Synthesis of pentafluorophenyl-substituted cyclopentadienes and their use as transition-metal ligands

Article abstract of DOI:10.1021/om9608216

The reaction of NaC₅H₅ (NaCp) and hexafluorobenzene (1:1 ratio) in THF at 25 °C for 15 h afforded, after hydrolysis, a mixture of regioisomeric (pentafluorophenyl)cyclopentadienes. This mixture was isolated as a monoisomeric dimer of 1-(pentafluorophenyl)cyclopentadiene. The structure of the dimer was determined crystallographically. Flash vacuum thermolytic cracking of the dimer at 200 °C regenerated (pentafluorophenyl)cyclopentadiene as a mixture of regioisomers. In contrast, the reaction of NaCp, NaH, and C₆F₆ (1:2:5 ratio) in THF at reflux for 3 d affords, after hydrolysis, 1,4-bis(pentafluorophenyl)cyclopentadiene, which does not dimerize. Either the mono- or the disubsubstituted diene reacts with NaH in THF to afford the corresponding stable substituted sodium cyclopentadienides in high yields. Sodium (pentafluorophenyl)cyclopentadienide, (C₆F₅)C₅H₄Na, reacted with FeBr₂, Re(CO)₅Br, and ZrCl₄(THF)₂, to afford the transition metal complexes (η⁵-C₅H₄C₆F₅) ₂Fe, (η⁵-C₅H₄C₆F ₅)Re(CO)₃, and (η⁵-C₅H₄C₆F₅) ₂ZrCl₂. Sodium 1,3-bis(pentafluorophenyl)cyclopentadienide reacted with FeBr₂ and Re(CO)₅Br to give the corresponding complexes [η⁵-1,3-C₅H₃(C₆F ₅)₂]₂Fe and [η⁵-1,3-C₅H₃(C₆F ₅)₂]Re(CO)3. Infrared spectroscopic analysis of the tricarbonylrhenium(I) complexes and cyclic voltammetric analysis of the substituted ferrocenes quantified the strong electron-withdrawing effects of the pentafluorophenyl substituents.

Full text of DOI:10.1021/om9608216

Organometallics 1996, 15, 5287-5291
5287
Articles
Syn th esis of P en ta flu or op h en yl-Su bstitu ted
Cyclop en ta d ien es a n d Th eir Use a s Tr a n sition -Meta l
Liga n d s
Paul A. Deck* and Woodward F. J ackson
Department of Chemistry, Virginia Polytechnic Institute and State University,
Blacksburg, Virginia 24061-0212
Frank R. Fronczek
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803-1804
Received September 25, 1996X
The reaction of NaC5H5 (NaCp) and hexafluorobenzene (1:1 ratio) in THF at 25 °C for 15
h afforded, after hydrolysis, a mixture of regioisomeric (pentafluorophenyl)cyclopentadienes.
This mixture was isolated as a monoisomeric dimer of 1-(pentafluorophenyl)cyclopentadiene.
The structure of the dimer was determined crystallographically. Flash vacuum thermolytic
cracking of the dimer at 200 °C regenerated (pentafluorophenyl)cyclopentadiene as a mixture
of regioisomers. In contrast, the reaction of NaCp, NaH, and C6F6 (1:2:5 ratio) in THF at
reflux for 3 d affords, after hydrolysis, 1,4-bis(pentafluorophenyl)cyclopentadiene, which does
not dimerize. Either the mono- or the disubsubstituted diene reacts with NaH in THF to
afford the corresponding stable substituted sodium cyclopentadienides in high yields. Sodium
(pentafluorophenyl)cyclopentadienide, (C6F5)C5H4Na, reacted with FeBr2, Re(CO)5Br, and
ZrCl4(THF)2, to afford the transition metal complexes (η5-C5H4C6F5)2Fe, (η5-C5H4C6F5)Re-
(CO)3, and (η5-C5H4C6F5)2ZrCl2. Sodium 1,3-bis(pentafluorophenyl)cyclopentadienide reacted
with FeBr2 and Re(CO)5Br to give the corresponding complexes [η5-1,3-C5H3(C6F5)2]2Fe and
[η5-1,3-C5H3(C6F5)2]Re(CO)3. Infrared spectroscopic analysis of the tricarbonylrhenium(I)
complexes and cyclic voltammetric analysis of the substituted ferrocenes quantified the strong
electron-withdrawing effects of the pentafluorophenyl substituents.
