Rational Syntheses Of Tetranuclear Metal Sulfur Clusters And Their Utility As Catalytic Precursors (molybdenum, Iron, Cobalt, Nickel, Carbonyl).

Bridged metal disulfide and cis-bridging sulfide dimers were found to be useful starting materials for the designed synthesis of tetranuclear M(,2)M(,2)' sulfido clusters. Reaction of the disulfide Fe(,2)((mu)-S(,2))(CO)(,6) with (Cp or MeCp)(,2)M(,2)(CO)(,4) (M = Mo,W) at room temperature resulted in formation of the clusters (Cp or MeCp)(,2)M(,2)Fe(,2)((mu)(,3)-S)(,2)(CO)(,8). For M = Mo, isomeric butterfly and rhomboidal clusters with the above formula were isolated and characterized crystallographically. For M = W, only the butterfly isomer was obtained along with the capped triangular cluster Cp(,2)W(,2)Fe((mu)(,3)-S)(CO)(,7). A new synthesis of the dimer MeCpMo(S)SH (,2) (2) was found to give 75% yield in 12 hours compared to the previously reported 14 day preparation. Complex 2 reacts with the metal carbonyls Fe(,2)(CO)(,9), Co(,2)(CO)(,8), and Ni(CO)(,4) at ambient temperatures to form the clusters (MeCp)(,2)Mo(,2)Fe(,2)((mu)(,3)-S)(,4)(CO)(,6) (rhomboidal), (MeCp)(,2)Mo(,2)Co(,2)((mu)(,3)-S)(,2)((mu)(,4)-S)(CO)(,4) (butterfly), and (MeCp)(,2)Mo(,2)Ni(,2)((mu)(,3)-S)(,4)(CO)(,2) (butterfly), respectively, all of which were structurally characterized by single crystal X-ray diffraction. The Mo(,2)Co(,2) cluster is electron deficient according to valence electron counting rules and displays delocalized bonding about the unusual (mu)(,4)-S ligand in order to satisfy the cluster valence orbital requirements. Variations in the observed Mo-Mo bond lengths in the reported clusters indicated a strong correlation between Mo-Mo distance and the number of bridging sulfur ligands. Cyclic voltammetry revealed a rich reduction chemistry for all of the tetranuclear clusters. Reaction of 2 or MeCpMo(SC(,3)H(,6)S) (,2) with Cp(,2)'Mo(,2)(CO)(,4) was found to yield diamagnetic, mixed-Cp ligand Mo(,4)S(,4) cubanes. Crystallographic characterization of (MeCp)(,2)(Me(,5)Cp)(,2)Mo(,4)S(,4) revealed nearly precise T(,d) symmetry for the Mo(,4)S(,4) core. EHMO calculations for the cubanes Cp(,4)M(,4)X(,4) (M = Cr,Mo; X = O,S) were found to support the bonding model developed by Dahl and co-workers for these types of clusters. Preliminary investigation of the catalytic properties of (MeCp)(,2)Mo(,2)Fe(,2)S(,2)(CO)(,8) (butterfly isomer) decomposed on alumina indicated low activity but high selectivity for CO methanation in 3:1 H(,2)/CO. Temperature programmed decomposition studies and steady state product distributions indicated that sulfur and carbon were strongly bound to the catalyst surface and were not removable under reducing conditions.PhDInorganic chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127782/2/8521011.pd