Ligand exchange processes in zirconocene dichloride-trimethylaluminum bimetallic systems and their catalytic properties in reaction with alkenes

Article abstract of DOI:10.1039/c8dt04156c

Ligand exchange processes in the systems L₂ZrCl₂-AlMe₃ (L₂ZrCl₂: Cp₂ZrCl₂, (CpMe)₂ZrCl₂, (C₅Me₅)₂ZrCl₂, Me₂SiCp₂ZrCl₂, Me₂Si(C₅Me₄)₂ZrCl₂, rac-Me₂C(2-Me-4-Bu^t-Cp)₂ZrCl₂, meso-Me₂C(2-Me-4-Bu^t-Cp)₂ZrCl₂, rac-Me₂C(3-Bu^t-Cp)₂ZrCl₂, Ind₂ZrCl₂, rac-H₂C(Ind)₂ZrCl₂, rac-Me₂C(Ind)₂ZrCl₂, rac-Me₂Si(Ind)₂ZrCl₂, rac-C₂H₄(Ind)₂ZrCl₂, rac-C₂H₄(THInd)₂ZrCl₂, rac-Me₂Si(THInd)₂ZrCl₂) and Cp₂ZrMeCl_2-n-AlMe₃ (n = 1, 2) were studied by NMR spectroscopy with the goal to establish the structures and dynamic features of probable intermediates in the zirconocene-catalyzed reactions of alkenes with AlMe₃. The effect of solvent, the organoaluminum compound concentration and the addition of (ClAlMe₂)₂ on the activation parameters of the alkyl exchange in the trimethylaluminum dimer was studied as well. The constants and activation parameters of the methyl group exchange in the monoalkyl-substituted ansa-complexes L₂ZrMeCl (L₂ = rac-Me₂C(2-Me-4-Bu^t-Cp)₂, rac-Me₂C(3-Bu^t-Cp)₂, rac-H₂CInd₂, rac-Me₂CInd₂, rac-Me₂SiInd₂, rac-H₄C₂Ind₂) were established for the first time. The catalytic activity and chemoselectivity of zirconocenes in the reaction of alkenes with AlMe₃ were evaluated and compared with the exchange and equilibrium constants of ligand exchange processes. A mechanism of the reaction was proposed.

Full text of DOI:10.1039/c8dt04156c

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PAPER
Ligand exchange processes in zirconocene
dichloride–trimethylaluminum bimetallic systems
and their catalytic properties in reaction with
alkenes†
Cite this: Dalton Trans., 2018, 47,
16918
Lyudmila V. Parfenova, *a Pavel V. Kovyazin,a Vener Z. Gabdrakhmanov,a
c,d
Galina P. Istomina,a,b Pavel V. Ivchenko,c,d Ilya E. Nifant’ev,
Leonard M. Khalilov a and Usein M. Dzhemileva
Ligand exchange processes in the systems L2ZrCl2–AlMe3 (L2ZrCl2: Cp2ZrCl2, (CpMe)2ZrCl2,
(C5Me5)2ZrCl2, Me2SiCp2ZrCl2, Me2Si(C5Me4)2ZrCl2, rac-Me2C(2-Me-4-But-Cp)2ZrCl2, meso-Me2C(2-Me-
4-But-Cp)2ZrCl2, rac-Me2C(3-But-Cp)2ZrCl2, Ind2ZrCl2, rac-H2C(Ind)2ZrCl2, rac-Me2C(Ind)2ZrCl2,
rac-Me2Si(Ind)2ZrCl2, rac-C2H4(Ind)2ZrCl2, rac-C2H4(THInd)2ZrCl2, rac-Me2Si(THInd)2ZrCl2) and
Cp2ZrMeCl2−n–AlMe3 (n = 1, 2) were studied by NMR spectroscopy with the goal to establish the struc-
tures and dynamic features of probable intermediates in the zirconocene-catalyzed reactions of alkenes
with AlMe3. The effect of solvent, the organoaluminum compound concentration and the addition of
(ClAlMe2)2 on the activation parameters of the alkyl exchange in the trimethylaluminum dimer was
studied as well. The constants and activation parameters of the methyl group exchange in the monoalkyl-
substituted ansa-complexes L2ZrMeCl (L2 = rac-Me2C(2-Me-4-But-Cp)2, rac-Me2C(3-But-Cp)2, rac-
H2CInd2, rac-Me2CInd2, rac-Me2SiInd2, rac-H4C2Ind2) were established for the first time. The catalytic
activity and chemoselectivity of zirconocenes in the reaction of alkenes with AlMe3 were evaluated and
compared with the exchange and equilibrium constants of ligand exchange processes. A mechanism of
the reaction was proposed.
Received 17th October 2018,
Accepted 4th November 2018
DOI: 10.1039/c8dt04156c
rsc.li/dalton
metallic homogeneous catalysts. From a mechanistic stand-
point, alkene hydro-, carbo-, and cyclometalation and
Introduction
The bimetallic catalytic systems based on zirconocene polymerization have the following common feature: the for-
dichlorides and organoaluminum compounds (OAC) L2ZrCl2– mation of active sites necessitates the presence of an activa-
AlR3 are classified as “neutral” organometallic catalytic tor, in particular, a Lewis acid (most often, aluminum or
systems. These systems show low activity towards polymeriz- boron compound).2 In the metallocene dichloride- and OAC-
ation; however, they are widely used to prepare functionalized based systems, σ-ligand exchange first takes place to give
low-molecular-weight products via hydro-, carbo-, and cyclo- hydride or alkyl metal complexes that are active towards
alumination of unsaturated compounds, which serve as hydro-, carbo- and cyclometalation of alkenes. The appear-
important synthons for organic and organometallic chem- ance of strong Lewis acids gives rise to active species such as
istry.1 The abovementioned reactions can also be intermedi- the [L2MR+⋯X−] ion pairs,3 which then either (a) dissociate,
ate or side steps of a polymerization process involving bi- thus providing a vacant coordination site at the transition
metal atom which is occupied by alkene (dissociation
requires a large amount of energy), or (b) do not dissociate,
aInstitute of Petrochemistry and Catalysis, Russian Academy of Sciences, 450075 Ufa,
the monomer being incorporated into the ion pair according
prosp. Oktyabrya, 141, Russian Federation. E-mail: luda_parfenova@ipc-ras.ru
to the substitution pattern.4 It has been noted that the reac-
tivity of Ziegler–Natta type systems may depend on the
dynamic processes of ion pair dissociation–association.5
The alkylation of the initial metallocene is a key step, result-
ing in the formation of active species and, hence, controlling
the transformation rates and chemoselectivity of catalytic
systems. For example, the formation of methyl-substituted
bUfa State Petroleum Technical University, ul. Kosmonavtov 1, 450062 Ufa,
Russian Federation
cDepartment of Chemistry, Lomonosov Moscow State University, 119991 Moscow,
1-3 Leninskiye Gory, Russian Federation
dA.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences,
Leninsky prosp. 29, 119991 Moscow, Russian Federation
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c8dt04156c
16918 | Dalton Trans., 2018, 47, 16918–16937
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complexes in the reaction of zirconocene dichlorides with
Thus, our work was aimed at a detailed investigation of the
AlMe3 was repeatedly proved in experiments.6 The rate of this structure and dynamics of the intermediates formed in the
step was shown to substantially depend on the π-ligand reaction of trialkylalanes with alkene catalyzed by L2ZrCl2
environment of the transition metal atom. Previously, we (1a–o) (Scheme 1) and an investigation of the activity and
studied the effects of the Zr π-ligand environment and the chemoselectivity of L2ZrCl2–AlMe3 catalytic systems towards
reaction conditions (solvent and reactant ratio) on the sub- alkenes, depending on the ligand environment of zirconium
strate conversion and the chemoselectivity of the reaction of and the solvent nature. The paper presents the results of
AlMe3 with alkenes catalyzed by L2ZrCl2 (1) [L = Cp, CpMe, dynamic NMR studies of ligand exchange processes and the
CpMe5, Ind (indenyl), Flu (fluorenyl), Ind* (1-neomenthylinde- structure of complexes formed in the L2ZrCl2–AlMe3 and
nyl)].7 The reaction gives the products of alkene hydro- and Cp2ZrMenCl2−n–AlMe3 systems (n = 1, 2). Since the reaction
carbometalation and dimerization, with the yield of carbo- conditions have a considerable effect on the alkene conversion
metalation products increasing for the reaction carried out in and chemoselectivity of the reaction, we also studied the alkyl
a chlorinated solvent (CH2Cl2) and for the presence of steric exchange in the trimethylaluminum dimer as a function of the
restrictions in the π-ligand (Cp < CpMe < Ind < Flu ≈ Cp* < nature of the solvent, the OAC concentration and the additions
Ind*). The dimerization products were also predominant in of (ClAlMe2)2.
the reaction mixture when the reaction was carried out in
CH2Cl2, but the catalysts used contained less bulky ligands
(Cp and CpMe). It was assumed that the bimetallic complex
(L2ZrMe(μ-Cl)AlMe3) formed in the first steps of the alkyl
exchange between L2ZrCl2 and AlMe3 is the key intermediate.
Results and discussion
Effect of the solvent nature and (ClAlMe2)2 on the (AlMe3)2 ⇄
2AlMe3 equilibrium
Despite the fact that the ligand exchange in L2ZrCl2–AlMe3
systems had been repeatedly studied,6 the structure of the
Trimethyl- and triethylaluminum are known to exist as
dimers.8 Previously, the exchange of bridging and terminal
possible intermediates and associates required further
alkyl groups in the trialkylalane dimers has been studied by
investigation.
dynamic NMR in various solvents; as a result, the rate con-
stants and thermodynamic parameters of the exchange of brid-
ging and terminal alkyl groups have been determined and
mechanisms for the alkyl exchange have been proposed,
implying the possibility of both intramolecular exchange and
intermolecular exchange via dissociation to monomers.9
It follows from quantum chemical studies (DFT, MP2, MP4)
of the self-association of trialkylalanes10 that the exchange of
alkyl groups in the trialkylalane dimers (2a,b) can occur along
three pathways with equal probability (Scheme 2): (a) an intra-
molecular pathway without preliminary dissociation of the
bridging bonds via a transition state (TS1) with three bridging
groups, (b) an intramolecular pathway with dissociation of one
bridging bond via structure (4a,b), and (c) an intermolecular
pathway with full dissociation of the (AlR3)2 dimers to mono-
mers (3a,b). Consideration of the influence of a solvent on
the OAC self-association using the polarized continuum
(non-specific solvation) model showed the presence of minor
solvation effects (solvation energy of ∼1 kcal mol−1). However,
Scheme 1
solvation was found to increase the self-association entropy.
