New tetradentate N,N,N,N-chelating α-diimine ligands and their corresponding zinc and nickel complexes: Synthesis, characterisation and testing as olefin polymerisation catalysts

Article abstract of DOI:10.1039/c0dt01308k

A series of zinc complexes of the general formula {[ZnCl(ArNC(An)-C(An)NAr) ]⁺}₂[Zn₂Cl₆]^2- (where Ar = 2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl 2a, 2-(1-(1-phenylethyl)-1H-1,2,3- triazol-4-yl)phenyl 2b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl 2c; An = acenaphthene backbone) were prepared by the condensation of acenaphthenequinone with the corresponding o-triazolyl-substituted anilines (2-(1-benzyl-1H-1,2,3- triazol-4-yl)aniline 1a, 2-(1-(1-phenylethyl)-1H-1,2,3-triazol-4-yl)aniline 1b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline 1c) which were formed by the copper(i)-catalyzed Huisgen[3+2] dipolar cycloaddition between 2-ethynylaniline and the corresponding azides in high yields, using anhydrous ZnCl₂ as the metal template, in boiling glacial acetic acid. Zinc complexes of the type [ZnCl(ArNC(An)-C(An)NAr)]⁺[ZnCl₃(NCCH₃)] ^- (4a-c) were synthesized by crystallisation of the corresponding complexes 2a-c in acetonitrile, at -20 °C. After removal of zinc dichloride from complexes 2a-c by the addition of potassium oxalate, in dichloromethane, the tetradentate N,N,N,N-chelating α-diimine ligands of the type ArNC(An)-C(An)NAr (5a-c) were obtained. The new ligand precursors and zinc complexes were characterised by elemental analysis, ¹H and ¹³C{¹H} NMR spectroscopy, two-dimensional NMR spectroscopy, and X-ray diffraction. Reaction of the ligand precursors 5a-c with [NiBr₂(DME)], in dichloromethane, gave nickel complexes of the type [NiBr₂(ArNC(An)-C(An)NAr)] (6a-c). The results of single crystal X-ray diffraction characterisation and magnetic susceptibility measurements demonstrated that nickel complexes 6a-c possess octahedral geometries around the nickel atoms with variable configurations, the Br atoms of which can be ionized when dissolved in methanol. In preliminary catalytic tests, complexes 6a-c revealed to be active as catalysts for the polymerisation of norbornene and styrene, when activated by cocatalyst MAO. The characterisation of the polymers by ¹H and ¹³C{¹H} NMR spectroscopy, gel permeation chromatography/size-exclusion chromatography (GPC/SEC) revealed that these polymers were formed by a coordination addition mechanism.

Full text of DOI:10.1039/c0dt01308k

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PAPER
New tetradentate N,N,N,N-chelating a-diimine ligands and their
corresponding zinc and nickel complexes: synthesis, characterisation and
testing as olefin polymerisation catalysts†
Lidong Li,a Clara S. B. Gomes,a Pedro T. Gomes,*a M. Teresa Duartea and Zhiqiang Fanb
Received 29th September 2010, Accepted 21st January 2011
DOI: 10.1039/c0dt01308k
A series of zinc complexes of the general formula {[ZnCl(ArN C(An)–C(An) NAr)]+}2[Zn2Cl6]2-
(where Ar = 2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl 2a, 2-(1-(1-phenylethyl)-1H-1,2,3-triazol-4-
yl)phenyl 2b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl 2c; An = acenaphthene backbone) were prepared
by the condensation of acenaphthenequinone with the corresponding o-triazolyl-substituted anilines
(2-(1-benzyl-1H-1,2,3-triazol-4-yl)aniline 1a, 2-(1-(1-phenylethyl)-1H-1,2,3-triazol-4-yl)aniline 1b,
2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline 1c) which were formed by the copper(I)-catalyzed
Huisgen[3+2] dipolar cycloaddition between 2-ethynylaniline and the corresponding azides in high
yields, using anhydrous ZnCl2 as the metal template, in boiling glacial acetic acid. Zinc complexes of the
type [ZnCl(ArN C(An)–C(An) NAr)]+[ZnCl3(NCCH3)]- (4a–c) were synthesized by crystallisation
of the corresponding complexes 2a–c in acetonitrile, at -20 ◦C. After removal of zinc dichloride from
complexes 2a–c by the addition of potassium oxalate, in dichloromethane, the tetradentate
N,N,N,N-chelating a-diimine ligands of the type ArN C(An)–C(An) NAr (5a–c) were obtained.
The new ligand precursors and zinc complexes were characterised by elemental analysis, 1H and
1
13C{ H} NMR spectroscopy, two-dimensional NMR spectroscopy, and X-ray diffraction. Reaction of
the ligand precursors 5a–c with [NiBr2(DME)], in dichloromethane, gave nickel complexes of the type
[NiBr2(ArN C(An)–C(An) NAr)] (6a–c). The results of single crystal X-ray diffraction
characterisation and magnetic susceptibility measurements demonstrated that nickel complexes 6a–c
possess octahedral geometries around the nickel atoms with variable configurations, the Br atoms of
which can be ionized when dissolved in methanol. In preliminary catalytic tests, complexes 6a–c
revealed to be active as catalysts for the polymerisation of norbornene and styrene, when activated by
1
cocatalyst MAO. The characterisation of the polymers by 1H and 13C{ H} NMR spectroscopy, gel
permeation chromatography/size-exclusion chromatography (GPC/SEC) revealed that these polymers
were formed by a coordination addition mechanism.
PdII-based complexes containing aryl a-diimine ligands, normally
when mixed with an activator such as methylaluminoxane (MAO),
led to highly active ethylene, propylene or a-olefin homo- and co-
Introduction
The use of catalysts based on late-transition metal complexes con-
taining Schiff base ligands was a major advance in the development
polymerisation catalytic systems for the production of polyolefins
of olefin polymerisation.1 The work of Brookhart and coworkers
with variable microstructures, such as branched polymers with
in the preparation of families of neutral and cationic NiII- or
controllable topological structures.2 The a-diimines used were
mainly based on DAB (DAB = 1,4-diaza-1,3-butadiene; Chart
aCentro de Qu´ımica Estrutural, Departamento de Engenharia Qu´ımica
e Biolo´gica, Instituto Superior Te´cnico, Av. Rovisco Pais, 1049-001,
Lisboa, Portugal. E-mail: pedro.t.gomes@ist.utl.pt; Fax: +351 218419612;
Tel: +351 218419612
1, A) and on BIAN (BIAN = bis(imino)acenaphthene; Chart 1, B)
backbones. Several aryl derivatives could be used in order to tune
the stereochemical and electronic features at the metal centres
and, therefore, influence the microstructure and the molecular
weight distributions. In particular, the aryl-BIANs proved to
be very efficient bidentate nitrogen ligands for the formation of
robust catalysts, not only in olefin polymerisation2a–c or CO/vinyl
arene copolymerisation3 but also in other useful transformations,
such as C–C cross-coupling reactions (Pd0- or PdII-aryl-BIAN
bDepartment of Polymer Science and Engineering, Zhejiang University,
Hangzhou, 310027, P. R. China
† Electronic supplementary information (ESI) available: Figures contain-
ing the definition of parameter t, the X-ray structures of complexes 2a,·4a
and 4c (containing the anionic counterparts), and of byproduct 3a. CCDC
reference numbers 789956–789965. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt01308k
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The other important synthetic route to aryl-BIANs is that in
which acenaphthenequinone is refluxed with the corresponding
amines in glacial acetic acid, as the solvent, in the presence of a
template such as ZnCl2 or NiBr2. This reaction leads directly to
the ZnII- or NiII-aryl-BIAN complexes, which, after removal of
ZnCl2 or NiBr2, give rise to the free ligands that are obtained in
moderate to high yields.11 This synthetic procedure has already
been broadly used in the literature,9,12 and has also been recently
extended to the synthesis of aryl-BIANs bearing strong electron-
withdrawing substituents on the aryl rings and mixed Ar,Ar¢-
BIANs.13 The latter authors found out that the real driving force
of this procedure is the lower solubility of the metal complexes
in the reaction medium in comparison with the starting reagents,
and not the formation of the template complexes. In the cases
where the metal complexes are more soluble, mixtures of acetic
acid with hydrocarbons (e.g. toluene) may induce this difference
in solubilities.13a
We have been interested in the chemistry of aryl-BIAN and its
corresponding metal complexes.10c,d,14 In view of the relevance of
the stereochemical and/or electronic features of the aryl-BIAN
framework vis-a`-vis the olefin polymerisation reaction and also its
potential use in biological applications,15 we set out the synthesis
of a series of a-diimine ligands modified by “Click Chemistry”,16
using the template method. In the present work, the newly
obtained triazole-aryl-BIAN ligands (Chart 2, D) and their corre-
sponding zinc and nickel complexes are structurally characterised
1
and discussed using 1H and 13C{ H} NMR spectroscopy, 2D
homo- and heteronuclear correlation NMR spectroscopy (COSY,
HSQC and HMBC), X-ray diffraction and magnetic susceptibility
measurements. Preliminary tests of the Ni complexes as potential
olefin polymerisation precatalysts, when activated by MAO, are
also presented.
Chart 1
complexes),4 the hydrosilylation of styrene (Pd0- or Pt0-aryl-BIAN
complexes containing p-coordinated unsaturated ligands),5 or the
allylic amination of olefins by nitroarenes, in the presence of CO
(Ru0-aryl-BIAN complex).6 More recently, ZnII or CuII complexes
containing a tetradentate bis(thiosemicarbazonato) ligand with
an acenaphthene backbone (An), which is structurally similar to
BIAN itself (Chart 1, C), were found to be good probes for in vitro
fluorescence imaging.7
The BIAN ligand can be regarded as a fusion of a naphthalene
ring with a DAB moiety, being more rigid in comparison
with the latter, which provides the ligand with both favourable
coordination geometry and high chemical stability. However, the
BIAN rigidity also leads to synthetic difficulties compared to
DAB, in which both alkyl- and aryl-derivatives are well known and
easily obtainable.8 While the synthesis of aryl-BIAN derivatives
is relatively straightforward, the alkyl-BIANs were only more
recently reported,9 which may stem from the ring strain of its
five-membered ring.9a
Chart 2
Results and discussion
Syntheses of triazolyl ortho-substituted aniline ligand synthons via
The majority of the presently known aryl-BIANs contain
electron-donating or moderately electron-withdrawing groups
on the aryl rings, and are easily prepared by condensation
of acenaphthenequinone with the corresponding amines in the
presence of catalytic amounts of Brønsted acids, such as formic
or toluenesulfonic acids.2e,10 Conversely, this same procedure
generally fails in the synthesis of aryl-BIANs bearing strong
electron-withdrawing groups on the aryl rings.
click chemistry
Click Chemistry is a term applied to chemical reactions whose
main features are: readily available starting materials and reagents,
mild reaction conditions, high or quantitative yield, no byprod-
ucts, no side reactions, simple workup, stereospecificity, and wide
applicability.16a,17 A typical click reaction is the copper(I)-catalyzed
Huisgen[3+2] dipolar cycloaddition between an alkyne and an
3366 | Dalton Trans., 2011, 40, 3365–3380
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◦
◦
azide, described by Sharpless,16b,18 which has been broadly used in
the fields of polymer chemistry and biochemistry.17b,19 Herein, we
introduced this click reaction to modify the BIAN ligands.
