Denis Ripoll

Bio: Denis Ripoll is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 100 citations.

Recent advances in the stereochemistry of metallotetrapyrroles

Abstract: Information pertaining to the stereochemistry of metalloporphyrins and other tetrapyrroles continues to expand. The present article reviews important developments of this structural chemistry. Detailed updates on the relationship of the structure and physical properties of iron derivatives are given. Metalloporphyrins with unusually high or low oxidation states are reviewed. Surveys of recent work on π-cation radical complexes, bound O2 species, tetrapyrroles with N-substituents, the stereochemistry of ring-reduced tetrapyrroles and a variety of novel species are given. Newly developed data concerning experimental electron density studies are summarized. Detailed reviews of porphyrin-porphyrin (π-π) interactions in the solid state are given. A variety of important conformational aspects of metalloporphyrins and their consequent results on physical properties are presented. Finally, a number of isomorphous series and crystal packing effects in tetrapyrroles have been detailed.

Organometallic Compounds Containing Oxygen Atoms

Abstract: Publisher Summary This chapter discusses the organometallic compounds containing oxygen atoms. At present, the range of organic ligands found in organometallic oxo compounds is quite restricted, the majority being either η-C 5 R 5 or alkyls or aryls having no β-hydrogen atom. Two basic routes to organometallic oxo compounds may be envisaged addition of an organic ligand to an inorganic oxo complex or addition of oxygen to an organometallic compound. Exhaustive decarbonylation with concomitant oxidation of a cyclopentadienyl metal carbonyl has proved to be a useful preparative route to cyclopentadienyl metal oxo compounds having no other ligands. In the ethylene complex, the oxo and ethylene ligands are cis to one another and the C–C axis of the ethylene is perpendicular to the M–O bond, a configuration that maximizes π bonding between the W(IV) (d 2 ) and the ethylene. Complexes containing cyclopentadienyl and oxygen as coligands are of two basic types: those containing a terminal double bond between a metal and oxygen, [M=O], and those containing one or more doubly bridging oxygen atoms, [M(μ 2 -O) n M]. The clusters are held together by M–O bonds and the M–( η 5 -C 5 H 5 ) bonding is of the usual type. Parallel to the development of organometallic clusters containing oxygen atoms has been the preparation of organometallic polyoxometallates. Although the organometallic groups are on the surface of the polyoxometallate, they are strongly and covalently bonded to the peripheral oxygen atoms.

Kinetics and mechanisms of decomposition reaction of hydrogen peroxide in presence of metal complexes

Abstract: Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [1]. H2O2 on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old [2]. However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent. Although the decomposition of hydrogen peroxide is often employed as a standard reaction to determine the catalytic activity of metal complexes and metal oxides [3,4], it has recently been extensively used in intrinsically clean processes and in end-of-pipe treatment of effluent of chemical industries [5,6]. Furthermore, the adoption of H2O2 as an alternative of current industrial oxidation processes offer environmental advantages, some of which are (1) replacement of stoichiometric metal oxidants, (2) replacement of halogens, (3) replacement or reduction of solvent usage, and (4) avoidance of salt by-products. On the other hand, wasteful decomposition of hydrogen peroxide due to trace transition metals in wash water in the fabric bleach industry, was also recognized [7]. The low intrinsic reactivity of H2O2 is actually an advantage, in that a method can be chosen which selectively activates it to perform a given oxidation. There are three main active oxidants derived from hydrogen peroxide, depending on the nature of the activator; they are (1) inorganic oxidant systems, (2) active oxygen species, and (3) per oxygen intermediates. Two general types of mechanisms have been postulated for the decomposition of hydrogen peroxide in the presence of transition metal complexes. The first is the radical mechanism (outer sphere), which was proposed by Haber and Weiss for the Fe(III)-H2O2 system [8]. The key features of this mechanism were the discrete formation of hydroxyl and hydroperoxy radicals, which can form a redox cycle with the Fe(II)/Fe(III) couple. The second is the peroxide complex mechanism, which was proposed by Kremer and Stein [9]. The significant difference in the peroxide complex mechanism is the two-electron oxidation of Fe(III) to Fe(V) with the resulting breaking of the peroxide oxygen-oxygen bond. It is our intention in this article to briefly summarize the kinetics as well as the mechanisms of the decomposition of hydrogen peroxide, homogeneously and heterogeneously, in the presence of transition metal complexes. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 643–666, 2000