Zwitterionic Metallocenes

Abstract

Ion pairing in cationic metallocenes capable of the polymerization of olefins affects the activity of these catalysts. One strategy for minimizing ion ± ion contacts is the preparation of zwitterionic analogues of the catalysts in which the counterion is affixed covalently to the ancillary or reactive ligand structure of the molecule. The concepts behind the varied synthetic approaches taken to three families of zwitterionic metallocenes, classified by the location of the counterion in the molecular structure, are discussed.

Reactivity of Metallocene Catalysts for Olefin Polymerization: Influence of Activator Nature and Structure

“…Another strategy towards controlling the ionic interactions is the use of zwitterionic analogs in which the counterion is attached covalently to the cationic species. [169] Zwitterionic complexes are active in olefin polymerization as they dissociate into ion pairs to form the active species. B(C 6 F 5 ) 3 reacts with one of the terminal butadiene carbon atoms of Cp 2 Zr(g 4 -butadiene) (67) to form the cationic (p-allyl)zirconocene complex 68, which is stabilized by the interaction between one of the ortho-C-F groups and the Zr center.…”

Zwitterionic complexes arising from the reaction of tucked-in titanocenes with tris(pentafluorophenyl)borane

“…The redox reaction of Ti(II) to Ti(III) is accompanied by elimination of the trimethylsilyl group [10b] (see Chart 1). The pendant double bonds attached to cyclopentadienyl rings were so far explored only sparingly: the allyl group at a cyclopentadienylamidozirconium complex was hydroborated by [BH(C 6 F 5 ) 2 ] [11], the allyldimethylsilyl group in dibenzylzirconocene was p-coordinated to a benzylzirconocene cation [12], x-alkenylpermethylzirconocene [13], and x-alkenyloxyzirconocene cations contained the pcoordinated double bond to the Zr cation [14].…”

Interaction of titanium(III) zwitterionic complex Cp[η5-C5H4B(C6F5)3]Ti with organic halides: Synthesis and X-ray crystal structure determination of zwitterionic titanocene monohalides Cp[η5-C5H4B(C6F5)3]TiX (X=Cl, Br) and their catalytic activity in the ring-opening polymerization of ε-caprolactone

“…The 1 H, 13 C and 11 B NMR spectra were recorded on a Bruker ARX-400 spectrometer, the 19 F NMR spectra were registered on a AC-250 spectrometer. 1 H and 13 C chemical shifts are given relative to TMS and are referenced to signals of the [D 6 ]benzene used (d H = 7.16 ppm, d C = 128.0 ppm); 19 F chemical shifts are given relative to CFCl 3 ; 11 B chemical shifts are given relative to BF 3 AE OEt 2 in CDCl 3 (N( 11 B) = 32.083971 MHz). The assignment of the NMR signals was conducted with the help of DEPT and shift correlation experiments.…”

“…Zwitterionic metallocenes of the Group IVB metals are of great interest as potential single-component catalysts for Ziegler-type olefin polymerization and other processes (see, e.g., reviews [1][2][3][4] and papers [5][6][7][8][9][10][11][12][13][14]). They represent uncharged analogues of the well-known cationic Group IVB metallocenes whose coordination and catalytic chemistry has received extensive development in the last decades (for reviews, see e.g., [15][16][17]).…”