Reactions of substituted zirconocene-bis(trimethylsilyl)ethyne complexes with terminal alkynes

The complexes [Zr(eta(2)-Me(3)SiCequivalent toCSiMe(3))(eta(5)-C5Me4R)(2)] (R = Me (5), H (6), SiMe3 (7)) reacted smoothly with terminal alkynes HCequivalent toCR' (R' = CMe3, SiMe3, ferrocenyl (Fc), Ph) to give the agostic alkenyl-alkynyl complexes [Zr(eta(1)-Cequivalent toCR'){eta(3)-C(SiMe3)=CH(SiMe3)}(eta(5)-C5Me4R)(2)] (R/ R'= Me/CMe3 (5a), Me/SiMe3 (5b), H/CMe3 (6a), H/SiMe3 (6b), H/Fc (6c), H/Ph (6d), SiMe3/ CMe3 (7a), SiMe3/Fc (7c)). Complex 7a, formed in situ from 7 and HCequivalent toCCMe(3), dimerized tert-butylethyne exclusively to give the head-to-tail dimer Me(3)CCequivalent toCC(CMe3)=CH2, and when all the terminal alkyne was consumed, 7 was restored. Complex 7 reacted similarly with 1-hexyne, phenylethyne, and (trimethylsilyl)ethyne, affording the respective alkenyl-alkynyl complexes, which also changed back to 7 on evaporation of the reaction solutions; none of these terminal alkynes was dimerized with 5-7. Heating of complex 6 with LiCequivalent toCSiMe(3) in toluene or THF yielded the diamagnetic zirconate complex Li[Zr(eta(1)-Cequivalent toCSiMe(3))(eta(2)-Me(3)SiCequivalent toCSiMe(3))(eta(5)-C5HMe4)(2)] (6e) and its solvatomorph Li[Zr(eta(1)-Cequivalent toCSiMe(3))(eta(2)-Me(3)SiCequivalent toCSiMe(3))( C5HMe4)(2)] . C4H8O (6f), respectively. The lithium cation in 6e and 6f is placed in a position at the side of the alkynyl triple bond and close to C-beta of the eta(2)-Me(3)SiCequivalent toCSiMe(3) ligand, apparently interacting with both moieties. All presented complexes were characterized by the standard spectral methods, and the structures of 5a, 6a, 6c, 6d, and 6e were determined by single-crystal X-ray diffraction.