Aliphatic and aromatic carbon-fluorine bond activation with Cp*2ZrH2: Mechanisms of hydrodefluorination

Article abstract of DOI:10.1021/ja016087l

Cp*₂ZrH₂ (1) (Cp* = pentamethylcyclopentadienyl) reacts with primary, secondary, and tertiary monofluorinated aliphatic hydrocarbons to give Cp*₂ZrHF (2) and/or Cp*₂ZrF₂ and alkane quantitatively through a radical chain mechanism. The reactivity of monofluorinated aliphatic C-F bonds decreases in the order 1° > 2° > 3°. The rate of hydrodefluorination was also greatly reduced with -CF₂H and -CF₃ groups attached to the hydrocarbon. An atmosphere of H₂ is required to stabilize 1 against C-H activation of the Cp*-methyl groups and subsequent dimerization under the thermal conditions employed in these reactions. Reaction of 1 with fluorobenzene cleanly forms a mixture of Cp*₂ZrHF, benzene, and Cp*₂Zr(C₆H₅)F. Detailed studies indicate that radicals are not involved in this aromatic C-F activation reaction and that dual hydrodefluorination pathways are operative. In one mechanism, hydridic attack by Cp*₂ZrH₂ on the aromatic ring and fluoride abstraction is involved. In the second mechanism, an initial ortho C-H activation occurs, followed by β-fluoride elimination to generate a benzyne complex, which then inserts into the zirconium-hydride bond.

Full text of DOI:10.1021/ja016087l

J. Am. Chem. Soc. 2001, 123, 10973-10979
10973
Aliphatic and Aromatic Carbon-Fluorine Bond Activation with
Cp*2ZrH2: Mechanisms of Hydrodefluorination
Bradley M. Kraft, Rene J. Lachicotte, and William D. Jones*
Contribution from the Department of Chemistry, UniVersity of Rochester, Rochester, New York 14627
ReceiVed April 26, 2001
Abstract: Cp*2ZrH2 (1) (Cp* ) pentamethylcyclopentadienyl) reacts with primary, secondary, and tertiary
monofluorinated aliphatic hydrocarbons to give Cp*2ZrHF (2) and/or Cp*2ZrF2 and alkane quantitatively through
a radical chain mechanism. The reactivity of monofluorinated aliphatic C-F bonds decreases in the order 1°
> 2° > 3°. The rate of hydrodefluorination was also greatly reduced with -CF2H and -CF3 groups attached
to the hydrocarbon. An atmosphere of H2 is required to stabilize 1 against C-H activation of the Cp*-methyl
groups and subsequent dimerization under the thermal conditions employed in these reactions. Reaction of 1
with fluorobenzene cleanly forms a mixture of Cp*2ZrHF, benzene, and Cp*2Zr(C6H5)F. Detailed studies indicate
that radicals are not involved in this aromatic C-F activation reaction and that dual hydrodefluorination pathways
are operative. In one mechanism, hydridic attack by Cp*2ZrH2 on the aromatic ring and fluoride abstraction
is involved. In the second mechanism, an initial ortho C-H activation occurs, followed by â-fluoride elimination
to generate a benzyne complex, which then inserts into the zirconium-hydride bond.
Introduction
Kiplinger and Richmond have demonstrated the catalytic
aromatization of cyclic perfluorocarbons using Cp2MF2 (M )
Ti, Zr) and activated magnesium or aluminum as the reductant
and fluoride sink (eqs 1 and 2).5 This study demonstrated for
Of all types of bonds in organic chemistry, the carbon-
fluorine bond is the most inert and resistant to oxidative degra-
dation.1 In addition, fluorocarbons have exceptional and unique
physical and chemical properties, and have found widespread
use in practical applications such as refrigerants, aerosol pro-
pellants, plastics, pharmaceuticals, oils, pesticides, and others.
Given the chemical inertness and long environmental lifetimes
of fluorocarbons, their distribution and accumulation in the
environment has raised concern of their effects and ultimate
fate in the biosphere. Recently, 3M company has discontinued
their Scotchguard products containing perfluorooctane sulfonate,
as trace amounts of this substance were found to linger in animal
and human tissue samples from all across the globe.2
Some of the research in fluorocarbon chemistry is aimed at
the development of non-ozone-depleting substitutes for CFCs
(chlorofluorocarbons) as well as effective methods for disposal
of the existing CFC stockpiles by conversion of CFCs to HFCs
(hydrofluorocarbons) or other non-ozone-depleting substances.3
In general, hydrodehalogenation reactions of fluorocarbons and
CFCs require strongly reducing conditions and formation of a
halide salt as necessary driving forces. In fact, the current com-
mercial method of CFC disposal is a slow process, using sodium
in liquid ammonia.3b An alternative route to dehalogenation and
C-F activation reactions involves the use of organometallic
complexes in homogeneous solution. Although rare, organo-
metallic systems serve as catalytic models which can circumvent
conventional hydrodehalogenation reaction requirements.4
the first time that early transition-metal complexes are capable
of catalytic activity in C-F activation, as formation of strong
metal-fluoride bonds is generally limiting to catalysis. The
authors were uncertain whether MII or MIII species were involved
in the reduction, but believed the metallocene fragment served
as an “electron shuttle” to transfer electrons from the terminal
reductant to the fluorinated organic substrate. Interestingly, the
reduction of perfluorocyclohexane to tetrafluorobenzene in-
volved hydrogen abstraction from the THF solvent.
We have recently reported that Cp2Zr(C6F5)2 decomposes
intramolecularly to form Cp2Zr(C6F5)F to release tetrafluo-
robenzyne. In the presence of C6F6, a competing reaction to
form perfluorophenylene oligomers was observed. The oligo-
mers were believed to form by a radical chain mechanism with
Cp2ZrIII(C6F5) proposed as the reactive species toward the C-F
bonds of C6F6.6
(1) Smart, B. E. In The Chemistry of Functional Groups, Supplement
D; Patai S., Rappoport, Z., Eds.; John Wiley & Sons: New York, 1983;
Chapter 14.
(2) Weber, J. Business Week 2000, June 5, 96-98.
(3) 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, 373. (b) Burdeniuc J.; Jedlicka, 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.
(4) Aizenberg, M.; Milstein, D. Science 1994, 265, 359. Aizenberg, M.;
Milstein, D. J. Am. Chem. Soc. 1995, 117, 8674.
