Syntheses and molecular structures of group 8 benzonitrile complexes

Article abstract of DOI:10.1016/j.jorganchem.2005.08.002

The molecular structures of eight nitrile complexes of general form [M(NCC₆H₄R-4)(L₂)Cp′]PF₆ [M = Fe, Ru; L₂ = dppe, (PPh₃)₂; Cp′ = Cp, Cp*] are reported and discussed in terms of the nature of the M-N interaction. Data are consistent with a predominantly σ-interaction, similar to that found in related acetylide complexes, with little evidence for metal to nitrile π-back bonding interactions.

Full text of DOI:10.1016/j.jorganchem.2005.08.002

Journal of Organometallic Chemistry 690 (2005) 4908–4919
www.elsevier.com/locate/jorganchem
Syntheses and molecular structures of group 8 benzonitrile complexes
´
Richard L. Cordiner, David Albesa-Jove, Rachel L. Roberts, Julian D. Farmer,
*
´
Horst Puschmann, Deborah Corcoran, Andres E. Goeta, Judith A.K. Howard, Paul J. Low
Department of Chemistry, University of Durham, South Rd, Durham DH1 3LE, UK
Received 12 April 2005; received in revised form 26 July 2005; accepted 3 August 2005
Available online 19 September 2005
Abstract
The molecular structures of eight nitrile complexes of general form [M(NCC6H4R-4)(L2)Cp0]PF6 [M = Fe, Ru; L2 = dppe, (PPh3)2;
Cp0 = Cp, Cp*] are reported and discussed in terms of the nature of the M–N interaction. Data are consistent with a predominantly
r-interaction, similar to that found in related acetylide complexes, with little evidence for metal to nitrile p-back bonding interactions.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Nitrile; Back-bonding; Molecular structure
1. Introduction
(TCNE), the cyanoacetylide complex is a much stronger
r-donor, and can be used in the formation of robust homo
and hetero-bimetallic compounds such as [{Ru(PPh3)2-
Cp}2(l-C„CC„N)][PF6] and [{Cp(PPh3)2Ru}(l-C„
CC„N){Fe(dppe)Cp}][PF6]. In the course of extending
this study to other half-sandwich metal systems, and
exploring the nature of the M–N„CC„CR bonding inter-
action, we found it necessary to have access to a range of
spectroscopic, electrochemical and structural parameters
from simple nitrile complexes of general form ½MðNCRÞ-
ðL2Þðg5-C5R05Þꢀþ. We report here a number of these half-
sandwich complexes featuring benzonitrile ligands, and
offer a comparison of the structural and electronic trends
within the series.
The interest in nitrile ligand chemistry has undergone
something of a renaissance in recent years, spurred on by
observations of significant second order non-linear optical
responses [1–8], the desire to rationalise and exploit the
greatly enhanced electrophilicity of the nitrile carbon cen-
tre when coordinated to an electron-rich metal centre [9–
11], and the rigid-rod like structure of the M–N–C moiety
[12]. Nitriles are isoelectronic with acetylide anions and,
unsurprisingly, similar interests have prompted many
investigations of the synthesis, molecular structure, reactiv-
ity, optical and magnetic properties and electronic struc-
ture of metal acetylide complexes [13–17].
We have recently undertaken an investigation of the
coordination and organometallic chemistry of a number
of unusual cyanocarbons [18], and have described the syn-
thesis of complexes [Ru(N„CC„CPh)(PPh3)2Cp][PF6]
and Ru(C„CC„N)(PPh3)2Cp, featuring the cyanoacety-
lene and cyanoacetylide ligands, respectively [19]. While
the phenylpropionitrile ligand is readily displaced by other
donor ligands including NCMe and tetracyanoethene
2. Results and discussion
A wide variety of nitriles have been shown to displace
the halide ligand (X) from iron and ruthenium complexes
MX(L2)Cp to afford cations [M(NCR)(L2)Cp]+, which
are readily isolated as the corresponding BFꢁ4 or PF6ꢁ salts
from reactions carried out in methanol or acetone [1–4,6,7,
17,20–22]. The complex salts [Ru(NCPh)(PPh3)2Cp]PF6
(1), [Ru(NCPh)(dppe)Cp*]PF6 (2) and [Fe(NCPh)(dppe)
Cp]PF6 (3) (Chart 1) were synthesised in good yield from
the reaction of the corresponding chloride complexes with
*
Corresponding author. Tel.: +44 0191 334 2114; fax: +44 0191 374
4737.
E-mail address: p.j.low@durham.ac.uk (P.J. Low).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.08.002