In tr od u ction
stituent effects on the physical properties or chemical
reactivity of Cp complexes are relatively sparse.2 Chal-
lenges to the design of Cp ligands with electron-
withdrawing substituents include (1) the isolation of the
ligands as stable cyclopentadienyl anions and (2) the
stability of the Cp ring substituents toward electrophilic/
oxophilic transition metal fragments, including the
reactive intermediates of important catalytic processes.
Circumventing the synthetic challenges by attaching
substituents to Cp ligands after formation of the metal
complex is reliable for only a few highly stable late
transition metal species.3
The physical and chemical properties of η5-C5H5 (Cp)
metal complexes may be widely varied or finely tuned
by changing the Cp ring substituents.1 However,
published accounts of electron-withdrawing ring sub-
X Abstract published in Advance ACS Abstracts, November 1, 1996.
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479, 1. (b) Maitlis, P. M. Acc. Chem. Res. 1978, 11, 301. (c) King, R. B.
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M. Organometallics 1990, 9, 3908. (b) Lee, I.-M.; Gauthier, W. J .; Ball,
J . M.; Iyengar, B.; Collins, S. Organometallics 1992, 11, 2115. (c)
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metallics 1991, 10, 148. (d) Bernheim, M.; Boche, G. Angew. Chem.,
Int. Ed. Engl. 1980, 19, 1010. (e) Baschky, M. C.; Sowa, J . R., J r.;
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Am. Chem. Soc. 1989, 111, 8938. (g) Finch, W. C.; Anslyn, E. V.;
Grubbs, R. H. J . Am. Chem. Soc. 1988, 110, 2406. (h) Herberich, G.
E.; Fischer, A. Organometallics 1996, 15, 58. (i) Schut, D. M.; Weakley,
T. J . R.; Tyler, D. R. New J . Chem. 1996, 20, 113. (j) Hughes, R. P.;
Trujillo, H. A. Organometallics 1996, 15, 286. (k) Oberoff, M.; Duda,
J . K.; Mohr, R.; Erker, G.; Fro¨hlich, R.; Grehl, M. Organometallics
1996, 15, 4005. (l) Barthel-Rosa, L. P.; Catalano, V. J .; Maitra, K.;
Nelson, J . H. Organometallics 1996, 15, 3924. (m) Miguel-Garcia, J .
A.; Adams, H.; Bailey, N. A.; Maitlis, P. M. J . Chem. Soc., Dalton Trans.
1994, 116, 385. (n) Wei, C.; Aigbirhio, F.; Adams, H.; Bailey, N. A.;
Hempstead, P. D.; Maitlis, P. M. J . Chem. Soc., Chem. Commun. 1991,
883. (o) Hauptman, E.; Waymouth, R. M.; Ziller, J . W. J . Am. Chem.
Soc. 1995, 117, 11586.
We now report the straightforward synthesis of pen-
tafluorophenyl-substituted cyclopentadienes from rou-
tinely available, relatively inexpensive starting mate-
(3) (a) Hughes, R. P.; Zheng, X.; Ostrander, R. L.; Rheingold, A. L.
Organometallics 1994, 13, 1567. (b) Paprott, G.; Seppelt, K. J . Am.
Chem. Soc. 1984, 106, 4060. (b) Bretschneider-Hurley, A.; Winter, C.
H. J . Am. Chem. Soc. 1994, 116, 6468. (c) Han. Y.-H.; Heeg, M. J .;
Winter, C. H. Organometallics 1994, 13, 3009. (d) Gassman, P. G.;
Winter, C. H. J . Am. Chem. Soc. 1988, 110, 6130. (e) Boche, G.;
Bernheim, M. Angew. Chem., Int. Ed. Engl. 1980, 92, 1043. (f) Stahl,
K. P.; boche, G.; Massa, W. J . Organomet. Chem. 1984, 277, 113. (g)
Hart, W. P.; Macomber, D. W.; Rausch, M. D. J . Am. Chem. Soc. 1980,
102, 1196. (h) Appel, A.; J a¨kle, F.; Priermeier, T.; Schmid, R.; Wagner,
M. Organometallics 1996, 15, 1188.
(4) (a) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015. (b) Goll, J . G.; Moore, K. T.; Chosh, A.; Therien, M. J .
Am. Chem. Soc. 1996, 118, 8344.
S0276-7333(96)00821-7 CCC: $12.00 © 1996 American Chemical Society

5288 Organometallics, Vol. 15, No. 25, 1996
Deck et al.
