Lithium species mechanistic studies

FIGURE 4.40 Mechanistic studies on transformation of lithium species 80. 

Most mechanistic studies have focused on elucidation of the role of alkali promoters. The addition of Li+ to MgO has been shown to decrease the surface area and to increase both methane conversion and selective C2 production.338,339 As was mentioned, however, besides this surface-catalyzed process, a homogeneous route also exists to the formation of methyl radicals.340-342 The surface active species on lithium-doped catalysts is assumed to be the lithium cation stabilized by an anion vacancy. The methyl radicals are considered to be produced by the interaction of methane with O- of the [Li+0-] center330,343 [Eq. (3.32)]. This is supported by the direct correlations between the concentration of [Li+0 ] and the concentration of CH3 and the methane conversion, respectively. The active sites then are regenerated by dehydration [Eq. (3.33)] and subsequent oxidation with molecular oxygen [Eq. (3.34)] ... 

Gp2TiCl2/NaBH4 mixtures have been studied as a convenient system for the hydroboration of alkenes. Mechanistic studies for these reactions are reported. These processes provide different regioselectivities and are catalyzed by the isolated Cp2Ti(/x-H)2BEl2 species. Lithium borohydride appears to be involved in the formation of the true catalytically active complex. Extensive nB NMR experiments indicated that the predominant products in the hydroboration reaction of Ph-CH=CH2 are a regiomeric mixture of tetraalkylborates, with minor amounts of trialkylborohydrides.1624,1625... 

Homoleptic metal alkoxides are of considerable interest as precursors to metal oxides. Both pyrolytic and hydrolytic methods have been employed for the conversion to the corresponding oxides [1]. As an example of the former procedure, oxide films have been created by the exposure of metal alkoxide vapors to hot surfaces [2]. Little, however, is known concerning the mechanistic steps involved in the thermal decomposition to metal alkoxides [3]. This contrasts with the extensive mechanistic information that is available for the decomposition of the corresponding metal alkyl species [4]. Herein, we report the results of our study of the pyrolysis of a series of cerium(III), lithium(I) and titanium(IV) alkoxides [5]. Depending on the... 

Intensive studies have been devoted to a mechanistic rationale of the conjugate addition of organocopper compounds and give a rather complex picture [141, 135, 136]. A simplified mechanistic model starts from dimeric lithium cuprates 131, wherein oxygen is assumed to coordinate to lithium and the carbon-carbon double bond to copper. The chelated cuprate 133, but also the nonchelated species 132 might function as intermediates for the formation of... 

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