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

The reactions of zirconocene-alkyne complexes Cp‘ 2 Zr(L)(η 2 -Me 3 SiC 2 SiMe 3 ) {Cp‘ 2 = (η 5 -C 5 H 5 ) 2: L = THF, 1; L = pyridine, 2; Cp‘ 2 = rac -ebthi, 3, [ebthi = 1,2-ethylene-1,1‘-bis(η 5 -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 Cp 2 Zr(C 14 H 16 ) ( 4 ) and rac -(ebthi)Zr(C 14 H 16 ) ( 5 ) (C 14 H 16 means two coupled NBDs) in good yields. NMR spectra of complexes 4 and 5 show the C 2 symmetry of the molecules, indicating that the two NBD components in the complexes are in exo − trans − exo conformation. An X-ray crystallographic structure determination of 5 confirms that the two NBD fragments are exo − trans − exo 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 Cp 2 Zr(C 22 H 20 ) ( 6 ) and rac -(ebthi)Zr(C 22 H 20 ) ( 7 ) (C 22 H 20 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(C 14 H 15 N) ( 9 ), bearing a free N coordinating site and a double bond, is formed from the coupling reaction of rac -(ebthi)Zr(C 7 H 7 N) ( 8 ) with NBD. All these reactions are stereospecific, and all new complexes are characterized by NMR, MS, and elemental analysis.