Enantiomerization Pathway and Atropochiral Stability of the BINAP Ligand: A Density Functional Theory Study

Abstract

A theoretical study of the enantiomerization pathway of BINAP, the paradigm of atropochiral ligands in asymmetric organometallic catalysis, is reported. Density functional theory was used with the B3PW91 functional and the 6-31G(d,p) basis set. The calculation level was validated through the study of the syn and anti enantiomerization pathways of the 1,1′-binaphthyl reference for which the enantiomerization barrier was calculated to be in good agreement with experimental data. Calculations were then performed on BINAP itself using the same level of theory, and showed that its enantiomerization mechanism follows the syn route through a concerted, yet highly asynchronous, all-chiral process. The enantiomerization barrier was computed at 213 kJ mol(−1) and proved little sensitive to the functional or to the basis set used, with values always larger than 200 kJ mol(−1). The configurational stability of BINAP was finally characterized by a computed Oki’s racemization temperature of 491 °C.

Optical Stability of 1,1′-Binaphthyl Derivatives

“…It would appear, then, that the dominating characteristic is the size of the substituent. Previous theoretical results obtained for large substituents are consistent with this assumption (computed rotational barriers for 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl and 2-amino-2′-hydroxy-1,1′-binaphthyl are 49.4 44 and 40.4 45 kcal/mol, respectively). The barrier for H is by far the lowest, whereas the highest barrier occurs for the bulky phenyl group.…”

Catalysis by Pure Graphene—From Supporting Actor to Protagonist through Shape Complementarity

“…For both compounds, the lowest activation energy was reported for racemization via the anti- C i pathway . These results are in general agreement with subsequent DFT studies of the uncatalyzed process. ,, Figure gives the molecular geometries as well as energies relative to the free compounds 1 and 2 obtained here at the PW6B95-D3­(BJ)/Def2-TZVPP level of theory − for all five possible transition structures for the chirality inversions of the binaphthyl systems of interest.…”

“…Being one of the most common motifs in the backbones of asymmetric metal and organocatalysts, − the racemizations of biaryl compounds have been studied extensively both computationally and experimentally. − Here, we focus on the racemizations of 1,1′-binaphthyl ( 1 ) and its synthetically highly relevant derivative 1,1′-binaphthyl-2,2′-diol (BINOL) ( 2 ) which forms the starting material to a myriad of chiral catalysts. − Table gives experimentally determined rotational barriers for compounds 1 and 2 .…”

“…The transition state geometries of binaphthyl inversions have been the focus of a number of computational mechanistic studies and a total of four general pathways have been proposed. ,,,− ,, These include two anti- type pathways with passage of the substituents in the 2 and 8 positions, and two syn- type routes corresponding to the passage of the 2 and 2′ and 8 and 8′ substituents. For both the syn and anti pathways, transition structures of two different symmetries, namely, anti- C i , anti- C 2 , syn- C 2 , and syn- C s , are conceivable.…”

Atropisomerism of 2,2′‐Diaryl‐1,1′‐binaphthalenes Containing Three Stereo­genic Axes: Experimental and Computational Study

“…ity of the binaphthalene unit [8] these compounds can each exist in the form of three diastereomeric atropisomers (Figure 2): two anti isomers (unlike,unlike and like,like, marked as u,u and l,l, respectively) and one syn isomer (pseudomeso form like,unlike, marked as l,u). We have also determined thermodynamic parameters of these atropisomers by variable-temperature (VT) NMR spectroscopy.…”