2-Hetaryl-Substituted Bis(indenyl)zirconium Complexes as Catalyst Precursors for Elastomeric Polypropylene Formation

Abstract

2-Indanone was treated with 2-lithio-5-methylfuran and the addition product dehydrated to yield the 2-(5‘-methyl-2‘-furyl)-substituted indene 2 . Deprotonation with n -butyllithium followed by transmetalation to zirconium gave the bis(2-furylindenyl)ZrCl 2 complex 4a . Subsequent reaction with methyllithium yielded the corresponding bis(2-furylindenyl)ZrMe 2 system 6a . The related bis[2-(5‘-methyl-2‘-furyl)indenyl]hafnium complexes ( 5a, 7a ) and the bis[2-(5‘-methyl-2‘-thienyl)indenyl]zirconium and -hafnium complexes 4b − 6b were synthesized analogously. In the crystal the bis(2-furylindenyl)ZrCl 2 ( 4a ) and -HfCl 2 ( 5a ) complexes exhibit meso -like metallocene conformations, as shown by X-ray diffraction. In contrast, the bis(2-furylindenyl)ZrMe 2 system ( 6a ) shows a chiral, close to C 2 -symmetric rac -like metallocene conformation in the solid state. Hydrolysis of 2-(5‘-methyl-2‘-furyl)indene ( 2a ) followed by Paal−Knorr pyrrole synthesis of the resulting 1,4-diketone 8 with methylamine gave (5‘-methyl-2‘- N -methylpyrrolyl)indene ( 9 ), which was deprotonated and transmetalated to yield the substituted bis(2-pyrrolylindenyl)ZrCl 2 ( 11 ), -HfCl 2 ( 12 ), and -ZrMe 2 ( 13 ) complexes. Treatment of the [2-(5‘-methyl-2‘-furyl)indenyl]- and [2-(5‘-methyl-2‘-thienyl)indenyl]ZrCl 2 systems 4a, b with excess methylalumoxane gave active homogeneous Ziegler catalysts for the production of elastomeric polypropylene. The catalyst derived from 11 yielded only propene oligomers.