Triphenylphosphine Complexes Research Articles

Thionitrosyl Complexes of Rhenium and Technetium with PPh3 and Chelating Ligands—Synthesis and Reactivity

In contrast to corresponding nitrosyl compounds, thionitrosyl complexes of rhenium and technetium are rare. Synthetic access to the thionitrosyl core is possible by two main approaches: (i) the treatment of corresponding nitrido complexes with S2Cl2 and (ii) by reaction of halide complexes with trithiazyl chloride. The first synthetic route was applied for the synthesis of novel rhenium and technetium thionitrosyls with the metals in their oxidation states “+1” and “+2”. [MVNCl2(PPh3)2], [MVNCl(PPh3)(LOMe)] and [MVINCl2(LOMe)] (M = Re, Tc; {LOMe}− = (η5-cyclopentadienyl)tris(dimethyl phosphito-P)cobaltate(III)) complexes have been used as starting materials for the synthesis of [ReII(NS)Cl3(PPh3)2] (1), [ReII(NS)Cl3(PPh3)(OPPh3)] (2), [ReII(NS)Cl(PPh3)(LOMe)]+ (4a), [ReII(NS)Cl2(LOMe)] (5a), [TcII(NS)Cl(PPh3)(LOMe)]+ (4b) and [TcII(NS)Cl2(LOMe)] (5b). The triphenylphosphine complex 1 is partially suitable as a precursor for ongoing ligand exchange reactions and has been used for the synthesis of [ReI(NS)(PPh3)(Et2btu)2] (3a) (HEt2btu = N,N-diethyl-N′-benzoyl thiourea) containing two chelating benzoyl thioureato ligands. The novel compounds have been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods including IR, NMR and EPR spectroscopy and (where possible) mass spectrometry. A comparison of structurally related rhenium and technetium complexes allows for conclusions about similarities and differences in stability, reaction kinetics and redox behavior between these 4d and 5d transition metals.

Synthesis and characterization of Ag(I) and Cu(I) complexes of triphenylphosphine: crystal structures, Hirshfeld surface analyses, and molecular docking with SARS-CoV-2 and its Omicron variant

Two new coordination complexes, a Ag(I) complex [Ag(PPh3)3(Sal)] (1) and a Cu(I) complex [Cu(PPh3)3Cl] (2), have been synthesized (PPh3 = triphenylphosphine, Sal = 3,5-dichlorosalicylaldehyde). Both complexes were characterized via single crystal X-ray crystallography. Complexes 1 and 2 were crystallized in monoclinic and trigonal crystal systems, respectively, in the P21/c and P3 space groups. Both possess tetrahedral coordination geometries. DFT calculations provided structure-property information. The Hirshfeld surface analyses and 2D fingerprint plots were performed to investigate the intermolecular interactions in the crystal structures. To explore potential SARS-CoV-2 drug candidates, we have examined the molecular docking of 1 and 2 with the SARS-CoV-2 spike protein (PDB ID: 8GOP) and with the SARS-CoV-2 Omicron spike protein (PDB ID: 7WRV). Complexes 1 and 2 showed good docking results with the SARS-CoV-2 spike protein (PDB ID: 8GOP) where the binding energies (ΔG) and respective inhibition constants (K i) correlation values are −7.4 kcal/mol (4.321 µM) and −7.9 kcal/mol (5.012 µM), respectively. The molecular docking results revealed that 1 and 2 with the SARS-CoV-2 Omicron spike protein (PDB ID: 7WRV) resulted in the binding energy (ΔG) of −7.6 kcal/mol and −8.2 kcal/mol with an inhibition constant (K i) of 4.639 and 5.742 µM, respectively. The study predicts that 1 and 2 may be used as anti-SARS CoV-2 agents.

Hydroboration of aldehydes with pinacolborane catalyzed by bulky 2‐iminopyrrolyl copper(I) triphenylphosphine complexes

