Autoinduced Catalysis and Inverse Equilibrium Isotope Effect in the Frustrated Lewis Pair Catalyzed Hydrogenation of Imines

Abstract

The frustrated Lewis pair (FLP)-catalyzed hydrogenation and deuteration of N-benzylidene-tert-butylamine (2) was kinetically investigated by using the three boranes B(C6F5)3 (1), B(2,4,6-F3-C6H2)3 (4), and B(2,6-F2-C6H3)3 (5) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol(-1)) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect.

Solid Molecular Frustrated Lewis Pairs in a Polyamine Organic Framework for the Catalytic Metal‐free Hydrogenation of Alkenes

“…It is highly likely that BCF forms a FLP with the substrate itself which is capable of splitting hydrogen to auto‐catalytically hydrogenate diethyl benzylidenemalonate. A similar behavior is already reported in literature for BCF in combination with imines . Experimental evidence of the autoinduced catalysis of imine reduction with BCF was reported by Tussing et al .…”

“…A similar behavior is already reported in literature for BCF in combination with imines . Experimental evidence of the autoinduced catalysis of imine reduction with BCF was reported by Tussing et al . However, as soon as substrate, H 2 and BCF are present during the reaction, the reduction of diethyl benzylidenemalonate occurs.…”

Evidence for Genuine Bimetallic Frustrated Lewis Pair Activation of Dihydrogen with Gold(I)/Platinum(0) Systems

“…Puzzled by this result we performed low-temperature NMR kinetics (-20 °C) for the activation of H2 with the 1b:2 couple and found an analogous strong inverse KIE that accounts for 0.50 ± 0.02, suggesting that both systems may share a common mechanism. Inverse KIEs are rather uncommon in the context of FLPs 37 and bimetallic systems, 38 though a very recent report from Mankad and Ess revealed an akin inverse KIE of 0.6 for the heterobimetallic trans-hydro(deutero)genation of alkynes using a polar ruthenium-silver complex containing a Ru-Ag bond. 39 For that system, formation of a terminal ruthenium hydride with low-energy binding modes that contributes to an inverse equilibrium isotopic effect (EIE) is proposed to be responsible of the measured inverse KIE.…”

Versatile Catalytic Hydrogenation Using A Simple Tin(IV) Lewis Acid

“…Interestingly,there is evidence for autocatalysis during the course of the reaction (16 %c onversion observed after 3h,6 0% after 6h); comparable observations have been made by Paradies et al for imine hydrogenations catalyzed by B(2,6-F 2 C 6 H 3 ) 3 ,a nd are attributed to the increased basicity of the product amines,r elative to the imine substrate,r endering H 2 activation more favorable as more product is formed. [25] Following success in the hydrogenation of imines,wewere interested to see whether [1]OTfm ight also be capable of mediating the hydrogenation of closely related carbonyl compounds.S atisfyingly,w hen acetone (4a)i se xposed to reaction conditions similar to those used to hydrogenate 2c catalytic conversion to 2-propanol (5a)i so bserved ( Table 2, entry 1). Whilst the reaction at 120 8 8Ci ss omewhat slow,a t 180 8 8Cn ear-quantitative conversion can be observed within 32 h( Table 2, entry 2).…”