Anionic fullerene-60 complexes of manganese(-I), cobalt(-I), and rhenium(-I): Thermal and photoinduced electron transfer processes between metal carbonylate anions and C60

Article abstract of DOI:10.1021/om020396i

Thermal and photochemical reactions of THF solutions of the carbonylate salts A[Mn(CO)₅], A[Co(CO)₄], and A[Re(CO)₅] (A = Na, PPN) with suspensions of C₆₀ result in electron transfer to give [C₆₀]^- and the transient 17-electron, metal-centered radicals Mn(CO)₅, Co(CO)₄, and Re(CO)₅, respectively. However, the ensuing secondary processes vary significantly, depending on the metal and the reaction conditions. With manganese and rhenium, self-coupling of M(CO)₅ (M = Mn, Re) to give the metal-metal bonded dimers M2(CO)₁₀ and coupling of M(CO)₅ with [C₆₀]^- to give the η²-C₆₀ complexes A[Mn(CO)₄(η²-C₆₀)] both occur under thermal and photochemical conditions. In contrast, the photochemical processes ultimately result also in complete homolysis of the dimers and regeneration of the metal-centered radicals, which then combine with fullende ion [C₆₀]^- still remaining in solution to form more of the η²-C₆₀ complexes. In the case of cobalt, no Co₂(CO)₈ is formed, but the η²-C₆₀ complex [Co(CO)₃(η²-C₆₀]^- is produced. While the latter is thermally unstable in refluxing THF, undergoing decarbonylation to the previously reported mixed metal fullende compound NaCoC₆₀·3THF, it is thermally stable under photochemical conditions at room temperature. Spectroscopic evidence suggests that much of the negative charge in [Mn(CO)₄(η²-C₆₀)]^- is delocalized onto the fullerene ligand; as a result, the η²-C₆₀-Mn bond is unusually strong and the complex [Mn(CO)₄(η²-C₆₀)]^- is very stable, exhibiting little of the chemistry associated with either neutral η²-C₆₀ complexes or the analogous [Mn(CO)₅]^-.

Full text of DOI:10.1021/om020396i

4762
Organometallics 2002, 21, 4762-4770
An ion ic F u ller en e-60 Com p lexes of Ma n ga n ese(-I),
Coba lt(-I), a n d Rh en iu m (-I): Th er m a l a n d
P h otoin d u ced Electr on Tr a n sfer P r ocesses betw een
Meta l Ca r bon yla te An ion s a n d C60
David M. Thompson, M. Bengough, and Michael C. Baird*
Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6
Received May 16, 2002
Thermal and photochemical reactions of THF solutions of the carbonylate salts A[Mn-
(CO)5], A[Co(CO)4], and A[Re(CO)5] (A ) Na, PPN) with suspensions of C60 result in electron
transfer to give [C60]- and the transient 17-electron, metal-centered radicals Mn(CO)5, Co-
(CO)4, and Re(CO)5, respectively. However, the ensuing secondary processes vary signifi-
cantly, depending on the metal and the reaction conditions. With manganese and rhenium,
self-coupling of M(CO)5 (M ) Mn, Re) to give the metal-metal bonded dimers M2(CO)10 and
coupling of M(CO)5 with [C60]- to give the η2-C60 complexes A[Mn(CO)4(η2-C60)] both occur
under thermal and photochemical conditions. In contrast, the photochemical processes
ultimately result also in complete homolysis of the dimers and regeneration of the metal-
centered radicals, which then combine with fulleride ion [C60]- still remaining in solution to
form more of the η2-C60 complexes. In the case of cobalt, no Co2(CO)8 is formed, but the
η2-C60 complex [Co(CO)3(η2-C60)]- is produced. While the latter is thermally unstable in
refluxing THF, undergoing decarbonylation to the previously reported mixed metal fulleride
compound NaCoC60‚3THF, it is thermally stable under photochemical conditions at room
temperature. Spectroscopic evidence suggests that much of the negative charge in [Mn-
(CO)4(η2-C60)]- is delocalized onto the fullerene ligand; as a result, the η2-C60-Mn bond is
unusually strong and the complex [Mn(CO)4(η2-C60)]- is very stable, exhibiting little of the
chemistry associated with either neutral η2-C60 complexes or the analogous [Mn(CO)5]-.
Metal-C60 compounds generally fall into one of three
behaves essentially as a weakly conjugated, electron-
deficient alkene ligand.3 While a few incompletely
characterized transition metal fulleride compounds are
known,2c-n none have as of yet been observed to exhibit
the high-temperature superconductivities of many alkali
metal fullerides. Nonetheless, one might anticipate that
transition metal fullerides, with the possibility of varia-
tions in d electron configurations, metal oxidation states,
and nuclearities, present enticing opportunities for
further research.
It is well established that C60 contains a low lying,
triply degenerate LUMO, thus making possible facile
reduction to the above-mentioned fullerides.2a,b We have
previously noted that transition metal carbonylate
anions have sufficiently low ionization potentials that
they should be capable of reducing C60 to radical anions
[C60]n- and have demonstrated that the reaction of Na-
[Co(CO)4] with C60 in refluxing THF results in the
formation of an insoluble, bimetallic fulleride compound
NaCoC60‚3THF.4 Although the latter could not be
characterized structurally, it exhibits antiferromagnetic
properties which confirm the possibility of magnetic
coupling in such materials. A small number of other
reports of reduction of C60 by electron-rich organome-
main categories: endohedral compounds in which the
metal atom is encapsulated by the fullerene sphere,1
exohedral alkali metal fulleride compounds containing
discrete anionic species [C60]n- (n ) 1-6),2a,b and η2-
transition metal complexes in which the fullerene
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10.1021/om020396i CCC: $22.00 © 2002 American Chemical Society
Publication on Web 09/24/2002

Anionic Fullerene-60 Complexes
Organometallics, Vol. 21, No. 22, 2002 4763
High-resolution ESMS experiments were carried out on a
Micromass Q-TOF-2 quadrupole time-of-flight mass spectrom-
eter. Mass-to-charge ratios reported below refer in all cases
to the strongest peak in what are always complex distributions
of isotopomers. 13C NMR were recorded on a Bruker AM-500
spectrometer and are referenced on the basis of comparisons
with the solvent resonances. Near-IR spectra (800-1300 nm)
were run on a Cary 17 UV-vis spectrophotometer; UV-vis
spectra (190 nm-820 nm), on a HP 8452A diode array spec-
trophotometer.
Chemicals were generally obtained from Aldrich, Fisher, or
Strem, while C60 was obtained from MER Corp. The com-
pounds Na[Co(CO)4],8a Na[Mn(CO)5],8b PPN[Mn(CO)5],8c and
PPN[Co(CO)4]8d were prepared as in the literature. We were
unable to prepare pure Na[Re(CO)5] using the methods
described in the literature, which involves stirring a solution
of Re2(CO)10 in diethyl ether or THF over sodium amalgam.8e,f
Complex (by IR) orange mixtures were invariably obtained,
and it seemed likely that Na[Re(CO)5] was reacting with Re2-
(CO)10 to form polynuclear anionic clusters.8e We therefore
developed a method that maintained a low concentration of
Re2(CO)10 in the presence of Na[Re(CO)5]. A solution of 2.0 g
of Re2(CO)10 (3.1 mmol) in 70 mL of THF was added dropwise
over 45 min to a flask containing 80 g of 1% sodium amalgam.
