Syntheses, characterisation and electrochemical properties of C 70-metal cluster complexes

Article abstract of DOI:10.3184/174751913X13639616845172

The complexes [Os₃(CO)₉(μ₃- ν²:ν²:ν²-C₇₀)] and [Re ₃(μ-H)₃(CO)₉(μ₃- ν²:ν²:ν²-C₇₀)] have be

Full text of DOI:10.3184/174751913X13639616845172

JOURNAL OF CHEMICAL RESEARCH 2013
RESEARCH PAPER 257
MAY, 257–262
Syntheses, characterisation and electrochemical properties of C70-metal
cluster complexes
Chang Yeon Lee*
Department of Energy and Chemical Engineering, Incheon National University, Incheon 406-772, Korea
The complexes [Os3(CO)9(µ3-η2:η2:η2-C70)] and [Re3(µ-H)3(CO)9(µ3-η2:η2:η2-C70)] have been prepared by reaction of C70
with [Os3(CO)10(NCMe)2] or [Re3(µ-H)3(CO)11(NCMe)] and their electrochemical properties studied by cyclic voltam-
metry in chlorobenzene solutions. The complex [Re3(µ-H)3(CO)8(CNCH2Ph)(µ3-η2:η2:η2-C70)] has also been synthesised
by reaction between [Re3(µ-H)3(CO)9(µ3-η2:η2:η2-C70)] and PhCH2N=PPh3.
Keywords: C70-metal cluster complexes, Re, Os, carbonyls, electrochemistry
Since the discovery of [60]fullerene and its synthesis in mass
quantities,1 many fullerene derivatives have been synthesised
and characterised to develop new nanomaterials and nanode-
vices.2–4 Among them, exohedral metallofullerenes have
received significant attention concerning the effects of metal
coordination on the chemical and physical properties of C60.5–14
In particular, C60-metal cluster complexes, including a face-
capping, cyclohexatriene-like bonding mode between metal-
cluster and C60, confer robust thermal and electrochemical
stabilities, as well as strong electronic communication
between C60 and metal cluster centres, to C60-metal cluster
complexes.15–23
In contrast to the well-defined studies about C60-metal clus-
ter complexes, research on C70-metal cluster complexes has
been rarely demonstrated and their electrochemical properties
have not been addressed so far. For example, Shapley and
coworkers have reported the preparation and structural charac-
terisation of the triruthenium-C70 complex, [Ru3(CO)9(µ3-η2:η2:
η2-C70)], in which the Ru3 triangle is coordinated to the
near polar C6 ring in C70 (Scheme 1).24 The same group have
published the triphenylphosphine-substituted derivatives of
[Ru3(CO)9(µ3-η2:η2:η2-C70)].25
reaction of [Re3(µ-H)3(CO)11(NCMe)] with 0.5 equiv. of C70 in
CB for 3h in 40% yield. Substitution of 2 with 1.2 equiv. of
PhCH2N=PPh3 in CB at room temperature for 12h afforded a
regioisomeric mixture (vide infra) of compound 3 in 53%
yield. The new compounds 1 and 2 are soluble in CS2 and
chlorinated benzene, whereas compound 3 is soluble in vari-
ous organic solvent such as CS2, dichloromethane, toluene,
and chlorinated benzenes. All the compounds were confirmed
by the molecular ion isotope patterns [m/z (highest peak): 1668
(1); 1656 (2); 1889 (3)] in the positive ion FAB mass spectra.
The IR spectra of 1 and 2 are identical to those of
[Os3(CO)9(µ3-η2:η2:η2-C60)],17 and [Re3(µ-H)3(CO)9(µ3-η2:η2:η2-
C60)]20 respectively. Furthermore, the IR spectra of 3 is similar
to that of [Re3(µ-H)3(CO)8(CNCH2Ph)(µ3-η2:η2:η2-C60)],20 in
which the benzyl isocyanide ligand occupies an axial position.
These results indicate that compounds 1–3 are isostructural
with their C60 analogues.
The 13C NMR spectrum of compound 1 at room temperature
is shown in Fig. 1. The carbonyl region in the 13C NMR spec-
trum of 1 shows two resonances at δ 176.1 and 175.6 in an
intensity ratio of 2:1 (Fig. 1a). The separate sets are presum-
ably due to the two different types of Os(CO)3 groups in 1,
assuming rapid local equilibration at each metal centre. On the
other hand, the sp3 carbon region of 1 shows three resonances
at δ 58.2, 54.8, and 51.0 with an intensity ratio of 1:1:1, which
is assigned to the six coordinated carbons (Fig. 1b). These
observations indicate that the triosmium cluster is bound to the
near-polar C6 ring in C70 as previously reported in [Ru3(CO)9
(µ3-η2:η2:η2-C70)],24 so that the symmetry of 1 is reduced to Cs
(Fig. 1b).
In order to investigate more specific characteristics and the
electrochemical properties of C70-metal cluster complexes, we
now report the synthesis and characterisation of the C70-metal
cluster complexes, [Os3(CO)9(µ3-η2:η2:η2-C70)] (1), [Re3(µ-H)3
(CO)9(µ3-η2:η2:η2-C70)](2)and[Re3(µ-H)3(CO)8(CNCH2Ph)(µ3-
η2:η2:η2-C70)] (3), as summarised in Scheme 2.
Results and discussion
Synthetic procedures for 1–3 are summarised in Scheme 2.
Compound 1 was prepared in 11% yield from the thermal reac-
tion of [Os3(CO)10(NCMe)2] with 1 equiv. of C70 in chloroben-
zene (CB). Compound 2 can be prepared from the thermal
1
The H NMR spectrum (hydride region) and the 13C NMR
spectrum of compound 2 at room temperature are shown in
Fig. 2. The NMR data indicate an idealised Cs symmetry for 2
in solution similar to compound 1 and previously reported in
1
[Ru3(CO)8(µ3-η2:η2:η2-C70)].24 The H NMR spectrum shows
two hydridic resonances at δ –16.1 and –16.3 in an intensity
ratio of 1:2 due to two different types of hydride in 2 (Fig. 2a).
Furthermore, the 13C NMR spectrum (sp3 carbon region, see
Fig. 2c) shows three resonances at δ 58.2, 54.8, and 51.0 with
an intensity ratio 1:1:1 as shown in compound 1. However,
the 13C NMR spectrum of compound 2 [carbonyl region see
Fig. 2(b)] shows five resonances at δ 184.9, 183.8, 182.6,
182.5, and 182.2 in an intensity ratio of 2:1:2:2:2 for nine
carbonyls, which implies the absence of a fast localised 3-fold
rotation of three carbonyl groups on each rhenium atom at
room temperature. The C60 analogue [Re3(µ-H)3(CO)9(µ3-η2:η2:
η2-C60)],20 however, has one resonances at δ 183.2 for the nine
carbonyl ligands due to the fast localised three-fold rotation of
three carbonyl groups on each rhenium centre.
1
The H NMR and 13C NMR spectra of complex 3 at room
Scheme 1 Projection diagram of [Ru3(CO)9(µ3-η2:η2:η2-C70)]24
temperature are shown in Figs 3 and 4, respectively. 1H NMR
(methylene region and hydride region) data of 3 appear as two
sets of resonances in an intensity ratio of 2:1, implying that 3
(Ru3 triangle marked in bold).
* Correspondent. E-mail: cylee@incheon.ac.kr

