The catalytic behavior of heterocenes activated by TIBA and MMAO under a low Al/Zr ratios in 1-octene polymerization

Article abstract of DOI:10.1016/j.apcata.2018.12.006

A series of SiMe₂-bridged ansa-zirconocenes LZrCl₂ derived from heterocyclic ligands such as cyclopenta[1,2-b:4,3-b’]dithiophene, 5,6-dihydroindeno[2,1-b]indole and 5,10-dihydroindeno[1,2-b]indole, called “heterocenes” were synthesized and characterized by NMR spectroscopy and by X-ray diffraction analysis. These complexes were activated by triisobutylaluminium (TIBA) at Al_TIBA/Zr ratio ～75 and then by MMАO-12 at Al_MAO/Zr ratio ～10, and were studied in the polymerization of 1-octene in the absence or presence of molecular hydrogen. In the absence of molecular hydrogen, derivatives of cyclopenta[1,2-b:4,3-b’]dithiophene and dihydroindeno[2,1-b]indole demonstrated high catalytic activity, while dihydroindeno[1,2-b]indole complexes catalyzed slow polymerization with the formation of ultrahigh molecular weight poly(1-octene)s. In the presence of molecular hydrogen, derivatives of dihydroindeno[1,2-b]indole showed an order of magnitude increase in the catalytic activity. β-Hydride elimination, β-hexyl elimination and Zr-Al transfer were detected as the main chain release mechanisms depending on the nature of the ligand used. A novel chain termination with selective formation of –C(Me)=CHCH₂– unsaturations was detected. It was found that heterocenes maintained a high catalytic activity up to 120 °C. Due to their high thermal stability and good hydrogen response, heterocenes are promising catalysts for the oligomerization and hydrooligomerization of α-olefins in the production of high-quality motor oil base stocks.

Full text of DOI:10.1016/j.apcata.2018.12.006

AppliedCatalysisA,General571(2019)12–24
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
The catalytic behavior of heterocenes activated by TIBA and MMAO under a
low Al/Zr ratios in 1-octene polymerization
⁎
Ilya E. Nifant'eva,b, , Alexander A. Vinogradova, Alexey A. Vinogradova, Andrei V. Churakovc,
Vladimir V. Bagrovb, Igor A. Kashulinb, Vitaly A. Roznyatovskyb, Yury K. Grishinb,
Pavel V. Ivchenkoa,b
a A. V. Topchiev Institute of Petrochemical Synthesis RAS, Lenuinsky avenue 29, Moscow, 119991, Russian Federation
b Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory 1–3, Moscow, 119991, Russian Federation
c N.S. Kurnakov Institute of General and Inorganic Chemistry RAS, Leninsky avenue 31, 119991, Moscow, Russian Federation
A R T I C L E I N F O
A B S T R A C T
Keywords:
1-Octene
Polymerization
Zirconocenes
Chain release mechanism
Heterocycle-annelated cyclopentadienes
A series of SiMe2-bridged ansa-zirconocenes LZrCl2 derived from heterocyclic ligands such as cyclopenta[1,2-
b:4,3-b']dithiophene, 5,6-dihydroindeno[2,1-b]indole and 5,10-dihydroindeno[1,2-b]indole, called "hetero-
cenes", were synthesized and characterized by NMR spectroscopy and by X-ray diffraction analysis. These
complexes were activated by triisobutylaluminium (TIBA) at AlTIBA/Zr ratio ∼75 and then by MMАO-12 at
AlMAO/Zr ratio ∼10, and were studied in the polymerization of 1-octene in the absence or presence of molecular
hydrogen. In the absence of molecular hydrogen, derivatives of cyclopenta[1,2-b:4,3-b']dithiophene and dihy-
droindeno[2,1-b]indole demonstrated high catalytic activity, while dihydroindeno[1,2-b]indole complexes
catalyzed slow polymerization with the formation of ultrahigh molecular weight poly(1-octene)s. In the presence
of molecular hydrogen, derivatives of dihydroindeno[1,2-b]indole showed an order of magnitude increase in the
catalytic activity. β-Hydride elimination, β-hexyl elimination and Zr-Al transfer were detected as the main chain
release mechanisms depending on the nature of the ligand used. A novel chain termination with selective for-
mation of –C(Me)=CHCH2– unsaturations was detected. It was found that heterocenes maintained a high cat-
alytic activity up to 120 °C. Due to their high thermal stability and good hydrogen response, heterocenes are
promising catalysts for the oligomerization and hydrooligomerization of α-olefins in the production of high-
quality motor oil base stocks.
1. Introduction
activation of indenyl or fluorenyl LZrCl2 complexes [24]. Reduction of
MАO for (C5H5)2ZrCl2 or (RC5H4)2ZrCl2 results in a decrease in the
Zirconocenes are exceptional single-site α-olefin polymerization
catalysts with high productivity, diversity of stereocontrol, and homo-
geneity in copolymerization [1–5]. Usually, zirconocene precatalysts
LZrCl2 are activated by methylalumoxane (MAO) [6–10], and high
catalytic performance is typically achieved at high AlMAO/Zr ratios (103
and more) [11], however, the formation of zirconium-aluminium
complexes at high Al/Zr ratios hampers the activation [12–16]. Similar
complexes that are the resting states of zirconocene-catalyzed poly-
merization [12,17–19] are intermediates in the chain transfer from
zirconium to aluminum [19–21] and presumably provoke the β-hydride
elimination [22,23]. Both side reactions lead to the significant decrease
degree of polymerization DPn [25–29], finally obtaining selective di-
merization with the formation of methylenealkanes [22,30–32].
Recently, while studying oligomerization of α-olefins, we found that
zirconocene 1 derived from heterocyclic thiapentalenyl ligand, being
activated by 20 eq. of triisobutylaluminium (TIBA) and then by 10 eq.
of MAO or MMAO-12, successfully catalyzed oligomerization of α-ole-
fins to lightweight products (Mn up to 103 Da) even at AlMAO/Zr ∼ 10
(Scheme 1) [33]. In addition, complex 2 was effectively used at rela-
tively low AlMAO/Zr ratios (∼ 50) in α-olefin/diene copolymerization
[34]. Complexes 1 and 2 represent a specific group of zirconocenes
composed of an η5-coordinated cyclopentadienyl ring annelated with a
heterocyclic fragment. The term "heterocenes" for these complexes was
introduced by J. Ewen, who obtained and studied the heteroanalogs of
bis-indenyl zirconium complexes in the late 1990s [35,36]. Heterocenes
in the molecular weight of poly-α-olefins. Thus, lowering of the AlMAO
Zr ratio is attractive for application of zirconocene catalysis.
/
However, MAO used with AlMAO/Zr ∼10 is ineffective for the
⁎ Corresponding author at: 119991, Leninskie Gory, 1–3, Moscow, Russian Federation.
E-mail address: inif@org.chem.msu.ru (I.E. Nifant'ev).
https://doi.org/10.1016/j.apcata.2018.12.006
Received 8 November 2018; Received in revised form 6 December 2018; Accepted 9 December 2018
Availableonline11December2018
0926-860X/©2018ElsevierB.V.Allrightsreserved.

I.E. Nifant'ev et al.
