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Inorganica Chimica Acta 358 (2005) 3513–3518
Note
Structure and spectroscopic studies of cis-bis(bipyridine)ruthenium(II) complexes of phenylcyanamide ligands
Anthony Baker, Joel Jaud, Jean-Pierre Launay, Jacques Bonvoisin *
NanoScience Group, CEMES-GNS/CNRS, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 4, France
Received 4 June 2004; accepted 22 September 2004
Available online 22 October 2004
Abstract
New ruthenium(II) complexes with cyanamide ligands, cis-[Ru(bpy)2(Ipcyd)2] (1) and [Ru(bpy)2(OHpcyd)2] (2) (bpy = 2,2 0-bipy-
ridine, Ipcyd = 4-iodophenylcyanamide anion, OHpcyd = 4-(3-hydroxy-3-methylbut-1-ynil)phenylcyanamide), have been prepared
and characterized by UV–Vis, IR and 1H NMR spectroscopies as well as electrochemical technique (CV). The complex cis-
[Ru(bpy)2(Ipcyd)2] (1) crystallized with empirical formula of C34H24I2N8Ru in a monoclinic crystal system and space group of
P21/c with a = 11.769(7) A, b = 24.188(12) A, c = 11.623(2) A, b = 91.63(3)�, V = 3308(3) A3 and Z = 4.
� 2004 Elsevier B.V. All rights reserved.
Keywords: Ruthenium compounds; Phenylcyanamide ligand; Bipyridine; Crystal structures
1. Introduction
Previous work [1] has shown that the X-ray structure
of a ru-cyanamide type complex shows a very specific
bent structure for the ligand. Starting from that, onequestion was to know if one could make ruthenium
dinuclear complexes bridged by two phenyldicyanamide
ligands, which could be of special interest in the field of
molecular electronics, and more precisely in the realiza-
tion of quantum interference [2]. The present work is a
first step towards this goal by synthesizing new com-
plexes of ruthenium(II) having two para-substituted
phenylcyanamide arms in cis conformation. We presenthere the di-iodo functionalized complex 1 and its struc-
ture and also the di-butinol derivative 2 issued from 1
after a Sonogashira cross-coupling reaction. Other X-
ray structures of complexes with two phenylcyanamide
ligands [3,16] appeared in the literature, but not with
0020-1693/$ - see front matter � 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.09.044
* Corresponding author. Tel.: +33 5 62 25 78 52; fax: +33 5 62 25 79
99.
E-mail address: [email protected] (J. Bonvoisin).
ruthenium atoms and a cis conformation for the above
cited ligands.
2. Experimental
2.1. Materials
All chemicals and solvents were of reagent grade or
better. Ru(bpy)2Cl2 and IpcydH (4-Iodophenylcyana-
mide) were prepared according to the literature proce-
dures [5,6]. 4-Iodoaniline was purchased from Aldrich.
Weakly acidic and neutral Brockmann I type alumina(Aldrich) was used. Where used, 100% argon implies
vacuum evacuation of apparatus before argon is intro-
duced to the system.
2.2. Physical measurements
1H NMR spectra were taken on Brucker AMD-400
MHz equipment. IR spectra were taken, using Perkin–
3514 A. Baker et al. / Inorganica Chimica Acta 358 (2005) 3513–3518
Elmer 1725 equipment, from a matrix of the subject
compound in KBr (1% dilution). UV–Vis absorbance
spectra were taken using a Shimadzu UV-3100 spec-
trometer and a 2 mm solution cell. Cyclic Voltammo-
grams were obtained with an Autolab system
(PGSTAT 100) in DMF (0.1 M tetrabutylammoniumhexafluorophosphate, TBAH) at 25� C. A three elec-
trode cell was used comprising a 1 mm Pt-disk working
electrode, a Pt wire auxiliary electrode, and an aqueous
saturated calomel (SCE) reference electrode. Electro-
spray (positive mode) and Electronic Impact mass spec-
tra were obtained with Perkin–Elmer Sciex (Nermag
R10-R10).
2.3. Syntheses
2.3.1. Preparation of cis-[Ru(bpy)2(Ipcyd)2] (1)Method 1. A violet solution of Ru(bpy)2Cl2 (992 mg,
2.1 mmol) and IpcydH (5 g, 20.5 mmol) in dichloro-
methane (150 cm3) was refluxed under argon and stirred
for 30 min. AgBF4 (1.6 g, 8.2 mmol) was added and the
solution was refluxed for 5 h, turning bright orange overthis time. A white precipitate of silver chloride was ob-
served to form in the reaction mixture. The reaction
mixture was cooled to room temperature and filtered
to remove the precipitate yielding a transparent orange
solution, which was evaporated to dryness leaving a
dark, sticky orange solid. The residue was purified on
acidic alumina column using a dichloromethane/ethanol
(99:1) eluent with the violet product being collected asthe second of three fractions. The third fraction contain-
ing the desired complex and impurity of the free ligand
was purified on a subsequent neutral alumina column
with the second crop of product being collected as the
only fraction. Crystallization occurred on standing and
the two crops were dried under vacuum (1.13 g, 62%).
