Synthesis, characterisation and reactivity of rare 46-electron tri-ruthenium clusters

Article abstract of DOI:10.1039/c8dt00189h

[Ru₃(CO)₁₂] reacts at room temperature with N-alkyl substituted 6-membered ring N-heterocyclic carbenes (6-NHC) to form [Ru₃(6-NHC)(CO)₁₀] (6-NHC = 6-ⁱPr 1, 6-Et 2 and 6-Me 4), rare examples of coordinatively unsaturated (46-electron) ruthenium clusters. Complexes 1, 2 and 4 have been structurally characterised, along with the tetranuclear ruthenium cluster [Ru₄(6-Et)₂(CO)₁₁] 3 that is formed along with 2. The degradation of the 6-ⁱPr derivative 1 by pyrimidinium salt elimination helped to explain the poor activity of the complex in the catalytic acylation of pyridine.

Full text of DOI:10.1039/c8dt00189h

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[Ru3(6-NHC)(CO)10]: Synthesis, Characterisation and Reactivity of Rare 46-Electron Tri-
ruthenium Clusters
Charles E. Ellul, John P. Lowe, Mary F. Mahon, Paul R. Raithby* and Michael K. Whittlesey*
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
1

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Abstract
[Ru3(CO)12] reacts at room temperature with Nꢀalkyl substituted 6ꢀmembered ring Nꢀ
heterocyclic carbenes (6ꢀNHC) to form [Ru3(6ꢀNHC)(CO)10] (6ꢀNHC = 6ꢀiPr 1, 6ꢀEt 2 and 6ꢀ
Me 4), rare examples of coordinatively unsaturated (46ꢀelectron) ruthenium clusters.
Complexes 1, 2 and 4 have been structurally characterised, along with the tetranuclear
ruthenium cluster [Ru4(6ꢀEt)2(CO)11] 3 that is formed along with 2. The degradation of the 6ꢀ
iPr derivative 1 by pyrimidinium salt elimination helped to explain the poor activity of the
complex in the catalytic acylation of pyridine.
2

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Introduction
Despite the unquestionable impact that Nꢀheterocyclic carbene (NHC) ligands have had
on organometallic chemistry over the last 25 years, their application to lowꢀvalent metal
cluster chemistry has received only limited attention.1 However, on the basis of what has
been observed, it is clear that combining NHCs with metal clusters frequently leads to very
interesting observations. Thus, there are examples in which cluster structure is retained upon
reaction with one type of NHC substitution pattern,2 but cleaved upon only relatively small
changes to either the substituents or reaction stoichiometry.3,4 In very recent cases, clusters
with unusually high NHC content have been identified as catalyst deactivation products.5
Arguably of most interest have been the observations of atypical NHC binding modes,6 the
detection of unprecedented reaction intermediates7 and the formation of multiply activated
carbene ligands.2b,8
The group 8 tricarbonyl precursors [M3(CO)12] (M = Fe,9 Ru,1b,2,3,5,7 Os)1b,2c,7,10,11 have
proven to be the most fertile area of cluster chemistry for reaction with NHCs, largely due to
their ease of accessibility and the wellꢀknown differences in properties that are seen upon
descending the group.12 For example, osmium exhibits a willingness to adopt 46ꢀelectron
counts in some Os3 clusters (e.g. [Os3(CO)10(ꢀꢀH)2], whereas ruthenium shows a greater
tendency to maintain coordinative saturation (i.e. 48 electrons) meaning that electronꢀ
deficient Ru3 systems are not very common.13 Indeed, [Ru3(CO)10(ꢀꢀH)2] has only been
generated photchemically14 and its chemistry explored only to a very limited extent.15
We16 (and others)17 have shown that NHCs with a ring size of >5 can be used to
stabilise low coordination numbers in a wide range of mononuclear transition metal
complexes, but as far as we are aware, reactions between this class of soꢀcalled ‘ringꢀ
expanded carbenes’18 and transition metal clusters have not been described.19 Herein, we
report that Nꢀalkylated, 6ꢀmembered ring NHCs (denoted as 6ꢀNHC) react with [Ru3(CO)12]
3

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at room temperature to afford novel 46ꢀelectron Ru3 clusters of general formula [Ru3(6ꢀ
NHC)(CO)10]. Their structures, together with studies of reactivity alongside other Ru3
clusters in catalytic CꢀH bond functionalisation, is described.
