Aminophosphine Ligands Research Articles

The Synthesis and Investigation of Liquid-Liquid Extraction Capability of N-Diphenylphosphino-N-ethylaniline and Its Chalcogenide Derivatives

The aminophosphine ligand was synthesized by the reaction of N-ethylaniline with chlorodiphenylphosphine in the presence of triethylamine at low temperature. Oxidation of the ligand with elemental sulfur or selenium afforded the corresponding aminophosphine sulfide and selenide. The compounds were characterized by elemental analyses, IR, 1H and 31P NMR. N-diphenylphosphino-N-ethylaniline and its chalcogen derivatives were used as ligands in solvent extraction of metal picrates such as Cd2+ and Ni2+ from the aqueous to the organic phase. Influences of parameters such as pH of the aqueous phase, solvent, extraction time, and extradant concentration were investigated to determine the extraction ability of ligands for metal ions. Results of the experiments showed that an extractability of 95.5 and 97.8%, respectively for Ni2+, and Cd2+ at pH 2 could be achieved.

Platinum(II) complexes containing hydrazide‐based aminophosphine ligands: Synthesis, molecular structures, computational investigation and evaluation as antitumour agents

Four new N,N‐bis(diphenylphosphino)amine ligands (where amine = 1‐amino‐4‐methylpiperazine (L1), N‐aminophthalimide (L2), 4‐aminomorpholine (L3) and hydrazine dihydrochloride (L4)) and their Pt(II) complexes C1, C2, C3 and C4 were synthesized and characterized using infrared and NMR spectroscopies. The crystal structures of C1, C2 and C3 were determined using single‐crystal X‐ray diffraction techniques. The antitumour activities of the synthesized complexes determined using MTT assay on MDA‐MB‐231 cell line revealed that the studied complexes, especially C2, significantly suppressed the proliferation of these cancer cells in a dose‐ and time‐dependent manner (e.g. at a complex concentration of 100 μg ml−1, in 24 h, the reduction of the cell viability was 88.00, 38.89, 83.35 and 64.28% for C1–C4, respectively). Theoretical approaches were also used to investigate the energy and the nature of metal–ligand and metal–chlorine interactions in the complexes, which could explain their biological activities. Results demonstrated that the interaction between ligand and Pt is stronger in C2, while the Pt–Cl interaction is weaker in this complex in comparison with the other complexes.

Synthesis and structure of methoxo-terminated molybdenum and tungsten M3S4 clusters containing aminophosphine ligands

Trinuclear [M3S4(OCH3)3](edpp)3]+ complexes, 1+ (M = Mo) and 2+ (M = W) bearing (2-aminoethyl)diphenylphosphine (edpp), have been isolated and fully characterized. Molybdenum and tungsten halide precursors react with methanol in the presence of Et3N, to yield the respective methoxo-terminated clusters. The crystal structures of complexes 1+ and 2+ confirm that methoxo ligands are coordinated to the metal centers. Gas-phase dissociation of the novel methoxo cluster cations using ESI tandem mass spectrometry reveals the sequential elimination of three neutral methanol molecules under collision induced dissociation (CID) conditions to form metal/imino M = NH cluster species.

Microwave-assisted synthesis of α-aminophosphonates and related derivatives by the Kabachnik-Fields reaction

In this paper, the solvent- and catalyst-free synthesis of α-aminophosphonate derivatives is presented by the microwave-assisted Kabachnik-Fields reaction of amines, paraformaldehyde and P-reagents. Starting from >P(O)H compounds bearing different substituents on the phosphorus atom, P-chiral α-aminophosphonates and α-aminophosphinates were prepared, while using an optically active amine, the synthesis of C-chiral derivatives was elaborated. An optically active bisaminophosphine, obtained after double deoxygenation, was utilized as a chiral bidentate aminophosphine ligand in the synthesis of an optically active cyclic platinum complex. As an extension towards α-aminophosphonates containing a functionalizable group, N-hydroxyethyl-α-aminophosphonates were also prepared.

