Bistable photochromic organometallics based on linkage isomerization: Photochemistry of dicarbonyl(η 5-methylcyclopentadienyl) manganese(I) derivatives with a bifunctional, nonchelating ligand


Cyclopentadienylmanganese complexes of the general formula (η 5-C 5H 4CH 3)Mn(CO) 2L, where L is a nonchelatable, bifunctional ligand, were found to be photochromic. Irradiation of (η 5-C 5H 4CH 3)Mn(CO) 2L(3-cyanomethylpyridme) with alternating visible and UV light produced alternating yellow and red solutions, and fatigue of this response was inhibited when free 3-(cyanomethyl)pyridine was present during irradiation. Similar results were observed when L is pyridine in the presence of dispersed acetonitrile. Irradiation of (η 5-C 5H 4CH 3)Mn(CO) 3 and a pyridine derivative RC 5H 4N (R = 3-CH 2CN, 2-CH 2CN, 4-CHCHPh, 4-CHCH 2) generated (η 5-C 5H 4CH 3)Mn(CO) 2L in situ, which likewise showed a photochromic response. The results demonstrate that the linkage isomerization occurs by unimolecular and bimolecular processes and that linkage isomerization is an effective photochromic mechanism for organometallics.

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