Nickel Complexes with New Bidentate P,N Phosphinitooxazoline and -Pyridine Ligands: Application for the Catalytic Oligomerization of Ethylene

Article abstract of DOI:10.1021/ic035132i

The phosphinitooxazoline 4,4-dimethyl-2-[1-oxy(diphenylphosphine)-1-methylethyl]-4,5-dihydrooxazole (9), the corresponding phosphinitopyridine ligands 2-ethyl-[1′-methyl-1′ -oxy(diphenylphosphino)]pyridine (11) and 2-ethyl-6-methyl-[1′ -methyl-1′-oxy(diphenylphosphino)]pyridine (12), which have a one-carbon spacer between the phosphinite oxygen and the heterocycle, and the homologous ligand 2-propyl-[2′-methyl-2′-oxy(diphenylphosphino)]pyridine (13), with a two-carbon spacer, were prepared in good yields. The corresponding mononuclear [NiCl₂(P,N)] complexes 14 (P,N = 9), 15 (P,N = 11), and 16 (P,N = 12) and the dinuclear [NiCl(μ-Cl)(P,N)]₂ 17 (P,N = 13) Ni(II) complex were evaluated in the catalytic oligomerization of ethylene. These four complexes were characterized by single-crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which indicated differences between the coordination spheres in the solution and the solid state. In the presence of methylalumoxane (MAO) or AlEt₃, only the decomposition of the Ni complexes was observed. However, complexes 14-17 provided activities up to 50 000 mol C₂H₄/(mol Ni)·h (16 and 17) in the presence of only 6 equiv of AlEtCl₂. The observed selectivities for ethylene dimers were higher than 91% (for 14 or 15 in the presence of only 1.3 equiv of AlEtCl₂). The activities for 14-17 were superior to that of [NiCl₂(PCy₃)₂], a typical dimerization catalyst taken as a reference. The selectivities of the complexes 14-17 for ethylene dimers and α-olefins were the same order of magnitude. From the study of the phosphinite 9/AlEtCl₂ system, we concluded that in our case ligand transfer from the nickel atom to the aluminum cocatalyst is unlikely to represent an activation mechanism.

Full text of DOI:10.1021/ic035132i

Inorg. Chem. 2004, 43, 1649−1658
Nickel Complexes with New Bidentate P,N Phosphinitooxazoline and
-Pyridine Ligands: Application for the Catalytic Oligomerization of
Ethylene†
,‡
Fredy Speiser,‡ Pierre Braunstein,* Lucien Saussine,§ and Richard Welter|
Laboratoire de Chimie de Coordination (UMR 7513 CNRS), UniVersite´ Louis Pasteur,
4 rue Blaise Pascal, F-67070 Strasbourg Ce´dex, France, Institut Franc¸ais du Pe´trole,
Direction Catalyse et Se´paration, CEDI Rene´ NaVarre, BP 3, F-69390 Vernaison, France, and
Laboratoire DECMET (UMR 7513 CNRS), UniVersite´ Louis Pasteur, 4 rue Blaise Pascal,
F-67070 Strasbourg Cedex, France
Received September 30, 2003
The phosphinitooxazoline 4,4-dimethyl-2-[1-oxy(diphenylphosphine)-1-methylethyl]-4,5-dihydrooxazole (9), the cor-
responding phosphinitopyridine ligands 2-ethyl-[1′-methyl-1′-oxy(diphenylphosphino)]pyridine (11) and 2-ethyl-6-
methyl-[1′-methyl-1′-oxy(diphenylphosphino)]pyridine (12), which have a one-carbon spacer between the phosphinite
oxygen and the heterocycle, and the homologous ligand 2-propyl-[2′-methyl-2′-oxy(diphenylphosphino)]pyridine (13),
with a two-carbon spacer, were prepared in good yields. The corresponding mononuclear [NiCl2(P,N)] complexes
14 (P,N ) 9), 15 (P,N ) 11), and 16 (P,N ) 12) and the dinuclear [NiCl(µ-Cl)(P,N)]2 17 (P,N ) 13) Ni(II) complex
were evaluated in the catalytic oligomerization of ethylene. These four complexes were characterized by single-
crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which indicated
differences between the coordination spheres in the solution and the solid state. In the presence of methylalumoxane
(MAO) or AlEt3, only the decomposition of the Ni complexes was observed. However, complexes 14−17 provided
activities up to 50 000 mol C H /(mol Ni)‚h (16 and 17) in the presence of only 6 equiv of AlEtCl2. The observed
2
4
selectivities for ethylene dimers were higher than 91% (for 14 or 15 in the presence of only 1.3 equiv of AlEtCl2).
The activities for 14−17 were superior to that of [NiCl2(PCy3)2], a typical dimerization catalyst taken as a reference.
The selectivities of the complexes 14−17 for ethylene dimers and R-olefins were the same order of magnitude.
From the study of the phosphinite 9/AlEtCl2 system, we concluded that in our case ligand transfer from the nickel
atom to the aluminum cocatalyst is unlikely to represent an activation mechanism.
Introduction
afford phosphinites in good yields.3-6 Among the best-known
examples are the TADDOP-type bisphosphonites 1 devel-
oped by Seebach and co-workers7 and the phosphinitoox-
azolines 2 recently reported by the groups of Pfaltz8 and
Richards.9 The TADDOP ligands 1 are used, e.g., in Pd-
catalyzed allylic substitutions,7 whereas the monophosphinite
systems 2 lead with great success to the Ir-catalyzed
Phosphinite ligands find widespread application in homo-
geneous catalysis,1,2 notably in asymmetric catalysis owing
to the availability of numerous chiral alcohols, which upon
reaction with a chlorophosphine in the presence of a base
† Dedicated to Professor E. Dinjus, on the occasion of his 60th birthday,
with our warmest congratulations.
* Author to whom correspondence should be addressed. E-mail: braunst@
chimie.u-strasbg.fr. Fax: +33 390 241 322.
(3) Ojima, I.; Clos, N.; Bastos, C. Tetrahedron 1989, 45, 6901.
(4) Brown, J. M.; Davies, S. G. Nature 1989, 342, 631-636.
(5) Blaser, H. U. Chem. ReV. 1992, 92, 935-952.
(6) Ohff, M.; Holz, J.; Quirmbach, M.; Bo¨rner, A. Synthesis 1998, 1391-
1417.
(7) Seebach, D.; Devaquet, E.; Ernst, A.; Hayakawa, M.; Ku¨hnle, F. N.
M.; Schweitzer, W. B.; Weber, B. HelV. Chim. Acta 1995, 78, 1636.
(8) Blankenstein, J.; Pfaltz, A. Angew. Chem., Int. Ed. 2001, 40, 4445-
4447.
‡ Laboratoire de Chimie de Coordination (UMR 7513 CNRS), Universite´
Louis Pasteur.
§ Institut Franc¸ais du Pe´trole, Direction Catalyse et Se´paration.
| Laboratoire DECMET (UMR 7513 CNRS), Universite´ Louis Pasteur.
(1) Agbossou, F.; Carpentier, J.-F.; Hapiot, F.; Suisse, I.; Mortreux, A.
Coord. Chem. ReV. 1998, 178-180, 1615-1645.
(2) Denis, P.; Croizy, J. F.; Mortreux, A.; Petit, F. J. Mol. Catal. 1991,
68, 159-175.
