Synthesis, structures and dynamic NMR spectra of η6-hexaethyl-benzene complexes of ruthenium(0) and ruthenium(II)

Article abstract of DOI:10.1039/b204875m

On reaction with the labile naphthalene complex [Ru(η⁶-C₁₀H₈)(η⁴-1,5-COD)], hex-3-yne undergoes stoichiometric cyclotrimerisation to form the hexaethylbenzene-ruthenium(o) complex [Ru(η⁶-C₆Et₆)(η⁴-1,5-COD)] 1. In the solid state and in solution the ethyl groups adopt a 1,4-proximal-2,3,5,6-distal arrangement, as shown by X-ray solid state and in solution the ethyl groups adopt a 1,4-proximal-2,3,5,6-distal arrangement, as shown by X-ray crystallography and NMR (¹H, ¹³C-{¹H}) spectroscopy. Treatment of 1 with HCl gives the binuclear ruthenium(II) complex [{RuCl(η⁶-C₆Et₆)}²(μ -Cl)₂] 2, whose arene ligands adopt a transoid arrangement about the Ru₂Cl₂ moiety; in turn 2 reacts with methanolic NH₄PF₆ to give the salt [Ru₂(μ-Cl)₃(η⁶-C₆ Et₆)₂]PF₆, [3]PF₆. The ethyl group conformations in crystalline 2 and [3]PF₆ are all-distal and 1,3,5-proximal-2,4,6-distal, respectively, whereas only the latter conformation is present in both compounds in dichloromethane or methanol solutions at low temperature according to ¹³C-{¹H} NMR spectroscopy. The v(Ru-Cl) band patterns in the IR spectra of 2 in the solid state and dichloromethane solution are almost identical, indicating that the neutral di-μ-chloro species predominates in solution at room temperature. However, the appearance at -50°C of a resonance due to free chloride ion in the ³⁵Cl NMR spectrum of complex 2 suggests that reversible formation of [3]Cl may be favoured at low temperature. Dilute (ca. 10^-3 M) solutions of 2 in dichloromethane and methanol behave as 1:1 electrolytes consistent with the presence of [3]Cl under these conditions. At room temperature the ethyl groups of η⁶-C₆Et₆ in 1, 2 and [3]PF₆ are equivalent on the NMR time-scale as a consequence of rotation about the arene-methylene bond and, possibly, rotation of the arene about the arene-metal bond. In the crystalline adducts [RuCl₂(η⁶-C₆Et₆)(L)] (L = PMe₃ 4, PPh₃ 5) the ethyl groups are all distal and remain equivalent on the NMR time-scale in solution from room temperature to -97°C. The results confirm conclusions, based primarily on studies of Group 6 carbonyl complexes, that the different conformations of η⁶-C₆Et₆ have very similar energies.

Full text of DOI:10.1039/b204875m

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Synthesis, structures and dynamic NMR spectra of ꢀ6-hexaethyl-
benzene complexes of ruthenium(0) and ruthenium(II)
Richard Baldwin,a Martin A. Bennett,*a David C. R. Hockless,a Paolo Pertici,b
Alessandra Verrazzani,b Gloria Uccello Barretta,b Fabio Marchettib and Piero Salvadorib
a Research School of Chemistry, Australian National University, Canberra, ACT 0200,
Australia
b Istituto per la Chimica dei Composti OrganoMetallici, ICCOM-CNR, Sezione di Pisa,
Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126
Pisa, Italy
Received 20th May 2002, Accepted 29th August 2002
First published as an Advance Article on the web 1st November 2002
On reaction with the labile naphthalene complex [Ru(η6-C10H8)(η4-1,5-COD)], hex-3-yne undergoes stoichiometric
cyclotrimerisation to form the hexaethylbenzene–ruthenium() complex [Ru(η6-C6Et6)(η4-1,5-COD)] 1. In the
solid state and in solution the ethyl groups adopt a 1,4-proximal-2,3,5,6-distal arrangement, as shown by X-ray
crystallography and NMR (1H, 13C-{1H}) spectroscopy. Treatment of 1 with HCl gives the binuclear ruthenium()
complex [{RuCl(η6-C6Et6)}2(µ-Cl)2] 2, whose arene ligands adopt a transoid arrangement about the Ru2Cl2 moiety;
in turn 2 reacts with methanolic NH4PF6 to give the salt [Ru2(µ-Cl)3(η6-C6Et6)2]PF6, [3]PF6. The ethyl group
conformations in crystalline 2 and [3]PF6 are all-distal and 1,3,5-proximal-2,4,6-distal, respectively, whereas only
the latter conformation is present in both compounds in dichloromethane or methanol solutions at low temperature
according to 13C-{1H} NMR spectroscopy. The ν(Ru–Cl) band patterns in the IR spectra of 2 in the solid state
and dichloromethane solution are almost identical, indicating that the neutral di-µ-chloro species predominates in
solution at room temperature. However, the appearance at Ϫ50 ЊC of a resonance due to free chloride ion in the 35Cl
NMR spectrum of complex 2 suggests that reversible formation of [3]Cl may be favoured at low temperature. Dilute
(ca. 10Ϫ3 M) solutions of 2 in dichloromethane and methanol behave as 1 : 1 electrolytes consistent with the presence
of [3]Cl under these conditions. At room temperature the ethyl groups of η6-C6Et6 in 1, 2 and [3]PF6 are equivalent
on the NMR time-scale as a consequence of rotation about the arene–methylene bond and, possibly, rotation of the
arene about the arene–metal bond. In the crystalline adducts [RuCl2(η6-C6Et6)(L)] (L = PMe3 4, PPh3 5) the ethyl
groups are all distal and remain equivalent on the NMR time-scale in solution from room temperature to Ϫ97 ЊC.
The results confirm conclusions, based primarily on studies of Group 6 carbonyl complexes, that the different
conformations of η6-C6Et6 have very similar energies.
Introduction
Hexaethylbenzene (C6Et6) is the smallest homosubstituted
hexa-alkylbenzene that shows the effects of steric hindrance
between the substituents. In the solid state the ethyl groups
project alternately above and below the plane of the six-
membered ring;1,2 on η6-coordination the ethyl groups can
point either towards the metal atom (proximal) or away from
it (distal). Extensive studies, especially of the Group 6 metal
tricarbonyl complexes of C6Et6 and their derivatives, have
shown the existence of a number of different conformations
Fig. 1 Possible rotational motions in [Cr(CO)3(η6-C6Et6)].
whose static and dynamic stereochemistry have attracted con-
siderable interest and some controversy; a detailed review has
appeared.3 In general, the favoured conformation or conform-
ations adopted in the solid state seem to be determined by a
balance of steric effects between the ethyl groups themselves
and between the ethyl groups and the ligands in the MLn unit.
Two dynamic processes are thought to occur in η6-C6Et6
metal complexes which render the distal and proximal ethyl
groups equivalent in solution at room temperature: (1) uncor-
related rotation of the ethyl groups about the arene–methylene
bond, and (2) rotation of the arene relative to the MLn frag-
ment. These processes are illustrated in Fig. 1 for [Cr(CO)3-
(η6-C6Et6)], which has a 1,3,5-proximal-2,4,6-distal arrange-
ment of ethyl groups in the solid state;2,4 the distal ethyl groups
in this compound eclipse the Cr–CO vectors. According to
variable temperature NMR studies of the complexes [Cr(CO)2-
(NO)(η6-C6Et6)]BF4 and [Cr(CO)(CS)(NO)(η6-C6Et6)]BF4, the
activation barriers ∆G≠ to the two processes are ca. 39.7 and
48.1 kJ molϪ1, respectively.5
Ruthenium in both zero and ϩ2 oxidation states forms
numerous η6-arene complexes with a variety of substituents in
the aromatic ring,6,7 but the only known η6-C6Et6 complex is
[Ru(η5-C5H5)(η6-C6Et6)]BF4, which was isolated in poor yield
from the reaction of [Ru(CO)2(η5-C5H5)]2 with an excess of
hex-3-yne in the presence of AgBF4.8,9 We describe here the
synthesis and structure of some hexaethylbenzene complexes
of ruthenium, with emphasis on the conformations adopted by
the ethyl groups.