The dominant carbonyl absorptions in the IR spectrum of the
resulting yellow solution were those characteristic of Na[Re-
(CO)]5 (1830, 1864, 1907 cm-1).8e,f The solution was filtered
through Celite and treated with 50 mL of pentanes to give a
yellow precipitate of the product. The solid was filtered,
washed with pentanes (3 × 25 mL), and dried under reduced
pressure.
F igu r e 1. Molecular structure of the anion of PPN[Mn-
(CO)4(η2-C60)].
tallics have also appeared,5 and we are investigating
the reactions of a variety of metal carbonylate complexes
with C60. We have in a communication6a and a confer-
ence proceeding6b reported that the carbonylate anion
[Mn(CO)5]- does indeed reduce C60 and have reported
the crystal structure of PPN[Mn(CO)4(η2-C60)], a product
of this reaction and the first well-characterized fullerene
complex of a metal in a negative oxidation state. The
structure of the complex anion is shown in Figure 1,
where it is seen that the C60 coordinates in conventional
η2-fashion. We now report fully on the η2-C60 complexes
formed during reactions of C60 with the carbonylate
complexes A[Mn(CO)5], A[Co(CO)4], and A[Re(CO)5] (A
) Na, PPN).
The compound NaC60 was prepared following a variation
on the literature procedure.9 C60 (260 mg, 0.36 mmol), Na
metal (7 mg, 0.33 mmol), and naphthalene (50 mg, 0.39 mmol)
were stirred together in 50 mL of THF under argon. The
solution quickly developed a deep burgundy color, and ESMS
monitoring revealed the expected peak at 720 Da/e. In addi-
tion, a near-IR spectrum exhibited the characteristic absorp-
tion at 1076 nm.2a,b The solution was filtered and the solvent
was removed from the filtrate under reduced pressure to give
the black product, which was washed with toluene and dried.
Exp er im en ta l Section
All reactions were carried out using standard Schlenk line
techniques or in Vacuum Atmospheres or Mbraun gloveboxes.
Argon and nitrogen were purified by passing through a column
of BASF catalyst heated to 140 °C and subsequently through
a second column containing 5 Å molecular sieves. Solvents
were purified by distillation from a drying agent under a
blanket of nitrogen or argon. In most cases Na wire was used
as the drying agent, the exceptions being dichloromethane and
acetonitrile, for which CaH2 and P2O5 were used, respectively.
Infrared (IR) spectra were recorded on a Bruker IFS 25
FTIR spectrometer, and negative ion mode electrospray mass
spectrometry (henceforth ESMS)7 experiments on a VG Quat-
tro with nitrogen as the nebulizing gas. Typical concentrations
of the species being studied were 1-5 mM, and the capillary
voltage, cone voltage, lens parameters, ionization energy and
ramp, position of the source, flow rate of the sample, and time
of acquisition were all varied in order to optimize the intensity
of the peak being studied. Low cone voltages < 30 V were
normally used to observe parent ions in solution, and higher
cone voltages (up to 150 V) to observe fragmentation products.
Th er m a l Rea ction s of A[Mn (CO)5], A[Co(CO)4], a n d
A[Re(CO)5] (A ) Na , P P N) w ith C60. In a typical reaction,
100 mg of C60 (0.14 mmol) was added to a solution containing
0.14 mmol of A[Co(CO)4], A[Mn(CO)5], or A[Re(CO)5] in 100
mL of THF under argon. The solution was refluxed, IR spectra
being recorded immediately and thereafter every half hour or
more. Workup procedures generally involved cooling the
reaction mixture followed by filtration. Addition of hexanes
to the filtrate resulted in precipitation of the product, which
was washed with toluene and hexanes and then dried under
reduced pressure.
P h otoch em ica l Rea ction s of A[Mn (CO)5], A[Co(CO)4],
a n d A[Re(CO)5] (A ) Na , P P N) w ith C60. In a typical
(7) For information on electrospray mass spectrometry and applica-
tions to organometallic and fullerene chemistry, see: (a) Gaskell, S.
J . J . Mass Spectrom. 1997, 32, 677. (b) Colton, R.; D’Agostino, A.;
Traeger, J . C. Mass Spectrom. Rev. 1995, 14, 79. (c) Henderson, W.;
Nicholson, B. K.; McCaffrey, L. J . Polyhedron 1998, 17, 4291. (d)
Henderson, W.; McIndoe, J . S.; Nicholson, B. K.; Dyson, P. J . J . Chem.
Soc., Dalton Trans. 1998, 519. (e) Ferrer, M.; Reina, R.; Rossell, O.;
Seco, M.; Segales, G. J . Organomet. Chem. 1996, 515, 205. (f)
Khairallah, G.; Peel, J . B. Chem. Commun. 1997, 253. (g) Barrow, M.
P.; Feng, X.; Wallace, J . I.; Boltalina, O. V.; Taylor, R.; Derrick, P. J .;
Drewello, T. Chem Phys. Lett. 2000, 330, 267.
(8) (a) Edgell, W. F.; Lyford, P. J . Am. Chem. Soc. 1971, 93, 6406.
(b) King, R. B.; Stone, F. G. A. Inorg. Synth. 1974, 15, 196. (c) Faltynek,
R.; Wrighton, M. S. J . Am. Chem. Soc. 1978, 100, 2701. (d) Lee, K. Y.;
Kochi, J . K. Inorg. Chem. 1989, 28, 567. (e) Ellis, J . E.; Flom, E. A. J .
Organomet. Chem. 1975, 99, 263. (f) Hileman, J . C.; Huggins, D. K.;
Kaesz, H. D. Inorg. Chem. 1962, 1, 933.
(5) (a) Bossard, C.; Rigaut, S.; Astruc, D.; Delville, M.-H.; Fe´lix, G.;
Fe´vrier-Bouvier, A.; Amiell, J .; Flandrois, S.; Delhae`s, P. J . Chem. Soc.,
Chem. Commun. 1993, 333. (b) Bochkarev, M. N.; Fedushkin, I. L.;
Nevodchikov, V. I.; Protchenko, A. V.; Schumann, H.; Girgsdies, F.
Inorg. Chim. Acta 1998, 280, 138. (c) Boyd, P. D. W.; Bhyrappa, P.;
Paul, P.; Stinchcombe, J .; Bolskar, R. D.; Sun, Y.; Reed, C. A. J . Am.
Chem. Soc. 1995, 117, 2907. (d) Mrzel, A.; Omerzu, A.; Umek, P.;
Mihailovic, D.; J aglicˇic´, Z.; Trontelj, Z. Chem Phys. Lett. 1998, 298,
329.
(6) (a) Bengough, M.; Thompson, D. M.; Baird, M. C. Organometal-
lics 1999, 18, 2950. (b) Thompson, D. M.; McLeod, J .; Baird, M. C.
