Convenient synthetic access to fluorescent rhodacyclopentadienes via ligand exchange reactions

Article abstract of DOI:10.1016/j.jorganchem.2017.02.028

We have previously reported the formation of fluorescent 2,5-bis(arylethynyl)rhodacyclopentadienes from the reaction of [Rh(κ²-O,O-acac)(PMe₃)₂] (acac = acetylacetonato) with α,ω-bis(arylbutadiynyl)alkanes. However, a second isomer series, namely phosphorescent rhodium biphenyl complexes, was also obtained from the same reaction mixture, which made purification of the 2,5-bis(arylethynyl)rhodacyclopentadienes challenging and led to low isolated yields. Herein, we describe a synthetic protocol to access the desired fluorescent rhodium complexes by reaction of [Rh(κ²-O,O-acac)(P(p-tolyl₃)₂)] with α,ω-bis(arylbutadiynyl)alkanes, which gives exclusively 2,5-bis(arylethynyl)rhodacyclopentadienes, and subsequent phosphine ligand exchange. The rhodacyclopentadienes bearing P(p-tolyl₃) ligands have been investigated and compared to their PMe₃ analogs with regard to their photophysical properties, showing that the aromatic phosphine ligands enhance non-radiative decay from the singlet excited state S₁, while no phosphorescence from T₁ is observed despite the presence of the heavy rhodium atom. One of the P(p-tolyl₃) ligands can also be exchanged for an N-heterocyclic carbene (NHC), leading to unsymmetrically coordinated rhodacyclopentadienes.

Full text of DOI:10.1016/j.jorganchem.2017.02.028

Journal of Organometallic Chemistry xxx (2017) 1e9
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Convenient synthetic access to fluorescent rhodacyclopentadienes via
*
ligand exchange reactions
Carolin Sieck, Daniel Sieh, Meike Sapotta, Martin Haehnel, Katharina Edkins,
*
Andreas Lorbach, Andreas Steffen, Todd B. Marder
a
Institut für Anorganische Chemie, Julius-Maximilians-Universit a€ t Würzburg, Am Hubland, 97074 Würzburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 February 2017
Received in revised form
We have previously reported the formation of fluorescent 2,5-bis(arylethynyl)rhodacyclopentadienes
2
from the reaction of [Rh(
k
-O,O-acac)(PMe
3
)
2
] (acac ¼ acetylacetonato) with
a,u-bis(arylbutadiynyl)al-
kanes. However, a second isomer series, namely phosphorescent rhodium biphenyl complexes, was also
17 February 2017
obtained from the same reaction mixture, which made purification of the 2,5-bis(arylethynyl)rhodacy-
Accepted 17 February 2017
Available online xxx
clopentadienes challenging and led to low isolated yields. Herein, we describe a synthetic protocol to
2
access the desired fluorescent rhodium complexes by reaction of [Rh(
k
-O,O-acac)(P(p-tolyl
3
)
2
)] with
a
,
u
-bis(arylbutadiynyl)alkanes, which gives exclusively 2,5-bis(arylethynyl)rhodacyclopentadienes, and
subsequent phosphine ligand exchange. The rhodacyclopentadienes bearing P(p-tolyl ) ligands have
been investigated and compared to their PMe analogs with regard to their photophysical properties,
showing that the aromatic phosphine ligands enhance non-radiative decay from the singlet excited state
, while no phosphorescence from T is observed despite the presence of the heavy rhodium atom. One
Keywords:
3
Metallacycle
Ligand exchange reaction
Phosphine
3
NHC
S
1
1
Luminescent
of the P(p-tolyl ) ligands can also be exchanged for an N-heterocyclic carbene (NHC), leading to un-
3
symmetrically coordinated rhodacyclopentadienes.
©
2017 Elsevier B.V. All rights reserved.
1
. Introduction
(M ¼ Fe, Ru) [4,5]. In addition, the spin-forbidden nature of the
radiative transition between T and the ground state (S ) is partially
removed by the SOC and, as a result, phosphorescence with life-
times of a few s and quantum yields ( ) of up to unity can be
observed [6e8].
1
0
0
Transition metal complexes bearing 2,2 -bipyridine- (bpy) and
-phenylpyridine-(ppy)-type chromophore ligands have success-
2
m
Ф
P
fully been employed in photocatalysis, light-emitting devices, and
biological imaging as a result of detailed investigations of their
structure-property relationships [1]. The prototypical compounds
In contrast to transition metal complexes of bpy and ppy, little is
known about the photophysical properties of metal-
2
þ
[Ru(bpy)
3
]
and [Ir(ppy)
3
], and derivatives thereof, have been
lacyclopentadienes as MC
4
analogs. Investigations have been
0
most extensively studied to understand their excited-state
behavior, and it soon became clear that the combination of heavy
metals exhibiting exceptionally high intrinsic spin-orbit coupling
focussed on the catalytic activity of 2,2 -biphenylene (bph) com-
plexes and only a limited number of bph complexes of Ir, Pd and Pt
were explored with regard to their photophysical properties,
although they show promising results with phosphorescence
(
SOC) with a variety of different ligands allows facile tuning of the
excited states [2,3]. As a consequence, the strong SOC of the metal
atom facilitates intersystem-crossing (ISC), which quenches the
quantum yields of up to 16% and lifetimes of
t
¼ 3e14
ms [9]. The
lack of photophysical reports in the literature is presumably due to
limited synthetic access to bph transition-metal complexes, which
are usually obtained via insertion of a low valent and electron-rich
1
fluorescence from the excited singlet state (S ). For example, ul-
trafast conversion of the S state to the T states on the timescale of
1
n
2
þ
vibrations (few femtoseconds) has been measured for [M(bpy)
3
]
metal fragment into a C-C bond of biphenylene or via reaction of a
0
2
,2 -dihaliated biphenyl with a metal dihalide [10,11]. In contrast,
4
structurally related main group EC systems such as boroles [12],
siloles [13], thiophenes [14] and phospholes [15] are well known
and have attracted significant attention due to their electron-
transporting and optical properties (linear and non-linear optical
*
Dedicated to Professor John Gladysz on the occasion of his 65th birthday.
Corresponding author.
E-mail address: todd.marder@uni-wuerzburg.de (T.B. Marder).
*
http://dx.doi.org/10.1016/j.jorganchem.2017.02.028
022-328X/© 2017 Elsevier B.V. All rights reserved.
