SYNTHETIC AND STRUCTURAL STUDIES ON (RC5H4)4RU4E40/2+ (E = S, SE, TE) - MOBILE METAL-METAL BONDS WITHIN A MIXED-VALENCE RUIV/RUIII CLUSTER

Thermolysis of solutions of (MeC5H4)Ru(PPh3)2EH (E = S, Se) gives the cubane clusters (MeC5H4)4Ru4E4. For the case for E = S, the coproducts were shown to be PPh3 and H-2. A rational synthesis of PPh4TeH is reported; this salt was employed in the preparation of (MeC5H4)4Ru4Te4. This Ru4Te4 cluster crystallizes in the monoclinic space group C2/c with a = 11.943(6) angstrom, b = 18.623(6) angstrom, c = 12.590(7) angstrom, V = 2792(4) angstrom3, and Z = 8. Structural trends show that the identity of the chalcogen more strongly affects the nonbonding Ru ... Ru, Ru ... E, and E ... E interactions than the bonding interactions. The clusters undergo 2e oxidations as demonstrated by cyclic voltammetry studies. Chemical oxidations using (MeC5H4)2Fe+ gave salts of the dications (MeC5H4)4Ru4E42+ (E = S, Se, Te). The dicationic S4 and Se4 clusters exhibit dynamic H-1 NMR properties such that at low temperatures signals for two CH3C5H4 groups were observed while at high temperatures the MeC5H4 groups appear equivalent. On the basis of coalescence temperatures, the barriers were estimated as approximately 52 kJ/mol. In a test of the possible influence of steric factors on the dynamics, the DNMR properties of the new derivative (Me3SiC5H4)4Ru4S4(PF6)2 were shown also to be very similar to the MeC5H4 clusters. The Me3SiC5H4 cluster crystallizes in the monoclinic space group P2(1)/c with a = 18.828(2) angstrom, b = 12.421 (1) angstrom, c = 21.451 (1) angstrom, beta = 92.442(1)-degrees, V = 5012 angstrom3, and Z = 4. The structure confirms the presence of three Ru-Ru bonding distances. Variable-temperature NMR experiments on (MeC5H4)4Fe4S42+ and (MeC5H4)4Ru4S4 gave no evidence of structural dynamics.