(5) Kiplinger, J. L.; Richmond, T. G. J. Am. Chem. Soc. 1996, 118,
1805-6.
10.1021/ja016087l CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/06/2001

10974 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Kraft et al.
Bercaw has shown that Cp*2HfH2 reacts with halogenated
hydrocarbons, such as CH3X (X ) Cl, Br, I), to give
Cp*2HfHX and Cp*2HfX2.7 Similarly, the neutral tungstenocene
dihydride, Cp2WH2, also reacts with a variety of aliphatic and
olefinic chloro- and bromocarbons to give hydrogenated prod-
ucts.8 Other early metal C-F activation has been observed in
reactions of fluoroethylene with complexes Cp2ZrHCl and
(tBu3SiO)3TaH2 by a â-F elimination mechanism.9,10 The
reduction of organic halides by the anionic complexes,
[(η5-C5H5)V(CO)3H]-, [HW(CO)5]-, [HW(CO)4P(OMe3)]-,
[HCr(CO)5]-, and [CpFe(CO)2]-, has been shown to occur by
SN2 and/or single electron-transfer processes.11,12
In the present study, it is demonstrated that reactions of
Cp*2ZrH2 with aliphatic fluorocarbons occur via a radical path-
way with Cp*2ZrIIIH as the reactive species toward aliphatic
C-F bonds. In contrast, reactions of Cp*2ZrH2 with aromatic
C-F bonds, such as in fluorobenzene and 1-fluoronaphthalene,
do not show evidence for radicals, and are believed to occur
through a nucleophilic displacement mechanism.
Figure 1. ORTEP drawings of Cp*2ZrH2, Cp*2ZrHF, and Cp*2ZrF2
showing 30% probability ellipsoids. The hydrides in Cp*2ZrH2 were
located and refined. The fluorine in Cp*2ZrHF is disordered over the
two equatorial sites (1/2 F each), and the hydride was not located. For
Cp*2ZrH2: Cp*-Zr-Cp* ) 144.2°, H-Zr-H ) 99(2)°, P21212.
For Cp*2ZrHF: Cp*-Zr-Cp* ) 141.4°, ‘F’-Zr-‘F’ ) 93.9(4)°,
P21212. For Cp*2ZrF2:
Cp*-Zr-Cp* ) 138.7°, F-Zr-F )
99.6(3)°, C2/c. Note the increase in metallocene bending with increased
fluorine substitution.
was observed, underscoring the lower reactivity of the tertiary
C-F bond.
Results and Discussion
Increasing geminal fluorine substitution also decreases the
reactivity toward hydrodefluorination. For example, 1,1-difluo-
roethane reacts with 1 under H2 to ∼90% completion after 1
day to produce ethane and Cp*2ZrHF upon heating to 150 °C.
1,1,1-Trifluoropropane was even more unreactive, reacting over
2 weeks at 150 °C to form Cp*2ZrHF in ∼57% yield by NMR
integration. Propane was not identified in the 1H NMR spectrum
and other unidentified decomposition products were observed.
Cp*2ZrH2 is unreactive with perfluorocarbons such as perfluo-
rohexane and perfluoroisobutane even with prolonged heating
at 150 °C. However, a reaction with perfluorocyclohexane to
give Cp*2ZrHF did occur, but the organic product(s) could not
be identified.
CFCs also react with 1 to give HFCs and subsequent
hydrogenated products. Dichlorofluoromethane reacted readily
at room temperature with 3 equiv of 1 to give fluoromethane,
Cp*2ZrHCl, and a small amount of Cp*2ZrCl2. Methane forms
when the sample is allowed to stand for 1 day at ambient
temperature, with 2, Cp*2ZrF2, and Cp*2ZrFCl also being
observed. Difluorodichloromethane and difluorochloromethane
were also found to give initially the dechlorinated organic
product, difluoromethane, upon reaction with 4 equiv of 1. As
with CF2HCH3, subsequent defluorination of CF2H2 was slow,
requiring heating to 120 °C under H2 over a period of >10 days
for complete dehalogenation to occur, giving methane.
The crystal structures of Cp*2ZrH2, Cp*2ZrHF, and
Cp*2ZrF2 have been characterized by single-crystal X-ray
crystallography (Figure 1). The structural data indicate that
increasing fluorine substitution on zirconium decreases the
Cp*-Zr-Cp* angle.
Decomposition of Cp*2ZrH2. As mentioned above, H2 is
required to stabilize 1 in reactions carried out at temperatures
above 85 °C. In the absence of H2, Cp*2ZrH2 decomposes in
solution above 85 °C to produce an extremely insoluble yellow
material. In the presence of 1.3 atm of H2, little or none of this
precipitate is observed. At 120 °C, a solution of 1 under vacuum
develops a red color within a few minutes followed by
precipitation of a substantial amount of the insoluble yellow
material within 30 min. A single crystal of this material was
mounted on the diffractometer and the unit cell constants were
obtained, matching those found for the dimeric species,
{Cp*(C5Me3(CH2)2Zr}2 (4), previously prepared by Pattiasina
by thermolysis (180 °C) of the allyl-diene complex,
Cp*(C5Me3(CH2)2)Zr (3), in benzene solution.14
Reactions of Monofluorinated Hydrocarbons and CFCs
with Cp*2ZrH2. Reaction of 1 equiv of Cp*2ZrH2 (1) with
1-fluorohexane in cyclohexane-d12 at 23 °C over a period of
∼2 days produces Cp*2ZrHF (2) and hexane quantitatively (eq
3). Subsequent addition of 1 equiv of 1-fluorohexane and heating
to 120 °C over 10 days produces Cp*2ZrF2 and hexane
quantitatively.
No deuterium was incorporated into the hexane as verified
by MS. 2 has been prepared previously by conproportionation
of Cp*2ZrH2 and Cp*2ZrF2.13 Fluorocyclohexane reacts similarly
to give a mixture of Cp*2ZrHF and Cp*2ZrF2, but elevated
temperatures were required (120 °C) and the reaction time must
be increased. At these temperatures, an atmosphere of H2 must
be present to stabilize 1 against loss of H2 and subsequent
dimerization (vide infra). Tertiary fluorine-substituted carbon
centers, such as in 1-fluoroadamantane, also react with 1, but
proceed only very slowly at 120 °C reaching ∼25% completion
after 1 week.
