Pyridinecarboxamidato-nickel(II) complexes

Article abstract of DOI:10.1021/om010576c

The synthesis, characterization, and reactivity toward ethylene of pyridinecarboxamidato complexes of nickel are reported. These compounds are isoelectronic to α-iminocarboxamidato complexes, which are useful ethylene polymerization catalysts. Addition of a benzene solution containing N-phenyl-2-pyridinecarboxamide and B(C₆F₅)₃ to bis(methallyl)nickel results in the formation of [N-phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ ²N,N]Ni(η³-CH₂CMeCH₂) (3) in 93% yield. A similar procedure using N-(2,6-diisopropyl) phenyl-2-pyridinecarboxamide provides [N-(2,6-diisopropyl) phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ² N,N]Ni (η³-CH₂CMeCH₂)(4) in 92% yield. The solid-state structures of 3 and 4 were determined by X-ray diffraction techniques. The intramolecular metrical parameters are consistent with substantial partial positive charge at the nickel atom. Deprotonation of N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide in THF with KH, followed by addition to Ni(η³-CH₂C₆H₅)Cl(PMe₃ ) and subsequent treatment with 2 equiv of B(C₆F₅)₃, produces [N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate- κ²N,N]Ni (η³-CH₂C₆H₅) (5). Compound 5 is obtained as a mixture of isomers. Deprotonation of N-(2,6-diisopropylphenyl)-6-triisopropylsilyl-2-pyridinecarboxamide, followed by addition to Ni(η³-CH₂C₆H₅)Cl(PMe₃ ), gives a product (7) which lacks a benzyl fragment. An X-ray diffraction study shows that metalation of one of the isopropyl groups and loss of the benzyl ligand takes place. The reactivity of 3, 4, 5, and 7 toward ethylene is presented. Considerably more activity is obtained with 5, probably as a result of faster initiation. The pyridine ligand leaves an open quadrant adjacent to nickel. As a result, the molecular weight of the product is not high.

Full text of DOI:10.1021/om010576c

Organometallics 2001, 20, 5425-5431
5425
P yr id in eca r boxa m id a to-Nick el(II) Com p lexes
Bun Yeoul Lee,†,‡ Xianhui Bu,† and Guillermo C. Bazan*,†
Departments of Chemistry and Materials, University of California,
Santa Barbara, California 93106, and Department of Molecular Science and Technology,
Ajou University, Suwon 442-749, Korea
Received J une 28, 2001
The synthesis, characterization, and reactivity toward ethylene of pyridinecarboxamidato
complexes of nickel are reported. These compounds are isoelectronic to R-iminocarboxamidato
complexes, which are useful ethylene polymerization catalysts. Addition of a benzene solution
containing N-phenyl-2-pyridinecarboxamide and B(C6F5)3 to bis(methallyl)nickel results in
the formation of [N-phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ2N,N]-
Ni(η3-CH2CMeCH2) (3) in 93% yield. A similar procedure using N-(2,6-diisopropyl)phenyl-
2-pyridinecarboxamide provides [N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamidatotris-
(pentafluorophenyl)borate-κ2N,N]Ni(η3-CH2CMeCH2) (4) in 92% yield. The solid-state structures
of 3 and 4 were determined by X-ray diffraction techniques. The intramolecular metrical
parameters are consistent with substantial partial positive charge at the nickel atom.
Deprotonation of N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide in THF with KH, followed
by addition to Ni(η3-CH2C6H5)Cl(PMe3) and subsequent treatment with 2 equiv of B(C6F5)3,
produces [N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-
κ2N,N]Ni(η3-CH2C6H5) (5). Compound 5 is obtained as a mixture of isomers. Deprotonation
of N-(2,6-diisopropylphenyl)-6-triisopropylsilyl-2-pyridinecarboxamide, followed by addition
to Ni(η3-CH2C6H5)Cl(PMe3), gives a product (7) which lacks a benzyl fragment. An X-ray
diffraction study shows that metalation of one of the isopropyl groups and loss of the benzyl
ligand takes place. The reactivity of 3, 4, 5, and 7 toward ethylene is presented. Considerably
more activity is obtained with 5, probably as a result of faster initiation. The pyridine ligand
leaves an open quadrant adjacent to nickel. As a result, the molecular weight of the product
is not high.
In tr od u ction
We discovered, during our efforts at developing tan-
dem catalytic processes,12-14 that the reactivity of
SHOP-type catalysts such as [(C6H5)2PC6H4C(O)O-κ2P,O]-
Ni(η3-CH2CMeCH2)15 toward ethylene increases sub-
stantially upon addition of B(C6F5)3. Carbonyl coordi-
nation to the borane gives the complex [(C6H5)2PC6H4C-
(OB(C6F5)3)O-κ2P,O]Ni(η3-CH2CMeCH2). Adduct forma-
tion removes electron density from the nickel atom.16
Nickel-based olefin polymerization and oligomeriza-
tion catalysts1 continue to attract considerable recent
attention.2,3 Depending on the ancillary ligand frame-
work, these catalysts participate in chain-walking reac-
tions,4,5 tolerate polar functionalities,6 and may even be
used in water.7 These properties provide materials with
unique topologies,8 could enable manufacturing alterna-
tives for the ever-growing polyolefin industry,9 and are
complementary in many ways to those of early metal-
based catalysts.10,11
(10) (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b)
Kaminsky, W., Sinn, H., Eds. Transition Metals and Organometallics
as Catalysts for Olefin Polymerization; Springer-Verlag: Berlin, 1988.
(c) Fink, G., Mu¨lhaupt, R., Brintzinger, H. H., Eds. Ziegler Catalysts;
Springer-Verlag: Berlin, 1995. (d) Togni, A., Halterman, R. L., Eds.
Metallocenes; Wiley-VCH: New York, 1998. (e) Britovsek, G. J . P.;
Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 429. (f)
Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 3, 255.
(11) (a) Espelid O, B. K. J . J . Catal. 2000, 195, 125. (b) Kohn, R. D.;
Haufe, M.; Mihan, S. Chem Commun. 2000, 1927. (c) Ajjou, J .; Scoott,
S. L. J . Am. Chem. Soc. 2000, 122, 8968. (d) Siemeling, U.; Kolling,
L.; Stammler, A. Chem. Commun. 2000, 1177. (e) Thune, P. C.; Loos,
J .; de J ong, A. M. Top. Catal. 2000, 67. (f) Voges, M. H.; Romming, C.;
Tilset, M. Organometallics 1999, 18, 529. (g) Kasani, A.; McDonald,
R.; Cavell, R. G. Chem. Commun. 1999, 1993. (h) Duchateau, R.;
Cremer, U.; Harmsen, R. J . Organometallics 1999, 18, 5447. (i) J ensen,
V. R.; Angermund, K.; J olly, P. W. Organometallics 2000, 19, 403. (j)
Dohring, A.; Gohre, J .; J olly, P. W. Organometallics 2000, 19, 388. (k)
Matare, C. J .; Foo, D. M.; Kane, K. M. Organometallics 2000, 19, 1534.
