Structural Analysis of Zincocenes with Substituted Cyclopentadienyl Rings

New zincocenes [ZnCp′₂] ( 2 – 5 ) with substituted cyclopentadienyl ligands C₅Me₄H, C₅Me₄tBu, C₅Me₄SiMe₂tBu and C₅Me₄SiMe₃, respectively, have been prepared by the reaction of ZnCl₂ with the appropriate Cp′‐transfer reagent. For a comparative structural study, the known [Zn(C₅H₄SiMe₃)₂] ( 1 ), has also been investigated, along with the mixed‐ring zincocenes [Zn(C₅Me₅)(C₅Me₄SiMe₃)] ( 6 ) and [Zn(C₅Me₅)(C₅H₄SiMe₃)] ( 7 ), the last two obtained by conproportionation of [Zn(C₅Me₅)₂] with 5 or 1 , as appropriate. All new compounds were characterised by NMR spectroscopy, and by X‐ray methods, with the exception of 7 , which yields a side‐product ( C ) upon attempted crystallisation. Compounds 5 and 6 were also investigated by ¹³C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp′ ligands, while 3 and 4 exhibit slipped‐sandwich geometries. Compounds 5 and 6 have rigid, η⁵/η¹(σ) structures, in which the monohapto C₅Me₄SiMe₃ ligand is bound to zinc through the silyl‐bearing carbon atom, forming a Zn? C bond of comparable strength to the Zn? Me bond in ZnMe₂. Zincocene 5 has dynamic behaviour in solution, but a rigid η⁵/η¹(σ) structure in the solid state, as revealed by ¹³C CPMAS NMR studies, whereas for 6 the different nature of the Cp′ ligands and of the ring substituents of the η¹‐Cp′ group (Me and SiMe₃) have permitted observation for the first time of the rigid η⁵/η¹ solution structure. Iminoacyl compounds of composition [Zn(η⁵‐C₅Me₄R)(η¹‐C(NXyl)C₅Me₄R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6‐dimethylphenylisocyanide) have also been obtained and characterised.