Diphenylphosphino Group Research Articles

Phosphorus‐Directed Rhodium‐Catalyzed C−H Arylation of 1‐Pyrenylphosphines Selective at the K‐Region

AbstractC−H arylation of 1‐pyrenylphosphine derivatives catalyzed by rhodium and directed by a diphenylphosphino group is selectively achieved at the K‐region, i. e. 4‐, 5‐, 9‐, or 10‐position of the pyrene moiety. This peri C−H activation/arylation of pyrenes using (hetero)aryl bromide coupling partners tolerates both electron‐donating and electron‐withdrawing groups on the arene, and provides isolated yields of products between 25% to 90%, including from bulky polyaromatic bromoarene substrates. We achieved investigations directed at the formation and reactivity of pertinent intermediate species in this C−H arylation reaction. The P‐ligand coordination at rhodium was established using 31P NMR and XRD analysis, and we isolated five‐membered rhodacycles as intermediates to the directed C−H functionalization. The data obtained overall supported the occurrence of a cationic rhodium catalytic process. We further described the access to a large class of pyrenylphosphine ligands and their selenated derivatives. Phosphine selenation allows to rapidly estimate from 1JP=Se values the basic character of the ligand in the perspective of their use for coordination. Accordingly, linear P‐coordinated Au(I) gold complexes were isolated, in addition to the variously coordinated Rh(III) complexes. The present methodology significantly extends the scope of polyaromatics that are functionalizable at the K‐Region by direct C−H activation, beyond smaller‐sized naphtalenes and aminopyrenes.magnified image

Phosphine-based push-pull AIE fluorophores: Synthesis, photophysical properties, and TD-DFT studies

Herein, we report the design and characterization of a novel series of four push-pull fluorophores using diphenylphosphino as an electron-donating terminal group (P-chromophores). The spectroscopic properties in solution, the aggregation-induced emission (AIE) properties, as well as the emission properties in the solid state were studied and compared with those of the diphenylamino-analogues (N-chromophores). Comparative analysis of the crystalline structures coupled with density functional theory calculations revealed that the diphenylphosphino group adopts a pyramidal geometry, whereas a trigonal planar configuration around the N-center is observed for the diphenylamino group. Consequently, the phosphorous lone pair is localized on the upper side of the average chromophore plan and considerable geometrical change of the P-center can occur between the ground state and the first excited state, explaining the much larger Stokes shift observed (10 000 cm−1) for the P-chromophores compared to the N-analogues.

Cross-Coupling Reaction of Allylic Ethers with Aryl Grignard Reagents Catalyzed by a Nickel Pincer Complex

A cross-coupling reaction of allylic aryl ethers with arylmagnesium reagents was investigated using β-aminoketonato- and β-diketiminato-based pincer-type nickel(II) complexes as catalysts. An β-aminoketonato nickel(II) complex bearing a diphenylphosphino group as a third donor effectively catalyzed the reaction to afford the target cross-coupled products, allylbenzene derivatives, in high yield. The regioselective reaction of a variety of substituted cinnamyl ethers proceeded to give the corresponding linear products. In contrast, α- and γ-alkyl substituted allylic ethers afforded a mixture of the linear and branched products. These results indicated that the coupling reaction proceeded via a π-allyl nickel intermediate.

An experimental and computational comparison of phosphorus- and selenium-based ligands for catalysis

To compare and contrast the bonding and reactivity of organoselenium ligands with organophosphines in coordination complexes, a new palladium(II) complex of the Se,N-chelating ligand o-(NH2)(X)C6H4(X = SePh, 2) was prepared. Its characterization by NMR spectroscopy, single-crystal X-ray diffraction, and density functional theory calculations is contrasted with the PdIIcomplex of the related P,N- chelating ligand (X = PPh2, 1). These techniques indicate that the phenylseleno moiety is a weaker σ donor to the PdCl2fragment than the diphenylphosphino group. Both complexes were suitable to catalyze the Suzuki–Miyaura coupling of p-tolylboronic acid and 4-bromobenzaldehyde.

Cracking cavitands: metal-directed scission of phosphinyl-substituted resorcinarenes.

Resorcinarene-derived tetramethylene cavitands bearing a diphenylphosphino group grafted to their wider rim undergo facile, directed C-O bond breaking upon reaction with transition-metal ions in the presence of nucleophiles. One possible reaction mechanism involves formation of a P,O-chelate complex, which weakens the adjacent O-CH2 bond, leading to the formation of an oxacarbenium intermediate.

