3-aminoiminoacrylate, 3-aminoacrylate, and 3-amidoiminomalonate complexes as catalysts for the dimerization of olefins

Article abstract of DOI:10.1021/om049075s

Nickel(II)-aminoacrylate, -aminoiminoacrylate, and -amidoiminomalonate complexes 1-4 are suitable precursors together with appropriate cocatalysts for the catalytic dimerization of ethylene, propylene, and α-olefins with short chain lengths such as 1-hexe

Full text of DOI:10.1021/om049075s

Organometallics 2005, 24, 4139-4152
4139
3-Aminoiminoacrylate, 3-Aminoacrylate, and
3-Amidoiminomalonate Complexes as Catalysts for the
Dimerization of Olefins
Martin E. Bluhm,† Cristina Folli, Daniela Pufky, Mario Kro¨ger, Olaf Walter, and
Manfred Do¨ring*
Forschungszentrum Karlsruhe, Institute for Technical Chemistry (ITC-CPV), P.O. Box 3640,
76021 Karlsruhe, Germany
Received November 26, 2004
Nickel(II)-aminoacrylate, -aminoiminoacrylate, and -amidoiminomalonate complexes
1-4 are suitable precursors together with appropriate cocatalysts for the catalytic dimer-
ization of ethylene, propylene, and R-olefins with short chain lengths such as 1-hexene.
Suitable ligands IV-VI, VIII, X, and XII generate nickel(II) compounds 1-4 active for these
catalytic dimerizations. The influence of different substituents attached to the coordinating
ligand backbone is tested in the catalytic reactions. Several novel monodentate and chelate
nickel(II) precursor complexes 1 and 3 were isolated and also characterized by X-ray structure
analysis.
1. Introduction
BP Chemicals5 with tricyclohexylphosphine and Ziegler-
type catalysts. In the Sumitomo process very high
selectivities of 2,3-dimethylbutenes (up to 85%) are
obtained at 20-50 °C using toluene as a solvent. On
the other hand, the BP Chemical process operates
without any solvent at lower temperature and with a
simpler catalyst composition, giving a lower selectivity
for 2,3-dimethylbutenes.
In the last years, discrete late-metal catalysts have
come into focus for ethylene poly- and oligomerization.6
Dimerization of ethylene has been carried out mainly
with complexes of iron,7 cobalt,8 palladium,9 and nickel,
while chromium complexes showed excellent activities
and selectivities in ethylene trimerization10 and tet-
ramerization.11 Most nickel-based oligomerization cata-
lysts contain bidentate P,N-,12 P,O-,13 N,N-,14 or N,O-
ligands.15
Olefins with short chain lengths are used as comono-
mers in the polymerization of ethylene to give linear
low-density polyethylene (LLDPE) or for the preparation
of detergents and synthetic lubricants. Especially the
dimerization of ethylene to butenes is used industrially
for generating powering components in fuel with ho-
mogeneous titanium catalysts and special cocatalysts
in the alphabutol process (IFP).1 2-Butene is also
produced with the Phillips Petroleum process by dimer-
ization of ethylene.2 Few technical processes are used
in industry for the dimerization of propylene. The
nonregioselective olefin dimerization3 (Dimersol, Insti-
tut Franc¸ais du Pe´trole), performed in the absence of
any phosphine ligand, affords propene dimers with a
composition of 22% n-hexenes, 72% 2-methylpentenes,
and 6% 2,3-dimethylbutenes. Dimers form 80% of the
oligomer mixture, a small amount of trimers (18%) and
tetramers (2%) being produced as well. The process
works at 50 °C under a pressure sufficient to maintain
the reactants in the liquid phase. The catalyst results
from the interaction of a nickel salt, soluble in a
paraffinic hydrocarbon solvent and an ethylaluminum
chloro compound; the active species is formed in situ
inside the dimerization reactor.
â-Diketiminates have an important role as spectator
ligands by virtue of their strong binding to the metal,
(4) (a) Nomura, K.; Itagaki, M.; Ishino, M.; Yamamoto, M.; Su-
zukamo, G. Catal. Lett. 1997, 47, 47-49. (b) Itagaki, M.; Suzukamo
G.; Nomura, K. Bull. Chem. Soc. Jpn. 1998, 71, 79-82. (c) Sato, H.;
Tojima, H.; Ikimi, K. J. Mol. Catal. 1999, 144, 285-293.
(5) (a) Olivier-Bourbigou, H.; Saussine, L. In Applied Homogeneous
Catalysis with Organometallic Compounds; Cornils, B., Herrmann, W.
A., Eds.; VCH: Weinheim, Germany, 1996; Vol. 1, pp 257-259. (b)
Wu, S.; Lu, S. Appl. Catal. A 2003, 246, 295-301.
(6) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169-1203.
Regioselective dimerization of propylene to 2,3-di-
methylbutenes is currently operated by Sumitomo4 and
(7) (a) Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120,
7143-7144. (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, 2221-2231. (c)
Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Mastroianni, S.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Dalton 2001,
1639-1644. (d) Small, B. L.; Marcucci, A. J. Organometallics 2001,
20, 5738-5744.
* To whom correspondence should be addressed. E-mail:
manfred.doering@itc-cpv.fzk.de. Tel: +49 7247-82 4385. Fax: +49
7247-82 2244.
† Current address: University of Pennsylvania, Department of
Chemistry, 231 South 34th Street. Philadelphia, PA 19104, USA.
(1) Commereuc, C.; Chauvin, Y.; Gaillard, J.; Le´onard, J.; Andrews,
J. Hydrocarbon Process 1984, 63(11), 118.
(8) (a) Small, B. L. Organometallics 2003, 22, 3178-3183. (b)
Tellmann, K. P.; Gibson, V. C.; White, A. J. P.; Williams, D. J.
Organometallics 2005, 24, 280-286.
(9) (a) Plentz Meneghetti, S.; Lutz, P. J.; Kress, J. Organometallics
1999, 18, 2734-2737. (b) Heinicke, J.; Kohler, M.; Peulecke, N.;
Kindermann, M. K.; Keim, W.; Kockerling, M. Organometallics 2005,
24, 344-352.
(10) (a) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H. J.
Organomet. Chem. 2004, 689, 3641-3668 and references therein. (b)
Bluhm, M. E.; Walter, O.; Do¨ring, M. J. Organomet. Chem. 2005,
690(3), 713-721.
(2) Weissermel, K.; Arpe, H.-J. Industrial Organic Chemistry; Wiley-
VCH: Weinheim, Germany, 1998; p 74.
(3) (a) Benedek, W. J.; Mauleon, J.-L. Hydrocarbon Process 1980,
59(5), 143. (b) Le´onard, J.; Gaillard, J. F. Hydrocarbon Process 1981,
60(3), 99. (c) Boucher, J. F.; Follain, G.; Fulop, D.; Gaillard, J. Oil Gas
J. 1982, 80, 84. (d) Chauvin, Y.; Gaillard, J.; Le´onard, J.; Bonnifay,
P.; Andrews, J. W. Hydrocarbon Process 1982, 61(5), 110. (e) Com-
mereux, D.; Chauvin, Y.; Leger, G.; Gaillard, J. Rev. Inst. Fr. Pet. 1982,
37, 639. (f) Gaillard, J. Pet. Technol. 1985, 314, 20.
10.1021/om049075s CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/16/2005

4140 Organometallics, Vol. 24, No. 17, 2005
Bluhm et al.
Figure 1. Formula of 3-aminoiminoacrylates.
their tunable and extensive steric demands, and their
diversity of bonding modes.16 Complexes with â-diketim-
inates are coordinately unsaturated, and this feature
is a key factor in their ability to function as catalysts
for several processes such as copolymerization of ep-
oxides and CO2,17 polymerization of lactide,18 polymer-
ization of methyl methacrylate,19 and oligo- and poly-
merization of olefins.20 N,N-â-Diketiminato complexes
of nickel, as well as N,O-ketiminato and Schiff base
derivatives, were active in the polymerization of nor-
bornene.21
Herein we report a new group of ligands: 3-ami-
noiminoacrylate, 3-aminoacrylate, and 3-amidoimino-
malonate ligands coordinate nickel(II) ions to give the
active precatalysts 1-4 (Figure 2). Together with the
cocatalysts methylaluminoxane (MAO) and ethylalumi-
num sesquichloride (EASC) 1-4 are suitable to dimerize
either ethylene or propylene with a high activity to give
butenes or hexenes. The nickel(II) aminoacrylate com-
pounds 3b,i are also able to oligomerize 1-hexene. The
results of the catalytic reactions with the precatalysts
1-4 and suitable cocatalysts will be presented.
2. Results and Discussion
Synthesis of Ligands and Nickel(II) Complexes.
As an extension of the class of well-known â-diketimi-
(11) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto,
S.; Overett, M.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S. J.
Am. Chem. Soc. 2004, 126, 14712-14713.
(12) (a) Keim, W.; Killat, S.; Nobile, C. F.; Suranna, G. P.; Englert,
U.; Wang, R. M.; Mecking, S.; Schroder, D. L. J. Organomet. Chem.
2002, 662, 150-171. (b) Speiser, F.; Braunstein, P.; Saussine, L.;
Welter, R. Organometallics 2004, 23, 2613-2624. (c) Speiser, F.;
Braunstein, P.; Saussine, L. Organometallics 2004, 23, 2633-2640.
(13) (a) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235-244.
(b) Heinicke, J.; He, M. Z.; Dal, A.; Klein, H. F.; Hetche, O.; Keim, W.;
Flo¨rke, U.; Haupt, H. J. Eur. J. Inorg. Chem. 2000, 431-440.
(14) (a) Killian, C. M.; Johnson, L. K.; Brookhart, M. Organometal-
lics 1997, 16, 2005-2007. (b) Svejda, S. A., Brookhart, M. Organome-
tallics 1999, 18, 65-74.
(15) (a) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich,
S. K.; Grubbs, R. H. Bansleben, D. A. Science 2000 287, 460-462. (b)
Carlini, C.; Isola, M.; Liuzzo, V.; Galletti, A. M. R.; Sbrana, C. Appl.
Catal. A: Gen. 2002, 231, 307-320. (c) Wu, S.; Lu, S. Appl. Catal. A:
Gen. 2003, 246, 295-301.
(16) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev.
2002, 102, 3031-3065.
(17) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738-
8749.
(18) (a) Cheng, M.; Attygalle, A. B.; Lobkovsky, E. B.; Coates, G.
W. J. Am. Chem. Soc. 1999, 121, 11583-11584. (b) Dove, A. P.; Gibson,
V. C.; Marshall, E. L.; White, A. J. P.; Williams, D. J. Chem. Commun.
2001, 283.
(19) Dove, A. P.; Gibson, V. C.; Marshall, E. L.; White, A. J. P.;
Williams, D. J. Chem. Commun. 2002, 1208-1209.
Figure 2. Molecular formulas of the precatalysts 1-4.
nates, we have synthesized novel 3-aminoiminoacrylates
that yield by deprotonation the corresponding monoan-
ionic ligands. An alkoxyl and a second functional group
R5 (i.e. nitrile or ester) are bound to the ligand backbone,
noticeably modifying the electronic distribution in the
metallacycle of the resulting transition-metal complex
compared to the classical â-diketiminates (Figure 1).
A wide range of different modifications is possible by
varying the substituents at the backbone. 3-Aminoimi-
noacrylates have been achieved through diverse multi-
step syntheses. These reactions required an optimiza-
tion of the reaction conditions according to the different
substituents R5 on the acryl backbone (Figure 1).
The cyano-substituted aminoiminoacrylates IVa,b
were obtained in a four-step reaction. The first step22
consists of a chlorination of cyanoacetic acid, followed
by condensation with 2,6-diisopropylaniline (Scheme 1).
The obtained amide I was then converted with an
oxonium salt to the related imino ester23 II, which was
refluxed with triethyl orthoformate in the presence of
acetic anhydride as solvent, in a Claisen reaction.24 The
(20) (a) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall,
W. J.; Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16(8),
1514-1516. (b) Wiencko, H. L.; Kogut, E.; Warren, T. H. Inorg. Chim.
Acta 2003, 345, 199-208. (c) Zhou, M. S.; Huang, S. P.; Weng, L. H.;
Sun, W. H.; Liu, D. S. J. Organomet. Chem. 2003, 665, 237-245. (d)
Gao, H. Y.; Guo, W. J.; Bao, F.; Gui, G. Q.; Zhang, J. K.; Zhu, F. M.;
Wu, Q. Organometallics 2004, 23, 6273-6280.
(21) Zhang, D.; Jin, G. X.; Weng, L. H.; Wang, F. S. Organometallics
2004, 23, 3270-3275.

