Synthetic and mechanistic studies of strained heterocycle opening reactions mediated by zirconium(IV) imido complexes

Article abstract of DOI:10.1021/om049105r

The reactions of the bis(cyclopentadienyl)(tert-butylimido)zirconium complex (Cp₂Zr=N-t-Bu)(THF) (1) with epoxides, aziridines, and episulfides were investigated. Heterocycles without accessible β-hydrogens undergo insertion/protonation of the C-X bond to produce 1,2-amino alcohols (X = O) and 1,2-diamines (X = NR), whereas heterocycles with accessible β-hydrogens undergo elimination/protonation to produce allylic alcohols (X = O) and allylic sulfides (X = S). Mechanistic investigations support a stepwise pathway with zwitterionic intermediates for the first reaction class and a concerted pathway for the second reaction class. Additionally, the feasibility of chirality transfer from the planar-chiral ebthi (ebthi = ethylenebis(tetrahydroindenyl)) ligand was demonstrated with a chiral analogue, (ebthi)Zr=NAr(THF) (Ar = 2,6-dimethylphenyl), 2, through the diastereoselective ring opening of meso epoxides.

Full text of DOI:10.1021/om049105r

Organometallics 2005, 24, 1647-1659
1647
Synthetic and Mechanistic Studies of Strained
Heterocycle Opening Reactions Mediated by
Zirconium(IV) Imido Complexes
Suzanne A. Blum, Vicki A. Rivera, Rebecca T. Ruck, Forrest E. Michael, and
Robert G. Bergman*
Department of Chemistry, University of California, Berkeley, California 94720
Received November 18, 2004
The reactions of the bis(cyclopentadienyl)(tert-butylimido)zirconium complex (Cp2ZrdN-
t-Bu)(THF) (1) with epoxides, aziridines, and episulfides were investigated. Heterocycles
without accessible â-hydrogens undergo insertion/protonation of the C-X bond to produce
1,2-amino alcohols (X ) O) and 1,2-diamines (X ) NR), whereas heterocycles with accessible
â-hydrogens undergo elimination/protonation to produce allylic alcohols (X ) O) and allylic
sulfides (X ) S). Mechanistic investigations support a stepwise pathway with zwitterionic
intermediates for the first reaction class and a concerted pathway for the second reaction
class. Additionally, the feasibility of chirality transfer from the planar-chiral ebthi (ebthi )
ethylenebis(tetrahydroindenyl)) ligand was demonstrated with a chiral analogue, (ebthi)-
ZrdNAr(THF) (Ar ) 2,6-dimethylphenyl), 2, through the diastereoselective ring opening of
meso epoxides.
Introduction
bifunctional reactivity allows for high levels of regio- and
stereoselectivity; in most cases, only one of several
possible products is obtained. The development of metal
complexes that exhibit bifunctional reactivity is an
active area of research for the design of new and highly
chemo- and stereoselective reactions.9-12 In contrast,
strained heterocycles with accessible â-hydrogens were
found to participate in elimination reactions, resulting
in allylic alkoxide complexes. The elimination reaction
of 2-methyl-2-propene oxide with imido complex 1 was
reported by our group previously.13 We now report the
full details of our original reports, including mechanistic
investigations and expansion of this reaction to include
aziridines, episulfides, and additional epoxide sub-
strates.
We have investigated the reactions of bis(cyclopen-
tadienyl)(tert-butylimido)zirconium complex 11 and its
chiral analogue (ebthi)ZrdNAr(THF) (ebthi ) ethyl-
enebis(tetrahydroindenyl), Ar ) 2,6-dimethylphenyl), 2,2
with strained heterocycles. Two different modes of
reactivity were observed, depending on the presence or
absence of â-hydrogens, where the â-hydrogen is defined
as being located two bonds away from the heterocyclic
ring. Strained heterocycles without accessible â-hydro-
gens participate in insertion chemistry of the C-X bond,
resulting in the formation of 1,2-aminoalkoxides (X )
O) and 1,2-diamides (X ) N) complexed to zirconium.3
Protonation of the 1,2-aminoalkoxide complexes releases
the corresponding 1,2-amino alcohol. Use of early tran-
sition metals as Lewis acids to promote the opening of
epoxides by amines and amine equivalents is an active
area of research,4-6 due to the importance of the amino
alcohol products in biologically active compounds and
as ligands for other transition-metal-mediated reac-
tions.7,8 Herein, we describe a mechanistically distinct
pathway for the opening of epoxides by amine equiva-
lents, in which imido complexes 1 and 2 act as both the
Lewis acid and the nucleophilic amine source. This
Results and Discussion
Reactions of Heterocycles without Accessible
â-Hydrogens. Imido complex 1 reacted cleanly with a
variety of strained heterocycles without accessible â-hy-
drogens. Scheme 1 shows a summary of the reactivity
of 1 with substrates of this class. In initial studies, we
found that complex 1 reacted with styrene oxide through
a highly regioselective ring opening, in 30 min at
ambient temperature, to give the orange azaoxazircona-
cyclopentane 3 (95% NMR yield, 44% isolated). Further
insight into the pathway for reaction of the imido moiety
* To whom correspondence should be addressed. E-mail: bergman@
cchem.berkeley.edu.
(1) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1988, 110, 8729.
(2) Sweeney, Z. K.; Salsman, J. L.; Andersen, R. A.; Bergman, R. G.
Angew. Chem., Int. Ed. 2000, 39, 2339.
(9) Hill, M.; Krker, G.; Kehr, G.; Frohlich, R.; Kataeva, O. J. Am.
Chem. Soc. 2004, 126, 11046.
(10) Ichikawa, E.; Suzuki, M.; Yabu, K.; Albert, M.; Kanai, M.;
Shibasaki, M. J. Am. Chem. Soc. 2004, 126, 11808.
(11) Kennedy-Smith, J. J.; Nolin, K. A.; Gunterman, H. P.; Toste,
F. D. J. Am. Chem. Soc. 2003, 125, 4056.
(12) Eldred, S. E.; Stone, D. A.; Gellman, S. H.; Stahl, S. S. J. Am.
Chem. Soc. 2003, 125, 3422.
(13) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. Organometallics
1993, 12, 3705.
(3) Blum, S. A.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc.
2003, 125, 14276.
(4) Bartoli, G.; Bosco, M.; Carlone, A.; Locatelli, M.; Massaccesi, M.;
Melchiorre, P.; Sambri, L. Org. Lett. 2004, 6, 2173.
(5) Larrow, J. F.; Schaus, S. E.; Jacobsen, E. N. J. Am. Chem. Soc.
1996, 118, 7420.
(6) Caron, M.; Sharpless, K. B. J. Org. Chem. 1985, 50, 1557.
(7) Bergmeier, S. C. Tetrahedron 2000, 56, 2561.
(8) Ager, D. J.; Prakash, I.; Schaad, D. R. Chem. Rev. 1996, 96, 835.
10.1021/om049105r CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/25/2005

1648 Organometallics, Vol. 24, No. 7, 2005
Scheme 1. Reactivity of 1 with Strained Heterocycles Lacking Accessible â-Hydrogens
Blum et al.
Table 1. Relative Rates of Reaction of
para-Substituted Styrene Oxides, Compared to σ+
Constants
with styrene oxide was gained by examining the reac-
tion of the chiral analogue, (rac)-2, with (S)-styrene
oxide. This ring opening proceeded with similar regio-
chemistry, to give product (rac)-9 (83%) (eq 1). The
relative rate
relative rate
2.0 equiv epoxide
p-X-Ar
σ+
10.0 equiv epoxide
MeO-
F-
-0.78
-0.07
0
0.11
0.15
0.61
100a
1.0
1.0
H-
1
1
Cl-
Br-
CF3-
0.85
0.70
0.15
0.80
0.73
0.15
a Reaction with 20.0 equiv of styrene oxide and 2.0 equiv of
p-methoxystyrene oxide.
structure of product 9 was confirmed by single-crystal
X-ray diffraction (Figure 1). The Zr-O and Zr-N bond
distances (1.966(3) and 2.112(3) Å, respectively) and the
O-Zr-N bond angle (80.27(8)°) were similar to those
of the other crystallographically characterized com-
plexes synthesized in this study (vide infra). A compari-
son of selected bond lengths and angles can be found in
Tables 2 and 3. The observed regio- and stereochemis-
tries of 3 and 9 provided our first insight into the
mechanism of this transformation. Formation of prod-
ucts containing a new N-C bond at the benzylic carbon
was consistent with the reaction proceeding through a
stepwise pathway that favored epoxide opening at the
benzylic site. Furthermore, (rac)-9 was formed as a
single diastereomer (R,R,R/S,S,S) (83% isolated yield),
which implicated a pathway that allowed for scrambling
of the original (S)-styrene oxide stereocenter. We con-
sidered both heterolytic and homolytic possibilities for
this process: (a) ring opening to form a benzylic car-
Figure 1. ORTEP diagram of 9.
bocation (10a), followed by trapping of the carbocation
by the anionic imido ligand, and (b) ring opening to form
a benzylic radical (10b), followed by trapping of the

