Synthesis, spectroscopic properties and theoretical calculations on methylene bridged 1,8-naphthyridine ligands and copper(I) complex through a non-catalyst C(sp3)–H methylenation

Abstract

Two 1,8-naphthyridine derivatives containing methylene, N-(5-methyl-7-((3-oxo-1,3-dihydroisobenzofuran-1-yl)methyl)-1,8-naphthyridin-2-yl)acetamide (L1) and 2-amino-3-((7-amino-4-methyl-1,8-naphthyridin-2-yl)methyl)isoindolin-1-one (L2), as well as a copper(I) complex CuI(L1)₂ (C1) have been synthesized through a non-catalyst C(sp³)–H methylenation process and characterized. The structure of C1 has been determined by X-ray diffraction analysis. The spectroscopic properties have been investigated by experimental as well as theoretical studies for all these compounds. The two ligands exhibit similar electronic absorption spectra with λ_max at about 340 nm, which can be tentatively assigned to π_naph→π_naph* transition. The electronic absorption spectra of C1 exhibits at ~335 nm except in n-hexane, which may be assigned tentatively to the intraligand charge transfer transition. The assignment is further supported by density functional theory calculations and cyclic voltammetry.