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-kappa P-2,kappa C-6)Mo(CO)(2)][OTf] (3 a[OTf]), [(2-kappa P-2,kappa ...
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-kappa P-2,kappa C-6)Mo(CO)(2)][OTf] (3 a[OTf]), [(2-kappa P-2,kappa C-6)Fe(CO)][OTf] (3 b[OTf]), and [(2-kappa P-2)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 (lambda=400 nm, 470 nm), the initially red-colored eta(2)-diphosphene complexes 3 a,b[OTf] readily undergo isomerization to form blue-colored eta(1)-complexes [(2-kappa P-1,kappa C-6)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 (kappa P-2,kappa C-6)-coordination mode gradually reverts back upon dissolution in coordinating solvents or more rapidly upon exposure to yellow or red irradiation (lambda=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.
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