Diphosphine Complexes Research Articles

Mechanism guided two-electron energy storage for redox-flow batteries using nickel bis(diphosphine) complexes.

The storage of multiple electrons per molecule can greatly enhance the energy density of redox-flow batteries (RFBs). Here, we show that nickel bis(diphosphine) complexes efficiently store multiple electrons through either sequential 1e- redox waves or a concerted 2e- redox wave, depending on their coordination environment. Mechanistic studies comparing ligand sterics (-Me vs. -Ph) and coordination of monodentate ligands (MeCN vs. Cl-) allow for selective control of the electron transfer pathway, steering electron storage toward the more favorable 2e- wave. Continuous charge-discharge cycling experiments show more negative charge-discharge potentials and improved capacity retention in the presence of Cl-, thus improving the energy storage of nickel bis(diphosphine) complexes as anolytes in RFBs. This work shows how mechanistic understanding of 2e- redox cycles for transition metal complexes can create new opportunities for multi-electron storage in RFBs.

Ligand and Metal Effects in the Gas‐Phase Fragmentation of Thiomethoxymethyl Complexes

AbstractWhile the collision‐induced dissociation (CID) of the mass‐selected cation [(Ph3P)2Pt(CH2SCH3)]+ causes the selective liberation of PPh3, the diphosphine complex [(dppe)Pt(CH2SCH3)]+ (dppe=1,2‐bis(diphenylphosphino)ethane) ejects C2H4, CH2S, and (CH3)2S upon CID. The analogous palladium complexes [(Ph3P)2Pd(CH2SCH3)]+ and [(dppe)Pd(CH2SCH3)]+ show similar reactivity, except that C−H‐bond activation is completely lacking. For other bidentate diphosphine ligands such as dppm, dppv, dppp, dppb, dppbz, dppf, and xantphos, a correlation of the dominant reaction channels with the bite angle is observed. For bite angles > 90°, hydrogen‐atom transfer is favored, as evidenced by an increase in dimethyl‐sulfide loss. For smaller bite angles (< 90°), intramolecular activation of the thiomethoxymethyl ligand predominates, thus resulting in increased losses of thioformaldehyde and ethene. The results of the CID experiments are compared with those for [(bipy)Pt(CH2SCH3)]+, for which the loss of C2H4 is observed as the main process. DFT calculations for the complexes [(dppe)Pt(CH2SCH3)]+ and [(bipy)Pt(CH2SCH3)]+ together with the experimental findings uncover subtle differences in the underlying reaction mechanisms.

Ball-Milling toward Nickel(II) Diphosphine Complexes for Direct Use in Catalysis.

Mechanochemistry turned out to be apowerful synthetic tool enabling the first efficient synthesis of nickel(II) complexes with diphosphines. It has been demonstrated that solventless ball-milling of nickel(II) halides with diphosphines leads to the [NiX2(diphosphine)] type compounds, which can be directly used in catalysis without any purification. Moreover, it was confirmed that despite the presence of impurities in the resulting complexes, their catalytic activity remains identical to those obtained via traditional solvent-based methods.

Understanding Ligand Effects on Bielectronic Transitions: Chemo‐ and Electroreduction of Rhodium Bis(Diphosphine) Complexes to Low Oxidation States

AbstractRhodium complexes in the −I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two‐electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(dxpy)2]NTf2 (x=P‐substituent, y=alkanediyl bridging P atoms). Through (electro)reductions from the RhI parents, Rh−I d10‐complexes were obtained and characterized spectroscopically, including 103Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E0(RhI/0) and second E0(Rh0/−I) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P−Rh‐P bite angles provide only partial correlations with the redox potentials. However, we identified the C−O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two‐electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.

Understanding Ligand Effects on Bielectronic Transitions: Chemo- and Electroreduction of Rhodium Bis(Diphosphine) Complexes to Low Oxidation States.

