A Redox-Switchable Germylene and its Ligating Properties in Selected Transition Metal Complexes

Article abstract of DOI:10.1002/chem.201605073

The synthesis, structure, and full characterization of a redox-switchable germylene based on a [3]ferrocenophane ligand arrangement, [Fc(NMes)₂Ge] (4), is presented. The mesityl (Mes)-substituted title compound is readily available from Fc(NHMes)₂(2) and Ge{N(SiMe₃)₂}₂, or from the dilithiated, highly air- and moisture-sensitive compound Fc(NLiMes)₂?3 Et₂O (3) and GeCl₂. Cyclic voltammetry studies are provided for 4, confirming the above-mentioned view of a redox-switchable germylene metalloligand. Although several 1:1 Rh^Iand Ir^Icomplexes of 4 (5–7) are cleanly formed in solution, all attempts to isolate them in pure form failed due to stability problems. However, crystalline solids of [Mo(κ¹Ge-4)₂(CO)₄] (8) and [W(κ¹Ge-4)₂(CO)₄] (9) were isolated and fully characterized by common spectroscopic techniques (8 by X-ray diffraction). DFT calculations were performed on a series of model compounds to elucidate a conceivable interplay between the metal atoms in neutral and cationic bimetallic complexes of the type [Rh(κ¹E-qE)(CO)₂Cl]^0/+(qE=[Fc(NPh)₂E] with E=C, Si, Ge). The bonding characteristics of the coordinated Fc-based metalloligands (qE/qE⁺) are strongly affected upon in silico oxidation of the calculated complexes. The calculated Tolman electronic parameter (TEP) significantly increases by approximately 20 cm^?1(E=C) to 25 cm^?1(E=Si, Ge) upon oxidation. The change in the ligand-donating abilities upon oxidation can mainly be attributed to Coulombic effects, whereas an orbital-based interaction appears to have only a minor influence.

Full text of DOI:10.1002/chem.201605073

A Journal of
Accepted Article
Title: A Redox-Switchable Germylene and its Ligating Properties in
Selected Transition Metal Complexes
Authors: Florian Walz, Eric Moos, Delphine Garnier, Ralf Köppe,
Christopher E. Anson, and Frank Breher
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201605073
Link to VoR: http://dx.doi.org/10.1002/chem.201605073
Supported by

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
A Redox-Switchable Germylene and its Ligating Properties in
Selected Transition Metal Complexes
Florian Walz,[a] Eric Moos,[a] Delphine Garnier,[a,b] Ralf Köppe,[a] Christopher E. Anson,[a]
and Frank Breher[a]*
Abstract: The synthesis, structure, and full characterization of a
redox-switchable germylene based on a [3]ferrocenophane ligand
arrangement, [Fc(NMes)2Ge] (4), is presented. The mesityl (Mes)-
substituted title compound is readily available from Fc(NHMes)2 (2)
and Ge{N(SiMe3)2}2, or from the dilithiated, highly air- and moisture-
sensitive compound Fc(NLiMes)2 · 3 Et2O (3) and GeCl2. Cyclic
voltammetry studies are provided for 4 confirming the above
mentioned view of a redox-switchable germylene metalloligand.
Although several 1:1 Rh(I) and Ir(I) complexes of 4 (5 – 7) are cleanly
formed in solution, all attempts to isolate them in pure form failed due
to stability problems. However, crystalline solids of [Mo(1Ge-
4)2(CO)4] (8) and [W(1Ge-4)2(CO)4] (9) were isolated and fully
characterized by common spectroscopic techniques (8 by X-ray
diffraction). DFT calculations were performed on a series of model
compounds in order to elucidate a conceivable interplay between the
metal atoms in neutral and cationic bimetallic complexes of the type
[Rh(1E-qE)(CO)2Cl]0/+ (qE = [Fc(NPh)2E] with E = C, Si, Ge). The
bonding characteristics of the coordinated Fc-based metalloligands
(qE/qE+) are strongly affected upon in silico oxidation of the calculated
complexes. The calculated Tolman electronic parameter (TEP)
significantly increase by ca. 20 cm-1 (E = C) to 25 cm-1 (E = Si, Ge)
upon oxidation. The change in the ligand donating abilities upon
oxidation can mainly be attributed to Coulombic effects, while an
orbital-based interaction appears to have only a minor influence.
Redox-active ligands offer the possibility to easily modify the
electronic properties of a metal complex. As an inherent feature,
they carry a fragment capable of gaining or losing electrons, with
a concomitant change of the ligation properties, which means that
the oxidation/reduction of the ligand affects the Lewis
acidity/basicity of both the ligand and coordinated metal center.[4]
Furthermore, uncommon reaction paths can be made available
by a ligand acting as an electron reservoir.[2c,5] In case the redox-
active fragment of the ligand is a metal center, the ligand is
frequently referred to as a redox-active metalloligand, that is, a
coordination complex as building block in lieu of simple organic
ligands.[6] Redox-active ligands of this type usually have a well-
defined number of electrons involved in mostly reversible
oxidation/reduction processes.
Introduction
In recent years, there has been a growing interest in studying
transition-metal complexes based on redox non-innocent
ligands.[1] The various types of non-innocent ligands known to
date, and the mechanisms through which they influence the
reactivity of a metal complex, with a particular attention to the field
of catalysis,[2] ion-sensing, or functional molecular materials,[2c,2d,3]
for instance, have been summarized in many reviews.
[a]
Dr. F. Walz, Dr. E. Moos, Dr. D. Garnier, Dr. R. Köppe, Dr. C. E.
Anson, Prof. Dr. F. Breher
Scheme 1. Selected redox-active metalloligands and their metal complexes (I–
VIII).
Institute of Inorganic Chemistry
Karlsruhe Institute of Technology (KIT)
Engesserstr. 15, 76131 Karlsruhe, Germany
E-mail: breher@kit.edu
[b]
Dr. D. Garnier (present address)
Institute of Organic Chemistry
University of Stuttgart
Pfaffenwaldring 55, 70569 Stuttgart, Germany
Seminal papers reported in this area focused, in particular, on
metallocene-based ligand scaffolds, most often containing
phosphine-[7] or N-donor-based[8] ligand entities attached to the
metallocenes. Carbene-based[9] redox-active ligands have also
been studied in recent years (Scheme 1).[10] For instance,
Siemeling and Bielawski have reported investigations on the
Supporting information for this article is given via a link at the end of
the document.
1
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
electronic properties and coordination chemistry of NHC
derivatives with 1,1’-ferrocenediyl backbones (I).[11] Structurally
related metal-containing NHC ligands have been published
before by Arduengo and co-workers (II)[12] and, more recently, by
Ganter et al.(III)[13] NHCs or related derivatives that feature redox-
active ferrocenyl substituents and that are ligated to catalytically
active metal fragments have recently been applied by the groups
of Sarkar (IV), Peris (V), and Bielawski (VI) as redox-switchable
catalysts.[14] Somehow related to these redox-active carbene
ligands, our research group has investigated the coordination
chemistry of Group 14-based tripodal ambidentate ligands,[15]
which contain a “free” pyramidal donor site (Scheme 1).[16] For
instance, we have recently reported on the synthesis of
divalent Group 14 element compounds containing N-ligands,[22a-d]
and ligands based on heavier group 14 element,[22e-k] we thought
to achieve this goal by substituting the carbene C atom in FcDAC
by a heavier, divalent Group 14 element, i.e. by a donor atom
featuring much larger and more diffuse valence orbitals, in
particular the -acceptor orbital.[23] Therefore, we became
interested in exploring the organometallic and coordination
chemistry of heavier analogs of FcDAC, in particular a redox-
switchable N-heterocyclic germylene (NHGe) based on the
[3]ferrocenophane ligand arrangement (target, Scheme 2).
Although several germylenes and their transition metal
complexes have been reported in recent years,[24] no redox-active
version has been published up to date, to the best of our
knowledge. Solely Inoue, Enthaler, Dries and co-workers[25] have
investigated a 1,1’-ferrocenyl-bridged bis(germylene) featuring
amidinate ligands on the Ge atoms, which in turn possess the
coordination number 3. In this particular case, however, the Fc
entity was introduced as flexible spacer and not for switching
purposes.
During the preparation of this manuscript it became apparent that
parallel to our studies[26a] the group of Siemeling[26b,27] also
prepared differently substituted NHGe (and NHSn) derivatives
with the 1,1’-ferrocenediyl backbone, focussing, however, not on
their redox-switchable ligating properties but on future
investigations on the reactivity of the free, uncoordinated NHGe
towards small molecules, also addressing the influence of the
redox state.[27] Herein we describe our results on the synthesis,
structure and electrochemical properties of the mesityl-
substituted diaminogermylene[3]ferrocenophane (4) and its first
transition metal complexes. Furthermore, quantum chemical
calculations on the electronic communication in the
heterobimetallic complexes are provided. We are particularly
interested in polynuclear complexes of this type in order to explore
cooperative effects between metal centers.[28,29]
heterobimetallic complexes containing
a redox-switchable,
carbanion-based metalloligand (VII).[17] In this case, the redox-
active, Ru-based ligand is the dominant electron reservoir.
Although DFT calculations predicted only marginal changes of the
bonding characteristics within the {MX} fragment upon electronic
excitation of the ruthenium-based metalloligand, some effect of
the influence of {MX} on the RuII/RuIII redox potential was detected
with the aid of cyclic voltammetry measurements. Related studies
have been perfomed for heterobimetallic cuprates consisting of a
redox-switchable, silicon-based metalloligand (VIII).[18]
The change in the ligand donating abilities upon oxidation of the
NHC-derived carbene ligand FcDAC[11a] in I was found to be
largely due to Coulombic effects, where removal of an electron
alters the overall molecular charge and increases the Tolman
electronic parameter (TEP)[19] by ca. +11 cm-1.[20] In line with this,
Ganter and co-workers showed that the inclusion of the
unipositive [RuCp*]+ fragment into the carbene ligand in III leads
to an experimental TEP of ca. 5 cm-1.[13] In previous studies,
however, Wrigthon and co-workers found for ferrocenyl-derived
phosphine ligands that both the coordinated and the redox-active
metal atom should be arranged in close spatial proximity in order
to attain an optimal intermetallic electronic interaction.[21] In this
line of thought, Bielawski et al. also proposed an orbital-based
explanation for the TEP upon oxidation (Scheme 2, top).
Results and Discussion
Diaminogermylene[3]ferrocenophane (4)
We initially focused on the mesityl-substituted derivative and used
1,1’-N-ferrocenyl diamine (Fc(NH2)2, 1) as starting material.[30]
The latter was employed in a literature-known Buchwald-Hartwig
coupling reaction with MesBr to provide Fc(NHMes)2 (2) in good
1
yield (Scheme 3).[31] The H and 13C NMR spectroscopic data
match with those published before by Arnold et al.[31] Orange
single crystals of 2 suitable for an X-ray diffraction study were
grown from Et2O at -30 °C (space group P21/c). The molecular
structure further confirmed the identity of the product (see Figure
S3-1 of the Supporting Information).
Deprotonation of 2 with BuLi in diethyl ether at -78 °C provided
the highly air- and moisture-sensitive compound 3 in 41 %
isolated yield as an orange, pyrophoric powder, which is only
hardly soluble in Et2O, toluene and benzene (Scheme 3). The
absence of an NH stretching band in the IR-ATR spectrum of solid
3 supported the successful dilithiation of the ferrocenyl diamine 2.
The 1H and 13C NMR spectra of 3 in C6D6, assigned with the aid
of various 2D NMR experiments (1H,13C-gHMQC, 1H,13C-gHMBC),
consist of several sets of signals that are attributed to N(Li)Mes
(1H = 2.09, 2.12, 2.46, 6.91, and 7.23 ppm) and Cp entities (1H
= 2.96, 3.38, 3.54, and 3.73 ppm). It has to be noted, however,
that the number of resonances are indicative for an unsymmetrical
structure of 3 in solution, in particular if compared with 2 (cf.
2
Scheme 2. Top: schematic illustration explaining the effect of oxidizing the
FcDAC ligand in I (Scheme 1) on the carbonyl stretching frequency (adapted
from ref. [11a]); bottom: proposal of this work, replacing C by Ge in order to
increase the possible orbital overlap; target molecule of this study. Note that the
Rh moiety has been truncated for clarity.
We speculated that the intermetallic communication in these
polynuclear scaffolds might be raised by increasing the overall
orbital overlap of the constituents. Based on our experience with
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
NHMes: 1H = 2.12, 2.17, and 6.78 ppm (4.05 ppm for NH); Cp:
cyclopentadienyl entities. The 1H NMR spectrum exhibits two
signals corresponding to the methyl group of the Mes ligands in
the ortho- and para-positions at 1H = 2.49 and 2.13 ppm,
respectively, while the respective signals for the aromatic CHMes
group appears at 6.81 ppm. The signal for the CHCp entities were
detected as two well-separated pseudo-triplets (AA’BB’ spin
system; for a simulation of the spectrum, see Figure S1-2 of the
Supporting Information) with chemical shifts of  = 3.89 and 4.33
ppm (Figure 1). The rather simple, symmetric structure of 4 in
solution was also confirmed by 13C NMR spectroscopy (see
Experimental Part for details).
