New titanium and hafnium complexes bearing [-NNN-] pyrrolylpyridylamido ligands as olefin polymerization catalysts

Article abstract of DOI:10.1021/om300519s

Four new complexes bearing either unsubstituted or substituted pyrrolylpyridylanilido ligands, with the general formula [^-NNN ^-]M(NMe₂)₂ (M = Ti(IV), Hf(IV)), were synthesized and fully characterized by NMR spec

Full text of DOI:10.1021/om300519s

Article
pubs.acs.org/Organometallics
New Titanium and Hafnium Complexes Bearing [−NNN−]
Pyrrolylpyridylamido Ligands as Olefin Polymerization Catalysts
Gang Li,† Marina Lamberti,† Giuseppina Roviello,‡ and Claudio Pellecchia†,*
†Dipartimento di Chimica e Biologia, Universita
̀
di Salerno, via Ponte don Melillo, I-84084 Fisciano (SA), Italy
‡Dipartimento per le Tecnologie, Universita
̀
di Napoli Parthenope, Centro Direzionale Napoli, Isola C4, 80143 Napoli, Italy
S
* Supporting Information
ABSTRACT: Four new complexes bearing either unsubsti-
tuted or substituted pyrrolylpyridylanilido ligands, with the
general formula [−NNN−]M(NMe2)2 (M = Ti(IV), Hf(IV)),
were synthesized and fully characterized by NMR spectroscopy
and elemental analyses. The solid-state structures of one Ti
and one Hf complex (both bearing the 2-isopropylphenyl
substituent on the carbon bridging the pyridine and the aniline
moieties) were obtained by single-crystal X-ray diffraction
analyses, showing in both cases slightly distorted square
pyramidal geometries, with the [−NNN−] ligand and one Me2N forming the base plane and the second Me2N as the apex. The
new complexes and, for comparison, their zirconium analogues were tested as precatalysts for olefin polymerization, after
activation with AliBu2H/methylalumoxane. Polymerization of ethylene under mild conditions (25 °C and 1 atm) was promoted
by all catalysts with high activities, resulting in highly linear polyethylenes with ultrahigh molecular weights (Mw up to 2.7 MDa).
Polymerization of propylene (at 25 °C and 6 atm) was promoted by all complexes, with activities decreasing in the order Ti > Zr
> Hf for the Cs-symmetric complexes and in the order Zr ≫ Ti > Hf for the C1-symmetric complexes. Concerning
stereoselectivity, catalysts based on Zr and Hf complexes behave similarly, with the C1-symmetric species of both metals affording
much more isotactic polymers than the Cs-symmetric species ([mmmm] 95% vs 73−79%) and performing better also in terms of
activities and production of high-molecular-weight polypropylenes (Mw up to 1.8 MDa for Hf). The Ti-based catalysts are less
stereospecific and produce polypropylenes having very high molecular weights and rather broad molecular weight distributions.
Solvent extraction of the raw samples showed the presence, in both cases, of an isotactic and an atactic fraction, also having
different regioerrors, suggesting the formation of at least two active species.
complexes bearing polydentate phenolate ligands, such as
bis(phenoxyimine) Ti(IV) catalysts,5 diaminobis(phenolate)
Zr(IV) catalysts,6 bis(phenolate)diether Zr(IV) or Hf (IV)
catalysts,7 trans-1,2-cyclooctanediylbis(thio)diphenolate Zr(IV)
catalysts,8 and mixed imino/aminobis(phenolate) Ti(IV)
catalysts.9 One of the rare examples of stereoselective catalysts
not displaying a phenolate moiety is the class of catalysts based
on arylpyridylamido Hf(IV) complexes, discovered and
optimized by researchers at Dow and Symyx using high-
throughput screening technologies.10 The excellent perform-
ance of these catalysts in the production of highly isotactic,
high-MW polypropylene at high temperature has been shown
to depend on arylcyclometalation reactions, changing a [NN−]
monoanionic ligand into a [−CNN−] dianionic tridentate ligand
(Scheme 1) and, possibly, by further ligand modifications such
as monomer insertion into a Hf−Caryl bond.10,11
INTRODUCTION
■
Although often considered a “mature” area or research, olefin
polymerization catalysis continues to attract great interest from
both industrial and academic scientists worldwide.1 In addition
to the obvious relevance related to the commercial production
of over 100 million tons per year of polyolefin-based plastics,
the degree of knowledge accumulated since the original
discoveries of Ziegler and Natta in the mid 1950s makes the
study of this reaction paradigmatic for goals such as rational
catalyst design, fine-tuning of polymer microstructure, control
of structure−property relationships, and so on. Following the
metallocene era,2 growing efforts have been directed to the
design of new non-metallocene coordination environments able
to stabilize better-performing organometallic catalysts.3 A large
variety of polydentate ligand frameworks based on nitrogen
and/or oxygen and/or sulfur donors has been explored,
sometimes resulting in catalysts displaying unprecedented
features, such as living polymerization above room temperature
or chain shuttling between two different active species, allowing
the synthesis of novel macromolecular architectures.1
Inspired by these results, we have recently reported
pentacoordinate Zr(IV) catalysts bearing dianionic pyrrolylpyr-
idylanilido [−NNN−] tridentate ligands,12 which do not appear
amenable to the aforementioned in situ modifications (Scheme
Significant results have also been achieved in the stereo-
selective polymerization of α-olefins by postmetallocene
catalyts,4 especially using C2-symmetric group 4 metal
Received: June 11, 2012
© XXXX American Chemical Society
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Scheme 1
Scheme 2
Figure 1. (a) ORTEP-3 view of [−NNN−]Ti(NMe2)2 (3). Selected bond distances (Å) and angles (deg): Ti−N1 = 1.985(1), Ti−N2 = 2.170(1),
Ti−N3 = 2.100(2), Ti−N4 = 1.889(2), Ti−N5 = 1.894(2); N2−Ti−N4 = 147.7(1), N1−Ti−N3 = 137.8(1). (b) ORTEP-3 view of one
independent molecule of [−NNN−]Hf(NMe2)2 (4). Selected bond distances (Å) and angles (deg): Hf−N1 = 2.096(3), Hf−N2 = 2.284(3), Hf−N3
= 2.180(4), Hf−N4 = 2.019(4), Hf−N5 = 2.022(4); N2−Hf−N4 = 131.5(1), N1−Hf−N3 = 140.4(1). Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms are omitted for clarity.
