Organometallic C70 chemistry. Preparation and crystallographic studies of (η2-C70)Pd(PPh3)2·CH 2Cl2 and (C70)·2{(η5-C5H5) 2Fe}

Article abstract of DOI:10.1016/S0022-328X(98)01108-5

Treatment of a solution of C₇₀ with solutions of Pd(PPh₃)₄ or ferrocene result in the formation of either black-brown (η²-C₇₀)Pd(PPh₃)₂·CH ₂Cl₂ or metallic-black C₇₀·2{(η⁵-C₅H₅) ₂Fe}, respectively. Crystallographic examination of the palladium complex reveals that the metal is coordinated to the a-b bond (a highly pyramidalized 6:6 ring junction) at the pole of the fullerene. The variable temperature ³¹P-NMR spectrum of the complex reveals the coalescence of the two doublets of the adduct at 80°C. This merging of the resonances results from a dynamic process that may involve rotation of the olefinic fullerene bond about the plane of the PdP₂ unit or phosphine dissociation. X-ray crystallography of the ferrocene-containing compound, C₇₀·2{(η⁵-C₅H₅) ₂Fe}, reveals that it involves co-crystallization of two ordered ferrocene molecules with an ordered C₇₀ molecule with no unusual interaction between these entities. The structure is similar in many aspects to that of C₆₀·2{(η⁵-C₅H₅) ₂Fe}.

Full text of DOI:10.1016/S0022-328X(98)01108-5

Journal of Organometallic Chemistry 578 (1999) 85–90
Organometallic C70 chemistry. Preparation and crystallographic studies
of (h2-C70)Pd(PPh3)2 · CH2Cl2 and (C70) · 2{(h5-C5H5)2Fe}
Marilyn M. Olmstead, Leijun Hao, Alan L. Balch *
Department of Chemistry, Uni6ersity of California, Da6is, CA 95616, USA
Received 8 July 1998
Abstract
Treatment of a solution of C70 with solutions of Pd(PPh3)4 or ferrocene result in the formation of either black–brown
(h2-C70)Pd(PPh3)2 · CH2Cl2 or metallic-black C70 · 2{(h5-C5H5)2Fe}, respectively. Crystallographic examination of the palladium
complex reveals that the metal is coordinated to the aꢀb bond (a highly pyramidalized 6:6 ring junction) at the pole of the
fullerene. The variable temperature 31P-NMR spectrum of the complex reveals the coalescence of the two doublets of the adduct
at 80°C. This merging of the resonances results from a dynamic process that may involve rotation of the olefinic fullerene bond
about the plane of the PdP2 unit or phosphine dissociation. X-ray crystallography of the ferrocene-containing compound,
C
70 · 2{(h5-C5H5)2Fe}, reveals that it involves co-crystallization of two ordered ferrocene molecules with an ordered C70 molecule
with no unusual interaction between these entities. The structure is similar in many aspects to that of C60 · 2{(h5-C5H5)2Fe}.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Fullerene; Ferrocene; Palladium; C70
two papers describe interactions of C84 with transition
metal complexes [11,12]. Here we report on the prepa-
ration of two new compounds that result from the
interaction of C70 with transition metal complexes. The
observed reactions reported here include one case of
h2-coordination and one case of co-crystallization.
As seen in Fig. 1, the structure of C70 is more
complex than that of C60; since the former contains five
distinct types of carbon atoms while the later contains
only one type of carbon atom. There are two types of
CꢀC bonds in C60, those at 6:6 ring junctions and those
at 6:5 ring junctions. C70 also has 6:6 and 6:5 ring
junctions, but there are four distinct 6:6 ring junctions
(aꢀb, cꢀc, dꢀe and eꢀe) and four 6:5 ring junctions (aꢀa,
bꢀc, cꢀd and dꢀd) in this fullerene. Previous work has
shown that metal complexes that coordinate to C70 in
an h2-fashion selectively add to the aꢀb bonds at the
ends of the fullerene [4,5,7]. These bonds involve the
most pyramidalized carbon atoms within the fullerene
[13], and these atoms undergo further pyramidalization
upon coordination.
1. Introduction
Considerable effort has been made in the investiga-
tion of the reactions of transition metal complexes with
C60 [1–3]. The major reactions encountered include (1)
coordination, generally in an h2-fashion to the olefinic
6:6 ring junctions of the fullerene, (2) reduction of the
fullerene to form fulleride salts, (3) addition of a ligat-
ing group on the metal complex to the fullerene so that
the metal is attached to the fullerene through some type
of covalent bridge, and (4) formation of a solid in
which a metal complex and the fullerene are co-crystal-
lized [1]. Considerably less attention has been give to
the behavior of the higher, but less abundant, fullerenes
with metal complexes. There are a few reports on the
behavior of C70 with transition metal complexes [4–9]
but only one in which C76 is utilized [10]. One paper
involving osmylation of C78 has also appeared [11], and
* Corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01108-5

