Ortho-5-methylfuran- and benzofuran-substituted η3- allyl(α-diimine)nickel(II) complexes: Syntheses, structural characterization, and the first polymerization results

Article abstract of DOI:10.1021/om0497902

Two representatives of a new family of ortho-furan-substituted N,N-phenyl α-diimine ligands [(Ar-N=C(Me)-(Me)C=N-Ar) Ar = 2,6-bis(5-methylfuran-2- yl)-4-phenylphenyl, 9; Ar = 2,6-bis(benzofuran-2-yl)phenyl, 17] have been synthesized by two alternative synthetic methodologies. 3,5-Bis(5-methylfuran-2- yl)biphenyl-4-ylamine (7) was prepared through a classical pyrylium salt approach. 2,6-Bis(5-methylfuran-2-yl)-4-phenylpyranylium tetrafluoroborate (4) was converted to 2,6-bis(5-methylfuran-2-yl)-4-phenylnitrobenzene (5) by reaction with nitromethane. Reduction of nitro compound 5 by zinc dust afforded aniline 7. The palladium-catalyzed cross-coupling reaction between 2,6-dibromophenylamine 13 and 2-benzofuranboronic acid 14 was used to prepare 2,6-bis(benzofuran-2-yl)phenylamine 15. The condensation of 2,2,3,3- tetramethoxybutane 8 with anilines 7 and 15 afforded α-diimines 9 and 17. The reaction of π-allylnickel chloride dimer 10, α-diimines 9 and 17, and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BAF) (11) or silver hexafluoroantimonate 18 led to three complexes, [η³-allyl(Ar-N= C(Me)-(Me)C=N-Ar)Ni]⁺X^- [Ar = 2,6-bis(5-methylfuran-2-yl)- 4-phenylphenyl, X = BAF, 12, Ar = 2,6-bis(benzofuran-2-yl)phenyl, X = BAF, 19, X = SbF₆, 20]. The steric repulsion of closely positioned benzofuran-2-yl groups in 20 caused distortion of the nickel square planar coordination by up to 11.4° according to X-ray analysis. Benzofuran-2-yl groups deviated up to 46.6° from the main planes of central phenyl rings in 20. Complexes 12 and 19 were tested as ethylene polymerization catalysts. The benzofuran-substituted η³-allyl (α-diimine)Ni complexes 19 afforded polyethylene with ultrahigh molecular weights (M_w) and was about three time more productive than complex 12.

Full text of DOI:10.1021/om0497902

3276
Organometallics 2004, 23, 3276-3283
or th o-5-Meth ylfu r a n - a n d Ben zofu r a n -Su bstitu ted
η3-Allyl(r-d iim in e)n ick el(II) Com p lexes: Syn th eses,
Str u ctu r a l Ch a r a cter iza tion , a n d th e F ir st
P olym er iza tion Resu lts†
Alex S. Ionkin* and William J . Marshall
DuPont Central Research & Development, Experimental Station,
Wilmington, Delaware 19880-0328
Received March 23, 2004
Two representatives of a new family of ortho-furan-substituted N,N-phenyl R-diimine
ligands [(Ar-NdC(Me)-(Me)CdN-Ar) Ar ) 2,6-bis(5-methylfuran-2-yl)-4-phenylphenyl, 9;
Ar ) 2,6-bis(benzofuran-2-yl)phenyl, 17] have been synthesized by two alternative synthetic
methodologies. 3,5-Bis(5-methylfuran-2-yl)biphenyl-4-ylamine (7) was prepared through a
classical pyrylium salt approach. 2,6-Bis(5-methylfuran-2-yl)-4-phenylpyranylium tetrafluo-
roborate (4) was converted to 2,6-bis(5-methylfuran-2-yl)-4-phenylnitrobenzene (5) by reaction
with nitromethane. Reduction of nitro compound 5 by zinc dust afforded aniline 7. The
palladium-catalyzed cross-coupling reaction between 2,6-dibromophenylamine 13 and 2-ben-
zofuranboronic acid 14 was used to prepare 2,6-bis(benzofuran-2-yl)phenylamine 15. The
condensation of 2,2,3,3-tetramethoxybutane 8 with anilines 7 and 15 afforded R-diimines 9
and 17. The reaction of π-allylnickel chloride dimer 10, R-diimines 9 and 17, and sodium
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BAF) (11) or silver hexafluoroantimonate 18
led to three complexes, [η3-allyl(Ar-NdC(Me)-(Me)CdN-Ar)Ni]+X- [Ar ) 2,6-bis(5-meth-
ylfuran-2-yl)-4-phenylphenyl, X ) BAF, 12, Ar ) 2,6-bis(benzofuran-2-yl)phenyl, X ) BAF,
19, X ) SbF6, 20]. The steric repulsion of closely positioned benzofuran-2-yl groups in 20
caused distortion of the nickel square planar coordination by up to 11.4° according to X-ray
analysis. Benzofuran-2-yl groups deviated up to 46.6° from the main planes of central phenyl
rings in 20. Complexes 12 and 19 were tested as ethylene polymerization catalysts. The
benzofuran-substituted η3-allyl (R-diimine)Ni complexes 19 afforded polyethylene with
ultrahigh molecular weights (Mw) and was about three time more productive than complex
12.
In tr od u ction
complexes with phosphine ligands bearing 2-furyl sub-
stituents have been found to be more efficient catalytic
systems in the cross-coupling of alkylstannanes with
aryl halogenides4,5 and in the palladium-catalyzed
alkoxycarbonylation of alkynes compared with the cor-
responding triphenylphosphine complexes.6
In this report, we describe two synthetic approaches
for making ortho-substituted furyl R-diimine ligands
and the corresponding nickel(II) complexes with 5-meth-
ylfuran-2-yl and benzofuran-2-yl moieties. The 5-methyl
substitution and benzo pattern of the furyl group
substitutions were chosen to provide bulk in the axial
sites of square planar nickel complexes and retard the
rate of chain transfer.7 The polymerization of ethylene
by the ortho-5-methylfuran- and benzofuran-substituted
η3-allyl(R-diimine)nickel(II) complexes is also the subject
of this report.
