Titanium isopropoxide complexes of a series of sterically demanding aryloxo based [N2O2]2- ligands as precatalysts for ethylene polymerization

Article abstract of DOI:10.1039/c0dt00407c

Several titanium isopropoxide complexes [N,N′-bis(2-oxo-3-R ₁-5-R₂-phenylmethyl)-N,N′-bis(methylene-p-R ₃-C₆H₄)-ethylenediamine]Ti(O ⁱPr)₂ [R₁ = t-Bu, R₂ = Me, R ₃ = H (1b); R₁ = R₂ = t-Bu, R₃ = H, (2b); R₁ = R₂ = Cl, R₃ = H, (3b), R₁ = t-Bu, R₂ = Me, R₃ = Cl (4b); R₁ = R ₂ = t-Bu, R₃ = Cl, (5b); R₁ = R₂ = R₃ = Cl, (6b)] supported over sterically demanding aryloxy based [N₂O₂]H₂ ligands have been designed as precatalysts for the ethylene polymerization. Specifically, the 1b-6b complexes, when treated with methylaluminoxane (MAO) under 88 ± 0.5 psi of ethylene at 30 °C for 3 h, produced polyethylene polymers of high molecular weight (M_w = ca. 7.2-8.3 × 10⁵ g mol^-1) having broad molecular weight distribution (PDI = ca. 13.1-14.6). The 1b-6b complexes were conveniently synthesized from the direct reaction of the [N ₂O₂]H₂ ligands, 1a-6a, with Ti(O ⁱPr)₄ in 69-86% yield. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00407c

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Titanium isopropoxide complexes of a series of sterically demanding aryloxo
based [N2O2]2- ligands as precatalysts for ethylene polymerization†
Manas K. Panda,a Sukhdeep Kaur,c Annapureddy Rajasekhar Reddy,a Mobin M. Shaikh,b Ray J. Butcher,d
Virendrakumar Gupta*c and Prasenjit Ghosh*a
Received 2nd May 2010, Accepted 17th August 2010
DOI: 10.1039/c0dt00407c
Several titanium isopropoxide complexes [N,N¢-bis(2-oxo-3-R1-5-R2-phenylmethyl)-
N,N¢-bis(methylene-p-R3-C6H4)-ethylenediamine]Ti(OiPr)2 [R1 = t-Bu, R2 = Me, R3 = H (1b); R1 = R2 =
t-Bu, R3 = H, (2b); R1 = R2 = Cl, R3 = H, (3b), R1 = t-Bu, R2 = Me, R3 = Cl (4b); R1 = R2 = t-Bu, R3 = Cl,
(5b); R1 = R2 = R3 = Cl, (6b)] supported over sterically demanding aryloxy based [N2O2]H2 ligands have
been designed as precatalysts for the ethylene polymerization. Specifically, the 1b–6b complexes, when
treated with methylaluminoxane (MAO) under 88 0.5 psi of ethylene at 30 ◦C for 3 h, produced
polyethylene polymers of high molecular weight (Mw = ca. 7.2–8.3 ¥ 105 g mol-1) having broad
molecular weight distribution (PDI = ca. 13.1–14.6). The 1b–6b complexes were conveniently
synthesized from the direct reaction of the [N2O2]H2 ligands, 1a–6a, with Ti(OiPr)4 in 69–86% yield.
of such initiators being rare, we became interested in designing
Introduction
simple monomeric titanium alkoxy initiators, like its isopropoxide
The area of early transition metal mediated Ziegler–Natta poly-
derivative, for ethylene polymerization and intended to do so by
merization is inundated with diverse initiators varying from the
employing sterically demanding chelating aryloxo based [N2O2]
metallocenes1 to half sandwich2 “constrained geometry”3 catalysts
ligand scaffolds. We rationalized the hard N and O donors of the
to a variety of non-metallocene ones4 like the diamides,5 phenoxy
aryloxo based [N2O2] and the alkoxy ligands on titanium together
imines6 and the amidinates7 etc. Over the years the rational
catalyst design approach was effectively employed in synthesizing
improved initiators and thus has enormously contributed to the
developments in the field. Notable among the post-metallocene
catalysts are the aryloxy ones,8 which are particularly known for
their special ability to stabilize the early transition metal complexes
by forming strong metal–O (aryloxy) bonds owing to the good
p-donor ability of the aryloxy-O atom, and have been shown
to be active in the ethylene homo-polymerization9 and in co-
polymerizations.10 Surprisingly enough, despite the more familiar
use of the aryloxy based precatalysts in ethylene polymerization,
the same use of the alkoxy counterparts is conspicuously less. The
alkoxy moiety, by virtue of being extremely basic, exhibits intrigu-
ing chemistry and is often found bridging between metal centres
resulting in agglomerated multinuclear frameworks and thus the
alkoxy ligands as such do not provide conducive platforms for the
design of discrete well-defined olefin polymerization initiators. As
the synthesis of mononuclear alkoxy initiators of early transition
metals poses a formidable challenge, with well-defined examples
would bring about additional stabilization of the diamagnetic d0
Ti(IV) center against any reduction to a paramagnet d1 Ti(III)
state particularly during the course of olefin polymerization in the
presence of the large excess of electron rich methylaluminoxane
(MAO) activator.
Furthermore, keeping the extreme reactivity of the simple
alkoxy moieties in mind, we chose to target the OiPr derivatives, as
opposed to the less bulkier OMe or OEt derivatives for designing
titanium initiators for ethylene polymerization, with the sole intent
of isolating well-defined discrete monomeric precatalysts. In this
regard it is worth noting that the use of simple alkoxy complexes
of group 4 metals is rare in ethylene polymerization with only a
handful of examples of the use of initiators like Ti(OBu)4,11 and
CpTi(OBz)3,12 existing, which when activated with coinitiators like
Et3Al or Et2Al2Cl3, exhibited ethylene polymerization as well as
copolymerization activities.
With our interest being in exploring the utility of transition
metal complexes in biomimetic chemistry13 and in chemical
catalysis namely, the C–C14 and C–N15 bond forming reactions,
the ring-opening polymerization (ROP) of L-lactide16 and the
sulfoxidation reaction,17 we set out to examine the potential of
titanium isopropoxy complexes in another important application
like the ethylene polymerization.
