Visible‐Light‐Triggered Photoswitching of Diphosphene Complexes
Clemens Taube, Jannis Fidelius, Kai Schwedtmann, Christopher J. Ziegler, Florian Kreuter, Leigh Loots, Leonard J. Barbour, Ralf Tonner, Robert Wolf, Jan J. Weigand
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.