Formation of tetrafluorobenzyne by β-fluoride elimination in zirconium-perfluorophenyl complexes

Article abstract of DOI:10.1021/om010888f

Cp*₂ZrH₂ (Cp* = pentamethylcyclopentadienyl) and Hg(C₆F₅)₂ react in pentane to form Cp*₂Zr(C₆F₂)H in high yield at room temperature. Cp*₂Zr(C₆F₅)H reacts intramolecularly at 120 °C under an atmosphere of H₂ to give Cp*₂Zr(o-C₆F₄H)F quantitatively by β-fluoride elimination and subsequent insertion of tetrafluorobenzyne into the Zr - H bond. Under vacuum, Cp*₂Zr(C₆F₅)H decomposes into a mixture of Cp*₂Zr(o-C₆F₄H)F and the ring methyl C - H activated product, Cp*(Fv)Zr(C₆F₅) (Fv = tetramethylfulvene). Upon further heating, Cp*(Fv)Zr(C₆F₅) reacts to form the novel complex Cp*(C₅Me₄CH₂(C₆F₄)) ZrF, formed by β-fluoride elimination and subsequent insertion of tetrafluorobenzyne into the Zr - CH₂ bond.

Full text of DOI:10.1021/om010888f

Organometallics 2002, 21, 727-731
727
F or m a tion of Tetr a flu or oben zyn e by â-F lu or id e
Elim in a tion in Zir con iu m -P er flu or op h en yl Com p lexes
Bradley M. Kraft, Rene J . Lachicotte, and William D. J ones*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received October 10, 2001
Cp*2ZrH2 (Cp* ) pentamethylcyclopentadienyl) and Hg(C6F5)2 react in pentane to form
Cp*2Zr(C6F5)H in high yield at room temperature. Cp*2Zr(C6F5)H reacts intramolecularly
at 120 °C under an atmosphere of H2 to give Cp*2Zr(o-C6F4H)F quantitatively by â-fluoride
elimination and subsequent insertion of tetrafluorobenzyne into the Zr-H bond. Under
vacuum, Cp*2Zr(C6F5)H decomposes into a mixture of Cp*2Zr(o-C6F4H)F and the ring methyl
C-H activated product, Cp*(Fv)Zr(C6F5) (Fv ) tetramethylfulvene). Upon further heating,
Cp*(Fv)Zr(C6F5) reacts to form the novel complex Cp*(C5Me4CH2(C6F4))ZrF, formed by
â-fluoride elimination and subsequent insertion of tetrafluorobenzyne into the Zr-CH2 bond.
In tr od u ction
Sm(C6F5)F, SmF2, Sm(C6F5)F2, Sm(C6F4-C6F5)F, and
organic 1H-perfluorobiphenyls and 1H-perfluoroterphe-
nyls. The observed products were explained by â-fluo-
ride elimination and subsequent insertion of tetrafluo-
robenzyne into the Sm-aryl bonds.3 Similarly, the
metallocene complexes Cp2M(C6F5)2 (M ) Ti, Zr) have
been shown to decompose with release of tetrafluoro-
benzyne and concomitant formation of Cp2M(C6F5)F.4,5
In the zirconium system, some of the tetrafluorobenzyne
was trapped using durene to give a Diels-Alder adduct.
In the absence of durene, tetrafluorobenzyne formed
adducts with the THF solvent.5
Interestingly, neither Cp2ZrHF nor Cp2Zr(C6F5)H has
been reported in the literature, and our attempts to
prepare these apparently unstable compounds by a
number of methods have been unsuccessful. However,
the pentamethylcyclopentadienyl analogues Cp*2ZrHF
and Cp*2Zr(C6F5)H are both stable. In this study, we
describe the synthesis and intramolecular reaction
modes of Cp*2Zr(C6F5)H.
The coordination and activation of fluorocarbons by
metal reagents has been a subject of interest for many
decades.1 The high electronegativity of fluorine imparts
low polarizability and weak σ-basicity to the lone pairs,
making saturated fluorocarbons unable to coordinate
strongly to metal centers. However, the presence of
fluorine on a coordinated ligand in close proximity to a
metal center may facilitate its coordination, making the
C-F bond more reactive and susceptible to chemical
attack. Ortho-substituted aryl fluorides are one class
of compounds that have been shown, in several cases,
to undergo C-F bond activation with release of benzyne.
