Synthesis and molecular structure of the trinuclear ruthenium cluster cations [H3Ru3{C6H5(CH2)2OC(O)C6H5}(C6Me6)2(O)]+ and [H3Ru3{C6H5(CH2) 2OC(O)(CH2)3C6H5}(C6Me6)2(O)]+

Article abstract of DOI:10.1016/j.ica.2003.09.008

Benzoic acid 2-cyclohexa-1,4-dienyl ethyl ester (1), and 4-phenylbutyric acid 2-cyclohexa-1,4-dienyl ethyl ester (2) are prepared by reacting, respectively, benzoic acid and 4-phenylbutyric acid with 2-cyclohexa-1,4-dienyl ethanol. These dienyl ester derivatives react with RuCl₃·n H₂O in refluxing ethanol to afford in good yield [Ru{C ₆H₅(CH₂)₂OC(O)C₆H ₅}Cl₂] ₂ (3), and [Ru{C₆H ₅(CH₂)₂OC(O)(CH₂)₃C ₆H₅}Cl₂]₂ (4). The trinuclear arene-ruthenium cluster cations [H₃Ru₃{C₆H ₅(CH₂)₂OC(O)C₆H₅}(C ₆Me₆)₂(O)]⁺ (5), and [H ₃Ru₃{C₆H₅(CH₂) ₂OC(O)(CH₂)₃C₆H₅}(C ₆Me₆)₂(O)]⁺ (6) are synthesised from the dinuclear precursor [H₃Ru₂(C₆Me ₆)₂]⁺, and the mononuclear complexes [Ru{C ₆H₅(CH₂)₂OC(O)C₆H ₅}(H₂O)₃]²⁺ and [Ru{C ₆H₅(CH₂)₂OC(O)(CH₂) ₃C₆H₅}(H₂O)₃] ²⁺, accessible, respectively, from 3 and 4 in aqueous solution. The water-soluble trinuclear cluster cations 5, and 6 possess a phenyl substituent attach to their side-arm which can act as a substrate for hydrogenation. The single-crystal X-ray structure analyses of [5][PF₆], and [6][PF ₆] have been determined.

Full text of DOI:10.1016/j.ica.2003.09.008

Inorganica Chimica Acta 357 (2004) 3437–3442
www.elsevier.com/locate/ica
Synthesis and molecular structure of the trinuclear ruthenium cluster
cations [H3Ru3{C6H5(CH2)2OC(O)C6H5}(C6Me6)2(O)]þ
and [H3Ru3{C6H5(CH2)2OC(O)(CH2)3C6H5}(C6Me6)2(O)]þ
*
*
€
Ludovic Vieille-Petit, Bruno Therrien , Georg Suss-Fink
Institut de Chimie, Universiteꢀ de Neucha^tel, Case postale 2, CH-2007 Neucha^tel, Switzerland
Received 4 September 2003; accepted 13 September 2003
Available online 21 November 2003
Abstract
Benzoic acid 2-cyclohexa-1,4-dienyl ethyl ester (1), and 4-phenylbutyric acid 2-cyclohexa-1,4-dienyl ethyl ester (2) are prepared by
reacting, respectively, benzoic acid and 4-phenylbutyric acid with 2-cyclohexa-1,4-dienyl ethanol. These dienyl ester derivatives react
with RuCl3 ꢀ n H2O in refluxing ethanol to afford in good yield [Ru{C6H5(CH2)2OC(O)C6H5}Cl2] (3), and [Ru{C6H5(CH2)2
2
OC(O)(CH2)3C6H5}Cl2]2 (4). The trinuclear arene–ruthenium cluster cations [H3Ru3{C6H5(CH2)2OC(O)C6H5}(C6Me6)2(O)]þ (5),
and [H3Ru3{C6H5(CH2)2OC(O)(CH2)3C6H5}(C6Me6)2(O)]þ (6) are synthesised from the dinuclear precursor [H3Ru2(C6Me6)2]þ,
and the mononuclear complexes [Ru{C6H5(CH2)2OC(O)C6H5}(H2O)3]2þ and [Ru{C6H5(CH2)2OC(O)(CH2)3C6H5}(H2O)3]2þ
,
accessible, respectively, from 3 and 4 in aqueous solution. The water-soluble trinuclear cluster cations 5, and 6 possess a phenyl
substituent attach to their side-arm which can act as a substrate for hydrogenation. The single-crystal X-ray structure analyses of
[5][PF6], and [6][PF6] have been determined.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Arene hydrogenation; Cluster catalysis; Intermolecular interactions; Ruthenium
1. Introduction
substrate and catalyst molecule, thus violating the
mechanistic doctrine of organometallic catalysis [3–5].
