Synthesis and reactivity of [penta(4-halogenophenyl)cyclopentadienyl] [hydrotris(indazolyl)borato]ruthenium(II) complexes: Rotation-induced fosbury flop in an organometallic molecular turnstile

Article abstract of DOI:10.1002/chem.200800689

The preparation of ruthenium(II) complexes coordinated to a penta(4-halogeno)phenylcyclopentadienyl ligand and to the hydrotris(indazolyl) borate ligand are detailed. Our strategy involves first the coordination of the penta(4-bromo)phenylcyclopentadienyl ligand by reaction with the ruthenium-carbonyl cluster followed by the coordination of the tripodal ligand. The pentabrominated precursor was successfully converted to the pentaiodinated derivative by using the Klapars-Buchwald methodology, applied for the first time on organometallic substrates. Cross-coupling reactions were performed on both pentabromo and pentaiodo complexes to introduce in a single step the five peripheric ferrocenyl fragments required to obtain a potential molecular motor. The two ligands present in the ruthenium complexes undergo a correlated rotation that was established both experimentally by NMR experiments and an Xray diffraction study, and theoretically by DFT calculations. The potentialenergy curve obtained by DFT revealed the energy barrier of the gearing mechanism to be only 4.5 kcal mol^-1. These sterically highly constrained complexes can be regarded as organometallic molecular turnstiles.

Full text of DOI:10.1002/chem.200800689

FULL PAPER
DOI: 10.1002/chem.200800689
Synthesis and Reactivity of [Penta(4-halogenophenyl)cyclopentadienyl]-
A
Fosbury Flop in an Organometallic Molecular Turnstile
Alexandre Carella,[a] Jean-Pierre Launay,[a] Romuald Poteau,[b] and
GwØnal Rapenne*[a]
Abstract: The preparation of rutheni-
um(II) complexes coordinated to
penta(4-halogeno)phenylcyclopenta-
dienyl ligand and to the hydrotris(inda-
zolyl)borate ligand are detailed. Our
strategy involves first the coordination
Klapars–Buchwald methodology, ap-
plied for the first time on organometal-
lic substrates. Cross-coupling reactions
were performed on both pentabromo
and pentaiodo complexes to introduce
in a single step the five peripheric fer-
rocenyl fragments required to obtain a
potential molecular motor. The two li-
gands present in the ruthenium com-
plexes undergo a correlated rotation
that was established both experimen-
tally by NMR experiments and an X-
ray diffraction study, and theoretically
by DFT calculations. The potential-
energy curve obtained by DFT re-
vealed the energy barrier of the gear-
G
a
of the penta(4-bromo)phenylcyclopen-
G
tadienyl ligand by reaction with the
ruthenium–carbonyl cluster followed
by the coordination of the tripodal
ligand. The pentabrominated precursor
was successfully converted to the penta-
iodinated derivative by using the
Keywords: cross-coupling · density
functional calculations · molecular
turnstiles · ruthenium · sandwich
complexes
ing
mechanism
to
be
only
4.5 kcalmolÀ1. These sterically highly
constrained complexes can be regarded
as organometallic molecular turnstiles.
Introduction
scopic objects at the molecular level, including the motions
these objects are able to undergo. Such systems that func-
tion in an analogous fashion to macroscopic mechanical sys-
tems have recently led to the synthesis and description of
many molecular-scale systems as innovative as molecular
gears,[3] wheels,[4] nanovehicles,[5] wheelbarrows,[6] and turn-
stiles.[7] These are providing a basis for the future design of
bottom-up nanoscale systems and materials to perform tasks
as varied as nanoscale manipulation, information storage,
molecular electronics and mechanics.
One of the earliest examples of a molecular gear was si-
multaneously reported by Mislow and Iwamura.[8] The mole-
cule consists of a bistriptycene linked by a methylene or an
oxygen bridge to give an analogue of a three-toothed bevel
gear. Simple carbon-derived rotors such as triptycene are
limited by valency to three cog-teeth. To increase the
number of cog-teeth available in the rotor and in the search
for the synthesis of a molecular motor,[9] we became inter-
ested in the possibility of utilising metallocenes, in particular
half-sandwich complexes with the “piano stool” structure.
They present interesting characteristics for our purpose: one
can build complex molecules presenting only one significant
degree of freedom in internal rotation, and it is possible to
The control of rotation is at the heart of the bottom-up
strategy to build molecular devices such as molecular ma-
chines and motors.[1,2] In the constant quest for novel molec-
ular components, multistep chemical synthesis is expected to
play a major role because it allows chemists to prepare
tailor-made compounds with predetermined shape and pro-
grammed movement or functions. This has stimulated the
design and synthesis of a variety of compounds that resem-
ble macroscopic machinery. We call such molecules “techno-
mimetic”[2] because they are designed to transpose macro-
[a] A. Carella, Prof. J.-P. Launay, Dr. G. Rapenne
NanoSciences Group, CEMES-CNRS
29 rue Jeanne Marvig, BP 94347
31055 Toulouse Cedex 4 (France)
Fax : (+33)562257841
E-mail: rapenne@cemes.fr
[b] R. Poteau
UniversitØ de Toulouse; INSA, UPS, CNRS; LPCNO
135 avenue de Rangueil, 31077 Toulouse (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200800689.
Chem. Eur. J. 2008, 14, 8147 – 8156
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8147

perform different chemistries on the upper and lower parts
of the molecule, giving access to a wide range of com-
pounds. Thus, we studied the synthesis of a family of ruthe-
nium complexes containing two different ligands, a penta-
phenyl-substituted cyclopentadienyl (Cp) and a hydrotris(in-
dazolyl)borate (Tp4Bo) ligand. This family of complexes is
much less common than the well-studied family of (cyclo-
pentadienyl)[hydrotris(pyrazolyl)borato]ruthenium
Results and Discussion
Synthesis of [penta(4-bromophenyl)cyclopentadienyl][hy-
drotris(indazolyl)borato]ruthenium complexes: Hydrotris-
(indazolyl)borate ligand (Tp4Bo) is a versatile ligand belong-
ing to the family of scorpionates developed by Trofimen-
ko.[10] It has been shown that Tp4Bo binds in a facial tripodal
mode and its geometry is particularly well suited to mimic
macroscopic gears.[3] Two routes have been described in the
literature to synthesise half-sandwich RuCpTp and
RuCp*Tp complexes. The most general one has been de-
scribed by Tocher and co-workers[11] and involves the coor-
dination of the scorpionate ligand followed by the coordina-
tion of the cyclopentadienyl ligand. For this purpose,
[Ru(h6-p-cymene)Tp4Bo] hexafluorophosphate was synthes-
[RuCpTp] complexes.[10]
In this paper, we present the synthesis of [penta(4-halo-
genophenyl)cyclopentadienyl][hydrotris(indazolyl)borato]ru-
thenium half-sandwich complexes. As halogens, bromine
and iodine were selected because of their potential in cross-
coupling reactions that enable the introduction of functional
building blocks. The brominated and iodinated derivatives
were prepared and cross-coupling reactions achieved on
both structures. The syntheses appeared to be relatively dif-
ficult and several strategies had to be explored. The combi-
ised by reaction of [{Ru
(p-cymene)Cl2}2] with KTp4Bo in ace-
A
tonitrile for 18 h at room temperature.