10.1021/ic035132i CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/04/2004
Inorganic Chemistry, Vol. 43, No. 5, 2004 1649

Speiser et al.
enantioselective hydrogenation of terminal olefins8,9 and to
Pd-catalyzed asymmetric alkylations.9
The basicity of the nitrogen donor will be increased by
replacing the oxazoline heterocycle in 9 with a pyridine in
11-13, and we will examine the influence of the ring size
of the metal chelate, which increases from six in 15 to seven
in 17, on the nature of the metal coordination sphere and on
the catalytic performances.
The bisphosphinite 3 was recently used with success by
Bedford and Welch in the Suzuki coupling reaction of
sterically hindered aryls.10 The bidentate aminophosphine
phosphinite ligand 4a was applied in Pd-catalyzed allylic
substitutions,11 and the bisphosphinite 4b, in asymmetric
Diels-Alder reactions.12 Notwithstanding these successes,8,10-12
only a few examples of the applications of phosphinites in
oligomerization, polymerization, copolymerization,13 or hy-
droformylation reactions have been reported.14 Thus, for
example, Keim and co-workers have used aryl bisphosphin-
ites 5 and 6 in ethylene/CO copolymerization and noted that
these ligands show increased stability in comparison to alkyl
phosphinites.13 Phosphinites 715 and 816 have been used in
hydroformylation reactions.
Results and Discussion
Synthesis of the Ligands. Phosphinites 9 and 10 were
prepared from 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)pro-
pan-2-ol (18), which was readily synthesized by heating
2-hydroxy-2-methylpropionic acid with 2-amino-2-methyl-
propan-1-ol at 160 °C in xylene.18 The reaction was com-
pleted when no further formation of water was observed in
a Dean-Stark trap (eq 1).
The phosphorus group was introduced by lithiation of 18
with 1 equiv of n-BuLi to give 19 and subsequent reaction
with either PPh2Cl or borane-protected P(i-Pr)2Cl. The
phosphinitooxazoline 9 was isolated in 76% yield (eq 2).
The borane-protected phosphinitooxazoline 20 (eq 3) de-
composed during deprotection, which may be due to the
strength of the base used (NHEt2) or the possible formation
of a stable carbocation upon breaking of the C-O bond.7
To investigate the potential of P,N-type phosphinite ligands
in the catalytic oligomerization of ethylene and compare them
with phosphinooxazolines and phosphinopyridines that we
have recently investigated,17 we have prepared the new
phosphinites 9-13 and their respective Ni complexes 14-
17, which were used as (pre)catalysts.
(13) Keim, W.; Maas, H. J. Organomet. Chem. 1996, 514, 271-276.
(14) Ungva´ry, F. Coord. Chem. ReV. 1999, 188, 263-296.
(15) Kostas, I. D. J. Organomet. Chem. 2001, 626, 221-226.
(16) Fuerte, A.; Iglesias, M.; Sa´nchez, F. J. Organomet. Chem. 1999, 588,
186-194.
(17) (a) Speiser, F. Ph.D. Thesis, Universite´ Louis Pasteur, Strasbourg,
France, 2002. (b) Speiser, F.; Braunstein, P.; Saussine, L.; Welter,
R. Organometallics 2004, in press. (c) Speiser, F.; Braunstein, P.;
Saussine, L. Organometallics 2004, in press.
(9) Jones, G.; Richards, C. J. Tetrahedron Lett. 2001, 42, 5553-5555.
(10) Bedford, R. B.; Welch, S. L. Chem. Commun. 2001, 129-130.
(11) Gong, L.; Chen, G.; Mi, A.; Jiang, Y.; Fu, F.; Cui, X.; Chan, A. S. C.
Tetrahedron: Asymmetry 2000, 11, 4297-4302.
(12) (a) Bruin, M. E.; Ku¨ndig, E. P. Chem. Commun. 1998, 2635-2636.
(b) Ku¨ndig, E. P.; Saudan, C. M.; Bernardinelli, G. Angew. Chem.,
Int. Ed. 1999, 38, 1219-1223.
(18) Pridgen, L. N.; Miller, G. M. J. Heterocycl. Chem. 1983, 20, 1223-
1230.
1650 Inorganic Chemistry, Vol. 43, No. 5, 2004

Catalytic Oligomerization of Ethylene
However, 20 can be stored under an inert atmosphere without
decomposition.
The synthesis of the phosphinitopyridines 11-13 required,
first, the metalation of either 2-bromopyridine, 2-bromo-6-
methylpyridine,19 or R-picoline with 1 equiv of n-BuLi,
followed by the addition of an excess of acetone to give
2-pyridin-2-ylpropan-2-ol (21),20-22 2-(6-methylpyridin-2-yl)-
propan-2-ol (22),20-22 or 2-methyl-1-pyridin-2-ylpropan-2-
ol (23) in yields of 60, 70, and 71%, respectively, after
vacuum distillation (eqs 4 and 5).
Figure 1. View of the molecular structure of 14 with thermal ellipsoids
drawn at the 50% probability level.
corresponding ligand for 12 h in CH2Cl2 at 25 °C. After
workup, the Ni complexes were isolated in 64-79% yields
(eqs 8-10). All of the complexes were paramagnetic and
were therefore best characterized by X-ray diffraction
(Figures 1-4). These structure determinations allowed one
to appreciate the differences resulting from changes in the
ring size and substituents brought about by the various
ligands. The coordination of ligand 9 in 14 was indicated in
The phosphorus moiety was then introduced by lithiation at
-78 °C and subsequent reaction with 1 equiv of PPh2Cl.
After workup, the pyridinyl phosphinites 11-13 were
isolated in 80, 91, and 85% yields, respectively, as transpar-
ent yellow oils, which solidified upon standing for a longer
period of time.
infrared spectroscopy by the shift of the νCN absorption from
1661 cm-1 (free ligand) to 1630 cm-1 (coordinated ligand).
Similarly, a comparison of the IR data obtained between
ligands 11-13 and the corresponding complexes 15-17
shows that the heterocyclic nitrogen is always coordinated
to the metal center (Table 1).23 The X-ray structure of 14
(Figure 1) shows a distorted, tetrahedral-coordination ge-
Synthesis of the Nickel Complexes. The nickel(II)
phosphinitopyridine complexes 14-17 were prepared by the
reaction of equimolar amounts of [NiCl2(DME)] with the
(19) Wang, Z.; Reibenspies, J.; Motekaitis, R. J.; Martell, A. E. J. Chem.
Soc., Dalton Trans. 1995, 1511-1518.
(20) Tsukahara, T.; Swenson, D. C.; Jordan, R. F. Organometallics 1997,
16, 3303-3313.
(21) Pasquinet, E.; Rocca, P.; Marsais, F.; Godard, A.; Que´guiner, G.
Tetrahedron 1998, 54, 8771-8782.
(22) Tre´court, F.; Breton, G.; Bonnet, V.; Mongin, F.; Marsais, F.;
Que´guiner, G. Tetrahedron 2000, 56, 1349-1360.
Inorganic Chemistry, Vol. 43, No. 5, 2004 1651

Speiser et al.
Figure 2. View of the molecular structure of 15 with thermal ellipsoids
drawn at the 50% probability level.
Figure 4. View of the molecular structure of 17 with thermal ellipsoids
drawn at the 50% probability level.
Table 1. Characteristic Vibrations (cm-1) for the Uncoordinated
Phosphinitopyridines 11-13 and the Corresponding Ni(II) Complexes
15-17
νCdC
νcycle
996
νR sens
νâ(C-H)
Figure 3. View of the molecular structure of 16 with thermal ellipsoids
drawn at the 50% probability level.
ligand 11
complex 15
1569
1599
695
692
1099
1107
1000, 1028
ometry for the metal center, and selected bond distances and
angles are given in Table 2. The six-membered chelate ring
shows a distorted boatlike conformation with the Ni atom
and Cl1 out of the P-O-C13-N plane. The opening of the
Cl1-Ni-Cl2 angle [125.71(3)°] compared to that in a
regular tetrahedron is accompanied by a closing of the
N-Ni-P angle.