The catalytic hydrogenation of benzene, taking place
inside the hydrophobic pocket, is supposed to proceed
stepwise via the formation of cyclohexadiene and cy-
clohexene, which are hydrogenated to give cyclohexane,
see Scheme 1. High-pressure NMR studies of the hy-
drogenation of benzene to give cyclohexane, catalysed
by the cluster cation [H3Ru3(C6H6) (C6Me6)2 (O)]þ,
reveals that the cyclohexadiene and cyclohexene are
hydrogenated more rapidly than benzene [6]. The hy-
drogenation reaction by supramolecular cluster catalysis
using [H3Ru3(C6H6)(C6Me6)2(O)]þ under biphasic
conditions works not only for benzene but also for not
too bulky benzene derivatives [1,2].
The complete characterisation of intermediary species
involved in a catalytic cycle represents one of the most
challenging task in organometallic chemistry. Recently,
we have postulated that the water-soluble cluster cation
[H3Ru3(C6H6)(C6Me6)2(O)]þ, active catalyst in the hy-
drogenation of benzene to cyclohexane under biphasic
conditions, to be involved in a catalytic mechanism in
which the catalytic reaction occurs within a host–guest
complex without prior coordination of the substrate
[1,2]. This new catalytic phenomenon, for which we
coined the term ‘‘supramolecular cluster catalysis’’, re-
lies entirely on weak intermolecular interactions between
In this context, it was interesting to attach the aro-
matic substrate to the catalyst molecule and to check if
the hydrogenation of the tethered phenyl group occurs
by an intra- or inter-molecular process. Changing the
length, and flexibility of the side-arm chain can allow the
* Corresponding authors. Tel.: +41-32-718-2499; fax: +41-32-718-
2511.
E-mail addresses: bruno.therrien@unine.ch (B. Therrien), georg.su-
€
ess-fink@unine.ch (G. Suss-Fink).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.09.008

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L. Vieille-Petit et al. / Inorganica Chimica Acta 357 (2004) 3437–3442
Scheme 1. Mechanism proposed for the hydrogenation of benzene within the hydrophobic pocket of cation [H3Ru3(C6H6)(C6Me6)2(O)]þ.
pharmaceutical chemistry, University of Geneva (Swit-
zerland). Electro-spray mass spectra were obtained in
positive-ion mode with an LCQ Finnigan mass spec-
trometer. The starting dinuclear dichloro complexes
[Ru(C6Me6)Cl2]2 [7], and [H3Ru2(C6Me6)2]þ [8,9] were
prepared according to published methods. 2-cyclohexa-
1,4-dienyl ethanol was synthesised by sodium reduction
of 2-phenyl ethanol in liquid ammonia [10].
2.2. Syntheses
2.2.1. Benzoic acid 2-cyclohexa-1,4-dienyl ethyl ester (1)
and 4-phenylbutyric acid 2-cyclohexa-1,4-dienyl ethyl
ester (2)
Scheme 2. Intra- and inter-molecular hydrogenation processes.
A solution of benzoic acid (1.25 g, 10.25 mmol) for
1 or 4-phenylbutyric acid (1.70 g, 10.48 mmol) for 2,
phenyl group to be hydrogenated via an intra- or inter-
molecular processes, see Scheme 2.
Herein, we report the synthesis, characterisation, and
N; N-dicyclohexylcarbodiimide (3.30 g, 15,99 mmol),
4-(dimethylamino)pyridine (1 g, 8.18 mmol), 4-pyrr-
olidinopyridine (1.20 g, 8.10 mmol), and 2-cyclohexa-
hydrogenation activity of the water-soluble cluster ca-
1,4-dienyl ethanol (1 g, 8.06 mmol) in CH2Cl2 (80 ml)
tions [H3Ru3{C6H5(CH2)2 OC(O)C6H5}(C6Me6)2(O)]þ
was stirred under nitrogen at room temperature during
(5), and [H3Ru3{C6H5ðCH2)2OC(O)(CH2)3C6H5}(C6
3 days. The resulting solution was filtered through
Me6)2 (O)]þ (6) possessing a side-arm substituent on
celite to remove N; N-dicyclohexylurea and the filtrate
which is attached a terminal phenyl group. The single-
concentrated under reduced pressure. A chromatogram
crystal X-ray structure analyses of [5][PF6], and [6][PF6]
have been determined.
of the residue was recorded on a silica gel column,
eluting with hexane/acetone (10:1). The pure product
was isolated from the first fraction, giving 1 or 2 as
clear yellow oils. Yield: 1.71 g (93%) for 1, 2.10 g
(95%) for 2.
