FORMATION AND STRUCTURE OF A NOVEL LARGE-RING GROUP-4 ANSA-METALLOCENE COMPLEX

1,12-Dodecanediol was treated with 2 molar equiv of methanesulfonyl chloride and then with indenyllithium to yield 1,12-bis(3-indenyl)dodecane (4). Double deprotonation of 4 with n-butyllithium gave the corresponding dilithio compound 5. Its reaction with ZrCl4(THF)2 in tetrahydrofuran under high dilution conditions gave the large-ring ansa-metallocene dihalide complex rac-6 in 15% isolated yield. Under similar conditions the reaction of 5 with ZrCl4(THF) 2 in toluene solvent allowed the isolation of the diastereoisomer meso-6 in 11% yield. The complex rac-6 was hydrogenated to yield the corresponding large-ring ansa-bis(tetrahydroindenyl)zirconium dichloride complex rac-8. Each of the complexes rac-6, meso-6, and rac-8 reacted cleanly with methyllithium to yield the corresponding ansa-metallocene dimethyl derivatives (rac-7, meso-7, rac-9). The organic compound 4 and the ansa-metallocene rac-6 were characterized by X-ray diffraction. In the solid state the metallocene precursor 4 exhibits a (-CH2-)12 chain at its maximal elongation, which separates the indenyl end groups intramolecularly as far as possible. In the large-ring ansa-metallocene dichloride complex rac-6 the 1,12-dodecanediyl chain that connects the two eta5-indenyl ligands is oriented in a nearly C2-symmetric arrangement in the central position in front of the bent-metallocene wedge. In this orientation the mean plane of the (-CH2-)12 loop is arranged orthogonal to the ZrCl2 sigma-ligand plane and spatially separates the two segments in front of the bent-metallocene unit where the reactive sigma-ligands are located.