Catalytic isomerization and disproportionation of olefins promoted by group 4/d0 benzamidinate complexes

Article abstract of DOI:10.1021/ja990011w

The group 4/d⁰ benzamidinate complexes cis-[p-CH₃-C₆H₄C(NSiMe₃) ₂]₂Zr(CH₃)₂ (1), C₃-tris([N-trimethylsilyl][N'-myrtanyl]benzamidinate)zirconium c

Full text of DOI:10.1021/ja990011w

J. Am. Chem. Soc. 1999, 121, 8755-8759
8755
Catalytic Isomerization and Disproportionation of Olefins Promoted
0
by Group 4/d Benzamidinate Complexes
Claudia Averbuj and Moris S. Eisen*
Contribution from the Department of Chemistry and Institute of Catalysis Science and Technology,
Technion-Israel Institute of Technology, Haifa 32000, Israel
ReceiVed January 4, 1999
0
Abstract: The group 4/d benzamidinate complexes cis-[p-CH3-C6H4C(NSiMe3)2]2Zr(CH3)2 (1), C3-tris([N-
trimethylsilyl][N′-myrtanyl]benzamidinate)zirconium chloride (2) and cis-[p-CH3C6H4C(NSiMe3)2]2Ti(CH3)2
(3) were found to be active catalytic precursors, in the presence of MAO (methylalumoxane), for the
isomerization of aliphatic olefins (1-octene, 2-E-octene, 3-methyl-1-butene, 2-methyl-1-butene, allylbenzene)
and the disproportionation of 1,4- and 1,3-cyclohexadienes. The active species was found to be the cationic
hydride complex obtained for aliphatic olefins by the insertion of the methyl ligand with concomitant â-hydrogen
elimination, and for the alicyclic dienes by an activation of the allylic hydrogen and accompanying elimination
of methane. Kinetic studies and Eyring analysis for the isomerization of allylbenzene show that the reaction
†
-1
†
is first order in both complex and olefin with ∆H ) 17.8(6) kcal‚mol and ∆S ) -25.1(2) eu. These
findings support the epimerization mechanism proposed for these types of cationic complexes, in the
polymerization of propylene, toward isotactic polypropylene. To the best of our knowledge, this is the first
study in which high oxidation state group 4 complexes are able to induce the catalytic isomerization of olefins
or the disproportionation of cyclic olefins.
Introduction
polymer. When the polymerization was conducted at high
monomer concentration, a highly isotactic polypropylene (mmmm
Recently, increased attention has been given to the chemistry
of complexes containing non-Cp-spectator ligands, such as
chelating benzamidinate complexes. For early-transition com-
plexes, the bis(benzamidinate) dichloride group 4 complexes
4
>
99%, mp ) 153 °C) was obtained. The resulting atactic
polypropylene was mechanistically rationalized by an intramo-
lecular epimerization reaction of the growing polypropylene
chain at the last inserted monomeric unit. This was found to be
faster (at low monomer concentrations) than the stereoregular
1,2
(A) are obtained as racemic mixtures of C2-symmetry cis-
5
insertion of propylene (Scheme 1a).
Additional corroboration indicating that the mechanism
presented in Scheme 1a is responsible for the stereo defects in
(2) For group 4 complexes, see: (a) M u¨ eller, E.; M u¨ eller, J.; Olbrich,
F.; Bruser, W.; Knapp, W.; Abeln, D.; Edelmann, F. T. Eur. J. Inorg. Chem.
1998, 87. (b) Stewart, P. J.; Blake, A. J.; Mountford, P. Organometallics
1998, 17, 3271. (c) Hagardon, J. R.; Arnold, J. Organometallics 1998, 17,
1355. (d) Hagardon, J. R.; Arnold, J. Inorg. Chem. 1997, 36, 2928. (e)
Ciruelo, G.; Cuenca, T.; Gomez, R.; Gomez-Sal, P.; Martin, A.; Rodriguez,
G.; Royo, P. J. Organomet. Chem. 1997, 547, 287. (f) Hagardon, J. R.;
Arnold, J. J. Chem. Soc., Dalton Trans. 1997, 3087. (g) Richter, J.; Belay,
M.; Brieser, W.; Edelmann, F. T. Main Group Met. Chem. 1997, 20, 191.