258 JOURNAL OF CHEMICAL RESEARCH 2013
Scheme 2 (1) Me3NO(2.2 equiv.)/MeCN, then C70, 132 °C, 2 h; (2) C70 (0.5 equiv.), 132 °C, 3 h; (3) PhCH2=PPh3 (1.2 equiv.), 12h
(carbonyl ligands are omitted for clarity).
Fig. 1 13C NMR spectrum (100 MHz, o-ODCB-d4, 298 K) of 1. (a) Carbonyl region (b) sp3 carbon region.

JOURNAL OF CHEMICAL RESEARCH 2013 259
1
Fig. 2 (a) H NMR spectrum (400Hz, CS2/CD2Cl2) of 2 (hydride region). (b) 13C NMR spectrum (100 MHz, CS2/CD2Cl2, 298 K) of 2
(carbonyl region). (c) 13C NMR spectrum (100 MHz, CS2/CD2Cl2, 298 K) of 2 (sp3 carbon region).
1
exists as two isomers in solution. H NMR of the methylene
region for the benzylic protons of the isocyanide ligand reveals
a singlet at δ 5.20 for the major isomer, along with a small
singlet at δ 5.17 for the minor isomer [see Fig. 3(a)]. Moreover,
The electrochemical properties of complexes 1 and 2 have
been examined by the cyclic voltammetric method in CB solu-
tions with tetrabutylammonium perchlorate as the supporting
electrolyte. Cyclic voltammograms (CVs) of 1 and 2 are shown
in Fig. 5. Half-wave potentials (E1/2) of 1 and 2, together with
free C70, are summarised in Table 1. All the CVs of 1 and 2
reveal four reversible redox waves that each correspond to a
one-electron process. The second reduction of 1 occurs at a
potential of –1.23 V, with a significant positive shift (210 mV)
relative to that of free C70 at –1.44 V. This unusually large
positive shift suggests that the one electron accepted through
the C70 ligand in [1]− is delocalised to the triosmium centre
with its strong π-acid carbonyl ligands, as previously proposed
for the triosmium-C60 analogue.18 Anionic species [1]− with
electron delocalisation to the osmium centre, therefore, under-
goes easier reduction via the C70 ligand than free C70− to afford
[1]2−. The fourth reduction potential (–1.65 V) of 1 is very
close to the third reduction potential (–1.51 V) and even more
positive than the third reduction of C70 (–1.88V), which implies
that further electron delocalisation from C70 to the triosmium
cluster occurred in [1]3− as well. In the same way, the second
(–1.19 V) and third (–1.38 V) reduction potentials of 2 are very
close to the first (–1.05 V) and second (–1.19 V) reduction
potentials and even more positive than the second (–1.44 V)
1
the H NMR spectrum [hydride region see Fig. 3(b)] of 3
shows three singlet resonances at δ –15.6, –15.8, and –16.2, in
an intensity ratio of 1:1:1, for the major isomer and two singlet
resonances at δ –15.8 and –16.0, in an intensity ratio of 2:1, for
1
the minor isomer. H NMR data would appear to correspond
to substitution of a benzyl isocyanide ligand on each of the
two possible rhenium centers (ratio 2:1) in the Cs symmetric
structure of 2 [see Fig. (3c)]. The major isomer may not have
the symmetry of the parent complex due to unsymmetrical
substitution of carbonyl on the rhenium centre, while the minor
isomer retains its symmetry as Cs.
The 13C NMR spectrum of 3 [carbonyl region see Fig. 4(a)]
shows 12 resonances for major and minor isomers, implying
the absence of any exchange process of carbonyl ligands on
each rhenium atom at room temperature. The 13C NMR spec-
trum of the sp3 carbon region [see Fig. 4(b)] also shows nine
resonances for the isomeric mixture of 3 and two resonances at
δ 49.5, and 49.4 in an intensity ratio of 2:1 for the methylene
carbons of the isocyanide ligand, which is consistent with
existence of an isomeric mixture with a ratio of 2:1.

260 JOURNAL OF CHEMICAL RESEARCH 2013
Fig. 3 1H NMR spectrum (400Hz, CDCl3) of 3. (a) methylene region. (b) hydride region. (c) projection diagrams of two possible
