PHOTOPHYSICAL BEHAVIOR OF A NEW CO2 REDUCTION CATALYST, RE(CO)(2)(BPY)(P(OET)(3))(2)(+)

The photophysical and photochemical properties of the cation Re(CO)(2)(2,2'-bipyridyl){P(OEt)(3)}(+)(2) (P+), which is an effective photochemical reductant of CO2, are examined by time-resolved infrared spectroscopy (TRIR) of the nu(CO) absorption bands, by UV/visible flash photolysis in both emission and absorption, and by spectroelectrochemistry in both infrared and UV/visible regions. It is shown that P+ is first excited into a metal to ligand charge transfer state (MLCT) in which the charge is localized on the bpy ligand, resulting in an upward shift in the nu(CO) bands. This excited state is quenched by 1,4-diazabicyclo[2.2.2]octane to form the neutral species P with lowered nu(CO) infrared bands; there is a rapid back-reaction between P and DABCO. The kinetics of these processes are obtained. Preliminary experiments suggest that P must be further activated before the CO2 reduction cycle starts.