Vanadium-based imido-alkoxide pro-catalysts bearing bisphenolate ligands for ethylene and ε-caprolactone polymerisation

Article abstract of DOI:10.1039/b902402f

The pro-catalysts [V(NAr)(L)(OR)] (Ar = p-tolyl, p-ClC₆H ₄, p-(OMe)C₆H₄, p-(CF₃)C ₆H₄; R = t-Bu, i-Pr, n-Pr, Et, C(CH₃)(CF ₃)₂) have been prepare

Full text of DOI:10.1039/b902402f

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www.rsc.org/dalton | Dalton Transactions
Vanadium-based imido-alkoxide pro-catalysts bearing bisphenolate ligands
for ethylene and e-caprolactone polymerisation†
Abdessamad Arbaoui,a Carl Redshaw,*a Damien M. Homden,a Joseph A. Wrighta and Mark R. J. Elsegoodb
Received 4th February 2009, Accepted 15th May 2009
First published as an Advance Article on the web 7th July 2009
DOI: 10.1039/b902402f
The pro-catalysts [V(NAr)(L)(OR)] (Ar = p-tolyl, p-ClC6H4, p-(OMe)C6H4, p-(CF3)C6H4; R = t-Bu,
i-Pr, n-Pr, Et, C(CH3)(CF3)2) have been prepared in good yields from the reaction of [V(NAr)(OR)3]
and the bisphenol 2,2¢-CH3CH[4,6-(t-Bu)2C6H2OH]2 (LH2). X-Ray crystal structure determinations for
the Ar = p-tolyl, R = t-Bu (1), R = C(CH3)(CF3)2 (2) and Ar = p-ClC6H4, R = t-Bu (3) derivatives
revealed monomeric complexes, whereas use of R = i-Pr, n-Pr or Et led to alkoxide-bridged dimeric
structures of the form [V(NAr)(L)(m-OR)]2 (R = i-Pr, Ar = p-tolyl (4), p-ClC6H4 (5), p-(CF3)C6H4 (6),
p-(OMe)C6H4 (7); R = n-Pr, Ar = p-tolyl (8), p-(CF3)C6H4 (9); R = Et, Ar = p-ClC6H4 (10), p-tolyl
(11)). Complexes 1–11 yield highly active ethylene polymerisation catalysts when treated with DMAC
(dimethylaluminium chloride) in the presence of ETA (ethyltrichloroacetate), with activities in the
range 38 800 to 75 200 g mmol-1 h-1 bar-1. The molecular weights of the resultant polymers were in the
range 37 000 to 411 000 g mol-1, with molecular weight distribution 2.2 to 4.7. The effect of the nature
of the para-arylimido substituent and the alkoxide group OR upon the catalytic activity has been
investigated. For e-caprolactone polymerisation, mononuclear 1–3 exhibit low conversion (≤25%; 0%
for 2), whereas use of the dimeric species 4–11 led to higher conversions (41–78%).
state.4 Amongst this group of aryloxide pro-catalysts were a new
family of dimeric vanadyl complexes bearing bisphenolate ligands
Introduction
Given the success of a number of investigators when examining
group IV metal chelating aryloxide systems for polymerisation
processes,1 we have subsequently screened a number of group V
of the type 2,2¢-CHR[4,6-(t-Bu)2C6H2OH]2 (R = H, Me (LH2)),
and possessing the structure I (Chart 1). We were interested in
how the electronic and steric factors associated with this type of
metal di- and triphenolate pro-catalysts. In the case of niobium
pro-catalyst structure might affect the catalytic activity/control
and tantalum, catalytic results were poor and such studies were
of the ethylene polymerization process. Given that the oxo group
discontinued.2 However, a number of vanadyl complexes bearing
is isoelectronic with the organoimido group, it was of interest to
chelating aryloxide ligands exhibited extremely high catalytic
investigate the related organoimido containing species. We note
activities (ca. 100 000 g mmol-1 h-1 bar-1) and, in the preceding
paper, we extended this family to include –S– and –SO2– bridged
chelating aryloxides.3 The exact nature of the active species is still
that recent reports by Moriuchi and Hirao have shown how the
imido group geometrical parameters can be controlled by the para
substituent of the aryl moiety (p-conjugation rather than inductive
effects) in a series of vanadium(V) complexes.5 We also note that in
the patent literature there is mention of [V(NAr)(bisphenolate)Cl]-
type pro-catalysts for olefin co-polymerisation and terpolymeri-
sation with other dienes, where a number of imido groups were
employed possessing a variety of electron-withdrawing groups, for
example 2,4,6-Cl3C6H2N.6
unknown, though it is thought to involve vanadium in the +3
aEnergy Materials Laboratory, School of Chemical Sciences and Pharmacy,
University of East Anglia, Norwich, UK NR4 7TJ. E-mail: carl.redshaw@
uea.ac.uk
bChemistry Department, Loughborough University Loughborough,
Leicestershire, UK LE11 3TU
Herein, we report our investigations using the readily available
vanadium precursors [V(NAr)(OR)3] (Ar = p-tolyl, p-ClC6H4,
p-(OMe)C6H4, p-(CF3)C6H4; R = t-Bu, C(CH3)(CF3)2, i-Pr,
n-Pr, Et),7 and their interaction with the chelating bisphenol 2,
† Electronic supplementary information (ESI) available: Selected poly-
merisation data, X-ray crystallographic files in CIF format for the structure
determinations of compound 1–10. CCDC reference numbers 718351–
718360. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b902402f
Chart 1 Pro-catalysts [V(O)(L)(m-OR)]2 (I), [V(NAr)(L)(OR)] (II) and [V(NAr)(L)(m-OR)]2 (III).
The Royal Society of Chemistry 2009 Dalton Trans., 2009, 8911–8922 | 8911
This journal is
©

2¢-ethylidene-bis(4,6-di-tert-butylphenol), which affords products
possessing one of two classes of structure (see II and III, Chart 1)
depending on the steric hindrance associated with the alkoxide
group R. The ability of the complexes to act as pro-catalysts
for ethylene polymerisation has been investigated and, given the
presence of the alkoxide ligand, we have also assessed their ability
to polymerise e-caprolactone. Chelating bisphenols such as LH2
have been employed previously as ancillary ligands in catalytic
systems for the ring opening of lactones and lactides, primarily
in conjunction with aluminium, zinc, titanium and lanthanide
centres.8
the analytically pure imido complex on the frit. Stoichiometrically
such complexes are formed via the loss of two molecules of alcohol
per vanadium centre.