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This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b204875m

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the substituents at the 1- and 4- positions of the C6Et6 ring are
Results
proximal, those at the 2,3,5,6-positions are distal. A similar
conformation has been observed in two other complexes of the
The usual starting compounds for entry into arene–ruthenium
chemistry are the di-µ-chloro dimers, [RuCl2(η6-arene)]2, which,
for mono- and di-substituted arenes, are generally most easily
made by reaction of RuCl3ؒxH2O with the appropriate 1,3-
or 1,4-cyclohexadiene. The dimeric RuCl2 complexes of
hexamethylbenzene,10 tetramethylbenzene,11,12 and 1,3,5-tri-
alkylbenzenes are readily obtained by heating or fusing
[RuCl2(η6-p-cymene)]2 with a large excess of the neat arene, but
hexaethylbenzene does not displace p-cymene at 180 ЊC, even
after 24 h, presumably because of steric hindrance. We
have, therefore, adopted an alternative approach13 based on
the labile, zerovalent ruthenium complex [Ru(η6-C10H8)-
(η4-1,5-COD)],14 the naphthalene ligand of which is displaced
by hex-3-yne in THF at room temperature to give [Ru(η6-
C6Et6)(η4-1,5-COD)] 1 as pale yellow crystals (eqn. (1)).
17
type ML2(η6-C6Et6), viz., M = Ta, L = OC6H3Pri2-2,6 and
M = Ir, L2 = η1,η3-C8H13,18 and in the cation of the salt
[MoCl(CO)3(η6-C6Et6)][MoCl6].19 In complex 1 the carbon
atoms carrying the distal arms almost eclipse the olefinic
carbon atoms of COD, while the proximal arms occupy the
space created by the saddle-shaped conformation of COD, thus
minimising steric hindrance between them and the diene. The
Ru–C(COD) distances in 1 [2.133(5)–2.138(5) Å] are similar to
those in [Ru(η6-C6H6)(η4-1,5-COD)] [2.127(4)–2.136(4) Å];20 in
contrast, the Ru–C(arene) distances are slightly greater in 1
[2.250(4)–2.265(4) Å vs. 2.195(7)–2.256(7) Å], presumably as
a consequence of the greater bulk of C6Et6. In the benzene
complex the aromatic ring is not completely planar but has
a shallow boat conformation, as is evident from the spread of
Ru–C(arene) bond lengths, whereas in 1 the Ru–C(arene)
distances do not differ significantly.
Treatment of complex 1 in hexane with HCl gives the
di-µ-chloro dimer [RuCl2(η6-C6Et6)]2 2 almost quantitatively
as an orange, air-stable solid. Unlike the C6H6 and C6Me6
analogues, 2 is very soluble in dichloromethane, and fairly
soluble in methanol and ethanol; solutions in CH2Cl2
decompose in air over a period of weeks. The peak of highest
mass in the EI-mass spectrum of 2 corresponds to the loss of
one chloride ion from the dimer. This process also occurs on
treatment of 2 with a saturated solution of NH4PF6 in meth-
anol, which gives the tri-µ-chloro salt [Ru2Cl3(η6-C6Et6)2]PF6
[3]PF6 as dark red crystals. The 1H and 13C-{1H} NMR spectra
of compounds 2 and [3]PF6 at room temperature show the
presence of equivalent ethyl groups; the arene carbon signal
appears as a broad singlet at δ 94–95 (2) and 93–95 (3), ca.
40 ppm to low frequency of that in free C6Et6.
(1)
The complex is obtained in almost quantitative yield after
chromatography and crystallisation from pentane at Ϫ78 ЊC
and has been characterised by elemental analysis, spectroscopic
measurements, and single crystal X-ray diffraction. The
EI-mass spectrum shows a parent-ion peak and the H NMR
spectrum at room temperature in C6D6 or CD2Cl2 shows a
1
quartet–triplet pattern due to apparently equivalent ethyl
groups. The COD resonances appear at δ 2.76 (br s, ᎐CH) and
᎐
2.36 (m, CH2); in CD2Cl2 the former shifts to δ 2.48 and
the latter appears as two 4H-multiplets centred at δ 2.04
and 1.88. These chemical shifts are similar to those of other
[Ru(η6-arene)(η4-1,5-COD)] complexes.15,16 Corresponding
resonances are observed in the 13C-{1H} NMR spectrum; the
signal due to the arene carbon atoms appears at δ 103.4,
ca. 30 ppm to low frequency of that in free C6Et6
The molecular structures of complexes 2 and 3, determined
by single-crystal X-ray diffraction, are shown in Fig. 3 and 4;
It should be noted that complexes such as [Ru(η6-C6H6)-
(η4-1,5-COD)] and [Ru(η6-p-cymene)(η4-1,5-COD)] do not
react with hex-3-yne even in refluxing THF. The possible
mechanism for this stoichiometric alkyne cyclotrimerisation
has been discussed elsewhere.13
The molecular structure of complex 1 is shown in Fig. 2;
significant bond distances and angles are listed in Table 1. The
molecule has a typical piano-stool structure and the η4-1,5-
COD ligand is in its usual puckered saddle conformation. The
plane containing the four olefinic carbon atoms C(19), C(20),
C(23) and C(24) is almost parallel with that of the C6Et6 carbon
atoms, the dihedral angle being 0.7(3)Њ. The methyl groups of
Fig. 3 An ORTEP diagram of [RuCl2(η6-C6Et6)] 2 showing selected
atom labelling and 20% probability ellipsoids; hydrogen atoms have
been omitted for clarity.
selected bond lengths and angles are listed in Tables 2 and 3.
Complex 2 has an edge-shared bioctahedral structure similar
to those of other [MCl2(η6-arene)]2 complexes [M = Os, arene =
p-cymene;21 M = Ru, arene = C6Me6,22 C6H5CO2Et,23 and
trindane24 (trindane = benzo(1,2:3,4:5,6)-1,2,3-trihydrocyclo-
pentene)]. The aromatic carbon atoms of each arene ligand are
coplanar, within experimental error, and these planes at the end
of each molecule are parallel. The two ruthenium atoms and
the two bridging chlorine atoms are coplanar; the terminal
chlorine atoms are orthogonal to this plane, one above and one
below it, so that the arene ligands adopt a mutually anti orient-
ation. In cation 3 three bridging chlorine atoms are arranged
Fig.
2
An ORTEP57 diagram of [Ru(η6-C6Et6)(η4-1,5-COD)]
1
showing selected atom labelling and 20% probability ellipsoids;
hydrogen atoms have been omitted for clarity.
