Synthesis and reactivity of ruthenium(II) complexes containing hemilabile phosphine-thiophene ligands

Article abstract of DOI:10.1039/b001898h

The syntheses of two new phosphine-thiophene ligands, 2-(2′-{diphenylphosphino}phenyl)thiophene (dpppth) and 3′-diphenylphosphino-2,2′ :5′,2-terthiophene (dppterth) are reported. These ligands react with [RuCl2(PPh₃)³] to give [RuCl₂(dpppth-P,₅)₂] and [RuCl-₄dppterth-P.S1-4], respectively, which both exist as a mixture of two isomers in solution. [RuCl₂(dpppth-P,₅)₂] reacts at 25 °C with carbon monoxide to yield a mixture of [RuCl2(CO)(dpppth-f)(dpppth-/′,₅)] and [RuCl₂(CO)₂(dpppth-.P)₂], while [RuCl-₄dppterth-.P.S¹-₄] reacts with CO under the same conditions to give only the monocarbonyl complex [RuCl₂(CO)(dppterth-P)(dppterth-P,5′)J. Displacement of one of the dppterth ligands in [RuQ₂(dppterth-.P,S₁)₂] with bis(diphenylphosphino)methane (dppm) yields c/5-[RuCl₂(dppm)(dppterth-.P.S¹)] which isomerizes in solution to fra;w-[RuCl2(dppm)(dppterth-.P,S1)J. These complexes react with carbon monoxide to give trans-[RuCl₂(CO)(dppm)(dppterth-/>)] and cw-[RuCl2(CO)(dppm)(dppterth-/>)], respectively, in which the thiophene end of the dppterth ligand is displaced by CO. The electronic spectra of these complexes are reported. Crystal structures for [RuCl₂(dpppth-.P,S)₂], [RuCl²(CO)(dppterth-.P)(dppterth-.P,S¹)] and cu-[RuCl₂(dppterth-.P,S¹)(dppm)] are reported. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b001898h

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Synthesis and reactivity of ruthenium(II) complexes containing
hemilabile phosphine–thiophene ligands
Olivier Clot,a Michael O. Wolf,*a Glenn P. A. Yapb and Brian O. Patricka
a Department of Chemistry, University of British Columbia, Vancouver, British Columbia,
Canada, V6T 1Z1. E-mail: mwolf@chem.ubc.ca
b Department of Chemistry, University of Ottawa, Ottawa, Canada, K1N 6N5
Received 8th March 2000, Accepted 13th June 2000
Published on the Web 20th July 2000
The syntheses of two new phosphine–thiophene ligands, 2-(2Ј-{diphenylphosphino}phenyl)thiophene (dpppth) and
3Ј-diphenylphosphino-2,2Ј:5Ј,2Љ-terthiophene (dppterth) are reported. These ligands react with [RuCl2(PPh3)3] to
give [RuCl2(dpppth-P,S)2] and [RuCl2(dppterth-P,S1)2], respectively, which both exist as a mixture of two isomers in
solution. [RuCl2(dpppth-P,S)2] reacts at 25 ЊC with carbon monoxide to yield a mixture of [RuCl2(CO)(dpppth-P)-
(dpppth-P,S)] and [RuCl2(CO)2(dpppth-P)2], while [RuCl2(dppterth-P,S1)2] reacts with CO under the same conditions
to give only the monocarbonyl complex [RuCl2(CO)(dppterth-P)(dppterth-P,S1)]. Displacement of one of the
dppterth ligands in [RuCl2(dppterth-P,S1)2] with bis(diphenylphosphino)methane (dppm) yields cis-[RuCl2(dppm)-
(dppterth-P,S1)] which isomerizes in solution to trans-[RuCl2(dppm)(dppterth-P,S1)]. These complexes react
with carbon monoxide to give trans-[RuCl2(CO)(dppm)(dppterth-P)] and cis-[RuCl2(CO)(dppm)(dppterth-P)],
respectively, in which the thiophene end of the dppterth ligand is displaced by CO. The electronic spectra of these
complexes are reported. Crystal structures for [RuCl2(dpppth-P,S)2], [RuCl2(CO)(dppterth-P)(dppterth-P,S1)] and
cis-[RuCl2(dppterth-P,S1)(dppm)] are reported.
such as PPh3 Ϫ xThx (Th = 2-thienyl, x = 1–3), in which only the
Introduction
phosphine coordinates, have also been reported.25–33
Conjugated polymers and oligomers are an interesting and
important class of materials which are of use in a wide range
of optoelectronic applications, including light-emitting diodes,
photovoltaics and field-effect transistors.1,2 Many approaches
are being explored to modify the optical and electronic proper-
ties of these materials, amongst them the attachment of metal
groups to the conjugated backbone.3
We elected to examine bidentate hemilabile ligands incor-
porating a phosphine and thiophene. This motif was recently
employed by Weinberger et al. to make polymerizable
ruthenium complexes;12 however, we chose to place the
phosphine directly on the oligothiophene backbone to provide
the most intimate contact between the metal and the ligand in
both mono- and bi-dentate coordination modes. We describe
here the syntheses and properties of two new phosphine–
thiophene ligands and a series of Ru() complexes which
incorporate these ligands. In addition, we demonstrate the
reactions of carbon monoxide with several of these com-
plexes, resulting in displacement of the thiophene.
We are interested in investigating materials in which metal
groups are coupled to oligothiophenes, and have recently
examined charge delocalization in compounds in which Fe
and Ru centers are inserted into a conjugated backbone.4–7
A complementary approach involves attaching metal groups
pendant to the oligothiophene, which permits electronic
coupling to the conjugated backbone providing the link
between the metal and oligomer is chosen appropriately.
A number of research groups have reported materials in which
conjugated oligomers or polymers are coordinated to metal
centers, and these efforts have been recently reviewed;3 however,
we are particularly interested in creating materials in which
the bonding and coordination environment of the metal can
be varied while still keeping the complex anchored to the
oligomer or polymer. One way in which this may be achieved
is via a backbone which functions as a hemilabile ligand8 on a
metal to which it is coordinated. The backbone may then be
switched between bidentate and monodentate coordination
modes, with the electronic coupling between the metal group
and the conjugated backbone depending on the coordination
mode.
