Vanadium complexes possessing N2O2S2-based ligands: Highly active procatalysts for the homopolymerization of ethylene and copolymerization of ethylene/1-hexene

Article abstract of DOI:10.1021/ic701461b

The family of ligands containing an N₂O₂S₂ core, namely, 1,2-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio)ethane (H ₂L¹), 1,3-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio) propane (H₂L²), 1,4-di(3-Me-5-t-Bu-salicylaldimino-o- phenylthio)-butane (H₂L³), and 1,2-di(3-Me-5-t-Bu- salicylaldamino-o-phenylthio)ethane (H₂L⁴), have been prepared and complexed with a variety of vanadium chlorides and alkoxides to afford complexes of the form [V(X)L¹] (X = O (1), Np-tol (2), Cl (3)), [V(O)(L^2,3)] (L² (4), L³ (5)), and [V(L⁴)] (6). Crystal structure determinations of H₂L ¹ and H₂L⁴ show the molecule to be centrosymmetric about the bridging ethane moiety, with structural determination of 1 and 3 revealing isostructural monomeric complexes in which the ligand chelates in such a way as to afford pseudo-octahedral coordination at the vanadium center. Prolonged reaction of H₂L¹ with [V(Np-tol)(OEt)₃] led, via oxidative cleavage of the C-S bond, to the bimetallic complex [V₂L¹(3-Me,5-t-Bu-salicylaldimino-o- phenylthiolate)₂] [VL′] (7), as characterized by single-crystal X-ray crystallography. 7 was also isolated from the reaction of H ₂L⁴ and [VO-(On-Pr)₃]. The ability of 1-7 to catalyze the homopolymerization of ethylene and the copolymerization of ethylene/1-hexene in the presence of dimethylaluminum chloride (DMAC) has been assessed: screening reveals that for ethylene homopolymerization 1-7 are all highly active (>1000 g/mmol·h·bar), with the highest activity (ca. 11 000 g/mmol·h·bar) observed using catalyst 3; the use of trimethyl aluminum (TMA) or methylaluminoxane (MAO) as the cocatalyst led only to poorly active systems producing negligible polymer. Analysis of the polyethylene produced showed high molecular weight linear polymers with narrow polydispersities. For ethylene/1-hexene copolymerization, activities as high as 1 190 g/mmol·h·bar were achieved (4); analysis of the copolymer indicated an incorporation of 1-hexene in the range of 5-13%.

Full text of DOI:10.1021/ic701461b

Inorg. Chem. 2007, 46, 10827−10839
Vanadium Complexes Possessing N2O2S2-Based Ligands:
Highly Active Procatalysts for the Homopolymerization of
Ethylene and Copolymerization of Ethylene/1-hexene
Damien M. Homden, Carl Redshaw,* and David L. Hughes
School of Chemical Sciences and Pharmacy, UniVersity of East Anglia, Earlham Road,
Norwich, Norfolk NR4 7TJ, UK
Received July 23, 2007
The family of ligands containing an N2O2S2 core, namely, 1,2-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio)ethane
(H2L1), 1,3-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio)propane (H2L2), 1,4-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio)-
butane (H2L3), and 1,2-di(3-Me-5-t-Bu-salicylaldamino-o-phenylthio)ethane (H2L4), have been prepared and complexed
with a variety of vanadium chlorides and alkoxides to afford complexes of the form [V(X)L1] (X
) O (1), Np-tol (2),
Cl (3)), [V(O)(L2,3)] (L2 (4), L3 (5)), and [V(L4)] (6). Crystal structure determinations of H2L1 and H2L4 show the
molecule to be centrosymmetric about the bridging ethane moiety, with structural determination of 1 and 3
revealing isostructural monomeric complexes in which the ligand chelates in such a way as to afford pseudo-
octahedral coordination at the vanadium center. Prolonged reaction of H2L1 with [V(Np-tol)(OEt)3] led, via oxidative
cleavage of the C
as characterized by single-crystal X-ray crystallography. 7 was also isolated from the reaction of H2L4 and [VO-
(On-Pr)3]. The ability of 1 7 to catalyze the homopolymerization of ethylene and the copolymerization of ethylene/
1-hexene in the presence of dimethylaluminum chloride (DMAC) has been assessed: screening reveals that for
ethylene homopolymerization 1 7 are all highly active (>1000 g/mmol bar), with the highest activity (ca. 11 000
g/mmol bar) observed using catalyst 3; the use of trimethyl aluminum (TMA) or methylaluminoxane (MAO) as
− ′] (7),
S bond, to the bimetallic complex [V2L1(3-Me,5-t-Bu-salicylaldimino-o-phenylthiolate)2] [VL
−
−
‚h‚
‚h‚
the cocatalyst led only to poorly active systems producing negligible polymer. Analysis of the polyethylene produced
showed high molecular weight linear polymers with narrow polydispersities. For ethylene/1-hexene copolymerization,
activities as high as 1 190 g/mmol
‚
h‚
bar were achieved (4); analysis of the copolymer indicated an incorporation
of 1-hexene in the range of 5 13%.
−
1. Introduction
group IV metal systems, the successful use of group V metals
has been somewhat limited,5,6 this despite the commercial
Group IV metallocenes, half-sandwich, and constrained
geometry catalysts have generated significant interest in the
field of Ziegler-Natta olefin polymerization, and as a result
numerous patents have been filed on such systems.1,2
Motivated by the desire from industry to gain increased
control over polymer properties and to steer away from well-
established licensed technology, focus into nonmetallocene-
based catalytic systems has steadily risen since the mid
1990s.3,4 In contrast to the high activities observed for the
use of the [V(acac)3] system in the production of ethylene-
propylene-diene elastomers.7 The beneficial properties of
vanadium-based catalysis were recognized at an early stage
by Natta et al.; [V(acac)3] or [VCl4] in combination with a
variety of different organoaluminum cocatalysts led to the
preparation of highly stereospecific syndiotactic polypropy-
lene polymers.8 More recently, vanadium catalysts have been
(4) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283.
(5) van Koten, G.; Hagen, H.; Boersma, J. Chem. Soc. ReV. 2002, 31,
357.
(6) Gambarotta, S. Coord. Chem. ReV. 2003, 237, 229.
(7) Kaminsky, W.; Arndt, M. Applied Homogeneous Catalysis with
Organometallic Compounds; Cornils, B., Hermann, W. A., Eds.; VCH
Publishers: Weinheim, Germany, 1996; Vol. 1, pp. 220.
(8) Natta, G.; Zambelli, A.; Pasquon, I. J. Am. Chem. Soc. 1962, 84, 1488.
* To whom correspondence should be addressed. E-mail: carl.redshaw@
uea.ac.uk, Tel +44 (0) 1603 593137.
(1) McKnight, A. L.; Waymouth, R. M. Chem. ReV. 1998, 98, 2587.
(2) Brintzinger, H. H. Angew. Chem., Int. Ed. Engl. 1995, 34, 1368.
(3) Gibson, V. C.; Britovsek, G. J. P.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428.
10.1021/ic701461b CCC: $37.00
Published on Web 11/09/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 25, 2007 10827

Homden et al.
Scheme 1. Recent Sulfur-Bridged Diphenolate Early Transition Metal Complexes of (a) Group IV and (b) Group V
utilized in both homo- and hetero-geneous systems and are
found to be capable of producing polymers with ultrahigh
molecular weights and narrow polydispersities.9-13 Redshaw
et al., Gibson et al., and Nomura et al. have demonstrated
highly active group V catalysts14-24 utilizing bi- or tridentate
ligands, whereas a MgCl2-supported vanadium phenoxy-
imine system has been reported by Fujita and Matsui.25 The
ease of reduction of the metal center to the lower inactive
state (divalent for vanadium) constitutes one of the intrinsic
problems associated with group V catalysts, though the use
of reactivating agents such as ethyltrichloroacetate (ETA)
or chlorinated hydrocarbons is a useful method for maintain-
ing the higher (active) oxidation states of vanadium sys-
tems.6,14,16,27 The situation is compounded by the highly
sensitive nature of cationic group V metal alkyls.15,26
(9) Casagrande, A. C. A.; dos Anjos, P. S.; Gamba, D.; Casagrande, O.
L.; dos Santos, J. H. Z. J. Mol. Catal. A: Chem. 2006, 255, 19.
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Catal. A: Chem. 2006, 260, 135.
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O. L.; dos Santos, J. H. Z.; Teranishi, T. J. Mol. Catal. A: Chem.
2004, 212, 267.
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4, 159.
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T.; Lemenovskii, D. A. J. Organomet. Chem. 2001, 640, 21.
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H. Chem. Commun. 2004, 1956.
Previous aryloxide-based chemistry carried out upon group
IV metals (titanium and zirconium) has shown enhanced
catalytic activity for diphenolate ligands bearing bridging
sulfur atoms, for example, I-IV (part a of Scheme 1).28-30
In particular, Schaverien et al.29 found that the additional
10828 Inorganic Chemistry, Vol. 46, No. 25, 2007