Catalysts for the Dimerization of Olefins
Organometallics, Vol. 24, No. 17, 2005 4141
Scheme 1. Synthesis of Cyano-Substituted 3-Aminoiminoacrylates IVa,b
Scheme 2. Synthesis of Cyano-Substituted Aminoacrylates Va-e
ethoxymethylene group in compound III finally reacted
This procedure was not effective for obtaining analog-
ous substances bearing an ester group instead of a
nitrile; for the synthesis of compounds VIa-c the
reagents had to be heated under stronger conditions and
ethanol produced during the reaction had to be distilled
away (Scheme 3).
Finally, a third modification of the backbone was
attained: the acyl-substituted aminoacrylates VIIIa,b
were synthesized in a two-step reaction from the â-keto
esters, using an adapted version of a procedure de-
scribed in the literature26 for similar compounds (Scheme
4).
An oxidative heterocyclization of VIIc with CuCl2
gave the imidazo[1,5-a]pyridyl derivative VIIIc in low
yields (Scheme 5). VIIIc was then reacted with sodium
bis(trimethylsilyl)amide and [(PPh3)2Ni(Mes)Br],27 as in
the previous cases, to give the nickel(II) complex 3i.
Another synthetic method was successful with com-
pounds Xa,b bearing two identically substituted aryl
rings. The route consists of a twofold condensation28a
with substituted anilines in refluxing methanol to give
the products IVa,b in good yields. The above-described
method was not successful with an ester in place of a
cyano group at the backbone; in fact, decomposition
occurred in the third step, because the imino ester was
not stable under these conditions.
A set of differently substituted 3-aminoacrylates Va-
e, VIa-c, and VIIIa,b was synthesized by aminolysis
of the Claisen adducts.25 The cyano-substituted ami-
noacrylates Va-e were easily prepared by condensation
of ethyl (ethoxymethylene)cyanoacetate with diverse
anilines in refluxing methanol, using an adapted version
of similar reactions already described in the literature
(Scheme 2).25
(22) Kuo, E. A.; Hambelton, P. T.; Kay, D. P.; Evans, P. L.; Matharu,
S. S.; Little, E.; McDowall, N.; Jones, C. B.; Hedgecock, J. R.; Yea, C.
M.; Chan, A. W. E.; Hairsine, P. W.; Ager, I. R.; Tully, W. R.;
Williamson, R. A.; Westwood, R. J. Med. Chem. 1996, 39, 4608-4621.
(23) Ahlbrecht, H.; Vonderheid, C. Chem. Ber. 1973, 106, 2009-
2016.
(24) (a) Claisen, L. Ber. Bunsen-Ges. Phys. Chem. 1893, 26(3), 2729-
2735. (b) Claisen, L.; Haase, E. Ber. Bunsen-Ges. Phys. Chem. 1895,
28 (1), 35-41. (c) Claisen, L. Justus Liebigs Ann. Chem. 1897, 297,
1-99. (d) Reidlinger, C.; Dworczak, R.; Junek, H.; Graubaum, H.
Monatsh. Chem. 1998, 129, 1313-1318. (e) Cuvigny, T.; Normant, H.
Bull. Soc. Chim. Fr. 1961, 2423-2432.
(26) Ife, R. J.; Brown, T. H.; Keeling, D. J.; Leach, C. A.; Meeson,
M. L.; Pearsons, M. E.; Reavill, D. R.; Theobald, C. J.; Wiggall, K. J.
J. Med. Chem. 1992, 35, 3413-3422.
(27) Klein, A. Z. Anorg. Allg. Chem. 2001, 627, 645-650.
(28) (a) Price, C. C.; Boekelheide, V. J. Am. Chem. Soc. 1946, 68,
1246-1250. (b) Price, C. C.; Roberts, R. M. J. Am. Chem. Soc. 1946,
68, 1204-1208. (c) Snyder, H. R.; Jones, R. E. J. Am. Chem. Soc. 1946,
68, 1253-1255.
(25) (a) Ja¨ger, E. G. Z. Anorg. Allg. Chem. 1968, 359(3-4), 147-
159. (b) Kristen, H.; Hamann, O. Pharmazie 1976, 31(4), 222-224. (c)
Ja¨ger, E.-G.; Kirchhof, B.; Schmidt, E.; Remde, B.; Kipke, A.; Mu¨ller,
R. Z. Anorg. Allg. Chem. 1982, 485, 141-172.

4142 Organometallics, Vol. 24, No. 17, 2005
Bluhm et al.
Scheme 3. Synthesis of Ester-Substituted Aminoacrylates VIa-c and the Nickel(II) Complexes 3d-f
Scheme 4. Synthesis of Acyl-Substituted Aminoacrylates VIIIa,b and the Nickel Complexes 3g,h
Scheme 5. Synthesis of Ethyl (2E)-Cyano(1-methylimidazo[1,5-a]pyridine-3(2H)-ylidene)acetate (VIIIc)
Scheme 6. Synthesis of Ester-Substituted
3-Aminoiminoacrylates Xa,b with Identically
Substituted Aryl Rings and Nickel(II)
Complexes 2a,b
condensation always took place only at the ethoxy-
methylene group and 2-cyano-3-aminoacrylates were
obtained. Ester-substituted 3-aminoiminoacrylates Xc-e
bearing differently substituted aryl rings were synthe-
sized as well. In method A (Scheme 7) diethyl (ethoxy-
methylene)malonate was condensed24 with two differ-
ently substituted anilines to the 3-aminoiminoacryla-
mides Xc-e, where the intermediates VI were formed.
The second condensation (amide formation, i.e., from VI
to IX) required stronger reaction conditions than the
first one. Method B, on the other hand, employed diethyl
malonate which was first condensed with 1 equiv of one
substituted aniline.29 The amide obtained subsequently
reacted with triethyl orthoformate and the other aniline
derivative.28,30
Method A has proven to be more efficient than method
B: the overall yields are higher and the first step in
method B requires a large excess of diethyl malonate
to prevent the immediate formation of the bisamide,
while the other reactions can be performed in equimolar
amounts.
in the absence of any solvent at high temperature with
simultaneous distillation of the produced ethanol. The
formed 3-aminoiminoacrylamides IXa,b reacted subse-
quently with an oxonium salt23 to the 3-aminoimi-
noacrylates Xa,b (Scheme 6).28b,c
Several attempts have been made to prepare com-
pound IVa using this method and starting from ethyl
(ethoxymethylene)cyanoacetate, but it was impossible
to obtain the intermediate 3-aminoacrylamide: the
Finally, the amidoiminomalonate XII was synthesized
from diethyl malonate by 2-fold condensation with
(29) Hodgkinson, A. J.; Staskun, B. J. Org. Chem. 1969, 34(6), 1709-
1713.
(30) Wolfbeis, O. S. Chem. Ber. 1981, 114(11), 3471-3484.

Catalysts for the Dimerization of Olefins
Organometallics, Vol. 24, No. 17, 2005 4143
Scheme 7. Syntheses of Ester-Substituted 3-Aminoiminoacrylates Xc-e with Differently Substituted Aryl
Rings and the Nickel(II) Complexes 2c-e
Scheme 8. Synthesis of the Amidoiminomalonate
XII and the Nickel(II) Complex 4
X, and XII with sodium bis(trimethylsilyl)amide. The
monoanions reacted subsequently with trans-(bromomes-
ityl)bis(triphenylphosphino)nickel(II) ((PPh3)2Ni(Mes)-
Br)27 to yield the metal complexes (Schemes 1 and 2).
Those compounds were all expected to act as bidentate
chelating ligands but, surprisingly, X-ray diffractometry
revealed a coordination of the monoanionic ligands
IVa,b to nickel(II) through the cyano group, the ligands
not acting as chelating units. The NMR spectra agree
with the structural data of 1a,b. The X-ray structure
of the complex 1a shows a tetracoordinated nickel atom
with a distorted-square-planar conformation (Figure
3): the angles N(1)-Ni-C(31) and P(1)-Ni-P(2) are
172.5(1) and 173.4(4)°, respectively. The Ni1-N1 bond
length is 1.888(3) Å; the nickel-phosphorus distances
are 2.243(1) and 2.252(1) Å, while the Ni1-C31 distance
is 1.919(3) Å. The observed C1-N2 (1.280(4) Å) and C3-
N3 (1.264(4) Å) bond lengths reveal bonds with a high
sp2 imine character. This is also confirmed by the
lengths observed for the C1-C2 (1.432(4) Å) and C2-
C3 (1.448(4) Å) bonds.
diisopropylaniline, followed by reaction with an oxonium
salt23 (Scheme 8).
The ligands IV-VI, VIII, X, and XII were used to
prepare nickel(II) complexes: all of them were employed
in their monoanionic form. Both the steric bulk at the
aryl rings and electronic effects of the ligand backbone
will affect the activity and selectivity of the correspond-
ing nickel catalyst precursors for catalytic oligomeriza-
tion reactions.
To our knowledge, no examples of any similar complex
have been described before. Several potential N,N- and
N,O-chelating compounds are published, bearing a
nitrile function at their backbone, but they are always
The monoanionic ligands were generated by depro-
tonation of the corresponding compounds IV-VI, VIII,

