Visible‐Light‐Triggered Photoswitching of Diphosphene Complexes

Abstract

Abstract Although 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 ‐κ 2 P, κ 6 C)Mo(CO) 2 ][OTf] ( 3 a [OTf]), [( 2 ‐κ 2 P, κ 6 C)Fe(CO)][OTf] ( 3 b [OTf]), and [( 2 ‐κ 2 P)Fe(CO) 4 ][OTf] ( 4 [OTf]) were prepared using the triflate salt [(L C )P=P(Dipp)][OTf] ( 2 [OTf) as a precursor (L C =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 η 2 ‐diphosphene complexes 3 a , b [OTf] readily undergo isomerization to form blue‐colored η 1 ‐complexes [( 2 ‐κ 1 P, κ 6 C)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 ( κ 2 P, κ 6 C)‐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 S 1 excited state and proceeds through a conical intersection.