We have recently observed such reactivity in the reac-
tion of Cp*2ZrH2 and fluorobenzene, forming a mixture
of Cp*2ZrHF, benzene, and Cp*2Zr(C6H5)F by competing
dual pathways.2 In one pathway, Cp*2ZrHF and ben-
zene form concurrently by hydride attack on the aro-
matic ring and fluoride abstraction by zirconium. In the
second pathway, Cp*2Zr(o-C6H4F)H forms by ortho C-H
activation of fluorobenzene, â-fluoride elimination to
form a zirconium-benzyne complex, and finally, inser-
tion of benzyne into the Zr-H bond to give Cp*2Zr-
(C6H5)F (eq 1).
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Cp *2Zr -
(C6F 5)H. The reaction of Cp*2ZrH2 with Hg(C6F5)2 (2:1
mole ratio) at room temperature in pentane afforded
Cp*2Zr(C6F5)H (1), H2, and elemental mercury (eq 2).
1 is isolated as an orange solid in 95% yield by
filtration of mercury and removal of the solvent. Crys-
tallization in pentane at -30 °C yields X-ray quality
crystals. The X-ray structure is shown in Figure 1,
The lanthanide complex Sm(C6F5)2 was shown to
decompose into a complex mixture of products including
(1) There are several recent reviews on C-F activation by metal
reagents, see: (a) Kiplinger, J . L.; Richmond, T. G.; Osterberg, C. E.
Chem. Rev. 1994, 94, 313. (b) Burdeniuc, J .; J edlicka, B.; Crabtree, R.
H. Chem. Ber./ Recl. 1997, 130, 145. (c) Richmond, T. G. In Topics in
Organometallic Chemistry; Murai, S., Ed.; Springer: New York, 1999;
Vol. 3, p 243.
(3) Deacon, G. B.; Koplick, A. J .; Raverty, W. D.; Vince, D. G. J .
Organomet. Chem. 1979, 182, 121.
(4) (a) Treichel, P. M.; Chaudhari, M. A. Stone, F. G. A. J .
Organomet. Chem. 1963, 1, 98. (b) Chaudhari, M. A.; Treichel, P. M.;
Stone, F. G. A. J . Organomet. Chem. 1964, 2, 206.
(5) Edelbach, B. L.; Kraft, B. M.; J ones, W. D. J . Am. Chem. Soc.
1999, 121, 10327.
(2) Kraft, B. M.; Lachicotte, R. J .; J ones, W. D. J . Am. Chem. Soc.
2001, 123, 10973.
10.1021/om010888f CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/18/2002

728 Organometallics, Vol. 21, No. 4, 2002
Kraft et al.
F igu r e 3. ORTEP drawing of Cp*(Fv)Zr(C6F5), 3, showing
30% probability ellipsoids.
F igu r e 1. ORTEP drawing of Cp*2Zr(C6F5)H, 1, showing
30% probability ellipsoids. The hydride ligand was located
and refined.
Ta ble 1. Str u ctu r a l P a r a m eter s for Cp *2Zr XY
Com p ou n d s
Cp*-Zr-Cp*, dZr-X
,
dZr-Y,
Å
compound
deg
Å
1
141.4
1.90(2) 2.355(2)
1.959(2) 2.306(3)
2.00(5) 2.294(5)
2.371(5) 2.348(6)
2.343(3) 2.339(6)
X ) H, Y ) C6F5
2
X ) F, Y ) o-C6F4H
2a
X ) H, Y ) o-C6F4H
3
X ) CH2-Cp*, Y ) C6F5
4a
140.7
142.2
142.8
137.5
X ) Cl, Y ) o-C6F4CH2-Cp*
by reaction of Cp*2Zr(o-C6F4H)H (2a )7 with 70% HF in
pyridine in 40% yield. The 19F NMR spectrum of 2 shows
four multiplets for the fluorines of the aryl group,
consistent with the presence of only one rotamer or with
rapid rotation around the Zr-aryl bond.
