligands for Transition Metal Complexes
Authors: Kirill V. Zaitsev, Kevin Lam, Viktor A. Tafeenko, Alexander A.
Korlyukov, and Oleg Kh. Poleshchuk
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10.1002/ejic.201801095
European Journal of Inorganic Chemistry
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Aryl Oligogermanes as Ligands for Transition Metal Complexes
Kirill V. Zaitsev,*[a] Kevin Lam,[b] Viktor A. Tafeenko,[a] Alexander A. Korlyukov[c] and Oleg Kh.
Poleshchuk[d, e]
Abstract: The ligand properties of a series of aryl oligogermanes
R3Ge-GeAr3, 3-7 (Me3Ge-GePh3 (3), Me3Ge-Ge(pTol)3 (4), Ph3Ge-
GePh3 (5), (C6F5)3Ge-GePh3 (6), Ph3Ge-GeMe2GePh3 (7)), for the
synthesis of transition metal carbonyl complexes such as R3Ge-
GeAr2(R’C6H4-η6)M(CO)3 (M = Cr, 3a-7a; M = Mo, 3b; M = W, 3c)
were investigated. The target complexes were obtained in moderate
yields using several different synthetic approaches. The
physicochemical properties of these new derivatives were
investigated by IR, UV/vis, NMR spectroscopy, electrochemistry and
DFT calculations. The molecular structures of 3c, 4a and 5a were
studied by single crystal X-ray diffraction analysis. A comparative
analysis of donor- and acceptor properties of aryl oligogermanes as
ligands for transition metal carbonyl complexes is reported.
derivatives with new properties. Bonding transition metal (M)
fragment to catenated Group 14 framework should impact on the
σ-delocalization and therefore, also on the physical properties of
the complex.[2] In addition, several possible modes to bonding
between the M and the Group 14 ligand could be expected,
each of them having a different impact on the σ-conjugation.
Compounds, containing a covalent bond between the E atom
and a transition metal, are numerous (leading references for Si
derivatives with M = rare earth metals;[3] Ti, Zr, Hf;[4] Ta;[5] Cr, Mo,
W;[6] Fe;[7] Pd;[8] Pt;[9] Au;[10] for special interest to Ge derivatives
for Hf, Zr;[4] W, Cr;[11] Pt;[9b, 12] Pd;[13] Au;[14] for Sn derivatives with
Ti;[4, 15] Mo, W;[16] Fe[17] etc.), but the present study is focusing on
the different types of bonding, including derivatives in which the
metal M fragment is connected through an organic group (ηn-
coordination). Only few studies on η5-C5R5 (Cp) catenated Ge
[19]
derivatives[18] and Cr[η6-C6H5GeMe2]2
have been reported to
Introduction
date while molecular oligosilane metal complexes have been the
subject of extensive studies[20] (complexed with η4-butadiene,[21]
η5-half-sandwich,[6c, 22] ferrocenyl[23] or other Cp ligands,[24] (η6-
aryl)M(CO)3,[25] sandwich Cr complexes,[26] η7-derivatives[27]);
this is also true for oligostannanes (Cp[28] derivatives) or for
polysilanes.[29] So the molecular oligogermanium complexes
bearing transition metals remain to be investigated in order to
complete the series. To the best of our knowledge, only 6
articles describing complexes of arylmonogermanes with
M(CO)3 have been reported up to this day.[19, 30]
Recently, derivatives of Group 14 elements bearing element –
element bonds (E(IV) = Si, Ge, Sn, Pb) have attracted significant
attention due to their unique and useful physical properties
(conductivity, light absorbance, luminescence etc.). These
properties are due to the presence of a σ-conjugation between
the E atoms within the framework of the molecule (Scheme 1).[1]
The number of E atoms in the chain, their nature, the electronic
properties of their substituents and conformation of the molecule
significantly affect on the σ-conjugation. The ability to finely tune
the electronic properties of these new compounds would allow to
synthesize substances and materials based on catenated
[a]
Dr. Kirill V. Zaitsev, Dr. Viktor A. Tafeenko
Chemistry Department
Moscow State University
B-234 Leninskie Gory, 1, 3, 119991 Moscow, Russia
E-mail: zaitsev@org.chem.msu.ru
Homepage:
http://www.chem.msu.ru/rus/chair/org_w/kmos/welcome.html
Dr. Kevin Lam
Department of Pharmaceutical, Chemical and Environmental
Sciences
University of Greenwich
Chatham Maritime, Kent, UK, ME4 4TB
Dr. Alexander A. Korlyukov
[b]
[c]
Scheme 1. Schematic representation of σ-conjugation between Group 14 E
atoms.
Russian Academy of Sciences
A.N.Nesmeyanov Institute of Organoelement Compounds
Vavilova Str., Moscow, Russia
Dr. Oleg Kh. Poleshchuk
National Research Tomsk Polytechnic University
Lenin Av., 30, Tomsk 634050, Russia
Dr. Oleg Kh. Poleshchuk
Tomsk State Pedagogical University
Kievskaya Str., 60, Tomsk 634061, Russia
Arene chromium tricarbonyl complexes are valuable
compounds that are used in organic synthesis and catalysis,[31]
the preparation of materials with non-linear properties,[32] etc. In
general, a Cr(CO)3 group, coordinated to an arene, acts as a
strong electron withdrawing substituent which reduces the
electron density of the aryl group. A priori, M(CO)3 would exhibit
electron-withdrawing properties similar in a magnitude to that of
a nitro group.[33] When the arene bears a functional group Y,
such as in (η6-C6H5Y)M(CO)3, the extent of the charge transfer
[d]
[e]
Supporting information for this article (Crystallographic data, NMR
and UV/vis spectra of the compounds obtained, and data of DFT
calculations) is given via a link at the end of the document.
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10.1002/ejic.201801095
European Journal of Inorganic Chemistry
FULL PAPER
to the metal strongly depends on the electron donating or
electron withdrawing properties of the group Y. This has been
shown by IR spectroscopy and is supported by theoretical
calculations. In this work, we are reporting the synthesis of
aryloligogermane carbonyl complexes 3a-c, 4a-7a (Scheme 2)
as well as an investigation of their structure - properties
relationship. Oligogermanes Me3Ge-GePh3 (3), Me3Ge-
Ge(pTol)3 (4), Ph3Ge-GePh3 (5), (C6F5)3Ge-GePh3 (6), and
[Ph3Ge]2GeMe2 (7) were used as simple and easily available
model compounds, differing in the number of Ge atoms, steric
and electronic properties of the substituents on the Ge centers.
Scheme 2. Structures of the compounds under investigation.
Scheme 3. Synthesis of 5a and 7a using Cr(CO)6 (1a) in decalin.
In order to improve the yields and simplify the isolation of
the desired compounds, new set of conditions was
Results and Discussion
a
investigated. Cr(CO)6 (1a) was reacted with Ph3GeGePh3 (5)
and (C6F5)3GeGePh3 (6) in a mixture of (nBu)2O/THF (10:1) at
reflux[34, 36] (Scheme 4). Similar conditions have been reported
for the synthesis of Group 14 derivatives using DME[37] or
dyglime.[38] When the unsymmetrical donor-acceptor digermane
6 was used, the exclusive formation of the product 6a was
observed, where the Cr(CO)3 coordinates to the electron rich Ph
ring. The isolation of pure 5a and 6a were performed by column
chromatography (for details, see Experimental part). The yields
of the target complexes depend not only on the type of
performed reaction but also on the structure of the oligogermane.
Insertion of an electron withdrawing group (like C6F5) results in a
decrease of the overall yields. Unfortunately, once again, the
target compounds were isolated in low yields. Furthermore,
when benzene was used as the eluent for the chromatographic
separation of 6a, a transmetallation was observed giving (η6-
C6H6)Cr(CO)3; therefore, a mixture of ether with petroleum ether
should be used instead of benzene for the isolation of the pure
complexes.
Synthesis. The synthesis of the new organometallic complexes
relied on the use of different metallic precursors, Cr(CO)6 (1a)
and M(CO)3(NCMe)3 (M = Cr (2a), M = Mo (2b), M = W (2c)).
At first, the method of thermolysis of Cr(CO)6 in a solvent
with a high boiling point (decalin)[34] in the presence of the
corresponding arene[35] (aryloligogermane
5 and 7) was
investigated (Scheme 3). Dimethylsuccinate is used here as an
agent promoting the abstraction of the CO group from the
chromium center.
Unfortunately, a significant amount of unreacted starting
material was recovered at the end of the reaction (conversion is
29-33 %), resulting to low yields of 5a and 7a. Increasing the
reaction time to 12 h did not show any improvement. Similarly,
using an excess of 1a did not improve the yield of the desired
complex. Therefore, the thermolysis approach for the synthesis
of 5a and 7a shown to have serious drawbacks due to the harsh
reaction conditions that have to be used to overcome the high
stability of Cr(CO)6. Moreover, tedious chromatographic
separations are needed in order to obtain the pure compounds.
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10.1002/ejic.201801095
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Scheme 4. Synthesis of 5a and 6a using Cr(CO)6 (1a) in (nBu)2O.
Scheme 6. Synthesis of complexes 3a-c, 4a and 7a using M(CO)3(NCMe)3 (2a-c).
When W(CO)6 was subjected to the same reaction
conditions in the presence of Me3GeGePh3 (3), the desired
complex Me3GeGePh2(η6-Ph)W(CO)3 (3c) was isolated only in a
trace amount; the major compound being the initial ligand 3. A
possible reason of this fact would be the decomposition of the
complex 3c under high temperature conditions. Therefore, in
order to perform the reaction at lower temperatures, M(CO)6 (1a-
c) (M = Cr, Mo, W) were replaced by 2a-c, M(CO)3(NCMe)3, in
which three carbonyl groups have been substituted by more
labile MeCN.[30b, 35b, 39]
Scheme 5. Synthesis of 2a-c.