Scheme 2
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Table 1 Solvent and (AlMe3)2 concentration effects on the rate and activation parameters of the alkyl exchange
δH, ppm
(T = 220 K)
kAlMe , s−1
(240 K)
ΔG‡240
,
ΔH‡240
,
ΔS‡240
,
3
Solvent
C, M/l
Meb
Met
kcal mol−1
kcal mol−1
cal mol−1 K−1
C6D5CD3
4.9
0.3
6.2
0.5
0.18
0.08
0.55
0.50
0.54
−0.62
−0.51
−0.65
−0.73
−0.68
−0.32
113
112
275
354
144
11.7 0.2a
11.7 0.1
11.2 0.1
11.1 0.1
11.0 0.1
13.0 1.0a
13.6 0.5
14.5 0.7
14.5 0.2
10.4 0.5
6.0 16.5a
8.2 8.5
13.6 12.4
14.2 3.2
−2.6 8.8
CD2Cl2
CD2Cl2 + (ClAlMe2)2
2.5 (AlMe3) 1.1 (ClAlMe2)
a Standard deviations calculated by earlier reported methods are given.11
Line shape analysis, carried out by standard dynamic NMR Ligand exchange in the Cp2ZrMenCl2−n–AlMe3 systems
procedures, resulted in the determination of alkyl exchange (n = 1, 2)
constants for (AlMe3)2 in concentrated and dilute solutions of
toluene and dichloromethane. The results demonstrated that According to the schemes proposed previously,6b,e,5 olefins are
the ΔH‡, ΔG‡, and ΔS‡ values that we found for the alkyl carbometalated with alkyl zirconocene derivatives. In order to
exchange of (AlMe3)2 in toluene are in line with published identify the possible intermediates of olefin carboalumination
data9b,c (Table 1). It was found that in toluene, the rate and with trimethylaluminum, we studied the bimetallic systems
activation parameters of the exchange between the bridging Cp2ZrMeCl–AlMe3 and Cp2ZrMe2–AlMe3 in C7D8 and CD2Cl2
and terminal methyl groups barely depend on the concen- by dynamic NMR. For this purpose, Cp2ZrMeCl (5a) and
tration of the solution.
It is known that the dissociation enthalpy and entropy of were reacted with AlMe3. As follows from Table 2, the proton
the (AlMe3)2 dimer to the monomer are chemical shifts of the Cp rings and the methyl group of the
Cp2ZrMe2 (6a) were synthesized by an alternative method and
Δ°dð1Þ ¼ 19:4 kcal molꢀ1, ΔSd°ð1Þ ¼ 29:3 (in aliphatic solvents)12a initial zirconocene complexes depend on the solvent polarity.
and Δ°dð1Þ ¼ 15:6 kcal molꢀ1 (in toluene).12b Since the Owing to the solvation effect in polar CD2Cl2 as compared
monomer energy level Δ°dð1Þ is higher than the transition state with that in toluene, the Cp proton signals are shifted down-
energy ΔH‡, the alkyl exchange process is likely to be mainly field, whereas both the proton and carbon signals of the
intramolecular (via 4a and TS1). This is also indicated by the methyl group are shifted upfield.
activation entropy of the exchange ΔS‡ being lower than ΔSd°ð1Þ
.
The replacement of one chlorine atom in Cp2ZrCl2 by the
The replacement of toluene by CD2Cl2 induces an almost methyl group induces upfield shifts of the 1H and 13C NMR
three-fold increase in the exchange rate kAlMe , which also signals of the Cp ring both in CD2Cl2 and in C7D8, which indi-
3
increases upon dilution of the (AlMe3)2 solution in CD2Cl2. cates an increase of electron density on the cyclopentadienyl
Since this is accompanied by only minor changes in the ligand and, hence, on the Zr atom due to the presence of the
thermodynamic parameters, one can conclude that the intra- methyl group, which, unlike chlorine, does not exhibit a nega-
molecular mechanism of the exchange is retained and the tive inductive effect.
increase in the rate can be attributed to the increasing pro-
The addition of (AlMe3)2 to Cp2ZrMe2 in either CD2Cl2 or
portion of exchange involving cleavage of one bridging bond C7D8 does not induce changes in the proton or carbon chemi-
(4a) or to the formation of solvent-caged monomers9a under cal shifts of the initial dimethylzirconocene, which indicates
the action of a more polar solvent. According to calculations,13 the absence of stable associates of this zirconium complex
the complex formation of trimethylaluminum with dichloro- with trialkylalane (Fig. S4†). However, as follows from the
methane or dichloroethane, although thermodynamically EXSY spectra (Fig. S6†), at temperatures below 320 K, inter-
favorable, is still inferior to dimerization.
molecular exchange of methyl groups takes place between 6a
When dimethylaluminum chloride, which exists in solution and (AlMe3)2, which is consistent with published data.15 Most
8
as a dimer, is added to a solution of (AlMe3)2 in CD2Cl2 at an likely, this exchange proceeds via a four-center associate
amount comparable to the amount of (AlMe3)2, the exchange (Scheme 3).
rate and activation enthalpy decrease. In the spectra of a
In the case of 5a, the appearance of (AlMe3)2 in solution in
mixture of (AlMe3)2 and (ClAlMe2)2 obtained in the 210–300 K either CD2Cl2 or C7D8, gives rise to two new Cp signals in the
temperature range, we did not identify structures such as NMR spectra. The signals of the initial 5a completely dis-
(Me2Al(μ-Me)(μ-Cl)AlMe2) with a bridging methyl group, which appear upon the addition of a ∼3-fold excess of trialkylalane.
is consistent with earlier reported data.14 However, associates One of the two new Cp signals coincides with the resonance
could be formed via the bridging chlorine atom (Me3Al(μ-Cl) lines of the Cp rings of dimethylzirconocene 6a, while the
AlMe2) and, by changing the effective monomer concentration, other signal is assigned to the AlMe3-associated Cp2ZrMeCl
they could affect the alkyl exchange parameters.
(7a). The appearance of an AlMe3 molecule associated with
16920 | Dalton Trans., 2018, 47, 16918–16937
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Table 2 1H and 13C NMR spectra of complexes 1a, 5–7a, and 5b–o (δ, ppm, 400.13 MHz (1H), 100.62 MHz (13C))
Complex
Solvent
T, K
Group
δ (1H)
δ (13C)
1a
C7D8
CD2Cl2
298
298
Cp
Cp
5.95 (s)
6.54 (s)
116.02
116.31
5a
C7D8
298
182
298
189
ZrMe
Cp
ZrMe
Cp
ZrMe
Cp
ZrMe
Cp
0.20 (s)
5.75 (s)
0.41 (s)
5.69 (s)
−0.01 (s)
5.98 (s)
−0.11 (s)
5.94 (s)
19.95
110.36
20.52
110.67
17.75
110.34
18.61
110.6
CD2Cl2
5aa
C7D8
298
298
ZrMe
AlMe3
Cp
ZrMe
AlMe3
Cp
0.38 (br.s)
−0.44
36.80
−9.47
112.75
34.01
−9.96
112.88
5.76
CD2Cl2
0.38 (br.s)
−0.55
6.31
6a
C7D8
298
182
298
190
ZrMe
Cp
ZrMe
Cp
ZrMe
Cp
ZrMe
Cp
−0.18 (s)
5.74 (s)
0.03 (s)
5.58 (s)
−0.38 (s)
6.13 (s)
−0.51 (s)
6.08 (s)
30.05
110.0
30.74
110.28
29.27
110.26
29.49
110.47
CD2Cl2
7ab
C7D8
298
182
298
189
ZrMe
AlMe3
Cp
ZrMe
AlMe3
Cp
ZrMe
AlMe3
Cp
ZrMe
AlMe3
Cp
n/a
n/a
5.81 (s)
0.50 (br.s)
−0.15 (br.s)
5.64
n/a
n/a
6.25 (s)
0.23 (br.s)
−0.64 (br.s)
6.19 (s)
n/a
n/a
112.29
28.98
−5.66
112.46
n/a
CD2Cl2
n/a
112.6
27.96
−5.92
112.70
5b
C7D8
298
298
ZrMe
L
0.35 (br.s)
33.94
14.67
109.35, 110.06
113.80, 115.04
126.16
36.12
15.09
110.13, 110.67
114.31, 115.27
127.48
2.01 (s, 6H, CH3)
5.51 (m, 4H, CH)
5.67 (m, 4H, CH)
CD2Cl2
ZrMe
L
0.35 (br.s)
2.25 (s, 6H, CH3)
6.08 (m, 4H, CH)
6.12 (m, 4H, CH)
5c
C7D8
285
298
ZrMe
L
−0.09 (s, 3H)
43.54
11.17
120.83
42.25
11.44
121.52
1.72 (s, 30H)
CD2Cl2
ZrMe
L
−0.09
1.98 (s, 30H, CH3)
5d
C7D8
260
ZrMe
L
0.44 (s, 3H)
39.98
5.09 (m, 2H, CH)
6.54 (m, 2H, CH)
6.60 (m, 2H, CH)
5.42 (m, 2H, CH)
115.37
123.59
124.58
110.95
103.82
−5.73
−6.80
38.72
−0.02 (s, 3H, SiMe)
0.13 (s, 3H, SiMe)
0.47 (s, 3H)
CD2Cl2
260
ZrMe
L
5.83 (m, 2H, CH)
115.88
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Table 2 (Contd.)
Complex
Solvent
T, K
Group
δ (1H)
δ (13C)
7.07 (m, 2H, CH)
6.84 (m, 2H, CH)
6.12 (m, 2H, CH)
123.81
124.88
111.33
104.80
−6.02
−4.98
0.56 (s, 3H, SiMe)
0.71 (s, 3H, SiMe)
5e
C7D8
299
ZrMe
L
−0.05 (s, 3H)
43.04
14.18
14.28
11.57
1.48 (s, 2H, CMe)
1.75 (s, 2H, CMe)
1.93 (s, 2H, CMe)
2.01 (s, 2H, CMe)
12.02
91.10, 123.48, 124.85
132.12, 133.12
2.32
2.82
n/a
0.53 (s, 3H, SiMe)
0.61 (s, 3H, SiMe)
n/a
CD2Cl2
260
ZrMe
L
1.82 (s, 2H, CMe)
2.00 (s, 2H, CMe)
2.06 (s, 2H, CMe)
2.13 (s, 2H, CMe)
14.44
14.56
11.99
11.82
91.37, 123.32, 124.88,
131.56, 132.67
3.17
3.26
0.88 (s, 3H, SiMe)
0.97 (s, 3H, SiMe)
5f
C7D8
300
ZrMe
L
0.50 (s, 3H)
36.20
101.99
101.74
120.11
122.24
30.23
29.92
26.46
26.46
17.79
17.13
5.03 (d, 2.8 Hz, 1H, CH1)
5.50 (d, 2.8 Hz, 1H, CH3)
6.09 (d, 2.8 Hz, 1H, CH4)
6.11 (d, 2.8 Hz, 1H, CH2)
1.28 (s, 9H, CMe3)
1.31 (s, 9H, CMe3)
1.40 (s, 3H, CMe)
1.46 (s, 3H, CMe)
1.77 (s, 3H, CpMe)
1.97 (s, 3H, CpMe)
32.80, 39.58, 101.74, 101.99, 110.38, 111.30,
117.91, 118.87, 140.76, 141.82
35.60
102.60
102.23
120.20
122.50
29.68
26.87
CD2Cl2
300
298
275
ZrMe
L
0.38 (s, 3H)
5.24 (d, 2.6 Hz, 1H, CH1)
5.69 (d, 2.6 Hz, 1H, CH3)
6.17 (d, 2.2 Hz, 1H, CH4)
6.37 (d, 2.2 Hz, 1H, CH2)
1.33 (s, 18H, CMe3)
1.78 (s, 3H, CMe)
1.85 (s, 3H, CMe)
2.22 (s, 6H, CpMe)
26.87
18.19
32.92, 39.93, 102.23, 102.60, 110.59, 111.52,
118.50, 119.24, 140.99, 142.08
5h
C7D8
ZrMe
L
0.49 (s, 3H)
34.88 (HSQC)
98.79
115.99
107.16
101.52
115.44
104.79
30.04
4.97 (d, 2.5 Hz, 1H, CH1)
6.22 (d, 2.4 Hz, 1H, CH2)
5.48 (d, 2.4 Hz, 1H, CH3)
5.11 (d, 2.4 Hz, 1H, CH4)
6.28 (d, 2.8 Hz, 1H, CH5)
5.44 (d, 2.8 Hz, 1H, CH6)
1.31 (s, 9H, CMe3)
1.33 (s, 9H, CMe3)
1.09 (s, 3H, CMe)
1.25 (s, 3H, CMe)
30.66
22.57
23.91
32.64, 35.84, 114.66, 116.04, 142.52, 144.55
34.79 (HSQC)
107.46
115.99
104.93
102.39
115.60
99.49
CD2Cl2
ZrMe
L
0.36 (s, 3H)
5.36 (m, 1H, CH1)
6.36 (m, 1H, CH2)
5.83 (m, 1H, CH3)
5.37 (m, 1H, CH4)
6.49 (m, 1H, CH5)
5.71 (m, 1H, CH6)
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Table 2 (Contd.)