1). Upon activation with AliBu2H/MAO, these complexes
exhibited excellent activity and stereoselectivity for polymer-
ization of propylene and 1-hexene, producing high-molecular-
weight (Mw up to 950 kg/mol) polypropylene with high
isotacticity ([mmmm] up to 95%), as well as isotactic poly(1-
hexene) ([mmmm] ≥ 99%).12b
It is well-known that the nature of the metal center can show
a not easily predicted influence on catalytic performance. For
example, tetrahedral dimethyltitanium complexes bearing
ancillary propylene-bridged aryl-substituted diamido ligands
proved to be highly active catalysts for polymerization of 1-
hexene and higher α-olefins, proceeding in a living fashion,
while zirconium catalysts did not.13 For diaminobis(phenolate)
(salan) group 4 metal catalysts14 bearing electron-withdrawing
halo groups, titanium catalysts showed much better perform-
ance than their zirconium analogues.
In the case of the aforementioned arylpyridylamido group 4
metal catalysts,10,15 hafnium complexes have been shown to
perform better than their zirconium analogues. We report here
the synthesis of four new bis(amido) Ti(IV) and Hf(IV)
complexes bearing pyrrolylpyridylanilido ligands and the
investigation of their performance in the polymerization of
ethylene and propylene in comparison with that of their Zr(IV)
counterparts.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Complexes 1−4.
Complexes 1 - 4 were prepared in benzene from the
corresponding proligand and the equimolar amounts of
tetrakis(dimethylamido)titanium or hafnium, and isolated as
yellow solid in high yields (86% for 1, 98% for 2, 94% for 3,
97% for 4, respectively) (Scheme 2). All complexes were fully
characterized by NMR spectroscopy and elemental analyses.
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The solid-state structures of complexes 3 and 4 were obtained
by single-crystal X-ray diffraction analyses.
In both complexes, the C-aryl group is oriented toward the
apex ligand, while the N-aryl group points toward the opposite
direction. Angles between the mean planes of the two aromatic
rings are 59.62(7) and 53.9(1)° for 3 and 4, respectively.
Ethylene and Propylene Polymerization. The new Ti
and Hf complexes 1−4 and, for comparison, the previously
reported Zr complexes 5 and 6 were tested as precatalysts for
the polymerization of ethylene under the same conditions,
using AliBu2H/solid methylaluminoxane (MAOd, obtained by
distilling off the solvent from the commercial solution) as the
cocatalytic system. The main data of ethylene polymerizations
are summarized in Table 1. Under mild conditions (25 °C and
The solution structures of complexes 1−4 were elucidated by
1
NMR analysis. The H NMR spectra of complexes 1 and 2
showed patterns of resonances compatible with “time averaged”
Cs symmetry in solution: e.g., the resonances of the methyl
protons of the dimethylamido groups (M−NMe2) appear as a
sharp singlet, one septet and two doublets are observed
respectively for the methine and methyl protons of isopropyl
groups (CHMe2), and one sharp singlet accounts for the
protons of the bridging methylene (see Figures S1 and S2 in
the Supporting Information). In contrast, the 1H NMR spectra
of complexes 3 and 4 indicated C1-symmetric structures, as
evidenced by three septets and six doublets of the methine and
the methyl protons of the isopropyl groups (CHMe2) and two
sharp singlets of methyl protons of dimethylamido groups (M−
NMe2) (see Figures S3 and S4 in the Supporting Information).
In any case, the patterns observed for the protons of the
isopropyl groups indicated that the rotation of N−Caryl bonds is
slow on the NMR time scale. 13C NMR spectra agree with the
above picture, as indicated for example by one singlet observed
for the methyl carbon atoms of M−NMe2 and three singlets of
carbon atoms of the isopropyl groups CHMe2 for complexes 1
and 2 vs two singlets observed for the methyl carbon atoms of
M−NMe2 and nine singlets of carbon atoms of the isopropyl
groups CHMe2 of complexes 3 and 4.
a
Table 1. Ethylene Polymerization Results
b
run precat. yield (g) activity
Tm (°C) Mw (×106) Mw/Mn
1
2
3
4
5
6
1
2
3
4
5
6
0.158
0.060
0.646
0.155
0.239
0.368
1.0
0.4
3.9
0.9
1.4
2.2
136
137
135
135
137
135
2.7
1.0
2.2
2.6
1.2
2.2
1.5
3.5
2.2
1.5
2.0
2.4
a
General conditions: precatalyst, 1 μmol; toluene, 100 mL; cocatalyst,
AliBu2H/M = 30, Al(solid MAO)/M = 2000; aging time, 10 min;
ethylene pressure, 1 atm; polymerization time, 10 min; polymerization
temperature, 25 °C; solid MAO (MAOd) obtained by distilling off the
b
solvent from the commercial solution. In units of kg of PE/((mmol
of cat.) h atm)).
X-ray Crystal Structures. The molecular structures of
complexes 3 and 4 are shown in Figure 1. Complex 3
crystallizes in the triclinic system (space group P1) and
̅
1 atm of monomer pressure) all catalysts promoted ethylene
polymerization with moderate to high productivities. Ti-based
catalysts showed activities comparable to or higher than those
of the corresponding Zr catalysts (in all cases exceeding 1 kg of
PE/((mmol of cat.) h atm)), while Hf-based catalysts were less
active (see Table 1).
complex 4 in the orthorhombic system (space group Pna21). In
4 the asymmetric unit is made up of two independent
molecules having opposite chirality at C1. In Figure 1 only one
independent molecule of 4 is shown and hereafter discussed,
since only minor differences in the geometrical parameters of
the two independent molecules are found, probably due to
packing effects.
Complexes 3 and 4 exhibit very similar molecular structures.
