Activation of open-cage fullerenes with ruthenium carbonyl clusters

Article abstract of DOI:10.1002/chem.201304186

Reactions of the open-cage fullerene C₆₃NO₂(Py)(Ph) ₂ (1) with [Ru₃(CO)₁₂] produce [Ru ₃(CO)₈(μ,η⁵-C₆₃NO ₂(Py)(Ph)₂)] (2), [Ru₂

Full text of DOI:10.1002/chem.201304186

DOI: 10.1002/chem.201304186
Communication
&
Cluster Compounds
Activation of Open-Cage Fullerenes with Ruthenium Carbonyl
Clusters
Chi-Shian Chen, Yu-Fang Lin, and Wen-Yann Yeh*[a]
In memory of Duward F. Shriver
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Abstract: Reactions of the open-cage fullerene
C63NO2(Py)(Ph)2 (1) with [Ru3(CO)12] produce [Ru3(CO)8(m,h5-
C63NO2(Py)(Ph)2)] (2), [Ru2H(CO)3(m,h7-C63N(Py)(Ph)(C6H4))]
(3), and [Ru(CO)(Py)2(h3-C63NO2(Py)(Ph)2)] (4), in which the
orifice sizes are modified from 12 to 8, 11, and 15-mem-
bered ring, through ruthenium-mediated CÀO and CÀC
bond activation and formation.
markably, the two ketone carbons of 1A are coupled to gener-
ate a vicinal dioxyl species, and the orifice of the open-cage
fullerene is changed to an 8-membered ring [Eq. (2)]. Similar
coupling of two adjacent carbonyl groups in an open-cage full-
erene compound under different conditions has been report-
ed.[9,21] The MALDI mass spectrum of 2 shows the molecular
ion peaks around m/z 1563, corresponding to combination of
1A and a [Ru3(CO)8] segment. An ORTEP diagram of 2, depict-
ed in Figure 1, consists of an open triangular [Ru3(CO)8] cluster
The discovery of fullerenes in 1985 marked the beginning of
a new field of chemical research,[1] and subsequent work has
been extensive thereafter.[2] Apart from fullerene adducts,[3] en-
dofullerenes,[4] and heterofullerenes,[5] open-cage fullerenes
present the fourth fundamental research topic of modified ful-
lerenes, whereby one or more bonds are removed chemically
to expose an orifice.[6] In this way, it is possible to insert into
them atoms or small molecules, such as noble gases (He, Ar,
Kr),[7,8] H2,[7,9] N2,[7a] H2O,[10] CO,[7,11] NH3,[12] and CH4.[13] Moreover,
they have been considered as new spherical molecules with
unique properties different from the closed fullerenes and
might find applications in photovoltaic components, electron-
ics, biomedicines, and molecular storage.[14] The first open-cage
fullerene was reported in 1995 by Wudl and co-workers.[15]
Since then, several methods for opening the fullerene cages
and expanding the orifice sizes have been developed, which
are mainly progressed by organic reactions and chalcogen re-
agents.[16] Recently, attachment of organometallic fragments to
fullerene cores becomes an important area within fullerene
chemistry.[17] One of the most fascinating aspects pertaining to
organometallic chemistry concerns the activation of organic
substrates at metal centers.[18] In particular, transition-metal
clusters have attracted increasing attention because of their
multimetal center activity in reactions involving substrates,
which are not activated by monometallic species.[19] This
unique feature should be applicable to tuning the orifice sizes
of open-cage fullerenes, too. Herein, we present the reactions
of [Ru3(CO)12] and C63NO2(Py)(Ph)2 to give mono-, di-, and tri-
ruthenium complexes, accompanied by variation of the fuller-
ene cavities.
Figure 1. Molecular structure of 2 with thermal elliposids shown at 30%.
The elegant open-cage fullerene, C63NO2(Py)(Ph)2 (1), con-
taining a 12-membered heterocyclic ring, was prepared by
treating C63N(Py)(Ph)2 with singlet-oxygen (1O2) according to
the method reported by Komatsu and co-workers.[20] Two iso-
mers, 1A and 1B, were obtained from cleavage of the C=C
double bond at the 3,4- and 5.6-position, respectively [Eq. (1)].