2. Experimental
Spectroscopic data for 1: IR (solution in CHCl3,
cmꢁ1): m ¼ 1712 (C@O ester). 1H NMR (200 MHz,
CDCl3): d ¼ 8:06 (m, 2H, Har), 7.52 (m, 3H, Har), 5.74
(m, 2H, ethylenic H), 5.59 (m, 1H, ethylenic H), 4.44 (t,
2H, –OCH2CH2–, 3J ¼ 13:92 Hz), 2.73 (m, 4H, –C@C–
CH2–), 2.46 (t, 2H,–OCH2CH2–, 3J ¼ 13:92 Hz).
13C{1H} NMR (50 MHz, CDCl3): d ¼ 166:85, 133.12,
131.40, 130.69, 129.83, 128.61, 124.42, 124.32, 121.28,
63.58, 36.83, 29.41, 27.06. MS (EI mode, acetone):
m=z ¼ 228 [M]þ. Anal. Calc. for C15H16O2: C, 78.92; H,
7.06. Found: C, 78.71; H, 6.98%.
2.1. General
All manipulations were carried out by routine under
nitrogen atmosphere. De-ionised water and organic
solvents were degassed and saturated with nitrogen
prior to use. NMR spectra were recorded using a Varian
Gemini 200 BB spectrometer and a Bruker 400 MHz
spectrometer. IR spectra were recorded on a Perkin–
Elmer 1720X FT-IR spectrometer (4000–400 cmꢁ1).
Microanalyses were performed by the Laboratory of

L. Vieille-Petit et al. / Inorganica Chimica Acta 357 (2004) 3437–3442
3439
Spectroscopic data for 2: IR (solution in CHCl3,
1
2.2.4. [H3Ru3{C6H5(CH2)2OC(O)C6H5}(C6Me6)2(O)]þ
(5)
cmꢁ1): m ¼ 1732 (C@O ester). H NMR (200 MHz, ac-
etone-d6): d ¼ 7:35 ꢁ 7:19 (m, 5H, Har), 5.73 (m, 2H,
ethylenic H), 5.52 (m, 1H, ethylenic H), 4.20 (t, 2H, –
OCH2CH2–), 2.72–2.64 (m, 6H, Ar–CH2CH2CH2– and
–C@C–CH2–), 2.39–2.29 (m, 4H, –OCH2CH2– and Ar–
CH2CH2CH2–), 1.98 (m, 2H, Ar–CH2CH2CH2–).
13C{1H}NMR (50 MHz, CDCl3): d ¼ 173:75, 141.72,
131.36, 126.24, 124.39, 124.30, 121.15, 62.81, 36.77,
35.39, 33.93, 29.31, 27.03, 26.83. MS (EI mode, ace-
tone): m=z ¼ 270 [M]þ. Anal. Calc. for C18H22O2: C,
79.96; H, 8.20. Found: C, 79.74; H, 8.13%.
To a solution of [H3Ru2(C6Me6)2][BF4] (70 mg, 0.11
mmol) in acetone (20 ml), and H2O (10 ml) was added 3
(64 mg, 0.08 mmol). The mixture was heated to 50 °C
for 24 h in a closed pressure Schlenk tube. The resulting
red solution was filtered through celite and evaporated
to dryness; the residue was dissolved in CH2Cl2 (10 ml),
and purified on silica-gel plates (eluent: CH2Cl2/acetone
2:1) to give pure [5][BF4] as red crystalline powder. Red
crystals suitable for X-ray analysis were obtained from
an acetone/n-hexane solution after addition of a small
amount of KPF6. Yield: 45 mg (43%).
