Silylamido

Si H M agostic interactions in silylamido complexes have been extensively studied to date. The earlier examples were prepared by halide displacement in the coordination sphere of a metal by a silylated amide, which puts severe limitations on the nature of the substituents at silicon (usually, robust methyl groups are used). More recently, a new route to p-agostic silylamides based on the direct coupling of silanes with imido ligands was discovered that allows one to trace the effect of substitution at silicon on the extent of the Si-H bond complexation (vide infra). 

The Sm silylamide surface species [(=SiO)Sm N(SiHMe2)2 (THF)] (28a-c, 29 and 30) (Scheme 12.11) readily undergo silylamido methanol and silylamido indenyl exchange reactions, affording materials [Sm(OMe)(THF)] MCM-41LP.280 (33c) and [Sm lnd(SiHMe2) (THF)J MGM-41LP.28o (34b) [126]. Notably, discrete Sm methoxy species are unknown in molecular chemistry due... 

Surface Ln-silylamido moieties lla- obtained via grafting of homoleptic silyl-amides Ln[N(SiMe3)2]3 on dehydroxylated silica Vulkasil S (BAYER AG, a = 175 ... 

A similar study with materials [Ln N(SiMe3)2 3] AS-380. (T = 250, 500, 700°C) revealed the implications of thermal pretreatment of the support for ethylene polymerization [117]. Materials featuring predominantly monopodal neodymium silylamido surface species produced the most achve catalysts [12b (100% monopodal) > 13b (40%)> 14b (25%), Table 12.6 cf, Nd[N(SiMe3)2]3 0.03 kg-PE molm h bar ]. Apparently, extensive replacement of silylamido by (surface) siloxo ligands, that is, an increase of podality of the supported species at... 

Y > Sm > Nd) [108]. Neodymium surface species 9 generated by silylamido alkoxo secondary ligand exchange was more efficient in e-CL polymerization, producing well-defined poly(CL)s with controllable molecular weight and polydis-persity [114]. 

Other monomeric silylamido complexes have also been obtained by the addition of tmeda (A, A, A A"-tetramethylethylenediamine) or pmdeta (N,N,N ,N" - pentamethyl-diethylenetriamine) to afford [(tmeda)LiN(SiMe3)2] which has three coordinate lithium Li—N(amide)= 1.893(3) A and [(pmdeta)LiN(SiMe3)2 with 4-coordinate Li and Li—N (amide = 1.988(6) A. The use of very large substituents at the amido ligand can also afford monomeric structures. Examples include [Li(thf)3N(SiMe2Ph)2], [Li(thf)2N(SiPh3)2l/ [Li(th )2N(SiBu 2F)2] [Li(thf)2N (C6F5)(SiBu 2F) ] and [Li(thf)3 NMes (SiPr 2X) ]... 

Two-coordinate monomeric amides. The silylamido derivative Mgj XTSiMea),, was first... 

Homoleptic silylamido-Ln compounds [Ln <(Si le j2 LI or the more readily displaceable [Ln N(SiHMe2)2 3(thf)n] have been widely used as substrates for reaction with protic reagents H L. Some examples have already been described in Sections 4.3.3 and 4.3.5 ... 

Very bulky silylamido ligands have been used to stabilize the monoamides [Me(Cl)AtN- Si(Ph)Bu 2 SiMeBu 2 ]4 (Al-N= 1.852(1) A) and Mc2AI., SiPhBii 2i SiMcBii, ... 

The aluminium is coordinated by three silylamido nitrogens in an essentially trigonal planar fashion ( °A1 = 359.7(3)) with coordination by the amine nitrogen in an axial position. The Al—N(amido) bond lengths average 1.809(3) A and the axial Al—N(amine) distance is 1.983(6) A The related podand derivatives [ HC(SiMe2NR)3 Al thf] (R CHsPh or C6H4Me-4 2), synthesized by salt elimination reactions, were reported recently. 

Pentavalent silylamido derivatives are limited to Ta, as reduction occurs with Nb.272,273 The bulkiness of the [N(SiMe3)2] ligand precluded complete chlorine substitution as well as formation of dimers. [TaCl3 N(SiMe2)2 2] has a trigonal bipyramidal structure with short equatorial Ta—N bonds (1.930 A av.). 

Bis(ruthenocenyl)allylium cation, characterization, 6, 644 Bis(silylamido) amines, with Zr(IV), 4, 790 Bis(silylamido) complexes, with Zr(IV), 4, 767 Bis-silylation... 

Cyclopentadienyl rings, in chromocenes with heteroatom substitutions, 5, 330 with pentalene rings, 5, 331 with substitutions, 5, 329 Cyclopentadienyl ruthenocenes, synthesis, 6, 639 Cyclopentadienyl—silylamido complexes, with Zr(IV) and Hf(IV) and monodentate ligands, 4, 852 Cyclopentadienyl—silylamido dienes, with Zr(IV) and Hf(IV),... 

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