Syntheses and molecular structures of some tricobalt carbonyl clusters containing 2,4,6-trimethyl-1,3,5-trithiane

Reactions of CCo₃ carbonyl clusters Co₃(μ₃-CR)(CO)₉ with 2,4,6-trimethyl-1,3,5-trithiane (S^Me3) have given Co₃(μ₃-CR)(μ₃-S^Me3)(CO)₆ [R = H (1), CCSiMe₃ (2)]. A small amount of the coupled-alkyne product Me₃SiC₂[Co₂(CO)₆]C₂[Co₂(μ-S^Me3)(CO)₄]CCSiMe₃ (3) was isolated from the latter reaction. The reaction of Co₃(μ₃-CCCSiMe₃)(μ₃-S^Me3)(CO)₆ (2) with AuCl(PPh₃) in the presence of NaOMe gave Co₃{μ₃-CCCAu(PPh₃)}(μ₃-S^Me3)(CO)₆ (4), which in turn reacts with Co₃(μ₃-CBr)(CO)₉ in the presence of catalytic amounts of Pd(PPh₃)₄ and CuI to give {(OC)₉Co₃}(μ-CCCC){Co₃(μ₃-S^Me3)(CO)₆} (5). Further substitution of 5 with S^Me3 gave symmetrical {Co₃(μ₃-S^Me3)(CO)₆}₂(μ-CCCC) (6), also obtained from a reaction between {Co₃(CO)₉}₂(μ-CCCC) and two equivalents of S^Me3. Similar substitution of Co₃{μ₃-C(CC)₂[Ru(dppe)Cp*]}(CO)₉ with S^Me3 gave Co₃{μ₃-C(CC)₂[Ru(dppe)Cp*]}(μ₃-S^Me3)(CO)₆ (7). In all of these compounds, the S^Me3 ligand caps the basal face of the CCo₃ cluster on the opposite side to the μ₃-CR group. The three S donors occupy axial sites, with all CO groups being in equatorial sites. Reactions of Co₃(μ₃-CBr)(CO)₉ with S^Me3 gave only Co₃(μ₃-CX)(μ₃-S^Me3)(CO)₆ [X = C(O)NMe₂ (8), CO₂H (9)]. The redox properties and electronic structure of the C₄-bridged bis-cluster 6 have been investigated through a combination of cyclic voltammetry, IR spectroelectrochemistry and DFT calculations, with comparisons made with suitable model systems. Single-crystal X-ray diffraction structure determinations of 1, 2, 3, 4 and 8 are reported.