Synthesis, characterization, and polymerization properties of bis(2-menthylindenyl)zirconium dichloride and bis(2-menthyl-4,7-dimethylindenyl)zirconium dichloride

The tetrakis(triphenylphosphine)palladium-ca cross coupling of 2-bromoinden e or 2-bromo-4,7-dimethylindene with menthylmagnesium chloride gave the nov el ligands 2-menthylindene (10) and 2-menthyl-4,7-dimethylindene (11) in 66 and 57% yields. These indenes were deprotonated with n-BuLi to give isolat ed indenyllithium complexes which were metalated with zirconium tetrachlori de to give bis(2-menthylindenyl)zirconium dichloride (14) and bis(2-menthyl -4,7-dimethylindenyl)zircon dichloride (15) in 40 and 66% yields. Both comp lexes formed as their single possible stereoisomer and were characterized b y X-ray crystallography and MS, NMR, and IR spectroscopy. The variable-temp erature H-1 NMR spectrum of bis(2-menthyl-4,7-dimethylindenyl)zircon dichlo ride (15) showed that it interconverts with a rotational activation barrier of about 12.5 +/- 0.5 kcal/mol, and that a 60:40 mixture of Ca-symmetric d iastereomeric conformations was present at -50 degreesC. The H-1 NMR spectr um of bis(2-menthylindenyl) zirconium dichloride (14) was invariant between -50 and +50 degreesC. Complexes 14 and 15 polymerized propene in the prese nce of methylaluminumoxane (MAO) and hydrogen (10 960 and 33 750 g PP/g Zr h, respectively). The molecular weights and stereoregularity of the polymer s produced were low.