81256-40-8Relevant academic research and scientific papers
Light-Promoted Transfer of an Iridium Hydride in Alkyl Ether Cleavage
Fast, Caleb D.,Schley, Nathan D.
supporting information, p. 3291 - 3297 (2021/10/12)
A catalytic, light-promoted hydrosilylative cleavage reaction of alkyl ethers is reported. Initial studies are consistent with a mechanism involving heterolytic silane activation followed by delivery of a photohydride equivalent to a silyloxonium ion generated in situ. The catalyst resting state is a mixture of Cp*Ir(ppy)H (ppy = 2-phenylpyridine-κC,N) and a related hydride-bridged dimer. Trends in selectivity in substrate reduction are consistent with nonradical mechanisms for C-O bond scission. Irradiation of Cp*Ir(ppy)H with blue light is found to increase the rate of hydride delivery to an oxonium ion in a stoichiometric test. A comparable rate enhancement is found in carbonyl hydrosilylation catalysis, which operates through a related mechanism also involving Cp*Ir(ppy)H as the resting state.
Selectivity and Mechanism of Iridium-Catalyzed Cyclohexyl Methyl Ether Cleavage
Fast, Caleb D.,Jones, Caleb A. H.,Schley, Nathan D.
, p. 6450 - 6456 (2020/07/13)
Cationic bis(phosphine)iridium complexes are found to catalyze the cleavage of cyclohexyl methyl ethers by triethylsilane. Selectivity for C-O cleavage is determined by the relative rates of SN2 demethylation versus SN1 demethoxylation, with the axial or equatorial disposition of the silyloxonium ion intermediate acting as an important contributing factor. Modulation of the electron-donor power of the supporting phosphine ligands enables a switch in selectivity from demethylation of equatorial methyl ethers to 2° demethoxylation. Applications of these accessible catalysts to the selective demethoxylation of the 3α-methoxy group of cholic acid derivatives is demonstrated, including a switch in observed selectivity controlled by 7α-substitution. The resting state of the catalyst has been characterized for two phosphine derivatives, demonstrating that the observed switch in C-O cleavage selectivity likely results from electronic factors rather than from a major perturbation of the catalyst structure.
Trioxorhena(VII)carborane anion and its methyl-substituted analogue: Synthesis, structure, DFT, and catalytic studies
Pichaandi, Kothanda Rama,Fanwick, Phillip E.,Abu-Omar, Mahdi M.
scheme or table, p. 1888 - 1896 (2012/04/23)
Synthesis and characterization of trioxorhena(VII)carborane [Bu 4N][(η1-C2B9H 11)ReO3] (1a) and its methyl-substituted analogue [Bu 4N][(7,8-Me2-η1-C2
Hydrosilylation of carbonyl-containing substrates catalyzed by an electrophilic η1-silane iridium(III) complex
Park, Sehoon,Brookhart, Maurice
experimental part, p. 6057 - 6064 (2011/02/26)
Hydrosilylation of a variety of ketones and aldehydes using the cationic iridium catalyst (POCOP)Ir(H)(acetone)+, 1 (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl), is reported. With triethyl silane, all but exceptionally bulky ketones undergo quantitative reactions employing 0.5 mol % catalyst in 20-30 min at 25 °C. Hydrosilylation of esters and amides results in over-reduction and cleavage of C-O and C-N bonds, respectively. The diastereoselectivity of hydrosilylation of 4-tert-butyl cyclohexanone has been examined using numerous silanes and is highly temperature dependent. Using EtMe2SiH, analysis of the ratio of cis:trans hydrosilylation products as a function of temperature yields values for ΔΔH ? (ΔH?(trans) - ΔH ?(cis)) and ΔΔS? (ΔS ?(trans) - ΔS?(cis)) of -2.5 kcal/mol and -6.9 eu, respectively. Mechanistic studies show that the ketone complex (POCOP)Ir(H)(ketone)+ is the catalyst resting state and is in equilibrium with low concentration of the silane complex (POCOP)Ir(H)(HSiR 3)+. The silane complex transfers R3Si + to ketone, forming the oxocarbenium ion R3SiOCR' 2+, which is reduced by the resulting neutral dihydride 3, (POCOP)Ir(H)2, to yield product R3SiOCHR'2 and (POCOP)IrH+, which closes the catalytic cycle.
One-step conversion of formate esters to O-silyl ethers by means of samarium diiodide in the presence of chlorosilane reagents
Honda, Toshio,Ishikawa, Fumihiro
, p. 3323 - 3328 (2007/10/03)
One-step conversion of various types of formate esters into the corresponding O-silyl ethers under neutral reaction conditions was established by employing samarium diiodide in the presence of chlorosilane reagents.
Group 6 anionic ·-hydride complexes [HM2(CO)10]- (M = Cr, Mo, W): New catalysts for hydrogenation and hydrosilylation
Fuchikami, Takamasa,Ubukata, Yumiko,Tanaka, Yasutaka
, p. 1199 - 1202 (2007/10/02)
Group 6 anionic ·-hydride complexes catalyze hydrogenation of conjugated olefins, aldehydes, ketoesters, and alkynes, and hydrosilylation of aldehydes and conjugated olefins with high regio- and stereoselectivity. Ketones are converted into silyl ethers and silyl enol ethers with monohydrosilanes and dihydrosilanes, respectively.