The compounds 2a-c are easy to prepare (Scheme 5) and
can either be isolated in high yields or even used without
isolation.[40]
As expected, using M(CO)3(NCMe)3 as more reactive
starting materials, allowed to prepare the desired complexes in
improved yields by refluxing 2a-c for
1 h with an aryl
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10.1002/ejic.201801095
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oligogermanes in THF (Scheme 6). For these reactions, the
conversion of the starting compounds proved to be much higher
(54-68 %). Increasing the reaction time (up to 3 h) resulted only
in a decrease of the yields probably due to the thermal instability
of M complexes. No conversion was observed when the reaction
was carried out either in MeCN (under reflux for 12 h) or in THF
at room temperature (for up to 3 days), indicating that MeCN is a
more donating ligand than the arenes (see below).
Using an excess of 2a (up to 2 eq.) resulted only to mono
Cr complexes (in the case of 7a) without any traces of the
expected di Cr complexes. In the case of Mo, the complex 3b
has shown to be unstable and to decompose during the various
attempts to isolate it. When other derivatives, such as
M(CO)3(Py)3[35b] were used as starting materials under the same
conditions in interaction with Ph3GeGeMe3 (3), only traces of the
target compound were observed. Nevertheless, Mo derivatives
are known to exhibit low stability.[41]
Under comparison the three methods used for the
synthesis of the target compounds 3a-c, 4a-7a (thermolysis of
M(CO)6 in decalin/dimethylsuccinate, reflux of M(CO)6 in
(nBu)2O/THF, reflux of M(CO)3(NCMe)3 in THF) the latest one
seems to be the most successful, giving the target products in
higher conversions and yields.
All complexes studied, 3a, 3c, 4a-7a, are yellow powders,
which are stable under an inert atmosphere, but get slowly
oxidized (and become greenish) upon exposure to air for several
months. In stark contrast, solutions of these compounds have
shown to be much more air-sensitive. All of these derivatives are
soluble in aromatic hydrocarbons (benzene, toluene), acetone,
ethers (THF, ether), but are insoluble in n-hexane, and
decompose very quickly in chloroform (or CDCl3). Among the
possible decomposition pathways, the rupture of Cr-Ar bonding
is the most probable, especially under harsh conditions. The
rupture of the Ge-Ge bond was also observed when NMR was
used to monitor the stability of the solutions of 6a in C6D6. After
3 days, the formation of 6, (C6F5)3GeGePh3, and (C6F5)3GeH
was observed.
Figure 1. Molecular structure of Me3GeGePh2(η6-Ph)W(CO)3 (3c).
Displacement ellipsoids are shown at 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and bond angles (deg):
Ge(1)-Ge(2) 2.4266(9), W-Cav(arene) 2.341(6), W-Cav(centroid) 1.867(6), W-
COav 1.967(7), Ge(1)-Cav 1.949(6), Ge(2)-Cav 1.957(6), Ge(2)-C(16) 1.972(6),
C-Oav 1.155(8); C-W-Cav(CO) 87.4 (3), C-Ge(1)-Ge(2)av 110.8(2), C-Ge(1)-Cav
108.1(3), C-Ge(2)-Ge(1)av 112.64(19), C-Ge(2)-Cav 106.2(2).
In 3c, the W(CO)3 group in relation to the coordinated C6H5
ring adopts an anti-eclipsed-conformation (Scheme 7; torsion
angles CGe-Ccentroid-W-CO are 55.4(7) and 71.1(7)o; 60o for ideal
anti- and 0o for ideal syn-). Due to the electronic interactions a
syn-eclipsed-conformation is typical for monosubstituted (η6-
R’C6H5)M(CO)3, bearing an electron donating R’ group. Such R’
groups increase the electron density in ortho- and para-positions
of the η6-Ar ring, where the octahedral set of Cr orbitals are
interacting.[44] Usually, an anti-eclipsed conformation is due to
steric reasons, but in our case, additional orbital interactions
between the d orbitals of the Cr and the σ-orbital of Ge-Ar and
Ge-Ge bonds may be observed (Scheme 7). The maximal
overlapping (torsion angle M-CArGe-Ge-Ge 180o is the most
profitable) is observed in 5a (see below); in 3c this value is
55.2(7)o, indicating that the electronic interactions between all
parts of the molecule are present to some extent. The
conformation along the Ge-Ge bond is staggered (torsion angles
C-Ge-Ge-Cav are 78.27/41.71o).
In 4a, the conformation of the Cr(CO)3 group in relation to
the coordinated C6H5 ring is close to be anti-eclipsed (torsions
CArGe-Ccentroid-Cr-CO are 52.9(8) and 68.7(8)o). The torsion angle
of Cr-CArGe-Ge-Ge is 46.5(8)o, indicating weak interactions
between Cr and Ge2. DFT calculations for 4a (see below)
showed that in the gas phase this torsion angle is 155o,
indicating an effect of the crystal packing on the conformation.
The conformation along the Ge-Ge bond is staggered (torsion
angles C-Ge-Ge-Cav are 70.5(8)/49.5(8)o).
All compounds were characterized by elemental analysis,
IR and NMR spectroscopy, mass spectrometry[42] and in the
case of 3c, 4a and 5a by single crystal X-ray diffraction (XRD)
analysis. The deviations in elemental analysis data are
explained by the sensitivity of the compounds and by the partial
combustion due to the presence of transition metals.
Solid state structure. A search in the CSD (Cambridge
Structural Database) (June 2018) for structures of
aryloligogermanes, coordinated with M(CO)3 showed no results.
Therefore, the structural investigation of 3c, 4a and 5a by XRD
reported in this work (Figures 1-3; Supporting Information, Table
S1) represents a significant contribution to the chemistry of
Group 14 derivatives. Moreover, only one structure of
monogermanium
compound,
N(CH2CH2O)3Ge(η6-
Ph)Cr(CO)3,[30d] has ever been studied by XRD to date.
For all of the structures studied in this work, the metal –
ligand core shown to adopt the well-known “piano stool”
geometry.[43]
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10.1002/ejic.201801095
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Scheme 7. Conformations of substituents in relation to η6-benzene.
Figure 3. Molecular structure of Ph3GeGePh2(η6-Ph)Cr(CO)3 (5a).
Displacement ellipsoids are shown at 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and bond angles (deg):
Ge(1)-Ge(2) 2.4316(13), Ge(1)-Cav 1.955(9), Ge(2)-Cav 1.953(10), Ge(2)-C(31)
1.974(9), Cr(1)-Cav(arene) 2.209(11), Cr-Cav(centroid) 1.698(11), Cr-COav
1.842(11), C-Oav 1.157(13); C-Cr-Cav(CO) 88.1(5), C-Ge(1)-Ge(2)av 110.0(3),
C-Ge(1)-Cav 108.9(4), C-Ge(2)-Ge(1)av 109.0(3), C-Ge(2)-Cav 109.9(4).
In all of the structures studied, 3c, 4a, and 5a, the η6-
coordinated arene ring is almost planar (the maximal deviations
from the mean square plane are 0.022(9) Å in 3c (C(19)-para to
Ge toward to W), 0.008(9) Å in 4a (C(8)-ipso and C(9)-ortho to
Ge out of Cr) and 0.012(9) Å in 5a (C(35)-meta to Ge out of
Cr).[43] In every case, the nearest Ge atom is slightly moved out
of the plane of the η6-Ar in the direction above M(CO)3 (0.228(9)
Ǻ for 3c, 0.131(9) Ǻ for 4a, 0.101(9) Ǻ for 5a; the angles of
deviation α are 6.4(7), 3.6(8), 3.0(9)o, respectively) due to the
electronic effects (Scheme 8), indicating a π-donor effect of the
oligogermanyl substituent. It should be noted that in 4a, the
methyl group of the p-tolyl ring is almost in the plane of aryl
group (the deviation is only 0.001(9) Å).
Figure 2. Molecular structure of Me3GeGe(pTol)2(η6-pTol)Cr(CO)3 (4a).
Displacement ellipsoids are shown at 50% probability level. Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and bond angles (deg):
Ge(1)-Ge(2) 2.4284(6), Ge(1)-Cav 1.952(5), Ge(1)-C(8) 1.970(4), Ge(2)-Cav
1.932(7), Cr(1)-COav 1.828(9), Cr(1)-Cav(arene) 2.212(5), Cr-Cav(centroid)
1.715(5), C-Oav 1.163(8); C-Cr-Cav(CO) 88.2(3), C-Ge(1)-Ge(2)av 112.66(13),
C-Ge(1)-Cav 106.1(2), C-Ge(2)-Ge(1)av 110.49(19), C-Ge(2)-Cav 108.5(3).
The structure of the complex 5a differs from the ones of 3c
and 4a. The conformation of the Cr(CO)3 group in relation to the
coordinated C6H5 ring is distorted staggered- (torsion angles
CArGe-Ccentroid-Cr-CO are 27.6(9) and 95.6(9)o), indicating electron
interactions between Cr(CO)3 and Ge2. The torsion angle Cr-
CArGe-Ge-Ge is 159.7(9)o, showing a very high interaction
between Cr, η6-Ph and Ge2. This significant difference,
observed in 5a, may be explained by the presence of Ph groups
at both Ge atoms, what is known to strongly affect the electronic
structure of the molecules.[45], [46] The conformation along the Ge-
Ge bond is staggered (torsion angles C-Ge-Ge-Cav are
59.6(9)/60.4(9)o).
The presence of the M(CO)3 increases the nonequivalence
of the aryl C-C bonds (approaching a hexadienyl character) and
shows an elongation of C1-C2 bond (Scheme 8), whereas the
electron density is partially transferred from the Ge-Ge bond
(HOMO-3, HOMO-4, HOMO-5; Figs. S26-S28, ESI) to the η6-
arene ring (LUMO+3, LUMO+4, LUMO+5; Figs. S32-S34, ESI).
