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 mu-alkyne complexes [Mo(2)(mu-R(1)C[triple bond]CR(2))(CO)(4)Cp(2)] (1a-c; Cp = eta-C(5)H(5), R(1) = R(2) = H, CO(2)Me; R(1) = H, R(2) = CO(2)Me) undergo oxidative decarbonylation on reaction with elemental sulfur in refluxing toluene to give good to excellent yields of the terminal dithiolene complexes [Mo(2)(S)(mu-S)(2)(SCR(1)=CR(2)S)Cp(2)] (2a-c). Further reaction of these complexes with 1 equiv of an alkyne R(3)C[triple bond]CR(4) (R(3) = R(4) = H, CO(2)Me; R(3) = H, R(4) = CO(2)Me) followed by oxidation with elemental sulfur produces the bis(dithiolene) complexes [Mo(2)(mu-S)(2)(SCR(1)=CR(2)S)(SCR(3)=CR(4)S)Cp(2)] (4a-d). Two examples, [Mo(2)(mu-S)(2)(S(2)C(2)H(2))(2)Cp(2)] and [Mo(2)(mu-S)(2){S(2)C(2)(CO(2)Me)(2)}(2)Cp(2)], have been structurally characterized. Reaction of 2 with an excess of an activated alkyne R(5)C[triple bond]CR(6) (R(5) = R(6) = CO(2)Me) and sulfur, or of 4 with the alkyne alone, affords good yields of the tris(dithiolene) complexes [Mo(2)(SCR(1)=CR(2)S)(SCR(3)=CR(4)S)(SCR(5)=CR(6)S)Cp(2)] (6a-e). The degree of control over the substituents in these complexes is demonstrated by the synthesis of [Mo(2)(S(2)C(2)H(2)){mu-S(2)C(2)(CO(2)Me)(2)}{mu-S(2)C(2)(CO(2)Et)(2)}Cp(2)] (6e), which contains three different dithiolene ligands, as a single isomer.

Phosphine-substituted dithiolene complexes as ligands: communication between ruthenium(II) centers through a dimolybdenum bis(dithiolene) core.

The reaction of Mo2(SCH2CH2S)2Cp2 (1; Cp=eta-C5H5) with an excess of an alkyne in refluxing dichloromethane affords the bis(dithiolene) complexes Mo2(micro-SCR1=CR2S)2Cp2 (2a, R1=R2=CO2Me; 2b, R1=R2=Ph; 2c, R1=H, R2=CO2Me) whereas with 1 equiv of alkyne at room temperature the mixed dithiolene-dithiolate species Mo2(micro-SCR1=CR2S)(micro-SCH2CH2S)Cp2 (3a, R1=R2=CO2Me; 3b, R1=R2=Ph) are formed. The remaining dithiolate ligand in 3 can then be converted into a different dithiolene by reaction with a second alkyne. Applying this methodology, we have used bis(diphenylphosphino)acetylene to prepare the first examples of complexes containing phosphine-substituted dithiolene ligands: Mo2{micro-SC(CO2Me)=C(CO2Me)S}{micro-SC(PPh2)=C(PPh2)S}Cp2 (2g) and Mo2{micro-SC(PPh2)=C(PPh2)S}2Cp2 (2h). Tri- and tetrametallic complexes can then be assembled by coordination of these diphosphines to CpRuCl units by reaction with CpRu(PPh3)2Cl. Electrochemical studies of the Ru(II)/Ru(III) couple in Mo2{micro-SC(PPh2)=C(PPh2)S}2Cp2(RuClCp)2 (4b) reveals that the two separate ruthenium centers are oxidized electrochemically at different potentials, demonstrating communication between them through the dimolybdenum bis(dithiolene) core. Density functional theory calculations were carried out to explore the electronic structures of these species and to predict and assign their electronic spectra.