J. Chem. Soc., Dalton Trans., 2002, 4488–4496
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Table 1 Selected distances (Å) and angles (Њ) in [Ru(η6-C6Et6)(η4-1,5-COD)] 1
Ru–C(19)
Ru–C(23)
Ru–C(1)
Ru–C(3)
Ru–C(5)
C(19)–C(20)
C(19)–C(26)
C(21)–C(22)
C(24)–C(25)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
Ru–C(Ar)a
CH2–CH3
2.127(4)
2.133(4)
2.265(3)
2.253(4)
2.250(3)
1.379(7)
1.490(8)
1.501(9)
1.518(9)
1.419(5)
1.431(5)
1.424(5)
1.750(1)
1.514(7)–1.528(5)
Ru–C(20)
Ru–C(24)
Ru–C(2)
Ru–C(4)
2.136(4)
2.130(4)
2.254(3)
2.260(4)
2.259(4)
1.401(7)
1.505(7)
1.494(8)
1.509(10)
1.425(5)
1.419(5)
1.431(5)
1.516(5)–1.530(5)
Ru–C(6)
C(23)–C(24)
C(20)–C(21)
C(22)–C(23)
C(25)–C(26)
C(2)–C(3)
C(4)–C(5)
C(1)–C(6)
C(arom.)–CH2
C(2)–C(1)–C(6)
C(2)–C(3)–C(4)
C(4)–C(5)–C(6)
C(8)–C(7)–C(1)
C(12)–C(11)–C(3)
C(16)–C(15)–C(5)
C(Ar)–Ru–C(COD)b
120.5(3)
119.3(3)
120.6(3)
114.3(4)
115.2(3)
113.4(4)
79.9(2)
C(1)–C(2)–C(3)
C(5)–C(4)–C(3)
C(5)–C(6)–C(1)
C(2)–C(9)–C(10)
C(4)–C(13)–C(14)
C(18)–C(17)–C(6)
120.3(3)
120.2(3)
119.1(3)
113.7(3)
114.3(4)
115.5(4)
a C(Ar) is the centroid of the aromatic ring. b C(COD) is the centroid of 1,5-COD.
Table 2 Selected distances (Å) and angles (Њ) in [RuCl2(η6-C6Et6)]2 2a
Ru(1)–Cl(1)
Ru(1)–Cl(2)
Ru(1)–C(1)
Ru(1)–C(3)
Ru(1)–C(5)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(ar)–CH2
2.454(2)
2.402(2)
2.163(7)
2.170(7)
2.190(7)
1.43(1)
1.44(1)
1.466(10)
1.50(1)–1.529(9)
Ru(1)–Cl(1)Ј
Ru–centroid
Ru(1)—C(2)
Ru(1)–C(4)
Ru(1)–C(6)
C(2)–C(3)
C(4)–C(5)
C(6)–C(1)
CH2–CH3
2.460(2)
1.638(3)
2.158(7)
2.193(7)
2.159(7)
1.405(10)
1.40(1)
1.42(1)
1.48(1)–1.52(1)
Cl(1)–Ru(1)–Cl(1)Ј
Cl(1)–Ru(1)–C(1)
Cl(1)–Ru(1)–C(3)
Cl(1)–Ru(1)–C(5)
Cl(1)Ј–Ru(1)–Cl(2)
Cl(1)Ј–Ru(1)–C(2)
Cl(1)Ј–Ru(1)–C(4)
Cl(1)Ј–Ru(1)–C(6)
Cl(2)–Ru(1)–C(2)
Cl(2)–Ru(1)–C(4)
Cl(2)–Ru(1)–C(6)
C(arom.)–CH2–CH3
80.23(7)
157.0(2)
92.7(2)
117.4(2)
87.37(8)
161.0(2)
114.4(2)
93.4(2)
Cl(1)–Ru(1)–Cl(2)
Cl(1)–Ru(1)–C(2)
Cl(1)–Ru(1)–C(4)
Cl(1)–Ru(1)–C(6)
Cl(1)Ј–Ru(1)–C(1)
Cl(1)Ј–Ru(1)–C(3)
Cl(1)Ј–Ru(1)–C(5)
Cl(2)–Ru(1)–C(1)
Cl(2)–Ru(1)–C(3)
Cl(2)–Ru(1)–C(5)
C–C–C(arom.)
86.97(7)
118.7(2)
92.8(2)
156.4(2)
122.5(2)
152.2(2)
90.1(2)
90.4(2)
91.6(2)
119.3(2)
154.7(2)
118.7(7)–121.0(6)
157.9(2)
115.6(2)
112.1(7)–115.7(7)
a Primed atom lies at Ϫx, Ϫy, Ϫz.
Y = AsF6,25 BF4;26 arene = toluene, Y = BF4;26 arene = p-cymene,
Y = BPh4;27 arene = 1,3,5-C6H3Me3,. Y = BF4;28 arene = C6Me6,
Y = PF6.29 When viewed along the Ru–Ru axis, three of the
arene carbon atoms of cation 3 eclipse the bridging chlorine
atoms; the same orientation is found in [Ru2Cl3(η6-C6H6)2]BF4,
whereas in the AsF6 salt and in most of the other analogues
mentioned above, the Ru–Cl vectors bisect the aromatic C–C
bonds to give a staggered conformation. Clearly, the energy
differences between different rotational isomers must be small.
Whereas the ethyl groups in complex 2 adopt an all-distal
arrangement, in cation 3 they are orientated in an alternating
1,3,5-proximal-2,4,6-distal conformation, with the three
proximal ethyl groups occupying the space between the bridg-
ing chloride ligands, and the aromatic carbon atoms carrying
the distal ethyl groups eclipsing the chloride ligands. The latter
conformation is commonly observed in the solid state struc-
tures of [M(CO)3(η6-C6Et6)] (M = Cr, Mo)2,4 and in derivatives
in which one or two CO ligands have been replaced by analo-
gous rod-like ligands, e.g. [Cr(CO)2(CS)(η6-C6Et6)],30 [Cr(CO)2-
(NO)(η6-C6Et6)]BF4,5 [Cr(CO)(CS)(NO)(η6-C6Et6)]BF4,5 and
[{Cr(CO)2(η6-C6Et6)}2(µ-N2)].31 whereas the all-distal conform-
ation is favoured in derivatives containing fairly bulky tertiary
phosphines, e.g. [Cr(CO)2(L)(η6-C6Et6)] (L = PPh3,2,4 PEt3 32).
Fig. 4 An ORTEP diagram of [Ru2Cl3(η2-C6Et6)2]PF6 [3]PF6 showing
selected atom labelling and 20% probability ellipsoids; hydrogen atoms
have been omitted for clarity.
