Photochemistry of Chromium Arene Tricarbonyl Complexes with Tethered Pyridinyl and Propenyl Groups: Investigations of the Effect of Ring Size on Chelate Formation, Structure, and Linkage Isomerization

Abstract

Chromium arene tricarbonyl complexes with tethered pyridinyl groups [Cr{η6-C6H5(CH2)n(2-Py)}(CO)3] (4–6) (2-Py = 2-pyridinyl, n = 1–3, respectively) were synthesized and irradiated to form the chelates [Cr{η6-C6H5(CH2)n(2-Py)-κN}(CO)2] (7–9). Studies examined the effect of ring size and structure on chromophore λmax, stability, and photosensitivity, which are factors important for photochromes based on linkage isomerization of tethered functional groups. The studies also include [Cr{η6-C6H5CH(2-Py)CH2CH═CH2}(CO)3] (3), which has a bifunctional tether of propenyl and pyridinyl groups, and irradiation produces the linkage isomers [Cr{η6-C6H5(CH(2-Py)CH2CH═CH2)-κN}(CO)2] (1) and [Cr{η6-C6H5(CH(2-Py)CH2CH═CH2)(η2-CH═CH2)}(CO)2] (2). X-ray crystal structures for 7–9 show that the dihedral angle between the coordinated pyridinyl groups and the phenyl-chromium centroid increases from 1 to 73° (n = 1–3, respectively). The experimental and TDDFT computed optical changes accompanying an increase in the dihedral ang...