After treatment with an ammonium hexafluorophosphate
solution and recrystallisation from methanol (with Et2O as a
non-solvent), (h6-p-cymene)[hydrotris(indazolyl)borato]ru-
thenium hexafluorophosphate was isolated as orange crys-
tals in 27% yield (Scheme 1).
nation of two bulky ligands (substituted Cp and Tp4Bo
)
around the metallic core revealed very interesting behav-
iour: a lateral gearing effect that was established experimen-
tally by NMR and X-ray experiments and theoretically by a
DFT study of the molecular motions. From a technomimetic
point of view, these complexes behave as organometallic
molecular turnstiles with two correlated rotations, that is,
the primary rotation of one ligand with respect to the other
induces a secondary rotation.
Scheme 1. Synthesis of (h6-p-cymene)[hydrotris(indazolyl)borato]rutheni-
Abstract in French: La prØparation de complexes de ruthØ-
nium coordinØ au ligand penta(4-halogØno)phØnyl cyclopen-
tadiØnyl et au ligand hydrotris(indazolyl)borate sont dØtail-
lØes. Notre stratØgie implique tout dꢀabord la coordination du
um hexafluorophosphate.
Photochemical[12] and thermal labilisation of the p-cymene
ligand were attempted in acetonitrile in the presence of
ligand penta(4-bromo)phØnylcyclopentadiØnyl par rØaction
A
1,2,3,4,5-penta
(phenyl)cyclopentadiene
without
success
avec le cluster de ruthØnium carbonyle suivie par la coordina-
tion du ligand tripode. Le prØcurseur pentabromØ a ensuite
ØtØ converti avec succ›s en dØrivØ pentaiodØ en utilisant la
mØthodologie dØveloppØe par Klapars et Buchwald qui a ØtØ
utilisØe pour la premi›re fois sur des substrats organomØtalli-
ques. Des rØactions de couplages croisØs ont ensuite ØtØ effec-
tuØes sur les dØrivØs pentabromØs et pentaiodØs afin dꢀintro-
duire simultanØment les cinq fragments ferrocØnyl pØriphØri-
ques requis pour obtenir un moteur molØculaire potentiel.
Les deux ligands prØsents dans les complexes de ruthØnium
sont le si›ge dꢀune rotation secondaire corrØlØe qui a ØtØ mise
en Øvidence expØrimentallement par des expØriences de RMN
et une Øtude de diffraction des rayons X, et thØoriquement
par des calculs DFT. La courbe dꢀØnergie potentielle obtenue
par DFT permet dꢀaccØder à la barri›re de rotation de ce mØ-
canisme dꢀengrenage qui nꢀest que de 4.5 kcalmolÀ1. Ces
complexes stØriquement tr›s contraints peuvent Þtre considØ-
rØs comme des tourniquets molØculaires organomØtalliques.
under various conditions, including microwave heating.
We subsequently investigated another synthetic route in-
volving the coordination of the Cp ligand in a first step. As
proposed by Mann and co-workers,[13] this strategy involves
the use of the (acetonitrile)(h5-cyclopentadienyltris)ruthe-
nium(II) complex in which the labile acetonitrile ligands can
be easily substituted by a Tp ligand. A similar strategy was
described by Singleton[14] using as intermediate the chloro-
A
A
complex, a versatile precursor because cycloocta-1,5-diene is
labile. However, both strategies failed with pentaphenylcy-
clopentadienyl ligands, possibly due to the strong steric hin-
drance in the neighbourhood of the coordination site.
These difficulties led us to follow an alternative strategy
that requires the synthesis of (h6-benzene)[h5-1,2,3,4,5-
penta(4-bromophenyl)cyclopentadienyl]ruthenium as a key
intermediate. Bromination of the commercially available
1,2,3,4,5-penta(phenyl)cyclopentadiene was achieved by
G
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Ruthenium(II) Complexes
FULL PAPER
Scheme 2. Synthesis of (h6-benzene)[h5-1,2,3,4,5-penta(4-bromophenyl)cyclopentadienyl]ruthenium hexafluorophosphate.
treatment with neat bromine at room temperature for 2 h,
which produced regioselectively 2, 1-bromo-1,2,3,4,5-
penta(4-bromophenyl)cyclopentadiene (Scheme 2). Similarly
to the oxidative addition of 1-bromo-1,2,3,4,5-pentaphenyl-
cyclopentadiene on the ruthenium–dodecacarbonyl clus-
ter,[15] the reaction of 2 with [Ru3(CO)12] yielded complex 3,
the bromidodicarbonyl[h5-1,2,3,4,5-penta(4-bromophenyl)-
cyclopentadienyl]ruthenium
complex,
[Ru
G
N
BrPh)5}Br(CO)2]. Moreover, the IR spectrum of complex 3
displayed two characteristic vibration bands of the carbonyl
ligands at 2003 and 2048 cmÀ1 comparable to the ones of
[RuCpBr(CO)2].[15] The substitution of the carbonyl and
bromine ligands was achieved in benzene at reflux in the
presence of aluminium chloride, as shown by Pauson and
McVey[16] for the synthesis of bromidodicarbonyl(h5-
Scheme 4. Synthesis of [Ru
A
G
column chromatography, 5 was obtained as a yellow solid in
30% yield.
1,2,3,4,5-penta(phenyl)cyclopentadienyl)iron. The photolabi-
A
lisation of the arene ligand and its substitution by a scorpio-
nate was demonstrated by Mann and co-workers.[17] After
counterion exchange by treatment with an excess of ammo-
nium hexafluorophosphate, (h6-benzene)[h5-1,2,3,4,5-penta-
Notably, two equivalents of KTp4Bo are needed to obtain
such a yield. The use of only one equivalent produced 5 in a
16% isolated yield, whereas a larger excess did not increase
the yield. Reaction time, temperature and solvent were
varied, but none of these changes resulted in an improved
yield. Nevertheless, it must be noted that the coordination
of the tripodal ligand is the result of two steps and the pres-
ence of various ligands (Tp4Bo, Cp, CO, Br) in the reaction
mixture may allow numerous side reactions. The slightest
ligand scrambling produces side products.