Monomeric tert-butoxides
In the case of the tert-butoxides (Ar = p-tolyl, R = t-Bu (1) and
C(CH3)(CF3)2 (2); Ar = p-(Cl)C6H4, R = t-Bu (3)), prisms suitable
for single-crystal X-ray structure determinations were grown from
saturated acetonitrile solutions on prolonged standing at ambient
temperature. The molecular structures are shown in Fig. 1 with
selected bond lengths and angles given in Table 1; crystallographic
data are presented in Table 10. The tert-butoxide complexes
obtained are all monomeric. The geometry about the vanadium
centre in 1–3 is pseudo tetrahedral with angles varying from ideal
in the ranges 105.15(5) to 113.39(9)◦ for 1, 103.81(6) to 114.00(5)◦
for 2, and 105.72(11) to 115.61(12)◦ for 3. The organomido groups
in each complex can be considered linear (V(1)–N(1)–C(5) =
175.73(17)◦ (1), 175.63(13)◦ (2) and 176.2(2)◦ (3)).9 The V–N bond
Results and discussion
General
Interaction of the arylimido-trialkoxides [V(NAr)(OR)3] with one
equivalent of the bisphenol LH2 in refluxing toluene afforded,
following work-up, complexes of the form [V(NAr)(L)(OR)]n (n =
1 or 2) as orange-red crystalline solids in moderate to high yield
(ca. 40–80%). Washing with cold acetonitrile removed any minor
vanadyl species of the form [V(O)(L)(OR)]n (n = 1 or 2), leaving
˚
lengths (1.657(2) (1), 1.6487(15) (2) and 1.653(3) A (3)) are in
the range of values reported for related arylimido vanadium(V)
complexes (1.644(3) to 1.678(3) A).5,7,9,10 In all of the tert-butoxide
˚
Fig. 1 CAMERON representation of the structures of 1, 2 and 3 showing spheres of arbitrary size; hydrogen atoms and t-Bu groups on the phenolates
have been omitted for clarity.
8912 | Dalton Trans., 2009, 8911–8922
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The Royal Society of Chemistry 2009
©

◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 1, 2 and 3
1
2
3
˚
Bond lengths/A
V(1)–N(1)
V(1)–O(1)
V(1)–Ophenolate
1.657(2)
1.7509(15)
1.8118(11)
1.6487(15)
1.8001(11)
1.7966(12) and 1.8097(12)
1.653(3)
1.738(2)
1.802(2) and 1.804(2)
Bond angles/◦
N(1)–V(1)–O(1)
113.39(9)
105.15(5)
112.44(4)
123.90(9)
147.73(14)
175.73(17)
112.94(7)
115.61(12)
N(1)–V(1)–Ophenolate
O(1)–V(1)–Ophenolate
V(1)–Ophenolate–Cphenolate
V(1)–O(1)–C(1)
105.45(7) and 103.81(6)
111.23(7) and 114.00(5)
120.68(10) and 131.04(10)
146.77(12)
105.72(11) and 105.92(12)
110.38(11) and 110.67(10)
124.22(18) and 124.83(18)
151.9(2)
V(1)–N(1)–C(5)
175.63(13)
176.2(2)
Fig. 2 Space filling diagrams of (left) [V(Np-tolyl)(hexahomotrioxacalix[3]arene)]2 (only half of dimer shown) and (right) 1.
complexes, the eight membered chelate rings adopt a flattened
chair conformation, in contrast to the reported flattened boat
conformation for the related chloro vanadium(V) oxo complex
bearing the bisphenol ligand 2,2¢-CH2(4-Me-6-t-BuC6H2OH)2.11
The V–O distances to the bisphenolate ligand (1.7966(12) to
structure/activity relationships (vide infra). As an entry point, we
chose the R = isopropoxy system [V(NAr)(Oi-Pr)3].7b For Ar =
p-tolyl (4), p-ClC6H4 (5), p-CF3C6H4 (6) and p-(OMe)C6H4 (7),
samples suitable for single-crystal X-ray diffraction studies were
grown from saturated solutions of acetonitrile at 0 ◦C. In all cases,
[V(NAr)(m-Oi-Pr)L]2 crystallizes as a centrosymmetric dimer (see
Fig. 3a–d). Selected bond lengths and angles are collected in
Table 2. The geometry at each vanadium is best described as
trigonal bipyramidal, with N(1) and O(1¢) occupying the apical
sites; the Reedijk criteria calculated for 4–7 (t ª 0.8) confirms
the geometry assignment.14 The three oxygen atoms O(1), O(2)
and O(3) occupy the equatorial sites, with the vanadium centre
˚
1.8118(11) A) are typical of those previously observed for vana-
dium(V) aryloxides (1.734(3) to 1.850(7) A).11,12 The V–O distances
˚
˚
˚
to the alkoxides are 1.7509(15) A in 1, 1.8001(11) A in 2 and
˚
1.738(2) A in 3 and are somewhat shorter than those reported
in other arylimido-alkoxy vanadium(V) complexes (1.842(1) to
3,5b,7
˚
1.888(3) A).
The alkoxo ligands adopt a bent arrangement
(V(1)–O(1)–C(1) 147.73(14)◦ (1), 146.77(12) (2) and 151.9(2)◦ (3)).
We note that the coordination environment about the vanadium
centre in complexes 1–3 shows a resemblance to the vanadium
environment in the highly active hexahomotrioxacalix[3]arene-
based vanadyl complexes as highlighted in Fig. 2.13
˚
located about 0.26 A out of the mean plane of the three oxygen
atoms in each case. As in 1–3, the eight membered ring chelates
in 4–7 adopt a flattened chair conformation, with O(2)–V(1)–
O(3) bite angles in the range 109.68(7) to 112.19(6)◦. These bite
angles are close to that reported by Toscano et al. (106.9(2)◦)
for a related oxo vanadium(V) complex bearing a bisphenolate
ligand.11 The arylimido group is bound to the metal almost directly
opposite the longer bridging isopropoxy group, and shows the
anticipated geometry with near linear V(1)–N(1)–C(5) angles in
the range 170.6(4)–173.3(3)◦. The V(1)–N(1) distances do not
Dimeric structures/variation of imido substituent
When the R group in the precursor vanadium complex is less
bulky than tert-butyl, an alkoxide-bridged dimeric structure is
favoured. Given the recent observations of Moriuchi and Hirao,5
we carried out single-crystal X-ray diffraction studies on a number
of organoimido derivatives with various combinations of alkoxide
group (OR) and arylimido group, in order that we might observe
˚
differ significantly, and are all about 1.66 A. In the case of 6, the
imido group shows disorder over two sets of positions. The major
component (approx. 55% occupancy) has an angle at nitrogen
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8911–8922 | 8913
©

Table 2 Selected bond lengths and angles for 4–7
4
5
6
7
˚
Bond lengths/A
V(1)–N(1)
V(1)–O(1)
V(1)–O(2)
V(1)–O(3)
V(1)–O(1¢)
V(1) ◊ ◊ ◊ V(1¢)
1.662(3)
1.879(3)
1.838(2)
1.840(2)
2.205(2)
3.294
1.658(2)
1.651(3)
1.880(2)
1.821(2)
1.821(2)
2.240(2)
3.337
1.6566(17)
1.8632(12)
1.8373(13)
1.8295(12)
2.2590(13)
3.311
1.8808(16)
1.8527(16)
1.8313(16)
2.1838(16)
3.301
Bond angles/◦
N(1)–V(1)–O(1)
N(1)–V(1)–O(2)
N(1)–V(1)–O(3)
N(1)–V(1)–O(1¢)
O(1)–V(1)–O(2)
O(1)–V(1)–O(3)
O(1)–V(1)–O(1¢)
O(2)–V(1)–O(3)
V(1)–O(1)–V(1¢)
V(1)–N(1)–C(5)
100.15(13)
98.25(13)
96.00(13)
171.87(14)
120.33(10)
122.65(11)
72.73(11)
110.98(11)
107.27(11)
173.3(3)
102.34(8)
97.97(9)
97.15(8)
173.97(8)
123.19(7)
119.40(7)
71.63(7)
109.68(7)
108.37(7)
172.54(17)
100.04(12)
97.49(11)
97.19(12)
172.14(11)
121.51(10)
122.21(10)
72.12(10)
110.06(10)
107.88(10)
170.6(4) and 172.6(3)
101.15(7)
95.82(7)
98.51(7)
174.32(6)
122.30(6)
118.96(6)
73.54(6)
112.19(6)
106.46(6)
171.47(15)
Fig. 3 CAMERON representation of the structures of 4, 5, 6 and 7 showing spheres of arbitrary size; hydrogen atoms and t-Bu groups on the phenolates
have been omitted for clarity.