At variance with related arylpyridylamido Hf complexes, which
were described in terms of a distorted-trigonal-bipyramidal
geometry,10c in our opinion the geometry is better described as
distorted square pyramidal, with the base plane constituted by
N1, N2, N3, and N4 (rmsd 0.015 for 3 and 0.232 for 4) and N5
as the apex atom. The metal lies 0.565(1) and 0.643(2) Å out
of the base plane for 3 and 4, respectively. A useful parameter16
to evaluate the extent of the distortion from square-pyramidal
geometry (sqp) versus the trigonal-bipyramidal geometry (tbp)
is τ = (β − α)/60°, where β and α are the two basal angles
N1−M−N3 and N2−M−N4, respectively. A value of 0 for this
simple geometric parameter suggests a sqp geometry and a
value of 1 a tbp geometry. In our case, we found τ = 0.16 for
complex 3 and 0.15 for complex 4, indicating a distorted-sqp
geometry for both complexes.
The pyrrolylpyridylanilido fragment is planar in both cases.
All the M−N bond distances fall in the range typical of similar
complexes11,12a,15c,17 and, in accord with the trend of the ionic
radii along group 4, those in the coordination sphere of Hf are
longer than the corresponding distances of the Ti complex and
shorter than those observed in similar Zr complexes.12a The
M−N(pyridyl) bond distance is longer than the other
distances, in accord with the different nature of the metal−
ligand bond. The geometry at the amido N1 atom is in
agreement with a substantially sp2 character.
The introduction of a 2-isopropylphenyl substituent on the
carbon bridging the pyridine and the aniline moieties resulted
in catalysts showing 2−4-fold increased activities for all the
metals. In all cases, the obtained polyethylene samples exhibited
ultrahigh molecular weights (Mw ranging between 1.0 and 2.7
MDa) and molecular weight distributions in the range of 1.5−
3.5. As reported in the literature, the polymers produced by the
related arylpyridylamido Hf catalysts exhibit rather broad
molecular weight distributions: this finding, even more relevant
for copolymers, was explained by the generation of multiple
active species by in situ ligand modification through monomer
insertion into an Hf−Caryl bond.10,11 In the case of
pyrrolylpyridylanilido Zr catalysts, the broadening of the
molecular weight was suggested to be mainly due to chain
transfer to aluminum and/or to slow initiation reactions.12b
Complexes 1−4 were also tested in the polymerization of
propylene after activation with AliBu2H/MAOd at 25 °C and
under 6 atm of monomer pressure. The main polymerization
data are summarized in Table 2, where the results previously
reported12 for Zr complexes 5 and 6 are also displayed for
comparison. The activity trends appear poorly predictable, as
previously observed in other papers comparing complexes of
different group 4 metals bearing the same ligands.13,14 In fact,
for the Cs-symmetric complexes, the activities decrease in the
order Ti > Zr > Hf (cf. runs 1, 2, and 5 of Table 2). In the case
of the C1-symmetric complexes, however, the activities decrease
in the order Zr ≫ Ti > Hf (cf. runs 3, 4, and 6 of Table 2). This
trend is very different from that observed in the case of
C
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a
Table 2. Propylene Polymerization Results
b
run
precat.
activity
[mmmm] (%)
regioinverted units
Tm (°C)
Mw (×105)
Mw/Mn
1
2
1
2
3
4
5
6
11.2
0.2
4.8
0.7
4.0
98
23
79
76
95
73
95
5.6
2.0
2.4
1.1
3.0
1.4
112
136
141
151
131
150
11.5
0.9
3.5
1.6
5.8
2.7
1.4
3.5
3
4.6
4
18.5
0.4
512
612
9.5
a
General conditions: precatalyst, 10 μmol; toluene, 100 mL; cocatalyst, AliBu2H/M = 30, Al(MAO)/M = 1000; dried MAO obtained by distilling off
the solvent from the commercial solution; aging time, 10 min; polymerization time, 60 min; polymerization temperature, 25 °C; propylene pressure,
b
6 atm. In units of kg of PP/((mol of [M]) h atm).
Chart 1. Isolated Regioinverted Units with Threo and Erythro Adjacent Methyls in a Fischer Projection
arylpyridylamido catalysts by Dow and Symyx, for which Hf-
based catalysts were reported to be the most active.15 Since it
has been suggested1a,18 that the lower activity of Hf-based
catalysts vs their Zr counterparts is due to the easier formation
of Hf−μ-Me2−Al adducts owing to the presence of free AlMe3
in commercial MAO, we note that in our polymerization runs
we always used solid MAO obtained by distilling off the solvent
from the commercial solution, which does not contain
appreciable amounts of free AlMe3. Moreover, a polymerization
run was carried out by adding to the catalytic system 4/
AliBu2H/MAO 10 equiv of 2,6-di-tert-butylphenol, a scavenger
for AlMe3, with no significant increase of activity.
A partial catalyst activation was indicated by the number of
polymer chains, estimated from the Mn values by GPC analysis,
with respect to the metal initiator employed. In particular, the
lowest values were found for the hafnium complexes, while the
most efficient catalyst activation was obtained with zirconium
complexes, confirming that, within the group 4 metal triad, the
zirconium catalysts are the best performing in these polymer-
ization reactions.
