Synthesis and structural characterization of heteroleptic dipyridophenazine–based [Cu(N^N)(P^P)]+ complexes.

Abstract

For the purposes of solar–induced multi–electron storage and charge transfer reactions, heteroleptic [Cu(N^N)(P^P)]+ type copper(I) complexes where (N^N)= diimine ligand and (P^P)= bulky diphosphine ligand, have become promising and viable alternatives to noble metal photosensitizers. In this thesis, the synthesis, structural and geometrical configurations of a series of electron–withdrawing para–substituted dipyrido–[3, 2–a: 2’, 3’–c]phenazine(dppz) copper complexes (inclusive of the non-substituted) are studied. With bromo, cyano and 4-methoxycarbonyl nitrophenyl as the substituents and (9,9-Dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane) (xantphos), 1,1'-Bis (diphenylphosphino)ferrocene (dppf) and ([1,1′-Binaphthalene]-2,2′ diyl)bis(diphenylphosphane) (binap) as the (P^P) ligands, the corresponding complexes were synthesized via a one–pot two–step method and characterized using multinuclear NMR, DOSY, FTIR and UV–Vis DR spectroscopy. The dppz ligands were obtained in quantitative yields via bromination, cyanation and Suzuki–type coupling reactions conducted on an intermediate benzothiadiazole scaffold. The cyano and alkyl benzoate derivatives were chosen for the prospective aim of incorporating the complexes into Zr–based MOFs UiO–66 and UiO–68 respectively. The free bromo– and cyano–dppz ligands exhibited severe solubility issues, with NMR characterization being possible upon strong acid addition. The complexes showed satisfying stability upon exposure to air and water with DOSY studies in N–donor solvents showing the fortunate absence of dissociative speciation and ligand exchange reactions leading to the formation of homoleptic species. Through–space correlations and solid– state structures defined by NOESY/ROESY NMR and SC–XRD indicated π–stacking properties among the complexes caused by a distorted tetrahedral coordination sphere around the Cu(I) metal. From the UV-Vis DRS studies, it was inferred that the presence of parasubstituted EWGs on the distal benzenoid ring promoted red-shifting of the absorption properties for both the ligands and complexes within the visible region.