Complex
Solvent
T, K
Group
δ (1H)
δ (13C)
1.31 (s, 9H, CMe3)
1.34 (s, 9H, CMe3)
1.51 (s, 3H, CMe)
1.67 (s, 3H, CMe)
29.99
30.64
23.03
24.44
32.76, 36.31, 114.84, 116.22, 142.97, 145.05
5i
C7D8
298
298
270
ZrMe
L
−0.52
43.88
101.53
117.72
103.18
125.53, 125.62
125.02
124.66
41.26
102.85
101.95
117.83
125.75, 125.71
125.15
124.46
46.55
111.75
5.74 (m, 2H, CH)
5.77 (m, 2H, CH)
5.80 (m, 2H, CH)
6.85–6.95 (m, 4H, CH(Ph))
7.08–7.28 (m, 4H, CH(Ph)
CD2Cl2
ZrMe
L
−0.61
6.18 (m, 2H, CH)
6.23 (m, 2H, CH)
6.26 (m, 2H, CH)
7.22–7.31 (m, 4H, CH(Ph))
7.46–7.62 (m, 4H, CH(Ph))
5j
C7D8
ZrMe
L
−0.64 (s, 3H)
4.97 (m, 1H, CH1)
5.45 (m, 1H, CH3)
111.22
103.52
106.22
6.30 (m, 1H, CH4)
6.23 (m, 1H, CH2)
6.58–6.71 (m, COSY, CH(Ph))
6.96–7.11 (m, COSY, CH(Ph))
7.27 (d, 8.4 Hz, 1H, CH(Ph))
7.30 (d, 8.4 Hz, 1H, CH(Ph))
119.63, 122.52
n/a
125.90
125.90
89.26, 118.31
3.69 (s, 2H, CH2)
−0.81 (s, 3H)
22.53
43.46
111.99
111.36
103.92
106.18
125.99
125.72, 126.06
CD2Cl2
280
ZrMe
L
5.71 (d, 3.1 Hz, 1H, CH1)
6.07 (d, 3.1 Hz, 1H, CH3)
6.39 (d, 2.8 Hz, 1H, CH4)
6.75 (d, 2.8 Hz, 1H, CH2)
7.10–7.19 (m, COSY, CH(Ph))
7.24–7.31 (m, COSY, CH(Ph))
7.59 (d, 9.2 Hz, 2H, CH(Ph))
7.51 (d, 8.5 Hz, 1H, CH(Ph))
7.45 (d, 8.5 Hz, 1H, CH(Ph))
4.55 (s, 2H, CH2)
125.34, 125.61
119.88
122.80
89.37, 89.47, 118.80, 118.41, 127.38, 128.02 23.33
5k
C7D8
300
ZrMe
L
−0.63 (s, 3H)
41.40
5.24 (d, 3.2 Hz, 1H, CH1)
5.76 (d, 3.2 Hz, 1H, CH3)
6.37 (d, 3.2 Hz, 1H, CH4)
6.41 (d, 3.2 Hz, 1H, CH2)
6.64–6.73 (m, COSY, CH(Ph))
6.72–6.82 (m, COSY, CH(Ph))
7.09–7.16 (m, COSY, CH(Ph))
7.19–7.27 (m, COSY, CH(Ph))
6.94–7.03 (m, COSY, CH(Ph))
7.02–7.09 (m, COSY, CH(Ph))
7.23–7.30 (m, COSY, CH(Ph))
7.27–7.34 (m, COSY, CH(Ph))
110.75
109.85
104.99
106.73
124.78
125.90
124.67
121.84
125.06
125.06
126.07
125.69
98.60, 100.41
27.10
1.64 (s, 3H, CMe)
1.70 (s, 3H, CMe)
27.10
40.22
44.75
CD2Cl2
300
ZrMe
L
−0.71 (s, 3H)
5.90 (d, 3.0 Hz, 1H, CH1)
6.29 (d, 3.0 Hz, 1H, CH3)
6.56 (d, 2.5 Hz, 1H, CH4)
6.91 (d, 2.5 Hz, 1H, CH2)
7.03–7.14 (m, COSY, CH(Ph))
7.22–7.32 (m, COSY, CH(Ph))
7.35–7.44 (m, COSY, CH(Ph))
7.60 (d, 8.4 Hz, 1H, CH(Ph))
7.62 (d, 8.4 Hz, 1H, CH(Ph))
111.95
110.63
105.37
107.90
126.23
125.66
125.93
125.75
125.75
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Table 2 (Contd.)
Complex
Solvent
T, K
Group
δ (1H)
δ (13C)
7.70 (d, 8.8 Hz, 1H, CH(Ph))
7.76 (d, 8.8 Hz, 1H, CH(Ph))
2.23 (s, 3H, CMe)
125.30
122.01
97.57, 99.55, 118.21, 128.15
2.29 (s, 3H, CMe)
27.56
27.56
40.82
5l
C7D8
270
ZrMe
L
−0.56 (s)
46.06
116.68
118.61
113.81
114.55
125.70
123.31
125.57
5.27 (m, 1H, CH1)
5.75 (m, 1H, CH3)
6.69 (d, 2.9 Hz, 1H, CH4)
6.64 (d, 2.5 Hz, 1H, CH2)
6.91–7.02 (m, COSY, CH(Ph))
7.09–7.19 (m, COSY, CH(Ph))
6.73–6.97 (m, COSY, CH(Ph))
6.80–6.89 (m, COSY, CH(Ph))
7.04–7.22 (m, COSY, CH(Ph))
7.46 (d, 8.7 Hz, 2H, CH(Ph))
126.75
n/a
126.43, 126.52
85.87, 86.98; 131.81, 125.86
0.43 (s, 3H, SiMe)
0.52 (s, 3H, SiMe)
−2.89
−2.51
42.70
119.08
116.92
114.01
114.34
CD2Cl2
300
ZrMe
L
−0.81 (s, 3H)
5.95 (d, 2.7 Hz, 1H, CH1)
6.27 (d, 2.7 Hz, 1H, CH3)
6.76 (d, 2.7 Hz, 1H, CH4)
7.06 (d, 2.7 Hz, 1H, CH2)
7.09–7.19 (m, COSY, CH(Ph))
7.37–7.48 (m, COSY, CH(Ph))
7.56–7.64 (m, COSY, CH(Ph))
7.68 (d, 8.5 Hz, 2H, CH(Ph))
125.94
126.25
123.83
125.54
87.02, 87.82; 125.57, 127.03; 131.85, 131.26
1.02 (s, 3H, SiMe)
1.11 (s, 3H, SiMe)
−2.17
−1.72
5m
C7D8
270
ZrMe
L
−0.52 (s)
44.97
113.96
112.24
107.06
107.78
125.29
125.07
125.87
126.67
126.10
122.29, 125.73
120.77
5.36 (d, 2.8 Hz, 1H, CH1)
5.74 (d, 3.1 Hz, 1H, CH3)
6.41 (d, 3.1 Hz, 1H, CH4)
6.31 (d, 2.8 Hz, 1H, CH2)
7.28 (d, 8.5 Hz, 1H, CH(Ph))
7.33 (d, 8.5 Hz, 1H, CH(Ph))
6.97–6.07 (m, 1H, CH(Ph))
6.89–6.96 (m, 1H, CH(Ph))
7.05–7.29 (m, 1H, CH(Ph))
6.80–6.86 (m, 2H, CH(Ph))
7.04–7.09 (m, 1H, CH(Ph))
117.22, 119.44; 122.74, 122.98; 127.15, 127.06
27.89
26.95
43.93
114.80
112.76
107.23
107.81
2.60–2.69, 2.84–2.95 (m, 2H, CH2)
2.69–2.78 (m, 2H, CH2)
−0.64 (s)
CD2Cl2
300
ZrMe
L
6.10 (d, 2.8 Hz, 1H, CH1)
6.36 (d, 2.8 Hz, 1H, CH3)
6.46 (d, 2.8 Hz, 1H, CH4)
6.78 (d, 2.8 Hz, 1H, CH2)
7.20–7.44 (m, 4H, CH(Ph))
7.49–7.60 (m, 2H, CH(Ph))
125.74, 125.90,
125.94, 126.22
125.01, 125.67
122.76
7.52 (m, 1H, CH(Ph))
7.72 (d, 8.6 Hz, 1H, CH(Ph))
121.22
118.30, 120.16; 122.97, 123.33; 126.81, 127.04
3.41–3.53, 3.65–3.76 (m, 2H, CH2)
3.52–3.61 (m, 2H, CH2)
28.63
27.76
5n
C7D8
300
ZrMe
L
0.34 (s)
40.7
4.73 (m, 1H, CH1)
112.87
111.04
122.65
120.60
22.11
5.28 (m, 1H, CH3)
6.46 (d, 2.8 Hz, 1H, CH4)
6.47 (d, 2.8 Hz, CH2)
1.36–1.49, 1.79–1.93 (m, 2H, CH2)
16924 | Dalton Trans., 2018, 47, 16918–16937
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Table 2 (Contd.)