As shown in Scheme 1, 2-ethynylaniline was reacted with substi-
tuted azides, in a 1 : 1 mixture of water and tert-butanol, at room
temperature, in the presence of the in situ generated Cu(I) catalyst,
derived from the reaction of copper(II) sulfate pentahydrate and
sodium ascorbate. Compounds 1a–c were obtained in very high
yields (91–95%), as off-white solids, although sometimes they may
acquire a deep brown colour when contaminated with residual
Cu(I) or Cu(II) species. However, they could be purified by repeated
crystallisation in methanol, at -20 ◦C, leading to the isolation of
white crystals.
˚
Table 1 Selected bond distances (A), angles ( ) and torsion angles ( ) for
compounds 1a and 1c
1a
1c
Distances
C1–N1
C6–C7
C7–C8
C7–N2
C8–N4
C9–N4
N2–N3
N3–N4
1.384(2)
1.472(2)
1.383(3)
1.370(2)
1.333(2)
1.474(2)
1.328(2)
1.347(2)
2.772(3)
0.87(2)
1.350(5)
1.473(4)
1.363(4)
1.363(4)
1.350(4)
1.431(4)
1.311(4)
1.352(4)
2.800(5)
0.98(4)
N1 ◊ ◊ ◊ N2
N1–H01
H01 ◊ ◊ ◊ N2
Angles
2.06(2)
2.11(6)
C7–C8–N4
C8–N4–N3
N4–N3–N2
N3–N2–C7
N2–C7–C8
N1–H01 ◊ ◊ ◊ N2
N1–C1–C6–C7
C1–C6–C7–C8
C1–C6–C7–N2
C1–N1–H01 ◊ ◊ ◊ N2
106.65(16)
110.83(16)
106.56(16)
109.88(16)
106.08(17)
138.5(17)
-1.3(2)
105.3(3)
110.0(3)
107.5(3)
108.8(3)
108.3(3)
127(4)
2.6(5)
-176.35(16)
150.8(4)
-28.5(5)
-25(8)
1.5(3)
-7(3)
Scheme 1 “Click” reaction between 2-ethynylaniline and azides.
Crystals of the anilines 1a and 1c suitable for single crystal X-ray
diffraction were grown from their dilute solutions in methanol, at
-20 ◦C. Compound 1a crystallised in the monoclinic system, space
group P21/n, while compound 1c, although crystallising also in the
monoclinic system, preferred space group P21/c. Each unit cell of
compounds 1a and 1c contains four molecules, the corresponding
bond distances and angles being comparable (including those
of the hydrogen bonds), as can been seen in Table 1. However,
in compound 1a (Fig. 1(a)), the aniline and triazolyl rings are
almost coplanar (dihedral angle of 3.14(10)◦), whereas for 1c
(Fig. 1(b)) the corresponding dihedral angle is 27.69(17)◦ (see
also the corresponding torsion angles C1–C6–C7–C8 or C1–C6–
C7–N2 in Table 1). Nevertheless, the coplanarity observed for 1a
is not driven by p-extended conjugation since the bond distance
Fig. 1 ORTEP diagrams of compounds (a) 1a and (b) 1c, with 50%
probability ellipsoid displacement. The calculated hydrogen atoms are
omitted for clarity. The dashed bonds represent the intramolecular
hydrogen bonds N1–H01 ◊ ◊ ◊ N2.
˚
C6–C7 (1.472(2) A) is typical of a C–C single bond, the same
˚
being observed for the corresponding distances of 1c (1.473(4) A).
Therefore, this coplanarity of the aromatic rings in 1a has its origin
in the existence of an intramolecular hydrogen bond interaction
N1–H01 ◊ ◊ ◊ N2, which is likewise observed for compound 1c (see
Table 1 and Fig. 1(a) and (b)).
In the 1H NMR spectra (CD2Cl2) of compounds 1a–c, the
NH2 chemical shifts lie at d 5.57 (1a), 5.64 (1b) and 5.54 (1c),
respectively. The characteristic 1H and 13C NMR signals of
triazolyl CC(H)N3 and CC(H)N3 are analogous for 1a (d 7.80
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and 120.0) and 1b (d 7.83 and 118.9), respectively, while the
difference in the molecular structures of the final complexes.
The Ar-BIAN ligands prepared by Elsevier and coworkers are
typically bidentate a-diimines that coordinate to ZnCl2 through
both iminic nitrogens, giving rise to four-coordinate [ZnCl2(Ar-
BIAN)] complexes. In the new complexes 2a–c, besides the iminic
nitrogens, two nitrogen atoms of each of the triazolyl groups
also coordinate to the metal centre and, as a result, one of the
chlorine atoms of the ZnCl2 moiety is expelled away from the
metal centre, leading to five-coordinate zinc(II) cations stabilised
by a ZnCl3- counterion, which exists in the dimeric form [Zn2Cl6]2-,
as displayed in Scheme 2. The amount of zinc dichloride used
has no influence on the formation of compounds 2a–c. Even
if one equivalent of zinc dichloride is used, compounds 2a–c
are the only products obtained. Complexes 2a–c are orange–
red solids. They are not soluble in common organic solvents,
such as n-hexane, diethyl ether, toluene, acetone, tetrahydrofuran,
and acetic acid, but are partially soluble in dichloromethane,
acetonitrile and methanol. Pyridine and dimethyl sulfoxide induce
the decomposition of compounds 2a–c.
1
corresponding H chemical shift of 1c (d 8.29) apparently shifts
downfield and its 13C chemical shift (d 118.1) is comparable.
Syntheses and characterisation of zinc complexes containing
N,N,N,N-chelating a-diimine ligands
The dehydrating condensations of compounds 1a–c with acenaph-
thenequinone in boiling glacial acetic acid in the presence of zinc
dichloride as a metal template gave rise to compounds 2a–c in
moderate to high yields (59–75%) (Scheme 2).
Along with the formation of compounds 2a–c (Scheme 2), the
amide byproducts 3a–c were isolated in very low yields (5–10%).
They are formed by dehydrating amidation reactions of acetic acid,
which is the reaction solvent, with the corresponding amines 1a–c.
The molecular structure of 3a is represented in Fig. S1 of the ESI.†
All of the 1H and 13C resonances in the NMR spectra of
3a–c (CD2Cl2) were assigned. In particular, those of the triazolyl
CC(H)N3 and CC(H)N3 of 3a–c are comparable with the corre-
sponding resonances of 1a–c (d 7.80–7.90 and 118.9–121.1, in 3a–c
vs. d 7.80–8.29 and 118.1–120.0, in 1a–c). The 1H and 13C NMR
resonances of the NH and C O groups in 3a–c are also similar
(d 11.22–11.39 and 168.7–168.8).
When compounds 2a–c were dissolved in acetonitrile, by heating
to reflux, and placed at room temperature or -20 ◦C to crystallise,
orange crystals of compounds 4a–c were obtained, as shown in
Scheme 2. The cationic counterparts of compounds 4a–c remained
intact in comparison with those of compounds 2a–c, while in 4a–
2-
c the dimeric Zn2Cl6 counteranions of 2a–c were split into the
acetonitrile adducts [ZnCl3(NCCH3)]-.
Crystals of compounds 2b and 4c suitable for single crystal
X-ray diffraction were obtained by slow diffusion of diethyl
ether into a dilute dichloromethane solution of 2b and a dilute
acetonitrile solution of 4c, respectively, at -20 ◦C, while those
of compound 4a were obtained by crystallisation in its dilute
acetonitrile solution, at -20 ◦C. Compounds 2b, 4a and 4c
¯
crystallise in the triclinic system, space group P1, each unit cell
containing two molecules. All the compounds 2b, 4a and 4c have
an ionic nature, being composed by cationic and anionic zinc
complexes. The structures of the corresponding cationic moieties
are represented in Fig. 2–4, and Table 2 lists their most relevant
bond distances and angles. All these species are cationic complexes
containing the new tetradentate N,N,N,N-ligands coordinated to
Zn1 metal atoms, which exhibit five-coordinate geometries, the
fifth position being occupied by a chlorine atom. The geometries
around Zn1 are intermediate between square pyramidal (SP) and
trigonal bipyramidal (TBP), which is pointed out by t values of
0.45, 0.47 and 0.50, respectively for cations 2b, 4a and 4c (the
parameter t20 is used to describe the degree of distortion of penta-
coordinated complexes: t = 0 for an ideal SP and t = 1 for an ideal
TBP – see Fig. S2 in ESI†).
Scheme 2 Synthesis of the zinc compounds 2 and 4, and of their corre-
sponding metal-free ligands 5, using the template method. Compounds 3
are reaction byproducts of the dehydrating amidation of acetic acid with
anilines 1.
This synthetic procedure is similar to that described in the
literature for simple Ar-BIAN ligands,11 however, there is a marked
3368 | Dalton Trans., 2011, 40, 3365–3380
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Fig. 2 ORTEP diagrams of the cation of compound 2b with 50% probability ellipsoid displacement: (a) top and (b) side views. Half of the anion
[Zn2Cl6]2-, two CH2Cl2 solvent molecules and all the hydrogen atoms are omitted for clarity.
◦
˚
Table 2 Selected bond distances (A) and angles ( ) for compounds 2b,
4a, 4c, 5a and 5c
type shape when coordinated to Zn, the metal sitting on top of
this structure with the Zn1–Cl1 axial bond pointing upwards. The
stereochemical hindrance exerted between the two triazolyl groups
of a ligand imposes different rotations of the aryl groups bonded
to both imine nitrogens, which are tilted by 44.8–52.9◦ or 64.5–
70.7◦, respectively, in relation to the bisimineacenaphthene plane.