Sch em e 1. Syn th esis of Sod iu m
(P en ta flu or op h en yl)cyclop en ta d ien id e
Sch em e 2. Syn th esis of Sod iu m
1,3-Bis(p en ta flu or op h en yl)cyclop en ta d ien id e
of the Diels-Alder dimer (2) is minimized if the workup
is carried out at 0 °C, and the diene mixture 1 may be
stored for 1-2 days at -20 °C. Recrystallization of the
crude mixture of dienes 1 from hot ethanol afforded the
monoisomeric dimer 2 in 60% yield. Flash vacuum
thermolysis of the dimer 2 regenerated the dienes 1,
which were treated immediately with NaH in THF to
afford sodium cyclopentadienide 3. Alternatively, the
anionic ligand 3 may be synthesized directly by carrying
out the reaction of NaCp and C6F6 in the presence of
NaH (1.1 equiv). This modification traps the dienes 1
by deprotonation in situ to afford 3 in one step, while
avoiding the formation of the byproduct, dicyclopenta-
diene. However, the crude product from the latter one-
pot procedure contains 5-10% of unreacted NaCp as
F igu r e 1. (a) Thermal ellipsoid plot of C22H10F10 (2). (b)
Thermal ellipsoid plot of the tricyclic core of C22H10F10 (2)
showing hydrogen atoms located and isotropically refined.
Only the ipso carbon atoms the C6F5 groups are shown at
C
11 and C17. Selected interatomic distances (Å): C(1)-C(2)
) 1.523(3), C(2)-C(3) ) 1.311(3), C(1)-C(11) ) 1.495(3),
C(1)-C(6) ) 1.599(3), C(6)-C(7) ) 1.498(3), C(6)-C(10) )
1.550(3), C(7)-C(8) ) 1.320(3), C(8)-C(9) ) 1.520(3), C(8)-
C(17) ) 1.478(3). Selected intramolecular conformational
angles (deg): C(5)-C(1)-C(11)-C(16) ) -14.8(3), C(7)-
C(8)-C(17)-C(22) ) -41.64.
1
determined by H NMR.
The structure proposed for the dimer 2 was verified
by single-crystal X-ray diffraction analysis. The thermal
ellipsoid plots shown in Figure 1 demonstrate the endo
stereochemistry of the tricyclic core and the regiochem-
istry of the double bonds, as well as the regiochemistry
and conformational disposition of the pentafluorophenyl
substituents on the tricyclo[5.2.1.02,6]deca-3,8-diene skel-
eton. These structural features were confirmed by
location and isotropic refinement of all the hydrogen
atoms in the molecule. The supporting information
contains complete crystal data and metric parameters
for 2.
As shown in Scheme 2, the reaction of NaCp with an
excess of C6F6 and 2 equiv of NaH in THF at reflux
afforded, after aqueous workup, the disubstituted diene
4 in 54% yield. The diene 4 reacted with sodium
hydride in THF to form sodium 1,3-bis(pentafluorophen-
yl)cyclopentadienide 5.
rials. We show that the C6F5-substituted cyclopenta-
dienes are readily converted into corresponding cyclo-
pentadienyl anions as thermally stable sodium salts in
high yield; in particular, fluoride elimination is not
observed. We then demonstrate the utility of the C6F5-
substituted cyclopentadienylsodium compounds as tran-
sition metal ligands by presenting the syntheses of four
late-transition-metal compounds and one early-transi-
tion-metal compound. Finally, we present spectroscopic
and electrochcmical data data unequivocally demon-
strating the additive electron-withdrawing influence of
the pentafluorophenyl substitutent(s).4
Resu lts a n d Discu ssion
As shown in Scheme 1, the reaction of NaCp with
C6F6 in THF at room temperature initially gave a
mixture of isomeric (pentafluorophenyl)cyclopentadienes
in 80% yield after hydrolysis (1).5 Immediate formation
As shown in Figure 2, common ligand-substitution
procedures6 for the syntheses of the corresponding
(5) (Pentafluorophenyl)cyclopentadiene was previously reported as
a product of the photolysis of Cp2Ti(C6F5)2. (a) Kligert, B.; Roloff, A.;
Urwyler, B.; Wirz, J . Helv. Chim. Acta 1988, 71, 1858. (b) Wahren,
R. J . Organometal. Chem. 1973, 57, 415. (c) Finter, J .; Riediker, M.;
Rohde, O.; Rotzinger, B. Makromol. Chem., Macromol. Symp. 1989,
24, 177.
