Editorial [Hot Topic: Organometallic Chemistry, Coordination Chemistry and Catalysis (Guest Editor: Julio Perez)]

This second issue of Current Organic Chemistry on the topic Organometallic Chemistry, Coordination Chemistry and Catalysis consists of eight reviews that I am sure will attract the interest of the readers. Robert Gossage (Acadia University, Canada) reviewed the applications of ZnBr2 in organic synthesis. The Lewis acid activity of this reagent is related with its structure in solution (where it is always complexed). An overview of the synthesis/availability, solid state structure, solubility and solution speciation of ZnBr2 in different solvents precedes a description of the reactions that it mediates: formation of C-C and C-O bonds, ring (including heterocycle) formation, ringopening of epoxides and aziridines, bromine transfer reagent, and selective removal of leaving or protecting groups. The paper by Markus Enders*(Universität Heidelberg, Germany) and Robert W. Baker*(University of Sydney, Australia) deals with the synthesis of aryl- and heteroaryl-substituted cyclopentadienes and indenes and their use in transition metal chemistry, mainly in olefin polymerization catalysis. The selective introduction of aryl substituents allows the design of a well-defined geometric environment around π-coordinated metals, which steric and electronic environment can be controlled further through the presence of an additional coordinating functionality within the aryl substituent and by freezing the rotation about the aryl-Cp C-C-bond. Kevin M. Smith (University of Prince Edward Island, Canada) focuses on recent advances in Cr(III) Cp, diketiminato, salicylaldiminato and other well-defined single component catalysts for olefin polymerization. The review (87 references, 38 from the 2004-05 period) highlights the difficulties in the study of these paramagnetic species, and the usefulness of high throughput screening strategies for rapid evaluation of structure-activity relationships, and of DFT studies both for rationalizing the observed reactivity of known catalysts and for suggesting new potential catalytic systems. Folami T. Ladipo (University of Kentucky, USA) reviews the low valent Ti-mediated reductive coupling of carbonyl compounds. The paper describes the range and selectivity of the Ti compounds that mediate pinacol and McMurry couplings, two powerful methods for the creation of C-C bonds that employ a low valent Ti reagent usually prepared by an in situ reduction of a Ti(IV) or Ti(III) precursor. The nature of the precursor, reductant, additives, conditions, etc. are discussed. Chemo- and stereolectivity deserve special attention. With regard to mechanistic information, the nature of the active species is discussed in the context of well characterized Ti compounds. Gerald B. Rowland, Emily B. Rowland, Qiang Zhang and Jon C. Antilla*(University of Mississippi and University of South Florida, USA) wrote on the stereoselective aza-Diels-Alder reaction, a powerful method to prepare nitrogen-containing natural products. The review addresses both diastereo- and enantioselective versions. Recent advances include the incorporation of more and more types of imines as useful substrates, the application of lanthanide-based Lewis acid catalysts, catalysts that are effective with low loadings, metal-free organic catalysts, catalysts that do not require anhydrized solvents or an inert atmosphere, and greater selectivities. Kate N. Fanning, Andrew G. Jamieson and Andrew Sutherland*(University of Glasgow, UK) reviewed the area of Pd (II)-catalyzed Cope, Claisen and aza-Claisen [3,3] sigmatropic rearrangements. Whereas non-catalyzed versions of these reactions, useful for the synthesis of biologically and medicinally important products, have been known for a long time, the employment of Pd(II) catalysis notably lowers the reaction temperatures and generally improves selectivity. Mechanism, stereochemical outcome (a high degree of chirality transfer results from a highly ordered transition state) and synthetic applications are considered. Bradley D. Fahlman (Central Michigan University, USA) has written a review of recent advances in chemical vapor deposition. CVD is the method of choice for thin film growth, allowing control of the properties of the resulting film, and is also useful to generate fiber-optic preforms, carbon nanotubes, etc. Metal β-diketonato, β-ketoiminato, β-diketiminato, amidinato, guanidinato, triazenido, azolato, allylimido complexes, and other precursors (such as ternary sulfides and heterometallic alkoxides) of stoichiometrically complex materials, are discussed. Kathryn B. Grant*and Miki Kassai (Georgia State University, USA) wrote on major advances in the hydrolysis of peptides and proteins using metal complexes. Under mild temperature and pH conditions, several metal complexes are able to promote the hydrolysis of the extremely stable amide bond of peptides and proteins....