Probing the Electron Accepting Ability of Phosphaphenalenes.

Phosphaphenalenes, extended π conjugates with the incorporation of phosphorus, are attractive avenues towards molecular materials for the applications in organic electronics, but their electron accepting ability have not been investigated. Herein we present systematic studies on the reductive behavior of a representative phosphaphenalene and its oxide by chemical and electrochemical methods. The chemical reduction of the phosphaphenalene by alkali metals reveals the facile P-C bond cleavage to form phosphaphenalenide anion, which functions as a transfer block for structure modification on the phosphorus atom. In contrast, the pentavalent P-oxide reacts with one or two equivalents of elemental sodium to form stable radical anion and dianion salts, respectively.

Alkylation and Arylation at Boron in NHC-Stabilized Phosphaborenes.

Phosphaborenes, featuring a phosphorus-boron multiple bond, remain a relatively untapped area in chemical research due to the limited synthetic methods. Introducing leaving groups as substituents to the phosphorus or boron can pave the way for enhanced functionalization and modification. In this study, we present the synthesis of phosphaborenes featuring an N-heterocyclic boryl group on phosphorus and halogen substituent on boron, with stabilization provided by an N-heterocyclic carbene. Straightforward alkylation/arylation of these phosphaborenes is achieved by substituting the halogen with benzyl and aryl groups at the boron terminus. Our approach offers an efficient route to produce a diverse array of phosphaborene structures.

An Isolable Radical Anion Featuring a 2-Center-3-Electron π-Bond without a Clearly Defined σ-Bond.

Featuring an extra electron in the π* antibonding orbital, species with a 2-center-3-electron (2c3e) π bond without an underlying σ bond are scarcely known. Herein, we report the synthesis, isolation and characterization of a radical anion salt [K(18-C-6)]+ {[(HCNDipp)2 Si]2 P2 }⋅- (i.e. [K(18-C-6)]+ 3⋅- ) (18-C-6=18-crown-6, Dipp=2,6-diisopropylphenyl), in which 3⋅- features a perfectly planar Si2 P2 four-membered ring. This species represents the first example of a Si- and P-containing analog of a bicyclo[1.1.0]butane radical anion. The unusual bonding motif of 3⋅- was thoroughly investigated via X-ray diffraction crystallography, electron paramagnetic resonance spectroscopy (EPR), and calculations by density functional theory (DFT), which collectively unveiled the existence of a 2c3e π bond between the bridgehead P atoms and no clearly defined supporting P-P σ bond.

Utilizing bis(imino)dihydroacridanide pincer ligands in p-block chemistry: synthesis and catalysis of an antimony monocation salt.

We present the synthesis and characterization of an Sb(III) monocation salt stabilized by a bulky bis(imino)dihydroacridanide pincer ligand. The Lewis acidity of the Sb cation is quantified using the Guttmann-Beckett method and confirmed by its reaction with 4-dimethylaminopyridine, which forms a Lewis acid-base adduct. This Sb cation exhibits catalytic activity in the cyanosilylation of arylketones. The electronic structure of the Sb cation as well as the mechanism of the catalytic transformation are explored by density functional theory computations.

Alkoxyphosphorane/Borane Cooperative Alkylations: A Frustrated Lewis Pair Version of the Mitsunobu Reaction.

The combination of the alkoxyphosphoranes, Ph2 P(OR)(O2 C6 Cl4 ) and the borane B(C6 F5 )3 generates the zwitterions 3 which act as FLP to effect the alkylation of several nucleophiles affording C-C, C-N, C-H and C-Cl coupling products. A DFT study shows the reaction proceeds via an FLP activation pathway generating an alkoxyphosphonium intermediate which effects the alkylation of the nucleophiles, akin to the Mitsunobu reaction.

Free Aluminylenes: An Emerging Class of Compounds.