Eight new copper(I) triphenylphosphine complexes of bulky 5‐substituted‐2‐iminopyrrolyl ligands [Cu{κ2N,N′‐5‐R‐NC4H2–2‐C(H) = N(2,6‐iPr2C6H3)}(PPh3)n] (for n = 2: R = 2,6‐Me2C6H3 (1), 3,5‐(CF3)2C6H3 (2); for n = 1: R = 2,4,6‐iPr3C6H2 (3), CPh3 (4), 2,6‐(OMe)2C6H3 (5), 2,4,6‐Ph3C6H2 (6), 2,6‐Me2C6H3 (7), 3,5‐(CF3)2C6H3 (8)) are presently reported. The complexes were prepared in good yields by: (1) the reaction of the previously reported binuclear complexes [Cu{κN,κN'‐5‐R‐NC4H2‐2‐C(H) = N(2,6‐iPr2C6H3)}]2 (D1–D6) with triphenylphosphine (PPh3); (2) the reaction of the respective 5‐R‐2‐iminopyrrolyl potassium salts (KL1–KL3 and KL5) and [Cu(NCMe)2(PPh3)2]BF4; or (3) the abstraction of one PPh3 ligand present in complexes 1 and 2 with one equivalent of tris(pentafluorophenyl)borane (only for complexes 7 and 8, respectively). All complexes were characterized by NMR spectroscopy, elemental analysis and, in selected cases, by single crystal X‐ray diffraction. The single crystal X‐ray diffraction structures of 1, 3, and 5–7 displayed tetrahedral (for 1) and trigonal planar (for 3 and 5–7) coordination geometries. All complexes catalyzed the 1,4‐hydroboration of some α,β‐unsaturated (E)‐2‐enals with pinacolborane (HBPin), with 1,4:1,2‐addition selectivities as high as 29:1, the maximum turnover frequencies being equal to 9.9 min−1, and the 1,4‐hydroboration selectivity being favored by increasing steric protection of the 5‐substituted‐2‐iminopyrrolyl scaffold. Additionally, these complexes also catalyzed the hydroboration of an array of other aldehydes, reaching TOFs as high as 9.9 min−1. A combination of control experiments suggests that the catalyst system operates via a non‐classical copper‐hydride outer sphere route.

Copper(I)/Triphenylphosphine Complexes Containing Naphthoquinone Ligands as Potential Anticancer Agents

Four new Cu/PPh3/naphtoquinone complexes were synthesized, characterized (IR, UV/visible, 1D/2D NMR, mass spectrometry, elemental analysis, and X-ray diffraction), and evaluated as anticancer agents. We also investigated the reactive oxygen species (ROS) generation capacity of complex 4, considering the well-established photochemical property of naphthoquinones. Therefore, employing the electron paramagnetic resonance (EPR) “spin trap”, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) technique, we identified the formation of the characteristic •OOH species (hydroperoxyl radical) adduct even before irradiating the solution containing complex 4. As the irradiation progressed, this radical species gradually diminished, primarily giving rise to a novel species known as •DMPO-OH (DMPO + •OH radical). These findings strongly suggest that Cu(I)/PPh3/naphthoquinone complexes can generate ROS, even in the absence of irradiation, potentially intensifying their cytotoxic effect on tumor cells. Interpretation of the in vitro cytotoxicity data of the Cu(I) complexes considered their stability in cell culture medium. All of the complexes were cytotoxic to the lung (A549) and breast tumor cell lines (MDA-MB-231 and MCF-7). However, the higher toxicity for the lung (MRC5) and breast (MCF-10A) non-tumoral cells resulted in a low selectivity index. The morphological analysis of MDA-MB-231 cells treated with the complexes showed that they could cause decreased cell density, loss of cell morphology, and loss of cell adhesion, mainly with concentrations higher than the inhibitory concentration of 50% of cell viability (IC50) values. Similarly, the clonogenic survivance of these cells was affected only with concentrations higher than the IC50 values. An antimigratory effect was observed for complexes 1 and 4, showing around 20–40% of inhibition of wound closure in the wound healing experiments.

Effect of Iodide on the pH-Controlled Hydrogenations of Diphenylacetylene and Cinnamaldehyde Catalyzed by Ru(II)-Sulfonated Triphenylphosphine Complexes in Aqueous–Organic Biphasic Systems

