Synthesis and structure of piano stool complexes derived from the tetrakis(pentafluorophenyl)cyclopentadienyl ligand

Article abstract of DOI:10.1021/om000805f

The reaction of NaCp (Cp = C₅H₅) with excess C₆F₆ and excess NaH in refluxing diglyme afforded a 57% yield of 1,2,3,4-tetrakis(pentafluorophenyl)cyclopentadiene (1). Treatment of 1 with NaH in THF afforded sodium tetrakis(pentafluorophenyl)cyclopentadienide (2) in 89% yield. Reactions of 2 with M(CO)₅Br (M = Mn, Re) yielded [(C₆F₅)₄C₅H]M(CO)₃ complexes (3, M = Mn, 33%, and 4, M = Re, 28%). Reactions of 2 with various iron(II) salts and with CoBr₂ however failed to afford the corresponding octaarylated metallocenes. Infrared spectroscopic analysis of 3 and 4 revealed an increase of 16(1) cm^-1 relative to CpM(CO)₃ in the A-symmetric C-O stretching frequency, suggesting that the C₆F₅ groups have a highly electron-withdrawing effect on the coordinated M(CO)₃ moieties. Crystal structures of 1, 1·1/2C₆D₆, 2, and 3 display a propeller-like arrangement of the C₆F₅ groups. Complexes 2 and 3 show elongation of the C₅(centroid)-M bond distances relative to CpMn(CO)₃ and CpRe(CO)₃, which is attributed to steric effects.

Full text of DOI:10.1021/om000805f

920
Organometallics 2001, 20, 920-926
Syn th esis a n d Str u ctu r e of P ia n o Stool Com p lexes
Der ived fr om th e
Tetr a k is(p en ta flu or op h en yl)cyclop en ta d ien yl Liga n d
Matthew P. Thornberry, Carla Slebodnick, Paul A. Deck,* and
Frank R. Fronczek
Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061-0212, and Department of
Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803-1804
Received September 19, 2000
The reaction of NaCp (Cp ) C5H5) with excess C6F6 and excess NaH in refluxing diglyme
afforded a 57% yield of 1,2,3,4-tetrakis(pentafluorophenyl)cyclopentadiene (1). Treatment
of 1 with NaH in THF afforded sodium tetrakis(pentafluorophenyl)cyclopentadienide (2) in
89% yield. Reactions of 2 with M(CO)5Br (M ) Mn, Re) yielded [(C6F5)4C5H]M(CO)3 complexes
(3, M ) Mn, 33%, and 4, M ) Re, 28%). Reactions of 2 with various iron(II) salts and with
CoBr2 however failed to afford the corresponding octaarylated metallocenes. Infrared
spectroscopic analysis of 3 and 4 revealed an increase of 16(1) cm-1 relative to CpM(CO)3 in
the A-symmetric C-O stretching frequency, suggesting that the C6F5 groups have a highly
electron-withdrawing effect on the coordinated M(CO)3 moieties. Crystal structures of 1,
1‚1/2C6D6, 2, and 3 display a propeller-like arrangement of the C6F5 groups. Complexes 2
and 3 show elongation of the C5(centroid)-M bond distances relative to CpMn(CO)3 and
CpRe(CO)3, which is attributed to steric effects.
In tr od u ction
previously that up to three pentafluorophenyl (C6F5)
groups are readily attached to cyclopentadiene and that
up to two C6F5 groups may be attached to indene by
one-pot procedures involving nucleophilic aromatic sub-
stitution of hexafluorobenzene.6,10 C6F5-substituted Cp
and indenyl anions are stable as sodium salts and can
Substituent effects on transition metal cyclopentadi-
enyl (Cp) complexes have been studied extensively.
Changes in the size, shape, and electron-donating
character of ring substituents influence molecular struc-
ture and crystal packing,1 physical and spectroscopic
properties,2 and fundamental aspects of inner coordina-
tion sphere reactivity.3 The wide-ranging influences of
Cp ligand substituents have been exploited in catalysis4
and in mechanistic studies.5 We have noted,6 however,
that the effects of highly electron-withdrawing substit-
uents are much less thoroughly studied than either
electron-donating substituent effects or steric effects.7,8
Nevertheless, electron-withdrawing substituents may
offer advantages for some catalytic applications.9
We are exploring the electron-withdrawing extreme
of substituent effects in Cp complexes. We showed
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10.1021/om000805f CCC: $20.00 © 2001 American Chemical Society
Publication on Web 01/27/2001

Tetrakis(pentafluorophenyl)cyclopentadienyl
Organometallics, Vol. 20, No. 5, 2001 921
Ta ble 1. Cr ysta llogr a p h ic Da ta
1
1‚1/2C6D6
3
4
empirical formula
fw
diffractometer
cryst dimens (mm)
cryst syst
a (Å)
C
29H2F20
2 C29H2F20‚C6D6
C32HF20MnO3
868.27
C32HF20ReO3
999.54
Nonius Kappa CCD
0.08 × 0.20 × 0.20
triclinic
8.1450(2)
13.1900(4)
14.4900(3)
75.9910(18)
81.0610(16)
79.9430(18)
1476.73(7)
P-1 (No. 2)
2
730.31
1544.72
Nonius Kappa CCD
