Some ruthenium complexes containing cyanocarbon ligands: Syntheses, structures and extent of electronic communication in binuclear systems

Article abstract of DOI:10.1016/j.jorganchem.2004.07.030

The preparation of several ruthenium complexes containing cyanocarbon anions is reported. Deprotonation (KOBu′) of [Ru(NCCH₂Ph₃)₂Cp]PF₆ (1) gives Ru{N=C=CH(CN)}(PPh₃)₂Cp (2), which adds a second [Ru(PPh₃)₂Cp]⁺ unit to give [{Ru(PPh₃)₂Cp}₂ (μ-NCCHCN)]⁺ (3). Attempted deprotonation of the latter to give the μ-NCCCN complex was unsuccessful. Similar chemistry with tricyanomethanide anion gives Ru{N=C=C(CN)₂} (PPh₃)₂Cp (4) and [{Ru(PPh₃) ₂Cp} 2 {μ-NCC(CN)CN}]PF₆(5), and with pentacyanopropenide, Ru{N=C=C(CN)C(CN)C(CN)₂} (PPh₃)₂Cp (6) and [{Ru(PPh₃)₂Cp}₂ {μ-NCC(CN)C(CN)C(CN)CN}]PF₆ (7). The Ru(dppe)Cp* analogues of 6 and 7 (8 and 9) were also prepared. Thermolysis of 6 (refluxing toluene, 12 h) results in loss of PPh₃ and formation of the binuclear cyclic complex {Ru(PPh₃) Cp[μ-N=C={C(CN)=C(CN)₂}CN]}₂ (10). The solid-state structures of 2-4 and 8-10 have been determined and the nature of the isomers shown to be present in solutions of the binuclear cations 7 and 9 by NMR studies has been probed using Hartree-Fock and density functional theory.

Full text of DOI:10.1016/j.jorganchem.2004.07.030

Journal of Organometallic Chemistry 689 (2004) 3308–3326
www.elsevier.com/locate/jorganchem
Some ruthenium complexes containing cyanocarbon
ligands: syntheses, structures and extent of electronic
communication in binuclear systems
a,
a
a
Michael I. Bruce *, Mark A. Buntine , Karine Costuas a,b, Benjamin G. Ellis ,
Jean-Franc¸ois Halet , Paul J. Low a,c, Brian W. Skelton , Allan H. White
b
d
d
a
Department of Chemistry, University of Adelaide, Adelaide, SA 5005, Auatralia
b
´
LCSIM UMR CNRS 6511, Institut de Chimie, Universite de Rennes 1, 35042, Rennes Cedex, France
c
Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, England
Department of Chemistry, University of Western Australia, Crawley, WA 6009, Australia
d
Received 10 May 2004; accepted 15 July 2004
Available online 28 August 2004
Abstract
The preparation of several ruthenium complexes containing cyanocarbon anions is reported. Deprotonation (KOBut) of
[Ru(NCCH2CN)(PPh3)2Cp]PF6 (1) gives Ru{N‚C‚CH(CN)}(PPh3)2Cp (2), which adds a second [Ru(PPh3)2Cp]+ unit to give
[{Ru(PPh3)2Cp}2(l-NCCHCN)]+ (3). Attempted deprotonation of the latter to give the l-NCCCN complex was unsuccessful. Sim-
ilar chemistry with tricyanomethanide anion gives Ru{N‚C‚C(CN)2}(PPh3)2Cp (4) and [{Ru(PPh3)2Cp}2{l-NCC(CN)CN}]PF6
(5), and with pentacyanopropenide, Ru{N‚C‚C(CN)C(CN)C(CN)2}(PPh3)2Cp (6) and [{Ru(PPh3)2Cp}2{l-NCC(CN)C(CN)C-
(CN)CN}]PF6 (7). The Ru(dppe)Cp* analogues of 6 and 7 (8 and 9) were also prepared. Thermolysis of 6 (refluxing toluene, 12 h)
results in loss of PPh3 and formation of the binuclear cyclic complex {Ru(PPh3)Cp[l-N‚C‚{C(CN)‚C(CN)2}CN]}2 (10). The
solid-state structures of 2–4 and 8–10 have been determined and the nature of the isomers shown to be present in solutions of
the binuclear cations 7 and 9 by NMR studies has been probed using Hartree–Fock and density functional theory.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Cyanocarbon; Redox properties; Conformations; DFT; Electronic interactions
1. Introduction
the first reports being given by Davies and coworkers
[6]. More recent applications linking these groups to
manganese or iron phthalocyanine centres [7], binuclear
Ru2(l-LL)4 [LL = MeCO2, 2-anilinopyridinate, 2-(2-
fluoroanilino)pyridinate] centres [8], metal hexafluoro-
acetylacetonates [8] and hexanuclear Cu6 aggregates [9]
have been reported. Cyanometallates [10] and carbonyl-
cyanometallates [11] have also been used as building
blocks for the assembly of a range of unusual manganese
derivatives. The ready coordination of organic nitrile
groups to metal centres has also resulted in the prepara-
tion of many complexes with these ligands bridging
two or more metal centres. Examples include various
The cyano group has been used as a ligand to bridge
transition metal centres since the early days of coordina-
tion chemistry [1–3]. A great deal of contemporary inter-
est is centred around the use of CN ligands in the design
and control of molecular shape, the cyanide-isocyanide
isomerism and electron-transfer processes [4,5]. Com-
monly used metal-containing building blocks include
the Fe(dppe)Cp and Ru(PPh3)2Cp groups, with one of
*
Corresponding author. Fax: +61 8 8303 4358.
E-mail address: michael.bruce@adelaide.edu.au (M.I. Bruce).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.030

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3309
dinitriles [12,13], while cyano-carbon and -nitrogen ani-
2. Results
ons have proved to be versatile constituents of electro-
and magnetically active materials [14]. The structure
and electrochemical properties of the anionic complex
[W{NCC(CN)C(CN)C(CN)2}(CO)5]ꢀ have been de-
scribed [15] and more recently, metal–metal interactions
through the CH2CN bridge in [M(NCCH2-
Fc)(L)2Cp]PF6 (M = Fe, Ru; L = PPh3, dppe/2) have
been claimed [16]. Vahrenkampꢀs perspective [2] allows
access to many relevant reviews and papers.
On an earlier occasion we described the preparation
of [Ru(NCCH2CN)(PPh3)2Cp]PF6 (1) from RuCl-
(PPh3)2Cp, malononitrile and NH4PF6 in methanol
[18]. Treatment of 1 with KOBut in thf gave the neutral
complex Ru(NCCHCN)(PPh3)2Cp (2) as a bright yellow
solid in nearly quantitative yield. Combination of equi-
molar amounts of 2 with [Ru(NCMe)(PPh3)2Cp]PF6 in
refluxing thf, followed by precipitation with hexane, af-
forded binuclear [{Ru(PPh3)2Cp}2(l-NCCHCN)]PF6
(3) in 91% yield (Scheme 1).
These compounds were readily characterised by ele-
mental analyses and from their spectroscopic data. For
example, the IR spectra contained m(CN) bands be-
tween 2100 and 2250 cmꢀ1. The cationic complex 1
gave rise to m(CN) bands at 2269 and 2259 cmꢀ1 which
may be compared with that in malononitrile
(2305 cmꢀ1) and indicates a limited mixing of the metal
and cyanocarbon p-type MOs. The predominant inter-
action is ligand ! metal r-donation through the nitro-
gen lone pair. The large shift to lower wavenumber
which accompanies deprotonation to 2 [m(CN) 2185,
2135 cmꢀ1] suggests a significant degree of mixing be-
tween the CN portion of the ligand with the orbital
of the same symmetry from the sp2-hybridisied C(1)
and an increase in the effective conjugation length.
Coordination of a second metal fragment in 3 has a
negligible effect on the m(CN) frequencies (now
2172 cmꢀ1) indicating limited p-donor/acceptor charac-
ter is associated with the cyanocarbon anion.
Some earlier studies were directed towards the synthe-
sis of complexes containing cyanocarbons, i.e., organic
compounds containing only cyano groups as substitu-
ents [17]. On an earlier occasion, we chose to examine
the chemistry of cyanocarbon anions and have described
several examples of these complexes [18]. Our work with
all-carbon bridging ligands, such as the C4 ligand found
in {Ru(PPh3)2Cp}2(l-C„CC„C) [19,20] and cyan-
oalkynes such as [C„CCN] and PhC„CCN [21] caused
us to reconsider the cyanocarbon complexes as possible
precursors of multi-nuclear derivatives which might exhi-
bit electronic communication between the metal centres.
This paper describes some studies of complexes derived
from cyanocarbon ligands of general form NC–X–CN,
including malononitrile (X = CH2) and its anion
(X = CHꢀ), and the tricyanomethanide [X = C(CN)ꢀ]
and pentacyanopropenide ½X ¼ C3ðCNÞꢀꢁ anions, con-
3
taining
Ru(PR3)2Cp0
[PR3 = PPh3,
Cp0 = Cp;
(PR3)2 = dppe; Cp0 = Cp*] groups. Comparisons are
also drawn with analogous complexes derived from dicy-
anamide (X = Nꢀ).
+
CN
N
Ru
PPh3
C
C
H2
Ph3P
KOBut
(R = H)
CH2(CN)2
(1)
CN
Ru
PPh3
N
C
C
Ru
Cl
K[C(CN)3] (R = CN)
R
Ph3P
Ph3P
PPh3
R
R = H (2), CN (4)
+
[RuX(PPh3)2Cp]n+
X= NCMe, n=1
X= Cl, n=0
C
C
N
C
N
Ru
Ph3P
Ru
PPh3
Ph3P
PPh3
R = H (3), CN (5), C(CN) = C(CN)2 (6)
Scheme 1.

