Nickel complexes with Phosphinito-Oxazoline Ligands: Temperature-Controlled formation of Mono- or Dinuclear complexes and catalytic oligomerization of ethylene and propylene

Article abstract of DOI:10.1021/om8009848

The complex [NiCl₂{Ph₂POCH₂ox ^Me2}] (Ph₂POCH₂ox^Me2 = 2-((diphenylphosphinooxy) methyl)-4,4-dimethy 1-4,5-dihydrooxazole) 14 has been synthesized by reaction of solid [NiCl_2<

Full text of DOI:10.1021/om8009848

1776
Organometallics 2009, 28, 1776–1784
Nickel Complexes with Phosphinito-Oxazoline Ligands:
Temperature-Controlled Formation of Mono- or Dinuclear
Complexes and Catalytic Oligomerization of Ethylene and Propylene
Patricia Chavez,† Itzel Guerrero Rios,‡ Anthony Kermagoret,† Roberto Pattacini,†
Andrea Meli,‡ Claudio Bianchini,‡ Giuliano Giambastiani,*,‡ and Pierre Braunstein*,†
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), UniVersite´ de Strasbourg,
4 rue Blaise Pascal, F-67070 Strasbourg Ce´dex, France, and Institute of Chemistry of OrganoMetallic
Compounds, ICCOM-CNR, Via Madonna del Piano, 10 - 50019 Sesto Fiorentino (Fi), Italy
ReceiVed October 12, 2008
The complex [NiCl2{Ph2POCH2oxMe2}] (Ph2POCH2oxMe2 ) 2-((diphenylphosphinooxy) methyl)-4,4-
dimethyl-4,5-dihydrooxazole) 14 has been synthesized by reaction of solid [NiCl2(DME)] (DME ) 1,2-
dimethoxyethane) with a CH2Cl2 solution of the P,N ligand. X-ray diffraction studies on its red crystals
established the mononuclear nature of the complex 14a, whose metal center has a distorted tetrahedral
coordination geometry. Recrystallization of 14a from a toluene-pentane/CH2Cl2 solution at temperatures
below 253 K afforded green crystals of the dinuclear, chloride-bridged, formula isomer complex 14b.
Conversion of 14b to 14a was observed as a function of temperature, both in the solid-state and in
solution. Together with other Ni(II) complexes containing a chelating P,N ligand of the type phosphino-
or phosphinito-oxazoline or phosphino-thiazoline, 14a has been evaluated as precatalyst in the
oligomerization of ethylene, with AlEtCl2 or MAO as cocatalyst, or propylene, with MAO as cocatalyst.
With AlEtCl2 as activator (6 equiv), the catalytic activities with ethylene were generally modest and
[NiCl2{Ph2PCH2ox}] (Ph2PCH2ox ) 2-((diphenylphosphinooxy)methyl)-4,5-dihydrooxazole) 1 was the
most active, with turnover frequencies (TOF) up to 7.9 × 104 mol of C2H4 (mol Ni × h)-1, whereas 14a,
activated with 2 equiv of AlEtCl2, was the most selective for ethylene dimers (up to 96%) and 1-butene
(up to 22%). With MAO as cocatalyst, complex 1 was again the most active, with TOF values up to 23
× 104 mol of C2H4 (mol Ni × h)-1. The highest selectivity for butenes was observed with complex
[NiCl2{Ph2PCH2thiazMe2}] 3. With propylene, TOFs up to 3.3 × 104 mol of C3H6 (mol Ni × h)-1 were
obtained with [NiCl2{Ph2POCH2pyridine}] 8 and selectivities for C6 products higher than 98.5% were
observed with precatalysts 3, [NiCl2{t-Bu2POCH2pyridine}] 9, and 14a.
of ethylene,3-5 a reaction of major industrial interest.6 Indeed,
since the seminal works of Ziegler and Natta on the oligomer-
Introduction
Heterofunctional ligands are much studied and applied in
coordination and organometallic chemistry owing to the often
unique properties of their metal complexes and their ability to
generate hemilabile systems endowed with enhanced reactivity.1
The combination of a hard nitrogen donor with a soft phosphorus
donor within a functional ligand leads to considerable chemical
and structural diversity and the resulting metal complexes often
display important applications in homogeneous catalysis, in
particular because of the stereoelectronic differentiation brought
about by the different donor functions and the stabilization of
the metal ion in optimum oxidation states.1-3 Chelating P,N
ligands containing N-heterocycles, such as pyridyl- and ox-
azolyl-, have been much investigated and their nickel complexes
are active catalyst precursors in the catalytic oligomerization
ization and polymerization of ethylene with metal catalysts
activated by alkyl aluminums,7 major industrial developments
(2) (a) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Zanobini, F.
Coord. Chem. ReV. 1992, 120, 193. (b) Newkome, G. R. Chem. ReV. 1993,
93, 2067. (c) Ajjou, A. N.; Alper, H. J. Am. Chem. Soc. 1998, 120, 1466.
(d) Espinet, P.; Soulantica, K. Coord. Chem. ReV. 1999, 193–195. (e) Qadir,
M.; Mochel, T.; Hii, K. K. Tetrahedron 2000, 56, 7975. (f) Hierso, J.-C.;
Amardeil, R.; Bentabet, E.; Broussier, R.; Gautheron, B.; Meunier, P.; Kalck,
P. Coord. Chem. ReV. 2003, 236, 143.
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784.
(4) (a) Bluhm, M. E.; Folli, C.; Walter, O.; Doering, M. J. Mol. Catal.
A., Chem. 2005, 229, 177. (b) Mukherjee, A.; Subramanyam, U.; Puranik,
V. G.; Mohandas, T. P.; Sarkar, A. Eur. J. Inorg. Chem. 2005, 1254. (c)
Sirbu, D.; Consiglio, G.; Gischig, S. J. Organomet. Chem. 2006, 691, 1143.
(d) Speiser, F.; Braunstein, P.; Saussine, L. Organometallics 2004, 23, 2625.
(e) Speiser, F.; Braunstein, P.; Saussine, L. Organometallics 2004, 23, 2633.
(f) Sun, W.-H.; Li, Z.; Hu, H.; Wu, B.; Yang, H.; Zhu, N.; Leng, X.; Wang,
H. New J. Chem. 2002, 26, 1474. (g) Tang, X.; Zhang, D.; Jie, S.; Sun,
W.-H.; Chen, J. J. Organomet. Chem. 2005, 690, 3918.
(5) Kermagoret, A.; Braunstein, P. Organometallics 2008, 27, 88.