AppliedCatalysisA,General571(2019)12–24
Scheme 1. The complexes that demonstrated high catalytic performance in α-olefin oligomerization (1 [33]) and copolymerization (2 [34]); benchmark bis-
fluorenyl complex 3 [60] and heterocenes 4–12 studied in this work in 1-octene polymerization.
activated by a large excess of MAO (100 eq. and more) were studied in
the polymerization of ethylene [37–39], propylene [35,36,40–47] 1-
butene [45,48–58] and 1-hexene [59]. To date, the catalytic properties
of heterocenes in the polymerization of higher α-olefins under low
AlMAO/Zr ratios (∼10) have not been studied in depth.
diphenylhydrazine, 1-indanone, 2-indanone, thiophene-2-carbalde-
hyde, fluorene, methyl iodide, ethyl N,N-dimethylcarbamate, 3-chlor-
opropanoyl chloride, p-TsOH, trimethylcetylammonium bromide, (1,3-
dppp)NiCl2, n-BuLi (1.6 M and 2.5 M solutions in hexane), MMAO-12
(1.54 M solution in toluene), TIBA (1 M solution in hexane), SiMe2Cl2,
SiEt2Cl2, AlCl3, ZrCl4, MgSO4 (powder), NaOH (pellets), KOH (powder)
and Br2 were used as purchased (Sigma-Aldrich). Hydrogen (99.999%,
Linde Gas, Russian Federation) was used without further purification.
5-Isopropyl-1-indanone and 5-(tert-butyl)-1-indanone were synthesized
according to previously reported procedures [61,62].
The control of the termination/propagation ratio, and the de-
termination of the chain release mechanism are crucial for the synthesis
of structurally uniform α-olefin oligomers and polymers with a given
DPn. To evaluate the catalytic potential of heterocenes in α-olefin
polymerization at low AlMAO/Zr ratio (∼10), we have chosen bis-
fluorenyl SiMe2-bridged ansa-complex 3 [60] as a structural prototype
and benchmark molecule, and prepared a series of heterocene pre-
catalysts based on 7H-cyclopenta[1,2-b:4,3-b']dithiophene (4, 5, 8),
5,6-dihydroindeno[2,1-b]indole (6, 9) and 5,10-dihydroindeno[1,2-b]
indole (7, 10–12, Scheme 1). We performed a series of 1-octene poly-
merization experiments using the TIBA followed by MMAO-12 cocata-
lyst both in the absence and in the presence of the molecular hydrogen,
compared the catalytic activities and mechanisms of chain release for
different complexes, and demonstrated the high applicability of het-
erocene catalysis in the synthesis of poly(1-octene)s with different DPn.
2.2. Analysis
CDCl3 and DMSO-d6 (Cambridge Isotope Laboratories, Inc., D
99.8%) were used as purchased. CD2Cl2 (JSC Isotope, Russian
Federation) was stored over CaH2 and condensed into NMR tubes. The
1H and 13C NMR spectra were recorded on a Bruker AVANCE 400
spectrometer (400 MHz) at 20 °C (spectra of ligands and complexes, 1H
NMR spectra of polymers) and at 55 °C (13C NMR spectra of polymers).
The chemical shifts are reported in ppm relative to the solvent residual
peaks.
Size exclusion chromatography (SEC) of poly(1-octene) samples was
performed using an Agilent PL-GPC 220 chromatograph equipped with
a PLgel column, and THF was used as the eluent (1 mL/min). The
measurements were recorded with universal calibration based on a
polystyrene standard at 40 °C. Elemental analysis (C, H, N, O) was
performed using a Perkin Elmer Series II CHNS/O Analyzer 2400. X-ray
diffraction studies were performed at the Center of Shared Equipment
of IGIC RAS.
2. Experimental section
2.1. Solvents and reagents
Benzene, toluene, n-hexane, n-heptane, and 1-octene (Sigma-
Aldrich) were stored over Na and distilled under argon. Diethyl ether,
THF, N,N,N',N'-tetramethylethylenediamine (TMEDA) and toluene
were refluxed over Na/benzophenone and distilled under argon.
Isopropylbenzene and tert-butylbenzene were distilled under reduced
pressure. CH2Cl2 was refluxed over CaH2 and distilled. Diethylene
glycol, ethanol, isopropanol, hydrazine hydrate, phenylhydrazine, 1,1-
13

I.E. Nifant'ev et al.
AppliedCatalysisA,General571(2019)12–24
2.3. Preparation of heterocycle-fused cyclopentadienes and indenes.
Synthesis of bridged ligands
of 19 without purification. 1H NMR (CDCl3, 20 °C) δ: 8.29 (bs, 1 H);
7.65 (m, 1 H); 7.61 (bc, 1 H); 7.41 (m, 1 H); 7.37 (bs, 2 H); 7.18 (m,
2 H); 3.72 (s, 2 H); 1.41 (s, 9 H). 13C NMR (101 MHz, DMSO-d6, 20 °C)
δ: 147.52; 147.30; 143.61; 140.59; 132.55; 124.28; 123.37; 122.51;
120.67; 119.45; 119.20; 118.41; 117.20; 112.33; 34.48; 31.43; 29.95.
The 1H and 13C NMR spectra of the product are provided in Appendix A,
Figs. S6 and S7, respectively.
2,5-Dimethyl-7H-cyclopenta[1,2-b:4,3-b']dithiophene 13 [41,63],
5-methyl-5,6-dihydroindeno[2,1- b]indole 14 [64], 5-phenyl-5,6-dihy-
droindeno[2,1- b]indole 15 [38], 5-methyl-5,10-dihydroindeno[1,2-b]
indole 16 [38], 5-phenyl-5,10-dihydroindeno[1,2-b]indole 17 [38],
(fluoren-9-yl)(2,5-dimethyl-7H-cyclopenta[1,2-b:4,3-b']dithiophen-7-
yl)dimethylsilane L4 [65], bis(2,5-dimethyl-7H-cyclopenta[1,2-b:4,3-
b']dithiophen-7-yl)dimethylsilane L5 [65], dimethylbis(5-methyl-5,6-
dihydroindeno[2,1-b]indol-6-yl)silane L6 [38], dimethylbis(5-methyl-
5,10-dihydroindeno[1,2-b]indol-10-yl)silane L7 [38], dimethylbis(5-
phenyl-5,6-dihydroindeno[2,1-b]indol-6-yl)silane L9 [38] and di-
methylbis(5-phenyl-5,10-dihydroindeno[1,2-b]indol-10-yl)silane L10
[38] were synthesized according to the previously reported procedures
(see Appendix A for details).
2.3.2.2. Tert -butyl-5-methyl-5,10-dihydroindeno[1,2-b]indole 19. This
compound was obtained by the same method from 2-tert-butyl-5,10-
dihydroindeno[1,2-b]indole (26.1 g, 0.1 mol), and recrystallized from
EtOH. The yield was 17.0 g (62%), white crystalline powder. Elemental
analysis (%): for C20H21N calc. C, 87.23; H, 7.69; N, 5.09; found C,
87.20; H, 7.74; N, 5.06. 1H NMR (CDCl3, 20 °C) δ: 7.68 (d, J = 7.4 Hz,
1 H); 7.65 (bs, 1 H); 7.61 (d, J = 7.6 Hz, 1 H); 7.43 (dd, J = 8.0 &
1.7 Hz, 1 H); 7.40 (d, J = 8.0 Hz, 1 H); 7.27 (t, J = 7.6 Hz, 1 H); 7.21 (t,
J = 7.4 Hz, 1 H). 13C NMR (101 MHz, CDCl3, 20 °C) δ: 148.45; 147.99;
144.99; 141.81; 132.96; 124.39; 123.45; 123.04; 120.93; 119.87;
119.56; 118.99; 117.14; 109.80; 34.89; 31.73; 31.13; 30.32. The 1H
and 13C NMR spectra are provided in Appendix A, Figs. S8 and S9,
respectively.