Vanadium Complexes Possessing N2O2S2-Based Ligands
Scheme 2. Synthesis of Ligands H2L1-4 a
a (i) Dry ethanol and Na. (ii) EtOH/H+(cat), reflux 12 h. (iii) THF, LiAlH4, room temperature, with stirring.
flexibility and potential π donation from the inclusion of a
sulfur atom in [Ti(tbmp)Cl2] (III, M ) Ti) (where tbmp )
2,2′-thiobis(6-t-Bu-4-methylphenolato)) led to a 10-fold
increase in catalytic activity for ethylene polymerization. The
procatalysts [Ti(tbmp)(NR2)] (R ) Me, Et) have been
evaluated for the polymerization of ꢀ-caprolactone;31 the
additional sulfur interaction led to a more efficient initiation
of the polymerization and a lower spread of molecular
weights of the resulting polymer. Furthermore, the complexes
[Ti(tmbp)X2] (X ) Cl, Oi-Pr) exhibit high activities (20 000-
43 000 g/mmol‚h‚bar) for the copolymerization of ethylene/
styrene (up to 100 times greater); the methylene analogue
(replacing the bridging sulfur atom) produces only a mixture
of homopolyethylene and homopolystyrene.28 In the case of
vanadium, Miyatake et al.32 showed that the complexes
[V(O)(tbmp)X] (X ) Cl, OC4H9) (part b of Scheme 1, V)
upon activation with methylaluminoxane produced activities
over 100 times greater for propylene polymerization than
their unsupported (e.g., VOCl3) vanadium counterparts; the
resulting polypropylene was isotactically enriched (mm %
> 35%), with a significantly narrower polydispersity.
Although no catalytic enhancement was observed in the
MgCl2-supported procatalysts [V2(µ-OEt)2(O)2(tbop-κ3O,S,O)2]
and [V2(µ-tbop-κ3O,S,O)2Cl2(CH3CN)2] (where tbop ) 2,2′-
thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol}(partbofScheme
1, VI and VII),33 it was found that the stability of the active
species during the polymerization reaction was increased and
displayed only a slight decrease in activity of the catalyst
over a 3 h period.
(15) Nomura, K.; Wang, W. Macromolecules 2005, 38, 5905.
(16) Redshaw, C.; Warford, L.; Dale, S. H.; Elsegood, M. R. J. Chem.
Commun. 2004, 1954.
(17) Redshaw, C.; Rowan, M. A.; Homden, D. M.; Dale, S. H.; Elsegood,
M. R. J.; Matsui, S.; Matsuura, S. Chem. Commun. 2006, 3329.
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Inorg. Chim. Acta 2005, 358, 4067.
(19) Mountford, P.; Bigmore, H. R.; Zuideveld, M. A.; Kowalczyk, R. M.;
Cowley, A. R.; Kranenburg, M.; McInnes, E. J. L. Inorg. Chem. 2006,
45, 6411.
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J. Inorg. Chem. 1998, 425.
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A. J. Organomet. Chem. 1998, 566, 111.
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Soc., Dalton Trans. 2000, 967.
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L.; da Costa, M. H. R.; Mastroianni, S. J. Organomet. Chem. 1999,
591, 78.
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Oshiki, T.; Tanaka, E. Organometallics 1995, 14, 2633.
(25) Fujita, T.; Matsui, S. Catal. Today 2001, 66, 63.
(26) Etienne, M.; Pritchard, H. M.; Vendier, L.; McGrady, G. S. Organo-
metallics 2004, 23, 1203.
To date, examples of complexes where the ancillary ligand
incorporates sulfur, nitrogen, and oxygen donors are prima-
rily focused on biological applications as bifunctional chelat-
ing agents for radioimaging with 99mTc34,35 or mimics for
iron(II/III) in enzymes within the body,36,37 whereas sulfur,
(27) Desmangles, N.; Gambarotta, S.; Bensimon, C.; Davis, S.; Zahalka,
H. J. Organomet. Chem. 1998, 562, 53.
(28) Mulhaupt, R.; Sernetz, F. G.; Fokken, S.; Okuda, J. Macromolecules
1997, 30, 1562.
(29) Schaverien, C. J.; Vanderlinden, A.; Meijboom, N.; Ganter, C.; Orpen,
A. G. J. Am. Chem. Soc. 1995, 117, 3008.
(30) Sobota, P.; Janas, Z.; Jerzykiewicz, L. B.; Przybylak, K.; Szczegot,
K. Eur. J. Inorg. Chem. 2004, 1639.
(32) Takaoki, K.; Miyatake, T. Macromol. Symp. 2000, 157, 251.
(33) Janas, Z.; Wisniewska, D.; Jerzykiewicz, L. B.; Sobota, P.; Drabent,
K.; Szczegot, K. Dalton Trans., 2007, 2065.
(34) Dhara, P. K.; Das, B.; Lo, J. M.; Chattopadhyay, P. Appl. Radiat.
Isot. 2005, 62, 729.
(35) Chhikara, B. S.; Kumar, N.; Tandon, V.; Mishra, A. K. Bioorg. Med.
Chem. 2005, 13, 4713.
(36) Sellmann, D.; Blum, D. C. F.; Heinemann, F. W.; Sutter, J. Eur. J.
Inorg. Chem. 2003, 418.
(31) Takashima, Y.; Nakayama, Y.; Hirao, T.; Yasuda, H.; Harada, A. J.
Organomet. Chem. 2004, 689, 612.
(37) Singh, A. K.; Mukherjee, R. Inorg. Chem. 2005, 44, 5813.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10829