(6) Vogt, D., Ed. Applied Homogeneous Catalysis with Organometallic
Compounds; VCH: Weinheim, 2002. (b) Gibson, V. C.; Spitzmesser, S. K.
Chem. ReV. 2003, 103, 283. (c) Ittel, S. D.; Johnson, L. K.; Brookhart, M.
Chem. ReV. 2000, 100, 1169.
* To whom correspondence should be addressed. E-mail: braunstein@
chimie.u-strasbg.fr, giuliano.giambastiani@iccom.cnr.it.
† Universite´ de Strasbourg, France.
‡ ICCOM-CNR, Sesto Fiorentino, Italy.
(1) (a) Bader, A.; Lindner, E. Coord. Chem. ReV. 1991, 108, 27. (b)
Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem. 1999,
48, 233. (c) Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336. (d)
Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680. (e)
McManus, H. A.; Guiry, P. J. Chem. ReV. 2004, 104, 4151. (f) Margraf,
G.; Pattacini, R.; Messaoudi, A.; Braunstein, P. Chem. Commun. 2006, 3098.
(g) Braunstein, P. Chem. ReV. 2006, 106, 134.
(7) (a) Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem.
1955, 67, 426. (b) Wilke, G. Angew. Chem., Int. Ed. 2003, 42, 5000. (c)
Bolton, P. D.; Mountford, P. AdV. Synth. Catal. 2005, 347, 355. (d) Bo¨hm,
L. L. Angew. Chem., Int. Ed. 2003, 42, 5010.
10.1021/om8009848 CCC: $40.75
2009 American Chemical Society
Publication on Web 02/12/2009

Nickel Complexes with Phosphinito-Oxazoline Ligands
Organometallics, Vol. 28, No. 6, 2009 1777
Scheme 1
Figure 1. ORTEP plot of the molecular structure of 14a. Hydrogen
atoms have been omitted for clarity. Selected distances (Å) and
angles (°): Ni1-N1 1.977(7), Ni1-Cl1 2.234(2), Ni1-Cl2 2.179(3),
Ni1-P1 2.264(2), N1-C5 1.25(1); N1-Ni1-Cl1 98.3(2), N1-
Ni1-Cl2 118.1(2), Cl1-Ni1-Cl2 127.5(1), N1-Ni1-P1 90.5(2),
Cl1-Ni1-P1 101.2(1), Cl2-Ni1-P1 113.9(1).
in the catalytic production of linear R-olefins (LAO) have taken
place. Complexes of the late transition metals such as Ni, Pd,
Co, and Fe give rise to oligomerization precatalysts by favoring
chain transfer over propagation during the catalytic cycle.3,8
Some of us have recently prepared a range of Ni(II)
complexes with a P,N chelating ligand containing a phosphine
or a phosphite donor associated with an oxazoline or a thiazoline
heterocycle and studied the catalytic properties of some of them
in ethylene oligomerization as a function of the chelate ring
size, the nature of the phosphorus function, the cocatalyst (MAO
or AlEtCl2) and in some cases compared them with their
analogues containing a pyridine donor in place of the oxazoline
(see 1-12, Scheme 1).3,5 The nuclearity of the complexes and
the coordination geometry around the Ni center(s) (square-
planar, tetrahedral, trigonal bipyramidal, with varying degrees
of distortion) were found to be very sensitive to the chelate
ring size and its substitution pattern.
methyl-4,5-dihydrooxazole) 14 was synthesized by reacting
[NiCl2(DME)] with a CH2Cl2 solution of the P,N ligand,10,11
similarly to its Co(II) analogue.11 A red powder was obtained
by addition of n-pentane and single crystals of 14a formed by
slow diffusion of a toluene-pentane mixture into a CH2Cl2
solution of the complex at 298 K. No NMR characterization of
the complexes described in this work was possible owing to
their paramagnetic nature.
It was also found that unprecedented tetranuclear complexes
of the type [{Ni2(µ2-Cl)2Cl(P,N)2}2(µ3-Cl)2] (13) could form and
undergo in the solid-state an irreversible pressure-induced
fragmentation into the corresponding mononuclear complex
[NiCl2(P,N)] (1 or 3).9 These observations triggered our interest
for further studies, reported below, on these classes of com-
pounds and their catalytic properties in ethylene and propylene
oligomerization.
In the molecular structure of 14a (Figure 1), the metal
center is chelated by a molecule of the P,N ligand Ph2-
POCH2CdNCMe2CH2O with a bite angle of 90.5(2)°. The
chelate ring defined by P1, O2, C6, C5, N1, Ni1 adopts a boat
conformation. Two terminal chlorides are also bound to the
metal center whose coordination geometry is distorted tetrahe-
dral. The structure is similar to that of the complex
[NiCl2{Ph2POCMe2oxMe2}] (Ph2POCMe2oxMe2 ) 2-(2-(diphe-
nylphosphinooxy)propan-2-yl)-4,4-dimethyl-4,5-dihydroox-
azole) 10 which contains a CMe2 group R to the oxygen
(Scheme 1)12 and to that of the Co(II) complexes [CoCl2-
{Ph2POCH2oxMe2}] or [CoCl2{Ph2POCMe2oxMe2}].11 The Ni1-
Cl1 distance in 14a (Ni1-Cl1 2.234(2) Å) is slightly longer
than Ni1-Cl2 (Ni1-Cl2 2.179(3) Å), and the Cl2-Ni1-P1
angle (113.9(1)°) is wider than Cl1-Ni1-P1 (101.2(1)°).
Results
Synthesis and X-Ray Crystal Structures of 14a and 14b and
Their Interconversion. The complex [NiCl2{Ph2POCH2oxMe2}]
(Ph2POCH2oxMe2 ) 2-((diphenylphosphinooxy)methyl)-4,4-di-
(8) (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428. (b) Mecking, S. Angew. Chem., Int. Ed. 2001, 40,
534. (c) Rieger, B., Saunders Baugh, L., Kacker, S., Striegler, S., Eds. Late
Transition Metal Polymerization Catalysis; Wiley-VCH: Weinheim, 2003.
(d) Bianchini, C.; Giambastiani, G.; Guerrero, I. R.; Mantovani, G.; Meli,
A.; Segarra, A. M. Coord. Chem. ReV. 2006, 250, 1391. (e) Bianchini, C.;
Gatteschi, D.; Giambastiani, G.; Rios, I. G.; Ienco, A.; Laschi, F.; Mealli,
C.; Meli, A.; Sorace, L.; Toti, A.; Vizza, F. Organometallics 2007, 26,
726. (f) Toti, A.; Giambastiani, G.; Bianchini, C.; Meli, A.; Luconi, L. AdV.
Synth. Catal. 2008, 350, 1855.
