Replacing chloride by alkoxide: Cp2Zr(H)OR, searching for alternatives to schwartz's reagent

Article abstract of DOI:10.1021/om8008734

Attempts to synthesize zirconocene hydrido alkoxide species, Cp ₂Zr(H)OR, via several synthetic pathways consistently failed to yield the targeted complexes, which seem prone to undergo disproportionation into Cp₂ZrH₂ and

Full text of DOI:10.1021/om8008734

4912 Organometallics 2009, 28, 4912–4922
DOI: 10.1021/om8008734
Replacing Chloride by Alkoxide: Cp2Zr(H)OR, Searching for
Alternatives to Schwartz’s Reagent
Philippe Perrotin, Ibrahim El-Zoghbi, Paul O. Oguadinma, and Frank Schaper*
ꢀ ꢀ ꢀ ꢀ ꢀ
Departement de Chimie, Universite de Montreal, Montreal, Quebec, H3C 3J7, Canada
Received September 8, 2008
Attempts to synthesize zirconocene hydrido alkoxide species, Cp2Zr(H)OR, via several synthetic
pathways consistently failed to yield the targeted complexes, which seem prone to undergo
disproportionation into Cp2ZrH2 and a bisalkoxide complex. Reaction of Cp2ZrH2 with HOR,
Me3SiOR, or Ph2CO yielded the corresponding bisalkoxide complexes Cp2Zr(OR)2, of which
Cp2Zr{OC(H)Ph2}2 was characterized by an X-ray diffraction study. Insertion of vinyl ethers into
Cp2ZrH2 yielded Cp2Zr(OR)2 and Cp2Zr(Et)OR. Attempted hydrogenation of Cp2Zr(Me)OR or
reaction of Cp2Zr(BH4)OR with NEt3 did not yield the targeted complexes. Cp2Zr(H)OC6H5 and
Cp2Zr(H)OC6F5 could be obtained, however, as transient species by β-H elimination from Cp2Zr-
(tBu)OR, ligand exchange between Cp2ZrH2 and Cp2Zr(OC6F5)2, or protonation in the presence of
olefin to yield the corresponding hydrozirconation products. In hydrozirconation reactions of
styrene both species are highly regioselective. The alkoxide substituent failed to inhibit β-H
elimination in hydrozirconations of trans-3-hexene or β-OR elimination in reactions with vinyl
ethers. On the other hand, it imparted a vastly increased thermal stability to the tert-butyl complexes
Cp2Zr(tBu)OR, which were stable for up to several months in solution, before they isomerize to the
respective isobutyl complexes. Cp2Zr(iBu)OC6H5 was characterized by X-ray crystallography.
Introduction
Secondary alkyl species were obtained in mixtures with the
terminal species when aromatic or polar substituents were
present.5-7 Attempts to control the regioisomeric ratio of
thermodynamic product mixtures or to trap kinetic products
met only limited success.7-9 The lack of access to secondary
alkyl complexes precluded enantioselective hydrozirconation
reactions, with the notable exception of Sita’s cyclopentadienyl
acetamidinate zirconium complexes.10 The reduced tendency of
this mixed ligand system to undergo β-H eliminations allowed
the isolation of a secondary alkyl zirconium complex as a
diastereomeric mixture due to the chirality of the zirconium
center.
Several attempts have been undertaken to improve on the
original Schwartz’s reagent, Cp2Zr(H)Cl. Substituted cyclo-
pentadienyl ligands, such as C5H4Me and C5Me5, have been
employed, mainly with the goal to increase solubility.8,9,11
Exchange of the chloride ligand with bromide proved
Hydrozirconation with Schwartz’s reagent, Cp2Zr(H)Cl,1
has found application in the direct functionalization of non-
activated olefins and alkynes, in particular when combined with
transmetalation.2 While the hydrozirconation of alkynes is
widely used, particularly in transmetalation reactions, hydro-
zirconation of olefins to generate valuable synthons is some-
what limited by the peculiarities of the hydrozirconation
reagent, Cp2Zr(H)Cl. One of its most noteworthy features is
that only primary zirconocene alkyl complexes are obtained.
Secondary alkyls, formed by hydrozirconation of internal
olefins or by putative 2,1-insertion of terminal olefins, isomerize
rapidly along the aliphatic chain to a terminal position, pre-
sumably via a β-H elimination/olefin reinsertion pathway.3,4
*Corresponding author. E-mail; Frank.Schaper@umontreal.ca.
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2009 American Chemical Society
pubs.acs.org/Organometallics
Published on Web 08/19/2009

Article
Organometallics, Vol. 28, No. 17, 2009 4913
to reduce reactivity,9 while exchange with a sulfonate
anion yielded highly active and soluble hydrozirconation
Scheme 1
reagents.12 Husgen and Luinstra found that hydrozircona-
€
tion of styrene with the latter complexes favored 1,2-inser-
tion products under kinetic control, while isomerization to
the thermodynamically controlled product mixture in-
creased the amount of secondary alkyl species present.12
Wipf et al. were able to trap secondary alkyl complexes,
formed initially in the hydrozirconation of 2- and 4-octene,
in mixtures with the thermodynamically favored terminal
alkyl species using in situ generated Cp2Zr(H)OTf.7
coordination of an oxygen atom to a zirconocene alkyl
or hydride complex has been evoked to explain the obser-
ved regiochemistry in hydrozirconations of unsaturated
alcohols.7,23
In the following we present our attempts to synthesize
unsubstituted Cp2Zr(H)OR complexes and our investiga-
tions into the reactivity of these complexes in hydrozircona-
tion reactions.
We decided to investigate the effects of replacing the
chloride ligand with alkoxide on reactivities and selectivities
in hydrozirconation. The more Lewis-basic alkoxide ligand
is supposed to render the zirconocene less prone to undergo
β-H eliminations, and the wide variety of available alcohols,
including chiral derivatives, would drastically increase the
possibilities to control the hydrozirconation reaction. Pre-
cedence for zirconocene hydrido alkoxide species has been
reported in the literature. Hydrido enolate complexes were
obtained after CO insertion into zirconacycles,13-15 while
hydrogenation after CO insertion in several cases yielded
hydrido alkoxide species.15-17 Bradley et al. obtained bis-
(indenyl)zirconium hydrido alkoxide complexes by oxidative
addition of ethers to Zr(II) complexes or reactions of dihy-
dride complexes with vinyl ether.18,19 Finally, in two cases
the direct synthesis of a Cp*2Zr(H)OR complex (Cp* =
Results and Discussion
Zirconocene Dihydride as Precursor. Protonation of com-
mercially available zirconocene dihydride by an alcohol,
following the procedure established by Schock and Marks
for the synthesis of Cp*2Zr(H)OtBu,21 would provide a
straightforward access to the targeted zirconocene hydrido
alkoxide complexes. In our case, room-temperature addition
of 1 equiv of ROH (R: Ph, C6F5, tBu) to a stirred suspension
of Cp2ZrH2 only resulted in the formation of the toluene-
soluble zirconocene dialkoxide complexes Cp2Zr(OR)2,
1a-c, and a white residue (Scheme 1). Compounds 1a-c
were identified by their NMR spectra in comparison to
literature data.21,24-26 The remaining insoluble material
isolated in these reactions was identified as Cp2ZrH2 by
treatment with excess acetone, which revealed only 1H
NMR signals associated with the formation of the 1,2-
insertion product of acetone: Cp2Zr(OiPr)2 (1H NMR:
δ 6.03 (s, 10H), 4.10 (q, 2H, J = 6 Hz), 1.07 (d, 12H, J =
6 Hz)).27 Treatment with acetone proved to be a convenient
and reliable technique to test for zirconium hydride bonds in
insoluble zirconocene complexes. Modifying the reaction
solvent (THF or toluene) or the rate of addition of the
alcohol to the Cp2ZrH2 suspension in THF did not affect
the outcome of the reaction.
21
C5Me5) by protonation of [Cp*2ZrH3]Li20 or Cp*2ZrH2
with alcohol was reported. It is noteworthy that isolated
zirconocene hydrido alkoxide complexes carried at least one
highly substituted cyclopentadienyl or indenyl ligand. For
applications as stoichiometric or catalytic reagents, however,
unsubstituted zirconocene complexes would be of much
higher interest, partly due to the reduced reactivity of sub-
stituted zirconocene complexes for insertion into the metal
hydride bond,22 partly due to economic reasons. To the best
of our knowledge, synthesis of Cp2Zr(H)OR complexes has
not been reported before, although their intermediate for-
mation has been postulated from NMR data,14,17 and
(12) Luinstra, G. A.; Rief, U.; Prosenc, M. H. Organometallics 1995,
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Grubbs, R. H.; Bercaw, J. E. J. Am. Chem. Soc. 1983, 105, 2068. Barger,
P. T.; Bercaw, J. E. Organometallics 1984, 3, 278. McDade, C.; Bercaw, J. E.
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A. L.; Geib, S. J. J. Organomet. Chem. 1988, 358, 169. Roddick, D. M.;
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Tilley, T. D. Organometallics 1989, 8, 324. Choukroun, R.; Douziech, B.;
Soleil, F. J. Chem. Soc., Chem. Commun. 1995, 2017. Karsch, H. H.;
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(15) Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E.
J. Am. Chem. Soc. 1978, 100, 2716.
Earlier success in the synthesis of Cp*2Zr(H)OR (R = 2,6-
iPr2C6H3,20 tBu21) might be related to the inaccessibility of the
sterically crowded dialkoxide complexes in the presence of the
Cp* ligands, while the less hindered unsubstituted zircono-
cenes favor the formation of a mixture of the dialkoxide
(23) Liu, X.; Ready, J. M. Tetrahedron 2008, 64, 6955. Zhang, D. H.;
Ready, J. M. J. Am. Chem. Soc. 2007, 129, 10288.
€
€
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Bercaw, J. E. J. Am. Chem. Soc. 1979, 101, 218. Threlkel, R. S.; Bercaw, J.
E. J. Am. Chem. Soc. 1981, 103, 2650. Vaughan, G. A.; Hillhouse, G. L.;
Rheingold, A. L. J. Am. Chem. Soc. 1990, 112, 7994.