In contrast to the situation in 14, the X-ray structure of
15 shows a slightly distorted square-planar-coordination
geometry for the Ni atom (Figure 2 and Table 3). The Ni
atom is in the mean plane passing through Cl1, Cl2, N, and
P [distance 0.0(3) Å]. The sum of the bond angles around
Ni is 360.69°. However, a magnetic moment of 2.87 µB was
determined in solution, which corresponds to a tetrahedral
coordination geometry.24-27
ligand 12
complex 16
1573
1604
997
1008, 1034
696
693
1099
1112
ligand 13
complex 17
1569
1602
997
1002, 1030
695
692
1099
1105
Table 2. Selected Bond Lengths (Å) and Angles (deg) in 14
Ni-P
Ni-N
Ni-Cl1
Ni-Cl2
2.2649(8)
1.987(2)
2.2229(7)
2.2078(9)
P-O1
1.623(2)
1.456(3)
1.509(3)
1.285(3)
O1-C13
C13-C16
N-C16
Cl1-Ni-Cl2
Cl1-Ni-P
Cl2-Ni-P
Cl1-Ni-N
Cl2-Ni-N
125.71(3)
109.87(3)
105.35(3)
104.68(6)
114.54(6)
P-Ni-N
91.30(7)
124.8(2)
109.3(2)
128.0(2)
P-O1-C13
O1-C13-C16
C16-N-Ni
conformation, which generates a sort of cavity limited by
one of the P-phenyl groups.
The X-ray structure of 16 also shows a distorted square-
planar-coordination geometry of the Ni atom, which is
slightly more distorted toward tetrahedral than that in 15
(Scheme 1 and Table 4).
The bond distances are similar to those in 14 except for
the Ni-P bond, which is 0.136 Å shorter. The folding of
the ligand around the Ni-C13 hinge creates a rooflike
(23) Pfeffer, M.; Braunstein, P.; Dehand, J. Spectrochim. Acta, Part A 1974,
30, 331-340.
(24) Sacconi, L.; Nannelli, P.; Nardi, N.; Campigli, U. Inorg. Chem. 1965,
4, 943-949.
(25) Venanzi, L. M. J. Chem. Soc. A 1958, 719-724.
(26) Dori, Z.; Gray, H. B. J. Am. Chem. Soc. 1966, 88, 1394-1398.
(27) Fro¨mmel, T.; Peters, W.; Wunderlich, H.; Kuchen, W. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 907-909.
1652 Inorganic Chemistry, Vol. 43, No. 5, 2004

Catalytic Oligomerization of Ethylene
Table 3. Selected Bond Lengths (Å) and Angles (deg) in 15
Cl1, and Cl1a, with the Cl2 atom occupying the apical
position. The Ni atom is out of this plane by 0.66(1) Å. In
the latter description, the atoms N, Cl1, and Cl2 would form
the basis of a trigonal bipyramid, with the Ni center being
situated in their plane [distance of 0.004(1) Å]. In comparison
to 14-16, 17 exhibits slightly longer metal-ligand bond dis-
tances, which is related to its increased coordination number.
Magnetic moments of 2.67 (14), 2.87 (15), 3.04 (16), and
2.82 (17) µB were observed in solution using the Evans
method.29-31 Literature values for tetrahedral Ni(II) com-
plexes are found in the range of 3.0-4.0 µB.25,28-32 Our
values are slightly different, but the magnetic moments of
Ni(II) complexes strongly depend on the ligand field in which
large differences can be observed.25,26,28,32,33 Furthermore,
equilibria between different structures may exist in solu-
tion.26,27,33 For 17, a change of the metal-coordination
geometry from square pyramidal to tetrahedral most likely
occurs in solution because a color change from ochre to violet
is observed. Many tetrahedral Ni(II) complexes are blue/
violet.28
Ni-P
2.129(1)
1.928(2)
2.223(1)
2.161(1)
P-O1
1.611(2)
1.477(3)
1.531(4)
1.355(3)
Ni-N
O1-C13
C13-C16
N-C16
Ni-Cl1
Ni-Cl2
Cl1-Ni-Cl2
Cl1-Ni-P
Cl2-Ni-P
Cl1-Ni-N
Cl2-Ni-N
93.59(4)
173.62(3)
90.67(3)
90.94(7)
171.04(7)
P-Ni-N
85.49(7)
122.8(2)
107.8(2)
126.5(2)
P-O1-C13
O1-C13-C16
C16-N-Ni
Scheme 1. Boat and Roof Conformations of the Six-Membered
Chelate Rings in the Nickel Phosphinite Complexes 14-16
Table 4. Selected Bond Lengths (Å) and Angles (deg) in 16
Ni-P
2.123(2)
1.916(7)
2.167(2)
2.231(2)
P-O
1.601(6)
1.476(9)
1.491(10)
1.370(10)
Ni-N
O-C13
C13-C16
N-C16
Ni-Cl1
Ni-Cl2
Catalytic Ethylene Oligomerization with the Nickel-
(II) Phosphinite Complexes 14-17. The nickel(II) phos-
phinitooxazoline complex 14 and the nickel phosphinitopy-
ridine complexes 15-17 were tested in the oligomerization
of ethylene in order to examine the influence of the basicity
of the nitrogen donor and the chelate ring size on the catalytic
characteristics of the complexes. In the presence of methyl-
alumoxane (MAO) or AlEt3, complexes 14-17 were inac-
tive. Only the formation of zerovalent nickel was observed.
However, complexes 14-17 were active for ethylene oli-
gomerization when 1.3, 2, or 6 equiv of AlEtCl2 was used
as a cocatalyst. For comparison, we also tested under the
same conditions the complex [NiCl2(PCy3)2], a typical
ethylene dimerization catalyst.34
For all of the catalytic tests, induction periods of ca. 3
min were observed. At the end of each catalysis, formation
of a black precipitate was observed. In the presence of 1.3
equiv of AlEtCl2, all complexes showed good activities
except for [NiCl2(PCy3)2], which was inactive. For 14-17,
turnover frequencies of 11 600 (14), 11 600 (15), 23 300 (16),
and 21 100 mol C2H4/(mol Ni)‚h (17) were observed (Tables
6-9). These values increased when 2 equiv of the cocatalyst
was used, and complexes 16 and 17 showed the highest
turnover frequencies (Figure 5). For [NiCl2(PCy3)2], only a
modest activity of 1600 mol C2H4/(mol Ni)‚h was observed.
Activities of 43 000 (15) and ca. 50 000 (14, 16, and 17)
mol C2H4/(mol Ni)‚h were obtained in the presence of 6
equiv of the cocatalyst (Figure 5).