Pure Appl. Chem. 2001, 273, 287.
(9) Chen, J .; Cai, R.-F.; Huang, Z.-E. Solid State Commun. 1995,
95, 239.

4764 Organometallics, Vol. 21, No. 22, 2002
Thompson et al.
reaction, 100 mg of C60 (0.14 mmol) was added to a solution
containing 0.14 mmol of A[Mn(CO)5], A[Co(CO)4], or A[Re-
(CO)5] in 100 mL of THF under argon. A Hanovia lamp, placed
inside a water-cooled quartz tube, was situated 10-12 cm
away from the reaction vessel, and the stirred reaction mixture
was photolyzed for several hours while being monitored as
above by IR spectroscopy and ESMS. Workup procedures were
generally as above.
P h otoch em ica l Rea ction s of Mn 2(CO)8 a n d Co2(CO)8
w ith Na C60. A solution of 100 mg of NaC60 (0.13 mmol) and
0.065 mmol of Mn2(CO)10 or Co2(CO)8 in 100 mL of THF was
photolyzed as above for several hours while being monitored
by IR spectroscopy and ESMS. Workup procedures were as
described above. Yields of Na[Mn(CO)4(C60)] and Na[Co(CO)3-
(C60)] were 36 mg (29%) and 45 mg (37%), respectively; the
products were characterized by IR spectroscopy and ESMS.
Rea ction s of A[Mn (CO)4(C60)] a n d A[Co(CO)3(C60)] (A
) Na , P P N) w ith Ter tia r y P h osp h in es. Solutions of 25-
50 mg of A[Mn(CO)4(C60)] or A[Co(CO)3(C60)] (A ) Na, PPN)
in 100 mL of THF were treated with a slight excess of PMe2-
Ph or PPh3 and then stirred for 3 h at 20 °C. IR monitoring
showed that in neither case had reaction occurred, and the
reaction mixtures were refluxed for 3 h and then photolyzed
as above for 12 h. Throughout this process, IR spectroscopy
showed slow loss of starting materials but no evidence for new
carbonyl compounds of any kind. In a separate experiment
PPN[Mn(CO)4(η2-C60)] was also found to be inert to PMe2Ph
in refluxing THF in the presence of anhydrous trimethylamine
oxide.
F igu r e 2. Mass spectrum of PPN[Mn(CO)4(η2-C60)]: (a)
full spectrum; (b) experimental isotope distribution; (c)
calculated isotope distribution.
In an effort to obtain better crystals, the reaction of
PPN[Mn(CO)5] with C60 was investigated. The reaction
was monitored by IR spectroscopy and ESMS as de-
scribed above, and PPN[Mn(CO)4(η2-C60)] was obtained
in 23% yield. This compound was better obtained by
photolysis of equimolar amounts of C60 and PPN[Mn-
(CO)5] in THF at room temperature. Monitoring by IR
spectroscopy and ESMS showed that the [Mn(CO)5]-
disappeared completely within 3 h, forming Mn2(CO)10
and PPN[Mn(CO)4(η2-C60)], while continued photolysis
(up to 48 h) resulted in a slower loss of the νCO of Mn2-
(CO)10 and an increase in the intensity of νCO of PPN-
[Mn(CO)4(η2-C60)]. The latter was eventually obtained
in 93% yield. As expected, photolysis of Na[Mn(CO)5]
with C60 proceeded in a similar fashion to form Na[Mn-
(CO)4(η2-C60)].
Rea ction of P P N[Mn (CO)4(C60)] w ith MeI. A solution of
50 mg of PPN[Mn(CO)4(η2-C60)] and 1 mL of CH3I in 100 mL
of THF was refluxed, the progress of the reaction being
monitored by IR spectroscopy and ESMS. After several hours,
the initial νCO of the starting material were replaced by new
ν
a
CO at 1929, 1972, 1995, and 2068 cm-1 and the ESMS revealed
strong peak at 421 Da/e with an isotope distribution
consistent with [Mn(CO)4I2]-. The pale amber colored solution
was filtered, and a black precipitate was separated from the
supernatant. The solvent was removed from the supernatant
to give a mixture containing PPN[Mn(CO)4I2], which was
identified by ESMS and IR spectroscopy (νCO ) 1929, 1972,
1995, and 2068 cm-1) (see below). The black precipitate was
insoluble in THF, toluene, benzene, and acetone and was not
investigated further.
It was unfortunately found to be impossible to obtain
analytically pure material; carbon analyses of several
samples were variable, as is often the case with fullerene
complexes.3b However, the identity of the [Mn(CO)4(η2-
C60)]- anion was verified unambiguously by a high-
resolution ESMS study of a THF solution of isolated
PPN[Mn(CO)4(η2-C60)]. The molecular ion was observed
at 886.9160 Da/e, differing by only 1.7 mDa (1.9 ppm)
from the theoretical mass of 886.9177 Da/e. In addition,
as noted previously,6a sufficiently good crystals were
obtained that a crystal structure could be obtained by
layering a THF solution with hexanes (see below).
Resu lts a n d Discu ssion
Syn th eses a n d P r op er ties of A[Mn (CO)4(η2-C60)]
(A ) Na , P P N). The thermal reaction of equimolar
amounts of C60 and Na[Mn(CO)5] in refluxing THF was
monitored by IR spectroscopy for 18 h. The solution
turned deep green, and νCO of [Mn(CO)5]- (1895, 1861,
1828 cm-1) decreased in intensity while those of Mn2-
(CO)10 (2044, 2010, 1979 cm-1) and of the complex anion
A
13C NMR spectrum of PPN[Mn(CO)4(η2-C60)] was
recorded in THF-d8, and the chemical shifts of all peaks
are listed in Table 1. Resonances at δ 134.7, 133.6,
130.5, and 128.4 are attributed to the phenyl ring
carbons of the PPN+ cation on the basis of comparison
with the 13C NMR spectrum of the chloride salt. To aid
in assignments, the relative intensities of the fullerene
resonances are presented arbitrarily as ratios of the
intensity of the peak at δ146.27. The reduction of
symmetry from the Ih of C60 results in many of the
fullerene carbon atoms becoming nonequivalent, and
hence, a complex 13C NMR spectrum is observed. While
complete assignments of the resonances are not possible,
the number and relative intensities of those between δ
135 and 176 can be used to determine the symmetry of
the anion.3b There are 17 peaks in the spectrum, and
the 13C NMR spectrum of a fullerene complex with C2v
symmetry is expected to exhibit 17 13C resonances.3b
[Mn(CO)4(η2-C60)]- (2023, 1938, 1900, cm-1 6a
) appeared
and steadily increased in intensity. ESMS revealed that
the peak of [Mn(CO)5]- (195 Da/e) disappeared and that
the peak of [C60]- (720 Da/e) appeared, grew, and then
decreased in intensity; a peak at 887 Da/e, attributable
to [Mn(CO)4(η2-C60)]-, grew in over the course of the
reaction and was the only anionic product present at
the end of the reaction (Figure 2a). Identification of the
new species as [Mn(CO)4(η2-C60)]- was strengthened by
comparison of its isotope distribution (Figure 2b) with
the calculated isotope pattern (Figure 2c). On workup,
black Na[Mn(CO)4(η2-C60)] was obtained in 26% yield;
while seemingly rather stable thermally and, surpris-
ingly, somewhat stable even in air, the compound could
not be obtained analytically pure nor could crystallo-
graphically useful crystals be obtained.

