Nickel and iron complexes with oxazoline- or pyridine-phosphonite ligands; synthesis, structure and application for the catalytic oligomerisation of ethylene

Article abstract of DOI:10.1039/b401792g

The bis(oxazolinyl)phenylphosphonite ligand 5 (bis(4,4-dimethyl-2-(1- hydroxy-1-methylethyl)-4,5-dihydrooxazole)phenylphosphonite, NOPON ^Me2)) and the new pyridine-phosphonite ligand 6 (2-ethyl(1′- methyl-1′hydroxy)pyridine-6H-dibenz[c,e][1,2]oxaphosphorin) have been used for the preparation of the mononuclear complexes [NiCl₂(NOPON ^Me2)] 18 and [NiCl₂(6)₂] 19, respectively, which catalyze the oligomerisation of ethylene with activities up to 57300 mol C₂H₄ mol Ni^-1 h^-1 (19 in the presence of only 6 equivalents of AlEtCl₂). The selectivities for C₄ dimers were as high as 90% (18 in the presence of only 2 equivalents of AlEtCl₂) with selectivities for 1-butene of 21-12% of the C₄ fraction. In the presence of 400 or 800 equivalents of MAO as cocatalyst, complex 19 yielded turnover frequencies of 7400 mol C ₂H₄ mol Ni^-1 h^-1 and 13200 mol C₂H₄ mol Ni^-1 h^-1, respectively. The selectivities for 1-butene and ethylene dimers were similar to those obtained with AlEtCl₂. The fact that 19 with a cyclic phosphonite moiety leads to higher activities and selectivities than 18 which contains an acyclic phosphonite group underlines the importance of the ligand on the catalytic properties of its metal complex. An unprecedented dinuclear iron complex [FeCl₂(4,4-dimethyl-2-{(1-hydroxy-1-methyl)ethyl}-4,5- dihydrooxazolate)]₂ 20 was also obtained which contains two pentacoordinated metal centers coordinated by a bridging-chelating oxazolinealcoholate. Complexes 18-20 are paramagnetic in solution, as determined by the Evans method.

Full text of DOI:10.1039/b401792g

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Nickel and iron complexes with oxazoline- or pyridine-phosphonite
ligands; synthesis, structure and application for the catalytic
oligomerisation of ethylene†
Fredy Speiser,a Pierre Braunstein*a and Lucien Saussineb
a Laboratoire de Chimie de Coordination (UMR 7513 CNRS), Université Louis Pasteur,
4 rue Blaise Pascal, F-67070 Strasbourg Cédex, France. E-mail: braunst@chimie.u-strasbg.fr.
b Institut Français du Pétrole, Direction Catalyse et Séparation, CEDI René Navarre, BP 3,
F-69390 Vernaison, France
Received 5th February 2004, Accepted 23rd March 2004
First published as an Advance Article on the web 20th April 2004
The bis(oxazolinyl)phenylphosphonite ligand 5 (bis(4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydro-
oxazole)phenylphosphonite, NOPONMe2)) and the new pyridine-phosphonite ligand 6 (2-ethyl(1Ј-methyl-1Ј-
hydroxy)pyridine-6H-dibenz[c,e][1,2]oxaphosphorin) have been used for the preparation of the mononuclear
complexes [NiCl2(NOPONMe2)] 18 and [NiCl2(6)2] 19, respectively, which catalyze the oligomerisation of ethylene
with activities up to 57300 mol C2H4 mol NiϪ1 hϪ1 (19 in the presence of only 6 equivalents of AlEtCl2). The
selectivities for C4 dimers were as high as 90% (18 in the presence of only 2 equivalents of AlEtCl2) with selectivities
for 1-butene of 21–22% of the C4 fraction. In the presence of 400 or 800 equivalents of MAO as cocatalyst, complex
19 yielded turnover frequencies of 7400 mol C2H4 mol NiϪ1 hϪ1 and 13200 mol C2H4 mol NiϪ1 hϪ1, respectively. The
selectivities for 1-butene and ethylene dimers were similar to those obtained with AlEtCl2. The fact that 19 with a
cyclic phosphonite moiety leads to higher activities and selectivities than 18 which contains an acyclic phosphonite
group underlines the importance of the ligand on the catalytic properties of its metal complex. An unprecedented
dinuclear iron complex [FeCl2(4,4-dimethyl-2-{(1-hydroxy-1-methyl)ethyl}-4,5-dihydrooxazolate)]2 20 was also
obtained which contains two pentacoordinated metal centers coordinated by a bridging-chelating oxazoline-
alcoholate. Complexes 18–20 are paramagnetic in solution, as determined by the Evans method.
