Formation of Di-tert-butylurea from a Mononuclear Iron Tris(isocyanide) Complex

We report the synthesis and characterization of the tripodal iron tris(isocyanide) complexes [TmR′Fe(CNR)3](OTf) (R = tBu, Ad; R′ = Me, Ph, Mes). These complexes generate the corresponding disubstituted ureas when treated sequentially with a reductant (KC8) and a proton source (H2O). A series of labeling experiments indicate air to be the source of the urea oxygen, while the urea carbon is derived from the isocyanide. Crossover experiments indicate a key role for H2NR in the formation of the disubstituted urea, and we propose a pathway for urea formation that involves a diaminocarbene intermediate that is formed from H2NR attack on a bound isocyanide ligand.