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1. Variation in pnictogen–oxygen bonding unlocks greatly enhanced Brønsted basicity for the monomeric stibine oxide

   https://doi.org/10.1039/D3DT02113K  

   Wenger, John S.; Getahun, Addis; Johnstone, Timothy C. (August 2023, Dalton Transactions)

   Phosphine oxides and arsine oxides feature highly polarized pnictoryl groups (Pn + –O − /Pn = O; Pn = P, As) and react as Brønsted bases through O-centered lone pairs. We recently reported the first example of a monomeric stibine oxide, Dipp 3 SbO (Dipp = diisopropylphenyl), allowing periodic trends in pnictoryl bonding to be extended to antimony for the first time. Computational studies suggest that, as the pnictogen atom becomes heavier, delocalization of electron density from the O-centered lone pairs to the Pn–C σ* orbitals is attenuated, destabilizing the lone pairs and increasing the donor capacity of the pnictine oxide. Herein, we assess the Brønsted basicity of a series of monomeric pnictine oxides (Dipp 3 PnO; Pn = P, As, and Sb). Stoichiometric reactivity between Dipp 3 PnO and a series of acids demonstrates the greatly enhanced ability of Dipp 3 SbO to accept protons relative to the lighter congeners, consistent with theoretical isodesmic reaction enthalpies and proton affinities. 1 H NMR spectrometric titrations allow for the p K aH,MeCN determination of Dipp 3 AsO and Dipp 3 SbO, revealing a 10 6 -fold increase in Brønsted basicity from Dipp 3 AsO to Dipp 3 SbO. The increased basicity can be exploited in catalysis; Dipp 3 SbO exhibits dramatically increased catalytic efficiency in the Brønsted base-catalyzed transesterification between p -nitrophenyl acetate and 2,2,2-trifluoroethanol. Our results unambiguously confirm the drastic increase in Brønsted basicity from Dipp 3 PO < Dipp 3 AsO < Dipp 3 SbO, a direct consequence of the variation in the electronic structure of the pnictoryl bond as the pnictogen atom increases in atomic number. 

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2. Self-assembly of reversed bilayer vesicles through pnictogen bonding: water-stable supramolecular nanocontainers for organic solvents

   https://doi.org/10.1039/d0sc00206b  

   Moaven, Shiva; Watson, Brandon T.; Thompson, Shelby B.; Lyons, Veronica J.; Unruh, Daniel K.; Casadonte, Dominick J.; Pappas, Dimitri; Cozzolino, Anthony F. (May 2020, Chemical Science)

   A new air and moisture stable antimony thiolate compound has been prepared that spontaneously forms stable hollow vesicles. Structural data reveals that pnictogen bonding drives the self-assembly of these molecules into a reversed bilayer. The ability to make these hollow, spherical, and chemically and temporally stable vesicles that can be broken and reformed by sonication allows these systems to be used for encapsulation and compartmentalisation in organic media. This was demonstrated through the encapsulation and characterization of several small organic reporter molecules. 

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3. The complicating role of pnictogen bond formation in the solution-phase and solid-state structures of the heavier pnictogen atranes

   https://doi.org/10.1039/D2DT01377K  

   Moaven, Shiva; Villanueva, Olivia H.; Unruh, Daniel K.; Cozzolino, Anthony F. (August 2022, Dalton Transactions)

   The structure of the simplest stibatrane has been a mystery since it was first prepared in 1966. This study reports the preparation and characterization of two stibatranes from triethanolamine and triisopropanolamine. Solid state structures reveal macrocycles that contain favourable inter- and intramolecular pnictogen bonds. Solution studies, corroborated by DFT analysis, reveal an equilibrium mixture assigned to monomer and pnictogen-bonded dimer. This allowed for the determination of an enthalpy associated with pnictogen bond formation of −27 kJ mol −1 , in line with the supramolecular nature of these interactions. 

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4. Expanding Pnictogen-Assisted Self-Assembly of Disulfide Macrocycles to Include Heteroarenes

   https://doi.org/10.1142/S1088424623500992  

   Zocchi, Luca J.; Davis, Willow A.; Zakharov, Lev N.; Johnson, Darren W. (October 2023, Journal of Porphyrins and Phthalocyanines)

   New routes to the formation of macrocyclic molecules are of high interest to the supramolecular chemistry community and the chemistry community at large. Here we describe the incorporation of heterocyclic core units into discrete macrocycles via the utilization of a pnictogen-assisted self-assembly technique. This method allows for the rapid and efficient formation of discreet macrocyclic units from simple dithiol precursors in high yields with good control over macrocycle size. Up to this point, this technique has been reported on primarily benzylic thiol systems with very little incorporation of endohedral heteroatoms in the resulting assemblies. This study demonstrates the effective incorporation of heterocyclic core molecules allowing for the formation of a more functional cavity, resulting in the formation and crystallization of novel furan- and thiophene-based disulfide dimer and trimer macrocycles, respectively, that are isolated from a range of other larger discrete macrocycles that assemble as well. These disulfide macrocycles can be trapped as their more kinetically stable thioether congeners upon sulfur extrusion. 

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5. Pnictogen Interactions with Nitrogen Acceptors

   https://doi.org/10.1002/anie.202304960  

   Lin, Binzhou; Liu, Hao; Karki, Ishwor; Vik, Erik C.; Smith, Mark D.; Pellechia, Perry J.; Shimizu, Ken D. (May 2023, Angewandte Chemie International Edition)

   Abstract Stabilizing nitrogen pnictogen bond interactions were measured using molecular rotors. Intramolecular C=O⋅⋅⋅N interactions were formed in the bond rotation transition states which lowered the rotational barriers and increased the rates of rotation, as measured by EXSY NMR. The pnictogen interaction energies show a very strong correlation with the positive electrostatic potential on nitrogen, which was consistent with a strong electrostatic component. In contrast, the NBO perturbation and pyramidalization analyses show no correlation, suggesting that the orbital‐orbital component is minor. The strongest C=O⋅⋅⋅N pnictogen interactions were comparable to C=O⋅⋅⋅C=O interactions and were stronger than C=O⋅⋅⋅Ph interactions, when measured using the sameN‐phenylimide rotor system. The ability of the nitrogen pnictogen interactions to stabilize transition states and enhance kinetic processes demonstrates their potential in catalysis and reaction design. 

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