Molecular Structures and Absorption Spectra Assignment of Corrole NH Tautomers

Abstract

The individual absorption spectra of the two NH tautomers of 10-(4,6-dichloropyrimidin-5-yl)-5,15-dimesitylcorrole are assigned on the basis of the Gouterman four-orbital model and a quantum chemical TD-DFT study. The assignment indicates that the red-shifted T1 tautomer is the one with protonated pyrrole nitrogen atoms N(21), N(22) and N(23), whereas the blue-shifted T2 tautomer has pyrrole nitrogen atoms N(21), N(22) and N(24) protonated. A wave-like nonplanar distortion of the macrocycle in the ground state is found for both NH tautomers, with the wave axis going through the pyrroles containing N(22) and N(24). The 7C plane determined by the least-squares distances to the carbon atoms C1, C4, C5, C6, C9, C16, and C19 is suggested as a mean corrole macrocycle plane for the analysis of out-of-plane distortions. The magnitude of these distortions is distinctly different for the two NH tautomers, leading to substantial perturbations of their acid-base properties, which are rationalized by the interplay of the degree of out-of-plane distortion of the macrocycle as a whole and the tendency of the pyrrole nitrogen atoms toward pyramidalization, with the former leading to a basicity increase whereas the latter enhances the acidity.

Synthesis, photophysical properties and spectroelectrochemical characterization of 10-(4-methyl-bipyridyl)-5,15-(pentafluorophenyl)corrole

“…The lower energy region, from 500 to 650 nm, have absorption peaks that correspond to transitions from the corrole p system to the p* molecular orbitals of both the tetrapyrrolic ring and bipyridine, and, at 416 nm, there are transitions from the HOMO to the p* molecular orbitals of the bipyridine and fluorophenyl groups. Those are commonly assigned as the S 0 -S 1 and S 0 -S 2 transitions, respectively [37]. The orbital picture suggesting an electron jump from the HOMO of corrole 2 to the bipyrine is of particular importance, for it demonstrates the possibility of excited state electron transfer in a possible bimetallic complex involving the central ring and a peripheral metal.…”

Origin of the Individual Basicity of Corrole NH-Tautomers: A Quantum Chemical Study on Molecular Structure and Dynamics, Kinetics, and Thermodynamics

“…pyrrolenic ring) in meso-aryl-substituted corroles determines the distinct optical properties and reactivity toward protons for the corresponding NH-tautomers (T1 and T2, see Scheme 1 for the particular structures and assignments). [22][23][24][25][26] Moreover, evidences of the coexistence of two NH-tautomers in fluid solutions at room temperature have been presented. 22,26 In particular, it was found that two NH-tautomers differ in their basicity, which was supposed to be due to different out-of-plane (oop) distortions of the corrole macrocycle and, more specifically, due to out-of-plane tilting of the pyrrolenic ring to be protonated in the different NH-tautomers.…”

“…[22][23][24][25][26] Moreover, evidences of the coexistence of two NH-tautomers in fluid solutions at room temperature have been presented. 22,26 In particular, it was found that two NH-tautomers differ in their basicity, which was supposed to be due to different out-of-plane (oop) distortions of the corrole macrocycle and, more specifically, due to out-of-plane tilting of the pyrrolenic ring to be protonated in the different NH-tautomers. 22,26 In our recent work we focused on experimental assignment and quantum chemical calculations of the UV-vis absorption spectra, as well as on the static ground state geometries of the NH-tautomers of meso-pyrimidinylcorroles.…”

“…22,26 In particular, it was found that two NH-tautomers differ in their basicity, which was supposed to be due to different out-of-plane (oop) distortions of the corrole macrocycle and, more specifically, due to out-of-plane tilting of the pyrrolenic ring to be protonated in the different NH-tautomers. 22,26 In our recent work we focused on experimental assignment and quantum chemical calculations of the UV-vis absorption spectra, as well as on the static ground state geometries of the NH-tautomers of meso-pyrimidinylcorroles. 22,23,[25][26][27][28][29] We have found indeed that the pyrrole ring to be protonated in the quickly reacting T1 tautomer is tilted out of the mean macrocyclic plane approximately three times more than in the slowly reacting T2 tautomer, where it lies almost in with the mean macrocycle plane.…”

“…22,26 In our recent work we focused on experimental assignment and quantum chemical calculations of the UV-vis absorption spectra, as well as on the static ground state geometries of the NH-tautomers of meso-pyrimidinylcorroles. 22,23,[25][26][27][28][29] We have found indeed that the pyrrole ring to be protonated in the quickly reacting T1 tautomer is tilted out of the mean macrocyclic plane approximately three times more than in the slowly reacting T2 tautomer, where it lies almost in with the mean macrocycle plane. 26 In the present work we give new insights in the origin of the basicity/reactivity difference between the two corrole NH-tautomers beyond the steady state geometry differences.…”