Manganese Oxidation Catalysts with 2-(2′-Hydroxyphenyl)oxazoline Ligands: Catalyst Intermediates and Degradation Products − Crystal Structure of Bis[{2-(2′-oxazolinyl)phenolato}bis(1-methylimidazole)manganese(III)] Perchlorate

Abstract

Manganese complexes with phox ligands [Hphox = 2-(2′-hydroxyphenyl)oxazoline] act as oxidation catalysts with dihydrogen peroxide. Their catalytic efficiency is strongly affected by the presence of a base, such as 1-methylimidazole (1-Meim). The crystal structure of an Mn−phox complex with two axial 1-Meim ligands, [Mn(phox)2(1-Meim)2](ClO4), is reported. The [Mn(phox)2]+ and [Mn(phox)2(1-Meim)]+ species have been detected in catalytic reaction mixtures by electrospray mass spectrometry. In the catalytic oxidation of styrene, turnover numbers of 428 and 456 have been obtained for styrene oxide in the presence of [Mn(phox)3] and of [Mn(5′-NO2phox)3], respectively. During these reactions, catalyst degradation occurs, and is the main obstacle to obtaining higher turnover numbers. GC-MS analysis of the degradation products of [Mn(5′-Clphox)3] after catalytic reactions indicates that the oxazoline group is decomposed. The same decomposition products are also observed with electrospray mass spectrometry at higher ionisation potentials. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)