Current Organic Chemistry - Volume 12, Issue 15, 2008

The issue number 15 of Curr. Org. Chem. 2008 (volume 15) consists of four reviews. Their subjects are the application of microwave irradiation to heterofunctionalization of alkenes and alkynes, the oxidative addition of RE-ER (E= S, Se, Te) compounds to transition metal complexes, metallomesogens based on alkane-rich metal complexes, and the dehydrogenative bond-forming catalysis involving phosphines. Daniela M. Ide, Marie P. Eastlund, Casie L. Jupe and Robert A. Stockland Jr.* (University of North Texas, USA) are the authors of the review Microwawe Assisted Heterofunctionalization of Alkenes and Alkynes. Microwave irradiation, compatible with a variety of solvents (and with solvent-free work) and catalysts, can reduce significantly the time and the secondary reactions of chemical reactions, sometimes leading to higher selectivity and functional group tolerance compared with conventional heating. Microwave reactors specifically designed for chemical synthesis, which are already commercially available, allow a precise real-time control of temperature, pressure and microwave power. The reactions covered by this review are the addition of N-H, P-H and O-H bonds, as well as the incorporation of S, Se, Sn and other elements, to alkenes and alkynes, as well as reactions leading to the formation of epoxides and aziridines. Details on the particular experiment, often including the type of reactor, are given in many cases. George C. Fortman, Tamas Kegl*, and Carl D. Hoff (University of Miami, USA, and University of Pannonia, Hungary) have written the paper Kinetic, Thermodynamic, and Mechanistic Aspects of Oxidative Addition Reactions of RE-ER (E = S, Se, Te) and Transition Metal Complexes, which, by means of selected examples, provides an overview of the chemistry of an area of relevance in both industrial and biological realms. The effect of the metal, sometimes within the Cr, Mo, W group, its oxidation state and accompanying ligands (e.g., molybdenum carbonyl complexes vs. tetrathiomolybdate) and the nature of the chalcogen are highlighted. Synthetic work, thermodynamic measurements, and kinetic studies are discussed as well as structural data and theoretical calculations in selected cases. Brenda Porta, Jamal Khamsi, and Juan C. Noveron* (University of Texas at El Paso, USA) wrote the paper Metallomesogens: Supramolecular Design via Alkane-rich Metal Complexes. This review updates the research on metal complexes containing long hydrocarbyl tails, molecules able to generate liquid crystals, organize themselves as micelles or liposomes in aqueous solution, or as Langmuir-Blodgett films on surfaces. The long hydrocarbyl tails, which function is to provide hydrophobic interactions, are usually present at substituents at the backbone of organic ligands. The review is organized by ligand denticity (monodentate, bidentate, etc.) and nature of the donor atoms (N-donors, O-donor, etc.) Rory Waterman (University of Vermont, USA) wrote the article Dehydrogenative Bond-Forming Catalysis Involving Phosphines. The reaction that makes the subject of this paper has been known since just 1995 but, as indicated by the 151 references, attracts much attention, in part due to the central role that phosphines play in coordination chemistry and catalysis. At the same time, this tendency of phosphines to coordinate metal centers is one of the difficulties in the search for catalytic procedures, because that coordination deprives the metal center of the unsaturation needed for catalytic activity. Both early- and late-transition metal complexes catalyze the reaction, and mechanistic studies have begun to provide useful information. The products of the reaction are compounds containing P-P bonds, ranging from diphosphines to cyclic compounds, including unique architectures and compounds that cannot be synthesized by other methods. In addition to these free products, mechanistic investigations highlighted the potential of ligands such as phosphinidenes in catalysis. Some of the catalysts used for the formation of P-P bonds are also effective for heterodehydrocoupling (P-B, P-Ga, P-C, P-Si, P-Ge, P-P (unsymmetric compounds) and P-S. I am sure that, thanks to the great job of the authors and the help of the anonymous reviewers, these reviews will be of interest to the broad readership of Curr. Org. Chem.

One of the most direct and powerful ways to prepare complex organic compounds containing N, P, O, S, and related elements is the addition of the heteroatom containing group to an unsaturated fragment. Hydroelementation, Michael additions, and oxidation processes provide scientists numerous ways to effect these changes. Microwave assisted synthesis has had a dramatic effect on how synthetic chemists approach the preparation of new compounds due to dramatic increases in reaction rates. The explanation for these rapid reaction rates has not been fully addressed, and the existence of non-thermal microwave effects continues to be the subject of great debate. The blending of microwave assisted chemistry with carbon heteroatom bond forming reactions has generated a host of new and intriguing compounds.

Mechanisms of oxidative addition of the RE-ER (E = S, Se, Te) bond to transition metal complexes are reviewed.

Molecules that use non-covalent interactions to self-organize into supramolecular structures have the potential to generate functional materials with a broad range of applications. This review article focuses on the design and synthesis of molecules that use transition metal ions and long alkyl chains to direct the formation of ordered supramolecular phases. This unique combination of coordination bonds and alkyl interdigitation provide exceptional control over intermolecular interactions and can generate nanoscale molecular order as liquid crystalline states, Langmuir-Blodgett films on surfaces, highly ordered lyotropic phases such as metallo-micelles in water and reverse metallo-micelles in organic media. The synthetic strategy for alkane-rich ligands and the coordination- and lipid-directed self-assembly of these molecules are described.

This review presents developments in the young field of dehydrogenative coupling reactions of phosphines. Catalytic phosphorus-element bond formation via dehydrocoupling has rapidly expanded since the first discoveries in the mid 1990s. A survey of the available catalysts, P-P and P-E products, and mechanistic understanding is presented with emphasis on the emerging synthetic applications of this reaction.