Photochemistry of π- and n-Donor Bifunctional Monosubstituted Derivatives of Cyclopentadienylmanganese Tricarbonyl Complexes Containing an Allyl Group and Photo- and Thermoisomerization of the Corresponding Dicarbonyl Chelates

Abstract

Photochemical properties of a series of bifunctional monosubstituted derivatives of cymantrene containing a C-, N-, or O-bound π-allyl group, along with n-donating carbamate, amide, or pyridine fragments were investigated. The results obtained demonstrate that the nature and thermodynamic stability of the cyclopentadienylmanganese dicarbonyl chelates derived from bifunctional monosubstituted cymantrene derivatives depend substantially on both the nature of the functional groups and on their position in the substituent at the Cp ring. Thus, for the six-membered chelates, the thermodynamic stability increases in the series carbamates < amides < pyridines < olefins. Some of the dicarbonyl chelates studied form reversible photochromic systems due to linkage isomerization between different donating groups of the bifunctional substituent and the manganese atom with a wide range of times of thermal isomerization.

Spectroscopic Studies of Photochemical Transformations of Cymantrenylquinazolinone Derivatives

“…IR monitoring of the irradiation of compounds 1 and 2 in benzene by a Hg lamp with λ = 365 nm showed that two MCO stretches of tricarbonyl complexes at 2019 and 1938 cm –1 disappear and two new bands of approximately equal intensities at 1931 and 1861 cm –1 appear in the ν(MCO) region of the IR spectra and the –NC=O band undergoes a low‐frequency shift of 54 cm –1 . The positions and intensity ratios are typical of the asymmetric and symmetric modes of MCO stretches in dicarbonyl complexes in which, according to our previous data,, , the manganese atom is coordinated to the –NC=O group; the low‐frequency shift of the ν(C=O) band also confirms the O ‐coordination. Thus, after photochemically induced CO loss, O ‐coordinated chelate complexes are formed (Figure , Scheme , Table ).…”

“…It is also well known that one of the basic properties of cyclopentadienyltricarbonyl manganese (cymantrene) complexes is the possibility of ligand exchange at the manganese atom under UV irradiation leading to a significant change in the spectral properties of the molecules . Earlier we found that the photolysis of cymantrenylalkylamides of carboxylic acids results in the formation of thermodynamically stable dicarbonyl chelates due to the coordination of the carbonyl fragment –NC=O to the Mn atom.…”

Synthesis and Spectroscopic Studies of the Photochromism of Bifunctional Derivatives of Cymantrene in Solution and without Solvent

“…The olefin chelates 19 and 21 were isolated as oils; the 1 H NMR spectra of these compounds confirm their structures and are in good agreement with the spectra of related olefin chelates , …”

“…The irradiation of a solution of 5 in benzene or THF results simultaneously in the formation of both chelate 19 with ν(CO) at ν̃ = 1975 and 1917 cm –1 and its isomer 20 with ν(CO) at ν̃ = 1930 and 1857 cm –1 in benzene (Scheme ). The band assignment in this region is based on our previous results , . For allylamides 6 – 8 , the simultaneous formation of olefin ( 21 – 23 ) and amide ( 24 – 26 ) chelates in ratios of 2:1 is observed in benzene.…”

“…We reported previously that the irradiation of yellow ( λ ≈ 333 nm) solutions of (allyl)dicarbonylmanganese chelates 1 and 2 with n‐donating amide substituent results in the formation of the crimson isomeric dicarbonyl amide compounds 3 and 4 , respectively ( λ ≈ 515 nm, Scheme ), which thermally fully isomerize back to the starting chelates 1 and 2 in 30–40 min. These are examples of intramolecular photochromic transformations between olefin chelates 1 and 2 and their amide isomers 3 and 4 , respectively.…”