In this contribution, we report a series of titanium iso-
propoxy complexes [N,N¢-bis(2-oxo-3-R1-5-R2-phenylmethyl)-
N,N¢-bis(methylene-p-R3-C6H4)-ethylenediamine]Ti(OiPr)2 [R1 =
t-Bu, R2 = Me, R3 = H (1b); R1 = R2 = t-Bu, R3 = H, (2b); R1 =
R2 = Cl, R3 = H, (3b); R1 = t-Bu, R2 = Me, R3 = Cl (4b); R1 =
R2 = t-Bu, R3 = Cl, (5b); R1 = R2 = R3 = Cl, (6b)] supported
over sterically demanding aryloxy based [N2O2]H2 ligands as
aDepartment of Chemistry,
bNational Single Crystal X-ray Diffraction Facility, Indian Institute of
Technology Bombay, Powai, Mumbai, 400 076, India
cReliance Technology Group, Hazira Manufacturing Division Reliance
Industries Limited, Surat, Gujarat, 395410, India
dDepartment of Chemistry, Howard University, 525 College Street,
NW, Washington DC, 20059, USA. E-mail: pghosh@chem.iitb.ac.in;
virendrakumar.gupta@ril.com; Fax: +91-22-2572-3480; Tel: +91-261-
6635879
† Electronic supplementary information (ESI) available: Fig. S1–S19.
CCDC reference numbers 643954, 709171, 715915 and 722297. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt00407c
11060 | Dalton Trans., 2010, 39, 11060–11068
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precatalysts for ethylene polymerization (Fig. 1). Specifically, when
activated with methylaluminoxane (MAO) the complexes 1b–6b
exhibited appreciable ethylene polymerization activities yielding
high molecular weight polyethylene polymers in presence of
ethylene gas at 30 ◦C.
Fig. 1 Titanium isopropoxide 1b–6b complexes supported over [N2O2]2-
ligands.
Results and Discussion
A set of sterically demanding aryloxy based [N2O2]H2 lig-
ands namely N,N¢-bis(2-hydroxo-3-R1-5-R2-phenylmethyl)-N,N¢-
bis(methylene-p-R3-C6H4)-ethylenediamine [R1 = t-Bu, R2 = Me,
R3 = H (1a); R1 = R2 = t-Bu, R3 = H, (2a); R1 = R2 = Cl, R3 =
H, (3a), R1 = t-Bu, R2 = Me, R3 = Cl (4a); R1 = R2 = t-Bu, R3 =
Cl, (5a); R1 = R2 = R3 = Cl, (6a)] were employed in stabilizing
the titanium isopropoxide 1b–6b complexes for their utility in
ethylene polymerization (Fig. 1). The 1a–6a ligands were obtained
by the Mannich condensation reaction of the N,N¢-bis(methylene-
p-R3-C6H4)-ethylenediamine (R3 = Cl, H), formaldehyde and the
respective 2,4-disubstituted phenols in 36–57% yield (Scheme 1).
The titanium isopropoxide complexes, 1b–6b, were synthesized
by the direct reaction of the 1a–6a ligands with Ti(OiPr)4 in 69–
86% yield (Scheme 1). Of particular interest are the titanium
bound two OiPr moieties that appeared as a septet at 4.86–
5.18 ppm (3JHH = 6 Hz) and as two doublets at 1.14–1.33 ppm
Scheme 1 General synthetic procedure of the 1b–6b complexes.
1b–6b complexes18 to be discrete monomers with the metal centers
residing in distorted octahedral environments. The two metal
bound OiPr moieties occupied adjacent cis positions while the
[N2O2]2- ligand occupied the remaining four sites in a C2 symmetric
fashion. (Tables 1–2, Fig. 2–3 and ESI Fig. S1–S2†).
1
(3JHH = 6 Hz) and 0.86–1.30 ppm (3JHH = 6 Hz) in the H NMR
spectrum and at 25.9–27.1 ppm and 25.7–26.7 ppm respectively
1
in the corresponding 13C{ H} NMR spectrum of the 1b–6b
complexes (ESI Fig. S4–S19†). More interestingly so, the hydrogen
resonances of the two of the three methylene (CH2) groups in the
1b–6b complexes were found to be diastereotopic in nature with
each appearing as two sets of doublets at 4.22–4.29 ppm (2JHH
=
13 Hz) and 3.23–3.41 ppm (2JHH = 13 Hz) and at 2.62–2.90 ppm
(2JHH = 10 Hz) and 2.29–2.44 ppm (2JHH = 10 Hz) consistent
with the C2 symmetric octahedral geometry of the complexes in
solution. The hydrogens of the third methylene (CH2) group were
however not diastereotopic and appeared as a singlet at 4.15–
4.22 ppm.
As intended with the incorporation of the OiPr moieties on
titanium, and also having further stabilization from the sterically
demanding aryloxy based [N2O2]2- ligand, the molecular structures
as determined by X-ray diffraction studies, indeed, revealed the
Fig. 2 ORTEP view of the solid state structure of 1b. The thermal
ellipsoids are shown in 50% probability level. Hydrogen atoms are
◦
˚
omitted for clarity. Selected bond lengths (A) and angles ( ) are given:
Ti1–O1 1.812(2), Ti1–O2 1.792(2), Ti1–O3 1.902(2), Ti1–O4 1.900(2),
Ti1–N1 2.373(3), Ti1–N2 2.378(2), O2–Ti1–O1 104.86(10), O2–Ti1–O4
97.23(10), O1–Ti1–O4 91.59(9), O2–Ti1–O3 92.28(10), O1–Ti1–O3
95.76(9), O4–Ti1–O3 166.09(9), O2–Ti1–N1 164.48(9), O1–Ti1–N1
89.78(9).
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Table 1 X-Ray crystallographic data for 1b, 4b–6b
Compound
1b, toluene
4b, benzene
5b, toluene
6b
Lattice
Formula
Formula weight
Triclinic
Triclinic
Monoclinic
C65.17H84.35Cl2N2O4 Ti
1078.56
C2/c
21.794(5)
20.558(3)
15.600(3)
90.00
117.09(3)
90.00
6223(2)
Trigonal
C53H72N2O4Ti
849.03
C55H71Cl2N2O4Ti
942.94
C36H38Cl6N2O4Ti
823.28
¯
¯
¯
Space group
P1
P1
R3c
˚
a/A
12.660(3)
14.159(10)
15.4004(16)
83.58(2)
12.046(4)
13.411(5)
17.802(6)
95.17(3)
25.591(4)
25.591(4)
29.747(6)
90.00
90.00
120.00
16871(5)
18
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
74.622(14)
64.80(5)
2408.4(19)
2
102.22(3)
110.10(3)
2597.8(15)
2
3
˚
V/A
Z
4
T/K
120(2)
0.71073
1.171
0.223
25.00
20221/8412
0.0951
8412/0/554
R1 = 0.0866, wR2 = 0.1717
R1 = 0.0617, wR2 = 0.1506
1.036
150(2)
0.71073
1.205
0.313
25.00
18346/9114
0.1056
9114/0/589
R1 = 0.2158, wR2 = 0.1803
R1 = 0.0918, wR2 = 0.1424
0.988
150(2)
0.71073
1.151
0.269
32.64
30359/10357
0.0677
10357/0/378
R1 = 0.1501, wR2 = 0.1456
R1 = 0.0577, wR2 = 0.1265
0.840
150(2)
0.71073
1.459
0.697
25.18
36190/3371
0.2525
3371/0/224
˚
Radiation (l/A)
r(calcd.),g cm-3
m(Mo-Ka)/mm-1
q max,deg.