Strained Heterocycle Opening Reactions
Organometallics, Vol. 24, No. 7, 2005 1649
Table 2. Comparison of Selected Bond Distances
(Å)
complex
4
5
Zr-N
Zr-N
Zr-N1
Zr-N
Zr-N
Zr-N
2.035(6)
2.066(5)
2.080(4)
2.112(3)
2.118(4)
1.836(3)
Zr-O
Zr-N2
Zr-O
Zr-O
Zr-O
1.972(4)
2.174(4)
1.966(3)
2.011(3)
2.265(3)
8
9
14
23
Table 3. Comparison of Selected Bond Angles
(deg)
complex
4
5
C-Zr-N
O-Zr-N
N1-Zr-N2
O-Zr-N
O-Zr-N
O-Zr-N
72.7(3)
80.1(2)
78.2(2)
80.27(8)
78.4(1)
96.8(1)
Figure 2. Hammett study showing correlation between
log(k/ko) and σ+.
8
9
14
23
substituent effects than an epoxide-opening reaction
known to proceed through a benzylic cation. However,
a conceptually similar set of radical reactions do not give
rise to viable Hammett correlations. Ingold and co-
workers performed a computational study on a series
of substituted toluene compounds (4-Y-C6H4CH2X, X )
H, Br, Cl, F) and report the complete absence of a
Hammett correlation between the bond dissociation
enthalpies of C-X and the relevant substituent con-
stants (either σ or σ+).16 An elegant review of this topic
exists, which provides analysis and summary of both
experimental and theoretical results in this area.16 For
this reason, the results of our Hammett study are most
consistent with the development of significant charge
separation in the transition state leading to formation
of the intermediates, and therefore with the intermedi-
ates themselves having zwitterionic character, despite
the lower absolute value of F+ observed in this reaction
than in the reported solvolysis reaction.
We considered the possibility that, due to the presence
of a large excess of epoxide, the THF-bound complex
might no longer be the ground state of the system.
Instead, an epoxide-bound complex might be the ground
state. The competition experiments using 20.0 equiv of
epoxide were too rapid to observe starting materials at
room temperature. Therefore, the nature of the ground
state was investigated by low-temperature 1H NMR
spectroscopy. When 20.0 equiv of styrene oxide was
added to imido complex 1 at -20 °C, complete displace-
ment of THF by the epoxide was observed. In contrast,
monitoring the reaction of imido complex 1 with 2.0
equiv of p-trifluoromethylstyrene oxide and 2.0 equiv
of styrene oxide at partial conversion showed that,
under these conditions, the ground state remained the
THF adduct. We next examined whether this difference
affected the outcome of the competition experiments.
The competition experiment was repeated for the series
of substrates using 2.0 equiv of each epoxide (Table 1,
column 4). Relative rates were found to be identical in
the experiments that employed 2.0 equiv of each epoxide
and 10.0 equiv of each epoxide, within the error of the
measurement ((10%). These identical relative rates
imply that the reaction operates under Curtin-Ham-
mett kinetics; that is, our measurement reflects ∆∆Gq,
Scheme 2. Proposed Mechanism, Involving a
Diradical or a Zwitterionic Intermediate
benzylic radical by the imido-based radical (Scheme 2).
In our initial communication,3 we hypothesized that the
reaction proceeded by pathway (a). However, since the
neighboring phenyl group in intermediates 10a and 10b
could help stabilize a charged or a radical species,
further experimentation was needed to examine this
issue.
Substituent Effects. A Hammett study was con-
ducted to determine the character of the intermediates
(zwitterionic or diradical) in the stepwise process. The
relative reaction rates of para-substituted styrene oxide
derivatives were assessed via competition experiments
in which a solution of imido complex 1 was added to a
rapidly stirred solution of 10.0 equiv of the substituted
styrene oxide and 10.0 equiv of the parent styrene oxide
1
in C6D6. These reactions were monitored by H NMR
spectroscopy and found to be complete in less than 10
min. The product ratios did not change upon standing.
The relative reaction rates determined under these
conditions are shown in Table 1, column 3.
A significantly better fit was obtained when the
relative reaction rates were plotted against σ+14 than
against σp, consistent with a direct resonance interaction
between the para position on the aromatic ring and the
reacting center. When electron-withdrawing (p-Cl, p-Br,
p-CF3), neutral (p-F), and electron-donating substituents
(p-OMe) were examined, a moderately good fit leading
to a F+-value of -2.2 was obtained (Figure 2). This low
absolute value of F+ contrasts with the higher absolute
value of F+ observed for the Brønsted-acid-catalyzed
aqueous solvolysis of para-substituted styrene oxides
(-4.2).15 Therefore, the zirconocene imido-mediated
opening of epoxides is significantly less sensitive to
(14) Takeuchi, K.; Takasuka, M.; Ohga, Y.; Okazaki, T. J. Org.
Chem. 1999, 64.
(15) Blumenstein, J. J.; Ukachukwu, V. C.; Mohan, R. S.; Whalen,
D. L. J. Org. Chem. 1993, 58, 924.
(16) Pratt, D. A.; Dilabio, G. A.; Mulder, P.; Ingold, K. U. Acc. Chem.
Res. 2004, 37, 334.

1650 Organometallics, Vol. 24, No. 7, 2005
Blum et al.
Scheme 3. Mechanism of Reaction of cis- and
trans-Stilbene Oxides with 1, Showing
Curtin-Hammett Kinetics
Figure 3. ORTEP diagram of 14 (obtained as the RRRR/
SSSS racemate).
same single diastereomer independent of the starting
stereochemistry of the epoxide (eq 2). An X-ray diffrac-
tion study revealed that (rac)-14 was the R,R,R,R/
S,S,S,S racemate, confirming the trans stereochemistry
(Figure 3). This offered support for our initial hypoth-
eses that 13 was the trans isomer (vide supra). The high
diastereoselectivity of this reaction suggested the pos-
sibility of a kinetic resolution of the racemic imido
compound (rac)-2 by readily available enantiopure
trans-stilbene oxide.18 Addition of 0.55 equiv of (R,R)-
trans-stilbene oxide (>98% ee) to a solution of 1.0 equiv
of (rac)-2 in C6H6 at ambient temperature resulted in a
modest product diastereoselectivity of 3:1, corresponding
to 50% ee of unreacted 2.19
Vinylcyclopropane Oxide. In an effort to gain
further support for the presence of a zwitterionic
intermediate, we investigated the ring opening of vi-
nylcyclopropane oxide20 (15) with imido complex 1. We
reasoned that if the reaction proceeds via a radical
pathway, we should observe a product corresponding to
ring opening of the cyclopropylcarbinyl radical.21 Un-
fortunately, the reaction of 1 with 15 led to a complex
mixture of products as determined by multiple Cp
resonances in the 1H NMR spectrum. Treatment of
N-TBS imido complex 1613 (TBS ) tert-butyldimethyl-
silyl), however, with epoxide 15 led to formation of a
single product, 17, that corresponded to simple ring
opening of the epoxide (Scheme 4). Given the fast rate
of cyclopropylcarbinyl radical ring opening,22 failure to
observe the corresponding cyclopropane ring-opened
product 18 suggests again that the reaction proceeds
via a zwitterionic mechanism (path a) as opposed to a
radical mechanism (path b).23
the difference in energy between the transition states
for the opening of styrene oxide and substituted styrene
oxide and does not reflect the energy difference between
ground states. This case would be expected for rapid and
reversible binding of each epoxide, prior to rate-
determining ring opening. Activation parameters sup-
porting the rapid and reversible binding of Lewis bases
to imido complex 1 at ambient temperature were
recently reported by our group.17
Stereochemistry of Metallacycle Formation. Fur-
ther support for the proposed stepwise mechanism was
obtained through examination of the reactivity of 1 with
cis- and trans-stilbene oxides in separate reactions. In
this case, 1H NMR analysis of the reaction mixture
showed formation of the same metallacycle, independent
of the stereochemistry of the starting material, consis-
tent with ring opening to form cis (11) and trans (12)
zwitterions, which interconverted rapidly relative to
trapping by the imido group (Scheme 3). Furthermore,
performing the reaction in the presence of excess
stilbene oxide showed that the unreacted epoxide did
not isomerize under the reaction conditions. This sup-
ports a mechanism that proceeds through rate-limiting
ring opening, since once the epoxide opens, it does not
revert to a bound epoxide, which would be expected to
rapidly dissociate from the metal. We initially assigned
product 13 as the trans isomer, since we theorized that
the lower steric interaction between the adjacent phenyl
groups would make the trans transition state more
favorable. This stereochemical assignment was later
confirmed for the ebthi system (vide infra).
The reaction of chiral ebthi complex (rac)-2 with cis-
or trans-stilbene oxide was also studied (eq 2). In theory,
Reactions with Other Strained Heterocyclic
Systems. We next examined the reaction of butadiene
monoepoxide with 1 (Scheme 5). Stepwise ring opening
would be expected to form allylic intermediate 19, in
which cationic character would be distributed between
the two terminal carbon atoms of the allylic system.
Trapping to form a five-membered ring or to form a
seven-membered ring would then produce metallacycle
(18) Tu, Y.; Wang, Z.-X.; Shi, Y. J. Am. Chem. Soc. 1996, 118, 9806.
(19) Priego, J.; Carratero, J. C. Synlett 1999, 1603.
(20) Kirmse, W.; Kornrumpf, B. Angew. Chem., Int. Ed. Engl. 1969,
8, 75.
this reaction could lead to the generation of four
different diastereomers, arising from both the planar
chirality of the ebthi ligand and from the benzylic
stereocenters. A 1H NMR spectrum of the crude reaction
mixture showed that product (rac)-14 was formed as the
(21) Nonhebel, D. C. Chem. Soc. Rev. 1993, 22, 347.
(22) Bowry, V. W.; Lusztyk, J.; Ingold, K. U. J. Am. Chem. Soc. 1991,
113, 5687.
(23) There was no evidence for the presence of olefinic resonances
(17) Blum, S. A.; Bergman, R. G. Organometallics 2004, 23, 4003.
in the 1H NMR spectrum.

