Phosphine Ligands Research Articles

Dithienylethene-Based Photoswitchable Phosphines for the Palladium-Catalyzed Stille Coupling Reaction.

Homogeneous transition metal catalysis is a constantly developing field in chemical sciences. A growing interest in this area is photoswitchable catalysis, which pursues in situ modulation of catalyst activity through noninvasive light irradiation. Phosphorus ligands are excellent targets to accomplish this goal by introducing photoswitchable moieties; however, only a limited number of examples have been reported so far. In this work, we have developed a series of palladium complexes capable of catalyzing the Stille coupling reaction that contain photoisomerizable phosphine ligands based on dithienylethene switches. Incorporation of electron-withdrawing substituents into these dithienylethene moieties allows variation of the electron density on the phosphorus atom of the ligands upon light irradiation, which in turn leads to a modulation of the catalytic properties of the formed complexes and their activity in a model Stille coupling reaction. These results are supported by theoretical computations, which show that the energy barriers for the rate-determining steps of the catalytic cycle decrease when the photoswitchable phosphine ligands are converted to their closed state.

Fluorinated Biphenyl Phosphine Ligands for Accelerated [Au(I)]-Catalysis

Fluorinated Biphenyl Phosphine Ligands for Accelerated [Au(I)]-Catalysis

Beyond Tertiary Amines: Introducing Secondary Amines via Palladium/Norbornene‐Catalyzed Ortho Amination

Since the discovery of the palladium/norbornene (Pd/NBE)‐catalyzed ortho amination in 2013, escaping the limitation of only yielding tertiary anilines has been a long‐standing challenge in the past decade. Here, we describe that, by carefully choosing the phosphine ligand and NBE mediator, installation of a N‐mono‐alkylamino group becomes feasible. The reaction tolerates a wide range of aryl iodide substrates and various N‐mono‐tertiary alkylamine‐derived electrophiles. Both ipso alkenylation and alkynylation can be realized. The synthetic utility of this method is exemplified in the formation of primary amino group via selective deprotection and streamlined access to N‐heterocycles. Preliminary success of installing a bulky N‐secondary alkylamino group and mechanistic understanding of the decomposition pathways of mono N‐alkylamine electrophiles have been obtained.

Interactions of phosphate, phosphine oxide and phosphoramide ligands with Th(IV)

The complexation behavior of phosphate, phosphine oxide, and phosphoramide ligands with Th(IV) is investigated at the Density Functional Theory (DFT) level. Employing Energy Decomposition Analysis (EDA), the study reveals significant contributions of geometric strain and dispersion interactions in determining the stability of these complexes. It is observed that the orbital interaction in the various Th(IV) complexes increases in the order phosphate < phosphine oxide < phosphoramide.

Synthesis, spectroscopic, DFT, anticancer evaluation and enzyme inhibition studies of platinum(II) complexes with 1-methyl-1H-1,2,3,4-tetrazole-5-thiol and phosphine ligands: Crystal structure of [Pt(mtzt)2(dppe)]

A number of Pt(II) complexes of 1-methyl-1H-1,2,3,4-tetrazole-5-thiol (Hmtzt) with phosphine ligands have been prepared and characterized and then evaluated as potential anti-cancer and ALP enzyme inhibitor agents. The complex [Pt(mtzt)2]2 was prepared by the reaction of 1-methyl-H1-tetrazole-5-thiol (Hmtzt) with K2PtCl4. This complex was treated with equivalent molar amounts of diphosphine ligands to afford complexes of the type [Pt(mtzt)2(PPh2(CH2)nPPh2)] in good yield, {PPh2(CH2)nPPh2, where n = 1 (dppm), n = 2 (dppe), n = 3 (dppp), n = 4 (dppb) and (PPh2((C5H4)2Fe)PPh2) (dppf)}. The prepared complexes were characterized by elemental analysis, IR, 1H-{31P} and 31P-{1H} NMR spectroscopy. The resulting data suggested that the prepared complexes were mononuclear with chelating diphosphines while the mtzt ligands were monodentate coordinating via the sulfur atom to give a square planner arrangement around the Pt(II) ion. This was confirmed by a single crystal structural analysis of the [Pt(mtzt)2(dppe)] complex. The Pt(II) complexes underwent structural optimization through the utilization of the DMol3 tool within the material studio package. A comparison of the results of molecular modelling with those of the X-ray structural analysis indicated that the structures were almost identical. The free ligand and two selected complexes were tested for inhibition activity against an alkaline phosphatase (ALP) enzyme, which was found to be active inhibitors, and the inhibition rate (37–88 %) range. Furthermore, the anticancer activity of the complexes (1, 3, and 6) was tested against human liver cancer (HepG2). The results showed that the prepared complexes have moderate activity but are lower than cis-platin. Complex 1 has the highest activity with an IC50 of 34.78 ± 1.75 M against the HepG2 cell line..

