2,6‐Bis(diazaboryl)pyridine – A Ligand with Hemilabile Donor and Lewis Acid Functionalities

Abstract

The coordination chemistry of 2,6‐bis(diazaboryl)pyridine (dab2py) is studied towards selected halides of aluminum(III), gallium(III) and germanium(II). Addition of dab2py to AlBr3 readily yielded the salt of ligand induced ionization [(dab2py)AlBr2][AlBr4]. The aluminum atom in the cation is coordinated by the pyridine's nitrogen atom and also by one nitrogen atom of each diazaboryl group, resembling the coordination motif found for tridentate pincer ligands, e.g. 2,6‐diiminopyridines. By NMR spectroscopic measurements a rapid exchange reaction between all four Ndab‐atoms was detected, showing that the tridentate coordination motif of dab2py is less rigid compared with 2,6‐diiminopyridines. The adduct formation of dab2py and GaCl3 does not proceed at room temperature in solution. Addition of GeCl2·dioxane to this mixture gave the salt [(dab2py)GeCl][GaCl4]. The germanium atom is coordinated by the pyridine's nitrogen atom and a nitrogen atom of one diazaboryl group. The product of partial hydrolysis of the cation [(dab2py)GeCl]+ was isolated as single crystals. The structure determination revealed the insertion of an oxygen atom between the germanium atom and a boron atom, showing that the diazaboryl groups do not only provide hemilabile Lewis donor but also weak Lewis acid functionalities that are involved in the stabilization of main group cations.