Results and discussion
Synthesis of phosphine–thiophene ligands
The phosphine–thiophene ligand dpppth 1 was prepared by
reaction of 2-(2Ј-bromophenyl)thiophene with Mg to yield the
Grignard reagent, followed by reaction with chlorodiphenyl-
phosphine (Scheme 1). Compound 1 could not be crystallized
An attractive approach towards this goal is to utilize thio-
phene, which coordinates weakly to most transition metals, in
combination with a strongly coordinating group to generate the
hemilabile ligand. Thiophene coordinates via several binding
modes, from η1 to η5,9–11 and there are several examples known
in which thiophene has been incorporated into multidentate
thiophene–nitrogen and thiophene–phosphine ligands.12–24
A
number of complexes containing phosphine–thiophene ligands,
Scheme 1
DOI: 10.1039/b001898h
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Table 1 Selected bond lengths (Å) and angles (Њ) for 3
and was isolated as a very thick oil. When stored at 0 ЊC,
the pale yellow product was stable in air for several months.
Compound 2 (dppterth) was synthesized by the reaction of
3Ј-bromo-2,2Ј:5Ј,2Љ-terthiophene with n-butyllithium followed
by reaction with chlorodiphenylphosphine. The product was
isolated as a light yellow solid which oxidized slowly in air.
Ru–Cl(1)
Ru–P(1)
2.4676(12)
2.3191(12)
1.461(7)
Ru–Cl(2)
Ru–P(2)
P(1)–C(10)
P(2)–C(32)
2.4080(12)
2.3392(12)
1.857(5)
C(4)–C(5)
C(26)–C(27)
1.462(8)
1.876(5)
Cl(1)–Ru–P(1)
Cl(2)–Ru–S(2)
S(2)–Ru–P(2)
Ru–S(1)–C(1)
Ru–S(2)–C(23)
Ru–P(1)–C(10)
S(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(1)–S(1)–C(4)
S(2)–C(26)–C(25)
169.62(5)
178.00(6)
81.48(5)
115.6(2)
131.0(3)
115.18(16)
112.8(5)
112.8(5)
91.7(3)
S(1)–Ru–P(2)
S(1)–Ru–P(1)
S(1)–Ru–S(2)
Ru–S(1)–C(4)
Ru–S(2)–C(26)
Ru–P(2)–C(32)
S(1)–C(4)–C(3)
C(2)–C(3)–C(4)
S(2)–C(23)–C(24)
165.93(5)
90.81(4)
95.44(6)
111.23(17)
119.7(2)
110.33(18)
110.1(4)
114.1(5)
106.0(6)
Synthesis and structures of 3 and 4
Ruthenium() complexes of dpppth and dppterth were pre-
pared by reaction of slightly more than two equivalents of
the ligands with [RuCl2(PPh3)3]. Complexes 3 and 4 were
106.7(6)
C(23)–C(24)–C(25) 114.3(8)
C(23)–S(2)–C(26) 98.8(3)
C(24)–C(25)–C(26) 113.6(8)
afforded in good yields as microcrystalline rust colored and
orange solids, respectively. Both complexes are air stable in the
solid state and are soluble in polar organic solvents such as
methylene chloride and acetone.
Solutions of 3 in methylene chloride are not stable in air
and turn green within 15 min unless kept under nitrogen. The
31P NMR spectrum of 3 consists of two doublets, indicating
that the phosphorus centers are in a cis arrangement. In
addition, a small singlet is observed at δP 39.72 indicating
the presence of a second structure in solution in which the
phosphorus nuclei are equivalent.
Fig. 1 ORTEP53 view of 3. Vibrational ellipsoids are drawn at the 30%
probability level.
dbt = dibenzothienyl) (132Њ)13 and 10Њ larger than for [ReCp*-
(CO)2(C4H4S)] (140.4Њ).34
Crystals of 3 were grown by slow diffusion of hexanes into
a solution of the compound in chloroform. The solid-state
structure of 3ؒ3CHCl3 is shown in Fig. 1 and selected bond
lengths and angles are presented in Tables 1 and 2. Redissolving
In the η1-coordination mode, thiophene acts primarily as a
σ donor, but has also been shown to act as a π acceptor.35 The
extent of π backbonding has been demonstrated to be related to
both the ring tilt angle and the Ru–S bond length. In 3, the
thienyl ring in dpppth2 has both a shorter Ru–S bond length
and a larger tilt angle than in dpppth1 indicating that π back-
bonding is more significant in dpppth2. The bond lengths in
the coordinated thienyl groups in 3 are different from those in
thiophene (Table 2) (vide infra).36
these crystals in CDCl3 shows the same ratio of isomers by 31
P
NMR as before crystallization suggesting that the isomers are
in equilibrium in solution. The geometry about the ruthenium
is a distorted octahedron where both dpppth ligands coordinate
in a bidentate fashion via the phosphorus and sulfur atoms.
Only one enantiomer was found in the crystal structure. Both
thiophenes are coordinated to the metal via the sulfur in an η1
binding mode and the two Ru–S bond lengths are in the range
reported for ruthenium complexes containing η1-coordinated
thiophene rings.9–11
The two dpppth ligands are not equivalent in this structure.
The phenyl and thienyl rings in the ligand containing P(2) and
S(2) (dpppth2) are coplanar. In the other ligand (dpppth1), the
phenyl and thienyl rings are twisted with respect to one another
with a dihedral angle of ca. 50Њ. The bite angle (P–Ru–S) of
dpppth1 is 81.5 and 90.8Њ for dpppth2. The Ru–S bond lengths
are within the range reported for η1-coordinated thiophenes,9–11
with a shorter bond for the ligand with the thienyl group trans
to Cl (dpppth2). In both ligands, the plane of the thiophene
ring is tilted with respect to the Ru–S axis with an angle of 128Њ
for dpppth1 and 150Њ for dpppth2 (Table 2). The tilt angle of
the thiophene in dpppth1 is in the range observed in other
ruthenium complexes containing η1 bound thiophenes.9–11 To
our knowledge, the tilt angle of the thiophene in dpppth2 is the
largest reported to date for S-coordinated thiophene. It is nearly
20Њ larger than for [RuCl2(P{dbt}{4-tol}2-P,S)2] (tol = tolyl,
Compound 4 is stable in solution and its 31P NMR spectrum
contains a singlet at δP 26.96 as well as a pair of doublets. Based
on the similarities to the spectrum of 3, the two doublets are
assigned to a cis isomer of 4, and the singlet assigned to a
second structure in which the phosphorus nuclei are equivalent.
Based on the crystal structure of 3 and the NMR spectra, we
assume that the cis form of 4 also has an all-cis geometry.
At room temperature, 60% of the mixture is the cis isomer, and
all attempts to isolate the isomers were unsuccessful, which
suggests that the two species may also be in equilibrium in
solution.
