457605-25-3Relevant academic research and scientific papers
Chromium complexes of an isomeric N-donor ligand, 2-[(N-arylamino)phenylazo]pyridine: Amination reactions, X-ray structure, and redox properties
Kamar, Kunal K.,Saha, Amrita,Castineiras, Alfonso,Hung, Chen-Hsiung,Goswami, Sreebrata
, p. 4531 - 4538 (2008/10/08)
The chromium chemistry of two positional isomers of the ligand 2-[(N-arylamino)phenylazo]pyridine (HL1 and HL2) are described. While the ligand HL1 coordinates as a bischelating tridentate N,N,N-donor, [L1]-, with deprotonation of the amine nitrogen, its isomer HL2 coordinates as a neutral bidentate N,N-donor. The amine nitrogen in this case remains protonated. Thus the reaction of CrCl3·nH2O with HL1 produced the brown cationic complex, [Cr- (L1)2]+, [1]+. The representative X-ray structure of [1a](ClO4) is reported. The two azo nitrogens of the anioinc tridentate ligand approach the metal center closest with Cr(1)-N(azo) av 1.862(6) A. There is a significant degree of ligand backbone conjugation in the coordinated ligands, which resulted in shortening of the C-N distances and also in lengthening of the diazo (N=N) distances. Two synthetic approaches for the synthesis of chromium complexes of HL2 are investigated. The first approach is based on the substitution reaction, wherein all the coordinated CO ligands of Cr(CO)6 were completely substituted by the three bidentate HL2 ligands to produce a violet complex [Cr(HL2)3]. The second approach is based on para-amination reaction of coordinated 2-(phenylazo)pyridine (pap). Thus the reaction of an inert complex, [CrCl2(pap)2], with ArNH2 yields a mixed ligand complex, [CrCl2(pap)(HL2)], 3. In this reaction one of the two coordinated pap ligands in [CrCl2(pap)2] undergoes amination at the para carbon (with respect to the diazo function) to yield HL2 in situ. This metal-promoted transformation is authenticated by the X-ray structure determination of a representative complex, [CrCl2(pap)(HL2a)], 3a. Notable differences in bond distances along the ligand backbones of the two coordinated ligands in 3a indicate different levels of metal-ligand overlap in this complex. All the chromium complexes of HL2 are characterized by their intense blue-violet color. The frequencies of the visible range transitions in these complexes linearly correlate with the Hammett's substitution constant. Intraligand charge-transfer transitions in the visible region are believed to be responsible for the intense color. Redox properties of all these complexes are reported.
