A full set of iridium(iv) pyridine-alkoxide stereoisomers: highly geometry-dependent redox properties

© The Royal Society of Chemistry. We introduce and characterize the complete set of possible isomers of IrIV(pyalk)2Cl2 (pyalk = 2-(pyridin-2-yl)propan-2-oate), providing valuable insights on the properties of Ir(iv) species. The pyridine alkoxide ligand strongly stabilizes high oxidation states, essential to accessing the catalytically relevant Ir(iv) state, and results in robust complexes that can be handled under ambient conditions, even permitting chromatographic separation. The redox properties are isomer-dependent, spanning a 300 mV range, rationalized with ligand-field theory and DFT calculations. The reported complexes exhibit very high kinetic inertness against isomerization, despite highly disparate predicted thermodynamic stabilities, presenting a unique opportunity to study all five possible isomeric complexes with the same ligand set

Heterogenized Iridium Water-Oxidation Catalyst from a Silatrane Precursor

A pentamethylcyclopentadienyl (Cp*) iridium water-oxidation precatalyst was modified to include a silatrane functional group for covalent attachment to metal oxide semiconductor surfaces. The heterogenized catalyst was found to perform electrochemically driven water oxidation at an overpotential of 462 mV with a turnover number of 304 and turnover frequency of 0.035 s^(–1) in a 0.1 M KNO3 electrolyte at pH 5.8. Computational modeling of the experimental IR spectra suggests that the catalyst retains its Cp* group during the first hour of catalysis and likely remains monomeric

Theoretical study of a nonpeptidic polydisulfide α-helix †

A carbon-sulfur molecule has been designed as a mimic of peptides. Density functional theory calculations showed that the oxidation of 10 moles of methanedithiol led to a polydisulfide oligomer, HS(CH 2 SS) 9 CH 2 SH. The polydisulfide can adopt an α-helix type of secondary structure, where the chain is coiled. Unlike proteins, the S-S bonds in the polydisulfide function as secondary rather than tertiary structural elements. The helix contains 8 non-hydrogen atoms per turn, 2.7 Å methylenes per turn, a pitch distance of 8.6 Å, and a radius of 1.00 Å. The methylene sites could carry R group residues similar to amino acids. Keywords: peptide mimics; carbon-sulfur polymers; α-helices; disulfides; secondary structure A challenging endeavor is the design of carbon-sulfur molecules as mimics of peptides. Secondary structural details of rubbery C-S polymers including helices, turns, and folds are often difficult to detect spectroscopically. For example, the elastic Thiokol polymer (CH 2 CH 2 SSSS) n formed from the condensation of Na 2 S 4 and 1,2-dichloroethane has many possible conformations (1). On the other hand, π -conjugated carbon-sulfur [n]helicenes are rigid due to the fused connections of the thiophene rings (2). We report here on computations of polydisulfide oligomers (1 and 2) bearing 1,3-SCH 2 S type bondin