New η2-formamidinyl zirconium complexes: Synthesis, characterization, and catalytic activity

Article abstract of DOI:10.1021/om030268+

The new η²-formamidinyl Zr complex Zr(NMeCyc)₂[C(NAr)NMeCyc]₂ (1) (Ar = 2,6-dimethylphenyl, Cyc = cyclohexyl) was prepared upon double insertion of 2,6-dimethyl phenyl isocyanide in the Zr-N bond of Zr(NMeCyc)₄. 1 was then converted into Zr(OC₆F₅)₂[C(NAr)N-MeCyc]₂ (2) and ZrCl₂[C(NAr)NMeCyc]₂ (3) by reacting it with C₆F₅OH and [NHMe₃]Cl, respectively. The crystal structure of 1 was established by X-ray analysis. All the complexes have been tested as catalysts for the polymerization of ethylene and 1-hexene in the presence of [NHMe₂Ph][B(C₆F₅)₄] as cocatalyst.

Full text of DOI:10.1021/om030268+

Organometallics 2003, 22, 3985-3990
3985
New η2-F or m a m id in yl Zir con iu m Com p lexes: Syn th esis,
Ch a r a cter iza tion , a n d Ca ta lytic Activity
Franco Benetollo,† Giovanni Carta,† Gianni Cavinato,‡ Laura Crociani,*,†
Gino Paolucci,§ Gilberto Rossetto,† Francesco Veronese,† and Pierino Zanella†
Istituto di Chimica Inorganica e delle Superfici, CNR, Area della Ricerca di Padova, C.so
Stati Uniti 4, 35127 Padova, Italy, Dipartimento di Chimica Inorganica, Metallorganica ed
Analitica, Universita` di Padova, Via Marzolo 1, 35131 Padova, Italy, and Dipartimento di
Chimica, Universita` Ca’ Foscari di Venezia, Dorsoduro 2137, 30123 Venezia, Italy
Received April 14, 2003
The new η2-formamidinyl Zr complex Zr(NMeCyc)2[C(NAr)NMeCyc]2 (1) (Ar ) 2,6-
dimethylphenyl, Cyc ) cyclohexyl) was prepared upon double insertion of 2,6-dimethyl phenyl
isocyanide in the Zr-N bond of Zr(NMeCyc)4. 1 was then converted into Zr(OC6F5)2[C(NAr)N-
MeCyc]2 (2) and ZrCl2[C(NAr)NMeCyc]2 (3) by reacting it with C6F5OH and [NHMe3]Cl,
respectively. The crystal structure of 1 was established by X-ray analysis. All the complexes
have been tested as catalysts for the polymerization of ethylene and 1-hexene in the presence
of [NHMe2Ph][B(C6F5)4] as cocatalyst.
In tr od u ction
must satisfy steric requirements both to increase the
stereoselectivity and to prevent termination reactions
such as â-H elimination, which would compromise the
chain growth. Nitrogen- and oxygen-based ligands to
form electronically unsaturated early transition metal
complexes have been reported to have more or less
remarkable effects.3
We focused our interest on the synthesis of zirconium
amides of general formula ZrX2(NRR′)2, to be used as
starting material for the new zirconium diamido di(η2-
formamidinyl) species formed by double migratory
insertion of isocyanides, CNR, into the Zr-N amide
bonds.
To date, the insertion of CNR into early transition
metal-amido bonds has been poorly investigated. To the
best of our knowledge only one paper has appeared
regarding specifically Zr-η2-formamidinyl complexes
starting from mixed silylamido-Zr compounds.4
Several years ago we started to study the reactivity
of ZrCl2(NMe2)2‚2THF with various isocyanides, and we
isolated the products of double insertion of isocyanides,
ZrCl2[C(NR)NMe2] (R ) p-tolyl, p-MeO-C6H4, t-Bu), as
red-orange powders, which exhibited appreciable cata-
lytic activity in the polymerization of ethylene by
activation with [NHMe2Ph][B(C6F5)4] and/or MAO.5
These results prompted us to extend our research to
other analogous substrates containing differently sub-
stituted zirconium amides.
Homogeneous catalysts for the olefin polymerization
have known a huge development after the first Ziegler-
Natta catalysts were discovered.1 In the last 20 years
group 4 element metallocenes offered to academic and
industrial research simple, structurally well defined,
and molecularly easily tunable models, very useful for
the study of the olefin polymerization parameters
controlling the activity, stereoselectivity, molecular
weight, polydispersivity, and the microstructure of the
polyolefins.2 However, the increasing demand for more
active and selective catalysts to provide greater control
over the properties of the polymers and to achieve the
possibility of introducing new monomer combinations
is forcing the research toward a new generation of olefin
polymerization catalysts that are an alternative to
metallocene-based systems.
At present the replacement of the Cp ligand by a less
electron-rich group would make the metal center more
electrophilic, thus affording a potentially more active
catalyst by favoring the coordination step of the Ziegler-
Natta polymerization. In addition the ligand selection
* Corresponding author. E-mail: crociani@icis.cnr.it.
† Istituto di Chimica Inorganica e delle Superfici, CNR.
‡ Universita` di Padova.
§ Universita` Ca’ Foscari di Venezia.
(1) For recent reviews and books see: (a) Buchmeiser, M. R.
