Synthetic, electrochemical, and theoretical studies of tetrairidium clusters bearing mono- and bis[60]fullerene ligands

Article abstract of DOI:10.1021/ja0616027

Heating a mixture of lr₄(CO)₉(PPh₃) ₃ (1) and 2 equiv of C₆₀ in refluxing chlorobenzene (CB) affords a butterfly tetrairidium-C₆₀ complex lr ₄(CO)₆{μ₃-κ³-PPh ₂(o-C₆H₄)P(o-C₆H₄) PPh(η¹-o-C⁶H⁴}}-(μ₃- η²:η²-C₆₀) (3, 36%). Brief thermolysis of 1 in refluxing chlorobenzene (CB) gives a butterfly complex lr₄(CO)₈{μ-k²-PPh₂(o-C ₆H₄)PPh}{μ₃-PPh₂(η ¹:η²-o-C₆H₄)} (2, 64%) that is both ortho-phosphorylated and ortho-metalated. Interestingly, reaction of 2 with 2 equiv of C₆₀ in refluxing CB produces 3 (41%) by C ₆₀-assisted ortho-phosphorylation, indicating that 2 is the reaction intermediate for the final product 3. On the other hand, reaction of lr ₄(CO)₈(PMe₃)4 (4) with excess (4 equiv) C ₆₀ in refluxing 1,2-dichlorobenzene, followed by treatment with CNCH₂Ph at 70 °C, affords a square-planar complex with two C ₆₀ ligands and a face-capping methylidyne ligand, lr ₄(CO)₃(μ₄-CH)(PMe₃) ₂(μ-PMe₂)(CNCH₂Ph)(μ-η²: η²-C₆₀)(μ₄-η¹: η¹:η²:η²-C₆₀) (5, 13%) as the major product. Compounds 2, 3, and 5 have been characterized by spectroscopic and microanalytical methods, as well as by single-crystal X-ray diffraction studies. Cyclic voltammetry has been used to examine the electrochemical properties of 2, 3, 5, and a related known butterfly complex lr₄(CO)₆(μ-CO){μ₃-k ²-PPh₂(o-C₆H₄)P(η¹-o- C₆H₄)}(η₃-η²: η²:η²-C₆₀) (6). These cyclic voltammetry data suggest that a C₆₀-mediated electron transfer to the iridium cluster center takes place for the species 3^3- and 6 ^2- in compounds 3 and 6. The cyclic voltammogram of 5 exhibits six well-separated reversible, one-electron redox waves due to the strong electronic communication between two C₆₀ cages through a tetrairidium metal cluster spacer. The electrochemical properties of 3, 5, and 6 have been rationalized by molecular orbital calculations using density functional theory and by charge distribution studies employing the Mulliken and Hirshfeld population analyses.

Full text of DOI:10.1021/ja0616027

Published on Web 08/05/2006
Synthetic, Electrochemical, and Theoretical Studies of
Tetrairidium Clusters Bearing Mono- and Bis[60]fullerene
Ligands
Bo Keun Park,† Gaehang Lee,† Kyoung Hoon Kim,‡ Hongkyu Kang,†
Chang Yeon Lee,† Md. Arzu Miah,† Jaehoon Jung,‡ Young-Kyu Han,*,‡ and
Joon T. Park*,†
Contribution from the Department of Chemistry and School of Molecular Science (BK 21),
Korea AdVanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Korea, and
Computational Chemistry Laboratory, AdVanced Materials R&D, LG Chem, Ltd. Research Park,
Daejeon, 305-380, Korea
Received March 16, 2006; E-mail: joontpark@kaist.ac.kr.; ykhan@lgchem.com
Abstract: Heating a mixture of Ir4(CO)9(PPh3)3 (1) and 2 equiv of C60 in refluxing chlorobenzene (CB)
affords a “butterfly” tetrairidium-C60 complex Ir4(CO)6{µ3-κ3-PPh2(o-C6H4)P(o-C6H4)PPh(η1-o-C6H4)}-
(µ3-η2:η2:η2-C60) (3, 36%). Brief thermolysis of 1 in refluxing chlorobenzene (CB) gives a “butterfly” complex
Ir4(CO)8{µ-k2-PPh2(o-C6H4)PPh}{µ3-PPh2(η1:η2-o-C6H4)} (2, 64%) that is both ortho-phosphorylated and
ortho-metalated. Interestingly, reaction of 2 with 2 equiv of C60 in refluxing CB produces 3 (41%) by C60-
assisted ortho-phosphorylation, indicating that 2 is the reaction intermediate for the final product 3. On the
other hand, reaction of Ir4(CO)8(PMe3)4 (4) with excess (4 equiv) C60 in refluxing 1,2-dichlorobenzene,
followed by treatment with CNCH2Ph at 70 °C, affords a square-planar complex with two C60 ligands and
a face-capping methylidyne ligand, Ir4(CO)3(µ4-CH)(PMe3)2(µ-PMe2)(CNCH2Ph)(µ-η2:η2-C60)(µ4-η1:η1:η2:η2-
C60) (5, 13%) as the major product. Compounds 2, 3, and 5 have been characterized by spectroscopic and
microanalytical methods, as well as by single-crystal X-ray diffraction studies. Cyclic voltammetry has been
used to examine the electrochemical properties of 2, 3, 5, and a related known “butterfly” complex
Ir4(CO)6(µ-CO){µ3-k2-PPh2(o-C6H4)P(η1-o-C6H4)}(µ3-η2:η2:η2-C60) (6). These cyclic voltammetry data suggest
that a C60-mediated electron transfer to the iridium cluster center takes place for the species 33- and 62-
in compounds 3 and 6. The cyclic voltammogram of 5 exhibits six well-separated reversible, one-electron
redox waves due to the strong electronic communication between two C60 cages through a tetrairidium
metal cluster spacer. The electrochemical properties of 3, 5, and 6 have been rationalized by molecular
orbital calculations using density functional theory and by charge distribution studies employing the Mulliken
and Hirshfeld population analyses.
Introduction
electrochemical properties of these complexes, and ultimately
to develop new electronic nanomaterials and nanodevices.3
Considerable research efforts have been devoted to [60]-
fullerene (C60), the most abundant representative of the fullerene
family, due to its potential application in materials science such
as optical, magnetic, electronic, catalytic, and biological fields.1
In recent years, seminal results with C60 research have been
achieved in various areas of light emitting diodes,2a nonlinear
optics,2b organic ferromagnets,2c superconductors,2d photovoltaic
cells,2e nitrogen fixation,2f and interaction with biological
targets.2g,h In particular, we have been interested in C60-metal
cluster exohedral metallofullerene complexes in order to inves-
tigate and understand the effects of metal cluster coordination
on the chemical and physical properties of C60, reactivities and
Metal clusters can potentially accommodate all the known
C60 π-bonding modes such as η2-,4 µ-η2:η2-,5 and η5-types,6
but the interaction of C60 with cluster framework has been
dominated by the face-capping cyclohexatriene-like, µ3-η2:η2:
η2-C60, bonding mode.3a The C60-metal cluster complexes with
(2) (a) Hutchison, K.; Gao, J.; Schick, G.; Rubin, Y.; Wudl, F. J. Am. Chem.
Soc. 1999, 121, 5611-5612. (b) Kuang, L.; Chen, Q.; Sargent, E. H.; Wang,
Z. Y. J. Am. Chem. Soc. 2003, 125, 13648-13649. (c) Makarova, T. L.;
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36, 807-815. (h) Bolskar, R. D.; Benedetto, A. F.; Husebo, L. O.; Price,
R. E.; Jackson, E. F.; Wallace, S.; Wilson, L. J.; Alford, J. M. J. Am. Chem.
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† Korea Advanced Institute of Science and Technology (KAIST).
‡ LG Chem, Ltd. Research Park.
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Goedert, R.; Templeton, D. Appl. Phys. Lett. 1994, 64, 2785-2787. (c)
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9
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J. AM. CHEM. SOC. 2006, 128, 11160-11172
10.1021/ja0616027 CCC: $33.50 © 2006 American Chemical Society

Tetrairidium Clusters Bearing Fullerene Ligands
A R T I C L E S
this relatively strong bonding mode exhibited remarkable
thermal and electrochemical stabilities, uniquely suitable for
various device applications3a in contrast to other previously
known C60-metal complexes. We have been interested in the
conversion of the existing C60 bonding modes to new ones, as
well as in the interconversion among them by changing the
coordination sphere of the metal cluster centers in C60-metal
cluster complexes. Our studies have revealed that π-type species
can transform into new σ-π mixed-type ones with µ3-η1:η2:
η1-C60 and µ3-η1:η1:η2-C60 ligands by modifying the coordina-
tion sphere of metals in the cluster, that is, the C60 bonding
mode can be remote-controlled by changing the metal cluster
environment.7 The C60-metal σ-complexes are known to be
very important starting materials for the selective functional-
ization of C60. By employing similar approaches, we have
observed the elusive µ-η2:η2-C60 bonding mode in the cluster
regime and furthermore have shown that the two bonding modes,
µ-η2:η2-C60 and µ3-η2:η2:η2-C60, are reversibly interconvertible
on an Os5C cluster framework.8 More importantly, we have
demonstrated an interesting strong electronic communication
between C60 and metal cluster centers, which can be readily
fine-tuned by control of electronic properties of the attached
ligands on the metal cluster center.3a In our previous work,
electrochemical studies of C60 derivatives of Re3,9 Os3,10 and
Rh611 clusters have revealed electronic communication between
cages. Thus far, however, a weak, through-space electronic
12
communication has been observed only for C120
,
C
120C,13
C
120O,14
C
120(CH2)2,15 and C120Si(C6H5)2,16 where the fullerenes
are directly bonded to each other or are separated by a single-
atom spacer such as carbon, oxygen, and silicon atoms. For
organic-based bisfullerenes with longer spacers, on the other
hand, no electronic communication has been observed.17 Inser-
tion of organic spacers between the two C60 cages results in
the transformation of the hybridization of C60 carbon atoms
involved in the spacer binding from sp2 to sp3, and consequently,
the electronic communication is possible only through space
via overlapped π-orbitals from the two separate C60 cages.
