Phosphole Units Research Articles

Synthesis and Properties of Dibenzo-Fused Naphtho[2,3-b:6,7-b']disilole and Naphtho[2,3-b:6,7-b']diphosphole.

Silole- and phosphole-containing polycyclic aromatic compounds have attracted significant attention in the field of organic functional materials. The structure of the aromatic units has great impact on the photophysical properties of the resulting silole- and phosphole-containing polycyclic aromatic compounds. Here, dibenzo-fused naphtho[2,3-b:6,7-b']disilole (NDS) and naphtho[2,3-b:6,7-b']diphosphole (NDP), where a naphthalene unit is arranged between two silole and phosphole units, respectively, were designed and synthesized. The solid-state structures of them were confirmed by X-ray crystallographic analysis. The photophysical properties were evaluated by UV-vis absorption and photoluminescence spectroscopies and compared with those of their related compounds, such as dibenzo-fused silolo[3,2-b]silole and benzo[1,2-b:4,5-b']disilole, ever reported. The longest wavelength absorption band of a series of silole-fused compounds was found to be red-shifted in the order benzo[1,2-b:4,5-b']disilole < NDS < silolo[3,2-b]silole derivatives. For a series of phosphole-fused compounds, π-extension from phospholo[3,2-b]phosphole to NDP derivatives induces the lower absorption coefficient of the longest wavelength absorption band and the red-shift of the second longest wavelength absorption band. Both NDS and NDP exhibit much lower fluorescence quantum yields than their related compounds.

Novel Metallo-Supramolecular Polymers with 1-Thioxophosphole Main-Chain Units and Remarkable Photoinduced Changes in Their Resonance Raman Spectra.

New low-bandgap unimers, with the central thiophene-(1-thioxophosphole)-thiophene (TPT) ring sequence and 2,2':6',2″-terpyridin-4'-yl (tpy) end groups connected to the central unit via conjugated linkers of different size, are prepared and assembled with Zn(II) and Fe(II) ions to metallo-supramolecular polymers (MSPs) that are studied regarding their properties. The most interesting feature of Zn-MSPs is the luminescence extended deep into the NIR region. Fe-MSPs not only show the metal-to-ligand charge transfer (MLCT) manifested by the MLCT band (an expected feature) but also an as-yet-undescribed remarkable phenomenon: specific damping of the bands of the TPT sequence in the resonance Raman spectra taken from solid Fe-MSPs using the excitation to the MLCT band (532 nm). The damping is highly reversible at the low laser power of 0.1 mW but gradually becomes irreversible as the power reaches ca. 5 mW. The revealed phenomenon is not shown by the same Fe-MSPs in solutions, nor by Fe-MSPs containing no phosphole units. A hypothesis is proposed that explains this phenomenon and its dependence on the irradiation intensity as a result of the interplay of three factors: (i) enhancement of the MLCT process by excitation radiation, (ii) the electron-acceptor character of the 1-thioxophosphole ring, and (iii) morphological changes of the lattice and their dependence on the population of new structures in the lattice.

Super-Photostable Phosphole-Based Dye for Multiple-Acquisition Stimulated Emission Depletion Imaging.

As stimulated emission depletion (STED) microscopy can provide structural details of cells with an optical resolution beyond the diffraction limit, it has become an indispensable tool in cell biology. However, the intense STED laser beam usually causes rapid photobleaching of the employed fluorescent dyes, which significantly limits the utility of STED microscopy from a practical perspective. Herein we report a new design of super-photostable dye, PhoxBright 430 (PB430), comprising a fully ring-fused π-conjugated skeleton with an electron-accepting phosphole P-oxide unit. We previously developed a super-photostable dye C-Naphox by combining the phosphole unit with an electron-donating triphenylamine moiety. In PB430, removal of the amino group alters the transition type from intramolecular charge transfer character to π-π* transition character, which gives rise to intense fluorescence insensitive to molecular environment in terms of fluorescence colors and intensity, and bright fluorescence even in aqueous media. PB430 also furnishes high solubility in water, and is capable of labeling proteins with maintaining high fluorescence quantum yields. This dye exhibits outstanding resistance to photoirradiation even under the STED conditions and allows continuous acquisition of STED images. Indeed, using a PB430-conjugated antibody, we succeed in attaining a 3-D reconstruction of super-resolution STED images as well as photostability-based multicolor STED imaging of fluorescently labeled cytoskeletal structures.

N,P]-pyrrole PdCl2 complexes catalyzed the formation of dibenzo-α-pyrone and lactam analogues.