Enantioselective synthesis of tunable chiral pyridine–aminophosphine ligands and their applications in asymmetric hydrogenation

A small library of tunable chiral pyridine-aminophosphine ligands were enantioselectively synthesized based on chiral 2-(pyridin-2-yl)-substituted 1,2,3,4-tetrahydroquinoline scaffolds, which were obtained in high yields and with excellent enantioselectivities via ruthenium-catalyzed asymmetric hydrogenation of 2-(pyridin-2-yl)quinolines. The protocol features a wide substrate scope and mild reaction conditions, enabling scalable synthesis. These chiral P,N ligands were successfully applied in the Ir-catalyzed asymmetric hydrogenation of benchmark olefins and challenging seven-membered cyclic imines including benzazepines and benzodiazepines. Excellent enantio- and diastereoselectivity (up to 99% ee and >20 : 1 dr), and/or unprecedented chemoselectivity were obtained in the asymmetric hydrogenation of 2,4-diaryl-3H-benzo[b]azepines and 2,4-diaryl-3H-benzo[b][1,4]diazepines.

Synthesis, structure, computational and catalytic activities of palladium complexes containing hydrazide based amino-phosphine ligands

Two new N, N-bis(diphenylphosphino)-amine ligands [where amine = N-Aminophthalimide (in L1) and Hydrazine dihydrochloride (in L2)] and their Pd(II) complexes, C1 and C2 have been synthesized and characterized by IR and NMR spectroscopies. Single crystal X-ray diffraction techniques have been used to determine the crystal structures of the complexes. Moreover, the catalytic activities of mentioned complexes in Heck coupling reactions have been assessed. The NBO analysis has been used to investigate the nature of the metal-ligand interactions. In the case of L2, preparation route could have produced two different products (Pro.1 and Pro.2), but only one structure has been gained which has been prepared in high purity. To address the reason for this manner, kinetics and thermodynamics of two different pathways that could have led to possible products have been investigated theoretically.

Monodentate aminophosphine nickel(II)‐ and palladium(II)‐catalyzed ethylene oligomerization and norbornene polymerization

Nickel(II) and palladium(II) complexes of monodentate aminophosphine ligands were prepared and characterized. In ethylene oligomerization and subsequent Friedel–Crafts alkylation of toluene, the Ni(II) complexes Ni‐1 and Ni‐2 were activated with aluminium co‐catalysts and generated tandem catalysts with high activities (up to 1.1 × 106 g (mol Ni)−1 h−1) which are comparable with those of previously reported bidentate Ni(II) catalysts. The Pd(II) precatalyst Pd‐1 showed high activities (up to 2.0 × 105 g (mol Pd)−1 h−1) in the polymerization of norbornene.

Palladium(II) catalyzed Suzuki C[sbnd]C coupling reactions with imino- and amino-phosphine ligands

A new series of bidentate PN type imino- (1–3) and amino-phosphine ligands (4–6) and their palladium(II) complexes [Pd(PN)Cl2] (1a–6a) have been synthesized and fully characterized using spectroscopic and analytical methods, including 31P, 1H, 13C NMR and FTIR spectroscopy and high resolution mass spectroscopy. The catalytic activities of the Pd(II) complexes were investigated for the Suzuki CC coupling reactions of phenylboronic acid with aryl bromides using a substrate to catalyst ratio of 500/1. The effect of base, temperature and solvent has been investigated, and the highest reaction rates were observed at 80 °C in dimethylformamide (DMF) with K2CO3 as the base in 12 h. Under optimized reaction conditions, generally higher coupled product was obtained with substituted aryl bromides, including both electron-withdrawing (-formyl and -aceto) or -donating groups (-methyl and -methoxy) at -ortho or -para positions, except 2-bromoacetophenone which has bulkier -aceto group compared to the other aryl bromides.

Sterically Demanding Phosphines with 2,6-Dibenzhydryl-4-methylphenyl Core: Synthesis of RuII, PdII, and PtII Complexes, and Structural and Catalytic Studies.