oligomerisation or polymerisation of α-olefins.10 These include
nickel complexes prepared in situ with the monodentate phos-
Introduction
Phosphonite ligands have found numerous applications in
phonites 4 which were patented by the Mitsubishi Chemical
homogeneous catalysis, especially in hydroformylation.1–7 The
Corporation for the dimerisation of trans-2-butene.11
bidentate phosphonites 1 and 2 were prepared by the group of
Börner and applied in the hydroformylation of 4-octene,5 and
Ru() complexes of the C2-symmetric tridentate phosphonite
3 catalyze the asymmetric cyclopropanation of olefins and
transfer hydrogenation of ketones.8
Olefin dimerisation and oligomerisation is typically per-
formed using homogeneous late-transition metal catalysts, with
nickel playing a central role.12 As part of our interest in the
development of new ethylene oligomerisation catalysts13 and
in order to examine the influence of a tridentate vs. a bidentate
functional phosphonite ligand on the catalytic activity and
selectivity of Ni() complexes in the oligomerisation of ethyl-
ene, the new pyridine-phosphonite ligand 6 was synthesized and
its properties compared to those of the tridentate ligand bis-
(oxazolinyl)phenylphosphonite 5.8
Despite the considerable current interest in the chemistry
of P,O- and P,N-type functional ligands and the catalytic
properties of their metal complexes,9 only few examples of
phosphonite complexes have been reported for the catalytic
This should also allow us to examine the influence of a cyclic
phosphonite moiety on the ligand and complex stability. Some
of the results presented here have given rise to a patent.13e
† Dedicated to Prof. F. Sécheresse on the occasion of his 60th birthday.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 1 5 3 9 – 1 5 4 5
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In addition, a new dinuclear Fe() complex was obtained,
originally from 5 after breaking of the P–O bonds, and subse-
quently directly prepared from the corresponding oxazoline-
alcohol ligand.
(4)
Results and discussion
Ligand synthesis
Bis(4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydro-
oxazole)phenylphosphonite 58 (abbreviated NOPONMe2 in the
following) was prepared by reaction of the oxazoline alcohol
713d,14 with PPhCl2 in the presence of triethylamine at Ϫ78 ЊC
(eqn. (1)):
(5)
(1)
When we attempted to extend this method to the synthesis of
the tridentate pyridine-phosphonite 8, only a product mixture
was obtained. The HCl liberated during the reaction leads
to the formation of 10 and 12 (eqns. (2) and (3)). Dehydration
of the pyridine-alcohol
9 leads to the corresponding
2-isopropenylpyridine 10 which was identified in 1H NMR
spectroscopy by the doublets for the olefinic protons at δ 5.25
and 5.92, respectively.
amounts of [NiCl2(DME)] (DME = 1,2-dimethoxyethane) with
5 or 6, respectively, in CH2Cl2 for 12 h at 25 ЊC. After work-up,
the complexes were isolated in 75 and 80% yields (eqns. (6) and
(7)).
(2)
(6)
(7)
The phosphonite 8 underwent an Arbuzov-like reaction15 in
the presence of HCl yielding a phosphonium ion 11 (31P{1H}
NMR δ Ϫ48) which quantitatively led to phosphonate 12
(31P{1H} NMR singlet at δ 16.5) (eqn. (3)).
Preliminary tests have shown that the presence of HCl in the
reaction medium can be avoided by replacing PPhCl2 with
PPh[N(CH3)2]16a,b as the phosphorus precursor.16c After reflux-
ing the latter with 2.3 equiv. of the pyridine-alcohol 9 in THF
for 24 h, 8 was formed as the major product (eqn. (4)). The
synthesis still has to be improved in order to use only stoichio-
metric quantities of pyridine alcohol since residual 9 proved
difficult to separate.
The bidentate phosphonite 6 was prepared by reacting the
lithium alcoholate 14 with one equivalent of 6-chloro-6H-
dibenz[c,e][1,2]oxaphosphorin17 15 at Ϫ78 ЊC. After workup,
racemic 6 was isolated as a white oil in 80% yield (eqn. (5))
Both Ni() complexes 18 and 19 are paramagnetic, with
magnetic moments of 2.85 and 1.7 µB, respectively, as deter-
mined by the Evans method.19 This indicates that 18 retains a