8914 | Dalton Trans., 2009, 8911–8922
This journal is
The Royal Society of Chemistry 2009
©

(C(34)–N(1)–V(1)) of 172.6(3)◦, whereas the minor component
shows an angle of 170.6(4)◦. This disorder is carried through the
whole imido ligand, with the entire aromatic ring and CF3 group
displaced. The two components are also rotated relative to one
another, with the angle between normals to the mean planes of
the aromatic rings being approximately 61◦.
Spectroscopy
The 1H NMR spectra of complexes 1–11 show little influence of the
complexation on the chemical shift for the ethylidene CH(CH3)
grouping of the diphenol ligand. For example, in 5 and 6 this
signal is shifted only ca. 0.1 ppm upfield compared with the
same signal for the free ligand. However, the influence of the
coordinationenvironmentis more markedonthe CH(CH3) proton
and is characterised by a ca. 1.0 ppm shift downfield compared
with the same signal for the free ligand. Similar effects have been
noted in other systems containing this ligand set.15 The dimeric or
monomeric nature of the complex had no influence on this feature.
Complex 2 displayed the largest shift, probably due to the presence
of the strong electron withdrawing groups on the alkoxide moiety.
The IR spectra of 1–11 all display a v(V–N) band at around
1160 cm-1, comparable to the IR stretch recorded for [CpVCl2{N-
2,6-(i-Pr)2C6H3}] (1157 cm-1) and [VCl3{N-2,6-(i-Pr)2C6H3}]
(1143 cm-1).16 The 51V NMR spectra of complexes bearing an
isopropoxide ligand (i.e. 4–7) were consistent with observations
made by Moriuchi and Hirao and previously by Maatta.5,7 When
the para-arylimido substituent is an electron donating group
Variation of alkoxide group
Replacement of Oi-Pr by the smaller On-Pr or OEt groups
leads to the formation of [V(NAr)(m-OR)L]2, R = n-Pr, Ar =
p-tolyl (8), p-CF3C6H4, (9); R = Et, Ar = p-ClC6H4 (10), Ar =
p-tolyl (11) (Fig. 4). Complexes 8–10 show the same general
dimeric structure as the Oi-Pr systems, although 10 is pseudo-
symmetrical and lacks a crystallographic centre of symmetry. All
three molecules crystallise with discrete solvent molecules in the
cell: 8 crystallises with two CH2Cl2 per dimer, 10 with one CH2Cl2
per dimer and 9 with one CH3CN per dimer. The geometric
parameters, summarised in Table 3, show the similarity between
these molecules and the Oi-Pr analogues.
Fig. 4 CAMERON representation of the structures of 8, 9 and 10 showing spheres of arbitrary size; hydrogen atoms, t-Bu groups on the phenolates
and solvent molecules of crystallisation have been omitted for clarity.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8911–8922 | 8915
©

Table 3 Selected bond lengths and angles for 8–10
Table 5 Ethylene polymerisation data for pro-catalysts 1–11a
8
9
10a
Polymer Activity/g PE
yield/g
Mn/g
Run Pro-catalyst
mmol-1 [V] h-1 bar-1 mol-1
PDI
˚
Bond lengths/A
1
2
3
4
5
6
7
8
9
1
0.94
0.40
1.17
0.97
1.27
1.36
1.20
1.88
0.68
0.42
1.52
37 600
15 850
46 800
38 800
50 800
54 400
48 000
75 200
27 200
16 800
60 800
115 000 2.6
2
58 000 4.0
146 000 4.1
165 000 2.2
196 000 2.4
200 000 2.3
160 000 2.4
162 000 2.6
78 300 2.6
161 000 2.2
137 000 2.4
V(1)–N(1)
V(1)–O(1)
V(1)–O(2)
V(1)–O(3)
V(1)–O(1¢)
V(1) ◊ ◊ ◊ V(1¢)
1.661(3)
1.885(3)
1.836(2)
1.856(3)
2.172(2)
3.281
1.677(3)
1.868(2)
1.844(2)
1.824(2)
2.193(2)
3.283
1.666(3)b
1.879(2)b
1.829(2)b
1.839(2)b
2.181(2)b
3.294
3
4
5
6
7
8
9
Bond angles/◦
10
11
10
11
N(1)–V(1)–O(1)
N(1)–V(1)–O(2)
N(1)–V(1)–O(3)
N(1)–V(1)–O(1¢)
O(1)–V(1)–O(2)
O(1)–V(1)–O(3)
O(1)–V(1)–O(1¢)
O(2)–V(1)–O(3)
V(1)–O(1)–V(1¢)
V(1)–N(1)–C(5)
99.34(13)
99.11(13)
98.05(14)
170.74(13)
117.55(11)
125.04(11)
72.27(11)
110.39(12)
107.73(11)
178.4(3)
101.17(11)
97.48(12)
97.48(12)
173.31(11)
124.05(10)
117.14(10)
72.37(10)
111.19(10)
107.63(10)
174.0(2)
100.72(14)b
98.46(14)b
98.43(14)b
171.97(14)b
118.29(13)b
124.34(12)b
71.76(11)b
109.67(13)b
108.24(11)b
175.7(3)b
a Conditions: 50 mL toluene, 0.1 mL ETA, co-catalyst DMAC 2 mL (40 000
equivalents), 0.05 mmol pro-catalyst, 45 ◦C, 30 min.