(24) Andra, K.; Hille, E. Z. Chem. 1968, 8, 65. Andra, K.; Hille, E. Z.
Naturforsch., B: Chem. Sci. 1969, 24, 169.
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ꢀ
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(17) Gell, K. I.; Posin, B.; Schwartz, J.; Williams, G. M. J. Am. Chem.
Soc. 1982, 104, 1846.
J. Organomet. Chem. 1995, 485, 153.
(27) Buchwald, S. L.; LaMaire, S. J.; Nielsen, R. B.; Watson, B. T.;
(18) Bradley, C. A.; Veiros, L. F.; Pun, D.; Lobkovsky, E.; Keresztes,
I.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128, 16600.
(19) Bradley, C. A.; Veiros, L. F.; Chirik, P. J. Organometallics 2007,
26, 3191.
(20) Hoskin, A. J.; Stephan, D. W. Organometallics 2000, 19, 2621.
(21) Schock, L. E.; Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.
(22) Chirik, P. J.; Bercaw, J. E. Organometallics 2005, 24, 5407.
King, S. M. Org. Synth. 1993, 71, 77.
(28) Averaged structural data from unsubstituted zirconocene dia-
lkoxide complexes in the CSD database: JAFYUK, JAQSOJ, JAQSUP,
KARKUJ, WEKYOB, XENXIX, YIVWUV, YUWDUP, ZIMXUO,
ZIMXUO01
(29) Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci. 2002, B58,
380.

4914 Organometallics, Vol. 28, No. 17, 2009
Perrotin et al.
Scheme 2
Scheme 3
complex and zirconocene dihydride. This might be due to
kinetic reasons (higher solubility and thus reactivity of Cp2Zr-
(H)OR compared with Cp2ZrH2), thermodynamic reasons
(disproportionation of Cp2Zr(H)OR into Cp2ZrH2 and
Cp2Zr(OR)2), or both.
Wipf et al. demonstrated the in situ formation of Cp2Zr-
(H)OTf from Cp2ZrH2 and TMSOTf.7 NMR-scale reactions
of Cp2ZrH2 with 1 equiv of PhOSiMe3 or C6F5OSiMe3 at
60 °C, however, again provided evidence only for the for-
mation of the respective dialkoxide complexes 1a and 1b,
respectively, along with the formation of Me3SiH (1H NMR:
δ 4.16 (m, 4 Hz), 0.01 (d, 4 Hz)) and an unidentified, benzene-
d6-insoluble precipitate (Scheme 2). The latter did not con-
tain any Zr-H bonds, as evidenced by the absence of a
reaction product with acetone. No reaction was observed
between Cp2ZrH2 and tBuOSiMe3 even at 80 °C.
Figure 1. Molecular structure of 1d. Disordered solvent and
hydrogen atoms (with the exception of H23 and H36) were
omitted for clarity. Thermal ellipsoids are drawn at the 50%
probability level. Selected structural data (average literature
values in square brackets, Z1: centroid C1-C5, Z2: centroid
C6-C10):28,29 Zr-O1: 1.961(2) A, Zr-O2: 1.984(2) A [1.993(5)],
˚
˚
˚
˚
O1-Zr-O2: 98.3(1)° [98.6(4)], Zr1-Z1: 2.25 A, Zr-Z2: 2.24 A
[2.24(1)], Z1-Zr-Z2: 127° [129(1)].
Alternatively to protonation by an alcohol, insertion of a
carbonyl bond into the Zr-H bond may provide a suitable
route to a Cp2Zr(H)OR complex. NMR spectra of the
reaction of Cp2ZrH2 with 1 equiv of benzophenone in
C6D6, however, displayed only signals for the dialkoxide
complex Cp2Zr(OCHPh2)2, 1d (Scheme 3). Reactions on a
preparative scale with 1 equiv of benzophenone yielded
Scheme 4
analytically pure 1d 1/2 toluene in moderate yields of
3
1
24%. The H NMR of the complex exhibits a singlet at
5.99 ppm (2H) for the CHPh2 protons, which shows correla-
tion by HSQC with a 13C NMR signal at 86.9 ppm.
Further confirmation of the assignment of 1d as a dialk-
oxide complex was obtained by X-ray crystallography
(Figure 1). As often observed in sterically more crowded
alkoxide complexes, the substituents at the oxygen atoms
aredirectedtotheoutside ofthe complex. BothCHPh2 groups
rotate in a way to orientate the hydrogen atom toward a
cyclopentadienyl ligand. Bond distances and angles around
the zirconium central atom are in the range observed for other
zirconocene dialkoxides (Figure 1). Despite the four phenyl
substituents present, neither intramolecular nor intermolecu-
lar π-π interactions were observed in the structure.
approximate 1:1 ratio that were assigned to Cp2Zr(OEt)2,
1e,5,30 and Cp2Zr(Et)OEt, 2e,31 by comparison to published
NMR data (Scheme 4). Reaction of Cp2ZrH2 with 1 equiv of
n-butyl vinyl ether under identical conditions afforded a
mixture of Cp2Zr(OnBu)2, 1f, and Cp2Zr(Et)OnBu, 2f, the
identity of which was established by NMR spectroscopy.
The 1H NMR resonances of the ethyl group in Cp2Zr-
(Et)OnBu exhibit a characteristic pattern with a triplet at
1.56 ppm and an upfield quadruplet at 1.02 ppm, which
integrate for 3H and 2H, respectively, relative to the 10
cyclopentadienyl protons. Confirmation of our assignment
for 1f was obtained by independent preparation from the
reaction of Cp2ZrH2 with excess n-butanol (Scheme 4).
The preparation of (η5-1,3-iPr2C9H5)2Zr(H)OMe by reac-
tion of the corresponding bis(indenyl)zirconium dihydride
complex with methyl vinyl ether18 drew our attention be-
cause of the commercial availability of various alkyl vinyl
ethers. Reaction of Cp2ZrH2 with 1 equiv of ethyl vinyl ether
in toluene at 60 °C in a sealed vessel afforded after 12 h
a homogeneous greenish solution. Formation of ethylene
(5.25 ppm) was established by monitoring the reaction by 1H
NMR. Removal of the volatiles yielded a thick brown oil, the
NMR spectra of which exhibit two sets of signals in an
(30) Gray, D. R.; Brubaker, C. H. Inorg. Chem. 1971, 10, 2143.
(31) Alt, H. G.; Denner, C. E. J. Organomet. Chem. 1990, 391, 53.

Article
Additional heating (5 days, 70 °C) of the 1e/2e mixture did
Organometallics, Vol. 28, No. 17, 2009 4915
Scheme 6
not affect their ratio, nor did the addition of further
EtOCHdCH2 (5 days, 70 °C). These results indicate that
Cp2Zr(H)OEt was indeed obtained as a transient species and
irreversibly trapped either by ethylene (formed during the
reaction) or by another molecule of vinyl ether.32 Reactions
of Cp2ZrH2 with n-butyl vinyl ether conducted under an
open N2 atmosphere in THF to decrease the partial pressure
of ethylene or in the presence of styrene to trap the zircono-
cene hydride intermediate afforded only mixtures of several
zirconocene complexes, with 2f as the main reaction product.
None of these reaction products indicated the presence of
an inserted styrene (NMR) or contained a Zr-H bond
(no reaction with acetone).
Hydrogenation of Zirconium Alkyls. Preparation of zirco-
nocene hydride and dihydride complexes has been reported
in the literature via hydrogenation of the corresponding
zirconocene methyl complexes with various degrees of suc-
cess. To this effect, following the reported procedure for the
preparation of Cp2Zr(Me)OtBu, 3c,33 the methyl alkoxide
zirconocenes Cp2Zr(Me)OPh, 3a, and Cp2Zr(Me)OC6F5,
3b, were prepared by reaction of Cp2ZrMe2 with 0.9 equiv
of the corresponding alcohol (Scheme 5). The reaction is
quantitative with respect to the alcohol (1H NMR), and
spectroscopic data were in agreement with literature values
for these complexes obtained by other pathways.26,34 NMR
spectra of benzene-d6 solutions containing these complexes
under an atmosphere of hydrogen remained, however,
unchanged even after prolonged heating (days) at 110 °C.
At the same time, NMR signals of residual Cp2ZrMe2,
present due to the slight excess employed in the preparation,
disappeared readily even at room temperature.
protonation of Cp2Zr(H)(BH4) with 1 equiv of phenol. The
equilibrium is readily displaced by providing 1a in excess,
and only traces of Cp2Zr(BH4)2 could be detected by NMR
after equilibration (48 h) of a 2:1 ratio solution of 1a and
Cp2Zr(BH4)2. Unfortunately, addition of triethylamine to
this reaction mixture resulted only in the formation of
Cp2Zr(H)(BH4) and re-formation of 1a. Presumably the
reaction of triethylamine with even trace amounts of Cp2Zr-
(BH4)2 is faster than with Cp2Zr(BH4)OPh, thus completely
displacing the ligand exchange reaction to the left.
Hydride Eliminations from tert-Butyl Complexes. Chirik
and co-workers reported the preparation of several ring-sub-
stituted zirconocene chloro hydride complexes by reaction of
the corresponding zirconocene dichloride with tBuLi, followed
by spontaneous β-H elimination of the unstable Zr-tBu inter-
mediate.35 Under comparable conditions, unsubstituted zirco-
nocene reinserts isobutene to form Cp2Zr(iBu)Cl,36 which can
react nevertheless as a hydrozirconation reagent.37 Motivated
by these reports, we investigated the possibility to generate a
Cp2Zr(H)OR species by isobutene elimination from the corre-
sponding tert-butyl complex. Initial reactions of the zircono-
cene chloro alkoxide complex Cp2Zr(OtBu)Cl38 with tert-
butyllithium afforded a mixture of products, presumably due
to unselective substitution of the chloride or the alkoxide
ligand. We thus turned our attention to the corresponding
dialkoxide complexes. Addition of 1 equiv of tBuLi (1.5 M in
pentane) to a cooled (-78 °C) solution of diphenolate complex
1a, followed by filtration of PhOLi, afforded a hexane-soluble,
bright yellow powder. The presence of a singlet at 1.43 ppm
integrating to 9H in the aliphatic region of its 1H NMR
spectrum and resonances at 50.0 and 37.3 ppm in its 13C
NMR spectrum indicate the presence of a tert-butyl group,
allowing the structural assignment of Cp2Zr(tBu)OPh, 5a
(Scheme 7). No indication for the formation of an isobutyl
or a hydride species could be gained from the NMR spectra.