(h) Hagardon, J. R.; Arnold, J. J. Am. Chem. Soc. 1996, 118, 893. (i) Gomez,
R.; Green, M. L. H.; Haggitt, J. L. J. Chem. Soc., Dalton Trans. 1996, 939
and references therein. For group 5 complexes, see: (j) Brussee, E. A. C.;
Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics, 1998, 17, 4090.
octahedral structures and, when activated with methyl alumox-
ane (MAO), were found to produce active catalytic cationic
complexes for the polymerization of ethylene, propylene,
(
(
k) Stewart, P. J.; Blake, A. J.; Mountford, P. Inorg. Chem. 1997, 36, 1982.
l) Dawson, D. Y.; Arnold, J. Organometallics, 1997, 16, 1111. For group
1
3 complexes, see: (m) Duchateau, R.; Meetsma, A,; Teuben, J. H. J. Chem.
3
norbornene, and for the cyclooligomerization of 1,5 hexadiene.
Soc., Chem. Comun. 1996, 223. (n) Barker, J.; Blacker, N. C.; Phillips, P.
R.; Alock, N. W.; Errington, W.; Wallbridge, M. G. H. J. Chem. Soc., Dalton
Trans. 1996, 431.
Interestingly, we have shown that, when the polymerization
was carried out at atmospheric pressure, polypropylene was
produced as an atactic oil, instead of the expected isotactic
(3) (a) Richter, J.; Edelmann, F. T.; Noltemeyer, M.; Schmidt, H.-G.;
Shmulinson, M.; Eisen, M. S. J. Mol. Catal. Part A 1998, 130, 149. (b)
Flores, J. C.; Chien, J. C. W.; Rausch, M. D. Organometallics 1995, 14,
1827. (c) Walther, D.; Fischer, R.; G o¨ rls, H.; Koch, J.; Schweder, B. J.
Organomet. Chem. 1996, 508, 13. (d) Walther, D.; Fischer, R.; Friedrich,
F.; Gebhardt, P.; G o¨ rls, H. Chem. Ber. 1996, 129, 1389. (e) G o´ mez, R.;
Duchateau, R.; Chernega, A. N.; Meetsma, A.; Edelmann, F. T.; Teuben,
J. H.; Green, M. L. H. J. Chem. Soc., Dalton Trans. 1995, 217. (f)
Herskovics-Korine, D.; Eisen, M. S. J. Organomet. Chem. 1995, 503, 307.
(4) Volkis, V.; Shmulinson, M.; Averbuj, C.; Lisovskii, A.; Edelmann,
F. T.; Eisen, M. S. Organometallics 1998, 17, 3155.
(1) For some group 3 and lanthanide complexes, see: (a) Edelmann, F.
T.; Richter, J. Eur. J. Solid State Inorg. Chem. 1996, 33, 157. (b) Hagardon,
J. R.; Arnold, J. Organometallics 1996, 15, 984. (c) Edelmann, F. T. Top.
Curr. Chem. 1996, 179, 113 and references therein. (d) Duchateau, R.; van
Wee, C. T.; Meetsma, A.; van Duijnen, P. Th.; Teuben, J. H. Organome-
tallics 1996, 15, 2279. (e) Duchateau, R.; van Wee, C. T.; Teuben, J. H.
Organometallics 1996, 15, 2291. (f) Edelmann, F. T. Coord. Chem. ReV.
1
994, 137, 403 and references therein.
