Ab Initio Studies of Proton Sponges. 3. 4,5-Bis(dimethylamino)fluorene and 4,5-Bis(dimethylamino)phenanthrene

摘要

The proton sponge properties of the title compounds 4,5-bis(dimethylamino)fluorene (DMAF) and 4,5-bis(di-methylamino)phenanthrene (DMAP) have been much discussed in the literature, with geometric effects of the ring system, linearity of the N-H···N linkage, and overlap of N lone pairs cited as possible sources of enhanced basicity. Certainly, both bases appear to have geometries more likely to result in proton sponge properties than does the archetypal proton sponge 1,8-bis-(dimethylamino)naphthalene (DMAN). The ring structure angles the nitrogens toward each other (an N···N separation of 2.31 A has been suggested for DMAF), forcing close lone pair-lone pair contact and allowing an almost linear H-bond. The primary aim of this paper is to establish the proton affinities (PA) and structures of DMAF and DMAP.