Reaction of 1A and equimolar [Ru3(CO)12] in chlorobenzene
at reflux for 30 min gave the cluster complex [Ru3(CO)8(m,h5-
C63NO2(Py)(Ph)2)] (2) in 24% yield after purification by TLC
(silica gel) and recrystallization from benzene/methanol. Re-
linked to the dioxyl, imine, and one 6:6-ring junction of the
modified fullerene. The metal parts contain 50 valence elec-
trons and require only two RuÀRu bonds to satisfy the 18-elec-
tron rule, with Ru1ÀRu3 2.7299(5) ꢁ slightly shorter than
Ru2ÀRu3 2.7614(5) ꢁ. Each ruthenium atom adopts a distorted
octahedral coordination. The Ru1 and Ru2 atoms are each as-
sociated with two terminal carbonyl ligands trans to the bridg-
ing oxygen atoms. The RuÀCO distances to Ru1 and Ru2
atoms, averaged 1.851(4) ꢁ, are significantly shorter than those
to the Ru3 atom, averaged 1.937(5) ꢁ. This can be ascribed to
an enhanced p back-donation from the Ru1 and Ru2 atoms,
which are linked to the stronger net electron-donating alkoxyl
ligands compared with CO, and/or trans influence of the alkox-
yl groups. The C9=C10 ring junction is coordinated to Ru1
atom asymmetrically with Ru1ÀC9 2.508(3) ꢁ and Ru1ÀC10
2.299(3) ꢁ. The imine linkage C24-C31-N1-C43 is about planar
(Æ0.02 ꢁ), in which the lone-paired electrons in nitrogen atom
[a] Dr. C.-S. Chen, Y.-F. Lin, Dr. W.-Y. Yeh
Department of Chemistry, National Sun Yat-Sen University
Kaohsiung 804 (Taiwan)
Fax: (+886)7-5253908
E-mail: wenyann@mail.nsysu.edu.tw
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304186.
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are donated to the Ru2 metal, with N1ÀRu2 2.220(3) ꢁ. The
Ru2 atom is 1.20 ꢁ away from the imine plane, with the tor-
sional angle C24-C31-N1-Ru2 138.0(4)8. It is important to
notice that the C11ÀC12 distance 1.670(5) ꢁ is unusually long
in comparison with normal carbon–carbon single bonds
(1.54 ꢁ), likely due to steric constraints of the dioxyl addends
to bridge two Ru atoms oppositely.
Compound 2 is robust enough to remain intact by heating
at reflux in chlorobenzene for several hours. A well thermal re-
action was achieved by pyrolyzing solid 2 at 3508C under
vacuum for 30 min, from which the dinuclear complex
[Ru2H(CO)3(m,h7-C63N(Py)(Ph)(C6H4))] (3) was isolated in 40%
yield after purification [Eq. (3)].
Figure 2. Molecular structure of 3 with thermal elliposids shown at 30%.
nation site, was not located but is believed to bind the Ru2
atom to satisfy the 18-electron rule. Therefore, the coordina-
tion around the Ru2 atom can be viewed as a four-legged
piano stool (including the hydride ligand) by considering the
(Ru1, N2, C10, C11, C12) unit as a metala-heterocyclopenta-
dienyl ring to bind the Ru2 atom in an h5-fashion, with Ru2À
N2 2.16(1), Ru2ÀC10 2.20(1), Ru2ÀC11 2.40(1), and Ru2ÀC12
2.46(1) ꢁ. The coordinated imine C10ÀN2 distance 1.35(2) ꢁ is
elongated by 0.09 ꢁ in comparison with the C31ÀN1 bond in
2, and the phenyl C11ÀC12 bond lengths 1.46(2) ꢁ is 0.12 ꢁ
longer than the C13ÀC14 and C15ÀC16 bonds (averaging
1.34(2) ꢁ), likely due to back donation from the Ru2 metal to
the p* orbitals of the ligands.
It is interesting that the two C(cage)ÀO bonds of 2 have
been cleaved, and the cage reformation from 1A to 3 is remi-
niscent to the McMurry reaction.[22] The phenyl group connect-
ed to the imine carbon has undergone an ortho-metalation re-
action on one Ru atom. Most strikingly, the other Ru atom is
inserted into the pentagon facing the imine group to generate
an eleven-membered ring. Insertion of a cobalt or an osmium
atom into one pentagon ring of the bisfulleroid C64H4 was pre-
viously described.[16a,23] The MALDI MS spectrum of 3 displays
the molecular ions around m/z 1288, with the isotope distribu-
tion matching a Ru2 pattern. The IR spectrum displays three
carbonyl stretches at u˜ =2032, 1996, and 1971 cmÀ1. The
1H NMR spectrum shows a complicated set of signals in the
range d=9.20–7.05 ppm for the phenyl and pyridyl protons,
and one upfield resonance at d=À6.89 ppm for the terminal
hydride. The ORTEP diagram of 3 is shown in Figure 2. The co-
ordination around the Ru1 atom can be described as a distort-
ed octahedron, which is linked to the Ru2 atom, two terminal
carbonyls, a pyridine, an imine, and a phenyl ring. The
Ru1ÀRu2 bond length, 2.790(2) ꢁ, is slightly longer than those
measured for 2. Three terminal carbonyls are linked to the
ruthenium metals with Ru1ÀC1 1.87(2), Ru1ÀC2 1.92(2), and
Ru2ÀC3 1.90(2) ꢁ. The hydride ligand, which occupies a coordi-
We then investigated the coordination reaction of 1B. It is
surprising that 1B displays a very different reactivity from 1A,
despite that their structures are closely resembling. Heating
1B and [Ru3(CO)12] at reflux in chlorobenzene led to a dark
brown solid, which was extracted with pyridine, purified by
TLC (silica gel, eluting with pyridine/CH2Cl2), and crystallized
from pyridine/n-hexane to give black crystals of [Ru(CO)-
(C5H5N)2(h3-C63NO2(Py)(Ph)2)] (4) in 46% yield [Eq. (4)]. In this re-
action, the Ru3 cluster is fragmented to become a mononuclear
complex, and the Ru atom is inserted into the pentagon far
away from the imine group, forming an orifice with a 15-mem-
bered ring. The IR spectrum of 4 in CH2Cl2 displays an absorp-
tion at u˜ =1936 cmÀ1 for the terminal carbonyl, and two ab-
sorptions at 1736 and 1605 cmÀ1 corresponding to the free
and coordinated ketone stretch, respectively. The ORTEP dia-
gram of 4 is depicted in Figure 3. The coordination around the
Ru1 atom can be described as a distorted octahedron, which is
bonded to a terminal carbonyl, two pyridines, and a ketone
and two carbon atoms of the fullerene cage. The ketone con-
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Figure 3. Molecular structure of 4 with thermal elliposids shown at 30%.