Spectroscopic data for 5: IR (KBr, cmꢁ1): m ¼ 1716
(C@O ester). 1H NMR (400 MHz, acetone-d6): d ¼ 8:06
(m, 2H, Har), 7.69 (m, 1H, Har), 7.55 (m, 2H, Har), 5.93
(m, 2H, Ru–C6H5), 5.62 (m, 3H, Ru–C6H5), 4.78 (t, 2H,
2.2.2. [Ru{C6H5(CH2)2OC(O)C6H5}Cl2]2 (3)
To a solution of ruthenium trichloride hydrate (530
mg, 2.03 mmol) in ethanol (40 ml) was added 1 (1.70
g, 7.46 mmol) and the mixture was refluxed over-
night. After cooling to room temperature, half of the
volume was evaporated in vacuo. The orange pre-
cipitate was filtered, washed with ether, and dried to
give pure [Ru{C6H5(CH2)2OC(O)C6H5}Cl2]2. Yield
750 mg (93%).
3
–OCH2CH2–, J ¼ 6:82 Hz), 2.97 (t, 2H, –OCH2CH2–,
3J ¼ 6:82 Hz), 2.32 (s, 36H, Ru–C6(CH3)6), )19.20 (d,
2H, Ru–Hydride, 2J ¼ 3:84 Hz), )19.88 (t, 1H, Ru–
2
Hydride, J ¼ 3:84 Hz). 13C{1H} NMR (100 MHz, ac-
etone-d6): d ¼ 166:18, 133.64, 130.58, 129.72, 129.05,
102.32, 95.13, 85.40, 80.60, 78.85, 64.88, 33.96, 17.54.
MS (ESI mode, acetone): m=z ¼ 874 [M + 2H]þ. Anal.
Calc. for C39H53B1F4O3Ru3: C, 48.80; H, 5.57. Found:
C, 48.64; H, 5.61%.
Spectroscopic data for 3: IR (KBr, cmꢁ1): m ¼ 1717
1
(C@O ester). H NMR (200 MHz, dmso-d6): d ¼ 7:97
(m, 4H, Har), 7.71–7.49 (m, 6H, Har), 6.08–5.95 (m, 8H,
Ru–C6H5), 5.81 (m, 2H, Ru–C6H5), 4.59 (t, 4H, –
3
OCH2CH2–, J ¼ 12:09 Hz), 2.93 (t, 4H, –OCH2CH2–,
2.2.5. [H3Ru3{C6H5(CH2)2OC(O)(CH2)3C6H5}(C6Me6)2
(O)]þ (6)
3J ¼ 12:09 Hz). 13C{1H} NMR (50 MHz, dmso-d6):
d ¼ 166:22, 134.16, 129.93, 129.52, 125.34, 103.71,
89.22, 86.94, 84.88, 64.23, 32.83. MS (EI mode, dmso):
m=z ¼ 760:5 [M ) Cl]þ. Anal. Calc. for C30H28Cl4
O4Ru2: C, 45.24; H, 3.54. Found: C, 45.12; H, 3.49%.
To a solution of [H3Ru2(C6Me6)2][BF4] (145 mg, 0.23
mmol) in acetone (30 ml), and H2O (15 ml) was added 4
(132 mg, 0.15 mmol). The mixture was heated to 50 °C
for 20 h in a closed pressure Schlenk tube. The resulting
red solution was filtered through celite and evaporated
to dryness; the residue was dissolved in CH2Cl2 (10 ml).
After chromatography on silica-gel plates (eluent:
CH2Cl2/acetone 5:2), [6][BF4] was isolated from the
most important red fraction. Red crystals suitable for
X-ray analysis were obtained from an acetone/n-hexane
solution after addition of a small amount of KPF6.
Yield: 46 mg (32%).
2.2.3. [Ru{C6H5(CH2)2OC(O)(CH2)3C6H5}Cl2]2 (4)
To a solution of ruthenium trichloride hydrate (485
mg, 1.85 mmol) in ethanol (35 ml) was added 2 (1.90 g,
7.04 mmol) and the mixture was refluxed overnight.
After cooling to room temperature, half of the volume
was evaporated in vacuo. The orange precipitate was
filtered, washed with ether, and dried to give pure
[Ru{C6H5(CH2)2OC(O)(CH2)3C6H5}Cl2]2. Yield: 680
mg (83%).