Highly oxidation resistant and organic dispersible ligand functionalized MXene for triggering performance of lithium ion batteries

Two-dimensional (2D) MXenes are one of the leading members of materials science due to their exceptional dispersion in water, metal-like conductivity, and promising applications in interdisciplinary fields. However, the ease of oxidation and poor dispersion in organic solvents have hindered the advancement of MXenes for futuristic applications. In this study, we developed oxidation-resistant, organic dispersible, environmentally stable, and conductive Ti3C2Tx MXene (Tx = –OH, –O, –F, etc.) by surface modification with 2-Ethylhexyl phosphate (EHP) ligand via a simple condensation reaction at room temperature by optimizing the pH value. The EHP functionalized MXene (MXene-EHP) has excellent dispersion stability in most organic solvents due to EHP ligands favoring excellent compatibility with counterparts. The MXene-EHP/lithium iron phosphate (LiFePO4, LFP) composite was prepared and investigated as an efficient cathode in lithium ion batteries (LIBs). The surface modification with EHP has impeded the surface oxidation of the MXene in MXene-EHP and enhanced the compatibility with the LFP cathode and ionic diffusion in LIBs. MXene-EHP/LFP has delivered an excellent specific capacity of 150 mAh g−1 and 136 mAh g−1 at the initial cycle and after the 500th cycle at 1C rate, respectively in comparison to the bare LFP electrodes with a specific capacity of 118 mAh g−1 and 101 mAh g−1.

Photoluminescence of Three- and Four-Coordinate Platinum(0) Phosphine Complexes

Abstract Six platinum complexes bearing monodentate phosphine ligands were prepared and their structures and photophysical properties examined. The complexes were photoluminescent in the solid state, with a maximum quantum yield of 72%. The tris(phosphine) platinum complexes displayed more red-shifted emissions than the tetrakis complexes. The nature of the emissive excited states is discussed based on the results of density functional theory and time-dependent density-functional theory calculations.

Palladium‐Catalyzed Chemoselective Amination of Chloro(hetero)aryl Triflates Enabled by Alkyl‐Pyrazole‐Based Phosphine Ligands.

Palladium‐Catalyzed Chemoselective Amination of Chloro(hetero)aryl Triflates Enabled by Alkyl‐Pyrazole‐Based Phosphine Ligands.

Exploiting Co(III)-Cyclopentadienyl Complexes To Develop Anticancer Agents.

In recent years, organometallic complexes have attracted much attention as anticancer therapeutics aiming at overcoming the limitations of platinum drugs that are currently marketed. Still, the development of half-sandwich organometallic cobalt complexes remains scarcely explored. Four new cobalt(III)-cyclopentadienyl complexes containing N,N-heteroaromatic bidentate, and phosphane ligands were synthesized and fully characterized by elemental analysis, spectroscopic techniques, and DFT methods. The cytotoxicity of all complexes was determined in vitro by the MTS assay in colorectal (HCT116), ovarian (A2780), and breast (MDA-MB-231 and MCF-7) human cancer cell lines and in a healthy human cell line (fibroblasts). The complexes showed high cytotoxicity in cancer cell lines, mostly due to ROS production, apoptosis, autophagy induction, and disruption of the mitochondrial membrane. Also, these complexes were shown to be nontoxic in vivo in an ex ovo chick embryo yolk sac membrane (YSM) assay.

