Tetramerization of BEB-Doped Phenalenyls to Obtain (BE)-[16]Annulenes (E = N, O).

Two (BE)-[16]annulenes were prepared and fully characterized by experimental and quantum-chemical means (, E = N; , E = O). The 1,8-naphthalenediyl-bridged diborane(6) served as their common starting material, which was treated with [Al(NH)]Cl to form (91% yield) or with 1,8-naphthalenediboronic acid anhydride to form (93% yield). As a result, the heteroannulenes and are supported by four aromatic "clamps" and may also be viewed as NH- or O-bridged cyclic tetramers of BNB- or BOB-doped phenalenyls. X-ray crystallography on mono-, di-, and tetraadducts ·thf, ·py, and ·py showed that is an oligotopic Lewis acid (thf/py: tetrahydrofuran/pyridine donor). The applicability of also as a Lewis basic ligand in coordination chemistry was demonstrated by the synthesis of the mononuclear Ag complex [Ag(py)(·py)] and the dinuclear Pb complex . During the assembly of , the rearrangement of led to the formation of two (BO)-macrocycles linked by two BOB-phenalenyls to form a nanometer-sized cage with four negatively charged, tetracoordinated B atoms. Both and show several redox waves in the cathodic regions of the cyclic voltammograms. An in-depth assessment of the consequences of electron injection on the aromaticity of and was achieved by electronic structure calculations. and are proposed to exhibit aromatic switching capabilities in the [16]annulene motif.