Synthesis of new tripodal tri-functionalized hydrotris(indazol-1-yl)borate ligands and x-ray structures of their cyclopentadieneruthenium complexes

Article abstract of DOI:10.1002/ejic.200500851

Two new tripodal ligands designed to anchor complexes onto surfaces have been synthesized. They integrate ester or thioether functions at the 6-position of the indazoles. Potassium hydrotris[6-(ethoxycarbonyl)indazolyl]borate and potassium hydrotris{6-[(ethylsulfanyl)methyl]indazolyl}borate exhibit three pendant groups oriented to anchor complexes onto an oxide and a metallic surface, respectively. Their complexation with [RuCp(CH₃CN) ₃]PF₆ yielded two piano-stool-shaped complexes that were characterized by X-ray diffraction. Comparison with the synthesized unfunctionalized analog showed that the three 6-substituted functions do not interfere with the coordination site and are particularly well oriented for surface deposition. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200500851

FULL PAPER
DOI: 10.1002/ejic.200500851
Synthesis of New Tripodal Tri-Functionalized Hydrotris(indazol-1-yl)borate
Ligands and X-ray Structures of Their Cyclopentadieneruthenium Complexes
Alexandre Carella,[a] Guillaume Vives,[a] Tara Cox,[a] Joël Jaud,[a] Gwénaël Rapenne,*[a] and
Jean-Pierre Launay*[a]
Keywords: Tripodal ligands / Ligand design / Ruthenium / Indazole / Stacking interactions
Two new tripodal ligands designed to anchor complexes onto
surfaces have been synthesized. They integrate ester or thio-
ether functions at the 6-position of the indazoles. Potassium
hydrotris[6-(ethoxycarbonyl)indazolyl]borate and potassium
shaped complexes that were characterized by X-ray diffrac-
tion. Comparison with the synthesized unfunctionalized ana-
log showed that the three 6-substituted functions do not in-
terfere with the coordination site and are particularly well
oriented for surface deposition.
hydrotris{6-[(ethylsulfanyl)methyl]indazolyl}borate
exhibit
three pendant groups oriented to anchor complexes onto an
oxide and a metallic surface, respectively. Their complex-
ation with [RuCp(CH3CN)3]PF6 yielded two piano-stool-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
ligands, have been used increasingly in bioinorganic, orga-
nometallic, and coordination chemistry.[9] This last aspect
has been extensively developed with a particular interest in
the modification of the functional groups connected to the
pyrazolyl moiety in order to control or modify the steric
and electronic environment surrounding the metal center.
However its analogue, hydrotris(indazolyl)borate (Tp4Bo),
has not stimulated intense studies since its synthesis in
1995.[10] Nevertheless tris(indazolyl)borate bears two ad-
vantages over trispyrazolylborate. First it is larger, but the
increase in size is not accompanied by a decrease in the
rigidity of the molecule. Furthermore, by withdrawing the
metal away from the surface, it allows interferences caused
by metal–surface interactions to be minimized, which is
particularly important for near-field microscopy experi-
ments. The rigidity of its indazolyl fragments, conjugated
with its tripodal shape, should make it a good candidate for
surface deposition of metal complexes onto surfaces.
Here we report the synthesis of two new scorpionate li-
gands incorporating functional groups on the indazole, de-
signed to interact with metallic or oxide surfaces. The func-
tionalized borate ligands were designed to have three func-
tional groups pointing in the opposite direction of the coor-
dination site in order not to interfere sterically with it. Each
of the three legs of the tripodal unit bears a functional
group connected at the 6-position of indazole, which should
be the optimal orientation for anchoring on a surface. The
ester function has been found to strongly interact with ox-
ide surfaces,[11] spontaneous deprotection yielding carbox-
ylic groups that covalently bind the metallic oxide. In order
to interact with a metallic surface, the thioether function
was chosen to alleviate the problem encountered with oxi-
datively unstable thiols. Acetyl-protected thiols were also
Introduction
In the last decade, the continuous improvement of near-
field microscopy techniques such as scanning tunneling mi-
croscopy (STM) and atomic force microscopy (AFM) has
led to the imaging and the study of physicochemical proper-
ties of various molecules.[1] These techniques allow the visu-
alization and manipulation of only one molecule and there-
fore the electrical[2] and mechanical properties[3] of a single
molecule deposited on a surface can be investigated. As sin-
gle-molecule experiments require the control of the shape
of the molecule deposited, the design and the synthesis of
rigid ligands able to be covalently attached on surfaces with
a minimum number of degrees of freedom is an active field
of research.[4] In particular, the movement of a molecule
can be efficiently restricted by attaching the molecule to a
surface with a tripod,[5] which prevents translation. Some
rigid organic molecules with three points of attachment
have already been used in AFM or STM studies.[6] How-
ever, the absence of coordination sites restricts their field
of application. Therefore, a structurally rigid bifunctional
molecule combining coordinating sites and anchoring
groups is of special interest. It would allow the covalent
attachment of coordination complexes on a surface, for in-
stance giving rise to surface-mounted molecular gears or
motors.[6,7]
Since their discovery by Trofimenko in the late 1960s,[8]
the trispyrazolylborate ligands, also known as scorpionate
[a] NanoSciences Group, CEMES-CNRS,
29 rue Jeanne Marvig, BP 94347,
31055 Toulouse Cedex 4, France
Fax: +33-5-62257999
E-mail: rapenne@cemes.fr
980
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Synthesis of New Tripodal Hydrotris(indazol-1-yl)borate Ligands
FULL PAPER
Figure 1. Structure of the triester-functionalized, trithioether-functionalized, and unfunctionalized ruthenium() complexes.
good candidates because of their spontaneous deprotection
on a gold surface,[12] but preliminary experiments showed
their incompatibility with the last step of the synthesis of
the borate ligand, which requires sodium borohydride,
yielding the reduction of the acetyl-protected thiol. The thio-
ether group is stable in a wider range of conditions and is
also known to interact strongly with a gold surface.[13] The
synthesis of the hydrotris[6-(ethoxycarbonyl)indazol-1-yl]-
borate ligand incorporating three ester functions and the
reaction with potassium borohydride to yield the potassium
hydrotris(indazol-1-yl)borate ligand. Purification methods
used in classical organic chemistry, such as column
chromatography, are not suited to the purification of salts.
