Synthesis and spectroscopic (H-1 NMR, ESR) characterization of new aryloxy-Mn(II) complexes: steric control over O- vs. phenyl-pi-coordination of ArO- ligands (ArO- = C6H5O-, 4-methyl-C6H4O-, 3,5-dimethyl-C6H3O-, 2,6-di-tert-butyl-C6H3O-, 2,6-dimethy

摘要

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(mu -OAr)(THF)](2) (ArO = C6H5O-, 4-(CH3)-C6H4O-, 3,5-(CH3)(2)-C6H3O-, 2,6-(CH3)(2)-C6H3O-) and [CpMn(eta (5)-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 pi -ligands. The latter bear the 2,6-substituted phenoxide pi -coordinated to the [Mn(Cp)](+) moiety. The different mode of bonding of the phenoxide ligands to Mn(II), substantiated by H-1 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 pi -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 pi -coordination to Mn(II). [References: 34]