Reactions of 3 and 4 with CO
Complexes 3 and 4 both react in solution with carbon
monoxide; however, the reaction is slower than with similar
complexes containing hemilabile phosphine–ether ligands,
such as [RuCl2({2-PPh2}C6H4OCH3-P,O)2].37 The reaction of 4
with carbon monoxide (Scheme 2) results in the formation of
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Table 2 Bond lengths and tilt angles of the η1-coordinated thienyl groups
Bond length/Å
Compound
Tilt angle/Њ
Ru–S
C–S
C᎐C
᎐
C–C
3/dpppth1
128
150
125
153
—
2.4106(12)
2.2790(15)
2.340(4)
2.3068(9)
—
1.738(4), 1.734(5)
1.671(6), 1.671(6)
1.738(13), 1.738(4)
1.728(4), 1.738(4)
1.714(1)
1.343(8), 1.349(7)
1.348(10), 1.361(11)
1.353(17), 1.321(15)
1.358(6), 1.364(6)
1.370(2)
1.420(8)
1.436(12)
1.457(17)
1.416(6)
1.424(2)
3/dpppth2
5
8
Thiophenea
a From ref. 36.
Table 3 Selected bond lengths (Å) and angles (Њ) for 5
Ru–Cl(1)
Ru–P(1)
Ru–C(1)
P(1)–C(7)
S(2)–C(6)
P(2)–C(32)
S(5)–C(30)
S(6)–C(37)
2.452(4)
2.367(4)
Ru–Cl(2)
Ru–P(2)
C(1)–O(1)
C(5)–C(6)
C(9)–S(2)
S(5)–S(33)
S(6)–C(34)
2.386(3)
2.401(4)
1.133(13)
1.406(15)
1.709(13)
1.748(13)
1.595(15)
1.810(15)
1.816(13)
1.709(13)
1.806(13)
1.702(13)
1.545(16)
S(1)–Ru–P(1)
P(1)–Ru–P(2)
Ru–C(1)–O(1)
Ru–P(2)–C(32)
S(1)–C(2)–C(3)
C(4)–C(5)–S(1)
91.8(5)
S(1)–Ru–Cl(2)
Cl(1)–Ru–C(1)
Ru–P(1)–C(7)
C(2)–S(1)–C(5)
C(2)–C(3)–C(4)
C(6)–S(2)–C(9)
178.68(13)
175.0(4)
112.8(4)
92.9(7)
112.3(13)
92.2(7)
172.89(13)
178.4(13)
115.9(4)
110.8(11)
110.4(11)
inner peaks of the two doublets are observed and the chemical
shift difference between the peaks increases with magnetic field,
consistent with this assignment.
Fig. 2 ORTEP53 view of 5. Vibrational ellipsoids are drawn at the 30%
probability level.
Although 4 exists as a mixture of isomers in solution, only
one product 5 results from the reaction with CO. This suggests
a reaction pathway that involves isomerization of the reactants
prior to reaction with CO. There is no evidence for the form-
ation of dicarbonyl complexes even when 4 is left to react with
CO for three days at 25 ЊC. The thiophene trans to the chloro in
5 may be too strongly coordinated to be displaced by a second
CO under these conditions.
Compound 5 contains both bidentate and monodentate
forms of dppterth; thus, it is possible to compare the bond
lengths and angles of both forms of the ligand in a single
structure. The bidentate dppterth ligand forms a six-membered
ring with a bite angle (P–Ru–S) of 91Њ. In this ligand, the Ru–S
bond length for the η1-bound thienyl ring is 2.340(4) Å, which
is comparable to the Ru–S bond lengths in 3. The thiophene
plane in 5 is tilted with respect to the Ru–S axis with an angle
of 125Њ, comparable to the tilt angle in dpppth1 in 3, suggesting
that there is a comparable degree of backbonding in these
thiophene–Ru bonds. Despite their different coordination
modes, there are only slight differences in bond lengths
and angles between the two dppterth ligands and these are
close to those observed in the structure of 3Ј-methyl-2,2Ј:5Ј,2Љ-
terthiophene.39 The bond lengths of the coordinated thienyl
group in 5 are similar to those observed for the dpppth1 ligand
in 3 (Table 2). The coordination of the sulfur of one of the rings
in the terthienyl moiety to the Ru does not introduce any major
perturbations in the structure of the oligomer.
When 3 reacts with CO, two major products are formed,
both of which appear as singlets (δP 17.7 and 10.9) in the 31P
NMR spectrum. The mixture of the two products has three
absorption bands in the carbonyl stretching region of the IR
spectrum, at 1976, 2015 and 2098 cmϪ1. By comparison with 5
(νCO = 1973 cmϪ1), we assign one product as the monocarbonyl
6 (νCO = 1976 cmϪ1 and δP 17.7) (Scheme 3). The second product
is assigned as the cis dicarbonyl 7 (νCO = 2015 and 2098 cmϪ1
and δP 10.9) by comparison to the IR spectrum of the closely
related dicarbonyl [RuCl2(CO)2(PPh3)2].40
Scheme 2
one major product 5 that exhibits two closely spaced resonances
at δP 5.89 and 5.52. The IR spectrum of this product contains
one sharp peak in the carbonyl stretching region at 1973 cmϪ1
.
Crystals of 5ؒCHCl3 were grown by slow diffusion of hexanes
into a chloroform solution of the compound, and the solid-
state crystal structure is shown in Fig. 2. Selected bond lengths
and angles are collected in Tables 2 and 3. The structure shows
that 5 is a monocarbonyl complex with the Ru in a slightly
distorted octahedral environment. The two phosphorus atoms
are oriented trans to each other and the carbonyl is trans to one
of the chloro ligands while the coordinated thienyl group is
trans to the other chloro group. The monocarbonyl complex
resulting from the reaction of [RuCl2(P{dbt}{4-tol}2-P,S)2]
with CO has the same geometry around the ruthenium center as
5.38 The 31P NMR spectrum of 5 consists of an AB spin pattern
where the difference in chemical shift is very small. Only the
J. Chem. Soc., Dalton Trans., 2000, 2729–2737
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Table 4 81.015 MHz 31P{1H} NMRa data for complexes with AMX spin pattern
δ
J/Hz
Complex
PA
PM
PX
2JAM
2JAX
2JMX
8
9
cis-[RuCl2(dppm)(dppterth-P,S)]
trans-[RuCl2(dppm)(dppterth-P,S)]
10 trans-[RuCl2(CO)(dppm)(dppterth-P)]
4.88
16.11
10.18
Ϫ10.64
Ϫ2.74
Ϫ8.19
2.97
Ϫ23.73
Ϫ14.99
Ϫ20.56
Ϫ9.30
24.5
27.5
21.0
27.8
41.3
61.2
42.7
33.4
363
322
364
273
11 cis-[RuCl2(CO)(dppm)(dppterth-P)]
Ϫ40.76
a Solvent: CDCl3.
