Photoinduced reactivity of titanium dioxide

The presence of transition metal ions in photocatalytic reactions is reviewed according to two main approaches: (a) the influence of transition metal ions on the rate of photocatalytic reactions (mainly oxidation) and (b) the transformation of the ions to less toxic species or their deposition on the semiconductor catalyst surface for recovery of expensive and useful metals. Most of the proposed mechanisms are discussed, together with experimental physicochemical evidences that support the involved pathways. Practical applications related to environmental protection and industrial processes are described.

Heterogeneous photocatalysis: Transition metal ions in photocatalytic systems

Surface modification of nanocrystalline metal oxide particles with enediol ligands was found to result in altered optical properties of nanoparticles. The surface modification results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The optical shift is correlated to the dipole moment of the Ti−ligand complexes at the particle surface and decreases with the ligand size. The binding was found to be exclusively characteristic of colloids in the nanocrystalline domain(<20 nm). X-ray near-edge structure measurements at Ti K edge indicate that in this size domain the surface Ti atoms adjust their coordination environment to form undercoordinated sites. These five-coordinated defect sites are the source of novel enhanced and selective reactivity of the nanoparticle toward bidentate ligand binding as observed using IR spectroscopy. Enediol ligands have the optimal geometry for chelating surface Ti atoms, resulting in a five-membered ring coordination complex and restored si...

Surface Restructuring of Nanoparticles: An Efficient Route for Ligand−Metal Oxide Crosstalk

The effects of surface chemistry on the morphology and phase stability of titanium dioxide nanoparticles have been investigated using a thermodynamic model based on surface free energies and surface tensions obtained from first principles calculations. It has been found that surfaces representing acidic and alkaline conditions have a significant influence on both the shape of the nanocrystals and the anatase-to-rutile transition size. The latter introduces the possibility of inducing phase transitions by changing the surface chemistry.

Prediction of TiO2 nanoparticle phase and shape transitions controlled by surface chemistry.

The direct functionalization of unactivated sp(3) C-H bonds is still one of the most challenging problems facing synthetic organic chemists. The appeal of such transformations derives from their capacity to facilitate the construction of complex organic molecules via the coupling of simple and otherwise inert building blocks, without introducing extraneous functional groups. Despite notable recent efforts, the establishment of general and mild strategies for the engagement of sp(3) C-H bonds in C-C bond forming reactions has proved difficult. Within this context, the discovery of chemical transformations that are able to directly functionalize allylic methyl, methylene and methine carbons in a catalytic manner is a priority. Although protocols for direct oxidation and amination of allylic C-H bonds (that is, C-H bonds where an adjacent carbon is involved in a C = C bond) have become widely established, the engagement of allylic substrates in C-C bond forming reactions has thus far required the use of pre-functionalized coupling partners. In particular, the direct arylation of non-functionalized allylic systems would enable access to a series of known pharmacophores (molecular features responsible for a drug's action), though a general solution to this long-standing challenge remains elusive. Here we report the use of both photoredox and organic catalysis to accomplish a mild, broadly effective direct allylic C-H arylation. This C-C bond forming reaction readily accommodates a broad range of alkene and electron-deficient arene reactants, and has been used in the direct arylation of benzylic C-H bonds.

The direct arylation of allylic sp(3) C-H bonds via organic and photoredox catalysis.

Data on molecular design of various types of mononuclear complexes of Schiff bases are generalized. Factors for variation of fine structure of Schiff-base ligand systems (metallocycle sizes and their number, nature of donor centers, aldehyde and amine fragments, co-ligands) are examined. A systematization of Salen complexes is offered. Electronic configurations of p- and d-metals in the coordination and organometallic compounds are taken into account in a series of chelate structures. Non-standard structures are emphasized, including various ligand chelates and molecular complexes.

Molecular design of mononuclear complexes of acyclic Schiff-base ligands

Data on the direct synthesis of coordination compounds from zerovalent metals and organic ligands are surveyed and described systematically. The preparation of metal complexes in the gas and liquid phases is considered. It is shown that the direct syntheses are single-stage processes and make it possible to obtain all types of coordination compounds — molecular and π-complexes, metal chelates, and dinuclear and polynuclear structures. Problems of competitive reactions in the course of the direct synthesis of complexes of ambident ligand systems are discussed. The bibliography includes 289 references.

http://iopscience.iop.org/article/10.1070/RC1995v064n03ABEH000145/pdf

Direct synthesis of coordination compounds from zerovalent metals and organic ligands

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Surface Modification of TiO2: Correlation between Structure, Charge Separation and Reduction Properties.

Synthesis of cobalt(II), nickel(II) and copper(II) complexes with 2-(2-hydroxyphenyliminomethyl)-1-(4-methyl-phenylsulfonamido)benzene and crystal structures of {bis(methanol)[2-(2′-N-tosylaminophenyl)iminomethyl]phenolato}nickel(II) and {bis(2,2′-bipyridine)[2-(2′-N-tosylaminophenyl)iminomethyl]phenolato}copper(II)

Publisher Summary This chapter discusses hetarylazomethine metal complexe. This reactivity pattern is illustrated by the interaction of the aforementioned metal sources with cyclic and acyclic azomethines. Complexes of acyclic azomethines involve chelates of Schiff bases, b-aminovinylketones, and b-aminovinylimines containing heterocyclic moieties. In the multinuclear coordination compounds under this chapter, the heterocyclic frameworks play the role of the aldehyde, amine, and/or adduct-forming constituents. In the oligonuclear structures, heterocycles may also play the role of the intermetal bridges. The data collected in this chapter are generalized and systematized with emphasis on the specified functions in the structure of azomethine ligands and heterocyclic frameworks.

D. A. Garnovskii

Papers

Molecular design of mononuclear complexes of acyclic Schiff-base ligands

Direct synthesis of coordination compounds from zerovalent metals and organic ligands

Surface Modification of TiO2: Correlation between Structure, Charge Separation and Reduction Properties.

Chapter 5 Hetarylazomethine Metal Complexes