Silylamide ligand

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). 

Scheme 12.8 (a) Introduction of bulky ligands (L ) by direct grafting of heteroleptic lanthanide silylamide complexes on mesoporous MCM-41 (22-25) (cf route A in Scheme 12.3) (b) grafting of (homoleptic) lanthanide silylamide complexes on a mesoporous material (cf route A in Scheme 12.3) followed by a subsequent ligand exchange (cf route C in Scheme 12.3) via protonolysis of the Ln-N bond with HL (A-L). 

The supported silylamide complexes display lower activities than the homogeneous counterparts Ln[N(SiMe3)2]3, with the yttrium (12c) and samarium surface complexes (12d) revealing the worst performance. Conversely, the yttrium sUyl-amide-based material 12c gave complete conversion of hept-l-yne after 15 h at 100 °C. It was speculated that the relatively high tail-to-head selectivity of 82% Pj, obtained for both fresh and recovered catalyst 12c, could be due to the bulky siloxo surface ligand [117]. 

Hybrid materials [Ln(fod) (THF)y] MCM-41.28o [Ln = Sc (18F), Y (19F) and La (26F)] and [Y(fod)3] MCM-41.28o (6) were used under standard conditions as catalysts for the Danishefsky transformation (Table 12.9). In these reactions 1.1 equivalents of benzaldehyde (Sj) were allowed to react with trans-l-methoxy-3-trimethylsilyloxy-1,3-butadiene (Si) in n-hexane at ambient temperature. The outcome of the reaction was highly dependent on the synthesis procedure used for the Ln-fod surface complexes. For materials [Ln(fod) ,(THF)y] MCM-41.28o. obtained by secondary ligand exchange from silylamide surface complexes 18,19 and 27 (via route C in Scheme 12.3 see also Table 12.3 and Scheme 12.8), the... 

The first well characterized thallium(I) derivative of a monodentate amide ligand was the silylamide [ TlN(SiMe3)2 2] obtained from LiN(SiMe3)2 and TlCl in toluene. It is a centro-symmetric dimer with an almost perfectly square planar TI2N2 core as shown in Figure 8.12. ... 

The use of the sterically demanding amido ligands such as N(SiMe3)2 and N( Pr)2 has given rise to an interesting variety of compounds with low coordination numbers (37, 38). For example, the tricoordinate silylamides,... 

A considerable number of adduct and heteroleptic silylamide complexes has been reported (Table 6) [124-137], In the following they are summarized with respect to their ligand combination. 

Limited application of the original silylamide route (Sect. 7.1) led to the exploration of the sterically less crowded bis(dimethylsilyl)amide (bdsa) ligand which is also readily available [138]. In contrast to the very similar NiPr2 ligand, the bdsa ligand enables the isolation of pure products via the stoichiometric LnCl3/Li(bdsa) procedure and this favors this system as a synthetic precursor. 

Now, back to the tritox-reaction. The reactivity-determining influence of the ligand constitution has been examined by introduction of the sterically less crowded bdsa amide ligand (Fig. 27) [114]. This ligand offers a valuable extension of the silylamide route ... 

Use of less basic triphenylsiloxide ligands also allowed the isolation of mononuclear complexes (Table 1) [46,47]. In addition to the silylamide route, anhydrous nitrates and isopropoxides were employed as synthetic precursors (Eqs. 1,2). The siloxide bridges in the solvent-free dimeric systems Ln2(OSiPh3)6 are readily disrupted by donor solvents like THF, OP Bu3 or DME. The m s-THF adducts of lanthanum, cerium (Fig. 5) and yttrium adopt an approximately /ac-octahedral geometry. 

The interplay of steric constraints and surplus Do functionalities create a ligand atmosphere which, for the first time, allowed the isolation of defined mixed ligand (amide/alkoxide) systems according the silylamide route. Both... 

A stabilizing option of the functionalized and highly hygroscopic ligand 2,4,6-tris(dimethylaminomethyl)phenol was demonstrated by the isolation of the remarkable water adduct complex Pr[0C6H2(CH2NMe2)3-2,4,6]3(H20)2 according to the silylamide route [129]. 

Solvent free LnL complexes (Type I) resulted from the silylamide route [184]. Crystals of Yb(trac) could be grown by sublimation (180 °C/10 2 Torr). The heptadentate ligand is wrapped around the ytterbium emerging in a disordered geometry. Both enantiomers, the right- (A) and left-handed (A) screw, are present in the unit cell. 

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