Concerning stereoselectivity, the behavior of catalysts based
on Hf complexes 2 and 4 parallels that of their Zr analogues 5
and 6, with the C1-symmetric species of both Hf and Zr
affording much more isotactic polymers than the Cs-symmetric
species (cf. runs 4 and 6 vs 2 and 5).12b The C1-symmetric Hf
and Zr complexes perform much better than the Cs-symmetric
complexes also in terms of activities, regioregularities, and
production of high-molecular-weight polypropylenes, with Hf
complexes being much less active, as stated above, but yielding
higher molecular weights (Mw up to 1.8 MDa, run 4) than Zr
analogues, as is often observed in the literature.1a 13C NMR
analysis of polypropylene samples produced by Hf complexes 2
and 4 revealed a microstructure similar to that of the polymers
produced by their Zr analogues,12b i.e. a 2/2/1 ratio of the
[mmmr]/[mmrr]/[mrrm] pentads in the methyl region, in
agreement with an “enantiomorphic sites” mechanism of the
stereospecific propagation,2,19 and some regioinverted units
(2.0 and 1.1 mol % for 2 and 4, respectively) in a threo
configuration (see Chart 1).10c,20
The behavior of Ti-based catalysts, on the other hand, was
significantly different. The Cs-symmetric catalyst 1 produced a
poorly isotactic enriched polypropylene ([mmmm] = 23%),
having high molecular weight and rather broad molecular
weight distribution (see Table 2, run 1). Also, detailed 13C
NMR analysis of the samples showed additional minor
resonances, having approximately the same intensity, attribut-
able to regioirregularly arranged monomer units. By compar-
ison with literature data,5d,21 the minor resonances at δ 15.47
and 15.02 ppm from hexamethyldisiloxane (HMDS) were
attributed to the adjacent methyl carbons (Pαβ and Pαγ) in the
erythro configuration, derived from tail-to-tail arrangements
(Chart 1). Accordingly, resonances were detected at 28.96 and
32.56 ppm (HMDS scale) for the methine carbons (Tβγ and
Sγ,α,β,δ) in the tail-to-tail sequence,22 while resonances at 33.34
and 33.60 ppm as multiplets could be attributed to methylene
carbons (Tαβ), coming from head-to-head misinsertion (see
Figure S5 in the Supporting Information). In summary, the
polypropylene produced by 1 is stereoirregular and poorly
regioregular (5.6 mol % regioinversions), but the regioerrors
are different from those found in polypropylenes produced by
the Zr and Hf analogues and are similar to those present in
polypropylenes prepared by C2-symmetric metallocene cata-
lysts.2
The raw polypropylene sample was subsequently fractioned
by stirring it in hexane at room temperature for 24 h. The
soluble fraction was a regioirregular, atactic polypropylene with
8.9 mol % erythro regioerrors, while the insoluble fraction (50
wt %) was constituted by a regioregular, prevailingly isotactic
polypropylene ([mmmm] = 56%) with ultrahigh molecular
weight (Mw = 1.8 MDa). 13C NMR analysis of the insoluble
fraction revealed a microstructure in agreement with an
“enantiomorphic sites” mechanism of the stereospecific
D
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propagation19 and the absence of detectable resonances
attributable to regioinverted monomer units.
polymerization performance, as paradigmatically demonstrated
by the case of arylpyridylamido Hf(IV) complexes, whose
performance depends on unpredictable arylcyclometalation
reactions, changing a [NN−] monoanionic ligand into a
[−CNN−] dianionic tridentate ligand, and, possibly, further
ligand modifications such as monomer insertion into a Hf−Caryl
bond.10,11 Additional levels of complexity, such as metalation of
an isopropylaniline substituent10e,15e and the formation of
different isomers,15c make identification of the true active
species in these systems difficult. Substitution of a [−CNN−]
arylpyridylamido ligand with a [−NNN−] pyrrolylpyridylamido
ligand should reduce the number of possible in situ
modifications in the catalyst coordination sphere. We are
currently studying the activation of alkylated [−NNN−] group 4
metal derivatives of this class with boron ionizing agents, such
as B(C6F5)3 and [Ph3C][B(C6F5)4], in a search for further
evidence on the elusive structure of the true active species
involved in pyridylamido catalysts.
The C1-symmetric catalyst 3 showed a lower activity but a
higher stereoselectivity, affording polypropylene with [mmmm]
= 76% pentads, high molecular weight (Mw = 460 kDa), and
broad molecular weight distribution (see run 3 of Table 2). In
this case, the polypropylene sample was fractioned by
sequential exhaustive Kumagawa extraction with boiling hexane.
13C NMR analysis and GPC analysis were carried out for each
fraction. The soluble fraction (36 wt %) was a stereoirregular
polypropylene with a very low amount of regioinverted units in
an erythro configuration, having ultrahigh molecular weight (Mw
= 1.3 MDa), while the insoluble fraction (64 wt %) was a highly
isotactic polypropylene ([mmmm] = 93%), having 4.4 mol %
regioinverted units with vicinal methyls in a threo configuration
(see Figure S6 and Table S2 in the Supporting Information),
much lower molecular weight (Mw = 157 KDa), and narrow
molecular weight distribution (Mw/Mn = 2.4).
The above findings suggest the formation of at least two
active species from the reaction of both Ti complexes 1 and 3
and the AliBu2H/MAO cocatalytic system, one isotactic-specific
and producing either no or threo regioerrors, the other not
stereospecific and producing erythro regioerrors. The different
behaviors of the Ti complexes with respect to the Zr and Hf
analogues could be related to the well-known greater tendency
of Ti(IV) toward reduction to lower oxidation species in the
presence of aluminum alkyls.
EXPERIMENTAL SECTION
■
All manipulations of air- and/or water-sensitive compounds were
carried out under a nitrogen atmosphere using standard Schlenk or
glovebox techniques. All solvents, purchased from Carlo Erba, were
refluxed over sodium/benzophenone or calcium hydride (CaH2) and
then freshly distilled under nitrogen atmosphere before use. 1-Bromo-
2-isopropylbenzene was purchased from Alfa Aesar without
purification before use. All other chemicals were purchased from
Sigma-Aldrich and used as received. MAO (10 wt % solution in
toluene) was dried by distilling off the volatile materials under reduced
pressure, and the excess of trimethylaluminium (AlMe3) was removed
by washing the resulting solid with dry hexane and drying under
vacuum the obtained white powder. Ethylene and propylene were
purchased from SON and used without further purification. 1-Hexene
was distilled over CaH2 prior to use.
CONCLUSIONS
■
We have reported the synthesis and characterization of four
new titanium and hafnium complexes bearing dianionic
pyrrolylpyridylanilido [−NNN−] tridentate ligands. The com-
plexes of the ligand carrying a 2-isopropylphenyl substituent on
the carbon bridging the pyridine and the aniline moieties have
C1-symmetric structures both in solution and in the solid state,
while those displaying an unsubstituted methylene bridge show
time-averaged Cs-symmetric structures in solution. The new Ti
and Hf complexes and, for comparison, the corresponding Zr
complexes have been tested as catalysts for ethylene and
propene polymerization after activation with AliBu2H/MAO.
All catalysts are highly active for ethylene polymerization under
mild conditions (25 °C and 1 atm of monomer pressure),
yielding ultrahigh-molecular-weight PE’s; Ti-based catalysts
show activities comparable to or higher than those of the
corresponding Zr catalysts, while Hf-based catalysts are less
active. Hf-based catalysts also show significantly lower activities
than their Zr and Ti analogues in the polymerization of
propene, a trend very different from that observed in the case of
arylpyridylamino catalysts developed by Dow and Symyx, for
which Hf-based catalysts were reported to be the most active.
