Perfluoroalkylated Main‐Group Element Lewis Acids as Catalysts in Transfer Hydrogenation

Abstract

Transfer hydrogenation plays an important part in organic chemistry. Recently, strong Lewis acids like B(C6F5)3 have been introduced as a catalyst for these reactions. We successfully employed the Lewis acid (C2F5)3PF2 as a catalyst in the transfer hydrogenation between 1,3,5‐trimethylcyclohexa‐1,4‐diene and 1,1‐diphenylethylene. Surprisingly, the treatment of the diene alone with a catalytic amount of (C2F5)3PF2 led to a quantitative dismutation to mesitylene and 1,3,5‐trimethylcyclohexane. With B(C6F5)3, there was a solvent‐dependency: in CH2Cl2 mainly the dismutation products were obtained, while in toluene the evolution of H2 was observed. Additionally, the catalytic activity of various perfluoroalkylated germanes and silanes was tested.

Alkene Transfer Hydrogenation with Alkaline‐Earth Metal Catalysts

“…The Stephan group reduced activated alkenes with a R 3 SiH/HNR 2 combination using a frustrated lewis pair (FLP) catalyst . Very recently, the groups of Melen and Morrill reported TH of silylenol ethers using a FLP catalyst and the groups of Paradies and Hoge introduced a Lewis‐acidic phosphine catalyst for TH of 1,1,‐diphenylethylene . Interestingly, high‐energy H 2 substitutes like NH 3 BH 3 or in situ generated HN=NH have been shown to reduce activated alkenes without using a catalyst …”

“…Although concomitant reduction of 1,3‐CHD also gave considerable quantities of cyclohexene, this reaction suggested the feasibility of Ae metal catalyzed alkene TH. Ketone TH, and to a lesser extent imine TH, are well‐studied procedures but there are hardly catalysts for the more challenging TH of the significantly less polar C=C bond . Herein we report first comprehensive investigations towards alkene reduction by TH using easily accessible AeN′′ 2 catalysts [N′′=N(SiMe 3 ) 2 ; Scheme ].…”

Tris(pentafluoroethyl)difluorophosphorane and N‐Heterocyclic Carbenes: Adduct Formation and Frustrated Lewis Pair Reactivity

“…It was applied as Lewis acidic catalyst in Diels-Alder reactions, [30] and Michael additions [31] or in transfer hydrogenations. [32] As a strong Lewis acid, PF 2 (C 2 F 5 ) 3 reacts with nucleophiles such as H À , [33] HO À , CH 3 C(=O)O À , [34] F À , [23,28] or Cl À . [35] The reaction with a fluoride source resulted in the formation of the corresponding fluorophosphate anion [PF 3 (C 2 F 5 ) 3 ] À (FAP anion), which has been found to be a highly valuable building block for materials applications, e. g. for preparation of the conducting salt Li[PF 3 (C 2 F 5 ) 3 ] (LiFAP) [36] and room temperature ionic liquids (RTILs).…”

Alkene Transfer Hydrogenation with Alkaline‐Earth Metal Catalysts

“…[11] Very recently,t he groups of Melen and Morrill reported TH of silylenol ethers using aF LP catalyst [12] and the groups of Paradies and Hoge introduced aL ewis-acidic phosphine catalyst for TH of 1,1,-diphenylethylene. [13] Interestingly, high-energy H 2 substitutes like NH 3 BH 3 or in situ generated HN=NH have been shown to reduce activated alkenes without using ac atalyst. [14,15] While early main-group metal catalysis is ar apidly developing field, [16] TH with these metals is currently restricted to transferring hydrogen from iPrOH to ketones with simple bulk catalysts like NaOH or KOH.…”

“…Ketone TH, and to al esser extent imine TH, are well-studied procedures but there are hardly catalysts for the more challenging TH of the significantly less polar C = Cbond. [13,19] Herein we report first comprehensive investigations towards alkene reduction by TH using easily accessible AeN'' 2 catalysts [N'' = N(SiMe 3 ) 2 ; Scheme 1].…”