0
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j.jorganchem.2017.02.028

2
C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
behaviour), motivating us to explore the potential of
metallacyclopentadienes.
orbitals, respectively, and the HOMO is energetically well separated
from the filled Rh d orbitals. This inhibits low-energy MLCT tran-
Synthetic access to MC
4
ring systems is possible by reductive
sitions, leading to a low triplet state density around S
hampering the ISC process [20,21]. In combination with that,
structural distortion toward a cumulenic geometry in the T state
leads to weak coupling of the different spin states and thus to
“organic-like” photophysical behavior. To investigate in more detail
the effect on the properties of the 2,5-bis(arylethynyl)rhodacyclo-
1
and
coupling of 1,3-butadiynes at a suitable transition-metal precursor
complex [16]. From a photophysical perspective, the most inter-
esting of the possible isomers are the 2,5-conjugated ring systems.
However, most of these reactions do not occur with the desired
regioselectivity, as found for cobalt, titanium [17] or ruthenium [18]
complexes. In 2001, Marder and co-workers successfully developed
a high-yield one-pot synthesis of luminescent 2,5-bis(arylethynyl)
rhodacyclopentadienes by reductive coupling of 1,4-diarylbuta-1,3-
diynes [16]. Over the past years, a variety of ligands and 1,4-bis(p-R-
1
pentadienes, another
p-electron-donating group, namely acac
(acetylacetonato), was introduced into the rhodium precursor.
2
3 2
Interestingly, reaction of [Rh(k -O,O-acac)(PMe ) ] [22] with linked
bis(diynes) led not only to the formation of fluorescent 2,5-
bis(arylethynyl)rhodacyclopentadienes (A), but also to isomeric
and phosphorescent rhodium biphenyl complexes (B) (Scheme 2)
[23].
The fundamentally different photophysical properties of B in
comparison of A arise from the energetic proximity of the filled
phenyl)-1,3-butadiynes (R ¼ H, Me, OMe, SMe, CO
used. Remarkably, reactions of [RhR(PMe
] (R ¼ C≡CSiMe
with two equivalents of 1,4-diarylbuta-1,3-diynes and also re-
2
Me, etc.) were
3
)
4
3
, Me)
2
actions of [Rh(C≡CSiMe
with different linked
the rhodacycle backbone) yields quantitatively, in all cases, only the
,5-bis(arylethynyl)rhodacyclopentadiene isomer (Scheme 1)
19,20].
Surprisingly, our rhodacyclopentadienes exhibit highly efficient
3
)(PMe
3
)
4
] or [Rh(
k
-S,S-S
2
CNEt
2
3
)(PMe )
2
]
a,u-bis(arylethynyl)alkanes (rigidification of
frontier orbitals in B, which are mixtures of ligand
p and metal
2
[
d orbitals. As a result, a number of triplet excited states with some
metal to ligand charge-transfer (MLCT) contribution can efficiently
connect the S
for isomer B is detected even at low temperature, it can be assumed
that S /T ISC must be faster than both fluorescence and non-
radiative decay from S [23]. This contrasts with the behavior of
1 1
state with the emitting T state. As no fluorescence
fluorescence with quantum yields of up to 69%, despite the pres-
ence of the heavy atom that would be expected to facilitate rapid
ISC and thus to quench the fluorescence. In 2014, we carried out a
detailed photophysical analysis of 2,5-bis(arylethynyl)rhodacyclo-
pentadienes to provide a full picture of their excited state behavior
in order to understand these unusual photophysical properties. The
origin of the fluorescence lies in the pure intra-ligand (IL) nature of
1
n
1
the isomeric rhodacyclopentadienes (A) for which we have previ-
ously shown that the unusual ISC occurs on a timescale that is
competitive with fluorescence, as mentioned above. Such long-
lived triplet excited states of the rhodium biphenyl complexes
(B), on a timescale of tens to hundreds of microseconds, can be very
useful for applications in color-tunable OLEDs, in which, at high
the excited states S
1
and T
1
, irrespective of the presence of a heavy
and * ligand
atom. The HOMO and the LUMO are nearly pure
p
p
Scheme 1. Synthesis of 2,5-bis(arylethynyl)rhodacyclopentadienes [19,21].
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j.jorganchem.2017.02.028

C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
3
Scheme 2. Synthesis of two isomers: Rhodacyclopentadiene (A) and rhodium biphenyl complex (B) [23].
voltages, the emissive excited state of a low-energy emitter must
have a long lifetime in order to become saturated by energy transfer
from a short-lived high-energy luminophore. Also, long-lived
excited states are of interest for photocatalysis, energy up-
conversion and non-linear optics, as has been shown for Pd(II)
porphyrin and Au(III) 2,6-diphenylpyridine complexes [24].
As already mentioned above, metal biphenyl complexes of type
B are difficult to prepare due to limited synthetic methods, and
their photophysical properties are typically hence rather less well
nearly full conversion to 2,5-bis(arylethynyl)rhodacyclopenta-
dienes 4 and 5 (Scheme 3), respectively. These were purified by
column chromatography and several recrystallizations to give
samples of very high purity for photophysical investigations,
resulting in moderate isolated yields. Rhodium complexes 4 and 5
were fully characterized by elemental analysis, mass spectrometry
and multi-nuclear NMR spectroscopy.
Inspection of the NMR spectroscopic data revealed the forma-
tion of a C2v symmetric complex on the NMR time scale as indicated
2
2
0
investigated then their {M(
k
-N,C-C
3
N)} or {M(
k
-N,N -C
2
N
2
)} an-
3
by only one resonance for the acac CH protons and only one
31
1
alogs (e.g. ppy or bpy complexes). We found that the product ratio
of isomers A and B (Scheme 2) depends on the temperature, with
isomer B being favored at higher temperatures. Different sub-
stituents at the aryl rings also lead to different isomer distributions.
phosphine signal. The P{ H} NMR resonances of the complexes 4
and 5 are observed at 24.6 and 24.8 ppm, respectively, with
rhodium phosphorus coupling constants of 114 (4) and 115 Hz (5),
the JRh-P values being in agreement with the data obtained for other
rhodacyclopentadiene complexes bearing trimethylphosphine li-
gands [23].
