| Abstract
| - The zirconocene−alkyne complex Cp2Zr(py)(η2-Me3SiC2SiMe3) reacts with methyl vinylketone to yield the zirconadihydrofuran (1). In contrast, rac-(ebthi)Zr(η2-Me3SiC2SiMe3) (ebthi = 1,2-ethylene-1,1‘-bis(η5-tetrahydroindenyl) reacts with methylvinyl ketone giving, for the first time, the 1,4-conjugated insertion product (2) in good yield. An X-ray crystallographic structuredetermination of 2 shows that the seven-membered ring is twisted in such a way to fit thesteric demands of the “ebthi” and SiMe3 groups. Treating rac-(ebthi)Zr(η2-Me3SiC2SiMe3)with tert-butyl acrylate gives the zirconadihydrofuran (3).The monomeric structure of 3 has been established by X-ray crystallography. A differenttype of zirconadihydrofuran, (4), resultsfrom the reaction with mesityl oxide. Complexes analogous to 4 and 2 were observedconsecutively by NMR in the reaction of Thi2Zr(η2-Me3SiC2SiMe3) (Thi = η5-tetrahydroindenyl) with methyl vinyl ketone. This lets one conclude that the carbonyl insertion products(e.g. 4) are formed first as intermediates. Finally, (5), azirconacyclopentene, is obtained from rac-(ebthi)Zr(η2-Me3SiC2SiMe3) and isoprene.
- The reactions of zirconocene−alkyne complexes with α,β-unsaturated carbonyl compounds give three different types of products: 1,2-insertion of the carbonyl into the zirconacyclopropene or 1,4-coordination connected with alkyne elimination leads to zirconadihydrofurans and 1,4-conjugated insertion of the heterodiene into the zirconacyclopropene produces novel seven-membered zirconacycles. The first type of complex was found to be the kinetically preferred one.
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