(6) (a) Organomet. Synth. 1965, 1, 64-121. King, R. B., ed. New
York: Acadamic Press. (b) Fischer, E. O.; Fellmann, W. J . Organomet.
Chem. 1963, 1, 191. (c) Nesmeyanov, A. N. Dokl. Akad. Nauk SSSR
Ser. Khim. 1964, 154, 646. (d) Gubin, S. P. Dokl. Akad. Nauk SSSR
Ser. Khim. 1972, 205, 346.

Pentafluorophenyl-Substituted Cyclopentadienes
Organometallics, Vol. 15, No. 25, 1996 5289
mV positive of ferrocene,7 we learned that the C6F5
group exerts an electron-withdrawing influence about
half that of the CF3 group on ferrocene. Another
noteworthy aspect of both the infrared spectroscopic and
electrochemical data is that the effect of four C6F5
groups is exactly twice the effect of two C6F5 groups,
within experimental errors, relative to the unsubsti-
tuted parent complex.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out using standard nitrogen-atmosphere techniques. Hexaflu-
orobenzene was purchased from PCR (Gainesville, FL). NaCp
was made by the reaction of freshly distilled cyclopentadiene
and NaH in THF or purchased from Aldrich as a 2.0 M solution
in THF. NMR spectra were recorded on a Varian Unity 400
MHz instrument. Melting points were obtained in open
capillaries and are uncorrected. Elemental analyses were
performed by Oneida Research Services (Whitesboro, NY). For
infrared spectroscopic measurements, a MIDAC M-Series FT-
IR operating at 0.5-cm-1 resolution was used to examine
n-octane solutions of the tricarbonylrhenium(I) complexes 7
and 8 in a NaCl-windowed cell.
Electr och em ica l Mea su r em en ts. Single-sweep cyclic
voltammetric data were obtained for substituted ferrocenes 6
and 7 at nominal concentrations of 5 µM in CH2Cl2 using 0.10
M [n-Bu4N][PF6] as the electrolyte and activated alumina as
an internal desiccant. The apparatus was a BAS 100B
potentiostat with a glassy Pt working electrode, a Pt wire
auxiliary electrode, and a Ag/AgCl reference electrode. The
sweep was initialized at 0 V, scanned to +2.0 V, reversed to
F igu r e 2. Synthesis of C6F5-substituted cyclopentadienyl-
metal complexes. Reagents and conditions: (a) 0.5 FeBr2,
THF, reflux, 6 h. (b) Re(CO)5Br, THF, reflux, 15 h. (c) 0.5
ZrCl4(THF)2, toluene, 100 °C, 1 h.
-1.8 V, and returned to 0 V, at a scan rate of 100 mV s-1
.
Reported E1/2 values represent the average of three experi-
ments. |Eox - Ered| ranged from 58 to 72 mV, and Ic/Ia was
within 7% of unity, both indicators of substantially reversible
oxidation. Increases in scan rate did not improve reversibility.
Cr ysta llogr a p h ic Stu d ies. Colorless prisms of diene
dimer (2) were grown by cooling a concentrated hexanes
solution to -20 °C. Relevant crystal data are summarized in
Table 1. Hydrogen atoms were located and isotropically
refined. Data were collected in a P21/a setting. Superlattice
reflections (with doubled a) exist, but refinement with Z ) 8,
A ) 30.1192 Å, was unsucessful. Complete details of the
crystallographic experiment, structure solution and refine-
ment, and metric and thermal parameters are provided in the
supporting information.
unsubstituted Cp complexes were readily adapted to the
new pentafluorophenyl-substituted ligands. The disub-
stituted ferrocene 6 forms hydrocarbon-soluble red-
orange flake crystals, while the tetrasubstituted fer-
rocene 7 is a sparingly soluble red-orange microcrystalline
solid. The mono- and disubstituted tricarbonylrhenium-
(I) complexes 8 and 9 form colorless, air-stable, hydro-
carbon-soluble crystalline solids. The disubstituted
zirconocene dichloride 10 forms very fine pale yellow
needles and is sparingly soluble in common solvents.
