Isonitrile reduction chemistry

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

To address the purification issue, which frequently is a bottle-neck in the fast microwave chemistry, a solid-phase catch and release methodology was utilized in a two-component, two-step synthesis of l-alkyl-4-imidazolecarboxylates [45]. In the first step, a collection of isonitriles 25 was immobilized onto a solid support by the reaction with the commercially available N-mclhyl aminomethylated polystyrene 26. Subsequent treatment with various amines brought about simultaneous derivatization and release of the desired imidazoles 27 back into solution. Significantly, only derivatized material was released from the resin, thus ensuring high purity of the desired product. Both steps of the reaction were substantially accelerated by microwave dielectric heating, resulting in the overall reaction time reduction from 60 hours to 70 minutes (Scheme 18). 

An important, but not widely recognized effect in electron transfer chemistry is the phenomenon that the thermochemical stability order of several tautomeric systems can be inverted upon one-electron oxidation. Hitherto, most of the data stem from gas-phase measurements (photoelectron and mass spectrometry data) or from calculations at several levels of theory (Table 2). While the explicit numbers still differ for each method they all agree on the inversion of the stability order for keto/enol, alkine/allene, imine/enamine, nitrile/isonitrile and aldimine/aminocarbene pairs. One-electron reduction, on the other hand, does not necessarily lead to a thermochemical stability inversion, as demonstrated in the case of acetaldehyde 7cthenol [41]. 

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