The C60-metal π-interaction in the µ3-η2:η2:η2-C60-metal
clusters little perturbs the C60 hybridization, as evidenced by
our earlier studies on the self-assembled monolayers,18 the
photovoltaic cell device application,19 and the X-ray structural
characterization of C60-metal cluster π-complexes.3a Thus, the
electronic properties of bisfullerene complexes with a metal
cluster spacer are expected to be drastically different from those
of organic-based bisfullerenes. In addition, C60-metal cluster
sandwich compounds should serve as direct models for two
carbon nanotubes connected by a heterogeneous inorganic
junction such as metal nanoparticles. We have recently dem-
onstrated that electron-withdrawing C60 cages can be connected
by a cluster bridge of octahedral hexarhodium, when the cluster
bridge is coordinated with electron-donating phosphine ligands.11
Cyclic voltammetric and theoretical studies of this bisfullerene-
Rh6 cluster sandwich complex, Rh6(CO)5(dppm)2(CNCH2Ph)-
(µ3-η2:η2:η2-C60)2, have shown the presence of unusually strong
electronic communication between the two C60 centers through
the hexarhodium cluster spacer, which is far stronger than that
observed for organic-based bisfullerenes (vide infra).11 Closely
following our report of the first hexarhodium bisfullerene
sandwich compound, Tang et al. reported the preparation of
monometallic bisfullerene sandwich compounds, [M(η2-C60)2-
(CO)2(dbcbipy)] (M ) W and Mo, dbcbipy ) 4,4′-di(butylcar-
boxyl)-2,2′-bipyridine), in which the two trans C60 ligands bind
to a single metal atom in an η2 fashion.20 This compound,
however, is electrochemically very unstable similarly as other
known η2-C60 metal complexes and reveals very weak inter-
fullerene electronic communication comparable to organic-based
bisfullerenes.21
C
60 and the metal cluster and also strong electronic interaction
between C60 cages through metal cluster spacers.
Bisfullerene compounds with two electroactive fullerene
centers are of special interest because the electronic com-
munication between the two C60 centers has practical implica-
tions for future applications. A number of bisfullerene com-
pounds with various organic spacers have been prepared in order
to effect the electronic communication between the two C60
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as Ir4(CO)9(PPh3)3 (1) and Ir4(CO)8(PMe3)4 (4) in the present
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A R T I C L E S
Park et al.
Scheme 1. Structures of 2, 3, 5, and 6a
Scheme 2. Syntheses of 2 and 3a
a Terminal carbonyl ligands are omitted for clarity.
reactions in satisfactory yield (64%). More interestingly, treat-
ment of 2 with 2 equiv of C60 in refluxing CB for 3 h allowed
for the formation of 3 in 41% yield by C60-assisted ortho-
phosphorylation reaction, demonstrating that 2 is indeed the
reaction intermediate leading to the product 3. The synthetic
details for 2 and 3 are given in Scheme 2. Attempted similar
reactions of tristrialkylphosphine-substituted complexes Ir4-
(CO)8(PR3)3 (R ) Me, Et) with C60, however, resulted in only
extensive decomposition of the starting materials. On the other
hand, reaction of the tetrakistrimethylphosphine-substituted
compound, 4, with excess C60 in refluxing 1,2-dichlorobenzene
(DCB) for 2 h afforded a new green band on TLC, presumably
a carbonyl analogue of 5 which could not be further character-
ized because of its marginal solubility after solvent removal.
Subsequent treatment of the carbonyl analogue with CNCH2Ph
at 70 °C for 2 h produced a green benzyl isocyanide-substituted
derivative, 5, as the major product in low yield (13%), which
is soluble enough to be fully characterized. A similar reaction
of the tetrakistriethylphosphine-substituted compound Ir4(CO)8-
(PEt3)4 with C60 gave the hydrido monometallic fullerene Ir(H)-
(CO)(PEt3)2(η2-C60) complex,25 but that of Ir4(CO)8(dppm)2 with
C60 did not afford any isolable product.
a Terminal carbonyl ligands are omitted for clarity.
work. The former reaction affords “butterfly” Ir4(CO)6{µ3-k3-
Ph2P(o-C6H4)PPh(η1-o-C6H4)}(µ3-η2:η2:η2-C60) (3) through the
intermediate of “butterfly” Ir4(CO)8{µ-κ2-Ph2P(o-C6H4)PPh}-
{µ3-PPh2(η1:η2-ï-C6H4)} (2) by a series of ortho-phospho-
rylation and ortho-metalation reactions. The latter reaction
produces a bisfullerene-tetrairidium complex, Ir4(CO)3(µ4-CH)-
(PMe3)2(µ-PMe2)(CNCH2Ph)(µ-η2:η2-C60)(µ4-η1:η1:η2:η2-C60)
(5), after treatment of the insoluble reaction intermediate with
CNCH2Ph. Herein we report the full details of syntheses,
characterization, and electrochemical properties of 2, 3, and 5,
together with electrochemistry of a related known C60-
tetrairidium “butterfly” complex Ir4(CO)6(µ-CO){µ3-κ2-Ph2P-
(o-C6H4)P(η1-o-C6H4)}(µ3-η2:η2:η2-C60) (6)22 (see Scheme 1).
To understand the nature of electronic communication between
C60 and tetrairidium metal cluster center in 3 and 6 and
interfullerene communication through a tetrairidium metal spacer
in 5, we have carried out molecular orbital (MO) calculations
on a set of face-capping C60-tetrairidium cluster complexes,
3, 5, and 6, by density functional theory (DFT) calculations
and charge distribution studies employing the Mulliken (MPA)
and Hirshfeld (HPA) population analyses. Preliminary accounts
of some of this work have already appeared.23,24
Compounds 2, 3, and 5 were formulated on the basis of
elemental analyses and mass spectroscopic data. The FAB+ mass
spectra showed the molecular ion isotope multiplets at m/z 1624
for 2 and 2210 for 3. Attempts to obtain mass spectroscopic
data for 5, however, with FAB+, FAB-, and MALDI-TOF
methods have not been successful. The synthesis and charac-
terization of complex 6 has been discussed in our earlier
account.22
Results and Discussion
Synthesis and Characterization of 2, 3, and 5. Heating of
tristriphenylphosphine-substituted tetrairidium carbonyl cluster
1 with 2 equiv of C60 in refluxing chlorobenzene (CB) for 2 h
after usual workup and chromatographic separation gave a novel
C60-tetrairidium “butterfly” complex with a triphoshine ligand,
3, in relatively low yield (36%). Refluxing 1 in CB briefly
afforded a “butterfly” tetrairidium complex, 2, with a diphos-
phine ligand by ortho-phosphorylation and ortho-metalation
1
The H NMR spectrum of 2 shows multiplets in the region
of δ 8.44-6.51 due to the 33 aromatic protons of five phenyl
and two o-phenylene moieties. The 31P{1H} NMR spectrum
displays two doublets for the diphosphine moiety and a singlet
for the monophosphine group. The low-field doublet at δ 24.2
(2JPP ) 22.1 Hz) accounts for the terminal phosphorus atom on
a “wing-tip” iridium atom, and the high-field doublet at δ -42.9
(22) Park, B. K.; Miah, M. A.; Kang, H.; Lee, K.; Cho, Y.-J.; Churchill, D. G.;
Park, S.; Choi, M.-G.; Park, J. T. Organometallics 2005, 24, 675-679.
(23) Lee, G.; Cho, Y.-J.; Park, B. K.; Lee, K.; Park, J. T. J. Am. Chem. Soc.
2003, 125, 13920-13921.
(24) Park, B. K.; Miah, M. A.; Lee, G.; Cho, Y.-J.; Lee, K.; Park, S.; Choi,
M,-G.; Park, J. T. Angew. Chem. Int. Ed. 2004, 43, 1712-1724.
(25) Compound Ir(H)(CO)(PEt3)2(η2-C60) was fully characterized by spectro-
scopic methods, cyclic voltammetry, and a single-crystal X-ray diffraction
study.
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Tetrairidium Clusters Bearing Fullerene Ligands
A R T I C L E S
Scheme 3 a
(2JPP ) 22.1 Hz) is assigned to the phosphorus atom that bridges
the two “wing-tip” iridium atoms. The singlet at δ 16.4 is
obviously assigned to the phosphorus atom on a “hinge” iridium
atom. The two resonances at δ 24.2 and 16.4 are consistent
with the chemical shift of the terminal phosphorus atom of the
triphenylphosphine ligands bonded to an iridium center, usually
observed in the region of δ -30 to +70.26 The 13C NMR
spectrum exhibits eight signals at δ 186.8, 185.7, 179.6, 176.4,
166.4, 165.7, 165.5, and 163.7 for eight carbonyl groups and
the multiplet resonances around δ 153.2-124.3 assignable to
the 42 aromatic carbon atoms.
1
The H NMR spectrum of 3 shows two sets of multiplet
resonances around δ 8.07-7.14 and 6.93-6.78 for the 27
aromatic protons of three o-phenylene bridges and three phenyl
moieties. The 31P{1H} NMR displays two doublets and a doublet
of doublet (dd) patterns for the three inequivalent phosphorus
atoms of the triphosphine group. The two doublets at δ 31.2
(2JPP ) 12.8 Hz) and at δ 21.5 (2JPP ) 4.0 Hz) are due to the
terminal phosphorus atoms on the two “wing-tip” iridium atoms,
whereas the dd pattern at δ -16.3 (2JPP ) 12.8 Hz, 2JPP ) 4.0
Hz) is assigned to the bridging phosphorus atom. The 13C NMR
spectrum reveals six carbonyl resonances at δ 188.4, 187.3,
179.9, 173.3, 172.4, and 161.2 and signals around δ 158.9-
143.6 for 54 sp2 carbon atoms and at δ 79.1, 68.0, 64.1, 62.7,
61.2, and 60.6 for the six π-bonded sp3 carbon atoms of the
C60 ligand.
a (1) -C6H6; 2) ortho-metalation of a phenyl group on the P3; (3) -C6H6,
-CO; (4) + C60; (5) -C6H6; (6) -2CO. Carbonyl ligands are omitted for
clarity.
