Trans influences, transition metal

In addition to routine spectroscopic characterization, transition metal silyls have been examined by a variety of physical methods, principally to determine (1) the definite presence of an Si—M bond, (2) the manner in which such a bond is influenced by other ligands, (3) whether such a bond possesses any w-component, and (4) the trans influence of the silyl ligand. 

The titanium trichloride-diethylaluminum chloride catalyst converted butadiene to the cis-, trans,-trans-cyclododecatriene. Professor Wilke and co-workers found that the particular structure is influenced by coordination during cyclization between the transition metal and the growing diene molecules. Analysis of the influence of the ionicity of the catalyst shows effects on the oxidation and reduction of the alkyls and on the steric control in the polymerization. The lower valence of titanium is oxidized by one butadiene molecule to produce only a cis-butadienyl-titanium. Then the cationic chain propagation adds two trans-butadienyl units until the stereochemistry of the cis, trans, trans structure facilitates coupling on the dialkyl of the titanium and regeneration of the reduced state of titanium (Equation 14). 

Porphyrins with metals other than iron (and cobalt) are not of particular direct relevance to the present section, although it should be noted that porphyrins have been extracted from coal and oil shales with metals such as gallium and the early transition metals coordinated. The biological significance of these observations is questionable. Nevertheless, detailed studies on a range of metalloporphyrins have contributed substantially to our appreciation of the bonding in such molecules, and the influence of cis and trans ligands on their structure and reactivity.599 609... 

There are many instances of the isomerisation of alkenes or alkenilic compounds under the influence of transition metal compound catalyst. Some examples arepent-l-ene into cis- and trans-pent-2-ene (RhCl3... 

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