The introduction of an isopropylphenyl substituent on the
carbon bridging the pyridine and the aniline moieties leads to a
higher regioselectivity, as an effect of the increased steric
congestion at the metal site. The same behavior was observed,
and studied by theoretical calculations,10c for the Dow and
Symyx catalysts. Concerning stereoselectivity, catalysts based
on Zr and Hf complexes behave similarly, with the C1-
symmetric species of both metals affording much more isotactic
PP’s than the Cs-symmetric species. The Ti-based catalysts are
less stereospecific, and the fractionation of the obtained
polypropylene samples suggested the formation of at least
two active species. These findings confirm that subtle
differences in catalyst structures can significantly affect their
1
The H and 13C NMR spectra were recorded on a Bruker Avance
spectrometer at 400 and 100.6 MHz. 13C NMR spectra of polymers
were recorded on a Bruker AM-250 spectrometer at 62.5 MHz in
1,1,2,2-tetrachloroethane-d2 (C2D2Cl4) at 100 °C and referenced vs
hexamethyldisiloxane (HMDS).
Molecular weights (Mn and Mw) and polydispersities (PDI) of
polymer were determined by high-temperature GPC using a Waters
GPC-V200 RI detector. The measurements were recorded at 135 °C
using 1,2-dichlorobenzene as a solvent and Styragel columns (range
107 to 103). Every value was the average of two independent
measurements.
Polymers melting points (Tm) were measured by differential
scanning calorimetry using a TA Instruments DSC 2920 in nitrogen
flow with a heating and cooling rate of 10 °C/min. Melting
temperatures were reported for the second heating cycle.
N-(6-(1H-Pyrrol-2-yl)pyridin-2-yl)methyl)-2,6-diisopropylbenzen-
amine and complex 512a and N-(6-(1H-pyrrol-2-yl)pyridin-2-yl)(2-
isopropylphenyl)methyl)-2,6-diisopropylbenzenamine and complex
612b were synthesized according to the previously reported protocols.
Synthesis of Complexes. General Procedures. A solution of
M(NMe2)4 in benzene (5 mL) was added dropwise into a stirred
solution of the corresponding ligand in benzene (10 mL). The
solution was stirred for 30 min at ambient temperature. All volatiles
were removed under vacuum to yield a yellow solid. The product was
crystallized from hexane (5 mL) at −20 °C and then washed with cold
pentane.
LTi(NMe2)2 (1). The yellow solid was obtained in 86% yield (277
mg, 0.59 mmol). 1H NMR (400 MHz; CD2Cl2): δ 1.13 (6H, d, J = 8.0
Hz, CH(CH3)2), 1.19 (6H, d, J = 8.0 Hz, CH(CH3)2), 2.99 (12H, s,
Ti−NMe2), 3.30 (2H, sept, CH(CH3)2), 5.00 (2H, s, NCH2), 6.18
(1H, m, NC4H3), 6.61 (1H, m, NC4H3), 6.98 (1H, d, J = 8.0 Hz, H-
Py), 7.02 (1H, m, NC4H3), 7.03 (1H, s, Ar-H), 7.08 (1H, d, J = 8.0 Hz,
Ar-H), 7.26 (1H, d, J = 8.0 Hz, H-Py), 7.70 (1H, t, H-Py). 13C NMR
E
dx.doi.org/10.1021/om300519s | Organometallics XXXX, XXX, XXX−XXX

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(400 MHz; CD2Cl2): δ 24.05 (CH(CH3)2), 27.37 (CH(CH3)2), 28.09
(CH(CH3)2), 44.77 (Ti−NMe2), 68.05 (NCH2), 107.70 (NC4H3),
111.10 (NC4H3), 113.44 (C-Py), 113.65, 123.52, 124.42, 133.53,
139.92, 143.90, 153.99, 162.35. Anal. Calcd for C26H37N5Ti (fw =
467.47): C, 66.80; H, 7.98; N, 14.98. Found: C, 66.98; H, 8.37; N,
15.32. Mass spectrometric data (EI 70 eV, m/z): 490.08 [M + Na]+,
427.10 [M − iPr + H]+.
LHf(NMe2)2 (2). The yellow solid was obtained in 98% yield (122
mg, 0.20 mmol). 1H NMR (400 MHz; CD2Cl2): δ 1.14 (6H, d, J = 8.0
Hz, CH(CH3)2), 1.17 (6H, d, J = 8.0 Hz, CH(CH3)2), 2.79 (12H, s,
Hf−NMe2), 3.45 (2H, sept, CH(CH3)2), 4.92 (2H, s, NCH2), 6.23
(1H, m, NC4H3), 6.75 (1H, m, NC4H3), 6.95 (1H, d, J = 8.0 Hz, H-
Py), 7.04−7.13 (4H, m, Ar-H), 7.35 (1H, d, J = 8.0 Hz, H-Py), 7.73
(1H, t, H-Py). 13C NMR (400 MHz; CD2Cl2): δ 24.36 (CH(CH3)2),
26.77 (CH(CH3)2), 28.19 (CH(CH3)2), 40.88 (Hf−NMe2), 65.84
(NCH2), 110.10 (NC4H3), 111.37 (NC4H3), 114.26 (C-Py), 114.76,
123.78, 124.77, 133.58, 140.74, 141.40, 146.99, 149.47,155.26, 164.42.
Anal. Calcd for C26H37HfN5 (fw = 599.25): C, 52.21; H, 6.24; N,
11.71. Found: C, 52.54; H, 6.13; N, 11.45. Mass spectrometric data
(EI 70 eV, m/z): 623.13 [M + Na]+, 600.98 [M + H]+, 578.97 [M +
Na − NMe2]+.