Chiral Phosphine Ligands of COAP and SKP Switched Regiodivergent Asymmetric Allylic Alkylation of MBH Adducts.

The palladium-catalyzed highly regioselective asymmetric allylic alkylation of 3'-indolyl-3-oxindole derivatives with Morita-Baylis-Hillman (MBH) carbonates was developed to facilely construct chiral 3,3'-bisindole derivatives under mild reaction conditions. The regioselectivity (α/γ) of MBH carbonates was efficiently switched in the presence of chiral oxalamide phosphine or spiroketal-based diphosphine/Pd(0) complexes as a chiral catalyst. A series of multifunctional 3,3'-bisindole derivatives with all-carbon quaternary stereogenic centers were obtained in high yields with good to excellent enantio-, diastereo-, and regioselectivity. The present process is endowed with some salient features such as broad substrate scope, N-protecting group-free, excellent stereoselectivity, as well as adjustable regioselectivity.

Isolation of Cationic η3-Allenylnickel(II) Key Intermediate Complexes: Origins of Enantioselectivity and Regioselectivity in Nickel(0)-Catalyzed Asymmetric Propargylic Substitutions.

Herein, we report the synthesis and isolation of cationic η3-allenylnickel(II) complexes that bear rac-BINAP as a bidentate ligand for the first time via Me3SiOTf-promoted C-O bond cleavage of propargylic tert-butyl carbonate. In contrast, in the presence of the monodentate phosphine ligand PEt3, treatment of propargylic tert-butyl carbonate with Ni(cod)2 resulted in a gradual C-O bond cleavage leading to η1-allenylnickel(II) complexes, i.e., trans-(PEt3)2Ni(η1-CPh═C═CHR)(OBoc). X-ray diffraction and NMR spectroscopy studies of [(η3-RCH-CCPh)Ni(rac-BINAP)](OTf) revealed that the complex adopts an η3-allenyl coordination mode both in the crystal lattice and in solution. A thorough structural comparison between [(η3-RCH-CCPh)Ni(rac-BINAP)](OTf) and palladium and platinum analogues revealed that the η3-allenyl moiety in the nickel complex is similar to that observed in palladium and platinum complexes, albeit that each Ni-C bond is shorter than the corresponding Pd-C and Pt-C bonds due to the smaller ionic radius of nickel to that of Pd or Pt. The reactions of either N-methylaniline or sodium N-methylanilide with [(η3-RCH-CCPh)Ni((R)-BINAP)](OTf) furnished (R)-PhC≡CCH(NMePh)Me as an asymmetric propargylic substitution (APS) product with excellent enantioselectivity. Furthermore, when the nickel-catalyzed APS reaction of propargylic tert-butyl carbonate with N-methylaniline was conducted in DMSO at 60 °C in the presence of 5 mol % of [(η3-RCH-CCPh)Ni((R)-BINAP)](OTf) and 7.5 mol % of sodium N-methylanilide as a catalytic precursor and an additive, respectively, (R)-PhC≡CCH(NMePh)Me was obtained in 79% yield with 90% ee. The experimental results and computational calculations strongly suggest that the nickel-catalyzed APS reaction might proceed via a cationic η3-allenylnickel(II) species as the key reaction intermediate.

Exploring the influence of bis-phosphine ligands on lanthanide complexes: A DFT study

This study employs density functional theory (DFT) calculation to investigate the bis-phosphine ligands interaction with lanthanide ions (La3+, Nd3+, Eu3+, Er3+ and Lu3+). Two distinct bridging modes are explored between two phosphine ligands: pyridine and methylene functional groups. The aim is to understand the structural, thermochemical, spectroscopic, and orbital properties of the bis-phosphine-Ln3+ complexes and compare the effects of different bridging modes. It is observed that bis-phosphine ligands form the most stable complexes with Er3+ and the least stable complexes with La3+, as evidenced by interaction energies, Gibb’s free energies and electrophilicity index values. Pyridine-bridged ligands form more stable complexes than methylene-bridged ligands, which is consistent with charge population analysis. Reduced density gradient analysis indicates the presence of strong hydrogen bond-like interactions between lanthanide ions and oxygen/nitrogen atoms of bis-phosphine complexes. Infrared spectra simulations reveal that Er3+ forms stronger bonds with oxygen atoms of bis-phosphine ligands than other lanthanide ions.