Infrared (IR) spectroscopic analysis of the mono- and
disubstituted tricarbonylrhenium(I) complexes 8 and 9,
respectively, and cyclic voltammetric analysis of the
substituted ferrocenes 6 and 7, respectively, were car-
ried out in order to quantify the electronic effects of the
pentafluorophenyl substituents in a manner that could
be compared to published data obtained with other
substituents. The IR analysis of 8 and 9 showed a
stepwise increase in the wavenumber of symmetric CO
stretch of 4 cm-1 for each C6F5 group relative to the
parent complex, (η5-C5H5)Re(CO)3. These data show
that the pentafluorophenyl substitutent has a strong
electron-withdrawing effect on the electronic properties
of the complexed Re(CO)3 fragment. The effect of the
C6F5 group is therefore comparable to that of an acetyl
substituent, which increases νCO by 3 cm-1 relative to
(η5-C5H5)Re(CO)3.6b,c
1,4-Bis(p en ta flu or op h en yl)tr icyclo[5.2.1.02,6]d eca -3,8-
d ien e (2). Under nitrogen, 3.7 g (0.020 mol) of C6F6 was
slowly added to a solution of NaCp (3.5 g, 0.040 mmol) in 20
mL of THF. The mixture was stirred at 25 °C for 15 h. The
solvent was removed under reduced pressure, and the residue
was washed with pentane (3 × 10 mL) to remove the dicyclo-
pentadiene byproduct. 1H NMR (THF-d8) analysis of the
residue found mainly Na(C6F5Cp) containing about 10% of
NaCp and a variable amount of THF. The residue was then
taken up in 20 mL of pentane, and the slurry was hydrolyzed
with 10 mL of ice-water. The layers were separated, and the
organic layer was dried over MgSO4 at 0 °C, filtered through
neutral alumina, and evaporated at 0 °C to afford 3.65 g (0.016
mol, 80%) of the complex diene mixture 1 as a sweet-smelling
white solid. Recrystallization twice from hot ethanol or
hexanes afforded an analytical sample of the dimer, C22H10F10
(2): 1H NMR (400 MHz, CDCl3) δ 6.31 (d, J ) 5.8 Hz, 1H),
6.20 (m, 1 H), 6.05 (m, 1 H), 3.64 (m, 1H), 3.12 (m, 2 H), 2.69
(m, 1 H), 2.11 (m, 3 H). {1H}13C NMR (CDCl3) δ 146.8 (d),
143.5 (d), 140.5 (d), 138.4 (d), 137.3, 137.2 (d), 135.8, 132.6,
131.3, 116.1 (t), 112.2 (t), 62.0, 56.4, 55.1, 45.8, 43.0, 37.7. Anal.
Calcd for C22H10F10 C, 56.91; H, 2.17. Found: C, 56.81; H,
1.93.
E1/2 of oxidation values of 345(5) mV and 678(5) mV
(relative to Cp2Fe+/Cp2Fe) for the disubstituted and
tetrasubstituted ferrocenes 6 and 7, respectively, were
obtained by cyclic voltammetry. As (η5-C5H4CF3)2Fe
was previously shown to have an E° of oxidation 640
(7) Gassman, P. G.; Winter, C. H. J . Am. Chem. Soc. 1986, 108, 4228.

5290 Organometallics, Vol. 15, No. 25, 1996
Deck et al.
3
19F NMR (CDCl3) δ -140.99 (d, J FF ) 22 Hz, 4 F), -157.44
Ta ble 1. Cr ysta l Da ta for C22H10F 10 (2)
3
(t, J FF ) 21 Hz, 2 F), -163.66 (m, 4 F). Anal. Calcd for
17H4F10: C, 51.28; H, 1.01. Found: C, 51.30; H, 0.93.
Sod iu m 1,3-Bis(p en ta flu or op h en yl)cyclop en ta d ien id e
formula
C22H10F10
C
formula weight
crystal system
space group
a, Å
464.3
monoclinic
P21/c
15.0596(10)
(5). A mixture of the 1,4-bis(pentafluorophenyl)cyclopen-
tadiene (4) and a 10% molar excess of NaH in THF was stirred
at room temperature for 3 h. Filtration to remove unreacted
sodium hydride and evaporation of the filtrate afforded the
crude product as a (THF)x solvate in yields exceeding 90%.
