Spectroelectrochemical studies on some new ruthenium(II) complexes containing both cyanide and isocyanide ligands

Article abstract of DOI:10.1016/S0020-1693(99)00581-2

New ruthenium(II) complexes trans, trans, trans-[RuCl₂(NCR)₂(CNR')₂] (R = Me or Ph, R' = Bu(t), xylyl or cyclohexyl (cy)) have been prepared by treating mer-[RuCl₃(NCR)₃] with the appropriate isocyanide ligand CNR' in EtOH/CH₂Cl₂. These complexes have been shown to be oxidisable electrochemically in situ to the analogous ruthenium(III) species trans, trans, trans[RuCl₂(NCR)₂(CNR')₂]⁺ in 0.5 mol dm^-3 [NBu₄/(n)][PF₆]/CH₂Cl₂ solution, the stereochemistry of the oxidised species being established by use of an infrared spectroelectrochemical (IRRAS) technique. The electronic absorption spectra of the ruthenium(III) species obtained by use of an OTTLE cell are also reported and discussed. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00581-2

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Inorganica Chimica Acta 300–302 (2000) 175–180
Spectroelectrochemical studies on some new ruthenium(II)
complexes containing both cyanide and isocyanide ligands
Joseph P. al Dulaimi, Robin J.H. Clark *, Marcia Saavedra S., Md. Abdus Salam
Christopher Ingold Laboratories, Uni6ersity College London, 20 Gordon Street, London, WC1H 0AJ, UK
Received 23 August 1999; accepted 11 November 1999
Abstract
New ruthenium(II) complexes trans, trans, trans-[RuCl2(NCR)2(CNR%)2] (R=Me or Ph, R%=But, xylyl or cyclohexyl (cy)) have
been prepared by treating mer-[RuCl3(NCR)3] with the appropriate isocyanide ligand CNR% in EtOH/CH2Cl2. These complexes
have been shown to be oxidisable electrochemically in situ to the analogous ruthenium(III) species trans, trans, trans-
[RuCl2(NCR)2(CNR%)2]+ in 0.5 mol dm−3 [NBun4 ][PF6]/CH2Cl2 solution, the stereochemistry of the oxidised species being
established by use of an infrared spectroelectrochemical (IRRAS) technique. The electronic absorption spectra of the rutheni-
um(III) species obtained by use of an OTTLE cell are also reported and discussed. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Spectroelectrochemical studies; Ruthenium(II) complexes; Cyanide ligand; Isocyanide ligand
1. Introduction
In this publication some new ruthenium(II) com-
plexes, [RuCl2(NCR)2(CNR%)2], containing both cya-
nide and isocyanide ligands, are described and their
redox behaviour investigated by means of infrared
reflection–absorption spectroscopy (IRRAS) [6] and by
electronic spectroscopy with an optically transparent
thin-layer electrochemical (OTTLE) [7] cell.
There is much interest in redox-active ruthenium
complexes which have been used, for example, as cata-
lysts, as electrochromic materials and in energy storage
devices. A wide range of such complexes can be formed
with cyanide and isocyanide ligands [1]; thus the mixed
chloride–cyanide complexes [RuCl6−n(NCR)n]z (R=
Me or Ph, n=0–6) have been prepared from
[RuCl6]2− by electrochemically induced displacement
of chloride [2]. The ruthenium(III) isocyanide com-
plexes trans-[NBu4n ][Ru(CNBut)2X4] (X=Cl or Br) un-
dergo halide displacement upon reduction in aceto-
nitrile [3,4], and their mixed-ligand environment also
permits access to the ruthenium(IV) oxidation state.
The ruthenium(II) isocyanide complexes trans-
[RuCl2(CNR)4] (R=But or xylyl) have been oxidised
electrochemically to trans-[RuCl2(CNR)4][ClO4] in a
[NBun4 ][ClO4]/MeCN solution [5]. Similar redox be-
haviour has also been reported for the complexes trans,
trans, trans-[RuCl2(CNR)2(PPh3)2] (R=But or xylyl)
[5].
2. Experimental
Commercial RuCl3·xH2O was obtained from John-
son Matthey. tert-Butylisocyanide and xylylisocyanide
were purchased from Fluka and cyclohexylisocyanide
was obtained from Aldrich. The complexes
[RuCl3(NCPh)3] and [RuCl3(NCMe)3] were prepared by
published methods [2] and their purity confirmed by
elemental analysis (C, H, N). All the ruthenium(II)
isocyanide complexes were prepared under a nitrogen
atmosphere using standard Schlenk-line techniques.
2.1. [RuCl2(NCMe)2(CNBut)2] (1)
[RuCl3(NCMe)3] (0.10 g, 0.30 mmol) and tert-
butylisocyanide (0.14 g, 1.64 mmol) were dissolved in
degassed 1:10 ethanol/dichloromethane (15 cm3). The
* Corresponding author. Tel.: +44-171-387 7050; fax: +41-171-
504 4603.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 9 9 ) 0 0 5 8 1 - 2

