Premium
Relative rates, relative activation parameters and substituent effects of lithium–metalloid exchange reactions
Author(s) -
Kanda Takahiro,
Kato Shinzi,
Kambe Nobuaki,
Kohara Yasuhisa,
Sonoda Noboru
Publication year - 1996
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199601)9:1<29::aid-poc752>3.0.co;2-q
Subject(s) - chemistry , steric effects , substituent , lithium (medication) , reactivity (psychology) , enthalpy , inorganic chemistry , reaction rate constant , medicinal chemistry , reaction rate , organic chemistry , kinetics , catalysis , thermodynamics , medicine , pathology , quantum mechanics , endocrinology , physics , alternative medicine
The relative reactivity of heteroatomic compounds (PhM; M = SeR, SnR 3 , TeR, I) towards BuLi was estimated by competitive experiments. The rates of exchange reactions in THF increase in the order I > Te ≫ Sn ≫ Se with a ratio of 1000:300:15:1 at − 70 °C when R = Bu. Me 3 SnPh underwent exchange much faster than Bu 3 SnPh, suggesting that the exchange reaction was largely affected by steric hindrance. The evidence that Bu 3 SnPh and BuTePh react with BuLi at almost the same rate in the presence of HMPA and that the relative exchange rates of Li‐Te/Li‐Sn increase in less polar solvents such as Et 2 O and hexane indicates that coordination of solvents towards lithium plays an important role in exchange reactions. Relative activation parameters obtained from competitive reactions of PhTeBu and PhSnBu 3 with BuLi showed that Li‐Te exchange was favored over Li‐Sn exchange by an enthalpy factor. Hammett treatment of Li‐Te exchange of ArTeBu with BuLi in THF showed a substantially large positive reaction constant (ρ) of 3·4, indicating that the anion charge was largely distributed on the leaving group in the transition state.