The mutual influence of ligands in transition metal coordination compounds with multiple metal-ligand bonds

Coordination chemistry of stibine and bismuthine ligands

Transition metal oxo complexes

Five-coordinate oxorhenium(V) anions with redox-active catecholate and amidophenolate ligands are shown to effect clean bimetallic cleavage of O2 to give dioxorhenium(VII) products. A structural homologue with redox-inert oxalate ligands does not react with O2. Redox-active ligands lower the kinetic barrier to bimetallic O2 homolysis at five-coordinate oxorhenium(V) by facilitating formation and stabilization of intermediate O2 adducts. O2 activation occurs by two sequential Re−O bond forming reactions, which generate mononuclear η1-superoxo species, and then binuclear trans-μ-1,2-peroxo-bridged complexes. Formation of both Re−O bonds requires trapping of a triplet radical dioxygen species by a cis-[ReV(O)(cat)2]− anion. In each reaction the dioxygen fragment is reduced by 1e−, so generation of each new Re−O bond requires that an oxometal fragment is oxidized by 1e−. Complexes containing a redox-active ligand access a lower energy reaction pathway for the 1e− Re−O bond forming reaction because the metal f...

Redox-active ligands facilitate bimetallic O2 homolysis at five-coordinate oxorhenium(V) centers.

Publisher Summary This chapter discusses the transition-metal alkoxides. Primary alkoxides of chromium (III) do not appear to undergo alcoholysis reactions, even under forcing conditions with other alcohols. This is rather unusual in view of the usually strong lability of the alkoxy groups exhibited in alkoxides of most of the metals studied; the main factor hindering such facile interchange has generally been explained on the basis of steric requirements. The general inertness of the primary alkoxides of chromium (III), a more detailed investigation of their substitution reactions has been carried out, and it has been shown that although these are inert to other simple alcohols they undergo interchange with chelating ligands such as ethanolamine, β-diketones and carboxylic acids.

C. J. L. Lock

Papers

204. Amine, phosphine, arsine, and stibine complexes of rhenium-(III), -(IV), and -(V)

Complexes of Rhenium(V)

77. β-Diketone complexes of rhenium