Late-metal catalysts for ethylene homo- and copolym-
erization based on Pd(II) and Ni(II) R-diimine complexes
(trademarked as the Versipol catalyst system by Du-
Pont)1 require moderately sterically hindered, ortho-
substituted anilines. Small deviations in the size and
electronic properties of the ortho-substituent have a
considerable impact on the amount of branching and
molecular weight of the resulting polymer. The furyl
group is comparable in size with the phenyl group, the
presence of which in the ortho-position has a consider-
able effect on the molecular weight of the polymer.2
Further modification of 2,6-diphenylaniline moieties by
para-methoxy or para-tert-butyl groups had a profound
effect on the polymerization process.3 The palladium
† Dedicated to Professor Maurice Brookhart on the occasion of his
62nd birthday. This is DuPont contribution #8529.
* Corresponding author. E-mail: alex.s.ionkin@usa.dupont.com.
(1) For recent reviews see: (a) Ittel, S. D.; J ohnson, L. K.; Brookhart,
M. Chem. Rev. 2000, 100, 1169. (b) Britovsek, G. J . P.; Gibson, V. C.;
Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (c) Mecking, S.
Coord. Chem. Rev. 2000, 203, 325. (d) Gibson, V. C.; Spitzmesser, S.
K. Chem. Rev. 2003, 103, 283.
(2) Moody, L. S.; MacKenzie, P. B.; Killian, C. M.; Lavoie, G. G.;
Ponasik, J . A.; Smith, T. W.; Pearson, J . C.; Barrett, A. G. M. U. S.
Pat. Appl., US 2002/0049135 A1.
(3) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskela, M.; Rieger, B.
Organometallics 2001, 20, 2321.
(4) Farina, V.; Krishnan, B. J . Am. Chem. Soc. 1991, 113, 9585.
(5) Amatore, C.; J utand, A.; Meyer, G.; Atmani, H.; Khalil, F.;
Chahdi, F. O. Organometallics 1998, 17, 2958.
(6) Scrivanti, A.; Beghetto, V.; Zanato, M.; Matteoli, U. J . Mol. Catal.
A 2000, 160, 331.
(7) J ohnson, L. K.; Killian, C. K.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414.
10.1021/om0497902 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 05/27/2004

η3-Allyl(R-diimine)nickel(II) Complexes
Organometallics, Vol. 23, No. 13, 2004 3277
Sch em e 1
Resu lts a n d Discu ssion
1.1. Syn th esis of 5-Meth ylfu r a n -2-yl or th o-Su b-
stitu ted r-Diim in e Liga n d a n d Cor r esp on d in g
Nick el(II) Com p lex. The classical approach through
a pyrylium salt was used to introduce a 5-methylfuran-
2-yl moiety in the structure of the desired R-diimine
ligand (Scheme 1).
The Michaelis condensation between 2-acetyl-5-meth-
ylfuran 1 and benzaldehyde 2 led to the formation of
1,5-bis(5-methylfuran-2-yl)-3-phenylpentane-1,5-dione
(3) with a 67% yield. The ring closure of the 1,5-diketone
3 was performed with triphenylcarbenium tetrafluo-
roborate in glacial acetic acid under reflux for 2 h. The
pyrylium salts with 2,6-furyl substituents are difficult
to isolate in a pure state due to the susceptibility of
furan rings to electrophilic attack of triphenylcarbenium
cation.8 For this reason, the X-ray analysis of compound
4 was conducted. A crystal of 4 suitable for X-ray
analysis was grown from acetic acid. An ORTEP draw-
ing of 4 without any incorporation of trityl fragments
in the molecule is shown in Figure 1.
The two 5-methylfuran-2-yl groups are almost planar
(deviations are 9.7° and 10.8°) with the central pyrylium
ring of compound 4. This implies the participation of
5-methylfuran-2-yl groups in the π-π conjugation with
the pyrylium core.
The reaction of 2,6-bis(5-methylfuran-2-yl)-4-phenyl-
pyranylium tetrafluoroborate (4) and nitromethane in
the presence of triethylamine resulted in the formation
of compounds 5 and 6. 2,6-Bis(5-methylfuran-2-yl)-4-
phenylnitrobenzene (5) was isolated as a major product
with a 56% yield. 2,6-Bis(5-methylfuran-2-yl)-4-nitro-
methyl-4-phenyl-4H-pyran (6) was a product of the
nucleophilic attack of nitromethane at the 4-position of
F igu r e 1. ORTEP drawing of 2,6-bis(5-methylfuran-2-yl)-
4-phenylpyranylium tetrafluoroborate, 4. Thermal ellip-
soids are drawn at the 50% probability level.
pyrylium salt 4.9-11 ORTEP drawings of 5 and 6 are
shown in Figures 2 and 3.
The reduction of the nitro group in 2,6-bis(5-methyl-
furan-2-yl)-4-phenylnitrobenzene (5) in the amino group
of substance 7 was accomplished by zinc dust in glacial
acetic acid.12 The condensation of 2,2,3,3-tetramethoxy-
butane13 8 with aniline 7 in the presence of an acid
catalyst led to the desired 2,3-bis[2,6-bis(5-methylfuran-
2-yl)-4-phenylphenylimino)]butane (8) (Scheme 2).14 The
ORTEP drawing of 9 (Figure 4) shows that CdN bonds
(9) Krohnke, F.; Dickore, K. Chem. Ber. 1959, 92, 46.
(10) Dimroth, K. B.; Neubauer, G. Angew. Chem. 1957, 69, 720.
(11) Dimroth, K.; Krafft, W.; Wolf, K. H. In Nitro-Compounds;
Urbanski, T., Ed.; Pergamon: Oxford, 1964; p 361.