In competitive reactions, a 5:5:1 mixture of fluorohexane,
fluorocyclohexane, and 1 reacted at 40 °C to give a 2.1:1 ratio
of hexane:cyclohexane. In comparison, when two separate but
parallel reactions were conducted at 40 °C with a stock solution
of 1 to which each fluorocarbon was added, a 2.3:1 ratio of
yields of hexane:cyclohexane reduction products was observed.
In a competition involving a 5:5:1 ratio of fluorocyclohexane:
1-fluoroadamantane:1, a 33:1 ratio of cyclohexane:adamantane
(6) Edelbach, B. L.; Kraft, B. M.; Jones, W. D. J. Am. Chem. Soc. 1999,
121, 10327-31.
(7) Roddick, D. M.; Fryzuk, M. D.; Deidler, P. F.; Hillhouse, G. L.;
Bercaw, J. E. Organometallics 1985, 4, 97-104.
(8) Green, M. L. H.; Knowles, P. J. J. Chem. Soc., Perkin Trans. 1 1973,
10, 989-91.
(9) Watson, L. A.; Yandulov, D. V.; Caulton, K. G. J. Am. Chem. Soc.
2001, 123, 603.
(10) Strazisar, S. A.; Wolczanski, P. T. J. Am. Chem. Soc. 2001, 123,
4728.
(11) Kinney, R. J.; Jones, W. D.; Bergman, R. G. J. Am. Chem. Soc.
1978, 100, 7902.
(12) Kao, S. C.; Spillett, C. T.; Ash, C.; Lusk, R.; Park, Y. K.;
Darensbourg, M. Y. Organometallics 1985, 4, 83.
(13) Barger, P. T.; Bercaw, J. E. Organometallics 1984, 3, 278.

Carbon-Fluorine Bond ActiVation with Cp*2ZrH2
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10975
The decomposition pathway is likely to involve a series of
reversible ring-metalation reactions of the Cp* methyl groups.
All 30 methyl protons are known to undergo intramolecular
exchange with the hydride positions of 1.15 In the absence of
H2, the intermediate fulvene or “tuck-in” complex may form
readily at higher temperatures, and could lead to a subsequent
C-H activation of a second methyl group to form 3. The
presence of 3 was confirmed by heating solid 1 for 19 h at 85
°C under dynamic vacuum to give a mixture of red and yellow
1
solid. The H NMR spectrum of a C6D12 solution of the solid
residue revealed ∼20% conversion to 3 and unreacted 1 only.
Addition of H2 to this solution formed 1 quantitatively. Once 3
is formed, a competing reaction to form the insoluble dimer, 4,
occurs (eq 4). Isolation of 4 and treatment with 1.3 atm of H2
Figure 2. Graph of kobs vs [1-fluorohexane] for reaction of 1 with
1-fluorohexane using initial rate data only.
in toluene at 95 °C for 1 day led to quantitative reformation of
Cp*2ZrH2. The reversibility of this decomposition pathway
explains why addition of H2 is required to stabilize 1 in reactions
at temperatures above 85 °C. However, because the reaction of
1 and 1-fluorohexane proceeds in the absence of H2, it is con-
cluded that H2 is not directly involved in the hydrodefluorina-
tion process.
Figure 3. Graph of ln(Cp*2ZrH2 Area) vs time showing the effect of
radical inhibitors: ([) 0.046 M 1-fluorohexane only; (9) 0.458 M
9,10-dihydroanthracene; (2) 0.458 M triphenylmethane; and (b) 5 mol
% n-propyl bromide.
Mechanism of Aliphatic Hydrodefluorination. The kinetics
of the reaction of 1 with fluorohexane were first examined as
a means of probing the mechanism of hydrodefluorination. The
reactions were performed in cyclohexane-d12 solvent at 45 °C.
The overall reaction does not follow a clean first-order rate law,
showing a decrease in rate after ∼80-90% of Cp*2ZrH2 is
consumed. However, with use of initial rate data, the rate
constant for reaction of 1 with fluorohexane was found to be
dependent on [fluorohexane]. A plot of kobs vs fluorohexane
concentration generated a second-order rate constant of 1.6 ×
10-6 M-1 s-1 (Figure 2).
The addition of sodium and naphthalene was effective for
initiation of the reaction, reaching completion within 45 min,
approximately 3 times faster than the control experiment. 2 was
formed in quantitative yield based on NMR integration and
formation of hexane was verified by GC/MS. The reaction also
proceeded at a more rapid rate in the presence of sodium only.
Na/naphthalene and fluorohexane were found to react in the
absence of added Cp*2ZrH2 under the same conditions but gave
only ∼5% conversion to hexane based on NMR integration. In
the beginning of the reactions initiated by a reducing agent,
1
severe broadening of the H NMR resonances was observed,
When a freshly prepared batch of Cp*2ZrH2 was prepared
and used for kinetic studies, the rate of the reaction was found
to be significantly slower under similar conditions. This was
the first indication that a radical mechanism may be operative
and could be initiated by a trace impurity in Cp*2ZrH2. In the
presence of the radical inhibitor isopropylbenzene (10 equiv),
no change in the rate of reaction was observed. However, in
the presence of radical inhibitors with weaker homolytic C-H
bond strengths, such as 9,10-dihydroanthracene or triphenyl-
methane, severe inhibition was observed, suggesting again that
radicals are involved in the mechanism (Figure 3). Addition of
n-propyl bromide (5 mol %) had essentially no effect on the
rate of the reaction. The possibility of a radical mechanism
stands in contrast to a concerted H/F exchange as was suggested
in our recent communication.16
but at the end of the reaction, the resonances had become sharp,
suggesting the presence of a transient paramagnetic ZrII or ZrIII
species early in the reaction. When the reaction was performed
in the presence of another potential radical initiator, TiCl3,
similar broadening of the resonances was observed, but no
apparent increase in the rate was observed and only a trace of
Cp*2ZrHCl was observed. Other initiators such as TEMPO and
VAZO were not suitable initiators as reaction with Cp*2ZrH2
occurred.
(14) (a) Pattiasina, J. W. Ph.D. Dissertation, University of Groningen,
1988. (b) Spek, A. L.; Pattiasina, J. W.; Teuben, J. H. Z. Kristallogr. 1996,
211, 643.
(15) Bercaw, J. E. AdV. Chem. Ser. 1978, 167, 136.
