Reactivity of cationic triruthenium carbonyl clusters: From pyrimidinium ligands to N-heterocyclic carbenes

Article abstract of DOI:10.1021/om101130g

The reaction of [Ru₃(CO)₁₂] with pyrimidine (Hpym) leads to the isomeric cyclometalated derivatives [Ru₃(μ-H)(μ- κ²N¹,C⁶-pym)(CO)₁₀] (1) and [Ru₃(μ-H)(μ-κ²N¹,C ²-pym)(CO)₁₀] (2), which have been treated with [Me ₃O][BF₄] to give the corresponding N-methylpyrimidinium derivatives [Ru₃(μ-H)(μ-κ²N¹,C ⁶-pymMe)(CO)₁₀][BF₄] (3[BF₄]) and [Ru₃(μ-H)(μ-κ²N¹,C ²-pymMe)(CO)₁₀][BF₄] (4[BF₄]). The reaction of 4[BF₄] with K-Selectride renders a separable mixture of two neutral trinuclear products, [Ru₃(μ-H){μ- κ²N¹,C²-(6-HpymMe)}(CO)₉] (5) and [Ru₃(μ-H){μ-κ²N¹,C ²-(4-HpymMe)}(CO)₉] (6), which arise from the nucleophilic attack of a hydride at the ligand C⁶ and C⁴ carbon atoms of 4⁺. This cationic complex can be reduced to the short-lived radical species 4^?, which spontaneously dimerizes by forming an intermolecular C-C bond between the ligands of two such radicals. Three hexanuclear derivatives, [Ru₆(μ-H)₂{μ₆- κ⁴N¹,N¹′,C²,C ²′-(4,6′-bipymMe₂)}(CO)₁₈] (isomers 7 and 8) and [Ru₆(μ-H)₂{μ₆- κ⁴N¹,N¹′,C²,C ²′-(4,4′-bipymMe₂)}(CO)₁₈] (isomer 9), have been isolated by reducing 4[BF₄] with cobaltocene. Molecular orbital calculations (at the DFT level) and electrochemical studies have helped rationalize the experimental results. The ligand-based character of the LUMO of 4⁺ and its atomic orbital composition account for the regiochemistry observed in the reactions of this cationic complex. The N-heterocyclic ligands of 5-9, which have two N atoms in a six-membered ring and a doubly metalated N atom, constitute novel types of N-heterocyclic carbenes.

Full text of DOI:10.1021/om101130g

1148 Organometallics 2011, 30, 1148–1156
DOI: 10.1021/om101130g
Reactivity of Cationic Triruthenium Carbonyl Clusters: From
Pyrimidinium Ligands to N-Heterocyclic Carbenes
†
‡
†
Javier A. Cabeza,*,† Ignacio del Rı
o, Enrique Perez-Carreno, and Vanessa Pruneda
ꢀ ~
´
†
´
ꢀ
ꢀ
Departamento de Quımica Organica e Inorganica-IUQOEM, Universidad de Oviedo-CSIC, E-33071
´
‡
´
´
Oviedo, Spain, and Departamento de Quımica Fısica y Analıtica, Universidad de Oviedo, E-33071 Oviedo,
Spain
Received December 2, 2010
The reaction of [Ru3(CO)12] with pyrimidine (Hpym) leads to the isomeric cyclometalated
derivatives [Ru3(μ-H)(μ-κ2N1,C6-pym)(CO)10] (1) and [Ru3(μ-H)(μ-κ2N1,C2-pym)(CO)10] (2), which
have been treated with [Me3O][BF4] to give the corresponding N-methylpyrimidinium derivatives
[Ru3(μ-H)(μ-κ2N1,C6-pymMe)(CO)10][BF4] (3[BF4]) and [Ru3(μ-H)(μ-κ2N1,C2-pymMe)(CO)10]-
[BF4] (4[BF4]). The reaction of 4[BF4] with K-Selectride renders a separable mixture of two neutral
trinuclear products, [Ru3(μ-H){μ-κ2N1,C2-(6-HpymMe)}(CO)9] (5) and [Ru3(μ-H){μ-κ2N1,C2-(4-
HpymMe)}(CO)9] (6), which arise from the nucleophilic attack of a hydride at the ligand C6 and C4
carbon atoms of 4þ. This cationic complex can be reduced to the short-lived radical species 4•, which
spontaneously dimerizes by forming an intermolecular C-C bond between the ligands of two such
4
1
1
2
2
0
0
radicals. Three hexanuclear derivatives, [Ru6(μ-H)2{μ6-κ N ,N ,C ,C -(4,60-bipymMe2)}(CO)18]
4
1
1
2
2
(isomers 7 and 8) and [Ru6(μ-H)2{μ6-κ N ,N ,C ,C -(4,40-bipymMe2)}(CO)18] (isomer 9), have been
isolated by reducing 4[BF4] with cobaltocene. Molecular orbital calculations (at the DFT level) and
electrochemical studies have helped rationalize the experimental results. The ligand-based character
of the LUMO of 4þ and its atomic orbital composition account for the regiochemistry observed in the
reactions of this cationic complex. The N-heterocyclic ligands of 5-9, which have two N atoms in a
six-membered ring and a doubly metalated N atom, constitute novel types of N-heterocyclic
carbenes.
0
0
Introduction
many NHCR5 carbenes are isolable as pure compounds or
can be prepared in situ by simple synthetic procedures.
Pyridylidenes (also named pyridinylidenes) and some ben-
zo-annulated relatives (derived from quinoline, isoquinoline,
acridine, etc.) are NHCR6 carbenes that contain only one N
atom in the carbenic ring (NHCR6-1N).2 Although their
isolation as free carbenes has been elusive, a few reports
describing indirect routes to various types of transition-
metal complexes containing NHCR6-1N ligands have been
published.2-7 In this context, we have recently communicated
Among the large and fast-growing family of N-hetero-
cyclic carbene (NHC) ligands known to date, those having
the carbene C atom in a five-membered ring (NHCR5) are far
more common than those having the carbene C atom in a six-
membered ring (NHCR6).1 This is mainly due to the fact that
*To whom correspondence should be addressed. E-mail: jac@
uniovi.es.
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pubs.acs.org/Organometallics
Published on Web 02/09/2011
2011 American Chemical Society

Article
Organometallics, Vol. 30, No. 5, 2011 1149
that pyrid-2-ylidenes, generated in situ by deprotonation
of pyridinium cations, can be trapped by [Ru3(CO)12],7 but
the great basicity of these ligands and the polynuclear
character of the ruthenium cluster trigger the room-
temperature ortho metalation of the initial κ1C2-pyrid-2-
ylidene ligands to give face-capping μ3-κ2C2,C3-pyrid-3-
yl-2-ylidene ligands (Scheme1).
Scheme 1
ꢀ
(6) (a) Rosello-Merino, M.; Dı
´
ez., J.; Conejero, S. Chem. Commun.
Considering that N-heterocyclic carbenes containing two
nitrogen atoms in a six-membered carbenic ring (NHCR6-2N)
2010, 46, 9247. (b) Song, G.; Li, Y.; Chen, S.; Li, X. Chem. Commun.