(l) Kim, W. K.; Fevola, M. J .; Liable-Sands, L. M. Organometallics 1998,
17, 4541.
† University of California.
‡ Ajou University.
(1) Ziegler, K.; Gellert, H.-G.; Holzkamp, E.; Wilke, G.; Duck, E. W.;
Kroll, W.-R. J ustus Liebigs Ann. Chem. 1960, 629, 172.
(2) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995 117, 6414.
(3) Reviews: (a) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem.
Rev. 2000, 100, 1169. (b) Mecking, S. Coord. Chem. Rev. 2000, 203,
325.
(4) Mo¨hring, V. M.; Fink, G. Angew. Chem., Int. Ed. Engl. 1985,
24, 1001.
(5) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J . Science 1999,
283, 2059.
(6) (a) Younkin, T. R.; Connor, E. F.; Henderson, J . I.; Friedrich, S.
K.; Grubbs, R. H.; Banselben, D. A. Science 2000, 287, 460.
(7) Held, A.; Bauers, F. M.; Mecking, S. Chem. Commun. 2000, 301.
(8) Cotts, P. M.; Guan, Z.; McCord, E.; McLain, S. Macromolecules
2000, 33, 6945.
(9) (a) Kissen, Y. V. Olefin Polymers-Polyethylene. In Kirk-Othmer
Encyclopedia of Chemical Technology, 4th ed.; Kroschwitz, J . I., Howe-
Grant, M., Eds.; Wiley-Interscience: New York, 1996. (b) Montagna,
A. A. Chemtech. 1995, 45. (c) Morse, P. M. Chem. Eng. News 1998,
J uly 6, p 11. (d) Tullo, A. H. Chem. Eng. News 2000, August 7, p 35.
(e) Short, P. Chem. Eng. News 2000, November 6, p 22.
(12) (a) Komon, Z. J . A.; Bu, X.; Bazan, G. C. J . Am. Chem. Soc.
2000, 122, 1830. (b) Barnhart, R. W.; Bazan, G. C.; Mourney, T. J .
Am. Chem. Soc. 1998, 120, 1082.
(13) Review: Komon, Z. J .; Bazan, G. C. Macromol. Rapid Commun.
2001, 22, 467.
10.1021/om010576c CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/10/2001

5426 Organometallics, Vol. 20, No. 25, 2001
Lee et al.
It is possible to extend this activation concept to the
design of polymerization catalysts by taking into account
mechanistic insight obtained from Brookhart’s diimine
complexes.17 Complexes 1 and 2, containing R-iminocar-
boxamide ligands, have been synthesized and their
reactivity toward ethylene has been studied.18 The two
resonance structures shown below illustrate the removal
of electron density from the nickel center upon Lewis
acid coordination. Attaching isopropyl groups at the 2,6
positions increases the rate of propagation relative to
the rate of chain transfer. Under identical reaction
conditions compound 1 produces oligomers, whereas 2
provides branched polymers. The η3-benzyl fragment
was selected, instead of the more frequently used
methallyl, because it leads to faster initiation rates.19
mide as a ligand for late transition metals.20 The bulkier
N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide can be
obtained in multigram quantities and in excellent yield
(92%) from 2-pyridinecarboxylic acid by addition of ethyl
chloroformate and triethylamine, followed by 2,6-diiso-
propylaniline (eq 1).
N-Phenyl-2-pyridinecarboxamide does not react di-
rectly with bis(methallyl)nickel. Apparently, the amide
N-H is not sufficiently acidic to protonate the methallyl
ligand.21 However, when B(C6F5)3, N-phenyl-2-pyridin-
ecarboxamide, and bis(methallyl)nickel are all mixed
simultaneously in benzene and allowed to react for 3 h,
one obtains [N-phenyl-2-pyridinecarboxamidatotris(pen-
tafluorophenyl)borate-κ2N,N]Ni(η3-CH2CMeCH2) in 93%
yield (compound 3 in eq 2). It is likely that in these
reactions the borane precoordinates to the carbonyl,
thereby lowering the pKa of the amide site. A similar
procedure using N-(2,6-diisopropyl)phenyl-2-pyridin-
ecarboxamide provides [N-(2,6-diisopropyl)phenyl-2-py-
ridinecarboxamidatotris(pentafluorophenyl)borate-κ2N,N]-
Ni(η3-CH2CMeCH2) in 92% yield (compound 4 in eq 2).
In this contribution we report on the synthesis and
reactivity of pyridinecarboxamidato nickel complexes
which are isoelectronic to 1 and 2. We examine the effect
on the reactivity toward ethylene of substitution at the
2,6 positions of the benzamide aryl ring as well as the
6 position of the pyridine ring. We also probe the effect
of methallyl versus η3-benzyl substitution on the rate
of initiation.
Compounds 3 and 4 have similar 1H, 11B, and 19F
1
NMR spectra. For example the H NMR signals for the
methylene protons appear at 2.00, 1.94, 1.71, and 1.44
ppm for 3 and 2.07, 1.88, 1.82, and 1.75 ppm for 4. In
the case of 4, at room temperature, two methine proton
resonances are observed (3.54 and 3.02 ppm), indicating
that the rotations of the phenyl ring and the methallyl
group are frozen with respect to the NMR time scale.22
The two ortho carbons are also inequivalent in the 13C
NMR spectrum (141.11 and 140.82 ppm). For 3, the two
ortho carbon resonances are equivalent, consistent with
a considerably faster rotation rate of the aryl unit.
Single crystals of 3 suitable for X-ray diffraction study
were obtained by allowing a hexane and benzene
solution (10:1) to stand at room temperature, and the
result of these studies is shown in Figure 1. A square
planar coordination geometry is observed, with the
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . Literature pre-
cedent exists for the use of N-phenyl-2-pyridinecarboxa-
(14) (a) Beach, D. L.; Kissin, Y. V. J . Polym. Sci. 1984, 22, 3027. (b)
Pettijohn, T. M.; Reagan, W. K.; Martin, S. J . U.S. Patent 5 331 070,
1994. (c) Starzewski, K. A. O.; Witte, J .; Reichert, K. H.; Vasiliou, G.