Anionic Fullerene-60 Complexes
Organometallics, Vol. 21, No. 22, 2002 4765
Ta ble 1. 13C NMR Da ta for P P N[Mn (CO)4(η2-C60)]
Ta ble 3. Ca r bon yl Str etch in g F r equ en cies of
Ma n ga n ese Ca r bon yl Com p lexes
chemical shift of peak (ppm) relative intensity
assignment
complex
ν(CO) cm-1 (average)
128.40 (doublet)
130.52 (multiplet)
133.40 (multiplet)
134.74
PPN+
PPN+
PPN[Mn(CO)4(η2-C60)]
PPN[Mn(CO)5]
Mn2(CO)10
2025, ∼2015 (sh), 1938, 1900 (1970)
PPN+
1894, 1861 (1878)
PPN+
2044, 2009, 1979 (2011)
2025, 1938 (1982)
2068, 1989, 1974, 1958 (1997)
sp3-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
sp2-C60
η5-C5H5Mn(CO)3
η3-C3H5Mn(CO)4
85.81
136.32
142.26
142.75
143.33
143.43
144.39
145.97
146.20
146.27
146.48
146.64
146.83
147.36
148.33
151.22
174.39
1.82
1.96
2.07
1.78
2.16
1.69
1.91
1.85
1.00a
2.21
1.90
0.95
1.54
0.69
1.98
1.86
and is postulated as well for the isoelectronic, neutral
fullerene complexes M(CO)4(η2-C60) (M ) Fe, Ru).13 The
question arises as to whether the [Mn(CO)4(η2-C60)]-
anion is better regarded as a complex of manganese(0)
with a coordinated [C60]- or as a complex of manganese-
(-I) with a coordinated C60. The latter mode of bonding
seems to be implied by the near-IR and UV-vis data,
and we feel this to be an appropriate description of the
bonding in this complex anion. However, the X-ray
structural data shed no light and the IR data are
surprisingly ambiguous.
Indeed, before the ESMS spectrum was obtained and
well before the crystal structure was available, the IR
evidence seemed to suggest that the new compound was
a neutral species related to η5-C5H5Mn(CO)3 or η3-C3H5-
Mn(CO)4 rather than to [Mn(CO)5]-. In Table 3 is a
comparison of νCO of PPN[Mn(CO)4(η2-C60)] with those
of several carbonyl complexes of manganese in the
formal oxidation states 0, I, and -I. As can be seen, νCO
of PPN[Mn(CO)4(η2-C60)] are more similar to those of
complexes containing Mn(0) or Mn(I) than those of the
Mn(-I) complex PPN[Mn(CO)5]. The implied possibility
of η3- or η5-modes of coordination of the C60 to the
manganese was initially quite exciting, as these modes
of coordination are unknown for fullerenes.3 However,
the crystal structure of PPN[Mn(CO)4(η2-C60)] ulti-
mately showed unambiguously that there is nothing
unprecedented structurally in the complex anion.
Considering, therefore, the C60-Mn bonding on the
basis of conventional η2-coordination of a neutral C60
to a [Mn(CO)4]- moiety, it is clear that there must be
significant π back-donation from the formally Mn(-I)
to the C60. The latter is widely regarded as a weakly
conjugated, electron-deficient alkene,3 and it seems from
comparisons of the IR data that its π acceptor properties
in [Mn(CO)4(η2-C60)]- actually exceed those of an equa-
torial CO in [Mn(CO)5]-.14a
a
Arbitrarily assigned.
Ta ble 2. 55Mn NMR of Or ga n om a n ga n ese
Com p lexes
compound
chemical shift
reference
KMnO4
0
-1844
-1850
-1895
-2325
-2578
-2780
10
PPN[Mn(CO)4(η2-C60)]
Mn(CF3CO)(CO)5
Mn(CH3CO)(CO)5
Mn2(CO)10
this work
10
10
10
10
10
MnH(CO)5
Na[Mn(CO)5]
The 55Mn NMR spectrum of a THF solution of PPN-
[Mn(CO)4(η2-C60)] exhibited a single resonance at δ
-1843.8 (relative to KMnO4), and a comparison of this
chemical shift with those of other manganese com-
plexes10 is made in Table 2. It is interesting to note that
the 55Mn chemical shift of PPN[Mn(CO)4(η2-C60)] is
much more similar to those of complexes of Mn(I) than
of Mn(-I), although it is clear from the data that
conclusions regarding oxidation state cannot be made
on the basis of such data.
The UV-vis spectrum of PPN[Mn(CO)4(η2-C60)] in
CH2Cl2 exhibited absorption bands at 221, 260, 332, and
450 nm, the latter being relatively broad. The spectrum
is thus very similar to that of C60 in hexanes, which
exhibits absorptions at 215, 270, and 335 nm with a
broad band between 440 and 640 nm.11 A near-IR
spectrum run on this solution revealed no absorptions
between 900 and 1400 nm, where fulleride anions
absorb strongly.2a,b
Returning to the ESMS study of a THF solution of
isolated PPN[Mn(CO)4(η2-C60)], in addition to the mo-
lecular ion observed at low cone voltages, we also found
that increasing the cone voltage to ∼30 V resulted in
the appearance of a new peak at 835 Da/e and with an
isotope distribution consistent with [Mn(CO)3(η2-C60)]-.
Molecu la r Str u ctu r e of a n d Bon d in g in [Mn -
(CO)4(η2-C60)]-. As we have shown previously,6a the
structure of PPN[Mn(CO)4(η2-C60)] contains a C60 ligand
coordinated to the metal via a [6-6] ring junction at an
equatorial position in a trigonal bipyramidal complex
(Figure 1). The same type of structure is generally
observed in complexes of the type Fe(CO)4(η2-alkene)12
(13) (a) Douthwaite, R. E.; Green, M. L. H.; Stephens, A. H. H.;
Turner, J . F. C. J . Chem. Soc., Chem. Commun. 1993, 1522. (b)
Raasinkangas, M.; Pakkanen, T. T.; Pakkanen, T. A. J . Organomet.
Chem. 1994, 476, C6.
(14) (a) Support for this conclusion may also be gleaned indirectly
from a comparison of the IR spectra of THF solutions of Na[Mn(CO)5],
PPN[Mn(CO)5], Na[Mn(CO)4(η2-C60)], and PPN[Mn(CO)4(η2-C60)]. While
the IR spectrum of PPN[Mn(CO)5] exhibits the anticipated two νCO
,
,
that of Na[Mn(CO)5] also exhibits a third broad peak at ∼1830 cm-1
(10) Pregosin, P. S. In Transition Metal Nuclear Magnetic Reso-
nance; Pregosin, P. S., Ed.; Elsevier: Amsterdam, 1991; p 90.