trigonal bipyramidal geometry in solution. The low magnetic
moment of 19 suggests a distorted square-planar coordination
geometry in solution.20–23 Literature values for pentacoord-
inated and tetrahedral Ni() complexes are usually found in the
range 3.0–4.0 µB.20,21,24 Our values are slightly different but
magnetic properties are strongly dependent on the ligand field
and considerable fluctuations of the magnetic moments are
often observed due to equilibria in solution.21,23,25
Synthesis of the metal complexes
Following earlier studies with the chiral NOPONiPr 3 or achiral
NOPONMe2 5 ligands in Ru() and Pd() chemistry and
asymmetric catalysis,8,18 and with Ni() phosphinito-oxazoline
and -pyridine complexes 16 and 17,13d the nickel phosphonite
complexes 18 and 19 were synthesised by reacting equimolar
(3)
D a l t o n T r a n s . , 2 0 0 4 , 1 5 3 9 – 1 5 4 5
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The complex [Ni(NOPONMe2)Cl2] 18 was characterized by
IR spectroscopy, elemental analysis and X-ray diffraction. In
the IR spectrum, a shift of the νCN absorption is observed from
1661 cmϪ1 (free ligand)8 to 1620 cmϪ1 (coordinated ligand). A
similar coordination shift of the νCN absorption was observed
in the corresponding [Ru(NOPONMe2)Cl2] complex.8 The X-ray
structure of 18 shows a trigonal bipyramidal coordination
geometry which is in accordance with the paramagnetic
character of the complex (Fig. 1). The Ni, P, N(1) and N(2)
atoms are almost coplanar, as in the ruthenium complex
[Ru(NOPONMe2)Cl2].8 The two chlorine atoms form an angle of
142.87(3)Њ with each other and are placed in a sort of cavity
formed by the four methyl groups on the oxazolines. The two
six-membered chelate rings are not identical, as shown by the
different bite angles P–Ni–N(1) of 80.48(6)Њ and P–Ni–N(2)
of 89.28(6)Њ. Except for a slight backward pinch of the phos-
phorus atom, the structure of the ligand is very similar to that
of the free ligand.8
Table
1 Selected bond distances (Å) and angles (Њ) in
[Ni(NOPONMe2)Cl2] 18
Ni–P
2.2210(7)
C(7)–O(1)
P–O(1)
P–O(3)
O(3)–C(15)
C(15)–C(18)
C(18)–N(2)
1.448(3)
1.606(2)
1.593(2)
1.458(3)
1.527(4)
1.259(3)
Ni–N(1)
Ni–N(2)
Ni–Cl(1)
Ni–Cl(2)
N(1)–C(10)
C(10)–C(7)
2.241(2)
2.133(2)
2.2736(7)
2.2954(8)
1.269(3)
1.515(4)
Cl(1)–Ni–Cl(2)
Cl(1)–Ni–P
Cl(2)–Ni–P
Cl(1)–Ni–N(2)
Cl(2)–Ni–N(2)
P–Ni–N(1)
P–Ni–N(2)
Ni–P–O(1)
P–O(1)–C(7)
O(1)–C(7)–C(10)
C(7)–C(10)–N(1)
142.87(3)
108.43(3)
108.60(3)
93.74(6)
89.31(6)
80.48(6)
89.28(6)
114.45(9)
127.5(1)
113.7(2)
130.9(2)
C(10)–N(1)–Ni
N(1)–Ni–Cl(1)
N(1)–Ni–Cl(2)
N(1)–Ni–N(2)
Ni–N(2)–C(18)
N(2)–C(18)–C(15)
C(18)–C(15)–O(3)
C(15)–O(3)–P
O(3)–P–Ni
125.32(1)
96.11(6)
87.38(6)
167.60(8)
126.65(5)
130.7(2)
111.3(2)
126.3(2)
109.52(4)
98.7(1)
Cl(1)–P–O(3)
O(3)–P–O(1)
101.02(9)
Table 2 Selected bond distances (Å) and angles (Њ) in [FeCl2(4,4-di-
methyl-2-{(1-hydroxy-1-methyl)ethyl}-4,5-dihydrooxazolate)]2 20
Fe–O(2)
Fe–O(2Ј)
Fe–Cl(1)
Fe–Cl(2)
1.987(1)
2.014(1)
2.2075(7)
2.2273(7)
Fe–N(1)
2.085(2)
1.277(3)
1.501(3)
1.432(3)
N(1)–C(4)
C(4)–C(1)
C(1)–O(2)
Cl(1)–Fe–Cl(2)
O(2)–Fe–Cl(1)
O(2Ј)–Fe–Cl(1)
O(2)–Fe–Cl(2)
O(2Ј)–Fe–Cl(2)
N(1)–Fe–Cl(1)
N(1)–Fe–Cl(2)
106.90(3)
104.66(5)
110.81(5)
98.42(5)
142.28(5)
100.94(6)
95.24(6)
Fe–N(1)–C(4)
N(1)–C(4)–C(1)
C(4)–C(1)–O(2)
C(1)–O(2)–Fe
C(1)–O(2)–Fe
O(2)–Fe–O(2Ј)
114.3(1)
122.3(2)
104.1(2)
132.6(1)
120.3(1)
72.97(7)
Fig.
1
View of the molecular structure of the complex
[Ni(NOPONMe2)Cl2] 18 with thermal ellipsoids drawn at the 50%
probability level.
Reaction of an equimolar amount of the ligand NOPONMe2
5 with anhydrous FeCl3 for 12 h at room temperature afforded
a product containing an oxazoline ligand (shift of the νCN
vibration from 1661 to 1637 cmϪ1). The paramagnetic nature
of the product prevented the observation of NMR signals. An
X-ray structure determination showed that scission of the P–O
bonds had taken place to yield a new complex 20 containing
oxazoline-alcoholate ligands. It was then prepared in a more
rational way and 85% yield by reaction of equimolar amounts
of the oxazoline alcohol 7 with FeCl3 under similar conditions
(eqn. (8)).
