Vanadium(V) Complexes Containing Unsymmetrical N-Heterocyclic Carbene Ligands: Highly Efficient Synthesis and Catalytic Behavior towards Ethylene/Propylene Copolymerization

Imidazolidin-2-iminato vanadium complexes for the synthesis of ethylene/propylene/5-ethylidene-2-norbornene (ENB) terpolymers with high ENB incorporation and ultra-high molecular weight

“…The molar fraction of X 3 (PEP sequences, 21.9%–22.5%) in the copolymers prepared with vanadium complexes Vi1–Vi4 containing imidazolidin-2-iminato ligands is higher than that of copolymers prepared with our reported vanadium complexes containing N-heterocyclic carbene ligands. 34 In addition, the molar fractions of X 5 (EEP or PEE sequences) in the copolymers prepared with Vi2 (17.8%) and Vi3 (15.8%) are higher than those of copolymers prepared with Vi1 (13.3%) and Vi4 (13.8%), indicating that ethylene–propylene copolymers with more randomly distributed monomer units could be prepared by using Vi2 or Vi3 as the precatalyst.…”

“…According to our previous reports, Et 3 Al 2 Cl 3 (EASC) serves as an efficient cocatalyst in the copolymerization of ethylene with propylene using vanadium complexes as precatalysts. 12,32,34 Therefore, the copolymerizations of ethylene with propylene were carried out using Vi1–Vi4 /EASC catalytic systems in hexanes under similar polymerization conditions. The results of catalytic activity and the propylene incorporation ratio are displayed in Table 1 and Fig.…”

“…The ethylene–propylene copolymers prepared with Vi1–Vi4 contain less X 2 content (tail-to-tail PP sequences, 6.0%–9.1%) than that in the copolymers prepared with vanadium complexes containing NHC ligands. 34 This could be attributed to the less steric bulk of imidazolidin-2-iminato ligands than NHC ligands in the V-based catalysts. The molar fraction of X 3 (PEP sequences, 21.9%–22.5%) in the copolymers prepared with vanadium complexes Vi1–Vi4 containing imidazolidin-2-iminato ligands is higher than that of copolymers prepared with our reported vanadium complexes containing N-heterocyclic carbene ligands.…”

“…7,26–31 We have reported that NHC ligands play important roles in the control of molecular weight of the resulting copolymers. 12,32–34 Vanadium complexes containing NHC ligands V1–V4 (as shown in Chart 1) display quasi-living characteristics in the copolymerization of ethylene with propylene, affording ethylene–propylene copolymers with ultra-high molecular weight ( M w = 1612 kg mol −1 ). 12 In order to synthesize UHMW EPDM with high ENB content, we sought to design the vanadium complexes with good catalytic activity and copolymerization ability by replacing the NHC ligands with electron-rich but less sterically hindered ligands.…”