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M.M. Olmstead et al. / Journal of Organometallic Chemistry 578 (1999) 85–90
a second isomer of (h2-C70)Pd(PPh3)2. Attempts to
separate and isolate the isomer responsible for these
low intensity resonances by selective crystallization
have not been successful.
The 31P-NMR spectrum of (h2-C70)Pd(PPh3)2 is sen-
sitive to temperature. Warming from −80 to 25°C
produces a broadening of the resonances so that the
doublet structure is no longer apparent, and further
warming produces added broadening until the reso-
nances coalesce into a broad singlet at 27.9 ppm at
80°C and then sharpen as the temperature is increased
to 100°C. Upon cooling the changes described here are
reversed. This behavior is attributed to a dynamic
process in which the environments of the two phospho-
rus atoms of the complex are rendered equivalent.
Simple rotation about the Pd–olefinic CꢀC bond of the
fullerene accomplishes such an interchange. This pro-
cess is shown diagramatically in Eq. (2). Alternatively,
the phosphine ligands may undergo dissociation and
reassociation.
Fig. 1. An drawing of an idealized C70 molecule that shows the five
types of carbon atoms (aꢀe) and the eight types of CꢀC bonds.
2. Results
2.1. Formation and solution properties of
(p2-C70)Pd(PPh3)2
Brown–black (h2-C70)Pd(PPh3)2 was readily formed
in high yield by mixing equimolar amounts of
Pd(PPh3)4 and C70 in benzene as shown in Eq. (1).
(2)
(1)
The reaction was monitored by 31P-NMR spectroscopy
and was complete almost immediately after mixing.
After evaporation of the solvent, the product was dis-
solved in dichloromethane, filtered and crystallized
through the addition of diethyl ether. The product,
(h2-C70)Pd(PPh3)2, is moderately stable in air in the
solid state but decomposes slowly in solution when
exposed to air. The 31P-NMR spectrum of the complex
in toluene-d8 consisted of a pair of doublets at 29.2 and
2.2. The crystal and molecular structure of
(p2-C70)Pd(PPh3)2
A view of the molecule, which has no crystallograph-
ically imposed symmetry, is shown in Fig. 2. Selected
bond distance and angles are contained in Table 1. The
complex consists of a Pd(PPh3)2 unit that is bonded
through palladium in an h2-fashion to one of the aꢀb
bonds of the C70 molecule. Coordination of the
C(1)ꢀC(6) bond of the fullerene results in an elongation
2
26.7 ppm at −80°C with J(Pa, Pb) of 8 Hz. Thus, the
two phosphorus atoms of the complex are inequivalent,
which is consistent with coordination of the palladium
to the 6:6 ring junctions that involve either the aꢀb or
cꢀd bonds (see Fig. 1) within the fullerene. Addition-
ally, the 31P-NMR spectrum of the reaction product
always also showed the presence of two resonances at
l=28.8 and 26.4, respectively, at −80°C. These reso-
nances had ca. 10% of the intensity of the major
doublet, and are believed to result from the presence of
˚
of that bond (bond length, 1.48(2) A) relative to the
˚
expected length (1.39 A) of such an aꢀb bond in C70.
The bond distances and angles reported here are all
similar to those found for (h2-C60)Pd(PPh3)2 [14]. The
overall structure is also similar to that reported earlier
from this laboratory for (h2-C70)Ir(CO)Cl(PPh3)2 [4].
Not only is the metal bonded to the fullerene in the two

