Mono- and dinuclear nickel complexes with phosphino-, phosphinito-, and phosphonitopyridine ligands: Synthesis, structures, and catalytic oligomerization of ethylene

Article abstract of DOI:10.1021/om7008759

The P,N-type ligands 2-[(diphenylphosphino)methyl]pyridine (12), 2-[2-(diphenylphosphino)ethyl]pyridine (13), 2-methyloxy(diphenylphosphino) pyridine (14), 2-methyloxy(dibenzyl-1,2-oxaphosphorino)pyridine (15), and 2-methyloxy(di-tert-butylphosphino)pyridine (16) have been prepared in good yields, and 12 and 13 have been used to synthesize Ni(II) complexes of formula [Ni(P,N)Cl₂], 17 (P,N = 12) and 18 (P,N = 13), by reaction with NiCl₂ in methanol. The crystal structure of 18 has been determined by X-ray diffraction to be dinuclear with a distorted square-base pyramidal geometry around the Ni(II) centers. To examine the possible influence of the nature of the spacer link between the P and N donor atoms, we compared ligand 13, with a CH₂CH₂ spacer, with 14 and 16, which have a isosteric CH₂-O spacer. Reactions of the phosphinitopyridine ligands 14 and 16 and of the phosphonitopyridine 15 with [NiX₂(DME)] (X = Cl or Br) afforded the complexes [Ni(P,N)Cl₂] 20 (X = Cl; P,N = 14), 21 (X = Br; P,N = 14), 22 (X = Cl; P,N = 16), and 23 (X = Cl; P,N = 15), respectively. The mononuclear structure of complex 22 has been established by X-ray diffraction and showed a distorted tetrahedral geometry around the metal center. Complexes 17, 18, and 20-22 have been tested as precatalysts in the oligomerization of ethylene, with AlEtCl₂ or MAO as cocatalyst, in order to evaluate the influence of the stereoelectronic properties of the phosphorus substituents. With only 6 equiv of AlEtCl₂ as cocatalyst and 4 × 10^-5 mol precatalyst, complex 18 was the most active, with turnover frequencies (TOF) up to 91 200 C₂H₄/(mol Ni·h), and 20 with 2 equiv of AlEtCl₂ showed the highest selectivities for ethylene dimers (up to 97%) and in 1-butene (up to 72%). When only 10^-5 mol precatalyst was used, the TOF values went up to 207 600 for 18 and 150 100 for 20. With only 25 equiv of MAO as cocatalyst, complex 18 was again the most active, with TOF values up to 20 600 C₂H ₄/(mpl Ni·h). Despite the high selectivity for C₄ olefins of 17, 18, 20, and 21 (up to 93% for 20), 22 presented the best selectivities for 1-butene (up to 73%) with MAO as cocatalyst, and its high reactivity for the reinsertion of 1-butene resulted in 2-ethyl- 1-butene being the main product of the catalytic reaction (up to 91%).

Full text of DOI:10.1021/om7008759

88
Organometallics 2008, 27, 88–99
Mono- and Dinuclear Nickel Complexes with Phosphino-,
Phosphinito-, and Phosphonitopyridine Ligands: Synthesis,
Structures, and Catalytic Oligomerization of Ethylene
Anthony Kermagoret and Pierre Braunstein*
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), UniVersité Louis Pasteur,
4 rue Blaise Pascal, F-67070 Strasbourg Cédex, France
ReceiVed August 31, 2007
The P,N-type ligands 2-[(diphenylphosphino)methyl]pyridine (12), 2-[2-(diphenylphosphino)ethyl]py-
ridine (13), 2-methyloxy(diphenylphosphino)pyridine (14), 2-methyloxy(dibenzyl-1,2-oxaphosphorino)py-
ridine (15), and 2-methyloxy(di-tert-butylphosphino)pyridine (16) have been prepared in good yields,
and 12 and 13 have been used to synthesize Ni(II) complexes of formula [Ni(P,N)Cl2], 17 (P,N ) 12)
and 18 (P,N ) 13), by reaction with NiCl2 in methanol. The crystal structure of 18 has been determined
by X-ray diffraction to be dinuclear with a distorted square-base pyramidal geometry around the Ni(II)
centers. To examine the possible influence of the nature of the spacer link between the P and N donor
atoms, we compared ligand 13, with a CH2CH2 spacer, with 14 and 16, which have a isosteric CH2-O
spacer. Reactions of the phosphinitopyridine ligands 14 and 16 and of the phosphonitopyridine 15 with
[NiX2(DME)] (X ) Cl or Br) afforded the complexes [Ni(P,N)Cl2] 20 (X ) Cl; P,N ) 14), 21 (X ) Br;
P,N ) 14), 22 (X ) Cl; P,N ) 16), and 23 (X ) Cl; P,N ) 15), respectively. The mononuclear structure
of complex 22 has been established by X-ray diffraction and showed a distorted tetrahedral geometry
around the metal center. Complexes 17, 18, and 20-22 have been tested as precatalysts in the
oligomerization of ethylene, with AlEtCl2 or MAO as cocatalyst, in order to evaluate the influence of the
stereoelectronic properties of the phosphorus substituents. With only 6 equiv of AlEtCl2 as cocatalyst
and 4 × 10-5 mol precatalyst, complex 18 was the most active, with turnover frequencies (TOF) up to
91 200 C2H4/(mol Ni · h), and 20 with 2 equiv of AlEtCl2 showed the highest selectivities for ethylene
dimers (up to 97%) and in 1-butene (up to 72%). When only 10-5 mol precatalyst was used, the TOF
values went up to 207 600 for 18 and 150 100 for 20. With only 25 equiv of MAO as cocatalyst, complex
18 was again the most active, with TOF values up to 20 600 C2H4/(mol Ni · h). Despite the high selectivity
for C4 olefins of 17, 18, 20, and 21 (up to 93% for 20), 22 presented the best selectivities for 1-butene
(up to 73%) with MAO as cocatalyst, and its high reactivity for the reinsertion of 1-butene resulted in
2-ethyl-1-butene being the main product of the catalytic reaction (up to 91%).
preference of this metal for the oligomerization of ethylene,10
Introduction
and many systems based on nickel complexes with P,O,11–18
N,N,19–21 N,O,22–27 P,P,28 and P,N8 chelating ligands have
The catalytic production of linear R-olefins (LAO) has
enjoyed major industrial developments since the seminal works
of Ziegler and Natta on the oligomerization and polymerization
of ethylene with metal catalysts activated by alkylaluminiums.1–4
By favoring chain transfer over propagation during the catalytic
cycle, late transition metals such as Ni, Pd, Co, and Fe are good
candidates for the formation of oligomerization catalysts.5–9 The
discovery of the “nickel effect” by Ziegler in 1953 proved the
(10) Ziegler, K.; Gellert, H. G.; Holzkamp, E.; Wilke, G. Brennst.-Chem.
1954, 35, 321.
(11) Keim, W.; Behr, A.; Gruber, B.; Hoffmann, B.; Kowaldt, F. H.;
Kürschner, U.; Limbäcker, B.; Sistig, F. P. Organometallics 1986, 5, 2356–
2359.
(12) Keim, W. Angew. Chem., Int. Ed. 1990, 29, 235–244.
(13) Heinicke, J.; He, M.; Dal, A.; Klein, H. F.; Hetche, O.; Keim, W.;
Flörke, U.; Haupt, H. J. Eur. J. Inorg. Chem. 2000, 431–440.
(14) Heinicke, J.; Köhler, M.; Peulecke, N.; He, M.; Kindermann, M. K.;
Keim, W.; Fink, G. Chem.-Eur. J. 2003, 9, 6093–6107.
(15) Braunstein, P.; Chauvin, Y.; Mercier, S.; Saussine, L. C. R. Chim.
2005, 8, 31–38.
* Corresponding author. E-mail: braunstein@chimie.u-strasbg.fr.
(1) Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem. 1955,
67, 426.
(2) Wilke, G. Angew. Chem., Int. Ed. 2003, 42, 5000–5008.
(3) Bolton, P. D.; Mountford, P. AdV. Synth. Catal. 2005, 347, 355–
366.
(16) Kuhn, P.; Semeril, D.; Jeunesse, C.; Matt, D.; Lutz, P.; Welter, R.
Eur. J. Inorg. Chem. 2005, 1477–1481.
(17) Malinoski, J. M.; Brookhart, M. Organometallics 2003, 22, 5324–
5335.
(4) Böhm, L. L. Angew. Chem., Int. Ed. 2003, 42, 5010–5030.
(5) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428–447.
(18) Kuhn, P.; Semeril, D.; Matt, D.; Chetcuti, M. J.; Lutz, P. Dalton
Trans. 2007, 515–528.
(6) Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 534–540.
(7) Rieger, B., Saunders Baugh, L., Kacker, S., Striegler, S., Eds. Late
Transition Metal Polymerization Catalysis; Wiley-VCH: Weinheim, 2003.
(8) Speiser, F.; Braunstein, P.; Saussine, L. Acc. Chem. Res. 2005, 38,
784–793.
(19) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169–1203.
(20) Killian, C. M.; Johnson, L. K.; Brookhart, M. Organometallics 1997,
16, 2005–2007.
(21) Svejda, S. A.; Brookhart, M. Organometallics 1999, 18, 65–74.
(22) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460–462.
(9) Bianchini, C.; Giambastiani, G.; Rios, I. G.; Mantovani, G.; Meli,
A.; Segarra, A. M. Coord. Chem. ReV. 2006, 250, 1391–1418.
10.1021/om7008759 CCC: $40.75
2008 American Chemical Society
Publication on Web 12/07/2007

