Joining the stable: The first examples of the highly instable selenenyl fluorides RSeF are prepared from the reaction on the tin selenide RSeSnMe(3) with XeF(2). Through the use of extremely large protecting groups (m-terphenyl ligands) which stabilizes the RSeF units against disproportionation, the compounds could be isolated and characterized by NMR spectroscopy and single-crystal structure analysis (see structure).

Isolation and structural characterization of hypervalent electron-rich pentacoordinate nitrogen species have not been achieved despite continuous attempts for over a century. Herein we report the first synthesis and isolation of air stable hypervalent electron-rich pentacoordinate nitrogen cationic radical (11-N-5) species from oxidation of their corresponding neutral (12-N-5) species. In the cationic radical species, the nitrogen centers adopt a trigonal bipyramidal geometry featuring a 3-center-5-electron hypervalent attractive interaction. The combination of single crystal X-ray diffraction analysis and computational studies revealed weak N-O interactions between the central nitrogen cation and oxygen atoms. This successful design strategy and isolation of air-stable pentacoordinate hypervalent nitrogen species allow further investigations on reactivity and properties resulting from these unusually weakly coordinating interactions in nitrogen compounds.Scheme 1 Preparation of neutral triarylamine precursors 2 Me a-b and 2 iPr a-b.This journal is

In order to examine differences in structure due to the electronic nature of the oxygen ligand, several organoboron compounds bearing ester 8a–8c and amide 13a and 13b ligands were prepared and crystallographically analyzed. In the ester ligand systems, the pinacolato derivative 8a and catecholato derivative 8b took a pentacoordinate structure, while fluorenyl derivative 8c took a tetracoordinate structure instead of pentacoordinate due to the strong electrophilic nature of the boron atom. In contrast to the ester ligand systems, no pentacoordinate species were found in the amide ligand systems. The pinacolato derivative 13a is tricoordinated, and catecholato derivative 13b is tetracoordinated. These results could be due to the steric effect of the diisopropylamide ligand together with the electronic effects. The VT NMR study and the DFT calculations reveal that the energy difference between the tetracoordinate and pentacoordinate structure in 8c is very small, and indicated that the electronic nature and steric effects of the ligand greatly affect the coordination state of the boron atom.

Several organoboron compounds having a tridentate ligand based on 2,6-bis(p-tolyloxymethyl)benzene (5) were prepared. X-ray crystallography revealed that the distances between the central boron and both oxygen atoms of the tridentate ligand varied from 2.50 Å to 3.16 Å . The boron atom of the pinacolato derivative (5a) was found to be tricoordinated, whereas those of the diphenyl (5b) and the catecholato derivative (5c) were pentacoordinated, although these molecular structures were unsymmetrical. Compound 5c was found to have the strongest BÀ ÀO interactions among this series because the BÀ ÀO distances of 5c (av. 2.60 Å ) are shorter than those for 5b (av. 2.65 Å ), and this could mainly come from the electronic effect of the substituents at the boron atom.

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