Multimetallic catalysis based on heterometallic complexes and clusters.

The chemistry of transition metals with three-membered ring heterocycles.

Hydrogenation, Hydrogenolysis, and Desulfurization of Thiophenes by Soluble Metal Complexes: Recent Achievements and Future Directions

Sulfur removal from petroleum is important from the standpoint of the global environment because the combustion of sulfur compounds leads to the production of sulfur oxides, which are the source of acid rain. As the regulations for sulfur in fuels become more stringent, the existing chemical desulfurizations are coming inadequate for the "deeper desulfurization" to produce lower-sulfur fuels without new and innovative processes. Biodesulfurization is rising as one of the candidates. Several microorganisms were found to desulfurize dibenzothiophene (DBT), a representative of the organic sulfur compounds in petroleum, forming a sulfur-free compound, 2-hydroxybiphenyl. They are promising as biocatalysts in the microbial desulfurization of petroleum because without assimilation of the carbon content, they remove only sulfur from the heterocyclic compounds which is refractory to conventional chemical desulfurization. Both enzymological and molecular genetic studies are now in progress for the purpose of obtaining improved desulfurization activity of organisms. The genes involved in the sulfur-specific DBT desulfurization were identified and the corresponding enzymes have been investigated. From the practical point of view, it has been proved that the microbial desulfurization proceeds in the presence of high concentrations of hydrocarbons, and more complicated DBT analogs are also desulfurized by the microorganisms. This review outlines the progress in the studies of the microbial desulfurization from the basic and practical point of view.

Microbial Desulfurization of Organic Sulfur Compounds in Petroleum

An overview of modeling studies in HDS, HDN and HDO catalysis

The kinetics of the reaction of a series of aromatic and aliphatic thiols with cluster 1 were determined. These reactions form cluster 2 and the arene or alkane corresponding to the thiol:  Cp‘2Mo2Co2S3(CO)4 (1) + RSH → Cp‘2Mo2Co2S4(CO)2 (2) + RH + 2CO. These reactions are first order in thiol and first order in cluster 1 with appreciable negative entropies of activation. These data suggest that the rate determining step of the desulfurization reaction is the initial association of the thiol to the cluster. The more nucleophilic thiolate anions react with 1 at −40 °C to form an adduct in which the thiolate anion is bound η1 to the Co atom. At −25 °C, the initial adduct rearranges to a fluxional μ2, η1-bound thiolate. The fluxional process is proposed to involve a concerted “walking” of the thiolate and a μ2-bound sulfide ligand on the surface of the cluster. Near 35 °C, the thiolate−cluster adduct undergoes C−S bond homolysis to give the paramagnetic anion of cluster 1 and the phenyl or alkyl radical. The...

Homolytic C−S Bond Scission in the Desulfurization of Aromatic and Aliphatic Thiols Mediated by a Mo/Co/S Cluster: Mechanistic Aspects Relevant to HDS Catalysis

Activation of C-S Bond Homolysis by Coordination to a Mo/Co/S-Containing Cluster

Structures of the Anionic Mo/Co/S Cluster Salts [BnNMe3][Cp‘2Mo2Co2S4(CO)2], [Na(15-crown-5)1.5][Cp*2Mo2Co2S4(CO)2], and [BnNMe3][Cp‘2Mo2Co2S3(CO)3(SAr)] (Bn = Benzyl, Cp* = C5Me4Et, Ar = p-Tolyl)

Scott H. Druker

Papers

Homolytic C−S Bond Scission in the Desulfurization of Aromatic and Aliphatic Thiols Mediated by a Mo/Co/S Cluster: Mechanistic Aspects Relevant to HDS Catalysis

Activation of C-S Bond Homolysis by Coordination to a Mo/Co/S-Containing Cluster

Structures of the Anionic Mo/Co/S Cluster Salts [BnNMe3][Cp‘2Mo2Co2S4(CO)2], [Na(15-crown-5)1.5][Cp2Mo2Co2S4(CO)2], and [BnNMe3][Cp‘2Mo2Co2S3(CO)3(SAr)] (Bn = Benzyl, Cp = C5Me4Et, Ar = p-Tolyl)