Developing more efficient catalysts remains one of the primary targets of organometallic chemists. To accelerate reaching this goal, effective molecular descriptors and visualization tools can represent a remarkable aid. Here, we present a Web application for analyzing the catalytic pocket of metal complexes using topographic steric maps as a general and unbiased descriptor that is suitable for every class of catalysts. To show the broad applicability of our approach, we first compared the steric map of a series of transition metal complexes presenting popular mono-, di-, and tetracoordinated ligands and three classic zirconocenes. This comparative analysis highlighted similarities and differences between totally unrelated ligands. Then, we focused on a recently developed Fe(II) catalyst that is active in the asymmetric transfer hydrogenation of ketones and imines. Finally, we expand the scope of these tools to rationalize the inversion of enantioselectivity in enzymatic catalysis, achieved by point mutation of three amino acids of mononuclear p-hydroxymandelate synthase.

Classical and frustrated Lewis pairs (LPs) of the strong Lewis acid (LA) Al(C₆F₅)₃ with several Lewis base (LB) classes have been found to exhibit exceptional activity in the Lewis pair polymerization (LPP) of conjugated polar alkenes such as methyl methacrylate (MMA) as well as renewable α-methylene-γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-butyrolactone (γ-MMBL), leading to high molecular weight polymers, often with narrow molecular weight distributions. This study has investigated a large number of LPs, consisting of 11 LAs as well as 10 achiral and 4 chiral LBs, for LPP of 12 monomers of several different types. Although some more common LAs can also be utilized for LPP, Al(C₆F₅)₃-based LPs are far more active and effective than other LA-based LPs. On the other hand, several classes of LBs, when paired with Al(C₆F₅)₃, can render highly active and effective LPP of MMA and γ-MMBL; such LBs include phosphines (e.g., P^tBu₃), chiral chelating diphosphines, N-heterocyclic carbenes (NHCs), and phosphazene superbases (e.g., P₄-^tBu). The P₄-^tBu/Al(C₆F₅)₃ pair exhibits the highest activity of the LP series, with a remarkably high turn-over frequency of 9.6 × 10⁴ h⁻¹ (0.125 mol% catalyst, 100% MMA conversion in 30 s, M_n = 2.12 × 10⁵ g mol⁻¹, PDI = 1.34). The polymers produced by LPs at RT are typically atactic (P_γMMBL with ∼47% mr) or syndio-rich (PMMA with ∼70–75% rr), but highly syndiotactic PMMA with rr ∼91% can be produced by chiral or achiral LPs at −78 °C. Mechanistic studies have identified and structurally characterized zwitterionic phosphonium and imidazolium enolaluminates as the active species of the current LPP system, which are formed by the reaction of the monomer·Al(C₆F₅)₃ adduct with P^tBu₃ and NHC bases, respectively. Kinetic studies have revealed that the MMA polymerization by the ^tBu₃P/Al(C₆F₅)₃ pair is zero-order in monomer concentration after an initial induction period, and the polymerization is significantly catalyzed by the LA, thus pointing to a bimetallic, activated monomer propagation mechanism. Computational study on the active species formation as well as the chain initiation and propagation events involved in the LPP of MMA with some of the most representative LPs has added our understanding of fundamental steps of LPP. The main difference between NHC and PR₃ bases is in the energetics of zwitterion formation, with the NHC-based zwitterions being remarkably more stable than the PR₃-based zwitterions. Comparison of the monometallic and bimetallic mechanisms for MMA addition shows a clear preference for the bimetallic mechanism.

Circular plastics defy traditional trade-offs in recyclability-performance and structure-property relationships.