The title compound [(µ-CH 2 )(ZrCp 2 Me) 2 ] (4) was prepared by the reaction of [Cp 2 Zr(Cl)Me] (6) with CH 2 (MgBr) 2 (5) or (CH 2 Mg) n (7). It had been expected that the carbon atom bridging the two zirconium atoms of 4 might be a candidate for a planar tetracoordinate carbon atom, but the X-ray crystal structures of two different modifications (crystals 1 and 2) showed it to be non-planar; however, the widened Zr−C−Zr angle of 132.7(1) and 134.0(3)°, respectively, and an unsymmetrical coordination of the central µ-CH 2 group (average: Zr1−CH 2 2.225 Å , Zr2−CH 2 2.242 Å ) indicates a tendency towards planarity. While 4 is relatively stable in THF solution, it disproportionates in toluene solution to give the 1,3-dizirconacyclobutane (Cp 2 ZrCH 2 ) 2 (8) and [Cp 2 ZrMe 2 ] (9), espe-