Zirconium and hafnium Salalen complexes in isospecific polymerisation of propylene

Article abstract of DOI:10.1039/c3dt00024a

The activity of dibenzylzirconium and dibenzylhafnium Salalen complexes in polymerisation of propylene with MAO as a cocatalyst is described. Three Salalen ligand precursors combining a bulky alkyl group (1-adamantyl) on the imine-side phenol and electron withdrawing halo groups of different sizes on the amine-side phenol were explored. All metal complexes were obtained as single diastereomers. An X-ray crystallographic structure of a hafnium complex of an additional ligand carrying the combination of tert-butyl and chloro substituted phenolates, 4-Hf, revealed a fac-mer wrapping of the Salalen ligand around the metal centre. All complexes led to active catalysts in propylene polymerisation and to isotactic polypropylene of high regioregularity. The zirconium complexes led to polypropylene having molecular weights of M_w = 132000-200000 and isotacticities of [mmmm] = 65.7-75.0%. The hafnium complexes led to polypropylene of higher molecular weights of M_w = 375000-520000 and higher stereoregularities of [mmmm] = 80.6-89.3%, the highest isotacticity obtained with 3-Hf.

Full text of DOI:10.1039/c3dt00024a

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Zirconium and hafnium Salalen complexes in
isospecific polymerisation of propylene†
Cite this: Dalton Trans., 2013, 42, 9096
Konstantin Press,a Vincenzo Venditto,b Israel Goldberga and Moshe Kol*a
The activity of dibenzylzirconium and dibenzylhafnium Salalen complexes in polymerisation of propylene
with MAO as a cocatalyst is described. Three Salalen ligand precursors combining a bulky alkyl group
(1-adamantyl) on the imine-side phenol and electron withdrawing halo groups of different sizes on the
amine-side phenol were explored. All metal complexes were obtained as single diastereomers. An X-ray
crystallographic structure of a hafnium complex of an additional ligand carrying the combination of tert-
butyl and chloro substituted phenolates, 4-Hf, revealed a fac–mer wrapping of the Salalen ligand around
the metal centre. All complexes led to active catalysts in propylene polymerisation and to isotactic poly-
propylene of high regioregularity. The zirconium complexes led to polypropylene having molecular
weights of Mw = 132 000–200 000 and isotacticities of [mmmm] = 65.7–75.0%. The hafnium complexes
led to polypropylene of higher molecular weights of Mw = 375 000–520 000 and higher stereoregulari-
ties of [mmmm] = 80.6–89.3%, the highest isotacticity obtained with 3-Hf.
Received 3rd January 2013,
Accepted 19th February 2013
DOI: 10.1039/c3dt00024a
www.rsc.org/dalton
Salans–{ONNO}-type diamine-diphenolate ligands featuring
Introduction
sp3 amine donors were first introduced in the year 2000.3 They
Octahedral complexes of group 4 metals have emerged as ver- were shown to wrap around group 4 metals in a fac–fac
satile non-metallocene catalysts for polymerisation of alpha mode,12,13 and their dibenzylzirconium complexes polymer-
olefins.1 Such catalysts typically include two labile monoden- ized 1-hexene upon activation with tris(pentafluorophenyl)-
tate groups of cis geometrical relationship, and a chelating borane. The presence of bulky substituents such as tert-butyl
ligand or ligands2 that control the electronic and steric in the ortho positions of the phenolate rings was found to be
environments thereby affecting the activity of the catalyst and crucial for high isoselectivity induction. Lower polymer iso-
the characteristics of the resulting polymer including its mole- tacticity was found when the same catalysts were employed in
cular weight and type and degree of stereoregularity. Among propylene polymerisation.14 Increasing the size of the ortho-
the ligand systems developed, the sequential tetradentate di- substituent from tert-butyl to 1-adamantyl led to polypropylene
anionic ligands of the {ODDO}-type, in which D represents a of higher tacticity,15 however, the activity of these catalysts was
neutral nitrogen,3,4 sulfur,5–7 phosphorus,8 or oxygen9 donor low.16 Higher activity catalysts were obtained with halo-substi-
atom and O represents a phenolate or alcoholate10 anionic tuted phenolates, however, their tacticity induction was not
donor, have emerged as particularly promising. The sequential high.17 Salan ligands featuring identical substituents on the
array of donors may lead to three wrapping modes of the two phenolate rings lead to complexes of C2-symmetry in
ligand around the metal: fac–fac (cis-α), fac–mer (cis-β) and which the two labile positions are homotopic, as schematically
mer–mer (trans), only the first two of which are suitable for represented in the quadrant description (Fig. 1, left).18 Aiming
polymerisation catalysis.11 The highly diastereoselective wrap- at catalysts that would combine high activities and isoselecti-
ping mode and the control of possible dynamic behavior are vities, we introduced the non-symmetric Salans that include a
crucial elements of ligand design.
bulky-alkyl substituted phenolate and a halo substituted
phenolate.19,20 These were also found to wrap in the fac–fac
mode, but their complexes were C1-symmetric (Fig. 1, middle).
It was found that averaging of the steric environments of the
two quadrants led to polymers of average tacticities. Trying to
overcome this averaging phenomenon, tetradentate-dianionic
ligands that wrap in a non-symmetric mode were sought.