Nickel Complexes with Phosphinopyridine Ligands
Organometallics, Vol. 27, No. 1, 2008 89
Scheme 1. Complexes with P,N-Type Ligands for the
Catalytic Oligomerization or Polymerization of Ethylene
(references given in the text)
provided very interesting catalytic results. The SHOP process,
which is based on neutral phenyl nickel complexes of type 1
and does not require any cocatalyst, remains a reference in
oligomerization of ethylene with its remarkable selectivity for
LAO and Schulz-Flory distribution.11,12 The R-diimine Ni(II)
complexes 2 and 3 also form very active and selective catalysts
for LAO when activated by a cocatalyst such as methylalu-
moxane (MAO).20,21
In combination with divalent nickel or palladium, P,N-type
ligands, such as phosphinoimines in 4 and 5,29,30 phosphino-
nicotine methyl esters in 6,31 phosphinosulfonamides in 7,32
phosphinidine-imines in 8,33 phosphinooxazolines in 9,34,35 and
phosphinopyrazole in 10,36 or derived from R-iminoazatri-
phenylphosphoranes in 11,37 result in active catalysts for
ethylene oligomerization or polymerization (Scheme 1).
The properties and applications of transition metal complexes
with phosphinopyridine ligands have been reviewed,38–41 and
some of their Ni(II) complexes catalyze the oligomerization of
ethylene in the presence of MAO42–45 or AlEtCl246 as cocatalyst.
We have recently reported Ni(II) complexes with phosphinopy-
ridine ligands that led to high selectivities for the dimerization
of ethylene but modest selectivities for R-olefins, and some
ethylene trimerization was also noted.47–50 We were therefore
interested in the synthesis of new Ni(II) catalyst precursors based
on phosphinopyridine ligands with different substituents on phos-
phorus to modify its electronic and steric effects and examine the
consequences for this catalytic reaction. Introducing tert-butyl
substituents on phosphorus will result in ligands with a larger cone
angle,51 and their influence on the stability of the complexes and
their catalytic properties has now been investigated.
(23) Jenkins, J. C.; Brookhart, M. Organometallics 2003, 22, 250–256.
(24) Sun, W.-H.; Tang, X.; Gao, T.; Wu, B.; Zhang, W.; Ma, H.
Organometallics 2004, 23, 5037–5047.
(25) Chen, Y.; Wu, G.; Bazan, G. C. Angew. Chem., Int. Ed. 2005, 44,
1108–1112.
(26) Speiser, F.; Braunstein, P.; Saussine, L. Inorg. Chem. 2004, 43,
4234–4240.
Results and Discussion
Synthesis of the Ligands. The ligand 2-[(diphenylphosphi-
no)methyl]pyridine (12) was prepared by deprotonation of
2-methylpyridine with n-BuLi, followed by reaction with excess
chlorotrimethylsilane at -78 °C and reaction with 1 equiv of
chlorodiphenylphosphine at -78 °C.52 This procedure is crucial
for a high-yield synthesis of the corresponding ligand because
the direct reaction of the carbanion with PPh2Cl gives rise to
byproducts. The ligand 2-[2-(diphenylphosphino)ethyl]pyridine
(13) was synthesized by reaction of 2-(pyridine)ethanol with
SOCl2 to give 2-chloroethylpyridine, which was then reacted
(27) Yang, Q.-Z.; Kermagoret, A.; Agostinho, M.; Siri, O.; Braunstein,
P. Organometallics 2006, 25, 5518–5527.
(28) Albers, I.; Alvarez, E.; Campora, J.; Maya, C. M.; Palma, P.;
Sanchez, L. J.; Passaglia, E. J. Organomet. Chem. 2004, 689, 833–839.
(29) van den Beuken, E. K.; Smeets, W. J. J.; Spek, A. L.; Feringa,
B. L. Chem. Commun. 1998, 223–224.
(30) Guan, Z.; Marshall, W. J. Organometallics 2002, 21, 3580–3586.
(31) Bonnet, M. C.; Dahan, F.; Ecke, A.; Keim, W.; Schulz, R. P.;
Tkatchenko, I. Chem. Commun. 1994, 615–616.
(32) Rachita, M. J.; Huff, R. L.; Bennett, J. L.; Brookhart, M. J. Polym.
Sci. Part A: Polym. Chem. 2000, 38, 4627–4640.
(33) Daugulis, O.; Brookhart, M.; White, P. S. Organometallics 2002,
21, 5935–5943.
(34) Speiser, F.; Braunstein, P.; Saussine, L.; Welter, R. Organometallics
2004, 23, 2613–2624.
(44) Bluhm, M. E.; Folli, C.; Walter, O.; Döring, M. J. Mol. Catal. A:
Chem. 2005, 229, 177–181.
(35) Tang, X.; Zhang, D.; Jie, S.; Sun, W.-H.; Chen, J. J. Organomet.
Chem. 2005, 690, 3918–3928.
(45) Sirbu, D.; Consiglio, G.; Gischig, S. J. Organomet. Chem. 2006,
691, 1143–1150.
(36) Mukherjee, A.; Subramanyam, U.; Puranik, V. G.; Mohandas, T. P.;
Sarkar, A. Eur. J. Inorg. Chem. 2005, 1254–1263.
(37) Braunstein, P.; Pietsch, J.; Chauvin, Y.; Mercier, S.; Saussine, L.;
DeCian, A.; Fischer, J. J. Chem. Soc., Dalton Trans. 1996, 3571–3574.
(38) Newkome, G. R. Chem. ReV. 1993, 93, 2067–2089.
(39) Zhang, Z.-Z.; Cheng, H. Coord. Chem. ReV. 1996, 147, 1–39.
(40) Espinet, P.; Soulantica, K. Coord. Chem. ReV. 1999, 193–195, 499–
556.
(46) de Souza, R. F.; Bernardo-Gusmao, K.; Cunha, G. A.; Loup, C.;
Leca, F.; Réau, R. J. Catal. 2004, 226, 235–239.
(47) Speiser, F.; Braunstein, P.; Saussine, L. Dalton Trans. 2004, 1539–
1545.
(48) Speiser, F.; Braunstein, P.; Saussine, L. Organometallics 2004, 23,
2633–2640.
(49) Speiser, F.; Braunstein, P.; Saussine, L. Organometallics 2004, 23,
2625–2632.
(41) Aucott, S. M.; Clarke, M. L.; Slawin, A. M. Z.; Woollins, J. D.
J. Chem. Soc., Dalton Trans. 2001, 972–976.
(50) Speiser, F.; Braunstein, P.; Saussine, L.; Welter, R. Inorg. Chem.
2004, 43, 1649–1658.
(42) Sun, W.-H.; Li, Z.; Hu, H.; Wu, B.; Yang, H.; Zhu, N.; Leng, X.;
Wang, H. New J. Chem. 2002, 26, 1474–1478.
(51) Tolman, C. A. Chem. ReV. 1977, 77, 313–348.
(52) Braunstein, P.; Heaton, B. T.; Jacob, C.; Manzi, L.; Morise, X.
Dalton Trans. 2003, 1396–1401.
(43) Chen, H.-P.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. Organometallics
2003, 22, 4893–4899.

90 Organometallics, Vol. 27, No. 1, 2008
Kermagoret and Braunstein
note the high 31P{1H} chemical shifts of 16 (δ 166.3 ppm)
compared to that of the phosphinite 14 (δ 117.7 ppm), which
results from the steric effect of the tert-butyl substituents.
Synthesis of the Ni(II) Complexes. To examine the possible
influence of the nature of the spacer link between the P and N
donor atoms, we compared ligand 13, which contains a CH2-
CH2 spacer, with 14 and 16, which have a isosteric CH2-O
spacer. The Ni(II) phosphinopyridine complexes 17 and 18 were
prepared by reaction of 1 equiv of the corresponding phosphine
with NiCl2 in methanol. The immediate color change, from
green to red, indicated a fast reaction. After workup, gray and
green powders of 17 and 18 were obtained in 83% and 80%
yields, respectively. Slow diffusion of pentane into a CH2Cl2
solution of 18 afforded single crystals suitable for X-ray
diffraction, which established its dinuclear structure (see below).
A red-violet complex has been reported from the reaction of
13 with NiCl2 in refluxing n-butanol.57
Figure 1. 1H NMR spectrum (300 MHz) of 13 showing the P-CH2
and the Py-CH2 protons.
1
with NaPPh2.53,54 The H NMR spectrum of 13 was analyzed
using the MestRec software55 by considering an AA′BB′X spin
system for the P-CH2 and Py-CH2 protons (Figure 1). The
reaction of (pyridin-2-yl)methanol with 1 equiv of PPh2Cl or
chloro(dibenzyl-1,2-oxa)phosphorine in the presence of excess
triethylamine (to neutralize the HCl liberated) afforded the new
ligands 2-methyloxy(diphenylphosphino)pyridine (14)56 and
2-methyloxy(dibenzyl-1,2-oxaphosphorino)pyridine (15),
respectively. Their properties are similar to those of their methyl
derivatives containing a POCMe2 instead of a POCH2 moiety.50
The complexation of NiCl2 by ligand 14 in methanol led to
cleavage of the phosphinite P-O bond and substituent exchange
at the phosphorus to form [Ni(µ-Cl)2(2-pyridine ethanol)2]Cl2
(19) and [NiCl2(PPh2OMe)2] (eq 2). The very low solubility of
19 in CH2Cl2 facilitated separation of the Ni(II) complexes. This
reaction is consistent with the sensitivity of phosphonites to the
presence of alcohols,58 and the breaking of the P-O bond does
not necessarily require the presence of a metal cation. Complex
19 has been obtained directly from (pyridin-2-yl)methanol and
NiCl2 and was shown by X-ray diffraction to have a dinuclear
structure.59
For the synthesis of 2-methyloxy(di-tert-butylphosphino)py-
ridine (16), 2-(pyridine)ethanol had to first be deprotonated and
reacted with di-tert-butyl(chloro)phosphine (eq 1), because the
phosphine is not electrophilic enough to react directly with a
pyridine-alcohol owing to the electron donor effect of the two
tert-butyl substituents.
(2)
The use of methanol for metal complexation with phosphinite
14 or 16 and phosphonite 15 should therefore be avoided, but
other solvents (MeCN, THF, or CH2Cl2) led to poor yields
owing to the very low solubility of NiCl2. However, reaction
of [NiCl2(DME)] or [NiBr2(DME)] in CH2Cl2 with 14-16 led
to the high-yield formation of the Ni(II) complexes 20–23,
respectively (up to 92%). Their colors in the solid state are
respectively gray, green, red, or maroon, but all complexes
afforded red CH2Cl2 solutions. Red single crystals of 22 suitable
for X-ray diffraction were obtained by slow diffusion of pentane
into a solution of the complex in chlorobenzene, and 22
presented a mononuclear structure (see below).
(1)
All the ligands have been characterized by 1H, 13C{1H},
31P{1H}, COSY, HMBC, and HMQC NMR spectroscopy. We
(53) Eisch, J. J.; Kovacs, C. A.; Chobe, P.; Boleslawski, M. P. J. Org.
Chem. 1987, 52, 4427–4437.
(54) Costella, L.; Del Zotto, A.; Mezzetti, A.; Zangrando, E.; Rigo, P.
J. Chem. Soc., Dalton Trans. 1993, 3001–3008.
(55) Cobas, J. C.; Sardina, F. J. Concepts Magn. Reson. 2003, 19A, 80–96.
(56) Van Haaren, R. J.; Druijven, C. J. M.; Van Strijdonck, G. P. F.;
Oevering, H.; Reek, J. N. H.; Kamer, P. C. J.; Van Leeuwen, P. W. N. M.
J. Chem. Soc., Dalton Trans. 2000, 1549–1554.
(57) Uhlig, E.; Maaser, M. Z. Anorg. Allg. Chem. 1966, 344, 205–213.
(58) Buckler, S. A. J. Am. Chem. Soc. 1962, 84, 3093–3097.
(59) To be published.

