Organometallics 1998, 17, 4541-4543
4541
[(P h )2n a cn a c]MCl2(THF )2 (M ) Ti, V, Cr ): A New Cla ss of
Hom ogen eou s Olefin P olym er iza tion Ca ta lysts F ea tu r in g
â-Diim in a te Liga n d s
Woo-Kyu Kim, Michael J . Fevola, Louise M. Liable-Sands,
Arnold L. Rheingold, and Klaus H. Theopold*
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716
Received J uly 30, 1998
Summary: [(Ph)2nacnac]MCl2(THF)2 ([(Ph)2nacnac] )
N,N-diphenyl-2,4-pentanediimine anion; M ) Ti (1a ),
V (1b), Cr (1c)) were prepared and their structures
determined by X-ray diffraction. In the presence of
excess methylaluminoxane (MAO), 1a -c catalyzed the
homopolymerization of ethylene and the copolymeriza-
tion of ethylene with R-olefins.
have been used as ligands before,6 but by comparison
with the analogous â-diketonates (“acac” complexes),
their chemistry is largely undeveloped. Herein we
describe our initial foray into the organometallic chem-
istry of “nacnac”-complexes of early transition metals,
which has yielded a novel class of homogeneous olefin
polymerization catalysts.
Heterogeneous catalysts containing early transition
metals (Ti, V, Cr) are widely used for the polymerization
of small olefins (ethylene, propene, etc.). The discovery
of homogeneous model systems has substantially im-
proved our understanding of the underlying organome-
tallic chemistry and is fueling the current round of
innovation hailed as “metallocene technology”.1 Despite
their commercial importance, chromium catalysts have
inspired less modeling activity,2 owing possibly to the
paramagnetism of relevant organometallic complexes.
We have previously created a homogeneous model
system for the so-called “Union Carbide catalyst” (i.e.
Cp2Cr/SiO2),3 which suggests that the active sites of this
catalyst are coordinatively unsaturated cyclopentadi-
enylchromium(III) alkyls.4 A notable feature of this
system is its extreme selectivity between ethylene and
R-olefins, making homopolymerizations of and copoly-
merizations with the latter impractical. In a bid to
overcome this limitation, we have now turned to model-
ing the “Phillips-catalyst” (i.e. CrO3/SiO2);5 which is
known to incorporate R-olefins. The ligand system we
have chosen to mimic the hard coordination environ-
ment of the silica surface (A) is a class of â-diiminates
(B); sterically demanding substituents on the nitrogen
should allow preservation of coordinatively unsaturated
mononuclear metal complexes, and the flexibility in the
choice of substituents (R, R′) will be useful to modify
the local symmetry of the catalytic sites. â-Diiminates
Reaction of [(Ph)2nacnac]Li ([(Ph)2nacnac] ) N,N-
diphenyl-2,4-pentanediimine anion with MCl3(THF)3 (M
) Ti, V, Cr) in THF yielded the chlorides [(Ph)2nacnac]-
MCl2(THF)2 (1a -c; see Scheme 1). Their molecular
structures have been determined by X-ray diffraction;7
all three are isomorphous, and the representative
chromium complex (1c) is depicted in Figure 1 with
selected interatomic distances and angles for all three
compounds listed in Table 1. The coordination environ-
ment of the metals is octahedral, with the oxygen atoms
of the THF ligands in the same plane as the nitrogen
atoms of the bidentate ligand. The nacnac moiety is
coordinated in the η2 mode, and the structural param-
eters show the expected gradual decrease in the size of
the metal atom with increasing atomic number. 1a -c
are paramagnetic, with effective magnetic moments
(6) (a) McGeachin, S. G. Can. J . Chem. 1968, 46, 1903-1912. (b)
Parks, J . E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408-1416. (c)
Honeybourne, C. L.; Webb, G. A. J . Chem. Soc., Chem. Commun. 1968,
740-741. (d) Healy, P. C.; Bendall, M. R.; Doddrell, D. M.; Skelton, B.
W.; White, A. H. Aust. J . Chem. 1979, 32, 727-735. (e) Bercaw, J . E.;
Davies, D. L.; Wolczanski, P. T. Organometallics 1986, 5, 443-450.
(f) Richeson, D. S.; Mitchell, J . F.; Theopold, K. H. J . Am. Chem. Soc.
1987, 109, 5868. (g) Richeson, D. S.; Mitchell, J . F.; Theopold, K. H.
Organometallics 1989, 8, 2570. (h) Hitchcock, P. B.; Lappert, M. F.;
Liu, D.-S. J . Chem. Soc., Chem. Commun. 1994, 2637-2638. (i)
Lappert, M. F.; Liu, D.-S. J . Organomet. Chem. 1995, 500, 203-217.
(j) Feldman, J .; McLain, S. J .; Parthasarathy, A.; Marshall, W. J .;
Calabrese, J . C.; Arthur, S. D. Organometallics 1997, 16, 1514-1516.
(k) Rahim, M.; Taylor, N. J .; Xin, S.; Collins, S. Organometallics 1998,
17, 1315-1323. (l) Qian, B.; Ward, D. L.; Smith, M. R., III. Organo-
metallics 1998, 17, 3070.
(1) (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
(b) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (c) Montagna,
A. A. CHEMTECH 1995, October, 44-47. (d) Stevens, J . C. In 11th
International Congress on Catalysis-40th Anniversary; Hightower, J .
W., Delgass, W. N., Iglesia, E., Bell, A. T., Eds.; Elsevier: Amsterdam,
1996; pp 11-20.
(2) (a) Feher, F. J .; Blanski, R. L. J . Chem. Soc., Chem. Commun.
1990, 1614-1616. (b) Coles, M. P.; Dalby, C. I.; Gibson, V. C.; Clegg,
W.; Elsegood, M. R. J . J . Chem. Soc., Chem. Commun. 1995, 1709-
1711.
(7) 1a : orthorhombic, Pna21, a ) 19.5601(8) Å, b ) 9.4959(4) Å, c
) 13.5555(5) Å, V ) 2517.8(2) Å3, Z ) 4, T ) 223(2) K, Dcalcd ) 1.352
g cm-3, R(F) ) 4.15% for 3912 observed independent reflections (4 e
2θ e 57°). 1b: orthorhombic, Pna21, a ) 19.5215(4) Å, b ) 9.5341(2)
(3) Karol, F. J .; Karapinka, G. L.; Wu, C.; Dow, A. W.; J ohnson, R.
N.; Carrick, W. L. J . Polym. Sci., Polym. Chem. Ed. 1972, 10, 2621-
2637.
Å, c ) 13.4898(3) Å, V ) 2510.72(9) Å3, Z ) 4, T ) 218(2) K, Dcalcd
)
1.363 g cm-3, R(F) ) 3.75% for 4948 observed independent reflections
(4 e 2θ e 57°). 1c: orthorhombic, Pna21, a ) 19.6220(4) Å, b ) 9.5971-
(2) Å, c ) 13.4509(3) Å, V ) 2533.00(9) Å3, Z ) 4, T ) 218(2) K, Dcalcd
) 1.354 g cm-3, R(F) ) 5.35% for 2408 observed independent reflections
(4 e 2θ e 57°).
(4) (a) Theopold, K. H. CHEMTECH 1997, October, 26-32. (b)
Theopold, K. H. Eur. J . Inorg. Chem. 1998, 15-24.
(5) (a) Hogan, J . P. J . Polym. Sci., Polym. Chem. Ed. 1970, 8, 2637-
2652. (b) McDaniel, M. P. Adv. Catal. 1985, 33, 47-98.
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Publication on Web 09/24/1998