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2008, 3558. (c) Gomez-Bujedo, S.; Alcarazo, M.; Pichon, C.; Alvarez, E.;
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are restricted to 1,3-dialkyl- and 1,3-diaryl-3,4,5,6-tetrahy-
dropyrimidin-2-ylidenes,8 the results shown in Scheme 1 led
us to attempt the synthesis of ruthenium cluster complexes
containing NHCR6-2N ligands derived from quinoxaline,
pyrazine, and pyrimidine, following an analogous synthetic
procedure. However, N-methylquinoxalinium,9 N-methyl-
pyrazinium,9 and N-methylpyrimidinium10 cations could
not be satisfactorily deprotonated with strong bases in the
presence of [Ru3(CO)12]. We then reasoned that previous
coordination of these cations would enhance their acidity,
but they failed to react with [Ru3(CO)12] even at tempera-
tures higher than 100 °C.9,10 Finally, we decided to attempt
the preparation of the desired cationic clusters by stepwise
treatment of [Ru3(CO)12] with the neutral heterocycles (this
would lead to heterocycle-derived neutral clusters) and then
with an electrophilic methylating reagent, such as methyl
triflate (this would lead to cationic derivatives if N-methylation
of the free N atom was achieved). A subsequent deprotonation
of these cationic clusters would lead to the desired products:
i.e., compounds containing NHCR6-2N ligands.
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´
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M. G.; Vazquez-Garcı
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690, 4433. (o) Zhang, Y.; Wang, D.; Wurst, K.; Buchmeiser, M. R.
In a previous paper,9 we have reported that, although we
have succeeded in preparing triruthenium clusters contain-
ing cationic pyrazinium- and quinoxalinium-derived ligands
by quaternization of neutral pyrazine- and quinoxaline-
derived clusters, the subsequent treatment of these cationic
clusters with some bases does not lead to isolable deprotona-
tion products but to clusters with neutral ligands that have
no significant carbene character and that arise from the
nucleophilic addition of the corresponding base to a ligand
ring carbon atom (see, for example, Scheme 2).
We now report the synthesis of cationic triruthenium
clusters having pyrimidinium-derived ligands and show
that their reactions with K-Selectride and cobaltocene
lead to neutral products that contain novel types of
NHCR6-2N ligands.
€
J. Organomet. Chem. 2005, 690, 5728. (p) Ozdemir, I.; Demir, S.;
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G. C.; Alder, R. W.; Owen-Smith, G. J. J. Chem. Eur. J. 2006, 12, 5361. (t)
Schneider, S. K.; Herrmann, W. A.; Herdtweck, E. J. Mol. Catal. A: Chem.
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Ong, T.-G.; O’Brien, J. S.; Lavoie, N.; Bell, E.; Yap, G. P. A.; Korobkov,
While we were preparing this paper, a report describing the
synthesis of rhodium(I) and iridium(I) complexes containing
monodentate phthalaz-2-ylidene ligands (Scheme 3) has
been published.11
€
I.; Richeson, D. S. Organometallics 2007, 26, 2885. (z) Ozdemir, I.; Demir,
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Khrustalev, V. N.; Nechaev, M. S. J. Organomet. Chem. 2009, 694,
2454. (cc) Iglesias, M.; Beetstra, D. J.; Kariuki, B.; Cavell, K. J.; Dervisi,
A.; Fallis, I. A. Eur. J. Inorg. Chem. 2009, 1913. (dd) Binobaid, A.; Iglesias,
M.; Beetstra, D. J.; Kariuki, B.; Dervisi, A.; Fallis, I. A.; Cavell, K. J.
Dalton Trans. 2009, 7099. (ee) Iglesias, M.; Beetstra, D. J.; Cavell, K. J.;
Dervisi, A.; Fallis, I. A.; Kariuki, B.; Harrington, R. W.; Clegg, W.;
Horton, P. N.; Coles, S. J.; Hursthouse, M. B. Eur. J. Inorg. Chem. 2010,
1604. (ff) Armstrong, R.; Ecott, C.; Mas-Marza, E.; Page, M. J.; Mahon,
M. F.; Whittlesey, M. K. Organometallics 2010, 29, 991. (gg) Newman,
P. D.; Cavell, K. J.; Kariuki, B. M. Organometallics 2010, 29, 2724. (hh)
Davies, C. J. E.; Page, M. J.; Ellul, C. E.; Mahon, M. F.; Whittlesey, M. K.
Chem. Commun. 2010, 46, 5151.
Results and Discussion
Synthesis of the Isomeric Cationic Clusters [Ru3(μ-H)(μ-K2N1,
C6-pymMe)(CO)10]þ (3þ) and [Ru3(μ-H)(μ-κ2N1,C2-pymMe)-
(CO)10]þ (4þ). These compounds were prepared following a
two-step synthetic protocol related to that reported previously
for the synthesis of the related complexes [Ru3(μ-H)(μ-κ2N1,
ꢀ ~
(9) Cabeza, J. A.; del Rıo, I.; Goite, M. C.; Perez-Carreno, E.;
´
Pruneda, V. Chem. Eur. J. 2009, 15, 7339.
(10) Cabeza, J. A.; Pruneda, V. Unpublished results.
ꢀ
Lassaletta, J. M. Organometallics 2010, 29, 5941.
ꢀ
(11) Magriz, A.; Gomez-Bujedo, S.; Alvarez, E.; Fernandez, R.;

1150 Organometallics, Vol. 30, No. 5, 2011
Cabeza et al.
Scheme 2
Scheme 4
Scheme 3
oxide, methyllithium, and potassium tris(sec-butyl)hydridobo-
rate (K-Selectride) was studied.
C2-LMe)(CO)10]þ (HLMe = N-methylpyrazinium, N-meth-
ylquinoxalinium): that is, treatment of [Ru3(CO)12] with the
N-heterocycle and subsequent methylation of the product
with methyl triflate.9 However, the reaction of [Ru3(CO)12]
with 1 equiv of pyrimidine (Hpym), in THF solution at reflux
temperature, did not lead to a single product but to a mixture
of the neutral cyclometalated hydrido derivatives [Ru3-
(μ-H)(μ-κ2N1,C6-pym)(CO)10] (1) and [Ru3(μ-H)(μ-κ2N1,
C2-pym)(CO)10] (2) (Scheme 4), which were satisfactorily
separated by thin-layer chromatography (TLC).12 The subse-
quent methylation of 1 and 2 with methyl triflate was
unsuccessful, because an equilibrium between the reactants
and the methylated products was established and this pre-
vented the isolation of the latter as pure compounds. For-
tunately, the use of trimethyloxonium tetrafluoroborate as
methylating reagent led to the desired cationic complexes,
[Ru3(μ-H)(μ-κ2N1,C6-pymMe)(CO)10]þ (3þ) and [Ru3(μ-H)-
(μ-κ2N1,C2-pymMe)(CO)10]þ (4þ) (Scheme 4).
Both 3[BF4] and 4[BF4] reacted readily with 1 equiv of
potassium tert-butoxide and methyllithium to give mixtures
of products, from which [Ru3(CO)12] was the only complex
that could be satisfactorily separated by TLC. Similar results
were obtained when 3[BF4] was treated with K-Selectride. It
seems that the initial products of these reactions are not
stable enough to be isolated and that they evolve to thermo-
dynamically driven mixtures that contain [Ru3(CO)12] and
other decomposition products.
However, although a mixture of products was also formed
when 4[BF4] was treated with K-Selectride at room tempera-
ture, a subsequent chromatographic workup allowed the
isolation of the yellow isomeric nonacarbonyl products
[Ru3(μ-H){μ-κ2N1,C2-(6-HpymMe)}(CO)9] (5) and [Ru3-
(μ-H){μ-κ2N1,C2-(4-HpymMe)}(CO)9] (6) (Scheme 5), which
contain novel NHCR6-2N ligands that arise from the nu-
cleophilic attack of the hydride ion at different C atoms of
the bridging N-heterocyclic ligand of 4þ. In the processes
that lead to 5 and 6, the nucleophilic attack of the hydride
ion at 4þ should precede the release of the CO ligand,
because the decacarbonyl cation 4þ is stable in solution at
room temperature.
