Distortional isomerism with copper(i) complexes of 3,7-diazabicyclo[3.3.1]nonane derivatives

Abstract

Two structural forms of the tetradentate bispidine ligand (3,7-diazabicyclo[3.3.1]nonane, pyridine-substituted at C2 and C4), coordinated to CuI, are known: a pentacoordinate square pyramidal structure with an acetonitrile completing the coordination sphere, and a tetracoordinate distorted tetrahedral structure, where one of the pyridine groups is dissociated. Similar structures are observed in crystals of the CuI complexes of another tetradentate and two pentadentate bispidine ligands. The structural dynamics in the CuI coordination sphere of the four ligands are probed by 1H-NMR spectroscopy, supported by approximate density functional theory (DFT) calculations. DFT and NMR spectroscopy indicate that there is an additional isomeric form, and experimental as well as computational data lead to the conclusion that the potential energy surfaces are very flat with various shallow minima.

Bispidine Coordination Chemistry

“…13(c)] (226). This behavior is nicely simulated by DFT calculations (226). The computed structures are in acceptable agreement with experimental data (see Table VII), and the energies indicate that for 14 the five-coordinate structure is slightly more stable while the four-coordinate structure is more stable for the methylated ligand 35 (here, the five-coordinate structure could only be located as a transition state).…”

“…There is a second form of this complex, however, which is assigned to a highly symmetrical four-coordinate complex with both pyridine donors coordinated [see Fig. 13(c)] (226). This behavior is nicely simulated by DFT calculations (226).…”

“…12(a)], in Fig. 12(c) with the methylated pyridine group of ligand 35 it is not, suggesting that it is still partially bonded (2.9 Å vs. 2.1-2.2 Å ) (70,226). This suggests that the rotational barrier is low and the orientation of the dangling pyridine group primarily depends on crystal lattice effects.…”

“…For copper(II), this leads to close-lying minima for various isomeric chromophores along Jahn-Teller-active vibrational coordinates (82,194) and for copper(I) this manifests itself in dynamic processes, which involve isomers with changes in coordination number (70,199,226). In both these and other cases, this is a result of a flat potential energy surface with various shallow minima and (in many cases) relatively low-energy barriers for isomer interconversion; that is, in both oxidation states a manifold of geometries are easily accessible.…”

The Mechanism of the (Bispidine)copper(II)‐Catalyzed Aziridination of Styrene: A Combined Experimental and Theoretical Study

“…This is not unexpected and is supported by NMR spectroscopy and DFT calculations of (bispidine)copper(I) complexes. [49,50] We therefore have not done any additional computational studies for these systems.…”