Table 6 Ethylene polymerisation data for complex 6a
Activity/g
Co-catalyst
equivalent
Polymer PE mmol-1
Mn/g
Run
T/◦C yield/g
[V] h-1 bar-1
mol-1
PDI
a Lacks a crystallographic centre of symmetry. b Average of two values in
non-symmetrical molecule.
1
2b
3
4
5
6
7
8
9
40 000
40 000
10 000
20 000
30 000
50 000
40 000
40 000
40 000
40 000
25
25
25
25
25
25
0
45
60
80
0.48
0.02
0.04
0.13
0.26
0.21
0.005
0.52
0.61
0.67
38 400
1600
3200
10 400
20 800
16 800
400
41 600
48 800
53 600
165 000 4.7
165 000 4.1
234 000 2.7
202 000 3.2
411 000 2.5
358 000 3.0
Table 4 Selected spectroscopic dataa
CH(CH3)
CH(CH3)
1
—
—
1
d H NMR/ d H NMR/
d
51V NMR/
ppm (w1/2/Hz) cm-1
IR v(V–N)/
216 000 2.2
124 000 2.4
37 000 2.6
Compound
ppm
1.63
1.67
ppm
5.51
5.64
10
1
2
-544 (120)
-538 (360)b
-315 (120)
-317 (500)b
-414 (514)
-384 (466)
-396 (470)
-413 (260)
-361 (365)
-443 (650)
-504 (428)
-503 (80)
-154 (1800)
—
1157
1157
a Conditions: 50 mL toluene, 0.1 mL ETA, co-catalyst DMAC (1 M in
hexanes), 0.05 mmol pro-catalyst, 15 min. b Without ETA.
3
1.61
1.62
1.55
1.59
1.62
1.67
1.67
1.60
1.65
1.69
5.46
5.46
5.43
5.43
5.46
5.45
5.42
5.47
5.50
4.45
1157
1156
1157
1156
1163
1157
1158
1156
1157
—
4
over a range of temperatures (0–80 ◦C) over 30 min unless
otherwise stated. Representative results are presented in Tables 5
and 6 (see ESI for complete set of polymerisation runs)† and
lifetime studies are presented in Fig. 5.
5
6
7
8
9
10
11
LH2
For complexes 1–11, it was found that treatment with DMAC
in the presence of ETA afforded highly active ethylene polymeri-
sation systems. Such a combination of reagents has proved to be
beneficial for producing highly active vanadium-based systems, as
reported by both us13,17 and others.18 Treatment of pro-catalyst
6 with either TMA or MAO resulted in little or no polymer
formation, even in the presence of the reactivator ETA. The
dramatic effect of ETA on the polymerisation is illustrated by
run 1 (Table 6), whereas in the absence of ETA, the activity of pro-
catalyst 6 is only approximately 4% of that obtained when ETA is
present in the system (Table 6, run 2).
A comparative study was conducted under the same conditions
for complexes 1 and 2 in order to assess their respective poly-
merisation behaviour due to their differing alkoxides, independent
of variation of other parameters. The results are collated in
Table 7, and reveal that whilst the initial activity is higher for
the hexafluoro-tert-butoxide pro-catalyst 2, the system utilising
the tert-butoxide 1 has a significantly enhanced performance
over time. Data from Table 5 also suggest that use of a p-CH3
substituent on the arylimido group is beneficial for enhanced
activity (Table 5, entries 8–11).
a NMR data collected in CDCl3 at room temperature; IR data collected in
nujol on KBr plates. b Collected in C6D6.
(i.e. OCH3 or CH3) a marked downfield shift for the 51V NMR
signal occurs (e.g. -361 ppm (7) and -384 ppm (4)), compared
with the 51V NMR signal recorded with electron withdrawing
groups such as Cl or CF3 (e.g. -396 ppm (5) and -413 (6) ppm).
Spectroscopic data relevant to this discussion have been collated
in Table 4.
Ethylene polymerisation
Complexes 1–11 have been evaluated as pro-catalysts for the
polymerisation of ethylene, employing either MAO (methylalu-
minoxane), TMA (trimethylaluminium) or DMAC (dimethyla-
luminium chloride) as co-catalyst, and with or without ETA
(ethyltrichloroacetate) present. Polymerisations were carried out
in toluene (50 mL) using 10 000–50 000 molar equiv. of co-catalyst
8916 | Dalton Trans., 2009, 8911–8922
This journal is
The Royal Society of Chemistry 2009
©

Fig. 5 Lifetime studies for pro-catalysts 1–11. Conditions: 50 mL toluene, 0.1 mL ETA, co-catalyst DMAC 2 mL (40 000 equivalents), 0.05 mmol
pro-catalyst, 45 ◦C.
Table 7 Comparative runs for pro-catalysts 1 and 2a
reactions. Interestingly, only low molecular weight polymers were
obtained using this alkoxy vanadium/benzyl alcohol system.
Polymer Activity/g PE
Pro-catalyst yield/g
mmol-1[V] h-1 bar-1
Mn/g
In order to investigate the influence of the co-initiator on the
catalyst performance, the polymerisation was run both in the
absence of benzyl alcohol (Table 8, entry 7) and with an excess
of benzyl alcohol present (Table 8, entry 8). Results revealed that
the concentration of benzyl alcohol had little effect on the catalytic
activity: after 24 h at 40 ◦C, the conversions obtained ranged from
41 to 50% (Table 8, entries 7, 2 and 8 for 0, 1 and 2 equivalents
of co-initiator, respectively). In the absence of benzyl alcohol, a
three-fold increase of the molecular weight was noted without
the increase in polydispersity index described with other metals
operating under such conditions.19
Run
mol-1
PDI
—
1b
2c
3b
4c
1
1
2
2
0.20
0.94
0.28
0.40
48 000
—
37 600
66 560
15 850
115 000 2.6
—
58 000 4.0
—
a Conditions: 50 mL toluene, 0.1 mL ETA, cocatalyst DMAC 2 mL (40
000 equivalents), 0.05 mmol procatalyst, 45 ◦C. b 5 min; c 30 min.
e-Caprolactone polymerisation
The screening of complexes 1–11 (Table 9) revealed that the
monomeric complexes (i.e. 1–3) showed lower activities than their
dimeric analogues (i.e. 4–11). After 24 h, complexes 1–3 afforded
only low conversions (≤25%), whereas higher conversions (41–
78%) were reached using complexes 4–11 under similar conditions.