Late-Stage Diversification of Phosphines by C-H Activation: A Robust Strategy for Ligand Design and Preparation.

ConspectusThe advent of the twenty-first century marked a golden era in the realm of synthetic chemistry, exemplified by groundbreaking advancements in the field of C-H activation, which is a concept that quickly transitioned from mere academic fascination to an essential element within the synthetic chemist's toolkit. This methodological breakthrough has given rise to a wealth of opportunities spanning a wide range of chemical disciplines. It has facilitated the late-stage diversification of elaborate organic frameworks, encompassing the spectrum from simple methane to complex polymers, thus refining the lead optimization process and easing the production of diverse molecular analogues. Among these strides forward, the development of phosphorus(III)-directed C-H activation stands out as an increasingly significant and inventive approach for the design and synthesis of ligands, substantially redefining the contours of synthetic methodology.Phosphines, renowned for their roles as ligands and organocatalysts, have become fundamentally important in modern organic chemistry. Their efficiency as ligands is significantly affected by coordination with transition metals, which is essential for their involvement in catalytic processes, influencing both the catalytic activity and the selectivity. Historically, the fabrication of phosphines predominantly relied on synthesis employing complex, multistep procedures. Addressing this limitation, our research has delved into ligand design and synthesis through innovative catalytic P(III)-directed C-H activation strategies. In this Account, we have explored a spectrum of procedures, including direct arylation using metal catalysis, and ventured further into domains such as C-H alkylation, alkenylation, aminocarbonylation, alkynylation, borylation, and silylation. These advances have enriched the field by providing efficient methods for the late-stage diversification of biaryl-type monophosphines as well as enabled the C-H activation of triphenylphosphine and its derivatives. Moreover, we have successfully constructed libraries of diverse axially chiral binaphthyl phosphine ligands, showcasing their potency in asymmetric catalysis. Through this Account, we aim to illuminate the exciting possibilities presented by P(III)-directed C-H activation in propelling the boundaries of organic synthesis. By highlighting our pioneering work, we hope to inspire further developments in this promising field of chemistry.

Regio- and Chemoselective Palladium-Catalyzed Additive-Free Direct C─H Functionalization of Heterocycles with Chloroaryl Triflates Using Pyrazole-Alkyl Phosphine Ligands.

A series of new pyrazole-alkyl phosphine ligands with varying cycloalkyl ring sizes that enable additive-free regio- and chemoselective C─H arylation of heterocycles are reported. Excellent α/β selectivity of various heterocycles such as benzo[b]thiophene, thiophene, furan, benzofuran, and thiazole can be achieved using these ligands, along with excellent chemoselectivity of C─Cl over C─OTf of chloroaryl triflates. Mechanistic studies supported by both experimental findings and density functional theory calculations indicate that the pyrazole phosphine ligands with optimal ring sizes allow the reaction to proceed with a lower energy barrier via a concerted metalation-deprotonation pathway.

Ruthenium Complexes with a Tridentate Anionic Bisfluoroalkoxy‐Carbene Ligand – Valuable Latent Olefin Metathesis Catalysts for Polymerisation Reactions

AbstractA Grubbs‐type ruthenium complex bearing a tridentate anionic bisfluoroalkoxy‐carbene was synthesised and fully characterised. Under standard conditions, it proved to be inactive in olefin metathesis reactions, but the addition of HCl triggers its activity and allows the synthesis of a series of cyclic olefins and ethers as well as a stereoregular polynorbornene with an unexpectedly high content of trans‐configured double bonds, as found in commercially available polynorbornene (Norsorex®). Detailed structural studies and DFT calculations showed that the complex enters the catalytic cycle, but instead of performing a full turnover, it is caught as a stable intermediate that does not undergo further reactions. The addition of HCl causes dissociation of the fluoroalkoxy units, resulting in a compound that behaves similarly to standard Grubbs‐type complexes. To further understand this phenomenon, the corresponding Hoveyda‐Grubbs complex was also obtained and studied in detail; due to the absence of the phosphine ligand, its behaviour was different from that of its Grubbs‐type counterpart.

