Allyl Complexes of Tungsten from the Rearrangement of Transient Cyclopropyl Precursors

This article explores the contrasting reactivity of cyclopropyl complexes of early transition metals. [Cp*W(NO)(CH2R)(c-C3H5)] (R = SiMe3, Ph, t-Bu) generated in THF solution from [Cp*W(NO)(CH2R)Cl] and [Mg(c-C3H5)(2)(dioxane)(x)] readily rearrange to eta(3)-allyl derivatives [Cp*W(NO)(CH2R)(eta(3)-C3H5)] by an intramolecular ring opening reaction. Both direct and catalyzed pathways are revealed by kinetic studies. Computational modeling indicates the ring opening reaction is preferred on thermodynamic grounds for tungsten whereas kinetic products arising from beta-H abstraction reactions of cyclopropane are observed for related zirconium and niobium complexes reported previously. The energetic accessibility and the nature of the LUMO in the tungsten complexes promote distal CC bond cleavage in the cyclopropyl ring.