Adamantane metal complexes

Bond angles C-S-C close to 100° are found in cyclic molecules based on strain-free 6-rings. All those studied have the chair conformation examples include l,4-dithiane/ 1,3,5-trithiane, and hexathia-adamantane. The last compound, S6(CH)4, is structurally similar to (CH2)eN4 and (CH2)6(CH)4. Trithiane forms many metal complexes the structure of S3(CH2)3. AgC104. H2O is mentioned in Chapter 3 (p. 90). 

A few mechanistic studies have been performed by Lebel and Huard to establish the catalytic cycle of this C—H amination reactions [77]. It has been shown that the deprotonation of the N-tosyloxycarbamate does not occur in the absence of the transition metal complex. Furthermore, the nature of the leaving group does not affect the amination pathway. For instance, the regioselectivity (tertiary vs. secondary C—H bonds) for the amination of adamantane is conserved, independent of the nature of the sulfonyloxy group (Eq. (5.27)). 

Other types of oxidative processes include the activation of saturated CH bonds. Such processes are especially interesting, from the practical point of view of processing the hydrocarbons from oil refining, and because such processes can occur in living organisms, and thus are definitely catalyzed by transition-metal complexes in aqueous environments. Among recent work on the development of model systems for such a purpose is the following. Water-soluble Ru(lll)-EDTA complexes are usable for activation of C(sp H bonds, e.g. in the oxidation of adamantane to a mixture of 1- and 2-adaman-tanols and adamantanone [184]. 

Cd(CN)2, is isomorphous. To prevent the interpenetration, relatively large species must be hosted into the diamondoid network. Indeed, the mixed metal complex NMe4[Cu Zn CN)4] shows no interpenetration because the tetra-methylammonium cations, whose size fits to that of the adamantane-like cavity, occupy half of these cavities (both Cu and Zn ions are tetracoordinated). The interpenetration of neutral M(CN)2 nets (M = Zn, Cd) can be hindered by hosting neutral molecules, structurally similar to NMe4. The solution of this problem is obvious and elegant The crystallization of Cd(CN)2 in the presence of Me4C leads to a single diamond-like net. ... 

A number of metal / -diketonates have been used to catalyze the oxidation of sulfides to sulfoxides, important synthetic intermediates for the construction of various biologically active molecules . For example, an elegant study by Ishii and coworkers demonstrated that VO(acac)2 (35) selectively catalyzed the sulfoxidation of adamantane (41) by SO2/O2 to give 1-adamantane sulfonic acid (42) (equation 10) . Although a number of metal acac complexes were examined as catalysts for this reaction, all but the vanadium compound failed to promote the sulfoxidation. The catalytic oxidation of triarylphosphines using the palladium complex Pd(acac)2 (29) has also been investigated . 

The skeletal isomerization of tetrabydrodicyclopentadiene into adamantane is an example of a very complex rearrangement diat is commercially carried out over strong Lewis acids with a hydride transfer initiator. The reaction can be catalyzed by rare earth (La, Ce, Y, Nd, Yb) exchanged faujasites (Scheme 1) in a Hj/HCl atmosphere at 25(yX3. Selectivities to adamantane of up to 50% have been reported, when a metal fimction, such as Pt, capable of catalyzing hydrogenation is added [54]. Initially acid catalyzed endo- to exo- isomerization of tetrahydro-dicyclopentadiene takes place and then a series of 1,2 alkyl shifts involving secondary and tertiary carbonium ions leads eventually to adamantane[55]. The possible mechanistic pathways of adamantane formation from tetrahydro-dicyclopentadiene are discussed in detail in ref [56]. 

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