Search for: All records

Abstract Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are persistent, bioaccumulative and anthropogenic pollutants that have attracted the attention of the public and private sectors because of their adverse impact on human health¹. Although various technologies have been deployed to degrade PFASs with a focus on non-polymeric functionalized compounds (perfluorooctanoic acid and perfluorooctanesulfonic acid)^2–4, a general PFAS destruction method coupled with fluorine recovery for upcycling is highly desirable. Here we disclose a protocol that converts multiple classes of PFAS, including the fluoroplastics polytetrafluoroethylene and polyvinylidene fluoride, into high-value fluorochemicals. To achieve this, PFASs were reacted with potassium phosphate salts under solvent-free mechanochemical conditions, a mineralization process enabling fluorine recovery as KF and K₂PO₃F for fluorination chemistry. The phosphate salts can be recovered for reuse, implying no detrimental impact on the phosphorus cycle. Therefore, PFASs are not only destructible but can now contribute to a sustainable circular fluorine economy. 

Photoredox catalysis driven by visible light has improved chemical synthesis by enabling milder reaction conditions and unlocking distinct reaction mechanisms. Despite the transformative impact, visible-light photoredox catalysis remains constrained by the thermodynamic limits of photon energy and inefficiencies arising from unproductive back electron transfer, both of which become particularly pronounced in thermodynamically demanding reactions. In this work, we introduce an organic photoredox catalyst system that overcomes these obstacles to drive chemical transformations that require super-reducing capabilities. This advancement is accomplished by coupling the energy of two photons into a single chemical reduction, whereas inefficiencies from back electron transfer are mitigated through a distinct proton-coupled electron transfer mechanism embedded in the catalyst design. The super-reducing capabilities of this organic catalyst system are demonstrated through efficient application in a broad scope of challenging arene reductions. 

Ni-catalyzed cross-electrophile coupling (XEC) reactions have gained prominence for the construction of C–C bonds. Prior studies of XEC routes to biaryls have invoked several different mechanisms for the formation of key Ni(Ar)2 intermediates. Here, we provide evidence for a previously unrecognized pathway involving reductively induced transmetalation between NiI(Ar) and NiII(Ar)X species. Chemical and electrochemical reduction of (tBubpy)NiII(2-tolyl)Br (tBubpy = 4,4’-di-tert-butyl-2,2’-bipyridine) to (tBubpy)NiI(2-tolyl) is shown to initiate rapid transmetalation of the 2-tolyl ligand to a second equivalent of (tBubpy)NiII(2-tolyl)Br, affording (tBubpy)NiII(2-tolyl)2 and (tBubpy)NiIBr as well defined products. Experimental and computational data show that the NiI-to-NiII transmetalation mechanism is much more favorable than NiII-to-NiII transmetalation. Oxidation of (tBubpy)NiII(2-tolyl)Br results in rapid reductive elimination of 2-tolyl–Br, rather than promoting the analogous oxidatively induced NiII/NiIII transmetalation. The NiII(2-tolyl)2 product of NiI-to-NiII transmetalation is stable at room temperature, while sterically less encumbered NiII(Ar)2 species undergo rapid reductive elimination to afford biaryl and a Ni0 byproduct. The latter species can serve as a source of electrons to promote further transmetalation and biaryl formation. The unhindered complex (tBubpy)NiII(4-CF3-phenyl)Br undergoes biaryl formation in the absence of added reductant; however, kinetic analysis reveals an induction period and autocatalytic time course. Addition of catalytic quantities of a cobaltocene-based reductant eliminates the induction period and accelerates biaryl formation, consistent with the NiI-to-NiII transmetalation pathway. The results of this study provide a new rationale for previously reported results in the literature and introduce an alternative pathway to consider in the development of Ni-catalyzed biaryl coupling reactions. 

DFT-level descriptor libraries were constructed to train 2D and 3D graph neural networks for on the-fly the prediction of carboxylic acid and alkyl amine descriptors suitable for statistical modeling of medicinally relevant molecules. 

Nickel-catalyzed cross-electrophile coupling (XEC) reactions of (hetero)aryl electrophiles represent appealing alternatives to palladium-catalyzed methods for biaryl synthesis, but they often generate significant quantities of homocoupling and/or proto-dehalogenation side products. In this study, an informer library of heteroaryl chloride and aryl bromide coupling partners is used to identify Ni-catalyzed XEC conditions that access high selectivity for the cross-product when using equimolar quantities of the two substrates. Two different catalyst systems are identified that show complementary scope and broad functional-group tolerance, and time-course data suggest the two methods follow different mechanisms. A NiBr2/terpyridine catalyst system with Zn as the reductant converts the aryl bromide into an aryl-zinc intermediate that undergoes in situ coupling with 2-chloropyridines, while a NiBr2/bipyridine catalyst system with tetrakis(dimethylamino)ethylene as the reductant uses FeBr2 and NaI as additives to achieve selective cross-coupling. 

Abstract Herein, we describe a new strategy for the carbonylation of alkyl halides with different nucleophiles to generate valuable carbonyl derivatives under visible light irradiation. This method is mild, robust, highly selective, and proceeds under metal‐free conditions to prepare a range of structurally diverse esters and amides in good to excellent yields. In addition, we highlight the application of this activation strategy for¹³C isotopic incorporation. We propose that the reaction proceeds by a photoinduced reduction to afford carbon‐centered radicals from alkyl halides, which undergo subsequent single electron‐oxidation to form a carbocationic intermediate. Carbon monoxide is trapped by the carbocation to generate an acylium cation, which can be attacked by a series of nucleophiles to give a range of carbonyl products.