Structural modification of phenoxyimine titanium complexes and activation studies with alkylaluminum compounds

Abstract

The synthesis and characterization of three complexes of the type (N-(3-tert-butylsalicylidene)-R) 2 TiCl 2 [R = 2,6-difluorophenyl 1, R = 2,6-dimethylphenyl 2, R = phenyl 3] is reported and compared with the highly active R = 2,3,4,5,6,-pentafluorophenyl 4. The complexes were tested for ethylene polymerization when activated with different co-catalysts, giving high catalytic activity when activated with methylaluminoxane for complexes 3 and 4. Complex 3 is the only catalyst to be inactive when activated with diethylaluminum chloride. Unexpectedly, for complexes 1 and 2, no catalytic activity is recorded when butylated hydroxytoluene in methylaluminoxane is used to remove the trimethylaluminum, while the catalytic activity for complex 3 is retained. NMR study on the activation of the four complexes in the presence of common alkyl aluminum cocatalysts suggests the formation of Ti(III) species in the presence of tri-iso-butylaluminum, and also the formation of NRÀ CH 2 (R: À Al(CH 2 CH(CH 3) 2) 2) bond from the N=CÀ H bond of the ligand explaining the absence of catalytic activity. Density functional theory calculations using B3LYP and a combination of basis sets (6-31 + G and cc-pVTZ) were performed on the catalyst precursors and the activated species showing insights into the frontier orbitals, localizing the LUMO on the imino bond elucidating their reactivity. Mulliken charges are also reported and an unexpected relationship between the nitrogen on the ligands and the molecular weight is observed.

Unprecedented Mechanical Properties in Linear UHMWPE Using a Heterogeneous Catalytic System

“…However, the reported procedure makes use of TiBA, which is found to deactivate the Cat. 1 used to produce dis -UHMWPE; moreover, there are no indications on the processability of the synthesized polymer and its entangled state. The magnesium chloride based activator used in this work was synthesized by slightly modifying the reported protocol; 1 equiv of MgCl 2 was refluxed in n -decane with 3 equiv of 2-ethyl-1-hexanol for 4 h, resulting in a clear solution of the MgCl 2 / 2-ethyl-1-hexanol adduct.…”

“…The catalytic system composed of a bis­[ N -(3- tert -butylsalicylidene)­pentafluoroanilinato] titanium­(IV) dichloride complex ( Cat. 1 ) has been proven to be an excellent candidate in producing UHMWPE with a reduced number of entanglements in high yields and with high molar masses and has established a well-defined route to unprecedented mechanical properties. − ,,− Therefore, it was appealing to use Cat. 1 for the synthesis of dis -UHMWPE in heterogeneous conditions.…”

Novel titanium(IV) diolate complexes with additional O‐donor as precatalyst for the synthesis of ultrahigh molecular weight polyethylene with reduced entanglement density: Influence of polymerization conditions and its implications on mechanical properties

“…In the overwhelming majority of cases, disentangled UHMWPE suitable for solid‐phase processing is synthesized on phenoxy‐imine Group 4 metal complexes (FI catalysts [ 9 ] ), activated with alkylaluminoxanes. [ 10–14 ] However, these activators have significant drawbacks that lie in the high Al/M ratios needed to achieve optimal catalytic performance and in its still ill‐defined structures (mixture of oligomers (AlO(Alk)) n evolving with time). In addition, these activators increase considerably the catalyst costs.…”

Effect of Activator and Outgoing Ligand Nature on the Catalytic Behavior of Bis(phenoxy-imine) Ti(IV) Complexes in the Polymerization of Ethylene and Its Copolymerization with Higher Olefins

“…Therefore, in recent years, significant efforts of researchers have been directed to the development of new types of activators. In particular, attempts have been made (generally not very successful) to use traditional trialkylaluminum and alkylaluminum chlorides for FI catalysts activation [ 12 , 13 , 14 , 15 ]. Many efforts have been made to replace MAO with non-coordinating anions (e.g., [B(C 6 F 5 ) 4 ] − ); however, their cost is also very high.…”