Method 2. A violet solution of Ru(bpy)2Cl2 (0.200 g,
0.41 mmol) and IpcydH (1 g, 4.1 mmol) in dichloro-methane (150 cm3) was refluxed under argon and stirred
for 30 min. Acidic alumina (10 g) and AgBF4 (1.6 g, 8.2
mmol) were added and the solution was refluxed for 5 h,
remaining violet. The reaction mixture was cooled to
room temperature, filtered to remove the alumina and
evaporated to dryness leaving a violet powder. The res-
idue was purified on acidic alumina column using a
dichloromethane/ethanol (99:1) eluent with the violetproduct being collected as the second of two fractions.
The product was dried under vacuum (0.161 g, 45%).
C34H24I2N8Ru requires C, 45.4; H, 2.7; N, 12.5; I,
28.2. Found: C, 44.7; H, 2.7; N, 12.2; I, 27.9%. IR
m/cm�1 2168s (NCN); ES mass spectrum (CH3OH)
m/z: 900.8 [M + H]+ requires 900.5; 657 [Ru(bpy)2 (Ip-
cyd) + H]+. 1H NMR (DMSO d = 2.50) 9.44 (2H, dd,
0.9, 5.6 Hz) 8.78 (2H, d, 8.0 Hz) 8.64 (2H, d, 8.1 Hz)8.21 (2H, td, 1.5, 7.8 Hz) 7.88 (4H, m) 7.72 (2H, d, 5.6
Hz) 7.30 (2H, m) 7.05 (4H, d, 8.7 Hz) 6.01 (4H, d, 8.7
Hz). UV–Vis (10�4 M, DMF) k /nm (e)/mol�1 dm3
cm�1 259s (33600), 293s (70200), 380br (10600), 532br
(6840).
2.3.2. Preparation of [Ru(bpy)2(OHpcyd)2] (2)To a mixture of Ru(bpy)2(Ipcyd)2 (0.200 g, 0.22
mmol), Pd(PPh3)4 (0.030 g, 0.026 mmol) and cop-
per(I)iodide (0.010 g, 0.053 mmol) in DMF (3 cm3),
under 100 % argon, was added, by syringe, 2-methyl-
3-butyn-2-ol (2.2 cm3, 2.2 mmol) and piperidine (1
cm3). The purple solution was stirred at room tempera-
ture for 2 1/2 h and then the solvent was evaporated un-
der vacuum leaving a purple residue. The product was
pre-adsorbed onto acidic alumina from dichlorometh-ane and purified on an acidic alumina column using a
dichloromethane/ethanol (95:5) eluent. The violet prod-
uct was collected as the second of two fractions and
dried under vacuum (0.167 g, 93%).
C44H38N8O2Ru requires C, 65.1; H, 4.7; N, 13.8.
Found: C, 64.2 H, 4.7; N, 13.5%. IR m/cm�1 2179s
(NCN); ES mass spectrum (CH3OH) m/z 813
[M + H]+ requires 812.9; 613 [Ru(bpy)2(OHpcyd)+ H]+. 1H NMR (DMSO d = 2.50) 9.44 (2H, d, 5.54
Hz) 8.79 (2H, d, 8.2 Hz) 8.64 (2H, d, 8.1 Hz) 8.23
(2H, td, 1.5, 7.74 Hz) 7.9 (4H, m) 7.73 (2H, d, 4.9 Hz)
7.28 (2H, m) 6.83 (4H, d, 8.5 Hz) 6.08 (4H, d, 8.5 Hz),
1.4 (12H, s). UV–Vis (10�4 M, DMF) k /nm (e)/mol�1
dm3 cm�1 259s (35650); 298s (58650), 329s (37500);
530br (6450).
