Allyl Complexes of Tungsten from the Rearrangement of Transient Cyclopropyl Precursors

Abstract

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 η3‐allyl derivatives [Cp*W(NO)(CH2R)(η3‐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 β‐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.

Highly Enantioselective Cobalt‐Catalyzed (3+2) Cycloadditions of Alkynylidenecyclopropanes

“…This step is not ac anonical b-carboelimination, but instead consists of adistal opening of the cyclopropyl ring (C•••C bond distance of 2.10 in TS2' '' '), ap rocess reminiscent to that previously proposed for cyclopropyl Rh III complexes and other transition metal derivatives. [25] Although the pathways proceeding through TS1 and TS1' ' cannot be discarded, the high stability of INT0' ',a nd Interestingly,t he computational study showed that the cyclopropyl to p-allyl rearrangement is also viable using an homologous Rh I complex (difference in activation barriers of approx. 1kcal mol À1 ).…”

Highly Enantioselective Cobalt‐Catalyzed (3+2) Cycloadditions of Alkynylidenecyclopropanes

“…This step is not ac anonical b-carboelimination, but instead consists of adistal opening of the cyclopropyl ring (C•••C bond distance of 2.10 in TS2' '' '), ap rocess reminiscent to that previously proposed for cyclopropyl Rh III complexes and other transition metal derivatives. [25] Although the pathways proceeding through TS1 and TS1' ' cannot be discarded, the high stability of INT0' ',a nd especially,t he low activation barriers associated with the subsequent steps,c learly favor the mechanism involving the cobaltacyclopentene INT1' '' '.…”

Regioselective C–F Bond Activation/C–C Bond Formation between Fluoropyridines and Cyclopropyl Groups at Zirconium

“…Deuterated solvents (benzene- d 6 , toluene- d 8 , cyclohexane- d 12 ) were degassed by freeze–pump–thaw cycles, dried over activated molecular sieves, and stored under argon. The syntheses of complex 1 , cyclopropyllithium, dicylopropylmagnesium, , dicyclopropylzinc, were carried out according to the reported procedures with limited modifications. Tricyclopropylaluminum was synthesized following a modified procedure used for triphenylaluminum …”