Regio‐ and Atroposelective Ring‐Opening of 1H‐Benzo[4,5]oxazolopyridinones

AbstractThe development of new methods for regio‐ and stereoselective activation of C−O bonds in ethers holds significant promise for synthetic chemistry, offering advantages in terms of environmental sustainability and economic efficiency. Moreover, the C−N atropisomers represent a fascinating and crucial chiral system, extensively found in natural products, pharmaceutical leads, and the frameworks of advanced materials. In this work, we have introduced a nickel‐catalyzed regio‐ and enantioselective carbon‐oxygen arylation reaction for atroposelective synthesis of N‐arylisoquinoline‐1,3(2H,4H)‐diones. The high regioselectivity of C−O cleavage benefits from the high stability of the in situ formed (amido)ethenolate via oxidative addition. Additionally, the self‐activation of the aryl C−O bond facilitates the reaction under mild conditions, leading to outstanding enantioselectivities. The diverse post‐functionalizations of the axially chiral isoquinoline‐1,3(2H,4H)‐diones further highlighted the utility of this protocol in preparing valuable C−N atropisomers, including the chiral phosphine ligands.

Regio- and Atroposelective Ring-Opening of 1H-Benzo[4,5]oxazolopyridinones.

The development of new methods for regio- and stereoselective activation of C-O bonds in ethers holds significant promise for synthetic chemistry, offering advantages in terms of environmental sustainability and economic efficiency. Moreover, the C-N atropisomers represent a fascinating and crucial chiral system, extensively found in natural products, pharmaceutical leads, and the frameworks of advanced materials. In this work, we have introduced a nickel-catalyzed regio- and enantioselective carbon-oxygen arylation reaction for atroposelective synthesis of N-arylisoquinoline-1,3(2H,4H)-diones. The high regioselectivity of C-O cleavage benefits from the high stability of the in situ formed (amido)ethenolate via oxidative addition. Additionally, the self-activation of the aryl C-O bond facilitates the reaction under mild conditions, leading to outstanding enantioselectivities. The diverse post-functionalizations of the axially chiral isoquinoline-1,3(2H,4H)-diones further highlighted the utility of this protocol in preparing valuable C-N atropisomers, including the chiral phosphine ligands.

Synthesis, anticancer activity, and molecular docking of half-sandwich iron(II) cyclopentadienyl complexes with maleimide and phosphine or phosphite ligands

In these studies, we designed and investigated the potential anticancer activity of five iron(II) cyclopentadienyl complexes bearing different phosphine and phosphite ligands. All complexes were characterized with spectroscopic analysis viz. NMR, FT–IR, ESI–MS, UV–Vis, fluorescence, XRD (for four complexes) and elemental analyses. For biological studies, we used three types of cells—normal peripheral blood mononuclear (PBM) cells, leukemic HL-60 cells and non-small-cell lung cancer A549 cells. We evaluated cell viability and DNA damage after cell incubation with these complexes. We observed that all iron(II) complexes were more cytotoxic for HL-60 cells than for A549 cells. The complex CpFe(CO)(P(OPh)3)(η1-N-maleimidato) 3b was the most cytotoxic with IC50 = 9.09 µM in HL-60 cells, IC50 = 19.16 µM in A549 and IC50 = 5.80 µM in PBM cells. The complex CpFe(CO)(P(Fu)3)(η1-N-maleimidato) 2b was cytotoxic only for both cancer cell lines, with IC50 = 10.03 µM in HL-60 cells and IC50 = 73.54 µM in A549 cells. We also found the genotoxic potential of the complex 2b in both types of cancer cells. However, the complex CpFe(CO)2(η1-N-maleimidato) 1 which we studied previously, was much more genotoxic than complex 2b, especially for A549 cells. The plasmid relaxation assay showed that iron(II) complexes do not induce strand breaks in fully paired ds-DNA. The DNA titration experiment showed no intercalation of complex 2b into DNA. Molecular docking revealed however that complexes CpFe(CO)(PPh3) (η1-N-maleimidato) 2a, 2b, 3b and CpFe(CO)(P(OiPr)3)(η1-N-maleimidato) 3c have the greatest potential to bind to mismatched DNA. Our studies demonstrated that the iron(II) complex 1 and 2b are the most interesting compounds in terms of selective cytotoxic action against cancer cells. However, the cellular mechanism of their anticancer activity requires further research.

