Current Organic Chemistry, 2011, Vol. 15, No. 11 Editorial 1669

Covalent Pseudohalides Editorial

Covalent pseudohalides (Scheme 1) are versatile tools in various chemical transformations and are widely used in various fields of chemistry as building blocks for synthesizing polymers, precursors, biologically active materials, and natural products. They occur in nature and smaller derivatives have been detected in the interstellar medium. Pseudohalides have a rich chemistry with a long and fascinating history, which goes back, for some derivatives, for centuries. Not only the chemistry and structure, but the stability of pseudohalides is very varied; there are stable molecules, what are easy to handle, and also reactive and short-lived species whose applications require special means.

RCN RNC nitrile isonitrile N O C R C R C R N O N O RCN O cyanate isocyanate fulminate nitrile oxide isofulminate N S C R C R C R N S N S RCN S thiocyanate isothiocyanate tiofulminate nitrile sulfide N Se C R C R C R N Se N Se RCN Se selenocyanate isoselenocyanate selenofulminate nitrile selenide N Te C R C R C R N Te N Te RCN Te tellurocyanate isotellurocyanate tellurofulminate nitrile telluride N R N N azide Scheme 1. Covalent pseudohalides (R= substituent atom or group, covalently linked to the pseudohalide frame). The present thematic issue includes six reviews, mainly focusing on the synthesis and chemical applications of covalent pseudohalides. Structural properties and spectroscopy are also briefly discussed. The first review of the issue discusses the chemistry of covalent cyanates, including their stability, synthesis, structure, spectroscopy, and chemical applications. Experimentally known derivatives are presented, namely the parent acid and its alkyl, aryl, silyl, SF5, and SeF5 derivatives. Covalent fulminates are regarded as unstable species and their chemistry is largely unexplored yet. This review also presents the available information on the chemistry of organic fulminates. In the second review, the chemistry of organic selenocyanates is summarized, focusing on their synthesis, spectroscopic characterization, and uses in preparative chemistry and biology. The synthesis of inorganic precursors is also discussed, as well as the application of organic selenocyanates in cancer therapy. Small covalent nitrile oxides are important transient species in organic synthesis and widely used for dipolar cycloaddition reactions. The third review focuses on the generation, spectroscopy, structural properties, and synthetic application of small nitrile oxides, XCNO, where the X substituent group is smaller than five atoms, viz. X = hydrogen, halogen, pseudohalogen, alkyl, vinyl, ethynyl, or nitro. The chemistry of nitrile sulfides is presented in the fourth review. The review presents a full coverage of stability, synthesis, spectroscopy, structure, and chemical applications of these unstable species. Nitrile selenides, analogously to nitrile sulfides, have the potential to become important dipolarophiles in preparative chemistry, however, their chemistry is largely unexplored yet. This review also summarizes the present knowledge about nitrile selenides.

Hetero-substituted isocyanates and isothiocyanates RX-NCY (X = R2N, RO, or RS; Y = O or S) and the isomeric cyanates RX-OCN, thiocyanates RX-SCN, nitrile oxides RX-CNO, and nitrile sulfides RX-CNS are highly reactive compounds, often transient at room temperature. The chemistry of these compounds, including their generation, identification, spectroscopy, structure, and rearrangement reactions, is reviewed in the fifth contribution. The chemistry of silicon and germanium azides is presented in the sixth review. This review article mainly focuses on the synthesis and synthetic applications of mono-, di-, tri-, and tetraazidosilanes and germanes, as well as their coordination complexes. The spectroscopy and structural properties of silicon and germanium azides are also briefly discussed.

Prof. Tibor Pasinszki Eötvös Loránd University Budapest, Hungary E-mail: [email protected]