R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
4909
a 3-fold excess of benzonitrile in methanol solutions
containing NH4PF6, and crystallised by slow diffusion of
methanol (1, 3) or hexane (2) into concentrated CH2Cl2
solutions. The substituted derivatives [Ru(NCC6H4NO2-4)-
(PPh3)2Cp]PF6 (4) and [Ru(NCC6H4NMe2-4)(PPh3)2Cp]-
PF6 (5) were readily prepared in an entirely analogous
procedure from the stoichiometric reaction of RuCl(PPh3)2
Cp with 4-nitrobenzonitrile or 4-(dimethylamino)benzonitrile,
respectively. In the case of the reaction with 1,4-dicyano-
benzene (terephthalonitrile), the stoichiometric reaction
to form [Ru(NCC6H4CN)(PPh3)2Cp]PF6 (6a) was compli-
cated by the tendency for further reaction and/or dispro-
portionation to afford the bimetallic dicationic complex
[{Ru(PPh3)2Cp}2(l-NCC6H4CN)][PF6]2 (7). In order to
prepare pure samples of 6a it proved necessary to employ
a large (10-fold) excess of terephthalonitrile to metal re-
agent, while complex 7 could be readily obtained either
by reaction of 6a with a further equivalent of RuCl(PPh3)2-
Cp, or directly from the reaction of terephthalonitrile with
one half equivalent of the ruthenium precursor. The iron
analogue of 7, [{Fe(dppe)Cp}2(l-NCC6H4CN)][PF6]2 (8)
was prepared directly from the stoichiometric reaction of
FeCl(dppe)Cp with terephthalonitrile in THF containing
NH4PF6, and isolated as a bright red crystalline material
following crystallisation (CH2Cl2/Et2O). The sample
analysed consistently with one molecule of CH2Cl2 per
formula unit, with the solvent of crystallisation also being
to lower energy relative to the respective free ligands in
many cases [2,4,6–8,22]. However, more recently computa-
tional studies have indicated only a minimal contribution
from p-back bonding to the overall electronic structure,
suggesting instead that the various spectroscopic and struc-
tural properties of these complexes may be attributed to
orbital polarisation and electrostatic effects transmitted
through the M–N r-bond [9–11].
In the ruthenium based complexes studied here, the
m(C„N) stretch in the coordinated nitrile ligand (recorded
with 2 cmꢁ1 resolution) was found to fall in the narrow
range 2221 (5, 6a)–2233 (1) cmꢁ1 and within ca. 10 cmꢁ1
of the m(C„N) band in the free ligand. The observed shifts
do not correlate with trends which might be expected on the
basis of the p-character of the nitrile ligand substituent. For
example, the m(C„N) band of 5, which features the electron
donating NMe2 group, was found at the same frequency as
the m(C„N) band in the CN substituted derivative 6a, and
at a slightly lower frequency than the NO2 substituted
derivative 4.
A more systematic variation was found in the position
of m(CN) band as a function of the metal fragment within
the series 1 (2233 cmꢁ1), 2 (2227 cmꢁ1), 3 (2217 cmꢁ1).
The decreased m(C„N) frequency in iron nitrile complexes
relative to ruthenium examples has previously been attrib-
uted to the greater p-donating ability of the iron centre and
enhanced back-bonding from the metal to ligand [4,6,7].
However, given the identical N–C bond lengths in the ser-
ies (see below) it may not be wise to simply analyse this
subtle decrease in m(C„N) stretching frequency in terms
of variations in p-back bonding effects alone [9–11].
The 31P NMR chemical shifts of the triphenylphosphine
ligands and the 1H and 13C resonances of the Cp ligand dis-
played a discernable variation in chemical shift with the
inductive nature of the para substituent. Such trends are
common in half-sandwich complexes of this type, and the
variations in chemical shift with electron density at the me-
tal centre correlate with those observed in the isoelectronic
acetylide complexes such as Fe(C„CC6H4X-4)(dppe)Cp*
[23] and Ru(C„CC6H4X-4)(PPh3)2Cp [24] with more elec-
tron donating substituents leading to lower frequency
resonances.
The electrochemical response of the complexes should
also reflect the relative donor ability of the ligands and
the metal centre. Cyclic voltammetry (CV) studies were
performed on each of the compounds 1–9 using a platinum
disc working electrode and platinum wire counter and
pseudo-reference electrodes, from CH2Cl2 solutions con-
taining 0.1 M [N(C4H9)4][BF4], with electrode potentials
cited against an internal ferrocene (Fc/Fc+ = 0.46 V vs.
SCE) or decamethylferrocene (Fc*/Fc*+ = ꢁ0.02 V vs.
SCE) standard [25]. The electrochemical response of 1 at
a platinum electrode was characterised by a single oxida-
tion event at +1.30 V, the chemical reversibility of which
was improved at sub-ambient temperatures. Compounds
2 and 3 both displayed reversible oxidation waves at
+1.10 and +0.83 V, respectively, with the lower oxidation
1
observed in the H NMR spectrum of the product.
Reaction of 4-ethynylbenzonitrile with RuCl(PPh3)2Cp
and NH4PF6 followed by treatment with NaOMe to
deprotonate the intermediate vinylidene, gave the acetylide
complex [Ru(C„CC6H4CN)(PPh3)2Cp] (6b), which is
isoelectronic with 6a. Complex 6b reacted smoothly with
a further equivalent of RuCl(PPh3)2Cp to give the bimetal-
lic complex [{Cp(PPh3)2Ru}2(l-C„CC6H4CN)]PF6 (9).
Complex 9 could also be prepared directly from 4-eth-
ynylbenzonitrile and two equivalents of RuCl(PPh3)2Cp
in the presence of NH4PF6 and subsequent treatment with
base.
The availability of the cluster substituted benzonitrile
[Co2(l-HC2C6H4CN-4)(CO)4(dppm)] prompted us to
examine the coordination reaction of this species to the
Ru(PPh3)2Cp as well. The reaction with RuCl(PPh3)2-
Cp proceeded in a manner entirely analogous to that
described above, although the low solubility of the cobalt
cluster Co2(l-HC2C6H4CN-4)(CO)4(dppm) in methanol
necessitated the use of a THF/methanol co-solvent in the
preparation of [Co2(l-HC2C6H4CN{Ru(PPh3)2Cp})(CO)4-
(dppm)] PF6 (10).
The complex salts were readily characterised by the
usual spectroscopic methods, and pertinent data are
summarised in Table 1. Some earlier studies suggested a
significant contribution from p-back bonding effects in
the nitrile complexes of strongly electron donating metal
fragments such as ML2Cp (M = Fe, Ru; L = phosphine)
to explain the spectroscopic properties of metal nitrile com-
plexes, which include shifts of the IR active m(C„N) bands

4910
R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
Me5
PF6
PF6
PF6
Ru
N
C
Ru
N
C
Fe
N
C
Ph2P
Ph2P
Ph3P
Ph3P
PPh2
PPh2
1
2
3
PF6
PF6
Ru
N
C
NMe2
Ru
N
C
NO2
Ph3P
Ph3P
Ph3P
Ph3P
5
4
PF6
Ru
C
C
CN
Ph3P
Ru
N
C
CN
Ph3P
Ph3P
Ph3P
6b
6a
[PF6]2
[PF6]2
Fe
N
C
C
N
Fe
Ru
N
C
C
N Ru
Ph2P
Ph3P
Ph3P
PPh2
PPh3
Ph2P
PPh3
PPh2
8
7
PF6
PF6
H
C
Ru
N
C
C
Co(CO)2
PPh2
Ru
C
C
C
N Ru
Ph3P
Ph3P
Ph3P
Ph3P
PPh3
(OC)2Co
Ph2P
PPh3
9
10
Chart 1. The complexes employed in this study.
potentials relative to 1 reflecting the more electron donat-
ing supporting ligands surrounding the metal centres.
Compounds 4, 5, 6a and 7 each displayed an irreversible,
poorly defined oxidation event, the shape of which could
not be improved even at sub-ambient temperatures and
scan rates up to 5 V/s.
The bis(iron) complex 8 gave rise to two sequential oxi-
dation processes (E1/2 = 0.84, 0.91 V), the separation of
which (DE ca. 70 mV) indicates the metal centres to be
essentially independent [26]. The small separation of the
electrochemical events contrasts dramatically with the rela-
tively large (DE = 260 mV, Kc = 2.6 · 104) separation of