(9) Kermagoret, A.; Pattacini, R.; Chavez Vasquez, P.; Rogez, G.;
Welter, R.; Braunstein, P. Angew. Chem., Int. Ed. 2007, 46, 6438.
(10) Agostinho, M.; Braunstein, P.; Welter, R. Dalton Trans. 2007, 759.
(11) Jie, S.; Agostinho, M.; Kermagoret, A.; Cazin, C. S. J.; Braunstein,
P. Dalton Trans. 2007, 4472.
(12) Speiser, F.; Braunstein, P.; Saussine, L.; Welter, R. Inorg. Chem.
2004, 43, 1649.

1778 Organometallics, Vol. 28, No. 6, 2009
ChaVez et al.
Recrystallization of 14a from a toluene-pentane/CH2Cl2
solution at temperatures below 253 K afforded a mixture of
red and green crystals, the latter corresponding to the dinuclear
formula isomer complex 14b. Its proportion increases when the
crystallization temperature is lowered to 238 K, where the ratio
14a/14b is approximately 1:1. An ORTEP plot of the molecular
structure of 14b in 14b · 2CH2Cl2 · 2CH3C6H5 is shown in Figure
2.
Complex 14b is a chloride-bridged dinuclear compound,
similar to the five-membered ring phosphino-oxazoline bromo
analog 11.13 The existence of a crystallographic C2 axis passing
through Cl2 and Cl3 results in the planarity of the central Ni2Cl2
unit. Each Ni atom is also coordinated by the P,N chelate
Ph2POCH2CdNCMe2CH2O and by a terminal chloride, giving
rise to a distorted square-pyramidal coordination geometry, the
base of the pyramid being defined by N1, Cl1, Cl2, and Cl3
and the vertex being occupied by the P1 atom. The distance
between Ni1 and the mean plane defined by the basal atoms is
0.330(7) Å. Only four [(NiCl2(P,N)]2 (P,N ) chelating ligand)
compounds similar to 14b appear to have been reported in the
literature, three of which sharing the same arrangement,5,14,15
while in the fourth, the dinuclear phosphinito-pyridine Ni(II)
complex 15, the P atom is in the base of the distorted square-
pyramidal structure whose vertex is occupied by a chlorine.12
Figure 2. ORTEP plot of the molecular structure of 14b in
14b · 2CH2Cl2 · 2CH3C6H5. Hydrogen atoms have been omitted and
only the phenyl ipso carbon atoms are depicted for clarity.
Symmetry operations generating equivalent atoms (′): -x, y, -1/
2-z. Selected distances (Å) and angles (deg): Ni1-N1 2.078(3),
Ni1-P1 2.292(1), Ni1-Cl1 2.292(1), Ni1-Cl2 2.334(1), Ni1-Cl3
2.415(1), N1-C5 1.265(5); N1-Ni1-Cl1 89.3(1), N1-Ni1-P1
91.2(1), Cl1-Ni1-P1 104.54(5), N1-Ni1-Cl2 89.4(1), Cl1-
Ni1-Cl2 151.33(4), P1-Ni1-Cl2 104.12(4), N1-Ni1-Cl3 172.5(1),
Cl1-Ni1-Cl3 95.50(4), P1-Ni1-Cl3 93.08(4), Cl2-Ni1-Cl3
83.66(5), Ni1-Cl2-Ni1′ 98.54(7), Ni1-Cl3-Ni1′ 94.15(6).
Although the structures of 14a and 14b display well-known
connectivities, this is the first time, to the best of our knowledge,
that the crystal structures of formula isomers of the type
[NiX2(P,N)]n (X ) Cl, Br; n ) 1, 2, or 4) have been determined.
According to the Cambridge Crystallographic database,16 there
are five different structural types encountered for complexes of
the general formula [NiX2(P,N)]n (Scheme 2).9
Compound 14a shows a type II structure, whereas 14b
belongs to the type III family whose structure contains a C2
symmetry axis. Intuitively, square planar structures (type I) are
possible when the steric hindrance in the metal coordination
plane is minimized (e.g., when P,N is Ph2PC(CH3)2-o-
pyridine).4e In 14a this arrangement would be disfavored
because of the presence of the two methyl groups in R position
with respect to the nitrogen atom. For similar reasons, the
centrosymmetricstructuresoftypesIV(e.g.,P,N)Ph2POCMe2CH2-
o-pyridine in 15)12 or V (e.g., P,N ) Ph2PCH2-2-oxazoline and
-thiazoline as in compounds 1 and 3, respectively, in Scheme
1)9 are disfavored with this ligand, being hindered in the position
cis to the phosphorus atom in the P, Ni, N plane. The P-Ni-N
angle can be larger and have more flexibility in a type III vs a
type IV structure.5 Type V structures require ligands with
relatively reduced steric hindrance, both in the chelation plane
and toward the axial positions (as with Ph2PCH2-2-thiazoline).
Figure 3. Comparison between the FTIR spectra in the 750-1800
cm-1 region of a single crystal of 14a (upper) and of the product
resulting from spontaneous transformation of 14b above 253 K
(lower spectrum).
Green crystals of 14b obtained at or below 253 K from a
toluene-pentane/CH2Cl2 solution turned red in their mother
liquor at room temperature. The product of this transformation
has been confirmed by FTIR spectroscopy to be 14a, thus
implying that dissociation of the dinuclear complex has occurred
in the solid-state. A comparison between the FTIR spectra of a
single crystal of 14a (Figure 3, upper spectrum) and of the red
product resulting from the spontaneous transformation of 14b
(Figure 3, lower spectrum) shows that they are superimposable.
The important role played by the crystallization solvent in
assisting the solid-state transformation of 14b to 14a is
noteworthy. The conversion is very slow when the crystals of
14b are protected by a perfluorinated oil, whereas it is fast when
the crystals are exposed to air. In the former case, the crystals
become opaque almost immediately, presumably because of
rapid loss of the most volatile species in the lattice, CH2Cl2. At
this stage, however, no color change occurs. This happens
slowly, suggesting that the loss of toluene may be a necessary
(13) Speiser, F.; Braunstein, P.; Saussine, L.; Welter, R. Organometallics
2004, 23, 2613.
(14) Sun, W.-H.; Li, Z.; Hu, H.; Wu, B.; Yang, H.; Zhu, N.; Leng, X.;
Wang, H. New J. Chem. 2002, 26, 1474.
(15) Faissner, R.; Huttner, G.; Kaifer, E.; Kircher, P.; Rutsch, P.; Zsolnai,
L. Eur. J. Inorg. Chem. 2003, 2219.
(16) CCDC database November 2007 Update.