F igu r e 2. ORTEP drawing of Cp*2Zr(o-C6F4H)F, 2, show-
ing 30% probability ellipsoids.
showing the perfluoroaryl group lying in the wedge of
the Cp*2Zr moiety (twist ) 6.8°). The 19F NMR spectrum
in cyclohexane-d12 for 1 shows five distinct fluorine
resonances, indicating hindered rotation about the Zr-
aryl bond. In the 1H NMR spectrum, the hydride
resonance at δ 7.71 is a doublet of doublets, arising from
coupling of the magnetically inequivalent ortho-substi-
tuted aryl fluorines. The rate of rotation of the Zr-aryl
bond could not be determined, as heating 1 at 105 °C
in the NMR probe in toluene-d8 did not result in
coalescense of the 19F NMR resonances. Perfluoroaryl
ligands attached to sufficiently bulky substituted zir-
conocenes generally show hindered rotation at room
temperature.6
Thermolysis of 1 at 80 °C for 28 days in cyclohexane-
d12 under vacuum produced mainly 2, but also produced
Cp*(Fv)Zr(C6F5) (3) (Fv ) tetramethylfulvene), Cp*-
(C5Me4CH2(C6F4))ZrF (4), and Cp*2ZrF2 in ∼14:36:3:1
ratio by NMR integration. 3 was prepared indepen-
dently in 56% yield by reaction of Cp*(Fv)ZrCl8 with
LiC6F5 in diethyl ether at low temperature and is
isolated as dark red crystals by crystallization from
pentane at -78 °C. The X-ray structure is shown in
Figure 3, with the aryl group once again lying in the
Cp*2Zr wedge (twist ) 1.0°). The 19F NMR spectrum of
3 shows five magnetically inequivalent fluorine reso-
nances, again caused by hindered rotation about the
Zr-aryl bond. As before, determination of the rate of
rotation could not be determined, as no indication of
coalescence was observed upon heating to 105 °C in
toluene-d8. The 1H NMR spectrum of 3 in toluene-d8
shows seven resonances at δ 2.21, 1.87, 1.71, 1.66, 1.56,
1.33, and 1.15 in 1:1:3:15:3:3:3 ratio. The separate
doublet of doublet resonances at δ 2.21 and 1.87
represent the magnetically inequivalent methylene
protons. Decoupling experiments show that only one of
the ortho fluorine atoms of the aryl group is coupled to
the methylene protons.
Th er m olysis of Cp *2Zr (C6F 5)H. Thermolysis of 1
at 100 °C for 20 days under 1.3 atm H2 in cyclohexane-
d
12 afforded Cp*2Zr(o-C6F4H)F (2) quantitatively (eq 3).
Th er m olysis of Cp *(F v)Zr (C6F 5). Thermolysis of 3
in cyclohexane-d12 at 120 °C for 4 days afforded Cp*-
(C5Me4CH2(C6F4))ZrF (4) in 58% yield (by NMR inte-
gration against an internal standard) along with other
1
2 was characterized by H and 19F NMR spectroscopy,
elemental analysis, and X-ray crystallography (Figure
2). Relevant structural details are summarized in Table
1, and the aryl group lies in the wedge of the Cp*2Zr
moiety (twist ) 0.7°). 2 was also prepared independently
(7) Cp*2Zr(o-C6F4H)H (2a ) is prepared by reaction of Cp*2ZrH2 with
Hg(o-C6F4H)2. See Experimental Section and Supporting Information
for details and the X-ray structure.
(6) Woodman, T. J .; Thornton-Pett, M.; Hughes, D. L.; Bochmann,
M. Organometallics 2001, 20, 4080.
(8) Pattiasina, J . W. Ph.D. Dissertation, University of Groningen,
1988.

Formation of Tetrafluorobenzyne
Organometallics, Vol. 21, No. 4, 2002 729
Sch em e 1. In tr a m olecu la r Rea ction Mod es of
Cp *2Zr (C6F 5)H In volvin g Tetr a flu or oben zyn e
In ter m ed ia tes
F igu r e 4. ORTEP drawing of Cp*(C5Me4CH2(C6F4))ZrCl,
4a , showing 30% probability ellipsoids.
unidentified products (eq 4). The unidentified products
are decomposition products of 4, as prolonged heating
of the reaction mixture at 120 °C resulted in decreased
yield.
sis of 3 to form 4 and also the observation of the durene-
tetrafluorobenzyne adduct in 36% yield upon thermol-
ysis of 3 in the presence of 10 equiv of durene. As before,
an intermediate tetrafluorobenzyne complex could not
be detected by NMR spectroscopy.
