Phenylsilane , catalytic

Diiodosilane l2SiH2 1872, prepared by treatment of phenylsilane PhSiHs with iodine, via PhSiH2l, in the presence of catalytic amounts of ethyl acetate at -20 °C, is much more electrophilic than Me3SiI 17 and therefore converts secondary alcohols such as 2-octanol 1871, at room temperature with Walden inversion, into iodides such as 1873 in 93% yield whereas the diol 1874 is nearly quantitatively converted into the monoiodobutane 1875 and only traces of the diiodobutane 1876 [88, 89] (Scheme 12.26). 

In the course of studying the reactions of Si-H compounds with dialkyltitanocenes, with a view to the synthesis of new hydridosilyltitanocene complexes, we adventitiously discovered that phenylsilane undergoes facile, quantitative dehydrogenative coupling to a linear poly(phenylsilylene) under the catalytic influence of dimethyltitanocene. The ease with which this reaction proceeds initially induced us to underestimate the significance of the observation. 

The compounds 2 and 3, have all been isolated from reactions of phenylsilane with either dimethyltitanocene (1 2) or dimethyl-zirconocene (r ). All of the evidence points to the fact that these compounds are probably resting species and are not involved in the catalytic cycle. They do nevertheless give some indication of the complex series of reactions that transform the dimethyl-metallocene to active catalyst. 

Treatment of this precatalyst with phenylsilane yields a very active catalytic system that can be used for the hydrosilylation of imines. This discovery was initiated by the observed hydrosilylation of imines when phenylsilane was added to Cp2TiF2. It was presumed that it might be possible to break the strong... 

Ti-F bond and generate a Ti-H species when 99 was treated with phenylsilane. The chirality transfer may take place through imine insertion into the Ti-H bond, similar to that in the catalytic hydrogenation process.1000 The reaction can be carried out by the subsequent addition of imines. The corresponding silylated amines can be obtained and further converted to enantiomerically enriched amines upon acid treatment. For example, in the presence of 99, N-methylimine 100 undergoes complete hydrosilylation within 12 hours at room temperature, with 97% ee and up to 5000 turnovers.103... 

Yttrium-catalyzed diene cyclization/hydrosilylation was applied to the synthesis of aliphatic nitrogen heterocycles such as the indolizidine alkaloid ( )-epilupinine. l-Allyl-2-vinylpiperidine 30 was synthesized in four steps in 59% overall yield from commercially available ( )-2-piperidinemethanol (Scheme 10). Treatment of 30 with phenylsilane and a catalytic amount of Gp 2YGH3(THF) gave silylated quinolizidine derivative 31 in 84% yield, resulting from selective hydrometallation of the A-allyl G=G bond in preference to the exocyclic vinylic G=G bond. Oxidation of the crude reaction mixture with tert-huVf hydrogen peroxide and potassium hydride gave (i)-epilupinine in 51-62% yield from 30 (Scheme 10). 

Isomerization of alkenes is catalyzed by bis(j7 -allyl)(jj -cyclopentadienyl)vanadium(IV). Cyclohexene nndergoes catalytic stereoselective aerobic oxidation with CpV(CO)4. Reductive coupling (see Reductive Coupling) of aldehydes and aldimines is catalyzed by a Cp-substituted vanadium compound in the presence of a chlorosilane and zinc or aluminum. Vanadocene or bis( ] -cyclopentadienyl)dimethylvanadium(IV) catalyzes the synthesis of 1,2-diphenyldisilane and 1,2,3-triphenyltrisilane from phenylsilane. ... 

A special one-pot deprotection-transacylation method involves coupling of activated Fmoc amino acids with Aloc-protected amino acid esters.The Aloc-deprotection proceeds with palladium/phenylsilane in the presence of the acylating species. Using Fmoc-Phe-F the synthesis of the sterically demanding dipeptide Fmoc-Phe-(Me)Aib-OMe was accomplished in a yield of 65% A similar one-pot approach to the acylation of the even more difficult hindered and weakly nucleophilic a-trifluoromethyl amino acid esters involves the intermediate A-Teoc protection. Thus treatment of ( )-Teoc-a-(a-CF3)Leu-OMe with Fmoc-Gly-F and a catalytic amount of tetraethylammonium fluoride in acetonitrile at 50 °C for 1-2 weeks gave ( )-Fmoc-Gly-(a-CF3)Leu-OMe (77%... 

Cyclosilylation of dienes. Phenylsilane with a catalytic amount of Cp 2YMe-THF... 

Iodosilane is readily prepared by the reaction of phenylsilane [Petrach Systems] with hydrogen iodide or by the reaction of silane [Matheson Gas Products] with hydrogen iodide in the presence of a catalytic amount of aluminum triiodide. Hydrogen selenide is conveniently prepared by the hydrolysis of... 

Fig. 7.16. Synthesis of short-chain poly(phenylsilane)s by the catalytic dehydrogenation ofPhSiHa...

Activation of the (7 ,f )-(EBTHI)TiF2 complex by PhSiH3 leads, in the first step, to the Li2TiH complex. Initial insertion of the imine in the Ti-H bond is followed by proton-transfer and departure of the chiral intermediate II, followed by formation of the Ti-N bond in V and the chiral product IV. The cycle is completed by the intervention of phenylsilane and regeneration of the L2TiH catalytic species. High enantioselectivity of the hydride transfer is controlled by the steric demand of the chiral ligand in the titanocene complex, in which diastereotopicity of the two sites of the C=N bond assures stereoselection. 

Following the development of group 2 complexes for the controlled polymerization of styrene, in 2006 Harder and coworkers reported the hydrosilylation of a series of activated alkenes with Ph SiH4 (n = 2 or 3) catalyzed by [ (Me2N-o-C6H4) CHSiMes 2M(THF)2] (M = Ca, Sr) and isolated the first calcium-hydride complex [ (ArNCMe)2CH Ca p-H)(THF)]2, a species relevant to the catalytic reaction [116, 117], In related studies, Okuda and coworkers have isolated a cationic trinuclear calcium hydride cluster and demonstrated its competency for the hydrosilylation of styrene with phenylsilane (Fig. 10) [118]. 

Asymmetric catalysis Initial attempts to develop non-racemic catalysts for the enantioselective hydrosilylation of alkenes have not been successful with C2-symmetric (5)-Ph-pybox and p-diketiminate calcium amide complexes catalyzing the addition of phenylsilane to styrene in the absence of solvent at 50 °C in, at best, 9 % e.e [69]. As with intramolecular hydroaminatiOTi catalysis, these results have been explained in terms of the loss of ligand control due to facile ligand redistribution reactions under the catalytic reaction conditions. 

Due to the toxicity of tin reagents, Fu developed a method using catalytic amounts of BusSnH that is regenerated by using phenylsilane or polymethylhydrosiloxane (PMHS) in alcoholic solvents (Scheme 8.43). Tributylgermanium hydride can substitute BusSnH in some reaction such as the reduction of arylazides to anilines. ... 

Marks reported that phenylsilane CeHsSiHs acts as a chain transfer agent for homogeneous olefin polymerization catalysts [16]. Newman found that CeHsSiHs increased the catalytic activity in the styrene polymerization [17]. The polymerization conversions with time are shown in Table 4.3. The data... 

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