Aluminylenes (R-Al) are aluminium analogs of carbenes. In contrast to isolable carbenes, aluminylenes are extremely rare species. In the past years, pioneered by Schnöckel, Roesky and Power, a few free aluminylenes and their complexes have been reported. Such compounds have the aluminium atom in the oxidation state +I, which contrasts with classical organoaluminium derivatives that contain the element in the +III oxidation state. Aluminylenes, either in their free state or in the coordination sphere of a Lewis base, are capable of coordinating to transition metals and activating inert chemical bonds. Free aluminylenes are emerging as potent synthetic platforms for unusual aluminium species.

Facile Synthesis of the Dicyanophosphide Anion via Electrochemical Activation of White Phosphorus: An Avenue to Organophosphorus Compounds.

Organophosphorus compounds (OPCs) have gained tremendous interest in the past decades due to their wide applications ranging from synthetic chemistry to materials and biological sciences. We describe herein a practical and versatile approach for the transformation of white phosphorus (P4) into useful OPCs with high P atom economy via a key bridging anion [P(CN)2]-. This anion can be prepared on a gram scale directly from P4 through an electrochemical process. A variety of OPCs involving phosphinidenes, cyclophosphanes, and phospholides have been made readily accessible from P4 in a two-step manner. Our approach has a significant impact on the future preparation of OPCs in laboratory and industrial settings.

Reversible Stereoisomerization of 1,3-Diphosphetane Frameworks Revealed by a Single-Electron Redox Approach.

The discovery of pyramidal inversion has continued to impact modern organic and organometallic chemistry. Sequential alkylation reactions of an N-heterocyclic carbene (NHC) ligated dicarbondiphosphide 1 with RI (R = Me, Et, or iBu) and ZnMe2 give rise to the highly stereoselective synthesis of cis-1,3-diphosphetanes 3. cis-3 is conformationally favorable at room temperature, whereas inversion to trans-3 is observed at 110 °C. One-electron oxidation of cis-3 with Fc+(BArF) (Fc = [Fe(C5H5)2]; BArF = [B(3,5-(CF3)2C6H3)4)]-) leads to the stereoselective formation of trans-1,3-diphosphetane radical cation salts 3•+(BArF), which can be reversibly transformed to cis-3 upon one-electron reduction. Salts 3•+(BArF) represent the first examples of 1,3-diphosphetane radical cations. These results provide a potential application of planar four-membered heterocycle-based building blocks for electrically fueled molecular switches.

Coordination-induced polymerization of P═C bonds leads to regular (P─C) n polycarbophosphanes.

The replacement of carbon in (C─C) n chains of polyolefins by phosphorus leads to polycarbophosphanes (P─C) n , which may possess unique chemical and physical properties. However, macromolecules with a regular (P─C) n chain have never been unambiguously identified. Here, we demonstrate that addition polymerization, a general concept to polymerize olefins, can be extended to P═C double bonds. The polymerization of monomeric 2-phosphanaphthalenes is mediated by copper(I) halides and leads to polycarbophosphanes with an M n of 14 to 34 kDa. Each phosphorus is coordinated to Cu(I), which can be easily removed. Unlike long-term durable polyolefins, the metal-free polymers depolymerize rapidly back to monomers under sunlight or ultraviolet irradiation at λ = 365 nm. The monomers can be recycled for repolymerization, demonstrating a cradle-to-cradle life cycle for polycarbophosphanes.

Salen supported Al-O-C[triple bond, length as m-dash]P and Ga-P[double bond, length as m-dash]C[double bond, length as m-dash]O complexes.

The first OCP adducts of aluminium and gallium are reported. The complexes are supported by sterically encumbered salen ligands and reveal a selective binding to O and P, respectively. Their reactivity with diazaphosphenium Lewis acids and N-heterocyclic carbene Lewis bases is described, in addition to cycloaddition reactions with s-tetrazines.

Transient Dipnictyl Analogues of Acrylamides, R-E=E'-CONR2 , and a Related Diphosphadigalletane from Na[OCP] and (R2 N)2 ECl (E, E'=P, As, Ga).

