The synthesis, crystal structure, and magnetic properties of [Cp2TiGi-OCH3)]2 (1) (Cp = tj5-C5H5) and [Cp2Ti-(m-OC2H5)]2 (2) are described. The two compounds are obtained from [Cp2Ti(CH3)2] and trimethoxy-and triethoxysilane, respectively, in hexane. Both crystallize in the tetragonal system, space group PAnl.
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).
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