Reflection collected/unique
R(int)
Data/restraints/parameters
R indices (all data)
Final R indices I > 2s(I)
GOF
R1 = 0.1305, wR2 = 0.2108
R1 = 0.0741, wR2 = 0.1939
0.959
◦
˚
Table 2 Comparison of bond lengths (A) and bond angles ( ) in the 1b–6b complexes
∠O (aryloxy)–Ti–
Complex Ti–O(iPr) bond
Ti–O (aryloxy) bond Ti–N bond
∠Ti–O(iPr)–C(iPr) ∠O (iPr)–Ti–O (iPr) O (aryloxy)
Reference
1b
2b
3b
4b
5b
6b
1.812(2), 1.792(2) 1.902(2), 1.900(2)
2.373(3), 2.378(2) 133.3(2), 165.2(3)
2.415(4), 2.419(5) 138.3(4), 148.9 (5) 105.07(9)
2.376(3), 2.331(3) 138.9(3), 142.8(3)
2.372(5), 2.395(5) 136.1(4), 157.7(4)
104.86(10)
166.09(9)
166.20(8)
164.16(12)
165.01(16)
168.70 (15)
162.9 (2)
this work
a
1.800(5), 1.818(4) 1.895(4), 1.890(4)
1.798(3), 1.782(3) 1.919(3), 1.916(3)
1.811(4), 1.796(4) 1.903(4), 1.884(4)
b
105.25(14)
106.09 (18)
108.72(15)
106.9(3)
this work
this work
this work
1.823(2)
1.767(4)
1.887(2)
1.909(4)
Ti1–N1 2.401(3)
Ti1–N1 2.354(4)
136.0(2)
158.9(7)
a S. H. Kim, J. Lee, D. J. Kim, J. H. Moon, S. Yoon, H. J. Oh, Y. Do, Y. S. Ko, J. H. Yim and Y. Kim, J. Organomet. Chem, 2009, 694, 3409–3417.
b M. K. Panda, M. M. Shaikh and P. Ghosh, Dalton Trans. 2010, 39, 2428–2440.
Table 3 The MAO: catalyst variation study for precatalyst 1b
Of particular interest are the Ti–O bond lengths in the 1b–
6b complexes that exhibited two different distances consisting
of a shorter Ti–O(isopropoxy) bond [1.767(4)–1.823(2) A] and
S. No
Al(MAO)/Ti
activity/g of PEmol-1Tih-1
˚
˚
a longer Ti–O(phenoxy) bond [1.884(4)–1.919(3) A] (Tables 1–2,
1.
2.
3.
4.
500
4010
Fig. 2–3 and ESI Fig. S1–S2†). The shorter Ti–O(isopropoxy)
bond lengths in 1b–6b can be ascribed to an additional p-type
interaction of an oxygen lone pair of the OiPr moiety with an
empty metal d orbital of titanium, common in many related
titanium isopropoxide complexes observed earlier by us17 as well
as by others.19 Additionally, the wide bond angles of the titanium
bound isopropoxy oxygens [∠ Ti–O–C 133.3(2)◦–165.2(3)◦] in the
1b–6b complexes further testified toward the presence of p-type
interaction between the isopropoxy group and the metal. The
Ti–O(phenoxy) distances of 1.884(4)–1.919(3) A were relatively
longer suggesting lesser degree of the p-type interaction prevalent
between the aryloxy group and titanium and so the Ti–O(phenoxy)
distances were slightly shorter than the sum of the individual
1000
1500
2000
24300
20000
20500
Polymerization conditions: polymerization pressure: 88 2 Psi, tempera-
ture: 30 1 ◦C, time: 3 h.
vation with MAO. In particular, the 1b–6b complexes exhibited
ethylene polymerization activity when treated with methylalumi-
noxane (MAO) in the presence of ethylene at 30 ◦C. The optimal
polymerization conditions were obtained for a representative
precatalyst 1b by varying the precatalyst to MAO mole ratio
from 1 : 500 to 1 : 2000 and which showed that the precatalyst
activity increased from 4.0 Kg of PE mol-1 h-1 to 20.5 Kg of PE
mol-1 h-1 respectively with the maximum activity of 24.3 Kg of PE
mol-1 h-1 observed for the 1 : 1000 ratio (Table 3). Furthermore,
the time dependence study performed with the same representative
precatalyst 1b showed similar increase of activity with time with
the maximum increase seen at 3 h after which it plateaued off
˚
20
˚
covalent radii of Ti and O (1.984 A). The Ti–N distances
[2.331(3)–2.413(2) A] on the other hand resembled elongated
single bond distances as these appeared even longer than the sum
˚
20
˚
of the individual covalent radii of Ti and N (2.024 A).
Significantly enough, all of the isopropoxy 1b–6b complexes
were found to be active for ethylene polymerization upon acti-
11062 | Dalton Trans., 2010, 39, 11060–11068
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(GPC) showed high molecular weight (Mw = ca. 7.2–8.3 ¥ 105 g
mol-1) with broad molecular weight distribution (PDI = ca. 13.1–
14.6) with long tailing in the low and high molecular weight
regions. Similar observation has been made for zirconium(IV)
complexes [(CF3)2C(O)CH2C(R1) = NPh]2ZrCl2 (R1 = Me, Ph,
ArF),21 a titanium(IV) complex, TpMs*TiCl3 and a titanium(III)
complex K[TpMs*TiCl3] {(TpMs* = HB(3-mesitylpyrazolyl) 2(5-
22
mesityl-pyrazolyl)} that also produced insoluble polyethylene
polymers when activated with MAO but for different metal and
ligand systems exhibiting different mechanisms and deactivation
pathways. In this regard, it should be noted that the direct
comparisons of 1b–6b with other systems, however, is difficult
since the polymerization conditions as well as the metal and ligand
systems vary drastically from each other. The observed broad PDI
values of the polymers may arise due to the long activation period
leading to low initiation efficiency in the alkylation step of the
1b–6b complexes by MAO. However, other factors like the change
in Rgrowth/Rtransfer ratio during polymerization as a result of chain-
transfer to MAO,23 or the presence of multiple active species or
even the heterogeneity of the reaction medium arising out of the
precipitation of the polyethylene polymer may also contribute to
the observed broadening of the PDI values.
Fig. 3 ORTEP view of the solid state structure of 4b. The thermal
ellipsoids are shown in 50% probability level. Hydrogen atoms are omitted
◦
˚
for clarity. Selected bond lengths (A) and angles ( ) are given: Ti1–O1
1.903(4), Ti1–O2 1.884(4), Ti1–O3 1.811(4), Ti1–O4 1.796(4), Ti1–N1
2.372(5), Ti1–N2 2.395(5), O4–Ti1–O3 106.09(18), O4–Ti1–O2 97.30(16),
O3–Ti1–O2 92.86(17), O4–Ti1–O1 93.79(17), O4–Ti1–N1 160.92(18),
O3–Ti1–N1 92.29(16), O2–Ti1–N1 86.62(15), O1–Ti1–N1 79.68(16).
