Zirconocenes and hafnocenes with boron-substituted cyclopentadie

Details Zirconocenes and hafnocenes with boron-substituted cyclopentadie Zirconocenes and hafnocenes with boron-substituted cyclopentadie

1998-04-16

1999-10-05

Leary, Louise N.

Organic compounds -- part of the class 532-570 series

Organic compounds

Heavy metal containing

556 7, 556 11, 556 1, C07F 700

Patent

active

059627182

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a generally applicable synthetic method for the preparation of as yet unknown zirconocenes and hafnocenes bearing a boron-containing substituent directly on the cyclopentadienyl ligand. These compounds will be used in a novel application in the polymerization of olefins with cocatalysis by aluminum alkyl compounds.
A wide variety of metallocene-based catalyst systems is known from the literature. They all share the necessity of a cocatalyst which converts the metallocene to an active form capable of polymerizing olefins. According to a generally accepted idea, a zirconium cation is generated thereby.


PRIOR ART

Metallocenes are usually activated as dichloride compounds with a large excess (1000-10,000:1) of methylalumoxane (MAO) (V. K. Gupta, S. Satish, I. S. Bhardwaj, J. M. S.--Rev. Macromol. Chem. Phys. 1994, C34(3), 439-514). MAO-free systems are based on the use of dialkylmetallocenes with "cationizing reagents". Good polymerization properties are only exhibited by "ligand-free" systems (R. F. Jordan, Adv. Organomet. Chem. 1991, 32, 325). Common cationizing reagents are ammonium compounds (H. W. Turner, Eur. Pat. Appl. 277004), acidic carboranes (D. J. Cowther, N. C. Baenziger, R. F. Jordan, J. Am. Chem. Soc. 1991, 113, 1455), boron Lewis acids (A. R. Siedle, R. A. Newmark, W. M. Lamanna, J. C. Huffman, Organometallics 1993, 12, 1491; X. Yang, C. L. Stern, T. J. Marks, J. Am. Chem. Soc. 1991, 113, 3623) or tritylium salts (M. Bochmann, S. J. Lancaster, J. Organomet. Chem. 1992, 434, C1).
Drawbacks of these methods are the often insufficient stabilities of the metallocene alkyl compounds and of the mixtures with cationizing reagents. In addition, the dependence of polymerization activity on the amount of cationizing reagent and preactivation time is a complex relationship which is not understood in detail.
One possibility of circumventing the synthesis is an in situ alkylation method (W.-M. Tsai, M. D. Rausch, J. C. W. Chien, Appl. Organomet. Chem. 1993, 7, 71). However, this method causes an effective polymerization catalysis only if the order of additions and the preactivation time are precisely observed.
Metallocenes with borylated cyclopentadienyl ligands represent potential polymerization catalysts since the attachment of a strong Lewis acid should enable the subsequently performed formation of a zwitterionic compound through the conjugated .pi. system of the ligand. ##STR1##
Borylated zirconocenes and hafnocenes are not described in the literature. They cannot be successfully synthesized by common methods of metallocene synthesis (D. J. Cardin, M. F. Lappert, C. L. Raston, Chemistry of Organo-Zirconium and -Hafnium Compounds, Ellis Horwood Ltd., Chichester, 1986) since the treatment of borylated cyclopentadienes with bases or metalization reagents will result in a cleavage of the B--C bond.
The transfer of silylated cyclopentadienyl ligands to zirconium is known (K. W. Krebs, H. Engelhard, G. E. Nischk (Bayer AG), Ger. Offen. 1,959,322, 1971; Chem. Abstr. 1971, 75, P88768P, and C. Winter, X.-X. Zhou, D. A. Dobbs, M. J. Heeg, Organometallics 1991, 10, 210). By the method described therein, the corresponding borylated zirconocenes and hafnocenes can be synthesized from precursors which are both borylated and silylated.
A systematic approach to the borylated and silylated cyclopentadienes does not exist. Alkoxyboranes or amine adducts of alkylboranes can be introduced via metallated precursors (B. M. Mikhailov, T. K. Baryshnikova, V. S. Bogdanov, Dokl. Akad. Nauk SSSR 1972, 202, 358, and H. Grundke, P. I. Paetzold, Chem. Ber. 1971, 104, 1136). Haloboranes are obtainable through Si--B exchange, and alkoxyboranes are obtainable through Sn--B exchange (P. Jutzi, A. Seufert, J. Organomet. Chem. 1979, 169, 327).
No generally applicable method exists for the synthesis of alkylboranes.
The above results have now been extended to a generally applicable method for the synthesis of zirconocenes and hafnocenes.
Starting from cyclopentadienes and substituted cyclopentadienes (s

REFERENCES:
patent: 5169818 (1992-12-01), Antberg et al.
patent: 5262498 (1993-11-01), Antberg et al.
patent: 5468889 (1995-11-01), Srebnik et al.
Bochmann et al; J. Chem. Soc., Chem. Commun; 1995; p. 2081.

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