R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
4911
Table 1
Selected spectroscopic data for complexes and ligands reported in this work (NMR spectra in CDCl3 unless otherwise indicated)
C2 C3
N
C
C1
C4 R
Compound
m(C„N) cmꢁ1
Cp dH/dC
C„N dC
C1
C2
C3
C4
PR3 dP
Reference
N„CC6H5
N„CC6H4NO2
N„CC6H4NMe2
N„CC6H4C„N
2229
2240
2210
118.39
116.69
120.48
116.96a
Not obs.
111.26
129.13
127.91
Not obs.
111.97
118.13
96.84
131.66
133.38
133.01
132.76
132.73
128.75
124.13
111.16
132.41
149.88
152.23
[6]
[6]
[6]
116.72a
111.50
1
2233
2227
2217
2228
2221
2221
2220c
2226
2223
2218d
4.55/84.38
129.49
133.82
42.89
76.15
98.32
42.97
42.82
42.58
51.25
42.58
2e
3
b
4.45
111.41
117.46
95.61
133.35
124.31
133.84
132.04
134.21
111.77
134.32
150.04
153.23
4
4.64/84.98
4.42/83.81
4.62
4.31/85.76
4.57
5
6a
6b
7f
8
120.70
115.91
131.07
131.92
135.29
4.47/80.45
4.34, 4.51/83.93, 85.79
Not obs.
Not obs.
114.69
116.96
131.39a
131.77
130.97a
131.05
97.90
42.84, 51.25
9
Not obs.
a
Or vice versa.
b
Cp* dH 1.51 ppm, dC 93.18, 9.68 ppm.
c
d
e
f
m(C„C) 2063, 2037sh cmꢁ1
.
2059, 2040sh cmꢁ1
In CD2Cl2.
.
Limited solubility precluded the observation of 13C NMR resonances in common solvents.
the oxidation processes observed in the related 1,4-diethy-
nyl benzene bridged species [{Fe(dppe)Cp*}2(l-C„CC6-
H4C„C)] [27], and consequently the high thermodynamic
stability of the mono-oxidised form of the bis(acetylide)
complex towards disproportionation [26].
Compound 9 displayed a reversible oxidation wave at
+0.73 V and a second irreversible wave (Ep = +1.45 V)
that resulted in the formation of a deposit on the electrode
precluding further characterisation of this wave. As the
analogous mononuclear acetylide complex 6b was charac-
terised by a single oxidation event at +0.71 V, the chemical
reversibility of which was improved at sub-ambient tem-
peratures, the reversible process observed in 9 is assigned
to an oxidation event predominantly localised on the metal
acetylide fragment.
insoluble in THF) were recorded as 0.1 mM solutions in
both CH2Cl2 and THF (Table 2). Each compound exhib-
ited an absorption band with a kmax in the range 240–
260 nm which displayed no solvatochromic behaviour
and was assigned to the localised p /p* transitions of
the phosphine ligands. Similar assignments have been
made previously for a series of closely related compounds
[28,29]. In addition, each compound gave rise to a broad
envelope between 300 and 450 nm. This envelope con-
tained two absorption bands, the relative positions and
intensities of which varied between complexes. In the case
of compounds 1, 4, 5 and 7 these bands overlapped to
such an extent that it was impossible to establish the posi-
tions of the two separate band maxima and the only
distinguishable maximum is reported here. In the remain-
ing cases, however, it was possible to distinguish two
band maxima in the 300–450 nm region. These were ten-
tatively assigned as MLCT Rudp–Cp for the higher energy
The electronic absorption spectra of each compound
with the exception of 6a (due to the disproportionation
problems described above) and 2 (which proved to be
Table 2
UV/Vis absorption data from complexes 1–5 and 7–10
Complex
k
max/nm (e/Mꢁ1 cmꢁ1) (CH2Cl2)
k
max/nm (e/Mꢁ1 cmꢁ1) (THF)
1
2
238 (52,900), 307 (13,600)
230 (70,400), 307 (13,500)
n/a
260 (17,100), 331 (5900), 391 (3200)
229 (51,000), 329 (6900)
249 (26,900), 310 (8400), 346 (6600)
258 (17,800), 328 (5600), 391 (2500)
237 (43,200), 384 (6900)
3
4
5
230 (62,700), 332 (55,000)
247 (85,400), 363 (20,900), 420 (17,100)
227 (1,38,500), 450 (4600)
240 (81,500), 415 (24,510)
270 (30,800), 360 (15,200), 550 (2400)
234 (45,400), 332 (45,000)
225 (55,600), 363 (10,300), 420 (8300)
210 (259,000), 463 (9000)
240 (29,100), 410 (26,000)
270 (55,400), 360 (29,500), 550 (1800)
7
8
9
10

4912
R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
transition, which seems to be too intense to be assigned to
ꢂ
d–d processes, and MLCT Rudp–NCRp for the lower.
Comparable transitions in the iron complexes 3 and 8
are assigned similarly. The marked solvatochromic nature
of the lowest energy band in compound 4 (which bears
the strongly electron-withdrawing NO2 group) supports
this assignment.
Single crystals of the nitrile complexes 2, 3, 4, 5, 7, 9 and
10 and the acetylide complex 6b were obtained by slow dif-
fusion of methanol or hexane into concentrated CH2Cl2
solutions of the complex salt. Crystallographic details are
summarised in Table 3, while important bond lengths
and angles are summarised in Table 4, together with those
of some closely related species reported earlier by others.
Plots of individual ions and molecules are illustrated in
Figs. 1–8 and show the atomic labelling schemes employed.
The structural analyses reveal the expected half-sandwich
metal fragments, with the average M–C (Cp or Cp*) dis-
tances being somewhat shorter in the case of the nitrile
complexes than the acetylides.
The structure of the benzonitrile complex 1 has been re-
ported on a previous occasion [19], and the metrical param-
eters of this compound provide a useful point for
comparison. Substitution of the Cp and PPh3 ligands in 1
for Cp* and dppe ligands in 2 (Fig. 1) results in an increase
in the electron density at the metal centre (as evidenced by
the lower oxidation potential of 2 vs. 1). Interestingly, this
increase in electron density results in contraction of the
Ru–P bonds through enhanced Ru ! P back bonding,
rather than any significant foreshortening of the Ru–N
contact. The coordinated nitrile N„C bond lengths are
identical in 1 and 2, and the only other significant change
in bond lengths and angles is the smaller P–Ru–P angle
in 2 which is a consequence of the ethyl bridge in the
diphosphine ligand.
The shorter Fe–N bond length in 3 (Fig. 2) compared
with the ruthenium species 1 and 2 reflects the smaller size
of the iron atom, and the bond parameters associated with
3 are better compared with those of the complex cation
[Fe(NCC6H4NO2)(dppe)Cp]+ (Fe–N 1.874(11) A [30]),
˚
and the Fe–N contacts in these two complexes are found
to be indistinguishable within the limits of precision of
the structure solutions.
˚
The C–N(O2) bond length in 4 [1.490(8)–1.523(11) A,
the NO2 group being disordered over three sites] (Fig. 3)
˚
is similar to that found in the free ligand [1.48(1) A] [31]
and significantly longer than in the related acetylide com-
˚
plex Ru(C„CC6H4NO2)(PPh3)2Cp [1.468(6) A] [24], and
˚
the iron complex Fe(C„CC6H4NO2)(dppe)Cp [1.455 A]
[23]. The Ru–N bond length in 4 is somewhat shorter than
in the parent benzonitrile species 1, although the difference
between 4 and 5, which features the NMe2 group, is at the
borderline of statistical significance and must therefore be
regarded with caution.
There are surprisingly few other examples of metal
complexes of N,N-dimethylaminobenzonitrile to facilitate
more detailed comparisons [32]. The C–NMe2 distance