rhenium centres regarding substitution reaction in complex 2.
Os3(CO)9(µ3-η2:η2:η2-C70) (1): An acetonitrile solution (3 mL) of
and third (–1.88 V) reduction potential of C70, respectively.
anhydrous Me3NO (12.0 mg, 0.156 mmol) to a dichloromethane/
acetonitrile (50/4 mL) solution of [Os3(CO)12] ( 65 mg, 0.071 mmol)
was added dropwise at room temperature, and the reaction mixture
was stirred for 1 h. After evaporation of the solvent in vacuo, the resi-
due was dissolved in chlorobenzene (5 mL). The resulting yellow
solution was added dropwise to a chlorobenzene (50 mL) solution
of C70 (50 mg, 0.060 mmol), and the reaction mixture was stirred at
80 °C for 30 min to give a blue-green solution. The solution was
concentrated to ca 10 mL under vacuum, and the resulting solution
was heated to reflux for 90 min. After solvent removal in vacuo, the
residue was purified by column chromatography (silica gel, CS2) to
afford the desired [Os3(CO)9(µ3-η2:η2:η2-C70)] (1) as a reddish-brown
solid (11 mg, 0.006 mmol, 11%). IR (CS2) ν (CO) 2082 (s), 2046 (vs),
2016 (m), 2002 (m), 1984 (sh) cm−1; 13C NMR (o-dichlorobenzene-d2,
298 K) δ 176.1 (s, 6CO), 175.6 (s, 3CO). The 13C NMR signal from
the unbounded sp2 carbon in the C70 ligand cannot be assigned because
it overlapped with solvent signal, 58.2 (2C, C70 sp3 carbon), 54.8
(2C, C70 sp3 carbon), 51.0 (2C, C70 sp3 carbon); MS (FAB+) m/z 1763
(M+).
Re3(µ-H)3(CO)9(µ3-η2:η2:η2-C70) (2): A chlorobenzene solution
(60 mL) of [Re3(µ-H)3(CO)11(NCMe)] (151.7 mg, 0.167 mmol) and
C70 (60.0 mg, 0.0833 mmol) was heated under reflux for 3 h. Evapora-
tion of the solvent and purification by preparative TLC (silicagel, CS2)
produced compound 2 (63.3 mg, 0.0413 mmol, 48%, Rf = 0.9) as a red
brown solid: IR (CS2) ν (CO) 2074 (s), 2048 (s), 2008 (m), 1987 (m),
1927 (m) cm−1; 1H NMR (400 MHz, CS2/ext.CD2Cl2, 298 K) –16.1 (s),
–16.3; 13C(1H) NMR (100 MHz, CS2/ext.CD2Cl2, 298 K) 184.9 (s,
2CO), 183.8 (1CO), 182.6 (2CO), 182.5 (2CO), 182.2 (2CO), 159.5
(1C), 154.6 (2C), 152.8 (1C), 152.1 (2C), 152.0 (2C), 150.8 (2C),
This observation also implies that electron delocalisation from
C70 to the trirhenium centre occurred in [2]− and [2]2− as well.
In conclusion, C70-triosmium and trirhenium complexes,
[Os3(CO)9(µ3-η2:η2:η2-C70)] (1), [Re3(µ-H)3(CO)9(µ3-η2:η2:η2-
C70)] (2), have been synthesised and characterised in this work.
1
From the spectroscopic data (IR, MS, H and 13C NMR), we
found that the metal cluster is coordinated to the near polar
C6 ring in C70, so that the symmetry of 1 and 2 were reduced to
Cs. Furthermore, a regioisomeric mixture was found in the
benzylisocyanide derivatives of 2, due to the two possible
rhenium centres (ratio 2:1) in the Cs symmetric structure of 2.
Electrochemical studies of compound 1 and 2 reveal that
C70-mediated electron transfer to metal cluster takes place
in C70-metal cluster complexes, which have the µ3-η2:η2:η2
bonding mode.
Experimental
All the reactions were carried out under a dinitrogen atmosphere with
use of standard Schlenk techniques. Solvents were dried over the
appropriate drying agents and distilled immediately before use. C70
(98%, SES research) was used without further purification. PhCH2N=
PPh326 and Re3(µ-H)3(CO)11(NCMe)27 were prepared according to the
literature methods. Preparative TLC plates were prepared with silica
gel GF254 (type 60, E. Merck). IR 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. Positive ion FAB mass spectra (FAB+) were obtained by
the staff of the Korea Basic Science Center, and all m/z values were
referenced to 192Os.

