NATURE OF THE SPECIES PRESENT IN THE ZIRCONOCENE DICHLORIDE BUTYLLITHIUM REACTION MIXTURE

The thermal decomposition of dibutylzirconocene (1) at room temperatur e affords paramagnetic butylzirconocene(III) (11), zirconocene(III) hy dride (12), the diamagnetic butenylzirconocene(IV) hydride dimer 5a, a nd the 1,1-bis(cyclopentadienyl)-2-methyl-3-(zirconocenyl hydride)-1-z irconacyclobutane(IV) dimer 9. Initially, decomposition furnishes crot ylzirconocene(IV) hydride (3a), followed by yclopentadienyl)-2-ethyl-1 -zirconacyclopropane(IV) (2a) and pentadienyl)-3,4-diethyl-1-zirconacy clopentane(IV) (4a), listed in the order of appearance. This order sug gests that the primary decomposition reaction is a gamma-H abstraction , which leads to the formation of yclopentadienyl)-2-methyl-1-zirconac yclobutane(IV) (6a). The latter was not observed experimentally but is postulated on the basis of secondary products. Reactions leading to t he above compounds are discussed from mechanistic and thermochemical p oints of view. The reported compounds have been characterized by eithe r EPR or multidimensional, multinuclear NMR spectroscopy. Compound 3a has also been synthesized independently from zirconocene chloride hydr ide and crotylmagnesium bromide and undergoes the same rearrangements into 2a and then 4a. The allyl analog 3b, synthesized from zirconocene chloride hydride and allylmagnesium bromide, exhibits the same behavi or and rearranges into clopentadienyl)-3,4-dimethyl-1-zirconacyclopent ane (4b).