Na-HMDS

It should be noted here that the lithium salt of hexamethyldisilazane li-HMDS 492 (and Na-HMDS-(486) and K-HMDS in Sections 5.1.2 and 5.1.3), which is readily obtained on treatment of a solution of HMDS 2 in hexane or THF with butyUithium at -78 °C, is not only a very useful and selective strong base, e.g. for Wittig reactions, but can also add to carbonyl groups to yield the silylated Schiff bases or nitriles (cf. Sections 4.7 and 5.1.3) or to nitriles to afford N-silylated ami-dines. Alkylation of the Li-HMDS 492, e.g. with allyl bromide, affords, furthermore, N,N-bis(trimethylsilylated) primary amines such as 43 [64]. The combina-... 

The carbonyl group of methyl benzoate condenses with Na-HMDS 486 to give methoxytrimethylsilane 13a and 51% yield of N,0-bis(trimethylsilyl)benzamide 296 [99], which is also accessible by silylation of benzamide with TCS 14/triethyla-mine. Benzamide or N-silylated benzamide, however, are converted by Na-HMDS 486 in benzene and subsequent quenching with MesSiCl 14 into 34% N,0-bis(trimethylsilyl)benzamide 296, 24% crystalline N-silylated benzamidine 524, and HMDSO 7 [99] (Scheme 5.32). 

On treatment of the ylide 1591 with HMDS-Na 486, the resulting sodium salt 1592 reacts with valeric aldehyde and subsequently with TCS 14 to give 1593, which eliminates trimethylsilanol 4 to give the ylide 1594. This ylide 1594 converts aldehydes such as butyraldehyde into dienes such as 1595 in up to 48% yield [9]. The ylide 1596 reacts with CO2 to give the ylide 1597 which, on heating to 110-120 °C, eliminates HMDSO 7 to give (oxovinyliden)phosphorane 1598 [10] (Scheme 10.3). 

The reaction kinetics In the case of HMDS suggests a two stage mechanism for the major dichloride consuming reaction. First a slow Na surface dependent build up of long lived active centers then a propagation step In which the Na surface is not rate determining. The reaction which occurs on the surface must be fast. 

The reaction was analyzed at the end of the PMDS reaction. The reaction mixture was washed, dried, and restarted with fresh Na and the second monomer, HMDS. 

Adhesion promoters evaluated are the newly developed TMSP, the formerly developed IPTMS and conventional HMDS (Fig.1). For e5q)osure, a KrF excimer laser stepper of a numerical aperture (NA) 0.50 was used. The alkaline development was done with 2.38wt% tetramethylammonium hydroxide solution, NMD-3 (Tokyo Ohka) for 60 sec. 

Projection lithography at 157 nm was performed on HMDS treated 8-inch silicon wafers with the Exitech 0.60-NA small field st er using either binary or phase shift masks. The resist thickness was 100 nm, the post apply bake (PAB) was for 140°C for 60 seconds on a hot plate and the post exposiue bake (PEB) was at 140°C for 90 seconds on a hot plate. Developmmit was by single puddle for 45 seconds with 2.38% TMAH (0.26 N) developer. 

The bis(amido) alkyl sodium magnesiate [NaMg(HMDS)2("Bu)]oo 28 (Fig. 20C) is also polymeric however, it adopts a one-dimensional chainlike infinite polymer through an almost linear Na—C( Bu)-Mg bridge. Two... 

The mixed sodium magnesium compounds [Na2(HMDS)2Mg( u)2 (donor)]oo (donor is TMEDA and (R,J .)-TMCDA for 33 and 34, respectively, Fig. 24) are isostructural and can be considered as the first examples of inverse sodium magnesium ate complexes. They can be rationally prepared by combining HMDS(H) with a mixture of BuNa and Bu2Mg in the presence of the corresponding donor molecule in a 2 2 1 1 molar ratio. Normally, ate complexes are associated with bimetallic systems, whereby one of the metals has higher Lewis acidity (ie. Mg ) than the other (ie, Na ), thus the former metal captures more Lewis basic anionic Hgands. 

In general terms, both the anionic [Mg(HMDS)3] and cationic [Na (donor) 2] moieties are typical structural motifs for solvent-separated alkali metal containing bimetallic magnesium complexes. 

Related thermodynamic enolization control has been observed using metallated hexamethyldisilazide to give the more substituted bromomagnesium ketone enolates. Metallation reactions of HMDS to yield Li, K, and Na derivatives are well known and the resulting nonnucleophilic bases have found extensive applications in organic synthesis. ... 

Complexes 50, which were characterized by a bis(NHC)-alkali metal cation and tris(HMDS)-coordinated alkaline earth metal anion, were the first examples of separated Group 1/Group 2 species that appeared to be labile in solution. As one might expect, larger alkaline earth metals (Sr and Ba) only formed stable complexes when larger alkali metals were used (Na or K for Sr, K for Ba), following hard-soft acid base theory. 

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