Bispidine-type ligand

Another interesting feature for the coordination chemistry of bispidine-type ligands is that diamines may be used in their synthesis. This hnding gives us access to ditopic ligand systems (see Chart 7) (24, 81, 82). 

Figure 2. Plots of the molecular cations of complexes with novel bispidine-type ligands ...

Borzel, H., Comba, P., Hagen, K. S. et al., Iron coordination chemistry with tetra-, penta- and hexaden-tate bispidine-type ligands, Inorg. Chem. Acta, 337 407-419, 2002. 

Build the bispidine complex using HyperChem and refine the corresponding co-balt(III) and cobalt(II) complexes with MOMEC (note that the force fields are not optimized for tetrahedral chromophores but our aim here is just to compute relative metal-ligand distances). Note, that all these structural optimizations need to be performed with 1,3-nonbonded interactions alone for the angular geometry around the metal ions (i.e., deactivate the Mult. Harm, functions for both metal atom types, either with the force field editor, in the interaction array or in the parameter array, where you can simply set the force constant to zero). Compare your results with those in Table 17.17.1. 

Aromatic substituents at C2 and C4 are to some extent hindered in rotation. This leads to a third type of isomerism in bispidine chemistry (i.e., atropisomer-ism). The activation energy for the rotation around the C2/C4—aryl bond for bispidones with various meta-substituted phenyl groups was determined by various NMR methods and found to be 70-75 kJ mol (23). For a rotation of 180°, which is usually necessary for the coordination of bispidine ligands to metal ions (e.g., 14, see Scheme 14), two energy barriers have to be overcome. The higher is the result of an interaction of the ortho-disposed proton of the aromatic ring with the proton or the alkyl substituent at the N3 amine nitrogen atom. The... 

In a recent example, based on a copper(II/I) couple of a tetradentate bispidine ligand, ivith knoivn copper(II) and copper(I) structures, the molecular mechanics-based analysis, supported in this case by similar DFT calculations, using the above-described free energy perturbation-type approach, indicated that the inner-sphere reorganization energy must be rather small = 18.6kJ see... 

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