Trituration with an apolar solvent can selectively dissolve
the indazole precursor, and an additional sublimation step
provides pure material. Potassium hydrotris[6-(ethoxycar-
bonyl)indazol-1-yl]borate (KTp4Bo,6-COOEt) was synthesized
in three steps starting with 3-amino-4-methylbenzoic acid
(1) (Scheme 1). The esterification of 1 in ethanol mediated
by thionyl chloride[14] afforded ethyl 3-amino-4-methylben-
zoate (2) quantitatively. The conversion of 2 into ethyl ind-
azole-6-carboxylate (3) was performed using the Jacobson
procedure[15] by reaction of 2 with potassium acetate, acetic
anhydride, and isopentyl nitrite in refluxing toluene to give
ethyl 1-acetylindazole-6-carboxylate, which was deprotected
with HCl, affording 3 in 64% yield.
The formation of the indazolyl ring was demonstrated by
1H NMR where the NH proton resonates with a character-
istic signal at δ = 11 ppm. Reaction of 3 at 180 °C for 5 h
with potassium borohydride gave the triester-functionalized
KTp4Bo,6-COOEt in 68% yield after purification by repetitive
trituration with hot toluene and sublimation of the unre-
acted ethyl indazole-6-carboxylate. It is noteworthy that by
conducting the reaction at 150 °C instead of 180 °C, the
bis(indazolyl)borate was mainly obtained. As known from
hydrotris{6-[(ethylsulfanyl)methyl]indazol-1-yl}borate
li-
gand with three pendant thioether arms is described, fol-
lowed by the preparation and X-ray structures of the corre-
sponding η5-cyclopentadienylruthenium complexes with
both functionalized tripodal ligands and also with the un-
functionalized ligand. Following Trofimenko’s scorpionate
nomenclature,[9] the 6-functionalized ligands can be noted
as KTp4Bo,6-COOEt for the ester-functionalized and
KTp4Bo,6-CH2SEt for the thioether-functionalized ligand,
and similarly the ruthenium complexes can be noted as
RuCpTp4Bo,6-COOEt, RuCpTp4Bo,6-CH2SEt, and RuCpTp4Bo
(Figure 1).
Results and Discussion
Ligand Syntheses
The strategy we followed consisted in the synthesis of a the literature,[16] the signal of the BH proton is very broad
functionalized indazole in a first step, and its subsequent and difficult to find but very informative to differentiate the
Scheme 1. Synthesis of potassium hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate.
Eur. J. Inorg. Chem. 2006, 980–987
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FULL PAPER
Scheme 2. Synthesis of potassium hydrotris{6-[(ethylsulfanyl)methyl]indazol-1-yl}borate.
bis (signal near 3.5 ppm) and tris (δ = 5 ppm) indazolylbor- the unfunctionalized ligand. For solubility reasons, the syn-
ates.
thesis of RuCpTp4Bo,6-COOEt required the use of anhydrous
Concerning the regiochemistry of the reaction, Trofi- DMF as cosolvent. The three complexes were fully charac-
menko has shown on the hydrotris(indazol-1-yl)borate li- terized.
gand[10] that the interplay of steric and electronic factors
The cyclic voltammogram of the unfunctionalized com-
tilts in favor of the latter, giving a product that is sterically plex exhibits a reversible metal-centered oxidation at
hindered around the boron atom but not on the coordina- 0.49 V/SCE, that is 100 mV higher than the pyrazolyl ana-
tion side. Similarly, we obtained exclusively the product re- log in the same conditions (Table 1). This shows that ruthe-
sulting from the fusion of the benzo ring at the 4–5-position nium() is more stabilized in RuCpTp4Bo than in its pyrazol-
(giving the Tp4Bo product) in which the boron atom is yl analog synthesized by Mann et al.,[17] which can be ex-
bound to the more hindered nitrogen atom and no trace plained by the more pronounced π-acceptor character of
of the 3–4 fusion product (Tp3Bo). This regiospecificity is the hydrotris(indazolyl)borate compared to its pyrazolyl an-
maintained with ester groups at the 6-position of the inda- alog. In the ruthenium complex RuCpTp4Bo,6-COOEt, which
zole, as confirmed by the X-ray structure of the ruthenium incorporates the triester-functionalized ligand, oxidation
complex.
occurs at a higher potential: 0.63 V/SCE, the ethoxycar-
The synthesis of 6-[(ethylsulfanyl)methyl]indazole (5) was bonyl electron-withdrawing groups stabilizing the rutheni-
achieved in two steps from 3 (Scheme 2). Reduction of the um() state further. The ester substituents decrease the σ-
ethyl ester function using LiAlH4 gave 6-(hydroxymethyl)- donor character and increase the π-acceptor character of
indazole (4) with a very good yield. Mesylation of the the scorpionate ligand. The combination of this low σ-do-
alcohol followed by reaction with thioethanol allowed the nor character and solubility problems could explain the
thioether-substituted indazole 5 to be obtained in a one-pot moderate yield of the coordination step. The coordinating
procedure. The same procedure used to obtain nitrogen of the ester-functionalized scorpionate ligand be-
KTp4Bo,6-COOEt was applied to 5, yielding potas- ing less donor than its unfunctionalized analog, is thus less
sium hydrotris{6-[(ethylsulfanyl)methyl]indazol-1-yl}borate efficient in the displacement of the acetonitrile ligands of
(KTp4Bo,6-CH2SEt).
the ruthenium precursor. In the ruthenium complex
RuCpTp4Bo,6-CH2SEt, which incorporates the thioether func-
tions, oxidation occurs at a slightly lower potential of
0.48 V/SCE, the slightly electron-donating (ethylsulfanyl)-
methyl groups destabilizing the ruthenium() state.
Complex Formation and Characterization
The coordination chemistry of the two ligands was con-
sistent with the absence of steric hindrance on the metal
coordination
face.
Complexation
of
KTp4Bo
,
KTp4Bo,6-COOEt, and KTp4Bo,6-CH2SEt with [RuCp(CH3CN)3]-
PF6 was performed by heating the scorpionate ligand with
1 equiv. of ruthenium complex in anhydrous and degassed
acetonitrile. The η5-cyclopentadienylruthenium() com-
plexes of each tripodal ligand were obtained; η5-
cyclopentadienyl(hydrotris{6-[(ethylsulfanyl)methyl]indazol-
1-yl}borato)ruthenium() (RuCpTp4Bo,6-CH2SEt) and η5-
cyclopentadienyl(hydrotris[6-(ethoxycarbonyl)indazol-1-yl]-
borato)ruthenium() (RuCpTp4Bo,6-COOEt) were obtained
Table 1. Cyclic voltammetry data.[a]
Compound
E1/2(ox) RuII–RuIII (V/SCE)[b]
RuCpTp4Bo,6-COOEt
0.63
0.49
RuCpTp4Bo
RuCpTp4Bo,6-CH2SEt
RuCpTp
0.48
0.39[c]
[a] Cyclic voltammograms were carried out at a scan rate of
100 mVs–1 in acetonitrile containing 0.1  Bu4NPF6 as supporting
electrolyte. Potentials were measured vs SCE using a Pt working
with a lower yield compared to the complex formed with electrode. [b] All couples are reversible. [c] Obtained from ref.[17]
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Synthesis of New Tripodal Hydrotris(indazol-1-yl)borate Ligands
1
FULL PAPER
Variable temperature H NMR experiments have shown Table 2. Selected bond lengths [Å] and angles [°] in the ruthenium
complexes.[a]
that the rotation of the Cp ligand in the complexes is fast
RuCpTp4Bo
RuCpTp4Bo,6-COOEt RuCpTp4Bo,6-CH2SEt
compared to the NMR timescale down to at least –90 °C
in deuterated dichloromethane, indicating that the coordi-
nation site is not sterically affected by the ethoxycarbonyl
or (ethylsulfanyl)methyl substituents.