(12) Matsouka, H.; Ohi, N.; Miharo, M.; Suzuki, H.; Miyamoto, K.;
Maruyama, K.; Tsuji, K.; Kato, N.; Akimoto, T.; Takeda, Y.; Yano, K.;
Kuroki, T. J . Med. Chem. 1997, 40, 105.
(13) Montchamp, J .-L.; Tian, F.; Hart, M. E.; Frost, J . W. J . Org.
Chem. 1996, 61, 3897.
(8) Reichardt, C.; Milart, P. Liebigs Ann. Chem. 1990, 4, 401.
(14) Ionkin, A. S. U.S. Pat. Appl. Publ., US 2003/130514.

3278 Organometallics, Vol. 23, No. 13, 2004
Ionkin and Marshall
Sch em e 2
F igu r e 3. ORTEP drawing of 2,6-bis(5-methylfuran-2-yl)-
4-nitromethyl-4-phenyl-4H-pyran, 6. Thermal ellipsoids are
drawn at the 50% probability level.
F igu r e 2. ORTEP drawing of 2,6-bis(5-methylfuran-2-yl)-
4-phenylnitrobenzene, 5. Thermal ellipsoids are drawn at
the 50% probability level.
1.2. Syn th esis of Ben zofu r a n -2-yl or th o-Su bsti-
tu ted r-Diim in e Liga n d a n d Cor r esp on d in g Nick -
el(II) Com p lexes. The palladium-catalyzed Suzuki
cross-coupling reaction between 2,6-dibromophenyl-
amine 13 and 2-benzofuranboronic acid 14 was used to
prepare 2,6-bis(benzofuran-2-yl)phenylamine 15 (Scheme
3).
The catalytic protocol involves Pd2dba3/tri-tert-Bu3P
as the catalyst16 in the presence of cesium carbonate in
1,4-dioxane as solvent. 2,6-Bis(benzofuran-2-yl)phenyl-
amine 15 was isolated with a 68% yield. [2,2′]Bibenzo-
furanyl 16 was a minor product of this reaction. The
X-ray analysis of compound 15 reveals intramolecular
hydrogen bonding of the amino hydrogen with the
oxygen atoms of the furyl rings (Figure 5).
are in the trans-configuration. The methyl groups are
pointed out in different directions, perhaps to minimize
steric overlap. The 5-methylfuran-2-yl moiety forms
angles of 30.6° and 27.0° with the central phenyl rings
(Table 1). The π-π conjugation between them should
be disrupted at those angles. Thus, any possible π-elec-
tronic effect of the oxygen atom on the furyl rings onto
the R-diimine core will be diminished and the steric
impact of the 5-methylfuran-2-yl moiety will be pre-
dominant.
The reaction between the π-allylnickel chloride dimer15
10, R-diimine 9, and sodium tetrakis[3,5-bis(trifluoro-
methyl)phenyl]borate (BAF) (11) led to η3-allyl(R-di-
imine)nickel complexes 12 (Scheme 2).
(15) Wilke, G.; Bogdanovic, B.; Hardt, P.; Heimbach, P.; Keim, W.;
Kroner, M.; Oberkirch, W.; Tanaka, K.; Steinbrucke, E.; Walter, D.;
Zimmerman, H. Angew. Chem., Int. Ed. Engl. 1966, 5, 151.
(16) Littke, A. F.; Dai, C.; Fu, G. C. J . Am. Chem. Soc. 2000, 122,
4020.

η3-Allyl(R-diimine)nickel(II) Complexes
Organometallics, Vol. 23, No. 13, 2004 3279
Ta ble 1. Selected Bon d Len gth s (Å) for 4-6, 9, 15-17, a n d 20
C-O furanyl (inner)
C-O furanyl (outer)
fur-phen tors
C-N
CdN
4
5
6
9
O11-C7 ) 1.367(6),
O17-C13 ) 1.363(6)
O10-C10 ) 1.351(2),
015-C15 ) 1.356(2)
O15-C14 ) 1.371(1),
O21-C20 ) 1.374(1)
O9-C9 ) 1.384(2),
O20-C20 ) 1.387(3)
O1-C5 ) 1.396(4)
O1-C1 ) 1.389(2)
O10-C9 ) 1.388(6),
O19-C18 ) 1.401(5)
O1-C12 ) 1.381(5),
O2-C20 ) 1.392(5),
O3-C34 ) 1.381(6),
O4-C42 ) 1.393(5)
O11-C10 ) 1.365(6),
O17-C16 ) 1.359(6)
O10-C13 ) 1.357(2),
O15-C18 ) 1.345(2)
O15-C16 ) 1.377(1),
O21-C22 ) 1.383(1)
O9-C12 ) 1.379(3),
O20-C23 ) 1.380(2)
O1-C6 ) 1.374(4)
9.7,
10.8
27.5,
18.4
3.6,
N1-C1 ) 1.452(2)
5.3
30.6,
27.0
35.6
N1-C3 ) 1.422(3)
N1-C1 ) 1.381(7)
N1-C3 ) 1.415(6)
N1-C1 ) 1.271(3)
N1-C1 ) 1.293(6)
15
16
17
O1-C4 ) 1.377(2)
O10-C11 ) 1.375(5),
O19-C20 ) 1.393(6)
O1-C13 ) 1.384(5),
O2-C21 ) 1.375(4),
O3-C35 ) 1.375(6),
O4-C43 ) 1.381(6)
5.1,
21.6
31.1,
31.1,
33.1,
46.6
20
N1-C6 ) 1.432(5)
N2-C28 ) 1.435(5)
N1-C1 ) 1.302(5)
N2-C2 ) 1.284(5)
F igu r e 4. ORTEP drawing of 2,3-bis[2,6-bis(5-methyl-
furan-2-yl)-4-phenylphenylimino)]butane, 9. Thermal el-
lipsoids are drawn at the 50% probability level.