Salalen ligands are tetradentate dianionic {ONNO}-type
ligands first introduced in 2004.21 As their name implies, they
are hybrids of Salan and Salen ligands featuring an sp3 amine
aThe School of Chemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
E-mail: moshekol@post.tau.ac.il; Fax: +972 3 6409293; Tel: +972 3 6407392
bDipartimento di Chimica, Università di Salerno, Via Ponte don Melillo, I-84084
Fisciano, Italy
†Electronic supplementary information (ESI) available: 13C NMR spectra of all
the polypropylene samples. A crystallographic cif file of 4-Hf. CCDC 917774. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt00024a
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Fig. 1 Schematic representation of quadrant occupancy formed by a fac–fac wrapping symmetric Salan ligand (left), a fac–fac wrapping non-symmetric Salan
ligand (middle), and a fac–mer wrapping Salalen ligand (right). Light spheres represent bulky alkyl groups; dark spheres represent halo groups. The monomer
approaches the centrally located metal in a horizontal fashion.
donor and an sp2 imine donor. Their coordination tendency halo groups in the ortho and para positions of the amine-side
around octahedral group 4 metal centres was found to reflect phenol.23 For those titanium complexes, the nature of the
the tendencies of their parent symmetric ligands: the {ONN} bulky alkyl substituent was found to play a significant role,
donor array around the amine donor tends to bind in a facial with the 1-adamantyl unit showing a higher stereodirecting
mode and the {ONN} donor array around the imine donor ability than the tert-butyl substituent. The nature of the halo
tends to bind in a meridional mode giving an altogether non- phenolate substituent, on the other hand, was found to play a
symmetric fac–mer wrapping.22 The two labile positions in less significant role. The three Salalen ligand precursors
these C1-symmetric octahedral complexes are cis-related, and Lig1–3H2 chosen for the current study in propylene polymeri-
reside in different steric environments, since the ligand wrap- sation catalysis by zirconium and hafnium complexes are out-
ping mode leads to inclusion of the substituents of the two lined in Scheme 1. All ligand precursors include the bulky
phenolate rings in a single quadrant (Fig. 1, right). Moreover, 1-adamantyl group in the ortho position of the imine-side
since one of these positions is trans to an anionic phenoxy phenol, and electron withdrawing halo groups of different
donor having a strong trans influence and the other position is sizes (Cl, Br, I) on the amine-side phenol, respectively. The
trans to the neutral imine donor having a less pronounced syntheses of Lig1H2 and Lig2H2 have not been described
trans influence, there is also a difference in their electronic before while Lig3H2 was previously described in regard to tita-
character. Recently, we developed a two-step synthesis that nium coordination and polymerisation catalysis. In addition,
affords Salalen ligand precursors of different skeletons and the previously described Lig4H2 including tert-butyl and Cl
substitution patterns. We have found that dibenzyltitanium substituents on the imine-side and the amine side phenols,
complexes of Salalen ligands led to active polymerisation cata- respectively, was employed for crystallographic characterisation
lysts of 1-hexene and propylene following activation with MAO. (vide infra). All ligand precursors were prepared in high to
The presence of a bulky substituent in the ortho position of quantitative yields via a two-step condensation and substi-
the imine side phenol and halo groups on the amine side tution synthesis starting from N-methyl-diaminoethane.
phenol was found to lead to highly isotactic polypropylene,
Zirconium and hafnium Salalen complexes
169.9 °C were Reacting the ligand precursors Lig1–3H2 with ZrBn4 and HfBn4
and for certain ligands, an ultra-high isotacticity of [mmmm] ≥
99.6% and the corresponding Tm
=
recorded.23–25 Aiming at further exploring the performance of led to the corresponding [(Salalen)MBn2] complexes 1-Zr, 2-Zr,
Salalen complexes and revealing structure–activity relation- 3-Zr, 1-Hf, 2-Hf, and 3-Hf, respectively, in high yields with
ships, we describe herein, for the first time, the synthesis and
activity in polymerisation catalysis of dibenzylzirconium and
dibenzylhafnium Salalen complexes.
Results and discussion
Design and synthesis of the Salalen ligand precursors
Our previous study on α-olefin polymerisation with Salalen
complexes of titanium revealed that a successful combination
of ligand substituents includes a bulky alkyl group in the ortho
position of the imine-side phenol, and electron withdrawing Scheme 1 Synthesis of ligand precursors employed in polymerisation catalysis.
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Scheme 2 Synthesis of dibenzylzirconium and dibenzylhafnium complexes.
elimination of toluene (Scheme 2, top). Significantly, all com-
plexes were obtained as single diastereomers of C1-symmetry,
as evident from their spectroscopic characterisation. The ten-
dency of the amine donor to orient its two neighboring donors
to form a fac-array of three donors, and that of the imine
donor to be a part of a mer-array of three donors26 should
promote an overall fac–mer ligand wrapping around the metal
centre. However, the non-symmetry of the Salalen skeleton
gives rise to C1-symmetric octahedral complexes irrespective of
the specific wrapping. To gain further evidence on the Salalen
ligand wrapping tendencies, we synthesized the hafnium
complex [Lig4Hf(OtBu)2] (4-Hf) by reacting the ligand precur-
sor Lig4H2 with Hf(OtBu)4 (Scheme 2, bottom). Single crystals
of 4-Hf suitable for X-ray crystallographic analysis were grown
from cold pentane and the structure was solved.‡ The structure
reveals a monomeric octahedral hafnium complex in which
the Salalen ligand wraps in the predicted fac–mer mode
around the hafnium centre, leading to a cis-geometrical
relationship between the two monodentate alkoxo groups. The
molecular structure and selected bond lengths and angles are
outlined in Fig. 2. The structure closely resembles that of the
titanium complex [Lig3Ti(OiPr)2]23 with the exception of longer
bond lengths for the hafnium. A longer amine–Hf bond rela-
tive to the imine–Hf bond is in line with those typically found
for the parent Salan and Salen ligands, respectively. A relatively
narrow angle of 151.16(12)° for the trans situated amine and
phenolate donors possibly results from the longer covalent
radius of hafnium relative to titanium for which an angle of
156.38(9)° was found. The bond length between the hafnium
and the tert-butoxo group trans to the phenoxy group (1.954(3)
Å) is slightly longer than that trans to the imine group (1.936(3)
Å) consistently with the bond lengths found for [Lig3Ti-
(OiPr)2]. The longer bond length corresponds to weaker
binding, possibly due to a stronger trans influence. The broad
Fig. 2 ORTEP representation of 4-Hf. Selected bond lengths (Å) and angles (°):
Hf–O(4) 1.936(3), Hf–O(3) 1.954(3), Hf–O(2) 2.003(3), Hf–O(5) 2.117(3), Hf–N(7)
2.307(3), Hf–N(6) 2.414(4), O(2)–Hf–N(6) 151.16(12), O(3)–Hf–O(4) 98.72(12).
