Cyclononatetraenyl‐Indenyl Transformation and a Zirconium(III) Trimer from Bulky Alkylcyclopentadienylzirconium Chlorides

Structure determinations of the known titanium, zirconium, and hafnium trichloro‐di(tert‐butyl)cyclopentadienyl complexes [Cp″MCl3] {Cp″ = η5‐C5H3tBu2, M = Zr (2), Ti (3), Hf (4)} on crystals obtained by sublimation show monomeric molecules in the solid state. Unlike the racemic di(tert‐butyl)(trimethylsilyl)cyclopentadienylzirconium trichloride 5, the 2,3‐diisopropyl‐1,4‐dimethylcyclopentadienylzirconium trichloride 7 is not a monomer according to its low volatility and the presence of two similar sets of signals in the NMR spectra. Reactions of 2 or its Cp″′ analogue [(η5‐C5H2tBu3‐1,2,4)ZrCl3] (1) with potassium cyclononatetraenide did not afford the desired cyclononatetraenyl complexes [Cp″′ (C9H9)ZrCl2] or its Cp″ analogue, but the indenyl complexes [Cp″′(C9H7)ZrCl2] (8) and [Cp″(C9H7)ZrCl2] (9). By reduction of the starting compound 1 with potassium a dark red, paramagnetic zirconium(III) complex was obtained and characterized as the cyclic trimer 10 with almost equal Zr···Zr distances of 3.384 Å.