Nickel Complexes with Phosphinito-Oxazoline Ligands
Organometallics, Vol. 28, No. 6, 2009 1779
Scheme 2
Ethylene Oligomerization Catalyzed by Nickel Complexes
Activated with AlEtCl2. Table 1 reports the results of a study
where the Ni(II) complexes 1-3,6,10-12, and14a (40 µmol)
were used to catalyze the oligomerization of ethylene in the
presence of 2, 4, or 6 equiv of AlEtCl2 as precatalyst activator.
All these catalytic systems gave almost exclusively butenes
and hexenes in ratios increasing with the amount of activator.
The selectivity in R-olefins was relatively modest (3-22 mol%
estimated on butenes) because of a fast isomerization process,
which is typical of Ni(II) oligomerization catalysts.6b,c,19 Pre-
catalyst 1 showed the highest activity with TOFs as high as 7.9
× 104 mol C2H4 converted (mol of Ni × h)-1 with 6 equiv of
AlEtCl2 (entry 2), while 14 activated by 2 equiv of AlEtCl2
gave the lowest ethylene conversion but the most selective
system, yielding 96% of C4 olefins with 22% of 1-butene (entry
14).
Since comparable activities were observed for the bis-chloride
1 and the bis-bromide 2 with either 2 or 6 equiv of AlEtCl2,
respectively, the halide coligand in the precursor seems to have
a negligible influence on the catalytic outcome (Table 1, entries
1 vs 3 and 2 vs 5). Replacing the oxygen atom with sulfur in
the azoline ring decreased the catalytic activity when only 2
equiv of AlEtCl2 were used (entry 6 vs entries 1 and 3), but
this effect was much less significant in the presence of 6 equiv
of this cocatalyst (entry 7 vs entries 2 and 5).
Compared to the catalytic results of the nickel complexes 6,
11 and 12 coordinated by dimethyl-substituted oxazoline
moieties,13 1-3 showed higher activities but lower selectivities
in butenes (entries 2 vs 13, 2 vs 9, and 5 vs 12).
step for the 14b f 2 14a fragmentation. This is reminiscent of
the pressure-induced isomerization of the tetranuclear complex
[NiCl2(Ph2PCH2-2-oxazoline)]4 (type V) in the solid state, which
afforded 1 (type I) only after solvent evaporation.9 In first
approximation, the voids created by the solvent loss facilitate
the conversion, as a lattice relaxation (when going from 14b to
14a) becomes then possible. A similar solid-state dissociation
has been observed with R-diimino complexes of the type
[NiBr2[(t - Bu)NdCHCHdN(t-Bu)]], however at higher tem-
Ethylene Oligomerization Catalyzed by Nickel Complexes
Activated with MAO. Complexes 1-5, 7-9, and 14 (Scheme
1) have been tested in the ethylene oligomerization using
methylaluminoxane (MAO) (2000 equiv) as activator. Table 2
summarizes the results of reactions carried out using 2 µmol of
precatalyst in 40 mL of a toluene/chlorobenzene mixture. Under
these conditions, no induction period was observed and the
maximum activity was attained within a few minutes, then the
consumption of ethylene remained practically constant for more
than half an hour. All complexes investigated have been found
to generate active systems for the production of short-chain
olefins, in the C4-C10 range, with a Schulz-Flory distribution
and turnover frequencies (TOFs) as high as 23 × 104 mol of
C2H4 converted (mol of Ni × h)-1 (entry 2). Analogously to
what was observed using AlEtCl2 as activator, the precatalysts
featured by the oxazoline system gave the best TOFs, showing
similar selectivity in R-olefins. Increasing the ethylene pressure
from 4 to 20 bar resulted in an appreciable increase of the
selectivity in linear olefins (estimated on the C6 products, Table
2, entries 4-7), whereas the R factor was independent of
the pressure, indicating that both the propagation and chain-
transfer rate are first order in ethylene concentration.20 Neither
saturated hydrocarbons nor odd carbon oligomers were produced
in a detectable amount, which indicates the absence of chain
transfer to aluminum.20b,21 Conversely, in all oligomerization
reactions, mixtures of linear and branched olefins were produced,
perature (378 K).17
In solution, a 14b / 2 14a equilibrium is established, since
a red dichloromethane/toluene solution becomes green below
ca. 220 K, similarly to what was observed with the aforemen-
tioned tetramer / monomer equilibrium and also observed with
other Ni complexes bearing P,N ligands.18 This is consistent
with the proposed equilibrium because of the role played by
entropy in dissociation reactions. Binuclear 14b is thus,
qualitatively, enthalpically favored with respect to 14a. A similar
test was performed on red dichloromethane solutions of 6 which
bears two exocyclic methyl groups. A color change to green
was observed at lower temperatures (ca. 180 K), but no crystal
of the corresponding dinuclear species could be grown.
The variable temperature visible/near IR spectra of 14a
(Figure 4) are consistent with the proposed equilibrium. At 298
K the spectrum contains a band at 500 nm in the visible region
and a weaker one at 890 nm in the near-infrared. The latter is
attenuated at lower temperature, while a new, strong band
appears at 440 nm. A shoulder is observed at 500 nm at 173 K,
possibly corresponding to the absorption observed at room
temperature. A further broad (possibly multiple) absorption
appears at 670 nm. This band is not present at 298 K, suggesting
that at this temperature the amount of dimer is negligible. The
spectrum change is reversible. When the solvent polarity was
lowered (by adding Et2O to the dichloromethane solution), the
440 and 670 nm bands appear at higher temperature, indicating
that the dimerization process is favored when the solvent polarity
is decreased. It should be mentioned that the band at 440 nm
was not observed for the tetranuclear octahedral derivative
observed for phosphino-methylthiazoline,9 which is consistent
with the different nature of the assembled oligomers.
(19) (a) Rieger, B.; Baugh, L. S.; Kacker, S.; Striegler, S. Late Transition
Metal Polymerization Catalysis; Wiley-VCH: Weinheim, 2003; p 331. (b)
Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995,
117, 6414. (c) Heinicke, J.; Ko¨hler, M.; Peulecke, N.; Kindermann, M. K.;
Keim, W.; Ko¨ckerling, M. Organometallics 2005, 24, 344. (d) Yang, Q.-
Z.; Kermagoret, A.; Agostinho, M.; Siri, O.; Braunstein, P. Organometallics
2006, 25, 5518.
(20) (a) Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143.
(b) Britovsek, G. J. P.; Mastroianni, S.; Solan, G. A.; Baugh, S. P. D.;
Redshaw, C.; Gibson, V. C.; White, A. J. P.; Williams, D. J.; Elsegood,
M. R. J. Chem. Eur. J. 2000, 6, 2221.
(17) Oswald, H. R.; Beer, H. R. Mater. Sci. Monogr. 1985, 28B, 893.