Scheme 3
Solutions of 7 are not stable in air and convert to 6 by loss of
CO, shown by the disappearance of the absorption at 2098
cmϪ1 and the concomitant growth of the band at 1976 cmϪ1
.
All attempts to precipitate the reaction products under a CO
atmosphere yielded mixtures with 6 as the dominant species.
Efforts to purify 6 by bubbling N2 through a mixture of 6 and 7
to remove the latter were unsuccessful owing to the presence of
several side-products which could not be separated. Similarly,
when N2 is bubbled through a solution of 6 for 12 h in an effort
to decarbonylate completely to 3, the 31P NMR spectrum of
the resulting reaction mixture is very complicated, showing 3
as a minor product along with several resonances that could not
be assigned to any known compounds.
Fig. 3 ORTEP53 view of 8. Vibrational ellipsoids are drawn at the
30% probability level. Phenyl groups have been omitted for clarity.
Synthesis and structure of 8 and 9
Treatment of a solution of 4 with one equivalent of bis(diphenyl-
phosphino)methane (dppm) at room temperature results in the
displacement of one of the dppterth ligands to yield complex 8
selected bond lengths and angles are shown in Tables 2 and 5. In
this structure, the ruthenium center is in a distorted octahedral
environment, due to the small bite angle (P–Ru–P) of the dppm
ligand. The chloro ligands are in a cis arrangement, and the
dppterth ligand chelates to form a six-membered ring with a
bite angle (P–Ru–S) close to 90Њ. Dppterth can form either
a six- or seven-membered ring depending on which terminal
thiophene in the terthienyl group is coordinated; however, we
do not see any evidence for formation of the seven-membered
ring isomer in 8. The thiophene is coordinated through the
sulfur atom with a Ru–S bond length of 2.3068(9) Å and a tilt
angle of 153Њ. This angle is even larger than the tilt angle of
dpppth2 in 3 indicating that the extent of π backbonding to the
thiophene in 8 is much larger than in 5 and comparable to
dpppth2 in 3. The bond lengths in the coordinated thienyl ring
in 8 are comparable to those in dpppth1 in 3 and in 5 (Table 2).
Overall, the terthienyl group in 8 is only slightly distorted with
respect to the structure of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene.39
It has been suggested that π backbonding with coordinated
thiophene rings should result in a slight weakening of the C–S
bonds in the ring.35 We observe this in all the structures in this
work with the exception of dpppth2 in 3. Despite a large tilt
angle, the C–S bonds in this ligand are shorter than the C–S
bonds in thiophene (Table 2). At this time we do not have an
explanation for this anomaly.
and a small amount of trans-[RuCl2(dppm)2]. The 31P NMR
spectrum of 8 consists of an AMX coupling pattern, and this
data is shown in Table 4. The assignment of the phosphorus
resonances is shown in Scheme 5.
Crystals of complex 8ؒ3CH2Cl2 were obtained by slow dif-
fusion of hexanes into a solution of the compound in methyl-
ene chloride. The solid-state structure is shown in Fig. 3 and
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Table 5 Selected bond lengths (Å) and angles (Њ) for 8
Ru–Cl(1)
Ru–P(1)
Ru–P(3)
P(1)–C(6)
2.4060(9)
2.3861(9)
2.3336(9)
1.825(4)
Ru–Cl(2)
Ru–P(2)
C(4)–C(5)
C(8)–C(9)
2.4854(9)
2.3122(9)
1.442(5)
1.448(5)
Cl(1)–Ru–S(1)
P(1)–Ru–P(3)
P(2)–Ru–P(3)
Ru–S(1)–C(1)
Ru–P(1)–C(6)
S(1)–C(4)–C(3)
C(1)–C(2)–C(3)
172.80(4)
174.43(3)
72.27(3)
131.7(1)
114.5(1)
109.3(3)
113.7(4)
Cl(2)–Ru–P(2)
S(1)–Ru–P(1)
Ru–S(1)–C(4)
S(1)–C(1)–C(2)
C(2)–C(3)–C(4)
S(1)–C(4)–C(5)
165.92(3)
90.33(3)
121.6(1)
109.9(3)
113.7(4)
120.3(3)
In the reaction of 4 with dppm, only one isomer 8 forms. It is
possible that this reaction proceeds via a two-step pathway,
in which the first step is dissociation of the thiophene end of
one of the dppterth ligands, followed by the monodentate
coordination of dppm. The second step would then involve
loss of the monodentate dppterth and the chelation of dppm.
It is interesting that one of the two dppterth ligands in 4 is
preferentially displaced by dppm to yield only the isomer 8. We
infer from the structure of 3 that the degree of π backbonding
and consequently the lability of the two dppterth ligands in 4
is likely quite different. The second dppterth ligand in 4 can
eventually be displaced by dppm, as evidenced by the small
amount of trans-[RuCl2(dppm)2] that forms.
When a solution of 8 is left in ambient laboratory light at
room temperature, the complex slowly isomerizes to 9 and
reaches equilibrium at a ratio close to 1:1. Under identical
conditions, 9 also slowly isomerizes to 8, reaching the same
equilibrium. The complex 9 can be isolated by passing the
mixture through a column of neutral alumina, and the 31P
NMR spectrum of this compound also consists of an AMX
coupling pattern (Table 4). The 31P NMR coupling constants
for 9 indicate a meridional arrangement of the phosphorus
atoms;41 therefore, the only possible structure for 9 that is con-
sistent with this data is the isomer in which the chloro groups
are trans.
