Grafting of peralkylated LnIIAlIII heterobimetallic complexes onto periodic mesoporous silica KIT-6

Abstract

Tetraethylaluminates of the divalent lanthanides ytterbium and samarium were grafted onto large-pore cubic periodic mesoporous silica (PMS) KIT-6, which had been dehydroxylated at 500 °C (specific surface area a_s: 500 m²g⁻¹; mesopore volume V_p: 1.06 cm³g⁻¹; main pore diameter: 85 Å). The bimetallic materials [Ln(AlEt₄)₂]@KIT-6₋₅₀₀ were analysed by DRIFT spectroscopy, elemental analysis, nitrogen physisorption and solid-state NMR. Upon heterogenization the surface area and pore volume of the KIT-6 materials dropped by 30–35% and 25%, respectively. The hybrid materials were compared to AlEt₃@KIT-6₋₅₀₀ since reaction of AlEt₃ with surface silanol groups is also a prominent reaction pathway when complexes [Ln(AlEt₄)₂]_n are immobilized. Reaction of the Ln(II) tetraalkylaluminates with tris(tert-butoxy)silanol HOSi(OtBu)₃ gave complexes Ln[(μ-OSi(OtBu)₃)(μ-R)AlR₂]₂ (Ln = Yb, Sm; R = Et; Ln = Yb; R = Me) which can be seen as molecular model complexes, evidencing alkane elimination, trialkylaluminium adduct formation, and Ln(II)–O(siloxane) bonding.