Rhodium complexes in the -I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two-electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(dxpy)2]NTf2 (x=P-substituent, y=alkanediyl bridging P atoms). Through (electro)reductions from the RhI parents, Rh-I d10-complexes were obtained and characterized spectroscopically, including 103Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E0(RhI/0) and second E0(Rh0/-I) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P-Rh-P bite angles provide only partial correlations with the redox potentials. However, we identified the C-O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two-electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.

Designing Nickel-based catalysts for the hydrogenation of CO2 under Ambient conditions: A computational study

Recent developments, industrialization, and modernization lead to production of more and more pollutants (such as CO2: ∼ 417.06 ppm) and such rapid growth of CO2 level results in global warming and the greenhouse effect. So, it is essential to conduct research on converting CO2 into fuels using carbon-neutral energy. Recent research on molecular catalysts has improved the rates of converting CO2 to formate. However, these catalysts require extremely high temperatures and pressures and are made of expensive metals like iridium, ruthenium, and rhodium. Herein, DFT-based computational studies have been performed on the catalytic hydrogenation of CO2 by different Ni(II) complexes in ambient conditions. Using state-of-the-art calculations, we demonstrate how the geometry and spin states of Ni(II) complexes containing different types of ligands affect their catalytic role in CO2 hydrogenation. It has been reported that hydride transfer is the most crucial step for such kind of hydrogenation reaction. We start with previously synthesised Ni-bis(diphosphine) complexes of type NiP4 and by extrapolating the concept, we propose a novel kind of Ni-PNP complex with a significantly lower hydride transfer barrier. We also calculate the hydricities of the nickel hydride complexes in order to correlate these thermodynamic parameters with the kinetic barrier of hydride transfer.

Chloroiridium Complexes of Biaryl-Based Diphosphines for Thermal Catalytic Transfer Dehydrogenation of Hindered 1,1-Disubstituted Ethanes

Chloroiridium Complexes of Biaryl-Based Diphosphines for Thermal Catalytic Transfer Dehydrogenation of Hindered 1,1-Disubstituted Ethanes

Backbone-functionalised ruthenium diphosphine complexes for catalytic upgrading of ethanol and methanol to iso-butanol.

Efficient catalysts for Guerbet-type ethanol/methanol upgrading to iso-butanol have been developed via Michael addition of a variety of amines to ruthenium-coordinated dppen (1,1-bis(diphenylphosphino)ethylene). All catalysts produce over 50% iso-butanol yield with >90% selectivity in 2 h with catalyst 1 showing the best activity (74% yield after this time). The selectivity and turnover number approach 100% and 1000 respectively using catalyst 6. The presence of uncoordinated functionalised donor groups in these complexes results in a more stable catalyst compared to unfunctionalised analogues.

Catalytic deoxydehydration of glycerol to allyl alcohol in the presence of mono-oxygenated rhenium diphosphine complexes

Allyl alcohol is a crucial organic intermediate in synthesizing polymeric compounds industrially produced by petroleum-derived propylene despite environmental concerns. In this study, we propose a system that utilizes cost-effective and renewable bio-resource, glycerol, as the starting material. In this regard, we conducted the reaction in the presence of mono-oxygenated rhenium diphosphine complexes as catalysts and alcohol as the solvent and hydrogen transfer agent. Among the tested complexes, the [ReOBr3(Xantphos)] complex combined with 2-propanol as a solvent and the reducing agent exhibited the most outstanding performance, yielding allyl alcohol with an exceptional efficiency of 100%. The structures of three newly synthesized complexes, [ReOBr3(Xantphos)], [ReOBr3(DPEphos)], and [ReOCl3(dppb)] were determined by X-ray single crystallography. These findings contribute to the advancement of allyl alcohol production, offering a more sustainable and environmentally friendly alternative to conventional petroleum-based methods.

