Decarboxylation labile metal ions

Marcus theory, first developed for electron transfer reactions, then extended to atom transfer, is now being applied to catalytic systems. Successful applications to catalysis by labile metal ions include such reactions as decarboxylation of oxaloacetate, ketonization of enolpyru-vate, and pyruvate dimerization (444). 

A number of reactions involving pyridoxal, an amino acid, and a metal ion have been attributed to the formation of a Schiff base chelate in which a hydrogen atom on the a-carbon of the amino acid is labilized, and the Schiff base can now undergo a variety of reactions resulting in a transamination, racemization, aldol condensation, a,/3-elimination, or decarboxylation reactions (188). 

In the presence of large metal ion concentrations, the decarboxylation of oxaloacetic acid is inhibited, probably because the labile carboxyl group is bound in a second six-membered metal chelate ring (structure LXXV) (91, 189). 

We have exploited this base catalysis of the oxygen exchange process to effect oxygen lability in the less electrophilic carbonyl sites of neutral metal carbonyl species. Because [MCOOH] intermediates are readily decarboxylated in the presence of excess hydroxide ion, in order to observe oxygen exchange processes in neutral metal carbonyl complexes it was convenient to carry out these reactions in a biphasic system employing phase transfer catalysis () (16, 17. 18). Under conditions (eq. 7) the... 

---