Spectroscopic data for 6: IR (KBr, cmꢁ1): m ¼ 1739
(C@O ester). 1H NMR (400 MHz, acetone-d6): d ¼ 7:31
(m, 2H, Har), 7.21 (m, 3H, Har), 5.91 (m, 2H,
Ru–C6H5), 5.53 (m, 3H, Ru–C6H5), 4.53 (t, 2H, –
OCH2CH2–), 2.81 (t, 2H, –OCH2CH2–), 2.67 (t, 2H, –
C(O)CH2CH2CH2–), 2.38 (t, 2H, –C(O)CH2CH2CH2–),
2.31 (s, 36H, Ru–C6(CH3)6), 1.94 (m, 2H, –C(O)
Spectroscopic data for 4: IR (KBr, cmꢁ1): m ¼ 1740
1
(C@O ester). H NMR (400 MHz, dmso-d6): d ¼ 7:28
(m, 4H, Har), 7.17 (m, 6H, Har), 5.98 (m, 6H, Ru–C6H5),
5.77 (m, 4H, Ru–C6H5), 4.33 (t, 4H, –OCH2CH2–,
3J ¼ 6:27 Hz), 2.77 (t, 4H, –OCH2CH2–, 3J ¼ 6:27 Hz),
2.58 (t, 4H, –C(O)CH2CH2CH2–), 2.30 (t, 4H,–C(O)
CH2CH2CH2–), 1.79 (m, 4H, –C(O)CH2CH2CH2–).
13C{1H} NMR (100 MHz, dmso-d6): d ¼ 173:20,
142.17, 129.19, 126.73, 105.96, 103.90, 89.27, 86.90,
84.47, 63.31, 37.02, 33.69, 32.91, 26.99. MS (EI mode,
dmso): m=z ¼ 844:5 [M ) Cl]þ. Anal. Calc. for
C36H40Cl4O4Ru2: C, 49.10; H, 4.58. Found: C, 49.02; H,
4.53%.
2
CH2CH2CH2–), )19.23 (d, 2H, Ru–Hydride, J ¼ 3:62
Hz), )19.90 (t, 1H, Ru–Hydride, 2J ¼ 3:62 Hz). 13C
{1H} NMR (50 MHz, acetone-d6): d ¼ 172:81, 141.90,
129.46, 127.79, 126.25, 102.25, 94.94, 85.27, 80.26,
78.59, 63.77, 34.96, 33.74, 33.30, 26.88, 16.73. MS (ESI
mode, acetone) : m=z ¼ 915 [M + H]þ. Anal. Calc. for
C42H59B1F4O3Ru3: C, 50.35; H, 5.94. Found: C, 50.23;
H, 5.82%.

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L. Vieille-Petit et al. / Inorganica Chimica Acta 357 (2004) 3437–3442
2.3. Hydrogenation reactions
riding atoms using the SHELXL default parameters. All
non-H atoms were refined anisotropically, using
weighted full-matrix least-square on F 2. Crystallo-
graphic details are summarised in Table 1. Figures were
drawn with ORTEP [13].
In a typical experiment, a solution of [5][BF4] or
[6][BF4] (10 mg) in 10 ml of degassed water was placed
in a 100 ml stainless-steel autoclave. After purging four
times with hydrogen, the autoclave was pressurised with
hydrogen (60 bar) and heated to 80 °C in an oil bath
under vigorous stirring. After 3 days, the autoclave was
placed in an ice-bath and the pressure released. The
aqueous solution containing the cluster was evaporated
to dryness under vacuum, and the residue was analysed
by NMR and mass spectrometry.
3. Results and discussion
Benzoic acid 2-cyclohexa-1,4-dienyl-ethyl ester (1),
and 4-phenylbutyric acid 2-cyclohexa-1,4-dienyl-ethyl
ester (2) are prepared by reacting, respectively, benzoic
acid and 4-phenylbutyric acid with 2-cyclohexa-1,4-die-
nyl-ethanol (see Scheme 3).
2.4. X-ray crystallography
The infrared spectra of 1 and 2 exhibit the character-
istic mCO absorption of the ester function at 1712 and 1732
cmꢁ1, respectively. In the 13C{1H} NMR spectrum, 1 and
2 give rise to a characteristic signal at 167 and 174 ppm
corresponding to the CO of the ester function. The dienyl
function of 1 and 2 reacts with RuCl3 ꢀ n H2O in refluxing
ethanol to afford in good yield [Ru{C6H5(CH2)2OC
(O)C6H5}Cl2]2 (3), and [Ru{C6H5(CH2)2OC(O)(CH2)3
C6H5}Cl2]2 (4) (see Scheme 4).