The structures of compounds 5 and 6 were determined by
X-ray diffraction (Figures 2 and 3, respectively). Table 1
contains a selection of bond lengths that permits a compar-
ison between related interatomic distances of compounds
4-6. Both structures comprise a closed [Ru3(CO)9] core that
is edge-bridged by a hydride ligand and face-capped by the
corresponding pyrimidinium-derived ligand, which bridges
the Ru2-Ru3 edge through the N1 atom while it is also
attached to the Ru1 atom through the carbene C1 atom. The
C1-Ru1 distances, 2.069(5) A in 5 and 2.04(1) A in 6,
are comparable to the Ru-Ccarbene distances reported for
tri- and tetraruthenium clusters containing NHCR5-N2
ligands.13 The main difference between compounds 5 and
6 is that the former results from the addition of the hydride
to the C6 carbon atom (C2 in Figure 2) of the original
The composition of 3[BF4] and 4[BF4] was established by
their microanalyses and FAB mass spectra. In addition, the
cationic character of the clusters was confirmed by their IR
and NMR spectra, since their ν(CO) absorptions are shifted
toward wavenumbers higher than those of their neutral
precursors 1 and 2 and the 1H and 13C NMR signals of their
heterocyclic ligands appear at chemical shifts higher than
1
those of 1 and 2. The high H (δ 4.35 ppm for 3[BF4] and
4.60 ppm for 4[BF4]) and 13C (δ 44.7 ppm for 3[BF4] and
50.3 ppm for 4[BF4]) chemical shifts of their methyl groups
corroborate the methylation of the uncoordinated N atoms
of 1 and 2. The solid-state structure of 4[BF4] was verified by
X-ray diffraction (Figure 1). A selection of bond lengths is
given in Table 1.
Reactions of Compounds 3[BF4] and 4[BF4] with Bases. The
reactivity of these ionic compounds with potassium tert-but-
(12) Compounds 1 and 2 have been previously prepared by treating
[Ru3(CO)10(MeCN)2] with Hpym: Foulds, G. A.; Johnson, B. F. G.;
Lewis, J. J. Organomet. Chem. 1985, 294, 123.

Article
Organometallics, Vol. 30, No. 5, 2011 1151
Figure 1. Structure of the cationic part of 4[BF4]. Thermal
ellipsoids are drawn at 30% probability level.
˚
Table 1. Selected Interatomic Distances (A) in Compounds
4[BF4], 5, and 6
Figure 2. Molecular structure of compound 5. Thermal ellip-
soids are drawn at the 30% probability level.
4[BF4]
5
6
Ru(1)-Ru(2)
Ru(1)-Ru(3)
Ru(2)-Ru(3)
C(1)-Ru(1)
N(1)-Ru(2)
N(1)-Ru(3)
C(1)-N(1)
C(1)-N(2)
C(2)-N(1)
C(2)-C(3)
2.8784(9)
2.8743(9)
2.8498(9)
2.090(7)
2.132(6)
2.7402(4)
2.7530(4)
2.7797(4)
2.069(4)
2.132(3)
2.170(3)
1.372(5)
1.345(5)
1.488(5)
1.506(6)
1.313(7)
1.423(6)
1.462(6)
2.747(2)
2.753(2)
2.767(2)
2.04(1)
2.19(1)
2.14(1)
1.43(2)
1.35(2)
1.39(2)
1.30(2)
1.50(2)
1.47(2)
1.44(2)
Scheme 5
1.339(10)
1.368(9)
1.334(10)
1.383(11)
1.351(12)
1.346(10)
1.492(10)
C(3)-C(4)
C(4)-N(2)
C(5)-N(2)
N-methylpyrimidinium ligand, whereas in complex 6, such
an addition has occurred on the C4 carbon atom (C4 in
Figure 3). While the C-C and C-N distances of the
pymMe ligand of compound 4þ are typical of an aromatic
system (they are in the range 1.34-1.38 A), those of the
6-HpymMe and 4-HpymMe ligands of 5 and 6 respectively
indicate that these ligands are no longer aromatic, since a
CdC double bond is clearly localized between the C3 and
C4 atoms of compound 5 (C3-C4 = 1.313(7) A) and
between the C2 and C3 atoms of compound 6 (C2-C3 =
1.30(2) A), while the remaining ring interatomic distances
are considerably longer, particularly those involving the
carbon atom of the corresponding CH2 group. While all six
ring atoms of the 4-HpymMe ligand of compound 6 are
nearly coplanar and the plane they define is perpendicular
to the Ru3 plane, the C2 carbon atom of the 6-HpymMe
ligand of compound 5 is 0.53(1) A away from the plane
defined by the remaining ligand ring atoms, which forms a
dihedral angle of 65.0(1)° with the Ru3 plane.
As expected, the IR spectra of 5 and 6 are almost identical
but are very different from that of their cationic decacarbo-
nyl precursor 4þ. Their 1H NMR spectra contain a hydride
resonance at -14.53 ppm for 5 and -14.07 ppm for 6 (that of
4
þ is observed at -14.12 ppm). While the 13C NMR signal
of the pymMe NCN carbon atom of 4þ is observed at
184.6 ppm, those of the Ccarbene atoms of 5 and 6 appear at
209.7 and 206.1 ppm, respectively, being in the upper part
of the range previously observed for many cyclic diamino-
carbene complexes (180-210 ppm).14
DFT calculations have already demonstrated that, in
cationic ligand-bridged triruthenium clusters, the greatest
positive atomic charges are located in the carbonyl C atoms.9
As no attack at the CO ligands of 4þ was observed when it
was treated with K-Selectride, this reaction should be orbi-
tal-controlled. Having this in mind, we performed a molec-
ular orbital study of 4þ aimed at rationalizing the experi-
mental results. Figure 4 shows (a) that the LUMO of 4þ is a
combination of π-type orbitals of atoms of the bridging
ligand, with negligible contributions from orbitals of the
remaining atoms of the cluster, (b) that the major contributors
(13) For examples of tri- and tetraruthenium cluster complexes
containing NHCR5-N2 ligands, see: (a) Cabeza, J. A.; Damonte, M.;
ꢀ
~
Garcı
´
a-Alvarez, P.; Kennedy, A. R.; Perez-Carreno, E. Organometallics
o,
I.; Fernandez-Colinas, J. M.; Perez-Carreno, E.; Sanchez-Vega, M. G.;
2011, 30, in press (DOI: 10.1021/om101021s). (b) Cabeza, J. A.; del Rı
´
ꢀ
ꢀ
~
ꢀ
ꢀ
Vazquez-Garcıa, D. Organometallics 2009, 28, 1832. (c) Zhang, C.; Luo,
´
F.; Cheng, B.; Li, B.; Song, H.; Xu, S.; Wang, B. Dalton Trans. 2009,
7230. (d) Bruce, M. I.; Cole, M. L.; Fung, R. S. C.; Forsyth, C. M.;
Hilder, M.; Junk, P. C.; Konstas, K. Dalton Trans. 2008, 4118.(e)
Critall, M. R.; Ellul, C. E.; Mahon, M. F.; Saker, O.; Whittlesey,
M. K. Dalton Trans. 2008, 4209. (f) Cabeza, J. A.; del Rı
´
D.; Perez-Carreno, E.; Sanchez-Vega, M. G. Organometallics 2008,
o, I.; Miguel,
ꢀ
27, 211. (g) Cabeza, J. A.; del Rı
ꢀ
~
ꢀ
ꢀ
o, I.; Miguel, D.; Perez-Carreno, E.;
Sanchez-Vega, M. G. Dalton Trans. 2008, 1937. (h) Cabeza, J. A.; del
~
´
ꢀ
´
o, I.; Miguel, D.; Sanchez-Vega, M. G. Angew. Chem., Int. Ed.
Rı
2008, 47, 1920. (i) Cabeza, J. A.; da Silva, I.; del Rı
Vega, M. G. Dalton Trans. 2006, 3966.