1H = 3.78 and 3.81 ppm; see also Figure S1-1 of the Supporting
Information). Integration of the signals revealed that solid 3
contains ca. three Et2O solvent molecules. Note that the dilithiated
compound should always be freshly prepared because
degradation products can already be detected after some days of
storage in an atmosphere of argon. Due to its high sensitivity, no
satisfactory elemental analysis could be obtained for 3.
Scheme 3. Synthesis of [Fc(NMes)2Ge] (4).
The target compound [Fc(NMes)2Ge] (4) is accessible via two
ways, either by reacting the dilithiated 3 with one equivalent of
GeCl2·dioxane in toluene at -78 °C and stirring for 15 hours at
room temperature (33 % isolated yield after work-up) or by
[32]
treating one equivalent of Ge{N(SiMe3)2}2 with 2 in toluene at
60 °C. Although the isolated yield of 4 is significantly higher in this
case (61 %), the reaction time is considerably longer (2 weeks). 4
is very soluble in toluene, benzene and tetrahydrofurane;
acetonitrile was found to react with the germylene under formation
of 2. Compound 4 is a (very) moisture and air-sensitive red solid
that is thermally stable (m.p. = 235-237 °C). Their UV/Vis
spectrum in THF shows broad bands around  = 456 ( = 962
dm3mol-1cm-1) and 294 nm ( = 16360 dm3mol-1cm-1), which
correspond to ferrocene-based d–d transitions[33] and fall in the
typical range found for 1,1’-ferrocene diamines.[34]
Figure 2. Molecular structure of 4 (a, displacement ellipsoids are drawn at the
30% probability level) and different top and side views (b and c). Selected bond
lengths and distances (pm) and angles (°): Fe1–C1 201.35(16), Fe1–C2
202.53(19), Fe1–C3 204.05(19), Fe1–C4 206.4(2), Fe1–C5 203.63(18), Fe1–
C6 201.68(16), Fe1–C7 203.60(18), Fe1–C8 205.49(18), Fe1–C9 203.93(19),
Fe1–C10 202.48(17), Fe1–Cpcent(1) 163.9, Fe1–Cpcent(2) 163.7, Ge1–N1
184.59(14), Ge1–N2 184.43(14), Ge1...Fe1 381.7, N1–C1 141.6(2), N2–C6
141.3(2), N1–C11 143.9(2), N2–C20 144.3(2); N1–Ge1–N2 103.67(6), Ge1–
N1–C1 131.10(11), Ge1–N2–C6 130.53(11), C1–Fe1–C6 100.70(7), C3–Fe1–
C8 113.24(9), C4–Fe1–C9 112.98(9). (Cpcent = centroids of the Cp rings)
Crystals of [Fc(NMes)2Ge] (4) suitable for X-ray crystallography
were obtained from a concentrated Et2O solution at -40 °C (Figure
2; space group P21/c). As expected, the germanium center in 4 is
bonded to two NMes entities (N1–Ge1–N2 = 103.67°). The
bridging of the 1,1’-N-ferrocenyldi(mesitylamido) scaffold by the
germanium(II) atom results in slightly inclined Cp rings, which can
be seen from the ca. 10 pm shorter iron–carbon bond lengths
Fe1–C1 (201.35 pm) and Fe1–C6 (201.68 pm) as compared to
those observed for
3 (see the Supporting Information).
Nevertheless, the ferrocene entity adopts an S-1,1’-synclinic
conformation (Figure 2b). The carbon–nitrogen bond lengths C1–
N1 and C6–N2 of 141.6 and 141.3 pm, respectively, are ca. 3 pm
longer than in 3. The Ge–N distances of 184.59 and 184.43 pm
fall in the typical range found for other five- and six-membered N-
heterocyclic germylenes (NHGe).[35] NHGes based on -
diketiminates or amidinates and halogermylenes derived from
1,3-diazaindanes usually show longer Ge–N distances.[36]
Figure 1. 1H NMR spectrum of 4 in C6D6 at room temperature. The inset is
showing the region of the CHCp signals.
Contrary to 3, the 1H and 13C NMR spectra of 4 in C6D6 consist of
simple sets of signals that are attributed to the mesityl and
3
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
Since we intended to employ 4 as redox-switchable ligand in
Metal complexes of 4
coordination chemistry, we became interested in quantifying its
Previous investigations on FcDAC-type carbene ligands have
revealed that such species can act as 1C ligands. Therefore, we
became interested in studying the coordination behavior of the
heavy analog 4 as well. 1H NMR spectroscopic monitoring of the
reaction of two equivs. of 4 with one equiv. of the dimers
[Rh(cod)Cl]2 and [Ir(cod)Cl]2 in C6D6 or d8-thf provided evidence
for the formation of [Rh(1Ge-4)(cod)Cl] (5) and [Ir(1Ge-
4)(cod)Cl] (6) (Scheme 5, Figure 4). Typical signal patterns for 1:1
complexes of 4 with Rh or Ir are observed (see Experimental Part
[37]
size. To this end, we have calculated the buried volume (%Vbur
)
on the basis of the molecular structure. The %Vbur value of 39.2
(d = 200 pm; r = 350.0 pm)[38] reasonably compares with those
obtained for the Fc-based NHC derivatives V1, V4 and V5
(Scheme 4) but is somewhat larger than those published for
purely organic N-heterocyclic carbenes (V6-V8) or the derivatives
V2 and V3 featuring smaller substituents on nitrogen.[39]
1
for details). The numbers of H and 13C NMR signals suggest
rather symmetrical structures in solution, which may be a result of
rapidly rotating metal and germylene entities around the Ge-M
bond on the NMR time scale. Pulsed gradient spin-echo (PGSE)
experiments were performed in d8-thf. The hydrodynamic radii
(rH(5)= 4.80 Å, rH(6)= 5.28 Å) and volumes (VH(5) = 463 Å3, VH(6)
= 616 Å3) in d8-thf solution were obtained by using the
experimental self-diffusion coefficients (D(5) = 9.7751010 m2 s1,
D(6) = 8.8881010 m2 s1) together with the Stokes-Einstein
equation. Note that both VH values for the complexes are very
close to the volume for an individual molecule of the free
germylene (4) estimated from X-ray crystallographic studies (VX-
ray = 610 Å3). However, close inspection of the diffusion properties
of, e.g., the Cp proton signals of the germylene unit and the cod
signals of the [M(cod)Cl] entities verified very similar results (see
Section S1 of the Supporting Information). Based on these data it
seems reasonable to assume that 4 indeed forms 1:1 complexes
with [M(cod)Cl]. However, all attempts to isolate 5 and 6 in pure
form failed. Only decomposition products have been obtained so
far.
Scheme 4. %Vbur values (d = 200 pm; r = 350.0 pm) of some selected
compounds. [a] calculated from the molecular structure of the Rh(cod)Cl
complex;[11] [b] calculated from the molecular structure of the Ir(CO)2Cl
complex;[11] [c] taken from the literature (based on Rh(I) and Ir(I) complexes).[39b]
Cyclic voltammetry studies on 4 were conducted in THF at room
temperature.
Although
the
THF/[nBu4N][Al{OC(CF3)3}4]
electrolyte was stored over sodium and thoroughly dried
glassware was used in a special setup for inert conditions
developed by Heinze,[40] 4 is rapidly hydrolyzed by trace amounts
of water to the parent amine 2 (Figure 3). The latter shows a
quasi-reversible redox process centered at E01/2 = -0.69 V (vs. the
ferrocene/ferrocenium couple, Fc/Fc+), which perfectly fits to
studies reported previously by Diaconescu[34] and Siemeling.[27]
In order to further substantiate the formation of the Rh(I) and Ir(I)
complexes 5 and 6, respectively, we have treated a solution of 6
with CO gas (p = ca. 1 bar) (Scheme 5, Figure 5). The signals for
The quasi-reversible oxidation of 4 detected at E0  0.15 V is
1/2
1
slightly more anodically shifted as compared to the value reported
by Siemeling and co-workers (E01/2 = -0.055 V),[27] which may be
be attributed to differences in the experimental conditions or
artefacts resulting from the relatively large Ep value of ca. 400
mV observed in our case. Note that the very limited publications
on the electrochemistry of NHGe derivatives only report
free 1,5-cyclooctadiene (cod) are immediately visible in the H
1
NMR spectrum (Figure 5). As compared to 6, the number of H
and 13C NMR signals observed for [Ir(1Ge-4)(CO)2Cl] (7) doubles,
which would be in accordance with a lower symmetry of 7. For
instance, the ortho-methyl protons of the Mes substituents gave
two signals with chemical shifts of 1H = 2.56 and 2.64 ppm and
four 1H NMR signals are detected for the Cp protons (Figure 5).
As expected, two resonances are found in the 13C{1H} NMR
spectrum for two different CO ligands (13C = 166.0 and 185.2
ppm; Figure 5). Albeit its clean and almost quantitative formation
in solution, all attempts to isolate 7 from the reaction mixtures
failed so far.
irreversible oxidation processes in THF at Ep  0.48 and 0.85 V
a
(vs. Fc/Fc+),[41] i.e. at much higher potentials. Quantum chemical
calculations performed by us (vide supra) and Siemelig et al.[27]
clearly showed that the spin density in the cationic complex, i.e.
4+, is largely located on the Fe atom of the ferrocenyl-backbone.
Attempts to prepare 4+ on a preparative scale have not yet been
successful but are still in the current focus of interest.
Figure 3. Cyclic voltammogram of 4 in THF at r.t. vs. the Fc/Fc+ couple; Scan
rate 250 mV s1, Pt/[nBu4N][Al{OC(CF3)3}4]/Ag.
Scheme 5. Synthesis of [Rh(1Ge-4)(cod)Cl] (5), [Ir(1Ge-4)(cod)Cl] (6), and
[Ir(1Ge-4)(CO)2Cl] (7). Note that all complexes have only been observed in
solution and decompose upon attempted isolation.
4
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
More successful attempts to isolate a metal complex of 4 have
been made by treating the germylene with the hexacarbonyls of
Both complexes are sparingly soluble in hexane or pentane, but
show a good solubility in toluene, benzene, and THF, and are
thermally stable with decomposition points > 230 °C. The NMR
spectra of the complexes are consistent with the formation of
symmetrical 1:2 metal-ligand species in all cases (Figure 6). For
instance, only one 13C NMR signal was detected for the CO
ligands at 13C = 207.7 (8) and 197.7 (9) ppm. The signals fall in
the expected range found for other 1:2 molybdenum or tungsten
germylene complexes in the literature.[43]
molybdenum and tungsten under irradiation for
2 h in
tetrahydrofuran (Scheme 6). Layering of the reaction solutions
with pentane or hexane furnished bright orange, crystalline solids
of [Mo(1Ge-4)2(CO)4] (8) and [W(1Ge-4)2(CO)4] (9) in 49 % and
14 % isolated yields, respectively. We were not able to detect or
isolate any hypothetical 1:1 metal-ligand complexes of the
general formula [M(1Ge-4)(CO)5], which may be a result of the
trans-effect exerted by 4.[42]
Scheme 6. Synthesis of [Mo(1Ge-4)2(CO)4] (8) and [W(1Ge-4)2(CO)4] (9).
Figure 4. 1H NMR spectra of [Rh(1Ge-4)(cod)Cl] (5, top) and [Ir(1Ge-
4)(cod)Cl] (6, bottom) in C6D6 at room temperature.
Figure 6. 1H NMR spectrum of [Mo(1Ge-4)2(CO)4] (8, bottom) and [W(1Ge-
4)2(CO)4] (9, top) in C6D6 at room temperature. Insets are showing sections of
the 13C NMR spectra, also overlaid with the 13C NMR spectrum of the starting
mateials [W(CO)6] and [Mo(CO)6].
Further evidence for the formation of 1:2 (instead of 1:1)
complexes was provided by IR and Raman investigations (Figure
7). Both complexes show a strong CO band at IR(8) = 1916 and
IR(9) = 1905 cm-1. Additional Raman investigations on 8 provided
two bands at RA(8) = 1971 and 2038 cm-1 (9 decomposes under
Figure 5. 1H NMR spectrum (top) and section of the 13C NMR spectrum (bottom)
of [Ir(1Ge-4)(CO)2Cl] (7) in C6D6 at room temperature.
