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

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.