We herein report the synthesis and catalytic application of a new family of [N,P] ligands based on the pyrrole ring with alpha-phosphine or phosphole units. Their palladium complexes (3a-d) were obtained in very good yields and their catalytic properties were evaluated in the direct intramolecular arylation to obtain both benzopyranones and phenanthridinones. The air stable complex 3a exhibited the best catalytic performance of this series of complexes, using 1 mol% of catalyst in combination with microwaves to promote this reaction.

Synthesis of π-Conjugated Polymers Containing Phosphole Units in the Main Chain by Reaction of an Organometallic Polymer Having a Titanacyclopentadiene Unit.

A regioregular organometallic polymer possessing titanacyclopentadiene units in the main chain, which was obtained by the reaction of terminal diyne and a low-valent titanium complex, was subjected to the reaction with dichlorophosphines to give π-conjugated polymers with phosphole or phosphole oxide units in the main chain. For example, a phenylphosphole-containing polymer was obtained in 76% yield by the reaction with dichlorophenylphosphine, whose number-average molecular weight (Mn) and molecular weight distribution (Mw/Mn) were estimated to be 6100 and 1.9, respectively, by GPC. The polymer was found to have an extended π-conjugated system, and its lowest unoccupied molecular orbital (LUMO) energy level was remarkably low (-3.28 eV) as supported by its UV-vis absorption spectrum and cyclic voltammetric (CV) analysis. Also, the polymer exhibits orange photoluminescence with an emission maximum (Emax) of 595 nm and a quantum yield (Φ) of 0.10.

Phosphathiahelicenes: synthesis and uses in enantioselective gold catalysis.

Enantiomerically pure thiahelicenes displaying a terminal phosphole unit and a stereogenic phosphorus center have been prepared by oxidative photocyclization of a diaryl-olefin precursor. Starting from one of these phosphathiahelicene oxides, the corresponding trivalent phosphine-Au(I) complex is obtained with complete diastereoselectivity. It affords a new, excellent precatalyst for the enantioselective cycloisomerization of N-tethered enynes (up to 96 % ee).

ChemInform Abstract: Helicenes with Embedded Phosphole Units in Enantioselective Gold Catalysis.

AbstractThe use of phosphahelicenes as chiral ligands in transition‐metal catalysis is described for the first time.

Helicenes with Embedded Phosphole Units in Enantioselective Gold Catalysis

This paper discloses the first uses of phosphahelicenes as chiral ligands in transition-metal catalysis. Unlike all known helical phosphines used so far in catalysis, the phosphorus function of phosphahelicenes is embedded in the helical structure itself. This crucial structural feature originates unprecedented catalytic behaviors and efficiency. An appropriate design and fine tuning allowed both high catalytic activity and good enantiomeric excesses to be attained in the gold promoted cycloisomerizations of N-tethered 1,6-enynes and dien-ynes.

Helicenes with Embedded Phosphole Units in Enantioselective Gold Catalysis

This paper discloses the first uses of phosphahelicenes as chiral ligands in transition-metal catalysis. Unlike all known helical phosphines used so far in catalysis, the phosphorus function of phosphahelicenes is embedded in the helical structure itself. This crucial structural feature originates unprecedented catalytic behaviors and efficiency. An appropriate design and fine tuning allowed both high catalytic activity and good enantiomeric excesses to be attained in the gold promoted cycloisomerizations of N-tethered 1,6-enynes and dien-ynes.

Room Temperature Multifunctional Organophosphorus Gels and Liquid Crystals

AbstractA new series of extended dithieno[3,2‐b:2',3'‐d]phospholes with dendritic and non‐dendritic architectures involving phenylenevinylene as well as Fréchet‐type dendrons is presented. Modification of the phosphorus center with Pd allows for the generation of a dimeric dendrimer with Pd‐center. The synthetic strategy employed balances the rigid main scaffold with the flexibility of the dendrons in order to keep control of supramolecular self‐organization features. All the structures show a high photoluminescence in both solution and solid state, which is further intensified via energy transfer from the dendrons to the core. In terms of self‐organization in solution, three of the derivatives which bear an extended phosphole unit as common moiety are able to gel a variety of organic solvents at room temperature independently from the nature of their substituents. Notwithstanding, the dimeric dendrimer with Fréchet‐type dendrons is only able to display gel properties at low temperature. All gels exhibit pronounced photoluminescence properties that can be tuned by variation of the solvent and the temperature. In absence of solvent, the phosphole derivatives exhibit, moreover, liquid‐crystalline mesomorphism features. While three of the compounds present stable and highly luminescent columnar hexagonal phases at room temperature, the fourth species was found to be crystalline in the thermal range up to its isotropic state. Finally as proof of concept, the multifunctionality of these materials is demonstrated in an electrochromic device.

