A zirconium complex having two phenoxy-imine chelate ligands, bis[N-(3-tert-butylsalicylidene)anilinato]zirconium(IV)dichloride (1), was found to display a very high ethylene polymerization activity of 550 kg of polymer/mmol of cat‚h with a viscosity average molecular weight (M v ) value of 0.9 × 10 4 at 25 °C at atmospheric pressure using methylalumoxane (MAO) as a cocatalyst. This activity is 1 order of magnitude larger than that exhibited by Cp 2 ZrCl 2 under the same polymerization conditions. The use of Ph 3 CB(C 6 F 5 ) 4 / i-Bu 3 Al in place of MAO as a cocatalyst resulted in extremely high molecular weight polyethylene, M v 505 × 10 4 , with an activity of 11 kg of polymer/mmol of cat‚h at 50 °C. This M v value is one of the highest values displayed by homogeneous olefin polymerization catalysts. Complex 1, using Ph 3 CB(C 6 F 5 ) 4 /i-Bu 3 Al as a cocatalyst, provided a high molecular weight ethylene-propylene copolymer, M v 109 × 10 4 , with 8 kg of polymer/mmol of cat‚h activity at a propylene content of 20.7 mol %. X-ray analysis revealed that complex 1 adopts a distorted octahedral coordination structure around the zirconium metal and that two oxygen atoms are situated in trans position while two nitrogen atoms and two chlorine atoms are situated in cis position. DFT calculations suggest that the active species derived from complex 1 possesses two available cis-located sites for efficient ethylene polymerization. Changing the tert-butyl group in the phenoxy benzene ring enhanced the polymerization activity. Bis[N-(3-cumyl-5-methylsalicylidene)cyclohexylaminato]zirconium(IV)dichloride ( 7) with MAO displayed an ethylene polymerization activity of 4315 kg of polymer/mmol of cat‚h at 25 °C at atmospheric pressure. This activity corresponds to a catalyst turnover frequency (TOF) value of 42 900/s‚ atm. This TOF value is one of the largest not only for olefin polymerization but also for any known catalytic reaction. Ligands with additional steric congestion near the polymerization reaction center gave increased M v values. The maximum M v value, 220 × 10 4 using MAO, was obtained with bis[N-(3,5-dicumylsalicylidene)-2′-isopropylanilinato]zirconium(IV)dichloride (15). Thus, polyethylenes ranging from low to exceptionally high molecular weights can be obtained from these zirconium complexes by changing the ligand structure and the choice of cocatalyst.

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New titanium complexes 1−4 having two nonsymmetric bidentate pyrrolide−imine chelate ligands, [2-(RNCH)C4H3N]2TiCl2 (1, R = Ph; 2, R = Et; 3, R = n-hexyl; 4, R = cyclohexyl), are prepared in good yields from the lithium salt of the corresponding ligands and TiCl4. Complex 1 is suggested by DFT calculations to adopt a distorted-octahedral structure in which the two pyrrolide-N atoms are situated in trans positions, while the two imine-N atoms and the two Cl atoms are located cis to one another. The spatial disposition elucidated by X-ray crystallographic analysis of complex 1 is consistent with the preferred structure predicted by DFT calculations. The molecular structures of complexes 2 and 4 established by X-ray analyses are very similar to that of complex 1. DFT calculations suggest that an active species derived from complex 1, for ethylene polymerization, possesses cis-located active sites trans to the imine-N atoms. These complexes were investigated as ethylene polymerization catalysts. Using methylalumoxane (MAO) as a cocatalyst, these complexes display very high activities and produce high-molecular-weight polyethylenes. Among them, complex 4 exhibits the highest activity (14 100 kg of polymer/((mol of Ti) h) comparable to that of Cp2TiCl2 with a very high molecular weight (M v) value of 2 601 000. Alternatively, using Ph3CB(C6F5)4/i-Bu3Al as a cocatalyst, these complexes produce ultrahigh-molecular-weight polyethylenes (M v > 4 000 000) with high activities (1500−2000 kg of polymer/((mol of Ti)/h).

We study electronic structure of the ͑0001͒ surfaces of graphite with a rhombohedral stacking arrangement by performing the first-principles total-energy calculations based on the density functional theory. We find that ferrimagnetic spin polarization occurs on the ͑0001͒ surfaces of rhombohedral graphite. Detailed analyses of energy bands, spin densities, and wave-function distribution unequivocally reveal the nature of the ferrimagnetic spin polarization, which is associated with the peculiar surface-localized state that possesses the same characteristics as the edge-localized states of graphite flakes.