The reaction of Na[OCP] with (R2 N)2 ECl (E=P or As; R=alkyl) granted direct access to transient amine-substituted diphospha- and arsaphospha-acrylamide analogues, (R2 N)E=P(CONR2 ) 1. Their facile formation allowed for a comprehensive reactivity study. Dimerization yielded the four-membered rings (R2 N)2 E2 P2 (CONR2 )2 , whereas in the presence of excess Na[OCP], a stepwise [2+2] cycloaddition occured, leading to the sodium salts of carboxotripnictides [(R2 N)EP2 CO(CONR2 )]- . These salts served as a reservoir of 1, either by extrusion of Na[OCP] or by reaction with the appropriate (R2 N)2 ECl, giving the [4+2]-cycloaddition products (R2 N)EP(C6 H10 )(CONR2 ) in the presence of 2,3-dimethylbutadiene. The formal conjugate addition product K[(tBuO)(R2 N)PP(CONR2 )] was obtained by reaction of Na[(R2 N)PP2 CO(CONR2 )] with tBuOK. In addition, a rare diphosphadigalletane with a ladder-type (R2 N)2 Ga2 P2 (CONR2 )2 core was isolated from the reaction of Na[OCP] with (R2 N)2 GaCl (R=alkyl). The unprecedented pnictogenyl carboxamide compounds were thoroughly characterized, including single-crystal X-ray structure determinations, and mechanisms for their formation were investigated by DFT calculations.

Simple Synthesis of Functionalized 2-Phosphanaphthalenes.

A simple synthesis of sodium 2-phosphanaphthalene-3-olate (1) based on the extrusion of N2 from phthalazine using Na[OCP] is reported. This heterocycle can be readily functionalized at the negatively charged oxygen center using a variety of electrophilic substrates. The coordination chemistry of both 1 and its neutral derivatives was explored, revealing their facile use as P-donor ligands for late-transition-metal complexes.

2,4,6-Tri(hydroxy)-1,3,5-triphosphinine, P3 C3 (OH)3 : The Phosphorus Analogue of Cyanuric Acid.

Cyanuric acid (C3 H3 N3 O3 ) is widely used as cross-linker in basic polymers (often in combination with other crosslinking agents like melamine) but also finds application in more sophisticated materials such as in supramolecular assemblies and molecular sheets. The unknown phosphorus analogue of cyanuric acid, P3 C3 (OH)3 , may become an equally useful building block for phosphorus-based polymers or materials which have unique properties. Herein we describe a straightforward synthesis of 2,4,6-tri(hydroxy)-1,3,5-triphosphinine and its derivatives P3 C3 (OR)3 which have been applied as strong π-acceptor η6 -ligands in piano stool Mo(CO)3 complexes.

The chemistry of parent phosphiranide in the coordination sphere of tungsten.

2-Chloroethylphosphine W(CO)5 complex readily reacts with sodium hydride. With one equivalent of NaH, the parent phosphirane complex is obtained. With more than two equivalents, the phosphiranide complex is exclusively formed. With 1.5 equivalents, a 1 : 1 mixture of and is obtained but readily attacks at the phosphorus atom by splitting of ethylene and by the formation of the P-P complex . In turn, the P-P bond of is split by NaH to yield the phosphide complex . The phosphiranide complex is a good source for a large variety of functional phosphirane complexes . With BrCN, the 1-cyanophosphirane complex is formed. Upon heating it loses its complexing group. Upon hydrolysis, it gives the 1-hydroxyphosphirane complex which dimerizes in basic medium by opening one P-C bond of the ring to give . The reaction of with PhPCl2 yields the triphosphorus complex whose molecular structure has been established by X-ray crystal structure analysis.

Palladium-catalyzed three-component domino reaction for the preparation of benzo[b]thiophene and related compounds.

A simple and efficient palladium-catalyzed three-component domino reaction of bromothiophenes with internal alkynes has been developed to produce benzo[b]thiophenes in moderate to good yields.