Elena Rychagova

Catecholase activity of Mannich-based dinuclear CuII complexes with theoretical modeling: new insight into the solvent role in the catalytic cycle

Four new dinuclear CuII complexes were synthesised from two Mannich-base ligands namely 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL1) and 2-[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL2): [Cu2(L1)(OH)](ClO4)2·CH3OH (1), [Cu2(L2)2](ClO4)2·H2O (2), [Cu2(L2)2(NO3)2] (3) and [Cu2(L2)2(OAc)2]·H2O (4) and well characterised. X-ray diffraction analysis of the complexes reveals a Cu⋯Cu distance of 2.9183(13), 2.9604(6), 3.0278(4) and 3.0569(11) A, respectively. In 1 the metal coordination geometry is intermediate between trigonal bipyramidal (TBP) and square pyramidal (SP) (τ = 0.488), in 2 the geometry is TBP (0.828 and 0.639) and in 3 and 4 is SP (τ = 0.188 and 0.083, respectively). Spectrophotometric investigations to evaluate the catecholase activity of complexes against 3,5-di-tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) in three different solvents (acetonitrile, methanol and DMSO) under completely aerobic conditions reveal that complexes 1–4 are able to oxidise 3,5-DTBC in all the solvents, while TCC can be oxidised only in acetonitrile (kcat = 0.0002–0.02 s−1). Intensive DFT calculations prove an ionic pathway for 1–3 while a unique neutral catalytic cycle for 4.

The Weakly Coordinating Tris(trichlorosilyl)silyl Anion

Closely following the procedure for the preparation of the base-stabilized dichlorosilylene complex NHCDipp ⋅SiCl2 reported by Roesky, Stalke, and co-workers (Angew. Chem. Int. Ed. 2009, 48, 5683-5686), a few crystals of the salt [NHCDipp -H⋅⋅⋅Cl⋅⋅⋅H-NHCDipp ]Si(SiCl3 )3 were isolated, aside from the reported byproduct [NHCDipp -H+ ⋅⋅⋅Cl- ], and characterized by X-ray crystallography (NHCDipp =N,N-di(2,6-diisopropylphenyl)imidazo-2-ylidene). They contain the weakly coordinating anion Si(SiCl3 )3- , which was also obtained in high yields upon deprotonation of the conjugate Brønsted acid HSi(SiCl3 )3 with NHCDipp or PMP (PMP=1,2,2,6,6-pentamethylpiperidine). The acidity of HSi(SiCl3 )3 was estimated by DFT calculations to be substantially higher than those of other H-silanes. Further DFT studies on the electronic structure of Si(SiCl3 )3- , including the electrostatic potential and the electron localizability, confirmed its low basicity and nucleophilicity compared with other silyl anions.

Singlet oxygen quantum yields and photostability of planar binuclear phthalocyanines

The singlet oxygen (1O2) quantum yield of the near-infrared absorbing (λmax = 839 nm) planar π-conjugated binuclear zinc phthalocyanine (ZnPc) was measured and compared to the 1O2 quantum yields of the mononuclear and the planar binuclear phthalocyanine without π-conjugation between Pc rings. In addition, the photooxidative stability of the π-conjugated binuclear Pc was determined and compared to the stabilities of the mononuclear ZnPc and the known near-infrared photosensitizer, zinc tetra-tert-butylnaphthalocyanine (λmax = 761 nm). The results are explained by DFT calculations and cyclic voltammetry.

Redox reactions of organic C60 derivatives

The redox reactions of organic polyadducts of fullerene RnC60 (R = But, n = 4, 8, 12; R = PhCH2, n = 12) with various oxidants (I2, AgBF4, tetracyanoethylene (TCNE), 3,6-di-tert-butyl-o-benzoquinone, 3,6-di-tert-butyl-4,5-difluoro-o-benzoquinone, C60) and the reductant (potassium) are reported. The oxidation of RnC60 proceeds under mild conditions, in contrast to the oxidation of pristine C60. The formation of radical oxidation products was confirmed by ESR spectroscopy. For But12C60 the reaction with excess of TCNE leads to further oxidation of the But12C60+· radical cation. The reduction of RnC60 with potassium does not occur at room temperature. Only on heating to 60 °C the corresponding radical anions were detected. To explain the experimental results the RnC60 molecules were studied by DFT. The calculations reveal an essential decrease in the ionization energies and electron affinities on going from C60 to RnC60.