2.3.1. Synthesis of 2-isopropyl-5-methyl-5,10-dihydroindeno[1,2-b]indole
18
2.3.1.1. 2-Isopropyl-5,10-dihydroindeno[1,2-b]indole. The solution of
PhNHNH2 (30.2 mL, 0.28 mol), 5-isopropyl-1-indanone (48.8 g,
0.28 mmol) and p-TsOH (0.5 g) in EtOH (250 mL) was refluxed for
40 min and cooled in an ice/water external bath. A solution of H2SO4
(100 mL) in EtOH (500 mL) was added. The mixture was refluxed for
12 h, cooled and poured into the solution of NaOH (40 g, 1 mol) in 2 L
of ice water. The precipitate was filtered off, washed with water and
dried. The yield was 60.1 g (87%), and the product was a beige powder.
Elemental analysis (%): for C18H17N calc. C, 87.41; H, 6.93; N, 5.66;
found C, 87.51; H, 6.96; N, 5.53. 1H NMR (400 MHz, CDCl3, 20 °C) δ:
8.23 (bs, 1 H); 7.65 (m, 2 H); 7.44 (bs, 1 H); 7.41 (m, 1 H); 7.37 (d,
J = 7.7 Hz, 1 H); 7.20 (m, 3 H); 3.72 (s, 2 H); 3.01 (sept, J = 6.9 Hz,
1 H); 1.34 (d, J = 6.9 Hz, 6 H). 13C NMR (101 MHz, CDCl3, 20 °C) δ:
148.34; 146.02; 143.59; 140.64; 132.95; 125.00; 124.78; 123.95;
121.47; 121.33; 120.25; 118.91; 117.21; 112.15; 77.48; 77.16; 76.84;
34.39; 30.43; 24.39. 13C NMR (101 MHz, DMSO-d6, 20 °C) δ: 147.80;
145.12; 143.71; 140.60; 132.98; 124.60; 124.29; 123.60; 120.66;
119.29; 119.22; 118.39; 117.51; 112.34; 33.62; 29.82; 24.16. The 1H
and 13C NMR spectra of the product are provided in Appendix A, Figs.
S1 and S2/S3, respectively.
2.3.3. Synthesis
of
bis(2,5-dimethyl-7H-cyclopenta[1,2-b:4,3-b']
dithiophen-7-yl)diethylsilane L8
BuLi (8.8 mL of 1.6 M in hexane, 14 mmol) was added dropwise to a
cooled (0 °C) solution of 13 (2.64 g, 14 mmol) in Et2O (20 mL). After 1 h
of stirring at room temperature, the mixture was cooled to –20 °C, and
SiEt2Cl2 (1.1 g, 7 mmol) in Et2O (10 mL) was added. The mixture was
allowed to warm to room temperature and was stirred for 4 h. NH4Cl
(10 mL of 10% aq.), was added, the organic phase was separated, and
the aqueous phase was extracted with CH2Cl2 (2 × 10 mL). The com-
bined organic phase was evaporated, and the residue was filtered off
and washed by cold Et2O and dried in vacuo. The yield was 2.2 g (63%).
M.p. 158–160 °C. Elemental analysis (%): for C26H28S4Si calc. C, 62.85;
H, 5.68; S, 25.81, found C, 62.94; H, 5.72; S, 25.69. 1H NMR (CDCl3,
20 °C) δ: 6.87 (bs, 4 H); 1.91 (s, 4 H); 2.56 (s, 12 H); 0.48 (t, J = 7.8 Hz,
6 H); 0.37 (q, J = 7.8 Hz, 4 H). 13C NMR (101 MHz, CDCl3, 20 °C) δ:
142.51; 141.84; 141.33; 116.72; 36.50; 16.25; 7.24; 0.83. The 1H and
13C NMR spectra of the product are provided in Appendix A, Figs. S10
and S11, respectively.
2.3.1.2. 2-Isopropyl-5-methyl-5,10-dihydroindeno[1,2-b]indole
18. 2-
Isopropyl-5,10-dihydroindeno[1,2-b]indole (24.7 g, 0.1 mol) and
methyl iodide (6.23 mL, 0.1 mol) were added to well-stirred biphase
mixture prepared from benzene (150 mL) and from the solution of
NaOH (150 g) and trimethylcetylammonium bromide (1.0 g, 2.5 mmol)
in water (150 mL). After 5 h of stirring, the organic layer was separated,
washed by 10% H3PO4 and by water, dried over MgSO4 and evaporated
under reduced pressure. The residue was recrystallized from EtOH/
benzene mixture (3:1, 200 mL). The yield was 20.0 g (76.5%).
Elemental analysis (%): for C19H19N calc. C, 87.31; H, 7.33; N, 5.36,
found C, 87.38; H, 7.40; N, 5.22. 1H NMR (400 MHz, CDCl3, 20 °C) δ:
7.63 (d, J = 7.6 Hz, 1 H); 7.58 (d, J = 7.6 Hz, 1 H); 7.44 (bs, 1 H); 7.38
(d, J = 7.4 Hz, 1 H); 7.23-7.21 (m, 2 H); 7.15 (d, J = 7.2 Hz, 1 H); 4.04
(s, 3 H); 3.70 (s, 2 H); 3.01 (sept, J = 6.9 Hz, 1 H); 1.34 (d, J = 6.9 Hz,
6 H). 13C NMR (101 MHz, CDCl3, 20 °C) δ: 148.71; 145.79; 145.05;
141.81; 133.37; 124.68; 124.37; 124.08; 120.92; 119.71; 119.58;
118.96; 117.45; 109.80; 34.34; 31.17; 30.21; 24.37. The 1H and 13C
NMR spectra of the product are provided in Appendix A, Figs. S4 and
S5, respectively.
2.3.4. Synthesis of bis(2-isopropyl-5-methyl-5,10-dihydroindeno[1,2-b]
indol-10-yl)dimethylsilane L11
BuLi (6.25 mL of 1.6 M in hexane, 10 mmol) was added dropwise to
a cooled (0 °C) solution of 18 (2.61 g, 10 mmol) in Et2O (50 mL). After
1 h of stirring at room temperature, the yellow solution was cooled to
–20 °C, and SiMe2Cl2 (0.6 mL, 5 mmol) in Et2O (10 mL) was added.
After 16 h of stirring at room temperature, 10 mL of 10% aq. NH4Cl was
added. The product was filtered off, washed with water and Et2O, and
dried in vacuo. The yield of the pure meso-form was 1.15 g (40%).
Elemental analysis (%): for C40H42N2Si calc. C 83.00, H 7.31, N 4.84,
found C 83.01, H 7.34, N 4.77. 1H NMR (CDCl3, 20 °C) δ: 7.71 (d,
J = 8.1 Hz, 2 H); 7.64 (d, J = 8.1 Hz, 2 H); 7.48 (bs, 2 H); 7.41 (d,
J = 8.1 Hz, 2 H); 7.25-7.19 (m, 4 H); 7.05 (t, 8.1 Hz, 2 H); 4.16 (s, 2 H);
4.12 (s, 6 H); 2.94 (quint, J = 6.9 Ha, 2 H); 1.28 (d, J = 6.9 Ha, 12 H);
–0.27 (s, 3 H); –0.43 (s, 3 H). 13C NMR (101 MHz, CDCl3, 20 °C) δ:
150.28; 145.14; 144.07; 142.05; 131.91; 123.96; 123.74; 123.58;
121.93; 120.87; 120.03; 119.32; 117.68; 109.71; 35.48; 34.35; 31.37;
24.49; 24.35; –4.97; –6.00. The 1H and 13C NMR spectra of the product
are provided in Appendix A, Figs. S12 and S13, respectively.
