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Nucleophilic addition versus electron transfer in carbonylmetallate salts. Donor–acceptor interactions in the precursor ion pairs
Author(s) -
Michael Bockman T.,
Kochi Jay K.
Publication year - 1997
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(199707)10:7<542::aid-poc918>3.0.co;2-o
Subject(s) - chemistry , nucleophile , isostructural , steric effects , delocalized electron , electron transfer , acceptor , pyridinium , photochemistry , redox , stoichiometry , electron acceptor , crystallography , inorganic chemistry , medicinal chemistry , stereochemistry , crystal structure , organic chemistry , catalysis , physics , condensed matter physics
The isostructural pentacarbonylmetallate anions M(CO) − 5 (M=Mn and Re) react with a series of N ‐methylpyridinium cations (Py + ) to yield products of nucleophilic addition [NA=Py–M(CO) 5 ] or of one‐electron redox reaction [ET=Py · +M(CO) · 5 ]. The partitioning of the reaction along the two reaction pathways is controlled by steric factors and the electronic structure of the pyridinium cation, with cations which form stable, delocalized radicals favoring the ET pathway. The central metal also plays a role in determining the stoichiometry, and the NA pathway is favored by the rhenate anion and ET by the manganate analogue. Rates of both reactions correlate with the driving force for electron transfer, and the differing reaction pathways are not distinguished on the basis of linear free energy relations, previously discussed by Bordwell and co‐workers. The contact ion pair [Py + , M(CO) − 5 ] is identified as the critical precursor for both electron transfer and nucleophilic coupling. Based on these observations, it is proposed that the rates and mechanisms of these interionic reactions are controlled by donor–acceptor bonding in the transition states, which in turn is directly related to the charge‐transfer interactions extant in the ion‐pair intermediate. © 1997 John Wiley & Sons, Ltd.