Shephard, Angus C.G., Bouammali, Amal, Delon, Aymeric, Guo, Zhifang, Chevreux, Sylviane, Niebel, Claude, Dautel, Olivier, Simler, Thomas, Deacon, Glen B., Junk, Peter C., and Jaroschik, Florian (2025) Ansa-effects in alkaline earth metal octaphenylmetallocenophanes and a derived ansa-ferrocene. Dalton Transactions, 54 (37). pp. 13918-13928.

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Abstract

The synthesis and structural characterisation of a series of alkaline earth ansa-octaphenylmetallocenes (Mg, Ca, Sr, Ba) bearing an ethylene bridge are described. The complexes [AE(C<inf>5</inf>Ph<inf>4</inf>CH<inf>2</inf>)<inf>2</inf>(thf)<inf>n</inf>] (AE = Mg (1), Ca (2) n = 1; AE = Sr (3), Ba (4), n = 2) were obtained through reductive dimerisation of 1,2,3,4-tetraphenylfulvene, facilitated by zero-valent metals and fully characterised by NMR spectroscopy. Single-crystal XRD studies reveal distinct binding differences of the Cp ligands to Mg in complex 1 compared to the heavier analogues (η³vs. η⁵). Complex 3 is the first structurally characterised ansa-metallocene complex of Sr. An ansa-effect was observed for the Ba complex 4 which showed good stability at room temperature in contrast to the previously described non-bridged analogue. Efficient transmetallation from the Ca ansa complex 2 to FeCl<inf>2</inf> provided the new ansa-ferrocene complex [Fe(C<inf>5</inf>Ph<inf>4</inf>CH<inf>2</inf>)<inf>2</inf>] (5). Structural, spectroscopic and electrochemical properties of this bent ferrocenophane complex were compared to those of the known unbridged octaphenylferrocene.

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