almost symmetrically between two ruthenium atoms in a face-
sharing bioctahedral structure, the two arenes being planar
and parallel to each other. Similar structures have been found
for other [Ru2Cl3(η6-arene)2]Y salts, where arene = C6H6,
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J. Chem. Soc., Dalton Trans., 2002, 4488–4496

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a
Table 3 Selected distances (Å) and angles (Њ) in [Ru2Cl3(η6-C6Et6)2]PF6 [3]PF6
Ru(1)–Cl(11)
Ru(1)–Cl(13)
Ru(1)Ј–Cl(11)
Ru(1)Ј–Cl(13)
Ru(1)–C(101)
Ru(1)–C(103)
Ru(1)–C(105)
Ru(1)Ј–C(101)Ј
Ru(1)Ј–C(103)Ј
Ru(1)Ј–C(105)Ј
C(101)–C(102)
C(103)–C(104)
C(105)–C(106)
2.445(1)
2.431(1)
2.447(1)
2.430(1)
2.190(4)
2.184(5)
2.189(5)
2.191(4)
2.187(4)
2.187(5)
1.434(6)
1.432(6)
1.426(6)
Ru(1)–Cl(12)
Ru–centroid
2.461(1)
1.649(2)
2.456(1)
3.3023(6)
2.173(4)
2.167(5)
2.169(5)
2.165(4)
2.163(4)
2.168(5)
1.418(6)
1.420(6)
1.418(6)
Ru(1)Ј–Cl(12)
Ru(1) ؒ ؒ ؒ Ru(1Ј)
Ru(1)–C(102)
Ru(1)–C(104)
Ru(1)–C(106)
Ru(1)Ј–C(102)Ј
Ru(1)Ј–C(104)Ј
Ru(1)–C(106)Ј
C(102)–C(103)
C(104)–C(105)
C(106)–C(101)
Cl(11)–Ru(1)–Cl(12)
Cl(12)–Ru(1)–Cl(13)
Ru(1)–Cl(12)–Ru(1)Ј
C–C–C(arom.)b
79.11(4)
79.52(4)
84.38(4)
117.9(4)–119.4(4)
115.8(4)–116.5(4)
Cl(11)–Ru(1)–Cl(13)
Ru(1)–Cl(11)–Ru(1)Ј
Ru(1)–Cl(13)–Ru(1)Ј
C–C–C(arom.)c
79.47(4)
84.91(4)
85.60(4)
120.1(4)–121.7(5)
108.2(4)–112.0(4)
d
e
C(arom.)–CH2–CH3
C(arom.)–CH2–CH3
a Values quoted for one independent molecule; those for second molecule do not differ significantly. b Carbon carrying proximal ethyl group.
c Carbon carrying distal ethyl group. d Proximal ethyl group. e Distal ethyl group.
Variable temperature NMR spectra
methyl carbon atoms are more shielded than the proximal ones,
as found also in the [M(CO)3(η6-C6Et6)] (M = Cr, Mo, W) com-
plexes.5,33 However, the proximal methylene carbon atoms in
complex 1 are more shielded than the distal ones, which is the
reverse of the order found in [M(CO)3(η6-C6Et6)].
Although the ethyl groups of the coordinated arene are
arranged differently in complexes 1–3, they are equivalent on
the NMR time-scale at room temperature. We have investigated
the fluxionality by variable temperature NMR spectroscopy.
On cooling a solution of complex 1 in CD2Cl2, the ethyl
resonances broaden progressively and decoalesce between
Ϫ70 ЊC and Ϫ80 ЊC (Fig. 5). At Ϫ100 ЊC the methyl resonance
splits into two broad triplets centred at δ 1.14 and 1.36 in a 2 : 1
intensity ratio. The methylene protons at this temperature give a
1
The H and 13C NMR spectra of complexes 2 and [3]PF6
behave identically with varying temperature, in both CD2Cl2
and CD3OD. The ethyl resonances at δ ca. 2.4 and 1.3 broaden
at ca. Ϫ5 ЊC, collapse into the baseline, and re-appear at
Ϫ30 ЊC; at Ϫ59 ЊC there are two triplets of equal intensity for
the methyl protons and two quartets of equal intensity for
the methylene protons. The average positions of each of the
two new resonances coincide approximately with the respective
chemical shifts at room temperature. Correspondingly, in the
13C-{1H} NMR spectra, the single methyl, methylene, and
aromatic carbon resonances broaden, collapse, and re-appear at
Ϫ30 ЊC; at Ϫ59 ЊC there are two triplets of equal intensity for
the methyl protons and two quartets of equal intensity for the
methylene protons. The average positions of each of the two
new resonances coincide approximately with the respective
chemical shifts at room temperature. For complex [3]PF6 these
observations are consistent with retention in solution of the
1,3,5-proximal-2,4,6-distal conformation of ethyl groups found
in the solid state, in which the bridging Ru–Cl bonds eclipse the
distal ethyl groups. In contrast, the variable temperature NMR
spectra of 2 are evidently not consistent with the all-distal ethyl
group conformation found in the solid state. If the molecule
had retained its solid state structure in solution at low tem-
perature, and if rotation about arene–methylene or arene–
ruthenium bonds had slowed on the NMR time-scale, there
should have been three different ethyl group environments in
a 1 : 1 : 1 ratio.
more complex pattern that overlaps with the ᎐CH and CH
᎐
2
resonances of COD: there are three groups of broad signals
centred at ca. δ 2.30, 2.04 and 1.88 together with an approx-
imate doublet at δ 1.72, the last being due to four CH2 protons
of COD. Homonuclear decoupling experiments established
that the resonance at δ 2.30 is coupled to the less intense CH3
signal at δ 1.36 and thus contains four equivalent CH2 (C6Et6)
protons. The other two broad triplets, at δ 2.04 and 1.88, are
coupled to each other and to the more intense methyl resonance
at δ 1.14, and must, therefore, be assigned to two sets of
CH2(C6Et6) protons that are inequivalent in pairs (CHH and
CHH).
Corresponding behaviour is observed in the variable tem-
perature 13C-{1H} NMR spectrum of 1. At room temperature
in CD2Cl2 the six equivalent ethyl groups give rise to signals at
δ 16.5 (CH3), 21.2 (CH2) and 104.0 (C6). At Ϫ40 ЊC the CH3 and
C6 signals are broad, while at Ϫ80 ЊC the C6 resonance has split
into two and two additional resonances appear close to the CH2
resonance at δ 21.2. Finally, at Ϫ100 ЊC, there are two groups of
sharp resonances, each in a 1 : 2 ratio, at δ 105.0 and 102.0 (C6),
20.0 and 21.2 (CH2) and 20.8 and 15.9 (CH3), the assignments
being established by a DEPT experiment.
The low temperature NMR spectra of complex 1 show that
there are two ethyl group environments in a 2 : 1 ratio and are
consistent with the retention in solution of the 1,4-proximal-
2,3,5,6-distal conformation found in the solid state. Since each
distal group is flanked by one proximal and one distal group,
whereas each proximal group in flanked by a pair of distal
groups, the diastereotopic methylene protons to which the
protons of the four equivalent methyl groups are coupled must
belong to the distal ethyl groups. The data are also consistent
with the alternative 1,4-distal-2,3,5,6-proximal conformation in
solution but it seems most unlikely that four methyl groups
would prefer to point towards the Ru(COD) fragment. It
should be noted that, if our assignment is correct, the aromatic
carbon atoms bearing the distal ethyl groups are more shielded
than those bearing the proximal ethyl groups and that the distal
Nature of [RuCl2(ꢀ6-C6Et6)]2 in solution
One possible explanation of the NMR result is that, in solution,
complex 2 exists predominantly as the chloride salt of cation 3,
i.e. [Ru2(µ-Cl)3(η6-C6Et6)2]Cl, the cation being assumed to have
the same 1,3,5-proximal-2,4,6-distal conformation of ethyl
groups found in the PF6 salt. We initially examined this possibil-
ity by carrying out conductivity measurements. Stephenson
et al.34,35 have reported that the molar conductivities (ΛM) of 10Ϫ3
M solutions of [Ru2Cl3(η6-C6H6)2]PF6 and [Ru2Cl3(η6-1,3,5-
C6H3Me3)2]BF4 in nitromethane are, respectively, 82 and 77 S
cm2 molϪ1, typical of 1 : 1 electrolytes in this solvent. Measure-
ments of ΛM for complexes 2 and [3]PF6 were made over a range
of concentrations (up to 2.6 × 10Ϫ3 M for 2 and 2.5 × 10Ϫ2M for
[3]PF6) in methanol. Plots of ΛM vs. c1/2 were linear, the derived
J. Chem. Soc., Dalton Trans., 2002, 4488–4496
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for 2 and [3]PF6 were ca. 50 S cm2 molϪ1, about double the
values reported previously for chloride salts of complex
rhodium() cations in CH2Cl2.38 Thus, solutions of complex 2
(ca. 10Ϫ3M) in CH2Cl2 or methanol appear to contain the ions
[Ru2Cl3(η6-C6Et6)2]ϩ and ClϪ in equilibrium with undissociated
2, although whether the latter is present as an ion-pair or
the neutral chloro-bridged dimer is not determined by the
experiments.
