Sequential Construction of One, Two, or Three Dithiolene Ligands from Alkynes and Sulfur in Dinuclear Cyclopentadienyl Molybdenum Complexes

This paper describes the sequential assembly of up to three dithiolene ligands from alkynes and elemental sulfur at a dimetal center. The dimolybdenum μ-alkyne complexes [Mo2(μ-R1CCR2)(CO)4Cp2] (1a−c; Cp = η-C5H5, R1 = R2 = H, CO2Me; R1 = H, R2 = CO2Me) undergo oxidative decarbonylation on reaction with elemental sulfur in refluxing toluene to give good to excellent yields of the terminal dithiolene complexes [Mo2(S)(μ-S)2(SCR1CR2S)Cp2] (2a−c). Further reaction of these complexes with 1 equiv of an alkyne R3CCR4 (R3 = R4 = H, CO2Me; R3 = H, R4 = CO2Me) followed by oxidation with elemental sulfur produces the bis(dithiolene) complexes [Mo2(μ-S)2(SCR1CR2S)(SCR3CR4S)Cp2] (4a−d). Two examples, [Mo2(μ-S)2(S2C2H2)2Cp2] and [Mo2(μ-S)2{S2C2(CO2Me)2}2Cp2], have been structurally characterized. Reaction of 2 with an excess of an activated alkyne R5CCR6 (R5 = R6 = CO2Me) and sulfur, or of 4 with the alkyne alone, affords good yields of the tris(dithiolene) complexes [Mo2(SCR1CR2S)(SCR3CR4S)(SCR5CR6S)Cp2] (6a−e). The degree of control over the substituents in these complexes is demonstrated by the synthesis of [Mo2(S2C2H2){μ-S2C2(CO2Me)2}{μ-S2C2(CO2Et)2}Cp2] (6e), which contains three different dithiolene ligands, as a single isomer.