Mono- and bi-nuclear phosphine-phenolate neutral nickel catalysts via simple Schiff-Base condensation for ethylene polymerization

In catalytic olefin polymerization, a significant amount of effort has been invested to modify either phosphine substituent or ligand backbone in recently advanced phosphine-phenolate [P,O] neutral nickel catalysts. Unlike other commonly used ligands like phenoxy-imines [N,O] and α-diimines [N,N], [P,O] ligands often require a laborious synthesis technique, which has hindered the rational design of ligand structures and the development of new catalysts. Here we present a novel and effective strategy for creating catalysts using [N,O,P] hybrid ligands. The substituent adjacent to the phenoxy group can be efficiently modified through straightforward Schiff-base condensation reactions with various amines that have established synthetic routes and diverse structures. This process results in the preparation of a series of highly active [P,O] nickel catalysts (up to 1.7 × 107 g mol-1h−1) that are capable of producing ultrahigh molecular weight polyethylene (UHMWPE) (Mw = 243.7 × 104 g/mol) in ethylene polymerization. The additional binding site greatly facilitates modulation of catalytic properties by additives, and parameters such as catalytic activity, polymer molecular weight, and polymer branching can be tuned in this way. Furthermore, binuclear [P,O] neutral nickel catalysts for olefin polymerization are synthesized for the first time using a sequence of diamines. The strategy presented in this work greatly improves the efficiency for the design and synthesis of [P,O] nickel and related catalysts. These findings will be advantageous for future catalyst design and screening.

Pinwheel-like tridentate phosphines for controlling divergent regioselectivity in Pd-catalyzed alkoxycarbonylation of alkenes

The elaborate control of regioselectivity regulated by the involved ligands with specific structural skeleton and compositions is always demanded in alkoxycarbonylation of alkenes. Herein, a series of pinwheel-like tridentate phosphine ligands with rotatable flexibility (L3) or hard rigidity (L5–L7) were synthesized and characterized for the first time, in which the incorporated three PPh2-fragments are located at meta-positions of phenyl groups. It was proved that the tridentate phosphine of L3 with the flexible configuration favorably corresponded to the linear regioselectivity with l/b ratio of 98/2, whereas L7 with the rigid configuration absolutely did favor to the branched regioselectivity with l/b ratio of 1/99. The presence of the three PPh2-frgaments in L3 did contribute to the remarkable performance of L3-Pd(TFA)2 system in terms of activity, linear regioselectivity and stability, subjected to 10-run recycling uses in anti-Markovnikov’s methoxycarbonylation of styrene without activity loss and Pd-black precipitation. In comparison, although the optimal L7-Pd(MeCN)2Cl2 system could catalyze Markovnikov’s alkoxycarbonylation of alkenes to afford the branched esters with excellent regioselectivity in the fresh use, its stability was too poor to support the recycling experiments. L3-Pd(TFA)2 and L7-Pd(MeCN)2Cl2 catalytic systems were both applicable to a wide range of substrates in alkoxycarbonylation of alkenes to afford the target esters in the isolated yields of 41–91 %, with the well maintained divergent regioselectivity.