In Transition Metals and Organometallics as Catalysts for Olefin Poly-
merization; Kaminsky, W., Sinn, H., Eds.; Springer-Verlag: Berlin,
1988; p 349. (d) Canich, J . A. M.; Licciardi, G. F. U.S. Patent 5 057 475,
1991. (e) Pellecchia, C.; Pappalardo, D.; Gruter, G. J . Macromolecules
1999, 32, 4491.
(15) Bonnet, M. C.; Dahan, F.; Ecke, A.; Keim, W.; Schultz, R. P.;
Tkatchenko, I. Chem. Commun. 1994, 615.
(16) For a recent review of activation of polymerization catalysts
with borane Lewis acids see: Chen, E. Y.-X.; Marks, T. J . Chem. Rev.
2000, 100, 1391.
(17) (a) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem.
Soc. 1996, 118, 11664. (b) Deng, L.; Woo, T. K.; Cavallo, L.; Margl, P.
M.; Ziegler, J . Am. Chem. Soc. 1997, 119, 6177. (c) Svejda, S. A.;
J ohnson, L. K.; Brookhart, J . Am. Chem. Soc. 1999, 121, 10634.
(18) Lee, B. Y.; Bazan, G. C.; Vela, J .; Komon, Z. J . A.; Bu, X. J .
Am. Chem. Soc. 2001, 123, 5352.
(20) Brunner, H.; Nuber, B.; Prommersberger, M. J . Organomet.
Chem. 1996, 523, 179.
(21) Ecke, A.; Keim, W.; Bonnet, M. C.; Tkatchenko, I.; Dahan, F.
Organometallics 1995, 14, 5302.
(22) Rotation about the metal-allyl axis is symmetrically forbidden.
See: J olly, P. W. In Comprehensive Organometallic Chemistry; Wilkin-
son, G., Stone, G. A., Abel, E. W., Eds.; Pergamon Press: New York,
1982; Vol. 6; p 145.
(19) Komon, Z. J . A.; Bu, X.; Bazan, G. C. J . Am. Chem. Soc. 2000,
122, 12379.

Pyridinecarboxamidato-Ni(II) Complexes
Organometallics, Vol. 20, No. 25, 2001 5427
F igu r e 1. ORTEP drawing of 3. Hydrogen atoms not
shown for clarity.
F igu r e 3. Comparison of the molecular structures of 3 and
4.
to decrease steric interference between the diisopropyl-
phenyl and B(C6F5)3 fragments.
Pyridinecarboxamidato-nickel compounds containing
the more reactive η3-benzyl ligand, instead of methallyl,
are readily obtained starting with Ni(η3-CH2C6H5)Cl-
(PMe3).26 Addition of KH to a solution of N-(2,6-
diisopropyl)phenyl-2-pyridinecarboxamide in THF re-
sults in clean deprotonation. Addition of this solution
to Ni(η3-CH2C6H5)Cl(PMe3), followed by 2 equiv of
B(C6F5)3, results in the precipitation of Me3P-B(C6F5)3
and two compounds in a 10:1 ratio. This ratio was
constant at a given temperature, regardless of reaction
and workup conditions. We propose that the product is
a mixture of the two isomers for [N-(2,6-diisopropyl)-
phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)-
borate-κ2N,N]Ni(η3-CH2C6H5) (5), as shown in eq 3.27
F igu r e 2. ORTEP drawing of 4. Hydrogen atoms not
shown for clarity.
amidato functionality coordinating via the nitrogen
atom. The C-OB distance (1.300(5) Å) is longer than
average C-O double bond lengths (∼1.22 Å), while the
C-NNi distance (1.298(5) Å) indicates considerable
partial double bond character.23 These data confirm a
strong contribution by a resonance structure similar to
B. That the pyridine N-Ni distance is nearly identical
(1.921(3) Å) to the amidato N-Ni distance (1.933(4) Å)
reflects the similarity in bonding between the two
nitrogen atoms. It is also interesting to note the in-
tramolecular “stacking” between one of the pentafluo-
rophenyl groups on boron and the phenyl group on
nitrogen.24 Interactions of this type have been observed
in the solid-state structures of the adducts of B(C6F5)3
and PhC(O)X compounds (X ) OEt and NPr).25
Figure 2 shows the solid-state structure of 4. The
coordination sphere around nickel is similar to that
observed for 3, with nearly identical intramolecular
bond distances and angles. The bulky isopropyl groups
bear their influence on two noteworthy distortions. The
methallyl ligand is “rotated” in such a way that the
methyl group points away from the diisopropylphenyl
fragment (Figure 3). One can obtain a measure of this
distortion by examining the pyN-Ni-Câ-CH3 torsional
angles (ca. -78° for 3 and ca. -67° for 4). In 4, the
C-O-B angle is larger (139.6(2)°) than in 3 (130.6(3)°)
The NMR spectroscopic features for the two isomers
of 5 are similar, and only those of the major species will
be discussed in detail. Signals for the aromatic hydro-
gens on the benzyl ligand occur in the 5.8-6.6 ppm
range, consistent with η3 coordination.18 The two me-
thine protons are equivalent, while the two methyl
(23) Sutton, L. E., Ed. Tables of Interatomic Distances and Con-
figurations in Molecules and Ions; The Chemical Society: London,
1958.
(24) Renak, M.; Bartholomew. G. P.; Wang, S.; Ricatto, P. J .;
Lachicotte, R. J .; Bazan, G. C. J . Am. Chem. Soc. 1999, 121, 7787.
(25) Parks, D. J .; Piers, W. E.; Parvez, M.; Atencio, R.; Zaworotko,
M. J . Organometallics 1998, 17, 1369.
(26) Carmona, E.; Paneque, M.; Poveda, M. Polyhedron 1989, 8, 285.
(27) Similar isomerization was observed in R-iminocarboxamide
ligands: see ref 18.

5428 Organometallics, Vol. 20, No. 25, 2001
Lee et al.
Ta ble 1. Rea ctivity Stu d ies w ith Eth ylen ea
B(C6F5)3 time consumed solid
Sch em e 1a
entry compound
(equiv)
(h) ethyleneb (g) fractionc (g)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
3
3
3
3
4
4
4
4
5
5
5
7
7
7
7
0
1
5
10
0
1
5
10
0
1
1.0
1.0
1.0
1.0
20
8
6.5
6.5
1.0
1.0
1.0
1.0
1.0
0.15
0.56
3.1
4.1
0.40
0.80
2.7
4.2
2.4
7.6
5.6
0
0
0
0
0
0.32
0.77
1.6
2.4
1.0
1.0
1.2
0
a
(i) n-BuLi, then CO2; (ii) ClC(O)OEt, NEt3, then 2,6-
diisopropylaniline.
