Ligand binding by metalloporphyrins. III. Thermodynamic functions for the addition of substituted pyridines to nickel(II) and zinc(II) porphyrins

Abstract

Here Aveq and Av&x are the contact shifts for a given proton in the "frozen" equatorial and axial environments and X\ and Xs are the mole fractions of the chelate rings in the X and conformations.28 The methylene protons in the Ni(II) complex of AT-methylethylenediamine are observed at -112 and -127 ppm.7 Our results suggest that the "frozen" contact shifts for the primary amine would be the same as for the ethylenediamine complex, namely, Aveq = -162 and = -10 ppm, and that the primary amine proton would be the one observed at Ajobad = -112 ppm. Making these substitutions and remembering = 1 -Xs, we can calculate Xs = 0.66 from eq 4. This means that twice as many methyl groups are in equatorial as axial (28) When a ring changes from the to the X conformation, a proton is moved from an equatorial to an axial position.Cole, Curthoys, Magnusson, and Phillips positions. Ho and Reilley reported 4 times as many equatorial as axial methyl groups for IV.iV'-dimethylethylenediamine, which has twice as many methyl groups and hence greater preference for the conformation. Using this value of Xs and assuming that the shift of the axial proton for the secondary amine is -6 ppm, as it is in N, '-dimethylethylenediamine, we can write eq 4 for the signal at -127 ppm with only Aveq as an unknown. We then find Aveq for the secondary amine is -189 ppm which is in excellent agreement with the -188 ppm reported by Ho and Reilley7 for N,Nfdimethylethylenediamine. Thus the assignment of the peak observed at -127 ppm to proton b is consistent with the reported shifts of ethylenediamine and N,N'dimethylethylenediamine and our calculations.

Coordination‐Induced Spin Crossover (CISCO) through Axial Bonding of Substituted Pyridines to Nickel–Porphyrins: σ‐Donor versus π‐Acceptor Effects

“…[5] The corresponding thermodynamic parameters for the system Ni-TPP/pyridine have also been determined. [10] For the design of a spin switch based on the coordinationinduced spin crossover (CISCO) effect, that is, by controlled coordination/decoordination of an axial ligand, we determined the thermodynamic parameters of both coordination stages by measuring the temperature dependence of K 1S and K 2 . In an ideal system K 1S should be considerably larger than K 2 to provide the possibility to switch the spin state by adding/removing a single ligand.…”

One-pot synthesis of nickel porphyrins with 2-pyridine-acetyl substituents: the unexpected Sonogashira cross-coupling products

“…Interestingly, adding extra water seemed to increase the yield of Zn 1 0 (Entry 6). The difference between the nickel and the zinc porphyrin reactions is possibly due to the facts that: (1) zinc(II) is a d 10 close-shell ion and nickel(II) is a d 8 open-shell ion, and (2) zinc(II) porphyrins form the 5-or 6-coordinated complex fairly easily [19] while nickel(II) porphyrins are usually 4-coordinated unless dissolved in strongly ligating solvents, such as pyridine or piperidine [20]. These two factors are likely to affect the geometry, the energy and the electronic structure of these porphyrins, resulting in the difference in the reactivities.…”

Metalloporphyrin receptors for bases

“…Data on the thermodynamic parameters of reactions (1) and (2) involving porphyrin complexes with Fe II , Co II , Zn II , Ni II , Hg II , Cd II , Cu II , and Mg II , as well as with Mn III , Fe III , and Co III , were obtained for a large number of additional ligands of different nature. [19][20][21][22][23][24] The influ ence of the nature of the molecular ligand on stability of mixed complexes was considered in several studies. 21- 25 The main conclusion drawn in these publications is that the thermodynamic constants of substitution (of anions and solvent molecules) in porphyrin complexes with mo lecular ligands of different nature does not, in the general case, linearly correlate with the basicity constants, except for sterically unhindered structurally similar ligands of similar nature.…”

“…(20) The reactions of (AcO)CrTPP with Im (21), (22), and Py (23), (24) are more complex than reaction (21). 37 The reaction with Im involves the reversible coordi nation of Im (K 1 = 2300 L mol -1 , the forward reaction rate constant k 1 = 2.18 s -1 mol -1 L), the replacement of AcO -in the six coordinate (AcO)(Im)CrTPP complex with Im (K 2 = 820 L mol -1 ), and the irreversible forma tion of the outer sphere complex [(Im)CrTPP] + (AcO) -(k = 2500 s -1 mol -2 L 2 ) after equilibration in the first reaction step (see Tables 6 and 7).…”