Macromol. Symp. 2002, 181, 23. (b) Blom, R., Follestad, A., Rytter,
E., Tilsel, M., Ystenes, M., Eds. Organometallic Catalyst and Olefin
Polymerization; Springer: Berlin, 2001. (c) Gladysz, J . A., Ed. Chem.
Rev. 2000, 100 (special issue on Frontiers in Metal-Catalyzed Polym-
erization). (c) Marks, T. J ., Stevens, J . C., Eds. Top. Catal. 1999, 7, 1
(special volume on Advances in Polymerization Catalysis, Catalysts
and Processes).
(2) For recent reviews and books see: (a) Scheirs, J ., Kaminsky, W.,
Eds. Metallocene-Based Polyolefins, Vol I and II; Wiley: Chichester,
2000. (b) Kaminsky, W. Metalorganic Catalysts for Synthesis and
Polymerization: Recent Results by Ziegler-Natta and Metallocene
Investigations; Springer-Verlag: Berlin, 1999. (c) J ordan, R. F. J . Mol.
Catal. 1998, 128, 1 (special issue on metallocene and single-site olefin
catalysts). (d) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998,
98, 2587.
Here we report our most recent results on the
synthesis of the new η2-formamidinyl complexes ZrX2-
[C(NAr)NMeCyc]2 (Ar ) 2,6-dimethylphenyl, Cyc )
(3) For recent reviews see: (a) Imanishi, Y.; Naga, N. Prog. Polym.
Sci. 2001, 26, 1147. (b) Britovsek, G. J . P.; Gibson, C. V.; Wass, F. D.
Angew. Chem., Int. Ed. 1999, 38, 428.
(4) Wu, Z.; Diminnie, J . B.; Xue, Z. Organometallics 1999, 18, 1002.
(5) Garon, S.; Carta, G.; Rossetto, G.; Zanella, P. Atti del XXVII
Congresso di Chimica, COMO 1999, 51.
10.1021/om030268+ CCC: $25.00 © 2003 American Chemical Society
Publication on Web 08/29/2003

3986 Organometallics, Vol. 22, No. 20, 2003
Benetollo et al.
prepared in situ from Lin-Bu and cyclohexylmethy-
lamine, and it was characterized via elemental analysis
1
and NMR spectroscopy. The H NMR spectrum of Zr-
(NCycMe)4 in C6D6 solution at 295 K (for the assign-
ments see the proton numbering in Figure 1) displays
a singlet at δ 3.05 (integrated for 12 H) assignable to
the N-CH3 protons and a multiplet (triplet of triplets)
centered at δ 3.00 assignable to the H1 protons of the
cyclohexyl groups both coupled with the neighboring
axial protons (H2, H6) (3J ) 11.05 Hz) and with the two
neighboring equatorial protons (H3, H11) (3J ) 3.06 Hz).
A series of multiplets ranging from δ 1.1 and 2.0 could
be assigned to the 40 residual cyclohexyl protons.
The tetra-amide Zr(NCycMe)4 was then reacted with
2 mol of 2,6-dimethylphenyl isocyanide at -90 °C in
F igu r e 1. Numbering scheme for the protons in the Zr-
(NCycMe)4 and related complexes containing the cyclohexyl
group.
cyclohexyl, X ) NMeCyc, OC6F5, Cl), their characteriza-
tion, and the catalytic activity in the polymerization of
1-hexene and ethylene in the presence of [NHMe2Ph]-
[B(C6F5)4].
Resu lts a n d Discu ssion
n-hexane (Scheme 1), giving the complex Zr(NMeCyc)2-
Syn th etic Ap p r oa ch es to th e Isocya n id e In ser -
tion P r od u cts. The synthetic approach to zirconium
complexes containing two η2-formamidinyl moieties
(FAM) of the type ZrX2(FAM)2 could be carried out in
two different ways by using either Zr diamide dichloride
or Zr tetra-amide complexes as starting materials. The
presence of the two η2-formamidinyl ligands helps
stabilize these complexes and their derivatives. By
varying the ancillary X groups, the catalytic behavior
of these electrophilic complexes can be modified as
needed.
First we tried to react ZrCl2(NMe2)2‚2THF and ZrCl2-
(NEt2)2‚2THF (more stable and easier to isolate and
purify than ZrCl2(NMe2)2‚2THF) with 2 equiv of 2,6-
dimethylphenyl isocyanide. However in both cases we
obtained mixtures of products which could not be readily
separated. Then, we reacted Zr(NMe2)4 with 2 equiv of
2,6-dimethylphenyl isocyanide: even at -90 °C, the
[C(NAr)NMeCyc]2 (1) as a white powder after workup
in 77% yield, according to the reaction in Scheme 1.
The IR spectrum in n-hexane shows an absorption at
1639 cm-1 characteristic of the stretching of a double
CdN bond.
Rea ctivity. The presence in complex 1 of two Zr-
amido groups which easily undergo substitution by
protonolysis suggests that complex 1 could be used as
a starting material to prepare other complexes. In fact,
complex 1 was then converted into the pentafluoro
phenoxide and chloride derivatives by reaction with 2
equiv of C6F5OH and [NMe3H]Cl in Et2O, respectively,
(Scheme 2): Zr(OC6F5)2[C(NAr)NMeCyc] (2) is a yellow
oil (yield 90%), while ZrCl2[C(NAr)NMeCyc] (3) is a
white powder (yield 83%).