In addition, modification of the
changing the linker length from 4 to 3 CH
a
,
u
-bis-(arylbutadiynyl)alkane, i.e.,
groups, dramatically
2
favors formation of the rhodium biphenyl isomer B for entropic
reasons, leading to an A:B ratio of 1:20 at room temperature and
Single-crystals suitable for X-ray diffraction analysis were ob-
tained by vapor diffusion of hexane into THF solutions of 4 and 5,
respectively, and the molecular structures are depicted in Fig. 1. The
molecular geometries of 4 and 5 are very similar, the rhodium atom
being in an octahedral coordination environment with trans-
disposed phosphine ligands. The Rh-P bond distances in 4 and 5 are
in the range of 2.3464(8) e 2.3637(8) Å and are therefore slightly
1
:25 at higher temperatures, which makes it challenging to isolate
isomer A in high yields [23]. These findings motivated us to develop
a different approach that selectively produces isomer A, and to
investigate the influence of the ligand sphere around the rhodium
center on the ISC processes by changing the phosphine ligands to
more
s-donating N-heterocyclic carbene (NHCs) ligands.
3
longer than in the corresponding PMe complexes (ca. 2.306 Å)
[23], or 1 (2.0549(14), 2.0857(14) Å; see Table S1), indicating
weaker metal phosphine bonding in 4 and 5. As the C-Rh-C angle
within the rhodacyclopentadiene ring is only 81 in both com-
2
. Results and discussion
ꢀ
plexes 4 and 5, the other angles within the ring are larger
(
2
2
.1. Synthesis, structural characterization and optical properties of
,5-bis(arylethynyl)rhodacyclopenta-2,4-dienes
ꢀ ꢀ
113e117 ) than the expected 108 for a regular planar, five
membered ring. However, the sum of angles in the rhodacycle is
ꢀ
5
40 in both compounds. At 1.358(5) e 1.368(4) Å, the C]C double
3 2
k ) ] (1), which was
2-O,O-acac)(P(p-tolyl)
The reaction of [Rh(
characterized by single-crystal X-ray diffraction (see S7), with
either -bis(arylbutadiynyl)alkane 2 or 3 in a 1:1 ratio leads to
bonds are basically the same than typical cyclopenta-1,3-diene
2
2
C(sp )¼C(sp ) bonds, and the single bond length of 1.431(4),
a,u
Scheme 3. Synthesis of 2,5-bis(arylethynyl)rhodacyclopentadienes 4 and 5 via reaction of [Rh(k2-O,O-acac)(P(p-tolyl
) ] (1) with a,u-bis(arylbutadiynyl)alkanes 2 and 3,
3 2
respectively.
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4
C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
Fig. 1. Molecular structures of 2,5-bis(arylethynyl)rhodacyclopentadienes 4 (left) and 5 (right) in the solid state determined by single-crystal X-ray diffraction with the anisotropic
displacement ellipsoids shown at the 50% probability level; H atoms are omitted for clarity.
2
2
1
.433(5) Å are also typical for endocyclic C(sp )-C(sp ) bonds [25].
In both complexes, one of the aryl rings at the alkyne groups is
ꢀ
nearly coplanar with the five membered metallacycle (9 ), while
ꢀ
the other one is slightly more twisted (23.47(13) in 4 and
ꢀ
1
6.02(17) in 5).
Being intrigued by the highly unusual fluorescence properties of
previously reported 2,5-bis(arylethynyl)rhodacyclopentadienes
containing PMe
3
ligands, we also explored the photophysical
properties of the tri(p-tolyl)phosphine complexes 4 and 5. Com-
pounds 4 and 5 show a low-energy absorption band in the visible
abs
region of the electromagnetic spectrum with
l
¼ 563 nm and
max
abs
l
¼
525 nm, respectively, and
a
broad emission with
¼ 550 nm, respectively. The CO Me-
max
em
em
l
¼ 583 nm and
l
2
max
max
substituted compound 4 shows a bathochromic shift in the ab-
sorption and emission spectrum in comparison to its SMe-
substituted congener 5, the influence of the acceptor substituent
exceeding that of the donor. The effect of donors and acceptors can
be explained by acceptors having a greater influence on the lowest
unoccupied molecular orbital (LUMO) than on the highest unoc-
cupied molecular orbital (HOMO), and donors showing an opposite
effect, therefore both decreasing the HOMOeLUMO gap, as previ-
Fig. 2. Absorption (dashed lines) and emission spectra (solid lines, excited at the
respective absorption maximum) of 4 (green) and 5 (blue) in degassed toluene at room
temperature. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
[
14g]
ously reported for related 2,5-bis(arylethynyl)thiophenes
,5-bis(arylethynyl)rhodacyclopentadienes [19,20].
The results from luminescence measurements suggest that the
emission occurs from the excited singlet state S , as small Stokes
and
2
1
ꢁ
1
ꢁ1
shifts 609 cm (4) and 866 cm (5) (Fig. 2) are observed [23]. The
rhodacyclopentadienes 4 and 5 exhibit very weak fluorescence
temperature, nearly full conversion of the starting material is
observed with only traces of complex 4 being left after only 10 min
with quantum yields
ФPL < 0.01, and very short emission lifetimes
(Fig. 3, top). The mono-substituted complex 6 is observed as the
in toluene at room temperature. However, for compounds 4 and 5,
no additional phosphorescence is observed, as previously reported
for our highly fluorescent 2,5-bis(arylethynyl)rhodacyclopenta-
dienes. Presumably, vibrational modes of the tri(p-tolyl)phosphine
ligands lead to the higher rate constants for non-radiative decay
and are thus responsible for the low quantum yields compared to
major product, giving rise to a doublet of doublets at 20.5 ppm (JRh-
P
P
¼ 103 Hz, JP-P ¼ 422 Hz) and at 4.7 ppm (JRh-P ¼ 122 Hz, JP-
¼ 422 Hz) for the P(p-tolyl) and the PMe ligand, respectively, the
3
3
trans disposition of the phosphines being clearly indicated of the
2
J
P-P coupling constant. The final product 8, with both tri(p-tolyl)
phosphine ligands being exchanged [23], is already being formed to
3
their corresponding PMe complexes [23].
a small extent as evidenced by the doublet at ꢁ1.0 ppm (JRh-
ꢀ
P
¼ 113 Hz). Upon warming the NMR sample to 60 C, the signals for
the starting compound 4 and the intermediate complex 6 disap-
pear, and full conversion to the 2,5-bis(arylethynyl)rhodacyclo-
pentadiene 7 as well as free tri(p-tolyl)phosphine occurs (Fig. 3,
bottom). Very similar kinetic behavior is found for the conversion of
2.2. Phosphine ligand exchange reactions of 4 and 5
The weak rhodium tri(p-tolyl)phosphine bond in 4 and 5
compared to that on related PMe complexes allows for facile
ligand exchange reactions. In the presence of an excess of PMe
3
5
to 9.