Table 4
Selected bond lengths and angles for compounds 1–5, 6b, 7, 9, 10 and related species
Compound
M–E
E„C
C–C(ipso)
M–P(1)
M–P(2)
M–E–C
E–C–C(ipso)
P(1)–M–P(2)
PhCN
NCC6H4NO2-4
NCC6H4NMe2-4
[Ru(NCPh)(PPh3)2Cp]PF6
[Ru(NCPh)(dppe)Cp*]PF6
[Ru(NCC6H4NO2)(PPh3)2Cp]PF6
[Ru(NCC6H4NO2){(+)-DIOP}Cp]PF6
[Ru(NCC6H4NMe2)(PPh3)2Cp]PF6
[Ru(NCC6H4OEt)(PPh3)2Cp]PF6
Ru(C„CPh)(PPh3)2Cp
1.137(14)
1.155(15)
1.145(3)
1.145(2)
1.146(7)
1.146(2)
1.137(18)
1.149(2)
1.152
1.215(4)/
1.214(7)
1.202(8)
1.219(3)
1.141(3)
1.129(14)
1.146(3)
1.201(7)a/
1.146(6)b
1.142(4)
1.401(14)
1.438(15)
1.434(4)
1.440(2)
1.438(7)
1.442(3)
1.42(2)
180.00
179(1)
179.49
[36]
[31]
[33]
This work
This work
This work
[8]
This work
[3]
1
2
2.037(1)
2.027(5)
2.023(2)
2.031(13)
2.031(1)
2.041(5)
2.016(3)/
2.017(5)
1.994(5)
2.011(2)
1.892(2)
1.874(11)
2.018(2)
1.994(5)a/
2.020(5)b
2.035(2)
2.334(1)
2.315(1)
2.329(1)
2.330(4)
2.325(1)
2.352
2.303/
2.229(3)
2.297(2)
2.3134(5)
2.207(1)
2.210(4)
2.348(1)
2.2903(14)a/
2.3104(14)b
2.3499(9)
2.335(1)
2.315(1)
2.330(1)
2.309(4)
2.321(1)
2.337
2.285/
2.228(3)
2.301(2)
2.3031(5)
2.206(1)
2.209(3)
2.344(1)
2.3046(13)a/
2.3218(14)b
2.3444(8)
171.70(12)
173.6(4)
171.24(15)
177.2(12)
173.52(14)
175.6
178.0(2)/
177.7(4)
175.9(4)
175.43(18)
172.16(18)
176.6(11)
166.9(2)
172.7(4)a/
172.0(4)b
176.7(2)
177.84(16)
174.9(6)
177.8(2)
178.6(15)
175.15(18)
175.1
171.9(3)/
170.6(5)
175.0(9)
175.1(2)
174.5(2)
177.4(15)
176.6(3)
175.1(5)a/
177.2(5)b
170.5(3)
97.46(1)
83.50(5)
100.30(2)
96.48(12)
104.24(2)
100.6
4
5
1.424(2)
1.405
1.456(4)/
1.462(8)
1.432(7)
1.432(3)
1.444(3)
1.42(2)
1.442(4)
1.419(7)a/
1.415(7)b
1.442(4)
100.5/
[37]/[38]
100.9(1)
101.17(7)
102.21(2)
84.37(6)
87.70(12)
102.89(2)
99.59(5)a/
97.25(5)b
102.62(3)
Ru(C„CC6H4NO2)(PPh3)2Cp 4
Ru(C„CC6H4CN)(PPh3)2Cp 6b
[Fe(NCPh)(dppe)Cp]PF6
[Fe(NCC6H4NO2)(dppe)Cp]PF6
[{Ru(PPh3)2Cp}2(l-NCC6H4CN)][PF6]2
[24]
This work
This work
[30]
This work
This work
3
7
[{Ru(PPh3)2Cp}2(l-CCC6H4CN)][PF6] 9
10
This work
a
Data from acetylide coordinated metal centre.
Data from nitrile coordinated metal centre.
b

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R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
Fig. 3. The cation from 4. For clarity only one of the disordered positions
of the NO2 is shown.
Fig. 4. The cation from the complex salt 5.
Fig. 5. The bimetallic dication from 7 showing the atom labelling scheme.
Fig. 6. A plot of the bimetallic cation 9 showing the atom labelling scheme.