singlets at δ 164.3, -44.9, and -47.9. The lowest-field signal
is assigned to the bridging phosphorus atom, commonly
observed in the downfield region of δ 130-300,26 whereas the
two high-field resonances are due to the terminal phosphorus
atoms of the trimethylphosphine ligands which usually appear
in the δ -30 to -70 region.26
The IR spectrum of complex 5 shows a weak absorption band
at 2159 cm-1 for the CN stretch of the benzyl isocyanide ligand
and a strong CO stretch at 1986 cm-1 for the three terminal
carbonyl groups. The 1H NMR spectrum contains a characteristic
doublet far downfield at δ 15.52 (1H, 3JPH ) 13.0 Hz), assigned
to the µ4-CH proton moiety. The phosphorus coupling is
assumed to be due to the phosphorus atom of the bridging
phosphido group, which is located approximately trans to the
methylidyne carbon (vide infra). Similar µ4-CH groups have
been previously reported in various metal clusters such as the
square planar complex Ru2Pt2(µ-H)(µ4-CH)(CO)3(PPri3)2(η5-
C5H5)2 (δH ) 14.87),27 the edge-sharing bitetrahedral complex
Co5Mo2(µ4-CH)(µ5-C)(CO)12(η5-C5H5)2 (δH ) 12.52),28 and the
square pyramidal complex Ru5(µ-H)(µ4-CH)(CO)10(µ-GePh2)2-
(µ3-GePh)2 (δH ) 11.21).29 The downfield region shows a
multiplet around δ 7.66-7.20 for the five aromatic protons of
the benzyl isocyanide ligand. An AB-type doublet around δ 5.18
A plausible reaction mechanism for the conversion of 1 f
2 f 3 is proposed in Scheme 3. The first step is an ortho-
phosphorylation in 1 to form the bidentate diphosphine inter-
mediate A. Ortho-metalation of a phenyl group on the P3 atom
in A results in the Ir1-Ir4 bond rupture to form the hydrido
butterfly intermediate B (62 valence electrons (VEs)); a similar
conversion was previously reported for tetrairidium clusters.22
Binuclear reductive elimination of C6H6 and loss of a carbonyl
ligand in B induces coordination of the P2 atom to the Ir4 center
and π-coordination of the ortho-metalated phenyl ring to the
Ir1 atom to form an η1:η2-o-C6H4 moiety in 2. The next step is
cleavage of the Ir3-P3 bond and subsequent coordination of
η2-C60 to produce the intermediate C. Another ortho-phospho-
rylation reaction in C takes place to form a triphosphine moiety,
and the π-interaction in the η1:η2-o-C6H4 ligand is replaced by
coordination of the P3 atom to the Ir1 center to give the
intermediate D. The final product 3 is produced by the loss of
two carbonyl ligands and formation of face-capping of the C60
ligand in µ3-η2:η2:η2 fashion. In this transformation, three PPh3
ligands are converted to the diphosphine µ-PPh2(o-C6H4)PPh
in 2 and in turn to the triphosphine µ3-PPh2(o-C6H4)P(o-C6H4)-
PPh(η1-o-C6H4) in 3 on the tetrairidium cluster framework by
successive ortho-phosphorylation and ortho-metalation pro-
cesses.
2
(2H, JHH ) 16.5 Hz) accounts for the two diastereotopic
benzylic protons of the benzyl isocyanide ligand. The two
2
2
doublets at δ 2.07 (9H, JPH ) 9.8 Hz) and 1.86 (9H, JPH
)
9.1 Hz) are due to the methyl protons of the two inequivalent
trimethylphosphine ligands. The two sets of doublet at δ 3.55
2
2
(3H, JPH ) 7.0 Hz) and 3.04 (3H, JPH ) 4.6 Hz) have been
assigned to the two diastereotopic methyl groups on the bridging
phosphido moiety. The 31P{1H} NMR spectrum exhibits three
(26) (a) Pregoein, P. S.; Kunz, R. W. 31P and 13C NMR Studies of Transition
Metal Phosphine Complexes; Springer-Verlag: New York, 1979. (b)
Garrou, P. E. Chem. ReV. 1981, 81, 229-266. (c) Goh, L. Y.; Weng, Z.;
Leong, W. K.; Vittal, J. J.; Haiduc, I. Organometallics 2002, 21, 5287-
5291. (d) Ziglio, C. M.; Vargas, M. D.; Braga, D.; Grepioni, F.; Nixon, J.
F. J. Organomet. Chem. 2002, 656, 188-198.
Synthesis of phosphine ligands with P-(C)n-P and P-(C)n-
P-(C)n-P donor sequences is of special interest because of
their ability to bridge metal-metal bonds and thus to stabilize
organometallic or metal cluster complexes. Such phosphine
ligands have usually been prepared by tedious multistep organic
synthesis.30 Instances in which phosphines couple to form a
diphosphine in transition metal complexes are extremely rare,
with only two other examples known, one for a Pd monomer31
(27) (a) Davies, D. L.; Jeffery, J. C.; Miguel, D.; Sherwood, P.; Store, F. G. A.
J. Chem. Soc., Chem. Commun. 1987, 454-456. (b) Davies, D. L.; Jeffery,
J. C.; Miguel, D.; Sherwood, P.; Stone, F. G. A. J. Organomet. Chem.
1990, 383, 463-480.
(28) Adams, H.; Guio, L. V. Y.; Morris, M. J.; Spey, S. E. J. Chem. Soc., Dalton
Trans. 2002, 2907-2915.
(29) Adams, R. D.; Captain, B.; Fu, W. Inorg. Chem. 2003, 42, 1328-1333.
9
J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006 11163

A R T I C L E S
Park et al.
Table 2. Selected Interatomic Distances (Å) and Bond Angles
Table 1. Selected Interatomic Distances (Å) and Bond Angles
(deg) for 2
(deg) for 3
Bond Distances
Bond Distances
Ir(1)-Ir(2)
Ir(2)-Ir(3)
Ir(3)-Ir(4)
Ir(3)-P(3)
Ir(4)-P(1)
Ir(1)-C(706)
P(1)-C(301)
P(3)-C(701)
2.6953(6) Ir(1)-Ir(3)
2.6689(6) Ir(2)-Ir(4)
2.8054(6) Ir(1)-P(2)
2.286(3) Ir(4)-P(2)
2.295(3) Ir(1)-C(701)
2.41(1)
1.81(1)
1.82(1)
2.7170(7)
2.7409(6)
2.297(3)
2.309(3)
2.55(1)
Ir(1)-Ir(2)
Ir(2)-Ir(3)
Ir(3)-Ir(4)
Ir(4)-P(2)
Ir(1)-P(2)
P(1)-C(301)
P(2)-C(401)
P(3)-C(501)
Ir(1)-C(2)
Ir(2)-C(4)
Ir(3)-C(6)
C(2)-C(3)
C(4)-C(5)
C(6)-C(1)
2.7598(8) Ir(1)-Ir(3)
2.8059(7) Ir(2)-Ir(4)
2.8094(7) Ir(4)-P(1)
2.300(2) Ir(1)-P(3)
2.281(2) Ir(2)-C(502)
1.826(9) P(2)-C(306)
1.831(9) P(3)-C(406)
1.812(9) Ir(1)-C(1)
2.222(8) Ir(2)-C(3)
2.150(8) Ir(3)-C(5)
2.161(8) C(1)-C(2)
2.7827(8)
2.7401(9)
2.318(2)
2.282(2)
2.089(8)
1.841(8)
1.807(9)
2.256(8)
2.241(8)
2.303(8)
1.44(1)
Ir(2)-C(706)
P(2)-C(306)
2.08(1)
1.86(1)
Bond Angles
Ir(2)-Ir(1)-Ir(3)
Ir(3)-Ir(2)-Ir(1)
Ir(2)-Ir(3)-Ir(4)
Ir(4)-Ir(3)-Ir(1)
P(2)-Ir(1)-Ir(2)
P(2)-Ir(4)-P(1)
P(1)-Ir(4)-Ir(3)
P(2)-Ir(4)-Ir(2)
P(3)-Ir(3)-Ir(2)
P(3)-Ir(3)-Ir(4)
59.09(2)
60.86(2)
60.03(2)
86.46(2)
76.79(8)
87.3(1)
96.58(8)
75.66(8)
83.51(8)
143.44(8)
Ir(3)-Ir(2)-Ir(4)
Ir(4)-Ir(2)-Ir(1)
Ir(2)-Ir(3)-Ir(1)
Ir(2)-Ir(4)-Ir(3)
P(2)-Ir(1)-Ir(3)
P(2)-Ir(4)-Ir(3)
Ir(1)-P(2)-Ir(4)
P(1)-Ir(4)-Ir(2)
P(3)-Ir(3)-Ir(1)
C(306)-P(2)-Ir(4)
C(301)-P(1)-Ir(4)
P(2)-Ir(1)-C(706)
Ir(3)-Ir(2)-C(706)
62.46(2)
88.20(2)
60.05(2)
57.51(2)
74.04(7)
72.12(7)
110.5(1)
152.18(8)
76.62(8)
106.4(3)
108.3(4)
123.1(3)
93.6(3)
1.49(1)
1.48(1)
1.51(1)
C(3)-C(4)
C(5)-C(6)
1.42(1)
1.43(1)
Bond Angles
Ir(2)-Ir(1)-Ir(3)
Ir(3)-Ir(2)-Ir(1)
Ir(2)-Ir(3)-Ir(4)
Ir(4)-Ir(3)-Ir(1)
P(2)-Ir(1)-Ir(2)
P(2)-Ir(4)-P(1)
P(1)-Ir(4)-Ir(3)
P(2)-Ir(4)-Ir(2)
P(3)-Ir(1)-Ir(2)
P(2)-Ir(1)-P(3)
Ir(4)-P(2)-C(306)
P(2)-C(306)-C(301) 119.2(7)
Ir(1)-P(3)-C(406) 108.8(3)
P(3)-C(406)-C(401) 115.9(7)
Ir(1)-Ir(2)-C(502) 94.7(2)
Ir(2)-C(502)-C(501) 122.6(6)
60.83(1)
59.99(2)
58.42(2)
83.30(2)
77.56 (6) P(2)-Ir(1)-Ir(3)
85.87(8)
101.28(6)
77.67 (6) P(1)-Ir(4)-Ir(2)
85.87(6)
84.53(8)
107.6(3)
Ir(3)-Ir(2)-Ir(4)
Ir(4)-Ir(2)-Ir(1)
Ir(2)-Ir(3)-Ir(1)
Ir(2)-Ir(4)-Ir(3)
60.86(1)
85.02(1)
59.18(2)
60.73(2)
76.57(7)
75.72(6)
108.45(9)
158.00(8)
144.33(6)
108.2(3)
C(301)-C(306)-P(2) 117.8(8)
C(306)-C(301)-P(1) 118.9(9)
P(2)-Ir(4)-Ir(3)
Ir(1)-P(2)-Ir(4)
P(2)-Ir(1)-C(701)
Ir(3)-P(3)-C(701)
145.7(3)
108.3(4)
P(3)-C(701)-C(706) 115.5(8)
C(701)-C(706)-Ir(2) 121.0(8)
P(3)-Ir(1)-Ir(3)
Ir(4)-P(1)-C(301)
P(1)-C(301)-C(306) 116.8(6)
Ir(1)-P(2)-C(401)
P(2)-C(401)-C(406) 118.4(7)
Ir(1)-P(3)-C(501) 114.2(3)
P(3)-C(501)-C(502) 119.9(6)
108.1(3)
and one for an Ir4 cluster.22 Further coupling leading to the
formation of triphosphine as assisted by C60 shown in the present
work is unprecedented and remarkable (Scheme 3).
