Phosphoramidate and Silyl Amine Mediated Synthesis of Isocyanide Cyclopentadienone Iron Complexes

ABSTRACT A synthetic procedure for the preparation of isocyanide cyclopentadienone iron complexes using the corresponding tricarbonyl complexes and primary amines as starting materials is described. By transforming the primary amines into deprotonated phosphoramidates or silyl amines, the CO ligands can be replaced by CNR ligands by abstracting the CO oxygen atom and replacing it with an NR fragment, with concomitant formation of phosphates or silanols as the thermodynamic driving force. The phosphoramidate route, using RNHP(O)(OEt) 2 , works well for R = alkyl, but fails for R = aryl, presumably due to the reduced nucleophilicity of the intermediate deprotonated phosphoramidate. Aromatic isocyanide ligands are accessible by using silyl amines ArNHTMS (Ar = aryl, TMS = trimethylsilyl) instead. The disclosed procedure has the advantage that the free isocyanide ligands themselves do not need to be isolated, which circumvents the use of strongly unpleasant smelling chemicals. Catalytic transfer hydrogenation reactions show that, under the same reaction conditions, the monoisocyanide complexes perform significantly worse than the corresponding tricarbonyl complexes. Kinetic monitoring revealed that fast catalyst decomposition is responsible for the lower performance. The reaction mechanism of the C≡O/C≡NR transformation was additionally investigated by DFT calculations.