3H-Benzophosphepine Complexes: Versatile Phosphinidene Precursors

Molecular-strain induced phosphinidene reactivity of a phosphanorcaradiene

Phosphanorcaradienes are an appealing class of phosphorus compounds that can serve as synthons of transient phosphinidenes. However, the synthesis of such species is a formidable task owing to their intrinsic high reactivity. Herein we report straightforward synthesis, characterization and reactivity studies of a phosphanorcaradiene, in which one of the benzene rings in the flanking fluorenyl substituents is intramolecularly dearomatized through attachment to the phosphorus atom. It is facilely obtained by the reduction of phosphorus(III) dichloride precursor with potassium graphite. Despite being thermally robust, it acts as a synthetic equivalent of a transient phosphinidene. It reacts with trimethylphosphine and isonitrile to yield phosphanylidene-phosphorane and 1-phospha-3-azaallene, respectively. When it is treated with one and two molar equivalents of azide, iminophosphane and bis(imino)phosphane are isolated, respectively. Moreover, it is capable of activating ethylene and alkyne to afford [1 + 2] cycloaddition products, as well as oxidative cleavage of Si-H and N-H bonds to yield secondary phosphines. All the reactions proceed smoothly at room temperature without the presence of transition metals. The driving force for these reactions is most likely the high ring-constraint of the three-membered PC2 ring and recovery of the aromaticity of the benzene ring.

Gallaphosphene L(Cl)GaPGaL: A novel phosphinidene transfer reagent

Gallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(Ar)]2 ; Ar=2,6-iPr2 C6 H3 ) reacts with N-heterocyclic carbenes R NHC (R NHC=[CMeN(R)]2 C; R=Me, iPr) to R NHC-coordinated phosphinidenes R NHC→PGa(Cl)L (R=Me 2 a, iPr 2 b) and with isonitriles RNC (R=iPr, Cy) to 1,3-phosphaazaallenes L(Cl)GaP=C=N-R (R=iPr 3 a, Cy 3 b), respectively. Quantum chemical calculations reveal that 2 a/2 b possess two localized lone pair of electrons, whereas 3 a/3 b only show one localized lone pair as was reported for gallaphosphene 1. 2 b reacts with 2.5 equivalents of a borane (THF ⋅ BH3 ) to the NHC-stabilized phosphinidene-borane complex [iPr NHC→P(BH2 )]2 (BH3 )3 4 with concomitant formation of LGa(H)Cl 5. 2-5 are characterized by heteronuclear (1 H, 13 C{1 H}, 31 P{1 H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD).

Synthesis and Unexpected Optical Properties of Ionic Phosphorus Heterocycles with P-Regulated Noncovalent Interactions

Optoelectronic properties of organic chromophores (OCPs) are to a large extent dictated by the chemical structures. Herein, we synthesized a new series of ionic phosphorus(P)-heteropines via the methylation of the P(III) center. Our studies revealed that methylation is highly dependent on the P(III) environments (NPN, NPC, and CPC), in which adjacent nitrogen atoms greatly withdraw electron density of the P(III) center. The observation of noncovalent interactions between solvent molecules and the molecular backbones of the related P-heterocycle in the single crystal structure implied tunable molecular conformations. Different from the red-shifted absorption and emission spectra of ionic P-OCPs induced by either decreased lowest unoccupied molecular orbital (LUMO) or intramolecular charge transfer (ICT) state in previous studies, current ionic P-heterocycles exhibit blue-shifted absorption and emission spectra compared to the nonionic counterparts. Our experimental and theoretical studies suggest that the unexpected photophysical characters are probably due to the counter-anion induced structure twisting via intermolecular noncovalent interactions between NH-indole and O(OTf), and/or strong intermolecular O···F bonding between O(MI) and F(OTf). Our studies also revealed that the P-environments (NPN, NPC, and CPC) conjunctly impact the photophysical properties of the ionic P-heteropines. Overall, the fact that the P-environment-regulated noncovalent interactions induce the rich structure dynamics and photophysics offers us with a new and effective strategy to fine-tune the optical properties of OCPs.