4144 Organometallics, Vol. 24, No. 17, 2005
Bluhm et al.
Figure 3. Molecular structures of 1a (left) and 1b (right). For 1a, red crystals suitable for X-ray diffractometry were
obtained in hexane/pentane/toluene (10/3/1). Selected bond distances (Å) and angles (deg): C3-N3 ) 1.264(4), C2-C3 )
1.448(4), C4-C2 ) 1.409(4), N1-C4 ) 1.152(4), C1-C2 ) 1.432(4), N2-C1 ) 1.280(4), Ni1-N1 ) 1.888(3), P2-Ni1 )
2.243(1), C31-Ni1 ) 1.919(3), P1-Ni1 ) 2.252(1); N1-Ni1-P2 ) 89.73(8), P2-Ni1-C31 ) 90.55(9), C31-Ni1-P1 )
87.82(9), P1-Ni1-N1 ) 92.72(8), N1-Ni1-C31 ) 172.5(1), P2-Ni1-P1 ) 173.4(4). For 1b, red crystals suitable for X-ray
diffractometry were obtained in pentane/toluene (15/1). Selected bond distances (Å) and angles (deg): C4-N1 ) 1.157(2),
C2-C4 ) 1.401(3), C3-C2 ) 1.427(3), N3-C3 ) 1.289(3), C1-C2 ) 1.445(3), O1-C1 ) 1.386(2), N2-C1 ) 1.278(3),
Ni1-N1 ) 1.894(2), Ni1-P2 ) 2.239(1), Ni1-C27 ) 1.899(2), Ni1-P1 ) 2.233(1); N3-C3-C2 ) 123.1(2), C3-C2-C1 )
125.8(2), C2-C1-N2 ) 132.8(2), C2-C4-N1 ) 178.8(2), N1-Ni1-P2 ) 91.00(5), P2-Ni1-C27 ) 89.18(6), C27-Ni1-P1
) 89.73(6), P1-Ni1-N1 ) 90.13(5), N1-Ni1-C27 ) 179.1(1), P2-Ni1-P1 ) 177.4(2).
reported to coordinate to the metal center as bidentate31
and not monodentate.
distances are markedly shorter compared to 1a-d. In
3a, the bite angle O1-Ni1-N1 is 92.0(1)°. The metal-
lacycle is planar, and the metal center has a distorted-
square-planar coordination sphere. The plane of the
mesityl substituent is oriented almost perpendicularly
to the plane of the metallacycle, the dihedral angle being
80.4°.
The 3-aminoacrylates Vd,e behaved analogously to
the corresponding imino-ligands IVa,b when reacting
with nickel(II), and gave similar complexes 1c,d (Scheme
3). On the other hand, under similar reaction conditions,
the 3-aminoacrylates Va-c yielded the expected N,O-
chelating complexes 3a-c by releasing one phosphine
ligand. On comparison of 1c to 3b,c, the increased steric
bulk on the aniline (i-Pr vs Et and Me) seems to make
binding via the cyano group more favorable. This
tendency is supported by the fact that the even bulkier
N,N ligands lead to similiar structures 1a,b. On the
other hand, the ligand on 1d is not sterically demand-
ing, especially compared to 3a,b (H vs Et and Me).
Hence, electronic effects must play an important role
as well. Overall, minor changes on the ligand have
drastic and difficult to predict effects on the complex
structure.
Crystals of the complexes 3a-c were obtained, and
their structure was revealed by X-ray structure analysis
(Figure 4). The triphenylphosphine ligand occupies the
position trans to the coordinated nitrogen atom, while
the mesityl group attached to the nickel center is bound
in a position trans to the oxygen. The Ni-O, Ni-N, Ni-
C, and Ni-P distances in 3a are similar to those of
previously described N,O chelate nickel(II) complex-
es.21,31,32 In 3a, the Ni1-N1 and Ni1-O1 bond lengths
are 1.947(3) and 1.940(3) Å and, therefore, are almost
identical with published data.33 The same is observed
for the carbon-carbon distances in the metallacycle:
C1-C2 (1.339(5) Å) and C2-C3 (1.410(5) Å), respec-
tively. The Ni1-P1 distance is 2.188(1) Å, while the
Ni1-C14 bond distance measures 1.892(4) Å. Both
Attempts to crystallize 1c,d were not successful, but
it was possible to nonetheless attribute their structure.
In fact, the ESI mass spectra of 1a,b and 1c,d clearly
showed the molecular peak corresponding to the com-
plex bearing two triphenylphosphines ((PPh3)2Ni(Mes)L),
while such a signal was always absent in the case of
the compounds 3a-c ((PPh3)Ni(Mes)L), where the mo-
lecular peak indicated the presence of only one tri-
phenylphosphine. In the region 2198-2207 cm-1, IR
spectra of the complexes 1a,b and 1c,d showed a weaker
absorption band for the CtN bond, in comparison to
the complexes 3a-c,i which exhibited strong absorp-
tions in the range of 2173-2204 cm-1
.
Even though compounds Va-e are very similar to
each other, they give different complexes under the
same reaction conditions. A factor which may explain
this behavior lies in the stability of the complexes
binding one or two triphenylphosphines, which is sig-
nificantly influenced by small changes in the ligands.
In case of the anionic ligands derived from IVa,b and
Vd,e, the complex [(PPh3)2Ni(Mes)L] is more stable,
whereas in the case of Va-c, [(PPh3)Ni(Mes)L] is
favored. Neither transformations of the complexes
[(PPh3)2Ni(Mes)L] in [(PPh3)Ni(Mes)L] through release
of triphenylphosphine were observed under the inves-
tigated conditions, nor the reverse reaction in the
presence of an excess of phosphine. In the case of the
ligands derived from VIa-c, VIIIa,b, and Xa-e, the
anions have no other good coordinating groups, which
would be able to bind to the nickel ion like the cyano
group does: for this reason, only chelate complexes
3d-h (Schemes 3 and 4) and 2a-e were obtained. In
the case of the nickel(II) complexes 3g,h, the anionic
(31) (a) Fritschi, H.; Leutenegger, U.; Siegmann, K.; Pfaltz, A. Helv.
Chim. Acta 1988, 71, 1541-1552. (b) Kla¨ui, W.; Bongards, J.; Reiss,
G. J. Angew. Chem., Int. Ed. 2000, 39(21), 3894-3896.
(32) Foley, S. R.; Stockland, R. A., Jr.; Shen, H.; Jordan, R. F. J.
Am. Chem. Soc. 2003, 125, 4350-4361.
(33) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G. J. Chem. Soc., Dalton Trans. 1989, S1.

Catalysts for the Dimerization of Olefins
Organometallics, Vol. 24, No. 17, 2005 4145
Figure 4. Molecular structures of 3a (left) and 3c (right). For 3a, red crystals suitable for X-ray diffractometry were
obtained in hexane/pentane/toluene (3/1/1). Selected bond distances (Å) and angles (deg): C1-O1 ) 1.254(5), C1-C2 )
1.399(5), C2-C3 ) 1.410(5), C3-N1 ) 1.313(4), Ni1-O1 ) 1.940(3), Ni1-N1 ) 1.947(3), Ni1-C14 ) 1.892(4), Ni1-P1 )
2.188(1); O1-C1-C2 ) 125.1(4), C1-C2-C3 ) 121.8(4), C2-C3-N1 ) 128.2(4), O1-Ni1-N1 ) 92.0(1), N1-Ni1-C14 )
93.8(1), C14-Ni1-P1 ) 88.0(1), P1-Ni1-O1 ) 87.0(1), O1-Ni1-C14 ) 171.7(2), P1-Ni1-N1 ) 171.7(1). For 3c, red
crystals suitable for X-ray diffractometry were obtained in pentane/toluene (8/1). Selected bond distances (Å) and angles
(deg): C4-O1 ) 1.244(5), C2-C4 ) 1.404(6), C1-C2 ) 1.406(6), N1-C1 ) 1.309(5), Ni1-O1 ) 1.941(3), Ni1-N1 ) 1.936(4),
Ni1-C17 ) 1.904(4), Ni1-P1 ) 2.185(2); O1-C4-C2 ) 124.9(4), C4-C2-C1 ) 121.0(4), C2-C1-N1 ) 127.8(4), N1-
Ni1-O1 ) 91.3(1), O1-Ni1-P1 ) 86.4(1), P1-Ni1-C17 ) 88.4(1), C17-Ni1-N1 ) 94.7(2), N1-Ni1-P1 ) 173.2(1), O1-
Ni1-C17 ) 169.9(2).
Figure 5. Molecular structures of 3g (left), 3h (right). For 3g, red crystals suitable for X-ray diffractometry were obtained
in pentane/hexane/toluene (10/2/1). Selected bond distances (Å) and angles (deg): C1-N1 ) 1.309(2), C2-C1 ) 1.420(2),
C3-C2 ) 1.395(3), O1-C3 ) 1.271(2), C4-C3 ) 1.504(2), Ni1-N1 ) 1.937(2), O1-Ni1 ) 1.901(1), P1-Ni1 ) 2.190(1),
C16-Ni1 ) 1.903(2); N1-C1-C2 ) 128.8(2), C1-C2-C3 ) 121.4(2), C2-C3-O1 ) 121.5(2), O1-C3-C4 ) 114.0(2), N1-
Ni1-O1 ) 90.55(6), O1-Ni1-P1 ) 86.41(4), P1-Ni1-C16 ) 88.24(5), C16-Ni1-N1 ) 95.48(6), N1-Ni1-P1 ) 174.0(1),
C16-Ni1-O1 ) 170.3(1). For 3h, red crystals suitable for X-ray diffractometry were obtained in pentane/toluene (7/1).
Selected bond distances (Å) and angles (deg): C1-N1 ) 1.327(9), C2-C1 ) 1.4461(0), C3-C2 ) 1.3911(1), O1-C3 )
1.270(9), C4-C3 ) 1.519(10), Ni1-N1 ) 1.909(6), Ni1-O1 ) 1.915(5), Ni1-P1 ) 2.184(3), Ni1-C18 ) 1.882(7); N1-C1-
C2 ) 125.8(7), C1-C2-C3 ) 121.5(7), C2-C3-O1 ) 122.3(7), N1-Ni1-O1 ) 90.4(2), O1-Ni1-P1 ) 88.1(2), P1-Ni1-
C18 ) 89.0(2), C18-Ni1-N1 ) 93.0(3), N1-Ni1-P1 ) 176.6(2), C18-Ni1-O1 ) 171.0(3).
ligand coordinates with its keto function, because that
oxygen atom has a stronger nucleophilic character than
the ester function in the same molecule.25c
In 3h, the triphenylphosphine occupies the trans
position of the coordinating nitrogen atom, while the
mesityl group attached to Ni is bound in a position trans
to the oxygen atom of the keto group (Figure 5). The
Ni-O, Ni-N, Ni-C, and Ni-P distances in complex 3h
are slightly shorter compared to the nickel complex 3a.
The Ni1-N1 and Ni1-O1 bond distances are almost
identical within the standard deviation range (1.909(6)
and 1.915(5) Å).18 The C1-C2 and C2-C3 distances in
the metallacycle are 1.446(10) and 1.391(11) Å, respec-
tively. The Ni1-P1 distance is 2.184(3) Å, while the

4146 Organometallics, Vol. 24, No. 17, 2005
Table 1. Dimerization of Ethylene with Nickel(II) Catalysts
Bluhm et al.
no. cat.a amt (µmol) cocat. time (h) T (°C) yield (g)b TON (×103) TOF (×103/h)
Rc
n-olefinsb (%) iso-olefinsb (%)
1
1a
1a
1a
1b
1c
1d
2a
2b
2c
2d
2e
2f
10
10
10
10
10
10
10
10
10
10
10
10
14
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
1
1
1
1
1
0.5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
25
0.08
6.46
0.29
0.29
43
27
57
73
2
MAO
EASC
MAO
MAO
MAO
MAO
EASC
EASC
EASC
EASC
EASC
MAO
EASC
MAO
EASC
EASC
MAO
MAO
25-45
25-74
25-33
22-25
23-35
23
25-70
25-70
25-71
25-72
25-64
23-28
25-70
25-31
25
23.06
23.06
0.04
3
4
0.65
31.80
1.88
2.33
113.49
6.71
2.33
113.49
13.41
71
22
27
29
78
73
5
0.11
0.04
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
3a
3a
3b
3b
3c
3d
3e
3f
25-70
23-42
23
7.51
4.43
13.06
25.95
26.79
15.80
46.60
92.59
26.79
15.80
46.60
92.59
24
58
30
28
76
42
70
72
23-30
23-70
25-72
25-43
25-70
25-34
25-70
25-31
25-62
25-47
27-70
3f
MAO
EASC
MAO
EASC
MAO
EASC
MAO
EASC
MAO
EASC
3f
3g
3g
3h
3h
3i
6.78
24.19
50.93
24.19
50.93
0.08
0.09
20
24
80
76
14.30
3i
4
5.8
20.53
20.53
0.11
54
46
4
a All precatalysts were dissolved in 30 mL of toluene and then activated either with 100 equiv of MAO (0.6 mL of a 10 wt % MAO
solution in toluene) or with 300 equiv of Et2AlCl‚EtAlCl2 (EASC) (3.3 mL of a 25 wt % solution in toluene); the ethylene pressure was 30
bar (No. 29, p ) 24 bar). b The yield and the 1-olefin content C4-C26 were determined by GC and a flame ionization detector using
calibration curves with standard solutions. c R is the probability of the chain propagation.
Table 2. Yield (%) of Oligomers in the
Table 3. Yield (%) of Oligomers in the
Experiments 18-21, 23, 25, and 29
Experiments 1, 2, and 4-6
expt no.
expt no.
1
2
4
5
6
18
19
20
21
23
25
29
C4
C6
C8
C10
100
95.9
4.1
100
89.1
9.9
95.9
4.1
C4
92.5
6.5
100
98.2
1.8
89.5
9.5
91.7
7.7
92.2
7.1
88.7
9.9
C6
0.9
C8
1.0
1.0
0.6
0.7
1.2
0.1
C10
C12
C14
C16
0.06
0.02
0.01
0.04
0.14
0.03
0.01
0.01
Ni1-C18 bond length measures 1.882(7) Å. The bite
angle O1-Ni1-N1 is 90.4°. The metallacycle is planar,
and the metal center shows a distorted-square-planar
coordination sphere. The plane of the mesityl ring is
oriented perpendicularly to the metallacycle plane, the
dihedral angle being 90.0°.
The complexes 2a-e and 4 were prepared in an
analogous manner by reaction of the anions with
[(PPh3)2Ni(Mes)Br]27 (Schemes 6-8).
Catalytic Oligomerizations with Ethylene and
Propylene. The precatalysts 1a-d are effective for
ethylene oligomerization when activated with MAO
(Table 1, runs 2-6), mostly giving dimeric products.
Without MAO the activity is very low (Table 1, run 1).
Youkin et al.15a have shown that N,O ligand Ni com-
plexes can be active for olefin polymerization without
MAO, with bulky substituents close to the chelating O
atom. The bulky surroundings seem to ease up dissocia-
tion of the PPh3 ligand. Since our system does not have
much steric bulk at this site, activation is necessary.
On the other hand, activation with EASC does not take
place in this case. In other experiments with alkylalu-
minum-based cocatalysts (Et3Al, Bu3Al) activation only
takes place within a very small range of Al/Ni ratios.15b
The complexes 1a,c bearing the isopropyl substituents
at the aryl rings are the most active among the nitrile-
bound complexes 1, thus indicating the importance of
bulky substituents in the ligand. Though these bulky
substituents are far away from the active metal center,
their steric demand has an impact on the position of
the PPh3 groups and, thus, the active metal center is
affected indirectly. The higher the activity, the lower
the selectivity for the produced olefins. 1a (Table 1, run
2) only yields C4-C6 with 95.9% butenes, while 1c
(Table 1, run 5) gives C4-C10 with 89.1% butenes. The
selectivity for R-olefins is rather poor, 25% for 1c, but
reaches 71% in the case of the less active 1b. The choice
of the cocatalyst is important. A good catalytic activity
is observed in the presence of MAO, whereas the
precatalyst is about 100 times less active in the absence
of any cocatalyst. EASC is not a suitable cocatalyst to
be used with the precatalysts 1a-d in the reactions
with ethylene, since all nickel complexes tested in the
presence of this organoaluminum compound did not
perform any oligomerization (Table 1). Complexes of
type 2 showed no activity either with MAO or with
EASC as cocatalyst.