The effect of NaI on hydrogenation of diphenylacetylene catalyzed by the water-soluble [{RuCl(mtppms-Na)2}2(µ-Cl)2] (1) (mtppms-Na = meta-monosulfonated triphenylphosphine sodium salt) is reported. Hydrogenations were performed under mild conditions (P(H2) = 1 bar, T = 50–80 ℃) in aqueous–organic biphasic reaction mixtures wherein the catalyst was dissolved in aqueous phase of various pHs. In acidic solutions, addition of NaI to 1 + mtppms-Na increased the selective conversion of diphenylacetylene to stilbenes from 10% to 90% but did not effect the high Z-selectivity (up to 98%). In contrast, in basic solutions the major product was diphenylethane (up to 70%), and the yield of E-stilbene exceeded that of the Z-isomer. 1H and 31P NMR measurements revealed that depending on the absence or presence of NaI, the catalytically active Ru(II)-hydride species in acidic solutions was [RuHCl(mtppms-Na)3], 2, or [RuHI(mtppms-Na)3], 5, respectively, while in basic solutions, both 2 and 5 were hydrogenated further to yield the same hydride species, cis,fac-[RuH2(H2O)(mtppms-Na)3]. [RuHI(mtppms-Na)3] proved superior to [RuHCl(mtppms-Na)3] as a catalyst for the selective hydrogenation of cinnamaldehyde to dihydrocinamaldehyde. This finding was explained by a facile formation of a (putative) dihydrogen complex [Ru(H2)I2(H2O)(mtppms-Na)2] intermediate, resulting in fast heterolytic activation of H2.

Vibrational spectra, force constants and quantum chemical calculations of μ-1,3-azide bridged triphenylphosphine complexes of copper(I) and silver(I)

The dimeric title compounds [(C6H5)3P]Cu2(N3)2 and [C6H5)3P]Ag2(N3)2 were synthesized and characterized by FT-Raman and IR spectroscopy. The two phases were not isotypic but possessed approximately the same molecular symmetry which was C2/2m. The assignment of the modes was supported by quantum chemical DFT calculations coupled with TED (Total Energy Distribution) analyses. The calculated (NN) force constants for the bridging --(NNN)-- groups were directly comparable (f(NN) = 11.75 (Cu) and 12.19 N cm−1(Ag)) and harmonized well with those of the free azide anion in the binary alkali azides. The (NN) bond orders were obtained based on the calculated force constants (Siebert Bond Order, SBO) and Density-dependent electrostatic and chemical (DDEC6) method yielding SBO = 1.92 (Cu) and 1.96 (Ag) and BO = 2.00 (Cu) and 2.03 (Ag), respectively, indicating the presence of double bonds. The results underlined that the (NN) force constants and bond orders in the bridging azide units were practically unaffected by the nature of the central metal atoms and that they could be regarded as quasi isolated anions similar to those in the binary azide compounds.

Organometallic flow chemistry: solvento complexes.

Photolysis under optimised flow conditions of metal carbonyls [{Ln}M(CO)x] [{Ln}M(CO)x = Cr(CO)6, Mo(CO)6, W(CO)6, Mn(CO)3(η-C5H4Me), Re(CO)3(η-C5H5)] in tetrahydrofuran (THF) conveniently affords the synthetically versatile and labile solvento complexes [{Ln}M(CO)x-1(THF)], thereby obviating many of the caveats associated with photochemical syntheses using either 'batch' or falling film techniques. Conversions were optimised and yields assayed by a combination of in situ infrared spectroscopy and derivatisation as the corresponding triphenylphosphine complexes [{Ln}M(CO)x-1(PPh3)].

Triboluminescence Phenomenon Based on the Metal Complex Compounds-A Short Review.

Triboluminescence (TL) is a phenomenon of light emission resulting from the mechanical force applied to a substance. Although TL has been observed for many ages, the radiation mechanism is still under investigation. One of the exemplary compounds which possesses triboluminescent properties are copper(I) thiocyanate bipyridine triphenylphosphine complex [Cu(NCS)(py)2(PPh3)], europium tetrakis dibenzoylmethide triethylammonium EuD4TEA, tris(bipyridine)ruthenium(II) chloride [Ru(bpy)3]Cl2, and bis(triphenylphosphine oxide)manganese(II) bromide Mn(Ph3PO)2Br2. Due to the effortless synthesis route and distinct photo- and triboluminescent properties, these compounds may be useful model substances for the research on the triboluminescence mechanism. The advance of TL studies may lead to the development of a new group of sensors based on force-responsive (mechanical stimuli) materials. This review constitutes a comprehensive theoretical study containing available information about the coordination of metal complex synthesis methodologies with their physical, chemical, and spectroscopic properties.

