Dimeric Hydrido Complexes of Rare-Earth Metals Containing a Linked Amido−Cyclopentadienyl Ligand:  Synthesis, Characterization, and Monomer−Dimer Equilibrium

Dimeric hydrido complexes of lutetium, ytterbium, and yttrium containing a linked amido−cyclopentadienyl ligand, [Ln(η5:η1-C5Me4SiMe2NCMe2R)(L)(μ-H)]2 (Ln = Lu, Yb, Y; R = Me, Et; L = THF, PMe3), were synthesized and characterized by elemental analysis and 1H, 13C 29Si, and 31P NMR spectroscopy. A single-crystal X-ray diffraction study of [Yb(η5:η1-C5Me4SiMe2NCMe2Et)(THF)(μ-H)]2 showed a homochiral dimeric structure with a trans configuration of the ancillary ligands, in analogy to the related yttrium complex. The PMe3 adducts of lutetium and yttrium [Ln(η5:η1-C5Me4SiMe2NCMe3)(PMe3)(μ-H)]2 (Ln = Lu, Y) were prepared in low yields by substitution of THF with a large excess of PMe3. Their crystal structures were determined and revealed a cisoid configuration of the linked amido−cyclopentadienyl ligands, isotypic with the scandium analogue previously described by Bercaw et al. On the NMR time scale fast dissociation of the Lewis base L is observed. Scrambling of the yttrium and lutetium hydrido complexes [Ln(η5:η1-C5Me4SiMe2NCMe3)(THF)(μ-H)]2 (Ln = Lu, Y) in C6D6 gave a mixture containing the heterobimetallic species [LuY(η5:η1-C5Me4SiMe2NCMe3)2(THF)2(μ-H)2] within 5 min, indicating the presence of monomeric species in solution. Chloro hydrido complexes of yttrium, [{Y(η5:η1-C5Me4SiMe2NCMe2R)(THF)}2(μ-H)(μ-Cl)], were formed by scrambling the chloro complex with the hydrido complex for 3 h. The dimeric chloro complexes [Y(η5:η1-C5Me4SiMe2NCMe2R)(THF)(μ-Cl)]2 could be synthesized by reacting in situ formed "Y(CH2SiMe3)2Cl(THF)n" with the amino−cyclopentadiene (C5Me4H)SiMe2NHCMe2R in a σ-bond metathesis. Single-crystal X-ray diffraction studies showed the chloro complex [Y(η5:η1-C5Me4SiMe2NCMe2Et)(THF)(μ-Cl)]2 to adopt a trans configuration of the ancillary ligands as a heterochiral dimer, whereas the chloro hydrido [{Y(η5:η1-C5Me4SiMe2NCMe2Et)(THF)}2(μ-H)(μ-Cl)] was found to be a homochiral dimer.