JOURNAL OF CHEMICAL RESEARCH 2013 261
Fig. 4 13C NMR spectrum (100 MHz, CDCl3, 298 K) of 3. (a) carbonyl region (b) sp3 carbon region.
Table 1 Half-wave potentials (E1/2 versus EoFc/Fc+) of free C70, 1
and 2
0/−1
−1/−2
−2/−3
−3/−4
Compound
C70
E1/2
E1/2
E1/2
E1/2
Solvent
–1.06 –1.44 –1.88 –2.34
CB
CB
[Os3(CO)9(µ3-η2:η2:η2-C70)] –1.05 –1.23 –1.51 –1.65
(1)
[Re3(µ-H)3(CO)9(µ3-η2:η2:
η2-C70)] (2)
–1.05 –1.19 –1.38 –1.75
CB
CB, Chlorobenzene.
Evaporation of the solvent and separation by TLC (CS2) afforded
compound 3 (16.7 mg, 0.0103 mmol, 53%, Rf = 0.5) as a red-brown
solid: IR (CS2) ν (NC) 2178 (m); ν (CO) 2060 (vs), 2043 (s), 2011 (s),
1986 (m), 1971 (s), 1954 (m) cm−1; 1H NMR (400 MHz, CDCl3, 298
K) Major isomer: 7.6–7.3 (m, 5H), 5.20 (s, 2H), –15.6 (s, 1H), –15.8
(s, 1H) –16.2 (s, 1H), Minor isomer: 7.6 – 7.3 (m, 5H), 5.17 (s, 2H),
–15.8 (s, 2H), –16.0 (s, 1H); MS (FAB+) m/z 1744 (M+).
Fig. 5 Cyclic voltammograms of 1 and 2 in dry deoxygenated
chlorobenzene (0.1 M [(n-Bu)4N][ClO4]). Scan rate = 5mV s−1.
Received 23 January 2013; accepted 14 February 2013
Paper 1301743 doi: 10.3184/174751913X13639616845172
Published online: 15 May 2013
150.6 (2C), 150.4 (2C), 150.2 (2C), 150.0 (1C), 149.5(2C), 149.3
(2C), 149.1 (1C), 148.9 (2C), 148.4 (2C), 148.0 (2C), 147.9 (2C),
147.5 (2C), 147.4 (2C), 147.2 (2C), 147.1 (2C), 146.6 (2C), 146.0
(2C), 145.6 (2C), 145.0 (2C) 144.4 (2C), 144.1 (2C), 143.4 (2C),
143.3 (2C), 133.3 (2C), 132.3 (2C), 132.1 (2C), 130.9 (2C), 129.8
(2C), 75.9 (2C, C70 sp3 carbon), 74.5 (2C, C70 sp3 carbon), 72.6 (2C,
C70 sp3 carbon); MS (FAB+) m/z 1656 (M+).
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