Strained Heterocycle Opening Reactions
Organometallics, Vol. 24, No. 7, 2005 1651
Scheme 4. Reaction of N-TBS Imido Complex 16 with Vinylcyclopropane Oxide
Scheme 5. Imidozirconium-Mediated Opening of Butadiene Monoepoxide
Scheme 6. Proposed Mechanism for the Opening
6 or 7, respectively. When 1 was added to a solution of
of exo-Norbornene Oxide by 1
butadiene monoepoxide in C6D6 at ambient tempera-
ture, the solution turned bright orange immediately. 1H
NMR spectroscopy showed formation of two metallacycle
isomers, assigned as 6 and 7 by proton coupling patterns
(43% and 41% NMR yields, respectively), and the
absence (6) or presence (7) of diastereotopic cyclopen-
tadienyl ligands. Metallacycle 6 exhibited fluxional
behavior that resulted in line broadening in the 1H NMR
spectrum at ambient temperature, possibly originating
from different, equilibrating ring conformations. Warm-
ing the sample to 70 °C resulted in a sharpening of the
resonances. Protonolysis by benzoic acid produced zir-
conocene dibenzoate 20 as well as the two previously
unknown amino alcohols 21 and 22, in a ratio identical
to the ratio of metallacycle 6 to 7. The structures of 21
and 22 were assigned by HRMS and 1H NMR spectros-
copy.
Although epoxide complexes with styrene oxide, stil-
bene oxide, or butadiene monoepoxide bound to zirco-
nium were not observed by 1H NMR spectroscopy in the
reactions with 1 or 2, we presumed that these complexes
were intermediates formed along the reaction pathway.
Therefore, we sought a system with a higher barrier for
ring opening that would allow for observation of an
epoxide complex. A C6D6 solution of 1 and exo-nor-
bornene oxide exhibited a broad 1H NMR spectrum,
consistent with exchange of the THF and exo-nor-
bornene oxide ligands at ambient temperature (Scheme
6). Removal of the THF in vacuo from this solution
produced exo-norbornene oxide complex 23 quantita-
the double-bond character of the imido moiety remains
and is similar to the Zr-N bond length in 1 (1.826(4)
Å).1 A comparison of selected bond lengths and angles
for the complexes reported in this study can be found
in Tables 2 and 3. This is one of the few examples of
proposed intermediate epoxide complexes that have
been isolated and structurally characterized.24,25
Heating either a solution of 1 and exo-norbornene
oxide (45 °C for 24 h) or a solution of 23 (45 °C for 5 h)
1
tively, as observed by H NMR spectroscopy. Crystals
of 23 were obtained at low temperature and character-
ized by X-ray diffraction (Figure 4). The long Zr-O bond
(2.265(3) Å) is consistent with the presence of a dative
interaction between the epoxide and the zirconium
center. The short Zr-N bond (1.836(3) Å) indicates that
(24) Darensbourg, D. J.; Wildeson, J. R.; Lewis, S. J.; Yarbrough,
J. C. J. Am. Chem. Soc. 2002, 124, 7075.
(25) Groves, J. T.; Han, Y.; Engen, D. J. Chem. Soc., Chem.
Commun. 1990, 436.

1652 Organometallics, Vol. 24, No. 7, 2005
Blum et al.
Scheme 7. Reaction of 1 with
7-Oxabenzonorbornadiene
Figure 4. ORTEP diagram of epoxide complex 23.
Figure 6. ORTEP diagram of 4.
broadening at ambient temperature, consistent with
establishment of an equilibrium between bound THF
and bound epoxide complexes, similar to the equilibrium
between 1 and 23. Heating this mixture to 75 °C,
however, did not produce ring-opened product. This lack
of reactivity corroborated the requirement for substan-
tial resonance stabilization from a group at the R
position to facilitate ring opening and therefore provided
indirect support for resonance-stabilized (“nonclassical”)
zwitterion 24 over the (“classical”) diradical structure.
Addition of ethylene oxide to 1 in C6D6 resulted in
rapid precipitation of a white solid, consistent with
polymerization of the epoxide. 1H NMR spectroscopy
performed on the remaining solution showed the forma-
tion of an intractable mixture of products, implying that
ethylene oxide accessed different reactivity than the
other epoxides in this study.
The reaction of imido complex 1 with 7-oxabenzonor-
bornadiene, which had been shown previously to un-
dergo metal-mediated ring opening and subsequent
trapping by nucleophiles,28 was investigated next
(Scheme 7). This substrate, however, reacted with imido
complex 1 to form the [2 + 2] cycloaddition product, 4,
in quantitative NMR yield. Removal of the solvent in
vacuo produced analytically pure material (87%). Com-
plex 4 was characterized by X-ray crystallography
(Figure 6). The X-ray crystal structure verified that
cycloaddition favors the exo face of the olefin exclusively,
which was observed previously in the reaction of 1 with
norbornene.13 Formation of 4 was found to be irrevers-
ible up to 75 °C, as evidenced by the stability of 4 in
the presence of styrene oxide. The stability of 4 con-
trasted sharply with the previously reported observation
that imido complex 1 formed highly labile [2 + 2]
cyclcoaddition products with ethylene and norbornene.13
The replacement of the methylene bridge of norbornene
with an oxygen therefore caused a marked shift in
reactivity, perhaps through the increase in strain of the
Figure 5. ORTEP diagram of cis-metallacycle 5.
yielded cis-metallacycle 5 (94% NMR yield, 46% iso-
lated). The stereochemistry of 5 was confirmed by X-ray
diffraction (Figure 5). The cis stereochemistry of 5
cannot result from “back side” SN2 displacement of the
epoxide oxygen and therefore is consistent with the
initial conversion of 23 to an intermediate that allows
for subsequent “front side” attack. This intermediate
may be the carbon-bridged (“nonclassical”) zwitterion
24 or the nonbridged (“classical”) diradical.26 Interest-
ingly, no trapping product 25, which would result from
the rearranged norbornyl framework, is observed. This
lack of rearrangement seems somewhat inconsistent
with the zwitterionic hypothesis. However, the possibil-
ity that closure to form 5 from zwitterion 24 proceeds
preferentially through a kinetically favored five-mem-
bered ring transition state instead of trapping at the
adjacent carbon atom, which would require a six-
membered ring transition state, cannot be ruled out.
Kinetic studies of the conversion of 23 to 5 were
performed, and the reaction was found to exhibit first-
order kinetics with respect to 23 (k ) 0.017 min-1 (59.8
°C), k ) 0.051 min-1 (69.8 °C), k ) 0.084 min-1 (79.8
°C), k ) 0.22 min-1 (89.9 °C)).27 The rate was zero-order
in concentration of excess epoxide, consistent with
unimolecular conversion of 23 to 5. Rates measured over
this temperature range gave activation parameters ∆Hq
) 19 ( 2 kcal mol-1 and ∆Sq ) -18 ( 4 cal mol-1 K-1
.
When 1 was treated with 1,2-epoxy-3,3-dimethylbu-
tane (Scheme 1), 1H NMR spectroscopy showed line
(26) Warner, C. R.; Strunk, R. J.; Kuivila, H. G. J. Org. Chem. 1966,
31, 3381.
(27) We estimate the error to be (0.006 min-1 at 69.5 °C, based on
(28) Lautens, M.; Fagnou, K.; Hiebert, S. Acc. Chem. Res. 2003, 36,
48.
a triplicate run.

Strained Heterocycle Opening Reactions
Organometallics, Vol. 24, No. 7, 2005 1653
elimination reaction was investigated in detail through
the reaction of 1 with the simpler substrate, 1,2-butene
oxide.
When a solution of 1,2-butene oxide in C6D6 was
1
added to imido complex 1 at ambient temperature, H
NMR spectroscopy showed the formation of two isomeric
zirconocene products in the ratio 2.0:1.0 (29). Identifica-
tion of these products was facilitated by cleavage of the
organic fragments from the metal center with 8 equiv
of benzoic acid. This produced the zirconocene diben-
zoate complex 20, tert-butylamine, and cis- and trans-
crotyl alcohol (>95% NMR yield; eq 4). Protic cleavage
Figure 7. ORTEP diagram of 8.
bicyclic ring system, which would destabilize the π-bond
of the starting heterocycle.
The reactivity of imido complex 1 with aziridines was
highly dependent on the nature of the substituent on
the nitrogen. For example, N-tosyl-2-phenylaziridine
reacted with 1 over 2 days at 75 °C to give the magenta
diazazirconacyclopentane 8 (>95% NMR yield, 84%
isolated; eq 3), while cis-1,2,3-triphenylaziridine did not
undergo ring opening. This discrepant behavior can be
did not change the ratio of isomers significantly (2.1:
1.0). Comparison with a commercially available mixture
of cis- and trans-crotyl alcohol by 1H NMR spectroscopy
and by 2-D TOCSY NMR spectroscopy showed that the
major isomer corresponded to trans-crotyl alcohol and
the minor isomer to cis-crotyl alcohol. Therefore, imido
complex 1 exhibited a modest preference for removal of
the proton corresponding to formation of the trans
olefin.
The substrate trans-phenylpropene oxide provided an
opportunity to examine the preference of imido complex
1 to participate in insertion (vide supra) or elimination
reactions, via an intramolecular competition experiment
(Scheme 9). The addition of trans-phenylpropylene oxide
to 1 in C6D6 at ambient temperature resulted in the
rapid (<30 min) formation of a single product 30 (82%
isolated) corresponding to an elimination reaction.
Product 32, which would form via insertion, was not
observed. Therefore, the elimination pathway has a
significantly lower barrier than the insertion pathway.
This has important consequences for the mechanism of
the elimination reaction. Since a reaction that proceeds
via significant charge buildup or radical character would
be expected to favor reactivity at the benzylic position,
the fact that elimination at a saturated center proceeds
more rapidly suggests a concerted process for this
reaction (Scheme 10).
explained by the better leaving group ability of tosyl-
amides over phenylamides. The structure of 8 was
confirmed by single-crystal X-ray diffraction (Figure 7).
The bond between the zirconium atom and the tert-
butylamide group was found to be shorter (2.080 Å) than
the bond between the zirconium and the tosylamide
(2.174 Å). This is consistent with partial donation of the
lone pair on the tert-butylamide to the electron-deficient
zirconium center, creating multiple bond character. The
lone pair on the tosylamide is less able to donate to the
zirconium center, due to interaction with the sulfonyl
group. Importantly, the observed regiochemistry of 8
supports a zwitterionic ring-opening mechanism analo-
gous to the one we have proposed for the reactions of 1
with epoxides.
Reactions of Strained Heterocycles with Acces-
sible â-Hydrogens. Imido complex 1 exhibited clean
elimination reactivity with a variety of epoxides with
accessible â-hydrogens. Scheme 8 shows a summary of
the reactivity of 1 with substrates of this class; the
individual reactions will be described in detail in the
subsequent paragraphs. Propylene oxide underwent
clean ring opening with 1 in C6D6 at ambient temper-
ature to give the corresponding allylic alkoxy amide 26.
Removal of the solvent produced analytically pure 26
(>95%). Similarly, cyclohexene oxide reacted with 1 to
give complex 27 (90% NMR yield, 37% isolated), and
cyclooctene oxide reacted with 1 to give complex 28 (>
95% NMR yield) as a mixture of cis and trans isomers
(88:12). Removal of the solvent produced analytically
The potential for chirality transfer from the planar-
chiral ebthi ligand set of (rac)-2 was investigated in the
ring-opening desymmetrization reaction of the meso
epoxide cis-2,3-butene oxide (eq 5). This ring-opening
reaction could theoretically result in the formation of
two possible diastereomers due to the chirality of the
ligand and that of the newly formed carbon-based
stereocenter. This is of interest due to the limited
number of methods currently available to enantioselec-
1
pure 28 (>95%). Due to the complexity of the H NMR
spectrum of the substrate, the isomer assignment was
not determined. Instead, the diastereoselectivity of the