ꢀ
o, I.; Sanchez-
´
(14) Tapu, D.; Dixon, D. A.; Roe, C. Chem. Rev. 2009, 109, 3385.

1152 Organometallics, Vol. 30, No. 5, 2011
Cabeza et al.
Figure 5. Cyclic voltammograms of 4[BF4] acquired at 20 °C in
0.1 M [NEt4][BF4] dichloromethane solutions at different scan
rates.
N-methylquinoxalinium-derived triruthenium clusters
contain ligands with no carbene character.9
It has been previously shown that, on treatment with
anionic nucleophiles, hydrido triruthenium carbonyl clusters
that have neutral N-heterocyclic ligands either undergo hyd-
ride deprotonation (when the starting clusters are neutral15
or cationic16) or a nucleophilic attack at a carbonyl C atom
(only observed for cationic starting clusters).16 Therefore, it
is clear that the cationic character of 4þ and of [Ru3(μ-H)
(μ-κ2N1,C2-LMe)(CO)10]þ (HLMe = N-methylpyrazinium,
N-methylquinoxalinium) and the fact that they have ligand-
based LUMOs account for the enhanced tendency of these
clusters to add anionic nucleophiles at the carbon atoms of
their bridging N-heterocyclic ligands. It has been reported that
coordinatively unsaturated triosmium clusters having neutral
N-heterocyclic bridging ligands undergo addition of anionic
carbon nucleophiles at a C atom of the bridging ligand,17 but
that chemistry has no parallel in ruthenium cluster chemistry.
Reductive Dimerization of 4þ. In an earlier report, we have
described that the cationic compounds [Ru3(μ-H)(μ-κ2N1,
C2-LMe)(CO)10]þ (HLMe=N-methylpyrazinium, N-meth-
ylquinoxalinium) can be reduced by cobaltocene to give
dimeric hexanuclear products that arise from the cou-
pling of two ligand-centered trinuclear radical species
(Scheme 6).18 These findings and the different results
obtained from the reactions of these two trinuclear catio-
nic clusters and compound 4þ with K-Selectride, noted
above, prompted us to study the reduction chemistry of 4þ.
The cyclic voltammograms of 4[BF4] in dichloromethane
(Figure 5) show a reduction peak at a potential, Ered = -0.70
at 0.200 V s-1, that is similar to those found for [Ru3(μ-H)
(μ-κ2N1,C2-LMe)(CO)10]þ: -0.74 V for HLMe = N-methyl-
pyrazinium and -0.77 V for HLMe = N-methylquinoxali-
Figure 3. Molecular structure of compound 6. Thermal ellip-
soids are drawn at the 30% probability level.
Figure 4. LUMOs of the cationic complexes 3þ and 4þ, shown
at an isosurface value of 0.05.
to this molecular orbital are the C4 and C6 carbon atoms,
and (c) that their contributions are very similar. The
composition of the LUMO of 4þ explains the selective
attack of the hydride ion at the ligand ring and accounts
for the isolation of the isomeric products 5 and 6 in similar
yields. However, it is not yet clear why the behavior of
methyllithium is so different from that of K-Selectride in
their reactions with 4þ.
Interestingly, Figure 4 also shows that the LUMO of 3þ
differs from that of 4þ in that the former has a non-negligible
participation of the metal atoms and that its major contri-
butor is the metal-coordinated C2 carbon atom. This may
account for the very different reactivities observed for these
two cationic compounds.
nium, at 0.200 V s-1 18
Figure 5 also illustrates that the
.
reduction processes are completely irreversible, even at fast
The above-described reaction of K-Selectride with 4þ
seems to follow a reactivity pattern similar to that observed
for the cationic compounds [Ru3(μ-H)(μ-κ2N1,C2-LMe)-
(CO)10]þ (HLMe = N-methylpyrazinium, N-methylquino-
xalinium), which also give nonacarbonyl products resulting
from the addition of a hydride to a ligand ring carbon atom
(see, for example, Scheme 2).9 However, the different
positions of the N atoms in the N-heterocyclic ligands
of these cationic clusters account for the different natures
of the final products of their reactions. While the ligands
of 5 and 6 are N-heterocyclic carbenes, the products of
the reactions of the related N-methylpyrazinium- and
(15) Lugan, N.; Laurent, F.; Lavigne, G.; Newcomb, T. P.; Liimata,
E. W. Organometallics 1992, 11, 1351.
(16) (a) Andreu, P. L.; Cabeza, J. A.; Riera, V.; Bois, C.; Jeannin, Y.
J. Chem. Soc., Dalton Trans. 1990, 3347. (b) Andreu, P. L.; Cabeza, J. A.;
Pellinghelli, M. A.; Riera, V.; Tiripicchio, A. Inorg. Chem. 1991, 30,
´ ´
4611. (c) Cabeza, J. A.; del Rıo, I.; Riera, V.; Garcıa-Granda, S.; Sanni,
S. B. Organometallics 1997, 16, 1743.
(17) See, for example: (a) Bergman, B.; Holmquist, R.; Smith, R.;
Rosenberg, E.; Ciurash, J.; Hardcastle, K. I.; Visi, M. J. Am. Chem. Soc.
1998, 120, 12818. (b) Smith, R.; Rosenberg, E.; Hardcastle, K. I.;
ꢀ
Vazquez, V.; Roh, J. Organometallics 1999, 18, 3519.
ꢀ ~
´
(18) Cabeza, J. A.; del Rıo, I.; Perez-Carreno, E.; Pruneda, V. Chem.
Eur. J. 2010, 16, 5425.

Article
Organometallics, Vol. 30, No. 5, 2011 1153
Scheme 6
Figure 6. Molecular structure of compound 7. Thermal ellip-
soids are drawn at the 30% probability level.
Scheme 7
Figure 7. Molecular structure of compound 8. Thermal ellip-
soids are drawn at the 30% probability level.
˚
Table 2. Selected Interatomic Distances (A) in Compounds
7 CH2Cl2 and 8
3
7 CH2Cl2
3
8
Ru(1)-Ru(2)
Ru(1)-Ru(3)
Ru(2)-Ru(3)
Ru(4)-Ru(5)
Ru(4)-Ru(6)
Ru(5)-Ru(6)
C(1)-Ru(1)
C(1)-N(1)
C(1)-N(2)
C(2)-N(1)
C(2)-C(3)
2.762(1)
2.747(1)
2.779(1)
2.747(1)
2.930(1)
2.662(1)
2.085(12)
1.39(2)
1.33(2)
1.40(2)
1.31(2)
1.50(2)
1.58(2)
1.48(2)
1.44(2)
1.36(2)
1.36(2)
1.49(2)
1.47(2)
1.33(2)
1.42(2)
1.45(2)
2.158(11)
2.158(9)
2.196(8)
2.136(10)
2.7498(5)
2.7340(5)
2.7671(5)
2.7325(5)
2.7378(5)
2.7853(5)
2.077(4)
1.373(6)
1.324(6)
1.428(5)
1.296(7)
1.494(7)
1.571(7)
1.494(6)
1.463(7)
1.372(6)
1.342(6)
1.484(7)
1.477(6)
1.313(9)
1.396(8)
1.470(8)
2.137(3)
2.160(4)
2.146(3)
2.197(4)
scan rates, indicating that the molecules of the reduced odd-
electron species 4• has a very short half-life in solution.
