Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Metal hydrocarbyl compounds

A reaction which is rather new and not mentioned in older textbooks is the so-called o-bond metathesis. It is a concerted 2+2 reaction immediately followed by its retrograde reaction giving metathesis. Both late and early transition metal alkyls are prone to this reaction, but for d° early transition metals there is no other mechanism than o-bond metathesis at hand. Many similar reactions such as the reaction of metal alkyls with other HX compounds could be described as if they would follow this pathway, but the use of the term o-bond metathesis is restricted to those reactions in which one reacting species is a metal hydrocarbyl or metal hydride and the other reactant is a hydrocarbon or dihydrogen. In Figure 2.30 the reaction has been depicted. [Pg.48]

Many organometallic compounds are moisture sensitive, a particularly important class from the catalytic viewpoint being transition metal hydrocarbyl derivatives (Mn+Rn). These compounds have been used as catalysts for or have been postulated as catalytic intermediates in many olefin reactions such as polymerization, oligomerization, and olefin disproportionation (23). Recent work has shown that compounds containing... [Pg.222]

Since many of these compounds are strongly colored and react instantly with oxide surfaces, the accessible surface hydroxyl concentration can be estimated by visually titrating a known amount of dried support with the metal hydrocarbyl solution until the supernatant liquid remains colored. [Pg.223]

All manipulations involving either the preparation of the metal hydrocarbyl compounds or their examination were made with the complete exclusion of oxygen and water. [Pg.224]

Reaction of Metal Hydrocarbyl Compounds with Support Surfaces. [Pg.231]

Disproportionation of 1-hexene did not occur with the above metal hydrocarbyl compounds in the absence of supports. Conditions for these experiments were 24 hrs at room temperature followed by several hours at >—68°C (refluxing 1-hexene). The support materials themselves also failed to catalyze the disproportionation reaction. [Pg.236]

The effect of drying temperature on the available surface hydroxyl concentration of a silica is shown in Figure 8. A constant slurry concentration of 4% silica/toluene was used in these experiments. These results are comparable with other data (20, 62), and they indicate that the surface hydroxyl group concentration is reduced with increasing drying temperatures. The reaction of metal hydrocarbyl compounds with strained siloxane groups is illustrated in Reaction 4. [Pg.239]

Syndiotactic polystyrene was first obtained only recently by Ishihara et al. [5] in polymerisation with a homogeneous catalyst derived from a transition metal compound such as monocyclopentadienyltitanium trichloride and methylalu-minoxane in toluene. Since then, several authors have reported on the synthesis of syndiotactic polystyrene promoted by different catalysts based on metal hydrocarbyls such as benzyl compounds, half-sandwich metallocenes (e.g. monocyclopentadienyl, monopentamethylcyclopentadienyl and monoindenyl metal derivatives), metal alkoxides, metallocenes and some other compounds. These catalysts are commonly derived from titanium or zirconium compounds, either activated with methylaluminoxane or aluminium-free, such as those activated with tris(pentafluorophenyl)boron, and promote the syndiospecific polymerisation of styrene and substituted styrenes [5-10,21,48-70], Representative examples of the syndiospecific polymerisation of styrene using catalysts based on various titanium compounds and methylaluminoxane are shown in Table 4.2 [6,52,53,56,58],... [Pg.251]

Metal hydrocarbyl or hydride-activated catalysts are in principle susceptible to deactivation by reactions with traces of moisture and other protic compounds however, the activity of soluble catalysts can be enhanced in some instances by the addition of a protic compound as the third component [107], It is also worthy noting that soluble catalyst precursors can give, after activation with organometallic compounds, soluble or finely divided heterogeneous catalysts. [Pg.351]

Metallaboranes mirror the metal hydrocarbyl complexes of organometallic chemistry and offer the promise of a similar rich chemistry.1 Indeed there are a number of strictly isoelectronic borane and hydrocarbon complexes in which a C atom is formally replaced with a B or BH moiety.2 Comparison of the structure and properties of these compound pairs highlights interesting similarities and differences between the organic and inorganic derivatives.3... [Pg.255]

Representing the third important method of C-C bond formation covered in Chapter 12, cross-coupling reactions constitute one of the most powerful and widely used tools available today to the synthesis chemist. Equation 12.52 shows the general overall reaction, which involves combination of two carbon fragments (R and R ), one typically originating from an organohalide and the other from a metal hydrocarbyl compound. A transition metal complex serves as catalyst and template for the coupling to occur. [Pg.584]

Crystallization in the presence of tmeda affords a tetrameric aggregate of composition [(tmeda)NaCH2C6H2Me2(OLi)]4, 205 [178]. A distorted U4O4 cube forms the central part of the molecule. Both the lithium and sodium atoms act as bridges between the methylene units and the oxygen atoms. The compound can be regarded as a model intermolecular superbase and overcomes the problem of differing solubilities of lithium alkoxides and the heavier alkali metal hydrocarbyls. [Pg.414]