Band‐gap engineering of polythiophenes via dithienophosphole doping

AbstractA series of polythiophenes doped with dithieno[3,2‐b:2′,3′‐d]phosphole units at varying levels (0–17%) were synthesized and characterized. Polymer work up provided two series of polymers from chloroform (C) and hexanes (H) for each doping level, respectively. Systematic structure–property studies revealed that the C‐series polymers generally had higher molecular weights than the H‐series, but also slightly higher relative dithienophosphole concentrations, both having a significant impact on the photophysical and electrochemical properties of the polymers. Furthermore, the presence of the dithienophosphole units also stabilizes the LUMO levels, whereas the HOMO levels remain dominated by the thiophene units, resulting in desirable electronics for an interaction with acceptor materials, such as 1‐(3‐methoxycarbonyl)propyl‐1‐phenyl[6,6]C61. Importantly, increasing amount of dithienophosphole doping results in increased conductivities for the polymers in their oxidized state, while concurrently significantly stabilizing the neutral polythiophenes toward oxidation under environmental conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Protonation of a Xantphos−Phosphole Ligand. Intramolecular Trapping of a P−H Phospholium Salt

Protonation of a bidentate xantphos-phosphole ligand by HBF(4) affords only one enantiomer of a cyclic phospholium dihydropholene structure. DFT calculations allowed us to establish that protonation initially takes place at the phosphorus atom of the phosphole moiety to afford a transient P-H phospholium salt, which in turn protonates the C=C double bond of the second phosphole unit.

Syntheses, Structures, and Coordination Chemistry of Phosphole-Containing Hybrid Calixphyrins: Promising Macrocyclic P,N2,X-Mixed Donor Ligands for Designing Reactive Transition-Metal Complexes

The syntheses, structures, and coordination chemistry of phosphole-containing hybrid calixphyrins (P,N2,X-hybrid calixphyrins) and the catalytic activities of their transition-metal complexes are reported. The 5,10-porphodimethene type 14pi-P,(NH)2,X- and 16pi-P,N2,X-hybrid calixphyrins (X = O, S, NH) are prepared via acid-promoted dehydrative condensation between a sigma4-phosphatripyrrane and the corresponding 2,5-bis[hydroxy(phenyl)methyl]heteroles followed by DDQ oxidation. Both spectroscopic and crystallographic data of the hybrid calixphyrins have revealed that the conformation and size of the macrocyclic platforms as well as the oxidation state of the -conjugated pyrrole-heterole-pyrrole (N-X-N) units vary considerably depending on the combination of heteroles. The sigma3-P,(NH)2,S- and sigma3-P,N2,S-hybrids react with Pd(OAc)2 and Pd(dba)2, respectively, to afford the same Pd(II)-P,N2,S-hybrid complex, in which the calixphyrin platform is regarded as a dianionic ligand. In the complexation with [RhCl(CO)2]2 in dichloromethane, the sigma3-P,N2,S-hybrid behaves as a neutral ligand to afford an ionic Rh(I)-P,N2,S-hybrid complex, whereas the sigma3-P,N2,NH-hybrid behaves as an anionic ligand to produce Rh(III)-P,N3-hybrid complexes. In the latter reaction, it is likely that a neutral Rh(I)-P,N3-hybrid complex, generated as a highly nucleophilic intermediate, undergoes C-Cl bond activation of the solvent. The complexation of AuCl(SMe2) with the sigma3-P,N2,X-hybrids (X = S, NH) leads to the formation of the corresponding Au(I)-monophosphine complexes. The spectral data and crystal structures of these metal complexes exhibit the hemilabile nature of the phosphole-containing hybrid calixphyrin platforms derived from the flexible phosphole unit and the redox active N-X-N units. The hybrid calixphyrin-palladium and -rhodium complexes catalyze the Heck reaction and hydrosilylations, respectively, implying that the metal center in the core is capable of activating the substrates under appropriate reaction conditions. The present results demonstrate the potential utility of the phosphole-containing hybrid calixphyrins as a new class of macrocyclic P,N2,X-mixed donor ligands for designing highly reactive transition-metal complexes.

