Generation of melded ligand (M = Mo) and mono(dithiolene) (M = Nb) complexes in the reactions of M(S-2)(S2CNEt2)(3) with dimethyl acetylenedicarboxylate

Reaction of brown Mo(S-2)(S2CNEt2)(3) with dimethyl acetylenedicarboxylate (DMAC) in refluxing I,2-dichloroethane results in the formation of Mo{SC(CO 2Me)=C(CO2Me)SCNEt2}{S2C2(CO2Me)(2)}(S2CNEt2) and Mo{SC(CO2Me)C(CO2Me)C(NEt 2)S}{S2C2(CO2Me)(2)}(S2CNEt2) (coordinating atoms italicised), which contai n ligands formed by melding dithiocarbamate and alkyne moieties (J. Chem. S ec., Chem. Commun. (1994) 2579). En contrast, reaction of orange Nb(S-2)(S2 CNEt2)(3) with DMAC in refluxing 1,2-dichloroethane produces purple, air-st able Nb{S2C2(CO2Me)(2)}(S2CNEt2)(3) which possesses an eight-coordinate, di storted mmmm dodecahedral structure closely related to that of the starting material. The related thio-niobium complex, NbS(S2CNEt2)(3) does not react with alkynes even under forcing conditions. (C) 2000 Elsevier Science B.V. All rights reserved.