1,3-Benzoyl migration of 2-benzoyl-2-phenylazoindane-1,3-dione. Molecular conformations and crystal structures of the rearrangement products, indane-1,2,3-trione 2-(N-benzoyl-N-phenylhydrazone) and indane-1,2,3-trione 2-(N-bromobenzoyl-N-phenylhydrazone)

Abstract

The solution and solid-state thermal rearrangement of 2-benzoyl-(4a) and 2-(p-bromobenzoyl)-2-phenylazoindane-1,3-dione (4b) have been studied. The expected product of the rearrangement of (4a), indane-1,2,3-trione 2-(N-phenylhydrazone)(6a) was found in high yield in the solution reaction, but only in trace amounts in the solid. The corresponding bromo-compound, indane-1,2,3-trione 2-(N-p-bromobenzoyl-N-phenylhydrazone)(6b) could only be detected in trace amounts in the solution rearrangement of (4b) and not at all in the solid-state rearrangement. To assign definitely the structure of this product of the solution rearrangement of (4a), crystal structures of both (6a) and (6b) were determined. Crystals of (6a) are monoclinic, with a= 6.774(2), b= 28.950(11), c= 9.018(3)Å, β= 96.08(1)°, space group P2₁/c; structure refined to R 0.063 on 2 951 non-zero reflections. Crystals of (6b) are triclinic, with a= 15.369(14), b= 13.917(17), c= 9.195(8)Å, α= 99.50(7), β= 85.12(7), and γ= 104.84(6)°, space group P, two molecules in the crystal asymmetric unit; structure refined R 0.081 on 4 425 non-zero reflections. The molecule of (6a), both when crystallized by itself and as a 1 : 1 complex with indane-1,2,3-trione 2-(N-phenylhydrazone), one of the molecules of (6b), and the p-t-butyl-derivative (6c), both when crystallized by itself and as a 1 : 1 acetone solvate, have a similar geometry and syn-arrangement of the two phenyl rings about the C(10)–N(2) amide bond. The other molecule of (6b) has an anti-arrangement about the C–N amide bond and is quite similar in conformation to those of the previously reported benzoylhydrazones (3a) and (3b). This group of molecules may be divided into two classes as evidenced by detailed analysis of the amide group geometry, the syn-class having very large pyramidal distortion at N (0.18–0.24 Å), and an intramolecular CO ⋯ CO interaction (2.67–2.84 Å), the anti-class being less overcrowded around the amide bond and showing less distortion at nitrogen. These features are reflected in ν(CO) values, being ca. 1 650 cm^–1 for (3a) and (3b), which are relatively undistorted, and for the syn-hydrazone (6a)ca. 1 700 cm^–1. The crystal structure of (6b) shows a short (3.168 Å) Br ⋯ O intermolecular contact, which may be partly responsible for the presence of two rotamers in the crystal.