1654 Organometallics, Vol. 24, No. 7, 2005
Scheme 8. Reactivity of 1 with Strained Heterocycles with Accessible â-Hydrogens
Blum et al.
Scheme 9. Intramolecular Competition
Experiment, Showing Preference for Elimination
Reactivity
NMR spectrum showed that the reaction proceeded with
a high degree of diastereoselectivity (>95:5). This
established the feasibility of using the ebthi ligand for
effective chirality transfer in the elimination reactions
of zirconium imido complexes.
Propene sulfide also underwent an ambient-temper-
ature elimination reaction with imido complex 1, pro-
ducing allylic sulfide complex 31 (72% NMR yield;
Scheme 11). Heating complex 1 in the presence of excess
propylene sulfide at 75 °C for 8 h resulted in catalytic
desulfurization of the substrate, producing propene
(510% NMR yield, relative to 1) and multiple other
products, both soluble and insoluble in the reaction
medium. Mass spectral analysis of the soluble products
indicated the presence of mass fragments corresponding
to oligomerization of the starting material. Previous
reports in the literature suggest that episulfides are
readily polymerized when treated with a variety of
Lewis acids and readily desulfurized to yield the cor-
responding olefin.30 Therefore, it seems unlikely that
catalysis specifically requires the presence of complex
1 or 31, but rather may involve minor amounts of
uncharacterized zirconocene products. Characterization
of 31 was facilitated by protic cleavage with benzoic acid,
which produced 20, tert-butylamine, and allyl sufide
(>95% NMR yield). In contrast to the insertion chem-
istry observed with 1 (vide supra), N-tosylaziridines
bearing accessible â-hydrogens did not participate in
ring-opening elimination reactions.
Scheme 10. Proposed Concerted Pathway for
Elimination Reaction of Propene Oxide
Conclusion
tively deprotonate meso epoxides.29 When 1 equiv of cis-
2,3-butene oxide was added to 1 equiv of (rac)-2, a H
Imidozirconocene complexes 1 and 2 underwent highly
regio- and stereoselective insertion and elimination
1
(29) For leading references, see: Eames, J. Eur. J. Inorg. Chem.
2002, 393.
(30) Adams, R. D.; Queisser, J. A.; Yamamoto, J. H. J. Am. Chem.
Soc. 1996, 118, 10674, and references therein.

Strained Heterocycle Opening Reactions
Organometallics, Vol. 24, No. 7, 2005 1655
Scheme 11. Ring Opening of Propene Sulfide and Subsequent Reactions
by Dr. Fred Hollander and Dr. Allen Oliver in the University
of California, Berkeley CHEXRAY facility.
reactions with a variety of epoxides. This reactivity can
be extended to properly substituted aziridines and
episulfides. Appropriately substituted substrate probes
were used to investigate the mechanisms of these
reactions and have provided strong evidence for a
stepwise reaction pathway for the ring-opening reaction
of heterocycles without â-hydrogens. This mechanism
was shown to involve rate-determining ring opening,
leading to stereochemically labile intermediates. A good
correlation between reaction rate and the Hammett
substituent constants (σ+) suggested that the intermedi-
ates in this process possessed substantial zwitterionic
character. The absence of cyclopropyl ring opening when
vinylcyclopropane oxide reacted with imido complex 16
further supported the action of a zwitterionic mecha-
nism. In contrast, the results of substrate probe experi-
ments were most consistent with the ring-opening
reaction of heterocycles with accessible â-hydrogens
proceeding through a concerted pathway. The results
demonstrate the bifunctional importance of the Lewis-
acidity of the zirconium center and the nucleophilicity
and basicity of the imido moiety in promoting these ring-
opening reactions.
Metallacycle 3. A solution of styrene oxide (28 mg, 0.23
mmol) in benzene (0.2 mL) was added to a solution of imido
complex 1 (75 mg, 0.21 mmol) in benzene (0.3 mL), producing
an orange solution. To remove the benzene, the volatile
materials were removed in vacuo to give a viscous orange oil,
which was dissolved in ether (0.2 mL) to form a clear orange
solution, and again the volatile materials were removed in
vacuo to give an orange oil. The oil was again taken up in ether
(0.75 mL) to form a cloudy solution and cooled to -35 °C. After
2 days, a red solid had precipitated. The mother liquor was
decanted, the solid was washed quickly with cold pentane, and
the volatile materials were removed in vacuo to leave the red
1
solid (38 mg, 44%). H NMR (300 MHz, C6D6): δ 7.63 (d, J )
7.0 Hz, 2H), 7.30 (t, J ) 7.8 Hz, 2H), 7.16 (m, 1H), 6.24 (s,
5H), 6.10 (s, 5H), 4.80 (dd, J ) 10.2, 5.3 Hz, 1H), 4.46 (d, J )
5.3 Hz, 1H) 3.99 (d, J ) 10.2 Hz, 1H), 0.80 (s, 9H). 13C{1H}
NMR (125 MHz C6D6): δ 151.4, 127.6, 127.0, 125.9, 113.6,
112.1, 78.6, 75.4, 55.8, 30.3. IR (Nujol): 1352, 1196, 1071, 1059,
1043, 1012, 965, 768, 761, 722, 707, 598, 552 (s), 529 (s), 508
(s) cm-1. Anal. Calcd for C22H27NOZr: C, 64.03; H, 6.59; N,
3.39. Found: C, 64.43; H, 6.67; N, 3.40.
p-Trifluoromethylstyrene Oxide Metallacycle. A solu-
tion of p-trifluoromethylstyrene oxide (16 mg, 0.082 mmol) in
benzene (0.3 mL) was added to imido complex 1 (30 mg, 0.082
mmol). After 4 days, the solution had turned bright orange,
and the volatile materials were removed in vacuo, producing
an orange gum. The gum was taken up in pentane (6 drops)
to form a cloudy orange solution, which was cooled to -35 °C.
After 2 days, clusters of pale orange crystals had formed. The
mother liquor was removed by pipet, and the residual solvent
was removed from the crystals in vacuo, yielding 32 mg (81%).
1H NMR (500 MHz, C6D6): δ 7.51 (m, 4H), 6.18 (s, 5H), 6.08
(s, 5H), 4.73 (dd, J ) 10, 5.0 Hz, 1H), 4.31 (d, J ) 5.5 Hz, 1H),
3.79 (d, J ) 10 Hz, 1H), 0.71 (s, 9H). 13C{1H} NMR (125 MHz,
C6D6): δ 156.1, 126.2, 124.6 (CF3), 113.7, 112.3, 78.0, 75.1, 55.8,
30.2. Anal. Calcd for C23H26F3NOZr: C, 57.47; H, 5.45; N, 2.91.
Found: C, 57.47; H, 5.27; N, 2.88.
Experimental Section
General Methods. All manipulations were carried out
under inert atmosphere, using a nitrogen-filled recirculating
glovebox or standard Schlenk line techniques. Solvents were
degassed using three freeze-pump-thaw cycles and dried over
3 Å activated molecular sieves (benzene-d6, toluene-d8), passed
through an activated alumina column and sparged with
nitrogen (benzene, toluene, pentane, THF, ether),31 or distilled
from purple Na/benzophenone ketyl (THF, ether), prior to use.
Bis(cyclopentadienyl)(tert-butylimido) zirconium complex 1,1
(ebthi)ZrdNAr(THF) (ebthi ) ethylenebis(tetrahydroindenyl,
Ar ) 2,6-dimethylphenyl), 2,2 bis(cyclopentadienyl)(tert-butyl-
dimethylsilylimido) zirconium complex 16,13 and vinylcyclo-
propane oxide20 were synthesized according to previously
published procedures. Liquid and low-melting-solid substrates
were degassed using three freeze-pump-thaw cycles and
vacuum transferred from CaH2 or distilled from CaH2 prior
to use. p-Methoxystyrene oxide was synthesized by dimethyl-
dioxirane (DMDO) epoxidation of p-methoxystyrene.32
p-Bromostyrene Oxide Metallacycle. A solution of p-
bromostyrene oxide (16 mg, 0.082 mmol) in benzene (0.3 mL)
was added to imido complex 1 (30 mg, 0.082 mmol). The
solution turned bright orange over 10 min. After 2 days, the
volatile materials were removed in vacuo, producing an orange
gum. The gum was taken up in ether (0.5 mL), producing a
cloudy orange solution. Pentane vapor diffusion was initiated
at -35 °C. After 6 days, orange crystals were present above
the solvent line and in the pale yellow mother liquor. The
mother liquor was removed by pipet, and the crystals were
washed quickly with cold pentane. The residual solvent was
All 1H NMR and 13C NMR spectra were recorded on Bruker
AV300, AV400, and DRX500 spectrometers. 1H NMR and 13C-
{1H} NMR chemical shifts (δ) are reported in parts per million
(ppm) downfield of tetramethysilane and referenced to the
residual protiated solvent peak. When listed, 13C{1H} NMR
peak assignments were determined by DEPT 135 experiments.
NMR yields were measured by integration of product reso-
nances in single-scan 1H NMR spectra, relative to integration
of THF resonances. X-ray structural analyses were performed
1
removed in vacuo, yielding 18 mg (45%). H NMR (300 MHz,
C6D6): δ 7.35 (m, 4H), 6.17 (s, 5H), 6.09 (s, 5H), 4.72 (dd, J )
9.5, 4.8 Hz, 1H), 4.26 (d, J ) 5.1 Hz), 3.81 (d, J ) 10.2 Hz,
1H), 0.72 (s, 9H). 13C{1H} NMR (125 MHz C6D6): δ 150.7,
130.7, 128.8, 119.5, 113.7, 112.3, 77.8, 75.3, 55.8, 34.1, 25.5.
Anal. Calcd for C22H26BrNOZr: C, 53.75; H, 5.33; N, 2.85.
Found: C, 53.92; H, 5.18; N, 2.77.
(31) Alaimo, P. J.; Peters, D. W.; Arnold, J.; Bergman, R. G. J. Chem.
Educ. 2001, 78, 64.
p-Chlorostyrene Oxide Metallacycle. A solution of p-
chlorostyrene oxide (23.4 mg, 0.151 mmol) in benzene (1.5 mL)
(32) Murray, R. W.; Singh, M. Organic Syntheses; Wiley: New York;
Vol. IX.

