Inhibition of the fac-(RCO2)ReI(CO3)(bis-azine) Photodecarboxylation of the Carboxylate Ligand, RCO2-, When R Is a Strongly Electron Donating Group:  Thermal and Photochemical Properties of Complexes Where R = Ferrocene, 4-(Dimethylamino)benzyl

The photophysical and phtochemical properties of fac-(RCO2)ReI(CO)3L (R = ferrocene, L = phen, 2,2‘-bpy; R = 4-(dimethylamino)benzyl (4-DMAB), L = phen) were investigated with continuous and flash photolyses. Their properties were compared with those of fac-(CH3CO2)ReI(CO)3L (L = phen, 2,2‘-bpy) complexes. On a femtosecond to 10 ps time scale, the transient spectra of the singlet Re(I) to L charge-transfer excited states, 1MLCTReL, of fac-(RCO2)ReI(CO)3L (R = ferrocene, 4-DMAB) transform into the spectra of two triplet excited states, the 3MLCTReL excited state and a Re(I) to RCO2- charge-transfer excited state, 3MLCTReRCO2. The 3MLCTReRCO2 and 3MLCTReL excited states have lifetimes that span 102 ns to several microseconds. The photodecarboxylation of fac-(RCO2)ReI(CO)3L, initiated in ligand-to-ligand charge-transfer excited states, 3LLCTReL, is markedly affected by the positions of the 3MLCTReRCO2 and 3MLCTReL excited states. In addition, the low energy of 3LLCTRCO2L in the fac-(RCO2)ReI(CO)3L (L = phen, 2,2‘-bpy) complexes, relative to those of fac-(CH3CO2)ReI(CO)3L (L = phen, 2,2‘-bpy) decreases the efficiency of the photodecarboxylation reaction.