Ag(I) symmetrical N,N′-diarylformamidine dithiocarbamate PPh3 complexes: Synthesis, structural characterization, quantum chemical calculations and in vitro biological studies

Three heteroleptic silver(I) dithiocarbamate triphenylphosphine complexes were developed in which triphenylphosphine was introduced as a bulky co-ligand and tested as antioxidant activity against the free radical of DPPH. All three complexes showed good antioxidant activity against the free radical of DPPH with compounds 1 and 2 having a better antioxidant activity when compared to ascorbic acid. All the complexes were found to be more active than ciprofloxacin against Gram (+) bacteria while they showed good to moderate activity against Gram (-) bacterial except S. typhimurium. The crystal structures of 2 and 3 were determined by single crystal X-Ray diffraction and confirmed distorted tetrahedral geometry around the Ag(I) center with coordination via two sulfur atoms of the dithiocarbamate ligand and two phosphorus atoms from the two triphenylphosphine ligands replacing the NO3– anion from the silver nitrate salt . The structures of the metal complexes were geometrically optimized, and the quantum chemical parameters were calculated using the density functional theory (DFT) at B3LYP/Lanl2dz basis set. Quantum chemical descriptors based on DFT calculations predicted the stability as well as reactivity of the complexes and there was a clear correlation with the biological activities.

Synthesis, characterization, electrochemistry, DFT and kinetic study of the oligothiophene-containing complex [Rh((C4H3S-C4H2S)COCHCOCF3)(CO)(PPh3)

The synthesis, electrochemistry, oxidative addition kinetics and computational chemistry study are presented for the [Rh((C4H3S-C4H2S)COCHCOCF3)(CO)(PPh3)] complex. Through chemical and electrochemical oxidation, this rhodium triphenylphosphine complex was converted from rhodium(I) to a rhodium(III) complex. The chemical kinetics, studied by the NMR, UV/Vis and IR, of the oxidative addition of CH3I to [Rh((C4H3S-C4H2S)COCHCOCF3)(CO)(PPh3)] indicated the formation of rhodium(III) alkyl 1, rhodium(III) acyl 1 and rhodium(III) alkyl 2 isomers respectively. A theoretical density functional theory study shed light on the geometry of the different reactants, transition states and reaction products. The second order rate constant of the [Rh((C4H3S-C4H2S)COCHCOCF3)(CO)(PPh3)] + CH3I oxidative addition reaction is 0.0027 mol−1 dm3 s−1 in CHCl3 at 25 °C. A linear relationship was established between the irreversible electrochemical oxidation potential of rhodium(I), Epa(Rh) and the second order rate constant of the oxidative addition reaction for a series of 17 different [Rh(β-diketonato)(CO)(PPh3)] complexes.

Ionic liquid immobilized Cu(I)–hydrazone–triphenylphosphine complex: an easily recyclable catalytic system for Suzuki and Heck cross couplings

A highly efficient, reusable, catalytic system of Heck and Suzuki cross-coupling reactions was observed for an inexpensive copper complex dispersed in ethyl-methyl imidazolium hexafluorophosphate medium, [EMIM]PF6. The reaction conditions were optimized by studying the effects of temperature, catalyst concentration, solvent, and time. This method functions for a variety of substrates towards the cross-coupling reactions. Most notably, the catalyst – ionic liquid mixture was easily recoverable and reused six times without much loss in the catalytic activity, causing a notably very low impact on the environment.

Correction: Mononuclear copper(i) complexes of triphenylphosphine and N,N′-disubstituted thioureas as potential DNA binding chemotherapeutics

Correction for ‘Mononuclear copper(i) complexes of triphenylphosphine and N,N′-disubstituted thioureas as potential DNA binding chemotherapeutics’ by Syed Ishtiaq Khan et al., New J. Chem., 2021, 45, 8925–8935, DOI: 10.1039/D0NJ06182D.

Mononuclear copper(i) complexes of triphenylphosphine and N,N′-disubstituted thioureas as potential DNA binding chemotherapeutics

Herein, nine copper(i) bromide complexes with N,N′-disubstituted thioureas and triphenylphosphine, were synthesized via a simple solution-based reaction at 60 °C and characterized, selected complexes were screened for DNA binding.

Stimuli‐Responsive Emission of Dinuclear Rhombic Copper(I) Iodide Complexes Having Triphenylarsine and N‐Heteroaromatic Co‐Ligands

Copper(I) iodide complexes of triphenylarsine with a series of N‐heteroaromatic co‐ligands, i.e., pyridine, 2‐picoline, 2,6‐lutidine, and quinoline, were synthesized. The structures of the complexes were analyzed by X‐ray crystallography, which revealed that they adopted dinuclear rhombic structures. It was found that the arsenic atom effectively worked for forming shorter cuprophilic interaction when compared with the corresponding triphenylphosphine complex. The N‐heteroaromatic co‐ligand highly affected Cu–Cu interactions, denoted as cuprophilic interactions, as well as emission behaviors. In addition, the emission color and/or efficiency were altered by thermal and mechanical stimuli, and the responsiveness was dependent on the complex structure.