Tailored Solvatochromic NIR Phosphorus-Chromophores via Selective P-N and P-C Chemistry in P-Heteropines

Herein we report selective P-C and P-N chemistry as a new synthetic tool for constructing phosphorus (P)-chromophores with rich chemical structures. Our studies reveal that isomeric structures significantly influence the chemical structure and electronic communication of P-heteropines, which results in efficient tunability of the photophysical properties. In particular, isomeric P-chromophores with a protic N-H (indole) are also capable of participating in intramolecular H bonding, offering a new strategy to access a near-infrared chromophore.

Insight into fragmentation of a phosphirane to form phosphinidene complexes: an illustration with the 1-phenylselenylphosphirane W(CO)5 complex

Density functional theory (DFT) calculations with 1-phenylselenylphosphirane complex 1 provide an insight into phosphirane fragmentation to phosphinidene complexes. FMO and ELF analyses show that the cleavage of two P-C σ bonds of phosphirane proceeds via an asynchronous concerted pathway. Transient [PhSeP-W(CO)₅] was generated by dissociation of 1 at 90 °C and trapped with different reagents. The 1-phenoxylphosphirane complex undergoes [1 + 2] retroaddition at a comparatively higher temperature which implies that the lone pair of the adjacent atom center of phosphorus plays a major role in phosphirane fragmentation.

1,1-Addition of α-C2-Bridged Biphospholes with Alkynes

An unusual chemoselective 1,1-addition of α-C₂-bridged biphospholes to terminal alkynes is reported. The developed protocol provides simple access to the unknown 1,3-diphosphepines, which has potential applications in the coordination and catalyst chemistry. Their Pd and Mo complexes were studied by single-crystal X-ray diffraction analysis. This method features excellent chemoselectivity, high step and atom economy, mild reaction conditions, and wide substrate scope.

π-Extended Phosphepines: Redox and Optically Active P-Heterocycles with Nonplanar Framework

In this letter, we present the synthesis of a new family of π-extended dithieno[ b, f]phosphepines. The Pd-catalyzed direct arylation allows the introduction of various substituents, which tune the absorption/emission in the visible range as well as the redox properties. All those modifications were rationalized through DFT calculations. The physical properties of ambipolar phosphepine with diphenylamino substituents inspired us to use it as a semiconductor in p-type organic field-effect transistors (OFETs).

A Room-Temperature-Stable Phosphanorcaradiene

A room-temperature-stable crystalline phosphanorcaradiene 2 has been synthesized via a C-C bond forming strategy induced by the demetalation of a phosphepine-Au complex 1 using a Lewis base (Ph₃P, IDipp or CyNC). Compound 2 undergoes photolysis to afford a 2 H-phosphirene 4. Ru(PPh₃)₃Cl₂ is shown to catalyze the equilibration of 2 and 4 in solution. In addition, the transformation of 2 to 4 can be achieved by a two-step strategy, namely cyclopropenylidene-induced ring opening to give cyclopropenylidene-stabilized vinylphosphinidene 7 followed by elimination of cyclopropenylidene by an electrophile including TMSOTf and Me₂SBH₃.

Evidence for Iron-Catalyzed α-Phosphinidene Elimination with Phenylphosphine

The ubiquitous half-sandwich iron complex [CpFe(CO)₂ Me] (Cp=η⁵ -C₅ H₅ ) appears to be a catalyst for α-phosphinidene elimination from primary phosphines. Dehydrocoupling reactions provided initial insight into this unusual reaction mechanism, and trapping reactions with organic substrates gave products consistent with an α elimination mechanism, including a rare example of a three-component reaction. The substrate scope of this reaction is consistent with generation of a triplet phosphinidene. In all, this study presents catalytic phosphinidene transfer to unsaturated organic substrates.

New porphyrin-based dendrimers with alkene linked fluorenyl antennae for optics

The biphotonic (σ₂) singlet oxygen generation capability (Φ_Δ) of new TFP-based photosensitizers peripherally functionalized with various dendrons containing 2-ethynylflorenyl chromophores is reported along with remarkable fluorescence yields (Φ_F) of up to 17%.

