Point seven-coordinate complexes

Most of the substitution reactions with the homoleptic Tc(I) isocyanide complexes presented in the preceding section had to be performed at elevated temperatures and were often characterized by low yield. The reason for this behaviour is the exceptionally high kinetic and thermodynamic stability of this class of compounds. From this point of view, 4a are not very convenient or flexible starting materials, although they are prepared directly from 3a in quantitative yield. The exceptionally high kinetic and thermodynamic stability is mirrored by the fact that it was not possible to substitute more than two isocyanides under any conditions. On the other hand, oxidation to seven-coordinated Tc(III) complexes occurs very readily. Technetium compounds of this type, which are not expected to be very inert, could open up a wide variety of new compounds, but this particular field has not been investigated very thoroughly. A more convenient pathway to mixed isocyanide complexes that starts with carbonyl complexes of technetium will be described in Sects. 2.3 and 3.2. 

Limiting kinetic behavior in the [IrCUf" oxidation of alcohols, R1R2CHOH (Ri, R2 = H, Me) points to formation of an intermediate complex which decomposes with C-H cleavage to give a carbon-centered radical in the rate-determining step. The absorbance at 488 nm increases and lack of CF inhibition points to a seven-coordinate geometry for the intermediate. 

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