Results and Discussion
Synthesis and Characterisation of [Ru3(6-NHC)(CO)10] (6-NHC = 6iPr, 6-Et, 6-
Me). Infraꢀred analysis of a reaction of 6ꢀiPr and Ru3(CO)12 (2:1 ratio, Scheme 1) in THF
showed replacement of the ν(CO) bands, characteristic of the starting material, by a new set
of terminal carbonyl stretches between 2084ꢀ1963 cmꢀ1, as well as a lower frequency feature
at 1802 cmꢀ1, over a period of ca. 2.5 days at room temperature. Removal of the solvent,
extraction of the redꢀbrown residue into hexane and slow evaporation confirmed that all of
the IR bands arose from the formation of a single product, the 46ꢀelectron cluster, [Ru3(6ꢀ
Et
N
Ru
Ru
N
(R = iPr, Me)
Et
Ru
R
R
N
N
N
N
R
R
Et
Et
2
N
N
Ru3(CO)12
Ru
Ru
Et
THF, RT
THF, RT
Et
Ru
N
N
Ru
Ru
Ru
N
N
= CO
1 (R = iPr)
4 (R = Me)
Et
Et
Ru
3
iPr)(CO)10] (1, Scheme 1), which could be isolated as a red crystalline product in 65% yield.20
Scheme 1. Summary of the reactivity of [Ru3(CO)12] with 6ꢀiPr, 6ꢀMe and 6ꢀEt.
The Xꢀray structure of 1 (Figure 1) revealed an asymmetric arrangement of the three Ru
atoms (Ru(1)ꢀRu(2) 2.7287(2) Å, Ru(1)ꢀRu(3) 2.8090(2) Å, Ru(2)ꢀRu(3) 2.8815(2) Å), a
single 6ꢀiPr ligand bound to Ru(1) (Ru(1)ꢀC(11) 2.1178(17) Å) and two asymmetrically
4

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bridging CO ligands (Ru(1)ꢀC(2) 1.9791(19) Å, Ru(2)ꢀC(2) 2.125(2) Å, Ru(1)ꢀC(2)ꢀRu(2)
83.26(7)°; Ru(1)ꢀC(3) 2.0128(19) Å, Ru(2)ꢀC(3) 2.118(2) Å, Ru(1)ꢀC(3)ꢀRu(2) 82.65(7)°) on
the Ru(1)ꢀRu(2) edge. The two shorter RuꢀC(bridging carbonyl) distances are associated with
Ru(1), which is also bound to the 6ꢀiPr ligand; this may result from the carbene exerting less
steric pressure than the two carbonyl ligands associated with Ru(2), or may alternatively
reflect a greater electron density on Ru(1) due to the strongly σꢀdonating NHC. As
anticipated, the carbene ligand lay in the equatorial plane of the Ru3 core, as is common for
the vast majority of nitrogen and phosphorus donor ligands coordinated to Ru3 triangular
clusters, although the dihedral twist between the pyrimidine ring and the Ru3 core is
significantly greater (87.3
; IMes = 1,3ꢀbis(2,4,6ꢀtrimethylphenyl)imidazolꢀ2ꢀylidene)2b or
[Ru3(abꢀItBu)(CO)11]6a (9.8 ; ab denotes an ‘abnormal’ (or mesionic) ligated NHC, ItBu =
°) than in either of the 5ꢀmembered ring NHC derivatives
[Ru3(IMes)(CO)11] (37.7
°
°
1,3ꢀdiꢀtertꢀbutylimidazolꢀ2ꢀylidene).21 As a consequence, the NꢀiPr groups lie in the same
plane as the axial carbonyl ligands. The inherent strain of this conformation may be alleviated
somewhat by the presence of the
ꢀꢀCO ligands. The RuꢀRu bond lengths in 1 are reminiscent
of the OsꢀOs bond lengths in [Os3(CO)10(ꢀꢀH)2] where the ‘unsaturated’ dihydridoꢀbridged
bond is substantially shorter, at 2.680(2) Å, than the mean of the other two bonds, at 2.814
Å.22 However, in a series of 48ꢀelectron triꢀruthenium clusters containing a ‘Ru(
ꢀꢀCO)2Ru’
unit, the dicarbonylꢀbridged RuꢀRu bond is also shorter than the two unbridged RuꢀRu
bonds.23
Changing to the less bulky 6ꢀEt ligand led to the formation of an analogous product,
[Ru3(6ꢀEt)(CO)10] (2, Scheme 1), albeit in much lower yield. Moreover, the crystallisation of
deep red 2 also afforded very small amounts of a second, less intensely coloured product,
which upon manual separation, was structurally characterised as the unusual Ru4 cluster,
[Ru4(6ꢀiPr)2(CO)11] 3 (Figure S7).