1
0.1021/ja990011w CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/10/1999

8756 J. Am. Chem. Soc., Vol. 121, No. 38, 1999
AVerbuj and Eisen
Scheme 1. (a) Proposed Mechanism for the Intramolecular
Epimerization Reaction of the Growing Polypropylene Chain
at the Last-inserted Monomeric Unit and (b). Plausible
Mechanism for the Expected Isomerization of Olefins
octene, 2-(Z)-octene, 3-(E)-octene, and 4-(E)-octene (Table 1,
entries 1, 2). The Z-isomer was formed exclusively with 2-octene
indicating that the enthalpy of activation toward both geometrical
isomers is similar. Starting from the 2-(E)-octene isomer (Table
1
, entries 3, 4), the isomerization proceeds toward the 3-(E)-
octene and 4-(E)-octene products as well as similar amounts of
-(Z)-octene, as found for the reaction with 1-octene, but without
2
traces of 1-octene. This result strongly argues for an equilibrium
between the two 2-octene isomers. Moreover, for complex 1,
the amount of the different isomerization products for either
starting alkene is similar, supporting the equilibrium process
proposed in Scheme 1b.
The isomerization of 3-methyl-1-butene yields the two
possible isomers 2-methyl-2-butene and 2-methyl-1-butene. We
have also studied the isomerization of 2-methyl-1-butene to
investigate if 2-methyl-1-butene is formed via the consecutive
isomerization from 2-methyl-2-butene. Thus, the isomerization
of 2-methyl-1-butene affords 2-methyl-2-butene in almost the
same yield (72%) as does 3-methyl-1-butene (Table 1, entries
5, 6), again supporting an equilibrium between the different
products, as expected from Scheme 1b. In Scheme 1b, the
cationic hydride complex is proposed as the active species,
whereas our starting isomerization catalysts are the correspond-
polypropylene obtained by C2-symmetry early transition metal
octahedral complexes was obtained by reacting the active
benzamidinate early transition metal hydride complexes with
an R-olefin which has an extremely low rate of polymerization
(Scheme 1b).
Thus, a â-hydrogen elimination is expected to occur either
from the terminal methyl group at the R-position in complex 1
Scheme 1b), causing no change in the alkene, or from the
8
(
ing alkyl complexes. We decided to study the formation of
R-position at the chain (CH2-CH2-R group), inducing isomer-
ization of the double bond. The efficacy of complementary
symmetric octahedral “template” ligation or even that of a C3
ligation, raises conceptual questions of applicability to the
this hydride complex, by performing the reaction with a small
excess of olefin. In the reaction of complex 1 with MAO and
5 equiv of 1-octene, similar stoichiometric amounts of 2-(E)-
nonene and 3-(E)-nonene were trapped and characterized. This
result clearly indicates that the methyl complex inserts regi-
oselectively into the olefin followed by a â-hydrogen elimination
leading to the formation of the active hydride complex (eq 1).9
0
isomerization of double bonds promoted by group IV/d
complexes. In this paper we report the reactivity and selectivity
of some well-defined early transition metal rac-benzamidinate
complexes with C2- and C3-symmetry in the isomerization and
disproportionation of alkenes. In addition to kinetic, thermo-
dynamic, and mechanistic studies, we present here the spec-
troscopic characterization of the products obtained in stoichi-
ometric reactions, allowing a rationalization of some of the key
organometallic intermediates. To the best of our knowledge,
0
this is the first example in which organometallic group 4/d
We decided to investigate whether this catalyst might isomerize
cyclic 1,3- and 1,4-dienes and induce their disproportionation
reactions to aromatic compounds. Reaction of 1,4-cyclohexa-
diene with 1/MAO does indeed give benzene, cyclohexene, and
cyclohexane with no trace formation of the conjugated 1,3-
isomer or the methylated cyclic compounds (Table 1, entry 7).