5
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
laser irradiation). The spectral data gave clear evidence of a local
space group P42212) and the crystallographic analyses
unambiguously confirm the 1:2 structures suggested by the
spectroscopic evidence.
D
4h symmetry around the metal atom and, thus, one IR-active (Eu)
and two Raman-active (A1g and B2g) CO stretches. Note that
compared to NHGe molybdenum complexes of the net formula
[L3Mo(CO)3] (L = NHGe), the CO band of 8, provided by the IR
investigation, was detected at lower frequencies (60-45 cm-1
less).[45]
The Mo center in 8 is coordinated by two germylene entities in
trans-position and four CO ligands. All structural parameters are
in good agreement with those observed for another 1:2
molybdenum complexes of a halogermylene.[43b] We are not
aware of any other reports on 1:2 molybdenum complexes of
germylenes featuring this trans arrangement. The Ge-Mo bond
length (249.40 pm) is very similar to the closely related 1:2
molybdenum complex of a halogermylene (249.90 pm).[43b]
Slightly longer Ge-Mo bond length were observed for five-
membered N-heterocyclic germylene complexes ([L3Mo(CO)3], L
= NHGe) (252.85, 254.45, 254.52 pm)[44a,b] and a chelate complex
featuring a bis(germylene) ([L2Mo(CO)4], L = NHGe) (252.04
pm).[44c] The Ge-N bond length (181.0) pm) is marginally shorter
than those observed in 4 (184.59, 184.43 pm), i.e. the free
germylene.
Cyclic voltammetry studies on 8 and 9 in THF at room
temperature showed that also the coordination compounds of
Fc(NMes)2Ge are extremely sensitive to moisture. Nevertheless,
apart from the typical redox process for the product of hydrolysis,
i.e. the amine 2, quasi reversible redox waves were detected at
E01/2(8) = -0.03 V and E01/2(9) = -0.02 V (vs. Fc/Fc+) with peak
potential differences of Ep(8) = 115 mV and Ep(9) = 91 mV,
respectively (See section S2 of the Supporting Information). From
these values it can be concluded that the redox potential of the
Fc-based NHGe (4) is only slightly affected upon coordination.
Furthermore, it has to be noted that we did not detect a
conceivable splitting of the half-wave potentials due to metal-to-
metal communcation between both ferrocenyl entities in the 1Ge-
coordinated germylenes in 8 and 9.[45]
Figure 7. FT-IR (black) and Raman spectrum (red) of solid [Mo(1Ge-4)2(CO)4]
(8).
Quantum Chemical Calculations
In order to elucidate a conceivable interplay between the metal
atoms in the bimetallic complexes, we initially focused on a
change of the bonding characteristics of the redox-switchable
germylene 4 upon oxidation. To this end, we have performed
some density functional theory (DFT) computations with the
Turbomole program package. We have chosen qGe as model
compound of 4 for this study containing phenyl instead of mesityl
substituents on nitrogen (Figure 9) and used the def2-TZVP basis
sets (see Experimental Part for details).
Figure 8. Molecular structure of [Mo(1Ge-4)2(CO)4] (8). Displacement
ellipsoids are drawn at the 30% probability level, carbon atoms of the Mes
ligands as spheres, for clarity reasons. Selected bond lengths (pm) and angles
(°): Ge1–Mo1 249.40(16), Mo1–C1 203.4(15), C1–O1 111.3(16), Ge1–N1
181.0(11), Ge1...Fe1 377.1, N1–C2 143.7(18), N1–C7 149.6(17), Fe1–C2
198.7(15), Fe1–C3 203.0(13), Fe1–C4 204.3(18), Fe1–C5 203.5(17), Fe1–C6
202.5(14), Fe1–Cpcent(1) 162.7; O1–C1–Mo1 178.8(15), C1–Mo1–C1’
178.6(16), C1–Mo1–C1’’ 91.9(8), C1–Mo1–C1’’’ 88.2(8), C1’–Mo1–C1’’’ 89.3(8),
C1’’–Mo1–C1’’’ 90.7(8), Ge1–Mo1–C1 90.7(8), Ge1–Mo1–C1’’ 89.3(8), Ge1–
Mo1–Ge1’ 180.0, N1–Ge1–Mo1 127.6(4), N1–Ge1–N1’’’ 104.8(7), Ge1–N1–C2
128.9(10), Ge1–N1–C7 119.7(9), C2–N1–C7 111.2(11), C2–Fe1–C2’’’ 100.7(9),
C3–Fe1–C3’’’ 166.4(8), C4–Fe1–C4’’’ 124.0(9), C5–Fe1–C5’’’ 137.5(9), C6–
Fe1–C6’’’ 141.6(8). (Cpcent = centroid of the Cp ligand). Atoms labeled with
apostrophes are generated by –x+1, -y+1, z ('), y, x, -z+1 (''), and –y+1, -x+1, -
z+1 (''').
Table 1. Selected geometry parameters (bond lengths in pm, angles in °) of the
model compounds qE/qE+ with E = C, Si, Ge.
Compound
4 (XRD)[a]
qGe
avg. Fe-C
202.8
206.5
212.2
206.2
211.5
205.4
210.8
avg. E-N
183.9
191.0
192.6
177.2
177.6
135.1
135.1
N-E-N
103.7
104.0
100.9
107.2
104.9
122.3
122.1
Fe...E
381.7
380.4
387.8
374.5
380.6
341.2
343.5
qGe+
qSi
qSi+
qC
qC+
[a] more detailed values are given in the caption of Figure 2.
In comparison with the experimental X-ray diffraction (XRD) data,
Crystals of 8 suitable for X-ray crystallography were obtained by
layering a concentrated THF solution with hexane (Figure 8;
Table 1 shows selected geometry parameters of the qGe and
qGe+. Note that Siemeling et al.[27] also found a second, strongly
6
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
distorted, thermodynamically disfavoured (G = 20.5 kcal mol-1)
bent structure for Fc(NMes)2Ge, which was, however, not
considered in our study. The agreement between computed bond
lengths for qGe and experiment (4) is satisfactory (4+ is not known
yet). The structural changes upon going from qGe to qGe+ are
relatively small, in accordance with Siemeling et al.[27] The
(mostly) germanium-centered lone-pair of electrons for the NHGe
qGe was found to be HOMO−4, i.e. much lower than typically
found for the related NHC derivatives,[11] whereas the lowest
unoccupied molecular orbital (LUMO) represents the expected p-
type acceptor orbital of the germylene. Note that Figure 9a
displays this Ge(4p) orbital analogous to the schematic drawing
in Scheme 2.
qSi, and qGe strongly decrease upon descending the Group 14
(cf. Figure 10, Table 2).
The HOMO (not shown) is centered on the iron atom of the
ferrocene backbone of qGe. Furthermore, spin density
calculations on the optimized geometry of the cationic germylene
qGe+ clearly suggests that the oxidation process seen in the cyclic
voltammogramm of 4 (cf. Figure 3) is also located on the iron
center (Figure 9b). Natural population analyses (NPA) further
support these findings (qGe: Fe: +0.25, Ge: +1.11; qGe+: Fe:
+1.23, Ge: +0.01). These computational results nicely confirm the
Figure 10. Compilation of the calculated orbital energies of qC, qSi and qGe
obtained at the B3LYP/def2-TZVP level; simplified visualization of the -
acceptor orbital (blue), the iron-centered HOMO (red) and the -donor orbital of
the ylene unit (green).
above mentioned view of
metalloligand.
a redox-switchable germylene
The results nicely correspond to orbital diagrams of benzo-
anellated NHC, NHSi, and NHGe compounds presented by
Heinicke et al.[44] The energy of the Fe-centered HOMO changes
only slightly within this series[46] and, consistently, the spin density
is located almost exclusively on the iron atom in the cationic
species qE+. Note that previous reports of Siemeling and co-
workers on the carbene system showed a slightly more
delocalized nature with the spin density distributed across the iron
and the carbene carbon atom.[27,11c]
Table 2. Calculated orbital energies [eV] of qC, qSi and qGe obtained at the
B3LYP/def2-TZVP level.
model comp.
-acceptor (ylene)
-0.59[b]
HOMO (Fe)
-5.36
-donor (ylene)
-5.77[c]
qC
qSi
qGe
-1.22[a]
-1.76[a]
-5.59
-5.91[d]
-6.21[e]
-5.55
[a] LUMO; [b] LUMO+1; [c] HOMO-1; [d] HOMO-3; [e] HOMO-4
Table 3. Selected geometry parameters (bond lengths in pm, angles in °) of the
model compounds qERh/qERh+ with E = C, Si, Ge.
avg.
avg.
Compound
N-E-N
E-Rh
Rh-Cl
E...Cl
Figure 9. Selected frontier orbitals of qGe (a), spin density of qGe+ (b), HOMO
of [Rh(1Ge-qGe)(CO)2Cl] (qGeRh, c), and spin density of [Rh(1Ge-
qGe)(CO)2Cl]+ (qGeRh+, d) obtained at the B3LYP/def2-TZVP level (C: black;
H: grey; N: blue; Cl: yellow; O: red; Fe: dark red; Ge: green). Note that for all
calculated model compounds the Mes substituents have been replaced by Ph.
For clarity reasons, we have only displayed positive spin density in the contour
plots b) and d). Small negative spin populations reside in all cases on the C
atoms of the Cp rings.
Fe-C
206.7
211.7
206.6
212.1
205.5
210.8
E-N
qGeRh
qGeRh+
qSiRh
qSiRh+
qCRh
185.5
188.7
173.1
175.3
134.8
135.2
108.1
104.9
111.9
107.3
122.8
122.3
243.7
241.8
231.9
229.2
211.6
209.4
240.8
244.2
245.5
249.6
240.6
241.8
269.0
253.8
236.9
228.3
306.7
289.2
qCRh+
In order to compare the results obtained for qGe and qGe+ with
the so-far unknown silicon derivatives and the previously
described FcDAC mentioned in the introduction, we have also
calculated the model compounds qSi/qSi+ and qC/qC+ (see
Section S4 of the Supporting Information). As expected, the
calculated energies of the -donor and -acceptor orbitals
centered on the ylene unit of the neutral model compounds qC,
To further explore the electronic alteration of the metalloligand
upon oxidation, we investigated in a next step the (hypothetical)
Rh(CO)2Cl complex of 4, namely [Rh(1Ge-qGe)(CO)2Cl]
(qGeRh) and its cationic counterpart qGeRh+ (Figure 9c and d,
respectively). Table 3 shows selected geometry parameters. Most
notably, the structural differences between qGeRh and qGeRh+
7
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
are much more pronounced as compared to the couple qGe/qGe+, reported, it appears that these calculated data for the gas-phase
in particular the tilting of the N-Ph entities with respect to the
planes defined by the Cp ligands (see Figure 9c and d).
Furthermore, the oxidized complex qGeRh+ shows a relatively
short contact between Ge and Cl of 253.8 pm (cf. 269.0 pm for
qGeRh). This structural aspect already hints to a significant
increase of the acceptor properties of the germanium(II) atom.
Again, spin density calculations verified the hypothesis of an Fe-
centered redox process (Figure 9d). Most importantly, the
calculated CO stretching frequencies considerably change from
1calc = 2073 cm-1 and 2calc = 2008 cm-1 for qGeRh (avcalc = 2041
species overestimate the effect of changing the redox-state of the
ligand. However, the former are solution processes, which are
much more complicated considering, for instance, the influence of
the solvent, the counter anions, etc. Nevertheless, the qualitative
trend to decreasing the donor and/or increasing the acceptor
properties of metalloligands upon oxidation is clear. For our
compound of interest, i.e. the redox-switchable germylene, the
calculated ligation properties for qGe+ (TEPqE+corr = 2084 cm-1) is
in the range of phosphite ligands and very electron-deficient
phosphines such as P(C6F5)3 (TEPexp = 2090.9 cm-1). Note that
Kühl et al.[50] has nicely shown by comprehensive calculations of
NHGe derivatives that such TEP values can only be achieved by
introducing strong acceptor substituents like cyano or nitro groups.
In our case, however, such values are accessible by simply
removing one electron from the redox-switchable germylene.
Considering the above mentioned overestimation for the gas-
phase calculation by the factor of ca. 2, we expect the
experimentally determined, solution-based TEP value for the
cationic germylene to be in the region of electron-deficient
phosphines and phosphites, i.e. around 2072 cm-1. This has,
however, to be confirmed by experiment, which is in the current
focus of our interest.
