Structural comparison of M(CO)3(dppe)(η2-C60) (M = Mo, W), Mo(CO)3(dppe)(η2-C70), and W(CO)3(dppe)(η2-trans-C2H 2(CO2Me)2)

Article abstract of DOI:10.1021/om971013x

The photolysis of M(CO)₄(dppe) (M = Mo, W) and C₆₀, C₇₀, or dimethyl fumarate (dmf) in chlorobenzene provides M(CO)₃(dppe)(η²-C₆₀) (M = Mo, 1; M = W, 2), Mo(CO)₃(dppe)(η²-C₇₀) (3), and W(CO)₃(dppe)(η²-dmf) (4), the structures of which have been determined by X-ray crystallography. Distorted octahedral geometries are found for the metal centers in all cases, with the dppe and olefin ligands in a mer configuration, and the C60 and C70 complexes display significant secondary interactions between the fullerene moiety and the phenyl groups of the diphosphine ligand. Furthermore, from ³¹P NMR studies, two isomers of 3 are observed.

Full text of DOI:10.1021/om971013x

1756
Organometallics 1998, 17, 1756-1761
Str u ctu r a l Com p a r ison of M(CO)3(d p p e)(η2-C60)
(M ) Mo, W), Mo(CO)3(d p p e)(η2-C70), a n d
W(CO)3(d p p e)(η2-tr a n s-C2H2(CO2Me)2)
Hsiu-Fu Hsu, Yuhua Du, Thomas E. Albrecht-Schmitt, Scott R. Wilson, and
J ohn R. Shapley*
School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801
Received November 17, 1997
The photolysis of M(CO)4(dppe) (M ) Mo, W) and C60, C70, or dimethyl fumarate (dmf) in
chlorobenzene provides M(CO)3(dppe)(η2-C60) (M ) Mo, 1; M ) W, 2), Mo(CO)3(dppe)(η2-C70)
(3), and W(CO)3(dppe)(η2-dmf) (4), the structures of which have been determined by X-ray
crystallography. Distorted octahedral geometries are found for the metal centers in all cases,
with the dppe and olefin ligands in a mer configuration, and the C60 and C70 complexes
display significant secondary interactions between the fullerene moiety and the phenyl groups
of the diphosphine ligand. Furthermore, from 31P NMR studies, two isomers of 3 are
observed.
Sch em e 1
In tr od u ction
The polyene-like C60 forms primarily η2 complexes
with single metal centers,1,2 although µ-η2:η2 complexes
with binuclear compounds3 and µ3-η2:η2:η2 complexes
with trinuclear and higher clusters4 have also been
reported. We have previously mentioned the prepara-
tion of a set of exceptionally stable C60 complexes
[M(CO)3(dppe)]nC60 (M ) Mo and W; n ) 1 and 2),5 and
we have extended this approach to the preparation of
an analogous C70 complex Mo(CO)3(dppe)(η2-C70). Here,
we wish to report the details of our X-ray crystal
structure studies of the C60 complexes M(CO)3(dppe)-
(η2-C60) (M ) Mo, 1; M ) W, 2), one isomer of the C70
complex Mo(CO)3(dppe)(η2-C70) (3), as well as of an
analogous complex of dimethyl fumarate (dmf) W(CO)3-
(dppe)(η2-dmf) (4). The general reaction for the forma-
tion of these compounds is shown in Scheme 1.
prepared as described in the literature.6 Separation of the
products was accomplished by thin-layer chromatography
(TLC) using SiO2 plates (Merck, Kieselgel 60 F254, 0.25 mm).
1H NMR spectra were recorded on a Varian U500 or General
Electric GE500 and GE300 spectrometers and were referenced
to CHCl3 at δ 7.24. 31P spectra were recorded on Varian U400
and General Electric GE500 spectrometers and were refer-
enced to external 85% H3PO4. Infrared spectra were recorded
on a Perkin-Elmer 1750 FT-IR spectrometer. Fast atom
bombardment (FAB) mass spectra were recorded on a VG ZAB-
SE spectrometer by the staff of the Mass Spectrometry
Laboratory of the School of Chemical Sciences. Microanalyses
were performed by the staff of the School Microanalytical
Laboratory.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were conducted under
an atmosphere of nitrogen using standard Schlenk techniques.
