Computational investigation of enantio‐ and regioselectivity of rhodium‐catalyzed asymmetric hydroformylation of vinyl formate with CHIRAPHOS‐type ligand

Abstract

The potential energy profile for Rh-catalyzed asymmetric hydroformylation of vinyl formate is mapped out using a nonlocal density functional method (B3LYP). This study focuses on the enantio-and regioselectivity of asymmetric hydroformylation. All the structures are optimized at the B3LYP/6-31G(d,p) level(LANL2DZ(d) for Rh, P). As illustrated by computation, the olefin insertion step is irreversible because of higher activation free energy of the reverse reaction than that of forward reaction, so it is the determining step for both the regioselectivity and enantioselectivity in asymmetric hydroformylation. The lowest activation free energy in vinyl insertion is the path 2a 3 TS1a (⌬G ϭ 47.92 kJ/mol), giving rise to the preferred product as (S)-1-formylenthyl formate. Throughout the catalytic cycle, the H 2 oxidative addition has the highest activation free energy, 77.24 kJ/mol, so it is the ratelimiting step for the whole catalytic cycle. The calculation results are in agreement with many experiment investigations.

Computational aspects of hydroformylation

“…The formation of Rh-alkyl intermediates was found as selectivity determining step and the branched (S)-1-formylethyl formate was predicted as main product. 120 For the competitive hydroformylation and hydrogenation of acrylaldehyde the hydrogen addition was proposed to be the rate-limiting step as well. Interestingly, for the branched intermediates the hydrogenation, whereas for the linear intermediates the hydroformylation is preferred kinetically.…”

Kinetics Assessment of the Homogeneously Catalyzed Hydroformylation of Ethylene on an Rh Catalyst

“…The obtained reaction enthalpy of the oxidative addition of H 2 amounts to 9 kJ mol −1 , which, combined with an entropy loss of −144 J mol −1 K −1 , leads to a reaction which is not thermodynamically favored, in line with what is reported in the literature. 28,29,32 The determined reaction enthalpy is relatively close to −11 kJ mol −1 , as obtained by Sparta et al, 28 and inside of the interval of −36 to 66 kJ mol −1 reported by Matsubara et al 33 Even though the oxidative addition of H 2 is difficult, the reverse reaction is slow, as the product has a low concentration, resulting from the quick and favorable occurrence of the consecutive reaction, i.e., the reductive elimination of propanal. The reaction enthalpy obtained for the oxidative addition of propanal amounts to −18 kJ mol −1 , which corresponds to an endothermicity of 18 kJ mol −1 for the reductive elimination of propanal.…”

“…Despite the consensus on the mechanism, there are still many uncertainties on the exact composition of the catalyst during reaction, i.e., which ligands are present on the catalyst and which reaction steps are kinetically relevant . The original consensus was that the oxidative addition of H 2 was rate determining, , but it is now understood that the kinetic relevance of the reaction steps depends on the reactant olefin(s), the reaction conditions, and the catalyst composition. , Numerous density functional theory (DFT) studies have been conducted to investigate the kinetics and thermodynamics of the various reaction steps in the hydroformylation mechanism. ,− Correspondingly, kinetic models have been constructed as well, ,− including a microkinetic one for the hydroformylation of styrene on a homogeneous Rh­(BDP) catalyst and the hydroformylation of ethylene on a heterogeneous Rh catalyst …”

Rational design of diphosphorus ligands – a route to superior catalysts

“…Consistently calculations have described the important intermediate as a pentacoordinate olefin complex; the olefin occupying an equatorial coordination site, in the same plane as the bidentate ligand, whilst the migrating hydride occupies one of the axial sites. [56][57][58] Successful regioselective control for the desired linear aldehyde product using the Xantphos series of ligands was a marked advance in hydroformylation research. However, broad application of asymmetric hydroformylation and structure/activity relationship studies are very much goals in pursuit.…”