Coordination‐Driven Terpyridyl Phosphine Pd(II) Gels

AbstractIncorporation of phosphine‐Pd catalytic centers in gel network is an important strategy to develop highly active catalysts. In this contribution we show that catalytically active phosphine‐Pd(II) gels can be readily obtained via reaction of rigid bridging terpyridyl phosphines and Pd(II). The terpyridyl phosphines, Py2P2 and Py2P, contain one 4,2′:6′,4′ ′‐terpyridyl group and two/one diphenylphosphino groups. Reactions of Py2P2/Py2P and Pd(II) in CHCl3‐MeOH afforded the corresponding phosphine‐Pd(II) gels at room temperature or at elevated temperature (40°C). The gelation is driven by formation of metal‐organic coordination. Mild heating is important in triggering the formation of Py2P‐Pd(II) gel. The gels have a coherent, rigid spongy porous network of continuous nanometer‐sized particles. The phosphine‐Pd(II) gels showed high activity in the Suzuki‐Miyaura reactions of aryl bromides under ambient conditions and could be recycled and reused.

Iron Catalysts Containing Amine(imine)diphosphine P-NH-N-P Ligands Catalyze both the Asymmetric Hydrogenation and Asymmetric Transfer Hydrogenation of Ketones

When activated with base, the iron(II) complexes with tetradentate amine(imine)diphosphine ligands, (S,S)-trans-[FeCl(CO)(PAr2-NH-N-PAr′2)]BF4 (1: Ar, Ar′ = Ph; 2: Ar = Ph, Ar′ = 4-MeC6H4; 3: Ar, Ar′ = 3,5-Me2C6H3), are very active for the asymmetric transfer hydrogenation (ATH) of ketones in KOtBu/2-propanol. For ATH, better enantioselectivity, but lower catalytic activity, was observed in general when using catalyst precursors with the bulkier dixylylphosphino groups compared to those with diphenylphosphino groups. The complexes were much less active for the pressure hydrogenation of ketones, where 1 and 2 produced racemic product alcohols, while 3 yielded chiral alcohols with an enantiomeric excess of up to 70% (R) at turnover frequencies up to 80 h–1 and turnover numbers of 100 for a range of ketones at 50 °C and 20 atm H2. This is a rare example of asymmetric pressure hydrogenation using an iron complex. Unlike the case of ATH, there is no effect on the rate upon the addition of KOtBu beyond the 2 eq...

Upper-rim calixarene phosphines consisting of multiple lower-rim OH functional groups: synthesis and characterisation

The synthetic approaches to mono-isopropoxytrihydroxycalix[4]arenes bearing two or three diphenylphosphino groups at the upper macrocycle rim were elaborated. Due to reactive hydroxyl groups at the lower rim capable of binding with silica gel surface, the calixarenes, especially the enantiomerically pure inherently chiral diphosphinocalixarene, are promissing ligands for creation of hybride organic–inorganic metallocomplexing catalysts of organic (asymmetric) reactions.

Tunable Asymmetric Catalysis through Ligand Stacking in Chiral Rigid Rods

Chiral benzene-1,3,5-tricarboxamide (BTA) ligands, comprising one diphenylphosphino group and one or two remote chiral 1-methylheptyl side chains, were evaluated in the rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate. Despite the fact that the rhodium atom and the chiral center(s) are separated by more than 12 covalent bonds, up to 82% ee was observed. A series of control and spectroscopic experiments confirmed that the selectivity arises from the formation of chiral helical polymers by self-association of the BTA monomers through noncovalent interactions. The addition of a phosphine-free chiral BTA, acting as a comonomer for the chiral BTA ligands, increases the level of enantioselectivity (up to 88% ee). It illustrates how the selectivity of the reaction can be increased in a simple fashion by mixing two different BTA monomers. The concept was further probed by performing the same experiment with an achiral BTA ligand, i.e. a phosphine-functionalized BTA that contains two remote octyl side chains. It afforded an encouraging 31% ee, thus demonstrating the catalytically relevant transfer of chirality between the self-assembled units. It constitutes a unique example of the sergeants-and-soldiers principle applied to catalysis.

Synthesis of an alkylthio-substituted dibenz[a,j]anthracene with improved solubility via the oxidative photocyclization of 1,3-distyrylbenzene derivatives

A series of 1,3-distyrylbenzene compounds bearing different substituents at the 2-position have been synthesized and subjected to an oxidative photocyclization process. The 1,3-distyrylbenzene compounds substituted with chloro, alkylthio, and diphenylphosphino groups at the 2-position afforded dibenz[a,j]anthracene derivatives, whereas those bearing methyl, trimethylsilyl, dimethylamino, butoxy, and fluoro groups gave benzo[c]chrysene derivatives. The solubility of dibenz[a,j]anthracene in organic solvents was improved by the introduction of alkylthio groups.

