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Group 12 metals Dihydrides

The racemization mechanism of sec-alcohols has been widely studied [16,17]. Metal complexes of the main groups of the periodic table react through a direct transfer of hydrogen (concerted process), such as aluminum complexes in Meerwein-Ponn-dorf-Verley-Oppenauer reaction. However, racemization catalyzed by transition metal complexes occurs via hydrogen transfer processes through metal hydrides or metal dihydrides intermediates (Figure 4.5) [18]. [Pg.94]

Scheme 13 Synthesis of group 14 element polysulfido complexes from the corresponding metal dihydrides... Scheme 13 Synthesis of group 14 element polysulfido complexes from the corresponding metal dihydrides...
For comparison, let us also consider the experimentally well-documented51 singlet reactions of H2 with group 9 metal carbene cations to give metal dihydride insertion products, e.g., for M = Ir,... [Pg.495]

The maj or exceptions to this simplified picture are probably CuH and ZnH2, which are reported to be stoichiometric, nonmetallic solids like the main group metal hydrides, but their crystal stmctures and physical properties are not well characterized. Borderline cases are the rare earth hydrides, which show a hydrogen concentration-dependent semiconductor-metal transition. E11H2 and YbH2 behave like alkaline earth dihydrides because of the special electron configuration of Eu + (4/ ) and Yb + (4/ " ). [Pg.254]

The halide groups can be replaced by other substituents like hydride or alkyl [86]. When the naphthyl (np) RuHnp(dmpe)2 is heated, the ligand undergoes an internal metallation to afford a dimer [87] (it was originally believed to be a monomer), though Ru(dmpe)2 has been isolated by photolysis of its dihydride, in matrixes at 12K (Figure 1.29) [88],... [Pg.33]

Certain dihydrides of main-group and transition metals are good precursors for metal polysulfides. The reactions of the dihydrides with Ss proceed without a change in the oxidation state of the metals. [Pg.162]

The dihydrides of the rare-earth metals are an unusual group of compounds with respect to defect structure, bonding mechanism, and electronic properties.1 These compounds usually show wide deviation from stoichiometry. In some individual cases the... [Pg.184]

Recent mechanistic studies on transition metal-catalysed hydrogen transfer reactions have been reviewed. Experimental and theoretical studies showed that hydrogen transfer reactions proceed through different pathways. For transition metals, hydridic routes are the most common. Within the hydridic family there are two main groups the monohydride and dihydride routes. Experimentally, it was found that whereas rhodium and iridium catalysts favour the monohydride route, the mechanism for ruthenium catalysts proceeds by either pathway, depending on the ligands. A direct hydrogen transfer mechanism has been proposed for Meerwein-Ponndorf-Verley (MPV) reductions.352... [Pg.137]

The earliest report of a rhenacyclopentane was that by Yang and Bergman52 in 1983. In this report, CpRe(CO)2H2 was treated with I(CH2)4I in THF at room temperature in the presence of the base l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to yield the rhenacyclopentane 54 (Fig. 17) as air-stable yellow-crystals in 53% yield. In this synthesis, the low pKa values of the dihydride of CpRe(CO)2H2 are exploited to allow attachment of the tetramethylene group to the metal centre. Thermolysis of the rhenacyclopentane at 100 °C resulted in the formation of CpRe(CO)3 (50%), methylcyclopropane (40%) and traces of 1-butene. The authors propose a decomposition pathway via loss of CO and/or r 5<->r 3 isomerisation of the Cp ligand (Scheme 19). [Pg.175]


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See also in sourсe #XX -- [ Pg.10 , Pg.11 ]




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