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Figure 1. Molecular structures of 1 (top), 2 (centre) and 4 (bottom). Ellipsoids are shown at
30% probability.
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The solution IR spectrum of 2 was essentially identical to that of 1. However, in
contrast to the sharp, wellꢀresolved room temperature 1H NMR spectrum of 1, the spectrum
of 2 comprised of three broad resonances at
δ 3.43, 3.27 and 2.07, together with a sharp
triplet at 1.31. The two higher frequency broad signals resolved into three sharper
δ
multiplets (relative integrals of 2:2:4) for the eight NCH2 protons upon cooling to 235 K.
The molecular geometry of 2 (Figure 1) is similar to that of 1 with the dicarbonylꢀ
bridged Ru(1)ꢀRu(2) bond (2.7277(2) Å) being the shortest, while the Ru(1)ꢀRu(3) and
Ru(2)ꢀRu(3) distances are 2.8018(2) and 2.8644(3) Å. The Ru(1)ꢀC(11) metalꢀcarbene
distance is 2.121(2) Å and, as for 1, the ligand lies close to the equatorial plane of the Ru3
core. The bridging carbonyl ligands display asymmetry (Ru(1)ꢀC(2) 1.993(3) Å, Ru(2)ꢀC(2)
2.121(2) Å, Ru(1)ꢀC(2)ꢀRu(2) 83.02(9)°; Ru(1)ꢀC(3) 1.985(2) Å, Ru(2)ꢀC(3) 2.115(3) Å,
Ru(1)ꢀC(3)ꢀRu(2) 83.36(9)°), again with the shortest RuꢀC(bridging carbonyl) distances
associated with Ru(1), which is also bound to the carbene ligand.
The NꢀMe substituted ligand 6ꢀMe behaved similarly to 6ꢀiPr in yielding only the
[Ru3(6ꢀNHC)(CO)10] product, [Ru3(6ꢀMe)(CO)10] 4 (Scheme 1). The carbonyl absorption
bands in the IR spectrum of 4 partially merged to give a total of nine bands compared to the
eleven bands seen for both 1 and 2. In the proton NMR spectrum, both the NꢀMe singlet and
NCH2C
H2 quintet were sharp, while the NCH2 triplet was noticeably broader, suggestive of
fluxionality (c.f. 2).
The molecular structure of 4 also closely resembles that of 1 and 2 with the three Ruꢀ
Ru distances following the same trend (Ru(1)ꢀRu(2) 2.7320(3) Å, Ru(1)ꢀRu(3) 2.8104(3) Å,
Ru(2)ꢀRu(3) 2.8688(3) Å), and the same distribution of the carbonyls and the carbene ligand.
The asymmetry in the bonding of the two bridging carbonyls is again apparent with the
shortest RuꢀC(carbonyl) distance being associated with Ru(1) which also has the carbene
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ligand bonded to it (Ru(1)ꢀC(11) (carbene) 2.107(3) Å; Ru(1)ꢀC(2) 1.980(3) Å and Ru(1)ꢀ
C(3) 1.996(3) Å for the two carbonyl bonds). By comparison the bridgingꢀcarbonyl Ru(2)ꢀC
bond lengths are 2.128(3) Å (Ru(2)ꢀC(2)) and 2.113(3) Å (Ru(2)ꢀC(3)).