R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
4915
centres. For example, substitution of the benzontrile
ligand in 1 with a stronger r-donating ligand such as phe-
nylacetylide [as in Ru(C„CPh)(PPh3)2Cp] results in a
contraction in the Ru–P bond lengths of approximately
˚
0.1 A, or about 4%. Similarly, the metal–phosphorus
bond lengths display some dependency on the degree of
electron density at the metal centre, with the more elec-
tron-rich species 2 giving rise to significantly shorter M–
P bonds than found in 1 (see above). The trends in Table
4 indicate that the electron-withdrawing NO2 group has
little effect on the M–P bond lengths in either metal acet-
ylide or nitrile complexes. The small contraction of the
Ru–P bond lengths in 5 relative to 1 and 4 likely reflects
the greater-donating properties of the NMe2 substituted
benzonitrile ligand.
In an effort to more clearly demarcate the electronic
properties of the nitrile ligand susbtitutent, we chose to
make an altogether less subtle change to the molecular
structure and introduced a second metal centre, which
would serve as a good r- and p- donor subsitutent with
little p-acceptor character. In the bimetallic complex 7
(Fig. 5) the metal fragments are related by an inversion
centre at the mid-point of the central aromatic ring,
and display shorter Ru–N bond lengths and longer
Ru–P bond lengths than found in the related
monometallic compound 1 (Table 4). The dication 7 also
exhibits the greatest deviation from linearity in the
M–N–C chain within this series, with the Ru–N(1)–
C(1) bond angle being distinctly non-linear (166.9(2)ꢁ),
although it is most likely that this distortion is due to
packing effects rather than any significant anomaly in
the electronic structure.
Fig. 7. A plot of a molecule of 6b showing the atom labelling scheme.
The C–N bond lengths across the series are independent
of both the nature of the para substituent on the nitrile li-
gand and the metal fragment and fall in the experimentally
˚
indistinguishable range 1.141(3)–1.149(2) A. The M–N
bond distances within the ruthenium based complexes var-
˚
ies between 2.023(2) and 2.041(5) A. While the shorter Ru–
N bond in 4 (which carries an electron accepting NO2
group) and 2 (which features a more electron donating me-
tal fragment) than in 1, together with the relative Fe–N
bond lengths in 3 and [Fe(NCC6H4NO2)(dppe)Cp]PF6, is
consistent with a back-bonding model, the bond length
alone cannot distinguish p-effects from the electrostatic ef-
fects highlighted by calculations on Re and Pt based sys-
tems [9–11].
The p-accepting properties of phosphines are well
established, and consequently within a set of structurally
similar complexes the M–P bond length is a modestly sen-
sitive probe of relative electron density at the metal
There appears to be little interaction between the metal
centres in 7 through the p-system with the N(1)–C(1) and
C(1)–C(11) bond lengths being identical with those of 1.
There is no obvious quinoidal character associated with
the aromatic portion of the dinitrile ligand. However,
Fig. 8. A plot of the heterometallic cation in 10 showing the atom labelling scheme.

4916
R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
the Ru–N(1) bond lengths are rather short and the Ru–P
bond lengths significantly elongated when compared with
the monometallic examples. Calculations on Re and Pt
systems in which p-back bonding is thought to be negligi-
ble suggest that the M–N bond is rather polarised, with a
considerable portion of the electronic charge residing on
the nitrogen atom. If one takes the elongated Ru–P bond
lengths in 7 relative to 1 to be indicative of less electron-
rich metal centres, the contraction in the Ru–N bonds can
be attributed to the better electrostatic attraction between
these centres.
nitrile p-back bonding effects to the M–N coordinate bond.
The variations in structure are more sensitive to r-donat-
ing substituents, in agreement with recent computational
work on rhenium and platinum complexes.
4. Experimental
All reactions were carried out in dry solvents, purified
using an Innovative Technology solvent purification
system, in oven dried glassware under an atmosphere
of nitrogen as a routine precaution. The complexes
RuCl(PPh3)2Cp [39], RuCl(dppe)Cp*[40], FeCl(dppe)Cp
[41], and Co2(l,g2-HC2C6H4CN-4)(CO)4(dppm) [35] were
prepared as described previously. Commercial benzonit-
