Ansa-metallocene complexes

A scandium complex, Cp ScH, also polymerizes ethylene, but does not polymerize propylene and isobutene [125]. On the other hand, a linked amidocyclo-pentadienyl complex [ Me2Si( / 5-C5 Me4)( /1 -NCMe3) Sc(H)(PMe3)] 2 slowly polymerizes propylene, 1-butene, and 1-pentene to yield atactic polymers with low molecular weight (Mn = 3000-7000) [126, 115]. A chiral, C2-symmetric ansa-metallocene complex of yttrium, [rac-Me2Si(C5H2SiMe3-2-Buf-4)2YH]2, polymerizes propylene, 1-butene, 1-pentene, and 1-hexene slowly over a period of several days at 25°C to afford isotactic polymers with modest molecular weight [114]. 

The butadiene ligand in the Group 4 metallocene complexes is very reactive towards olefins attached at the Cp rings. A typical example is the system 9 that instantaneously reacts further to yield 10 when generated from 8 (see Scheme 4). In contrast, the unsaturated (butadiene)ansa-metallocene complexes s-cis-13 and s-trans-13 are stable when prepared from 12 under similar conditions.15 Complex 12 was obtained by a ring closing olefin metathesis reaction from 11. 

The ansa-metallocene complex (CpCMe2Flu)Nd(C3H5)(THF) is an effective single-component catalyst for the production of syndiotactic styrene-rich co-polymer materials modified by isoprene and/or ethylene. The properties of the final polymer could be tuned by altering the monomer ratio.55... 

The catalysts are Tim hydrides which are generated in situ by reduction of enantio-merically pure L TiCl2 with butyllithium and PhSiH3 they are also highly effective in the asymmetric hydrogenation of imines and enamines.20 The lutetium ansa-metallocene complex (22-XVII) catalyzes the deuteration of 1-pentene (63% e.e.)21 Related samarium compounds hydrogenate imines.22... 

Jordan and coworkers have recently prepared several ansa-bis(indenyl) compounds (AlMe2L)indenyl 2SiMe2 and 1,2- (AlMe2L)indenyl 2C2H4 (L = THE, Et20, 1,4-dioxane) by a salt metathesis route. These were reacted with M(NMc2)4 (M = Zr, Hf) to eliminate [Me2AlNMc2]2 and form ansa-metallocene complexes of bis(dimethylamido)zirconium and bis(dimethylamido)hafmum. A simple tris(indenyl)aluminum compound has been prepared by reaction of bis(indenyl)mer-cury with aluminum metal. ... 

Boron-bridged group-4 ansa-metallocene complexes 01EJI321. 

Substituents at the Fluorenyl Fragment in ansa-Metallocene Complexes of the Type (Flu -CMe2-Cp)ZrCl2... 

In most cases the catalyst precursor is a metallocene dichloride complex consisting of two aromatic five-membered ring systems that can be tethered by a bridging unit ansa metallocene complexes) or not. The two aromatic ligands at the metal can be of the same type. i.e.. cyclopentadienyl. indenyl. or fluorenyl. The introduction of substituents at certain positions of the two aromatic ligands and/or the bridge modifies not only the steric and electronic conditions in the molecule but also the symmetry of such a metallocene dichloride complex. Another variable parameter is the metal M = Ti. Zr. Hf. 

In this review, no ansa metallocene complexes with indenyl ligands are incorporated due to the already existing comprehensive literature. Furthermore, it would have been necessary to repeat all polymerization experiments with these complexes in order to obtain results for a comparison with the already established parameters. 

Ansa-metallocene complexes have been studied for olefin polymerization, e.g., polymerizing i-PP with an ansa-titanocene. The bridged ligands change the catalysts and the polymer structures, also affecting MW and MWD... 

Group 4 Phosphorus-Bridged ansa-Metallocene Complexes. 145... 

The following abbreviations are used for the n-ligands of the ansa-metallocene complexes cyc-lopentadienyl (Cp), substituted cyclopentadienyl (Cp ), indenyl (Ind), 2-methyl-4-phenyl-indenyl (2-Me-4-PhInd), and fluorenyl (Flu). 

A boron bridge offers more functionality than silicon or carbon bridges to the chemistry of group 4 ansa-metallocene complexes because it can reversibly bind a variety of Lewis basic moieties that are designed to influence the electronic and stereochemical properties of the complex. By coordinating an anionic Lewis base, the boron can potentially serve as an internal, counteranion to the catalytically active, cationic group 4 metal alkyl, as in the hypothetical zwitterionic complex shown in Figure 5.1. The polymerization activity of the zwitterionic catalyst should benefit from the remote location of the counteranion from the active site, where it will not compete with the alkene monomer for a coordination site on the metal. 

GROUP 4 DONOR-ACCEPTOR-BRIDGED ANSA-METALLOCENE COMPLEXES... 

Abstract The development of a sa-metallocene catalysts is considered along several lines of interest - ansa-metallocene complexes with different ligand frameworks, insights gained with regard to relevant reaction intermediates and contributions of ansa-metallocene catalysts to industrial polymer production -with a view toward the present state of the art in these fields of catalysis research. 

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