Redox-active ligands - a viable route to reactive main group metal compounds

Anionic redox-active ligands such as o-amidophenolates, catecholates, dithiolenes, 1,2-benzendithiolates, 2-amidobenzenethiolates, reduced α-diimines, ferrocenyl and porphyrinates are capable of reversible oxidation and thus have the ability to act as sources of electrons for metal centres. These and other non-innocent ligands have been employed in coordination complexes of base transition metals to influence their redox chemistry and afford compounds with useful catalytic, optical, magnetic and conducting properties. Despite the focus in contemporary main group chemistry on designing reactive compounds with potential catalytic activity, comparatively few studies exploring the chemistry of main group metal complexes incorporating redox-active ligands have been reported. This article highlights relevant chemical reactivity and electrochemical studies that probe the oxidation/reduction of main group metal compounds possessing redox-active ligands and comments on the prospects for this relatively untapped avenue of research.

Radical non-radical states of the [Ru(PIQ)] core in complexes (PIQ = 9,10-phenanthreneiminoquinone)

9,10-Phenanthreneiminosemiquinonate anion radical (PIQ˙(-)) complexes of ruthenium of types trans-[Ru(II)(PIQ˙(-))(PPh3)2(CO)Cl] () and trans-[Ru(III)(PIQ˙(-))(PPh3)2Cl2] () are reported. Reactions of and with I2 afford trans-[Ru(III)(PIQ˙(-))(PPh3)2(CO)Cl](+)I3(-)·½CH2Cl2 ((+)I3(-)·½CH2Cl2) and trans-[Ru(PIQ˙(-))2(PPh3)2(μ-Cl)3](+)I3(-)·¼I2·¼toluene) ((+)I3(-)·¼I2·¼toluene), while the reaction of with Br2 yields a 9,10-phenanthreneiminoquinone (PIQ) complex of the type mer-[Ru(III)(PIQ)(PPh3)Br3]·½CH2Cl2 (·½CH2Cl2). In comparison, the reaction of trans-[Ru(III)(PQ˙(-))(PPh3)2Cl2] (PQ), a 9,10-phenanthrenequinone (PQ) analogue of affords only trans-[Ru(III)(PQ)(PPh3)2Cl2](+)Br3(-) ((+)Br3(-)). Considering the X-ray bond parameters, EPR spectra and the atomic spin densities obtained from the density functional theory (DFT) calculations, is defined as a PIQ˙(-) (average C-O/N and C-C lengths, 1.280(2) and 1.453(3) Å) complex of ruthenium(ii) while is a neutral PIQ (average C-O, C-N, C-C and C-O/N lengths, 1.248(7), 1.284(7), 1.485(8) and 1.266(7) Å) complex of the ruthenium(iii) ion. The single crystal X-ray bond parameters proposed that (+)I3(-) (average C-O/N and C-C lengths, 1.294(8) and 1.449(9) Å) and (average C-O/N and C-C lengths, 1.289(2) and 1.447(4) Å) are PIQ˙(-) complexes of ruthenium(iii), while the (+) ion (average C-O/N and C-C lengths, 1.288 ± 0.004 and 1.450 ± 0.017 Å) is a co-facial bi-octahedral complex of ruthenium(iii). In contrast, the (+) ion is a PQ complex of the ruthenium(iii) ion. EPR spectra and the calculated atomic spin densities authenticated that the (+) ion obtained after constant potential coulometric oxidation of is a PIQ complex of ruthenium(iii), while the (-) ion is a hybrid state of [Ru(II)(PIQ˙(-))] and [Ru(III)(PIQ(2-))] states. It is observed that the PIQ˙(-) state in which spin is more localized on the nitrogen (∼38% in and ∼35% in (-) ion) is stable and the coordination of the PIQ(2-) state is not observed in this study. Redox activities, UV-vis/NIR absorption spectra and their origins and the spectroelectrochemical measurements for → (+), → (-) and (+) → (2+) conversions are analyzed.

Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate, 4,4′-di-tert-butyl-2,2′-bipyridine and 1,10-phenanthroline anion radicals to oxidovanadium(iv)

Coordination of semiquinonate and heterocyclic α-diimine anion radicals to oxidovanadium(iv) is authenticated.