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ABSTRACT A series of bridled chiroporphyrins (BCP) and their metal complexes were prepared, in which two n-methylene straps connect adjacent meso substituents by ester linkages. These compounds can exist as four atropisomers (αααα, αβαβ, αααβ, or ααββ) depending on the position of the meso groups relative to the macrocycle (α when above and β when below). We characterized the conformation of these chiral porphyrins and their metal (Zn, Ni, Mn) complexes by vibrational circular dichroism (VCD) associated with ab initio calculations. VCD spectra of the three metalloporphyrins were recorded in CDCl3 and benzene solutions and ab initio calculations of their four atropoisomers were performed at the Density Functional Theory (DFT) level. The bridled chiroporphyrin with the longer straps (9 CH2) and its nickel(II) complex can be isolated as the αβαβ atropisomer in the solid state and were found with the same conformation in CDCl3 and benzene solutions. The bridled chiroporphyrin with the shortest straps (8 CH2) and its zinc(II) complex can be isolated as the αααα atropisomer in the solid state, but in solution they are subject to atropisomeric equilibria, resulting in atropisomer distributions that are strongly solvent-dependent. Comparison of the experimental VCD spectra with the predicted spectra of the four atropisomers allowed the quantification of these distributions. Finally, the manganese(III) complex also exhibits an atropisomeric equilibria in solution which is slightly solvent-dependent. Chirality 25:480-486, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Infrared spectral study of bistable chiral porphyrins. Chiral porphyrins in which adjacent meso substituents are connected by a strap via ester linkages and their metal complexes have been examined by infrared spectroscopy. These compounds can adopt several conformations depending on the length of the strap as well as on the nature of the complexing metal. The multiplicity of the carbonyl stretching vibration is correlated to the symmetry of these complexes, and therefore it provides information on their conformation. This observation is potentially useful in the case of paramagnetic complexes where NMR spectroscopy is uninformative. To cite this article: A. Castaings et al., C. R. Chimie 9 (2006) . [Copyright &y& Elsevier]