5
0
2
0
0
1.6
0
0
0
2 Ni(COD)2 1.0
10 1.0
a
Polymerization conditions: 25 µmol Ni, 30 mL of toluene, 100
b
psig ethylene. Consumed ethylene monitored by a mass flow
controller. c Precipitated polymer in acetone.
F igu r e 4. ORTEP drawing of 7. Hydrogen atoms not
shown for clarity.
groups on each isopropyl remain inequivalent. These
data are consistent with a fast suprafacial motion of the
benzyl ligand, as shown in eq 4 below.26
Rea ctivity Stu d ies. Table 1 summarizes the reac-
tivity of compounds 3, 4, 5, and 7 toward ethylene.
Entries 1-4 show that the addition of additional
B(C6F5)3 increases the total amount of ethylene con-
sumed by 3 over a period of 1 h. There is no change in
1
the H NMR spectra of 3 after the addition of 20 equiv
of B(C6F5)3 at similar concentrations ([Ni] ) 0.010 M).
Therefore the equilibrium constant overwhelmingly
favors coordination of the borane.29 Increased product
formation is likely due to scrubbing of impurities by the
additional borane. Examination of the product obtained
by using 3 shows that it is a distribution of ethylene
oligomers; no precipitate is observed. GC/MS analysis
shows that, in addition to 1-alkenes, the product con-
tains a substantial fraction of internal alkenes and
1-alkene dimers. The active species derived from 3 thus
reacts further with the 1-alkene product.30 One can
examine the rate of ethylene consumption as a function
of time by using a mass flow controller designed to keep
a constant pressure. As shown in Figure 5, for the
reaction in entry 4, there is a steady increase of activity
for the first 30 min. After this period of time a substan-
tial decline is observed.
Efforts to study the effect of substitution on the
pyridine ligand focused on the synthesis of N-(2,6-
diisopropylphenyl)-6-triisopropylsilyl-2-pyridinecarboxa-
mide (6). Ligand synthesis begins with the quenching
of 2-lithio-6-triisopropylsilylpyridine28 with CO2, which
gives 6-triisopropylsilyl-2-pyridinecarboxylic acid in 93%
yield (Scheme 1). Addition of triethylamine and ethyl-
chloroformate to this acid, followed by 2,6-diisopropyl-
aniline and purification by chromatography, provides
6 in 71% yield.
Deprotonation of 6 using KH in THF, followed by
addition to Ni(η3-CH2C6H5)Cl(PMe3) in toluene, results
in the immediate precipitation of KCl. The 1H NMR
spectrum of the resulting red organometallic pro-
duct shows five unique methyl resonances at 1.58 (d),
1.38 (d), 1.29 (d), 1.08 (d), and 1.04 (s) ppm in a 1:1:1:
1:1 ratio. No signals due to a benzyl fragment were
detected, while the 31P NMR spectrum displayed a
signal at -24 ppm. A single-crystal X-ray diffrac-
tion study (Figure 4) confirms loss of the benzyl ligand
and metalation of one of the isopropyl groups. The
product is thus compound 7, as shown in eq 5. It is
noteworthy that the carboxamide ligand continues to
prefer N-coordination, despite the crowded ligand en-
vironment.
Entries 5-8 in Table 1 show that the reactions with
4/C2H4 differ from those with 3/C2H4 in two important
respects. First, substantially longer reaction times are
required with 4/C2H4 to obtain similar quantities of
product. Figure 5 also shows the activity versus time
profile for entry 8. Substantial reactivity is observed
(29) Drago, R. S. Physical Methods in Chemistry, 2nd ed.; Saun-
ders: New York, 1992; p 257.
(30) For homogeneous catalysts that are selective for 1-alkene
formation see: (a) Rogers, J . S.; Bazan, G. C.; Sperry, C. K. J . Am.
Chem. Soc. 1997 119, 9305. (b) Small, B. L.; Brookhart, M. J . Am.
Chem. Soc. 1998, 120, 7143. (c) Barnhart, R. W.; Bazan, G. C.;
Mourney, T. J . Am. Chem. Soc. 1998, 120, 1082. (d) Review: Skupin-
ska, J . Chem. Rev. 1991, 91, 3.
(28) Corey, E. J .; Zheng, G. Z. Tetrahedron Lett. 1998, 39, 6151.

Pyridinecarboxamidato-Ni(II) Complexes
Organometallics, Vol. 20, No. 25, 2001 5429
propylsilyl group resulted in metalation of one of the
isopropyl groups and a concomitant deactivation of the
metal center.
Exp er im en ta l Section
Gen er a l Rem a r k s. All manipulations were performed
under an inert atmosphere using standard glovebox and
Schlenk techniques.33 Toluene, THF, hexane, and pentane
were distilled from benzophenone ketyl. N-Phenyl-2-pyridin-
ecarboxamide20 and 2-bromo-6-triisopropylpyridine28 were syn-
thesized according to the literature methods. Tris(pentafluo-
rophenyl)boron was provided by Boulder and purified by
sublimation. NMR spectra were obtained using a Varian Unity
400 or 500 spectrometer. 1H NMR spectra were calibrated
using signals from the solvent and are reported downfield from
SiMe4. 11B NMR and 19F NMR spectra were calibrated and
reported downfield from external BF3‚OEt2 and R,R,R-trifluo-
rotoluene, respectively. Mass spectrometric analyses were
obtained using a VG-70E double-focusing magnetic sector
instrument operated with a OPUS/SIOS data system. Desert
Analytics, Inc., Tucson, AZ, performed elemental analyses. The
use of the mass flow controller has been described elsewhere.34
F igu r e 5. Ethylene consumption rate monitored by a mass
flow controller.
only after ∼3.5 h, and the maximum activity is consid-
erably lower than that observed for 3/C2H4 under
identical conditions. Similar observations were made for
the reaction in entry 7. That a solid product is obtained
with 4/C2H4 is a second important difference relative
1
to 3/C2H4. This solid product was shown by H NMR
spectroscopy to be low molecular weight branched
polyethylene (Mn, 860; branch number/1000C, 80).31
Low molecular weight ethylene oligomers are also
obtained. The fraction of the solid is also given in Table
1.
