Current Organic Chemistry - Volume 11, Issue 16, 2007

The Number 16, 2007 Organometallic Chemistry, Coordination Chemistry and Catalysis thematic issue of Current Organic Chemistry comprises five review papers having synthesis, reactivity and applications of metal complexes as the unifying theme. Organometallic catalysis, activation of C-H and C-C bonds, cooperation of hydrogen bonds and metals, recognition and selective cleavage of nucleic acids by metal-based systems, and the luminiscence of lanthanide complexes are some of the topics dealt with in this issue. Andrei N. Vedernikov (University of Maryland, USA) authored Recent advances in the platinum-mediated C-H bond functionalization. Metal-mediated C-H activation is a topic of intense research activity, and one that has been the subject of several previous reviews. Most of the 79 references of the present paper come from the 2005-06 period. The Pt(II)-catalyzed oxidation of methane by stoichiometric hexachloroplatinic (IV) acid in water to MeOH or MeCl (Shilov reaction) was historically important in homogeneous C-H functionalization by metal complexes. Subsequent efforts to use practical oxidants, protect the products from overoxidation, achieve high activity, and employ mild conditions, continue up to the present time. Examples of catalytic formation of C-O, C-C and C-Si bonds, and functionalization of relevant Pt-C bonds are discussed, as well as selectivity issues and mechanistic studies. Finally, current efforts to improve the design of Pt catalysts for C-H activation based on mechanistic information and theoretical calculations are summarized. Ola F. Wendt (Lund University, Sweden) wrote Transmetallation reactions involving group 10 metals, an account that focuses on the transfer of an organic group from a main group metal (including boron and group 12 metals) to group 10 metals. The paper provides an overview of two areas that have been dealt with separately in most previous publications: (a) applications of the stoichiometric transmetallation reaction to the synthesis of group 10 organometallic complexes, and (b) transmetallation as one step of the group 10-catalyzed cross-coupling between organic electrophiles and main group (mainly B, Si and Sn) nucleophiles. Juan C. Mareque Rivas (University of Edinburgh, UK) is the author of the review Cooperation of metals and hydrogen bonding groups in metal-promoted reactions. Selected examples are used to illustrate how the presence of groups able to participate in the formation of hydrogen bonds can contribute to a higher efficiency of metal-based catalysts, in an approach to the mode of action of enzymes. While most examples are taken from areas reminiscent of the activity of some enzymes (peptide and phosphodiester bonds, the reaction of carbon dioxide and water, or oxidations catalyzed by metal complexes, notably by iron-porphyrin complexes), others come from reactions that are typically catalyzed by organometallic complexes. Akinori Kuzuya (New York University, USA) and Makoto Komiyama* (University of Tokyo, Japan) wrote Site-selective Artificial Ribonucleases and Their Applications. In this case, the target of the artificial nucleases is RNA, and the emphasis is on systems in which the elements, the “sequence-recognizing moieties” (that bind to a particular region of RNA), and the “molecular scissors” (either a metal complex or a metal-free polyamine) that catalyze RNA hydrolysis) are not covalently bonded. Applications to genotyping are discussed. Ana de Bettencourt-Dias (Syracuse University; currently at the University of Nevada, Reno, USA) contributed Small Molecule Luminiscent Lanthanide Ion Complexes-Photophysical Characterization and Recent Developments. This paper provides an introduction to the luminiscence displayed by lanthanide ions and their complexes and some of their most important applications. Then, recent examples of the solid state structure of the complexes of the Ln3+ ions (which often reach high coordination numbers) with a variety of ligands (that also act as sensitizers), their solution speciation, and the luminiscent behavior are discussed. It has been a privilege and a pleasure to help in putting together this issue. I wish to express my deepest appreciation to the authors, and to the many anonymous reviewers, for their great job.

Platinum complexes have played an important role in our understanding the mechanisms of arene and alkane CH activation and developing catalytic methods for hydrocarbon CH functionalization. Knowledge of the factors controlling the reactivity of the metal center acquired over the past few years enabled significant progress in the field. Among the most challenging problems which have to be solved yet are i) the use of more readily available oxidants, ideally, oxygen from the air; ii) selective functionalization of CH bonds, iii) protection of the oxygenation products against overoxidation and iv) designing more water-tolerant systems. The most recent examples of platinum mediated catalytic functionalization of alkane and arene CH bonds in water and non-polar solvents, mechanistic studies of alkane and arene CH activation, computational and experimental design of new efficient platinum complexes are reported. The review covers mostly publications appeared in 2005-2006.

This review gives an overview of the early development of transmetallation reactions for synthetic purposes and presents some recent results on the transmetallation reaction as a part of cross-coupling reactions and the mechanism of these reactions.

A major challenge in chemistry is the design of catalysts that can carry out important chemical transformations with the extraordinary efficiency of enzymes. In many cases nature does this by making metals and hydrogen bonding groups to work cooperatively. This review provides a description of recent work inspired by nature where the combination of metal ions and hydrogen bonding groups has been used to enhance the properties of synthetic metal complexes in metal-mediated reactions. It covers a range of strategies, hydrogen bond types, effects and chemical transformations.

Recent developments in artificial enzymes for site-selective scission of RNA have been reviewed, and their advantages over ribozymes are discussed. Most of previous reports involve covalent fixation of molecular scissors to sequence- recognizing moieties. However, non-covalent strategy, in which these two components are never covalently bound each other, has made remarkable progresses. When oligonucleotide bearing an acridine (site-selective activator) forms duplex with RNA substrate, the phosphodiester linkage of the RNA in front of the acridine is selectively activated and hydrolyzed by various metal ions (e.g., Lu(III). These non-covalent artificial ribonucleases are simple enough to be used for various more complicated systems. For example, tandem activator for clipping of desired fragment from long RNA substrate is obtained by attaching two acridines to an oligonucleotide. By analyzing the resultant RNA fragment with MALDI-TOFMS, the RNA substrate is accurately genotyped in terms of both single nucleotide polymorphisms (SNPs) and insertion/deletion polymorphisms (Indels).

The luminescence of lanthanide ions makes them interesting for a wide variety of applications and several researchers try to optimize this property. In this paper we give a brief overview of the luminescence process and of the techniques utilized to characterize the photophysical properties. Several recent examples of luminescent complexes with small molecule sensitizers will also be discussed.