rile was distilled prior to use, other reagents were used
as received. IR spectra were recorded from nujol mulls
on NaCl plates using a Nicolet Avatar spectrometer
fitted with an MCT detector (2 cmꢁ1 resolution). NMR
spectra were recorded on Varian Unity – 300 (1H,
299.91 MHz; 31P, 121.40 MHz) or INOVA 500 (13C,
125.69 MHz) spectrometers from solutions in CDCl3
unless indicated otherwise, and referenced against
residual solvent resonances or an external H3PO4
reference. Electrochemical measurements were made
from solutions in CH2Cl2 containing 0.1 M NBu4BF4
supporting electrolyte, using a conventional three elec-
trode cell and recorded on an AutoLab PGSTAT-30
potentiostat. A platinum dot working electrode was
employed together with Pt wire counter and pseudo
reference electrodes. All potentials are reported against
SCE, being referenced against an internal ferrocene/ferr-
ocenium couple (0.46 V).
More interesting are the changes that result from dimet-
allation of 4-ethynylbenzonitrile, and the mixed acetylide/
nitrile ligand present in 9 (Fig. 6), together with the struc-
tural data from 1, Ru(C„CPh)(PPh3)2Cp and 6b (Fig. 7),
provides the basis for an informative comparison of the
metrical parameters associated with the M–C„CR and
M–N„CR motifs. Each metal centre in 9 adopts the ex-
pected arrangement of Cp and PPh3 ligands, which to-
gether with the acetylide or nitrile fragment give rise to
pseudo-octahedral geometry. The aromatic portion of the
bridging 4-ethynylbenzonitrile ligand lies in a plane which
almost bisects the P–Ru–P angle at each metal centre,
and therefore provides a conjugation pathway between dp
orbitals on each metal centre. Whilst the C(9)„N(1) and
C(1)„C(2) bond lengths in 9 are essentially unchanged
relative to the respective model mononuclear complexes,
within the C(3)–C(8) ring system there is some evidence
for a degree of quinoidal character, which is supported
˚
by the short C(2)–C(3) [1.419(7) A] and C(6)–C(9)
˚
[1.415(7) A] bond lengths.
A comparison of the Ru(1)–P(1,2) bond lengths
˚
[2.290(1), 2.305(1) A] with the Ru–P bond lengths of
˚
Ru(C„CPh)(PPh3)2Cp [2.229(3), 2.228(3) A], and of
4.1. Preparation of [Ru(NCC6H5)(PPh3)2 Cp][PF6] (1)
˚
Ru(2)–P(3, 4) [2.310(1), 2.322(1) A] with those of 1
˚
[2.334(1), 2.335(1) A] reveals Ru(1)–P(1,2) to be rather
A flask was charged with RuCl(PPh3)2Cp (250 mg,
0.345 mmol), benzontrile (0.1 ml, 0.97 mmol), and NH4-
PF6 (200 mg, 1.22 mmol). The solids were suspended in
MeOH (20 ml) and the mixture heated to reflux under
a nitrogen atmosphere. After 30 min the yellow solution
that had formed was allowed to cool to room tempera-
ture and was then further cooled using an ice/water bath.
The resulting yellow precipitate was collected by filtra-
tion and washed with cold methanol to give 1 as a yel-
low solid (146 mg, 0.156 mmol, 45%). Crystals suitable
for X-ray diffraction studies were obtained by slow diffu-
sion of MeOH into a CH2Cl2 solution of 1. Found: C,
61.29; H, 4.30; N, 1.52. RuC48H40P3F6N requires: C,
61.41; H, 4.29; N, 1.49. 1H NMR: d 4.55 (s, 5H, Cp);
7.09–7.57 (m, 35H, Ph). 13C {1H} NMR: d 135.9 (m,
JCP = 23 Hz, Cipso PPh3); 133.8 (s, C4); 133.5 (t,
JCP = 5 Hz, Cortho PPh3); 132.7 (s, C2); 130.4 (s, Cpara
elongated in 9, and the corresponding bonds on the nitrile
coordinated metal centre being amongst the shortest re-
ported for this class of complex. When taken as a whole,
these structural parameters provide clear evidence for the
donation of electron density from Ru(1) to Ru(2) via the
polarised r-bond framework of the ethynylbenzonitrile
bridge.
The cluster pendant group in 10 has little influence on
the geometry of the ruthenium fragment (Fig. 8). The struc-
ture of the Ru(NCR)(PPh3)2Cp portion of 10 is essentially
identical to that of 1, save for a small elongation of the Ru–
P bond lengths and expansion of the P–Ru–P angle in the
case of the cluster complex. The small differences in the
structural parameters in related acetylide complexes have
been commented upon previously [35].
3. Conclusion
PPh3); 129.5 (s, C3); 128.7 (t, JCP = 5 Hz, Cmeta PPh3);
111.5 (s, C1); 84.4 (s, Cp).
31
P {1H} NMR: d 42.9 (s,
Structural data from a series of half-sandwich metal
complexes featuring substituted benzonitrile ligands are
inconsistent with a significant contribution from metal to
PPh3); ꢁ143 (ht, JPF = 713 Hz PF6). ES(+)-MS (m/z):
794 [Ru(NCC6H5)(PPh3)2Cp]+; 691 [Ru(PPh3)2Cp]+. IR:
m(C„N) 2233 cmꢁ1
.

