Organometallic compounds complex formation

In addition, a catalytic version of Tt-allylpalladium chemistry has been devel-oped[6,7]. Formation of the Tr-allylpalladium complexes by the oxidative addition of various allylic compounds to Pd(0) and subsequent reaction of the complex with soft carbon nucleophiles are the basis of catalytic allylation. After the reaction, Pd(0) is reformed, and undergoes oxidative addition to the allylic compounds again, making the reaction catalytic.-In addition to the soft carbon nucleophiles, hard carbon nucleophiles of organometallic compounds of main group metals are allylated with 7r-allylpalladium complexes. The reaction proceeds via transmetallation. These catalytic reactions are treated in this chapter. 

The stereochemistry of the Pd-catalyzed allylation of nucleophiles has been studied extensively[5,l8-20]. In the first step, 7r-allylpalladium complex formation by the attack of Pd(0) on an allylic part proceeds by inversion (anti attack). Then subsequent reaction of soft carbon nucleophiles, N- and 0-nucleophiles proceeds by inversion to give 1. Thus overall retention is observed. On the other hand, the reaction of hard carbon nucleophiles of organometallic compounds proceeds via transmetallation, which affords 2 by retention, and reductive elimination affords the final product 3. Thus the overall inversion is observed in this case[21,22]. 

The formation of surface compounds of low-valent ions of transition metals on the surface of the support. In particular, fixing organometallic compounds on the support surface, it may be possible to stabilize coordi-natively insufficient complexes of transition metals and to obtain highly active catalysts. In the ideal case a complete use of the transition metal in the formation of the propagation centers can be achieved. 

Formation constants for complex species of mono-, di-, and trialkytin(rV) cations with some nucleotide-5 -monophosphates (AMP, LIMP, IMP, and GMP) are reported by De Stefano et al. The investigation was performed in the light of speciation of organometallic compounds in natural fluids (I = 0.16-1 moldm ). As expected, owing to the strong tendency of organotin(IV) cations to hydrolysis (as already was pointed above) in aqueous solution, the main species formed in the pH-range of interest of natural fluids are the hydrolytic ones. ... 

Organometallic compounds are considered only with strong restrictions, namely when organic ligands, e.g., methyl groups, are introduced to avoid formation of coordination polymers, as is the case with mononuclear metallo-onium complexes. 

Based upon analogies between surface and molecular coordination chemistry outlined in Table 1, we have recently set forth to investigate the interaction of surface-active and reversibly electroactive moieties with the noble-metal electrocatalysts Ru, Rh, Pd, Ir, Pt and Au. Our interest in this class of compounds is based on the fact that chemisorption-induced changes in their redox properties yield important information concerning the coordination/organometallic chemistry of the electrode surface. For example, alteration of the reversible redox potential brought about by the chemisorption process is a measure of the surface-complex formation constant of the oxidized state relative to the reduced form such behavior is expected to be dependent upon the electrode material. In this paper, we describe results obtained when iodide, hydroquinone (HQ), 2,5-dihydroxythiophenol (DHT), and 3,6-dihydroxypyridazine (DHPz), all reversibly electroactive... 

The three phases that are present in the Ziegler-Natta polymerisation are (i) the monomer (ii) the solvent and (iii) the catalyst. Reactions take place at certain points on the surface of catalyst particles. The polymer molecule grows as the monomer units join the chain where earlier monomer is attached to the catalyst particle. The precise nature of the action of catalyst is not yet known. However, the first step in the polymerisation process proposed is the formation of a monomer-catalyst complex between the organometallic compound and the monomer. 

As highly reactive heterocycles, the thietes are well suited for the formation of metal complexes. Takahashi and Dittmer both individually and in collaboration have been involved with the interaction of thietes and iron or cobalt carbonyls. During the thermally or photochemically induced complexation process, ring opening takes place so that the resultant thioacrolein is the actual ligand in the organometallic compound (Scheme i7)/ 3-203,204... 

Any reaction of the type to be considered here begins with the interaction of an organometallic compound with O2. This may lead to the formation of a dioxygen complex, however fleeting its existence. Further reactions may ensue. In the following sections we summarize the available results, organized by type of transformation. We begin with the evidence for coordination of O2. 

Much effort has been devoted to activate hydrocarbons, particularly saturated compounds, through the formation of organometallic compounds and transformation of the latter to substituted derivatives. A number of transition-metal complexes have been found to insert into carbon-hydrogen bonds leading to stable alkyl metal hydrides ... 

It was later found that stable organometallic compounds of transition metals exhibiting very low polymerization activity could be transformed into high-activity catalysts when deposited on silica, alumina, or silica-alumina.287-289 Interaction of surface hydroxyl groups with the organometallic compounds such as chromocenes, benzyl, and Tt-allyl complexes results in the formation of surface-bound organometallic complexes (41-43) 289-291... 

The chemistry of alkyne complexes is somewhat more complicated than that of alkene complexes because of the greater possibilities for -n bonding by alkynes and the tendency of some of die complexes to act as intermediates in the formation of other organometallic compounds. 

Main-group organometallic compounds are versatile tools in organic synthesis, but their structures are complicated by the involvement of the multicenter, two-electron bonds and ion-dipole interactions that are involved in aggregate formation (5). Electron deficiency or Lewis acidity of the metallic center and nucleophilicity or basicity of the substituents are important considerations in synthesis. The complexity of the structures and interactions is, however, the origin of much of the unique behavior of these organometallic compounds. 

The reaction of bis-phenylpropargyl ether (321) with tris(triphenylphosphine)rhodium chloride in benzene or toluene led to the formation of the unusual organometallic compound (322), which can be viewed as a derivative of an oxygen-rhodium pentalene system. Reaction of the rhodium complex (322) with sulfur leads to the corresponding 4,6-diphenyl-l,3-dihydro[3,4-c]furan (323). The selenium and tellurium analogs (324) and (325) were made in a similar manner (Scheme 111) (76LA1448). 

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