Fig. 2 View of the molecular structure of the dinuclear FeIII complex
20 with thermal ellipsoids drawn at the 50% probability level.
bipyramidal [FeIII(O,N)Cl2]n complexes.26 According to the
Cambridge Structure Database, 20 appears to be the first
dinuclear Fe() complex with a trigonal bipyramidal coordin-
ation sphere of the metal centers. A magnetic moment of 5.98
µB was determined for complex 20 in solution, which is
in accord with literature values of 5.90 µB for other trigonal
bipyramidal iron() complexes.26–28
(8)
Catalytic oligomerisation of ethylene with the Ni(II) complexes
Complexes 18 and 19 were tested in the oligomerisation of
ethylene using MAO or AlEtCl2 as cocatalyst and the data are
given in Tables 3 and 4. For all catalytic tests an induction
period of about 3 min was observed. The catalysts were still
active when the oligomerisation reactions were stopped, as
indicated by monitoring of the ethylene consumption. For
comparison of activities and selectivities, [NiCl2(PCy3)2] was
chosen as a reference since it is a typical precatalyst used in the
dimerisation of ethylene with AlEtCl2 as cocatalyst.29
Complex 20 is a centrosymmetric dinuclear complex and the
coordination sphere of the Fe() centers is distorted trigonal
bipyramidal (Fig. 2, Table 2). The Fe–O(2) distance of 1.987(1)
Å is shorter than the Fe–O(2Ј) distance with 2.014(1) Å which is
in accord with observations made for mononuclear trigonal
D a l t o n T r a n s . , 2 0 0 4 , 1 5 3 9 – 1 5 4 5
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Table 3 Ethylene oligomerisation with complexes 18, 19 and [NiCl2(PCy3)2] using AlEtCl2 as cocatalyst
18a
18b
19a
[NiCl2(PCy3)2]a
AlEtCl2 (equiv.)
Selectivity C4 (%)
Selectivity C6 (%)
Selectivity C8 (%)
1.3
81
17
1.5
0.1
2
76
22
2
6
70
27
2.5
0.1
0.1
2
90
9
6
75
23
2
2
82
17
6
75
23
2
88
12
6
86
14
0.08
1.5
2.5
–
–
–
0.4
Selectivity C10 (%)
0.1
0.1
12700
26500
9
–
–
0.1
–
–
–
–
–
–
Selectivity C12 (%)
–
–
Productivity/g C2H4 g NiϪ1 hϪ1
TOF/mol C2H4 mol NiϪ1 hϪ1
α-Olefin (C4) (%)
8100
17000
21
15000
31400
9
7900
16500
19
18100
37900
10
21100
44200
22
27400
57300
12
700
1500
12
13000
27200
9
c
kα
0.16
0.21
0.26
<0.10
0.21
0.16
0.21
0.11
0.13
a Conditions: T = 30 ЊC, 10 bar C2H4, 35 min, 4.0 × 10Ϫ2 mmol Ni complex, solvent 15 mL toluene. b Conditions: T = 30 ЊC, 10 bar C2H4, 35 min, 4.0
× 10Ϫ2 mmol Ni complex, solvent 50 mL toluene. c kα = hexenes [mol]/butenes [mol].
Table 4 Ethylene oligomerisation with complex 19 using MAO as
cocatalysta, b
MAO (equiv.)
Selectivity C4 (%)
Selectivity C6 (%)
400
94
7
800
90
5
Selectivity C8 (%)
0.5
2
1.5
6300
13200
17
Selectivity C10 (%)
–
Productivity/g C2H4 g NiϪ1 hϪ1
TOF/mol C2H4 mol NiϪ1 hϪ1
α-Olefin (C4) (%)
3500
7400
19
c
kα
< 0.10
< 0.10
a Conditions: T = 30 ЊC, 10 bar C2H4, 35 min, 4.0 × 10Ϫ2 mmol Ni
complex, 20 mL toluene. b No C12 oligomers were detected. c kα
hexenes [mol]/butenes [mol].
=
In the presence of 1.3 equiv. of AlEtCl2, complex 18 showed
an activity of 17000 mol C2H4 mol NiϪ1 hϪ1 whereas 19 was
inactive (Fig. 3). With two equivalents of AlEtCl2, turnover
frequencies of 26500 mol C2H4 mol NiϪ1 hϪ1 (18) and 44200
mol C2H4 mol NiϪ1 hϪ1 (19) were obtained. Activities of up to
31400 mol C2H4 mol NiϪ1 hϪ1 (18) and 57300 mol C2H4 mol
NiϪ1 hϪ1 (19) and 27200 mol C2H4 mol NiϪ1 hϪ1 ([NiCl2(PCy3)2])
were observed when using 6 equiv. of cocatalyst.
Fig. 4 Selectivity of complex 18 for C4 oligomers in the presence of
different quantities of solvent. Conditions: T = 30 ЊC, 10 bar C2H4,
35 min, 4 × 10Ϫ2 mmol Ni.
Fig. 5 1-Butene selectivity within the C4 fraction of the complexes 18,
19 and [NiCl2(PCy3)2] using different quantities of AlEtCl2. Ref.:
[NiCl2(PCy3)2]. Conditions: T = 30 ЊC, 10 bar C2H4, 35 min, 4 × 10Ϫ2
mmol Ni, 15 mL toluene.
