101377-16-6Relevant articles and documents
Ruthenium complexes of N,S- and C,N,S-coordinating azo ligands: Synthesis, reactions, and structure
Mahapatra, Amiya K.,Datta, Sachchidananda,Goswami, Sreebrata,Mukherjee, Monika,Mukherjee, Alok Kumar,Chakravorty, Animesh
, p. 1715 - 1721 (2008/10/08)
The reaction of ruthenium trichloride with 2-(arylazo)phenyl thioethers (ArNNC6H4SR: Ar = Ph, p-tolyl; R = Me, CH2Ph) (HL, 4) in methanol affords blue-violet Ru(HL)(L)Cl (8) and red-violet RuL2 (6), the former being the major product. If lithium bromide is added to the reaction mixture, the bromo analogue of 8 is formed. Both 8 and 6 contain pseudooctahedral ruthenium(H): HL is bidentate, coordinating via thioether sulfur and an azo nitrogen, but L is meridionally tridentate (coordination at sulfur, nitrogen, and the ortho carbon of Ar). All chelate rings are five-membered. The dissimilar binding of HL and L is reflected in infrared and 1H NMR data. Considerable lowering of vN=N occurs in going from HL to 6 and 8 due to Ru-azo π-back-bonding. The conversion 8 → 6 is very effectively catalyzed (yield of 6 60%) by a mildly hot (323 K) silica gel surface. The same conversion can be achieved but in poorer yield by reaction with silver perchlorate in methanol solution. A mechanism is suggested involving ortho-metalative edge displacement assisted by electrophilic (silver(I), silica gel) halide displacement. With two HL-like moieties bridged as in ArNNC6H4S(CH2)3SC6H 4NNAr (Ar = Ph, p-tolyl, m-tolyl; H2LL, 9), octahedral hexadenticity of the type RuC2N2S2 is readily achieved in violet Ru(LL) (10). The ortho metalation of the Ar groups (i.e. absence of two ortho protons) in 10 is unequivocally revealed by the spin-spin structure of the 1H NMR spectrum of 10. All three types of complexes (6, 8, and 10) exhibit reversible or nearly reversible ruthenium(III)/ruthenium(H) couples in cyclic voltammetry (platinum electrode, MeCN solvent). The formal potentials are as follows: RuL2+/RuL2, ～0.52 V; Ru(LL)+/Ru(LL), ～0.60 V; Ru(HL)(L)-Cl+/Ru(HL)(L)Cl, ～0.70 V. The oxidized complexes are relatively unstable and have not been isolated in the pure state. However the electronic structure of coulometrically produced Ru(HL)(L)Cl+ and RuL2+ in solution could be studied with the help of EPR and near-IR spectra. In frozen dichloromethane (77 K) the EPR spectrum of Ru(HL)(L)Cl+ is rhombic (gx = 2.291, gy = 2.173, and gz = 1.963 in the case Ar = Ph and R = CH2Ph) and corresponds to axial (Δ) and rhombic (V) splitting parameters of 10 200 and 4700 cm-1 respectively. On the other hand the spectrum of the corresponding RuL2+ complex is axial (g⊥ = 2.213 and g∥ = 1.965), with Δ = 9800 cm-1. The predicted near-IR absorptions due to transitions within Kramers doublets are experimentally observable. The ruthenium(II) complexes 6, 8, and 10 show multifeatured absorptions in the region 450-750 nm believed to be due to MLCT excitations. The axial splittings here (estimated to be -1) are much less than those in the oxidized complexes.