Therefore, when coordinated to Zn, the triazolyl nitrogens N3 and
N6 do not lie in the same plane of the iminic nitrogens N1 and N2
and, thus, the triazolyl groups are not coplanar, appearing shifted
in relation to each other by 16.9–20.7◦, which is on the basis of
the observed distortion of the square pyramidal geometry around
Zn1. Therefore, all the three cations 2b, 4a and 4c are chiral at the
Zn centre but, since each of the corresponding asymmetric unit
cells has an inversion centre, the therein existing pair of molecules
is a racemate. Additionally, since a racemic mixture of 1b was
employed in the synthesis of compound 2b, its corresponding
cation has two asymmetric carbons with different chiralities, C22
(mainly S) and C38 (R) (see Fig. 2), although the methyl group
bonded to C22 is disordered over two positions (probabilities of
61% (C21) and 39% (C21b) for S and R configurations, respec-
tively). Despite no X-ray structural data of ZnCl pentacoordinate
complexes, containing neutral tetradentate N,N,N,N-ligands with
a-diimine moieties, being found in the literature, two structures of
cationic pentacoordinate [ZnCl(N,N,S,S-cyclohexane-1,2-dione-
bis(4-methyl-3-thiosemicarbazone)]Cl showing true SP geome-
tries about the Zn(II) ion (t values of 0.01221 and 0.03522) with
axial Zn–Cl bonds are reported. The observation of these pure
SP geometries is likely due to the fact that these ligands define
three five-membered metallacycles (instead of one five-membered
and two six-membered rings in compounds 2b, 4a and 4c) when
complexed to Zn and, also, because the sulfur donor atoms do not
exert important stereochemical hindrance on the Zn coordination
2b
4a
4c
5a
5c
Distances
Zn1–N1
Zn1–N2
Zn1–N3
Zn1–N6
Zn1–Cl1
N1–C1
N2–C12
C1–C12
N3–N4
2.158(8)
2.192(7)
2.120(8)
2.068(9)
2.229(3)
1.264(11) 1.274(3)
1.275(11) 1.286(3)
1.495(13) 1.518(3)
1.350(10) 1.321(3)
1.323(10) 1.333(3)
1.374(13) 1.370(3)
1.354(10) 1.321(3)
1.307(11) 1.327(2)
2.1153(17) 2.147(3)
2.2019(18) 2.182(3)
2.1185(18) 2.135(3)
2.0492(18) 2.090(3)
2.2638(6) 2.2308(10)
—
—
—
—
—
—
—
—
—
—
1.275(5)
1.283(5)
1.507(6)
1.326(4)
1.341(5)
1.357(6)
1.313(4)
1.341(4)
—
1.281(4) 1.282(2)
1.272(4) 1.277(2)
1.518(4) 1.519(2)
1.333(4) 1.314(2)
1.332(4) 1.363(2)
1.373(4) 1.367(2)
1.326(4) 1.313(2)
1.346(4) 1.356(2)
N4–N5
C19–C20
N6–N7
N7–N8
C35–C36
C34–C35
C33–C34
Angles
N1–Zn1–N2 75.8(3)
N2–Zn1–N3 123.5(3)
N2–Zn1–N6 82.7(3)
N3–Zn1–N6 97.9(3)
N1–Zn1–N6 150.4(3)
Cl1–Zn1–N1 102.9(2)
Cl1–Zn1–N2 122.7(2)
1.382(13)
—
—
—
1.372(3)
—
—
1.378(4)
—
—
—
1.372(2)
—
1.368(5)
76.80(7)
76.57(12)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
125.24(7) 119.99(12)
83.45(7)
97.52(7)
83.51(11)
93.63(12)
153.67(7) 150.03(12)
102.45(5) 106.26(9)
127.40(5) 124.69(8)
Cl1–Zn1–N3 111.39(19) 105.78(5) 114.28(9)
Cl1–Zn1–N6 105.8(2)
C1–N1–C13 124.0(8)
C12–N2–C29 122.8(8)
C12–N2–C28 —
103.35(5) 103.46(9)
124.05(18) 121.0(3)
117.8(3) 118.91(14)
—
120.6(3)
—
—
—
—
121.8(3)
—
—
121.38(18)
—
C12–N2–C27 —
122.53(15)
Side views of the molecular structures of complexes 2b, 4a and
4c (Fig. 2(b)–4(b)) show the tetradentate ligands acquire a saddle-
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Fig. 3 ORTEP diagram of the cation of compound 4a with 50% probability ellipsoid displacement: (a) top and (b) side views. The anion [ZnCl3(NCCH3)]-,
two acetonitrile solvent molecules and all the hydrogen atoms are omitted for clarity.
Fig. 4 ORTEP diagram of the cation of compound 4c with 50% probability ellipsoid displacement: (a) top and (b) side views. The anion [ZnCl3(NCCH3)]-
and all the hydrogen atoms are omitted for clarity.
sphere. The zinc anionic counterparts of compounds 2b, 4a and
4c can be observed in Figs. S3–S5 of the ESI.†
c). Despite the NMR measurements being performed in different
deuterated solvents, these large shifts may be attributed to the
coordination of the triazolyl groups to the metal centres. The 13
C
NMR resonances of the imine C N groups in 2a–c are d 162.3,
162.1 and 162.5, respectively. Since the coordinated acetonitrile
molecules of compounds 4a–c are removed when their samples
are subjected to vacuum, these compounds cannot be dried and
In the 1H and 13C NMR spectra of 2a–c, in CD3OD or
CD3OD/CD3CN (4 : 1 (v/v)), the resonances of the triazolyl
CC(H)N3 and CC(H)N3 appear shifted downfield (by ca. 1 and 4
ppm, respectively) when compared with those of 1a–c (d 8.74–9.26
and 122.0–124.2, in 2a–c vs. d 7.80–8.29 and 118.1–120.0, in 1a–
3370 | Dalton Trans., 2011, 40, 3365–3380
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Fig. 5 ORTEP diagrams of ligands (a) 5a and (b) 5c, with 50% probability ellipsoid displacement. The hydrogen atoms are omitted for clarity.
isolated as such, and their NMR samples were prepared in situ by
dissolution of compounds 2a–c in deuterated acetonitrile. The 1H
and 13C NMR resonances of the triazolyl CC(H)N3 and CC(H)N3
in 4a–c, in CD3OD or CD3OD/CD3CN (4 : 1 (v/v)), are similar
to those of 2a–c (d 8.60–9.14 and 122.5–124.3, in 4a–c vs. d 8.74–
9.26 and 122.0–124.2, in 2a–c). The 13C NMR resonances of the
imine C N groups in 4a–c appear at d values very similar to
those of 2a–c. Since the steric hindrance hampers the free rotation
of the benzyl groups in 4a, it is worth to note that, the benzyl
methylene hydrogens (CH2Ph) are diastereotopic, their 1H NMR
resonances appearing as an AB pattern, at d 5.76 and 5.69, with a
geminal coupling constant of 14.4 Hz. Likewise, due to the use of
a racemic C*H(Me)Ph group in the synthesis of compound 1b, the
characteristic 1H and 13C NMR resonances of the triazolyl groups
(CC(H)N3 and CC(H)N3) of 4b split into two superimposed peaks
(d 8.72–8.61), and into two broad resonance peaks (d 123.6 and
123.1), respectively. However, such a splitting is not observed for
2b in CD3OD.
both showing isomers of the type (E,E) (configurations around
the imine C N bonds resulting from nitrogen inversion) and
an anti configuration of the arylimine groups in relation to the
acenaphtheneimine plane. Their corresponding bond distances
and angles are comparable, as displayed in Table 2. In typical
Ar-BIAN ligands,11 (E,E) and (E,Z) isomers with anti and syn
configurations can exist depending on their substituents, in which
less bulky substituents often lead to a mixture of different isomers
and bulkier substituents generally give rise to a predominant
isomer. Apparently, compounds 5a–c fall in the latter category,
their structure details being consistent with the 1H and 13C NMR
data. In the metal-free ligands 5a and 5c, the absence of the
strain imposed by chelation to Zn, observed in 4a and 4c, leads
to a more perpendicular orientation of the phenyl groups in
relation to the bisimineacenaphthene plane and, also, to an anti
configuration of the two triazolyl groups, due to minimisation
of the steric hindrance. In fact, the dihedral angles between
the phenyl ring planes and the bisimineacenaphthene plane are
80.20(13)◦/57.41(14)◦ and 76.09(7)◦/58.59(7)◦, respectively in 5a
and 5c.
Synthesis and characterisation of the metal-free
N,N,N,N-chelating a-diimine ligands
The characteristic 1H and 13C NMR resonances of the triazolyl
CC(H)N3 and CC(H)N3, in CD2Cl2, are comparable in 5a
(d 7.95 and 123.4) and 5b (d 8.10, 8.09, and 122.5), while
the corresponding 1H chemical shift of 5c (d 8.90) markedly
shifts downfield compared to those of 5a and 5b, and its 13C
After removal of ZnCl2 from the complexes 2a–c, by addition
of potassium oxalate in dichloromethane, the new tetradentate
N,N,N,N modified a-diimine ligands 5a–c were prepared as
orange solids in moderate to high yields (52–85%), as represented
in Scheme 2.
chemical shift (d 121.6) is close. All of the imine C
N
13C
NMR resonances of the metal-free ligands 5a–c are analogous
(d 160.37–160.7) and appear to be shifted upfield (ca. 1.6–1.9
ppm) in relation to the values exhibited in their corresponding
Zn complexes (measurements performed in different solvents). It
is worthy of note that due to the use of racemic C*H(Me)Ph
groups in the synthesis of compound 5b, the triazolyl CC(H)N3
Crystals of compound 5a suitable for single crystal X-ray
diffraction were grown from a dilute hexane–ethyl acetate (1 : 4)
solution, at -20 ◦C, while those of compound 5c were obtained by
crystallisation in ethyl acetate, at -20 ◦C. Compound 5a crystallises
¯
in a triclinic system, space group P1, each unit cell containing 2
1
resonances, appear as two peaks in the H NMR spectrum, at
molecules, while compound 5c preferred a monoclinic system,
space group P 21/c, each unit cell containing 4 molecules. The
molecules of compounds 5a and 5c are structurally similar (Fig. 5),
d 8.10 and 8.09, corresponding to the magnetically inequivalent
protons of the racemic molecules, and the 13C resonance of
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Scheme 3 Synthesis of the nickel compounds 6.
◦
˚
Table 3 Selected bond distances (A) and angles ( ) for compounds 6a
and 7a
C
N group splits as well into two resonances at d 160.39 and
160.37.
6a
7a
Syntheses and characterisation of nickel complexes containing
N,N,N,N-chelating a-diimine ligands
Molecule 1 Molecule 2
Distances
Ni1–N1/Ni1A–N1Aa
Ni1–N2/Ni1A–N2Aa
Ni1–N3/Ni1A–N3Aa
Ni1–N6/Ni1A–N6Aa
Ni1–Br1
2.078(5)
2.062(4)
2.052(5)
2.044(4)
2.7368(10)
2.5313(10)
—
2.066(4)
2.085(5)
2.076(5)
2.050(5)
—
—
2.104(4)
2.070(3)
2.079(4)
2.103(4)
2.141(5)
2.047(5)
—
—
2.066(4)
2.084(4)
The reactions of compounds 5a–c with [NiBr2(DME)] in
dichloromethane gave complexes 6a–c in very good yields (80–
91%) (Scheme 3). Complexes 6a–c were characterised by elemental
analysis, magnetic susceptibility measurements, and the crystal
structure of 6a was determined by X-ray diffraction. They are
very soluble in methanol, sparingly soluble in dichloromethane
and acetonitrile, and insoluble in THF, diethyl ether, toluene and
n-hexane.
Attempts were made to obtain single crystals suitable for
X-ray diffraction of compounds 6, by slow evaporation of their
acetonitrile solutions in air, at room temperature. Upon complete
evaporation of the solvent from the vials (ca. a week), only in
the case of 6a was it possible to separate good quality diffracting
crystals from the resulting material, the corresponding molecular
structure being that of complex 7a, where substitution of the
coordinated Br atoms by water molecules from moisture occurred
(see Scheme 3 and below). Although this is an indication that
compounds 6 might be sensitive to moisture, the resulting bulk
powders remained uncharacterised. Nevertheless, the examination
of the crystal structure of 7a shows that Ni chelates of 5 may have
different conformations (see below).
Ni1–Br2
Ni1–O1/Ni1A–O3a
Ni1–O2/Ni1A–O4a
Angles
—
N1–Ni1–N2/N1A–Ni1A–N2Aa 79.70(18)
N2–Ni1–N6/N2A–Ni1A–N6Aa 88.46(18)
78.89(19)
79.34(19)
78.79(17)
86.74(17)
N3–Ni1–N6/N3A–Ni1A–N6Aa 102.92(18) 174.45(18) 89.66(18)
N1–Ni1–N3/N1A–Ni1A–N3Aa 87.36(18)
78.22(17)
—
98.43(16)
94.24(17)
90.76(14)
77.48(17)
—
99.44(17)
82.40(17)
89.18(17)
Br1–Ni1–Br2
174.45(3)
N1–Ni1–O1/N1–Ni1A–O3a
N2–Ni1–O2/N2–Ni1A–O4a
O1–Ni1–O2/O3–Ni1A–O4a
—
—
—
a For 7a (molecule 2).
