1,1′-Biisoquinolines—Neglected Ligands in the Heterocyclic Diimine Family That Provoke Stereochemical Reflections

Abstract

1,1′-Biisoquinolines are a class of bidentate nitrogen donor ligands in the heterocyclic diimine family. This review briefly discusses their properties and the key synthetic pathways available and then concentrates upon their coordination behaviour. The ligands are of interest as they exhibit the phenomenon of atropisomerism (hindered rotation about the C1–C1′ bond). A notation for depicting the stereochemistry in coordination compounds containing multiple stereogenic centers is developed. The consequences of the chirality within the ligand on the coordination behaviour is discussed in detail.

Through a Glass Darkly—Some Thoughts on Symmetry and Chemistry

“…I note that when multiple different stereogenic motifs are present in a compound, IUAPC is not yet helpful in defining in what sequence or where in the name the variousdescriptors should be placed. I have discussed this in detail in the context of chiral metal complexes containing both stereogenic metal centers and chiral ligands [321]…”

Stereoelectronic Profiling of Neutral and Monoanionic Biimidazoles and Mixed Diimines

“…Aromatic six-membered 1,2-diimines, such as 2,2′-bipyridine and 1,10-phenanthroline, are among the most widely used bidentate ligands in coordination chemistry due to their versatility and aromatic character. − …”

Synthesis and Coordination Chemistry of a Benzannulated Bipyridine: 6,6′-Biphenanthridine

“…Benzannulation can also impart axial chirality by restricting rotation about a single bond, as seen in prototypical ligands based on 1,1′-binaphthalene such as BINOL and BINAP. 13,14 With respect to benzannulated derivatives of the canonical, bidentate N-heterocyclic ligand 2,2′-bipyridine (bpy) and its annulated analogue 1,10phenanthroline, 15 the ligands 2,2′-biquinoline and 1,1′biisoquinoline 16 have been among the more popular (Figure 1). 17 In the context of ruthenium polypyridyl complexes, the benzannulation in 2,2′-biquinoline ligands has been exploited in the design of photochemical molecular devices, 18 longwavelength sensitizers for dye-sensitized solar cells, 19,20 and DNA binders and photocleavage agents.…”

“…Extending the π-system of conjugated ligands through benzannulation is a widely used strategy for influencing electronic transitions in transition metal − and main-group complexes. − This strategy provides flexibility in the design of new emissive molecules and photosensitizers by enabling photophysical properties to be controlled without extensive changes to molecular shape. Benzannulation can also impart axial chirality by restricting rotation about a single bond, as seen in prototypical ligands based on 1,1′-binaphthalene such as BINOL and BINAP. , With respect to benzannulated derivatives of the canonical, bidentate N -heterocyclic ligand 2,2′-bipyridine (bpy) and its annulated analogue 1,10-phenanthroline, the ligands 2,2′-biquinoline and 1,1′-biisoquinoline have been among the more popular (Figure ). In the context of ruthenium polypyridyl complexes, the benzannulation in 2,2′-biquinoline ligands has been exploited in the design of photochemical molecular devices, long-wavelength sensitizers for dye-sensitized solar cells, , and DNA binders and photocleavage agents. , Ruthenium­(II) complexes of 1,1′-biisoquinolines have found application as water oxidation catalysts and hydrogenation catalysts, while endotopic, sterically non-hindering 3,3′-biisoquinolines have been employed to construct molecular shuttles and rotors .…”