Scheme 4
cmϪ1),40 while the CO stretching frequency for 11 (2020 cmϪ1) is
consistent with a trans phosphorus ([RuCl2(PPh2Me)3(CO)],
1991 cmϪ1).43
At room temperature, 10 is thermally converted to the
isomer 11, without formation of 8 or 9 (Scheme 4). The reverse
reaction (11 to 10) does not proceed at room temperature in
ambient light. Similar isomerizations have been reported for
related complexes such as [RuCl2(PR3)3(CO)] (PR3 = PMe3,
PPhMe2 and PPh2Me).43 In ruthenium() complexes containing
carbonyl ligands, the thermodynamic stability is directed in
part by the nature of the ligand found trans to the carbonyl
group. Since CO is a strong π-acceptor, any trans ligand com-
peting for electron density from the metal center will weaken
the M–CO bond and this trans influence decreases in the order
CO > P > Cl.44 Thus, complexes containing a chloro trans to a
carbonyl are thermodynamically more stable than isomers with
either a phosphine or a CO trans to a carbonyl, as reported in
the literature.43,45,46
When 8 reacts with CO at room temperature, only 10 forms
while the reaction of 9 with CO yields only 11. It is possible that
10 forms via a pentacoordinate intermediate resulting from
dissociation of the thiophene sulfur (Scheme 5). Such inter-
mediates have been proposed in many displacement reactions
involving Ru complexes containing hemilabile ligands.47,48 The
CO then reacts on the less hindered face of the bipyramidal
intermediate, which would yield the observed product. The
reaction of 9 with CO probably proceeds via a different inter-
mediate than for 8 since the product is not the same. One
possibility is a pathway involving an intermediate in which
the Ru–S bond weakens but does not completely dissociate
when the CO approaches, due to the lower temperature of this
reaction. The thiophene only fully dissociates when the CO
reacts with the face which yields the more stable product, with
the chloro group trans to the CO. Further experiments to fully
elucidate these reaction mechanisms are needed.
Reactions of 8 and 9 with CO
Complex 8 reacts slowly with CO in solution at room tem-
perature (Scheme 4). The reaction vessel was kept in the dark
to prevent isomerization of the starting material to 9 and
approximately 30% conversion to the monocarbonyl 10 is
achieved after 14 h. This complex was separated from the
reaction mixture by chromatography on a column of neutral
alumina. Complex 9 also reacts with CO at Ϫ8 ЊC in the dark to
yield a different monocarbonyl complex 11. These conditions
were necessary to prevent the isomerization of the starting
material to 8 and in this case, the conversion was complete
after 14 h. Compounds 10 and 11 both have an AMX coupling
pattern in their 31P NMR spectra (Table 4) and their IR spectra
contain single sharp bands in the carbonyl stretching region
at 2020 and 1975 cmϪ1, respectively.
The structures of 10 and 11 (Scheme 4) are assigned based
on the IR and 31P NMR spectral data for those compounds.
By comparison to the number and position of the bands in the
far-IR spectra of related complexes,42 the RuCl2 stretching
frequencies indicate that the chloro group are trans in 10 and
cis in 11. The coupling constants (JPP) in the 31P NMR spectra
show that the phosphorus atoms in both complexes are in a
meridional arrangement around the metal.41 In 10, PA is shifted
upfield due to the trans carbonyl group, and similar shifts have
been observed in the trans isomers of complexes such as
[RuCl2(PR3)3(CO)] (PR3 = PMe3, PPhMe2 and PPh2Me).43 The
carbonyl stretching frequency for 10 (1975 cmϪ1) is in the range
observed for closely related complexes in which CO is trans to
Cl such as 5 (1973 cmϪ1) and [RuCl2(AsPh3)3(CO)] (1961
J. Chem. Soc., Dalton Trans., 2000, 2729–2737
2733

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Table 6 UV–VIS spectral data
UV–VIS
a
Complex
λmax/nm (ε/MϪ1 cmϪ1
)
1
2
3
4
8
9
5
6
dpppth
dppterth
[RuCl2(dpppth-P,S)2]
[RuCl2(dppterth-P,S)2]
cis-[RuCl2(dppm)(dppterth-P,S)]
trans-[RuCl2(dppm)(dppterth-P,S)]
[RuCl2(CO)(dppterth-P)(dppterth-P,S)]
[RuCl2(CO)(dpppth-P)(dpppth-P,S)]
228 (2.14 × 104), 266 (1.66 × 104)
254 (2.08 × 104), 354 (1.77 × 104)
318 (sh) (1.73 × 104), 356 (sh) (7.32 × 103), 484 (sh) (9.5 × 102)
356 (br) (2.13 × 104)
322 (1.17 × 104), 374 (1.78 × 104), 510 (1.10 × 103)
316 (sh) (1.14 × 104), 382 (1.48 × 104), 518 (2.91 × 102)
238 (1.22 × 105), 254 (sh) (1.17 × 105), 286 (sh) (8.21 × 104), 346 (6.65 × 104)
252 (sh) (1.11 × 105), 308 (sh) (3.19 × 104), 390 (sh) (3.25 × 103)
276 (sh) (2.66 × 104), 340 (1.37 × 104)
10 cis-[RuCl2(CO)(dppm)(dppterth-P)]
11 trans-[RuCl2(CO)(dppm)(dppterth-P)]
246 (sh) (8.68 × 104), 336 (4.07 × 104)
a Solvent: CH2Cl2; sh = shoulder; br = broad.
The weak bands at 510 nm in 8 and 518 nm in 9 are assigned to
d–d transitions.
Upon reaction of the complexes with CO, substantial
changes occur in the electronic spectra. In the spectrum of com-
plex 5, multiple overlapping bands are observed, and it is likely
that the different electronic transitions are due to the two
coordination modes of the two dppterth ligands. The spectrum
of 6 (also containing 7 and other impurities) shows only
poorly resolved UV absorptions tailing into the visible. In the
spectrum of 10 and 11, the d–d band observed in 8 and 9 at
ca. 500 nm is absent. The higher energy bands are assigned to
ligand-based π–π* transitions. In both complexes, the ligand
absorptions are blue-shifted with respect to 8 and 9. This is
due to the reduction of electron donation from the Ru and
removal of the rigidity in the terthienyl moiety when dppterth
is monodentate. The ligand-based absorptions of 10 and 11 are
also slightly blue-shifted with respect to dppterth. This may be
due to a small electron withdrawing effect of the ruthenium
carbonyl group in 10 and 11.
Scheme 5
Experimental
General
Electronic spectra
2-(2Ј-Bromophenyl)thiophene,54 3Ј-bromo-2,2Ј:5Ј,2Љ-terthio-
phene55 and [RuCl2(PPh3)3]40 were all prepared according to
The UV–VIS spectral data for all the complexes are shown in
Table 6. Compound 1 has an absorption in the UV region at
266 nm, which is comparable in position and intensity to the
π–π* transition of 2-phenylthiophene (282 nm).49 The free
ligand dppterth has an absorption at 354 nm, similar to the
π–π* transition of terthiophene (351 nm).49 In complex 3, high
energy bands can be observed in the UV region of the spectrum
along with a weak band at 484 nm. The latter is assigned to a
Ru d–d transition and the higher energy bands to ligand-based
π–π* transitions. The spectrum of complex 4 contains a broad
band with a maximum at 356 nm. Since the complex is present
in solution as a mixture of two isomers, it is likely that the
absorption bands of the two species overlap and cannot be
resolved.
literature procedures. Diethyl ether and THF were distilled
from sodium/benzophenone; methylene chloride was distilled
from CaCl2. All other reagents were purchased from either
Aldrich or Strem Chemicals and used as received. Electronic
absorption spectra were obtained on an UNICAM UV-2
spectrometer. IR spectra were obtained on a Bomem MB-series
spectrometer on either methylene chloride solutions or caesium
1
iodide pellets. H and 31P NMR experiments were performed
on either a Bruker AC-200E or a Varian XL-300 spectrometer,
and spectra were referenced to residual solvent (1H) or external
85% H3PO4 (31P).
