Reductions of Challenging Organic Substrates by a Nickel Complex of a Noninnocent Crown Carbene Ligand

The first crown-tetracarbene complex of Ni(II) has been prepared, and its crystal structure determined. The complex can be reduced by Na/Hg, with an uptake of two electrons. The reduced complex reductively cleaves arenesulfonamides, including those derived from secondary aliphatic amines, and effects Birch reduction of anthracenes as well as reductive cleavage of stilbene oxides. Computational studies show that the orbital that receives electrons upon reduction of the complex <b>2</b> is predominantly based on the crown carbene ligand and also that the HOMO of the parent complex <b>2</b> is based on the ligand

Reductions of Challenging Organic Substrates by a Nickel Complex of a Noninnocent Crown Carbene Ligand

The first crown-tetracarbene complex of Ni(II) has been prepared, and its crystal structure determined. The complex can be reduced by Na/Hg, with an uptake of two electrons. The reduced complex reductively cleaves arenesulfonamides, including those derived from secondary aliphatic amines, and effects Birch reduction of anthracenes as well as reductive cleavage of stilbene oxides. Computational studies show that the orbital that receives electrons upon reduction of the complex <b>2</b> is predominantly based on the crown carbene ligand and also that the HOMO of the parent complex <b>2</b> is based on the ligand

KO<i>t</i>Bu: A Privileged Reagent for Electron Transfer Reactions?

Many recent studies have used KO<i>t</i>Bu in organic reactions that involve single electron transfer; in the literature, the electron transfer is proposed to occur either directly from the metal alkoxide or indirectly, following reaction of the alkoxide with a solvent or additive. These reaction classes include coupling reactions of halobenzenes and arenes, reductive cleavages of dithianes, and S_RN1 reactions. Direct electron transfer would imply that alkali metal alkoxides are willing partners in these electron transfer reactions, but the literature reports provide little or no experimental evidence for this. This paper examines each of these classes of reaction in turn, and contests the roles proposed for KO<i>t</i>Bu; instead, it provides new mechanistic information that in each case supports the <i>in situ</i> formation of organic electron donors. We go on to show that direct electron transfer from KO<i>t</i>Bu can however occur in appropriate cases, where the electron acceptor has a reduction potential near the oxidation potential of KO<i>t</i>Bu, and the example that we use is CBr₄. In this case, computational results support electrochemical data in backing a direct electron transfer reaction