Zirconium Complexes with Cyclopentadienyl Ligands Involving Fused a Thiophene Fragment

The following cyclopentadienes (Cp‘H) with fused thiophene and benzothiophene fragments were synthesized:  4,5-dimethyl-6H-cyclopenta[b]thiophene (2), 5,6-dimethyl-4H-cyclopenta[b]thiophene (4), 1,3,5-trimethyl-4H-cyclopenta[c]thiophene (6), 2-methyl-1(and 3)H-cyclopenta[b][1]thiophenes (9), 2,3-dimethyl-1H-cyclopenta[b][1]benzothiophene (11), 1,2-dimethyl-3H-cyclopenta[b][1]benzothiophene (14). After a deprotonation of 2, 4, 11, and 14 with n-BuLi, followed by treatment of the resulting lithium salts with (η⁵-C₅Me₅)ZrCl₃, complexes (η⁵-Cp‘)(η⁵-C₅Me₅)ZrCl₂ were obtained. The ligand 6 gave a mixture of undesirable products instead of the respective metallocene. Two of them were isolated and turned out to be the polynuclear hydride complex {(Cp*Zr)(μ-H)(μ-Cl)₂(Cp*ZrCl)}₂(μ-Cl)₆Li₂ and a binuclear complex containing an unusual bridged bis[1,5-dimethyl-3-methylene-1,3-dihydro-η⁵-cyclopenta[c]thien-1-yl] ligand. Starting from the cyclopentadienes 2, 4, 11, and 14, several bis(cyclopentadienyl)dimethylsilanes were obtained and further used for the synthesis of the respective ansa-zirconocenes, which were isolated and unambiguously characterized either as pure diastereomeres or as rac/meso mixtures. Unbridged complex Cp‘₂ZrCl₂ was prepared in a similar manner from the ligand 9.