F igu r e 6. ORTEP drawing of nickel(1+), [N,N′-(1,2-di-
methyl-1,2-ethanediylidene) (2,6-bis(benzofuran-2-yl)phen-
yl-N],[(η3-2-propenyl]-, hexafluoroantimonate(1-), 20. Ther-
mal ellipsoids are drawn at the 50% probability level.
yl)phenyl]borate (NaBAF) (11) or silver hexafluoroan-
timonate 18 led to η3-allyl(R-diimine)nickel complexes
19 and 20 (Scheme 4). The hexafluoroantimonate de-
rivative 20 afforded single crystals suitable for X-ray
analysis from chlorobenzene solution.
F igu r e 5. ORTEP drawing of 2,6-bis(benzofuran-2-yl)-
phenylamine, 15. Thermal ellipsoids are drawn at the 50%
probability level.
X-ray analysis of complex 20 reveals that the central
nickel atom is four-coordinate with the bidentate R-di-
imine and π-allyl ligands. The ORTEP drawing of 20
(Figure 6) shows that the nickel square planar coordi-
nation has been distorted. This distortion can be mea-
sured by the dihedral angle Σ between the two sets of
planes defined by N1-Ni-N2 and C5-Ni-C3. The
tetrahedral twist angles for the two independent mol-
ecules of 20 in the asymmetric unit are 5.2° and 11.4°
(Figure 6). There are no short contacts between the
oxygen atoms of the benzofuran-2-yl moieties and the
nickel atom in complex 20. Benzofuran-2-yl groups
deviated from the main planes of central phenyl rings
in 20 from 31.1° to 46.6° (Table 1). Upon complexation
the deviation of benzofuran-2-yl groups increased, be-
cause the starting ligand 17 has corresponding values
at 21.6° and 5.1°. At these rotation angles between the
central phenyl ring and the benzofura-2-yl groups,
possible conjugation should be minimized. However,
Sch em e 3
The condensation of 2,2,3,3-tetramethoxybutane 8
with aniline 15 and a few crystals of para-toluene-
sulfonic acid led to the desired R-diimine ligand 17
(Scheme 4).
The reaction between π-allylnickel chloride dimer 10,
R-diimine 17, and sodium tetrakis[3,5-bis(trifluorometh-

3280 Organometallics, Vol. 23, No. 13, 2004
Ionkin and Marshall
Sch em e 4
Ta ble 2. Eth ylen e P olym er iza tion Resu lts w ith Ca ta lysts 12 a n d 19
temp
(°C)
1H NMR
mp (°C),
(∆Hf*) (J /g)
productivitya
25.4
branchingb
Mw
Mw/Mn
3.4
c
entry
1
catalyst
12
60
90
8.3
21.2
69.8
7.4
651
318
121.1
(110.6)
97.9
(84.6)
65.9
(8.4)
127.5
(97.6)
2
3
4
12
12
19
15.7
3.8
3.3
2.3
120
60
64
90.0
3 050
111.1
bimodal
(insolubles)
36.8
(insolubles)
6.2
5
6
7
8
9
19
19
19
19
19
70
80
76.2
71.9
59.3
69.2
20.3
14.2
17.0
26.3
36.8
59.9
2 486
685
765
55
116.5
(75.6)
111.1
(85.9)
94.9
(41.5)
86.8
(67.5)
89.6
90
4.9
2.7
3.2
120
150
23
(1.2)
a
b
kg polymer/g Ni. Total CH3 per 1000 CH2. c 103 g mol-1
.
angles are not at 90°, which would prevent π-conjuga-
tion completely. Further analysis of bond lengths of
oxygen atoms in the furanyl part of the molecules 17
and 20 (Table 1, second and third columns) did not
reveal substantial differences, which could indicate
limited, if any, conjugation between those moieties. The
most flat molecules are the pyrylium salt 4 and 2,6-
bis(5-methylfuran-2-yl)-4-nitromethyl-4-phenyl-4H-py-
ran (6) with a potentially higher degree of π-conjugation
between the central rings and the furanyl moieties. The
bond lengths of the oxygen atoms in the furanyl part of
these molecules can be used as an indicator of the
conjugation. For example, C-O bonds have a tendency
to be longer with smaller torsion angles between furanyl
groups and central rings (compound 5 versus compound
6). It may be concluded from the above structural
studies that benzofuran-2-yl moieties in 20 provide
considerable steric protection for the nickel above and
below the square plane.
Table 1 summarizes the bond lengths of furanyl
derivatives 4-6, 9, 15-17, and 20 for the furan oxygen
and R-diimine cores of the molecules.
