Palladium catalysis, general discussion

The use of palladium catalysis to synthesize aromatic heterocydes has been reviewed in a number of recent publications [1], As such, rather than a complete discussion of this large field, the thrust of this review will be to highlight general examples of how palladium catalysis has become used in heterocyde synthesis. This will focus on routes that direcdy assemble the aromatic heterocyclic core, rather than their subsequent functionalization or the use of palladium to assemble precursors for traditional cydocondensations, and on processes that involve generation of carbon-heteroatom bonds. 

The results discussed in this article were mostly obtained with ultrahigh vacuum systems at total pressures not exceeding 10"4 Torr, whereas real catalysis is performed in the atmospheric pressure regime. This general pressure gap raises the serious question to which extent experiments of the type described using the spectroscopic techniques of "surface science are relevant at all for real-life catalysis. A general answer to this problem can certainly not yet be offered. However, a rather favorable situation is found in the present case, as long as the discussion is confined to temperatures below 7 ax at which the reaction rate reaches is maximum rmax (cf., for example, Fig. 35). This situation has been discussed in detail in Section IV for palladium and holds as well for the other platinum metals since the shape of the r(T) curve is always quite similar. It has been shown that the kinetics may then approximately be described by... 

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