3310
M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
Chart 1. NMR data for ligands.
1
The H NMR spectra contained the expected reso-
nances for Cp and Ph protons. The CH2 group in 1 gave
a broad singlet at d 3.96, while sharp singlets at d 2.35 or
4.46 are assigned to the CH protons in 2 and 3, respec-
tively. In the 13C NMR spectrum of 2, a low intensity
CN resonance was present at d 143.39, while the CH
resonances are at d 4.48 (2) and 9.42 (3). No resonance
assignable to the free CN group could be found. These
values may be compared with those for CH2(CN)2 itself
[d 8.62 (CH2), 109.21 (CN)] (Chart 1). The electrospray
(ES) mass spectrum of 1 contained M+ at m/z 757, to-
gether with fragment ions [Ru(PPh3)nCp]+ (n = 1, 2) at
m/z 429 and 691, respectively. The spectrum of a solu-
tion of 2 containing NaOMe contained the ions
[2M + Na]+ and [M + Na]+ at m/z 1535 and 779, respec-
tively, together with [Ru(PPh3)Cp]+ at m/z 429. Com-
plex 3 showed M+ and loss of up to three PPh3 ligands.
The compound Ru{NCC(CN)2}(PPh3)2Cp (4) has
also been described before and its structure reported
[18,22,23]. On this occasion, we give an improved prep-
aration, details of the 13C NMR and ES mass spectra
which were not previously available, and the X-ray
structure of a second, solvated, polymorph. In the IR
spectrum, only a single m(CN) band is found at 2172
cmꢀ1, which is virtually unchanged from that in
K[C(CN)3] at 2178 cmꢀ1. Resonances of interest in the
13C NMR spectrum are at d 11.29 (central C) and
118.74 (CN) (cf. d 5.18 and 120.71, respectively, in
K[C(CN)3]), both being consistent with the shielding
of the central carbon which results from the relatively
high electron density on this centre. The Ru–NC reso-
nance is found significantly downfield at d 133.37. Of
interest in the mass spectrum is the presence of binuclear
cations at m/z 1472, 1209 and 948, corresponding to
[{Ru(PPh3)2Cp}2C(CN)3]+ („M+), [M ꢀ PPh3]+ and
[M ꢀ 2PPh3]+, respectively.
and the spectral properties are unexceptional, the central
carbon being found at d 15.89 (see Section 7). The m(CN)
bands from free and coordinated CN moieties could be
resolved in this case, being found at 2204 and 2189
cmꢀ1, respectively. During the course of this work, re-
lated studies of iron and ruthenium complexes contain-
ing dicyanamido and tricyanomethanide groups were
described, including 4 and 5 [23]. All attempts using a
variety of conditions to add a third Ru(PPh3)2Cp group
to 5 were unsuccessful, probably for steric reasons.
The bright orange pentacyanopropenide derivative
Ru{NCC(CN)C(CN)‚C(CN)2}(PPh3)2Cp (6; Scheme 1)
was obtained from equivalent amounts of RuCl
(PPh3)2Cp and [NMe4][C3(CN)5] via a minor modifica-
tion of the method previously described [18]. Use of
two equivalents of RuCl(PPh3)2Cp with NH4PF6 as an
additional halide abstracting reagent afforded dark pur-
ple [{Ru(PPh3)2Cp}2{l-C3(CN)5}]PF6 (7), characterised
by elemental analysis and from its ES mass spectrum,
which contained ions at m/z 1548 [{Ru(PPh3)2Cp}2C3-
(CN)5]+ („M+), 1286 ([M ꢀ PPh3]+) and 1024
([M ꢀ 2PPh3]+). Similar reactions of one or two equiva-
lents of RuCl(dppe)Cp* with [C3(CN)5]ꢀ afforded
Ru{NCC(CN)C(CN)‚C(CN)2}(dppe)Cp* (8) or [{Ru-
(dppe)Cp*}2{l-C3(CN)5}]PF6 (9), respectively. In addi-
tion to the molecular ion (m/z 802) and a fragment ion
formed by loss of the cyanocarbon ligand, the ES mass
spectrum of 8 also featured an isotopic envelope arising
from the binuclear complex 9. As detailed in Section 7,
the IR spectra of these complexes contain between one
and four m(CN) bands, in contrast to the free
[C3(CN)5]ꢀ anion, which has only one at 2199 cmꢀ1
.
The NMR spectra of the pentacyanopropenide com-
plexes revealed the presence of two isomers of the mono-
nuclear complexes 6 and 8 and three isomers of the
binuclear complexes 7 and 9 (Table 1). For 7, the five
Cp signals can be assigned to one symmetrical (singlet
Cp, relative intensity 0.15) and two unsymmetrical iso-
mers (two pairs of Cp resonances, relative intensities
0.12 and 0.73). For 9, while only four Cp resonances
are found (one signal comprises an overlapping pair),
the 31P NMR spectrum contains five resonances which
The binuclear cation was obtained directly in excel-
lent yield as its PFꢀ6 salt (5) from 4 and a single equiva-
lent amounts of RuCl(PPh3)2Cp and NH4PF6, or
directly from the reaction between RuCl(PPh3)2Cp with
half an equivalent of K[C(CN)3] in the presence of
NH4PF6. Again, characterisation was straight-forward

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3311
Table 1
Partial NMR spectra of complexes 7, 9 and 10
Complex
Isomer
7
1
9
1
10
1
2
3
2
3
2
3
4
Ratio
1H (Cp)
31P (PPh3)
0.73
4.49, 4.55
40.98, 41.23
0.15 0.12
4.52 4.54, 4.59
41.10 39.99a
0.54 0.30
1.45 1.41a
74.87 74.77, 76.87 76.69, 77.89 11.88 11.43, 12.35
0.16
0.59 0.27
4.58 4.52, 4.62
0.09
4.54, 4.60
0.05
4.74, 4.78
1.38a
b
b
13C (Ru-NC) 123.25,
126.79
126.88 123.87,
124.29
122.77 120.57,
122.67
9.44 9.31, 9.37
119.64,
121.43
9.08a
13C (Cp)
13C (C2)
a
83.84, 83.87
60.18, 60.92
83.94 83.76, 85.91
61.09 58.18, 59.90
78.05 77.71, 78.36 78.20, 78.53 79.90, 80.22
b
b
59.30 59.07, 59.46 56.56, 57.71 57.91 62.04
Overlapping peaks.
b
Not observed.
(a)
[Ru]
N
C
N
C
[Ru]
N
N
NC
C
C
CN
C
C
CN
C
C
C
C
NC
C
CN
C
C
C
N
C
N
C
N
C
N
C
N
C
N
[Ru]
(a) [- / 0]
(b) [- / 12.5]
(c) [- / 14.4]
[Ru]
N
C
[Ru]
N
C
N
C
N
C
NC
C
CN
[Ru]
C
C
NC
C
CN
NC
C
C
CN
NC
C
CN
C
C
C
C
C
C
N
C
N
C
N
C
N
C
N
C
N
C
N
C
N
[Ru]
[Ru]
[Ru]
[Ru]
[Ru]
(ad) [13.4 / 2.0]
(ae) [- / 36.8]
(ab) [35.1 / 0.3]
(ac) [14.9 / 0.0 ]
[Ru]
[Ru]
N
C
[Ru]
N
N
[Ru]
N
C
C
C
C
N
C
C
C
C
C
CN
C
C
N
C
N
C
N
C
N
(bc) [99.5 / 40.6]
(bd) [0 / 13.7]
(b)
N
C
N
N
C
C
C
CN
CN
N
C
C
C
N
C
C
C
C
N
[Ru]
C
[Ru}
CN
C
N
(g)
(f)
Chart 2. Conformations of [Ru]x-C3(CN)5, [Ru] = Ru(PPh3)2Cp (x=1, 6; x=2, 7). (a) N-bonded; (b) C-bonded. [Hartree–Fock/DFT calculated
relative energies (kJ molꢀ1) are given in brackets for 6 and 9 or 9-H given in brackets (see text).]