M.M. Olmstead et al. / Journal of Organometallic Chemistry 578 (1999) 85–90
87
Fig. 3. A view of the structure of C70 · 2{(h5-C5H5)2Fe} showing the
face-to-face interactions of the poles of the fullerene with adjacent
ferrocene molecules.
tances within the C70 molecule are given in Table 2,
where they are compared with related structure deter-
minations of C70 in various forms. Fig. 3 shows the way
in which two ferrocene molecules pack near the ends of
the oblong C70 molecule so that the two pentagonal
faces on the C5 axis of the fullerene make van der
Waals p–p contact with ferrocene molecules. The dis-
tances between the carbon atoms of the fullerene and
Fig. 2. A perspective view of (h2-C70)Pd(PPh3)2 · CH2Cl2. The dis-
tances from the dichloromethane molecule to the fullerene are:
˚
˚
˚
˚
Cl(2)···C(47), 3.31 A, Cl(2)···C(57), 3.50 A; Cl(1)···C(31%), 3.41 A,
Cl(1)···C(40%), 3.41 A.
complexes in the same h2-fashion, but two of the
phenyl rings of the triphenylphosphine ligands make
face-to-face contact with the surface of the C70 portion
of both the palladium and the iridium complex.
˚
the ferrocene molecule fall in the range 3.3–3.4 A,
which is what is expected from contacts between aro-
matic molecules and the separation of planes in
˚
graphite (3.35 A). Fig. 4 is a stereoscopic view of the
molecular organization within the solid.
Ferrocene forms a similar crystalline compound with
C60 [15]. Although C70 · 2{(h5-C5H5)2Fe} and
C60 · 2{(h5-C5H5)2Fe} crystallize in different space
groups, the two structures are similar. Fig. 5 shows the
two structures from a perspective that demonstrates the
similarities between them. In both solids there are
face-to-face p contacts between the fullerene and the
ferrocene molecules. Additionally, in both structures
the ferrocene molecules have an eclipsed conformation
of the two cyclopentadienyl rings. In crystalline fer-
rocene itself the two rings are eclipsed [16]. However,
the barrier to rotation is low (ca. 5 kJ mol−1 or less)
and in the gas phase the rings are eclipsed [17]. Conse-
quently, either eclipsed or staggered configurations can
be found for ferrocene-based compounds [18].
2.3. Formation and structure of C70 · 2{(p5-C5H5)2Fe}
Gradual evaporation of a solution of C70 and fer-
rocene in carbon disulfide results in the deposition of
large thin plates of C70 · 2{(h5-C5H5)2Fe} which are
co-mingled with orange crystals of ferrocene itself. The
plates of C70 · 2{(h5-C5H5)2Fe}, which have a silvery
sheen, were manually separated form the orange fer-
rocene
crystals
for
examination
by
X-ray
crystallography.
Views of the structure of C70 · 2{(h5-C5H5)2Fe} are
shown in Figs. 3 and 4. The solid is comprised of
individual molecules of the two components with no
covalent bonding between these molecules. Despite the
tendency of individual fullerene molecules to display
disorder in the solid state, both the C70 and the fer-
rocene molecules are ordered within this solid. Dimen-
sions within the ferrocene portion are normal; the
3. Discussion
˚
average FeꢀC distance is 2.04 A. Average CꢀC dis-
Structural characterization of (h2-C70)Pd(PPh3)2
confirms our earlier studies of addition patterns of
metal complexes to C70 [4,5,7]. Addition of Pt(PPh3)2
units to C70 was shown to produce four compounds,
(h2-C70){Pt(PPh3)2}n (with n=1, 2, 3 and 4) [7]. Spec-
troscopic data suggested that the first and second plat-
inum atoms are bound to the aꢀb bonds at opposite
ends of the fullerene, while the third and fourth added
to the cꢀc bonds. Crystallographic characterizations of
(h2-C70)Pd(PPh3)2 and (h2-C70){Pt(PPh3)2}4 support
this suggestion. The structure of (h2-C70)Pd(PPh3)2 re-
veals coordination to the aꢀb bond at one end of the
Table 1
Selected bond distances and angles for (h2-C70)Pd(PPh3)2 · CH2Cl2
˚
Bond length (A)
PdꢀC(1)
PdꢀP(1)
C(1)ꢀC(6)
2.106(11) PdꢀC(6)
2.123(11)
2.340(3)
2.328(3)
1.48(2)
PdꢀP(2)
Bond angles (°)
C(1)ꢀPdꢀC(6)
C(1)ꢀPdꢀP(2)
C(6)ꢀPdꢀP(2)
41.1(4)
143.6(3)
102.5(3)
C(1)ꢀPdꢀP(1)
C(6)ꢀPdꢀP(1)
P(1)ꢀPdꢀP(2)
100.2(3)
140.6(3)
115.62(11)