This was observed for each of the new complexes studied
(Scheme 9), indicating that the presence of a M(CO)3 moiety
lowers the bond order of the aromatic ring due to its acceptor
properties. Furthermore,
hybridization for the arene carbon atoms bonded to Ge is
observed.
a
deviation from the ideal sp2
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Table 1. Comparison structural parameters of complexes 3c, 4a, 5a with parent oligogermanes 3, 4 and 5.
Compound [a]
Me3GeGePh3 (3) [47]
3c
d(Ge-Ge)
2.418(1)
2.4266(9)
d(Ge-C)
1.943(4)
1.949(6)
d(GeM-C)
1.957(2)
1.972(6)
C-Ge-GeM
110.2(1)
110.8(2)
C-Ge-C
108.7(1)
108.1(3)
C-GeM-Ge
C-GeM-C
108.6(1)
106.2(2)
110.3(1)
112.64(19)
Me3GeGe(pTol)3 (4) [48]
2.4292(7)
2.4284(6)
1.936(7)
1.932(7)
1.948(4)
1.970(4)
115.6(2)
107.2(4)
108.5(3)
110.90(12)
112.66(13)
107.97(17)
106.1(2)
4a
110.49(19)
Ph3GeGePh3 (5) [49]
2.437
1.959
1.959
110.80
108.10
110.80
108.10
5a
2.4316(13)
1.955(9)
1.974(9)
110.0(3)
108.9(4)
109.0(3)
109.9(4)
[a] Bond lengths (Å) and bond angles (deg); GeM is a nearest to M(CO)3 germanium atom; average values are used
(2.4266(9) vs. 2.4284(6) vs. 2.4316(13) Å in 3c, 4a, 5a,
respectively) and Ge-C bond length (for example, Ge-CArM
1.972(6) vs. 1.970(6) vs. 1.974(9) Å). Furthermore, the d(Ge-
CArM) is longer than the other Ge-C bonds; this may be explained
as by steric reasons (introduction of a more voluminous M(CO)3
substituent) and by electronic effects (similar to ones, which
have
been
earlier
observed
for
donor-acceptor
oligogermanes).[46, 50] In general, the geometry at each of Ge
atom may be described as a slightly distorted tetrahedral.
A
comparison between the structural parameters of
complexes 3c, 4a, 5a and the ones of the parent oligogermanes
3,[47] 4[48] and 5,[49] respectively (Table 1), shows minimal
differences, indicating a strong mutual influence of the Ge2, aryl
and M(CO)3 fragments in the molecule, where the acceptor
properties of M(CO)3 are counterbalanced by a Ge2 donation.
Structure in solution. The NMR spectra of complexes 3a-3c
and 4a-7a were recorded in C6D6 or acetone-d6. Due to the
weaker π-acceptor properties of the η6-coordinated arene ligand
in comparison with CO, a quenching of the ring current is
observed in such compound. The electron density is transferred
from arene to the M(CO)3. This phenomenon is reflected in the
NMR spectra by upfield shifts of the coordinated aryl group
Scheme 8. Donor effects of oligogermyl substituent.
Scheme 9. Values of d(C-C) bond lengths in η6-arene for 3c, 4a and 5a.
1
signals in comparison with the parent oligogermanes 3-7. In H
NMR (C6D6) the signals of the η6-coordinated Ar appeared
between δ 4.0-5.3 ppm (an upfield shift of ca. 2 ppm), and the
signals of the uncoordinated Ar were shifted toward downfield by
ca. 0.2 ppm in comparison with the free oligogermane (for
details, see Experimental Part and Supporting Information, Figs.
S1-S16). A comparison with the parent (η6-C6H6)Cr(CO)3 (vs. δ
4.31 ppm)[51] showed that for oligogermanes 3a-7a the proton
signals are shifted toward lower fields. Furthermore, the signal
for each position of the coordinated Ar group (ortho-, para- and
meta-) appeared as well resolved multiplets (doublets, triplets
The Ge-Ge moiety is cisoid- in relation to the M(CO)3
group in 3c (the value of the torsion angle for Ge-Ge-C(16)Ar-W
is 55.2(7)o) and 4a (torsion Ge-Ge-C(8)Ar-Cr is 46.5(8)o),
whereas in 5a this same feature is transoid- (torsion Ge-Ge-
C(31)Ar-Cr is 159.7(9)o). These data, along with the conformation
of M(CO)3 along the Ar, indicate that there is a stronger electron
interaction between the octahedrally directed metal’s orbitals
and the η6-arene in 5a. The values of the torsion angles for Ge-
Ge-CAr-CAr and Ge-Ge-CAr-M (-39.2(7)/55.2(7)o for 3c; 46.0(8)/-
46.5(8)o for 4a; -67.1(9)/-159.7(9)o for 5a) indicate the presence
of an σ-π-conjugation between the Ge-Ge and η6-Ar fragments
(90o for an ideal conjugation).
In all of the structures 3c, 4a and 5a the values of d(C-O)
are very similar (1.155(8) vs. 1.163(8) vs. 1.157(13) Å), showing
an acceptor properties across different oligogermanes and
metals. The values of d(Cr-CO) in 4a and 5a are almost identical
(1.828(9) vs. 1.842(11) Å). Variation of the substituents on the
Ge atom or of the nature of M resulted only in small changes of
the main structural parameters, i.e. Ge-Ge bond length
3
4
etc., JH-H = 6.6 Hz, JH-H = 1.0 Hz). The weakest upfield shifts
were observed for Mo and the largest ones for W (3b vs. 3a vs.
3c).
The 13C NMR spectra of Cr compounds have shown a
single signal for CO (δ 232.1-234.1 ppm), indicating the rapid
(on the NMR time scale) rotation along the M-Arcentroid axis
resulting in the equivalence of the 3 carbonyls. The 13C NMR
spectra are characterized by the presence of 4 signals typical for
coordinated carbon arene at δ 110.6-90.8 ppm (upfield shift of
ca. 35 ppm in comparison with non-coordinated Ar); ipso-, ortho-
/meta- and para-carbon signals are easily distinguished. In
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10.1002/ejic.201801095
European Journal of Inorganic Chemistry
FULL PAPER
Table 2. Data of the UV/vis spectra according to experiment and DFT Calculations for the compounds 4, 4’, 4’’, 4’’’ and 4a.
compound
λexp, nm [a]
232 (2.3)
220 (1.74)
253 (0.76)
λcalc, nm [b]
229 (0.282)
-
transition
HOMO→LUMO+2
Me3GeGe(pTol)3 (4) [c]
(η6-pTolH)Cr(CO)3 (4’)
-
286 (0.2228)
321 (0.0017)
327 (0.0030)
343 (0.0010)
288 (0.2091)
322 (0.0022)
327 (0.0019)
295 (0.1044)
318 (0.0037)
323 (0.0032)
333 (0.0028)
337 (0.0027)
350 (0.0025)
382 (0.0025)
391 (0.0071)
-
279 (0.0132)
298 (0.1452)
326 (0.0029)
328 (0.0156)
336 (0.0092)
357 (0.0016)
383 (0.0024)
394 (0.0107)
HOMO→LUMO+1, HOMO-1→LUMO
HOMO-2→LUMO+1
HOMO-2→LUMO
317 (0.95) [d]
HOMO-1→LUMO+1
HOMO→LUMO+1, HOMO-1→LUMO
HOMO-2→LUMO+1
HOMO→LUMO+1, HOMO-2→LUMO
HOMO-1→LUMO+1
HOMO-2→LUMO+2
HOMO-1→LUMO+2
HOMO-1→LUMO+1
HOMO-2→LUMO+1
HOMO→LUMO+2
Me3Ge(η6-pTol)Cr(CO)3 (4’’)
-
MeGe(pTol)2(η6-pTol)Cr(CO)3 (4’’’)
-
HOMO-1→LUMO
HOMO→LUMO
Me3GeGe(pTol)2(η6-pTol)Cr(CO)3 (4a)
233 (4.55)
267 (0.80)
321 (0.87)
-
HOMO-3→LUMO
HOMO-1→LUMO+1
HOMO-2→LUMO+1
HOMO-1→LUMO+2
HOMO-2→LUMO+1
HOMO→LUMO+1
HOMO-1→LUMO
HOMO→LUMO
[a] Absorptivity ε (104 M-1 cm-1) in parentheses; data in CH2Cl2. [b] Oscillator strength in parentheses. [c] Data from [48]. [d] Data from [52]
.
general these signals are shifted toward lower fields in
comparison with the parent (C6H6)Cr(CO)3 (vs. δ 92.36 ppm).[51]
DFT calculations. Theoretical investigation has been
localized on the (Tol)Cr(CO)3 fragment. All of this indicates a full
conjugation between the different parts of the molecule and a
distribution of the electron density over the whole molecule. This
situation differs significantly from what is observed for the parent
aryloligogermanes, where the HOMO is mainly localized on the
Ge-Ge bond and the LUMO mainly on Ar substituents,[45], [46] as it
was confirmed for 4. It means that the electron density is
transferred from Ge2 to ArCr(CO)3 through an intramolecular
conjugation.
performed
pTol)Cr(CO)3
for
model
(4a),
compounds
Me3GeGe(pTol)2(η6-
(4’),
Me3Ge(η6-
(η6-TolH)Cr(CO)3
pTol)Cr(CO)3 (4’’), MeGe(pTol)2(η6-pTol)Cr(CO)3 (4’’’) and
Me3GeGe(pTol)3 (4) (Supporting Information, Figs. S17-S62,
Tables S2-S4); the results obtained are typical for all series of
compounds 3a-7a. DFT calculations were carried out to estimate
electron density distributions in occupied and antibonding
orbitals; furthermore, these calculations are useful to assign
experimental transitions in the UV spectra, which can not be
carried out only on the basis of the experimental spectra.