Complex
Solvent
T, K
Group
δ (1H)
δ (13C)
1.42–1.52, 1.59–1.69 (m, 2H, CH2)
1.59–1.71 (m, 4H, CH2)
1.95–2.06, 2.24–2.38 (m, 2H, CCH2)
2.51–2.62, 2.87–2.98 (m, 2H, CCH2)
1.56–1.66, 2.11–2.19 (m, 2H, CCH2)
2.58–2.67, 2.71–2.83 (m, 2H, CCH2)
0.27 (s, 3H, SiMe)
22.01
22.77, 22.56
25.90
24.41
25.61
23.95
−2.89
−2.89
0.36 (s, 3H, SiMe)
98.68, 99.47, 127.25, 134.27
CD2Cl2
280
ZrMe
L
0.20 (s)
39.91
5.22 (d, 2.8 Hz, 1H, CH1)
5.63 (d, 2.8 Hz, 1H, CH3)
6.49 (m, 1H, CH4)
113.04
111.16
120.58
122.65
6.76 (m, 1H, CH2)
1.52–1.89 (m, 8H, CH2CH2)
2.02–2.14, 2.51–2.64 (m, 2H, CCH2)
2.31–2.45, 2.59–2.71 (m, 2H, CCH2)
1.68–1.89, 2.83–2.89 (m, 2H, CCH2)
2.71–2.94 (m, 2H, CCH2)
0.64 (s, 3H, SiMe)
21.91, 22.15, 22.65, 22.89, 25.50, 25.83
24.05, 24.56
−2.64
−2.49
0.72 (s, 3H, SiMe)
98.81, 100.01, 127.77, 128.01, 134.47, 134.74
5o
C7D8
270
298
ZrMe
L
0.43 (s)
41.09
109.07
107.04
114.00
116.43
22.11, 22.23, 22.46
23.72, 24.14, 23.15, 23.38
27.66, 27.21
123.24, 126.89, 129.78, 130.01
39.11
108.97
106.85
114.21
116.40
4.75 (d, 2.7 Hz, 1H, CH1)
5.30 (d, 2.7 Hz, 1H, CH3)
6.20 (m, 1H, CH4)
6.15 (m, 1H, CH2)
1.19–1.64 (m, 8H, CH2CH2)
2.32–2.63, 2.71–2.97 (m, 4H, CCH2)
1.92–2.12 (m, 4H, CCH2)
2.18–2.43 (m, 4H, bridge CH2CH2)
0.33 (s)
CD2Cl2
ZrMe
L
5.37 (d, 2.8 Hz, 1H, CH1)
5.77 (d, 2.8 Hz, 1H, CH3)
6.16 (m, 1H, CH4)
6.48 (m, 1H, CH2)
1.52–2.04 (m, 8H, CH2CH2)
2.44–3.05 (m, 8H, CCH2)
2.86–2.95, 2.98–3.10 (m, 4H, bridge CH2CH2)
22.35, 22.39, 22.63
23.48, 23.74, 23.82, 24.23
27.64, 28.02
123.42,123.35, 127.79, 129.24, 129.82, 129.90
a The complex is obtained in the reaction of Cp2ZrCl2 with (AlMe3)2. b The complex is obtained in the reaction of Cp2ZrMeCl with (AlMe3)2.
Concentration [Zr]0 = 0.13 mol l−1, [(AlMe3)2]0 = 0.29 mol l−1 (C7D8); [Zr]0 = 0.09 mol l−1, [(AlMe3)2]0 = 0.43 mol l−1 (CD2Cl2).
Scheme 3
Cp2ZrMeCl induces considerable downfield shifts of the
The equilibrium constants K1 and K2 for two parallel reac-
signals for the methyl group at Zr and Cp rings, which attests tions can be represented in the following form:
to deshielding of these groups of atoms. The addition of di-
½Cp2ZrMeCl ꢁ AlMe3ꢂ
methylaluminum chloride to 6a gave again the initial 5a. The
K1 ¼
½Cp2ZrMeClꢂ½AlMe3ꢂ
reaction of 5a with (Me2AlCl)2 aimed at generating the
(Cp2ZrMe(μ-Cl)Al(Cl)Me2) intermediate6c resulted in Cp2ZrCl2
and AlMe3 even at temperatures below 200 K (Scheme 4, reac-
½Cp2ZrMe2ꢂ½ClAlMe2ꢂ
tion (3)). Thus, the reaction of 5a with (AlMe3)2 involves two
equilibrium processes (Scheme 4, reactions (1) and (2)):
K2 ¼
;
½Cp2ZrMeClꢂ½AlMe3ꢂ
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Scheme 4
if one assumes that [Cp2ZrMe2] = [ClAlMe2], then
K1 ½Cp2ZrMeCl ꢁ AlMe3ꢂ
¼
:
2
K2
½Cp2ZrMe2ꢂ
The equilibrium concentrations of 5a and 6a are pro-
portional to the integrated intensities of the Cp-ring signals in
1
the H NMR spectra. Thus, it is possible to estimate the vari-
ation of the ratio of the equilibrium constants of these steps as
a function of the solvent. Indeed, for equal initial concen-
trations of 5a, the K1/K2 ratio is 0.65 in CD2Cl2 and 0.08 in
C7D8. Since K1/K2 < 1, the reaction pathway producing 6a
always predominates, this pathway being more significant in
toluene than in CD2Cl2. The lower proportion of reaction (1) in
CD2Cl2 can be explained both in terms of solvation of the
initial 5a and in terms of the increasing rate of the reverse
reaction between 6a and ClAlMe2 as a result of increasing pro-
portion of the OAC monomer formed upon dissociation of the
(ClAlMe2)2 dimer in the polar solvent.
The existence of complex 7a in solutions of C7D8 and
1
CD2Cl2 was confirmed by low-temperature 1D H NMR spectra
(Fig. 1 and S7†) and 2D EXSY spectra (Fig. 2 and S8†) recorded
in the temperature range of 170–200 K.
In the temperature range of 170–200 K in CD2Cl2 or C7D8,
complex 7a showed slow exchange of the methyl group
between the Zr and Al atoms, as indicated by the cross-peaks
of the ZrMe signals [δZrMe(C7D8) = 0.50 ppm, δZrMe(CD2Cl2) =
Fig. 1 Variable-temperature 1H NMR study of the 5a–(AlMe3)2 system
(1 : 3) in CD2Cl2 ((AlMe3)2 was added at 220 K).
0.23 ppm] with the AlMe3 signals [δAlMe(C7D8) = −0.15 ppm, exhibits lines for the unreacted (AlMe3)2 dimer. As for pure
δAlMe(CD2Cl2) = −0.64 ppm] in the EXSY spectra. The rate of (AlMe3)2, the EXSY spectra of this mixture in the temperature
methyl group exchange between Zr and Al for 7a proved to be range of 170 to 200 K show a slow exchange of bridging and
lower in CD2Cl2 (ΔW1/2 = 9 Hz, T = 190 K) than that in C7D8 terminal methyl groups (Fig. 2). A study of the system
(ΔW1/2 = 17 Hz, T = 190 K). Under the assumption that the dynamics in toluene (Fig. S7†) revealed an unusual type of
exchange proceeds via dissociation of the complex or via reac- exchange in the (AlMe3)2 dimer: as the temperature increases
tion with one more AlMe3 molecule, the deceleration of this in the 175–240 K range, the signals of bridging and terminal
process in CD2Cl2 may be due to the solvation of Cp2ZrMeCl methyl groups are broadened. However, they do not coalesce,
and trialkylalane.
as in the case of pure (AlMe3)2, but, conversely, move apart. It
Apart from the signals for zirconocene complexes 6a and 7a was found that in (AlMe3)2 containing a Cp2ZrMeCl admixture,
observed in the equilibrium system, the 1H NMR spectrum the exchange rate between the terminal and bridging methyl
16926 | Dalton Trans., 2018, 47, 16918–16937
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peaks with the Me resonance line for Cp2ZrMe2. The second,
1
narrower H NMR signal at −0.22 ppm correlates with the 13C
NMR line at −0.66 ppm. We interpreted this signal as an aver-
aged line for the methyl group involved in the fast exchange
with ZrMeCl, the associated AlMe3 monomer, and the (AlMe3)2
dimer. A similar picture is observed in CD2Cl2. However, in
this case, the proportion of the dimer is approximately 1.5
times lower than that in C7D8 (for equal initial concentrations
of 5a), apparently as a result of the increasing proportion of
the AlMe3 monomer involved in the exchange.
Thus, one can conclude that 5a reacts with the AlMe3
monomer, which is thus withdrawn from the (AlMe3)2 dimer–
monomer equilibrium. This withdrawal of the AlMe3
monomer is more pronounced in dichloromethane, which
results in a higher content of complex 7a in the chlorinated
solvent than in toluene.
Ligand exchange in the L2ZrCl2–(AlMe3)2 systems
Fig. 2 EXSY spectrum of the 5a–(AlMe3)2 system (1 : 3) in CD2Cl2 at
199 K (τ = 0.08 s).
For the identification of intermediates formed in the reaction
of alkenes with trimethylaluminum, we studied the reactions
of L2ZrCl2 (1a–o) with (AlMe3)2 in toluene and dichloro-
methane. It was found that complete conversion of the initial
groups (k) is higher and ΔH‡ is lower than that for pure zirconium complex occurs with at least a 20–80-fold excess of
(AlMe3)2 both in CD2Cl2 and in C7D8 (Table 3). Furthermore, OAC. Apparently, the large excess is needed for providing the
ΔS‡ substantially decreases as compared with the activation monomer concentration necessary for alkylation of metallo-
entropy of exchange in pure (AlMe3)2 (Table 3). All of these are cene dichloride. A high probability of the reaction of metallo-
attributable to increasing proportion of intramolecular cene dichloride with the AlMe3 monomer was also revealed in
exchange in the (AlMe3)2 dimer (pathway b in Scheme 1), a theoretical study.16 The reactions of 1a–o with trimethyl-
which is caused by the decrease in the effective concentration aluminum give only zirconocene methyl chlorides L2ZrMeCl,
of the monomer upon association with Cp2ZrMeCl. The ΔH‡ which is consistent with published data.6b,c,f,g The NMR
value is greater in CD2Cl2 than that in C7D8, probably due to spectra of the L2ZrCl2–(AlMe3)2 system in both toluene and di-
the increasing proportion of the monomer involved in the chloromethane exhibit broadened signals for the Me groups of
exchange.
L2ZrMeCl and (AlMe3)2 and the Me group of the trimethyl-
In the temperature range of 230–240 K, the resonance lines aluminum moiety, which we assigned to the AlMe3 monomer
of ZrMe, the associated AlMe3, and bridging and terminal Me (Fig. 3, Fig. S9†). The study showed that the proton and carbon
groups in the residual (AlMe3)2 are markedly broadened, signals for the methyl groups of the AlMe3 monomer are
which is indicative of the increasing exchange rate. A further located at a higher field than the dimer signals at δH −0.5 to
temperature rise to 300 K could be expected to give rise to one −0.4 ppm and δC −10 to −8 ppm. According to EXSY experi-
averaged, narrow (because of fast exchange) signal for the Me ments (Fig. 3, Fig. S10†), at temperatures below 310 K, the Zr-
group. However, two resonance lines are observed in experi- bound methyl group in the formed L2ZrMeCl is involved in
ments (Fig. 1 and S7†) for the Al-bound Me groups (one line is slow exchange with both the AlMe3 monomer and the (AlMe3)2
broadened). At 300 K, the more intense broad 1H NMR line dimer. Apparently, this exchange proceeds via the AlMe3
recorded at −0.34 ppm in C7D8 (Fig. S2†) is correlated with the monomer, which is in equilibrium with the (AlMe3)2 dimer
carbon signal at −7.4 ppm in the HSQC experiment; therefore, and with zirconium complexes 5 and 7 (Scheme 5). The EXSY
the signal at −0.34 ppm was assigned to the (AlMe3)2 dimer. In spectra also exhibit cross-peaks between the signals for the
the EXSY spectrum at T = 300 K, this signal produces cross- ligands of complexes 1 and 5 (7). It should be noted that the
Table 3 Solvent and Cp2ZrMeCl effects on the rate and activation parameters of the alkyl exchange in (AlMe3)2 at T = 220 K
Solvent
C([Al]) (mol l−1
)
k (s−1
)
ΔG‡ (kcal mol−1
)
ΔH‡ (kcal mol−1
)
ΔS‡ (cal mol−1 K−1
)
C7D8 a
C7D8
0.3
0.3
0.4
0.5
59.0
10.0
45.7
21.0
10.9 0.1
11.7 0.1
11.1 0.1
11.4 0.1
8.8 0.5
13.6 0.5
9.8 0.4
−10.3 9.8
8.2 8.5
−6.0 8.9
14.2 3.2
CD2Cl2 a
CD2Cl2
14.5 0.2
a Rate and activation parameters of the alkyl exchange in pure (AlMe3)2.
