Silyl amides

The reactivity of epoxides can be modified by various proximal functionality. For example, 2,3-epoxy sulfides 118 are converted to the corresponding TMS-thiiranium species 119 upon treatment with TMS triflate. This intermediate reacts with O-silyl amides regiospecifically to form l-substituted-3-hydroxy-2-thioethers (e.g., 120). Simple primary amines undergo polyalkylation, but imines can be used as an indirect amine equivalent <96TET3609>. 

The mono-silylated or free acetamides, which are liberated during silylation with 22 a, can, furthermore, interfere with any subsequent reaction, e.g. with electrophiles. Thus in the one-pot/one-step silylation, Friedel-Crafts catalyzed, nucleoside synthesis starting from protected sugar derivatives and pyrimidine or purine bases, the mono- or bis-silylated amides such as 22 a can compete with less reactive silylated heterocycHc bases for the intermediate electrophilic sugar cation to form protected 1-acetylamino sugars in up to 49% yield [42, 47]. On silylation with trimethylsilylated urea 23 a the Hberated free urea is nearly insoluble in most solvents, for example CH2CI2, and thus rapidly precipitated [43]. 

Free carboxylic acids such as benzoic acid, phenylacetic acid, or 4-hydroxyben-zoic acid 297 are converted on heating with HMDS 2 or OMCTS 52, via their N,0-bis(silylated) amides such as 22a, into nitriles such as 298 [99, 100] (Scheme 4.38). 

AU these results indicate that silylated amides and, in particular, silylated lactams such as 388 will react with methyl or ethyl cyanoacetate or malonate and malodinitrile in the presence of HMDS 2 (to convert the leaving group MeaSiOH 4 into HMDSO 7) via the O-silylated forms such as 384b or 389 to give similar products such as 385 and HMDSO 7 (Scheme 4.54). 

The N-silylated amide 1558 reacts with diketene vio the O-silylated intermediate 1559 to give the pyrone 1560, which rearranges when treated with 10% HCl to give pyridin-2-one 1561 [74] (Scheme 9.43). 

Metalloporphyrinosilicas as a new class of hybrid organic-inorganic materials were prepared by polymerization of 3- er -butyl-5-vinylsalicylaldehyde with styrene and divinylbenzene and used as selective biomimetic oxidation catalyst.27 Synthesis and structural characterization of rare-earth bisfdimethyl-silyl)amides and their surface organometallic chemistry on mesoporous silicate MCM-41 have been reported.28... 

Silylation of AN with Silylated Amides One of the most important approaches to the synthesis of SENAs is based on silylation of AN with neutral silylating agents, that is, in the absence of bases. N-Silylated amides presented... 

The mechanism of silylation of AN with silylated amides was not systematically studied, but some data on this problem have been reported (204). 

Chart 3.1 A possible mexanistic models for electrocyclic silylation of AN with N-silyl-amides. 

Aminocarbonylation can also be carried out by use of CO and a silyl amide. Watanabe et al. reported the cobalt-catalyzed aminocarbonylation of epoxides [55]. Some silyl amides such as PhCH2NHSiMe3 and Et2NSiMe3 were applicable to the reaction to give the /i-siloxy amide in good yields, whereas high reaction temperature was required. The use of 4-(trimethylsilyl) morpholine was found to be crucial for a milder and more efficient carboami-nation here, the reaction proceeded at ambient temperature under 0.1 MPa of CO. However, N-(2-hydroxyalkyl)morpholines, a product without carbonyla-tion, were yielded as by-products (Scheme 18) [56]. 

An unusual rearrangement with elimination of acetonitrile to give (100) occurs on heating the silylated amide (99).76... 

Silyl Acid Linker 4-[l-Hydroxy-2-(trimethylsilyl)ethyl]-benzoic acid Silyl Amide Linker 4-[(l-Amino)-2-(trimethylsilyl)ethyl]-phenoxyace-... 

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). 

Immobilization of Rare-Earth Metal (Silyl)amide Complexes... 

Surface Organolanthanide Chemistiy SOLnC 467 Table 12.3 Trivalent and divalent amide- and (silyl)amide-based SOLnCtgiSiOj. 

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 ... 

For the use of lithium and sodium bis(trimethyl-silyl)amide respectively in carbonyl enolate chemistry see Barton (reference 15). 

Ethylene, aluminum catalyst A1PO-1, heptane, chromium(III) tris(bis(trimethyl-silyl)amide), nonane, chromium(III) tris(bis(trimethylsilyl)amide)... 

Density functional theory computational studies have been used to determine die importance of secondary orbital interactions for the stability of transition-state structures for die 4 + 2-cycloaddition of furan with cyclopropene.175 Kinetic studies of die 2 + 4-cycloaddition of 2-cyclopropylidene acetates with furan and dimethylful-vene suggest a mechanism involving diradicals or zwitterions as intermediates.176 Cyclopropene, produced by die reaction of allyl chloride with sodium bis(bimediyl-silyl)amide, reacts with 1,3-diphenylisobenzofuran to produce both endo- and exo-Diels-Alder cycloadducts isolated for the first tune.177... 

At low temperature (-78 °C) deprotonation with the bulky silyl amide KHMDS runs under kinetic control - enolization takes place regio-and stereoselectively at the terminal methyl group of ketone 4. The sterically less hindered enolate is transformed to enol triflate 22, which has all-trans configuration. 

For such experiments, however, liquid ammonia is not suitable. A much more promising reaction offered by that discovered by Wannagat and Seyffert (149) involves treatment of sodium bis(trimethylsilyl)amide with mononuclear metal carbonyls in which nucleophilic attack of the silyl amide on a CO ligand leads to monocyanocarbonyl metalates. 

In its reactions with metal carbonyl derivatives having ligands bearing acidic C—H bonds, NaN(SiMe3)2 behaves as a proton acceptor as the silyl amide is a strong base (161). 

Starting from /V-trimethylsilylated amides or lactams is not necessary as these chelates can be formed directly from the non-silylated amide or lactam in a one-pot reaction with the same chloromethylchlorosilane in the presence of hexamethyldisilazane.45... 

This last result is in contrast with the one of silylation of amide with LDA in solvent THF that give a-silylated amides.138... 

The historical sketch outlines the class of lanthanide amides this article is to deal with and which is further manifested in Scheme 1. Organometallic amides which can be classified as dialkyl (-aryl, -silyl) amides and amides derived from unsaturated heterocyclic ligands are seen with respect to N-unsubstituted (primary, inorganic) amides. The consideration of more classic coordination compounds like acid amides or sulfonamides, often ascribed as wet chemistry , is excluded. The historical data also demonstrate the relatively late start of lanthanide amide chemistry reflecting the late industrial establishment of the lanthanide elements (separation, purification, etc.) [9], However, lanthanide amides are still the youngest class in conjunction with the most important pillars of organometallic lanthanide chemistry, namely the alkyls/cyclopentadienyls (LnCp3, 1954, [10]) and the alkoxides (Ce(OR)4 1956 [11a] La(OR)3 , 1958 [lib]). Indeed most of the work has been conducted in the last ten years. 

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