In contrast, for 1,3-cyclohexadiene, in addition to the dispro-
portionation products, 1,4-cyclohexadiene, saturated and unsat-
urated dimers, trimers, and tetramers were also found. A
plausible mechanism for the disproportionation of 1,4-cyclo-
hexadiene is described in Scheme 2. In this mechanism, the
cationic form of complex 1, which was obtained by the reaction
complexes are able to perform catalytic isomerization and
disproportionation of alkenes.6
Results and Discussion
The reaction of cis-[p-CH3-C6H4C(NSiMe3)2]2Zr(CH3)2 (1)4
or C3-tris([N-trimethylsilyl][N′-myrtanyl]benzamidinate)zirco-
7
nium chloride (2) with an excess of MAO in toluene (catalyst:
MAO ) 1:400) catalyzes the isomerization of 1-octene (cat:
-
1
olefin ) 1:180; TON ) ca. 25 h at 90 °C) yielding 2-(E)-
(5) (a) Busico, V.; Cipullo, R.; Caporaso, L.; Angelini, G.; Segre, A. L.
J. Mol. Catal. Part A 1998, 128, 53 and references therein. (b) Busico, V.;
Brita, D.; Caporaso, L.; Cipullo, R.; Vacatello, M. Macromolecules 1997,
4
of 1 and MAO, is activated by the allylic hydrogen, producing
3
0, 3971. (c) Busico, V.; Caporaso, L.; Cipullo, R.; Landriani, L.; Angelini,
methane and the active cyclohexadienyl complex B. Elimination
G.; Margonelli, A. Segre, A. L. J. Am. Chem. Soc. 1996, 118, 2105. (d)
Leclerc, M.; Brinzinger, H. H. J. Am. Chem. Soc. 1996, 118, 9024 and
references therein. (e) Leclerc, M.; Brinzinger, H. H. J. Am. Chem. Soc.
1
0
of a hydrogen in a 1,4-fashion produce benzene and the
hydride complex C. Complex C may either insert into 1,4-
cyclohexadiene or cyclohexene, forming complex D or E,
respectively. Allylic activation of complex D or E by 1,4-
cyclohexadiene allows the formation of cyclohexene and
cyclohexane, respectively.
1
995, 117, 1651. (f) Busico, V.; Cipullo, R. J. Am. Chem. Soc. 1994, 116,
9
329.
(
6) The stoichiometric isomerization of olefins via the hydrozirconation
reaction is well-known, see: (a) Schwartz, J. Pure Appl. Chem. 1980, 52,
33 and references therein. (b) Schwartz, J.; Labinger, J. A. Angew. Chem.,
7
Int. Ed. Engl. 1976, 15, 333 and references therein. (c) Hart, D. W.;
Schwartz, J. J. Am. Chem. Soc. 1974, 96, 8115. For group 4 complexes,
the catalytic isomerization of alkenes is known only for low-valent
complexes, see: (a) Ohff, A.; Burlakov, V. V.; Rosenthal, U. J. Mol. Catal.
Part A 1996, 105, 103. (b) Rao, S. A.; Periasamy, M. J. Organomet. Chem.
(8) See refs 4 and 7 for the formation of the corresponding cationic
benzamidinate complexes.
(9) 2-Methyl-1-octene is also an expected isomer although it was not
detected either due to a difference in reactivity favoring the 2,1-insertion
or because the methyl elimination of such an organometallic moiety is much
faster than the â-hydrogen elimination. For the polymerization of propylene
catalyzed by octahedral complexes we have shown that the methyl
elimination is the only effective termination pathway at atmospheric
pressure. See ref 4.
1
3
1
988, 342, 15 (c) Yanlong, Q.; Jiaqui, L.; Weihua, X. J. Mol. Catal. 1986,
4, 31. (d) Cohen, S. A.; Auburn, P. R.; Bercaw, J. E. J. Am. Chem. Soc.
983, 105, 1136.
(7) Averbuj, C.; Tish, E.; Eisen, M. S. J. Am. Chem. Soc. 1998, 120,
8
640.