The stretching frequency of the double CdN bond
does not change significantly (1638 cm-1 for 2 and 1639
cm-1 for 3 in n-hexane).
The synthetic approach based on the double insertion
of 2,6-dimethylphenylisocyanide into two Zr-N bonds
of Zr(NMeCyc)4 afforded the η2-formamidinyl Zr com-
plex 1, which had been shown to be a versatile reagent
for the preparation of 2 and 3.
main product was Zr[C(NAr)NMe2]4 (Ar ) 2,6-dimeth-
ylphenyl) derived by the tetra-insertion of the isocyanide
into the Zr-N bond, already described in the literature.4
Since the doubly inserted product has never been
isolated from the reaction mixture, such results have
shown that the double-insertion reaction is strictly
governed by the reactivity of the substrates and their
steric hindrance. In view of these results we increased
the steric bulk of the amido ligands by incorporation of
a cyclohexyl group to see if the additional steric hin-
drance could be used to control the extent of isocyanide
insertion. The tetra-amide Zr(NCycMe)4 was synthe-
sized by reacting ZrCl4 with 4 mol of LiNCycMe,
NMR Ch a r a cter iza tion . The assignments of the
1
signals of the H and 13C NMR spectra of compounds
1-3 in C6D6 solution at 298 K have been carried out by
means of HMQC experiments. In some cases the broad-
ening of the signals suggests the fluxional behavior of
the compounds. The presence of common ancillary
ligands in the complexes 1-3 contributes to the assign-
Sch em e 1

η2-Formamidinyl Zirconium Complexe
Organometallics, Vol. 22, No. 20, 2003 3987
Sch em e 2
ments of the 1H and 13C NMR spectra in addition to
the HMQC experiments. The 1H NMR spectrum of 1
displays in the range δ 6.89-δ 7.05 a combination of
triplets and doublets assignable to the meta- and para-
phenyl protons of the two -CdN-C6H3-2,6-(CH3)2
group. The multiplet (triplet of triplets) centered at δ
3.85 could be assigned to the H1 cyclohexyl protons of
the two -N(CH3)C6H11 units (see Figure 1), and the
multiplet at δ 3.60 to the H1 cyclohexyl protons of the
two -NdC-N(CH3)C6H11 groups. In fact the H1 cyclo-
hexyl protons of the -N(CH3)C6H11 undergo a greater
deshielding than the corresponding H1 cyclohexyl pro-
tons of the -NdC-N(CH3)C6H11, as they are closer to
the zirconium ion. A sharp singlet at δ 3.19 was
assigned to the Zr-N(CH3)C6H11, and the strong singlet
at δ 2.28 could be assigned to the methyl protons of the
two -CdN-C6H3(CH3)2 units and a series of broad
signals ranging from δ 1.8 to 1.02 due to the remaining
cyclohexyl protons. Correspondingly on the basis of the
HMQC experiment the signals of the 13C NMR spectrum
of 1 were assigned as follows: the signals at δ 213.36
and 211.03 are due to the imino carbon atoms of the
two -NdC-NRR′ (R ) CH3; R′ ) C6H11). The series of
signals at δ 151.17, 130.73, 127.48, and 122.49 were
assigned to the phenyl carbon atoms of the 2,6-dimeth-
ylphenyl groups. The signal at δ 66.11 was assigned to
the C1 atom of the cyclohexyl group of the Zr-N(CH3)-
C6H11 residue, whereas the signal at δ 61.13 is due to
the C1 atom of the cyclohexyl group of the -NdCN-
(CH3)C6H11 molecule fragment. The signals at δ 33.44
and 31.23 are due to the methyls of the groups
-NdCN(CH3)C6H11 and Zr-N(CH3)C6H11, respectively,
and the resonance at δ 19.65 was assigned to the
methyls bonded to the aromatic groups. The substitution
of the methylcyclohexylamino groups in complex 1 with
NMR spectrum of 2 at 298 K showed a doublet centered
at δ 7.14 (J ) 7.6 Hz) assignable to the meta-phenyl
protons and a triplet at δ 6.99 (J ) 7.6 Hz) due to the
para-phenyl protons. A broad signal centered at δ 2.81
was assigned to the N-CH3; the H1 protons of the two
cyclohexyl groups give rise to a broad signal centered
at δ 2.48, while the sharp singlet at δ 2.30 is due to the
methyls of the 2,6-dimethylphenyl groups. A series of
unresolved broad signals in the range δ 1.70-0.80 are
assigned to the remaining cyclohexyl protons. The
1
broadness of the signals in the H NMR spectrum of 2
could be attributable to the lesser steric hindrance of
the ligands than in complex 1, which exhibits more
