Carborane Guests for Cucurbit[7]uril Facilitate Strong Binding and on Demand Removal

High affinity guest have been reported for the macrocyclic host cucurbit[7]uril (CB[7]), enabling widespread applications, but preventing CB[7] materials from being returned to their guest-free state for reuse. Here we present polyhedral boron clusters (carboranes) as strongly-binding, yet easily removable, guests for CB[7]. Aided by a Pd-catalyzed coupling of an azide anion, we prepared boron-functionalized 9<i>-</i>amino and 9-ammonium modified <i>ortho-</i>carboranes that bind to CB[7] with a <i>K_a</i>=10¹⁰ M^-1. Upon treatment with base, the <i>ortho</i>-carboranes<i> </i>readily undergo deboronation to yield anionic <i>nido</i>-carborane, a poor guest of CB[7], facilitating recovery of guest-free CB[7]. We showcase the utility of the modified <i>ortho</i>-carborane guest by recycling a CB[7]-functionalized resin. With this report, we introduce stimuli-responsive decomplexation as an additional consideration in the design of high affinity host-guest complexes.

Carborane Guests for Cucurbit[7]uril Facilitate Strong Binding and on Demand Removal

High affinity guest have been reported for the macrocyclic host cucurbit[7]uril (CB[7]), enabling widespread applications, but preventing CB[7] materials from being returned to their guest-free state for reuse. Here we present polyhedral boron clusters (carboranes) as strongly-binding, yet easily removable, guests for CB[7]. Aided by a Pd-catalyzed coupling of an azide anion, we prepared boron-functionalized 9<i>-</i>amino and 9-ammonium modified <i>ortho-</i>carboranes that bind to CB[7] with a <i>K_a</i>=10¹⁰ M^-1. Upon treatment with base, the <i>ortho</i>-carboranes<i> </i>readily undergo deboronation to yield anionic <i>nido</i>-carborane, a poor guest of CB[7], facilitating recovery of guest-free CB[7]. We showcase the utility of the modified <i>ortho</i>-carborane guest by recycling a CB[7]-functionalized resin. With this report, we introduce stimuli-responsive decomplexation as an additional consideration in the design of high affinity host-guest complexes.

A Practical Synthesis of 5-Substituted 1H-Tetrazoles from Aldoximes Employing the Azide Anion from Diphenyl Phosphorazidate

5-Substituted 1H-tetrazoles were effectively synthesized from aldoximes and diphenyl phosphorazidate (DPPA) under reflux conditions in xylenes. Various aldoximes underwent the cycloaddition reaction to afford the corresponding 5-substituted 1H-tetrazoles in short reaction times and in good yields. Chiral aldoximes derived from amino acids also gave aminotetrazoles with almost no racemization.

The vibrational spectroscopy of the coordinated azide anion; a theoretical study

DFT has been used to model azide complexes and related model systems, in order to provide an understanding of azide vibrational spectra. The spectra are controlled by the charge distributions and the metal involved. This means that a group theory-based approach will seldom enable an interpretation, even though the azide groups are commonly vibrationally coupled.