Photo-substitution reactions of Cr(CO)4(1,10-phenanthroline). Mechanistic information from entering nucleophile, irradiation wavelength and pressure dependences

Article abstract of DOI:10.1016/s0020-1693(96)05288-7

Quantum yields for the photo-substitution of Cr(CO)₄phen (phen = 1,10-phenanthroline) by PMe₃ and PPh₃ (L) to produce Cr(CO)₃(L)phen were determined as a function of nucleophile concentration, irradiation wavelength and pressure. The results show that LF photolysis is decelerated significantly on increasing pressure, which is in line with a limiting dissociative mechanism. There is a steady decrease in the corresponding volume of activation on increasing the irradiation wavelength from 366 to 546 nm. The results obtained from MLCT photolysis indicate that ligand substitution proceeds according to a dissociative interchange (I_d) mechanism. The results for PMe₃ and PPh₃ are rather similar and demonstrate that relatively little bond formation occurs with the entering nucleophile during MLCT photolysis.