0.23 × 0.32 × 0.38
triclinic
Nonius Kappa CCD
0.18 × 0.20 × 0.30
monoclinic
10.6760(4)
10.8820(5)
Siemens P4
0.13 × 0.29 × 0.48
triclinic
10.515(2)
11.345(3)
13.910(3)
93.097(16)
97.264(18)
117.174(17)
1452.6(6)
P-1 (No. 2)
2
11.1190(2)
14.7360(3)
15.6200(3)
82.1670(13)
80.2890(11)
79.7970(15)
2467.78(8)
P-1 (No. 2)
4
b (Å)
c (Å)
24.4400(12)
R (deg)
â (deg)
94.266(3)
γ (deg)
V (Å)3
2831.5(2)
P21/n (No. 14)
2
1.812
0.199
space group
Z
D
calc (Mg m-3
)
1.966
0.221
1424
1.985
0.622
844
2.248
4.3
944
abs coeff (mm-1
F000
)
1508
λ (Mo KR) (Å)
temp (K)
0.71073
100
0.71073
150
0.71073
293
0.71073
120
θ range for collection
no. of reflns colld
no. of indep reflns
abs corr method
max, min transm
no. of data/restrnts/params
R [I > 2σ(I)]
1.4-27.9
2.7-27.5
10 584
6259
2.0-27.5
2.5-32.6
18 771
7744
15 805
11 729
none
6649
ψ scans
0.550, 0.487
6649/0/509
0.041
0.077
0.81
0.26, -0.22
10 352
none
multiscan
0.726, 0.521
10 352/0/506
0.031
0.063
1.00
11 729/0/884
0.068
0.184
1.56
0.61, -0.44
6259/0/470
0.036
0.082
0.84
0.21, -0.21
Rw [I > 2σ(I)]
GoF on F2
peak, hole (e Å-3
)
1.28, -1.71
Database (CSD) was searched using ConQuest software (ver-
sion 1.0) from the Cambridge Crystallographic Data Centre.
be used in various standard synthetic procedures to
prepare complexes of both early and late transition
metals.
Cr ysta llogr a p h ic Stu d ies. Crystals of 1 were obtained by
allowing a solution of 1 in ethyl acetate/hexane to evaporate
completely. Crystals of 1 were also obtained serendipitously
during NMR-scale experiments in which 1 was reacted with
(C6F5C5H4)CpZr(CH3)2 and B(C6F5)3 in benzene-d6. The reac-
tion afforded a red, viscous oil that we were unable to
characterize and a few colorless crystals. X-ray diffraction
analysis of the colorless crystals found 1‚1/2C6D6. These
crystals were found to be highly unstable toward solvent loss,
so crystals were removed quickly from the mother liquor,
mounted on a fiber under oil, and transferred to the cold
stream of the diffractometer. Crystals of 3 and 4 were grown
by cooling warm, concentrated toluene solutions to 25 °C.
Crystallographic data are assembled in Table 1.
This contribution reports our extension of these
studies to the tetrakis(pentafluorophenyl)cyclopentadienyl
ligand. We first present an efficient synthesis of 1,2,3,4-
tetrakis(pentafluorophenyl)cyclopentadiene, and we char-
acterize its molecular structure using two crystal struc-
tures, one of which contains a “stacked” benzene solvate
molecule. The syntheses and characterization of the
corresponding sodium salt as well as two complexes,
[(C6F5)4C5H]M(CO)3 (M ) Mn and Re), are reported. We
also briefly discuss our failure to prepare either
[(C6F5)4C5H]2Fe or [(C6F5)4C5H]2Co using methods that
were successful for the corresponding triarylated Cp
ligands.6
1,2,3,4-Tetr akis(pen taflu or oph en yl)cyclopen tadien e (1).
A mixture of NaCp (2.00 g, 22.7 mmol), NaH (3.27 g, 136
mmol), and diglyme (250 mL) was stirred at reflux. Using a
syringe, C6F6 (25.6 g, 138 mmol) was added cautiously to the
refluxing reaction mixture over a period of 5 min. The mixture
was stirred at reflux for 2 days. The diglyme was then removed
by heating the dark mixture under vacuum. The black residue
was taken up in 200 mL of THF and added, using a canulla,
to an aqueous solution of NH4Cl (10.0 g in 400 mL). The
biphasic mixture was evaporated, and the resulting dark, oily
residue was extracted with CH2Cl2, filtered through Celite, and
evaporated to yield a brown, oily solid. The crude solid was
triturated with warm hexane, collected on a filter, and dried
under vacuum to afford 9.44 g (12.9 mmol, 57%) of a brown
Exp er im en ta l Section
Gen er a l P r oced u r es. Standard inert-atmosphere tech-
niques were used for all reactions. C6F6 (99% purity), FeBr2,
Mn(CO)5Br, Re(CO)5Br, KH, and 18-crown-6 were used as
received from Aldrich. NaH was purchased as a 60% mineral
oil dispersion from Aldrich, washed with hexanes, dried under
vacuum, and stored in a glovebox. Anhydrous CoBr2 was
prepared by heating the red commercial hydrate (from Fisher)
under vacuum to obtain a bright green powder. NaCp was
prepared from freshly distilled cyclopentadiene and excess
NaH in THF. Fe(acac)2 was prepared by a published method.11
Melting points were obtained using a Mel-Temp apparatus and
are uncorrected. Infrared spectra were recorded on a Midac
M-series instrument operating at 1 cm-1 resolution, using
dilute hexane or octane solutions and KBr-windowed cells.