(18) Christopher, R. E.; Gordon, I. R.; Venanzi, L. M. J. Chem. Soc.
1968, 205.

1780 Organometallics, Vol. 28, No. 6, 2009
ChaVez et al.
Figure 4. Visible/near IR solution spectra at variable temperature of complex 14a in the region 400-1000 cm-1. The spectra were recorded
in CH2Cl2 (4 mM), except the top one, which was recorded in a CH2Cl2/Et2O 1:1 v/v mixture. For clarity, the top spectrum has been shifted
by ca. +0.08 absorbance units.
Table 1. Catalytic Results for Complexes 1-3, 6, 10-12, and 14a in Ethylene Oligomerization using AlEtCl2 as Activatora
entry
precatalyst
AlEtCl2 (equiv)
prod.b
TOFc(× 10-4
)
Rd
C4 g %
C6 g %
C8 g %
1-butene mol %
1
2
3
4
5
6
7
8
1
1
2
2
2
3
3
2
6
2
4
6
2
6
2
6
2
6
6
6
2
4
6
22200
37650
21120
30530
37170
5060
34350
12300
22000
21200
23800
traces
18400
900
4.65
7.88
4.42
6.39
7.78
1.06
7.19
2.54
4.59
4.44
4.99
traces
3.81
0.19
4.86
6.32
0.16
0.53
0.25
0.31
0.38
0.11
0.44
0.28
0.50
0.22
0.51
80
53
71
68
62
86
58
67
54
81
64
100
64
96
73
69
19
42
26
29
34
13
39
28
40
18
33
1
5
3
3
4
1
3
3
1
1
3
9
4
10
4
3
15
4
25
20
14
8
613
613
1012
1012
1113
1213
14ae
14ae
14ae
9
10
11
12
13
14
15
16
0.34
<0.10
0.23
33
3
25
30
3
<1
2
13
22
6
23220
30200
0.29
1
7
a Reaction conditions: stainless steel-reactor, 145 mL; precatalyst: 40 µmol; solvent: chlorobenzene, 14 or 13 or 12 mL + 1 or 2 or 3 mL of
cocatalyst in toluene solution for 2 or 4 or 6 equiv of AlEtCl2, respectively; 10 bar of C2H4; stirring rate: 450 rpm; time 35 min; initial temperature,
25-30 °C. b Grams C2H4 converted (g of Ni × h)-1
.
c Mol of C2H4 converted (mol of Ni x h)-1; products quantified by GC (average value over two
d
runs at least). R ) mol of C6 (mol of C4)-1
.
e Presence of 14a under the catalytic conditions is favored by the increased temperature.
Table 2. Catalytic Results for Complexes 1-5, 7-9, and 14a in Ethylene Oligomerization using MAO as Cocatalysta
entry
precatalyst
pressure (bar)
TOFb (× 10-4
)
Rc
C4 g %
C6 g%
C8 g %
C10 g %
1-hexene mol %
linear C6 (%)d
1
1
1
2
3
3
3
3
10
10
10
4
10
15
20
10
10
10
10
10
10
10.82
22.86
6.44
1.93
5.92
8.61
14.95
5.36
2.76
6.09
5.33
3.15
6.43
0.12
0.12
0.14
0.07
0.07
0.08
0.07
0.11
0.13
0.16
0.08
0.11
0.11
75.3
74.3
69.7
89.8
89.1
83.5
90.9
77.1
72.9
67.9
81.8
76.6
76.5
19.8
20.4
25.6
9.3
10.2
14.3
8.4
18.7
21.2
23.8
15.5
19.0
19.1
4.1
4.4
4.1
0.8
0.6
1.9
0.6
3.6
4.9
6.6
2.3
3.7
3.7
0.7
0.8
0.5
<0.1
<0.1
0.2
<0.1
0.5
0.9
1.4
14.0
15.3
14.8
9.6
13.8
15.1
17.3
15.4
12.2
14.6
14.6
11.8
16.7
79.3
75.6
77.1
80.7
70
91.2
92.6
78.8
73.4
80.7
80.3
72.5
73.6
2e
3
4
5
6
7
8
9
10
11
12
13
4
5f
7
8
0.3
0.6
0.6
9
14ag
a Reaction conditions: stainless steel-reactor, 1 L; precatalyst: 2 µmol; cocatalyst: MAO, 4 mmol (2000 equiv); toluene, 39 mL + 1 mL of
chlorobenzene as cosolvent; stirring rate: 1500 rpm; time 30 min; temperature 30 ( 1 °C. b Mol of C2H4 converted (mol of Ni × h)-1; products
quantified by GC using n-heptane as internal standard (average value over three runs). c Schulz-Flory parameters, R ) mol of Cn+2 (mol of Cn)-1
.
d Determined after hydrogenation of the final reaction mixture using 10% Pd/C and 10 bar of H2 at room temperature. e Ten minutes. f This complex
was prepared in situ. g Presence of 14a under the catalytic conditions is favored by the increased temperature.
as shown by the analysis of the hydrogenated reaction mixtures
(see Table 2). A rationale for the observed selectivity may be
proposed by assuming that the isomerization rate of the Ni-
alkyl intermediate prevails over the associative displacement
and the migratory insertion. On the other hand, the concomitant
occurrence of reincorporation of the olefins produced at the early
stages of the reactions, although unlikely, cannot be definitively
ruled out. Experiments with the most active system 1/MAO
showed the composition of the oligomerization mixture (linear
and branched isomers) to be independent of the reaction time

Nickel Complexes with Phosphinito-Oxazoline Ligands
Organometallics, Vol. 28, No. 6, 2009 1781
Scheme 3. Propylene Dimerization Pathways and Isomerization of Primary Products
Table 3. Propene Oligomerization with Nickel(II) Catalysts 1-5, 7-9, and 14a
C6 product distribution (%)c
pathway Ad
pathway Be/Cf
pathway Dd
pre
catalyst
product
mass (g)
TOFb
C6
(%)
C9
(%)
linear
dimers
1-hexene and
3-(Z)-hexene
2-(E)-
hexene
2-(Z)-
hexene
3-(E)-
hexene
methyl
2,3-dimethyl
butenes
entry
(× 10-4
)
pentenesh
1
2
3
4
5
6
7
8
9
1
2
3
3.0
3.2
2.3
2.2
1.2
0.3
6.9
1.7
2.2
1.42
1.52
1.10
1.04
0.58
0.18
3.29
0.82
1.04
96.3
96.2
98.5
97.3
95.0
98.3
96.7
98.7
98.6
3.7
3.8
1.5
2.7
5.0
1.7
3.3
1.3
1.4
18.4
18.4
18.2
17.7
23.4
13.2
13.1
21.5
17.5
1.1
1.1
0.7
0.7
1.8
2.1
2.1
4.0
2.2
10.1
10.9
11.0
10.6
14.0
3.9
5.5
12.5
6.2
5.9
5.1
5.3
5.2
5.9
7.2
6.7
5.0
8.3
1.2
1.4
1.2
1.3
1.8
0.1
0.8
0.0
0.9
76.4
76.2
71.7
71.2
72.4
82.5
77.9
74.6
75.0
5.2
5.3
10.1
11.1
4.2
4.3
7.0
3.9
7.4
4
5i
7
8
9
14
a Reaction conditions: glass-reactor, 250 mL; precatalyst: 10 µmol; cocatalyst: MAO, 6 mmol (600 equiv); propylene, 17.5-42.2 g; toluene, 40 mL;
stirring rate: 1500 rpm; time 30 min; initial temperature, room temp. b Mol of C3H6 converted (mol of Ni × h)-1; average value over three runs.