Cl1-Ni-Cl2
Cl1-Ni-P
Cl2-Ni-P
Cl1-Ni-N
Cl2-Ni-N
95.08(9)
P-Ni-N
85.6(2)
125.5(4)
108.8(6)
124.8(5)
93.94(9)
158.75(10)
164.8(2)
90.6(2)
P-O-C13
O-C13-C16
C16-N-Ni
Table 5. Selected Bond Lengths (Å) and Angles (deg) in 17
Ni-P
Ni-N
Ni-Cl1
Ni-Cl1a
Ni-Cl2
2.362(1)
2.041(2)
2.367(1)
2.418(1)
2.287(1)
P-O
1.611(2)
1.470(2)
1.532(3)
1.513(3)
1.352(3)
O-C13
C13-C16
C16-C17
N-C17
Cl1-Ni-Cl2
Cl1a-Ni-Cl2
Cl1a-Ni-Cl1
Cl1-Ni-P
Cl1a-Ni-P
Cl2-Ni-P
Cl1-Ni-N
109.95(4)
95.85(2)
86.67(2)
90.00(2)
167.58(2)
96.53(2)
142.23(6)
Cl1a-Ni-N
Cl2-Ni-N
P-Ni-N
89.95(5)
107.82(5)
85.37(5)
129.1(1)
115.1(2)
119.3(2)
117.4(1)
P-O-C13
O-C13-C16
C13-C16-C17
C17-N-Ni
This increased distortion in 16 is assigned to the presence
of the methyl substituent in the 6 position of the pyridine
ring, although the Ni atom is in the mean plane passing
through the atoms Cl1, Cl2, N, and P [distance of 0.0(3) Å].
The sum of the bond angles around Ni is 365.22°. Complex
16 shows a magnetic moment of 3.04 µB in solution, which
corresponds to a tetrahedral-coordination sphere, as observed
for compounds 14 and 15.24-27
To examine the influence of an increased chelate ring size
on the Ni-coordination sphere and the catalytic properties
of the resulting complex, we prepared ligand 13 and its
Ni(II) complex 17. In contrast to complexes 14-16, 17 is a
centrosymmetric dinuclear complex with a pentacoordinated
Ni(II) center (Figure 4 and Table 5). This underlines the
considerable influence that the chelate ring size may exert
on the coordination geometry of the metal. The metal is out
of the N-Cl1-Cl2 plane by 0.004(1) Å and out of the
P-Cl1-Cl2 plane by 0.021(1) Å. Its coordination sphere
may be viewed as an intermediate between distorted square
pyramidal and trigonal bipyramidal. In the former case, the
base of the square pyramid is formed by the atoms P, N,
(28) Holleman, A. F.; Wiberg, E. Holleman-Wiberg Lehrbuch der Anor-
ganischen Chemie, 91-100 ed.; Walter de Gruyter: Berlin, 1985; pp
1152-1156.
(29) Evans, D. F. J. Chem. Soc. 1959, 2003.
(30) Lo¨liger, J.; Scheffold, R. J. Chem. Educ. 1972, 49, 646-647.
(31) Sur, S. K. J. Magn. Reson. 1989, 82, 169-173.
(32) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon
Press: Oxford, 1984; pp 1337-1349.
(33) Hayter, R. G.; Humiec, F. S. Inorg. Chem. 1965, 4, 1701-1706.
(34) (a) Knudsen, R. D. Prepr.sAm. Chem. Soc., DiV. Pet. Chem. 1989,
572-576. (b) Commereuc, D.; Chauvin, Y.; Le´ger, G.; Gaillard, J.
ReV. Inst. Fr. Pet. 1982, 37, 639-649.
Inorganic Chemistry, Vol. 43, No. 5, 2004 1653

Speiser et al.
Table 6. Ethylene Oligomerization with Precatalyst 14 Using AlEtCl2
Table 9. Ethylene Oligomerization with Precatalyst 17 Using AlEtCl2
as the Cocatalyst, in 15a and 50 mLb of Toluenec
as the Cocatalysta,b
14a
14b
AlEtCl2 (equiv)
selectivity C4 (%)
selectivity C6 (%)
selectivity C8 (%)
productivity (g
C2H4/(g Ni)‚h)
TOF (mol
6
59
35
5
2
61
35
0
1.3
79
20
AlEtCl2 (equiv)
selectivity C4 (%)
selectivity C6 (%)
selectivity C8 (%)
selectivity C10 (%)
productivity (g
C2H4/(g Ni)‚h)
TOF (mol
6
2
1.3
92
8
6
2
1.3
91
9
64
33
3
81
18
1
82
16
2
87
13
0.1
0
1
23 800
19 500
12 400
0
0
0
0.2
0
49 400
40 800
21 100
23 600 14 000 5500
17 700 13 700 11 600
C2H4/(mol Ni)‚h)
R-olefin (C4) (%)
6
0.33
8
0.31
17
0.22
c
49 500 30 100 11 600 37 100 28 600 24 300
kR
C2H4/(mol Ni)‚h)
a Conditions: T ) 30 °C, 10 bar of C2H4, 35 min, 4 × 10-2 mmol of Ni
complex, solvent ) 15 mL of toluene. b No C10-C12 oligomers were
detected. c kR ) 1-hexene (mol)/1-butene (mol).
R-olefin (C4) (%)
8
14
16
7
17
17
a Conditions: T ) 30 °C, 10 bar of C2H4, 35 min, 4 × 10-2 mmol of Ni
complex, solvent ) 15 mL of toluene. b Conditions: T ) 30 °C, 10 bar of
C2H4, 35 min, 4 × 10-2 mmol of Ni complex, solvent ) 50 mL of toluene.
c No C12 oligomers were detected.
Table 7. Ethylene Oligomerization with Precatalyst 15 Using AlEtCl2
as the Cocatalyst, in 15a and 50 mL of Tolueneb,c
15a
15b
AlEtCl2 (equiv)
selectivity C4 (%)
selectivity C6 (%)
selectivity C8 (%)
selectivity C10 (%)
productivity (g
C2H4/(g Ni)‚h)
TOF (mol
6
64
33
3
0.1
20 900
2
1.3
92
13
6
79
19
2
0.2
18 500
87
13
0.1
0.1
7800
16 300
18
5500
11 600
19
43 700
5
38 700
7
C2H4/(mol Ni)‚h)
R-olefin (C4) (%)
Figure 5. Activity of complexes 14-17 in the oligomerization of ethylene
using different quantities of AlEtCl2 as the cocatalyst. Conditions: T ) 30
°C, 10 bar of C2H4, 35 min, 4 × 10-2 mmol of Ni, toluene (15 mL); ref )
[NiCl2(PCy3)2].
a Conditions: T ) 30 °C, 10 bar of C2H4, 35 min, 4 × 10-2 mmol of Ni
complex, solvent ) 15 mL of toluene. b Conditions: T ) 30 °C, 10 bar of
C2H4, 35 min, 4 × 10-2 mmol of Ni complex, solvent ) 50 mL of toluene.
c No C12 oligomers were detected.
Table 8. Ethylene Oligomerization with Precatalyst 16 Using AlEtCl2
as the Cocatalysta,b
AlEtCl2 (equiv)
selectivity C4 (%)
selectivity C6 (%)
productivity (g
C2H4/(g Ni)‚h)
TOF (mol
6
71
29
23 800
2
80
20
21 200
1.3
80
20
11 100
49 900
9
44 400
10
23 300
15
C2H4/(mol Ni)‚h)
R-olefin (C4) (%)
a Conditions: T ) 30 °C, 10 bar of C2H4, 35 min, 4 × 10-2 mmol of Ni
complex, solvent ) 15 mL of toluene. b No C8-C12 oligomers were
detected.
Replacement of the oxazoline heterocycle with a pyridine
led to significantly higher activities for complexes 16 and
17 only when either 1.3 or 2 equiv of AlEtCl2 was used. No
notable difference was observed in the presence of 6 equiv
of the cocatalyst. Thus, an increase of the chelate ring size
from six to seven membered leads to the formation of more
active species in the presence of small amounts of AlEtCl2.
The influence of a larger chelate ring size on the catalytic
activity remains however modest, which may be due to
similar coordination polyhedra for 15-17 in solution.
