Remarkable isolation, structural characterisation and electrochemistry of unexpected scrambling analogues of 5-ferrocenyl-10,20-diphenylporphyrin

Abstract

Selective condensation of 5-ferrocenyldipyrromethane, 1, and dipyrromethane, 2, with benzaldehyde, 3, led to 5-ferrocenyl-10,20-diphenylporphyrin, 5. During the condensation, an unusually large amount of scrambling was observed which led to the isolation of two further ferrocenylated porphyrin analogues 6 and 7. The structure of 6 was confirmed by a single-crystal X-ray study. A mechanism is proposed for this atypical scrambling which is likely to involve acid-catalysed reversion of the dipyrromethane synthesis. (1)H NMR further elucidated the structures of each complex and showed the existence of atropisomerism. An electrochemical study (cyclic voltammetry, Osteryoung square wave and linear sweep voltammetry) showed that there exists a linear relationship between the sum of the group electronegativities of meso substituents of the obtained porphyrins and the formal reduction potentials of the two observed ring-centred reduction processes, the meso substituent ferrocenyl-based oxidation process and the first ring-centred oxidation wave. These four relationships could be mathematically quantified. Due to the strong electron-withdrawing properties of the oxidised ferrocenium group, the second ring centred oxidation wave fell outside the potential window of dichloromethane as solvent.

Metal-free and transition-metal tetraferrocenylporphyrins part 1: synthesis, characterization, electronic structure, and conformational flexibility of neutral compounds

“…In most cases, the iron centers should be located at a distance of less than 5.4 Å to achieve effective metal-metal coupling between the ferrocene units in the same molecule, while examples of long range (∼10 Å ) metal-metal couplings in polyferrocenyl containing systems are still rare. [17][18][19][20][21][22] Meso-ferrocenyl substituted porphyrins have so far received little attention, although they seem very promising in terms of their photochemical properties. [21][22][23] For instance, during our investigation of the efficient and fast electron transfer from zinc 5,10,15,20-tetraferrocenylporphyrin (ZnTFcP, strong electron donor) to 2-pyridyl-3,4-fulleropyrrolidine (electron acceptor), ZnTFcP showed interesting photoinduced electron-transfer features.…”

Ferrocenyl end capped molecular rods: synthesis, structure, and properties

“…Sonogashira cross-coupling reaction of ethynyl ferrocene 23 and 1-ethynyl-4-ferrocenyl-benzene ( 16) with 1,4-diiodobenzene 18, in the presence of Pd(PPh 3 ) 4 as a catalyst, CuI as cocatalyst, and diisopropylamine as a base, resulted 4-iodo-1-ferrocenylethynylbenzene (19) and 4-iodo-1-ferrocenyl-phenylethynylbenzene (21) in 80%, and 88% yield, respectively (Scheme 2).…”

“…18 The reversibility was also observed with peak current ratios close to 1 for all processes, and the deviation from 1 is the result of baseline uncertainty due to the onset of solvent decomposition at these low potentials. 19 The anodic and cathodic peak potential difference DE p (mV), for 1-11 was found in the range of 60-96 mV (Table 1). This shows that all oxidations are almost reversible.…”

Ferrocene-appended porphyrins: Syntheses and properties

“…The poor solubility of the mixture components precluded their efficient separation by chromatography and only 2H 2 and 5H 2 could be obtained as pure samples. Using similar synthetic strategies, the introduction of 4-methyl-, mesityl-or 4-tert-butyl-benzyl-groups at the meso positions proved later to allow cleaner and easier separations of all these components [17,26,27,29].…”

“…The interest towards molecules showing multiple interacting redox centres prompted the development of strategies enabling the synthesis of various partially meso-substituted ferrocene porphyrins [27]. A mixture of mono-, bis-and trisferrocenyl-substituted porphyrins could especially be obtained from the reaction of 5-ferrocenyldipyrromethane with benzaldehyde (2H 2 , 3H 2 , 4H 2 , 5H 2 , Fig.…”