3312
M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
can also be assigned to one symmetrical (intensity 0.54)
and two unsymmetrical isomers (intensities 0.30, 0.16).
These data are collected in Table 1, which also confirms
that all nuclei (1H, 13C, 31P) give consistent spectra.
There is no detectable resonance from free PPh3 and
there is no coalescence of any of the resonances on cool-
ing the solutions. Careful t.l.c. did not separate these iso-
mers, nor were products with different NMR spectra
obtained after fractional crystallisation.
Consideration of possible points of attachment of the
metal centres to the cyanocarbon ligand (Chart 2) indi-
cates that there are three possible isomers of 6 or 8, and
six possible isomers of 7 or 9. It would appear that facile
equilibria between the various components are rapidly
set up in solution, although no change in isomeric pro-
portions occurs on cooling or warming the solutions
(temperature range ꢀ50 to +50 ꢁC). However, different
isomeric ratios are found in different solvents, e.g., in
C6D6 (0.87/0.13), in CDCl3 (0.71/0.29) or in d6-acetone
(0.79/0.21).
It has not been possible to assign any definitive struc-
tures to these isomers. Theoretical calculations (see be-
low) suggest that coordination to the central CN
group is likely to be hindered by steric constraints so
the isomeric forms involving this arrangement are likely
to be those present in minor amounts. Two possible iso-
mers of 6 and 8 are those in which the ruthenium frag-
ment is attached either to one of the cyano groups of
the C(CN)2 group (as in a or b) or to the C(CN) group
(as in c) and found in the mononuclear derivatives
(Chart 2) [3b,15,22,23]. In the cases of 7 and 9, where
several isomers can be detected, the situation is less obvi-
ous. On steric grounds it is unlikely that two rutheniums
would be attached one to each of the CN groups of one
C(CN)2 moiety (isomer ab). Assuming then that the first
Ru group is attached to one C(CN)2 moiety, the second
Ru group can be attached either to the central C(CN)
group (ac or bc), or to one of the cyano groups of the
second C(CN)2 moiety (ad, ae or bd). In isomer ae, steric
hindrance between the ligands precludes this being
formed (see below). Conformational isomerism appears
to be inconsistent with the temperature independence of
the isomer ratio. While the isomer ratio is solvent-
dependent, inter-conversion of the various forms by a
dissociative process seems to be excluded by (a) there
being no free PPh3 detected in solution and (b) there
being no change upon addition of [Ru(thf)(PPh3)2Cp]+
to a solution of 7.
On heating 6 in refluxing toluene, one PPh3 ligand is
displaced from one molecule by a free CN group of the
C3(CN)5 ligand of a second molecule of complex to
give the bright red cyclic complex {Ru(PPh3)Cp[l-
N‚C‚C{C(CN)‚C(CN)2}CN]}2 (10; Scheme 2). This
complex is not one of the isomeric products discussed
1
above, as evidenced by its unique H NMR spectrum.
This complex was characterised by elemental analysis
and (limited) spectroscopic studies, the NMR spectra
showing the presence of two major isomers (ratio 0.53/
0.47), with two other isomers also present in minor
amounts. The two major isomers may arise by simple
rotation of one of the free C(CN)‚C(CN)2 groups rel-
ative to the other to give either symmetrical or asymmet-
rical conformations. The NMR spectra contain three
signals for the Cp groups, one a singlet and the other
Scheme 2.

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3313
a pair of equal intensity signals, which can be assigned
to the symmetrical and asymmetrical isomers,
respectively.
C‚C(CN)C(CN)‚C(CN)2}{P(OMe)3}(PPh3)Cp (6a)
[18] and the macrocyclic complex {Ru[C{‚C-
(CN)2}C{C„C[Ru(PPh3)2Cp]}C(CN)2](PPh3)Cp}2 (11)
[19], all containing N-bonded cyano groups. In the latter
case, the CNgroupsarebondedasnitriles, while in thefirst
two, the ketenimine structure is adopted by the (formally)
anionic ligands. On this occasion, we report the structures
of complexes 2–4 and 8–10. Plots of single molecules or
cations are given in Figs. 1–3 and selected structural
parameters are collected in Tables 2 and 3.
3. Molecular structures
In previous work, we or others have described X-ray
determinations of the molecular structures of
Ru{N‚C‚C(CN)2}(PPh3)2Cp (4) [22,23], Ru{N‚
1111
1112
1131
P(11)
1121
1112
1111
1122
1132
103
1132
102
11
1126
104
P(11)
102
111
N(111)
Ru(1)
112
N(112)
1131
Ru(1)
N(11)
105
11
1
2232
103
P(12)
1231
1231 P(12)
101
12
2222
104
1232
1212
2231
1221
1226
1232
N(12)
2221
2211
2132
1211
Ru(2)
2131
P(21)
1212
P(22)
1221
1211
1222
2122
2212
2121
201
204
203
202
(b)
(a)
132
121
131
112
P(1)
122
111
02
CN(12)
1
03
CN(13)
04
222
Ru
CN(11)
01
05
221
Cl(3)
212
P(2)
211
C(0)
231
Cl(1)
Cl(2)
232
(c)
Fig. 1. (a)–(d) Projections of 2 (molecule 1), 3, 4 [molecule 1, with associated (ordered) solvent] and 8 in common orientation down the Ru–Cp
˚
centroid line. 50% amplitude displacement parameters are shown for the non-hydrogen atoms, hydrogen atoms having arbitrary radii of 0.1 A. (e)
Unit cell contents of 2 projected down a. (f) Unit cell contents of 3 projected down a.

3314
M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
112
111
122
041
031
121
P(1)
04
CN(12)
2
10
05
03
CN(11)
1
3
051
Ru
20
CN(32)
CN(21)
02
P(2)
01
222
021
212
221
211
CN(31)
011
(d)
Ru1
P11
P12
Ru2
P22
P21
b
cSinβ
(e)
b
cSin
Ru1
Ru2
(f)
Fig. 1 (continued)

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3315
N
CN(31’)
CN(31)
3
C
CN(32’)
3’
CN(21’)
Ru
N
C
C
C
C
2
L
C
C
C
N
L
CN(21)
N(32)
2’
N
122
1
CN(12)
121
N
CN(11)
P(1)
111
05
L2 = (PPh3)2 (6), dppe (8)
04
Ru
112
03
+
01
02
L
132
Ru
L
N
C
N
C
C
C
C
C
C
C
N
(a)
N
N
Ru
L
L
04
02
03
CN(21’)
05
CN(32’)
3’
L2 = (PPh3)2 (7), dppe (9)
Ru
2
01
122
P(1)
111
112
121
132
3.1. Ru(NCCRCN)(PPh3)2Cp [R = H (2), CN (4)]
131
These complexes adopt the usual piano-stool configu-
ration, with the cyano ligands being attached via a nitro-
gen atom. No unusual bond parameters were found. Thus
˚
Ru–P [2.319(1)–2.3338(9) A], Ru–C(Cp) [2.185–2.239(5)
(b)
˚
˚
A] and Ru–N [2.047(4), 2.072(5) (2), 2.051(3) A (4)] are
within ranges previously found, while angles at Ru
[P(1)–Ru–P(2) 98.05(4), 99.71(5); 101.18(3); P–Ru–N
88.02(9)–92.7(1), Ru–N–C 173.1–176.5(4)ꢁ] are close to
those expected for a distorted octahedral geometry. The
cyanocarbon ligands are planar, with C–C and C–N dis-
tances consistent with the structural representations given
above.
Fig. 2. Projections of 10, (a) normal to and (b) through, the central
ring ꢁplaneꢀ.
3.3. Ru{NCC(CN)C(CN)C(CN)2}(dppe)Cp* (8)
The anionic cyanocarbon is attached via a nitrogen,
leading to the ketenimine configuration with approxi-
mate linear Ru–N–C arrangement, as found in the
analogous complex described earlier [Ru–N 2.012(2)
3.2. {Ru(PPh3)2Cp}2(l-NCCHCN) (3)
˚
The binuclear formulation for 3 is confirmed by the
structural determination, which shows that the cyano-
carbon chain is bent at C(1) [C(11)–C(1)–C(12)
121.2(8)ꢁ]. Other parameters within this group are nor-
(8), 2.033(6) A (8b); Ru–N(11)–C(11) 166.9(2)ꢁ (8),
176.3(4)ꢁ (8b)] [18]. In this case, the Ru–P [2.3066,
2.3072(6) A] and Ru–C(Cp*) distances [2.223–2.255(2)
˚
A] are similar to those found in other examples, the
chelating phosphine resulting in a smaller P–Ru–P an-
gle [83.65(2)ꢁ] and P–Ru–N angles [85.59ꢁ, 90.52(6)ꢁ],
˚
˚
mal: N–C 1.163(9), 1.17(1); C–C 1.38, 1.37(1) A, angles
Ru(1)–N–C 173.8ꢁ; N–C–C 178.0ꢁ.