2.3.2. Synthesis of 2-tert-butyl-5-methyl-5,10-dihydroindeno[1,2-b]indole
19
2.3.2.1. 2-Tert-butyl-5,10-dihydroindeno[1,2-b]indole. This compound
was obtained by the same method from 5-tert-butyl-1-indanone
(57.5 g, 0.3 mol) and PhNHNH2 (33 mL, 0.3 mol). The yield of the
crude product was 78 g (> 98%). The product was used in the synthesis
2.3.5. Synthesis of bis(2-(tert-butyl)-5-methyl-5,10-dihydroindeno[1,2-b]
indol-10-yl)dimethylsilane L12
This compound was obtained by the same method from 19. The
yield of the pure meso-form was 58%. Elemental analysis (%): for
C42H46N2Si calc. C, 83.12; H, 7.64; N 4.62, found C, 83.17; H, 7.69; N,
14

I.E. Nifant'ev et al.
AppliedCatalysisA,General571(2019)12–24
4.56. 1H NMR (CDCl3, 20 °C) δ: 7.84 (bs, 2 H); 7.79 (d, J = 8.1 Hz, 2 H);
7.74 (d, J = 8.1 Hz, 2 H); 7.49 (d, J = 8.6 Hz, 2 H); 7.47 (d, J = 8.4 Hz,
2 H); 7.27 (t, J = 7.9 Hz, 2 H); 7.13 (t, J = 7.8 Hz, 2 H). 13C NMR
(101 MHz, CDCl3, 20 °C) δ: 150.00; 147.37; 144.06; 142.09; 131.55;
123.98; 122.65; 122.53; 122.08; 120.92; 120.00; 119.39; 117.39;
109.76; 35.68; 34.92; 31.78; 31.35; –5.50; –6.10. The 1H and 13C NMR
spectra of the product are provided in Appendix A, Figs. S14 and S15,
respectively.
58.33; 34.73; 31.38; 31.29; 29.78; 4.65. The 1H and 13C NMR spectra
are provided in Appendix A, Figs. S35 and S36, respectively.
2.5. X-ray diffraction study
Single crystals of heterocenes 8, rac-9 and rac-10 were obtained by
low-temperature crystallization from CH2Cl2 solutions. The reflections
were measured with a Bruker SMART APEX II diffractometer (graphite
monochromatized MoKα radiation, λ = 0.71073 Å) using the ω-scan
mode at 150 K. An absorption correction based on the measurements of
equivalent reflections was applied [66]. The structure was solved by
direct methods and was refined by full matrix least-squares on F2 with
anisotropic thermal parameters for all nonhydrogen atoms [67]. In 8
and rac-10 all of the hydrogen atoms were found from the difference
Fourier synthesis and were refined with isotropic thermal parameters.
As for rac-9, all of the hydrogen atoms were placed in calculated po-
sitions and were refined using a riding model. The crystallographic data
for 8, rac-9 and rac-10 were deposited with the Cambridge Crystal-
lographic Data Center as supplementary publications under the CCDC
numbers 1876661, 1875030 and 1870989, respectively. This informa-
tion may be obtained free of charge from the Cambridge Crystal-
lographic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
2.4. Preparation of zirconocene precatalysts 2-12
All of the synthetic experiments were performed in argon atmo-
sphere using the glovebox and Schlenk techniques. Zirconocene pre-
catalysts 2 [42], 3 [60], 4 [65], 5 [65], 6 [65], 7 [65], 9 [65] and 10
[65] were prepared according to the previously reported procedures
(see the Appendix A for details). New complexes 8, 11 and 12 were
synthesized as described below.
2.4.1. Synthesis of [μ-diethylsilylenebis(η5-2,5-dimethyl-7H-cyclopenta
[1,2-b:4,3-b']dithiophen-7-yl)]dichlorozirconium (IV) 8
BuLi (1.9 mL of 2.5 M in hexane, 4.75 mmol) was added to a cooled
(–70 °C) suspension of L8 (1.135 g, 2.3 mmol) in Et2O (50 mL). The
mixture was allowed to warm to room temperature. After 5 h of stirring,
the mixture was cooled to –40 °C, and ZrCl4 (0.536 g, 2.3 mmol) was
added. After 16 h of stirring at room temperature, the mixture was
filtered, and the precipitate was washed with Et2O (2 × 30 mL) and
recrystallized from CH2Cl2. The yield was 0.720 g (47%), orange crys-
tals. Elemental analysis (%): for C26H26Cl2S4SiZr calc. C, 47.53; H, 3.99;
S, 19.52; found C, 47.55; H, 4.04; S, 19.47. 1H NMR (CDCl3, 20 °C) δ:
6.68 (q, 4J = 1.3 Hz, 4 H); 2.49 (d, 4J = 1.3 Hz, 12 H); 1.73 (q,
3J = 7.9 Hz, 4 H); 1.47 (t, 3J = 7.9 Hz, 6 H). 13C NMR (CD2Cl2, 20 °C) δ:
149.61; 135.22; 133.30; 116.28; 65.82; 16.83; 6.78; 4.11. The 1H and
13C NMR spectra are provided in Appendix A, Figs. S16 and S17, re-
spectively.
2.6. Polymerization and polymer analysis
All of the synthetic experiments were conducted under an argon
atmosphere.
Polymerization of 1-octene was carried out in argon or in hydrogen
atmosphere (1 bar). TIBA solution (0.3 mL of 1.0 M in hexane,
0.3 mmol) was added to 1-octene (31.4 mL, 200 mmol), the mixture was
heated to defined temperature. Then, zirconocene precatalyst (4 μmol)
was added. After 20 min of stirring, MMAO-12 (26 μL of 1.54 M in to-
luene, 40 μmol) was added, and the mixture was stirred at a given
temperature. After a certain period of time, the reaction flask was
cooled, and dry oxygen was bubbled through the stirred mixture within
5 min for the oxidation of the polymeryl–Al species. Then, 5% aq. HCl
was added until the aluminum hydroxide was completely dissolved.
The organic layer was separated, and the aqueous layer was washed
with hexane. The combined organic phase was evaporated and dried
under 10–2 Torr at 100 °C with stirring to completely remove the vo-
latiles including 1-octene dimerization products and isobutanol.
End-group analysis was performed using the 1H NMR spectra of the
polymer solutions in CDCl3. Polymer tacticity was analyzed using 13C
NMR spectroscopy [68,69]. The 1H and 13C NMR spectra of the poly-
mers are provided in Appendix A.
2.4.2. Synthesis of [μ-dimethylsilylenebis(η5-2-isopropyl-5-methyl-5,10-
dihydroindeno[1,2-b]indol-10-yl)]dichlorozirconium (IV) 11
This compound was obtained by the same method from L11 (1.05 g,
1.81 mmol), BuLi (1.50 mL, 3.75 mmol) and ZrCl4 (0.422 g,
1.81 mmol). The yield of rac-11 was 0.55 g (41%), dark red crystals.