conformational rigidity than 2. These signals become
sharp by increasing the temperature as a consequence
of the increased rotational freedom, which makes the
methyl groups equivalent to one another. The HMQC
experiments made possible the assignments of the
signals in the 13C NMR spectrum of 2 as follows: the
two signals at δ 214.52 and 213.02 are due to the two
-NdC-N(CH3)C6H11; the four signals at δ 152.46,
129.50, 128.13, 122.03 are assigned to the carbon atoms
of the disubstituted phenyl groups. A series of signals
in the range δ 140.00-135.00 are assigned to the carbon
atoms of the two pentafluorophenyl groups. The signal
of the C1 atoms of the two cyclohexyl groups are at δ
58.49, the C atoms of the methyl groups bonded to the
nitrogen are at δ 31.45, and those of the two 2,6-
(CH3)2C6H3 are at δ 18.85. Finally a series of signals
ranging between δ 32.00 and 24.80 are assigned to the
remaining cyclohexyl carbon atoms. A further confirma-
tion of the assignments of the previous complexes 1 and
2 comes from the comparison with the 1H and 13C NMR
spectra of the complex 3, having only the two -NdC-
N(CH3)C6H11 groups in common with the other com-
plexes. The 1H NMR showed a doublet centered at δ
1
pentafluorophenoxy groups affords complex 2. The H

3988 Organometallics, Vol. 22, No. 20, 2003
Benetollo et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Zr (NMeCyc )2[C(NAr )NMeCyc]2 (1)
Zr-N(1)
2.064(3)
2.259(4)
1.452(7)
1.464(6)
1.321(5)
Zr-N(3)
2.221(3)
1.459(6)
1.341(5)
1.463(6)
1.425(5)
Zr-C(8)
N(1)-C(1)
N(2)-C(8)
N(2)-C(15)
N(3)-C(16)
N(1)-C(7)
N(2)-C(9)
N(3)-C(8)
N(3)-Zr-C(8)
N(1)-Zr-N(3)
N(1)-Zr-N(1)a
C(8)-Zr-C(8)a
Zr-N(1)-C(1)
C(9)-N(2)-C(15)
C(8)-N(2)-C(9)
Zr-N(3)-C(8)
N(1)-C(1)-C(6)
N(2)-C(8)-N(3)
Zr-C(8)-N(2)
N(2)-C(9)-C(10)
N(3)-C(16)-C(17)
34.3(1)
N(1)-Zr-C(8)
102.1(1)
89.7(2)
134.0(2)
111.4(3)
89.7(2)
114.5(4)
123.9(4)
152.8(3)
132.5(3)
113.9(4)
71.3(2)
120.5(1)
100.0(2)
108.4(2)
134.1(3)
118.2(4)
117.8(4)
74.5(2)
114.0(4)
127.6(4)
161.1(3)
111.9(4)
120.3(3)
N(3)-Zr-N(1)a
N(3)-Zr-N(3)a
Zr-N(1)-C(7)
N(3)-Zr-N(1)a
C(1)-N(1)-C(7)
C(8)-N(2)-C(15)
Zr-N(3)-C(16)
C(8)-N(3)-C(16)
N(1)-C(1)-C(2)
Zr-C(8)-N(3)
N(2)-C(9)-C(14)
N(3)-C(16)-C(21)
112.8(4)
118.6(4)
F igu r e 2. ORTEP view of the Zr(NMeCyc)2[C(NAr)N-
MeCyc]2 (1) with the atom nomenclature.
a
At -x, -y, z.
consistent with the planarity of the C(8)-N(2)-C(9)-
C(15) group and with the sum of the angles around N(2)
of 360°. The same behavior has been observed in Zr[η2-
C(NMe2)dNAr]3{η2-C[Si(SiMe3)3]dNAr},4 where all the
ligands are η2-bonded to the central metal ion.
7.15 (J ) 7.6 Hz) due to the meta-phenyl protons and
the triplet at δ 7.00 (J ) 7.6 Hz) of the para-phenyl
protons, a broad singlet at δ 2.82 assignable to the
-N(CH3)C6H11, a broad multiplet at δ 2.44 due to the
H1 protons bonded to the C1 carbon atom of the
cyclohexyl groups, a singlet at δ 2.31 of the methyl
groups of the -CdN-C6H3(CH3)2 units, and finally a
series of broad signals ranging from δ 1.85 to 0.90
assignable to the remaining cyclohexyl protons. The
signals of the 13C NMR spectrum were assigned on the
basis of the HMQC experiments as follows: δ 209.62,
208.44 to the two NdC-N quaternary carbon atoms, δ
152.31, 130.69, 127.48, 121.79 to the phenyl carbon
atoms -C6H3(CH3)2, δ 65.67 assignable to the C1 carbon
atoms of the cyclohexyl groups, δ 31.73 to the methyl
group bonded to the nitrogen atom of the NdC-N(CH3)-
C6H11 residue, δ 18.92 assigned to the carbon atoms of
the methyl substituents in the phenyl rings [CdNC6H3-
(CH3)2], and a series of signals between δ 22.8 and 26.1
assignable to the remaining cyclohexyl carbon atoms.
X-r a y Cr ysta l Str u ctu r e of 1. An ORTEP view of
The insertion of the monodentate amide is character-
ized by a short Zr-N distance (Zr-N(1) 2.064(3) Å), as
7
found for other amido complexes such as Zr(NMe2)4
(electron diffraction) (Zr-N 2.07 Å) and [(C5Me4)SiMe2-
(N-t-Bu)]Zr[N(R)C(Me)dC(Me)N(R)] (R ) tert-butyl and
2,6-xylyl)8 with Zr-N bond distances ranging between
2.06 and 2.07 Å, reflecting again N π-donation to the
electrophilic d0 Zr center.