A
hexafluoro-
A
1H NMR analysis showed a free rotation of the h5-1,2,3,4,5-
penta(4-bromophenyl)cyclopentadienyl and h6-benzene li-
gands with only a singlet for the benzene ring.
Unfortunately, by following a standard procedure, irradia-
tion of complex 4 in acetonitrile with a 400-W UV lamp did
not allow us to obtain the target complex (Scheme 3). TLC
analysis showed the formation of numerous side products,
indicating a probable generation of bromine radicals during
the experiment.
The piano-stool structure of the [h5-1,2,3,4,5-penta(4-bro-
mophenyl)cyclopentadienyl][hydrotris(indazol-1-yl)borato]-
1
A
The three indazoles are chemically equivalent, resonating at
the same frequency. Moreover, the signals for protons 1 and
4 are largely shifted downfield indicating a strong shielding
effect of the phenyls of the h5-1,2,3,4,5-penta(4-bromophe-
nyl)cyclopentadienyl ligand on the indazole of Tp4Bo, as ex-
pected for such interpenetrated ligands.
X-ray structure of 5: Crystals of [Ru
N
N
(5) suitable for X-ray diffraction were obtained from the
slow diffusion of methanol in a benzene solution of the com-
plex [Ru
N
N
zene molecules. The X-ray structure of [Ru
N
N
Scheme 3. Attempted photolabilisation of the benzene in acetonitrile.
BrPh)5}Tp4Bo] confirmed the coordination of both ligands, as
shown in Figure 1.[18] As shown by Trofimenko,[19] Tp4Bo
binds in a facial tripodal mode (i.e., k3-N,N’,N’’). The com-
plex has a piano-stool structure with the Cp substituents fit-
ting in the vacant spaces of the tripodal ligand. The distance
between the Cp ligand and the ruthenium atom is 1.79 Š
In order to obtain complex 5, as shown in Scheme 4, com-
plex 4 and KTp4Bo were heated in THF at reflux under
argon atmosphere for 24 h. After purification by silica-gel
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8149

G. Rapenne et al.
Table 1. Selected bond lengths in [Ru
[RuCpTp4Bo].
A
(4-BrPh)5}Tp4Bo
]
and
[Ru
G
(4-BrPh)5}Tp] (5)
[RuCpTp4Bo
]
À
Ru N(1)
2.158(5)
2.159(4)
2.131(5)
2.192(5)
2.186(5)
2.186(5)
2.142(5)
2.207(5)
2.142(7)
2.108(7)
2.098(7)
2.140(10)
2.155(13)
2.166(11)
2.143(13)
2.131(11)
À
Ru N(3)
À
Ru N(5)
À
Ru C(1)
À
Ru C(2)
À
Ru C(3)
À
Ru C(4)
À
Ru C(5)
Figure 1. Crystal structure of 5: space-filling (side view, left) and ORTEP
(bottom view, right) representations.
Reactivity of the pentabrominated derivative [Ru
N
N
and the average distance between the three coordinated ni-
trogen atoms and the ruthenium centre is 2.16 Š.
BrPh)5}Tp4Bo]: Our research on electron-triggered molecular
motors involves an active part based on a ruthenium–cyclo-
pentadienyl (Cp) complex. In this design the Cp ligand is
substituted by five linear and rigid arms, each terminated by
an electroactive group. Ferrocene was selected as an electro-
active group because it exhibits reversible oxidation in vari-
ous solvents.[21] The molecule is intended to be deposited be-
tween two electrodes of a nanojunction and should trans-
form a current of electrons into a unidirectional rotation
motion.[9] The quintuple Sonogashira coupling reaction[22]
By analogy with ethane, as shown in Figure 2, two re-
markable conformations can be defined: the eclipsed confor-
mation, in which the dihedral angle between a CH bond of
the h5-cyclopentadienyl ligand and one indazole of the scor-
pionate ligand is 08, and the staggered conformation, in
which this dihedral angle is 128.
was attempted between [Ru
N
N
ethynylferrocene without success. Different alkynes and cat-
alytic systems were tested, but even the use of very elec-
tron-rich and hindered phosphines such as tris(tert-butyl-
phosphine) did not allow us to obtain the coupling product.
This may be due to the high electron density of the bromide
derivative, which is covalently linked to a formal anionic
entity (Cp). The electron-rich character of the carbon–bro-
mide bond precludes the oxidative addition on the palladi-
um catalyst.
Figure 2. Eclipsed (left) and staggered (right) conformations of a complex
bearing a C3 and a C5 symmetry ligand. Interconversion occurs upon a
128 rotation (represented counterclockwise on the figure). For symmetry
reasons, the staggered conformation appears every 248.
In accordance with the results obtained by Tobe et al.[23]
for the synthesis of differentially substituted hexaethynyl-
benzenes based on tandem Sonogashira and Negishi[24]
cross-coupling reactions, we tried to overcome the poor re-
activity of the aryl bromide centres by using Negishi condi-
tions. The specificity of this protocol lies in the use of a
freshly prepared alkynyl zinc chloride solution instead of an
alkynyl cuprate generated in situ. In contrast to the Sonoga-
shira conditions, the five ferrocenyl groups were simultane-
ously covalently attached to the pentaphenyl Cp ligand by a
quintuple coupling of ethynylferrocene with 5 with a 32%
yield, which corresponds to a yield of 80% per coupling
(Scheme 5). 1H NMR spectroscopy clearly showed an
AA’BB’ pattern for the phenyl groups attached to the cen-
tral Cp ring and the signals of the ferrocene units integrating
for 45 protons. The presence of the five ethynylferrocene
units was also confirmed by mass spectrometry.
The [Ru
A
N
conformation close to the staggered one. For symmetry con-
siderations, the superimposition of a tripodal ligand bearing
a C3 axis and a penta-substituted Cp of C5 symmetry causes
differentiation of the five 4-bromophenyl rings, considering
the dihedral angle between the plane of the phenyl ring and
the plane of the Cp ring. One is exactly perpendicular (908),
and the two groups that are not located above indazole are
almost perpendicular (818). Due to steric hindrance with the
tripodal ligand, the remaining two phenyl rings have to be
tilted at 358 and 368 to minimise steric interactions.
