Sb-to-P Metathesis: A Direct Route to Structurally Constrained, Cationic P Compound.

Structurally constrained, cationic P compound [LP][SbCl] with an OCO pincer-type ligand (L) having a central carbene donor was directly synthesized via an Sb-to-P metathesis reaction between PCl and LSb-Cl. [LP][SbCl] was isolated and its reactivity with small molecules (ROH and RNH) was studied, showing that [SbCl] is not an innocent counter anion, but an active participant in these reactions. When the [SbCl] was replaced with the [CBH] ([Cb]) anion, the reactions were redirected to [LP] cation only.

Hydrogen splitting at a single phosphorus centre and its use for hydrogenation.

Catalytic processes are largely dominated by transition-metal complexes. Main-group compounds that can mimic the behaviour of the transition-metal complexes are of great interest due to their potential to substitute or complement transition metals in catalysis. While a few main-group molecular centres were shown to activate dihydrogen via the oxidative addition process, catalytic hydrogenation using these species has remained challenging.

Polyaromatic Calixarene Hosts: Calix[4]pyrenes.

Calixpyrenes, calix[4]arenes incorporating one or two pyrene moieties as a part of their hydrophobic cavities, have been prepared and fully characterized. Distally di--propoxy diether of the calix dipyrene, which exists in the pinched cone conformation with nearly parallel pyrene moieties, demonstrates strongly enhanced binding of an organic cation (-methylpyridinium) compared with the analogous diethers of the parent calix[4]arene.

Long Range Electronic Effects on the Host-Guest Complexation within the Oxygen Depleted 5,5'-Bicalixarene Cavities.

We report the synthesis of a series of the oxygen-depleted conjugated 5,5'-Bicalix[4]arene compounds bearing various substituents at the terminal positions of the conjugated chain and their fluorescence response to the presence of a cationic -methylpyridinium guest. The complexation of this cation within the bicalixarene cavity results in the fluorescence quenching, with the host molecules bearing electron-donating groups demonstrating a stronger fluorescence response. These results show the importance of the electronic effects on the host-guest complexation within the hydrophobic calixarene scaffolds.

Polymeric architecture as a tool for controlling the reactivity of palladium(II) loaded nanoreactors.

Self-assembled systems, like polymeric micelles, have become great facilitators for conducting organic reactions in aqueous media due to their broad potential applications in green chemistry and biomedical applications. Massive strides have been taken to improve the reaction scope of such systems, enabling them to perform bioorthogonal reactions for prodrug therapy. Considering these significant advancements, we sought to study the relationships between the architecture of the amphiphiles and the reactivity of their Pd loaded micellar nanoreactors in conducting depropargylation reactions.

Highly Chemoselective Zn -Catalyzed Hydrosilylation of Alkynes.

Hydrosilylation of C=C double and C≡C triple bonds is one of the most widely used processes in organosilicon chemistry, mostly catalyzed by Pt-based complexes. Herein, the synthesis of a dicationic Zn -based complex with a tripodal tris(2-pyridylmethyl)amine (TPA) ligand is reported which was found to be a highly chemoselective catalyst for hydrosilylation reactions of alkynes. Mechanistic studies revealed that unlike typical Zn-catalyzed hydrosilylation reactions where the key step is the activation of the Si-H bond, this system catalyzes the hydrosilylation reaction through the activation of C≡C triple bonds, which presumably is the reason for its high chemoselectivity.

Metallomimetic Chemistry of a Cationic, Geometrically Constrained Phosphine in the Catalytic Hydrodefluorination and Amination of Ar-F Bonds.

The synthesis, isolation, and reactivity of a cationic, geometrically constrained σ-P compound in the hexaphenyl-carbodiphosphoranyl-based pincer-type ligand () are reported. reacts with electron-poor fluoroarenes via an oxidative addition-type reaction of the C-F bond to the P-center, yielding new fluorophosphorane-type species (P). This reactivity of was used in the catalytic hydrodefluorination of Ar-F bonds with PhSiH, and in a catalytic C-N bond-forming cross-coupling reactions between fluoroarenes and aminosilanes.

Carbon-Nitride Popcorn-A Novel Catalyst Prepared by Self-Propagating Combustion of Nitrogen-Rich Triazenes.

The interest in development of non-graphitic polymeric carbon nitrides (PCNs), with various C-to-N ratios, having tunable electronic, optical, and chemical properties is rapidly increasing. Here the first self-propagating combustion synthesis methodology for the facile preparation of novel porous PCN materials (PCN3-PCN7) using new nitrogen-rich triazene-based precursors is reported. This methodology is found to be highly precursor dependent, where variations in the terminal functional groups in the newly designed precursors (compounds 3-7) lead to different combustion behaviors, and morphologies of the resulted PCNs.