To address the origin of the face-capping µ4-CH unit in 5,
the reaction of deuterated Ir4(CO)8(P(CD3)3)4 with C60, followed
by treatment with benzyl isocyanide, was carried out. The µ4-
CH signal at δ 15.52 is absent in the 1H NMR spectrum of the
formed deuterium-labeled phosphine analogue of 5 (5d), imply-
ing that a methyl group in a PMe3 ligand is the source of the
resultant methylidyne moiety by P-C and C-H bond activation.
Since three phosphorus atoms remain in 5, reaction of stoichi-
ometrically precise Ir4(CO)9(PMe3)3 with C60 was attempted,
but resulted in severe decomposition of the starting material.
Additional PMe3 ligand in the starting material, 4, apparently
plays a crucial role in the formation of 5. Efforts to prepare a
µ4-CCH3 complex have not been successful by employing Ir4-
(CO)8(PEt3)4, but the hydrido monoiridium Ir(H)(CO)(PEt3)2-
(η2-C60) compound was produced by extensive fragmentation
of the tetrairidium framework, which will be reported else-
where.25
Ir-Ir distances of 2.7255(6) and 2.7796(8) Å of 2 and 3 are
comparable to those observed in other known “butterfly”
tetrairidium clusters.32 Each iridium atom of 2 has two terminal
carbonyl groups. The P1 atom bearing two phenyl groups in 2
is coordinated to the Ir4 center, and the two “wing-tip” Ir atoms
are almost symmetrically bridged by the P2 atom (Ir1-P2 )
2.297(3) Å and Ir4-P2 ) 2.309(3) Å) with Ir1-P2-Ir4 )
110.5(1)°. An o-phenylene group bridges the P1 and P2 atoms
in the bidentate diphosphine moiety Ph2P(ï-C6H4)PPh, which
in turn forms a five-membered metalacyclic P1-C301-C306-
P2-Ir4 moiety on the cluster. Another interesting feature of 2
is the presence of µ3-PPh2(η1:η2-o-C6H4) ligand (a five-electron
donor), which is coordinated through P3 to the Ir3 atom, by an
Ir-C(phenylene) σ-bond to the Ir2 center, and by an η2
interaction of the o-C6H4 ring to the Ir1 atom to form another
metalacycle Ir3-P3-C701-C706-Ir2. A similar five-electron-
donor bonding mode was previously observed in (µ-H)Os3(CO)8-
{µ3-PPhMe(η1:η2-C6H4)}33 and (µ-H)Ru3(CO)8{µ3-PPh(η1:η2-
C6H4)(η-C5H4)Fe(η-C5H4PPh2)}.34 In compound 3, one terminal
carbonyl group is bonded to each of Ir1 and Ir2 atoms, whereas
each of the Ir3 and Ir4 centers is ligated by two terminal
carbonyl groups. The P1 atom bearing two phenyl groups is
X-ray Crystal Structures of 2, 3, and 5. Selected interatomic
distances and angles of 2, 3, and 5 are listed in Tables 1-3,
respectively.
The molecular structures of 2 and 3 are shown in Figures 1
and 2, respectively. Both complexes exhibit a “butterfly”
geometry of four iridium atoms as expected for 62 VE metal
clusters. The two “wings” are nearly perpendicular to each other
( Ir4-Ir2-Ir1 ) 88.20(2)° for 2 and 85.02(1)° for 3), as was
observed in previously reported “wing-tip” bridged tetrairidium
“butterfly” complexes.32a The bond length of the Ir3-Ir4 is
relatively longer (2.8054(6) Å for 2 and 2.8094(7) Å for 3) than
the other Ir-Ir distances in both 2 and 3. However, the average
(32) (a) Stuntz, G. F.; Shapley, J. R.; Pierpont, C. G. Inorg. Chem. 1978, 17,
2596-2603. (b) Vargas, M. D.; Pereira, R. M. S.; Braga, D.; Grepioni, F.
J. Chem. Soc., Chem. Commun. 1993, 1008-1010. (c) Benvenutti, M. H.
A.; Vargas, M. D.; Braga, D.; Grepioni, F.; Mann, B. E.; Naylor, S.
Organometallics 1993, 12, 2947-2954. (d) Benvenutti, M. H. A.; Vargas,
M. D.; Braga, D.; Grepioni, F.; Parisini, E.; Mann, B. E. Organometallics
1993, 12, 2955-2961 and references therein; (e) Pereira, R. M. S.; Fijiwara,
F. Y.; Vargas, M. D.; Braga, D.; Grepioni, F. Organometallics 1997, 16,
4833-4838. (f) Araujo, M. H.; Hitchcock, P. B.; Nixon, J. F.; Vargas, M.
D. J. Braz. Chem. Soc. 1998, 9, 563-570.
(33) Deeming, A. J.; Kabir, S. E.; Powell, N. I.; Bates, P. A.; Hursthouse, M.
B. J. Chem. Soc., Dalton Trans. 1987, 1529-1534.
(34) Bruce, M. I.; Humphrey, P. A.; Shawkataly, O. B.; Snow, M. R.; Tiekink,
E. R. T.; Cullen, W. R. Organometallics 1990, 9, 2910-2919.
(30) (a) Bianchini, C.; Frediani, P.; Sernau, V. Organometallics 1995, 14, 5458-
5459. (b) Hietkamp, S.; Sommer, H.; Stelzer, O. Inorg. Synth. 1989, 25,
120-122. (c) Hartley, J. G.; Venanzi, L. M.; Goodall, D. C. J. Chem. Soc.
1963, 3930-3936.
(31) Estevan, F.; Garc´ıa-Bernabe´, A.; Lahuerta, P.; Sanau´, M.; Ubeda, M. A.;
Gala´n-Mascaros, J. R. J. Organomet. Chem. 2000, 596, 248-251.
9
11164 J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006

Tetrairidium Clusters Bearing Fullerene Ligands
A R T I C L E S
Table 3. Selected Interatomic Distances (Å) and Bond Angles
(deg) for 5
Bond Distances
Ir(1)-Ir(2)
Ir(2)-Ir(3)
Ir(3)-P(3)
Ir(4)-P(3)
Ir(1)-C(1)
Ir(1)-C(2)
Ir(2)-C(3)
Ir(2)-C(4)
Ir(3)-C(5)
C(1′)-C(2′)
C(2′)-C(3′)
C(4′)-C(5′)
C(1)-C(2)
C(3)-C(4)
C(5)-C(6)
C(100)-H(100)
3.0388(7)
2.9116(7)
2.313(4)
2.284(3)
2.20(1)
2.16(1)
2.17(1)
2.19(1)
2.17(1)
1.46(2)
1.50(2)
1.50(2)
1.44(2)
1.49(2)
1.55(2)
1.10(2)
Ir(1)-Ir(4)
Ir(3)-Ir(4)
Ir(3)-P(1)
Ir(4)-P(2)
Ir(1)-C(3′)
Ir(1)-C(4′)
Ir(2)-C(1′)
Ir(2)-C(2′)
Ir(4)-C(6)
C(1′)-C(6′)
C(3′)-C(4′)
C(5′)-C(6′)
C(2)-C(3)
C(4)-C(5)
C(1)-C(6)
2.8574(7)
2.7819(7)
2.372(4)
2.318(4)
2.11(1)
2.20(1)
2.19(1)
2.14(1)
2.19(1)
1.52(2)
1.48(2)
1.36(2)
1.49(2)
1.50(2)
1.54(2)
Bond Angles
Ir(3)-Ir(2)-Ir(1)
Ir(3)-Ir(2)-Ir(1)
P(3)-Ir(3)-P(1)
P(3)-Ir(3)-Ir(4)
P(3)-Ir(3)-Ir(2)
P(3)-Ir(4)-Ir(3)
Ir(4)-P(3)-Ir(3)
P(2)-Ir(4)-Ir(1)
87.41(2)
87.41(2)
100.2(2)
52.28(9)
143.67(9)
53.3(1)
Ir(4)-Ir(1)-Ir(2)
Ir(4)-Ir(3)-Ir(2)
P(1)-Ir(3)-Ir(4)
P(3)-Ir(4)-P(2)
P(1)-Ir(3)-Ir(2)
P(2)-Ir(4)-Ir(3)
P(3)-Ir(4)-Ir(1)
Ir(3)-Ir(4)-Ir(1)
87.47(2)
91.47(2)
112.3(1)
103.8(1)
95.91(9)
154.35(9)
146.8(1)
93.64(2)
74.5(1)
107.75(9)
Figure 2. Molecular geometry and atomic-labeling scheme for 3.
bonds in the µ3-η2:η2:η2-C60 ligand alternate in length, with an
average long distance of 1.49(1) Å and average short distance
of 1.43(1) Å. The formal electron counts for Ir1, Ir2, Ir3, and
Ir4 of 2 and 3 are 18, 17, 18, and 19, respectively. The formal
electron deficiency at the Ir2 center appears to be compensated
for by a strong σ-interaction (2.08(1) Å) between Ir2 and C706
in 2 and similarly between Ir2 and C502 (2.089(8) Å) in 3.
The molecular structure of 5 is shown in Figure 3. Extensive
structural changes have occurred for the tetrairidium metal
framework and ligand coordination environments from the
starting complex. The tetrairidium metal framework in 5 now
has a square-planar geometry, whereas the starting material Ir4-
(CO)8(PMe3)4 adopts a tetrahedral core. The overall VE count
is 64 VEs for 5, as expected for a four-metal cluster compound
with a square-planar geometry. The tetrairidium framework is
face-capped, surprisingly, by a methylidyne unit which formally
acts as a three-electron donor. The C-H bond vector is almost
perpendicular to the square-planar tetrairidium plane, and the
bond length is 1.10(2) Å, which compares with those of Ru2-
Pt2(µ-H)(µ4-CH)(CO)3(PPri3)2(η5-C5H5)2 (1.0(1) Å)27 and Ru5-
(µ-H)(µ4-CH)(CO)10(µ-GePh2)2(µ3-GePh)2 (0.89(2) Å).29 The Ir3
and Ir4 metal atoms, each coordinated with a terminal PMe3
ligand, are bridged by a PMe2 moiety. A benzyl isocyanide
ligand is coordinated to the Ir4 atom, and one terminal carbonyl
ligand is bonded to each of the Ir1, Ir2, and Ir3 atoms. Interesting
structural features are observed for the C60-metal interactions;
two adjacent metals, Ir1 and Ir2, bridge the two C60 units via a
µ-η2:η2-C60 bonding mode. The inner carbon atoms, C(2, 3)
and C(2′, 3′), of the butadiene-like moieties of the two C60 units
exhibit stronger interactions with metal atoms than the outer
carbon atoms, C(1, 4) and C(1′, 4′), as was previously observed
for Os5C(CO)12 (PPh3)(µ-η2:η2-C60):8 Ir1-C2 ) 2.16(1) Å; Ir2-
C3 ) 2.17(1) Å; Ir2-C2′ ) 2.14(1) Å; Ir1-C3′ ) 2.11(1) Å;
Ir1-C1 ) 2.20(1) Å; Ir2-C4 ) 2.19(1) Å; Ir2-C1′ ) 2.19(1)
Å; Ir1-C4′ ) 2.20(1) Å. More importantly, the other two metal
atoms, Ir3 and Ir4, bind to two carbon atoms (C5 and C6) of
one C60 unit in a σ-fashion, which is the first example of a novel
σ-π mixed-type µ4-η1:η1:η2:η2-C60 bonding mode. The σ-in-
Figure 1. Molecular geometry and atomic-labeling scheme for 2.