Synthesis of novel dihydroxydiphosphines and dihydroxydicarboxylic acids having a tetra(thio-1,3-phenylene-2-yl) backbone

Novel tetradentate PPh2–OH hybrid ligands 5 and CO2H–OH hybrid ligands 6 have been successfully synthesised from tetra(thio-5-tert-butyl-2-hydroxy-1,3-phenylene) (2 4 ) by replacing the hydroxy groups at both the 2-position and either the 2′-, 2″- or 2‴-position with diphenylphosphino or carboxy groups, after converting into bistriflates 8; the substitution positions of newly introduced substituents are denoted hereafter by superscript 1,n as 5 1, n . Bistriflates 8 1,3 and 8 1,4 can be readily prepared by the regioselective detriflation of tetrakistriflate 7 with tetrabutylammonium fluoride (TBAF), conducted under different conditions. On the other hand, the preparation of bistriflate 8 1,2 requires a four-step process through protection/deprotection. Thus, the silylation of tetraol 2 4 with an excess of 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane gives O,O′- and O″,O‴-disiloxane-1,3-diyl-capped derivative 9. One of the two disiloxane bridges is removed by the treatment with 0.5 mol equiv. of TBAF to give diol 10. Triflation of diol 10, followed by the removal of the remaining disiloxane bridge, affords bistriflate 8 1,2 . Bistriflates 8 are subjected to palladium-catalysed phosphorylation, followed by the reduction of the resulting phosphine oxide 12 1, n to give PPh2–OH hybrid ligands 5 1, n (n = 2–4), while CO2H–OH hybrid ligands 6 1, n (n = 3,4) are obtained from 8 via acetylation of the remaining hydroxy groups, followed by palladium-catalysed methoxycarbonylation of the TfO moieties, and subsequent hydrolysis of the resulting tetraesters 14. X-ray structural analyses of dicarboxylic acids 6 1,3 and 6 1,4 reveal that they form quite different 3D network structures to each other. Interestingly, 6 1,4 constructs a porous channel with a potential for serving as a supramolecular host, by the stacking of its cyclic dimer that is formed by intermolecular hydrogen bondings between the carboxy groups.

N,N-Bis(diphenylphosphanyl)cyclopropylamine

In the title compound, C27H25NP2, the diphenyl­phosphino groups are staggered relative to the PNP backbone. The dihedral angles between the phenyl rings bonded to each P atom are 51.74 (5) and 68.23 (4)°. The coordination around the N atom deviates from trigonal-pyrimidal geometry towards an almost planar arrangement between the N atom and the adjacent P and C atoms; the distance between the N atom and the plane formed by the adjacent C/P/P atoms is 0.098 (2) Å.

Synthesis of 1‐Methyl‐6,10‐diphenylheptalene Derivatives

AbstractThe reduction of heptalene diester 1 with diisobutylaluminium hydride (DIBAH) in THF gave a mixture of heptalene‐1,2‐dimethanol 2a and its double‐bond‐shift (DBS) isomer 2b (Scheme 3). Both products can be isolated by column chromatography on silica gel. The subsequent chlorination of 2a or 2b with PCl5 in CH2Cl2 led to a mixture of 1,2‐bis(chloromethyl)heptalene 3a and its DBS isomer 3b. After a prolonged chromatographic separation, both products 3a and 3b were obtained in pure form. They crystallized smoothly from hexane/Et2O 7 : 1 at low temperature, and their structures were determined by X‐ray crystal‐structure analysis (Figs. 1 and 2). The nucleophilic exchange of the Cl substituents of 3a or 3b by diphenylphosphino groups was easily achieved with excess of (diphenylphospino)lithium (=lithium diphenylphosphanide) in THF at 0° (Scheme 4). However, the purification of 4a/4b was very difficult since these bis‐phosphines decomposed on column chromatography on silica gel and were converted mostly by oxidation by air to bis(phosphine oxides) 5a and 5b. Both 5a and 5b were also obtained in pure form by reaction of 3a or 3b with (diphenylphosphinyl)lithium (=lithium oxidodiphenylphospanide) in THF, followed by column chromatography on silica gel with Et2O. Carboxaldehydes 7a and 7b were synthesized by a disproportionation reaction of the dimethanol mixture 2a/2b with catalytic amounts of TsOH. The subsequent decarbonylation of both carboxaldehydes with tris(triphenylphosphine)rhodium(1+) chloride yielded heptalene 8 in a quantitative yield. The reaction of a thermal‐equilibrium mixture 3a/3b with the borane adduct of (diphenylphosphino)lithium in THF at 0° gave 6a and 6b in yields of 5 and 15%, respectively (Scheme 4). However, heating 6a or 6b in the presence of 1,4‐diazabicyclo[2.2.2]octane (DABCO) in toluene, generated both bis‐phosphine 4a and its DBS isomer 4b which could not be separated. The attempt at a conversion of 3a or 3b into bis‐phosphines 4a or 4b by treatment with t‐BuLi and Ph2PCl also failed completely. Thus, we returned to investigate the antipodes of the dimethanols 2a, 2b, and of 8 that can be separated on an HPLC Chiralcel‐OD column. The CD spectra of optically pure (M)‐ and (P)‐configurated heptalenes 2a, 2b, and 8 were measured (Figs. 4, 5, and 9).

