Photohydroxylation of 1,4-benzoquinone in aqueous solution revisited.

In water, photolysis of 1,4-benzoquinone, Q gives rise to equal amounts of 2-hydroxy-1,4-benzoquinone HOQ and hydroquinone QH(2) which are formed with a quantum yield of Phi=0.42, independent of pH and Q concentration. By contrast, the rate of decay of the triplet (lambda(max)=282 and approximately 410 nm) which is the precursor of these products increases nonlinearly (k=(2-->3.

o-Iminobenzosemiquinonato(1-) and o-amidophenolato(2-) complexes of palladium(II) and platinum(II): a combined experimental and density functional theoretical study.

From the reaction mixture of [M(II)(bpy)Cl(2)], the ligand 2-anilino-4,6-di-tert-butylphenol, H[L(AP)], and 2 equiv of a base (NaOCH(3)) in CH(3)CN under anaerobic conditions were obtained the blue-green neutral complexes [M(II)(L(AP)-H)(bpy)] (M = Pd (1), Pt (2)). (L(AP)-H)(2)(-) represents the o-amidophenolato dianion, (L(AP))(1)(-) is the o-aminophenolate(1-), (L(ISQ))(1)(-) is its one-electron-oxidized, pi-radical o-iminobenzosemiquinonate(1-), and (L(IBQ))(0) is the neutral quinone. Complexes 1 and 2 can be oxidized by ferrocenium hexafluorophosphate, yielding the paramagnetic salts [M(II)(L(ISQ))(bpy)]PF(6) (S = (1)/(2)) (M = Pd (1a), Pt (2a)).

Ligand-Based Redox Isomers of [Zn(II)(C(28)H(40)NO(2))(2)]: Molecular and Electronic Structures of a Diamagnetic Green and a Paramagnetic Red Form.

The tridentate trianion of N,N-bis(2-hydroxy-di-3,5-tert-butylphenyl)amine, H(3)L(3), forms 1:1 and 2:1 complexes with di-, tri-, or tetravalent transition metal ions where it can exist in four oxidation levels (C(28)H(40)NO(2))(3)(-)(,2)(-)(,1)(-)(,0), which are herein designated as L(3), L(2), L(1), and L(0), respectively; (L(2))(2)(-) and (L(0))(0) are paramagnetic (S = (1)/(2)), whereas the other two are diamagnetic (S = 0). We have synthesized the complexes [Zn(L(2))(NEt(3))] (1), green [Zn(L(1))(2)] (2), and red [Zn(L(2))(L(0))] (3). Complexes 1, 2 (Girgis, A.

Metal- versus Ligand-Centered Oxidations in Phenolato-Vanadium and -Cobalt Complexes: Characterization of Phenoxyl-Cobalt(III) Species.

The coordination chemistry of the pendent-arm macrocycles 1,4,7-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane, L(Me)H(3), 1,4,7-tris(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane, L(Bu)H(3), 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane, L(OCH)()3H(3), and Tolman's ligand 1,4-diisopropyl-7-(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane, L(Pr)H, with vanadium and cobalt(III) has been studied. The following complexes containing a fac-N(3)O(3) donor set have been synthesized: [L(Me)V(III)] (1), [L(Me)V(IV)]PF(6) (2), [(L(Me)H)V(V)(O)]PF(6) (3), [L(Bu)V(IV)]PF(6) (4), [L(OCH)()3V(IV)]PF(6) (5), [L(Me)Co(III)] (6), [L(Bu)Co(III)] (7), [L(OCH)()3Co(III)] (8). In addition, two complexes containing the L(Pr)Co(III) fragment have been prepared: [L(Pr)Co(III)(acac)](ClO(4)) (9) and [L(Pr)Co(III)(Cl(4)cat)].