coordinated to the Ir4 atom, and the two “wing-tip” Ir1 and Ir4
atoms are spanned slightly asymmetric by P2 (Ir4-P2 ) 2.300-
(2) Å and Ir1-P2 ) 2.281(2) Å) with an angle of 108.45(9)°
( Ir4-P2-Ir1). The phenyl group on the P2 atom has been
ortho-phosphorylated by the P3 atom, and a phenyl group on
the P3 center underwent ortho-metalation to form two five-
membered Ir1-P2-C401-C406-P3 and Ir1-Ir2-C502-
C501-P3 metalacycles, respectively. Overall, the three phos-
phine ligands in 1 are converted to a triphosphine ligand PPh2(o-
C6H4)P(o-C6H4)PPh(η1-o-C6H4) in 3. The C60 ligand in 3 is
coordinated to the lower “wing” of the “butterfly” composed
of the Ir1-Ir2-Ir3 triangle in a typical µ3-η2:η2:η2-C60 arene-
type fashion, which has recently been reviewed.3a The C-C
9
J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006 11165

A R T I C L E S
Park et al.
Figure 4. CVs of 2, 3, and 6 in chlorobenzene (scan rate ) 50 mV/s).
Figure 5. CV of 5 in chlorobenzene (scan rate ) 10 mV/s).
Electrochemical Studies of 2, 3, 5, and 6. The electrochemi-
cal properties of compounds 2, 3, 5, and 6 in CB have been
examined by cyclic voltammetry with tetrabutylammonium
perchlorate as the supporting electrolyte. Cyclic voltammograms
(CVs) of 2, 3, and 6 are shown in Figure 4, and that of 5 is
shown in Figure 5. Half-wave potentials (E1/2) of all the new
compounds, together with free C60,36 Os3(CO)8(PMe3)(µ3-η2:
η2:η2-C60) (7),10 Os3(CO)8(CN(CH2)3Si(OEt)3)(µ3-η2:η2:η2-C60)
(8),18 and Rh6(CO)5(dppm)2(CNCH2Ph)(µ3-η2:η2:η2-C60)2 (9),11
are provided in Table 4.
The CV of tetrairidiumcomplex 2 exhibits an irreversible two-
electron reduction at -2.04 V and reoxidation at -1.53 V of
the material formed during the reduction, which has been
evidenced by the observation that no waves were observed by
scanning between -0.4 and -1.7 V. Similar irreversible
behaviors have been commonly observed for metal carbonyl
cluster complexes, where loss of a carbonyl and structural
changes are generally accompanied by a two-electron reduc-
tion.37 The CV of triphosphine-coordinated C60-tetrairidium
complex 3 reveals four reversible redox couples that each
correspond to a one-electron processes with the third and fourth
waves overlapped within the CB solvent potential window. The
general features of the CV of 3 are similar to those of the
previously reported complexes 710 and 8,18 as listed in Table 4.
All the four-half-wave potentials of 3, however, appear at much
Figure 3. (a) Molecular geometry and atomic-label scheme for 5. (b)
Expanded view of ligated C6 rings of the two C60 ligands.
teractions (Ir3-C5 ) 2.17(1) Å and Ir4-C6 ) 2.19(1) Å) are
comparable to the σ-type interactions (2.11(1)-2.20(1) Å) unlike
other known σ-π mixed complexes such as Os3(CO)8(L)(µ3-
CNR)(µ3-η1:η2:η1-C60) (L ) CO, CNR; R ) CH2Ph) and Os3-
(CO)7(CNR)(µ3-CNR)(L)(µ3-η1:η2:η1-C60) (L ) (µ-H)2, CNR,
PMe3; R ) CH2Ph), in which shorter bond distances are
commonly observed for σ-bonds (2.19(2)-2.25(2) Å) compared
to π-bonds (2.31(2)-2.50(2) Å).7 The C6 ring in the µ-η2:η2-
C60 ligand shows alternation in C-C bond distances (av 1.43-
(2) and 1.51(2) Å, respectively). However, the other C6 ring in
the µ4-η1:η1:η2:η2-C60 ligand exhibits 1,3-cyclohexadiene-like
nature; the bond lengths, C1-C2 (1.44(2) Å) and C3-C4 (1.49-
(2) Å), are shorter than the other four C-C bonds (av 1.52(2)
Å). The sums of three angles around sp3-hybridized C5 (334°)
and C6 (333°) are considerably smaller than those of the other
four carbon atoms (av 347°) with sp2 hybridization. Similar
protrusion of sp3-hybridized carbons from the smooth curvature
of the C60 ligand has been previously observed for related σ-π
mixed-type C60-cluster complexes.7 To our knowledge, the only
previously known square-planar tetrairidium compound is Ir4-
(CO)8{C2(CO2Me)}435 with 64 VEs which contains four acety-
lene ligands: two functions as four-electron donors and two as
two electron donors.
(36) (a) Xie, Q.; Perez-Cordero, E.; Echegoyen, L. J. Am. Chem. Soc. 1992,
114, 3978-3980. (b) Ohsawa, Y.; Saji, T. J. Chem. Soc., Chem. Commun.
1992, 781-782. (c) Zhou, F.; Jehoulet, C.; Bard, A. J. J. Am. Chem. Soc.
1992, 114, 11004-11006.
(37) (a) Geiger, W. E.; Connelly, N. G. AdV. Organomet. Chem. 1985, 24, 87-
130. (b) Johnson, B. F. G.; Lewis, J.; Nelson, W. J. H.; Nicholls, J. N.;
Puga, J.; Raithby, P. R.; Rosales, M. J.; Schro¨der, M.; Vargas, M. D. J.
Chem. Soc., Dalton Trans. 1983, 2447-2457. (c) Clark, R. J. H.; Dyson,
P. J.; Humphrey, D. G.; Johnson, B. F. G. Polyhedron 1998, 17, 2985-
2991. (d) Shephard, D. S.; Johnson, B. F. G.; Harrison, A.; Parsons, S.;
Smidt, S. P.; Yellowlees, L. J.; Reed, D. J. Organomet. Chem. 1998, 563,
113-136.
All the bond distances and angles for 2, 3, and 5, including
those for the carbonyl and C60 ligands, are within the expected
ranges.
(35) Heveldt, P. F.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R.; Sheldrick, G.
M. J. Chem. Soc., Chem. Commun. 1978, 340-341.
9
11166 J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006

Tetrairidium Clusters Bearing Fullerene Ligands
A R T I C L E S
Table 4. Half-Wave Potentials (E1/2 vs E°Fc/Fc+) of C60, 2, 3, 5, 6, 7, 8, and 9
0/-1
-1
/-2
-2/-3
-3/-4
-4/-5
-5/-6
/2
compound
E1
/
E1
E1
/
E1
/
E1
/
E1
solvent
ref
2
/
2
2
2
2
C60
2
3
7
8
6
5
9
-1.06
-1.43
-1.91
-2.38
CB
CB
CB
DCB
DM
CB
CB
CB
9
b
b
10
18
b
23
11
-2.04a
-1.53
-1.42
-1.37
-1.46
-1.32
-1.38
-1.18
-1.06
-1.01
-1.13
-1.25
-1.19
-2.11
-1.93
-1.81
-1.54
-1.66
-1.62
-2.11
-1.95
-1.81
-1.88
-1.82
-1.86
-2.35
-2.12
-2.58
-2.41
a Two-electron process and peak potential of irreversible process. b This work.
more negative potentials, at least by ca. 120 mV, compared to
those of 7 and 8, since compound 3 contains a strongly electron-
donating triphosphine ligand. The first through third reduction
potentials of 3 (-1.18, -1.53, and -2.11 V), show large
cathodic shifts compared to those of free C60 (-1.06, -1.43,
and -1.91 V) due to donor effects of both iridium metals and
the triphosphine ligand, which indicates that compound 3
undergoes three successive C60-localized reductions to produce
3-, 32-, and 33- (vide infra). The third and fourth reductions
of 3, however, take place at the same potential (-2.11 V), which
is even more positive than the fourth redox wave of free C60 at
-2.38 V. The overlap of the third and fourth waves in 3, 7,
and 8 support the general conclusion that the electron density
of C60 in the species 33-, 73-, and 83- is significantly delocalized
to the metal cluster center.3a,38 Accordingly, the fourth electron
can add to the C60 moiety of 33-, 73-, and 83- more easily
compared to free C603-, which results in a large positive shift
of the fourth reduction potential of 3 (270 mV), 7 (430 mV),
and 8 (570 mV) relative to free C60, as shown in Table 4. The
CV of diphosphine-coordinated C60-tetrairidium complex 6
reveals four reversible redox waves, each corresponding to a
one-electron process. The second and third redox waves are very
close but could be resolved into two one-electron redox couples
at half-wave potentials of -1.46 and -1.54 V by simulation
using PeakFit 4.11 software,39 as listed in Table 4. The third
redox wave at -1.54 V appears at a much more positive
potential than that of free C60 at -1.91 V, which also implies
that the electron density in dianionic species 62- is significantly
delocalized from C60 to the tetrairidium cluster center, resulting
in an unusually large anodic shift (370 mV) of the third redox
wave compared to that of the free C60. The following redox
wave at -1.88V is due to one-electron C60-localized reduction
to form 64- (vide infra). The electron delocalization from C60
to the tetrairidium cluster is also reflected in the fourth reduction
(-1.88 V) of 6 with an anodic shift (500 mV) compared to
free C60 reduction (-2.38 V).
with the triphosphine ligand in 3. The half-wave potential data
in Table 4 indicate that corresponding reduction potentials of
each compound generally decrease as 8 > 7 > 6 > 3, implying
that electron-donating power of ligands decreases as triphosphine
> diphosphine > PMe3 > CN(CH2)3Si(OEt)3, as commonly
expected for a ligand donor effect. Furthermore, these data
suggest that half-wave potentials of C60-metal cluster com-
plexes can be readily fine-tuned by changing the coordinated
ligands. This class of complexes, therefore, would certainly
invoke an increased interest in future electronic application.
