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Catalytic and electrochemical properties of new manganese(III) compounds of 2-(2′-hydroxyphenyl)-oxazoline (Hphox or HClphox). Molecular structures of [Mn(Clphox)2(MeOH)2](ClO4) and [Mn(phox)2(MeOH)2][Mn(phox)2(ClO4)2](H2O)2 |
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| Authors: | Marcel Hoogenraad Kevita Ramkisoensing Willem L Driessen Huub Kooijman Anthony L Spek Elisabeth Bouwman Jaap G Haasnoot Jan Reedijk |
| Institution: | a Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands b Bijvoet Center for Biomolecular Research, Crystal and Structural Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands |
| Abstract: | New manganese(III) complexes of Hphox (2-(2′-hydroxyphenyl)-oxazoline) and HClphox (2-(5′-chloro-2′-hydroxyphenyl)-oxazoline) have been synthesised. The X-ray structures of Mn(phox)2(MeOH)2]Mn(phox)2(ClO4)2](H2O)2 and Mn(Clphox)2(MeOH)2](ClO4) show the manganese(III) ions to be octahedrally coordinated with methanol or perchlorate at the axial coordination sites. The cyclic voltammograms of the complexes, with the exception of Mn(phox)2(acac)] (Hacac=2,4-pentanedione), show an irreversible reduction wave of manganese(III) to manganese(II). After addition of an excess of 1-methylimidazole (1-Meim), the reduction process shifts towards lower potentials and becomes (quasi-) reversible, indicating that the presence of 1-Meim affects the catalytic efficiency of the complexes. The complexes catalyse the epoxidation of styrene by dihydrogen peroxide. The cumulative turnover numbers towards styrene oxide obtained after 15 min. vary from 16 for Mn(Clphox)2(MeOH)2](ClO4) to 26 for Mn(phox)2(acac)]. Ligand degradation appears to be the limiting factor for obtaining higher turnover numbers. |
| Keywords: | Manganese complexes Oxazoline complexes Crystal structures Electrochemistry |
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