Ruthenium-azoimine-chloranilates Synthesis, Spectra and Electrochemistry of Ruthenium(II)-1-alkyl-2-(arylazo)imidazole-chloranilate Complexes

Abstract

Ag + -assisted dechlorination of blue cis-trans-cis Ru(R-aai-R¢) 2 Cl 2 followed by the reaction with chloranilic acid (H 2 CA) in the presence of Et 3 N, gives a neutral mononuclear violet complex [Ru(R-aai-R¢) 2 (CA)]. [R-aai-R¢=p-R-C 6 H 4 AN@NAC 3 H 2 ANN, abbreviated as an N,N¢ chelator where N(imidazole) and N(azo) represent N and N¢, respectively; R = H (a), OMe (b), NO 2 (c) and R¢= Me (4), Et(5), Bz (6)]. All the complexes exhibit strong intense MLCT transitions in the visible region and weak broad bands at higher wavelength (>700 nm). Visible transitions (580-595 nm) show a negative solvatochromic effect. The cyclic voltammograms show two quasireversible to irreversible couples positive to SCE and are due to CA ) /CA 2) (1.2-1.35 V) and Ru(III)/Ru(II) (1.6-1.8 V) redox processes. Three couples, negative to SCE, are assigned to CA 2) /CA 3) ()0.2 to )0.3 V), and azo reductions ()0.5 to )0.7, )0.8 to )0.9 V) of the chelated R-aai-R¢.

Ruthenium-mediated Selective Aromatic Thiolation in the Complex [RuII{o-S—C6H4-(p-R-)—N=N—C3H2NN(1)—R′}2]. Synthesis, Spectroscopic, e.p.r., Electro-chemical Characterization and Spectro-electrochemical Correlation

“…imidazoles were synthesized by the reported procedure [4][5][6]. KS 2 COR¢¢ (R¢¢ = Me, Et, Pr, Bu or CH 2 Ph), NaS 2 -P(OEt) 2 and NaS 2 PPh 2 were prepared according to the reported procedures.…”

“…Commercially available silica gel (60-120 mesh) and alumina (neutral) from Sisco Research Lab, (SRL) India were used for chromatographic separation. The purification of solvents for electrochemical and spectral work and [n-Bu 4 N]-[ClO 4 ](TBAP) were prepared as described earlier [7]. All other solvents and chemicals were of reagent grade and were used without further purification.…”

“…The starting parent complexes Ru II {C 6 H 4 (pOMe-)AN@NAC 3 H 2 NN(1)AMe} 2 Cl 2 were prepared as described in our previous paper [6][7][8][9][10]. The ctc isomer (100 mg, 0.177 mmol) was dissolved in DMF (15 cm 3 ) and heated to reflux for 5 min.…”

“…The reaction was repeated with benzenethiol, carbon disulphide, S 8 , thiirane, dithiocarbamate, NaS 2 P(OEt) 2 and NaS 2 PPh 2 instead of (2) but these reagents failed to give the desired product (4). The free ligands also did not undergo the transformation.…”

“…Because of the biological involvement of imidazole we are interested in synthesizing arylazoimidazoles. The ruthenium chemistry of 1-alkyl-2-(arylazo)imidazole (RaaiR¢, Scheme 1) is known in some detail [4][5][6]. Herein I report a detailed synthetic account of the formation of thiolated complexes and the spectroscopic and electrochemical properties of these nine complexes (4a-4i).…”