Homden et al.
Table 1. Crystallographic Data and Results of X-ray Analysis
compound
formula
H2L1
H2L4
1
3
7
C38H44N2O2S2
624.9
monoclinic
P21/a
C38H48N2O2S2
628.9
monoclinic
C2/c
C38H42N2O3S2V.MeCN
C38H42ClN2O2S2V.MeCN
C74H80N4O4S4V2.2Et2O
fw
730.8
triclinic
P1h
750.3
triclinic
P1h
1467.8
triclinic
P1h
cryst syst
space group
unit cell dimensions
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
9.3754(7)
17.3669(11)
11.1490(7)
90
116.819(7)
90
16.5584(15)
7.7388(6)
27.125(3)
90
100.499(8)
90
9.6480(1)
11.9119(2)
16.9911(3)
83.830(1)
85.870(1)
73.428(1)
1859.01(5)
2
9.6892(7)
11.7442(10)
17.1594(8)
84.560(6)
84.449(6)
76.692(7)
1885.9(2)
2
11.567(3)
12.515(3)
14.789(4)
73.40(2)
80.22(2)
65.98(2)
1870.4(8)
1
1620.04(19)
2
3417.6(6)
4
Z
T (K)
D
140(1)
1.281
140(1)
1.222
120(1)
1.306
140(1)
1.321
140(1)
1.303
calcd (g cm-3
)
absorption coefficient
0.202
0.191
0.420
0.483
0.417
(mm-1
)
cryst size (mm3)
2θ max (deg)
0.6 × 0.24 × 0.06
0.64 × 0.40 × 0.13
50
18 200
2990
0.056
2454
0.986-1.015
203
0.12 × 0.06 × 0.04
55
42 231
8520
0.055
6828
0.816-1.00
445
0.73 × 0.24 × 0.10
60
28 521
10 633
0.072
6842
0.945-1.064
445
0.48 × 0.22 × 0.14
40
11 010
3434
0.100
2648
0.972-1.031
444
55
reflns measured
unique reflns
Rint
21 255
3699
0.047
3382
reflns with F2 > 2σ(F2)
transmission factors
number of params
R1 [F2 > 2σ(F2)]
wR2, R1 (all data)
largest difference
204
0.049
0.125, 0.056
0.35 and -0.27
0.055
0.105, 0.077
0.46 and -0.35
0.044
0.107, 0.061
0.39 and -0.52
0.044
0.093, 0.089
0.63 and -0.51
0.100
0.190, 0.132
0.42 and -0.36
peak and hole (e Å-3
)
nitrogen, and oxygen donor ligands in combination with
vanadium are limited to the use of thiosemicarbazones.38-40
It is noteworthy that a number of vanadium-based catalytic
systems for use in R-olefin polymerization have appeared
in the patent literature. In particular, systems of the type
V2X3(ED)n where X ) halogen and ED ) electron-donating
groups such as ethers, phosphine, ketones, isocyanides, or
esters in conjunction with organoaluminum cocatalysts and
a halocarbon promoter41,42 have been reported, as well as
systems supported on silica.43
Taking into account the high activity afforded by phe-
noxyimine ligands and the beneficial effects imparted by
donor sulfur atoms in the aforementioned diphenolate-based
systems, we decided to examine a family of ligands
incorporating both of these potentially desirable features and
to screen for possible beneficial effects in vanadium-
catalyzed R-olefin polymerization. Herein, the synthesis and
characterization of four new ligands H2L1-H2L4 (Scheme
2, section 3.1), the new vanadium complexes [V(X)L1] (X
) O (1), Np-tol (2), Cl (3)), [V(O)(L2,3)] (L2 (4), L3 (5))
and [V(L4)] (6), together with the bimetallic complex [V2L1-
(3-Me,5-t-Bu-salicylaldimino-o-phenylthiolate)2] (7) (Scheme
4, section 3.3) are reported. In addition, 1-7 have been
screened for ethylene homopolymerization and ethylene/1-
hexene copolymerization in the presence of the organoalu-
minum cocatalyst dimethylaluminum chloride (DMAC) and
the reactivating substance ETA.
2. Experimental Section
All of the manipulations were carried out under an atmosphere
of nitrogen using standard Schlenk line and cannula techniques or
a conventional N2-filled glovebox. Solvents were refluxed over the
appropriate drying agents and distilled and degassed prior to use.
Elemental analyses were performed at London Metropolitan
University. NMR spectra were recorded on a Varian VXR 400 S
spectrometer at 400 MHz, a Gemini at 300 MHz, or a Bruker
DPX300 spectrometer at 300 MHz (1H) and 75.5 MHz (13C) at
298 K; chemical shifts are referenced to the residual protio impurity
of the deuterated solvent. EPR spectroscopy was performed on an
X-band ER200-D spectrometer (Bruker Spectrospin) interfaced to
an ESP1600 computer and fitted with a liquid-helium flow cryostat
(ESR-900; Oxford Instruments), and the spectra were simulated
with Simfonia. IR spectra (nujol mulls, KBr windows) were
recorded on a PerkinElmer 577 or 457 grating spectrophotometer.
DSC analyses of polymer samples were performed on a TA
Instruments DSC Q 1000. Magnetic moments were recorded
following the Evans’ NMR method.44 1,2-Bis(2-aminophenylthio)-
ethane (A), 1,3-bis(2-aminophenylthio)propane (B), 1,4-bis(2-
aminophenylthio)butane (C), and the known procatalysts 8 and 9
were synthesized following the reported procedures;35,45,46 [VO-
(On-Pr)3] was purchased from Aldrich and used as received. [V(Np-
tol)(OEt)3] and [VCl3‚3THF] were synthesized following the
reported procedures by van Koten et al.47 and Kurras.48 All of the
(38) Sreekanth, A.; Sivakumar, S.; Kurup, M. R. P. J. Mol. Struct. 2003,
655, 47.
(39) Khuhawar, M. Y.; Arain, G. M. Talanta 2006, 68, 535.
(40) Maurya, M. R.; Kumar, A.; Abid, M.; Azam, A. Inorg. Chim. Acta
2006, 359, 2439.
(41) Stakem, F. G. Eur. Pat. Appl. 1990, 9 pp, EP 374595 A1.
(42) Beran, D. L.; Cann, K. J.; Jorgensen, R. J.; Karol, F. J.; Maraschin,
N. J.; Marcinkowsky, A. E. Eur. Pat. Appl. 1984, 35 pp. EP 120501
A1.
(44) Evans, D. F. J. Chem. Soc. 1959, 2003.
(45) Donaldson, P. B.; Tasker, P. A.; Alcock, N. W. J. Chem. Soc., Dalton
Trans. 1976, 2262.
(46) Nakayama, Y.; Bando, H.; Sonobe, Y.; Suzuki, Y.; Fujita, T. Chem.
Lett. 2003, 32, 766.
(43) Wagner, B. E.; Samuels, Sari, B.; Karol, F. J. Eur. Pat. Appl. 1992,
16 pp, EP 464744 A2.
(47) Lutz, M.; Hagen, H.; Schreurs, A. M. M.; Spek, A. L.; van Koten, G.
Acta Crystallogr. 1999, C55, 1636.
10830 Inorganic Chemistry, Vol. 46, No. 25, 2007

Vanadium Complexes Possessing N2O2S2-Based Ligands
Figure 1. (a) View of a molecule of H2L1 showing the atom numbering scheme. Thermal ellipsoids are drawn at the 50% probability level. (b) Packing
diagram showing the intercalation of planar phenoxy-imine groups.
Figure 2. (a) View of a molecule of H2L4, showing disorder in the methyl group at C(4). Thermal ellipsoids are drawn at the 50% probability level. (b)
Packing diagram looking down the b axis.
other chemicals were obtained commercially and used as received
unless stated otherwise.
Mass Spec. (ESI): 639 (M)+. IR (cm-1): ν 3582 m, 3457 bm,
3370 bm, 3057 m, 2956 s, 2921 s, 2863 m, 2359 m, 2325 m, 2245
m, 1936 w, 1726 w, 1614 s, 1573 s, 1563 s, 1469 s, 1435 s, 1390
m, 1360 m, 1264 s, 1235 m, 1205 m, 1162 m, 1067 m, 1029 m,
980 m, 908 s, 864 m, 801 m, 753 m, 732 m, 666 m, 648 m.
2.1. Synthesis of Ligands. 2.1.1. Preparation of 1,2-Di(4-Me-
6-t-Bu-salicylaldimino-o-phenylthio)ethane (H2L1). 1,2-Bis(2-
aminophenylthio)ethane (2.20 g, 7.96 mmol) and 3-Me-5-t-Bu-
salicaldehyde (1.53 g, 7.96 mmol) were brought to reflux in ethanol
(25 mL). A drop of formic acid was added to catalyze the reaction,
and the reflux maintained for 12 h. Upon cooling, the solvent was
removed in vacuo, affording H2L1 as an orange solid. Yield 3.63
g (73%). Mp 153-155 °C. Anal. Found: C, 73.0; H, 7.1; N, 4.5.
C38H44N2O2S2 requires: C, 72.6; H, 7.1; N, 4.4. 1H NMR
(CDCl3): δ 8.52 (s, 2H, CHdN), 7.11-7.40 (m, 12H, ArH), 7.02
(s, 2H, OH), 3.15 (s, 3H, Me), 2.31 (s, 4H, CH2), 1.46 (s, 18H,
t-Bu). Mass Spec. (ESI): 625 (M)+. IR (cm-1): ν 3580 m, 1615
m, 1588 m, 1574 m, 1559 m, 1463 s, 1377 m, 1322 m, 1267 m,
1231 w, 1203 m, 1153 m, 1126 w, 1060 w, 1040 s, 1021 s, 959 w,
893 w, 854 m, 772 m, 749 m, 718 m, 665 m.
2.1.3. Preparation of 1,4-Di(3-Me-5-t-Bu-salicylaldimino-o-
phenylthio)butane (H2L3). As for H2L1 but using 1,4-bis(2-
aminophenylthio)butane (2.00 g, 6.57 mmol) and 3-Me-5-t-Bu-
salicaldehyde (2.65 g, 13.79 mmol) to give a yellow oil. This was
further purified by extraction into hexane (30 mL) and stored at
0 °C for 1 week to give H2L3 as a yellow solid. Yield 1.71 g (40%).
Mp 81-84 °C. Anal. Found: C, 73.5; H, 7.6; N, 4.2. C40H48N2O2S2
1
requires: C, 73.6; H, 7.4; N, 4.3. H NMR (CDCl3): δ 8.48 (s,
2H, CHdN), 7.39-6.85 (m, 12H, ArH), 2.81 (s, 4H, CH2), 2.23
(s, 6H, Me), 1.78 (s, 4H, CH2), 1.47 (s, 18H, t-Bu). Mass Spec.
(ESI): 653 (M)+. IR (cm-1): ν 3146 bm, 2361 m, 2341 m, 1745
w, 1617 m, 1594 m,1575 m, 1563 m,1322 m, 1263 m, 1236 m,
1205 m, 1162 m, 1067 m, 981 m, 961 w, 927 w, 857 m, 800 s,
770 m, 751 m, 740 m, 721 m, 668 w.
2.1.2. Preparation of 1,3-Di(3-Me-5-t-Bu-salicylaldimino-o-
phenylthio)propane (H2L2). As for H2L1 but using 1,3-bis(2-
aminophenylthio)propane (2.00 g, 6.89 mmol) and 3-Me-5-t-Bu-
salicaldehyde (2.78 g, 14.46 mmol) to give a yellow oil. This was
further purified by extraction into hexane (30 mL) and stored at
0 °C for 1 week to give H2L2 as a yellow oil. Yield 3.70 g (84%).
Anal. Found: C, 73.4; H, 7.2; N, 4.2. C39H46N2O2S2 requires: C,
2.1.4. Preparation of 1,2-Di(3-Me-5-t-Bu-salicylaldamino-o-
phenylthio)ethane (H2L4). To a solution of H2L1 (1.35 g, 2.16
mmol) in THF (50 mL) was added LiAlH4 (0.33 g, 8.64 mmol) in
small portions at room temperature. Over 5 min, the solution turns
from a dark orange/yellow to a very light yellow. Once the color
change had ceased, the solution was stirred for a further 30 min.
The solvents were removed in vacuo, and the residue cooled to
0 °C. Chilled water (100 mL) was added slowly, followed by the
addition of Et2O (200 mL). The organic phase was collected,
1
73.3; H, 7.3; N, 4.4. H NMR (CDCl3): δ 8.54 (s, 2H, CHdN),
7.35-7.05 (m, 12H, ArH), 3.08 (t, 4H 3JHH 7.0 Hz, CH2), 2.31 (s,
3
6H, Me), 2.06 (quin, 2H JHH 7.2 Hz, CH2), 1.46 (s, 18H, t-Bu).
(48) Kurras, E., Naturwissenschaften 1959, 46, 171.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10831