3316
M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
1021
1031
102
101
1011
1041
104
105
Ru(1)
1051
1112
CN(12)
CN(21’)
1111
1211
CN(11)
P(11)
1121
1
1212
CN(32)
2’
110
P(12)
1222
1221
2
3’
CN(21)
120
3
CN(32’)
2222
220
210
2221
CN(31)
2122
P(21)
2051
Ru(2)
205
2211
2212
2011
2112
2111
201
2041
203
202
2021
2031
Fig. 3. Projection of 9 approximately through the Cp* ring planes, showing the disorder associated with the central cyanocarbon ligand.
Table 2
Selected bond parameters for 2–4
2 (mols 1, 2)
3a
4b
˚
Bond lengths (A)
Ru–P(1)
Ru–P(2)
2.322, 2.327(1)
2.319(2)
2.327(2)
2.192–2.239(8)
2.22(2)
2.3338(9)
2.327(1)
2.185–2.236(5)
2.21(2)
2.327(1), 2.319(1)
2.206–2.239(5), 2.212–2.225(6)
2.22(1), 2.217(5)
Ru–C(cp)
(av.)
Ru–N(11)
N(11)–C(11)
C(1)–C(11)
C(1)–C(12)
C(12)–N(12)
2.047(4), 2.072(5)
1.149(6), 1.152(8)
1.383(8), 1.47(1)
2.053(6)
1.163(9)
1.38(1)
2.051(3)
1.150(5)
1.389(6)
1.396(7)
1.159(8)
1.386(8), 1.27(1)
1.158(8), 1.25(2)
1.37(1)
1.17(1)
Bond angles (ꢁ)
P(1)–Ru–P(2)
P(1)–Ru–N(11)
P(2)–Ru–N(11)
Ru–N(11)–C(11)
N(11)–C(11)–C(1)
C(11)–C(1)–C(12)
C(1)–C(12)–N(12)
a
98.05(4), 99.71(5)
90.2(1), 90.0(1)
92.7(1), 91.9(1)
173.1(4), 176.5(4)
177.6(5), 171.6(8)
118.4(5), 124.9(9)
179.4(6), 173(1)
100.96(6)
87.0(2)
88.1(2)
101.18(3)
89.99(9)
88.02(9)
174.8(3)
176.6(5)
118.7(4)
177.6(6)
173.8(5)
178.0(7)
121.2(8)
176.2(9)
Ru(1) ambience only; Ru(2) is similar but disordered.
b
˚
C(1)–C(13) 1.388(7), C(13)–N(13) 1.144(8) A; C(11)–C(1)–C(13) 122.1(4)ꢁ, C(1)–C(13)–N(13)178.5(6)ꢁ.
than those found in 2 and 4 above. The cyanocarbon
ligand is planar.
(Fig. 3). As discussed below, these appear to be related
to the minimum energy conformations 9bd and 9bd0
found by theoretical calculations, which are related by a
ca 180ꢁ rotation about the Ru–N bond (Fig. 4).
3.4. {Ru(PPh3)2Cp}2{l-NC(CN)C(CN)C(CN)CN} (9)
Although this structure is imprecise and further discus-
sion of the molecular parameters is thereby precluded, the
determination confirms the formulation, being modelled
in terms of two conformations with equal occupancies
3.5. {Ru(PPh3)Cp[l-NCC[C(CN)C(CN)2]CN]}2 (10)
Although formally the cyanocarbon ligand is
attached by a ketenimine group to one ruthenium and

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3317
Table 3
Selected bond parameters for 8–10
8
9 [Ru(1, 2)]
Calc.a
10
˚
Bond lengths (A)
Ru–P(1)
Ru–C(cp)
(av.)
2.3066, 2.3072(6)
2.223–2.255(2)
2.24(1)
2.306(6); 2.280(6)
2.22–2.24(3); 2.19–2.24(2)
2.23(1); 2.22(2)
2.325(1)
2.164–2.212(5)
2.18(2)
Ru–N(11)
N(11)–C(11)
C(1)–C(11)
C(1)–C(12)
C(1)–C(2)
C(2)–C(3)
C(2)–C(21)
C(3)–C(31)
C(3)–C(32)
C(12)–N(12)
C(21)–N(21)
C(31)–N(31)
C(32)–N(32)
2.012(2)
1.149(3)
1.420(4)
1.426(5)
1.386(4)
1.345(5)
1.552(5)
1.458(5)
1.382(5)
1.133(5)
1.125(5)
1.111(5)
1.121(4)
2.00(2); 2.01(2)
1.06(4); 1.15(4)
2.16; 2.17
1.15; 1.15
2.042(4)
1.136(7)
1.419(7)
1.419(5)
1.37(2)
1.55(5); 1.40(7)
1.31(11); 1.51(13)
1.39(4); 1.50(9)
1.37(13)
1.44; 1.44
1.41; 1.41
1.44; 1.44
1.47; 1.47
1.38(2)
1.46(1)
1.46(2)
1.42(2)
1.146(5)
1.14(3)
1.09(2)
1.12(2)
Bond angles (ꢁ)
P(1)–Ru–P(2)
83.65(2)
85.59(6)
90.52(6)
166.9(2)
170.8(3)
126.0(3)
116.6(2)
129.2(3)
116.6(2)
175.5(3)
118.3(3)
122.5(3)
176.0(4)
174.9(4)
170.9(4)
83.4(2); 84.3(2)
92.4(6); 87.7(6)
89.4(6); 86.4(6)
167(2); 159(3)
168(3)
P(1)–Ru–N(11)
P(2)–Ru–N(11)
Ru–N(11)–C(11)
N(11)–C(11)–C(1)
C(11)–C(1)–C(2)
C(11)–C(1)–C(12)
C(1)–C(2)–C(3)
C(1)–C(2)–C(21)
C(1)–C(12)–N(12)
C(2)–C(3)–C(31)
C(2)–C(3)–C(32)
C(2)–C(21)–N(21)
C(3)–C(31)–N(31)
C(3)–C(32)–N(32)
88.5(1)
175.9; 178.0
175.7; 175.7
169.2(4)
172.9(4)
113.4(6)
115.3(4)
124.3(8)
120(1)
101(6); 121(6)
121.2; 121.2
113.6; 113.7
174.5(6)
119.9(9)
123(1)
115.4; 115.4
175(2)
175(2)
176(2)
˚
For 9: Ru–P(2) 2.308(6); 2.279(7) A.
For 10: Values for the ligand are for the major component; values for C(N)(3, 31, 32), C(N)(4, 41, 42) are tabulated as the second component of
˚
C(N)(2, 21, 22), C(N)(1, 11, 12). P(1)–Ru–N(12) 91.1(2), N(11)–Ru–N(12) 84.8(2) A; Ru–N(12)–C(12) 171.0(3)ꢁ.
See text.
a
a nitrile group to the other, the complex is centrosym-
metric and therefore both Ru–NC bond distances are
equivalent. The cyanocarbon ligand and two Ru atoms
4. Electrochemistry
With a view to assessing the degree to which the me-
tal centres might interact via the various cyanocarbon
ligands NC–X–CN, we have briefly examined the electr-
ochemical properties of these complexes, determining
their cyclic voltammograms using similar conditions
(see Section 7 and Table 4).
˚
are coplanar. The Ru–P [2.325(1) A] and Ru–N
˚
[2.042(4) A] distances closely resemble those mentioned
above, as do the angles at Ru [N–Ru–N 84.8(2)ꢁ,
N–Ru–P 88.5ꢁ, 91.1(2)ꢁ], but the Ru–C(Cp) [2.164–
2.212(5) A] distances are somewhat shorter, probably
˚
as a result of decreased steric hindrance (only one
PPh3 group). An alternative explanation for the change
in bond length may be related to the altered electronic
environment around the metal centre, which with only
one PPh3 ligand is less electron-rich, resulting in in-
creased electron donation from the Cp ligand and shorter
Ru–C(Cp) bond lengths. Apparently, metal ! ligand
back-donation is not important here.
The mononuclear cation 1 undergoes a single par-
tially reversible oxidation at E0 = +1.38 V, which is sim-
ilar to that found for [Ru(NCPh)(PPh3)2Cp]+ under
comparable conditions (+1.30 V [21]). As expected, neu-
tral
2
is oxidised at much lower potentials
(E0 = +0.51 V; irreversible), the CV also containing a
partially reversible oxidative wave (E0 = +1.38 V) which
we ascribe to the oxidation of 1 formed at the electrode

3318
M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
Fig. 4. Projections of the structures of the three lowest-energy conformers (a) 9bd, (b) 9bd0 and (c) 9ad, determined at the ab initio Hartree–Fock level
of theory. Hydrogen atoms have been omitted for clarity.
Table 4
Some electrochemical data for ruthenium–cyanocarbon complexes
Complex/X
E1 (V)
E2 (V)
DE (mV)
E3 (V)
1/CH2
2/CHꢀ
3/CHꢀ
1.38 (part rev.)
0.51 (irrev.)
0.59
–
1.09
500
230
300
–
4/C(CN)ꢀ
5/C(CN)ꢀ
6=C3ðCNÞꢀ
7=C3ðCNÞꢀ3
8=C3ðCNÞꢀ3
0.97
0.95
–
1.18
–
–
1.14
1.17
–
1.34
ꢀ1.30
ꢀ1.15
ꢀ1.33
ꢀ1.23
ꢀ1.41. ꢀ1.25
0.92
0.91
–
9=C3ðCNÞꢀ3
1.13 (irrev.)
1.28 (part rev.)
220
180
3
10=C3ðCNÞꢀ
1.10
3
surface after oxidation of 2. Introduction of an addi-
tional electron-withdrawing CN group in the tricya-
nomethanide complex 4 raises the oxidation potential
to +0.97 V. In comparison with the other ligands in this
series, the poorer r-donor properties of the pentacya-
nopropenide group are clearly shown by the oxidation