Comparison of 4 vs 5 (entries 9-11) reveals that the
formally isoelectronic replacement of methallyl for η3-
benzyl yields a precatalyst that more quickly converts
to the catalytically important species. This improved
reactivity is readily evident upon comparison of the data
in Figure 5. For 5/C2H4, there is no induction period.
Note that for entry 10, the reaction reaches an activity
at 50 min of 600 kg/mol‚h. This rate is the maximum
flow rate that can be measured under our experimental
conditions.
Finally, entries 12-15 show that compound 7 does
not produce an effective catalyst. Efforts to use Ni-
(COD)2 in the expectation that PMe3 would be removed
from 7 to give an active species were not successful.32
Only in the presence of a large excess of B(C6F5)3 is
ethylene consumed. The product under these conditions
is a distribution of low molecular weight oligomers
consisting of 1-alkenes, internal alkenes, and 1-alkene
dimers.
[N-P h en yl-2-p yr id in eca r boxa m id a totr is(p en ta flu or o-
p h en yl)bor a te-κ2 N,N](η3-m eth a llyll)n ick el (3). N-Phenyl-
2-pyridinecarboxamide (0.198 g, 1.00 mmol) and tris(pen-
tafluorophenyl)boron (0.512 mg, 1.00 mg) were weighed into
a vial and dissolved in benzene (4.0 g). Bis(methallyll)nikel-
(II) (0.173 mg, 1.05 mmol) in benzene (2.0 g) was added at
room temperature, and the solution was stirred for 3 h.
Removal of solvent under vacuum gave a yellow oily residue,
which solidified by trituration with pentane (4 g) overnight.
The yellow powder was isolated by filtration, washed with
pentane (∼10 g), and placed under vacuum overnight. The
product is obtained as a yellow powder in 93% yield. 1H NMR
spectroscopy showed that 0.37 molecules of pentane were
retained for each molecule of 3. Single crystals for elemental
analysis and X-ray diffraction studies were grown from hexane
and benzene (∼10:1) at room temperature overnight. Half a
molecule of hexane was incorporated for each molecule of 3 in
1
the crystal lattice. H NMR (400 MHz, C6D6): δ 7.71 (d, J )
8.0 Hz, 1 H, py-H3), 7.03 (t, J ) 8.0 Hz, 2 H, ph-H2,6), 7.00-
6.83 (m, 4 H, py-H3, ph-H3-5), 6.65 (td, J ) 8.0, 1.6 Hz, 1 H,
py-H4), 6.06 (ddd, J ) 8.0, 5.2, 1.2 Hz, 1 H, py-H5), 2.00 (d, J
) 2.8 Hz, 1 H, methallyl-CH2), 1.94 (dd, J ) 2.8, 1.2 Hz, 1 H,
methallyl-CH2), 1.71 (s, 1 H, methallyl-CH2), 1.58 (s, 3 H,
methallyl-CH3), 1.44 (s, 1 H, methallyl-CH2). 13C NMR (100
MHz, C6D6): δ 166.92 (carbonyl), 152.13 (py-C2), 151.98 (py-
C6), 149 (dm, J ) 250 Hz, p-CF), 147.73 (ph-C1), 140 (dm, J )
240 Hz, o-CF), 138.81 (py-C4), 138 (dm, J ) 260 Hz, m-CF),
130.64 (ph-C4), 128.88 (ph-C3,5), 127.90 (py-C5), 126.46 (py-C3),
126.21 (methallyl-CCH3), 123.70 (ph-C2,6), 121 (m, i-BC), 61.63
(methallyl-CH2), 54.19 (methallyl-CH2), 23.09 (methallyl-CH3).
19F NMR (C6D6, 376 MHz): δ -75.7 (br, o-F), -101.3 (t, J )
20 Hz, p-F), -107.2 (td, J ) 20, 4 Hz, m-F). 11B NMR (toluene,
128 MHz): δ -0.75. Anal. Calcd (C34H16B1F15N2O1Ni‚C3H7):
C, 51.3; H, 2.68; N, 3.27. Found: C, 51.0; H, 2.58; N, 3.27.
Su m m a r y Discu ssion
In summary, the synthesis and characterization of
pyridinecarboxamidato-nickel complexes has been dem-
onstrated. The ligand environment of these complexes
provides bonding to the metal similar to the R-iminocar-
boxamide ligands in complexes 1 and 2. Considerably
more efficient formation of the propagating species
occurs with the use of the η3-benzyl ligand, compared
to methallyl. While the pyridinecarboxamidate and
R-iminocarboxamide ligands are similar in an electronic
sense, the pyridine ring leaves an open quadrant
adjacent to the metal center. It is not possible to obtain
a similar congestion of the axial sites,2 and a result the
average molecular weight of the product obtained with
4 is considerably smaller than the product obtained with
2 under similar reaction conditions. Attempts to in-
crease steric hindrance by addition of the bulky triiso-
N-(2,5-Diisop r op ylp h en yl)-2-p yr id in eca r boxa m id e. 2-
Pyridinecarboxylic acid (3.1 g, 25 mmol) was dissolved in THF
(100 mL) and cooled to -15 °C. Triethylamine (3.5 mL, 25
mmol) and ethyl chloroformate (2.4 mL, 25 mmol) were then
added successively. The resulting suspension was stirred for
30 min, and 2,6-(diisopropyl)aniline (4.43 g, 25 mmol) was
added. The reaction mixture was warmed to room temperature
slowly and stirred for 4 h, whereupon evolution of CO2 gas
(33) Burger, B. J .; Bercaw, J . E. In Experimental Organometallic
Chemistry; Wayda, A. L., Darensbourg, M. Y., Eds.; ACS Symposium
Series 357; American Chemical Society: Washington, D.C., 1987.
(34) Bazan, G. C.; Rogers, J . S.; Fang, C. C. Organometallics 2001,
20, 2059.
(31) This number is not corrected for end group contribution.
(32) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R.
H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.

5430 Organometallics, Vol. 20, No. 25, 2001
Lee et al.
was detected. The mixture was filtered and washed with THF.
