New ionic half-metallocenes of early lanthanides

We present in this study a new and one-step method allowing the preparation of an unprecedented family of stable half-lanthanidocenes. X-ray analysis shows that the isolated compounds all display the same ionic Ln–Mg bimetallic structure consisting of two anionic (Cp R)Ln(BH 4) 3 species and one cationic Mg(THF) 6 (Cp R = C 5Me 5, Ln = Nd, 1a, Ln = La, 1b; Cp R = C 5H 5, Ln = Nd, 2a; Cp R = C 5H 2Ph 3, Ln = Nd, 3a). Such complexes display high stability with respect to disproportionation in solution. Combined with dialkylmagnesium, neodymium complexes provide powerful catalysts for stereospecific isoprene polymerisation.