Nickel Complexes with Phosphinopyridine Ligands
Organometallics, Vol. 27, No. 1, 2008 91
Although some nickel complexes with P,N- or P,N,P-type
ligands are diamagnetic in solution,60 complexes 17, 18, 20,
22, and 23 proved to be paramagnetic in CDCl3, CD2Cl2,
CD3CN, CD3CD2OD, or CD3OD solution. Their magnetic
moments per Ni atom, determined by the Evans method in
CD2Cl2,61–64 were 2.2 (17), 2.7 (18), 2.8 (20), 3.0 (22), and 1.9
(23) µB, respectively.65,66 These values are similar to those
recently reported for other Ni(II) complexes with P,N-type
ligands.34,47–50 Relatively low magnetic moments, such as those
for 17 and 23, may also be due to equilibria with their square-
planar, diamagnetic isomer.67
Figure 2. ORTEP view of the molecular structure of 18 (ellipsoids
enclose of 50% electronic density; only the phenyl ipso carbons
are shown and the H atoms are omitted for clarity).
These complexes have also been characterized by IR,
elemental analysis, and mass spectrometry, but no NMR spectra
could be recorded. High-resolution mass spectrometry (HRMS)
with the electrospray ionization method afforded spectra where
the main peak corresponds to [Ni(P,N)Cl]+. The structures of
18 and 22 are shown in Figures 2 and 3, and selected bond
distances and angles are given in Tables 1 and 2.
Figure 3. ORTEP view of the molecular structure of 22 (ellipsoids
enclose 50% electronic density; H atoms are omitted for clarity).
Complex 18 has a dinuclear structure with pentacoordinated
metal centers and six-membered-ring chelates. The cisoid
coordination of the two pyridine functions with respect to the
Ni-Ni axis makes the structure non-centrosymmetric, but it
possesses a C2 symmetry axis passing through Cl2 and Cl3.
The coordination geometry around the metals is distorted square-
pyramidal, with the square base being formed by N and the
three chlorides (Scheme 2). The Ni atom is out of this plane by
0.3777(1) Å.
It is interesting to compare the structure of 18 with those of
the distorted square-pyramidal dinuclear Ni(II) complexes 24
and 25, which contain five- and seven-membered-ring P,N
chelates.42,50
In contrast to 18, complexes 24 and 25 have centrosymmetric
structures and their square bases contained the atoms P, N, and
the two bridging chlorides Cl(1) and Cl(1a) (Scheme 2). The
larger N-Ni-P coordination angle (96.18(9)°, Table 1) of 18
compared to 24 (84.48(9)°) or 25 (85.37(5)°) leads to the apical
position being occupied by the phosphorus donor atom instead
of a chloride ligand. The Ni-P and Ni-N distances in 18, of
2.305(1) and 2.061(3) Å, respectively, are similar to those in
the dinuclear complexes 24 and 25 but are longer than in related
mononuclear Ni(II) complexes.50
Complex 22 has a mononuclear structure with a distorted
tetrahedral geometry similar to that of complex 26, in contrast
to the square-planar geometry of complexes 27 and 28 (Figure
3).50 The Ni-P and Ni-N distances of 22, 2.304(1) and
2.006(3) Å (Table 2), are significantly longer than in complexes
26–28. The large Cl-Ni-Cl angle (123.47(5)°) and the small
N-Ni-P angle (92.1(1)°, Table 2) result in complex 22
adopting a distorted tetrahedral geometry instead of a square-
planar geometry. The steric properties of the tert-butyl substit-
uents on phosphorus probably explain the tetrahedral coordi-
nation in 22. Tetrahedral Ni(II) complexes coordinated by
phosphinopyridine43,44 or phosphinoimine ligands30 have been
used previously in ethylene oligomerization, and we shall now
examine the catalytic properties of complexes 17, 18, and 20–22
in this reaction.
(60) Jalil, M. A.; Fujinami, S.; Senda, H.; Nishikawa, H. J. Chem. Soc.,
Dalton Trans. 1999, 1655–1661.
(61) Evans, D. F. J. Chem. Soc. (A) 1959, 2003–2005.
(62) Deutsch, J. L.; Poling, S. M. J. Chem. Educ. 1969, 46, 167–168.
(63) Löliger, J.; Scheffold, R. J. Chem. Educ. 1972, 49, 646–647.
(64) Sur, S. K. J. Magn. Reson. 1989, 82, 169–173.
This structural study emphasizes the influence of sometimes
seemingly minor variations in the stereoelectronic properties
of the ligands on the structure of their corresponding Ni(II)
complexes. With related phosphino-oxazoline and -thiazoline
ligands, it was recently found that tetranuclear Ni(II) complexes
(65) Venanzi, L. M. J. Chem. Soc. (A) 1958, 719–724.
(66) Hayter, R. G.; Humiec, F. S. Inorg. Chem. 1965, 4, 1701–1706.
(67) Kermagoret, A.; Pattacini, R.; Vasquez, P. C.; Rogez, G.; Welter,
R.; Braunstein, P. Angew. Chem., Int. Ed. 2007, 46, 6438–6441.

92 Organometallics, Vol. 27, No. 1, 2008
Kermagoret and Braunstein
Table 1. Selected Bond Lengths (Å) and Angles (deg) in 18
in toluene (Al/Ni ratios of 2, 4, or 6, respectively), and the
catalytic results are presented in Table 3 and shown in Figures
4-6.
Ni-P
2.305(1)
2.061(3)
2.291(1)
2.4227(9)
2.3508(9)
1.822(4)
C6-C7
C5-C6
C5-N
P-C8
1.543(5)
1.500(5)
1.357(4)
1.821(4)
1.818(4)
Ni-N
The highest activities when 4 × 10-5 mol precatalyst was
used were obtained for complex 18 with turnover frequencies
(TOF) of 78 200 and 91 200 mol C2H4/(mol Ni · h), with either
4 or 6 equiv of AlEtCl2, respectively. Complexes 17, 20, 21,
and 22 had similar activities (Figure 4), which increased with
the amount of cocatalyst, between 17 000 and 20 400 mol C2H4/
(mol Ni · h) with 2 equiv of AlEtCl2, 43 500 and 46700 mol
C2H4/(mol Ni · h) with 4 equiv, and 56600 and 63 600 mol C2H4/
(mol Ni · h) with 6 equiv. However, 20 showed very low activity
with 2 equiv of AlEtCl2 (1100 mol C2H4/(mol Ni · h)).
The selectivity for 1-butene was modest and less than 17%
for all the complexes except for 20 with 2 equiv of AlEtCl2
(72%, Figure 6). The high concentration of 2-butene indicates
that isomerization of 1-butene is largely favored. The exother-
micity of the catalytic reaction (temperatures up to 115 °C) with
very active systems is most likely responsible for the lower
selectivity in 1-butene.70 The selectivities for C4 olefins were
between 97% and 50% for complexes 17, 18, and 20–22 (Figure
5), and this showed that dimerization is much favored over chain
growth. The second largest is constituted by the hexenes (Table
3), with the reinsertion of 1-butene and 2-butene being very
significant on the basis of the branched olefins formed
(Table 4).
Ni-Cl1
Ni-Cl2
Ni-Cl3
P-C7
P-C14
Cl1-Ni-Nl2
Cl1-Ni-Cl3
Cl1-Ni-N
Cl1-Ni-P
Cl2-Ni-Cl3
Cl2-Ni-N
Cl2-Ni-P
158.69(4)
Cl3-Ni-N
Cl3-Ni-P
N-Ni-P
Ni-P-C7
C7-C6-C5
C6-C5-N
C5-N-Ni
162.92(9)
100.18(3)
96.18(9)
105.5(1)
113.4(3)
118.5(3)
126.8(3)
92.09(4)
87.97(8)
106.28(4)
84.53(3)
89.23(8)
95.03(3)
Table 2. Selected Bond Lengths (Å) and Angles (deg) in Complex
22
Ni-P
2.304(1)
2.005(3)
2.217(2)
2.227(1)
1.865(5)
P-0
1.626(3)
1.454(6)
1.505(6)
1.350(5)
1.860(5)
Ni-N
O-C6
C5-C6
C5-N
P-C11
Ni-Cl1
Ni-Cl2
P-C7
N-Ni-P
Ni-P-O
P-O-Cl
O-C1-C2
C1-C2-N
C2-N-Ni
92.2(1)
105.9(1)
118.8(2)
112.1(3)
116.8(4)
122.5(3)
N-Ni-Cl1
N-Ni-Cl2
Cl1-Ni-Cl2
Cl1-Ni-P
C12-Ni-P
102.9(1)
108.3(1)
123.47(5)
112.74(5)
111.77(5)
Increasing the amount of AlEtCl2 had a significant influence
on the catalytic results by forming a more active but less
selective system. Higher activities were associated with an
increasing isomerization of 1-butene to 2-butene. With 18, for
example, the fraction of 1-butene decreased from 13% to 2%.
The higher concentration of 2-butene favored its reinsertion to
give C6 oligomers (Table 4).
Scheme 2. Representation of the Square-Pyramidal Coordi-
nation Geometries around the Metals in 18, 24, and 25
To study the influence of the concentration of the complexes
on the oligomerization of ethylene, precatalysts 18 and 20 have
been tested with only 1 × 10-5 mol of complex in 15 mL of
solution instead of 4 × 10-5 mol for the standard procedure.
The catalytic results with 6 equiv of AlEtCl2 showed that the
complexes are more active and selective for C4 oligomers under
these conditions (Table 3). Under these conditions, the TOF
values went up to 207 600 for 18 and 150 100 for 20.
To determine the robustness of the P-O bond of complex
20 and the lifetime of the catalyst, we increased the reaction
time to 120 min and compared the catalytic results with those
for complex 18 (Table 3). The high and constant activities during
the catalytic run (the ethylene consumption was constant, no
plateau of activity was observed, and the final activities were
104 100 and 83 100 mol C2H4/(mol Ni · h) for 18 and 20,
respectively) suggested a reasonable lifetime for the catalysts.
The lower TOF values calculated for these experiments com-
pared with those where the reaction time was 35 min are due
to the nonlinearity of the ethylene consumption as a function
of time.
Use of MAO as Cocatalyst. Complexes 17, 18, and 20–22
have also been evaluated in the presence of 12.5, 25, 50, 100,
and 200 equiv of MAO in toluene as cocatalyst, and the catalytic
results are given in Tables 5 and 6 and shown in Figures 7-10.
In contrast to analogous Ni(II) complexes with pyridine-
phosphine and pyridine-phosphinite ligands tested under
similar conditions,8 the precatalysts 17, 18, and 20–22
presented high activities with very small amounts of MAO
(Figures 7-9). In particular, 18 showed activities up to
are formed and a dramatic effect of pressure was evidenced,
which results in its breaking into four mononuclear complexes.67
Catalytic Oligomerization of Ethylene. Complexes 17, 18,
and 20–22 have been tested as precatalysts in the oligomerization
of ethylene with variable amounts of AlEtCl2 or MAO as
cocatalyst. In previous studies, [NiCl2(PCy3)2], which is a typical
R-olefin dimerization catalyst,68 was used to compare the
catalytic results, but considering the sensitivity of this complex,
we choose another reference compound, [NiCl2{P(n-Bu3)}2],
which is diamagnetic and thus readily amenable to purity check
by NMR spectroscopy and is also highly active in oligomer-
ization with AlEtCl2.69 The analysis of the different C6 oligomers
was performed in order to differentiate between a chain growth
mechanism and the reinsertion of butenes. The formation of
2-hexene, 3-hexene, and 2-ethyl-1-butene by reinsertion of
1-butene and the formation of 3-methyl-2-pentene and 3-methyl-
1-pentene by reinsertion of 2-butene depending on the insertion
mode (2,1- or 1,2-insertion) have been discussed previously.27
Isomerization of 1-hexene leads to the formation of 2-hexene
and 3-hexene.
Use of AlEtCl2 as Cocatalyst. Complexes 17, 18, and 20–22
have been tested in the presence of 2, 4, or 6 equiv of AlEtCl2
(68) Commereuc, D.; Chauvin, Y.; Le´ger, G.; Gaillard, J. ReV. Inst. Fr.
Pét. 1982, 37 (6), 39–649.
(69) Bergem, N.; Blindheim, U.; Onsager, O. T.; Wang, H. Fr. Patent
1519181, 1968.
(70) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414–6415.