Homden et al.
Figure 3. View of a molecule of 1 showing the atom numbering scheme.
Thermal ellipsoids are drawn at the 50% probability level.
Table 2. Comparison of Selected Bond Lengths (Angstroms) and
Angles (Degrees) in 1 and 3
Figure 4. View of a molecule of 3 showing the atom numbering scheme.
1
3
Thermal ellipsoids are drawn at the 50% probability level.
V(1)-O(1)
1.6193(14) V-Cl
2.3717(6)
1.9096(13)
1.8704(13)
2.1006(16)
2.0788(16)
2.5403(6)
171.00(4)
91.43(4)
95.40(4)
92.08(4)
88.275(19)
172.01(6)
82.76(4)
V(1)-O(1A)
V(1)-O(1B)
V(1)-N(1A)
V(1)-N(1B)
V(1)-S(1B)
2.0294(14) V-O(1B)
1.9209(14) V-O(1A)
2.1037(16) V-N(8B)
2.0883(16) V-N(8A)
Scheme 3. Proposed Mechanism for C-S Bond Cleavage55
2.5252(6)
168.27(7)
100.47(7)
95.66(7)
98.68(7)
88.92(5)
164.93(7)
79.55(4)
91.24(6)
167.94(5)
V-S(17A)
O(1)-V(1)-O(1A)
O(1)-V(1)-O(1B)
O(1)-V(1)-N(1A)
O(1)-V(1)-N(1B)
O(1)-V(1)-S(1B)
N(1A)-V(1)-N(1B)
S(1B)-V(1)-O(1A)
O(1A)-V(1)-O(1B)
O(1B)-V(1)-S(1B)
Cl-V-O(1B)
Cl-V-O(1A)
Cl-V-N(8B)
Cl-V-N(8A)
Cl-V-S(17A)
N(8A)-V-N(8B)
S(17A)-V-O(1B)
O(1A)-V-O(1B)
O(1A)-V-S(17A)
97.31(6)
171.03(4)
2.2.2. Preparation of [V(Np-tol)L1] (2). As described above
for 1, but using [V(Np-tol)(OEt)3] (0.51 g, 1.76 mmol) and H2L1
(1.00 g, 1.60 mmol) to give 2 as a brown solid. Yield 0.79 g, 63%
Mp decomposed at 103 °C. Anal. Found: C, 69.4; H, 6.3; N, 5.4.
C45H49N3O2S2V requires: C, 69.5; H, 6.5; N, 5.6. Mass Spec. 778
(M)+, 689 (M-C7H7)+. IR (cm-1): ν 1615 m, 1588 m, 1537 m,
1499 w, 1417 m, 1014 s, 928 m, 858 m, 800 s, 757 w. EPR (toluene,
298 K): giso ) 1.98, Aiso ) 95 G, (toluene, 40 K) g ) 1.96, A )
168 G, g| ) 1.99, A|) 58 G, µeff ) 1.63 µB.
washed with a 10% HCl solution (50 mL) and water (2 × 50 mL),
respectively, and dried over MgSO4. Removal of the Et2O in vacuo
and recrystallization of the solid from ethanol gave H2L4 as yellow
blocks. Yield of crystals, 500 mg (30%). Total yield (1.11 g, 82%).
Mp 115 °C. Anal. Found: C, 72.6; H, 7.7; N, 4.5. C38H48N2O2S2
1
requires: C, 72.5; H, 7.6; N, 4.5. H NMR (CDCl3): δ 8.06 (s,
2H, OH), 6.60-7.40 (m, 12H, ArH), 5.16 (s, 2H, NH), 4.32, (s,
4H, CH2N), 2.80, (s, 4H, SCH2), 1.40, (s, 18H, t-Bu). Mass Spec.
(ESI): 629 (M)+. IR (cm-1): ν 3156 m, 3107 m, 1580 m, 1300 m,
1269 m, 1231 w, 1215 w, 1192 m, 1153 w, 1075 w, 1029 w, 1005
m, 966 w, 932 w, 897 w, 854 w, 800 w, 745 m, 717 m.
2.2.3. Preparation of [V(Cl)L1] (3). (a). As for 1, but using
[V(O)(On-Pr)3] (0.40 mL, 1.76 mmol), H2L1 (1.00 g, 1.60 mmol),
and dimethylaluminum chloride (1.76 mL, 1.0 M, 1.76 mmol) to
give dark-brown blocks of 3. Yield 0.89 g, 78%.
2.2. Synthesis of Complexes. 2.2.1. Preparation of [V(O)L1]
(1). [V(O)(On-Pr)3] (0.40 mL, 1.76 mmol) and H2L1 (1.00 g, 1.60
mmol) were refluxed for 12 h in toluene (40 mL). After cooling,
the solvent was removed in vacuo, and the residue was extracted
into warm acetonitrile (40 mL), affording 1 as deep-red prisms.
Yield 786 mg (71%). Mp > 250 °C. Anal. Found: C, 65.7; H,
6.2; N, 5.8. C38H42N2O3S2V‚MeCN requires: C, 65.3; H, 6.2; N,
5.8. Mass Spec. (EI): 689 (M)+. IR (cm-1): ν 2960 w, 2912 w,
2866 w, 2253 w, 1614 m, 1598 m, 1577 m, 1535 m, 1474 m, 1416
m, 1385 m, 1351 w, 1316 w, 1216 w, 1241 w, 1200 m, 1165 m,
1095 w, 1029 w, 907 s, 815 w, 788 w, 732 w, 665 s, 650 s. EPR
(b) As for 1, but using [VCl3‚3THF] (0.66 g, 1.76 mmols) and
H2L1 (1.00 g, 1.60 mmol) to give deep-red blocks of 3. Yield 1.05
g (93%). Mp 195 °C. Anal. Found: C, 63.9; H, 6.1; N, 5.0. C38H42-
ClN2S2O2V‚1/2MeCN requires: C, 64.2; H, 6.0; N, 4.8. Mass Spec.
(MALDI): 709 (M)+. IR (cm-1): ν 2359 m, 2330 m, 1533 s, 1398
m, 1261 m, 1231 s, 1203 s, 1165 s, 1092 m, 1018 m, 866 s, 800
m, 667 m. µeff ) 2.52 µB.
2.2.4. Preparation of [V(O)L2] (4). As for 1, but using [V(O)-
(On-Pr)3] (0.39 mL, 1.72 mmol) and H2L2 (1.00 g, 1.57 mmol),
giving 4 as a brown solid. Yield 0.93 g, 84% Mp decomposed at
148 °C. Anal. Found: C, 67.0; H, 6.5; N, 3.9. C39H44N2O3S2V
requires: C, 66.6; H, 6.3; N, 4.0. Mass Spec. 704 (M)+. IR (cm-1):
ν 1615 m, 1533 w, 1261 s, 1093 bs, 1020 bs, 864 m, 800 s. EPR
(toluene, 298 K): giso ) 1.98, Aiso ) 94G, (toluene, 40 K) g
1.96, A ) 169 G, g| ) 1.99, A|) 60 G, µeff ) 1.76 µB.
)
10832 Inorganic Chemistry, Vol. 46, No. 25, 2007

