PERIODIDES OF PYRIDINE.²

Abstract

PYRIDINE ALKYL PERIODIDES.i. Pyridine Methyl Pentiodide.-This was obtained in the manner given in detail below, very satisfactorily in preparation I, and with slight impurity in two other preparations, II and III, by different ways, through separation from other periodides. 1 The substance isolated was a condensation-product of this with a second molecule of nitrotoluene ; but this is undoubtedly the primary reduction-product.2 Read at the Springrield meeting of the American Association for the Advancement of Science, September 2, 1895.

Halogen Bonding: An Odd Chemistry?

“…This structure was initially virtually ignored, but following the discovery of its synthetic applicability, [19] halogen(I) complexes have drawn increased attention [20] . Hassel's route to the crystal structure of [bis(pyridine)iodine(I)] + complex might have been serendipitous, as his initial purpose was to investigate a pyridine ⋅ 2I 2 complex; [18,21] nevertheless, he found it to be of “considerable interest” [18] . The high amount of iodine in the sample brought some practical challenges for structural determination, for example, the N−I distances could not be accurately measured.…”

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

“…44 The bond has occasionally also been named a halonium bond 45 and the complexes superhalides. 21,22 We note that halogen(I) com-plexes should not be misconceived with λ 3 -halogane (λ 3iodane, λ 3 -bromane, λ 3 -chlorane) compounds, which sometimes are also termed halonium complexes yet encompass a halogen(III). 46,47 In a 3c4e halogen bond, [D•••X•••D] + , the positive charge of the halenium ion, X + , is transferred to a large extent to the coordinating Lewis bases (D), 13,17,19 and therefore, we recommend the use of the term "halogen(I) complex" as it was initially introduced by Lin and Hope in 1972.…”

“…Importantly, this procedure is unlikely to provide pure product in the presence of protic solvents, such as alcohols or water, which have been used in some initial protocols. 21,57,58 In protic solvents, the protonated Lewis base, or the halogen(I) complex contaminated with it, is formed according to D 2 I + + H 2 O → 2DH + + OI − , where D is the Lewis base. Due to the high electrophilicity of halogen(I), these complexes rapidly react with moisture when not properly dried solvents and glassware are used.…”

“…A further option for the formation of halogen(I) complexes is to mix a strong Lewis base, such as DMAP or a thione, with a dihalogen to generate a halogen(I) complex. 42 This reaction was used in the very first reports on the structural investigation of halogen(I) complexes by Prescott and Trowbridge in 1895 21 as well as by Hope and Hassel in 1961, 58 whose impact on this research field cannot be overstated. 20 This redox reaction does not generate a pure product in high yield, but the product can be isolated through careful crystallization.…”

“…19,20 Halogen-bonded halenium ions, [D•••X•••D], are halogen(I) species that are frequently termed halonium ions. Halogen-bonded halogen(I) ions have been known and been in use for decades 21,22 but for a long time without an understanding of the nature of their bonding. The triiodide ion, […”