1656 Organometallics, Vol. 24, No. 7, 2005
Blum et al.
was added to imido complex 1 (50.0 mg, 0.137 mmol). The
solution turned bright orange over 10 min. After 1 day, the
volatile materials were removed in vacuo, producing an orange
gum. The gum was taken up in ether (1.5 mL), producing a
cloudy orange solution. Pentane vapor diffusion was initiated
at -35 °C. After 9 days, orange crystals were present above
the solvent line and in the pale yellow mother liquor. Some
fine white powder (presumably decomposition products) had
settled to the bottom of the solution. The mother liquor was
removed by pipet, concurrently removing the fine white powder
as a suspension. The crystals were washed quickly with cold
pentane and the residual solvent was removed in vacuo,
yielding 18 mg (30%). 1H NMR (500 MHz, C6D6): δ 7.37 (d, J
) 8.5 Hz, 2H), 7.22 (d, J ) 8.5 Hz, 2H), 6.17 (s, 5H), 6.08 (s,
5H), 4.73 (dd, J ) 10.5, 5.0 Hz, 1H), 4.29 (d, J ) 5.5 Hz, 1H),
3.83 (d, J ) 10 Hz, 1H), 0.74 (s, 9H). 13C{1H} NMR (125 MHz
C6D6): δ 150.4 (C), 131.8 (C), 128.4 (CH), 127.8 (CH), 113.7
(CH), 112.3 (CH), 78.0 (CH), 75.6 (CH2), 56.1 (CH), 30.6 (CH3).
Anal. Calcd for C22H26ClNOZr: C, 59.10; H, 5.86; N, 3.13.
Found: C, 58.99; H, 5.93; N, 2.97.
p-Fluorostyrene Oxide Metallacycle. A solution of p-
fluorostyrene oxide (20.8 mg, 0.151 mmol) in benzene (1.5 mL)
was added to imido complex 1 (50.0 mg, 0.137 mmol). The
solution turned bright orange over 10 min. After 1 day, the
volatile materials were removed in vacuo, producing an orange
gum. The gum was taken up in ether (1.5 mL), producing a
cloudy orange solution. Pentane vapor diffusion was initiated
at -35 °C. After 6 days, red crystals were present above the
solvent line and in the mother liquor. Some fine white powder
(presumably decomposition products) had settled to the bottom
of the solution. The mother liquor was removed by pipet,
concurrently removing the fine white powder as a suspension.
The crystals were washed quickly with cold pentane, and the
residual solvent was removed in vacuo, yielding 36.5 mg (62%).
1H NMR (500 MHz, C6D6): δ 7.42 (dd, J ) 8.0, 2.5 Hz, 2H),
6.93 (t, J ) 9 Hz, 2H), 6.19 (s, 5H), 6.09 (s, 5H), 4.75 (dd, J )
10.0, 5.0 Hz, 1H), 4.35 (d, J ) 5.0 Hz, 1H), 3.87 (d, J ) 10.0
Hz, 1H), 0.75 (s, 9H). 13C{1H} NMR (125 MHz C6D6): δ 162.1
(d, JC-F ) 220 Hz, C), 147.4 (d, JC-F ) 3.8 Hz, C), 128.6 (d,
JC-F ) 7.5, CH), 114.6 (d, JC-F ) 20 Hz, CH), 113.9 (CH), 112.5
(CH), 78.0 (CH), 75.8 (CH2), 56.1 (C), 30.6 (CH3). Anal. Calcd
for C22H26FNOZr: C, 61.35; H, 6.09; N, 3.25. Found: C, 61.27;
H, 6.29; N, 3.45.
p-Methoxystyrene Oxide Metallacycle. A solution of
p-methoxystyrene oxide (28.2 mg, 0.188 mmol) in benzene (3
mL) was added to imido complex 1 (65.4 mg, 0.188 mmol). The
solution turned bright orange with dissolution of 1. After 15
min, the volatile materials were removed in vacuo, producing
an orange gum. The complex decomposed upon attempted
purification. 1H NMR (500 MHz, C6D6): δ 7.54 (d, J ) 8.5 Hz,
2H), 6.93 (d, J ) 8.5 Hz, 2H), 6.26 (s, 5H), 6.09 (s, 5H), 4.81
(dd, J ) 10.0, 5.0 Hz, 1H), 4.46 (d, J ) 5.0 Hz, 1H), 4.02 (d, J
) 10 Hz, 1H), 0.84 (s, 9H). 13C{1H} NMR (125 MHz C6D6): δ
158.8 (C), 143.6 (C), 128.3 (CH), 113.9 (CH), 112.5 (CH), 78.3
(CH), 76.1 (CH2), 56.2 (C), 54.8 (CH3), 30.7 (CH3).
Hammett Study General Procedures. 10.0 Equiv of
Epoxide. A solution of imido complex 1 (10.0 mg, 0.0274
mmol) in benzene-d6 (0.5 mL) was added dropwise to a rapidly
stirred solution of substituted styrene oxide (0.274 mmol, 10.0
equiv) and styrene oxide (0.274 mmol, 10.0 equiv) in benzene-
d6 (0.7 mL). The solution turned bright orange upon addition.
The reaction was monitored by 1H NMR spectroscopy and
found to be complete in <30 min. The product ratios did not
change upon standing.
and found to be complete in 2-8 h. The product ratios did not
change upon standing.
Low-Temperature 1H NMR Study of THF Displace-
ment by Excess Epoxide. In the glovebox, a NMR tube was
charged with a solution of imido complex 1 (15 mg, 0.041
mmol) in toluene-d8
and capped with a rubber septum. A 250
µL gastight syringe was charged with styrene oxide (94 µL,
0.82 mmol, 20 equiv), and the tip was protected from air by
insertion into a plastic stopper. Both items were removed from
the box.
The NMR tube was placed in a -78 °C bath for 10 min, at
which time styrene oxide was injected into the solution through
the septum. After 2 min, the NMR tube was removed from
the bath, the viscous solution was quickly shaken, and the tube
was dropped into a precooled (-20 °C) spectrometer probe. A
1H NMR spectrum obtained at this temperature showed
complete displacement of THF by styrene oxide (no formation
of metallacycle product 3 was observed).
Metallacycle 4. 7-Oxabenzonorbornadiene (19.7 mg, 0.137
mmol) was dissolved in benzene (1.0 mL) and added to a
solution of imido complex 1 (50.0 mg, 0.137 mmol) in benzene
(1.0 mL), producing a dark orange solution. The solvent was
1
removed in vacuo, to give an orange glass (52 mg, 87%). H
NMR (500 MHz, C6D6): δ 7.20 (d, J ) 6.0 Hz, 1H), 7.15 (m,
1H), 7.12 (dt, J ) 7.0, 1.0 Hz), 7.04 (dt, J ) 7.0, 1.0 Hz, 1H),
6.04 (s, 5H), 5.56 (s, 5H), 5.36 (s, 1H), 5.25 (s, 1H), 2.67 (d, J
) 7.5 Hz, 1H), 2.17 (d, J ) 7.0 Hz, 1H). 13C{1H} NMR (125
MHz C6D6): δ 150.7, 144.4, 126.3, 125.0, 111.2, 110.2, 84.6,
83.2, 67.8, 55.9, 42.9, 31.8. Satisfactory elemental analysis
could not be obtained on this compound.
Procedure for Obtaining Crystals Suitable for X-ray
Diffraction Analysis. 7-Oxabenzonorbornadiene (19.7 mg,
0.137 mmol) was dissolved in benzene (1.0 mL) and added to
a solution of imido complex 1 (50.0 mg, 0.137 mmol) in benzene
(1.0 mL), producing a dark orange solution. The solvent was
removed in vacuo, to give an orange powder. The powder was
taken up in ether (3 mL), and pentane vapor diffusion was
started at -35 °C. After 3 days, orange crystals were present
along the solvent front and on the bottom of the solution. The
mother liquor was removed by pipet. Satisfactory elemental
analysis could not be obtained on this compound.
Metallacycle 5. A solution of exo-norbornene oxide (19 mg,
0.17 mmol) in benzene (1 mL) was added to a solution of imido
complex 1 (58 mg, 0.16 mmol), in benzene (1 mL), producing
a tan solution. The solution was transferred to a resealable J.
Young NMR tube, sealed, and removed from the box. The NMR
tube was heated at 45 °C for 3 days, and the solvent was then
removed in vacuo to produce a red gum. The gum was dissolved
in pentane (0.2 mL), and orange crystals suitable for X-ray
diffraction analysis formed upon standing at ambient temper-
ature for 5 days. The mother liquor was removed by pipet, and
1
the residual solvent was removed in vacuo (30 mg, 46%). H
NMR (300 MHz, C6D6): δ 6.13 (d, J ) 16.2 Hz, 10H), 4.25 (d,
J ) 3.3 Hz, 1H), 3.38 (d, J ) 3.3 Hz, 1H), 2.39 (d, J ) 5.7 Hz,
1H), 2.24 (s, 1H), 2.14 (s, 1H), 1.30-1.11 (m, 6H), 0.96 (s, 9H).
13C{1H} NMR (125 MHz, C7D8): δ 113.2, 111.8, 83.8, 81.3, 55.2,
44.1, 42.8, 34.0, 27.0, 23.6, 30.9. Anal. Calcd for C21H29NOZr:
C, 62.64; H, 7.26; N, 3.48. Found: C, 62.53; H, 7.38; N, 3.45.
Metallacycles 6 and 7. A solution of butadiene mono-
epoxide (42 mg, 0.60 mmol) in benzene-d6 (0.5 mL) was added
to a solution of imido complex 1 (200 mg, 0.548 mmol) in
1
benzene-d6 (1 mL), producing a bright orange solution. A H
NMR spectrum showed formation of two metallacycle isomers,
assigned as 6 and 7 via proton coupling patterns (43% and
41% NMR yields, respectively), and via the distinctive absence
(6) or presence (7) of diastereotopic cyclopentadienyl ligands.
Spectral information for 6: 1H NMR (300 MHz, C6D6): δ 6.09
(s, 10H), 5.37 (m, 2H), 4.69 (br, 2H), 3.45 (br, 2H), 1.00 (s, 9H).
Spectral information for 7: 1H NMR (300 MHz, C6D6): δ 6.10
(s, 5H), 6.01 (s, 5H), 4.36 (dd, J ) 6.0, 4.8 Hz, 1H), 3.83 (dd, J
) 6.0, 4.8 Hz, 1H), 0.99 (s, 9H).
2.0 Equiv of Epoxide. A solution of imido complex 1 (10
mg, 0.027 mmol) in benzene-d6 (0.5 mL) was added dropwise
to a rapidly stirred solution of substituted styrene oxide (0.055
mmol, 2.0 equiv) and styrene oxide (0.055 mmol, 2.0 equiv) in
benzene-d6 (0.7 mL). The solution turned bright orange over
1
5 min. The reaction was monitored by H NMR spectroscopy