In several systems involving the formation of nonflu-
orinated benzyne complexes, both ortho C-H activation
and elimination of arene or alkane occur.10,11 In a
relevant system involving benzyne formation and ring
methyl C-H activation, Cp*2Zr(C6H5)2 reacts to give
Cp*(Fv)Zr(C6H5) and benzene quantitatively.12 Strong
evidence was presented in support of aryl C-H activa-
tion to give the ZrII benzyne intermediate Cp*2Zr(C6H4)
prior to ring methyl hydrogen atom transfer. A similar
reaction sequence involving initial aryl C-F activation
in the reaction of 1 to form 4 is highly unlikely.
Independent experiments show that 3 forms 4 directly,
and therefore ring methyl hydrogen atom transfer
occurs prior to â-fluoride elimination. For the ring
methyl C-H activation of 1, a ring methyl hydrogen
atom transfer to give H2 and 3 is proposed followed by
subsequent reaction to form 4. Addition of 1.3 atm H2
to 3 gave 1 cleanly and quantitatively. This observation
clearly illustrates the equilibrium between 1 and 3 and
explains why 2 is formed exclusively in the thermolysis
of 1 in the presence of added H2.
An alternative mechanism to explain the formation
of 4 from 1 involves â-fluoride elimination to give free
tetrafluorobenzyne and Cp*2ZrHF. Cp*2ZrHF could
then undergo fast ring methyl C-H activation to give
Cp*(Fv)ZrF followed by insertion of tetrafluorobenzyne
into the Zr-CH2 bond. This mechanism was ruled out
with independent experiments showing that 3 reacts to
give 4 in the absence of H2, Cp*(Fv)ZrF is not observed
at any time during the reaction, and last, Cp*2ZrHF
remains stable against ring methyl C-H activation
under the same reaction conditions. A pathway involv-
1
The H NMR spectrum shows a Cp* resonance, four
singlet methyl resonances, and two doublets for the
inequivalent methylene protons. The 19F NMR spectrum
shows four aromatic fluorine resonances and one Zr-F
resonance shifted far downfield. 4 could not be ef-
fectively separated from the other unidentified reaction
products, but could be derivatized into Cp*(C5Me4CH2-
(C6F4))ZrCl (4a ) by heating the product mixture con-
taining 4 with LiCl. A single crystal of 4a was isolated
for characterization by X-ray crystallography (Figure 4),
showing the formation of the C-C bond between the
aryl group and the fulvene. The aryl group now lies at
an angle of 28.5° to the plane of the Cp*2Zr wedge.
Mech a n istic Con sid er a tion s. The mechanism for
formation of 2 from 1 can be explained by initial
â-fluoride elimination to generate tetrafluorobenzyne or
a tetrafluorobenzyne complex followed by insertion of
tetrafluorobenzyne into the Zr-H bond. Evidence for
free tetrafluorobenzyne was confirmed by independent
thermolysis of 1 in the presence of 10 equiv of durene,
a benzyne trap,5 which formed the durene-tetrafluo-
robenzyne adduct in 20% yield by NMR integration.
Very recently, the first transition-metal complex of
tetrafluorobenzyne, Ir(η5-C5Me5)(PMe3)(η2-C6F4), has
been isolated and structurally characterized.9 However,
in the current system, no intermediate tetrafluoroben-
zyne complex could be detected by NMR spectroscopy.
The mechanism for formation of 4 from 1 can be
explained by an initial ring methyl C-H activation to
give 3 and H2, followed by â-fluoride elimination to
release tetrafluorobenzyne followed by insertion of
tetafluorobenzyne into the Zr-CH2 bond (Scheme 1).
This mechanism is supported by independent thermoly-
(10) Buchwald, S. L.; Watson, B. T.; Huffman, J . C. J . Am. Chem.
Soc. 1986, 108, 7411.
(11) McLain, S. J .; Schrock, R. R.; Sharp, P. R.; Churchill, M. R.;
Youngs, W. J . J . Am. Chem. Soc. 1979, 101, 263.
(12) Schock, L. E.; Brock, C. P.; Marks, T. J . Organometallics 1987,
6, 232.
(9) Hughes, R. P.; Williamson, A.; Sommer, R. D.; Rheingold, A. L.
J . Am. Chem. Soc. 2001, 123, 7443.

730 Organometallics, Vol. 21, No. 4, 2002
Kraft et al.
Syn th esis of Cp *2Zr (o-C6F 4H)F , 2. In the drybox, a
solution of 60 mg (0.117 mmol) of Cp*2Zr(o-C6F4H)H in ∼1 mL
of pentane was prepared in a polyethylene reaction vessel.
