Redox properties of two new ruthenium(III) isocyanide complexes, trans-[NBu4][RuX4(CNTM)2](X = Cl or Br, CNTM = p-tolylsulfonylmethylisocyanide)

Article abstract of DOI:10.1016/S0020-1693(99)00587-3

New ruthenium(III) complexes trans-[NBu₄][RuX₄(CNTM)₂] (X=Cl or Br, CNTM = p-tolylsulfonylmethylisocyanide) have been prepared by treating [NBu₄]₂[RuX₆] with the isocyanide ligand CNTM in EtOH-CH₂Cl₂ solution. In situ IR and UV-Vis spectroelectrochemical studies have shown that reduction of trans-[RuX₄(CNTM)₂] in acetonitrile and subsequent oxidation yields mer,trans-[RuX₃(CNTM)₂(NCMe)]. Similar studies have shown, interestingly, that oxidation of trans-[RuX₄(CNTM)₂]^- and subsequent reduction also yields the same product. Differences between the redox behaviour of trans-[RuX₄(CNTM)₂]^- and trans-[RuX₄(CN(t)Bu)²]^- (X = Cl or Br, CN(t)Bu = tert-butylisocyanide) in the presence of free isocyanide ligand have also been identified. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00587-3

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Inorganica Chimica Acta 300–302 (2000) 525–530
Redox properties of two new ruthenium(III) isocyanide complexes,
trans-[NBu4][RuX4(CNTM)2](X=Cl or Br,
CNTM=p-tolylsulfonylmethylisocyanide)
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 15 November 1999; accepted 28 November 1999
Abstract
New ruthenium(III) complexes trans-[NBu4][RuX4(CNTM)2] (X=Cl or Br, CNTM=p-tolylsulfonylmethylisocyanide) have
been prepared by treating [NBu4]2[RuX6] with the isocyanide ligand CNTM in EtOH–CH2Cl2 solution. In situ IR and UV–Vis
spectroelectrochemical studies have shown that reduction of trans-[RuX4(CNTM)2]− in acetonitrile and subsequent oxidation
yields mer,trans-[RuX3(CNTM)2(NCMe)]. Similar studies have shown, interestingly, that oxidation of trans-[RuX4(CNTM)2]−
and subsequent reduction also yields the same product. Differences between the redox behaviour of trans-[RuX4(CNTM)2]− and
trans-[RuX4(CNtBu)2]− (X=Cl or Br, CNtBu=tert-butylisocyanide) in the presence of free isocyanide ligand have also been
identified. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Redox properties; Ruthenium(III) complexes; Isocyanide complexes; Spectroelectrochemical studies; IRRAS and OTTLE cell
measurements
electrochemical (IR and UV–Vis) studies have shown
that these complexes can also undergo halide substi-
1. Introduction
tution upon oxidation [7,8]. This unexpected result
means that reduction followed by oxidation or oxida-
tion followed by reduction, of trans-[RuX4(CN-
tBu)2]− in the presence of certain ligands may ulti-
mately lead to the formation of the same substituted
product.
In this publication, the isocyanide ligand p-tolylsul-
fonylmethylisocyanide, CH3(C6H4)·SO2CH2NC, has
been investigated since it is a poorer s-donor than
tert-butylisocyanide and thus its ruthenium(III) com-
plexes may be expected to display different redox prop-
erties from those of tert-butylisocyanide. Two new
ruthenium(III) complexes of p-tolylsulfonylmethyliso-
cyanide have been prepared and their redox behaviour
investigated by means of infrared reflection-absorption
spectroscopy (IRRAS) [9] and, in an optically transpar-
ent thin-layer electrochemical (OTTLE) cell [10], by
electronic spectroscopy. The results of these spec-
troelectrochemical (IR and UV–Vis) studies are pre-
sented and discussed herein.
Isocyanide ligands are isoelectronic with carbon
monoxide and form transition metal complexes
analogous to metal carbonyls [1]. However, in general,
they are better s-donors than CO but poorer p-accep-
tors [2] and consequently isocyanide cations are well-
known, but homoleptic isocyanide anions [3] are rare.