(16) Kraft, B. M.; Lachicotte, R. J.; Jones, W. D. J. Am. Chem. Soc.
2000, 122, 8559.

10976 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Kraft et al.
Scheme 1
Scheme 2
Figure 4. ORTEP drawing of Cp*2Zr(o-C6H4F)H showing 30%
probability ellipsoids.
hydride positions of Cp*2ZrH2 below -80 °C.15 When 1 is in
the presence of H2, severe broadening of the zirconium-hydride
resonance is observed in the 1H NMR spectrum. Free H2 is never
observed in the presence of 1 even when excess H2 (∼5 equiv)
is present. Attempts to observe an H2 complex with use of low-
temperature NMR spectroscopy in methylcyclohexane-d14 showed
no evidence for a static H2 complex even at -125 °C, as very
little change in the 1H NMR spectrum was observed. Although
an H2 complex could not be observed, it may still exist
transiently and defluorination could be inhibited by H2 coor-
dination. Another possibility is that H2 forms a complex with
the Cp*2ZrIIIH radical to inhibit the fluorine abstraction step.
A similar decrease in rate (∼8-fold) was also observed when
the reaction of 1-fluorohexane was performed in THF-d8 solvent.
Again, this inhibition is attributed to occupation of the vacant
coordination site of Cp*2ZrH2.
Reaction of 1 with Fluorobenzene. Reaction of 1 with 1
equiv of fluorobenzene and 1.3 atm of H2 in cyclohexane-d12
at 85 °C over 40 days resulted in a clean mixture of Cp*2ZrHF,
benzene, and Cp*2Zr(C6H5)F in 1:1:0.75 ratio. When the
reaction was performed in THF-d8 solvent, only traces of 2 were
observed in addition to small amounts of other unidentified
product(s) after 7 days at 85 °C. A similar reaction involving
(Cp*2YH)2 with halobenzenes was reported. In a reaction with
fluorobenzene, a complex mixture of products formed instantly,
two of which were identified as 2-fluorobiphenyl and Cp*2Y-
(-C6H4-C6H4F).19 The observed products were suggestive of
benzyne formation. In the present study with fluorobenzene,
an intermediate species was observed during the course of the
reaction and has been assigned to the ortho C-H activated
product, Cp*2Zr(o-C6H4F)H. Although this species could not
be isolated directly from the reaction mixture, independent
synthesis of this compound confirmed its identity. Cp*2Zr(o-
C6H4F)H was prepared in nearly quantitative yield by reaction
of 1 with Hg(o-C6H4F)2 in pentane (eq 5). The reaction is
Definitive evidence for radical formation was obtained by
reaction of 1 with cyclopropylcarbinyl fluoride. The cyclopro-
pylcarbinyl radical is known to ring-open irreversibly to give
the butenyl radical at a rate of 2.70 × 108 s-1 at 30 °C.17
Cyclopropylcarbinyl fluoride reacted with 1 within 15 min to
give a clean 1:1 mixture of Cp*2Zr(n-butyl)H and 2. No
1
methylcyclopropane was observed in the H NMR spectrum.
These products can be accounted for by a mechanism in which
a fluorine radical abstraction by a small amount of Cp*2ZrIIIH
gives the cyclopropylcarbinyl radical. This radical quickly ring
opens to form the butenyl radical, which then abstracts a
hydrogen atom from 1 to continue the radical chain. Butene
undergoes insertion with another equivalent of 1 to give the
observed butyl hydride complex (Scheme 1). Cp*2Zr(n-butyl)H
1
was characterized by H NMR spectroscopy and reacted with
1
H2 to form 1 and butane, which was confirmed by H NMR
and GC/MS. Full characterization of Cp*2Zr(n-butyl)H was not
possible due to the inherent instability of these types of alkyl
hydride derivatives.18 In a control experiment, 1 was found to
be unreactive with methylcyclopropane at room temperature.
The reactivity trends observed with increasing geminal
fluorine substitution on carbon are consistent with known
characteristics of fluorocarbons. Increasing geminal fluorination
is known to greatly increase the C-F bond strength. For
example, the C-F bond dissociation energies for the fluo-
romethanes (CH3F, CH2F2, CHF3, and CF4) increase from 109,
122, 128, to 130 kcal/mol, respectively.1 However, based on
radical stability, the C-F bond dissociation energy for mono-
fluorinated substrates should decrease with increasing substi-
tution at carbon (1°, 2°, 3°), but the opposite reactivity trend is
observed. It is likely but unsubstantiated that steric repulsion
with the Cp* ligands governs the ease of fluorine abstraction.
The mechanism in Scheme 2 best fits the observations. The
reaction could be initiated by a trace unidentified impurity in
Cp*2ZrH2. As shown above, the initial rate is proportional to
the fluorohexane concentration. The rate-determining step
therefore involves fluorohexane and a steady-state concentration
of the Cp*2ZrIIIH radical. The chain is continued by hydrogen
abstraction by the alkyl radical from another Cp*2ZrH2 molecule
rather than from the deuterated NMR solvent, as no deuterium
was incorporated into the hexane. Similarly, the reactions with
other fluorocarbons and CFCs are likely to occur by the same
mechanism. Radical chains of this type involving metal hydrides
and alkyl halides are well-known.11,12
complete within minutes and elemental mercury and H2 gas are
observed. The product was characterized by 19F and 1H NMR,
X-ray, and elemental analysis. The X-ray structure is shown in
Figure 4. Heating Cp*2Zr(o-C6H4F)H in the presence of H2 led
(17) Mathew, L.; Warkentin, J. J. Am. Chem. Soc. 1986, 108, 7981.
(18) Miller, F. D.; Sanner, R. D. Organometallics 1988, 7, 818.
(19) Booij, M.; Deelman, B.; Duchateau, R.; Postma, D. S.; Meetsma,
A.; Teuben, J. H. Organometallics 1993, 12, 331-40.
Effect of H2 and THF. Addition of 1.3 atm of H2 to the
reaction of 1-fluorohexane significantly inhibited the reaction
by ∼11-fold. It is well-known that H2 exchanges with the

Carbon-Fluorine Bond ActiVation with Cp*2ZrH2
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10977
more slowly than fluorobenzene, but the opposite is observed.