Catalytic Isomerization and Disproportionation of Olefins
J. Am. Chem. Soc., Vol. 121, No. 38, 1999 8757
Table 1. Distribution Ratio for the Isomerization of Olefins Promoted by Benzamidinate Complexes Activated with MAO
products (%)
entry catalyst
substrate
1-octene
1-octene
2-E-octene
2-E-octene
3-methyl-1-butene 2-methyl-2-butene (76.0)
2-methyl-1-butene 2-methyl-2-butene (72.0)
1,4-cyclohexadiene benzene (55.5)
1
2
3
4
5
6
7
8
1
2
1
2
1
1
1
1
2-(Z)-octene (15.9)
2-(Z)-octene (20.3)
2-(Z)-octene (13.5)
2-(Z)-octene (14.3)
2-(E)-octene (24.3)
2-(E)-octene (53.4)
2-(E)-octene (27.0)
2-(E)-octene (31.2)
2-methyl-1-butene (24.0)
2-methyl-1-butene (28.0)
cyclohexene (43.1)
cyclohexene (21.1)
3-(E)-octene (41.3) 4-(E)-octene (18.5)
3-(E)-octene (23.8) 4-(E)-octene (2.5)
3-(E)-octene (41.6) 4-(E)-octene (17.9)
3-(E)-octene (37.8) 4-(E)-octene (16.7)
cyclohexane (1.4)
cyclohexane (4.3)
1,3-cyclohexadiene benzene (24.3)
1,4-cyclohexadiene (4.1)
dimers (20.4)
trimers (17.7)
tetramers (8.1)
9
0
1
1
2
3
allylbenzene
allylbenzene
allylbenzene
trans-â-methylstyrene (68.0) cis-â-methylstyrene (32.0)
trans-â-methylstyrene (90.0) cis-â-methylstyrene (10.0)
trans-â-methylstyrene (100)
1
1
Scheme 2. Plausible Mechanism for the Disproportionation
of 1,4-Cyclohexadiene
activation of the allylic hydrogen in the starting substrate with
the concomitant elimination of methane. A final question
concerns the mechanistic pathway for an alkene, such as
allylbenzene, with both a benzylic and an allylic position. Thus,
the isomerization of allylbenzene to cis- and trans-â-methyl-
styrene was studied with complexes 1, 2, and with the analogous
complex cis-[p-CH3-C6H4C(NSiMe3)2]2Ti(CH3)2 (3) (Table 1,
entries 9-11). In contrast to the well-known isomerization of
allylbenzene catalyzed by late transition metal complexes in
which the isomerized products are in equilibrium,12 no equi-
librium between the products is achieved for our octahedral
complexes (entries 9 and 11). This result indicates that the
insertion of the cationic hydride complex does not occur at the
conjugated double bonds, but only with the starting material.
To elucidate which of the two possible mechanisms is respon-
sible for the formation of the hydride complex, the reaction of
complex 1/MAO and 10 equiv of allylbenzene was carried out.
Besides the expected isomerization products, 1-phenyl-2-butene,
1
-phenyl-1-butene, and 2-methyl-3-phenyl-1-propene were ob-
It is important to point out the mechanistic difference between
the two cyclic dienes. The insertion of 1,3-cyclohexadiene with
complex C may follow two routes: (1) preferential formation
of the allylic organometallic moiety F, which seems to be
responsible for the formation of higher oligomers, or (2)
formation of the intermediate D. â-hydrogen elimination from
complex D will yield 1,4-cyclohexadiene and the starting
hydride complex C (eq 2). 11
tained in similar amounts (ca. 30-34%), with no traces of
methane. The formation of these three compounds is in
agreement with insertion of the methyl ligand into the double
bond of the starting allylbenzene with no regioselectivity and
the subsequent â-hydrogen elimination, producing the cationic
hydride complex (eq 3).
Kinetic measurements on the isomerization of allylbenzene with
1
1
were undertaken by in situ H NMR spectroscopy. The
reaction was monitored with constant catalyst concentration until
complete substrate consumption. The disappearance of the
We have observed two different pathways that are effective for
rac-octahedral benzamidinate complexes yielding the cationic
active hydride complex. For aliphatic alkenes, an insertion
reaction between the Zr-CH3 complex and the double bond
followed by â-hydrogen elimination; and for alicyclic dienes,
1
benzylic H resonance (doublet at δ ) 3.10 ppm) and the
1
appearance of the methyl H resonance of the product (doublet
at δ ) 2.08 ppm) were followed and normalized. The kinetic
shows a linear dependence of the rate of the reaction on
allylbenzene concentration over a ∼10-fold substrate concentra-
tion range, which indicates a first order dependence of the
catalytic rate on substrate concentration under these conditions
(Figure 1).