Calculations of the UV/vis spectra were performed for 4, 4’,
4’’, 4’’’ and 4a (Table 2).
[25c, 52-53]
The UV/vis spectra of (η6-C6H6)Cr(CO)3
has been
reported to exhibit 3 bands, corresponding to a π-π* transition (~
220 nm with ε~1-3x104 M-1 cm-1), a M→ArH charge transfer
(~250 nm with ε<104 M-1 cm-1) and a M→π* CO charge transfer
(~ 315 nm with ε~104 M-1 cm-1).[38a, 53c]
According to the calculations using B3LYP/6-311+G(2d,p)
in THF, 4a has three bands, active in IR for carbonyl groups,
1960 and 1884/1855 cm-1. This correlates well with the
experimental results (1961, 1887 cm-1, see below), confirming
the validity of the model used. In the gas phase, using 6-31G(d),
a different set of values (2107, 2056/2052 cm-1) was obtained,
showing the high dependence of these values on the solvent
used. These calculations have also shown that the presence of
a Ge2 fragment increases the donor properties of the aryl group
(vs. 2117, 2066/2060 cm-1 for (η6-TolH)Cr(CO)3 (4’)).
The most hypsochromic bands of the UV/vis absorption
spectrum (220 nm for 4’; 233 nm for 4a) correspond to an
intraligand charge transfers (ILCT) for Ar, where the transition is
observed from a low HOMO (such as HOMO-4 and lower) to a
higher LUMO (such as LUMO+5 and higher), which are located
on the Ar groups. Due to DFT restrictions, these transitions have
not been taken into account during the calculations.
For 4a, due to the presence of the metal, an electron
acceptor, the HOMO is mainly localized on the Cr(CO)3 fragment
(bonding Cr-CO), whereas the HOMO-1, HOMO-2 are mainly
localized on the TolCr(CO)3. The lower energy HOMO-3 orbital
is bonding and localized on the Ge-Ge fragment; the other
bonding orbitals, HOMO-4, HOMO-5, HOMO-6, HOMO-7 are all
located on the non-coordinated Tol rings. Furthermore, the
LUMO as well as the LUMO+1, are π-antibonding orbitals and
localized on the non-coordinated Tol rings. The LUMO+2 is
characterized by a contribution to the antibonding orbital on
TolCr(CO)3. The higher energy orbital LUMO+3 is mainly
The data obtained for 4a show a significant orbital mixing,
and all bands are significantly bathochromically shifted in
comparison with the model compounds. The following bands
attributions could be made: 267 nm (metal-to-arene charge
transfer, MACT, from Ge2 to Ar, and MACT from TolCr(CO)3 to
the antibonding orbital of Tol; in general from a lower HOMO to
LUMO and near) and 321 nm (metal-to-carbonyl charge transfer,
MCCT,[54] from TolCr(CO)3 to the antibonding orbitals of
Cr(CO)3; from a lower HOMO to higher LUMO orbitals).
UV/vis spectroscopy. UV/vis spectroscopy is an
important method for characterization of catenated Group 14
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10.1002/ejic.201801095
European Journal of Inorganic Chemistry
FULL PAPER
compounds and for the estimation of their HOMO-LUMO gaps.
For the compounds 3a-7a, one might expect a shift of the bands
compared to the parent compounds. The introduction of
aromatic groups within an oligogermane framework is known to
lead to a bathochromic shift of the UV/vis absorbance bands due
to the σ-π-conjugation. The effect of the insertion of transitional
metal fragments remains less evident to predict.
Table 3. UV/vis spectroscopy data for 3a-7a and related compounds.
compound [a]
(η6-EtO2CC6H5)Cr(CO)3
(η6-C6H6)Cr(CO)3
λ (nm), σ→σ* [b]
λ (nm), ILCT [b]
223 (2.23)
213 (3.00)
220 (1.74)
212 (2.17)
231 (1.9)
232 (1.9)
232 (2.1)
213 (2.87)
λ (nm), MACT [b]
255 (0.82)
256 (0.75)
253 (0.76)
256 (0.71)
256
λ (nm), MCCT [b]
323 (1.00)
317 (1.06)
317 (0.95)
317 (1.03)
318 (1.1)
326 (2.1)
321 (1.9)
327 (1.56)
reference
[52]
[52]
[52]
(η6-MeC6H5)Cr(CO)3
(η6-Et3SiC6H5)Cr(CO)3
[52]
Me3SiSiMe2(η6-C6H5)Cr(CO)3
Me3SiSiMe2(η6-C6H5)Mo(CO)3
Me3SiSiMe2(η6-C6H5)W(CO)3
PhSiMe2SiMe2(η6-C6H5)Mo(CO)3
Me3GeGePh3 (3)
[25c]
[25c]
[25c]
[53d]
[55]
286 (4.1)
278 (5.1)
[c]
230
Me3GeGePh2(η6-C6H5)Cr(CO)3 (3a)
Me3GeGePh2(η6-C6H5)W(CO)3 (3c)
Me3GeGe(pTol)3 (4)
232 (2.47)
233 (1.96)
263 (0.53)
291 (0.38)
320 (0.67)
322 (0.46)
this work
this work
[48]
232 (2.3)
241
-
-
Me3GeGePh2(η6-C6H5)Cr(CO)3 (4a)
Ph3GeGePh3 (5)
233 (4.55)
238 (3.57)
234 (2.15)
244 (3.60)
267 (0.80)
321 (0.87)
this work
[56]
-
-
Ph3GeGePh2(η6-C6H5)Cr(CO)3 (5a)
(C6F5)3GeGePh3 (6)
267 (1.64) (sh)
322 (0.64)
this work
[46]
226 (3.70)
245 (3.02)
-
261 (0.78)
-
-
(C6F5)3GeGePh2(η6-C6H5)Cr(CO)3 (6a)
Ph3GeGeMe2GePh3 (7) [d]
322 (0.41)
-
321 (0.38)
this work
[57]
Ph3GeGeMe2GePh2(η6-C6H5)Cr(CO)3 (7a)
261 (2.10) (sh)
this work
[a] Performed in solution in CH2Cl2 unless otherwise stated. [b] ε (104 M-1 cm-1) in parentheses. [c] Solution in THF. [d] Solution in cyclohexane.
Table 4. IR spectroscopy data for arene M (M = Cr, Mo, W) tricarbonyl complexes.
Compound
Cr(CO)6
νCO, cm-1
1987
solvent
hydrocarbons
reference
Compound
νCO, cm-1
1991,
solvent
cyclohexane
reference
[58]
[34]
Cr(CO)3(η6-C6H5Cl)
1929, 1925
1969,
[59]
[34]
fac-Cr(CO)3(PF3)3
2062, 1998
not given
Cr(CO)3(η6-C6H5NMe2)
cyclohexane
1894, 1888
1990, 1927
1992, 1929
[60]
[61]
[34]
[54]
fac-Cr(CO)3[(MeO)3P]3
1962, 1875
1966,
CS2
hexadecane
Cr(CO)3(η6-C6H5COOMe)
Cr(CO)3(η6-C6H5COOMe)
cyclohexane
heptane
1888/1879
1939, 1849
1935, 1842
1911, 1887
[62]
[61]
[63]
[30a]
[30a]
[30c]
fac-Cr(CO)3[Me3P]3
fac-Cr(CO)3[NH3]3
not given
hexadecane
MeCN
Cr(CO)3(η6-PhSiMe3)
Cr(CO)3(η6-PhGeMe3)
Cr(CO)3(η6-PhGeMe2Ph)
1987, 1911
1985, 1910
1980,
cyclohexane
cyclohexane
nujol
1915/1870
1984, 1908
1977, 1911
1972, 1906
[40b]
[64]
[30a]
[25c]
[25d]
fac-Cr(CO)3[NCMe]3
fac-Cr(CO)3[Py]3
1910, 1782
1910, 1778
1983, 1914
nujol
not given
cyclohexane
Cr(CO)3(η6-PhSnMe3)
Cr(CO)3(η6-PhSiMe2SiMe3)
Cr(CO)3(η6-
cyclohexane
isooctane
hexane
[53b]
Cr(CO)3(η6-С6H5CH3)
PhSiMe2SiMe2C≡CPh)
[65]
[34]
[66]
[34]
[67]
[34]
[25d]
1962, 1893
1980, 1908
nujol
cyclohexane
nujol
Cr(CO)3(η6-
1975, 1909
1974, 1897
1970, 1894
1975, 1900
1976, 1901
1972, 1896
1983, 1913
hexane
nujol
nujol
nujol
nujol
nujol
PhSiMe2SiMe2SiMe2C≡CPh)
Cr(CO)3(η6-PhGePh2GeMe3)
(3a)
Cr(CO)3(η6-С6H5OCH3)
Cr(CO)3(η6-C6H6)
this work
this work
this work
this work
1975/1945,
1903/1857
1982, 1915
Cr(CO)3(η6-
pTol)Ge(pTol)2GeMe3 (4a)
Cr(CO)3(η6-PhGePh2GePh3)
(5a)
cyclohexane
nujol
1978, 1910
Cr(CO)3(η6-
PhGePh2Ge(C6F5)3) (6a)
Cr(CO)3(η6-C6H5F)
1990,
1929, 1926
1915, 1783
cyclohexane
nujol
Cr(CO)3(η6-
this work
PhGePh2GeMe2GePh3) (7a)
Mo(CO)3(η6-C6H5SiMe3)
[40b], [68]
[53d]
fac-Mo(CO)3(NCMe)3
petroleum
ether
isooctane
KBr
fac-Mo(CO)3(PMe3)3
Mo(CO)3(η6-C6H6)
1927, 1828
1987, 1916
not given
heptane
Mo(CO)3(η6-PhSiMe2SiMe3)
Mo(CO)3(η6-
1981, 1912
1953, 1871
[69]
[70]
[25c]
[53d]
PhSiMe2SiMe2Ph)
[30e]
[30e]
[30e]
[30e]
[30e]
1985, 1912
1980, 1910
nujol
nujol
nujol
Mo(CO)3(η6-C6H5GeMe3)
1986/1958,
1909/1867
1979/1951,
1909/1862
1978, 1900
nujol
nujol
nujol
Mo(CO)3(η6-C6H5Me)
Mo(CO)3(η6-C6H5SnMe3)
Mo(CO)3(η6-C6H5SiMe3)
1986/1944,
1916/1874
Mo(CO)3(η6-
this work
PhGePh2GeMe3) (3b)
[40b]
[61]
[71]
[72]
fac-W(CO)3(NCMe)3
fac-W(CO)3[(MeO)3P]3
1885, 1778
1973,
nujol
hexadecane
W(CO)3(η6-C6H6)
1968, 1886
1985, 1910
CH2Cl2
heptane
W(CO)3(η6-MeC6H5)
1894/1880
1940, 1845
[61]
[25c]
fac-W(CO)3[Me3P]3
hexadecane
W(CO)3(η6-PhSiMe2SiMe3)
W(CO)3(η6-PhGePh2GeMe3)
(3c)
1980, 1909
1980, 1904
isooctane
nujol
this work
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10.1002/ejic.201801095
European Journal of Inorganic Chemistry
FULL PAPER
The σ-σ* transition in the Ge-Ge bonds is usually observed
around 230-250 nm for di- and trigermanes with very high
absorptivity (ε~2-5x104 M-1 cm-1). Due to solubility reasons all
UV/vis spectra in this work were recorded in CH2Cl2 which allow
to get data at λ>230 nm. For oligogermane 3a-7a, three main
bands (Table 3) were observed. Other bands were presented
but were either weak or overlapped with the main absorptions or
with the solvent.