c Products quantified by GC using n-heptane as internal standard. d Propylene 1,2-insertion followed by propylene 2,1-insertion. e Propylene
1,2-insertion, followed by propylene 1,2-insertion. f Propylene 2,1-insertion, followed by propylene 2,1-insertion. g Propylene 2,1-insertion followed by
propylene 1,2-insertion. h 4-Methyl-pent-1-ene (E + Z)-4-methyl-pent-2-ene, 2-methyl-pent-1-ene, and 2-methyl-pent-2-ene; total amount determined
after hydrogenation of final reaction mixture using 10% Pd/C and 10 bar H2. i This complex was prepared in situ.
(entries 1 vs 2), which is consistent with a prevalent isomer-
ization path of the Ni-alkyl intermediate.
Under comparable experimental conditions, precatalyst 8 gave
the best TOFs (Table 3, entry 7), while the selectivity in hexenes
was similar to that of the other catalysts. Like for the ethylene
oligomerization, alkyl substituents at phosphorus decreased the
catalytic performance (entries 8 vs 7 and 5 vs 4) while a
negligible influence of the nature of the halide coligand was
generally observed (entries 2 vs 1 and 4 vs 3).
Finally, it is noteworthy that alkyl substituents on the
phosphorus atom have a detrimental effect on the catalytic
performance (entries 5 vs 9 and 11 vs 12), while the dibromide
precursors are from slightly to moderately less active than their
dichloride congeners (entries 1 vs 3 and 5 vs 8).
Propene Dimerization Catalyzed by Nickel Complexes
Activated with MAO. On treatment with MAO in toluene, the
Ni(II) bishalides P,N complexes 1-5, 7-9, and 14 (Scheme 1)
were found to generate active and selective systems for the
dimerization of propene to internal and branched C6 products
(up to 99%). The total amount of branched isomers was
determined after the reaction mixtures were hydrogenated in
the presence of an heterogeneous catalyst (10 bar H2 pressure,
Pd/C 10% catalyst). The catalytic results are summarized in
Table 3.
Discussion
The results obtained in the oligomerization of ethylene clearly
show that both AlEtCl2 and MAO are excellent activators of
Ni(II) bis-halides modified with hybrid P,N ligands. Although
the different experimental conditions used with either activator
do not allow for a reliable comparison of the two catalytic
systems, it appears that AlEtCl2 and MAO generate distinct
catalytic systems as shown by the different distribution of the
olefins produced (non Schulz-Flory with AlEtCl2 and Schulz-
Flory with MAO).
(21) (a) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem.
Soc. 1998, 120, 4049. (b) Chen, Y.; Chen, R.; Qian, C.; Dong, X.; Sun, J.
Organometallics 2003, 22, 4312.
The mechanism of ethylene oligomerization by Ni(II) com-
plexes supported by the chelating ligands and activated by

1782 Organometallics, Vol. 28, No. 6, 2009
ChaVez et al.
AlEtCl2 or MAO is well established and does not deserve any
comment. Instead it may be worthwhile to comment on the
specific steps leading to the formation of various hexene isomers
upon propene dimerization on the basis of the structural isomers
obtained.22 It is well-known that the isomer distribution depends
on several factors, which include the alternative migration of
either n-propyl or isopropyl groups and the way this migration
occurs (either 1,2- or 2,1-), and finally the regioselectivity of
the ꢀ-H elimination steps when two possibilities exist (Scheme
3, paths A and C). Since linear products and dimethyl butenes
account for 17-29% of the total products while methyl-pentenes
constitute the major product (up to 83%), some mechanistic
conclusions can be drawn from the quantitative analysis of the
primary products.
which in the presence of MAO (Al:Ni ratio ) 700), gave TOFs
23
up to 1.2 × 106 h-1
.
Experimental Part
General Considerations. All air- and/or water-sensitive reactions
were performed under nitrogen in flame-dried flasks using standard
Schlenk-type techniques. Anhydrous toluene was obtained by means
of a MBraun Solvent Purification Systems, while chlorobenzene
was obtained by distillation under nitrogen from sodium. Solid
MAO for oligomerization was prepared by removing toluene and
AlMe3 under vacuum from a commercially available MAO solution
(10 wt% in toluene, Crompton Corp.). The MAO solution was
filtered on a D4 funnel and evaporated to dryness at 50 °C under
vacuum. The resulting white residue was heated further to 50 °C
under vacuum overnight. A stock solution of MAO was prepared
by dissolving solid MAO in toluene (100 mg mL-1). The solution
was used within three weeks to avoid self-condensation effects of
the MAO. AlEtCl2 as a 1 M solution in hexane was used as provided
by the supplier. All the other reagents and solvents were used as
purchased from commercial suppliers. Catalytic reactions were
performed in a 250 mL glass reactor or 500 or 1000 mL stainless
steel reactors, equipped with a magnetic drive stirrer and a Parr
4842 temperature and pressure controller. For ethylene oligomer-
ization, the reactor was connected to an ethylene reservoir to
maintain a constant pressure throughout the catalytic runs. IR spectra
in the range 4000-650 cm-1 were recorded on a Thermo Nicolet
6700 instrument, equipped with SMART Orbit Diamond ATR
accessory. Single crystals FTIR spectra were recorded in a diamond
window microcompression cell, on a Thermo Nicolet Centaurus
microscope. The variable temperature visible spectra of 14a were
recorded on a VARIAN Cary05E, equipped with a OXFORD
INSTRUMENTS DN1704 cryostat. Elemental C, H, N analyses
were performed by the “Service de microanalyses”, Universite´ de
Strasbourg, on a Flash EA 1112 microanalyzer. GC analyses of
the reaction products were performed on a Shimadzu GC-17 gas
chromatograph equipped with a flame ionization detector and a
Supelco SPB-1 fused silica capillary column (30 m length, 0.25
mm i.d., 0.25 µm film thickness) for the C4-C12 fraction. In the
propene dimerization experiments, the yields of dimers and trimers
were determined by comparing the integrals of the products to those
of the internal standard (n-heptane) and by assuming equal response
factors of the standard and the products. Specific GC analyses for
the C6 isomers were performed with a Varian PLOT fused silica
capillary column with stationary phase PLOT Al2O3/KCl (50 m,
0.32 mm i.d., 5 µm film thickness). The GC/MS analyses were
performed on a Shimadzu QP2010S apparatus equipped with a
column identical with that used for GC analysis.