The increased reactivity with 1-fluoronaphthalene over fluo-
robenzene can be explained by the decreased loss of resonance
energy in fluoronaphthalene in the intermediate/transition state.
Further support for this mechanism is derived from the X-ray
structure of a cationic TiIII fluorobenzene complex, Cp*2Ti-
(FC6H5)+, recently reported by Teuben et al.21 The structure
illustrates the effects of a neutral fluorocarbon ligand coordinated
to a cationic center. In comparison with free fluorobenzene,
lengthening of the C-F bond was observed that provides good
evidence that coordination to a cationic center may cause a
weakening of the C-F bond. In fact, heating Cp*2Ti(FC6H5)+
was shown to cause C-F activation of the coordinated fluo-
robenzene.
Figure 5. ORTEP drawing of Cp*2Zr(C6H5)F showing 30% probability
ellipsoids.
to a mixture of fluorobenzene, Cp*2ZrH2, and Cp*2Zr(C6H5)F,
indicating that the ortho C-H activation step is reversible.
However, heating Cp*2Zr(o-C6H4F)H in the absence of H2
formed Cp*2Zr(C6H5)F quantitatively. Cp*2Zr(C6H5)F was
characterized by 19F and 1H NMR, X-ray, and elemental
analysis. The X-ray structure is shown in Figure 5. Regarding
this reaction, it is likely that a â-fluoride elimination occurs to
generate a benzyne complex that quickly inserts into the Zr-H
bond to give Cp*2Zr(C6H5)F (eq 6). The reaction was performed
Conclusions
A series of fluorocarbons react with Cp*2ZrH2 to give
primarily Cp*2ZrHF and alkane by a radical chain mechanism
involving Cp*2ZrIIIH as the reactive species toward C-F bonds.
Radical inhibitors and initiators are shown to severely affect
the rate of reaction. Last, the reaction with cyclopropylcarbinyl
fluoride to produce Cp*2Zr(n-butyl)H provides good evidence
that alkyl radicals are generated in the reactions with aliphatic
fluorocarbons. However, Cp*2ZrH2 reacts with monofluoro-
arenes by a different mechanism involving hydridic attack on
the aromatic ring and subsequent fluoride abstraction to yield
Cp*2ZrHF and hydrogenated arene. In the reaction with fluo-
robenzene, an additional pathway occurs to form Cp*2Zr-
(C6H5)F. The complex was shown to form by an initial ortho
C-H activation, subsequent fluoride elimination to generate a
benzyne complex, and finally, insertion of benzyne into the
zirconium-hydride bond.
in the presence of 10 equiv of 1,2,4,5-tetramethylbenzene, a
benzyne trap, but no benzyne adduct was observed in this
reaction. Unlike the decomposition of Cp2Zr(C6F5)2 to release
tetrafluorobenzyne,6 it is possible that the nonfluorinated ben-
zyne remains fully coordinated to zirconium as in the decom-
position of Cp2ZrPh2.20
Several other mechanisms to explain the formation of
Cp*2Zr(C6H5)F were discounted: (1) Reaction of Cp*2ZrHF
and benzene did not produce Cp*2Zr(C6H5)F after 12 h at 120
°C. (2) [Cp*2Zr]2(N2)3 did not react with 2 equiv of fluoroben-
zene at 77 °C to give Cp*2Zr(C6H5)F, suggesting that an
oxidative addition to “Cp*2ZrII” does not occur. (3) Cp*2ZrHF
and Cp*2Zr(C6H5)H do not conproportionate after 3 days at 120
°C. Cp*2Zr(C6H5)F was prepared independently in 41% yield
by addition of 1 equiv of phenyllithium to Cp*2ZrF2 and
subsequent recrystallization. Cp*2Zr(C6H5)F was treated with
1.3 atm of H2 and heated to 120 °C for 3 days, but resulted in
no reaction. This observation eliminated the possibility that
benzene and Cp*2ZrHF were formed by this pathway.
The reaction of 1 with 1-fluoronaphthalene proceeded much
faster than that with fluorobenzene, and produced naphthalene
and Cp*2ZrHF over 4 days at 85 °C with no Cp*2Zr(naphthyl)F
being observed. Unlike the reactions with aliphatic fluorocar-
bons, this reaction showed no inhibition by 9,10-dihydroan-
thracene or triphenylmethane. Also, no increase in rate was
observed when the reaction was performed in the presence of
sodium/naphthalene initiator, suggesting that a radical mecha-
nism is not involved for these aromatic C-F bond-activation
reactions. The formation of Cp*2ZrHF and arene in the reactions
with fluorobenzene and fluoronaphthalene is therefore best
explained by a direct nucleophilic attack by hydride on the
aromatic ring (SNAr2) and fluoride abstraction by zirconium
(eq 7). Sterically, 1-fluoronaphthalene might be expected to react
Experimental Section
General Considerations. All manipulations were performed inside
a N2-filled Vacuum Atmospheres glovebox or on a high-vacuum line.
NMR solvents, cyclohexane-d12, and toluene-d8 (Cambridge) were dried
and vacuum distilled from purple solutions of benzophenone ketyl. UHP
grade H2 (Air Products) was purified by passage over activated 4 Å
molecular sieves and MnO on vermiculite. D2 (Cambridge) was used
as received. 1-Fluorohexane, fluorobenzene, and 1-fluoronaphthalene
were purchased from Aldrich and used as received. Fluorocyclohexane
was purchased from Matrix Scientific. CFCs were purchased from
Matheson. All liquids were degassed by the freeze-pump-thaw
method. 1H and 19F NMR spectra were recorded with a Bruker
Avance400 spectrometer. 19F NMR spectra were referenced to R,R,R-
trifluorotoluene (δ 0.00 with downfield chemical shifts taken to be
positive). GC/MS analyses were conducted with use of a 5890A Series
GC equipped with a Restek RTX-5 column (0.25 mm ID, 0.25 µm, 13
m) and a HP 5970 series mass selective detector. Cp*2ZrH2, 1-fluo-
roadamantane, and Hg(o-C6H4F)2 were prepared according to the
literature procedures.22-24 Caution: Organomercury derivatives are
highly poisonous and should be handled with great care.25
Reaction of 1-Fluorohexane with 1. A resealable NMR tube was
charged with 20 mg (0.055 mmol) of 1 and dissolved in cyclohexane-
d12. 1-Fluorohexane (7.2 µL, 0.055 mmol, F ) 0.80) was added via
(21) Plenio, H. Chem. ReV. 1997, 97, 3363. de Wolf, J. M.; Gercama,
J.; del Hierro Morales, I.; Troyanov, S. I.; Meetsma, A.; Hessen, B.; Teuben,
J. H., submitted for publication.
(20) Erker, G. J. Organomet. Chem. 1977, 134, 189.

