Visible Light-Induced Cis/trans Isomerization of Dicarbonyl Fe(II) PNP Pincer Complexes

The synthesis and characterization of dicarbonyl Fe(II) PNP pincer complexes of the type cis-[Fe(PNP-iPr)(CO)2(X)]+ (X=Br, Cl) is described. These complexes are slowly formed when solutions of complexes trans-[Fe(PNP-iPr)(CO)2(X)]+ are kept in the dark for 9h (X=Br) and 3days (X=Cl). Upon exposure to visible light these complexes isomerize to the respective trans-dicarbonyl complexes within a few hours. The visible-light reaction seems to involve reversible CO dissociation. The isomerization can be repeated serval times. A mechanistic rationale for this isomerization process is established by means of DFT calculations.