Catalysts for the Dimerization of Olefins
Organometallics, Vol. 24, No. 17, 2005 4147
Table 4. Dimerization of Propene with Nickel(II) Catalysts
no.
cata
amt (µmol)
cocat.
time (h)
p (bar)
T (°C)
yield (g)b
TON (×103)
TOF (×103/h)
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
1a
1a
1b
1c
1c
1d
2a
2a
2b
2f
10
10
10
10
10
10
10
10
10
10
10
14
10
10
10
10
10
10
10
10
MAO
1
8
25
EASC
EASC
MAO
0.8
1
8
26-52
24-36
25
12.6
9.7
30.00
23.09
36.15
23.09
8
1
8
EASC
EASC
EASC
EASC
EASC
EASC
EASC
EASC
EASC
EASC
MAO
EASC
EASC
EASC
EASC
EASC
1
8
25-50
25-49
27-50
25-52
26-43
25-44
25
7.8
14.0
5.4
17.1
15.7
22.0
11.8
23.4
19.0
8.0
18.56
33.25
12.88
40.73
37.41
52.41
28.09
39.76
45.25
18.93
18.56
33.25
12.88
40.73
37.41
52.41
28.09
39.76
45.25
18.93
1
8
1
8
1
9.5
8
1
1
8
8
3a
3b
3c
3e
3f
1
1
9.5
8
25-54
26-44
24-44
25
1
1
8
1
8
3f
1
8
25
11.5
26.5
7.7
15.5
11.5
27.43
63.09
18.34
36.93
27.34
27.43
63.09
18.34
36.93
27.34
3g
3h
3i
1
9.5
8
25-54
26-42
25-43
25-50
1
1.2
1
9.5
8
4
a All precatalysts were first dissolved in 30 mL of toluene in an ultrasonic bath and then activated either with 100 equiv of MAO (0.6
mL of a 10 wt % MAO solution in toluene) or with 300 equiv of Et2AlCl‚EtAlCl2 (3.3 mL of a 25 wt % solution in toluene). b The yield and
the 1-olefin content C6-C18 were determined by GC and a flame ionization detector using calibration curves with standard solutions.
The N,O-chelated complexes 3a-i exhibit very dif-
ferent catalytic properties for the oligomerization of
ethylene. While 3a-c and 3i are completely inactive
(Table 1, runs 13-17 and 27 and 28), 3d-h oligomerize
ethylene with good turnover frequencies (Table 1, runs
18-26). Apparently, the presence of the noncoordinating
cyano group in place of an ester group is an inhibiting
factor in the catalysis.
The chelate complexes 3d-f are active with MAO as
cocatalyst at 30 bar (runs 18, 19, and 21). The precursor
3f bears the most bulky groups (i.e. isopropyl) at the
2,6-positions of the aryl ring and is the most active
among the N,O-chelate complexes 3 for the oligomer-
ization reaction. The main products are butenes ranging
from 89.5% for 3f (C4-C10) to 100% for 3e (only C4). The
precatalyst 3d produces the brightest range of oligomers
(C4-C14), although it is more selective for butenes than
3f (92.5% vs 89.5%). Selectivity toward R-olefins varies
in the range of 24-58%. The precatalyst 3f maintains
a good catalytic activity even in the absence of any
cocatalyst (Table 1, run 20), its TOF being just half of
the value reached in the presence of MAO (4.7 × 104 vs
9.3 × 104 h-1). 3f is fully inactive when EASC is
employed (Table 1, run 22).
When activated with MAO, both complexes 3g,h
oligomerize ethylene to C4-C14 oligomers (Table 1, runs
23 and 25), where the main fraction consists of butenes
(92%). The length of the alkyl chain R3 of 3g,h influ-
ences the activity: in fact, the turnover frequency of 3h
(R3 ) n-propyl) is twice as much as 3g (R3 ) methyl,
5.1 × 104 vs 2.4 × 104 h-1). The selectivities are very
similar to each other. ESAC does not give active
catalytic species with 3g,h (Table 1, runs 22 and 24).
2f and 3i with ligands bearing one or two imidazo-
[1,5-a]pyridines were inactive for catalytic oligomeriza-
tions with ethylene (Table 1, runs 12, 27, and 28) in
the presence of both MAO and EASC as cocatalyst. The
amidoiminomalonate complex 4 shows good perfor-
mances in the presence of MAO as cocatalyst, yielding
oligomers in the range of C4-C16 with prevailing dimers
(Table 1, run 29). It possesses one of the best R-selec-
tivities with MAO (54%) of all procatalysts tested herein,
although the selectivity for dimerization is not very
satisfactory (88.7%).
In summary, 3-aminoacrylate, 3-aminoiminoacrylate,
and amidoiminomalonate nickel(II) complexes 1-4 form
a versatile class of successful ethylene oligomerization
catalysts. The catalytic properties are strongly affected
by many factors such as coordination mode of the ligand
(chelate or monodentate), the steric hindrance of sub-
stituents at the aryl rings, electronic characteristics of
functional groups at the backbone (ester, nitrile, or
simply hydrogen), and the groups sideways to the
coordinating atoms (ester, ketone, imino ester, or imi-
dazopyridine). The best results were obtained in the
presence of MAO as cocatalyst. The best activity for
ethylene oligomerization was shown by the CN-coordi-
nated 2-cyano-3-aminoacrylate nickel(II) complex 1c
(TOF 1.13 × 105 h-1), followed by the chelate ester-
substituted 3-aminoacrylate 3f (TOF 9.3 × 104 h-1). The
most selective catalysts for generating n-olefins were
the nonchelate 2-cyano-3-aminoiminoacrylate nickel(II)
complex 1b (71%) and the chelate ester-substituted
3-aminoacrylate 3e (58%).
Some of the described nickel(II) complexes were also
tested for the reaction with propylene. The precatalysts
tested were not catalytically active when treated with
MAO (Table 4, runs 31, 34, and 45). Nevertheless, they
exhibited good performances when activated with EASC;
the turnover frequency was ranging from 7500 to 63 000
h-1. The influence of the organoaluminum activator
corresponds to literature published about the dimeriza-
tion of propylene by â-ketiminate nickel(II) complexes
(TOF up to 1.3 × 105 h-1).15c
All catalysts tested behaved similarly to each other
and the main products mostly consisted of dimers,
ranging between 85 and 95% (Tables 5-7). The ten-
dency of the nickel(II) catalysts to dimerize propylene
rather than to form higher oligomers is due to their
strong propensity for â-elimination.14,34
Methylpentenes were the main products (Table 5),
followed by hexenes. Mostly internal olefins were pro-
duced. The GC spectra of the fractions C6 usually
showed the presence of many different isomers, thus

4148 Organometallics, Vol. 24, No. 17, 2005
Bluhm et al.
Table 5. Distribution of Dimers (mol %)
Some other catalysts have a different behavior toward
ethylene and propylene oligomerization. For example,
the imidazo[1,5-a]pyridyl chelate complexes 2f and 3i
also exhibit high activities in dimerizing propylene (5.2
× 104 and 3.7 × 104 h-1, respectively). 2f gave oligomers
in the range of C6-C18, while 3i yielded olefins up to
C24. Among the C6 fraction, the main products consisted
of methylpentenes (Tables 5-7).
The cyano-coordinated complexes 1a,b and 1c,d also
mostly produced dimers in good yields (Table 4, runs
32, 33, 35, and 36) and exhibited moderately better
selectivities for the generation of linear hexenes (Table
5, runs 32, 33, 35, and 36). Among this class of
compounds, 1a was the most active and most selective
catalyst to produce dimers (93.0%, Table S1 in the
supplement): this trend is inverted to that of the
ethylene oligomerizationsthere, 1c was the most active
and selective precatalyst.
methyl- dimethyl-
no. cat. dimera 1-hexeneb hexenesc pentenes butenes
32 1a
33 1b
35 1c
36 1d
37 2a
38 2a
39 2b
40 2f
41 3a
42 3b
43 3c
44 3e
46 3f
47 3g
48 3h
49 3i
93.0
84.8
87.5
87.6
95.2
92.5
89.6
91.6
95.7
91.5
89.8
86.0
92.2
92.0
95.2
91.4
84.7
0.06
0.06
0.07
0.07
0.06
39.4
38.0
43.0
38.0
20.1
33.2
35.7
32.7
41.0
28.9
33.0
39.4
30.2
32.9
31.1
32.7
33.6
58.1
61.6
53.9
59.3
73.9
65.0
63.1
66.5
50.9
67.9
65.8
60.1
68.3
65.5
67.7
66.5
64.5
2.5
0.4
3.1
2.7
6.0
1.8
1.2
0.8
8.1
3.2
1.2
0.5
1.5
1.6
1.2
0.8
1.9
0.06
0.08
50
4
a Values for higher oligomers can be found in Tables S1 and S2
in the supplement. b Calculated over the whole amount. c 1-Hexene
included.
The precatalysts 3a-c did not work for ethylene
oligomerization, but they reacted with propylene when
activated with EASC (Table 4, runs 41-43). The most
selective precatalyst to generate dimers was 3a, produc-
ing only olefins in the range of C6-C12. Hence, also in
this case the catalytic activity was influenced by the
steric hindrance of the substituents at the aryl groups.
The behaviors of the chelate complexes 3a-c and the
nonchelate complexes 1a-d were very similar in the
propylene dimerization with regard to both the activity
and selectivity (Tables 4-7). With 4, a lower tendency
to generate dimers was observed (84.7%, Table S2 in
the Supporting Information), but the distribution of the
formed dimers did not change significantly in compari-
son with the other precatalysts tested (Table 5).
At 8 bar of ethylene pressure, the most active nickel
catalyst was the imidazopyridyl complex 2f (5.2 × 104
h-1, Table 4), while the best selectivity to generate
dimers was observed with the 3-aminoacrylate complex
3a (95.7%, Table S1). 1c exhibited the highest selectivity
for the formation of linear hexenes (43.0%, Table 5),
while 2a and 3f were the most selective for the forma-
tion of methylpentenes (74 and 68%, respectively).
Additionally, a few tests with 1-hexene were per-
formed to verify if some complexes are active for the
oligomerization of higher R-olefins (Table 6). 3b,i were
tested in the presence of EASC and gave oligomers
consisting of C12, C18, and C24 with rather low yields.
The main products were dimers, and the oligomer
distribution depended on the ligands used (runs 51 and
52) and on the reaction conditions (runs 52 and 53):
more dimers were obtained when the reaction was
performed only in 1-hexene and fewer dimers in a
diluted solution of 1-hexene in toluene.
Table 6. Results of 1-Hexene Oligomerization with
Nickel(II) Catalysts
amt
t
yield TON
TOF
no. cat.a (µmol) cocat. (h) T (°C) solvent (g)c (×103) (×103/h)
51 3ia
52 3ba
53 3bb
10
10
10
EASC
EASC
EASC
1
1
1
25-29
24-28
0.7
0.84
1.58
0.32
0.84
1.58
0.32
1.3
23-28 toluene 0.3
a The precatalysts were first dissolved in 30 mL of 1-hexene in
an ultrasonic bath and then activated with 360 equiv of EASC.
b The precatalyst was first dissolved in 30 mL of toluene in an
ultrasonic bath; then 5 mL of 1-hexene was added and the catalysis
was activated with 360 equiv of EASC. c The yield and the olefin
content of C6-C24 were determined by FID-GC using calibration
curves with standard solutions.
Table 7. Yield (%) of Oligomers in Experiments
51-53
expt
fraction
51
52
53
C12
C18
C24
41.6
32.3
26.2
88.4
7.0
4.6
68.2
27.0
4.8
indicating that the catalysts are able to isomerize the
olefin produced. When the propylene pressure was
increased, catalytic activity was improved, too (Table
4, runs 37 and 38). As shown in the case of complex 2a,
the higher pressure also influences the ratio of the
dimers produced: at lower pressure the catalyst is more
selective for generating methylpentenes.
Even complexes not active for ethylene oligomeriza-
tion provided good results with propylene. For example,
complexes 2a,b were not effective in oligomerizing
ethylene, but they worked well with propylene and
When the oligomerization was performed in bulk, the
complexes 3b,i also worked as isomerization catalysts
for 1-hexene and gave a mixture of internal olefins. Less
than 10% of the 1-hexene was oligomerized under these
test conditions, while most of it underwent isomeriza-
tion.
exhibited good activities (1.3 × 104 and 3.7 × 104 h-1
,
respectively, at 8 bar of pressure). The increased steric
hindrance of the isopropyl groups at the aryl substitu-
ents of the precatalyst 2b provides a better catalytic
performance compared to 2a, which bears less bulky
methyl groups. However, 2a exhibited the highest
selectivity for methylpentenes of all tested precatalysts.
3. Conclusions
(34) (a) Johnson, L. K.; Killian, C. M.; Brookhart M. J. Am. Chem.
Soc. 1995, 117, 6414-6415. (b) Johnson, L. K.; Mecking, S.; Brookhart,
M. J. Am. Chem. Soc. 1996, 118, 267-268. (c) Killian, C. M.; Tempel,
D. J.; Johnson, L. K.; Brookhart, M. J. Am. Chem. Soc. 1996, 118,
11664-11665. (d) Tempel, D.; Brookhart, M. Organometallics 1998,
17(11), 2290-2296.
Novel 3-aminoiminoacrylate, 3-aminoacrylate, and
amidoiminomalonate ligands have been synthesized and
coordinated with nickel(II) ions to give active precata-
lysts 1-4 suitable for dimerization reactions with small