23a–c
23d,24
˚
˚
distances (e.g. 2.32–2.38 A
the Ni1–Br1 distance (2.7368(10) A) being markedly longer than
that of Ni1–Br2 (2.5313(10) A), which can be attributed to the large
steric hindrance around the metal centre. Alternatively, compound
6a could be regarded as a five-coordinate cationic NiII complex
with square pyramidal geometry (t = 0.01), where the Ni1–Br2
occupies the apical position of the pyramid, the Br1 atom acting
as a very tight anion. A third possibility could be a structure of
square planar Ni(II) complex where the two Br atoms were present
as very tight anions.
and 2.41–2.47 A,
respectively),
˚
˚
Crystals of complex 6a suitable for single crystal X-ray diffrac-
tion were obtained by slow diffusion of diethyl ether into a dilute
acetonitrile solution of 6a, under dinitrogen, at -20 ◦C, while
those of complex 7a were obtained by slow evaporation of a dilute
acetonitrile solution of 6a, in air, at room temperature. Complexes
¯
6a and 7a crystallised in the triclinic system, space group P1, each
unit cell containing 2 molecules. Although all of the molecules of
6a and 7a adopt octahedral geometries (Fig. 6 and 7, Table 3), their
configurations are totally different, as illustrated in Scheme 4.
Complex 6a is a six-coordinate nickel species, where the metal
atom is bonded to two iminic N atoms (N1 and N2), two triazolyl
N atoms (N3 and N6), and two Br atoms (Br1 and Br2). The
four N atoms occupy the equatorial plane, since they are coplanar
Conversely, in Fig. 7(a), in one of the molecules of complex 7a
(molecule 1, configuration II of Scheme 4), the two iminic N atoms
(N1 and N2) and the two aqueous O atoms (O1 and O2) stay in the
equatorial plane, but present a considerable mean deviation from
˚
their least square plane (0.209(5) A), and the two triazolyl N atoms
(N3 and N6) occupy the axial positions in a trans fashion (N3–
Ni1–N6, 174.45(18)◦), leading to a distorted octahedral geometry.
As can be observed in Fig. 7(a), in the second molecule coexisting
in the crystal structure of 7a (molecule 2, configuration III of
Scheme 4), the two iminic N atoms (N1A and N2A), one of the
aqueous O atoms (O3) and one of the triazolyl N atoms (N6A)
constitute a distorted square plane (mean deviation from their
˚
within a small mean deviation (0.025(5) A) from their least square
plane, giving a slightly distorted square plane, and the two Br
atoms occupy the axial directions in a trans fashion (Br1–Ni1–
Br2, 174.45(3)◦), as displayed in Fig. 6 and in configuration I
of Scheme 4. However, the Ni–Br bond distances in complex 6a
are much longer than typical terminal or bridging NiII–Br bond
˚
least square plane, 0.214(5) A), the remaining aqueous O (O4) and
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Fig. 6 ORTEP diagrams of complex 6a, with 50% probability ellipsoid displacement. The hydrogen atoms are omitted for clarity.
Fig. 7 ORTEP diagrams of complex 7a: (a) molecule 1, and (b) molecule 2 of unit cell, with 50% probability ellipsoid displacement. The hydrogen atoms
are omitted for clarity.
triazolyl N (N3A) atoms occupying the two axial positions (N3A–
Ni1A–O4, 166.88(18)◦), and leading to an even more distorted
octahedral geometry. In complexes 6a and 7a, the corresponding
bond distances and angles are comparable, as can be seen in Table
3.
can rearrange in solution, giving rise to interconversion between
isomers (see Scheme 4), that might also include form I. By analogy,
one can suppose that the same type of stereochemically non-
rigidity and equilibrium can exist also in the case of compound
6a. This could either occur by internal pseudo-rotation of the
chelating ligands, by coordination/de-coordination25 of one or
more of the N-donor atoms of the tetradentate ligands, in
The existence of two types of octahedral isomeric forms II and
III shows that 7a is a stereochemically non-rigid complex and
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Scheme 4 Schematic representation of the different configurations around the Ni centre found in complexes 6a (I) and 7a (II and III). NTA refers to the
coordinating nitrogen atoms of the triazolyl groups.
Scheme 5 Schematic representation of the possible configurations resulting from the ionisation of complex 6a in methanol.
Table 4 Effective magnetic moments meff (mB) for complexes 6a–c, mea-
sured in methanol solution (Evans method-NMR), at 303 K
steric hindrance of the corresponding ligand (configuration V of
Scheme 5).
Complex
meff (mB)
Polymerisation tests
6a
6b
6c
4.38
4.60
4.64
It is apparent that the molecular structures and formal electron
count of complexes 6a–c are considerably different from the
more unsaturated typical tetrahedral Brookhart NiII-a-diimine
complexes, which are very active for ethylene polymerisation.2a,c
In fact, attempts to polymerize ethylene (PC = 2 bar (absolute
H
2
4
◦
particular, those of the triazolyl groups that may be labile due
to the strained character of the chelates, and also by the existence
of ionisation equilibria of the Br atoms from the complexes.
Complexes 6a–c are paramagnetic compounds. The effective
magnetic moments (meff), derived from the measurement of the
corresponding magnetic susceptibilities in methanol solution (by
the Evans method-NMR), are summarized in Table 4, for 303 K,
but were also found to be approximately constant with temperature
down to 193 K. The values obtained are considerably higher than
expected for typical S = 1 octahedral Ni(II) geometries (2.9–3.4
mB26). In fact, the results obtained in solution lie closer to the
upper limit values of the range of meff found typically for S =
1 tetrahedral Ni(II) complexes (3.2–4.1 mB26), which are much
larger than the spin-only magnetic moment value of 2.83 mB (S =
1), due to some significant orbital contribution from low energy
excited states. However, we also managed to measure the effective
magnetic moment of a solid powdered sample of complex 6a, using
the Gouy method, at 291 K. A value of meff = 2.46 mB was obtained,
better conforming to an octahedral molecular geometry (probably
“contaminated” by a low extent of S = 0 square planar molecules).
This is in a better agreement with the crystal structure of 6a
discussed above of an octahedral geometry with elongated Ni–
Br bond distances. This difference in magnetic moments obtained
for 6a, in solution and in the solid state, may thus indicate that,
in a polar and protic solvent such as methanol, the Br atoms
are ionised giving rise to a tetradentate-N,N,N,N Ni2+ dication
(configuration IV of Scheme 5) whose configuration may be shifted
to a more stable distorted tetrahedral configuration, due to the
pressure); T = 20, 50 and 70 C; t = 1 and 24 h; [Ni] = 10-4
M; [Al]:[Ni] = 1000; solvent, toluene) or 1-hexene ([1-hexene] =
0.48, 0.95 and 1.43 M; T = 30 and 50 ◦C; t = 1, 5 and 8 h; [Ni] =
10-4 M; [Al]:[Ni] = 500; solvent, toluene or dichloromethane), with
complexes 6a–c did not succeed when MAO was used as cocatalyst.
Nevertheless, these same systems behaved efficiently as catalysts
for the addition polymerisation of norbornene (NB) and styrene
(Sty), respectively, in dichloromethane and toluene. These very
different catalytic reactivities may be related to the more reduced
electrophilic character of Ni centres (in relation to Brookhart’s
catalysts), which are coordinated to four nitrogen atoms, being
able only to polymerise monomers containing activated double
bonds.
The preliminary polymerisation tests are summarised in Table 5.
Blank experiments proved that, under the experimental conditions
used in the polymerisation tests, neither the cocatalyst MAO
(entries 1 and 6, Table 5) nor the Ni precatalysts acting alone
were active towards the polymerisation of norbornene or styrene.
Complexes 6a–c exhibit high catalytic activities for norbornene
polymerisation, at 30 ◦C, when activated with MAO. The obtained
activities, ca. 3 ¥ 106 g PNB mol Ni-1 h-1 (entries 2–4, Table 5),
are of the same order of magnitude of those of other tetradentate
chelating nickel(II) complexes,27,28 but significantly much higher
than those exhibited by the related Brookhart-type [NiBr2(2,6-
iPr2C6H3-BIAN)]/MAO catalyst system (ca. 5.3 ¥ 103 g PNB
mol Ni-1 h-1).29 The different substituents of complexes 6a–c,
which possess similar steric and electronic properties, have a slight
influence on the polymerisation activities and molecular weights
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Table 5 Polymerisation of norbornene (NB) and styrene (Sty) with nickel complexes 6a–c/MAO catalytic systemsa,b
Activityd (¥ 10-5)
Mn
Mw/Mn
c
e
e
Entry
Catalyst
NB (g)
Sty (g)
nAl:nNi
Yield (g)
Conversion (%)
1
2
3
—
6a
6b
6c
6a
—
6a
6b
6c
6b
6b
2.0
1.0
1.0
1.0
1.0
—
—
—
—
—
—
—
—
—
500 : 0
500 : 1
500 : 1
500 : 1
0
0
0
—
—
0.42
0.49
0.42
0.30
traces
1.50
2.53
1.48
0.96
0.78
42.0
49.0
42.0
30.0
25.2
29.4
25.2
18.0
294000
282000
288000
2.32
2.65
2.36
4
5f
6
—
500 : 1
5.0
5.0
5.0
5.0
5.0
5.0
1000 : 0
1000 : 5
1000 : 5
1000 : 5
1000 : 5
1000 : 5
7
8
30.0
50.6
29.6
19.2
15.6
1.00
1.69
0.99
0.64
0.52
15500
14800
14800
15700
14500
1.71
1.69
1.75
1.70
1.75
9
11g
10h
—
a Norbornene polymerisation conditions: nickel complex, 1.0 mmol; solvent, dichloromethane; reaction temperature, 30 ◦C; reaction time = 10.0 min;
total volume, 25 ml. b Styrene polymerisation conditions: nickel complex, 5.0 mmol; solvent, toluene; reaction temperature, 30 ◦C; reaction time =
c
3.0 h; total volume, 25 ml. nAl:nNi, in mmol Al:mmol Ni. d In g polymer mol Ni-1 h-1. e In g mol-1, determined by GPC/SEC. f 10 equivalents of
2,6-di-tert-butyl-4-methyl-phenol (BHT) were added. g 5 equivalents of BHT were added. h 5 equivalents of galvinoxyl were added.
of the resulting monomodal polynorbornenes. Although high
number-average molecular weights are produced with the catalysts
6a–c/MAO, these values are considerably lower than those found
in the literature for the related Brookhart-type catalyst mentioned
above (ca. 1.8 ¥ 106 g mol-1) and the polydispersities approximately
the same.29
In general, norbornene can be polymerized via three routes:
(a) ring-opening metathesis polymerisation (ROMP), (b) radi-
cal/cationic polymerisation, and (c) addition (vinyl) polymerisa-
tion, giving rise to polymers with three different types of structures
(Chart 3).30 Since the addition of 2,6-di-tert-butyl-4-methylphenol
(BHT) as a free radical trap (10 equivalents in relation to the Ni
catalyst; entry 5, Table 5) did not lead to a complete deactivation,
but just to some decrease of polymerisation activity, a radical
Chart 4 Polymerisation of styrene.
as [NiBr2(2,6-iPr2C6H3-BIAN)]/MAO, and the number-average
molecular weights of the monomodal polystyrenes obtained are
very similar to those reported for the latter system.31 However,
the corresponding distributions are much narrower (ca. 1.7 in the
present work vs. 2.4–2.931).