The CV of bisfullerene complex 5 exhibits six well-separated,
reversible, one-electron redox waves at -1.25, -1.32, -1.66,
-1.82, -2.35, and -2.58 V within the solvent window, as
shown in Figure 5. Redox waves of 5 correspond to sequential,
pairwise addition of six electrons into the two C60 moieties to
form C60-Ir4-C60-, C60--Ir4-C60-, C60--Ir4-C602-, ..., and
ultimately C603--Ir4-C603- (vide infra). All three pairs of redox
waves are shifted to more negative potentials (190 and 260;
230 and 390; 440 and 670 mV) compared to those of the
corresponding free C60. The first redox wave in each pair of
the CV is ascribed to reduction of the µ-η2:η2-C60 ligand because
the other µ4-η1:η1:η2:η2-C60 ligand bonded to four metal atoms
and even phosphine-coordinated metal atoms would certainly
experience a higher degree of metal-to-C60 π-back-donation.
Overall, the redox waves of 5 are shifted to more negative
potentials relative to those of the related bisfullerene complex
Rh6(CO)5(dppm)2(CNCH2Ph)(µ3-η2:η2:η2-C60)2 (9)11 (-1.19,
-1.38, -1.62, -1.86, -2.12, and -2.41 V) due to the stronger
metal-to-C60 π-back-bonding in 5. The second redox wave in
each pair in the CV of 5 becomes increasingly separated from
the first wave (∆ (E1/21, E1/22) ) 0.07 V, ∆ (E1/23, E1/24) ) 0.16
V, ∆ (E1/2,5 E1/26) ) 0.23 V) as the reduction proceeds. Similar
3
behavior was observed for 9 (∆ (E1/21, E1/22) ) 0.19 V, ∆ (E1/2
,
E1/24) ) 0.24 V, ∆ (E1/2,5 E1/26) ) 0.29 V), in which the larger
separations are proposed to stem from an increasing Coulombic
repulsion between the two C60 moieties.11 This larger increase
in the separation within the redox pairs of 9, however, cannot
be explained solely by stronger Coulombic repulsion because
the distance between the two C60 units in 5 (d(C2-C3′) ) 3.23
Å; d(C3-C2′) ) 3.25 Å) is shorter than that (ca. 3.56 Å) in 9.
The first two reductions for 3 and all four reductions of 6
occur at much more positive potentials compared to the
“butterfly” tetrairidium cluster reduction (Ered ) -2.04 V) of
2, and thus could be confidently assigned to the C60-localized
successive reductions. The overlapped third and fourth one-
electron reductions of 3 were assigned to redox processes also
localized on the C60 ligand, based on MO calculation results
(vide infra). All the corresponding half-wave-potentials of 6 are
more positive than those of 3, revealing a clearly less electron-
donating nature of the diphosphine ligand in 6 in comparison
Furthermore, only small redox pair separation is observed for
14
compounds, such as C
O
120
and C120Si(C6H5)2,16 with much
shorter interfullerene distances of ∼1.5 Å (C120O: ∆ (E1/21, E1/2
)
2
) 0.039 V; ∆ (E1/23, E1/24) ) 0.061 V; ∆ (E1/2,5 E1/26) ) 0.138
V;14 C120(SiPh2): ∆ (E1/21, E1/22) ) 0.09 V; ∆ (E1/23, E1/24) )
0.08 V; ∆ (E1/2,5 E1/26) ) 0.14 V16). For comparison, separations
between stepwise reduction pairs of various organic and
inorganic bisfullerenes reported to date are summarized in Table
5 which clearly indicate remarkably efficient electronic com-
(38) Park, J. T.; Cho, J.-J.; Song, H.; Jun, C.-S.; Son, Y.; Kwak, J. Inorg. Chem.
1997, 36, 2698-2699.
(39) PeakFit, Version 4.11; Jandel Scientific Software: San Rafael, CA.
9
J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006 11167

A R T I C L E S
Park et al.
ref
Table 5. Separations (mV) between Stepwise Reduction Pairs of Various Organic and Inorganic Bisfullerenes
2
4
6
compound
∆
(E1 1, E1
)
∆
(E1 3, E1
)
∆
(E1 5, E1
)
solvent
/
2
/
2
/
2
/
2
/
2
/2
C120
80
80
39
70
90
70
70
DCB
DCB
DCB
DCB
DCB
DCM
CB
12
13
14
15
16
21
23
11
C
C
C
C
120C
120O
96
61
75
80
80
172
138
90
120(CH2)2
120SiPh2
140
Mo(η2-C60)2(CO)2(dbcbipy)
5
9
160
240
230
290
190
CB
Table 6. Energies and Contributions of Component Parts for
Selected MOs for 3 and 6 in CB Solvent
orbital
C60
cluster
orbital no.
energy (eV)
character (%)
character (%)
3
6
LUMO+3
LUMO+2
LUMO+1
LUMO
-2.92
-3.41
-3.49
-3.68
-4.80
46
91
89
97
36
54
9
11
3
HOMO
64
LUMO+3
LUMO+2
LUMO+1
LUMO
-3.47
-3.48
-3.71
-3.77
-5.02
68
91
43
92
40
32
9
57
8
HOMO
60
munication between C60 cages through metal cluster spacers in
bisfullerenes such as 5 and 9, in contrast to the other organic
and monometallic bisfullerenes.
Theoretical Calculations of 3, 5, and 6. Theoretical studies
on C60-metal cluster complexes are very scarce. We have
previously performed calculations on triosmium40 and hexa-
rhodium systems,11b while others have done so for the Ru3(CO)9-
(µ3-η2:η2:η2-C60) complex.41 Previous theoretical reports, except
for the triosmium system, were limited to a MO analysis of
neutral complexes without considering the changes of geometry
and electronic structures caused by successive reductions. In
the present work, DFT using the BPW9142 functional was
employed to investigate the MOs of 5 and both neutral and
anionic species of 3 and 6 in CB solvent, in an effort to
understand electrochemical properties observed in the CVs of
these complexes. Furthermore, the MPA43 and HPA44 were
performed to obtain the charge distributions for 3, 6, and their
anions in CB solvent.
Table 6 lists orbital energies and contributions of C60 and
metal cluster parts for selected MOs of monofullerene com-
plexes, 3 and 6, in CB solvent. The corresponding MO diagrams
for 3 and 6 are displayed in Figure 6. Highest occupied
molecular orbitals (HOMOs) for 3 and 6 are largely metal
cluster-based (64% for 3, and 60% for 6) with significant C60
contributions (36% for 3, and 40% for 6), which implies a strong
ground-state interaction between C60 and Ir4 cluster centers.
Similar ground-state interactions were previously reported for
hexarhodium clusters such as Rh6(CO)9(dppm)2(µ3-η2:η2:η2-C60)
and Rh6(CO)7(dppm)2(CNCH2Ph)2(µ3-η2:η2:η2-C60).11b Energies
of lowest unoccupied MOs (LUMOs) of 6 are generally lower
Figure 6. MO diagrams for (a) 3 and (b) 6.
than those of 3, which explains that all the reduction potentials
of 6 are shifted to more positive potentials than those of 3 and
proves the weaker donor effect of the diphosphine ligand in 6
in comparison with the triphosphine ligand in 3.
Assuming that added electrons sequentially fill the unoccupied
molecular orbitals, LUMO and LUMO+1 orbitals of 3 are
responsible for the first and second one-electron and for the
third and fourth one-electron reduction steps observed in the
CV of 3, respectively. LUMO+1 of 3 is C60-based (89%), but
the metal cluster contribution is not negligible (11%), namely,
the electron density in 33- is delocalized on the metal cluster
center. This fact is clearly indicated by the charge increments
for 32- f 33-, average values of ∆Q(2-/3-) ) 37% for C60
and 63% for the metal cluster, as shown in Table 7. This
explains a large anodic shift of the fourth redox wave of 3, which
essentially overlapped with the third one-electron redox wave
at -2.11 V. On the other hand, the LUMO and LUMO+1
orbitals of 6 are responsible for the first one-electron and for
(40) Kim, K. H.; Jung, J.; Han, Y.-K. Organometallics 2004, 23, 3865-3869.
(41) Lynn, M. A.; Lichtenverger, D. L. J. Cluster Sci. 2000, 11, 169-188.
(42) (a) Becke, A. D. Phys. ReV. A 1988, 38, 3098-3100. (b) Perdew, J. P.;
Wang, Y. Phys. ReV. B 1992, 45, 13244-13249.
(43) Mulliken, R. S. J. Chem. Phys. 1955, 23, 1833-1840.
(44) Hirshfeld, F. L. Theor. Chim. Acta 1977, 44, 129-138.
9
11168 J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006

Tetrairidium Clusters Bearing Fullerene Ligands
A R T I C L E S
Table 7. Charges and Charge Increments of C60 and Cluster
Parts for 3 and 6 in CB Solvent
MPA
HPA
total charge
C60
cluster
C60
cluster
3
Q
0
-0.25
-0.98
-1.71
-2.10
-2.59
0.73
0.73
0.39
0.49
0.25
-0.02
-0.29
-0.90
-1.41
0.27
0.27
0.61
0.51
-0.32
-1.05
-1.79
-2.13
-2.61
0.73
0.74
0.34
0.48
0.32
0.05
-0.21
-0.87
-1.39
0.27
0.26
0.66
0.52
-1
-2
-3
-4
∆Q
0/-1
-1/-2
-2/-3
-3/-4
6
Q
0
-0.21
-0.85
-1.07
-1.64
-2.29
0.64
0.22
0.57
0.65
0.21
-0.15
-0.93
-1.36
-1.71
0.36
0.78
0.43
0.35
-0.32
-0.97
-1.12
-1.70
-2.38
0.65
0.15
0.58
0.68
0.32
-0.03
-0.88
-1.30
-1.62
0.35
0.85
0.42
0.32
-1
-2
-3
-4
∆Q
0/-1
-1/-2
-2/-3
-3/-4
the second one-electron steps observed in the CV of 6,
respectively, since the energy difference between the LUMO
and LUMO+1 orbitals is very small (0.06 eV) in this complex.
The metal cluster contribution to the LUMO+1 orbital of 6 is
large (57%), which implies that the electron density in 62- is
significantly delocalized on the metal cluster center. This is also
clearly shown by the charge increments for 6- f 62-, average
values of ∆Q(1-/2-) ) 19% for C60 and 81% for the metal
cluster (see Table 7). These theoretical results are consistent
with the observation in the CV of 6 that the second (-1.46 V)
and the third (-1.54 V) redox waves are very close to each
other and the fourth wave, accordingly, reveals a large anodic
shift (230 mV) compared to that of 3.