NMR experiments used J EOL ECP500, Varian U400, and
Bruker EM360 instruments. THF-d8 (Isotec) was vacuum-
transferred from NaK2 alloy. 19F NMR spectra were referenced
to external C6F6 in CDCl3 (-163.00 ppm) at 25 °C. C-F
coupling constants were approximated from apparent split-
tings. Elemental analyses were performed by Desert Analytics
(Tucson, AZ). Version 5.19 of the Cambridge Structural
1
powder, which was found by H and 19F NMR analysis to be
about 95% pure. An analytically pure sample was obtained
by sublimation (125 °C, 5 × 10-6 Torr): mp 196-197 °C (open
capillary). 1H NMR (CDCl3): δ 4.17 (s, 2 H). 19F NMR
3
5
(CDCl3): δ -140.02 (dd, J ) 22 Hz, J ) 8 Hz, 4 F), -140.29
3
5
3
(dd, J ) 23 Hz, J ) 8 Hz, 4 F), -151.10 (t, J ) 21 Hz, 2 F),
3
-152.00 (t, J ) 21 Hz, 2 F), -160.18 (m, 4 F), -160.62 (m, 4
F). {19F}13C NMR (CDCl3): δ 144.1 (s, CF), 144.0 (s, CF), 141.8
(s, CF), 141.7 (s, CF), 138.1 (s, CF), 137.7 (s, CF), 136.1 (t, J )
6 Hz, C-C6F5), 134.5 (t, J ) 4 Hz, C-C6F5), 109.3 (s, Cipso), 108.3
(s, Cipso), 48.1 (t, J ) 132 Hz, CH2). {1H}13C NMR (CDCl3): δ
1
1
144.1 (d, J CF ) 240 Hz, CF), 141.6 (d, J CF ) 250 Hz, CF),
138.1 (d, J CF ) 260 Hz, CF), 137.7 (d, J CF ) 260 Hz, CF),
136.1 (s, C-C6F5), 134.5 (s, C-C6F5), 109.3 (m, Cispo), 108.3 (m,
1
1
(11) Bunel, E. E.; Valle, L.; Manriquez, J . M.; Organometallics 1985,
4, 1680.

922 Organometallics, Vol. 20, No. 5, 2001
Thornberry et al.
Cipso), 48.1 (s, CH2). Anal. Calcd for C29H2F20: C, 47.70; H, 0.28.
Found C, 48.01; H, 0.29.
Sch em e 1
Sodiu m 1,2,3,4-Tetr akis(pen taflu or oph en yl)cyclopen ta-
d ien id e (2). A mixture of 1,2,3,4-tetrakis(pentafluorophenyl)-
cyclopentadiene (1, 2.05 g, 2.81 mmol), NaH (0.17 g, 7.08
mmol), and THF (50 mL) was stirred at 25 °C for 1 day and
then filtered to remove unreacted NaH. The filtrate was
evaporated, and the residue was triturated with hexane,
collected on a fritted filter, and dried under vacuum to afford
1.88 g (2.50 mmol, 89%) of a tan powder. (The potassium salt
can be prepared analogously by using KH in place of NaH).
1H NMR (THF-d8): δ 6.43 (p, 5J ) 1.6 Hz, 1 H). 19F NMR (THF-
d8): δ -143.95 (dd, 3J ) 25 Hz, 5J ) 7 Hz, 4 F), -144.86 (d, 3J
) 25 Hz, 5J ) 6 Hz, 4 F), -165.00 (t, 3J ) 21 Hz, 2 F), -167.52
(m, 6 F, two unresolved signals), -167.83 (m, 4 F). {19F}13C
NMR (THF-d8): δ 144.3 (s, CF), 143.8 (s, CF), 138.0 (s, CF),
137.8 (s, CF), 137.5 (s, CF), 137.1 (s, CF), 117.7 (s, Cispo), 117.6
(s, Cispo), 115.5 (d, J ) 165 Hz, CH), 106.6 (d, J ) 4.2 Hz,
C-C6F5), 106.4 (d, J ) 8.3 Hz, C-C6F5). {1H}13C NMR (THF-
d8): δ 144.3 (d, J ) 243 Hz, CF), 143.8 (d, J ) 241 Hz, CF),
137.7 (d, J ) 243 Hz, three unresolved CF), 137.1 (d, J ) 233
Hz, CF), 117.6 (m, two unresolved Cispo), 115.5 (s, CH), 106.6
(s, C-C6F5), 106.4 (C-C6F5). Satisfactory microanalytical data
1
were not obtained. H and 19F NMR spectra of 2 are provided
in the Supporting Information as evidence of substantial bulk
purity.
Tr ica r bon yl[η5-1,2,3,4-tetr a k is(p en ta flu or op h en yl)cy-
clop en ta d ien yl]m a n ga n ese(I) (3). A mixture of Mn(CO)5Br
(0.223 g, 0.811 mmol), sodium 1,2,3,4-tetrakis(pentafluorophe-
nyl)cyclopentadienide (2, 0.597 g, 0.794 mmol), NaH (20 mg),
and toluene (50 mL) was stirred under reflux for 1 day. The
mixture was then filtered while still warm, and the filtrate
was evaporated. The resulting residue was triturated with
hexane, collected on a filter, and dried under vacuum to afford
0.197 g (0.259 mmol, 33%) of a yellow solid. An analytically
pure sample was obtained by recrystallization from toluene.