Furthermore, isocyanide ligands can stabilise metal ions
in relatively high oxidation states, for example as in
[Cr(CNR)6]3+ [4] and [Mo(CNR)7]2+ [5], for which the
carbonyl analogues are unknown. This means that a
wider range of oxidation states is usually accessible for
isocyanide than carbonyl systems.
Recently, the redox properties of the complexes
trans-[NBu4][RuX4(CNtBu)2] (X=Cl or Br) [6–8] were
reported. These complexes readily undergo halide sub-
stitution upon reduction with neutral donor ligands
such as acetonitrile or pyridine. In addition, spectro-
* Corresponding author. Tel.: +44-171-387 7050; fax: +44-171-
504 4603.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00587-3

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2. Experimental
(A−); 733 (A−ꢀBr); 617 (A−ꢀCNTM); 538 (A−
ꢀBrꢀCNTM); 422 (A−ꢀ2CNTM) amu. A− refers to the
ion fragment trans-[RuBr4(CNTM)2]− (assignments are
based on 102Ru and 79Br).
Commercial RuCl3·xH2O was obtained from
Johnson–Matthey. The isocyanide ligand p-tolylsul-
fonylmethylisocyanide (CNTM) was purchased from
Avocado. The complexes [NBu4]2[RuCl6] [11] and
[NBu4]2[RuBr6] [12] were prepared by published meth-
ods. Both ruthenium(III) isocyanide complexes were
prepared under a nitrogen atmosphere using standard
Schlenk-line techniques.
Cyclic voltammetric experiments utilised a PAR
174A polarographic analyzer and a PAR 175 waveform
generator in conjunction with a Bryans Instruments
60000 Series X-Y/t chart recorder. The experiments
were performed using a cell comprising a platinum
working electrode, a platinum counter-electrode, and
an Ag/AgCl reference electrode [13] calibrated against
the ferrocenium–ferrocene couple (+0.55 V) [14]. The
voltammetric data were not corrected for the IR drop
across the working and reference electrodes. The sol-
vents dichloromethane [13] and acetonitrile [15] were
dried and distilled from CaH2 prior to use; the support-
ing electrolyte, tetra-n-butylammonium hexafluoro-
phosphate, was prepared as described previously [13].
Infrared (IR) spectroelectrochemical experiments
were performed using an IRRAS cell [9] mounted on a
modified Specac specular reflectance attachment located
in the sample compartment of a Nicolet Magna 750
FTIR spectrometer. 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 spec-
troelectrochemical 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 [10] 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.
2.1. Preparation of trans-[NBu4][RuCl4(CNTM)2]
[NBu4]2[RuCl6] (0.10 g, 0.13 mmol) and CNTM (0.10
g, 0.50 mmol) were dissolved in a degassed 1:20
ethanol–dichloromethane (30 cm3) solution. The mix-
ture was stirred for 24 h at room temperature where-
upon it changed from dark brown to dark yellow. Then
the insoluble by-products were filtered off under gravity
and the filtrate volume was reduced to approximately 5
cm3. A dark yellow solid was precipitated on adding
diethyl 1:1 ether–hexane solution to the filtrate. The
product was recrystallised twice from CH2Cl2–diethyl
ether solution. Yield: 51%. Anal. Calc. for
C34H54N3S2O4Cl4Ru: C, 46.6; H, 6.2; N, 4.8; Cl, 16.2;
S, 7.3. Found: C, 46.3; H, 6.0; N, 4.7; Cl, 16.9; S, 7.5%.
IR spectrum (KBr disc): wNC=2168 cm−1. Electronic
absorption spectrum (CH2Cl2 solvent): wmax (m (dm3
mol−1 cm−1)) 19 300 (500), 22 700 (6700), 32 000
(2500), 38 000 (15 000), 42 000 (20 000) cm−1. Nega-
tive-ion FAB mass spectrum: major m/z peaks at 634
(A−); 599 (A−ꢀCl); 439 (A−ꢀCNTM); 244 (A−ꢀ2
CNTM) amu. A− refers to the ion fragment trans-
[RuCl4(CNTM)2]− (assignments are based on 102Ru
and 35Cl).
