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Herein, we present the formation of transient radical ion pairs (RIPs) by single-electron transfer (SET) in phosphine-quinone systems and explore their potential for the activation of C-H bonds. PMes 3 (Mes=2,4,6-Me 3 C 6 H 2 ) reacts with DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) with formation of the P-O bonded zwitterionic adduct Mes 3 P-DDQ (1), while the reaction with the sterically more crowded PTip 3 (Tip=2,4,6-iPr 3 C 6 H 2 ) afforded C-H bond activation product Tip 2 P(H)(2-[CMe 2 (DDQ)]-4,6-iPr 2 -C 6 H 2 ) (2). UV/Vis and EPR spectroscopic studies showed that the latter reaction proceeds via initial SET, forming RIP [PTip 3 ]⋅ + [DDQ]⋅ - , and subsequent homolytic C-H bond activation, which was supported by DFT calculations. The isolation of analogous products, Tip 2 P(H)(2-[CMe 2 {TCQ-B(C 6 F 5 ) 3 }]-4,6-iPr 2 -C 6 H 2 ) (4, TCQ=tetrachloro-1,4-benzoquinone) and Tip 2 P(H)(2-[CMe 2 {oQ tBu -B(C 6 F 5 ) 3 }]-4,6-iPr 2 -C 6 H 2 ) (8, oQ tBu =3,5-di-tert-butyl-1,2-benzoquinone), from reactions of PTip 3 with Lewis-acid activated quinones, TCQ-B(C 6 F 5 ) 3 and oQ tBu -B(C 6 F 5 ) 3 , respectively, further supports the proposed radical mechanism. As such, this study presents key mechanistic insights into the homolytic C-H bond activation by the synergistic action of radical ion pairs., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Frustrated Lewis pairs (FLPs) are well known for their ability to activate small molecules. Recent reports of radical formation within such systems indicate single-electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride, or tetrachloro-1,4-benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single-electron transfer (SET) events; that is, being direct SET to B(C 6 F 5 ) 3 or not. The reactions of H 2 and Ph 3 SnH with archetypal P/B FLP systems do not proceed via a radical mechanism. In contrast, reaction with TCQ proceeds via SET, which is only feasible by Lewis acid coordination to the substrate. Furthermore, SET from the Lewis base to the Lewis acid-substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical main-group chemistry., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