Strained Heterocycle Opening Reactions
Organometallics, Vol. 24, No. 7, 2005 1657
The high solubility of these complexes hampered purifica-
tion; therefore, protic cleavage of the alkoxide moiety from the
metal was used to corroborate the product assignments. To
the crude reaction mixture containing 6 and 7 was added
benzoic acid (669 mg, 5.5 mmol) in benzene (3 mL). The
reaction mixture became colorless immediately. The solution
was diluted with ether (3 mL) and extracted with aqueous 1
M HCl (10 mL × 3). The combined aqueous layers were back
extracted with ether (7 mL × 3), and then aqueous NaOH was
added until pH ) 9, producing a white precipitate. The
aqueous layer was extracted with ether (20 mL × 3). The
combined organic layers were dried over Na2SO4, filtered, and
concentrated in vacuo to a cloudy oil. The oil was extracted
for C36H41NOZr: C, 72.68; H, 6.95; N, 2.35. Found: C, 72.42;
H, 6.95; N, 2.46.
Procedure for Obtaining Crystals Suitable for X-ray
Diffraction Analysis. A solution of styrene oxide (13 mg, 0.11
mmol) in toluene (6 drops) was added to solid (rac)-2 (50 mg,
0.091 mmol), producing a cloudy orange solution. After 20 min,
vapor diffusion of pentane into the solution was started and
the system was cooled to -35 °C. After 5 days, nonsuitable
yellow crystals had formed. The mother liquor was removed,
and a new vapor diffusion of pentane into this mother liquor
was started. After 4 days, yellow crystals suitable for X-ray
diffraction analysis had formed. The mother liquor was
removed by pipet, and the residual solvent was removed in
vacuo.
1
with benzene-d6 (1 mL). A H NMR spectrum showed amino
Metallacycle 13. trans-Stilbene oxide (22 mg, 0.11 mmol)
and imido complex 1 (38 mg, 0.10 mmol) were dissolved in
toluene (4 drops), producing an orange solution after 15 min.
Vapor diffusion of ether into the solution at -35 °C was
started. After 1 day, clusters of red-orange crystals had formed.
The mother liquor was removed by pipet, and the residual
solvent was removed in vacuo (18 mg, 37%). 1H NMR (300
MHz, C6D6): δ 7.13-7.02 (m, 10H), 6.22 (d, J ) 3.3 Hz, 10H),
5.67 (d, J ) 9.0 Hz, 1H), 4.80 (d, J ) 9.0 Hz, 1H), 0.76 (s, 9H).
13C{1H} NMR (125 MHz, C6D6): δ 146.1, 144.4, 129.8, 127.9,
127.2, 126.9, 126.8, 126.4, 113.5, 113.1, 88.6, 86.7, 55.9, 30.4.
Anal. Calcd for C28H31NOZr: C, 68.80; H, 6.39; N, 2.87.
Found: C, 69.04; H, 6.53; N, 2.95.
alcohols 21 and 22 and tert-butylamine (>90% purity). Spectral
information for 21: 1H NMR (300 MHz, C6D6): δ 5.82 (m, 2H),
4.21 (d, J ) 5.7 Hz, 1H), 4.08 (d, J ) 4.5 Hz, 1H), 3.16 (d, J )
4.5 Hz, 1H), 2.93 (d, J ) 5.7 Hz, 1H), 0.95 (s, 9H). Spectral
information for 22: 1H NMR (300 MHz, C6D6): δ 5.49 (m, 2H),
4.90 (m, 1H), 3.48 (m, 1H), 0.97 (s, 9H). HRMS (EI): m/z calcd
(C8H17NO) 144.1388, found 144.1393 [M+].
Metallacycle 8. N-Tosyl-2-phenylaziridine (24 mg, 0.086
mmol) was dissolved in toluene-d8 (0.8 mL) and added to solid
imido complex 1 (100 mg, 0.27 mmol), producing a pale tan
solution. The solution was transferred to a resealable J. Young
NMR tube, sealed, and removed from the box. The NMR tube
was heated at 75 °C for 1 day, producing a deep purple-brown
Metallacycle 14. A solution of cis-stilbene oxide (40 mg,
0.20 mmol) in benzene (4 mL) was added to an orange
suspension of (rac)-2 (100 mg, 0.18 mmol) in benzene (1 mL),
to produce a dark red solution after 5 min. The solution was
layered with pentane (15 mL) and cooled to -35 °C. After 4
weeks the pale orange mother liquor was decanted to reveal
clusters of orange crystals, suitable for X-ray diffraction
analysis, of a 1:1 mixture of the desired product and benzene
(65 mg, 48%). Purified material therefore contained 1 equiv
1
solution. A H NMR spectrum obtained at this time showed
product 8 (98% NMR yield). The volatile materials were
removed in vacuo to produce a magenta gum. The gum was
taken up in ether (0.5 mL), and pentane vapor diffusion was
started at -35 °C. After 3 days, deep purple crystals suitable
for X-ray diffraction analysis had formed. The mother liquor
was removed by pipet, and the residual solvent was removed
in vacuo, yielding 42 mg of crystals. A 1H NMR spectrum
showed 1 equiv of ether, and a X-ray diffraction study showed
inclusion of ca. 0.5 equiv ether into the crystal lattice. An
adjusted yield taking this ether into account was calculated:
1
of benzene. H NMR (500 MHz, C6D6): δ 7.51 (d, J ) 7.5 Hz,
1H), 7.27 (d, J ) 7 Hz, 1H), 7.19-6.90 (m, 16H), 6.76 (t, J )
5 Hz, 1H), 6.61 (d, J ) 10.5 Hz, 1H), 6.45 (d, J ) 3 Hz, 1H),
5.72 (d, J ) 6 Hz, 1H), 5.72 (s, 1H), 5.41 (d, J ) 3 Hz, 1H),
4.39 (d, J ) 3 Hz, 1H), 3.53 (m, 1H), 2.90 (m, 1H), 2.95-2.25
(m, 1H), 2.52 (s), 2.07-2.04 (m, 1H), 2.04 (s), 1.94-1.90 (m,
1H), 1.60-1.50 (m, 2H), 1.45-1.32 (m, 1H), 1.30-1.19 (m, 1H).
13C{1H} NMR (125 MHz, C6D6): δ 156.7, 146.6, 144.5, 132.7,
131.5, 131.4, 131.0, 129.5, 126.4, 126.3, 126.2, 122.6, 120.6,
119.6, 115.7, 111.9, 110.5, 108.6, 28.4, 27.6, 25.2, 25.1, 24.7,
23.4, 23.0, 22.9, 22.6, 22.4, 22.3. Anal. Calcd for C48H49NOZr:
C, 77.16; H, 6.61; N, 1.87. Found: C, 76.78; H, 6.96; N, 1.83.
Metallacycle 17. Vinylcyclopropane oxide (20 mg, 0.24
mmol) was added to a solution of imido complex 16 (100 mg,
0.24 mmol) in benzene (2.5 mL), producing a yellow solution.
The reaction mixture was allowed to sit for 24 h, at which time
pentane (2.5 mL) was added to the solution and the reaction
mixture was filtered to remove a white insoluble byproduct.
The solvent was removed in vacuo, and the resultant yellow
solid was taken up in ether (1.0 mL), layered with pentane
(1.0 mL), and cooled to -35 °C. After 1 day, a yellow crystalline
solid had precipitated. The mother liquor was decanted, and
the volatile materials were removed in vacuo to leave the
1
38 mg of 8 (82%). H NMR (500 MHz, C6D6): δ 7.55 (d, J )
8.0 Hz, 2H), 7.24 (d, J ) 7.0 Hz, 2H), 6.99 (m, 3H), 6.63 (d, J
) 8.0 Hz, 2H), 6.44 (s, 5H), 6.40 (s, 5H), 3.86 (d, J ) 5.0 Hz,
1H), 3.78 (dd, J ) 12.5. 5.0 Hz, 1H), 3.22 (d, J ) 12.5 Hz, 1H),
1.91 (s, 3H), 0.63 (s. 9H). 13C{1H} NMR (125 MHz, C6D6): δ
149.9 (C), 140.2 (C), 140.1 (C), 128.7 (CH), 127.3 (CH), 126.9
(CH), 126.5 (CH), 125.5 (CH), 115.1 (CH), 114.0 (CH), 65.6 (C),
57.3 (C), 54.8 (CH2), 30.2 (CH3), 20.8 (CH3). The elemental
composition is not altered significantly upon inclusion of 0.5
equiv of ether. Anal. Calcd for C29H34N2O2SZr: C, 61.55; H,
6.06; N, 4.95. Found: C, 61.57; H, 6.30; N, 4.83.
Metallacycle 9. A solution of styrene oxide (13 mg, 0.11
mmol) in toluene (0.3 mL) was added to solid orange imido
complex (rac)-2 (50 mg, 0.091 mmol), producing a deep red-
brown solution. After 10 min, the solution was concentrated
in vacuo to a viscous red oil. Ether (3 drops) was added to
dissolve the oil, and pentane vapor diffusion was started at
-35 °C. After 24 h, orange crystals had formed. The mother
liquor was removed, the crystals were washed with cold
pentane, and the residual solvent was removed in vacuo (45
1
1
mg, 83%). H NMR (500 MHz, C6D6): δ 7.01 (d, J ) 5.0 Hz,
yellow solid (52 mg, 43%). H NMR (400 MHz, C6D6): δ 6.21
1H), 7.00-6.92 (m, 1H), 6.88 (t, J ) 7.5 Hz, 1H), 6.28 (d, J )
3.0 Hz, 1H), 6.21 (d, J ) 2.5 Hz, 1H), 6.03 (dd, J ) 5.0, 4.5 Hz,
1H), 5.51 (t, J ) 9.5 Hz, 1H), 5.43 (d, J ) 3.0 Hz, 1H), 5.24 (d,
J ) 3.0 Hz, 1H), 5.16 (dd, J ) 5.0, 4.5 Hz, 1H), 3.14 (dt, J )
16 Hz, 1H), 2.98-2.94 (m, 1H), 2.91-2.84 (m, 1H), 2.70-2.63
(m, 2H), 2.57 (m, 2H), 2.38 (s, 3H), 2.34 (s, 3H), 2.2-2.0 (m,
1H), 1.94-1.90 (m, 2H), 1.64-1.54 (m, 3H), 1.40-1.37 (m, 2H),
0.90-0.85 (m, 2H). 13C{1H} NMR (125 MHz, C6D6): δ 153.6,
140.3, 135.1, 133.8, 133.1, 131.0, 130.5, 128.3, 128.1, 127.0,
122.1, 121.2, 119.6, 112.2, 110.5, 110.3, 106.4, 83.5, 72.9, 29.0,
27.8, 25.3, 24.5, 23.6, 23.4, 23.0, 22.4, 22.1, 21.9. Anal. Calcd
(s, 5H), 6.14 (s, 5H), 4.71 (dd, 1H, J ) 4.0, 9.6 Hz), 3.97 (d,
1H, J ) 9.6 Hz), 3.17 (dd, 1H, J ) 4.0, 7.6 Hz), 1.51 (m, 1H),
1.02 (s, 9H), 0.62 (m, 1H), 0.48 (m, 1H), 0.32 (m, 1H), 0.26 (s,
3H), 0.16 (m, 1H), -0.27 (s, 3H). 13C{1H} NMR (100 MHz,
C6D6): δ 113.9, 113.4, 80.0, 76.1, 28.4, 20.3, 18.5, 7.8, 3.7, 0.2,
-0.5. Anal. Calcd for C21H33NOSiZr: C, 58.01; H, 7.65; N, 3.22.
Found: C, 58.12; H, 7.70; N, 3.14.
Complex 23. A solution of exo-norbornene oxide (22 mg,
0.20 mmol) in toluene (1.2 mL) was added to imido complex 1
(50 mg, 0.14 mmol), producing a tan solution. The volatile
materials were removed in vacuo, yielding tan crystals. An