Elemental analysis (%): for C40H40Cl2N2SiZr calc.C, 65.01; H, 5.46; N,
3.79; found C, 65.09; H, 5.81; N, 3.77. 1H NMR (CDCl3, 20 °C) δ: 8.16
(d, 3J = 8.0 Hz, 2 H); 7.58 (d, 3J = 8.9 Hz, 2 H); 7.44 (s, 2 H); 7.34
(ddd, 3J = 8.1 and 7.1 Hz, 4J = 1.1 Hz, 2 H); 7.27 (br. d, 3J = 8.1 Hz,
2 H); 7.19 (ddd, 3J = 8.0 and 7.1 Hz, 4J = 1.3 Hz, 2 H); 6.94 (dd,
3J = 8.9 Hz, 4J = 1.3 Hz, 2 H); 3.90 (s, 6 H); 2.45 (sept, 3J = 6.9 Hz,
2 H); 1.76 (s, 6 H); 0.88 (d, 3J = 6.9 Hz, 6 H); 0.53 (d, 3J = 6.9 Hz, 6 H).
13C NMR (CD2Cl2, 20 °C) δ: 147.53; 146.30; 138.78; 130.90; 125.73;
124.83; 122.79; 122.60; 122.49; 122.35; 119.84; 119.52; 113.10;
109.85; 58.89; 35.37; 31.88; 23.58; 22.33; 5.05. The 1H and 13C NMR
spectra are provided in Appendix A, Figs. S31 and S32, respectively.
3. Results and discussions
3.1. Heterocene preparation
3.1.1. Synthesis of the ligands
In our research, we aimed to study heterocyclic analogs of bis-
fluorenyl ansa-zirconocene 3. Among the variety of heteroanalogs of
fluorene [70] we chose 2,5-dimethyl-7H-cyclopenta[1,2-b:4,3-b']di-
thiophene, substituted 5,6-dihydroindeno[2,1-b]indoles and substituted
5,10-dihydroindeno[1,2-b]indoles (Scheme 2). 2,5-Dimethyl-7H-cyclo-
penta[1,2-b:4,3-b']dithiophene 13 was prepared by a modified pre-
viously reported method [63], and the synthesis of indeno-indoles
14–19 was performed using the Fischer rearrangement of the corre-
sponding hydrazones prepared from 2-indanone, 1-indanone or 5-alkyl-
1-indanones. 5,10-Dihydroindeno[1,2-b]indole derivatives 18 and 19
are new compounds (for experimental details see 2.3.1 and 2.3.2, re-
spectively, the NMR spectra of 18 and 19 are provided in Appendix A).
The synthesis of dimethylsilanydiyl-bridged precursors of ansa-li-
gands L3–L12 was performed under argon atmosphere by the reaction
of the lithium derivative of 13–19 with a half equivalent of SiMe2Cl2
2.4.3. Synthesis of [μ-dimethylsilylenebis(η5-2-tert-butyl-5-methyl-5,10-
dihydroindeno[1,2-b]indol-10-yl)]dichlorozirconium (IV) 12
This compound was obtained by the same method from L12 (1.15 g,
1.89 mmol), BuLi (1.55 mL, 3.87 mmol) and ZrCl4 (0.44 g, 1.89 mmol).
The yield of rac-12 was 0.38 g (26%), dark red crystals. Elemental
analysis (%): for C42H44Cl2N2SiZr calc. C, 65.77; H, 5.78; N, 3.65; found
C, 65.84; H, 5.86; N, 3.60. 1H NMR (CDCl3, 20 °C) δ: 8.16 (ddd,
3J = 8.0 Hz, 4J = 1.1 Hz, 5J = 0.8 Hz, 2 H); 7.58 (dd, 3J = 9.1 Hz,
4J = 0.8 Hz, 2 H); 7.54 (dd, 4J = 1.6 Hz, 5J = 0.8 Hz, 2 H); 7.32 (ddd,
3J = 8.3 and 6.9 Hz, 4J = 1.1 Hz, 2 H); 7.27 (br. d, 3J = 8.3 Hz, 2 H);
7.18 (ddd, 3J = 8.3 and 7.1 Hz, 4J = 1.1 Hz, 2 H); 7.14 (dd, 3J = 9.1 Hz,
4J = 1.6 Hz, 2 H); 3.91 (s, 6 H); 1.77 (s, 6 H); 0.95 (s, 18 H). 13C NMR
(CD2Cl2, 20 °C) δ: 147.85; 146.87; 138.47; 131.39; 125.10; 124.48;
122.33; 122.16; 121.69; 120.21; 119.53; 117.24; 112.43; 109.31;
15

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Scheme 2. Synthesis of fluorene heteroanalogs used in this work.
Scheme 3. Synthesis of SiMe2-bridged ansa-ligand precursors L4–L12 (A) and heterocenes 4–12 (B).
(Scheme 3). Compounds L8, L11 and L12 are novel (see 2.3.3–2.3.5,
the NMR spectra are provided in Appendix A). Indenoindole ligand
precursors were obtained as rac-/meso- mixtures. Less soluble diaster-
eomers, namely, rac- for L6, L7, L9 and meso- for L11, L12 were se-
parated by recrystallization and were characterized by 1H and 13C NMR
(see Appendix A for details).
solubilities of both reaction components provided the conditions of the
principle of dilution that resulted in the high yields of the ansa-products
with minimal polymer formation. Indenoindole complexes 6, 7, 10–12
were obtained as mixtures of diastereomers, and rac-forms of these
heterocenes were separated by recrystallization (see 2.4). Special at-
tention should be paid to the high yield of rac-9 (82%), because such a
high stereoselectivity is unusual for Li-Zr transmetallations in the
synthesis of ansa-zirconocenes that typically yields ∼1:1 rac-/meso-
mixtures [71]. Zirconocenes 8, 11 and 12 are novel compounds (see
2.3.3–2.3.5, the NMR spectra are provided in Appendix A).
3.1.2. Synthesis of heterocenes
The synthesis of heterocenes 4–12 by the reaction of dilithium de-
rivatives of the ligands with ZrCl4 (Scheme 3) was complicated by the
extremely low solubility of both dilithium salts and LZrCl2 products,
and the reactions required 10–15 h for completion. However, the low
The known heterocene complex 5 is poorly soluble in polar organic
solvents. The synthesis of its analog 8 was performed to increase the
16

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AppliedCatalysisA,General571(2019)12–24
Fig. 1. Molecular structure of 8.
solubility. As a result, we successfully obtained the single crystals of 8
and carried out an X-ray diffraction study. The molecular structure of 8
is shown in Fig. 1.
Complexes 9 and 10 were characterized for the first time by NMR
spectroscopy in this work (see the Appendix A, 3.6 and 3.7), X-ray
diffraction analysis was carried out to compare the molecular structures
of rac-9 and rac-10. The molecular structures of rac-9 and rac-10 are
shown in Fig. 2.
