A Supramolecular Palladium Catalyst Displaying Substrate Selectivity by Remote Control

Zwitterionic Aqua Palladacycles with Noncovalent Interactions for meta-Selective Suzuki Coupling of 3,4-Dichlorophenol and 3,4-Dichlorobenzyl Alcohol in Water

The site-selective reaction of substrates with multiple reactive sites has been a focus of the current synthetic chemistry. The use of attractive noncovalent interactions between the catalyst and substrate is emerging as a versatile approach to address site-selectivity challenges. Herein, we designed and synthesized a series of palladacycles, to control meta-selective Suzuki coupling of 3,4-dichlorophenol and 3,4-dichlorobenzyl alcohol. Noncovalent interactions directed zwitterionic aqua palladacycles catalyzed meta-selective Suzuki couplings of 3,4-dichloroarenes bearing hydroxyl in water have been developed. Experiments and density functional theory (DFT) calculations demonstrated that the electrostatic interactions play a critical role in meta-selective coupling of 3,4-dichlorophenol, while meta-selective coupling of 3,4-dichlorobenzyl alcohol arises due to the hydrogen-bonding interactions.

Stepwise Oxidative C-C Coupling and/or C-N Fusion of Zn(II) meso-Pyridin-2-ylthio-porphyrins

The synthesis and characterization of zinc(II) meso-pyridin-2-ylthio-porphyrins are presented in this manuscript. The (electro)chemical oxidation of [5-(pyridin-2-ylthio)-10,20-bis(p-tolyl)-15-phenylporphyrinato] zinc(II) or [5,15-bis(pyridin-2-ylthio)-10,20-bis(p-tolyl)porphyrinato] zinc(II) leads to the formation of one or two C-N bond(s) by intramolecular nucleophilic attack of the peripheral thiopyridinyl fragment(s) on the neighboring β-pyrrolic position(s) (C-N fusion reaction). In addition, the chemical oxidation of [5-(pyridin-2-ylthio)-10,20-bis(p-tolyl)porphyrinato] zinc(II), i.e., bearing one free meso position, mainly affords the meso,meso-dimer. Further stepwise electrochemical oxidation selectively produces the mono and bis C-N fused meso,meso-dimer. The resulting pyridinium derivatives exhibit important changes in their physicochemical properties (NMR, UV-vis, CV) as compared to their initial unfused precursors. Also, the X-ray crystallographic structures of three unfused monomers, one unfused meso,meso-dimer, and two C-N fused monomers are presented.

Enzyme-like Supramolecular Iridium Catalysis Enabling C-H Bond Borylation of Pyridines with meta-Selectivity

The use of secondary interactions between substrates and catalysts is a promising strategy to discover selective transition metal catalysts for atom-economy C-H bond functionalization. The most powerful catalysts are found via trial-and-error screening due to the low association constants between the substrate and the catalyst in which small stereo-electronic modifications within them can lead to very different reactivities. To circumvent these limitations and to increase the level of reactivity prediction in these important reactions, we report herein a supramolecular catalyst harnessing Zn⋅⋅⋅N interactions that binds to pyridine-like substrates as tight as it can be found in some enzymes. The distance and spatial geometry between the active site and the substrate binding site is ideal to target unprecedented meta-selective iridium-catalyzed C-H bond borylations with enzymatic Michaelis-Menten kinetics, besides unique substrate selectivity and dormant reactivity patterns.

Modular Synthesis of trans-A2 B2 -Porphyrins with Terminal Esters: Systematically Extending the Scope of Linear Linkers for Porphyrin-Based MOFs

Differently functionalized porphyrin linkers represent the key compounds for the syntheses of new porphyrin-based metal-organic frameworks (MOFs), which have gathered great interest within the last two decades. Herein we report the synthesis of a large range of 5,15-bis(4-ethoxycarbonylphenyl)porphyrin derivatives, through Suzuki and Sonogashira cross-coupling reactions of an easily accessible corresponding meso-dibrominated trans-A2 B2 -porphyrin with commercially available boronic acids or terminal alkynes. The resulting porphyrins were fully characterized through NMR, MS, and IR spectroscopy and systematically investigated through UV/Vis absorption. Finally, selected structures were saponified to the corresponding carboxylic acids and subsequently proven to be suitable for the synthesis of surface-anchored MOF thin films.