Mp (sealed, nitrogen-filled capillary): 190-192 °C. IR (octane)
Resu lts a n d Discu ssion
Ligan d Syn th esis. Sodium cyclopentadienide (NaCp)
reacts with a large excess of hexafluorobenzene (C6F6)
and excess sodium hydride (NaH) under forcing condi-
tions (Scheme 1) to afford, after aqueous workup, a 57%
yield of 1,2,3,4-tetrakis(pentafluorophenyl)cyclopenta-
diene (1). Initially, we had failed to detect 1 as a minor
impurity in the synthesis of the triarylated cyclopen-
tadienes (A and B),10b simply because 1 does not elute
from silica gel with hexanes, a procedure used in the
purification of A and B. Subsequent adjustment of the
reaction conditions and isolation procedures enabled us
to obtain 1 directly, with A and B as minor impurities.
We have attempted unsuccessfully to prepare the
corresponding pentaarylated cyclopentadiene (C) by
using longer reaction times, by using solvents with
higher boiling points, and by carrying out the reactions
under pressure in a stirred autoclave. We have found
that C6F5-substituted cyclopentadienes exclusively adopt
regiochemical arrangments in which all of the C6F5
groups are conjugated with the diene moiety (e.g., A and
B). Conjugation of a fifth C6F5 group is not possible in
the neutral cyclopentadiene. Steric effects12 may also
impede the formation of C. Finally, each added C6F5
group renders the cyclopentadienyl anion less nucleo-
philic in the subsequent arylation.
1
νCO ) 2044, 1980, 1970 cm-1. H NMR (THF-d8): δ 6.29 (s, 1
3
H). 19F NMR (THF-d8): δ -131.53 (m, 2 F), -135.82 (d, J )
3
3
21 Hz, 4 F), -140.30 (d, J ) 21 Hz, 2 F), -151.57 (t, J ) 24
Hz, 2 F), -153.27 (t, 3J ) 22 Hz, 2 F), -161.51 (m, 2 F),
-162.04 (m, 2 F), -162.47 (m, 4 F). Anal. Calcd for C32HF20
MnO3: C, 44.27; H, 0.12. Found: C, 44.09; H, 0.05.
-
Tr ica r bon yl[η5-1,2,3,4-tetr a k is(p en ta flu or op h en yl)cy-
clop en ta d ien yl]r h en iu m (I) (4). A mixture of Re(CO)5Br
(0.325 g, 0.800 mmol), sodium 1,2,3,4-tetrakis(pentafluorophe-
nyl)cyclopentadienide (2, 0.603 g, 0.802 mmol), NaH (20 mg),
and toluene (50 mL) was refluxed for 1 day and then filtered
while still warm. The filtrate was evaporated, and the result-
ing residue was triturated with hexane, collected on a filter,
and dried under vacuum to afford 0.196 g (0.220 mmol, 28%)
of an off-white solid. An analytically pure sample was obtained
by recrystallization from toluene. Mp (sealed, nitrogen-filled
capillary): 205-207 °C. IR (hexane) νCO ) 2047, 1970, 1959
1
cm-1. H NMR (THF-d8): δ 6.95 (s, 1 H). 19F NMR (THF-d8):
3
δ -131.89 (d, J ) 24 Hz, 2 F), -135.88 (m, 4 F), -140.94 (d,
3
3
3J ) 22 Hz, 2 F), -151.30 (t, J ) 21 Hz, 2 F), -153.23 (t, J
) 22 Hz, 2 F), -161.21 (m, 2 F), -161.93 (m, 2 F), -162.34
(m, 4 F). Anal. Calcd for C32HF20O3Re: C, 38.45; H, 0.10.
Found: C, 38.60; H, 0.05.
Rea ction s of Ir on Sa lts a n d CoBr 2 w ith 2. Several
reactions were attempted in order to prepare metallocenes
using 2 equiv of 2 and either (a) 1 equiv of FeBr2 in THF at 25
°C, (b) 1 equiv of FeBr2 in THF at 65 °C, (c) 1 equiv of FeBr2
in DME at 85 °C, (d) 1 equiv of Fe(acac)2 in toluene at 110 °C
with catalytic 18-crown-6 (the potassium congener of 2 was
used), or (e) 1 equiv of CoBr2 in THF at 65 °C. Crude product
mixtures, obtained after cooling the reactions to 25 °C and
removing the solvents under reduced pressure, were analyzed
Treatment of the diene (1) with either NaH or KH in
THF (Scheme 1) affords high yields of the corresponding
1
by H and 19F NMR spectroscopy. These spectra showed only
(12) Burkey, D. J .; Alexander, E. K.; Hanusa, T. P. Organometallics
1994, 13, 2773.
unreacted ligand.