The comparison of the X-ray crystal structures of
[RuCpTp4Bo
]
[20]
À
lengths in the latter: +0.02 Š for the Ru C bonds, and
À
À
À
+0.02 Š for the Ru N bonds. The Ru C and Ru N bond
lengths are summarised in Table 1. This trend is reproduced
by DFT calculations on both systems (+0.05 Š and +0.01 Š
Synthesis of [penta(4-iodophenyl)cyclopentadienyl][hydro-
tris(indazolyl)borato]ruthenium complexes by halogen-ex-
change reaction: Because the conversion to organozinc pre-
cursors is not quantitative and not compatible with all the
organic functions or organometallic building blocks, we de-
cided to substitute the bromine atoms for iodine centres to
À
À
for the Ru C and Ru N bonds, respectively). This stretch-
ing of the metal–ligand bonds reflects the steric hindrance in
5 due to the interactions of the 4-bromophenyl substituents
with the indazole rings of the tripodal ligand, but the magni-
tude of the effect is small.
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Ruthenium(II) Complexes
FULL PAPER
Scheme 5. Palladium-catalysed coupling strategy.
overcome the lack of reactivity of the polybrominated pen-
taphenylcyclopentadienyl moiety. A halogen-exchange reac-
tion was investigated to activate the penta(4-bromo)phenyl-
G
cyclopentadienyl ligand towards palladium-catalysed cou-
pling reactions. The pentaiodinated analogue of complex 5
was envisaged because aryl iodides are more reactive in pal-
ladium-catalysed cross-coupling reactions. The most com-
monly used reaction to convert an aryl bromide into an aryl
iodide consists of the preparation of the organolithium de-
rivative in a first step followed by quenching with iodine.
However, this reaction is not universal and, in particular, it
is not suited for polybromide precursors because polyanion-
ic species are difficult to generate and are often accompa-
nied by solubility problems.
In 2002, Klapars and Buchwald described a very efficient
copper-catalysed halogen–exchange reaction in aryl halides,
consisting of an aromatic Finkelstein reaction.[25] They
showed it was possible to exchange a bromide with an
iodide by treatment of the substrate with copper iodide,
sodium iodide and a catalytic amount of N,N’-dimethyl-
trans-cyclohexanediamine, with 93–99% yield for the con-
version of monohalogen derivatives. The reaction seems to
tolerate many organic functions and is efficient with various
electrodonating or electrowithdrawing groups. Nevertheless,
it must be noted that, to our knowledge, there are no exam-
ples of this halogen-exchange reaction on organometallic or
coordination compounds.
Scheme 6. Iodination reactions performed on the ruthenium complexes.
a) 2.5 equiv CuI, 20 equiv NaI, 0.5 equiv (rac)-trans-N,N’-dimethyl-1,2-cy-
clohexanediamine, dioxane, Ar, 1108C, 24 h.
1
This reaction was first tested on [Ru
G
N
This complex was characterised by H- and 13C NMR spec-
BrPh)5}Tp4Bo] (5), but the result was not satisfactory because
an analysis of the crude mixture by mass spectrometry
showed partial conversion of the starting complex and pro-
duction of all the possible products resulting from 1-to-5
halogen exchange. Performing the same reaction on the pre-
cursor complex 3 gave access to the pentaiodinated ana-
logue 7 which, after coordination of ligand Tp4Bo as shown
troscopy, mass spectrometry and infrared spectroscopy. The
carbonyl vibrations (nC O =2000 and 2042 cmÀ1) are similar
=
to those of the brominated complex 3 (nC O =2003 and
=
2048 cmÀ1).
Compound 7 was converted into the pentaiodinated 8 by
reaction with KTp4Bo (2 equiv) in refluxing THF for 24 h.
Compound 8 was isolated in 14% yield by column chroma-
tography, and this compound was also fully characterised by
1H and 13C NMR spectroscopy, and mass spectrometry. The
in Scheme 6, yielded [Ru
The periodination
A
ACHTREUNG
G
N
1
BrPh)5}Br(CO)2] (3) was achieved at 1108C in dioxane in
the presence of sodium iodide (20 equiv), copper iodide
(2.5 equiv) and N,N’-dimethyl-trans-cyclohexanediamine in
catalytic amount (Scheme 6). After 24 h of heating, the de-
sired compound 7 was obtained in a 45% isolated yield.
comparison of the H NMR spectra of the pentabrominated
and the pentaiodinated complexes (5 and 8) showed a shift
of the phenyl signals due to the effect of the iodine centres.
Indeed, the protons located ortho to the halogen atom are
shifted downfield by 0.20 ppm and the protons meta to the
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G. Rapenne et al.
1
halogen atom are shifted upfield by 0.17 ppm in the case of
the iodine derivatives. Interestingly, these shifts are very
close to the values given in the commonly used incremental
tables, 0.21 and 0.13 ppm, respectively.
symmetry, chemical equivalence in the H NMR spectrum is
a proof of free rotation of one ligand with respect to the
1
other one. For instance, in the H NMR spectrum of 5, the
rotational freedom of the Cp ring was evidenced because
the three indazolyl groups are equivalent, as shown in
Figure 3. The 4-bromophenyl rings are also free to rotate, as
evidenced by the chemical equivalence of the two ortho pro-
tons (Ho) and of the two meta protons (Hm).
Reactivity of the pentaiodinated derivative [Ru
N
N
IPh)5}Tp4Bo]: As shown in Scheme 5, the Sonogashira cou-
pling conditions were very efficient with the pentaiodinated
precursor (whereas the pentabrominated analogue gave no
reaction) and allowed the direct connection of the five ethy-
nylferrocene moieties onto complex 8. This was accom-
plished in a single step, leading to complex 6 after a quintu-
ple coupling reaction with a 44% yield corresponding to an
excellent 85% per coupling. This is the best yield obtained
to date for this family of molecules involving a quintuple
coupling in the last synthetic step.
Electrochemistry: Cyclic voltammetry of complex 6 showed
two reversible oxidation waves corresponding to the succes-
sive oxidation of the iron centres and the ruthenium centre.
The 5:1 ratio between these two waves is consistent with the
ratio between the iron and ruthenium atoms in the complex.
In complex 6, the five iron centres are first reversibly[21] and
simultaneously oxidised at a potential of 0.52 V/saturated
calomel electrode (SCE) (Table 2), followed by the reversi-
ble oxidation of the ruthenium centre at 0.82 V/SCE, which
is similar to the value obtained with 1. The lower oxidation
potential for the iron moiety in 6 versus ethynylferrocene
(Ethynyl–Fc) is in line with the replacement of a hydrogen
atom by an electron-rich aromatic substituent.
Figure 3. 1H NMR (CD2Cl2, 250 MHz) spectrum of 3 (bottom) compared
to [RuCpTp4Bo] (top) at 258C.
