Synthesis and properties of hypervalent electron-rich pentacoordinate nitrogen compounds.

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.

Imidazole-stabilized, electron-deficient boron cations.

The borenium cations [(C7H5N2Ad)B(C6F5)2][AlCl4/Al2Cl7] 2a, and [(C7H5N2Me)B(C6F5)2][B(C6F5)4] 2b were prepared and are shown to feature a high Lewis acidity, the capability to activate hydrogen and to effect the 1,1-carborations of terminal and internal alkynes under mild conditions.