Organometallic compounds ligands

Precursor of Useful Chiral Ligands. OPEN is widely used for the preparation of chiral ligands. Organometallic compounds with these ligands act as useful reagents or catalysts in asymmetric induction reactions such as dihydroxylation of olefins, transfer hydrogenation of ketones and imines, Diels-Alder and aldol reactions, desymmetrization of meso-diols to produce chiral oxazolidinones, epoxidation of simple olefins, benzylic hydroxylation, and borohydride reduction of ketones, imines, and a,p-unsaturated carboxylates. ... 

The preparation and structure determination of ferrocene marked the beginning of metallocene chemistry Metallocenes are organometallic compounds that bear cyclo pentadiemde ligands A large number are known even some m which uranium is the metal Metallocenes are not only stucturally interesting but many of them have useful applications as catalysts for industrial processes Zirconium based metallocenes for example are the most widely used catalysts for Ziegler-Natta polymerization of alkenes We 11 have more to say about them m Section 14 15... 

Zirconium tetrachloride is instantly hydrolyzed in water to zirconium oxide dichloride octahydrate [13520-92-8]. Zirconium tetrachloride exchanges chlorine for 0x0 bonds in the reaction with hydroxylic ligands, forming alkoxides from alcohols (see Alkoxides, METAl). Zirconium tetrachloride combines with many Lewis bases such as dimethyl sulfoxide, phosphoms oxychloride and amines including ammonia, ethers, and ketones. The zirconium organometalLic compounds ate all derived from zirconium tetrachloride. 

P. Skinner, M. W. Howard, I. A. Oxton, S. F. A. Ketde, D. B. Powell, and N. Sheppard./ Chem. Soc., Faraday Trans. 2,1203, 1981. Vibrational spectroscopy (infrared) studies of an organometallic compound containing the ethylidyne ligand. 

In recent years this simple picture has been completely transformed and it is now recognized that the alkali metals have a rich and extremely varied coordination chemistry which frequently transcends even that of the transition metals. The efflorescence is due to several factors such as the emerging molecular chemistry of lithium in particular, the imaginative use of bulky ligands, the burgeoning numbers of metal amides, alkoxides, enolates and organometallic compounds, and the exploitation of multidentate... 

In the case of organometallic compounds the most satisfactory way of classifying the ligands... 

Organometallic compounds apart, oxidation states below - -2 are best represented by complexes with tris-bidentate nitrogen-donor ligands such as 2,2 -bipyridyl. Reduction by LiAlH4 in thf yields tris(bipyridyl) complexes in which the formal oxidation state of vanadium is -1-2 to —1. Magnetic moments are compatible with low-spin configurations of the metal but. 

Besides [Ni(CO)4] and organometallic compounds discussed in the next section, nickel is found in the formally zero oxidation state with ligands such as CN and phosphines. Reduction of K2[Ni (CN)4] with potassium in liquid ammonia precipitates yellow K4[Ni (CN)4], which is sensitive to aerial oxidation. Being... 

Furan is typically tiVC) coordinated in a series of organometallic compounds. However, it is its ti (C=C) coordination that opened a perspective toward a broad series of derivatized furans. It can be a bridging ligand forming (C=C)... 

The ethylene polymerization was observed (9a) also in the presence of c-organometallic compounds of titanium and zirconium, containing such ligands as -CH i(CH3) , -CH(C H6)Si(CH3)3, -CH2C(CH3)3,... 

Here M is the transition metal and L are other ligands of the initial organometallic compounds. In this case individual organometallic compounds are considered to be true catalysts, and the question of the dependence of the polymerization rate on the character of metal-ligand bonds in the initial organometallic compounds is discussed (123). 

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 participation of siloxane groups in the reaction increases with the temperature of dehydration of Si02 and quantity of organometallic compound introduced in the reaction. According to the data of infrared spectroscopy (139), the allyl ligands formed in the surface organometallic complexes of Ni and Cr keep the 7r-allyl character of the metal-ligand bond. 

The availability of organic ligands in the surface complexes obtained by the reaction of organometallic compounds with supports allows us to consider two possibilities of the initiation process (1) the monomer insertion into the organic ligand-metal bond (bensyl, allyl, etc.) (9a) ... 

As with the reduction of aldehydes and ketones (16-23), the addition of organometallic compounds to these substrates can be carried out enantioselectively and diastereoselectively. Chiral secondary alcohols have been obtained with high ee values by addition to aromatic aldehydes of Grignard and organolithium compounds in the presence of optically active amino alcohols as ligands. ... 

Study of the recoil chemistry of organometallic compounds for its own sake, began really in 1955 with the publication of a study (56) by Mad-dock and Sutin on neutron activation of triphenylarsene. Since this time, most of the published work has been focussed on those radioactive atoms which did not permanently escape their ligands. Thus, in one way or another, they end up in molecular form. It is with these that this review is largely concerned. 

The second edition of the well-known Red Book, the definitive recommendations of the lUPAC Commission on Nomenclature of Inorganic Chemistry, appeared in Pure Appl. Chem., 28, 1-110 (1971). It is also available separately as a hard-bound reprint. In this edition, the rules for naming organometallic compounds have been completely revised and extended, with introduction of the rj nomenclature for organic ligands. 

A discussion of ligand exchange reactions of organometallic compounds associated with oxidation-reduction processes leading to free-radical formation will be found in Volume 14 (Free-radical polymerization). 

The key to the successful development of homogeneous catalysts has been the exploitation of the effects that ligands exert on the properties of metal complexes by tailoring the electronic and steric properties of a catalytically active metal complex, activities and selectivities can be altered considerably. This especially holds for phosphorus based ligands, which are the most commonly encountered ligands as.sociated with organometallic compounds. 

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