Isomerism and Stereochemical Change

In this section we mention the paramagnetic monocationic complexes [Mo(CO)2(dppe)2]+ and [Mo(CO)2(bipy)2]+, both of which are produced by oxidation of the parent Mo° complexes. In the former case, the oxidants used include [MeCftKUNJfBFj,46 NO[PF6], I2 and AgIla-47 and a variety of analogues [Mo(CO)2L2]+ has been obtained (L2 - dppm, dmpe, diars, etc.).1 47 Electrochemical oxidation has also been used, with other measurements, to show that a rapid cis — trans isomerization follows oxidation and an explanation for this phenomenon has been proposed on the basis of extended Huckel molecular orbital calculations, the stereochemical change being dependent on the number of valence electrons and the nature of the coligand jr-donor or -acceptor capacity. Similar studies have been made upon the compounds [Mo(CO)2L2]+ (L = bipy or phen).47... 

Mannose usually exists as the pyranoside shown below, This is in equilibrium with the furanoside. What is the conformation of the pyranoside and what is the stereochemistry of the furanoside What other stereochemical change will occur more quickly than this isomerization ... 

Whereas Scheme 13.6 focuses on the kinetics of stereochemical changes to R)-3h induced by its photolyses. Scheme 13.7 focuses on regiochemical considerations of product formation. Scheme 13.7 links in-cage formation of 2-BN and 4-BN to specific, regio-isomeric radical pairs, [radical pair]2B and [radical pair]4B, and Equation 13.16 can be derived from it. 

In addition to the stereochemical changes that accompany chemical reaction, these systems can be rearranged without chemical change. Several such examples of geometrical and of optical rearrangements are known for metal complexes. A brief account is given of some examples of geometrical (or cis-trans) isomerization in this section, and the next section contains a few examples of optical isomerization (or racemization). 

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