New heterometallic sulfido clusters and their redox chemistry related to desulfurization catalysis.

Abstract

The reactivity of the cluster $\rm Cp\sp{Et}\sb2Mo\sb2Co\sb2S\sb4(CO)\sb2$ (2) $\rm(Cp\sp{Et}=EtMe\sb4C\sb5)$ with organic sulfur compounds was studied to aid our understanding of the commercial hydrodesulfurization process. Cluster 2 reacted with thiiranes and thietanes to give the corresponding organic alkene and insoluble solids which analyzed consistently for $\rm Cp\sp{Et}\sb2Mo\sb2Co\sb2S\sb{x}$ (x = 5-8). When a suspension of $\rm Cp\sp{Et}\sb2Mo\sb2Co\sb2S\sb{x}$ was reacted with CO at elevated pressure and temperature, 2 was recovered in $\sim$40% yield. In the presence of H$\sb2$ (200 psi) at 125$\sp\circ$C, a 50 fold excess of trans-2,3-diphenylthiirane reacted with 2 to give trans-stilbene in 83% yield. When a 100 fold excess of thietane was reacted with 2 and H$\sb2$ (500 psi) at 130$\sp\circ$C, complete and exclusive conversion to propane thiol was observed. The reaction of 2 with excess trans-2,4-diphenylthietane gave a mixture corresponding to C-S bond hydrogenolysis and desulfurization products. Elemental Hg does not act as a poison in the catalytic reactions with 2, nor in reactions with the conventional Co-Mo-S/$\rm Al\sb2O\sb3$ catalyst. Oxidative substitution of CO in 2 was observed when it was reacted with halogens, disulfides, and benzene thiol to form the paramagnetic 58 VSE clusters $\rm Cp\sp{Et}\sb2Mo\sb2Co\sb2S\sb4(X)\sb2$ (X = I (9), Br (10), Cl (11), SPh (12)). The molecular structures of 9, 11, and 12 were determined by X-ray analysis. The structures are consistent with the removal of a pair of electrons from a predominantly metal-metal bonding orbital and cleavage of a Co-Co bond. Clusters 9, 10, and 11 exhibited complex spin equilibria with S = 1, 2, and 3 states and simple paramagnetism was observed for cluster 12, with an S = 1 spin state. Cluster 12 reacted with CO to regenerate 2 and PhSSPh. Cluster 2 reacted with excess PhSH in a CO atmosphere at high pressure and temperature to give 12 and PhSSPh and PhS(CO)Ph in excess of the stoichiometric amounts based on 2. When 10 was reacted with excess Na, reductive aggregation of the cluster occurred to give $\rm\lbrack Cp\sp{Et}\sb2Mo\sb2Co\sb2S\sb4Br\rbrack\sb3.$ An X-ray structural determination revealed a triangular arrangement of three cubane moieties mutually bound by a Co atom coordinated to a CoS$\sb2$ "pocket" on an adjacent cubane unit. The clusters $\rm Cp\sp{Et}\sb2Mo\sb2Co\sb2S\sb4(NO)\sb2$ (20a), $\rm Cp\sp{Et}\sb2Mo\sb2Fe\sb2S\sb4(NO)\sb2$ (19a), $\rm Cp\sp*\sb2W\sb2Co\sb2S\sb4(NO)\sb2$ (22), $\rm Cp\sp*\sb2W\sb2Fe\sb2S\sb4(NO)\sb2$ (21), and $\rm Cp\sp{Et}\sb2W\sb2Co\sb2S\sb3(CO)\sb5$ (24) were synthesized and their structures were solved by X-ray analysis. The structures for 19a, 20a, 21, and 22 show that the clusters consist of a cubane core skeleton. The structure of 24 shows a butterfly arrangement of metal atoms with a terminal CO on the early transition metal atom, W. Cyclic voltammetry of all clusters revealed that they have multiple, stable oxidation states.