Supramolecular axial chirality in [N–I–N]⁺-type halogen bonded dimers

Abstract

The [N–I–N]+-type halogen bond performed as a powerful tool for the construction of functional axial chiral compounds, enriching the toolbox for asymmetric synthesis and optics.

A zinc porphyrin-based halogen-bonded organic framework with the heavy atom effect as a highly efficient photocatalyst for oxidative coupling of amines

“…2e and S22†), revealing that [(ZnTPP) 2 I] + possessed a smaller Δ E ST , which could benefit from the existence of I + with the HAE. 50 According to these results, the efficient excited state relaxation and 1 O 2 generation route of XOF-ZnTPP was further illustrated (Fig. 2f).…”

“…The peak at 1594 cm −1 corresponding to the pyridine groups in ZnTPP shifted to 1605 cm −1 after the reaction, which resulted from the formation of [N⋯I + ⋯N] complexes which lowered the electron density of pyridine, confirming the coordination of pyridine groups between I + . 50 The UV-vis spectroscopy analysis of XOF-ZnTPP in the solid state unveiled a minor red shift when compared to the ZnTPP monomer (Fig. S4†).…”

Mono- and Bis-Carbonyl Hypoiodites of the Tertiary Amines Quinuclidine and DABCO

“…23−28 32 While a few examples of heteroleptic, [L1−I−L2] + , iodine(I) complexes do exist in the solid state, 33,34 these have been found to be susceptible to ligand scrambling in solution, often resulting in mixtures also containing the disproportionation products [L1−I−L1] + and [L2−I−L2] + , 33,35 though recently this problem has been deftly side-stepped for pairs of monotopic ligands via the inducement of axial chirality in homoleptic complexes. 36 On the other hand, hypoiodites of the form the RC(O)O−I−L are inherently heteroleptic in their substituents, offering a greater variety of options for modifying their substituents and ultimately tuning their properties, such as the first chiral hypoiodite complexes being recently reported based on chiral N-protected amino acids. 37 A handful of examples of [N−I−N] + iodine(I) complexes incorporating tertiary amines as the Lewis base have been synthesized, 38 though only the bicyclic tertiary amines quinuclidine (quin), 39−41 34,42 and hexamethylenetetramine (HMTA) 43 have been structurally characterized due to their relative stability in comparison to their acyclic counterparts.…”

“…Historically, the [N–I–N] + iodine­(I) complexes have overwhelmingly existed as homoleptic species incorporating aromatic Lewis bases, ,,,,− i.e., [L1–I–L1] + (L = Lewis base), including the eponymous Barluenga’s reagent [py–I–py]­BF 4 (py = pyridine) . While a few examples of heteroleptic, [L1–I–L2] + , iodine­(I) complexes do exist in the solid state, , these have been found to be susceptible to ligand scrambling in solution, often resulting in mixtures also containing the disproportionation products [L1–I–L1] + and [L2–I–L2] + , , though recently this problem has been deftly side-stepped for pairs of monotopic ligands via the inducement of axial chirality in homoleptic complexes . On the other hand, hypoiodites of the form the RC­(O)­O–I–L are inherently heteroleptic in their substituents, offering a greater variety of options for modifying their substituents and ultimately tuning their properties, such as the first chiral hypoiodite complexes being recently reported based on chiral N-protected amino acids …”

Iodine(I) pnictogenate complexes as Iodination reagents

“…The utility of halogen bonding as a productive non-covalent interaction has been realised over the last few decades, with applications in a myriad of host–guest systems (e.g., chemical or biomolecular separations) and the preparation of functional materials (e.g., liquid-crystalline, magnetic, phosphorescent, porous) 1 – 4 . Halogen bonding, defined as the interaction between an electrophilic region of a halogen atom with neutral or anionic nucleophiles 5 , is also adept toward the assembly of supramolecular architectures 6 – 11 , largely owing to its highly directional bonding. This is especially true for the sub-class of halogen bonded species, halogen(I) (halenium) ions, which are fully polarised halogen atoms (X + ; X = I, Br, Cl) that demonstrate linear 2-coordinate complexes of the form [L─X─L] + in the presence of a pair of suitable Lewis bases (L) 12 – 18 , which have also been incorporated into supramolecular iodine(I) architectures 19 – 23 .…”