10978 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Kraft et al.
syringe. The tube was allowed to stand for 2 days at room temperature.
The reaction was ∼93% complete with formation of Cp*2ZrHF and
hexane. For Cp*2ZrHF: 1H NMR (C6D12) δ 1.92 (s, 30 H, Cp*), 6.23
(s, 1 H, ZrHF); 19F NMR δ 141.4 (s, 1 F). For C6H14: 1H NMR δ 0.89
(t, 6 H), 1.28 (m, 8 H); MS (m/z) 86 (M+). An additional equivalent of
1-fluorohexane (7.2 µL, 0.055 mmol) was added to the tube and heated
at 120 °C for 10 days. The reaction mixture now consisted of a mixture
of Cp*2ZrF2 and hexane. For Cp*2ZrF2: 1H NMR (C6D12) δ 1.86 (s,
30 H, Cp*); 19F NMR δ 97.8 (s, 2 F).
Reaction of 1,1,1-Trifluoropropane with 1. Cyclohexane-d12 and
∼13 mg of 10% palladium on carbon was added to a resealable NMR
tube. In a 56-mL calibrated glass bulb, 55 Torr (0.17 mmol) of 3,3,3-
trifluoropropene was condensed at -196 °C followed by admission of
1.3 atm of H2. The mixture was thawed and stirred for 1 h at room
temperature yielding 1,1,1-trifluoropropane cleanly and quantitatively.
For CF3CH2CH3: 1H NMR (C6D12) δ 1.97 (m, 2 H), 1.06 (t, 3 H); 19
F
NMR δ -5.48 (t, JH-F ) 11.3 Hz). The contents of the tube were
vacuum transferred into another resealable NMR tube containing 17
mg of Cp*2ZrH2 (0.047 mmol). H2 (1.3 atm) was admitted into the
tube and the contents were heated at 150 °C for 2 weeks. At this point,
Cp*2ZrH2 was ∼80% consumed with formation of Cp*2ZrHF in ∼57%
yield by NMR integration. Other unidentified decomposition products
of Cp*2ZrH2 were also observed. Propane was not unambiguously
Kinetics for Reaction of 1-Fluorohexane with 1. In the drybox,
400 µL of a 0.0687 M stock cyclohexane-d12 solution of 1 containing
0.057 M of hexamethyldisilane standard was syringed into resealable
NMR tubes. Fluorohexane was added with a microliter syringe and
the total volume was brought to 0.600 mL. The reactions were
monitored at 45 °C in the NMR probe. From initial rate data, the rate
constants (kobs) obtained for 458, 687, 916, and 1370 mM 1-fluoro-
1
identified in the H NMR spectrum.
Reaction of Difluorodichloromethane with 1. In a resealable NMR
tube, 27 mg (0.074 mmol) of 1 was dissolved in cyclohexane-d12. On
the vacuum line, the tube was freeze-pump-thaw degassed three times.
In a 56-mL calibrated glass bulb, 7 Torr (0.021 mmol) of CF2Cl2 was
condensed at -196 °C. Hydrogen (1.3 atm) was admitted into the tube.
Upon thawing, a yellow precipitate formed. 1H and 19F NMR re-
vealed formation of a mixture of Cp*2ZrCl2, Cp*2ZrHCl, and CF2H2.
For Cp*2ZrCl2: 1H NMR (C6D12) δ 1.94 (s). For Cp*2ZrHCl: 1H NMR
hexane were 3.7 × 10-4, 7.3 × 10-4, 1.1 × 10-3, and 1.8 × 10-3 s-1
,
respectively.
Reaction of 1-Fluorohexane and 1 in the Presence of Radical
Inhibitors. A 160-µL aliquot (0.027 mmol) of a 0.172 M Cp*2ZrH2
stock solution in cyclohexane-d12 was added to a resealable NMR tube
followed by addition of 9,10-dihydroanthracene (50 mg, 0.27 mmol)
or triphenylmethane (67 g, 0.27 mmol). Additional cyclohexane-d12
was added to bring the total volume to 0.60 mL. The reaction mixture
was heated at 45 °C in the NMR probe and analyzed periodically over
the course of the reaction.
δ 1.97 (s, 30 H), 6.54 (s, 1 H). For CF2H2: 1H NMR δ 5.44 (t, JH-F
)
50.2 Hz); 19F NMR δ -77.8 (t, JH-F ) 51.9 Hz). The mixture was
then heated at 120 °C for 11 days. The reaction mixture now consisted
of a mixture of Cp*2ZrCl2, Cp*2ZrHCl, Cp*2ZrHF, and methane. For
CH4: 1H NMR δ 0.19 (s). The identity of methane was further
characterized by spiking with an authentic sample.
Reaction of 1-Fluorohexane with 1 in the Presence of Sodium
and Naphthalene. A 160-µL aliquot of a 0.137 M Cp*2ZrH2 stock
solution in cyclohexane-d12 was added to a resealable NMR tube
containing ∼3 mg of sodium metal and ∼5 mg of naphthalene.
1-Fluorohexane (120 µL) was then added via syringe. The reaction
mixture was heated at 45 °C in the NMR probe. The reaction was
complete within 45 min, forming Cp*2ZrHF in nearly quantitative yield
Reaction of Difluorochloromethane with 1. In a resealable NMR
tube, 25 mg (0.069 mmol) of 1 was dissolved in cyclohexane-d12. On
the vacuum line, the tube was freeze-pump-thaw degassed three times.
In a 56-mL calibrated glass bulb, 8 Torr (0.024 mmol) of CHClF2 was
condensed at -196 °C. Hydrogen (1.3 atm) was admitted into the tube.
Upon thawing, a yellow precipitate formed. 1H and 19F NMR revealed
formation of a mixture of Cp*2ZrCl2, Cp*2ZrHCl, and CF2H2. The
mixture was then heated at 120 °C for 10 days. The reaction mixture
now consisted of a mixture of Cp*2ZrCl2, Cp*2ZrHCl, Cp*2ZrHF, and
methane.
