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

The complexes [Zr(η 2 -Me 3 SiC⋮CSiMe 3 )(η 5 -C 5 Me 4 R) 2 ] (R = Me ( 5 ), H ( 6 ), SiMe 3 ( 7 )) reacted smoothly with terminal alkynes HC⋮CR‘ (R‘ = CMe 3, SiMe 3, ferrocenyl (Fc), Ph) to give the agostic alkenyl−alkynyl complexes [Zr(η 1 -C⋮CR‘){η 3 -C(SiMe 3 ) CH(SiMe 3 )}(η 5 -C 5 Me 4 R) 2 ] (R/R‘ = Me/CMe 3 ( 5a ), Me/SiMe 3 ( 5b ), H/CMe 3 ( 6a ), H/SiMe 3 ( 6b ), H/Fc ( 6c ), H/Ph ( 6d ), SiMe 3 /CMe 3 ( 7a ), SiMe 3 /Fc ( 7c )). Complex 7a, formed in situ from 7 and HC⋮CCMe 3, dimerized tert -butylethyne exclusively to give the head-to-tail dimer Me 3 CC⋮CC(CMe 3 ) CH 2, 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 LiC⋮CSiMe 3 in toluene or THF yielded the diamagnetic zirconate complex Li[Zr(η 1 -C⋮CSiMe 3 )(η 2 -Me 3 SiC⋮CSiMe 3 )(η 5 -C 5 HMe 4 ) 2 ] ( 6e ) and its solvatomorph Li[Zr(η 1 -C⋮CSiMe 3 )(η 2 -Me 3 SiC⋮CSiMe 3 )(η 5 -C 5 HMe 4 ) 2 ]·C 4 H 8 O ( 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 β of the η 2 -Me 3 SiC⋮CSiMe 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.