Developing a New Class of Axial Chiral Phosphorus Ligands: Preparation and Characterization of Enantiopure Atropisomeric Phosphinines

Abstract

Both enantiomers of the first atropisomeric phosphinine (1) have been isolated by using analytical HPLC on a chiral stationary phase. The enrichment of one enantiomer and a subsequent investigation into its racemization kinetics revealed a barrier for internal rotation of DeltaG(298)(double dagger) = (109.5+/-0.5) kJ mol(-1), which is in excellent agreement with the theoretically predicted value of DeltaG(298)(double dagger) =116 kJ mol(-1). Further analysis with UV and circular dichroism spectroscopies and density functional theory calculations led to the determination and assignment of the absolute configurations of both enantiomers. These results are the basis for future investigations into this new class of axially chiral phosphinine-based ligands and their possible applications in asymmetric homogeneous catalysis.

Cyclometalation of Aryl‐Substituted Phosphinines through CH‐Bond Activation: A Mechanistic Investigation

“…Synthesis and characterization: We have recently shown in several cases that the original synthetic route for the preparation of 2,4,6-triphenylphosphinine (1) is a modular procedure that can be used to access substituted and functionalized 2,4,6-triarylphosphinines. [15][16][17][18][19][22][23][24][25][26][27] We therefore started to introduce electron-withdrawing and electron-donating groups in specific positions of the heterocyclic framework by making use of the corresponding commercially available substituted acetophenones, benzaldehydes, and HBF 4 ·Et 2 O. In this way, symmetrically substituted pyrylium salts were synthesized in a one-pot procedure in good yields and the corresponding phosphinines could be obtained by subsequent reaction with PA C H T U N G T R E N N U N G (SiMe 3 ) 3 , according to Scheme 1.…”

“…The pyrylium salt route, originally reported by Märkl, [22] provides an easy way to introduce electron-withdrawing and electrondonating substituents in specific positions of the phosphinine core. [15][16][17][18][19][23][24][25][26][27] This makes a facile tuning of the ligand properties possible.…”

The Synthesis of Chiral Phosphorus Ligands for use in Homogeneous Metal Catalysis

“…[94] The cyclic phosphine was prepared by condensation of 2,3-dimethylpropiophenone with transbenzylideneacetophenone to give the relevant pyrylium salt. [94] The cyclic phosphine was prepared by condensation of 2,3-dimethylpropiophenone with transbenzylideneacetophenone to give the relevant pyrylium salt.…”

“…Müller and co-workers achieved the separation of atropoisomeric phosphinine enantiomers (Scheme 43). [94] The cyclic phosphine was prepared by condensation of 2,3-dimethylpropiophenone with transbenzylideneacetophenone to give the relevant pyrylium salt. Replacement of the oxygen by phosphorus with an excess of P(CH 2 OH) 3 afforded the enantiomeric phosphinines.…”

Phosphorus Heterocycles

“…Finally, another noteworthy result concerns the synthesis of the first enantiopure atropisomeric phosphinines using the original synthesis of M€ arkl (Scheme 23.26) [252]. The enantiomers are separated by HPLC on a chiral stationary phase.…”