Tetrakis(pentafluorophenyl)cyclopentadienyl
Organometallics, Vol. 20, No. 5, 2001 923
Ta ble 2. Ca r bon yl Str etch in g Wa ven u m ber s of
P ia n o Stool Com p lexes
a
wavenumbers (cm-1
)
entry
complex
vCO (A)
vCO (E)
1944
1954
1966, 1960
1973, 1965
1975, 1963
1980, 1970
1939
1947
1953
1963, 1957
1965, 1954
1970, 1959
b
1
2
3
4
5
6
7
8
9
CpMn(CO)3
2028
2032
2035
2040
2041
2044
2031
2034
2038
2042
2043
2047
c
(C6F5C5H4)Mn(CO)3
[(1,3-C6F5)2C5H3]Mn(CO)3
c
c
c
[(1,2,4-C6F5)3C5H2]Mn(CO)3
[(1,2,3-C6F5)3C5H2]Mn(CO)3
[(C6F5)4C5H]Mn(CO)3 (3)
b
CpRe(CO)3
c
(C6F5C5H4)Re(CO)3
[(1,3-C6F5)2C5H3]Re(CO)3
[(1,2,4-C6F5)3C5H2]Re(CO)3
[(1,2,3-C6F5)3C5H2]Re(CO)3
c
c
10
11
12
c
[(C6F5)4C5H]Re(CO)3 (4)
a
Recorded in octane or hexane solution. Reproducibility is
F igu r e 1. Thermal ellipsoid plot of 1 shown at 50%
probability. One of two nearly identical independent mol-
ecules is shown. Fluorine atoms are numbered the same
as the carbon atoms to which they are attached.
within 1 cm-1
.
Values of 2030 and 1946 cm-1 for CpMn(CO)3 and
b
2032 and 1940 for CpRe(CO)3 were reported elsewhere.23 We re-
prepared these complexes for direct comparisons with our com-
pounds. c Prior results from our laboratories.6,10
pentadiene13 and 1,2,3,4-tetra(isopropyl)cyclopentadi-
ene12 reveals only one significant feature, an elongation
of the C2-C3 bond in the tetra(isopropyl)cyclopentadi-
ene, which we ascribe to steric congestion.
sodium or potassium tetrakis(pentafluorophenyl)cy-
clopentadienide (2). Both the diene (1) and the anion
(2) are characterized by a single 1H NMR resonance and
six signals in the 19F NMR assigned to the ortho, meta,
and para fluorine atoms of the “inner” and “outer” C6F5
groups, clear indicators of time-averaged C2v symmetry
in solution.
The C6F5 groups of 1 are splayed in a propeller-like
array relative to the C5 ring. The “outer” C6F5 groups
(C11-C16 and C41-C46) tend to show greater copla-
narity with the C5 ring than the “inner” groups (C21-
C26 and C31-C36), reflecting the greater congestion of
the latter. The value of 64° for â1 in 1‚1/2C6D6 (Table 3)
was therefore surprising. Our efforts to rationalize this
angle by examining the packing diagrams for specific
intermolecular interactions were inconclusive. Although
the unfluorinated counterpart (1,2,3,4-tetraphenylcy-
clopentadiene) does not show a propeller-like struc-
ture,14 that feature is found in both tetraphenylcyclo-
pentadienone15 and tetraphenylcyclopentadienyl anion.16
The benzene solvate in 1‚1/2C6D6 is incorporated in a
C6F5-C6D6-C6F5 “stacking” motif (Figure 2). The stack-
ing is defined by a C6F5-centroid to C6D6-centroid
distance of 3.558(4) Å, a C6F5-centroid to C6D6-plane
distance of 3.456(4) Å, a C6D6-centroid to C6F5-plane
distance of 3.360(4) Å, and an interplanar angle of 5.2°.
The stacking motif involves the C41-C46 C6F5 group.
The relative orientations of the two six-membered rings
are nearly eclipsed. These parameters are nearly identi-
cal to the observations we reported earlier for [1,2,4-
(C6F5)3C5H2]Mn(CO)3‚1/2C6D6.6
Syn th esis of P ia n o Stool Com p lexes. The tet-
raarylated ligand (2) reacts with either Mn(CO)5Br or
Re(CO)5Br (Scheme 1) to afford moderate yields of the
corresponding [(C6F5)4C5H]M(CO)3 complexes (3, M )
Mn, 33%; and 4, M ) Re, 28%). Both complexes are
relatively thermally stable, crystalline solids. The major
difficulty in the synthesis of these complexes is that in
small-scale experiments moisture must be rigorously
excluded, otherwise 2 is converted to 1, which is the
most significant side-product observed. Unlike previous
syntheses of related compounds, we find that the use
of THF as a reaction solvent affords 3 and 4 in low
yields. Using toluene as the reaction solvent and a small
amount of added NaH to scavenge adventitious moisture
affords the reported yields, which we consider optimized.
In fr a r ed Sp ectr oscop ic An a lysis. The trend that
we have established (Table 2),10 whereby the symmetric
(A) stretching mode increases in frequency by 4 cm-1
per C6F5 group, continues with complexes 3 and 4. We
have long been curious about the possibility of reaching
a substituent effect “limit” in which so many electron-
withdrawing groups are attached to a Cp ligand that
the M(CO)3 moiety can no longer “adjust” to their
combined effects. The nearly linear trends implied by
the data in Table 2 suggest that we are not approaching
such a “limit” in the CpM(CO)3 system. The principle
of “additivity” therefore is reliable even when the
complexes are as electronically “stressed” as 3 and 4.
