Titanocene Silylpropyne Complexes: Promising Intermediates en route to a Four‐Membered 1‐Metallacyclobuta‐2,3‐diene?

Coordination of the alkyl‐substituted alkynes Me 3 SiC 2 CH 2 R ( 1 : R=SiMe 3 ; 2 : R=N(SiMe 3 ) 2 ) to titanocene centres [Cp′ 2 Ti] (Cp′=Cp, Cp*) yields stable alkyne complexes of the type Cp′ 2 Ti(η 2 ‐Me 3 SiC 2 CH 2 R) ( 3 : Cp′=Cp, R=SiMe 3 ; 5 : Cp′=Cp, R=N(SiMe 3 ) 2 ; 6 : Cp′=Cp*, R=SiMe 3 ) that are not prone to alkyne/allene isomerisation. When reacting alkyne  2 with Cp * 2 TiCl 2 and Mg formation of the complex Cp* 2 Ti(III)(η 3 ‐Me 3 SiC 2 CH 2 ) ( 7 ) which displays a propargylic unit coordinated to the Ti III centre takes place. All complexes were fully characterised, the molecular structures for 5 , 6 , and 7 are discussed.