2.2. Preparation of trans-[NBu4][RuBr4(CNTM)2]
Negative-ion FAB mass spectra were recorded on a
VG ZAB 2SE mass spectrometer.
[NBu4]2[RuBr6] (0.10 g, 0.09 mmol) and CNTM (0.07
g, 0.36 mmol) were dissolved in a degassed 1:20
ethanol–dichloromethane (30 cm3) solution. The mix-
ture was stirred for 7 h at room temperature whereupon
it changed from dark blue to violet. Then the insoluble
by-products were filtered off under gravity and the
filtrate volume was reduced to approximately 5 cm3. A
violet solid was precipitated on adding diethyl ether to
the filtrate. The product was recrystallised twice from
CH2Cl2/diethyl ether. Yield: 78%. Anal. Calc. for
C34H54N3S2O4Br4Ru: C, 38.8; H, 5.2; N, 4.0; Br, 30.3;
S, 6.1. Found: C, 38.9; H, 5.0; N, 4.0; Br, 30.2; S, 6.2%.
IR spectrum (KBr disc): wNC=2161 cm−1. Electronic
absorption spectrum (CH2Cl2 solvent): wmax (m (dm3
mol−1 cm−1)) 14 000 (500), 16 500 (6700), 18 000
(4800), 19 700 (1300), 21 400 (1700), 26 000sh (1800),
30 500 (7500), 38 500 (17 000), 42 000 (24 000). Nega-
tive-ion FAB mass spectrum: major m/z peaks at 812
3. Results and discussion
3.1. Reducti6e chemistry of
trans-[NBu4][RuBr4(CNTM)2] in acetonitrile
The cyclic voltammogram of trans-[NBu4][RuBr4-
(CNTM)2] recorded in 1:1 acetonitrile–dichloro-
methane solution displays a one-electron reduction
(E1/2= −0.01 V) to trans-[RuBr4(CNTM)2]2− (Fig.
1(a)). The trans-[RuBr4(CNTM)2]−/2− couple is quasi-
reversible since it displays DEp values which increase with
increasing scan rates. The reduced species reacts rapidly
with acetonitrile to form an electroactive species which

J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 525–530
527
Fig. 1. Cyclic voltammograms showing (a) reductive cycle, (b) oxidative cycle of trans-[NBu4][RuBr4(CNTM)2] in 1:1 acetonitrile–
dichloromethane containing 0.25 mol dm−3 [NBu4][PF6] at r.t. vs. AgꢀAgCl, scan rate=100 mV s−1. Arrows indicate commencement of scan
direction.
shifted to 2194 cm−1 and wCN to 2335 cm−1. The
can be detected on the return scan (Epa= +0.54 V).
changes in the wNC throughout this redox sequence
imply that the coordinated CNTM ligands remain in
the trans configuration, i.e. that the ultimate product of
reduction is mer,trans-[RuBr3(CNTM)2(NCMe)]−,
which can be reversibly oxidised to mer,trans-
[RuBr3(CNTM)2(NCMe)] (Table 1)2. The halide
The latter is not observed if the cathodic scan is
switched prior to the detection of the trans-[RuBr4-
(CNTM)2]−/2− reduction wave nor if the solution is
held throughout the redox cycle below 273 K. These
observations indicate that trans-[RuBr4(CNTM)2]− dis-
plays EC-type [16] behaviour whereby electron trans-
fer(E) is followed by
a homogeneous chemical
reaction(C) which gives rise to a new species (Epa=
+0.54 V) in solution. The shift in E1/2(Ru(III/II)) (ca.
+0.6 V) between trans-[RuBr4(CNTM)2]2− and the
newly formed species indicates that the latter is
[RuBr3(CNTM)2(NCMe)] [17]. Two irreversible waves
are detected at : +0.9 and +1.2 V, observations
which relate to the oxidation of bromide expelled from
trans-[RuBr4(CNTM)2]2−
.