2.0. Eth ylen e P olym er iza tion Activity of or th o-
5-Meth ylfu r a n - a n d Ben zofu r a n -Su bstitu ted η3-
Allyl(r-d iim in e)n ick el(II) Com p lexes 12, 19, a n d
20. The general procedure for ethylene polymerization
is as follows. In a nitrogen-purged drybox, a 20 mL glass
insert was loaded with the nickel compound (0.001
mmol) and 20 equiv of cocatalyst (B(C6F5)3). Next, the
solvent (para-xylene (10 mL)) was added to the glass
insert. The glass insert was then loaded in a pressure
tube inside the drybox. The pressure tube was then
sealed, brought outside of the drybox, connected to the
pressure reactor, placed under the desired ethylene

η3-Allyl(R-diimine)nickel(II) Complexes
Organometallics, Vol. 23, No. 13, 2004 3281
Ta ble 3. Su m m a r y of Cr ysta l Da ta , Da ta Collection , a n d Str u ctu r e Refin em en t P a r a m eter s of 4-6 a n d 9
4
5
6
9
empirical formula
fw
C
23H21O5B1F4
C22H17N1O4
718.73
C22H19N1O5
377.38
C48H40N2O4
473.78
464.21
cryst color, form
cryst syst
space group
a (Å)
b (Å)
c (Å)
colorless needle
monoclinic
P21/c
7.477(1)
13.615(2)
21.374(3)
colorless needle
monoclinic
P21/n
7.270(3)
23.042(5)
20.403(4)
colorless block
triclinic
P1h
gold rod
monoclinic
P21/n
8.5187(8)
14.515(2)
18.523(2)
9.931(1)
10.418(1)
10.524(1)
100.436(2)
93.297(2)
117.185(2)
940.2(2)
2
R (deg)
â (deg)
92.363(3)
93.01(3)
99.470(2)
γ (deg)
V (Å3)
2173.9(5)
4
1.418
0.12
960
3413.1(2)
4
1.399
0.10
1504
2265.2(4)
4
1.389
0.43
980
Z
density (g/cm3)
1.333
0.09
396
abs, µ (mm-1
F(000)
)
cryst size (mm)
temp (°C)
scan mode
detector
θmax (deg)
0.27 × 0.04 × 0.05
0.30 × 0.005 × 0.005
0.40 × 0.38 × 0.23
0.43 × 0.16 × 0.16
-100
-100
-100
-100
ω
ω
ω
ω
BrukerCCD
22.98
MarCCD
26.39
BrukerCCD
28.27
BrukerCCD
28.28
no. obsd reflns
no. unique reflns
no. params
Sb
8970
3007
306
0.87
R1 ) 0.057
wR2 ) 0.124
R1 ) 0.186
wR2 ) 0.167
0.307, -0.243
24 363
6800
491
0.95
R1 ) 0.053
wR2 ) 0.140
R1 ) 0.066
wR2 ) 0.146
0.643, -0.375
11 103
4422
256
1.06
R1 ) 0.041
wR2 ) 0.112
R1 ) 0.051
wR2 ) 0.120
0.318, -0.228
11 389
5268
283
0.83
R1 ) 0.045
wR2 ) 0.089
R1 ) 0.108
wR2 ) 0.103
0.339, -0.373
R indices [I>2σ(I)]a
R indices (all data)a
max diff peak, hole (e/Å3)
R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2 (sometimes denoted as Rw2). GooF ) S ) {∑[w(Fo - Fc2)2]/
a
2
b
2
(n - p)}1/2, where n is the number of reflections, and p is the total number of refined parameters.
Ta ble 4. Su m m a r y of Cr ysta l Da ta , Da ta Collection , a n d Str u ctu r e Refin em en t P a r a m eter s of 15-17 a n d 20
15
16
17
20
empirical formula
C
22H15O2N1
C16H10O2
117.12
C48H32N2O4
C60H44.5CL1.5F6N2
Ni1O4Sb1
1205.11
fw
325.35
700.76
cryst color, form
cryst syst
space group
a (Å)
b (Å)
c (Å)
colorless plate
orthorhombic
Fdd2
43.515(8)
6.263(1)
colorless parallelpiped
monoclinic
P21/n
9.4234(6)
5.9391(3)
colorless prism
orthorhombic
Pbca
10.1345(6)
17.4948(4)
19.2433(6)
dark red wedge
monoclinic
P21/c
18.768(4)
26.982(5)
11.651(3)
10.9880(6)
21.791(4)
R (deg)
â (deg)
114.399(2)
107.80(3)
γ (deg)
V (Å3)
3175.6(1)
8
560.04(5)
4
3411.9(2)
4
10507(4)
8
Z
density (g/cm3)
1.361
0.09
1360
1.389
0.09
244
1.364
0.09
1464
1.524
1.02
4872
abs, µ(mm-1
F(000)
)
cryst size (mm)
temp (°C)
scan mode
detector
θmax (deg)
0.40 × 0.38 × 0.01
0.31 × 0.08 × 0.01
0.07 × 0.05 × 0.02
0.25 a 0.04 a 0.01
-173
-100
-100
-100
ω
ω
ω
ω
BrukerCCD
23.77
Raxis-Image plate
24.09
Raxis-Image plate
24.09
MarCCD
28.28
91 307
25 003
1369
no. obsd reflns
no. unique reflns
no. params
Sb
3432
1097
145
1.04
R1 ) 0
wR2 ) 0
R1 ) 0
wR2 ) 0
0.135, -0.144
2952
851
102
1.04
R1 ) 0.039
wR2 ) 0.100
R1 ) 0.044
wR2 ) 0.102
0.131, -0.174
7934
2333
245
0.81
R1 ) 0.056
wR2 ) 0.073
R1 ) 0.097
wR2 ) 0.177
0.184, -0.246
0.99
R indices [I>2σ(I)]a
R1 ) 0.072
wR2 ) 0.207
R1 ) 0.080
wR2 ) 0.217
1.730, -1.594
R indices (all data)a
max diff peak, hole (e/Å3)
a
2
b
2
R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2 (sometimes denoted as Rw2). GooF ) S ) {∑[w(Fo - Fc2)2]/
(n - p)}1/2, where n is the number of reflections, and p is the total number of refined parameters.
pressure (600 psig), and shaken mechanically. After the
stated reaction time (18 h), the ethylene pressure was
released and the glass insert was removed from the
pressure tube. The polymer was precipitated by the
addition of MeOH (∼20 mL). The polymer was then
collected on a fritted filter and rinsed with MeOH. The
polymer was transferred to a preweighed vial and dried
under vacuum overnight. Table 2 summarizes the

3282 Organometallics, Vol. 23, No. 13, 2004
Ionkin and Marshall
2,6-Bis(5-m eth ylfu r a n -2-yl)-4-p h en ylp yr a n yliu m ; tet-
r a flu or obor a te (4). 1,5-Bis(5-methylfuran-2-yl)-3-phenylpen-
tane-1,5-dione (3) (2.6 g, 0.0077 mol), 3.06 g (0.0093 mol) of
triphenylcarbenium tetrafluoroborate, and 20 mL of glacial
acetic acid were refluxed for 2 h. The reaction mixture was
allowed to cool to ambient temperature and diluted with 200
mL of ethyl ether. The precipitate was collected and recrystal-
lized from acetic acid. Yield of 2,6-bis(5-methylfuran-2-yl)-4-
phenylpyranylium tetrafluoroborate (3) was 0.89 g (29%) with
mp 91 °C. Anal. Calcd for C21H17BF4O3 (Mw 404.16): C, 62.41;
results on the ethylene polymerization catalyzed by
nickel complexes 12 and 19. Complex 20 was insoluble
in para-xylene.