The reaction of 4[BF4] with 1 equiv of cobaltocene led to a
mixture of products from which three neutral hexanuclear
C(3)-C(4)
C(4)-C(7)
C(4)-N(2)
C(5)-N(2)
C(6)-N(3)
C(6)-N(4)
C(7)-C(8)
4
1
1
2
2
0
0
derivatives, namely, [Ru6(μ-H)2{μ6-κ N ,N ,C ,C -(4,60-
bipymMe2)}(CO)18] (isomers 7 and 8) and [Ru6(μ-H)2{μ6-
4
1
1
2
2
0
0
κ N ,N ,C ,C -(4,40-bipymMe2)}(CO)18] (isomer 9), were
separated by TLC (Scheme 7). They were all characterized
by analytical and spectroscopic techniques and, in the cases
of 7 and 8, also by X-ray diffraction.
C(7)-N(3)
C(8)-C(9)
C(9)-N(4)
C(10)-N(4)
N(1)-Ru(2)
N(1)-Ru(3)
N(3)-Ru(5)
N(3)-Ru(6)
The solid-state molecular structures of compounds 7 and 8
(Figures 6 and 7, Table 2) have many features in common.
Both molecules comprise two closed trimetallic units, each
edge-bridged by a hydride and face-capped by a ligand, 4,60-
bipymMe2, that arises from the intermolecular formation of
a C-C bond between the pymMe ligands of two molecules of
the radical 4•. In 7 and 8, the new C-C bond involves the
heterocyclic C4 carbon atom (C4 in Figures 6 and 7) of one
trinuclear unit, Ru3H(4-pymMe)(CO)9, and the heterocyclic
C6 carbon atom (C7 in Figures 6 and 7) of the other tri-
nuclear unit, Ru3H(60-pymMe)(CO)9. The key difference

1154 Organometallics, Vol. 30, No. 5, 2011
Cabeza et al.
between both molecules is that their C7 carbon atoms have
opposite stereochemistries, while the stereochemistries of
their C4 carbon atoms are the same. The coordination of
the bridging ligand to the metal atoms of the Ru3H-
(4-pymMe)(CO)9 units of 7 and 8 is essentially identical with
that found in compound 6 (Figure 3); however, the different
stereochemistry of the C7 carbon atom of each molecule
induces a different arrangement of the atoms of the corre-
sponding Ru3H(60-pymMe)(CO)9 unit. While that of 7 is analo-
gous to that found in [Ru6(μ-H)2{μ6-κ N ,N ,C ,C -(3,30-
biquinoxMe2)}(CO)18] (HquinoxMe = N-methylquinoxa-
line) (Scheme 6),18 that of 8 is the same as that found in
compound 5 (Figure 2). We believe that the coordination mode
found for the bridging ligand 4,60-bipymMe2 in the Ru3H(60-
pymMe)(CO)9 unit of 7minimizes steric interactions (involving
CO ligands and C-H groups) that would be more intense if it
had the coordination mode found for the same trinuclear unit
in compound 8. In both molecules, the rotation about the
C4-C7 bond is sterically impeded. This steric hindrance should
also be responsible for the very long C4-C7 interatomic
distances: 1.58(2) A in 7 and 1.571(7) A in 8.
compounds 7-9, it can be deduced that each enantiomer of
4• may couple through its C4 atom to the C6 atom of both
enantiomers (thus leading to compounds 7 and 8 as racemic
mixtures) and to the C4 atom of the opposite enantiomer
(thus leading to compound 9 as a racemic mixture). Most
probably, steric factors are responsible for the nonoccur-
rence (at least to an observable extent) of C6-C6 couplings
between molecules of any enantiomer and C4-C4 couplings
between molecules of the same enantiomer.
The cyclic voltammogram of compound 3[BF4] also shows
an irreversible reduction at any scan rate, but the reduction
potential, Ered ≈ -0.86 at 0.200 V s-1, is lower than that of
4[BF4] (Ered ≈ -0.70 at 0.200 V s-1), in agreement with the
fact that the LUMO of 3þ, which has a DFT-calculated
energy of -6.841 eV, is more stable than the LUMO of 4þ
(-6.371 eV). The reaction of 3[BF4] with cobaltocene was also
performed, but [Ru3(CO)12] was the only metal-containing
product that could be isolated.
4
1
1
0
2
2
0
The reductive intermolecular formation of C-C bonds
between ligands of transition-metal clusters has only been
previously observed for [Ru3(μ-H)(μ-κ2N1,C2-LMe)(CO)10]þ
(HLMe = N-methylpyrazinium, N-methylquinoxalinium),18
but there are a few examples of related couplings in mono-
nuclear chemistry. In general, these metal complexes are catio-
nic and have ligand-based LUMOs. This is the case for the
diazoalkane amido complexes [Mo{4-RC6H4C(H)NN}(NtBu-
Ar)3]þ (various R and Ar), which dimerize at the diazoalkane C
atom,19 the salophen derivatives [M(salophen)]nþ (M = Ni,20
Ti,21 V,21 Mn22), which undergo a reversible dimerization at a
ligand C atom, the 2,20-bipyridine alkylidyne complex [W(t
CC6H4NMe2)(κ2N2-bipy)(NCMe)(CO)2]þ, which dimerizes at
a bipy C atom,23 some propargyl cobalt complexes, which
dimerize at a ligand C atom,24 and the carbene derivative [Cr(d
CNEt2)(CO)5]þ, which dimerizes at the carbene C atom.25 It
has been reported that the reaction of the titanium complex
trans-[TiCl2(κ2N2-tmeda)2] (tmeda = Me2NCH2CH2NMe2)
with acetonitrile leads to the reductive coupling of the latter,
affording the dimetallic eneimido derivative trans-[Ti2Cl4-
{μ-κ2N2-NC(Me)d(Me)CN}(κ2N2-tmeda)2].26 In contrast,
the reductive dimerization of complexes with metal-based
LUMOs leads to dimers with a new metal-metal bond,
as is the case for the trinuclear clusters [Ru3(μ3-κ2N2-
Hampy)(CO)10]þ (H2ampy = 2-amino-6-methylpyridine)27
Although no crystals of compound 9 suitable for X-ray
diffraction could be obtained, its atom connectivity (see
Scheme 7) was satisfactorily inferred from its spectroscopic
data. The νCO region of its IR spectrum is comparable to
those of compounds 7 and 8, which are almost identical
despite corresponding to compounds with different, but
1
related, molecular structures. Both the H and 13C NMR
spectra of compound 9 contain duplicated resonances, in-
dicating that the compound consists of two essentially
identical parts that are not symmetry related. The C4-C4
0
coupling was unambiguously confirmed by its 135-DEPT
and 13C{1H} NMR spectra, which in addition to the
resonances of the HC4-HC4 group (δ 59.9 and 57.7 ppm)
0
contain the resonances of the remaining ring CH (δ 147.3,
146.7, 101.5, and 100.0 ppm) and carbene C atoms (δ 210.8
and 210.0 ppm) at chemical shifts very close to those found
for 6 and for the Ru3H(4pymMe)(CO)9 units of 7 and 8,
whose structures have been established by X-ray diffraction.
This confirms that the CdC double bond of the heterocyclic
ring is located between the C5 and C6 carbon atoms.
The fact that both trinuclear units of this compound are
not symmetry related implies that the C4 and C4 carbon
0
atoms have different stereochemistries (R,S or S,R), because
otherwise (R,R or S,S) the molecule would have C2 symme-
try. In 0addition, there should be no free rotation about the
C4-C4 bond, because for 0°-eclipsed or 180°-alternated
conformations there would be a mirror plane bisecting the
and [Pd3(μ3-κ7-C7H7)2(MeCN)3]2þ 28
, which give hexanuclear
products with seven metal-metal bonds.
(19) Curley, J. J.; Murahashi, T.; Cummings, C. C. Inorg. Chem.
2009, 48, 7181.