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Fig. 3 EXSY spectra of the reaction mixture L2ZrCl2–(AlMe3)2: (a) L = Cp, T = 300 K, CD2Cl2 (τ = 0.3 s); (b) L = Me2SiInd2, T = 300 K, CD2Cl2 (τ = 0.3 s).
Scheme 5
processes of intermolecular exchange by the methyl group
between the Zr and Al or B atoms are characteristic of homo-
geneous Ziegler–Natta type catalytic systems and were also
investigated using the EXSY method.17
The low-field region of the 2D COSY spectra of methyl
Scheme 6
chloride ansa-complexes 5f,h,j–n contains two pairs of corre-
lated proton signals of the cyclopentadienyl moieties (H1–H2,
H3–H4, Scheme 6, Table 2). The magnetic non-equivalence of
these four protons is caused by the replacement of one Cl
atom by the Me group (Fig. 4a). The exchange correlation
spectra (EXSY) show the exchange of protons from different
indenyl moieties of the same molecule of the complex
(Fig. 4b). Since the molecule is conformationally rigid and the
rotation of the indenyl moieties of the ansa-ligand is imposs-
ible, in addition to the Zr–Ind bond cleavage and the sub-
sequent ligand reorientation and reattachment to the metal
atom, providing the meso-isomer, the observed dynamics is
attributable to the change in the spatial environment of H1–H4
atoms due to the alteration of the methyl group position rela-
tive to the indenyl parts of the ansa- ligand (Scheme 6). The
NOE effect that we found between the Zr-bound methyl
protons and the H1, H2, and H4 protons attests to the spatial
proximity of these atoms; the greatest chemical shift difference
was observed for the H1–H2 pair, which can also be associated
with the proximate position of the methyl group. The magnetic
non-equivalence and dynamic behavior of the ansa-cyclopenta-
dienyl protons are also typical of complexes 5d–h.
An interesting picture of NOE effects was found for the
ethylidene-bridged bis-indenyl complex (Scheme 6). This was
observed in both CD2Cl2 and C7D8. Here the signals for the H5
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Fig. 4 Low-field part of the spectra of the 1l–(AlMe3)2 system in CD2Cl2 at T = 300 K: (a) COSY HH; (b) EXSY (τ = 0.3 s).
and H6 protons of the ethanediyl bridge form a multiplet at δH erature, conformation (a), in which the ligands are rotated rela-
3.44–3.58 ppm, while the chemical shift difference between tive to each other virtually through 180°, is preferred for
the diastereotopic H7 and H8 protons is greater; as a result, complex 5m. This conclusion is also confirmed by quantum
they show two multiplets at δH 3.35–3.43 ppm and chemical calculations. Geometry optimization for the com-
3.66–3.74 ppm (the chemical shifts are given for T = 240 K, plexes revealed that conformer 5m-a is predominant over 5m-b
CD2Cl2). The NOESY spectra exhibit coupling of the H5 and H6 (Scheme 7). These calculations for the initial form of the cata-
protons with the H1 proton and the aromatic H10 atom of the lyst, dichloride complex 1m, showed the predominance of con-
opposite part of the ligand. The H7 and H8 atoms correlate formation (b). According to published data,18 in the liquid
with H3 and H10; both H1 and H2 correlate with the Me group medium, the conformers exist in fast exchange, whereas in the
at Zr. It should be noted that the form of the H5–H8 proton crystalline state, the molecules have conformation 1m-b,
signals virtually does not change as the temperature varies in according to X-ray diffraction data.18a Thus, while investigating
the 230–300 K range. Hence, it follows that even at room temp- the stereoselectivity of alkene coordination to this complex,
Scheme 7
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one should take into account both conformations, with (6). A study of the dynamic processes in the system containing
primary attention being given to conformation 5m-a, which is the ansa-complex with the bis-tetrahydroindenyl ligand (1n)
predominant in solution.
demonstrated that the intermolecular exchange involves the
The hydrogenation of the ligand in the compound 1m initial dichloride, as indicated by the cross-peaks between
causes a loss of its conformational mobility. Thus, a compari- proton signals of the ligands in the EXSY spectra.
son of the NOESY spectra of complexes 1o and 5o indicates
Thus, our study of the dynamics of alkyl chloride inter-
the invariance of the spatial configuration of the ansa-ligand mediates with the conformationally rigid ligands that specify
in both toluene and methylene chloride in the course of sub- the planar chirality of the complexes shed light on the most
stitution of one of the chlorine atoms by the methyl group. probable mechanism of alkyl exchange in the bimetallic Zr,Al-
The conformation of the complexes 1o and 5o was assigned to catalytic systems and gives information about its rate and acti-
b according to the NOE correlations between the atoms indi- vation parameters (Table 4). As follows from Table 2, going
cated in Scheme 6, which corresponds to the conformation in from the more electron-donating sterically crowded bis-cyclo-
the crystals19a,c and in the solution.19b
pentadienyl ligand in intermediate 5 to the more electron-
As possible mechanisms of methyl–chloride exchange, deficient bis-indenyl substituent results in an increase in the
intramolecular and intermolecular ones can be considered. If rate of methyl group exchange in the alkyl chloride complexes,
the exchange is assumed to follow the intramolecular mecha- probably due to a decrease in the activation barrier. This
nism realized via intermediate 7, then, as can be seen from means that the lifetime of the methyl group bound to the tran-
the reaction equation, this does not lead to the change of the sition metal atom is lower in complexes with bis-indenyl
environment of H1–H4 protons in the alkyl chloride ansa-com- ligands than in the sterically hindered cyclopentadienyl
plexes, which is at variance with the observed EXSY spectra analogues.
(Scheme 8). The intermolecular pathway can be accomplished
Unfortunately, the calculated constant cannot be used to
in two ways, namely, via the dichloride (1) and dialkyl complex evaluate the reactivity of the whole catalytic system, because it
Scheme 8
Table 4 Rate constants and activation parameters of the methyl group exchange in L2ZrMeCl (5f, h, and j–m)
Complex
Solvent
T, K
k, s−1
ΔG‡, kcal mol−1
ΔH‡, kcal mol−1
ΔS‡, cal mol−1 K−1
5f
5h
5j
CD2Cl2
C7D8
CD2Cl2
C7D8
CD2Cl2
C7D8
CD2Cl2
C7D8
297.3
300.4
297.7
298.3
291.2
296.5
299.4
297.9
297.8
300.7
0.9
9.2
6.9
9.3
2.7
2.9
7.2
2.5
4.6
4.8
17.5 0.02
16.2 0.02
16.3 0.04
16.1 0.04
16.4 0.07
16.7 0.02
16.3 0.01
16.9 0.03
16.5 0.01
16.6 0.03
25.2 1.2
13.6 0.5
7.9 0.3
4.0 0.2
5.2 0.8
8.7 0.4
8.5 0.04
8.0 0.3
8.1 0.07
8.4 0.15
26.1 17.1
−8.8 7.9
−28.0 4.7
−40.4 3.3
−38.2 11.9
−26.9 6.0
−26.1 0.5
−29.7 4.4
−28.1 1.2
−27.5 2.4
5k
5l
5m
CD2Cl2
C7D8
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reflects only the overall lifetime of the methyl group at the Zr dichloromethane can be attributed to the increasing rate of
atom in intermediates 5 and 7, which are in equilibrium with reverse reaction between 5 and (ClAlMe2)2 as a result of the
each other (Scheme 4). Of these intermediates, only 7, the pro- increasing proportion of the OAC monomer upon dimer dis-
portion of which cannot be determined in a real catalytic sociation in a polar solvent, similarly to solutions of (AlMe3)2
system, seems to participate in the alkene coordination.
in dichloromethane.
Since at room temperature, the equilibrium 5 ⇄ 7 is almost
The calculation of the integrated intensity of the Me lines
entirely shifted towards 5, the equilibrium constant K3 in for the L2ZrMeCl moiety, the AlMe3 monomer, and unreacted
Scheme 5 can be calculated using the formula proposed pre- (AlMe3)2 showed that for all the complexes chosen for the
viously.6f
study, the monomer proportion depends on the solvent and
the type of π-ligand. The maximum proportion of AlMe3 was
observed in CD2Cl2. The proportion of the monomer also
increases in the series Cp < CpMe < Ind; however, its content
decreases with increasing initial concentration of trimethyl-
aluminum. This is quite understandable because its existence
is directly related to the appearance of zirconocene
dichlorides.
Q
K3 ¼
;
ðIð1 þ 1=QÞ ꢀ 1Þ
where Q = [L2ZrMeCl]/[L2ZrCl2] (equilibrium concentration
ratio), I = [(AlMe3)2]0/[L2ZrCl2]0 (ratio of the initial concen-
trations of trimethylaluminum and the zirconocene complex).
The proton chemical shifts of the methyl substituent at Zr
and the equilibrium constant and, hence, the intermolecular
exchange rate depend, under the chosen conditions, first of all
on the type of η5-ligand in the complex (Table 5). As the
number of methyl groups in the Cp ligand increases, the
protons of the ZrMe moiety become more shielded in the H
NMR spectra and K3 decreases, which can be caused by both
steric and electronic factors.
It follows from Table 2 that for most of the complexes, the
constant K3 is somewhat higher in toluene than in dichloro-
methane. This indicates that the equilibrium concentration of
complexes 5 (7) is higher in a non-polar solvent than in a polar
solvent. The decrease in the proportion of forward reaction in
Zirconocene structure–activity relationships in the catalytic
reaction of alkenes with AlMe3
1
The reaction of 1-octene with AlMe3 in the presence of com-
plexes 1a–o at the AlMe3 : alkene : L2ZrCl2 reactant ratio of
60 : 50 : 1 and at room temperature gives carbo- (8) and hydro-
alumination (10) products, 2-methyl-1-octene (9) and dimers
(11) (Scheme 9, Table 6).