Heating the product at 80 °C under high vacuum (10-5 torr)
for several hours affords a THF-free sample: 1H NMR (THF-
d8) δ 6.99 (m, 1 H), 6.44 (m, 2 H). {1H}13C NMR (THF-d8) δ
144.0 (d, 1J CF ) 241 Hz, CF), 138.9 (d, 1J CF )245 Hz, CF), 135.0
b, Å
c, Å
11.0688(13)
10.9452(7)
93.112(5)
1821.8(10)
â, deg
V, Å3
Z
4
cryst dimens, mm
cryst color, habit
0.28 × 0.18 × 0.15
colorless rectangular prism
D
calc, g cm-3
1.693
15.1
295
1
2
µ(Cu KR), cm-1
temp, K
(d, J CF ) 241 Hz, CF), 118.5 (t, J CF ) 16 Hz, C6F5 ipso C),
113.2 (m, CC6F5), 111.6 (CH), 106.9 (CH). 19F NMR (THF-d8)
δ -143.9 (d, 3J FF ) 20 Hz, 4 F), -166.03 (m, 4 F), -170.86 (tt,
diffractometer
monochromator
radiation
2θ scan range, deg
index ranges
no. of collcd rflns
no. of ind rflns
no. of ind obsd rflns
solution
Enraf-Nonius CAD-4
graphite
3J FF ) 21 Hz, J FF ) 5 Hz, 2 F). Anal. Calcd for C17H3F10Na
4
Cu KR (λ ) 1.54184 Å)
C, 48.59; H, 0.72. Found: C, 48.12; H, 0.65.
2-75
Bis[η5-(p en t a flu or op h en yl)cyclop en t a d ien yl]ir on (II)
(6). A mixture of FeBr2 (216 mg, 1.00 mmol), sodium (pen-
tafluorophenyl)cyclopentadienide (3, 533 mg, 2.10 mmol), and
THF (25 mL) was stirred under reflux for 6 h. The solvent
was then removed under reduced pressure, water (50 mL) was
added, and the crude product was extracted with benzene (50
mL). Evaporation of the organic layer gave an orange residue,
from which the analytically pure product (6, 445 mg 0.86
mmol, 86%) was obtained as three crops of red-orange flakes
by crystallization from hexanes: mp 183-185 °C. 1H NMR
-13 e h e 0, -13 e k e 0, -37 e l e 37
8324
3747
2747
direct methods (MULTAN)7
refinement software
R(F)
MolEN
0.043
0.047
2.092
R(wF)
GOF
a
Scattering factors and anomalous dispersion (∆f′, ∆f′′) data
were from (a) International Tables for X-ray Crystallography;
Lonsdale, K., Ed.; Reidel: Boston, 1985. For a discussion of
anomalous dispersion effects, see: (b) Ibers, J . A.; Hamilton, W.
C. Acta Crystallogr. 1964, 17, 781.
3
5
(CDCl3) δ 4.78 (tt, J HH ) 2.0 Hz, J FF ) 2.0 Hz, 4 H), 4.42 (t,
3J HH ) 2.0 Hz, 4 H). {1H}13C NMR (CDCl3) δ 144.2 (d, J CF
)
1
1
1
251 Hz), 138.9 (d, J CF ) 252 Hz), 137.8 (d, J CF ) 252 Hz),
2
3
112.53 (t, J CF ) 15 Hz), 72.7 (t, J CF ) 6 Hz), 71.1 (t, J CF ) 2
Hz), 70.8 (t, J CF ) 6.0 Hz). 19F NMR (CDCl3) δ -140.67 (d,
3J FF ) 22 Hz, 4 F), -159.17 (t, 3J FF ) 21 Hz, 2 F), -164.07 (m,
4 F). Anal. Calcd for C22H8F10Fe: C, 51.00; H, 1.56. Found:
C, 51.12; H, 1.60.
Sod iu m (P en ta flu or op h en yl)cyclop en ta d ien id e (3). A
solution of 1-(pentafluorophenyl)cyclopentadiene dimer (2, 2.5
g, 5.4 mmol) in pentane (10 mL) was subjected to flash vacuum
thermolysis in a 20-cm Pyrex tube at 200 °C to afford 2.1 g
(9.1 mmol, 84%) of an approximately 1:1 mixture of 1- and
2-(pentafluorophenyl)cyclopentadienes, as determined by 1H
NMR. This colorless oil was dissolved in THF (10 mL) and
added to a stirred suspension of NaH (500 mg, 0.021 mol) in
THF (20 mL) maintained at 0 °C. After stirring for 2 h, during
which the mixture warmed to 25 °C, the solvent was evapo-
rated, and the residue was triturated with several 10-mL
portions of pentane to obtain 2.2 g (8.7 mmol, 96%) of
Na(C6F5C5H5) (3) as a violet solid: 1H NMR (THF-d8) δ 6.45
(m, 2 H), 5.93 (m, 2 H). {1H}13C NMR (THF-d8) δ 146.2 (d,
Bis[η5-1,3-b is(p en t a flu or op h en yl)cyclop en t a d ien yl]-
ir on (II) (7). A mixture of sodium 1,3-bis(pentafluorophenyl)-
cyclopentadienide (5, 105 mg, 0.25 mmol) and FeBr2 (27 mg,
0.12 mmol) in THF (20 mL) was stirred at reflux under
nitrogen for 12 h. Removal of the solvent under reduced
pressure, extraction of the residue with hot benzene, and
evaporation of the solvent afforded 90 mg (0.11 mmol, 88%) of
(7) as a red-orange solid. An analytical sample was obtained
by sublimation (80 °C, 0.050 torr): mp 237-241 °C. 1H NMR
(CDCl3) δ 5.41 (br s, 2 H), 5.04 (br s, 4 H). The compound
was not sufficiently soluble for 13C NMR analysis. 19F NMR
1
1J CF ) 240 Hz, CF), 141.4 (d, J CF ) 244 Hz, CF), 137.0 (d,
3
3
1J CF ) 228 Hz, CF), 121.7 (t, 2J CF ) 17 Hz, C6F5 ipso C), 111.3
(CDCl3) δ -139.96 (d, J FF ) 22 Hz, 8 F), -156.88 (t, J FF
21 Hz, 4 F), -162.98 (m, 8 F). Anal. Calcd for C34H6F20Fe:
C, 48.03; H, 0.71. Found: C, 48.36; H, 0.76.