nected to the ruthenium atom has the bond lengths O2ÀRu1
2.124(5) and O2ÀC12 1.279(8) ꢁ, whereas the uncoordinated
ketone O3ÀC44 bond lengths is 1.200(8) ꢁ. The C38ÀC42 edge
has been broken by oxidative insertion of the ruthenium atom
with Ru1ÀC38 1.971(7) and Ru1ÀC42 2.040(7) ꢁ, and the non-
bonding C38···C42 distance is 2.56(6) ꢁ. The 15-membered ring
orifice traverses 6.60 ꢁ from C27 to C40 atoms, which is close
to the diameter of C60 (7.1 ꢁ)[2a] and 4.67 ꢁ from C13 to C43
atoms.
Figure 4. Cyclic voltammograms for 1A-4 in o-dichlorbenezene. The poten-
tials are versus the Fc/Fc+ couple.
such as b-elimination and oxidative cleavage at the last
stage.[22] Our preliminary studies revealed that treating com-
plexes 2–4 with H2O2 or I2 can result in decomposition of the
ruthenium complexes and release new open-cage fullerenes.
Characterization of these fullerene derivatives is in progress
and will be described elsewhere.
In conclusion, three new ruthenium complexes of open-cage
fullerenes were prepared and structurally characterized. The
transformation from 1 to 4 is of interest within the context of
the chemistry of fullerenes and of the ability of transition-
metal clusters to promote fullerene-cage modification. It may
provide an attractive general strategy for tuning the orifice
sizes of open-cage fullerenes. Recently, preparation of endohe-
dral fullerenes encapsulating transition metals in isolable and
stable form remains great challenges to chemists. Traditional
metal/graphite laser and arc evaporation methods are limited
in the fullerene size and low product yield.[26] An alternative
approach by opening the fullerene cages, followed by metal
complexation and insertion, might provide a promising path-
way, in which the orifice size is an important factor. We are cur-
rently investigating the activity of 2–4 with an aim to include
ruthenium atom(s) inside the fullerene cages.
The electrochemical properties of 1A-4 were studied by
cyclic voltammetry (CV) in dry, oxygen-free o-dichlorobenzene
solution at 278C (Figure 4). Within the solvent cutoff, C60,
C63N(Py)(Ph)2, 1A, and 1B exhibited four quasi-reversilbe redox
waves in the negative scan upon CV.[24] Complex 2 also dis-
plays four reduction waves at E1/2 =À1095, À1463, À1904, and
À2201 mV (vs. Fc/Fc+ couple), which are shifted anodically by
approximately 200 mV compared to C63N(Py)(Ph)2 (the parent
compound having a similar eight-membered ring; see [Eq. (1)])
and may be ascribed to the presence of two electron-with-
drawing oxyl addends and/or delocalization of negative charg-
es to the Ru3 cluster, making the fullerene cage more ease to
reduce. In contrast, complexes 3 and 4 have a ruthenium atom
inserted into the fullerene rim to form metallofullerenes with
distinct skeletons. Their LUMO might carry some Ru characters
and are different from 2, thus, presenting dissimilar CV profiles.
Modern organic syntheses often involve several transition-
metal-catalyzed steps.[25] Frequently, the functionalized organic
substrates are released from metal by numerous methods,
Experimental Section
Details on the reaction procedures, characterization data, and
structural determination for 2–4 are given in the Supporting Infor-
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These data can be obtained free of charge from The Cambridge
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Acknowledgements
The authors are grateful for support of this work by the Na-
tional Science Council of Taiwan and thank Mr. Ting-Shen Kuo
(National Taiwan Normal University, Taipei) for X-ray diffraction
analysis.
Keywords: CÀC activation · cluster compounds · fullerenes ·
ruthenium · structure elucidation
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Received: October 27, 2013
Published online on January 2, 2014
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