American Chemical Society
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Synthesis and Structural Investigation of Stable Zirconacyclopentanes Which Bear Additional Functional Groups

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journal contribution
posted on 2001-11-13, 00:00 authored by Hongsui Sun, Vladimir V. Burlakov, Anke Spannenberg, Wolfgang Baumann, Perdita Arndt, Uwe Rosenthal
The reactions of zirconocene-alkyne complexes Cp‘2Zr(L)(η2-Me3SiC2SiMe3) {Cp‘2 = (η5-C5H5)2:  L = THF, 1; L = pyridine, 2; Cp‘2 = rac-ebthi, 3, [ebthi = 1,2-ethylene-1,1‘-bis(η5-tetrahydroindenyl)]} with 2 equiv (or excess) of bicyclo[2.2.1]hepta-2,5-diene (NBD) in THF at 50 °C result in five-membered zirconacyclopentane complexes Cp2Zr(C14H16) (4) and rac-(ebthi)Zr(C14H16) (5) (C14H16 means two coupled NBDs) in good yields. NMR spectra of complexes 4 and 5 show the C2 symmetry of the molecules, indicating that the two NBD components in the complexes are in exotransexo conformation. An X-ray crystallographic structure determination of 5 confirms that the two NBD fragments are exotransexo linked to form a racemate. Both optical isomers are present in a 1:1 ratio in the crystals. Reactions of 1 and 2 with 1 equiv of NBD have also been investigated, and only zirconacyclopentane complex 4 was isolated from the reactions. The analogous zirconacyclopentane complexes Cp2Zr(C22H20) (6) and rac-(ebthi)Zr(C22H20) (7) (C22H20 means two coupled BNBDs) are obtained from the reactions of 1 (or 2) and 3 with an excess of 1,4-dihydro-1,4-methanonaphthalene (BNBD), respectively. The X-ray structure of the orange complex 7 shows that the geometry of the Zr coordination sphere can be described as a distorted tetrahedron and similar to that of 5. The zirconacyclopentane complex rac-(ebthi)Zr(C14H15N) (9), bearing a free N coordinating site and a double bond, is formed from the coupling reaction of rac-(ebthi)Zr(C7H7N) (8) with NBD. All these reactions are stereospecific, and all new complexes are characterized by NMR, MS, and elemental analysis.