Given that the propagating species is likely to be monomeric
(the growing polymeric chain is bulkier than a tert-butyl group),
we propose that the beneficial effect evidenced here involves the
initiation step of the polymerisation, when the first monomer is
coordinated to the metal and inserted into the V–OR bond. For
complexes bearing the same alkoxide ligand, the para-arylimido
substituent has little effect on the polymerisation activity; however,
some activity trends can be drawn here. For instance, when the
alkoxy group is an isopropoxide, the catalytic activity followed
the order: CH3 ª CF3 > Cl > OCH3. For dimeric complexes (i.e.
Complexes 1–11 were also screened for their ability to polymerise
e-caprolactone. Complex 7 was subjected to temperature and
co-initiator concentration studies. The polymerisation data are
presented in Table 8.
Complex 7 was active for the ring opening polymerisation of
e-caprolactone. However, it was only moderately active at room
temperature, leading to low conversions after 24 h (Table 8,
entry 1). The conversion increased dramatically with temperature,
without noticeable increase of polydispersity index. (Table 8,
entries 2 and 3). Complex 7 was also active at low catalyst
loading leading to 29% conversion after 24 h for 900 equivalents
of monomer.
All polymers obtained were of low polydispersity (IP ≤ 1.3),
which suggested that these polymerisations occurred without side
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8911–8922 | 8917
©

Table 8 e-Caprolactone polymerisation data for complex 7a
Run
Monomer/metal
T/◦C
Conversionb(%)
Mn calculated/g mol-1
Mn measuredc/g mol-1
PDI
1
2
3
4
500
500
500
300
700
900
500
500
25
40
60
40
40
40
40
40
7
41
82
77
42
29
50
47
4000
23 450
46 900
26 430
33 640
29 860
28 600
13 440
—
—
5510
9420
7410
8690
5760
16 900
5760
1.1
1.2
1.1
1.1
1.3
1.1
1.1
5
6
7d
8e
a Conditions: 40 mL of toluene; 5 mL of e-caprolactone; 1 equivalent of benzyl alcohol (from a 0.97 M solution in toluene). b Calculated by 1H NMR.
c Mn measured = 0.45 ¥ Mn GPC. d No benzyl alcohol. e 2 equivalents of benzyl alcohol.
Table 9 e-Caprolactone polymerisation data for complexes 1–11a
However, the electronic effect alone is not sufficient to explain
the variations in activity. Other factors, relating to the nature of the
alkoxide ligand have an influence on the polymerisation process.
Conversionb Mn calculated/ Mn measuredc/
Run Pro-catalyst (%)
g mol-1
g mol-1
PDI
For example, we noted that complexes with an ethoxide ligand
displayed better activities (in terms of conversion) than complexes
with the longer alkoxy group n-propoxide (Table 9, entries 8 and
11). Furthermore, the position of the electron withdrawing groups
on the ligand framework is of key importance. Most notably, the
use of the fluorinated alkoxide OC(CH3)(CF3)2 led to complete
de-activation of the complex for e-caprolactone polymerisation
(Table 9, entry 2 vs. entry 1). In this particular case, the enhanced
Lewis acidity of the metal centre is counter-balanced by the
reduced nucleophilicity of the alkoxide group.
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
13
0
7440
—
4390
—
1.1
—
25
64
53
60
41
65
78
74
73
14 300
36 610
30 320
34 320
23 450
37 180
44 620
42 330
41 760
8460
7830
8110
8050
5510
10 940
7920
15 040
11 860
1.1
1.1
1.3
1.1
1.1
1.1
1.2
1.3
1.1
10 10
11 11
In conclusion, crystal structure determinations for complexes
of the form [V(NAr)L(OR)]n have shown that when the alkoxide is
tert-butoxide (or the fluorinated derivative thereof), a monomeric
(n = 1) structure results, whereas for less bulky alkoxides, such as
ethoxy or propoxy groups, a dimeric structure (n = 2) is formed.
In combination with DMAC and ETA, such arylimido vanadium
complexes afford highly active (up to 75 000 g mmol-1 h-1 bar-1)
systems for polyethylene production. The use of fluorinated tert-
butoxides leads to improved initial activity, whilst the variation
a Conditions: monomer/metal = 500; 40 mL of toluene; 5 mL of e-
caprolactone; 1 equivalent of benzyl alcohol (from a 0.97 M solution
in toluene); 40 ◦C. b Calculated by 1H NMR. c Mn measured = 0.45 ¥ Mn
GPC.
4–10), the observed catalytic activity increased with the upfield
shift of the 51V NMR signal (Fig. 6). Complex 11 was excluded
from this correlation because of the atypical wide broadening of
the 51V NMR signal (w1/2 = 1800 Hz).
Fig. 6 Monomer conversion (%) with the 51V NMR chemical shift (ppm) for complexes 4–10.
8918 | Dalton Trans., 2009, 8911–8922 This journal is The Royal Society of Chemistry 2009
©

of the para substituent on the arylimido group revealed higher
activities for p-CF3 and p-Cl. In the case of e-caprolactone
polymerisation, better conversions (≥ 60%) were achieved using
dimeric pro-catalysts possessing propoxide bridges (complexes 4–
8), whereas far poorer conversions (≤ 25%) were observed when
using monomeric pro-catalysts (complex 2 was inactive).
Experimental
General
All manipulations were carried out under an atmosphere of
dinitrogen using standard Schlenk and cannula techniques or in
a conventional nitrogen-filled glove-box. Solvents were refluxed
over an appropriate drying agent and distilled and degassed prior
to use. Elemental analyses were performed by the microanalytical
services at London Metropolitan University. NMR spectra were
recorded on a Varian VXR 400 S spectrometer at 400 MHz
(1H) and 105.1 MHz (51V) or a Gemini 300 NMR spectrometer
at 300 MHz (1H) and 282.4 MHz (19F) at 298 K; chemical
shifts are referenced to the residual protio impurity of the
deuterated solvent (1H NMR) or to an external VOCl3/CDCl3
reference (51V NMR). IR spectra (Nujol mulls, KBr windows)
were recorded on Perkin-Elmer 577 and 457 grating spectropho-
tometers. Number and weight average molecular weights (Mn and
Mw) for all poly(e-caprolactone) samples were measured by gel
permeation chromatography (GPC) on a Polymer Laboratories
˚
PL GPC 220 instrument equipped with PL gel 5 A mixed C
column eluted in tetrahydrofuran at 1.0 mL min-1 at 40 ◦C
and calibrated using nine monodisperse polystyrene standards
in the range 580–1 233 000 Da. The complexes [V(NAr)(Ot-
Bu)3], [V(NAr)(OC(CH3)(CF3)2)3] and [V(NAr)(OR)3] (R = Et,
n-Pr, i-Pr) were prepared as described in the literature.7 All other
chemicals were obtained commercially and used as received unless
stated otherwise.
