Helical chirality of pyrrolo[1,2-a][1,10]phenanthroline derivatives

The objective of the study was to confirm by X-ray analysis the phenomenon of helical chirality inferred from solution H-1-NMR data for a series of derivatives based on the novel pyrrolo[1,2-a][1,10] phenanthroline system. The syntheses of the title compounds and their H-1-NMR data are presented. Crystals of the representative compound ethyl, 1( 4-phenylbenzoyl)-pyrrolo[ 1,2-a][ 1,10] phenanthroline-3-carboxylate, with molecular formula C31H22N2O3, were found to crystallize in the triclinic system, space group P (1) over bar with a = 7.8541( 1), b = 11.2605( 2), c = 13.4093( 3) angstrom, alpha = 92.244( 1), beta = 90.292( 1), gamma = 106.475( 1)degrees and Z = 2. The X-ray analysis revealed the predicted helicity of the phenanthroline system as well as its origin, namely the proximity of the pyridine N atom and the carbonyl C atom of the phenylbenzoyl residue, with non-bonded distance N center dot center dot center dot C of only 2.465( 2) angstrom. A secondary, but significant distortion, involving displacement of the carbonyl C atom by more than 0.5 angstrom from the pyrrole ring, was evident. The crystal structure is maintained by C-H center dot center dot center dot O hydrogen bonds and pi - pi interactions.