1658 Organometallics, Vol. 24, No. 7, 2005
Blum et al.
additional portion of toluene (0.5 mL) was added, and the
volatile materials were again removed in vacuo, to remove
residual THF. The resulting tan crystals were redissolved in
minimal toluene (1.2 mL), and the solution was filtered. The
tan solution was then layered with pentane (3.5 mL) and
cooled to -35 °C. After 9 days the mother liquor was decanted
to reveal tan crystals suitable for X-ray diffraction analysis
(28 mg, 38%). 1H NMR (300 MHz, C6D6): δ 6.15 (s, 10 H), 3.35
(s, br, 2H), 1.96 (s, 2H), 0.95 (br, 2H), 0.88 (m, br, 4 H), 0.58
(m, br, 4 H), 0.25 (d, J ) 9.6 Hz, 2H). 13C{1H} NMR (125 MHz,
C7D8): δ 137.0, 110.0, 61.4, 36.0, 34.1, 26.1, 23.6. Anal. Calcd
for C21H29NOZr: C, 62.64; H, 7.26; N, 3.48. Found: C, 62.48;
H, 7.25; N, 3.38.
(125 MHz C6D6): δ 138.5, 125.6, 110.6, 78.8, 54.8, 39.9, 34.2,
29.3, 26.1, 23.8. Anal. Calcd for C22H33NOZr: C, 63.10; H, 7.94;
N, 3.35. Found: C, 63.36; H, 7.71; N, 3.18.
Complex 29. 1,2-Butene oxide (9.9 mg, 0.14 mmol) was
dissolved in benzene (1.0 mL) and added to a solution of imido
complex 1 (50 mg, 0.14 mmol) in benzene (1.0 mL). After 30
min, the solvent was removed in vacuo, to give a light yellow
1
oil (14 mg, 28%). H NMR analysis showed a 2.0:1.0 mixture
of isomers. Trans isomer (major): 1H NMR (500 MHz, C6D6):
δ 6.19 (s, 10H), 5.62 (m, 2H), 4.39 (br, 1H), 1.63 (m, 3H), 1.21
(s, 9H). Cis isomer (minor): 1H NMR (500 MHz, C6D6): δ 5.92
(s, 10H), 5.69 (m, 1H), 5.43 (m, 1H), 4.52 (d, J ) 6.3), 3.79 (br,
1H), 1.53 (d, J ) 6.6 Hz), 1.21 (s, 9H). Anal. Calcd for C18H27-
NOZr: C, 59.29; H, 7.46; N, 3.84. Found: C, 58.61; H, 7.29;
N, 3.39.
Kinetic Analysis of Formation of Metallacycle 25 from
Complex 23. Epoxide complex 23 (7.0 mg, 0.017 mmol), exo-
norbornene oxide (3.7 mg, 0.034 mmol), and 1,3,5-trimethoxy-
benzene internal standard (8.0 mg, 0.048 mmol) were dissolved
in toluene-d8 and transferred to a resealable J. Young NMR
tube (total solution volume 0.380 mL). Product formation was
Assignment of Isomers Was Facilitated by Protic
Cleavage of the Alkoxide Moiety from the Complex. A
solution of benzoic acid (26 mg, 0.22 mmol) in benzene-d6 (0.5
mL) was added to a solution of complex 29 (10 mg, 0.027 mmol)
in benzene-d6 (0.5 mL). After 20 min, 1H NMR and TOCSY
spectra showed the formation of trans- and cis-crotyl alcohol
(2.1:1.0), which were compared to a commercially available
sample of 90:10 trans:cis-crotyl alcohol to confirm isomer
assignment.
Complex 30. Phenylpropene oxide (19 mg, 0.15 mmol) was
dissolved in benzene (1.0 mL) and added to a solution of imido
complex (50 mg, 0.14 mmol) in benzene (1.0 mL), producing a
pale yellow solution. After 20 min, the solvent was removed
in vacuo, to give a brown oil (48 mg, 82%). 1H NMR (500 MHz,
C6D6): δ 7.38 (d, J ) 7.0 Hz, 2H), 7.26 (t, J ) 7.5 Hz, 2H),
7.12 (t, J ) 7.5 Hz, 1H), 5.96 (m, 1H), 5.92 (s, 5H), 5.91 (s,
1H), 5.26 (m, 2H), 5.01 (d, J ) 10 Hz, 1H), 4.10 (s, br, 1H),
1.20 (s, 9H). 13C{1H} NMR (125 MHz C6D6): δ 145.8 (C), 143.7
(CH), 126.6 (CH), 126.3 (CH), 111.7 (CH2), 110.7 (CH), 85.1
(CH), 55.3 (C), 34.2 (CH3). One of the Cp resonances was not
found, presumably due to overlap with the solvent resonance.
Anal. Calcd for C23H29NOZr: C, 64.74; H, 6.85; N, 3.28.
Found: C, 64.52; H, 6.75; N, 3.21.
1
monitored by H NMR spectroscopy, and the probe tempera-
ture was calibrated with an ethylene glycol standard. The
reaction exhibited clean first-order kinetics: k ) 0.017 (
0.000086 min-1 (59.8 °C), k ) 0.051 ( 0.00033 min-1 (69.8 °C),
k ) 0.084 ( 0.00021 min-1 (79.8 °C), k ) 0.22 ( 0.0016 min-1
(89.9 °C). Error limits are reported at one standard deviation
for each k and were calculated by comparison between the
actual and simulated data. The rate constants were indepen-
dent of the initial concentration of complex 23 and of excess
epoxide: k ) 0.048 ( 0.00034 min-1 (3.0 mg 23, 69.5 °C), k )
0.048 ( 0.0059 min-1 (10 mg exo-norbornene oxide, 0.265 mL
total solvent volume, 69.8 °C). The reproducibility was con-
servatively estimated by doubling the difference in the k values
for a triplicate run at 69.5 °C (i.e., error ) 2 × [0.051 min-1
-
0.048 min-1] ) 0.006 min-1). Errors in ∆Hq and ∆Sq were
calculated from this estimation.
Complex 26. Propylene oxide (8.7 mg, 0.15 mmol) was
dissolved in benzene (1.0 mL) and added to a solution of imido
complex 1 (50 mg, 0.14 mmol) in benzene (1.0 mL), producing
a pale yellow solution. After 5 min, the solution was concen-
trated in vacuo to a cloudy oil that solidified upon standing
(40 mg, 82%). 1H NMR (500 MHz, C6D6): δ 5.97-5.90 (m, 1H),
5.89 (s, 10H), 5.31 (dq, J ) 17, 2.5 Hz, 1H), 5.08 (dt, J ) 11,
2.0 Hz, 1H), 3.92 (s, br, 1H), 1.22 (s, 1H). 13C{1H} NMR (125
MHz C6D6): δ 140.2, 111.8, 110.7, 73.7, 55.1, 34.2. Anal. Calcd
for C17H25NOZr: C, 58.24; H, 7.19; N, 3.99. Found: C, 58.15;
H, 6.99; N, 4.00.
Complex 31. Propene sulfide (6.1 mg, 0.082 mmol) was
dissolved in benzene-d6 (0.3 mL) and added to a solution of
imido complex (30 mg, 0.082 mmol) in benzene-d6 (0.2 mL),
producing a bright yellow solution. Analysis of the crude
1
reaction mixture by H NMR spectroscopy showed 69% yield
of complex 31. The complex decomposed upon attempted
1
purification. H NMR (300 MHz, C6D6): δ 6.20 (m, 1H), 5.78
(s, 10H), 5.48 (s, br, 1H), 5.29 (d, J ) 12.9 Hz, 1H), 5.02 (d, J
) 7.5 Hz, 1H), 3.57 (d, J ) 3.3 Hz, 2H), 1.14 (s, 9H).
Complex 27. Cyclohexene oxide (29 mg, 0.30 mmol) was
dissolved in benzene (0.3 mL), and the resulting solution was
added to solid imido complex 1 (100 mg, 0.27 mmol), producing
a pale tan solution. After 10 min, pentane was layered on top,
and the sample was cooled to -35 °C. After 14 days, a scant
amount of powder had precipitated on the bottom of the vial.
The colorless mother liquor was removed carefully by pipet
so as not to disturb the fine precipitate. The mother liquor
was concentrated in vacuo, yielding a white powder (39 mg,
Assignment of the Product Was Facilitated by Protic
Cleavage of the Sulfide Moiety from the Complex. A
solution of benzoic acid (30 mg, 0.25 mmol) in benzene-d6 (0.5
mL) was added to the crude solution of complex 31. The
solution became colorless immediately. Analysis of the solution
by 1H NMR spectroscopy showed formation of allyl sulfide
(>95% from 31). Comparison with commercially available allyl
sulfide confirmed the assignment.
1
37%). H NMR (500 MHz, C6D6): δ 5.95 (s, 5H), 5.94 (s, 5H),
5.76 (m, 1H), 5.67 (m, 1H), 4.37 (m, 1H), 3.62 (s, 1H), 1.9-1.3
(m, 6 H), 1.25 (s, 9H). 13C{1H} NMR (125 MHz C6D6): δ 133.1,
126.9, 110.7, 75.3, 54.8, 34.3, 33.3, 25.3, 19.8. Anal. Calcd for
C20H29NOZr: C, 61.49; H, 7.48; N, 3.59. Found: C, 61.43; H,
7.43; N, 3.86.
Complex 28. Cyclooctene oxide (19 mg, 0.15 mmol) was
dissolved in benzene (1.0 mL), and the resulting solution was
added to a solution of imido complex 1 (50 mg, 0.14 mmol) in
benzene (1.0 mL), producing a pale yellow solution. After 5
min, the solvent was removed in vacuo to give a clear gel (58
mg, 99%). 1H NMR analysis showed a 88:12 mixture of
isomers. Major isomer: 1H NMR (500 MHz, C6D6): δ 5.97 (s,
10H), 5.63 (ddd, J ) 10.5, 6.5, 1.0 Hz, 1H), 5.51 (m, 1H), 4.81
(quintet, J ) 5.5, 1H), 3.68 (s, br, 1H), 2.20 (m, 1H), 1.92 (m,
2H), 1.6-1.4 (m, 6H), 1.31 (m 1H), 1.27 (s, 9H). 13C{1H} NMR
NMR Desymmetrization Experiment: Formation of
Complex 34. To a solution of imido complex (rac)-2 (5.5 mg,
0.010 mmol) in benzene-d6 (0.4 mL) was added 2,3-butene
oxide (0.97 µL, 0.011 mmol), producing a yellow solution. A
1H NMR spectrum obtained on this solution after 1 h showed
that all (rac)-2 had been consumed, to produce complex 34 as
one diastereomer (>95:5). A 1H NMR spectrum obtained after
1 day showed no change. Structural assignment of 34 was
made by analogy to complexes 26-31. 1H NMR (300 MHz,
C6D6): δ 7.16 (m, 2H), 6.91 (t, J ) 7.6 Hz, 1H), 6.16 (d, J )
3.0 Hz, 1H), 6.01 (ddd, J ) 17.2, 10.4, 7.2 Hz, 1H), 5.52 (d, J
) 3.0 Hz, 1H), 5.39 (d, J ) 3.0 Hz, 1H), 5.27 (d, J ) 3.0 Hz,
1H), 5.06 (dm, J ) 17.4 Hz, 1H), 4.96 (dm, J ) 11.1 Hz, 1H),
4.86 (s, br, 1H), 4.65 (p, J ) 6.4 Hz, 1H), 2.38 (s, 1H), 1.32 (d,
J ) 6.3 Hz, 3H).