With stirring, HF-pyridine (70% HF, 30% pyridine) (∼0.1 mL)
was added via syringe and vigorous H2 evolution occurred. The
solution was transferred to a glass vial to neutralize excess
HF and stripped to dryness. The residue was redissolved in
pentane, filtered, and stripped to dryness, yielding analytically
ing reductive elimination of an aryl-methylene bond
in 3 followed by C-F activation is also inconsistent with
the formation of benzyne-trapped products.
Con clu sion s
The thermal decomposition of Cp*2Zr(C6F5)H occurs
by dual pathways to give Cp*2Zr(o-C6F4H)F and Cp*-
(Fv)Zr(C6F5) by competing C-F and C-H bond activa-
tion pathways. Further reaction with Cp*(Fv)Zr(C6F5)
leads to formation of Cp*(C5Me4CH2(C6F4))ZrF, formed
by insertion of tetrafluorobenzyne into the Zr-CH2 bond
of the fulvene complex. In both C-F bond activation
reactions, tetrafluorobenzyne was trapped with durene
to form the Diels-Alder adduct.
pure Cp*2Zr(o-C6F4H)F (25 mg, 40%). Anal. Calcd for C26H31
-
ZrF5: C, 58.95; H, 5.90. Found: C, 58.70; H, 6.18.
Th er m olysis of Cp *2Zr (C6F 5)H u n d er H2. In a resealable
NMR tube, 12 mg (0.033 mmol) of Cp*2Zr(C6F5)H was added,
dissolved in cyclohexane-d12, and freeze-pump-thaw degassed
three times. H2 (1.3 atm) was admitted into the tube, and the
solution was heated in a thermostated 100 °C oil bath for 20
days, leading to quantitative conversion of Cp*2Zr(o-C6F4H)F.
1H NMR (C6D12): δ 1.786 (s, 30 H, Cp*), 6.63 (m, 1 H, Arf-H).
19F NMR (C6D12): δ 90.5 (s, 1 F, Zr-F), -113.9 (m, 1 F), -139.3
(m, 1 F), -157.9 (m, 1 F), -158.8 (m, 1 F).
Exp er im en ta l Section
Th er m olysis of Cp *2Zr (C6F 5)H u n d er Va cu u m . In a
sealable NMR tube, 29 mg of Cp*2Zr(C6F5)H was added and
dissolved in cyclohexane-d12. The solution was freeze-pump-
thaw degassed three times and sealed under vacuum. The tube
was then heated in a 80 °C oil bath. After 28 days, the starting
material was ∼92% depleted, yielding a 36:14:3:1 mixture of
Cp*(C5Me4CH2)Zr(C6F5), Cp*2Zr(C6F4H)F, Cp*(C5Me4CH2-
(C6F4))ZrF, and Cp*2ZrF2, respectively. For Cp*(C5Me4CH2)-
Zr(C6F5), 1H NMR (toluene-d8): δ 2.21 (dd, 1 H), 1.87 (dd, 1
H), 1.71 (d, 3 H), 1.66 (s, 15 H), 1.56 (s, 3 H), 1.33 (s, 3 H),
1.15 (d, 3 H). 19F NMR (toluene-d8): δ -114.6 (m, 1 F), -124.4
(d, 1 F), -156.0 (t, 1 F), -161.0 (quin, 1 F), -161.6 (quin, 1
F). For Cp*(C5Me4CH2(C6F4))ZrF, 1H NMR (C6D12): δ 3.75 (d,
J H-H ) 17.5 Hz, 1 H), 3.57 (d, J H-H ) 17.5 Hz, 1 H), 2.13 (s, 3
H), 2.12 (s, 3 H), 1.86 (s, 15 H), 1.73 (s, 3 H), 1.51 (s, 3 H). 19F
NMR (C6D12): δ 87.6 (br s, 1 F), -108.4 (m, 1 F), -140.6 (t, 1
F), -158.9 (m, 1 F), -160.1 (m, 1 F).
Gen er a l Con sid er a tion s. All manipulations were per-
formed inside a N2-filled Vacuum Atmospheres glovebox or on
a high-vacuum line. Cyclohexane and cyclohexane-d12 were
dried and vacuum distilled from purple solutions of benzophe-
none ketyl. UHP grade H2 (Air Products) was purified by
passage over activated 4 Å molecular sieves and MnO on
vermiculite. 1H and 19F NMR spectra were recorded using a
Bruker Avance400 spectrometer. 19F NMR spectra were ref-
erenced to R,R,R-trifluorotoluene (taken as δ -63.73 relative
to CFCl3 with downfield chemical shifts taken to be positive).
