Studies on the reactivity of cis-RuCl2 fragment in Ru(PPh3)2 (TaiMe)Cl2 with N,N-chelators (TaiMe=1-methyl-2-(p-tolylazo)imidazole): Spectral and electrochemical characterisation of the products

Dechlorination of Ru(PPh3)2(TaiMe)Cl2 (TaiMe = p-Me-C6H4-N=N- C3H2NN(1)-Me (1), l-methyl-2-(p-tolylazo)imidazole) has been carried out in acetone solution by Ag+ and reacted with N,N'-chelators to synthesise [Ru(PPh3)2 (TaiMe)(N,N')2+. The complexes have been isolated as their perchlorate salts. The N,N' chelators are l-alkyl-2-(phenylazo)imidazoles (PaiX, X = Me, Et, CH2Ph); 2- (arylazo)pyridines, (Raap, p-R-C6H4- N=N-C5H4N; R = H, Me, Cl); 2- (arylazo)pyrimidines (Raapm, p-R-C6 H4-N=N-C3N2H2; R = H, Me, Cl); 2,2'- bipyridine (bpy) and 1,10-phenanthroline (o-phen). Unsymmetrical N,N' chelators may give two isomers and this is indeed observed. The 1H NMR spectral data refer to the presence of two isomers in the mixture in different proportions. With consideration of coordination pairs in the order of PPh3, PPh3; N,N (N refers to N(immidazole) and N',N (N' refers to N(azo), the complexes have been characterised as trans-cis-cis and trans-trans-trans configuration; the former predominates in the mixture. Electrochemical studies exhibit high potential Ru(III)/Ru(II) couple and quasireversible N=N reduction. Electronic spectra show high intensity (ε104) MLCT transition in the visible region (520 ± 10) nm along with a shoulder ( ε 103) in the longer wavelength region. (author)