Nickel Complexes with Phosphinopyridine Ligands
Organometallics, Vol. 27, No. 1, 2008 93
Table 3. Comparative Catalytic Data for Complexes 17, 18, and 20-22 in the Oligomerization of Ethylene with AlEtCl2 as Cocatalysta
selectivityb (%)
quantity of complex
(10-5 mol)
AlEtCl2
(equiv)
productivity
(g C2H4/(g Ni · h))
TOF
d
time (min)
C4
C6
C8
(mol C2H4/(mol Ni · h))
1-butenec (%)
kR
17
17
17
18
18
18
18
18
20
20
20
20
20
21
21
22
22
22
refe
refe
refe
4
4
4
4
4
4
1
1
4
4
4
1
1
4
4
4
4
4
4
4
4
2
4
6
2
4
6
6
6
2
4
6
6
6
4
6
2
4
6
2
4
6
35
35
35
35
35
35
35
120
35
35
35
35
120
35
35
35
35
35
35
35
35
87
71
55
76
52
50
69
70
97
75
63
71
72
74
59
85
68
66
83
60
61
12
28
43
21
44
43
30
28
2
24
35
27
27
24
38
14
28
31
15
35
34
<1
<1
2
3
4
7
1
2
<1
1
2
2
1
2
3
1
9700
22 300
30 300
8400
37 300
43 500
99 000
49 700
500
20 700
27 900
71 600
39 700
21 100
24 800
8200
21 500
27 200
4000
20 400
46 700
63 600
17 600
78 200
91 200
207 600
104 100
1100
43 500
58 500
150 100
83 100
44 100
56 600
17 000
45 100
57 000
8400
17
14
7
13
3
2
1
9
72
5
<0.10
0.26
0.53
0.19
0.57
0.59
0.31
0.27
<0.10
0.21
0.38
0.24
0.25
0.21
0.43
0.11
0.27
0.31
0.12
0.39
0.37
3
11
14
6
4
16
6
6
13
3
4
3
2
5
35 300
35 000
74 100
73 600
5
3
a Conditions: T ) 25–30 °C, 10 bar C2H4, solvent 14 mL of chlorobenzene and 1 mL of cocatalyst solution in toluene, 13 mL of chlorobenzene and
2 mL of cocatalyst solution, and 12 mL of chlorobenzene and 3 mL of cocatalyst solution for 2, 4, or 6 equiv of AlEtCl2, respectively. b No C10
oligomers were detected. c Within the C4 fraction. d kR ) hexenes [mol]/butenes [mol]. e reference: [NiCl2{P(n-Bu)3}2].
Figure 6. Selectivity of the complexes 17, 18, and 20–22 for
1-butene using AlEtCl2 as cocatalyst, ref: [NiCl2{P(n-Bu)3}2].
Figure 4. Catalytic activities of the complexes 17, 18, and 20–22
in the oligomerization of ethylene using AlEtCl2 as cocatalyst, ref:
[NiCl2{P(n-Bu)3}2].
and 20–22 had similar activities, between 14 100 and 19 600
mol C2H4/(mol Ni · h). The precatalyst 17, with a smaller bite
angle ligand than 18–22, presented slightly lower activities
but better selectivities for 1-butene.
In contrast to complex 20, which has phenyl substituents
on the phosphorus atom, complex 22 has tert-butyl groups
and their steric and electronic donor effects significantly
affected the catalytic results. Under standard conditions,
precatalyst 20 led to a low selectivity for 1-butene (less than
11% of the C4 fraction), which is characteristic of an
isomerizing catalyst, and to a high concentration of C6
oligomers formed by reinsertion of 2-butene (up to 68%,
Table 6). In contrast, 22 did not favor the isomerization of
1-butene and had a selectivity up to 42% for 1-butene within
the C4 fraction. However 22 led overall to a low selectivity
in C4 products (less than 23%) owing to the reinsertion of
1-butene to form 2-ethyl-1-butene (up to 77%, Table 6) and
presented a very different mass distribution of oligomers
compared to 20 (Figure 10). Heinicke et al. have observed
similar effects with cationic methallylnickel phosphinophenol
complexes where cyclohexyl substituents on the phosphorus
donor function favored the formation of 2-ethyl-1-butene,
in contrast to the phenyl substituents, which favored the
formation of cis-3-methyl-2-pentene.72
Figure 5. Selectivity of the complexes 17, 18, and 20–22 for C4
compounds using AlEtCl2 as cocatalyst (1-butene and 2-butene),
ref: [NiCl2{P(n-Bu)3}2].
18 400 and 20 600 mol C2H4/(mol Ni · h) with only 12.5 and
25 equiv of MAO, respectively. The use of fresh MAO under
strict conditions could explain these high activities of 17,
18, and 20–22, respectively, since MAO is known to be very
sensitive to air and moisture and can rapidly evolve to a poor
cocatalyst.71 Increasing the amount of cocatalyst did not have
a major impact on the catalytic results. Precatalysts 17, 18,
(72) Heinicke, J.; Köhler, M.; Peulecke, N.; Kindermann, M. K.; Keim,
W.; Köckerling, M. Organometallics 2005, 24, 344–352.
(71) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391–1434.