Vanadium Complexes Possessing N2O2S2-Based Ligands
Table 3. Selected Bond Lengths (A° ngstroms) and Angles (Degrees) for
2347 w, 1595 s, 1575 m, 1536 s, 1419 m, 1353 m, 1305 m, 1261
s, 1202 m, 1168 m, 938 w, 904 w, 859 m, 798 s, 755 s, 732 w, 687
w, µeff ) 2.50 µB.
7
V(1)-O(1A)
1.915(7)
1.876(6)
2.104(8)
88.3(3)
97.5(3)
162.3(2)
84.6(2)
94.0(3)
V(1)-N(1B)
2.061(8)
2.367(3)
2.559(3)
90.8(3)
170.9(2)
171.3(3)
80.74(10)
V(1)-O(1B)
V(1)-S(1A)
2.3. Crystallographic Analysis. For each sample, a crystal was
mounted in oil on to a glass fiber and fixed in a cold nitrogen
stream, on either a Bruker-Nonius Kappa CCD diffractometer (for
crystal 1) or an Oxford Diffraction Xcalibur-3 CCD diffractometer
(for all other samples); both systems were equipped with Mo KR
radiation (λ ) 0.71073 Å) and a graphite monochromator. In all
of the cases, intensity data were measured by thin-slice ω- and
æ-scans. Data were processed using the CrysAlis-CCD and -RED49
programs or, for 1, the DENZO/SCALEPACK50 programs, with
absorption corrections applied in SADABS.51 The structures were
determined by the direct methods routines in the SHELXS program51
and refined by full-matrix least-squares methods, on F 2’s, in
SHELXL.52 The non-hydrogen atoms were refined with anisotropic
thermal parameters. In H2L1 and H2L4, the phenolic hydrogen atoms
were located in difference maps and were refined freely; all of the
other hydrogen atoms in all of the samples were included in
idealized positions, and their Uiso values were set to ride on the
V(1)-N(1A)
V(1)-S(1B)
O(1A)-V(1)-N(1A)
O(1A)-V(1)-N(1B)
O(1A)-V(1)-S(1A)
O(1A)-V(1)-S(1B)
O(1A)-V(1)-O(1B)
O(1B)-V(1)-N(1B)
O(1B)-V(1)-S(1B)
N(1A)-V(1)-N(1B)
S(1A)-V(1)-S(1B)
Table 4. Ethylene Polymerization Runs for 1-7
catalyst weighta activityb
Mw Mn
P.D.I. M.P.c
1
2
0.65
1.44
1.86
1.60
1.53
0.26
1.03
1.36
1.00
2580
5744
11 130
7675
6108
1052
2068
10 880
8000
246 000 84 500
183 000 45 500
213 000 57 900
244 000 77 900
256 000 105 000
160 000 67 900
207 000 61 600
2.9
4.0
3.7
3.1
2.5
2.4
3.4
2.5
3.2
137.6
135.2
134.6
134.3
137.3
134.1
134.4
134.6
134.2
3d
4e
5
6
7
8f
9f
98 700
40 300
155 000 48 700
a Polymer weight in grams. b Units: g/mmol vanadium‚hr‚bar. c Degrees
Celcius, measured by DSC. d Run time of 20 min. e Run time of 25 min.
f Run time of 15 min. All runs were completed with 0.5 µmol of vanadium,
4000 equiv of DMAC, and 0.1 mL of ETA in 50 mL of toluene at 60 °C
for 30 min.
Ueq values of the parent carbon atoms. Scattering factors for neutral
atoms were taken from reference.53 Crystal data and refinement
results are collated in Table 1. Computer programs used in this
analysis have been noted above and were run through WinGX54 on
a Dell Precision 370 PC at the University of East Anglia.
2.4. Ethylene Polymerization Procedure. Ethylene polymeriza-
tions were performed in a flame-dried glass flask (250 mL) equipped
with a magnetic stirrer bar. The flask was evacuated and filled with
ethylene gas at 1 bar, which was maintained throughout the
polymerization. The flask was further purged several times with
ethylene, and then 50 mL of dry, degassed toluene was added via
a glass syringe. If applicable, the reactivating agent ETA was added
(0.1 mL, 0.72 mmol) at this stage. The solution was then stirred
for 10 min to allow ethylene saturation, and the correct temperature
was acquired via the use of a water bath. The cocatalyst was added,
and the solution was stirred for a further 5 min. The procatalyst
was injected as a toluene solution (stock solutions of 1 µmol mol-1
were prepared immediately prior to use). The polymerization time
was measured from procatalyst injection; the polymerization was
quenched by the injection of 5 mL of methanol. The resulting
polymer was transferred into a 500 mL beaker containing acidified
methanol, and the solid polyethylene was collected via filtration
and dried at 90 °C overnight.
(toluene, 298 K): giso ) 1.99, Aiso ) 98 G, (toluene, 40 K), g )
1.95, A ) 173 G, g| ) 1.99, A| ) 61 G, µeff ) 1.42 µB.
2.2.5. Preparation of [V(O)L3] (5). As for 1 but using [V(O)-
(On-Pr)3] (0.38 mL, 1.69 mmol) and H2L3 (1.00 g, 1.53 mmol),
giving 5 as dark-brown blocks. Yield: 0.47 g (42%). Mp >
250 °C. Anal. Found: C, 67.0; H, 6.5; N, 3.9. C40H46N2O3S2V
required: C, 67.0; H, 6.5; N, 3.9. Mass Spec. (MALDI): 717 (M)+.
IR (KBr, cm-1): ν 1611 m, 1592 m, 1533 m, 1308 m, 1262 m,
1238 m, 1200 m, 1172 m, 1102 m, 1067 m, 1021 m, 994 m, 928
m, 854 m, 803 m, 749 w, 737 w. EPR (toluene, 298 K): giso
)
1.99, Aiso ) 98 G, (toluene, 40 K), g ) 1.95, A ) 175 G, g| )
1.99, A| ) 61 G, µeff ) 1.35 µB.
2.2.6. Preparation of [VL4] (6). A solution of [V(O)(On-Pr)3]
(0.40 mL, 1.75 mmol) and H2L4 (1.00 g, 1.59 mmol) in diethyl
ether (30 mL) was stirred at room temperature for 15 min, after
which the solvent was removed in vacuo. A further portion of
diethyl ether (30 mL) was added, and the solution was stirred for
15 min. This process was repeated 5 times, after which the solid
residue was extracted into warm dichloromethane (30 mL) and
filtered. Removal of the solvent in vacuo gave 6 as a brown solid.
Yield 0.74 g, 67% Mp 118-120 °C. Anal. Found: C, 66.0; H,
6.4; N, 3.8. C38H44N2O2S2V‚1/4CH2Cl2 requires: C, 65.7; H, 6.7;
N, 4.0. Mass Spec. 676 (M)+. IR (cm-1): ν 2361 w, 1574 m, 1537
m, 1305 m, 1261 s, 1239 m, 1200 m, 1167 m, 984 m, 937 w, 860
2.5. Ethylene/1-Hexene Polymerization. Copolymerizations
were performed in a flame-dried glass flask (250 mL) equipped
with a magnetic stirrer bar. The flask was evacuated and filled with
ethylene gas at 1 bar, which was maintained throughout the
polymerization. The flask was further purged several times with
ethylene and then 40 mL of dry, degassed toluene was added via
m, 802 s, 750 m, 731 m, 669 w. EPR (toluene, 298 K): giso
1.98, Aiso ) 97 G, (toluene, 40 K) g ) 1.96, A ) 168 G, g| )
1.99, A| ) 60 G, µeff ) 1.36 µB.
)
(49) CrysAlis-CCD and -RED, Oxford Diffraction Ltd.: Abingdon, U.K.,
2005.
(50) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in the Oscillation Mode. In Methods in Enzymology,
Macromolecular Crystallography, Part A; Carter, C. W., Jr., Sweet,
R. M., Eds.; Academic Press: New York, 1997; Vol. 276, pp 307-
326.
(51) Sheldrick, G. M. SADABS: Program for Calculation of Absorption
Corrections for Area-Detector Systems, version 2.10; Bruker AXS
Inc.: Madison, WI, U.S.A., 2003.
(52) Sheldrick, G. M. SHELX-97: Programs for Crystal Structure Deter-
mination (SHELXS) and Refinement (SHELXL); University of Go¨t-
tingen: Go¨ttingen, Germany, 1997.
2.2.7. Preparation of [VL′] (7). (i) [V(O)(On-Pr)3] (0.24 mL,
1.06 mmol) and H2L4 (1.00 g, 1.59 mmol) were combined in a
Schlenk flask. Toluene (40 mL) was added, and the solution was
refluxed for 24 h. On cooling, the solvent was removed in vacuo,
and the residue extracted into either warm acetonitrile (40 mL) or
diethyl ether (40 mL). Prolonged standing at room temperature gave
dark-brown blocks of 7. Yield 580 mg (83%). Mp decomposes at
∼161 °C. Anal. Found: C, 67.5; H, 6.2; N, 4.3. C74H80O4S4N4V2
requires: C, 67.4; H, 6.1; N, 4.3. Mass Spec. (MALDI): 971 (M-
[SC6H4NCH-3-Me-5-tBuC6H2O]-V)+, 645 (M-2[SC6H4NCH-3-
Me-5-tBuC6H2O]-V)+, 624 (ligand H2L1)+ IR (cm-1): ν 2730 w,
(53) International Tables for X-ray Crystallography; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1992; Vol. C, pp 500, 219,
and 193.
(54) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10833

