Cooperative Metal–Ligand Assisted <i>E/Z</i> Isomerization and Cyano Activation at Cu<sup>II</sup> and Co<sup>II</sup> Complexes of Arylhydrazones of Active Methylene Nitriles
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New (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzoic acid (H2L4) and known sodium 2-(2-(dicyanomethylene)hydrazinyl)benzenesulfonate (NaHL1), 2-(2-(dicyano-methylene)hydrazinyl)benzoic acid (H2L2), and sodium (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzenesulfonate (NaHL3) were used in the template synthesis of a series of CuII and CoII complexes [Cu(H2O)2L1a]·H2O (1), [Cu(H2O)(3-pyon)L1b]·H2O (2), [Cu(H2O)(4-pyon)L1b] (3), [Co(H2O)((CH3)2NCHO)(μ-L2a)]2·(CH3)2NCHO (4), [Cu3(μ3-OH)(NO3)(CH3OH)(μ2-X)3(μ2-HL3)] (5), [Cu(H2O)(py)L3]·H2O (6), [Cu(H2O)2(μ-L4)]6·6H2O (7), [Cu(2-cnpyb)2(L1b)2]·2H2O (8), [Cu(2-cnpya)2(L1a)2]·2H2O (9), and [Cu(H2O)(4-cnpy)(L1a)2] (10), where 3-pyon = 1-(pyridin-3-yl)ethanone, 4-pyon = 1-(pyridin-4-yl)ethanone, py = pyridine, HX = syn-2-pyridinealdoxime, 4-cnpy = 4-cyanopyridine; 2-cnpya, 2-cnpyb, L1a, L1b, L2a are the ligands derived from nucleophilic attack of methanol (a) or water (b) on a cyano group of 2-cyanopyridine (2-cnpy), L1 or L2, respectively, giving the corresponding iminoesters (2-cnpya, L1a or L2a) or carboxamides (2-cnpyb or L1b). An auxiliary ligand, namely syn-2-pyridinealdoxime or pyridine, acting cooperatively with the metal ion (CuII in this case), induced an E/Z isomerization of the H2L4 ligand; the E- and Z-isomers were isolated separately and fully characterized (compounds 9 and 10, respectively). A one-pot activation of nitrile groups in different molecules was achieved in the syntheses of 8 and 9. Complexes 1–10 are catalyst precursors for the solvent-free microwave (MW)-assisted selective oxidation of secondary alcohols to the corresponding ketones, with typical yields in the 29–99% range (TOFs up to 4.94 × 103 h–1) after 30 min of MW irradiation.