1.3 and 2 equivalents of cocatalyst (Fig. 5). This is probably
due to the exothermic character of the catalytic reaction and is
consistent with observations reported by other groups.30 The
limited selectivity for α-olefins could be due to (i) reversible β-H
elimination after ethylene insertion, followed by a reinsertion of
the olefin with the opposite regiochemistry and chain transfer
to give 2-butene, or (ii) a re-uptake mechanism leading to
isomerisation of 1-butene. This has not been further examined
in the present work. On the other hand, it has already been
reported that Ni() complexes can isomerise α-olefins.31
Fig. 3 Activity of the complexes 18 and 19 in the oligomerisation of
ethylene using different quantities of AlEtCl2. Ref.: [NiCl2(PCy3)2].
Conditions: T = 30 ЊC, 10 bar C2H4, 35 min, 4 × 10Ϫ2 mmol Ni, 15 mL
toluene.
Complexes 18 and 19 showed high selectivities, up to 76%
(18) and 82% (19) for ethylene dimers in the presence of only
2 equiv. of AlEtCl2 (Fig. 4). An increase in the amount of
cocatalyst from 2 to 6 equiv. led to selectivities of 70% (18) and
75% (19) for the C4 dimers, the remaining products were C6
and C8 oligomers and only for 18 were very small quantities of
C10 and C12 products observed.
In order to increase the selectivity of complex 18 for
1-butene, it was tested using 50 mL instead of 15 mL of toluene
as solvent in order to control better the reaction temperature.
The formation of C4 products was increased (Fig. 4), but no
Complexes 18 and 19 led to selectivities for 1-butene within
the C4 fraction of only 21% (18) and 22% (19) in the presence of
D a l t o n T r a n s . , 2 0 0 4 , 1 5 3 9 – 1 5 4 5
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noticeable influence on the selectivity for 1-butene was
observed. A similar effect upon catalyst dilution has been
observed recently with the related P,N chelate complexes 16 and
17.13d
presence of bridging-chelating oxazoline-alcoholates around
two pentacoordinated metal centres. It was inactive in the
catalytic conversion of ethylene, which may be related to the
stability of the bridging alkoxide ligand. All complexes were
paramagnetic in solution, as determined with the Evans
method.
When going from the tridentate 18 to the bidentate phos-
phonite ligand 19, the corresponding Ni() complexes display
higher turnover frequencies in the presence of 2 equiv. AlEtCl2,
26500 and 44200 mol C2H4 mol NiϪ1 Ϫ1, respectively, and the
h
Experimental
selectivity for 1-butene within the C4 fraction increases: 9% (18)
< 12% ([NiCl2(PCy3)]) < 22% (19), but remains modest.
All solvents were dried and distilled using common techniques
unless otherwise stated. All manipulations were carried out
When MAO was used as cocatalyst with complexes 18, 19
and [NiCl2(PCy3)2], only decomposition of 18 and [NiCl2-
(PCy3)2] and formation of zerovalent nickel was observed.
Complex 19 showed turnover frequencies of 7400 mol C2H4
mol NiϪ1 hϪ1 and 13200 mol C2H4 mol NiϪ1 hϪ1 in the presence
of 400 and 800 equiv. of MAO, respectively (Table 4). Select-
ivities of 94 or 90% for the ethylene dimers and of 19 or 17% for
1-butene within the C4 fraction were observed, respectively.
The iron complex 20 showed no activity in the oligomeris-
ation or polymerisation of ethylene with AlEtCl2 or MAO as
cocatalysts and the reasons for this are not established. In
general, the nature of the active species for the iron-based
bis(imino)pyridine and related catalysts are not as well under-
stood as those for the α-diimine nickel and palladium systems.10
Both Fe() and Fe() precursors have been reported to
produce identical polyethylene with similar activities.10b In our
case, it is possible that the stability of the Fe2O2 rhombus
accounts, at least in part, for the inactivity of complex 20.
using Schlenk techniques. NiCl2
ؒ6H O was dried by heating
2
for 6 h at 160 ЊC under vacuum. [NiX2
(DME)] (DME = 1,2-
dimethoxyethane; X = Cl, Br),33
2-pyridin-2-yl-propan-2-ol
11,34
6-chloro-6H-dibenz[c,e][1,2]oxaphosphorin 1717 and
bis(4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydro-
oxazole)phenylphosphonite 58 were prepared according
to the literature. Other chemicals were obtained from com-
mercial sources and were used without further purification
unless otherwise stated. The
1H, 31P{1H} and 13C{1H} NMR
spectra were recorded at 500.13 or 300.13, 121.5 and 76.0 MHz,
respectively, on FT Bruker AC300, Avance 300 and Avance
500 instruments. IR spectra in the range 4000–400 cmϪ1 were
recorded on a Bruker IFS66FT and a Perkin Elmer 1600 Series
FTIR. Gas chromatographic analyses were performed on a
Thermoquest GC8000 Top Series gas chromatograph using
a HP Pona column (50 m, 0.2 mm diameter, 0.5 µm film
thickness).