2.4. X-ray diffraction studies
Dark red parallelepiped crystals of cis-[Ru(bpy)2-
(Ipcyd)2] (1) were grown by slow evaporation of a mix-
ture of an ethanol/dichloromethane solution of the
complex. A summary of crystal data is given in Table
1. The selected crystal for the measurement was a long
needle with the following size: 0.012, 0.030 and 0.655mm. It was very anisotropic and very thin. It was not
possible to cut the crystal in order to give it a more rea-
sonable size. Taking into account the interest of this
study and in spite of the fact that the measurement could
not be optimum, the diffraction intensities were collected
on a Nonius Kappa CCD diffractometer at room tem-
perature, using graphite monochromated Mo Ka radia-
tion (k = 0.71073 A) at a detector distance of 4 cm. Thecompound crystallizes in monoclinic system with the P21/c space group. The crystallographic cell was found by
using EVAL-CCD [7]. The structure was solved using
DIRDIFDIRDIF [8] and refined in the maXus software package
[9]. The measure was made up to h = 27.5�. We have
tried to measure the totality of the sphere with a redun-
dancy of 3, which led us to collect 20874 reflections
spots. This led us to 6433 independent reflections outof which only 1469 revealed to be used for refinement
after absorption correction. These were performed using
Table 1
Crystallographic data and refinement parameters
Formula C34H24I2N8Ru
Crystal system monoclinic
Fw (g mol�1) 899.5
Space group P21/c
a (A) 11.769(7)
b (A) 24.188(12)
c (A) 11.623(2)
b (�) 91.63(3)
V (A3) 3308(3)
Z 4
l(Mo Ka) (mm�1) 2.38
qcalc (g cm�3) 1.806
2h max (�) 64
Total number of reflections 6433
Rint 0.064
Number of unique reflections with I > 3r(I) 1469
Number of variables 113
Absorption correction multi-scan
Tmin/max 0.859/1.015
Rfa 0.081
Rwb 0.160
GOF 2.564
a Rf =P
||Fo| � |Fc||/P
|Fo|.b Rw=(
Pw|Fo| � |Fc|)
2/(P
w|Fo|2)1/2.
A. Baker et al. / Inorganica Chimica Acta 358 (2005) 3513–3518 3515
the SORTAV program [10]. Besides the fact that this
method gave the best results, the poor quality of the
crystal led to errors on the intensities and did not allow
suitable refinements. This was solved by adding rigid
block constraints and by doing independent refinements
only on heavy atoms (ruthenium and iodine atoms) with
anisotropic thermal agitation factors. This method al-
lowed us to reach the right geometry around the ruthe-nium atom, the distances and the angles around this
atom being freely refined. The remainder of the mole-
cule�s geometry being largely predictable, it has been
possible to obtain, from a rather poor quality crystal,
a realistic structure. The chemically relevant informa-
tion is obtained without ambiguities. The hydrogen
NN
NN
RuCl
Cl
IHN
CN
+
NN
NN
R
AgB
CH2
Purification on acidicalumina column
Scheme 1. Synthesis o
atoms were calculated and fixed at 0.97 A from the cor-
responding atoms. The full experimental details, atomic
parameters and the complete listing of bond lengths and
angles are available as supplementary data.
3. Results and discussion
The synthesis of the ruthenium Ipcyd complex 1 is
shown in Scheme 1. It is likely that the first stage of
the reaction, the ligand displacement, yields the charged
IpcydH complex, with the chlorides retained as counter-
ions. This is shown by the fact that the crude product,
when evaporated to dryness, is obtained as a viscous or-ange liquid rather than a solid, a behaviour typical of
charged complexes. Purification of this product on
acidic alumina seems, counter-intuitively, to deproto-
nate the ligands yielding the neutral, solid complex. This
deprotonation has been identified in previous work on
phenyl-cyanamide ligands [4] but no satisfactory expla-
nation for the behaviour has been put forward although
it is most likely due to the wealth of active sites on alu-mina in addition to acidity.
Overall, the product was obtained in yields between
28% and 60%. The highest yield obtained was probably
due to the use of new, pure AgBF4, which is a highly
hygroscopic reagent and can deteriorate easily. It was
noticed that during the reaction, the solution became
increasingly protic, an effect due to the large excess of
the ligand used and the facile liberation of the protonattached to one of the nitrogens on that ligand by the
Cl� or BF4� moiety. It was thought that this could be
reducing the yield and so a method was devised which
could keep the reaction neutral. Due to the de-protonat-
ing effect on the column noticed earlier, it was decided to
add a small amount of slightly acidic alumina to the
reaction mixture. Whilst this did not produce a yield in-
crease, it did allow easier isolation of the final complex.
NN
NN
Ru N
N
C
HN
C NH
I
I
u N
N
CN
C N
I
I
Cl2
F4
Cl2
1
f the Complex 1.
3516 A. Baker et al. / Inorganica Chimica Acta 358 (2005) 3513–3518
The presence of the alumina meant that the complex was
obtained in the neutral form. This allowed the isolation
of the pure compound on a single column rather than
the two needed previously.