The analysis of UV/vis spectra of the compounds obtained
within this study with the spectra of the initial oligogermanes
shows that the introduction of a M(CO)3 group has a strong
influence on the absorption (Table 3; DFT section above). The
bands, corresponding to the σ→σ* transition in the parent
oligogermanes did not appear due to a mixing of the MO. The
two bands, corresponding to an ILCT and an MACT in the
parent chromium complexes are significantly bathochromically
shifted in 3a-7a; at the same time the bands located at λ 320-
322 nm (MCCT) are weakly red shifted. This indicates an
increase of the donor properties of the η6-Ar ligand (HOMO
increase) due to the presence of a Ge2 group. The weak bands
at 260-270 nm (MACT) appeared as a shoulder for Cr and as a
distinct peak for the heavier analogs Mo[25c] and W.[73] This
indicates an orbitals mixing of the Ge-Ge σ-bonds, π-aryl and π-
CO, where Ge-Ge acts as a strong electronic donor. This band
may be attributed to a transfer of electronic density from Ge-Ge
to Ar.
For the complexes studied, the nature of the metal M
(compare 3a and 3c) has shown to have little effect on the
UV/vis absorption, whereas only the MACT is significantly
bathochromically shifted when replacing Cr by Mo or W.[74]
In contrast with the free molecular oligogermanes[75], [48] all
complexes showed a total absence of luminescence both in
solution and in solid form. The presence of transition metal
fragments, M(CO)3 (M = Cr, Mo, W), within the complexes
results in a quenching of the emissive properties. The electronic
conjugation between Ge2, η6-arene and M(CO)3 occurs through
direct interaction between a filled Cr d-orbitals and a σ* of Ge2
bond, metal-ring σ-π-delocalization (π-conjugation) and a back-
donation from Cr d-orbitals to a π*-orbitals of the arene, a
solvents due to Lewis acidic interaction between the solvent and
the carbonyl ligands.[51]
Comparing the IR data for the compounds 3a-c, 4a-7a with
the parent compound (η6-C6H6)Cr(CO)3 shows a decrease of the
stretching absorption due to the electron donating properties of
the catenated Group 14 fragment; its insertion within the Ar
framework results in
a small increase in the σ-donating
properties and a decrease in the π-acceptor ability. Using the
literature data and the ones obtained in this work (Table 4)
allows to place the aryloligogermanes among ligands that
increase the π-back acceptor properties: [Py]3 < [MeCN]3
<
[NH3]3 < [PMe3]3 < [P(OMe)3]3 < ArGe(Ar2)GeR3 < [CO]3 < [PF3]3.
The catenated germanium fragment may be considered as a
donor group in next row of substituted arenes: NMe2
<
ArGe(Ar2)GeR2GeR3 < ArGe(Ar2)GeR3 ≤ Ar(SiR2)2SiR’3 < OMe
< ArSiR2SiR’3 < Ar2GeMe2 < Me < H < PhSnMe3 < PhGeMe3 <
PhSiMe3 < CO2Me < F < Cl. In addition, the Ge atoms have
shown to exhibit greater electron donating abilities than Si.
Increasing the length of the Ge chain increased the donor
properties of the aryloligogermane. This suggests that Ge2
fragments have σ- as well as π-donating properties.
In comparison, it is known that the introduction of disilane
fragment decreases the donor properties of the Ar ligand
(Me3Si(η6-Ph)Mo(CO)3 and PhSiMe2SiMe2(η6-Ph)Mo(CO)3 in
KBr: 1946, 1865 vs. 1953, 1871 cm-1).[53d]
The comparison of the IR data between 3a-7a (weak
increase of the donor properties in 6a<5a<3a<7a<4a) shows a
similar trend as the one observed in other spectroscopies. A
similar trend could be observed when comparing the NMR
chemical shifts of the 13CO groups, where increased donor
properties correspond to a deshielding.[78] Increasing the donor
properties in η6-coordinated Ar groups results to a decrease of
the acceptor properties (4a in Tol vs. Ph in 3a); the same effect
is observed when increasing the Ge chain length (Ge3 in 7a vs.
Ge2 3a) and during the metal transition W<Mo<Cr. Varying the
substituent nature on the Ge atom, neighbouring the η6-
coordinated Ar group also influence on the donor properties, but
this effect remains relatively weak; therefore, the introduction of
an electron withdrawing groups resulted only in
a small
donation from Ar to Cr (due to the withdrawing effect of Cr(CO)3). decrease of the donor properties (3a vs. 5a; 5a vs. 6a).
This resulted in a bathochromic shift of the metal absorption
bands (at 220 nm) with a small increase in absorbance.
Changing the nature of substituent on the central Ge atom has a
more significant effect (compare PhGeMe3 and Ph2GeMe2,
Table 4). Therefore, in order to maximize the donor properties of
the complex, one has to use long chained oligogermane,
containing aryl groups bearing electron donating groups.
IR spectroscopy and donor properties. For each of the
compound studied the IR spectrum contains the expected 2
bands in the carbonyl region, including a non-degenerated
symmetric A1 (at higher wave numbers, νCO ~2000-1970 cm-1)
and a doubly-degenerated asymmetric E (νCO ~1950-1900 cm-1)
vibrations (local C3v symmetry)[76] (Table 4). In the experiment
there is no possible splitting of the E bands, which may be
observed due to a small perturbation of the general symmetry of
the arene substituent[77] (compare with DFT calculations, see
above). The analysis of the IR data (mainly, A1 band) could be
used to assess the donor (a decrease of the IR value) or the
acceptor (an increase of the IR value) properties of a ligand. A
strong dependence of the IR bands on the solvent has also been
observed; broadened red shifted bands are observed in polar
Electrochemistry. In this work compound 4a was studied
as a typical example of the new complexes (Figure 4).
Compound 4a displays a reversible one electron oxidation
of the organometallic center Cr(0)→Cr(1+)[44, 79] that results to
the formation of a stable cation-radical (on the voltammetric
experiment timescale);[80] the presence of the a Ge-Ge donor
group offer an additional stabilization to the cationic oxidized
product;[81] no further oxidation has been observed. This differs
from the parent oligogermanes, where an irreversible Ge-Ge
oxidation is observed usually. The oxidation of the chromium
center into a cationic species is pushing any possible further
This article is protected by copyright. All rights reserved.

10.1002/ejic.201801095
European Journal of Inorganic Chemistry
FULL PAPER
oxidation towards higher potentials, in this case, making a
second oxidation of the compound much more difficult. The
oxidation of 4a has the shape of a typical slow electron transfer
and occurs at E1/2 = 0.32 V vs. Fc/Fc+. The oxidation of the
Experimental Section
Experimental Details. All manipulations were performed under a dry,
oxygen-free argon atmosphere using standard Schlenk techniques. 1H
NMR (400.130 MHz), 13C NMR (100.613 MHz) and 19F (376.498 MHz)
parent compound (η6-MeC6H5)Cr(CO)3 has been reported to
78-79]
occur at E1/2 = 0.38 V vs. Fc/Fc+,[53b,
indicating that the
spectra were recorded with
a Bruker 400 or Agilent 400MR
spectrometers at 298 K. Chemical shifts are given in ppm relative to
internal Me4Si (1H and 13C NMR spectra) or external CFCl3 (19F NMR
spectra). Mass spectra (EI-MS, 70 eV) were recorded on a quadrupole
mass spectrometer FINNIGAN MAT INCOS 50 with direct insertion; all
assignments were made with reference to the most abundant isotopes.
