Article
Organometallics, Vol. 28, No. 14, 2009 4171
Chart 1. Ligand Evolution from Salicylaldimine to Hydroxy-
indanimine
catalysts bearing salicylaldiminato ligands for ethylene oligo-
merization.18
Recently, our group designed and synthesized a series of
nickel, copper, and iridium complexes based on hydroxy-
indanimine ligands (II) (Chart 1), which have the same basic
fragment as salicylaldimine for norbornene, MMA, and
styrene polymerization with high activity.19 Herein we report
the half-sandwich chromium(III)complexes bearinghydroxy-
indanimine ligands, which show high activity for ethylene
polymerization to produce high molecular weight PE acti-
vated with only a small amount of triethylaluminum
(Scheme 1).
ethylene.5a Half-sandwich salicylaldiminato chromium(III) cata-
Results and Discussion
lysts, Cp*Cr[2,4-tBu2-6-(CHdNR)-C6H2O]Cl/AlR03 [R=tBu,
i
Ph, 2,6-iPr2C6H3; R0 =Me, Et, Bu], were reported, and they
The ligands 1a-1e were synthesized according to the
literature.19,20 Reactions of Cp*Cr(THF)Cl2 with the corre-
sponding sodium salts of the hydroxyindanimine ligands
1a-1e (Scheme 1) in THF at -78 °C resulted in the green-
colored half-sandwich Cr(III) complexes 2a-2e in ca. 50-
70% yields. In a similar synthesis method, we also synthe-
sized the Cp (cyclopentadienyl)-based chromium complex 2f
bearing ligand 1e for comparing to complex 2e, which
contains a Cp* ligand. All the chromium complexes 2a-2f
are soluble in common solvents such as CH2Cl2, THF,
toluene, diethyl ether, and hexane. These Cr(III) complexes
can catalyze ethylene polymerization to produce linear high
molecular weight PE.11 Recently we synthesized a series of
half-sandwich chromium complexes with β-ketoiminato and β-
diketiminate ligands. Upon activation with a small amount of
triethylaluminum, these chromium complexes exhibited high
activity for ethylene polymerization to produce linear high
molecular weight PE.12
Salicylaldiminato ligands (I) (Chart 1), which were used for
high performance olefin polymerization catalysts, are of wide
interest in academic and industrial fields.3a Grubbs reported
neutral nickel catalysts bearing salicylaldiminato ligands that
showed high activity for ethylene homopolymerization and
copolymerization.13 Fujita and Coates independently developed
a family of highly active non-metallocene group IV catalysts with
bis(salicylaldiminato) ligands.14,15 Carlini studied nickel and
copper complexes bearing bis(salicylaldiminato) ligands for the
polymerization of olefin and polar monomers.16 Our group also
synthesized a series of nickel and group IV catalysts based on
salicylaldiminato ligands for ethylene and norbornene polymeri-
zation.17 Gibson reported a series of non-metallocene chromium
1
were characterzed by IR and elemental analysis. H NMR
analysis indicated the paramagnetic character of the Cr(III)
complexes.21 Crystals of 2c suitable for X-ray diffraction
were obtained by recrystallization from CH2Cl2/hexane
solution at low temperature. The molecular structure of 2c
along with selected bond lengths and angles is depicted in
Figure 1.
X-ray crystallographic analysis shows that the crystal of 2c
contains one CH2Cl2 solvent per molecule. Complex 2c
adopts a three-legged piano stool geometry with a pseudo-
octahedral coordination environment, containing a hydro-
xyindanimine ligand, a Cp* ligand, and chloride, which
is similar to the Cp*Cr(acac)Cl, half-sandwich salicylal-
diminato and β-ketoiminato and β-diketiminate chromium
complexes.5a,11,12 In complex 2c, the bond length of Cr-O
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˚
(1.935(2) A) is longer than that of the half-sandwich salicylal-
˚
diminato (1.9185(16)-1.927(3) A) and β-ketoiminato (1.922
˚
˚
(13) A) complexes; the Cr-N bond length (2.082(3) A) is in
the range of the salicylaldiminato complexes (2.049(4)-
2.097(2) A), but longer than that of chromium complexes
˚
˚
bearing β-ketoiminato (2.042(4) A) and β-diketiminate
(1.995(3)-2.001(3) A) ligands. The O(1)-Cr(1)-N(1) angle
˚
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