Two additional pieces of evidence suggest that dissociation
of chloride ion from complex 2 may also occur at higher
concentrations. First, the molecular weight of a 1.9 × 10Ϫ2
M
solution of 2 in CH2Cl2 measured by vapour pressure osmom-
etry at 37 ЊC was 670 (calc. 836). Second, although the 35Cl
NMR spectrum of 2 in CD3OD is very broad at room temper-
ature, as expected for a compound containing covalently bound
chloride (35Cl: I = 3/2; Q = Ϫ8.2 × 10Ϫ30 m2),39,40 at Ϫ50 ЊC a
new, much sharper signal appears that can be assigned to
unbound chloride ion. Complex [3]PF6 does not show this
resonance under the same conditions. In CD2Cl2 the new signal
is again evident at Ϫ50 ЊC, though observation is hampered
by the large excess of covalently bound chloride in the
solvent. At Ϫ75 ЊC the line-width is ca. 200 Hz, which is much
less than expected for covalently bound chloride. The same
sharp resonance is observed at room temperature in a
solution of [Et4N]Cl in CH2Cl2, but it does not appear in
CH2Cl2 alone.
There are two possible interpretations of these observations:
(a) dissociation of chloride ion from complex 2 is rapid on the
NMR time-scale at room temperature and slow below Ϫ50 ЊC,
and (b) dissociation is slow on the NMR time-scale even at
room temperature but the equilibrium shifts in favour of
[Ru2Cl3(η6-C6Et6)2]ϩClϪ as the temperature is lowered, so that
only at Ϫ50 ЊC can the resonance due to free chloride ion
be detected. The second interpretation is supported by the
observation that solutions of [RuCl2(η6-trindane)]2 in CD2Cl2
contain two species in equilibrium that McGlinchey et al.24
assigned to [RuCl2(η6-trindane)]2 and [Ru2Cl3(η6-trindane)2]Cl
on the basis that the second species is favoured at lower
temperatures and in the more polar solvent CD3NO2. If this
interpretation is correct, reversible loss of chloride ion must be
slow on the NMR time-scale.
The most clear-cut information about the nature of
[RuCl2(η6-C6Et6)]2 in dichloromethane solution comes from
IR spectroscopy. The IR spectrum of complex 2 in the region
500–150 cmϪ1 is essentially identical in the solid state and in
CH2Cl2, and contains three strong absorptions at 365, 310 and
240 cmϪ1 due to v(Ru–Cl) vibrations. In the same region, com-
plex [3]PF6 shows just two strong bands at 310 and 240 cmϪ1
,
which must be due to bridging Ru–Cl modes [v(Ru–Clbr)];
hence, the band at 365 cmϪ1 in the spectrum of 2 is due to a
terminal Ru–Cl mode [v(Ru–Clt)]. Similarly, the spectrum of
[RuCl2(η6-C6Me6)]2, both as a solid and in CH2Cl2, shows three
strong bands at ca. 340 cmϪ1 [v(Ru–Clt)], 300 cmϪ1 [v(Ru–Clbr)]
and 240 cmϪ1 [v(Ru–Clbr)], whereas [Ru2Cl3(η6-C6Me6)2]PF6
shows only two strong bands at ca. 280 cmϪ1 and 230 cmϪ1
1
Fig. 5 Variable temperature H NMR spectrum of [Ru(η6-C6Et6)(η4-
1,5-COD)] 1.
values of ΛM (10Ϫ3M) and Λ0 (the molar conductivity at infinite
dilution) being 75 and 117 S cm2 molϪ1, respectively, for 2,
103 and 112 S cm2 molϪ1 respectively, for [3]PF6; these
values are in the expected range for 1 : 1 electrolytes in meth-
anol.36 The linearity of the plots confirms that the complexes
do not undergo multiple dissociations.37 In the case of [3]PF6,
the slope of the Λ0 Ϫ ΛM vs. c1/2 plot is 266, which compares
well with reported values for 1 : 1 electrolytes in methanol,
e.g., 288 for [Ru2Cl3(PEt2Ph)6]Cl;37 however, for 2 the slope
is greater, 1245, presumably reflecting greater ion-pairing
or covalent binding of Cl compared with PF6. Ion pairing is
likely to be even more significant in dichloromethane in which
solvent ΛM values were measured over a range up to 4 × 10Ϫ3 M
for 2 and 1 × 10Ϫ3 M for [3]PF6; plots of ΛM vs. c1/2 were again
[Pandey et al.29 report a band due to v(Ru–Cl) at 265 cmϪ1
,
similar to the values obtained for other [Ru2Cl3(η6-arene)2]ϩ
salts41]. Surprisingly, the v(Ru–Clt) frequencies for [RuCl2(η6-
C6Me6)]2, and especially [RuCl2(η6-C6Et6)]2, are considerably
higher than those reported for [RuCl2(η6-arene)]2 complexes
containing less highly substituted arenes (ca. 300 cmϪ1),41
but the assignment seems secure and there is no obvious
explanation.
In summary, the main species present in dichloromethane
solutions of [RuCl2(η6-C6Et6)]2 is the chloro-bridged dimer,
although [Ru2Cl3(η6-C6Et6)2]Cl may become
a significant
component in very dilute solutions and at low temperature. In
solution, the ethyl groups in the dimer adopt the 1,3,5-distal-
2,4,6-proximal conformation, in contrast to the all-distal
conformation found in the solid state.
linear. The derived values of Λ0 were 68 and 100 S cm2 molϪ1
,
respectively, to be compared with 120 S cm2 molϪ1 for [Et4N]Cl
measured under similar conditions. The values of ΛM (10Ϫ3 M)
4492
J. Chem. Soc., Dalton Trans., 2002, 4488–4496

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Tertiary phosphine derivatives of [RuCl2(ꢀ6-C6Et6)]2 2
Replacement of one of the carbonyl ligands of [Cr(CO)3-
(η6-C6Et6)] by tertiary phosphines of increasing bulk causes a
systematic change in the original 1,3,5-distal-2,4,6-proximal
conformation of ethyl groups. Thus, the solid-state conform-
ations in [Cr(CO)2(L)(η6-C6Et6)] are 1,2,3,5-distal-2,4-proximal
(L = PMe3),42 1,2,3,4,5-distal-6-proximal and all-distal (equal
populations) (L = PEt3),32 and all-distal (L = PPh3).2,4 In the
PMe3 derivative, four stereoisomers can be detected by 31P-{1H}
NMR spectroscopy at low temperature, that found in the solid
state being the least populated in solution. It was of interest
to see whether the Ru–C6Et6 system would show similar
behaviour.
Complex 2 reacts with a stoichiometric amount of PMe3 in
refluxing toluene, or with a slight excess of PPh3 in refluxing
dichloromethane, to give the adducts [RuCl2(L)(η6-C6Et6)]
(L = PMe3 4, PPh3 5) as orange-red, air-stable, crystalline solids.
