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Ruthenium(II) Tris-Pyrazolylmethane Complexes in Transfer Hydrogenation Reactions |
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| Authors: | Dr Alberto Gobbo Dr Xinyuan Ma Prof Gianluca Ciancaleoni Prof Stefano Zacchini Dr Lorenzo Biancalana Dr Massimo Guelfi Prof Guido Pampaloni Prof Steven P Nolan Prof Fabio Marchetti |
| Institution: | 1. University of Pisa, Department of Chemistry and Industrial Chemistry, Via G. Moruzzi 13, I-56124 Pisa, Italy
A.?G. and X.?M. contributed equally to this work.;2. Ghent University, Department of Chemistry and Centre for Sustainable Chemistry, Krijgslaan 281, S-3, 9000 Ghent, Belgium A.?G. and X.?M. contributed equally to this work.;3. University of Pisa, Department of Chemistry and Industrial Chemistry, Via G. Moruzzi 13, I-56124 Pisa, Italy;4. University of Bologna, Department of Industrial Chemistry “Toso Montanari”, Viale Risorgimento 4, I-40136 Bologna, Italy;5. Ghent University, Department of Chemistry and Centre for Sustainable Chemistry, Krijgslaan 281, S-3, 9000 Ghent, Belgium |
| Abstract: | While ruthenium(II) arene complexes have been widely investigated for their potential in catalytic transfer hydrogenation, studies on homologous compounds replacing the arene ligand with the six-electron donor tris(1-pyrazolyl)methane (tpm) are almost absent in the literature. The reactions of RuCl(κ3-tpm)(PPh3)2]Cl, 1 , with a series of nitrogen ligands (L) proceeded with selective PPh3 mono-substitution, affording the novel complexes RuCl(κ3-tpm)(PPh3)(L)]Cl (L=NCMe, 2 ; NCPh, 3 ; imidazole, 4 ) in almost quantitative yields. Products 2 – 4 were fully characterized by IR and multinuclear NMR spectroscopy, moreover the molecular structure of 4 was ascertained by single crystal X-ray diffraction. Compounds 2 – 4 were evaluated as catalytic precursors in the transfer hydrogenation of a series of ketones with isopropanol as the hydrogen source, and 2 exhibited the highest activity. Extensive NMR experiments and DFT calculations allowed to elucidate the mechanism of the transfer hydrogenation process, suggesting the crucial role played by the tpm ligand, reversibly switching from tri- to bidentate coordination during the catalytic cycle. |
| Keywords: | coordination switching homogeneous catalysis ruthenium transfer hydrogenation tris(pyrazol-1-yl)methane |