Re(CO)₃‑Templated Synthesis of α‑Amidinoazadi(benzopyrro)methenes

α-Amidinoazadi­(benzopyrro)­methenes were synthesized using the Re­(CO)₃ unit as a templating agent. The products of these template reactions are six-coordinate rhenium complexes, with a facial arrangement of carbonyls, a noncoordinating anion, and a tridentate α-amidinoazadi­(benzopyrro)­methene ligand. The tridentate ligand shows the conversion of one diiminoisoindoline sp² carbon to a sp³ carbon, which has been seen in the “helmet” and bicyclic phthalocyanines. The bidentate diiminoisoindoline fragment tilts out of the plane of coordination. Five examples of α-amidinoazadi­(benzopyrro)­methenes produced from these reactions using different nitrile solvents, including the nitrile activation of acetonitrile, propionitrile, butyronitrile, cyclohexanecarbonitrile, and benzonitrile

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>]⁺

Re(CO)₃‑Templated Synthesis of Semihemiporphyrazines

Half-hemiporphyrazine macrocycles, which can be called “semihemiporphyrazines”, were synthesized using the Re­(CO)₃ unit as a templating agent. The products of these template reactions are six-coordinate rhenium complexes, with a facial arrangement of carbonyls, a halide, and a bidentate semihemiporphyrazine chelate that tilts out of the plane of coordination. Three types of semihemiporphyrazines can be produced from these reactions, depending on the alternate heterocycle to the isoindoline unit; structures including pyridine, thiazole, and benzimidazole were formed. The electronic structures of these compounds were probed using spectroscopy as well as density functional theory methods

Visible-Light-Driven Photosystems Using Heteroleptic Cu(I) Photosensitizers and Rh(III) Catalysts To Produce H₂

The synthesis of two new heteroleptic Cu­(I) photosensitizers (PS), [Cu­(Xantphos)­(NN)]­PF₆ (NN = biq = 2,2′-biquinoline, dmebiq = 2,2′-biquinoline-4,4′-dimethyl ester; Xantphos = 4,5-bis­(diphenylphosphino)-9,9-dimethylxanthene), along with the associated structural, photophysical, and electrochemical properties, are described. The biquinoline diimine ligand extends the PS light absorbing properties into the visible with a maximum absorption at 455 and 505 nm for NN = biq and dmebiq, respectively, in CH₂Cl₂ solvent. Following photoexcitation, both Cu­(I) PS are emissive at low energy, albeit displaying stark differences in their excited state lifetimes (τ_MLCT = 410 ± 5 (biq) and 44 ± 4 ns (dmebiq)). Cyclic voltammetry indicates a Cu-based HOMO and NN-based LUMO for both complexes, whereby the methyl ester substituents stabilize the LUMO within [Cu­(Xantphos)­(dmebiq)]⁺ by ∼0.37 V compared to the unsubstituted analogue. When combined with H₂O, <i>N,N</i>-dimethylaniline (DMA) electron donor, and <i>cis</i>-[Rh­(NN)₂Cl₂]­PF₆ (NN = Me₂bpy = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine, dmebpy = 2,2′-bipyridine-4,4′-dimethyl ester) water reduction catalysts (WRC), photocatalytic H₂ evolution is only observed using the [Cu­(Xantphos)­(biq)]⁺ PS. Furthermore, the choice of <i>cis</i>-[Rh­(NN)₂Cl₂]⁺ WRC strongly affects the catalytic activity with turnover numbers (TON_Rh = mol H₂ per mol Rh catalyst) of 25 ± 3, 22 ± 1, and 43 ± 3 for NN = Me₂bpy, bpy, and dmebpy, respectively. This work illustrates how ligand modification to carefully tune the PS light absorbing, excited state, and redox-active properties, along with the WRC redox potentials, can have a profound impact on the photoinduced intermolecular electron transfer between components and the subsequent catalytic activity

Magnetic Circular Dichroism of Transition-Metal Complexes of Perfluorophenyl-N-Confused Porphyrins: Inverting Electronic Structure through a Proton

Neutral and deprotonated anionic Ni­(II), Pd­(II), Cu­(II), and Cu­(III) complexes of tetrakis­(perfluorophenyl)-N-confused porphyrin (PF-NCP) were prepared and investigated by UV–visible and magnetic circular dichroism (MCD) spectroscopies. As in the previously reported Ni­(II) adduct of tetraphenyl N-confused porphyrin, we observe sign reverse (positive to negative intensities with increasing energy) features in the MCD spectra of the neutral Ni­(II), Pd­(II), and Cu­(II) complexes of PF-NCP, which is indicative of rare ΔHOMO < ΔLUMO relationships. Upon deprotonation of Ni­(II), Pd­(II), and Cu­(II) complexes, these features revert to those of more typical porphyrin MCD spectra consistent with a ΔHOMO > ΔLUMO condition. The Cu­(III) PF-NCP complex shows features similar to those of the deprotonated divalent metal systems. Spectroscopic features in all target complexes as well as previously published metal-free and Ni­(II) NCP systems were correlated with the density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. Calculation data are consistent with the tautomeric rearrangement of the electronic structures of NCP cores playing dominant roles, with smaller contribution from the central metal ions in the observed optical and magneto-optical properties. This is true for all described NCP systems to date, as they affect the stabilization/destabilization of the N-confused porphyrin-centered Gouterman orbitals