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- Oxorhenium complexes bearing the water-soluble tris(pyrazol-1-yl)methanesulfonate, 1,3,5-triaza-7-phosphaadamantane, or related ligands, as catalysts for baeyer-villiger oxidation of ketonesPublication . Martins, Luisa; Alegria, Elisabete; Smolenski, Piotr; Kuznetsov, Maxim L.; Pombeiro, ArmandoNew rhenium(VII or III) complexes [ReO3(PTA)(2)][ReO4] (1) (PTA = 1,3,5-triaza-7-phosphaadamantane), [ReO3(mPTA)][ReO4] (2) (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane cation), [ReO3(HMT)(2)] [ReO4] (3) (HMT = hexamethylenetetramine), [ReO3(eta(2)-Tpm)(PTA)][ReO4] (4) [Tpm = hydrotris(pyrazol-1-yl)methane, HC(pz)(3), pz = pyrazolyl), [ReO3(Hpz)(HMT)][ReO4] (5) (Hpz = pyrazole), [ReO(Tpms)(HMT)] (6) [Tpms = tris(pyrazol-1-yl)methanesulfonate, O3SC(pz)(3)(-)] and [ReCl2{N2C(O)Ph} (PTA)(3)] (7) have been prepared from the Re(VII) oxide Re2O2 (1-6) or, in the case of 7, by ligand exchange from the benzoyldiazenido complex [ReCl2(N2C-(O)Ph}(Hpz)(PPh3)(2)], and characterized by IR and NMR spectroscopies, elemental analysis and electrochemical properties. Theoretical calculations at the density functional theory (DFT) level of theory indicated that the coordination of PTA to both Re(III) and Re(VII) centers by the P atom is preferable compared to the coordination by the N atom. This is interpreted in terms of the Re-PTA bond energy and hard-soft acid-base theory. The oxo-rhenium complexes 1-6 act as selective catalysts for the Baeyer-Villiger oxidation of cyclic and linear ketones (e.g., 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone, and 3,3-dimethyl-2-butanone or pinacolone) to the corresponding lactones or esters, in the presence of aqueous H2O2. The effects of a variety of factors are studied toward the optimization of the process.
- Molybdenum complexes bearing the tris(1-pyrazolyl)methanesulfonate ligand: synthesis, characterization and electrochemical behaviourPublication . Dinoi, Chiara; Guedes Da Silva, M. Fátima C.; Alegria, Elisabete; Smolenski, Piotr; Martins, Luisa; Poli, Rinaldo; Pombeiro, ArmandoThe tris(1‐pyrazolyl)methanesulfonate lithium salt Li(Tpms) [Tpms = SO3C(pz)3–] reacts with [Mo(CO)6] in NCMe heated at reflux to yield Li[Mo(Tpms)(CO)3] (1 ), which, upon crystallization from thf, forms the coordination polymer [Mo(Tpms)(CO)2(μ‐CO)Li(thf)2]n (2 ). Reaction of 1 with I2, HBF4 or AgBF4 yields [Mo(Tpms)I(CO)3] (3 ), [Mo(Tpms)H(CO)3] (5 ) or [Mo(Tpms)O2]2(μ‐O) (7 ), respectively. The high‐oxidation‐state dinuclear complexes [{Mo(Tpms)O(μ‐O)}2] (4 ) and [{Mo(tpms)OCl}2](μ‐O) (6 ) are formed upon exposure to air of solutions of 3 and 5 , respectively. Compounds 1 –7 , which appear to be the first tris(pyrazolyl)methanesulfonate complexes of molybdenum to be reported, were characterized by IR, 1H and 13C NMR spectroscopy, ESI‐MS, elemental analysis, cyclic voltammetry and, in the cases of Li(Tpms) and compounds 2 , 4· 2CH3CN, 6· 6CHCl3 and 7 , by X‐ray diffraction analyses. Li(Tpms) forms a 1D polymeric structure {i.e., [Li(tpms)]n } with Tpms as a tetradentate N2O2 chelating ligand that bridges two Li cations with distorted tetrahedral coordination. Compound 2 is a 1D coordination polymer in which Tpms acts as a bridging tetradentate N3O ligand and each Li(thf)2+ moiety is coordinated by one bridging CO ligand and by the sulfonyl group of a contiguous monomeric unit. In 4 , 6 and 7 , the Tpms ligand is a tridentate chelator either in the NNO (in 4 ) or in the NNN (in 6 and 7 ) fashion. Complexes 1 , 3 and 5 exhibit, by cyclic voltammetry, a single‐electron oxidation at oxidation potential values that indicate that the Tpms ligand has an electron‐donor character weaker than that of cyclopentadienyl.