Elemental Magnesium as an Early Transition Metal Substitute: From Pentafulvene Coordination to Deprotonation of Amines.

The reaction of magnesium turnings and 6,6-di-para-tolylpentafulvene was investigated. Under mild conditions, the magnesium dissolves, forming the MgII complex 1 with a π-η5  : σ-κ1 coordinating ligand of the dimerized pentafulvene, analyzed by NMR and XRD investigations. As a magnesium pentafulvene complex was a possible intermediate, amines were employed as intercepting agents. Thereby, the amines were formally deprotonated by elemental magnesium, yielding the first examples of Cp'Mg(THF)2 NR2 complexes. This reaction competes with the formation of 1 and a consecutive formal [1,5]-H-shift forming an ansa-magnesocene. Employing amines with low basicity gave quantitative conversion to the amide complexes.