Crystals of [5][PF6], and [6][PF6] were mounted on a
Stoe image plate diffraction system equipped with a /
circle goniometer, using Mo Ka graphite monochro-
ꢁ
mated radiation (k ¼ 0:71073 A) with / range 0–200°,
increment of 1.5° and 1.2°, Dmax ꢁ Dmin ¼ 12:45 ꢁ 0:81
ꢁ
A. The structures were solved by direct methods using
the program SHELXS-97 [11]. The refinement and all
further calculations were carried out using SHELXL-97
[12]. In [5][PF6], and [6][PF6], the hydrogen atoms have
been included in calculated positions and treated as
The complexation of the dienyl ester derivatives 1 and
2 to a ruthenium atom in an g6-fashion is conveniently
monitored by H NMR spectroscopy: the coordinated
1
arene gives rise to a set of signals between 5–6 ppm
corresponding to the arene protons.
Table 1
Crystallographic and selected experimental data of [5][PF6] and
[6][PF6]
The trinuclear cations [H3Ru3{C6H5(CH2)2OC(O)C6
H5}(C6Me6)2(O)]þ (5), and [H3Ru3{C6H5(CH2)2OC(O)
(CH2)3C6H5}(C6Me6)2(O)]þ (6) have been synthesised
in solution (acetone/water) from [Ru{C6H5(CH2)2OC
[5][PF6] ꢀ acetone
42H59F6O4PRu3
[6][PF6]
Chemical formula
Formula weight
Crystal system
Space group
C
C42H59F6O3PRu3
1060.07
triclinic
(O)C6H5}(H2O)3]2þ
,
and
[Ru{C6H5(CH2)2OC(O)-
1076.07
triclinic
(CH2)3C6H5}(H2(O)3]2þ, and from the known dinuclear
precursor [H3Ru2(C6Me6)]þ [8,9], see Scheme 5. The 1H
ꢂ
ꢂ
P1
red block
P1
orange plate
Crystal colour and
shape
Crystal size
0.48 ꢂ 0.45 ꢂ 0.40
11.884(1)
13.129(1)
15.166(2)
89.14(1)
74.02(1)
69.43(1)
2120.9(4)
2
0.25 ꢂ 0.25 ꢂ 0.08
10.3849(9)
14.286(1)
14.890(1)
84.43(1)
74.50(1)
84.39(1)
2112.7(3)
2
ꢁ
a (A)
ꢁ
b (A)
ꢁ
c (A)
a (°)
b (°)
c (°)
3
ꢁ
Scheme 3.
V (A )
Z
T (K)
153(2)
1.685
1.159
293(2)
1.666
1.160
Dc (g cmꢁ3
)
l (mmꢁ1
)
Scan range (°)
Unique reflections
Reflections used
½I > 2rðIÞꢃ
4:04 < 2h < 51:84
7683
6261
4:20 < 2h < 51:76
7642
5876
Rint
0.0460
0.0309, wR2 0.0761
0.0728
0.0406, wR2 0.1027
Final R indices
½I > 2rðIÞꢃ
R indices (all data)
Goodness-of-fit
0.0411, wR2 0.0801
0.956
0.0532, wR2 0.1077
0.934
Maximumꢁ, 3Minimum 0.561, )0.465
0.803, )0.898
ꢁ
Dq (e A
)
Scheme 4.

L. Vieille-Petit et al. / Inorganica Chimica Acta 357 (2004) 3437–3442
3441
Scheme 5.
NMR spectra of 5 and 6 give rise to two hydride signals,
a triplet (d ¼ ꢁ19:88 ppm for 5 and )19.90 ppm for 6)
and a doublet (d ¼ ꢁ19:20 ppm for 5 and )19.23 ppm
for 6) integrating for 1 and 2 protons, respectively, and a
characteristic singlet at 2.3 ppm for the methyl groups of
the hexamethylbenzene ligands, the rest of the signals
correspond to the protons of the phenylester–arene–
ruthenium moiety.