High resolution mass spectra (HRMS) were measured on a Bruker
micrOTOF II instrument using electrospray ionization (ESI). Elemental
analyses were carried out in the Microanalytical Laboratory of the
Chemistry Department of the Moscow State University using
HeraeusVarioElementar instrument. UV/visible spectra were obtained
using two ray spectrophotometer Evolution 300 «Thermo Scientific» with
cuvette of 1.00 cm long. The IR spectra were recorded using a 200
Thermo Nicolet apparatus. Flash chromatography was performed using
SiO2 (0.015-0.040 mm).
presence of the Ge2 fragment in conjugation with (η6-
MeC6H5)Cr(CO)3 framework resulted to small HOMO
a
destabilization.[82] This decrease in the oxidation potential differs
slightly from what is observed for monogermanium fragments
(compare with E1/2 0.827 V vs. Ag/AgCl (0.377 V vs. Fc/Fc+) for
Me2Ge[(η6-Ph)Cr(CO)3]).[44] Based on the electrochemical data,
the effect of a Ge2 fragment is comparable to the introduction of
four methyl groups on the η6-benzene ring (for (η6-Me4C6H2-
1,2,4,5)Cr(CO)3 E1/2 = 0.33 V vs. Fc/Fc+). Furthermore, these
data indicate that the orbitals of Cr(CO)3 are located on the
HOMO of the whole molecule. The parent digermane 4 is
oxidized irreversibly at a much higher potential Eox 1.65 V vs.
Ag/AgCl[48] (1.20 V vs. Fc/Fc+).
Solvents were dried by standard methods and distilled prior to use.
Tetrahydrofuran, diethyl ether were stored under solid KOH and then
distilled over sodium/benzophenone. Toluene and n-hexane were
refluxed and distilled over sodium. Dichloromethane and acetonitrile were
distilled over CaH2. C6D6 was distilled over sodium under argon.
Starting materials, Me3GeGePh3 (3),[56b] Me3GeGe(pTol)3 (4),[48]
83]
Ph3GeGePh3 (5),[56b,
(C6F5)3GeGePh3 (6)[46] were synthesized
according to the literature procedures. Metal carbonyls, M(CO)6 (M = Cr
(1a), M = Mo (1b), M = W (1c)), were sublimed under vacuum before
using. Other reagents were used as supplied.
Attention! The work with metal carbonyl compounds should be performed
under special conditions (under fume hood) due to volatility and
formation of CO.
Figure 4. Electrochemical data for Me3GeGe(pTol)2(η6-pTol)Cr(CO)3
(4a), 1.00 mM in [TBA][PF6] in CH2Cl2. Sweeping rate: 250 mV/s.
X-Ray crystallography. Crystal data for 3c, 4a and 5a are given in
Table S1 (Supporting Information). These data have been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publications no. 1865890 (3c), 1865473 (4a), 1865889 (5a). They can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Conclusions
Several synthetic routes for the synthesis of the 3a-3c, 4a-7a,
R3Ge-GeAr2(R’C6H4-η6)M(CO)3, were developed and studied.
Among them, the reaction between aryloligogermane and
M(CO)3(NCMe)3 was found to be the best synthetic strategy.
The analysis of the experimental and literature data for (η6-
arene)M(CO)3 complexes, including derivatives of catenated
Group 14 compounds, indicates that electronic interaction (π-, d-
and σ-interactions) between all parts of the molecule (Ge-Ge,
arene, M(CO)3) are observed and affects the physical properties
of the whole molecule even though it remains weak.
Oligogermanyl substituents on aromatic ring show the behavior
typical for electron donating substituents, so the complexes like
R3Ge-GeAr2(R’C6H4-η6)M(CO)3 are of donor-acceptor nature.
Introduction of oligogermanyl group bathochromically shifted
UV/vis absorption bands due to a significant mixing of the atomic
orbitals. The electrochemical oxidation of (η6-ArGe2R5)M(CO)3 is
reversible since to the oxidation is happening on the metallic
center M rather than on the Ge-Ge bond.
Electrochemistry. Electrochemical measurements were carried out
using an Autolab 302N potentiostat interfaced through Nova 2.0 software
to a personal computer. Electrochemical measurements were performed
in a glovebox under oxygen levels of less than 5 ppm using solvent that
had been purified by passing through an alumina-based purification
system. Diamond-polished glassy carbon electrodes of 3 mm diameter
were employed for cyclic voltammetry (CV) scans. CV data were
evaluated using standard diagnostic criteria for diffusion control and for
chemical and electrochemical reversibility. The experimental reference
electrode was a silver wire coated with anodically deposited silver
chloride and separated from the working solution by a fine glass frit. The
electrochemical potentials in this article are referenced to
ferrocene/ferrocenium couple. The ferrocene potential was obtained by
its addition to the analyte solution.
Data for initial compounds
Me3GeGePh3 (3). 1H NMR (400.130 MHz, C6D6): δ = 7.55-7.50 (m, 6H),
7.16-7.10 (m, 9H) (aromatic protons), 0.36 (s, 9H, GeMe3) ppm. 13C NMR
This article is protected by copyright. All rights reserved.

10.1002/ejic.201801095
European Journal of Inorganic Chemistry
FULL PAPER
(100.613 MHz, C6D6): δ = 138.49 (ipso-C6H5), 135.61 and 128.67 (o- and
m-C6H5), 128.84 (p-C6H5), -0.88 (GeMe3) ppm.
Me3GeGePh2(Ph-η6)Mo(CO)3 (3b). Analogously to 3a using
Mo(CO)3(NCMe)3 (2b) (0.70 g, 2.30 mmol) and Me3GeGePh3 (3) (0.89 g,
2.11 mmol). The reaction was accompanied by
a
noticeable
1
decomposition (precipitation of a black precipitate). After evaporation,
dissolving in ether and passing through a pad of SiO2, H NMR analysis
Ph3GeGePh3 (5). H NMR (400.130 MHz, C6D6): δ = 7.60-7.56 (m, 12H),
1
7.09-7.01 (m, 18H) (aromatic protons) ppm. 13C NMR (100.613 MHz,
C6D6): δ = 137.92 (ipso-C6H5), 135.98 and 128.74 (o- and m-C6H5),
129.19 (p-C6H5) ppm.
of the mixture obtained indicates the presence of initial compound 3
(major) and complex 3b (trace amounts). For complex 3b: 1H NMR
3
4
(400.130 MHz, C6D6): δ = 5.22 (dd, JH-H= 6.5 Hz, JH-H= 0.8 Hz, 2H, o-
C6H5*Mo(CO)3), 4.75 (tt, JH-H
3
4
= 6.5 Hz, JH-H= 0.8 Hz, 1H, p-
(C6F5)3GeGePh3 (6). 1H NMR (400.130 MHz, C6D6): δ = 7.41-7.33 (m,
6H), 7.06-6.98 (m, 3H), 6.95-6.87 (m, 6H) (aromatic protons) ppm. 13C
NMR (100.613 MHz, C6D6): δ = 135.08 and 128.73 (o- and m-C6H5),
133.21 (ipso-C6H5), 130.13 (p-C6H5) ppm. 19F NMR (376.498 MHz,
C6D6): δ = -124.52 – (-124.60) (2F), 149.03 – (-149.13) (1F), -159.68 – (-
159.78) (2F) ppm.
C6H5*Mo(CO)3), 4.44 (t, 3JH-H= 6.5 Hz, 2H, m-C6H5*Mo(CO)3) ppm. Other
signals are overlapped with the signals of Me3GeGePh3 (3). IR (nujol) ν,
cm-1: 1978 (s) (A1, CO), 1900 (s) (E, CO). HRMS (ESI), m/z [M-H]+, calcd.
600.6565, found 600.6548.
Me3GeGePh2(Ph-η6)W(CO)3 (3c). Method 1. Analogously to 3a using
W(CO)3(NCMe)3 (2c) (0.78 g, 1.99 mmol) and Me3GeGePh3 (3) (0.59 g,
1.40 mmol). After chromatography (SiO2) initial 3 (0.27 g, Rf 0.6,
ether/petroleum ether 1:4) and target complex 3c (0.14 g, 27 %,
conversion 54 %, Rf 0.3, ether/petroleum ether 1:3, orange powder) were
isolated.
Synthesis of Ph3GeGeMe2GePh3 (7). At -78 oC the solution of nBuLi in
hexane (2.5 M, 2.0 mL, 5.00 mmol) was added dropwise to the solution
of Ph3GeH (1.52 g, 5.00 mmol) in ether (50 mL). After stirring at the same
temperature for 2 h the solution of Ph3GeLi generated in situ was used
further without isolation. Then Me2GeCl2 (0.43 g, 2.50 mol) was added to
the solution of Ph3GeLi obtained as described above, reaction mixture
was slowly warmed to room temperature and stirred overnight. Then
water (50 mL) was added, aqueous phase was extracted with ether
(3x20 mL), combined organic phases were dried over MgSO4, and then
all volatile materials were removed under reduced pressure. After
recrystallization from toluene/n-heptane mixture compound 7 (1.49 g,
Method 2. Solid W(CO)6 (1c) (0.42 g, 1.19 mmol) was added to the
solution of Me3GeGePh3 (3) (0.50 g, 1.19 mmol) in a mixture of
(nBu)2O/THF (10:1) (30 mL). The mixture obtained was frozen in liquid
nitrogen, evacuated in high pressure and warmed to room temperature
(procedure was repeated three times). Then it was refluxed on oil bath
(150 oC) for 5 h, whereas significant decomposition (black precipitate)
was observed. Then all volatile materials were removed under reduced
pressure, the residue was dissolved in ether and the residue was passed
through a pad of SiO2 indicating the decomposition. 1H NMR (400.130
MHz, C6D6): δ = 7.57-7.53 (m, 6H), 7.24-7.17 (m, 4H) (aromatic protons),
1
84 %) was isolated as white crystals. H NMR (400.130 MHz, C6D6): δ =
7.46-7.39 (m, 12H), 7.14-7.03 (m, 18H) (aromatic protons), 0.70 (s, 6H,
GeMe2) ppm. 13C NMR (100.613 MHz, C6D6): δ = 138.10 (ipso-C6H5),
135.85 and 128.61 (o- and m-C6H5), 128.84 (p-C6H5), -2.00 (GeMe2) ppm.