As follows from Table 6, the alkene conversion and reaction
chemoselectivity depend to a large extent on the structure of
the η5-ligands in the zirconium complex and the solvent
nature. The highest activity was found for complexes with non-
bound ligands 1a–c,i and for the silicon-bound ansa-complex
Table 5 Effect of the nature of the η5 ligand and the solvent on K3 in 1l. Linking of the cyclopentadienyl ligands by the silicon (com-
the reaction of L2ZrCl2 with (AlMe3)2
plexes 1d,e) or using bis-indenyl ligands with hydrocarbon
bridges leads to a considerable decrease in the substrate con-
[L2ZrCl2]0,
mol l−1
[(AlMe3)2]0,
mol l−1
version, and the greatest decrease in activity occurs in the case
of complexes with single carbon bridges. However, the silicon
bridged bis-indenyl catalyst 1l showed the highest activity,
among all complexes studied in this work, towards the reac-
tion carried out in toluene (∼99% conversion). This fact agrees
with the conclusion20 that dimension of the large silicon
bridge matches well with the coordination requirement of the
large zirconium atom. This provides the largest reaction space
of the metal center while retaining the stability of the metallo-
cene complexes, and, therefore, higher activities of such type
of complexes than the unbridged and other bridged metallo-
cenes. Moreover, the reaction catalyzed by complex 1l gives
predominantly the carbometalation products (8) (∼63%). The
ethylene-bis-indenyl complex 1m has the highest chemo-
selectivity: carboalumination products (8) are predominant
after the reaction, but the alkene conversion is low in this case
(∼26%). The complex almost completely loses its activity in
toluene upon hydrogenation of the ligand, i.e. in the case of
catalyst 1o. A similar trend is observed when going from cata-
lyst 1l to its hydrogenated analog 1n. Sterically hindered cyclo-
pentadienyl complexes 1e–h do not show catalytic activity in
the alkene reaction with AlMe3. An interesting issue is the
solvent effect on alkene conversion. The highest activity was
Complex
Solvent
K3
1a
CD2Cl2
C7D8
0.059–0.061
0.050–0.053
0.040–0.058
0.045–0.050
0.027–0.036
0.024–0.041
0.050–0.061
0.079–0.095
0.045–0.056
0.038–0.046
0.056–0.065
0.050–0.057
0.048–0.061
0.047–0.057
0.058–0.060
0.045–0.047
0.035–0.10
0.058–0.068
0.043–0.057
0.019–0.029
0.053–0.067
0.018–0.033
0.029–0.031
0.028–0.035
0.052–0.061
0.048–0.053
0.059–0.061
0.039–0.045
0.96–1.23
1.18–1.62
0.85–1.63
0.60–1.53
3.02–4.66
2.45–4.93
0.98–1.56
0.81–1.23
1.09–1.87
1.26–1.98
0.78–2.04
0.77–1.89
1.50–2.06
0.94–1.85
0.24–0.47
0.57–0.78
0.31–1.00
0.98–1.74
1.82–2.46
0.59–0.94
0.84–1.33
1.36–1.97
0.29–0.74
0.38–0.85
1.61–2.20
1.70–2.15
1.01–1.35
0.78–1.24
0.25(1)
0.18(1)
1b
1c
1d
1e
1f
CD2Cl2
C7D8
CD2Cl2
C7D8
CD2Cl2
C7D8
CD2Cl2
C7D8
0.042(1)
0.056(6)
0.0033(3)
0.0048(4)
0.058(2)
4.15(5)
0.0033(2)
0.0065(6)
0.0011(1)
0.0014(2)
0.0039(3)
0.0051(2)
0.57(3)
2.83(14)
0.10(1)
0.25(2)
0.099(5)
12.20(4)
0.55(1)
CD2Cl2
C7D8
1h
1i
CD2Cl2
C7D8
CD2Cl2
C7D8
1j
CD2Cl2
C7D8
1k
1l
CD2Cl2
C7D8
CD2Cl2
C7D8
0.29(3)
0.35(2)
2.10(5)
0.0010(3)
0.0066(4)
0.0067(3)
0.033(6)
1m
1n
1o
CD2Cl2
C7D8
CD2Cl2
C7D8
CD2Cl2
C7D8
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Scheme 9
Table 6 Conversion of 1-octene and product yields in the reaction of
the alkene with AlMe3 in the presence of mol% L2ZrCl2
2
(L2ZrCl2 : alkene : AlMe3 = 1 : 50 : 0, 20 °C, the reaction time of 24 h)
Product yield, %
L2ZrCl2
Solvent
Conversion, %
8
9
10
11
1a7a
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
92
69
84
39
68
44
24
13
89
70
0
3
3
11
9
53
15
<1
<1
31
38
14
21
14
9
8
14
5
4
19
14
7
7
7
9
7
14
5
6
—
10
68
38
52
12
—
1
13
2
39
8
1b7a
1c7a
1d
1i7a
1j
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
CH2Cl2
C6H5CH3
11
2
4
9
—
—
0.7
1
<1
—
<1
1
—
—
<1
<1
9
<1
5
2
—
1
1k
0.6 0.3
<1
20
63
15
22
1
13
16
1
1.6
1
2
1l
30
99
16
26
3a
9
34
<1
3
—
—
—
—
18
4
1m
—
—
—
—
<1
<1
16
2
1n
35a
17
2
Scheme 10 Probable mechanism of the L2ZrCl2-catalyzed reaction of
alkenes with trimethylaluminum.
1o
Cp2ZrMeCl (5a)
Cp2ZrMe2 (6a)
58b
52b
16b
9b
15
46
6
4
3
1
<1
L2ZrMeCl with AlMe3 gives intermediate 7 in which the Zr–Me
bond is more polarized as a result of association with an elec-
tron-deficient Lewis acid, in particular, the trimethylaluminum
monomer. It is worth noting that the addition of the alkene to
the Cp2ZrMeCl–(AlMe3)2 system (1 : 3 ratio) does not result in
the formation of methylalumination products over a period of
24 hours. The alkene reacts only in the catalytic version of the
reaction. Indeed, the complexes 5a and 6a obtained by an
alternative synthetic route were tested as catalysts for the reac-
tion of 1-hexene with (AlMe3)2 (Scheme 9, Table 6). It was
found that 6a has low catalytic activity in this reaction,
3
<1
a Dimers and oligomers were identified as the main reaction products.
b 1-Hexene was used in the reaction.
observed in dichloromethane for complexes with non-bound
ligands and in toluene for the ansa-complexes.
The probable mechanism of the L2ZrCl2-catalyzed reaction of
alkenes with trimethylaluminum
The results allow us to propose a mechanism of the reaction of whereas 5a provides the previously observed set of products
alkenes with trimethylaluminum catalyzed by L2ZrCl2, which 8–11, with the alkene conversion being somewhat higher in di-
includes the following catalytic cycles (Scheme 10). In the first chloromethane and the chemoselectivity towards carbometala-
step, complex 1 reacts with AlMe3, the equilibrium concen- tion being higher in toluene.
tration of which is higher in the chlorinated solvent, to give
Apparently, 5a activated by the associated AlMe3 molecule
alkyl chloride complex 5. The subsequent reaction of (complex 7) serves as the catalytically active site. As shown
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above, complex 7a exists in the associated state at temperatures substrate carbozirconation and β-C–H elimination in the car-
below 230 K. At room temperature, it dissociates to 5a and bozirconation product; and the reactivity of hydride zircono-
AlMe3 and its concentration becomes negligibly low; hence, cene intermediates. By the way, the reactivity can increase with
the alkene does not react. Switching to the catalytic reaction increasing electron-donating properties and steric restrictions
shifts the equilibrium towards complex 7a, and products 8–11 in the ligand.23 Apparently, additional investigations of these
are thus formed in the system. The obtained results are also steps, in particular, by quantum chemical methods, are
consistent with the data of theoretical calculations of the needed in this case.
activity of complexes 5a–7a,21 according to which the carbo-
zirconation ability of the complexes increases in the series
Cp2ZrMeCl (5a) (the barrier of ethylene insertion is 40.2 kcal
Conclusions
mol−1) < Cp2ZrMeCl·AlMe3 (7a) (34.7 kcal mol−1) < Cp2ZrMe2
(6a) (33.3 kcal mol−1). Moreover, the tendency of the barrier to Thus, the investigation of the zirconocene dichloride reaction
increase when going from metallocene methyl chloride with trimethylaluminum and the study of zirconocene dichloride
(L2MMeCl·AlMe3, L = Cp, Me2CCpFlu, M = Zr, Hf) to metallo- catalytic activity provided the following conclusions. According to
cene dimethyl (L2MMe2·AlMe3) was shown in ref. 16. Since 6a dynamic NMR data, the rates and thermodynamic parameters
is not formed in the reaction of Cp2ZrCl2 with AlMe3, a major of the exchange of bridging and terminal alkyl groups in the
role is played by intermediate 7a. The degree of association of (AlMe3)2 dimers depend on the nature of the solvent and the
L2ZrMeCl with AlMe3, that is, the stability and the equilibrium concentration of the solution. The replacement of a less polar
concentration of complex 7, depend also on the π-ligand solvent (toluene) by a more polar one (dichloromethane) or
environment of Zr and the nature of the solvent. Moreover, as dilution of trialkylalanes with a chlorinated solvent leads to a
judged by the barrier value and reaction time, the step of higher exchange rate because of the increasing proportion of
alkene insertion into complex 7 is apparently rather slow for the monomer due to solvation and to the intermolecular
neutral complexes.
exchange mechanism. The addition of (ClAlMe2)2 to trimethyl-
Then the alkene is inserted into the Zr–C bond to give aluminum in dichloromethane decreases the rate and
complex 14, which undergoes transmetalation with AlMe3 or enthalpy and entropy of activation of the exchange, which is
Me2AlCl to give carboalumination product 8, thus closing the attributable to the increasing proportion of the intramolecular
catalytic cycle A. Simultaneously, a β-hydride transfer takes exchange, caused by the decrease in the monomer content via
place in complex 14 to give the substituted alkene and hydride the formation of short-lived (Me3Al(μ-Cl)AlMe2) associates.
complex 15. This intermediate is responsible for the existence Since the AlMe3 monomer is a Lewis acid, its effective concen-
of the catalytic cycle B, which affords hydrometalation pro- tration can influence the rates of formation of the key
ducts and dimers. The alkyl complex 16 obtained upon alkene intermediates.
hydrometalation with intermediate 15 can be rapidly transme-
On the other hand, the catalyst is also a Lewis acid, due to a
tallated, like 14, to give saturated product 10, which brings the free nonbonding orbital;24 therefore, it disturbs the above
reaction back to the beginning of cycle C or A. Thus, three balance by reacting with the trialkylalane monomer. Thus, one
catalytic cycles, in which the alkyl complex 14 may also play a of the important roles of the catalyst besides the formation of
key role, coexist in the catalytic reaction involving AlMe3. It is active species is to accelerate the exchange through the dis-
worth noting that the high conversion of the alkene may be sociation with the release of the OAC active monomer. It was
largely provided by catalytic cycles B and C and, hence, by the shown that the L2ZrMeCl complexes formed in the methyl–
propensity of 14 to β-C–H elimination and by the reactivity of chloride exchange can be coordinated to the AlMe3 monomer
intermediates 15 and 16. One way to decrease the quantity of to give the (L2ZrMe(μ-Cl)AlMe3) associates, while the Zr-bound
hydroalumination and dimerization products is to introduce alkyl group can exchange with the (AlMe3)2 alkyl groups via
bulky substituents into the π-ligand, which prevent β-C–H monomer formation. The parameters of the methyl group
elimination22 in complex 14. However, there are problems of exchange (constants, activation enthalpies and entropies) in
slowing down of the initial step of alkyl exchange, the stability the monoalkyl-substituted ansa-complexes L2ZrMeCl (L2
of intermediate 7, and the rate of alkene insertion into the Zr– Me2CInd2, Me2SiInd2, H4C2Ind2, H2C(CpMetBu)2) were estab-
Me bond of 7 (Scheme 10). lished for the first time. It was found that the exchange is
=
Unfortunately, we failed to establish a correlation between intermolecular and involves zirconocene dichlorides.