They show singlets in their 31P-{1H} NMR spectra in CD2Cl2 at
δ 3.1 and 24.0, respectively, which are fairly close to the values
reported for the corresponding C6Me6 complexes (δ 0.6 in
CDCl3 for L = PMe3,43 δ 29.3 in CDCl3, 30.4 in CD2Cl2 for
L = PEt3 44), and the spectrum of 4 remained unchanged down
to Ϫ60 ЊC. The 1H and 13C-{1H} NMR spectra show the
presence of equivalent ethyl groups and the signal due to the
coordinated arene carbon atoms appears at δ ca. 100 without
discernible 31P coupling. Unlike the spectra of complexes 1–3,
those of 4 and 5 are invariant with temperature.
Fig. 7 An ORTEP diagram of [RuCl2(PPh3)(η6-C6Et6)] 5 showing
selected atom labelling and 20% probability ellipsoids; hydrogen atoms
have been omitted for clarity.
Table 4 Selected distances (Å) and angles (Њ) in [RuCl2(PMe3)(η6-
C6Et6)] 4
Ru(1)–Cl(1)
Ru(1)–C(1)
Ru(1)–C(3)
C(1)–C(2)
2.4181(9)
2.200(3)
2.251(3)
1.416(4)
1.416(6)
Ru(1)–P(1)
Ru(1)–C(2)
C(1)–C(1a)
C(2)–C(3)
2.343(1)
2.196(3)
1.431(6)
1.440(4)
The X-ray structures of complexes 4 and 5 are shown in Fig.
6 and 7; selected bond distance and angles are listed in Tables 4
C(3)–C(3a)
Cl(1)–Ru(1)–Cl(1a)
Cl(1)–Ru(1)–C(1)
Cl(1)–Ru(1)–C(3)
Cl(1)–Ru(1)–C(2a)
P(1)–Ru(1)–C(1)
P(1)–Ru(1)–C(3)
90.35(5)
115.83(8)
89.81(7)
154.03(8)
99.51(8)
160.08(8)
Cl(1)–Ru(1)–P(1)
Cl(1)–Ru(1)–C(2)
Cl(1)–Ru(1)–C(1a)
Cl(1)–Ru(1)–C(3a)
P(1)–Ru(1)–C(2)
82.11(3)
88.96(8)
153.79(8)
116.28(8)
123.43(8)
Table 5 Selected distances (Å) and angles in [RuCl2(PPh3)(η6-C6Et6)] 5
Ru(1)–Cl(1)
Ru(1)–P(1)
Ru(1)–C(2)
Ru(1)–C(4)
Ru(1)–C(6)
C(2)–C(3)
C(4)–C(5)
2.423(1)
2.388(1)
2.242(5)
2.234(5)
2.217(5)
1.454(8)
1.423(7)
Ru(1)–Cl(2)
Ru(1)–C(1)
Ru(1)–C(3)
Ru(1)–C(5)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
2.412(1)
2.235(5)
2.207(5)
2.252(5)
1.403(7)
1.395(7)
1.414(7)
Cl(1)–Ru(1)–Cl(2)
Cl(1)–Ru(1)–C(1)
Cl(1)–Ru(1)–C(3)
Cl(1)–Ru(1)–C(5)
Cl(2)–Ru(1)–P(1)
Cl(2)–Ru(1)–C(2)
Cl(2)–Ru(1)–C(4)
Cl(2)–Ru(1)–C(6)
P(1)–Ru(1)–C(2)
P(1)–Ru(1)–C(4)
P(1)–Ru(1)–C(6)
87.99(4)
113.3(2)
89.3(1)
154.4(1)
82.63(4)
114.9(1)
154.3(2)
89.7(1)
Cl(1)–Ru(1)–P(1)
Cl(1)–Ru(1)–C(2)
Cl(1)–Ru(1)–C(4)
Cl(1)–Ru(1)–C(6)
Cl(2)–Ru(1)–C(1)
Cl(2)–Ru(1)–C(3)
Cl(2)–Ru(1)–C(5)
P(1)–Ru(1)–C(1)
P(1)–Ru(1)–C(3)
P(1)–Ru(1)–C(5)
86.83(5)
87.6(1)
117.6(2)
150.9(2)
89.3(1)
153.0(2)
117.4(1)
158.1(2)
124.0(2)
99.2(1)
Fig. 6 An ORTEP diagram of [RuCl2(PMe3)(η6-C6Et6)] 4 showing
selected atom labelling and 20% probability ellipsoids; hydrogen atoms
have been omitted for clarity.
and 5. Both complexes have the expected half-sandwich, piano-
stool structure with the arene ethyl groups in the all-distal
conformation. When viewed along the arene–Ru bond axis, the
ligand tripod is staggered relative to the arene carbon atoms.
The Ru–arene(centroid) distance is significantly greater in 5
[1.720(2) Å] than in 4 [1.696(1) Å], possibly reflecting greater
steric hindrance to arene coordination induced by the larger
tertiary phosphine. In agreement, the Ru–P distance in 5
[2.388(1) Å] is greater than that in 4 [2.343(1) Å], cf. 2.3637(12)
Å in [RuCl2(PPh3)(η6-C6H6)].45 The Ru–C(arene) distances span
the ranges 2.196(3)–2.251(3) Å for 4 and 2.207(5)–2.252(5) Å
for 5 but, in contrast to the η6-benzene complexes [RuCl2(L)-
(η6-C6H6)] (L = PMePh2,46 PPh3 45), there is no systematic
lengthening to the carbon atoms trans to the tertiary phosphine.
161.4(2)
100.3(1)
121.6(1)
ruthenium() and is easily converted into [RuCl2(η6-C6Et6)]2 2.
The availability of this precursor should enable the conform-
ational and dynamic properties of hexaethylbenzene in its
ruthenium and Group 6 transition metal complexes to be
compared. The 1,4-proximal-2,3,5,6-distal arrangement of
ethyl groups found in complex 1 has not been observed so far in
any complexes of the [M(CO)3(η6-C6Et6)] class, thus illustrating
how the conformation is determined primarily by the auxiliary
ligand array (bipodal in the case of 1). While complexes 1 and
[3]PF6 appear to retain in solution the ethyl group conform-
ations found in the solid state (1,3,5-proximal-2,4,6-distal for
the latter), the evidence suggests that in complex 2 the conform-
ation changes from all-distal in the solid to 1,3,5-proximal-
Discussion
The compound [Ru(η6-C6Et6)(η4-1,5-COD)] 1 is readily pre-
pared by the stoichiometric cyclotrimerisation of hex-3-yne on
J. Chem. Soc., Dalton Trans., 2002, 4488–4496
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2,4,6-distal in solution at low temperature. The energies of the
various conformations are clearly similar and several examples
of similar changes are known. For example, the cation
[Fe(η5-C5H5)(η6-C6Et6)]ϩ adopts a 1,3-proximal-2,4,5,6-distal
Conductivities were measured on a digital conductivity meter
LF DIGI 550 from Wissenschaft-Technische Werkstätten with
a CDC 344 platinum electrode from Radiometer. The cell con-
stant was determined by calibration with a standard aqueous
solution of KCl. The Λ0 values were obtained from a plot of ΛM
against the square root of concentration. The linear portion of
the graph was extrapolated and Λ0 was taken as the intercept
with the axis where the concentration was zero.
