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Misregulation of transmembrane ion transport in biological systems has been linked to a variety of diseases. As a result, supramolecular chemists have been trying to develop small molecules that facilitate the transmembrane transport of several ionic species. However, ion transport by small molecules is a passive process and needs to be overall charge neutral (i.e., when an ion is transported across a membrane, another ion needs to be transported as well to avoid charge separation). Ion pair receptors could therefore have great potential as transmembrane ion transporters because they can facilitate transport of an overall neutral species. Furthermore, ditopic ion pair receptors also have the potential to transport biologically important zwitterionic species, such as amino acids. In this manuscript, we report the synthesis of a series of ditopic receptors based on squaramides as the anion binding unit and 18-crown-6 as the cation binding unit. UV-vis and NMR titrations revealed that these compounds can bind a variety of chloride salts, especially KCl. Furthermore, liquid–liquid extractions and transport experiments using bulk liquid membranes and liposomes indicate that these ditopic receptors are capable of transporting chloride salts and hydrophilic amino acids. In fact, compound 5 was even able to facilitate the transport of amino acids with charged side chains at physiological pH (arginine and glutamate), making it the first example of a small molecule that can transport these highly polar and charge-dense species. These findings open up the possibility of using these receptors in a wide range of biological applications. 

Iron hydrides are proposed reactive intermediates for N2 and CO conversion in industrial and biological processes. Here, we report a reactivity study of a low-coordinate di(μ-hydrido)diiron(II) complex, Fe2(μ-H)2L, where L2– is a bis(β-diketiminate) cyclophane, with isocyanides, which have electronic structures related to N2 and CO. The reaction outcome is influenced by the isocyanide substituent, with 2,6-xylyl isocyanide leading to H2 loss, to form a bis(μ-1,1-isocyanide)diiron(I) complex, whereas all of the other tested isocyanides insert into the Fe–H bond to give (μ-1,2-iminoformyl) complexes. Steric bulk of the isocyanide substituent determines the extent of insertion (i.e., into one or both Fe–H–Fe units) with tert-butyl isocyanide reacting to yield the mono-(μ-1,2-iminoformyl)diiron(II) complex, exclusively, and isopropyl- and methyl isocyanides affording the bis(μ-1,2-iminoformyl)diiron(II) products. Treatment of Fe2(μ-1,2-CHNtBu)(μ-H)L with 2,6-xylyl isocyanide (or XylNC) yields Fe2(μ-XylNC)2L and tert-butylaldimine as one of the organic products. 

Cyclooctyne reacts with the trianionic pincer ligand supported alkylidyne [^tBuOCO]WCC(CH₃)₃(THF)₂(1) to yield tungstacyclopropene (3) and tungstacyclopentadiene (4) complexes.