Ru–N(1)
Ru–N(3)
Ru–N(5)
Ru–C(22)
Ru–C(23)
Ru–C(24)
Ru–C(25)
Ru–C(26)
N(1)–Ru–N(3)
N(3)–Ru–N(5)
N(5)–Ru–N(1)
N(2)–B–N(4)
N(4)–B–N(6)
N(6)–B–N(2)
2.141(8)
2.108(7)
2.099(7)
2.141(10)
2.156(11)
2.166(11)
2.145(11)
2.131(11)
84.4(3)
84.2(3)
85.6(3)
108.3(8)
110.2(7)
106.8(7)
2.113(4)
2.129(4)
2.103(4)
2.166(5)
2.152(5)
2.148(5)
2.162(5)
2.161(5)
83.46(14)
84.97(14)
86.46(14)
107.3(4)
108.4(4)
108.9(4)
2.128(5)
2.126(5)
2.120(5)
2.140(6)
2.160(6)
2.159(5)
2.154(5)
2.147(6)
83.55(18)
85.87(17)
84.01(17)
107.5(4)
108.3(4)
108.5(4)
Crystal Structures of the Complexes
Crystals suitable for X-ray diffraction were grown by the
slow diffusion of methanol over a dichloromethane solution
of the complex. The ORTEP representations with atom
numbering are shown in Figure 2, while selected bond
lengths and angles are listed in Table 2.
RuCpTp4Bo,6-COOEt and RuCpTp4Bo crystallized in the
Pccn space group while RuCpTp4Bo,6-CH2SEt crystallized in
[a] Numbers in parentheses are estimated standard deviations.
¯
the P1 group. The triester-functionalized complex cocrys-
tallized with molecules of methanol (0.5 equiv. per ruthe-
nium complex), which are located on a symmetry axis and tion of the coordination site, which is thus free of any steric
1
1
are highly disordered. In line with the H NMR spectro- hindrance as seen in solution by a variable temperature H
scopic data, the three complexes have a piano stool shape NMR experiment. The lack of interference between the co-
where the scorpionate ligand binds the ruthenium center ordination site and the attaching groups suggests that this
in a facial tripodal mode (i.e. κ3-N,NЈ,NЈЈ), as shown by molecule can be expected to be truly bifunctional, acting
Trofimenko for scorpionate complexes. The crystal struc- both as ligand and anchor to fix metal complexes onto a
ture of complexes with the triester- and (ethylsulfanyl)- surface.
methyl-functionalized ligands confirmed the regiochemistry
It must be noted that these complexes combine a C5-
of the scorpionate formation, which is the expected Tp4Bo symmetry cyclopentadienyl ligand and a C3-symmetry tri-
isomer. Moreover, the functional groups at the 6-position podal ligand, and as a result, have a low symmetry. In order
of indazole are well oriented, pointing in the opposite direc- to facilitate the discussion and by analogy with ethane, two
Figure 2. Thermal ellipsoid diagram of (RuCpTp4Bo,6-COOEt) (left), (RuCpTp4Bo) (center), and (RuCpTp4Bo,6-CH2SEt) (right), side view
(top) and top view (bottom). The ellipsoids are drawn at the 50% probability level and the molecules of cocrystallizing solvent (MeOH)
have been removed for clarity.
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A. Carella, G. Vives, T. Cox, J. Jaud, G. Rapenne, J.-P. Launay
FULL PAPER
significant conformations can be defined (Figure 3). The
Moreover, average Ru–C distances of 2.15 Å (for cyclo-
first one can be considered as an eclipsed conformation in pentadienyl) and Ru–N bond lengths of 2.11 Å (for trisind-
which one of the dihedral angles between a CH bond of the azolylborate) are found in the three complexes, showing
cyclopentadienyl ligand and one indazole of the scorpionate that the coordination of the tripodal ligand is not influ-
ligand is 0°. In the second one, the staggered conformation, enced by the presence of the functional groups at the 6-
two of these dihedral angles are equal to 12°. Because of position of the indazole rings. The moderate reactivity of
the symmetry of each ligand, a rotation of 24° is invariant. the triester-functionalized ligand towards complexation
A 12° rotation of one ligand with respect to the other allows with [RuCp(CH3CN)3]PF6 is thus justified purely by elec-
the interconversion between staggered and eclipsed confor- tronic considerations, while steric hindrance due to the ester
mations.
groups can be ruled out.
Conclusions
In summary, we have described the preparation and co-
ordination of two new tripodal ligands that bear functional
groups suitable for surface deposition. The orientation of
the three anchoring groups, as shown by the X-ray struc-
tures, seems to be ideal for surface deposition of organome-
tallic complexes. Work is underway to anchor these com-
plexes on surfaces and integrate the triester-functionalized
ligand into molecular machines such as a molecular rotary
motor[7] designed to be studied as a single molecule de-
posited on an oxide surface.
Figure 3. Eclipsed (left) and staggered (right) conformations of a
complex containing both C3- and C5-symmetry ligands. Intercon-
version occurs upon a 12° rotation. For symmetry reasons, the stag-
gered conformation appears every 24°.
On purely steric grounds, the staggered conformer is ex-
pected to be the most stable, as obtained in the case of the
pyrazolyl analog RuCpTp.[15] On the contrary, RuCpTp4Bo
adopts an almost eclipsed conformation in the solid state,
with a dihedral angle between the C(24)–H(24) bond and
the plane of the N(1)-containing indazole equal to 0.3°
(Figure 2, bottom view). An explanation for a favored
eclipsed conformation must be found in the crystal packing
and in the intermolecular forces involved in the solid state.