94 Organometallics, Vol. 27, No. 1, 2008
Kermagoret and Braunstein
Table 4. Catalytic Data and Distribution of the C6 Oligomers for
Complexes 17, 18, and 20-22 in the Oligomerization of Ethylene
with AlEtCl2 as Cocatalysta
Conclusion
New P,N ligands with a pyridine function have been
synthesized in good yields and characterized by H, 31P{1H},
1
selectivity (mass %)
and 13C{1H} NMR spectroscopy. These ligands present various
bite angles and phosphorus functions (phosphine, phosphinite,
or phosphonite functions) with different substituents on the
phosphorus atom (phenyl or tert-butyl groups). The Ni(II)
complexes 17, 18, and 20–22, prepared in 70–92% yields from
ligands 12–16, respectively, were characterized by IR, elemental
analysis, and high-resolution mass spectroscopy. Whereas
complex 18 was shown by X-ray diffraction to have a dinuclear
structure with a distorted square-base pyramidal geometry, 22,
in which a CH2 group of the spacer between the pyridine and
the phosphorus has been replaced with an oxygen and the
phenyls on phosphorus by t-Bu substituents, has a mononuclear
structure with a distorted tetrahedral geometry. One should of
course keep in mind that the nuclearity of a complex may be
different in the solid state and in solution. Related Ni(II)
complexes with phosphino-oxazoline and -thiazoline ligands
have been recently found to form unprecedented tetranuclear
structures, which illustrates the considerable diversity of this
chemistry. A dramatic effect of pressure on the solid was
evidenced that resulted in breaking of the complex into four
mononuclear entities.67
The precatalysts 17, 18, and 20–22 have been evaluated in
the catalytic oligomerization of ethylene with AlEtCl2 or MAO
as cocatalyst. All the complexes presented high activities with
AlEtCl2 as cocatalyst, and the most active was 18 (91 200 mol
C2H4/(mol Ni · h)) with 6 equiv of AlEtCl2. 20 with 2 equiv of
AlEtCl2 showed the best selectivities in butenes (97%) and in
1-butene (72%). The high activities of 18 and 20 when the
reaction time was increased to 120 min suggested a good
stability of the catalysts. Precatalysts 17, 18, and 20–22 favored
the dimerization and trimerization of ethylene, but the high
proportions of branched oligomers suggested a significant
contribution of 1-butene and 2-butene reinsertion. The generally
modest selectivity for 1-butene is consistent with the isomerizing
character of 17, 18, and 20–22.
c
d
AlEtCl2
C6
C6
b
(equiv) 1-hexene linear C6 from 1-butene from 2-butene
17
17
17
18
2
4
6
2
4
6
6
6
2
4
6
6
6
4
6
2
4
6
3
1
1
37
37
30
27
19
19
18
22
15
29
25
40
45
22
26
49
32
31
17
20
14
15
13
13
14
15
15
14
11
6
6
13
9
11
7
7
43
42
55
57
67
67
67
62
3
56
63
53
46
63
62
22
60
61
1
18
<1
<1
<1
1
67
1
<1
1
3
2
18
18e
18e, f
20
20
20
20e
20e,f
21
21
22
22
22
3
18
1
1
a Conditions: T ) 25–30 °C, 10 bar C2H4, 35 min, 4 × 10-5 mol of
complex, solvent 14 mL of chlorobenzene and 1 mL of cocatalyst
solution in toluene, 13 mL of chlorobenzene and 2 mL of cocatalyst
solution, and 12 mL of chlorobenzene and 3 mL of cocatalyst solution
for 2, 4, or 6 equiv of AlEtCl2, respectively. b Sum of 2-cis-hexene,
2-trans-hexene, 3-cis-hexene, and 3-trans-hexene. c Corresponding to
2-ethyl-1-butene. d Sum of 3-methyl-1-pentene, 3-methyl-2-cis-pentene,
and 3-methyl-2-trans-pentene. e 1 × 10-5 mol of complex. f Reaction
time: 120 min.
When the quantity of precatalyst 20 and 22 was decreased
to 10-5 mol, very high activities were still observed. Under
these conditions, 20 showed a slightly better selectivity for
C4 products and 22 a slightly higher selectivity for 1-butene.
Increasing the pressure to 30 bar resulted in increased
catalytic activities with 20 and 22, from 30 100 to 36 800
mol C2H4/(mol Ni · h) with 20 and from 24 200 to 45 500
mol C2H4/(mol Ni · h) with 22. It has been shown with related
systems that TOF can be independent or not of ethylene
pressure.20,70 In the former case, the alkyl olefin species is
The precatalysts 17, 18, and 20–22 presented high activities
already with small amounts of MAO as cocatalyst. Complex
18 was the most active under 10 bar of ethylene with 25 equiv
(20 600 C2H4/(mol Ni · h)) and 17 the most selective in C4
oligomers (89%) and in 1-butene (35%) in the presence of 50
equiv of MAO. In contrast to 17, 18, 20, and 21, complex 22,
with tert-butyl substituents on phosphorus, largely favored
1-butene reinsertion over isomerization and afforded 2-ethyl-
1-butene as the main product. Increasing the pressure to 30 bar
made the precatalysts 20 and 22 more active and increased their
selectivity for C4 products and for 1-butene.
the catalyst resting state.73 According to the literature,20
a
higher ethylene concentration favors the formation of R-ole-
fins, and the selectivities for 1-butene with 20 (34%) and 22
(73%) were indeed higher. The selectivity for C4 products
with 20 increased to 93% (Table 5), but the mass distribution
of the oligomers produced by 22 did not change. The high
concentration of 1-butene resulted in a marked increase of
the concentration in 2-ethyl-1-butene (up to 91%). These
rather surprising results with 22 suggest that the tert-butyl
substituents on the P donor atom favor the formation of
1-butene and that its isomerization to 2-butene is disfavored
with respect to formation of the C6 product 2-ethyl-1-butene.
One could envisage that the latter originates from unselective
insertion of 1-butene into the Ni-ethyl bond of a primarily
formed intermediate72 (Scheme 3, route A) or by ꢀ-elimina-
tion of a metallacyclic intermediate resulting from the
coupling of 1-butene with ethylene (Scheme 3, route B).
Although this remains speculative in the absence of, for
example, H/D labeling experiments, Ni(II) metallacyclic
compounds have been previously considered in olefin chem-
istry.74
Experimental Section
General Considerations. All solvents were dried and freshly
distilled under nitrogen prior to use using common techniques.
All manipulations were carried out using Schlenk techniques.
1
The H, 31P{1H}, and 13C{1H} NMR spectra were recorded at
300.13, 121.5, and 76 MHz, respectively, on a Bruker AC300
instrument. Elemental analyses were performed by the “Service
de Microanalyse, Université Louis Pasteur (Strasbourg, France)”.
IR spectra in the range 4000–400 cm-1 were recorded on a
Bruker IFS28FT. Mass spectra were recorded with a Bruker
Daltonics microTOF (ESI; positive mode; capillary voltage: 4.8
kV; nebulizer pressure: 0.2 bar; desolvation temperature: 180
°C; desolvation gas flow rate: 4.5 L/min). Magnetic moments
were determined by the Evans method in CD2Cl2 using a solution
(73) Doherty, M. D.; Trudeau, S.; White, P. S.; Morken, J. P.; Brookhart,
M. Organometallics 2007, 26, 1261–1269.
(74) Grubbs, R. H.; Miyashita, A. J. Am. Chem. Soc. 1978, 100, 7416–
7418.

Nickel Complexes with Phosphinopyridine Ligands
Organometallics, Vol. 27, No. 1, 2008 95
Table 5. Comparative Catalytic Data for Complexes 17, 18, and 20-22 in the Oligomerization of Ethylene with MAO as Cocatalysta
selectivity (%)
amount of complex
(10-5 mol)
amt of
MAO (equiv)
productivity (g C2H4/
TOF (mol C2H4/
(mol Ni · h))
c
C4
C6
C8
>C8
(g Ni · h))
1-buteneb (%)
kR
17
17
17
17
18
18
18
18
18
20
20
20
20
20
20e
21
22
22
22
22
22e
refd
ref
ref
ref
4
4
4
4
4
4
4
4
4
4
4
4
4
1
1
4
4
4
4
1
1
4
4
4
4
50
100
200
400
12.5
25
89
61
64
72
70
69
72
65
64
79
72
75
72
84
93
65
17
20
23
26
27
43
25
26
41
10
32
29
23
28
30
23
28
28
17
22
20
21
13
6
30
52
49
52
47
50
46
54
52
45
1
6
6
5
2
1
4
6
7
4
5
5
6
2
1
4
20
22
20
17
15
8
14
16
10
0
<1
0
0
0
1300
5700
6800
5700
8800
9800
8300
8400
8200
8400
7000
6700
9400
14 300
17 500
9000
7000
7900
2800
12 000
14 300
12 000
18 400
20 600
17 300
17 600
17 300
17 00
14 800
14 100
19 600
30 100
36 800
18 900
14 800
16 600
13 600
24 200
45 500
40 000
41 300
36 900
39 600
35
19
19
25
10
8
11
14
16
11
10
11
9
13
34
11
38
42
42
56
73
3
<0.10
0.36
0.31
0.21
0.27
0.29
0.21
0.29
0.30
0.14
0.21
0.18
0.19
0.10
<0.10
0.49
2.00
1.60
1.50
1.18
1.22
0.72
1.47
1.31
0.72
0
50
<1
<1
<1
0
<1
0
1
<1
0
1
11
9
5
10
8
3
7
6
4
100
200
25
50
100
200
100
100
200
25
50
100
100
100
50
100
200
400
6500
11 500
21 700
18 600
19 200
17 600
18 900
3
3
4
a Conditions: T ) 25–30 °C, 10 bar C2H4, solvent 10 mL of chlorobenzene and 0.5, 1, 2, 4, or 8 mL of cocatalyst solution in toluene for 12.5, 25,
50, 100, or 200 equiv of MAO, respectively. b Within the C4 fraction. c kR ) hexenes [mol]/butenes [mol]. d Reference: [NiCl2{P(n-Bu)3}2]. e Pressure:
30 bar.
Table 6. Catalytic Data and Distribution of the C6 Oligomers for
Complexes 17, 18, and 20-22 in the Oligomerization of Ethylene
with MAO as Cocatalysta
selectivity (mass %)
c
d
MAO
C6
C6
b
(equiv) 1-hexene linear C6
from 1-butene from 2-butene
17
17
17
17
18
18
18
18
18
20
20
20
20
20e
50
100
200
400
12.5
25
50
100
200
25
14
3
4
37
43
46
47
38
46
40
42
45
17
29
20
29
25
27
14
5
17
10
10
11
15
14
10
9
10
15
14
11
10
12
12
10
77
75
75
83
91
43
44
40
37
47
39
38
36
42
67
56
68
60
61
53
76
16
21
21
9
5
<1
<1
2
3
3
1
1
1
2
2
8
1
2
1
1
3
5
Figure 7. Catalytic activities with 17, 18, 20, and 22 in the
oligomerization of ethylene using MAO as cocatalyst, ref: [NiCl2{P(n-
Bu)3}2].
50
100
200
100
20e,f 100
°C, respectively, and degassed with nitrogen before use. A
solution of NaPPh2 was prepared according to the literature,75
by addition of PPh2Cl (7.40 g, 6 mL, 33.4 mmol) to a suspension
of Na (4.00 g, 174.0 mmol) in THF (100 mL). After the mixture
was stirred at reflux for 4 h, the solution became red and a gray
precipitate of NaCl appeared. The salt and unreacted Na were
eliminated by filtration through a canula, and the compound was
kept in THF. 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). Details of the synthesis and analytical data for known
compounds are given below because of slight modifications or
new data introduced.
21
22
22
22
22e
200
25
50
100
100
3
3
5
2
22e,f 100
2
a Conditions: T ) 25–30 °C, 10 bar C2H4, 35 min, 4 × 10-5 mol of
complex, solvent 10 mL of chlorobenzene and 0.5, 1, 2, 4, and 8 mL of
cocatalyst solution in toluene for 12.5, 25, 50, 100, or 200 equiv of MAO,
respectively. b Sum of 2-cis-hexene, 2-trans-hexene, 3-cis-hexene, and
3-trans-hexene. c Corresponding to 2-ethyl-1-butene. d Sum of 3-methyl-
1-pentene, 3-methyl-2-cis-pentene, and 3-methyl-2-trans-pentene. e 1 ×
10-5 mol of complex. f Pressure: 30 bar.
2-[(Trimethylsilyl)methyl]pyridine...76 A solution of n-BuLi
(96.0 mmol, 1.6 M in hexane) was added dropwise over 15 min to
a solution of 2-picoline (8.94 g, 96.0 mmol) in 100 mL of THF at
of CH3NO2 in CD2Cl2 (20:80, v/v) as reference.61–64 Corrections
for diamagnetic susceptibility were done for the solvent but not
for the ligands. The complexes NiCl2 · 6H2O and NiBr2 · 6H2O
were dried by heating at 160 °C overnight under vacuum to give
anhydrous NiCl2 and NiBr2. The commercial compounds 2-pi-
coline and (pyridin-2-yl)methanol were distilled at 130 and 115
(75) Issleib, K.; Tzschach, A. Chem. Ber. 1959, 92, 704–711.
(76) van den Ancker, T. R.; Raston, C. L.; Skelton, B. W.; White, A. H.
Organometallics 2000, 19, 4437–4444.