)
4
5
(t, J CF ) 7 Hz, CH), 110.3 (t, J CF ) 2 Hz, CH), 105.8 (3J CF
)
3
3 Hz, CC6F5). 19F NMR (THF-d8) δ -144.51 (d, J FF ) 23 Hz,
2 F), -166.43 (t, 3J FF ) 24 Hz, 2 F), -172.51 (tt, 3J FF ) 21 Hz,
4J FF ) 5 Hz, 1 F). Variable small quantities of THF in the
product (as determined by 1H NMR) prevented us from
obtaining satisfactory elemental analysis. Heating the product
under vacuum to remove residual THF leads to slow decom-
position.
Tr ica r bon yl[η5-(pen ta flu or oph en yl)cyclop en ta d ien yl]-
r h en iu m (I) (8). A mixture of Re(CO)5Br (Aldrich, 203 mg,
0.500 mmol), sodium (pentafluorophenyl)cyclopentadienide (3,
140 mg, 0.55 mmol), and THF (25 mL) was stirred at reflux
under nitrogen for 2 h. After the solvent was removed under
reduced pressure, the brown residue was extracted with
hexanes (50 mL). The solution was eluted through neutral
alumina and evaporated to afford 180 mg (0.36 mmol, 72%) of
crude 8. Crystallization from hexanes at -20 °C afforded an
analytical sample: mp 66.0-66.5 °C; IR (octane) νCO ) 2034,
1,4-Bis(pen ta flu or oph en yl)cyclopen ta dien e (4). A mix-
ture of NaCp (2.0 g, 0.023 mmol), NaH (1.1 g, 0.046 mol), C6F6
(42 g, 0.23 mol), and THF (100 mL) was stirred at reflux under
nitrogen for 3 d. The solvent was then removed under reduced
pressure, and the residue was washed with pentane (3 × 50
mL). Pentane (100 mL) and water (20 mL) were added, the
layers were separated, and the organic layer was dried over
MgSO4, filtered through neutral alumina, and evaporated to
afford 4.9 g (54% based on NaCp) of the 4. An analytical
sample was obtained by recrystallization from hot ethanol or
1947 cm-1
. )
1H NMR (CDCl3) δ 6.00 (tt, J HH ) 2.4 Hz, J HF
3
3
1.6 Hz, 2 H), 5.47 (t, 3J ) 2.4 Hz, 2 H). {1H}13C NMR (CDCl3)
1
1
δ 192.6 (CO), 144.1 (d, J CF ) 251 Hz, CF), 140.3 (d, J CF
)
1
2
251 Hz, CF), 138.0 (d, J CF ) 252 Hz, CF), 108.2 (t, J CF ) 16
4
Hz, C6F5 ipso C), 87.8 (m, CC6F5), 87.4 (t, J CF ) 6 Hz, CH),
84.05 (s, CH). 19F NMR (CDCl3) δ -138.95 (m, 2 F), -155.47
3
4
hexanes: mp 104-106 °C; 1H NMR (CDCl3) δ 7.31 (tt, 4J HH
)
(tt, J FF ) 21 Hz, J FF ) 2 Hz, 1 F), -162.15 (m, 2 F). IR
(octane) νCO ) 2038, 1954 cm-1. Anal. Calcd for C14H4F5O3-
Re C, 33.54; H, 0.80. Found: C, 33.50; H, 0.63.
