Ligands, especially phosphines and carbenes, can play a key role in modifying and controlling homogeneous organometallic catalysts, and they often provide a convenient approach to fine-tuning the performance of known catalysts. The measurable outcomes of such catalyst modifications (yields, rates, selectivity) can be set into context by establishing their relationship to steric and electronic descriptors of ligand properties, and such models can guide the discovery, optimisation and design of catalysts.In this review we present a survey of calculated ligand descriptors, with a particular focus on homogeneous organometallic catalysis. A range of different approaches to calculating steric and electronic parameters are set out and compared, and we have collected descriptors for a range of representative ligand sets, including 30 monodentate phosphorus(III) donor ligands, 23 bidentate P,Pdonor ligands and 30 carbenes, with a view to providing a useful resource for analysis to practitioners. In addition, several case studies of applications of such descriptors, covering both maps and models, have been reviewed, illustrating how descriptor-led studies of catalysis can inform experiments and highlighting good practice for model comparison and evaluation.

Computers have become closely involved with most aspects of modern life and these developments are tracked in the chemical sciences. Recent years have seen the integration of computing across chemical research, made possible by investment in equipment, software development, improved networking between researchers and rapid growth in the application of predictive approaches to chemistry, but also a change of attitude rooted in the successes of computational chemistry -it is now entirely possible to complete research projects where computation and synthesis are cooperative, integrated, and work in synergy to achieve better insights and so improved results. It remains our ambition to put computational prediction before experiment, and we have been working towards developing the key ingredients and workflows to achieve this.The ability to precisely tune selectivity along with high catalyst activity make organometallic catalysts using transition metal (TM) centres ideal for high value-added transformations, and this can make them appealing for industrial applications. However, mechanistic variations of TM-catalysed reactions across the vast chemical space of different catalysts and substrates are not fully explored, nor is such an exploration feasible with current resources. This can lead to complete synthetic failures when new substrates are used, but more commonly we see outcomes that require further optimisation, such as incomplete conversion, insufficient selectivity, or the appearance of unwanted side products. These processes consume time and resources, but the insights and data generated are usually not tied to a broader predictive workflow where experiments test hypotheses quantitatively, reducing their impact.These failures suggest at least a partial deviation of the reaction pathway from that hypothesised, hinting at quite complex mechanistic manifolds for organometallic catalysts which are affected by the combination of input variables. Mechanistic deviation is most likely when challenging, multifunctional substrates are being used, and the quest for so-called privileged catalysts is quickly replaced by a need to screen catalysts libraries until a new "best" match between catalyst and substrate can be identified and reaction conditions optimised. As a community we remain confined to broad interpretations of the substrate scope of new catalysts and focus on small changes based on idealised catalytic cycles, rather than working towards a "big data" view of organometallic homogeneous catalysis, with routine use of predictive models and transparent data sharing.Databases of DFT-calculated steric and electronic descriptors can be built for such catalysts, and we summarise here how these can be used in the mapping, interpretation, and prediction of catalyst properties and reactivities. Our motivation is to make these databases useful as tools for synthetic chemists, so they challenge and validate quantitative computational approaches. In this account we demonstrate their application to different aspects of cataly...

Both E‐ and Z‐N′‐alkenyl urea derivatives of imidazolidinones may be formed selectively from enantiopure α‐amino acids. Generation of their enolate derivatives in the presence of K+ and [18]crown‐6 induces intramolecular migration of the alkenyl group from N′ to Cα with retention of double bond geometry. DFT calculations indicate a partially concerted substitution mechanism. Hydrolysis of the enantiopure products under acid conditions reveals quaternary α‐alkenyl amino acids with stereodivergent control of both absolute configuration and double bond geometry.

Iron‐catalyzed isomerization of alkenes is reported using an iron(II) β‐diketiminate pre‐catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H3N⋅BH3). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre‐catalyst activation step that gives access to an η2‐coordinated alkene FeI complex, followed by oxidative addition of the alkene to give an FeIII intermediate, which then undergoes reductive elimination to allow release of the isomerization product.

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Three new carboranylphosphines, [1-(1′-closo-1′,7′-C2B10H11)-7-PPh2-closo-1,7-C2B10H10], [1-(1′–7′-PPh2-closo-1′,7′-C2B10H10)-7-PPh2-closo-1,7-C2B10H10], and [1-{PPh-(1′-closo-1′,2′-C2B10H11)}-closo-1,2-C2B10H11], have been prepared, and from a combination of these and literature compounds, eight new carboranylphosphine selenides were subsequently synthesized. The relative basicities of the carboranylphosphines were established by (i) measurement of the 1 J PSe NMR coupling constant of the selenide and (ii) calculation of the proton affinity of the phosphine, in an attempt to establish which of several factors are the most important in controlling the basicity. It is found that the basicity of the carboranylphosphines is significantly influenced by the nature of other substituents on the P atom, the nature of the carborane cage vertex (C or B) to which the P atom is attached, and the charge on the carboranylphosphine. In contrast, the basicity of the carboranylphosphines appears to be relatively insensitive to the nature of other substituents on the carborane cage, the isomeric form of the carborane, and whether the cage is closo or nido (insofar as that does not alter the charge on the cluster). Such information is likely to be of significant importance in optimizing future applications of carboranylphosphines, e.g., as components of frustrated Lewis pairs.

Both E‐ and Z‐N′‐alkenyl urea derivatives of imidazolidinones may be formed selectively from enantiopure α‐amino acids. Generation of their enolate derivatives in the presence of K+ and [18]crown‐6 induces intramolecular migration of the alkenyl group from N′ to Cα with retention of double bond geometry. DFT calculations indicate a partially concerted substitution mechanism. Hydrolysis of the enantiopure products under acid conditions reveals quaternary α‐alkenyl amino acids with stereodivergent control of both absolute configuration and double bond geometry.

The passage of stock solutions through stainless-steel needles during sample preparation or introduction into the apparatus led to rapid oxidative decay rates due to metal leaching. What practical measures should be taken in this and related systems and what would be the best alternative to stainless-steel needles?Guy Lloyd-Jones answered: For this system, use of glass or polymer seems to work ne. For other systems, this is a difficult question to answer. It will always be a balance of practicality over 'purity'. Just like using glass reaction vessels (which are not always as inert as we would expect), stainless steel needles and cannulae are very convenient, and do not oen interfere with reactions. A few controls should hopefully elucidate if there is any interference, and if so, then other nominally inert materials (e.g. PTFE, ceramic, titanium, etc.) can be used, if required.Jennifer Love continued the discussion of the paper: It's great that you have gured this out. We've seen in other systems that decomposition is a lot more complex than one would think and our problem was that we couldn't isolate and measure our product. Were you able to measure and fully characterise the product 282