Preparation of half-titanocenes of thiophene-fused trimethylcyclopentadienyl ligands and their ethylene copolymerization reactivity

Methylthiophene-fused or dimethylthiophene-fused trimethylcyclopentadienyltitanium trichloride complexes, (η5-Me4RC7S)TiCl3 (R = Me or H), are prepared, from which a chloride ligand is replaced with 2,6-diisopropylphenoxy, di(tert-butyl)ketimide, or tri(tert-butyl)phosphinimide ligand to yield (η5-Me4RC7S)TiXCl2 (11, R = Me, X = iPr2C6H3O–; 12, R = H, X = iPr2C6H3O–; 13, R = Me, X = tBu2C = N–; 14, R = H, X = tBu2C = N–; 15, R = Me, X = tBu3P = N–; 16, R = H, X = tBu3P = N–). The molecular structures of 11, 14, and 16 are confirmed by X-ray crystallography. The Cp(centroid)–Ti–N angles of 11, 14, and 16 (119.83°, 111.98°, and 125.34°, respectively) are significantly larger than the corresponding angle observed for the related thiophene-fused and tetrahydroquinaldine-linked cyclopentadienyl complex (1), [(η5-(Me4C7S)-(2-MeC9H9N-κN)]TiMe2 (106.6°). The phenoxy complexes 11 and 12 show negligible activity, while the ketimido and phosphinimido complexes 13–16 exhibit good activities (5–20 × 106 g/molTi h) for ethylene/1-octene copolymerization. The ketimido-complexes 13 and 14 are able to incorporate a high amount of 1-octene (15–16 mol%), while the phosphinimido-complexes 15 and 16 are not as capable (8 mol% 1-octene) under the identical polymerization conditions. The catalytic performance of 13–16 is inferior to 1 in terms of activity and comonomer incorporation.

Graphical abstractHalf-titanocenes constructed with thiophene-fused trimethylcyclopentadienyl ligands and bearing aryloxo, ketimido, or phosphinimide ligands are prepared, and their catalytic activity for ethylene/1-octene copolymerization studied. Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Half-titanocenes of thiophene-fused cyclopentadienyl were prepared. ► Molecular structures of aryloxy, ketimide, and phosphinimide complexes were determined. ► They were screened for ethylene/1-octene copolymerization. ► Their catalytic performances were inferior to the analogous bridged complexes.