Fixation and spontaneous dehydrogenation of methanol on a triruthenium-iridium framework: Synthesis and structure of the cluster anion [HRu3Ir(CO)12(OMe)]-

Article abstract of DOI:10.1039/a905487a

The anionic mixed-metal cluster [RU₃Ir(CO)₁₃]^- 1, found to be catalytically active in the carbonylation of methanol, reacts with methanol at 70°C to give, with O-H activation of the substrate, the cluster anion [HRu₃Ir(CO)₁₂(OMe)]^- 2, which upon prolonged reaction loses formaldehyde to give the cluster anion [H₂RU₃Ir(CO)₁₂]^- 3; both anions 2 and 3 crystallise together as the double-salt [N(PPh₃)₂]₂[HRu₃Ir(CO)₁₂(OMe)][H₂Ru₃Ir(CO)₁₂] the single-crystal X-ray structure analysis of which reveals a butterfly Ru₃Ir skeleton for 2 and a tetrahedral Ru₃Ir skeleton for 3.

Full text of DOI:10.1039/a905487a

Fixation and spontaneous dehydrogenation of methanol on a
triruthenium–iridium framework: synthesis and structure of the cluster anion
2
[
HRu Ir(CO) (OMe)]
3
12
Susanne Haak,† Antonia Neels, Helen Stœckli-Evans, Georg Süss-Fink* and Christophe M. Thomas
Institut de Chimie, Université de Neuchâtel, Avenue de Bellevaux 51, CH-2000 Neuchâtel, Switzerland.
E-Mail: GEORG.SUESS-FINK@ICH.UNINE.CH
Received (in Basel, Switzerland) 7th July 1999, Accepted 19th August 1999
The anionic mixed-metal cluster [Ru
3
Ir(CO)13]2 1, found to
solution, and the double-salt [N(PPh
3 2 2 3
) ] [HRu Ir(CO)12(O-
be catalytically active in the carbonylation of methanol,
Me)][H Ru Ir(CO)12] can be isolated by crystallisation of the
2
3
reacts with methanol at 70 °C to give, with O–H activation of
reaction residues from a 4+1 mixture of diethyl ether and
hexane.
2
the substrate, the cluster anion [HRu
3
Ir(CO)12(OMe)] 2,
which upon prolonged reaction loses formaldehyde to give
A suitable crystal§ of this double-salt revealed the molecular
structure of both anions 2 and 3 (Fig. 1 and 2), disordered over
the same position. Three of the four metal positions are
occupied by metal atoms of both anions 2 and 3, whereas one
ruthenium atom splits into Ru(1) for anion 2 and Ru(1a) for
anion 3, the refinement of the occupancy factors giving a 1+1
2
the cluster anion [H
crystallise together as the double-salt [N(PPh
CO)12(OMe)][H Ru Ir(CO)12 the single-crystal X-ray
structure analysis of which reveals a butterfly Ru Ir skeleton
for 2 and a tetrahedral Ru Ir skeleton for 3.
2 3
Ru Ir(CO)12
]
3; both anions 2 and 3
3
)
2
]
2
[HRu Ir-
3
(
2
3
]
3
3
3
ratio. In contrast to anion 2, anion 3 is already known, its
Mixed-metal clusters have received steadily increasing atten-
tion over the last three decades owing to their inherent catalytic
structure in the double-salt being very similar to that we found
3 2 2 3
in the salt [N(PPh ) ][H Ru
Ir(CO)12].3
1
potential. The presence of different metals in the same complex
In anion 2, the dihedral angle Ru(1)–Ir(1)–Ru(3)–Ru(2), that
is to say the spreading of the wing tips is relatively small (82.9°)
2
may have synergistic effects in the catalytic activity. Recently
we reported a series of Ru
3
Ir and Os
3
Ir mixed-metal clusters
compared to those in other chalcogen- or halogen-bridged
5
which show reasonable catalytic activity in the carbonylation of