Bearing in mind that the fast ligand exchange reaction is a result
of the weaker rhodium-phosphine bond in 4 and 5 due to the lesser
-donation of tri(p-tolyl)phosphine compared to trimethylphos-
phine [26], we also studied the reaction of the P(p-tolyl )-based
rhodium complex 5 with NHCs as even stronger -donors [27].
Addition of an excess of either 1,3-di(methyl)imidazol-2-ylidene
3
a
stepwise reaction can be observed, giving first the mono-
substituted, mixed phosphine intermediates 6 and 7 and, subse-
quently, full conversion to the 2,5-bis(arylethynyl)rhodacyclo-
pentadienes 8 and 9 bearing only trimethylphosphine ligands
s
3
s
(Scheme 4).
Monitoring the reaction by 31P{ H} NMR spectroscopy at room
1
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C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
5
Scheme 4. Synthesis of 2,5-bis(arylethynyl)rhodacyclopentadienes 8 and 9 by stepwise ligand exchange.
n
(
Me
2
Im, 10) or 1,3-di(n-propyl)imidazol-2-ylidene ( Pr
2
Im, 11) to a
stepwise, facile ligand exchange of P(p-tolyl)
3
by PMe
3
provides
solution of 5 in toluene at room temperature led to the release of
one equivalent of P(p-tolyl ) and to the quantitative formation of
convenient access to highly fluorescent 2,5-bis(arylethynyl)rhoda-
cyclopentadienes, of which the optical properties have been re-
ported previously [19e23]. In contrast to the very efficient
3
the mono-substituted NHC rhodium complexes 12 and 13,
respectively (Scheme 5). However, due to very similar solubility
properties of the released phosphine ligand and the rhodium
compounds, the products could only be isolated in ca. 6% yield.
Interestingly, no conversion was observed in the case of bulkier
fluorescence S
P(p-tolyl) analogs show enhanced non-radiative decay rates, but
still weak fluorescence in the visible region of the spectrum, being
competitive with intersystem-crossing S /T . The ligand ex-
change reaction is also possible with one equivalent of more s-
1 0 3
/S observed in the PMe -based complexes, their
3
1
n
iPr
2
Im.
For both complexes 12 and 13 a doublet is detected in the 31P
donating NHC ligands, yielding unsymmetrically NHC/phosphine-
substituted rhodacyclopentadienes.
1
{
H} NMR spectrum at 21.7 and 21.8 ppm, respectively. The
103
31
Rh- P coupling constant of 101 Hz for both compounds is
decreased by 15 Hz compared to that of the starting material 4 (JRh-
¼ 116 Hz), which can be attributed to a weakening of the Rh-P
bond [28], fully consistent with the enhanced trans influence of
the stronger -donating NHC ligand in a trans-position to the
phosphine. The C{ H} NMR spectra of both complexes 12 and 13
display a doublet of a doublet at
4
. Experimental
P
General considerations: The compounds [Rh(
m
-Cl)(COE)
2
]
2
s
2
13
1
(COE ¼ cyclooctene) [35] [Rh(
k
-O,O-acac)(PMe ) ] [22], 1,11-bis(p-
3 2
carbomethoxyphenyl)undeca-1,3,9,11-tetrayne (2) and 1,11-bis(p-
methylthiophenyl)undeca-1,3,9,11-tetrayne (3) [23], 2,5(aryle-
thynyl)rhodacyclopentadienes (8) and (9) [23], 1,3-di(methyl)imi-
d
¼ 174 ppm with coupling con-
stants of JP-C ¼ 146 Hz and JRh-C ¼ 48 Hz, which we assign to the
carbene carbon atoms bound to the rhodium metal center. Similar
rhodium-C(NHC) coupling constants in the range of 40e60 Hz have
2
dazolin-2-ylidene (Me Im) (10) [36], and 2,6-di(n-propyl)
imidazolin-2-ylidene ( Pr Im) (11) [36] were prepared according to
the literature. All other starting materials were purchased from
n
2
been reported [29e31], and J phosphorus-carbene-carbon atom
2
couplings above 100 Hz are commonly observed if the phosphine
ligand is trans to the NHC ligand [32]. Respective cis P-C couplings,
on the other hand, are often not larger than 20 Hz [32].
commercial sources and used without further purification. All
solvents for synthetic reactions were HPLC grade, further treated to
remove traces of water using an Innovative Technology Inc. Pure-
Solv Solvent Purification System and deoxygenated using the
freeze-pump-thaw method. All reactions and subsequent manip-
ulations were performed under an argon atmosphere in an Inno-
vative Technology Inc. glovebox or using standard Schlenk
techniques. NMR spectra were recorded on Bruker Avance 300 or
Single-crystals suitable for X-ray diffraction were obtained for
complex 12. The molecular structure is shown in Fig. 4, with
selected bond distances and angles being tabulated in Table S1. The
molecular structure of 12 in the solid state (Fig. 4) confirms the
conclusion from the NMR spectroscopic data that only one phos-
phine ligand was exchanged for a NHC ligand and that the phos-
phine and carbene ligands are mutually trans. The distance of the
rhodium metal center to the carbene carbon atom (Rh1-C26) of
1
3
5
6 6
00 spectrometers, using C D as the solvent. C NMR spectra were
1
3
1
broad-band proton-decoupled ( C{ H}). Chemical shifts are listed
in parts per million (ppm) and were determined relative to internal
C
C
Coupling constants are quoted in Hertz. Aromatic peaks in the H
NMR spectra quoted as d are approximated as doublets resulting
from more complex spin systems. Mass spectra were recorded on a
Bruker Daltonics autoflex II LRF mass spectrometer operating in the
MALDI mode. Elemental analyses were performed by the micro-
analytical laboratory of the Institute of Inorganic Chemistry of the
2
.0889(17) Å is in the typical range for octahedral rhodium(III) NHC
1
6
D
D
5
H ( H,
d
¼ 7.16; C
6 6
D ), to natural-abundance carbon resonances
complexes, but longer than reported for rhodium(I) complexes [33].
