η3‐Diphosphavinylcarbene: A P2 Analogue of the Dötz Intermediate

Do the twist : The reaction of in situ generated phosphinidenes with phosphaalkynes is a facile route to the new metal‐coordinated η³‐diphosphavinylcarbene 1 , which shows facile ligand‐exchange reactions and undergoes an unprecedented rearrangement that involves phosphinidene complex 2 and η³‐phosphaalkenylphosphinidene complex 3 , the 1,3 isomer of 1 .

     

Pyridyl‐Functionalised 3H‐1,2,3,4‐Triazaphospholes: Synthesis,Coordination Chemistry and Photophysical Properties of Low‐Coordinate Phosphorus Compounds

Novel conjugated, pyridyl‐functionalised triazaphospholes with either tBu or SiMe₃ substituents at the 5‐position of the N₃PC heterocycle have been prepared by a [3+2] cycloaddition reaction and compared with structurally related, triazole‐based systems. Photoexcitation of the 2‐pyridyl‐substituted triazaphosphole gives rise to a significant fluorescence emission with a quantum yield of up to 12 %. In contrast, the all‐nitrogen triazole analogue shows no emission at all. DFT calculations indicate that the 2‐pyridyl substituted systems have a more rigid and planar structure than their 3‐ and 4‐pyridyl isomers. Time‐dependent (TD) DFT calculations show that only the 2‐pyridyl‐substituted triazaphosphole exhibits similar planar geometry, with matching conformational arrangements in the lowest energy excited state and the ground state; this helps to explain the enhanced emission intensity. The chelating P,N‐hybrid ligand forms a Re^I complex of the type [(N^N)Re(CO)₃Br] through the coordination of nitrogen atom N² to the metal centre rather than through the phosphorus donor. Both structural and spectroscopic data indicate substantial π‐accepting character of the triazaphosphole, which is again in contrast to that of the all‐nitrogen‐containing triazoles. The synthesis and photophysical properties of a new class of phosphorus‐containing extended π systems are described.     

A Phosphorus Analogue of p-Quinodimethane with a Planar P4 Ring: A Metal-Free Diphosphorus Source

Para-quinodimethane (pQDM) is a fundamental structural component in many π-conjugated organic molecules and materials. The incorporation of phosphorus atom into π-conjugated frameworks offers unique opportunities for controlling the properties of derived species. A phosphorus analogue of p-quinodimethane (pQDM), (IPrC)₂P₄ [ 5 , IPr=C{N(Ar)CH₂}₂; Ar=2,6-iPr₂C₆H₃] featuring a planar P₄ ring, was readily accessible by KC₈-reduction of (IPrC)(PCl₂)₂ ( 2 ). Base-mediated C−H functionalization of IPrCH₂ ( 1 ) with PCl₃ afforded 2 . The formation of 5 was expected to occur through a dimerization of the transient 3H-diphosphirene (IPrC)P₂ ( 4 ), which was theoretically suggested to have an intermediate diradical character. Compound 5 underwent photo-induced ring-contraction reaction to form the singlet diradicaloid (IPrCP)₂ VI and white phosphorus (P₄). The formation of and VI and P₄ suggested the formal diphosphorus (P₂) elimination from 5 . Indeed, photolysis of a mixture of 1,3-cyclohexadiene (CHD) and 5 led to the formation of P₂-entrapped product (CHD)₂P₂ ( 6 ). The compound 5 represents the first organophosphorus species that functions as a P₂ source.     

A Phosphorus Analogue of Bis(η4‐cyclobutadiene)iron(0)

P makes it possible : The convenient oxidative synthesis of the 16‐electron organophosphorus iron sandwich complex [Fe(η⁴‐P₂C₂tBu₂)₂] (see structure) suggests that the elusive all‐carbon complex [Fe(η⁴‐C₄H₄)₂] is a viable synthetic target.

     

Borane Adducts of Aromatic Phosphorus Heterocycles: Synthesis,Crystallographic Characterization and Reactivity of a Phosphinine-B(C6F5)3 Lewis Pair

A phosphinine-borane adduct of a Me₃Si-functionalized phosphinine and the Lewis acid B(C₆F₅)₃ has been synthesized and characterized crystallographically for the first time. The reaction strongly depends on the nature of the substituents in the α-position of the phosphorus heterocycle. In contrast, the reaction of B₂H₆ with various substituted phosphinines leads to an equilibrium between the starting materials and the phosphinine–borane adducts that is determined by the Lewis basicity of the phosphinine. The novel phosphinine borane adduct ( 6 -B(C₆F₅)₃) shows rapid and facile insertion and [4+2] cycloaddition reactivity towards phenylacetylene. A hitherto unknown dihydro-1-phosphabarrelene is formed with styrene. The reaction with an ester provides a new, facile and selective route to 1-R-phosphininium salts. These salts then undergo a [4+2] cycloaddition in the presence of Me₃Si−C≡CH and styrene to cleanly form unprecedented derivatives of 1-R-phosphabarrelenium salts.     

