Transition metals building block approach

Further examples of the modular Tinkertoy approach includes the synthesis of (hetero)penta- to nona-metallic complexes. An important family of Tinkertoys are halide-, pseudohalide-, cyanoacetylide-, heterocyclic- and/or di- and tricarboxylic acid-funtionalized transition metal building blocks. 

In the last decades, cyanohydrins have become versatile chiral building blocks, not only for laboratory synthesis, but also for a range of pharmaceuticals and agrochemicals. Several methods for the enantioselective preparation of these compounds have been published [1, 2]. The most important synthetic approaches are catalysis by oxynitrilases, also termed hydroxynitrile lyases (HNLs), wording used in this chapter, [3] and by transition metal complexes [4], whereas the relevance of cyclic dipeptides as catalysts is decreasing [2]. 

Extending this approach, using hexacyanometalate building blocks together with divalent transition metal complexes containing labile positions has afforded a variety of one-, two- and three-dimensional compounds with very different physical properties from those of the face-centred Prussian blues [20-22],... 

There is an interest in these types of ionic liquids as green media for chemical reactions, this reaction provides a useful approach to the synthesis of finely tuned ionic liquids, using imidazolium salts as building blocks. Functionalization of heterocyclic substrates via transition metals is an important extension of this work (Equation (6.14)). Bergman has shown that these species can be successfully reacted with olefins in the presence of a rhodium catalyst via an NHC intermediate [55, 56). 

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