The changes in the IR spectra accompanying the
reduction and subsequent oxidation of trans-
[RuBr4(CNTM)2]− in 1:1 acetonitrile–dichloromethane
solution in an IRRAS cell are also informative. The wNC
band of the coordinated isocyanide ligand in trans-
[RuBr4(CNTM)2]− occurs at 2170 cm−1 and, upon
reduction at Eapp= −0.20 V1, it collapses with the
growth of bands at 2282, 2109 and 2038 cm−1 (Fig. 2,
Table 1). The bands at 2109 and 2038 cm−1 can be
assigned to wNC of the isocyanide in the reduced species
whilst the band at 2282 cm−1 is due to wCN of newly
coordinated acetonitrile. Oxidation of the reduced spe-
cies occurs at Eapp= +0.75 V, whereupon wNC is
Fig. 2. Changes in the IR differential absorbance spectra accompany-
ing the reduction of trans-[NBu4][RuBr4(CNTM)2] (ca. 10 mmol
dm−3) in 1:1 acetonitrile–dichloromethane (2 cm3) containing 0.25
mol dm−3 [NBu4][PF6] at 298 K.
2 The complex mer,trans-[RuBr3(CNTM)2(NCMe)] has skeletal C26
symmetry and therefore should display two wNC (a1+b1) bands in its
IR spectrum. However, the dipole moment change for the a1 mode is
nearly zero and usually only the strong b1 band is detected. The
reduced species has lower symmetry on account of back-bonding
(Ru(II) to CN(p*)) along its RuꢀCNꢀC axes and consequently its a1
mode becomes detectably IR active.
1 Eapp refers to the potential at which the electrolysis was per-
formed in the IRRAS or OTTLE cell.

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J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 525–530
Table 1
IR spectroelectrochemical data
a
a
Complex (z=charge)
Band maxima (cm−1
)
Ru(II)
Band maxima (cm−1
)
Ru(III)
wNC
wCN
wNC
wCN
[RuCl3(CNTM)2(NCMe)]z b
[RuBr3(CNTM)2(NCMe)]z b
[RuCl3(CNTM)3]z c
2110 (s) 2043 (m)
2109 (s) 2038 (m)
2141 (w) 2086 (m) 2034 (m)
2144 (m) 2088 (m) 2035 (m)
2275 (w)
2282 (w)
2202 (s)
2194 (s)
2242 (w) 2208 (m) 2178 (s)
2235 (w) 2199 (m) 2169 (s)
2332(w)
2335(w)
[RuBr3(CNTM)3]z c
a Recorded in an IRRAS cell under conditions stated in the text. Relative band intensities: s=strong, m=medium and w=weak.
b mer,trans-isomer.
c mer-isomer.
3.3. Redox chemistry of trans-[NBu4][RuCl4(CNTM)2]
in acetonitrile
configuration of the latter is confirmed by UV–Vis
spectroscopy since such ruthenium(III)-halide species
display diagnostic halide-to-metal charge-transfer spec-
tra [11]. The reduction of trans-[RuBr4(CNTM)2]−
The redox behaviour of the analogous chloride is
qualitatively very similar. Cyclic voltammetric experi-
(Eapp= −0.20 V) and its subsequent oxidation (Eapp
=
+0.75 V) in an OTTLE cell produces a spectrum
characteristic of a complex with a meridional arrange-
ment of bromide ions (Fig. 3, Table 2).
3.2. Oxidati6e chemistry of
trans-[NBu4][RuBr4(CNTM)2] in acetonitrile
The species trans-[RuBr4(CNTM)2]− in 1:1 acetoni-
trile–dichloromethane solution undergoes irreversible
oxidation (Epa= +1.58 V) and ultimately forms an
electroactive species detected at Epc= +0.54 V on the
return scan (Fig. 1(b)). Both IR and UV–Vis spec-
troelectrochemical experiments show that the product
of oxidation followed by reduction of trans-
[RuBr4(CNTM)2]−
is
mer,trans-[RuBr3(CNTM)2-
(NCMe)] since the final spectra thus formed are identi-
cal to those obtained following reduction and subse-
quent oxidation of trans-[RuBr4(CNTM)2]− in
acetonitrile.
