Niobium dithiocarbamate complexes

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

Dinuclear niobium xanthato complexes, Nb2S4(S2COR)4 (R = Et, Pr1, Cy also dithiocarbamates and dithiophosphates) have been prepared from [NEt4][Nb2S4(NCS)8] by replacing the thio-cyanato ligands.76... 

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. ... 

Addition of thiuram disulfides to the niobium(IV) dimethyl complex [Cp2NbMe2] results in cleavage of the sulfur-sulfur bond and addition to the metal center (734). The nature of the final product is dependent on the alkyl substituents. With tetraethylthiuram disulfide, the molecular niobium(V) dithiocarbamate complex [Cp2NbMe2(ri -S2CNEt2)2] results, which is believed to contain a monodentate dithiocarbamate ligand. In contrast, tetramethylthiuram disulfide affords a 1 1 electrolyte, believed to be [Cp2NbMe(S2CN-... 

Dinuclear niobium sulfido and selenido dithiophosphates, Nb2Q4[S2P(OR)2]4,75,76 (Q = S, Se R = Et) (also xanthates and dithiocarbamates) have been prepared but no crystal structure was reported. Optically active chromium complexes, Cr[S2P(OR)2]3 derived from Z)-borneol and L-menthol, have been described.77... 

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. 

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