Synthesis of Imino-Enamido Hafnium and Zirconium Complexes: A New Family of Olefin Polymerization Catalysts with Ultrahigh-Molecular-Weight Capabilities

Abstract

Bidentate, nitrogen-containing molecules are of interest as ligands in transition-metal-catalyzed olefin polymerization. A computational evaluation of a series of 1,2-bis-imines, 1,2-imine-enamines, and 1,2-bis-enamines of cyclic and acyclic derivatives was conducted to understand the relative thermodynamic stabilities of these compounds. The five- and six-membered-ring 1,2-imine-enamines were found to be more stable than the other tautomers, while the 1,2-bis-imines were calculated to have the lowest energy among four- and seven-membered-ring and acyclic derivatives. On the basis of the computational results, literature examples, and prior experience with imino-amido catalysts, 1,2-imine-enamines containing a cyclohex-2-enylidene backbone were targeted as ligands for a new family of polyolefin catalysts. The desired ligands were prepared in three steps, starting from the commercially available 1,2-cyclohexanedione, and subsequently converted into hafnium and zirconium complexes. An ethylene/1-octene copolymerization study conducted at 120 °C demonstrated that the hafnium complex possessed very good activity for the production of polymers with ultrahigh molecular weight (M w of 1037 kDa) and moderate 1-octene incorporation. This molecular weight is 20 times higher than that produced by the titanium constrained geometry catalyst (CGC) under the same polymerization conditions. The imino-enamido zirconium complex exhibited slightly lower activity than that observed for the hafnium catalyst, yielding an ethylene/1-octene copolymer with M w and mol % 1-octene incorporation of 509 kDa and 6.4, respectively. The polymerization reactions with these catalysts conducted in the presence of diethylzinc led to a sharp decrease in the observed polymer molecular weights, indicative of effective chain transfer. These imino-enamido complexes exhibit higher activity, produce higher molecular weight polymers, incorporate higher levels of 1-octene, and demonstrate significantly improved thermal stability relative to analogous imino-amido complexes reported previously.

Preparation of [bis(amido)-phosphine] and [amido-phosphine sulfide or oxide] hafnium and zirconium complexes for olefin polymerization

“…After oxidation, the 31 P NMR signal was shifted significantly from À21 to 35 ppm. The 1 H, 13 C, 31 P NMR and IR spectra were in agreement with the expected structures. When the phosphine compounds were treated with sulfur in toluene, the desired phosphine sulfide compounds 4, 6, and 7 were also afforded in good yields (54e61%).…”

“…Single crystals of the tribenzyl hafnium complex of the sulfide ligand (13) were grown in a cosolvent comprising toluene and hexane at À35 C, and the structure of the complex was confirmed by X-ray crystallography (Fig. 1).…”

“…The IR spectrum was recorded from the solid itself using attenuated total reflection (ATR) FTIR. The 1 H NMR (400 MHz), 13 C NMR (100 MHz), and 31 P NMR (162 MHz) spectra were recorded on a Varian Mercury plus 400. Elemental analyses were carried out at the Analytical Center, Kyunghee University.…”

“…), 1.05 (d, J ¼ 6.4 Hz, CH 3 ) ppm 13. C{ 1 H} NMR (C 6 D 6 ): d 157.04 (d, J PC ¼ 32 Hz), 150.63, 133.82, 133.55 (d, J PC ¼ 2.2 Hz), 132.74 (d, J PC ¼ 2.2 Hz), 132.17 (d, J PC ¼ 12 Hz), 130.55, 128.53, 128.17, 126.73, 126.01, 124.12, 121.47 (d, J PC ¼ 9.9 Hz), 120.91, 119.48, 119.10 (d, J PC ¼ 2.3 Hz), 119.06, 68.91, 63.29 (d, J PC ¼ 9.1 Hz), 45.60 (d, J PC ¼ 4.6 Hz), 26.34, 22.59, 19.28 ppm.…”

“…ppm 13. C{ 1 H} NMR (C 6 D 6 ): d 158.16 (d, J PC ¼ 3.8 Hz), 147.22, 135.59, 133.33 (d, J PC ¼ 14 Hz), 133.09 (d, J PC ¼ 2.3 Hz), 132.70 (d, J PC ¼ 11 Hz), 128.91 (d, J PC ¼ 13 Hz), 128.62, 128.44, 127.53, 121.50, 117.06 (d, J PC ¼ 6.9 Hz), 116.92 (d, J PC ¼ 14 Hz), 114.69, 113.58, 80.62,…”