156813-99-9Relevant academic research and scientific papers
Dynamic Cross-Exchange in Halophosphonium Species: Direct Observation of Stereochemical Inversion in the Course of an SN2 Process
Nikitin, Kirill,Jennings, Elizabeth V.,Al Sulaimi, Sulaiman,Ortin, Yannick,Gilheany, Declan G.
supporting information, p. 1480 - 1484 (2018/02/06)
The complex fluxional interconversions between otherwise very similar phosphonium bromides and chlorides R3PX+X? (R=Alk, Ar, X=Cl or Br) were studied by NMR techniques. Their energy barriers are typically ca. 11 kcal mol?1, but rise rapidly as bulky groups are attached to phosphorus, revealing the importance of steric factors. In contrast, electronic effects, as measured by Hammett analysis, are modest (ρ 1.46) but still clearly indicate negative charge flow towards phosphorus in the transition state. Most significantly, detailed analysis of the exchange pathways unequivocally, and for the first time in any such process, shows that nucleophilic attack of the nucleophilic anion on the tetrahedral centre results in inversion of configuration.
Catalytic phosphorus(V)-mediated nucleophilic substitution reactions: Development of a catalytic appel reaction
Denton, Ross M.,An, Jie,Adeniran, Beatrice,Blake, Alexander J.,Lewis, William,Poulton, Andrew M.
, p. 6749 - 6767 (2011/10/02)
Catalytic phosphorus(V)-mediated chlorination and bromination reactions of alcohols have been developed. The new reactions constitute a catalytic version of the classical Appel halogenation reaction. In these new reactions oxalyl chloride is used as a consumable stoichiometric reagent to generate the halophosphonium salts responsible for halogenation from catalytic phosphine oxides. Thus, phosphine oxides have been transformed from stoichiometric waste products into catalysts and a new concept for catalytic phosphorus-based activation and nucleophilic substitution of alcohols has been validated. The present study has focused on a full exploration of the scope and limitations of phosphine oxide catalyzed chlorination reactions as well as the development of the analogous bromination reactions. Further mechanistic studies, including density functional theory calculations on proposed intermediates of the catalytic cycle, are consistent with a catalytic cycle involving halo- and alkoxyphosphonium salts as intermediates.