47
ethyl group conformation in its PF6 salt and a 1-proximal-
2,3,4,5,6-distal conformation in its BPh4 salt,48 while in solution
at low temperature these co-exist with a third isomer having
an all-distal conformation.49 In contrast, [Ru(η5-C5H5)-
(η6-C6Et6)]PF6 appears to adopt the 1,3,5-proximal-2,4,6-distal
conformation in solution, though the conformation in the solid
state in unknown.8,9 It seems likely that conformations, such
as 1,3-proximal-2,4,5,6-distal, 1-proximal-2,3,4,5,6-distal, and
all-distal are present in equilibrium with 1,3,5-proximal-2,4,6-
distal in solutions of complexes 2 and [3]PF6 above ca. Ϫ50 ЊC;
interconversion at an intermediate rate on the 13C-NMR time
scale at room temperature could account for the apparent
broadness of the arene carbon resonances. Studies over a wider
temperature range on a higher frequency instrument combined
with detailed line-shape analysis will probably be necessary to
provide further information. Like [Cr(CO)2(PPh3)(η6-C6Et6)],2,4
complexes 4 and 5 adopt an all-distal arrangement of ethyl
groups and the temperature-independence of their NMR
spectra indicates cessation of ethyl group rotation consistent
with retention of the all-distal arrangement in solution. Pre-
sumably, steric repulsion between the phosphine substituents
and the proximal ethyl groups is sufficient to overcome the
repulsion between mutually distal groups. In contrast to 4,
however, the ethyl groups in [Cr(CO)2(PMe3)(η6-C6Et6)] adopt
predominantly a 1,3-proximal-2,4,5,6-distal arrangement in
the solid state, although there is a small proportion of the
1-proximal-2,3,4,5,6-distal conformer in the lattice.42 Moreover,
in solution these conformers co-exist with the 1,3,5-proximal-
2,4,6-distal and all-distal compounds. Since the M–P and M–C
(arene) distances in 4 and in [Cr(CO)2(L)(η6-C6Et6)] (L =
PMe3,42 PEt3 32) are very similar, there is no obvious reason
based on steric effects for these differences.
Preparations
[Ru(ꢀ6-C6Et6)(ꢀ4-1,5-COD)] 1. A solution of [Ru(η6-C10H8)-
(η4-1,5-COD)] (0.20 g, 0.59 mmol) in THF (10 cm3) was treated
with hex-3-yne (0.4 cm3, 3.52 mmol) and the mixture was stirred
at room temperature for 3 h. The solvent was evaporated in
vacuo and the residue was dissolved in n-pentane (10 cm3). The
dark brown solution was transferred to an alumina column
(20 × 1.5 cm, activity III). The yellow band that eluted with
n-pentane was concentrated under reduced pressure to a
volume of ca. 5 cm3 and set aside at Ϫ78 ЊC to give pale yellow,
air sensitive crystals of 1 (0.25 g, 93%). 1H NMR (C6D6, 23 ЊC,
200 MHz) δ 2.76 (br s, 4 H, ᎐CH), 2.36 (br s, 8 H, CH of
᎐
2
3
COD), 2.1 (q, 12H, J = 7.5 Hz, CH2 of C6Et6), 1.82 (t, 18 H,
CH ); (CD Cl , 23 ЊC, 200 MHz) δ 2.48 (m, 4 H, ᎐CH), 2.24 (q,
᎐
3
2
2
12 H, 3J = 7.5 Hz, CH2 of C6Et6), 2.04 (m, 4 H, CHH of COD),
1.88 (m, 4 H, CHH of COD), 1.30 (t, 18 H, 3J = 7.5 Hz, CH3);
(CD Cl , Ϫ100 ЊC, 200 MHz) δ 2.32 (br s, 8 H, ᎐CH, proximal
᎐
2
2
CH2 of C6Et6), 2.04, 1.87 (dq, 8 H, distal CH2 of C6Et6), 1.92
(br m, 4 H, CHH of COD), 1.72 (approx d, 4 H, CHH of
COD), 1.36 (br t, 6 H, proximal CH3), 1.14 (t, 12 H, distal
CH3); 13C-{1H}NMR (C6D6, 23 ЊC, 75.4 MHz) δ 103.4(C6), 64.3
(᎐CH), 34.6 (CH of COD), 21.1 (CH2 of C6Et6); (CD2Cl2,
᎐
2
Ϫ100 ЊC, 75.4 MHz) δ 105.0 (1), 102.0 (2) (C ), 62.5 (᎐CH), 34.6
᎐
6
(CH2 of COD), 21.2–20.8 (overlapping distal CH2, proximal
CH3 of C6Et6), 20.0 (proximal CH2 of C6Et6), 15.8 (distal CH3
of C6Et6); EI-MS (70 eV) m/z 456 (Mϩ). Anal. Found: C, 68.7;
H, 9.0. C26H42Ru requires: C, 68.6; H, 9.2%.
[RuCl2(ꢀ6-C6Et6)]2 2. A stirred solution of freshly prepared
1 (0.19 g, 0.40 mmol) in acetone (10 cm3) was treated dropwise
with conc. aq. HCl (0.3 cm3). The colour changed from yellow
to orange-brown. After 30 min the orange air-stable precipitate
of 2 was separated by filtration, washed with acetone, and dried
in vacuo. The yield was 0.16 g (95%). The same complex was
obtained similarly in 87% yield from 1 (50 mg, 0.11 mmol) in
hexane (ca. 100 cm3) and conc. aq. HCl. Single crystals of
2 suitable for X-ray structural analysis were obtained by layer-
ing a CH2Cl2/diethyl ether solution with hexane over a 3 d
period. The red cubic crystals lost solvent on exposure to air. 1H
Experimental
All operations were performed under argon with use of
standard Schlenk techniques. Pentane, hexane, thf, diethyl
ether, benzene and toluene were pre-dried over sodium wire,
distilled from sodium–benzophenone under nitrogen, and
stored under nitrogen or argon. Hex-3-yne was degassed before
use and stored under argon. Dichloromethane was distilled
from CaH2; acetone and methanol were dried over 3 Å molec-
ular sieves. The complex [Ru(η6-C10H8)(η4-1,5-COD)] was
prepared by a literature method.14
NMR (1H, 13C and 31P) spectra were measured on Varian XL
200, VXR 300 and Gemini 300 BB spectrometers (Canberra)
and on Varian Gemini 200 and VXR 300 spectrometers (Pisa).
Chemical shifts are reported relative to internal Me4Si (1H, 13C)
and to external 85% H3PO4 (31P). The 35Cl NMR spectra were
measured with a Varian VXR 300 instrument at an operating
frequency of 29.396 MHz with a spectral window of 100,000
Hz on solutions containing ca. 15 mg of compound in 0.5 cm3
of solvent. Times to collect enough scans for a spectrum ranged
from 5 min for [Et4N]Cl in CD2Cl2 to several hours for
[RuCl2(η6-C6Et6)]2 2 in CD2Cl2. Mass spectra were recorded on
a VG Micromass 7070 spectrometer (EI, 70 eV) or on a VG
ZAB2-SEQ spectrometer (FAB, positive ion). Infrared spectra
were measured on Perkin-Elmer 683 or Perkin-Elmer FTIR
1800 spectrometers. Spectra in the range 450–150 cmϪ1 were
measured on the latter, either as polythene discs or as CH2Cl2
solutions, in a polythene cell of 0.1 mm path length. Elemental
analyses were carried out by the staff at the Australian National
University Analytical Services Unit, Canberra and of the
Facoltà di Farmacia, Università di Pisa. The former also per-
formed a molecular weight determination on complex 2 by
means of a Knauer vapour pressure osmometer.