LTi(NMe2)2 (3). The light yellow solid was obtained in 94% yield
(487 mg, 0.832 mmol). 1H NMR (400 MHz; CD2Cl2): δ 0.21 (3H, d,
J = 6.84 Hz, CH(CH3)2), 0.66 (3H, J = 6.72 Hz, CH(CH3)2), 0.99
(3H, J = 6.92 Hz, CH(CH3)2), 1.05 (3H, J = 6.92 Hz, CH(CH3)2),
1.08 (3H, d, J = 6.72 Hz, CH(CH3)2), 1.25 (3H, d, J = 6.6 Hz,
CH(CH3)2), 2.27 (1H, sept, CH(CH3)2), 2.64 (1H, sept, CH(CH3)2),
2.94 (3H, s, Ti−NMe2), 3.16 (3H, s, Ti−NMe2), 3.46 (1H, sept,
CH(CH3)2), 5.98 (1H, s, NCH), 6.20 (1H, m, NC4H3), 6.49 (1H, d, J
= 7.6 Hz, H-Py), 6.65 (1H, m, NC4H3), 6.94−7.14 (7H, m, Ar-H),
7.24 (1H, m, NC4H3), 7.28 (1H, d, J = 7.88 Hz, H-Py), 7.59 (1H, t, H-
Py). 13C NMR (400 MHz; CD2Cl2): δ 21.73 (CH(CH3)2), 24.22
(CH(CH3)2), 24.89 (CH(CH3)2), 26.06 (CH(CH3)2), 26.42 (CH-
(CH3)2), 26.80 (CH(CH3)2), 27.80 (CH(CH3)2), 28.57 (CH(CH3)2),
28.67 (CH(CH3)2), 45.76 (Ti−NMe2), 47.85 (Ti−NMe2), 77.81
(NCH), 107.74 (NC4H3), 111.38 (NC4H3), 113.70 (C-Py), 115.28 (C-
Py), 123.91, 124.35, 124.54, 125.47, 126.34, 127.89, 131.42, 133.35,
140.17, 140.34, 141.00, 143.13, 145.04, 148.03, 153.93, 154.04, 167.98.
Anal. Calcd for C35H47N5Ti (fw = 585.65): C, 71.78; H, 8.09; N,
11.96. Found: C, 72.17; H, 8.07; N, 11.75. Mass spectrometric data
(EI 70 eV, m/z): 1151.95 [2M − NMe2 + Na]+, 580.13 [M − NMe2 +
K]+, 541.09 [M − NMe2]+.
methods (SIR 97 package)24 and refined by the full-matrix least-
squares method (SHELXL program of SHELX97 package)25 on F2
against all independent measured reflections, using anisotropic thermal
parameters for all non-hydrogen atoms. H atoms were placed in
calculated positions with Ueq values equal to those of the carrier atom
and refined by the riding method. Data for complex 3: R1 = 0.0438;
wR2 = 0.0992 (on reflections with I > 2σ(I)). Data for complex 4: R1
= 0.0297; wR2 = 0.0501 (on reflections with I > 2σ(I)). All plots were
generated by using the program ORTEP-3.26 Crystal data and details
of the data collections are reported in the Supporting Information.
CCDC 864410 (Ti) and 868521 (Hf) contain supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
General Procedures for Ethylene and Propylene Polymer-
ization. The polymerizations were carried out in a magnetically stirred
flask (250 mL) or in a Buchi glass autoclave (500 mL). Under a
̈
nitrogen atmosphere, the required amount of AliBu2H (0.06 mM in
toluene) was added to solutions of the complexes in toluene (1 mL),
and then the mixtures were stirred for 10 min at room temperature.
The reactor vessels were charged sequentially with toluene, dried
MAO, and the solution of the precatalyst in toluene. The stirred
mixture was thermostated at the required temperature, and then the
monomer gas feed was started. After the prescribed time, the
polymerization mixture was poured into acidified methanol. The
polymers were filtered, washed with ethanol, and dried in a vacuum
oven at 60 °C overnight.
Fractionation Experiment. Polypropylene samples (Table 2, runs
1 and 3) were packed into a thimble and capped with filter paper
(Whatman 1#). A 250 mL round-bottom flask attached to a
Kumagawa extractor was charged with 100 mL of hexane. Extraction
was conducted overnight. After the extraction, the solvent was
removed under reduced pressure. The polymer fractions were dried
under vacuum at 60 °C overnight.
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures, tables, and CIF files giving 1H NMR spectra of
complexes 1−4, details on fractionation experiments, and X-ray
crystallographic data of complexes 3 and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
LHf(NMe2)2 (4). The light yellow solid was obtained in 97% yield
(620 mg, 0.87 mmol). 1H NMR (400 MHz; CD2Cl2): δ 0.11 (3H, d, J
= 6.84 Hz, CH(CH3)2), 0.57 (3H, J = 6.72 Hz, CH(CH3)2), 1.04 (9H,
m, CH(CH3)2), 1.30 (3H, d, J = 6.76 Hz, CH(CH3)2), 2.52 (1H, sept,
CH(CH3)2), 2.63 (3H, s, Hf−NMe2), 2.93 (1H, sept, CH(CH3)2),
3.04 (3H, s, Hf−NMe2), 3.31 (1H, sept, CH(CH3)2), 6.10 (1H, s,
NCH), 6.26 (1H, m, NC4H3), 6.49 (1H, d, J = 7.64 Hz, H-Py), 6.76
(1H, m, NC4H3), 6.95 (1H, m, NC4H3), 6.99−7.15 (6H, m, Ar-H),
7.36 (1H, d, J = 8.6 Hz, H-Py), 7.62 (1H, t, H-Py). 13C NMR (400
MHz; CD2Cl2): δ 22.19 (CH(CH3)2), 23.88 (CH(CH3)2), 25.16
(CH(CH3)2), 25.69 (CH(CH3)2), 25.99 (CH(CH3)2), 26.07 (CH-
(CH3)2), 27.92 (CH(CH3)2), 28.59 (CH(CH3)2), 28.86 (CH(CH3)2),
41.19 (Hf−NMe2), 42.62 (Hf−NMe2), 75.08 (NCH), 109.95
(NC4H3), 112.57 (NC4H3), 114.33 (C-Py), 116.67 (C-Py), 123.99,
124.58, 124.72, 125.61, 126.47, 127.76, 130.49, 133.59, 141.00, 141.33,
142.03, 146.61, 147.19, 147.63, 148.04, 155.14, 169.50. Anal. Calcd for
C35H47HfN5 (fw = 717.33): C, 58.69; H, 6.61; N, 9.78. Found: C,
58.95; H, 6.83; N, 9.67. Mass spectrometric data (EI 70 eV, m/z):
1412.93 [2M − NMe2 + Na]+.