Catalysts for the Dimerization of Olefins
Organometallics, Vol. 24, No. 17, 2005 4149
mL of absolute toluene, sodium bis(trimethylsilyl)amide solu-
tion in toluene (1.23 g, 0.8 mmol), [(PPh3)2Ni(Mes)Br]27 (0.66
g, 0.8 mmol) in 35 mL of absolute toluene. Yield: 0.27 g (0.2
mmol, 27%). 1H NMR (DMSO-d6): δ 7.49-7.17 (m, 37H, HPhenyl
+ NCH), 6.08 (s, 2H, HMes), 3.32 (s, 24H, CH3), 2.86 (bs, 4H,
CH), 2.72 (bs, 2H, CH2), 2.29 (bs, 6H, CH3), 2.02 (bs, 3H, CH3),
1.23 (bs, 3H, CH3). IR (KBr): ν 3436 cm-1 (CdN), 3054 (C-H,
aryl), 2961, 2911 (C-H, CH3), 2198 (CtN, w), 1618 (CdC),
1456 (CdC), 1434 (P-Ph, PPh3), 1363 (C-H, C(CH3)2), 1262
(C-O-C), 1093 (C-O), 1028 (C-O-C), 846 (C-H, mesityl),
803 (C-H, aryl), 693 (C-H, phenyl). ESI+-MS: m/z 1161 (M+).
Anal. Calcd for C75H81N3NiOP2: C, 77.58; H, 7.03; N, 3.62.
Found: C, 77.43; H, 6.91; N, 3.32.
[Ethyl 2-Cyano-3-[(2,6-dimethylphenyl)amino]-N-(2,6-
diisopropylphenyl)prop-2-enimidoatetoluyl]bis(triphen-
ylphosphino)nickel(II) (1b) was obtained from ethyl 2-cyano-
3-[(2,6-dimethylphenyl)amino]-N-(2,6-diisopropylphenyl)prop-
2-enimidoate (IVb; 0.13 g, 0.3 mmol) in 10 mL of absolute
toluene, sodium bis(trimethylsilyl)amide solution in toluene
(0.50 g, 0.3 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.26 g, 0.3 mmol)
in 10 mL of absolute toluene. Yield: 0.14 g (0.1 mmol, 38%).
1H NMR (CDCl3): δ 7.56-7.07 (m, 37H, HPhenyl + NCH), 6.10
(s, 2H, HMes), 4.34 (q, 2H, CH2), 3.10 (s, 6H, CH3), 2.94 (m7,
2H, CH), 2.16 (s, 6H, CH3), 1.98 (s, 3H, CH3), 1.38 (t, 3H, CH3),
1.20 (d, 6H, CH3), 1.17 (d, 6H, CH3). IR (KBr): ν 3448 cm-1
(CdN), 3058 (C-H, aryl), 2964 (C-H, CH3), 2204 (CtN, w),
1647 (CdC), 1621 (CdC), 1589 (CdC, phenyl), 1478 (CdC),
1435 (P-Ph, PPh3), 1370 (C-H, C(CH3)2), 1273 (C-O-C),
1095 (C-O), 1027 (C-O-C), 847 (C-H, mesityl), 796 (C-H,
aryl), 773 (CdC-H), 693 (C-H, phenyl). ESI+-MS: m/z 1105
(M+).
olefins: e.g., ethylene, propylene, and 1-hexene. The
ligands IVa,b and Vd,e did not act as chelating units
but instead coordinated to the nickel(II) ion through the
cyano group to give 1a-d. If the cyano group was
replaced by less suitable coordinating groups such as
esters, only bidentate chelate complexes 2a-e and
3d-h were obtained.
Catalytic properties of the precatalysts 1-4 for the
dimerization and oligomerization of ethylene and pro-
pylene depend on the coordination mode and the sub-
stituted backbone of the ligand, the steric hindrance of
the substituents at the aryl rings, and the nickel(II)-
coordinated functional groups. For the dimerization of
ethylene, the best results were obtained with MAO as
cocatalyst. The highest activity in the reaction with
ethylene provided 1c and 3f, whereby 1b acted as the
most selective precatalyst. Some nickel(II) complexes did
not work for ethylene oligomerization, but they reacted
with propylene when activated with EASC (e.g. 2a,b,f,
3a-c,i). 2f and 3g were the most active precatalysts
with EASC and propylene, while the best selectivity to
generate dimers was observed with 3a. 1c showed the
highest selectivity for the formation of linear hexenes,
while 2a and 3f are most selective for the formation of
methylpentenes. 3b,i were also active for the oligomer-
ization of 1-hexene with EASC as cocatalyst. The main
products were isomerized internal dodecenes.
[Ethyl 2-cyano-3-[(2,6-diisopropylphenyl)amino]acryl-
atemesityl]bis(triphenylphosphino)nickel(II) (1c) was
obtained from ethyl 2-cyano-3-[(2,6-diisopropylphenyl)amino]-
acrylate (Vd; 0.21 g, 0.7 mmol) in 15 mL of absolute toluene,
sodium bis(trimethylsilyl)amide solution in toluene (1.06 g, 0.7
mmol), and [(PPh3)2Ni(Mes)Br]27 (0.55 g, 0.7 mmol) in 30 mL
4. Experimental Section
General Considerations. All manipulations were carried
out under an atmosphere of argon using standard Schlenk
techniques. NMR spectra were recorded on Bruker 250 MHz
(1H) and 62.9 MHz (13C) spectrometers at 293 K. Mass spectra
were obtained using electron ionization (EI), electron spray
ionization (ESI), or field ionization (FI). FI and EI spectra were
recorded with Micromass GCT and Finnigan MAT GCQ
spectrometers, ESI spectra were recorded with a Hewlett-
Packard 1100 MSD spectrometer. Melting points were either
determined by using capillaries and a Bu¨chi apparatus or with
differential scanning calorimetry (DSC) with a Mettler Toledo
DSC822e instrument. IR spectra were recorded with a Perkin-
Elmer System 2000 FT-IR. Oligomer products were analyzed
by GC with a flame ionization detector, using a 50 m DB1
column, injector temperature 40 °C, and the following tem-
1
of absolute toluene. Yield: 0.17 g (0.2 mmol, 24%). H NMR
(DMSO-d6): δ 7.47-7.14 (m, 34H, HAryl + NCH), 6.19 (s, 2H,
HMes), 3.32 (s, 12H, CH3), 2.86 (bs, 4H, CH), 2.77 (bs, 2H, CH2),
2.28 (bs, 6H, CH3), 2.02 (bs, 3H, CH3), 0.62 (t, 3H, CH3). IR
(KBr): ν 3434 cm-1 (CdN), 3055 (C-H, aryl), 2962 (C-H,
CH3), 2207 (CtN, w), 1615 (CdC), 1480 (CdC), 1435 (P-Ph,
PPh3), 1370 (C-H, C(CH3)2), 1262 (C-O-C), 1094 (C-O), 1027
(C-O-C), 844 (C-H, mesityl), 694 (C-H, phenyl). ESI+-MS:
m/z ) 1001 (M+). Anal. Calcd for C63H64N2NiO2P2: C, 75.53;
H, 6.44; N, 2.80. Found: C, 75.20; H, 6.10; N, 2.47.
[Ethyl 2-cyano-3-[(4-methylphenyl)amino]acrylate-
mesityl]bis(triphenylphosphino)nickel(II) (1d) was ob-
tained from ethyl 2-cyano-3-[(4-methylphenyl)amino]acrylate
(Ve; 0.29 g, 1.3 mmol) in 20 mL of absolute toluene and sodium
bis(trimethylsilyl)amide solution in toluene (1.86 g, 1.3 mmol),
with [(PPh3)2Ni(Mes)Br]27 (1.00 g, 1.3 mmol) in 50 mL of
absolute toluene being added dropwise to the solution. Yield:
0.69 g (0.7 mmol, 58%). 1H NMR (CDCl3): δ 7.60 (bs, 1H,
NCH), 7.52-7.16 (m, 30H, HPhenyl), 6.54 (d, 2H, HAryl), 6.43 (d,
2H, HAryl), 5.75 (s, 2H, HMesityl), 2.82 (q, 2H, CH2), 2.64 (q, 2H,
CH2), 2.06 (s, 3H, CH3), 1.84 (s, 3H, CH3), 0.75 (t, 3H, CH3).
IR (KBr): ν 3463 cm-1 (CdN), 3042 (C-H, aryl), 2963 (C-H,
CH3), 2200 (CtN, w), 1671 (CdC), 1629 (CdC), 1479 (CdC),
1434 (P-Ph, PPh3), 1379 (C-H, CH3), 1261 (C-O-C), 1094
(C-O), 1027 (C-O-C), 843 (C-H, mesityl), 817 (C-H, aryl),
694 (C-H, phenyl). ESI+-MS: m/z 932 (M+). C54H54N2NiO2P2:
C, 73.40; H, 6.16; N, 3.17. Found: C, 73.13; H, 6.04; N, 3.54.
[Ethyl 2-{ethoxy[(2,6-dimethylphenyl)imino]-methyl}-
3-[(2,6-dimethylphenyl)amino]acrylatemesityl](triphen-
ylphosphino)nickel(II) (2a) was obtained from ethyl 2-{eth-
oxy[(2,6-dimethylphenyl)imino]methyl}-3-[(2,6-dimeth-
ylphenyl)amino]acrylate (Xa; 0.29 g, 0.7 mmol) in 15 mL of
absolute toluene, sodium bis(trimethylsilyl)amide solution in
toluene (1.15 g, 0.8 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.58 g,
perature program: 40 °C/5 min, 40-300 °C, 5 °C/10 min-1
The individual products were integrated, using n-tridecane as
internal standard.
Materials. MAO (10% solution in toluene), EASC (25%
solution in toluene), and all other anilines were purchased
commercially and used as received.
.
3. Synthesis of Nickel(II) Complexes 1-4. General
Procedure. The corresponding ligand was dissolved in abso-
lute toluene. Then a 0.6 M solution of sodium bis(trimethyl-
silyl)amide in toluene was added. The resulting solution was
added dropwise to a solution of [(PPh3)2Ni(Mes)Br]27 in abso-
lute toluene. If not otherwise noted, the mixture was stirred
under argon at room temperature for 16-24 h, and then it
was filtered on Celite under argon and the filtrate was
concentrated under vacuum to 1-5 mL. After that, 15-50 mL
of an absolute pentane/hexane mixture was added and the
precipitate was filtered, dried under vacuum, and finally stored
under argon.
[Ethyl 2-cyano-3-[(2,6-diisopropylphenyl)amino]-N-
(2,6-diisopropylphenyl)prop-2-enimidoatemesityl]bis-
(triphenylphosphino)nickel(II) (1a) was obtained from
ethyl 2-cyano-3-[(2,6-diisopropylphenyl)-amino]-N-(2,6-diiso-
propylphenyl)prop-2-enimidoate (IVa; 0.38 g, 0.8 mmol) in 20