angle of 98.72(12)° between the two tert-butoxo groups sig-
nifies a relatively open space for polymeryl growth and
monomer approach. We propose that all the dibenzylzirco-
nium and dibenzylhafnium complexes described herein share
this fac–mer Salalen ligand wrapping around the metal centre.
Propylene polymerisation
The three dibenzylzirconium and three dibenzylhafnium com-
plexes of the Salalen ligands were employed in propylene poly-
merisation with 500 equiv. of dried MAO as a cocatalyst. Neat
liquid propylene was employed in all cases, by cryogenically
condensing gaseous propylene in a stainless steel reactor pre-
charged with the precatalyst and the cocatalyst, sealing the
reactor and allowing it to warm to RT. The polymerisations
were allowed to proceed for ca. 14 hours, following which the
excess propylene was released and the polymer was worked up
and characterized as described in the Experimental section.
The polymerisation results are summarized in Table 1.
All the zirconium and hafnium complexes were found to be
active catalysts for polymerisation of propylene. While this
polymerisation setup does not enable calculation of catalyst
activity, it is noteworthy that, in all the polymerisation runs,
most of the propylene had reacted, forming insoluble polypro-
pylene as the only product. The molecular weights of the poly-
mers ranged between 110 < Mw < 200 kD for the zirconium
and 375 < Mw < 520 kD for hafnium. Consistently with their
high molecular weights, no chain ends could be detected in
the 1H NMR spectra of the polymer samples. The higher mole-
cular weights for hafnium relative to zirconium are in accord-
ance with general trends regarding these metals.16,17 The
molecular weight distributions are around 2.0 for several poly-
merisations and higher for others, possibly reflecting the slow
catalyst dissolution at the early stages of the polymerisation,
‡Crystal data for complex 4-Hf: C33H50Cl2O4N2Hf; M = 788.14; triclinic; space
ˉ
group P1; a = 11.09040(10) Å, b = 13.4696(2) Å, c = 13.6674(2) Å, α = 114.1734(5)°,
β = 105.5292(6)°, γ = 92.2735(11)°, V = 1768.57(4) Å3; T = 110(2) K; Z = 2; Dc
=
1.480 g cm−3; μ (Mo Kα) = 3.137 mm−1; R1 = 0.0408 and wR2 = 0.0965 for 7322
reflections with I > 2σ(I); R1 = 0.0503 and wR2 = 0.1026 for all 8349 unique
reflections.
9098 | Dalton Trans., 2013, 42, 9096–9103
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Table 1 Summary of propylene polymerisation resultsa
Catalyst
Monomer (g)
Polymer (g)
Tm b (°C)
ΔHb (J g−1
)
Mw
Mw/Mn
[mmmm]
1-Zr
2-Zr
3-Zr
1-Hf
2-Hf
3-Hf
8.26
9.03
7.87
7.73
7.67
9.91
7.86
6.67
5.51
6.05
7.06
9.21
100
112
120.6
136.6
142.4
145.5
30
50
48.5
68.7
83.3
98.1
132 000
113 000
200 000
520 000
375 000
405 000
4.72
3.13
2.15
2.94
2.08
2.16
65.7
70.3
75.0
80.6
86.1
89.3
a Polymerisations of liquid propylene employing 10 μmol of dibenzylmetal complex and 500 equiv. of MAO run for 14 h. b Melting transition and
heat of fusion from DSC.
Fig. 3 13C NMR of polypropylene prepared with 1-Zr, [mmmm] = 65.7% (left), and with 3-Hf, [mmmm] = 89.3% (right), and the corresponding quadrant represen-
tations of the complexes.
and the precipitation of the polymer from the liquid pentad (which is typical of the mmrm and the rmrr
propylene.
pentads)31–33 with an intensity of 0.5%. An mmrm pentad is
All polymer samples were obtained as crystalline solids con- consistent with a stereoblock-isotactic microstructure that may
sistently with their high molecular weights and their isotacti- result either from a fluxional catalyst6,34,35 or from a shuttling
city.27 13C NMR characterisation of the polymer samples at of the polymeryl chains36 (e.g., by traces of trialkylaluminum
high temperatures revealed that they were all isotactic as indi- in the MAO) between catalyst enantiomers. This phenomenon
cated by the dominance of the mmmm pentad. A clear 2 : 2 : 1 is currently under investigation. Based on previous findings of
ratio for the [mmmr], [mmrr], and [mrrm] pentads is indicative Salan and Salalen ligands, we propose a highly regular 1,2-
of the enantiomorphic site control mechanism of isotacticity.28 insertion by the current catalysts. For the polypropylene
Two clear trends emerge from the data in Table 1: (a) a gradual sample prepared with 3-Hf,
a slight regioirregularity is
increase in isotacticity is found as the size of the ortho halo observed in the form of 2,1-misinsertion peaks with intensities
phenolate substituent increases from chloro through bromo to of ca. 0.2%.37,38
iodo. This gradual increase occurs both for the zirconium and
In comparison, the titanium catalysts of Salalen ligands fea-
the hafnium catalysts. (b) Higher tacticities are observed for turing bulky substituents on the imine-side phenolate and
the hafnium series of catalysts ([mmmm] = 80.6–89.3%) than halo substituents on the amine-side phenolate led to regio-
for the zirconium series of catalysts ([mmmm] = 65.7–75.0%). error-free polypropylene of higher isotacticities, and the only
For representative 13C NMR spectra, see Fig. 3.