Synthesis and characterization of a new ruthenium (II) terpyridyl diphosphine complex

Ruthenium complexes have been prepared for several applications, mostly for electrocatalysis, catalytic hydrogenation, energy conversion, photolysis, medicinal chemistry, among other fields. Bipyridine and terpyridine ligands are commonly found in the metal coordination sphere, including ruthenium, largely due to the high stability exhibited by the resulting complex and the possibility of greater stereochemical control during synthesis. The combination of substituted terpyridine ligands with diphosphine ligands to the metal ruthenium occurs to a lesser extent and its catalytic potential has been examined in several studies. This paper describes the synthesis of a new ruthenium (II) aqua complex containing aryl diphosphine and substituted terpyridine ligands: [Ru(L)(totpy)(OH2)](ClO4)2 (L=Ph2PCH2CH2PPh2); (totpy=4´-(4-tolyl)-2,2´:6´,2´´-terpyridine). The synthesis route was conducted in three steps; the final and the intermediate products have shown good reaction yields; the results of the characterization of the aqua complex by cyclic voltammetry, UV-visible spectroscopy and elemental analysis are consistent with the proposed chemical structure.

When 3+1 is Less Than 2+2: Surprisingly Moderate Hydricities in Heteroleptic Rhodium Complexes Containing Triphosphine and Monophosphine Ligands

Rhodium(I) complexes with the formula [Rh(PP2)(PR3)]+ (PP2 = PhP(CH2CH2PPh2)2; R = Ph, Et, or Me) were synthesized and characterized. Their reactions with H2 in the presence of strong bases, forming rhodium(I) hydrides with the formula HRh(PP2)(PR3), were studied, and the structure of HRh(PP2)(PPh3) was determined by X-ray crystallography. These are the first structurally characterized rhodium complexes with this combination of triphosphine and monophosphine ligands. Their thermodynamic hydricities were determined from the equilibrium constants of their heterolytic H2 activation equilibria. The values of ΔG°H– range from 37.3 kcal/mol for HRh(PP2)(PMe3) to 42.4 kcal/mol for HRh(PP2)(PPh3) in MeCN. These hydricities are surprisingly modest in comparison to their close analogues with the HRh(diphosphine)2 ligand framework, which are among the most powerful known hydride donors. Due to this decreased reactivity, the hydricities are in a nearly optimal range for CO2 hydrogenation, balancing the favorability of hydride transfer with the free energy for H2 activation. The structural factors underlying the thermodynamic trends, including the relatively small variation in hydricity imparted by the monophosphine and the higher overall ΔG°H– values compared to electronically similar bis(diphosphine) complexes, are largely attributable to the small bite angles within the chelate rings of the triphosphine ligand in these complexes.

Construction of Monophosphine–Metal Complexes in Privileged Diphosphine-Based Covalent Organic Frameworks for Catalytic Asymmetric Hydrogenation

Privileged diphosphine ligands that chelate many transition metals to form stable chelation complexes are essential in a variety of catalytic processes. However, the exact identity of the catalytically active moieties remains ambiguous because the chelated metal catalysts may undergo rearrangement during catalysis to produce monophosphine-metal complexes, which are hard to isolate and evaluate the activities. By taking advantage of the isolation of two phosphorus atoms, we demonstrate here the successful construction of chiral monophosphine-Ir/Ru complexes of diphosphine ligands in covalent organic frameworks (COFs) for enantioselective hydrogenation. By condensation of the tetraaldehyde of enantiopure MeO-BIPHEP and linear aromatic diamines, we prepare two homochiral two-dimensional COFs with ABC stacking, in which the two P atoms of each diphosphine are separated and fixed far apart. Post-synthetic metalations of the COFs thus afford the single-site Ir/Ru-monophosphine catalysts, in contrast to the homogeneous chelated analogues, that demonstrated excellent catalytic and recyclable performance in the asymmetric hydrogenation of quinolines and β-ketoesters, affording up to 99.9% enantiomeric excess. Owing to the fact that the porous catalyst is capable of adsorbing and concentrating hydrogen, the catalytic reactions are promoted under ambient/medium pressure, which are typically performed under high pressure for homogeneous catalysis. This work not only shows that monophosphine-metal complexes of diphosphines can be catalytically active centers for asymmetric hydrogenation reactions but also provides a new strategy to prepare new types of privileged phosphine-based heterogeneous catalysts.

