Visible‐Light‐Triggered Photoswitching of Diphosphene Complexes

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‐κ2P,κ6C)Mo(CO)2][OTf] (3a[OTf]), [(2‐κ2P,κ6C)Fe(CO)][OTf] (3b[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 ƞ2‐diphosphene complexes 3a,b[OTf] readily undergo isomerization to form blue‐colored ƞ1‐complexes [(2‐κ1P,κ6C)M(CO)n][OTf] (5a,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 3a,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.

Formation of a Hexaphosphido Cobalt Complex through P−P Condensation

“…[7] Additionally, compounds 1 and 1[Cl] have proven to be excellent precursors for the preparation of transition metal carbonyl η 2 -diphosphene complexes (D, Scheme 1iv), which undergo light-induced haptotropic rearrangement to η 1 -complexes upon irradiation with blue light (λ = 470 nm). [8] These results highlight the potential of compounds 1 and 1[Cl] as precursors for various new phosphorus species.…”