Substantial differences in the productivity, the mo-
lecular weight average of the polyethylene formed, and
the thermal stability of the 5-methylfuran-2-yl-substi-
tuted catalyst 12 and benzofuran-substituted catalyst
19 were observed. The nickel catalyst 19 was about 3
times more productive than catalyst 12 within the
tested temperature range (fourth column). The benzo-
furan-substituted catalyst 19 produced ultrahigh mo-
lecular weight ethylene polymers in the runs at 60 °C
and 70 °C (sixth column, entries 4 and 5). Broad,
bimodal molecular weight distributions were observed
in those cases. Ultrahigh molecular weight ethylene
polymers were observed for the para-tert-butylphenyl-
substituted catalysts of Rieger’s research.3 The 5-meth-
ylfuran-2-yl-substituted catalyst 12 produced polyeth-
ylenes having a molecular weight somewhat higher than
ortho-methyl-substituted nickel catalysts,1 but below
ortho-phenyl-substituted nickel catalysts.1 The thermal
stability of the catalyst 19 is noteworthy. It is still active
up to temperatures as high as 150 °C. The catalyst 12
is less thermally stable; it deactivates around 120 °C.
The molecular weight and catalyst productivity decrease
upon increasing the temperatures of polymerization.
The branching is low, but it increases at higher tem-
peratures. The polyethylene produced at 60 and 70 °C
is crystalline (eighth column, entries 1, 4, and 5). The
crystallinity of the polymers declines at higher temper-
atures. These observations would constitute normal
dependencies in the Versipol polymerization technol-
ogy.1
1
H, 4.24. Found: C, 62.22; H, 4.23. H NMR (CD3CN): δ 2.21
(s, 6H), 5.90-7.50 (m, 11H). The structure was proven by X-ray
analysis (Figure 1).
2,6-Bis(5-m eth ylfu r a n -2-yl)-4-p h en yln itr oben zen e (5)
a n d 2,6-Bis(5-m eth ylfu r a n -2-yl)-4-n itr om eth yl-4-p h en yl-
4H-p yr a n (6). 2,6-Bis(5-methyl-2-furyl)-4-phenylpyrylium tet-
rafluoroborate (4) (0.75 g, 0.00186 mol), 2.0 g (0.033 mol) of
nitromethane, 2.0 g (0.020 mol) of triethylamine, and 2 mL of
ethyl alcohol were stirred at ambient temperature for 3 days.
The solvent was removed in a vacuum (0.1 mm) at room
temperature, and the residue was purified by chromatography
on silica with petroleum ether/ethyl ether (10:2) as eluent.
Compound 5 was eluted from the column first. Yield of 2,6-
bis(5-methylfuran-2-yl)-4-phenylnitrobenzene (5) was 0.37 g
(56%) with mp 107 °C. Anal. Calcd for
C22H17NO4 (Mw
359.37): C, 73.53; H, 4.77; N, 3.90. Found: C, 73.30, H, 4.70;
1
N, 3.80. H NMR (CDCl3): δ 2.30 (s, 6H), 6.01 (m, 2H), 6.51
(m, 2H), 7.20-7.75 (br, 7H). The structure of 5 was proved by
X-ray analysis (Figure 2). Yield of 2,6-bis(5-methylfuran-2-yl)-
4-nitromethyl-4-phenyl-4H-pyran (6) was 0.033 g (5%), mp 153
°C. Anal. Calcd for C22H19NO5 (Mw 377.39): C, 70.02; H, 5.07;
1
N, 3.71. Found: C, 70.22; H, 5.16; N, 3.72. H NMR (CDCl3):
δ 2.32 (s, 6H), 4.90 (s, 2H), 5.60 (s, 2H), 6.03 (m, 2H), 6.50 (m,
2H), 7.10-7.55 (br, 5H). The structure of 6 was proved by
X-ray analysis (Figure 3).
3,5-Bis(5-m eth ylfu r a n -2-yl)bip h en yl-4-yla m in e (7). 2,6-
Bis(5-methylfuran-2-yl)-4-phenylnitrobenzene (5) (1.84 g,
0.00512 mol), 5.0 g (0.077 mol) of zinc dust, and 70 mL of
glacial acetic acid were stirred at room temperature for 24 h.
The reaction mixture was filtered, and the liquid part was
washed with water and extracted with ethyl ether. After
removal of the solvent, the residue was purified by chroma-
tography on silica with petroleum ether/ethyl ether (10:2) as
eluent. Yield of 3,5-bis(5-methylfuran-2-yl)biphenyl-4-ylamine
In conclusion, 5-methylfuran-2-yl-substituted catalyst
12 and benzofuran-substituted catalyst 19 were found
to be robust catalysts for ethylene polymerization. The
catalyst 19 shows superior thermal stability and pro-
ductivity and led to polyethylene with ultrahigh molec-
ular weights. This could be attributed to steric protec-
tion, created by the four benzofuranyl moieties of the
ligand, for the nickel atom above and below the square
plane.
(7) was 0.79 g (45%) with mp 54 °C. Anal. Calcd for C22H19
-
NO2 (Mw 329.39): C, 80.22; H, 5.81; N, 4.25. Found: C, 80.37;
H, 5.82; N, 4.16. 1H NMR (CDCl3): δ 2.31 (s, 6H), 6.03 (m,
2H), 6.50 (m, 2H), 7.19-7.65 (broad lines, 7H).
