Shapeshifting xantphos

No abstract availabl

Density Functional Theory Studies of the Catalyst Structure–Activity and Selectivity Relationships in Rh(I)-Catalyzed Transfer C–H Borylation of Alkenes

International audienceWe report the results of a computational investigation that shed light on the catalyst structure–activity and selectivity relationships for our recently developed Rh(I)-xantphos-catalyzed transfer C–H borylation of alkenes. Our study uncovered the influence that the ligand properties have on the free energy surfaces of the reactions catalyzed by a series of Rh catalysts bearing derivatives of the xantphos ligand with varied electronic features and steric demands. We present the full reaction profiles and provide a closer look on how different modifications to the ligand structure influence each step of the catalytic reaction. We observed that the increased steric effects have a large effect on the free energy surfaces, increasing the energy barriers, thereby decreasing the rates of the reaction. In turn, the electronic effects can stabilize key transition states and destabilize crucial intermediates, such as the resting of the catalyst, thus accelerating the overall catalytic process. Additionally, the electronic effects can modify the relative rates of the alternative pathways and therefore affect the selectivity preferences. In general, our study provides guidelines for the rational development of new catalysts to further enhance the performance of the catalytic system and address the remaining challenges

Multicatalysis enables turning plastic waste into chemical commodities

International audienc

Dual-Catalytic Transition Metal Systems for Functionalization of Unreactive Sites of Molecules

Catalytic reactions occur readily at sites of starting materials that are both innately reactive and sterically accessible or that are predisposed by a functional group amenable to direct a catalyst. However, selective reactions at unbiased sites of substrates remain challenging and typically require additional pre-activation steps or the use of highly reactive reagents. Herein, we report dual-catalytic transition metal systems that merge a reversible activation cycle with a functionalization cycle, together enabling functionalization of substrates at their inherently unreactive sites. By engaging the Ru- or Fe-catalyzed equilibrium between an alcohol and an aldehyde, Pd-catalyzed b-arylation of aliphatic alcohols and Rh-catalyzed g-hydroarylation of allylic alcohols were developed. The mild conditions, functional group tolerance and broad scope of the methodologies (81 examples) demonstrate the synthetic applicability of the dual-catalytic systems. In a broader context, this work highlights the potential of the multi-catalytic approach to address challenging transformations to circumvent the multi-step procedures and the use of highly reactive reagents in organic synthesis.</b

Isoselective Hydroformylation of Propylene by Iodide‐Assisted Palladium Catalysis

Isobutanal is a high value bulk material that, in principle, could be produced with 100 % atom-economy by isoselective hydroformylation of propylene with syngas. However, leading industrial Rh- and Co-catalyzed hydroformylation methods preferentially form n-butanal over the iso-product, and methods offering isoselectivity remain underdeveloped. Here we report an iodide-assisted Pd-catalyzed hydroformylation of propylene that produces isobutanal with unprecedented levels of selectivity. The method involves PdI2 , simple alkyl monophosphines, such as tricyclohexylphosphine, and common green solvents, enabling the title reaction to occur with isoselectivity in up to 50 : 1 iso/n product ratios under industrially relevant conditions (80-120 °C). The catalytic and preliminary mechanistic experiments indicate a key role of the iodide anions in both the catalytic activity and the isoselectivity

A Merger of Relay Catalysis with Dynamic Kinetic Resolution Enables Enantioselective β-C(sp3)-H Arylation of Alcohols.

The conceptual merger of relay catalysis with dynamic kinetic resolution strategy is reported to enable regio- and enantioselective C(sp3)-H bond arylation of aliphatic alcohols, forming enantioenriched β-aryl alcohols typically with >90:10 enantiomeric ratios (up to 98:2 er) and 36-74% yields. The starting materials bearing neighbouring stereogenic centres can be converted to either diastereomer of the β-aryl alcohol products, with >85:15 diastereomeric ratios determined by the catalysts. The reactions occur under mild conditions, ensuring broad compatibility, and involve readily available aryl bromides, an inorganic base, and commercial Ru- and Pd-complexes. Mechanistic experiments support the envisioned mechanism of the transformation occurring through a network of regio- and stereoselective processes operated by a coherent Ru/Pd-dual catalytic system

Multi-Stimuli-Responsive Network of Multicatalytic Reactions using a Single Palladium/Platinum Catalyst.