(20) Gambarotta, S.; Urso, F.; Floriani, C.; Chiesi-Villa, A.; Guastini,
C. Inorg. Chem. 1983, 22, 3966.
(21) (a) Franceschi, F.; Solari, E.; Floriani, C.; Rosi, M.; Chiesi-Villa,
A.; Rizzoli, C. Chem. Eur. J. 1999, 5, 708. (b) Rosi, M.; Sgamellotti, A.;
Franceschi, F.; Floriani, C. Chem. Eur. J. 1999, 5, 2914.
(22) Gallo, E.; Solari, E.; Re, N.; Floriani, C.; Chiesi-Villa, A.;
Rizzoli, C. J. Am. Chem. Soc. 1997, 119, 5144.
(23) Duplessis, E. A.; Jelliss, P. A.; Kirkpatrick, C. C.; Minteer, S. D.;
Wampler, K. M. J. Organomet. Chem. 2006, 691, 4660.
(24) Melikyan, G. G.; Deravakian, A. J. Organomet. Chem. 1997,
544, 143.
4
4
0
C4-C4 bond or an inversion center between the C and C
0
atoms, respectively, and molecular models have shown that
the steric repulsion between the atoms of the two parts of the
molecule is stronger at the 0°-eclipsed and 180°-alternated
conformations than at any other intermediate conformation.
Upon addition of one electron, the LUMO of 4þ
(Figure 4) is converted to the SOMO of the odd-electron
species 4•, which should have an atomic orbital composition
analogous to that of the LUMO of 4þ: i.e., with the ligand C4
and C6 atoms as the major contributors. In this radical, the
endo face of the N-heterocyclic ligand is protected by one of
the axial CO ligands of the Ru(CO)4 moiety and, therefore,
its dimerization is expected to occur only through the exo
face of its ligand. In addition, as this radical species is
asymmetric, it is in fact a racemic mixture (dextro and levo
enantiomers). Considering these facts and the structures of
(25) Fischer, E. O.; Wittmann, D.; Himmelreich, D.; Neugebauer, D.
Angew. Chem., Int. Ed. 1982, 21, 1036.
(26) Duchateau, R.; Williams, A. J.; Gambarotta, S.; Chiang, M. Y.
Inorg. Chem. 1991, 30, 4863.
(27) Cabeza, J. A.; del Rıo, I.; Riera, V.; Grepioni, F. Organometallics
´
1995, 14, 3124.
(28) Murahashi, T.; Hashimoto, Y.; Chiyoda, K.; Fujimoto, M.;
Uemura, T.; Inoue, R.; Ogoshi, S.; Kurosawa, H. J. Am. Chem. Soc.
2008, 130, 8586.

Article
Organometallics, Vol. 30, No. 5, 2011 1155
Concluding Remarks
solid (178 mg, 81%). Anal. Calcd for C15H7BF4N2O10Ru3
(765.24): C, 23.54; H, 0.92; N, 3.66. Found: C, 23.58; H, 0.97;
N, 3.62. (þ)-FAB MS: m/z 679 [M - BF4]þ. IR (CH2Cl2): νCO
2108 (w), 2074 (s), 2062 (vs), 2028 (s), 2016 (s). 1H NMR
(acetone-d6, 293 K): δ 9.81 (d, J = 1.2 Hz, 1 H, CH), 8.51 (dd,
J = 6.3, 1.2 Hz, 1 H, CH), 8.47 (d, J = 6.3 Hz, 1 H, CH), 4.35
(s, 3 H, CH3), -14.44 (s, 1 H, μ-H). 13C{1H} NMR (acetone-d6,
293 K): δ 203.1, 202.9, 200.4, 199.5, 197.2, 194.0, 192.6, 191.6,
190.7, 188.4 (10 COs), 184.2 (C), 154.4 (CH), 140.5 (CH), 135.7
(CH), 44.7 (CH3). Cyclic voltammetry: Ered (scan rate) -0.83 V
(0.05 V s-1), -0.84 V (0.10 V s-1), -0.86 V (0.20 V s-1).
[Ru3(μ-H)(μ-K2N1,C2-pymMe)(CO)10][BF4] (4[BF4]). This
product was prepared as described above for 3[BF4], using
compound 2 (134 mg, 0.202 mmol) and [Me3O][BF4] (138 mg,
0.933 mmol) as starting materials. It is a yellow-orange solid
(101 mg, 65%). Anal. Calcd for C15H7BF4N2O10Ru3 (765.24):
C, 23.54; H, 0.92; N, 3.66. Found: C, 23.55; H, 0.94; N, 3.63. (þ)-
FAB MS: m/z 679 [M - BF4]þ. IR (CH2Cl2): νCO 2113 (w), 2079
(s), 2067 (vs), 2044 (w) 2020 (m, br), 2016 (s). 1H NMR (acetone-
d6, 293 K): δ 9.32 (dd, J = 5.1, 1.5 Hz, 1 H, CH), 9.23 (dd, J = 6.6,
1.5 Hz, 1 H, CH), 7.85 (dd, JH-H = 6.6, 5.1 Hz, 1 H, CH), 4.60 (s,
3 H, CH3), -14.12 (s, 1 H, μ-H). 13C{1H} NMR (acetone-d6,
293 K): δ 206.8, 205.8, 202.9, 200.1, 199.9, 193.6, 192.3, 190.2,
189.9, 187.6 (10 COs), 184.6 (C), 164.2 (CH), 153.6 (CH), 119.1
(CH), 50.3 (CH3). Cyclic voltammetry: Ered (scan rate) -0.66
V (0.05 V s-1), -0.68 V (0.10 V s-1), -0.70 V (0.20 V s-1).
[Ru3(μ-H){μ-K2N1,C2-(6-HpymMe)}(CO)9] (5) and [Ru3(μ-H)-
{μ-κ2N1,C2-(4-HpymMe)}(CO)9] (6). A THF solution of K-Selec-
tride (78 μL, 1 M, 0.078 mmol) was added dropwise to a solution of
4[BF4] (60 mg, 0.078 mmol) in the same solvent. The color changed
from yellow to orange. After the mixture was stirred for 1 h, the
solvent was removed under reduced pressure and the resulting
residue was redissolved in dichloromethane (3 mL) and was
supported on preparative silica gel TLC plates. Dichloromethane/
hexane (2/1) eluted four yellow bands. The first and fourth bands
contained small amounts of [Ru3(CO)12] and compound 2, respec-
tively. The second and third bands contained compounds 5 (8 mg,
16%) and 6 (12 mg, 24%), respectively.
Data for 5 are as follows. Anal. Calcd for C14H8N2O9Ru3
(651.43): C, 25.81; H, 1.24; N, 4.30. Found: C, 25.88; H, 1.30; N,
4.21. (þ)-FAB MS: m/z 653 [M]þ. IR (CH2Cl2): νCO 2083 (w),
2055 (s), 2029 (vs), 1999 (m, br), 1967 (w, sh), 1950 (w, br). 1H
NMR (CD2Cl2, 293 K): δ 6.04 (dt, J = 7.6, 1.6 Hz, 1 H, CH),
5.17 (dt, J = 7.6, 4.0 Hz, 1 H, CH), 3.65 (dd, J = 4.0, 1.6 Hz, 2 H,
CH2), 3.40 (s, 3 H, CH3), -14.53 (s, 1 H, μ-H). 13C{1H} and DEPT
NMR (CD2Cl2, 293 K): δ 209.7 (C), 204.2 (br, COs), 195.5 (br,
COs), 128.3 (CH), 107.0 (CH), 62.4 (CH2), 42.7 (CH3).
