Organometallic compounds of chromium

Table 26. Selected bond enthalpy contributions, D (M-L) and (M-L) kJ mol-1, in organometallic compounds of chromium, manganese, iron cobalt and nickel and related compounds (An asterisk ( ) denotes the average value in a series)...

There are many examples of organometallic compounds of chromium in oxidation states -II to III. 

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]. 

A78. M. J. Udy, ed., Chromium, ACS Monograph No. 132. Reinhold, New York, 1956. Volume 1 Chemistry of chromium and its compounds. Chapter 6, M. C. Udy The physical and chemical properties of compounds of chromium. The last section, pp. 240-246, organometallic chromium compounds, is almost entirely concerned with a discussion of polyphenylchromium compounds, at the time of writing not recognized as bis-7r-arenechromium derivatives. 

The spectrum of the organometallic compound dimesitylene chromium, [C Hj(CHs)3]2Cr, has relatively high amplitude. The location of the principal peak, 18 ev., corresponds to that of divalent chromium. 

The extensive organometallic chemistry of chromium, i.e. the hexacarbonyl and its derivatives, organochromium compounds without carbonyl ligands, cyanide and isocyanide complexes, alkene, allyl, diene, cyclopentadiene and arene derivatives, and complexes of a-donor carbon ligands, has been recorded in Chapters 26.1 and 26.2 of Volume 3 of Comprehensive Organometallic Chemistry .1 In the present section, chromium complexes... 

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. 

Ziegler-Natta Catalysts (Heterogeneous). These systems consist of a combination of a transition metal compound from groups IV to VIII and an organometallic compound of a group I—III metal.23 The transition metal compound is called the catalyst and the organometallic compound the cocatalyst. Typically the catalyst is a halide or oxyhalide of titanium, chromium, vanadium, zirconium, or molybdenum. The cocatalyst is often an alkyl, aryl, or halide of aluminum, lithium, zinc, tin, cadmium, magnesium, or beryllium.24 One of the most important catalyst systems is the titanium trihalides or tetra-halides combined with a trialkylaluminum compound. 

Chromium complexes exist in a very wide range of formal oxidation states (-IV to +VI). The extremely low ones are stabilized by jr-acid ligands, notably carbon monoxide these are described in the article on organometallic compounds (see Chromium Organometallic Chemistry). The extensive coordination chemistry of Cr spans coordination numbers 3-7, but is dominated by octahedral complexes. Complexes of... 

There are also catalysts known in which ACs are formed during the direct interaction between the transition metal compound and the monomer without participation of special cocatalysts (so-called one-component catalysts). Examples of one-component catalysts are chromium oxide catalysts, lower halides of transition metals (titanium dichloride) and catalysts prepared by precipitating organometallic compounds of transition elements on oxide carriers... 

Cocondensation of metal vapor and organic ligands at liquid nitrogen temperature has proved to be a very useful method for preparing organometallic compounds of the first-row transition elements 409), as exemplified by the synthesis of bisbenzene chromium 408) ... 

This class of organometallics originates from chemistry of the chromium-carbon bond developed only within the last two decades.Illustrative of this fact is the observation that a comprehensive reference published in 1982 makes no mention of compounds of chromium (III) bearing both cyclopentadienyl and alkyl ligands. Within this class are... 

The most commonly used transition metal compounds are those of titanium, vanadium, chromium, and zirconium. The transition metal-carbon bond is formed by the action of an organometallic compound of the main group elements, leading to the formation of the complex which has catalytic properties. 

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... 

Organometallic Complexes. The range of chromium(iii) o-bonded carbon derivatives has been extended this year. Treatment ofCr(OBu )4 with RMgX (R = Me, Et, Ph, or mesityl) affords CrR3 via the corresponding CrR4 compound. Tris(2,2,3-trimethylbicyclo[2,2,l]hept-l-yl)chromium (67) has been obtained... 

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