(10) The 1,4-elimination producing benzene is favored over an isomer-
ization of the organometallic complex with consecutive 1,2-elimination. If
isomerization occurs before the elimination, an intermediate complex similar
to the one obtained for the disproportionation of 1,3-cyclohexadiene would
be expected, leading also to oligomeric products. For favoring 1,4-
eliminations over 1,2-eliminations in alicyclic compounds see: Mandelbaum,
A. Mass Spectrom. ReV. 1983, 2, 223.
(12) Crabtree, R. H. In The Organometallic Chemistry of the Transition
Metals; John Wiley & Sons Inc.: New York, 1988; Chapter 9.
(13) No isomerization products were observed in blank reactions,
performed under the same conditions, for both olefin and cyclic olefins
with MAO.
(11) In Scheme 2, the allylic activation of either complexes D and E by
cyclohexene is possible, although it seems not to be a competing reaction
since complex F would be formed allowing oligomerization products.

8758 J. Am. Chem. Soc., Vol. 121, No. 38, 1999
AVerbuj and Eisen
Figure 3. Eyring plot for the isomerization of allylbenzene to trans-
8
â-methylstyrene with complex 1 as the precatalyst in toluene-d . The
line represents the least-squares fit to the data points.
Figure 1. Plot of the observed reaction rate vs allylbenzene concentra-
tion for the isomerization of allylbenzene with complex 1 as the pre-
8
catalyst in toluene-d . The line represents the least-squares fit to the
data points.
Scheme 3
The results presented here demonstrate for the first time that
early transition metal octahedral cationic complexes are active
catalysts for the isomerization of alkenes by a mechanism that
consists of several Zr-H insertions and â-hydrogen eliminations
to the most stable alkene (Saytzeff rule). In addition, these
complexes are active in the disproportionation of cyclic dienes,
producing the active cationic hydride species by a mechanism
that consists of activation of an allylic hydrogen in the starting
diene with the concomitant elimination of methane.
Figure 2. Plot of the observed reaction rate vs catalyst concentration
for the isomerization of allylbenzene with complex 1 as the precatalyst
8
in toluene-d . The line represents the least-squares fit to the data points.
Experimental Section
When the concentration of the allylbenzene is maintained
constant and the concentration of the precatalyst is varied over
a 10-fold concentration range, a plot of reaction rate vs
precatalyst concentration indicates that the reaction is first-order
dependent in precatalyst (Figure 2).
Materials and Methods. All manipulations of air-sensitive materials
were performed with rigorous exclusion of oxygen and moisture in
flamed Schlenk-type glassware on a dual manifold Schlenk line, or
interfaced to a high-vacuum (10 Torr) line, or in a nitrogen-filled
Vacuum Atmospheres glovebox with a medium capacity recirculator
-5
The rate law expression for the isomerization of allylbenzene
promoted by the precatalyst 1 is given by eq 4.
(1-2 ppm O ). Argon and nitrogen were purified by passage through
2
a MnO oxygen-removal column and a Davison 4 Å molecular sieve
8 6
column. Hydrocarbon solvents (toluene-d , benzene-d ) were distilled
1
1
ν ) k[L Zr-H] [allylbenzene]
(4)
under nitrogen from Na/K alloy. All solvents for vacuum line
manipulations were stored in vacuo over Na/K alloy in resealable bulbs.
