Bistable Photochromic Organometallics Based on Linkage Isomerization:  Photochemistry of Dicarbonyl(η⁵-methylcyclopentadienyl)manganese(I) Derivatives with a Bifunctional, Nonchelating Ligand

Abstract

Cyclopentadienylmanganese complexes of the general formula (η 5 -C 5 H 4 CH 3 )Mn(CO) 2 L, where L is a nonchelatable, bifunctional ligand, were found to be photochromic. Irradiation of (η 5 -C 5 H 4 CH 3 )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 (η 5 -C 5 H 4 CH 3 )Mn(CO) 3 and a pyridine derivative RC 5 H 4 N (R = 3-CH 2 CN, 2-CH 2 CN, 4-CHCHPh, 4-CHCH 2 ) generated (η 5 -C 5 H 4 CH 3 )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.