(11) Leach, S.; Vervloet, M.; Despres, A.; Brehert, E.; Hare, J . P.;
Dennis, T. J .; Kroto, H. W.; Taylor, R.; Walton, D. R. M. Chem. Phys.
1992, 160, 451.
(12) Deeming, A. J . In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: New York,
1982; Chapter 31.3, and references therein.
a result of lowering of the symmetry because of Na-OC ion pairing in
solution between a carbonyl ligand and the sodium ion.14b In contrast,
the IR spectra of Na[Mn(CO)4(η2-C60)] and PPN[Mn(CO)4(η2-C60)] are
essentially identical, implying an absence of strong Na-OC ion pairing
in Na[Mn(CO)4(η2-C60)]. A reasonable conclusion is that the negative
charge is sufficiently delocalized onto the fullerene that Na-OC ion
pairing is negligible. (b) Darensbourg, M. Y. Prog. Inorg. Chem. 1985,
33, 221.

4766 Organometallics, Vol. 21, No. 22, 2002
Thompson et al.
F igu r e 3. Intensity of [Mn(CO)5]- daughter ions as a function of center of mass collision energy with Ar as determined
by CID.
F igu r e 4. Intensity of [Mn(CO)4(η2-C60)]- daughter ions as a function of center of mass collision energy with Ar as
determined by CID.
Further increasing the cone voltage to ∼60 V also
resulted in the appearance of peaks at 803 and 720 Da/e
with isotope patterns consistent with [Mn(CO)(C60)]-
and [C60]-, respectively. Successive decarbonylation of
metal carbonylate complexs with increasing cone voltage
is an established phenomenon,7c and the loss of one or
more CO ligands from [Mn(CO)4(C60)]- is to be antici-
pated.
In view of the conclusions, discussed above, that there
is less π back-donation to the carbonyl ligands in
[Mn(CO)4(C60)]- than in [Mn(CO)5]-, it follows that the
metal-carbonyl bonds should be weaker in [Mn(CO)4-
(η2-C60)]- than in [Mn(CO)5]-. To gain further insight
into the matter, ESMS collision-induced dissociation
(CID)15 experiments were performed on these two
complex ions. In these experiments a specific ion is
selected using the first quadropole of the mass spec-
trometer and is passed through with a specific energy
into a collision cell containing argon gas; the daughter
ions from the collision are then analyzed in a second
quadrupole. By plotting the intensity of peaks attribut-
able to specific daughter ions versus the center of mass
(C of M) collision energy and extrapolating the data back
toward zero intensity, a threshold energy for the dis-
sociation process can be determined.
Figures 3 and 4 show plots of the intensities of the
daughter ions versus the center of mass collision energy
for [Mn(CO)5]- and [Mn(CO)4(η2-C60)]-, respectively.
The extrapolated threshold energies for the first carbo-
nyl ligand dissociation were found to be ∼0.1 eV for
[Mn(CO)4(C60)]- and ∼1 eV for [Mn(CO)5]-, and thus
the energy required to dissociate a carbonyl ligand from
[Mn(CO)4(η2-C60)]- in the gas phase is significantly less
than that required to accomplish the same dissociation
from [Mn(CO)5]-. Thus the mass spectrometry data
concur qualitatively with the IR data, which suggest
that there are weaker Mn-CO bonds in the fullerene
complex.
Syn th esis a n d P r op er ties of A[Co(CO)4] (A ) Na ,
P P N). In an attempt to learn more about the mode of
formation of the previously reported NaCoC60‚3THF,4
a mixture of equimolar amounts of Na[Co(CO)4] and C60
was refluxed in THF while the progress of the reaction
was monitored using IR spectroscopy. As with the
manganese system, the νCO of Na[Co(CO)4] slowly
disappeared as new, weak νCO at 1920, 1966, and 1992
cm-1 appeared. Monitoring of the reaction by ESMS
revealed that changes in the intensity of the νCO of the
[Co(CO)4]- anion correlated well with a decrease in the
intensity of the peak of the [Co(CO)4]- anion at 171 Da/e
(15) (a) McLuckey, S. A. J . Am. Soc. Mass Spectrom. 1992, 3, 599.
(b) Anderson, S. G.; Blades, A. T.; Klassen, J .; Kebarle, P. Int. J . Mass
Spectrom. Ion Processes 1995, 141, 217. (c) Sunderlin, L. S.; Wang,
D.; Squires, R. R. J . Am. Chem. Soc. 1992, 114, 2788. (d) Sunderlin,
L. S.; Wang, D.; Squires, R. R. J . Am. Chem. Soc. 1993, 115, 12060.

Anionic Fullerene-60 Complexes
Organometallics, Vol. 21, No. 22, 2002 4767
Ta ble 4. Ca r bon yl Str etch in g F r equ en cies of P P N+
Sa lts
and the appearance of peaks at 720 and 863 Da/e,
attributable respectively to [C60]- and the new anionic
complex [Co(CO)3(C60)]-. Although the intensity of the
peak at 863 Da/e was generally relatively weak, we were
able by focusing on that region and adjusting the cone
voltage to maximize the peak intensity to observe an
isotope distribution consistent with [Co(CO)3(C60)]-.
Interestingly, at the cone voltage that optimized the
intensity of this peak (43 V), we also observed a peak
at 835 Da/e with an isotope distribution consistent with
the formulation [Co(CO)2(C60)]-, and thus partial de-
carbonylation had occurred. After 4 h, all carbonyl
intensity had disappeared and the previously reported
NaCoC60‚3THF4 was obtained.
The thermal reaction of PPN[Co(CO)4] with C60
proceeded similarly, a green solution of PPN[Co(CO)3-
(C60)] being obtained within 3 h, although further
refluxing resulted again in complete loss of carbonyl
intensity over 10 h. Workup as before resulted in a small
amount of crude PPN[Co(CO)3(C60)], which could not be
obtained analytically pure. However, a high-resolution
ESMS study of a THF solution revealed a peak at
862.9245 Da/e, differing by only 7.6 ppm from the
calculated value of 862.9179 Da/e and thus confirming
the identity of the species.
species
νCO (cm-1
)
νCO (average, cm-1
)
[Co(CO)4]-
1886
1920, 1992
1861, 1894
1886
1956
1878
1954
[Co(CO)3(η2-C60)]-
[Mn(CO)5]-
[Mn(CO)4(η2-C60)]-
1900, 1938, 2023
frequency on going from the starting carbonylate anions
to the fullerene products are almost identical, 70 and
76 cm-1. Thus in both cases substitution apparently has
a similar effect on the degree of π back-donation from
the metal to the carbonyl ligand, and it seems reason-
able to assume that C60 is coordinated to the two metals
in the same way.
Syn th esis a n d P r op er ties of Na [Re(CO)4(η2-C60)].
