Oligo- and polymerization of ethylene by pyrrolide-imine chromium catalysts bearing pendant O-, S- and N-donor groups. Synthesis, characterization and DFT studies

• Published in: Molecular catalysis Vol. 528; p. 112495
• Main Authors: da Silva, Sabrina M., Pinheiro, Adriana C., da Costa, Miriã T., Alves, Thiago C.G., Oliboni, Robson S., Stieler, Rafael, Casagrande, Adriana C.A., Casagrande, O.L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2022
• Subjects: Chromium(III) complexes; DFT studies; Ethylene oligomerization; Ethylene polymerization; Pyrrolide-imine ligands; Ethylene polymerization; Chromium(III) complexes; Ethylene oligomerization; Pyrrolide-imine ligands; DFT studies
• ISSN: 2468-8231; 2468-8231
• DOI: 10.1016/j.mcat.2022.112495

•New set of chromium(III) catalysts supported by pyrrolide-imine ligands with pendant O-, S- and N-donor groups has been synthesized.•Upon activation with MAO, chromium precatalysts generated active species affording a nonselective distribution of α‐olefins along with the production of varied amounts of polymers.•The nature of the donor atom at the pendant group of the pyrrolide-imine ligand has a strong influence on the product distribution.•DFT calculations suggested that the type of donor atom induce the formation of different species in the reactional medium. The synthesis and ethylene reactivity of a new set of chromium(III) complexes supported by pyrrolide-imine ligands bearing pendant O-, S- and N-donor groups [Cr{(C4H3N-2-CH=N)Z}(THF)Cl2] (Z = CH2Ph-2-OMe, Cr1; Z = Ph-2-OPh, Cr2; Z = Ph-2-OMe, Cr3; Z = Ph-2-SPh, Cr4; Z = Ph-2-SMe, Cr5; Z = CH2Py, Cr6; Z = C2H4Py, Cr7) are described. Activation of Cr1-Cr7 with MAO generates active systems affording a full range oligomerization of ethylene (C4-C12+) with turnover frequencies (TOFs) in the range of 13,900–94,200 mol(ethylene)·mol(Cr)–1·h–1 along with production of a varied amount of polymer (6.9 - 91.5 wt.%). The nature of the pendant group has a significant impact on the catalytic performances of these Cr complexes. Particularly, catalytic precursors containing pendant O-donor groups (Cr1-Cr3) produce mostly oligomers (up to 89.0 wt%) while those bearing sulfur-base donor groups (Cr4 and Cr5) are primarily polymerization systems. DFT calculations suggested the presence of two different CrIII catalytic species, the mononuclear species responsible for production of polymer and one dinuclear species that have been ascribed for production of oligomers. By tunning the reactional conditions, higher TOF and higher selectivities for production of α-olefins were achieved. Notably, the use of high MAO loading (1500 equiv.) enhanced the activity of Cr2 [TOF = 389,800 (mol ethylene)⋅(mol Cr)−1⋅h−1] producing mostly oligomers (97.7 wt% of total products) with high selectivity for α-olefins (>95.5 wt.%). [Display omitted]