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 degrees C (specific surface area a(s): 500 m(2)g(-1); mesopore volume V(p): 1.06 cm(3)g(-1); main pore diameter: 85 A). 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[(mu-OSi(OtBu)(3))(mu-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.