observable stereoerrors were the mmmr, mmrr, and mrrm
A higher isotacticity for hafnium vs. zirconium catalysts peaks.23 For example, [Lig3TiBn2] yielded high molecular-
bound to the same ligands is a familiar phenomenon,16,17 weight highly isotactic polypropylene with [mmmm] ≥ 99% and
albeit the similarity in size of these two metals.29,30 The a corresponding Tm of 164 °C. In contrast to the current zirco-
melting transitions and the high heats of fusion closely match nium and hafnium catalysts for which the increase in halo
the degrees of isotacticity for these relatively high molecular substituent size resulted in increase in polymer isotacticity,
weight polypropylene samples, and the highest Tm of 145.5 °C the isotacticity induced by the titanium catalysts was almost
and heat of fusion of ΔH = 98.1 (J g−1) were obtained for the independent of the nature of the halo-group. This difference
sample having the highest degree of isotacticity of [mmmm] = might be related to the difference in size of these metals: For
89.3%. A close inspection of the 13C NMR spectra of the poly- the larger zirconium and hafnium, a summation of a bulky
propylene samples prepared by the hafnium complexes reveals alkyl group and a bulky halo group may better occupy a given
the presence of another peak at 0.17 ppm upfield of the mmrr large quadrant and assist in orienting a bound polymeryl
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group and an approaching monomer. For the smaller tita- as received. Polymerisation grade propylene purchased from
nium, the bulky alkyl group may already occupy most of the Maxima was used as received. Tetrabenzylzirconium was
volume of that smaller quadrant, so the added volume of the synthesized according to a published procedure.39 2-(Bromo-
halo group would only play a minor role.
methyl)-4,6-dichlorophenol, 2-(bromomethyl)-4,6-dibromophe-
It is also instructional to compare the current Salalen cata- nol,23 2-(bromomethyl)-4,6-diiodophenol,17 2-(((methylamino)-
lysts with the corresponding catalysts of the non-symmetric ethylimino)methyl)-4-methyl-6-adamantylphenol, and the
Salan ligands which wrap around the metal in a fac–fac mode ligand precursors Lig3H2 and Lig4H2 were synthesized accord-
leading to opposite quadrant occupancy (Fig. 1, middle) and ing to published procedures.23 Solid methylaluminoxane
for which an average isoselective induction was observed.19 (MAO) was obtained by solvent removal from a 10 wt% solu-
Very recently, we described the polymerisation of propylene by tion in toluene purchased from Aldrich. NMR data for the
such zirconium catalysts.20 All catalysts yielded polypropylene intermediate organic compounds, ligand precursors, and
of very low molecular weight. A zirconium complex featuring a metal complexes were recorded on a Bruker AC-400 spec-
Salan ligand combining an adamantyl-phenolate and a chloro- trometer. C6D6 was employed as a solvent for the metal com-
phenolate yielded polypropylene with a low degree of isotacti- plexes (protio impurities in benzene-d6 at δ 7.15 and 13C
city of [mmmm] = 44%, and a zirconium complex featuring a chemical shift of benzene at δ 128.70 were used as reference).
Salan ligand combining an adamantyl-phenolate and an iodo- CDCl3 was used as a solvent for the other samples (chemical
phenolate yielded polypropylene with a higher degree of isotac- shift of TMS at δ 0.00, and 13C NMR chemical shift of the
ticity of [mmmm] = 74%. Notably, the zirconium Salalen com- solvent at δ 77.16 were used as reference). X-ray diffraction
plexes featuring the same combinations of phenolate measurements for complex 4-Hf were performed using a
substituents described herein lead to polymers of significantly Nonius Kappa CCD diffractometer system, using MoKα (λ =
higher molecular weights and higher isotacticities. Thus, the 0.7107 Å) radiation. The analyzed crystal grown from a pentane
fac–mer ligand wrapping appears to be a successful design solution at −35 °C was embedded within a drop of viscous oil
motif for isoselective catalysts.
and freeze-cooled to ca. 110 K. The structure was solved by a
combination of direct methods and Fourier techniques using
SIR-9740 software, and was refined by full-matrix least squares
with SHELXL-97.41 Elemental analyses were performed in the
microanalytical laboratory in the Hebrew University of
Conclusions
The Salalen ligands introduced in this work which combine an Jerusalem.