1
by H NMR integration. Hexane was verified by GC/MS.
Reaction of Fluorocyclohexane with 1. A resealable NMR tube
was charged with 20 mg (0.055 mmol) of 1 and dissolved in
cyclohexane-d12. Fluorocyclohexane (5.9 µL, 0.055 mmol, F ) 0.95)
was added via syringe. The tube was then freeze-pump-thaw degassed
three times and 1.3 atm of H2 was admitted into the tube. The tube
was heated at 120 °C for 4 days. The reaction mixture consisted of a
12:1 mixture of Cp*2ZrHF and Cp*2ZrF2, and cyclohexane. For
C6H12: 1H NMR (C6D12) δ 1.44 (s). C6H12 was not distinguishable
from C6D12 solvent by GC/MS.
Reaction of 1-Fluoroadamantane with 1. A resealable NMR tube
was charged with 20 mg (0.055 mmol) of 1 and 1-fluoroadamantane
(8 mg, 0.052 mmol) and dissolved in cyclohexane-d12. The tube was
freeze-pump-thaw degassed three times and 1.3 atm of H2 was
admitted into the tube. The tube was heated to 120 °C for 6 days. The
reaction was ∼25% complete, producing Cp*2ZrHF and adamantane.
For C10H16: 1H NMR (C6D12) δ 1.86 (br, 4 H), 1.78 (br, 12 H); MS
(m/z) 136 (M+).
Reaction of 1,1-Difluoroethane with 1. Cyclohexane-d12 and ∼10
mg of 10% palladium on carbon was added to a resealable NMR tube.
In a 56-mL calibrated glass bulb, 13 Torr (0.039 mmol) of 1,1-
difluoroethylene was condensed at -196 °C followed by admission of
1.3 atm of H2. The mixture was thawed and stirred for 1 h at room
temperature yielding 1,1-difluoroethane cleanly and quantitatively. For
CF2HCH3: 1H NMR (C6D12) δ 5.75 (tq, JH-F ) 56.7 Hz, 1 H), 1.43
(td, JH-F ) 19.9 Hz, 3 H); 19F NMR (C6D12) δ -45.4 (m). The contents
of the tube were vacuum transferred into another resealable NMR tube
containing 28 mg of 1 (0.078 mmol). H2 (1.3 atm) was admitted into
the tube and the contents were heated at 150 °C for 24 h. At this point,
Cp*2ZrH2 was ∼90% depleted with formation of Cp*2ZrHF, ethane,
and a trace amount of Cp*2ZrF2. For ethane: 1H NMR (C6D12) δ 0.852
(s). The identity of ethane was further characterized by spiking with
an authentic sample.
Reaction of Dichlorofluoromethane with 1. In a resealable NMR
tube, 20 mg (0.055 mmol) of 1 was dissolved in cyclohexane-d12. On
the vacuum line, the tube was freeze-pump-thaw degassed three times.
In a 56-mL calibrated glass bulb, 6 Torr (0.018 mmol) of CHFCl2 was
condensed at -196 °C. Hydrogen (1.3 atm) was admitted into the tube.
Upon thawing, a yellow precipitate formed. 1H and 19F NMR revealed
formation of a mixture of Cp*2ZrCl2, Cp*2ZrHCl, CH3F, and a trace
amount of Cp*2ZrHF. The mixture was allowed to stand at room
temperature for 1 day. The reaction mixture then consisted mostly of
Cp*2ZrHCl and Cp*2ZrClF and methane. Only small amounts of
Cp*2ZrHF and Cp*2ZrF2 were present. For CH3F: 1H NMR (C6D12) δ
4.08 (d, JH-F ) 46.4 Hz); 19F NMR δ -205.0 (q, JH-F ) 45.2 Hz).
For Cp*2ZrClF: 1H NMR δ 1.901 (s); 19F NMR δ 129.5 (s).
Preparation of Cyclopropylcarbinyl Fluoride. Cyclopropylcarbi-
nyltosylate (3.59 g, 0.0159 mmol) was added to “anhydrous” tetrabu-
tylammonium fluoride26 (prepared from 10 g [0.038 mmol] of TBAF‚
3H2O), and the oily mixture was stirred for 2 h. The solution was
freeze-pump-thawed three times on the vacuum line and the volatiles
of the reaction were vacuum transferred into an empty ampule. About
1 mL of material was collected, consisting of an organic and aqueous
1
layer. The organic layer was separated by removal with a syringe. H
NMR analysis of the organic layer showed ∼50% cyclopropylcarbinyl
fluoride along with olefin(s) and other unidentified impurities. Pure
cyclopropylcarbinyl fluoride was obtained by treating 7 µL of the crude
material with 50 mg of Cp*2ZrH2 in cyclohexane-d12. Immediately
following mixing, the solution was freeze-pump-thawed three times
and the volatiles were transferred to an empty NMR tube. This sample
analyzed as >95% pure cyclopropylcarbinyl fluoride in C6D12. 19F NMR
(22) Schock, L. E.; Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.
(23) Yoneda, N.; Fukuhara, T.; Nagata, S.; Suzuki, A. Chem. Lett. 1985,
1693.
(25) Blayney, M. B.; Winn, J. S.; Nierenberg, D. W. Chem. Eng. News
1997, 75 (19), 7.
(24) Nesmeyanov, A. N.; Vanchikov, A. N.; Lisichkina, I. N.; Lazarev,
V. V.; Tolstaya, T. P. Dokl. Akad. Nauk SSSR Ser. Khim. 1980, 255, 1136.
(26) Cox, D. P.; Terpinski, J.; Lawrynowicz, W. J. Org. Chem. 1984,
49, 3216.

Carbon-Fluorine Bond ActiVation with Cp*2ZrH2
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10979
1
(C6D12): δ -144.4 (td, JH-F ) 51 Hz); H NMR δ 4.05 (dd, JH-F
)
NMR tube was charged with 12 mg of Cp*2Zr(o-C6H4F)H, dissolved
in cyclohexane-d12. The tube was heated at 80 °C for 18 days producing
Cp*2Zr(C6H5)F cleanly and quantitatively. The volatiles were removed
in vacuo and the residue was recrystallized in pentane at -30 °C to
yield a single crystal that was sent for elemental analysis. Anal. Calcd
for C26H35ZrF: C, 68.22; H, 7.71. Found: C, 67.91; H, 7.58.
