Simple route to bis(3-indenyl)methanes and the synthesis, characterization, and polymerization performance of selected racemic-dichloro[methylenebis(R-n-1-indenyl)]-zirconium complexes

A large range of bis(R-n-3-indenyl)methanes were obtained in good to fair y ields with the base-catalyzed condensation between formaldehyde and (substi tuted) indenes. For example, bis(indenyl)methane and bis(4,7-dimethylindeny l)methane have been synthesized in 70% and 50% yield, respectively, from th e 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 temperatur e. This process provides an inexpensive and atom-efficient protocol for the synthesis of methylene-bridged ligands, providing a facile entry into meth ylene-bridged ansa-zirconocenes: MAO-activated Ca-symmetric rac-dichloro[me thylenebis(eta(5)-1-indenyl)]zirconium (1) and rac-dichloro[methylenebis(4, 7-dimethyl-eta(5)-1-indenyl)]zirconium (2) polymerize ethylene to low molec ular weight, vinyl-terminated linear polyethylene, and liquid propylene to low molecular weight, low isotacticity polypropylene. The microstructure, m olecular 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 c ompared to those of 3-6. In liquid monomer at 50 degrees C, the amount of s econdary insertions increases on going from the more open to the more hinde red systems. At the same time, there is an increase of the fraction of seco ndary units undergoing isomerization from the normal 2,1 unit to the 3,1 un it (tetramethylene sequence).