Metallocycles ruthenium

A mechanistic pathway is proposed based upon the observed regioselectivities and other results that were obtained during the exploration of the scope and limitations of the Alder-ene reaction.38 Initially, coordination of the alkene and alkyne to the ruthenium catalyst takes place (Scheme 5). Next, oxidative addition affords the metallocycles 42 and 43. It is postulated that /3-hydride elimination is slow and that the oxidative addition step is reversible. Thus, the product ratio is determined by the rate at which 42 and 43 undergo /3-hydride elimination. 

A different variation on this theme has been developed by Ito, where the TRAP ligands (37) form a nine-membered metallocycle [157-162]. The ruthenium catalysts seem to function best at low pressures, but highly functionalized dehydroamino esters can be reduced with high degrees of asymmetric induction [157, 159-164], as well as indoles [165]. 

A series of novel ruthenium(IV) dioxolene complexes, formally [3 + 2] cycloadducts, have been obtained via the reaction of cix-[Ru (0)2(Me3tacn)(CF3C02)] with trimethylsilylacetylenes (Scheme 14). " These dark blue complexes display a characteristic UV-vis absorption band at 550-680 nm. They are also characterized by electrospray mass spectrometry. The X-ray structure of the complex formed with bis(trimethylsilyl)acetylene has been determined the two Ru—O bonds of the metallocycle are of the same length (1.978 A). 

Rhodium(I) complexes of pyrazole, such as (81) have been studied by H and C NMR the boat conformation of the metallocycle was thus established <84JCPB25l>. Ruthenium(II) complexes of pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, and indazole were described (x-ray crystallography and a careful H and C NMR study) in <90JCS(D)1463>. 

Reactions of ruthenium and osmium cluster carbonyls with heteroatom-substituted and functionalized alkynes (metallocycles) 00IZV1. 

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