GC/MS analyses were conducted using a 5890A Series GC
equipped with a Restek RTX-5 column (0.25 mm i.d., 0.25 µm,
13 m) and a HP 5970 series mass selective detector. Cp*2ZrH2,
Hg(C6F5)2, Hg(o-C6F4H)2, and Cp*(C5Me4CH2)ZrCl were pre-
pared according to the literature procedures.8,13-15 Ca u tion :
Or ga n om er cu r y d er iva tives a r e h igh ly p oison ou s a n d
sh ou ld be h a n d led w ith gr ea t ca r e.14,16
Th er m olysis of Cp *2Zr (C6F 5)H in th e P r esen ce of
Du r en e (1,2,4,5-tetr a m eth ylben zen e). In a resealable NMR
tube, 18 mg (0.034 mmol) of Cp*2Zr(C6F5)H and 46 mg (0.34
mmol) of durene were dissolved in cyclohexane-d12. The tube
was then placed in a 120 °C oil bath for 4 days. Both Cp*2Zr-
(o-C6F4H)F and Cp*(C5Me4CH2(C6F4))ZrF were formed along
with the Diels-Alder adduct C6H2(CH3)4(C6F4) in 20% yield
by NMR integration. The solvent was replaced with THF-d8
for direct comparison of known chemical shifts.4 For C6H2-
(CH3)4(C6F4), 1H NMR (THF-d8): δ 4.57 (t, 2 H), 1.80 (s, 12
H). 19F NMR (THF-d8): δ -151.1 (m, 2 F), -163.6 (m, 2 F).
GC/MS (m/z): 282 (M+).
Syn th esis of Cp *(C5Me4CH2)Zr (C6F 5), 3. Into a 100 mL
Schlenk flask, 800 mg (2.01 mmol) Cp*(C5Me4CH2)ZrCl was
added and dissolved in ∼40 mL of diethyl ether. Into a second
round-bottomed flask, 246 µL (2.21 mmol, d ) 1.514 g/mL) of
pentafluorobenzene and ∼15 mL of diethyl ether were added
and cooled to -78 °C. n-Butyllithium (1.41 mL, 2.26 mmol,
1.60 M in hexanes) was added dropwise with stirring and
allowed to warm slowly to -20 °C followed by cooling to -78
°C. The resulting LiC6F5 solution was transferred via cannula
into the Cp*(C5Me4CH2)ZrCl solution at -78 °C, upon which
the solution gradually turned from orange to deep red. The
mixture was allowed to warm slowly to room temperature over
5 h. The solvent was replaced with pentane, filtered over
Celite, and concentrated. Crystallization and filtration at -78
°C afforded dark red crystals of Cp*(C5Me4CH2)Zr(C6F5) (600
mg, 56%). Anal. Calcd for C26H29ZrF5: C, 59.17; H, 5.54.
Found: C, 59.05; H, 5.71.
Syn th esis of Cp *2Zr (C6F 5)H, 1. In the drybox, a solution
of 200 mg (0.55 mmol) of Cp*2ZrH2 in ∼5 mL of pentane was
added dropwise to a slurry of 147 mg (0.275 mmol) of Hg(C6F5)2
in ∼5 mL of pentane at room temperature. Vigorous evolution
of H2 occurred, and elemental mercury was formed. The
mixture was stirred for 30 min, filtered over Celite, and
stripped to dryness, giving an orange crystalline mass of Cp*2-
Zr(C6F5)H (415 mg, 95%). Cp*2Zr(C6F5)H was recrystallized
from pentane at -30 °C to yield X-ray quality crystals. 1H
NMR (C6D12): δ 1.88 (s, 30 H, Cp*), 7.71 (dd, 1H, Zr(C6F5)H).
19F NMR (C6D12): δ -116.3 (m, 1 F), -117.7 (m, 1 F), -155.2
(t, 1 F), -160.2 (m, 1 F), -161.9 (m, 1 F). Anal. Calcd for
C
26H31ZrF5: C, 58.95; H, 5.90. Found: C, 59.04; H, 5.76.
P r ep a r a tion of Cp *2Zr (o-C6F 4H)H. A solution of 200 mg
(0.55 mmol) of Cp*2ZrH2 in ∼5 mL of pentane was added
dropwise to a slurry of 137 mg (0.275 mmol) of Hg(o-C6F4H)2
in ∼5 mL of pentane at room temperature. Vigorous evolution
of H2 and elemental mercury was observed. The mixture was
stirred for 30 min, filtered over Celite, and stripped to dryness.
