Stereoselective Halogenation of Integral Unsaturated C‐C Bonds in Chemically and Mechanically Robust Zr and Hf MOFs

Metal–organic frameworks (MOFs) containing Zr^IV‐based secondary building units (SBUs), as in the UiO‐66 series, are receiving widespread research interest due to their enhanced chemical and mechanical stabilities. We report the synthesis and extensive characterisation, as both bulk microcrystalline and single crystal forms, of extended UiO‐66 (Zr and Hf) series MOFs containing integral unsaturated alkene, alkyne and butadiyne units, which serve as reactive sites for postsynthetic modification (PSM) by halogenation. The water stability of a Zr–stilbene MOF allows the dual insertion of both ?OH and ?Br groups in a single, aqueous bromohydrination step. Quantitative bromination of alkyne‐ and butadiyne‐containing MOFs is demonstrated to be stereoselective, as a consequence of the linker geometry when bound in the MOFs, while the inherent change in hybridisation and geometry of integral linker atoms is facilitated by the high mechanical stabilities of the MOFs, allowing bromination to be characterised in a single‐crystal to single‐crystal (SCSC) manner. The facile addition of bromine across the unsaturated C?C bonds in the MOFs in solution is extended to irreversible iodine sequestration in the vapour phase. A large‐pore interpenetrated Zr MOF demonstrates an I₂ storage capacity of 279 % w/w, through a combination of chemisorption and physisorption, which is comparable to the highest reported capacities of benchmark iodine storage materials for radioactive I₂ sequestration. We expect this facile PSM process to not only allow trapping of toxic vapours, but also modulate the mechanical properties of the MOFs.     

Structurally Defined Molecular Hypervalent Iodine Catalysts for Intermolecular Enantioselective Reactions

Molecular structures of the most prominent chiral non‐racemic hypervalent iodine(III) reagents to date have been elucidated for the first time. The formation of a chirally induced supramolecular scaffold based on a selective hydrogen‐bonding arrangement provides an explanation for the consistently high asymmetric induction with these reagents. As an exploratory example, their scope as chiral catalysts was extended to the enantioselective dioxygenation of alkenes. A series of terminal styrenes are converted into the corresponding vicinal diacetoxylation products under mild conditions and provide the proof of principle for a truly intermolecular asymmetric alkene oxidation under iodine(I/III) catalysis.     

A Cooperative Strategy for the Highly Selective Intermolecular Oxycarbonylation Reaction of Alkenes using a Palladium Catalyst

A novel method for intermolecular functionalization of terminal and internal alkenes has been designed. The electrophilic reagent, hypervalent iodine, plays a key role in this process by activating the alkene C=C bond for nucleophilic addition of the palladium catalyst. This process generates an iodonium‐containing palladium species which undergoes CO insertion. The new approach, intermolecular oxycarbonylaton reactions of alkenes, has been achieved and carried out under mild reaction conditions to produce the corresponding β‐oxycarbonylic acids with excellent efficiencies and levels of regio‐ and diastereoselectivity.     

Iodine-catalyzed N-sulfonylation of benzotriazoles with sodium sulfinates under mild conditions

A new and convenient procedure is developed for the preparation of N-sulfonylbenzotriazoles from sodium sulfinates and benzotriazoles using molecular iodine as catalyst via the S–N bond formation reaction. This catalytic radical sulfonylation proceeds efficiently in air at room temperature under neutral conditions, and in short reaction time, to afford the corresponding N-sulfonylbenzotriazoles in good yields, thus extending the catalytic application of molecular iodine in organic synthesis.     

Unusual oxidative cleavage of the aryl—ethynyl bondsin (arylethynyl)polymethylbenzenes with iodine in dimethyl sulfoxide

While heating 1,2,4,5-tetramethyl-3,6-bis(phenylethynyl)benzene, 1,3,5-trimethyl-2,4-bis(phenylethynyl)benzene, and 1,2,4,5-tetramethyl-3-(phenylethynyl)benzene with iodine in DMSO in the absence of oxygen, the triple bonds are oxidized to give the corresponding 1,2-diketones. In the presence of oxygen, the previously unknown competitive oxidative process causes the cleavage of the aryl—ethynyl bonds so that duroquinone and the corresponding 4-hydroxybenzils are formed. This cleavage is produced by oxygen only in the presence of iodine and DMSO. It was shown that the key stage of the process is the formation of intermediate charge-transfer complexes between polymethylbenzene rings and iodine.     

An advantageous synthesis of new indazolone and pyrazolone derivatives

The synthesis of new indazolone and pyrazolone derivatives starting from methyl anthranilate type substrates is presented. This general approach constitutes a novel and advantageous alternative for the synthesis of the target heterocycles, which implies the use of the environmentally friendly oxidizer PIFA. The synthetic design includes the oxidation of N-arylamides by the hypervalent iodine reagent to the corresponding N-acylnitrenium ions, which can be intramolecularly trapped by an amine moiety to furnish the title compounds by formation of a new N-N single bond.     

Characterization of iodine species in the marine aerosol: To understand their roles in particle formation processes

In this contribution, iodine chemistry in the Marine Boundary Layer (MBL) is introduced. A series of methodologies for the measurements of iodine species in the gas and particle phases of the coastal atmosphere has been developed. Iodine species in the gas phase in real air samples has been determined in two field campaigns at the west coast of Ireland, indicating that gaseous iodo-hydrocarbons and elemental iodine are the precursors of new particle formation. Particulate iodine speciation from the same measurement campaigns show that the non-water-soluble iodine compounds are the main iodine species during the marine particle formation. A seaweed-chamber experiment was performed, indicating that gaseous I₂ is one of the important precursors that lead to new particle formation in the presence of solar light in the ambient air at the coastal tidal area.     

A study on the species present in solutions of hypervalent iodine(III) reagents by electrospray ionization mass spectrometry

Solutions of iodobenzene diacetate in CH₃CN, AcOH, MeOH/H₂O and MeOH (with or without base) were analyzed by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). The major species in CH₃CN, AcOH and MeOH/H₂O solutions are [PhI(OAc)₂Na]⁺, [PhI(OAc)₂K]⁺, [PhI]⁺, [PhIOAc]⁺, [PhIOH]⁺, [PhIO₂Ac]⁺, [PhIO₂H]⁺ and the dimer [Ph₂I₂O₂Ac]⁺. On the other hand, MeOH solutions showed [PhIOMe]⁺ as the most abundant species. A similar result was observed adding 2, 3 or 4 equiv of KOH to MeOH solutions. However, in the presence of 10 equiv of KOH, probably occurs the formation of a polymeric material. Similarly, ESI-MS analysis of the MeOH solution of iodobenzene bis(trifluoroacetate) showed a pattern analogous to that observed for the corresponding solutions of PhI(OAc)₂. However, ESI-MS spectral data of PhI(O₂CCF₃)₂ of CH₃CN suggests that the main species in solutions is iodosylbenzene, which contrasts with the results obtained for PhI(OAc)₂.     

Artifact formation from the use of potassium-iodide-based ozone traps during atmospheric sampling of trace organic gases

Trace atmospheric gases have been sampled using potassium-iodide-based reactant traps for ozone removal. GC-MS analysis revealed the presence of organic iodine compounds which were present neither in the atmosphere nor as contaminants of the materials used, but more likely arose from reactions of organic gases or aerosols sampled with reactive iodine or hypoiodite released from reaction of ozone with potassium iodide in the traps. Losses of the individual organic trace gases measured were not, however, observed as a result of this mechanism. Several cautions in identifying unknown compounds from the atmosphere when using potassium iodide ozone traps are discussed.