Cooperative bond activations by a tucked-in iron complex.

Herein, we report the first example of a 'tucked-in' iron diphosphine complex, formed through deprotonation of a Cp*-(CH̲3) (Cp* = C5Me5-) group by n-butyllithium. The reactivity of this complex was demonstrated by activation of organic and metal-containing substates, including CO2, benzaldehyde, Br-AuI-PPh3, B(C6F5)3, and HBCy2 (Cy = cyclohexyl).

Organic group decorated heterogeneous Pd complex on mesoporous silica toward catalytic allylation in aqueous media

The use of water as a reaction solvent is ideal for green chemistry. However, carrying out catalytic reactions with transition metal catalysts in aqueous media is challenging. To enhance the scope of transition-metal-catalyzed allylation reactions in aqueous media, a series of Pd diphosphine complexes co-immobilized with organic groups onto mesoporous silica (MS) supports was synthesized. The synthesized catalysts were characterized via FT-IR, XAFS, and hydrophobicity determined via contact angle measurements. The newly synthesized catalyst demonstrated improved catalytic allylation performance in water. Aqueous catalytic allylation between allyl methyl carbonate and ethyl acetoacetate produced disubstituted product yields greater than 99%. Moreover, an MS pore size of 3.1 nm and phenyl/Pd ratio of 15 demonstrated the highest activity among the synthesized catalyst library. The results significantly expand the toolkit of transition-metal-catalyzed reactions in aqueous media; we believe they will have far-reaching consequences owing to the wide use and scope of allylation reaction in academia as well as industry.

Ferroptosis‐Enhanced Cancer Immunity by a Ferrocene‐Appended Iridium(III) Diphosphine Complex

AbstractFerroptosis is a programmed cell death pathway discovered in recent years, and ferroptosis‐inducing agents have great potential as new antitumor candidates. Here, we report a IrIII complex (Ir1) containing a ferrocene‐modified diphosphine ligand that localizes in lysosomes. Under the acidic environments of lysosomes, Ir1 can effectively catalyze Fenton‐like reaction, produce hydroxyl radicals, induce lipid peroxidation, down‐regulate glutathione peroxidase 4, and result in ferroptosis. RNA sequencing analysis shows that Ir1 can significantly affect pathways related to ferroptosis and cancer immunity. Accordingly, Ir1 can induce immunogenic cells death and suppress tumor growth in vitro, regulate T cell activity and immune microenvironments in vivo. In conclusion, we show the potential of small molecules with ferroptosis‐inducing capabilities for effective cancer immunotherapy.

Ferroptosis-Enhanced Cancer Immunity by a Ferrocene-Appended Iridium(III) Diphosphine Complex.

Ferroptosis is a programmed cell death pathway discovered in recent years, and ferroptosis-inducing agents have great potential as new antitumor candidates. Here, we report a IrIII complex (Ir1) containing a ferrocene-modified diphosphine ligand that localizes in lysosomes. Under the acidic environments of lysosomes, Ir1 can effectively catalyze Fenton-like reaction, produce hydroxyl radicals, induce lipid peroxidation, down-regulate glutathione peroxidase 4, and result in ferroptosis. RNA sequencing analysis shows that Ir1 can significantly affect pathways related to ferroptosis and cancer immunity. Accordingly, Ir1 can induce immunogenic cells death and suppress tumor growth in vitro, regulate T cell activity and immune microenvironments in vivo. In conclusion, we show the potential of small molecules with ferroptosis-inducing capabilities for effective cancer immunotherapy.

How solvents affect the stability of cationic Rh(I) diphosphine complexes: a case study of MeCN coordination.

