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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: jbonvoisin@cemes.fr (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-

quest@ccdc.cam.ac.uk, 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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