We also note in passing that the increase of the TEP values upon
oxidation is slightly more pronounced for the heavier ylenes as
compared to the carbene ligand. Although it is too early for a final
statement, this might be due to a better orbital overlap in these
polynuclear scaffolds induced by the larger valence orbitals of the
donor atom, in this case the 3p and 4p acceptor orbitals of silicon
and germanium, respectively. Nevertheless, the change in the
ligand donating abilities upon oxidation can, as previously
noted,[20] mainly be attributed to Coulombic effects while an
orbital-based interaction appears to have only a minor influence.
calc
cm-1) to 1calc= 2102 cm-1 and 2calc= 2044 cm-1 in qGeRh+ (av
= 2073 cm-1). Although these computed vibrational frequencies
avcalc had to be scaled in order to be compared with experimental
values,[47] the avcalc data appear to suffer from a systematic error
because the calculated data would justify a categorization of the
germylene (4) among good donor ligands if compared to
Rh(CO)2Cl complexes of both electron-rich and electron-deficient
calc
NHC ligands.[48,19d] For the above mentioned av
TEPqGe
values a
for qGe of 2051 cm-1 would result (Table 4).[49] This
calc
would be comparable to classical NHC ligands like IAd or IPr.
However, the calculated orbital energies for the series qC, qSi
and qGe clearly showed that qGe should be a (much) weaker
donor as compared to qC, for instance, which would also be in
line with the common view in the literature.[50]
In order to overcome this problem, we have again also calculated
the lighter congeners, namely qSiRh and qCRh, both for
comparison and, more importantly, to calibrate the results
obtained for this series with the experiment, which is known for
the [Rh(CO)2Cl] complex of FcDAC (TEPFcDAC = 2048.5 cm-
exp
1).[11] A direct comparison of TEPFcDAC
with the calculated
exp
TEPqCcalc of 2040 cm-1 gave the correction factor F = 1.0039 (and
this TEPqC = 2049 cm-1).[51] The correction was applied to all
corr
model compounds to furnish TEPqSicorr of 2052 cm-1 and TEPqGe
corr
of 2059 cm-1, respectively (Table 4). To put these numbers into
perspective, the genuine carbene ligand FcDAC shows donor
properties comparable to classical NHC ligands like IAd (Figure
11). The so-far unknown silicon derivative qSi is still a good donor,
in the range of electron-rich phosphine ligands such as PCyc3 or
the carbene IPr (Figure 11). As expected, the germanium
compound qGe is a weaker ligand and falls in the typical region
found for phosphine ligands such as PiPr3 or PCyc3 (Figure 11).
corr
corr
Table 4. Calculated TEPqE
and TEPqE+
values [cm-1] using a correction
factor of F = 1.0039 in order to calibrate the calculated results with the
experiment.
Figure 11. Tolman electronic parameter (TEP) of qE and qE+ (calculated, E =
C, Si, Ge) and selected NHC and phosphine ligands (experimental values taken
from the literature).
corr
corr
corr
model comp.
qC/qC+
qSi/qSi+
TEPqE
TEPqE+
2069
TEPqE/qE+
2049[a]
20
25
25
2052
2077
qGe/qGe+
2059
2084
[a] calibrated to the experiment, TEPFcDACexp = 2048.5 cm-1.
Conclusions
In this work we have described the synthesis and characterization
of a redox-switchable germylene based on a 1,1’-ferrocenediyl
backbone, [Fc(NMes)2Ge] (4), which is readily available from
Fc(NHMes)2 (2) and Ge{N(SiMe3)2}2, or from the dilithiated
compound Fc(NLiMes)2 ·3 Et2O (3) and GeCl2 in 61 and 33 %
Last but not least, we were very much interested in estimating the
difference in the TEP values upon switching the redox-state of the
metalloligands. Table 4 summarizes the TEPqE+corr of the oxidized
ylenes qC+, qSi+ and qGe+ in the complexes qCRh+, qSiRh+ and
qGeRh+, respectively. Most notably, upon in silico one-electron
oxidation to qERh+, the TEPqE+corr values for all model compounds
are significantly increased by 20-25 cm-1 to 2069 cm-1 for qC+,
2077 cm-1 for qSi+, and 2084 cm-1 for qGe+, respectively. As
experimental TEPexp values of only up to ca. 11 cm-1 have been
isolated yield, respectively. The calculated buried volume (%Vbur
)
of 4 amounts to 39.2 and reasonably compares with those
reported for the Fc-based NHC derivatives. Cyclic voltammetry
studies are provided for 4 confirming the above mentioned view
8
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
respectively. The abbreviation br. is given for broadened signals.
Assignments were confirmed if necessary with the use of two-dimensional
correlation experiments. Pulsed field-gradient spin-echo (PGSE)
measurements were conducted as previously described.[52] All diffusion
and molecular size estimations were performed using the DiffAtOnce
software package.[52c]
of a redox-switchable germylene metalloligand. Several attempts
to isolate the 1:1 Rh(I) and Ir(I) complexes of 4, [Rh(1Ge-
4)(cod)Cl] (5), [Ir(1Ge-4)(cod)Cl] (6), and [Ir(1Ge-4)(CO)2Cl] (7),
failed so far. However, as evidenced with the aid of various NMR
spectroscopic techniques, all complexes are cleanly formed in
solution. On the other hand, the 1:2 metal-ligand complexes
[Mo(1Ge-4)2(CO)4] (8) and [W(1Ge-4)2(CO)4] (9) are stable and
were isolated in 49 % and 14 % yield, respectively. The structural
parameters of 8 were determined by X-ray diffraction showing a
trans arrangement of both germylene ligands. The local D4h
symmetry around the metal atom in 8 and 9 were also confirmed
by IR and Raman investigations. Density functional theory (DFT)
calculations have been provided on a series of model compounds
in order to elucidate a conceivable interplay between the metal
atoms in bimetallic complexes of the type [Rh(1E-qE)(CO)2Cl]0/+
(E = C, Si, Ge). The bonding characteristics of the coordinated
Fc-based metalloligands (qE/qE+) are strongly affected upon in
silico oxidation of the calculated complexes. The calculated
Tolman electronic parameter (TEP) significantly increase by 20-
25 cm-1 upon oxidation. Although this dependence suggests an
interaction between both metals due to their close spatial
proximity, only small differences in the TEP values have been
observed by substituting the carbene (E = C; TEP = 20 cm-1) for
the silylene or the germylene (E = Si, Ge; TEP = 25 cm-1). The
change in the ligand donating abilities upon oxidation can thus
mainly be attributed to Coulombic effects, while an orbital-based
interaction appears to have only a minor influence.
Computational details. The calculations were performed with the
TURBOMOLE program package[53] in the framework of density functional
theory (DFT). The functional B3LYP[54] was used in conjunction with the
def2-TZVP basis sets.[55] Vibrational frequencies were computed by using
Turbomole’s module Aoforce.
Starting materials. Fc(NH2)2 (1) was prepared according to literature
procedures.[30] The different transition metal compounds employed were
used as obtained from commercial sources without further purification.
2:[31] A mixture of Pd2dba3 (672 mg, 0.73 mmol) and dppf (630 mg, 1.14
mmol) in toluene (70 ml) was placed in a 500 ml round bottom flask.
NaOtBu (2.35 g, 24.50 mmol), 2-Bromomesitylene (5.87 g, 4.50 ml, 29.50
mmol) and 1,1‘-N-ferrocenyldiamine (2.10 g, 9.72 mmol) were added
subsequently to the dark orange solution. The resulting suspension was
diluted with THF (140 ml) and heated to 95 °C for 64 h. The following work-
up procedure was performed under air. After cooling to room temperature,
the dark red suspension was poured into water (140 ml) and extracted 5
times with 200 ml of diethyl ether. The combined ethereal layers were dried
over magnesium sulfate. All volatile components were removed in vacuo.
The red oily residue was taken up in diethyl ether and filtered through a
pad of Florisil®. After reducing the filtrate to dryness, the residue dissolved
in dry toluene (15 ml). 2 was collected as a brownish, micro crystalline solid
(2.23 g, 4.93 mmol, 51 %) at -40 °C. Suitable crystals for X-ray diffraction
can be obtained by recrystallization from diethyl ether. 1H NMR
(300.1 MHz, C6D6, 25°C): δ = 2.12 (s, 12 H, Mes-oCH3), 2.17 (s, 6 H, Mes-
pCH3), 3.78 (m, 4 H, Cp-CH(2,5)), 3.81 (m, Cp-CH(3,4)), 4.05 (s, 2 H, NH,
W1/2 = 3.5 Hz), 6.78 (s, Mes-CH). 13C NMR (75.5 MHz, C6D6, 25°C): δ =
18.7 (s, Mes-oCH3), 20.8 (s, Mes-pCH3), 60.3 (s, Cp-CH(3,4)), 64.6 (s, Cp-
CH(2,5)), 108.2 (s, Cp-C(1)), 129.9 (s, Mes-C-oCH3), 131.0 (s, Mes-CH),
132.4 (s, Mes-C-pCH3), 139.8 (s, N-C-Mes). FT-IR (ATR): ν = 410 s, 429
s, 449 vs, 458 s, 484 s, 501 m, 510 m, 526 w, 558 m, 578 w, 602 w, 614
w, 646 w, 664 w, 693 m, 729 w, 763 w, 800 s, 838 m, 858 s, 882 w, 937
m, 958 w, 1009 s, 1029 w, 1037 m, 1051 w, 1063 vw, 1098 vw, 1122 w,
1155 w, 1221 m, 1261 s, 1276 w, 1305 m, 1347 w, 1377 m, 1435 m, 1471
s, 1500 vs, 1586 vw, 1736 vw, 1776 vw, 2732 br, vw, 2853 w, 2910 w,
2941 w, 2962 vw, 3024 vw, 3083 vw, 3096 vw, 3404 m cm-1.
3: A solution of 2 (2.00 g, 4.42 mmol) in diethyl ether (80 ml) was treated
carefully with BuLi in hexane (2.50 M, 3.90 mL, 9.73 mmol) at -78 °C. The
resulting suspension was raised to ambient temperature and stirred for 18
h. The yellowish orange precipitate was filtered, washed twice with diethyl
ether (10 ml) and dried in vacuo. The content of ether was determined (3
diethyl ether molecules per ferrocenyl moiety) by 1H NMR measurements
in C6D6 (yield: 1.256 g, 1.82 mmol, 41 %). M. p. (sealed tube under Ar):
>189°C (dec.). 1H NMR (300.1 MHz, C6D6, 25°C): δ = 1.11 (t, 18 H,
(CH3CH2)2O), 2.09 (s, 6 H, Mes-oCH3), 2.12 (s, 6 H, Mes-oCH3), 2.46 (s,
6 H, Mes-pCH3), 2.96 (m, 2 H, Cp-CH), 3.26 (q, 12 H, (CH3CH2)2O), 3.38
(m, 2 H, Cp-CH), 3.54 (m, 2 H, Cp-CH) 3.73 (m, 2H, Cp-CH), 6.91 (s, 2 H,
Mes-CH), 7.23 (s, Mes-CH). 7Li NMR (116.6 MHz, C6D6, 25°C): δ = 2.6 (s,
broad, Li), 0.9 (s, broad, Li). 13C NMR (75.5 MHz, C6D6, 25°C): δ [ppm] =
15.1 ((CH3CH2)2O), 19.0 (2 signals, Mes-oCH3), 20.6 (Mes-pCH3), 55.0
(Cp-CH), 58.8 (Cp-CH), 62.3 (Cp-CH), 64.1 (Cp-CH), 65.5 ((CH3CH2)2O),
not detected (Cp-C(1), 130.2 (Mes-CH), 131.6 (Mes-CH), 130.8 (s, Mes-
C-oCH3), 133.9 (s, Mes-C-oCH3), 133.6 (Mes-C-pCH3), 149.8 (N-C-Mes).
FT-IR (ATR): ν = 443 s, 460 s, 449 vs, 489 m, 507 m, 534 s, 561 s, 580 m,
607 w, 632 m, 643 m, 686 w, 710 w, 735 w, 761 w, 772 m, 782 m, 791 m,
806 s, 824 w, 853 s, 880 w, 916 w, 936 m, 957 w, 977 vw, 1002 w, 1021
m, 1046 m, 1069 br, m, 1100 w, 1150 m, 1200 m, 1219 m, 1243 s, 1264 s,
1298 m, 1323 w, 1356 w, 1375 m, 1387 m, 1422 m, 1454 vs, 1518 br, vw,
1607 br, vw, 1726 vw, 2727 br, vw, 2857 vw, 2873 vw, 2910 vw, 2923 w,
2968 w, 3020 vw, 3073 vw, 3082 vw, 3094 vw, 3130 vw cm-1. Elemental
analysis: varying values.
Experimental Section
General methods and instrumentation. The reactions were performed
under an inert atmosphere of argon using Schlenk techniques, unless
stated otherwise. Air sensitive compounds were stored and weighed in a
glovebox. All solvents (THF, toluene, benzene) were freshly distilled under
argon from sodium/benzophenone (THF, benzene, toluene) prior to use.
