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A series of kinetic and thermodynamic deuterium isotope effects pertaining to the reactions of ansa-molybdenocene and -tungstenocene complexes of the type [Me2Si(C5Me4)(sub 2)]MRH (M = Mo, R=Ph, M = W, R = Me, Ph) is reported. It is demonstrated that the KIEs are highly dependent on the nature of the metal indicating that the energy surface for the reductive elimination of RH varies significantly for two otherwise similar systems.

Hydrodenitrogenation (HDN), the process by which nitrogen is removed form fossil fuels, is essential for minimizing NO(sub s) emissions. The reaction of Mo(PMe3)(sub 6) towards a variety of five and six-membered heterocyclic nitrogen compounds provide a series of complexes, including the first structurally characterized eta(super 6)-indolyl and eta(super 6)-(C5N)-quinoline derivatives, that may serve as structural models for the coordination of such heterocycles to molybdenum in heterogeneous HDN catalysts.

Research has been conducted on the hydrodesulfurization. The formation of the molybdenum thiophene adduct and butadiene-thiolate complex which are relevant to this hydrodesulfurization are described.

The reactivity of thiophenes to molybdenum compounds was studied to determine the molybdenum chemistry of hydrodesulfurization.

The overall reductive elimination of RH from the ansa-molybdenocene and -tungstenocene complexes [Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]Mo(Ph)H and [Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]W(R)H (R = Me, Ph) is characterized by an inverse primary kinetic isotope effect (KIE) for the tungsten system but a normal KIE for the molybdenum system. Oxidative addition of Phil to {[Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]M} also differs for the two systems, with the molybdenum system exhibiting a substantial intermolecular KIE, while no effect is observed for the tungsten system. These differences in KIEs indicate a significant difference in the reactivity of the hydrocarbon adducts [Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]M(RH) for the molybdenum and tungsten systems. Specifically, oxidative cleavage of [Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]M(RH) is favored over RH dissociation for the tungsten system, whereas RH dissociation is favored for the molybdenum system. A kinetics analysis of the interconversion of [Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]W(CH[sub 3])D and [Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]W(CH[sub 2]D)H, accompanied by elimination of methane, provides evidence that the reductive coupling step in this system is characterized by a normal KIE. This observation demonstrates that the inverse KIE for overall reductive elimination is a result of an inverse equilibrium isotope effect (EIE) and is not a result of an inverse KIE for a single step. A previous report of an inverse kinetic isotope effect of 0.76 for C-H reductive coupling in the [Tp]Pt(CH[sub 3])H[sub 2] system is shown to be erroneous. Finally, a computational study provides evidence that the reductive coupling of [Me[sub 2]Si(C[sub 5]Me[sub 4])[sub 2]]W(Ph)H proceeds via the initial formation of a benzene σ-complex, rather than an η²-π-benzene complex. [ABSTRACT FROM AUTHOR]

Examines the reaction of a molybdenum (Mo) compound with six-membered heterocyclic nitrogen compounds. Molecular structure of Mo compounds; Binding of the indolyl ligand to the six-membered arene ring; Coordination through the six-membered ring.