The coordination chemistry of phenoxide ligands, such as C6H5O, 4-(CH3)-C6H4O, 3,5-(CH3)2-C6H3O, 2,6-(tert-butyl)2-C6H3O, 2,6-(CH3)2-C6H3O, to Mn(II) has been investigated because of the possible implication of Mn(II)phenoxide complexes as intermediates in the phenylphosphate carboxylase enzyme, a protein which catalyses the selective carboxylation of phenylphosphate to 4-OH-benzoic acid using CO2. We report here the synthesis and characterization of [CpMn(µ-OAr)(THF)]2 (ArO = C6H5O, 4-(CH3)-C6H4O, 3,5-(CH3)2-C6H3O, 2,6-(CH3)2-C6H3O) and [CpMn(η5-ArO)] (ArO = 2,6-(tert-butyl)2-C6H3O and 2,6-(CH3)2-C6H3O) complexes, the first examples of mixed-sandwich complexes with Cp and phenate as π-ligands. The latter bear the 2,6-substituted phenoxide π-coordinated to the [Mn(Cp)]+ moiety. The different mode of bonding of the phenoxide ligands to Mn(II), substantiated by 1H NMR and electron spin resonance (ESR) spectroscopy, is controlled by the steric hindrance of substituents at the 2- and 6-position. The reactivity of the π-bonded ligand towards CO2 is also reported as a quite rare example of nucleophilic attack at the cumulene by the ring-carbon of the phenoxide, which is driven by electron density localization at the 4-position generated upon π-coordination to Mn(II).Key words: Mn(II)-complexes, phenoxide ligands, 1H NMR spectroscopy, ESR spectroscopy, reaction with carbon dioxide.
