Electronic spectra and photoreactivity of (cyclopentadienyl)rhenium(I)(dicarbonyl)(nitrosyl) cation

The complex [CpReI(CO)2(NO)]+ with Cp=cyclopentadienyl shows two long-wavelength absorptions at λmax=380 and 330 nm which are assigned to ReI→NO+ metal-to-ligand charge transfer (MLCT) transitions. In the solid state [CpReI(CO)2(NO)]PF6 displays a luminescence at λmax=570 nm which is assumed to originate from the lowest-energy ReI→NO+ MLCT triplet. In solution the complex is not emissive but photoreactive. In the presence of PPh3, MLCT excitation leads to a photosubstitution yielding [CpRe(CO)(PPh3)(NO)]+. The dependence of the quantum yield on the PPh3 concentration is consistent with an associative mechanism.