Predictive catalysis was applied to the reaction of pyridinium 1,4‐zwitterionic thiolates with a copper carbene. Theoretical calculations were first performed to determine the suitability of their annulation reaction and to make predictions about the performance of different copper salts, diazo species, and pyridinium derivatives. With calculations in hand, the experimental conditions were optimized, the scope of the reaction was assessed, and the precision of the predictions was evaluated. Yields up to 90% were obtained for the synthesis of indolizine scaffolds in the reactivity of pyridinium 1,4‐zwitterionic thiolates with a metal carbene. magnified image

Inverse sandwich complexes of Yb and Sm stabilized by a bulky β‐diketiminate (BDI) ligand have been prepared: (BDI)Ln(η⁶,η⁶‐C₆H₆)Ln(BDI); Ln=lanthanide. Coordinated benzene ligands can be neutral, di‐anionic or, often controversially discussed, even tetra‐anionic. The formal charge on benzene is correlated to assignment of the metal oxidation state which generally poses a problem. Herein, we take advantage of the structural similarities found when comparing Ca^II with Yb^II, and Sr^II with Sm^II complexes. In this work, we found an excellent overlap of the Ca/Yb inverse sandwich structures but a striking difference for the Sr/Sm pair. The much shorter Sm−N and Sm‐C₆H₆ distances are strong evidence for a Sm^III‐benzene⁻⁴‐Sm^III assignment. This was further supported by NMR spectroscopy, magnetic susceptibility, reactivity and comprehensive computational investigation.

The trapping of the elusive vinylogous position of a vinyl carbene with an aliphatic C(sp³)−H bond has been achieved for the first time during a silver‐catalyzed carbene/alkyne metathesis (CAM) process. A Tp^x‐containing silver complex first promotes the generation of a donor‐acceptor silver carbene which triggers CAM, generating a subsequent donor‐donor vinyl silver carbene species, which then undergoes a selective vinylogous C(sp³)−H bond insertion, leading to the synthesis of a new family of benzoazepines. Density functional theory (DFT) calculations unveil the reaction mechanism, which allows proposing that the C−H bond insertion reaction takes place in a stepwise manner, with the hydrogen shift being the rate determining step.

The thermodynamic stability of 11 complexes of Cu(II) and 26 complexes of Fe(III) is studied, comprising the ligands pyridoxamine (PM), ascorbic acid (ASC), and a model Amadori compound (AMD). In addition, the secondary antioxidant activity of PM is analyzed when chelating both Cu(II) and Fe(III), relative to the rate constant of the first step of the Haber-Weiss cycle, in the presence of the superoxide radical anion $(O_2^{•-}$) or ascorbate (ASC⁻). Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. The aqueous environment is modeled by making use of the SMD solvation method in all calculations. This level of theory accurately reproduces the experimental data available. When put in perspective with the stability of various complexes of aminoguanidine (AG) (which we have previously studied), the following stability trends can be found for the Cu(II) and Fe(III) complexes, respectively: ASC < AG < AMD < PM and AG < ASC < AMD < PM. The most stable complex of Cu(II) with PM (with two bidentate ligands) presents a $\Delta G_f^0$ value of −35.8 kcal/mol, whereas the Fe(III) complex with the highest stability (with three bidentate ligands) possesses a $\Delta G_f^0$ of −58.9 kcal/mol. These complexes can significantly reduce the rate constant of the first step of the Haber-Weiss cycle with both $O_2^{•-}$ and ASC⁻. In the case of the copper-containing reaction, the rates are reduced up to 9.70 × 10³ and 4.09 × 10¹³ times, respectively. With iron, the rates become 1.78 × 10³ and 4.45 × 10¹⁵ times smaller, respectively. Thus, PM presents significant secondary antioxidant activity since it is able to inhibit the production of ·OH radicals. This work concludes a series of studies on secondary antioxidant activity and allows potentially new glycation inhibitors to be investigated and compared relative to both PM and AG.

The thermodynamic stability of twenty-nine Fe(III) complexes with various deprotonated forms of lipoic (LA) and dihydrolipoic (DHLA) acids, with coordination numbers 4, 5 and 6, is studied at the M06(SMD)/6-31++G(d,p) level of theory in water under physiological pH conditions at 298.15 K. Even though the complexes with LA^- are more stable than those with DHLA⁻, the most thermodynamically stable Fe(III) complexes involve DHLA²⁻. The twenty-four exergonic complexes are used to evaluate the secondary antioxidant activity of DHLA and LA relative to the Fe(III)/Fe(II) reduction by ${\mathrm{O}}_2^{•-}$ and ascorbate. Rate constants for the single-electron transfer (SET) reactions are calculated. The thermodynamic stability of the Fe(III) complexes does not fully correlate with the rate constant of their SET reactions, but more exergonic complexes usually exhibit smaller SET rate constants. Some Cu(II) complexes and their reduction to Cu(I) are also studied at the same level of theory for comparison. The Fe(III) complexes appear to be more stable than their Cu(II) counterparts. Relative to the Fe(III)/Fe(II) reduction with ascorbate, DHLA can fully inhibit the formation of ^•OH radicals, but not by reaction with ${\mathrm{O}}_2^{•-}$. Relative to the Cu(II)/Cu(I) reduction with ascorbate, the effects of DHLA are moderate/high, and with ${\mathrm{O}}_2^{•-}$ they are minor. LA has minor to negligible inhibition effects in all the cases considered.