4150 Organometallics, Vol. 24, No. 17, 2005
Bluhm et al.
0.7 mmol) in 15 mL of absolute toluene. Yield: 0.33 g (0.4
mmol, 53%). 1H NMR (CDCl3): δ 7.32-7.06 (m, 15H, HPhenyl),
6.94 (t, 1H, HAryl), 6.67 (d, 2H, HAryl), 6.63 (bs, 1H, NCH), 5.79
(s, 2H, HMesityl), 4.28 (q, 2H, CH2), 2.61 (q, 2H, CH2), 2.45 (s,
6H, CH3), 2.23 (s, 6H, CH3), 2.08 (s, 6H, CH3), 1.92 (s, 3H,
CH3), 1.31 (t, 3H, CH3), 0.53 (t, 3H, CH3). IR (KBr): ν 3449
cm-1 (CdN), 3058 (C-H, aryl), 2968, 2923 (C-H, CH3), 1642
(CdO), 1610 (CdC), 1465 (C-H, CH3), 1435 (P-Ph, PPh3),
1379 (C-H, CH3), 1238 (C-O-C), 1086 (C-O), 1037 (C-O-
C), 844 (C-H, mesityl), 804 (C-H, aryl), 693 (C-H, phenyl).
ESI+-MS: m/z ) 834 (M+). Anal. Calcd for C51H55N2NiO3P:
C, 73.48; H, 6.65; N, 3.36. Found: C, 73.12; H, 6.38; N, 3.10.
[Ethyl 2-{ethoxy[(2,6-diisopropylphenyl)imino]methyl}-
3-[(2,6-diisopropylphenyl)amino]acrylate-mesityl](tri-
phenylphosphino)nickel(II) (2b) was obtained from ethyl
2-{ethoxy[(2,6-diisopropylphenyl)imino]methyl}-3-[(2,6-diiso-
propylphenyl)amino]acryl-ate (Xb; 0.23 g, 0.4 mmol) in 20 mL
of absolute toluene, sodium bis(trimethylsilyl)amide solution
in toluene (0.68 g, 0.5 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.35
g, 0.4 mmol) in 10 mL of absolute toluene. Yield: 0.12 g (0.1
mmol, 28%). 1H NMR (DMSO-d6): δ 7.62 (s, 1H, NCH), 7.63-
7.16 (m, 21H, HAryl), 6.08 (s, 2H, HMes), 3.32 (s, 24H, CH3), 2.97
(bs, 4H, CH), 2.88 (bs, 2H, CH2), 2.72 (bs, 2H, CH2), 2.28 (bs,
6H, CH3), 1.93 (bs, 3H, CH3), 1.22 (bs, 3H, CH3), 1.08 (bs, 3H,
CH3). ESI+-MS: m/z 946 (M+). Anal. Calcd for C59H71N2-
NiO3P: C, 74.92; H, 7.57; N, 2.96. Found: C, 74.72; H, 7.53;
N, 2.91.
[Ethyl 3-[(2,6-diethylphenyl)amino]-2-{ethoxy[(4-meth-
ylphenyl)imino]methyl}acrylatemesityl](triphenylphos-
phino)nickel(II) (2c) was obtained from ethyl 3-[(2,6-di-
ethylphenyl)amino]-2-{ethoxy[(4-methylphenyl)imino]-
methyl}acrylate (Xc; 0.10 g, 0.3 mmol) in 20 mL of absolute
toluene, sodium bis(trimethylsilyl)amide solution in toluene
(0.37 g, 0.3 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.20 g, 0.3 mmol)
in 5 mL of absolute toluene. Yield: 0.20 g (0.2 mmol, 91%).
1H NMR (CDCl3) δ 7.32-6.54 (m, 23H, HPhenyl+Aryl + NCH),
5.73 (s, 2H, HMesityl), 3.98 (q, 2H, CH2), 2.61 (q, 2H, CH2), 2.43
(q, 4H, CH2), 2.41 (s, 6H, CH3), 2.29 (s, 3H, CH3), 1.83 (s, 3H,
CH3), 1.06 (t, 3H, CH3), 0.89 (t, 3H, CH3), 0.67 (t, 3H, CH3).
IR (KBr): ν 3459 cm-1 (CdN), 3054 (C-H, aryl), 2964 (C-H,
CH2, CH3), 1646 (CdO), 1479 (C-H, CH2, CH3), 1435 (P-Ph,
PPh3), 1094 (C-O), 1029 (C-O-C), 847 (C-H, mesityl), 804
(C-H, aryl), 692 (C-H, phenyl). ESI+-MS: m/z 847 (M+).
[Ethyl 2-{ethoxy[(2,6-dimethylphenyl)imino]-methyl}-
3-[(4-methylphenyl)amino]acrylatemesityl](triphen-
ylphosphino)nickel(II) (2d) was obtained from ethyl 2-{eth-
oxy[(2,6-dimethylphenyl)imino]methyl}-3-[(4-methyl-
phenyl)amino]acrylate (Xd; 0.14 g, 0.4 mmol) in 20 mL of
absolute toluene, sodium bis(trimethylsilyl)amide solution in
toluene (0.54 g, 0.4 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.29 g,
0.4 mmol) in 20 mL of absolute toluene. Yield: 0.07 g (0.1
mmol, 23%). 1H NMR (CDCl3): δ 7.29-6.91 (m, 15H, HPhenyl),
6.70-6.49 (m, 8H, HAryl + NCH), 5.79 (s, 2H, HMesityl), 4.30 (q,
2H, CH2), 2.63 (q, 2H, CH2), 2.45 (s, 6H, CH3), 2.33 (s, 3H,
CH3), 2.18 (s, 6H, CH3), 1.90 (s, 3H, CH3), 1.33 (t, 3H, CH3),
0.54 (t, 3H, CH3). IR (KBr): ν 3456 cm-1 (CdN), 3054 (C-H,
aryl), 2964 (C-H, CH3), 1636 (CdO), 1480 (C-H, CH3), 1435
(P-Ph, PPh3), 1095 (C-O), 1029 (C-O-C), 847 (C-H, mesi-
tyl), 804 (C-H, aryl), 744 (C-H, aryl), 693 (C-H, phenyl).
ESI+-MS: m/z 819 (M+).
CH2), 3.55 (m7, 2H, CH), 2.71 (q, 2H, CH2), 2.46 (s, 6H, CH3),
1.91 (s, 6H, CH3), 1.84 (s, 3H, CH3), 1.14 (t, 3H, CH3), 0.86 (s,
6H, CH3), 0.82 (s, 6H, CH3), 0.79 (t, 3H, CH3). IR (KBr): ν
3455 cm-1 (CdN), 3054 (C-H, aryl), 2963 (C-H, CH3), 1635
(CdO), 1481 (C-H, CH3), 1435 (P-Ph, PPh3), 1095 (C-O),
1029 (C-O-C), 847 (C-H, mesityl), 805 (C-H, aryl), 693 (C-
H, phenyl). ESI+-MS: m/z 889 (M+).
[1-Methyl-3-[(1-methylimidazo[1,5-a]pyridin-3-yl)me-
thyl]imidazo[1,5-a]pyridylmesityl](triphen-ylphosphino)-
nickel(II) (2f) was obtained from 1-methyl-3-[(1-methylimidazo-
[1,5-a]pyridin-3-yl)methyl]imidazo[1,5-a]pyridine (Xf; 0.08 g,
0.3 mmol) in 25 mL of absolute toluene, sodium bis(trimeth-
ylsilyl)amide solution in toluene (0.51 g, 0.4 mmol), and
[(PPh3)2Ni(Mes)Br]27 (0.24 g, 0.3 mmol) in 15 mL of absolute
toluene. Yield: 0.10 g (1 mmol, 45%). 1H NMR (CDCl3): δ 8.06
(bs, 2H, HAryl), 7.68 (bs, 2H, HAryl), 7.56-7.10 (m, 15H, HPhenyl),
6.53 (bs, 2H, HAryl), 6.43 (bs, 2H, HAryl), 4.79 (s, 2H, HMesityl),
3.11 (bs, 1H, CH), 2.50 (s, 6H, CH3), 1.69 (s, 6H, CH3), 1.27 (s,
3H, CH3). IR (KBr): ν 3455 cm-1 (CdN), 2963, 2917 (C-H,
CH3), 1631 (CdC), 1435 (P-Ph, PPh3), 1102 (C-N), 847 (C-
H, mesityl), 738 (C-H, heterocycle), 707 (C-H, heterocycle).
ESI+-MS: m/z 715 (M+). Anal. Calcd for C44H41N4NiP: C,
73.86; H, 5.78; N, 7.83. Found: C, 73.53; H, 5.49; N, 8.18.
[Ethyl 2-cyano-3-[(4-methoxyphenyl)amino]acrylate-
mesityl](triphenylphosphino)nickel(II) (3a) was obtained
from ethyl 2-cyano-3-[(4-methoxyphenyl)amino]acrylate (Va;
0.17 g, 0.7 mmol) in 15 mL of absolute toluene, sodium bis-
(trimethylsilyl)amide solution in toluene (1.00 g, 0.7 mmol),
and [(PPh3)2Ni(Mes)Br]27 (0.52 g, 0.7 mmol) in 20 mL of
absolute toluene. Yield: 0.32 g (0.5 mmol, 71%). 1H NMR
(CDCl3): δ 7.61 (d, 1H, NCH), 7.40-7.20 (m, 15H, HAryl), 6.44
(d, 2H, HAryl), 6.28 (d, 2H, HAryl), 5.78 (d, 2H, HMes), 3.59 (s,
3H, CH3), 2.83 (q, 2H, CH2), 2.63 (s, 6H, CH3), 1.86 (s, 3H,
CH3), 0.75 (t, 3H, CH3). IR (KBr): ν 3465 cm-1 (CdN), 3055
(C-H, aryl), 2960, 2911 (C-H, CH3), 2832 (C-H, OCH3), 2198
(CtN, s), 1664, 1618 (CdC), 1479 (CdC, phenyl), 1429 (P-
Ph, PPh3), 1372 (C-H, CH3), 1095 (C-O), 1029 (C-O-C), 843
(C-H, mesityl), 832 (C-H, aryl), 749 (C-H, phenyl), 696 (C-
H, phenyl). ESI+-MS: m/z 685 (M+). Anal. Calcd for C40H39N2-
NiO3P: C, 70.09; H, 5.74; N, 4.09. Found: C, 69.89; H, 5.79;
N, 4.12.
[Ethyl 2-cyano-3-[(2,6-dimethylphenyl)amino]acryl-
atemesityl](triphenylphosphino)nickel(II) (3b) was ob-
tained from ethyl 2-cyano-3-[(2,6-dimethylphenyl)amino]-
acrylate (Vb; 0.17 g, 0.7 mmol) in 15 mL of absolute toluene,
sodium bis(trimethylsilyl)amide solution in toluene (1.10 g, 0.8
mmol), and [(PPh3)2Ni(Mes)Br]27 (0.55 g, 0.7 mmol) in 30 mL
1
of absolute toluene. Yield: 0.23 g (0.3 mmol, 48%). H NMR
(DMSO-d6): δ 7.50-7.15 (m, 16H, HPhenyl + NCH), 6.73-6.62
(m, 3H, HAryl), 5.77 (s, 2H, HMes), 3.32 (s, 6H, CH3), 3.01 (q,
2H, CH2), 2.09 (s, 6H, CH3), 1.87 (s, 3H, CH3), 0.67 (t, 3H, CH3).
IR (KBr): ν 3456 cm-1 (CdN), 3057 (C-H, aryl), 2962, 2914
(C-H, CH3), 2205 (CtN, s), 1703 (CdO), 1615 (CdC), 1435
(P-Ph, PPh3), 1371 (C-H, CH3), 1267 (C-O-C), 1094 (C-
O), 1019 (C-O-C), 844 (C-H, mesityl), 747 (C-H, phenyl),
695 (C-H, phenyl). ESI+-MS: m/z 684 (M+). Anal. Calcd for
C41H41N2NiO2P: C, 72.05; H, 6.05; N, 4.10. Found: C, 71.84;
H, 5.91; N, 3.94.
[Ethyl 2-cyano-3-[(2,6-diethylphenyl)amino]acrylate-
mesityl](triphenylphosphino)nickel(II) (3c) was obtained
from ethyl 2-cyano-3-[(2,6-diethylphenyl)amino]acrylate (Vc;
0.20 g, 0.7 mmol) in 20 mL of absolute toluene, sodium bis-
(trimethylsilyl)amide solution in toluene (1.08 g, 0.7 mmol),
and [(PPh3)2Ni(Mes)Br]27 (0.56 g, 0.7 mmol) in 15 mL of
absolute toluene. Yield: 0.30 g (0.4 mmol, 58%). 1H NMR
(CDCl3): δ 7.41-7.16 (m, 16H, HPhenyl + NCH), 6.82 (t, 1H,
HAryl), 6.66 (d, 2H, HAryl), 5.78 (s, 2H, HMesityl), 2.99 (q, 2H, CH2),
2.57 (q, 2H, CH2), 2.50 (s, 6H, CH3), 1.89 (s, 3H, CH3), 1.03 (t,
3H, CH3), 0.79 (t, 3H, CH3). IR (KBr): ν 3461 cm-1 (CdN),
3064 (C-H, aryl), 2960, 2933 (C-H, CH3, CH3), 2206 (CtN,
s), 1614 (CdC), 1498 (CdC), 1431 (P-Ph, PPh3), 1367 (C-H,
[Ethyl 2-[[(2,6-diisopropylphenyl)imino](ethoxy)me-
thyl]-3-[(2,6-dimethylphenyl)amino]acrylatemesityl]-
(triphenylphosphino)nickel(II) (2e) was obtained from
ethyl 2-[[(2,6-diisopropylphenyl)imino]-(ethoxy)methyl]-3-[(2,6-
dimethylphenyl)amino]acryl-ate (Xe; 0.09 g, 0.2 mmol) in 20
mL of absolute toluene, sodium bis(trimethylsilyl)amide solu-
tion in toluene (0.34 g, 0.2 mmol), and [(PPh3)2Ni(Mes)Br]27
(0.15 g, 0.2 mmol) in 20 mL of absolute toluene. The mixture
was stirred under argon at room temperature for 2 days.
Yield: 0.07 g (0.1 mmol, 41%). 1H NMR (CDCl3): δ 7.03-6.55
(m, 22H, HPhenyl+Aryl + NCH), 5.80 (s, 2H, HMesityl), 4.22 (q, 2H,

