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

Abstract

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.

Accurate Prediction of the Excited States in the Fully Conjugated Porphyrin Tapes across the Full Spectral Range: A Story of the Interplay between π–π* and Intramolecular Charge-Transfer Transitions in Soft Chromophores

“…For instance, in the case of parent porphyrin 1 , all geometry optimizations in the gas phase and solution resulted in a stable structure of the D 4 point group with a nearly (but not exactly) planar macrocycle and phenyl groups, which were tilted from the perpendicular position by ∼20°. Such a D 4 point group geometry is in agreement with the previous reports on MTPP complexes optimized by the DFT method . When the geometry of ZnTPP 1 was forced into the D 4 h point group during geometry optimizations, the frequency calculations on converged geometries were suggestive of the transition state (negative predicted frequencies) rather than local or global minima and this was also the case for the ZINDO/1 optimized geometry of 1 .…”

“…Such a D 4 point group geometry is in agreement with the previous reports on MTPP complexes optimized by the DFT method. 67 When the geometry of ZnTPP 1 was forced into the D 4h point group during geometry optimizations, the frequency calculations on converged geometries were suggestive of the transition state (negative predicted frequencies) rather than local or global minima and this was also the case for the ZINDO/1 optimized geometry of 1. In the case of porphyrin tapes 2−12, with the DFT calculations, we found that the highest symmetry that converged to the stationary point belongs to the D 2 point group.…”

“…Time-dependent density functional theory (TDDFT) methodology offers a reasonable computational cost, a variety of specifically tuned exchange-correlation functionals, and good accuracy for the large π-extended systems. − The TDDFT approach was successfully applied for the accurate prediction of the vertical excitation energies in porphyrins, phthalocyanines, and their structural analogues. Two research groups have recently attempted to find the best TDDFT methodology for a large group of phthalocyanines and their analogues substituted with electron-donating groups. , These systems have UV–vis spectra that are composed of the combination of the macrocycle-centered π–π* transitions and interligand charge-transfer bands.…”

Ruthenium N‐Confused Porphyrins: Selective Reactivity for Ambident 2‐Heteroatom‐Substituted Pyridines Serving as Axial Ligands

“…These two forms along with the third tautomeric 3H′‐form (three inner protons, two from sp 3 ‐CH 2 and one from NH) of NCP play an important role when complexing the metal ions inside of the core. That is, the 2H‐form and 3H′‐form serve as dianionic ligands, whereas the 3H‐form serves as a trianionic ligand (Figure b) . Although the 3H′‐form is not isolated as a genuine form but by tethering the substituent at the inner sp 3 ‐carbon atom, the dianionic coordination environment can be easily formed…”

“…That is, the 2H-form and 3H'-form serve as dianionic ligands, whereas the 3H-form serves as a trianionic ligand ( Figure 1b). [3,4] Although the 3H'-form is not isolated as a genuine form but by tethering the substituent at the inner sp 3carbon atom, the dianionic coordination environment can be easily formed. [5][6][7][8][9][10][11] The inner carbon atom, particularly in the form of a carbonÀ metal bond in the NCP core, is susceptible to various reactions such as alkylation, [5,6] fluoroalkylation, [7] nitration, [8] oxygenation, [9] sulfurization, [10,11] and phosphorization.…”