Solvents for preparative use were dried and distilled. The
compounds 1,2-diphenylphosphinoethane (dppe, Aldrich), Mo-
(CO)6 and W(CO)6 (Strem Chemicals), and C60 and C70 (98%,
BuckyUSA and Southern Chemical Group) were used as
received. The precursors M(CO)4(dppe) (M ) Mo, W) were
Syn th esis a n d Ch a r a cter iza tion of M(CO)3(d p p e)(η2-
C
60) (M ) Mo a n d W), W(CO)3(d p p e)(η2-C2H2(CO2Me)2),
(1) (a) Fagan, P. J .; Calabrese, J . C.; Malone, B. Acc. Chem. Res.
1992, 25, 134. (b) Stephens, A. H. H.; Green, M. L. H. In Advances in
Inorganic Chemistry; Sykes, A. G., Ed.; Academic: New York, 1997;
Vol. 44, p 1.
(2) (a) Park, J . T.; Cho, J .-J .; Song, H. J . Chem. Soc., Chem.
Commun. 1995, 15. (b) Nagashima, H.; Nakazawa, M.; Itoh, K. Chem.
Lett. 1996, 405. (c) Green, M. L. H.; Stephens, H. H. Chem. Commun.
1997, 793.
(3) (a) Rasinkangas, M.; Pakkanen, T. T.; Pakkanen, T. A.; Ahlgre´n,
M.; Rouvinen, J . J . Am. Chem. Soc. 1993, 115, 4901. (b) Mavunkal, I.
J .; Chi, Y.; Peng, S.-M.; Lee, G.-H. Organometallics 1995, 14, 4454.
(4) (a) Hsu, H.-F.; Shapley, J . R. J . Am. Chem. Soc. 1996, 118, 9192.
(b) Lee, K.; Hsu, H.-F.; Shapley, J . R. Organometallics 1997, 16, 3876.
(5) (a) Shapley, J . R.; Du, Y.; Hsu, H.-F.; Way, J . J . Proc.-
Electrochem. Soc. 1994, 94-24, 1255. (b) Hsu, H.-F.; Shapley, J . R.
Proc.-Electrochem. Soc. 1995, 95-10, 1087.
a n d Mo(CO)3(d p p e)(η2-C70). The preparations of M(CO)3-
(dppe)(η2-C60) (M ) Mo and W) and W(CO)3(dppe)(η2-C2H2(CO2-
Me)2) were conducted by photolysis of M(CO)4(dppe) (M ) Mo
or W) and olefin in chlorobenzene followed by chromatographic
isolation as briefly described previously.5 The preparation of
Mo(CO)3(dppe)(η2-C70) was analogous, and the details are
presented here.
Syn th esis of Mo(CO)3(d p p e)(η2-C70) (3). Mo(CO)4(dppe)
(21.6 mg, 0.0356 mmol) and C70 (30 mg, 0.0357 mmol) were
(6) Grim, S. O.; Briggs, W. L.; Barch, R. C.; Tolman, C. A.; J esson,
J . P. Inorg. Chem. 1974, 13, 1095.
S0276-7333(97)01013-3 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/25/1998

Structural Comparison of Mo and W Complexes
Organometallics, Vol. 17, No. 9, 1998 1757
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p ou n d s 1-4
1‚CS2
2‚2C6H4Cl2‚C6H12
3‚3CHCl3
4‚H2O
chem formula
fw
cryst syst
space group
temp (K)
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
90H24MoO3P2S2
C107H44Cl4O3P2W
1765.0
triclinic
P1h
198(2)
13.801(5)
14.779(4)
20.144(4)
74.28(2)
71.57(2)
96.03(2)
3513(2)
2
C102H27Cl9O3MoP2
1777.17
monoclinic
P21/c
C35H34O8P2W
1828.41
orthorhombic
Pbca
198(2)
16.634(4)
17.858(4)
22.573(7)
90
90
90
6705(3)
8
1.641
1375.09
triclinic
P1h
198(2)
198(2)
13.1645(6)
14.2060(6)
15.6949(7)
89.782(4)
71.021(1)
84.071(1)
2759.6(2)
2
1.655
4.37
0.0610
0.0707
10.6694(1)
29.0158(4)
22.317(3)
90
96.685(1)
90
6862(1)
4
1.720
6.50
0.0990
0.0817
0.2025
Z
F(calc), (g cm-3
)
1.668
19.06
0.0275
0.0411
µ (cm-1
Rint
)
36.67
0.0333
0.0339
0.0881
R(Fo)a
2
b
Rw(Fo
)
0.1591
0.1192
R(Fo) ) Σ|(Fo - Fc)|Σ|Fo|. Rw(Fo2) ) {Σ[w(Fo - Fc2)2]/Σw(Fo2)2]}1/2
.