Stoichiometric and catalytic reactions of 1 involving CO. The comparatively poor
yields of 2 and 4, as well as the need to manually separate 2 from 3, led us to use 1 for
investigations into the reactivity of the [Ru3(6ꢀNHC)(CO)10] complexes. Given the
coordinative unsaturation, we were surprised to find that there was no reaction of [Ru3(6ꢀ
iPr)(CO)10] with CO (1atm in THFꢀ
to 1 atm 13CO led to the appearance of a 13C enhanced carbonyl signal at
d8), even upon heating to 80 °C. However, exposure of 1
δ
200 in the
13C{1H} NMR spectrum at room temperature (Figure S11), implying that although [Ru3(6ꢀ
iPr)(CO)10] will not add CO, it can undergo facile CO exchange.24
The stability of 1 to CO led us to test it as a precursor in the catalytic acylation of
pyridine (Table 1). Moore and coꢀworkers reported in 199225 that the insertion of CO and a
terminal alkene into the ortho CꢀH position of pyridine was catalysed by [Ru3(CO)12] at high
pressure (10 atm CO) under forcing conditions (150 °C, 16 h) to give predominantly linear
acylation products. In our hands, we were unable to achieve the 65% yield with 1ꢀhexene
described by Moore using [Ru3(CO)12], achieving instead a more modest 31% average
yield.26 Disappointingly, 1 exhibited lower activity than [Ru3(CO)12], as did the
coordinatively saturated, abnormally bound 5ꢀmembered ring NHC clusters, [Ru3(abꢀ
ItBu)(CO)11]6a and [Ru3(abꢀIAd)(CO)11] (IAd = 1,3ꢀbis(adamantyl)imidazolꢀ2ylidene).6b
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Table 1. Ru3 cluster catalysed acylation of pyridine.a
Ru precursor
[Ru3(CO)12]
Product yield (%)b
31
12
23
6
1
[Ru3(abꢀItBu)(CO)11]
[Ru3(abꢀIAd)(CO)11]
aReaction conditions: Ru3 precursor (0.026 mmol), 1ꢀhexene (0.25 mL), pyridine (7.5 mL), CO (10 atm), 150°C,
16 h. bYields (average of at least two runs) determined by integration of 1H NMR product resonances at δ 3.22
and/or δ 1.74 (linear product)25 and δ 4.1 (branched product)25 versus the OMe resonance of 2,4,6ꢀ(MeO)3C6H3
as an internal standard.
Degradation of 1 through loss of [6-iPrH]+ and 6-iPr. In an effort to rationalise the
poor catalytic activity, 1 was heated in the presence of 4 equiv pyridine in an NMR tube scale
reaction. Warming to 85 °C brought about loss of the 1H NMR resonances of 1 and
appearance of signals due to the pyridinium cation [6ꢀiPrH]+.27 The presence of low
frequency proton signals at δ ꢀ15.5 and δ ꢀ19.2 suggested that this was partnered with anionic
ruthenium carbonyl hydride species and, indeed, an Xꢀray study of a small number of orangeꢀ
yellow crystals isolated from the reaction yielded a structure of [6ꢀiPrH]2[Ru4(CO)12H2]
(Figure S14).28 The diꢀpotassium salt of [Ru4(CO)12H2]2ꢀ has a hydride chemical shift of δ ꢀ
19.3.29
A likely pathway to [6ꢀiPrH]+ formation involves CꢀH activation of pyridine by 1,23a,30
followed by reductive elimination from a resulting {(6ꢀiPr)RuH} moiety. Support for
reductive elimination from such a species came upon reacting 1 with H2 at 60 °C (THFꢀd8),
which again generated pyrimidinium proton NMR signals, together with hydride signals at δ ꢀ
12.1 and ꢀ12.5, in < 1 h.
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Further evidence for the low stability of the [Ru3(6ꢀNHC)(CO)10] complexes, comes
from the reaction of 1 with phosphines, where we found that 1 reacted with 1ꢀ3 equiv PPh3 at
60 °C with complete loss of the starting material and the formation of multiple phosphorus
containing species. Efforts to characterise the product mixture led to isolation of just the
known phosphine carbonyl cluster, [Ru3(PPh3)3(CO)9] (Figure S18),31 indicating that 1 also
appears to be susceptible to loss of free carbene under quite mild conditions.
Conclusions
The synthesis and structural characterisation of rare examples of 46ꢀelectron triꢀ
ruthenium clusters has been achieved upon reacting [Ru3(CO)12] with Nꢀalkyl substituted, 6ꢀ
membered ring Nꢀheterocyclic carbenes under very mild conditions. Reactivity studies of the
[Ru3(6ꢀNHC)(CO)10] complexes carried out using the 6ꢀiPr derivative 1 indicated that loss of
the carbene ligand took place upon addition of PPh3, mild heating under H2 or in the presence
of pyridine, thereby, limiting the potential of these complexes in catalytic applications.
The formation of very different products in the reaction of [Ru3(CO)12] with 6ꢀNHCs to
those formed with 5ꢀmembered ring analogues is notable,1b suggesting that (i) investigations
with 6ꢀ and/or 7ꢀmembered ring NHCs bearing, for example, Nꢀaryl substituents, and/ or (ii)
the use of other group 8 carbonyl clusters as precursors, is worthy of investigation.
