Abstract
The origin of the enantio- and regioselectivity of ring-opening reaction of oxabicyclic alkenes catalyzed by rhodium/Josiphos has been examined using M06-2X density functional theory(DFT). DFT calculations predict a 98% ee for the enantioselectivity and only the 1,2-trans product as one regio- and diastereomer, in excellent agreement with experimental results. The solvent tetrahydrofuran(THF) plays a key role in assisting nucleophilic attack. Orbital composition analysis of the LUMO and the NPA atomic charge calculations were conducted to probe the origins of the regioselectivity. The orbital composition analysis reveals two potential electrophilic sites of the Rh–π-allyl intermediate M3 and the NPA atomic charges demonstrate that Cα carries more positive charges than Cγ, which suggests that Cα is the electrophilic site.
Highlights
The origin of the enantio- and regioselectivity of ring-opening reaction of oxabicyclic alkenes catalyzed by rhodium/Josiphos has been examined using M06-2X density functional theory(DFT)
Among enormous transition metal catalysts used in organic synthesis, catalytic active rhodium has been of great significance in this regard
The π-allyl or enyl rhodium alkoxide complex II or III was generated by oxidative insertion with retention into a bridgehead C–O bond, which is regarded as the enantiodiscriminating step in the catalytic cycle
Summary
The M06-2X functional[20,21] was used for the gas-phase geometry optimization of all species, which was demonstrated to be suitable for studying transition metal catalysis[22,23]. Frequency analysis at the same level was performed to ensure the stationary point as minimum or transition state. The single-point calculations on the gas-phase optimized geometry with SMD solvation model[25] www.nature.com/scientificreports/. The single-point calculations were carried out using M06-2X with GEN2 (LANL2DZ for Rh and Fe, and 6–311 +G(d,p) for other atoms). The reported Gibbs free energy in this study was calculated by adding the gas-phase Gibbs free energy correction with the solution-phase single-point energy[26]. Fragment distortion and interaction energies were computed at the M06-2X/6–311 + G(d,p)-LANL2DZ level of theory using the M06-2X/6–31 G(d)-LANL2DZ geometries in the gas phase. The 3D structures were prepared using CYLView[28]
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