A careful examination of the crystal packing of the unfunc-
tionalized and both functionalized complexes showed π-
stacking interactions between the two indazoles of neighb-
oring complexes. As shown for the unfunctionalized com-
plex in Figure 4, the two indazoles face each other in a
head-to-tail mode, the electron-rich part of one indazole
being exactly above the electron-poor part of the other in-
dazole, which provides further stabilization by donor–ac-
ceptor interactions. The distance between the planes of two
consecutive indazoles is ideal for stacking: 3.62 Å for the
triester complex, 3.59 Å for the tris (ethylsulfanyl)methyl
complex, and 3.56 Å for the unfunctionalized complex.
Experimental Section
All commercially available chemicals were of reagent grade and
were used without further purification. [RuCp(CH3CN)3]PF6 was
purchased from Strem. Potassium hydrotris(indazol-1-yl)borate
(KTp4Bo) was prepared according to a literature procedure.[10]
NMR spectra were recorded with Bruker AM 250 or Avance 500
spectrometers and full assignments were made using COSY,
ROESY, HMBC, and HMQC methods when necessary. The num-
bering scheme for the indazol derivatives is given in molecule 3 (see
Scheme 1 and Scheme 2). Chemical shifts are defined with respect
to TMS = 0 ppm for 1H and 13C NMR spectra and were measured
relative to residual solvent peaks. UV/Vis spectra were recorded
with a Shimadzu UV-3100 spectrometer. FAB and DCI mass spec-
trometry was performed using a Nermag R10–10. The melting
points were measured on a Kofler Reichert apparatus and are not
corrected.
Ethyl 3-Amino-4-methylbenzoate (2): 3-Amino-4-methylbenzoic
acid (1) (2.00 g, 13.3 mmol, 1 equiv.) was dissolved in absolute eth-
Figure 4. Stabilization in the crystal structure of RuCpTp4Bo by π-stacking interactions between neighboring indazolyl pairs. Zooming
in shows the donor–acceptor interactions between two indazolyl groups positioned in a head-to-tail arrangement with an interplane
distance of 3.56 Å.
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Synthesis of New Tripodal Hydrotris(indazol-1-yl)borate Ligands
FULL PAPER
1.34 (t, J = 7 Hz, 9 H, CH2CH3) ppm. 13C NMR (63 MHz, [D6]-
DMSO): δ = 166.3 (CO), 144.3, 133.0 (Ca), 126.3, 123.2, 120.6 (Cc),
120.3 (Cb), 112.7 (Cd), 61.0 (CH2), 14.3 (CH3).
3
anol (50 mL). Thionyl chloride (2 mL, 27.4 mmol, 2 equiv.) was
added dropwise and the reaction mixture was heated at reflux over-
night, during which the color of the solution turned from purple
to pink. Ethanol was removed under reduced pressure, and the re-
sidual oil was dissolved in ethyl acetate (50 mL) and washed with
a saturated sodium carbonate solution (3×20 mL). The combined
aqueous phases were extracted with ethyl acetate (20 mL). Then the
combined organic phases were dried with MgSO4 and the solvent
removed under reduced pressure to afford ethyl 3-amino-4-methyl-
benzoate (2) (2.33 g, 13.0 mmol, 98%) as a pink oil which was used
without further purification. DCI-MS (NH3): m/z (%) = 180 [M +
H]+, 197 [M + NH4]+. 1H NMR (250 MHz, CDCl3): δ = 7.26–7.30
(m, 2 H, Hc–d), 6.92 (d, 3J = 7.8 Hz, 1 H, Hb), 4.31 (q, 3J = 6.9 Hz,
2 H, CH2CH3), 3.91 (broad s, 2 H, NH2), 2.00 (s, 3 H, Me), 1.21
η5-Cyclopentadienyl(hydrotris[6-(ethoxycarbonyl)indazol-1-yl]bor-
ato)ruthenium(II) (RuCpTp4Bo,6-COOEt): Potassium hydrotris[6-(eth-
oxycarbonyl)indazol-1-yl]borate (KTp4Bo,6-COOEt) (62 mg,
0.1 mmol, 1 equiv.) was dissolved in dry DMF (2 mL), dry acetoni-
trile was added (20 mL), and the mixture was purged with argon.
[RuCp(CH3CN)3]PF6 (43 mg, 0.1 mmol, 1 equiv.) was added to this
solution, which was then refluxed overnight. Evaporation of the
solvent followed by a purification by column chromatography
(SiO2: cyclohexane/ethanol 0–20%) afforded η5-cyclopentadienyl-
[hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borato]ruthenium()
(RuCpTp4Bo,6-COOEt) (39 mg, 0.052 mmol, 52%) as a yellow solid.
DCI-MS (NH3): 747 [M + H]+, 764 [M + NH4]+. High resolution
LSI calculated [M + H]+: 747.1676 (C35H34BN6O6Ru); found:
747.1700 (100% [M + H]+). M.p. 212 °C dec. 1H NMR (250 MHz,
3
(t, J = 6.9 Hz, 3 H, CH2CH3) ppm.
Ethyl 1H-Indazole-6-carboxylate (3): In a three-necked round-bot-
tomed flask, ethyl 3-amino-4-methylbenzoate (2) (2.30 g,
12.8 mmol, 1 equiv.), potassium acetate (1.3 g, 13.2 mmol,
1.1 equiv.), and acetic anhydride (4.4 mL, 47 mmol, 3.6 equiv.) were
suspended in toluene (50 mL). Isopentyl nitrite (3.6 mL,
24.6 mmol, 2.1 equiv.) was added dropwise to this suspension over
a 15-min period. The gelatinous mixture was heated at reflux over-
night giving an orange solution, which was evaporated to dryness.
HCl (5 , 10 mL) and concentrated HCl (5 mL) were added and
the red solution was heated at 50 °C for 1 h followed by 10 min at
60 °C. After cooling down, the acid layer was extracted twice with
toluene (20 mL) to remove neutral compounds. The red combined
organic phases were washed three times with concentrated HCl.
