Zirconacyclopropanes and zirconacyclopropenes: Their formation and reactivity

Douglas Ray Swanson, Purdue University

Abstract

A convenient procedure to generate a zirconocene equivalent, Cp$\sb2$Zr(1-butene), from Cp$\sb2$ZrCl$\sb2$ and 2 equiv of n-BuLi allowed a facile exploration of the reactivity of zirconocene and organic substrates. This zirconocene equivalent displayed a $\pi$-reactivity with enynes, diynes, non-conjugated dienes by a $\pi$-displacement of 1-butene followed by cyclization. Alkenes and conjugated dienes displayed a $\sigma$-reactivity by carbometalation of the zirconacyclopropane to give 1-butene incorporated products. The corresponding conjugated diene-zirconocene complexes could be produced without incorporation of 1-butene by generating a new zirconocene equivalent, Cp$\sb2$Zr(isobutylene), from Cp$\sb2$ZrCl$\sb2$ and 2 equiv of t-BuLi. A facile $\pi$-displacement of the isobutylene allowed entry into a general synthesis of zirconocene-diene complexes and zirconocene-olefin-PMe$\sb3$ complexes. The decomposition of dialkylzirconocenes in the presence of phosphines to form zirconocene-olefin-PMe$\sb3$ complexes is shown to occur via a non-dissociative mechanism. The mechanistic details are presented. A convenient procedure to generate a Cp$\sb2$Zr(H)Cl equivalent, Cp$\sb2$Zr(isobutyl)Cl, was presented. Alkynes and alkenes were found to hydrozirconate cleanly in high yields upon heating to 50$\sp\circ$C, releasing isobutylene. A novel mechanism for olefin isomerization is presented for the zirconocene catalyzed (Z)- to (E)-stilbene isomerization. A dipolar 16-electron zirconocene intermediate containing two stilbene molecules is proposed. The mechanistic details of this reaction are presented.

Degree

Ph.D.

Advisors

Negishi, Purdue University.

Subject Area

Organic chemistry

COinS