Computational Approaches to Activity in Rhodium‐Catalysed Hydroformylation

We have undertaken theoretical investigations of the asymmetric hydroformylation of styrene by the [Rh{(R,S)-BINAPHOS}(CO)(2)H] catalyst, focusing on the origin of the ligand coordination preferences and stereoinduction. We evaluated the different factors governing the preference of the BINAPHOS ligand to coordinate with the phosphane moiety at the equatorial site and the phosphite moiety at the apical site. The donor-acceptor interactions, obtained using a modified version of energy decomposition analysis (EDA) based on orbital deletion, favour the phosphite moiety at the equatorial site. However, the electronic distortion and the steric effects inverse this tendency. Calculations also suggest that the coordination preference was transferred to the selectivity-determining transition state. We propose a stereochemical model based on quantitative quadrant maps obtained from a new molecular descriptor, the distance-weighted volume (V(W)), which is easily computed from ground-state structures. Repulsive interactions between the substrate and the apical phosphite were responsible for the enantiodifferentiation. The axial chirality of the phosphite discriminated one of the competitive equatorial-apical paths, whereas the axial chirality of the backbone discriminated one of the two enantiomers. Transition-state calculations revealed that the placement of phosphane at the apical site would lower enantioselectivity, explaining the poor performance of other phosphane-phosphite ligands. Finally, comparison with previous studies allowed the definition of several prerequisites for diphosphane ligands for high stereoselectivity: 1) specific equatorial-apical coordination bringing chirality to the apical site, 2) combination of two stereogenic centres and 3) rigid structures.

Section: Wwwchemeurjorgmentioning

confidence: 99%

Theoretical Studies of Asymmetric Hydroformylation Using the Rh(R,S)‐BINAPHOS Catalyst—Origin of Coordination Preferences and Stereoinduction

Aguado-Ullate

Saureu

Guasch

et al. 2011

“…Most of the work has been reviewed, [11][12][13] but several aspects of hydroformylation are still under investigation. [14][15][16][17][18][22][23][24] The entire catalytic cycle for rhodium/ phosphane-catalyzed hydroformylation has been examined at different levels of calculation by using simplified model phosphanes and ethene as model alkene. [14][15][16] Recently, Rocha and Almeida used propene instead of ethene as substrate to investigate the regioselectivity on HRh(CO)(PH 3 ) 2 model rhodium/phosphane catalysts, [17a] and on HRh(CO) 3 unmodified rhodium catalysts.…”

Section: Introductionmentioning

confidence: 99%

“…In line with these arguments, recent high-level calculations on related model systems showed that barriers for alkene association/ dissociation are negligible, and when free-energy corrections are considered, alkene complexes and their dissociation products are almost isoenergetic. [14] Substrate-ligand interactions: To more deeply analyze the factors governing enantioselectivity, we investigated ligandsubstrate interactions in more detail. We stated above that the difference between phenyl-phenyl and phenyl-methyl interactions may be crucial in sterodifferentiation.…”

mentioning

confidence: 99%

Origin of Stereoinduction by Chiral Aminophosphane Phosphinite Ligands in Enantioselective Catalysis: Asymmetric Hydroformylation

Carbó¹,

Lledós²,

Vogt³

et al. 2006

The origin of stereoinduction by chiral aminophosphane phosphinite (AMPP) ligands in asymmetric hydroformylation was investigated with a theoretical approach. The roles of the stereogenic center at the aminophosphane phosphorus atom (NP*) and of the chirality of the backbone were analyzed by considering three experimentally tested cases: 1) P-stereogenic yielding high ee, 2) P-nonstereogenic yielding low ee, and 3) P-stereogenic yielding low ee. We succeeded in reproducing the experimentally observed trends for the three studied AMPP ligands. Our results indicated that alkene insertion into the rhodium-hydride bond is the selectivity-determining step, and not alkene coordination. Additional calculations on model systems revealed that the different nonbonding weak-type interactions of styrene with the substituents of the NP* stereogenic center in an axial position is responsible for stereodifferentiation. The chirality of the AMPP backbone plays a secondary role. The rationalization of the stereochemical outcome is not straightforward, because two competitive equatorial/axial reaction paths, showing opposite asymmetric induction, must be considered. Construction of stereochemical models and evaluation of stereoinduction for novel ligand systems suggested that two prerequisites are required to improve the performance of AMPP-type ligands in asymmetric hydroformylation: 1) combination of stereorecognition and stereohindrance by substituents at the NP* atom, and 2) more rigid backbones.

“…Indeed, previous theoretical studies on the hydride migration step of the hydroformylation reaction have shown that the geometry of the transition state is far from linear. [15][16][17][18][19][20] Furthermore, because the hydride migration step in the hydroformylation reaction involves the breaking of a rhodium À hydride bond, which is significantly different from a carbon À hydrogen bond, interpretations purely based on a single small 1 H/ 2 H kinetic isotope effect can be misleading. A more detailed discussion is provided below.…”

mentioning

confidence: 96%

The Rate‐Determining Step in the Rhodium–Xantphos‐Catalysed Hydroformylation of 1‐Octene

Zuidema¹,

Escorihuela²,

Eichelsheim³

et al. 2008

The rate-determining step in the hydroformylation of 1-octene, catalysed by the rhodium-Xantphos catalyst system, was determined by using a combination of experimentally determined (1)H/(2)H and (12)C/(13)C kinetic isotope effects and a theoretical approach. From the rates of hydroformylation and deuterioformylation, a small (1)H/(2)H isotope effect of 1.2 was determined for the hydride moiety of the rhodium catalyst. (12)C/(13)C isotope effects of 1.012(1) and 1.012(3) for the alpha-carbon and beta-carbon atoms of 1-octene were determined, respectively. Both quantum mechanics/molecular mechanics (QM/MM) and full quantum mechanics calculations were carried out on the key catalytic steps, for "real-world" ligand systems, to clarify whether alkene coordination or hydride migration is the rate-determining step. Our calculations (21.4 kcal mol(-1)) quantitatively reproduce the experimental energy barrier for CO dissociation (20.1 kcal mol(-1)) starting at the (bisphosphane)RhH(CO)(2) resting state. The barrier for hydride migration lies 3.8 kcal mol(-1) higher than the barrier for CO dissociation (experimentally determined trend approximately 3 kcal mol(-1)). The computed (1)H/(2)H and (12)C/(13)C kinetic isotope effects corroborate the results of the energy analysis.