Prototype of a class of neutral aromatic diamines with exceptionally high basicity known as proton sponges. Prepn: W. G. Brown, N. J. Letang, J. Am. Chem. Soc. 63, 358 (1941); and basicity study: R. W. Alder et al., J. Chem. Soc. Chem. Commun. 1968, 723. X-ray crystal structure: H. Einspahr et al., Acta Crystallogr. B29, 1611 (1973). Proton transfer studies: F. Hibbert, J. Chem. Soc. Perkin Trans. 2 1974, 1862. Ab initio structural studies: J. A. Platts et al., J. Org. Chem. 59, 4647 (1994); and fluorescence spectroscopy: A. Szemik-Hojniak et al., J. Am. Chem. Soc. 120, 4840 (1998). Charge distribution: P. R. Mallinson et al., ibid. 121, 4640 (1999). 13C NMR study of hydrogen bonding: M. Pietrzak et al., ibid. 123, 4338 (2001). Catalytic activity: I. Rodriguez et al., J. Catal. 183, 14 (1999). Review of chemistry: H. A. Staab, T. Saupe, Angew. Chem. Int. Ed. 27, 865-879 (1988); R. W. Alder, Chem. Rev. 89, 1215-1223 (1989).