Elemental analyses consistent with this formula were obtained,
but despite repeated efforts, we were unable to obtain a single
crystal to confirm the rather unusual presence of a Zr-bonded
tBu group by X-ray diffraction. Derivatization of 5a by
insertion of 2,6-xylyl isonitrile into the Zr-tBu bond, however,
afforded crystals of Cp2Zr(OPh)C(tBu)dN(C6Me2H3), 6, sui-
table for an X-ray diffraction study (Scheme 7, Figure 2).
Unlike most literature examples,39 insertion of isonitrile into
5a required heating to proceed.
Scheme 5
€
Synthesis via a Borohydride Complex. Husgen and Luin-
stra reported the preparation of several zirconocene hydrido
sulfonate complexes by a two-step procedure:12 the borohy-
dride complex Cp2Zr(BH4)OSO2R, prepared by ligand re-
distribution between an equimolar mixture of Cp2Zr-
(OSO2R)2 and Cp2Zr(BH4)2, was reacted with triethylamine
to generate in high yield the corresponding hydrido sulfonate
Cp2Zr(H)OSO2R. NMR-scale reactions of Cp2Zr(BH4)2
with 1 equiv of 1a in benzene-d6 showed the formation of a
novel zirconocene of the formula Cp2Zr(BH4)OPh, 4, as
1
revealed by the appearance of new resonances in the H
NMR spectrum for the Cp protons (5.80 ppm) and the meta
protons of the phenoxide substituent (6.63 ppm) (Scheme 6).
After 2 days at room temperature, 4 was found to be in
equilibrium with the starting material: Cp2Zr(BH4)2 and 1a.
The same product mixture could be obtained directly by
An X-ray diffraction study confirmed the structure of
the insertion product 6 and thus the initial assignment of
5a (Figure 2). The main feature of this structure is the
(32) The proposed course of the reaction would require that approxi-
mately one-third of Cp2ZrH2 remains unreacted. However, neither did
we observe any remaining precipitate nor did the spectra exhibit
resonances of the sparingly soluble dihydride complex. While we did
not investigate the fate of the dihydride in detail, coloration of the
solution seems to indicate a certain amount of reductionto zirconium(II)
species.
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4916 Organometallics, Vol. 28, No. 17, 2009
Perrotin et al.
Scheme 7
three-membered ring formed by a dative donation of the N
lone pair to the metal center. Structural data of 6, in
particular of the three-membered ring, are comparable to
those for similar insertion products of isonitriles into a Zr-C
bond (see Figure 2, caption).
Figure 2. Molecular structure of 6. Hydrogen atoms and the
disorder of a cyclopentadienyl ring were omitted for clarity.
Thermal ellipsoids are drawn at the 50% level. Selected geome-
trical data (averaged literature values in square brackets):29,40
Zr1-C25: 2.247(3) [2.240(5)]; Zr1-N1: 2.254(2) [2.238(7)];
In benzene-d6 solution at room temperature, all signals
associated with 5a disappeared over a period of 2 months.
At 65 °C, complete decomposition of 5a was observed in
3 days. The colorless, benzene-insoluble precipitate formed
during the reaction showed no further reaction with acet-
one. Of the benzene-soluble fraction, which accounts for
approximately half of the initial zirconocene concentration,
the major decomposition species (60%) was identified
˚
C25-N1: 1.279(3) [1.274(2)], Zr1-O1: 2.075(2) A, O1-C11:
˚
1.323(3) A, Zr1-O1-C11: 143.3(2)°.
instead a conformation minimizing steric interactions of the
isobutyl group with the phenoxide and cyclopentadienyl
ligands. The zirconium carbon bond of the isobutyl ligand
1
by H and 13C NMR as Cp2Zr(iBu)OPh, 7a (Scheme 7),
˚
of 2.307(3) A is at the longer end of the range observed in
41
accompanied by 1a (40%). The zirconium-bound isobutyl
group in 7a gives rise to a multiplet at 2.21 ppm and two
˚
zirconocene neo-pentyl complexes (2.256-2.296 A), but
still close to the average for zirconocene alkyl com-
1
doublets at 1.15 and 1.05 ppm in the H NMR spectra,
˚
plexes (2.243-2.397 A) in general, or (C5R5)2Zr(CH2R)OR
integrating for one, six, and two protons, respectively. To
confirm this assignment, 7a was prepared independently by
reaction of 1a with iBuMgCl in Et2O and obtained as a
thick oil in 90% purity. Although small amounts of
colorless crystals suitable for X-ray diffraction analysis
(vide infra) formed after 2 weeks at room temperature
(accompanied by extensive decomposition), several at-
tempts to obtain analytically pure, solid samples of 7a
failed. Heating of solid 5a under a dynamic vacuum for
20 h at 90 °C to force elimination of isobutene yielded only
unchanged 5a, traces of 7a, and a precipitate, which showed
no reaction with acetone. When 1 atm of H2 was added to a
sample of 5a in benzene-d6, no hydrogenation of the tert-
butyl group was observed either at room temperature or at
110 °C. After 5 days at this temperature only decomposition
products were obtained, namely, 1a, isobutene, CpH,
PhOH, and some insoluble materiel (no reaction with
acetone).
29,42
˚
complexes in particular (2.265-2.337 A).
The observed stability of the obtained zirconocene tert-
butyl complex 5a is quite remarkable. As a matter of fact, we
are aware of only two other zirconium complexes carrying
tert-butyl substituents that do not readily decompose or
rearrange at room temperature: a tetrahedral complex bear-
ing a tripodal triamide ligand prepared by Gade and co-
workers43 and Sita’s cyclopentadienyl zirconium acetamidi-
nates.44 Both complexes include N donors in their ligand
framework, which suggests a crucial influence of π-donation
from the N to the metal center. Our results advocate that the
alkoxide ligand reduces the propensity of the complexes to
undergo β-H elimination in the same way, presumably by
filling the a1 orbital of the transition metal,45 thus reducing
(41) Jeffery, J.; Lappert, M. F.; Luong-Thi, N. T.; Webb, M.; At-
wood, J. L.; Hunter, W. E. J. Chem. Soc., Dalton Trans. 1981, 1593.
Dreier, T.; Bergander, K.; Wegelius, E.; Frohlich, R.; Erker, G. Organome-
tallics 2001, 20, 5067. Chirik, P. J.; Dalleska, N. F.; Henling, L. M.; Bercaw, J.
E. Organometallics 2005, 24, 2789.
(42) Determined from a structural search on Cp and Ind zirconium
complexes with unchelated terminal alkyl ligands in the Cambridge
Structural Database.
(43) Gade, L. H.; Renner, P.; Memmler, H.; Fecher, F.; Galka, C. H.;
Laubender, M.; Radojevic, S.; McPartlin, M.; Lauher, J. W. Chem.;
Eur. J. 2001, 7, 2563. Renner, P.; Galka, C.; Memmler, H.; Kauper, U.; Gade,
L. H. J. Organomet. Chem. 1999, 591, 71.
(44) Harney, M. B.; Keaton, R. J.; Fettinger, J. C.; Sita, L. R. J. Am.
Chem. Soc. 2006, 128, 3420. Keaton, R. J.; Koterwas, L. A.; Fettinger, J. C.;
Sita, L. R. J. Am. Chem. Soc. 2002, 124, 5932.
Compound 7a is the first isobutyl zirconocene complex
characterized by X-ray diffraction (Figure 3). The alkyl
ligand displays neither β- nor γ-agostic interactions with
the metal center, as expected for a bulky alkyl substituent
and in the presence of a π-donating alkoxide ligand. It adopts
(40) Values determined from 16 comparable complexes in the CSD
database with the following ref codes: BEHWAM, CUYHIN, FAZ-
MUO, GERSEC, ICAJUS, IGOCAI, KIHLES, LIFVAX, NETYOA,
NETYUG, NIKXEK, NIYXEY, PUXSUW, RAQXEM, UKIBEV,
YUVMAD
(45) Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729.

Article
Organometallics, Vol. 28, No. 17, 2009 4917
Scheme 8
Figure 3. Molecular structure of 7a. Hydrogen atoms and the
disorder of a cyclopentadienyl ring were omitted for clarity.
Thermal ellipsoids are drawn at the 50% level. Selected geome-
trical data (Z1: centroid C1-C5, Z2: centroid C6-C10):
˚
˚
˚
˚
Zr-C20: 2.307(3) A, Zr1-Z1: 2.19 A, Zr1-Z2: 2.23 A,
˚
(Scheme 7). Reactions of 5a with 1 equiv of benzophenone at
65 °C for 3 days afforded a mixture of 1a (22-24%), 1d
(21-23%), and a new species (53-57%) identified as Cp2Zr-
(OPh)(OCHPh2), 8, based on resonances at 5.93 ppm (10H)
for the cyclopentadienyl protons, at 6.02 ppm (1H) for
CHPh2, and the associated resonances for the aromatic
protons. In agreement with this assignment, the same mix-
ture of products was obtained by ligand exchange reactions
between 1a and 1d (Scheme 7). Reaction between 5a and
styrene or 1-hexene did not afford the corresponding inser-
tion products.
The fact that reaction of 5a with phenol generates iso-
butene rather than isobutane indicates that direct proton-
ation of the alkyl group is only a minor process and 1a is
instead predominately formed by protonation of the zirco-
nocene hydride 9a after isobutene elimination. Hydride 9a
can also be trapped by benzophenone to yield the corre-
sponding alkoxide complexes. Only a statistical mixture
of the dialkoxide complexes 1a, 1d, and 8 was obtained,
indicating facile exchange of the alkoxide ligands under these
conditions. The lack of reactivity of 5a toward hexene and
particularly (vide infra) styrene is somewhat surprising, but
might be related to the rather harsh reaction conditions
required for the elimination of isobutene (70 °C, days).
