Visible‐Light‐Triggered Photoswitching of Diphosphene Complexes

Abstract

AbstractAlthough diphosphene transition metal complexes are known to undergo E to Z isomerization upon irradiation with UV light, their potential for photoswitching has remained poorly explored. In this study, we present diphosphene complexes capable of reversible photoisomerizations through haptotropic rearrangements. The compounds [(2‐κ2P,κ6C)Mo(CO)2][OTf] (3 a[OTf]), [(2‐κ2P,κ6C)Fe(CO)][OTf] (3 b[OTf]), and [(2‐κ2P)Fe(CO)4][OTf] (4[OTf]) were prepared using the triflate salt [(LC)P=P(Dipp)][OTf] (2[OTf) as a precursor (LC=4,5‐dichloro‐1,3‐bis(2,6‐diisiopropylphenyl)‐imidazolin‐2‐yl; Dipp=2,6‐diisiopropylphenyl, OTf=triflate). Upon exposure to blue or UV light (λ=400 nm, 470 nm), the initially red‐colored η2‐diphosphene complexes 3 a,b[OTf] readily undergo isomerization to form blue‐colored η1‐complexes [(2‐κ1P,κ6C)M(CO)n][OTf] (5 a,b[OTf]; a: M=Mo, n=2; b: M=Fe, n=1). This haptotropic rearrangement is reversible, and the (κ2P,κ6C)‐coordination mode gradually reverts back upon dissolution in coordinating solvents or more rapidly upon exposure to yellow or red irradiation (λ=590 nm, 630 nm). The electronic reasons for the reversible visible‐light‐induced photoswitching observed for 3 a,b[OTf] are elucidated by DFT calculations. These calculations indicate that the photochromic isomerization originates from the S1 excited state and proceeds through a conical intersection.