Metal-cation-directed synthesis

However, the practical, direct synthesis of functionalized linear polyolefins via coordination copolymerization olefins with polar monomers (CH2 = CHX) remains a challenging and industrially important goal. In the mid-1990s Brookhart et al. [25, 27] reported that cationic (a-diimine)palladium complexes with weakly coordinating anions catalyze the copolymerization of ethylene with alkylacrylates to afford hyperbranched copolymers with the acrylate functions located almost exclusively at the chain ends, via a chain-walking mechanism that has been meticulously studied and elucidated by Brookhart and his collaborators at DuPont [25, 27], Indeed, this seminal work demonstrated for the first time that the insertion of acrylate monomers into certain late transition metal alkyl species is a surprisingly facile process. It spawned almost a decade of intense research by several groups to understand and advance this new science and to attempt to exploit it commercially [30-33, 61]. 

This reaction is widely utilised in organic synthesis, when carbonyl groups may be protected as the thioacetals or thioketals. Unlike acetals or ketals, the thio compounds do not undergo acid catalysed hydration, and may be used in acidic reaction conditions. The metal-directed hydrolysis is rationalised in terms of the soft-soft interaction of the sulfur with the metal cation, in contrast to the hard-soft interaction with a proton. Hydrolysis is readily achieved on treatment with aqueous mercury(n) or silver(i) salts. Once again, the... 

Here we report a technique of direct synthesis of the photocatalytically active mesoporous composites Ti02/M (M = Cu, Ni, Co, Fe, Zn, Ag etc.) via photochemical reduction of the metal cations adsorbed on highly developed surface of a mesoporous titanium dioxide. The Ti02/M composites were found to be efficient photocatalysts of hydrogen evolution from water-alcohol mixtures. 

The first step in the study of metal complexes is the synthesis or preparation of the complex of interest followed by physicochemical characterization of the complex. Lanthanides rarely behave like transition metal cations and hence the need for different precautions in handling them. The fundamental characteristics and behavior of lanthanides in solution is useful for embarking on the synthesis of lanthanide complexes. Some properties of lanthanides, which are useful, and of direct interest for practical purposes will be recalled here. 

A more direct, 2 + 2 approach to the synthesis of cobalt(III) corroles has been described. It involves condensing a diformyl bipyrrole such as 2.140 with a diacid dipyrrylmethane such as 2.36. This approach is thus similar to the one used to obtain the bifuran-containing corroles 2.3 2.40 described earlier. In the present instance, the diacid bipyrrole 2,141 may also be reacted with a diformyl dipyrrylmethane such as 2.142. This affords corrole 2.125b (Scheme 2.1.37). In either case, the reaction must be carried out in the presence of Co(II) and PPhs. This requirement for a presumably coordinating metal cation is in stark contrast to what is seen in the case of the bifuran analog there, no metal is needed to template the reaction. ... 

Flanigen believed that the components of alkali metal cations of the synthetic system would play an important role in two aspects in the synthesis of zeolites [55] (1) supply of base, i.e., OH and (2) structure directing. Recently, Dutta and colleagues concluded that the hydrated cations can stabilize aluminosilicate ions via static electric and steric interactions.[56] In a word, alkali metal cations or alkaline earth metal cations mainly play the roles of structure direction, framework charge balancing, and pH adjustment in the synthesis of aluminosilicate zeolites. 

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