2,6,10-Tris(dialkylamino)trioxatriangulenium ions. Synthesis, structure, and properties of exceptionally stable carbenium ions

A general synthetic route to a novel type of triamino-substituted planar ca rbenium ions (5) is reported. The synthetic method is based on a facile and selective nucleophilic aromatic substitution on the tris(2,4,6-trimethoxyp henyl)carbenium ion (1) with amines and gives access to a wide variety of m ore complex amino-substituted carbenium ions. X-ray crystallography shows t hat the 2,6,10-tris(N-pyrrolidinyl)-4,8,12-trioxatriangulenium ion (5b) is planar and forms segregated stacks of cations and PF6 anions in the solid p hase. The stability of the 2,6, 10-tris(diethylamino)-4,8,12-trioxatriangul enium ion 5a is expressed as the pK(R+) value, which is determined in stron gly basic nonaqueous solution on-the basis of a new acidity function C-. Th e pK(R+) value of 5a is measured to be 19.7, which is 10 orders of magnitud e higher than the values found for the most stable carbenium ions previousl y reported. Electrochemical reduction of compound 5a leads to rapid dimeriz ation. Two consecutive one-electron oxidations are identified by cyclic vol tammetry.