Xanthene-Phosphole Ligands: Synthesis, Coordination Chemistry, and Activity in the Palladium-Catalyzed Amine Allylation

Two new xanthene-phosphole derivatives, 3 and 4, were synthesized through the nucleophilic substitution of the cyano group in 1-P-cyano-2,5-diphenylphosphole (1) and 1-P-cyano-3,4-dimethylphosphole (2) by the 4,5-dilithium salt of 9,9‘-dimethylxanthene. For this, a new synthetic procedure was developed, allowing the synthesis of the required 1-P-cyano-2,5-diphenylphosphole from the 1,2,5-triphenylphosphole. Both ligands (DPP-Xantphos 3 for the diphenyl derivative and DMP-Xantphos 4 for the dimethyl derivative) react with [Pd(allyl)Cl]2 to afford the corresponding cationic complexes 5Cl and 6Cl. Using AgOTf, stable triflate complexes 5OTf and 6OTf could be isolated. The chloride complexes, on the other hand, exhibit a limited stability in solution. The DPP-Xantphos derivative 5Cl eliminates allyl chloride to yield the dimeric palladium(0) complex 7 of general formula [Pd(3)]2, in which each palladium is coordinated to the two phosphorus atoms of the same ligand and to one double bond of one phosphole unit of the second ligand. Decomposition of complex 6Cl furnished a mixture of compounds featuring a dimeric trinuclear species of general formula [Pd3(4)2Cl2]. This complex was also synthesized directly. Reaction of the DMP-Xantphos ligand 4 with 1 equiv of [Pd(COD)Cl2] and 2 equiv of [Pd(dba)2] afforded dimer 8, which features one 18-VE Pd0 center and two Pd-Cl fragments, which are coordinated to the dienic system of the two phosphole ligands and connected through a single Pd−Pd bond. The catalytic activity of the triflate complexes 5OTf and 6OTf was evaluated in the allylation of aniline. Whereas the DMP-Xantphos derivative 6OTf exhibited a poor catalytic activity, very good conversion yields were obtained with the DPP-Xantphos complex 5OTf. On the basis of X-ray structure data and DFT calculations, it was concluded that the high catalytic activity of the DPP-Xantphos derivative complex [Pd(allyl)3][OTf] (6OTf) results from the combination of two effects: a large P−Pd−P bite angle, which enhances the reactivity of the allyl ligand, and the strong π-accepting capacity of the diphenylphosphole moiety, which allows the easy formation of a 14-VE complex.

Structure, magnetizability, and nuclear magnetic shielding tensors of bis‐heteropentalenes. IV. Dihydrophospholophosphole isomers

The geometry of the heteropentalenes formed by two phosphole units has been determined at the DFT level. The magnetic susceptibility and the nuclear magnetic shielding at the nuclei of these systems have also been calculated using gauge-including atomic orbitals and a large Gaussian basis set to achieve near Hartree-Fock estimates. A comparative study of the various isomers, of their flattened analogs, and of the parent phosphole molecule, shows that the [3,4-c] isomer is the most aromatic system in the set considered, assuming diatropicity and degree of planarity as indicators, even if it is the less stable in terms of total molecular energy. Plots of magnetic field-induced current densities confirm diatropicity of P-containing bis-heteropentalenenes, showing, however, significant differences from the analogous systems with distinct heteroatoms. The maps give evidence of spiral flow nearby C-C bonds, compatible with prevalent distortive behavior of pi electrons exalted by pyramidalization at P, and competing against the sigma electron compression, which would favor planar structure.

Synthesis and Properties of First Well-Defined Phosphole-Containing π-Conjugated Polymers

Novel π-conjugated polymers 10a−c having the phosphole unit were prepared by palladium complex-catalyzed coupling of bis(p-bromophenyl)phosphole (7) with diethynylarenes 9a−c. The obtained polymers 10a−c were regio-regulated with the 2,5-substituted phosphole unit and characterized by 1H and 31P NMR. Polymers 10a−c were found to be an extended π-conjugated system according to the results of the UV−vis absorption spectra. In the fluorescence emission spectra of 10, moderate emission peaks were observed in the visible region. These polymers showed electron-donating properties in cyclic voltammometry measurements.

X-Ray crystal structure and Diels–Alder reactivity of the 3,4-dimethyl-2H-phosphole dimer

The [4 + 2] P–P bonded dimer of 3,4-dimethyl-2H-phosphole has the ecdo geometry with long, weak P–P and C–C bridges between the two phosphole units; it can therefore act as generator of monomeric 3,4-dimethyl-2H-phosphole at ca. 100 °C and gives the expected [4 + 2] and [2 + 4] cycloadducts with diphenylacetylene and 2,3-dimethylbutadiene.