a
b
2
dissolved in 30 mL of dried and degassed chlorobenzene in a
100 mL Pyrex Schlenk tube under a nitrogen atmosphere. The
flask was evacuated to a pressure of ca. 0.1 mmHg with the
reaction mixture frozen and then closed. The solution was
allowed to melt, and then the tube was irradiated with a
tungsten sunlamp (GE, 275 W) for a total of 24 h, with periodic
evacuation of CO. The solution was evaporated under vacuum,
and the residue was separated by thin-layer chromatography,
eluting with n-hexane/dichloromethane (1:1). In order of
elution, a burgundy band of unreacted C70 was trailed by a
green-brown band of 3 with Rf values of ca. 1 and 0.8,
respectively. Following the band containing 3 were multiple
bands attributed to isomers of {Mo(CO)3(dppe)}2(η2-C70) as well
as more highly substituted derivatives. Yield: 21 mg of 3
(0.015 mmol, 42% based on C70).
X-r a y Cr ysta llogr a p h y. For X-ray crystallography, dark
green crystals of 1 were obtained by crystallization from
methanol/carbon disulfide. Dark green crystals of 2 were
grown by diffusion of a mixture of cyclohexane/hexane into a
concentrated solution of 2 in 1,2-dichlorobenzene. Black
crystals 3 were grown from a concentrated solution of chloro-
form that was allowed to stand for several days. The yellow
crystals of 4 were obtained by diffusion of n-hexane into a
solution of 4 in a mixture of carbon tetrachloride/chloroform/
dichloromethane (1:1:1).
A summary of selected crystallographic data for 1-4 is given
in Table 1. Diffraction data for 1 and 3 were collected on a
Siemens Platform/CCD automated diffractometer. Intensity
data for 2 and peak-profile data for 4 were collected on an
Enraf-Nonius CAD4 diffractometer. The structures of 1-3
were solved by direct methods.8 Hydrogen atoms were fixed
on calculated positions, and full-matrix least squares refine-
ment (SHELXL-93)9 was based on F2. The data for compounds
2-4 were corrected for absorption analytically.9 The structure
of 4 was solved by Patterson methods.8 In 4, positions for H(3)
and H(4) were independently refined. Methyl H atom posi-
tions, O-CH3, were optimized by rotation about O-C bonds
with idealized C-H, O-H, and H-H distances. The remain-
ing H atoms were included as fixed idealized contributors.
Successful convergence of the full-matrix least-squares refine-
ment on F2 was indicated by the maximum shift/error for the
last cycle. The highest peak in the final difference Fourier
map was in the vicinity of the W atom; the final map had no
other significant features.
Mo(CO)3(dppe)(η2-C60) (1). Anal. Calcd for C89H24O3P2Mo:
C, 82.29; H, 1.86. Found: C, 81.90; H, 1.59. FAB(+)-MS
(98Mo): m/z 1300 (M+). IR (CH2Cl2): ν(CO) 2006 (m), 1939
(m), 1896 (s) cm-1 1H NMR (400 MHz, CDCl3): δ 7.53 (20H,
.
m, C6H5), 2.92 (4H, app tr, CH2). 31P NMR (202.5 MHz,
CDCl3): δ 62.64 (1P, d, J (P-P) ) 15.2 Hz), 54.21 (1P, d, J (P-
P) ) 15.2 Hz).
W(CO)3(dppe)(η2-C60) (2). Anal. Calcd for C89H24O3P2W: C,
77.07; H, 1.74; W, 13.26. Found: C, 76.70; H, 1.84; W, 13.59.
FAB(-)-MS (184W): m/z 1386 (M-). IR (CH2Cl2): ν(CO) 2002
(m), 1937 (m), 1884 (s) cm-1 1H NMR (300 MHz, CDCl3, 20
.
°C): δ 7.45 (20H, m, C6H5), 2.99 (4H, m, CH2). 31P NMR (202.5
MHz, CDCl3): δ 41.48 (1P, d, J (P-P) ) 5.4 Hz, J (P-W) )
228.1 Hz), 38.11 (1P, d, J (P-P) ) 5.4 Hz, J (P-W) ) 218.4
Hz).