Experimental
All manipulations were carried out using standard Schlenk, high vacuum and glovebox
techniques using dried and degassed solvents. NMR spectra were recorded on a Bruker
Avance 500 and 400 MHz NMR spectrometers and run in THFꢀd8 (referenced to δ 3.58 (1H)
and δ 67.6 (13C)). IR spectra were recorded in hexane solution on a Nicolet Nexus
spectrometer. Elemental analyses were performed by Elemental Microanalysis Ltd,
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Okehampton, Devon, UK. [Ru3(CO)12] (Sigma Aldrich) was used as received, while the
[PF6]ꢀ salts of [6ꢀiPrH]+, [6ꢀEtH]+ and [6ꢀMeH]+ were prepared according to the literature.32
[Ru3(6-iPr)(CO)10] 1. [6ꢀiPrH][PF6] (108 mg, 0.34 mmol) and KHMDS (66 mg, 0.33
mmol) were stirred in THF for 1 h in a J. Young’s resealable ampoule. The suspension was
then reduced to dryness, [Ru3(CO)12] (110 mg, 0.17 mmol) added and the mixture redissolved
in THF (6 mL). After stirring at room temperature for 3ꢀ4 days, the solvent was removed and
the residue extracted exhaustively with warm hexane (4 x 25 mL). The hexane was removed
under vacuum and the residue allowed to slowly evaporate in an argonꢀfilled glovebox from
ca. 2 mL hexane/THF (90:10) to afford deepꢀred crystalline 1. Yield 84 mg, 65 %. 1H NMR
(500 MHz, 298 K): δ = 3.59 (sept, 2H, 3JHH = 6.50 Hz, CHMe2), 3.40 (m, 2H, NCH2), 3.18
(m, 2H, NCH2), 2.11 (m, NCH2CHH, 1H), 1.88 (m, 1H, NCH2CHH), 1.36 (d, 6H, 3JHH
=
6.50 Hz, CHMe2), 1.21 (d, 6H, 3JHH = 6.50 Hz, CHMe2). 13C{1H} NMR (101 MHz, 298 K):
δ = 198.7 (s, RuꢀCNHC), 57.5 (s, NCHMe2), 40.6 (s, NCH2), 21.6 (s, NCH2CH2), 20.6 (s,
CHMe2), 20.0 (s, CHMe2). IR (cmꢀ1): 2084, 2061, 2041, 2031, 2022, 2009, 2001, 1984, 1976,
1963, 1802 (all νCO)
C, 31.92; H, 2.77; N, 3.60.
[Ru3(6-Et)(CO)10] 2 and [Ru4(6-Et)2(CO)11] 3. As for 1 but with [6ꢀEtH][PF6] (100
. Analysis found: C, 31.96; H, 2.68; N, 3.73. C20H20N2O10Ru3 requires:
mg, 0.35 mmol), KHMDS (69 mg, 0.35 mmol) and [Ru3(CO)12] (111 mg, 0.17 mmol).
Combined yield of 2 and 3: 24 mg. Selected spectroscopic data for 2. 1H NMR (500 MHz,
235 K): δ = 3.47 (m, 2H, NCH2CH3), 3.39 (m, 2H, NCH2CH3), 3.26 (m, 4H, NCH2CH3),
2.07 (m, 2H, NCH2CH2), 1.31 (t, 6H, 3JHH = 6.99 Hz, NCH2CH3). 13C{1H} NMR (126 MHz,
235 K): δ 206.1 (s), 201.0 (s), 199.1 (s), 198.2 (s), 189.5 (s), 186.8 (s), 52.5 (s, NCH2), 45.1
(s, NCH2), 20.9 (s, NCH2CH2), 13.9 (s, CH2CH3). IR (cmꢀ1): 2085, 2061, 2042, 2031, 2022,
2009, 2002, 1984, 1977, 1964, 1803 (all νCO). Analysis found: C, 30.01; H, 2.20; N, 3.93.
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C18H16N2O10Ru3 requires: C, 29.87; H, 2.23; N, 3.87. Only a few single crystals of 3 could be
isolated, restricting characterisation to just an Xꢀray crystal structure (Figure S7).
[Ru3(6-Me)(CO)10] 4. As for 1 but with [6ꢀMeH][PF6] (60 mg, 0.23 mmol), KHMDS
(46 mg, 0.23 mmol) and [Ru3(CO)12] (75 mg, 0.12 mmol) to afford deepꢀred crystals of 4.
