Coordination compounds base-catalyzed reactions

Palladium-catalyzed allylic oxidations, in contrast, are synthetically useful reactions. Palladium compounds are known to give rise to carbonyl compounds or products of vinylic oxidation via nucleophilic attack on a palladium alkene complex followed by p-hydride elimination (Scheme 9.16, path a see also Section 9.2.4). Allylic oxidation, however, can be expected if C—H bond cleavage precedes nucleophilic attack 694 A poorly coordinating weak base, for instance, may remove a proton, allowing the formation of a palladium rr-allyl complex intermediate (89, path by694-696 Under such conditions, oxidative allylic substitution can compete... 

There are various procedures for the preparation of polyethers. These procedures typically start with oxirane or oxirane derivatives (e.g. propylene oxide, etc.). Base catalyzed anionic polymerization, acid initiation, or complex coordination catalysis can be used for the reaction [1-3], Not only oxiranes can generate polyethers. Diols also can be used for polyether synthesis. Other source compounds include tetrahydrofuran, which can be polymerized to a polyether using fluorosulfonic acid (HSO3F) as a catalyst, oxetane (trimethylene oxide) or oxetane derivatives, which can be polymerized to generate polyethers with practical applications such as poly[bis(chloromethyl)oxetane], etc. 

The efficiency of a catalytic system based on an organometallic coordination compound depends on the number of metal-atom orbitals that can be involved in bonding. Therefore derivatives of the reare earths, especially the lanthanides with their partially filled d- and f-orbitals, should provide interesting new opportunities for catalyzing a great variety of organic reactions. 

Alumina prepared by conventional hydrolysis of aluminum compound precursors is covered by surface hydroxyl groups. High-temperature calcination is needed in order to expose the surface coordination unsaturation of A1 ions. A new method, which involves stoichiometric hydrolysis of an amine-Al alkoxide monomeric complex, can generate alumina with a surface that is covered with far fewer hydroxyls without high-temperature postsynthesis treatment. In this method, the coordination unsaturation site of A1 is protected with an amine throughout the preparation process. The bound amine on the alumina surface can be exchanged with other bases, and the final solid is a Lewis-acid catalyst and catalyzes reactions such as aminolysis of epoxide. The chemistry in the preparation of such an alumina is described. 

New challenges were then made to develop useful Lewis base-catalyzed aldol reactions of trimethylsilyl enolates, simple and the most popular silicon enolates. It has recently been found that aldol reactions of trimethylsilyl enolates with aldehydes proceed smoothly under the action of a catalytic amount of lithium diphenylamide or lithium 2-pyrrilidone in DMF or pyridine (Eq. (38)) [57]. This Lewis base-catalyzed aldol reaction of trimethylsilyl enolates [58] has an advantage over acid-catalyzed reactions in that aldol reaction of carbonyl compounds with highly-coordinative functional groups with Lewis acid catalysts are smoothly catalyzed by Lewis bases to afford the desired aldol adducts in high yields. 

There are three principal ionic ring-opening polymerization reactions of epoxides acid-initiated, base-initiated, and coordinate-initiated polymerizations. The acid-initiated reaction involves addition of an active hydrogen compound, HY, such as ethanol, to an epoxide ring and is catalyzed by an acid, HX, such as perchloric acid. The reaction sequence involves formation of an oxonium complex, followed by ring opening by an 8 2 cleavage of an oxonium carbon bond. 

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