Reduction of Carbon-rich Compounds

Studies of metal reduction of polycyclic aromatic hydrocarbons (PAHs) [1] were reported as early as 1867 by Berthelot [2], where he described the fusion of metallic potassium with naphthalene 1. Studies in solution of electron transfer from Na and K to PAHs started as early as 1913 with Schlenk et al. [3] who reported that when anthracene reacted with the alkali metal in ether, 1 1 and 2 1 metal anthracene adducts were obtained. Not understanding what the 1 1 adduct really was, it was termed radical and later on it was suggested by Hvickel that the radical is a singly charged species [4], 

In this chapter we concentrate on reduction processes of carbon-rich systems. The formation of anions and radical anions of -conjugated monocyclic systems, cyclophanes, bowls and fullerenes is described. Carbon-rich compounds can be reduced directly by contact with alkali metals Li, Na, K, Rb and Cs, which have a low reduction potential. Proton, carbon and lithium NMR and EPR spectroscopies are the main methods used to gain a better understanding of the mono- and polycyclic systems in solution. Special attention will be given to modes of electron delocalization, aromaticity, anti-aromaticity, as well as aggregation, bond formation and bond cleavage processes of diamagnetic electron transfer products. Electrochemical reductions will be briefly discussed. 

The electron transfer method and the reducing metal are very significant, since they can infiuence the reduction products. This affects the reduction state of the anions formed, the electronic and magnetic spectra, and the dynamic and structural changes that the negatively charged molecules undergo [Ib-dj. 

Carbon-Rich Compounds. Edited by Michael M. Haley and Rik R. Tykwinsld Copyright 2006 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-31224-2 

---

Upon reaction with a metal, the NMR spectrum of a neutral hydrocarbon first disappears, due to one-electron transfer from the metal. This step can be studied by EPR spectroscopy [la, 5j. The reduction of carbon-rich compounds usually occurs stepwise by one-electron transfers as depicted in Scheme 13.1 [lb]. The same set of events occurs in electrochemical processes and in alkali metal reductions. This reaction has become the main synthetic route to i-conjugated anions. 

---