New Acridine-Based Tridentate Ligand for Ruthenium(II): Coordination with a Twist

Abstract

A new tridentate ligand based on acridine has been synthetized. The central acridine heterocycle bears two pyridine coordinating units at positions 4 and 5. The terdentate 2,7-di-tert-butyl-4,5-di(pyridin-2-yl)acridine (dtdpa) was then coordinated to a ruthenium(II) cation. The corresponding homoleptic complex could only be obtained where both ligands coordinate to the ruthenium in a fac fashion. Thus, a heteroleptic compound (2) was constructed in combination with a terpyridine ligand in order to constrain the ligand to adopt a mer geometry. Such a coordination imposes a dramatic twist on the acridine heterocycle, resulting in an unexpected photophysical behavior. The electrochemical and photophysical properties of both complexes were studied, and the molecular structure of 2 was determined by X-ray diffraction. The two compounds absorb at low energy wavelengths, and a very weak luminescence is detected only for complex 2 in the near-infrared region.

One-step synthesis of ball-shaped metal complexes with a main absorption band in the near-IR region

“…Although the structure of the auxiliary ligand is rigid and planar, significant bond length alternation was observed. The bond length between the central metal and nitrogen is consistent with typical M–X bonds of hexacoordinated metal complexes 40,41 . Therefore, other metals that favor octahedral hexacoordinated structures might also be used for the synthesis of corresponding Temari-shaped complexes.

Figure 4X-ray crystal structure of ( a ) ruthenium complex 1d and ( b ) iron complex 3 .

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Closed Shell Iron(IV) Oxo Complex with an Fe–O Triple Bond: Computational Design, Synthesis, and Reactivity

“…[45] Unfortunately,upon mixing the neutral ligand with iron(III) nitrate,w ed id not observe any formation of an iron(III) complex, but only the protonated ligand [(L1)H] + appeared in the mass spectrum (Figure S2 in the Supporting Information). To make the ligand less rigid and thus to facilitate accommodation of the iron center, we considered modification of existing acridine-based dtdpa (2,7-di-tert-butyl-4,5-di(pyridin-2-yl)acridone) ligand [46] to acridone L2-H ( Figure 3). We have generated [(L2)Fe III -(NO 3 )] + which lost NO 2 upon collisional activation ( Figure S3 in the Supporting Information).…”

Acridine Variations for Coordination Chemistry

“…Selected acridine-based ligands. [7,8,19] carbon monoxide, and metal catalyst at elevated temperatures and pressures. [15] The Friedel-Crafts alkylation of acridone itself yields 2,7-di-tert-butylacrid-9(10H)-one.…”

“…Jouvenot, Loiseau and coworkers reported this acridone as a precursor to a 4,5-di (pyridin-2yl)acridine ligand, prepared by Stille cross-coupling of a dibromoacridine. [19] We wondered whether cross-coupling of the CÀ Br bonds in acridone 2 could be carried out effectively in the presence of the moderately acidic NH bond. Suzuki-Miyaura coupling successfully installed the p-tolyl group at both positions, giving a 68 % yield of the diarylated product 3 (Scheme 2).…”

“…Reaction of acridone 1 with bromine in acetic acid gives the 4,5‐dibromo derivative 2 (Scheme ). Jouvenot, Loiseau and coworkers reported this acridone as a precursor to a 4,5‐di(pyridin‐2yl)acridine ligand, prepared by Stille cross‐coupling of a dibromoacridine . We wondered whether cross‐coupling of the C−Br bonds in acridone 2 could be carried out effectively in the presence of the moderately acidic NH bond.…”