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J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 175–180
solution was heated under reflux for 2 h whereupon it
changed from red to dark yellow. The insoluble by-
products in the reaction flask were then filtered off
under gravity and the filtrate volume was reduced to
approximately 5 cm3. A yellow product was precipi-
tated on adding diethyl ether to the filtrate, separated
off and recrystallised twice from CH2Cl2/diethyl ether
solutions. Yield: 59%. Anal. Calc. for C14H24N4Cl2Ru:
C, 40.0; H, 5.8; N, 13.3. Found: C, 39.8; H, 5.6; N,
12.7%.
2.4. [RuCl2(NCPh)2(CNBut)2] (4)
The complex was prepared in a similar manner to
that used for [RuCl2(NCMe)2(CNBut)2]. [RuCl3-
(NCPh)3] was used instead of [RuCl3(NCMe)3] and the
reactants were heated under reflux for 3 h. The product
is
a yellow solid. Yield: 78%. Anal. Calc. for
C24H28N4Cl2Ru: C, 52.9; H, 5.2; N, 10.3. Found: C,
52.5; H, 5.0; N, 10.3%.
The 1H NMR spectrum of 1 recorded in CDCl3
solution shows only the two signals (l=1.66 and 2.42
ppm), as expected.
2.5. [RuCl2(NCPh)2(CNcy)2]·CH2Cl2 (5)
The complex was prepared in a similar manner to
that used for [RuCl2(NCPh)2(CNBut)2] except that the
reactants were heated under reflux for 4 h. The product
2.2. [RuCl2(NCMe)2(CNcy)2] (2)
is
a yellow solid. Yield: 87%. Anal. Calc. for
The complex was prepared in a similar manner to
that used for [RuCl2(NCMe)2(CNBut)2] except that the
reactants were heated under reflux for 4 h. The product
C29H34N4Cl4Ru: C, 51.1; H, 5.0; N, 8.2. Found: C,
51.7; H, 5.1; N, 8.3%.
is
a yellow solid. Yield: 81%. Anal. Calc. for
2.6. [RuCl2(NCPh)2(CNxylyl)2] (6)
C18H28N4C2Ru: C, 45.7; H, 6.0; N, 11.8. Found: C,
45.2; H, 6.0; N, 11.4%.
The complex was prepared in a similar manner to
that used for [RuCl2(NCMe)2(CNxylyl)2]. [RuCl3-
(NCPh)3] was used instead of [RuCl3(NCMe)3]. The
product is a yellow solid. Yield: 78%. Anal. Calc. for
C32H28N4Cl2Ru: C, 60.0; H, 4.4; N, 8.7. Found: C,
59.6; H, 4.3; N, 8.4%.
Cyclic voltammetric experiments involved the use of
a PAR 174A polarographic analyzer and a PAR 175
waveform generator in conjunction with a Bryans In-
struments 60000 Series X-Y/t chart recorder. The ex-
periments were performed using a cell comprising a
platinum working electrode, a platinum counter-elec-
trode, and an Ag/AgCl reference electrode [8,9] cali-
brated against the ferrocenium–ferrocene couple
(+0.55 V) [10]. The voltammetric data were not cor-
2.3. [RuCl2(NCMe)2(CNxylyl)2] (3)
[RuCl3(NCMe)3] (0.10 g, 0.30 mmol) and xylyliso-
cyanide (0.20 g, 1.52 mmol) were dissolved in degassed
1:10 ethanol/dichloromethane (15 cm3) and approxi-
mately 0.2 g of mercury added. The mixture was heated
under reflux for 1 h. The insoluble by-products and
unreacted mercury in the reaction flask were filtered off
under gravity and the filtrate volume reduced to ap-
proximately 5 cm3. The yellow product which was
precipitated on adding diethyl ether to the filtrate was
recrystallised twice from CH2Cl2/diethyl ether solu-
tions. Yield: 54% Anal. Calc. for C22H24N4Cl2Ru: C,
51.2; H, 4.7; N, 10.8. Found: C, 51.2; H, 4.4; N, 10.2%.
Table 1
Analytical data on the complexes
Complex
number a
FAB mass spectral data b,c (m/z)
13C NMR signal
(ppm) d
NC
420 (M); 379 (M−MeCN); 344 (M−ClꢀMeCN); 337 (M−CNBut); 263 (M−ClꢀMeCNꢀCNBut) 152
CN
1
2
123
122
472 (M); 431 (M−MeCN); 396 (M−ClꢀMeCN); 355 (M−Clꢀ2MeCN); 286
(M−ClꢀCNcyꢀMeCN)
151
3
516 (M); 481 (M−Cl); 434 (M−2MeCN); 362 (M−2Clꢀ2MeCN); 307
(M−ClꢀMeCNꢀCNxylyl)
164
122
4
5
544 (M); 509 (M−Cl); 461 (M−CNBut); 441 (M−PhCN); 406 (M−ClꢀPhCN)
596 (M−CH2Cl2); 561 (M−Cl); 493 (M−PhCN); 458 (M−ClꢀPhCN); 349
(M−ClꢀPhCNꢀCNcy)
150
151
113
112
6
640 (M); 605 (M−Cl); 537 (M−PhCN); 502 (M−ClꢀPhCN); 473 (M−ClꢀCNxylyl)
163
112
a Refer to Section 2 for the identification of the complexes.
b Recorded in 3-nitrobenzyl alcohol matrix.
c M=molecular ion.
d Recorded in CDCl3 solvent.

