The synthesis of two Ru-dmso complexes containing the ligands 2-(3-pyrazolyl)pyridine (pypz-H), and pyrazole (pz-H), [Ru(II)Cl2(pypz-H)(dmso)2], (2) and [Ru(II)Cl2(pz-H)(dmso)3], (3), has been described. Both complexes have been fully characterized in solution through (1)H-NMR and UV-Vis techniques and also in the solid state through monocrystal X-ray diffraction analysis. The redox properties of both complexes have also been studied by means of cyclic voltammetry. Exposure of 2 to visible light in acetonitrile produces a substitution of one dmso ligand by a solvent molecule generating a new complex, [Ru(II)Cl2(MeCN)(pypz-H)(dmso)] (4). Also, UV-visible spectroscopy points out that complex 2 presents a thermal and photochemical substitution of dmso ligands in aqueous solution. Finally, the reactivity of complexes 2 and 3 has been tested with regard to the hydration of nitriles using water as a single solvent, displaying good efficiency and selectivity for the corresponding amide derivatives. In general, better performance is achieved with complex 3. Reuse of these catalysts in water and glycerol has been explored for the first time in ruthenium-mediated nitrile hydration catalysis.
The synthesis of a family of new Ru complexes containing the facial tridentate ligand with general formula [Ru(II)(T)(D)(X)](n+) (T = trispyrazolylmethane (tpm); D = ((4S,4'S)-(-)-4,4',5,5'-tetrahydro-4,4'-bis(1-methylethyl)-2,2'-bioxazole) (iPr-box-C) or N-(1-hydroxy-3-methylbutan-(2S)-(-)-2-yl)-(4S)-(-)-4-isopropyl-4,5-dihydrooxazole-2-carbimidate (iPr-box-O); X = Cl, H(2)O) has been described. All complexes have been spectroscopically characterized in solution through (1)H NMR and UV-vis techniques, and the redox properties of complexes have also been studied by means of cyclic voltammetry (CV). Furthermore, the chloro complexes presented here have been characterized in the solid state through monocrystal X-ray diffraction analysis. The oxazolinic iPr-box-C ligand undergoes a Ru-assisted hydrolysis reaction generating the corresponding amidate anionic ligand iPr-box-O, that keeps coordinated to the Ru metal center and that produces a strong σ-donation effect over it. The reactivity of the Ru-OH(2) complexes described in this paper together with other similar ones, previously synthesized by us, has been tested with regard to the epoxidation of different olefins. Complexes [Ru(II)(R-box-C)(tpm)OH(2)](BF(4))(2), R = Bz, 3'c/iPr, 3c, show high stereoselectivity in the epoxidation of cis-β-methylstyrene, with the exclusive formation of the cis-epoxide. However, there is a significant difference in regioselectivity between the two catalysts in the epoxidation of 4-vinylcyclohexene; complex 3'c leads to the regioselective oxidation at the ring alkene position, whereas complex 3c leads to the oxidation at the terminal position. Computational calculations indicate only small energy differences between the two possible products of 4-vinylcyclohexene epoxidation, but the energy barriers for the interaction of the catalytic systems with the alkene groups of 4-vinylcyclohexene agree with the reactivity differences found for the two catalysts having isopropyl or benzyl as substituent of the oxazole ligand. Computed local Fukui functions help to explain the observed reactivity trends.
The reaction of cis,fac-[RuCl2(dmso-S)3(dmso-O)], 1, with different azole (L) ligands leads to new [RuCl2(L)(dmso-S)3] compounds (L = CH3-pz-H, 2; NO2-pz-H, 3; CF3-pz-H, 4 and Br-Hind, 5). Complexes 2-5 have been characterized by analytical, spectroscopic and electrochemical techniques as well as by monocrystal X-ray diffraction analysis. Upon oxidation to Ru(iii) the complexes undergo linkage isomerization of a S-bound dmso ligand and the corresponding kinetic rates as well as the thermodynamic properties have been determined for compound 2 and also for the previously described [Ru(II)Cl2(pypz-H)(dmso-S)2] (pypz-H = 2-(3-pyrazolyl)pyridine), 6, from cyclic voltammetries performed at different scan rates. The exposure of compound 2 to visible light in acetonitrile produces the substitution of one dmso ligand by a solvent molecule generating a new compound, 2'. The irradiation of solutions of compounds 2 and 6 in chloroform leads in both cases to the substitution of one dmso by a chlorido ligand in parallel to the oxidation of Ru(ii) to Ru(iii) generating complexes 2'' and 6' respectively. The reactivity of compounds 2-6 has been tested with regard to the hydration of nitriles in water as a solvent, displaying in all cases good performance and selectivity for the corresponding amides.
The preparation and characterization of complexes with a phosphonated terpyridine (trpy) ligand (trpy-P-Et) and a bidentate pyridylpyrazole (pypz-Me) ligand, with formula [Ru (trpy-P-Et)(pypz-Me)X] (2: X=Cl, n=1; 3: X=H O, n=2), is described, together with the anchoring of 3 on two types of supports: mesoporous silica particles (SP) and silica-coated magnetic particles (MSP). Aqua complex 3 is easily obtained by heating 2 in refluxing water and exhibits a two-electron Ru redox process. It was anchored on SP and MSP supports by two different synthetic strategies, yielding the heterogeneous systems SP@3 and MSP@3, which were fully characterized by IR and UV/Vis spectroscopy, SEM, cyclic voltammetry, and differential pulse voltammetry. Catalytic olefin epoxidation was tested with molecular complex 3 and its SP@3 and MSP@3 heterogeneous counterparts, including reuse of the heterogeneous systems. The MSP@3 material can be easily recovered by a magnet, which facilitates its reusability.
In the present work, we describe an efficient method for the covalent anchoring of a Ru-dmso complex onto two types of supports: mesoporous silica particles (SP) and silica coated magnetic particles (MSNP). First, we have prepared and characterized the molecular complexes containing the bidentate pyridylpyrazole ligands pypz-Me and pypz-CH2COOEt, with the formula [RuIICl2(pypz-R)(dmso)2] (R = Me, 1; CH2COOEt, 2). Complex 2 was anchored onto the silica supports, yielding the heterogeneous systems SP@2 and MSNP@2 which were fully characterized by IR, UV–vis, SEM, TEM, TGA, and XPS techniques. Hydration of representative nitriles has been tested with the molecular complexes and their SP@2 and MSNP@2 heterogeneous counterparts, in aqueous medium under neutral conditions. The heterogeneous catalysts display high yields and excellent selectivity values. Both systems can be reused throughout several cycles for benzonitrile and acrylonitrile substrates, without any significant loss in reactivity. The MSNP@2 material can be easily recovered by a magnet, facilitating its reusability.
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