Ca ta lytic Tests. Complexes 1, 2, and 3, when treated
with stoichiometric amounts of [HNMe2Ph]B(C6F5)4 as
activator and with Al(i-Bu)3 as scavenger, were found
to promote the polymerization of 1-hexene and ethylene.
The specific reaction conditions, the catalytic activity,
and some properties of the polymers such as average
molecular weights (by viscometry) and melting points
are reported in Tables 2 and 3 for the polymerization
of 1-hexene and ethylene, respectively.
These complexes catalyze the polymerization of 1-hex-
ene and ethylene exhibiting low to moderate activity,
respectively. The activity decreases on going from the
amido to the chloride derivatives. By comparison to the
zirconocene, ZrCp2Cl2, these complexes showed a lower
activity but higher reproducibility of the results under
the same polymerization conditions. This trend of activ-
ity, 1 > 2 > 3, could be assigned to the electronic and
steric properties of the different groups X of the com-
the molecular structure of Zr(NMeCyc)2[C(NAr)N-
MeCyc]2, 1, together with the atom numbering is in
Figure 2.
Selected bond distances and angles are given in Table
1. The molecular structure of 1 has C2 symmetry. The
zirconium atom lies on the 2-fold crystallographic axis,
and it is coordinated to two η2-(NdC) moieties as well
as to two η1-(NMeCyc), both symmetry related. The
coordination sphere around Zr can be described as a
pseudotetrahedron with each η2-formamidinyl unit oc-
cupying a single coordination site.
plexes ZrX2[C(NAr)NMeCyc]2.
The Zr-C(8) (2.259(4) Å) and Zr-N(3) (2.221(3) Å)
bond distances are comparable to those found in (Me3-
CCH2)3Zr{η2-C[Si(SiMe3)3]dNAr}6 (Zr-C(1) 2.255(4),
Zr-N(1) 2.175(3)Å) despite the different hindrance of
the cyclohexyl with respect to the substituted xylyl
group. The C-N(Me)Cyc bond distance of 1.341(5) Å is
between the double bond -CdN- [C(8)-N(3) 1.321(5)
Å] and N-Car (1.463(6) Å) single bond, suggesting some
degree of π-π bonding in the (Me)Cyc-N-CdN moiety
On the other hand, the physical properties of the poly-
(1-hexenes) and polyethylenes obtained, which have
been evaluated by means of viscometry and differential
scanning calorimetry (DSC), deserve a deeper insight.
The poly(1-hexenes) show high molecular weights,
higher than those already reported in the literature: in
the temperature range -30 to +300 °C no vitreous
transition is observed as well as crystallization or
(7) Hagen, K.; Holwill, C. J .; Rice, D. A.; Runnacles, J . D. Inorg.
Chem. 1998, 27, 2032.
(8) Kloppenburg, L.; Petersen, J . L. Organometallics 1997, 16, 3548.
(6) Wu, Z.; McAlexander, L. H.; Diminnie, J . B.; Xue, Z. Organo-
metallics 1998, 17, 4852.

η2-Formamidinyl Zirconium Complexe
Organometallics, Vol. 22, No. 20, 2003 3989
Ta ble 2. Con d ition s a n d Resu lts of th e P olym er iza tion of 1-Hexen ea
b
c
d
g
complex
(mol)
Tinit.
Tfin.
treact.
activitye
(kgp/molcat‚h‚bar)
% conversion of
Mwv
run
(°C)
(°C)
(min)
1-hexenef [yield (g)]
(g/mol)
1
2
3
1
2
3
1
2
3
1 (5 × 10-5
1 (5 × 10-5
1 (5 × 10-5
2 (5 × 10-5
2 (5 × 10-5
2 (5 × 10-5
3 (5 × 10-5
3 (5 × 10-5
3 (5 × 10-5
)
)
)
)
)
)
)
)
)
24.5
23.0
21.2
22.5
23.0
22.0
21.5
23.0
22.0
28.8
27.7
25.0
26.0
26.9
26.1
24.0
25.7
24.9
60
60
60
60
60
60
60
60
60
14
3.47 [0.70]
3.86 [0.78]
3.12 [0.63]
2.48 [0.50]
2.87 [0.58]
2.33 [0.47]
1.49 [0.30]
1.88 [0.38]
1.09 [0.22]
423 000
402 000
442 000
578 000
590 000
512 000
953 000
915 000
897 000
15.6
12.6
10.0
11.6
9.4
6.0
7.6
9.4
a
b
c
Conditions: solvent, toluene 10 mL, nAl(-Bu)3/ncat) 8, 1-hexene 30 mL. Tinit. ) initial temperature. Tfin. ) temperature at the end
of the polymerization. treact. ) reaction time. e kgp ) kilograms of polymer, molcat ) moles of catalyst. f conversion ) 100‚gpolymer/g1-hexene
.
d
g
Mwv ) average molecular weight of the polymer measured via viscometry.
Ta ble 3. Con d ition s a n d Resu lts of th e
P olym er iza tion of Eth ylen ea
agreement with the fact that the crystallinity degree
tends to decrease by increasing the polymerization and
molecular weight.