The 13C NMR data in CDCl3 corresponds to known from the literature.[84]
HRMS (ESI), m/z [M-H]+, calcd. 709.6045, found 709.6036.
3
4
3
4.98 (dd, JH-H= 6.3 Hz, JH-H= 1.2 Hz, 2H, o-C6H5*W(CO)3), 4.50 (tt, JH-
H= 6.3 Hz, 4JH-H= 1.2 Hz, 1H, p-C6H5*W(CO)3), 4.17 (tt, 3JH-H= 6.3 Hz, 4JH-
H= 1.2 Hz, 2H, m-C6H5*W(CO)3), 0.45 (s, 9H, GeMe3) ppm. 13C NMR
(100.613 MHz, C6D6): δ = 209.95 (W(CO)3), 136.98 (ipso-C6H5), 135.50
and 128.91 (o- and m-C6H5), 129.54 (p-C6H5), 97.63 (ipso-C6H5*W(CO)3),
97.23 and 89.19 (o- and m-C6H5*W(CO)3), 91.86 (p-C6H5*W(CO)3), -0.57
(GeMe3) ppm. MS (EI) m/z (%): 690 ([M]+, 4), 606 ([M – 3CO]+, 22), 544
([M – CO - GeMe3]+, 16), 488 ([M – 3CO - GeMe3]+, 2), 422 ([M –
W(CO)3]+, 46), 304 ([Ph3Ge]+, 100), 227 ([Ph2Ge]+, 27), 52 ([Cr]+, 2).
UV/vis (CH2Cl2), λmax, nm (ε, М-1 cm-1): 233 (sh) (1.96x104), 291
(0.38x104), 322 (0.46x104). IR (nujol) ν, cm-1: 2924 (s), 2862 (m), 1980
(s) (A1, CO), 1904 (s) (E, CO), 1460 (m). HRMS (ESI), m/z [M-H]+, calcd.
688.5565, found 688.5567. С24H24Ge2O3W (689.5634): Calcd. С 41.80,
H 3.51; Found: C 39.68, H 2.87 %.
Synthesis of the initial complexes
Synthesis of fac-(MeCN)3M(CO)3 (M = Cr (2a), Mo (2b), W (2c)).
Synthesis was performed using literature procedure,[40] by refluxing
corresponding M(CO)6 in MeCN, what allows to obtain (MeCN)3M(CO)3
(72 % for 2a; 67 % for 2b; 76 % for 2c) as a yellow powder.
Synthesis of the target aryloligogermane carbonyl complexes
Me3GeGePh2(Ph-η6)Cr(CO)3 (3a). Solid (MeCN)3Cr(CO)3 (2a) (0.34 g,
1.31 mmol) was added to the solution of Me3GeGePh3 (3) (0.46 g, 1.09
mmol) in THF (20 mL), the mixture obtained was refluxed for 1 h. Then
all volatile materials were removed under reduced pressure and the
residue was purified by flash-chromatography (SiO2, petroleum
ether/toluene 4:1) giving target compound 3a (Rf 0.3, 0.25 g, 42 %) as a
yellow powder. 1H NMR (400.130 MHz, C6D6): δ = 7.59-7.53 (m, 4H),
Me3GeGe(pTol)2(pTol-η6)Cr(CO)3 (4a). Analogously to 3a using
Cr(CO)3(NCMe)3 (2a) (0.27 g, 1.04 mmol) and Me3GeGe(pTol)3 (4) (0.48
g, 1.04 mmol). After chromatography (SiO2) initial 4 (0.15 g, Rf 0.8,
toluene/petroleum ether 1:3) and target complex 4a (0.24 g, 56 %, Rf 0.3,
toluene/petroleum ether 1:3, conversion 68 %) were isolated as yellowish
crystals. 1H NMR (400.130 MHz, C6D6): δ = 7.58, 7.11 (2d, JH-H = 6.7 Hz,
each 4H, 2p-C6H4), 5.23, 4.23 (2d, JH-H = 5.1 Hz, each 2H, p-
C6H4*Cr(CO)3), 2.10 (s, 6H, 2C6H4Me), 1.58 (s, 3H, C6H4Me*Cr(CO)3),
0.58 (s, 9H, GeMe3) ppm. 13C NMR (100.613 MHz, C6D6): δ = 234.06
(Cr(CO)3), 139.17, 133.52 (2 ipso-C6H4Me-p), 135.64, 129.72 (2 o-
C6H4Me-p), 110.60, 98.21 (2 ipso-C6H4Me-p*Cr(CO)3), 101.05, 91.98 (2
o-C6H4Me-p*Cr(CO)3), 21.31 (C6H4Me-p), 20.26 (C6H4Me-p*Cr(CO)3), -
0.46 (GeMe3) ppm. MS (EI) m/z (%): 600 ([M]+, 2), 516 ([M – 3CO]+, 100),
464 ([M – Cr(CO)3]+, 454 ([M – CO - GeMe3]+, 18), 398 ([M – 3CO -
GeMe3]+, 1), 38), 346 ([(pTol)3Ge]+, 14), 255 ([(pTol)2Ge]+, 32), 52 ([Cr]+,
4). IR (THF) ν, cm-1: 1961 (s) (A1, CO), 1887 (s) (E, CO). IR (nujol) ν, cm-
1: 1970 (s) (A1, CO), 1894 (s) (E, CO). UV/vis (CH2Cl2), λmax, nm (ε, М-1
cm-1): 233 (sh) (4.55x104), 267 (sh) (0.80x104), 321 (0.87x104). HRMS
3
4
7.26-7.17 (m, 6H) (aromatic protons), 5.03 (dd, JH-H= 6.6 Hz, JH-H= 1.0
Hz, 2H, о-C6H5*Cr(CO)3), 4.56 (tt, JH-H= 6.3 Hz, JH-H= 1.0 Hz, 1Н, p-
C6H5*Cr(CO)3), 4.23 (t, JH-H= 6.3 Hz, 2Н, m-C6H5*Cr(CO)3), 0.49 (s, 9H,
3
4
3
GeMe3) ppm. 13C NMR (100.613 MHz, C6D6): δ = 233.52 (Cr(CO)3),
136.94 (ipso-C6H5), 135.61 and 128.84 (o- and m-C6H5), 129.43 (p-C6H5),
100.25 (ipso-C6H5*Cr(CO)3), 100.11 and 90.79 (o- and m-C6H5*Cr(CO)3),
94.80 (p-C6H5*Cr(CO)3), -0.49 (GeMe3) ppm. MS (EI) m/z (%): 558 ([M]+,
2), 474 ([M – 3CO]+, 100), 422 ([M – Cr(CO)3]+, 42), 412 ([M – CO -
GeMe3]+, 22), 356 ([M – 3CO - GeMe3]+, 4), 304 ([Ph3Ge]+, 34), 227
([Ph2Ge]+, 24), 52 ([Cr]+, 3). UV/vis (CH2Cl2), λmax, nm (ε, М-1 cm-1): 232
(sh) (2.47x104), 263 (sh) (0.53x104), 320 (0.67x104). IR (KBr) ν, cm-1:
1971 (s) (A1, CO), 1910/1894 (s) (E, CO). IR (nujol) ν, cm-1: 1974 (s) (A1,
CO), 1897 (s) (E, CO). HRMS (ESI), m/z [M-H]+, calcd. 556.7121, found
556.7107. С24H24CrGe2O3 (557.7200): Calcd. С 51.68, H 4.34; Found: C
51.26, H 4.12 %.
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10.1002/ejic.201801095
European Journal of Inorganic Chemistry
FULL PAPER
(ESI), m/z [M-H]+, calcd. 598.7924, found 598.7911. С27H30CrGe2O3
(599.7998): Calcd. С 54.07, H 5.04; Found: C 52.78, H 4.22 %.
nitrogen, evacuated in vacuum and warmed to room temperature (three
times); then it was heated at 190 oC for 2 h. Then all volatile materials
were removed under high vacuum, residue was purified by
chromatography (SiO2), giving unreacted [Ph3Ge]2GeMe2 (7) (0.48 g, Rf
0.6, ether/petroleum ether 1:3) and target compound 7a (0.10 g, 34%, Rf
0.3, ether/petroleum ether 1:2, conversion 33 %) as a yellow powder.
Ph3GeGePh2(Ph-η6)Cr(CO)3 (5a). Method 1. Dimethyl succinate (0.46 g,
3.10 mmol) and Cr(CO)6 (1a) (0.76 g, 3.44 mmol) were added to the
suspension of Ph3GeGePh3 (5) (1.90 g, 3.10 mmol) in decalin (20 mL).
Reaction mixture was frozen in liquid nitrogen, evacuated in vacuum and
o
warmed to room temperature (three times); then it was heated at 190 C
Method 2. Trigermane [Ph3Ge]2GeMe2 (7) (0.24 g, 0.33 mmol) was
added to the solution of Cr(CO)3(NCMe)3 (2a) (0.19 g, 0.73, 2.2 eq.) in
THF (20 mL), the solution was refluxed for 2 h, then all volatile materials
were removed under reduced pressure. The residue was purified by
chromatography (SiO2, ether/petroleum ether 1:2) giving initial compound
7 (Rf 0.7, 0.09 g) and target complex 7a as a yellow powder (Rf 0.2, 0.08
for 2 h. Then all volatile materials were removed under high vacuum,
residue was purified by chromatography (SiO2, petroleum ether, then
petroleum ether/benzene 3:2), giving target compound 5a (Rf 0.4, 0.18 g,
28 %, conversion 29 %) as a yellow powder and unreacted Ph3GeGePh3
(5a) (Rf 0.7 in benzene, 1.37 g).
