Metal-Mediated CH Bond Activation in a Carbon-Substituted Hemiporphyrazine

A Switchable Near-Infrared-Absorbing Dye Based on Redox-Bistable Benzitetraazaporphyrin

Activatable near-infrared (NIR) dyes responsive to external stimuli are used in medical and other applications. Here, we describe the design and synthesis of bench-stable 18π- and 20π-electron benzitetraazaporphyrins (BzTAPs) possessing redox-switchable NIR properties. X-Ray, NMR, and UV/Visible-NIR analyses revealed that 20π-electron BzTAP 1 exhibits NIR absorption and antiaromaticity with a paratropic ring-current, while 18π-electron BzTAP 2 shows weakly aromatic character with NIR inertness. Notably, the NIR-silent BzTAP 2 was readily converted to the NIR-active BzTAP 1 in the presence of mild reducing agents such as amine. The intense NIR absorption band of BzTAP 1 is in sharp contrast to the very weak absorption bands of previously reported antiaromatic porphyrinoids. Molecular orbital analysis revealed that symmetry-lowering perturbation of the 20π-electron porphyrinoid skeleton enables the HOMO-LUMO transition of 1 to be electric-dipole-allowed. BzTAPs are expected to be useful for constructing activatable NIR probes working in reductive environments.

Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems

The unique environment within the core of carbaporphyrinoid systems provides a platform to explore unusual organometallic chemistry. The ability of these structures to form stable organometallic derivatives was first demonstrated for N-confused porphyrins but many other carbaporphyrin-type systems were subsequently shown to exhibit similar or complementary properties. Metalation commonly occurs with catalytically active transition metal cations and the resulting derivatives exhibit widely different physical, chemical and spectroscopic properties and range from strongly aromatic to nonaromatic and antiaromatic species. Metalation may trigger unusual, highly selective, oxidation reactions. Alkyl group migration has been observed within the cavity of metalated carbaporphyrins, and in some cases ring contraction of the carbocyclic subunit takes place. Over the past thirty years, studies in this area have led to multiple synthetic routes to carbaporphyrinoid ligands and remarkable organometallic chemistry has been reported. An overview of this important area is presented.

N-Substituted Azacalixphyrins: Synthesis, Properties, and Self-Assembly

Pre- and postintroduction of substituents with respect to the macrocyclization step leads to previously unknown N-substituted azacalixphyrins. The stepwise synthetic approach has been studied in detail to highlight the key role of the N-substituents of the precursors and/or intermediates in terms of reactivity. Based on a combined experimental and theoretical investigation, the relationship between the properties of the macrocycles and their degree of substitution is rationalized. Depending on the nature of the N-substituents, the formation of supramolecular ribbon-like structures could also be observed, as demonstrated by combined TEM, SEM, AFM, and FTIR experiments.

A Chiral Hemiporphyrazine Derivative: Synthesis and Chiroptical Properties

The synthesis of an optically active hemiporphyrazine with chiral binaphthyl substituents (1) is reported, providing the first example of the incorporation of an intrinsically chiral moiety into the macrocyclic core of a hemiporphyrazine analogue. A negative circular dichroism (CD) signal is observed in the 325-450 nm region of the CD spectrum of (S,S)-1, while mainly positive bands are observed in the 220-325 nm region. Mirror symmetry is observed across the entire wavelength range of the CD spectra of (R,R)-1 and (S,S)-1. An irreversible one-electron oxidation wave with an onset potential at 1.07 V is observed by cyclic voltammetry, along with a reversible one-electron reduction wave at -0.85 V. Density functional calculations reproduce the experimentally observed data and trends, and provide further insight into the nature of the electronic transitions.

Boron templated synthesis of a BODIPY analogue from a phthalocyanine precursor

The synthesis of aza(dibenzopyrro)methenes (ADBMs) using aryl boron compounds as templates is described. Compounds (1–3) are structurally related to the BODIPYs and were isolated with terminal imine, oxo, or mixed imine-oxo groups. Compounds 1–3 were investigated for their absorption/emission properties, and were probed by DFT and TDDFT methods.

Benziporphyrins, a unique platform for exploring the aromatic characteristics of porphyrinoid systems

Benziporphyrins and related systems exhibit a wide range of properties and may possess nonaromatic, strongly aromatic or even antiaromatic characteristics.

The synthesis and metal binding chemistry of carbahemiporphyrazines with an electron withdrawing substituent

Benziphthalocyanine (bzpc) and dicarbahemiporphyrazine (dchp) are phthalocyanine analogs where one and two of the isoindoline units have been replaced with benzene rings. In this report, we present dchp and bzpc analogs 1 and 2 where CF3 groups have been placed on the 5-position of the benzene rings. Compounds 1 and 2 have identical structural features as their unmodified parent macrocycles, but some differences are observed in their metal adducts. Complex 1Ag shows few differences with the analogous dchp complex, but compounds 1Cu and 2Co exhibit reductions in M – C bond lengths arising from the electron withdrawing nature of the CF3 unit.

The metal chemistry of the carbahemiporphyrazines

Over fifty years ago, Linstead and Elvidge described the syntheses of phthalocyanine-like macrocycles in which one or two of the interior metal-binding nitrogen atoms were replaced with aromatic C - H groups. We review here the coordination chemistry of two of these systems, dicarbahemiporphyrazine and benziphthalocyanine, and we emphasize the unusual reactivity displayed by these macrocycles and the varying extent to which the C - H groups are activated by metal-binding.

Low-Coordinate Transition-Metal Complexes of a Carbon-Substituted Hemiporphyrazine

The metallation of the core-modified phthalocyanine analogue dicarbahemiporphyrazine with manganese, iron, and cobalt results in the formation of low-coordinate metal(II) complexes. All three compounds are produced by the reaction of metal carbonyls with the free base macrocycle. As in many other carbaporphyrinoids, the internal C-H bonds remain intact upon metallation, resulting in the formation of two long-range agostic-type interactions. Each metal can thus be considered as a three-coordinate ion, where two inner isoindolene nitrogens and a single axial pyridine are bound to the metal. The manganese and cobalt complexes, Mn(dchp)py and Co(dchp)py, are nearly isostructural, but the iron complex, Fe(dchpH2)py, exhibits a reduction at an iminic double bond upon metallation.