The acid phase was then carefully neutralized with ammonia, caus-
ing precipitation of the compound. After filtration, the product
was dissolved in dichloromethane then dried with MgSO4 and the
solvent removed under reduced pressure to afford 3 (1.56 g,
8.2 mmol, 64%) as a brown solid. The product can be sublimed
(0.1 Torr, 160 °C) or used without further purification. DCI-MS
(NH3): m/z (%) = 191 [M + H]+. High resolution LSI calculated
[M + H]+: 191.0821 (C10H11N2O2); found: 191.0827 (100% [M +
H]+). M.p. 125 °C. 1H NMR (250 MHz, CDCl3): δ = 11.15 (s, 1 H,
NH), 8.27 (d, 4J = 1 Hz, 1 H, Ha), 8.14 (s, 1 H, Hd), 7.88–7.77 (m,
4
4
CD2Cl2): δ = 8.66 (d, J = 0.9 Hz, 3 H, Ha), 8.62 (d, J = 1.2 Hz,
3 H, Hd), 7.69 (dd, 3J = 8.5 Hz, J = 1.2 Hz, 3 H, Hc), 7.62 (dd, 3J
4
= 8.5 Hz, J = 0.9 Hz, 3 H, Hb), 4.63 (s, 5 H, Cp), 4.42 (q, 3J =
4
7 Hz, 6 H, CH2CH3), 1.43 (t, 3J = 7.2 Hz, 9 H, CH2CH3) ppm.
13C NMR (63 MHz, CD2Cl2): δ = 167.6 (CO), 143.1, 140.2 (Ca),
129.2, 126.8, 122.0 (Cc), 119.7 (Cb), 114.6 (Cd), 72.8 (Cp), 62.0
(CH2), 15.0 (CH3) ppm. ERuII:RuIII (V/SCE): +0.63 rev (sweep rate:
100 mV s–1). UV/Vis (CH2Cl2): λmax (ε in L mol–1 cm–1) = 222
(60300), 256 (14000), 334 (12800), 418 nm (6900).
η5-Cyclopentadienyl[hydrotris(indazol-1-yl)borato]ruthenium(II
)
(RuCpTp4Bo): A solution of potassium hydrotris(indazol-1-yl)bo-
rate (KTp4Bo) (81 mg, 0.2 mmol, 1 equiv.) in acetonitrile (20 mL)
was purged with argon and [RuCp(CH3CN)3]PF6 (87 mg,
0.2 mmol, 1 equiv.) was added. The solution was refluxed for 1.5 h.
The solution, initially yellow, turned to orange-brown. Upon cool-
ing to room temperature, an orange precipitate appeared.
Recrystallization from chloroform/methanol gave pure RuCpTp4Bo
(70 mg, 0.132 mmol, 65%) as an orange microcrystalline product.
DCI-MS (NH3): m/z (%) = 548 [M + NH4]+, 531 [M + H]+. High
resolution LSI calculated [M + H]+: 531.1042 (C26H22BN6Ru);
found: 531.1061 (100% [M + H]+). M.p. 222 °C dec. 1H NMR
3
3
2 H, Hb–c), 4.42 (q, 2 H, J = 7.0 Hz, CH2CH3), 1.44 (t, 3 H, J =
7.2 Hz, CH2CH3) ppm. 13C NMR (63 MHz, CDCl3): δ = 166.8
(CO), 139.5, 135.0 (Ca), 129.0, 125.7, 121.6 (Cc), 120.7 (Cb), 112.1
(Cd), 61.3 (CH2), 14.4 (CH3) ppm. C10H10N2O2: calcd. C 63.2, H
5.30, N 14.7; found: C 62.8, H 5.11, N 14.5.
3
(250 MHz, CDCl3): δ = 8.61 (s, 3 H, Ha), 7.90 (d, J = 8.75 Hz, 3
3
3
H, Hb), 7.6 (d, J = 7.25 Hz, 3 H, Hd), 7.32 (t, J = 7.25 Hz, 3 H,
Hc), 7.05 (t, 3J = 7.25 Hz, 3 H, H6), 4.56 (s, 5 H, Cp) ppm. 13C
NMR (63 MHz, CDCl3): δ = 138.9 (Ca), 125.9, 123.7, 120.5 (Cc),
119.2 (Cb), 111.5 (Cd), 70.7 (Cp) ppm. UV/Vis (CH2Cl2): λmax (ε in
Lmol–1 cm–1) = 231 (21400), 298 (15000), 307 (12200), 325 (9700),
388 nm (4600). CV (CH3CN, Bu4NPF6) ERuII:RuIII (V/SCE): +0.49
rev (sweep rate: 100 mVs–1).
Potassium
Hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate
(KTp4Bo,6-COOEt): Ethyl indazole-6-carboxylate (3) (700 mg,
3.68 mmol, 3.5 equiv.) and potassium borohydride (56 mg,
1.05 mmol, 1 equiv.) were ground up in a mortar then dried under
vacuum and the vessel was filled with argon. The mixture was
heated in a sand bath at 180 °C until the gas evolution had ceased
(5–6 h). The reaction was then quenched by addition of toluene.
The solid was filtered off and purified by trituration with hot tolu-
ene, which dissolved the unreacted 3. After drying under vacuum,
the solid was ground in a mortar and any remaining unreacted
indazole was removed by sublimation, by heating the sample at
160 °C under vacuum. By repeating alternating trituration and sub-
limation, potassium hydrotris[6-(ethoxycarbonyl)indazol-1-yl]bo-
rate (KTp4Bo,6-COOEt) (440 mg, 0.712 mmol, 68%) was obtained as
a pale yellow solid. FAB-MS (MeOH, Gly-Thio, negative mode):
m/z (%) = 579 [M – K]–. High resolution LSI calculated [M – K]–:
6-(Hydroxymethyl)-1H-indazole (4): LiAlH4 (1.6 g, 42.5 mmol,
4 equiv.) was added carefully in portions to a solution of 3 (2 g,
10.5 mmol, 1 equiv.) in freshly distilled THF (100 mL) at 0 °C. Af-
ter 2 h of vigorous stirring, TLC analysis showed a complete disap-
pearance of the starting material and the presence of a single prod-
uct. The reaction mixture was carefully quenched with water
(1.6 mL) followed by a 15% NaOH solution (1.6 mL) and then
water (4 mL). The mixture was filtered through Celite and the filter
cake was washed several times with dichloromethane. The filtrate
was dried with MgSO4 and the solvent was removed under reduced
pressure, affording 6-(hydroxymethyl)indazole (4) (1.45 g,
9.8 mmol, 93%). This compound was used without further purifi-
1
cation. ESI-MS: m/z (%) = 149 [M + H]+. M.p. 159 °C. H NMR
578.2085 (C30H27BN6O6); found: 578.2099 (100% [M – K]–). 1H (250 MHz, [D6]DMSO): δ = 12.97 (s, 1 H, NH), 8.00 (s, 1 H, Ha),
4
NMR (250 MHz, [D6]DMSO): δ = 8.20 (s, 3 H, Ha), 8.15 (d, J = 7.65 (d, 3J = 8.4 Hz, 1 H, Hd), 7.46 (s, 1 H, Hb), 7.04 (d, 3J =
1 Hz, 3 H, Hd), 7.81 (d, 3J = 8.5 Hz, 3 H, Hc), 7.59 (dd, 3J =
8.5 Hz, 4J = 1 Hz, 3 H, Hb), 4.33 (q, 3J = 7 Hz, 6 H, CH2CH3),
8.4 Hz, 1 H, Hc), 5.28 (br. s, 1 H, OH), 4.61 (d, J = 5.9 Hz, 2 H,
3
CH2).