An assessment about the degree of crystallinity in the polyethy-
lene polymer was obtained using differential scanning calorimetry
(DSC) studies that showed the polymer melting temperature (Tm)
of 137–139 ◦C and the crystallization temperature (Tc) of 112–
114 ◦C (Table 4) indicating the presence of linear polymer chains
1
with little branching contents. The 13C{ H} NMR analysis of the
(Table 4). Based on the above observations, the 1b–6b complexes,
thus, when activated with 1000 equivalents of methylaluminoxane
(MAO) and subjected to 88 psi of ethylene for 3 h, yielded high
molecular weight polyethylene polymers with broad molecular
weight distributions (Table 5). The most of the polyethylene
polymers were found to be insoluble in the 1,2,4-trichlorobenzene
at 150 ◦C thereby suggesting the formation of very high molec-
ular weight polymers. The polyethylene polymers that could be
analyzed by high temperature gel permeation chromatography
polymer showed no minor peak except for only one strong peak
assignable to the backbone methylene (CH2) resonance suggesting
the formation of linear polymer chains.6h,i
More interestingly so, the methylaluminoxane (MAO) activated
ethylene polymerization of the titanium isopropoxide 1b–6b
precatalysts proceeded via a coordination-insertion pathway by
the elimination of two cis labile isopropoxide groups while the
other possibility of a radical pathway was ruled out based on
EPR studies. Specifically, the EPR analysis of a solution of
a representative precatalyst 2b containing a large excess (226
equivalents) of methylaluminoxane (MAO) in toluene showed no
presence of any radical species, thereby ruling out the radical
pathway (see ESI Fig. S3†). The lack of any reduction of the
diamagnetic d0 Ti(IV) 2b precatalyst to a paramagnetic d1 Ti(III)
radical species in presence of the large excess of the electron rich
methylaluminoxane (MAO) coinitiator can be attributed to the
stabilization of the Ti(IV) 2b precatalyst by the hard N and O
donors of the aryloxy based [N2O2]2- ligand.24
Table 4 Time dependent study of ethylene polymerization by 1b
S. No
Time/h
Activity/g of PEmol-1Tih-1
1
2
3
4
0.5
3
4
0
4010
4600
5000
5
Polymerization conditions: polymerization pressure: 88 2 Psi, tempera-
ture: 30 1 ◦C, Al(MAO)/Ti: 500.
Table 5 Ethylene polymerization by precatalysts 1b–6b activated by methylaluminoxane (MAO)
S. No.
precatalyst
Activity/g of PEmol-1Tih-1
Mw ¥ 10-5/g mol-1
Mw/Mn
13.1
Tm/◦C
Tc/◦C
1
2
3
4
5
6
1b
2b
3b
4b
5b
6b
24300
13400
3400
3660
14600
15100
7.2
138
139
137
139
137
138
113
112
112
114
112
114
insolublea
insolublea
8.3
14.6
insolublea
insolublea
Polymerization conditions: polymerization pressure: 88 2 Psi, temperature: 30 1 ◦C, Al(MAO)/Ti: 1000, time 3 h.a GPC could not be carried out due
to insolubility of polymer in 1,2,4-trichlorobenzene at 150 ◦C.
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The comparison of the 1b–6b precatalysts with other reported
titanium isopropoxy complexes for olefin polymerization is impor-
tant. Although titanium halide complexes have long been studied
for olefin polymerization,25 the reports of titanium isopropoxy
based ones are relatively rare. In this regard we are aware of
only a handful of reports of the titanium isopropoxide based
initiators for the styrene26 and ethylene polymerizations21,27 and the
ethylene-styrene copolymerization.10g Of particular interest are the
[(CF3)2C(O)CH2C(R1) = NPh]2Ti(OiPr)2 (R1 = Me, Ph) complexes,
which when activated with MAO (MAO/Ti = 1100–1500), pro-
duced polyethylene polymers of high molecular weight (Mw = 3.7–
4.3 ¥ 105 g mol-1) having a narrow polydispersity index (PDI) range
of 2.7–4.7,21 and which is only similar to the molecular weight
(Mw = 7.2–8.3 ¥ 105 g mol-1) but different from the broad molecular
weight distribution (PDI = 13.1–14.6) observed for the 1b–6b
precatalysts. Also, another isopropoxy complex, [1-di-R-amino-
contain the supplementary crystallographic data for the palladium
1b, 4b–6b complexes respectively. The data can be obtained free
of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or in the
ESI.† Elemental analysis was carried out on Thermo Quest
FLASH 1112 SERIES (CHNS) Elemental Analyzer.
Synthesis of N,N¢-Bis(2-hydroxo-3-t-butyl-5-
methylphenylmethyl)-N,N¢-dibenzylethylenediamine (1a)
A
solution of N,N¢-dibenzylethane-1,2-diamine (1.50 g,
6.25 mmol), 2-t-butyl-4-methylphenol (2.05 g, 12.5 mmol) and
aqueous formaldehyde (37% w/v, 2.06 g, 25.0 mmol) in methanol
(ca. 20 mL) was refluxed for 24 h. A white precipitate was
formed which was filtered and washed with methanol (ca. 4 ¥
20 mL) and then vacuum dried to obtain product 1a as white
solid (1.50 g, 41%). 1H NMR (CDCl3, 400 MHz, 25 ◦C), d
i
3
3-(3,5-dimethyl-pyrazol-1-yl)-propan-2-olate]2Ti(OiPr)2, (R = Pr,
10.5 (s, 2H, OH), 7.26-7.24 (m, 6H, C6H5), 7.14 (d, 4H, JHH
=
CH2Ph, tBu),28 polymerized ethylene in presence of MAO
(MAO/Ti = 500–1000) giving extremely high molecular weight
(Mw = 1.11–1.50 ¥ 106 g mol-1) polyethylene polymer exhibiting a
modestly broad polydispersity index (PDI = 2.1–6.3).
