Preparation and characterization of Cp-functionalized cycloheptatrienyl–cyclopentadienyl titanium sandwich complexes (troticenes)

Cp-functionalized monotroticenes [(η7-C7H7)Ti(η5-C5H4E)] (2, E = Ph2SiCl; 3, E = tBu2SnCl; 12, E = I) and bitroticenes [(η7-C7H7)Ti(η5-C5H4)]2E′ (5, E′ = PPh; 6, E′ = BN(SiMe3)2; 7, E′ = Cp2Ti) were prepared by salt elimination metathesis between the monolithiated troticene [(η7-C7H7)Ti(η5-C5H4Li)]·pmdta (1b) (pmdta = N,N′,N′,N″,N″-pentamethyldiethylene-triamine) and the appropriate electrophile. The troticenyl-substituted zirconocene monochloride [(η7-C7H7)Ti(η5-C5H4ZrClCp*2)] (Cp* = η5-C5Me5) (8) and hafnocene ethoxide [(η7-C7H7)Ti{η5-C5H4Hf(OEt)Cp2}] (Cp = η5-C5H5) (11), and the heterobimetallic μ-oxo complexes [(η7-C7H7)Ti(η5-C5H4MCp2)]2O (9, M = Zr; 10, M = Hf) were obtained instead of the expected zircona- and hafna[1]troticenophanes by reaction of the dilithiated troticene [(η7-C7H6Li)Ti(η5-C5H4Li)]·pmdta (1a) with [Cp2MCl2] (M = Zr, Hf) or [Cp*2ZrCl2] in stoichiometric amounts. These compounds were characterized by single crystal X-ray diffraction analyses and, in the case of 2, 3, 5–7, 9, 10 and 12, also by elemental analyses and 1H, 13C and 119Sn NMR spectroscopy. Exposure of the troticenyl organotin chloride 3 to moisture resulted in its partial hydrolysis and formation of the organostannoxane-bridged bitroticene 4, while palladium-catalyzed Negishi C–C cross-coupling reaction between the troticenylzinc chloride [(η7-C7H7)Ti(η5-C5H4ZnCl)] (13) and the iodotroticene 12 or iodobenzene (PhI) led to the fulvalene complexes [(η7-C7H7)Ti(η5-C5H4)]2 (14) and [(η7-C7H7)Ti(η5-C5H4Ph)] (15). Compound 4 displays an unsymmetrical structure with the troticenyl fragments cis with respect to the Sn–O–Sn core, whereas compound 14 is centrosymmetrically trans oriented.

Graphical abstractSalt metathesis reactions between monolithiated troticene and various electrophiles lead to Cp-functionalized troticenes, some of which can be further used as synthons to afford pentafulvalene complexes. The reaction of the dilithiated troticene with metallocene dichlorides presumably provided metalla[1]troticenophanes, which undergo a regioselective cleavage by traces of water to afford heterobimetallic μ-oxo complexes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Functionalized cycloheptatrienyl–cyclopentadienyl titanium complexes were prepared. ► Selective lithiation and functionalization at the five-membered ring was achieved. ► Attempted preparation of metalla[1]troticenophanes afforded highly reactive species. ► Selective cleavage of the in situ formed strained troticenophanes was observed.