These protons are referred to as an AA’BB’ spin system.
Table 2. Oxidation potentials of iron and ruthenium in V vs SCE. All
waves were reversible (CH2Cl2, nBu4NPF6 0.1m, Pt working and counter
electrode).
In addition, there are striking differences between the spec-
trum of [Ru
(h5-Cp)Tp4Bo], which we have also synthesised,
A
and the spectrum of 5. Protons a and b (see numbering
scheme in Scheme 5) are significantly shielded from 8.62 to
7.86 ppm for protons a and from 7.60 to 7.39 ppm for pro-
tons b. This shielding is explained by the location of these
protons in the shielding cones of the 4-bromophenyl rings,
evidencing the two ligands fitting into each other in solution,
just like in the solid state. Variable-temperature 1H NMR
spectroscopy from À908C to 1208C did not show any signifi-
cant differences in terms of equivalence of protons. Thus,
the rotation barrier could not be measured by NMR analysis
and must be low.
The apparent paradox of the free rotation evidenced by
NMR analysis and the embedding of the aromatics high-
lighted by X-ray diffraction can only be explained by two
correlated rotation processes. Because the two ligands are
interpenetrated, the rotation of the Cp ring should only be
possible if the 4-bromophenyl groups tip over to settle in
the vacant spaces of the tripodal ligand. Figure 4 represents
the rotation of the upper Cp ligand (action 1) inducing the
secondary rotation of the 4-bromophenyl rings (action 2).
DFT calculations were performed to support this hypothesis
in order to elucidate the molecular motions that correspond
to a lateral gearing effect.
5
6
Ethynyl–Fc
E1/2(ox) FeII/FeIII
E1/2(ox) RuII/RuIII
–
0.80
0.52
0.82
0.59
–
The relative oxidation potentials are compatible with our
objective, in the sense that the ruthenium centre will remain
inert towards the redox cycles of the peripheral electroactive
groups. Indeed, the cyclic voltammogram (see Supporting
Information) shows that the two oxidation processes do not
overlap, which means that oxidation of the ferrocene frag-
ments will not affect the ruthenium centre.
Study of the rotation in solution—evidence for a lateral
gearing effect: The rotation was studied both experimentally
and theoretically on complex 5. In this complex, an addi-
tional steric interference exists relative to the case of
[RuCpTp4Bo] due to the interaction between the bromo-
phenyl units and the indazolyl paddles, so that one could an-
ticipate a slow or restricted rotation.
The dissymmetry of the complex was exploited to study
the dynamics of the rotation in 5. Because the tripodal
ligand bears a C3 axis and the penta-substituted Cp is of C5
8152
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Chem. Eur. J. 2008, 14, 8147 – 8156

Ruthenium(II) Complexes
FULL PAPER
tion can be explained by the dispersion interaction, which
favours weak CH/p attractive interactions[26] between the
leg and the paddle overhanging. Hybrid DFT functionals
are able to describe this particular dispersion interaction, al-
though it is underestimated with respect to the MP2 and
CCSD(T) level of theories.
The potential-energy curve obtained by DFT gave access
to the energy barrier of the gearing mechanism. A transition
state, corresponding to an intermediate during the rotation
process, was found by DFT at 4.5 kcalmolÀ1 above the mini-
mum. It resembles the staggered geometry (Figure 5b), but
one paddle (*) starts to interact with a leg, prefigurating the
nearby minimum geometry (Figure 5c). The differences be-
tween the X-ray structure and the computed minimum and
transition-state structures are subtle and also involve differ-
ences in orientation of the phenyl rings with respect to the
Cp ring. Thus, we can conclude that the upper part remains
strongly linked to the lower part during the rotation process,
while being almost free to rotate.
Closer inspection of the structure strongly suggests that
the rotation must involve some “ gearing effect”, that is, a
correlated motion of the upper part with respect to the
lower part (Figure 4, motion 1), and of a paddle around the
Cp–phenyl single bond (Figure 4, motion 2). This is reminis-
cent of the “Fosbury flop”.[27]
Figure 4. Representation of the secondary rotation: the rotation of the
upper Cp ligand (action 1) results in the paddles tipping over (action 2).
DFT analysis: The symmetry of the two parts of the mole-
cule suggests that the potential-energy curve should have a
high periodicity. If we start from a conformation in which a
4-bromophenyl group (paddle) sits just above an indazol
ring (leg), it is clear that a rotation by 248 (1/15th of a turn)
makes another coincidence happen (Figure 2). Hence, we
predict that the potential-energy curve should present close-
ly spaced extrema. To systematise the analysis, we define an
eclipsed and a staggered conformation from the value of the
smallest dihedral angle between a paddle and a leg, that is,
08 and 128, respectively (see above). Simple steric considera-
tions suggest that the staggered conformation should be an
energy minimum, whereas the eclipsed one should be a tran-
sition state. The geometry close to the staggered one ob-
tained for the X-ray crystal structure (Figure 1) is not exact-
ly reproduced by DFT calculations. At this level, it is found
that the most stable conformation is the eclipsed one (Fig-
ure 5a). The paddle that sits exactly above a leg is tilted
with respect to the Cp ring plane by 318 only, that is, by
much less than the others (53 to 858). This privileged posi-
Conclusion
The synthesis of the active part of molecular motors was
achieved through cross-coupling reactions performed on a
polyhalogenated ruthenium complex. The coupling reactions
involving the polybrominated complex were either ineffec-
tive (Sonogashira) or successful (Negishi), however, the
latter requires in a first step the conversion of a terminal
alkyne into an organozinc intermediate, which restricts the
scope of this reaction. To overcome this problem, the poly-
brominated complex was successfully converted into its
polyiodinated analogue by using the Klapars–Buchwald
G
methodology, which was applied, to the best of our knowl-
edge, for the first time to an organometallic substrate.
Under Sonogashira conditions, an excellent 85% yield per
coupling was achieved with the pentaiodinated complex.
An X-ray diffraction study showed that the two ligands
coordinated to ruthenium were strongly embedded, howev-
er, free rotation was evidenced both experimentally by
NMR analysis and theoretically by DFT. This is reminiscent
of macroscopic molecular turnstiles that undergo correlated
rotation motions.
Work is now underway to anchor analogous complexes
onto oxide surfaces for the observation of molecular mo-
tions on the unimolecular scale; however, the demonstration
of a controlled rotary movement requires further experi-
mental developments by scanning probe microscopy. More-
over, the lateral gearing effect may be exploited in nanome-
chanics to use the work produced during rotation of the
molecule.
