Cobalt metallocene compounds

Probably the first report on the use of a metaUocene in zeolite synthesis dates back more than ten years [124]. In the past few years, however, essentially two groups reported on the influence (i.e. structure directing properties) of cobalt metallocene compounds in the synthesis of zeolites and zeolite-like materials [e.g. 125-128]. In none of these studies had a new framework topology been synthesized. However, very recently Balkus and coworkers reported the synthesis of the first fourteen-membered ring zeolite, which they called UTD-1 (University of Texas at Dallas No. 1) [129-132]. UTD-1 was synthesized with a quite unusual template, viz. with bis(pentamethyl-cyclopentadienyl)cobalt(III) hydroxide [129-132]. Both the essentially pure-silica version and high-silica derivatives have been prepared. A typical synthesis of the all-silica version com-... 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Because of their reversible electrochemical properties, ferrocene [biscyclopentadie-nyl-iron(II), FeCp2 and cobaltocenium [biscyclopentadienyl-cobalt(III), CoC p2 1 I are the most common electroactive units used to functionalize dendrimers. Both metallocene residues are stable, 18-electron systems, which differ on the charge of their most accessible oxidation states zero for ferrocene and + 1 for cobaltocenium. Ferrocene undergoes electrochemically reversible one-electron oxidation to the positively charged ferrocenium form, whereas cobaltocenium exhibits electrochemically reversible one-electron reduction to produce the neutral cobaltocene. Both electrochemical processes take place at accessible potentials in ferrocene- and cobaltocenium-containing compounds. 

Ferrocene is only one of a large number of compounds of transition metals with the cyclopentadienyl anion. Other metals that form sandwich-type structures similar to ferrocene include nickel, titanium, cobalt, ruthenium, zirconium, and osmium. The stability of metallocenes varies greatly with the metal and its oxidation state ferrocene, ruthenocene, and osmocene are particularly stable because in each the metal achieves the electronic configuration of an inert gas. Almost the ultimate in resistance to oxidative attack is reached in (C5H5)2Co , cobalticinium ion, which can be recovered from boiling aqua regia (a mixture of concentrated nitric and hydrochloric acids named for its ability to dissolve platinum and gold). In cobalticinium ion, the metal has the 18 outer-shell electrons characteristic of krypton. 

Other late transition metals used in special cases of hydrosilation include cobalt, iron, ruthenium (vide infra for reactions with alkynes), osmium, chromium, molybdenum, tungsten and copper. Metallocenes (see Metallocene Complexes) of early transition metals and lanthanides have also been found to catalyze the hydrosilation of a number of unsaturated compounds including alkenes and esters (vide infra). 

Cobalt and its heavier homologs form paramagnetic metallocenes Mcp2 (Tabele 9.14). Biscyclopentadienylcobalt(II) is relatively stable, while compounds of rhodium and iridium are stable only at low (liquid nitrogen) or high (above 393 K) temperatures in gaseous state. At room temperature, they dimerize to afford the diene-dienyl complexes (9.91). 

In addition, several metallocenes, [biscyclopentadienylmetal(II) derivatives] in which the metal atom does not have the inert gas configuration (those of vanadium, chromium, cobalt, and nickel are known). However, these compounds are much less stable and more reactive than the analogous ferrocene, in which the iron atom has the inert gas configuration. 

There are some examples of the use of so-called photobase generators in the preparation of polymers by anionic means. Photobase generators are compounds that produce bases upon irradiation with light, examples include cobalt complexes 0-acyloximines and benzyloxycarbonyl derivatives. PBGs are generally important in polymer science due to their application in photoinitiated transformation of polymeric materials and epoxy resins. Kutal et al. have reported the anionic polymerization of alkyl 2-cyanoacrylates initiated by anionic species upon the irradiation of group 8 metallocenes [YAM 98, YAM 99, YAM 00, SAN 02, BRI 02, DIN 03, SAN 05,... 

Similar divalent metallocene complexes of ytterbium, i.e., (Cp),Yb(base/ligand) y, were also shown to act as mild, one-electron reducing agoits toward transition metal carbonyl compounds such as Co2(CO)g (Tilley and Andarsen, 1981), CpCo(CO)2 (Boncella and Andersen, 1984) and other organometallic derivatives of cobalt. 

Metalcarbonyls, organo- s. Acyl-cobaltcarbonyl complexes Metal complex compounds cobalt porphyrin complexes complex salts manganese complex compounds, ar. metalcarbonyl, organo-metallocenes... 

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