The 1H and 13C NMR spectra show the polystyrenes ob-
tained are heterotactic, although containing an enhanced isotactic
content (Pm = 0.71), which points to a coordination addition
mechanism rather than a cationic or free radical mechanism. In
fact, polymerisation tests performed in the presence of excess
amounts of radical traps, such as BHT or the very strong
galvinoxyl (5 equivalents in relation to the Ni catalyst; entries 10
and 11, Table 5), did not lead to a complete deactivation, but only
to a decrease in the polymerisation activity, the polymer molecular
weight features (Mn and Mw/Mn) remaining constant in relation
to the reactions in the absence of radical traps.32
1
mechanism can in principle be ruled out. Additionally, the H
NMR spectra of the resulting polymers gave resonances within the
range of d 2.38–0.94 typical of homopolynorbornenes obtained by
an addition mechanism (migratory insertion), and no resonances
of vinylene protons (–CH CH–), in the range of d 5.15–5.31,
typical of ROMP polynorbornenes were observed (see Fig. S6 in
ESI†).29
It is generally accepted that, for the homogenous a-diimine
NiII or PdII-based catalysts, the polymerisation initiators are
unsaturated 14-electron cationic methyl complexes of the type
[L2MMe]+ (M = Ni, Pd, L2 = bidentate chelating a-diimine
ligand), which are formed by the reaction of the catalyst pre-
cursors with MAO.33 An olefin can bind to this species to give
a 16-electron [L2MMe(olefin)]+ complex, which is followed by
migratory insertion into the metal-alkyl bond and formation of
a new alkyl complex [L2MR(olefin)]+. The coordination of further
olefins and their subsequent insertion lead to chain propagation
and to the polymer growth. In the whole process, the electron-
count of all the active species is lower than 18. In the present
case, the reaction of catalyst precursors 6a–c with MAO may
originate cationic methyl complexes [L4NiMe]+ (L4 = N,N,N,N-
tetradentate chelating ligands). However, these are still 18-electron
species and, if no de-coordination of some of the N-donor atoms
takes place, the coordination of a further olefin and subsequent
Chart 3 Types of norbornene polymerisation.
The styrene can also be polymerized by 6a–c/MAO catalysts
(Chart 4), the corresponding activities and molecular weights be-
ing both ca. 20–25 times lower than those obtained for norbornene
(entries 7–9, Table 5). These activities are ca. 3–5 times lower
than those reported for related Brookhart-type catalysts, such
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migratory insertion would be hampered. In the present case, we
should think that the triazolyl groups behave somehow as labile
moieties of these chelating ligands, which could be attested by
the observed stereochemical non-rigidity of these complexes. The
norbornene and styrene monomers could then be able to substitute
such groups, thus generating 18-electron [LŸL3MMe(olefin)]+ or
prior to use. Methanol was purified by treatment with a small
amount of sodium with vigorous stirring, and distilled prior to
use. Norbornene was refluxed over sodium for 2 days, distilled,
and kept by storage at -20 ◦C. Styrene was dried over calcium
hydride for 2 days, distilled trap-to-trap under vacuum, at room
temperature, and kept by storage at -20 ◦C. Methylaluminoxane
(MAO) of the type PMAO-IP (7 wt% Al) was purchased from
AkzoNobel. Deuterated solvents (acetonitrile-d3, chloroform-d1,
dichloromethane-d2, methanol-d4, and 1,1,2,2-tetrachloroethane-
16-electron [L2 L2MMe(olefin)]+ species that could account for
Ÿ
the initiation and activity of 6a–c/MAO catalytic systems in
their polymerisation. However, taking into account all these
plausible problems of stereochemical crowding of the coordination
sphere of the metal, it is remarkable that these systems still have
activities comparable to those of the Brookart-type bidentate a-
diimine Ni precatalysts or even higher (in the case of norbornene
polymerisation).
˚
d2) were dried by storage over 4 A molecular sieves and degassed
by the freeze-pump-thaw method. Solvents and solutions were
transferred using a positive pressure of nitrogen through stainless
steel cannulae and mixtures were filtered in a similar way using
modified cannulae that could be fitted with glass fiber filter disks.
Elemental analyses were obtained from the IST elemental
analysis service.
Conclusions
Nuclear magnetic resonance (NMR) spectra were recorded on
Bruker Avance III 300 (1H, 300.130 MHz; 13C, 75.4753 MHz),
Bruker Avance III 400 (1H, 400.132 MHz; 13C, 100.623 MHz) or
Bruker Avance III 500 (1H, 500.130 MHz; 13C, 125.758 MHz)
(UltraShield magnet) spectrometers. Spectra were referenced
internally using the residual protio solvent resonance relative
to tetramethylsilane (d = 0). All chemical shifts are quoted
in d (ppm) and coupling constants given in Hz. Multiplicities
were abbreviated as follows: broad (br), singlet (s), doublet (d),
triplet (t), quartet (q) and multiplet (m). For air- and moisture-
sensitive materials, NMR solutions were prepared in a glovebox.
Three new tetradentate chelating a-diimine ligands of the general
formula ArN C(An)–C(An) NAr (where Ar = 2-(1-benzyl-
1H-1,2,3-triazol-4-yl)phenyl 5a, 2-(1-(1-phenylethyl)-1H-1,2,3-
triazol-4-yl)phenyl 5b, 2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl
5c) were synthesised, through the modification of Brookhart-type
a-diimine ligands by using Click Chemistry.
These ligands were obtained by the condensation of ace-
naphthenequinone with the corresponding o-triazolyl-substituted
anilines, using ZnCl2 as template, followed by subsequent de-
coordination Zn with K2C2O4. It was demonstrated by elemen-
tal analysis, NMR spectroscopy and X-ray diffraction that, in
compounds 2a–c and 4a–c, these ligands appear tetracoordi-
nated to Zn in cationic square pyramidal complexes of the
type [ZnCl(ArN C(An)–C(An) NAr)]+, the counteranions of
which are either dimers [Zn2Cl6]2- (2a–c) or acetonitrile adducts
[ZnCl3(NCCH3)]- (4a–c).
The reaction of [NiBr2(DME)] with ligands 5a–c originates
the Ni(II) complexes 6a–c having distorted octahedral geometries
around the Ni atoms, which are sterochemically non-rigid and may
appear in variable configurations. Preliminary experiments show
that complexes 6a–c are active in the coordination addition poly-
merisation of norbornene and styrene, when activated with MAO.
The catalytic activities of these systems are significantly higher
(for norbornene) or somewhat lower (for styrene) than those of
the typical Brookhart-type catalyst systems, and the molecular
weight features considerably different, although monomodal
distributions typical of single-site catalysts are obtained.
1
The 1H and 13C{ H} NMR spectra of the polynorbornenes
and polystyrenes in 1,1,2,2-tetrachloroethane-d2 solutions were
obtained, respectively, at 110 ◦C, at 300 and 500 MHz respectively.
Magnetic susceptibility measurements of complexes 6a–c in
solution were carried out by the Evans method34 in the Bruker
Avance III 300 spectrometer, using a 3% solution of hexamethyl-
disiloxane (reference) in methanol-d4. The magnetic susceptibility
of complex 6a in the solid state was determined for a powdered
sample using a Sherwood Scientific magnetic susceptibility bal-
ance, based on the Gouy method; a diamagnetic correction for
Ni2+, Br- and ligand 5a was applied.
The number-average molecular weight (Mn), weight-
average molecular weight (Mw), and polydispersity indexes
(Mw/Mn) of polynorbornene were analysed by Gel Permeation
Chromatography/Size-exclusion Chromatography (GPC/SEC),
using
a
Polymer Laboratories GPC220 gel permeation
chromatograph, equipped with a series of a PLgel 10 mm
guard column (50 ¥ 7.5 mm) and two PLgel 10 mm mixed-B
(300 ¥ 7.5 mm), using 1,2,4-trichlorobenzene (with anti-oxidant)
as eluent and a flow-rate of 1.0 mL min-1 (nominal), at
150 ◦C (nominal); the detector was a differential refractometer.
The polystyrenes’ molecular weight were also determined by
GPC/SEC, using a Waters 150CV gelpermeation chromatograph,
equipped with a series of a PL Polypore guard column (50 ¥
7.5 mm) and two PL Polypore columns (300 ¥ 7.5 mm), usi◦ng
THF as eluent and a flow-rate of 1.0 mL min-1 (nominal), at 35 C
(nominal); the detector was a differential refractometer. Both the
GPC/SEC systems were calibrated with polystyrene standards.
Experimental
General
All manipulations dealing with air- or moisture-sensitive ma-
terials were carried out under inert atmosphere using a dual
vacuum/nitrogen line and standard Schlenk techniques. Unless
otherwise stated, all reagents were purchased from commercial
suppliers (e.g., Acros, Aldrich, Fluka) and used as received. All
solvents were used under inert atmosphere and purified prior
to use. Toluene and diethyl ether were purified by refluxing
over sodium/benzophenone ketyl, and distilled prior to use.
Dichloromethane and acetonitrile were purified over calcium
hydride and phosphorus pentoxide, respectively, and distilled
Syntheses of the triazole ortho-functionalised anilines 1a–c.
The synthetic procedure is adapted from that reported in the
literature.16b A typical procedure is described as follows: water
3376 | Dalton Trans., 2011, 40, 3365–3380
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(20 ml) and tert-butanol (20 ml) were mixed in a 100 ml flask and
degassed by bubbling gaseous dinitrogen. 2-Ethynylaniline (20.0
mmol) and, respectively, (azidomethyl)benzene (for 1a), (R,S)-(1-
azidoethyl)benzene (for 1b) and azidobenzene (for 1c) (22.0 mmol,
1.1 equiv) were added with vigorous stirring, and followed by
the sequential addition of a 1.0 M aqueous solution of sodium
ascorbate (2.0 ml) and a 1.0 M aqueous solution of CuSO4·5H2O
(1.0 ml). In approximately half an hour, the solution colour turned
brown, changing to orange–yellow for a few minutes and, finally,
to light yellow. Simultaneously, a large amount of white solid
precipitated. The suspension was stirred for 24 h, 50 ml of CH2Cl2
was added and the two phases separated. The aqueous phase
was extracted with CH2Cl2 (3 ¥ 50 ml). The organic phases were
combined and dried with anhydrous Na2SO4. After removal of
the solvent, an off-white solid was isolated and dried in vacuum.
The crude products were obtained with yields of 95% (1a), 91%
(1b) and 94% (1c), and were pure enough to be used as such
in the subsequent reactions. These solids were further purified by
crystallisation in methanol, at -20 ◦C, and colourless crystals were
obtained. Final yields: 89% (1a), 64% (1b) and 91% (1c).
Calcd for C42H30Cl4N8Zn2: C, 54.87; H, 3.29; N, 12.19. Found: C,
54.62; H, 3.29; N, 12.10.
