Alkane derivatives activation

We restrict our attention to the reactions of CH bonds with low-valent transition metals that avoid radical or elecfrophihc selectivity patterns and are therefore considered CH activation in the sense considered at the outset of the review. A number of non-alkane CH activation reactions are included where they derive from concepts developed in alkane work and where they have proved particularly usefrd. 

We had previously determined isotopic distribution patterns for alkanes derived from the deuterogenation of several olefins on an amorphous catalyst activated to 300° in hydrogen followed by activation in nitrogen to 470° (52). For reactions at about 60°, the patterns for the alkanes from j)ropylene, 1-butene, cyclopentene, and 1-hexene closely resemble those obtained for hexane from 1-hexene on amorphous catalysts in the present work that for pentane from 2-pentene resembles that for hexane from lower selectivity for alkane-d2. We consider it important that the previous work showed that ethylene led to no ethane containing more than two deuterium atoms. In the previous investigation, the effect of the temperature of... 

The alkane metathesis with the W-alkyhdyne/alkyl complexes supported on alumina or sihca-alumina yielded a different distribution of branched, neopentyl alkane derivatives, albeit in lower amounts. These results suggest a different mechanism than the alkyhdene-supported metal complexes depicted above. A chrect, C - H bond activation of propane on the alkyhdyne species [91,92] or, alternatively, the formation of bisalkylidene intermediates [93] have been proposed [71]. 

In a seminal contribution, C.-J. Li reported in 2007 the first iron-catalyzed CDC reaction between alkanes and activated methylene derivatives such as p-ketoesters or p-diketones. A simple FeCl2 catalytic system (20 mol%) can promote the coupling reaction in the presence of 2 equiv. of di-fert-butyl peroxide ( BuOO Bu) as the oxidant in an alkane as the solvent (Scheme 4.2). The CDC reaction is efficient with cycloalkanes and p-ketoesters (48-88% yields). It is worth mentioning that linear alkanes such as n-hexane produce moderate yields (42%) with a mixture of two regio-isomers in a 1.2 1 ratio. By contrast, the reaction with p-diketones is a more difficult task, and only low yields (10-15%) are obtained. 

Scheme 4.2 CDC reaction between alkanes and activated methylene derivatives.

As in the alkanes, it is possible for carbon atoms to align themselves in different orders to form isomers. Not only is it possible for the carbon atoms to form branches which produce isomers, but it is also possible for the double bond to be situated between different carbon atoms in different compounds. This different position of the double bond also results in different structural formulas, which, of course, are isomers. Just as in the alkanes, isomers of the alkenes have different properties. The unsaturated hydrocarbons and their derivatives are more active chemically than the saturated hydrocarbons and their derivatives. 

Scheme 7 summarizes the synthesis of (7JR,llS)-7,ll-dimethylheptadecane (1), the female sex pheromone of the spring hemlock looper (Lambdina athasaria) by Mori [ 18]. Enantiopure alkanes are usually synthesized by coupling enantio-pure building blocks derived from natural products or compounds prepared by asymmetric synthesis. Even among hydrocarbons, chirality is very important for pheromone activity, and in this particular case meso-1 was bioactive, while neither (7R,11R)-1 nor (7S,11S)-1 showed bio activity. 

Late transition metal boratabenzene complexes can catalyze C-H activation thus, the bis(ethylene)rhodium derivatives (HsCsB-R)Rh(C2H4)2 (R = Ph, NMe2) promote boration of alkanes faster than does the Cp analog Cp Rh(C2H4)2, although the boratabenzene compounds are thermally less stable.110... 

The success of derivatives of 1 and 2 as dehydrogenation catalysts has led to the investigation of numerous different pincer ligands for iridium-catalyzed alkane dehydrogenation. The Anthraphos pincer iridium complex (3-H2) was expected to afford even greater thermal stability (Eig. 1), and indeed, the catalyst can tolerate reaction temperatures up to 250°C [42]. The catalytic activity of 3-H2, however, is much less than that of I-H2 under comparable conditions. 

The hydrosilylation of alkenes with trialkylsilanes in the presence of Lewis acid catalysts under mild conditions gives the corresponding (trialkylsilyl)alkanes [Eq. (22)]. Reaction with terminal alkenes such as 1-hexene and 1-dodecene at room temperature gives hydrosilylation products in 57 and 58% yields, respectively. Reactions with activated styrene derivatives such as styrene, / -chlorostyrene, and a-methylstyrene at —20°C afford hydrosilylated products in 55-61% yields. ... 

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