96 Organometallics, Vol. 27, No. 1, 2008
Kermagoret and Braunstein
-78 °C. After complete deprotonation, the red anion precipitated,
and after further stirring for 1 h at -78 °C, degassed chlorotrim-
ethylsilane (TMSCl, 14.00 g, 112.0 mmol) was added dropwise to
the solution. The brown mixture was allowed to reach room
temperature overnight, and the solvents and unreacted TMSCl were
evaporated under reduced pressure. The residue was distilled (120
°C, 12 mbar) to afford pure, liquid 2-[(trimethylsilyl)methyl]pyri-
dine. Yield: 6.61 g, 42%. 1H NMR (CDCl3): δ 0.00 (s, 9H,
Si(CH3)], 2.32 (s, 2H, SiCH2), 6.93 (m, 2H, Py), 7.45 (m, 1H, Py),
3
8.39 (d, 1H, JH-H ) 4.2 Hz, HCN). 13C{1H} NMR (CDCl3): δ
-1.7 (s, SiCH3), 30.25 (s, SiCH2), 119.04 (s, Py), 122.06 (s, Py),
135.72 (s, Py), 148.94 (s, Py), 161.28 (s, HCN).
2-[(Diphenylphosphino)methyl]pyridine, 12..52 To a solution
of 2-[(trimethylsilyl)methyl]pyridine (4.21 g, 25.5 mmol) in 50 mL
of THF was added 4.70 mL of PPh2Cl (5.62 g, 25.5 mmol) at -78
°C, and the mixture was stirred overnight at room temperature. After
filtration and solvent removal under reduced pressure, 12 was
isolated as a colorless oil. Yield: 5.60 g, 79%. Spectroscopic data
are consistent with the literature values.
Figure 8. Selectivity of 17, 18, 20, and 22 for 1-butene using MAO
as cocatalyst (1-butene and 2-butene), ref: [NiCl2{P(n-Bu)3}2].
2-(2-Chloroethyl)pyridine.53,54 Pure SOCl2 (4.10 g, 2.5 mL,
34.2 mmol) was added to a solution of 2-pyridine-ethanol (2.50 g,
20.3 mmol) in THF and stirred at reflux for 2 h. After reaction, the
THF was removed under reduced pressure and 2-(2-chloroethyl)py-
ridine was extracted with 50 mL of CH2Cl2 and washed with water
saturated with NaHCO3 (3 × 20 mL). After elimination of CH2Cl2
under reduced pressure, 2-(2-chloroethyl)pyridine was isolated as
1
a dark oil. Yield: 2.40 g, 84%. H NMR (CDCl3): δ 3.24 (t, 2H,
3JHH ) 6.8 Hz, ClCH2), 3.92 (t, 2H, 3JHH ) 6.8 Hz, Py-CH2), 6.97
(d, 1H, 3JHH ) 7.8 Hz, Py), 7.22 (m, 2H, Py), 7.65 (t, 1H, 3JHH
)
3
5.8 Hz, Py), 8.55 (d, 1H, JHH ) 5.4 Hz, NCH).
2-[2-(Diphenylphosphino)ethyl]pyridine, 13.53,54 A solution of
2-(2-chloroethyl)pyridine (2.40 g, 17.0 mmol) in 30 mL of THF
was added to a solution of NaPPh2 in THF (100 mL, 33.4 mmol)
and stirred overnight. After reaction, NaCl was eliminated by
filtration and THF was removed under reduced pressure. Compound
13 was purified by column chromatography (length of the stationary
phase 50 cm, column diameter 2.5 cm) over silica gel using a
mixture of pentane/ethylacetate (3:1 and 5% diethylamine) and was
isolated as a white powder. Yield: 2.17 g, 45%. 1H NMR (CDCl3):
δ AA′BB′X spin system (A ) A′ ) B ) B′ ) H, X ) P) 2.51 (m,
Figure 9. Selectivity of 17, 18, 20, and 22 for C4 compounds using
MAO as cocatalyst (1-butene and 2-butene), ref: [NiCl2{P(n-
Bu)3}2].
2
2
2
2
2H, JAA′ ) 13.5 Hz, JAB ) 5.2 Hz, JAB′ ) 11 Hz, JA′B ) 11
2
2
2
Hz, JAB′ ) 5.2 Hz, JAP ) 0.7 Hz, JA′P ) 0.7 Hz, PCH2), 2.90
2
2
2
2
(m, 2H, JBB′ ) 13.5 Hz, JAB ) 5.2 Hz, JAB′ ) 11 Hz, JA′B
)
2
2
2
11 Hz, JAB′ ) 5.2 Hz, JBP ) 8.5 Hz, JA′P ) 8.5 Hz, CH2Py),
3
7.10 (d, 2H, JHH ) 7.0 Hz, Py) 7.26 (m, 6H, Ph), 7.33 (m, 4H,
Ph), 7.45 (dt, 1H, 3JHH ) 7.6 Hz, 4JHH ) 2.0 Hz, Py), 8.52 (d, 1H,
3JHH ) 4.5 Hz). 13C{1H} NMR (CDCl3): δ 28.0 (d, JPC ) 12.5
1
2
Hz, PCH2), 28.0 (d, JPC ) 18.0 Hz, PyCH2),121.2 (s, Py), 122.8
(s, Py), 128.5 (d, 3JPC ) 14.1 Hz, m-Ph), 128.5 (s, p-Ph), 132.8 (d,
Figure 10. Mass distribution of the oligomers produced by 20 and
22 (4 × 10-5 mol of complex, 25 equiv of MAO, 10 bar, 35 min).
2JPC ) 18.5 Hz, o-Ph), 136.4 (s, Py), 138.4 (d, JPC ) 13.0 Hz,
1
ipso-Ph), 149.4 (s, Py), 161.8 (d, 3JPC ) 13.4 Hz, NCCH). 31P{1H}
NMR (CDCl3): δ -14.2 (s).
3
2
(d, JPC ) 6.9 Hz, m-Ph), 129.6 (s, p-Ph), 130.6 (d, JPC ) 21.9
Synthesis of 2-Methyloxy(diphenylphosphino)pyridine, 14...56
To a solution of (pyridin-2-yl)methanol (3.04 g, 27.9 mmol) in
THF containing 3 equiv of triethylamine (12 mL, 85.0 mmol)
was added 5 mL of PPh2Cl (6.15 g, 27.9 mmol) at -78 °C. The
solution was stirred for 2 h from -78 °C to room temperature,
and all volatiles were removed under reduced pressure. The
residue was dissolved in diethyl ether to precipitate triethylammo-
nium chloride. After filtration, the solvents were removed under
reduced pressure and 14 was isolated as a pale yellow oil. Yield:
1
Hz, o-Ph), 136.7 (s, Py), 141.4 (d, JPC ) 18.3 Hz, ipso-Ph),
149.1 (s, Py), 158.7 (d, JPC ) 8.8 Hz, NCCH). 31P{1H} NMR
2
(CDCl3): δ 117.7 (s); IR (KBr) 1592 (s), 1477 (m), 1435 (s),
1096 (s), 1050 (s), 751 (s), 697 (s) cm-1
.
2-Methyloxy(dibenzyl-1,2-oxaphosphorino)pyridine, 15. To a
solution of (pyridin-2-yl)methanol (1.08 g, 10.0 mmol) in THF
containing 3 equiv of triethylamine (4.2 mL, 30.0 mmol) was added
chloro(dibenzyl-1,2-oxa)phosphorine (2.34 g, 10.0 mmol) at -78
°C. The solution was stirred for 2 h from -78 °C to room
temperature, and then the volatiles were removed under reduced
pressure. The residue was dissolved in diethyl ether to precipitate
triethylammonium chloride. After filtration, the solvents were
removed under reduced pressure and 15 was isolated as a pale
3
7.52 g, 92%. 1H NMR (CDCl3): δ 2.50 (t, 2H, JHH ) 8.7 Hz,
3
3
PCH2), 7.17 (dd, 1H, JHH ) 7.6 Hz, JHH ) 4.8 Hz, CHCHN),
3
7.36(m, 6H, Ph), 7.47 (d, 1H, JHH ) 7.6 Hz CCH), 7.55(m, 4H,
Ph), 7.67(dt, 1H, 3JHH ) 7.6 Hz, 4JHH ) 1.8 Hz, CHCHCH), 8.53
(d, 1H, JHH ) 4.8 Hz, CHN). 13C{1H} NMR (CDCl3): δ 72.2
3
1
yellow oil. Yield: 2.70 g, 88%. H NMR (CDCl3): δ ABX spin
2
2
(d, JPC ) 16.2 Hz, POCH2), 121.2 (s, Py), 122.4 (s, Py), 128.4
system (A, B, X ) P) 4.86 (1H, dd, JAB ) 13.8 Hz, JXB ) 8.7

