Intramolecular C–H Bond Activation by Lanthanoid Complexes Bearing a Bulky Aminopyridinato Ligand

Abstract

Abstract The present work is aimed towards the synthesis of C–H activation products of various group 3 and lanthanoid metals bearing a bulky aminopyridinato ligand, (2,6‐diisopropylphenyl)[6‐(2,6‐dimethylphenyl)pyridin‐2‐yl]amine ( 1 , Ap′H). Deprotonation of 1 using KH leads to polymeric [Ap′K] n ( 2 ), which undergoes clean salt metathesis reaction with MX 3 [M = Sc, Nd and Sm, and X = Cl or M = La and X = Br] forming mono thf adducts [Ap′ 2 ScCl(thf)] ( 3 ), [Ap′ 2 LaBr(thf)] ( 4 ), [Ap′ 2 NdCl(thf)] ( 5 ), and [Ap′ 2 SmCl(thf)] ( 6 ). However, reacting 2 with LuCl 3 leads to mono‐ as well as bis(aminopyridinato)lutetium complexes [Ap′LuCl 2 (thf) 2 ] ( 7 ) and [Ap′ 2 LuCl(thf)] ( 8 ), respectively, while the analogous reaction with LaCl 3 at 50 °C produces the tris(aminopyridinato)lanthanum complex [Ap′ 3 La] ( 9 ). For the selective synthesis of 8 in good yield amine elimination route was adopted. X‐ray diffraction studies revealed a distorted octahedral coordination for the bis(aminopyridinato) complexes 3 , 4 and 6 , despite the differences in their ionic radii. Alkylation of the bis(aminopyridinato) monohalide complexes with equimolar amounts of LiCH 2 SiMe 3 in hexane allowed the isolation of the corresponding alkyl derivatives. For the smaller metals like Sc and Lu affording [Ap′ 2 ScCH 2 SiMe 3 (thf)] ( 10 ) and [Ap′ 2 LuCH 2 SiMe 3 (thf)] ( 11 ), respectively. However, lanthanoids with large ionic radii such as La and Nd resulted in the formation of methyl group C–H bond activation products [Ap′(Ap′ –H )La(thf) 2 ] ( 12 ) and [Ap′(Ap′ –H )Nd(thf)] ( 13 ), respectively. Most likely an alkyl species was formed which then undergoes intramolecular C–H activation and C–H activation runs fast with regard to the rate of alkyl complex formation. The alkylation of 6 (Sm) with LiCH 2 SiMe 3 did not give a clear product. The reaction of 11 with PhSiH 3 (Ph = phenyl) led via intramolecular C–H bond activation to [Ap′(Ap′ –H )Lu(thf)] ( 14 ). In this case most likely a hydride species was formed which then undergoes rapid C–H activation. The alkyl complex 10 (Sc) did not react with PhSiH 3 . The molecular structures of 11 , 12 and 13 have been confirmed by X‐ray crystal structure analysis.