adamantyl substituted phenolate and ortho, para-halo substi-
tuted phenolate were found to wrap in a diastereoselective fac–
mer manner around octahedral zirconium and hafnium
Synthesis of ligands and metal complexes
Synthesis of the ligand precursor Lig1H2. A solution of
centres. All complexes led to active catalysts for propylene poly- 2-(bromomethyl)-4,6-dichlorophenol (0.60 g, 2.3 mmol) in THF
merisation upon activation with MAO yielding polypropylene (20 mL) was added dropwise to a solution of 2-(((methylamino)-
featuring a degree of isotacticity which depended both on the ethylimino)methyl)-4-methyl-6-adamantylphenol
(0.77
g,
metal and on the size of the halo group. The degree of 2.3 mmol) and triethylamine (3 mL) in THF (20 mL) and
induced tacticity was lower than that achieved with the corres- stirred for 2 h. The solid that formed was filtered out and the
ponding complexes of titanium, but higher than that solvent was removed under vacuum. The crude product was re-
achieved with the corresponding Salan complexes featuring crystallized from cold methanol yielding the ligand precursor
1
identical phenolate substituents. This work gives further Lig1H2 as a bright yellow solid quantitatively. H NMR (CDCl3,
support for the success of the non-symmetric fac–mer ligand 400 MHz): δ = 8.33 (s, 1H, NCH), 7.24 (d, 1H, J = 1.5 Hz, ArH),
wrapping as a structural motif in stereoselective catalyst 7.08 (d, 1H, J = 2.5 Hz, ArH), 6.89 (d, 1H, J = 1.5 Hz, ArH), 6.86
design. The search for other systems exhibiting high isoselec- (d, 1H, J = 1.5 Hz, ArH), 3.77 (t, 2H, J = 6.9 Hz, NCH2), 3.76 (s,
tivity is currently underway.
2H, ArCH2N), 2.89 (t, 2H, J = 6.9 Hz, NCH2), 2.40 (s, 3H,
NCH3), 2.27 (s, 3H, ArCH3), 2.16 (bs, 6H, adamantyl), 2.07 (bs,
3H, adamantyl), 1.78 (m, 6H, adamantyl). 13C NMR (CDCl3,
100.67 MHz): δ = 167.4 (CN), 158.6 (CO), 157.9 (CO), 137.4
(CH), 130.9 (C), 129.6 (CH), 128.8 (CH), 126.9 (CH), 126.6 (C),
123.7 (C), 123.4 (C), 121.7 (C), 118.2 (C), 61.1 (CH2), 57.3 (CH2),
Experimental
General
All experiments employing metal complexes were performed 57.2 (CH2), 42.0 (NCH3), 40.3 (CH2), 37.2 (CH2), 36.9 (C), 29.1
under an atmosphere of dry nitrogen in a nitrogen-filled glove- (ArCH3), 20.7 (CH). MS(ESI): Calcd for C28H34N2O2Cl2: 501.5,
box. Pentane was washed with HNO3/H2SO4 prior to distilla- found: 501.3.
tion from Na/benzophenone/tetraglyme. Diethyl ether and
Anal. Calcd for C28H34N2Cl2O2: C, 67.06; H, 6.83; N, 5.59.
toluene were refluxed over Na/benzophenone and distilled Found: C, 66.97; H, 6.77; N, 5.11.
under an argon atmosphere. Triethylamine was purchased
Synthesis of the ligand precursor Lig2H2. Lig2H2 was pre-
from Aldrich and used as received. Hafnium(IV) tert-butoxide pared in
a quantitative yield from 2-(bromomethyl)-4,6-
and tetrabenzylhafnium were purchased from Strem and used dibromophenol (0.80 g, 2.3 mmol) and 2-(((methylamino)-
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ethylimino)methyl)-4-methyl-6-adamantylphenol
(0.76
g, (CH2), 56.3 (CH2), 55.7 (CH2), 45.8 (NCH3), 40.7 (CH2), 37.4
2.3 mmol) following the same procedure employed for making (C), 37.3 (CH2), 30.7 (CH), 20.5 (ArCH3).
Lig1H2. 1H NMR (CDCl3, 400 MHz): δ = 8.33 (s, 1H, NCH), 7.54
Synthesis of complex 3-Zr. 3-Zr was prepared according to
(d, 1H, J = 2.2 Hz, ArH), 7.08 (d, 1H, J = 1.8 Hz, ArH), 7.02 (d, the synthesis of 1-Zr from Lig3H2 (54 mg, 0.08 mmol) and
1H, J = 2.5 Hz, ArH), 6.88 (d, 1H, J = 1.8 Hz, ArH), 3.78 (t, 2H, J ZrBn4 (36 mg, 0.08 mmol). The final yield was 67 mg (89%).
= 6.8 Hz, NCH2), 3.71 (s, 2H, ArCH2N), 2.86 (t, 2H, J = 6.8 Hz, 1H NMR (C6D6, 400 MHz): δ = 8.01 (d, 1H, J = 2.1 Hz, ArH),
NCH2), 2.38 (s, 3H, NCH3), 2.30 (s, 3H, ArCH3), 2.22 (bs, 6H, 7.27 (d, 1H, J = 1.9 Hz, ArH), 7.21 (s, 1H, NCH), 7.09–7.07 (m,
adamantyl), 2.15 (bs, 3H, adamantyl), 1.77 (m, 6H, adaman- 3H, ArH), 7.02–6.95 (m, 4H, ArH), 6.94 (d, 1H, J = 1.9 Hz, ArH),
tyl). 13C NMR (CDCl3, 100.67 MHz): δ = 167.3 (CN), 158.1 (CO), 6.72–6.65 (m, 3H, ArH), 6.60 (d, 1H, J = 2.1 Hz, ArH), 3.10 (d, J
154.1 (CO), 137.3 (CH), 134.1 (C), 130.7 (CH), 130.0 (CH), 129.5 = 9.0 Hz, 1H), 2.86 (d, J = 9.0 Hz, 1H), 2.54 (d, J = 10.2 Hz, 1H),
(CH), 126.8 (C), 124.0 (C), 118.1 (C), 110.9 (C), 110.4 (C), 60.9 2.48–2.34 (m, 6H, CH2), 2.19 (m, 6H, adamantyl), 2.06 (s, 3H,
(CH2), 57.1 (CH2), 57.0 (CH2), 41.7 (NCH3), 40.2 (CH2), 37.1 CH3), 2.02 (m, 6H, adamantyl), 1.83 (s, 3H, CH3), 1.79 (m, 3H,
(CH2), 36.8 (C), 29.0 (ArCH3), 20.6 (CH). MS(ESI): Calcd for adamantyl), 1.48 (m, 1H, CH2). 13C NMR (CDCl3, 100.67 MHz):
C28H34N2O2Br2: 590.4, found: 591.2. Anal. Calcd for δ 168.5 (CN), 159.2 (CO), 158.2 (CO), 146.3 (CH), 146.2 (CH),
C28H34N2Br2O2: C, 56.96; H, 5.80; N, 4.74. Found: C, 56.81; H, 137.7 (C), 137.5 (CH), 134.2 (CH), 133.8 (CH), 132.1 (C), 131.8
5.56; N, 4.20.
