(Spectro)Electrochemistry of 3‐(Pyrid‐2‐yl)‐s‐Tetrazine‐ and 1,2‐ (Dihydro)pyridazine Tricarbonylrhenium(I)chloride

Abstract

The electrochemistry and spectroelectrochemistry (SEC) of the three [ReCl(CO)3(N1.69998pt N)], N1.69998pt N=3‐(pyrid‐2‐yl)‐1,2,4,5‐tetrazine [1], 3‐(pyrid‐2‐yl)‐4‐ferrocenyl‐4,5‐dihydropyridazine [1H2Fc], and 3‐(pyrid‐2‐yl)‐4‐ferrocenyl‐pyridazine [1Fc], are reported. The ligand's conjugation affects the reduction potentials as well as intramolecular charge transfers observed in the UV‐vis‐NIR spectrum. The spectroscopic observations were further supported by DFT calculations.

Red Light Absorption of [ReI(CO)3(α-diimine)Cl] Complexes through Extension of the 4,4′-Bipyrimidine Ligand’s π-System

“…In particular, metal-to-ligand charge transfer (MLCT) energies could be shifted towards lower energies via either increased π-conjugation in the α-diimine acceptor ligand [ 21 , 22 , 23 ], the introduction of electron-withdrawing substituents on the α-diimine ligands [ 24 , 25 , 26 , 27 ], or the use of electron-poor ligands, e.g., bidiazines [ 28 , 29 ]. The reported maxima of MLCT transitions in such Re(I) complexes range by up to 529 nm [ 30 , 31 ]. However, biomedical applications in living tissue, such as photodynamic therapy [ 32 ] or light-triggered ligand release [ 33 ], require significant absorbances within the so-called therapeutic window of 600 to 800 nm [ 34 ].…”

Preparation of 3‐Bromo‐1,2,4,5‐tetrazine

“…[24,25] Metal complexes of monosubstituted pyridyl-tetrazines accessible from the title compound 7 were shown to feature excellent rate constants in biorthogonal chemistry. [26,27] Beyond the many biological and biomedical applications of tetrazines, [28] mono substituted halogenated tetrazines have been used in high energy material applications, [29] such as tris(tetrazine)amine [30] or polynitro-alkoxy-tetrazines. [31] Overall, the documented and potential use of bromotetrazine 7 led to its recent commercialization (Note 36).…”