The structure refinements of 1-4 were straightforward
except for the presence of two unresolved chloroform solvent
molecules in 3. Consequently, the SQUEEZE10 subroutine in
the program package PLATON11 was used to account for these
molecules. With this procedure, potential solvent regions in
the unit cell are identified from considerations of space filling.
The contributions to the total structure factors of the observed
electron densities in these regions are calculated by a discrete
Fourier transform, and the results are incorporated into the
structure factors for further least-squares refinement of the
ordered part of the structure. The process is iterated.
Mo(CO)3(dppe)(η2-C70) (3). Anal. Calcd for C99H24MoO3P2‚
CS2: C, 79.18; H, 1.82; P, 3.85. Found: C, 79.25; H, 1.87; P,
3.61. FAB(+)-MS (98Mo): m/z 1420 (M+). IR (CH2Cl2): ν(CO)
2008 (m), 1942 (m), 1897 (s) cm-1
.
1H NMR (400 MHz,
CDCl3): δ 7.45 (20H, m, phenyl), 2.85 (4H, app tr, CH2). 31P
NMR (161.9 MHz, CDCl3): δ 62.54 (1P, two overlapped
doublets, average J (P-P) ) 15.8), 57.55 and 57.35 (1P, two
doublets with the ratio of 4:1, average J (P-P) ) 15.8 Hz).
W(CO)3(dppe)(η2-C2H2(CO2Me)2) (4). Anal. Calcd for
C
35H32O7P2W: C, 51.87; H, 3.98; P, 7.64. Found: C, 51.54; H,
3.90; P, 7.39. IR (CH2Cl2): ν(CO) 2006 (m), 1936 (m), 1887
(s) cm-1 (lit.7 ν(CO) (CH2Cl2) 2006 (s), 1934 (m), 1887 (vs) cm-1).
1H NMR (300 MHz, CDCl3, 20 °C): δ 7.60 (20H, m, C6H5), 3.46
(2H, s, -HCdCH-), 3.30 (6H, s, CH3), 2.47 (4H, m, CH2) (lit.7
(CD2Cl2) δ 7.40 (m, C6H5), 3.48 (d, -HCdCH-), 3.30 (s, OCH3),
2.56 (CH2)). 31P NMR (121.7 MHz, CDCl3): δ 45.37 (1P, d,
J (P-P) ) 10.0 Hz, J (P-W) ) 219.2 Hz), 43.19 (1P, d, J (P-P)
) 10.0 Hz, J (P-W) ) 219.0 Hz).
Resu lts a n d Discu ssion
Syn th eses a n d Ch a r a cter iza tion of 1-4. Com-
pounds 1-4 were prepared by photolysis of M(CO)4-
(8) Sheldrick, G. M. SHELX-76. Program for crystal structure
determination; University of Cambridge: Cambridge, England, 1976.
(9) Sheldrick, G. M. SHELXL-93; University of Go¨ttingen: Go¨ttin-
gen, Germany, 1993.
(10) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(11) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(7) Schenk, W.; Mu¨ller, H. Chem. Ber. 1982, 115, 3618.

1758 Organometallics, Vol. 17, No. 9, 1998
Hsu et al.
F igu r e 1. View of the molecular structure of 2 (50%
probability ellipsoids).
F igu r e 2. View of the molecular structure of 3 (50%
probability ellipsoids).
(dppe) and the respective olefin (C60, C70, or dimethyl
fumarate) in chlorobenzene followed by TLC separation.
As indicated previously,5 these six-coordinate, 18-
electron, M(0) fullerene complexes are quite stable
toward air, moisture, and heat. This is presumably due
to both steric and electronic inhibition of substitution
reactions. The direct reaction of W(CO)4(dppe) with
dimethyl fumarate under photolysis provides 4 in 38%
yield, which compares with 45% reported for the initial
preparation of W(CO)3(dppe)(acetone) followed by reac-
tion with dimethyl fumarate.7
The ν(CO) infrared spectra of 1-4 are very similar
in pattern and peak frequencies. Upon changing the
metal center from Mo to W in 1 to 2, a red shift of 2-4
cm-1 is observed; this is consistent with stronger π-base
character for the third-row metal. A comparison of the
spectra of 1 and 3 shows a slight blue shift of 1-3 cm-1
as C60 is replaced with C70. The blue shift from 1 to 3
indicates that C70 is more electronegative than C60,
which agrees with results reported by Albrecht.12 The
infrared spectrum of 4 is almost identical to that of 2,
with a small blue shift of 1-4 cm-1. The two 31P NMR
signals shift 21 and 16 ppm upfield from 1 to 2, while
only a 2 ppm downfield shift is observed from 1 to 4.
