Diazaphospholene-Catalyzed Hydrodefluorination of Polyfluoroarenes with Phenylsilane via Concerted Nucleophilic Aromatic Substitution

Metallomimetic C-F Activation Catalysis by Simple Phosphines

Delivering metallomimetic reactivity from simple p-block compounds is highly desirable in the search to replace expensive, scarce precious metals by cheap and abundant elements in catalysis. This contribution demonstrates that metallomimetic catalysis, involving facile redox cycling between the P(III) and P(V) oxidation states, is possible using only simple, cheap, and readily available trialkylphosphines without the need to enforce unusual geometries at phosphorus or use external oxidizing/reducing agents. Hydrodefluorination and aminodefluorination of a range of fluoroarenes was realized with good to very good yields under mild conditions. Experimental and computational mechanistic studies show that the phosphines undergo oxidative addition of the fluoroaromatic substrate via a Meisenheimer-like transition state to form a fluorophosphorane. This undergoes a pseudotransmetalation step with a silane, via initial fluoride transfer from P to Si, to give experimentally observed phosphonium ions. Hydride transfer from a hydridosilicate counterion then leads to a hydridophosphorane, which undergoes reductive elimination of the product to reform the phosphine catalyst. This behavior is analogous to many classical transition-metal-catalyzed reactions and so is a rare example of both functional and mechanistically metallomimetic behavior in catalysis by a main-group element system. Crucially, the reagents used are cheap, readily available commercially, and easy to handle, making these reactions a realistic prospect in a wide range of academic and industrial settings.

Pentafluorobenzene: Promising Applications in Diagnostics and Therapeutics

Pentafluorobenzene (PFB) represents a class of aromatic fluorine compounds employed exclusively across a spectrum of chemical and biological applications. PFBs are credited with developing various chemical synthesis techniques, networks and biopolymers, bioactive materials, and targeted drug delivery systems. The first part of this review delves into recent developments in PFB-derived molecules for diagnostic purposes. In the latter segment, PFB's role in the domain of theragnostic applications is discussed. The review elucidates different mechanisms and interaction strategies applied in leveraging PFBs to formulate diagnostic and theragnostic tools, substantiated by proper examples. The utilization of PFBs emerges as an enabler, facilitating manifold reactions, improving materials' properties, and even opening avenues for explorative research.

Direct C(sp3)-H Polyfluoroarylation: Access to Polyfluoroaryl Amino Acids via Rh-Catalyzed Selective C-F Bond Cleavage

A catalytic selective C-F bond alkylation method for polyfluoroarene with glycinates and derivatives in the presence of a DavePhos-ligated Rh catalyst was developed. This method avoids the preactivation of alkylating reagents and provides an efficient and straightforward route to synthesize a series of polyfluoroaryl amino acids via C(sp³)-H functionalization. This reaction proceeds under mild conditions and exhibits high reactivity and excellent chemoselectivities. Meanwhile, the synthetic potential of this method was demonstrated by gram-scale synthesis, and further transformations proved the application value of the products as well.

Bimetallic Metal-Organic Coordination Polymers Facilitated the Selective C-F Cleavage of Polyfluoroarenes

Selective C-F bond cleavage of polyfluoroarenes has attracted tremendous interest due to its promising applications in introducing fluorinated building blocks into organic molecules. However, it remains a challenge to achieve highly site-selective C-F bond cleavage because of the intrinsic inertness of the C-F bond and the difficulty in distinguishing specific C-F bonds on the aromatic ring. Herein we report an efficient nucleophilic aromatic substitution (S_NAr) reaction of polyfluoroarenes with Grignard reagents that employs MnFe-based bimetallic metal-organic coordination polymers (MOCPs) as recyclable and reusable heterogeneous catalysts. Significantly, in this reaction, the prepared MOCP (Mn-Fe) catalyst exhibited excellent activity in selective C-F bond cleavage and afforded a series of functionalized polyfluoroarenes in moderate to excellent yields (up to 96%). This work highlights the potential of MOCP catalysts to serve as a tunable platform in Lewis acid catalysis.

1,3,2‐Diazaphospholene‐Catalyzed Reductive Cyclizations of Organohalides**

1,3,2‐diazaphospholenes hydrides (DAP‐Hs) are highly nucleophilic organic hydrides serving as main‐group catalysts for a range of attractive transformations. DAP hydrides can act as stoichiometric hydrogen atom transfer agents in radical reactions. Herein, we report a DAP‐catalyzed reductive radical cyclization of a broad range of aryl and alkyl halides under mild conditions. The pivotal DAP catalyst turnover was achieved by a DBU‐assisted σ‐bond metathesis between the formed DAP halide and HBpin, which rapidly regenerates DAP‐H. The transformation is significantly accelerated by irradiation with visible light. Mechanistic investigations indicate that visible light irradiation leads to the formation of DAP dimers, which are in equilibrium with DAP radicals and accelerate the cyclization. The direct use of (DAP)₂ enabled a catalytic protocol in the absence of light.

Synthetic applications of NHPs: from the hydride pathway to a radical mechanism

We briefly summarized synthetic applications of N-heterocyclic phosphines in both hydridic and radical reductions with an emphasis on their recently discovered radical reactivity.