Data for 6 are as follows. Anal. Calcd for C14H8N2O9Ru3
(651.43): C, 25.81; H, 1.24; N, 4.30. Found: C, 25.85; H, 1.31; N,
4.24. (þ)-FAB MS: m/z 653 [M]þ. IR (CH2Cl2): νCO 2082 (w),
2054 (vs), 2020 (vs), 1998 (m, a), 1969 (w, sh), 1948 (w, br). 1H
NMR (CD2Cl2, 293 K): δ 5.27 (dt, J = 7.8, 2.0 Hz, 1 H, CH),
4.93 (dt, J = 7.8, 3.2 Hz, 1 H, CH), 4.04 (dd, J = 3.2, 2.0 Hz,
2 H, CH2), 3.33 (s, 3 H, CH3), -14.07 (s, 1 H, μ-H). 13C{1H} and
DEPT NMR (CD2Cl2, 293 K): δ 206.1 (C), 205.0 (br, COs) (COs),
196.0 (br, COs), 144.2 (CH), 103.4 (CH), 46.8 (CH2), 44.3 (CH3).
The present work has demonstrated that triruthenium
cluster compounds having cationic ligands derived from
N-methylpyrimidinium (compounds 3þ and 4þ) can be pre-
pared by methylation with [Me3O][BF4] of the uncoordinated N
atoms of neutral precursors containing ortho-metalated pyrimidine
ligands (compounds 1 and 2). DFT calculations have shown that
these cationic complexes have ligand-based LUMOs. The ligand of
4þ has been transformed into various NHC ligands by treating the
complex with K-Selectride (compounds 5 and 6) and cobaltocene
(compounds 7-9). The N-heterocyclic ligands of 5-9, which have
two N atoms in a six-membered ring and a doubly metalated N
atom, constitute novel types of N-heterocyclic carbenes.
Experimental Section
General Data. Solvents were dried over sodium diphenyl ketyl
(hydrocarbons, diethyl ether, THF) or CaH2 (dichloromethane)
and distilled under nitrogen before use. The reactions were
carried out under nitrogen, using Schlenk-vacuum-line tech-
niques, and were routinely monitored by solution IR spectros-
copy (carbonyl stretching region) and/or spot TLC. IR spectra
were recorded in solution on a Perkin-Elmer Paragon 1000 FT
1
spectrophotometer. H NMR spectra were run on a Bruker
DPX-300 instrument, using the dichloromethane solvent reso-
nance as internal standard (δ 5.30). Microanalyses were ob-
tained from the University of Oviedo Analytical Service. (þ)-
FAB mass spectra were obtained from the University of Santia-
go de Compostela Mass Spectrometric Service; data given refer
to the most abundant molecular ion isotopomer.
[Ru3(μ-H)(μ-K2N1,C6-pym)(CO)10] (1) and [Ru3(μ-H)(μ-κ2N1,
C2-pym)(CO)10] (2). A solution of [Ru3(CO)12] (500 mg, 0.782
mmol) and pyrimidine (68 μL, 0.860 mmol) in THF (50 mL) was
stirred at reflux temperature for 2.5 h. The solvent was removed
under reduced pressure, and the resulting residue was redis-
solved in dichloromethane (4 mL). This solution was supported
on preparative silica gel TLC plates. Hexane/diethyl ether (2/1)
eluted three yellow bands. The first one contained a small
amount of [Ru3(CO)12]. The second and third bands contained
compounds 1 (190 mg, 37%) and 2 (134 mg, 26%), respectively.
Data for 1 are as follows. Anal. Calcd for C14H4N2O10Ru3
(663.40): C, 25.35; H, 0.61; N, 4.22. Found: C, 25.42; H, 0.66; N,
4.18. (þ)-FAB MS: m/z 665 [M]þ. IR (CH2Cl2): νCO 2101 (w), 2064
(s), 2051 (vs), 2024 (m), 2012 (m), 1983 (sh). 1H NMR (CD2Cl2, 293
K): δ 8.51 (d, J = 1.6 Hz, 1 H, CH), 7.99 (d, J = 5.0 Hz, 1 H, CH),
7.49 (dd, J = 5.0, 1.6 Hz, 1 H, CH), -14.53 (s, 1 H, μ-H). 13C{1H}
NMR (CD2Cl2, 293 K): δ 207.4 (CO), 205.9 (CO), 200.7 (CO),
200.4 (CO), 199.2 (2 COs), 195.6 (CO), 195.4 (CO), 191.7 (CO),
190.8 (CO), 189.4 (C), 160.5 (CH), 150.0 (CH), 136.0 (CH).
Data for 2 are as follows. Anal. Calcd for C14H4N2O10Ru3
(663.40): C, 25.35; H, 0.61; N, 4.22. Found: C, 25.34; H, 0.61; N,
4.17. (þ)-FAB MS: m/z 665 [M]þ. IR (CH2Cl2): νCO 2101 (w),
1
2064 (s), 2051 (vs), 2024 (m), 2012 (m), 1983 (sh). H NMR
4
1
1
2
2
0
0
[Ru6(μ-H)2{μ6-K N ,N ,C ,C -(4,60-bipymMe2)}(CO)18
]
(CD2Cl2, 293 K): δ 8.44 (dd, J = 4.8, 2.4 Hz, 1 H, CH), 8.07 (dd,
J = 5.6, 2.4 Hz, 1 H, CH), 6.86 (dd, J = 5.6, 4.8 Hz, 1 H,
CH), -14.48 (s, 1 H, μ-H). 13C{1H} NMR (CD2Cl2, 293 K): δ
207.9, 205.9, 200.8, 200.6, 195.4, 195.1, 194.5, 192.3, 191.2, 189.6
(10 COs), 185.9 (C), 157.7 (CH), 155.7 (CH), 117.3 (CH).
[Ru3(μ-H)(μ-K2N1,C6-pymMe)(CO)10][BF4] (3[BF4]). Solid
[Me3O][BF4] (200 mg, 1.352 mmol) was added to a solution of
compound 1 (190 mg, 0.286 mmol) in dichloromethane (40 mL).
After it was stirred at room temperature for 24 h, the solution
changed from yellow to orange and contained some orange
solid. The solvent was removed under reduced pressure, and the
resulting residue was redissolved in acetone (2 ꢀ 15 mL). The
filtered solution was evaporated to dryness, and the residue was
washed with diethyl ether (2 ꢀ 10 mL) to give 3[BF4] as a yellow
4
1
1
2
2
0
(Isomers 7 and 8) and [Ru6(μ-H)2{μ6-κ N ,N ,C ,C -(4,40-
bipymMe2)}(CO)18] (Isomer 9). Solid cobaltocene (20 mg,
0.105 mmol) was added to a solution of 4[BF4] (80 mg,
0.105 mmol) in THF (30 mL). The color changed immediately
from yellow to dark orange. After it was stirred for 10 min, the
mixture was concentrated to ca. 3 mL and the resulting solution
was supported on silica gel TLC plates. Hexane/dichloro-
methane (2/1) eluted seven yellow bands. The first one contained
a small amount of [Ru3(CO)12]. The second and third bands con-
tained compounds 7 (6 mg, 8%) and 8 (6 mg, 8%), respectively. The
fourth and fifth bands contained small amounts of mixtures of un-
identified compounds. The sixth band contained compound 9(12mg,
18%). The seventh band contained a small amount of compound 2.
0

1156 Organometallics, Vol. 30, No. 5, 2011
Cabeza et al.
Data for 7 are as follows. Anal. Calcd for C28H14N4O18Ru6
(1300.86): C, 25.85; H, 1.08; N, 4.31. Found: C, 25.92; H, 1.15;
N, 4.24. (þ)-FAB MS: m/z 652 [M/2]þ. IR (CH2Cl2): νCO 2083
(w), 2050 (vs), 2034 (s), 2001 (m, br), 1972 (w, sh), 1953 (w, sh).