The Rh1-P1 distance of 2.3406(5) Å is almost identical to the Rh1-
phosphine distances of complex 5 (Avq. ¼ 2.351 Å). Considering the
1
3
31
6
6
(
C,
d
¼ 128.06; C
6
D
6
) or external 85% H
3
PO
4
(
P,
d
¼ 0).
1
strong s-donating abilities of NHC ligands, a strong trans influence
would be expected, so this observation is rather counterintuitive.
However, phosphines and carbenes are both considered moderate
trans influence ligands [28,34] and indeed similar observations
have been made by other groups. Nolan and co-workers for
example observed only small elongations of the Rh-P bond length
of about 0.015 Å in rhodium complexes where a trans phosphine
ligand is exchanged for a NHC ligand [32].
University of Würzburg with an Elementar vario micro cube.
2
[
Rh(k
-O,O-acac)(P(p-tolyl
3
)
2
] (1): A suspension of acetylace-
tone (0.20 g, 9 mmol) and KOH (0.50 g, 8.5 mmol) in degassed THF
50 mL) was added to a solution of [Rh( -Cl)(COE) (1.5 g,
.18 mmol) in degassed THF (5 mL) and the reaction mixture was
(
4
m
2 2
]
3
. Conclusion
We have reported the reaction of Rh( 2
stirred for 1.5 h at room temperature. The volatiles were removed in
vacuo and the resulting residue was extracted with hexane (25 mL)
2
k
-O,O-acac)(P(p-tolyl
3
)
2
)]
to give, after evaporation of the solvent, [Rh(
k
-O,O-acac)(COE)
(2.52 g,
8.3 mmol) in degassed toluene (20 ml). The reaction mixture was
2
]
with -bis(arylbuta-diynyl)alkanes, which leads to full conver-
sion to 2,5-bis(arylethynyl)rhodacyclopentadienes. Subsequent
a,u
[35]. The extract was added to a solution of P(p-tolyl)
3
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6
C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
Fig. 3. In situ 31P{ H} NMR spectra (202 MHz) of the reaction of 4 with an excess PMe
1
3
6 6
in C D . Top: The mono-substituted complex 6 is the major product after 10 min at room
ꢀ
temperature. Bottom: full conversion to 8 after heating at 60 C.
stirred and heated to reflux for 1 h and then the solvent was
Calcd. (%) for C47
H
49
P
2
O
2
Rh: C, 69.63; H, 6.09. Found: C, 69.77; H,
þ
þ
removed in vacuo. Compound 1 was isolated as an orange solid.
6.50. MS (ES ) m/z ¼ 810 [M ].
1
2,5-Bis(arylethynyl)rhodacyclopentadiene (4): [Rh(k
2-O,O-
Yield: 0.81 g (96%) H NMR (300 MHz, C
6
D
6
, r.t., ppm)
d
: 7.86 (m,
1
2
2H, CHarom), 6.80 (d, J ¼ 7 Hz, 12H, CHarom), 5.38 (s, 1H, acac-CH),
3 2
acac)(P(p-tolyl ) ] (1) (0.30 g, 0.37 mmol) and 1,11-bis(p-carbo-
methoxyphenyl)undeca-1,3,8,10-tetrayne (2) (0.19 g, 0.37 mmol)
were suspended in THF (10 mL) and the reaction mixture was
31
1
.00 (s, 18H, p-tolyl-CH
, r.t., ppm)
3
), 1.58 (s, 6H, acac-CH
3
). P{ H} NMR
(
121 MHz, C
6
D
6
d
: 54.8 (d, JRh-P ¼ 195 Hz, 2 P). Elem. Anal.
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j.jorganchem.2017.02.028

C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
7
Scheme 5. Treatment of rhodacyclopentadiene 5 with an excess of NHC giving the mono-substituted complexes 12 and 13.
13
1
C{ H} NMR (125.75 MHz, C
6
D
6
, r.t., ppm)
d
: 185.6 (s), 171.2 (t,
J ¼ 3 Hz), 139.1 (s), 137.4(s), 136.0 (t, J ¼ 5 Hz), 135.9 (s), 130.2 (s),
30.0 (t, J ¼ 23 Hz), 126.8 (s), 124.6 (s), 109.1 (d, J ¼ 1 Hz), 99.3 (s),
8.7 (s), 31.9 (s), 30.1 (s), 28.2 (s), 27.9 (s), 21.2 (s), 15.3 (s). Elem.
1
9
Anal. Calcd. (%) for C72
H
69
O
6
P
2
RhS
2
: C, 72.35; H, 5.82; S, 5.37.
þ
Found: C, 72.56; H, 5.96; S, 5.25. MS (MALDI-TOF) m/z: 1095 [M -
þ
acac], 890 [M -P(p-tolyl)
3
].
2,5-Bis(arylethynyl)rhodacyclopentadiene (8): Compound 4
(0.20 g, 0.16 mmol) was dissolved in THF (20 mL). After the addition
of PMe
3
(0.03 mL, 0.32 mmol), the reaction mixture was stirred at
ꢀ
60
C. After one day, the volatiles were removed and n-hexane
(10 mL) was added and then removed in vacuo in order to evaporate
any remaining uncoordinated PMe . For purification, gradient-
3
flash-chromatography was performed. The crude product was
Fig. 4. Molecular structure of mono-substituted complex 12 in the solid state deter-
mined by single-crystal X-ray diffraction with the anisotropic displacement ellipsoids
shown at the 50% probability level; H atoms are omitted for clarity. Selected bond
distances (Å): Rh1-C26 2.0889(17), Rh1-P1 2.3406(5).
further purified by recrystallization from THF/hexane to yield 8 as a
1
red solid (0.12 g, 86%). H NMR (300 MHz, C
6
D
6
, r.t., ppm)
d: 7.58 (d,
J ¼ 8 Hz, 4 H, CHarom), 7.18 (br s, 4 H, CHarom), 5.07 (s, 1 H, CH), 2.71
m, 4 H, CH ), 2.27 (s, 6 H, CH ), 2.10 (m, 2 H, CH ), 1.76 (s, 6 H, CH ),
). C{ H} NMR (126 MHz, C , r.t.,
: 186.4, 156.5, 144.6, 132.9, 129.6, 128.4, 98.2, 30.9, 30.5, 28.3,
(
0
2
3
2
3
2
13
1
.95 (vt, JP-H ¼ 3 Hz, 18 H, PMe
3
6 6
D
ꢀ
31
1
stirred at 60 C and monitored by P{ H} NMR spectroscopy. Once
ppm)
2
d
the reaction was complete, the volatiles were removed in vacuo.