88
M.M. Olmstead et al. / Journal of Organometallic Chemistry 578 (1999) 85–90
Fig. 4. A stereo view of the structure of C70 · 2{(h5-C5H5)2Fe}.
fullerene, while the structure of (h2-C70){Pt(PPh3)2}4
showed that the four platinum atoms were arranged in
a C26 symmetric fashion with coordination at two aꢀb
and two cꢀc bonds [7].
C5H5)2Fe}, the single crystal X-ray diffraction study of
C70 · 6(S8) [26], a pulsed neutron diffraction study of C70
powder at 300 K, an electron diffraction study of a C70
film at room temperature [27], and a gas phase electron
diffraction study of C70 at 825°C [28]. While there is
generally good agreement among the parameters ob-
tained from these five studies of unaltered C70, the
studies do show variation in the length of the equatorial
eꢀe bond. Thus, this bond is unusually short in the
solid state electron diffraction study and considerably
elongated in the high temperature, gas phase electron
diffraction study. Theoretical calculations on the struc-
ture of C70 at 825°C do not reproduce the electron
diffraction data and do not show any cause for excep-
tional lengthening of the eꢀe bond [29].
In the absence of a coordinated group, which lowers
the symmetry of the fullerene, molecules of C70 tend to
form crystals that display some degree of disorder and
dynamical processes involving various rotations of the
fullerene [19–25]. However, in the two co-crystallized
materials, C70 · 2{(h5-C5H5)2Fe}and C70 · 6(S8), the C70
molecules assume fully ordered positions and are free of
rotational dynamics that complicate structure determi-
nations. Table 2 presents a comparison of bond lengths
within C70 that are taken from a variety of sources.
These include the present structure of C70 · 2{(h5-
Table 2
Bond lengths within C70
Bond
C70 · 2{(h5-C5H5)2Fe}a
C70 · 5(S8)b
C70 (solid)c
C70 (solid)d
C70 (gas phase)e
aꢀa
aꢀb
bꢀc
cꢀc
cꢀd
dꢀd
dꢀe
eꢀe
1.451(13)
1.397(12)
1.436(16)
1.391(16)
1.441(12)
1.439(14)
1.416(10)
1.469(10)
1.451(3)
1.387(4)
1.445(3)
1.378(3)
1.447(2)
1.426(3)
1.414(2)
1.462(10)
1.464(9)
1.37(1)
1.47(1)
1.37(1)
1.46(1)
1.47(3)
1.39(1)
1.41(3)
1.460(4)
1.382(6)
1.449(5)
1.396(6)
1.464(7)
1.420(4)
1.415(5)
1.477(6)
1.461(8)
1.388(16)
1.453(11)
1.386(25)
1.405(13)
1.425(14)
1.405(13)
1.538(19)
a This work, single crystal X-ray diffraction.
b From Ref. [22], single crystal X-ray diffraction.
c From Ref. [23], powder electron diffraction.
d From Ref. [16], powder pulsed neutron diffraction.
e From Ref. [24], gas phase electron diffraction.