(C), 126.4 (CH), 126.2 (CH), 125.7 (CH), 125.3 (CH), 122.9 (C),
Synthesis of complex 1-Zr. Lig1H2 (24 mg, 0.05 mmol) was 122.4 (C), 120.2 (C), 120.0 (C), 119.6 (C), 72.5 (CH2), 71.6 (CH2),
dissolved in 1 mL of toluene chilled to −35 °C and the solution 60.9 (CH2), 56.6 (CH2), 54.7 (CH2), 45.5 (NCH3), 40.7 (CH2),
was added dropwise to a stirring solution of ZrBn4 (22 mg, 37.3 (CH2), 29.1 (CH), 20.5 (ArCH3).
0.05 mmol) in 1 mL of chilled toluene. The reaction mixture
Synthesis of complex 1-Hf. Lig1H2 (56 mg, 0.11 mmol) was
was allowed to warm to room temperature and after 1 h the dissolved in 1 mL of toluene chilled to −35 °C and the solution
solvent was removed under vacuum, yielding a yellow solid, was added dropwise to a stirring solution of HfBn4 (61 mg,
which was washed with 1 mL of pentane and dried in vacuo. 0.11 mmol) in 1 mL of toluene chilled to the same temp. The
The final yield was 31 mg (86%). 1H NMR (C6D6, 400 MHz): δ = reaction mixture was allowed to warm to room temperature,
7.32 (d, 1H, J = 1.5 Hz, ArH), 7.28 (d, 1H, J = 2.5 Hz, ArH), 7.21 and after 2 h the solvent was removed under vacuum, yielding
(s, 1H, NCH), 7.13–6.92 (m, 11H, ArH), 6.59 (d, 1H, J = 1.5 Hz, a white solid, which was washed with 1 mL of pentane and
ArH), 2.77 (d, J = 9.5 Hz, 1H), 2.66 (d, J = 9.5 Hz, 1H), 2.61 (m, dried in vacuo. The final yield was 96 mg (100%). 1H NMR
1H, CH2), 2.49–2.40 (m, 6H, CH2), 2.34 (d, J = 11.5 Hz, 1H), (C6D6, 400 MHz): δ = 7.29 (d, 1H, J = 1.7 Hz, ArH), 7.24 (s, 1H,
2.25 (d, J = 11.5 Hz, 1H), 2.19 (m, 6H, adamantyl), 2.17 (m, 1H, NCH), 7.06–6.94 (m, 7H, ArH), 6.78–6.71 (m, 4H, ArH), 6.62 (d,
CH2), 2.13 (s, 3H, CH3), 2.00 (m, 3H, adamantyl), 1.98 (s, 3H, 1H, J = 1.7 Hz, ArH), 6.57 (d, 1H, J = 2.0 Hz, ArH), 3.10 (d, J =
CH3), 1.81 (m, 4H, adamantyl), 1.67 (m, 1H, CH2). 13C NMR 11.4 Hz, 1H), 2.90 (d, J = 11.4 Hz, 1H), 2.61 (d, J = 10.3 Hz, 1H),
(CDCl3, 100.67 MHz): δ 168.6 (CN), 158.0 (CO), 154.6 (CO), 2.55 (d, J = 10.3 Hz, 1H), 2.50–2.44 (m, 6H, CH2), 2.22 (m, 6H,
152.3 (CH), 149.4 (CH), 139.8 (C), 138.8 (CH), 137.7 (CH), 134.8 adamantyl), 2.20 (m, 3H, CH3), 2.01 (m, 4H, adamantyl), 1.87
(CH), 131.9 (C), 130.1 (CH), 129.9 (C), 129.1 (CH), 128.7 (CH), (s, 3H, CH3), 1.82 (m, 5H, adamantyl). 13C NMR (CDCl3,
128.4 (CH), 128.2 (CH), 127.7 (CH), 126.7 (CH), 126.1 (CH), 100.67 MHz): δ 168.5 (CN), 158.4 (CO), 154.8 (CO), 142.9 (CH),
124.5 (CH), 124.2 (C), 123.1 (C), 122.6 (C), 120.2 (C), 120.0 (C), 139.3 (CH), 134.2 (C), 131.8 (CH), 130.9 (CH), 130.0 (CH), 129.4
71.2 (CH2), 69.2 (CH2), 61.3 (CH2), 56.3 (CH2), 54.8 (CH2), 46.3 (C), 129.1 (CH), 128.5 (C), 128.1 (CH), 127.4 (CH), 126.6 (CH),
(NCH3), 40.7 (CH2), 37.5 (C), 37.4 (CH2), 29.4 (CH), 20.6 125.4 (CH), 124.3 (C), 123.7 (C), 123.1 (C), 122.9 (C), 122.7 (C),
(ArCH3).