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3319
potential of neutral 6 (+1.14 V). Introduction of a more
electron-rich metal centre [Ru(dppe)Cp*] lowers the oxi-
dation potential of 8 (+0.92 V) compared with the
Ru(PPh3)2Cp analogue 6.
tions. We assume that one ruthenium fragment is at-
tached to a CN group of one of the C(CN)2 moieties,
as found in the structure of the mononuclear complex
8. Six isomeric arrangements of the two Ru fragments
can then be drawn (Chart 2, ab, ac, ad, ae, bc and bd).
The second Ru group can be bonded either to the cen-
tral C(CN) group or to a CN group of the second
C(CN)2 group. With restricted rotation about the
C(CN)–C(CN)2 bond, related structures ac and bc give
a symmetrical structure which may be responsible for
the singlet resonance. Isomer ab arises by coordination
of Ru moieties to both CN groups of a single C(CN)2
group. Although sterically congested, theoretical calcu-
lations suggest that it is possible for this to form, unlike
isomer ae, for which no sensible structure can be
calculated.
Our studies have shown that the isomer ratios are sol-
vent dependent, but are not affected by temperature.
Interconversion of various isomers by a dissociative
process seems to be excluded by (a) there being no reso-
nance assignable to free PPh3 present and (b) there being
no change in ratio upon addition of [Ru(thf)-
(PPh3)2Cp]+.
For the binuclear complex 3, we find two fully revers-
ible oxidation waves at E0 = +0.59 and +1.09 V, while 4
gives only one reversible wave at E0 = +0.97 V. Two
processes at E0 = +0.95 and +1.18 V were found for 5.
Introduction of the extensively delocalised bridging
C3(CN)3 moiety in 7 and 9 also results in two oxidation
processes separated by 300 or 220 mV, respectively,
reflecting the differing electron richness of the two metal
centres. The doubly-bridged system in 10 gives two oxi-
dation potentials, separated by ca 180 mV. Complexes
6–10 also exhibit reduction waves at potentials between
ꢀ1.23 and ꢀ1.41 V, the extended polycyanocarbon lig-
and allowing electron delocalisation onto the CN groups
and thus stabilisation of the anionic species formed by
population of the ligand p* MOs. The similarity of the
reduction potentials found for 6 and 8, and for 7 and
9, confirms the limited metal ! ligand back-donation
suggested by the IR m(CN) spectra.
5. Discussion
5.1. Hartree–Fock and density functional theory calcula-
tions
We have examined the coordinating abilities of
the free CN groups in some ruthenium cyanocarbon
Conformers 9ab, 9ac, 9ad, 9bc and 9bd (see Chart 2)
were first investigated via the ab initio Hartree–Fock
(HF) approach. The close proximity of the Ru(dp-
pe)Cp* groups makes isomer 9ae sterically disfavoured
and this structure was not considered further. The rela-
tive energies calculated for the complexes investigated
are given in parentheses in Chart 2. According to the
HF results, the energetically most stable structure is
9bd. In this structure the two Cp* groups are oriented
in the same direction. The next lowest energy structure
is denoted as 9bd0, in which the molecular conformation
has the relative orientation of one Ru(dppe)Cp* group
rotated by ꢂ180ꢁ about the cyanocarbon quasi-plane.
The small difference in energies (6.5 kJ molꢀ1) between
9bd and 9bd0 suggests that rotation of the Ru(dppe)Cp*
group about the adjacent C–N bond axes is relatively
unhindered.
complexes towards
a
second Ru(PP)Cp0 moiety
[PP = (PPh3)2, Cp0 = Cp; PP = dppe, Cp0 = Cp*], find-
ing that binuclear complexes are formed readily in essen-
tially quantitative yield. Indeed, in solution, the ES mass
spectra suggest that such species form readily even when
a deficiency of ruthenium is present, at least under ES
mass spectroscopic conditions. X-ray structure determi-
nations confirm the anticipated N-bonding of the cyan-
1
ocarbon ligand, as found in several earlier examples.
As mentioned above, three isomers can be detected
by NMR spectroscopy for both 7 and 9 (Table 1). While
definitive assignments of these resonances to particular
isomers cannot be made, it is informative to consider
the particular structures which are possible (Chart 2)
and to compare their energies by theoretical calcula-
The next two lowest energy conformers are 9ad and
9ac, lying, respectively, 13.4 and 14.9 kJ molꢀ1 higher
in energy than 9bd. Conformer 9ab, which has the two
Ru(dppe)Cp* moieties on adjacent CN groups, lies
35.1 kJ molꢀ1 higher in energy, while conformer 9bc
[also having Ru(dppe)Cp* moieties on adjacent CN
groups] is calculated to be the least favoured structure,
lying 99.5 kJ molꢀ1 higher than 9bd.
Conformers of the analogous model complex
{Ru(dHpe)Cp}2C3(CN)5 (9-H; dHpe = PH2CH2CH2-
PH2; see Fig. 4) were also computed via density func-
tional theory (DFT) for comparison. Their relative
1
It is rare for transition metal derivatives of the cyanocarbons to be
other than N-bonded, with the exception of the g2-alkene complexes
formed by tetracyanoethene [24]. However, the Ru(PPh3)2Cp complex
derived from (phenylsulfonyl)acetonitrile has recently been shown to
exist in the N- and C-bonded forms, the former being the more stable
[25]. Interconversion by intra- and inter-molecular mechanisms were
demonstrated. The rates of isomerisation of related complexes carrying
different tertiary phosphine ligands appear to depend on the cone angle
of the phosphine, i.e., to be influenced by steric effects, there being no
correlation with the basicity of the phosphine. In the present case, two
C-bonded isomers can be formulated (f and g, Chart 2). We have been
able to isolate only one form of the complexes, although solutions of
extensively purified material show the same ratio of isomers.

3320
M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
energies are also given in brackets in Chart 2. The fact
that structure 9-Hbd is not the most stable arrangement
according to DFT results clearly indicates that steric
hindrance, e.g., between ligand phenyl groups, is a ma-
jor factor in determining the stabilities of the different
isomers. Interestingly enough, the energies of the other
conformers of 9-H, namely ab, ac, ad and bd, track those
obtained at the HF level of theory (see Chart 2).
than the related complexes [{Cp(R3P)2M}‚C‚
C‚CHC„C{M(PR3)2Cp}]BF4 [M = Fe, (PR3)2 =
dppe; M = Ru, Os, PR3 = PPh3], whose syntheses were
described by Jia [26]. Attempts to prepare complexes
containing the l-C5 ligand by treating the cations with
[CPh3]+ or with strong bases were unsuccessful.
Different possible conformations of hydrogenated
models of mononuclear 6 [Ru{C3(CN)5}(PH3)2Cp, (6-
H)] were also computed at the DFT level of theory.
The results indicate that structure 6-Ha is energetically
preferred over structures 6-Hb and 6-Hc by 12.5 and
14.5 kJ molꢀ1, respectively.
As can be seen from Fig. 4, the conformations found
experimentally in the X-ray crystal structure determina-
tion for 9 closely resemble those of 9ad and 9bd. The ob-
served disorder confirms the presence of both
conformers and provides evidence for the relatively
unhindered rotation described above. The calculated
structural parameters are compared with the values
determined from the X-ray structural study (Table 3)
which, however, are of relatively low precision. The
cyanocarbon groups in the two conformers 9bd and
9bd0 are almost unaltered by the rotation about the
Ru(1)–N(1) bond. In addition, the distance between
the centroids of the two Cp* groups differs by only
5.2. Electrochemistry
Single oxidation processes were found in the CVs of
the mononuclear complexes 1, 2, 4, 6 and 8, that for 1
being at a much higher potential as expected for a cati-
onic complex. The oxidation potentials are consistent
with the differing electron densities at the metal centres
in the end-capping Ru(PPh3)2Cp and Ru(dppe)Cp*
groups, and with the poorer electron-donor properties
of bridging groups with more CN substituents.
Some indication of the degree of interaction between
the metal centres through the bridging ligand can be ob-
tained by considering differences between the two 1-elec-
tron redox potentials (DE0) found for the binuclear
complexes. Previous studies have shown that this is a
feature of many complexes containing electron-rich me-
tal centres linked by a C4 chain [27]. Others have shown
that electronic interactions diminish as the carbon chain
length increases [28]. Electrochemical measurements on
the binuclear complexes 3, 5, 7, 9 and 10 confirmed that
there is an electronic interaction between the two ruthe-
nium centres, which is mediated by the cyanocarbon
chain. However, the oxidised species could not be iso-
lated after treatment of the complexes with ferrocenium
ion or Ag+, for example, only intractable brown solids
being obtained.
Further consideration of the differences in redox pot-
entials in terms of the bridging group X in the ligands
[NC–X–CN]ꢀ shows a decrease in the order X = H (3;
500 mV) > C3(CN)5 (300 for 7, 200 for 9) > CN (5;
230) > N (180 [23]). Corresponding values for KC for 3
and 5 are 2.8 · 108 and 7.7 · 103, respectively. While
the HOMO is likely to be similar to that found in
{Ru(dppe)Cp*}2(l-C4), in that it is derived from mixing
of the filled d orbital with the filled ligand set [20a], the
substituent on the central carbon exerts an inductive ef-
fect to moderate the contribution of the central carbon
to the HOMO, in turn moderating the degree of pertur-
bation between the metal centres.
˚
1.84 A. As expected, the calculated bond lengths are
somewhat longer than those found in the structure
determination.
The conformational study was carried out, in part, to
try to cast light on the mixture of conformers which
were detected in solution by NMR methods. While no
quantitative conclusions can be drawn, it is interesting
to find that of the five conformers (Chart 2) which could
be calculated, the relative energies appear to correlate
quite well with the relative concentrations of each con-
former found in solutions of 9. Indeed, conformer 9bd
could tentatively be assigned to the symmetrical NMR
isomer, whereas 9ac and 9ad could correspond to the
two unsymmetrical NMR isomers (see above). We must
mention, however, that calculations were performed on
isolated molecules without taking into account polar
solvent effects which may play a role in favouring one
isomer or another. No doubt similar conformational
isomers are responsible for the several resonances also
found in solutions of the other complexes described
above.
The possibility of further deprotonation of 2 to the
neutral species, which would contain the conjugated
Ru–N‚C‚C‚C‚N–Ru sequence, resembling similar
complexes containing Cn chains, was explored. How-
ever, we have been unable to perform this transforma-
tion (using NaOMe, LiMe, KOBut or LiH as bases),
since the presence of the two nitrogen atoms would
undoubtedly make this species considerably more basic
For complexes 1, 2 and 3, no reduction processes
were observed within the solvent limits.
In the binuclear derivatives 7 and 9, a fully reversible
reduction wave is observed, presumably from a ligand-
centred event. As expected, the reduction process is
more negative for the Ru(dppe)Cp* complexes as a con-
sequence of the greater inductive electron-donating
properties of this fragment, i.e., they are more readily
oxidised than the Ru(PPh3)2Cp complexes.

