This Feature Article reviews the structural motifs and catalytic applications of crown ether-containing catalysts and details the development of “pincer-crown ether” ligands for applications in controlled catalysis.

The catalytic transposition of double bonds holds promise as an ideal route to alkenes with value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst is developed for the selective production of either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on non-covalent modifications. File list (9) download file view on ChemRxiv Camp_SwitchableRegioselectivity_Manuscript_ChemRxiv... (2.31 MiB) download file view on ChemRxiv Camp_SwitchableRegioselectivity_SI_ChemRxiv_Submis... (3.22 MiB) download file view on ChemRxiv 215c5b.cif (1.97 MiB) download file view on ChemRxiv 218c6a.cif (1.67 MiB) download file view on ChemRxiv 315c5b.cif (1.89 MiB) download file view on ChemRxiv 318c6a.cif (3.47 MiB) download file view on ChemRxiv 318c6b.cif (1.97 MiB) download file view on ChemRxiv Na118c6a.cif (1.31 MiB) download file view on ChemRxiv 218c6b.cif (3.23 MiB)

A series of 1,1′-bis(sulfonyl)ferrocene compounds were produced via the 1,1′-bis(sulfonate)ferrocene ammonium salt. This compound can be readily converted to 1,1′ bis(sulfonylchloride)ferrocene. Varying stoichiometry and reaction times, both mono- and bis-sulfonamide derivatives can be synthesized. All new compounds presented in this report have been structurally characterized. The structures of the bis-sulfonamide systems are similar to the well-studied bis(amide) ferrocene compounds. Intermolecular hydrogen bonding is observed, typically between NH and SO groups of neighboring sulfonamides. However in the bis(GABA) derivative, intermolecular NH to CO hydrogen bonding interactions are present.