A study of the rhenium system was initiated to comple-
ment our findings with manganese. A reaction of Na-
[Re(CO)5] with C60 in refluxing THF was monitored by
IR spectroscopy and ESMS, and over several hours, νCO
of the Na[Re(CO)5] were replaced by those of Re2(CO)10
in addition to several others. ESMS measurements
revealed peaks at 720 and 838 Da/e, the former at-
tributable to [C60]-, the latter apparently to the tri-
nuclear species [Re3(CO)10]-. Photolysis of a THF solu-
tion of Na[Re(CO)5] with C60 was also carried out, and
again the νCO of Na[Re(CO)5] were replaced by a number
of new peaks between 1850 and 2050 cm-1, including
those of Re2(CO)10, which appeared almost immediately.
Interestingly, the νCO of both Re2(CO)10 and [Re(CO)5]-
disappeared within 48 h, while ESMS experiments
revealed many peaks, including a strong peak at 1019
Da/e and exhibiting an isotope distribution consistent
with [Re(CO)4(C60)]-. Other peaks in the spectrum at
895 and 867 are probably attributable to cluster anions
such as [Re3(CO)12]- and [Re3(CO)11]-, respectively.
Increasing the cone voltage resulted in significant loss
of intensity of these peaks and appearance of new peaks
at 783 and 755 Da/e, tentatively attributed to [Re3(CO)8]-
and [Re3(CO)7]-, respectively. The species [Re3(CO)11]-,
[Re3(CO)8]-, and [Re3(CO)7]- all appear to result from
fragmentation of [Re3(CO)12]-, a complex that does not
appear to have been reported previously.17 We suspect
that all arise from secondary processes, possibly within
the mass spectrometer, rather than directly from the
initial electron-transfer process.
While we were not able to isolate Na[Re(CO)4(η2-C60)],
we were able to recover a solid that exhibited solubility
in THF (green solution) and exhibited the same IR
spectrum as that observed after 48 h of photolysis. A
high-resolution ESMS study of this material revealed
a peak at 1018.9423 Da/e, differing by 6.3 ppm from the
theoretical mass of [Re(CO)4(η2-C60)]- (1018.93545 Da/
e) and thus confirming the identity of this species.
Interestingly, muliplets centered at ∼658 and ∼644
Da/e were also observed. The separations between these
multiplets of only 14 Da/e in addition to separations
within each multiplet of 0.5 Da/e suggest that these
species are both doubly charged and differ only by one
CO ligand. The mass-to-charge ratios of 658 and 644
Given the superiority of the photochemical over the
thermal procedure with the manganese system, a brief
study was also made of the photochemical reactions of
equimolar amounts of A[Co(CO)4] (A ) Na, PPN) with
C
60 in THF. IR and ESMS monitoring of the reaction of
PPN[Co(CO)4] showed that νCO of [Co(CO)4]-1 steadily
lost intensity, while those of [Co(CO)3(C60)]- grew in and
gained substantially in intensity over 48 h. ESMS
monitoring of the reaction revealed the presence of the
anticipated peak at 863 Da/e when the peaks at 1992
and 1920 cm-1 were present in the IR spectrum.
Similarly photolysis of solutions of Na[Co(CO)4] in THF
with C60 resulted in a loss of intensity from the carbonyl
peaks attributable to Na[Co(CO)4] and the appearance
of peaks attributable to [Co(CO)3(η2-C60)]-. Interest-
ingly, the photochemical reaction of Co2(CO)8 with Na-
[C60] was also found to result in the formation of
[Co(CO)3(C60)]-, identified via ESMS and IR spectro-
scopic monitoring.
In view of the close similarities between the manga-
nese and cobalt systems, we believe that the fullerene
in the latter is also coordinated in η2-fashion. In contrast
to manganese, analogous alkene complexes of cobalt
have been reported previously and the IR spectrum of
Na[Co(CO)3(η2-C60)] in THF (νCO at 1920, 1966, and
1992 cm-1) is comparable to those of the complexes Na-
[Co(CO)3(η2-alkene)] (alkene ) maleic anhydride, dim-
ethylmaleate, fumaronitrile), which exhibit νCO in the
regions 1896-1904, 1910-1971, and 1992-2011 cm-1
in THF.16 These results seem to confirm the nature of
C60 as an electron-deficient alkene.3
The IR data also imply that the presence of C60 in
both [Mn(CO)4(η2-C60)]- and [Co(CO)3(η2-C60)]- has a
similar effect on the electron density on the metal. In
Table 4 we compare νCO data for the two metals. As can
be seen, not only are the average νCO of the two fullerene
complexes very similar, but the changes in average
(17) For summaries of rhenium carbonyl cluster anions, see: (a)
Holloway, C. E.; Melnik, M. Organomet. Chem. Rev. 1988, 20, 249. (b)
Henly, T. J . Coord. Chem. Rev. 1989, 93, 269. (c) Hillary, K. M.;
Hughes, A. K.; Peat, K. L.; Wade, K. Polyhedron 1998, 17, 2803. (d)
Hughes, A. K.; Wade, K. Coord. Chem. Rev. 2000, 197, 191.
(16) Ungva´ry, F.; Gallucci, J .; Wojcicki, A. Organometallics 1991,
10, 3053.

4768 Organometallics, Vol. 21, No. 22, 2002
Thompson et al.
substitution labile.23 This substitution reaction would
probably also be facilitated by electron pairing as the
two radicals combine. In this scenario, radical pairing
of Mn(CO)5 and [C60]- is competitive with Mn(CO)5
dimerization and results in the formation of [Mn(CO)4-
(η2-C60)]-, as shown in Scheme 1.
Sch em e 1. P r op osed Mech a n ism for th e Th er m a l
a n d P h otoch em ica l Rea ction s of A[Mn (CO)5] w ith
C60 (A ) Na , P P N)
Evidence for this mechanism is also inferred from the
results of the photochemical syntheses of A[Mn(CO)4-
(η2-C60)] (A ) Na, PPN). It is known that Mn2(CO)10 is
photosensitive, undergoing reversible homolysis to Mn-
(CO)5 radicals on irradiation.24 Thus the Mn2(CO)10
formed during the photochemical process should be
converted to monomer (step d of Scheme 1), which can
then react with the [C60]- already in solution to produce
a higher yield of the [Mn(CO)4(η2-C60)]-. As indicated
above, the Mn2(CO)10 formed within the first 3 h does
indeed react further to give [Mn(CO)4(η2-C60)]-, and
isolated yields soared from ∼25% in the thermal process
to almost quantitative.
We note also that photoinduced charge transfer from
the transition metal carbonylate anion to C60 is a
possible first step in the photochemical synthesis. Car-
bonylate anions have long been known to participate
in photoinduced electron-transfer reactions,25 and outer-
sphere interactions between the mild oxidant C60 and
a wide variety of reducing agents have also been
demonstrated to generate new optical transitions in-
volving charge transfer from the electron donor to the
fullerene.26 Irradiation at the frequencies of these
transitions results in electron transfer,26 and it is
possible that photoinduced charge-transfer phenomena
explain the fact that all of the PPN[Mn(CO)5] is con-
sumed within 3 h in the photochemical reaction, while
consumption of the anion requires 12 h in the thermal
reaction. While no charge-transfer transitions were
identified, that Mn(CO)5 and [C60]- can react directly
was confirmed by an experiment in which Mn2(CO)10
and a solution of Na[C60] in THF were photolyzed. Over
the course of 8 h, νCO of Mn2(CO)10 disappeared while
those of PPN[Mn(CO)4(η2-C60)] grew in, demonstrating
clearly that the [C60]- radical anion can indeed substi-
tute a CO ligand in the Mn(CO)5 radical to form the
[Mn(CO)4(η2-C60)]- anion.
