Metallocene dichloride, group

Most of the Group 4 dehydrocoupling catalysts just listed are photochemi-cally and/or thermally unstable with short shelf lives at room temperature. They are also generally not commercially available and have to be synthesized from a metallocene dichloride. There are, therefore, obvious advantages to catalysts that can be generated in situ. Corey and co-workers49,50... 

Dialkyl metallocenes and other dialkyl Group 4 transition metal complexes are useful as precatalysts in combination with co-catalysts such as tris(perfluoro-aryl)boranes or tetrakis(periluoroaryl)borate salts [18]. Recently, an expedient procedure for the production of dimethyl metallocenes and Cp-amido dimethyl metal complexes in high yields and purity has been reported. The direct synthesis of Group 4 dimethylmetallocenes [19] consists of the one-pot reaction between the r-ligand, a 2-fold excess of MeLi, and MtCU. This simple method produces the dimethylated complexes in higher overall yield, and saves on reaction time and solvents, compared to the classic two-step route, which consists in the synthesis of the metallocene dichloride followed by its methylation with 2 equiv. MeLi. 

The reduction potential of a metallocene dichloride complex is one indicator of the electron density at the metal center. A systematic study of the one-electron reduction potential for the series (C5H5 Me )2ZrCl2 ( = 0 — 4) revealed a shift to more negative potential by 0.071 V per methyl group. The deviation from this trend for n = 5 was... 

Vitamin K3, progesterone, and androstadienedione were converted to their dioximes. These dioximes were reacted with Group IVB metallocene dichlorides forming products with the... 

Titanium tetrachloride has been studied in the hydrodefluorination reaction of trifluorotoluene derivatives in the presence of lithium aluminium hydride as hydride source, giving excellent yields. Rieger et al. studied group (iv) metallocenes dichlorides in carbon-fluorine activation reactions and they found higher catalytic activities for zirconocene and hafnocene complexes compared to the titanocene complex probably due to the tendency toward reduction of titanium(iv). ... 

If, however, one of the trimethylsilyl groups in the tris(trimethylsilyl)silylanion reagent is replaced by methyl, the reaction with the metallocene dichlorides does not work cleanly any more. 

The reason for this seems to be the enhanced reduction properties of the silyl anion, which are caused by the removal of a charge-stabilizing group. This called for a reactivity moderation, which can easily be accomplished via the transmetallation of potassium against magnesium [6], The reagent obtained then reacts smoothly with the metallocene dichloride (Scheme 2). 

HPIX is a macrocycUc tetrapyrrole structure with four methyl, two propionic acid, and two ethanolic sidechains. The two propionic acid and two ethanolic chains react with Group IVB metallocene dichlorides, giving crosslinked polymers as 11. 

In the present study Ni ion is being absorbed. The adsorbent species (solid phase) are the three Group IVB products obtained from the interfacial polycondensation reaction between HPIX and the Group IVB metallocene dichlorides " and two commercially available ion exchange resins. Adsorption is the physical or chemical bonding to the surface. 

FIGURE 4.1 Group 4 metallocenes can be unlinked, singly linked, or doubly linked. These metallocene dichloride complexes are common precatalysts for olefin polymerization. 

RCM was also efficiently performed for 16-electron, early transition metal metallocene dichlorides. Two research groups concurrently [15, 25] reported the intramolecular Ru-catalyzed reactions of bis(cyclopentadienylalkenyl) group IV bent metallocene derivatives shown on Scheme 12.17. 

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