β‐Diketiminato Rare‐Earth Metal Complexes: The Influence of Monoatomic Substituents in the N‐aryl Moieties on Structures and Properties

Treatment of β‐diketiminate ligands bearing different N‐aryl monoatomic substituents [HLH = (C6H5)N = C(Me)CH=C(Me)NH(C6H5), HLF = (2,6‐F2C6H3)N=C(Me)CH=C(Me)NH(2,6‐F2C6H3), and HLCl = (2,6‐Cl2C6H3)N=C(Me)CH=C(Me)NH(2,6‐Cl2C6H3)] with Ln(CH2SiMe3)3(THF)2 (Ln = Y and Lu) afforded a variety of β‐diketiminato rare‐earth metal complexes depending on substituents, namely, phenyl ring C–H bond activated complexes (L')(LH)Lu(THF) (1b, L' = (C6H4)N = C(Me)CH=C(Me)N(C6H5)), six‐coordinate homoleptic complexes (LH)3Ln [Ln = Y (1aa), Lu (1bb)], five‐coordinate monoalkyl complexes (LF)2Ln(CH2SiMe3) [Ln = Y (2a), Lu (2b)], and four‐coordinate dialkyl complexes (LCl)Ln(CH2SiMe3)2 [Ln = Y (3a), Lu (3b)]. All these complexes were characterized with NMR spectroscopy, and lutetium complexes 1b, 1bb and 3b were structurally validated by single‐crystal X‐ray diffraction analysis. Moreover, dialkyl complexes 3 promoted the polymerization of 2‐vinylpyridine (2‐VP) to produce atactic poly(2‐vinylpyridine) (P2VP) with quantitative yield. On activation with an equimolar amount of [Ph3C][B(C6F5)4], complexes 3 afforded highly isotactic P2VP with an mm value up to 94 %. Both 1H NMR spectrum and MALDI‐TOF mass analysis of an oligomer indicate that the polymerization was initiated by coordination insertion of 2‐VP into the Y‐CH2SiMe3 bond.