Highly reducible π-extended copper corroles

Abstract

Di- and octa-phenylethynyl (PE) substituted π-extended copper corroles were synthesized and characterized as to their structural, electrochemical and spectroscopic properties. The addition of two or eight PE groups to the β-pyrrole positions of the corrole results in dramatic red shifts in the electronic absorption spectra and new reductions which are not seen for the parent compound lacking PE substituents. CuCor(PE) is reduced in four reversible one-electron transfer steps to give derivatives of [CuCor(PE)] where n = 1, 2, 3 or 4. Variable temperature H NMR and EPR measurements were carried out and suggest that the octa- and di-PE substituted Cu-corroles can both be described as an antiferromagnetically coupled Cu corrole cation radical which is in equilibrium with a triplet state, possibly due to a lower singlet-triplet energy gap as compared to 1 and 2 at room temperature. The EPR spectra of one-electron oxidized and one electron reduced species exhibited the characteristics of Cu(ii) corroles. The products generated in the first two reductions of each π-extended corrole were characterized by thin-layer spectroelectrochemistry, thus providing new insights into how UV-vis spectra of highly reduced corroles vary as a function of the number of PE groups and overall charge on the molecule. The singly reduced and singly oxidized copper corroles were also chemically generated in CHCN and shown to have UV-visible spectra almost identical to the spectra obtained by electroreduction or electrooxidation in PhCN or THF containing 0.1 M tetrabutylammonium perchlorate.

Electrochemistry of Bis(pyridine)cobalt (Nitrophenyl)corroles in Nonaqueous Media

“…Earlier electrochemical studies of cobalt corroles have often assigned the oxidation states and sites of electron transfer based on what was known for the related cobalt porphyrins, namely, cobalt­(III)/cobalt­(II), cobalt­(II)/cobalt­(I), or cobalt­(III)/cobalt­(IV) in the case of the metal-centered reactions and π-cation or π-anion radicals when the electrode reaction involves the conjugated macrocycle . However, the site of electron transfer is not so clear in the case of transition-metal corroles, which have been characterized as possessing a noninnocent macrocycle, the most-often-cited examples of which have been given for corrole derivatives containing copper or iron ions. ,,,,,− …”

Old Dog, New Tricks: Innocent, Five-coordinate Cyanocobalt Corroles

“…The electrochemical and spectroscopic properties of numerous corroles possessing a wide variety of meso - and β-pyrrole substituents have been reported over the last three decades. − Many of these reports have focused on the use of these compounds for applications as redox and bioinspired catalysts − or sensors, − with the focal point of cobalt corrolate application involving oxygen reduction ,− and carbon monoxide detection. − Moreover, a particular emphasis of corrole research has been placed on unveiling the electronic configuration of the molecule ,− to aid in the design of new catalysts . The propensity of the corrole macrocycle to behave as a noninnocent ligand under specific conditions has often hindered the ability to definitively assign an exact metal and ligand oxidation state, but published reports from our laboratory ,,− and others ,,,,,− have clearly demonstrated that noninnocent corrole macrocycles are significantly easier to reduce than innocent macrocyclic systems having the same formal oxidation state of the central metal ion, thus providing insights into the electronic configuration of the molecule.…”

“…Both direct and indirect spectroscopic criteria, such as X-ray absorption spectroscopy (XAS), electron paramagnetic resonance spectroscopy, and UV–visible spectroscopy, laid out by Ganguly and Ghosh have been used to classify ligand noninnocence. In our own reports, we established an electrochemical litmus test, where the existence of extremely facile reductions (∼0.00 to −0.20 V vs saturated calomel electrode (SCE)) for transition-metal corroles can be used as one criterion to establish the presence of a noninnocent ligand in the case of metallocorroles with iron, cobalt, nickel, or copper. ,,,− For example, in the case of cobalt triarylcorroles, the four-coordinate complexes are reduced at the macrocycle (eq ), while the six-coordinate species are reduced at the central metal ion (eq ), giving, in both cases, the same cobalt­(II) reduction product. …”

Versatile Synthesis of Siloxy Silicon Tetrabenzotriazacorroles and Insight into the Mode of Macrocycle Formation

“…Both bands of Tbc compounds exhibit high extinction coefficients and on the same order of magnitude (∼10 5 L mol –1 cm –1 ). , Thus, Tbcs have the unique ability to absorb light at high intensities in two regions of the visible spectrum, both the blue and red regions. In contrast, the absorbance of corroles, a similar family of well-studied asymmetric compounds, is skewed having Soret-bands with extinction coefficients an order of magnitude higher than the Q-bands . Triazacorroles, on the other hand, have relatively matching absorbance intensities between their Soret- and Q-bands but with lower extinction coefficients relative to Tbcs …”