Simple Route to Bis(3-indenyl)methanes and the Synthesis, Characterization, and Polymerization Performance of Selected racemic-Dichloro[methylenebis(Rn-1-indenyl)]-zirconium Complexes

A large range of bis(R-n-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 Ca-symmetric rac-dichloro[methylenebis(eta(5)-1-indenyl)]zirconium (1) and rac-dichloro[methylenebis(4,7-dimethyl-eta(5)-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 degrees 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).