To confirm the electronic structures of 3 and 6 in the reduction
processes unambiguously, HOMOs of their anions were also
investigated and presented in Figure 7. The HOMOs of 3- and
32- show that the first and second reductions are mainly
localized on the C60 ligand. The HOMO of 33- indicates that
the electron density in 33- is somewhat delocalized on the metal
cluster part, while the HOMO of 34- is exclusively localized
on the C60 cage as well. The HOMO of 6- is also C60-based,
but the metal cluster contribution is much larger than that of
3-. More electron density in 6- is delocalized on the metal
cluster center as compared to 3-, which serves to explain the
anodic shift of the second wave for 6 (-1.46 V) compared to
that of 3 (-1.53 V). Furthermore, the shape of HOMO of 62-
reveals that the electron density in 62- is significantly delocal-
ized on the metal cluster part, but HOMOs of 63- and 64- are
again exclusively localized on the C60 part. These orbital
analyses for anions of 3 and 6 clearly support that reduction
processes usually undergo through the C60 moiety and the two
overlapped or close redox waves in 3 or 6 are correlated with
the electron delocalization from the C60 unit to the metal cluster
moiety.
Figure 7. HOMO diagrams for (a) 3 and its anions and (b) 6 and its anions.
Table 8. Orbital Energies and Contributions of C60 and Cluster
Parts for Selected Molecular Orbitals of 5 in CB Solvent
C60 character (%)
orbital
cluster
orbital no.
energy (eV)
C60 (left)
C60 (right)
character (%)
LUMO+5
LUMO+4
LUMO+3
LUMO+2
LUMO+1
LUMO
-3.24
-3.27
-3.28
-3.43
-3.52
-3.59
-4.54
69
31
68
1
67
26
33
7
61
27
88
31
71
18
24
8
5
11
2
3
HOMO
49
5 is metal cluster-based (49%) with two significant C60
contributions (33% (left) and 18% (right)), as similarly observed
for Rh6(CO)5(dppm)2(CNCH2Ph)(µ3-η2:η2:η2-C60)2.11b The LUMO
is C60(right)-based (71%), which evidently indicates that the
first reduction is ascribed to the µ-η2:η2-C60 moiety. This
theoretical result confirms that the µ-η2:η2-C60 moiety is more
electropositive than the µ4-η1:η1:η2:η2-C60 moiety due to less
metal-to-C60 back-donation in the µ-η2:η2-C60 moiety. Further-
more, LUMO contributions from the two C60 units alternate from
LUMO to LUMO+5, which explains the alternating electron
additions to the two C60 units in the six successive reductions,
as observed in the CV of 5. Metal cluster contributions to the
MOs are not negligible, up to 24% for LUMO+5, suggesting
that the electronic information of one C60 ligand is efficiently
communicated through the metal cluster spacer to the other C60
ligand. The spin-pairing energies apparently exceed the energy
gaps (0.01-0.15 eV) among LUMOs of 5. The metal cluster
contribution to LUMOs overall increases as the reduction
Theoretical studies of 5 in CB solvent have been similarly
carried out to address details of its electrochemical properties
shown in Figure 5. MO energies and contributions of metal
cluster and two C60 parts for selected MOs are listed in Table
8, and MO diagrams are depicted in Figure 8. The HOMO for
proceeds, which could be related to the increase in the separation
4
within the redox pairs [∆ (E1/21, E1/22) ) 0.07 V, ∆ (E1/23, E1/2
)
) 0.16 V, ∆ (E1/2,5 E1/26) ) 0.23 V] in the CV of 5.
9
J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006 11169

A R T I C L E S
Park et al.
thin layer plates were prepared with silica gel GF254 (Type 60, E.
Merck). Infrared spectra were obtained on a Bruker EQUINOX-55 FT-
IR spectrophotometer. 1H(400 MHz) and 13C(100 MHz) NMR spectra
were recorded on a Bruker AVANCE-400 spectrometer and 31P(122
MHz) NMR spectra on a Bruker AM-300 spectrometer. Positive-ion
FAB mass spectra (FAB+) were obtained by the staff of the Korea
Basic Science Institute (KBSI), and all m/z values are referenced to
193Ir. Elemental analyses were performed by the staff of the Energy &
Environment Research Center at KAIST.
Preparation of 2. A CB solution (30 mL) of 1 (50 mg, 0.028 mmol)
was heated to reflux for 40 min. Evaporation of the solvent and
purification by preparative TLC (CH2Cl2/C6H14 ) 1:1) produced 2 (29.6
mg, 0.018 mmol, 64%, Rf ) 0.8) as an orange solid: IR(C6H12): νCO
2062 (w), 2049 (s), 2029 (vs), 2011 (vs), 1993 (vs), 1956 (m), 1946
(m) cm-1; 1H NMR (400 MHz, CDCl3, 298 K): δ 8.44 (dd, 1H, JPH
)
8.0 Hz, JPH ) 2.5 Hz), 7.89 (m, 1H), 7.63(m, 4H), 7.46-6.88 (m, 24H),
6.62 (m, 2H), 6.51 (t, 1H, JPH ) 7.6 Hz) (all C6H5 + C6H4); 13C NMR
(100 MHz, CDCl3, 298 K): δ 186.8 (s, 1CO), 185.7 (s, 1CO), 179.6
(s, 1CO), 176.4 (s, 1CO), 166.4 (s, 1CO), 165.7 (s, 1CO), 165.5 (d,
1CO, 2JCP ) 3.5 Hz), 163.7 (d, 1CO, 2JCP ) 4 Hz), 153.2-124.3 (42C,
C6H5 + C6H4); 31P{H} NMR (122 MHz, CDCl3, 298 K): δ 24.2 (d,
2
2
1P, JPP ) 22.1 Hz), 16.4 (s, 1P), -42.9 (d, 1P, JPP ) 22.1 Hz); MS
(FAB+): m/z: 1624 [M+]. Anal. Calcd for C50H33Ir4O8P3: C, 36.99;
H, 2.05. Found: C, 36.76; H, 2.19.
Preparation of 3. A CB solution (30 mL) of 1 (30 mg, 0.017 mmol)
and C60 (2 equiv, 24 mg, 0.033 mmol) was heated to reflux for 3 h.
Evaporation of the solvent and purification by preparative TLC (CS2/
CH2Cl2 ) 8:1) produced compound 3 (13.2 mg, 0.006 mmol, 36%,
Rf ) 0.7) as a greenish-black solid: IR(CH2Cl2): νCO 2045 (vs), 2016
(vs), 1998 (s), 1985 (sh), 1970 (m) cm-1; 1H NMR (400 MHz, CDCl3,
298K): δ 8.07-7.14 (m, 24H), 6.93-6.78 (m, 3H) (all C6H4 + C6H4);
13C NMR (100 MHz, C6D4Cl2, 298K): δ 188.4 (d, 1CO, JPC ) 2.5
Hz), 187.3 (d, 1CO, JPC ) 3.2 Hz), 179.9 (s, 1CO), 173.3 (t, 1CO,
Figure 8. MO diagrams for 5.
Concluding Remarks
In conclusion, we have found remarkable phosphine conver-
sion: 1(phosphine) f 2(diphosphine) f 3(triphosphine). We
have also demonstrated that facile ortho-phosphorylation and
ortho-metalation reactions can take place on a tetrairidium
framework during the conversion of 1 f 2 f 3 and, more
importantly, that the multifunctional C60 ligand can assist the
ortho-phosphorylation step in the conversion of 2 f 3. In
addition, we have prepared a square planar C60-tetrairidium
cluster sandwich complex 5 with two metal centers bridging
two C60 units, which contains an unprecedented µ4-η1:η1:η2:
η2-C60 bonding mode and an unusual face-capping µ4-CH
moiety. Electrochemical studies, charge population analyses, and
DFT MO calculation of 3, 5, 6, and their anions nicely match
and clearly allow for the electrochemical pathways of C60-
tetrairidium cluster complexes to be understood in detail. In
particular, compound 5 reveals an enhanced electronic com-
munication through a wide channel of two metal centers for
efficient electronic interactions between C60 cages. This work
explicitly proves that the electrochemical properties of C60-Ir4
cluster complexes can be controlled by changing attached
ligands on the metal cluster center. These new discoveries may
lead to future electronic nanomaterials applications with com-
plexes of this class.
JPC ) 3.9 Hz), 172.4 (d, 1CO, JPC ) 12.2 Hz), 161.2(dd, 1CO, JPC
)
51.2 Hz, JPC ) 5.5 Hz), 158.9-143.6 (54C, C60 sp2 region), 79.1 (d,
1C, JPC ) 6.3 Hz, C60 sp3 π-bonded carbon) 68.0 (t, 1C, JPC ) 4.9 Hz,
C
60 sp3 π-bonded carbon), 64.1 (d, 1C, JPC ) 2.4 Hz, C60 sp3 π-bonded
carbon), 62.7 (s, 1C, C60 sp3 π-bonded carbon), 61.2 (d, 1C, JPC
4.5 Hz, C60 sp3 π-bonded carbon), 60.6 (dd, 1C, JPC ) 13.8 Hz, JPC
)
)
2.3 Hz, C60 sp3 π-bonded carbon); 31P{H} NMR (122 MHz, CS2/ext.
CD2Cl2, 298K): δ 31.2 (d, 1P, 2JPP ) 12.8 Hz), -16.3 (dd, 1P, 2JPP
)
2
2
12.8 Hz, JPP ) 4.0 Hz), -21.5 (d, 1P, JPP ) 4.0 Hz); MS (FAB+):
m/z: 2210 [M+]. Anal. Calcd for C102H27Ir4O6P3: C, 55.43; H, 1.23.
Found: C, 55.64; H, 1.42.
Conversion of 2 to 3. A CB solution (30 mL) of 2 (30 mg, 0.018
mmol) and C60 (2 equiv, 26 mg, 0.036 mmol) was heated to reflux for
3 h. Evaporation of the solvent and purification by preparative TLC
(CS2/CH2Cl2 ) 8:1) afforded compound 3 (15.1 mg, 0.007 mmol, 41%,
Rf ) 0.7) as a greenish-black solid.
