ansa-Chromocenes: An alternative route to Me2Si(C5Me4)2Cr

The mechanism for the preparation of Me2Si(C5Me4)2Cr, 1, from CrCl2(THF)x and Me2Si(C5Me4)2Li2 was investigated and – in contrast to earlier claims – no evidence was found for the participation of an auxiliary ligand. The formation and stability of 1 is attributed to the combination of correct reaction conditions and a highly substituted ligand framework. Reactions with other ligands under identical conditions did not lead to the formation of ansa-chromocenes. Reaction with H4C2Ind2Li2 afforded the η3-Ind bridged dimer {H4C2(η5-Ind)(μ-,η3-Ind)Cr}2, 9. Complex 1 does not coordinate PPh3 or carbenes, but from reaction with two equivalents of xylyl isocyanide the CH-activated complex Me2Si(C5Me4)(η3-C5Me3(H)(CH2)Cr(CNC6MeH3)2, 7, was obtained. Complexes 7 and 9 were characterised by X-ray crystallography.