J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 175–180
177
rected for the IR drop across the working and reference
electrodes. The dichloromethane solvent was dried over
KOH and distilled from CaH2 prior to use; the sup-
porting electrolyte, tetra-n-butylammonium hexafluoro-
phosphate, was prepared as described previously [8,9].
Voltammetric and spectroelectrochemical experiments
were carried out in 0.5 mol dm−3 [NBu4n ][PF6]/CH2Cl2.
Infrared (IR) spectroelectrochemical experiments
were performed using an IRRAS cell mounted on a
modified Specac specular reflectance attachment located
in the sample compartment of a Nicolet Magna 750
FTIR spectrometer [6]. The electrode arrangement con-
sisted of a highly polished platinum disc electrode (5
mm diameter), a platinum gauze counter-electrode, and
a platinum wire pseudo-reference electrode. All spectro-
electrochemical experiments were performed by first
stepping to a potential of approximately 0.2 V past the
appropriate E1/2 and then collecting single-scan IR
spectra (resolution=1 cm−1) as a function of time.
Ultraviolet–visible (UV–Vis) spectroelectrochemical
experiments were performed using a cryostated OTTLE
cell [7] positioned in the sample compartment of a
Perkin–Elmer Lambda 16 spectrophotometer. The cell
contained a platinum gauze working electrode (ca. 75%
transmission), a platinum wire counter-electrode, and a
platinum pseudo-reference electrode.
NMR spectra were recorded on a Bruker AMX 400
MHz spectrometer. Positive-ion FAB mass spectra were
obtained with a VG ZAB 2SE mass spectrometer.
3. Results and discussion
The cyclohexylisocyanide and tert-butylisocyanide
derivatives were prepared according to the following
reaction scheme:
NCR
CNR%
RuCl3 ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁ RuCl3(NCR)3 ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁ
MeOH reflux
EtOH/CH Cl reflux
2 2
RuCl2(NCR)2(CNR%)2
Reduction of [RuCl3(NCR)3] under the stated condi-
tions results in the elimination of a chloride and the
facile replacement of one cyanide by isocyanide.
[RuCl3(NCR)3] complexes are thus found to be conve-
nient precursors for the preparation of certain com-
plexes of the type [RuCl2(NCR)2(CNR%)2]. It was found
that mercury had to be used in the preparation of the
xylylisocyanide derivatives because this ligand does not
coordinate to ruthenium(III) under the specified condi-
tions. However, the ruthenium(II) species produced by
the mercury reduction readily coordinates to xylyliso-
cyanide since the latter is a better p-acceptor than either
cyclohexylisocyanide or tert-butylisocyanide [11]. All
the products are stable in air and moderately soluble in
dichloromethane. They were characterised by elemental