Intramolecular C-N bond activation by a geometrically constrained P-centre.

In this work the first examples of C-N bond activation by insertion into a geometrically constrained P-centre are shown. The mechanisms of these activation processes leading to new P species were studied both experimentally and computationally. Interestingly, in the case of insertion of the P-centre into an N-C(O)H bond, an unstable phosphoranyl-formaldehyde intermediate is probably formed, which undergoes decarbonylation in the presence of a catalytic amount of HCl producing a hydrophosphorane.

Dual Reactivity of a Geometrically Constrained Phosphenium Cation.

A geometrically constrained phosphenium cation in bis(pyrrolyl)pyridine based NNN pincer type ligand (1 ) was synthesized, isolated and its preliminary reactivity was studied with small molecules. 1 reacts with MeOH and Et NH, activating the O-H and N-H bonds via a P-center/ligand assisted path. The reaction of 1 with one equiv.

Geometrically constrained square pyramidal phosphoranide.

Geometrical constriction of main group elements leading to a change in the reactivity of these main group centers has recently become an important tool in main group chemistry. A lot of focus on using this modern method is dedicated to group 15 elements and especially to phosphorus. In this work, we present the synthesis, isolation and preliminary reactivity study of the geometrically constrained, square pyramidal (SP) phosphoranide anion (1).

Benzylic Dehydroxylation of Echinocandin Antifungal Drugs Restores Efficacy against Resistance Conferred by Mutated Glucan Synthase.

Each year, infections caused by fungal pathogens claim the lives of about 1.6 million people and affect the health of over a billion people worldwide. Among the most recently developed antifungal drugs are the echinocandins, which noncompetitively inhibit β-glucan synthase, a membrane-bound protein complex that catalyzes the formation of the main polysaccharide component of the fungal cell wall.

Phosphorus mediated imidazolinium to oxazolium ring rearrangement.

An unexpected rearrangement occurred when an imidazolinium based OCO pincer-type ligand (1) reacted with PCl producing a chlorophosphine with a pendant oxazolium "arm" (3). The mechanism of this rearrangement was studied both experimentally and by density functional theory (DFT) computations. The deprotonation of 3 led to further unexpected results.

Allenic phosphonium borate zwitterions via a phosphonium allenylidene intermediate.

We describe the synthesis of alkynyl phosphanes of the type RP-C[triple bond, length as m-dash]C-C(OCH)Ph (R = Ph, Cy) and investigate their transformation to geminally substituted phosphonium borato-allene zwitterions upon their reaction with B(CF). The mechanism for this transformation was studied experimentally and by density functional theory computations (DFT), suggesting the intermediacy of an unsaturated 3-coordinate phosphonium electrophile akin to a methylene phosphonium cation.

Low-Power Laser Ignition of an Antenna-Type Secondary Energetic Copper Complex: Synthesis, Characterization, Evaluation, and Ignition Mechanism Studies.

In recent years, development of new energetic compounds and formulations, suitable for ignition with relatively low-power lasers, is a highly active and competitive field of research. The main goal of these efforts is focused on achieving and providing much safer solutions for various detonator and initiator systems. In this work, we prepared, characterized, and studied thermal and ignition properties of a new laser-ignitable compound, based on the 5,6-bis(ethylnitroamino)-'2,'3-dihydroxypyrazine-2,3-bis(carboximidamide) (DS3) proligand.

Carborane Stabilized "19-Electron" Molybdenum Metalloradical.

Paramagnetic metal complexes gained a lot of attention due to their participation in a number of important chemical reactions. In most cases, these complexes are dominated by 17-e metalloradicals that are associatively activated with highly reactive paramagnetic 19-e species. Molybdenum paramagnetic complexes are among the most investigated ones.

Facile proton-coupled electron transfer enabled by coordination-induced E-H bond weakening to boron.

We report the facile activation of aryl E-H (ArEH; E = N, O, S; Ar = Ph or C6F5) or ammonia N-H bonds via coordination-induced bond weakening to a redox-active boron center in the complex, (1-). Substantial decreases in E-H bond dissociation free energies (BDFEs) are observed upon substrate coordination, enabling subsequent facile proton-coupled electron transfer (PCET). A drop of >50 kcal mol-1 in H2N-H BDFE upon coordination was experimentally determined.

An air-stable, Zn-based catalyst for hydrosilylation of alkenes and alkynes.

