<i>Ansa</i>-effects in alkaline earth metal octaphenylmetallocenophanes and a derived <i>ansa</i>-ferrocene

The synthesis and structural characterisation of a series of alkaline earth <i>ansa</i>-octaphenylmetallocenes (Mg, Ca, Sr, Ba) bearing an ethylene bridge are described. The complexes [AE(C₅Ph₄CH₂)₂(thf)_<i>n</i>] (AE = Mg (1), Ca (2) <i>n</i> = 1; AE = Sr (3), Ba (4), <i>n</i> = 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 (η³<i>vs.</i> η⁵). Complex 3 is the first structurally characterised <i>ansa</i>-metallocene complex of Sr. An <i>ansa</i>-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 <i>ansa</i> complex 2 to FeCl₂ provided the new <i>ansa</i>-ferrocene complex [Fe(C₅Ph₄CH₂)₂] (5). Structural, spectroscopic and electrochemical properties of this bent ferrocenophane complex were compared to those of the known unbridged octaphenylferrocene.