Oxides rational synthesis

Non-aqueous synthetic methods have recently been used to assemble mesoporous transition metal oxides and sulfides. This approach may afford greater control over the condensation-polymerization chemistry of precursor species and lead to enhanced surface area materials and well ordered structures [38, 39], For the first time, a rational synthesis of mesostructured metal germanium sulfides from the co-assembly of adamantanoid [Ge4S ()]4 cluster precursors was reported [38], Formamide was used as a solvent to co-assemble surfactant and adamantanoid clusters, while M2+/1+ transition metal ions were used to link the clusters (see Fig. 2.2). This produced exceptionally well-ordered mesostructured metal germanium sulfide materials, which could find application in detoxification of heavy metals, sensing of sulfurous vapors and the formation of semiconductor quantum anti-dot devices. 

The other more rational synthesis of inverted porphyrins was reported recently by Dolphin and coworkers. This approach has as its key macrocycle-forming step a McDonald-type 2 -t- 2 condensation between the a-p-linked dipyrrylmethane 3.168 and the diformyl dipyrrylmethane 3.169. Following oxidation with air, the heptaalkyl N-inverted porphyrin system 3.170 is isolated in ca. 25% yield (Scheme 3.5.4). 

Oxidative cyclization of acyclic trimer 45 under high dilution conditions gave us the first rational synthesis of the exploded [3]pericyclyne, 42, which was isolated in 39% yield (Fig. 9-15) [18]. Varying amounts (up to 8%) of the cyclic hexamer, 54, were also obtained... 

There are many examples of rational synthesis. A good example is Sialon, in which A1 and oxygen were partly substituted for Si and nitrogen in silicon nitride, Si3N4. The fast Na+ ion conductor Nasicon was synthesized based on understanding the coordination preferences of cations and the nature of oxide networks formed by them. The zero-expansion ceramic CaQ5Ti2P30j2, possessing the Nasicon framework, was later synthesized based on the idea that the property of zero expansion would be exhibited by two- or three-coordination polyhedra linked in to leave substantial empty space in the network [3]. 

A rational synthesis of 9-methylenebicyclo[6.1.0]nona-2,4,6-triene by pyrolysis of an amine oxide led to 4-methylenebicyclo[5.2.0]nona-2,5,8-triene which upon further pyrolysis gave c/ -l-methylene-8,9-dihydroindene (Scheme 11.52). ... 

Rational Synthesis of Lanthanide Oxide/Hydroxide Complexes... 

The title complexes are the first well-characterized multiiron sandwich compounds prepared via rational synthesis from lacunary or defect species. They have possible applications as catalysts for the oxidation of organic compounds with the environmentally friendly oxidant H202 and constitute a well-defined multiiron species to facilitate the further investigation and delineation of magnetic interactions in such systems." ... 

In conclusion, the few examples provided above show that powder perovskite-type oxides prepared by USS demonstrate in general enhanced structural properties compared to more conventional synthesis methods. However, a rational synthesis by design is desirable that should be based on a systematic research of the effect of synthesis parameters on structural and morphological properties of the product... 

Arena oxides have great importance in biosynthetic schemes and in the metabolism of foreign compounds in mammals. A new approach to the rational synthesis of substituted arena oxides has been investigated culminating in the total synthesis of the natural products senepoxide and seneol (Scheme 8). ... 

In an extension of this work, the Shibasaki group developed the novel transformation 48—>51 shown in Scheme 10.25c To rationalize this interesting structural change, it was proposed that oxidative addition of the vinyl triflate moiety in 48 to an asymmetric palladium ) catalyst generated under the indicated conditions affords the 16-electron Pd+ complex 49. Since the weakly bound triflate ligand can easily dissociate from the metal center, a silver salt is not needed. Insertion of the coordinated alkene into the vinyl C-Pd bond then affords a transitory 7t-allylpalladium complex 50 which is captured in a regio- and stereocontrolled fashion by acetate ion to give the optically active bicyclic diene 51 in 80% ee (89% yield). This catalytic asymmetric synthesis by a Heck cyclization/ anion capture process is the first of its kind. 

In the following we will concentrate on three important cases, i.e. CO oxidation on alkali doped Pt, ethylene epoxidation on promoted Ag and synthesis gas conversion on transition metals. We will attempt to rationalize the observed kinetic behaviour on the basis of the above simple rules. 

The above methodology has been extremely useful for the synthesis of a variety of INOC precursors. For instance, treatment of 0-trimethylsilyl a-bro-moaldoximes 52b, e, f with F ion in presence of unsaturated alcohols 57 produces oximino ethers 58 which can be readily oxidized using NaOCl (Scheme 8) [29]. The transient nitrile oxide intermediates formed undergo spontaneous cyclization to fused isoxazolines 59. The preferred stereoisomer in the formation of the five-membered ring ethers is trans whereas in the six-membered ring ethers the cis isomer predominates (see Table 5). MM2 calculations helped rationalize the experimentally observed stereoselectivites (see Table 5). 

This simple procedure resulted in 2H-azirines exclusively in high yields and with retention of chirality at C-2 [24]. Mechanistically, this oxidative synthesis of azirines can be rationalized by invoking the intermediacy of chloro-dimethyl-sulfonium chloride (Me2SCl+- Cl ), which then reacts with the aziridine as indicated in Scheme 12. 

Besides current development of new catalysts and related functional materials, oxidation tools have always played an important role in their synthesis, activation, and functionalization. After a separate discussion per technique we have rationalized our literature findings (Table 6.2) as five principal oxidative functions with many proven applications. 

Table 6.2 Rationalization of the oxidation chemistry applied in the synthesis of heterogeneous catalysts and related functional materials.

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