Given her unrivalled proficiency in the synthesis of all molecules of life, nature has been an endless source of inspiration for developing new strategies in organic chemistry and catalysis. However, one feature that remains beyond chemists' grasp is her unique ability to adapt the productivity of metabolic processes in response to triggers that indicate the temporary need for specific metabolites. To demonstrate the remarkable potential of such stimuli-responsive systems, we present a metabolism-inspired network of multicatalytic processes capable of selectively synthesising a range of products from simple starting materials. Specifically, the network is built of four classes of distinct catalytic reactions - cross-couplings, substitutions, additions, and reductions, involving three organic starting materials - terminal alkyne, aryl iodide, and hydrosilane. All starting materials are either introduced sequentially or added to the system at the same time, with no continuous influx of reagents or efflux of products. All processes in the system are catalysed by a multifunctional heteronuclear PdII/PtII complex, whose performance can be controlled by specific additives and external stimuli. The reaction network exhibits a substantial degree of orthogonality between different pathways, enabling the controllable synthesis of ten distinct products with high efficiency and selectivity through simultaneous triggering and suppression mechanisms

Transfer C-H Borylation of Alkenes under Rh(I)-Catalysis: In-sight into the Mechanism, Selectivity-Control & Synthetic Capacity

Transfer C-H borylation of alkenes bears the potential to unlock a range of attractive transformations for modular synthe-sis and late-stage derivatization of complex molecules. However, its scarce precedence associated with a limited mechanistic understanding hinders the development of practical synthetic protocols. Here we report a Rh(I)-catalyzed transfer C-H borylation reaction that is founded on an unprecedented yet crucial elementary step of the beta-boryl elimination engaging the Rh(I)-(beta-borylalkyl) intermediate. A thorough mechanistic investigation involving a series of catalytic and stoichiometric experiments and complementary computational studies revealed that this step proceeds with a considerably low free energy barrier, further elucidated the full catalytic cycle, and provided insight into the features con-trolling the activity and the selectivity. Driven by this mechanistic understanding, we devised a protocol that is compatible with a plethora of functional groups, including often problematic motifs, and applicable not only to terminal but also inter-nal alkenes and varied electronic and steric properties. The method proved also to be effective in complex settings of the late-stage borylation of derivatives of macrocyclic mycoestrogen Zearalenol, bioactive Brompheniramine, Chlorpromazine, and CD3254, and the synthesis of the boronic acid bio¬isostere of the drug Ozagrel. Besides the valuable new method, these mechanistic investigations set the stage for the development of other hydrogen-for-functional group exchange reactions undergoing a similar pathway

Multi-Catalytic Approach to One-Pot Stereoselective Synthesis of Secondary Benzylic Alcohols

One-pot multi-step procedures bear the potential to rapidly build up molecular complexity while avoiding the wasteful and costly isolations and purifications of consecutive intermediates. Here we report multi-catalytic protocols that convert alkenes, unsaturated aliphatic alcohols, and aryl boronic acids into secondary benzylic alcohols with high stereoselectivities under sequential catalysis that integrates alkene cross-metathesis, isomerization, and nucleophilic addition. Because each transformation of the sequence is executed by an independent catalyst, without any catalytic cross-reactivity, allylic alcohols bearing a prochiral double bond can be converted to any stereoisomer of the product with high stereoselectivity (>98:2 er and >20:1 dr). Overall, with the aid of up to four catalysts operating in a single vessel, the protocols directly convert simple starting materials into a range of value-added products with high stereocontrol and excellent material efficiency, demonstrating both the efficacy and the advantages of the one-pot synthesis employing multiple transition-metal catalysts