Fig. 3. The UV–Vis spectra of trans-[NBu4][RuBr4(CNTM)2] (—)
and mer,trans-[RuBr3(CNTM)2(NCMe)] (---). The initial complex
(ca. 1.6 mmol) was dissolved in 1:1 acetonitrile–dichloromethane (1.4
cm3) containing 0.25 mol dm−3 [NBu4][PF6] at 298 K.
Table 2
UV–Vis spectroelectrochemical data
a
a
Complex (z=charge)
Band maxima (cm−1
)
Ru(II)
Band maxima (cm−1
)
Ru(III)
[RuCl3(CNTM)2(NCMe)]z b
[RuBr3(CNTM)2(NCMe)]z b
[RuCl3(CNTM)3]z c
35700 (s), 41000 (vs)
38000 (m), 43000 (vs)
18800 (m), 22400 (s), 39000 sh
14300 (m), 16800 (s), 29000 sh, 32800 (s)
17200 (m), 19700 (s), 33000 sh, 38000 (vs)
18900 (s), 24100 (w), 36000 (vs), 40000 (vs)
33000 sh, 38000 (vs), 42000 (vs)
25000 sh, 33000 (w), 37000 (vs)
23500 (w), 31000 sh, 38000 (vs), 42000 (vs) 12400 (s), 17900 (w), 37500 (vs), 40500 (vs)
[RuCl2(CNTM)4]z d
[RuBr2(CNTM)4]z d
a Recorded in an OTTLE cell under conditions stated in the text. Relative band intensities: vs=very strong, s=strong, m=medium and
w=weak.
b mer,trans-isomer.
c mer-isomer.
d trans-isomer.

J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 525–530
529
ments show that reduction of trans-[RuCl4(CNTM)2]
in 1:1 acetonitrile–dichloromethane solution at −0.10
V leads to the formation of an electroactive species
detected at E1/2= +0.51 V on the return scan. Oxida-
tion of the same complex at +1.70 V also leads to the
formation of an electroactive species detected at the
same potential (E1/2= +0.51 V). Both IR and UV–Vis
spectroelectrochemical studies indicate that the species
formed upon either reduction followed by oxidation or
oxidation
followed
by
reduction
of
trans-
[RuCl4(CNTM)2]− in the presence of acetonitrile is
mer,trans-[RuCl3(CNTM)2(NCMe)] (Table 1). The visi-
ble spectrum of mer,trans-[RuCl3(CNTM)2(NCMe)]
shows bands at 22400 and 18800 cm−1 arising from
transitions of the type Cl(pp)“Ru(dp) [11] (Table 2). It
Fig. 4. The electrogeneration of mer-[RuCl3(CNTM)3]− from trans-
[NBu4][RuCl4(CNTM)2] in an IRRAS cell. The initial complex (ca.
10 mmol dm−3) and CNTM ligand (ca. 15 mmol dm−3) were
dissolved in dichloromethane (2 cm3) containing 0.5 mol dm−3
[NBu4][PF6] at 243 K.
is
proposed
that
the
complexes
mer,trans-
[RuX3(CNTM)2(NCMe)] are formed by the same free
radical mechanism as that discussed for the formation
of mer,trans-[RuBr3(CNtBu)2(NCMe)] [7].
3.4. Redox chemistry of trans-[NBu4][RuX4(CNTM)2]
in the presence of uncoordinated CNTM
Both complex ions trans-[RuX4(CNTM)2]− (X=Cl
or Br) also undergo reduction-induced halide substitu-
tion with neutral donor ligands other than acetonitrile.
