Tetramerization of BEB-Doped Phenalenyls to Obtain (BE) 8 -[16]Annulenes (E = N, O).

Two (BE) 8 -[16]annulenes were prepared and fully characterized by experimental and quantum-chemical means ( 1 , E = N; 2 , E = O). The 1,8-naphthalenediyl-bridged diborane(6) 3 served as their common starting material, which was treated with [Al(NH 3 ) 6 ]Cl 3 to form 1 (91% yield) or with 1,8-naphthalenediboronic acid anhydride to form 2 (93% yield). As a result, the heteroannulenes 1 and 2 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 2 ·thf, 2 ·py 2 , and 2 ·py 4 showed that 2 is an oligotopic Lewis acid (thf/py: tetrahydrofuran/pyridine donor). The applicability of 2 also as a Lewis basic ligand in coordination chemistry was demonstrated by the synthesis of the mononuclear Ag + complex [Ag(py) 2 ( 2 ·py 4 )] + and the dinuclear Pb 2+ complex 6 . During the assembly of 6 , the rearrangement of 2 led to the formation of two (BO) 9 -macrocycles linked by two BOB-phenalenyls to form a nanometer-sized cage with four negatively charged, tetracoordinated B atoms. Both 1 and 2 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 1 and 2 was achieved by electronic structure calculations. 1 and 2 are proposed to exhibit aromatic switching capabilities in the [16]annulene motif.