Preparation of 5 and 5d. A DCB solution (30 mL) of 4 (30 mg,
0.023 mmol) and C60 (67 mg, 0.093 mmol, 4 equiv) was prepared in
a 100 mL Schlenk flask equipped with a reflux condenser, and the
solution was heated to reflux for 2 h. The reaction mixture was purified
by preparative TLC to give a green band (CS2/CH2Cl2 ) 4:1, Rf )
0.35), which was dissolved in CB (50 mL). Benzyl isocyanide (2.0
mg, 0.0038 mmol) in 0.25 mL of CB was added to the green solution
of the green band via a syringe, and the resulting solution was stirred
at 70 °C for 2 h. Solvent removal under vacuum and purification by
preparative TLC (CS2/CH2Cl2 ) 2:1) gave 5 (8 mg, 0.0023 mmol, 13%)
as a dark green solid. IR(CH2Cl2) νCN 2159 (w) cm-1; νCO 1986 (s)
Experimental Section
General Comments. All reactions were carried out under a nitrogen
atmosphere with use of standard Schlenk techniques. Solvents were
dried over the appropriate drying agents and distilled immediately before
use. C60 (99.5%, SES Research), Ir4(CO)12 (98%, Strem), PPh3 (99%,
Aldrich), KOH (85%, Junsei), PMe3 (97%, Aldrich), deutrated-PMe3
(99+atom %D, Aldrich), and benzylisocyanide (98%, Aldrich) were
used without further purification. Ir4(CO)9(PPh3)3,45 Ir4(CO)9(PMe3)3,46
Ir4(CO)9(PEt3)3,46 Ir4(CO)8(PMe3)4,46 Ir4(CO)8(P(CD3)3)4,46 Ir4(CO)8-
(dppm)2,47 and 622 were prepared by the literature methods. Preparative
(45) Drakesmith, A. J.; Whyman, R. J. Chem. Soc., Dalton Trans. 1973, 362-
367.
(46) (a) Darensbourg, D. J.; Baldwin-Zuschke, B. J. Inorg. Chem. 1981, 20,
3846-3850. (b) Darensbourg, D. J.; Baldwin-Zuschke, B. J. J. Am. Chem.
Soc. 1982, 104, 3906-3910.
(47) Ros, R.; Scrivanti, A.; Albano, V. G.; Braga, D.; Garlaschelli, L. J. Chem.
Soc., Dalton Trans. 1986, 2411-2421.
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11170 J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006

Tetrairidium Clusters Bearing Fullerene Ligands
A R T I C L E S
Table 9. Crystallographic Data for 2, 3, and 5
2
3
5
formula
fw
cryst syst
space group
a, Å
C50H33P3O8Ir4
1623.47
triclinic
P1h
11.087(1)
11.472(1)
21.576(2)
91.925(2)
101.719(2),
116.070(1)
2390.1(4)
2
C
102H27P3O6Ir4‚4CS2
C140H32NO3P3Ir4‚C6H4Cl2‚1.75CS2
2514.47
monoclinic
P21/c
17.472(5)
20.071(6)
22.639(6)
90
100.739(5)
90
7800(4)
4
2917.60
monoclinic
P21/n
18.139(2)
24.386(3)
22.478(3)
90
110.283(2)
90
9327(2)
4
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
D
calcd, g cm-3
2.256
2.141
2.078
temp, K
293(2)
293(2)
173(2)
λ(Mo KR), Å
0.71073
11.254
1.95° < θ < 28.02°
14 826
10 924
0.0394
1.044
0.0576
0.71073
7.144
0.71073
5.948
µ, mm-1
θ range for collection
no. of rflns measd
no. of unique rflns
Rint
1.69°< θ < 25.52°
40 827
14 530
0.0716
0.953
1.25°< θ < 28.28°
53 694
21 663
0.0748
1.034
GOF
R1a
0.0422
0.0859
0.0646
0.1528
wR2b
0.1476
2
2
2
a R1 ) ∑|Fo| - |Fc|/∑ |Fo|. b wR2 ) [∑ω(Fo - Fc )2/∑ω(Fo )2]1/2
.
1
cm-1; H NMR (1,2-C6D4Cl2, 298K) δ 15.52 (d, 1H, JPH ) 13.0 Hz,
µ4-CH), 7.66-7.20 (m, 5H, CNCH2C6H5), 5.18 (AB pattern, 2H, J )
16.5 Hz, CNCH2C6H5), 3.55 (d, 3H, JPH ) 7.0 Hz, CH3-µ-P-CH3),
3.04 (d, 3H, JPH ) 4.6 Hz, CH3-µ-P-CH3), 2.07 (d, 9H, JPH ) 9.8 Hz,
PMe3), 1.86 (d, 9H, JPH ) 9.1 Hz, PMe3); 31P{1H} NMR (1,2-C6D4Cl2,
298 K) δ 164.3 (s, 1P, µ-PMe2), -44.9 (s, 1P, PMe3), -47.9 (s, 1P,
PMe3); Anal. Calcd for C147H32O3NP3Ir4: C, 63.75; H, 1.22; N, 0.53.
Found: C, 63.40; H, 1.59; N, 0.81.
Systems, Inc.), a platinum counter wire electrode (5 cm length of 0.5
mm diameter wire), and a Ag/Ag+ reference electrode (0.1 M AgNO3/
Ag in acetonitrile with a Vycor salt bridge). All measurements were
performed at ambient temperature under nitrogen atmosphere in a dry,
deoxygenated 0.1 M CB solution of [(n-Bu)4N]ClO4. The concentrations
of compounds were ca. 3 × 10-4 M. All potentials were referenced to
the standard ferrocene/ferrocenium (Fc/Fc+) scale. The relative number
of electrons involved in each reduction process was obtained from the
graph of current vs (time)-1/2 according to the Cottrell equation.51
Computational Details. Our calculations were based on the DFT
at the generalized gradient approximation (GGA) level (Becke’s 1988
functional for exchange and Perdew-Wang’s 1991 functional for
correlation, BPW9142). The energy-consistent relativistic effective core
potential (RECP) was used for Ir atoms.52 Double numerical plus
polarization (DNP) basis sets were used for the C, H, O, N, and P
atoms, and the VEs for Ir were also expanded using the DNP basis set.
All the structures of 3, 5, and 6 were optimized without any symmetry
restriction using the analytical gradients of the energies. We have
performed the MPA43 and the HPA44 for 3, 6, and their anions in order
to obtain the charge distributions. The geometry optimization and the
population analysis were performed using the DMol3 software.53
The MOs for 3, 5, and 6 were calculated at the optimized structures
using the Gaussian03 software package.54 The energy-consistent RECP
with corresponding basis sets52 was used for the Ir atoms, and 6-31G(d)
basis sets were used for the other atoms. Solvation energies were
calculated using the conductor-like screening model (COSMO)55 to
consider bulk solvent effects effectively. The dielectric constant value
(ꢀ ) 5.6) of CB was employed in the COSMO calculations.
A similar treatment of Ir4(CO)8(P(CD3)3)4 to 5 gave a deuterium-
labeled analogue, 5d: 1H NMR (1,2-C6D4Cl2, 298K) δ 7.66-7.20 (m,
5H, CNCH2C6H5), 5.18 (AB pattern, 2H, J ) 16.5 Hz, CNCH2C6H5);
31P{1H} NMR (1,2-C6D4Cl2, 298 K) δ 163.4 (s, 1P, µ-P(CD3)2), -46.6
(s, 1P, P(CD3)3), -49.6 (s, 1P, P(CD3)3).
X-ray Crystallographic Studies. Crystals of 2, 3, and 5 suitable
for an X-ray analysis were grown by slow solvent diffusion: for 2
with methanol into dichloromethane at room temperature, for 3 with
heptane into carbon disulfide at room temperature, and for 5 with
methanol into carbon disulfide/DCB (1:1) at room temperature.
Diffraction data of 2 and 3 were collected on a Siemens SMART
diffractometer/CCD area detector at room temperature. Diffraction data
of 5 were collected on a Bruker SMART diffractometer/CCD area
detector at 173 K. Preliminary orientation matrix and cell constants
were determined from three series of ω scans at different starting angles.
The hemisphere of reflection data was collected at scan intervals of
0.3° ω with an exposure time of 10 s per frame. The data were corrected
for Lorentz and polarization effects, but no correction for crystal decay
was applied. Absorption corrections were performed using SADABS.48
Each structure was solved by direct49 and difference Fourier methods
and was refined by full-matrix least-squares methods based on F2
(SHELX 97).50 All non-hydrogen atoms were refined with anisotropic
thermal coefficients. Details of relevant crystallographic data for 2, 3,
and 5 are summarized in Table 9.
Acknowledgment. This work was supported by the Korea
Research Foundation Grant funded by the Korean Government
(MOEHRD) (KRF-2005-201-C00021) and by the Nano R&D
Electrochemical Measurements. Cyclic voltammetry was carried
out on a AUTOLAB (PGSTAT 10, Eco Chemie, Netherlands) elec-
trochemical analyzer using the conventional three-electrode system of
a platinum working electrode (1.6 mm diameter disk, Bioanalytical
(51) Bard, A. J.; Faulkner, L. R. Electrochemical Methods; John Wiley and
Sons: New York, 1980; pp 142-146.
(52) Andrae, D.; Ha¨ussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim.
Acta 1990, 77, 123-141.
(53) (a) Delley, B. J. Chem. Phys. 1990, 92, 508-517. (b) Delley, B. J. Chem.
Phys. 1991, 94, 7245-7250. (c) Delley, B. J. Phys. Chem. 1996, 100,
6107-6110. (d) Delley, B. J. Chem. Phys. 2000, 113, 7756-7764.
(54) Frisch, M. J., et al. Gaussian 03, Revision C.02; Gaussian, Inc.; Wallingford,
CT, 2004.
(48) Sheldrick, G. M. SADABS, A program for area detector absorption
corrections; University of Go¨ttingen: Go¨ttingen, Germany, 1994.
(49) Sheldrick, G. M. Acta Crystallogr. A 1990, 46, 467-473.
(50) Sheldrick, G. M. SHELX97, Program for Crystal Structure Refinement;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(55) Klamt, A.; Schu¨u¨rmann, G. J. Chem. Soc., Perkin Trans. 2 1993, 799-
805.
9
J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006 11171

A R T I C L E S
Park et al.
program (2005-02618) of the Korea Science and Engineering
Foundation (KOSEF) funded by Korean Ministry of Science
& Technology (MOST). This work was also supported in part
by the SRC program (R11-2005-008-03001-0) of the KOSEF
through the Center for Intelligent Nano-Bio Materials at Ewha
Womans University.
Supporting Information Available: Details of the crystal-
lographic studies of 2, 3, and 5 (PDF); X-ray crystallographic
files for 2, 3, and 5 (CIF); and complete ref 54. This material
is available free of charge via the Internet at http://pubs.acs.org.
JA0616027
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11172 J. AM. CHEM. SOC. VOL. 128, NO. 34, 2006