Da/e are those anticipated for [Re2(CO)8(C60)]2- and
[Re2(CO)7(C60)]2-, respectively, but the poor signal-to-
noise ratios made assignment of these peaks tenuous.
While it is not possible to make an unambiguous
identification of the νCO of [Re(CO)4(η2-C60)]-, one would
expect them to have frequencies and relative intensities
similar to those of [Mn(CO)4(η2-C60)]-. Assuming a slight
shifting of IR-active carbonyl absorptions to lower
frequencies on moving from first to third row metals,18
we tentatively assign νCO at 2005, 1931, and 1891 cm-1
to [Re(CO)4(η2-C60)]-, although there is, in fact, consid-
erable overlap with absorptions of the polynuclear
complexes. The assigned bands are quite different from
those of the thermally unstable, neutral compound C60-
{Re(CO)5}2 (νCO 2134, 2130, 2036, 1993 cm-1), prepared
by reacting C60 at low temperatures with the 17-
electron, metal-centered radical Re(CO)5, which was
prepared via photolysis of Re2(CO)10.19
Mech a n ism s of th e Rea ction s of A[Mn (CO)5)],
A[Co(CO)4] (A ) Na , P P N), a n d Na [Re(CO)5)] w ith
C
60. Mech a n ism s of F or m a tion of η2-C60 Com -
p lexes. The high electron affinity of C60 (2.65 eV2a)
coupled with the strongly reducing nature of carbonylate
anions20 makes it likely that electron transfer from, for
example, [Mn(CO)5]- to C60 takes place in the thermal
reactions to generate the radical anion [C60]- and the
neutral 17-electron, metal-centered radical Mn(CO)5
(step a of Scheme 1). The presence of the Mn(CO)5
radical in solution would be expected to result in the
formation of Mn2(CO)10 (step b of Scheme 1) since Mn-
(CO)5 is known to dimerize at near diffusion-controlled
rates.21 In agreement with this, we do indeed observe
Mn2(CO)10 as a major reaction product.
The stability of PPN[Mn(CO)4(η2-C60)] during pho-
tolysis is interesting, as a control experiment showed
that similar photolysis of a THF solution of [Mn(CO)5]-
resulted in loss of all νCO intensity over several hours.
Fullerenes exhibit very strong absorptions in the UV-
vis region,26 however, and the presence of a coordinated
fullerene may well create pathways other than CO
dissociation for the relaxation of excited states of a
complex carbonylate anion.
The formation of comparable amounts of [Mn(CO)4-
(η2-C60)]- could conceivably involve direct substitution
of a carbonyl ligand on [Mn(CO)5]- by C60, or even direct
nucleophilic attack by the anion on the fullerene, as
occurs with carbanions,22 followed by loss of a CO.
However, the reaction more likely involves substitution
by [C60]- of a carbonyl ligand on the Mn(CO)5 radical
(step c of Scheme 1), which is known to be very
The reactions of A[Co(CO)4] and A[Re(CO)5] with C60
presumably also involve initial electron transfer fol-
(18) (a) Adams, D. M. Metal-Ligand and Related Vibrations;
Edward Arnold Publishers: London, 1967. (b) Braterman, P. S. Metal
Carbonyl Spectra; Academic Press: London, 1975.
(19) Zhang, S.; Brown, T. L.; Du, Y.; Shapley, J . R. J . Am. Chem.
Soc. 1993, 115, 6705.
(23) Trogler, W. C. In Organometallic Radical Processes; Trogler,
W. C., Ed.; Elsevier: Amsterdam, 1990; p 306.
(24) Baird, M. C. Chem. Rev. 1988, 88, 1217.
(20) (a) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877.
(b) Lai, C.-K.; Feighery, W. G.; Zhen, Y.; Atwood, J . D. Inorg. Chem.
1989, 28, 3929. (c) Corraine, M. S.; Atwood, J . D. Organometallics 1991,
10, 2315. (d) Lai, C. K.; Corraine, M. S.; Atwood, J . D. Organometallics
1992, 11, 582.
(21) Brown, T. L. In Organometallic Radical Processes; Trogler, W.
C., Ed.; Elsevier: Amsterdam, 1990; p 70.
(22) (a) Fukuzumi, S.; Suenobu, T.; Hirasaka, T.; Arakawa, R.;
Kadish, K. M. J . Am. Chem. Soc. 1998, 120, 9220. (b) Kitagawa, T.;
Takeuchi, K. Bull. Chem. Soc. J pn. 2001, 74, 785.
(25) (a) Bockman, T. M.; Kochi, J . K. J . Am. Chem. Soc. 1989, 111,
4669. (b) Wei, C.-H.; Bockman, T. M.; Kochi, J . K. J . Organomet. Chem.
1992, 428, 85. (c) Kochi, J . K.; Bockman, T. M. Adv. Organomet. Chem.
1991, 33, 51.
(26) (a) Mittal, J . Pure Appl. Chem. 1995, 67, 103. (b) Martin, N.;
Sa´nchez, L.; Illescas, B.; Pe´rez, I. Chem. Rev. 1998, 98, 2527. (c)
Konarev, D. V.; Lyubovskaya, R. N. Russ. Chem. Rev. (Engl. Transl.)
1999, 68, 19. (d) Konarev, D. V.; Lyubovskaya, R. N.; Drichko, N. V.;
Yudanova, E. I.; Shul’ga, Y. M.; Litvinov, A. L.; Semkin, V. N.; Tarasov,
B. P. J . Mater. Chem. 2000, 10, 803.

Anionic Fullerene-60 Complexes
Organometallics, Vol. 21, No. 22, 2002 4769
lowed by CO substitution to give [Co(CO)3(η2-C60)]- and
[Re(CO)4(η2-C60)]-, respectively. The former is thermally
unstable in refluxing THF as the sodium salt and
decarbonylates to yield the fulleride, NaCoC60‚3THF,4
but its synthesis via the photolysis of Co2(CO)8 in the
presence of Na[C60] clearly demonstrates that the [C60]-
anion can react with the Co(CO)4 radical to form [Co-
(CO)3(η2-C60)]-. As the 17-electron radical Co(CO)4 is
known to dimerize readily to Co2(CO)8,21 it is not clear
why the latter is not formed as an intermediate.