Cationic rhodium(I) diphosphine complexes, referred to as Schrock-Osborn catalysts, are privileged homogeneous catalysts with a wide range of catalytic applications. The coordination of solvent molecules can have a significant influence on reaction mechanisms and kinetic scenarios. Although solvent binding is well documented for these rhodium species, comparative quantifications for structurally related systems are not available to date. We present a method for systematic investigation and quantification of this important parameter, using MeCN which replaces diolefins and forms stable Rh(I) MeCN complexes. Using UV-vis and 31P{1H} NMR spectroscopy we determine and compare stability constants of different [Rh(PP)(NBD)]BF4 and [Rh(PP)(COD)]BF4 complexes (PP = diphosphine; COD = 1,5-cyclooctadiene; NBD = 2,5-norbornadiene) and discuss the influence of PP ligands and reaction temperature. A DFT study reveals the dependence of the stability on the thermodynamics of the exchange reaction. Using variable temperature NMR spectroscopy, the first mixed solvate complex could be verified as an intermediate in the MeCN-MeOH exchange.

Ruthenium(II)-diphosphine complexes containing acylthiourea ligands are effective against lung and breast cancers.

We have synthesized and characterized three new ruthenium(II) diphosphine complexes containing an acylthiourea ligand, with the general formula [Ru(DPEPhos)(O,S)(bipy)]PF6, where DPEPhos = bis(2-(diphenylphosphino)phenyl)ether, bipy = 2,2'-bipyridine, and O,S = N,N-dimethyl-N'-(benzoyl)thiourea (1), N,N-dimethyl-N'-(furoyl)thiourea (2), and N,N-dimethyl-N'-(thiophenyl)thiourea (3), by several physicochemical techniques. We evaluated the ruthenium complexes for their cytotoxicity against two human cancer cell lines, A549 (lung) and MDA-MB-231 (breast), and two corresponding lines of non-cancer cells, MRC-5 (lung) and MCF-10A (breast). All the complexes are cytotoxic against the cancer cell lines; the IC50 values lie in the micromolar range (0.07-0.70 μM). Ruthenium complex 1 is more selective (7 times more active) toward lung cancer cells (A549) than toward non-cancer cells (MRC-5) and is 160 times more cytotoxic than cisplatin against A549 cells. Investigations of the mechanism of action of complex 1 in A549 cells demonstrated that it inhibits colony formation and promotes cell cycle arrest in the G1 phase and apoptotic cell death. DNA binding studies revealed that complexes 1-3 interact with the biomolecule via minor grooves. These complexes also interact with human serum albumin (HSA) and have affinity for site I by hydrophobic forces. Therefore, this new class of ruthenium complexes can act as cytotoxic agents, mainly for lung cancer treatment.

Ethynyl π-coordinated and non-coordinated mononuclear Cu(i) halide diphosphine complexes: synthesis and photophysical studies

Complexes 4 and 5 emit yellow green delayed fluorescence and complexes 1–3 and 6 and 7 show yellow green to greenish yellow prompt fluorescence.

The One‐pot Encapsulation of Palladium Complexes into Covalent Organic Frameworks Enables the Alkoxycarbonylation of Olefins

AbstractIn this study, palladium‐based heterogeneous catalysts were successfully prepared by encapsulating the palladium diphosphine complexes into an imine‐linked 2D‐COF (TPB‐DMTP‐COF) through a one pot self‐assembly approach. It not only prevents the oxidation of phosphine‐based ligand during the stepwise impregnation but also suppresses the coordination of imine linkers at the COF host to the palladium guest, thus enabling highly efficient encapsulation of the active bidentate phosphine chelated palladium complex by the widely explored imine‐linked COF. Besides, the dosage of diphosphine ligand (Xantphos‐SO3H, L) and the ratio of palladium to L in the preparation of [Pd]@COF hybrids can be readily adjusted under such one pot procedure to satisfy the requirement of crystallinity, porosity, active sites, and CO adsorption capacity for the catalytic performance in the methoxycarbonylation of olefins. The resultant [Pd]@COF‐A‐0.25‐0.5 provides satisfied catalytic performance for both aliphatic and aromatic olefins with total esters up to 92.1 % under optimized conditions. These findings provide the basis for a novel design concept to design heterogeneous catalysts with high efficiency for reaction processes comprising the alkoxycarbonylation of olefins.