Both infrared and 31P NMR data for 1-4 demonstrate
that C60, C70, and dimethyl fumarate have very similar
electronic properties as η2-ligands bound to these ze-
rovalent metal centers.
Cr ysta l Str u ctu r es of 1-4. Drawings of the mo-
lecular structures of 2, 3, and 4 are shown in Figures
1, 2, and 3, respectively. The structure of 1 is essentially
superimposable on that of 2. Selected bond distances
and bond angles are given in Table 2 for compounds 1,
2, and 4 and in Table 3 for compound 3. The metal
centers are distorted octahedra in all four cases, and
the olefin ligands are η2-coordinated to the metal
centers. A mer configuration is adopted for the dppe
and olefin ligands, where one phosphorus atom of the
chelating diphosphine ligand is trans and the other cis
to the olefinic center. The trans effect is observed in
the M-P(2) bond distances, which are cis to the olefin
ligand and trans to CO(102). The M-P(2) bonds are
uniformly longer than the M-P(1) bonds, which are cis
F igu r e 3. View of the molecular structure of 4 (50%
probability ellipsoids).
to the carbonyl and trans to the olefin. The bite angles
of the dppe ligands, P(1)-M-P(2), are comparable
among the three compounds, and they are almost
identical for 2 (79.0°) and 4 (78.8°). The most significant
difference among the three is the P(2)-M-C(102) angle.
For the dimethyl fumarate compound 4 (154.4°), it is
ca. 10° smaller than those of the three fullerene
compounds 1, 2, and 3 (162.1°, 164.1°, and 161.8°,
respectively). This distortion may be due to interactions
between the phenyl rings of the dppe ligands and
fullerenes as described below.
Upon coordination of an olefin to a metal center, the
double bond distance increases and the four groups
attached to the olefin bend away from the metal, as
explained by the Dewar-Chatt bonding model.1a,13 The
(12) Burba, M. E.; Lim, S. K.; Albrecht, A. C. J . Phys. Chem. 1995,
99, 11839.
(13) Kumar, A.; Lichtenhan, J . D.; Critchlow, S. C.; Eichinger, B.
E.; Borden, W. T. J . Am. Chem. Soc. 1990, 112, 5633. (b) Ittel, S. D.;
Ibers, J . A. Adv. Organomet. Chem. 1976, 14, 33.

Structural Comparison of Mo and W Complexes
Organometallics, Vol. 17, No. 9, 1998 1759
those in other η2-C60 complexes (e.g., 1.50(3) Å in Pt-
(PPh3)2C60,14a 1.53(3) Å in Ir(CO)Cl(PPh3)2C60,14b and
1.48(1) Å in RhH(CO)(PPh3)2C6014c). The CdC bond
distance in 4 is similar to that (1.41(1) Å) in a closely
related compound [mer-W(CO)3{CH3N(P(OCH3)2)2}]2(µ-
η2:η2-C7H8),15 and it is comparable with those reported
for other dimethyl fumarate compounds, such as 1.439(4)
Å in Ru(CO)2(i-Pr-DAB)(η2-dmf)16a and 1.429(6) Å in Mo-
(CO)2(phen)(η2-dmf)2.16b
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for Com p ou n d s 1, 2, a n d 4
1
2
4
Bond Lengths
2.309(7)
2.306(7)
2.475(2)
2.545(2)
2.010(10)
2.013(9)
2.053(9)
1.483(10)
1.475(10)
1.476(10)
1.493(11)
M-C(1)
2.291(6)
2.296(5)
2.484(2)
2.533(2)
2.009(6)
2.026(7)
2.037(6)
1.497(8)
1.478(8)
1.476(8)
1.477(8)
2.279(7)
2.273(7)
2.495(2)
2.524(2)
1.986(8)
2.045(8)
2.033(8)
1.455(10)
M-C(2)
M-P(1)
M-P(2)
M-C(102)
M-C(101)
M-C(103)
C(1)-C(2)
C(1)-C(9)
C(2)-C(3)
C(2)-C12
The olefin C-C vectors of the ligands in 1-4 are in
each case parallel to the P(2)-M-C(102) axis. Theo-
retical analysis of octahedral olefin complexes has
confirmed that such an eclipsed orientation is more
stable than the staggered one and that the energy
barrier to interconverting these configurations is ca.