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3321
Complex 10 shows two reduction and two oxidation
waves, all fully reversible. The first oxidation potential
is found at relatively high potentials for a neutral
complex within this series, a consequence of both the pres-
ence of a poorly electron-donating pentacyanopropenide
ligand and the decrease in the number of phosphine lig-
ands about each metal centre. The observation of two dis-
tinct reduction potentials in this complex, but only one in
the related binuclear complexes 7 and 9, suggests that
these processes are a consequence of a through-space
interaction between ligand-centred anions.
It is therefore apparent that the degree of interaction
between the metal centres in complexes of general form
[{Ru(PP)Cp0}2{l-X(CN)2}]+ can be tuned by subtle
changes in the ligand structure, with electron-withdraw-
ing substituents decreasing both the electron density be-
tween the metal centres and the magnitude of the
through-bond coupling component.
clude oxygen during work-up. Common solvents were
dried and distilled under nitrogen before use. Elemental
analyses were performed by the Canadian Microanalyt-
ical Service, Delta, B.C., Canada. Preparative t.l.c. was
carried out on glass plates (20 · 20 cm) coated with silica
gel (Merck 60 GF254, 0.5 mm thickness).
7.2. Instrumentation
IR: Perkin–Elmer 1720X FT IR. NMR: Bruker
CXP300 or ACP300 (1H at 300.13 MHz, 13C at 75.47
MHz, 31P at 121.105 MHz) or Varian Gemini 200 (1H
at 199.8 MHz, 13C at 50.29 MHz) spectrometers. Unless
otherwise stated, spectra were recorded using solutions
in CDCl3 in 5 mm sample tubes. ES mass spectra: Finn-
igan LCQ. Solutions were directly infused into the
instrument. Chemical aids to ionisation were used as re-
quired [29]. Electrochemistry was carried out with a
MacLab 400 instrument. The CVs were determined un-
der standard conditions at room temperature (1.0 mM
solutions in CH2Cl2 containing 0.1 M [NBu4]PF6 as sup-
porting electrolyte). A three-electrode system was used,
consisting of a Pt-dot working electrode and Pt counter
and pseudo-reference electrodes. Potentials (see Table 4)
are given in V vs SCE, the ferrocene–ferrocinium couple
being used as internal calibrant for the measured poten-
tials (E0 = +0.46 V vs SCE) [30].
6. Conclusions
We have prepared several complexes containing
Ru(PP)Cp0 groups attached to various cyanocarbon frag-
ments. In the case of complexes where two of these frag-
ments are bridged by the cyanocarbon ligand,
electrochemical measurements demonstrated that there
is a moderate to high degree of electronic interaction be-
tween the two metal centres. After the completion of this
study, Chen and coworkers [8a] published an independent
study of dicyanamide and tricyanomethanide-bridged
iron and ruthenium complexes, which contained a struc-
tural study of the monohydrate of 4 (which is isomor-
phous with the CHCl3-solvate reported here). Where
they overlap, there is substantial agreement between our
two sets of results. Finally, Hartree–Fock and density
functional theory calculations on the conformers of 6
and 9, carried out to provide information concerning
the various species detected by NMR in solution, predict
several conformations close in energy, two of which are
found in the crystal structure. This series, taken together
with the related dicyanamide complex {Ru(PPh3)2Cp}2-
{l-N(CN)2} allows for a comparison of the electronic
interactions between the metal centres mediated by the
ligand series NC–X–CN (X = CH2, [CH]ꢀ, [C(CN)]ꢀ,
[C3(CN)3]ꢀ), which are attenuated by the more electron-
withdrawing substituents.
7.3. Reagents
The compounds K[C(CN)3] [17a], [NMe4][C3(CN)5]
[17a], RuCl(PPh3)2Cp [31] and RuCl(dppe)Cp* [20b]
were prepared by literature methods.
7.3.1. [Ru(NCCH2CN)(PPh3)2Cp][PF6] (1)
A suspension of RuCl(PPh3)2Cp (400 mg, 0.55
mmol), NH4PF6 (200 mg, 1.22 mmol) and malononitrile
(80 mg, 1.05 mmol) in degassed MeOH (15 ml) was stir-
red for 3 h. The resulting bright yellow precipitate was
collected on a sintered glass funnel and washed with
benzene (20 ml) followed by Et2O (20 ml) before being
dried under vacuum to give [Ru(NCCH2CN)-
(PPh3)2Cp][PF6] (1) (421 mg, 85%). IR (nujol): m(CN)
1
2259, 2269; m(PF) 839 cmꢀ1. H NMR: d 7.02–7.40 (m,
30H, Ph), 4.52 (s, 5H Cp), 3.96 (br, 2H, CH2). 13C
NMR: d 128.34–135.53 (m, Ph), 121.06 (s, Ru-NC),
108.65 (s, CN), 83.90 (s, Cp), 10.58 (s, CH2). 31P
NMR: d 41.65 (s, PPh3), ꢀ143.11 (septet, PF6). ES mass
spectrum (positive ion mode, m/z): 757, M+; 691,
[Ru(PPh3)2Cp]+; 429, [Ru(PPh3)Cp]+. Lit. values [18]:
1
IR (nujol) 2267 cmꢀ1; H NMR (CDCl3): d 7.31 (Ph),
7. Experimental
4.56 (Cp), 3.96 (CH2).
7.1. General reaction conditions
7.3.2. Ru(NCCHCN)(PPh3)2Cp (2)
To a solution of 1 (980 mg, 1.09 mmol) in thf (20 ml)
was added KOBut (123 mg, 1.09 mmol) and the solution
Reactions were carried out under an atmosphere of
nitrogen, but no special precautions were taken to ex-