Nickel Complexes with Phosphinopyridine Ligands
Organometallics, Vol. 27, No. 1, 2008 97
Scheme 3. Proposed Pathways to Explain the Formation of
2-Ethyl-1-butene
nitrogen flux. Yield: 135.0 g, 80%. Anal. Calcd for C4H10Cl2NiO2:
C, 21.87; H, 4.59. Found: C, 21.26; H, 4.68.
[NiBr2(DME)]..78 This compound was prepared using a method
similar to that described for [NiCl2(DME)] starting from NiBr2 (10.0
g, 45.8 mmol). It was isolated as an orange powder. Yield: 12.3 g,
87%. Anal. Calcd for C4H10Br2NiO2: C, 15.57; H, 3.27. Found: C,
15.72; H, 3.73.
[Ni{2-{(diphenylphosphino)methyl}pyridine}Cl2], 17. A solu-
tion of 12 (1.36 g, 4.9 mmol) in methanol was added to a solution
of NiCl2 (0.63 g, 4.9 mmol) at room temperature. The solution
became red and was stirred for 1 h. Methanol was removed under
reduced pressure, and the residue was dissolved in 30 mL of
CH2Cl2. Unreacted NiCl2 was eliminated by filtration. The solution
was concentrated to 10, and 40 mL of pentane was added to
precipitate 17. After filtration, 17 was washed with 20 mL of diethyl
ether, dried under vacuum, and isolated as a gray powder. Yield:
1.66 g, 84%. Anal. Calcd for C18H16Cl2NNiP: C, 53.13; H, 3.96;
N, 3.44. Found: C, 53.39; H, 4.11; N, 3.45. HRMS: Mass Calcd
for C18H16ClNNiP: 362.0006. Found: 361.9984 [Ni(P,N)Cl]+. IR
(KBr): 1604 (vs), 1566 (w), 1476 (vs), 1435 (vs), 1310 (m), 1158
(s), 1101 (vs), 1021 (m), 998 (m), 843 (s), 743 (vs), 692 (vs), 603
2
Hz, POCH2) and 4.93 (1H, dd, JAB ) 13.8 Hz, JXA ) 10.2 Hz,
POCH2), 7.04 (d, 1H, 3JHH ) 7.8 Hz), 7.10 (t, 2H, 3JHH ) 5.1 Hz),
3
7.19 (dt, 1H, JHH ) 7.5 Hz, JPH ) 1.5 Hz), 7.30 (m, 1H,), 7.50
3
(m, 2H), 7.64 (m, 1H), 7.98 (dd, 1H, JHH ) 7.8 Hz, JPH ) 1.8
3
3
Hz), 8.02 (d, 1H, JHH ) 7.8 Hz), 8.46 (dq, 1H, JHH ) 3.9 Hz,
JPH ) 0.9 Hz, Py). 13C{1H} NMR (CDCl3): δ 70.6 (d, 2JPC ) 10.8
Hz, POCH2), 120.6 (s, Ph), 120.8 (s, Py), 122.3 (s, Py), 122.5 (d,
2JPC ) 6.2 Hz, PCCC), 123.4 (s, Ph), 123.5 (s, Ph), 124.9 (s, Ph),
(w), 522 (m), 487 (m) cm-1
.
127.7 (d, 3JPC ) 13.4 Hz, PCCHCH), 129.6 (s, Ph), 131.5 (d, 2JPC
3
) 48.2 Hz, PCCH), 131.7 (s, Ph), 131.9 (s, Ph), 132.2 (d, JPC
)
[Ni(µ-Cl)2{2-{2-(diphenylphosphino)ethyl}pyridine}2]2Cl2, 18.
This compound was prepared using a method similar to that
described for 17 by reaction of ligand 13 (2.17 g, 6.0 mmol) with
NiCl2 (0.78 g, 6.0 mmol). 18 was isolated as a green powder. Yield:
2.19 g, 80%. Anal. Calcd for C38H36Cl4N2Ni2P2: C, 54.21; H, 4.31;
N, 3.33. Found: C, 53.92; H, 4.39; N, 3.10. HRMS: Mass Calcd
for C19H18ClNNiP: 384.0213. Found: 384.0227 [Ni(P,N)Cl]+. IR
(KBr): 1605 (vs), 1484 (vs), 1437 (vs), 1377 (m), 1158 (m), 1101
(s), 1025 (m), 998 (m), 869 (m), 757 (s sh), 743 (s), 718 (m), 698
2
2.8 Hz, POCC), 136.5 (s, Py), 141.9 (s, Py), 149.7 (d, JPC ) 9.3
Hz, POC Ph), 158.1 (d, JPC ) 4.7 Hz, NCCH2). 31P{1H} NMR
2
(CDCl3): δ 130.5 (s).
Chloro-di-tert-butylphosphine...77 It was synthesized according
to the literature77 by dropwise addition of a solution of t-BuLi (60.0
mL, 102.0 mmol, 1.7 M in pentane) to a solution of PCl3 (7.00 g,
51.0 mmol) in 100 mL of pentane at -78 °C. The mixture was
stirred overnight from -78 °C to room temperature. LiCl was
removed by filtration, and pentane was slowly removed under
reduced pressure. The residue was distilled under reduced pressure
(70 °C, 10 mbar), and chloro-di-tert-butylphosphine was isolated
as a colorless liquid. Yield: 2.90 g, 32%. 1H NMR (CDCl3): δ 1.24
(vs), 526 (s), 500 (m), 475 (m) cm-1
.
[Ni(µ-Cl)2{(pyridin-2-yl)methanol}2]2Cl2, 19, and [Ni{P(OMe)-
Ph2}2Cl2]. A MeOH solution of ligand 14 (0.89 g, 3.0 mmol) was
added to a MeOH solution of NiCl2 (0.39 g, 3.0 mmol). The
resulting red solution was stirred at reflux for 1 h. After reaction,
the solvent was removed under vacuum, and 20 mL of CH2Cl2
was added. A green precipitate was isolated from the red solu-
tion by filtration and was identified as [Ni(µ-Cl)2{(pyridin-2-
yl)methanol}2]2Cl2, 19. Yield: 0.52 g, 98%. Anal. Calcd for
C24H28Cl4N4Ni2O4: C, 41.43; H, 4.06; N, 8.05. Found: C, 41.82;
H, 4.37; N, 7.86. HRMS: Mass Calcd for C12H14ClN2O2Ni:
311.0092. Found: 311.0099 [Ni(N,O)2Cl]+. IR (KBr): 1608 (s),
1571 (m), 1483 (m), 1444 (s), 1286 (m), 1237 (m), 1156 (m), 1033
(d, 18H, JPH ) 12.1 Hz, CH3). 31P{1H} NMR (CDCl3): δ 148.0
3
(s).
2-Methyloxy(di-tert-butylphosphino)pyridine, 16. A solution
of t-BuLi (4.00 mL, 6.7 mmol, 1.7 M in pentane) was added to a
solution of (pyridin-2-yl)methanol (0.725 g, 6.7 mmol) in 30 mL
of THF at -78 °C. The solution became red and was stirred for 30
min. Di-tert-butylchlorophosphine (1.20 g, 6.7 mmol) in 20 mL of
THF was added to the mixture to afford a pale yellow solution,
which was stirred overnight from -78 °C to room temperature.
THF was removed under reduced pressure, and diethyl ether was
added to precipitate LiCl. After filtration and removal of the solvents
under reduced pressure, 16 was isolated as a pale yellow oil. Yield:
(s), 765 (s), 727 (m) cm-1
.
All the volatiles of the red solution were removed under reduced
pressure, and the residue was dissolved in 20 mL of diethyl ether.
Then 80 mL of pentane was added to the solution, and a red powder
precipitated, which was characterized as [Ni{P(OMe)Ph2}2Cl2].
Yield: 0.71 g, 84%. Anal. Calcd for C26H26Cl2NiO2P2: C, 55.56;
H, 4.66. Found: C, 55.40; H, 4.69.
1
3
1.52 g, 89%. H NMR (CDCl3): δ 1.13 (d, 18H, JPH ) 11.7 Hz,
CH3), 4.93 (d, 2H, 3JPH ) 5.7 Hz, CH2), 7.18 (m, 1H, Py), 7.55 (d,
3
3
4
1H, JHH ) 7.8 Hz, Py), 7.70 (dt, 1H, JHH ) 7.5 Hz JHH ) 1.8
Hz, Py), 8.53 (d, 1H, 3JHH ) 4.8 Hz, Py). 13C{1H} NMR (CDCl3):
2
2
δ 27.4 (d, JPC ) 15.1 Hz, CH3), 35.4 (d, JPC ) 24.3 Hz, PC),
76.1 (d, 2JPC ) 21.7 Hz, OCH2), 120.9 (s, Py), 122.1 (s, Py), 136.6
(s, Py), 149.0 (s, Py), 159.5 (d, 3JPC ) 10.6 Hz, NCCH). 31P{1H}
NMR (CDCl3): δ 166.3 (s).
[Ni{2-methyloxy(diphenylphosphino)pyridine}Cl2], 20. Solid
[NiCl2(DME)] (2.51 g, 11.5 mmol) was added to a solution of 14
(3.21 g, 11.0 mmol) in 30 mL of CH2Cl2. The solution became red
and was stirred for 2 h. After reaction, unreacted [NiCl2(DME)]
was eliminated by filtration. The solution was concentrated to 10
mL, and 40 mL of pentane was added to precipitate 20. After
filtration, 20 was washed with diethyl ether, dried under vacuum,
and isolated as a green powder. Yield: 4.28 g, 92%. Anal. Calcd
for C18H16Cl2NNiOP: C, 51.12; H, 3.81; N, 3.31. Found: C, 50.81;
H, 4.04; N, 3.00. HRMS: Mass Calcd for C18H16ClNNiOP:
386.0006. Found: 386.0007 [Ni(P,N)Cl]+. IR (KBr): 1606 (s), 1571
(m), 1484 (s), 1438 (vs), 1380 (w), 1313 (m), 1232 (w), 1185 (w),
1158 (m), 1130 (m), 1010 (vs), 833 (w), 741 (vs), 696 (vs) 618
[NiCl2(DME)]...78 NiCl2 (100 g, 771.6 mmol) was dissolved in
a mixture of 300 mL of methanol and 50 mL of trimethylortho-
formate and stirred at reflux overnight. After reaction, unreacted
NiCl2 was eliminated by filtration and 80% of the solution was
removed under reduced pressure to obtain a green gel. It was
dissolved in a minimum of methanol, and 300 mL of DME was
added. The solution was stirred at reflux overnight. A yellow powder
of [NiCl2(DME)] precipitated and was isolated by filtration through
a canula. The powder was washed with pentane and dried under a
(m), 539 (s), 486 (s) cm-1
.
(77) Naiini, A. A.; Han, Y.; Akinc, M.; Verkade, J. G. Inorg. Chem.
1993, 32, 5394–5395.
(78) Ward, L. G. L. Inorg. Synth. 1971, 13, 154–164.
[Ni{2-methyloxy(diphenylphosphino)pyridine}Br2], 21. This
compound was prepared using a method similar to that described