Solubility of the Ipcyd complex was limited. Whilst a
dichloromethane/ethanol eluent was used successfully incolumn purification, the solubility of the pure complex
was poor in these and many other common solvents.
Complete solubility was limited to DMF and DMSO
solvents, which created problems with further reactions.
This was surprising as very similar complexes with only
one Ipcyd ligand [6] have been shown to enjoy high sol-
ubility in most common solvents.
The reaction can be easily followed using the IRspectrum of the complex by examination of the triple
bond CN band region at around 2200 cm�1. The un-
complexed, protonated IpcydH ligand displays the
m(CN) stretch at 2229 cm�1. In the compound 1, the
same stretch is observed at 2168 cm�1, a value typical
of the stretch of the deprotonated complexed ligand.
NMR of the complex 1 was completed successfully
(see Section 2.3.1). The characteristic Ipcyd peaks werepresent with the integration values confirming that the
compound contained two cyanamido ligands and hence
that the complex isolated had successfully undergone the
double substitution. The spectrum also showed the char-
acteristic pattern of the bipyridine ligand, i.e., seven
peaks between 9.5 and 7.2 ppm.
Cyclic voltammetry showed primarily that the oxida-
tion potential of the ruthenium centre in the complex is0.43 V and that the ligand oxidation is �1 V. Scans to
negative potential show the characteristic reduction of
the bipyridine ligands. The oxidation of the metal is dis-
tinguished from that of the ligand by inspection of the
differential pulse spectrum, which shows the higher peak
to be approximately double the intensity of the lower
and so implies that it represents the oxidation of the
two ligands. The metal oxidation is perfectly reversibleif the voltammetry is run only as far as 0.8 V. Interest-
ingly, however, if a full sweep to 1.5 V is performed
and the ligand is also oxidized then no reverse reduction
is observed. This implies that some fundamental elec-
tronic change is occurring in the complex upon oxida-
tion of the ligands. The presence of irreversible
oxidation of the ligand would be a problem should this
NN
NN
Ru N
N
CN
C N
I
I
OH
Pd(PPh3)4 (10%CuI(10%),Piperidine,DMF
1
Scheme 2. Sonogashira coupling of 2-methyl-3-b
molecule be considered as a candidate for a molecular
wire. One characteristic that a wire has to have is that
it should be robust. Whilst the irreversible oxidation will
not necessarily affect electron transfer, the fact that re-
peated exposure to harsh conditions may lead to
destruction of the wire means that, perhaps, this ligandwould not be the ideal choice for use in an electronic
component.
The ruthenium butynol complex 2 was prepared by
the Sonogashira reaction (Scheme 2) [11]. The reaction
was found to proceed very efficiently with yields of over
90% obtained in every experiment.
The characteristic m(CN) stretch in the IR spectrum is
seen to move to 2179 from the 2168 cm�1 found with thecomplex 1. This can be rationalized by the fact that one
side of the bond has become slightly heavier from the
substitution of the iodine by the acetylene function
and thus vibrates at a lower frequency. In theory, the
CC triple bond should also vibrate in this area creating
either two peaks or a shoulder to the CN stretch. The IR
spectrum, however, shows no shoulder or second peak.
This implies that the CC bond is vibrating at exactlythe same frequency as the CN, which is unlikely, but if
we consider that the frequencies will be defined in each
case by the amount of bonding and the relative masses
of the bodies involved possible.
Solubility tests on the butynol complex again showed
the complex to be poorly soluble in all solvents but not
in DMF and DMSO. This was again unexpected as the
hydroxyl function usually imparts good solubility tomolecules. The poor solubility was this time more prob-
lematic as the next step, deprotecting the alkyne, is usu-
ally performed in freshly distilled THF, a solvent that
did not readily dissolve the butynol complex.
Electrochemistry, again by cyclic and differential
pulse voltammetry showed a very similar profile to that
for the complex 1. The metal oxidation at 0.42 V was
observed with the ligand oxidation peak shifting slightlyto lower potential, reflecting the replacement of the io-
dide group by the acetylene function. The same behav-
iour regarding the reversible and irreversible oxidation
was observed as for the Ipcyd complex. Varying the
speed of the cyclic voltammetry between from 0.05 to
1 V also allowed the formation of the classic spread of
cyclic voltammetry curves, where the current flowing
NN
NN
Ru N
N
CN
C N
OH
OH),
2
utyn-2-ol with complex 1 to get complex 2.
Fig. 1. ORTEP drawing of the [Ru(bpy)2(Ipcyd)2] complex (proba-
bility level of 30%).