Synthesis of [V(Np-tolyl)(L)(Ot-Bu)] (1). [V(Np-tolyl)(Ot-
Bu)3] (0.94 g, 2.51 mmol) and LH2 (1.00 g, 2.28 mmol) were
refluxed in toluene (40 mL) for 12 h. Upon cooling the solution,
the volatiles were removed in vacuo and the residue was washed
with cold acetonitrile (40 mL). Recrystallisation from a saturated
acetonitrile solution, after standing at ambient temperature for
1–2 d afforded 1 as orange prisms. Yield: 0.68 g, 45%; mp. 186 ◦C
(decomposition). Elemental analysis calculated for C41H60NO3V:
1
C 73.96, H 9.08, N 2.10; found: C 73.91, H 8.93, N 2.05%. H
NMR (CDCl3, 400 MHz) d: 7.57 (s, 2 H, C6H2), 7.02 (s, 2 H,
C6H2), 6.45 (d, 2 H, J = 8.1 Hz, NC6H4), 5.67 (d, 2 H, J =
8.1 Hz, NC6H4), 5.51 (q, 1 H, J = 7.3 Hz, CHCH3), 2.12 (s, 3 H,
CH3C6H4N), 1.63 (m, 12 H, OC(CH3)3 and CHCH3), 1.30 (s, 36
H, C(CH3)3) ppm. 51V NMR (C6D6, 105.1 MHz) d: -538.10 ppm
(w1/2 360 Hz). 51V NMR (CDCl3, 105.1 MHz) d: -543.73 ppm
(w1/2 120 Hz). MS (MALDI): m/z 665 [M+], 591 [M+ - Ot-Bu].
IR (KBr, Nujol mull): 1596 (w), 1359 (s), 1258 (s), 1227 (m), 1157
(s), 1106 (m), 1005 (s), 887 (m), 846 (m), 800 (s), 772 (m), 753 (m),
687 (m), 664 (m), 652 (m), 629 (m), 617 (m), 590 (m) cm-1.
Synthesis of [V(Np-tolyl)(L)(OC(CF3)2Me)] (2). As for 1, but
using [V(Np-tolyl)(OC(CF3)2Me)3] (1.49 g, 2.1 mmol) and LH2
(0.85 g, 1.9 mmol) affording 2 as orange/red prisms. Yield:
0.60 g, 40%; mp. 128 ◦C. Elemental analysis calculated for
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8911–8922 | 8919
©

C41H54F6NO3V: C 63.64, H 7.03, N 1.81; found: C 63.77, H 6.97,
N 1.90%. 1H NMR (CDCl3, 400 MHz) d: 7.62 (s, 2 H, C6H2), 6.90
(s, 2 H, C6H2), 6.11 (d, 2 H, J = 8.2 Hz, NC6H4), 5.64 (q, 1 H,
J = 7.2 Hz, CH(CH3)), 4.66 (d, 2 H, J = 8.2 Hz, NC6H4), 2.00
(s, 3 H, CH3C6H4N), 1.96 (s, 3 H, C(CH3)(CF3)2), 1.67 (d, 3 H,
J = 7.2 Hz, CH(CH3)), 1.36 (s, 18 H, C(CH3)3), 1.29 (s, 18 H,
C(CH3)3) ppm. 51V NMR (CDCl3, 105.1 MHz) d: -315.40 ppm
(w1/2 120 Hz). 51V NMR (C6D6, 105.1 MHz) d: -316.53 ppm (w1/2
500 Hz).19F NMR (CDCl3, 282.4 MHz) d: -77.81 ppm. MS (EI):
m/z 773.2 [M+]. IR (Nujol mull, KBr): 1599 (w), 1514 (m), 1309
(m), 1293 (m), 1262 (s), 1214 (w), 1192 (w), 1157 (m), 1094 (s),
1021 (s), 975 (m), 934 (w), 879 (w), 800 (s), 735 (w), 722 (m) cm-1.
N 1.94%. 1H NMR (CDCl3, 400 MHz) d: 7.57 (s, 2 H, C6H2), 7.04
(s, 2 H, C6H2), 6.93 (d, 2 H, J = 8.3 Hz, NC6H4), 5.79 (d, 2 H, J =
8.3 Hz, NC6H4), 5.43 (m, 2 H, CHCH3 and CH(CH3)2), 1.59 (d,
3 H, J = 7.2 Hz, CHCH3), 1.55 (d, 6 H, J = 6.1 Hz, CH(CH3)2),
1.31 (s, 18 H, C(CH3)3), 1.29 (s, 18 H, C(CH3)3) ppm. 51V NMR
(105.1 MHz, CDCl3) d: -413.17 ppm (w1/2 260 Hz). MS (EI): m/z
705.3 [M]+. IR (Nujol mull, KBr): 1238 (m), 1294 (m), 1261 (s),
1245 (w), 1226 (m), 1212 (w), 1156 (m), 992 (m), 922 (w), 907 (m),
877 (w), 864 (w), 851 (m), 769 (w), 689 (w), 661 (m), 638 (w), 595
(w) cm-1.
Synthesis of [V(Np-(OMe)C6H4)(L)(Oi-Pr)]2 (7). As for 1, but
using [V(Np-(OMe)C6H4)(Oi-Pr)3] (1.05 g, 3.0 mmol) and LH2
(1.18 g, 2.7 mmol) affording 7 as orange/red prisms. Yield: 1.38 g,
77%; mp. 92 ◦C. Elemental analysis calculated for C40H58NO4V: C
71.94, H 8.75, N 2.10; found: C 71.84, H 8.83, N 1.90%. 1H NMR
(300 MHz, CDCl3) d: 7.59 (s, 2 H, C6H2), 7.02 (s, 2 H, C6H2), 6.15
(d, 2 H, J = 8.9 Hz, NC6H4), 5.72 (d, 2 H, J = 8.9 Hz, NC6H4),
5.46 (m, 2 H, CH(CH3) and CH(CH3)2), 3.60 (s, 3 H, CH3OC6H4),
1.62 (d, 3 H, J = 7.3 Hz, CH(CH3)), 1.55 (d, 6 H, J = 6.2 Hz,
CH(CH3)2), 1.30 (s, 36 H, C(CH3)3) ppm. 51V NMR (105.1 MHz,
CDCl3) d: -360.5 ppm (w1/2 365 Hz). MS (EI): m/z 667.3 [M]+.IR
(Nujol mull, KBr): 1587 (m), 1512 (w), 1299 (w), 1261 (m), 1228
(w), 1163 (m), 1105 (s), 1035 (s), 914 (w), 802 (s), 722 (w), 635
(w) cm-1.
