Arene extrusion as an approach to reductive elimination at boron: implication of carbene-ligated haloborylene as a transient reactive intermediate.

Herein, we report boron-centered arene extrusion reactions to afford putative cyclic(alkyl)(amino) carbene (CAAC)-ligated chloroborylene and bromoborylene intermediates. The borylene precursors, chloro-boranorbornadiene (ClB(CMe), 2) and bromo-boranorbornadiene (BrB(CMe), 2) were synthesized through the reaction of the corresponding 1-halo-2,3,4,5-tetramethylborole dimer (XBCMe) (X = Cl, 1; X = Br, 1) with 2-butyne. Treatment of 2 with CAACs resulted in the release of di-coordinate chloro-borylene (CAAC)BCl from hexamethylbenzene (CMe) at room temperature.

Pentaphosphorylation via the Anhydride of Dihydrogen Pentametaphosphate: Access to Nucleoside Hexa- and Heptaphosphates and Study of Their Interaction with Ribonuclease A.

Pentametaphosphate is the little studied cyclic pentamer of the metaphosphate ion, [PO] . We show that the doubly protonated form of this pentamer can be selectively dehydrated to provide the anhydride [PO] (). This trianion is the well-defined condensed phosphate component of a novel reagent for attachment of a pentaphosphate chain to biomolecules all in one go.

Synthesis and reactivity of an N-heterocyclic carbene-stabilized diazoborane.

Diazo compounds and organic azides are widely used as reagents for accessing valuable molecules in multiple areas of fundamental and applied chemistry. Their capacity to undergo versatile chemical transformations arises from the reactive nature of an incipient dinitrogen molecule at the terminal position. In this work, we report the synthesis and characterization of an N-heterocyclic carbene (NHC)-stabilized diazoborane-a boron-centered analog of organic azides and diazoalkanes.

Synthesis of Phosphet-2-one Derivatives via Phosphinidene Transfer to Cyclopropenones.

We report the first synthesis and structural characterization of free, uncomplexed phosphet-2-ones. These unsaturated four-membered phosphacycles were prepared by phosphinidene transfer from dibenzo-7-phosphanorbornadiene compounds, RP ( = CH, anthracene), to cyclopropenones in yields of up to 89%. Theoretical studies suggest that the reaction proceeds through ketene-ylide and ketene-phosphaalkene intermediates.

Mechanochemical Phosphorylation of Acetylides Using Condensed Phosphates: A Sustainable Route to Alkynyl Phosphonates.

In pursuit of a more sustainable route to phosphorus-carbon (P-C) bond-containing chemicals, we herein report that phosphonates can be prepared by mechanochemical phosphorylation of acetylides using polyphosphates in a single step, redox-neutral process, bypassing white phosphorus (P) and other high-energy, environmentally hazardous intermediates. Using sodium triphosphate (NaPO) and acetylides, alkynyl phosphonates can be isolated in yields of up to 32%, while reaction of sodium pyrophosphate (NaPO) and sodium carbide (NaC) engendered, in an optimized yield of 63%, ethynyl phosphonate , an easily isolable compound that can be readily converted to useful organophosphorus chemicals. Highly condensed phosphates like Graham's salt and bioproduced polyphosphate were also found to be compatible after reducing the chain length by grinding with orthophosphate.

Binding of Nitriles and Isonitriles to V(III) and Mo(III) Complexes: Ligand vs Metal Controlled Mechanism.

The synthesis and structures of nitrile complexes of V(N[Bu]Ar), (Ar = 3,5-MeCH), are described. Thermochemical and kinetic data for their formation were determined by variable temperature Fourier transform infrared (FTIR), calorimetry, and stopped-flow techniques. The extent of back-bonding from metal to coordinated nitrile indicates that electron donation from the metal to the nitrile plays a less prominent role for than for the related complex Mo(N[Bu]Ar), .

Stabilized Molecular Diphosphorus Pentoxide, POL (L = -Donor Base), in the Synthesis of Condensed Phosphate-Organic Molecule Conjugates.

Commercial phosphorus pentoxide reacts with some -donor bases to give the adducts POL and POL (L = DABCO, pyridine, 4--butylpyridine). The DABCO adducts were structurally characterized by single-crystal X-ray diffraction. It is proposed that POL and POL undergo interconversion through a "phosphate-walk" mechanism, which was evaluated using DFT calculations.

Synthesis of phosphiranes organoiron-catalyzed phosphinidene transfer to electron-deficient olefins.

Herein is reported the structural characterization and scalable preparation of the elusive iron-phosphido complex FpP( Bu)(F) (2-F, Fp = (Fe(η-CH)(CO))) and its precursor FpP( Bu)(Cl) (2-Cl) in 51% and 71% yields, respectively. These phosphide complexes are proposed to be relevant to an organoiron catalytic cycle for phosphinidene transfer to electron-deficient alkenes. Examination of their properties led to the discovery of a more efficient catalytic system involving the simple, commercially available organoiron catalyst Fp.