Preparations
The spectra of 8 and 9 are very similar to one another, both
showing high energy bands which are due to ligand-based π–π*
transitions. A small red-shift is observed for these absorptions
relative to dppterth, which can be attributed to electronic or
steric effects in the terthienyl fragment of dppterth. Com-
parison of the bond lengths and angles of dppterth in 8 with
those of 3Ј-methyl-2,2Ј:5Ј,2Љ-terthiophene39 shows that the
structure of the terthienyl moiety is only slightly perturbed. The
red-shift is, therefore, due to a combination of two factors:
(a) electron donation from the metal to the terthienyl group
and (b) a more rigid backbone in the coordinated oligomer.
It has been reported that the absorption bands of thiophene
oligomers with rigid backbones are red-shifted owing to the
reduction in rotational disorder relative to less rigid analogs.50
2-(2Ј-{Diphenylphosphino}phenyl)thiophene (dpppth) 1. 2-(2Ј-
Bromophenyl)thiophene (7.70 g, 32.2 mmol) and Mg (0.850 g,
35.4 mmol) were added to dry THF (45 mL) at 60 ЊC and
allowed to react for 1 h at room temperature after which time
chlorodiphenylphosphine (7.71 g, 35.0 mmol) was added drop-
wise. The reaction mixture was stirred for 1 h and was then
quenched with 0.5 M HCl (100 mL). The organic layer was
washed with water, dried over anhydrous MgSO4 and the
solvent removed in vacuo to yield the crude product, which was
purified by chromatography on silica gel with a hexanes–
acetone mixture (98/2 v/v). The yellow band was collected
and the solvent removed, leaving pure 1 as a thick yellow oil.
1
Yield: 7.90 g (71%). H NMR (200 MHz, CDCl3): δ 7.57–7.46
2734
J. Chem. Soc., Dalton Trans., 2000, 2729–2737

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(m, 1H), 7.44–7.18 (m, 13H), 7.08–6.82 (m, 3H). 31P{1H} NMR
(81.015 MHz, CDCl3): δ Ϫ15.13. Anal. C22H17PS requires C,
76.74; H, 4.94. Found: C, 76.83; H, 4.95%.
a mixture of acetone and methylene chloride (2/3 v/v). Removal
of the solvent and crystallization from methylene chloride–
hexanes yielded pure 8 as a red powder. Yield: 0.70 g (73%).
1H NMR (200 MHz, CDCl3): δ 8.22–8.30 (m, 2H), 7.94–8.02
(m, 4H), 7.50–6.60 (m, 28H), 6.55 (d, 1H), 6.16–6.24 (m,
1H), 5.18 (d, 1H), 4.98–5.06 (m, 1H), 4.64–4.70 (m, 1H). FIR
(CsI): νas(RuCl2) = 319 cmϪ1, νs(RuCl2) = 271 cmϪ1. Anal.
C49H39Cl2P3S3Ru requires C, 59.50; H, 3.95. Found: C, 59.22;
H, 3.98%.
3Ј-Diphenylphosphino-2,2Ј:5Ј,2Љ-terthiophene (dppterth) 2. A
solution of n-butyllithium in hexanes (1.6 M, 0.38 mL, 0.61
mmol) was added dropwise to a solution of 3Ј-bromo-
2,2Ј:5Ј,2Љ-terthiophene (0.20 g, 0.61 mmol) in dry diethyl ether
(7 mL) at Ϫ15 ЊC. The mixture was stirred for 1 h at Ϫ15 ЊC
and then allowed to warm to room temperature. A solution of
chlorodiphenylphosphine (0.14 g, 0.62 mmol) in diethyl ether
was then added dropwise. The resulting solution was stirred for
another 30 min at room temperature, after which time 1 M HCl
(25 mL) was added to quench the reaction. The organic layer
was washed with water, dried over anhydrous MgSO4 and
the solvent removed to yield an oily solid. The crude solid
was purified by chromatography on silica gel using a hexanes–
acetone mixture (8/2 v/v) as eluant. The yellow band was
collected and the solvent removed to give a solid, which was
dissolved in a small amount of methylene chloride to which
hexanes were added to yield 2 as a yellow powder. Yield: 0.20 g
(76%). 1H NMR (200 MHz, CDCl3): δ 7.36 (m, 10H), 7.29 (m,
1H), 7.17 (m, 2H), 7.07 (m, 1H), 6.98 (m, 2H), 6.06 (m, 1H).
31P{1H} NMR (81.015 MHz, CDCl3): δ Ϫ25.79. Anal.
C24H17PS3 requires C, 66.67; H, 3.94. Found: C, 66.05; H,
4.01%.
trans-[RuCl2(dppm)(dppterth-P,S1)] 9.
A solution of 8
(556 mg, 0.560 mmol) in dry methylene chloride (30 mL)
was stirred at room temperature for 24 h in ambient room light.
The mixture was then eluted on a neutral alumina column with
methylene chloride and the red–brown band collected. Removal
of the solvent and recrystallization from methylene chloride–
hexanes yielded 9 as a rust colored powder. Unreacted 8 was
recovered by washing the column with an acetone–methylene
chloride mixture (2/3 v/v). Yield: 150 mg (27%). 1H NMR
(200 MHz, CDCl3): δ 7.56–7.64 (m, 4H), 7.40–6.85 (m, 32H),
6.42 (d, 1H), 4.74–4.82 (m, 2H). FIR (CsI): νas(RuCl2) = 325
cmϪ1. Anal. C49H39Cl2P3S3Ru requires C, 59.50; H, 3.95. Found:
C, 59.26; H, 4.12%.