Preparation of 2-ethyl(1Ј-methyl-1Ј-hydroxy)pyridine-6H-
dibenz[c,e][1,2] oxaphosphorin 6
Conclusion
The new bidentate pyridine-phosphonite ligand 6 was prepared
in good yields and used, together with the tridentate bis-
(oxazolinyl)phenylphosphonite 5, for the preparation of the
mononuclear Ni() complexes 18 and 19. These complexes
catalyze the oligomerisation of ethylene with activities up to
57300 mol C2H4 mol NiϪ1 hϪ1 (19 in the presence of only 6
equiv. of AlEtCl2) (Table 3). The selectivities for ethylene
dimers were as high as 90% (18 in the presence of only 2 equiv.
of AlEtCl2). Similar activities have been reported for the
dimerisation of ethylene and propene with Ni() catalysts only
when 200 or more equivalents of MAO were used.32 Complex
19 yielded turnover frequencies of 7400 mol C2H4 mol NiϪ1 hϪ1
and 13200 mol C2H4 mol NiϪ1 hϪ1 in the presence of 400 and
800 equivalents of MAO, respectively (Table 4). The selectivities
for 1-butene and ethylene dimers were similar to those obtained
with AlEtCl2. The kα values given in Tables 3 and 4 correspond
to the ratio hexenes [mol]/butenes [mol] and not to a Schultz–
Flory constant since our catalysts are mainly dimerisation
catalysts. The fact that this value varies for a given catalyst as a
function of the nature or quantity of cocatalysts used and
increases as the turnover number increases suggests that some
incorporation of the butene formed occurs during chain growth
(a fraction of the C6 products results from consecutive reaction
of butene and ethylene).
Previous results with Ni() complexes of N,O ligands of the
type pyridine-alcohol or oxazoline-alcohol have illustrated
the influence of the basicity of the nitrogen donor ligand and a
less basic nitrogen moiety led to an increased α-olefin selectivity
and to higher turnover frequencies.13c The fact that complex 19
with a pyridine donor is more active and selective for 1-butene
than 18 which contains an oxazoline donor could be due to
the presence of a cyclic phosphonite moiety in the former.
However, it remains difficult to generalize such considerations
and it was recently found with other Ni() complexes that
phosphinitopyridine chelates led to more active catalysts than
phosphinitooxazolines, in which the nitrogen donor is less
basic.13d
To a solution of the pyridine alcohol 11 (0.580 g, 4.26 mmol) in
THF (30 mL) was added one equiv. of n-BuLi (1.6 molar
solution in hexanes, 4.26 mmol, 2.67 mL) at Ϫ78 ЊC. The solu-
tion was stirred for 1 h at Ϫ78 ЊC before a solution containing
one equiv. of 17 (1.00 g, 4.26 mmol) in THF (20 mL) was added
dropwise. The reaction mixture was heated to room temper-
ature overnight and the solution was hydrolyzed by addition of
degassed water (10 mL). The organic phase was separated and
the aqueous phase was extracted twice with Et2O (20 mL). The
organic phases were pooled and dried over MgSO4, filtered and
taken to dryness under reduced pressure affording the product
as a yellow oil. Yield: 1.16 g, 3.46 mmol, 80%. 1H NMR
(CDCl3): δ 1.72 (s, 3H, C(CH3)2), 1.79 (s, 3H, C(CH3)2), 7.17–
7.35 (m, 4 H, OPPh), 7.44 (m, 1H, py-H5), 7.65 (m, 1H, py-H4),
7.60 (m, 1H, py-H3), 7.43–8.04 (m, 4H, PPh), 8.04 (t, 1H, py-
3
3
H4, J(H,H) = 6.0 Hz), 9.2 (d, 1H, py-H6, J(H,H) = 8.1 Hz).
13C{1H} NMR (CDCl3): δ 28.9 (s, C(CH3)2), 79.5 (s, C(CH3)2)
114.8 (s, py-C5), 117.0 (s, POPh Co), 120.0 (m, POPh Cp, py-C3),
126.6 (d, PPh Co, 2J(P,C) = 13 Hz), 127.3 (s, PPh Cm), 128.8 (d,
1
PPh Cipso, J(P,C) = 24.0 Hz), 130.0 (m, POPh Cm, PPh Cp),
135.2 (s, py-C4), 137.0 (m, Ph–Co–Ph) 150.2 (s, py-C6), 156.1 (s,
POPh Cipso) 163.7 (s, py-C2). 31P{1H} NMR (CDCl3): δ 119.8 (s).
Anal. Calc. for C20H18NO2P: C, 71.63; H, 5.41; N: 4.18. Found:
C, 71.79; H, 5.72; N, 4.40%.
Preparation of 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-
ol (7)
This was prepared according to the literature,14 except that the
reaction mixture was heated for 20 min at 70 ЊC, 30 min at
120 ЊC and for 1 h at 150 ЊC before it was heated at 170 ЊC until
no further formation of water was observed in a Dean–Stark
trap.