Ru
N
C
N
N
C
N
θ1 θ2
A. Baker et al. / Inorganica Chimica Acta 358 (2005) 3513–3518 3517
through the solution increases with the rate of change of
voltage.
NMR of the complex was as expected with the main
body of the Ipcyd and bipyridine peaks now comple-
mented by the strong singlet peak at low (1.4) ppm cor-
responding to the 12 tert-butyl group hydrogens.UV–Vis spectroscopy showed a very similar spectrum
to the one observed for the Ipcyd complex. This is as ex-
pected as the only difference between the molecules is the
exchange of an iodide group for the protected acetylene.
Neither of these groups is likely to be UV active and so
the measured absorbencies should be the same.
Crystal structure data for [Ru(bpy)2(Ipcyd)2] (1) and
selected bond lengths and angles are, respectively, givenin Tables 1 and 2. Fig. 1 shows the ORTEP drawing of
the [Ru(bpy)2(Ipcyd)2] entity and the numbering scheme
used in Table 2. In the molecular structure, the two
cyanamido ligands adopt a cis disposition. As in most
examples of Ru–cyanamido complexes [1,6,12–15], the
Ru–N–C–N moiety is almost linear, while the ligand is
bent around the nitrogen atom linked to the phenyl ring
(N12 and N9 on Fig. 1). (Note, however, the curiousexception of [Co(bpy)2(Cl-pcyd)2]
+ where the structure
is bent around the two nitrogens of each cyanamido lig-
and [16].)
The terminal phenyl rings and the NCN groups are in
the same plane, as already observed [1]. On the other
hand, there is certainly an almost free rotation around
the RuNCN axes (Scheme 3), since a variety of confor-
mations have been already observed. (Note that sincethe Ru–N–C–N chain is linear, it is not possible to say
around which particular bond of the chain the rotation
occurs). In the present case, the adopted disposition
could be due to crystal packing forces. Thus, it can be
assumed that in solution, the two cyanamido ligands
Table 2
Selected bond lengths (A) and bond angles (�)
Bond lengths (A)
Ru(1)–N(2) 2.06(2) N(7)–C(8) 1.11(3)
Ru(1)–N(3) 2.11(4) N(9)–C(8) 1.28(3)
Ru(1)–N(4) 2.07(3) N(9)–C(34) 1.43(2)
Ru(1)–N(5) 2.08(4) N(6)–C(11) 1.11(2)
Ru(1)–N(6) 2.085(14) N(12)–C(11) 1.28(2)
Ru(1)–N(7) 2.07 (2) N(12)–C(40) 1.43(2)
Bond Angles (�)N(2)–Ru(1)–N(3) 79.0 (12) N(2)–Ru(1)–N(4) 99.2(14)
N(2)–Ru(1)–N(5) 176.1(16) N(2)–Ru(1)–N(6) 94.9(12)
N(2)–Ru(1)–N(7) 84.6(13) N(3)–Ru(1)–N(4) 92.9(14)
N(3)–Ru(1)–N(5) 99.0(9) N(3)–Ru(1)–N(6) 173.8(18)
N(3)–Ru(1)–N(7) 93.6(15) N(4)–Ru(1)–N(5) 77.5(12)
N(4)–Ru(1)–N(6) 87.1(8) N(4)–Ru(1)–N(7) 173.0(12)
N(5)–Ru(1)–N(6) 87.1(9) N(5)–Ru(1)–N(7) 99.0(10)
N(6)–Ru(1)–N(7) 86.7(10) Ru(1)–N(6)–C(11) 161.3(18)
N(6)–C(11)–N(12) 177(2) C(11)–N(12)–C(40) 121.4(11)
Ru(1)–N(7)–C(8) 169(3) N(7)–C(8)–N(9) 179(4)
C(8)–N(9)–C(34) 121(2)
Scheme 3. Free rotations around the RuNCN axes. See text for
discussion.
can adopt a number of different conformations. Inspec-
tion of a molecular model shows that by rotationaround h1 and h2 (see Scheme 3), it is possible to bring
the cyanamido ligands in a position where a dimeriza-
tion with another complex should be possible. Work is
in progress to exploit this possibility.
4. Supplementary material
CCDC No. 235067 contains the supplementary crys-
tallographic data for this paper. These data can be ob-
tained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, by emailing data_re-
[email protected], or by contacting The Cambridge
Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033.
3518 A. Baker et al. / Inorganica Chimica Acta 358 (2005) 3513–3518
Acknowledgements
We thank the European Union for an ERASMUS
scholarship (A.B.) and Christine Viala (CEMES) for
technical help and the synthesis of Ru(bpy)2Cl2.
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