Extraplanar ligand-exchange dynamics in (tetraphenylporphinato)zinc(II) and the conformation of zinc(II) porphyrins in solution

Abstract

The extraplanar ligand-exchange dynamics of (tetraphenylporphinato)zinc(II) with pyridine and /V-methylimidazole have been studied at 21 °C in CDC13. For the ZnTPP-py system we find kon = 4.90 X 10s M'1 s'1, ko[f = 1.98 X 105 6s'1, and K = 2300 ± 400 M'1. For the ZnTPP-/V-MeIm system we find kon = 1.67 X 108 M'1 s'1, koñ = 4.78 X 104 s'1, and K = 10 200 ± 600 M"1. An analysis of the steric limitations of ZnTPP and the ligands (pyridine and /V-methylimidazole) suggests that kon is close to, if not at, the diffusion-controlled rate limit. Since the ZnTPP-L complexes are known to have the Zn(II) displaced some 0.3 Á out of the mean plane of the porphyrin ring, a diffusion-controlled kon requires that the unligated ZnTPP also be nonplanar.

FRET Sensitization of Tungsten–Alkylidyne Complexes by Zinc Porphyrins in Self-Assembled Dyads

“…Benesi–Hildebrand analysis of the spectra provides the binding constants K b = 7700 M –1 for ZnTPP( 1 ) and K b = 9100 M –1 for ZnTP Cl P( 1 ); these are of the same magnitude as that for ZnTPP(py) in toluene ( K b = 6000 M –1 ) . The association/dissociation equilibrium for ZnPor( 1 ) is rapid on the NMR time scale, as indicated by the fact that their 1 H NMR spectra exhibit several resonances with concentration-dependent chemical shifts (Figure S12); similar behavior is observed for ZnTPP(py) . Thus, the coordination chemistry of the ZnPor( 1 ) dyads in solution appears to be typical of those of axially ligated zinc–porphyrin complexes.…”

“…83 The association/ dissociation equilibrium for ZnPor(1) is rapid on the NMR time scale, as indicated by the fact that their 1 H NMR spectra exhibit several resonances with concentration-dependent chemical shifts (Figure S12); similar behavior is observed for ZnTPP(py). 84 Thus, the coordination chemistry of the ZnPor(1) dyads in solution appears to be typical of those of axially ligated zinc−porphyrin complexes. The calculated (DFT) molecular structure of ZnTPP(1) (Figure 6) shows a geometry about the zinc center similar to that for other axially substituted zinc−porphyrin compounds 85 and a geometry about the WC(dppe) 2 Cl fragment essentially identical with that of 1 (Table S4).…”

Dipyrrin Zn<SUP>II</SUP> Complexes with Functional Aryl Groups: Formation, Characterization, and Structures in the Solid State

“…[22][23][24] On the other hand, intermolecular interactions such as CH-interactions between pyridyl-2-CH to pyrrole plane (C(H) · · · distance: 3.32 Å) and those from pyridyl-3-CH and pyrrole-CH to pyridyl ring (the respective C(H) · · · distances: 3.51 and 3.50 Å) are observed. Similarly, (Mes-DPR) 2 Zn shows the CH-interactions between methyl-CH to mesityl plane with the C(H) · · · distance of 3.51 Å and those from methyl-CH and pyrrole-3-CH to pyrrole plane with the C(H) · · · distances of 3.…”

One-Step Template-Directed Synthesis of a Macrocyclic Tetraarylporphyrin Hexamer Based on Supramolecular Interactions with a C3-Symmetric Tetraarylporphyrin Trimer

“…Table ), assuming that the maximum possible association rate constant is diffusion controlled, and therefore it cannot exceed the value 10 10 M -1 s -1 (cf. refs f and ). Therefore, as the equilibrium constant equals the quotient of this maximum on-rate divided by the off-rate, an upper limit of the latter should be k = 3.7 s -1 , a value which, within the margin of error, is close to the rate constant ( k 293 = 6.5 s -1 ) derived from the kinetic experiment as explained above.…”