Complexes 14-17 are very good dimerization catalysts
with selectivities for C4 products of 64-92% (14) (Figure
6). In all cases, the formation of C6 oligomers was observed
in the presence of 2 or 6 equiv of AlEtCl2, whereas C8
oligomers were also observed, although in small quantities,
except with 16, and C10 oligomers only with 14 and 15 as
Figure 6. Selectivities of the complexes 14-17 for ethylene dimers.
Conditions: T ) 30 °C, 10 bar of C2H4, 35 min, 4 × 10-2 mmol of Ni,
toluene (15 mL); ref ) [NiCl2(PCy3)2].
catalysts. The phosphinitopyridine complex 16 with a more
basic nitrogen donor showed a lower selectivity for ethylene
dimers than complex 15 with 1.3 and 2 equiv of the
cocatalyst (Figure 6). The behavior of 17 contrasts with that
of 14 and 15, which gave selectivities between 81 and 87%
for the dimerization products in the presence of 2 equiv of
the cocatalyst (Figure 6).
Complexes 14-17 led to selectivities for 1-butene of only
15-19% of the C4 fraction in the presence of 1.3 equiv of
the cocatalyst. This may be due to the exothermic character
1654 Inorganic Chemistry, Vol. 43, No. 5, 2004

Catalytic Oligomerization of Ethylene
cocatalyst in the oligomerization of ethylene using 14 as a
precatalyst in order to check whether the transfer of the
phosphinite ligand 9 from the nickel complex to AlEtCl2
would be the reason for the activity of complexes 14-17.
Using the same ratio of Al/Ni as in the other experiments,
the activity observed in this test was very low, and the
product distribution was shifted toward C6 and C8 oligomers
when compared to the results obtained for the complex 14
under similar conditions. Therefore, we do not believe that
the activation pathway involves direct interaction between
the Ni-coordinated ligand and the AlEtCl2 cocatalyst.
Figure 7. Selectivities of the complexes 14 and 15 for ethylene dimers in
the presence of different quantities of solvent. Conditions: T ) 30 °C, 10
bar of C2H4, 35 min, 4 × 10-2 mmol of Ni, 6 equiv of AlEtCl2.
of the catalytic reactions, which favors isomerization to
internal olefins.35,36 Therefore, complexes 14 and 15 were
tested using 50 mL instead of 15 mL of toluene as the solvent
in order to better control the reaction temperature (Tables
6 and 7). The reactions were less exothermic (by about
10-15 °C), but no significant influence on the amount of
1-butene formed could be detected. Surprisingly, the product
distribution with both complexes was shifted toward ethylene
dimers (Figure 7). The turnover frequencies decreased by
ca. 20% with 6 equiv of the cocatalyst but doubled in the
case of 14 with 1.3 equiv of the cocatalyst.
The stability of the phosphinite ligands may be of concern
in homogeneous catalysis. Such ligands may lead to Arbuzov
rearrangement, while Smith and co-workers reported the
rupture of a R-O bond in phosphates, phosphonates, and
phosphites in the presence of organoaluminum compounds
such as AlEtCl2 and the resulting formation of the aluminum
adduct 25 and alkyl or aryl chloride (eq 11).37 For a given
Conclusion
The new phosphinitooxazoline 9 and the phosphinitopy-
ridine ligands 11-13 were prepared in good yields for the
synthesis of the mononuclear 14-16 and dinuclear 17
Ni(II) complexes. These complexes were characterized by
single-crystal X-ray diffraction in the solid state and in
solution with the help of the Evans method, which indicated
differences between the metal-coordination spheres in the
solution and the solid state. These metal complexes were
evaluated for the catalytic oligomerization of ethylene. In
the presence of MAO and AlEt3, only the decomposition of
the Ni complexes was observed. However, complexes
14-17 provided activities up to 50 000 mol of C2H4/(mol
of Ni)‚h (16 and 17) in the presence of 6 equiv of AlEtCl2.
The selectivities for ethylene dimers were as high as 92%
(14 and 15) in the presence of only 1.3 equiv of AlEtCl2.
The precatalysts 14-17 led to a selectivity for 1-butene of
only 14-19%. The activities for 14-17 were superior to
that of [NiCl2(PCy3)2], a typical dimerization catalyst, which
was taken as a reference.34
At this stage, it is difficult to strictly relate the catalytic
performances of a Ni(II) complex to its coordination geom-
etry, in particular because structures intermediate between
square planar and tetrahedral are often encountered. The
subtle ligand or packing effects that may be responsible for
these structural changes in the solid state cannot be easily
extrapolated or do not apply to the structures in solution,
and the latter are difficult if not impossible to assess in situ.
Recent theoretical studies on the structures and energies of
the transition states for the insertion of the CdC bond of
various (functional) olefins into the metal-carbon bond of
generic models for the Ni(II) and Pd(II) complexes with
diimine (Brookhart) and salicylaldiminato (Grubbs) ligands
have shown that nickel systems show lower insertion barriers
than their palladium counterparts owing to their easier access
to the required tetrahedral transition state.38
alkyl group, the ease of elimination decreased in the series
as follows: (RO)2RPO/AlEtCl2 > (RO)3PO/AlEtCl2
>
(EtO)3P/AlEtCl2. Therefore, we felt it necessary to test the
stability of the phosphinite ligands using the diphenylphos-
phinitooxazoline 9 as an example. This ligand was reacted
at room temperature with 1 equiv of AlEtCl2 in toluene, and
the reaction was followed by 31P NMR spectroscopy. A
singlet at 34.6 ppm indicates the formation of a phosphinite/
AlEtCl2 complex whose suggested structure 26 is shown
below. After 3 days, slow decomposition of 26 was observed,
and new 31P NMR signals were observed between -10 and
-17 ppm, which correspond to PPh2Et species. The alumi-
num phosphinitooxazoline complex 26 was also tested as a
(35) Brown, S. J.; Masters, A. F. J. Organomet. Chem. 1989, 367, 371-
374.
(36) Abeywickrema, R.; Bennett, M. A.; Cavell, K. J.; Kony, M.; Masters,
A. F.; Webb, A. G. J. Chem. Soc., Dalton Trans. 1993, 59-68.
(37) Cohen, B. M.; Smith, J. D. J. Chem. Soc. A 1969, 2087-2089.
From the study of the phosphinite 9/AlEtCl2 system, we
concluded that in our case ligand transfer from the nickel
(38) Deubel, D. V.; Ziegler, T. Organometallics 2002, 21, 4432-4441.
Inorganic Chemistry, Vol. 43, No. 5, 2004 1655

Speiser et al.
Preparationof2-Ethyl-[1′-methyl-1′-oxy(diphenylphosphino)]-
pyridine (11). A solution of the pyridine alcohol 21 (1.73 g, 13
mmol) in 30 mL of THF was cooled to -78 °C and stirred for
30 min before 1 equiv of n-BuLi (1.6 M solution in hexanes,
8.13 mL, 13 mmol) was slowly added. After the solution was
stirred for 1 h at -78 °C, 1 equiv of PPh2Cl (2.30 mL, 2.78 g, 13
mmol) was added. The reaction mixture was brought to room
temperature overnight and then hydrolyzed by the addition of
degassed water (10 mL). The organic phase was separated, and
the aqueous phase was extracted twice with diethyl ether (20
mL). The organic fractions were dried over MgSO4, filtered, and
taken to dryness under reduced pressure, yielding the product as a
transparent oil (3.81 g, 12 mmol, 91%). 1H NMR (CDCl3) δ: 1.79
(s, 3H, C(CH3)2), 7.14 (m, 1H, py-H5), 7.34 (d, 1H, py-H3,
3J(H3,H4) ) 8.1 Hz), 7.35-7.50 (m, 10H, PPh2), 7.65 (m, 1H,
py-H4), 8.50 (d, 1H, py-H6, 3J(H6,H5) ) 8.1 Hz). 13C{1H}
NMR (CDCl3) δ: 28.4 (s, C(CH3)2), 80.0 (s, C(CH3)2), 114.8
atom to the aluminum cocatalyst is unlikely to represent an
activation mechanism.