Transition-metal phosphors with cyclometalating ligands: fundamentals and applications

One goal of this critical review is to provide advanced methodologies for systematic preparation of transition-metal based phosphors that show latent applications in the field of organic light emitting diodes (OLEDs). We are therefore reviewing various types of cyclometalating chelates for which the favorable metal-chelate bonding interaction, on the one hand, makes the resulting phosphorescent complexes highly emissive in both fluid and solid states at room temperature. On the other hand, fine adjustment of ligand-centered pi-pi* electronic transitions allows tuning of emission wavelength across the whole visible spectrum. The cyclometalating chelates are then classified according to types of cyclometalating groups, i.e. either aromatic C-H or azolic N-H fragment, and the adjacent donor fragment involved in the formation of metallacycles; the latter is an N-containing heterocycle, N-heterocyclic (NHC) carbene fragment or even diphenylphosphino group. These cyclometalating ligands are capable to react with heavy transition-metal elements, namely: Ru(II), Os(II), Ir(III) and Pt(II), to afford a variety of highly emissive phosphors, for which the photophysical properties as a function of chelate or metal characteristics are systematically discussed. Using Ir(III) complexes as examples, the C--N chelates possessing both C-H site and N-heterocyclic donor group are essential for obtaining phosphors with emission ranging from sky-blue to saturated red, while the N--N chelates such as 2-pyridyl-C-linked azolates are found useful for serving as true-blue chromophores due to their increased ligand-centered pi-pi* energy gap. Lastly, the remaining NHC carbene and benzyl phosphine chelates are highly desirable to serve as ancillary chelates in localizing the electronic transition between the metal and remaining lower energy chromophoric chelates. As for the potential opto-electronic applications, many of them exhibit remarkable performance data, which are convincing to pave a broad avenue for further development of all types of phosphorescent displays and illumination devices (94 references).

Luminescent platinum complexes containing phosphorus-linked silole ligands

A series of Pt(ii) complexes containing silole-based ligands with diphenylphosphino groups terminally bound to a conjugated organic linker unit coordinated to the silole ring in the 2- or 2,5-positions, 1,1-dimethyl-2-(5'-diphenylphosphino-2'-thienyl)-3,4-diphenylsilole (4), 1,1-dimethyl-2,5-bis(5'-diphenylphosphino-2'-thienyl)-3,4-diphenylsilole (5), and 1,1-dimethyl-2,5-bis(4'-diphenylphosphinophenyl)-3,4-diphenylsilole (8), have been prepared from (cod)PtX(2) (X = Cl, Me, C(2)Ph) precursors. Mononuclear, cis-P(2)PtX(2) (P = 4) complexes 6-7 were produced from silole 4 whereas dinuclear macrocyclic, cis-cis-X(2)Pt(P-P)(2)PtX(2) (P-P = 5 or 8) complexes 9-13 were produced from siloles 5 and 8. The solid state structure of the dinuclear complex 13 obtained from reaction of (cod)Pt(C(2)Ph)(2) with silole 8, was confirmed by X-ray crystallography. The optical properties of the siloles and the platinum complexes were studied by UV-vis and fluorescence spectroscopy in solution and were found to exhibit long wavelength absorption and emission bands attributed to the π-π* transitions of the silole core.

