Redox induced electron transfer in doublet azo-anion diradical rhenium(II) complexes. Characterization of complete electron transfer series.

Reactions of dirhenium decacarbonyl with the two azoaromatic ligands, L(a) = (2-phenylazo)pyridine and L(b) = (4-chloro-2-phenylazo)pyridine (general abbreviation of the ligands is L) afford paramagnetic rhenium(II) complexes, [Re(II)(L(*-))(2)(CO)(2)] (1) (S = 1/2 ground state) with two one-electron reduced azo-anion radical ligands in an octahedral geometrical arrangement. At room temperature (300 K) the complexes 1a-b, showed magnetic moments (mu(eff)) close to 1.94 mu(B), which is suggestive of the existence of strong antiferromagnetic interactions in the complexes. The results of magnetic measurements on one of the complexes, 1b, in the temperature range 2-300 K are reported. The above complexes showed two cathodic and two anodic responses in cyclic voltammetry where one-electron oxidation leads to an unusual redox event involving simultaneous reduction of the rhenium(II) and oxidation of the second ligand via intramolecular electron transfer. The oxidized complexes 1a(+) and 1b(+) are air stable and were isolated as crystalline solids as their tri-iodide (I(3)(-)) salts. The structures of the two representative complexes, 1b and [1b]I(3), as determined by X-ray crystallography, are compared. The anionic complexes, [1](-) and [1](2-) were characterized in solution by their spectral properties.

1,4-Alkyl migration associated with simultaneous S-C bond cleavage and N-C bond formation in platinum complexes of 2-aminothioethers. Characterization of intramolecular interligand charge transfer phenomenon.

Chemical reactions of Pt(pap)Cl(2) [pap = 2-(phenylazo)pyridine] with the N,S-donor atom ligands, 2-alkylthioanilines (HL, (H(2)N--SR), where R = Me, -CH(2)Ph, -CH(2)-CH=CH(2)) in acetonitrile solvent under alkaline conditions yielded mixed chelate donor-acceptor complexes, [Pt(pap)(HN--SR)](+) (1(+), R = Me), [Pt(pap)(HN--S)] (2, HN--S = 2-amidothiophenolate, R = Me, -CH(2)Ph, -CH(2)-CH=CH(2)) and [Pt(pap)(RN--S)] (RN--S = 2-(N-alkyl)amidothiophenolate 3 and 4, R = -CH(2)Ph, -CH(2)-CH=CH(2)). Unusual types of 1,4-alkyl group migration associated with simultaneous S-C bond cleavage and N-C bond formation were observed for R = -CH(2)Ph, -CH(2)-CH=CH(2). However, for R = Me, only S-C bond cleavage occurred producing compound 2 at a higher temperature. Under identical experimental conditions the reaction of Pt(bpy)Cl(2) [bpy = 2,2'-bipyridine] with 2-methylthioaniline afforded [Pt(bpy)(HN--SR)](+) (5(+), R = Me) as the only product with no S-C bond activation. The complexes have been characterized by (1)H NMR, UV-vis-NIR, ESI-MS, EPR and cyclic voltammetry studies. Single-crystal X-ray structures of the complexes, [1][OTf] (OTf = trifluoromethanesulfonate), 2, 3, 4 and [5][OTf] are reported. The Pt-pap complexes (1(+) and 2-4) showed intense interligand charge transfer (ILCT) transition in the NIR-region (>800 nm). This band in the Pt-bpy analogue, [5](+) shifted to a much higher energy, at 545 nm. The cationic complex, [1][OTf] displayed two reversible responses at -0.21 and -0.94 V along with two irreversible anodic responses at 0.48 and 0.90 V. The molecular compounds, 2, 3 and 4 showed two reversible waves near -0.60 and -1.30 V and an irreversible anodic response near 0.5 V. The response at the anodic potential is presumably due to oxidation of 2-amidothioether/2-amidothiophenolate ligand while the reversible responses at cathodic potentials are due to successive reductions of the azo chromophore of the coordinated pap ligand. The redox processes are characterized by EPR and spectroelectrochemistry. Density-functional theory calculations were employed to confirm the structural features and to support the spectral and redox properties of the complexes.