Anionic products of the two‐electron reduction of aromatic nitriles in liquid ammonia

Abstract

The reduction of Bcyanonnthracene by two equivalents of potassium in liquid ammonia was shown to yield the 9cyanoanthracene dianion, whereas 1-naphtho-and benzonitrile gave the cyanodihydroaryl anions corresponding to the protonation of nitrile dianions at a position para to the cyano group. The 9-cyanoanthracene dianion underwent the same transformation in the presence of a stronger protonating agent, methanol. According to I3C NMR spectral data of the generated species, the cyano group extracts the negative charge from the *-electronic system: ca 0.20:0*25 e in the case of the 9-cyanoanthracene dianion and ca 0-140.17 e in the case of cyanodihydroaryl anions. These estimations and the general NMR pattern of r-charge distribution in all the anionic species under investigation are in accordance with data from quantum molecular orbital calculations at the PM3 and INDO levels, being reflected by the fairly good linear relationships between the changes of ring carbon chemical shifts on going to the anionic species from the respective neutral precursors on the one hand and the calculated nsharges on the other. The para-orienting effect of the cyano group in the protonation of nitrile dinnions is discussed in terms of the r-charge distribution in the starting dianion and the tendency to form a most stable cyanodihydroaryl anion isomer. RESULTSThe reduction was performed just before recording NMR spectra by adding two equivalents of potassium 'Part5 of the series 'Reductive Alkylation of Arenes.' For Parts 1-4, see Refs 1 and 2. t Present address:

The formation of dicyanoterphenyls by the interaction of terephthalonitrile dianion with biphenylcarbonitriles in liquid ammonia

“…Both these DAs are stabilized by electron-withdrawing effects of cyano and phenyl groups, however the steric hindrance exerted by a phenyl group ortho to the site of coupling obviously causes DA 12 to be less stable compared with the "straight-shaped" DA 11. As indicated above, further conversions of DAs 11 and 12 into products 8 and 9 include rapid cyanide-ion elimination 7,8 resulting in cyclohexadienyl anions 13 and 14. Having no a good leaving group at the saturated carbon, these anions are stable 10 under inert reaction conditions but undergo oxidative aromatisation by exposing to air (Scheme 2).…”

Substituent-induced polarization of charge in phenalenyl anions

“…In the remaining AMX spectrum belonging to H-7, H-8 and H-9, the signal with two ortho couplings can be assigned to H-8. The 13 C NMR signals belonging to these positions can be found using the C-H HETCOR spectrum. A distinction between the two remaining tertiary 13 C signals, C-7 and C-9, could be made by recording a 75 MHz gated decoupled 13 C NMR spectrum (Fig.…”

“…Cyanoarenes have only recently been used for the first time in Birch-like reactions 12,13 and little is known about the effect of this substituent on the charge distribution of delocalized anions. In order to compare the effect of a CN triple bond with that of a CC triple bond, the 1-(3,3-dimethylbutynyl) derivative ( Fig.…”

“…9 An example of this is the reduction of 1-methylnaphthalene in the absence or presence of a 4-trimethylsilyl (TMS) substituent. 10 A useful way of studying the effect of a specific substituent on the charge distribution of an anion is by generating the anion in an NMR tube and measuring and interpreting its 1 H and 13 C NMR spectra. 4 This has been done previously in order to study the effect of methyl, methoxy and vinyl substituents on the charge distribution of the phenalenyl anion.…”

“…Anions 2 À , 3 À and 4 À were generated in an NMR tube and examined by means of 1 H and 13 C NMR spectroscopy. The charge distribution and the HOMO coefficients of these anions were calculated by means of semiempirical calculations.…”