Data for 2b.1H NMR (400 MHz, CD3OD): d 8.80 (s, 2H), 8.23
(d, 2H, J = 8.4 Hz), 8.05 (d, 2H, J = 7.6 Hz), 7.82–7.75 (br, 4H),
7.66–7.60 (m, 6H), 7.27 (br, 10H), 5.98 (q, 2H, J = 7.2 Hz), 2.00–
1
1.97 (m, 2H). 13C { H} NMR (100 MHz, CD3OD): d 162.1, 146.1,
144.9, 141.8, 139.7, 139.6, 132.3, 131.39, 131.36, 129.8, 129.41,
129.37, 128.7, 128.3, 128.2, 126.1, 126.0, 125.7, 125.0, 122.9, 122.6,
121.6, 61.8, 20.2. Anal. Calcd for C44H34Cl4N8Zn2: C, 55.78; H,
3.62; N, 11.83. Found: C, 55.73; H, 3.75; N, 11.80.
1
Data for 2c. H NMR (400 MHz, CD3OD): d 9.26 (s, 2H),
8.28 (d, 2H, J = 8.4 Hz), 8.19 (d, 2H, J = 6.8 Hz), 7.90–7.67 (m,
1
14H), 7.52 (br, 6H). 13C { H} NMR (100 MHz, CD3OD): d 162.5,
146.7, 145.0, 142.1, 136.3, 132.4, 131.5, 130.0, 129.7, 129.6, 129.4,
128.3, 125.8, 125.1, 122.7, 122.0, 121.5, 120.6. Anal. Calcd for
C40H26Cl4N8Zn2: C, 53.90; H, 2.94; N, 12.57. Found: C, 53.85; H,
3.21; N, 12.56.
Isolation of amide byproducts 3a–c. Compounds 3a–c were
isolated as byproducts of each of the synthetic procedures of
compounds 2a–c, respectively. A typical isolation procedure is
described as follows: after the synthetic reactions of 2a–c, the
suspensions were filtered off, and the filtrates were collected,
evaporated in vacuum, and extracted with diethyl ether. The
diethyl ether solutions were stored at -20 ◦C to crystallise. Crystals
of 3a (light yellow), 3b (orange) and 3c (pink) were isolated,
respectively, and dried in vacuum. Yields: 5% (3a), 10% (3b) and
6% (3c).
Data for 1a. 1H NMR (400 MHz, CD2Cl2): d 7.80 (s, 1H), 7.44–
7.42 (m, 3H), 7.37–7.35 (m, 3H), 7.14 (t, 1H, J = 7.8 Hz), 6.80 (d,
1H, J = 8.0 Hz), 6.72 (t, 1H, J = 7.2 Hz), 5.61 (s, 2H), 5.57 (br,
1
2H). 13C { H} NMR (100 MHz, CD2Cl2): d 148.7, 145.2, 135.0,
129.0, 128.9, 128.6, 128.1, 127.7, 120.0, 117.1, 116.5, 113.4, 54.1.
Anal. Calcd for C15H14N4: C, 71.98; H, 5.64; N, 22.38. Found: C,
71.95; H, 6.03; N, 22.04.
Data for 1b. 1H NMR (400 MHz, CD2Cl2): d 7.83 (s, 1H), 7.44–
7.37 (m, 6H), 7.16 (t, 1H, J = 7.4 Hz), 6.82 (d, 1H, J = 8.0 Hz),
6.75 (t, 1H, J = 7.6 Hz), 5.91 (q, 1H, J = 6.8 Hz), 5.64 (br, 2H),
1
Data for 3a. H NMR (300 MHz, CD2Cl2): d 11.35 (br, 1H),
8.63 (d, 1H, J = 8.1 Hz), 7.90 (s, 1H), 7.43 (m, 7H), 7.10 (t, 1H, J =
1
7.5 Hz, J = 1.2 Hz), 5.63 (s, 2H), 2.25 (s, 3H). 13C { H} NMR (75
1
2.07 (d, 3H, J = 6.8 Hz). 13C { H} NMR (100 MHz, CD2Cl2): d
MHz, CD2Cl2): d 168.8, 147.9, 136.7, 134.5, 129.1, 128.9, 128.8,
128.2, 127.1, 123.1, 121.1, 121.0, 117.2, 54.4, 25.1. Anal. Calcd for
C17H16N4O: C, 69.85; H, 5.52; N, 19.17. Found: C, 69.87; H, 5.68;
N, 19.22.
148.3, 145.3, 140.3, 129.0, 128.9, 128.5, 127.6, 126.5, 118.9, 117.0,
116.5, 113.5, 60.4, 21.2. Anal. Calcd for C16H16N4: C, 72.70; H,
6.10; N, 21.20; Found: C, 72.36; H, 6.10; N, 20.91.
1
Data for 1c. H NMR (300 MHz, CD2Cl2): d 8.29 (s, 1H),
1
Data for 3b. H NMR (300 MHz, CD2Cl2): d 11.39 (br, 1H),
7.86–7.83 (m, 2H), 7.63–7.58 (m, 2H), 7.54–7.49 (m, 2H), 7.19 (t,
8.62 (d, 1H, J = 8.4 Hz), 7.88 (s, 1H), 7.50–7.30 (m, 7H), 7.10 (t,
1H, J = 7.5 Hz, J = 1.2 Hz), 5.93 (q, 1H, J = 7.2 Hz), 2.25 (s, 3H),
1H, J = 7.8 Hz, J = 1.5 Hz), 6.85–6.79 (m, 2H), 5.54 (br, 2H).
1
13C { H} NMR (75 MHz, CD2Cl2): d.148.9, 145.4, 137.0, 129.8,
1
2.09 (d, 3H, J = 6.9 Hz). 13C { H} NMR (75 MHz, CD2Cl2): d
129.2, 128.9, 127.8, 120.6, 118.1, 117.2, 116.6, 113.1. Anal. Calcd
for C14H12N4: C, 71.17; H, 5.12; N, 23.71. Found: C, 71.02; H,
5.02; N, 23.83.
168.7, 147.5, 139.8, 136.7, 129.0, 128.7, 128.6, 127.0, 126.5, 123.0,
121.0, 119.9, 117.3, 60.7, 25.1, 21.1. Anal. Calcd for C18H18N4O:
C, 70.57; H, 5.92; N, 18.29; Found: C, 70.58; H, 6.06; N, 17.95.
1
Data for 3c. H NMR (400 MHz, CD2Cl2): d 11.22 (br, 1H),
8.64 (d, 1H, J = 8.4 Hz), 8.38 (s, 1H), 7.88–7.85 (m, 2H), 7.67–7.63
(m, 3H), 7.59–7.55 (m, 1H), 7.41 (t, 1H, J = 7.2 Hz, J = 1.6 Hz),
Syntheses of zinc complexes 2a–c. The synthetic procedure is
adapted from that reported in the literature.11 A typical procedure
is described as follows: 40 ml of glacial acetic acid was added to a
mixture of acenaphthenequinone (4.0 mmol), compounds 1a, 1b
(racemate) or 1c (8.0 mmol), respectively, and ZnCl2 (8.0 mmol).
The mixtures were heated to reflux for 5 h, and then cooled down
to room temperature. Orange–red solids precipitated. These solids
were filtered off, washed with acetic acid (3 ¥ 50 ml) and diethyl
ether (3 ¥ 50 ml), and dried in vacuum. Yields: 59% (2a), 75% (2b)
and 65% (2c).
1
7.19 (t, 1H, J = 7.6 Hz, J = 1.2 Hz), 2.28 (s, 3H). 13C { H} NMR
(100 MHz, CD2Cl2): d 168.7, 148.1, 136.83, 136.76, 129.9, 129.3,
129.1, 127.2, 123.3, 121.3, 120.7, 119.2, 117.1, 25.1. Anal. Calcd
for C16H14N4O: C, 69.05; H, 5.07; N, 20.13. Found: C, 69.01; H,
5.10; N, 20.11.
Syntheses of zinc complexes 4a–c. Compounds 2a–c were
dissolved in acetonitrile, and refluxed for 2 h, respectively. The
solutions were cooled down and crystallised at -20 ◦C, leading to
orange crystals of 4a–c, the elemental compositions of which were
unstable under vacuum due to loss of acetonitrile.
Data for 2a. 1H NMR (400 MHz, CD3OD/CD3CN (4 : 1 v/v)):
d 8.74 (s, 2H), 8.30 (d, 2H, J = 8.4 Hz), 8.04 (d, 2H, J = 7.2 Hz),
7.90–7.86 (br, 4H), 7.72–7.68 (m, 6H), 7.38–7.34 (br, 10H), 5.70 (s,
Data for 4a. 1H NMR (400 MHz, CD3CN): d 8.60 (s, 2H), 8.28
(d, 2H, J = 8.0 Hz), 7.98 (d, 2H, J = 7.6 Hz, J = 2.0 Hz), 7.93–
7.89 (m, 4H), 7.71–7.64 (m, 6H), 7.44–7.42 (m, 4H), 7.39–7.36 (m,
1
4H). 13C { H} NMR (100 MHz, CD3OD/CD3CN (4 : 1 v/v)): d
162.3, 146.3, 145.0, 141.7, 134.4, 132.5, 131.3, 130.1, 129.6, 128.9,
128.7, 128.3, 128.1, 125.8, 125.2, 124.2, 122.8, 121.4, 54.8. Anal.
1
6H), 5.76 (d, 2H, J = 14.4 Hz), 5.69 (d, 2H, J = 14.4 Hz). 13C { H}
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NMR (100 MHz, CD3CN): d 162.3, 146.3, 145.0, 141.5, 134.2,
132.7, 131.2, 130.4, 129.9, 129.8, 129.1, 128.9, 128.5, 128.4, 125.8,
125.4, 124.3, 122.8, 121.1, 55.1.
Data for 4b. H NMR (400 MHz, CD3CN): d 8.72–8.61 (m,
2H), 8.24 (d, 2H, J = 8.4 Hz), 8.01 (m, 2H), 7.90–7.88 (d, 4H),
Syntheses of nickel complexes 6a–c. 40 ml of CH2Cl2 were
added to mixtures of compounds 5a–c (1.34 mmol), respectively,
and NiBr2(DME) (1.34 mmol). The mixtures were stirred for 24 h
at room temperature. After filtration, brown solids were isolated,
washed with diethyl ether (3 ¥ 100 ml), and dried in vacuum.
Yields: 90% (6a), 80% (6b) and 91% (6c).
Data for 6a. Anal. Calcd for C42H30Br2N8Ni: C, 58.30; H, 3.49;
N, 12.95. Found: C, 57.90; H, 3.36; N, 12.85.
Data for 6b. Anal. Calcd for C44H34Br2N8Ni: C, 59.16; H, 3.84;
N, 12.54. Found: C, 59.46; H, 3.71; N, 12.42.
1
7.72–7.62 (m, 6H), 7.37–7.34 (br, 10H), 6.10–5.94 (m, 2H), 2.03
1
(d, 6H, J = 6.8 Hz). 13C { H} NMR (100 MHz, CD3CN): d 162.2,
146.1, 144.9, 141.5, 139.8, 139.5, 132.7, 131.1, 130.4, 129.9, 129.8,
129.1, 128.7, 128.5, 126.5, 125.8, 125.3, 123.6, 123.1, 122.8, 121.2,
62.0, 20.5.