clusters, such as HRu
3
Co(CO)12(m-SMe
2
) (96.1°) or HRu
3
Ir-
methanol to give acetic acid.3
,4
The cluster anions
(CO)12(m-Cl) (89.3°). A similar dihedral angle as in 2 has been
6
[Ru
3
Ir(CO)13]2 1 and [Os Ir(CO)13]2 4, used as catalyst
3
observed in the hydroxy-bridged osmium cluster cation [H Os -
4
4
+
7
precursors in this process, are however unstable under the
reaction conditions, which has been confirmed by the isolation
(CO)12(m-OH)] (82.3°). As a result of the small dihedral
angle, the distance between the wing tip metal atoms Ru(1) and
Ru(2) is only 3.3536(2) Å. The hydride-bridged edge Ru(1)–
Ru(3), at 3.095(5) Å, is significantly longer than all the other
metal–metal bonds. The wing tips are bridged asymmetrically
by the methoxy group, the Ru–O bond distances being 2.02(2)
and 2.16 (2) Å, respectively. This is well in line with the bond
of
the
fragmentation
products
Ir
4
(CO)12
and
4
[N(PPh
3
)
2
][M(CO) ] (M = Ru, Os). In this context we were
3 3
I
interested in the behaviour of these anionic clusters towards
reagents participating in the catalytic process, especially in the
reaction with methanol.
The anion [Ru
3
Ir(CO)13]2 1 (as its [N(PPh
3
)
2
]+ salt) reacts
lengths found in other methoxy-bridged clusters, such as
8
with methanol at 70 °C within 2 h to give the anionic cluster
3
HOs Pt
2
(CO)10(m
5
-C)(m-OMe)(PCy
3
)
2
3
or Os (CO)10(m-
2
[
3
HRu Ir(CO)12(OMe)] 2 [eqn. (1)], as indicated by a colour
change of the solution from red to orange. The formation of 2
involves O–H activation of the methanol molecule, which is
split into m-H and m-OMe ligands, replacing a carbonyl group of
the starting compound. Anion 2 can be isolated as the
+
[N(PPh
3
)
2
] salt by extraction with diethyl ether after evapora-
tion of the reaction solution to dryness, washing of the residue
with hexane–dichloromethane (5+1) and recrystallisation from
ethanol–pentane (1+3) at 218 °C.‡
[Ru
3
Ir(CO)13]2 + MeOH ? [HRu
3
Ir(CO)12(OMe)]2 + CO
1
2
(1)
Upon prolonged reaction (48 h) in methanol, especially at
higher temperature (90 °C), anion 2 is transformed into the
2
anion [H
2
Ru
3
Ir(CO)12
]
3 with liberation of formaldehyde
[
eqn. (2)]. The formation of formaldehyde is evidenced by the
H NMR spectrum of the reaction mixture, which shows the
1
signal for HCHO at d 9.75 as well as a signal at d 5.31 attributed
to the formaldehyde trimer trioxane (by comparison with an
authentic sample).
[HRu
3
Ir(CO)12(OMe)]2 ? [H
2
Ru
3
Ir(CO)12]2 + HCHO
3
2
(2)
Fig. 1 Molecular structure of [HRu
3
Ir(CO)12(OMe)]2 2 showing the atom
numbering scheme. Selected bond distances (Å) and angles (°): Ir(1)–Ru(1)
2.854(2), Ir(1)–Ru(2) 2.758(1), Ir(1)–Ru(3) 2.737(1), Ru(1)–Ru(3)
If the thermal reaction of 1 with methanol at 90 °C is stopped
half-way (after 12 h), both anions 2 and 3 are present in the
3
.095(5), Ru(2)–Ru(3) 2.797(1), Ru(1)–H(1) 1.47(1), Ru(3)–H(1) 1.77(1),
†
Present address: Department of Chemistry, University of Sheffield,
Ru(1)–O(13) 2.02(2), Ru(2)–O(13) 2.16(2), O(13)–C(13) 1.39(3), Ru(1)–
O(13)–C(13) 119.3(16), Ru(2)–O(13)–C(13) 125.7(16).
Sheffield, UK S3 7HF.
Chem. Commun., 1999, 1959–1960
This journal is © The Royal Society of Chemistry 1999
1959

