Thomas R. Halbert

Synthesis and activity of hydrotreating catalysts prepared via promotion by low-valent transition-metal complexes

A new family of hydrotreating catalysts is developed via low-temperature chemical reaction of the edge of preformed MoS2 particles. Specifically, an “edge decoration” is achieved via reaction of MoS2 with low-valent organometallic complexes such as Co2(CO)8. This approach is suggested by the reactivity of similar low-valent organometallics with molecular complexes whose structure contains fragments that resemble those in transition-metal sulfides. Activity tests with pure compounds and commercial feedstocks have shown that these catalysts are active for hydrodesulfurizatlon.

Ligand and induced internal redox processes in Mo- and W-S systems

Abstract This paper reviews recent work from our laboratory on redox chemistry of Mo-S systems. Mo and S are each capable of existing in multiple oxidation states. When found together in the same compound, these elements elicit numerous redox possibilities. The classical situation involving simple changes in the oxidation state of Mo is well known. Recent work has also documented the ability of coordinated S ligands (e.g. S2−, S2−2 and S2−4) to undergo redox while Mo remains in a given state of oxidation. In this paper cases are presented wherein both the Mo and S oxidation states change. For example, the reaction of the red MoS2−4 ion with organic disulfides gives the purple Mo2S2−8 ion in high yield. The oxidizing disulfide added to the hexavalent MoS2−4 ion leads quantitatively to the reduced pentavalent dinuclear Mo2S2−8 ion. Mechanistically, this reaction proceeds in two stages involving a green intermediate of yet unknown structure. The net reaction embodies an induced internal electron transfer from S to Mo in the same sense that Taube et al. elucidated in the chemistry of cobalt. Application of the concept of induced internal electron transfer allows access to new low-valent Mo-S systems by adding oxidants to Mo(VI)-S species. For example, the reactions of MoS2−4 with thiuram disulfides give compounds of the form MoS2(S2CNR2)3 (R = Et or iBu). These are mononuclear EPR-active Mo(V) complexes containing eight-coordinate Mo. As expected, W shows distinctly less reactivity than Mo in S → M redox processes. The ability of S2− ligands to act as donors and Mo and W atoms to act as acceptors of electron density has also been exploited in the synthesis of new heteronuclear “thiocubane” clusters.

Molecules, clusters, solids and catalysts in early transition metal sulphide systems

Inorganic syntheses starting with the tetrathiometallates of molybdenum, tungsten, vanadium and rhenium produce new homonuclear transition metal sulphide (TMS) complexes and clusters by utilizing internal redox processes. The resultant molecular structures often contain features or fragments that resemble those in TMS solids. The homonuclear complexes serve synthetically as excellent ligands, particularly to low-valent organometallic metals. The resulting heteronuclear TMS clusters serve as precursors to TMS solids that are active hydrodesulphurization catalysts. Moreover, the same reactions that lead to the heteronuclear TMS clusters allow decoration of the edges of preformed MoS2 catalysts, leading to active catalytic materials.

Intercalation of organometallic compounds into layered transition metal oxyhalides

Abstract The syntheses of the new intercalate compounds FeOCl[(EtMe 4 Cp) 2 Fe] 0.16 , VOCl(CoCp 2 ) 0.16 , and TiOCl(CoCp 2 ) 0.16 are reported. Their structures are found by X-ray powder diffraction to be qualitatively the same as those of the previously reported complexes FeOCl(CoCp 2 ) 0.16 and FeOCl(FeCp 2 ) 0.16 . Results of 57 Fe Mossbauer and magnetic susceptibility studies on the latter two compounds are reported, and shown to be consistent with electron transfer from the metallocene to the host upon intercalation.