Homden et al.
Figure 5. View of a molecule of 7 showing the atom numbering scheme. Thermal ellipsoids are drawn at the 50% probability level.
Scheme 4. Representation of the New Procatalysts 1-7 and the Known Phenoxy-imine (F.I.) Procatalysts 8 and 9 46
a glass syringe. The reactivating agent, ETA, was added (0.1 mL,
0.72 mmol) along with 1-hexene (5 mL, 4000 equiv). The solution
was then stirred for 10 min, to allow ethylene saturation, and the
correct temperature was acquired via the use of a water bath. DMAC
(4 mL, 1M solution, 400 equiv) was added via a glass syringe, and
the solution was stirred for a further 5 min. The procatalyst was
injected as a toluene solution (stock solutions of 1 µmol mL-1 were
prepared immediately prior to use). The polymerization time was
set at 30 min, after which the reaction was quenched by the injection
of 5 mL of methanol. The resulting polymer was transferred into
500 mL of acidified methanol, and the precipitate was collected
via filtration and dried at 90 °C overnight.
3. Results and Discussion
3.1. Synthesis and Structure of Proligands H2L1-H2L4.
The proligand H2L1 was readily synthesized in good yield
(73%) via an adaptation of the method reported by Rajeskhar
et al.55 The reaction of 1,2-bis(2-aminophenylthio)ethane (A)
in a 1:2 ratio with 3-Me-5-t-Bu-salicaldehyde in refluxing
10834 Inorganic Chemistry, Vol. 46, No. 25, 2007

Vanadium Complexes Possessing N2O2S2-Based Ligands
Figure 6. Lifetime graph of ethylene polymerization for 1-7. Conditions: 50 mL toluene at 60 °C, 0.1 mL ETA, 4 000 equiv DMAC, 0.5 µmol of
vanadium.
ethanol produced H2L1 as a pure (by 1H NMR) orange solid.
X-ray quality crystals were grown from a saturated ethanol
solution upon slow evaporation of the solvent. A molecule
of proligand H2L1 is depicted in part a of Figure 1.
The molecule has Ci symmetry, with the center of
inversion between C18 and C18′. The phenoxy-imine
moieties are close to planar and linked via the bridging ArS-
C2H4-SAr group. The planarity of the phenoxy-imine group
is aided by a single hydrogen bond from the phenolic
OH to the nitrogen of the imine group [H(1)‚‚‚N(8) bond
length of 1.82(3) Å with a corresponding O(1)-H(1)‚‚‚N(8)
angle of 156(3)°]. The torsion angle about the S(17)-C(18)
bond, 169.49(15)°, indicates an anti arrangement of the
phenoxy-imine moiety. Most of one-half of the molecule
forms a good mean-plane; the other half forms a parallel
plane, which is removed by a step (perpendicular distance
3.040 Å) through the S-CH2-CH2-S link. Either side of
the first plane, there are overlapping planes of adjacent
molecules, related by a-glide symmetry. Hence, a series of
half-molecule planes, spaced along the a axis, slot between
a neighboring series of symmetry-related planes (part b of
Figure 1). The angle between the normals of neighboring
planes is 11.64(4)°, and the distance between these planes
is ca. 3.45 Å.
formation of H2L4 can easily be monitored by the loss of
the initial bright-orange coloration (indicating the presence
of H2L1) and the appearance of a clear pale-yellow solution.
Crystals suitable for X-ray crystallography were obtained on
slow cooling of a warm, saturated acetonitrile solution to
ambient temperature. The molecular structure of H2L4 is
given in Figure 2.
The molecule is centrosymmetric; however, unlike H2L1,
the phenoxy-amine moiety is not planar because of the
reduction of the imine groups leading to increased flexibility
around the C-N bond and the formation of a weaker
hydrogen bond [H1a‚‚‚N1 2.11(4) Å with an O1a-H1a‚‚‚
N1 angle of 148(3)°]. There is additional hydrogen bonding
[H(1)‚‚‚S(1) 2.63 Å with N(1)-H(1)‚‚‚S(1) at 108°] to the
bridging thioether group; this further affects the conformation
of the H2L4. Rather than adopting an anti arrangement as
previously seen in H2L1, the torsion angle C(14′)-C(14)-
S(1)-C(13) [68.6(3)°] indicates that the phenoxy-amine
moiety adopts a gauche conformation. A difference in the
packing is also observed (part b of Figure 2) with no overlap
of extended planar moieties. Only van der Waals interactions
are observed intermolecularly.
The length of the ethane bridge can be readily varied by
selection of the appropriate dibromoalkane precursor (Scheme
2). The propane- (H2L2) and butane- (H2L3) bridged
molecules were isolated (and characterized) as yellow oils
in 84 and 40% yield, respectively. Both are highly soluble
in hydrocarbon solvents, and in the case of H2L3, trituration
with hexane afforded a yellow solid.
The reduction of the imine moieties of H2L1 is facile at
room temperature in THF using 2 or more equiv of LiAlH4
per imine (isolated yield of H2L4, 82%). The complete
(55) Rajsekhar, G.; Rao, C. P.; Saarenketo, P.; Nattinen, K.; Rissanen, K.
New J. Chem. 2004, 28, 75.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10835

Homden et al.
Table 5. Ethylene Screening for 1
cocatalyst
equiv
run cocatalyst
Ta weightb activityc
Mw
Mn
P.D.I.
1
2
3
4
5
6
7
8
9
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
2000
2000
2000
2000
2000
1000
2000
3000
4000
5000
2000
2000
2000
2000
2000
2000
2000
2000
0
0.049
196 340 000 112 000 3.0
412
25 0.103
45 0.118
60 0.597
80 0.044
25 0.474
25 0.501
25 0.562
25 0.475
25 0.431
25 0.696
25 0.824
25 0.103
25 0.101
25
472 229 000 78 900
2388
176 75 300 13 700
2.9
5.5
1896 482 000 227 000 2.1
2004
2248 439 000 204 000 2.2
1900
1724 445 000 206 000 2.2
2784 420 000 142 000 3.0
Figure 7. Example of V-Cl-Al motif postulated as an active species in
vanadium-based R-olefin polymerization.
10 DMAC
11 MAC
12 MACd
13 DMAC
14 DMACd
15 TMA
16 TMAd
17 MAO
18 MAOd
3.2. Synthesis and Structure of 1-7. The reaction of
H2L1 with [VO(On-Pr)3] in refluxing toluene affords, fol-
lowing work up, brown block crystals of [V(O)L1] (1) in
good yield (ca. 70%). Crystals suitable for single-crystal
X-ray analysis were obtained from a saturated acetonitrile
solution upon prolonged standing (2-3 days) at ambient
temperature. The molecular structure of 1 is shown in Figure
3, with selected bond lengths and angles given in Table 2.
Because of the constrained nature of the ligand, the binding
of the salicylaldimine groups is such that the nitrogens are
bound trans [N1B-V-N1A 164.93(7)°] with respect to each
other, with the oxygens being bound in the cis fashion
[O1A-V-O1B 91.24(6)°]. The binding of the vanadyl
oxygen atom and one of the bridging thioether groups
completes the pseudo-octahedral geometry of the vanadium-
(IV) center. The V-O [1.9209(14) and 2.0294(14) Å] and
V-N [2.0883(16) and 2.1037(16) Å] bond distances are
typical of values observed previously for vanadium phenoxy-
imine complexes,17 whereas the V-S bond distance [2.5252-
3296 308 000 62 500
4.9
412 489 000 205 000 2.4
406 595 000 270 500 2.2
25
25
25
a Degrees Celcius. b Polymer weight in grams. c Units: g/mmol
vanadium‚hr‚bar. d Without ETA. All runs were completed with 1 µmol of
vanadium and 0.1 mL of ETA in 50 mL of toluene for 30 min.
verified empirically using a standard halide test with AgNO3.
An effective magnetic moment of 2.52 µB (Evans’ method),
consistent with a vanadium(III) (d2) high-spin system was
observed; the spin-only value is 2.83 µB, with the large
deviation attributed to the possible contribution of orbital
angular momentum possible in 3d2 systems, but is compa-
rable with other vanadium(III) complexes (e.g., 2.52 µB for
[V(OC6H2(CH2NMe2)2-2,6-Me-4)3]).59 3 can also be synthe-
sized by refluxing [VCl3‚3THF] and H2L1 in toluene, with
the loss of 2 equiv of HCl. After workup and prolonged
standing at ambient temperature (2-3 weeks), red rectangular
crystals of 3 as the acetonitrile solvate formed in good yield
(78%).
(6) Å] is slightly shorter than that observed in [VLS ]
2
[2.5306(4) Å] [LS ) 2,2′-S{4,6-(t-Bu)2C6H2O}2].56 The
2
vanadyl VdO bond length, 1.6193(4) Å, is typical53 and
gives a strong absorption in the IR spectrum at υ 1029 cm-1.
4 and 5 being the vanadyl-bearing propane-bridged and
butane-bridged analogues, respectively, were prepared as
described for 1; however, high solubility in common organic
solvents has, to-date, thwarted attempts to obtain crystals
suitable for single-crystal X-ray diffraction.
A similar reaction of H2L1 with [V(Np-tol)(OEt)3] pro-
duced the imido analogue of 1, namely [V(Np-tol)L1] (2),
as characterized by elemental analysis, mass spectrometry,
EPR, and magnetic moment. Reaction of H2L1 with [V(O)-
(On-Pr)3] in the presence of excess DMAC, led to isolation
of the vanadium(III) complex [V(Cl)L1] (3) in ca. 90% yield.
Crystals suitable for an X-ray diffraction study were isolated
from a saturated solution of acetonitrile on standing at
ambient temperature for 7 days. A molecule of 3 is shown
in Figure 4 (selected bond lengths and angles are given in
Table 2) and is found to be essentially isostructural to that
of 1.
The vanadium ethane-bridged amine complex, 6, was
ultimately isolated in good yield (67%) under less-forcing
conditions than previously employed for 1-5. It was found
that the reaction could be driven at room temperature in
diethyl ether by repeatedly stirring for 15 min, followed by
the removal in solvent in vacuo. Over four or five cycles, a
deep red/brown coloration developed, at which point the
crude material was extracted into dichloromethane. A binding
motif similar to that seen in 1 and 3 is tentatively suggested,
whereby both phenolate groups are bound to the metal center,
as well as in this case, both amine nitrogens; the presence
of a vanadium-sulfur interaction cannot be directly proven
in the absence of a crystal structure determination. The
vanadium center has no extra functionality by way of a bound
oxygen atom (i.e., no vanadyl group); the magnetic moments
and EPR results providing corroborating evidence for the
presence of a d1 vanadium(IV) species. The mass spectrum
for this compound displays a peak at 676, which can be
attributed to the molecular ion peak for the above suggested
structure (see also Scheme 4); however, without conclusive
The V-Cl bond length [2.3717(6) Å] is slightly longer
than that found in previously reported vanadium(III) com-
plexes [2.227(1) to 2.2923(16) Å],58,59 possibly due to the
presence of three dative bonds increasing the electron density
at the metal center. The presence of the chlorine atom was
(56) Chaudhuri, P.; Paine, T. K.; Weyhermuller, T.; Slep, L. D.; Neese,
F.; Bill, E.; Bothe, E.; Wieghardt, K. Inorg. Chem. 2004, 43, 7324.
(57) Redshaw, C.; Rowan, M. A.; Warford, L.; Homden, D. M.; Arbaoui,
A.; Elsegood, M. R. J.; Dale, S. H.; Yamato, T.; Casas, C. P.; Matsui,
S.; Matsuura, S. Chem. Eur. J. 2007, 13, 1090.
(58) Berreau, L. M.; Hays, J. A.; Young, V. G.; Woo, L. K. Inorg. Chem.
1994, 33, 105.
(59) Hagen, H.; Boersma, J.; Lutz, M.; Spek, A. L.; van Koten, G. Eur. J.
Inorg. Chem. 2001, 117.
10836 Inorganic Chemistry, Vol. 46, No. 25, 2007