Data for 4c. 1H NMR (400 MHz, CD3CN/CD3OD (4 : 1 v/v)):
d 9.14 (s, 2H), 8.28 (d, 2H, J = 8.4 Hz), 8.14 (d, 2H, J = 6.8 Hz),
Data for 6c. Anal. Calcd for C40H26Br2N8Ni: C, 57.39; H, 3.13;
N, 13.38. Found: C, 57.60; H, 3.21; N, 13.52.
1
7.89 (br, 8H), 7.73–7.67 (m, 6H), 7.56 (br, 6H). 13C { H} NMR
(100 MHz, CD3CN/CD3OD (4 : 1 v/v)): d 162.6, 146.6, 145.0,
141.9, 136.2, 132.7, 131.2, 130.5, 130.1, 129.9, 129.7, 128.5, 125.8,
125.4, 122.8, 122.5, 121.2, 120.8.
X-ray diffraction
Crystallographic and experimental details of crystal structure
determinations are given in Table S2 of the ESI.† In each case,
a specimen crystal was selected under an inert atmosphere,
covered with polyfluoroether, and mounted on the end of a
nylon loop. All of crystal data was collected in a Bruker
AXS-KAPPA APEX II diffractometer equipped with an Ox-
ford Cryosystems open-flow nitrogen cryostat, at 150 K, using
Syntheses of metal-free ligands 5a–c. The synthetic procedure
is adapted from those reported in the literature.13a A typical
procedure is described as follows: compounds 2a–c (0.65 mmol),
respectively, were suspended in 100 ml of CH2Cl2, and solutions
of K2C2O4 (1.95 mmol) in water (10 ml) were added. The
mixtures were vigorously stirred for 4 h until the suspensions
completely turned clear. White precipitates of ZnC2O4 could be
seen suspended in the aqueous phases. For each reaction, the
two phases were separated, and the organic layer was washed
with water (3 ¥ 30 ml) and dried with anhydrous Na2SO4. After
removal of the solvent, orange solids were isolated. These solids,
in the cases of both 5a and 5b, were further purified by column
chromatography (silica gel 60 A, hexane–ethyl acetate (1 : 4 and
1 : 1 v/v, respectively, for 5a and 5b) as eluents) or also, in the
case of 5a, by recrystallisation from a dilute solution in hexane
and ethyl acetate (1 : 4 v/v), at -20 ◦C, and, in the case of 5c, by
recrystallisation from a dilute solution in ethyl acetate. Yields: 80%
(5a), 52% (5b) and 85% (5c).
˚
graphite monochromated Mo-Ka radiation (l = 0.71073 A).
Cell parameters were retrieved using Bruker SMART software
and refined using Bruker SAINT on all observed reflections.
Absorption corrections were applied using SADABS.35 Structure
solution and refinement were performed using direct methods with
the programs SIR92,36 SIR200437 and SHELXL,38 all included
in the package of programs WINGX-Version 1.70.01.39 Non-
hydrogen atoms were refined with anisotropic thermal parameters.
Except NH and NH2, that were found in the difference electron
density maps and were allowed to refine freely, all hydrogens
were inserted in idealised positions and allowed to refine riding
˚
˚
in the parent C atoms, with C–H distances of 0.93 A, 0.96 A and
˚
0.98 A for aromatic, methyl and methine H atoms, respectively,
Data for 5a. 1H NMR (300 MHz, CD2Cl2): d 8.35–8.32 (m, 2H),
7.95 (s, 2H), 7.83 (d, 2H, J = 7.8 Hz), 7.36–7.28 (m, 6H), 7.03–
and with Uiso(H) = 1.2Ueq(C). All the structures refined to a
perfect convergence, even though some of the crystals were of
poorer quality, such as 2b and 5a that presented high Rint and
relatively low ratio of observed/unique reflections. Some of the
crystal showed the presence of disordered solvent molecules,
the PLATON/SQUEEZE40 routine being applied whenever a
good disorder model was impossible to attain (4c, 6a and 7a).
Graphic presentations were prepared with ORTEP-III.41 Data
was deposited in CCDC under the deposit numbers 789956 (1a),
789957 (1c), 789958 (2b), 789959 (3a), 789960 (4a), 789961 (4c),
789962 (5a), 789963 (5c), 789964 (6a), and 789965 (7a).
1
6.83 (m, 14H), 5.29 (s, 4H). 13C { H} NMR (75 MHz, CD2Cl2): d
160.7, 147.8, 144.7, 141.7, 135.1, 131.1, 129.3, 128.7, 128.6, 128.2,
127.9, 127.7, 127.6, 125.2, 123.7, 123.4, 121.0, 118.0, 53.8. Anal.
Calcd for C42H30N8: C, 78.00; H, 4.68; N, 17.33. Found: C, 77.47;
H, 4.68; N, 17.19.
1
Data for 5b. H NMR (400 MHz, CD2Cl2): d 8.41–8.38 (m,
2H), 8.10 (s, 1H), 8.09 (s, 1H), 7.85 (d, 2H, J = 8.4 Hz), 7.35–
7.30 (m, 6H), 7.03–6.81 (m, 14H), 5.60 (q, 2H, J = 7.2 Hz, J =
1
2.8 Hz), 1.71 (d, 6H, J = 7.2 Hz, J = 2.4 Hz). 13C { H} NMR
(100 MHz, CD2Cl2): d 160.39, 160.37, 147.4, 144.2, 141.8, 140.43,
140.42, 131.2, 129.3, 128.6, 128.3, 128.1, 128.0, 127.74, 127.73,
126.0, 125.3, 123.7, 122.5, 121.58, 121.55, 117.67, 117.64, 60.0,
21.06, 21.04. Anal. Calcd for: C44H34N8: C, 78.32; H, 5.08; N,
16.61. Found: C, 78.32; H, 5.20; N, 16.24.
Polymerisation reactions
The polymerisation of ethylene was attempted by using the same
experimental conditions and procedures described elsewhere.14e,42
The polymerisations of norbornene and styrene (and the
1-hexene polymerisation attempts) were conducted in 100 ml
Schlenk tubes, which were flamed in vacuum and back-filled with
nitrogen. The desired amounts of solvent (dichloromethane and
toluene, respectively, for norbornene and styrene), monomer and
catalyst suspension in the corresponding solvent (1.0 mmol ml-1)
were injected, by this order, via syringe. The polymerisation was
initiated by addition of MAO in toluene via syringe. At the desired
Data for 5c. 1H NMR (400 MHz, CD2Cl2): d 8.90 (s, 2H), 8.68–
8.65 (m, 2H), 7.98 (d, 2H, J = 8.0 Hz), 7.68 (d, 4H, J = 8.0 Hz, J =
2.0 Hz), 7.57–7.54 (m, 4H), 7.47 (t, 2H, J = 8.0 Hz), 7.39–7.37 (m,
1
6H), 7.27–7.23 (m, 4H). 13C { H} NMR (100 MHz, CD2Cl2): d
160.7, 147.7, 144.8, 142.2, 136.9, 131.2, 129.6, 128.8, 128.2, 128.0,
127.9, 127.8, 125.5, 123.9, 121.6, 121.2, 119.5, 117.4. Anal. Calcd
for C40H26N8: C, 77.65; H, 4.24; N, 18.11. Found: C, 77.63; H,
4.27; N, 18.11.
3378 | Dalton Trans., 2011, 40, 3365–3380
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reaction time, the polymerisation was terminated by the addition
of HCl-acidified methanol (5% (v/v)). The polymer was isolated
by filtration, washed with methanol, and dried in vacuum at 50 ◦C.
J. Polym. Sci., Part A: Polym. Chem., 1999, 37, 2471–2480; (b) M. M.
Marques, S. Fernandes, S. G. Correia, J. R. Ascenso, S. Caroc¸o, P. T.
Gomes, J. Mano, S. G. Pereira, T. Nunes, A. R. Dias, M. D. Rausch and
J. C. W. Chien, Macromol. Chem. Phys., 2000, 201, 2464–2468; (c) M.
M. Marques, S. Fernandes, S. G. Correia, S. Caroc¸o, P. T. Gomes, A. R.
Dias, J. Mano, M. D. Rausch and J. C. W. Chien, Polym. Int., 2001, 50,
579–587; (d) S. Fernandes, J. R. Ascenso, P. T. Gomes, S. I. Costa, L.
C. Silva, P. T. Gomes, J. C. W. Chien and M. M. Marques, Polym. Int.,
2005, 54, 249–255; (e) V. Rosa, P. J. Gonzalez, T. Avile´s, P. T. Gomes,
R. Welter, A. C. Rizzi, M. C. G. Passeggi and C. D. Brondino, Eur. J.
Inorg. Chem., 2006, 23, 4761–4769; (f) V. Rosa, S. A. Carabineiro, T.
Avile´s, P. T. Gomes, R. Welter, J. M. Campos and M. R. Ribeiro, J.
Organomet. Chem., 2008, 693, 769–775; (g) L.-D. Li, C. S. B. Gomes,
P. T. Gomes and M. T. Duarte, Synth. Commun., 2008, 38, 4415–
4425.
Acknowledgements
We thank the Fundac¸a˜o para Cieˆncia
financial support (Projects PPCDT/QUI/59025/2004,
PTDC/QUI/65474 and PTDC/EQU-EQU/110313/2009,
co-financed by FEDER) and fellowships to L.L. and C.S.B.G.
(SFRH/BPD/30733/2006 and SFRH/BPD/64423/2009,
e Tecnologia for
respectively). We also thank the Portuguese NMR Network
(IST-UTL Centre).
15 See, for example: (a) T. J. Wadas, E. H. Wong, G. R. Weisman and C.
J. Anderson, Chem. Rev., 2010, 110, 2858–2902; (b) E. L. Quea and C.
J. Chang, Chem. Soc. Rev., 2010, 39, 51–60; (c) R. E. Mewis and S. J.
Archibald, Coord. Chem. Rev., 2010, 254, 1686–1712.
16 (a) H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int.
Ed., 2001, 40, 2004–2021; (b) V. V. Rostovtsev, L. G. Green, V. V. Fokin
and K. B. Sharpless, Angew. Chem., Int. Ed., 2002, 41, 2596–2599.
17 T. P. Lodge, Macromolecules, 2009, 42, 3827–3829.
References
1 (a) S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev., 2000,
100, 1169–1203; (b) G. P. Britovsek, V. C. Gibson and D. F. Wass,
Angew. Chem., Int. Ed., 1999, 38, 428–447; (c) V. C. Gibson and S. K.
Spitzmesser, Chem. Rev., 2003, 103, 283–315.
18 P. Wu, A. K. Feldman, A. K. Nugent, C. J. Hawker, A. Scheel, B. Voit, J.
Pyun, J. M. J. Fre´chet, K. B. Sharpless and V. V. Fokin, Angew. Chem.,
Int. Ed., 2004, 43, 3928–3932.
2 (a) L. K. Johnson, C. M. Killian and M. Brookhart, J. Am. Chem.
Soc., 1995, 117, 6414–6415; (b) L. K. Johnson, S. Mecking and M.
Brookhart, J. Am. Chem. Soc., 1996, 118, 267–268; (c) C. M. Killian,
D. J. Tempel, L. K. Johnson and M. Brookhart, J. Am. Chem. Soc.,
1996, 118, 11664–11665; (d) D. J. Tempel, L. K. Johnson, R. L. Huff, P.
