Anion-Activated Bases and Nucleophiles Characterized by Photoelectron Spectroscopy.

Negative ion photoelectron spectra at 20 K along with ab initio [CCSD(T)] and M06-2X density functional theory calculations are reported for a series of six basic and nucleophilic pyridine derivatives with an anionic substituent [i.e., 3- and 4-PyrBX 3 - , where X = F, 4- t -BuC 6 H 4 , 4-MeOC 6 H 4 , and 3,5-(MeO) 2 C 6 H 3 ]. Vertical detachment energies (VDEs) of these charge-activated reagents span from 4.50-5.85 eV and are well reproduced by M06-2X/aug- cc -pVTZ and CCSD(T)/maug- cc -pVTZ computations. Surprisingly, the VDEs are found to correlate with the S N 2 reactivity of the PPh 4 + salts of the substituted pyridine anions with 1-iodooctane in dichloromethane. This provides an experimental measure of the nucleophilicity of these charge-activated anions, which represent a new class of chemical reagent.