However, this dimerization process is an order of
magnitude slower than dimerization of Mn(CO)5,21 and
it may be that self-coupling is just not kinetically
competitive with Co(CO)4-[C60]- coupling. The reaction
of Na[Re(CO)5] with C60 proceeds similarly to the
manganese system, but identification of the νCO of [Re-
(CO)4(η2-C60)]- is complicated by the concomitant for-
mation of polynuclear carbonylate anions. While crys-
tallographically useful crystals of the rhenium complex
could not be obtained, the high-resolution MS studies
confirmed unambiguously its identity and it seems
reasonable to assume that the C60 is bound as in [Mn-
(CO)4(η2-C60)]-, i.e. via a [6-6] ring junction.
incoming ligand can coordinate. While this type of
reaction cannot generally be applied to metal carbony-
late complexes because of the negative charges and the
increased metal carbonyl bond strengths, the νCO of [Mn-
(CO)4(η2-C60)]- are in the range of typically active
neutral carbonyls, and we therefore attempted to induce
CO substitution in this way. Again, we were unable to
induce substitution.
The anionic [Mn(CO)5]- is a good nucleophile and
reacts with MeI to form MeMn(CO)5 and I-.28a However,
the analogous chemistry of PPN[Mn(CO)4(η2-C60)] with
CH3I was quite different, as IR monitoring revealed that
the thermal reaction resulted in a new anionic species
with νCO at 2068, 1995, 1972, and 1929 cm-1 and a peak
in the mass spectrum at 421 Da/e. The latter exhibited
an isotope pattern consistent with [Mn(CO)4I2]-, and
[Bu4N][Mn(CO)4I2] was synthesized for purposes of
comparison according to a procedure described pre-
viously.28b The IR spectrum of the latter complex
compared well with νCO observed in the IR spectrum of
the reaction between PPN[Mn(CO)4(η2-C60)] and CH3I,
although other νCO were also observed and thus the
reaction was complex. There was also a black precipitate
recovered from the reaction, but this did not exhibit
solubility in THF, toluene, benzene, or acetone and was
not examined further. If MeI does indeed react with
[Mn(CO)4(η2-C60)]- to give an iodo-manganese rather
than a methyl-manganese species, i.e., in the opposite
sense of the reaction of MeI with [Mn(CO)5]-, which
gives MeMn(CO)5 and iodide ion,28a then a fullerene
product should be [C60Me]-, a known compound soluble
in THF.29 We did not detect [C60Me]-, and thus the
course of the reaction remains somewhat mysterious.
Reactions of PPN[Mn(CO)4(η2-C60)] with trifluoroacetic
acid were also investigated, but the results were erratic
and the reactions were not pursued further.
Som e Ch em istr y of [Mn (CO)4(η2-C60)]-. All of the
(η2-fullerene)metal carbonylate salts described above are
insoluble in pentane, hexanes, benzene, toluene, ac-
etone, thiophene, benzonitrile, and acetonitrile, but
exhibit limited solubility in THF and CH2Cl2 (5-10 mg/
mL) to give very deep green solutions. We have therefore
investigated a few reactions of the most available
complex, [Mn(CO)4(η2-C60)]-, with representative nu-
cleophilic and electrophilic reagents.
Although PPh3 reacts readily at room temperature
with Ru(CO)4(η2-C60) to give Ru(CO)4PPh3 and C60,13b
we find that the isoelectronic [Mn(CO)4(η2-C60)]- anion
is inert to substitution in refluxing THF; [Co(CO)3(C60)]-
is similarly inert to thermal substitution. Presumably
the negative charge on the metal anions increases the
back-donation of electron density to the fullerene,
resulting in stronger metal-fullerene bonds than is the
case with the neutral ruthenium(0) compound.
It has been reported that the photochemical reaction
of [Mn(CO)5]- with PPh3 results in dissociative phos-
phine substitution of one of the carbonyl ligands to yield
[Mn(CO)4(PPh3)]-.7c Under identical reaction conditions,
however, we were unable to induce photochemical CO
substitution by PPh3 on any of the complexes A[Mn-
(CO)4(η2-C60)] or A[Co(CO)3(η2-C60)] (A ) Na, PPN). The
metal-CO bonds are relatively weak in the latter
complexes, and it seems that the presence of a coordi-
nated fullerene somehow permits relaxation of the
absorbed energy via nondissociative pathways. How-
ever, the possibility of the added steric encumbrance of
C60 discouraging PPh3 coordination also seemed plau-
sible, and a less sterically hindered phosphine, PMe2-
Ph, was tried; again no substitution was observed.
Phosphine substitution of carbonyl ligands in neutral
metal carbonyls having νCO greater than 2000 cm-1 can
often be induced thermally by the addition of Od
N(CH3)3.27 The latter reacts with electron-poor carbonyl
ligands to produce trimethylamine and carbon dioxide,
thus generating a vacant site on the metal at which an
Su m m a r y. Thermal and photochemical reactions of
the carbonylate salts A[Mn(CO)5], A[Co(CO)4], and
A[Re(CO)5] (A ) Na, PPN) with C60 result in all cases
in electron transfer to give [C60]- and the transient 17-
electron, metal-centered radicals Mn(CO)5, Co(CO)4, and
Re(CO)5, respectively. Subsequent self-coupling of M(CO)5
(M ) Mn, Re) then gives the metal-metal bonded
dimers M2(CO)10 competitively with coupling of M(CO)5
with [C60]-, which gives the η2-C60 complexes A[Mn-
(CO)4(η2-C60)]. Interestingly, the photochemical pro-
cesses ultimately result also in complete homolysis of
the dimers and regeneration of the metal-centered
radicals, which then combine with the [C60]- still
remaining in solution to form more of the η2-C60
complexes. In the case of cobalt, no Co2(CO)8 is formed,
but the thermally labile η2-C60 complex [Co(CO)3(η2-
C60)]- is produced and decarbonylation in refluxing THF
gives the previously reported mixed fulleride compound
NaCoC60‚3THF. Much of the negative charge in [Mn-
(CO)4(η2-C60)]- (and the cobalt and rhenium analogues)
is delocalized onto the fullerene ligand; as a result, the
η2-C60-Mn bond is unusually strong and the complex
[Mn(CO)4(η2-C60)]- is very stable, exhibiting little of the
(28) (a) King, R. B. Acc. Chem. Res. 1970, 3, 417. (b) Abel, E. W.;
Butler, J . J . Chem. Soc. 1964, 434.
(29) (a) Hirsch, A.; Gro¨sser, T.; Skiebe, A.; Soi, A. Chem. Ber. 1993,
126, 1061. (b) Caron, C.; Subramanian, R.; D’Souza, F.; Kim, J .; Kutner,
W.; J ones, M. T.; Kadish, K. M. J . Am. Chem. Soc. 1993, 115, 8505.
(27) (a) Albers, M. O.; Coville, N. J . Coord. Chem. Rev. 1984, 53,
227. (b) Luh, T.-Y. Coord. Chem. Rev. 1984, 60, 255.

4770 Organometallics, Vol. 21, No. 22, 2002
Thompson et al.
chemistry associated with either neutral η2-C60 com-
ALCAN for a Graduate Fellowship to D.M.T. We also
thank Prof. J . A. Stone, Mr. T. Hunter, and Dr. I.
Galetich for assistance with the mass spectrometry
measurements, and Prof. Gang Wu for assistance in
obtaining the 55Mn NMR spectrum.
plexes or the analogous [Mn(CO)5]-.
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council for a Research Grant
to M.C.B. and a Graduate Fellowship to D.M.T., and
OM020396I