To decrease the electron-donating properties of the OPh
ligand in 5a, we prepared the pentafluorophenolate deriva-
tive Cp2Zr(tBu)OC6F5, 5b, by addition of 1 equiv of tBuLi to
a cooled (-78 °C) solution of 1b in Et2O (Scheme 8). The
hexane-soluble product was isolated in moderate yield after
filtration to remove the C6F5OLi formed during the reaction.
Complex 5b is remarkably moisture sensitive, as evidenced
by the formation of [Cp2Zr(OC6F5)]2(μ-O)26 in sealed J.
Young tubes despite rigorously anhydrous handling and
the use of carefully dried benzene-d6.
Z1-Zr1-Z2: 129°, Zr1-O1: 1.993(2) A, O1-C11: 1.334(3) A,
Zr1-O1-C11: 145. 9(2)°.
its availability for the β-H elimination step.46 The resistance
of Cp2Zr(Me)OR complexes 3a-c and of 5a to undergo
hydrogenation (vide supra), which was also observed in Sita’s
acetamidinate complexes,10 is in agreement with these re-
sults. Jordan et al. observed a 4 times faster hydrogenation of
[Cp2ZrMe(THF)]BPh4 in CH2Cl2 than in THF and attrib-
uted the difference to the π-donation of the THF-oxygen,
which raises the energy of the Zr LUMO required for
effective hydrogenation.47 Since phenoxide coordination is
strongly influenced by steric considerations,48 there is no
direct evidence for an increased π-donation in the structural
data of 7a. Complex 6 shows a longer Zr-O and a shorter
˚
O-C bond than 7a (Zr1-O1: 2.075(2) and 1.993(2) A,
˚
O1-C11: 1.323(3) and 1.334(3) A), which would be in
agreement with reduced π-donation to the less Lewis-acidic
metal center in 6, but the differences are barely significant.
Nevertheless, but extremely slowly at room temperature
(2 months), 5a does reorganize itself to the sterically less
demanding isobutyl complex 7a. Most likely, formation of
7a occurs by β-H elimination and reinsertion of isobutene.3,4
It is unknown at the moment if in this or comparable systems
the isomerization rather involves rotation of a zirconium-
bonded isobutene or dissociation and reassociation of the
olefin. For the sake of simplicity, we propose dissociation of
isobutene and transient formation of Cp2Zr(H)OPh, 9a, but
formation of the corresponding olefin complex Cp2Zr(H)-
(H2CdCMe2)OPh cannot be excluded.
Further indirect evidence agrees with the existence of an
intermediary hydride species. Heating of a C6D6 solution of
5a in the presence of 1.6 equiv of phenol quantitatively (1H
NMR) yielded the diphenolate 1a along with free isobutene
(δ 4.75, 1.60 ppm) and isobutane in approximate 4:1 ratio
Monitoring the decomposition of 5b in benzene-d6 by
NMR spectrometry reveals the formation of Cp2Zr(iBu)-
OC6F5, 7b, in 13 days at room temperature or 3 h at 70 °C
(Scheme 8). Again, 7b could be prepared independently by
reacting 1b with iBuMgCl in diethyl ether as a viscous oil,
which could not be further purified by crystallization. Inter-
estingly, thermolysis (70 °C, 3 h) of 5b in C6D6 in the presence
of excess styrene (4 equiv) afforded Cp2Zr(CH2CH2Ph)-
OC6F5, 10, and in the presence of ethyl vinyl ether (4 equiv)
Cp2Zr(OEt)(OC6F5), 11, and free ethylene. The identity of
(46) In the rare cases where stable zirconocene complexes with β-H-
containing alkyl substiuents were obtained in the absence of π-donor
ligands, their relative stability is attributed to steric crowding of the
metal center. Wendt, O. F.; Bercaw, J. E. Organometallics 2001, 20,
3891.
(47) Jordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.
Organometallics 1987, 6, 1041.
(48) Cf. the Zr-O-CAr angle in Cp2Zr(OPh)2 and Cp*2Zr(OPh)2 of
147° and 173°, respectively. Howard, W. A.; Trnka, T. M.; Parkin, G.
Inorg. Chem. 1995, 34, 5900.

4918 Organometallics, Vol. 28, No. 17, 2009
Perrotin et al.
Scheme 9
co-workers reported the activity of a mixture of Cp02ZrH2
and Cp02ZrCl2 (Cp0 = C5H4Me), obtained in the attempted
synthesis of Cp02Zr(H)Cl, in hydrozirconation reactions,
most probably via Cp02Zr(H)Cl formed in equilibrium.11
Reactions between Cp2ZrH2 and 1 or 2 equiv of 1a in
C6D6, however, did not show any indication for the forma-
tion of 9a, and reactions effectuated in the presence of 1 equiv
of styrene afforded after 3 days at room temperature only
traces of an olefin insertion product (CH2Ph: 2.97 ppm) that
could not be identified with certainty as Cp2Zr(CH2CH2Ph)-
OPh. Reaction of an equimolar mixture of Cp2ZrH2 and 1.2
equiv of 1b with styrene in C6D6, however, cleanly afforded
after 3 days at room temperature the styrene 1,2-insertion
product 10 as the major species (58%, Scheme 9), accom-
panied by 31% of 1b and minor amounts of decomposition
or side products ({Cp2Zr(OC6F5)}2(μ-O): 1%, others: 10%,
based on Cp resonances). 1H NMR spectra of 10 contained
two multiplets of identical intensity at 2.90 and 1.43 ppm,
which showed cross-peaks in the COSY spectra.49 The
corresponding signals in the 13C spectra at 50.5 and
40.1 ppm were identified as CH2 groups (DEPT). All of
these observations agree with the assignment of 10 as Cp2Zr-
(CH2CH2Ph)OC6F5.50
10 was established by NMR spectroscopy and its subsequent
reaction with 2,6-xylyl isonitrile (vide infra). Assignment of
11 was confirmed by reaction of 5b with 1 equiv of ethanol in
C6D6 at 70 °C. In the presence of trans-3-hexene, thermolysis
of 5b afforded a mixture of the n-hexyl complex Cp2Zr-
(OC6F5)(CH2)5Me, 12 (vide infra), and 7b in a ratio of 60:40.
In the presence of 1-hexene, the same product mixture was
obtained, albeit in a ratio of 93:7. The rate of disappearance
of 5b during the formation of 7b, 10, and 11 in benzene-d6
was monitored by 1H NMR at 70 °C. All reactions observed
similar kinetics consistent with a first-order reaction and
with comparable rate constants of k343K = 1.4-1.6 h-1. On
the other hand, reaction of the iso-butyl complex 7b with
EtOCHdCH2 at 70 °C yielded 11 with a lower first-order
rate constant of k343K = 0.13 h-1, and only traces of 11 were
detected (1H NMR) after 10 was reacted for 5 days with
EtOCHdCH2 at 70 °C.
Substitution of the hydrogen atoms of the phenolate
ligand by fluorine in 5b reduces O-π-donation to the metal
center and thus increases the lability of the tert-butyl group
versus β-H elimination. Consequently, at 25 or 70 °C for-
mation of the corresponding isobutyl derivative is about
1 order of magnitude faster from 5b than from 5a. The
putative hydride intermediate Cp2Zr(H)OC6F5, 9b, could
be trapped in the presence of either styrene or ethyl vinyl
ether to yield the corresponding insertion products
(Scheme 8). No traces of the isobutyl complex 7b were
observed in these reactions, which is in agreement with
relative insertion rates into M-H bonds of styrene and
isobutene, reported by Bercaw and Chirik.22 An internal
olefin, such as trans-3-hexene, is barely able to compete with
isobutene for 9b, while reactions with 1-hexene contain only
small amounts of the isobutyl complex. Identical rate con-
stants for the formation of 7b, 10, and 11 indicate that
formation of the zirconocene hydride 9b is rate-determining,
followed by trapping of 9b with the appropriate olefin. A
mechanism involving prior isomerization to the isobutyl
complex 7b can be ruled out due to its significant lower
reaction rate with ethyl vinyl ether under the same condi-
tions. Assuming that β-H elimination is also rate-determin-
ing in reactions of 7b and 10 with vinyl ethyl ether to yield 11,
β-H eliminations in Cp2Zr(OR)R complexes follow the trend
tBu>iPr>CH2CH2Ph.
The reduced amount of decomposition products obtained
here, when compared to the preparation of 10 by thermolysis
of 5b in the presence of styrene, allowed the observation of a
doublet of minor intensity at 1.56 ppm, coupled to an
unresolved resonance at 2.9 ppm beneath the CH2Ph signal
of 10 (COSY). Both resonances shifted (1.13, 3.59 ppm) after
reaction with xylyl isonitrile. These signals were putatively
assigned to the 2,1-insertion product of styrene Cp2Zr-
(OC6F5)CH(Me)(Ph), 13 (Scheme 9). The ratio of 10:13
was approximately 95:5 and remained unchanged after
heating for 20 h at 70 °C. Coordination of the zirconium to
the R-position of styrene was attributed to a stabilizing
coordination of the aryl ring to the metal center, and hydro-
zirconations of aryl alkenes usually yield a mixture of
regioisomers.5-7 While the formation of a 2,1-insertion
product can be suppressed by extensive substitution of the
cyclopentadienyl ring,22 1b/Cp2ZrH2 is to our knowledge the
most regioselective hydrozirconation reagent for styrene
with unsubstituted cyclopentadienyl ligands. Increased
π-donation of the alkoxy ligand as well as steric effects might
disfavor the formation of the secondary alkyl species 13.
The absence of isobutene in hydrozirconations with 1b/
Cp2ZrH2 allowed the preparation of single products with less
reactive olefins as substrates. Reactions of trans-3-hexene
with 1b/Cp2ZrH2 in C6D6 afforded after 3 days at room
temperature only the 1-hexyl species Cp2Zr(OC6F5)-
1
(CH2)5Me, 12 (Scheme 9). H spectra of 12 contained four
signals for the hexyl protons with an integral ratio of 2:8:2:3,
and COSY spectra allowed the identification of the CH2
(49) Addition of 2,6-xylylisonitrile to the C6D6 solution gave rise to a
new zirconocene species, which contained the two now resolved triplets,
shifted to 2.77 and 2.45 ppm, in addition to peaks assigned to inserted
isonitrile.