R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
4917
4.2. Preparation of [Ru(NCC6H5)(dppe)Cp*][PF6] (2)
117.5 (s, C1); 85.0 (s, Cp). 31P {1H} NMR: d 43.0 (s,
PPh3); ꢁ142.9 (ht, JPF = 713 Hz PF6). ES(+)-MS (m/z):
839 [Ru(NCC6H4NO2)(PPh3)2Cp]+; 691 [Ru(PPh3)2Cp]+.
In a manner similar to that described for the preparation
of 1, a suspension of RuCl(dppe)Cp* (200 mg, 0.299 mmol),
benzonitrile (0.1 ml, 0.97 mmol), and NH4PF6 (195 mg,
1.20 mmol) in refluxing MeOH (10 ml) was allowed to react
for 1 h. The resulting yellow solution was cooled to room
temperature and solvent removed. The yellow residue was
dissolved in the minimum quantity of CH2Cl2, filtered and
the product crystallised by slow diffusion of hexane into a
CH2Cl2 solution, affording yellow crystals of 2 (207 mg,
0.235 mmol, 78%). This compound repeatedly analysed
IR: m(C„N) 2228 cmꢁ1
.
4.5. Preparation of [Ru(NCC6H4NMe2)(PPh3)2Cp][PF6]
(5)
Reaction of RuCl(PPh3)2Cp (100 mg, 0.138 mmol), 4-
N,N-dimethylaminobenzonitrile (20 mg, 0.138 mmol), and
NH4PF6 (80 mg, 0.49 mmol) yielded 5 as a yellow solid
(65 mg, 0.066 mmol, 48%). Crystals suitable for X-ray dif-
fraction were obtained from slow diffusion of hexane into a
solution of 5 in CHCl3. Found: C, 60.69; H, 4.61; N, 2.84.
1
low in carbon. H NMR (CD2Cl2): d 1.51 (s, 15H, Cp*);
2.46, 2.50 (2 · br, 4H, dppe); 6.54, 6.57 (pseudo-d, 2Hortho
,
PhCN); 7.26–7.62 (m, 23H, Ph). 13C {1H} NMR (CD2Cl2):
d 134.6–126.2 (m, Ph); 111.3 (s, C„N); 93.2 (s, C5Me5);
28.8–28.4 (m, dppe); 9.7 (s, C5 Me5). 31P {1H} NMR
(CD2Cl2): d 76.2 (s, dppe); ꢁ143.4 (ht, JPF = 710 Hz PF6).
ES(+)-MS (m/z): 794 [Ru(NCC6H5)(dppe)Cp*]+; 635
RuC50H45N2P3F6 requires: C, 61.16; H, 4.62; N, 2.85. H
1
NMR: d 4.42 (s, 5H, Cp); 7.00–7.30 (m, 37H, Ph); 2.97
(s, 6H, N(CH3)2). 13C {1H} NMR: d 153.2 (s, C4) 136.1
(t, JCP = 23 Hz, Cipso PPh3); 133.8 (s, C2) 133.48 (t,
JCP = 5 Hz, Cortho PPh3); 130.3 (s, Cpara); 128.6 (t,
JCP = 5 Hz, Cmeta PPh3); 111.8 (s, C3); 95.6 (s, C1); 83.8
(s, Cp); 40.2 (s, Me). 31P {1H} NMR: d 42.8 (s, PPh3);
ꢁ143.0 (ht, JPF = 713 Hz PF6). ES(+)-MS (m/z): 837
[Ru(NCC6H4NMe2)(PPh3)2Cp]+; 691 [Ru(PPh3)2Cp]+.
[Ru(dppe)Cp*]+. IR: m(C„N) 2227 cmꢁ1
.
4.3. Preparation of [Fe(NCC6H5)(dppe)(Cp)][PF6] (3)
An analogous procedure using FeCl(dppe)(Cp) (200 mg,
0.361 mmol), benzonitrile (0.1 ml, 0.97 mmol) and NH4PF6
(235 mg, 1.44 mmol) followed by recrystallisation by diffu-
sion of MeOH into a CH2Cl2 solution resulted in the for-
mation of red crystals of 3 (163 mg, 0.213 mmol, 59%).
Found: C, 59.87; H, 4.45; N, 1.80. C38H34P3NF6Fe re-
quires: C, 59.47; H, 4.47; N, 1.82.1H NMR: d 4.45 (s,
IR: m(C„N) 2221 cmꢁ1
.
4.6. Preparation of [Ru(NCC6H4CN-4)(PPh3)2Cp][PF6]
(6a)
A flask was charged with RuCl(PPh3)2Cp (100 mg,
0.138 mmol), 1,4-dicyanobenzene (173 mg, 1.38 mmol),
and NH4PF6 (80 mg, 0.49 mmol). Methanol (20 ml) was
added and the suspension was heated to reflux under a
nitrogen atmosphere. After 30 min the yellow solution
was cooled and the solvent removed on a rotary evapora-
tor. The yellow residue was dissolved in the minimum
quantity of CH2Cl2, filtered and precipitated into Et2O.
The precipitate formed was collected and dried to obtain
6a as a pale yellow powder (100 mg, 0.104 mmol, 75%),
but could not be obtained in an analytically pure form, pre-
sumably due to the complications of disproportionation
5H, Cp); 2.45, 2.63 (2 · br, 4H, dppe); 6.46 (s, 2Hortho
,
PhCN); 7.16–7.86 (m, 23H, Ph).13C {1H} NMR: d 136.7
(m, 2 · Cipso); 134.3 (s, C4); 133.4 (s, C2); 133.0 (br, Cortho);
132.0 (s, C3); 131.5 (br, Cortho); 131.3 (s, Cpara); 130.9 (s,
C
para); 129.7 (br, Cmeta); 129.5 (br, Cmeta); 129.1 (s, CN);
111.4 (s, C1); 79.9 (s, Cp); 28.1 (m, dppe). 31P {1H}
NMR: d 98.3 (s, dppe); ꢁ143.1 (ht, JPF = 713 Hz PF6).
ES(+)-MS (m/z): 622 [Fe(NCC6H5)(dppe)Cp]+; 519
[Fe(dppe)Cp]+. IR: m(C„N) 2217 cmꢁ1
.
1
4.4. Preparation of [Ru(NCC6H4NO2)(PPh3)2Cp][PF6]
(4)
described in the text. H NMR: d 4.62 (s, 5H, Cp); 6.98–
7.37 (m, 74H, Ph). 31P {1H} NMR: d 42.6 (s, PPh3);
ꢁ142.9 (ht, JPF = 713 Hz, PF6). ES(+)-MS (m/z): 819
[Ru(NCC6H4CN)(PPh3)2Cp]+; 691 [Ru(PPh3)2Cp]+. IR:
The reaction between RuCl(PPh3)2Cp (100 mg,
0.138 mmol), 4-nitrobenzonitrile (20.4 mg, 0.138 mmol),
and NH4PF6 (80 mg, 0.49 mmol) in refluxing MeOH
(20 ml) afforded an orange solution after 30 min which
was cooled (ice/water) to afford 4 as an orange precipitate
(90 mg, 0.092 mmol, 66%). Crystals suitable for X-ray dif-
fraction studies were obtained from slow diffusion of
MeOH into a solution of 4 in CH2Cl2. Found: C, 54.57;
H, 3.84; N, 2.66. RuC49H41N2P3F6Cl2O2 requires: C,
55.07; H, 3.87; N, 2.62.1H NMR: d 4.64 (s, 5H, Cp);
7.11–7.39 (m, 40H, Ph). 13C {1H} NMR: d 150.0 (s, C4)
135.6 (m, JCP = 22 Hz, Cipso PPh3); 134.21 (s, C2) 133.5
(t, JCP = 5 Hz, Cortho PPh3); 130.5 (s, Cpara); 128.8 (t,
JCP = 5 Hz, Cmeta PPh3); 127.9 (s, CN); 124.3 (s, C3);
m(C„N) 2221 cmꢁ1
.
4.7. Preparation of Ru(CCC6H4CN)(PPh3)2Cp (6b)
A suspension of RuCl(PPh3)2Cp (200 mg, 0.275 mmol),
HC„CC6H4CN (150 mg, 1.18 mmol), and NH4PF6
(100 mg, 0.61 mmol) in methanol (20 ml) was heated at re-
flux under a nitrogen atmosphere. After 1 h the red solu-
tion formed was treated with DBU and the yellow
precipitate formed was collected and washed (MeOH)
and dried to give 6b as a bright yellow powder (202 mg,
0.247 mmol, 90%). Despite repeated efforts, the compound
analysed consistently low in carbon (ca. 0.8%). 1H NMR: d