Eur. J. Inorg. Chem. 2006, 980–987
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
985

A. Carella, G. Vives, T. Cox, J. Jaud, G. Rapenne, J.-P. Launay
FULL PAPER
6-[(Ethylsulfanyl)methyl]-1H-indazole (5): Mesyl chloride (0.65 mL,
8.4 mmol, 1 equiv.) was added dropwise to a solution of 6-(hy-
droxymethyl)indazole (4) (1.24 g, 8.4 mmol, 1 equiv.) and triethyl-
amine (2.5 mL) in ethyl acetate (170 mL) at 0 °C. The mixture was
stirred at room temperature for 12 h, the organic phase was washed
three times with water (50 mL), and the combined aqueous phases
were extracted once with ethyl acetate. The combined organic
phases were dried with MgSO4 and the solvent removed under re-
duced pressure, giving a pale yellow solid that was used without
purification in the next step. The mesylate yellow solid was dis-
solved in dry THF (75 mL) and added dropwise to a solution of
ethane thiol (0.62 mL, 8.4 mmol, 1 equiv.) in ethanol (75 mL) with
KOH (0.7 g, 12.5 mmol, 1.5 equiv.). The solvent was removed un-
der reduced pressure and the crude material was purified by col-
umn chromatography (SiO2, cyclohexane/Et2O 40 %) to give 6-
[(ethylsulfanyl)methyl]indazole (5) (400 mg, 2.08 mmol, 25%) as a
white solid. DCI-MS (NH3): m/z (%) = 193 [M + H]+. High resolu-
tion LSI calculated [M + H]+: 193.0799 (C10H13N2S); found:
193.0804 (100 % [M + H]+). M.p. 61 °C. 1H NMR (250 MHz,
(d, 3 H, 3J = 8.3 Hz, Hc), 4.55 (s, 5 H, Cp), 3.87 (s, 6 H, CH2),
2.15 (q, 6 H, 3J = 7.3 Hz, CH2CH3), 1.22 (t, 9 H, 3J = 7.3 Hz,
CH2CH3) ppm. 13C NMR (126 MHz, CD2Cl2): δ = 143.0, 138.9
(Ca), 136.9, 122.7, 122.3 (Cc), 119.3 (Cb), 111.0 (Cd), 70.7 (Cp), 36.4
(CH2S), 25.2 (CH2), 14.3 (CH3) ppm. ERuII:RuIII (V/SCE): +0.49 rev
(sweep rate: 100 mVs–1). UV/Vis (CH2Cl2): λmax (ε in Lmol–1 cm–1)
= 231 (30500), 309 (14700), 327 (13500), 390 nm (6200).
X-ray Crystallographic Study: Crystal data for η5-cyclopentadienyl-
(hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borato)ruthenium()
(RuCpTp4Bo,6-COOEt). Orange prismatic crystals suitable for X-ray
analysis were obtained by slow evaporation of a solution of the
complex in a pentane/methanol (1:1) mixture. C35H33BN6O6Ru·
0.5CH3OH: Mr = 1523.17, orthorhombic, space group Pccn, a (Å)
= 22.682(6), b (Å) = 15.0415(13), c (Å) = 19.813(3), V (Å3) =
6760(2), Z = 4, ρcalcd. = 1.497 gcm–3, µ(Mo-Kα) (mm–1) = 0.521.
Data were collected on a Nonius-Kappa CCD diffractometer using
Mo-Kα graphite-monochromated radiation (λ = 0.71073 Å) at
200 K; 3983 reflections having I Ͼ 2σ(I) were used for structure
determination (4.06° Ͻ θ Ͻ 27.00°). For all computations the
Bruker maXus software package was used. Final results: R(F) =
0.0507, Rw(F) = 0.1004, Gof = 1.032.
3
CD2Cl2): δ = 11.35 (s, 1 H, NH), 8.01 (s, 1 H, Ha), 7.68 (d, J =
3
8.3 Hz, 1 H, Hd), 7.44 (s, 1 H, Hb), 7.08 (d, J = 8.3 Hz, 1 H, Hc),
3
3
3.86 (s, 2 H, CH2), 2.39 (q, J = 7.3 Hz, 2 H, CH2CH3), 1.15 (t, J
= 7.3 Hz, 3 H, CH2CH3) ppm. 13C NMR (63 MHz, CD2Cl2): δ =
140.4, 138.0 (Ca), 134.4, 122.7 (Cc), 120.8 (Cb), 109.6 (Cd), 36.3
(CH2S), 25.4 (CH2), 14.3 (CH3) ppm. C10H12N2S: calcd. C 62.5, H
6.29, N 14.6; found C 62.2, H 6.14, N 14.5.
Crystal Data for η5-Cyclopentadienyl[hydrotris(indazol-1-yl)borato]-
ruthenium(II) (RuCpTp4Bo): Orange prismatic crystals suitable for
X-ray analysis were obtained by dissolution of the compound in
dichloromethane and slow liquid diffusion of methanol.
C26H21BN6Ru: Mr = 529.377, orthorhombic, space group Pccn, a
(Å) = 13.2676(12), b (Å) = 18.891(2), c (Å) = 19.4177(13), V (Å3)
= 4866.8(7), Z = 8, ρcalcd. = 1.445 gcm–3, µ(Mo-Kα) (mm–1) = 0.67.
Data were collected on a Nonius-Kappa CCD diffractometer using
Mo-Kα graphite-monochromated radiation (λ = 0.71073 Å) at
298 K; 2103 reflections having I Ͼ 3σ(I) were used for structure
determination (0° Ͻ θ Ͻ 35.00°). For all computations the Bruker
maXus software package was used. Final results: R(F) = 0.047,
Rw(F) = 0.108, Gof = 1.055.