Exp er im en ta l Section
2,3-Bis[2,6-bis(5-m eth ylfu r a n -2-yl)-4-p h en ylp h en ylim -
in o)]bu tan e (9). 3,5-Bis(5-methylfuran-2-yl)biphenyl-4-ylamine
(7) (0.79 g, 0.0024 mol), 0.21 g (0.0011 mol) of 2,2,3,3-
tetramethoxybutane (8), 20 mL of toluene, and a few crystals
of para-toluenesulfonic acid were refluxed under nitrogen for
18 h. The solvent and formed methanol were removed under
vacuum. The resulting yellow solid was recrystallzed from
ethanol. Yield of 2,3-bis[2,6-bis(5-methylfuran-2-yl)-4-phen-
ylphenylimino)]butane (9) was 0.47 g (55%) with mp 310 °C
Gen er a l P r oced u r es. All the operations related to cata-
lysts were carried out under an argon atmosphere using
standard Schlenk techniques. Anhydrous solvents were used
in the reactions. Solvents were distilled from drying agents
or passed through alumina columns under an argon or nitro-
gen atmosphere. 2,6-Dibromophenylamine, 2-benzofuranbo-
ronic acid, Pd2dba3, silver hexafluoroantimonate, benzalde-
hyde, 2-acetyl-5-methylfuran, and triphenylcarbenium tetra-
fluoroborate were purchased from Aldrich. Sodium tetrakis-
[3,5-bis(trifluoromethyl)phenyl]borate (NaBAF) was purchased
from Boulder Scientific.
1
(dec). H NMR (CDCl3): δ 1.20 (s, 6H), 2.40 (s, 12H), 6.01 (m,
4H), 6.30 (m, 4H), 7.15-8.10 (m, 14H). 13C NMR (CDCl3)
(assignment only for selected bonds due to complexity of
spectra): δ 170.55 ppm (CdN bonds). Anal. Calcd for C48H40
-
1,5-Bis(5-m et h ylfu r a n -2-yl)-3-p h en ylp en t a n e-1,5-d i-
on e (3). Benzaldehyde 2 (5.3 g, 0.05 mol), 18.60 g (0.15 mol)
of 2-acetyl-5-methylfuran 1, 2.07 g (0.038 mol) of sodium
methylate, and 50 mL of dry methanol were stirred at room
temperature for 3 days. The precipitate was filtered and
recrystallized from ethanol. The yield of 1,5-bis(5-methylfuran-
2-yl)-3-phenylpentane-1,5-dione (3) was 11.29 g (67%) with mp
110 °C. 1H NMR (CDCl3): δ 2.34 (s, 6H), 3.20 (m, 4H), 3.95
(m, 1H), 6.17-7.49 (broad lines, 9H). 13C NMR (CDCl3 selected
bond): δ 186.73 ppm. LC/MS MW is 337 (M + H). Anal. Calcd
for C21H20O4: C, 74.98; H, 5.99. Found: C, 74.87; H, 5.79.
N2O4 (Mw 708.84): C, 81.33; H, 5.69; N, 3.95. Found: C, 81.28;
H, 5.77; N, 3.59. The structure was proven by X-ray analysis.
Nick el(1+), [N,N′-(1,2-Dim eth yl-1,2-eth a n ed iylid en e)-
(3,5-bis(5-m et h ylfu r a n -2-yl)bip h en yl-4-yla m in e ],[(η3-2-
p r op en yl]-, tetr a k is[3,5-bis(tr iflu or om eth yl)p h en yl]bo-
r a t e(1-) (12). 2,3-Bis[2,6-bis(5-methylfuran-2-yl)-4-phenyl-
phenylimino)]butane (9) (0.025 g, 0.000035 mol), 0.0047 g
(0.000017 mol) of allyl nickel chloride dimer 10, 0.031 g
(0.000035 mol) of sodium tetrakis[3,5-bis(trifluoromethyl)-
phenyl]borate 11, and 20 mL of ethyl ether were stirred at

η3-Allyl(R-diimine)nickel(II) Complexes
Organometallics, Vol. 23, No. 13, 2004 3283
RT for 12 h. The resulting reaction mixture was filtered
through Celite, and the solvent was evaporated in a vacuum.
The residue was washed with 10 mL of pentane and dried,
affording 0.050 g (85%) of nickel compound 12 as a brown
powder. 1H NMR (CD2Cl2): δ 1.10 (s, 6H, CH3), 1.79 (br,
2-allyl-H), 2.10 (s, 12 H, CH3), 2.55 (br, 2-allyl-H), 4.95 (br,
1H central allyl-H), 5.45-7.50 (m, arom. and furyl 30H). 13C
NMR (CD2Cl2) (selected signals): δ 177.86 (s, CdN). Anal.
Calcd for C83H57BF24N2NiO4 (Mw 1671.82): C, 59.63; H, 3.44;
N, 1.68. Found: C, 59.85; H, 3.61; N, 1.79.
were stirred at RT for 12 h. The resulting reaction mixture
was filtered through Celite, and the solvent was evaporated
in a vacuum. The residue was washed with 10 mL of pentane
and dried, affording 0.43 g (91%) of nickel compound 19 as a
1
brown powder. H NMR (CD2Cl2): δ 1.50 (br, 2-allyl-H), 2.05
(s, 6H, CH3), 2.40 (br, 2-allyl-H), 4.35 (br, 1H central allyl-H);
6.50-8.00 (m, arom. 38H). 13C NMR (CD2Cl2) (selected sig-
nals): δ 177.79 (s, CdN). Anal. Calcd for C85H55BF24N2NiO4
(Mw 1693.82): C, 60.27; H, 3.27; N, 1.65. Found: C, 60.42; H,
3.50; N, 1.74.