Vanadium Complexes Possessing N2O2S2-Based Ligands
Table 6. Ethylene/1-Hexene Copolymerization Results
1-hexene
equiv
run
catalyst
weighta
activityb
C6 ) mol %c
Mw
Mn
P.D.I.
2.2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19d
1
1
1
1
1
1
1
1
1
1
1
2
3
4
5
6
7
1
1
400
800
1.16
1.01
0.82
0.42
0.41
0.22
0.14
0.11
0.18
0.21
230
200
164
85
82
43
28
21
36
42
88 100
39 400
1600
2400
3200
4000
4800
5600
6400
7200
8000
4000
4000
4000
4000
4000
4000
4000
4000
7.3
11.3
13.6
11.8
12.1
11.6
39 800
21 000
21 000
10 800
1.9
1.9
2.58
3.31
5.95
2.86
1.48
1.22
4.35
0.44
516
662
1190
572
148
244
870
89
6.3
8.4
5.9
8.3
5.1
7.6
13.0
10.2
38 100
41 700
24 400
36 900
62 800
47 000
39 800
5780
19 200
19 000
8 520
18 900
33 300
23 000
21 000
2980
2.0
2.2
2.9
2.0
1.9
2.0
1.9
1.9
1
d
a Polymer weight in grams. b Units: g/mmol vanadium‚hr‚bar. c Calculated by H NMR. T ) 45 °C. All runs completed with 10 µmol of vanadium,
0.1 mL of ETA, 400 equiv of DMAC and 40 mL of toluene at 25 °C for 30 min.
X-ray data, the possibility of a bridging dinuclear species
similar to that of 7 or an amido-hydroxo species cannot be
completely ruled out.
moment of 2.50 µB, which is consistent with a vanadium-
(III) system (vide infra). In contrast to 3, 7 is highly unstable,
producing a high degree of fragmentation when analyzed
using mass spectrometry, and only a very weak signal for
the molecular ion is observed; peaks due to the loss of ligands
around the metal centers dominate.
The reaction between H2L4 and [V(O)(On-Pr)3] in reflux-
ing toluene, following extraction into hot acetonitrile, gave
brown crystals of 7 in 19% yield. Single-crystal X-ray
analysis of the complex (Figure 5) unexpectedly revealed
the binding of two metal centers to one S2N2O2 molecule,
with the meridonal binding of an SNO group to each
vanadium center (Scheme 4, 7). Additionally, each vanadium
atom is coordinated, also meridonally, through the SNO
atoms by a thiolate ligand produced by the cleavage of an
H2L1 molecule. Selected bond lengths and angles for 7 are
given in Table 3.
An analogous ligand to the parent ligand H2L4 has recently
been shown to undergo cleavage of one of the C-S bonds
for a cobalt(II) system (Scheme 3).55
We invoke a similar mechanism for 7; however, in the
case of 7, the fragment L1b (see Scheme 3) does not appear
in the isolated product 7. Rather, this product is the result
of the combination of two [L1aV]-type fragments, which are
bound by an intact L1 ligand. We have not be able to isolate
(or identify) other products in this reaction. The reformation
of the imine arms in 7 is most likely driven by the reductive
elimination of dihydrogen and water.
In light of the characterization of 7, the stoichiometry of
the reaction was altered accordingly such that the reaction
involving [V(O)(On-Pr)3] and H2L4 was carried out in a 2:3
(metal/ligand) ratio, resulting in the isolation of the desired
product 7 in good yield (83%).
As in the proligands H2L1 and H2L4, 7 contains a center
of symmetry at the midpoint of the ethane bridge (between
C14b and C14b′). The vanadium centers are pseudo octa-
hedral, each with two phenolate bonds, to O(1A) and O(1B),
three dative bonds, to N(1A), N(1B), and S(1B), and a
thiolate bond to S(1A). The V-S dative bond is comparable
to that found in 1. The complex displayed a magnetic
3.3. Polymerization Results. 3.3.1. Ethylene Homopo-
lymerization. Procatalysts 1-7 (Scheme 4) were screened
for R-olefin polymerization in the presence of a variety of
organoaluminum cocatalysts, namely, methylaluminoxane
(MAO), trimethylaluminum (TMA), methylaluminum dichlo-
ride (MAC), and dimethylaluminum chloride (DMAC). In
the presence of DMAC and the reactivating agent ETA, 1-7
exhibited very good activities (>1000 g/mmol‚h‚bar) for
ethylene polymerization as defined by the Gibson criteria.3
Lifetime studies (Table 4 and Figure 6) carried out upon
systems 1-7 as well as the known 8 and 9, showed in
general, a steady decrease in catalytic activity over the first
15 min period (up to 50% reduction in activity). The lower
level of activity is maintained throughout the polymerization
screening lifetime (∼30 min). Only in the case of 3 was there
a pronounced decrease in catalytic activity, where initial
values of ca. 40 000 g/mmol‚h‚bar at 5 min fell sharply to
around 11 000 g/mmol‚h‚bar at ca. 15 min; again this lower
activity is maintained throughout the remainder of the
polymerization run. The greater activity observed by 3 could
be attributed to the lower oxidation state of the vanadium
center, a theory supported by Allegra et al.60 In the case of
7, the instability of the complex is thought to produce lower
activities observed when compared to those of 3. All of the
polymers produced using 1-7 were of high molecular weight
(Mw ) 160 000-256 000) with narrow polydispersity in-
dexes (2.4-4.0) with melting points of 134-138 °C being
typical of values for linear polyethylene. Under analogous
polymerization conditions, the known 8 and 9 also displayed
very good activities. In particular, vanadium(IV) complex 8
(60) Zambelli, A.; Allegra, G. Macromolecules 1980, 13, 42.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10837

