We describe the synthesis of new manganese (II) and manganese (III) complexes containing the bidentate ligands 2-(3-pyrazolyl)pyridine, pypz-H, and 3 (5) These observations have been explained through computational calculations. The reutilization of catalysts 1 and 6 for the epoxidation of alkenes has been evaluated in [bmim]:acetonitrile mixture (bmim = 1-butyl-3-methylimidazolium), allowing the effective recyclability of the catalytic system and keeping high conversion and selectivity values up to 12 successive runs, in all cases.
Different synthetic routes have been developed to obtain the aqua complex trans‐[RuII(trpy)(pypz‐H)(OH2)](PF6)2, Ru6. This complex, together with the chlorido intermediate complexes cis‐ and trans‐[RuIICl(pypz‐H)(trpy)]+, Ru5a and Ru5b, have been fully characterized by analytical, spectroscopic, and electrochemical methods. Furthermore, the trans‐Ru5b complex has been characterized in the solid state through single‐crystal X‐ray diffraction analysis. The aqua complex Ru6 was tested as catalyst in the photooxidation of alcohols in water and in the chemical oxidation of alkenes, displaying a good performance with high selectivity values in both catalytic processes.
The catalytic oxidation of a series of alkenes by three MnII complexes, MnCl2[(-)-L]2 (1), ({MnCl[(-)-L]}2(-Cl)2) (2), and Mn(CF3SO3)2[(-)-L]2 (3), having the bidentate N-ligand (-)-pinene[5,6]bipyridine, (-)-L, and using peracetic acid as oxidant in acetonitrile is described. The performance of catalysts 1 and 2 is enhanced by the use of additives (NaHCO3 and imidazole) and also using a [bmim]/acetonitrile mixture as reaction media. The latter conditions allow recyclability of the catalytic system, keeping good selectivity and conversion values in some cases. The nature of the species formed in acetonitrile after the addition of peracetic acid has been investigated through EPR and UV/Vis spectroscopy. The results point to the formation of high-valent manganese species, among which a di--oxo-bridged Mn2(III,IV) binuclear species was unambiguously identified for complex 3 through a typical 16-line EPR signatureThis research has been financed by the Spanish Ministerio de Ciencia e Innovacion (MICINN) through project CTQ2010-21532-C02-01. J. R. thanks the Universitat of Girona for a predoctoral grant. F. M., C. D. and M. N. C. acknowledge the Reseau National de RPE Interdisciplinaire TGE CNRS for EPR measurements facilities and the Labex programm ARCANE (grant number ANR-11-LABX-0003-01
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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