Cyclooctatetraene complexes of yttrium and the lanthanides with Bis(phosphinimino)methanides: Synthesis, structure, and hydroamination/ cyclization catalysis

A series of cyclooctatetraene bis(phosphinimino)methanide complexes of yttrium and the lanthanides, [{CH(PPh₂NSiMe₃) ₂}Ln(η⁸-C₈H₈)] (Ln = Y, Sm, Er, Yb, Lu), were synthesized via three different pathways. The title compounds can be obtained either from [(η-C₈H₈)-LnI(THF) ₃] and K{CH(PPh₂NSiMe₃)₂} or from K₂C₈H₈ and [{CH(PPh₂NSiMe ₃)₂}LnCl₂]₂. In a third approach the title compounds were synthesized in a one-pot reaction starting from K{CH(PPh₂NSiMe₃)₂}, LnCl₃, and K₂C₈H₈. All complexes have been characterized by crystal X-ray diffraction. The solid-state structures of these complexes show that both ligands completely shield the metal center. As a result of the steric crowding, both ligands are slightly asymmetrically attached to the metal. Even though the title compounds are noncharged lanthanide complexes with no obvious leaving group and no coordinated solvent molecules, the compounds were tested as catalysts for the hydroamination/cyclization reaction. A moderate catalytic activity at elevated temperature is observed.