1
g, 44 %, conversion 63 %). H NMR (400.130 MHz, C6D6): δ = 7.44-7.34
(m, 10H), 7.15-7.07 (m, 15H) (aromatic protons), 4.80 (d, JH-H = 5.9 Hz,
2H, o-C6H5*Cr(CO)3), 4.53 (br t, JH-H = 5.9 Hz, 1H, p-C6H5*Cr(CO)3), 4.17
(br t, J = 5.9 Hz, 2H, m-C6H5*Cr(CO)3), 0.81 (s, 6H, GeMe2) ppm. 13C
NMR (100.613 MHz, C6D6): δ = 233.36 (Cr(CO)3), 137.62 (Ge(ipso-
C6H5)3), 136.52 (Ge(ipso-C6H5)2Ph*Cr(CO)3), 135.91 and 128.81 (Ge(o-
and m-C6H5)2Ph*Cr(CO)3), 135.78 and 128.71 (Ge(o- and m-C6H5)3),
129.53 (Ge(p-C6H5)2Ph*Cr(CO)3), 129.01 (Ge(p-C6H5)3), 100.54
(Ge(ipso-C6H5)*Cr(CO)3), 99.95 and 90.80 (Ge(o- and m-C6H5)*Cr(CO)3),
Method 2. Analogously to 3c (Method 2) using Cr(CO)6 (1a) (0.31 g, 1.40
mmol) and Ph3GeGePh3 (5) (0.80 g, 1.32 mmol) in (nBu)2O/THF (10:1)
mixture (20 mL), heating for 26 h. The residue was purified by
chromatography (SiO2, Rf 0.3, benzene/petroleum ether 1:3) giving 5a
(0.31 g, 32 %) as a yellow powder. 1H NMR (400.130 MHz, C6D6): δ =
7.75-7.70 (m, 4H), 7.61-7.54 (m, 6H), 7.14-7.06 (m, 15H) (aromatic
protons), 5.05 (d, JH-H = 6.3 Hz, 2H, o-C6H5*Cr(CO)3), 4.48 (t, JH-H = 6.3
Hz, 1H, p-C6H5*Cr(CO)3), 4.14 (t, JH-H = 6.3 Hz, 2H, m-C6H5*Cr(CO)3)
ppm. 13C NMR (100.613 MHz, C6D6): δ = 233.10 (Cr(CO)3), 136.84
(Ge(p-C6H5)2(Ph*Cr(CO)3)), 136.14 (Ge(p-C6H5)3), 135.94 and 128.90
(Ge(o- and m-C6H5)3), 135.79 (Ge(ipso-C6H5)3), 129.89 and 129.52
94.52 (Ge(p-C6H5)*Cr(CO)3), -1.68 (GeMe2) ppm. UV/vis (CH2Cl2), λmax
,
nm (ε, М-1 cm-1): 244 (sh) (3.60x104), 261 (sh) (2.10x104), 321 (0.38x104).
IR (nujol) ν, cm-1: 2942 (s), 1972 (s) (A1, CO), 1896 (s) (E, CO), 1452 (m).
MS (EI) m/z (%): 847 ([M]+, 1), 763 ([M – 3CO]+, 22), 711 ([M – Cr(CO)3]+,
100), 407 ([Ph3GeGeMe2]+, 12), 304 ([Ph3Ge]+, 22), 52 ([Cr]+, 2). HRMS
(ESI), m/z [M-H]+, calcd. 845.6298, found 845.6281. С41H36CrGe3O3
(846.6372): Calcd. С 58.16, H 4.29; Found: C 60.12, H 4.52 %.
(Ge(o-
and
m-C6H5)2(Ph*Cr(CO)3)),
128.53
(Ge(ipso-
C6H5)2(Ph*Cr(CO)3)), 100.60 (Ge(ipso-C6H5)*Cr(CO)3)), 99.82 and 90.74
(Ge(o- and m-C6H5)*Cr(CO)3)), 94.27 (Ge(p-C6H5)*Cr(CO)3)) ppm. MS
(EI) m/z (%): 744 ([M]+, 2), 660 ([M – 3CO]+, 43), 608 ([M – Cr(CO)3]+, 38),
412 ([M – CO - GePh3]+, 2), 357 ([M – 3CO - GePh3]+, 2), 304 ([Ph3Ge]+,
100), 227 ([Ph2Ge]+, 21), 151 ([PhGe + H]+, 18), 52 ([Cr]+, 2). UV/vis
(CH2Cl2), λmax, nm (ε, М-1 cm-1): 238 (sh) (3.57x104), 267 (sh) (1.04x104),
322 (0.64x104). IR (nujol) ν, cm-1: 2932 (s), 1975 (s) (A1, CO), 1900 (s) (E,
CO), 1454 (s), 1370 (m). HRMS (ESI), m/z [M-H]+, calcd. 742.9208,
found 742.9211. С39H30CrGe2O3 (743.9282): Calcd. С 62.97, H 4.06;
Found: C 60.72, H 3.66 %.
Acknowledgments
We thank Dr. V.A. Korolyov (IOC RAS, Moscow, Russia) for
mass spectral investigations. This work was supported in part by
M.V. Lomonosov Moscow State University Program of
Development and by the University of Greenwich. The DFT
calculations are carried out at Tomsk Polytechnic University
within the framework of Tomsk Polytechnic University
Competitiveness Enhancement Program grant.
(C6F5)3GeGePh2(Ph-η6)Cr(CO)3 (6a). Analogously to 3c (Method 2)
using Cr(CO)6 (1a) (0.15 g, 0.69 mmol) and (C6F5)3GeGePh3 (6) (0.58 g,
0.66 mmol) in (nBu)2O/THF (10:1) mixture (20 mL), heating for 30 h. The
residue was purified by chromatography (SiO2, Rf 0.3, ether/petroleum
ether 1:3), giving 6a (0.11 g, 16 %) as an orange powder. 1H NMR
(400.130 MHz, C6D6): δ = 7.58-7.54 (m, 4H), 7.04-7.00 (m, 6H) (aromatic
3
3
rotons), 4.91 (d, JH-H = 6.3 Hz, 2H, о-C6H5*Cr(CO)3), 4.35 (t, JH-H = 6.3
Keywords: Germanium • Oligogermanes • X-ray Diffraction
Analysis • Carbonyl Complex • Chromium
3
Hz, 1H, p-C6H5*Cr(CO)3), 4.06 (t, JH-H = 6.3 Hz, 2H, m-C6H5*Cr(CO)3)
ppm. 13C NMR (100.613 MHz, C6D6): δ = 232.17 (Cr(CO)3), 149.85-
149.66, 147.42-147.24, 144.88-144.78, 142.39-142.13, 139.16-138.85,
136.63-136.27 (6m, Ge(C6F5)3), 135.19 and 129.04 (o- and m-C6H5),
131.25 (ipso-C6H5), 130.86 (p-C6H5), 97.79 and 90.94 (o- and m-
C6H5*Cr(CO)3), 95.16 (ipso-C6H5*Cr(CO)3), 93.51 (p-C6H5*Cr(CO)3) ppm.
19F NMR (376.498 MHz, C6D6): δ = -124.29 – (-124.34) (2F), 148.61 – (-
148.72) (1F), -159.46 – (-159.56) (2F) ppm. MS (EI) m/z (%): 1014 ([M]+,
1), 930 ([M – 3CO]+, 32), 878 ([M – Cr(CO)3]+, 22), 575 ([(C6F5)3Ge]+, 8),
[1]
a) R. D. Miller, J. Michl, Chem. Rev. 1989, 89, 1359-1410; b) M. L.
Amadoruge, C. S. Weinert, Chem. Rev. 2008, 108, 4253-4294; c) C.
Marschner, in Functional Molecular Silicon Compounds I, 155 (Ed.: D.
Scheschkewitz), Springer International Publishing, 2014, pp. 163-228;
d) C. Marschner, J. Hlina, in Comprehensive Inorganic Chemistry II
(Second Edition) (Eds.: J. Reedijk, K. Poeppelmeier), Elsevier,
Amsterdam, 2013, pp. 83-117.
304 ([Ph3Ge]+, 100), 167 ([C6F5]+, 16), 52 ([Cr]+, 2). UV/vis (CH2Cl2), λmax
,
nm (ε, М-1 cm-1): 234 (sh) (2.15x104), 261 (0.78x104), 322 (0.41x104). IR
(nujol) ν, cm-1: 2852 (s), 1976 (s) (A1, CO), 1901 (s) (E, CO), 1650 (m),
1462 (s), 1372 (m), 1082 (s). HRMS (ESI), m/z [M-H]+, calcd. 1012.7777,
found 1012.7782. С39H15CrF15Ge2O3 (1013.7851): Calcd. С 46.20, H
1.49; Found: C 44.64, H 1.07 %.
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Entry for the Table of Contents
FULL PAPER
A series of transition metal carbonyl
complexes with aryloligogermanes
Oligogermanium Complexes
Kirill V. Zaitsev,* Kevin Lam, Viktor A.
Tafeenko, Alexander A. Korlyukov, Oleg
Kh. Poleshchuk
was
obtained
and
thoroughly
IR, UV/vis
investigated
(NMR,
spectroscopy, electrochemistry, DFT,
XRD). Oligogermanyl substituents
have an electron donor behaviour,
whereas the M(CO)3 group is
characterized as electron withdrawing.
The dependences of the properties
from the nature of M, R, Ar, number of
Ge atoms were established.
Page No. – Page No.
Aryl Oligogermanes as Ligands for
Transition Metal Complexes
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