Technology Centre (United Kingdom) for a generous loan of
ruthenium trichloride hydrate.
Notes and references
‡
Analytical and spectroscopic data: for [N(PPh
Analysis. Found: C, 41.97; H, 2.65; N, 1.00. Calc. for C49
C, 41.97; H, 2.44; N, 1.00%. IR(thf): 2071vw, 2035w, 2016s, 2006s,
3
)
2
][HRu
3
Ir(CO)12(OMe)].
H
34IrNO13 Ru
P
3
3
:
2
1 1
1
2
968vs, 1817m, 1805m cm
.
H NMR (200 MHz, 294 K, CDCl
14.28 (s, 1H), 2.94 (s, 3H), 7.39–7.70 (m, 30H).
For [N(PPh ][H Ru Ir(CO)12]. Analysis. Found: C, 41.93; H, 2.17; N,
32IrNO12Ru : C, 42.02; H, 2.35; N, 1.02%. IR(thf):
074w, 2038s, 2005vs, 1968m, 1952m, 1819w, 1805w cm
): d 220.64 (s, 2H), 7.40–7.70 (m, 30H).
Crystallographic data for [N(PPh [HRu Ir(CO)12(OMe)][H
Ir(CO)12], C117 Ir Ru , M = 1387.18, monoclinic, space
/c, a = 14.966(1), b = 19.743(1), c = 17.07781) Å, b =
3
): d
3
)
2
2
3
1
.08. Calc. for C48
H
3
2
1 1
2
.
H NMR
(200 MHz, 294 K, CDCl
3
§
Ru
group P2
3
)
2
]
2
3
2
-
3
H N
66 2
O P
2 25 4
6
1
3
23
9
3
8.541(10)°, V = 4989.8(7) Å , Z = 2, D
c
= 1.846 g cm , m(Mo-Ka) =
2
1
.675 mm , 38776 reflections measured (2qmax = 52.08°), 5302 observed
data [I > 2s(I)] used in the refinement, R1 = 0.0588, wR2 = 0.1501 (R1
= 0.1042, wR2 = 0.1674 for all data). Intensity data were collected at
293(2) K on a Stoe Imaging Plate Diffractometer system (IPDS) equipped
with a one-circle goniometer using Mo-Ka graphite-monochromated
radiation (l = 0.71073 Å). 200 exposures (3 min per exposure) were
obtained at an image plate distance of 70 mm with 0 < o < 200° with the
crystal oscillating through 1° in o. The structure was solved by direct
2 3
Fig. 2 Molecular structure of [H Ru
Ir(CO)12]2 3 showing the atom
numbering scheme. Selected bond distances (Å): Ir(1)–Ru(1A) 2.689(6),
Ru(1A)–Ru(2) 2.878(4), Ru(1A)–Ru(3) 2.866(6), Ru(3)–H(1) 1.77(1),
Ru(1A)–H(1) 1.37(1). The second hydride ligand spanning Ru(1A)–Ru(2),
only having an occupancy factor of 50%, could not be located in the double-
3
3 2 2 3
salt, but was found in [N(PPh ) ][H Ru Ir(CO)12].
10
methods (SHELXS-97 ) and refined using weighted full-matrix least
2
11
squares on F (SHELXL-97 ). A high disorder was found in the double-salt
resulting in refined occupancies of 0.5 for Ru(1), Ru(1a) and the
corresponding CO ligands. The methoxy group which is coordinated to
Ru(1) and Ru(2) also has an occupancy of 0.5. Despite an empirical
absorption correction being applied using DIFABS12 (Tmin = 0.168, Tmax
=
0
.640), a large peak of electron density near one of the ruthenium atoms
remained, which may be due to the disorder.
CCDC 182/1387. See http://www.rsc.org/suppdata/cc/1999/1959/ for
crystallographic files in .cif format.
1
2
P. Braunstein and J. Rose, in Comprehensive Organometallic Chemistry
2
1
, ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Elsevier, Oxford,
995, vol. 10, p. 351.
E. Rosenberg and R. M. Laine, in Catalysis by Di- and Polynuclear
Metal Complexes, ed. R. D. Adams and F. A. Cotton, Wiley–VCH, New
York, 1998, p. 1; G. Süss-Fink and M. Jahncke, in Catalysis by Di- and
Polynuclear Metal Complexes, ed. R. D. Adams and F. A. Cotton,
Wiley–VCH, New York, 1998, p. 167.
Scheme 1
3
G. Süss-Fink, S. Haak, V. Ferrand and H. Stœckli-Evans, J. Chem. Soc.,
Dalton Trans., 1997, 3861.
OMe)
.9 The methyl group sticks out of the Ru(1)–Ru(2)–O(13)
plane with an angle of 13.7°, in accordance with observations
Anion 2 is consistent with the
effective atomic number rule which requires an electron count
of 62 valence electrons for butterfly clusters.
The reaction sequence involving the cluster anions 1, 2 and 3
and the oxidation of methanol to formaldehyde is very
interesting (Scheme 1). Anion 1 contains a closed tetrahedral
4 G. Süss-Fink, S. Haak, V. Ferrand and H. Stœckli-Evans, J. Mol. Catal.
A, 1999, 143, 163.
5 S. Rossi, J. Pursianen and T. A. Pakkanen, Organometallics, 1991, 10,
2
9
for Os
3
(CO)10(m-OMe)
2
.
1
390.
6
7
8
A. U. Härkönen, M. Ahlgrèn, T. A. Pakkanen and J. Pursianen,
J. Organomet. Chem., 1996, 519, 205.
B. F. G. Johnson, J. Lewis, P. R. Raithby and C. Zuccaro, J. Chem. Soc.,
Dalton Trans., 1980, 716.
L. J. Farrugia, A. D. Miles and F. G. A. Stone, J. Chem. Soc., Dalton
Trans., 1985, 2437.
Ru
3
Ir metal framework, which is opened by the reaction with
Ir skeleton,
methanol to give anion 2 containing a butterfly Ru
3
9 V. F. Allen, R. Mason and P. B. Hitchcock, J. Organomet. Chem., 1977,
140, 297.
the wing tips of which are bridged by the methoxy ligand. The
elimination of formaldehyde in going from 2 to 3 implies the
1
1
0 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
1 G. M. Sheldrick, SHELXL-97, University of Göttingen, Germany,
3
reclosing of the butterfly Ru Ir skeleton to a closed metal
tetrahedron.
1
997.
1
2 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1990, 46, 158.
We are grateful to the BASF AG (Germany) for financial
support of this work. We also thank the Johnson Matthey
Communication 9/05487A
1960
Chem. Commun., 1999, 1959–1960