0—Bond metathesis radical processes

Harrod s most recent mechanistic proposal for cation-like silylzirco-nocenes is the redox mechanism, one variation of which is shown in Fig. 5.3d>60>81>83 jn caSes where Zr(IV) is not reduced to Zr(III), c-bond metathesis is likely. However, if Zr(III) is produced, Harrod favored generation of silyl radicals through a Zr(III)/Zr(IV) redox cycle and subsequent coupling of silyl radicals produced the silicon oligomer or polymer. Additional arguments for possible radical processes will be provided in a later section. 

The most important discoveries in ruthenium catalysis are highlighted and innovative activation processes, some of which are still controversial, are presented in this volume. They illustrate the usefulness in organic synthesis of specific reactions including carbocyclization, cyclopropanation, olefin metathesis, carbonylation, oxidation, transformation of silicon containing substrates, and show novel reactions operating via vinylidene intermediates, radical processes, inert bonds activation as well as catalysis in water. 

A theoretical analysis of the reaction kinetics was given in the study by Jodkowski et a/.31 A hydrogen-bonded molecular complex was found for the hydroxymethyl reaction channel. The formation of this complex may be a ratedetermining process in the two-step reaction mechanism of the H-abstraction from methyl group. On the other hand, the reaction channel which produces methoxy radicals is a simple metathesis reaction. The profile of the potential energy surface obtained by Jodkowski et al at the G2 level is shown in Fig. 14. 

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