Synthesis and structural characterisation of rare-earth bis(dimethylsilyl)amides and their surface organometallic chemistry on mesoporous MCM-41†

Abstract

Rare-earth silylamides of type [Ln{N(SiHMe₂)₂}₃(thf)_x] (Ln = Sc, Y, La, Nd, Er or Lu) have been prepared in high yield by reaction of 2.9 equivalents of Li[N(SiHMe₂)₂] with [LnCl₃(thf)_x] in n-hexane or thf, depending on the solubility of the rare-earth halide precursor. The complexes [Ln{N(SiHMe₂)₂}₃(thf)₂] (Ln = Y, La to Lu) are isostructural in the solid state, adopting the preferred (3 + 2, distorted) trigonal bipyramidal geometry, whilst [Sc{N(SiHMe₂)₂}₃(thf)] has a distorted tetrahedral co-ordination geometry and short Sc· · ·Si contacts in the solid state. The reaction of [Y{N(SiHMe₂)₂}₃(thf)₂] with varying amounts of AlMe₃ resulted in desolvation and alkylation with formation of AlMe₃(thf), {AlMe₂[µ-N(SiHMe₂]₂}₂ and heterobimetallic (Y/Al) species. The generation of surface-bonded ‘(SiO)_xY[N(SiHMe₂)₂]_y’ and ‘SiOSiHMe₂’ moieties via the grafting of [Y{N(SiHMe₂)₂}₃(thf)₂] onto the mesoporous silicate MCM-41 is described in detail. Consideration is given to the factors governing the siloxide formation and silylation reactions, and the thermal stability of the surface species.