1
1.4, 12.5 (vt, JC-P ¼ 14 Hz). Due to the low intensity two carbon
The product was purified via column chromatography (Al
2
O
3
)
31 1
signals coupled to Rh and/or P were not observed. P{ H} NMR
eluting with hexane/THF (2:1), recrystallized and washed with hot
1
(
121 MHz, C
Anal. Calcd. (%) for C38
H, 5.97. MS (MALDI-TOF) m/z: 762 [M ], 663 [M - acac] [23].
,5-Bis(arylethynyl)rhodacyclopentadiene (9): Compound 5
0.2 g, 0.17 mmol) was dissolved in THF (20 mL). After the addition
6
D
6
, r.t., ppm)
d
: ꢁ3.0 (d, JRh-P ¼ 113 Hz, 2 P). Elem.
1
hexane to give pure 4 as a red solid. Yield: 0.3 g (38%). H NMR
H O P Rh: C, 59.85; H, 5.95. Found: C, 59.55;
45 6 2
(
1
300 MHz, C
2 H, p-tolyl-CHarom), 7.90 (d, J ¼ 8 Hz, 4 H, CHarom.), 6.93 (d,
J ¼ 8 Hz, 12 H, p-tolyl-CHarom), 4.65 (s, 1 H, acac-CH), 3.52 (s, 6 H,
CO Me-CH ), 2.06 (m, 4 H, CH ), 1.96 (s, 18 H, p-tolyl-CH ), 1.63 (m,
H, CH ), 1.55 (s, 6 H, acac-CH ). P{ H} NMR (121 MHz, C , r.t.,
ppm)
: 24.6 (d, JRh-P ¼ 114 Hz, 2 P). C{ H} NMR (125.75 MHz,
, r.t., ppm)
6
D
6
, r.t., ppm)
d
: 8.28 (d, J ¼ 8 Hz, 4 H, CHarom.), 8.00 (m,
þ
þ
2
(
2
3
2
3
of PMe
3
(0.04 mL, 0.34 mmol), the reaction mixture was stirred at
31
1
2
2
3
6 6
D
ꢀ
60
C. After one day, the volatiles were removed and n-hexane
13
1
d
(10 mL) was added and removed in vacuo in order to evaporate any
C
6
D
6
d: 185.8 (s), 173.1 (t, J ¼ 3 Hz), 166.6 (s), 139.4 (d,
remaining uncoordinated PMe . For purification, gradient-flash-
3
J ¼ 5 Hz), 135.8 (t, J ¼ 5 Hz), 132.4 (s), 130.9 (s), 130.1 (s), 129.7 (t,
chromatography was performed. The crude product was further
J ¼ 23 Hz),109.6 (d, J ¼ 1 Hz),102.2 (s), 99.5 (s), 51.5 (s), 30.5 (s), 30.1
purified by recrystallization from THF/hexane to yield 9 as a red
(
s), 28.1 (s), 27.9 (s), 21.2 (s). Elem. Anal. Calcd. (%) for
1
solid (0.10 g, 84%). H NMR (300 MHz, C
6
D
6
, r.t., ppm)
d
: 7.60 (d,
74 69 6 2
C H O P Rh: C, 72.90; H, 5.70. Found: C, 72.79; H, 5.60. MS
J ¼ 8 Hz, 4 H, CHarom), 7.05 (br s, 4 H, CHarom), 5.15 (s, 1 H, CH), 2.74
m, 4 H, CH ), 2.19 (m, 2 H, CH ), 1.96 (s, 6 H, CH ), 1.92 (s, 6 H, CH ),
). C{ H} NMR (126 MHz, C , r.t.,
: 186.3, 165.9, 136.8, 131.0, 126.4, 124.0, 107.0, 98.5, 94.9, 30.1,
þ
þ
(
MALDI-TOF) m/z: 1119 [M -acac], 914 [M -P(p-tolyl)
,5-Bis(arylethynyl)rhodacyclopentadiene (5): [Rh(
acac)(P(p-tolyl ] (1) (0.20 g, 0.41 mmol) and 1,11-bis(p-thioanisyl)
3
].
(
1
2
2
3
3
2
k
2-O,O-
2
13
1
.03 (vt, JP-H ¼ 3 Hz, 18 H, PMe
3
6 6
D
3 2
)
ppm)
2
d
undeca-1,3,8,10-tetrayne (3) (0.33 g, 0.41 mmol) were suspended in
1
9.9, 28.2, 15.0, 10.7 (vt, JC-P ¼ 14 Hz). Due to the low intensity two
ꢀ
THF (10 mL) and the reaction mixture was stirred at 60 C and
31 1
carbon signals coupled to Rh and/or P were not observed. P{ H}
NMR (121 MHz, C
Elem. Anal. Calcd. (%) for C36
Found: C, 58.92; H, 6.19 S, 8.23. MS (MALDI-TOF) m/z: 738 [M ]
monitored by 31P{ H} NMR spectroscopy. Once the reaction was
1
1
6
D
6
, r.t., ppm)
d
: ꢁ1.14 (d, JRh-P ¼ 114 Hz, 2 P).
complete, the volatiles were removed in vacuo. The product was
H
45
O
2
P
2
RhS
2
: C, 58.53; H, 6.14; S, 8.68.
purified via column chromatography (Al
2
O
3
) eluting with hexane/
þ
THF (2:1), recrystallized and washed with hot hexane to give pure 5
[23].
1
as a red solid. Yield: 0.4 g (44%). H NMR (300 MHz, C
: 8.07 (m, 12 H, p-tolyl-CHarom), 7.85 (d, J ¼ 8 Hz, 4 H, CHarom.), 7.21
d, J ¼ 8 Hz, 4 H, CHarom.), 6.96 (d, J ¼ 8 Hz, 12 H, p-tolyl-CHarom.),
.65 (s, 1 H, acac-CH), 2.07 (m, 4H, CH ) 1.98 (s, 6 H, SMe-CH ), 1.97
s, 18 H, p-tolyl-CH ), 1.61 (s, 6 H, acac-CH ) 1.58 (m, 2 H, CH
H} NMR (121 MHz, C , r.t., ppm)
: 24.8 (d, JRh-P ¼ 115 Hz, 2 P).