98 Organometallics, Vol. 27, No. 1, 2008
Kermagoret and Braunstein
Table 7. Crystallographic Data for Complexes 18 and 22
18
22
chemical formula
Mr
C38H36Cl4N2Ni2P2
841.85
C14H24Cl2NNiOP
382.92
cell setting, space group
temperature (K)
a (Å)
b (Å)
c (Å)
monoclinic, C2/c
173(2)
monoclinic, P21/n
173(2)
20.4250(8)
15.5080(7)
11.9040(6)
103.913(2)
3660.0(3)
4
1.528
Mo KR
1728
8.8770(3)
17.1160(6)
12.0180(5)
102.7270(12)
1781.14(11)
4
1.428
Mo KR
800
ꢀ (deg)
V (Å3)
Z
Dx (Mg m-3
radiation
F(000)
)
µ (mm-1
)
1.44
1.47
cryst size (mm)
0.12 × 0.03 × 0.02
9382, 5331, 3826
I > 2σ(I)
0.078
0.12 × 0.10 × 0.08
7317, 4076, 3133
I > 2σ(I)
0.064
no. of measd, indept, and obsd reflns
criterion for obsd reflns
Rint
θmax (deg)
30.0
27.5
data set (h; k; l)
-28/28; -19/21; -16/16
0.096, 0.116, 1.21
5331
-11/11; -22/20; -15/15
0.083, 0.117, 1.19
4076
R[F2 > 2σ(F2)], wR(F2), S
no. of reflns
no. of params
218
181
for 20 by reaction of [NiBr2(DME)] (0.77 g, 2.6 mmol) with ligand
14 (0.65 g, 2.6 mmol). 21 was isolated as a green powder. Yield:
0.92 g, 72%. Anal. Calcd for C14H24Br2NNiOP: C, 42.24; H, 3.15;
N, 2.74. Found: C, 42.05; H, 3.33; N, 2.68. IR (KBr): 1605 (s),
1484 (s), 1438 (s), 1157 (m), 1131 (m), 1102 (s), 758 (s), 696 (s)
With MAO in toluene as a cocatalyst, 1 × 10-2 or 4 × 10-2
mmol of Ni complex was dissolved in 10 mL in chlorobenzene
and injected into the reactor under an ethylene flux. Then 0.5, 1, 2,
4, 8, or 16 mL of a cocatalyst solution, corresponding to 12.5, 25,
50, 100 (4 mL for 4 × 10-2 mmol of Ni complex or 1 mL for
10-2 mmol of Ni complex), 200, or 400 equiv of MAO,
respectively, was added.
cm-1
.
[Ni{2-methyloxy(di-tert-butylphosphino)pyridine}Cl2], 22.
This compound was prepared using a method similar to that
described for 20 by reaction of [NiCl2(DME)] (0.57 g, 2.6 mmol)
with ligand 17 (0.65 g, 2.6 mmol). 22 was isolated as a red powder.
Yield: 0.70 g, 70%. Anal. Calcd for C14H24Cl2NNiOP: C, 43.91;
H, 6.32; N, 3.66. Found: C, 43.25; H, 6.37; N, 3.62. HRMS: Mass
Calcd for C14H24ClNNiOP: 346.0632. Found: 346.0677 [Ni(P,N)
Cl]+. IR (KBr): 1607 (s), 1479 (s), 1438 (m sh), 1370 (m), 1315
(m), 1060 (w), 1026 (vs), 999 (vs), 808 (m), 780 (s), 764 (s), 743
All catalytic tests were started between 25 and 30 °C, and no
cooling of the reactor was done during the reaction. After injection
of the catalytic solution and of the cocatalyst under a constant low
flow of ethylene, the reactor was pressurized to 10 or 30 bar. A
temperature increase was observed, which resulted solely from the
exothermicity of the reaction. The 10 or 30 bar working pressure
was maintained during the experiments through a continuous feed
of ethylene from a reserve bottle placed on a balance to allow
continuous monitoring of the ethylene uptake. At the end of each
test (35 or 120 min) a dry ice bath, and in the more exothermic
cases also liquid N2, was used to rapidly cool the reactor, thus
stopping the reaction. When the inner temperature reached 0 °C,
the ice bath was removed, allowing the temperature to slowly rise
to 10 °C. The gaseous phase was then transferred 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 amount of ethylene not consumed was thus deter-
mined. Although this method is of limited accuracy, it was used
throughout and gave satisfactory reproducibility. The products in
the reactor were hydrolyzed in situ by the addition of ethanol (1
mL), transferred into a Schlenk flask, and separated from the metal
complexes by trap-to-trap evaporation (20 °C, 0.8 mbar) into a
second Schlenk flask previously immersed in liquid nitrogen in
order to avoid loss of product.
(m), 622 (s) cm-1
.
[Ni{2-methyloxy(dibenzyl-1,2-oxa-phosphorino)pyridine}Cl2],
23. This compound was prepared using a method similar to that
described for 20 by reaction of [NiCl2(DME)] (1.93 g, 8.8 mmol)
with ligand 15 (2.70 g, 8.8 mmol). 23 was isolated as a maroon
powder (2.88 g, 6.6 mmol). Yield: 2.88 g, 75%. Anal. Calcd for
C14H24Cl2NNiOP: C, 49.49; H, 3.23; N, 3.21. Found: C, 47.64; H,
4.27; N, 2.90 (despite several attempts, better analysis were not
obtained). HRMS: Mass Calcd for C14H24ClNNiOP: 399.9804.
Found: 399.9815 [Ni(P,N)Cl]+. IR (KBr): 1675 (s sh), 1638 (s),
1608 (vs), 1583 (m sh), 1560 (w), 1476 (vs), 1443 (m), 1430 (s),
1278 (m), 1203 (vs), 1116 (s), 1060 (vs), 913 (s), 758 (vs), 716
(m), 619 (m), 605 (m), 531 m) cm-1
.
Oligomerization of Ethylene. All catalytic reactions were carried
out in a magnetically stirred (900 rpm) 145 mL stainless steel
autoclave. A 125 mL glass container was used to protect the inner
walls of the autoclave from corrosion. The preparation of the
solution of the precatalyst is dependent on the nature and the amount
of the cocatalyst.
Crystal Structure Determinations. Diffraction data were col-
lected on a Kappa CCD diffractometer using graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å) (Table 7).
Data were collected using phi-scans, the structures were solved
by direct methods using the SHELX 97 software,79,80 and the
refinement was by full-matrix least-squares on F2. No absorption
correction was used. All non-hydrogen atoms were refined aniso-
When AlEtCl2 in toluene was used as a cocatalyst, 4 × 10-2
mmol of Ni complex was dissolved in 14, 13, or 12 mL of
cholorobenzene depending on the amount of the cocatalyst and
injected into the reactor under an ethylene flux. Then 1, 2, or 3 mL
of a cocatalyst solution, corresponding to 2, 4, or 6 equiv,
respectively, was added to form a total volume of 15 mL with the
precatalyst solution. When 10-2 mmol of precatalyst was used, a
solution of the complex in 14 mL of chlorobenzene was injected
into the reactor, followed by 0.75 mL of a solution of the cocatalyst
(6 equiv).
tropically with H atoms introduced as fixed contributors (dC-H
)
(79) Kappa CCD Operation Manual, Nonius BV: Delft, The Nether-
lands, 1997.
(80) Sheldrick, G. M. SHELXL97, Program for the refinement of crystal
structures; University of Göttingen: Germany, 1997.

Nickel Complexes with Phosphinopyridine Ligands
Organometallics, Vol. 27, No. 1, 2008 99
0.95 Å, U11 ) 0.04). Crystallographic data (excluding structure
factors) have been deposited in the Cambridge Crystallographic
Data Centre as Supplementary publication no. CCDC 668689 and
668690. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: (+44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
are grateful to Dr. A. DeCian and Prof. R. Welter (ULP
Strasbourg) for the crystal structure determinations and to
M. Mermillon-Fournier and P. Chavez (LCC Strasbourg) for
experimental assistance. We thank a referee for useful
comments.
Supporting Information Available: CIF files giving crystal data
for the complexes 18 and 22. This material is available free of
charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank the Centre National de la
Recherche Scientifique (CNRS), the Ministère de l’Education
Nationale et de la Recherche (Paris) (Ph.D. grant to A.K.),
and the Institut Français du Pétrole (IFP) for support. We
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