Hydrosilylation of C[double bond, length as m-dash]C double and C[triple bond, length as m-dash]C triple bonds is one of the most widely used processes in organosilicon chemistry, mostly catalyzed by Pt-based complexes. We report here the synthesis of an air-stable dicationic Zn2+-based complex in a hemilabile tris(2-methyl-6-pyridylmethyl) phosphine (TmPPh) ligand, 12+[B(C6F5)4]2. When heated, 12+[B(C6F5)4]2 activates Si-H bonds reversibly via ligand/metal cooperation between Lewis acidic Zn2+ and Lewis basic N centers in a frustrated Lewis pair (FLP) type fashion.

Fluorophore-Appendant 5,5'-Bicalixarene Scaffolds for Host-Guest Sensing of Nitric Oxide.

Conjugated 5,5'-Bicalixarene scaffolds having fluorophores at the chain termini have been prepared and tested in the supramolecular detection of nitric oxide. Scaffolds bearing electron-rich fluorophores demonstrated a stronger turn-off response to the presence of NO than the fluorophore-free analogue in both organic and aqueous media, while no fluorescence quenching happened when the electron-deficient fluorophores were employed. Unprecedented ratiometric supramolecular sensing was observed when fluorophores of the opposite electronic demands were placed at the scaffold's termini.

Redox-Controlled Reactivity at Boron: Parallels to Frustrated Lewis/Radical Pair Chemistry.

We report the synthesis of new Lewis-acidic boranes tethered to redox-active vanadium centers, (PhN)V(μ-N)B(CF) () and (N(CHCHN(CF)))V(μ-N)B(CF) (). Redox control of the V couple resulted in switchable borane versus "hidden" boron radical reactivity, mimicking frustrated Lewis versus frustrated radical pair (FLP/FRP) chemistry, respectively. Whereas heterolytic FLP-type addition reactions were observed with the V complex () in the presence of a bulky phosphine, homolytic peroxide, or Sn-hydride bond cleavage reactions were observed with the V complex, [CoCp][(N(CHCHN(CF)))V(μ-N)B(CF)] (), indicative of boron radical anion character.

Base- and Catalyst-Induced Orthogonal Site Selectivities in Acylation of Amphiphilic Diols.

Seeking to selectively functionalize natural and synthetic amphiphiles, we explored acylation of model amphiphilic diols. The use of a nucleophilic catalyst enabled a remarkable shift of the site selectivity from the polar site, preferred in background noncatalyzed or base-promoted reactions, to the apolar site. This tendency was significantly enhanced for organocatalysts comprising an imidazole active site surrounded by long/branched tails.

Phosphorylation Organocatalysts Highly Active by Design.

The activity of nucleophilic organocatalysts for alcohol/phenol phosphorylation was enhanced through attaching oligoether appendages to a benzyl substituent on imidazole- or aminopyridine-based active units, presumably because of stabilizing -cation interactions of the ethereal oxygens with the positively charged aza-heterocycle in the catalytic intermediates, and was substantially higher than that of known benchmark catalysts for a range of substrates. Density functional theory calculations and the study of analogues having a lower potential for such stabilizing interactions support our hypothesis.

Redox-switchable carboranes for uranium capture and release.

The uranyl ion (UO; U(VI) oxidation state) is the most common form of uranium found in terrestrial and aquatic environments and is a central component in nuclear fuel processing and waste remediation efforts. Uranyl capture from either seawater or nuclear waste has been well studied and typically relies on extremely strong chelating/binding affinities to UO using chelating polymers, porous inorganic or carbon-based materials, as well as homogeneous compounds. By contrast, the controlled release of uranyl after capture is less established and can be difficult, expensive or destructive to the initial material.

Isolable cyclic (alkyl)(amino)carbene-phosphonyl radical adducts.

Phosphonyl radicals ([RP[double bond, length as m-dash]O]˙) and their adducts are proposed as intermediates in a number of important chemical and biological processes. Despite the great interest in these species, there are no examples of stable, isolated phosphonyl radicals or their adducts reported in the literature. Here we report the synthesis, EPR and theoretical study of stable, isolable cyclic (alkyl)(amino)carbene (cAAC)-phosphonyl radical adducts, [cAAC-P(O)R]˙ (R = OPr, Ph).

A self-catalyzed reaction of 1,2-dibenzoyl-o-carborane with hydrosilanes - formation of new hydrofuranes.

The activation of Si-H bonds is a very important transformation both in organic and inorganic chemistry. Herein we report that 1,2-dibenzoyl-o-carborane (1) reacts with Si-H bonds, yielding new hydrofurane-type products. The mechanism of this Si-H bond activation was studied both experimentally and by DFT calculations, and supposedly proceeds in an FLP-type manner.