R-Olefins (1-octene, 2-octene, 1,3- and 1,4-cyclohexadiene, 3-methyl-
1-butene, 2-methyl-1-butene, and allylbenzene) (Aldrich) were dried
and stored over activated molecular sieves (4 Å), degassed, and freshly
vacuum-distilled. Complexes 1, 2, and 3 were prepared according to
n
An enthalpy of activation, ∆H† 17.8 (6) kcal‚mol , and a
)
-1
†
large negative entropy of activation, ∆S ) -25.1 (2) e.u.,
characterize the activation parameters derived from an Eyring
analysis for the isomerization of allylbenzene (Figure 3). These
parameters suggest a highly ordered transition state with
considerable bond making to compensate for bond breaking.
A plausible mechanism for the isomerization of allylbenzene
is given in Scheme 3. This mechanism consists of two well-
established elementary reactions: (1) insertion of a hydride
M-H σ-bond as a turnover-limiting step and (2) rapid â-hy-
drogen elimination of the products.
4
literature procedures. NMR spectra were recorded on Bruker AM 200
1
and Bruker AM 400 spectrometers. Chemical shifts for H-NMR and
13
C-NMR are referenced to internal solvent resonances and are reported
relative to tetramethylsilane. GC/MS experiments were conducted in a
(14) (a) The Aldrich Library of NMR Spectra; Pouchert, C. J., II, Ed.;
Aldrich Chemical Co.: Milwaukee, WI; 1983; Vols. 1, 2. (b) The Aldrich
13
1
Library of C and H FT NMR Spectra; Pouchert, C. J., Behnke, J. Eds.;
Aldrich Chemical Co.: Wilwaukee, WI; 1993.

Catalytic Isomerization and Disproportionation of Olefins
J. Am. Chem. Soc., Vol. 121, No. 38, 1999 8759
GCMS (Finnigan Magnum) spectrometer. The NMR experiments were
conducted in Teflon valve-sealed tubes (J-Young) after vacuum transfer
of the liquids in a high-vacuum line.
plots. Typical initial olefin concentrations were in the range 0.42-4.2
M and typical catalyst concentrations were in the range 7.9-7.7 mM.
General Procedure for the Catalytic Isomerization of r-Olefins
and the Disproportionation of Cyclic Dienes. In a typical procedure,
the specific amount of an olefin or a cyclic diene was vacuum
transferred into an J-Young NMR tube containing 10 mg of the specific
Kinetic Study of the Isomerization of Allylbenzene. In a typical
experiment, a NMR sample was prepared as described in the typical
NMR scale catalytic reactions section but maintained at -78 °C until
kinetic measurements were started. The sealed tube was heated in a
temperature-controlled oil bath and at suitable time intervals NMR data
were acquired using eight scans with a long pulse delay to avoid
saturation of the signal. The kinetic studies were usually monitored by
the intensity changes in the substrate resonances and in the product
catalyst and a specific amount of MAO (keeping the ratio catalyst:
MAO:olefin as 1:400:180) in 0.6 mL of toluene-d8.13 The sealed tube
was then heated in an oil bath at 85 °C for 6 h. The organic products
-6
were vacuum transferred (10 mmHg) to another J-Young NMR tube
1
and sealed, and both residue and volatiles were characterized by H-
resonances over 3 or more half-lives. The substrate concentration (C)
13
and C-NMR and 2D-NMR spectroscopy and GC-MS spectroscopy
1
was measured from the area (A
solvent (A
by least squares to eq 5 where C
s
) of the H-normalized signal of the
14
and by comparing with known compounds.
b
). All the data collected could convincingly fit (R > 0.98)
(C ) Aso/Abo) is the initial
) is the substrate concentration
o
o
Acknowledgment. This research was supported by The
Israel Science Foundation, administered by The Israel Academy
of Sciences and Humanities under contract 69/97-2, by the
Technion Vice President for Research Lowengart Research
Fund, by the Fund for the Promotion of Research at the
Technion, and by The E. and J. Bishop Research Fund
administered by the Technion Vice President for Research.
concentration of substrate and C (A
s b
/A
at time, t.
mt ) log(C/Co)
(5)
The ratio of catalyst to substrate was accurately measured by using
stock solutions of both catalyst and substrate. Turnover frequencies
-1
(
N
t
, h ) were calculated from the least-squares slope (m) of the resulting
JA990011W