The orange crystalline mass was dissolved in a minimum of
pentane and crystallized at -30 °C to yield X-ray quality
crystals of Cp*2Zr(o-C6F4H)H (177 mg, 63%). The X-ray
structure is included in the Supporting Information. For Cp*2-
1
Zr(o-C6F4H)H, H NMR (C6D12): δ 1.847 (s, 30 H, Cp*), 5.98
(m, 1 H, Zr-C6F4H), 6.83 (br, 1 H, ZrH). 19F NMR (C6D12): δ
-118.1 (m, 1 F), -139.8 (m, 1 F), -157.4 (m, 1 F), -159.0 (m,
1 F). Anal. Calcd for C26H32ZrF4: C, 61.02; H, 6.30. Found: C,
60.84; H, 6.08.
Th er m olysis of Cp *(C5Me4CH2)Zr (C6F 5). Into a reseal-
able NMR tube, 12 mg (0.023 mmol) of Cp*(C5Me4CH2)Zr(C6F5)
was dissolved in cyclohexane-d12. R,R,R-Trifluorotoluene (1.0
µL) was added as an internal standard. The tube was im-
mersed in a 120 °C oil bath for 4 days to give Cp*(C5Me4CH2-
(C6F4))ZrF in 58% yield by NMR integration with other
(13) Schock, L. E.; Marks, T. J . J . Am. Chem. Soc. 1988, 110, 7701.
(14) Albrecht, H. B.; Deacon, G. B.; Tailby, M. J . J . Organomet.
Chem. 1974, 70, 313.
(15) Tamborski, C.; Soloski, E. J . J . Organomet. Chem. 1979, 17,
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1997, 75, (19), 7.

Formation of Tetrafluorobenzyne
Organometallics, Vol. 21, No. 4, 2002 731
unidentified products. NMR data are given above. MS (m/z):
526 (M+). The solution contents were transferred to an ampule
along with dry LiCl (24 mg) and heated with stirring for 3
days at 100 °C for conversion of 4 into Cp*(C5Me4CH2(C6F4))-
ZrCl, 4a . 4a was isolated by repeating the reaction in an
ampule using 190 mg of 3. The resulting solution was filtered
over Celite, stripped to dryness, and extracted with 4 mL of
pentane. The extract was concentrated and cooled to -30 °C
to give 10 mg of a yellow powder. Although the 19F NMR
of Cp*(C5Me4CH2)Zr(C6F5) and 36 mg (0.27 mmol) of durene
were dissolved in cyclohexane-d12. The mixture was freeze-
pump-thawed three times and sealed with a torch. The tube
was placed in a 125 °C oil bath for 2 days. Cp*(C5Me4CH2-
(C6F4))ZrF was formed along with the Diels-Alder adduct,
C6H2(CH3)4(C6F4), in 36% yield by NMR integration.
Ack n ow led gm en t is made to the U.S. Department
of Energy, Grant FG02-86ER13569, for their support
of this work.
1
spectrum showed the product cleanly, the H NMR spectrum
contained small impurities. 1H NMR (C6D12): δ 1.89 (s, 15 H),
2.20 (s, 3 H), 1.99 (s, 3 H), 1.95 (s, 3 H), 1.63 (s, 3 H), 3.75 (d,
J H-H ) 17.5 Hz, 1 H), 3.53 (d, J H-H ) 17.5 Hz, 1 H). 19F NMR:
δ -105.4 (m, 1 F), -140.6 (m, 1 F), -158.8 (m, 1 F), -159.9
(m, 1 F). MS (m/z): 542 (M+). Anal. Calcd for C26H29F4ZrCl:
C, 57.38; H, 5.37. Found: C, 57.11; H, 5.63.
Su p p or tin g In for m a tion Ava ila ble: Includes tables giv-
ing details of the crystallographic procedures along with
intramolecular distances and angles, and positional and
thermal parameters for 1, 2, 2a , 3, and 4a . This material is
available free of charge via the Internet at http://pubs.acs.org.
Th er m olysis of Cp *(C5Me4CH2)Zr (C6F 5) in th e P r es-
en ce of Du r en e. In a sealable NMR tube, 14 mg (0.027 mmol)
OM010888F