Reductive Eliminations of Amines from Pd II Amido Complexes

3 Reductive Eliminations of Amines from Pd(II) Amido Complexes 

Reductive elimination of amines is the key bond-forming step in the catalytic ami-nation processes. These reactions were unknown a couple of years ago, but several examples of this reaction now exist, and the factors that control the rates of this process are beginning to be understood. The identity of the intermediates in some of these reductive elimination reactions has recently been uncovered. 

The dimeric amido complexes underwent reductive elimination after cleavage to form two monomeric, 3-coordinate, 14-electron amido complexes. In the case of the anilido dimer 20, a half-order rate dependence in the palladium complex showed that the reductive elimination occurred after reversible cleavage of the dimer to form two monomers. In the case of the f-butylamido complex 21, rapid reductive elimination occurred after irreversible dimer cleavage. This conclusion was supported by reaction rates that were first order in palladium dimer and by the lack of crossover during the reductive elimination reactions containing two doubly-labeled dimers. 

4 Competing 3-Hydrogen Elimination from Amido Complexes 

The amination chemistry depends on the absence of irreversible P-hydrogen elimination from the amido complexes before reductive elimination of amine. At the early stages of the development of the amination chemistry, it was remarkable that the unknown reductive elimination of arylamines could be faster than the presumed rapid [57,58] P-hydrogen elimination from late metal amides. In fact, directly-observed P-hydrogen elimination from late metal amido complexes was rare, and no examples were observed to occur irreversibly from a simple monomeric amido species [69], At this point, it is clear that C-N bond-forming reductive elimination of amines and ethers can be rapid, and that P-hydrogen elimination can be slow. 

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