For all catalysts, paths A and D, involving either 2,1- or 1,2-
insertion into the n-propyl and iso-propyl complex, respectively,
are less favorable. On the other hand, there is little doubt that
paths B and C prevail over paths A and D for propene
dimerization, accounting for 77-88% of the C6 mixture (4-
methyl-1-pentene, cis-4-methyl-2-pentene, and trans-4-methyl-
2-pentene and 2-methyl-1-pentene). Unfortunately, the propene
insertion selectivity is further complicated by our inability to
distinguish by GC the methyl-pentene isomers (2-methyl-1-
pentene and cis,trans-4-methyl-2-pentene). Indeed, peak over-
lapping did not allow for a reliable assignment of most favorable
insertion path of propene to produce the branched isomers.
Conclusions
We have found in this work that the structure of Ni(II)
complexes containing functional P,N-type ligands can experi-
ence dramatic changes as a function of relatively minor
modifications of the ligand or of the crystallization conditions.
This was recently highlighted with the unprecedented intercon-
version between a mono- and a tetranuclear Ni(II) system.9 The
complex [NiCl2{Ph2POCH2oxMe }] 14 was isolated in the form
2
of red crystals corresponding to its mononuclear form 14a, in
which the metal center has a distorted tetrahedral coordination
geometry, and its recrystallization from a toluene-pentane/
CH2Cl2 solution at temperatures below 253 K afforded green
crystals of the dinuclear, chloride-bridged, formula isomer
complex 14b. Conversion of 14b to 14a was observed as a
function of temperature, both in the solid-state and in solution.
The catalytic performance of Ni(II) phosphino- or phosphinito-
oxazoline or phosphino-thiazoline, bishalides in the oligomer-
ization of ethylene and propylene has been evaluated using
AlEtCl2 or MAO as activators. These systems have shown from
low to fairly good activity for the oligomerization of ethylene
leading almost exclusively to the production of dimers and
trimers with relatively modest percentages of R-olefins. The
precatalysts containing the oxazoline ligands have shown the
highest activity with either activator, but the different distribution
of the olefins produced (non Schulz-Flory with AlEtCl2 and
Schulz-Flory with MAO) is consistent with the generation of
different catalytic systems. The dimerization of propylene to
internal and branched hexenes has been achieved by activation
of the precatalysts with MAO. The highest TOF for the
dimerization of propylene has been obtained with the pyridine-
phosphite Ni(II) complex 8. One of the currently most active
Ni(II) catalyst precursor for propene oligomerization is a
dinuclear complex containing a (bis-amido)phosphine ligand,
Preparation of [Ni{2-((diphenylphosphinooxy)methyl)-4,4-di-
methyl-4,5-dihydrooxazole}Cl2] (14a). Solid [NiCl2(DME)] (3.26
g, 14.8 mmol) was added to a solution of the ligand 2-((diphe-
nylphosphinooxy)methyl)-4,4-dimethyl-4,5-dihydrooxazole (4.64 g,
14.8 mmol)10,11 in 100 mL of CH2Cl2. The solution became red
and was stirred overnight. After reaction, unreacted [NiCl2(DME)]
was eliminated by filtration. The solution was concentrated to 30
and 120 mL of pentane were added to precipitate 14a. After
filtration, 14a was washed with diethylether, dried under vacuum,
and isolated as a red powder. Yield: 4.80 g (10.8 mmol, 73%). IR
(KBr) cm-1: 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 (vs), 526 (s), 500 (m), 475 (m). HRMS: exp. 406.0268 (M+ -
Cl),theor.for[C18H20ClNNiO2P]+406.0278.Anal.calcdforC18H20NCl2-
NiPO2: C, 48.81; H, 4.55; N, 3.16. Found: C, 48.97; H, 4.80; N,
2.91.
General Procedure for the Ethylene Oligomerization. AlEtCl2
as Activator. The catalytic reactions were carried out in a magneti-
cally stirred (450 rpm) 145 mL stainless steel autoclave. A 125
mL glass container was used to protect the inner walls of the
(22) Bianchini, C.; Giambastiani, G.; Guerrero Rios, I.; Meli, A.; Segarra,
A. M.; Toti, A.; Vizza, F. J. Mol. Cat. A: Chem. 2007, 277, 40.

Nickel Complexes with Phosphinito-Oxazoline Ligands
Organometallics, Vol. 28, No. 6, 2009 1783
Table 4. Selected Data Collection and Refinement Parameters for
autoclave from corrosion; 40 µmol of Ni complex were dissolved
in 14, 13, or 12 mL of cholorobenzene depending of the amount
of the activator and injected into the reactor under an ethylene flux.
Then 1, 2, or 3 mL of AlEtCl2 in toluene, corresponding to 2, 4, or
6 equiv respectively, were introduced into the reactor to achieve a
total volume of 15 mL with the precatalyst solution.
14a and 14b · 2CH2Cl2 · 2CH3C6H5
compound
14a
14b · 2CH2Cl2 · 2CH3C6H5
Chemical formula
C18H20Cl2NNiO2P
C36H40Cl4N2Ni2O4P2 ·
2CH2Cl2,2C7H8
1239.98
Mr
442.93
Cell setting, space
group
Temperature (K)
a, b, c (Å)
Orthorhombic, Pna21
Monoclinic, P2/c
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 bar. A
temperature increase was observed due to the remarkable exother-
micity of the reactions. The 10 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 min) a dry ice
bath, and in the more exothermic cases, also liquid N2, was used
to rapidly cool down the reactor and quench 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 the GC analysis. The products in
the reactor were treated in situ by 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 to
avoid any loss of product.