Experimental Section
General Procedures. All solvents were dried and distilled using
common techniques unless otherwise stated. NiCl2‚6H2O was dried
by heating for 6 h at 160 °C under vacuum to afford anhydrous
NiCl2. NiX2(DME) (X ) Cl, Br),39 18,18 and 2-bromo-6-methylpy-
ridine19 were prepared according to the literature. Other chemicals
were commercially available and were used without further puri-
fication unless otherwise described. 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, or Avance
500 instruments. IR spectra in the range of 4000-400 cm-1 were
recorded on Bruker IFS66FT and Perkin-Elmer 1600 Series FTIR
instruments. 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). For
all complexes whose magnetic moments were determined with the
help of the Evans method, a CH3NO2-CD2Cl2 solution (80:20, v/v)
was used as the reference. The solvents were degassed and dried
using standard techniques. For a standard NMR experiment, a
0.055-0.10 M solution of the paramagnetic substance in CD2Cl2
was prepared.
2
(s, py-C5), 120.0 (s, py-C3), 126.6 (d, Ph-Co, J(P,C) ) 12.5
1
Hz), 127.3 (s, P-Phm), 128.8 (d, P-Cipso, J(P,C) ) 25.0 Hz),
130.0 (s, Ph-Cp), 135.2 (s, py-C4), 150.2 (s, py-C6), 163.7 (s,
py-C2). 31P{1H} NMR (CDCl3) δ: 89.3 (s). Anal. Calcd for
C20H20NOP: C, 74.75; H, 6.27; N, 4.36. Found: C, 74.32; H, 6.20;
N, 4.30.
Preparation of 2-Ethyl-6-methyl-[1′-methyl-1′-oxy(diphen-
ylphosphino)]pyridine (12). A solution of the pyridine alcohol 22
(1.79 g, 12 mmol) in 60 mL of THF was cooled to -78 °C, and 1
equiv of n-BuLi (1.6 M solution in hexanes, 7.4 mL, 12 mmol)
was slowly added. After the solution was stirred for 1 h at -78
°C, 1 equiv of PPh2Cl (2.64 g, 2.20 mL, 12 mmol) was added. The
reaction conditions and workup are similar to those for 11, yielding
the product as a transparent viscous liquid, which solidified upon
standing (5.7 g, 17 mmol, 85%). 1H NMR (CDCl3) δ: 1.78 (s, 6H,
Preparation of 4,4-Dimethyl-2-[1-oxy(diphenylphosphine)-1-
methylethyl]-4,5-dihydrooxazole (9). The oxazoline alcohol18 18
(1.083 g, 6.89 mmol) was dissolved in THF (50 mL), and the
solution was cooled to -78 °C before 1 equiv of n-BuLi (1.6 M
solution in hexanes, 4.30 mL, 6.89 mmol) was slowly added. After
the reaction mixture was stirred for 1 h at -78 °C, 1.0 equiv of
PPh2Cl (1.52 g, 1.3 mL, 6.89 mmol) was added. The solution was
further stirred for 2 h at -78 °C before it was brought to room
temperature overnight. The reaction mixture was hydrolyzed by
the addition of degassed water (10 mL), and the organic phase was
separated. The aqueous phase was extracted twice with diethyl ether
(20 mL). The organic phase was dried over MgSO4 and filtered.
The solvent was evaporated under reduced pressure, yielding the
product as a white oil (1.78 g, 6.89 mmol, 76%). IR (CH2Cl2):
3
C(CH3)2), 2.48 (s, 3H, py-CH3), 7.00 (d, 1H, py-H5, J(H,H) )
7.8 Hz), 7.10 (d, 1H, py-H3, 3J(H3,H4) ) 7.8 Hz), 7.20-7.30 (m,
10H, PPh2), 7.50 (t, 1H, py-H4, 3J(H,H) ) 7.8 Hz). 13C{1H} NMR
(CDCl3) δ: 23.1 (s, py-CH3), 28.4 (s, C(CH3)2), 80.0 (s, C(CH3)2),
2
114.8 (s, py-C5), 120.0 (s, py-C3), 126.6 (d, Ph-Co, J(P,C) )
1
15.5 Hz), 127.3 (s, Ph-Cm), 128.8 (d, Ph-Cipso, J(P,C) ) 25.6
Hz), 130.0 (s, P-Cp), 135.2 (s, py-C4), 150.2 (s, py-C5), 163.7
(s, py-C2). 31P{1H} NMR (CDCl3) δ: 88.8 (s). Anal. Calcd for
C21H22NOP: C, 75.21; H, 6.61; N, 4.18. Found: C, 75.55; H, 7.00;
N, 4.25.
1
1661 cm-1. H NMR (CDCl3) δ: 1.27 (s, 6H, C(CH3)2), 1.64 (s,
6H, OC(CH3)2), 3.75 (s, 2H, OCH2), 7.28-7.51 (m, 10H, PPh2).
13C{1H} NMR (CDCl3) δ: 26.5 (s, NC(CH3)2), 28.1 (s, OC(CH3)2),
67.3 (s, NC(CH3)2), 75.4 (s, OC(CH3)2), 79.0 (s, OCH2), 128.0-
131.7 (m, PPh2), 167.2 (s, CdN). 31P{1H} NMR (CDCl3) δ: 95.4
(s). Anal. Calcd for C20H24NO2P: C, 70.37; H, 7.09; N, 4.10.
Found: C, 70.61; H, 7.32; N, 4.23.
Preparation of 2-Propyl-[2′-methyl-2′oxy(diphenylphosphi-
no)]pyridine (13). A solution of the pyridine alcohol 23 (3.0 g, 20
mmol) in 60 mL of THF was cooled to -78 °C, and 1 equiv of
n-BuLi (1.6 M solution in hexanes, 12.4 mL, 20 mmol) was slowly
added. After the solution was stirred for 1 h at -78 °C, 1 equiv of
PPh2Cl (4.4 g, 3.70 mL, 20 mmol) was added. The reaction
conditions and workup were similar to those for 11, yielding the
product as a transparent viscous liquid, which solidified upon
Preparation of 4,4-Dimethyl-2-[1-oxy(diisopropylphosphine)-
1-methylethyl]-4,5-dihydrooxazole (10). The oxazoline alcohol
1818 (1.96 g, 12.5 mmol) was dissolved in 50 mL of toluene, and
3 equiv of NEt3 (3.79 g, 5.2 mL, 37.5 mmol) was added. After the
reaction mixture was cooled to 0 °C, 1.0 equiv of P(BH3)(i-Pr)2Cl
(1.92 g, 2.0 mL, 12.5 mmol) was added. The solution was further
stirred for 30 min at 0 °C before it was brought to room temperature.
After 1 h, the formation of a white precipitate was observed. The
reaction mixture was stirred for 10 h at room temperature before
the solution was filtered through Celite. The Celite was washed
twice with toluene (20 mL). The organic fractions were pooled and
evaporated under reduced pressure, yielding a transparent oil.