8 Hz, C6H5), 6.97 (s, 2H, C6H2{2-OH,3-C(CH3)3,5-CH3}), 6.59
(s, 2H, C6H2{2-OH,3-C(CH3)3,5-CH3}), 3.59 (s, 4H, CH2), 3.47
(s, 4H, CH2), 2.63 (s, 4H, CH2), 2.22 (s, 6H, CH3), 1.40 (s,
18H, C(CH3)3). 13C{ H} NMR (CDCl3, 100 MHz, 25 ◦C),
1
d 154.1 (C6H2{2-OH,3-C(CH3)3,5-CH3}), 136.8 (C6H2{2-OH,3-
C(CH3)3,5-CH3}), 136.5 (C6H5), 129.7 (C6H5), 128.7 (C6H5), 127.7
(C6H5), 127.6 (C6H2{2-OH,3-C(CH3)3,5-CH3}), 127.4 (C6H2{2-
OH,3-C(CH3)3,5-CH3}), 126.9 (C6H2{2-OH,3-C(CH3)3,5-CH3}),
121.9 (C6H2{2-OH,3-C(CH3)3,5-CH3}), 58.9 (CH2), 58.3 (CH2),
50.0 (CH2), 34.7 (C(CH3)3), 29.7 (C(CH3)3), 20.8 (CH3). IR Data
(KBr pellet cm-1): 3428 (w), 3066 (w), 3030 (w), 2951 (s), 2905
(s), 2866 (s), 2807 (m), 1885 (w), 1760 (w), 1605 (m), 1481 (s),
1457 (s),1445 (s), 1361 (s), 1304 (m), 1239 (s), 1203 (m), 1165 (m),
1076 (m), 1029 (w), 968(w), 880 (m), 824 (m), 742 (s), 701 (s), 679
(w), 466 (w). HRMS (ES): m/z 593.4097 [(ligand+H)]+, Calcd.
593.4107. Anal. Calcd. for C40H52N2O2: C, 81.04; H, 8.84; N, 4.73.
Found: C, 81.41; H, 9.20; N, 5.13.
Conclusion
In summary, relatively rare titanium isopropoxide based pre-
catalysts, 1b–6b, supported over sterically demanding [N2O2]H2
ligands have been designed for the ethylene polymerization. The
1b–6b complexes when activated with methylaluminoxane (MAO)
produced high molecular weight (Mw) polyethylene polymers
with broad molecular weight distributions. The EPR studies
indicated that the ethylene polymerization by the 1b–6b complexes
proceeded via a coordination-insertion pathway.
Experimental Section
General Procedures
Synthesis of [N,N¢-Bis(2-oxo-3-t-butyl-5-methylphenylmethyl)-
N,N¢-dibenzylethylenediamine]Ti(OiPr)2 (1b)
All manipulations were carried out using standard Schlenk
techniques and glove box. Solvents were purified and de-
gassed by standard procedures. The 2,4-di-t-butylphenol, 2-
t-butyl-4-methylphenol and Ti(OiPr)4 were purchased from
Sigma Aldrich, Germany and used without any further pu-
rification. The 2,4-di-chlorophenol was purchased from Spec-
trochem, India. The N,N¢-di-benzylethylenediamine and N,N¢-
di-p-chlorobenzylethylenediamine were prepared according to
literature procedure.29 The 2a,30 2b,30 3a17 and 3b17 were prepared
To
a
solution of ligand N,N¢-bis(2-hydroxo-3-t-butyl-5-
methylphenylmethyl)-N,N¢-dibenzylethylenediamine 1a (0.153 g,
0.258 mmol) in toluene (ca. 5 mL), a solution of Ti(OiPr)4 (0.147 g,
0.516 mmol) in toluene (ca. 1 mL) was added. The resulting
solution was stirred at 50 ◦C for 4 h after which the volatiles
were removed under reduced pressure. The residue was washed
with hexane (ca. 2 ml) and dried under vacuum to obtain product
1b as a yellow solid (0.168 g, 86%). 1H NMR (CDCl3, 400 MHz,
25 C), d 7.23 (br, 8H, C6H5), 7.16 (t, 2H, JHH = 7 Hz, C6H5),
6.91 (s, 2H, C6H2O{3-C(CH3)3,5-CH3}), 6.43 (s, 2H, C6H2O{3-
C(CH3)3,5-CH3), 4.86 (sept, 2H, 3JHH = 6 Hz, OCH(CH3)2), 4.24
◦
1
1
3
by following a modified literature procedures. H and 13C{ H}
NMR spectra were recorded on a Varian 400 MHz NMR
1
spectrometer. H NMR peaks are labelled as singlet (s), doublet
2
(d), triplet (t) and septet (sept). Infrared spectra were recorded
on a Perkin Elmer Spectrum One FT-IR spectrometer. Mass
spectrometry measurements were done on a Micromass Q-Tof
spectrometer. X-Ray diffraction data were collected on a Bruker
P4 difractometer equipped with a SMART CCD detector. The
crystal data collection and refinement parameters are summarized
in Table 1. The structures were solved using direct methods and
standard difference map techniques and were refined by full-matrix
least-squares procedures on F2 with SHELXTL (version 6.10).31
CCDC 643954, CCDC 709171, CCDC 722297 and CCDC 715915
(d, 2H, JHH = 13 Hz, CH2), 4.15 (s, 4H, CH2), 3.23 (d, 2H,
2JHH = 13 Hz, CH2), 2.86 (d, 2H, JHH = 10 Hz, CH2), 2.29
2
2
(d, 2H, JHH = 10 Hz, CH2), 2.11 (s, 6H, CH3), 1.42 (s, 18H,
3
C(CH3)3), 1.21 (d, 6H, JHH = 6 Hz, OCH(CH3)2), 1.08 (d, 6H,
3JHH = 6 Hz, OCH(CH3)2). 13C{ H} NMR (CDCl3, 100 MHz,
1
25 ◦C), d 159.7 (C6H2O{3-C(CH3)3,5-CH3}), 136.8 (C6H5), 132.7
(C6H5), 129.2 (C6H2O{3-C(CH3)3,5-CH3}), 128.5 (C6H2O{3-
C(CH3)3,5-CH3}), 128.3 (C6H5), 128.2 (C6H2O{3-C(CH3)3,5-
CH3}), 127.4 (C6H5), 125.5 (C6H2O{3-C(CH3)3,5-CH3}), 124.0
(C6H2O{3-C(CH3)3,5-CH3}), 77.8 (OCH(CH3)2), 59.6 (CH2),
11064 | Dalton Trans., 2010, 39, 11060–11068
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59.1 (CH2), 44.9 (CH2), 35.0 (C(CH3)3), 30.5 (C(CH3)3), 26.9
(OCH(CH3)2), 26.6 (OCH(CH3)2), 21.0 (CH3). IR Data (KBr
pellet cm-1): 3432 (m), 3027 (w), 2963 (s), 2922 (m), 2860 (s), 2548
(s), 1776 (w), 1603 (w), 1541 (m), 1467 (s),1439 (s), 1376 (w), 1358
(w), 1293 (m), 1263 (s), 1202 (w), 1157 (s), 1124 (s), 1076 (w), 1056
(w), 1002 (s), 989 (s), 915 (w), 861 (m), 842 (s), 797 (w), 783 (w),
731 (w), 705 (m), 630 (w), 609 (m), 582 (w), 564 (s). Anal. Calcd.
for C46H64N2O4Ti∑C6H5CH3: C, 74.98; H, 8.55; N, 3.30. Found: C,
74.94; H, 8.97; N, 3.18.