X-ray Crystallography. Single crystals of 3 and 4 suitable for X-
ray analysis were obtained from n-hexane at 253 K. Data collections
were performed in flowing N2 at 173 K on a Bruker-Nonius
kappaCCD diffractometer (Mo Kα radiation, CCD rotation images,
thick slices, φ scans + ω scans to fill the asymmetric unit). Cell
parameters were determined from 90 reflections in the range 3.59° ≤ θ
≤ 23.04° and 406 reflections in the range 3.459° ≤ θ ≤ 23.045° for 3
and 4, respectively. Semiempirical absorption corrections (multiscan
SADABS)23 were applied. The structures were solved by direct
AUTHOR INFORMATION
Corresponding Author
*Tel: +39 089 969576. Fax: +39 089 969603. E-mail:
cpellecchia@unisa.it.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We are grateful to Professors Angela Tuzi and Roberto Centore
■
(Universita
(Universita
̀
“Federico II di Napoli”) and Dr. Consiglia Tedesco
di Salerno) for valuable discussions of the X-ray
̀
analysis. The contributions of Dr. Mariagrazia Napoli and Dr.
Patrizia Oliva for GPC analyses and for some NMR
experiments, respectively, are also acknowledged. G.R. thanks
̀
the CRdC ”Nuove Tecnologie per le Attivita Produttive” of
Campania Region (Italy) for use of Bruker-Nonius X-ray
equipment. This work was supported by the University of
Salerno (FARB Grant).
REFERENCES
■
(1) (a) Busico, V. Dalton Trans. 2009, 8794−8802. (b) Sita, L. R.
Angew. Chem., Int. Ed. 2009, 48, 2464−2472.
(2) For a collection of reviews on metallocene catalysts, see the issue:
Chem. Rev. 2000, 100 (4).
F
dx.doi.org/10.1021/om300519s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(3) (a) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283−
316. (b) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428−447.
(4) Lamberti, M.; Mazzeo, M.; Pappalardo, D.; Pellecchia, C. Coord.
Chem. Rev. 2009, 253, 2082−2097.
N. C.; Vittal, J. J. Macromolecules 1996, 29, 5241−5243. (c) Scollard, J.
D.; McConville, D. H. J. Am. Chem. Soc. 1996, 118, 10008−10009.
(14) (a) Segal, S.; Goldberg, I.; Kol, M. Organometallics 2005, 24,
200−202. (b) Cohen, A.; Kopilov, J.; Lamberti, M.; Venditto, V.; Kol,
M. Macromolecules 2010, 43, 1689−1691.
(15) (a) Diamond, G. M.; LaPointe, A. M.; Leclerc, M. K.; Longmire,
J.; Nava-Salgado, V.; Shoemaker, J. A. W.; Sun, P. (Symyx
Technologies, Inc.) U.S. Patent 7,256,296, 2007. (b) Diamond, G.
M.; LaPointe, A. M.; Leclerc, M. K.; Longmire, J.; Nava-Salgado, V.;
Shoemaker, J. A. W.; Sun, P. (Symyx Technologies, Inc.) U.S. Patent
7,387,980, 2008. (c) Frazier, K. A.; Froese, R. D.; He, Y.; Klosin, J.;
Theriault, C. N.; Vosejpka, P. C.; Zhou., Z. Organometallics 2011, 30,
3318−3329. (d) Diamond, G. M.; Hall, K. A.; LaPointe, A. M.;
Leclerc, M. K.; Longmire, J.; Shoemaker, J. A. W.; Sun, P. ACS Catal.
2011, 1, 887−900. (e) Luconi, L.; Rossin, A.; Tuci, G.; Tritto, I.;
Boggioni, L.; Klosin, J. J.; Theriault, C. N.; Giambastiani, G. Chem. Eur.
J. 2012, 18, 671−687.
(16) (a) Addison, A. W.; Nageswara Rao, T.; Reedijk, J.; van Rijn, J.;
Veschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1355.
(b) Bukowska-Strzyzewska, M.; Maniukiewicz, W.; Sieron, L. Acta
Crystallogr. 1997, B53, 466−475. (c) Munoz-Hernandez, M. A.;
Keizer, T. S.; Wei, P.; Parkin, S.; Atwood, D. A. Inorg. Chem. 2001, 40,
6782−6787.
(5) (a) Tian, J.; Coates, G. W. Angew. Chem., Int. Ed. 2000, 39,
3626−3629. (b) Saito, J.; Mitani, M.; Mohri, J.; Ishii, S.; Yoshida, Y.;
Matsugi, T.; Kojoh, S.; Kashiwa, N.; Fujita, T. Chem. Lett. 2001, 576−
577. (c) Saito, J.; Mitani, M.; Onda, M.; Mohri, J.; Ishii, S.; Yoshida, Y.;
Nakano, T.; Tanaka, H.; Matsugi, T.; Kojoh, S.; Kashiwa, N.; Fujita, T.
Macromol. Rapid Commun. 2001, 22, 1072−1075. (d) Tian, J.; Hustad,
P. D.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 5134−5135.
(e) Lamberti, M.; Pappalardo, D.; Zambelli, A.; Pellecchia, C.
Macromolecules 2002, 35, 658−663. (f) Mitani, M.; Furuyama, R.;
Mohri, J.; Saito, J.; Ishii, S.; Terao, H.; Nakano, T.; Tanaka, H.; Fujita,
T. J. Am. Chem. Soc. 2003, 125, 4293−4305. (g) Lamberti, M.;
Consolmagno, M.; Mazzeo, M.; Pellecchia, C. Macromol. Rapid
Commun. 2005, 26, 1866−1871. (h) Mazzeo, M.; Strianese, M.;
Lamberti, M.; Santoriello, I.; Pellecchia, C. Macromolecules 2006, 39,
7812−7820. (i) Edson, J. B.; Wang, Z.; Kramer, E. J.; Coates, G. W. J.
Am. Chem. Soc. 2008, 130, 4968−4977. (j) For a recent review see:
Makio, H.; Terao, H.; Iwashita, A.; Fujita, T. Chem. Rev. 2011, 111,
2363−2449.
(17) For titanium complexes: (a) Westmoreland, I.; Munslow, I. J.;
O’Shaughnessy, P. N.; Scott, P. Organometallics 2003, 22, 2972−2976.
(b) Fuhrmann, H.; Brenner, S.; Arndt, P.; Kempe, R. Inorg. Chem.
1996, 35, 6742−6745.