μ-Bis(diphenylphosphino)methane-1:2κ2P:P′]nonacarbonyl-1κ3C,2κ3C,3κ3C-[tris(4-methylphenyl)arsine-3κAs]-triangulo-triruthenium(0)

In the title triangulo-triruthenium compound, [Ru3(C21H21As)(C25H22P2)(CO)9], the bis­(diphenyl­phos­phino)methane ligand bridges an Ru—Ru bond and the monodentate arsine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. Additionally, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. The three arsine-substituted phenyl rings make dihedral angles of 87.36 (10), 81.96 (10) and 73.37 (11)° with each other. The dihedral angles between the two phenyl rings are 88.08 (12) and 80.15 (10)° for the two diphenyl­phosphino groups. In the crystal packing, the mol­ecules are linked together as dimers via inter­molecular C—H⋯O hydrogen bonds. These dimers are stacked down b axis. Inter­molecular C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.6383 (13) Å] further stabilize the crystal structure.

N,N-Bis(diphenylphosphino)ethylamine

In the title compound, C26H25NP2, the diphenyl­phosphino groups are staggered relative to the PNP backbone, even though the ethyl substituent coordinated to the N atom is not sterically bulky. The N atom adapts an almost planar geometry with two P atoms and a C atom of the allyl group attached to it in order to accommodate the steric bulk of the phenyl groups and the alkyl group. The distortion of the trigonal-pyramidal geometry of the nitro­gen is further illustrated by the bond angles which range between 114.0 (1) and 123.7 (1)°. There are no classical inter­molecular inter­actions.

Boronation of 1,8-Bis(diphenylphosphino)naphthalene: Formation of Cyclic Boronium Salts

Treatment of 1,8-bis(diphenylphosphino)naphthalene (1) with borane−dimethyl sulfide complex in THF/Et2O solution affords monoborane adduct 3 irrespective of the molar ratio of the reagents. The monoboronation product has been characterized by multinuclear (1H, 31P, 13C, 11B) NMR spectroscopy and MS-FAB measurements. Optimization of its structure with DFT methods at the B3LYP/6-31+G(d) level of theory revealed that steric hindrance around the diphenylphosphino group prevents formation of the bis-borane adduct. In dichloromethane or chloroform solution boronation of bis-phosphine 1 with H3B·Me2S results in the unexpected formation of a cyclic dihydroboronium chloride, 4·Cl. The corresponding cyclic iodide 4·I and triflate 4·TfO are formed by treatment of bis-phosphine 1 with H3B·Me2S followed by methyl iodide and methyl triflate, respectively, in THF/Et2O solution. The hexafluorophosphate 4·PF6 prepared by anion exchange from the chloride 4·Cl has also been characterized by single-crystal X-ray diffraction....

Calixarene-monophosphines as supramolecular chelators

The calix[4]arenes 5-diphenylphosphino-17-R1-11,23-diR2-25,26,27,28-tetrapropoxycalix[4]arene (1, R1 = R2 = Br; 2, R1 = Br, R2 = H; 3, R1 = R2 = p-tolyl; 4, R1 = p-tolyl, R2 = H; 5, R1 = R2 = H; 20, R1 = p-tolyl, R2 = H), all bearing a diphenylphosphino group attached to the calixarene upper rim, have been synthesised starting from 5,11,17,23-tetrabromo-25,26,27,28-tetrapropoxycalix[4]arene. Reaction of 1-5 with [RuCl2(p-cymene)]2 leads quantitatively to monophosphine complexes, [RuCl2(p-cymene)L], in which the endo-oriented ruthenium atom unit sits inside the cone delineated by the four phenoxy rings. The particular orientation of the P-Ru vector appears to result from pi-pi interactions between the p-cymene ligand and two aromatic cavity walls. Overall, in each case the calixarene end of the ligand behaves as a supramolecular receptor towards the Ru(p-cymene) fragment. Formation of complexes with exo-oriented P-M bonds were observed in the complexes cis-[PtCl2 x 1(2)] and in [RuCl2(p-cymene) x 20]. As shown by a variable temperature study carried out on [RuCl2(p-cymene) x 3], in which the ruthenium is embedded in an expanded cone, the p-cymene ring undergoes a fast oscillation about the Ru-arene bond which can be frozen out at low temperatures. Reaction of [RuCl2(p-cymene) x 3] with AgBF4 in CH3CN results in an intra-cavity reaction, with one chloride ligand being replaced by acetonitrile.

First Catenane‐Containing Phosphino Groups: A Step toward a Catenane Ligand

A novel [2] catenane containing a diphenylphosphino group on each ring was prepared. Synthesis of the new catenane involved the use of tetraamide rings to form an efficient pseudorotaxane intermediate. The catenane was found to be applicable as a ligand for metal-catalyzed reactions such as Suzuki-Miyaura coupling.