We have prepared 1,8-naphthyridines substituted at the 2,7 positions with imines comprising various N-alkyl and N-aryl "R" groups, These compounds constitute tetradentate chelating ligands, N4L, that are "crescent" shaped and quite symmetrical -- leading to diagnostic yet simple 1H-NMR spectra. Iodo and bromo-bridged dicopper(I) complexes N4LCu2X2 have been characterized crystallographically with R = cyclohexyl to reveal short copper-copper distances of ca 2.62 angstroms (X = iodo) vs. 2.69 angstroms (X = bromo). These values are notably short and comparable to those determined in several dicopper enzyme sites (for instance copper A and pMMO - particulate methane monooxygenase). Examples of N4LCu2X2 with X = mercapto have also been prepared though isolation as crystalline solid appears conditional on the steric and electronic features of the imine R group, and the identity of the mercapto R' group. (Crystallographic characterization of bridging mercapto groups has possible relevance to the copper A site, but in this case continues to remain elusive). Herein, we report 1H-NMR spectra of N4LCu2X2 comprising various bridging ligands, with the chemical shifts of the phenyl hydrogens of R' = benzyl and 2,4,6-trimethylbenzyl appearing notably upfield at ca. 5.4 ppm, while the hydrogens on the alpha carbon of the R group are shifted considerably downfield.

Recent developments in the chemistry of dicopper(I)-naphthyridinediimine crescent complexes hosting various bridging ligands

254th National Meeting (2017)

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