Diethyl ether was distilled from sodium/potassium alloy/benzophenone
immediately prior use. [D8]THF and C6D6 were vacuum transferred from
potassium/benzophenone into thoroughly dried glassware equipped with
Young teflon valves. Elemental analyses were carried out in the
institutional technical laboratories of the Karlsruhe Institute of Technology
(KIT). Due to the air- and moisture-sensitive nature of 3, no satisfactory
elemental analyses could be obtained. For the complexes 8 and 9, the
obtained results are outside the range viewed as establishing analytical
purity. This is due to the varying solvent content of crystalline samples
dried in vacuo. IR spectra were recorded on a Bruker Alpha spectrometer
in the range from 4000 cm−1 to 400 cm−1 using a KBr beamsplitter.
Samples were measured by using the ATR technique (attenuated total
reflection) on bulk material, and the data are quoted in wavenumbers
(cm−1). The intensity of the absorption band is indicated as vw (very weak),
w (weak), m (medium), s (strong), vs (very strong), and br (broad). FT-
Raman spectra were taken using a Bruker MultiRam spectrometer; the
excitation wavelength of the Nd-YAG laser was 1064 nm. Cyclic
voltammetry measurements were performed with a suitable potentiostat
and an electrochemical cell within a glovebox. We used a freshly polished
Pt disk working electrode, a Pt wire as counter electrode, and a Ag wire as
(pseudo)
reference
electrode
{[nBu4N][PF6]
(0.05
M)
or
[nBu4N][Al{OC(CF3)3}4] (0.05 M) as electrolyte}. Potentials were calibrated
against the Fc/Fc+ couple (internal standard). UV-VIS spectra were
recorded in dry THF on a Varian Cary 100 Scan spectrometer in the range
from 800 nm to 260 nm using a quarz cuvette (d = 1 cm). Solution NMR
spectra were recorded with NMR instruments operating at 1H Larmor
frequencies of 300 and 400 MHz. The spectral reference used was TMS
for 1H and 13C. Coupling constants J are given in Hertz as positive values
regardless of their real individual signs. The multiplicity of the signals is
indicated as s, d, q, or m for singlets, doublets, quartets, or multiplets,
9
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
4: Route 1: During a time period of 15 min, a solution of GeCl2 (424 mg,
1.83 mmol) in toluene (40 ml) was added dropwise to a suspension of 3
(1.256 g, 1.83 mmol) in toluene (60 ml) at -78 °C. The mixture was brought
to ambient temperature and stirred for 18 h. The red brownish suspension
was filtered. All volatile components of the filtrate were removed in vacuo
and diethyl ether (30 ml) was added. A further filtration provided the
separation of a greyish green precipitate from the red filtrate. The volume
of the filtrate was reduced and compound 4 was obtained as a red,
crystalline solid at -40 °C (255 mg, 0.49 mmol, 27 %). A second crop of 4
was obtained by further concentration of the mother liquor (65 mg, 0.12
mmol, 7 %). Total yield: 320 mg, 0.61 mmol, 33 %.
25°C): δ = 20.3 (s, Mes-oCH3), 20.9 (s, Mes-pCH3), 29.0 (s, COD-CH2),
34.4 (s, COD-CH2), 50.8 (s, COD-CH), 67.9 (s, Cp-CH(3,4)), 68.6 (s, Cp-
CH(2,5)), 87.8 (s, COD-CH), 104.9 (s, Cp-C(1)), 130.1 (s, Mes-C-oCH3),
136.2 (s, Mes-CH), 137.3 (s, Mes-C-pCH3), 141.9 (s, N-C-Mes). 13C NMR
(75.5 MHz, [D8]THF, 25°C): δ = 20.4 (s, Mes-oCH3), 21.0 (s, Mes-pCH3),
29.6 (s, COD-CH2), 34.9 (s, COD-CH2), 51.5 (s, COD-CH), 68.2 (s, Cp-
CH(3,4)), 69.1 (s, Cp-CH(2,5)), 87.3 (s, COD-CH), 105.6 (s, Cp-C(1)),
130.2 (s, Mes-C-oCH3), 136.7 (s, Mes-CH), 137.9 (s, Mes-C-pCH3), 142.4
(s, N-C-Mes).
7: In a J. Young NMR tube, a mixture of 4 (24.0 mg, 0.05 mmol) and
[Ir(COD)Cl]2 (12.4 mg, 0.018 mmol) were dissolved in [D8]THF (0.7 ml).
The solution was degassed by three cycles of a freeze-pump-thaw
procedure using liquid nitrogen. The frozen mixture was treated with ~ 1.5
bar of carbon monoxide. After allowing to warm to ambient temperature, a
color change from red to reddish orange took place. The selectively formed
compound 7 could not be isolated since decomposition takes place in the
process of in vacuo solvent removal. 1H NMR (400.1 MHz, [D8]THF, 25°C):
δ = 2.18 (s, 6 H, Mes-pCH3), 2.33 (m, broad, 8 H, free COD-CH2), 2.56 (s,
6 H, Mes-oCH3), 2.64 (s, 6 H, Mes-oCH3), 3.88 (m, 2 H, Cp-CH), 4.10 (m,
2 H, Cp-CH), 4.38 (m, 2 H, Cp-CH), 4.77 (m, 4H, Cp-CH), 5.50 (m, 4 H,
free COD-CH), 6.75 (s, 4 H, Mes-CH), 6.85 (s, 4 H, Mes-CH). 13C NMR
(100.6 MHz, [D8]THF, 25°C): δ = 20.9 (s, Mes-oCH3), 21.2 (s, Mes-oCH3),
21.5 (s, Mes-pCH3), 28.9 (s, free COD-CH2), 66.8 (s, Cp-CH(3,4)), 68.2 (s,
Cp-CH(2,5)), 68.4 (s, Cp-CH(2,5)), 71.3 (s, free COD-CH), 103.8 (s, Cp-
C(1)), 130.0 (s, Mes-C-oCH3), 130,.8 (s, Mes-C-oCH3), 136.7 (s, Mes-CH),
138.6 (s, Mes-CH), 141.6 (s, Mes-C-pCH3), 144.4 (s, N-C-Mes) 166.0 (s,
CO), 185.2 (s, CO).
8: 4 (100 mg, 0.19 mmol) and Mo(CO)6 (26 mg, 0.10 mmol) were dissolved
in THF (10 ml). The mixture was irradiated for 2 h with a mercury vapor
lamp while being stirred. Orange, rod shaped crystals of 8 were isolated
by layering the solution with hexane (20 ml) (59 mg, 0.047 mmol, 49 %).
M. p. (sealed tube under Ar): 233 – 235°C (dec.). 1H NMR (400.1 MHz,
C6D6, 25°C): δ = 2.15 (s, 12 H, Mes-pCH3), 2.47 (s, 24 H, Mes-oCH3), 3.77
and 4.18 (AA’BB’ spin system, 2  4 H, Cp-CH(3,4) and Cp-CH(2,5)), 6.81
(s, 8 H, Mes-CH). 13C NMR (100.6 MHz, C6D6, 25°C): δ = 20.1 (s, Mes-
oCH3), 21.0 (s, Mes-pCH3), 67.6 (s, broad, Cp-CH(3,4), Cp-CH(2,5)),
106.1 (s, Cp-C(1)), 130.5 (s, Mes-C-oCH3), 135.9 (s, Mes-CH), 137.0 (s,
Mes-C-pCH3), 143.1 (s, N-C-Mes), 207.7 (s, Mo-CO). FT-IR (ATR): ν =
403 s, 440 m, 452 m, 491 s, 506 s, 522 s, 541 s, 560 vs, 580 m, 606 vs,
647 s, 716 m, 786 s, 804 s, 818 m, 850 m, 887 s, 914 m, 944 s, 1024 m,
1036 m, 1068 m, 1145 s, 1198 s, 1209 m, 1249 s, 1303 w, 1335 w, 1372
s, 1392 w, 1443 br, s, 1475 m, 1536 w, 1608 w, 1731 w, 1760 w, 1772 w,
1916 vs, 2035 vw, 2075 vw, 2115 vw, 2148 vw, 2727 w, 2854 w, 2917 m,
2948 w, 2999 w, 3086 w, 3101 w cm-1. Raman: ν = 132, 236, 297, 379,
407, 422, 542, 579, 651, 890, 1058, 1152, 1215, 1252, 1303, 1375, 1447,
1609, 1971, 2038, 2918, 3088, 3107 cm-1. Elemental analysis:
C60H60Fe2Ge2MoN4O4 (1326.18); C 58.27 (calcd. 57.47); H 5.50 (4.82); N
3.84 (4.47) %.
9: 4 (100 mg, 0.19 mmol) and W(CO)6 (34 mg, 0.10 mmol) were dissolved
in THF (10 ml). The mixture was irradiated for 2 h with a mercury vapor
lamp while being stirred. Orange, rod shaped crystals of 8 were isolated
by layering the solution with pentane (20 ml) (18.5 mg, 0.014 mmol, 14 %).
M. p. (sealed tube under Ar): 235-238°C (dec.). 1H NMR (400.1 MHz, C6D6,
25°C): δ = 2.14 (s, 12 H, Mes-pCH3), 2.47 (s, 24 H, Mes-oCH3), 3.77 and
4.18 (AA’BB’ spin system, 2  4 H, Cp-CH(3,4) and Cp-CH(2,5)), 6.82 (s,
8 H, Mes-CH). 13C NMR (100.6 MHz, C6D6, 25°C): δ = 20.2 (s, Mes-oCH3),
21.1 (s, Mes-pCH3), 67.7 (s, broad, Cp-CH(3,4), Cp-CH(2,5)), 105.8 (s,
Cp-C(1)), 130.5 (s, Mes-C-oCH3), 135.9 (s, Mes-CH), 137.0 (s, Mes-C-
pCH3), 143.0 (s, N-C-Mes), 197.7 (s, W-CO). FT-IR (ATR): ν = 398 s, 441
m, 454 m, 491 s, 506 m, 521 s, 541 s, 559 vs, 580 m, 600 s, 647 s, 716 m,
786 s, 803 s, 828 m, 847 m, 888 s, 944 s, 1024 s, 1037 m, 1066 m, 1145
s, 1197 s, 1209 m, 1249 br, s, 1303 w, 1335 vw, 1372 s, 1393 w, 1444 br,
s, 1474 m, 1537 w, 1608 w, 1905 br, vs, 1957 w, 2024 vw, 2072 vw, 2727
vw, 2853 w, 2915 m, 2947 m, 3086 w cm-1. Elemental analysis:
C60H60Fe2Ge2WN4O4 (1341.95 g/mol); C 54.12 (calcd. 53.70); H 5.162
(4.51); N 3.58 (4.18) %.
Route 2: A mixture of Ge{N(SiMe3)2}2 (197 mg, 0.50 mmol) and 2 (226 mg,
0.50 mmol) in toluene (10 ml) was stirred 14 days at 60 °C. All volatile
components were removed in vacuo and was crystallized from diethyl
ether at -40 °C (5 ml). 4 was obtained as orange prisms (160 mg, 0.31
mmol, 61 %). M. p. (sealed tube under Ar): 235-237°C. 1H NMR (300.1
MHz, C6D6, 25°C): δ = 2.13 (s, 6 H, Mes-pCH3), 2.49 (s, 12 H, Mes-oCH3),
3
3
3.89 and 4.33 (AA’BB’ spin system, J[1,1] = 1.04 Hz, J[1,2] = 2.67 Hz,
3J[2,1] = 1.17 Hz, 3J[2,2] = 5.14 Hz, 2  4 H, Cp-CH(3,4) and Cp-CH(2,5),
see the Supporting Information), 6.81 (s, 4 H, Mes-CH). 1H NMR (300.1
MHz, [D8]THF, 25°C): δ = 2.20 (s, 6 H, Mes-pCH3), 2.47 (s, 12 H, Mes-
oCH3), 3.93 and 4.35 (AA’BB’ spin system, 3J[1,1] = 1.04 Hz, 3J[1,2] = 2.67
Hz, 3J[2,1] = 1.17 Hz, 3J[2,2] = 5.14 Hz, 2  4 H, Cp-CH(3,4) and Cp-
CH(2,5), see the Supporting Information), 6.87 (m, 4 H, Mes-CH). 13C NMR
(75.5 MHz, C6D6, 25°C): δ = 20.5 (s, Mes-oCH3), 21.3 (s, Mes-pCH3), 67.4
(s, Cp-CH(3,4)), 68.4 (s, Cp-CH(2,5)), 109.6 (s, Cp-C(1)), 130.3 (s, Mes-
C-oCH3), 135.5 (s, Mes-CH), 137.3 (s, Mes-C-pCH3), 143.7 (s, N-C-Mes).
