SILICON-PHOSPHORUS ANALOGIES. PARTICIPATION OF EXTERNAL NUCLEOPHILES TO ACTIVATED PROCESSES OF RACEMIZATION AND HYDROLYSIS OF CHLOROPHOSPHONO DERIVATIVES

Article abstract of DOI:10.1016/S0040-4020(01)83131-8

Kinetic and stereochemical studies show nucleophilic assistance by dimethylformamide (DMF), dimethylacetamide (DMA), hexamethylphosphotriamide (HMPT) and N-methylimidazole (NMI) in racemization and solvolysis of menthylchloro(phenyl)phosphonate, 1a, and O-ethylchloro(phenyl)thiophosphonate, 2.Similar orders of nucleophilic reactivity (Nu = NMI >> HMPT > DMF> DMA), and identical rate laws (v_rac = k ² and v_H2O = k') are consistent with a common mechanism, governed by entropy (-60 u.e<ΔS^/= <-40 u.e.).Analogies between reaction mechanisms at silicon and phosphorus are clearly evidenced.A two step process, involving rate-determining attack on a pentacoordinate complex is discussed.