P-yramids: Tetrahedranes are highly strained molecules, and the all-carbon (CtBu) 4 and all-phosphorus species P 4 have been known for decades and centuries, respectively. Despite this, the mixed P/C tetrahedranes were unknown until recently when the syntheses of the phosphatetrahedranes P(CtBu) 3 and P 2 (CtBu) 2 were reported by the research groups of Cummins and Wolf., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H 2 outside of the usual Lewis acid/base chemistry described by the concept of frustrated Lewis pairs (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly hindered boranes: tris(3,5-dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway. This radical-based, redox pathway involves the homolytic cleavage of H 2 , in contrast to conventional models of FLP chemistry, which invoke a heterolytic cleavage pathway. This represents a new mode of chemical reactivity for hydrogen activation by borane Lewis acids., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Inspired by the commercially available azoimidazolium dyes (e.g., Basic Red 51) that can be obtained from aryldiazonium salts and N-heterocyclic carbenes, we developed the synthesis of a unique set of arylazophosphonium salts. A range of colours were obtained by applying readily tuneable phosphine donor ligands and para-substituted aryldiazonium salts as nitrogen-based Lewis acids. With cyclic voltammetry, a general procedure was designed to establish whether the reaction between a Lewis acid and a Lewis base occurs by single-electron transfer or electron-pair transfer., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Avoiding white phosphorus: Cummins and Geeson have recently described the conversion of phosphoric acid into the novel bis(trichlorosilyl)phosphide anion, which serves as a key intermediate in the synthesis of organophosphines, hexafluorophosphate, and phosphine gas in a reaction sequence that does not rely on white phosphorus., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The phosphorus analogues of cyclopentadienone, tricyclopentanone, and housene were accessed from bis(cyclopropenyl)diphosphetanedione 3, which was prepared by mixing 1,2,3-tris-tert-butylcyclopropenium tetrafluoroborate (1) and sodium phosphaethynolate [Na(OCP)(dioxane) n ]. While photolysis of 3 results in decarbonylation, yielding bis(cyclopropenyl)diphosphene 4 and after rearrangement diphosphahousene 5, thermolysis of 3 leads to phosphatricyclo[2.1.0.0]pentanone 7. Metal-mediated valence isomerization of 7 and subsequent demetalation provides access to phosphacyclopentadienone 12., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Phosphinidenes [R-P] are convenient P 1 building blocks for the synthesis of a plethora of organophosphorus compounds. Thus far, transition-metal-complexed phosphinidenes have been used for their singlet ground-state reactivity to promote selective addition and insertion reactions. One disadvantage of this approach is that after transfer of the P 1 moiety to the substrate, a challenging demetallation step is required to provide the free phosphine. We report a simple method that enables the Lewis acid promoted transfer of phenylphosphinidene, [PhP], from NHC=PPh adducts (NHC=N-heterocyclic carbene) to various substrates to produce directly uncoordinated phosphorus heterocycles that are difficult to obtain otherwise., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two [3+1] fragmentations of the Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutanide Li[Mes*P 4 ⋅ BPh 3 ] (Mes*=2,4,6-tBu 3 C 6 H 2 ) are reported. The reactions proceed by extrusion of a P 1 fragment, induced by either an imidazolium salt or phenylisocyanate, with release of the transient triphosphirene Mes*P 3 , which was isolated as a dimer and trapped by 1,3-cyclohexadiene as a Diels-Alder adduct. DFT quantum chemical computations were used to delineate the reaction mechanisms. These unprecedented pathways grant access to both P 1 - and P 3 -containing organophosphorus compounds in two simple steps from white phosphorus., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The transient bicyclo[1.1.0]tetraphosphabutane anion, generated from white phosphorus (P4) and Mes*Li (Mes*=2,4,6-tBu3C6H2), can be trapped by BPh3 in THF. This Lewis acid stabilized anion can be used as an [RP4](-) transfer agent, reacting cleanly with neutral Lewis acids (B(C6F5)3, BH3, and W(CO)5) to afford unique singly and doubly coordinated butterfly anions, and with the trityl cation to form a neutral, nonsymmetrical, all-carbon-substituted P4  derivative. This reaction path enables a simple, stepwise functionalization of white phosphorus., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reacting white phosphorus (P4 ) with sterically encumbered aryl lithium reagents (aryl=2,6-dimesitylphenyl or 2,4,6-tBu3 C6 H2 ) and B(C6 F5 )3 gives the unique, isolable Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutane anion. Subsequent alkylation of the nucleophilic site of the RP4 anion gives access to non-symmetrical disubstituted bicyclic tetraphosphorus compounds. This novel method enables PC bond formation in a controlled fashion using white phosphorus as starting material., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Readily accessible nitrilium triflates are convenient imine building blocks for the expedient synthesis of a novel class of 1,3-P,N ligands as demonstrated for the reaction with primary phosphanes. This procedure allows variation of all substituents. X-ray crystal structures are reported for nitrilium ions, phosphaamidines, and three phosphaamidinate complexes. The lithium phosphaamidinate is N coordinated and its reaction with [AuCl(tht)] (tht = tetrahydrothiophene) gives a unique P-bridged gold trimer, while a P,N-bidentate complex results from [{RhCl(cod)}2]. The nitrilium ion methodology allows extension of the 1,3-P,N motive to bis(imino)phosphanes, which are the neutral phosphorus analogues of the valuable β-diketiminate ligand., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Syntheses, properties, and reactivities of nucleophilic phosphinidene complexes [L(n)M=P-R] are reviewed. Emphasis is placed on the electronic tuning of this emerging class of phosphorus reagents, using different ancillary ligands and coordinatively unsaturated transition-metal moieties. The difference in applicability of the established stable 18-electron and transient 16-electron phosphinidenes is addressed.

Do the twist: The reaction of in situ generated phosphinidenes with phosphaalkynes is a facile route to the new metal-coordinated eta(3)-diphosphavinylcarbene 1, which shows facile ligand-exchange reactions and undergoes an unprecedented rearrangement that involves phosphinidene complex 2 and eta(3)-phosphaalkenylphosphinidene complex 3, the 1,3 isomer of 1.

P makes it possible: The convenient oxidative synthesis of the 16-electron organophosphorus iron sandwich complex [Fe(eta(4)-P(2)C(2)tBu(2))(2)] (see structure) suggests that the elusive all-carbon complex [Fe(eta(4)-C(4)H(4))(2)] is a viable synthetic target.