13C NMR (75.5 MHz, [D8]THF, 25°C): δ = 20.3 (s, Mes-oCH3), 20.9 (s, Mes-
pCH3), 67.2 (s, Cp-CH(3,4)), 68.4 (s, Cp-CH(2,5)), 109.9 (s, Cp-C(1)),
130.1 (s, Mes-C-oCH3), 135.7 (s, Mes-CH), 137.5 (s, Mes-C-pCH3), 144.0
(s, N-C-Mes). FT-IR (ATR): ν = 416 m, 458 m, 490 s, 508 m, 522 s, 534 m,
560 s, 579 w, 594 w, 637 m, 644 m, 716 w, 764 w, 799 s, 837 m, 848 m,
861 w, 881 s, 946 s, 1011 m, 1020 m, 1037 w, 1071 vw, 1123 w, 1144 s,
1194 s, 1223 w, 1257 m, 1303 w, 1331 w, 1372 m, 1445 s, 1474 m, 1504
w, 1595 vw, 1607 vw, 1629 vw, 1667 vw, 1729 vw, 1769 vw, 2727 vw,
2851 w, 2912 w, 2941 w, 2974 w, 3081 vw, 3098 vw, 3404 w cm-1. UV-VIS
(THF): max (ε): 456 nm ( = 962 dm3mol–1cm–1), 294 nm ( = 16360
dm3mol–1cm–1). Elemental analysis: C28H30FeGeN2 (523.03); C 64.54
(calcd. 64.30); H 5.76 (5.78); N 5.35 (5.36) %.
5: In a typical experiment, a mixture of 4 (15.7 mg, 0.03 mmol) and
[Rh(COD)Cl]2 (7,4 mg, 0,015 mmol) were dissolved in C6D6 ([D8]THF) (0.7
ml) in a J. Young NMR tube. The selectively formed compound 5 could not
be isolated since decomposition takes place in the process of in vacuo
solvent removal. 1H NMR (400.1 MHz, C6D6, 25°C): δ = 1.29 (m, 2 H, COD-
CH2), 1.41 (m, 2 H, COD-CH2), 1.56 (m, 2 H, COD-CH2), 1.61 (m, 2 H,
COD-CH2), 2.15 (s, 6 H, Mes-pCH3), 2.65 (s, 12 H, Mes-oCH3), 3.79 (m, 2
H, COD-CH), 3.86 and 4.39 (AA’BB’ spin system, 2  4 H, Cp-CH(3,4) and
Cp-CH(2,5)), 5.05 (m, 2 H, COD-CH), 6.84 (s, 4 H, Mes-CH). 1H NMR
(400.1 MHz, [D8]THF, 25 °C): δ = 1.49-1.87 (m, 8 H, COD-CH2), 2.25 (s, 6
H, Mes-pCH3), 2.50 (s, 12 H, Mes-oCH3), 3.65 (m, 2 H, COD-CH), 4.00 (m,
4 H, Cp-CH(3,4)), 4.43 (m, 4H, Cp-CH(2,5)), 4.71 (m, 2 H, COD-CH). 13
C
NMR (100.6 MHz, C6D6, 25°C): δ = 20.5 (s, broad, Mes-oCH3), 20.9 (s,
Mes-pCH3), 28.3 (s, COD-CH2), 33.3 (s, COD-CH2), 67.6 (d, 1JC,Rh = 13.1
Hz, broad, COD-CH), 67.7 (s, broad, Cp-CH(3,4)), 68.6 (s, broad, Cp-
CH(2,5)), 99.5 (d, 1JC,Rh = 8.7 Hz, broad, COD-CH), 105.1 (s, broad, Cp-
C(1)), 130.0 (s, Mes-C-oCH3), 136.0 (s, Mes-CH), 137.8 (s, Mes-C-pCH3),
142.2 (s, N-C-Mes).
6: In a typical run, a mixture of 4 (15.7 mg, 0.03 mmol) and [Ir(COD)Cl]2
(10.1 mg, 0,015 mmol) were solved in C6D6 ([D8]THF) (0.7 ml) in a J.
Young NMR tube. The selectively formed compound 5 could not be
isolated since decomposition takes place in the process of in vacuo solvent
removal. 1H NMR (400.1 MHz, C6D6, 25°C): δ = 1.00 (m, 2 H, COD-CH2),
1.21 (m, 2 H, COD-CH2), 1.39 (m, 2 H, COD-CH2), 1.59 (m, 2 H, COD-
CH2), 2.12 (s, 6 H, Mes-pCH3), 2.63 (s, 12 H, Mes-oCH3), 3.61 (m, 2 H,
COD-CH), 3.84 (m, 4 H, Cp-CH(3,4)), 4.33 (m, 4H, Cp-CH(2,5)), 4.72 (m,
2 H, COD-CH), 6.81 (s, 4 H, Mes-CH). 1H NMR (400.1 MHz, [D8]THF,
25°C): δ = 1.19 (m, 2 H, COD-CH2), 1.30 (m, 2 H, COD-CH2), 1.52 (m, 4
H, COD-CH2), 2.24 (s, 6 H, Mes-pCH3), 2.52 (s, 12 H, Mes-oCH3), 3.45 (m,
2 H, COD-CH), 4.04 (m, 4 H, Cp-CH(3,4)), 4.31 (m, 2 H, COD-CH), 4.47
(m, 4H, Cp-CH(2,5)), 6.90 (s, 4 H, Mes-CH). 13C NMR (75.5 MHz, C6D6,
Crystal structure determinations of 2, 4 and 8. Crystal data collection
and processing parameters are given below. In order to avoid degradation,
single crystals were mounted in perfluoropolyalkyletheroil on top of the
10
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
edge of an open Mark tube and then brought into the cold nitrogen stream
of a low-temperature device (Oxford Cryosystems Cryostream unit) so that
the oil solidified. Diffraction data were measured using a Stoe IPDS II
diffractometer and graphite-monochromated MoK (0.71073 Å) radiation.
The structures were solved by dual-space direct methods with SHELXT,[56]
followed by full-matrix least-squares refinement using SHELXL-2014/7.[57]
All non-hydrogen atoms were refined anisotropically, with organic
hydrogen atoms placed in calculated positions using a riding model.
Crystals of 8 were generally of rather poor quality, reflected in the rather
high R(int). The lattice solvent (7 MeCN per complex molecule) occupies
cavities centred on special positions, and is badly disordered. Its
contribution to the observed structure factors was calculated using
SQUEEZE.[58] Structure factors therefore included contributions from
the .fab file, and the quoted molecular formula includes these MeCN
molecules. The structure was refined taking inversion twinning into
account.
R. H. Crabtree, Chem. Soc. Rev. 2013, 42, 1440; e) V. Blanco, D. A.
Leigh, V. Marcos, Chem. Soc. Rev. 2015, 44, 5341; f) S. M. Guillaume,
E. Kirillov, Y. Sarazin, J.-F. Carpentier, Chem. Eur. J. 2015, 21, 7988.
a) U. Siemeling, Z. Anorg. Allg. Chem. 2005, 631, 2957; b) Z. Liu,
Science 2003, 302, 1543; c) J. W. Sibert, P. B. Forshee, V. Lynch, Inorg.
Chem. 2005, 44, 8602; d) H. Wang, D. Qi, Z. Xie, W. Cao, K. Wang, H.
Shang, J. Jiang, Chem. Commun. 2013, 49, 889; e) K. Green, N Gauthier,
H. Sahnoune, G Argouarch, L. Toupet, K. Costuas, A. Bondon, B. Fabre,
J.-F. Halet, F. Paul, Organometallics 2013, 32, 4366.
[3]
[4]
Another approach uses ferrocenyl substituents as oxidisable entities to
modify the solubility of
a complex. Plenio and co-workers have
demonstrated in a seminal paper that the activity of Fc-decorated
Grubbs-Hoveyda catalysts can be switched by one-electron
oxidation/reduction. Loss of activity is attributed to the low solubility of
the cationic complex catalyst: M. Süßner, H. Plenio, Angew. Chem. 2005,
117, 7045, Angew. Chem. Int. Ed. 2005, 44, 6885; see also b) C. A.
Fleckenstein, H. Plenio, Adv. Synth. Catal. 2006, 348, 1058.
Crystallographic data (excluding structure factors) for the structures in this
paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC 1497719-1497721.
[5]
[6]
For a recent study on the effect of a ferrocene moiety as redox active site,
see: S. Kuriyama, K. Arashiba, K. Nakajima, H. Tanaka, K. Yoshizawa,
Y. Nishibayashi, Chem. Sci. 2015, 6, 3940.
Copies
of
the
data
can
be
obtained
from
https://summary.ccdc.cam.ac.uk/structure-summary-form.
Metalloligands have been used to prepare multimetallic complexes. See
e.g.: a) T. T. Nadasdi, D. W. Stephan, Organometallics 1992, 11, 116; b)
T. Sue, Y. Sunada, H. Nagashima, Eur. J. Inorg. Chem. 2007, 2897; c)
D. L. Reger, J. R. Gardinier, S. Bakbak, R. F. Semeniuc, U. H. F. Bunz,
M. D. Smith, New J. Chem. 2005, 29, 1035; d) T. Matsumoto, M.
Wakizaka, H. Yano, A. Kobayashi, H.-C. Chang, M. Kato, Dalton Trans.
2012, 41, 8303; e) M.-G. Alexandru, D. Visinescu, A. M. Madalan, F.
Lloret, M. Julve, M. Andruh, Inorg. Chem. 2012, 51, 4906. For several
applications in MOF chemistry see e.g.: f) S. R. Halper, L. Do, J. R. Stork,
S. M. Cohen, J. Am. Chem. Soc. 2006, 128, 15255; g) S. Kitagawa, R.
Kitaura, S. Noro, Angew. Chem. Int. Ed. 2004, 43, 2334; general review:
h) G. Kumar, R. Gupta, Chem. Soc. Rev. 2013, 42, 9403.
2: C28H32FeN2, 452.40 g mol-1, monoclinic, P21/c, a = 1453.10(11), b =
803.35(4), c = 1025.73(7) pm,  = 105.266(6)°, V = 1155.13(13) 106 pm3,
T = 200(2) K, Z = 2, (Mo-K) = 0.670 mm1, Dcalcd. = 1.301 g cm–3; crystal
dimensions 0.50×0.15×0.10 mm3, 12455 reflections, 2753 unique data,
Rint = 0.0457; 160 parameters, wR2 (all data) = 0.0828, S = 1.070 (all data),
R1= 0.0303 (2307 data with I > 2σ(I)), max/min residual electron density:
+0.29/–0.23 e 10–6 pm–3
.
4: C28H30FeGeN2, monoclinic, P21/c, a = 1551.22(11), b = 1904.20(11), c
= 834.31(6) pm,  = 91.128(6)°, V = 2463.9(3) 106 pm3, T = 200(2) K, Z =
4, (Mo-K) = 1.826 mm1, Dcalcd. = 1.41 g cm–3; crystal dimensions
0.41×0.38×0.35 mm3, 41884 reflections, 5859 unique data, Rint = 0.0508;
319 parameters, wR2 (all data) = 0.0877, S = 1.028 (all data), R1= 0.0298
(4930 data with I > 2σ(I)), max/min residual electron density: +0.68/-0.81
[7]
[8]
Selected examples of metallocene-based ligand scaffolds containing
phosphine donors with a strong focus on redox-switchable catalysis
(RSC): a) I. M. Lorkovic, R. R. Duff, M. S. Wrighton, J. Am. Chem. Soc.
1995, 117, 3617; b) R. T. Hembre, J. S. McQueen, V. W. Day, J. Am.
Chem. Soc. 1996, 118, 798; c) P. Neumann, H. Dib, A.-M. Caminade, E.
Hey-Hawkins, Angew. Chem. 2015, 127, 316; d) M. Chen, B. Yang, C.
Chen, Angew. Chem. Int. Ed. 2015, 54, 15520.
e 10–6 pm–3
.
8: C74H81Fe2Ge2MoN11O4, 1541.31 g mol-1, tetragonal, P42212, a =
1696.1(2), , c = 1156.8(2) pm, V = 3327.8(12) 106 pm3, T = 200(2) K, Z =
2, (Mo-K) = 1.562 mm1, Dcalcd. = 1.538 g cm–3; crystal dimensions
0.30×0.10×0.09 mm3, 28263 reflections, 3288 unique data, Rint = 0.2328;
171 parameters, wR2 = 0.1969, S = 1.021, Flack  = 0.44(7) (all data), R1=
0.0739 (1919 data with I > 2σ(I)), max/min residual electron density:
Selected examples of metallocene-based ligand scaffolds containing
nitrogen donors with a strong focus on redox-switchable catalysis (RSC):
a) C. K. A. Gregson, V. C. Gibson, N. J. Long, E. L. Marshall, P. J. Oxford,
A. J. P. White, J. Am. Chem. Soc. 2006, 128, 7410; b) E. M. Broderick,
N. Guo, T. Wu, C. S. Vogel, C. Xu, J. Sutter, J. T. Miller, K. Meyer, T.
Cantat, P. L. Diaconescu, Chem. Commun. 2011, 47, 9897; c) E. M.