The synthesis of sterically demanding aminophosphine and phosphinite ligands Ar*NHPPh2 (1) and Ar*OPPh2 (2), based on 2,6-dibenzhydryl-4-methylphenyl core having bulky benzhydryl groups, and their RuII, PdII and PtII complexes is described. The reactions of 1 and 2 with [Ru(η6- p-cymene)Cl2]2 in 2:1 molar ratios produced mononuclear complexes [RuCl2{(η6- p-cymene)PPh2-EAr*}-κ1-P] (E = NH (3) and O (4)). Interestingly, complexes 3 and 4, upon refluxing in chlorobenzene, displace the p-cymene ring by one of the phenyl rings of side arms, forming rare η6-arene coordinated tethered complexes [RuCl2{(PPh2-EAr*)-κ1-P-η6-arene}] (E = NH (5) and O (6)). Treatment of 1 and 2 with [M(COD)Cl2] [M = Pd, Pt] in 2:1 ratios afforded mononuclear complexes [MCl2{(PPh2EAr*)-κ1-P}2] (E = NH, M= Pd (7), Pt (8); E = O, M= Pd (9), Pt (10)). Similarly, 1:1 reactions of 1 and 2 with [Pd(COD)Cl2] produced chloro-bridged dinuclear complexes [PdCl2{(PPh2EAr*)-κ1-P}]2 (E = NH (11) and O (12)), whereas [Pt(COD)Cl2] yielded only the mononuclear complexes 8 and 10. The reactions of 1 and 2 with [Pd(η3-C3H5)Cl]2 in 2:1 molar ratios produced the mononuclear complexes [PdCl{(η3-C3H5)(PPh2EAr*)-κ1-P}] (E = NH (13) and O (14)). Many of these complexes have been structurally characterized, which show C-H···π interactions between the methine hydrogen of the benzhydryl and with one of the carbon atoms of the phenyl ring attached to the phosphorus center. The complex [RuCl2{(η6- p-cymene)PPh2-NHAr*}-κ1-P] (3) shows very short C-H···π interactions of 2.36 Å; in addition, C-H···M interactions were observed between the methine hydrogen of one of the benzhydryl groups and palladium centers in 11 and 13. The tethered ruthenium complex 5 is found to be an excellent catalyst for the catalytic oxidation of various styrene derivatives.

Studies on heavy metal removal efficiency and antibacterial activity of 2-(diphenylphosphino)aminopyridine

The solvent extraction of metal picrates such as Ni2+, Cu2+, Co2+, Pb2+ and Cd2+ from the aqueous to the organic phase was studied using 2-(diphenylphosphino)aminopyridine (Ph2PNHpy). The effects of parameters including the pH of the aqueous phase and the ligand solution volume were investigated to determine the extraction ability of the ligand for metal ions. The results showed that the extraction percentages of metal ions were high at low pH values. The antibacterial activity of the aminophosphine was also screened against Escherichia coli (E. coli) ATCC 25922, Staphylococcus aureus (S. aureus) ATCC 25923, Pseudomonas syringae pv. tomato (P. syringae) DC300, Salmonella enterica serotype Typhmurium (S. typhmurium) SL 1344 and Streptococcus mutans (S. mutans) ATCC 25175. From the studies of antibacterial activity, it was observed that the ligand exhibited a potent inhibitory effect against all Gram-negative and Gram-positive bacteria with a diameter of inhibition zone ranging from 3.86 to 18.10 mm. The aminophosphine ligand (Ph2PNHpy) should be considered as a suitable bio-active molecule for antimicrobial material design and next-generation, non-toxic drug fabrication. The Ph2PNHpy obtained may have the potential for use as an antimicrobial additive for bioengineering applications.

Disentangling Ligand Effects on Metathesis Catalyst Activity: Experimental and Computational Studies of Ruthenium-Aminophosphine Complexes.

Second-generation ruthenium olefin metathesis catalysts bearing aminophosphine ligands were investigated with systematic variation of the ligand structure. The rates of phosphine dissociation ( k1; initiation rate) and relative phosphine reassociation ( k-1) were determined for two series of catalysts bearing cyclohexyl(morpholino)phosphine and cyclohexyl(piperidino)phosphine ligands. In both cases, incorporating P-N bonds into the architecture of the dissociating phosphine accelerates catalyst initiation relative to the parent [Ru]-PCy3 complex; however, this effect is muted for the tris(amino)phosphine-ligated complexes, which exhibit higher ligand binding constants in comparison to those with phosphines containing one or two cyclohexyl substituents. These results, along with X-ray crystallographic data and DFT calculations, were used to understand the influence of ligand structure on catalyst activity. Especially noteworthy is the application of phosphines containing incongruent substituents (PR1R'2); detailed analyses of factors affecting ligand dissociation, including steric effects, inductive effects, and ligand conformation, are presented. Computational studies of the reaction coordinate for ligand dissociation reveal that ligand conformational changes contribute to the rapid dissociation for the fastest-initiating catalyst of these series, which bears a cyclohexyl-bis(morpholino)phosphine ligand. Furthermore, the effect of amine incorporation was examined in the context of ring-opening metathesis polymerization, and reaction rates were found to correlate well with catalyst initiation rates. The combined experimental and computational studies presented in this report reveal important considerations for designing efficient ruthenium olefin metathesis catalysts.

