Zirconium-promoted carbon-carbon and carbon-heteroatom bond-forming and -cleaving reactions

Christophe Jacques Rousset, Purdue University

Abstract

n-Bu$\sb2$ZrCp$\sb2$ decomposes as ($\eta\sp2$-1-butene)ZrCp$\sb2$ which has been shown to bicyclize non-conjugated dienes in a stereoselective manner. The resulting zirconabicycles could be converted to the corresponding 1,2-dimethylcycloalkanes and 1,2-bis(iodomethyl)cycloalkanes via hydrolysis and iodinolysis, respectively, or to bicyclic ketones and bicyclic alcohols via a carbonylation/iodinolysis and a carbonylation/hydrolysis sequence, respectively. In contrast with its reaction with non-conjugated dienes which proceeds via extrusion of 1-butene, ($\eta\sp2$-1-butene)ZrCp$\sb2$ reacts with 1-alkenes with incorporation of the 1-butene moiety to give regio- and stereoselectively the corresponding trans-3,4-dialkylzirconacyclopentanes. However, the reaction is not "pair"-selective. Interestingly, the reaction of ($\eta\sp2$-1-butene)ZrCp$\sb2$ with styrene is "pair"-selective and produces trans-2-aryl-4-ethylzirconacyclopentane. All these reactions which presumably involve a reaction of carbometallation between zirconacyclopropanes and alkenes to produce zirconacyclopentanes have been shown to lead to the thermodynamically equilibrated products suggesting that the formation of three- and five-membered zirconacycles is reversible. The latter ones appear to be useful intermediates in various catalytic processes as their reactions with Grignard reagents led to the development of several Zr-catalyzed carbon-carbon bond-forming reactions such as carbomagnesation of alkenes, cyclization of non-conjugated dienes and head to tail dimerization of 1-alkenes. It was also found that dialkylzirconocenes, e.g., Cp$\sb2$Zr(Et)$\sb2$ or Cp$\sb2$Zr(Bu-n)$\sb2$, are active catalyst precursors for the hydrosilation reaction of alkenes which is believed to proceed via silyl(hydrido)zirconocene derivatives. Finally, and in an effort to develop enantioselective procedures, two enantiomerically pure zirconium and hafnium dichloride complexes were prepared from a $\beta$-pinene derived cyclopentadiene. 1,2-Migratory insertion reaction is another impotant fundamental pattern for C-C bond formation via organotransition metals. It has been found that alkynylzirconium derivatives can undergo facile 1,2-migratory insertion reaction which, unlike some other known 1,2-migrations such as those involving $\alpha$,$\beta$-unsaturated organoborates, proceeds without the assistance of an external electrophile.

Degree

Ph.D.

Advisors

Negishi, Purdue University.

Subject Area

Organic chemistry

COinS