the exchange constant k or equilibrium constant K3 and the Moreover, the exchange rate substantially decreases on going
catalytic activity of the complexes in these reactions, since it from bis-indenyl to substituted cyclopentadienyl ligands. It
was impossible to experimentally assess the effective concen- was shown that neither the constants of the methyl group
tration of key intermediate 7 and the reactivity of 7 towards the exchange between methyl chloride ansa-complexes nor the
alkene as functions of the ligand and solvent natures. These L2ZrCl2 ↔ (L2ZrMe(μ-Cl)AlMe3) equilibrium constants can
factors determine important aspects of the reaction such as serve as an activity measure for a catalytic system towards
the zirconocene dichloride alkylation rate; the lifetimes of the alkenes. This is due to the fact that the activity of catalytic
methyl group at the zirconium atom and intermediate 7 systems depends on the lifetimes of the associated complexes,
associated with the trimethylaluminum molecule; the rates of the effective concentration of which depends on the methyl–
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chloride exchange rate in the early stage of the reaction and on exchange were found using lineshape analysis of NMR spectra
the stability of the associates, which are prone to dissociation. in the program Bruker TopSpin 3.2. Rate constants of the
The rates of these steps can be controlled by varying the OAC, methyl group exchange in L2ZrMeCl (5f, h, j–m) were found via
η5-ligand, and solvent natures. However, variation of these the analysis of two-site exchange between H1 and H3 protons
components would change the reactivity of active sites towards of the ansa-η5-ligands in EXSY spectra in the temperature
the alkene and the probability for side β-C–H elimination of range 230–310 K according to the procedure described in ref.
the carbozirconation products to occur. For example, if one 34.
increases the electrophilicity of the zirconium center by chan-
The hydrolysis products of the reaction mixtures were ana-
ging the η5-ligand, this can accelerate the chloride–methyl lyzed on a Chrom-5 chromatograph (flame ionization detector,
exchange in the first step; however, the lifetime of the methyl a 2 m × 3 mm column, 15% Peg-6000, 50–190 °C). The deute-
group at the zirconium atom in the resulting complex will be rated products were analyzed by GC/MS on an automated QP
very short because of the fast exchange of this group with the 2010 Ultra GC/MS assembled with a TD-20 Shimadzu thermal
OAC and the chlorine atom of L2ZrCl2. On the other hand, desorber.
the alkene insertion would be, most likely, accelerated in
the (L2ZrMe(μ-Cl)AlMe3) active complex, but the rate of β-C–H
elimination to give hydrocarbons containing methylene
A study of the exchange processes in the trialkylalane dimer
(AlMe3)2
groups and more reactive zirconocene hydride intermediates An argon-filled NMR tube was charged with C7D8
may also increase. An efficient way to slow down this process is (0.25–0.52 ml) or CD2Cl2 (0.23–0.49 ml) and 97% AlMe3
to use bulky substituents in the η5-ligand.
(0.22–6.67 mmol, 16–480 mg) (1 : 1–30 molar ratio of AlMe3 to
Thus, regulation of the activity and chemo- and stereo- the solvent). To study the effect of dimethylaluminum chloride
selectivity of the studied systems is a problem of fine-tuning addition on the exchange process in the trimethylaluminum
the catalytically active site in which a balance is needed dimer, the following amounts of components were used:
between the electronic and steric factors of the catalyst, OAC, 0.53 ml of CD2Cl2, 2.07 mmol of AlMe3 (0.20 ml) and
the substrate and the reaction conditions.
0.94 mmol of ClAlMe2 (0.09 ml). The NMR spectra were
recorded in the temperature range of 180 K to 300 K.
A study of the structure of intermediates of the reaction
between L2ZrCl2 and (AlMe3)2 by dynamic NMR spectroscopy
Experimental
General procedures
An argon-filled NMR tube was charged with L2ZrCl2
All experiments were carried out under argon using Schlenk (0.010–0.059 mmol), C7D8 or CD2Cl2, and AlMe3
techniques. Toluene was dried by refluxing over HAlBui2 and (0.052–6.69 mmol). The ampoule was weighed after each
freshly distilled prior to use. Methylene chloride was dried addition of the components. The measurements were carried
over P2O5. Commercially available 97% AlMe3 (Aldrich) and out in an NMR tube in the temperature range of 180 to 300 K.
97% ClAlMe2 (Aldrich) were involved in the reactions.
Synthesis of Cp2ZrMe2
CAUTION: Pyrophoric nature of aluminum alkyl compounds
requires special safety precautions in their handling. Complexes Cp2ZrMe2 was synthesized by a procedure described in ref. 35.
Cp2ZrCl2 (1a),25 (CpMe)2ZrCl2 (1b),26 Me2SiCp2ZrCl2 (1d),27 An argon-filled flask equipped with a magnetic stirrer was
Me2Si(C5Me4)2ZrCl2 (1e),28 rac-Me2C(2-Me-4-But-Cp)2ZrCl2 (1f) charged with Cp2ZrCl2 (1.7 mmol, 500 mg) and diethyl ether
(contains ∼7% of 1g),29 meso-Me2C(2-Me-4-But-Cp)2ZrCl2 (1g) (1.5 ml). A solution of MeLi (3.42 mmol) in diethyl ether (c =
(contains ∼17% of 1f),29 rac-Me2C(3-But-Cp)2ZrCl2 (1h),29 1.9 mol l−1, 1.8 ml) was added dropwise with continuous stir-
Ind2ZrCl2 (1i),30 rac-H2C(Ind)2ZrCl2 (1j),31 and rac-Me2C ring to the suspension of Cp2ZrCl2 in diethyl ether cooled to
(Ind)2ZrCl2 (1k)32 were synthesized from ZrCl4 (Aldrich, −20 °C. The temperature of the reaction mixture was brought
99.5%). Zirconocenes (C5Me5)2ZrCl2 (1c) (97%, Acros), rac- to 0 °C and maintained for 30 min. The solvent was evaporated
Me2Si(Ind)2ZrCl2 (1l) (97%, Strem), rac-C2H4(Ind)2ZrCl2 (1m) in vacuo, and the dry residue was sublimed at 110 °C for 1.5 h.
(Strem), and rac-C2H4(THInd)2ZrCl2 (1o) (Strem) were pur- The sublimation gave Cp2ZrMe2 as a white crystalline solid in
chased and used as received. The complex rac-Me2Si 150 mg (35%) yield.
(THInd)2ZrCl2 (1n) was synthesized from 1l according to ref.
33. Terminal alkenes 1-hexene (97%, Acros) and 1-octene
Synthesis of Cp2ZrMeCl
(99%, Acros) were used.
An argon-filled flask equipped with a magnetic stirrer was
The 1H and 13C NMR spectra were recorded on a Bruker charged with Cp2ZrCl2 (1.7 mmol, 500 mg) and diethyl ether
AVANCE-400 spectrometer (400.13 MHz (1H), 100.62 MHz (1.5 ml). A solution of MeLi (1.71 mmol) in diethyl ether (c =
(13C)). As the solvents and the internal standards, toluene-d8 1.9 mol l−1, 0.9 ml) was added dropwise with continuous stir-
and methylene chloride-d2 were employed. 1D and 2D NMR ring to the suspension of Cp2ZrCl2 in diethyl ether cooled to
spectra (COSY HH, HSQC, HMBC, EXSY (NOESY)) were −20 °C. The temperature of the reaction mixture was brought
recorded using standard Bruker pulse sequences. The con- to 0 °C and maintained for 30 min. The solvent was evaporated
stants and activation parameters of trimethylaluminum in vacuo, and the dry residue was sublimed at 110 °C for 1.5 h.
16934 | Dalton Trans., 2018, 47, 16918–16937
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The sublimation gave Cp2ZrMeCl as a white crystalline solid in
280 mg (60%) yield.
P. G. Andresson and J. J. Munslou, Wiley-VCH, Weinheim,
Germany, 2008, pp. 447–489; (c) G. A. Tolstikov,
U. M. Dzhemilev and A. G. Tolstikov, Aluminiyorganicheskie
soedineniya v organicheskom sinteze (Organoaluminum com-
pounds in organic synthesis), Akad. izd. GEO, Novosibirsk,
2009, 645 p. (in Russian); (d) U. M. Dzhemilev and
A. G. Ibragimov, J. Organomet. Chem., 2010, 695, 1085–
1110; (e) V. A. D’yakonov, Dzhemilev Reaction in Organic and
A study of the reaction of Cp2ZrMeCl or Cp2ZrMe2 with
(AlMe3)2
An argon-filled NMR tube was charged with Cp2ZrMeCl
(0.04–0.06 mmol, 12–17 mg) or Cp2ZrMe2 (0.04–0.06 mmol,
10–15 mg), C7D8 (or CD2Cl2) (0.5 ml), and 97% AlMe3
(0.14–0.2 mmol, 10–15 mg). NMR spectra were recorded in the
temperature range of 180 to 300 K.
Organometallic
Synthesis
(Chemistry
Research
and
Applications), Nova Science Pub Inc, NY, 2010, 96 p;
(f) E.-i. Negishi, in Catalytic Asymmetric Synthesis, ed. I.
Ojima, Wiley-VCH, New York, 2000, pp. 165–189;
(g) E.-i. Negishi, Bull. Chem. Soc. Jpn., 2007, 80, 233–257;
(h) E.-i. Negishi, B. Liang, T. Novak and Z. Tan, in
Asymmetric Synthesis - The Essentials, ed. M. Christmann
and S. Brase, Wiley-VCH, Weinheim, 2008, p. 126;
(i) E.-i. Negishi, ARKIVOC, 2011, 8, 34–53.
Reaction of 1-alkene with (AlMe3)2 in the presence of L2ZrCl2
A 10 ml argon-filled glass reactor mounted on a magnetic
stirrer was charged with L2ZrCl2 (2 mmol), CH2Cl2 or C6H5CH3
(1 ml), 1-hexene or 1-octene (100 mmol), and AlMe3
(120 mmol). The reaction was carried out at 22 °C with con-
tinuous stirring. After 24 hours, the reaction mixture was
quenched with 10% HCl or DCl at 0 °C. The products were
extracted with benzene and the organic phase was dried with
Na2SO4. The product yield was determined by GLC and GC/MS
analysis.
2 E. Y.-X. Chen and T. J. Marks, Chem. Rev., 2000, 100, 1391–
1434.
3 (a) H. G. Alt and A. Koppl, Chem. Rev., 2000, 100, 1205–
1222; (b) L. Resconi, L. Cavallo, A. Fait and F. Piemontesi,
Chem. Rev., 2000, 100, 1253–1346; (c) G. G. Hlatky, Chem.