[RuCl2(CO)(dppterth-P)(dppterth-P,S1)] 5. Carbon monoxide
was bubbled through a solution of 4 (200 mg, 0.190 mmol)
in methylene chloride. After 4 h, the orange solution turned
dark orange–yellow, and the flask was sealed and left overnight
under a CO atmosphere. The resulting bright yellow mixture
was concentrated to 1–2 mL and hexanes were added to precipi-
tate a yellow powder. This solid was dissolved in methylene
chloride under CO and hexanes were added yielding 5 as a
yellow powder. Yield: 128 mg (58%). 1H NMR (200 MHz,
CDCl3): δ 8.80 (m, 1H), 8.40–7.73 (m, 10H), 7.61–6.76 (m,
19H), 6.64–6.25 (m, 3H), 5.9–5.73 (m, 1H). 31P{1H} NMR
(81.015 MHz, CDCl3): δ 5.89 (s), 5.52 (s). IR (CH2Cl2):
νCO = 1973 cmϪ1. Anal. C49H34Cl2OP2S6Ru requires C, 55.26;
H, 3.20. Found: C, 54.79; H, 3.50%.
[RuCl2(dpppth-P,S)2] 3. [RuCl2(PPh3)3] (1.00 g, 1.04 mmol)
and 1 (1.08 g, 3.13 mmol) were added to dry methylene chloride
(60 mL) under a N2 atmosphere. After the reaction mixture was
stirred at room temperature for 13 h, the solvent was removed.
The resulting solid was extracted with diethyl ether to leave a
red powder which was collected. The crude product was dis-
solved in methylene chloride and a small amount of hexanes
added until a fine gray precipitate appeared. The residual
solution was filtered off and the gray precipitate was discarded.
More hexanes were added to the mother-liquor to precipitate
the product as a rust colored powder. The product was isolated
as a mixture of cis and trans isomers. Yield: 0.68 g (76%).
1H NMR (200 MHz, CDCl3): δ 8.00–8.12 (m, 2H), 7.80–7.31
(m, 12H), 7.28–7.00 (m, 8H), 6.92–6.40 (m, 9H), 6.00–6.08 (m,
2H), 5.67–5.75 (m, 1H). 31P{1H} NMR (81.015 MHz, CDCl3):
δ 36.36 (d, 1P, JPP = 160 Hz), 34.83 (d, 1P, JPP = 160 Hz), 39.72
(s). Anal. C44H34Cl2P2S2Ru requires C, 61.39; H, 3.95. Found:
C, 61.71; H, 4.23%.
trans-[RuCl2(CO)(dppm)(dppterth-P)] 10. In a foil-wrapped
reaction flask, carbon monoxide was bubbled through a solu-
tion of 8 (190 mg, 0.190 mmol) in methylene chloride for 4 h,
then the mixture was left under a CO atmosphere overnight.
The resulting orange solution was concentrated to 2–3 mL by
blowing CO over the solution and then filtered through a short
neutral alumina column. To remove residual 8, the column was
first washed thoroughly with ethyl acetate until the eluent was
colorless. A bright yellow band left on the top of the column
was then eluted with neat methanol. Removal of the solvent
left a yellow powder which was recrystallized from methylene
chloride–hexanes at Ϫ8 ЊC. Pure 10 was collected as a yellow
powder which was dried under vacuum. Yield: 55 mg (28%).
1H NMR (200 MHz, CDCl3): δ 7.86 (m, 1H), 7.72–7.96 (m,
33H), 6.76 (m, 3H), 6.62 (d, 1H), 5.16 (d, 1H). IR (CH2Cl2):
ν(CO) = 2020 cmϪ1. FIR (CsI): νas(RuCl2) = 326 cmϪ1. Anal.
C50H39Cl2OP3S3Ru requires C, 59.05; H, 3.84. Found: C, 58.78;
H, 4.03%.
[RuCl2(dppterth-P,S1)2] 4. [RuCl2(PPh3)3] (1.8 g, 1.9 mmol)
and 2 (2.0 g, 4.6 mmol) were added to dry methylene chloride
(80 mL) under a N2 atmosphere. After the reaction mixture was
stirred at room temperature for 15 h, the solvent was removed
and the resulting solid extracted with diethyl ether to leave a
dark orange powder which was collected. The crude product
was dissolved in a small amount of methylene chloride and
hexanes added to precipitate the product as an orange powder.
The product was isolated as a mixture of isomers. Yield: 1.9 g
(97%). 1H NMR (200 MHz, CDCl3): δ 8.21–7.96 (m, 3H), 7.80–
6.78 (m, 28H), 6.68–5.92 (m, 3H). 31P{1H} NMR (81.015 MHz,
CDCl3): δ 23.89 (d, 1P, Jpp = 137 Hz), 22.75 (d, 1P, Jpp = 137
Hz), 26.94 (s). Anal. C48H34Cl2P2S6Ru requires C, 55.60; H,
3.28. Found: C, 55.33; H, 3.30%.
cis-[RuCl2(CO)(dppm)(dppterth-P)] 11. Carbon monoxide
was bubbled through a solution of 9 (200 mg, 0.193 mmol) in
methylene chloride (4–5 mL) for 20 min. The flask was then
sealed and left overnight in the dark at Ϫ8 ЊC, during which
time the mixture changed from orange–red to yellow. Hexanes
were added to precipitate a yellow solid which was collected and
recrystallized from methylene chloride–hexanes at Ϫ8 ЊC. The
pure product was obtained as yellow crystals which were dried
under vacuum. Yield: 145 mg (71%). 1H NMR (200 MHz,
CDCl3): δ 8.21–8.01 (m, 2H), 7.96–7.56 (m, 8H), 7.49–6.8
(m, 26H), 6.71 (d, 1H), 6.42–6.32 (m, 1H), 5.00–4.56 (m, 1H).
cis-[RuCl2(dppm)(dppterth-P,S1)] 8. Bis(diphenylphosphino)-
methane (dppm) (0.371 g, 0.965 mmol) was added to a solution
of 4 (1.00 g, 0.965 mmol) in dry methylene chloride (50 mL).
The mixture was stirred at room temperature for 10 h after
which time the solvent was removed in vacuo. The resulting
solid was purified by chromatography on neutral alumina. The
column was first eluted with methylene chloride to remove
excess dppm, dppterth and trans-[RuCl2(dppm)2] until the
eluent was colorless, then the product eluted as a red band with
J. Chem. Soc., Dalton Trans., 2000, 2729–2737
2735

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Table 7 Crystallographic data for 3, 5 and 8
3ؒ3CHCl3
5ؒCHCl3
8ؒ3CH2Cl2
Formula
M
C47H37Cl11P2RuS2
1218.85
C50H35Cl5OP2RuS6
1184.40
C52H45Cl8P3RuS3
1243.72
T/K
Crystal system
Space group
213(2)
Orthorhombic
P212121
238(2)
Monoclinic
P21/n
173.2
Monoclinic
P21/n
a/Å
b/Å
c/Å
11.1896(8)
19.063(1)
23.732(2)
17.069 (7)
12.857(7)
24.092(7)
105.325(9)
5099.4
15.7595(6)
15.5059(5)
22.323(1)
93.506(3)
5444.8(3)
4
β/Њ
V/Å3
5062.0(6)
4
Z
4
Refl. collected/unique
12164/8639
0.0486
0.1225
4244/2354
0.0621
0.1584
11329/9328
0.076
0.129
a
R1
b
wR2
¹
2 2

²
2
2
2
a R = Σ Fo| Ϫ |Fc /Σ|Fo| (observed data). b wR2 = (Σ(Fo Ϫ Fc ) /Σw(Fo ) ) (all data).