Addition of a Cyclophosphine to Nitriles: An Inorganic Click Reaction Featuring Protio,Organo, and Main‐Group Catalysis

The addition of a cyclotriphosphine to a broad range of nitriles gives access to the first examples of free 1‐aza‐2,3,4‐triphospholenes in a rapid, ambient temperature, one‐pot, high‐yield protocol. The reaction produces electron‐rich heterocycles (four lone pairs) and features homoatomic σ‐bond heterolysis, thereby combining the key features of the 1,3‐dipolar cycloaddition chemistry of azides and cyclopropanes. Also reported is the first catalytic addition of P−P bonds to the C≡N bond. The coordination chemistry of the new heterocycles is explored.     

Single‐Step Microwave‐Mediated Synthesis of Oxazoles and Thiazoles from 3‐Oxetanone: A Synthetic and Computational Study

The direct microwave‐mediated condensation between 3‐oxetanone and primary amides and thioamides has delivered moderate to good yields of (hydroxymethyl)oxazoles and (hydroxymethyl)thiazoles. The reactions use a sustainable solvent and only require short reaction times. These are highly competitive methods for the construction of two classes of valuable heteroarenes, which bear a useful locus for further elaboration. Electronic structure calculations have shown that the order of events involves chalcogen atom attack at sp³ carbon and alkyl–oxygen cleavage. The critical role of acid catalysis was shown clearly, and the importance of acid strength was demonstrated. The calculated barriers were also fully consistent with the observed order of thioamide and amide reactivity. Spontaneous ring opening involves a modest degree of C? O cleavage, moderating the extent of strain relief. On the acid‐catalysed pathway, C? O cleavage is less extensive still, but proton transfer to the nucleofuge is well advanced with the carboxylic acid catalysts, and essentially complete with methanesulfonic acid.     

Dendrimeric Oligo(phenylenevinylene)‐Extended Dithieno[3,2‐b:2′,3′‐d]phospholes—Synthesis,Self‐Organization,and Optical Properties

A boost from the branches : Incorporation of the dithieno[3,2‐b:2′,3′‐d]phosphole system as a core in oligo(phenylenevinylene) dendrimers (an example is shown here) provides materials that exhibit energy‐transfer features relaying incoming photons from the dendrons towards the core, which in turn shows enhanced emission intensity. The optical properties and self‐assembly features of the dendrimers can be impacted by the terminal groups (‐H, ‐CF₃, or ‐NPh₂) employed.

     

2‐(2′‐Pyridyl)‐4,6‐diphenylphosphinine versus 2‐(2′‐Pyridyl)‐4,6‐diphenylpyridine: Synthesis,Characterization, and Reactivity of Cationic RhIII and IrIII Complexes Based on Aromatic Phosphorus Heterocycles

The bidentate P,N hybrid ligand 1 allows access for the first time to novel cationic phosphinine‐based Rh^III and Ir^III complexes, broadening significantly the scope of low‐coordinate aromatic phosphorus heterocycles for potential applications. The coordination chemistry of 1 towards Rh^III and Ir^III was investigated and compared with the analogous 2,2′‐bipyridine derivative, 2‐(2′‐pyridyl)‐4,6‐diphenylpyridine ( 2 ), which showed significant differences. The molecular structures of [RhCl(Cp*)( 1 )]Cl and [IrCl(Cp*)( 1 )]Cl (Cp*=pentamethylcyclopentadienyl) were determined by means of X‐ray diffraction and confirm the mononuclear nature of the λ³‐phosphinine–Rh^III and Ir^III complexes. In contrast, a different reactivity and coordination behavior was found for the nitrogen analogue 2 , especially towards Rh^III as a bimetallic ion pair [RhCl(Cp*)( 2 )]⁺[RhCl₃(Cp*)]^? is formed rather than a mononuclear coordination compound. [RhCl(Cp*)( 1 )]Cl and [IrCl(Cp*)( 1 )]Cl react with water regio‐ and diastereoselectively at the external P?C double bond, leading exclusively to the anti‐addition products [MCl(Cp*)( 1 H ? OH)]Cl as confirmed by X‐ray crystal‐structure determination.     

2,4,6‐Tri(hydroxy)‐1,3,5‐triphosphinine,P3C3(OH)3: The Phosphorus Analogue of Cyanuric Acid

Cyanuric acid (C₃H₃N₃O₃) 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, P₃C₃(OH)₃, may become an equally useful building block for phosphorus‐based polymers or materials which have unique properties. ¹ Herein we describe a straightforward synthesis of 2,4,6‐tri(hydroxy)‐1,3,5‐triphosphinine and its derivatives P₃C₃(OR)₃ which have been applied as strong π‐acceptor η⁶‐ligands in piano stool Mo(CO)₃ complexes.     