For example, in dichloromethane solution, the wNC
band of the coordinated isocyanide in trans-
[RuCl4(CNTM)2]− occurs at 2176 cm−1 and, upon
reduction at Eapp= −0.30 V in the presence of free
CNTM, it collapses with the growth of bands at 2141,
2086 and 2034 cm−1 arising from the formation of
mer-[RuCl3(CNTM)3]− (Fig. 4, Table 1). Oxidation at
Eapp= +1.30 V leads to the collapse of these bands
and the growth of new ones at 2242, 2208 and 2178
cm−1 corresponding to the formation of mer-
[RuCl3(CNTM)3] (Fig. 5, Table 1). Under the same
conditions trans-[RuBr4(CNTM)2]− can be reduced to
mer-[RuBr3(CNTM)3]− which in turn can be oxidised
to mer-[RuBr3(CNTM)3] (Table 1). These results differ
from those established for the analogous complexes of
tert-butylisocyanide, viz. trans-[NBu4][RuX4(CNtBu)2]
in dichloromethane, since the reduction and subsequent
oxidation of the latter in the presence of free CNtBu
yields the disubstituted species trans-[RuX2(CNtBu)4]+
[9]. This implies that CNtBu is capable of exerting a
stronger trans-influence than CNTM when present in
complexes of the type trans-[NBu4][RuX4(CNR)2]. Oxi-
dation and subsequent reduction of trans-
[RuX4(CNTM)2]− in dichloromethane in the presence
of free CNTM also leads to the formation of mer-
[RuX3(CNTM)3]. The shorter timescale of an IRRAS
experiment compared to one performed using an OT-
TLE cell favours the detection of monosubstituted spe-
cies such as mer-[RuX3(CNTM)3] which may be
short-lived.
Fig. 5. Electrogeneration of mer-[RuCl3(CNTM)3] from mer-
[RuCl3(CNTM)3]− in an IRRAS cell under the conditions indicated
in the caption for Fig. 4.
Fig. 6. The UV–Vis spectra of trans-[NBu4][RuCl4(CNTM)2] (—)
and mer-[RuCl3(CNTM)3] (---). The initial complex (ca. 1.6 mmol)
and CNTM ligand (ca. 5 mmol) were dissolved in dichloromethane
(2 cm3) containing 0.5 mol dm−3 [NBu4][PF6] at 298 K.

530
J.P. al Dulaimi et al. / Inorganica Chimica Acta 300–302 (2000) 525–530
In an OTTLE cell, reduction of trans-
[RuCl4(CNTM)2]− in dichloromethane in the presence
of free CNTM at Eapp= −0.30 V leads to the forma-
tion of a ruthenium(II) species which upon oxidation at
E
app= +1.70 V yields trans-[RuCl2(CNTM)4]+. The
visible spectrum of the latter is typical of a complex
with a trans arrangement of chloride ions [11], showing
a single band at 18 900 cm−1 arising from a halide-to-
metal charge transfer (XMCT) (Table 2). However,
under the same conditions, oxidation of trans-
[RuCl4(CNTM)2]− at Eapp= +1.90 V followed by re-
duction yields mer-[RuCl3(CNTM)3], which shows
XMCT bands at 19 700 and 17 200 cm−1 in its visible
spectrum (Fig. 6, Table 2).
In an OTTLE cell, reduction of the analogous
bromo species, trans-[RuBr4(CNTM)2]−, in dichloro-
methane in the presence of CNTM at Eapp= −0.20 V
followed by oxidation at Eapp= +1.70 V yields trans-
[RuBr2(CNTM)4]+ (Table 2). However, trans-
[RuBr4(CNTM)2]−, differs from trans-[RuCl4(CN-
TM)2]− in that, under the same conditions, its oxidative
cycle leads to the formation of the same species, viz.
trans-[RuBr2(CNTM)4]+, as obtained in the reductive
cycle described above. Limiting the amount of free
ligand present in solution does not yield mer-
[RuBr3(CNTM)3] but only a decrease in the amount of
disubstituted species formed.
In general, the complexes trans-[NBu4][RuX4-
(CNTM)2] have similar redox properties to the
analogous ones formed by tert-butylisocyanide. How-
ever, there is one significant difference; the reduction
and subsequent oxidation of trans-[RuX4(CNTM)2]− in
an IRRAS cell and in the presence of free CNTM
yields mer-[RuX3(CNTM)3], whereas the reduction and
subsequent oxidation of trans-[RuX4(CNtBu)2]- in the
presence of free CNtBu yields trans-[RuX2(CNtBu)4]+.
Acknowledgements
J.P.A. thanks the EPSRC for a postgraduate award.
M.A.S. is indebted to the Commonwealth Scholarship
Commission for an award of a Commonwealth Fellow-
ship. M.S.S. thanks CONICYT for funding her re-
search at University College London.
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