The details of the X-ray diffraction experiments are provided in
section 2.5, and the structural parameters of heterocenes are given in
Appendix A. The coordination environment of the Zr atom may be
treated as a distorted tetrahedron (assuming that the η5-C5 rings occupy
a single coordination site). The Zr–C distances vary in a wide range of
2.438(1)–2.710(1) Å. The main geometric parameters for 8, 9 and 10
(Table 1) are close to those previously determined for the SiMe2-
bridged complexes containing the indenyl and fluorenyl ligands that
were retrieved from CSD [72]; these parameters for close structural
analog of 3–5 and 8, bis(fluorenyl) complex [Me(CH2=CHCH2)Si(η5-
3.2. Polymerization experiments
3.2.1. End-group analysis for α-olefin polymers and mechanisms of chain
release
The control of termination events is an important problem in single-
site α-olefin polymerization catalysis. Traditional mechanisms of chain
release that are discussed in the literature [74] are illustrated in Scheme
4. In the presence of organoaluminum cocatalysts, chain release may
occur via Zr-Al transfer (Scheme 4, A) or by different routes that result
in different end-group unsaturations. Generally, for higher α-olefins,
chain release by β-hydride elimination with a formation of vinylidene
chain ends (Scheme 4, B) is the main termination route. Unlike pro-
pylene, higher α-olefins usually do not demonstrate the tendency to β-
alkyl elimination (Scheme 4, C) with a formation of allyl chain ends. To
the best of our knowledge, route C has been reported in only two works
in the field of metallocene-catalyzed higher olefin polymerization
[75,76]. The internal double bond formation (Scheme 4, D, E) can be
interpreted through either an allyl or secondary alkyl metal species
[77–80]. Brintzinger and Babushkin demonstrated that cationic allyl
complexes (Scheme 4, route D, right) dominate as intermediates in 1-
hexene polymerization catalyzed by [Me2Si(Indenyl)2]ZrR+/per-
fluoroborate [81], but Crowther et al. proposed 1,2-rearrangements
(Scheme 4, route D, left) as a possible pathway for the formation of
C
13H8)2]ZrCl2 20 [73] are presented in the Table 1 for comparison. The
only structural parameter that differ the complex 10 among the zirco-
nocenes 8–10 is Cl1-Zr-Cl2 angle that is minimal in 10 (94.73° vs 98.32°
in 8 and 99.27° in 9).
17

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AppliedCatalysisA,General571(2019)12–24
Fig. 2. Molecular structures of rac-9 and rac-10.
[82]. Unsaturated chain ends were detected in the 1H NMR spectra of
the polymer solutions in CDCl3 by the analysis of the characteristic
signals at 4.65–4.80 ppm for vinylidene groups > C = CH2, at
4.95–5.05 ppm (2 H) and 5.70–5.85 ppm (1 H) for vinyl groups
–CH = CH2, at 5.10–5.20 ppm for trisubstituted fragments > C = CH–,
and at 5.30–5.40 ppm for internal –CH = CH– fragments. Finally, hy-
drogenolysis of Zr-polymeryl Scheme 4, route H), resulting in > CH-
CH3 formation, was detected in some cases by the presence of the
characteristic doublets at 0.82 ppm.
Table 1
Selected bond length (Å)a) and angles (deg) in 8, rac-9 rac-10 and bis(fluorenyl)
complex 20 [73].
8
9
10
20
Bond length, Å
Zr-C1
Zr-C2
Zr-C3
Zr-C4
3.2.2. 1-Octene polymerization in the absence of the molecular hydrogen
The use of 102–104 eq. of MAO is typical for catalytic experiments
with LZrCl2 as catalyst precursors. Lower amounts of pure MAO are
ineffective for activation of indenyl or fluorenyl complexes. The alter-
native way of activation of LZrCl2 use TIBA that easily transforms in-
soluble LZrCl2 into zirconium-dialuminium hydride alkyl derivatives
[83]. The formation of Zr-Al hydrides was detected in zirconocene/
MAO reaction mixtures even at high Al/Zr ratios (∼500) after the
addition of TIBA [84]. Specific catalytic activity of cationic zirconocene
hydrides was demonstrated by Marks et al. in 1992 [85], cationic Zr-Al2
hydride-alkyls stabilized by counter-ions were characterized by Bercaw,
Brintzinger and coll. [86]. The rates of polymerization in the presence
of such complexes are significantly lower in comparison with "pure"
zirconocene cations, and the nature of the real catalytic particles in
TIBA-MAO system remains unclear.
In our experiments with a series of heterocenes LZrCl2 included
extremely low soluble complexes 3–5 and 7, we applied two-stage ac-
tivation. Treatment of LZrCl2 by 75 eq. of TIBA in 1-octene media at
60 °C resulted in complete dissolution of the complexes, polymerization
was not detected in all cases. The reactions were started after the ad-
dition of 10 eq. of MMAO-12. The results of our experiments are
summarized in Table 2.
Under these conditions, the mixed-ligand heterocene 2 demon-
strated high productivity with a formation of poly(1-octene) with Mn
7.4·104 Da (Table 2, run 1). Benchmark complex 3 had low activity
(Table 2, run 2). After the replacement of the fluorenyl fragments by
cyclopenta[1,2-b:4,3-b']dithiophene (complex 5), both the catalytic
productivity and polymer molecular weight increased (Table 2, run 4).
The catalytic properties of SiMe2-bridged ansa-complexes based on di-
hydroindeno[2,1-b]indole (6) and 5,10-dihydroindeno[1,2-b]indole (7)
are substantially different: complex 6 was highly active, and the
2.455
2.510
2.700
2.710
2.520
2.276
1.861
1.426
1.426
2.454
2.500
2.642
2.661
2.603
2.265
1.886
1.443
1.418
2.438
2.475
2.668
2.674
2.548
2.251
1.874
1.451
1.423
2.424
2.545
2.708
2.706
2.548
2.282
1.871
1.422
1.424
Zr-C5
Zr-Cenb)
Si-C1
C2-C3
C4-C5
Angles, deg
Cen-Zr-Cen
Cp-Cpc)
C1-Si-C1'
Cl1-Zr-Cl2
130.68
65.08
96.28
98.32
130.80
60.76
95.62
99.27
131.18
63.28
95.32
94.73
130.86
65.76
95.49
95.39
a)
Average values for both η5-coordinated rings.
Cen – centroid of the cyclopentadienyl ring.
Dihedral angle between cyclopentadienyl rings.
b)
c)
trisubstituted olefins [74,75]. Reactivation of the allyl species required
the presence of molecular hydrogen. For –CH = CH– formation, 2,1-
misinsertion with subsequent β-hydride elimination (Scheme 4, route
E) was proposed as an appropriate reaction pathway [77,80]. Finally, in
the presence of molecular hydrogen, the chain breaks via the hydro-
genolysis of the Zr–Alkyl bond with a formation of saturated macro-
molecules (Scheme 4, route H).
To detect both Zr-Al transfer and chain release with the formation of
unsaturated groups in the 1H NMR spectra, in our experiments, we
oxidized the reaction mixtures prior to hydrolysis, allowing us to ana-
lyze polymeryl-CH2OH end-groups after the elimination of volatiles
from the polymers by the comparative integration of the signals in the
1H NMR spectra at ∼3.5 ppm. A similar approach was previously
suggested in the study of Zr-Al transfer in propylene polymerization
18

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AppliedCatalysisA,General571(2019)12–24
Scheme 4. Traditional mechanisms of chain release in α-olefin polymerization with the formation of characteristic chain-end groups (routes AeE) [74,75] and
saturated polyolefin species (route H).
productivity was comparable to that of complex 2 but the MW of poly
(1-octene) was two times lower (Table 2, run 5). Complex 7 (Table 2,
runs 6–8) demonstrated very low activity, with only 30% conversion
observed after two days, but the formed poly(1-octene) had extremely
high molecular weight (Mn = 8.9·105 Da) and remarkably low dispersity
(ÐM = 1.2). N-phenyl substituted complex 9 was less active than N-
methyl analog 6 (only 60% conversion after 4 h, Table 2, run 10). N-
phenyl 5,10-dihydroindeno[1,2-b]indole complex 10 was inactive, and
only traces of poly(1-octene) were formed after 4 h (Table 2, run 11),
after 48 h polymer with moderate Mn and ÐM = 2.2 was obtained
(Table 2, run 12). Complexes 11 and 12 also demonstrated low catalytic
activities (Table 1, runs 13 and 14, respectively). There was no no-
ticeable difference in the catalytic behavior of heterocene 8 and its low-
solubility analog 5. To summarize, in an inert atmosphere, heterocenes
activated by TIBA and MMAO-12, catalyzed 1-octene polymerization
with the formation of poly(1-octene)s in a wide Mn interval (104–106
Table 2
1-Octene homopolymerization (10 eq. MMAO-12, 75 eq. TIBA, 60 °C, 1-octene/Zr = 5·104).