Broderick, N. Guo, C. S. Vogel, C. Xu, J. Sutter, J. T. Miller, K. Meyer, P.
Mehrkhodavandi, P. L. Diaconescu, J. Am. Chem. Soc. 2011, 133, 9278;
d) X. Wang, A. Thevenon, J. L. Brosmer, I. Yu, S. I. Khan, P.
Mehrkhodavandi, P. L. Diaconescu, J. Am. Chem. Soc. 2014, 136, 11264.
Selected reviews: a) A. J. Arduengo, Acc. Chem. Res. 1999, 32, 913; b)
D. Bourissou, O. Guerret, F. P. Gabbaï, G. Bertrand, Chem. Rev. 2000,
100, 39; c) W. A. Herrmann, Angew. Chem. Int. Ed. 2002, 41, 1290; d)
F. E. Hahn, M. C. Jahnke, Angew. Chem. Int. Ed. 2008, 47, 3122; e) J.
Vignolle, X. Cattoën, Didier Bourissou, Chem. Rev. 2009, 109, 3333; f)
P. de Frémont, N. Marion, S. P. Nolan, Coord. Chem. Rev. 2009, 253,
862; g) K. Öfele, E. Tosch, C. Taubmann, W. A. Herrmann, Chem. Rev.
2009, 109, 3408; h) L. Mercs, M. Albrecht, Chem. Soc. Rev. 2010, 39,
1903; i) T. Dröge, F. Glorius, Angew. Chem. Int. Ed. 2010, 49, 6940; j)
N-Heterocyclic Carbenes−Effective Tools for Organometallic Synthesis;
S. P. Nolan (Ed.); Wiley−VCH Weinheim, Germany, 2014; k) M. N.
Hopkinson, C. Richter, M. Schedler, F. Glorius, Nature 2014, 510, 485.
+0.56/–1.06 e 10–6 pm–3
.
Acknowledgements
We thank Prof. Ulrich Siemeling for his very collegial handling of
the overlapping interests in this research area and Prof. Rainer
Winter for very helpful comments and hints regarding the redox
behaviour of the title compound. Financial support by the DFG
Collaborative Research Centre CRC/Transregio 88, “Cooperative
effects in homo- and heterometallic complexes (3MET)” is
gratefully acknowledged (Project B4).
[9]
Keywords: Germylene • Ferrocene • Metalloligands • Redox-
active Ligands
References
[10] Selected reviews on singlet carbenes derived from ferrocene and closely
related sandwich complexes: a) B. Bildstein, J. Organomet. Chem. 2001,
617-618, 28; b) U. Siemeling, Eur. J. Inorg. Chem. 2012, 3523.
[11] Studies on diaminocarbene[3]ferrocenophanes and closely related Fc-
decorated NHC ligands and their complexes: a) D. M. Khramov, E. L.
Rosen, V. M. Lynch, C. W. Bielawski, Angew. Chem. 2008, 120, 2299;
b) U. Siemeling, C. Färber, C. Bruhn, Chem. Commun. 2009, 98; c) U.
Siemeling, C. Färber, M. Leibold, C. Bruhn, P. Mücke, R. F. Winter, B.
Sarkar, M. von Hopffgarten, G. Frenking, Eur. J. Inorg. Chem. 2009,
11
[1]
a) A. M. Allgeier,C. A. Mirkin, Angew. Chem. Int. Ed. 1998, 37, 894; b)
W. Kaim, Inorg. Chem. 2011, 50, 9752; c) P. J. Chirik, Inorg. Chem. 2011,
50, 9737; d) K. Hindson, B. de Bruin, Eur. J. Inorg. Chem. 2012, 340; e)
W. Kaim, Eur. J. Inorg. Chem. 2012, 343.
[2]
a) R. H. Crabtree, New J. Chem. 2011, 35, 18; b) W. I. Dzik, J. I. van der
Vlugt, J. N. H. Reek, B. de Bruin, Angew. Chem. Int. Ed. 2011, 50, 3356;
c) V. Lyaskovskyy, B. de Bruin, ACS Catal. 2012, 2, 270; d) O. R. Luca,
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
4607; d) E. L. Rosen, C. D. Varnado Jr., A. G. Tennyson, D. M. Khramov,
J. W. Kamplain, D. H. Sung, P. T. Cresswell, V. M. Lynch, C. W.
Bielawski, Organometallics 2009, 28, 6695; e) C. D. Varnado, V. M.
Lynch, C. W. Bielawski, Dalton Trans. 2009, 7253; f) K. Arumugam, J.
Chang, V. M. Lynch, C. W. Bielawski, Organometallics 2013, 32, 4334;
j) U. Siemeling, C. Färber, C. Bruhn, S. Fürmeier, T. Schulz, M.
Kurlemann, S. Tripp, Eur. J. Inorg. Chem. 2012, 1413; k) C. D. Varnado
Jr, E. L. Rosen, M. S. Collins, V. M. Lynch, C. W. Bielawski, Dalton Trans.
2013, 42, 13251; l) K. Arumugam, J. Chang, V. M. Lynch, C. W. Bielawski,
Organometallics 2013, 32, 4334; m) A. R. Petrov, A. Derheim, J. Oetzel,
M. Leibold, C. Bruhn, S. Scheerer, S. Oßwald, R. F. Winter, U. Siemeling,
5335; e) F. Armbruster, I. Fernández, F. Breher, Dalton Trans. 2009,
5612; f) F. Armbruster, T. Augenstein, P. Oña-Burgos, F. Breher, Chem.
Eur. J. 2013, 19, 17899; g) T. Augenstein, F. Dorner, K. Reiter, H. E.
Wagner, D. Garnier, W. Klopper, F. Breher, Chem. Eur. J. 2016, 22,
7935; h) M. Zimmer, F. Rupp, P. Singer, F. Walz, F. Breher, W. Klopper,
R. Diller, M. Gerhards, Phys. Chem. Chem. Phys. 2015, 17, 14138; i) Y.
Schmitt, K. Chevalier, F. Rupp, M. Becherer, A. Grün, A. M. Rijs, F. Walz,
F. Breher, R. Diller, M. Gerhards, W. Klopper, Phys. Chem. Chem. Phys.
2014, 16, 8332; j) F. Armbruster, J. Meyer, A. Baldes, P. Oña-Burgos, I.
Fernández, F. Breher, Chem. Commun. 2011, 47, 221; k) D. Nied, E.
Matern, H. Berberich, M. Neumaier, F. Breher, Organometallics 2010, 29,
6028.
Inorg. Chem. 2015, 54, 6657; n) U. Siemeling, C. Farber, C. Bruhn, M.
̈
Leibold, D. Selent, W. Baumann, M. von Hopffgarten, C. Goedecke, G.
Frenking, Chem. Sci. 2010, 1, 697; o) S. Rittinghaus, C. Färber, C. Bruhn,
U. Siemeling, Dalton Trans. 2014, 43, 3058.
[23] M. Kaupp, J. Comput. Chem. 2006, 28, 320.
[24] Selected reviews: a) W. Petz, Chem. Rev. 1986, 86, 1019; b) M. F.
Lappert, R. S. Rowe, Coord. Chem. Rev. 1990, 100, 267; c) O. Kühl,
Coord. Chem. Rev. 2004, 248, 411; d) S. Nagendran, H. W. Roesky,
Organometallics 2008, 27, 457; e) M. Asay, C. Jones, M. Driess, Chem.
Rev. 2011, 111, 354; f) J. Barrau, G. Rima, Coord. Chem. Rev. 1998,
178-180, 593; g) N. Tokitho, R. Okazaki, Coord. Chem. Rev. 2000, 210,
251; h) M. F. Lappert, Main Group Metal Chem. 1994, 17, 183; i) W.-P.
Leung, K.-W. Kan, K.-H. Chong, Coord. Chem. Rev. 2007, 251, 2253; j)
L. Álvarez-Rodríguez, J. A Cabeza, P. García-Álvarez, D. Polo, Coord.
Chem. Rev. 2015, 300, 1; k) A. V. Zabula, F. E. Hahn, Eur. J. Inorg.
Chem. 2008, 5165; l) J. Baumgartner, C. Marschner, Rev. Inorg. Chem.
2014, 34, 119. Pioneering papers in the area of NHGe: m) Ref [32]; n)
Ref. [35h]. For attempts of Wrackmeyer and co-workers to prepare the
Fc-based NHSn, see: o) B. Wrackmeyer, E. V. Klimkina, W. Milius, Z.
Anorg. Allg. Chem. 2006, 632, 2331; p) B. Wrackmeyer, W. Milius, H. E.
Maisel, H. Vollrath, M. Herberhold, Z. Anorg. Allg. Chem. 2003, 629,
1169. For a successfull synthesis, see q) ref. [27].
[12] a) A. J. Arduengo, D. Tapu, W. J. Marshall, Angew. Chem. Int. Ed. 2005,
44, 7240; b) A. J. Arduengo, D. Tapu, W. J. Marshall, J. Am. Chem. Soc.
2005, 127, 16400.
[13] a) B. Hildebrandt, W. Frank, C. Ganter, Organometallics 2011, 30, 3483;
b) B. Hildebrandt, S. Raub, W. Frank, C. Ganter, Chem. Eur. J. 2012, 18,
6670.
[14] a) L. Hettmanczyk, S. Manck, C. Hoyer, S. Hohloch, B. Sarkar, Chem.
Commun. 2015, 51, 10949; b) S. Ibáñez, M. Poyatos, L. N. Dawe, D.
Gusev, E. Peris, Organometallics 2016, 35, 2747; c) K. Arumugam, C. D.
Varnado, Jr., S. Sproules, V. M. Lynch, C. W. Bielawski, Chem. Eur. J.
2013, 19, 10866.
[15] I. Kuzu, I. Krummenacher, J. Meyer, F. Armbruster, F. Breher, Dalton
Trans. 2008, 5836.
[16] Selected examples: a) F. Breher, J. Grunenberg, S. Lawrence, P.
Mountford, H. Rüegger, Angew. Chem. Int. Ed. 2004, 43, 2521; b) I.
Krummenacher, H. Rüegger, F. Breher, Dalton Trans. 2006, 1073; c) H.
R. Bigmore, J. Meyer, I. Krummenacher, H. Rüegger, E. Clot, P.
Mountford, F. Breher, Chem. Eur. J. 2008, 14, 5918; d) I. Kuzu, I.
Krummenacher, I. J. Hewitt, Y. Lan, V. Mereacre, A. K. Powell, P. Höfer,
J. Harmer, F. Breher, Chem. Eur. J. 2009, 15, 4350; e) I. Fernández, P.
Oña-Burgos, F. Armbruster, I. Krummenacher, F. Breher, Chem.
Commun. 2009, 2586; f) M. G. Cushion, J. Meyer, A. Heath, A. D.
Schwarz, I. Fernández, F. Breher, P. Mountford, Organometallics 2010,
29, 1174; g) D. Kratzert, D. Leusser, D. Stern, J. Meyer, F. Breher, D.
Stalke, Chem. Commun. 2011, 47, 2931; h) J. Meyer, I. Kuzu, S.
González-Gallardo, F. Breher, Z. Anorg. Allg. Chem. 2013, 639, 301; i)
J. Meyer, S. González-Gallardo, S. Hohnstein, D. Garnier, M. K.
Armbruster, K. Fink, W. Klopper, F. Breher, Chem. Eur. J. 2015, 21,
2905; j) I. Trapp, S. González-Gallardo, S. Hohnstein, D. Garnier, P.
Oña-Burgos, F. Breher, Dalton Trans. 2014, 43, 4313; k) I. Kuzu, A.
Baldes, F. Weigend, F. Breher, Polyhedron 2016, in press
(http://dx.doi.org/10.1016/j.poly.2016.09.017).
[25] W. Wang, S. Inoue, S. Enthaler, M. Driess, Angew. Chem. 2012, 124,
6271; Angew. Chem. Int. Ed. 2012, 51, 6167.
[26] a) Florian Walz, Dissertation, Karlsruher Institut für Technologie (KIT),
September 2015 (ISBN 978-3-8325-4208-5); b) Jan Oetzel, Dissertation,
Universität Kassel, September 2015.
[27] J. Oetzel, N. Weyer, C. Bruhn, M. Leibold, B. Gerke, R. Pöttgen, M. Maier,
R. F. Winter, M. C. Holthausen, U. Siemeling, Chem. Eur. J. submitted.
[28] See, e.g. a) R. M. Haak, S. J. Wezenberg, A. W. Kleij, Chem. Commun.
