Formation of a Novel Yttrium Hydride with Bridging 1,2,3,4-Tetramethylfulvene and

Thermolysis of [(C5Me5)2YH]2 in n-octane or benzene yields (C5Me5)2Y(µ-H)Y(η5-C5Me4CH2)(C5Me5), a bis-yttrium-monohydride in which a tetramethylfulvene ligand bridges in a σ-η5 manner between the yttrium atoms; the hydride bridge is asymmetric showing two yttrium-hydrogen coupling constants in the 1H n.m.r. spectrum. Hydrogen abstraction from a pentamethylcyclopentadienyl group to give a tetramethylfulvene ligand probably plays a crucial role in processes like H-D-exchange and C-H-activation with permethylmetallocene derivatives of early transition metals and f elements.1 The tetramethylfulvene ligand is interesting since it can bond in several ways: as a ‘tucked in ’ cyclopentadienyl-alkyl (I),2 as a six-co-ordinate fulvene (II),3 and also as a bridging η5-cyclopentadienyl-σ-alkyl (III).4 As part of a project on permethylyttrocene derivatives we tried to prepare yttrium-fulvene systems. We followed an approach that proved to work well for titanium, e.g. thermo