86646-01-7Relevant academic research and scientific papers
Chemistry of ruthenium. 12. Reactions of bidentate ligands with diaquobis[2-(arylazo)pyridine]ruthenium(II) cation. Stereoretentive synthesis of tris chelates and their characterization: Metal oxidation, ligand reduction, and spectroelectrochemical correlation
Goswami, Sreebrata,Mukherjee, Rabindranath,Chakravorty, Animesh
, p. 2825 - 2832 (2008/10/08)
Two isomers of the diaquo complex Ru(OH2)IL22+, viz., trans-cis (tc) and cis-cis (cc) in the pairs N(pyridine), N(pyridine) and N(azo), N(azo), have been used to carry out the title reaction in the cases of both symmetrical and unsymmetrical bidentate ligands (B): major emphasis is given on the tc isomer [L = 2-(phenylazo)pyridine (pap) or 2-(m-tolylazo)pyridine (tap)]. The tris chelates thus formed are of type RuBL2x+ (x = 1 or 2). Using 1H NMR data (δMe of tap complexes), one can demonstrate that the stereochemistry of the RuL2 fragment in the tris chelates is the same as that in the parent diaquo complex. In the particular case of RuL32+, the tc parent gives only the meridional isomer, but the cc isomer produces both meridional and facial isomers, the latter being formed in less than statistical quantities due to steric inhibition. The metal oxidation and ligand reduction behavior of the complexes are studied electrochemically in acetonitrile. High (0.7-2.3 V) formal potentials for the ruthenium(III)-ruthenium(II) couple are generally observed. In the case of Ru(acac)(tap)2+, the ruthenium(IV)-ruthenium(III) couple occurs near 2 V. In Ru(en)(tap)22+, secondary oxidation of en follows electrochemical metal oxidation. Short Ru-N distances are correlated with high ruthenium(III)-ruthenium(II) formal potentials. The Ru-N(azo) bond is shorter than the Ru-N(pyridine) bond due to greater π-back-bonding in the former case. The high potentials of the present complexes are thus related to the strong Ru-N(azo) π-bonding. For the triazene 1-oxide complexes Ru(EtN(O)NNC6H4R-p)(pap)2+, R has been systematically varied from strongly electron donating (OMe) to strongly electron withdrawing (NO2). The formal potentials obey the Hammett relationship very well. Ligand-based reductions are investigated at hanging mercury drop electrode in the range O to -2.7 V. In RuL32+, six such reductions constitute the complete electron-transfer series. The electrons are believed to be added successively to the three azo functions. In the mixed chelates Ru(bpy)L22+ and Ru(bpy)2L2+, both bpy and L reductions are observed. A correlation of MLCT transition energy with the difference between the formal potentials of the ruthenium(III)-ruthenium(II) couple and the first ligand reduction couple is noted. The energy of the MLCT band is predictable to within ± 1000 cm-1 of the experimental value.