Ligand Modification for Selectivity Control in Selective Ethylene Oligomerization

A series of aminophosphine ligands were synthesized by in situ combination of CrCl3(THF)3 and dry methylaluminoxane and examined for their catalytic behavior in chromium-catalyzed selective ethylene oligomerization. Variations of the ligand scaffold obtained by modifying the diarylphosphine moiety affected the steric bulkiness, which resulted in remarkable changes in the selectivity for 1-hexene vs. 1-octene. Based on our experimental results, we evaluated two different mechanisms proposed for selective ethylene oligomerization.

Synthesis and characterisation of fluorescent aminophosphines and their coordination to gold(i).

Three novel fluorescent aminophosphine ligands have been synthesised that incorporate napthyl (L1), pyrenyl (L2) and anthraquinone (L3) chromophores into their structures. The ligands react with [AuCl(tht)] (tht = tetrahydrothiophene) to give neutral complexes of the form [AuCl(L1-3)]. Solid state, X-ray crystallographic data was obtained for the anthraquinone derivative, [AuCl(L3)], and showed a distorted linear coordination geometry at Au(i). The packing structure also revealed a number of intermolecular π-π interactions that involve the anthraquinone and phenyl units of the aminophosphine ligand. 31P NMR spectroscopic data revealed δP values of +42.2 (L1), +42.1 (L2) and +26.1 (L3) ppm, which shifted downfield upon coordination to Au(i) to +64.6, +64.7, and +55.8 ppm, respectively. Supporting TD-DFT studies were able to reproduce the structure and 31P NMR chemical shifts of [AuCl(L3)] as well as rationalise the HOMO-LUMO compositions. Photophysical studies showed that the appended fluorophore dominates the absorption and emission properties for the ligands and complexes, with the anthraquinone derivatives showing visible emission at ca. 570 nm which was attributed to the intramolecular charge transfer character of the phosphinoaminoanthraquinone fragment.

Catalytic stereoselective total synthesis of a spiro-oxindole alkaloid and the pentacyclic core of tryptoquivalines.

An expedient route to the pentacyclic core of the tryptoquivaline alkaloids and the total synthesis of natural product (+)-3'-(4-oxoquinazolin-3-yl)spiro[1H-indole-3,5'-oxolane]-2,2'-dione (1) have been achieved. The route is enabled by a key, highly stereoselective, aldol reaction catalysed by a Ag(i) and cinchona-derived aminophosphine ligand system, forming a highly substituted oxazoline ring, and setting the C1 spirocyclic stereocentre for downstream manipulation.

Synthesis, characterization, and application of palladium complexes containing bis(aminophosphine) ligands

Two palladium complexes containing bis(aminophosphine) ligands have been prepared and characterized. Their solid structures were determined by X-ray single crystal diffraction studies. They were successfully employed in the Suzuki coupling reactions of phenylboronic acid and various aryl chlorides.

Diiron Dithiolate Hydrides Complemented with Proton-Responsive Phosphine-Amine Ligands.