74.1 (CH2), 73.2 (CH2), 62.0 (CH2), 61.1 (CH2), 56.7 (CH2), 45.8
Synthesis of complex 2-Zr. 2-Zr was prepared according to (NCH3), 40.8 (CH2), 38.0 (C), 37.6 (CH2), 29.4 (CH), 20.6
the synthesis of 1-Zr from Lig2H2 (36 mg, 0.06 mmol) and (ArCH3).
ZrBn4 (27 mg, 0.05 mmol). The final yield was 47 mg (93%).
Synthesis of complex 2-Hf. 2-Hf was prepared according to
1H NMR (C6D6, 400 MHz): δ = 7.60 (d, 1H, J = 2.0 Hz, ArH), the synthesis of 1-Hf from Lig2H2 (37 mg, 0.06 mmol) and
7.27 (d, 1H, J = 1.6 Hz, ArH), 7.22 (s, 1H, NCH), 7.04–6.91 (m, HfBn4 (34 mg, 0.06 mmol). The final yield was 57 mg (95%).
10H, ArH), 6.74 (d, 1H, J = 2.0 Hz, ArH), 6.61 (d, 1H, J = 1.6 Hz, 1H NMR (C6D6, 400 MHz): δ = 7.59 (d, 1H, J = 2.0 Hz, ArH),
ArH), 3.11 (d, J = 8.8 Hz, 1H), 2.87 (d, J = 8.8 Hz, 1H), 2.58 (d, J 7.30 (d, 1H, J = 1.6 Hz, ArH), 7.18 (s, 1H, NCH), 7.10–6.97 (m,
= 9.6 Hz, 1H), 2.44 (m, 3H, adamantyl), 2.41 (s, 3H, CH3), 2.34 5H, ArH), 6.94 (d, 1H, J = 2.0 Hz, ArH), 6.72–6.67 (m, 5H, ArH),
(d, J = 11.2 Hz, 1H), 2.20 (m, 6H, adamantyl), 2.29 (d, J = 6.58 (d, 1H, J = 1.6 Hz, ArH), 2.76 (d, J = 9.6 Hz, 1H), 2.63 (d,
11.2 Hz, 1H), 2.18 (d, J = 9.6 Hz, 1H), 2.02 (m, 3H, adamantyl), 1.99 J = 9.6 Hz, 1H), 2.57 (d, J = 11.8 Hz, 1H), 2.47 (s, 3H, CH3),
(m, 6H, CH2, adamantyl), 1.83 (s, 3H, CH3), 1.80 (m, 4H, ada- 2.41–2.37 (m, 4H, CH2), 2.32 (d, J = 10.8 Hz, 1H), 2.23 (d, J =
mantyl), 1.68 (m, 1H, CH2). 13C NMR (CDCl3, 100.67 MHz): δ 10.8 Hz, 1H), 2.19 (m, 6H, adamantyl), 2.13 (d, J = 11.8 Hz,
168.4 (CN), 158.1 (CO), 156.0 (CO), 149.9 (CH), 148.5 (CH), 1H), 2.01 (m, 3H, adamantyl), 1.93 (s, 3H, CH3), 1.79 (m, 6H,
139.1 (C), 138.2 (CH), 137.7 (CH), 134.8 (CH), 131.9 (C), 130.8 adamantyl), 1.60 (s, 2H, CH2). 13C NMR (CDCl3, 100.67 MHz):
(CH), 129.8 (C), 129.1 (CH), 128.5 (CH), 128.3 (CH), 128.2 (CH), δ 168.5 (CN), 157.8 (CO), 155.9 (CO), 141.8 (CH), 135.7 (CH),
127.1 (CH), 126.4 (CH), 126.2 (CH), 124.5 (CH), 124.3 (C), 122.9 131.9 (C), 131.4 (CH), 130.6 (CH), 129.8 (C), 129.2 (CH), 128.9
(C), 122.7 (C), 120.1 (C), 119.7 (C), 69.7 (CH2), 64.7 (CH2), 62.1 (C), 128.3 (CH), 127.2 (CH), 125.9 (CH), 124.6 (C), 123.1 (C),
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122.8 (C), 121.5 (C), 72.8 (CH2), 70.3 (CH2), 62.1 (CH2), 60.8
NMR, DSC and GPC analyses were carried out on un-
(CH2), 56.6 (CH2), 45.8 (NCH3), 40.5 (CH2), 37.9 (C), 37.5 extracted samples. The 13C NMR spectra of the polypropylene
(CH2), 29.4 (CH), 20.9 (ArCH3).
