Oxo- and hydroxomanganese(IV) adducts: a comparative spectroscopic and computational study.
The electronic structures of the bis(hydroxo)manganese(IV) and oxohydroxomanganese(IV) complexes [Mn(IV)(OH)(2)(Me(2)EBC)](2+) and [Mn(IV)(O)(OH)(Me(2)EBC)](+) were probed using electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD spectroscopies. The d-d transitions of [Mn(IV)(OH)(2)(Me(2)EBC)](2+) were assigned using a group theory analysis coupled with the results of time-dependent density functional theory computations. These assignments permit the development of an experimentally validated description for the pi and sigma interactions in this complex. A similar analysis performed for [Mn(IV)(O)(OH)(Me(2)EBC)](+) reveals that there is a significant increase in the ligand character in the Mn pi* orbitals for the Mn(IV)=O complex relative to the bis(hydroxo)manganese(IV) complex, whereas the compositions of the Mn sigma* orbitals are less affected. Because of the steric features of the Me(2)EBC ligand, we propose that H-atom transfer by these reagents proceeds via the sigma* orbitals, which, because of their similar compositions among these two compounds, leads to modest rate enhancements for the Mn(IV)=O versus Mn(IV)OH species.
Chattopadhyay
Swarup
S
Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, USA.
Geiger
Robert A
RA
Yin
Guochuan
G
Busch
Daryle H
DH
Jackson
Timothy A
TA
D000042:Absorption; D002942:Circular Dichroism; D004583:Electrons; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D013057:Spectrum Analysis
D009942:Organometallic Compounds; D008345:Manganese