Quantitative Estimates of Steric Effects. Intramolecular Strain Energy Effects on the Stability and Dissociation Rate Constant of Polythia Ether Macrocycle Complexes of Copper(II)
Intramolecular strain energies for a homologous series of copper(I1) polythia ether macrocycle complexes have been calculated and compared with experimentally determined stability constants, dissociation rates, and free energies of formation. For the complexes with the tetrathia macrocycles 1,4,7,10-tetrathiacyclododecane ([ 121-ane-S4), 1,4,7,10-tetrathiacyclotridecane ([ 1 31-ane-S4), 1,4,8,1l-tetrathiacyclotetradecane ([ 14]-ane-S4), 1,4,8,12-tetrathiacyclopentadecane ([ 151-ane-S,), and 1,5,9,13-tetrathiacyclohexadecane ([ 1 61-ane-S4), stability constants and dissociation rate constants decrease with increasing intramolecular strain. The free energy of formation within this series is inversely proportional to intramolecular strain, yielding a “strain-free” free energy of formation of -8.65 (0.66) kcal mol-’ for tetrathia ether macrocycle complexes of copper(I1). The anomalous behavior of the pentathia ether ligand 1,4,7,10,13-pentathiacyclopentadecane ([ 1 5]-ane-S5) is ascribed to entropic terms. The observed agreement with experimentally determined parameters indicates that, while there is no evidence for systematic variations in intramolecular strain with the number of atoms or interactions in a chosen force field model, molecular-mechanics techniques are readily adapted to systems with a variety of nuclei.
American Chemical Society
Brubaker, George R. and Johnson, David W., "Quantitative Estimates of Steric Effects. Intramolecular Strain Energy Effects on the Stability and Dissociation Rate Constant of Polythia Ether Macrocycle Complexes of Copper(II)" (1984). Chemistry Faculty Publications. 28.