d
159.6 (C6H2O{3-C(CH3)3,5-CH3}), 136.8 (C6H4Cl), 134.4
(C6H4Cl), 133.8 (C6H2O{3-C(CH3)3,5-CH3}), 131.0 (C6H2O{3-
C(CH3)3,5-CH3}), 128.5 (C6H4Cl), 128.4 (C6H2O{3-C(CH3)3,5-
CH3}), 127.5 (C6H4Cl), 125.6 (C6H2O{3-C(CH3)3,5-CH3}), 123.7
(C6H2O{3-C(CH3)3,5-CH3}), 77.9 (OCH(CH3)2), 59.6 (CH2),
58.3 (CH2), 44.9 (CH2), 35.0 (C(CH3)3), 30.5 (C(CH3)3), 26.9
(CH(CH3)2), 26.6 (CH(CH3)2), 21.0 (CH3). IR Data (KBr pel-
let cm-1): 2963 (s), 1467 (s), 1262 (s), 1124 (m), 986 (m), 840 (s),
607 (m), 565 (s). Anal. Calcd. for C55H71Cl2N2O4Ti: C, 66.91; H,
7.57; N, 3.39. Found: C, 66.84; H, 7.35; N, 3.09.
Synthesis of N,N¢-bis(2-hydroxo-3-t-butyl-5-methylphenylmethyl)-
N,N¢-bis(p-chlorobenzyl)ethylenediamine (4a)
Synthesis of N,N¢-bis(2-hydroxo-3,5-di-t-butylphenylmethyl)-
N,N¢-bis(p-chlorobenzyl)ethylenediamine (5a)
A solution of N,N¢-di-p-chlorobenzylethylenediamine (0.403 g,
1.31 mmol), 2-t-butyl-4-methylphenol (0.425 g, 2.62 mmol) and
aqueous formaldehyde (37% w/v, 0.432 g, 5.25 mmol) in methanol
(ca. 30 mL) was refluxed for 24 h. A white precipitate was formed
which was filtered and washed with methanol (ca. 4 ¥ 20 mL) and
then vacuum dried to obtain product ◦4a as a white solid (0.358 g,
41%). 1H NMR (CDCl3, 400 MHz, 25 C), d 10.2 (s, 2H, OH), 7.23
(d, 4H, 3JHH = 8 Hz, C6H4Cl), 7.06 (d, 4H, 3JHH = 8 Hz, C6H4Cl),
6.95 (s, 2H, C6H2{2-OH,3-C(CH3)3,5-CH3}), 6.57 (s, 2H, C6H2{2-
OH,3-C(CH3)3,5-CH3}), 3.58 (s, 4H, CH2), 3.42 (s, 4H, CH2),
2.59 (s, 4H, CH2), 2.22 (s, 6H, CH3), 1.38 (s, 18H, C(CH3)3).
A solution of N,N¢-di-p-chlorobenzylethylenediamine (0.603 g,
1.95 mmol), 2,4-di-t-butylphenol (0.804 g, 3.92 mmol) and aque-
ous formaldehyde (37% w/v, 0.652 g, 7.92 mmol) in methanol
(ca. 50 mL) were refluxed for 24 h. A white precipitate formed
which was filtered and washed with methanol (ca. 4 ¥ 20 mL)
and then vacuum dried to obtain product 5a as a white solid
(0.503 g, 36%). H NMR (CDCl3, 400 MHz, 25 ◦C), d 10.2 (s,
1
2H, OH), 7.23 (d, 4H, 3JHH = 8 Hz, C6H4Cl), 7.16 (s, 2H, C6H2{2-
3
OH,3,5-C(CH3)3}), 7.07 (d, 4H, JHH = 8 Hz, C6H4Cl), 6.73 (s,
2H, C6H2{2-OH,3,5-C(CH3)3}), 3.61 (s, 4H, CH2), 3.45 (s, 4H,
CH2), 2.63 (s, 4H, CH2), 1.39 (s, 18H, C(CH3)3), 1.25 (s, 18H,
13C{ H} NMR (CDCl3, 100 MHz, 25 ◦C), d 153.9 (C6H2{2-
1
C(CH3)3). 13C{ H} NMR (CDCl3, 100 MHz, 25 ◦C), d 153.8
1
OH,3-C(CH3)3,5-CH3}), 136.6 (C6H2{2-OH,3-C(CH3)3,5-CH3}),
135.4 (C6H4Cl), 133.6 (C6H2{2-OH,3-C(CH3)3,5-CH3}), 130.9
(C6H4Cl), 128.9 (C6H4Cl), 127.6 (C6H2{2-OH,3-C(CH3)3,5-
CH3}), 127.1 (C6H2{2-OH,3-C(CH3)3,5-CH3}), 127.0 (C6H2{2-
OH,3-C(CH3)3,5-CH3}), 121.7 (C6H4Cl), 59.0 (CH2), 57.8 (CH2),
50.4 (CH2), 34.7 (C(CH3)3), 29.7 (C(CH3)3), 20.9 (CH3). IR Data
(KBr pellet cm-1): 3378 (s), 3049 (w), 3000 (w), 2949 (s), 2913 (w),
2863 (w), 2823 (m), 1755 (s), 1599 (w), 1544 (w), 1493 (s), 1446 (s),
1408 (w), 1390 (w), 1357 (m), 1302 (w), 1240 (s), 1206 (w), 1144
(m), 1091 (m), 1016 (m), 927 (m), 865 (m), 849 (w), 801 (m), 759
(w), 716 (m), 666 (w), 592 (w), 563 (w), 516 (w), 469 (w). HRMS
(ES): m/z 661.3355 [ligand+H]+, Calcd. 661.3328. Anal. Calcd.
for C40H50Cl2N2O2: C, 72.60; H, 7.62; N, 4.23. Found: C, 72.38;
H, 7.75; N, 4.20.
(C6H2{2-OH,3,5-C(CH3)3}), 141.1 (C6H2{2-OH,3,5-C(CH3)3}),
136.0 (C6H4Cl), 135.4 (C6H2(OH){3,5-C(CH3)3}), 133.6 (C6H2{2-
OH,3,5-C(CH3)3}), 130.9 (C6H4Cl), 128.9 (C6H4Cl), 123.8
(C6H2{2-OH,3,5-C(CH3)3}), 123.4 (C6H2{2-OH,3,5-C(CH3)3}),
121.0 (C6H4Cl), 59.4 (CH2), 57.7 (CH2), 50.5 (CH2), 35.0
(C(CH3)3), 34.3 (C(CH3)3), 31.9 (C(CH3)3), 29.8 (C(CH3)3). IR
Data (KBr pellet cm-1): 2951 (s), 2862 (m), 1599 (w), 1480 (s), 1462
(s), 1404 (m), 1364 (m), 1304 (w), 1241 (s), 1205 (w), 1165 (w), 1089
(m), 986 (w), 825 (w). HRMS (ES): m/z 745.4283 [ligand+H]+,
Calcd. 745.4267. Anal. Calcd. for C46H62Cl2N2O2: C, 74.07; H,
8.38; N, 3.76. Found: C, 73.97; H, 8.57; N, 4.08.