The reaction of Fe2(pdt)(CO)6 with two equivalents of Ph2PC6H4NH2 (PNH2) affords the amido hydride HFe2(pdt)(CO)2(PNH2)(PNH) {[H1H]0, pdt2- = CH2(CH2S-)2}. Isolated intermediates in this conversion include Fe2(pdt)(CO)5-(κ1-PNH2) and Fe2(pdt)(CO)4(κ2-PNH2). X-ray crystallographic analysis of [H1H]0 shows that the chelating amino/amido-phosphine ligands occupy trans-dibasal positions. The 31P NMR spectrum indicates that [H1H]0 undergoes rapid proton exchange between the amido and amine centers. No exchange was observed for the hydride. Protonation of [H1H]0 gives [HFe2(pdt)(CO)2(PNH2)2]+ ([H21H]+), which contains two equivalent amino-phosphine ligands. Single-crystal X-ray crystallographic analysis of [H21H]+ also reveals hydrogen bonds between the exo amine protons with a THF molecule and BF4. Deprotonation of [H1H]0 with potassium tert-butoxide gave [HFe2(pdt)(CO)2(PNH)2]- ([1H]-), which was characterized spectroscopically. The complex has time-averaged C2 symmetry with two amido-phosphine ligands. FTIR spectroscopic measurements show that υCO shifts by approximately 20 cm-1 in the series [1H]-, [H1H]0, and [H21H]+. These shifts are comparable to those seen for the S-protonation of the (NC)2(CO)Fe-(μ-Scys)2Ni(Scys)2 site in the [NiFe]-hydrogenases.[1].

CH2 Linkage Effects on the Reactivity of Bis(aminophosphine)\u2013Ruthenium Complexes for Selective Hydrogenation of Esters into Alcohols

A novel ruthenium complex binding to two subtly different aminophosphine ligands, (o-PPh2C6H4CH2NH2)(o-PPh2C6H4NH2)RuCl2, was successfully isolated. This bis(aminophosphine)–ruthenium complex shows efficient activity in both dimethyl oxalate (DMO) and methyl benzoate (MB) hydrogenation. On the contrast, similar complexes (o-PPh2C6H4NH2)2RuCl2 and (o-PPh2C6H4CH2NH2)2RuCl2, can only effectively catalyze the hydrogenation of DMO and MB, respectively. Our experimental studies in combination of theoretical calculations reveal that the remarkable substrate selectivity in the hydrogenation of esters arises from the nonbonding interactions operated by the CH2 linkage of the ligand.

Enantioselective Silver and Amine Co-catalyzed Desymmetrizing Cycloisomerization of Alkyne-Linked Cyclohexanones.

A silver(I) and amine co-catalyzed desymmetrization of 4-propargylamino cyclohexanones for the direct enantioselective synthesis of 2-azabicyclo[3.3.1]nonanes is described. Exploiting reactivity arising from dual activation of the pendant terminal alkyne by silver(I) and the ketone moiety through transient enamine formation, this synthetically relevant transformation is easy to perform, efficient and broad in scope. High enantioselectivity (up to 96 % ee) was achieved by exploiting a significant matching effect between the chirality of a cinchona alkaloid-derived aminophosphine ligand for the silver(I) salt and the 2-bis(aryl)methylpyrrolidine catalyst which was rationalized by DFT calculations. This allowed for the preparation of both enantiomers of the bicyclic product with near-identical stereocontrol.

Non‐Pincer‐Type Manganese Complexes as Efficient Catalysts for the Hydrogenation of Esters

AbstractCatalytic hydrogenation of carboxylic acid esters is essential for the green production of pharmaceuticals, fragrances, and fine chemicals. Herein, we report the efficient hydrogenation of esters with manganese catalysts based on simple bidentate aminophosphine ligands. Monoligated Mn PN complexes are particularly active for the conversion of esters into the corresponding alcohols at Mn concentrations as low as 0.2 mol % in the presence of sub‐stoichiometric amounts of KOtBu base.

Enantioselective Silver and Amine Co‐catalyzed Desymmetrizing Cycloisomerization of Alkyne‐Linked Cyclohexanones

AbstractA silver(I) and amine co‐catalyzed desymmetrization of 4‐propargylamino cyclohexanones for the direct enantioselective synthesis of 2‐azabicyclo[3.3.1]nonanes is described. Exploiting reactivity arising from dual activation of the pendant terminal alkyne by silver(I) and the ketone moiety through transient enamine formation, this synthetically relevant transformation is easy to perform, efficient and broad in scope. High enantioselectivity (up to 96 % ee) was achieved by exploiting a significant matching effect between the chirality of a cinchona alkaloid‐derived aminophosphine ligand for the silver(I) salt and the 2‐bis(aryl)methylpyrrolidine catalyst which was rationalized by DFT calculations. This allowed for the preparation of both enantiomers of the bicyclic product with near‐identical stereocontrol.