(50) Assignment of 10 and 12 was further confirmed by reaction of
the benzene-d6 solutions with I2. 1H NMR and GC-MS analyses showed
the formation of 1-iodo-2-phenylethane and iodohexane, respectively, in
51% and 90% yield (relative to initial olefin). 1-Iodo-1-phenylethane
(expected upon reaction of 13 with iodine) was not identified in the
obtained reaction mixtures, although a minor, iodine-containing com-
pound was observed in GC-MS analyses, which showed identical
fragmentation patterns and similar retention times to 1-iodo-2-pheny-
lethane.
The evidence for the intermediate existence of the hydrides
9a and 9b prompted us to investigate other methods to
generate the hydride as a transient species. Erker and

Article
Organometallics, Vol. 28, No. 17, 2009 4919
groups in R- and β-position relative to the zirconium center
at 1.23 and 1.66 ppm, respectively. The aliphatic region of the
13C spectra of 12 displayed six signals, five of which were
identified by DEPT as CH2 groups, the Zr-bound methylene
appearing at 50.0 ppm. Consequently, complex 12 could be
prepared as well by reaction of 1b/Cp2ZrH2 with 1-hexene
for 3 days at room temperature or 3 h at 60 °C. The presence
of a Zr-bound alkyl group was further confirmed by the
reaction of 12 with 2,6-xylylisonitrile. When the reaction of
substoichiometric amounts of trans-3-hexene with 1b/
Cp2ZrH2 in C6D6 was followed by NMR, the aliphatic
region of the NMR spectra contained no signals that could
be assigned to other Zr alkyl species than 12, even at <5%
conversion. Instead, resonances assigned to 2-hexene by
comparison with literature data and by GC-MS analysis
were observed in increasing amounts,51 which however never
exceeded 25% of that of trans-3-hexene. After 21 h, all olefin
had reacted and only resonances of 12, 1b, and (Cp2ZrH2)2
remained. To test the involvement of Cp2ZrH2, its reaction
with trans-3-hexene was investigated under the same condi-
tions. No indication for the formation of any zirconocene
alkyl species could be obtained, but the NMR spectra
indicated isomerization of trans-3-hexene to an approxi-
mately 1:1 mixture of 3-hexene and 2-hexene after 21 h,51
accompanied by approximately 5% of hexane. Continued
reaction for 4 days afforded exclusively hexane. In repeated
experiments, isomerization of trans-3-hexene by Cp2ZrH2
was subject to an induction period ranging from 2 to 24 h,
indicating that, rather than by Cp2ZrH2 itself, the isomeriza-
tion is catalyzed by one of its decomposition products. In
agreement with the assignment of the reaction products with
Cp2ZrH2 as mixture of isomerized olefins, addition of 1b to
such a mixture yielded again exclusively the 1-hexyl species
12 (accompanied by small amounts of hexane).
Formation of 12 (and other zirconocene alkyl complexes)
by reaction of olefins with 1b/Cp2ZrH2 can be envisioned by
two mechanisms: Comproportionation between 1b and
Cp2ZrH2 yields 9b, which inserts 3-hexene, followed by iso-
merization to the 1-hexyl product (Scheme 10, A). Alterna-
tively, insertion of olefin might occur into Cp2ZrH2, which
would lead to the corresponding Cp2Zr(H)R complexes
(Scheme 10, B). Isomerization by β-H elimination/reinsertion
into Cp2ZrH2 leads to the formation of Cp2Zr(H)(CH2)5Me,
which is now irreversibly trapped by 1b to form 12. Observed
relative reactivities seem to disfavor pathway B: only minor
isomerization to 2-hexene (∼5%) was observed in reactions
between Cp2ZrH2 and trans-3-hexene after 3 h, while ∼40%
of trans-3-hexene was converted into 12 by 1b/Cp2ZrH2 after
the same time, in addition to the formation of ∼5% 2-hexene.
The available data did not allow to distinguish if 2-hexene was
derived via pathway A or B. Formation of 12, however,
proceeds faster than possible via pathway B (maximum twice
as fast as the rate of isomerization to 2-hexene), which argues
strongly in favor of the formation ofthe morereactivehydrido
species 9b. The absence of significant amounts of 2-hexene
formed during hydrozirconation of trans-3-hexene indicates
that the olefin remains to a certain extent attached to the
zirconium center during the isomerization, which is in agree-
ment with hydrozirconations with Schwartz’s reagent, where
isomerized olefins are rarely observed, mainly in the case of
less reactive olefins.3
Scheme 10
In light of these results, we revisited the direct protonation
in the presence of olefin, which proved unsuccessful when
phenol was employed. Addition of C6F5OH to a mixture of
Cp2ZrH2 and excess 1-hexene in C6D6 yielded after heating
for 1.5 h at 70 °C a dark solution. The only species present in
its 1H NMR spectrumwere12and 1 (6%). Hydrozirconations
with 9b can thus be achieved on a reasonable time scale by
preparing 9b in situ from commercially available precursors.
Conclusions
Hydrido alkoxide complexes of unsubstituted zircono-
cene, Cp2ZrH(OR), remained elusive synthetically, most
likely due to fast disproportionation to Cp2ZrH2 and Cp2Zr-
(OR)2. They can be accessed, however, as a transient species
by thermolysis of Cp2Zr(tBu)OR or comproportionation
between Cp2ZrH2 and Cp2Zr(OC6F5)2. Their formation in
the presence of olefins or ketone yields the corresponding
hydrozirconation products. While exchange of chloride with
alkoxide was expected to impede β-H elimination reactions,
experimental evidence in this regard is so far inconclusive.
tert-Butyl complexes 5a,b with OPh and OC6F5 ligands
displayed drastically increased stabilities when compared
to their chloride counterparts. On the other hand, no alkyl
species other than n-hexyl could be identified in reactions of
trans-3-hexene with 1b/Cp2ZrH2, which is in apparent dis-
agreement with the slow isomerization of Cp2Zr(Cl)C(H)-
(Me)R complexes reported by Chirik and Bercaw.4 Overall,
thermolysis of 5b, comproportionation of 1b/Cp2ZrH2, and,
in particular, reaction of Cp2ZrH2 with C6F5OH in the
presence of olefins gave access to Cp2Zr(H)OC6F5 as a new
hydrozirconation reagent, whose properties differ notably
from Schwarz’s reagent, e.g., a strongly increased regiospe-
cificity in styrene hydrozirconation. We are currently inves-
tigating the reactivities and selectivities of these hydro-
zirconations in general and in particular the conflicting
evidence with regard to β-H elimination and the suitability
of other alcohols than the “pseudo-halogen” C6F5OH.
Experimental Section
All reactions were carried out under an inert atmosphere
using Schlenk and glovebox techniques. Cp2Zr(OPh)2,24 Cp2Zr-
(BH4)2,52 Cp2Zr(H)(BH4),53 Cp2ZrMe2,54 Cp2Zr(OPh)2,24
(52) Nanda, R. K.; Wallbridge, M. G. H. Inorg. Chem. 1964, 3, 1798.
(53) James, B. D.; Nanda, R. K.; Walbridge, M. G. H. Inorg. Chem.
1967, 6, 1979.
(54) Frauenrath, H. Polymerization of Olefins and Functionalized
Monomers with Zirconocene Catalysts; Techn. Hochsch. Aachen, 2001.
Samuel, E.; Rausch, M. D. J. Am. Chem. Soc. 1973, 95, 6263.
(51) Neither NMR nor GC-MS data allowed a complete assignment
of the cis- and trans-isomers for 2- or 3-hexene, respectively.

4920 Organometallics, Vol. 28, No. 17, 2009
Perrotin et al.
Cp2Zr(OC6F5)2 PhOSiMe3,55 C6F5OSiMe3,26 and tBuO-
26
sent out of the glovebox, and the suspension was stirred 12 h at
60 °C. Over the reaction time the reaction mixture turned dark
orange-green. Removal of the volatiles yielded a light brown,
thick oil. Analysis of the cyclopentadienyl proton integration
(1H NMR) of the crude mixture showed a ∼1:1 ratio of Cp2Zr-
(OEt)2, 1e, and Cp2Zr(Et)OEt, 2e.
56
SiMe3 were prepared according to literature procedures.
Cp2ZrH2, Cp2ZrCl2, and other chemicals were purchased from
common commercial suppliers. 1H and 13C NMR spectra were
acquired on a Bruker AMX 300 spectrometer (300 MHz 1H) or
on a Bruker Avance 500 spectrometer (500 MHz 1H). 19F NMR
spectra were acquired on a Bruker Avance 300 (300 MHz 1H).
Chemical shifts were referenced to the residual signals of the
deuterated solvent (C6D6: 1H: δ 7.16 ppm, 13C: δ 128.38 ppm).
Relaxation delays of 15 s were used in 1H NMR to obtain
Cp2Zr(OEt)2, 1e. 1H NMR (300 MHz, C6D6): δ 6.01 (s, 10H,
C5H5), 3.95 (t, 4H, OCH2, J=7 Hz), 1.12 (m, 8H, CH3, J =
7 Hz) ppm. 13C NMR: δ 111.9 (C5H5), 68.9 (OCH2), 20.5
(CH2CH2CH3) ppm.
1
reliable integration data. Complete assignments of the H and
Cp2Zr(Et)OEt, 2e. 1H NMR (300 MHz, C6D6): δ 5.76 (s,
10H, C5H5), 3.81 (q, OCH2, J=7 Hz), 1.59 (t, 3H, CH2CH3,
J = 7.5 Hz), 1.06 (q, 2H, CH2CH3, J = 7.5 Hz), 0.99 (t, 3H,
OCH2CH3, J = 7 Hz) ppm. 13C NMR: δ 110.6 (C5H5), 69.0
(OCH2), 32.0 (H2CH3)), 20.4 (OCH2CH3), 18.2 (CH2CH3) ppm.