6 6
D , r.t., ppm)
2,5-Bis(arylethynyl)rhodacyclopentadiene (12): Rhodacyclo-
d
pentadiene 5 (0.10 g, 0.08 mmol) was dissolved in dry toluene and
,3-di(methyl)imidazol-2-ylidene (10) (0.02 g, 0.22 mmol) was
(
4
1
2
3
added. The reaction mixture was stirred at room temperature and
monitored by NMR spectroscopy. After 7 days, no starting material
could be detected anymore. The volatiles were removed in vacuo
31
(
{
3
3
2
).
P
1
6
D
6
d
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j.jorganchem.2017.02.028

8
C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
and the solid residue was washed three times with hexane. The
dark orange crude product was removed from insoluble by-
space group P-1, Z ¼ 2, 35722 reflections measured, 12977 inde-
pendent reflections (Rint ¼ 0.0322). The final R values were 0.0382
1
2
products by dissolving in toluene and purified by precipitation
(I > 2
(I > 2
Crystal data for 5:
s(I)) and 0.0636 (all data). The final wR(F ) values were 0.0994
1
2
from toluene/hexane at low temperature. Yield: 4.2 mg (5%).
NMR (500 MHz, C , r.t., ppm)
.61e7.59 (m, 4H, CHarom), 7.18e7.16 (m, 4H, CHarom), 6.99e6.97 (m,
H, CHarom), 5.77 and 5.76 (2s, 2H, NCHCHN), 4.88 (s, 1H, acaceH),
.11 (s, 6H, NCH ), 2.68e2.62 (m, 2H, CH ), 2.38e2.30 (m, 2H, CH ),
.00 (s, 9H, tolꢁCH ), 1.99 (s, 6H, SCH ), 1.95e1.86 (m, 2H, CH ) 1.84
). C{ H} NMR (125 MHz, C , r.t., ppm) : 185.4
H
s
(I)) and 0.1276 (all data). The goodness of fit on F was 1.087.
RhS 1195.24,
20.0940(10) Å,
6
D
6
d
: 8.02e7.98 (m, 6H, CHarom),
C
72
H
69
O
2
P
2
2
c
,
M
¼
7
a
a
¼
12.6624(7) Å,
¼ 103.554(3) ,
b
¼
13.6745(7) Å,
¼
ꢀ
ꢀ
ꢀ
3
6
4
2
b
¼ 103.458(3) ,
g
¼ 104.558(3) , V ¼ 3112.6(3) Å ,
3
2
2
T ¼ 100(2) K, space group P-1, Z ¼ 2, 77862 reflections measured,
12235 independent reflections (Rint ¼ 0.0656). The final R values
3
3
2
1
1
3
1
2
(
s, 6H, acaceCH
3
6
D
6
d
were 0.0425 (I > 2
were 0.0906 (I > 2
F was 1.026.
s
(I)) and 0.0668 (all data). The final wR(F ) values
(I)) and 0.1034 (all data). The goodness of fit on
(
s), 174.0 (dd, JRhꢁC ¼ 144 Hz, JPꢁC ¼ 46 Hz), 170.5 (s), 138.8 (d,
s
2
J ¼ 2 Hz), 136.8 (s), 135.7 (d, J ¼ 10 Hz), 131.2 (s), 130.8 (dd, J ¼ 34 Hz,
J ¼ 12 Hz), 130.2 (d, J ¼ 40 Hz), 126.9 (s), 124.9 (s), 121.9 (s), 107.5 (d,
J ¼ 1 Hz), 100.5 (d, J ¼ 1 Hz), 98.5 (s), 39.0 (s) 30.2 (s), 28.6 (s), 28.6
Crystal data for 12:
C
56
H
56
N
2
O
2
PRhS
2
,
M
¼
987.02,
a ¼ 10.9365(10) Å, b ¼ 11.6313(11) Å, c ¼ 19.2589(17) Å,
3
1
1
ꢀ
ꢀ
ꢀ
3
(
s), 21.2 (s), 15.5 (s). P{ H} NMR (202 MHz, C
6
D
H
6
, r.t., ppm)
d
: 21.7
: C,
a
¼ 78.182(3) ,
b
¼ 87.291(3) ,
g
¼ 81.362(3) , V ¼ 2370.4(4) Å ,
(
6
d, JRhꢁP ¼ 101 Hz). Elem. Anal. Calcd. (%) C56
8.14; H, 5.72; N, 2.84. Found: C, 68.26; H, 6.09; N, 3.18.
,5-Bis(arylethynyl)rhodacyclopentadiene (13): Rhodacyclo-
56
N
2
O
2
PRhS
2
T ¼ 100(2) K, space group P-1, Z ¼ 2, 55675 reflections measured,
10320 independent reflections (Rint ¼ 0.0230). The final R
1
values
2
2
were 0.0274 (I > 2
s(I)) and 0.0329 (all data). The final wR(F ) values
pentadiene 5 (0.10 g, 0.08 mmol) was dissolved in dry toluene. After
the addition of 1,3-di(n-propyl)imidazol-2-ylidene (11) (0.05 g,
were 0.0662 (I > 2
F was 1.070.
s
(I)) and 0.0712 (all data). The goodness of fit on
2
0
.34 mmol), the reaction mixture was stirred at room temperature
General photophysical measurements: UVevisible absorption
spectra were obtained on an Agilent 1100 Series Diode Array
spectrophotometer using standard 1 cm path length quartz cells.