Cr ysta l Str u ctu r es of P ia n o Stool Com p lexes 3
a n d 4. Figures 3 and 4 present the molecular structures
of 3 and 4. Metric data are presented in Table 5. Both
complexes adopt similar M(CO)3 conformations (R val-
ues in Table 5) despite having crystallized in qualita-
tively different unit cells and in different packing
arrangements (see below). Neither complex exhibits a
significantly “slipped” Cp ligand,17 and the carbonyl
ligands are substantially linear, with relatively uniform
Cr ysta l Str u ctu r es of 1. Figure 1 shows a diagram
of the molecular structure of 1. The compound crystal-
lizes with two independent but substantially isostruc-
tural molecules in the asymmetric unit. We also ob-
tained a crystal structure of 1 in which a molecule of
benzene is included in the lattice. Metric data for these
three molecular structures are provided in Table 3. A
comparison (Table 4) of the bond lengths in the cyclo-
pentadiene “core” with corresponding data from cyclo-
(13) Haumann, T.; Benet-Buchholz, J .; Boese, R. J . Mol. Struct.
1996, 299, 374.
(14) Evrard, G.; Piret, P.; Germain, G.; Van Meerssche, M. Acta
Crystallogr. 1971, B27, 661.
(15) (a) Alvarez-Toledano, C.; Baldovino, O.; Espinoza, G.; Toscano,
R. A.; Gutierrez-Perez, R.; Garcia-Mellado, O. J . Organomet. Chem.
1997, 41, 540. (b) Barnes, J . C.; Horspool, W. M.; Mackie, F. I. Acta
Crystallogr. 1991, C47, 164.
(16) Bock, H.; Hauck, T.; Nather, C.; Haulas, Z. Z. Naturforsch.
1997, B52, 524.

924 Organometallics, Vol. 20, No. 5, 2001
Ta ble 3. Selected Metr ic Da ta for 1 a n d 1‚1/2C6D6
Thornberry et al.
distance (Å)
1a
1‚1/2C6D6
angle (deg)b
1a
1‚1/2C6D6
C1-C2
C2-C3
C3-C4
C4-C5
C5-C1
C1-C11
C2-C21
C3-C31
C4-C41
1.355(4)
1.481(5)
1.358(5)
1.499(4)
1.495(5)
1.479(4)
1.475(5)
1.487(4)
1.464(5)
1.349(4)
1.472(4)
1.359(4)
1.498(4)
1.505(4)
1.505(4)
1.485(4)
1.483(5)
1.470(4)
1.349(3)
1.476(3)
1.354(3)
1.506(3)
1.502(3)
1.502(3)
1.472(3)
1.478(3)
1.475(3)
C1-C2-C3
C2-C3-C4
C3-C4-C5
C4-C5-C1
C5-C1-C2
â1
108.6(3)
109.8(3)
107.8(3)
104.9(3)
108.8(3)
39.7(5)
53.7(5)
53.3(5)
41.2(5)
109.3(3)
109.3(3)
108.6(3)
104.0(3)
108.8(3)
40.0(5)
58.5(5)
55.7(5)
45.9(5)
109.2(2)
109.0(2)
109.0(2)
103.5(2)
109.3(2)
64.0(3)
57.5(3)
58.8(3)
47.4(3)
â2
â3
â4
a
b
Two independent molecules in the unit cell. â angles are interplanar torsion angles (0-90°) between the (C1-C5) least-squares
planes and the least-squares planes of C11-C16 (â1), C21-C26 (â2), C31-C36 (â3), and C41-C46 (â4).
Ta ble 4. Com p a r ison of Metr ic Da ta for
1,2,3,4-Tetr a su bstitu ted Cyclop en ta d ien es
average for
average for
C5H6
average for
C5H2(iPr)4
b
c
1a
C1-C2, C3-C4
C2-C3
C4-C5, C5-C1
1.354
1.476
1.501
1.344
1.460
1.498
1.351
1.502
1.489
a
Both independent molecules of crystalline
1
as well as
1‚1/2C6D6 were included in the average. Ref 13. c Ref 12.
b
F igu r e 4. Thermal ellipsoid plot of 4 shown at 50%
probability. Hydrogen, fluorine, and oxygen atoms are
numbered the same as the carbon atoms to which they are
attached.
Ta ble 5. Selected Metr ic Da ta for P ia n o Stool
Com p lexes (3 a n d 4)
distance
(Å)
bond anglea
(deg)
F igu r e 2. Stacking of benzene solvate in 1‚1/2C6D6.
