Photoanation reactions

The Strasbourg group extended their studies to highly hindered derivatives of terpy. The ligand 6,6"-Ph2terpy is very hindered, but forms a bis complex with ruthenium(II) the NMR and photophysical properties of this complex have been reported 168, 279). The steric requirements of the ligand are expressed in dissociative photoanation reactions. 

Chromium(in) complexes also undergo photoanation reactions. When aqueous solutions of Cr(H20)6 are photolyzed in the wavelength range of 40Q-575 nm in the presence of Cl" or SCN" ion, replacement of a water molecule by the anionic ligand occurs ... 

The quantum yields are in the region of 10 for this photoanation reaction. A comparative study of the photoaquation and photoanation reactions has been carried out by photolyzing Cr(NH3)6 in an aqueous solution containing added chloride ion. For a series of solutions covering a chloride ion concentration range from 0-8 M, the total quantum yield is independent of the chloride ion concentration. Aquation and anation therefore only compete with each other for the vacant coordination position in Cr(NH3)i that is formed by the photodissociation of an ammonia molecule. Since the lowest excited quartet state that leads to photodissociation is very short-lived (t < 10" only those molecules present in the... 

Finally, IPA or interfacial photoanation reactions have been observed at liquid-liquid interfaces by measurement of photocurrents. The photoinduced exchange of ligands in the bulk is a well-characterized process. Brown has observed... 

PC-doubling Reactions PC doubling refers to a type of charge-transfer reaction in which both bands of the semiconductor are involved, thus emphasizing the distinctive features of semiconductor electrochemistry. The first examples of such reactions relate to the photoan-odic oxidation of species such as formate and tartrate at wide band gap -type electrodes [74, 75]. A photon generates an electron-hole pair in the semiconductor. The electron and hole are separated by the electric field of the depletion layer. The electron is detected as photocurrent in the external circuit. The hole oxidizes a species from solution producing an intermediate... 

An associative mechanism is also proposed for the photoanation of [Cr(DMSO)e] ion by N3- and NCS ions. The quantum yield for the reaction with N3- ion is greater than that for the reaction with NCS, even at anion concentrations near to... 

---