696
However, use of β-diiminato ligands, such as [ArNC(R)CHC(R)NAr]-[R = Me,
tBu; Ar = Ph, 2,6-iPr 2 C 6 H 3 , 2,4,6-Me 3 C 6 H 2 ], displayed insignificant catalytic
activities.
The catalyst systems based on V(III) possessing (dimethylamino)ethylfunctionalized benzamidinate ligand (Fig. 10a) along with Et 2 AlCl displayed modest catalytic activity for polymerization of ethylene. The activity for above
polymerization at 30 °C was 447 kg polymer/mol V h bar for ethylene loading of 6
bar. The activity (447 kg polymer/mol V h bar) of the complex based on
{[PhC(NSiMe 3 ) 2 ]VCl 2 (THF)} 2 (Fig. 10b) was somewhat lower under the same conditions [50]. On increasing the temperature, the activity of 10b increased, whereas
10a exhibited a decrease in catalytic activity. The V(III) complex based on 10b and
10a when placed on MgCl 2 /AlEt n (OEt) 3-n support exhibited exceptional catalytic
activity of 1490 kg polymer/mol V h bar and 3120 kg polymer/mol V h bar, respectively. V(III) methyl bis(amidinate) complex oligomerized ethylene (M n = 1780,
M w /M n = 2.3) without any additional co-catalyst. Replacing the Ph group with C 6 F 5
further improved the catalytic activity (8.1 kg oligomer/(mol V h)) [51].
Subsequently, dinuclear catalyst systems were developed and analyzed. A dinuclear vanadium(III) chloride complex possessing a bis(amido)amine [(Me 3 Si)
NCH 2 CH 2 ] 2 N(SiMe 3 ) in presence of Me 2 AlCl (activity = 660 kg polymer/(mol V h)
or methylaluminoxane (activity = 237 kg polymer/(mol V h) exhibited strong catalytic activity for ethylene polymerization at 50 °C [52]. However, the lifetime of the
catalyst was limited to 20–30 min only; this may be attributed to the conversion of
V(III) to inactive V(II) species (Scheme 12). Similarly, other complexes based on
V(III) species were synthesized and utilized for polymerization of ethylene (Fig. 11).
For example, dithiolate ligand (11a, 11b, and 11c)-based complexes displayed catalytic activity up to 1990 kg PE/mol V h in presence of Et 2 AlCl and MgCl 2 as
N
N
V
Cl 2(THF)
Me Me
N
Ph
SiMe 3
(a)
Me 3 Si
N
VCl 2(THF)
N
Ph
Me 3 Si
(b)
Me 3 Si
N
V
N
R
Me 3 Si
(c)
Me
R = Ph or C 6 F 5
O
O
V
3
V(acac) 3
O
O
V
3
V(Cy-acac) 3
O
O
tBu
tBu
V
3
V(tBu-acac) 3
O
O
F 3 C
F 3 C
V
3
V(CF3-acac) 3
Fig. 10 (a–c) V(III)-based complexes utilized for olefin polymerization
A. S. K. Sinha and U. Ojha
However, use of β-diiminato ligands, such as [ArNC(R)CHC(R)NAr]-[R = Me,
tBu; Ar = Ph, 2,6-iPr 2 C 6 H 3 , 2,4,6-Me 3 C 6 H 2 ], displayed insignificant catalytic
activities.
The catalyst systems based on V(III) possessing (dimethylamino)ethylfunctionalized benzamidinate ligand (Fig. 10a) along with Et 2 AlCl displayed modest catalytic activity for polymerization of ethylene. The activity for above
polymerization at 30 °C was 447 kg polymer/mol V h bar for ethylene loading of 6
bar. The activity (447 kg polymer/mol V h bar) of the complex based on
{[PhC(NSiMe 3 ) 2 ]VCl 2 (THF)} 2 (Fig. 10b) was somewhat lower under the same conditions [50]. On increasing the temperature, the activity of 10b increased, whereas
10a exhibited a decrease in catalytic activity. The V(III) complex based on 10b and
10a when placed on MgCl 2 /AlEt n (OEt) 3-n support exhibited exceptional catalytic
activity of 1490 kg polymer/mol V h bar and 3120 kg polymer/mol V h bar, respectively. V(III) methyl bis(amidinate) complex oligomerized ethylene (M n = 1780,
M w /M n = 2.3) without any additional co-catalyst. Replacing the Ph group with C 6 F 5
further improved the catalytic activity (8.1 kg oligomer/(mol V h)) [51].
Subsequently, dinuclear catalyst systems were developed and analyzed. A dinuclear vanadium(III) chloride complex possessing a bis(amido)amine [(Me 3 Si)
NCH 2 CH 2 ] 2 N(SiMe 3 ) in presence of Me 2 AlCl (activity = 660 kg polymer/(mol V h)
or methylaluminoxane (activity = 237 kg polymer/(mol V h) exhibited strong catalytic activity for ethylene polymerization at 50 °C [52]. However, the lifetime of the
catalyst was limited to 20–30 min only; this may be attributed to the conversion of
V(III) to inactive V(II) species (Scheme 12). Similarly, other complexes based on
V(III) species were synthesized and utilized for polymerization of ethylene (Fig. 11).
For example, dithiolate ligand (11a, 11b, and 11c)-based complexes displayed catalytic activity up to 1990 kg PE/mol V h in presence of Et 2 AlCl and MgCl 2 as
N
N
V
Cl 2(THF)
Me Me
N
Ph
SiMe 3
(a)
Me 3 Si
N
VCl 2(THF)
N
Ph
Me 3 Si
(b)
Me 3 Si
N
V
N
R
Me 3 Si
(c)
Me
R = Ph or C 6 F 5
O
O
V
3
V(acac) 3
O
O
V
3
V(Cy-acac) 3
O
O
tBu
tBu
V
3
V(tBu-acac) 3
O
O
F 3 C
F 3 C
V
3
V(CF3-acac) 3
Fig. 10 (a–c) V(III)-based complexes utilized for olefin polymerization
A. S. K. Sinha and U. Ojha