Catalysts for the Dimerization of Olefins
Organometallics, Vol. 24, No. 17, 2005 4151
CH3), 1273 (C-O-C), 1094 (C-O), 1019 (C-O-C), 845 (C-
H, mesityl), 745 (C-H, phenyl), 694 (C-H, phenyl). ESI+-MS:
m/z 711 (M+). Anal. Calcd for C43H45N2NiO2P: C, 72.59; H,
6.37; N, 3.94. Found: C, 72.24; H, 6.13; N, 3.63.
740 (C-H, phenyl), 694 (C-H, phenyl). ESI+-MS: m/z 700
(M+). Anal. Calcd for C42H44NNiO3P: C, 72.02; H, 6.33; N, 2.00.
Found: C, 71.67; H, 5.98; N, 1.79.
[Ethyl 2-butyryl-3-[(2,6-dimethylphenyl)amino]acryl-
atemesityl](triphenylphosphino)nickel(II) (3h) was ob-
tained from ethyl 2-butyryl-3-[(2,6-dimethylphen-yl)amino]-
acrylate (VIIIb; 0.20 g, 0.7 mmol) in 10 mL of absolute toluene,
sodium bis(trimethylsilyl)amide solution in toluene (1.04 g, 0.7
mmol), and [(PPh3)2Ni(Mes)Br]27 (0.52 g, 0.7 mmol) in 10 mL
of absolute toluene. The mixture was stirred under argon at
room temperature for 5 days. Yield: 0.08 g (0.1 mmol, 16%).
1H NMR (CDCl3): δ 7.79 (d, 1H, NCH), 7.38-7.16 (m, 15H,
HPhenyl), 6.79-6.65 (m, 3H, HAryl), 5.84 (s, 2H, HMesityl), 4.14 (q,
2H, CH2), 2.50 (t, 2H, CH2), 2.46 (s, 6H, CH3), 2.10 (s, 6H, CH3),
1.94 (s, 3H, CH3), 1.22 (t, 3H, CH3), 0.74 (m6, 2H, CH2), 0.49
(t, 3H, CH3). IR (KBr): ν 3446 cm-1 (CdN), 3054 (C-H, aryl),
2964, 2935 (C-H, CH2, CH3), 1706 (CdO), 1583 (CdC), 1457
(C-H, CH2, CH3), 1434 (P-Ph, PPh3), 1387 (C-H, CH3), 1272
(C-O-C), 1072 (C-O), 1035 (C-O-C), 846 (C-H, mesityl),
786 (C-H, aryl), 693 (C-H, phenyl). ESI+-MS: m/z 728 (M+).
Anal. Calcd for C44H48NNiO3P: C, 72.54; H, 6.64; N, 1.92.
Found: C, 72.18; H, 6.33; N, 1.68.
[Ethyl cyano(1-methylimidazo[1,5-a]pyridin-3(2H)yl-
idene)acetatemesityl](triphenylphosphino)nickel(II) (3i)
was obtained from ethyl cyano(1-methylimidazo[1,5-a]pyridin-
3(2H)-ylidene)acetate (VIIIc; 0.11 g, 0.4 mmol) in 15 mL of
absolute toluene, sodium bis(trimethylsilyl)amide solution in
toluene (0.70 g, 0.5 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.33 g,
0.4 mmol) in 20 mL of absolute toluene. The mixture was
stirred at room temperature for 3 days. Yield: 0.09 g (0.1
mmol, 31%). 1H NMR (CDCl3) δ 7.39-7.06 (m, 18H, HPhenyl+Pyr),
6.59 (t, 1H, HPyr), 6.05 (s, 2H, HMes), 4.27 (q, 2H, CH2), 2.75 (s,
6H, CH3), 2.01 (s, 3H, CH3), 1.27 (s, 3H, CH3), 0.62 (t, 3H, CH3).
IR (KBr): ν 3437 cm-1 (CdN), 3055 (C-H, aryl), 2964, 2923
(C-H, CH3), 2174 (CtN, s), 1742 (CdO), 1581 (CdC), 1497
(CdC), 1435 (P-Ph, PPh3), 1374 (C-H, CH3), 1261 (C-O),
1094 (C-O), 1029 (C-O-C), 846 (C-H, mesityl), 729 (C-H,
heterocycle), 694 (C-H, heterocycle). ESI+-MS: m/z 682 (M+).
Anal. Calcd for C40H38N3NiO2P: C, 70.40; H, 5.61; N, 6.16.
Found: C, 70.03; H, 5.30; N, 5.82.
[N-(2,6-Diisopropylphenyl)-3-[(2,6-diisopropyl-phen-
yl)amino]-3-oxopropanimidoatemesityl](tri-phenylphos-
phino)nickel(II) (4) was obtained from ethyl N-(2,6-diiso-
propylphenyl)-3-[(2,6-diisopropylphen-yl)amino]-3-oxopro-
panimidoate (XII; 0.21 g, 0.4 mmol) in 20 mL of absolute
toluene, sodium bis(trimethylsilyl)amide solution in toluene
(0.65 g, 0.4 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.35 g, 0.4 mmol)
in 20 mL of absolute toluene. Yield: 0.16 g (0.2 mmol, 41%).
1H NMR (CDCl3): δ 7.77-6.91 (m, 21H, HAryl+Phenyl), 6.10 (s,
2H, HMes), 3.10 (s, 6H, CH3), 3.03 (bs, 1H, CH), 2.92 (bs, 1H,
CH), 2.62 (bs, 2H, CH2), 2.36 (s, 2H, CH2), 1.98 (s, 3H, CH3),
1.20 (bs, 12H, CH3), 1.09 (bs, 12H, CH3), 0.97 (bs, 3H, 1.20
(bs, 12H, CH3). IR (KBr): ν 3359 cm-1 (CdN), 3054 (C-H,
aryl), 2964 (C-H, CH3), 2869 (C-H, CH), 1595 (CdC), 1550
(C(O)-N), 1480 (CdC), 1459 (C-H, CH2, CH3), 1435 (P-Ph,
PPh3), 1385 (C-H, C(CH3)2), 1260 (C-O-C), 1095 (C-O), 846
(C-H, mesityl), 801 (C-H, aryl), 744 (C-H, phenyl), 693 (C-
H, phenyl). ESI+-MS: m/z 889 (M+). Anal. Calcd for C56H67N2-
NiO2P: C, 75.59; H, 7.59; N, 3.15. Found: C, 75.21; H, 7.23;
N, 2.78.
Oligomerization Procedure. (a) Oligomerizations with
Propylene (8-9.5 bar). The precatalyst was dissolved in 30
mL of solvent in a Schlenk flask under argon. A complete
solution was obtained by leaving the flask in an ultrasonic bath
for several minutes. A 150 mL glass reactor was evacuated
and then filled with argon. The precatalyst solution was added
under argon into the reactor vessel. The cocatalyst (MA,
approximately 100 equiv, 0.6 mL of a 10 wt % MAO solution
in toluene; EASC, approximately 300 equiv, 3.3 mL of a 25 wt
% solution in toluene) and n-tridecane standard solution were
added with stirring under argon. For several minutes propyl-
[Diethyl {[(4-methylphenyl)amino]methylene}malo-
natemesityl](triphenylphosphino)nickel(II) (3d) was ob-
tained from diethyl {[(4-methylphenyl)amino]methylene}-
malonate (VIa; 0.08 g, 0.3 mmol) in 25 mL of absolute toluene,
sodium bis(trimethylsilyl)amide solution in toluene (0.47 g, 0.3
mmol), and [(PPh3)2Ni(Mes)Br]27 (0.22 g, 0.3 mmol) in 10 mL
of absolute toluene. The mixture was stirred under argon at
room temperature for 48 h. Yield: 0.10 g (0.1 mmol, 48%). 1H
NMR (CDCl3): δ 8.23 (d, 1H, NCH), 7.32-7.07 (m, 15H,
HPhenyl), 6.97 (d, 2H, HAryl), 6.83 (d, 2H, HAryl), 5.78 (s, 2H,
HMesityl), 4.11 (q, 2H, CH2), 3.09 (q, 2H, CH2), 2.93 (s, 6H, CH3),
2.46 (s, 6H, CH3), 1.83 (s, 3H, CH3), 1.16 (t, 3H, CH3), 0.72 (t,
3H, CH3). ESI+-MS: m/z 717 (M+). Anal. Calcd for C42H44-
NNiO4P: C, 70.41; H, 6.19; N, 1.95. Found: C, 70.19; H, 5.99;
N, 1.73.
[Diethyl {[(2,6-diethylphenyl)amino]methylene}mal-
onatemesityl](triphenylphosphino)nickel(II) (3e) was
obtained from diethyl {[(2,6-diethylphenyl)amino]methylene}-
malonate (VIb; 0.14 g, 0.4 mmol) in 10 mL of absolute toluene,
sodium bis(trimethylsilyl)amide solution in toluene (0.66 g, 0.4
mmol), and [(PPh3)2Ni(Mes)Br]27 (0.35 g, 0.4 mmol) in 10 mL
1
of absolute toluene. Yield: 0.14 g (0.2 mmol, 40%). H NMR
(CDCl3): δ 7.92 (d, 1H, NCH), 7.42-7.10 (m, 15H, HPhenyl), 6.75
(t, 1H, HAryl), 6.61 (d, 2H, HAryl), 5.72 (s, 2H, HMesityl), 4.03 (q,
2H, CH2), 2.91 (q, 2H, CH2), 2.78 (q, 2H, CH2), 2.50 (q, 2H,
CH2), 2.41 (s, 6H, CH3), 1.82 (s, 6H, CH3), 1.10 (t, 3H, CH3),
0.96 (t, 3H, CH3), 0.75 (t, 3H, CH3). IR (KBr): ν 3443 cm-1
(CdN), 3056 (C-H, aryl), 2965, 2933 (C-H, CH2, CH3), 1698
(CdO), 1600 (CdC), 1462 (C-H, CH2, CH3), 1435 (P-Ph,
PPh3), 1381 (C-H, CH3), 1241 (C-O-C), 1071 (C-O), 1027
(C-O-C), 845 (C-H, mesityl), 789 (C-H, aryl), 747 (C-H,
phenyl), 722 (C-H, CH2), 695 (C-H, phenyl). ESI+-MS: m/z
758 (M+). Anal. Calcd for C45H50NNiO4P: C, 71.25; H, 6.64;
N, 1.85. Found: C, 70.89; H, 6.51; N, 1.77.
[Diethyl {[(2,6-diisopropylphenyl)amino]methylene}-
malonatemesityl](triphenylphosphino)nickel(II) (3f) was
obtained from diethyl {[(2,6-diisopropylphenyl)amino]methyl-
ene}malonate (VIc; 0.22 g, 0.6 mmol) in 10 mL of absolute
toluene, sodium bis(trimethylsilyl)amide solution in toluene
(1.00 g, 0.7 mmol), and [(PPh3)2Ni(Mes)Br]27 (0.48 g, 0.6 mmol)
in 10 mL of absolute toluene. Yield: 0.16 g (0.2 mmol, 34%).
1H NMR (CDCl3): δ 7.86 (d, 1H, NCH), 7.33-7.09 (m, 15H,
HPhenyl), 6.93 (t, 1H, HAryl), 6.81 (d, 2H, HAryl), 5.80 (s, 2H,
HMesityl), 4.03 (q, 2H, CH2), 3.61 (m7, 2H, CH), 3.05 (q, 2H, CH2),
2.46 (s, 6H, CH3), 1.84 (s, 3H, CH3), 1.09 (t, 3H, CH3), 0.91 (d,
6H, CH3), 0.89 (d, 6H, CH3), 0.67 (t, 3H, CH3). IR (KBr): ν
3468 cm-1 (CdN), 3057 (C-H, aryl), 2962 (C-H, CH3), 1697
(CdO), 1599 (CdC), 1461 (C-H, CH3), 1436 (P-Ph, PPh3),
1381 (C-H, C(CH3)2), 1260 (C-O-C), 1070 (C-O), 1029 (C-
O-C), 846 (C-H, mesityl), 802 (C-H, aryl), 744 (C-H, phenyl),
693 (C-H, phenyl). ESI+-MS: m/z 787 (M+). Anal. Calcd for
C47H54NNiO4P: C, 71.77; H, 6.92; N, 1.78. Found: C, 71.61;
H, 6.43; N, 1.63.
[Ethyl 2-acetyl-3-[(2,6-dimethylphenyl)amino]acryl-
atemesityl](triphenylphosphino)nickel(II) (3g) was ob-
tained from ethyl 2-acetyl-3-[(2,6-dimethylphen-yl)amino]-
acrylate (VIIIa; 0.17 g, 0.6 mmol) in 10 mL of absolute toluene,
sodium bis(trimethylsilyl)amide solution in toluene (1.03 g, 0.7
mmol), and [(PPh3)2Ni(Mes)Br]27 (0.50 g, 0.6 mmol) in 15 mL
1
of absolute toluene. Yield: 0.08 g (0.1 mmol, 19%). H NMR
(CDCl3): δ 7.80 (d, 1H, NCH), 7.39-7.16 (m, 15H, HPhenyl),
6.78-6.67 (m, 3H, HAryl), 5.83 (s, 2H, HMesityl), 4.14 (q, 2H, CH2),
2.47 (s, 6H, CH3), 2.11 (s, 6H, CH3), 1.92 (s, 3H, CH3), 1.20 (t,
3H, CH3), 0.89 (t, 3H, CH3). IR (KBr): ν 3441 cm-1 (CdN),
3055 (C-H, aryl), 2964, (C-H, CH3), 1688 (CdC), 1635 (Cd
C), 1480 (C-H, CH3), 1435 (P-Ph, PPh3), 1262 (C-O-C), 1094
(C-O), 1022 (C-O-C), 843 (C-H, mesityl), 803 (C-H, aryl),

