Metallo-ring compounds

It is remarkable that LDF theory also describes the bond length and vibrational frequency of the fluorine molecule with the same error bar as the other systems discussed here. This finding is significant as it shows that the error made in the LDF approach appears to be consistent in a wide class of different systems. In fact, recent calculations on ferrocene (52) show that also this type of metallo-organic compound does not present an exception - the Fe/ring distance agrees within 0.002 A with experiment. 

On the other hand, the use of [Rh(CO)2Cl]2 as a catalyst results in ring opening of the siloxycyclopropanes 13 to the silyl enol ethers 14 with high stereoselectivity [10]. The 2-siloxyrhodacyclobutane 15a is proposed to undergo j8-elimination to give jr-allylrhodium 16a followed by reductive elimination to the silyl enol ether 14a. 1-Trimethylsiloxybicyclo[n.l.0]alkanes serve as / -metallo-carbonyl compounds via desilylation with a variety of transition metals [11]. The palladium-catalyzed reaction of the siloxycyclopropanes 17 under carbon monoxide in chloroform provides a route to the 4-keto pimelates 18. In the presence of aryl triflates, the 1,4-dicarbonyl compounds 19 are... 

Syntheses of 1-Fimctionalized-l-Metallo Small Ring Compounds... 

The investigation of organic substances must often include tests for metals if the latter are likely to be present in the organic molecule (metallo-organic compounds) or as mere admixtures. The ring oven method devised by Weisz may be used in such cases it permits separations from as little as one drop of the test material. 

The halogen atoms remaining can then be replaced by organic residues such as trifluoroethoxy units. High polymers can also be prepared by ring-opening polymerization of the chlorocyclo-phosphazene, XXVIII. Compounds of this type can be converted to nldo-carboranes in the presence of base, but these do not form metallo-derivatlves, presumably for sterlc reasons (29). 

In a slightly different approach, the introduction of a metal complex is also possible as a metallo amino acid. For example, ferrocenyl-alanine (Fer) was prepared as early as 1957 [67]. Also, stereoselective preparations [68-71] and its biological activity were reported [72], and the compound has been inserted into peptide sequences just as a normal amino acid would (see Fig. 7 for an example) [35, 71]. In this case, the metallocene constitutes the side chain. Alternatively, the amino and carboxylic acid function can be on two different Cp rings, yielding, in the simplest possible case, l -aminoferrocene-l-carboxylic acid (Fca, see Fig. 7 for an example). This compound has also been reported in the literature, although it was difficult to obtain in pure form [73,74], It has since been incorporated into oligomers... 

The structure of 5 consists of a nine-membered (Cu —N—N)3 metallo-cyclic ring similar to the ones of the isostructural silver(I) and gold(I) compounds (15). Significant deviations from planarity, as found in the silver(I) tri-mer, are present. 

As in recent years, the synthesis of new chiral phosphines and related chiral tervalent phosphorus esters and amides continues to be a major preoccupation, being driven by the need for improved performance in metal-catalysed processes. It is very pleasing to note that two of the recipients of the 2001 Nobel Prize for Chemistry, William S. Knowles, and Ryoji Noyori, are honoured for their work in the synthesis and application in catalysis of chiral phosphine ligands. Interest in the structures of metallo-organophosphide systems, noted in the previous volume, has continued to develop. The chemistry of heteroaromatic ring systems, notably that of phospholes, and of low coordination number p -bonded compounds, also remain active areas. 

Several groups have investigated the synthesis of such compounds, for instance the cationic metallo-macrocycles [(t -ring)M(Aa)]3[BF4]3 (Aa = amino acidate) act as catalysts for hydrogen transfer to ketones while the neutral metallo-macrocycles [( -ring)ML]3 are efficient hosts for alkali metals (Li and Na). However, the chiral aspect of these species in solution was not investigated and only Yamanari and coworkers have reported diastereomeric separations, but no NMR studies have been made to differentiate these chiral macrocycles by the use of a chiral auxiliary. Recently the chemistry of these macrocycles was reviewed by Severin, who contributed largely to the development of this field. 

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