3
NMR (CD2Cl2, 23 ЊC, 300 MHz) δ 2.40 (q, 12 H, J = 8 Hz,
CH2), 1.30 (t, 18 H, CH3); (CD3CN, 23 ЊC, 200 MHz) δ 2.50 (q,
12 H, 3J = 7.6 Hz, CH2), 1.35 (t, 18 H, CH3); (CD2Cl2, Ϫ59 ЊC,
300 MHz) δ 2.45 (q, 6 H, 3J = 8 Hz, CH2), 2.14 (q, 6 H, 3J = 8
Hz, CH2), 1.28 (t, 9 H, CH3), 1.18 (t, 9 H, CH3); 13C-{1H} NMR
(CD2Cl2, 23 ЊC, 75.4 MHz) δ 94–95 (br, C6), 21.1 (CH2), 14.7
(CH3); (CD2Cl2, Ϫ59 ЊC, 75.4 MHz) δ 101.7 (1), 87.6 (1) (C6),
22.7, 20.0, 17.3, 11.3 (CH2, CH3); EI-MS (70 eV) m/z 800 (Mϩ
Ϫ Cl, 420 [RuCl2(C6Et6)ϩ]. Anal. Found: C, 51.45; H, 7.4; Cl,
16.8; M (osmometry, CH2Cl2, 37 ЊC, 1.6198 mg cmϪ3), 670;
C36H60Cl4Ru2 requires: C, 51.7; H, 7.2; Cl 17.0%; M, 837.
[Ru2Cl3(ꢀ6-C6Et6)2]PF6 [3]PF6. Solid NH4PF6 was added
slowly to a stirred solution of complex 2 (50 mg, 0.06 mmol) in
ethanol or methanol (3 cm3) until no more would dissolve.
When the solution was set aside without stirring for 3 d, red
cubic crystals of [3]PF6 deposited that were of X-ray quality.
The supernatant liquid was removed and the crystals were
washed by decantation with hexane and cold ethanol. The yield
1
was 44 mg (78%). H NMR (CD3OD, 23 ЊC, 200 MHz) δ 2.50
(q, 12 H, 3J = 7.6 Hz, CH2), 1.33 (t, 18 H, CH3); 13C-{1H} NMR
4494
J. Chem. Soc., Dalton Trans., 2002, 4488–4496

View Article Online
Table 6 Crystal and structure refinement data for complexes 1–5
1
2
3
4
5
Compound
M
C26H42Ru
455.67
C36H60Cl4Ru2
836.82
C36H60Cl3F6PRu2
946.33
C21H39Cl2PRu.H2O
512.50
C36H45Cl2PRu.C6H6
758.81
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
Triclinic
P1 (no. 2)
Monoclinic
P21/n (no. 14)
10.900(3)
9.566(3)
18.439(3)
Triclinic
P1 (no. 2)
13.913(3)
14.132(3)
21.625(3)
90.97(1)
90.56(1)
100.89(2)
4175(1)
Monoclinic
P21/m (no. 11)
8.698(2)
14.618(4)
9.613(2)
Orthorhombic
P212121 (no. 19)
9.358(2)
19.226(1)
20.478(2)
¯
¯
9.578(3)
10.712(3)
13.336(4)
68.61(3)
84.16(3)
64.32(3)
1145.6(6)
2
101.99(2)
99.01(2)
γ/Њ
V/Å3
Z
1880.7(7)
2
1.478
92.85(Cu-Kα)
864
1207.1(4)
2
1.410
9.45(Mo-Kα)
536
3684.2(6)
4
1.368
53.97(Cu-Kα)
1584
4
Dc/g cmϪ3
1.321
6.92(Mo-Kα)
484
1.506
10.05(Mo-Kα)
1936
µ/mmϪ1
F(000)
)
Reflections measured
Unique reflections(Rint
Used reflections
4241
3179
15431
2399
3131
3111
2857[I > 3σ(I )]
0.025, 0.027b
0.39, Ϫ0.23
)
3981(0.0409)
3979[I > 2σ(I )]
0.040, 0.099a
0.80, Ϫ0.62
3004(0.053)
1953[I > 3σ(I )]
0.039, 0.040b
0.89, Ϫ1.07
14767(0.019)
10182[I > 3σ(I )]
0.037, 0.030b
1.03, Ϫ1.13
2246(0.029)
2008[I > 3σ(I )]
0.028, 0.024b
0.58, Ϫ0.44
R,Rw(obs.data)
ρmax, ρmin/e Å3
2
2
a R = Σ||Fo Ϫ |Fc||/Σ|Fo|; Rw = {Σw(|Fo|2 Ϫ |Fc|2)2/ΣwFo }1/2
.
b R = Σ||Fo| Ϫ |Fc||/Σ|Fo|; Rw = {Σw(|Fo| Ϫ |Fc|)2/ΣwFo }1/2
.
(CD2Cl2, 23 ЊC, 75.4 MHz) δ 93–95 (br, C6), 21.5 (CH2), 15.0
(CH3); (CD2Cl2, Ϫ59 ЊC, 75.4 MHz) δ 101.1 (1), 87.1 (1) (C6),
22.1, 19.4, 16.7, 12.7 (CH2, CH3); 31P-{1H} NMR (CD3OD,
2–551) and expanded by standard Fourier syntheses (SHELX 93
for 1,52 DIRDIF 92 for 2–551). Non-hydrogen atoms were
refined anisotropically by full-matrix least-squares. In the case
of 4 the PMe3 group refined with one carbon atom disordered
equally over two positions. Hydrogen atoms were included in
calculated positions except for those on one of the PMe3 methyl
groups [C(10)] in 4, which were located on a difference map.
Calculations were carried out with the PARST program53
for 1 and the software package TEXSAN54 for 2–5. Neutral
atom scattering factors,55 the values of ∆f Ј and ∆f Љ,56 and
the mass attenuation coefficients56 were taken from standard
compilations.
1
23 ЊC, 81.0 MHz) δ Ϫ142.7 (sept, JPF = 708 Hz, PF6); EI-MS
(70 eV) m/z 383 [RuCl(C6Et6)ϩ]. Anal. Found: C, 44.3; H, 6.5.
C36H60Cl3F6PRu2 requires: C, 45.7; H, 6.3%.
[RuCl2(PMe3)(ꢀ6-C6Et6)] 4. A suspension of complex 2
(36 mg, 0.43 mmol) in toluene (10 cm3) was treated with PMe3
(0.087 cm3, 0.86 mmol). The mixture was stirred at 60 ЊC for
2 h to give a deep red solution. This was filtered to remove a
small amount of solid and evaporated to dryness in vacuo.
The orange-red residue was dissolved in the minimum volume
of dichloromethane and the solution was layered with hexane.
After 12 h at room temperature a crop of red, air-stable, X-ray
quality needles of 4 had deposited. The yield was 32 mg (78%).
1H NMR (CD2Cl2, 23 ЊC, 200 MHz) δ 2.40 (q, 12 H, 3J = 7.6 Hz,
CH2), 1.26 (d, 9 H, 2JPH = 10.4 Hz, PMe3), 1.08 (t, 18 H, CH3 of
C6 Et6); 13C-{1H}NMR (CD2Cl2, 23 ЊC, 75.4 MHz) δ 100.5 (C6),
CCDC reference numbers 186313–186317.
See http://www.rsc.org/suppdata/dt/b2/b204875m/ for crys-
tallographic data in CIF or other electronic format.
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4496
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