Electrophilic Phosphonium Cation-Mediated Phosphane Oxide Reduction Using Oxalyl Chloride and Hydrogen
The metal-free reduction of phosphane oxides with molecular hydrogen (H2) using oxalyl chloride as activating agent was achieved. Quantum-mechanical investigations support the heterolytic splitting of H2 by the in situ formed electrophilic phosphonium cation (EPC) and phosphane oxide and subsequent barrierless conversion to the phosphane and HCl. The reaction can also be catalyzed by the frustrated Lewis pair (FLP) consisting of B(2,6-F2C6H3)3 and 2,6-lutidine or phosphane oxide as Lewis base. This novel reduction was demonstrated for triaryl and diaryl phosphane oxides providing access to phosphanes in good to excellent yields (51–93 %).
Stepen, Arne J.,Bursch, Markus,Grimme, Stefan,Stephan, Douglas W.,Paradies, Jan
supporting information
p. 15253 - 15256
(2018/10/24)
Electronic and steric effects of ligands as control elements for rhodium-catalyzed asymmetric hydrogenation
Chiral diphosphine ligands analogous to bdpp have been synthesized and tested in order to study the effect of the electronic nature of the ligands in Rh-catalyzed asymmetric hydrogenation of some prochiral olefins. The results are compared with those obtained with the analogous unsubstituted ligand (bdpp). The rhodium-catalyzed asymmetric hydrogenation of olefins was influenced by ligand-based electronic effects, as well as substrate based ones. Excellent ee's (up to 98.3%) have been obtained in the rhodium-catalyzed hydrogenation of (Z)-α-acetamidocinnamic acids and esters.
A concise synthesis of a new xylyl-biaryl diphosphine ligand for asymmetric hydrogenation of ketones
A concise synthesis of a symmetrical biaryl diphosphine ligand bearing 3,5-dimethylphenyl substituents at phosphorus is described. The ruthenium catalysts [diphosphine RuCl2 diamine] containing the new ligand Xyl-TetraPHEMP were found to be as active and as selective as the state-of-the-art catalysts for homogeneous asymmetric ketone hydrogenation.
Henschke, Julian P.,Zanotti-Gerosa, Antonio,Moran, Paul,Harrison, Paul,Mullen, Brendan,Casy, Guy,Lennon, Ian C.
p. 4379 - 4383
(2007/10/03)
Anodic Bahavior of Crowded Triarylphosphines. ESR Study of Triarylphosphoniumyl Radicals, Ar3P.+
A large number of triarylphosphines exhibiting different steric hindrance has been prepared.The pyramidalization angle α of these compounds was calculated with use of the MM2 force field and was shown to depend almost exclusively on the number of ortho substituents on the phenyl rings.In a series of isosteric (same α) phosphines, the oxidation potential correlates with the sum of the ?+ Hammett parameters of the phenyl substituents.In the absence of oxygen, anodic oxidation of all the triarylphosphines bearing two o-methyl substituents on each phenyl ring is reversible and yields very persistent phosphoniumyl radicals.These radicals are easly detected by ESR in liquid solution and were shown to retain a pyramidal geometry that is significantly flattened compared to that of the parent phosphine.
Culcasi, Marcel,Berchadsky, Yves,Gronchi, Gerard,Tordo, Paul
p. 3537 - 3542
(2007/10/02)
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