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 2 is predominantly based on the crown carbene ligand and also that the HOMO of the parent complex 2 is based on the ligand.

Super-electron donors: bis-pyridinylidene formation by base treatment of pyridinium salts.

Deprotonation of bispyridinium salt 7b affords bispyridinylidene 10, a very powerful neutral organic two-electron donor [E1/2 (DMF)=-1.13 V vs Ag/AgCl/KCl (sat)], presumably via the pyridinylidene 8. Donor 10 reduces aryl iodides and bromides to aryl anions in excellent yield and also reductively cleaves selected phenylalkylsulfones very efficiently.