3
4
3
4
M-C1
M-C2
M-C3
M-C4
M-C5
2.193(3) 2.343(2) M-C6-O6 176.8(3) 178.0(3)
2.196(3) 2.345(2) M-C7-O7 175.9(3) 175.8(3)
2.191(3) 2.332(3) M-C8-O8 176.9(3) 178.8(3)
2.159(3) 2.309(3)
R
34.0(3)
50.0(3)
56.9(3)
46.9(3)
47.8(3)
9.7(3)
36.1(3)
61.0(3)
56.8(3)
49.3(3)
45.8(3)
11.6(3)
7.7(3)
2.158(3) 2.317(3) â1
M-Cpb 1.812(3) 1.983(3) â2
M-C6
M-C7
M-C8
1.770(3) 1.893(3) â3
1.787(3) 1.919(3) â4
1.797(3) 1.921(3) γ1
C6-O6 1.158(4) 1.151(3) γ2
C7-O7 1.150(4) 1.147(4) γ3
C8-O8 1.150(4) 1.148(5) γ4
7.0(3)
7.6(3)
7.6(3)
5.2(3)
5.4(3)
R is the smallest CCO-M-Cpb-C5 torsion angle, defining the
disposition of the M(CO)3 group relative to the Ar4C5H ligand. â
angles are interplanar torsion angles (0-90°) between the (C1-
C5) least-squares planes and the least-squares planes of C11-
C16 (â1), C21-C26 (â2), C31-C36 (â3), and C41-C46 (â4). γ
angles are the angle formed between the C1-C5 least-squares
plane and the Cp-C6F5 bonds: C1-C11 (γ1), C2-C21 (γ2), C3-
a
F igu r e 3. Thermal ellipsoid plot of 3 shown at 50%
probability. Hydrogen, fluorine, and oxygen atoms are
numbered the same as the carbon atoms to which they are
attached.
b
C31 (γ3), and C4-C41 (γ4). Cp is the C1-C5 centroid.
1.780(4) Å observed in [1,2,4-(C6F5)3C5H2]Mn(CO)3.6 The
Cp-Re distance of 1.983(3) Å in 4 is long compared to
the values of 1.955(8) Å observed in [1,3-(C6F5)2C5H3]-
Re(CO)3 and of 1.968(6) Å observed in [1,2,4-(C6F5)3C5H2]-
Re(CO)3.6 Ordinarily, electron-deficient carbocyclic ligands
are closer to the metal than their electron-rich coun-
terparts.19 However, no clear substituent effects were
M-C and C-O distances in both M(CO)3 tripods. The
Cp-Mn distance of 1.812(3) Å in 3 is relatively long
compared to the values of 1.762 and 1.766 Å obtained
18
for CpMn(CO)3 as well as the Cp-Mn distance of
(17) (a) Marder, T. B.; Calabrese, J . C.; Roe, C. D.; Tulip, T. H.
Organometallics 1987, 6, 2012. (b) Wescott, S. A.; Kakkar, A. K.;
Stringer, G.; Taylor, N. J .; Marder, T. B. J . Organomet. Chem. 1990,
394, 777. (c) Faller, J . W.; Crabtree, R. H.; Habib, A. Organometallics
1985, 4, 929. (d) Carl, R. T.; Hughes, R. P.; Rheingold, A. L.; Marder,
T. B.; Taylor, N. J . Organometallics 1988, 7, 1613. (e) Baker, R. T.;
Tulip, T. H. Organometallics 1986, 5, 839.
(18) (a) Fitzpatrick, P. J .; LePage, Y.; Sedman, J .; Butler, I. S. Inorg.
Chem. 1981, 20, 2852. (b) Cowie, J .; Hamilton, E. J . M.; Laurie, J . C.
V.; Welch, A. J . J . Organomet. Chem. 1990, 394, 1. (c) A value of 1.794
was found earlier: Berndt, A. F.; Marsh, R. E. Acta Crystallogr. 1963,
16, 118.

Tetrakis(pentafluorophenyl)cyclopentadienyl
Organometallics, Vol. 20, No. 5, 2001 925
Ch a r t 1
F igu r e 5. Correlation of â and γ for C6F5-substituted
CpM(CO)3 complexes (M ) Mn, Re). Parameters are
defined in Table 5. Additional data are taken from ref 6.
evident from an examination of the 120 substituted
CpMn(CO)3 compounds (Cp-Mn distances ranging from
1.749-1.795 Å) or the 12 substituted CpRe(CO)3 com-
pounds (Cp-Re distance ranging from 1.944-1.982 Å)
retrieved from the Cambridge Structural Database.20
The trends observed here may be due simply to weak
steric interactions of the C6F5 groups with the M(CO)3
moieties.
As in the diene 1, both piano stool complexes 3 and 4
hold the C6F5 groups in propeller-like arrays relative
to their respective Cp rings; however, all the torsion
angles (â1-â4) fall into the range 45-61°, with no
pronounced tendency for the “inner” C6F5 groups to
adopt more perpendicular conformations. A search of
the Cambridge Structural Database showed that all of
the crystallographically characterized transition metal
complexes of the η5-tetraphenylcyclopentadienyl ligand
adopt propeller-like conformations also.
The C6F5 ipso carbon lies slightly out of the C5 least-
squares plane of the cyclopentadienyl ligand and is
directed away from the M(CO)3 fragment (exo). The
angle between the C-C6F5 bond and the C5 least-
squares plane is reported as the angle γ in Table 5. We
noticed that γ appears to correlate with the Cp-C6F5
torsion angle (â). This prompted us to reexamine the
crystal structures of [1,3-(C6F5)2C5H3]Re(CO)3, [1,2,4-
(C6F5)3C5H2]Mn(CO)3‚1/2C6D6, and [1,2,4-(C6F5)3C5H2]-
Re(CO)36 in order to double the number of points in our
correlation. The result of this analysis is presented in
Figure 5. The â-γ plot shows a correlation coefficient
of 0.8, which is surprisingly high considering the soft-
ness of the Cp-C6F5 conformational potentials and the
likely susceptibility of â to deformation by weak inter-
molecular (packing) interactions. The positive â-γ
correlation could arise from the same steric interactions
proposed to account for the elongated Cp-M bonds in
3 and 4. As â increases, interactions between the endo
ortho fluorine atoms and the M(CO)3 moiety push the
C6F5 groups in the exo direction.
bond length and Mn-CtO angles, however, are identi-
cal to those of the other carbonyl ligands, suggesting
that the donor-acceptor interaction is just a weak
packing interaction.