MAO as Activator. A 1 L stainless steel reactor was heated to
60 °C under vacuum overnight and then cooled to room temperature
under a nitrogen atmosphere. A MAO solution, prepared by diluting
2.65 mL of a stock toluene solution of MAO (4 mmol) with toluene
(36.5 mL), was introduced by suction into the reactor, previously
evacuated by a vacuum pump. The system was pressurized with
ethylene to 10 bar and stirred for 5 min. Afterward, the ethylene
pressure was released slowly and 1 mL of a precatalyst solution,
prepared by dissolving the solid precatalyst (20 µmol) in 10 mL of
chlorobenzene, was syringed into the reactor. The system was
repressurized to the final ethylene pressure and stirred at 1500 rpm.
Ethylene was continuously fed to maintain the reactor pressure at
the desired value. The temperature inside the reactor increased solely
from the exothermicity of the reaction and reached a maximum
value within 5-7 min. After 30 min, the reaction was stopped by
cooling the reactor to -20 °C, depressurizing, and introducing 2
mL of acidic MeOH (5% HCl). n-Heptane was injected into the
reactor as the GC internal standard and the reactor contents were
stirred for 10 min further. The solution was analyzed by GC and
GC-MS. The moles of the C6 and C8 fractions were determined
by GC using calibration curves with standard toluene solutions
containing concentrations of 1-hexene and 1-octene as close as
possible to those in the sample under analysis. Schulz-Flory R
constants were determined by the molar ratio of the couple C8/C6.
173(2)
17.4440(3),
13.5450(8), 8.459(1)
90
1998.7 (3)
4
1.472
173(2)
11.7438(5),
12.3426(9), 22.748(1)
118.647 (3)
2893.7 (3)
2
1.423
Mo KR
1.12
ꢀ (deg)
V (Å3)
Z
Dx (Mg m-3
)
Radiation type
Mo KR
1.33
µ (mm-1
)
Crystal size (mm)
No. of meas., indep.
and obsvd. Refl.
Rint
0.05 × 0.04 × 0.03
0.08 × 0.03 × 0.03
12329, 3642, 2660
17643, 6614, 3124
0.081
25.5
0.084, 0.202, 1.18
0.086
27.5
0.059, 0.149, 1.01
θmax (°)
R[F2 > 2s(F2)],
wR(F2), S
No. of parameters
228
290
1 mL of chlorobenzene was syringed under nitrogen atmosphere.
The reactor was then cooled at -15 °C and liquid propene
(17.5-42.2 g) was transferred from a 1.5 L cylinder into the reactor
via a flexible hose while the internal pressure raised 4-5 bar. The
amount of propene used for each run was determined by measuring
the cylinder weight difference before and after the propene addition.
MAO (6 mmol, ca. 600 equiv, 4 mL) was injected into the reactor
via a syringe and the system was warmed to room temperature and
the solution stirred. The reactor internal pressure rapidly reached
10 bar. After the desired reaction time, the reactor was depressurized
and the mixture was quenched by introducing acidic MeOH (5%
HCl, 1 mL). Finally, the reactor mixture was cooled at 0 °C and
the unreacted propene was carefully evaporated under vigorous
stirring. A solution of n-heptane (1 mL) was added into the reactor
as the GC internal standard and an aliquot of the resulting solution
was sampled for the GC analyses of the products.
Hydrogenation of the r-Olefin Oligomerization Products. The
hydrogenation of the reaction mixtures was carried out in a 20 mL
stainless steel autoclave equipped with a magnetic stirrer at room
temperature and 10 bar H2 pressure for 10 h, using Pd/C 10% (80
mg) as catalyst. The quantification of both linear and branched
hydrocarbon species was achieved by GC.
X-Ray Data Collection, Structure Solution, and Refinement
for Compounds 14a and 14b · 2CH2Cl2 · 2CH3C6H5. Suitable crys-
tals for the X-ray analysis of 14a and 14b · 2CH2Cl2 · 2CH3C6H5
were obtained as described above. The intensity data were collected
at 173(2) K on a Kappa CCD diffractometer24 (graphite mono-
chromated Mo KR radiation, λ ) 0.71073 Å). Crystallographic and
experimental details for the structures are summarized in Table 4.
The structures were solved by direct methods (SHELXS-97) and
refined by full-matrix least-squares procedures (based on F2,
SHELXL-97)25 with anisotropic thermal parameters for all the non-
hydrogen atoms. The hydrogen atoms were introduced into the
geometrically calculated positions (SHELXS-97 procedures) and
refined riding on the corresponding parent atoms. CCDC 704525
(14a) and 704526 (14b) contain the supplementary crystallographic
data for this paper that can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
The moles of C4 were calculated by the Schulz-Flory R constant
and the moles of C6 by the formula moles of C4 ) (moles of C6)/
R, whereas the moles of the higher oligomers were calculated by
the Schulz-Flory R constant and the moles of C8 by the general
formula moles of Ci ) (moles of C8)R(i-8)/2. The total moles of
converted ethylene were obtained by the formula moles of C2H4 )
Σ(moles of Ci)(i/2) with i ) 4-14; therefore, the TOFs were
obtained.
Oligomerization of Propene. A 250 mL glass reactor equipped
with a mechanical stirrer and an external jacket for the temperature
control and previously evacuated by a vacuum pump, was charged
by suction with 10 mL of toluene. Afterward, a solution of the
precatalyst (10 µmol) prepared by dissolving the solid complex in
(24) Bruker-Nonius Kappa CCD Reference Manual, Nonius BV: The
Netherlands, 1998.
(23) Majoumo-Mbe, F.; Lo¨nnecke, P.; Volkis, V.; Sharma, M.; Eisen,
M. S.; Hey-Hawkins, E. J. Organomet. Chem. 2008, 693, 2603.
(25) Sheldrick, G. M. SHELXL-97, Program for crystal structure
refinement; University of Go¨ttingen: Germany, 1997.

1784 Organometallics, Vol. 28, No. 6, 2009
ChaVez et al.
Acknowledgment. We thank the Centre National de la
RechercheScientifique(CNRS),theMiniste`redel’Education
Nationale et de la Recherche (Paris), the Institut Franc¸ais
du Pe´trole (IFP), the European Commission (NoE IDE-
CAT,NMP3-CT-2005-011730),andtheMinisterodell’Istruzione,
dell’Universita` e della Ricerca of Italy (NANOPACK-
FIRB project n. RBNE03R78E) for support. We are
grateful to the COST-D30 programme for a mobility grant
to P.C.V. We thank Dr. D. Mandon for assistance with
the variable-temperature vis/near IR measurements and
M. Mermillon-Fournier (LCC Strasbourg) for technical
assistance.
OM8009848