摘要
Addition of an anionic donor to an Mn V (O) porphyrinoid complex causes a dramatic increase in 2-electron oxygen-atom-transfer (OAT) chemistry. The 6-coordinate [Mn V (O)(TBP 8 Cz)(CN)] - was generated from addition of Bu 4 N + CN - to the 5-coordinate Mn V (O) precursor. The cyanide-ligated complex was characterized for the first time by Mn K-edge X-ray absorption spectroscopy (XAS) and gives Mn-O = 1.53 Å, Mn-CN = 2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN - complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e - -reduced Mn III (CN) - complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000-fold versus the same reaction for the parent 5-coordinate complex. An Eyring analysis gives ΔH± = 14 kcalmol -1 , ΔS± = -10 cal mol -1 K -1 . Computational studies fully support the structures, spin states, and relative reactivity of the 5- and 6-coordinate Mn V (O) complexes.