The solvent was removed to give an oily residue, which was
purified by passing through a short silica gel column using
methylene chloride. The oily compound solidifies from hexane
at room temperature. Overall yield was 92% (6.52 g). 1H NMR
(400 MHz, CDCl3): δ 9.46 (br, 1 H, NH), 8.66 (ddd, J ) 4.8,
1.6, 1.2 Hz, 1 H, py-H6), 8.31 (dt, J ) 7.6, 1.2 Hz, 1 H, py-H3),
7.92 (td, J ) 7.6, 1.6 Hz, 1 H, py-H4) 7.51 (ddd, J ) 7.6, 4.8,
1.2 Hz, py-H5), 7.33 (t, J ) 8.0 Hz, 1 H, ph-H4), 7.23 (d, J )
8.0 Hz, 2 H, ph-H3,5), 3.15 (septet, J ) 13.6 Hz, 2 H, iPr-CH),
1.23 (d, J ) 13.6 Hz, 6 H, iPr-CH3). 13C NMR (100 MHz,
CDCl3): δ 163.71 (carbonyl), 149.99 (py-C2), 148.41 (py-C6),
146.43 (ph-C2,6), 137.73 (py-C4), 131.38 (ph-C1), 128.41 (py-C5),
126.60 (py-C3), 123.67 (ph-C3,5), 122.84 (ph-C4), 29.12 (iPr-CH),
23.86 (iPr-CH3). IR (neat): 3350, 3294 (br, NH), 1688 (carbo-
nyl) cm-l. HRMS-EI m/z M+ calcd (C15H22N2O1), 282.1705;
found, 282.1718.
1 H, ph-H4), 7.09 (t, J ) 8.0 Hz, 1 H, benzyl-ph-H4), 7.04, 6.91
(d, J ) 8.0 Hz, 2 H, ph-H3,5), 6.65 (dd, J ) 5.2, 0.8 Hz, py-H6),
6.64 (t, J ) 8.0, 2 H, benzyl-ph-H3,5), 6.13, 6.21 (td, J ) 8.0,
1.6 Hz, 1 H, py-H4), 5.94-5.89 (br, 2 H, benzyl-ph-H2,6), 5.89
(ddd, J ) 8.0, 5.2, 1.2 Hz, 1 H, py-H5), 3.52, 3.19 (septet, J )
6.8 Hz, 2 H, iPr-CH), 1.33, 1.49 (s, 2 H, benzyl-CH2), 1.26, 0.98
(d, J ) 6.8 Hz, 6 H, iPr-CH3), 1.13, 0.88 (d, J ) 6.8 Hz, 6 H,
iPr-CH3). 13C NMR (100 MHz, C6D6): δ 166.62 (carbonyl),
164.81, 143.16, 140.94, 137.49, 135.06, 128.51, 128.28, 127.66,
127.17, 126.36, 124.23, 117.47, 37.56 (benzyl-CH2), 28.83 (iPr-
CH), 25.43, 23.67 (iPr-CH). 11B NMR (toluene, 128 MHz): δ
-0.66. Anal. Calcd (C43H28B1F15N2O1Ni): C, 54.8; H, 3.00; N,
2.97. Found: C, 54.9; H, 3.03; N, 2.57.
6-Tr iisop r op ylsilyl-2-p yr id in eca r boxylic Acid . A solu-
tion of nBuLi (1.5 M, 2.5 mL, 3.8 mmol) was added dropwise
to a solution of 2-bromo-6-triisopropylpyridine (1.0 g, 3.2 mmol)
in THF (10 mL) at -78 °C. The resulting orange solution was
stirred at -78 °C for 10 min and then warmed to -45 °C for
15 min. After recooling to -78 °C, the solution was poured
onto solid CO2 via cannula. After stirring for 1 h at room
temperature, the mixture was poured into a separatory funnel
containing aqueous concentrated NH4Cl (50 mL). The product
was extracted twice with diethyl ether (30 mL). The combined
organic fractions were dried over MgSO4, and the solvent was
removed to give a white crystalline solid (0.83 g, 93%). The
compound was used without further purification. 1H NMR (400
MHz, CDCl3): δ 8.15 (d, J ) 7.2 Hz, 1 H, py-H3), 7.88 (t, J )
7.2 Hz, 1 H, py-H4), 7.76 (d, J ) 7.2 Hz, 1 H, py-H5), 1.51
(septet, J ) 7.6 Hz, 3 H, iPr-CH), 1.01 (d, J ) 7.6 Hz, 18 H,
iPr-CH3). 13C NMR (100 MHz, CDCl3): δ 164.81 (carbonyl),
136.30, 134.86, 122.51 (py-C3,4,5), 18.66 (iPr-CH3), 10.91 (iPr-
CH). IR (neat): 3250 (br, OH), 1775 (carbonyl) cm-l. HRMS-
EI m/z M+ calcd (C15H25N1O2Si1), 279.1655; found, 279.1658.
N-(2,6-Diisop r op ylp h en yl)-6-tr iisop r op ylsilyl-2-p yr id i-
n eca r boxa m id e (6). Triethylamine (0.42 mL, 3.0 mmol) and
ethyl chloroformate (0.29 mL, 3.0 mmol) were added succes-
sively at -15 °C to a solution of 6-triisopropylsilyl-2-pyridin-
ecarboxylic acid (0.83 g, 3.0 mmol). The mixture was stirred
for 15 min at -15 °C, at which time a white precipitate
(presumably HCl‚NEt3) formed. 2,6-Diisopropylaniline (0.53
g, 3.0 mmol) was added and the cooling bath removed. After
stirring at room temperature for 4 h, the mixture was filtered
and the solvent was removed to give a residue. Purification
was accomplished by column chromatography on silica gel with
hexane and ether (5:1). The compound solidified upon standing
at room temperature. Overall yield was 0.93 g (71%). 1H NMR
(400 MHz, CDCl3): δ 9.63 (br s, 1 H, NH), 8.22 (dd, J ) 7.6,
1.2 Hz, 1 H, py-H3), 7.83 (t, J ) 7.6 Hz, 1 H, py-H4), 7.69 (dd,
J ) 7.6, 1.2 Hz, 1 H, py-H5), 7.34 (dd, J ) 8.0, 6.8 Hz, 1 H,
ph-H4), 7.25 (d, J ) 7.6 Hz, 2 H, ph-H3,5), 3.17 (septet, J ) 6.8
Hz, 2 H, iPr-CH), 1.53 (septet, J ) 7.6 Hz, 3 H, SiCH), 1.22
(d, J ) 6.8 Hz, 12 H, SiCHCH3) 1.23 (d, J ) 7.6 Hz, 18 H,
iPr-CH3). 13C NMR (100 MHz, C6D6): δ 164.18, 163.87 (car-
bonyl, py-C6), 149.72 (py-C2), 146.41 (ph-C2), 135.38, 133.47,
121.49 (py-C3,4,5), 131.79 (ph-C1), 128.35 (ph-C4), 123.69 (ph-
C3,5), 29.15 (iPr-CH), 23.75 (iPr-CH3), 18.68 (SiCHCH3), 10.06
(SiCH). IR (neat): 3350 (br, NH), 1694 (carbonyl) cm-l. HRMS-
EI m/z M+ calcd (C27H42N2O1Si1), 438.3066; found, 438.3058.