Bond Angles
37.5(2)
77.5(1)
85.3(2)
162.1(2)
89.5(3)
C(1)-M-C(2)
38.1(2)
79.0(1)
83.0(2)
164.1(1)
89.6(2)
178.9(2)
91.2(2)
37.3(3)
78.8(1)
80.6(2)
154.4(2)
90.5(3)
174.3(3)
86.2(3)
7-10 kcal mol-1 17
rotation barrier for the dmf ligand in 4 to be 11 kcal
mol-1 5a
The preferred alignment with the P(2)-M-
.
We have previously reported the
P(1)-M-P(2)
C(102)-M-P(1)
C(102)-M-P(2)
C(102)-M-C(101)
C(101)-M-C(103)
C(102)-M-C(103)
.
C(102) axis instead of the C(101)-M-C(103) axis can
be rationalized by the net lower π acid competition for
the metal d orbital involved in the π back-bonding with
the olefin.18
177.4(3)
89.0(3)
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 3
Fullerene/arene interactions are observed in both
fullerene compounds 1 and 2, and the interactions are
essentially identical in the two cases. Figure 4 shows
the details for compound 1, in which the phenyl ring
(C(19P)-C(24P)) of P(2) is parallel to the C60 moiety’s
surface and is roughly centered over a “double bond”
(C(8)-C(24)) to form an offset π-stacked geometry. The
distances from the center of the phenyl ring to the
closest carbon atom of C60 are 3.30 Å for 1 and 3.29 Å
for 2. The other phenyl ring (C(13P)-C(18P)) is per-
pendicular to C60, resulting in an edge-on geometry, and
the distances calculated between C(18P) and the nearest
carbon atom of C60 are 3.75 and 3.55 Å for 1 and 2,
respectively. Since the H atoms are at fixed positions
with a C-H bond distance of 0.95 Å, the resulting
H(18P)-C(C60) distances are 2.84 and 2.60 Å for 1 and
2, respectively.
Bond Lengths
Mo-C(1)
2.290(7)
2.478(2)
2.040(8)
2.033(8)
1.502(10)
1.505(9)
Mo-C(6)
2.278(6)
2.542(2)
2.019(8)
1.460(9)
1.488(9)
1.472(9)
Mo-P(1)
Mo-P(2)
Mo-C(101)
Mo-C(103)
C(1)-C(2)
C(6)-(11)
Mo-C(102)
C(1)-C(6)
C(1)-C(5)
C(6)-C(20)
Bond Angles
C(1)-Mo-C(6)
C(2)-C(1)-C(5)
37.3(2)
102.8(6)
P(1)-Mo-P(2)
C(11)-C(6)-C(20)
79.3(1)
101.8(5)
Sch em e 2
Both intra- and intermolecular π-π interactions have
been reported for fullerene complexes, with distances
comparable to those in compounds 1 and 2.19 These
interactions have been used to design supramolecular
aggregates of fullerene-containing complexes, as dem-
onstrated in the crystal structure of Ir(CO)Cl(bobPPh2)2-
(η2-C60).19a In this structure, the closest intramolecular
contact between the phenyl rings and the C60 moiety is
degree of bending can be described by the pyramidal-
ization angle,13 defined as the angle between the exten-
sions of the CdC bond and the plane containing the
substituents, as shown in Scheme 2. For all three
fullerene compounds, the two coordinated carbon atoms,
C(1) and C(2) for the C60 compounds and C(1) and C(6)
for the C70 compound, are pulled away from the fullerene
cage. Coincident with this is a lengthening of the four
bonds adjacent to C(1) and C(2) (average 1.48 Å) for
compounds 1 and 2 or C(1) and C(6) (average 1.49 Å)
for compound 3. The pyramidalization angles for the
fullerene compounds are approximately 43°, 42°, and
41° for compounds 1, 2, and 3, respectively. The
dimethyl fumarate compound 4 has an approximate
pyramidalization angle of 33°. These angles are not
directly suitable for comparing the degree of dπ-π*
back-bonding for the fullerene compounds 1, 2, and 3
with 4, since free C60 and C70 are already nonplanar (ca.
