707 citations for the Gibson group published on April 7 [13] and 983 for the
Brookhart group published on April 29 [14]. Industrial trials were extensively
conducted on the process of ethylene oligomerization in a joint adventure between
DuPont and PetroChina, and on the process of ethylene polymerization targeting
HDPE by BP with the assistance of Albemarle. The catalytic system of bis(imino)
pyridyliron chlorides commonly proceed with ethylene oligomerization and polymerization together, but only the selective process producing either oligomerization
or polymerization would be applicable in the petrochemical industry. Further
modifications of the bis(imino)pyridyliron chloride complexes have been
researched, and significant progress was made when revisiting the ambient-temperature-inactive benzhydryl-substituted bis(imino)pyridylmetal (iron or cobalt) chloride complexes (Scheme 3) [31, 49–52] [53, and unpublished data]. The exploration
was inspired by the temperature-switching catalytic system of the 2-benzoxazolyl6-iminopyridylcobalt chlorides, with ethylene oligomerization at room temperature, but ethylene polymerization at elevated reaction temperature [43]. These
benzhydryl-substituted bis(imino)pyridylmetal (iron or cobalt) complex
pre-catalysts [31, 49–52] [53, and unpublished data] do not show activity towards
ethylene at room temperature; however, when the reaction temperature is elevated,
they perform with high activities [up to 10
5 kg PE mol
–1 (Fe) h
–1 ] in ethylene
polymerization without any oligomers in the products.
The metal (iron or cobalt) complex pre-catalysts showed significant differences
in their catalytic activities and resultant polyethylenes, depending on the
substituents used in the ligands. Small fine tuning of the ancillary ligand set,
even sometimes distant from the metal center, can result in dramatic changes to
the resultant catalysis. For example, the iron analog pre-catalysts can give different
options of polymerization conditions and properties of the obtained polyethylenes
(Table 1). Although the molecular weights of these polyethylenes ranged from
thousands to millions, high linearity is generally observed for these polyethylenes
and, more importantly, narrow polydispersity for the obtained polyethylenes could
be achieved through controlling the reaction parameters. Therefore, the bis(imino)
pyridylmetal (iron or cobalt) complex pre-catalysts could potentially provide a
catalytic process for producing HDPE or polyethylene waxes, though one more
parameter should be considered as the operation temperature is between 70
C and
90
C for most olefin polymerization processes.
N
N
N
M
Cl
Ar
Ph-BBPh
Cl
M = Fe or Co
Ph-BBPh:
R
Q
Q
Q
Q
Ph
Ph
Ph
Ph
R = Me or Cl
Q = Ph or p-fluorophenyl (FPh)
3A
3B
R
1
R
1
R
2
Ar represents the
followings in whole
text
Scheme 3 Benzhydryl-substituted bis(imino)pyridylmetal complex pre-catalysts
Novel Polyethylenes via Late Transition Metal Complex Pre-catalysts
167
Brookhart group published on April 29 [14]. Industrial trials were extensively
conducted on the process of ethylene oligomerization in a joint adventure between
DuPont and PetroChina, and on the process of ethylene polymerization targeting
HDPE by BP with the assistance of Albemarle. The catalytic system of bis(imino)
pyridyliron chlorides commonly proceed with ethylene oligomerization and polymerization together, but only the selective process producing either oligomerization
or polymerization would be applicable in the petrochemical industry. Further
modifications of the bis(imino)pyridyliron chloride complexes have been
researched, and significant progress was made when revisiting the ambient-temperature-inactive benzhydryl-substituted bis(imino)pyridylmetal (iron or cobalt) chloride complexes (Scheme 3) [31, 49–52] [53, and unpublished data]. The exploration
was inspired by the temperature-switching catalytic system of the 2-benzoxazolyl6-iminopyridylcobalt chlorides, with ethylene oligomerization at room temperature, but ethylene polymerization at elevated reaction temperature [43]. These
benzhydryl-substituted bis(imino)pyridylmetal (iron or cobalt) complex
pre-catalysts [31, 49–52] [53, and unpublished data] do not show activity towards
ethylene at room temperature; however, when the reaction temperature is elevated,
they perform with high activities [up to 10
5 kg PE mol
–1 (Fe) h
–1 ] in ethylene
polymerization without any oligomers in the products.
The metal (iron or cobalt) complex pre-catalysts showed significant differences
in their catalytic activities and resultant polyethylenes, depending on the
substituents used in the ligands. Small fine tuning of the ancillary ligand set,
even sometimes distant from the metal center, can result in dramatic changes to
the resultant catalysis. For example, the iron analog pre-catalysts can give different
options of polymerization conditions and properties of the obtained polyethylenes
(Table 1). Although the molecular weights of these polyethylenes ranged from
thousands to millions, high linearity is generally observed for these polyethylenes
and, more importantly, narrow polydispersity for the obtained polyethylenes could
be achieved through controlling the reaction parameters. Therefore, the bis(imino)
pyridylmetal (iron or cobalt) complex pre-catalysts could potentially provide a
catalytic process for producing HDPE or polyethylene waxes, though one more
parameter should be considered as the operation temperature is between 70
C and
90
C for most olefin polymerization processes.
N
N
N
M
Cl
Ar
Ph-BBPh
Cl
M = Fe or Co
Ph-BBPh:
R
Q
Q
Q
Q
Ph
Ph
Ph
Ph
R = Me or Cl
Q = Ph or p-fluorophenyl (FPh)
3A
3B
R
1
R
1
R
2
Ar represents the
followings in whole
text
Scheme 3 Benzhydryl-substituted bis(imino)pyridylmetal complex pre-catalysts
Novel Polyethylenes via Late Transition Metal Complex Pre-catalysts
167