[N-(2,6-d iisop r op ylp h en yl)-6-(t r iisop r op ylsilyl-KC2)-
p yr id in e ca r b oxa m id a t o-κN ,N ](t r im e t h ylp h osp h in e )-
n ick el (7). N-(2,6-Diisopropylphenyl)-6-(triisopropylsilyl)-2-
pyridinecarboxamide (78.9 mg, 0.180 mmol) and KH (22 mg,
3.0 equiv) were weighed in a vial inside a glovebox. THF (1.0
g) was added, and the mixture was stirred for 3 h at room
temperature. NMR spectra indicate at this stage the clean
formation of the potassium salt. 1H NMR (400 MHz, THF-d6):
δ 8.44 (d, J ) 8.0 Hz, 1 H, py-H3), 7.55 (t, J ) 7.6 Hz, 1 H,
py-H4), 7.44 (d, J ) 7.6 Hz, 1 H, py-H5), 7.06 (d, J ) 7.6 Hz, 2
H, ph-H3,5), 6.89 (t, J ) 7.6 Hz, 1 H, ph-H4), 3.24 (septet, J )
6.8 Hz, 2 H, iPr-CH), 1.32 (septet, J ) 7.6 Hz, 3 H, SiCH),
1.20-1.05 (m, 30 H, iPr-CH3, SiCHCH3). 13C NMR (100 MHz,
[N-(2,6-Diisop r op ylp h en yl)-2-p yr id in eca r b oxa m id a -
totr is(p en ta flu or op h en yl)bor a te-κ2 N,N](η3-m eth a llyl)-
n ick el (4). This compound was prepared using a procedure
similar to the synthesis of 3 from N-(2.6-diisopropylphenyl)-
2-pyridinecarboxamide. This reaction works best when 1.2
equiv of ligand is used, instead of 1.0 equiv. The product is
obtained as a yellow powder in 93% yield. Single crystals for
elemental analysis and X-ray diffraction studies were grown
from pentane and benzene (∼1:3) at room temperature 2 days.
Two and a half benzene molecules were incorporated in the
1
single crystals. H NMR (400 MHz, C6D6): δ 7.41 (d, J ) 8.0
Hz, 1 H, py-H3), 7.18 (t, J ) 8.0 Hz, 1 H, ph-H4), 7.13 (dd, J )
5.2, 1.2 Hz, py-H6), 6.97 (d, J ) 8.0 Hz, 1 H, ph-H3or5), 6.96 (d,
J ) 8.0 Hz, ph-H3or5), 6.27 (td, J ) 8.0, 1 Hz, 1.2 H, py-H4),
6.00 (ddd, J ) 8.0, 5.2, 1.2 Hz, 1 H, py-H5) 3.54 (septet, J )
6.8 Hz, 1 H, iPr-CH), 3.02 (septet, J ) 6.8 Hz, 1 H, iPr-CH),
2.07 (d, J ) 2.8 Hz, 1 H, methallyl-CH2), 1.88 (t, J ) 2.4, 1 H,
methallyl-CH2), 1.82 (d, J ) 2.0 Hz, 1 H, methallyl-CH2), 1.75
(s, 1 H, methallyl-CH2), 1.56 (s, 3 H, methallyl-CH3), 1.17 (d,
J ) 6.8 Hz, 3 H, iPr-CH3), 1.09 (d, J ) 6.8 Hz, 3 H, iPr-CH3),
1.07 (d, J ) 6.8 Hz, 3 H, iPr-CH3), 1.05 (d, J ) 6.8 Hz, 3 H,
iPr-CH3). 13C NMR (100 MHz, C6D6): δ 166.08 (carbonyl),
152.18 (py-C6), 150.71 (py-C2), 149 (dm, J ) 250 Hz, p-CF),
142.58 (ph-C1), 141.11, 140.82 (ph-C2,6), 140 (dm, J ) 240 Hz,
o-CF), 138 (dm, J ) 260 Hz, m-CF), 137.58 (py-C4), 131.43 (py-
C5), 127.61 (ph-C3,5), 126.61 (methallyl-CCH3), 126.26, 124.00
(py-C3, ph-C4), 121 (m, i-BC), 58.37, 56.70 (methallyl-CH2),
28.85, 28.56 (iPr-CH), 25.53, 25.22 (iPr-CH3), 23.95, 23.17 (iPr-
CH3), 22.74 (methallyl-CH3). 19F NMR (C6D6, 376 MHz): δ
-75.3 (br, o-F), -100.1 (br, p-F), -106.8 (br, m-F). 11B NMR
(toluene, 128 MHz): δ -0.34. Anal. Calcd (C40H28B1F15N2O1-
Ni‚C15H15): C, 59.9; H, 3.94; N, 2.54. Found: C, 60.1; H, 4.02;
N, 2.76.
[N-(2,6-Diisop r op ylp h en yl)-2-p yr id in eca r b oxa m id a -
totr is(p en ta flu or op h en yl)-bor a te-κ2N,N](η3-ben zyl)n ick -
el (5). N-(2.6-Diisopropyl)phenyl-2-pyridinecarboxamide (0.282
g, 1.00 mmol) and KH (0.040 g, 1.0 equiv) were weighed in a
vial inside a glovebox. THF (6.0 g) was added at room
temperature, and the mixture was stirred overnight. After
cooling to -30 °C, the solution was added to a solution of Ni-
(η3-CH2C6H5)Cl(PMe3) (261 mg, 1.0 mmol) in THF (10 g) which
had been cooled to -30 °C. The solvent was removed slowly
under vacuum for 30 min. The residue was extracted with
toluene (30 mL), and the solvent was then removed to give a
red solid. A cooled solution (-30 °C) of tris(pentafluorophenyl)-
boron (1.024 g, 2.0 equiv) in toluene (15 g) was added to the
red solid, and the solution was stirred for 30 min at room
temperature. The byproduct, (C6F5)3B-PMe3, was filtered off.