Yield 16 mg, 20 %. 1H NMR (500 MHz, 298 K): δ = 3.32 (br t, 4H, 3JHH = 4.8 Hz, NCH2),
3.14 (s, 6H, NMe), 2.09 (quint, 2H, 3JHH = 6.0 Hz, NCH2CH2). 13C{1H} NMR (101 MHz,
298 K): δ = 202.7 (s, RuꢀCNHC), 47.5 (s, NCH2), 43.9 (s, NMe), 21.1 (s, NCH2CH2). IR (cmꢀ
1): 2086, 2061, 2043, 2023, 2010, 2003, 1981, 1962, 1806 (all νCO)
. Analysis found: C, 28.02;
H, 1.66; N, 3.82. C16H12N2O10Ru3 requires: C, 27.63; H, 1.74; N, 4.03.
Reactivity studies of 1. (a) with C5H5N: 1 (17.1 mg, 0.023 mmol) was combined with
pyridine (7.5 ꢀL, 0.093 mmol) in THFꢀd8 in a J. Young’s resealable NMR tube and the
reaction followed by 1H NMR spectroscopy. (b) with H2: 1 (11.1 mg, 0.015 mmol) was
dissolved in THFꢀd8 in a J. Young’s resealable NMR tube, the solution freezeꢀpumpꢀthaw
degassed (x3), placed under 1 atm H2 and the reaction followed by 1H NMR spectroscopy. (c)
with PPh3: 1 (6.5 mg, 0.009 mmol) was combined with 3 equiv PPh3 (6.8 mg, 0.026 mmol) in
THFꢀd8 in a J. Young’s resealable NMR tube and the reaction followed by 1H and 31P NMR
spectroscopy.
Catalysis. Solid samples of Ru3 precursors (0.0265 mmol), togther with 2,4,6ꢀ
(MeO)3C6H3 (0.0265 mmol) as an internal standard, were weighed into a Parr autoclave
inside a glovebox. A solution of 1ꢀhexene (2 mmol) in pyridine (7.5 mL, dried over activated
3 Å molecular sieves) was added by cannula, and the autoclave assembly put together under a
flow of argon. After purging twice with CO, the autoclave was pressurised to 10 atm and
heated at 150 °C for 16 h. After cooling and depressurising, a small amount of the redꢀorange
solution was diluted with CDCl3 and analysed by 1H NMR spectroscopy. Product resonances
were assigned by comparison to the literature.25
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X-ray crystallography. Data for 1 were collected on a Nonius kappaCCD
diffractometer using MoꢀKα radiation, while those for 2, 3 (ESI) and 4 were obtained using
using a CuꢀKα source and an Agilent SuperNova instrument. Refinements, achieved using
SHELXL33 via Olex234 were relatively straightforward and only points of note are mentioned
hereafter. In 3 (ESI), C22 was refined subject to taking 75:25 disorder with C22A into
account. Meanwhile, the asymmetric unit in 4 was seen to comprise 2 molecules, which differ
in the relative orientation of the apical carbeneꢀcarbon atoms within the respective molecules
to which they belong.
Crystallographic data for all compounds have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publications CCDC 1559943 (1), 1559944
(2), 1559945 (3, ESI) and 1559946 (4), 1816567 ([6ꢀiPrH]2[Ru4(CO)12H2], ESI) and 1816568
([Ru3(PPh3)3(CO)9], ESI) respectively. Copies of these data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax(+44) 1223 336033, eꢀ
mail: deposit@ccdc.cam.ac.uk.
Acknowledgements.
We thank EPSRC/University of Bath for support (DTA to CEE). PRR is grateful to the
EPSRC for continued support through a Programme Grant (EP/K004956/1). MKW would
like to thank Dr Matthew Jones for assistance with the catalysis.
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This represents the average value from six catalytic runs, including ones in which (i)
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Graphical Abstract
Ru3(6-NHC)(CO)10: Synthesis, Characterization and Reactivity of Rare 46-Electron Tri-
ruthenium Clusters
Charles E. Ellul, John P. Lowe, Mary F. Mahon, Paul R. Raithby and Michael K.
Whittlesey
The room temperature reaction of 6-membered ring N-heterocyclic carbenes with
[Ru3(CO)12] affords [Ru3(6-NHC)(CO)10], rare examples of coordinatively unsaturated,
46-electron tri-ruthenium clusters. Upon mild heating in the presence of C5H5N, H2 or
PPh3, these compounds lose carbene.
N
N
R
R
R
R = iPr, Et, Me
Ru3(CO)12
N
N
Ru
Ru
RT
R
Ru
= CO
1