In conclusion, the polymers produced with this new
family of η2-formamidinyl catalysts showed interesting
rheological properties and high molecular weight with
low dispersivity.
b
d
complex treact.
activityc
yield Mwv
mpe
run
(mol) (min) (kgp/molcat‚h‚bar) (g) (g/mol) (°C)
1
2
3
1
2
3
1
2
3
1
1 (10-5
1 (10-5
1 (10-5
2 (10-5
2 (10-5
2 (10-5
3 (10-5
3 (10-5
3 (10-5
ZrCp2Cl2
(10-5
ZrCp2Cl2
(10-5
)
20
20
20
20
20
20
20
20
20
20
58.8
66.7
54.5
45.5
49.7
41.2
22.4
33.3
26.7
0.97 n.d.
1.10 n.d.
0.90 n.d.
0.75 n.d.
0.82 n.d.
0.68 n.d.
0.37 n.d.
0.55 n.d.
0.44 n.d.
134.5
134.9
135.1
135.7
135.4
136.1
136.7
136.4
136.9
)
)
)
)
)
)
)
)
Exp er im en ta l Section
All manipulations were performed in an oxygen- and
moisture-free atmosphere in a Braun MB 200 G-II drybox.
Cyclohexylmethylamine and all the solvents were purified and
dried following standard procedures.10 ZrCl4 (Aldrich), 2,6-
dimethyl phenyl isocyanide (Fluka), Lin-Bu (Aldrich), C6F5-
OH (Aldrich), [HNMe2Ph]B(C6F5)4 (Montell), Al(i-Bu)3 (TIBA)
(Schering), and ethylene (SIAD, “ethylene polymerization
grade”) were used as received; [HNMe3]Cl (Aldrich) was
purified by precipitation from saturated CHCl3 (previously
distilled on CaH2) solutions. 1-Hexene (Aldrich) was fraction-
ally distilled on CaH2 and kept on molecular sieves (NaA
zeolites, 8-12 mesh). Microanalyses were performed at Istituto
di Chimica Inorganica e delle Superfici, CNR, Padova. The IR
spectra were recorded on a Galaxy Series FT-IR 3000 Mattson
454
7.5
13 400 126.3
)
2
20
254
4.2
12 950 125.9
)
a
Conditions: solvent, toluene 20 mL, nal(-Bu)3/ncat) 20, pressure
b
) 5 atm, temperature 55-60 °C. treact. ) reaction time. c kgp
)
d
kilograms of polymer, molcat ) moles of catalyst. Mwv ) average
molecular weight of the polymer measured via viscometry; n.d.)
not determined. e mp ) melting point, determined via differential
scanning calorimetry.
melting processes. However at T > 275 °C decomposi-
tion took place. The poly(1-hexenes) are atactic, amor-
phous materials with viscoelastic properties. The pres-
ence of an n-butyl side chain lowers the molecular
cohesion (internal plasticization), suggesting a consider-
able flexibility even at low temperature so that vitreous
transitions are expected to occur in our case at temper-
atures below -30 °C.
1
in Nujol. The H and 13C NMR spectra were obtained as C6D6
solutions on a Bruker AMX-300 spectrometer operating at 300
and 100.61 MHz, respectively. The assignments of the proton
resonances were performed by standard chemical shift. The
13C resonances were attributed through 2D-heterocorrelated
COSY experiments (HMQC with bird sequence11 and quadra-
ture along F1 achieved using the TPPI method12 for the
H-bonded carbon atoms). The determination of the average
molecular weight of the polymer was carried out on a Hubbe-
hold viscometer in toluene solutions at 55 °C. The analysis
via differential scanning calorimetry was done with a TA DSC
2920 instrument.
Zr (NMeCyc)4. Li(NMeCyc) was prepared in situ by adding
dropwise a solution of NHMeCyc (3.13 mL, 24 mmol) in toluene
(5 mL) to a solution of Lin-Bu (15 mL, 1.6 M in hexane, 24
mmol) in toluene (20 mL) and stirring for 2.5 h at room
temperature. To this suspension was added gradually ZrCl4
(1.398 g, 6 mmol) in 30 min. After stirring for 18 h the solution
was filtered and the filtrate was reduced to a dark yellow oil
under reduced pressure. Yield: 3.20 g (98.7%). Anal. Calcd
(Found) for C28H56N4Zr: C 62.26 (62.00), H 10.47 (10.01), N
10.38 (10.11). 1H NMR (C6D6, δ ppm, 295 K): 3.05 (s, 12H,
CH3), 3.00 (tt, 4H, 3J ) 11.07 Hz, 3J ) 3.6 Hz), 1.1-2.0 (m,
40H, H4C2-C-C3H6). 13C NMR (C6D6, δ ppm, 295 K): 63.22
(N-CH3), 34.22 (C2, C6), 33.18 (C1), 26.63 (C3, C5), 26.59 (C4).
The polyethylenes (PEs) obtained using the η2-for-
mamidinyl complexes as catalysts were characterized
by high molecular weights (magnitude order 106g/mol).
Their insolubility in several solvents or mixtures of
solvents prevented the average molecular weight de-
termination via viscometry. On the contrary, the poly-
ethylenes obtained using ZrCp2Cl2, more active cata-
lysts, are characterized by low molecular weights, and
are industrially less interesting. The PEs polymers show
neat high melting points, suggesting that they are high-
density polyethylenes (HDPE). The crystallinity degree
X is calculated as
∆Hfus
X )
∆Hft
(9) Pella, E. Laboratorio di Microanalisi; Carlo Erba: Milano, 1970.