To deprotect the phosphinite 22, it was dissolved in 30 mL of
degassed NHEt2 and stirred for 10 h. After all volatiles were
evaporated, only the decomposition of the phosphinitooxazoline
was observed.
standing (5.7 g, 17 mmol, 85%). 1H NMR (CDCl3) δ: 1.42 (s, 6H,
3
C(CH3)2), 3.19 (s, 2H, py-CH2), 7.12 (t, 1H, py-H5, J(H5,H6,4
)
) 7.8 Hz), 7.30 (m, 1H, py-H3), 7.20-7.30 (m, 10H, PPh2), 7.75
(d, 1H, py-H4, 3J(H4,H5,3) ) 7.8 Hz), 8.51 (d, 1H, py-H6,
3J(H6,H5) ) 7.8 Hz. 13C{1H} NMR (CDCl3) δ: 26.5 (s, C(CH3)2),
49.9 (s, py-CH2), 69.2 (s, C(CH3)2), 119.9 (s, py-C5), 124.0 (s,
py-C3), 126.6 (d, Ph-Co, 2J(P,C) ) 16.5 Hz), 127.3 (s, Ph-Cm),
1
128.6 (d, Ph-Cipso, J(P,C) ) 22.3 Hz), 130.0 (s, Ph-Cp), 136.0
(s, py-C4), 147.0 (s, py-C5), 164.0 (s, py-C2). 31P{1H} NMR
(CDCl3) δ: 88.8 (s). Anal. Calcd for C21H22NOP: C, 75.21; H,
6.61; N, 4.18. Found: C, 74.75; H, 6.10; N, 3.95.
Preparation of [Nickel{1-[4,4-dimethyl-2-[1-oxy(diphenylphos-
phino)-1-methylethyl]]-4,5-dihydrooxazole} Dichloride] (14). To
(39) Cotton, F. A. Inorg. Synth. 1971, 13, 160-164.
1656 Inorganic Chemistry, Vol. 43, No. 5, 2004

Catalytic Oligomerization of Ethylene
a solution of the phosphinitooxazoline 9 (1.01 g, 2.97 mmol) in
CH2Cl2 (30 mL) was added 0.9 equiv of [NiCl2(DME)] (0.582 g,
2.67 mmol), and the reaction mixture was stirred for 2 h at room
temperature. After 15 min, a color change from orange to violet
was observed. The solution was then filtered through Celite to
separate unreacted [NiCl2(DME)], and the Celite was washed with
CH2Cl2 (30 mL). The organic phases were pooled, and the solvent
was evaporated. The violet solid was dissolved in 20 mL of toluene
and precipitated by the addition of hexane (40 mL). The violet
precipitate was allowed to settle, and the supernatant organic phase
was separated with a glass pipet. The solid was taken to dryness
under reduced pressure and dried under vacuum for 10 h, yielding
a violet powder (1.04 g, 2.27 mmol, 75%). IR (CH2Cl2): 1630 cm-1
(νCdN). Anal. Calcd for C20H24Cl2NNiO2P: C, 51.00; H, 5.14; N,
2.97. Found: C, 50.80; H, 4.85; N, 2.79.
Preparation of [Nickel{2-ethyl-[1′-methyl-1′-oxy(diphenylphos-
phino)]pyridine} Dichloride] (15). To a solution of the phos-
phinitopyridine 11 (0.896 g, 2.78 mmol) in CH2Cl2 (30 mL) was
added 0.9 equiv of [NiCl2(DME)] (0.546 g, 2.50 mmol), and the
reaction mixture was stirred for 2 h at room temperature. After 15
min, a color change from orange to brick red was observed. The
reaction conditions and workup were similar to those for 14,
affording a violet solid, which was dissolved in 20 mL of toluene
and precipitated by the addition of hexane (40 mL). The supernatant
organic phase was separated, and the solid was dried under vacuum
for 12 h, yielding a brick-red powder (0.77 g, 1.69 mmol, 68%).
1H NMR (CDCl3) δ: 2.58 (s, vbr, 6H, C(CH3)2), 7.1-9.1 (5 s,
vbr, 14H, 4(py-H), 10 PPh2). Anal. Calcd for C20H20Cl2NNiOP:
C, 53.27; H, 4.47; N, 3.11. Found: C, 52.93; H, 4.49; N, 2.87.
Preparation of [Nickel{2-ethyl-6-methyl-[1′-methyl-1′-oxy-
(diphenylphosphino)]pyridine} Dichloride] (16). To a solution
of the phosphinitopyridine 12 (1.420 g, 4.23 mmol) in CH2Cl2 (40
mL) was added 0.9 equiv of [NiCl2(DME)] (0.830 g, 3.81 mmol),
and the reaction mixture was stirred for 2 h at room temperature.
After 15 min, a color change from orange to violet was observed.
The reaction conditions and workup were similar to those for 14,
affording a violet solid, which was dissolved in 20 mL of toluene
and precipitated by the addition of hexane (40 mL). The supernatant
organic phase was separated, and the solid was dried under vacuum
for 12 h, yielding a violet-red powder (1.39 g, 2.99 mmol, 79%).
1H NMR (CDCl3) δ: 3.01 (s, 6H, C(CH3)2), 5.28 (s, 3H, py-CH3)
7.2-7.8 (m, 13H, 3(py-H), 10 PPh2). Anal. Calcd for C21H22Cl2-
NNiOP: C, 54.24; H, 4.77; N, 3.01. Found: C, 52.51; H, 4.95; N,
2.82.
Preparation of [Nickel{2-propyl-[2′-methyl-2′-oxy(diphen-
ylphosphino)]pyridine} Dichloride]2 (17). To a solution of the
phosphinitopyridine 13 (1.212 g, 3.62 mmol) in CH2Cl2 (40 mL)
was added 0.9 equiv of [NiCl2(DME)] (0.769 g, 3.50 mmol), and
the reaction mixture was stirred for 2 h at room temperature. After
15 min, a color change from orange to violet was observed. The
reaction conditions and workup were similar to those for 14,
affording a violet solid, which was dissolved in 20 mL of toluene
and precipitated by the addition of hexane (40 mL). The supernatant
organic phase was separated, and the solid was dried under vacuum
for 12 h, yielding an ochre-colored powder (1.26 g, 2.72 mmol,
75%). Anal. Calcd for C42H44Cl4N2Ni2O2P2: C, 54.24; H, 4.77; N,
3.01. Found: C, 54.00; H, 4.95; N, 3.15.
Preparation of 2-Pyridin-2-ylpropan-2-ol (21). A solution of
2-bromopyridine19 (11.0 mL, 17.87 g, 113 mmol) in 100 mL of
THF was cooled to -78 °C and stirred for 30 min before 1 equiv
of n-BuLi (1.6 M solution in hexanes, 70.71 mL, 113 mmol) was
slowly added over a period of 15 min. The reaction mixture was
stirred for 2 h at -78 °C before 40 mL of distilled acetone was
added, and the solution was brought to room temperature overnight.
After 4 h, the formation of an orange precipitate was observed.