Stishovite's Relative: A Post‐Coesite Form of Phosphorus Oxonitride

Phosphorus oxonitride (PON) is isoelectronic with SiO₂ and may exhibit a similar broad spectrum of intriguing properties as silica. However, PON has only been sparsely investigated under high‐pressure conditions and there has been no evidence on a PON polymorph with a coordination number of P greater than 4. Herein, we report a post‐coesite (pc) PON polymorph exhibiting a stishovite‐related structure with P in a (5+1) coordination. The pc‐PON was synthesized using the multianvil technique and characterized by powder X‐ray diffraction, solid‐state NMR spectroscopy, TEM measurements and in situ synchrotron X‐ray diffraction in diamond anvil cells. The structure model was verified by single‐crystal X‐ray diffraction at 1.8 GPa and the isothermal bulk modulus of pc‐PON was determined to K₀=163(2) GPa. Moreover, an orthorhombic PON polymorph (o‐PON) was observed under high‐pressure conditions and corroborated as the stable modification at pressures above 17 GPa by DFT calculations.     

3‐Bromo‐2‐Pyrone: An Alternative and Convenient Route to Functionalized Phosphinines

The facile access to 3‐bromo‐2‐pyrone allows the preparation of 6‐bromo‐2‐trimethylsilyl‐phosphinine by a [4+2] cycloaddition with Me₃Si‐C≡P for the first time. The regioselectivity of this reaction could be verified by means of single crystal X‐ray diffraction of the corresponding W⁰ complex. In the presence of ZnBr₂ and dppp (1,3‐bis(diphenylphosphino)propane) as a bidentate ligand, the bromo‐phosphinine quantitatively undergoes a Negishi cross‐coupling reaction with PhLi that selectively leads to 6‐phenyl‐2‐trimethylsilyl‐phosphinine. This heterocycle could again be characterized by means of X‐ray diffraction as a W⁰ complex. These results describe a new and convenient route to 2,6‐disubstituted phosphinines that makes use of readily available starting materials.     

Energetic Salts Based on an Oxygen‐Containing Cation: 2,4‐Diamino‐1,3,5‐triazine‐6‐one

A family of energetic salts with high thermal stability and low impact sensitivity based on an oxygen‐containing cation, 2,4‐diamino‐1,3,5‐triazine‐6‐one, were synthesized and fully characterized by IR and multinuclear (¹H, ¹³C) NMR spectroscopy, elemental analysis, and differential scanning calorimetry. Insights into their sensitivities towards impact, friction, and electrostatics were gained by submitting the materials to standard tests. The structures of 2,4‐diamino‐1,3,5‐triazine‐6‐one nitrate, 2,4‐diamino‐1,3,5‐triazine‐6‐one sulfate, 2,4‐diamino‐1,3,5‐triazine‐6‐one perchlorate, 2,4‐diamino‐1,3,5‐triazine‐6‐one 5‐nitrotetrazolate were determined by single‐crystal X‐ray diffraction; their densities are 1.691, 1.776, 1.854, and 1.636 g cm^?3, respectively. Most of the salts decompose at temperatures over 180 °C; in particular, the salts 2,4‐diamino‐1,3,5‐triazine‐6‐one nitrate and 2,4‐diamino‐1,3,5‐triazine‐6‐one perchlorate, which decompose at 303.3 and 336.4 °C, respectively, are fairly stable. Furthermore, most of the salts exhibit excellent impact sensitivities (>40 J), friction sensitivities (>360 N), and are insensitive to electrostatics. The measured densities of these energetic salts range from 1.64 to 2.01 g cm^?3. The detonation pressure values calculated for these salts range from 14.6 to 29.2 GPa, and the detonation velocities range from 6536 to 8275 m s^?1; these values make the salts potential candidates for thermally stable and insensitive energetic materials.     

Photolytic Reductive Elimination of White Phosphorus from a Mononuclear cyclo‐P4 Transition Metal Complex

Elemental white phosphorus (P₄) is well recognized as a critical precursor to organophosphorus compounds. However, regulatory constraints stemming from the toxic and pyrophoric nature of white phosphorus have significantly limited its accessibility. Herein is described a new approach to white phosphorus storage and release based on a unique example of photolytic reductive elimination of the tetrahedral P₄ molecule from a mononuclear cyclo‐P₄ molybdenum complex. The latter functions as an air‐stable, chemically‐deactivated source of white phosphorus. The system features efficient photo‐release of white phosphorus using inexpensive violet LED sources. Additionally, high‐yield recapture of unspent white phosphorus by the molybdenum center can be achieved by post‐photolysis heating at convenient temperatures.     

Redox‐Triggered Reversible Interconversion of a Monocyclic and a Bicyclic Phosphorus Heterocycle

Molecules which change their structures significantly and reversibly upon an oxidation or reduction process have potential as future components of smart materials. A prerequisite for such an application is that the molecules should undergo the redox‐coupled transformation within a reasonable electrochemical window and lock into stable redox states. Sodium phosphaethynolate reacts with two equivalents of dicyclohexylcarbodiimide (DCC) to yield an anionic, imino‐functionalized 1,3,5‐diazaphosphinane [ 3 a ]^?. The oxidation of this anion with elemental iodine causes an intramolecular rearrangement reaction to give a bicyclic 1,3,2‐diazaphospholenium cation [ 6 ]⁺. This umpolung of electronic properties from non‐aromatic to highly aromatic is reversible, and the cation [ 6 ] ⁺ is reduced with elemental magnesium to reform the 1,3,5‐diazaphosphinanide anion [ 3 a ]^?. Theoretical calculations suggest that phosphinidene species are involved in the rearrangement processes.