Preparation of [Ni(NOPONMe2)Cl2] 18
To a solution of NOPONMe2 5 (0.420 g, 0.99 mmol) in THF
(30 mL) was added one equiv. of [NiCl2(DME)] (0.217 g,
0.99 mmol). The reaction mixture was stirred for 24 h at room
The unprecedented dinuclear Fe() complex 20 was fully
characterized by X-ray diffraction, which established the
D a l t o n T r a n s . , 2 0 0 4 , 1 5 3 9 – 1 5 4 5
1543

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Table 5 X-Ray experimental data for [Ni(NOPONMe2)Cl2] 18 and [FeCl3(4,4-dimethyl-2-{(1-hydroxy-1-methyl)ethyl}-4,5-dihydrooxazolate)]2 20
Formula
Mr
C22H33Cl2N2NiO4P
550.11
C16H28Cl4N2Fe2O4
565.90
Crystal system
Space group
Monoclinic
P21/c
Orthorhombic
Pbca
a/Å
b/Å
c/Å
18.2474(6)
9.4918(2)
15.6567(7)
102.837(5)
2644.0(3)
4
12.5227(3)
9.4272(2)
20.3311(5)
–
2400.17(3)
4
β/Њ
V/Å3
Z
Colour
Green
0.20 × 0.20 × 0.12
1.38
Green
0.15 × 0.15 × 0.12
1.566
Crystal dimensions/mm
Dc/g cmϪ3
F(000)
1152
1.026
1160
1.677
µ/mmϪ1
T /K
λ/Å
294
0.71073
180
0.71073
Radiation
Diffractometer
Scan mode
hkl Limits
θ Limits/Њ
Number of data meas.
Mo-Kα graphite monochromated
KappaCCD
Phi scans
Ϫ20,20/Ϫ11,10/Ϫ23,23
2.5/27.49
10258
0,16/0,12/0,26
2.88/27.50
2752
2152 (n = 2)
128
No. data with I > nσ(I )
Number of variables
3781 (n = 3)
289
R
Rw
0.033
0.048
0.0362
0.0837
GOF
1.019
0.330
1.067
0.447
Largest peak in final diff. map/e ÅϪ3
temperature. After 2 h a colour change from yellow to green
was observed. The green solution was filtered through Celite.
The Celite was washed with toluene (15 mL) and the organic
phase was evaporated to dryness. Finally the green solid was
dried in vacuo overnight. Yield: 0.660 g, 0.75 mmol, 75%. IR
(KBr): 1620 cmϪ1. Anal. Calc. for C22H33Cl2N2NiO4P: C, 48.04;
H, 6.05; N, 5.09. Found: C, 47.86; H, 6.30, N, N: 4.93%.
unreacted FeCl3. The solvent was evaporated and the solid was
dissolved in toluene (15 mL) and reprecipitated by addition of
hexane (25 mL). Filtration of the solid afforded the product as
a yellow solid. Yield: 1.29 g, 2.30 mmol, 85%.
Oligomerisation of ethylene
All catalytic reactions were carried out in a magnetically stirred
(900 rpm) 100 mL stainless steel autoclave. The interior of the
autoclave was protected from corrosion by a protective coating.
All catalytic tests were started at 30 ЊC and no cooling of the
reactor was done during reaction. The complex [NiCl2(PCy3)2]
was taken for comparative purposes (4 × 10Ϫ2 mmol of Ni). The
amount of precatalyst needed for six catalytic runs was dis-
solved in 60 mL of toluene. For each catalysis, 10 mL of this
solution were injected into the reactor. Depending on the
amount of cocatalyst added, between 0 and 5 mL of solvent
were added so that the total volume of all solutions was 15 mL.
This can be summarised by the following equation: 10 mL
(Ni-solution) ϩ y mL (solvent) ϩ z mL (cocatalyst solution) =
15 mL
Preparation of [NiCl2(2-ethyl(1Ј-methyl-1Ј-hydroxy)pyridine)-
6H-dibenz[c,e] [1,2]oxaphosphorin)] 19
To a solution of 6 (1.166 g, 3.47 mmol) in CH2Cl2 (40 mL) was
added one equiv. of [NiCl2(DME)] (0.739 g, 3.47 mmol) and the
solution was stirred for 12 h at room temperature. Then the
solution was filtered through Celite to separate unreacted
[NiCl2(DME)]. The solvent was evaporated and the brown solid
was dissolved in toluene (40 mL) and reprecipitated by addition
of hexane (60 mL). The solid was filtered off and dried under
vacuum for 12 h yielding the product as a brown solid. Yield:
1.29 g, 2.77 mmol, 80.0%. Anal. Calc. for C20H18Cl2NNiO2P: C,
51.67; H, 3.90; N, 3.01. Found: C, 51.90; H, 4.10; N, 3.20%.