Taming phosphorus mononitride.

Phosphorus mononitride (PN) only has a fleeting existence on Earth, and molecular precursors for the release of this molecule under mild conditions in solution have remained elusive. Here we report the synthesis of an anthracene-based precursor-an anthracene moiety featuring an azidophosphine bridge across its central ring-that dissociates into dinitrogen, anthracene and P≡N in solution with a first-order half-life of roughly 30 min at room temperature. Heated under reduced pressure, this azidophosphine-anthracene precursor decomposes in an explosive fashion at around 42 °C, as demonstrated in a molecular-beam mass spectrometry study.

Beyond Triphosphates: Reagents and Methods for Chemical Oligophosphorylation.

Oligophosphates play essential roles in biochemistry, and considerable research has been directed toward the synthesis of both naturally occurring oligophosphates and their synthetic analogues. Greater attention has been given to mono-, di-, and triphosphates, as these are present in higher concentrations biologically and easier to synthesize. However, extended oligophosphates have potent biochemical roles, ranging from blood coagulation to HIV drug resistance.

Reactions of Tri--Butylphosphatetrahedrane as a Spring-Loaded Phosphinidene Synthon Featuring Nickel-Catalyzed Transfer to Unactivated Alkenes.

Cage-opening reactions of the highly strained tri--butylphosphatetrahedrane (), shown here to function as a synthon of (tri--butylcyclopropenyl)phosphinidene, are described. Treatment of with a base-stabilized silylene led to the corresponding phosphasilene, which was isolated in 72% yield as a red crystalline solid. Phosphinidene transfer was also observed when (2 equiv) was combined with the Wittig reagent PhPCH to form a diphosphirane (50% isolated yield).

Sustainable Production of Reduced Phosphorus Compounds: Mechanochemical Hydride Phosphorylation Using Condensed Phosphates as a Route to Phosphite.

In pursuit of a more sustainable production of phosphorous acid (HPO), a versatile chemical with phosphorus in the +3 oxidation state, we herein report that condensed phosphates can be employed to phosphorylate hydride reagents under solvent-free mechanochemical conditions to furnish phosphite (HPO ). Using potassium hydride as the hydride source, sodium trimetaphosphate (NaPO), triphosphate (NaPO), pyrophosphate (NaPO), fluorophosphate (NaPOF), and polyphosphate ("(NaPO) ") engendered phosphite in optimized yields of 44, 58, 44, 84, and 55% based on total P content, respectively. Formation of overreduced products including hypophosphite (HPO ) was identified as a competing process, and mechanistic investigations revealed that hydride attack on in-situ-generated phosphorylated phosphite species is a potent pathway for overreduction.

Staudinger Reactivity and Click Chemistry of Anthracene ()-Based Azidophosphine NP.

11-Azido-9,10-dihydro-9,10-phosphanoanthracene (NP) has been demonstrated recently as a transfer reagent for molecular phosphorus mononitride (PN) because it easily dissociates at room temperature into dinitrogen (N), PN, and anthracene (). Here we report further reactivity studies of the NP molecule including strain-promoted 1,3-dipolar cycloaddition with cyclooctyne and Staudinger-type reactivity. Calculations at the DLPNO-CCSD(T)/cc-pVTZ//PBE0-D3(BJ)/cc-pVTZ level of theory indicate that the click reaction is faster than the dissociation of NP.

Lithium superoxide encapsulated in a benzoquinone anion matrix.

Lithium peroxide is the crucial storage material in lithium-air batteries. Understanding the redox properties of this salt is paramount toward improving the performance of this class of batteries. Lithium peroxide, upon exposure to p-benzoquinone (-CHO) vapor, develops a deep blue color.

Frustrated Lewis Pair Stabilized Phosphoryl Nitride (NPO), a Monophosphorus Analogue of Nitrous Oxide (NO).

Phosphoryl nitride (NPO) is a highly reactive intermediate, and its chemistry has only been explored under matrix isolation conditions so far. Here we report the synthesis of an anthracene () and phosphoryl azide based molecule (NP(O)) that acts as a molecular synthon of NPO. Experimentally, NP(O) dissociates thermally with a first-order kinetic half-life that is associated with an activation enthalpy of Δ = 27.

Lost in Condensation: Poly-, Cyclo-, and Ultraphosphates.

