17336-23-1Relevant academic research and scientific papers
B(C6F5)3-Catalyzed Silation of Alcohols: A Mild, General Method for Synthesis of Silyl Ethers
Blackwell, James M.,Foster, Katherine L.,Beck, Victoria H.,Piers, Warren E.
, p. 4887 - 4892 (2007/10/03)
The commercially available borane tris(pentafluorophenyl)borane, B(C6F5)3, is an effective catalyst for the dehydrogenative silation of alcohols using a variety of silanes, R3SiH, R2SiH2, and R2R′SiH. Generally, the reactions occur in a convenient time frame at room temperature using 2 mol % of the borane and are clean and high yielding, with dihydrogen as the only byproduct. Primary aliphatic alcohols are silated cleanly but slowly, with reaction times ranging from 20 to 144 h. Faster reaction times can be achieved by increasing the catalyst loading to 8 mol % or by heating the reaction to ～60°C. Secondary and tertiary alcohols react more rapidly, with most reactions being complete in 0.5-2 h. The reaction is tolerant of many functional groups including C=C, C=C, -Br, aliphatic ketones, C(O)OR, lactones, furans, OBn, OMe, and NO2; examples of each are given. Using the phenolic substrate 2,4,6-trimethylphenol, a number of different silanes were tested. Only the most bulky silanes (Bn3SiH and Pri3SiH) were not reactive under these conditions. The selectivity of the silation reactions are roughly governed by the relative basicity of the alcohols (and other functions in the molecule) with more basic groups being selectively silated. These observations are rationalized on the basis of a mechanism that invokes borane activation of the silane by hydride abstraction. The resulting intermediate silylium/hydridoborate ion pair then reacts with alcohols to give the observed silyl ether and dihydrogen products.
A study of the silanolysis of triphenylsilane and p-methoxyphenolcatalysed by (PMe3)4RuH2 and the stoichiometric reactions of (PMe3)4Ru(H)(OC6H4-p-X) (X = Me, OMe) with Ph3SiH
Burn, Melinda J.,Bergman, Robert G.
, p. 43 - 54 (2007/10/02)
The ruthenium dihydride cis-(PMe3)4Ru(H)2 (1) catalytically converts PH3SiH and HOC6H4-p-OMe to the alcoholysis products Ph3SiOC6H4-p-OMe and H2.This reaction was studied kinetically and the rate was found to be first-order in , first-order in , and independent of .The stoichiometric reactions of cis-(PMe3)4Ru(H)(OC6H4-p-X) (X = Me, 2; OMe, 3) with Ph3SiH were also studied in the presence of varying amounts of free para-substituted phenol.In the absence of the free phenol, compounds 2 and 3 reacted with Ph3SiH to give Ph3SiOC6H4-p-X and a compound we believe to be (PMe3)3Ru(H)3(SiPh3) (4).In the presence of large amounts of phenol (> equiv.), (PMe3)4Ru(H)2 (1) was formed.However, at intermediate concentrations of free phenol, compounds 2 and 3 exhibited divergent behavior.Complex 2 gave dihydride 1 in a reaction whose rate was found to be first-order in the concentration of the starting aryloxy hydride 2, first-order in phenol and independent of .In contrast, complex 3 reacted with less than 0.5 equiv. of p-methoxyphenol to form 1, but when approximately 1 equiv. of p-methoxyphenol was added to the solution of 3 and Ph3SiH a mixture of trihydride 4 and dihydride 1 were formed.The mechanisms of these complicated transformations, and their potential relationship to the dihydride-catalyzed silanolysis reaction, are discussed. Key words: Silicon; Ruthenium; Silanolysis; Silane; Phenol