When MAO was used as cocatalyst the total volume was
increased to 20 mL. After injection of the catalyst solution
under a constant low flow of ethylene, the reactor was brought
to working pressure and continuously fed with ethylene using a
reserve bottle placed on a balance to allow continuous monitor-
ing of the ethylene uptake. The temperature increase observed
resulted solely from the exothermicity of the reaction. The
oligomerisation products and remaining ethylene were only
collected from the reactor at the end of the catalytic experi-
ment. At the end of each test, the reactor was cooled to 10 ЊC
before transferring the gaseous phase into a 10 L polyethylene
tank filled with water. An aliquot of this gaseous phase was
transferred into a Schlenk flask, previously evacuated, for GC
analysis. The products in the reactor were hydrolyzed in situ by
addition of ethanol (10 mL), transferred in a Schlenk flask and
separated from the metal complexes by trap-to-trap distillation
(120 ЊC, 20 Torr). All volatiles were evaporated (120 ЊC, 20
Torr static pressure) and recovered in a second flask previously
immersed in liquid nitrogen in order to avoid any loss of
product. For gas chromatographic analyses, 1-heptene was used
as internal reference. The catalytic results are presented in
Tables 3 and 4.
Preparation of [FeCl2(4,4-dimethyl-2-{(1-hydroxy-1-methyl)-
ethyl}-4,5-dihydrooxazolate)]2 20
To a solution of NOPONMe2 5 (0.150 g, 0.36 mmol) in CH2Cl2
(30 mL) was added 0.8 equiv. of FeCl3 (0.045 g, 0.28 mmol) and
the solution was stirred for 14 h. After 2 h the opaque solution
became transparent. In order to separate unreacted FeCl3 the
yellow reaction mixture was filtered through Celite and the
Celite was washed with CH2Cl2 (40 mL). After the solvent was
evaporated, the yellow–white solid was dissolved in toluene (20
mL) and precipitated by the addition of hexane (50 mL). The
supernatant organic phase was separated with the help of a
cannula equipped with a filter cap. Finally the solid was dried
under vacuum for 12 h. Yield: 0.095 g, 0.17 mmol, 60%. IR
(CH2Cl2): 1637 cmϪ1. Anal. Calc. for C16H28Cl4Fe2N2O4: C,
33.96; H, 4.99; N, 4.95. Found: C, 34.21; H, 5.10; N, 5.00%.
Alternatively, 20 was better prepared by addition of one
equiv. of the oxazoline-alcohol 7 (0.424 g, 2.70 mmol) to a
suspension of anhydrous FeCl3 (0.438 g, 2.70 mmol) in CH2Cl2
(30 mL). The solution was stirred for 12 h at room temperature
and was then filtered through Celite in order to separate
D a l t o n T r a n s . , 2 0 0 4 , 1 5 3 9 – 1 5 4 5
1544

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10 (a) Late Transition Metal Polymerization Catalysis, ed. B. Rieger,
X-Ray structure determinations on 18 and 20
L. Saunders Baugh, S. Kacker and S. Striegler, Wiley-VCH,
Weinheim, 2003; (b) V. C. Gibson and S. K. Spitzmesser, Chem. Rev.,
2003, 103, 283; (c) S. D. Ittel, L. K. Johnson and M. Brookhart,
Chem. Rev., 2000, 100, 1169; (d ) G. J. P. Britovsek, V. C. Gibson and
D. F. Wass, Angew. Chem., Int. Ed., 1999, 38, 428, and references
therein.
Diffraction data were collected on a Kappa CCD diffract-
ometer using graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å). The relevant data are summarized in Table 5.
Data were collected using phi-scans and the structures were
solved by direct methods using the SHELX 97 software,35,36 and
the refinement was by full-matrix least squares on F 2. No
absorption correction was used. All non-hydrogen atoms were
refined anisotropically with H atoms introduced as fixed
contributors (dC–H = 0.95 Å, U11 = 0.04).
11 Y. Kawaragi and Y. Nakajima, Jpn. Kokai Tokkyo Koho,
JP 09268132 A2, 1996 (to Mitsubishi Chemical Industries Ltd.,
Japan).
12 (a) S. Muthukumaru Pillai, M. Ravindranathan and S. Sivaram,
Chem. Rev., 1986, 86, 353; (b) J. Skupinska, Chem. Rev., 1991, 91,
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13 (a) P. Braunstein, Y. Chauvin, S. Mercier, L. Saussine, A. DeCian
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43, in press; (d ) F. Speiser, P. Braunstein, L. Saussine and R. Welter,
Inorg. Chem., 2004, 43, 1649; (e) F. Speiser, P. Braunstein and
L. Saussine, Fr. Pat., FR 2837725 A1, 2003 (to Institut Francais
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Organometallics, 2004, 23, in press.
CCDC reference numbers 224561 and 224562.
See http://www.rsc.org/suppdata/dt/b4/b401792g/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We are grateful to the CNRS and the Ministère de la Recherche
et des Nouvelles Technologies (Paris) for support and to the
Institut Français du Pétrole for a PhD grant (F. S.) and financial
support. We thank Professor R. Welter, Dr A. DeCian and
N. Gruber (Service de diffraction des rayons X, Institut de
Chimie Strasbourg) for the determination of the crystal
structures.
14 L. N. Pridgen and G. M. Miller, J. Heterocycl. Chem., 1983, 20,
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