Neutral and Cationic Alkyl and Amido Group 3 Metal Complexes of Amidine‐Amidopyridinate Ligands: Synthesis, Structure, and Polymerization Catalytic Activity

Abstract

AbstractAlkane and amine elimination reactions between the amidine‐aminopyridine proligands (NR1NNR1CMeNR2)H [R1 = R2 = Me (1a), R1 = H, R2 = Me (1b), R1 = Me, R2 = iPr (1c)] and the precursors [Ln(CH2SiMe3)3(thf)2] (Ln = Sc and Y) and [Ln{N(SiHMe2)2}3(thf)x] (Ln = Sc, Y, and La) have been investigated. Bulky 1c and [Ln(CH2SiMe3)3(thf)2] (Ln = Sc and Y) selectively afforded dialkyl complexes 2c‐Sc and 2c‐Y. Yttrium and lanthanum diamido complexes 3a‐Y, 3b‐Y, 3c‐Y, and 3c‐La were synthesized and isolated in high yields; however, similar aminolysis reactions to prepare the scandium analogues were unsuccessful. Detailed 29Si NMR spectroscopic studies combined with X‐ray crystallography revealed the presence of β‐Si–H···Ln agostic interactions in the diamido complexes. Cationic monoamido complex 4a‐Y was obtained from the reaction of 3a‐Y with [Et3NH]+[BPh4]–. Both the dialkyl and diamido complexes, activated with [Ph3C]+[B(C6F5)4]–/AliBu3 or [PhNMe2H]+[B(C6F5)4]–/AliBu3, were found to be moderately active at 60 °C in the trans‐1,4‐selective polymerization of isoprene, and the diamido complexes promoted the ring‐opening polymerization of rac‐lactide with moderate activities.