Silyl substituted alkanes

The two main groups of silyl substituted alkane ligands HC(SiMe3)3 and HCH(SiMe3)2 demonstrate significantly different steric demands, and we will discuss the two groups of alkali metal complexes separately. Only select compounds will be discussed. 

Recently the unprecedented example of stereoselective C—Si bond activation in cu-silyl-substituted alkane nitriles by bare CQ+ cations has been reported by Hornung and coworkers72b. Very little is known of the gas-phase reactions of anionic metal complexes with silanes. In fact there seems to be only one such study which has been carried out by McDonald and coworkers73. In this work the reaction of the metal-carbonyl anions Fe(CO) (n = 2, 3) and Mn(CO) (n = 3, 4) with trimethylsilane and SiH have been examined. The reactions of Fe(CO)3 and Mn(CO)4 anions exclusively formed the corresponding adduct ions via an oxidative insertion into the Si—H bonds of the silanes. The 13- and 14-electron ions Fc(CO)2 and Mn(CO)3 were observed to form dehydrogenation products (CO) M(jj2 — CH2 = SiMe2) besides simple adduct formation with trimethylsilane. The reaction of these metal carbonyl anions with SiFLj afforded the dehydrogenation products (CO)2Fe(H)(SiII) and (CO)3Mn(II)(SiII). ... 

The reaction of silylborane with 1-halo-l-lithio-l-alkenes yields 1-boryl-l-silyl-l-alkenes via borate formation followed by 1,2-migration of silyl group (Equation (90)).76,240 The mechanism seems to be closely related to that proposed for the silaboration of isocyanide (Figure 2). Vinyl-substituted carbenoids, l-chloro-l-lithio-2-alkenes, react with silylpinacolborane to give l-boryl-l-silyl-2-alkanes in good yield (Equation (91)).241 This methodology is applied to the synthesis of l-boryl-l-silyl-2-cyclobutene.2 2 Similar reactions are carried out with other carbenoid... 

Systems and conditions that proceed cleanly by route c (Scheme 6.62) are efficient for catalytic dehydrogenative silation. A M-SiRs source is necessary and this can be a silane, with concomitant reduction of the alkene to give an alkane (Scheme 6.62, c). /l-SiRa elimination has been artfully used to produce a M-SiRs moiety from vinylsilanes or allylsilanes. Scheme 6.63 depicts the use of allylsilanes described by Murai et ai. to produce silyl substituted alkenes and propene as byproduct [194b]. 

Functional groups such as silyl ether, ester, acetal and halide, are compatible with hydroformylation conditions. Thus, (O-fimctionaUzed 3-substituted alkanals are synthesized from 2-alkyl-1-alkenes, and this methodology has been apphed to the synthesis of muscone (14) (Figure 5). [20],... 

Cleavage of l-(trimethylsilyloxy)bicyclo[n.l.O]alkanes (8, 269-270). Lead tetraacetate fragmentation of the exo- and endo-methyl substituted silyl cyclopropyl ethers (1) is essentially stereospecific.2 Thus exo-1 is fragmented to the (E)-alke-noate 2 exclusively and endo-1 is converted into (Z)-2 exclusively. 

Fig. 1.47. Myers synthesis of atkanes from aldehydes via the sulfonylated hydrazones B and their silyl derivatives C. This procedure provides a skeletongenerating three-step synthesis of alkanes from aldehydes. In terms of Figure 1.2, the chain reaction F —> I involved is a "substitution reaction by fragmentation." (The sulfonylated hydrazide anion, which here results from the addition of R3-Li to the sulfonyl hydrazone C, does—at this reaction s temperature of-78 °C—not release toluene sulfinate. Compare the different behavior of the sulfonylated hydrazide anion C in the reaction of Figure 17.69, where a mesitylene sulfinate residue is eliminated at a temperature that is higher by 160 °C).

Substituted bicyclo[ . 1.0]alkanes may also be obtained by condensation of secondary amines with 2-haloketones. A variety of nucleophilic reactions can be carried out on the intermediate cyclopropaniminium salt 116251 (Scheme 108). Competing alkene scission and cyclopropanation occurs on reaction of enamines with pentacarbonyl-chromium carbene complexes252 (Scheme 109). N-Silylated allylamines and their derived N-silylated enamines undergo rhodium or copper catalysed cyclopropanation by methyl diazoacetate253 (Scheme 110). 

Z)-1,5-Hexadienyl carboxylates. C substituted 1,3-butadienes proceeds in higl reaction involves the disubstituted double ho Sulfur compounds. Displacement of room temperature. Linear products also ] carbonates. l,2-Bis(phenylthio)alkanes an diphenyl disulfide under eatalytic condiuc functional groups (ester, silyl, etc.) directh I... 

Substituting oxygen by carbon in the above silyl ethers results in 1,2-bis(silyl)alkanes lacking heteroatoms. Thus, coordination between sili-... 

Recently Ito and coworkers have prepared, structurally determined and interconverted bis(silyl)alkane palladium(II) (98) and bis(silyl)paUadium(0) (99) complexes, supporting the postulated mechanism for the bis(silylation) of triple bonds (equation 53) . Similar supporting evidence has been recently obtained using mixed sUyl-stannyl compounds, by the unsymmetrical substituted disilane MesSiSiFaPh, and by theoretical studies by Sakaki " M rquez - and others ". ... 

Fig. 5a) with the analogous carbonyl hydrosilylation shown in Fig. 4. Formation of a pentacoordinate silyl-H oxonium complex 7 from 2 by addition of the alkoxysi-lane is followed by substitution at the SiH partner with inversion. Rearrangement to an alkane complex 8 is foUowed by decomposition to product. 

TBDMSCl-Assisted Reactions. Nitro aldol (Henry) reactions have been reported to be promoted by TBDMSCl. To a THF solution of tetra-n-butylammonium fluoride is added sequentially equimolar amounts of the nitro compound, aldehyde, and EtsN, followed by an excess of TBDMSCl (eq 11). Substitution of TMSCl for TBDMSCl reduces the yield of nitro aldol product. The authors speculate that TBDMSCl is responsible for activation of the aldehyde while n-Bu4NF activates the nitro compound. In a related method, primary and secondary nitro alkanes were treated with LDA in THF followed by addition of TBDMSCl to give the corresponding silyl nitronates. The silyl nitronates reacted with a variety of aliphatic and aromatic aldehydes which gave vicinal nitro TBDMS aldol products. ... 

Silyl ketene acetal adds photolytically to C50 give a-fullerene-substituted carboxylic esters and are used in L-quebrachitol and statine synthesis They induce the first highly asymmetric Pummerer-type reaction of acyclic sulphoxides, giving siloxy(arylthio)alkanes with >99% ee541. 

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