Homden et al.
Figure 8. 13C NMR (CDCl3) of ethylene/1-hexene copolymer using procatalyst 1.
upon activation with DMAC afforded a system with a
catalytic activity of ca. 10 500 g/mmol‚h‚bar; cf. 8 000 under
analogous conditions using 9. The activity of some of the
catalysts was such that mass transport problems were
encountered, leading to the shorter runs times quoted;
however, from these results it is interesting to note that
although the vanadium(IV) species from procatalysts 1-7,
notably 4, give activities comparable to that of 8, the
vanadium(III) procatalysts 3 and 9 give quite different
activities. This suggests that additional π donation from the
sulfur atom in 3 helps to stabilize the lower oxidation state,
producing the higher activity. However, any structure-
activity relationship discussions are best restricted to the
procatalyst because the exact nature of the active species in
these vanadium-based systems still remains a mystery.
Recent studies have shown that the nature of the cocatalyst
is crucial for vanadium-based polymerization catalysis.16,17
Here, the use of alkyl aluminum compounds (TMA and
MAO; Table 5, runs 15 and 17) with 1 led to negligible
activites, whereas the chlorinated cocatalysts (MAC and
DMAC; Table 5, run 11 vs run 13) produced moderate-to-
high activities. The use of DMAC as a cocatalyst in
combination with 3 produced the highest activity (ca. 11 000
g/mmol‚h‚bar). The necessity of a chloro-organoaluminum
cocatalyst is supported by the work of Gambarotta et al.,6
who have postulated that the catalytically active species in
vanadium-based R-olefin polymerization utilizes bridging
chloro groups in V-Cl-Al-type motifs (Figure 7). In no
instance here was any polymer produced in the absence of
an aluminum cocatalyst, and the cocatalyst alone produced
only negligible polymer.
erization temperature resulted in a decrease in the molecular
weight of the polyethylene and broader polydispersity. A
significant decrease in the molecular weight was observed
with 8 (Mw ) 98 700) compared to molecular weights
produced by the other vanadium(IV) procatalysts herein;
upon increasing the temperature to 80 °C, a further decrease
in molecular weight was observed (Mw ) 37 900) and also
a broadening of the range of molecular weights (P.D.I.
increases from 3.5 to 17) indicating the presence of more
than one active species, while also displaying the thermal
instability of the active species. 9, a vanadium(III) system,
faired better under the same conditions, producing a polymer
with a narrow distribution (P.D.I. in the range 2.3-3.4) even
at elevated temperature. However, an even more-drastic
decrease in molecular weight was observed from Mw
155 000 at 60 °C to Mw ) 13 400 at 80 °C.
)
A maximum in activity is also observed with varying
cocatalyst concentration (Table 5, runs 6-10), with 3 000
equiv producing the highest activity ([Al:V] range ) 1000-
5000). However, the influence of the Al:V ratio is not
dramatic; the lowering of the Al:V ratio to 1 000 equiv (run
6) still produced a highly active polymerization system.
Unlike previously observed for more-active vanadium sys-
tems, the removal of ETA from the polymerization system
(Table 5, runs 11 vs 12) did not result in a dramatic change
in activity; however, it did lead to a broadening of the P.D.I.
of the polymers, suggesting its role herein to be that of
maintaining a single active species.
Within the vanadyl family of catalysts presented here (1,
4, and 5), there is no clear trend for activity on increasing
the length of the backbone. The lowest activity is exhibited
by procatalyst 1, for which n ) 2, with procatalyst 4 (n )
3) affording the highest activity, whereas 5 (n ) 4) falls
Maximum catalytic activities for 1 were observed at ca.
60 °C (Table 5, runs 1-5), and, as previously found in
vanadium-based ethylene catalysis,16 the increase in polym-
10838 Inorganic Chemistry, Vol. 46, No. 25, 2007

Vanadium Complexes Possessing N2O2S2-Based Ligands
between 1 and 4. After t ) 25 min, the activities of 4 and 5
are comparable.
4. Conclusions
A new family of highly active vanadium procatalysts
bearing a ligand featuring sulfur, nitrogen, and oxygen donor
ligands has been synthesized and screened for the homopo-
lymerization of ethylene and copolymerization of ethylene/
1-hexene. Catalytic studies suggest that a single active species
is responsible for the polymerization and that this species
has a certain degree of thermal stability. The nature of the
cocatalyst is crucial, with aluminum species containing both
alkyl and chloro substituents producing the highest activities;
the exclusion of ETA in the reactions leads to a negligible
change in activities but does result in a noticeable broadening
of the P.D.I.’s of the resulting polymer products. However,
any structure-activity relationship discussions are best
restricted to the procatalyst because the exact nature of the
active species in these vanadium-based systems still remains
a mystery. Reduction of the imine function in the procatalyst
resulted in poorer activities, a trend that has been noted
elsewhere in other systems.65 When compared with the
known FI catalysts reported by Fujita et al.,46 the inclusion
of the additional sulfur atom resulted in higher activities for
the vanadium(III) species and comparable activites for the
vanadium(IV) species. Furthermore, the polymer produced
was found to have a higher molecular weight, particularly
at elevated temperatures; in the case of vanadium(IV), a
much-narrower P.D.I. was suggestive of a more-controlled
polymerization process. Increasing the alkane chain length
in the ligand backbone did not result in any noticeable
beneficial effects for ethylene homopolymerization.
3.3.2. Ethylene/1-Hexene Copolymerization. To date, the
use of vanadium-based complexes for the copolymerization
of R-olefins is somewhat limited. Recent investigations have
examined the vanadium-catalyzed copolymerization of eth-
ylene-propylene,61 ethylene-norbornene, and ethylene/1-
alkenes.15,62,63
Procatalysts 1-7 in the presence of DMAC catalyze the
polymerization of ethylene/1-hexene with activities, levels
of incorporation, molecular weights, and polydispersities all
within a narrow range (Table 6), suggestive of single-site
catalysis and a common active species. The highest activity
(run 14), ca. 1 200 g/mmol‚h‚bar, produced a low-molecular-
weight polymer with a narrow P.D.I. In the case of 1, it was
found that a minimum of 3 200 equiv of 1-hexene were
required for successful copolymerization; with a smaller
amount of 1-hexene, only polyethylene was isolated. Upon
increasing the concentration of 1-hexene above this threshold,
both the activity of 1 and the level of monomer incorporation
(11.0-13.6%) remained fairly constant; the molecular weight
of the polymer, however, was shown to decrease (runs
1-11). Above 8 000 equiv of 1-hexene, no material is
recovered, most probably due to catalyst poisoning.
An increase in temperature from 25 to 45 °C led to an
order of magnitude decrease in the activity of the system
and the molecular weight of the resulting polymer, for
example runs 18 and 19. The 1-hexene incorporation fell by
3% (to ca. 10%); however, the P.D.I. of the resulting polymer
remained constant. Analysis of the copolymer was carried
out by 13C NMR in CDCl3 at room temperature, with the
assignment of the microstructure following previous work
reported by Hsieh and Randall64 (Figure 8).
For the copolymerization of ethylene/1-hexene, the result-
ing polymer properties and levels of incorporation are again
suggestive of a common active species, which in this case
is independent of the ligands employed.
The polymer produced appears to be long chains of
polyethylene with isolated units of hexene. The lack of any
peaks at ∼40 ppm (indicating the absence of polyhexane
blocks within the polymer) and at ∼24 ppm (indicative of
alternating sequences of monomers) supports the idea of
single incorporation of a 1-hexene monomer into a predomi-
nantly polyethylene polymer, which can be explained due
to steric crowding around the metal center. 1H NMR analysis
indicated an incorporation of ca. 1 unit of 1-hexene for every
10 units of ethylene polymerized.
Acknowledgment. The University of East Anglia and the
EPSRC are thanked for financial support. We thank the
EPSRC Mass Spectrometry Service Centre (Swansea, U.K.).
We would also like to thank Rapra Scientific Ltd. for GPC
measurements and Dr. Myles Cheesman (UEA) for help with
recording EPR spectra.
Supporting Information Available: Structures of H2L1, H2L4,
1, 3, and 7 in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
(61) Ma, Y. L.; Reardon, D.; Gambarotta, S.; Yap, G. Organometallics
1999, 18, 2773.
IC701461B
(62) Gambarotta, S.; Reardon, D.; Guan, J.; Yap, G. P. A.; Wilson, D. R.
Organometallics 2002, 21, 4390.
(63) Bialek, M.; Czaja, K. Polymer 2000, 41, 7899.
(64) Hsieh, E. T.; Randall, J. C. Macromolecules 1982, 15, 1402.
(65) Britovsek, G. J. P.; Gibson, V. C.; Mastroianni, S.; Oakes, D. C. H.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Eur. J.
Inorg. Chem. 2001, 431.
Inorganic Chemistry, Vol. 46, No. 25, 2007 10839