[766-77-8] · C8H12Si · Dimethyl(phenyl)silane · (MW 136.29)
(hydrosilylating reagent; reductant in combination with acid or F-)
Physical Data: bp 157 °C/744 mmHg; d 0.889 g cm-3.
Solubility: sol common organic solvent such as chloroform, 1,2-dichloroethane, benzene, ether, acetone, dioxane, THF; insol H2O.
Form Supplied in: oil, commercially available.
Analysis of Reagent Purity: 1H NMR (CDCl3-Me4Si) d 7.6-7.4 (m, 2 H), 7.4-7.2 (m, 3 H), 4.42 (septet, J = 3.6 Hz, 1 H), 0.34 (d, J = 3.6 Hz, 6 H). 13C and 29Si NMR have also been reported.2
Preparative Method: see Benkeser and Foster.1
Handling, Storage, and Precautions: moisture sensitive; evolves H2 when added to wet piperidine.
Dimethyl(phenyl)silane reduces aldehyde and ketone carbonyls with the aid of fluoride ion or acid. a-Acylpropionamides, 1-aminoethyl ketones, and 1-alkoxyethyl ketones are readily converted into the corresponding b-hydroxy amides, a-amino alcohols, and a-alkoxy alcohols, respectively. The stereoselectivity is complementary and generally high: erythro (or syn) isomers are obtained with Trifluoroacetic Acid (TFA), whereas threo (or anti) isomers are obtained with fluoride ion activator (eq 1). The erythro selectivity in the acid-promoted carbonyl reduction is ascribed to a proton-bridged Cram's cyclic transition state. On the other hand, the threo selectivity in the fluoride-mediated reduction is explained in terms of the Felkin-Anh type model, wherein a penta- or hexacoordinated fluorosilicate is involved. No epimerization at the chiral center is observed during the reaction.
With a transition metal catalyst, the hydrosilane adds to carbon-carbon double or triple bonds to give alkylsilanes or alkenylsilanes. Hydrosilylation of deoxydiisopropylidene-arabino-hexenopyranose (1) catalyzed by [Rh(norbornadiene)Cl]2 (Bis(bicyclo[2.2.1]hepta-2,5-diene)dichlorodirhodium) gives 6-deoxy-6-phenyldimethylsilyldiisopropylidenealtrose (2), which is desilylated by Tetra-n-butylammonium Fluoride to yield 6-deoxydiisopropylidenealtrose (3) (eq 2).5
In the presence of a Pt complex like bis(h-divinyltetramethyldisiloxane)tri-t-butylphosphineplatinum(0) (4), phenyldimethylsilane reacts with 1-butyn-3-ol to give an 8:1 mixture of alkenylsilanes (5 and 6) (eq 3). The major product 1-dimethylphenylsilyl-1-buten-3-ol (5) is separated and resolved by lipase-catalyzed esterification.6
Hydrosilylation of 1,4-bis(trimethylsilyl)-1,3-butadiyne (7) gives 1,4-bis(trimethylsilyl)-1,3-bis(dimethylphenylsilyl)-1,2-butadiene (8) (Chlorotris(triphenylphosphine)rhodium(I), 100 °C) or 1,4-bis(trimethylsilyl)-2-(dimethylphenylsilyl)-1-buten-3-yne (9) (Pt(PPh3)4, 100 °C) (eq 4) depending on the catalyst.7 The enyne (9) is considered to be a precursor of the allene (8).
Transition metal-catalyzed hydrosilylation of a,b-unsaturated ketones and aldehydes with PhMe2SiH proceeds in a 1,4-fashion to give silyl vinyl ethers, which are hydrolyzed to give ketones and aldehydes. Asymmetric 1,4-reduction has been studied using a chiral transition metal catalyst, but with little success (eq 5).8
Dimethyl (Z,Z)-2,4-hexadienedioate is hydrosilylated with PhMe2SiH/RhCl(PPh3)3 to give the 1,6-hydrosilylation product, methyl (3E)-6-methoxy-6-(phenyldimethylsilyloxy)-3,5-hexadienoate (eq 6).9
Under a Carbon Monoxide atmosphere (1-4 MPa), silylformylation of alkynes occurs in the reaction of alkynes and PhMe2SiH to give b-silyl enals in the presence of a rhodium catalyst (eq 7).10 Terminal alkynes exclusively give products having the SiMe2Ph group at the terminal carbon. Depending on the structure of the alkyne, the isomer ratio (E/Z) varies from 0:100 to 100:0. Hydroxyl groups survive these conditions; however, in the presence of a tertiary amine, alkynols are converted into a-(dimethylphenylsilylmethylene) b-lactones (eq 8).11
Silylformylation of N-propargyl tosylamides gives normal b-silyl enal products, whereas the same reaction in the presence of 1,8-Diazabicyclo[5.4.0]undec-7-ene or Triethylamine affords a-(dimethylphenylsilyl)methylene b-lactams (eq 9).12 Propargylamines are transformed to 2-(dimethylphenylsilyl)methyl-2-propenals (eq 10).13
Tamejiro Hiyama & Manabu Kuroboshi
Tokyo Institute of Technology, Yokohama, Japan