Organometallic complexes sulfides

The selective insertion of diphenylacetylene in the cyciopaiiadated sulfide complex 1 leads to the stable organometallic complex 2, which can be depalladated with silver(I) tetrafluoroborate to give a mixture of the dibenzothiepinium salt 3 and the dibenzo[Z>,z ]thiepin 4.91 Demethyla-tion of 3 to yield 4 is complete after refluxing overnight in chlorobenzene. The synthetic scope of this method for thiepin derivatives is limited due to their thermal instability, but the method is very suitable for the synthesis of 1//-2-benzothiopyrans.91... 

Catalysts may be metals, oxides, zeolites, sulfides, carbides, organometallic complexes, enzymes, etc. The principal properties of a catalyst are its activity, selectivity, and stability. Chemical promoters may be added to optimize the quality of a catalyst, while structural promoters improve the mechanical properties and stabilize the particles against sintering. As a result, catalysts may be quite complex. Moreover, the state of the catalytic surface often depends on the conditions under which it is used. Spectroscopy, microscopy, diffraction and reaction techniques offer tools to investigate what the active catalyst looks like. 

Of several procedures for the stereoselective oxidation of sulfides using organometallic complexes, two adaptations of Kagan s original process have gained prominence. In the first method the diol (36) is reacted with Ti(0 Pr)4 to form the catalyst. With cumyl hydroperoxide as the stoichiometric oxidant, methyl para-tolyl sulfide was converted into the optically active sulfoxide in 42 % yield (98 % ee)[109]. 

Catalysts are heterogeneous sulfided nickel (or cobalt) molybdenum compounds on a y-alumina. The reaction has been extensively studied with substrates such as thiophene (Figure 2.40) as the model compound mainly with the aims of improving the catalyst performance. The mechanism on the molecular level has not been established. In recent years the reaction has also attracted the interest of organometallic chemists who have tried to contribute to the mechanism by studying the reactions of organometallic complexes with thiophene [41], Many possible co-ordination modes for thiophene have been described. 

Odta — see Acetic acid, octamethylenediaminetetra-Optical resolution amine metal complexes, 25 Ore-forming solutions metal sulfides, 525 Organometallic complexes solubility... 

As the edge sites of sulfide slabs are generally known as active sites in hydrotreating reactions [1], it seemed thus possible to us that reactions take place preferentially between sulfide edge sites and organometallic complexes, if placed in contact each other. Selective modification of edge sites could then be made by different metals like cobalt or tin. In this study, we applied SOMC to the modification of the conventional hydrotreating catalysts alumina-supported molybdenum sulfides with or without cobalt promoter. The Co and Sn... 

Two-electron redox processes are facile in metal sulfide surfaces, and thus M-S bond breaking and re-making in such extended arrays may provide an energetically favorable pathway to modify the electron count at a particular metal center. Although Tl -bonded thiophenes have not been invoked in heterogeneous HDS mechanisms, T T transformations such as the ones defined in organometallic complexes could be envisaged to take place at the active sites of HDS catalysts, as possible routes for... 

Note - In inorganic chemistry, the most common monodentate L ligands are water, amines, ethers, thiols and sulfides (Chap. 1.1). They are all good donors, because they are not n acceptors. Thus, they are weakly bound to metals, and, as such, also frequently used in organometallic complexes for facile substitution chemistry (see Chap. 5) and catalysis (see Parts IV and V). 

Hydrogenations and oxidations form two important classes of catalytic reactions. In heterogeneous catalysis, the metals from the groups Vin and IB of the periodic system, as well as oxides or sulfides, catalyze such reactions. In view of their unique reaction mechanisms, acid-catalyzed reactions are considered as a separate class, while a fourth category is formed by reactions that are catalyzed by coordination complexes or organometallic complexes in solution, as in homogeneous catalysis. Heterogeneous catalytic reactions will be the focus, however. 

Organometallic compounds asymmetric catalysis, 11, 255 chiral auxiliaries, 266 enantioselectivity, 255 see also specific compounds Organozinc chemistry, 260 amino alcohols, 261, 355 chirality amplification, 273 efficiency origins, 273 ligand acceleration, 260 molecular structures, 276 reaction mechanism, 269 transition state models, 264 turnover-limiting step, 271 Orthohydroxylation, naphthol, 230 Osmium, olefin dihydroxylation, 150 Oxametallacycle intermediates, 150, 152 Oxazaborolidines, 134 Oxazoline, 356 Oxidation amines, 155 olefins, 137, 150 reduction, 5 sulfides, 155 Oxidative addition, 5 amine isomerization, 111 hydrogen molecule, 16 Oxidative dimerization, chiral phenols, 287 Oximes, borane reduction, 135 Oxindole alkylation, 338 Oxiranes, enantioselective synthesis, 137, 289, 326, 333, 349, 361 Oxonium polymerization, 332 Oxo process, 162 Oxovanadium complexes, 220 Oxygenation, C—H bonds, 149... 

In another process for the synthesis of PPS, as well as other poly(arylene sulfide)s and poly(arylene oxide)s, a pentamethylcyclopentadienylmthenium(I) 71-complex is used to activate/>-dichlorobenzene toward displacement by a variety of nucleophilic comonomers (92). Important facets of this approach, which allow the polymerization to proceed under mild conditions, are the tremendous activation afforded by the -coordinated transition-metal group and the improved solubility of the resultant organometallic derivative of PPS. Decomplexation of the organometaUic derivative polymers may, however, be complicated by precipitation of the polymer after partial decomplexation. 

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