(10) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press: New York, 1980.
(11) Bax, A.; Subramian, S. J . Magn. Reson. 1986, 67, 565.
(12) Otting, G.; Wu¨trich, J . J . Magn. Reson. 1988, 76, 569. Drobny,
G.; Pines, A.; Sinton, S.; Weitkamp, D.; Wemmer, D. Faraday Symp.
Chem. Soc. 1979, B33, 49.
where ∆Hfus is the experimental enthalpy of fusion
(J /g) and ∆Hft ) 276.27 J /g reference value of the
enthalpy of fusion of a sample of 100% crystalline
polyethylene9 ranges from 17% for the polymer obtained
with 1 to 13% for the polymer obtained with 3, in

3990 Organometallics, Vol. 22, No. 20, 2003
Benetollo et al.
Ta ble 4. Cr ysta llogr a p h ic Da ta for
Zr (NMeCyc)2[C(NAr )NMeCyc]2 (1)
Zr (NMeCyc)2[C(NAr )NMeCyc]2, Ar ) 2,6-dim eth ylph en -
yl, 1. To a solution of Zr(NMeCyc)4 (1.080 g, 2 mmol) in
n-hexane (30 mL) at -90 °C was gradually added 2,6-
dimethylphenyl isocyanide (0.525 g, 4 mmol). The reaction was
checked via IR spectroscopy. After stirring for 2.5 h the
mixture was filtered and the filtrate was concentrated and put
in the freezer at -31 °C to give a white precipitate, which was
collected by filtration and washed with cold n-hexane. Yield:
1.24 g (77%). Anal. Calcd (Found) for C46H74N6Zr: C 68.86
(69.72), H 9.29 (9.64), N 10.47 (9.95). IR (Nujol): 1639 cm-1
ν(CdN). 1H NMR (C6D6, δ ppm, 295 K): 7.05-6.89 [m, 6H,
CdNC6H3(Me)2], 3.85 [m, 2H, ZrN(CHC5H10)], 3.60 [m, 2H, Nd
CN(CHC5H10)], 3.19 (s, 6H, Zr-NCyCH3), 2.28-2.17 [m, 18H,
NdCNC6H11CH3 and CdNC6H3(CH3)2], 1.82-1.02 (m, 40H,
cyclohexyl protons). 13C NMR (C6D6, δ ppm, 295 K): 213.36,
211.03 (NdCNCycMe), 151.17, 130.73, 127.48, 122.49 (C6H3),
66.11 [Zr-N(CHC5H10)Me], 61.13 [NdCN(CHC5H10)Me], 33.44
(NdCNCycCH3),31.23(Zr-NCycCH3),25.90-22.82[N(CHC5H10)-
Me], 19.65 [CdNC6H3(CH3)2].
formula
fw
cryst syst
space group
a (Å)
C46H74N6Zr
802.35
orthorhombic
P21212
12.399(3)
19.467(3)
9.607(3)
2318.9(8)
2
b (Å)
c (Å)
V (Å3)
Z
Dc (g cm-3
)
1.149
µ (mm-1
F(000)
)
0.272
864
cryst dimens (mm)
T, K
0.48 × 42 × 0.38
293(2)
θmax (deg)
26
no. of reflns measd
no. of reflns obsd [I g 2σ(I)]
R (on F)a
4790
4346
0.045
Rw (on F2)a
0.131
goodness-of-fit on F2
largest diff peak/hole (e Å-3
1.231
)
0.662/-0.755
Zr (OC6F 5)2[C(NAr )NMeCyc]2, Ar ) 2,6-d im eth ylp h en yl,
2. To a solution of 1 (0.401 g, 0.5 mmol) in Et2O (30 mL) was
added dropwise a solution of C6F5OH (0.184 g, 1 mmol) in Et2O
(10 mL): the reaction occurs instantaneously and exother-
mally, and the color changed to dark yellow. After 2 h the
solution was dried under reduced pressure, giving a yellow
R ) ∑|Fo| - |Fc|/∑|Fo|, Rw ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
2
another flask a solution of the complex (5 × 10-3 M, 1 mL)
and of the cocatalyst (1.25 × 10-3 M, 4 mL) in toluene were
mixed together before being transferred to the autoclave. The
autoclave was then heated at 55-60 °C and pressurized with
ethylene (p ) 5 atm) for 20 min. At the end MeOH (2 mL)
was added.
oil. Yield: 0.424 g (90%). Anal. Calcd (Found) for C44H46N4F10
-
Zr: C 55.98 (56.78), H 4.91 (5.10), N 5.94 (6.19). IR (Nujol):
1
1638 cm-1 ν(CdN). H NMR (C6D6, δ ppm): 7.14 [d, 4H, J )
P u r ifica tion of P oly(eth ylen e). After venting the auto-
clave, the polymer was filtered and washed several times with
a solution of MeOH-HCl, 1:1, and then with water and
acetone and dried at 90 °C under vacuum.
