Structural modification of phenoxyimine titanium complexes and activation studies with alkylaluminum compounds. Issue 20 (8th September 2020)

• Record Type: Journal Article
• Authors: Yang, Huaqin; van Ingen, Yara; Blom, Burgert; Rastogi, Sanjay; Romano, Dario
• Is Part Of: ChemCatChem. Volume 12:Issue 20(2020)
• Page Start: 5209
• Page End: 5220
• Publication Date: 2020-09-08
• Subjects: Activation -- Alkylaluminum -- DFT -- FI catalysts -- UHMWPE; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.202000731
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: The synthesis and characterization of three complexes of the type (N‐(3‐ tert ‐butylsalicylidene)‐R)2 TiCl2 [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 co‐catalysts suggests the formation of Ti(III) species in the presence of tri‐ iso ‐butylaluminum, and also the formation of NR−CH2 (R: −Al(CH2 CH(CH3 )2 )2 ) bond from the N=C−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. Abstract : Structure affects : Complex 4 /TiBA system, shows the lowest distance between the fluorine atom and aluminum (2.247 Å) and lowest calculated energy (−35 Kcal/mol) for the reaction between 4 and TiBA, revealing a stabilizing interaction of the ortho‐atom with the aluminum. A general correlation between Mulliken charges bore by the nitrogen in the complexes 1 –4 with the calculated energy, the catalytic activity and reactivity towards aluminum‐based co‐catalysts is revealed.