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(SiHMe 2 ) 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(SiHMe 2 ) 2 ] with [LnCl 3 (thf) x ] in n-hexane or thf, depending on the solubility of the rare-earth halide precursor. The complexes [Ln{N(SiHMe 2 ) 2 } 3 (thf) 2 ] (Ln = Y, La to Lu) are isostructural in the solid state, adopting the preferred (3 ϩ 2, distorted) trigonal bipyramidal geometry, whilst [Sc{N(SiHMe 2 ) 2 } 3 (thf)] has a distorted tetrahedral co-ordination geometry and short Sc ؒ ؒ ؒ Si contacts in the solid state. The reaction of [Y{N(SiHMe 2 ) 2 } 3 (thf) 2 ] with varying amounts of AlMe 3 resulted in desolvation and alkylation with formation of AlMe 3 (thf), {AlMe 2 [µ-N(SiHMe 2 ] 2 } 2 and heterobimetallic (Y/Al) species. The generation of surface-bonded '(᎐ ᎐ ᎐ SiO) x Y[N(SiHMe 2 ) 2 ] y ' and '᎐ ᎐ ᎐ SiOSiHMe 2 ' moieties via the grafting of [Y{N(SiHMe 2 ) 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.Rare-earth amides, and in particular silylamides, 1 are of potential relevance in catalysis 2 and the material sciences. 3 Furthermore, the synthetic versatility of the Ln᎐N(SiMe 3 ) 2 moiety is well established in amine elimination reactions known as the silylamide route (Scheme 1). 1,4 Rare-earth amides are also capable of alkylation reactions via Lewis acid-base derived heterobimetallic species. 5,6 Advantages of the Ln᎐N(SiMe 3 ) 2 -based silylamide route are (i) facile availability of mono-and heterobi-metallic amide precursors, (ii) favourable (mild) reaction conditions including non-co-ordinating solvents, ambient temperature, smooth work-up procedures and 'quantitative' yield, (iii) avoidance of halide contamination and (iv) donor ligand-free products due to the weak donor capability of the released silylamine. 1 Complexes [Ln{N(SiHMe 2 ) 2 } 3 (thf) 2 ] derived from the sterically less bulky bis(dimethylsilyl)-amide ligand were introduced better to cope with the steric requirements of catalytically relevant, bulky and chelating ancillary ligands such as salen or linked cyclopentadienyl derivatives. 7 We report here a detailed synthetic and structural examination of these versatile synthetic building blocks. In addition, AlMe 3 -directed desolvation and alkylation reactions are discussed.Very recently, we found that many features of the homogeneously performed silylamide route can be transferred to a heterogeneous medium (Scheme 1). 8 Such a supramolecular approach allowed the grafting of rare-earth silylamide complexes onto a mesoporous aluminosilicate of type MCM-41 9,10 via surface organometallic chemistry. 11 The presence of 'Si᎐H' as a spectroscopic probe helped to unravel the chemical anchoring of the silylamides which proceeds via siloxide formation and silylation reactions. In this work more light will be shed on the surface organometallic chem...

Bis(phosphinimino)methanide Rare Earth Amides: Synthesis, Structure, and Catalysis of Hydroamination/Cyclization, Hydrosilylation, and Sequential Hydroamination/Hydrosilylation

“…Lu (1 e)] (Anwander amides) [33] were prepared in a modified synthesis similar to that published by Anwander et al, although in a one-pot synthesis, in contrast to the published two-step procedure, which first required the preparation of the THF solvates [LnCl 3 A C H T U N G T R E N N U N G (thf) x ]. Treatment of LnCl 3 (Ln = Y, La, Sm, Lu) with KNA C H T U N G T R E N N U N G (SiHMe 2 ) 2 (2.9 equiv) gave 1 a-e in high yields.…”

Rare‐Earth Metal Mixed Chloro/Methyl Compounds: Heterogeneous–Homogeneous Borderline Catalysts in 1,3‐Diene Polymerization

“…When the initially formed and isolated 1 + 2/4 product mixtures were treated with an excess of AlMe 3 in hexane, instantaneous precipitation of amorphous solids [5,9] The monoamido derivatives 3 might form mixed chloro/methyl compounds 8 with lower methyl content than 5 (i.e. d @ c).…”

Highlights in the Renaissance of Amidometal Chemistry

“…[71] Interesting applications in catalysis are promised by immobilizing amidolanthonide complexes on surfaces of mesoporous silicates. [72] Amine elimination reactions of silyl amides of lanthanoids with dehydrated MCM-41 [73] led to immobilized lanthanoid complexes (Scheme 13). These are remarkable precatalysts in Danishefsky hetero-Diels ± Alder reactions.…”