31°),1a in contrast to free fumarate. The CdC distances
for 1, 2, 3, and 4 are 1.48(1), 1.50(1), 1.460(9), and
1.46(1) Å, and they are significantly longer than those
in free C60 (6,6 ring fusion ) 1.36(1) Å12) and free olefins
(1.34 Å in ethylene, and 1.34 Å in tetracyanoethylene).
The length of the CdC bond in 1 and 2 is similar to
(14) (a) Fagan, P. J .; Calabrese, J . C.; Malone, B. Science 1991, 252,
1160. (b) Balch, A. L.; Lee, J . W.; Noll, B. C.; Olmstead, M. M. Inorg.
Chem. 1993, 32, 3577. (c) Bashilov, V. V.; Petrovskii, P. V.; Sokolov,
V. I.; Lindeman, S. V.; Guzey, I. A.; Struchkov, Y. T. Organometallics
1993, 12, 991.
(15) Mague, J . T.; J ohnson, M. P. Organometallics 1991, 10, 349.
(16) (a) van Wijnkoop, M.; de Lange, P. P. M.; Fru¨hauf, H.-W.;
Vrieze, K.; Smeets, W. J . J .; Spek, A. L. Organometallics 1995, 14,
4781. (b) Lai, C.-H.; Cheng, C.-H.; Chou, W.-C.; Wang, S.-L. Organo-
metallics 1993, 12, 1105.
(17) Albright, T. A.; Hoffmann, R.; Thibeault, J . C.; Thorn, D. L. J .
Am. Chem. Soc. 1979, 101, 3803.
(18) Templeton, J . L.; Winston, P. B.; Ward, B. C. J . Am. Chem.
Soc. 1981, 103, 7713.
(19) (a) Balch, A. L.; Catalano, V. J .; Lee, J . W.; Olmstead, M. M. J .
Am. Chem. Soc. 1992, 114, 5455. (b) Balch, A. L.; Lee, J . W.; Noll, B.
C.; Olmstead, M. M. J . Am. Chem. Soc. 1992, 114, 10984. (c) Balch, A.
L.; Lee, J . W.; Olmstead, M. M. Angew. Chem., Int. Ed. Engl. 1992,
31, 1356. (d) Meidine, M. F.; Hitchcock, P. B.; Kroto, H. W.; Taylor,
R.; Walton, D. R. M. J . Chem. Soc., Chem. Commun. 1992, 1534. (e)
Fedurco, M.; Olmstead, M. M.; Fawcett, W. R. Inorg. Chem. 1995, 34,
390.

1760 Organometallics, Vol. 17, No. 9, 1998
Hsu et al.
F igu r e 5. 31P NMR spectrum showing the presence of
isomers 3a and 3b. Superimposed is a diagram showing
the near-polar binding sites a and b in C70
.
spectra recorded up to 100 °C showed no signal broad-
ening and, in particular, no coalescence of the major and
minor doublets near 55 ppm. This implies a barrier to
interconversion of these two forms of greater than 21
kcal/mol (k < 10 s-1 at T ) 398 K; ∆Gq ) (4.575 ×
10-3)T{10.319 + log(T/k)} ) 21.7 kcal/mol), which is not
consistent with rotational isomerism. As noted earlier,
the barrier to rotation about the metal-olefin axis is
expected to be ca. 11 kcal/mol, which is sufficiently low
that any such rotational isomers should be in rapid
exchange at room temperature. This expectation is
consistent with the observation of only one pair of
doublets for both 1 and 2.
F igu r e 4. View of the interactions of C60 and both phenyl
rings on P(2) in 1. Top: Edge-on view of π-stacked ring
C(19P)-C(24P). Bottom: View perpendicular to ring
C(19P)-C(24P).
3.10 Å, whereas the intermolecular offset π-stacked
interactions between the bobPPh2 ligand and the C60
ligand of an adjacent molecule range from 3.3 to 3.4 Å.