7.6 Hz, meta-C6H3(Me)2], 6.99 (t, 2H, J ) 7.6 Hz, para-C6H3-
(Me)2), 2.81 (bs, 6H, NdCN(CH3)Cyc), 2.48 [bm, 2H, NdCN-
(CHC5H10)], 2.30 (s, 12H, CdNC6H3(CH3)2), 1.70-0.80 (m, 20H,
cyclohexyl protons). 13C NMR (C6D6, δ ppm): 214.52, 213.02
(NdCNCycMe), 152.46, 129.50, 128.13, 122.03 (C6H3), 140.0-
135.0 (C6F5O), 58.49 [NdCN(CHC5H10)Me], 31.45 (NdCN-
CycCH3), 32.0-24.8 [N(CHC5H10)Me], 18.85 [CdNC6H3(CH3)2].
X-r a y Mea su r em en t s a n d St r u ct u r e Det er m in a t ion .
Crystals of 1 suitable for X-ray analysis were grown upon
cooling n-pentane solutions. Crystal data were collected using
a Philips PW1100 diffractometer, with graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å) following the standard
procedures. All intensity data were corrected for Lorentz-
polarization effects and absorption.13 The refined lattice
parameters and other pertinent crystallographic information
are given in Table 4. The structure was solved by direct
methods using SIR-92.14 All non-hydrogen atoms were located
in the subsequent Fourier maps. The structure was refined
by full-matrix least-squares methods using anisotropic tem-
perature factors for all non-hydrogen atoms. Hydrogen atoms
were introduced at calculated positions in their described
geometries and during refinement were allowed to ride on the
attached carbon atoms with fixed isotropic thermal parameters
(1.2Ueq of the parent carbon atom). The Flack parameters15
have been refined for the structure. The calculations were
performed with the SHELXL-97 program,16 implemented in
the WinGX package.17 The program for the ORTEP drawing
was taken from ref 18.
Zr Cl2[C(NAr )NMeCyc]2, Ar ) 2,6-d im eth ylp h en yl, 3. To
a solution of 1 (0.401 g, 0.5 mmol) in Et2O (30 mL) was added
gradually [Me3NH]Cl (0.096 g, 1 mmol); the color changed
slowly to light yellow. After 12 h the solution was dried under
reduced pressure, dissolved in n-hexane, and filtered. The
filtrate was cooled at -31 °C, giving a white precipitate.
Yield: 0.270 g (83%). Anal. Calcd (Found) for C32H46N4ClZr:
C 59.23 (58.11), H 7.15 (7.41), N 8.63 (8.87). IR (Nujol): 1638
cm-1 ν(CdN). 1H NMR (C6D6, δ ppm, 295 K): 7.15 [d, 4H, J )
7.6 Hz, CdNC6H3(Me)2], 7.00 [t, 2H, J ) 7.6 Hz, CdNC6H3-
(Me)2], 2.82 [bs, 6H, NdCN(CH3)Cyc], 2.44 [bm, 2H, NdCN-
(CHC5H10)], 2.31 (s, 12H, CdNC6H3(CH3)2), 1.80-0.90 (m, 20H,
cyclohexyl protons). 13C NMR (C6D6, δ ppm, 295 K): 209.62,
208.44 (NdCNCycMe), 152.31, 130.69, 127.48, 121.79 (C6H3),
65.67 [NdCN(CHC5H10)Me], 31.73 (NdCNCycCH3), 26.1-22.8
[NdCN(CHC5H10)Me], 18.92 [CdNC6H3(CH3)2].
P olym er iza tion of 1-Hexen e. In a three-neck round-
bottom flask were introduced 1-hexene (30 mL), TIBA (0.1 mL),
and toluene (5 mL). In another flask a solution of the complex
(5 × 10-3 M, 1 mL) and of the cocatalyst (1.25 × 10-3 M, 4
mL) in toluene were mixed together before being transferred
to the flask containing the olefin and the scavenger. The
reaction was carried out at room temperature for 1 h.
Ack n ow led gm en t. We thank CNR, Consiglio Na-
zionale delle Ricerche, Italia, for financial support.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for 1. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM030268+
P u r ifica tion of P oly(1-h exen e). After adding MeOH (1
or 2 mL) at the end of the reaction, the reaction solution was
evaporated under reduced pressure and the polymer was dried
at 60-70 °C under vacuum. The polymer (0.5 g) was dissolved
in toluene (50-60 mL), and the solution washed three times
with a solution of MeOH-HCl, 1:1 (3 × 50 mL). The addition
of a MeOH-acetone solution, 1:1 (50 mL), and shaking
vigorously caused the coagulation of the polymer, which was
separated and dried at 90 °C for 3 h under vacuum.
(13) North, A. T. C.; Philips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A24 1968, 351.
(14) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. SIR-92. J . Appl. Crystallogr. 1994,
27, 435.
(15) (a) Flack, H. D. Acta Crystallogr., Sect. A 1983, 39, 876. (b)
Bernardinelli, G.; Flack, H. D. Acta Crystallogr., Sect. A41 1985, 500.
(16) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Germany, 1997.
(17) Farrugia, L. J . J . Appl. Crystallogr. 1999, 32, 837.
(18) Burnett, M. N.; J ohnson, C. K. ORTEP-III; Report ORNL-6895;
Oak Ridge National Laboratory: Oak Ridge, TN, 1996.
P olym er iza tion of Eth ylen e. A stainless steel autoclave
was charged with toluene (20 mL) and TIBA (0.05 mL). In