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The synthesis and propene polymerization performance of the novel rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2 (2) and rac-[CH2(3-tert-butyl-1-indenyl)2]ZrMe2 (2-Me2) are described. The ligand precursor, bis(1-tert-butyl-3-indenyl)methane (L2), is obtained in ca. 80% conversion from the condensation of 3-tert-butylindene and formaldehyde in DMF at room temperature and is isolated as a yellow powder by washing with pentane. Red 2 is obtained in 50−60% yield and free from its meso stereoisomer by reacting an Et2O solution of the ligand dianion, (L2)Li2(Et2O)x, with a slurry of ZrCl4 in either pentane or toluene. Yellow 2-Me2 is prepared in 90% yield by reaction of 2 with excess MeMgCl in toluene. Alternatively, 2-Me2 (contaminated with about 5% of its meso isomer) can be obtained directly from the ligand L2, by reacting L2 in Et2O with 4 equiv of MeLi and then 1 equiv of ZrCl4 in toluene. Both 2 and 2-Me2 are remarkably soluble in pentane (2, ca. 1.7 g/L; 2-Me2, ca. 13 g/L) and toluene (2, ca. 50 g/L). 2/MAO and 2-Me2/MAO polymerize liquid propene with good activities to highly isotactic (mmmm = 95−98%), fully regioregular polypropene with medium-high molecular weights (&Mmacr;w = 70 000−780 000) and high melting points (Tm = 154−163 °C) in the Tp range 30−70 °C. The behavior of 2 is compared to that of the prototypical Montell zirconocene rac-[Me2C(3-t-Bu-Ind)2]ZrCl2 (1). 2 is the first example of a highly efficient and at the same time simple and inexpensive zirconocene catalyst for isotactic polypropene. The molecular structures of 2 and its Hf analogue (Hf-2) have been determined and compared to that of 1.

A large range of bis(Rn-3-indenyl)methanes were obtained in good to fair yields with the base-catalyzed condensation between formaldehyde and (substituted) indenes. For example, bis(indenyl)methane and bis(4,7-dimethylindenyl)methane have been synthesized in 70% and 50% yield, respectively, from the corresponding indenes. Typical reaction conditions are as follows:  indene in DMF or DMSO, 0.5 equiv of CH2O, 0.2−0.5 equiv of EtONa, room temperature. This process provides an inexpensive and atom-efficient protocol for the synthesis of methylene-bridged ligands, providing a facile entry into methylene-bridged ansa-zirconocenes:  MAO-activated C2-symmetric rac-dichloro[methylenebis(η⁵-1-indenyl)]zirconium (1) and rac-dichloro[methylenebis(4,7-dimethyl-η⁵-1-indenyl)]zirconium (2) polymerize ethylene to low molecular weight, vinyl-terminated linear polyethylene, and liquid propylene to low molecular weight, low isotacticity polypropylene. The microstructure, molecular weight, and end-group structure of these isotactic polypropylenes (i-PP) are compared to those from rac-[isopropylidenebis(1-indenyl)]ZrCl2 (3), rac-[ethylenebis(1-indenyl)]ZrCl2 (4), rac-[ethylenebis(4,7-dimethyl-1-indenyl)]ZrCl2 (5), and the silicon-bridged rac-[dimethylsilylbis(1-indenyl)]ZrCl2 (6). The molecular structures of 1 and 2 have been determined and compared to those of 3−6. In liquid monomer at 50 °C, the amount of secondary insertions increases on going from the more open to the more hindered systems. At the same time, there is an increase of the fraction of secondary units undergoing isomerization from the normal 2,1 unit to the 3,1 unit (tetramethylene sequence).

The known rac-[ethylenebis(4,7-dimethyl-η⁵-1-indenyl)]ZrCl2 (2r) and its meso isomer (2m) have been compared with the prototypal chiral isospecific rac-[ethylenebis(η⁵-1-indenyl)]ZrCl2 (1r) and its aspecific meso isomer 1m in terms of molecular structures, solution dynamics, and ligand substitution effect on polymerization performance. In liquid propene at 50 °C, 2r/MAO produces iPP with appreciably higher isotacticity but lower molecular weight and regiospecificity than 1r/MAO. The lower molecular weight obtained with 2r in liquid monomer is due to predominant chain transfer to the monomer after a secondary propene insertion, producing >90% cis-2-butenyl− end groups. At lower propene concentration, 2r/MAO allows both β-hydrogen transfer after a primary insertion and β-methyl transfer. The low-activity 2m/MAO catalyst produces low molecular weight aPP. The diastereoselective synthesis of 2r,m via the corresponding rac- and meso-bis(4,7-dimethyl-1-(trimethylsilyl)-3-indenyl)ethane is reported. The crystal and molecular structures of meso-bis(4,7-dimethyl-1-(trimethylsilyl)-3-indenyl)ethane, 2r,m, have been determined.