S. White and M. Brookhart, J. Am. Chem. Soc., 2000, 122, 6686–6700;
(e) D. P. Gates, S. A. Svejda, E. On˜ate, C. M. Killian, L. K. Johnson, P.
S. White and M. Brookhart, Macromolecules, 2000, 33, 2320–2334.
3 A. Scarel, M. Rosa Axet, F. Amoroso, F. Ragaini, C. J. Elsevier, A.
Holuigue, C. Carfagna, L. Mosca and B. Milani, Organometallics, 2008,
27, 1486–1494.
4 (a) R. van Asselt and C. J. Elsevier, Organometallics, 1992, 11, 1999–
2001; (b) R. van Asselt and C. J. Elsevier, Tetrahedron, 1994, 50, 323–
334.
5 (a) R. van Asselt, C. J. Elsevier, W. J. J. Smeets and A. L. Spek, Inorg.
Chem., 1994, 33, 1521–1531; (b) J. W. Sprengers, M. Greef, M. A. Duin
and C. J. Elsevier, Eur. J. Inorg. Chem., 2003, 3811–3819.
6 (a) F. Ragaini, S. Cenini, S. Tollari, G. Tummolillo and R. Beltrami,
Organometallics, 1999, 18, 928–942; (b) F. Ragaini, S. Cenini, E.
Borsani, M. Dompe´, E. Gallo and M. Moret, Organometallics, 2001,
20, 3390–3398.
19 (a) A. J. Link and D. A. Tirrell, J. Am. Chem. Soc., 2003, 125, 11164–
11165; (b) Q. Wang, T. R. Chan, R. Hilgraf, V. V. Fokin, K. B. Sharples
and M. G. Finn, J. Am. Chem. Soc., 2003, 125, 3192–3193; (c) K. D.
Bodine, D. Y. Gin and M. S. Gin, J. Am. Chem. Soc., 2004, 126, 1638–
1639; (d) J. A. Opsteen and J. C. M. V. Hest, Chem. Commun., 2005,
57–59; (e) M. Malkoch, K. Schleicher, E. Drockenmuller, C. J. Hawker,
T. P. Russell, P. Wu and V. V. Fokin, Macromolecules, 2005, 38, 3663–
3678; (f) A. E. Daugaard, S. Hvilsted, T. S. Hansen and N. B. Larsen,
Macromolecules, 2008, 41, 4321–4327; (g) J. Sinha, R. Sahoo and A.
Kumar, Macromolecules, 2009, 42, 2015–2022.
20 (a) A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and G. C. Verschoor,
J. Chem. Soc., Dalton Trans., 1984, 1349–1356; (b) C. O’Sullivan, G.
Murphy, B. Murphy and B. Hathaway, J. Chem. Soc., Dalton Trans.,
1999, 1835–1844.
21 M. C. Rodriguez-Arguelles, L. P. Battaglia, M. B. Ferrari, G. G. Fava,
C. Pelizzi and G. Pelosi, J. Chem. Soc., Dalton Trans., 1995, 2297–2303.
22 A. J. M. Al-Karawi, W. Clegg, R. W. Harrington and R. A. Henderson,
Dalton Trans., 2009, 564–570.
23 (a) J. Feldman, S. J. McLain, A. Parthasarathy, W. J. Marshall, J. C.
Calabrese and S. D. Arthur, Organometallics, 1997, 16, 1514–1516;
(b) J.-C. Yuan, L. C. Silva, P. T. Gomes, P. Valerga, J. M. Campos, M. R.
Ribeiro, J. C. W. Chien and M. M. Marques, Polymer, 2005, 46, 2122–
2132; (c) D. M. Spasyuk, D. Zargarian and A. Est, Organometallics,
2009, 28, 6531–6540; (d) H.-R. Liu, P. T. Gomes, S. I. Costa, M. T.
Duarte, R. Branquinho, A. C. Fernandes, J. C. W. Chien, R. P. Singh
and M. M. Marques, J. Organomet. Chem., 2005, 690, 1314–1323.
24 H. Gao, W. Guo, F. Bao, G. Gui, J. Zhang, F. Zhu and Q. Wu,
Organometallics, 2004, 23, 6273–6280.
7 S. I. Pascu, P. A. Waghorn, T. D. Conry, B. Lin, H. M. Betts, J. R.
Dilworth, R. B. Sim, G. C. Churchill, F. I. Aigbirhio and J. E. Warren,
Dalton Trans., 2008, 2107–2110.
8 G. Van Koten and K. Vrieze, Adv. Organomet. Chem., 1982, 21, 151–
239.
9 (a) F. Ragaini, M. Gasperini, E. Gallo and P. Macchi, Chem. Commun.,
2005, 1031–1033; (b) J. A. Moore, K. Vasudevan, N. J. Hill, G. Reeske
and A. H. Cowley, Chem. Commun., 2006, 2913–2915; (c) F. Ragaini,
M. Gasperini, P. Parma, E. Gallo, N. Casati and P. Macchi, New J.
Chem., 2006, 30, 1046–1057; (d) M. Hagar, F. Ragaini, E. Monticelli,
A. Caselli, P. Macchib and N. Casatic, Chem. Commun., 2010, 46,
6153–6155.
10 For instance: (a) S. A. Svejda and M. Brookhart, Organometallics,
1999, 18, 65–74; (b) D. Pappalardo, M. Mazzeo, S. Antinucci and C.
Pellecchia, Macromolecules, 2000, 33, 9483–9487; (c) H.-R. Liu, S. I.
Costa, P. T. Gomes, M. T. Duarte, R. Branquinho, A. C. Fernandes,
J. C. W. Chien and M. M. Marques, J. Organomet. Chem., 2005, 690,
1314–1323; (d) J.-C. Yuan, L. C. Silva, P. T. Gomes, P. Valerga, J. M.
Campos, M. R. Ribeiro, J. C. W. Chien and M. M. Marques, Polymer,
2005, 46, 2122–2132.
25 M. L. Tobe, J. Burgess, Inorganic Reactions Mechanisms, Adison Wesley
Longman, 1999, Ch. 5.
26 (a) N. N. Greenwood, A. Earnshaw, Chemistry of the Elements,
Butterworth-Heinemann, 2nd edn, 1997, pp. 1157–1158; (b) A. F.
Orchard, Magnetochemistry, Oxford University Press, 2003, p. 114.
27 V. Lozan, P.-G. Lassahn, C. Zhang, B. Wu, C. Janiak, G. Rheinwald
and H. Lang, Z. Naturforsch. B, 2003, 58, 1152–1164.
28 D. H. Lee, J. Y. Lee, J. Y. Ryu, Y. Kim, C. Kim and I.-M. Lee, Bull.
Korean Chem. Soc., 2006, 27, 1031–1037.
29 (a) M. C. Sacchi, M. Sonzogni, S. Losio, F. Forlini, P. Locatelli, I. Tritto
and M. Licchelli, Macromol. Chem. Phys., 2001, 202, 2052–2058; (b) L.-
D. Li, P. T. Gomes, M. A. N. D. A. Lemos, F. Lemos and Z.-Q. Fan,
Macromol. Chem. Phys., 2011, 212, 367–374.
30 See, for example, the following papers and the references therein
contained: (a) C. Janiak and P. G. Lassahn, J. Mol. Catal. A: Chem.,
2001, 166, 193–209; (b) C. Janiak and P. G. Lassahn, Macromol. Rapid
Commun., 2001, 22, 479–492; (c) F. Blank and C. Janiak, Coord. Chem.
Rev., 2009, 253, 827–861; (d) Q. Shi, S. Jie, S. Zhang, H. Yang and
W.-H. Sun, Macromol. Symp., 2007, 260, 74–79; (e) R. Ma, Y. Hou, J.
Gao and F. Bao, J. Macromol. Sci. C: Polym. Rev., 2009, 49, 249–287.
31 J. Schellenberg, Eur. Polym. J., 2006, 42, 487–494.
11 R. van Asselt, C. J. Elsevier, W. J. J. Smeets, A. L. Spek and R. Benedix,
Recl. Trav. Chim. Pays-Bas, 1994, 113, 88–98.
12 K. V. Vasudevan, M. Findlater and A. H. Cowley, Chem. Commun.,
2008, 1918–1919.
13 (a) M. Gasperini, F. Ragaini and S. Cenini, Organometallics, 2002, 21,
2950–2957; (b) M. Gasperini, F. Ragaini, E. Gazzola, A. Caselli and
P. Macchi, Dalton Trans., 2004, 3376–3382; (c) M. Gasperini and F.
Ragaini, Organometallics, 2004, 23, 995–1001.
14 (a) S. G. Correia, M. M. Marques, J. R. Ascenso, A. F. G. Ribeiro, P.
T. Gomes, A. R. Dias, M. Blais, M. D. Rausch and J. C. W. Chien,
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3365–3380 | 3379
©

View Online
32 (a) D. M. Haddleton, M. C. Crossman, K. H. Hunt, C. Topping,
C. Waterson and K. G. Suddaby, Macromolecules, 1997, 30, 3992–
3998; (b) M. Nagel, W. F. Paxton and A. Sen, Macromolecules, 2004,
37, 9305–9307; (c) P. M. Castro, M. P. Lankinen, M. Leskela¨ and
T. Repo, Macromol. Chem. Phys., 2005, 206, 1090–1097; (d) Y.-J.
Kwark, J. Kim and B. M. Novak, Macromol. Res., 2007, 15, 31–
38.
33 (a) D. G. Musaev, R. D. J. Froese, M. Svensson and K. Morokuma, J.
Am. Chem. Soc., 1997, 119, 367–374; (b) D. G. Musaev, M. Svensson,
K. Morokuma, S. Stro¨mberg, K. Zetterberg and P. E. M. Siegbahn,
Organometallics, 1997, 16, 1933–1945.
36 A. Altomare, G. L. Cascarano, C. Giacovazzo and A. Guagliardi, J.
Appl. Crystallogr., 1993, 26, 343–50.
37 M. C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G. L. Cascarano,
L. De Caro, C. Giacovazzo, G. Polidori and R. Spagna, J. Appl.
Crystallogr., 2005, 38, 381–388.
38 G. M. Sheldrick, Shelxl-97-A Computer Program for Refinement of
Crystal Structure, University of Go¨ttigen, Go¨ttigen, 1997.
39 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837–838.
40 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13.
41 M. N. Burnett, C. K. Johnson, ORTEP-III: Oak Ridge Thermal
Ellipsoid Plot Program for Crystal Structure Illustration, Oak Ridge
National Laboratory Report ORNL-6895, 1996.
34 (a) D. F. Evans, J. Chem. Soc., 1959, 2003–2005; (b) S. K. Sur, J. Magnet.
Res., 1989, 82, 169–173.
35 G. M. Sheldrick, SADABS, Program for Empirical Absorption Correc-
tion, University of Go¨ttingen, Go¨ttingen, 1996.
42 J. Houghton, S. Simonovic, A. C. Whitwood, R. E. Douthwaite, S.
A. Carabineiro, J.-C. Yuan, M. M. Marques and P. T. Gomes, J.
Organomet. Chem., 2008, 693, 717–724.
3380 | Dalton Trans., 2011, 40, 3365–3380
This journal is
The Royal Society of Chemistry 2011
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