1H NMR (CD2Cl2, 293 K): δ 6.22 (d, J = 8.0 Hz, 1 H, CH), 5.38
(d, J = 7.5 Hz, 1 H, CH), 4.98 (dd, J = 8.0, 5.1 Hz, 1 H, CH),
4.67 (dd, J = 7.5, 4.3 Hz, 1 H, CH), 4.30 (d, J = 4.3 Hz, 1 H,
CH), 3.93 (d, J = 5.1 Hz, 1 H, CH), 3.29 (s, 3 H, NCH3), 3.24 (s,
3 H, NCH3), -14.06 (s, 1 H, μ-H), -15.45 (s, 1 H, μ-H). 13C{1H}
and DEPT NMR (CD2Cl2, 293 K): δ 210.1 (C), 204.3 (br, COs),
200.3 (br, COs), 193.5 (br, COs), 192.5 (br, COs), 173.5 (C),
145.2 (CH), 131.2 (CH), 103.7 (CH), 103.3 (CH), 75.6 (CHR),
67.9 (CHR), 44.2 (NCH3), 43.1 (NCH3).
using Becke’s three-parameter hybrid exchange-correlation
functional30 and the B3LYP nonlocal gradient correction.31
The LanL2DZ basis set, with relativistic effective core poten-
tials, was used for the Ru atoms.32 The basis set used for the
remaining atoms was 6-31G, with addition of (d,p)-polari-
zation.33 The optimized structures were confirmed as energy minima
by analytical calculation of frequencies (all positive eigenvalues).
Molecular orbital data were obtained from the natural bond order
(NBO) analysis of the data.34 Cartesian atomic coordinates for the
optimized structures are given in the Supporting Information.
X-ray Diffraction Analyses. Diffraction data for 4[BF4] were
collected on a Nonius Kappa-CCD diffractometer, using gra-
phite-monochromated Mo KR radiation. A semiempirical ab-
sorption correction was performed with SORTAV.35 Diffrac-
Data for 8 are as follows. Anal. Calcd for C28H14N4O18Ru6
(1300.86): C, 25.85; H, 1.08; N, 4.31. Found: C, 25.94; H, 1.14; N,
4.22. (þ)-FAB MS: m/z 652 [M/2]þ. IR (CH2Cl2): νCO 2083 (w),
tion data for 5, 6, 7 CH2Cl2, and 8 were collected on a Oxford
3
Diffraction Xcalibur Nova diffractometer, using graphite-
monochromated Cu KR radiation. Empirical absorption cor-
rections were applied using the SCALE3 ABSPACK algorithm
as implemented in the program CrysAlis Pro RED.36 Structures
were solved by Patterson interpretation using the program
DIRDIF.37 Isotropic and full-matrix anisotropic least-squares
refinements were carried out using SHELXL.38 After many
crystallization attempts, low-quality crystals of compound 6
were obtained from CH2Cl2/hexane. Its molecular structure
could be completely solved from one of these crystals, but
anisotropic refinement led to nonpositive-definite ellipsoids
for several atoms. Therefore, all nonruthenium atoms were
isotropically refined in the final model. All non-H atoms of all
the other structures were refined anisotropically. Hydride atom
positions were calculated with the program XHYDEX.39 The
remaining hydrogen atoms were set in calculated positions and
refined riding on their parent atoms. The molecular plots were
made with the PLATON program package.40 The WINGX
program system41 was used throughout the structure determi-
nations. A selection of crystal, measurement, and refinement
data is given as Supporting Information. CCDC deposition
numbers: 807868 (4[BF4]), 807869 (5), 807870 (6), 807871
1
2050 (vs), 2033 (s), 2002 (m, br), 1972 (w, sh), 1953 (w, sh). H
NMR (CD2Cl2, 293 K): δ 6.25 (d, J = 7.7 Hz, 1 H, CH), 5.44 (dd,
J = 7.9, 1.0 Hz, 1 H, CH), 5.00 (dd, J = 7.7, 5.5 Hz, 1 H, CH), 4.54
(dd, J = 7.9, 4.0 Hz, 1 H, CH), 4.21 (ddd, J = 4.3, 4.0, 1.0 Hz, 1 H,
CH), 3.40 (dd, J = 5.5, 4.3 Hz, 1 H, CH), 3.37 (s, 3 H, NCH3), 3.21
(s, 3 H, NCH3), -13.96 (s, 1 H, μ-H), -15.07 (s, 1 H, μ-H).
13C{1H} and DEPT NMR (acetone-d6, 293 K): δ 208.8 (C),
205.4 (C), 205.1 (br, COs), 204.4 (br, COs), 202.4 (br, COs), 195.2
(br, COs), 193.8 (br, COs), 147.3 (CH), 131.8 (CH), 106.4 (CH),
101.8 (CH), 68.5 (CHR), 66.5 (CHR), 43.6 (NCH3), 42.9 (NCH3).
Data for 9 are as follows. Anal. Calcd for C28H14N4O18Ru6
(1300.86): C, 25.85; H, 1.08; N, 4.31. Found: C, 25.92; H, 1.13;
N, 4.25. (þ)-FAB MS: m/z 652 [M/2]þ. IR (CH2Cl2): νCO
2083 (w), 2057 (vs), 2032 (s), 2001 (m, br), 1972 (w, sh), 1952
(w, sh). 1H NMR (CD2Cl2, 293 K): δ 5.49 (d, J = 7.3 Hz, 1 H,
CH), 5.45 (dd, J = 7.7, 1.3 Hz, 1 H, CH), 4.73 (dd, J = 7.7, 3.2
Hz, 1 H, CH), 4.65 (m, 2 H, CH), 4.37 (m, 1 H, CH), 3.45 (s, 3 H,
NCH3), 3.40 (s, 3 H, NCH3), -14.04 (s, 1 H, μ-H), -14.05 (s,
1 H, μ-H). 13C{1H} and DEPT NMR (CD2Cl2, 293 K): δ 210.6
(C), 209.8 (C), 203.9 (br, COs), 195.3 (br, COs), 195.1 (br, COs),
147.3 (CH), 146.7 (CH), 101.5 (CH), 100.0 (CH), 59.9 (CHR),
57.7 (CHR), 42.9 (NCH3), 42.5 (NCH3).
(7 CH2Cl2), and 807872 (8).
3
Electrochemical Studies. Cyclic voltammetric measurements
were carried out by using an AUTOLAB-III potentiostat con-
nected to a homemade single-compartment micro cell contain-
ing a 1 mm platinum disk as working electrode, a platinum wire
as auxiliary electrode, and a silver wire as pseudoreference
electrode. All measurements were carried out in deoxygenated
0.1 M [NEt4][BF4] dichloromethane (freshly distilled from CaH2)
solutions. The concentration of each cluster complex analyte
was 0.5 ꢀ 10-3 M. To measure potentials, ferrocene was used as
internal standard. The [FeCp2]0/þ couple was referenced to
Acknowledgment. This work has been supported by
the European Union (FEDER grants) and the Spanish
MICINN (projects CTQ2007-60865 and MAT2006-
1997) and Principado de Asturias (project IB09-093).
Fellowships from the University of Oviedo and Princi-
pado de Asturias (to V.P.) are gratefully acknowledged.
Supporting Information Available: Atomic coordinates of the
structures optimized by DFT calculations (Tables S1 and S2), a
selection of crystal, measurement, and refinement data for the
compounds studied by X-ray diffraction (Table S3), and CIF
files giving crystallographic data. This material is available free
of charge via the Internet at http://pubs.acs.org.
E1/2 = 0.59 V versus SCE. As the reductions of both 3[BF4] and
4[BF4] were completely irreversible, the given Ered values corre-
spond to the reduction peaks at the corresponding scan rate.
Theoretical Calculations. Density functional theory (DFT)
calculations were carried out with the Gaussian03 package,29
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A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma,
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