4152 Organometallics, Vol. 24, No. 17, 2005
Table 8. Crystallographic Data
Bluhm et al.
1a
1b
3a
3c
3g
3h
empirical formula
CCDC no.
fw
C
77H85.80N3NiOP2
C
71H73N3NiOP2
C
40H39N2NiO3P
C43H45N2NiO2P
256367
C42H44NNiO3P
256363
C44H47NNiO3P
256362
1189.94
240(2)
256366
256364
256365
727.51
1104.97
200(2)
0.710 73
monoclinic
P21/c (No. 14)
685.41
200(2)
0.710 73
monoclinic
P21/c (No. 14)
711.49
700.46
temp (K)
wavelength, λ (Å)
cryst syst
space group
unit cell dimens
a, Å
200(2)
200(2)
0.710 73
monoclinic
P21/c (No. 14)
200(2)
0.710 73
triclinic
P1h (No. 2)
0.710 73
triclinic
0.710 73
triclinic
P1h (No. 2)
P1h (No. 2)
12.674(1)
14.702(1)
18.808(1)
101.815(1)
91.609(1)
102.356(1)
3341.3(4)
2
14.978(1)
24.131(1)
17.469(1)
90
15.220(1)
9.616(1)
24.915(1)
90
10.822(5)
12.157(6)
14.632(7)
99.202(7)
94.050(7)
98.805(7)
1868.9(1)
2
20.493(1)
17.590(1)
10.144(1)
90
10.749(10)
13.812(13)
14.233(14)
100.826(17)
99.922(16)
104.049(15)
1960(3)
b, Å
c, Å
R, deg
â, deg
101.839(1)
90
106.896(1)
90
91.436(1)
90
γ, deg
V (Å3)
6179.6(7)
4
3489.2(3)
4
3655.3(4)
4
Z
2
F
calcd (g cm-3
)
1.183
1.188
1.305
1.264
1.273
1.233
µ (mm-1
F(000)
)
0.384
0.411
0.642
0.600
0.614
0.575
1270
2344
1440
752
1480
770
cryst size (mm3)
θ range for data
collecn (deg)
0.3 × 0.25 × 0.1
0.3 × 0.2 × 0.2
0.25 × 0.07 × 0.07 0.25 × 0.2 × 0.1
0.4 × 0.4 × 0.3
0.30 × 0.05 × 0.05
1.63-28.31
1.39-28.32
1.40-28.28
1.42-28.45
1.53-28.30
1.50-28.61
index ranges
-16 e h e 16,
-19 e k e 19,
-25 e l e 25
40 555
16 042 (R(int) )
0.0741)
-19 e h e 19,
-31 e k e 32,
-23 e l e 23
74 003
15 125 (R(int) )
0.0741)
15 125/0/724
-20 e h e 20,
-12 e k e 12,
-32 e l e 33
41 775
8602 (R(int) )
0.1978)
8602/0/437
-14 e h e 14,
-15 e k e 16,
-19 e l e 19
18 820
8853 (R(int) )
0.0731)
8853/2/472
-27 e h e 27,
-23 e k e 23,
-13 e l e 13
43 174
8977 (R(int) )
0.0282)
8977/0/448
-14 e h e 14,
-18 e k e 18,
-18 e l e 18
24 010
9499 (R(int)
) 0.1733)
9499/0/467
no. of rflns collected
no. of indep rflns
no. of data/restraints/ 16 042/6/777
params
goodness of fit on F2
final R indices
(I > 2σ(I)]a
0.856
0.941
0.776
0.924
1.063
0.868
R1 ) 0.0480,
wR2 ) 0.1157
R1 ) 0.1495,
wR2 ) 0.1326
R1 ) 0.0413,
wR2 ) 0.0915
R1 ) 0.0921,
wR2 ) 0.1087
R1 ) 0.0500,
wR2 ) 0.0921
R1 ) 0.1967,
wR2 ) 0.1232
R1 ) 0.0725,
wR2 ) 0.1675
R1 ) 0.1366,
wR2 ) 0.1971
R1 ) 0.0368,
wR2 ) 0.0966
R1 ) 0.0516,
wR2 ) 0.1032
R1 ) 0.1058,
wR2 ) 0.2405
R1 ) 0.2670,
wR2 ) 0.3194
R indices
(all data)a
2
a R1 ) [∑||Fo| - |Fc||]/∑|Fo|, wR2 ) [[∑w(|Fo2 - Fc |)2]/[∑w(Fo2)]]1/2, w ) 1/[(σFo)2 + (aP)2]. The value of aP was obtained from structure
refinement.
ene was introduced while streaming through the reactor to
displace the argon. Then the reactor was closed and pressur-
ized to 8 bar (or 9.5 bar) with propylene. The reactor pressure
was maintained constant throughout the oligomerization run
by manually controlled addition of propylene. Runs were
terminated by venting off volatiles and extracting the solution
with dilute hydrochloric acid and water. Quantitative GC
analysis of the organic layer was performed immediately after
the extraction.
(b) Oligomerizations with Ethylene (30 bar). The
precatalyst was dissolved in 30 mL of solvent in a Schlenk
flask under argon. A complete solution was obtained by leaving
the flask in an ultrasonic bath for several minutes. A 150 mL
stainless steel reactor with cooling mantle was evacuated and
then filled with argon. The precatalyst solution was added
under argon into the reactor vessel. The cocatalyst (MAO,
approximately 100 equiv, 0.6 mL of a 10 wt % MAO solution
in toluene; EASC, approximately 300 equiv, 3.3 mL of a 25 wt
% solution in toluene) and n-tridecane standard solution were
added with stirring under argon. For several minutes ethylene
was introduced while streaming through the reactor to displace
the argon. Then the reactor was closed and pressurized to 30
bar with ethylene. The reactor pressure was maintained
constant throughout the oligomerization run by manually
controlled addition of ethylene. The temperature of the reac-
tion was controlled by cooling the reactor vessel with water.
Runs were terminated by venting off volatiles and extracting
the solution with dilute hydrochloric acid and water. Quantita-
tive GC analysis of the organic layer was performed im-
mediately after the extraction.
tion. Data were corrected for Lorentz and polarization effects
but not for absorption.35,36
The structures were resolved by direct methods (SHELXS37)
2
and refined by full-matrix least-squares techniques against Fo
(SHELXL-9738). The hydrogen atoms were localized by differ-
ence Fourier synthesis and refined isotropically. The data are
deposited in the Cambridge Crystallographic Data Centre.39
All non-hydrogen atoms were refined anisotropically.38 XP
(SIEMENS Analytical X-ray Instruments, Inc.) and Ortep40
were used for structure representations. Crystal data for all
compounds are given in Table 8.
Supporting Information Available: Text giving syn-
thetic details and characterization data for the ligands used
in this study and tables giving additional yield data. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM049075S
(35) COLLECT, Data Collection Software; Nonius BV, Delft, The
Netherlands, 1998.
(36) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology; Carter, C.
W., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276
(Macromolecular Crystallography, Part A), pp 307-326.
(37) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467-473.
(38) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1993.
(39) The files CCDC 256362-256367 contain the supplementary
crystallographic data of the structure analyses given in this paper.
These data can be obtained free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, U.K.; fax (+44) 1223-
336-033; deposit@ccdc.cam.ac.uk).
Crystal Structure Determination. The intensity data for
the compounds were collected by a Siemens Smart 1000 CCD
diffractometer using graphite-monochromated Mo KR radia-
(40) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.