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M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
was stirred at r.t. for 15 min. Solvent was removed under
vacuum and a CH2Cl2 extract of the solid was filtered
into rapidly stirred hexane to give a bright yellow precip-
itate that was collected on a sintered glass funnel to give
Ru(NCCHCN)(PPh3)2Cp (2) (797 mg, 97%), which was
characterised by comparison with the published data. IR
Solvent was removed under vacuum and the solid was
extracted in the minimum amount of CH2Cl2 and added
dropwise to rapidly stirred hexane to give yellow
[{Ru(PPh3)2Cp}2{(l-NC)2C(CN)}][PF6] (5) (750 mg,
91%). Anal. Calc (C86H38F6N3P5Ru2): C, 63.89; H,
4.36; N, 2.59; M (cation), 1472. Found: C, 63.29; H,
1
1
(nujol): m(CN) 2185, 2135 cmꢀ1. H NMR (C6D6): d
4.50; N, 2.55%. IR (nujol): m(CN) 2204, 2189 cmꢀ1. H
6.95–7.28(m, 30 H, Ph), 4.00 (s, 5H, Cp), 2.35 (s, 1H,
CH). 13C NMR: d 143.39 (s, NC-Ru), 127.30–136.92
(m, Ph), 82.07 (s, Cp), 4.48 (s, CH). 31P NMR: d 42.15
(s, PPh3). ES mass spectrum (positive ion mode, with
NaOMe, m/z): 1535, [2M + Na]+; 779, [M + Na]+; 429
[Ru(PPh3)Cp]+. (Lit. values [18]: IR m(CN) 2231vw,
NMR: d 7.03–7.31 (m, 60H, Ph), 4.34 (s, 10H, Cp).
13C NMR: d 130.01 (s, NC-Ru), 128.08–136.51 (m,
Ph), 83.04 (s, Cp), 15.89 (s, C). 31P NMR: d 41.54 (s,
PPh3), ꢀ143.12 (septet, PF6). ES mass spectrum (posi-
tive ion mode, m/z): 1472, M+; 1210, [M ꢀ PPh3]+;
948, [M ꢀ 2PPh3]+; 691, [Ru(PPh3)2Cp]+.
1
2161 (sh), 2137s cmꢀ1; H NMR: d 4.24s, 7.24m).
7.3.6. Ru{N‚C‚C(CN)C(CN)‚C(CN)2}(PPh3)2Cp
(6)
7.3.3. [{Ru(PPh3)2Cp}2(l-NCCHCN)][PF6] (3)
A mixture of 2 (870 mg, 1.08 mmol) and [Ru(NC-
Me)(PPh3)2Cp][PF6] (940 mg, 1.08 mmol) was heated
in refluxing thf (60 ml) for 90 min. The cooled yellow
solution was slowly added to rapidly stirred hexane
(300 ml) to give a fine yellow precipitate that was col-
lected and dried to give [{Cp(PPh3)2Ru}2(l-
NCCHCN)][PF6] (3) (1.57 g, 91%). Anal. Calc.
(C85H71F6N2P5Ru2): C, 64.07; H, 4.46; N, 1.76; M,
1146. Found: C, 64.07; H, 4.43; N, 1.76%. IR (nujol):
A suspension of RuCl(PPh3)2Cp (500 mg, 0.69 mmol)
and [NMe4][C3(CN)5] (166 mg, 0.69 mmol) in methanol
(15 ml) was heated at reflux point for 1 h. Solvent was
removed and the bright red residue was chromato-
graphed (alumina, 20 · 2 cm column, CH2Cl2/Et2O
1/2). The bright orange fraction was collected, evapo-
rated and dissolved in the minimum amount of CH2Cl2.
Dropwise addition to stirred hexane gave bright orange
Ru{N‚C‚C(CN)C(CN)‚C(CN)2}(PPh3)2Cp (6) (490
mg, 83%). Anal. Calc. (C49H35N5P2Ru): C, 68.70; H,
4.10; N, 8.20; M, 857. Found: C, 68.70; H, 4.11; N,
8.09%. IR (nujol): m(CN) 2199 cmꢀ1. ES mass spectrum
(positive ion mode, m/z): 1548, [{Ru(PPh3)2Cp}2-
C3(CN)5]+; 1286, [{Ru(PPh3)2Cp}2C3(CN)5 ꢀ PPh3]+,
1024, [{Ru(PPh3)Cp}2C3(CN)5 ꢀ 2PPh3]+; 691, [Ru-
(PPh3)2Cp]+; 430, [Ru(PPh3)Cp]+.
m(CN) 2172; m(PF) 838 cmꢀ1 1H NMR: d 7.09–7.28
.
(m, 60H, Ph), 4.46 (s, 1H, CH), 4.23 (s, 10H, Cp). 13C
NMR: d 139.54 (s, Ru-NC), 127.78–136.75 (m, Ph),
82.39 (s, Cp), 9.42 (s, CH). 31P NMR: d 42.11 (s,
PPh3), ꢀ143.11 (septet, PF6). ES mass spectrum (posi-
tive ion mode, m/z): 1146, M+, 1184, [M ꢀ PPh3]+;
922, [M ꢀ 2PPh3]+; 660, [M ꢀ 3PPh3]+.
The 1H and 13C NMR spectra showed the presence of
1
7.3.4. Ru{NCC(CN)2}(PPh3)2Cp (4)
two isomers in solution in 5/2 ratio. Major isomer: H
A mixture of RuCl(PPh3)2Cp (500 mg, 0.69 mmol)
and KC(CN)3 (89 mg, 0.69 mmol) was heated in reflux-
ing thf/MeOH (1:1, 50 ml) for 1 h. Solvent was removed
under vacuum and the solid extracted in the minimum
quantity of CH2Cl2 and filtered dropwise into rapidly
stirred hexane to give a bright yellow precipitate of
Ru{NCC(CN)2}(PPh3)2Cp (4) (526 mg, 97%). IR (nu-
NMR: d 7.07–7.34 (m, 30H, Ph), 4.52 (s, 5H, Cp). 13C
NMR: d 128.26–135.92 (m, Ph), 124.86 (s, Ru-NC),
115.48, 114.93, 114.14, 113.28 (4 · s, CN), 83.47 (s,
Cp), 60.54, 57.75 [2 · s, C(CN)2]. 31P NMR: d 41.39
(s, PPh3). Minor isomer: 1H NMR: d 7.07–7.34 (m,
30H, Ph), 4.40 (s, 5H, Cp). 13C NMR: d 128.26–135.92
(m, Ph), 124.86 (s, Ru-NC), 115.54, 114.32, 112.51,
112.06 (4 · s, CN), 83.47 (s, Cp), 62.15, 57.70 [2 · s,
C(CN)2]. 31P NMR: d 41.06 (s, PPh3).
1
jol): m(CN) 2172 cmꢀ1. H NMR: d 7.03–7.31 (m, 30H,
Ph), 4.28 (s, 5H, Cp). 13C NMR: d 133.37 (s, NC-Ru),
127.88–136.65 (m, Ph), 118.74 (s, CN), 82.35 (s, Cp),
11.29 (s, C). 31P NMR: d 41.45 (s, PPh3). ES mass
spectrum (positive ion mode, m/z): 1472, [{Ru(PPh3)2-
7.3.7. [{Ru(PPh3)2Cp}2{l-[N‚C‚CN]2C(CN)}][PF6] (7)
A suspension of RuCl(PPh3)2Cp (500 mg, 0.69
mmol), [NMe4][C3(CN)5] (82 mg, 0.34 mmol) and
NH4PF6 (112 mg, 0.69 mmol) in methanol (25 ml) was
heated at reflux point for 30 min. Solvent was removed
and the dark purple solid was chromatographed (20 cm
alumina column). Elution with acetone/hexane (3/7)
gave a bright orange band containing 6 (52 mg, 9%).
The major band was eluted with acetone–hexane (1/1)
to give red [{Ru(PPh3)2Cp}2{l-[N‚C‚C(CN)]2-
C(CN)}][PF6] (7) (490 mg, 77%). Anal. Calc.
(C90H70F6N5P5Ru2): C, 63.86; H, 4.16; N, 4.13; M
Cp}2C(CN)3]+;
1209,
[{Ru(PPh3)2Cp}2C(CN)3 ꢀ
P-Ph3]+; 948, [{Ru(PPh3)2Cp}2C(CN)3 ꢀ 2PPh3]+; 691,
[Ru(PPh3)2-p]+. Lit. values [6]: IR (nujol) 2175 cmꢀ1
1H NMR (CDCl3): d 7.21–7.30 (Ph), 4.29 (Cp); 13C
NMR (CDCl3): 128.5–136.4 (Ph), 82.8 (Cp).
;
7.3.5. [{Ru(PPh3)2Cp}2{(NC)2C(CN)}][PF6] (5)
A mixture of 4 (400 mg, 0.51 mmol), RuCl(PPh3)2Cp
(372 mg, 0.51 mmol) and NH4PF6 (84 mg, 0.51 mmol) in
MeOH/thf (1:1, 40 ml) was heated at reflux point for 3 h.