2010, 46, 2713; b) J. I. van der Vlugt, Eur. J. Inorg. Chem. 2012, 363; c)
J. Park, S. Hong, Chem. Soc. Rev. 2012, 41, 6931; d) I. Bratko, M.
Gómez, Dalton Trans. 2013, 42, 10664.
[29] For a recent study on differential many-body cooperativity in electronic
spectra of oligonuclear transition-metal complexes, see J. Chmela, M. E.
Harding, D. Matioszek, C. E. Anson, F. Breher, W. Klopper, Chem. Phys.
Chem. 2016, 17, 37.
[30] a) A. Shafir, M. P. Power, G. D. Whitener, J. Arnold, Organometallics
2000, 19, 3978; b) A. R. Petrov, K. Jess, M. Freytag, P. G. Jones, M.
Tamm, Organometallics 2013, 32, 5946; c) M. A. Abdulmalic, T. Rüffer,
Bull. Chem. Soc. Jpn. 2013, 86, 724.
[17] a) S. González-Gallardo, I. Kuzu, P. Ona-Burgos, T. Wolfer, C. Wang, K.
W. Klinkhammer, W. Klopper, S. Bräse, F. Breher, Organometallics 2014,
33, 941.
[31] a) A. Shafir, J. Arnold, Inorg. Chim. Acta 2003, 345, 216; b) J. A. Lee, B.
N. Williams, K. R. Ogilby, K. L. Miller, P. L. Diaconescu, J. Organomet.
Chem. 2011, 696, 4090; c) U. Siemeling, T.-C. Auch, O. Kuhnert, M.
Malaun, H. Kopacka, B. Bildstein, Z. Anorg. Allg. Chem. 2003, 629, 1334.
[32] a) J. D. Cotton, C. S. Cundy, D. H. Harris, A. Hudson, M. F. Lappert, P.
W. Lednor, J. Chem. Soc., Chem. Commun. 1974, 651; b) D. H. Harris,
M. F. Lappert, J. Chem. Soc., Chem. Comm. 1974, 895.
[18] S. Styra, S. González-Gallardo, F. Armbruster, P. Oña-Burgos, E. Moos,
M. Vonderach, P. Weis, O. Hampe, A. Grün, Y. Schmitt, M. Gerhards, F.
Menges, M. Gaffga, G. Niedner-Schatteburg, F. Breher, Chem. Eur. J.
2013, 19, 8436.
[19] a) C. A. Tolman, Chem. Rev. 1977, 77, 313; b) S. Wolf, H. Plenio, J.
Organomet. Chem. 2009, 694, 1487; c) R. A. Kelly III, H. Clavier, S.
Giudice, N. M. Scott, E. D. Stevens, J. Bordner, I. Samardjiev, C. D. Hoff,
L. Cavallo, S. P. Nolan, Organometallics 2008, 27, 202; d) D. J. Nelson,
S. P. Nolan, Chem. Soc. Rev. 2013, 42, 6723.
[33] D. R. Scott, R. S. Becker, J. Organomet. Chem. 1965, 4, 409.
[34] S. Duhović, P. L. Diaconescu, Polyhedron 2013, 52, 377.
[35] Selected examples: a) W. A. Herrmann, M. Denk, J. Behm, W. Scherer,
F.-R. Klingan, H. Bock, B. Solouki, M. Wagner, Angew. Chem. Int. Ed.
Engl. 1992, 31, 1485; b) P. Bazinet, G. P. A. Yap, D. S. Richeson, J. Am.
Chem. Soc. 2001, 123, 11162; c) S. Krupski, R. Pöttgen, I. Schellenberg,
F. E. Hahn, Dalton Trans. 2014, 43, 173; d) J. Pfeiffer, W. Maringgele, M.
Noltemeyer, A. Meller, Chem. Ber. 1989, 122, 245; e) O. Kühl, P.
Lönnecke, J. Heinicke, Polyhedron 2001, 20, 2215; f) S. Krupski, J. V.
Dickschat, A. Hepp, T. Pape, F. E. Hahn, Organometallics, 2012, 31,
2078; g) F. E. Hahn, A. V. Zabula, T. Pape, A. Hepp, Z. Anorg. Allg.
Chem. 2008, 634, 2397; h) M. Veith, M. Grosser, Z. Naturforsch. 1982,
37b, 1375; h) P. Bazinet, G. P. A. Yap, D. S. Richeson, J. Am. Chem.
Soc. 2001, 123, 11162; i) M. Stender, A. D. Phillips, P. P. Power, Inorg.
12
[20] As summarized in ref. [11d], „the redox tunability of these ligands does
not strongly depend on the specific chemical identity of the redox-active
functional group. Rather, the overall charge imparted to the molecule
upon redox changes appears to be the origin of the ligand’s attenuated
donating ability.“
[21] T. M. Miller, K. J. Ahmed, M. S. Wrighton, Inorg. Chem. 1989, 28, 2347.
[22] a) F. Breher, H. Rüegger, Angew. Chem. 2005, 117, 477; Angew. Chem.
Int. Ed. 2005, 44, 473; b) I. Krummenacher, F. Breher, Z. Anorg. Allg.
Chem. 2006, 632, 965; c) I. Krummenacher, C. Oschwald, H. Rüegger,
F. Breher, Z. Anorg. Allg. Chem. 2007, 633, 2354; d) I. Krummenacher,
I. Fernández, H. Rüegger, F. Weigend, F. Breher, Dalton Trans. 2009,
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
Chem. 2001, 40, 5314; j) M. Driess, S. Yao, M. Brym, C. van Wüllen,
Angew. Chem. 2006, 118, 4455; Angew. Chem., Int. Ed. 2006, 45, 4349;
k) S. Krupski, C. Schulte to Brinke, H. Koppetz, A. Hepp, F. E. Hahn,
Organometallics, 2015, 34, 2624.
F. Breher, I. Fernández, Chem. Eur. J. 2013, 19, 691; c) DiffAtOnce
Molecular Diffusion, available at www.diffatonce.com.
[53] TURBOMOLE, V6.0, 2009; a development of University of Karlsruhe
(TH) and Forschungszentrum Karlsruhe GmbH 1989-2007:
[36] Selected exampes: a) M. Driess, S. Yao, M. Brym, C. Van Wüllen, D.
Lentz, J. Am. Chem. Soc. 2006, 128, 9628; b) H. V. R. Dias, Z. Wang,
W. Jin, Coord. Chem. Rev. 1998, 176, 67; c) B. Gehrhus, M. F. Lappert,
J. Organomet. Chem. 2001, 617-618, 209; d) Y. Ding, H. W. Roesky, M.
Noltemeyer, H.-G. Schmidt, P. P. Power, Organometallics 2001, 20,
1190; e) A. E. Ayers, T. M. Klapötke, H. V. R. Dias, Inorg. Chem. 2001,
40, 1000; for a related four-membered germylene, see e.g. f) M. Veith,
R. Lisowski, Angew. Chem. 1988, 100, 1124; Angew. Chem., Int. Ed.
Engl. 1988, 27, 1087
TURBOMOLE
GmbH,
since
2007,
available
from
http://www.turbomole.com.
[54] a) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785; b) A. D.
Becke, J. Chem. Phys. 1993, 98, 5648.
[55] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005, 7, 3297.
[56] G. M. Sheldrick, Acta Cryst. 2015, A71, 3.
[57] G. M. Sheldrick, Acta Cryst. 2015, C71, 3.
[58] A. L. Spek, Acta Cryst., 2015, C71, 9.
[37] a) A. Poater, B. Cosenza, A. Correa, S. Giudice, F. Ragone, V. Scarano,
L.
Cavallo,
Eur.
J.
Inorg.
Chem.
2009,
1759;
b)
https://www.molnac.unisa.it/OMtools/sambvca.php.
[38] Note that we had to substitute Ge for Si in the calculation of the %Vbur
value because Ge is not available in the sambvca database.[37b] However,
since germanium and silicon are very similar in size, we expect only slight
deviations from the „true“ value for 4.
[39] a) Ref. [3]; b) H. Clavier, S. P. Nolan, Chem. Commun. 2010, 46, 841; c)
O. Diebolt, G. C. Fortman, H. Clavier, A. M. Z. Slawin, E. C. Escudero-
Adán, J. Benet-Buchholz, S. P. Nolan, Organometallics 2011, 30, 1668;
d) N. Fey, M. F. Haddow, J. N. Harvey, C. L. McMullin, A. G. Orpen,
Dalton Trans. 2009, 8183.
[40] a) K. Hinkelmann, J. Heinze, H.-T. Schacht, J. S. Field, H. Vahrenkamp,
J. Am. Chem. Soc. 1989, 111, 5078; b) J. Heinze, Angew. Chem. 1984,
96, 823; Angew. Chem. Int. Ed. 1984, 23, 831.
[41] Epa values of 0.84 and 1.20 V vs. Ag/AgCl (THF/[Bu4N][ClO4]) have been
reported for unsaturated and saturated germylenes (CHNtBu)2Ge and
(CH2NtBu)2Ge, respectively, which corresponds to Epa  0.48 and 0.85 V
vs. Fc/Fc+. Interestingly, (CHNtBu)2Ge gave a reversible redox process
centred at E0 = 0.41 V vs. Ag/AgCl in 1,2-DCB using [Bu4N][ClO4] as
1/2
electrolyte, i.e. ca. 0.06 V vs. Fc/Fc+. A. Dhiman, T. Müller, R. West, J. Y.
Becker, Organometallics 2004, 23, 5689.
[42] F. Basolo, R. G. Pearson, Progr. Inorg. Chem. 1962, 4, 381.
[43] See, e.g.: a) O. Kühl, P. Lönnecke, J. Heinicke, Inorg. Chem. 2003, 42,
2836; b) D. Matioszek, N. Katir, N. Saffon, A. Castel, Organometallics
2010, 29, 3039; c) I. Saur, S. Garcia Alonso, H. Gornitzka, V. Lemierre,
A. Chrostowska, J. Barrau, Organometallics 2005, 24, 2988.
[44] a) F. Ullah, O. Kühl, G. Bajor, T. Veszprémi, P. G. Jones, J. Heinicke,
Eur. J. Inorg. Chem. 2009, 221; b) F. Ullah, G. Bajor, T. Veszprémi, P.
G. Jones, J. Heinicke, Angew. Chem. 2007, 119, 2751; Angew. Chem.
Int. Ed. 2007, 46, 2697; c) A. V. Zabula, F. E. Hahn, T. Pape, A. Hepp,
Organometallics 2007, 26, 1972.
[45] Typically, the metal-to-metal communication is assessed by
electrochemical experiments. For a nice review article on the triumphs
and defeats of half-wave potential splittings ΔE1/2 as a measure of
electronic coupling in mixed-valent systems, see: R. Winter,
Organometallics 2014, 33, 4517.
[46] Small deviations of the HOMO energy levels have to be expected due to
the different tilting of the Cp rings in the model compounds: J. C. Green,
Chem. Soc. Rev. 1998, 27, 263.
[47] In order to compare calculated harmonic frequencies with experimental
values the computed vibrational frequencies have to be scaled. A typical
empirical factor for the chosen theoretical method is 0.9671
(B3LYP/def2-TZVP): M. K. Kesharwani, B. Brauer, J. M. L. Martin, J.
Phys. Chem. A 2015, 119, 1701.
[48] W. A. Herrmann, J. Schütz, G. D. Frey, E. Herdtweck, Organometallics
2006, 25, 2437.
[49] For the TEP calculations, we have consistently used the equations given
in ref. [19b] and [19c].
[50] Germylenes are usually categorized among the weak -donor and good
-acceptor ligands. See Ref. [24] and O. Kühl, K. Lifson, W. Langel, Eur.
J. Org. Chem. 2006, 2336.
[51] We refrain from giving any dicimal places and quote rounded values.
[52] a) M. W. Löble, P. Oña-Burgos, I. Fernández, C. Apostolidis, A.
Morgenstern, O. Walter, F. Bruchertseifer, P. Kaden, T. Vitova, J. Rothe,
K. Dardenne, N. L. Banik, A. Geist, M. A. Denecke, F. Breher, Chem. Sci.
2013, 4, 3717; b) M. Casimiro, P. Oña-Burgos, J. Meyer, S. Styra, I. Kuzu,
13
This article is protected by copyright. All rights reserved.

10.1002/chem.201605073
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents:
FULL PAPER
The redox-switchable germylene
[Fc(NMes)2Ge] based on a
[3]ferrocenophane ligand
Florian Walz, Eric Moos, Delphine
Garnier, Ralf Köppe, Christopher E.
Anson, Frank Breher*
arrangement, alongside some
transition metal complexes, are
reported. The change in the ligating
properties upon oxidation were
elucidated by DFT calculations on
neutral and cationic bimetallic model
complexes.
1 – 13
A Redox-Switchable Germylene and
its Ligating Properties in Selected
Transition Metal Complexes
14
This article is protected by copyright. All rights reserved.