Syntheses and structures of 10-trimethylelement-substituted 1,8-dichloroanthracenes

1,8-Dichloroanthracenes bearing EMe₃ substituents at the 10-position (E = Si, Ge, Sn) have been synthesised by salt elimination reactions. The key compound, 10-bromo-1,8-dichloroanthracene (2), was quantitatively obtained by conversion of 1,8-dichloroanthracene with elemental bromine in dichloromethane. The EMe₃-substituted anthracene compounds 1,8-dichloro-10-(trimethylsilyl)-(3), 1,8-dichloro-10-(trimethylgermyl)-(4) and 1,8-dichloro-10-(trimethylstannyl)anthracene (5) were completely characterised by multinuclear NMR spectroscopy and mass spectrometry. Their molecular structures in the crystalline state were analysed by X-ray diffraction experiments and compared with the crystal structure of 10-tert-butyl-1,8- dichloroanthracene (1). It was found that the level of deformation of the anthracene backbone continuously increases along the series of anthracene substituents SnMe₃ < GeMe₃ < SiMe₃ < CMe₃. Owing to the good agreement of experimental structural parameters with the results of quantum chemical calculations, the molecular deformations can be regarded as inherent molecular properties. 10-Bromo-1,8-dichloroanthracene was quantitatively obtained by bromination of 1,8-dichloroanthracene and converted into 1,8-dichloro-10-(trimethylelement) anthracenes (with E = Si, Ge, Sn). Their crystal structures show a butterfly-like deformation of the molecules, which is also observed in case of the tert-butyl compound (E = C).