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3323
(cation), 1548. Found: C, 63.75; H, 4.24; N, 4.06%. IR
(nujol): m(CN) 2192, 2204; m(PF6) 837 cmꢀ1. ES mass
spectrum (positive ion mode, m/z): 1548, [{Ru(PPh3)2-
Cp}2C3(CN)5]+; 1286, [{Ru(PPh3)2Cp}2C3-(CN)5 ꢀ PPh3]+,
1024, [{Ru(PPh3)Cp}2C3(CN)5]+; 691, [Ru(PPh3)2Cp]+;
429, [Ru(PPh3)Cp]+.
The NMR spectra of 7 showed the presence of three
species in solution (Table 1). In the 13C NMR spectrum,
the following peaks could not be individually assigned: d
128.32–135.86 (m, Ph), 111.24, 112.57, 113.89, 114.19,
114.58, 115.18, 115.90 (7 · s, CN).
2186, 2179, m(PF6) 835 cmꢀ1. ES mass spectrum (posi-
tive ion mode, m/z): 1437, [{Ru(dppe)Cp*}2C3(CN)5]+;
635 [Cp(dppe)Ru]+.
The NMR spectra of 9 showed the presence of three
species in solution (Table 1). In the 13C NMR spectrum,
the following peaks could not be individually assigned: d
128.12–135.32 (m, Ph), 107.25, 111.55, 112.78, 112.94,
113.08, 115.10, 115.55, 115.77 (8 · s, CN); 28.04–29.65
(m, CH2).
7.3.10. {Ru(PPh3)2Cp[l-NCC{C(CN)‚C(CN)2}-
CN]}2 (10)
Asolutionof6(100mg, 0.12mmol)washeatedinreflux-
ing toluene (50 ml) for 12 h. Solvent was removed and the
residue was purified by preparative TLC plates using chlo-
roform as the solvent. A bright red band (Rf 0.6) was
collected and after replating afforded {Ru(PPh3)2Cp
[l-NCC{C(CN)‚C(CN)2}CN]}2 (10) (8 mg, 11%). Anal.
Calc. (C62H40N10P2Ru2): C, 62.52; H, 3.36; N, 11.76; M,
1190. Found: C, 62.59; H, 3.30; N, 11.74%. IR (nujol):
m(CH2Cl2): 2209, 2189 cmꢀ1. ES mass spectrum (with
NaOMe, m/z): 1213, [M + Na]+; 1024, [M ꢀ C3(CN)5]+.
The NMR spectra (Table 1) showed the presence of
four isomers in solution. Other peaks: 1H NMR: d
7.34–7.48 (m, 30H, Ph). 13C NMR: d 121.46, 124.04 [iso-
mer 1, C(3)], 121.07, 124.42 [isomer 2, C(3)], 132.88 [iso-
mer 1, C(1)], 132.73, 132.93 [isomer 2, C(1)], 112.84,
112.89, 113.13, 114.88 (4 · s, CN), 128.52–133–83 (m,
7.3.8. Ru{N‚C‚C(CN)C(CN)C(CN)2}(dppe)Cp* (8)
A mixture of RuCl(dppe)Cp* (100 mg, 0.15 mmol)
and [NMe4][C3(CN)5] (35 mg, 0.15 mmol) were stirred
in MeOH (10 ml) at r.t. for 1 h. Solvent was removed
and the bright orange residue was chromatographed
(20 cm silica-gel column, acetone/hexane 35/65). The
bright orange band was evaporated, extracted into the
minimum of CH2Cl2 and precipitated by hexane to give
Ru{N‚C‚C(CN)C(CN)C(CN)2}(dppe)Cp* (8) (92
mg, 76%). Anal. Calc. (C44H39N5P2Ru): C, 65.91;
4.86; N, 8.74; M, 801. Found: C, 65.79; H, 4.84; N,
8.69%. IR (nujol): m(CN): 2168, 2191, 2211 cmꢀ1. ES
mass spectrum (positive ion mode, m/z): 1437, [{Ru(dp-
pe)Cp*}2C3(CN)5]+; 802, [Ru{C3(CN)5}(dppe)Cp*]+;
635, [Ru(dppe)Cp*]+.
The 1H and 13C NMR spectra showed the presence of
1
Ph). 31P NMR: d 49.86 (s). Minor isomer: H NMR:
1
two isomers in solution in 5/2 ratio. Major isomer: H
dH 7.34–7.48 (m, 30H, Ph), 4.58 (s, 5, Cp), 4.47 (s, 5,
NMR: d 7.22–7.54 (m, 20H, Ph), 2.2–2.9 (m, 4H, CH2),
1.46 [t, 3J(HP) = 1.5 Hz, 15H, Cp*]. 13C NMR: d
128.27–135.81 (m, Ph), 124.11 (s, Ru-NC), 115.61,
113.30, 112.67, 112.25 (4 · s, CN), 92.37 (s, Cp*), 59.98,
Cp). 31P NMR: d 51.04 (s), 48.74 (s).
7.4. Structure determinations
1
57.51 [2 · s, C(CN)2], 28.28 [t, J(CP) = 22.3 Hz, CH2],
Full spheres of data to 2h = 58ꢁ were measured at ca
153 K using a Bruker AXS CCD area-detector instru-
ment, merged to unique sets after ‘‘empirical’’/multiscan
absorption corrections, Ntot data merging to N unique
(Rint quoted), N0 with F > 4r(F) being used in the refine-
ments. All data were measured using monochromatic
9.48 (s, Cp*). 31P NMR: d 74.98 (s, dppe). Minor isomer:
1H NMR: d 7.22–7.54 (m, 20H, Ph), 2.2–2.9 (m, 4H,
3
CH2), 1.44 [t, J(HP) = 1.8 Hz, 15H, Cp*]. 13C NMR: d
128.26–135.92 (m, Ph), 121.87 (s, Ru-NC), 115.61,
115.30, 113.30, 112.95 (4 · s, CN), 92.76 (s, Cp), 57.98,
57.36 [2 · s, C(CN)2], 29.27 [t, 1J(CP) = 22.34 Hz, CH2],
9.48 (s, Cp*). 31P NMR: d 76.88 (s, dppe).
˚
Mo Ka radiation, k = 0.71073 A. In the refinements,
anisotropic thermal parameter forms were used for the
non-hydrogen atoms, (x, y, z, Uiso)H being constrained
7.3.9. [{Ru(dppe)Cp*}2{l[N‚C‚C(CN)]2C(CN)}]-
[PF6] (9)
at estimated values. Conventional residuals R, Rw on
jFj are quoted, weights being [r2(F) + 0.0004F2]ꢀ1. Neu-
tral atom complex scattering factors were used; compu-
tation used the XTAL 3.4 program system [32].
Pertinent results are given in Figs. 2–4 (which show
non-hydrogen atoms with 50% probability amplitude
displacement ellipsoids) and Tables 2, 3 and 5.
In a number of the determinations, specimen quality
and disorder presented significant difficulties, impacting
adversely on the precision of the determinations. Spe-
cific variations in procedure:
A mixture of RuCl(dppe)Cp* (100 mg, 0.15 mmol),
[NMe4][C3(CN)5] (18 mg, 0.075 mmol) and NH4PF6
(25 mg, 0.15 mmol) was stirred in MeOH (10 ml) at
r.t. for 1 h. Solvent was removed and the dark purple
residue chromatographed (20 cm silica gel column). Elu-
tion with acetone/hexane (35/65) gave 8 (13 mg, 11%).
The purple fraction eluted with acetone/hexane (1/1)
contained
[{Ru(dppe)Cp*}2{l[N‚C‚C(CN)]2C-
(CN)}][PF6] (9) (88 mg, 74%). Anal. Calc. (C80H78F6-
N5P5Ru2): C, 60.79; H, 4.97; M (cation), 1437. Found:
C, 61.09; H, 5.12%. IR (nujol): m(CN) 2213, 2195,
2. The solvent dichloromethane (molecule 2) was
modelled as disordered over two sets of sites, accupan-

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M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
cies refining to 0.713(5) and complement. C,N in the
cyano-ligand were assigned in molecule 1 on the basis
of refinement behaviour and geometries, the hydrogen
on C(1) being refinable in (x, y, z, Uiso); the same ligand
in molecule 2 is oriented differently with high displace-
ment parameters (isotropic) on C(2) and beyond unreal-
istically large and presumably a foil for disorder, each
ligand lying in association with a solvent molecule, dis-
ordered in the latter case.
3. The question of disorder and its nature, e.g., the
possibility of co-crystallisation of closely related species,
is raised more seriously here. Ru(1) and associated lig-
ands, together with the PFꢀ6 anion refine convincingly
and unproblematically, these moieties comprising layers
disposed about y = 0.25, 0.75. Displacement parameters
of N(2), Ru(2), C(201–205) and two of the three solvent
molecules are high, but with no resolution of associated
disorder; the two PPh3 ligands from the P atom and be-
yond are modelled in terms of superimposed displaced
components of equal occupancy, these being disposed
about y = 0.5, together with solvent 3, modelled as a ri-
gid body.
4. T was 300 K for this study. The occupancy of the
CHCl3, despite hydrogen-bonding to the cyano-ligand,
refined only to 0.705(4).
9. Weak and limited data would permit meaningful
anisotropic displacement parameter refinement for Ru,
P, F only. The central ligand was modelled as disordered
over a pair of sites of equal occupancy.
10. Somewhat similar disorder was resolved in the
central ligand, the two components refining to occupan-
cies of 0.63(1) and complement, the inner, ordered part
of the ligand lying close to and parallel with, one of the
Ph rings.
7.5. Ab initio Hartree–Fock and density functional theory
calculations
Quantum chemical ab initio calculations were per-
formed using GAMESS-US [33] at the restricted Har-
tree–Fock level of theory with the in-built SBKJC
effective core potential-containing basis set [34–36].
The number of core electrons replaced with appropriate
core potential functions for each atom type are: C = 2,
N = 2, P = 10, Ru = 28. All calculations were performed
on an Intel-based Beowulf computing cluster [37]. The
representation of the models used MOLDEN [38].
Density functional theory calculations using the
Amsterdam Density Functional (ADF) package [39] with
the Becke–Perdew function were carried out on hydro-
genated model complexes (Cp, PH3 and dHpe in place
of Cp*, PPh3 and dppe) to reduce computational effort.
The atomic basis sets used were a double-Slater-type or-
bital (STO) (ADF basis set II) for C, P, H of the Cp, PH3
and dHpe ligands, and a triple-Slater-type orbital
(STO) + single-STO set (ADF Basis set IV) for the rest

M.I. Bruce et al. / Journal of Organometallic Chemistry 689 (2004) 3308–3326
3325
(b) Z.N. Chen, R. Appelt, H. Vahrenkamp, Inorg. Chim. Acta
309 (2000) 65.
of the molecule, with a frozen core approximation for the
orbitals up to 1s for C and N, 2p for P and 4p for Ru.
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8. Supplementary material
(b) N.G. Connelly, O.M. Hicks, G.R. Lewis, A.G. Orpen, A.J.
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(c) N.G. Connelly, G.R. Lewis, M.T. Moreno, A.G. Orpen, J.
Chem. Soc., Dalton Trans. (1998) 1905;
Full details of the structure determinations have been
deposited with the Cambridge Crystallographic Data
Centre as CCDC 237211–237216 (complexes 2–4 and
8–10, respectively). Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44
1223 336 033; e-mail: deposit@ccdc.cam.ac.uk or
www:http//www.ccdc.cam.ac.uk).
(d) N.G. Connelly, O.M. Hicks, G.R. Lewis, M.T. Moreno, A.G.
Orpen, J. Chem. Soc., Dalton Trans. (1998) 1913.
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Acknowledgements
We thank the Australian Research Council for sup-
port of this work and Johnson Matthey plc, Reading,
UK, for a generous loan of RuCl3 Æ nH2O. These studies
were facilitated by travel grants [ARC IREX, Australia,
and the Centre National de la Recherche Scientifique
(CNRS), France].
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