The thermal decomposition of dibutylzirconocene (1) at room temperature affords paramagnetic butylzirconocene(III) (11), zirconocene(III) hydride (12), the diamagnetic butenylzirconocene(IV) hydride dimer 5a, and the 1,1-bis(cyclopentadienyl)-2-methyl-3-(zirconocenyl hydride)-1-zirconacyclobutane(IV) dimer 9. Initially, decomposition furnishes crotylzirconocene(IV) hydride (3a), followed by 1,1-bis(cyclopentadienyl)-2-ethyl-1-zirconacyclopropane(IV) (2a) and 1,1-bis(cyclopentadienyl)-3,4-diethyl-1-zirconacyclopentane(IV) (4a), listed in the order of appearance. This order suggests that the primary decomposition reaction is a γ-H abstraction, which leads to the formation of 1,1-bis(cyclopentadienyl)-2-methyl-1-zirconacyclobutane(IV) (6a). The latter was not observed experimentally but is postulated on the basis of secondary products. Reactions leading to the above compounds are discussed from mechanistic and thermochemical points of view. The reported compounds have been characterized by either EPR or multidimensional, multinuclear NMR spectroscopy. Compound 3a has also been synthesized independently from zirconocene chloride hydride 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 behavior and rearranges into 1,1-bis(cyclopentadienyl)-3,4-dimethyl-1-zirconacyclopentane (4b).

A kinetic study of the photochemical reaction of [Cp 2 Zr(µ-SiH 2 Ph)] 2 2+ 2[BBu n (C 6 F 5 ) 4-n ] -(1) with PhCH 2 SiH 3 to give the analogous PhCH 2 SiH 2 complex 2 was carried out using a combination of NMR and EPR spectroscopy to follow the rates of disappearance of reactants and the appearance of intermediates and products. The paramagnetic intermediate [Cp 2 Zr III ] + [BBu n (C 6 F 5 ) 4-n ] -(3) is produced with a quantum efficiency of 0.96 ( 0.16 on irradiation of 1 with light having λ < 450 nm. The rate law and analysis of intermediates supports a Zr(IV)/Zr(III) redox mechanism in which the rate-determining step is photodecomposition of 1 to generate 3 and silyl radicals by homolytic dissociation. In the presence of excess PhCH 2 SiH 3 3 reacts rapidly to give products.