Dyn a m ic NMR Stu d ies. Figure 6 shows several 19
F
NMR spectra of 4 obtained at temperatures ranging
from -100 to +25 °C. In the room-temperature (top)
spectrum, the two signals at -132 and -141 ppm are
assigned to the ortho fluorines of the “inner” C6F5
groups, for which the exo and endo positions (Cp-C6F5)
are in slow exchange at all temperatures. In contrast,
the signal at -135 ppm, which we assign to the ortho
fluorines of the “outer” C6F5 groups, is in fast exchange
at 25 °C but decoalesces at -75 °C. Application of eqs
1-3 enables the measurement of first-order exo-endo
exchange rate constants across a wide temperature
range.21 These rates lead to the construction of an
Eyring plot (Figure 7), from which activation param-
eters are determined to be ∆Hq ) 7(1) kcal mol-1 and
∆Sq ) -5(5) cal mol-1 K-1. A similar analysis of 3
generates exactly the same activation parameters.
These values are consistent with activation parameters
for Cp-C6F5 rotation of the vicinal pair of C6F5 groups
in [1,2,4-(C6F5)3C5H2]Re(CO)3 that we obtained earlier.6
Details of the Eyring analyses are deposited in the
Supporting Information. In neither 3 nor 4 did we find
evidence for “restricted” rotation of the M(CO)3 groups,22
which could result in loss of time-averaged Cs symmtery
of the complexes.
kcoal ) (π/x2)∆v ) 2.22∆v
(1)
(2)
The packing diagram of the manganese complex 3
(but not of 4) reveals that the oxygen atom of one of the
CO ligands (a Lewis-basic “donor”) interacts with a C6F5
“acceptor” in a pairwise fashion (Chart 1). The CtO
k(T) ) π[fwhm(T) - fwhm(natural)]
k(T) ) π(∆v)2/[fwhm(T) - fwhm(natural)] (3)
Con clu sion s. Tetrakis(pentafluorophenyl)cyclopen-
(19) (a) Gassman, P. G.; Winter, C. H. J . Am. Chem. Soc. 1988, 110,
6130. (b) Gassman, P. G.; Deck, P. A. Organometallics 1994, 13, 1934.
(c) Gassman, P. G.; Winter, C. H. Organometallics 1991, 10, 1592.
(20) Compounds having additional rings fused to the Cp ligand (such
as indenyl complexes) were excluded from the CSD search.
(21) Hore, P. J . Nuclear Magnetic Resonance; New York: Oxford,
1995; pp 44-47.

926 Organometallics, Vol. 20, No. 5, 2001
Thornberry et al.
F igu r e 6. 19F NMR spectra of 4 at several temperatures (°C).
corresponding ferrocene by standard methods failed.
The effect of four C6F5 groups on the carbonyl stretching
wavenumbers is linearly additive. Compounds 1, 3, and
4 adopt propeller-like conformations in the solid state.
A correlation between Cp-C6F5 torsion angle and the
angular displacement of the C6F5 group from the C5
least-squares plane of the CpM(CO)3 core in C6F5-
substituted CpM(CO)3 complexes (M ) Mn, Re) is
ascribed to steric interaction between the endo ortho
fluorine atoms and the M(CO)3 tripod. Cp-C6F5 rotation
barriers are identical to those observed in homologous
C6F5-substituted CpM(CO)3 complexes.
Ack n ow led gm en t. This project was supported by
the Petroleum Research Fund (30738-G).
F igu r e 7. Eyring plot of Cp-C6F5 rotation rates in 4.
tadiene (1) may be prepared in one pot from sodium
cyclopentadienide, excess hexafluorobenzene, and excess
NaH in diglyme. The corresponding sodium salt 2 is a
useful ligand for the formation of Mn(CO)3 and Re(CO)3
complexes 3 and 4, although attempts to form the
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for 1 (Tables S1-S8), 1‚1/2C6D6 (Tables S9-S16), 3
1
(Tables S17-S24), and 4 (Tables S25-S32). H and 19F NMR
spectra of 2 (Figures S1 and S2) showing bulk purity of the
sample. Variable-temperature 19F NMR spectra of 3 (Figure
S3) and 4 (Figure S4). Eyring analysis of dynamic NMR data
for 3 (Chart S1) and 4 (Chart S2). This material is available
free of charge via the Internet at http://pubs.acs.org.
(22) (a) Hardcastle, K.; Siegel, J . S. J . Am. Chem. Soc. 1993, 115,
6138. (b) Kilway, K. V.; Siegel, J . S. Organometallics 1992, 11, 1426.
(23) (a) Benson, I. B.; Knox, S. A. R.; Stansfield, R. F. D.; Woodward,
P. J . Chem. Soc., Dalton Trans. 1981, 51. (b) Casey, C. P.; Rutter, E.
W. Inorg. Chem. 1990, 29, 2333.
OM000805F