Visible light-induced cis/trans isomerization of dicarbonyl Fe(II) PNP pincer complexes

Abstract The synthesis and characterization of dicarbonyl Fe(II) PNP pincer complexes of the type cis -[Fe(PNP- i Pr)(CO) 2 (X)] + (X = Br, Cl) is described. These complexes are slowly formed when solutions of complexes trans -[Fe(PNP- i Pr)(CO) 2 (X)] + are kept in the dark for 9 h (X = Br) and 3 days (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.