M.M. Olmstead et al. / Journal of Organometallic Chemistry 578 (1999) 85–90
89
Fig. 5. A comparison of the molecular packing in C70 · 2{(h5-C5H5)2Fe} and C60 · 2{(h5-C5H5)2Fe}. Data for C60 · 2{(h5-C5H5)2Fe} were taken
from Ref. [22].
4. Experimental
25°C, l=29.3 [s, 1P], 26.9 [s, 1P]; at 80°C, l=27.9 [s,
br, 2P]; at 100°C, l=28.2 [s, sharp, 2P].
The reactions were performed under a purified atmo-
sphere of dinitrogen with the use of Schlenk techniques
unless otherwise noted. The solvents were degassed
before use. Pd(PPh3)4 was synthesized according to a
reported procedure [30]. Infrared spectra were recorded
on a Galaxy Series FTIR 3000 spectrometer as KBr
pellets. NMR spectra were recorded on a QE-300 in-
strument. 31P{1H}-NMR spectra were referenced to
external 85% H3PO4 in H2O, with downfield chemical
shifts reported as positive.
4.2. Preparation of C70 · 2{(p5-C5H5)2Fe}
A saturated carbon disulfide solution of C70 was
mixed with an equal volume of a saturated carbon
disulfide solution of ferrocene. The resulting reddish
solution was allowed to slowly evaporate without dis-
turbing for two weeks. Shiny black crystals of product,
Table 3
Crystal data and data collection parameters
4.1. Preparation of (p2-C70)Pd(PPh3)2
(h2-C70)Pd(PPh3)2 · CH2Cl2 (C70) · 2{h5-C5H5)2Fe}
Empirical formula
Formula weight
T (K)
C
107H32Cl2P2Pd
C180H40Fe4
2425.52
130(2)
To a solution of C70 (36 mg, 0.043 mmol) in benzene
(7 ml), Pd(PPh3)4 (49 mg, 0.043 mmol) was added. The
red–brown solution was stirred for 10 min. The solvent
was then removed under vacuum. The brown solid was
redissolved in dichloromethane (1 ml), and the solution
was filtered. Diethyl ether (40 ml) was added to the
filtrate to precipitate the product as a black crystalline
solid in 91% yield. IR (KBr pellet): 1431 (vs), 1411 (m),
1092 (m), 742 (s), 692 (vs), 673 (m), 579 (m), 534 (m),
513 (s, br), 457 (m). For comparison, IR spectrum of
C70 in KBr pellet displayed bands at 1429 (vs), 1414 (s),
1134 (m), 795 (s), 674 (s), 642 (m), 577 (s), 564 (m), 534
(s), 459 (m). NMR (in toluene-d8): at −80°C, l=29.2
1556.57
130(2)
Color, habit
Crystal system
Space group
Black, plate
Monoclinic
P21/n
Black, plate
Monoclinic
C2
˚
a (A)
18.309(2)
14.325(2)
23.796(2)
92.428(7)
4
27.752(5)
10.056(2)
19.603(6)
124.19(2)
2
˚
b (A)
˚
c (A)
i (°)
Z
z (g cm−3
)
1.658
1.780
v (mm−1
)
4.175
5.666
Ra (obsd data)
0.093
0.076
wR2
0.202
0.201
2
2
[d, 1P, J(P, P)=8 Hz], 26.7 [d, 1P, J(P, P)=8 Hz]; at
a R1=SꢀFo−Fcꢀ/SꢁFoꢁ; wR2=[S[ꢀ(Fo2−Fc2)2]/S[ꢀ(F2o)2]]1/2
.

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M.M. Olmstead et al. / Journal of Organometallic Chemistry 578 (1999) 85–90
C70 · 2{(h5-C5H5)2Fe}, were separated from the orange
crystals of ferrocene by hand.
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C
70 · 2{(h5-C5H5)2Fe}. Copies of this information may
be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK (Fax:
+44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or
www:http://www.ccdc.cam.ac.uk).
Acknowledgements
[30] D.R. Coulson, Inorg. Synth. 28 (1990) 107.
[31] A.J.C. Wilson (Ed.), International Tables for Crystallography,
Volume C, Kluwer Academic Publishers, Dordrecht, 1992.
[32] S. Parkin, B. Moezzi, H. Hope, J. Appl. Crystallogr. 28 (1995)
53.
The authors thank the US National Science Founda-
tion (Grant CHE 9610507) for support and Johnson
Matthey for a loan of palladium(II) chloride.
.