samples were recorded on a Bruker AC-500 spectrometer. The
Synthesis of complex 3-Hf. 3-Hf was prepared according to NMR samples of the polypropylene produced with complexes
the synthesis of 1-Hf from Lig3H2 (58 mg, 0.08 mmol) and 1-Zr–3-Zr were prepared by dissolving a maximum weight of
HfBn4 (46 mg, 0.08 mmol). The final yield was 81 mg (92%). 15 mg of polymer in 0.5 mL of 1,1,2,2-tetrachloroethane-d2
1H NMR (C6D6, 400 MHz): δ = 8.08 (d, 1H, J = 2.1 Hz, ArH), and the spectra were recorded at a temperature of 100 °C. The
8.03 (d, 1H, J = 2.1 Hz, ArH), 7.37 (s, 1H, NCH), 7.08–6.95 (m, NMR samples of the polypropylene produced with complexes
11H, ArH), 6.93 (d, 1H, J = 2.0 Hz, ArH), 5.42 (d, J = 13.2 Hz, 1-Hf–3-Hf were prepared accordingly with 1,2-dichloroben-
1H), 5.35 (d, J = 13.2 Hz, 1H), 5.10 (d, J = 13.4 Hz, 1H), 5.00 (d, zene-d4 as a solvent and the spectra were recorded at a temp-
J = 13.4 Hz, 1H), 3.18 (d, J = 12.6 Hz, 1H), 2.78 (d, J = 12.6 Hz, erature of 140 °C. The following parameters were employed:
1H), 2.54–2.30 (m, 9H, adamantyl), 2.26 (m, 3H, adamantyl), 5 mm dual 13C/1H probe; acquisition time, 1.445 s; spectral
2.21 (s, 3H, CH3), 2.18–2.14 (m, 2H, CH2), 2.09 (s, 3H, CH3), width, 180 ppm; time domain, 32 K; size, 32 K; relaxation
1.79 (m, 3H, adamantyl), 1.85–1.81 (m, 2H, CH2). 13C NMR delay, 1 s; 30° pulse angle. Composite pulse proton decoupling
(CDCl3, 100.67 MHz): δ 167.2 (CN), 166.6 (CO), 159.8 (CO), was achieved with the WALTZ 16 sequence. Molecular weights
146.5 (CH), 145.8 (CH), 144.3 (C), 141.7 (CH), 137.4 (CH), 134.1 and molar mass distributions were measured by gel per-
(CH), 133.0 (C), 132.1 (C), 128.9 (CH), 128.3 (CH), 126.8 (CH), meation chromatography (GPC) at 135 °C by a Waters GPCV
126.6 (CH), 126.2 (C), 125.3 (C), 124.8 (C), 119.5 (C), 118.9 (C), 2000 instrument equipped with refractive index and visco-
72.3 (CH2), 71.6 (CH2), 62.1 (CH2), 57.7 (CH2), 56.2 (CH2), 41.2 meter detectors, using a set of four PSS columns: 106, 105,
(NCH3), 40.7 (CH2), 37.3 (CH2), 29.4 (CH), 20.4 (ArCH3).
104, 103 Å pore size with 10 μm particle size. o-Dichloroben-
Synthesis of complex 4-Hf. Ligand precursor Lig4H2 (51 mg, zene was the carrier solvent used with a flow rate of 1.0 mL
0.11 mmol) was dissolved in 1 mL of toluene and added drop- min−1. A calibration curve was established with polystyrene
wise to a stirring solution of Hf(OtBu)4 (52 mg, 0.11 mmol) in standards. Differential scanning calorimetry analysis was per-
1 mL of toluene. The reaction mixture was stirred for 2 h and formed using a TA 2920 DSC (TA Instruments). Melting tran-
the solvent was removed under vacuum, yielding a white solid, sitions were determined on the second heating run at 10 °C
which was washed with about 1 mL of pentane and dried in min−1 with a nitrogen purge at a flow rate of 40 mL s−1. The
vacuo. The final yield was 83 mg (96%). 1H NMR (C6D6, instrument was calibrated for temperature and enthalpy by the
400 MHz): δ = 7.71 (d, 1H, J = 2.5 Hz, ArH), 7.37 (s, 1H, NCH), high purity indium (156.60 °C, 28.45 J g−1) standard.
7.34 (d, 1H, J = 2.6 Hz, ArH), 6.97 (d, 1H, J = 2.6 Hz, ArH), 6.76
(d, 1H, J = 2.5 Hz, ArH), 3.25 (d, J = 12.8 Hz, 1H), 3.01 (d, J =
12.8 Hz, 1H), 2.94 (m, 1H, CH2), 2.58 (m, 1H, CH2), 2.40 (s,
3H, NCH3), 1.93 (m, 1H, CH2), 1.76 (s, 9H, (CH3)3), 1.47 (m,
Acknowledgements
1H, CH2), 1.36 (s, 9H, (CH3)3), 1.31 (s, 9H, (CH3)3), 1.13 (s, 9H,
(CH3)3). 13C NMR (CDCl3, 100.67 MHz): δ 166.8 (CN), 159.7
We thank the Israel Science Foundation for financial support.
We thank Dr Maria Grazia Napoli for the HT-GPC analysis.
(CO), 159.0 (CO), 139.1 (C), 138.7 (C), 130.0 (CH), 129.7 (CH),
128.6 (CH), 126.9 (CH), 125.2 (C), 124.2 (C), 121.9 (C), 118.7
(C), 61.6 (CH2), 57.2 (CH2), 55.4 (CH2), 47.2 (NCH3), 35.4 (C),
33.9 (C), 32.6 ((CH3)3), 32.5 ((CH3)3), 31.3 ((CH3)3), 30.9 (C),
29.7 ((CH3)3). Anal. Calcd for C33H50Cl2O4N2Hf (with 2 mole-
cules of H2O): C, 48.09; H, 6.60; N, 3.40. Found: C, 47.65; H,
5.86; N, 3.35.
Notes and references
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A stainless steel reactor equipped with an inner glass sleeve
and a magnetic stir-bar was charged with 10 μmol of the corres-
ponding dibenzylzirconium or dibenzylhafnium complex and
500 equiv. of dried MAO and was cooled with a liquid nitrogen
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Dalton Trans., 2013, 42, 9096–9103 | 9103