In the structure of {Ir(CO)Cl(PMe2Ph)2}2C60‚C6H6,19b
the phenyl rings of the phosphine ligands form an offset
π-stacked configuration with the C60 cage within the
same molecule. In the structure of the C70 derivative
{Ir(CO)Cl(PPhMe2)2}2C70‚C6H6, both intra- and inter-
molecular interactions are observed in which the phenyl
rings are found to be sandwiched by two adjacent C70
cages.19c
However, in contrast to the single type of “double
bond” site for C60, the possibilities for coordination to
C70 are more varied. Additions to C70 occur preferen-
tially at the more pyramidalized sites near the poles,20
predominantly at site a nearest the pole and secondarily
at the next nearest site b (see diagram in Figure 5). The
structure of 3 determined by X-ray diffraction corre-
sponds to the Mo center binding at site a , and we,
therefore, assign the major 31P NMR signal to structure
3a . The minor signal is assigned to an isomer of
structure 3b. We assume that 3a crystallized prefer-
entially from the bulk sample containing both forms.
Unfortunately, there was not a sufficient quantity of
these X-ray-quality crystals to dissolve and monitor
whether pure 3a isomerizes to the observed 3a , 3b
mixture.
As observed in the analogous C60 compounds 1 and
2, fullerene/arene interactions involving both phenyl
rings are also observed in the structure of 3. There is
an offset π-stacked geometry for the C(19P)-C(24P) ring
and an edge-on geometry for the C(13P)-C(18P) ring
with the C70 core. The separation distance from the
center of the C(19P)-C(24P) phenyl ring to the nearest
carbon atom in the fullerene cage is 3.27 Å, which is
shorter than the 3.37 Å distance found in 1.
Ack n ow led gm en t. This work was supported by
grants from the National Science Foundation, Grant
Nos. CHE 94-14217 (to J .R.S.) and DMR 8920538 (to
the Materials Research Laboratory at the University of
Illinois). We acknowledge J im Elfering for obtaining the
single crystals of compound 1. Purchase of the Siemens
Platform/CCD diffractometer by the School of Chemical
Obser va tion of Isom er s in 3. In the 31P NMR
spectra of compounds 1, 2, and 4, two well-separated
signals, corresponding to the two distinct phosphorus
centers in these molecules, are observed; each signal is
split into a narrow doublet due to coupling between the
two 31P nuclei. In contrast, for compound 3, two pairs
of doublets are seen, partially superimposed as shown
in Figure 5, corresponding to a major (80%) form 3a and
a minor (20%) form 3b. We considered that these two
forms might be rotational isomers, i.e., that the major
species had the olefin C-C vector oriented parallel to
the P(2)-Mo-C(102) axis, as seen in the crystal struc-
ture of 3, and the minor species had the C-C vector
rotated 90° to be oriented parallel to the C(101)-Mo-
C(103) axis. However, variable-temperature 31P NMR
(20) (a) Hawkins, J . M.; Meyer, A.; Solow, M. A. J . Am. Chem. Soc.
1993, 115, 7499. (b) Herrmann, A.; Diederich, F.; Thilgen, C.; ter Meer,
H.-U.; Muller, W. H. Helv. Chim. Acta 1994, 77, 1689. (c) Seiler, P.;
Herrmann, A.; Diederich, F. Helv. Chim. Acta 1995, 78, 344. (d) Balch,
A. L.; Catalano, V. J .; Lee, J . W.; Olmstead, M. M.; Parkin, S. R. J .
Am. Chem. Soc. 1991, 113, 8953. (e) Balch, A. L.; Costa, D. A.;
Olmstead, M. M. Chem. Commun. 1996, 2449. (f) Smith, A. B., III.;
Strongin, R. M.; Brard, L.; Furst, G. T.; Atkins, J . H.; Romanow, W.
J .; Saunders, M.; J ime´nez-Va´zquez, H. A.; Owens, K. G.; Goldschmidt,
R. J . J . Org. Chem. 1996, 61, 1904.

Structural Comparison of Mo and W Complexes
Organometallics, Vol. 17, No. 9, 1998 1761
Su p p or tin g In for m a tion Ava ila ble: Tables of the details
of crystallographic data, atomic coordinates, thermal coef-
ficients, bond distances, and bond angles from the structure
determination of 1-4 (43 pages). Ordering information is
given on any current masthead page.
Sciences at the University of Illinois was supported
National Science Foundation Grant No. CHE 9503145.
NMR spectra were obtained using instruments in the
Varian Oxford Instrument Center for Excellence in
NMR Laboratory in the School of Chemical Sciences;
external funding for this instrumentation was obtained
from the Keck Foundation, NIH, and NSF.
OM971013X