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J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 175–180
analysis, fast atom bombardment mass spectroscopy,
13C NMR, IR and UV–Vis spectroscopy (Tables 1
and 2). The complexes gradually decompose over 24
h in air in dichloromethane solution. All attempts to
grow single crystals of the complexes were unsuccess-
ful.
Vibrational data for the complexes are reported in
Table 2. Bands arising from cyanide (wCN) and iso-
cyanide (wNC) stretching vibrations occur in the region
2100–2300 cm−1. Each complex shows a single wCN
and wNC band both in solution and in the solid state,
implying that the complexes have a common structure
in which each pair of the same ligands has the trans
arrangement.
The electronic absorption spectra of the complexes
(Table 2) each show a band in the 23 000–27 000
cm−1 region and two or more intense bands above
30 000 cm−1. The less intense bands arise from
MLCT transitions of the type Ru(dp)“CNR%(p*),
i.e. they involve excitation of metal dp electrons into
low-lying antibonding p orbitals of the isocyanide lig-
ands. The charge transfer energies associated with
these bands reflect the different p-acceptor capacities
of the ligands, viz. CNBut, CNcyBCNxylyl. The
more intense bands may arise from either MLCT or
intraligand transitions.
The redox behaviour of the complexes was studied
by cyclic voltammetry and the results are given in
Table 2. The complexes exhibit quasi-reversible
Ru(II)/Ru(III) oxidations in 0.5 mol dm−3
[NBun4 ][PF6]/CH2Cl2. Departure from reversible be-
haviour is indicated by DEp values which increase
with increasing scan rates and which are greater than
the ideal Nernstian value of 59 mV (DEp=separation
between anodic and cathodic peak potentials). The
E1/2 values of the Ru(II)/Ru(III) oxidations also
reflect the different p-acceptor capacities of the lig-
ands, viz. NCMeBNCPh and CNBut, CNcyBCNxy-
lyl.
Data relating to the IR spectroelectrochemical ex-
periments on the complexes are reported in Table 2.
The wNC and wCN bands in trans, trans, trans-
[RuCl2(NCPh)2(CNcy)2] occur at 2150 and 2251
cm−1, respectively (Fig. 1). Upon oxidation at +1.2
V these bands collapse and new ones grow at 2223
and 2278 cm−1, the former being assigned to wNC and
the latter to wCN. The fact that only a single band
occurs in each region implies that each product, like
its precursor, has the trans, trans, trans-octahedral ge-
ometry. Each of the complexes could be reversibly
oxidised in an IRRAS cell at room temperature, al-
though the ratio, I(wCN)/I(wNC), of the cyanide/iso-
cyanide band intensities is less for the methylcyanide
than for the phenylcyanide complexes (Fig. 2). The
increase in both wNC and wCN on oxidation of Ru(II)
to Ru(III) is consistent with generally accepted bind-
ing differences between these oxidation states.
Data relating to the UV–Vis spectroelectrochemical
experiments are also reported in Table 2. The spec-
trum of trans, trans, trans-[RuCl2(NCPh)2(CNcy)2]
shows bands arising from MLCT and intraligand
transitions mainly in the UV region. Upon oxidation
at +1.2 V these bands collapse with the growth of
bands at 22 600, 20 300 and 19 000 cm−1 (Fig. 3).
The band at 19 000 cm−1 arises from a transition of
the type Cl(p)“Ru(dp) while that at 20 300 cm−1 is
due to a CN(p)“Ru(dp) transition [2,12]. The band
observed at 22 600 cm−1 arises from a NC(p)“
Ru(dp) transition, and in the spectrum of the
analogous methylcyanide derivative, it is red-shifted
as expected (Fig. 4). The other ruthenium complexes
likewise each show intense bands in the 19 000–
Fig. 1. Changes in the IR differential absorbance spectra upon oxidation of trans, trans, trans-[RuCl2(NCPh)2(CNcy)2] in an IRRAS cell at r.t.

J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 175–180
179
Fig. 2. Changes in the IR differential absorbance spectra of trans, trans, trans-[RuCl2(NCMe)2(CNcy)2] upon oxidation in an IRRAS cell at r.t.
A solvent peak (*) occurs at 2307 cm−1
.
Fig. 3. Changes in the electronic spectrum of trans, trans, trans-[RuCl2(NCPh)2(CNcy)2] upon oxidation in an OTTLE cell at r.t.
Fig. 4. Changes in the electronic spectrum of trans, trans, trans-[RuCl2(NCMe)2(CNcy)2] upon oxidation in an OTTLE cell at r.t.

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J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 175–180
26 000 cm−1 region arising from similar LMCT transi-
tions. Each of the ruthenium(II) complexes could be
oxidised reversibly in an OTTLE cell at r.t. (Fig. 4).
Council for the award of a Commonwealth Fellowship.
M.S.S. thanks CONICYT and the British Council for
funding her research at University College London.
4. Conclusion
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Acknowledgements
The authors thank Dr D.G. Humphrey (CSIRO
Forestry and Forest Products, Victoria, Australia) for
useful comments. J.P.A. is grateful to the EPSRC for a
postgraduate studentship. M.A.S. thanks the British
.