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

The issue number 16 of Curr. Org. Chem. 2008 (volume 12) features four reviews. Their subjects are iron catalysis in organic synthesis, chiral diaminocarbene metal complexes for asymmetric catalysis, the reactivity of early transition metal M-C bonds with N-heterocycles, and the Ti- or Zr-mediated or catalyzed umpolung reactions. Eike B. Bauer (University of Missouri at Saint Louis, USA) contributed the paper Recent Advances in Iron Catalysis in Organic Synthesis, which deals with developments in the field of homogeneous catalysis with iron compounds since 2004, avoiding overlap with previous reviews. C-C forming reactions (including cyclizations, cyanohidrin formation, and allylation reactions), formation of C-O and C-N bonds, reactions involving sulfur, polymerizations, redox reactions, and biomimetic oxidations are included. The catalysts range from simple mixtures of FeCl3 and ligands such as amines to well-characterized complexes, including porphirine complexes and organometallic well-characterized complexes. Ligands used in combination with iron sources include phosphines and N-heterocyclic carbenes as well as polymer-inmobilized ligands. For all these transformations, advantages of iron-based catalysts over more widely used systems are low price and low toxicity. David R. Snead, Hwimin Seo and Sukwon Hong* (University of Florida, USA) wrote Recent Developments of Chiral Diaminocarbene-Metal Complexes for Asymmetric Catalysis. N-heterocyclic carbenes are the type of ligands deserving more attention in recent times, due to their desirable properties in catalysis. This paper reviews, with special attention to the most recent literature not covered in previous reviews, asymmetric reactions catalyzed by transitions metal complexes of chiral monodentate or bidentate NHC (and some isolated example of non-cyclic analog) ligands. These are classified by metal (Ru, Rh, Ir, Pd, Cu and Ni) and, within each metal, reactions type. Some of these reactions show excellent enantioselectivities. Paula L. Diaconescu (University of California at Los Angeles, USA) is the author of Reactions of Early Transition Metal- Carbon Bonds with N-Heterocycles, a review divided into two sections: (a) reactions of early transition metal (groups 3-5 and fblock metals) complexes featuring M-C σ bonds leading to ortho-metalation or insertion to yield functionalized heterocycles, and (b) heterocycle ring-opening via reaction with metal complexes containing metal-element multiple bonds. The interest in these processes stems from the search of methods that allow heterocycle functionalization, and from the difficulty of cleaving the C-N bonds of nitrogen heterocycles, a process that takes place during industrially-relevant, heterogeneously-catalyzed hydrodenitrification (HDN), required to avoid catalyst poisoning in subsequent industrial steps and generation of toxic nitrogen oxides. Hairong Guan (University of Cincinnati, USA) is the author of Titanium and Zirconium Mediated or Catalyzed Umpolung Reactions, centered on polarity reversal of carbonyl and imine derivatives. Acyl anions, a-amino carbanion or a-hydroxy carbanion equivalents, homoenolates and homoenolate equivalents are the most useful organometallic reagents in C-C bond forming reactions. Due to the high electropositive character of Ti and Zr, the carbanionic character of the metal-bonded carbon overcomes the electronegativity of N or O atoms, achieving the polarity reversal. The selectivity (chemo-, regio- and stereo-) is highlighted as an advantage of some reactions. 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.