Reaction of Cp2ZrH2 with nBuOCHdCH2. In a N2-filled
glovebox a 25 mL glass bomb was charged with Cp2ZrH2
(200 mg, 0.90 mmol), nBuOCHdCH2 (90 mg, 0.90 mmol), a
magnetic stir bar, and toluene (8 mL). The vessel was hermeti-
cally sealed and sent out of the glovebox, and the suspension was
stirred 12 h at 65 °C. Over the reaction time the reaction mixture
turned brown-gray. The volatiles were removed under vacuum,
and the residue was taken into 10 mL of hexanes. Filtration and
evaporation of the filtrate afforded a brown, thick oil. Analysis
of the cyclopentadienyl proton integration (1H NMR) of the
crude mixture showed a ∼1:1 ratio of Cp2Zr(OnBu)2, 1f (NMR
data vide supra), and Cp2Zr(Et)OnBu, 2f.
13C NMR resonances of the zirconocene products were
obtained using information from COSY, DEPT 135, HSQC
(heteronuclear single quantum coherence), and/or HMBC
(heteronuclear multiple bond coherence) spectra. 13C reso-
nances of the OC6F5 group could not be detected using acquisi-
tion times sufficient to observe all other resonances. THF was
distilled from sodium/benzophenone; all other solvents were
dried by passage through activated aluminum oxide (MBrown
SPS) and deoxygenated by repeated extraction with nitrogen.
Benzene-d6 was dried over sodium and distilled under reduced
pressure, then degassed by three freeze-pump-thaw cycles.
Reagents were dried using the suitable drying agent and distilled
under reduced pressure prior to use (tert-butanol: K2CO3; ethyl
vinyl ether, n-butyl vinyl ether, 1-hexene, 3-hexene: CaH2;
˚
C6F5OH, 1-butanol; ethanol: activated 4 A molecular sieves).
Phenol and 2,4-di-tert-butylphenol were sublimed under re-
duced pressure prior to use. Styrene was evacuated under
Cp2Zr(Et)OnBu, 2f. 1H NMR (300 MHz, C6D6): δ 5.77
(s, 10H, C5H5), 3.78 (t, 4H, OCH2), 1.56 (t, ZrCH2CH3),
1.46-1.25 (m, 4H, CH2CH2CH3), 1.02 (q, ZrCH2CH3), 0.90
(t, 3H, CH2CH2CH3) ppm. 13C NMR: δ 110.7 (C5H5), 73.4
(OCH2), 36.8 (CH2CH2CH3), 32.1 (ZrCH2CH3), 19.8 (CH2-
CH2CH3), 18.1 (ZrCH2CH3), 14.6 (CH2CH2CH3) ppm.
NMR-Scale Preparation of Cp2Zr(Me)OR, 3a. In a nitrogen-
filled glovebox, a C6D6 solution of Cp2ZrMe2 (ca. 10 mg in
0.6 mL) was added at one time to 0.9 equiv of the alcohol in
a small test tube. Vigorous bubbling ensued (C6F5 > Ph ∼
C6tBu2H3 > tBu). After 30 s, the bubbling ceased and the
colorless solution was transferred to a J. Young tube and
allowed to stand 30 min at room temperature. NMR spectra
matched those obtained in preparations by other pathways
(3a and 3b)26,34 or the same protocol (3c).33
˚
vacuum and dried over 4 A molecular sieves. Elemental analyses
ꢀ
ꢀ
were performed by the Laboratoire d’Analyse Elementaire at
the University of Montreal. Some zirconocene complexes were
obtained as noncrystallizable oils, precluding appropriate pur-
ifications for elemental analyses. Analyses of the oils returned
inconsistent results, indicating a high tendency to decompose.
Cp2Zr(OCHPh2)2, 1d. THF (10 mL) was added at room
temperature to a Schlenk flask containing Cp2ZrH2 (200 mg,
0.90 mmol) and benzophenone (163 mg, 0.90 mmol). The gray
suspension was stirred overnight at room temperature, yielding
a pale yellow solution. The solution was filtered, the filtrate
evaporated, and the residue recrystallized from a concentrated
toluene/hexane (ca. 1:1) solution chilled to -30 °C. The color-
less crystals (137 mg, 24%) were washed with cold hexane and
briefly dried under vacuum. Cp2Zr(OCHPh2)2 cocrystallized
with 0.5 molecule of toluene (1H NMR).
Cp2Zr(Me)OPh, 3a. 34 1H NMR (300 MHz, C6D6): δ 7.19 (t,
2H, J = 7 Hz, meta OPh), 6.85 (t, 1H, J = 7 Hz, para OPh), 6.59
(d, 2H, J = 7.5 Hz, ortho OPh), 5.74 (s, 10H, C5H5), 0.49 (s, 3H,
Zr-CH3) ppm. 13C NMR (C6D6): δ 165.8 (ipso OPh), 123.0
(ortho OPh), 119.9 (para OPh), 118.6 (meta OPh), 111.5 (C5H5),
22.8 (Zr-CH3) ppm.
1H NMR (300 MHz, C6D6): δ 7.40 (d, 8H, J = 7 Hz, ortho
Ar), 7.20 (t, 8H, J = 7.5 Hz, meta Ar), 7.10 (d, 4H, J = 7.5 Hz,
para Ar), 5.99 (s, 1H, OCHPh2), 5.89 (s, 10H, C5H5) ppm. 13
C
NMR: δ 147.6 (ipso Ar), 128.9 (Ar), 127.4 (Ar), 127.2 (Ar), 112.5
(C5H5), 86.9 (CHPh2) ppm. Anal. Calcd for C39.5H36O2Zr: C,
74.84; H, 5.72. Found: C, 74.50; H, 5.05.
Cp2Zr(Me)OC6F5, 3b. 26 1H NMR (300 MHz, C6D6): δ 5.69 (s,
10H, C5H5), 0.54 (s, 3H, Zr-CH3) ppm. 13C NMR (C6D6): δ
112.5 (C5H5), 27.2 (Zr-CH3) ppm. 19F(C6D6): δ-165.55 (m, ortho
C6F5), -167.52 (m, meta C6F5), -174.25 (m, para C6F5) ppm.
Cp2Zr(BH4)OPh, 4a. (a) A J. Young NMR tube was char-
ged with 1a (24.3 mg, 0.060 mmol), Cp2Zr(BH4)4 (7.5 mg,
0.030 mmol), and 0.6 mL of benzene-d6. The colorless solution
was allowed to stand 2 days at room temperature to yield a
mixture of 1a, 4a, and traces (ca. 1%) of Cp2Zr(BH4)4.
(b) In a N2-filled glovebox, a PhOH (6.7 mg, 0.072 mmol)
solution in benzene-d6 (0.6 mL) was added to Cp2Zr(H)(BH4)
(17.0 mg, 0.072 mmol). Vigorous bubbling ensued. After 5 min
the colorless solution was transferred to a J. Young NMR tube.
NMR analysis revealed a mixture of 4a (42%), Cp2Zr(BH4)2
(20%), and 1a (31%).
Cp2Zr(OnBu)2, 1f. At room temperature, a 4 mL toluene
solution of 1-butanol (90 mg, 1.21 mmol) was added at one time
to a suspension of Cp2ZrH2 in 10 mL of toluene. A vigorous
bubbling ensued, and the reaction mixture was allowed to stir
15 h at room temperature, yielding a pale yellow solution. The
volatiles were removed in vacuo (3 h, 25 °C). Then 15 mL
of hexanes was added, the mixture filtered, and the solvent
removed in vacuo, affording 1f as a yellow oil.
1H NMR (benzene-d6): 6.02 (s, 10H, C5H5), 3.91 (t, 4 H,
OCH2), 1.43 (m, 8H, CH2CH2), 0.96 (t, 6H, CH3) ppm. 13C
NMR (benzene-d6): 112.0 (C5H5), 73.5 (OCH2), 37.2
(OCH2CH2CH2), 20.0 (OCH2CH2CH2) 14.7 (CH3) ppm.
Reaction of Cp2ZrH2 with EtOCHdCH2. In a N2-filled glove-
box a 25 mL glass bomb was charged with Cp2ZrH2 (50 mg,
0.22 mmol), EtOCHdCH2 (16 mg, 0.22 mmol), a magnetic stir
bar, and toluene (5 mL). The vessel was hermetically sealed and
1
Cp2Zr(BH4)OPh, 4a. H NMR (300 MHz, C6D6): δ 7.19 (t,
2H, J = 8 Hz, meta OPh), 6.87 (t, 1H, J = 7, para OPh), 6.63 (d,
2H, J = 8, ortho OPh), 5.80 (s, 10H, C5H5), 1.04 (q, J = 80 Hz,
Zr-BH4) ppm. 13C NMR (C6D6): δ 166.4 (ipso OPh), 130.1 (ortho
OPh), 120.9 (para OPh), 119.0 (meta OPh), 113.1 (C5H5) ppm.
Reaction of Cp2Zr(BH4)OPh, 4a, with Triethylamine. In a N2-
filled glovebox, a J. Young tube was charged with 1a (27.7 mg,
(55) Poisson, T.; Dalla, V.; Papamicael, C.; Dupas, G.; Marsais, F.;
Levacher, V. Synlett 2007, 0381.
(56) Langer, S. H.; Connell, S.; Wender, I. J. Org. Chem. 1958, 23, 50.

Article
Organometallics, Vol. 28, No. 17, 2009 4921
0.0674 mmol), Cp2Zr(BH4)2 (8.6 mg, 0.034 mmol), and 0.6 mL
of benzene-d6. The mixture was allowed to stand 2 days, and
NMR was taken to ensure completion of the reaction. The
spectrum showed a mixture of 1a (57%), 4a (40%) and 3% of
Cp2Zr(BH4)2/Cp2Zr(H)(BH4). Et3N (9.4 μL, 0.0674 mmol) was
added to the NMR tube with a microsyringe and the reaction
-78 °C, some white crystals formed. To this cooled suspension
was added dropwise iBuMgCl (0.490 mL, 0.98 mmol, 2 M
solution in Et2O) with a syringe. After 1 h at -78 °C, the
colorless solution was allowed to warm to room temperature
and stirred an additional 2 h. The solution turned yellow with
formation of some precipitate. The solvent was removed under
reduced pressure, yielding a yellow foam, to which 10 mL of
hexanes was added, stirred, and removed under vacuum to
facilitate removal of the volatiles. The resulting yellow-brown
residue was then dried for 2 h under dynamic vacuum. Addition
of hexane, subsequent filtration, and evaporation of the filtrate
to dryness yielded an orange oil that turned brown upon
standing (at room temperature or -30 °C).
