Dibenzo-7-phosphanorbornadiene compounds, RPA (A = CH or anthracene), are investigated as phosphinidene sources upon thermally induced (70-90 °C) anthracene elimination. Analysis of substituent effects reveals that π-donating dialkylamide groups are paramount to successful phosphinidene transfer; poorer π-donors give reduced or no transfer. Substituent steric bulk is also implicated in successful transfer. Molecular beam mass spectrometry (MBMS) studies of each derivative reveal dialkylamide derivatives to be promising precursors for further gas-phase spectroscopic studies of phosphinidenes; in particular, we present evidence of direct detection of the dimethylamide derivative, [MeN═P]. Kinetic investigations of PrNPA thermolysis in 1,3-cyclohexadiene and/or benzene-d are consistent with a model of unimolecular fragmentation to yield free phosphinidene [PrN═P] as a transient reactive intermediate. This conclusion is probed by density functional theory (DFT) calculations, which favored a mechanistic model featuring free singlet aminophosphinidenes. The breadth of phosphinidene acceptors is expanded to unsaturated substrates beyond 1,3-dienes to include olefins and alkynes; this provides a new synthetic route to valuable amino-substituted phosphiranes and phosphirenes, respectively. Stereoselective phosphinidene transfer to olefins is consistent with singlet phosphinidene reactivity by analogy with the Skell hypothesis for singlet carbene addition to olefins.

Super-reducing excited states have the potential to activate strong bonds, leading to unprecedented photoreactivity. Excited states of radical anions, accessed via reduction of a precatalyst followed by light absorption, have been proposed to drive photoredox transformations under super-reducing conditions. Here, we investigate the radical anion of naphthalene monoimide as a photoreductant and find that the radical doublet excited state has a lifetime of 24 ps, which is too short to facilitate photoredox activity. To account for the apparent photoreactivity of the radical anion, we identify an emissive two-electron reduced Meisenheimer complex of naphthalene monoimide, [NMI(H)] − . The singlet excited state of [NMI(H)] − is a potent reductant (−3.08 V vs Fc/Fc + ), is long-lived (20 ns), and its emission can be dynamically quenched by chloroarenes to drive a radical photochemistry, establishing that it is this emissive excited state that is competent for reported C−C and C−P coupling reactivity. These results provide a mechanistic basis for photoreactivity at highly reducing potentials via singlet excited state manifolds and lays out a clear path for the development of exceptionally reducing photoreagents derived from electron-rich closed-shell anions.

What is the strongest acid? Can a simple Brønsted acid be prepared that can protonate an alkane at room temperature? Can that acid be free of the complicating effects of added Lewis acids that are typical of common, difficult-to-handle superacid mixtures? The carborane superacid H-(CHB11F11) is that acid. It is an extremely moisture-sensitive solid, prepared by treatment of anhydrous HCl with [Et3Si–H–SiEt3][CHB11F11]. It adds H2O to form [H3O][CHB11F11] and benzene to form the benzenium ion salt [C6H7][CHB11F11]. It reacts with butane to form a crystalline tBu+ salt and with n-hexane to form an isolable hexyl carbocation salt. Carbocations, which are thus no longer transient intermediates, react with NaH either by hydride addition to re-form an alkane or by deprotonation to form an alkene and H2. By protonating alkanes at room temperature, the reactivity of H(CHB11F11) opens up new opportunities for the easier study of acid-catalyzed hydrocarbon reforming.

The transannular diphosphorus bisanthracene adduct P2A2 (A = anthracene or C14H10) was synthesized from the 7-phosphadibenzonorbornadiene Me2NPA through a synthetic sequence involving chlorophosphine ClPA (28-35%) and the tetracyclic salt [P2A2Cl][AlCl4] (65%) as isolated intermediates. P2A2 was found to transfer P2 efficiently to 1,3-cyclohexadiene (CHD), 1,3-butadiene (BD), and (C2H4)Pt(PPh3)2 to form P2(CHD)2 (>90%), P2(BD)2 (69%), and (P2)[Pt(PPh3)2]2 (47%), respectively, and was characterized by X-ray diffraction as the complex [CpMo(CO)3(P2A2)][BF4]. Experimental and computational thermodynamic activation parameters for the thermolysis of P2A2 in a solution containing different amounts of CHD (0, 4.75, and 182 equiv) have been obtained and suggest that P2A2 thermally transfers P2 to CHD through two competitive routes: (i) an associative pathway in which reactive intermediate [P2A] adds the first molecule of CHD before departure of the second anthracene, and (ii) a dissociative pathway in which [P2A] fragments to P2 and A prior to addition of CHD. Additionally, a molecular beam mass spectrometry study on the thermolysis of solid P2A2 reveals the direct detection of molecular fragments of only P2 and anthracene, thus establishing a link between solution-phase P2-transfer chemistry and production of gas-phase P2 by mild thermal activation of a molecular precursor.