An Electrocatalytic Reduction Cycle using Low-valent Tungsten

2 An Electrocatalytic Reduction Cycle using Low-valent Tungsten 

Schrocks group has spent a great deal of experimental effort trying to demonstrate the chemical feasibihty of such a cycle at Mo and has most recently focused its attention on ttiamidoamine [RN3N]Mo platforms (Fig. 3.2) to specifically test whether catalytic N2 fixation might proceed from a well-defined [RN3N]Mo(III)-N2 species. They have in fact reported one such system that is 

In this regard the Schrock system is distinct from aU previously developed molybdenum N2 systems. 

Several molybdenum complexes that are invoked as intermediates of the N2 fixation cycle can be used as the initial catalyst precursors, instead of the starting N2 complex. That these species provide similar overall results with respect to yields of reduced N2 is consistent with the cyde proposed. Therefore, they are either (i) spedes generated along the N2 fixation path or possibly (ii) precatalysts that can be chemically converted to the relevant active catalyst 

Prior to their emphasis of [RNsNJMo systems for N2 fixation, Schrock and coworkers had extensively studied Cp MMe3(N2) systems (M = Mo, W) that mediated the reduction of N2 to ammonia in nearly quantitative fashion (but not catalyticaUy) under certain conditions [33-39]. A possible mechanistic difference between systems of this latter type and the now better known [RNsNjMo systems concerns the terminal nitride intermediate. Ammonia release was presumed to proceed without generation of a terminal nitride species in the Cp MMe3(N2) systems, as illustrated in Fig. 3.7. Note the similarity between this proposed pathway and the secondary Chatt pathway illustrated in Fig. 3.3. A detailed mechanistic study by Norton regarding the protonation of the species 

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