49 Hz, 2 H), 1.10 (m, 1 H), 0.52 (m, 2 H), 0.23 (m, 2 H); MS (m/z) 74
(M+). To this solution, 0.40 µL of Me3SiSiMe3 was added as a standard
to determine the amount of cyclopropylcarbinyl fluoride present in
solution.
Reaction of Cyclopropylcarbinyl Fluoride with 1. To a resealable
NMR tube, 1 (10 mg, 0.027 mmol) was added and dissolved in a
solution of cyclopropylcarbinyl fluoride (0.028 mmol) [see preparation
of cyclopropylcarbinyl fluoride] in C6D12. After 15 min at room
temperature, NMR analysis revealed a clean 1:1 mixture of Cp*2ZrHF,
Cp*2Zr(n-butyl)H, and unreacted cyclopropylcarbinyl fluoride. No
methylcyclopropane was observed. For Cp*2Zr(n-butyl)H: 1H NMR
(C6D12) δ 5.20 (s, ZrH, 1 H), 1.90 (s, Cp*, 30 H), 0.85 (t, ZrCH2CH2-
CH2CH3, 3 H), 1.17 (sex, ZrCH2CH2CH2CH3, 2 H), 0.10 (m, ZrCH2CH2-
CH2CH3, 2 H), -0.04 (m, ZrCH2CH2CH2CH3, 2 H). For further
characterization of Cp*2Zr(n-butyl)H, the solution was freeze-pump-
thawed three times and 1.3 atm of H2 was admitted into the tube. After
5 min, Cp*2Zr(n-butyl)H had fully reacted to form butane and
Cp*2ZrH2. For butane: 1H NMR (C6D12) δ 1.29 (m, 4 H), 0.89 (m, 6
H); MS (m/z) 58 (M+).
Reaction of Fluorobenzene with Cp*2ZrH2. A resealable NMR
tube was charged with 21 mg (0.058 mmol) of 1 and dissolved in
cyclohexane-d12. Fluorobenzene (5.4 µL, 0.058 mmol, F ) 1.02) was
added via syringe. The tube was then freeze-pump-thaw degassed
three times and 1.3 atm of H2 was admitted into the tube. The tube
was heated at 85 °C for 40 days, monitoring periodically over this time.
At the end, the reaction mixture consisted of a 1:1:0.75 mixture of
Cp*2ZrHF, benzene, and Cp*2Zr(C6H5)F. For Cp*2Zr(C6H5)F: 1H NMR
(C6D12) δ 1.72 (s, 30 H), 6.89 (m, 2 H), 7.00 (m, 3 H); 19F NMR δ
139.7 (s). For C6H6: 1H NMR δ 7.21 (s). Cp*2Zr(o-C6H4F)H was
observed as a transient species.
Preparation of Cp*2Zr(C6H5)F. Into an ampule, 100 mg of
Cp*2ZrF2 (0.25 mmol) and 23 mg of phenyllithium (0.27 mmol) were
added and suspended in ∼10 mL of toluene. The mixture was freeze-
pump-thawed and heated to 85 °C for 5 h with stirring. The reaction
mixture was stripped to dryness and ∼10 mL of pentane was added.
Filtration over dried Celite, concentration, and crystallization at -30
°C yielded 47 mg (41%) of Cp*2Zr(C6H5)F. (See NMR data above.)
Reaction of 1-Fluoronaphthalene with Cp*2ZrH2. A resealable
NMR tube was charged with 15 mg (0.041 mmol) of 1 and dissolved
in cyclohexane-d12. 1-Fluoronaphthalene (4.52 µL, 0.041 mmol, F )
1.33) was added via syringe. The tube was freeze-pump-thaw
degassed three times and 1.3 atm of H2 was admitted into the tube.
The tube was heated to 85 °C for 4 days producing Cp*2ZrHF and
naphthalene in quantitative yield. For C10H8: 1H NMR (C6D12) δ 7.33
(m, 4 H), 7.70 (m, 4 H); MS (m/z) 128 (M+).
Thermal Decomposition of Cp*2ZrH2. A resealable NMR tube was
charged with 10 mg of Cp*2ZrH2 and placed under high vacuum on
the vacuum line. The tube was immersed in an 85 °C oil bath for 19
h over which time a small amount of red solid had formed. The solid
residue was dissolved in C6D12 and analyzed by 1H NMR spectroscopy
revealing a 5:1 ratio of Cp*2ZrH2 and Cp*(C5Me3(CH2)2)Zr. For
Cp*(C5Me3(CH2)2)Zr: 1H NMR (C6D12) δ 2.01 (s, 15 H), 1.72 (s, 3
H), 1.31 (s, 6 H), 0.80 (d, 2 H, J ) 6.2 Hz), 0.47 (d, 2 H, J ) 6.2 Hz).
Acknowledgment. The authors thank the U.S. Department
of Energy, Grant FG02-86ER13569 for support of this work.
Synthesis of Cp*2Zr(o-C6H4F)H. In the drybox, 50 mg (0.137
mmol) of 1 and 27 mg (0.069 mmol) of Hg(o-C6H4F)2 were added to
a vial. Pentane (∼5 mL) was added and the mixture was stirred for 30
min at room temperature. Vigorous evolution of H2 occurred and
elemental mercury was formed. The product mixture was filtered over
Celite and stripped to dryness leaving a yellow microcrystalline mass
of >95% pure Cp*2Zr(o-C6H4F)H (62 mg, 98%). X-ray quality crystals
Supporting Information Available: A description of the
X-ray experimental procedures and tables giving crystallographic
data, intramolecular distances and angles, and positional and
thermal parameters for 1, 2, Cp*2ZrF2, Cp*2Zr(o-C6H4F)H, and
Cp*2Zr(C6H5)F (PDF) and X-ray crystallographic data (CIF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
1
were obtained by crystallization from pentane at -30 °C. H NMR
(C6D12) δ 1.82 (s, 30 H), 6.34 (m, 1H), 6.59 (s, 1 H, ZrH), 6.61 (m, 1
H), 6.85 (m, 2H). 19F NMR δ -28.0 (m). Anal. Calcd for C26H35ZrF:
C, 68.22; H, 7.71. Found: C, 68.15; H, 7.91.
Thermolysis of Cp*2Zr(o-C6H4F)H. In the drybox, a resealable
JA016087L