Figure 5. a) DFT minimum, b) transition state and c) DFT minimum sim-
ilar to that in a) after 1/15th of a turn.
Chem. Eur. J. 2008, 14, 8147 – 8156
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8153

G. Rapenne et al.
(2 g, 2.1 mmol; 98%). 1H NMR (CDCl3): d=7.44–7.18 (m, 12H), 6.85–
6.70 ppm (m, 8H); 13C NMR (CDCl3): d=147.7, 140.9, 134.0, 132.5,
132.1, 131.8, 131.7, 131.5, 131.4, 131.1, 129.1, 128.0, 122.5, 122.24,
122.15 ppm; MS (DCI/NH3): m/z (%): 914.6 (100) [M+H]+; HRMS
(FAB): m/z calcd for C35H20Br6: 913.6665 [M]+; found: 913.6688; elemen-
tal analysis calcd (%) for C35H20Br6: C 45.70, H 2.19; found: C 45.81, H
2.22.
Experimental Section
Computational details: All calculations were performed with the Gaussi-
an03 suite of programs,[28] using the B3PW91[29] hybrid functionals. Rela-
tivistic effective core potentials developed by the Stuttgart group and
their associated basis sets were used for all atoms.[30] Geometry optimisa-
tions were achieved in the gas phase without symmetry constraints. Cal-
culations of vibrational frequencies were systematically done to charac-
terise the nature of stationary points. The path of the chemical reaction
was traced from the transition state to the products and reactants by
using the intrinsic reaction coordinate method.[31] Gibbs free energies
were calculated by means of the harmonic frequencies, that is, by a
straightforward application of the statistical thermodynamics equations
given in standard textbooks.[32]
Bromoidodicarbonyl
ACHTREUNG
A
N
ACHTREUNG
(256 mg, 0.4 mmol, 1 equiv) and 2 (1.1 g, 1.2 mmol, 3 equiv) were heated
under reflux for 2 h in freshly distilled toluene (20 mL). The solution
turned rapidly from yellow to dark green and then to cherry red. The
crude reaction mixture was evaporated under vacuum. A dichlorome-
thane solution of the crude product was passed over a plug of silica to
remove red polar side products. The product was adsorbed onto silica
and then purified by flash column chromatography (silica gel: cyclohex-
Synthesis: All commercially available chemicals were of reagent grade
and were used without further purification. Ethynylferrocene was pur-
ane/dichloromethane 40%) to give
3 as a yellow solid (1.006 g,
chased from Aldrich. Ruthenium carbonyl, [{Ru(p-cymene)Cl2}2] and
A
1
3
0.934 mmol, 78%). H NMR (CD2Cl2): d=7.29 (d, J=8.7 Hz, 10H; Hm),
6.88 ppm (d, 3J=8.7 Hz, 10H; Ho); 13C NMR (CDCl3): d=196.4, 134.5,
1,2,3,4,5-pentaphenylcyclopentadiene were purchased from Strem. Potas-
sium hydrotris(indazol-1-yl)borate,[19] [(ferrocenyl)ethynyl]zinc chloride[9a]
were prepared according to literature procedures. Toluene was dried
over CaH2 and THF over sodium with benzophenone. All reactions were
carried out using standard Schlenk techniques under an argon atmos-
phere. Flash column chromatography was carried out on silica gel 230–
400 mesh from SDS.
132.2, 128.6, 124.0, 106.0 ppm; IR: nC O =2003 (s) and 2048 cmÀ1 (s); MS
=
(DCI/NH3): m/z: 1096 [M+NH4]+.
(h6-Benzene)[h5-1,2,3,4,5-penta(4-bromophenyl)cyclopentadienyl]ruthe-
nium(II) hexafluorophosphate [Ru(h6-benzene)
N
N
(4): A solution 3 (410 mg, 0.4 mmol) and aluminium chloride (67 mg) in
freshly distilled benzene (15 mL) was purged with argon. The solution
was stirred under reflux for 6 d. Benzene was evaporated and the reac-
tion mixture was redissolved in dichloromethane (100 mL). A solution of
NH4PF6 (700 mg) in acetonitrile (100 mL) was added to this solution.
After 1 h stirring the solvents were removed under vacuum. The product
was redissolved in dichloromethane and salts were filtered. The solution
was evaporated under vacuum and redissolved in acetonitrile. Crystallisa-
tion of the compound was started by adding water and evaporating part
of the acetonitrile. Allowing to cool to 08C gave 4 as analytically pure
yellow crystals (248 mg, 0.239 mmol, 60%). 1H NMR (CDCl3): d=7.36
NMR spectra were recorded by using Bruker AM250 or Avance500
spectrometers and full assignments were made using COSY, ROESY,
HMBC and HMQC methods. Chemical shifts are defined with respect to
TMS=0 ppm for 1H, and 13C NMR spectra and were measured relative
to residual solvent peaks. The following abbreviations were used to de-
scribe the signals: s for singlet; d for doublet; t for triplet; q for quadru-
plet; m for multiplet. The numbering schemes are given in Scheme 1 (for
hydrotris(indazol-1-yl)borate and coordinated p-cymene) and Scheme 5
(for ferrocenes and pentaphenylcyclopentadienyl). UV/Vis-near infra-red
spectra were recorded by using a Shimadzu UV-3100 spectrometer. FAB
and DCI mass spectrometry was performed by using a Nermag R10–10.
Cyclic voltammetry was performed by using an AUTOLAB PGSTAT100
potentiostat using a Pt disc (1 mm diameter) as working electrode and a
Pt counter electrode. The reference electrode used was the saturated cal-
omel electrode (SCE).
3
3
(d, J=8.2 Hz, 10H; Hm), 6.76 (d, J=8.4 Hz, 10H; Ho), 6.47 ppm (s, 6H;
Ha); 13C NMR (CDCl3): d=132.9, 132.2, 127.3, 124.2, 100.2, 91.7 ppm;
MS (DCI/NH3): 1037 [M+NH4]+.
