Selective Synthesis of rac-C₂H₄-(η⁵-Ind)₂ZrCl₂ Assisted by Ancillary Directing Ligands

A series of ancillary directing ligands bearing O, S, N atoms were used to react with ZrCl4 to get the intermediate complexes, which showed certain diastereoselectivity when reacting with the dilithium salts of ethenebridged bis(indene). To carry out the selective synthesis, the ancillary directing ligand was firstly reacted with equal molar amount of ZrCl4 in toluene under argon overnight. The resultant suspension was transferred to the solid salts of C2H4［(η5Ind)Li］2 (molar ratio 1∶1) at 0 ℃. The reaction mixture was warmed up and stirred for 48 h at 30 ℃. Then the solvent was removed under vacuum and the residue was analyzed directly by 1HNMR spectroscopy to detect the relative amount of racC2H4(η5Ind)2ZrCl2 and mesoC2H4(η5Ind)2ZrCl2. Most of these ancillary directing ligands assisted the formation of racemic isomers, racC2H4(η5Ind)2ZrCl2, with the molar ratio of racC2H4(η5Ind)2ZrCl2 to mesoC2H4(η5Ind)2ZrCl2 as high as 74∶26. Further research demonstrated that the diastereoselectivity was significantly influenced by the structure, coordination atoms and substituents thereon of the intermediate complexes.