Methylene-bridged, intramolecular donor-acceptor systems based on rare-earth metals and phosphinomethanides

New geminally bonded intramolecular donor-acceptor systems, Cp₂LnCH₂PR₂ (Ln = Y, Ho, Er, R = CHMe₂, CMe₃), were prepared by salt elimination reactions between the dicyclopentadienyl-element chlorides (Cp₂LnCl, Ln = Y, Ho, Er) and diorganylphosphinomethanides (R₂PCH₂Li; R = CHMe₂, CMe₃). These compounds, 1-6, were characterized by elemental analyses, mass spectrometry and X-ray diffraction experiments and the yttrium species additionally by NMR spectroscopy. In the solid state the molecular structures differ from each other, depending on the steric demand of the phosphorus substituents. For all iso-Pr-substituted compounds, dimers [Cp₂LnCH₂P(CHMe₂)₂]₂ with six-membered Ln-C-P-Ln-C-P rings in a chair-like conformation were observed. The sterically more demanding tert-butyl groups prevent dimerization but instead lead to species that undergo complexation of LiCl units by two monomers: [Cp₂LnCH₂P(CMe₃)₂·LiCl]. The solution NMR data for the yttrium compounds are consistent with the solid-state structures. Conversion with phenylacetylene afforded heteroleptic cyclobutane-like alkynyl-rare-earth metal complexes [Cp₂Ln(μ-C[triple bond, length as m-dash]CPh)]₂ [Ln = Y (7), Ho (8), Er (9)]. Treatment of compounds 1-6 with 1,8-diethynylanthracene led to single metalation and dimerization and products with similar structural motifs as observed for complexes 7-9. Reactions with dihydrogen and carbon dioxide resulted in Y-C bond breaking, yielding Cp₂YH/R₂PCH₃ and CO₂ insertion products, respectively.