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- Donor functionalized iron(II) N-Heterocyclic carbene complexes in transfer hydrogenation reactionsPublication . Lopes, Rita; Raya-Baron, Alvaro; Robalo, M. Paula; S. Vinagreiro, Carolina; Barroso, Sonia; Romão, Maria João; Fernandez, Ignacio; Pereira, Mariette M.; RoyoTwo piano-stool iron(II) complexes bearing N-heterocyclic carbene ligands outfitted with acetamide- and amine-pendant arms [Cp*Fe(NHC(R))(CO)I] {Cp* = eta(5)-tetramethylcyclopentadienyl; R = CH2CONEt2(3), (CH2)(2)NEt2(4)}, have been prepared and fully characterized. Their catalytic activity in transfer hydrogenation (TH) of ketones usingiPrOH as a hydrogen source and catalytic amounts of base (LiOtBu) has been explored, along with that of previously reported [CpFe(NHC(R))(CO)I] {R =nBu (5), (CH2)(2)OH (6), Et (7), and (CH2)(3)OH (8)} complexes containing hydroxyl and nonfunctionalized alkyl arms. Complex3displayed the highest catalytic activity of the whole series3-8, reaching a TOF(50)value of 533 h(-1). NMR monitoring of the stoichiometric reaction of3with LiOtBu, allowed the identification of a new species3'containing a deprotonated amidate moiety, which has been fully characterized by(1)H,C-13, and(15)N NMR. Finally, a green protocol for the reduction of ketones through TH using glycerol as a hydrogen source, under microwave irradiation in the presence of catalytic amounts of3and base has been developed.
- Wasteful azo dyes as a source of biologically active building blocksPublication . Fernandes, Ana; Pinto, Bruna; Bonardo, Lorenzo; Royo, Beatriz; Robalo, M. Paula; Martins, Lígia O.In this work, an environment-friendly enzymatic strategy was developed for the valorisation of dye-containing wastewaters. We set up biocatalytic processes for the conversion of azo dyes representative of the main classes used in the textile industry into valuable aromatic compounds: aromatic amines, phenoxazinones, phenazines, and naphthoquinones. First, purified preparations of PpAzoR azoreductase efficiently reduced mordant, acid, reactive, and direct azo dyes into aromatic amines, and CotA-laccase oxidised these compounds into phenazines, phenoxazinones, and naphthoquinones. Second, whole cells containing the overproduced enzymes were utilised in the two-step enzymatic conversion of the model mordant black 9 dye into sodium 2-amino-3-oxo-3H-phenoxazine-8-sulphonate, allowing to overcome the drawbacks associated with the use of expensive purified enzymes, co-factors, or exquisite reaction conditions. Third, cells immobilised in sodium alginate allowed recycling the biocatalysts and achieving very good to excellent final phenoxazine product yields (up to 80%) in water and with less impurities in the final reaction mixtures. Finally, one-pot systems using recycled immobilised cells co-producing both enzymes resulted in the highest phenoxazinone yields (90%) through the sequential use of static and stirring conditions, controlling the oxygenation of reaction mixtures and the successive activity of azoreductase (anaerobic) and laccase (aerobic).