The migration of the hydrocarbyl ligand to the coordinated Lewis base such as CO, RNC, etc., or CO insertion into the metal-hydrocarbyl bond, usually takes place in the case of 18 complexes via 6e compounds or solvated lie compounds " (see Chapter 2) ... [Pg.255]

The past decade has witnessed a dramatic expansion in what we know about the organometallic compounds of the 5f elements. It is now evident that the actinides have a very rich, intricate, and instructive organo-metallic chemistry, and that we have much to learn about the basic principles governing structure, bonding, and reactivity. Nowhere is this situation more obvious than in the area of metal hydrocarbyls (i.e., alkyls, aryls, alkenyls, etc.) and hydrides, and the growth in this area since our last ASI review in 1978 [ll has been phenomenal. [Pg.115]

Table II indicates the stoichiometry of the reaction of metal hydro-carbyls with the surface of silicas and aluminas dried at various temperatures. The results indicate that at lower drying temperatures approximately 2 moles of hydrocarbon are liberated per mole of hydrocarbyl compound. Subsequent reaction with the proton source, n-butyl alcohol, generates 1 or 2 moles of hydrocarbon, depending on whether a tris- or tetrahydrocarbyl compound is used. The formation of 2 moles of hydrocarbon can arise as a fortuitous combination of metal species singly, doubly, and triply bonded to the support surface. Table II indicates the stoichiometry of the reaction of metal hydro-carbyls with the surface of silicas and aluminas dried at various temperatures. The results indicate that at lower drying temperatures approximately 2 moles of hydrocarbon are liberated per mole of hydrocarbyl compound. Subsequent reaction with the proton source, n-butyl alcohol, generates 1 or 2 moles of hydrocarbon, depending on whether a tris- or tetrahydrocarbyl compound is used. The formation of 2 moles of hydrocarbon can arise as a fortuitous combination of metal species singly, doubly, and triply bonded to the support surface.
Hydrocarbonyl compounds, lanthanide complexes, 4, 4 ( -Hydrocarbyl)bis(zirconocene), preparation, 4, 906 Hydrocarbyl-bridged cyclopentadienyl-amido complexes, with Zr(IV), 4, 864 Hydrocarbyl complexes bis-Cp Ti hydrocarbyls reactions, 4, 551 structure and properties, 4, 551 synthesis, 4, 542 cobalt with rf-ligands, 7, 51 cobalt with rf-ligands, 7, 56 cobalt with ]4-ligands, 7, 59 cobalt with rf-ligands, 7, 71 heteroleptic types, 4, 192 homoleptic types, 4, 192 into magnetic metal nanoparticles via ligand stabilization, 12, 87 via polymer stabilization, 12, 87 into noble metal nanoparticles... [Pg.122]

Of great importance as precatalysts in organolanthanide-catalyzed processes are lanthanide hydrocarbyls containing the bulky bis(trimethylsilyl)methyl ligand. They are also the most suitable precursors for the preparation of the dimeric hydrides [(C5Me5)2Ln(/t-H)]2. Such compounds can be isolated completely free of coordinating solvents and alkali metal halides Eq. (2) [19-25. ... [Pg.251]

Higher 43-hydrocarbyl derivatives of transition metals can be obtained by partial protolysis of the bis(7i-allyl)metal compounds formed from cyclo-octa-1,5-diene metal complexes and 1,3-butadiene with one equivalent of the Bronsted acid in the presence of the proper ligand in a polar solvent at lowered temperature (e.g. — 40°C). For instance, Ni [43-(CxHn)l and Ni—[43-(Ci2Hig)] derivatives have been yielded by the reaction of Ni(CxH 2)2 [(Ni(Cod)2] with 1,3-butadiene (C4H6), followed by treatment with a Bronsted acid, according to scheme (1) [132] and scheme (2) [37] respectively ... [Pg.293]


See other pages where Metal hydrocarbyl compounds is mentioned: [Pg.58]    [Pg.224]    [Pg.238]    [Pg.239]    [Pg.244]    [Pg.122]    [Pg.371]    [Pg.377]    [Pg.444]    [Pg.225]    [Pg.333]    [Pg.268]    [Pg.21]    [Pg.23]    [Pg.103]    [Pg.100]    [Pg.223]    [Pg.9]    [Pg.10]    [Pg.248]    [Pg.249]    [Pg.218]    [Pg.222]    [Pg.333]    [Pg.152]    [Pg.40]    [Pg.40]    [Pg.117]   
See also in sourсe #XX -- [ Pg.215 , Pg.222 ]




SEARCH



Hydrocarbyl

Hydrocarbyls

© 2024 chempedia.info