Enantioselectivity in the Iridium-Catalyzed Hydrogenation of Unfunctionalized Olefins

Abstract

The iridium-catalyzed asymmetric hydrogenation of largely unfunctionalized olefins has been studied by DFT calculations using a full, experimentally tested combination of ligand and substrate. All possible diastereomeric pathways were considered within four different hydrogenation mechanisms. The effect of a solvent continuum was also considered, and both the gas-phase and solventcontinuum calculations favored the same mechanism. This mechanism passed through Ir III and Ir V intermediates and was consistent with the sense of stereoselection observed experimentally. Comparing the calculations to those performed on a model system permitted an evaluation of the model system's utility in representing the full one. A simple, general method for predicting the sense of stereoselection in iridium-catalyzed olefin hydrogenation was developed and tested against published data.

DFT Methods to Study the Reaction Mechanism of Iridium‐Catalyzed Hydrogenation of Olefins: Which Functional Should be Chosen?

“…This is followed by its reductive elimination (RE), as the second-H hydrogenation step, leading to the final hydrogenated product, and consequently,r egenerating the iridium(I) complex to finalize the catalytic cycle. [29][30][31][32][33][34] Furthermore, this type of Ir III /Ir V catalytic cycle is also supported by ar ecent NMR spectroscopy study carried out by Pfaltz and Gruber. [24] Moreover,t he Ir I /Ir III mechanism was recently supported by NMRe xperiments and DFT computational analysis.…”

“…[12][13][14] Initiated by this groundbreaking discovery, hundreds of chiral iridium-based catalystsh ave been developed and tested for variousalkene hydrogenations. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] In this regard, theoretical computation and modeling could potentially contribute to solving this conundrum, due to the lack of much relevant experimentald ata. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] In this regard, theoretical computation and modeling could potentially contribute to solving this conundrum, due to the lack of much relevant experimentald ata.…”

Asymmetric Hydrogenation of Olefins Using Chiral Crabtree-type Catalysts: Scope and Limitations

“…This is illustrated in Figure 20a and center of the R-group, as shown in Figure 20c. 41 The angle is negative for ligands in Class 1 and positive for those in Class 2, indicating that the quadrant accommodating the R group will be in the lower and upper corner respectively, for catalysts bearing these ligands. The quadrant system can be used to predict the absolute configuration of the products obtained in the asymmetric hydrogenation of trisubstituted alkenes by chiral N,P-ligated iridium catalysts.…”

“…41 For instance, an Ir center bearing the ligand ent-9a phenyl-2-butene to (S)-2-phenylbutane as the major product (96% ee);…”

SpinPhox/Iridium(I)‐Catalyzed Asymmetric Hydrogenation of Cyclic α‐Alkylidene Carbonyl Compounds

“…On the basis of the the crystal structure information of the SpinPhox/Ir I complexes (R,S)-and (S,S)-1 [14e] and the observed asymmetric induction in the catalysis, as well as the related mechanism reported by Andersson, [16] a plausible asymmetric induction model is proposed for the present catalytic system. As shown in Figure 3, the hydrogen bonding between the lactam carbonyl moieties and the upper Ir À H probably has significant impact on the approach of the C = C double bond to the iridium center during the catalysis.…”