Liu has provided the link between pure the prototype organic aromatic compound (benzene) and the prototype pure inorganic aromatic (borazine).1 His group has prepared 1,2-dihydro1,2-azaborine 1. Dixon has performed computations to support the identification of the molecule. For example, the computed and experimental chemical shifts are in nice agreement (see Table 1). The B3LYP/DZVP2 optimized structure of 1 is shown in Figure 1.


1

Table 1. Computeda and experimental chemical shifts (ppm) of 1.1

atom

expt

computed

B-H

4.9

5.4

N-H

8.44

7.8

C3–H

6.92

7.3

C4–H

7.70

8.0

C5–H

6.43

6.6

C6–H

7.40

7.4

B

31.0

26.9

aB3LYP/Alhrichs-vTZP.

Figure 1. B3LYP/DZVP2 optimized structure of 1.1

The computations support the notion that 1 is truly aromatic. Its NICS(1) value is -7.27 ppm, close that of benzene (-10.39 ppm), and much more negative that that of borazine (-3.01 ppm). Reactions 1 and 2 compare the stability of 1 to benzene. These indicate that the resonance stabilization energy of 1 is about 13 kcal mol-1 less than that of benzene, whose RSE is about 34 kcal mol-1. Liu and Dixon thus consider 1 to be an aromatic compound and one that helps create a sort of organic, mixed organic-inorganic and inorganic aromatic continuum.

References

(1) Marwitz, A. J. V.; Matus, M. H.; Zakharov, L. N.; Dixon, D. D.; Liu, S.-Y., "A Hybrid Organic/Inorganic Benzene," Angew. Chem. Int. Ed. 2009, 48, 973-977, DOI: 10.1002/anie.200805554

InChIs

1: InChI=1/C4H6BN/c1-2-4-6-5-3-1/h1-6H
InChIKey=OGZZEGWWYQKMSO-UHFFFAOYAN