The reaction mixture was hydrolyzed by transferring it into a
saturated NH4Cl solution (200 mL). The organic phase was
separated, and the aqueous phase was extracted twice with diethyl
ether (200 mL). The organic fractions were collected and dried over
Na2SO4. After filtration, the solvent was evaporated, and the
remaining orange-brown oil was distilled under vacuum (2 Torr,
1
45 °C), yielding a transparent liquid (9.30 g, 67 mmol, 60%). H
NMR (CDCl3) δ: 1.53 (s, 6H, C(CH3)2), 5.0 (s, 1H, OH), 7.14
3
(m, 1H, py-H5), 7.34 (d, 1H, py-H3, J(H3,H4) ) 8.1 Hz), 7.65
(m, 1H, py-H4), 8.50 (d, 1H, py-H6, 3J(H5,H6) ) 8.1 Hz). These
data are consistent with the literature values.20,22
Preparation of 2-(6-Methylpyridin-2-yl)propan-2-ol (22). A
solution of 2-bromo-6-methylpyridine19 (19.66 g, 114 mmol) in 150
mL of THF was cooled to -78 °C and stirred for 30 min before 1
equiv of n-BuLi (1.6 M solution in hexanes, 71.40 mL, 114 mmol)
was slowly added over a period of 15 min. The reaction conditions
and workup were similar to those for 21, yielding an orange-brown
oil that was distilled under vacuum (2 Torr, 75 °C) to afford a
1
transparent liquid (12.08 g, 80 mmol, 70%). H NMR (CDCl3) δ:
1.56 (s, 6H, C(CH3)2), 2.53 (s, 3H, py-CH3), 5.58 (s, 1H, OH),
3
7.00 (d, 1H, py-H3, J(H,H) ) 7.8 Hz), 7.10 (d, 1H, py-H5,
3J(H,H) ) 7.8 Hz), 7.57 (t, 1H, py-H4, 3J(H,H) ) 7.8 Hz). These
data are consistent with the literature values.20,22
Preparation of 2-Methyl-1-pyridin-2-ylpropan-2-ol (23). A
solution of R-picoline (21.20 g, 230 mmol) in 200 mL of THF
was cooled to -78 °C and stirred for 30 min before 1 equiv of
n-BuLi (1.6 M solution in hexanes, 142.0 mL, 230 mmol) was
slowly added over a period of 30 min. The reaction conditions and
workup were similar to those for 21, affording an orange-brown
oil that was distilled under vacuum (2 Torr, 60 °C) to give a
transparent liquid (24.67 g, 163 mmol, 71%). 1H NMR (CDCl3) δ:
1.21 (s, 6H, C(CH3)2), 2.92 (s, 2H, CH2), 5.60 (s, 1H, OH), 7.1 (d,
3
3
1H, py-H3, J(H,H) ) 7.7 Hz), 7.12 (d, 1H, py-H5, J(H,H) )
7.7 Hz), 7.65 (t, 1H, py-H4, 3J(H,H) ) 7.8 Hz), 8.53 (m, 1H, py-
H6). These data are consistent with the literature values.40
Oligomerization 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 °C, and no cooling of the reactor was done during the reaction.
After injection of the catalyst solution under a constant low flow
of ethylene, the reactor was pressurized to the desired pressure.
The temperature increase that was observed resulted solely from
the exothermicity of the reaction. When the alkylaluminum
compounds were used as cocatalysts, the activator was also injected
under a constant ethylene flow and finally brought to working
pressure. The reactor was continuously fed with ethylene by a
reserve bottle placed on a balance to allow continuous monitoring
of the ethylene uptake. In all of the catalytic experiments with MAO
and AlEtCl2, 4.0 × 10-2 mmol of the Ni complex were used. The
oligomerization products and remaining ethylene were only col-
lected from the reactor at the end of the catalytic experiment. At
the end of each test, the reactor was cooled to 10 °C 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 the addition of ethanol
(10 mL), transferred in a Schlenk flask, and separated from the
(40) Koning, B.; Buter, J.; Hulst, R.; Stroetinga, R.; Kellogg, R. M. Eur.
J. Org. Chem. 2000, 15, 2735-2743.
Inorganic Chemistry, Vol. 43, No. 5, 2004 1657

Speiser et al.
Table 10. Crystallographic Data for Complexes 14-17
14
15
16
17
formula
fw
crystal system
space group
a (Å)
C20H24Cl2NNiO2P
470.98
monoclinic
P21/c
8.999(2)
14.579(2)
16.535(2)
2166.0(6)
90
C20H20Cl2NNiOP
450.95
triclinic
P1h
9.151(5)
10.262(5)
11.874(5)
1020.4(9)
99.29(1)
108.43(1)
98.44(1)
2
C21H22Cl2NNiOP
464.98
monoclinic
P21/n
10.2634(3)
16.9550(5)
11.8716(4)
2045.34(11)
90
C42H44Cl4N2Ni2O2P2
929.95
triclinic
P1h
9.267(5)
9.280(5)
13.987(5)
1038.2(9)
96.05(1)
94.42(1)
118.67(1)
1
b (Å)
c (Å)
V (Å3)
R (deg)
â (deg)
γ (deg)
Z
93.16(5)
90
4
98.08(1)
90
4
color
violet
red
violet
ochre
crystal size, mm
0.10 × 0.10 × 0.08
0.10 × 0.10 × 0.08
0.10 × 0.10 × 0.08
0.11 × 0.14 × 0.08
D
calcd (g‚cm-3
)
1.444
1.468
1.510
1.487
µ (mm-1
)
1.231
1.86/27.49
4950
1.300
1.85/27.52
4645
1.299
2.11/27.51
4659
1.280
2.54/34.99
9028
θ limits (deg)
no. of data measured
no. of data with I > 2σ(I)
no. of variables
3521
245
3774
235
3521
245
6146
245
R
0.0369
0.0803
1.015
0.0357
0.1109
1.073
0.0888
0.2310
1.176
0.0677
0.0973
1.093
Rw
GOF on F2
correction was used. All non-hydrogen atoms were refined aniso-
tropically with H atoms mathematically introduced as fixed
contributors (SHELXL procedure). Full data-collection parameters
and structural data are available as the Supporting Information.
Crystallographic data for all of the structures in this paper have
been deposited with the Cambridge Crystallographic Data Centre,
CCDC 224957-224960. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, +44 1223 336033; e-mail,
deposit@ccdc.cam.ac.uk; web, http://www.ccdc.cam.ac.uk).
metal complexes by trap-to-trap distillation (120 °C, 20 Torr). All
volatiles were evaporated (120 °C, 20 Torr static pressure) and
recovered in a second flask previously immersed in liquid nitrogen
in order to avoid any loss of product. For GC analyses, 1-heptene
was used as an internal reference. The necessary amount of complex
for six catalytic runs was dissolved in 60 mL of toluene. For each
catalysis, 10 mL of this solution was injected into the reactor.
Depending on the amount of cocatalyst added, between 0 and 5
mL of the solvent was added so that the total volume of all of the
solutions was 15 mL. This can be summarized by the following
equation:
Acknowledgment. We are grateful to the CNRS and the
Ministe`re de la Recherche (Paris) for support and to the
Institut Franc¸ais du Pe´trole for a Ph.D. grant (F.S.) and
financial support.
10 mL (Ni solution) + y mL (solvent) +
z mL (cocatalyst solution) ) 15 mL
Supporting Information Available: X-ray data for 14-17
available in CIF format and ORTEP plots of all of the structures
with complete atom numbering. This material is available free of
charge via the Internet at http://pubs.acs.org.
When MAO was used as the cocatalyst, the total volume was
increased to 20 mL.
X-ray Structure Determinations of 14-17. Diffraction data
were collected at 180 K on a Kappa CCD diffractometer using
graphite-monochromatized Mo KR radiation (λ ) 0.710 73 Å) and
a φ-scan mode. The relevant data are summarized in Table 10. Data
were collected using φ scans, and the structures were solved by
direct methods using the SHELX-97 software.41,42 The refinements
were conducted by full-matrix least squares on F2. No absorption
IC035132I
(41) Kappa CCD Operation Manual; Nonius B. V.: Delft, The Netherlands,
1997.
(42) Sheldrick, G. M. SHELXL-97: Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
1658 Inorganic Chemistry, Vol. 43, No. 5, 2004