Synthesis of [N,N¢-bis(2-oxo-3,5-di-t-butylphenylmethyl)-N,N¢-
bis(p-chlorobenzyl)ethylenediamine]Ti(OiPr)2 (5b)
Synthesis of [N,N¢-bis(2-oxo-3-t-butyl-5-methylphenylmethyl)-
N,N¢-bis(p-chlorobenzyl)ethylenediamine]Ti(OiPr)2 (4b)
To a solution of N,N¢-bis(2-hydroxo-3,5-di-t-butylphenylmethyl)-
N,N¢-bis(p-chlorobenzyl)ethylenediamine
5a
(0.515
g,
To a solution of N,N’-bis(2-hydroxo-3-t-butyl-5-methylphenyl-
methyl)-N,N¢-bis(p-chlorobenzyl)ethylenediamine 4a (0.203 g,
0.307 mmol) in toluene (ca. 5 mL), a solution of Ti(OiPr)4 (0.174 g,
0.614 mmol) in toluene (ca. 2 mL) was added. The resulting
solution was stirred at 50 ◦C for 4 h after which the volatiles
were removed under reduced pressure. The residue was washed
with hexane (ca. 2 mL) and dried under vacuum to obtain product
4b as a yellow solid (0.181 g, 72%). 1H NMR (CDCl3, 400 MHz,
0.690 mmol) in dichloromethane (ca. 10 mL), Ti(OiPr)4
(0.353 g, 1.38 mmol) in dichloromethane (ca. 2 mL) was added.
The resulting solution was stirred for 3 h after which the volatiles
were removed under reduced pressure. The residue was washed
with hexane (ca. 2 mL) and dried under vacuum to obtain
product 5b as yellow solid (0.539 g, 86%). 1H NMR (CDCl3,
◦
3
400 MHz, 25 C), d 7.29 (d, 4H, JHH = 8 Hz, C6H4Cl), 7.21 (s,
3
2H, C6H2O{3,5-C(CH3)3}), 6.94 (d, 4H, JHH = 8 Hz, C6H4Cl),
25 ◦C), d 7.29 (d, 4H, 3JHH = 8 Hz, C6H4Cl), 6.99 (d, 4H, 3JHH
=
6.65 (s, 2H, C6H2O{3,5-C(CH3)3}), 4.94 (sept, 2H, JHH = 6 Hz,
3
2
7 Hz, C6H4Cl), 6.96 (s, 2H, C6H2O{3-C(CH3)3,5-CH3}), 6.51 (s,
OCH(CH3)2), 4.22 (d, 2H, JHH = 13 Hz, CH2), 4.19 (s, 4H,
3
2
3
2H, C6H2O{3-C(CH3)3,5-CH3}), 4.92 (sept, 2H, JHH = 6 Hz,
CH2), 3.26 (d, 2H, JHH = 13 Hz, CH2), 2.72 (d, 2H, JHH =
3
OCH(CH3)2), 4.28 (d, 2H, 2JHH = 13 Hz, CH2), 4.18 (s, 4H, CH2),
10 Hz, CH2), 2.35 (d, 2H, JHH = 10 Hz, CH2), 1.49 (s, 18H,
2
3
3
3.25 (d, 2H, JHH = 13 Hz, CH2), 2.90 (d, 2H, JHH = 10 Hz,
CH2), 2.30 (d, 2H, 3JHH = 10 Hz, CH2), 2.19 (s, 6H, CH3), 1.48 (s,
18H, C(CH3)3), 1.26 (d, 3H, 3JHH = 6 Hz, CH(CH3)2), 1.21 (d,◦3H,
C(CH3)3), 1.25 (s, 18H, C(CH3)3), 1.21 (d, 6H, JHH = 6 Hz,
CH(CH3)2), 1.13 (d, 6H, JHH = 6 Hz, CH(CH3)2). 13C{ H}
NMR (C6D6, 100 MHz, 25 ◦C), d 160.0 (C6H2O{3,5-C(CH3)3}),
139.9 (C6H4Cl), 136.7 (C6H2O{3,5-C(CH3)3}), 134.7 (C6H2O{3,
3
1
1
3JHH = 6 Hz, CH(CH3)2. 13C{ H} NMR (CDCl3, 100 MHz, 25 C),
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1461 (s), 1374 (w), 1312 (w), 1217 (w), 1124 (m), 1016 (m),
866 (m), 780 (w), 608 (m), 540 (w), 486 (w). Anal. Calcd. for
C36H38Cl6N2O4Ti∑CH2Cl2: C, 48.93; H, 4.44; N, 3.08. Found: C,
48.77; H, 4.31; N, 2.90.
5-C(CH3)3}), 134.0 (C6H4Cl), 131.1 (C6H4Cl), 128.9 (C6H4Cl),
124.9 (C6H2O{3,5-C(CH3)3}), 124.4 (C6H2O{3,5-C(CH3)3}),
123.8 (C6H2O{3,5-C(CH3)3}), 78.2 (OCH(CH3)2), 60.8 (CH2),
59.0 (CH2), 45.6 (CH2), 35.8 (C(CH3)3), 34.5 (C(CH3)3), 32.1
(C(CH3)3), 31.0 (C(CH3)3), 27.2 (CH(CH3)2), 26.9 (CH(CH3)2).
IR Data (KBr pellet cm-1): 2962 (s), 1597 (w), 1471 (s), 1360 (w),
1276 (m), 1203 (w), 1125 (s), 988 (m), 846 (s), 811 (m), 749 (w), 609
(m), 553 (s), 472 (m). Anal. Calcd. for C52H74Cl2N2O4Ti·CH2Cl2:
C, 63.99; H, 7.70; N, 2.82. Found : C, 63.22; H, 7.89; N, 2.23.
Ethylene polymerization
A mechanically stirred stainless steel 400 ml autoclave was heated
under vacuum for at least 1 h at 120 ◦C and cooled to room
temperature prior to being charged with 150 ml toluene, MAO,
and the 1b–6b catalyst precursor. After addition of required
amount of MAO and precursor, the reaction mixture was heated
Synthesis of N,N¢-bis(2-hydroxo-3,5-di-chlorophenylmethyl)-
N,N¢-bis(p-chlorobenzyl)ethylenediamine (6a)
to 30
1
◦C; ethylene was introduced to a pressure of 88 psi.
The reactor pressure was maintained at 88 2 psi throughout the
polymerization. At the end of the polymerization, the unreacted
ethylene was vented and the reaction quenched with acidified
methanol. After filtration, the polymer was washed with methanol,
and then dried at 60 ◦C under vacuum to constant weight.