Tr ica r b on yl[η5-1,3-b is(p en t a flu or op h en yl)cyclop en -
ta d ien yl]r h en iu m (I) (9). This complex was prepared from
Re(CO)5Br and 5, following the same method as for the
1.3 Hz, 5J HF ) 0.9 Hz, 2 H), 4.05 (tp, 5J HF ) 1.8 Hz, 4J HH ) 1.3
1
Hz, 2 H). {1H}13C NMR (CDCl3) δ 144.5 (d, J CF ) 253 Hz,
1
1
CF), 139.5 (d, J CF ) 253 Hz, CF), 138.0 (d, J CF ) 251 Hz,
CF), 136.3 (t, 4J ) 8 Hz, CH), 133.7 (m, CC6F5), 110.9 (td, 2J CF
) 14 Hz, 4J CF ) 4 Hz, C6F5 ipso C), 46.5 (p, 4J CF ) 5 Hz, CH2).

Pentafluorophenyl-Substituted Cyclopentadienes
Organometallics, Vol. 15, No. 25, 1996 5291
3
4
monosubstituted complex (8); a 78% yield of [η5-1,3-C5H3-
(C6F5)2]Re(CO)3 (9) was obtained: mp 107.0-107.5 °C. IR
F), -155.21 (tt, J FF ) 22 Hz, J FF ) 3 Hz, 2 F), -163.50 (m,
4 F). Anal. Calcd for
Found: C, 42.58, H, 1.01.
C22H8Cl2F10Zr C, 42.32; H, 1.29.
(octane) νCO ) 2038, 1953 cm-1 1H NMR (CDCl3) δ 6.56 (br
.
s, 1 H), 6.08 (br s, 2 H). {1H}13C NMR (CDCl3) δ 191.6 (s,
1
1
Con clu sion s
CO), 144.1 (d, J CF ) 251 Hz, CF), 140.6 (d, J CF ) 250 Hz,
1
2
CF), 138.0 (d, J CF ) 251 Hz, CF), 107.4 (td, J CF ) 13 Hz,
Formal nucleophilic aromatic substitution of fluoride
with cyclopentadienyl anions in hexafluorobenzene
provides a simple route to new Cp ligands for use in
preparing transition metal complexes with electron-
deficient metal centers. We are presently exploring the
scope of this method with respect to other cyclopenta-
dienes, fluoroarenes, and transition metal fragments.
4J CF ) 4 Hz, C6F5 ipso), 89.1 (t, J CF ) 5 Hz, CH), 87.6 (s,
4
CC6F5), 86.5 (t, 4J CF ) 5 Hz, CH). 19F NMR (CDCl3) δ -138.80
3
3
4
(d, J FF ) 23 Hz, 4 F), -151.40 (tt, J FF ) 21 Hz, J FF ) 3 Hz,
2 F), -161.60 (m, 4 F). Anal. Calcd for C20H3F10O3Re: C,
35.99; H, 0.45. Found: C, 36.17; H, 0.44.
Dich lor obis[η5-(p en ta flu or op h en yl)cyclop en ta d ien yl]-
zir con iu m (IV) (10). A mixture of ZrCl4(THF)2 (350 mg, 0.93
mmol), sodium (pentafluorophenyl)cyclopentadienide (3, 320
mg, 1.00 mmol), and toluene (50 mL) was stirred at 100 °C
for 1 h. The hot mixture was filtered through Celite, which
was washed with additional hot toluene. Fine needles sepa-
rated from the yellow filtrate upon cooling to room tempera-
ture. The crystalline product was collected by filtration and
washed with pentane to afford 427 mg (0.68 mmol, 73%) of
Ack n ow led gm en t. We thank Prof. K. J . Brewer and
G. N. A. Nallas for providing electrochemical instru-
mentation and expertise, and Prof. B. E. Hanson for
providing the FT-IR instrument.
Su p p or tin g In for m a tion Ava ila ble: Crystal data for
22H10F10 (2) (10 pages). Ordering information is given on any
current masthead page.
C
3
pure 10: 1H NMR (C6D6) δ 6.48 (m, 4 H), 5.81 (t, J HH ) 3.2
Hz, 4 H). The complex was not sufficiently soluble for 13C
NMR analysis. 19F NMR (C6D6) δ -140.52 (d, 3J FF ) 20 Hz, 4
OM9608216