1
allowed to stand at room temperature. After 20 h, H NMR
showed a mixture of 1a (70%), 4a (13%), and Cp2Zr(H)(BH4)
(18%). After 40 h no residual 4a was detected and the remaining
mixture consisted of 1a (77%) and Cp2Zr(H)(BH4) (23%).
Cp2Zr(tBu)OPh, 5a. 1a (550 mg, 1.35 mmol) was dissolved in
40 mL of Et2O. Upon cooling to -78 °C, a fair amount of the
zirconocene precipitated out of the solution as a white powder.
A tBuLi solution (900 μL, 1.5 M solution in pentane) was added
dropwise over 5 min to the reaction flask. The white precipitate
rapidly disappeared, and the resulting bright yellow solution
was stirred for 1 h at -78 °C. The dry ice bath was removed and
the reaction mixture stirred an additional hour. After evapora-
tion of the volatiles, 10 mL of hexanes was added, stirred, and
removed under vacuum. Addition of 30 mL of hexanes to the
yellow residue, followed by filtration and removal of the solvent
under vacuum, afforded 5a (343 mg, 68%) as a yellow powder.
1H NMR (300 MHz, C6D6): δ 7.18 (m, 2H, meta OPh), 6.86
(t, 1H, J = 7, para OPh), 6.58 (d, 2H, J = 9, ortho OPh), 5.78 (s,
10H, C5H5), 1.43 (s, 9H, Zr-C(CH3)) ppm. 13C NMR (C6D6): δ
165.5 (ipso OPh), 129.9 (ortho OPh), 120.1 (para OPh), 118.6
(meta OPh), 112.1 (C5H5), 50.0 (Zr-C(CH3)3), 37.3 (Zr-C-
(CH3)3) ppm. Anal. Calcd for C20H24OZr: C, 64.64; H, 6.51.
Found: C, 64.68; H, 6.24.
Cp2Zr(tBu)OC6F5, 5b. A tBuLi solution (340 μL, 1.5 M
solution in pentane) was added dropwise to a cooled (-78 °C)
solution of 1b (300 mg, 0.51 mmol) in 25 mL of Et2O (some
precipitation of 1b occurred). The mixture was stirred 2 h at
-78 °C, then allowed to gradually warm to room temperature
and stirred an additional hour. The bright yellow solution was
evaporated to dryness. The following procedure was repeated
twice: hexane (ca. 10 mL) was added, the reaction mixture was
vigorously stirred, and the volatiles were stripped off. The bright
yellow residue was then extracted with 20 mL of hexane, filtered,
and dried under vacuum, yielding Cp2Zr(OC6F5)(tBu), 5b
(131 mg, 56%), as a bright yellow powder.
1H NMR (300 MHz, C6D6): δ 7.18 (t, 2H, J = 7 Hz, meta
OPh), 6.85 (t, 1H, J = 7 Hz, para OPh), 6.58 (d, 2H, J = 8 Hz,
ortho OPh), 5.75 (s, 10H, C5H5), 2.21 (m, 1H, CH2CH), 1.15 (d,
6H, J = 7 Hz, CH(CH3)2), 1.05 (d, 2H, J = 7 Hz, ZrCH2) ppm.
13C NMR (C6D6): δ 165.8 (ispo OPh), 130.0 (o-OPh), 120.0
(para OPh), 118.7 (meta OPh), 111.5 (C5H5), 56.0 (CH(CH3)2),
33.2 (ZrCH2), 28.8 (CH(CH3)2) ppm.
On one occasion, small amounts of colorless crystals formed
from the oil that showed identical 1H and 13C NMR spectra, but
could not be separated from the oil for elemental analysis.
Cp2Zr(iBu)OC6F5, 7b. An Et2O (20 mL) solution of 1b
(300 mg, 0.51 mmol) was cooled to -78 °C, which induced some
precipitation of the starting material. Isobutyl magnesium
chloride (260 μL, 2.0 M solution in Et2O) was added dropwise
to the cooled reaction mixture and the solution stirred 1 h at
-78 °C, then 1.5 h at room temperature, yielding a bright yellow
solution with a white precipitate. The volatiles were removed
under vacuum, and the yellow residue was dried an additional
15 min. Hexane (10 mL) was added, stirred, and evaporated.
The product was extracted with hexane (20 mL), filtrated, and
evaporated to dryness, affording 7b (80 mg, 35%) as a thick
yellow oil.
1H NMR (300 MHz, C6D6): δ 5.72 (s, 10H, C5H5), 2.17 (m,
1H, CH2CH(CH3)2), 1.11 (d, 2H, CH2CH(CH3)2, J = 7 Hz),
1.06 (d, 6H, CH2CH(CH3)2) ppm. 13C NMR: δ 112.5 (C5H5),
61.2 (s, CH2), 33.7 (s, CHMe2), 28.4 (CH2CH(CH3)2) ppm.δ
112.5 (C5H5), 61.2 (CH2CH(CH3)2), 33.7 (CH2CH(CH3)2),
28.4 ppm. 19F NMR (C6D6): δ -166.18 (m, ortho C6F5),
-167.50 (m, meta C6F5), -174.22 (m, para C6F5) ppm.
Cp2Zr(OCHPh2)OPh, 8. (a)A J. Youngtubewaschargedwith
1a (26.1 mg, 0.064 mmol), 1e (40.5mg, 0.064 mmol), and0.6mLof
benzene-d6. The tube was heated 3 days to 65 °C, yielding a pale
orange solution. The relative abundance of the zirconocene com-
plexes was obtained from analysis of the intensity of the Cpsignals
in 1H NMR: 1a (28%) 1d (17%), and 8 (58%).
(b) A J. Young tube was charged with 5a (25.4 mg, 0.068
mmol), benzophenone (12.5 mg, 0.068 mmol), and 0.6 mL of
benzene-d6. The tube was heated 3 days to 65 °C in an oil bath. The
initiallybright yellowsolutiondiscoloredtoa paleyellow solution.
The relative abundance of the zirconocene complexes was ob-
tainedfromanalysisofthe intensity ofthe Cpsignals:1a (22%), 1d
(21%), and Cp2Zr(OCHPh2)OPh, 8 (54%). Another experiment
using about half the initial concentrations (0.033 mmol of 5a and
benzophenone in 0.6 mL of C6D6) yielded after 3 days at 65 °C the
same product mixture in a comparable ratio of 24:23:57.
Cp2Zr(OCHPh2)OPh, 8. 1H NMR (300 MHz, C6D6): δ 7.42
(m, 4H, ortho Ar), 7.28-7.17(m, meta Ar), 7.09 (m, 2H, para
Ar), 6.89 (m, 1H, para OPh), 6.72 (d, 2H, J = 7 Hz, ortho OPh),
6.02 (s, 1H, OCHPh2), 5.93 (s, 10H, C5H5) ppm. 13C NMR: δ
166.7 (ipso OPh), 147.1 (ipso Ar), 130.1 (ortho OPh), 128.9 (Ar),
127.6 (Ar), 127.3 (Ar), 119.5 (para OPh), 118.9 (meta OPh),
113.0 (C5H5), 87.5 (CHPh2) ppm.
1H NMR (300 MHz, C6D6): δ 5.74 (s, 10H, C5H5), 1.36 (s,
9H, C(CH3)3) ppm. 13C NMR (C6D6): δ 113.2 (C5H5), 53.8
(C(CH3)3), 36.6 (C(CH3)3) ppm. 19F (C6D6): δ -164.12 (m,
ortho C6F5), -167.37 (m, meta C6F5), -173.97 (m, para C6F5)
ppm. Anal. Calcd for C20H19F5OZr: C, 52.04; H, 4.15. Found:
C, 52.08; H, 4.00.
Cp2Zr(OPh)C(tBu)dN(2,6-Me2C6H3), 6. In a nitrogen-filled
glovebox, a Schlenk flask was charged with 5a (150 mg, 0.40
mmol), 2,6-dimethylphenylisocyanide (52 mg, 0.40 mmol), a
magnetic stir bar, and toluene (15 mL). The reaction flask was
closed and stirred 15 h at 65 °C under N2. The resulting dark
orange solution was decanted and evaporated to dryness, yielding
an orange residue. Colorless crystals of the desired product suitable
for X-ray analyses were obtained from a cooled (-30 °C) toluene/
hexane solution. The crystals were washed twice with cold hexanes
(0.5 mL) and briefly dried under vacuum (62 mg, 31%).
1H NMR (300 MHz, C6D6): δ 7.16 (m, 2H, meta OPh),
6.81-6.90 (m, 3 H, C6H3), 6.72 (tt, 1H, J = 7, 1 Hz, para OPh),
6.52 (dm, ortho OPh), 5.90 (s, 10H, C5H5), 1.93 (s, 6H, C6H3-
(CH3)3), 0.95 (s, 9H, C(CH3)3) ppm. 13C NMR (C6D6): δ 168.20
(ipso OPh), 146.8, 129.0, 128.4, 128.3, 124.6, 119.1, 116.2, 109.4
(C5H5), 42.4 (C(CH3)3), 27.7 (C6H3(CH3)2), 19.5 (C(CH3)3)
ppm. The 13C NMR signal for Zr-C(tBu)dN) could not be
observed after a reasonable acquisition time; however the
HMBC exhibits a cross-peak for C-C(CH3)3. Anal. Calcd for
C29H33NOZr: C, 69.23; H, 6.62; N, 2.79. Found: C, 68.93; H,
5.93; N, 2.94.
Reaction of 5b with Olefins. A J. Young NMR tube was
charged with ca. 10 mg of 5b, 4 equiv of the corresponding olefin,
and 0.6 mL of C6D6. The tube was hermetically closed and heated
3 h at 70 °C. The solution gradually discolored, and the disap-
pearance of signals for 5b indicated complete conversion
Cp2Zr(iBu)OPh, 7a. 1a (400 mg, 0.98 mmol) was dissolved in
40 mL of Et2O, yielding a colorless solution. Upon cooling to

4922 Organometallics, Vol. 28, No. 17, 2009
Perrotin et al.