(18) Busico, V.; Cipullo, R.; Pellecchia, R.; Talarico, G.; Razavi, A.
Macromolecules 2009, 42, 1789−1791.
(6) (a) Tshuva, E. Y.; Goldberg, I.; Kol, M. J. Am. Chem. Soc. 2000,
122, 10706−10707. (b) Busico, V.; Cipullo, R.; Friederichs, N.; Ronca,
S.; Talarico, G.; Togrou, M.; Wang, B. Macromolecules 2004, 37,
8201−8203. (c) Busico, V.; Cipullo, R.; Pellecchia, R.; Ronca, S.;
Roviello, G.; Talarico, G. Proc. Natl. Acad. Sci. U.S.A. 2006, 103,
15321−15326. (d) Strianese, M.; Lamberti, M.; Mazzeo, M.;
Pellecchia, C. Macromol. Chem. Phys. 2008, 209, 585−592. (e) Gendler,
S.; Zelikoff, A. L.; Kopilov, J.; Goldberg, I.; Kol, M. J. Am. Chem. Soc.
2008, 130, 2144−2145. (f) Cohen, A.; Kopilov, J.; Goldberg, I.; Kol,
M. Organometallics 2009, 28, 1391−1405.
(19) (a) Shelden, R. A.; Fueno, T.; Tsunetsugu, T.; Furokawa, J. J.
Polym. Sci., Part B 1965, 3, 23. (b) Wolfsgruber, C.; Zannoni, G.;
Rigamonti, E.; Zambelli, A. Makromol. Chem. 1975, 176, 2765−2769.
(20) Paolucci, G.; Zanella, A.; Sperni, L.; Bertolasi, V.; Mazzeo, M.;
Pellecchia, C. J. Mol. Catal. A: Chem. 2006, 258, 275−283.
(21) (a) Asakura, T.; Nishiyama, Y.; Doi, Y. Macromolecules 1987, 20,
616−620. (b) Grassi, A.; Zambelli, A.; Resconi, L.; Albizzati, E.;
Mazzocchi, R. Macromolecules 1988, 21, 617−622. (c) Busico, V.;
Cipullo, R. Prog. Polym. Sci. 2001, 26, 443−533. (d) Busico, V.;
Cipullo, R.; Polzone, C.; Talarico, G.; Chadwich, J. C. Macromolecules
2003, 36, 2616−2622.
(7) (a) Boussie, T. R.; Brummer, O.; Diamond, G. M.; LaPointe, A.
̈
M.; Leclerc, M. K.; Micklatcher, C.; Sun, P.; Bei, X. U.S. Patent US
7,241,714 B2, 2007. (b) Kiesewetter, E. T.; Randoll, S.; Radlauer, M.;
Waymouth, R. M. J. Am. Chem. Soc. 2010, 132, 5566−5567.
(8) (a) Ishii, A.; Toda, T.; Nakata, N.; Matsuo, T. J. Am. Chem. Soc.
2009, 131, 13566−13567. (b) Nakata, N.; Toda, T.; Ishii, A. Polym.
Chem. 2011, 2, 1597−1610.
(22) For the nomenclature of the carbons, see: Carman, C.; Wilkes,
C. E. Rubber Chem. Technol. 1971, 44, 781.
(23) Sheldrick, G. M. SADABS, Program for empirical absorption
(9) Press, K.; Cohen, A.; Goldberg, I.; Venditto, V.; Mazzeo, M.; Kol,
M. Angew. Chem., Int. Ed. 2011, 50, 3529−3532.
(10) (a) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.;
LaPointe, A. M.; Leclerc, M. K.; Lund, C.; Murphy, V. PCT Pat. Appl.
WO 038628, 2002. (b) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall,
K. A.; LaPointe, A. M.; Leclerc, M. K.; Lund, C.; Murphy, V.;
Shoemaker, J. A. W.; Tracht, U.; Turner, H.; Zhang, J.; Uno, T.;
Rosen, R. K.; Stevens, J. C. J. Am. Chem. Soc. 2003, 125, 4306.
(c) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A.
M.; Leclerc, M. K.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.;
Rosen, R. K.; Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R.;
Talarico, G. Angew. Chem., Int. Ed. 2006, 45, 3278−3283.
(d) Zuccaccia, C.; Macchioni, A.; Busico, V.; Cipullo, R.; Talarico,
G.; Alfano, F.; Boone, H. W.; Frazier, K. A.; Hustad, P. D.; Stevens, J.
C.; Vosejpka, P. C.; Abboud, K. A. J. Am. Chem. Soc. 2008, 130,
10354−10368. (e) Zuccaccia, C.; Busico, V.; Cipullo, R.; Talarico, G.;
Froese, R. D. J.; Vosejpka, P. C.; Hustad, P. D.; Macchioni, A.
Organometallics 2009, 28, 5445−5458. (f) Busico, V.; Cipullo, R.;
Pellecchia, R.; Rongo, L.; Talarico, G.; Macchioni, A.; Zuccaccia, C.;
Froese, R. D. J.; Hustad, P. D. Macromolecules 2009, 42, 4369−4373.
(11) Domski, G. J.; Lobkovsky, E. B.; Coates, G. W. Macromolecules
2007, 40, 3510−3513.
correction; University of Gottingen, Gottingen, Germany, 1996.
̈
̈
(24) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J. Appl. Crystallogr. 1999, 32, 115−119.
(25) Sheldrick, G. M. SHELX-97; University of Gottingen,
̈
Gottingen, Germany, 1997.
̈
(26) Ortep-3: Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(12) (a) Annunziata, L.; Pappalardo, D.; Tedesco, C.; Pellecchia, C.
Macromolecules 2009, 42, 5572−5578. (b) Li, G.; Lamberti, M.;
D’Amora, S.; Pellecchia, C. Macromolecules 2010, 43, 8887−8891.
(c) Li, G.; Lamberti, M.; Mazzeo, M.; Pappalardo, D.; Roviello, G.;
Pellecchia, C. Organometallics 2012, 31, 1180−1188.
(13) (a) Scollard, J. D.; McConville, D. H.; Vittal, J. J. Organometallics
1995, 14, 5478−5480. (b) Scollard, J. D.; McConville, D. H.; Payne,
G
dx.doi.org/10.1021/om300519s | Organometallics XXXX, XXX, XXX−XXX