Bistable photochromic organometallics based on linkage isomerization:: Photochemistry of dicarbonyl(η5-methylcyclopentadienyl)manganese(I) derivatives with a bifunctional, nonchelating ligand

Cyclopentadienylmanganese complexes of the general formula (eta(5)-C5H4CH3)Mn(CO)(2)L, where L is a nonchelatable, bifunctional ligand, were found to be pbotochromic. Irradiation of (eta(5)-C5H4CH3)Mn(CO)(2)L(3-cyanomethylpyridine) 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 (eta(5)-C5H4CH3)Mn(CO)(3) and a pyridine derivative RC5H4N (R = 3-CH2CN, 2-CH2CN, 4-CHCHPh, 4-CHCH2) generated (eta(5)-C5H4CH3)Mn(CO)(2)L 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.