a)
a)
Run
Cat
H2, bar
React. time, h
Conv., %
Mn ·103 SEC
ÐM
RH, %b)
Mechanism of chain releasec)
Polymer tacticityd)
Polymerization in inert atmosphere
1
2
3
4
5
6
7
8
2
3
4
5
6
7
7
7
8
9
10
10
11
12
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
4
4
4
1
4
24
48
4
4
4
48
4
4
80
22
15
32
79
10
14
30
82
60
2
74.0
65.4
74.6
138.9
44.0
98.2
241.4
890.0
69.6
41.4
–
2.8
3.0
3.6
3.2
2.4
2.6
2.8
1.2
3.6
2.7
–
1
2
0
0
0
2
aB
BC
aBc
A
isotactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
Ab
Ab
Ab
Ab
Ab
aB
Bd
aBd
aB
AB
e)
–
–
)
9
6
4
–
0
0
0
10
11
12
13
14
22
15
35
52.4
54.8
87.5
2.2
2.3
3.5
Polymerization in hydrogen atmosphere
15
16
17
18
19
20
21
22
23
24
25
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
4
4
4
4
4
82
12
10
78
83
73
83
84
48
72
70
30.0
31.7
30.4
17.3
53.4
7.3
34.3
17.9
2.8
2.2
2.3
2.4
2.9
2.6
3.0
2.4
2.2
3.2
3.2
2.8
17
69
87
70
8
61
91
0
Ab
isotactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
atactic
bC H
aBc H
aBC H
AB
BC H
abC H
BCde
ABC H
BC H
Bcd H
10
11
12
74
69
72
5.6
6.9
a)
b)
c)
d)
e)
Number average molar mass Mn and dispersity ÐM were determined by SEC (THF, PS standard).
Relative hydrogenation value RH was determined by the analysis of the end-groups signals in the 1H NMR spectra.
Uppercase letters indicate the main chain release reaction pathways, lowercase letters indicate the minor reaction pathways.
Determined by 13C NMR.
Not determined.
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AppliedCatalysisA,General571(2019)12–24
Fig. 3. 1H NMR spectra (end group region) of poly(1-octene)s obtained in bulk at 60 °C in the presence of benchmark complex 3 and heterocenes 5, 6 and 7 activated
by 10 eq. MMAO-12 under inert atmosphere.
Da). Particular attention should be paid to complexes 4 and 7 that al-
lowed us to achieve the Mn values that were previously obtained under
extremely high pressure [87–89].
octene. Unexpectedly, C2-symmetrical racemic heterocenes 6, 7, 9–12
also acted as catalysts of atactic polymerization (13C NMR spectra are
provided in the Appendix A, Figs. S42–S54).
The results of the 1H NMR end-group analysis of poly(1-octene)s are
also provided in Table 2. β-Hydride elimination is the main chain re-
lease mechanism for complex 2. For bis-fluorenyl benchmark complex
3, β-hydride (B) and β-alkyl (C) eliminations were detected (Fig. 3,
spectrum 1). For heterocenes 5, 6 and 7, the transfer of the polymer
chain to aluminum was the main chain termination pathway (Fig. 3,
spectra 2–4); moreover, the formation of polymeryl-Al species was the
only mechanism of chain release for complex 5, and the signals of
unsaturated groups were not detected by 1H NMR (Fig. 3, spectrum 2).
Special attention should be given to the stereochemistry of poly(1-
octene)s obtained. In the case of C1 symmetrical complex 2 highly
isotactic polymer formed. As expected, complexes 3, 5 and 8 (C2v
symmetry) and 4 (Cs symmetry) catalyzed atactic polymerization of 1-
3.2.3. 1-Octene polymerization in the presence of the molecular hydrogen
Molecular hydrogen in zirconocene-catalyzed polymerization of α-
olefins can play at least two roles. First, hydrogen can cleave a Zr–C
bond with the formation of saturated hydrocarbons (Scheme 4, route
H); this reaction has a low activation barrier [90] and is controlled by
the hydrogen concentration in the reaction mixture. This pathway is
promising for the development of one-stage synthesis of hydrogenated
oligomers that does not incur the high energy cost of the hydrogenation
of unsaturated products of the traditional α-olefin oligomerization. To
evaluate the contribution of the route H in the chain release processes,
we calculated relative hydrogenation (RH) value for obtained polymers
(the corresponding formula are provided in the Appendix A). When 1-
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AppliedCatalysisA,General571(2019)12–24
Fig. 4. 1H NMR spectra (end group region) of poly(1-octene)s obtained in polymerization experiments under 1 bar H2 atmosphere catalyzed by heterocenes 7 (top)
and 10 (bottom).
Table 3
1-Octene homopolymerization at elevated temperatures (10 eq. MMAO-12, 75 eq. TIBA, 1-octene/Zr = 5·104).
Mn ·103 SECa)
ÐM
RH, %b)
Mechanism of chain releasec)
a)
Run
Cat
T, °C
H2, bar
React. time, h
Conv., %
1
2
3
4
5
6
7
8
3
3
3
5
5
5
6
6
6
7
7
7
9
9
9
80
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4
4
4
4
4
4
1
4
4
2
2
2
1
1
1
2
2
2
18
13
10
75
78
80
78
82
84
85
80
82
84
84
86
52
76
72
24.4
19.6
10.6
12.3
5.3
2.1
1.8
2.0
2.8
3.8
2.8
2.0
3.7
2.5
2.1
1.7
1.6
1.8
2.3
2.6
3.3
2.0
2.6
56
32
12
75
23
21
0
B H
B H
B h
aBcde h
aBcde h
BCde h
aBc
aBc
aBc
ABC h
BCd
BCd
B 18% dimer
BF 40% dimer
bF 60% dimer
ABC H
aBC h
100
120
80
100
120
80
100
120
80
100
120
80
100
120
80
100
120
3.9
47.0
19.6
29.8
9.7
4.5
4.5
11.6
4.5
5.5
3.9
3.8
4
0
9
10
11
12
13
14
15
16
17
18
29
13
2
d)
–
–
–
54
42
20
10
10
10
3.1
aBC h
a)
Number average molar mass Mn and dispersity ÐM were determined by SEC (THF, PS standard).
Relative hydrogenation value RH was determined by analysis of end-groups signals in 1H NMR spectra.
Uppercase letters indicate the main reaction pathways of chain release, lowercase letters indicate the minor reaction pathways.
Not determined.
b)
c)
d)
octene was polymerized under an inert atmosphere, the value of RH
was roughly equal to 0% (Table 2, runs 1–12).
dihydroindeno[2,1-b]indole derivatives 6 and 9 in the presence of H2
was unchanged with the minimal lowering of the molecular weight. By
contrast, even at 1 bar, molecular hydrogen effectively activated dihy-
droindeno[2,1-b]indole derivatives 7, 10, 11 and 12 (Table 2, runs 20,
23–25). The productivity increased by an order of magnitude, with a
proportional decrease in the molecular weights.
