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Reactions of Substituted Zirconocene−Bis(trimethylsilyl)ethyne Complexes with Terminal Alkynes

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journal contribution
posted on 05.07.2004, 00:00 authored by Michal Horáček, Petr Štěpnička, Jiří Kubišta, Róbert Gyepes, Karel Mach
The complexes [Zr(η2-Me3SiC⋮CSiMe3)(η5-C5Me4R)2] (R = Me (5), H (6), SiMe3 (7)) reacted smoothly with terminal alkynes HC⋮CR‘ (R‘ = CMe3, SiMe3, ferrocenyl (Fc), Ph) to give the agostic alkenyl−alkynyl complexes [Zr(η1-C⋮CR‘){η3-C(SiMe3)CH(SiMe3)}(η5-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 HC⋮CCMe3, dimerized tert-butylethyne exclusively to give the head-to-tail dimer Me3CC⋮CC(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 57. Heating of complex 6 with LiC⋮CSiMe3 in toluene or THF yielded the diamagnetic zirconate complex Li[Zr(η1-C⋮CSiMe3)(η2-Me3SiC⋮CSiMe3)(η5-C5HMe4)2] (6e) and its solvatomorph Li[Zr(η1-C⋮CSiMe3)(η2-Me3SiC⋮CSiMe3)(η5-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 Cβ of the η2-Me3SiC⋮CSiMe3 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.