Rev., 2000, 100, 1347–1376; (d) A. K. Rappe, W. M. Skiff and
C. J. Casewit, Chem. Rev., 2000, 100, 1435–1456;
(e) J.-N. Pedeutour, K. Radhakrishnan, H. Cramail and
A. Deffieux, Macromol. Rapid Commun., 2001, 22, 1095–
1123; (f) V. Busico, Dalton Trans., 2009, 8794–8802;
(g) M. Bochmann, Organometallics, 2010, 29, 4711–4740;
(h) A. Shamiri, M. H. Chakrabarti, S. Jahan, M. A. Hussain,
W. Kaminsky, P. V. Aravind and W. A. Yehye, Materials,
2014, 7, 5069–5108; (i) R. A. Collins, A. F. Russell and
P. Mountford, Appl. Petrochem. Res., 2015, 5, 153–171.
4 M. Bochmann, J. Organomet. Chem., 2004, 689, 3982–3998.
5 (a) X. Yang, C. L. Stern and T. J. Marks, J. Am. Chem. Soc.,
1994, 116, 10015–10031; (b) D. E. Richardson,
N. G. Alameddin, M. F. Ryan, T. Hayes, J. R. Eyler and
A. R. Siedle, J. Am. Chem. Soc., 1996, 118, 11244–11253;
(c) F. Schaper, A. Geyer and H. H. Brintzinger,
Organometallics, 2002, 21, 473–483; (d) R. A. Petros and
J. R. Norton, Organometallics, 2004, 23, 5105–5107;
(e) J. M. Camara, R. A. Petros and J. R. Norton, J. Am. Chem.
Soc., 2011, 133, 5263–5273.
6 (a) R. J. Pudderhatt and M. A. Stalteri, Organometallics,
1983, 2, 1400–1405; (b) D. E. Van Horn and E.-i. Negishi,
J. Am. Chem. Soc., 1978, 100, 2252–2254; (c) T. Yoshida and
E.-i. Negishi, J. Am. Chem. Soc., 1981, 103, 4985–4987;
(d) E.-i. Negishi, D. E. Van Horn and T. Yoshida, J. Am.
Chem. Soc., 1985, 107, 6639–6647; (e) E.-i. Negishi,
D. Y. Kondakov, D. Choueiri, K. Kasai and T. Takahashi,
J. Am. Chem. Soc., 1996, 118, 9577–9588; (f) S. Beck and
H. H. Brintzinger, Inorg. Chim. Acta, 1998, 270, 376–381;
(g) I. Tritto, D. Zucchi, M. Destro, M. C. Sacchi, T. Dall’Occo
and M. Galimberti, J. Mol. Catal. A: Chem., 2000, 160, 107–
114.
Computational details
All calculations were carried out at the DFT level. The geometry
optimization of the minima, vibrational frequency analysis,
and calculation of thermodynamic corrections to the total
energy of the compounds were carried out using the Gaussian
09 software package, Revision D.01, program.36 The density
functional M06-2X37 with the cc-pVDZ basis set for the main
group elements (H, C, Cl)38 and the cc-pVDZ-PP basis set for a
transitional metal (Zr)39 were employed as the methods for the
description of Zr-containing systems.40 The calculated thermo-
dynamic parameters were determined at 298 K.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors thank the Russian Foundation of Basic Research
(Grant No. 16-33-60203mol_a_dk, Dr Kovyazin P. V.) for finan-
cial support. Part of the studies were carried out in accordance
with the Federal Program No. AAAA-A17-117012610062-1. The
work was also supported by the TIPS RAS State Plan (in part of
the synthesis of zirconocene dichloride complexes). The authors
acknowledge the use of equipment in the Agidel Collective Use
Centre at the Institute of Petrochemistry and Catalysis of RAS.
Notes and references
1 (a) U. M. Dzhemilev and A. G. Ibragimov, Russ. Chem. Rev.,
2000, 69, 121–135; (b) U. M. Dzhemilev and
A. G. Ibragimov, in Modern Reduction Methods, ed.
7 (a) L. V. Parfenova, V. Z. Gabdrakhmanov, L. M. Khalilov
and U. M. Dzhemilev, J. Organomet. Chem., 2009, 694,
This journal is © The Royal Society of Chemistry 2018
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Paper
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3725–3731; (b) L. V. Parfenova, T. V. Berestova, 22 (a) P. J. Chirik, M. W. Day, J. A. Labinger and J. E. Bercaw,
T. V. Tyumkina, P. V. Kovyazin, L. M. Khalilov, R. J. Whitby
and U. M. Dzhemilev, Tetrahedron: Asymmetry, 2010, 21,
299–310.
8 T. Mole and E. A. Jeffery, Organoaluminium Compounds,
Elsevier publishing company, Amsterdam, London,
J. Am. Chem. Soc., 1999, 121, 10308–10317; (b) P. J. Chirik
and J. E. Bercaw, Organometallics, 2005, 24, 5407–5423.
23 L. V. Parfenova, P. V. Kovyazin, I. E. Nifant’ev,
L. M. Khalilov and U. M. Dzhemilev, Organometallics, 2015,
34, 3559–3570.
New York, 1972, pp. 85–128; H.-G. Stammler, S. Blomeyer, 24 J. W. Lauher and R. Hoffmann, J. Am. Chem. Soc., 1976, 98,
R. J. F. Berger and N. W. Mitzel, Angew. Chem., Int. Ed.,
2015, 54, 13816–13820.
9 (a) K. C. Williams and T. L. Brown, J. Am. Chem. Soc., 1966,
1729–1742.
25 R. Kh. Freidlina, E. M. Brainina and A. N. Nesmeyanov,
Dokl. Acad. Nauk SSSR, 1969, 138, 1369–1372 (in Russian).
88, 5460–5465; (b) K. C. Ramey, J. F. O’Brien, I. Hasegawa 26 L. T. Reynolds and G. Wilkinson, J. Inorg. Nucl. Chem.,
and A. E. Borchert, J. Phys. Chem., 1965, 69, 3418–3423; 1959, 9, 86–92.
(c) O. Yamamoto, K. Hayamizu and M. Yanagisawa, 27 C. S. Bajgur, W. R. Tikkanen and J. L. Petersen, Inorg.
J. Organomet. Chem., 1974, 73, 17–25. Chem., 1985, 24, 2539–2546.
10 E. Yu. Pankratyev, T. V. Tyumkina, S. L. Khursan, 28 P. Jutzi and R. Dickbreder, Chem. Ber., 1986, 119, 1750–
L. V. Parfenova, L. M. Khalilov and U. M. Dzhemilev, 1754.
Vestnik Bashkirskogo universiteta, 2008, 13(3(I)), 802–809 (in 29 L. Resconi, F. Piemontesi, I. E. Nifant’ev and
Russian). P. V. Ivchenko, U.S. Patent 6051728, 2000.
11 (a) J. Sandström, Dynamic NMR Spectroscopy, Academic 30 N. Piccolrovazzi, P. Pino, G. Consiglio, A. Sironi and
Press, NY, 1982, 226p; (b) G. M. Wilmes, M. B. France, M. Moret, J. Am. Chem. Soc., 1990, 9, 3098–3105.
S. R. Lynch and R. M. Waymouth, Organometallics, 2004, 31 V. A. Dang, L.-Ch. Yu, D. Balboni, T. Dall’Occo, L. Resconi,
23(10), 2405–2411.
12 (a) M. B. Smith, J. Organomet. Chem., 1972, 46,
P. Mercandelli, M. Moret and A. Sironi, Organometallics,
1999, 18, 3781–3791.
31–49; (b) M. B. Smith, J. Organomet. Chem., 1972, 46, 211– 32 I. E. Nifant’ev and P. V. Ivchenko, Organometallics, 1997,
217. 16, 713–715.
13 I. V. Vakulin, A. E. Zagidullina, R. F. Talipov and 33 (a) W. A. Herrmann, J. Rohrmann, E. Herdtweck, W. Spaleck
O. S. Vostrikova, J. Struct. Chem., 2006, 47(6), 1170–1176.
14 Yu. Sakurada, M. L. Huggins and W. R. Anderson, J. Phys.
Chem., 1964, 68, 1934–1943.
15 I. Tritto, R. Donetti, M. C. Sacchi, P. Locatelli and
G. Zannoni, Macromolecules, 1997, 30(5), 1247–1252.
16 A. Laine, M. Linnolahti and T. A. Pakkanen, J. Organomet.
Chem., 2012, 716, 79–85.
and A. Winter, Angew. Chem., Int. Ed. Engl., 1989, 28, 1511–
1512; (b) H. J. G. Luttikhedde, R. P. Leino, J. H. Nasman,
M. Ahlgren and T. Pakkanen, Acta Crystallogr., Sect. C: Cryst.
Struct. Commun., 1995, 51, 1488–1490.
34 Ch. L. Perrin and T. J. Dwyer, Chem. Rev., 1990, 90(6), 935–
967.
35 (a) P. C. Wailes, H. Weigold and A. P. Bell, J. Organomet.
Chem., 1972, 34, 155–164; (b) E. Samuel and M. D. Rausch,
J. Am. Chem. Soc., 1973, 95(19), 6263–6266.
17 (a) P. A. Deck and T. J. Marks, J. Am. Chem. Soc., 1995,
117(22), 6128–6129; (b) P. A. Deck, C. L. Beswick and
T. J. Marks, J. Am. Chem. Soc., 1998, 120(8), 1772–1784; 36 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
(c) S. Beck, S. Lieber, F. Schaper, A. Geyer and
H.-H. Brintzinger, J. Am. Chem. Soc., 2001, 123(7), 1483–
1489; (d) G. Theurkauff, A. Bondon, V. Dorcet,
J.-F. Carpentier and E. Kirillov, Angew. Chem., Int. Ed., 2015,
54(21), 6343–6346.
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford CT,
2009.
18 (a) F. Piemontesi, I. Camurati, L. Resconi, D. Balboni,
A. Sironi, M. Moret, R. Zeigler and N. Piccolrovazzi,
Organometallics, 1995, 14, 1256–1266; (b) M. Linnolahti,
T. A. Pakkanen, R. Leino, H. J. G. Luttikhedde, C.-E. Wilén
and J. H. Näsman, Eur. J. Inorg. Chem., 2001, 2001(8), 2033–
2040.
19 (a) F. R. W. P. Wild, M. Wasiucionek, G. Huttner and
H. H. Brintzinger, J. Organomet. Chem., 1985, 288, 63–67;
(b) R. M. Waymouth, F. Bangerter and P. Pino, Inorg.
Chem., 1988, 27(4), 758–759; (c) S. Collins, B. A. Kuntz,
N. J. Taylor and D. G. Ward, J. Organomet. Chem., 1988, 342,
21–29.
20 B. Wang, Coord. Chem. Rev., 2006, 250, 242–258.
21 E. Yu. Pankratyev, S. L. Khursan and U. M. Dzhemilev, 37 Y. Zhao and D. G. Truhlar, Theor. Chem. Acc., 2008, 120,
Dokl. Chem., 2012, 443(1), 67–71.
215–241.
16936 | Dalton Trans., 2018, 47, 16918–16937
This journal is © The Royal Society of Chemistry 2018

View Article Online
Dalton Transactions
Paper
38 (a) T. H. Dunning, Jr., J. Chem. Phys., 1989, 90, 1007–1023; 39 K. A. Peterson, D. Figgen, M. Dolg and H. Stoll, J. Chem.
(b) D. E. Woon and T. H. Dunning Jr., J. Chem. Phys., 1993, Phys., 2007, 126, 124101.
98, 1358–1371; (c) E. R. Davidson, Chem. Phys. Lett., 1996, 40 Y. Sun and H. Chen, J. Chem. Theor. Comput., 2013, 9,
260, 514–518.
4735–4743.
This journal is © The Royal Society of Chemistry 2018
Dalton Trans., 2018, 47, 16918–16937 | 16937