Strained Heterocycle Opening Reactions
Organometallics, Vol. 24, No. 7, 2005 1659
Catalytic Desulfurization of Propene Sulfide. Propene
sulfide (50 mg, 0.68 mmol) was dissolved in benzene-d6 (0.3
mL) and added to a solution of imido complex 1 (10 mg, 0.027
mmol) in benzene-d6 (0.2 mL), producing a bright yellow
solution. The solution was transferred to a NMR tube, which
was fitted with a Cajon adaptor, sealed, and removed from
the glovebox. The NMR tube was flame sealed under vacuum
and heated at 75 °C for 8 h. The dark brown, heterogeneous
reaction mixture was then analyzed by 1H NMR spectroscopy,
which showed the formation of propene (5.1 equiv, relative to
1), multiple products giving rise to baseline resonances, and
unreacted propene sulfide (3.6 equiv). The NMR tube was
opened to air, and the solution was flushed through a silica
plug and diluted with THF. GC-MS analysis of the resultant
solution indicated the presence of mass fragments correspond-
ing to oligomerization of the starting material.
Acknowledgment. This work was supported by the
NSF though a graduate fellowship to S.A.B, and by the
NIH through grant no. GM-25459 to R.G.B. and post-
doctoral fellowships to R.T.R. and F.E.M. We thank Dr.
Fred Hollander and Dr. Allen Oliver of the UC Berkeley
CHEXRAY facility for the X-ray structure determina-
tions, Dr. Herman van Halbeek for help with NMR
experiments, and Mr. Jordan Markham for the gift of
N-tosyl-2-phenylaziridine.
Supporting Information Available: Kinetics data for the
conversion of 23 to 5; X-ray structural data for compounds 5,
7, 8, 9, 14, and 23. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM049105R