REDUCTIVE ALKYLATION OF ARENES .5. ANIONIC PRODUCTS OF THE 2-ELECTRONREDUCTION OF AROMATIC NITRILES IN LIQUID-AMMONIA

The reduction of 9-cyanoanthracene by two equivalents of potassium in liquid ammonis was shown to yield the 9-cyanoanthracene dianion, where as 1-naphtho- and benzonitrile gave the cyanodihydroaryl anions corres ponding to the protonation of nitrile dianions at a position para to t he cyano group. The 9-cyanoanthracene dianion underwent the same trans formation in the presence of a stronger protonating agent, methasol. A ccording to C-13 NMR spectral data of the generated specks, the cyano group extracts the negative charge from the pi-electronic system: ca 0 .20:0.25 e in the case of the 9-cyanoanthracene dianion and ca 0.14:0. 17 e in the case of cyanodihydroaryl anions. These estimations and the general NMR pattern of pi-charge distribution in all the anionic spec ies under investigation are in accordance with data from quantum molec ular orbital calculations at the PM3 and INDO levels, being reflected by the fairly good linear relationships between the changes of ring ca rbon chemical shifts on going to the anionic species from the respecti ve neutral precursors on the one hand and the calculated pi-charges on the other. The para-orienting effect of the cyano group in the proton ation of nitrile dianions is discussed in terms of the pi-charge distr ibution in the starting dianion and the tendency to form a most stable cyanodihydroaryl anion isomer.