Grafting of peralkylated Ln~(II)Al~(III) heterobimetallic complexes onto periodic mesoporous silica KIT-6

摘要

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 m~2g~(-1); mesopore volume V_p: 1.06 cm ~3g~(-1); main pore diameter: 85 ?). The bimetallic materials [Ln(AlEt_4)_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 AlEt_3@KIT-6_(-500) since reaction of AlEt_3 with surface silanol groups is also a prominent reaction pathway when complexes [Ln(AlEt_4)_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)AlR_2]_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.