Ansa-Effects in Alkaline Earth Metal Octaphenylmetallocenophanes and a Derived Ansa-Ferrocene

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(C5Ph4CH2)2(thf)n] (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 (η 3 vs.η 5 ). Complex 3 is the first structurally characterised ansametallocene 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 FeCl2 provided the new ansa-ferrocene complex [Fe(C5Ph4CH2)2] (5). Structural, spectroscopic and electrochemical properties of this bent ferrocene complex were compared to the known unbridged octaphenylferrocene.