[h5-1,2,3,4,5-Penta-(4-bromophenyl)cyclopentadienyl][hydrotris(indazol-
1-yl)borato]ruthenium(II) [Ru
N
N
(h6-p-Cymene)[hydrotris(indazol-1-yl)borato]ruthenium(II) hexafluoro-
(107 mg, 0.1 mmol, 1 equiv) and potassium hydrotris(indazol-1-yl)borate
(80 mg, 0.2 mmol, 2 equiv) were heated under reflux for 24 h in freshly
distilled THF (4 mL). The crude reaction mixture was evaporated under
vacuum. The product was adsorbed onto silica and purified by column
chromatography (silica gel: cyclohexane/dichloromethane 0–20%) to
give compound 5, which was recrystallised in dichloromethane/methanol
to afford yellow crystals (39 mg, 0.030 mmol, 30%). 1H NMR (CD2Cl2):
d=8.04–7.98 (dd, 3J=8.57, 4J=0.84 Hz, 3H; He), 8.86 (d, 4J=0.84 Hz,
3H; Ha), 7.44–7.34 (m, 6H; Hb, Hc), 7.27–7.17 (m, 20H; Ho, Hm), 7.06–
6.98 ppm (ddd, 3J=7.10, 3J=6.90, 4J=0.84 Hz, 3H; Hd); 13C NMR
(CDCl3): d=143.6 (CM), 140.4, 135.3, 132.3, 130.8, 126.8, 123.1 (CN),
122.0, 120.7, 120.1, 111.6, 87.2 ppm; UV/Vis (CH2Cl2) lmax (e)=295
phosphate [Ru
U
A
0.32 mmol, 1 equiv) was stirred in degassed acetonitrile (40 mL) for
20 min and potassium hydrotris(indazol-1-yl)borate (260 mg, 0.64 mmol,
2 equiv) was added. The mixture was stirred at RT in the dark overnight.
Acetonitrile was then removed under reduced pressure and the reaction
mixture was redissolved in methanol. A solution of ammonium hexa-
fluorophosphate was then added (407 mg, 2.5 mmol, 8 equiv). The reac-
tion mixture was filtered trough a pad of neutral alumina. Compound 1
was obtained by recrystallisation from methanol/Et2O, affording the de-
sired product (130 mg, 0.17 mmol, 27%). 1H NMR ([D6]acetone): d=
9.11 (d, 4J=0.8 Hz, 3H; Ha), 7.82 (dd, 3J=8.7, 4J=0.9 Hz, 3H; Hb), 7.74
3
4
3
4
(dd, J=8.7, J=0.9 Hz, 3H; Hd), 7.41 (dd, J=7.25, J=6.8 Hz, 3H; He),
II
III
(300300), 311 (268700), 396 nm (34800); ERu
(V/SCE): +0.80 rev.;
:Ru
3
3
7.16 (dt, J=7.25, 4J=6.8 Hz, 3H; Hc), 6.61 (d, J=6.4 Hz, 2H; Hg), 6.38
(d, 3J=6.4 Hz, 2H; Hh), 3.32 (m, 1H; Hi), 2.62 (s, 6H; Hj), 1.37 ppm (d,
3J=6.9 Hz, 3H; Hf); 13C NMR ([D6]acetone): d=141.8 (CM), 138.8 (CA),
128.9 (CC), 124.4 (CN), 121.0 (CD), 119.3 (CE), 112.5 (CB), 105.9 (CK),
101.8 (CL), 84.0 (CH), 83.1 (CG), 31.5 (CI), 22.3 (CJ), 18.3 ppm (CF); MS
(MNBA-FAB): m/z (%): 599 (100) [MÀPF6]+; HRMS (FAB): m/z calcd
for C31H30BN6Ru: 599.1668 [M]+; found: 599.1686.
MS (DCI/NH3): m/z (%): 1305 (100) [M+H]+; HRMS LSI: m/z calcd for
C56H37BBr5N6Ru: 1300.8133 [M+H]+; found: 1300.8177 [M+H]+.
AHCTREUNG
AHCTREUNG
ACHTREUNG
(30 mg, 26 mmol, 0.5 equiv) in freshly distilled THF (10 mL) was de-
gassed. A solution of [(ferrocenyl)ethynyl]zinc chloride (1 mmol, 4 equiv
per bromide) was prepared as described in the literature[9a] was then
added. The mixture was heated under reflux for 24 h. Additional catalyst
(30 mg) and reactants (1 mmol of [(ferrocenyl)ethynyl]zinc chloride)
were added by using a syringe under argon and the mixture was kept
under reflux for 24 h. The crude reaction mixture was evaporated under
vacuum. The product was adsorbed onto silica and purified by flash
column chromatography (silica gel: cyclohexane/CH2Cl2 0–30%, Rf
1-Bromo-1,2,3,4,5-penta(4-bromophenyl)cyclopentadiene (2): Br2 (2 mL,
45 mmol, 20 equiv) was slowly added to 1,2,3,4,5-pentaphenylcyclopenta-
diene (1 g, 2.2 mmol, 1 equiv) in a two-necked flask connected to a KOH
solution to quench the acid vapors formed during the reaction. The solu-
tion was stirred for 2 h after the end of the bubbling. The reaction mix-
ture was then diluted with dichloromethane (50 mL) and washed with po-
tassium thiosulfate solution (1 m, 4”100 mL). After drying over MgSO4,
the product was purified by flash column chromatography (silica gel:
cyclohexane/dichloromethane 0–10%) to give 2 as a pale-yellow solid
8154
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Chem. Eur. J. 2008, 14, 8147 – 8156

Ruthenium(II) Complexes
FULL PAPER
(silica gel, cyclohexane/CH2Cl2 30%)=0.12) to give 6 as an orange solid
(33 mg, 0.017 mmol, 32%).
Acknowledgements
This work was supported by the CNRS, the University Paul Sabatier
(Toulouse) and the European Community. A.C. thanks the French Minis-
try of National Education and the Institut Universitaire de France for a
PhD Fellowship. One of us (R.P.) thanks the Centre Informatique Na-
tional de lꢁEnseignement SupØrieur (CINES) for allocation of computa-
tional resources. Dr Isabelle M. Dixon is warmly acknowledged for her
corrections and comments on this manuscript.
From the pentaiodide derivative (8) by means of a Sonogashira coupling:
In a Schlenk tube, 8 (24 mg, 0.016 mmol, 1 equiv), ethynylferrocene
(33 mg, 0.16 mmol, 10 equiv), diisopropylamine (2 mL) and freshly dis-
tilled THF (166 mL) were degassed under argon during 20 min. CuI
(1 mg, 5 mmol, 30 mol%) and [Pd(PPh3)4] (3.3 mg, 2.5 mmol, 15 mol%)
N
were added and the mixture was heated at 808C overnight. The same
amounts of additional CuI, ethynylferrocene and Pd0 were added and the
mixture was heated at 808C for another 24 h. Solvents were removed
under reduced pressure and the crude material was subjected to column
chromatography (silica gel, cyclohexane/CH2Cl2 0–30%) to give 6 as an
orange solid (7.0 mg, 44%).
