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

Reactions of CCo3 carbonyl clusters Co3(mu3-CR)(CO)9 with 2,4,6-trimethyl-1,3,5-trithiane (SMe3) have given Co3(mu3-CR)(mu3-SMe3)(CO)6 [R = H (1), C[triple bond]CSiMe3 (2)]. A small amount of the coupled-alkyne product Me3SiC2[Co2(CO)6]C2[Co2(mu-SMe3)(CO)4]C[triple bond]CSiMe3 (3) was isolated from the latter reaction. The reaction of Co3(mu3-CC[triple bond]CSiMe3)(mu3-SMe3)(CO)6 (2) with AuCl(PPh3) in the presence of NaOMe gave Co3{mu3-CC[triple bond]CAu(PPh3)}(mu3-SMe3)(CO)6 (4), which in turn reacts with Co3(mu3-CBr)(CO)9 in the presence of catalytic amounts of Pd(PPh3)4 and CuI to give {(OC)9Co3}(mu-C[triple bond]CC[triple bond]C){Co3(mu3-SMe3)(CO)6} (5). Further substitution of 5 with SMe3 gave symmetrical {Co3(mu3-SMe3)(CO)6}2(mu-C[triple bond]CC[triple bond]C) (6), also obtained from a reaction between {Co3(CO)9}2(mu-C[triple bond]CC[triple bond]C) and two equivalents of SMe3. Similar substitution of Co3{mu3-C(C[triple bond]C)2[Ru(dppe)Cp*]}(CO)9 with SMe3 gave Co3{mu3-C(C[triple bond]C)2[Ru(dppe)Cp*]}(mu3-SMe3)(CO)6 (7). In all of these compounds, the SMe3 ligand caps the basal face of the CCo3 cluster on the opposite side to the mu3-CR group. The three S donors occupy axial sites, with all CO groups being in equatorial sites. Reactions of Co3(mu3-CBr)(CO)9 with SMe3 gave only Co3(mu3-CX)(mu3-SMe3)(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.