Tuning of the Properties of Transition-Metal Bispidine Complexes by Variation of the Basicity of the Aromatic Donor Groups

Abstract

Bispidines (3,7-diazabicyclo[3.3.1]nonanes) as very rigid and highly preorganized ligands find broad application in the field of coordination chemistry, and the redox potentials of their transition-metal complexes are of importance in oxidation reactions by high-valent iron complexes, aziridination catalyzed by copper complexes, and imaging by (64)Cu positron emission tomography tracers. Here, we show that the redox potentials and stability constants of the copper(II) complexes of 15 tetradentate bispidines can be varied by substitution of the pyridine rings (variation of the redox potential over ca. 450 mV and of the complex stability over approximately 10 log units). It is also shown that these variations are predictable by the pKa values of the pyridine groups as well as by the Hammett parameters of the substituents, and the density functional theory based energy decomposition analysis also allows one to accurately predict the redox potentials and concomitant complex stability. It is shown that the main contribution emerges from the electrostatic interaction energy, and the partial charges of the pyridine donor groups therefore also correlate with the redox potentials.

C–H Bond Oxidation Catalyzed by an Imine-Based Iron Complex: A Mechanistic Insight

“…4-Methoxy-2-picolyl aldehyde and 4-nitro-2-picolyl aldehyde were synthesized following a literature procedure. 40 Ligand L6H was prepared according to a published procedure. 30 Synthesis of Ligands.…”

Optimization of Hexadentate Bispidine Ligands as Chelators for 64CuII PET Imaging

“…Note that for the MM calculations a method was used in which the direction of the Jahn–Teller axis is, in contrast to the DFT calculations, pre‐imposed). A DFT‐based energy decomposition analysis (EDA) was also performed to compute the relative energies of the copper(II) complexes with L 1 and L 2 (see Table ).…”

“…The redox potentials of Cu II/I couples have been correlated with the copper(II) complex stabilities, under the assumption that Cu I complex stabilities are nearly constant for a large range of ligand systems . The computed release of strain due to substitution of one pyridine group by a pyridazine is supported by the solid‐state and solution structural properties.…”

“…Approaches for optimizing the selectivity of bispidine‐type ligands for forming Cu II complexes and the stability of these complexes have included the design of macrocyclic bispidine derivatives, substitution of the pyridine donors as the classical bispidine ligands (Figure ) and ligands with pyridine donors substituted by picolinate or phosphonate groups . Here, we describe the Cu II and related Zn II chemistry of a hexadentate bispidine ligand L 1 , in which py3 is replaced by a pyridazine .…”

Studies towards development of asymmetric double-Mannich reactions of chiral 2-oxocyclohexanecarboxylate derivatives with bis(aminol)ethers

“…HRMS (EI þ ) Found: 345.1575 calcd: 345.1576. Diastereomer B: R f ¼0.23 (3:1 n-hexanes/EtOAc); C, C]O); IR: n max (film)/cmÀ1 ; 3417, 2937, 2866, 1779, 1698, 1455, 1388, 1343, 1219, 1196, 1164, 1117, 1088, 1068; MS m/z (EI þ ) 345 (M þ , 1), 279(18), 167 (40), 149 (100), 113 (10), 71(23), 57 (32), 43(21). HRMS (EI þ ) Found: 345.1575 calcd: 345.1576.4.4.8.2.…”