Synthesis, Redox Properties, and Electronic Coupling in the Diferrocene Aza-dipyrromethene and azaBODIPY Donor–Acceptor Dyad with Direct Ferrocene−α-Pyrrole Bond

3,3′-Diferrocenylazadipyrromethene (<b>3</b>) and corresponding difluoroboryl (azaBODIPY) complex (<b>4</b>) were synthesized in several steps from ferrocenecarbaldehyde, following the well-explored chalcone-type synthetic approach. The novel diiron complexes, in which ferrocene groups are directly connected to the α-pyrrolic positions were characterized by a variety of spectroscopic techniques, electrochemistry, spectroelectrochemistry, and X-ray crystallography, while their electronic structure, redox properties, and UV–vis spectra were correlated with the density functional theory (DFT) and time-dependent DFT calculations

Re(CO)₃‑Templated Formation of Aza(dibenzo)dipyrromethenes

The Re­(CO)₃ unit was used to template the formation of aza­(dibenzopyrro)­methene (ADBM) in the presence of pyridine or <i>N</i>-methylimidazole. The products of these template reactions are six-coordinate complexes, with a facial arrangement of the carbonyls, a bidentate ADBM, and a sixth ligand (pyridine or <i>N</i>-methylimiadozle). Three types of ADBM ligands are produced from these reactions, depending on the degree of hydrolysis; bis­(imine)-terminated, bis­(oxo)-terminated, and mixed-imine/oxo chelates were formed

Re(CO)₃‑Templated Formation of Aza(dibenzo)dipyrromethenes

The Re­(CO)₃ unit was used to template the formation of aza­(dibenzopyrro)­methene (ADBM) in the presence of pyridine or <i>N</i>-methylimidazole. The products of these template reactions are six-coordinate complexes, with a facial arrangement of the carbonyls, a bidentate ADBM, and a sixth ligand (pyridine or <i>N</i>-methylimiadozle). Three types of ADBM ligands are produced from these reactions, depending on the degree of hydrolysis; bis­(imine)-terminated, bis­(oxo)-terminated, and mixed-imine/oxo chelates were formed

Observation of the Strong Electronic Coupling in Near-Infrared-Absorbing Tetraferrocene aza-Dipyrromethene and aza-BODIPY with Direct Ferrocene−α- and Ferrocene−β-Pyrrole Bonds: Toward Molecular Machinery with Four-Bit Information Storage Capacity

The 1,3,7,9-tetraferrocenylazadipyrromethene (<b>3</b>) and the corresponding 1,3,5,7-tetraferrocene aza-BODIPY (<b>4</b>) were prepared via three and four synthetic steps, respectively, starting from ferrocenecarbaldehyde using the chalcone-type synthetic methodology. The novel tetra-iron compounds have ferrocene groups directly attached to both the α- and the β-pyrrolic positions, and the shortest Fe–Fe distance determined by X-ray crystallography for <b>3</b> was found to be ∼6.98 Å. These new compounds were characterized by UV–vis, nuclear magnetic resonance, and high-resolution electrospray ionization mass spectrometry methods, while metal–metal couplings in these systems were probed by electro- and spectroelectrochemistry, chemical oxidations, and Mössbauer spectroscopy. Electrochemical data are suggestive of the well-separated stepwise oxidations of all four ferrocene groups in <b>3</b> and <b>4</b>, while spectroelectrochemical and chemical oxidation experiments allowed for characterization of the mixed-valence forms in the target compounds. Intervalence charge-transfer band analyses indicate that the mixed-valence [<b>3</b>]⁺ and [<b>4</b>]⁺ complexes belong to the weakly coupled class II systems in the Robin–Day classification. This interpretation was further supported by Mössbauer spectroscopy in which two individual doublets for Fe­(II) and Fe­(III) centers were observed in room-temperature experiments for the mixed-valence [<b>3</b>]^<i>n</i>+ and [<b>4</b>]^<i>n</i>+ species (<i>n</i> = 1–3). The electronic structure, redox properties, and UV–vis spectra of new systems were correlated with Density Functional Theory (DFT) and time-dependent DFT calculations (TDDFT), which are suggestive of a ferrocene-centered highest occupied molecular orbital and chromophore-centered lowest unoccupied molecular orbital in <b>3</b> and <b>4</b> as well as predominant spin localization at the ferrocene fragment attached to the α-pyrrolic positions in [<b>3</b>]⁺ and [<b>4</b>]⁺