Potassium Hydrotris{6-[(ethylsulfanyl)methyl]indazol-1-yl}borate
(KTp4Bo,6-CH2SEt): 6-[(Ethylsulfanyl)methyl]indazole (5) (300 mg,
1.56 mmol, 3.4 equiv.) and potassium borohydride (25 mg,
46 mmol, 1 equiv.) were ground up in a mortar, dried under vac-
uum and the vessel was filled with argon. The mixture was heated
in a sand bath at 200 °C; 5 h were needed until the gas evolution
had ceased. The solid was ground in a mortar and any remaining
unreacted indazole was removed by sublimation, by heating the
sample at 160 °C under vacuum. By repeating alternating tritura-
tion with toluene and sublimation, potassium hydrotris{6-[(ethyl-
sulfanyl)methyl]indazol-1-yl}borate (KTp4Bo,6-CH2SEt) (160 mg,
0.25 mmol, 55%) was obtained as a pale yellow sticky solid. FAB-
MS (MeOH, Gly-Thio, negative mode): m/z (%) = 584 [M – K]–.
High resolution LSI calculated [M – K]–: 584.2022 (C30H33BN6S3);
found: 584.2042 (100 % [M – K]–). 1H NMR (250 MHz, [D6]-
Crystal Data for η5-Cyclopentadienyl(hydrotris{6-[(ethylsulfanyl)-
methyl]indazol-1-yl}borato)ruthenium(II) (RuCpTp4Bo,6-CH2SEt): Yel-
low prismatic crystals suitable for X-ray analysis were obtained by
dissolution of the compound in dichloromethane and slow liquid
diffusion of methanol. C35H39BN6RuS3: Mr = 751.81, triclinic,
¯
4
3
DMSO): 7.82 (d, J = 1 Hz, 3 H, Ha), 7.52 (d, J = 8.0 Hz, 3 H,
space group P1, a (Å) = 9.883(3), b (Å) = 14.032(3), c (Å) =
14.889(4), V (Å3) = 1802.7(7), Z = 2, ρcalcd. = 1.385 gcm–3, µ(Mo-
Kα) (mm–1) = 0.642. Data were collected on a Nonius-Kappa CCD
diffractometer using Mo-Kα graphite-monochromated radiation (λ
= 0.71073 Å) at 298 K; 3927 reflections having I Ͼ 2σ(I) were used
for structure determination (0° Ͻ θ Ͻ 27.00°). For all computations
the Bruker maXus software package was used. Final results: R(F)
= 0.072, Rw(F) = 0.131, Gof = 1.064.
Hc), 6.92 (s, 3 H, Hd), 6.84 (dd, J = 8.0 Hz, J = 1 Hz, 3 H, Hb),
3.57 (s, 2 H, CH2S), 2.05 (q, J = 7.4 Hz, 6 H, CH2CH3), 0.97 (t,
3
4
3
3J = 7 Hz, 9 H, CH2CH3), 5.73 (br. s, 1 H, BH) ppm. 13C NMR
(63 MHz, [D6]DMSO): δ = 143.8, 133.3 (Ca), 131.9, 121.9, 120.0
(Cc), 119.5 (Cb), 112.6 (Cd), 35.2 (CH2S), 24.0 (CH2), 14.2 (CH3)
ppm. 11B NMR (160 MHz, [D6]DMSO): –2.57 (s, 1 H) ppm.
η5-Cyclopentadienyl(hydrotris{6-[(ethylsulfanyl)methyl]indazol-1-
yl}borato)ruthenium(II) (RuCpTp4Bo,6-CH2SEt): Potassium
hydrotris{6-[(ethylsulfanyl)methyl]indazol-1-yl}borate (KTp4Bo,6-
CH2SEt) (62 mg, 0.1 mmol, 1 equiv.) was dissolved in dry acetonitrile
(20 mL) and the mixture was purged with argon. [RuCp(CH3CN)
3]PF6 (43 mg, 0.1 mmol, 1 equiv.) was added to this solution and it
was then refluxed for 2 h. Evaporation of the solvent followed by
a purification by column chromatography (SiO2: cyclohexane/
CCDC-254040 (for RuCpTp4Bo), -254041 (for RuCp-
Tp4Bo,6-COOEt), and -284359 (for RuCpTp4Bo,6-CH2SEt) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Electrochemistry: The voltammetric experiments were measured
dichloromethane 0–50 %) afforded η5-cyclopentadienyl(hydro- with an AUTOLAB PGSTAT 100 potentiostat using a Pt disc
tris{6-[(ethylsulfanyl)methyl]indazol-1-yl}borato)ruthenium()
(RuCpTp4Bo,6-CH2SEt) (10 mg, 0.013 mmol, 13%) as a yellow solid.
DCI-MS (NH3): 753 [M + H]+. High resolution LSI calculated
[M + H]+: 753.1613 (C35H40BN6RuS3); found: 753.1637 (100% [M
(1 mm diameter) as working electrode and a Pt counter electrode.
The reference electrode used was the saturated calomel electrode
(SCE). Tetra-n-butylammonium hexafluorophosphate (Bu4NPF6,
0.1 ) acted as the electrolyte. All solutions were degassed thor-
oughly for at least 15 min with argon and an inert gas blanket was
1
+ H]+). M.p. 206 °C dec. H NMR (500 MHz, CD2Cl2): δ = 8.57
3
(s, 3 H, Ha), 7.78 (s, 3 H, Hd), 7.55 (d, 3 H, J = 8.3 Hz, Hb), 7.08 maintained over the solution during the measurements.
986
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 980–987

Synthesis of New Tripodal Hydrotris(indazol-1-yl)borate Ligands
FULL PAPER
[8] a) S. Trofimenko, J. Am. Chem. Soc. 1966, 88, 1842–1844; b)
S. Trofimenko, J. Am. Chem. Soc. 1967, 89, 6288–6294.
[9] a) S. Trofimenko, Scorpionates – Polypyrazolylborate Ligands
and Their Coordination Chemistry, Imperial College Press, Lon-
don, 1999; b) S. Trofimenko, Chem. Rev. 1993, 93, 943–980; c)
A. Shaver, in Comprehensive Coordination Chemistry (Eds.: G.
Wilkinson, R. D. Gillard, J. McCleverty), Pergamon, Oxford,
1987, vol. 13, pp. 245–259; d) C. Pettinari, C. Santini, in: Com-
prehensive Coordination Chemistry II (Ed.: A. B. P. Lever), El-
sevier, Amsterdam, 2003, vol. 1, pp. 159–210; e) D. L. Reger,
Coord. Chem. Rev. 1996, 147, 571–595; f) G. Parkin, Adv. Inorg.
Chem. 1995, 42, 291–393; g) M. Etienne, Coord. Chem. Rev.
1996, 156, 201–236; h) P. K. Byers, A. J. Canty, R. T. Honey-
man, Adv. Organomet. Chem. 1992, 34, 1–65.
[10] a) A. L. Rheingold, G. P. A. Yap, S. Trofimenko, Inorg. Chem.
1995, 34, 759–760; b) A. L. Rheingold, B. S. Haggerty, G. P. A.
