84049-25-2Relevant academic research and scientific papers
Chemistry of ruthenium. 7. Aquo complexes of isomeric bis[2-(arylazo)pyridine]ruthenium(II) moieties and their reactions: Solvolysis, protic equilibria, and electrochemistry
Goswami, Sreebrata,Chakravarty, Akhil R.,Chakravorty, Animesh
, p. 602 - 609 (2008/10/08)
The two blue isomers of RuCl2L2 are trans,cis (2) and cis,cis (3) in the following sequence: N(pyridine), N(pyridine); N(azo), N(azo) [L = 2-(phenylazo)pyridine (pap) or 2-(m-tolylazo)pyridine (tap)]. Both 2 and 3 undergo facile and stereoretentive displacement of Cl- by H2O in the presence of aqueous Ag+, affording the corresponding isomers 5 and 6 of Ru(OH2)2L22+ (isolated as the perchlorate hydrate). Conversely, 5 and 6 regenerate 2 and 3, respectively, in chloride media. Deprotonation of 5 (L = pap; pK1 = 6.80, pK2 = 8.66) affords Ru(OH)(OH2)(pap)2+ (8) and Ru(OH)2(pap)2 (9), both of which have been isolated in the pure form (the former as a perchlorate salt). The t2g → π*(L) MLCT transition energies as well as the N=N stretching frequencies decrease on deprotonation (5 > 8 > 9) due to t2g-p(OH-) and t2g-π*(L) interactions. Both 5 and 6 (but not 8 and 9) undergo stereoretentive solvolysis in donor solvents (S), furnishing RuS2L22+, of which one, viz., Ru(PhCN)2(tap)22+, is isolated as a crystalline perchlorate. Reaction of 5 (L = pap) with pyridine (py) and subsequent acidification and processing furnishes the perchlorate salt of the monobasic acid (pK1 = 6.80) Ru(OH2)(py)(pap)22+ (7). The pK values of 5 and 7 reflect the strong π acidity of L. The consequent stability of the t2g level in turn leads to high redox potentials in Ru-L complexes. Complexes 8 (in MeCN) and 9 (in CH2Cl2) display quasi-reversible Ru(IV)/Ru(III) and Ru(III)/Ru(II) couples: 82+ + e- ? 8+, 8+ + e- ? 8; 92+ + e- ? 9+, 9+ + e- ? 9. The respective E°298 values are as follows: 1.18, 1.89 V; 1.07, 1.53 V (vs. SCE). For 7 (in MeCN) the couple 7+ + e- ? 7 is observed (E°298 = 1.5 V) initially but it is rapidly replaced by a couple with E°298 of 1.88 V due to solvolysis. In acidic (pH 1-4) aqueous media the 2e--2H+ couple RuIV(O)(py)(pap)22+ + 2e- + 2H+ ? 7 occurs (E°298 = 1.20 V).
