Organometallic complexes, transition metal chromium

A large number of organometallic compounds are based on transition metals Examples include organic derivatives of iron nickel chromium platinum and rhodium Many important industrial processes are catalyzed by transition metals or their complexes Before we look at these processes a few words about the structures of transition metal complexes are m order... 

Recently some information became available on a new type of highly active one-component ethylene polymerization catalyst. This catalyst is prepared by supporting organometallic compounds of transition metals containing different types of organic ligands [e.g. benzyl compounds of titanium and zirconium 9a, 132), 7r-allyl compounds of various transition metals 8, 9a, 133), 7r-arene 134, 185) and 71-cyclopentadienyl 9, 136) complexes of chromium]. 

The synthetic potential of transition metal atoms in organometallic chemistry was first demonstrated by the formation of dibenzenechrom-ium (127). Apart from chromium, Ti, V, Nb, Mo, W, Mn, and Fe atoms each form well-defined complexes with arenes on condensation at low temperatures. Interaction has also been observed between arenes and the vapors of Co, Ni, and some lanthanides. Most important, the synthesis of metal-arene complexes from metal vapors has been successful with a wide range of substituted benzenes, providing routes to many compounds inaccessible by conventional reductive preparations of metal-arene compounds. 

The works by Volpin and Shur [160] as well as by Shilov [161] on molecular nitrogen fixation via complexing with transition metals indicates nitrogen readily reacting with low-valence organometallic compounds of titanium, chromium, molybdenum, wolfram and iron. 

Apart from the metal atom aggregation reactions described below, bis(arene)metal complexes of the early transition metals are resistant to ligand displacement The rings on the corresponding bis(naphthalene)metal species (41) are by, contrast, labile. Polymer-supported analogs of these naphthalene compounds with vanadium and chromium are known (42), but Ti atoms attack the polymer at the silicon ether linkage. These and other hybrid polymers can be further modified once the metal atom is incorporated. Thus a-methyl naphthalene is displaced from the hybrid organometallic polymer shown in Scheme 7 (43). 

Many cation-exchanged clays are suitable for the production of metal-oxide-pillared clays. The hydrolysis of the cation helps the pillaring step, so, at first, the aluminum ion was applied as a pillaring agent. Later, other elements were also used, for example, zirconia chromium iron transition metal elements and some lantanoids, organometallic complexes, surfactants, and polymers. 

Chromium Organometallic Chemistry Coordination Organometallic Chemistry Principles Magnetism of Transition Metal Ions Metal Ion Toxicity Nutritional Aspects of Metals Trace Elements Oxidation Catalysis by Transition Metal Complexes. 

Reactions of metal carbonyls with Zintl phases do not always yield the desired result. An example is the reaction of KSi with the metal carbonyls M(CO)6 (M = Cr, Mo, W) and the chromium complex Cr(CO)sNMe3. Instead of forming a structure with a Si4 anion, KSi reduces these transition metal compounds to form the anions, [M2(CO)io] . In addition, certain organometallic transition metal clusters have been synthesized that contain Zintl anions coordinated to the metal, but Zintl compounds are not used as the reagents. 

Chromium, molybdenum, and tungsten are the transition metals in Group 6 of the periodic table. Chromium metal has the outer electronic configuration. W54,yl and forms compounds in oxidation states II- to VI+.1 The extensive organometallic chemistry of Cr is covered in the accompanying Comprehensive Organometallic Chemistry series, and this review is generally restricted to the coordination complexes (oxidation states 0 to VI+). 

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