CoIII and CuII complexes of reduced Schiff bases: Generation of phenoxyl radical species

A redox active switch for lanthanide luminescence in phenolate complexes

The reversible oxidation of coordinated phenolates into phenoxyl radicals results in a dramatic quenching (>95%) of the luminescence of the f metal ion.

Synthesis, Characterization, and Cu(2+) Coordination Studies of a 3-Hydroxy-4-pyridinone Aza Scorpiand Derivative

The synthesis, acid-base behavior, and Cu(2+) coordination chemistry of a new ligand (L1) consisting of an azamacrocyclic core appended with a lateral chain containing a 3-hydroxy-2-methyl-4(1H)-pyridinone group have been studied by potentiometry, cyclic voltammetry, and NMR and UV-vis spectroscopy. UV-vis and NMR studies showed that phenolate group was protonated at the highest pH values [log K = 9.72(1)]. Potentiometric studies point out the formation of Cu(2+) complexes of 1:2, 2:2, 4:3, 1:1, and 2:1 Cu(2+)/L1 stoichiometries. UV-vis analysis and electrochemical studies evidence the implication of the pyridinone moieties in the metal coordination of the 1:2 Cu(2+)/L1 complexes. L1 shows a stronger chelating ability than the reference chelating ligand deferiprone. While L1 shows no cytotoxicity in HeLa and ARPE-19 human cell lines (3.1-25.0 μg/mL), it has significant antioxidant activity, as denoted by TEAC assays at physiological pH. The addition of Cu(2+) diminishes the antioxidant activity because of its coordination to the pyridinone moiety phenolic group.

Development of Highly Active and Regioselective Catalysts for the Copolymerization of Epoxides with Cyclic Anhydrides: An Unanticipated Effect of Electronic Variation

Recent developments in polyester synthesis have established several systems based on zinc, chromium, cobalt, and aluminum catalysts for the ring-opening alternating copolymerization of epoxides with cyclic anhydrides. However, to date, regioselective processes for this copolymerization have remained relatively unexplored. Herein we report the development of a highly active, regioselective system for the copolymerization of a variety of terminal epoxides and cyclic anhydrides. Unexpectedly, electron withdrawing substituents on the salen framework resulted in a more redox stable Co(III) species and longer catalyst lifetime. Using enantiopure propylene oxide, we synthesized semicrystalline polyesters via the copolymerization of a range of epoxide/anhydride monomer pairs.

Crystal structure of an eight-coordinate terbium(III) ion chelated by N,N'-bis-(2-hy-droxy-benz-yl)-N,N'-bis-(pyridin-2-ylmeth-yl)ethyl-enedi-amine (bbpen(2-)) and nitrate

The reaction of terbium(III) nitrate penta-hydrate in aceto-nitrile with N,N'-bis-(2-hy-droxy-benz-yl)-N,N'-bis-(pyridin-2-ylmeth-yl)ethyl-enedi-amine (H2bbpen), previously deprotonated with tri-ethyl-amine, produced the mononuclear compound [N,N'-bis-(2-oxidobenzyl-κO)-N,N'-bis-(pyridin-2-ylmethyl-κN)ethylenedi-amine-κ(2) N,N'](nitrato-κ(2) O,O')terbium(III), [Tb(C28H28N4O2)(NO3)]. The mol-ecule lies on a twofold rotation axis and the Tb(III) ion is eight-coordinate with a slightly distorted dodeca-hedral coordination geometry. In the symmetry-unique part of the mol-ecule, the pyridine and benzene rings are both essentially planar and form a dihedral angle of 61.42 (7)°. In the mol-ecular structure, the N4O4 coordination environment is defined by the hexa-dentate bbpen ligand and the bidentate nitrate anion. In the crystal, a weak C-H⋯O hydrogen bond links mol-ecules into a two-dimensional network parallel to (001).

Synthesis of imine and reduced imine compounds containing aromatic sulfonamide: use as catalyst for in situ generation of ruthenium catalysts in transfer hydrogenation of acetophenone derivatives

Three imine and three reduced imine ligands containing aromatic sulfonamide (2-7) were isolated by a simple method and characterized by FT-IR, NMR, and elemental analysis. Meanwhile, the interaction of 2-7 ligands with [(p-cymene)RuCl2]2 was analyzed in situ by UV-vis spectrophotometer. The in situ generated catalytic system derived from N-(2-(benzylideneamino)phenyl)-2,4,6-trimethyl-benzenesulfonamides and N-(2-(benzylamino)phenyl)-2,4,6-trimethyl-benzenesulfonamides with [(p-cymene)RuCl2]2 was used as a catalyst in the transfer hydrogenation (TH) of p-substituted acetophenone derivatives. The catalytic systems displayed high activities, which increased in the order 7<4<5<6<1<2<3. The best activity for the TH of 4-chloroacetophenone was provided with the [(p-cymene)RuCl2]2/ligand (3) catalytic system (turnover frequency values: 720 h(-1) for 10 min on S/C: 500/1).

Ligand contributions to the electronic structures of the oxidized cobalt(II) salen complexes

Square planar cobalt(II) complexes of salen ligands N,N'-bis(3-tert-butyl-5R-salicylidene)-1,2-cyclohexanediamine), where R = OMe (1) and tert-butyl (2), were prepared. 1 and 2 were electrochemically reversibly oxidized into cations [1-H(2)O](+) and [2-H(2)O](+) in CH(2)Cl(2). The chemically generated [1-H(2)O](SbF(6))·0.68 H(2)O·0.82CH(2)Cl(2) and [2-H(2)O](SbF(6))·0.3H(2)O·0.85CH(2)Cl(2) were characterized by X-ray diffraction and NIR spectroscopy. Both complexes are paramagnetic species containing a square pyramidal cobalt ion coordinated at the apical position by an exogenous water molecule. They exhibit remarkable NIR bands at 1220 (7370 M(-1) cm(-1)) and 1060 nm (5560 M(-1) cm(-1)), respectively, assigned to a CT transition. DFT calculations and magnetic measurements confirm the paramagnetic (S = 1) ground spin state of the cations. They show that more than 70% of the total spin density in [1-H(2)O](+) and [2-H(2)O](+) is localized on the metal, the remaining spin density being distributed over the aromatic rings (30% phenoxyl character). In the presence of N-methylimidazole 1 and 2 are irreversibly oxidized by air into the genuine octahedral cobalt(III) bis(phenolate) complexes [1-im(2)](+) and [2-im(2)](+), the former being structurally characterized. Neither [1-im(2)](+) nor [2-im(2)](+) exhibits a NIR feature in its electronic spectrum. 1 and 2 were electrochemically two-electron oxidized into [1](2+) and [2](2+). The cations were identified as Co(III)-phenoxyl species by their characteristic absorption band at ca. 400 nm in the UV-vis spectrum. Coordination of the phenoxyl radical to the cobalt(III) metal ion is evidenced by the EPR signal centered at g = 2.00.