Synthesis of [V(Np-(Cl)C6H4)(L)(Ot-Bu)] (3). As for 1, but
using [V(Np-(Cl)C6H4)(Ot-Bu)3] (1.27 g, 3.2 mmol) and LH2
(1.27 g, 2.9 mmol) affording 3 as orange/red prisms. Yield: 1.17 g,
59%;mp. 122 ◦C. Elementalanalysis calculatedfor C40H57ClNO3V:
C 70.01, H 8.37, N 2.04; found: C 69.86, H 8.38, N 1.90%. 1H NMR
(CDCl3, 400 MHz) d: 7.56 (s, 2 H, C6H2), 7.03 (s, 2 H, C6H2), 6.62
(d, 2 H, J = 8.6 Hz, NC6H4), 5.66 (d, 2 H, J = 8.6 Hz, NC6H4),
5.46 (q, 1 H, J = 7.2 Hz, CHCH3), 1.61 (m, 12 H, OC(CH3)3 and
CHCH3), 1.29 (s, 36 H, C(CH3)3) ppm. 51V NMR (105.1 MHz,
CDCl3) d: -414.2 ppm (w1/2 514 Hz). MS (EI): m/z 686.3 [M]+.
IR (Nujol mull, KBr): 1260 (s), 1228 (w), 1200 (w), 1157 (m), 907
(m), 878 (w), 869 (w), 849 (m), 770 (w), 757 (w), 737 (w), 689 (w),
654 (w), 636 (m), 6199 (w), 594 (m) cm-1.
Synthesis of [V(Np-tolyl)(L)(On-Pr)]2 (8). As for 1, but using
[V(Np-tolyl)(On-Pr)3] (0.70 g, 2.1 mmol) and LH2 (0.84 g,
1.9 mmol) affording 8·2(CH2Cl2) as orange/red prisms after
recrystallisation from CH2Cl2. Yield: 0.98 g, 79%; mp. 118 ◦C. Ele-
mental analysis calculated for C40H58NO3V (sample dried in-vacuo
for 12 h, -2 CH2Cl2): C 73.70, H 8.97, N 2.15; found: C 73.82, H
8.88, N 2.23%. 1H NMR (400 MHz, CDCl3) d: 7.61 (s, 2H, C6H2),
6.99 (s, 2H, C6H2), 6.42 (d, 2 H, J = 8.2 Hz, NC6H4), 5.62 (d, 2 H,
J = 8.2 Hz, NC6H4), 5.45 (q, 1 H, J = 7.1 Hz, CH(CH3)), 5.34 (m,
2 H, OCH2CH2CH3), 2.34 (m, 2 H, OCH2CH2CH3), 2.13 (s, 3 H,
CH3C6H4N), 1.67 (d, 3 H, J = 7.1 Hz, CH(CH3)), 1.41 (s, 18 H,
C(CH3)3), 1.30 (s, 18 H, C(CH3)3), 0.85 (t, 3 H, OCH2CH2CH3)
ppm. 51V NMR (105.1 MHz, CDCl3) d: -442.93 (w1/2 650 Hz).
MS (EI): m/z 651.3 [M]+. IR (Nujol mull, KBr): 1295 (m), 1261
(w), 1245 (w), 1227 (m), 1202 (w), 1157 (m), 1112 (m), 1038 (m),
1009 (m), 976 (m), 909 (w), 889 (w), 880 (w), 867 (w), 834 (s), 816
(m), 803 (m), 783 (w), 774 (m), 753 (m), 650 (w), 624 (w), 613 (m),
583 (m) cm-1.
Synthesis of [V(Np-tolyl)(L)(Oi-Pr)]2 (4). As for 1, but us-
ing [V(Np-tolyl)(Oi-Pr)3] (0.70 g, 2.1 mmol) and LH2 (0.85 g,
1.9 mmol) affording 4 as orange/red prisms. Yield: 0.86 g, 68%;
mp. 98 ◦C. Elemental analysis calculated for C40H58NO3V: C 73.70,
H 8.97, N 2.15; found: C 73.62, H 8.43, N 2.15%. 1H NMR (CDCl3,
400 MHz) d: 7.57 (s, 2 H, C6H2), 7.02 (s, 2 H, C6H2), 6.46 (d, 2 H,
J = 8.2 Hz, NC6H4), 5.65 (d, 2 H, J = 8.2 Hz, NC6H4), 5.46 (m,
2 H, CHCH3 and CH(CH3)2), 2.12 (s, 3 H, CH3C6H4), 1.62 (d, 3
H, J = 7.3 Hz, CHCH3), 1.55 (d, 6 H, J = 6.1 Hz, CH(CH3)2),
1.30 (s, 36 H, C(CH3)3) ppm. 51V NMR (105.1 MHz, CDCl3) d:
-383.5 ppm (w1/2 466 Hz). MS (EI): m/z 651.3 [M]+. IR (Nujol
mull, KBr): 1260 (s), 1227 (m), 1201 (w), 1156 (w), 910 (m), 867
(m), 752 (w), 638 (m), 614 (w), 580 (w) cm-1.
Synthesis of [V(Np-ClC6H4)(L)(Oi-Pr)]2 (5). As for 1, but
using [V(Np-(Cl)C6H4)(Oi-Pr)3] (0.74 g, 2.1 mmol) and LH2
(0.84 g, 1.9 mmol) affording 5 as orange/red prisms. Yield: 0.98 g,
76%; mp. 96 ◦C. Elemental analysis calculated for C39H55ClNO3V:
1
C 69.68, H 8.25, N 2.08; found: C 69.82, H 8.36, N 2.02%. H
Synthesis of [V(Np-(CF3)C6H4)(L)(On-Pr)]2 (9). As for 1, but
using [V(Np-(CF3)C6H4)(On-Pr)3] (0.46 g, 1.2 mmol) and LH2
(0.48 g, 1.1 mmol) affording 9·CH3CN as orange/red prisms.