IR (CH2Cl2): ν(CO) = 1975 cmϪ1. FIR (CsI): νas(RuCl2) =
301 cmϪ1, νs(RuCl2) = 273 cmϪ1. C50H39Cl2OP3S3Ru requires
C, 59.05; H, 3.84. Found: C, 58.77; H, 4.06%.
9 R. J. Angelici, NATO ASI Series, Ser. 3, 1998, 60, 89.
10 R. J. Angelici, Bull. Soc. Chim. Belg., 1995, 104, 265.
11 T. B. Rauchfuss, Prog. Inorg. Chem., 1991, 39, 259.
12 D. A. Weinberger, T. B. Higgins, C. A. Mirkin, L. M. Liable-Sands
and A. L. Rheingold, Angew. Chem., Int. Ed., 1999, 38, 2565.
13 T. B. Rauchfuss, S. M. Bucknor, M. Draganjac, C. Ruffig,
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14 M. Draganjac, C. Ruffig and T. B. Rauchfuss, Organometallics,
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15 J. Amarasekera and T. B. Rauchfuss, Inorg. Chem., 1989, 28, 3875.
16 S. Ng, K. Mok and B. Chen, J. Chem. Soc., Dalton Trans., 1998, 23,
4035.
X-Ray crystallographic analysis
Suitable crystals of 3 and 5 were selected and mounted on thin,
glass fibers using paraffin oil. Data were collected on a Bruker
AX SMART 1k CCD diffractometer using 0.3Њ ω-scans at 0, 90
and 180Њ in φ at Ϫ60 ЊC for 3 and Ϫ35 ЊC for 5. The Flack
parameter for 3 was refined to nil, which indicates that the
true hand of the data has been determined correctly. Three of
the thiophene rings in 5 were disordered; however, because
of the close proximity of the atomic positions of the contribu-
ting disordered rings, only the disordered sulfur atoms could be
located with a refined site occupancy distribution of 90/10, 85/
15, and 70/30. All scattering factors and anomalous dispersion
factors are contained in the SHEXTL 5.10 program library.51
A crystal of 8 was mounted on a glass fiber, and data were
collected at Ϫ100 ЊC on a Rigaku/ADSC CCD area detector in
two sets of scans (ψ = 0.0–190.0Њ, χ = 90Њ and ω = Ϫ18.0 to
23.0, χ = Ϫ90Њ), using 0.50Њ oscillations with 27.0 s exposures.
All calculations were performed using the teXsan52 crystallo-
graphic software package of the Molecular Structure Corpor-
ation. The uncoordinated thiophene is disordered by rotation
about the C(8)–C(9) bond causing S(3) and C(10) to exchange
positions. Subsequent refinement of the occupancies of S(3)
and C(10) led to values of 0.69 and 1.9, respectively, which
corresponds to 0.5 S and 0.5 C at each site. Crystallographic
data are shown in Table 7.
17 R. Mathieu, M. Alvarez and N. Lugan, Inorg. Chem., 1993, 32,
5652.
18 R. Mathieu, M. Alvarez, N. Lugan and B. Donnadieu, Organo-
metallics, 1995, 14, 365.
19 F. Neve, M. Ghedini and A. Crispini, J. Organomet. Chem., 1994,
466, 259.
20 L. Latos-Grazynski, J. Lisowski, M. M. Olmstead and A. L. Blach,
Inorg. Chem., 1989, 28, 1183.
21 L. Latos-Grazynski, M. M. Olmstead and A. L. Blach, Inorg.
Chem., 1989, 28, 4066.
22 G. van Stein, G. van Koten, F. Blank, L. C. Taylor, K. Vrieze,
A. L. Spek, A. J. M. Duisenberg, A. M. M. Scheurs, B. Kojic-Prodic
and C. Brevard, Inorg. Chim. Acta, 1985, 98, 107.
23 E. C. Constable, R. P. G. Henney and D. A. Tocher, J. Chem. Soc.,
Chem. Commun., 1986, 913.
24 E. C. Constable, S. J. Dunne, D. G. F. Rees and C. X. Schmitt, Chem.
Commun., 1996, 1196.
25 A. Varshney and G. M. Gray, Inorg. Chim. Acta, 1988, 148, 215.
26 T. M. Räsänen, S. Jääskeläinen and T. A. Pakkanen, J. Organomet.
Chem., 1998, 553, 453.
27 M. C. Barral, R. Jimenez-Aparicio, R. Kramolowsky and
I. Wagner, Polyhedron, 1993, 12, 903.
CCDC reference number 186/2045.
See http://www.rsc.org/suppdata/dt/b0/b001898h/ for crystal-
lographic files in .cif format.
28 D. G. Dick and D. W. Stephan, Can. J. Chem., 1986, 64, 1870.
29 U. Bodensieck, H. Vahrenkamp, G. Rheinwald and H. Stoekli-
Evans, J. Organomet. Chem., 1995, 488, 85.
30 A. J. Deeming, S. N. Jayasuriya, A. J. Arce and Y. De Sanctis,
Organometallics, 1996, 15, 786.
31 A. J. Deeming, S. N. Jayasuriya, A. J. Arce and Y. De Sanctis,
J. Chem. Soc., Dalton Trans., 1999, 1153.
32 J. D. King, M. Monari and E. Nordlander, J. Organomet. Chem.,
1999, 573, 272.
Acknowledgements
We thank the Natural Sciences and Engineering Research
Council of Canada for support of this research.
33 A. R. Sanger, Can. J. Chem., 1984, 62, 2168.
34 M.-G. Choi and R. J. Angelici, Organometallics, 1992, 11, 922.
35 S. Harris, Polyhedron, 1997, 16, 3219.
36 B. Bak, D. Christensen, L. Hansen-Nygaard and J. Rastrup-
Andersen, J. Mol. Spectrosc., 1961, 6, 61.
37 T. B. Rauchfuss, D. M. Roundhill and F. T. Patino, Inorg. Chem.,
1975, 14, 652.
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