Clusters 5 and 6, which possess a phenyl substituent at
the end of a tethered side-arm, have been tested in various
hydrogenation reaction conditions (60 bar of H2, 50–110
°C, 12–72 h) to generate the corresponding cyclohexyl
derivatives [H3Ru3{C6H5(CH2)2OC(O) C6H11}(C6Me6)2
(O)]þ, and [H3Ru3{C6H5(CH2)2OC(O)(CH2)3C6H11}
(C6Me6)2 (O)]þ. A modelling study had suggested that, in
the case of 5, the phenyl can be only hydrogenated in the
hydrophobic pocket of a neighbouring molecule, whereas
in 6 a longer and more flexible chain could as well allow
the phenyl substituent to be incorporated into its own
hydrophobic pocket, suggesting a possible auto-hydro-
genation mechanism, see Scheme 2.
Fig. 1. ORTEP drawing of cation 5, displacement ellipsoids are drawn
at the 50% probability level. Hydrogen atoms acetone molecule, and
hexafluorophosphate anion are omitted for clarity.
Table 2
ꢁ
Selected bond lengths (A) and angles (°) for [5][PF6] and [6][PF6]
[5][PF6]
[6][PF6]
Interatomic distances
O(1)–Ru(1)
O(1)–Ru(2)
2.007(2)
2.000(2)
2.002(2)
2.7473(5)
2.7489(6)
2.7791(5)
2.002(3)
1.993(3)
1.984(3)
2.7470(5)
2.7374(5)
2.7922(6)
O(1)–Ru(3)
Ru(1)–Ru(2)
Ru(1)–Ru(3)
Ru(2)–Ru(3)
Angles
However, compounds [5][BF4] and [6][BF4] turned
out to be inactive for the hydrogenation of the pheny-
lester group in water, they show partial decomposition
without hydrogenation under the conditions; 50–110 °C
under 60 bar H2 during 12–72 h. It appears that mono-
and di-nuclear species, among which, we identified by
NMR spectroscopy [H3Ru2(C6Me6)2]þ, are formed
during the hydrogenation reaction. The fate of the
phenylester–arene–ruthenium moiety is unclear, no de-
composition products containing a phenylester group
have been identified so far by 1H NMR and mass
spectrometry. To gain further insight on the instability
of 5 and 6 under hydrogenation conditions, X-ray
structure analyses of [5][PF6] and [6][PF6] have been
performed.
Ru(1)–Ru(2)–Ru(3)
Ru(1)–Ru(3)–Ru(2)
Ru(2)–Ru(1)–Ru(3)
Ru(1)–O(1)–Ru(2)
Ru(1)–O(1)–Ru(3)
Ru(2)–O(1)–Ru(3)
59.655(13)
59.598(13)
60.748(14)
86.58(9)
59.225(14)
59.565(13)
61.210(15)
86.89(11)
86.73(12)
89.18(11)
86.58(8)
87.95(9)
bouring molecules form a strong p stacking interactions
in a parallel mode, see Fig. 2. The carbon–carbon dis-
ꢁ
tances [3.379(5), 3.373(5), and 3.358(5) A] are in good
agreement with the theoretical value calculated for this
ꢁ
kind of p stacking [3.77 A] [14].
The molecular structure of 6 is shown in Fig. 3. The
ruthenium atoms possess a pseudo-octahedral geometry,
and the metrical parameters around the metallic
framework compare well with those of similar [H3Ru3
(g6-arene)3(O)]þ tri-nuclear ruthenium cluster cations
[15–23]. As in [5][PF6], the metal core consists of three
ruthenium atoms capped by a l3-oxo ligand. Selected
bond lengths and angles are listed in Table 2.
The molecular structure of 5 is shown in Fig. 1. The
metal core consists of three ruthenium atoms capped
by a l3-oxo ligand. The three hydrido ligands bridging
the three ruthenium–ruthenium single bonds were lo-
cated from a difference Fourrier map and their posi-
tions fixed. Selected bond lengths and angles are listed
in Table 2.
In the crystal structure, the phenylester moiety shows
no interaction with the triruthenium framework. An
intramolecular hydrogen contact is observed between
In the crystal structure of [5][PF6] ꢀ acetone, two g6-
C6H5{(CH2)2OCOC6H5} arene ligands of two neigh-

3442
L. Vieille-Petit et al. / Inorganica Chimica Acta 357 (2004) 3437–3442
UK, deposition numbers: [5][PF6] 218286, [6][PF6]
218287.
Acknowledgements
The authors are grateful to the Fonds National Suisse
de la Recherche Scientifique for financial support. A
generous loan of ruthenium chloride hydrate from the
Johnson Matthey Technology Centre is gratefully
acknowledged.
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