Yield: 0.40 g, 52%; mp. 100 ◦C. Elemental analysis calculated
for C40H55F3NO3V (sample dried in-vacuo for 12 h, -CH3CN): C
68.07, H 7.85, N 1.98; found: C 68.16, H 7.76, N 1.91%. 1H NMR
(CDCl3, 400 MHz) d: 7.61 (s, C6H2), 7.00 (s, 2 H, C6H2), 6.91 (d,
2 H, J = 8.3 Hz, NC6H4), 5.76 (d, 2 H, J = 8.3 Hz, NC6H4),
5.42 (q, 1 H, J = 7.3 Hz, CHCH3), 5.35 (m, 2 H, OCH2CH2CH3),
2.33 (m, 2 H, OCH2CH2CH3), 1.67 (d, 3 H, J = 7.3 Hz, CHCH3),
1.42 (s, 18 H, C(CH3)3), 1.29 (s, 18 H, C(CH3)3), 0.88 (t, 3 H, J =
7.3 Hz, OCH2CH2CH3) ppm. 51V NMR (105.1 MHz, CDCl3) d:
-503.5 ppm (w1/2 428 Hz). MS (EI): m/z 705.3 [M]+. IR (Nujol
mull, KBr): 1324 (m), 1261 (m), 1227 (w), 1158 (m), 1129 (m),
1105 (m), 1069 (w), 1036 (w), 1007 (m), 977 (w), 907 (w), 881 (w),
NMR (CDCl3, 400 MHz) d: 7.57 (s, 2 H, C6H2), 7.04 (s, 2 H,
C6H2), 6.63 (d, 2 H, J = 8.6 Hz, NC6H4), 5.65 (d, 2 H, J = 8.6 Hz,
NC6H4), 5.43 (m, 2 H, CH(CH3) and CH(CH3)2), 1.62 (d, 3 H, J =
7.3 Hz, CHCH3), 1.55 (d, 6 H, J = 6.1 Hz, CH(CH3)2), 1.30 (s, 36
H, C(CH3)3) ppm. 51V NMR (105.1 MHz, CDCl3) d: -395.9 ppm
(w1/2 470 Hz). MS (EI): m/z 672.3 [M]+. IR (Nujol mull, KBr):
1568 (w), 1261 (m), 1224 (w), 1157 (w), 1109 (m), 1090 (m), 1014
(m), 932 (w), 881 (w), 866 (w), 824 (m), 802 (s), 773 (w), 752 (w),
731 (m), 689 (w), 637 (m), 596 (w), 580 (m), 570 (m) cm-1.
Synthesis of [V(Np-(CF3)C6H4)(L)(Oi-Pr)]2 (6). As for 1, but
using [V(Np-(CF3)C6H4)(Oi-Pr)3] (0.81 g, 2.1 mmol) and LH2
(0.85 g, 1.9 mmol) affording 6 as orange/red prisms. Yield:
0.62 g, 45%; mp. 100 ◦C. Elemental analysis calculated for
C40H55F3NO3V: C 68.07, H 7.85, N 1.98; found: C 68.12, H 7.75,
8920 | Dalton Trans., 2009, 8911–8922
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The Royal Society of Chemistry 2009
©

868 (w), 840 (m), 802 (m), 772 (w), 722 (w), 694 (w), 646 (w), 635
(m), 585 (m) cm-1.
C(6)–C(10) in the imido group were modelled as disordered over
two sets of positions with major occupancy of 68.8(8)%. Where
disorder was modelled, restraints were applied to both geometry
and anisotropic displacement parameters.
Synthesis of [V(Np-ClC6H4)(L)(l-OEt)]2 (10). As for 1, but
using [V(Np-(Cl)C6H4)(OEt)3] (0.53 g, 1.7 mmol) and LH2 (0.68 g,
1.5 mmol) affording 10·CH2Cl2 as orange/red prisms after recrys-
tallisation from CH2Cl2. Yield: 0.52 g, 51%; mp. 97 ◦C. Elemental
analysis calculated for C38H53ClNO3V (sample dried in-vacuo for
12 h, -CH2Cl2): C 69.34, H 8.12, N 2.13; found: C 69.15, H 7.98,
N 2.12%. 1H NMR (CDCl3, 400 MHz) d: 7.59 (s, 2 H, C6H2), 7.00
(s, 2 H, C6H2), 6.61 (d, 2 H, J = 8.6 Hz, NC6H4), 5.67 (d, 2 H, J =
8.6 Hz, NC6H4), 5.47 (m, 3 H, CH(CH3) and CH2CH3), 1.74 (t,
3 H, J = 6.3 Hz, CH2CH3), 1.60 (d, 3 H, J = 7.4 Hz, CH(CH3)),
1.42 (s, 18 H, C(CH3)3), 1.30 (s, 18 H, C(CH3)3) ppm. 51V NMR
(105.1 MHz, CDCl3) d: -503 ppm (w1/2 80 Hz). MS (EI): m/z
658.3 [M]+. IR (Nujol mull, KBr): 1593 (m), 1567 (w), 1293 (m),
1261 (m), 1231 (m), 1201 (w), 1156 (m), 1112 (w), 1087 (m), 1027
(s), 1004 (m), 999 (m), 974 (w), 881 (m), 856 (w), 841 (w), 831 (w),
824 (w), 803 (m), 780 (w), 773 (w), 758 (w), 731 (m), 665 (w), 636
(w) cm-1.
Several of the crystals were weakly diffracting, leading to high
Rint values for 4, 8 and a low ratio of observed to unique reflections
for 5. In 6, a short contact between two tert-butyl hydrogen atoms
˚
was observed: H(19B) ◊ ◊ ◊ H(35B) 2.03 A. Neither tert-butyl group
is disordered, and in both cases the hydrogen atoms are in the local
optimal positions. This contact is therefore likely to be a packing
artefact.
Acknowledgements
The EPSRC is thanked for financial support. The EPSRC Mass
Spectrometry Service (Swansea, UK) and Rapra Smithers Ltd
(GPC on polyethylene samples) are thanked for data collection.
The EPSRC’s National Crystallography Service at the University
of Southampton is thanked for the collection of X-ray diffraction
data for 3.
Synthesis of [V(Np-tolyl)(L)(l-OEt)]2 (11). As for 1, but using
[V(Np-tolyl)(OEt)3] (0.61 g, 2.1 mmol) and LH2 (0.84 g, 1.9 mmol)
affording 11 as orange/red prisms. Yield: 0.96 g, 79%; mp.
128 ◦C. Elemental analysis calculated for C39H56NO3V: C 73.44, H
8.85, N 2.20; found: C 73.36, H 8.80, N 2.14%. 1H NMR (CDCl3,
400 MHz) d: 7.60 (s, 2 H, C6H2), 6.98 (s, 2 H, C6H2), 6.42 (d, 2 H,
J = 7.6 Hz, NC6H4), 5.66 (d, 2 H, J = 7.6 Hz, NC6H4), 5.50 (m,
3 H, CH(CH3) and CH2CH3), 2.13 (s, 3 H, CH3C6H4N), 1.74 (t,
3 H, J = 6.7 Hz, CH2CH3), 1.65 (d, 3 H, J = 7.0 Hz, CH(CH3)),
1.42 (s, 18 H, C(CH3)3), 1.29 (s, 18 H, C(CH3)3) ppm. 51V NMR
(105.1 MHz, CDCl3) d: -154.2 ppm (w1/2 1800 Hz). MS (EI): m/z
637.3 [M]+. IR (Nujol mull, KBr): 1292 (w), 1261 (w), 1244 (w),
1230 (m), 1201 (m), 1157 (m), 1134 (m), 1112 (m), 1088 (m), 977
(m), 932 (w), 919 (w), 907 (m), 890 (m), 882 (w), 868 (w), 834 (s),
816 (w), 783 (w), 774 (w), 753 (m), 687 (w), 668 (w), 649 (w), 636
(m), 617 (w), 605 (s), 585 (m) cm-1.
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