title: The unexpected role of pyridine-2-carboxylic acid in manganese based oxidation catalysis with pyridin-2-yl based ligands.
abstract: A number of manganese-based catalysts employing ligands whose structures incorporate pyridyl groups have been reported previously to achieve both high turnover numbers and selectivity in the oxidation of alkenes and alcohols, using H(2)O(2) as terminal oxidant. Here we report our recent finding that these ligands decompose in situ to pyridine-2-carboxylic acid and its derivatives, in the presence of a manganese source, H(2)O(2) and a base. Importantly, the decomposition occurs prior to the onset of catalysed oxidation of organic substrates. It is found that the pyridine-2-carboxylic acid formed, together with a manganese source, provides for the observed catalytic activity. The degradation of this series of pyridyl ligands to pyridine-2-carboxylic acid under reaction conditions is demonstrated by (1)H NMR spectroscopy. In all cases the activity and selectivity of the manganese/pyridyl containing ligand systems are identical to that observed with the corresponding number of equivalents of pyridine-2-carboxylic acid; except that, when pyridine-2-carboxylic acid is used directly, a lag phase is not observed and the efficiency in terms of the number of equivalents of H(2)O(2) required decreases from 6-8 equiv. with the pyridin-2-yl based ligands to 1-1.5 equiv. with pyridine-2-carboxylic acid.
authors.affiliation: Stratingh Institute for Chemistry, Faculty of Mathematics and Natural Sciences, University of Groningen, Nijenborgh 4, 9747AG, Groningen, The Netherlands.
authors.forename: Dirk
authors.initials: D
authors.lastname: Pijper
authors.forename: Pattama
authors.initials: P
authors.lastname: Saisaha
authors.forename: Johannes W
authors.initials: JW
authors.lastname: de Boer
authors.forename: Rob
authors.initials: R
authors.lastname: Hoen
authors.forename: Christian
authors.initials: C
authors.lastname: Smit
authors.forename: Auke
authors.initials: A
authors.lastname: Meetsma
authors.forename: Ronald
authors.initials: R
authors.lastname: Hage
authors.forename: Ruben P
authors.initials: RP
authors.lastname: van Summeren
authors.forename: Paul L
authors.initials: PL
authors.lastname: Alsters
authors.forename: Ben L
authors.initials: BL
authors.lastname: Feringa
authors.forename: Wesley R
authors.initials: WR
authors.lastname: Browne
mesh_terms: D000475:Alkenes / Q000737:chemistry; D000588:Amines / Q000737:chemistry; D002384:Catalysis; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D010848:Picolinic Acids / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*
chemical_list: D000475:Alkenes; D000588:Amines; D008024:Ligands; D010848:Picolinic Acids; D011725:Pyridines; D008345:Manganese; D007501:Iron; C023666:pyridine; C030614:picolinic acid