A Masked Phosphinidene Trapped in a Fluxional NCN Pincer

The trapping of a phosphinidene (R-P) in an NCN pincer is presented. Stabilized phosphinidene 1 was characterized by ³¹ P{¹ H}, ¹ H, and ¹³ C{¹ H} NMR spectroscopy, exhibiting an averaged C_2v symmetry in solution between -60 and 60 °C. In the solid state, the phosphinidene is coordinated by one adjacent N atom featuring a formal P-N bond (1.757(2) Å) to give a five-membered ring with some aromatic character, confirmed by DFT calculations (B3LYP-D3/6-311G**++) to be the ground-state structure. Equilibration of the two N ligands occurs rapidly in solution via a "bell-clapper"-type process through an associative symmetric transition state calculated to lie 4.0 kcal mol^-1 above the ground state.

Optically active P5-deltacyclenes: selective oxidation, ligand properties, and a diastereoselective rearrangement reaction

Cage-chiral tetra-tert-butyl-P5-deltacyclene is accessible as a pair of highly enriched enantiomers and . The only secondary phosphorus atom P1 of the cage can be selectively oxidized by reaction with t-BuOOH. The P1-oxo species and , allow the direct determination of their ee values. Oxidation occurs with the complete retention of the optical activity of the compounds. The chiroptical properties of and are strongly dominated by their cage chirality, the oxygen atom does not contribute significantly. Elemental sulfur and selenium oxidize P5 with high preference to yield P5-thio- and P5-seleno-P5-deltacyclenes and of the intact cages again. Longer reaction time and more than stoichiometric amounts of selenium, leads to tri-seleno-P5-tetracycloundecane , a partially opened oxidized rearrangement product. The ligand properties of racemic were determined. Diphosphetane phosphorus atom P2 of is the active donor center to bind a Cr(CO)5 fragment, but a tautomerization of takes place if [(benzene)RuCl2]2 is added. A hydrogen atom migrates from P1 to the oxygen atom to form a phosphinous acid ligand. The lone pair of P1 is regenerated and acts as the active ligand function of the cage in this case. As for , the base n-BuLi induces an efficient cage rearrangement reaction of , where P1 and the neighboring carbon atom C4 containing its t-Bu substituent change places. C4 moves to its new position without breaking the bond with P5, this way forming the novel P1-oxo-P5-norsnoutene cage in a highly diastereoselective process.

Effect of metal complexation on the equilibrium between methylphosphepine and methylphosphanorcaradiene and their benzo analogues

Methylphosphepine and its norcaradiene isomer as well as their benzo-derivatives are predicted to form energetically closely spaced η⁴-tetrahapto and η³-trihapto complexes with the transition metal units.

Sequential electrophilic P-C bond formation in metal-coordinated chlorophosphines

In the presence of chloride abstractors, metal-coordinated chlorophosphines undergo facile room-temperature electrophilic substitution reactions with unsaturated organic substrates, leading to P-C bond formation. This methodology can be applied sequentially two or three times, stepwise or in one-pot reactions, to form phosphines with three different substituents. The reactions are rapid and high-yielding, and can be applied to a wide range of organic substrates, making them valuable tools for P-C bond formation.

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta-1,3,5-triene into the corresponding bicyclo[4.1.0]hepta-2,4-dienes is reviewed to show the impact of the heteroatom on the stability of both valence isomers. The focus is on the parent systems and their synthetic applications.

Remarkable metal-complexed phosphorus analogues of the cyclopropenylcarbene-cyclobutadiene rearrangement

In situ-generated metal carbonyl-complexed cyclopropenylphosphinidenes undergo a sequence of structural changes leading to phosphorus analogues of Pettit's seminal (η(4)-cyclobutadiene)iron tricarbonyl complex via multiple valence isomers along the reaction pathway and the elimination of one molecule of carbon monoxide.

Developing the chemistry of monovalent phosphorus

Electrophilic terminal phosphinidene complexes can be seen as singlet phosphinidenes stabilized by complexation with electron withdrawing metallic centers. They allow the development of an original P(I) chemistry whose latest results are summarized. These include the description of the first stable electrophilic terminal phosphinidene complexes, new precursors for the widely used transient [RP-M(CO)5] complexes (M = Cr, Mo, W), new substituents at phosphorus, new reactions and new decomplexation techniques. Finally, a different approach is proposed for stabilizing singlet phosphinidenes by formation of adducts with nitrogen bases such as N-methylimidazole. The resulting zwitterions are potentially equivalent to singlet nucleophilic phosphinidenes. Their synthetic potential remains to be explored.