Tantalum, dithiocarbamate complexes

Scheme 4 Mechanism of the production of bridging dinitrogen in niobium and tantalum dithiocarbamate complexes (R2dtc, etc. Omitted for clarity)...

The development of niobium and tantalum dithiocarbamate chemistry is relatively recent, the first well authenticated examples coming from the insertion of carbon disulfide into metal amide complexes to give [M(S2CNR2)4] (193, 666). Dithiocarbamates are now known to stabilize niobium and tantalum in the +3 to +5 oxidation states. 

A range of other cationic niobium and tantalum tetrakis(dithiocarbamate) complexes, [M(S2CNR R )4]X (M = Nb, Ta R = R = Me, f-Bu R = Me, R = I -Pr, Ph, Cy, Bz), have been prepared from the metal pentachlorides and anhydrous dithiocarbamate salts (719). They are fluxional on the NMR time scale, a polytopal mechanism being proposed via a cubic or square antiprismatic transition state. The kinetics of this process has been studied by total line shape analysis, giving AG values of 42-50 kJ moP. ... 

Figure 70. Tantalum(V) tris(dithiocarbamate) sulfido and disulfido complexes.

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