(1H NMR). The volatiles were removed under vacuum, and the
residue was taken up in 0.6 mL of benzene-d6. NMR spectra
showed the reaction product and small amounts of decomposi-
tion products (1a: <15%, {Cp2Zr(OC6F5)2](μ-O): <5%).
Cp2Zr(CH2CH2Ph)OC6F5, 10. 1H NMR (300 MHz, C6D6): δ
7.32 (m, 5H, Ar), 5.69 (s, 10H, C5H5), 2.90 (m, 2H, CH2Ph), 1.43
(m, 2H, ZrCH2) ppm. 13C NMR: δ 148.9 (Ar), 129.6 (Ar), 125.9
(Ar), 115.5 (Ar), 112.6 (C5H5), 50.5 (ZrCH2), 40.1 (CH2Ph)
ppm. 19F (C6D6): δ -165.32 (m, ortho C6F5), -167.34 (m, meta
C6F5), -174.08 (m, para C6F5) ppm.
(7 or 8) to ensure mixing of the reactants (Cp2ZrH2 is mostly
insoluble). After 3 days the reaction is nearly completed (little
precipitate left). After 6 days the volatiles were removed under
vacuum, and the residue was redissolved in C6D6. The 1H NMR
displayed signals for 10 (vide supra) and 1b (used in excess).
A doublet of minor intensity (5%) was observed at 1.56 ppm
(d, J = 7 Hz), whichdisplayeda COSY cross-peakto a resonance
at 2.90 ppm, buried under the CH2Ph resonance of 10. Both
resonances were putatively assigned to the 2,1-insertion product
13. No 13C resonances could be observed for 13, nor did NOESY
experiments identify which of resonances of minor intensity in
the Cp region of the spectra could be associated with 13.
To the obtained C6D6 was added a solution of 2,6-dimethy-
lisocyanide (4.0 mg, 0.030 mmol) in C6D6, and the tube closed
and shaken. After 30 min at room temperature the reaction is
nearly complete (1H NMR), and all signals of 10 (and 13)
disappeared after 16 h.
Cp2Zr(OC6F5)(OEt), 11. 1H NMR (300 MHz, C6D6): δ 5.90
(s, 10H, C5H5), 3.90 (q, 2H, J = 7 Hz OCH2CH3), 1.05 (t, 3H,
J = 7 Hz, OCH2CH3) ppm. 13C NMR: δ 113.6 (C5H5), 70.6
(OCH2CH3), 19.8 (CH2CH3) ppm. 19F NMR (C6D6): δ -165.71
(m, ortho C6F5), -168.02 (m, meta C6F5), -175.63 (m, para
C6F5) ppm.
Cp2Zr(OC6F5)(OEt), 11, by Reaction of 5b with EtOH. A J.
Young NMR tube was charged with 5b (15.0 mg, 0.032 mmol),
2 μL of EtOH (0.054 mmol), and 0.6 mL of benzene-d6. The tube
was closed and heated 17 h at 70 °C, during which time the
solution turned colorless. After cooling to room temperature, the
1H NMR spectra revealed the formation of 11, isobutene, and
isobutane (in 4:1 ratio) and decomposition products (C5H6, 1b).
Cp2Zr(OC6F5)(CH2)5CH3, 12. (a) By Ligand Exchange. A J.
Young tube was charged with Cp2ZrH2 (5.0 mg, 0.022 mmol),
Cp2Zr(OC6F5)2 (17.0 mg, 0.030 mmol), trans-3-hexene (4.0 mg,
0.048 mmol), and 0.6 mL of benzene-d6. The NMR tube was
closed and allowed to stand at room temperature for 6 days,
during which the tube was shaken a few times (7 or 8) to ensure
mixing of the reactants (Cp2ZrH2 is mostly insoluble). After
removal of the volatiles in vacuo, the residue was redissolved in
C6D6. The solution contained excess 1b (25%), [Cp2Zr-
(OC6F5)]2O (4%), and 12 (71%).
Cp2Zr(OC6F5)(C(CH2CH2Ph)dN(Xylyl)). 1H NMR (C6D6):
δ 7.13-7.04 (m, 3H, C6H5), 6.93 (m, 2H, C6H5), 6.81 (m, 1H,
C6H3), 6.74 (d, 2H, J = 7 Hz, C6H3), 5.82 (s, 10H, C5H5), 2.77 (t,
2H, J = 8 Hz, CH2CH2Ph), 2.45 (t, 2H, J = 8 Hz, CH2CH2Ph),
1.74 (s, 6H, CH3) ppm. 13C NMR (C6D6): 144.0 (Ar), 141.2 (Ar),
129.5 (Ar), 128.9 (Ar), 128.7 (Ar), 127.2 (Ar), 126.8 (Ar), 110.7
(C5H5), 39.8 (CH2CH2Ph), 33.2 (CH2CH2Ph), 18.9 (CH3) ppm.
The doublet assigned to the insertion product of 13 appeared
at [1H NMR (C6D6)] 1.14 (d, J = 7 Hz) ppm. No 13C resonance
was observed after a reasonable time of acquisition. A NOESY
experiment did not show any correlation between this doublet
and the methyl groups of the N(C6H3(CH3)2).
Kinetic Experiments. A 0.6 mL amount of a stock solution
(0.036 M) of 5b (0.0216 mmol) and hexamethylbenzene (0.050 M)
in benzene-d6 was added to 4 equiv of the corresponding olefin,
and the resulting solution was transferred to a J. Young tube. The
tubes were heated to 70 °C in an oil bath, and 1H NMR spectra
were acquired every 35 min.
X-ray Diffraction Studies. Diffraction data were collected on a
Bruker Smart 6000 (4K) (1e, 7a) and a Bruker Microstar/
Platinum 135 diffractometer (6), both equipped with a rotating
anode source and Mirror Montel 200-monochromated Cu KR
radiation. Cell refinement and data reduction were done using
APEX2.57 Structures were solved by direct methods using
SHELXS9758 and refined on F2 by full-matrix least-squares
using SHELXL97.58 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were refined isotropically on
calculated positions using a riding model. The structure of 1e
contained one molecule of toluene disordered around an inver-
sion center. In 6 and 7a one cyclopentadienyl ring was found to
be slightly disordered, as indicated by elevated thermal para-
meters for the CCp atoms. All disorders have been resolved and
refined anisotropically with appropriate restraints. Further
experimental details are given in the Supporting Information.
Cp2Zr(OC6F5)(CH2)5CH3. 1H NMR (C6D6): δ 5.73 (s, 10H,
C5H5), 1.66 (m, 2H, ZrCH2CH2), 1.47 (m, 6H, (CH2)3Me), 1.23
(m, 2H, ZrCH2), 1.02 (m, 2H, CH3) ppm. 13C NMR (C6D6): δ
112.5 (C5H5), 50.0 (ZrCH2), 36.9 (CH2), 34.1 (ZrCH2CH2), 32.5
(CH2), 23.7 (CH2), 14.9 (CH3) ppm.
Addition of an excess of 2,6-dimethylisocyanide (8.1 mg,
0.060 mmol) to the C6D6 solution yielded in 30 min the insertion
product Cp2Zr(OC6F5)(C(hexyl)dN(xylyl)): 1H NMR (C6D6):
δ 6.90-6.69 (m, 3H, C6H3), 5.90 (s, 10H, C5H5), 2.13 (m, 2H,
Zr-CCH2), 1.77 (s, 6H, C6H3(CH3)2), 1.52 (m, 2H, CH2), 1.24
(m, 2H, CH2), 1.14 (m, 4H, CH2), 0.89 (t, 3H, J = 7 Hz,
CH2CH3) ppm. 13C NMR (C6D6): δ 110.6 (C5H5), 38.1 (CH2),
32.2 (CH2), 30.3 (CH2), 27.5 (CH2), 23.3 (CH2), 18.9 (C6H3-
(CH3)2), 14.6 (CH3) ppm.
(b) By Reaction of 5b with 1-Hexene. A J. Young NMR tube
was charged with 5b (20.4 mg, 0.044 mmol), 1-hexene (15.1 mg,
0.179 mmol), and 0.6 mL of benzene-d6. The tube was closed and
the solution heated in an oil bath 3 h at 70 °C, during which time
the bright yellow solution turned pale yellow. The volatiles were
removed in vacuo, and the residue was taken up in benzene-d6.
The 1H NMR spectra of the mixture confirmed the presence of
7b (7%) and 12 (93%).
(c) By Reaction of 5b with 3-Hexene. A J. Young NMR tube
was charged with 5b (24.3 mg, 0.052 mmol), trans-3-hexene
(12.4 mg, 0.147 mmol), and 0.6 mL of benzene-d6. The sealed tube
was heated in an oil bath for 3 h at 70 °C, during which time the
solution turned from bright yellow to pale yellow. The volatiles were
removed in vacuo, and the residue was taken up in benzene-d6. The
NMR spectra revealed a mixture of 7b (40%) and 12 (60%).
Cp2Zr(CH2CH2Ph)OC6F5, 10, from Cp2ZrH2 and 1b. In a
nitrogen-filled glovebox, a J. Young NMR tube was charged
with Cp2ZrH2 (7.0 mg, 0.031 mmol), 1b (21.2 mg, 0.036 mmol),
styrene (10.0 mg, 0.096 mmol), and 0.6 mL of benzene-d6. The
NMR tube was closed and allowed to stand at room tempera-
ture several days, during which the tube was shaken a few times
Acknowledgment. We thank Dr. P. V. M. Tan and S.
Bilodeau for assistance with NMR experiments, Dr. D.
Zargarian and D. Spasyuk for GC-MS analyses, and M.
Teillard for the synthesis of several compounds. Funding
for this research was provided by the Natural Sciences
and Engineering Research Council of Canada and the
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Universite de Montreal.
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Supporting Information Available: NMR spectra of noniso-
lated products or NMR reactions. Details of the X-ray structure
determinations. This material is available free of charge via the
Internet at http://pubs.acs.org.
(57) APEX2, Release 2.1-0; Bruker AXS Inc.: Madison, WI, 2006.
(58) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.