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R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
1
4.31 (s, 5H, Cp); 7.43–6.99 (m, 34H, Ph). 31P {1H} NMR: d
51.3 (s, PPh3). ES(+)-MS (m/z): 818 [M + H]+; 691
[Ru(PPh3)2Cp]+. IR: m(C„N) 2220 cmꢁ1, m(C„C) 2063,
4.90; N, 0.79. H NMR: d 4.52 (s, 5H, Cp); 4.35 (s, 5H,
Cp); 7.41–6.96 (m, 64H, Ph). 31P {1H} NMR: d 51.3 (s,
PPh3); 42.8 (s, PPh3); ꢁ143.0 (ht, JPF = 713 Hz PF6).
ES(+)-MS (m/z): 1508 [{Ru(PPh3)2Cp}2(l-C„CC6H4-
CN-4)]+, 818 [Ru(C„CC6H4CN)(PPh3)2Cp + H]+; 691
[Ru(PPh3)2Cp]+. IR: m(C„N) 2218 cmꢁ1, m(C„C) 2059,
2037(sh) cmꢁ1
.
4.8. Preparation of [{Ru(PPh3)2Cp}2(l-1,4-NCC6H4-
CN)][PF6]2 (7)
2040(sh) cmꢁ1
.
The reaction of RuCl(PPh3)2Cp (200 mg, 0.276 mmol),
1,4-dicyanobenzene (18 mg, 0.136 mmol), and NH4PF6
(160 mg, 0.98 mmol) in the usual manner yielded 7 as a yel-
low solid (140 mg, 0.078 mmol, 57%) which was recrystal-
lised from CH2Cl2/MeOH. Found: C, 56.03; H, 3.79; N,
1.40. Ru2C92H78N2P6F12Cl4 requires: C, 56.11; H, 3.99;
N, 1.42. 1H NMR: d 4.57 (s, 10H, Cp); 6.98–7.37 (m,
74H, Ph). 31P {1H} NMR: d 42.6 (s, PPh3); ꢁ142.8 (ht,
JPF = 713 Hz, PF6). ES(+)-MS (m/z): 1655 [M ꢁ PF6]+;
819 [Ru(NCC6H4CN)(PPh3)2Cp]+; 691 [Ru(PPh3)2Cp]+.
4.11. Preparation of [Co2(l,g2-HC2C6H4CN-4)-
{Ru(PPh3)2Cp}(CO)4(dppm)](PF6) (10)
A solution of RuCl(PPh3)2Cp (97.9 mg, 0.135 mmol),
Co2(l,g2-HC2C6H4CN-4)(CO)4(dppm) (100 mg, 0.135
mmol), and NH4PF6 (80 mg, 0.49 mmol), were allowed tore-
act in refluxing MeOH (15 ml) and THF (5 ml) for 2.5 h after
which time the solvent was removed and the residue recrys-
tallised from CH2Cl2/MeOH affording 10 as dark red crys-
tals (141 mg, 0.089 mmol, 66C80H64Co2RuO4P5NF6Cl2
1
IR: m(C„N) 2226 cmꢁ1
.
requires: C, 57.81; H, 3.88; N, 0.84. H NMR: d 3.06 (dt,
1H, JHP = 13 Hz, JHH = 9 Hz, CHP2); 3.60 (dt, 1H,
JHP = 13 Hz, JHH = 10 Hz, CHP2); 4.47 (s, 5H, Cp); 5.80
(s, 1H, JHP = 7 Hz, Co2C2H); 7.05–7.50 (m, 54H, Ph). 13C
{1H} NMR: d 84.0 (s, Cp); 128.5–133.2 (m, Ph). 31P {1H}
NMR: d 42.8 (s, dppm); 43.8 (br, PPh3). ES(+)-MS (m/z):
4.9. Preparation of [{Fe(dppe)Cp}2(l-NCC6H4CN-4)]-
[PF6]2 (8)
A solution of FeCl(dppe)Cp (150 mg, 0.27 mmol) and
1,4-dicyanobenzene (17.3 mg, 0.13 mmol) in THF (15 ml)
was treated with NH4PF6 (90 mg, 0.55 mmol) and the dark
blue-black solution heated at reflux point for 2 h, during
which time a red precipitate gradually formed. The solid
was collected by filtration, and washed with hexane before
being recrystallised from CH2Cl2 and diethyl ether, afford-
ing the title material (63 mg, 0.043 mmol, 32 %). Found: C,
55.31; H, 4.20; N, 1.87. Fe2C71H64N2P6F12Cl2 requires: C,
55.31; H, 4.18; N, 1.82. 1H NMR: d 2.42, 2.60 (2 · m,
2 · 2H, dppe); 4.47 (s, 5H, Cp); 5.32 (CH2Cl2 of recrystal-
lisation, 1H); 6.24 (s, 2H, NCC6H4CN); 7.32–7.78 (m, 20H,
Ph). 13C NMR: d 136.5 (t, JCP = 19 Hz, Cipso dppe); 136.2
(t, JCP = 19 Hz, Cipso dppe); 132.9 (t, JCP = 5 Hz, Cortho
dppe); 132.0 (s, Cpara dppe); 131.4 (t, JCP = 5 Hz, Cortho
dppe); 131.3 (s, C2/C3); 131.0 (s, C2/C3); 129.6 (t,
JCP = 5 Hz, Cmeta dppe); 129.5 (t, JCP = 5 Hz, Cmeta dppe);
114.7 (s, C1); 80.5 (s, Cp), 28.0 (m, dppe). 31P {1H} NMR:
d 97.9 (s, dppe). ES(+)-MS (m/z): 1311, [M ꢁ PF6]+; 519,
1432
[Co2(l,g2-HC2C6H4CN-4){Ru(PPh3)2Cp}(CO)4-
(dppm)]+; 691 [Ru(PPh3)2Cp]+. IR: m(CO) 2021, 1993,
1973 1955 cmꢁ1. The m(CN) band could not be detected.
4.12. Crystallographic studies
Diffraction data were collected on Bruker 3-circle dif-
fractometers with SMART 6K (for 2, 3, 5 and 7) or
SMART 1K (for 4, 6b, 9 and 10) CCD area detectors,
using graphite-monochromated sealed-tube Mo Ka radia-
tion. The data collection was carried out at 120 K (for 2,
3, 4, 5, 6b, 7 and 9) and 100 K (for 10) using cryostream
(Oxford cryosystem) open flow N2 cryostats. Reflection
intensities were integrated using the SAINT V6.45 program
[42] (for 2, 3, 5 and 9) and SAINT V6.02a [43] (for 4, 6b, 7
and 10).
The crystal structures were solved using direct-methods
and refined by full matrix least-squares against F2 of all
data using SHELXTL [44] software. All non-hydrogen atoms
where refined in anisotropic approximation, except the dis-
ordered nitro group in 4 and the carbon atom of a dichlo-
romethane molecule in 10, which were isotropically refined.
Hydrogen atoms were either located by a difference map
(for 2, 3, 5 and 7) or placed in calculated positions (4, 6b,
9 and 10) and refined isotropically using a riding model.
For compound 10 the position of the hydrogen atom
(H4) in the dicobalt moiety was freely refined.
[Fe(dppe)Cp]+. IR: m(C„N) 2223 cmꢁ1
.
4.10. Preparation of [{Ru(PPh3)2Cp}2(l-CCC6H4CN-4)]-
(PF6) (9)
A suspension of RuCl(PPh3)2Cp (200 mg, 0.275 mmol),
HC„CC6H4CN (18 mg, 0.142 mmol), and NH4PF6
(70 mg, 0.43 mmol) in methanol (20 ml) was heated at re-
flux point under a nitrogen atmosphere. After 30 min the
orange solution formed was treated with a methanolic solu-
tion of NaOMe and refluxed for a further 30 min. The yel-
low precipitate formed was collected and washed with
MeOH and hexane and dried to give 9 as a yellow powder
(180mg, 0.11mmol, 80%). Found: C, 65.48; H, 4.48; N,
1.03. Ru2C91H74NP5F6.2C3H6O requires: C, 65.87; H,
Disorder is present in all the structures except 6b and 7.
The PF6 anion is disordered in compounds 2, 5, and 9. In
the crystal structure of 3, the alkane chain of the dppe moi-
ety is disordered between two positions, partially populated
with occupancies of ca. 0.8 and 0.2. The nitro group in
compound 4 is highly disordered, and the electron density

R.L. Cordiner et al. / Journal of Organometallic Chemistry 690 (2005) 4908–4919
4919
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distribution was modeled by locating this group at three
different positions. In compound 10, a phenyl ring of the
dppm moiety presents rotational disorder. In the crystal
structure of 2, disordered solvent molecules are present,
and Platonꢀs Squeeze tool was applied [45]. Crystal data
and experimental details are listed in Table 3.
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Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic Data
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We are grateful to the EPSRC, ONE-North East and
the University of Durham for financial support of this
work and to Johnson Matthey Plc for a generous loan of
RuCl3 Æ nH2O. RLC and RLR hold studentships from the
Department of Chemistryꢀs EPSRC Doctoral Training
Account.
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