Melting points of polyethylene were determined by differen-
tial scanning calorimetry (DSC) using a Perkin-Elmer DSC-7
A solution of N,N¢-di-p-chlorobenzylethylenediamine (0.503 g,
1.62 mmol), 2,4-di-chlorophenol (0.530 g, 3.25 mmol) and aque-
ous formaldehyde (37% w/v, 0.535 g, 6.50 mmol) in methanol
(ca. 30 mL) was refluxed for 24 h. A white precipitate formed
which was filtered and washed with methanol (ca. 6 ¥ 20 mL)
and then vacuum dried to obtain product 6a as a white solid
(0.613 g, 57%). 1H NMR (CDCl3, 400 MHz, 25 ◦C), d 11.0
◦
calorimeter operating at the rate of 10 C min-1. For polymer
3
(s, 2H, OH), 7.34 (d, 4H, JHH = 8 Hz, C6H4Cl), 7.26 (d, 2H,
molecular weights, gel permeation chromatography (GPC) was
performed on a Polymer Laboratories PL-GPC220 High Temper-
ature Chromatograph instrument (columns: 3 ¥ PLgel Mixed-B
10 mm) with two detectors (viscometer and refractometer) in 1,2,4
- trichlorobenzene at flow rate of 1 mL min-1 at 160 ◦C. The
system was calibrated with polystyrene standards using universal
calibration. The NMR spectra were recorded on a Bruker Avance-
400 spectrometer in 50% (v/v) 1,2,4-trichlorobenzene and d2-
tetrachloroethane solution with 10% (w/v) at frequencies of
100 MHz for 13C. A delay time of 2 s was given for recording
3
4JHH = 2 Hz, C6H2{2-OH,3,5-Cl2}), 7.07 (d, 4H, JHH = 8 Hz,
C6H4Cl), 6.79 (d, 2H, 4JHH = 2 Hz, C6H2{2-OH,3,5-Cl2}), 3.62 (s,
1
4H, CH2), 3.49 (s, 4H, CH2), 2.60 (s, 4H, CH2). 13C{ H} NMR
(CDCl3, 100 MHz, 25 ◦C), d 152.1 (C6H2{2-OH,3,5-Cl2}), 134.4
(C6H4Cl), 133.8 (C6H2{2-OH,3,5-Cl2}), 130.8 (C6H4Cl), 129.3
(C6H4Cl), 127.1 (C6H2{2-OH,3,5-Cl2}), 127.0 (C6H2{2-OH,3,5-
Cl2}), 124.3 (C6H2{2-OH,3,5-Cl2}), 123.5 (C6H2{2-OH,3,5-Cl2}),
121.9 (C6H4Cl), 58.5 (CH2), 58.1 (CH2), 50.4 (CH2). IR Data
(KBr pellet cm-1): 2955 (w), 2842 (w), 1598 (w), 1455 (s), 1387
(m), 1237 (w), 1171 (m), 1089 (m), 1015 (w), 970 (w), 863 (m),
803 (m), 731 (m). HRMS (ES): m/z 657.0208 [ligand+H]+, Calcd.
657.0204. Anal. Calcd. for C30H26Cl6N2O2: C, 54.66; H, 3.98; N,
4.25. Found: C, 54.12; H, 3.62; N, 4.43.
1
13C{ H} NMR spectra.
ESR experiment for detecting Ti(III) radical species in the catalytic
cycle
Synthesis of [N,N¢-bis(2-oxo-3,5-di-chlorophenylmethyl)-N,N¢-
bis(p-chlorobenzyl)ethylenediamine]Ti(OiPr)2 (6b)
In order to rule out the involvement of Ti(III) radical in the
catalytic cycle we recorded an ESR spectrum of representative
titanium precatalyst 2b after activating with methylaluminoxane
MAO. Specifically, in a typical experiment, MAO (300 mL,
4.52 mmol) was added to a solution of 2b (0.015 g, 0.018 mmol) in
toluene (ca. 2 mL) and the ESR spectrum of the resulting solution
was recorded at 77 K. However, as no signal corresponding to
the radical Ti(III) species was observed, the possibility of a radical
pathway for the ethylene polymerization was thus ruled out.
To a solution of N,N¢-bis(2-hydroxo-3,5-di-chlorophenylmethyl)-
N,N¢-bis(p-chlorobenzyl)ethylenediamine
6a
(0.256
g,
0.388 mmol) in dichloromethane (ca. 10 mL), Ti(OiPr)4
(0.220 g, 0.775 mmol) in dichloromethane (ca. 2 mL) was added.
The resulting solution was stirred for 3 h after which the volatiles
were removed under reduced pressure. The residue was washed
with hexane (ca. 2 mL) and dried under vacuum to obtain
product 6b as yellow solid (0.248 g, 78%). 1H NMR (CDCl3,
◦
3
Acknowledgements
400 MHz, 25 C), d 7.34 (d, 4H, JHH = 8 Hz, C6H4Cl), 7.26 (s,
2H, C6H2O{3,5-Cl2}), 7.06 (d, 4H, 3JHH = 8 Hz, C6H4Cl), 6.84 (s,
2H, C6H2O{3,5-Cl2}), 5.15 (sept, 2H, 3JHH = 6 Hz, OCH(CH3)2),
4.26 (d, 2H, 2JHH = 14 Hz, CH2), 4.23 (s, 4H, CH2), 3.39 (d, 2H,
2JHH = 14 Hz, CH2), 2.64 (d, 2H, 3JHH = 10 Hz, CH2), 2.36 (d, 2H,
3JHH = 10 Hz, CH2), 1.31 (d, 6H, 3JHH = 6 Hz, CH(CH3)2), 1.28 (d,
We thank Reliance Industries Limited for financial support of
this research. We are grateful to the National Single Crystal
X-ray Diffraction Facility and Sophisticated Analytical Instru-
ment Facility (SAIF) at IIT Bombay, India, for the crystallo-
graphic and other characterization data. MP thanks CSIR, New
Delhi, and RR thanks Reliance Industries Limited for research
fellowships.
1
6H, 3JHH = 6 Hz, CH(CH3)2). 13C{ H} NMR (CDCl3, 100 MHz,
25 ◦C), d 158.1 (C6H2O{3,5-Cl2}), 134.8 (C6H2O{3,5-Cl2}), 133.6
(C6H4Cl), 130.7 (C6H4Cl), 129.5 (C6H4Cl), 128.8 (C6H4Cl), 128.2
(C6H2O{3,5-Cl2}), 126.4 (C6H2O{3,5-Cl2}), 122.6 (C6H2O{3,5-
Cl2}), 121.5 (C6H2O{3,5-Cl2}), 80.1 (OCH(CH3)2), 58.8 (CH2),
57.1 (CH2), 48.6 (CH2), 26.1 (CH(CH3)2), 25.9 (CH(CH3)2).
IR Data (KBr pellet cm-1): 3436 (m), 2967 (m), 2859 (w),
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