Efficient Syntheses of New Super Lewis Basic Tris(dialkylamino)-Substituted Terpyridines and Comparison of Their Methyl Cation Affinities.

Syntheses of very electron-rich dialkylamino-substituted 2,2':6',2"-terpyridines (TPYs) were adapted to moderate scale preparation without tedious purification of intermediates. The key 4'-bromo-6,6"-dimethyl-2,2':6',2"-terpyridine-4,4"-diyl bisnonaflate is now available in gram quantities. Its nucleophilic aromatic substitution with dimethylamine provided mixtures of 4'-bromo-substituted 4,4"-bis(dimethylamino)-TPY and the tris(dimethylamino)-TPY. The bromo compound was used in a Buchwald-Hartwig amination to provide the tris(dimethylamino)-TPY in excellent yield. The 4'-bromo substituent was reductively removed to furnish the bis(dimethylamino)-TPY. The same sequence of reactions with pyrrolidine as nucleophile leads to the hitherto unknown pyrrolidino-TPYs. Calculations at the MP2(FC)/6-31+G(2d,p)//B98/6-31G(d) level predict very high methyl cation affinities for compounds of this type, with the 4,4',4"-tri(pyrrolidin-1-yl)-TPY being the most Lewis basic TPY synthesized to date. The efficiently prepared electron-rich TPYs should be excellent ligands for many applications.