End-group analysis of the poly(1-octene)s obtained in the presence
of H2 showed the changes in the main chain release routes. For bis
(fluorenyl) complex 3, the formation of vinyl end-groups became the
main pathway in the formation of unsaturations. Apparently, the
Zr–Alkyl hydrogenolysis replaced the β-hydride elimination.
Heterocene 5 that did not form unsaturated groups without H2 showed
a tendency to both hydride and alkyl elimination processes in the
presence of hydrogen (Scheme 4, routes B and C). Vinyl end-group
formation was also used for both dihydroindeno[1,2-b]indole and di-
hydroindeno[2,1-b]indole complexes. Mechanism E (elimination after
2,1-monomer insertion) was detected for complex 9. We note that
formation of Zr–Al transfer products was reduced in all of the
The second role of the molecular hydrogen is the reactivation of the
"dormant sites" by hydrogenolysis of the secondary alkyl–Zr or allyl–Zr
species. The presence of internal > C = CH– and –CH = CH– end
fragments in polymerization products provides experimental evidence
of the formation of allyl-Zr intermediates. We studied 1-octene poly-
merization catalyzed by 2–12 (10 eq. MMAO-12) under 1 bar of the
molecular hydrogen. We found that H2 slightly affected the catalysis by
heterocene 2. A minor increase in the polymer yield was accompanied
by a twofold decrease in its molecular weight (Table 2, run 15). The
benchmark catalyst 3 was partially inactivated by H2 (Table 2, run 16),
and more than half of the polymer was hydrogenated. The productivity
of mixed-ligand complex 4 in the presence of H2 was also lower than
that in its absence, and saturated polymers were mostly formed
(Table 2, run 17). The activity of 5 under the hydrogen atmosphere
increased, and the molecular weight of the poly(1-octene) was reduced
by almost an order of magnitude (Table 2, run 18). Catalytic activity of
21

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AppliedCatalysisA,General571(2019)12–24
Fig. 5. 1H NMR spectra of poly(1-octene)s obtained in polymerization experiments under 1 bar H2 atmosphere in the presence of 9 at 60 (top), 100 (middle) and
120 °C (bottom). C16 fraction eliminated in vacuo, –C(Me)=CHCH2– groups detected.
Scheme 5. The possible pathway for the formation of –C(Me)=CHCH2– unsaturations.
experiments.
In some experiments, we demonstrated the influence of steric en-
hydride elimination was the main route of chain release for 7, and three
reaction pathways were detected for 10 in equal parts.
vironment on the chain release mechanisms. The end-group region of
the 1H NMR spectra of poly(1-octene)s, obtained in the presence of
heterocenes 7 and 10 under hydrogen atmosphere, is shown in Fig. 4. β-
The residual unsaturation values calculated by formula (2) depend
on the structure of the heterocenes. Route H plays a minor role for 2,
and dihydroindeno[2,1-b]indole complexes 6 and 9 (Table 2, runs 14,
22

I.E. Nifant'ev et al.
AppliedCatalysisA,General571(2019)12–24
17 and 20). By contrast, Zr–Alkyl hydrogenolysis contributes sig-
nificantly to chain termination for benchmark complex 3, for its cy-
clopenta[1,2-b:4,3-b']dithiophene analogs 4, 5 and 8, as well as for
dihydroindeno[1,2-b]indole complexes 7, 10–12 (Table 2, runs 14–16,
18, 19, 21–23). Lowering of the Mn of polymerization products in the
presence of H2 allows to consider molecular hydrogen as an effective
tool for the control of the degree of polymerization DPn for these
complexes.
The role of the molecular hydrogen in activation of indeno[1,2-b]
indole complexes 7, 10–12 is not clear. The absence of trisubstituted
olefin end-groups (Scheme 4, routes D) indicates that conventional
mechanism of the reactivation of allyl dormant species by H2 is not
actial for these complexes. Recently, Bercaw and Brintzinger demon-
strated that diisobutylalyminium hydride (that easily forms from TIBA
at elevated temperatures) reacts with zirconocene dialkyls with a for-
mation of inactive formally Zr (III) species [91]. We can only propose
that the formation of such species (maybe, dimeric) is more substantial
for indeno[1,2-b]indole derivatives, and the possible role of the mole-
cular hydrogen is in reactivation of inactive Zr complexes in low oxi-
dation states.
(AlMMAO/Zr = 10). We performed a series of polymerization experi-
ments in the absence and in the presence of molecular hydrogen in the
temperature range of 60–120 °C.
We found that in the absence of molecular hydrogen, cyclopenta
[1,2-b:4,3-b']dithiophene derivatives 2, 5 and 8 and 5,6-dihydroindeno
[2,1-b]indole derivatives 6 and 9 are highly active catalysts. 5,10-
Dihydroindeno[1,2-b]indole complexes 7, 10–12 are low-active cata-
lysts, and ultrahigh molecular weight poly(1-octene) with sharp MWD
was obtained in the presence of 7. End-group analysis by 1H NMR
spectroscopy shown a substantial diversity in the polymer chain release
mechanisms for the different heterocenes.
We found that catalytic activity of dihydroindeno[1,2-b]indole
complexes increases by an order of magnitude in the presence of mo-
lecular hydrogen. Hydrogenolysis of the Zr–C bond makes a significant
contribution to chain release for these complexes and dominates at
relatively low temperatures. Increasing the temperature gives rise to a
wide range of spectra of the different chain termination processes in-
cluding the novel reaction with the formation of –C(Me)=CHCH2–
unsaturations. In contrast to bis(fluorenyl) zirconium complex 3, het-
erocenes maintain high catalytic activity up to 120 °C.
Reaction temperature is another effective tool for DPn control.
Clearly, an increase in temperature leads to the lowering of the ratio of
propagation and termination rate constants, and decreases DPn. We
performed a series of 1-octene polymerizations at 80, 100 and 120 °C
for six complexes, namely, benchmark complex 3 and complexes 5, 6,
7, 9 and 10 that represent different structural types of heterocenes. The
results of these experiments are provided in the Table 3.
Due to their high catalytic activity even at AlMMAO/Zr ∼10, good
hydrogen response, high thermal stability, and variability of the
structures of the complexes that allow us to obtain both isotactic and
atactic polymers, heterocenes are promising single-site catalysts for the
hydrooligomerization of α-olefins.
Acknowledgment
The benchmark bis(fluorenyl) complex 3 demonstrated the max-
imum of productivity at 80 °C. At 120 °C, the activity of 3 was two times
lower (Table 3, run 3). β-Hydride elimination was the main reaction
pathway for chain termination in the high-temperature 1-octene poly-
merization catalyzed by 3. With decreasing DPn and increasing of the
residual unsaturation, heterocyclic analog 5 at elevated temperatures
maintained its activity at a constant level, and demonstrated the whole
spectrum of termination reactions (Table 3, runs 4–6). Complex 6 also
remained highly active to 120 °C (Table 3, runs 7–9). For heterocene 7,
with increasing temperature, we detected a decrease in of DPn and in
hydrogenated polymer (Table 3, runs 10–12). The increasing of the
resudial unsaturations at elevated temperatures can be explained by
decrease of the solubility of the molecular hydrogen. The increase of the
pressure of molecular hydrogen should increase the degree of hydro-
genation of the polymer with decreasing of the Mn. We believe that a
rational combination of both tools, temperature and hydrogen pressure,
will allow us to achieve the desired DPn values with a formation of
highly hydrogenated oligomers.
The authors are thankful to the Russian Science Foundation, Grant
No. 18-13-00351 for financial support.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.apcata.2018.12.006.
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