Reduction of Alkyl Halides by Triethylsilane Based on a Cationic Iridium Bis(phosphinite) Pincer Catalyst: Scope, Selectivity and Mechanism

Abstract

A highly efficient procedure for the reduction of a broad range of alkyl halides by triethylsilane based on a cationic iridium bis(phosphinite) pincer catalyst has been discovered and developed. This reduction chemistry is chemoselective and has unique selectivities compared with conventional radical-based processes and the aluminum trichloride/ triethylsilane (AlCl 3 /Et 3 SiH) and triphenylmethyl tetrakis [pentafluorophenyl]borate/triethylsilane {[Ph 3 C] [BA C H T U N G T R E N N U N G (C 6 F 5 ) 4 ]/Et 3 SiH} systems. Reductions use three equivalents of triethylsilane relative to the halide and can be carried out with very low catalyst loadings and in a solvent-free manner, which may provide an environmentally attractive and safe alternative to many currently practiced methods for reduction of alkyl halides. Mechanistic studies reveal a unique catalytic cycle. The cationic iridium hydride

Preferential α‐Hydrosilylation of Terminal Alkynes by Bis‐N‐Heterocyclic Carbene Rhodium(III) Catalysts

“…Other examples of ionic mechanisms involving hydrosilanes include substrates such as carbonyl [8] and ether [9] compounds (C-O and C=O bonds), halogenated compounds [10] (Chalide bonds) and N-heterocycles [11] (C=N bonds). In these cases the splitting of the Si-H bond takes places by interaction of a metal center with the hydrogen atom, and the substrate with the silicon atom.…”

Copper‐Catalyzed Reduction of Alkyl Triflates and Iodides: An Efficient Method for the Deoxygenation of Primary and Secondary Alcohols

“…Thus far, investigations into the reduction of halides and sulfonates using Pd, [15] Ni, [16] and Ir [17] have mostly been focused on unfunctionalized substrates. Thus far, investigations into the reduction of halides and sulfonates using Pd, [15] Ni, [16] and Ir [17] have mostly been focused on unfunctionalized substrates.…”

“…[23] The reaction is compatible with aryl chlorides, bromides, and iodides, all of which are typically reactive in both transition-metal-catalyzed and free-radical reductions (14)(15)(16)(17). We found that, with slight modifications to existing methods, primary triflates can be efficiently prepared with minimal purification.…”

“…We were surprised to find that relatively few attempts have been made to address these challenges through the use of transition-metal catalysis, especially given its role in the selective reduction of alkenes, alkynes, and carbonyls. Thus far, investigations into the reduction of halides and sulfonates using Pd, [15] Ni, [16] and Ir [17] have mostly been focused on unfunctionalized substrates. Recently, we reported the use of copper hydride in a chemoselective catalytic semireduction of alkynes.…”

“…High yields were obtained in the presence of substituents that are susceptible to reduction, including cyano, carbomethoxy, nitro, and alkenyl groups (10-12 and 21). [23] The reaction is compatible with aryl chlorides, bromides, and iodides, all of which are typically reactive in both transition-metal-catalyzed and free-radical reductions (14)(15)(16)(17). The reduction of compounds 18 and 19 shows that the selective reduction of triflates can be accomplished even in the presence of alkyl bromides or tosylates.…”