Much like linear, branched, and cyclic alkanes, condensed phosphates exist as linear, branched, and cyclic structures. Inasmuch as alkanes are the cornerstone of organic chemistry, generating an inexplorably large chemical space, a comparable richness in structures can be expected for condensed phosphates, as also for them the concepts of isomerism apply. Little of their chemical space has been charted, and only a few different synthesis methods are available to construct isomers of condensed phosphates.

Alleviating Strain in Organic Molecules by Incorporation of Phosphorus: Synthesis of Triphosphatetrahedrane.

Phosphatetrahedranes (BuCP) and (BuC)P were recently reported and represent the first tetrahedranes containing a mixed carbon/phosphorus core. Herein, we report that tetrahydrofuran (THF) solutions of the parent triphosphatetrahedrane HCP may be generated in 31% yield (NMR internal standard yield) by combining [Na(THF)][PNb(ODipp)] (Dipp = 2,6-diisopropylphenyl), INb(ODipp)(THF), and bromodichloromethane in thawing THF. While HCP was found to be stable in dilute THF solutions for extended periods of time, the concentration of the solution at -40 °C led to the formation of a black precipitate, which has been tentatively assigned as a polymerized form of HCP.

Dimerization and Cycloaddition Reactions of Transient Tri--butylphosphacyclobutadiene Generated by Lewis Acid Induced Isomerization of Tri--butylphosphatetrahedrane.

Tri--butylphosphatetrahedrane () is shown here to act as a synthon of isomeric tri--butylphosphacyclobutadiene in the presence of a Lewis acid or transition-metal complex. When it is combined with a substoichiometric amount of triphenylborane, compound forms a ladderane-type dimer of tri--butylphosphacyclobutadiene in 72% isolated yield. Trapping of a generated intermediate was achieved by repeating the experiment in the presence of excess styrene (20 equiv) or ethylene (1 atm), and the corresponding [4 + 2] cycloadducts of tri--butylphosphacyclobutadiene were isolated in 88% and 74% yields, respectively.

Dihydrogen cleavage by a dimetalloxycarbene-borane frustrated Lewis pair.

A frustrated Lewis pair of dititanoxycarbene [(Ti(N[Bu]Ar))(μ-CO)] (Ar = 3,5-MeCH) and B(CF) cleaved dihydrogen under ambient conditions to give the zwitterionic formate [(Ti(N[Bu]Ar))(μ-OCHO-ηO:ηO')(B(CF))] and the hydrido borate [Ti(N[Bu]Ar)][HB(CF)].

Understanding the Nature and Properties of Hydrogen-Hydrogen Bonds: The Stability of a Bulky Phosphatetrahedrane as a Case Study.

Recently, the first mixed C/P phosphatetrahedranes (BuC)P and (BuCP) were reported. Unlike (BuCP), (BuC)P exhibits remarkable thermal stability, which can be partially attributed to a network of nine hydrogen-hydrogen bonds (HHBs) localized between the -butyl substituents. The stabilizing contribution arising from this network of HHBs was obtained from local energy decomposition (LED) analysis calculated at the domain-based local pair natural orbital CCSD(T) (DLPNO-CCSD(T)) level of theory.

P NMR Chemical Shift Tensors: Windows into Ruthenium Phosphinidene Complex Electronic Structures.

A series of octamethylcalix[4]pyrrole/ruthenium phosphinidene complexes (Na[=PR]) can be accessed by phosphinidene transfer from the corresponding RP ( = CH, anthracene) compounds (R = Bu, Pr, OEt, NH, NMe, NEt, NPr, N, dimethylpiperidino). Isolation of the -butyl and dimethylamino derivatives allowed comparative studies of their P nuclear shielding tensors by magic-angle-spinning solid-state nuclear magnetic resonance spectroscopy. Density functional theory and natural chemical shielding analyses reveal the relationship between the P chemical shift tensor and the local ruthenium/phosphorus electronic structure.

An Azophosphine Synthetic Equivalent of Mesitylphosphaazide and Its 1,3-Dipolar Cycloaddition Reactions.

Dibenzo-7-phosphanorbornadiene-substituted diazene MesNP (, where Mes = mesityl, = anthracene, or CH), a synthetic equivalent of mesitylphosphaazide (MesNP) and anthracene, was synthesized by treatment of [PhBP][Na(OEt)] with [MesN]OTf (OTf = CFSO) in thawing tetrahydrofuran (14% isolated yield). Treatment of with unsaturated molecules cyclooctyne, [Na(dioxane)][OCP] (phosphaethynolate), and Ad-C≡P (Ad = adamantyl) results in the corresponding [3 + 2] phosphaazide-(phospha)alkyne cycloadducts, with concomitant loss of anthracene in 65%, 49%, and 38% isolated yield, respectively. Structural data for the phosphaethynolate cycloadduct ([][Na(12-crown-4)]) were obtained in a single-crystal X-ray diffraction study.