Nick el(1+), [N,N′-(1,2-d im eth yl-1,2-eth a n ed iylid en e)-
(2,6-bis(ben zofu r an -2-yl)ph en yl-N],[(η3-2-pr open yl]-, h exa-
flu or oa n tim on a te(1-) (20). 2,3-Bis(2,6-bis(benzofuran-2-
yl)phenylimino)butane (17) (0.21 g, 0.00030 mol), 0.0445 g
(0.000168 mol) of allyl nickel chloride dimer 10, 0.113 g
(0.000379 mol) of silver hexafluoride 18, and 20 mL of ethyl
ether were stirred at RT for 12 h. The resulting reaction
mixture was filtered through Celite, and the solvent was
evaporated in a vacuum. The residue was recrystallized from
10 mL of toluene, affording 0.27 g (85%) of nickel compound
2,6-Bis(ben zofu r a n -2-yl)p h en yla m in e (15) a n d [2,2′]-
Biben zofu r a n yl (16). 2-Benzofuranboronic acid 14 (10.0 g,
0.0617 mol), 6.97 g (0.0278 mol) of 2,6-dibromoaniline 13, 24.14
g (0.069 mol) of cesium carbonate, 0.848 g (0.00093 mol) of
tris(dibenzylideneacetone)dipalladium, 0.45 g (0.0022 mol) of
tri-tert-butylphosphane, and 120 mL of dioxane were stirred
at room temperature for 24 h under argon. The reaction
mixture was filtered, and the solvent was removed under
vacuum. The resulting mixture was purified by chromatogra-
phy on silica with petroleum ether/ethyl ether (10:2) as eluent.
The yield of the 2,6-bis(benzofuran-2-yl)phenylamine 15 was
6.1 g (68%) with mp 128 °C. 1H NMR (CDCl3): δ 5.30 (br, 2H),
6.60-7.80 (m, 13H). Anal. Calcd for C22H15NO2 (Mw 325.36):
C, 81.21; H, 4.65; N, 4.30. Found: C, 80.97; H, 4.41; N, 4.12.
The structure of 15 was proved by X-ray analysis (Figure 5).
The yield of [2,2′]bibenzofuranyl 1617 was 0.20 g (3% on
2-benzofuranboronic acid). 1H NMR (CDCl3): δ 7.10-7.70 (m,
10H). Anal. Calcd for C16H10O2 (Mw 234.25): C, 82.04; H, 4.30.
Found: C, 81.87; H, 4.38.
2,3-Bis(2,6-b is(b en zofu r a n -2-yl)p h en ylim in o)b u t a n e
(17). 2,6-Bis(benzofuran-2-yl)phenylamine (15) (2.20 g, 0.0068
mol), 0.60 g (0.0034 mol) of 2,2,3,3-tetramethoxybutane 8, 30
mL of xylenes, and a few crystals of para-toluenesulfonic acid
were refluxed under nitrogen for 3.5 h. The resulting yellow
precipitate was filtered, washed with 20 mL of ethyl ether,
and dried in a vacuum. Yield of 2,3-bis(2,6-bis(benzofuran-2-
yl)phenylimino)butane (17) was 0.31 g (13%) with mp 316 °C.
1H NMR (DMSO-d6): δ 0.95 (s, 6H), 6.50-8.60 (m, 26H). Anal.
Calcd for C48H32N2O4 (Mw 700.78): C, 82.27; H, 4.60; N, 4.00.
Found: C, 82.12; H, 4.58; N, 4.11. The structure of 2,3-bis-
(2,6-bis(benzofuran-2-yl)phenylimino)butane was proved by
X-ray analysis.
1
20 as a black powder. H NMR (CD2Cl2): δ 1.45 (br, 2-allyl-
H), 2.10 (s, 6H, CH3), 2.40 (br, 2-allyl-H), 4.35 (br, 1H central
allyl-H); 6.50-8.00 (m, arom. 26H). Anal. Calcd for C53H43F6N2-
NiO4Sb (Mw 1066.36): C, 59.70; H, 4.06; N, 2.63. Found: C,
59.83; H, 4.10; N, 2.67. The structure of 20 was proved by X-ray
analysis.
Ack n ow led gm en t. X-ray analysis of complex 20
was performed at the DuPont-Northwestern-Dow Col-
laborative Access Team (DND-CAT) Synchrotron Re-
search Center located at Sector 5 of the Advanced
Photon Source at Argonne National Laboratory. DND-
CAT is supported by the E.I. DuPont de Nemours & Co.,
The Dow Chemical Company, the U.S. National Science
Foundation through Grant DMR-9304725, and the State
of Illinois through the Department of Commerce and
the Board of Higher Education Grant IBHE HECA
NWU 96. Use of the Advanced Photon Source was
supported by the U.S. Department of Energy, Basic
Energy Sciences, Office of Energy Research, under
Contract No. W-31-102-Eng-38. The authors wish to
thank Kurt Adams for funding X-ray research, Zdzislaw
Wawrzak for help with synchrotron experiments, and
Steve Ittel for valuable suggestions and proofreading
the manuscript.
Nick el(1+), [N,N′-(1,2-d im eth yl-1,2-eth a n ed iylid en e)-
(2,6-bis-ben zofu r a n -2-yl-p h en yl-N], [(η3-2-p r op en yl]-, tet-
r a k is[3,5-bis(tr iflu or om eth yl)p h en yl]bor a te(1-) (19). 2,3-
Bis(2,6-bis(benzofuran-2-yl)phenylimino)butane (17) (0.20 g,
0.00029 mol), 0.0039 g (0.000144 mol) of allyl nickel chloride
dimer 10, 0.25 g (0.00028 mol) of sodium tetrakis[3,5-bis-
(trifluoromethyl)phenyl]borate 11, and 20 mL of ethyl ether
Su p p or tin g In for m a tion Ava ila ble: The crystallographic
information files (CIF) of compounds 4-6, 9, 15-17, and
20 are available free of charge via the Internet at http://
pubs.acs.org.
(17) Oae, S.; Inubushi, Y.; Yoshihara, M. Phosphorus, Sulfur Silicon
Relat. Elem. 1995, 103, 101.
OM0497902