Linear bis-Coordinate Silver(I) and Iodine(I) Complexes with R3 R2 R1 N Tertiary Amines

Stabilisation of Bromenium Ions in Macrocyclic Halogen Bond Complexes

Halenium ions (X+) are highly reactive electron deficient species that are prevalent transient intermediates in halogenation reactions. The stabilisation of these species is especially challenging, with the most common approach to sequester reactivity through the formation of bis-pyridine (Py) complexes; [(Py)2X]+. Herein, we present the first example of a macrocyclic stabilisation effect for halenium species. Exploiting a series of bis-pyridine macrocycles, we demonstrate that preorganised macrocyclic ligands stabilise bromenium cations via endotopic complexation, impressively facilitating the isolation of a bench stable 'Br+ NO3 -' species. Solid state X-ray crystallographic structural comparison of macrocyclic Br(I) complexes with Ag(I) and Au(I) analogues provides insightful information concerning similarities and stark contrasts in halenium/metal cation coordination behaviors. Furthermore, the first chemical ligand exchange reactions of Br(I) complexes are reported between acyclic [(Py)2Br]+ species and a bis-pyridine macrocyclic donor ligand which importantly highlights a macrocycle effect for halenium cation stabilisation in the solution phase.

Iodine(I) pnictogenate complexes as Iodination reagents

Halogen(I) complexes are widely used as halogenation reagents and traditionally feature homoleptic stabilising Lewis bases, though the recent revitalisation of iodine(I) carboxylate chemistry has provided isolable examples of heteroleptic iodine(I) complexes. This work reports iodine(I) pnictogenate complexes stabilised by a Lewis base (L), Ph2P(O)O─I─L, synthesised via cation exchange from the silver(I) precursor, (Ph2P(O)OAg)n. The complexes were characterised in both solution (1H, 1H-15N HMBC, 31P) and the solid state, and supplemented computationally by DFT studies. Interestingly, these iodine(I) pnictogenates demonstrate a range of stabilities, and have been found to excel as iodination reagents in comparison to carbonyl hypoiodites, with comparable reactivity to the eponymous Barluenga's reagent in the iodination of antipyrine.

Halogen Bonds of Halogen(I) Ions─Where Are We and Where to Go?

Halenium ions, X+, are particularly strong halogen-bond donors that interact with two Lewis bases simultaneously to form linear [D···X···D]+-type halonium complexes. Their three-center, four-electron halogen bond is both fundamentally interesting and technologically valuable as it tames the reactivity of halogen(I) ions, opening up new horizons in a variety of fields including synthetic organic and supramolecular chemistry. Understanding this bonding situation enables the development of improved halogen(I) transfer reactions and of advanced functional materials. Following a decade of investigations of basic principles, the range of applications is now rapidly widening. In this Perspective, we assess the status of the field and identify its key advances and the main bottlenecks. Clearing common misunderstandings that may hinder future progress, we aim to inspire and direct future research efforts.