Yap, S. Trofimenko, Inorg. Chem. 1997, 36, 5097–5103; c) C.
Janiak, S. Temizdemir, S. Dechert, Inorg. Chem. Commun.
2000, 3, 271–275.
[11] a) K. Kalyanasundaram, M. Grätzel, Coord. Chem. Rev. 1998,
177, 347–414; b) E. Galoppini, W. Guo, P. Qu, G. J. Meyer, J.
Am. Chem. Soc. 2001, 123, 4342–4343; c) P. G. Hoertz, R. A.
Carlisle, G. J. Meyer, D. Wang, P. Piotrowiak, E. Galoppini,
Nano Lett. 2003, 3, 325–330.
Acknowledgments
A. C. thanks the French Ministry of National Education and the
Institut Universitaire de France for a Ph.D. Fellowship. T. C.
thanks the European Union for an ERASMUS Fellowship. G. V.
thanks the French Ministry of National Education and the Ecole
Normale Supérieure of Lyon for a Ph.D. Fellowship. Drs André
Gourdon and Christophe Coudret are gratefully acknowledged for
useful discussions. Christine Viala is also thanked for the measure-
ment of the NMR spectra.
[1] a) F. Moresco, Phys. Rep. 2004, 399, 175–225; b) A. Gourdon,
Eur. J. Org. Chem. 1998, 2797–2801.
[2] a) C. Joachim, J. K. Gimzewski, A. Aviram, Nature 2000, 408,
541–548; b) C. Joachim, J. K. Gimzewski, Chem. Phys. Lett.
1997, 265, 353–357.
[3] a) C. Joachim, J. K. Gimzewski, Struct. Bonding (Berlin) 2001,
99, 1–18; b) V. L. Popov, Phys. Rev. E 2003, 68, 026608; c) F.
Moresco, G. Meyer, K.-H. Rieder, H. Tang, A. Gourdon, C.
Joachim, Phys. Rev. Lett. 2001, 86, 672–675; d) G. Rapenne,
Org. Biomol. Chem. 2005, 3, 1165–1169.
[4] a) J. K. Whitesell, H. K. Chang, Science 1993, 261, 73–76; b)
Q. Li, A. V. Rukavishnikov, P. A. Petukhov, T. O. Zaikova, C.
Jin, J. F. W. Keana, J. Org. Chem. 2003, 68, 4862–4869; c) E.
Galoppini, W. Guo, W. Zhang, P. G. Hoertz, P. Qu, G. J. Meyer,
J. Am. Chem. Soc. 2002, 124, 7801–7811; d) E. Galoppini, Co-
ord. Chem. Rev. 2004, 248, 1283–1297; e) Q. Li, C. Jin, P. A.
Petukhov, A. V. Rukavishnikov, T. O. Zaikova, A. Phadke,
D. H. LaMunyon, M. D. Lee, J. F. W. Keana, J. Org. Chem.
2004, 69, 1010–1019.
[12] a) J. M. Tour, L. Jones, D. L. Pearson, J. J. S. Lamba, T. P. Bur-
gin, G. M. Whitesides, D. L. Allara, A. N. Parikh, S. Atre, J.
Am. Chem. Soc. 1995, 117, 9529–9534; b) D. T. Gryko, C.
Clausen, J. S. Lindsey, J. Org. Chem. 1999, 64, 8635–8647.
[13] a) E. B. Troughton, C. D. Bain, G. M. Whitesides, R. G. Nuzo,
D. L. Allara, M. D. Porter, Langmuir 1988, 4, 365–385; b) J.
Noh, T. Murase, K. Nakajima, H. Lee, M. Hara, J. Phys.
Chem. B 2000, 104, 7411–7416; c) K. W. Kittredge, M. A. Min-
ton, M. A. Fox, J. K. Whitesell, Helv. Chim. Acta 2002, 85,
788–798; d) K. Furukawa, K. Ebata, H. Nakashima, Y. Kashi-
mura, K. Torimitsu, Macromolecules 2003, 36, 9–11.
[5] a) A. V. Rukavishnikov, A. Phadke, M. D. Lee, D. H. LaMun-
yon, P. A. Petukhov, J. F. W. Keana, Tetrahedron Lett. 1999, 40,
6353–6356; b) Y. Yao, J. M. Tour, J. Org. Chem. 1999, 64, 1968–
1971; c) W. Guo, E. Galoppini, G. Rydja, G. Pardi, Tetrahedron
Lett. 2000, 41, 7419–7421; d) D. Hirayama, K. Takimiya, Y.
Aso, T. Otsobu, T. Hasobe, H. Yamada, H. Imahori, S. Fuku-
zumi, Y. Sakata, J. Am. Chem. Soc. 2002, 124, 532–533; e) Q.
Li, A. V. Rukavishnikov, P. A. Petukhov, T. O. Zaikova, J. F. W.
Keana, Org. Lett. 2002, 4, 3631–3634.
[14] B. D. Hosangadi, R. H. Dave, Tetrahedron Lett. 1996, 37,
6375–6378.
[15] a) C. Ruechardt, V. Hassmann, Synthesis 1972, 375–376; b)
D. G. Batt, J. J. Petraitis, G. C. Houghton, D. P. Modi, G. A.
Cain, M. H. Corjay, S. A. Mousa, P. J. Bouchard, M. S. For-
sythe, P. P. Harlow, F. A. Barbera, S. M. Spitz, R. R. Wexler,
P. K. Jadhav, J. Med. Chem. 2000, 43, 41–58.
[6] a) J. Vacek, J. Michl, New J. Chem. 1997, 21, 1259–1268; b)
M. C. Hersam, N. P. Guisinger, J. W. Lyding, Nanotechnology [16] C. Lopez, R. M. Claramunt, D. Sanz, C. F. Foces, F. H. Cano,
2000, 11, 70–76; c) R. Yasuda, H. Noji, K. Kinosita, M. Yosh-
ida, Cell 1998, 93, 1117–1124; d) R. Yasuda, H. Noji, K. Kino-
sita, H. Itoh, Nature 2001, 410, 898–904; e) H. Jian, J. M. Tour,
J. Org. Chem. 2003, 68, 5091–5103.
R. Faure, E. Cayon, J. Elguero, Inorg. Chim. Acta 1990, 176,
195–204.
[17] A. N. McNair, D. C. Boyd, K. R. Mann, Organometallics 1986,
5, 303–310.
[7] A. Carella, G. Rapenne, J.-P. Launay, New J. Chem. 2005, 29,
288–290.
Received: September 23, 2005
Published Online: January 16, 2006
Eur. J. Inorg. Chem. 2006, 980–987
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
987