Emission spectra were recorded on an Edinburgh Instruments
FLSP920 spectrometer, equipped with a 450 W Xenon arc lamp,
double monochromators for the excitation and emission pathways,
and a red-sensitive photomultiplier tube (R928-P PMT) as the de-
tector. All spectra were fully corrected for the spectral response of
the instrument. Unless otherwise mentioned, the longest-
wavelength absorption maximum of the compound in the respec-
tive solvent was chosen as the excitation wavelength for the
solution-state emission spectra. The emission spectra are inde-
pendent of the excitation wavelength, and the absorption and
excitation spectra are comparable across the measured range. All
solutions used in photophysical measurements had a concentration
lower than 10 М to minimize inner filter effects during photo-
luminescence measurements. The emission quantum yields were
measured using a calibrated integrating sphere from Edinburgh
Instruments combined with the FLSP920 spectrometer described
above. The emission was collected at right angles to the excitation
source with the emission wave-length selected using a double
grated monochromator and detected by a R928-P PMT.
and monitored by NMR spectroscopy. After 7 days, no starting
material could be detected. The volatiles were removed in vacuo
and the solid residue was washed three times with hexane. The red
crude product was removed from insoluble by-products by dis-
solving in toluene and further purified by precipitation from
1
toluene/hexane at low temperature. Yield: 4.9 mg (6%). H NMR
(
500 MHz, C
6 6
D , r.t., ppm) d: 7.98e7.95 (m, 6H, CHarom), 7.58e7.56
(
m, 4H, CHarom), 7.17e7.14 (m, 4H, CHarom), 6.98e6.96 (m, 6H,
CHarom), 6.22 (2s, 2H, NCHCHN), 4.91 (s, 1H, acaceH), 4.73 (s, 4H,
NCH ), 2.62e2.56 (m, 2H, CH ), 2.37e2.30 (m, 2H, CH ), 2.00 (s, 9H,
tol-CH ), 2.00 (s, 6H, SCH ),1.96e1.88 (m, 2H, CH ),1.86 (s, 6H, acac-
CH ), 1.64 (m, 4H, NCH CH CH CH CH ).
), 1.02 (t, 3H, J ¼ 7 Hz, NCH
C{ H} NMR (125 MHz, C , r.t., ppm) : 185.4 (s), 174.1 (dd,
RhꢁC ¼ 146 Hz, JPꢁC ¼ 48 Hz), 170.5 (s), 138.7 (d, J ¼ 2 Hz), 136.7 (s),
35.7 (d, J ¼ 10 Hz), 131.3 (s), 130.8 (dd, J ¼ 34 Hz, J ¼ 13 Hz), 130.2
d, J ¼ 40 Hz), 126.7 (s), 124.4 (s), 120.1 (s), 120.0 (s), 106.8 (d,
J ¼ 1 Hz), 100.5 (d, J ¼ 1 Hz), 98.5 (s), 51.7 (s), 30.2 (s), 28.7 (s), 28.5
2
2
2
3
3
2
3
2
2
3
2
2
3
13
1
6
D
6
d
J
1
(
ꢁ
6
31
1
(
s), 25.7 (s), 21.2 (s), 15.5 (s), 11.8 (s) ppm. P{ H} NMR (202 MHz,
C
C
6
6
D
6
, r.t., ppm) : 21.3 (d, JRhꢁP ¼ 101 Hz). Elem. Anal. Calcd. (%)
d
60
H
64
N
2
O
2
PRhS : C, 69.08; H, 6.18; N, 2.69. Found: C, 69.48; H,
2
.27; N, 2.92.
Crystallographic Details: The crystal data were collected on a
Bruker X8-APEX II diffractometer with a CCD area detector and
graphite monochromated Mo radiation. The structures were
Acknowledgements
K
a
solved using the intrinsic phasing method (ShelXT) or the olex2.-
solve structure solution program using Charge Flipping [37],
refined with the ShelXL program [38] and expanded using Fourier
techniques. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in structure factor calculations. All
hydrogen atoms were assigned to idealized geometric positions.
CCDC 1531337 for 1,1531334 for 4,1531336 for 5 and 1531335 for 12
contain the supplementary crystallographic data for this paper,
which can be obtained free of charge from the Cambridge Crys-
tallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
We thank the DFG (MA 4471/4-1) and the Julius-Maximilians-
Universitat Würzburg for support. A.L. thanks the DFG for a post-
doctoral fellowship.
€
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2017.02.028.
References
Crystal data for 1: C47
H
49
O
2
P
2
Rh, M ¼ 810.71, a ¼ 13.9553(6) Å,
ꢀ
ꢀ
b ¼ 22.5210(10) Å, c ¼ 14.2399(7) Å,
a
¼ 90 ,
b
¼ 114.662(2) ,
[
1] (a) P.G. Bomben, K.C.D. Robson, B.D. Koivisto, C.P. Berlinguette, Coord. Chem.
ꢀ
3
g
¼ 90 , V ¼ 4067.2(3) Å , T ¼ 100(2) K, space group P2 /c, Z ¼ 4,
1
Rev. 256 (2012) 1438e1450;
(b) R.H. Crabtree, Organometallics 30 (2011) 17e19;
6
8252 reflections measured, 14603 independent reflections
(
c) P.-T. Chou, Y. Chi, M.-W. Chung, C.-C. Lin, Coord. Chem. Rev. 255 (2011)
653e2665;
d) W.-Y. Wong, C.-L. Ho, Acc. Chem. Res. 43 (2010) 1246e1256;
(e) A.F. Rausch, H.H.H. Homeier, H. Yersin, Top. Organomet. Chem. 29 (2010)
93e235;
(
(
(
R
int ¼ 0.1070). The final R
1
values were 0.0419 (I > 2
s
(I)) and 0.0781
2
(
2
all data). The final wR(F ) values were 0.0823 (I > 2
all data). The goodness of fit on F was 1.003.
s(I)) and 0.0938
2
1
Crystal data for 4: C74
H
69
O
6
P
2
Rh, M ¼ 1219.14, a ¼ 11.9993(7) Å,
(
(
f) A.J. Morris, G.J. Meyer, E. Fujita, Acc. Chem. Res. 42 (2009) 1983e1994;
g) M. Gr a€ tzel, Acc. Chem. Res. 42 (2009) 1788e1798;
ꢀ
b
b
¼
14.1960(8) Å,
c
¼
19.5690(11) Å,
a
¼
103.2998(16) ,
ꢀ
ꢀ
3
¼ 104.3165(17) ,
g
¼ 100.1056(17) , V ¼ 3046.4(3) Å , T ¼ 100 K,
(h) A.S. Polo, M.K. Itokazu, N.Y. Murakami Iha, Coord. Chem. Rev. 248 (2004)
Please cite this article in press as: C. Sieck, et al., Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.02.028

C. Sieck et al. / Journal of Organometallic Chemistry xxx (2017) 1e9
9
1
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Please cite this article in press as: C. Sieck, et al., Journal of Organometallic Chemistry (2017), http://dx.doi.org/10.1016/
j.jorganchem.2017.02.028