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3
1H NMR (250 MHz, CDCl3): d=8.0 (d, J=8.4 Hz, 3H; He), 7.94 (s, 3H;
Ha), 7.5–7.3 (d, 16H; Hm, Hb, Hc), 7.20–7.10 (d, 3J=8.0 Hz, 10H; Ho),
7.02 (t, 3J=7.5 Hz, 3H; Hd), 4.43 (t, 3J=2 Hz, 10H; Hr), 4.21 (s, 25H;
Hn), 4.19 ppm (t, 3J=2 Hz, 10H; Hs); 13C NMR (66 MHz, CDCl3): d=
143.4 (CM), 140.2, 133.4, 133.2, 130.4, 126.4, 123.0 (CN), 122.7, 122.4,
120.0, 111.7, 89.3, 87.5, 85.5, 71.4, 70.0, 68.8, 65.0 ppm; UV/Vis (CH2Cl2):
lmax (e)=264 (225000), 306 (169200), 359 (58000), 436 nm (10400);
II III
:Fe
II
III
CV(CH2Cl2, nBu4NPF6,), EFe
(V/SCE): +0.52 rev, (5 e); ERu
:Ru
[4] a) L. Grill, K. H. Rieder, F. Moresco, G. Rapenne, S. Stojkovic, X.
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Mal, Chem. Commun. 2008, 960.
(V/SCE): +0.82 rev (1 e); MS (MALDI-TOF): m/z (%): calcd for
C
116H81BN6Fe5Ru: 1950.2463 [M]+; found: 1950.3480 [M]+ (100); HRMS
LSI calcd for C116H82BN6Fe5Ru 1951.2599 [M+H]+; found: 1951.2631
[5] a) Y. Shirai, Y. Zhao, L. Chen, J. M. Tour, Org. Lett. 2004, 6, 2129;
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[M+H]+.
Dicarbonyliodido[h5-1,2,3,4,5-penta-(4-iodophenyl)cyclopentadienyl]ru-
thenium(II) [Ru
N
N
with CuI (95 mg, 0.5 mmol, 2.5 equiv), 3 (200 mg, 0.2 mmol, 1 equiv) and
NaI (600 mg, 4.0 mmol, 20 equiv). Under an argon atmosphere, racemic
trans-N,N’-dimethyl-1,2-cyclohexanediamine (15 mg, 0.1 mmol, 0.5 equiv)
and dioxane (3.0 mL) were added. The Schlenk tube was sealed with a
Teflon valve and the reaction mixture was stirred at 1108C for 24 h. The
solvent was removed and the crude material was purified by column
chromatography (silica gel: cyclohexane/dichloromethane (0–10%)) to
give 124 mg (0.09 mmol, 45%) of 7 as an orange-brown solid. MS (DCI/
NH3): m/z: 1339 [MÀ2CO+N2H7]+; 1H NMR (CDCl3): d=7.49
(AA’BB’ pattern, 3J=8.5 Hz, 10H; Hm), 6.71 ppm (AA’BB’ pattern, 3J=
8.5 Hz, 10H; Ho); 13C NMR (CD2Cl2): d=196.1, 137.7, 134.3, 131.8,
128.8, 128.3, 123.6, 95.5 ppm; IR: nC O =2000 (s), 2040 cmÀ1 (s).
=
[h5-1,2,3,4,5-Penta-(4-iodophenyl)cyclopentadienyl][hydrotris(indazol-1-
yl)borato]ruthenium(II) [Ru
N
N
By halogen exchange (not isolated): A Schlenk tube was charged with
CuI (18 mg, 0.075 mmol, 2.5 equiv), 5 (40 mg, 0.03 mmol, 1 equiv) and
NaI (90 mg, 0.6 mmol, 20 equiv). Under an argon atmosphere, racemic
trans-N,N’-dimethyl-1,2-cyclohexanediamine (4.8 mL, 0.03 mmol, 1 equiv)
and dioxane (1.0 mL) were added under argon. The Schlenk tube was
sealed with a Teflon valve and the reaction mixture was stirred at 1108C
for 24 h. The solvent was removed and the crude material was purified
by column chromatography (silica gel: cyclohexane/dichloromethane (0–
10%)) to give partially iodinated h5-1,2,3,4,5-penta-(4-halogenophenyl)-
cyclopentadienyl complex.
By reaction of dicarbonyliodido
[h5-(1,2,3,4,5-penta-(4-iodophenyl)cyclo-
A
pentadienyl)] with Tp4Bo: A mixture of 7 (144 mg; 0.12 mmol; 1 equiv)
and potassium hydrotris(indazol-1-yl)borate (100 mg, 0.24 mmol, 2 equiv)
was heated under reflux for 24 h in freshly distilled THF (8 mL). The
crude reaction mixture was evaporated under vacuum. The product was
adsorbed onto silica and then purified by flash column chromatography
(silica gel: cyclohexane/dichloromethane 0–20%) to give 24 mg
(0.016 mmol, 14%) of 8. 1H NMR (CDCl3): d=7.97 (d, 3J=8.5 Hz, 3H;
He), 7.78 (s, 3H; Ha), 7.42–7.30 (m, 16H; Hm, Hb, Hc), 7.08–6.98 ppm (m,
13H; Ho, Hd); 13C NMR (CDCl3): d=142.8 (CM), 139.4, 134.3, 132.1,
130.4, 126.2, 122.5 (CN), 121.2, 120.1, 119.9, 111.1, 86.4 ppm; MS (DCI/
NH3): m/z (%): 1541 (100) [M+H]+; HRMS LSI: m/z calcd for
C56H37BI5N6Ru: 1540.7440 [M+H]+; found: 1540.7497 [M+H]+.
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orthorhombic, space group Pbca
40.875(5) Š, a=90 b=90 g=908, V=12333(5) Š3, Z=8, 1calcd
1.573 gcmÀ3, m(MoKa)=3.48 mmÀ1. Data were collected on a Nonius
, a=14.271(2) b=21.144(7) c=
=
ACHTREUNG
Kappa CCD diffractometer using MoKa graphite monochromated
radiation (l=0.71073 Š) at 298 K. 2938 reflections having I>3s(I)
were used for structure determination (0.008<q<28.008). For all
computations the Bruker maXus software package was used. Final
results: R(F)=0.088, Rw(F)=0.139, GoF=4.39.
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[27] The year 2008 celebrates not only the 40th anniversary of the events
of May ꢁ68 in France, but also the 40th anniversary of the first “Fos-
bury” flop, from the name of the high-jump athlete, Dick Fosbury,
who initiated this jumping style at the Olympic Games in Mexico.
Received: April 10, 2008
Published online: July 24, 2008
8156
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 8147 – 8156