The solvent was removed under vacuum. Crystallization from
toluene and pentane (∼3:1) overnight at -30 °C gave an
1
orange solid (0.810 g, 86%). H NMR spectra showed that the
product is a mixture of two isomers (10:1 ratio). The peaks of
1
the minor isomer are reported in italics. H NMR (400 MHz,
C6D6): δ 7.26 (d, J ) 8.0 Hz, 1 H, py-H3), 7.22 (t, J ) 8.0 Hz,

Pyridinecarboxamidato-Ni(II) Complexes
Organometallics, Vol. 20, No. 25, 2001 5431
Ta ble 2. Cr ysta llogr a p h ic P a r a m eter sa
3
4
7
formula
fw
a, Å
b, Å
C
34H16BF15N2NiO
C110H86B2F30N4Ni2O2
2204.87
12.732(2)
13.421(2)
16.698(2)
71.222(2)
72.959(2)
73.756(2)
2528.2(6)
P1h
C30H49N2NiOPSi
571.48
19.317(9)
16.997(8)
20.064(9)
90
101.925(8)
90
6446(5)
C2/c
1.178
8
0.712
33 018
7472
823.01
11.130(2)
12.247(2)
14.698(2)
71.396(2)
68.835(2)
73.809(2)
1740.0(5)
P1h
1.571
2
0.669
15 391
6110
c, Å
R, deg
â, deg
γ, deg
V, Å3
space group
d(calc), g cm-1
Z
1.448
1
µ, mm-1
no. of data collected
no. of unique data
no. of variables
R (%)
0.481
26 351
11 277
681
515
6.80
338
4.45
4.76
R
w (%)
19.3
9.97
10.8
goodness of fit
1.401
0.936
1.026
All data collected at 150 K with Mo KR radiation, R(F) ) ∑||Fo| - |Fc||/∑|Fo| with Fo > 4.0σ(F), Rw ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
a
2
with Fo > 4.0σ(F).
CDCl3): δ 165.50, 162.51, 162.07, 153.59, 141.14, 133.82,
131.41, 125.53, 122.85, 120.92, 29.31 (iPr-CH), 23.85 (iPr-CH3),
19.38 (SiCHCH3), 12.51 (SiCH). The excess KH was filtered
off, and to the filtrate was added a solution of Ni(η3-CH2C6H5)-
Cl(PMe3) (47 mg, 0.18 mmol) in THF (2.0 g) at room temper-
ature. KCl precipitated immediately upon mixing the two
solutions. The mixture was stirred for an additional 5 h. The
solvent was removed by vacuum, and the product was ex-
tracted using pentane. The compound was purified by recrys-
tallization from a concentrated pentane solution at room
temperature and was obtained as dark red crystals in 50%
yield. The crystals are analytically pure and suitable for X-ray
controller. The reaction was quenched by release of ethylene
pressure, and the solution was analyzed by GC-MS. The
reaction mixture was poured into a flask containing 100 mL
of acetone, and the precipitated polyethylene was collected by
filtration. The catalytic activities are summarized in Table 1.
Cr ysta llogr a p h y. Crystals were mounted onto a thin glass
fiber with paratone-8277 and immediately placed in a cold
nitrogen stream at 150 K on a Bruker SMART CCD diffrac-
tometer equipped with a normal focus, 2.4 kW sealed tube
X-ray source (Mo KR radiation) operating at 45 kV and 40 mA.
A full sphere of intensity data for each structure was collected
in 2252 frames with a scan width of 0.30° and an exposure
time of 30 s. The number of reflections used for the least-
squares refinement of unit cell parameters (at 150 K) was
6649, 7176, and 8192 for 3, 4, and 7, respectively. The
empirical absorption corrections based on the equivalent
reflections were performed using the program SADABS. The
structures were solved by direct methods followed by succes-
sive difference Fourier methods. Full-matrix refinements were
against F2. Hydrogen atoms were calculated at idealized
positions, and their atomic positions were refined as riding
atoms of their parent carbon atoms. The crystal data and
refinement results are summarized in Table 2.
1
diffraction studies. H NMR (400 MHz, C6D6): δ 8.04 (ddd, J
) 7.2, 2.0, 0.8 Hz, 1 H, py-H3), 7.21 (s, 3 H, ph-H2-4), 7.03 (t,
J ) 7.2 Hz, 1 H, py-H4), 6.99 (ddd, J ) 7.2, 2.0, 0.8 Hz, 1 H,
py-H5), 4.46 (septet, J ) 6.8 Hz, 2 H, iPr-CH), 1.58 (d, J ) 6.8
Hz, 6 H, iPr-CH3), 1.38 (d, J ) 6.8 Hz, 6 H, iPr-CH3), 1.29 (d,
J ) 6.8 Hz, 6 H, SiCHCH3), 1.20-1.10 (m, 2 H, SiCH), 1.08
(d, J ) 6.8 Hz, 6 H, SiCHCH3) 1.04 (s, 6 H, NiCCH3), 0.59 (d,
J ) 8.4 Hz, 9 H, PCH3). 13C NMR (100 MHz, CDCl3): δ 169.96
(carbonyl), 165.35 (py-C6), 155.33 (ph-C1) 148.60 (py-C2), 145.08
(ph-C2), 136.34, 132.07 (d, J ) 2.3 Hz), 125.10 (py-C3,4,5), 123.58
(ph-C3.5), 123.48 (ph-C4), 30.06 (iPr-CH), 29.29 (d, J ) 5.4 Hz,
NiC), 26.29, 23.44 (iPr-CH3), 20.40, 19.91 (SiCHCH3), 15.71
(d, J ) 25 Hz, NiCCH3), 12.25 (SiCH). 31P NMR (162 MHz,
C6D6): δ -24.03 ppm. Anal. Calcd: C, 63.0; H, 8.66; N, 4,90.
Found: C, 63.1; H, 8.65; N, 5.10.
Ack n ow led gm en t. The authors are grateful to the
Department of Energy and the Petroleum Research
Fund for financial assistance. B.Y.L. is thankful to the
Korea Science and Engineering Foundation for partial
financial support.
Gen er a l P olym er iza tion P r oced u r e. In a typical reac-
tion, 25 µmol of catalyst (3, 4, 5, or 7) and optionally a certain
amount of B(C6F5)3 was (were) weighed into a 50 mL Erlen-
meyer flask containing a stirring bar in a glovebox. To the
above flask was added 30 mL of toluene. The flask was then
placed inside a Parr bomb reactor. The bomb was assembled
and brought out of the glovebox. The ethylene was fed
continuously under a pressure of 100 psig without temperature
control. The ethylene flow rate was monitored by a mass flow
Su p p or tin g In for m a tion Ava ila ble: Complete details for
crystallographic studies of 3, 4, and 7. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM010576C