In vitro biological studies of heteroleptic Ag(I) and Cu(I) unsymmetrical N,N′-diarylformamidine dithiocarbamate phosphine complexes; the effect of the metal center

A series of five dithiocarbamate and their respective Ag(I) and Cu(I) triphenylphosphine complexes of the general formula [Ag/Cu(PPh3)2L] were synthesized and characterized. The dithiocarbamate ligands were synthesized from formamidines with substituents in the 2 and/or 6 positions of the phenyl rings, intentionally keeping substituents on one ring different from those of the second phenyl ring while investigating the structure-activity relationship of Ag(I) and Cu(I) dithiocarbamate complexes. All Ag(I) and Cu(I) complexes with the general formula [Ag(PPh3)2L] (1–5) or [Cu(PPh3)2L] (6–10), displayed distorted tetrahedral geometry around the metal centers with coordination via two S atoms of the dithiocarbamate ligand and two P atoms from the PPh3 units. Complexes 1–5 showed better inhibition values against Gram-positive, Staphylococcus aureus (methicillin resistant) and Staphylococcus aureus than the standard used, ciprofloxacin. Complexes 1 and 2 generally had good activity against all bacterial strains but were not active against Salmonella typhimurium. All Cu(I) complexes were either of low activity or inactive against all bacterial strains tested. Complex 2 was found to be more active with IC50 values of 1.34 × 10−3 mM and 0.25 mM as agents for antioxidant activity against DPPH and NO free radical scavengers, respectively. The metal center played a vital role in their biological activity as the Ag(I) complexes displayed better antibacterial and antioxidant activity than Cu(I) complexes.

Synthesis, Characterization, DFT Studies and Biological Activity of Ru(III), La(III) and Ce(III) Triphenylphosphine Complexes Containing 2-Aminothiazole and 2-Aminotriazole

In the present paper a series of triphenylphosphine complexes containing mixed ligands like 2-aminothiazole (Ath) and 2-aminotriazole (Atz) have been prepared. The complexes are of the formula [MCl3((Pph3)(Ath)2] and [MCl3((Pph3)(Atz)2], [M = Ru(III), Ce(III) and La(III)]. These complexes were characterized by different spectral techniques. Additionally, the computational study has been performed using density functional theory (DFT) and the calculation is used to examine the electronic structure of the synthesized complexes. The biological activities of all the synthesized complexes were evaluated and the comparative account in properties between the triphenylphosphine metal complexes containing 2-aminothiazole and 2-aminotriazole ligands has been made. The DNA-binding property of these metal complexes was investigated using electronic absorption spectroscopy and fluorescence spectroscopy. The antibacterial and antifungal activity against bacterial species (Gram −ve bacteria: Escherichia coli, Salmonella typhi) and (Gram +ve bacteria: (Staphylococcus aureus and Bacillus subtilis) and fungi (Aspergillus niger and Candida albicans). The antioxidant study was carried out against the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·) which showed that the metal complexes are good antioxidant, as compared to BHT. Further, the in-silico molecular docking study was performed to predict the possible binding sites of the metal complexes.

Antiproliferative Activity of Gold(I) N‐Heterocyclic Carbene and Triphenylphosphine Complexes with Ibuprofen Derivatives as Effective Enzyme Inhibitors

A series of gold(I) complexes of ligand ibuprofen‐alkynyl (but‐3‐yn‐1‐yl 2‐(4‐isobutylphenyl)propanoate, LE) with N‐heterocyclic carbene (LC: 1,3‐dimethylimidazol‐2‐ylidene) and triphenylphosphine (PPh3) ligands with formula (LE)Au (LC) (complex 1) and (LE)Au (PPh3) (complex 2) were synthesized and fully characterized by spectroscopic methods. In order to reveal the cytotoxicity mechanism, the interaction of complex 1 or 2 with cysteine (HCys) has been studied by experimental and density functional theory (DFT) methods. The compounds were investigated for their anticancer activity against MCF‐7, MDAMB 231 breast cancer cells, HT‐29 colon cancer cells and MCF‐10A non‐tumor breast cell line. The results were compared with cisplatin and auranofin as reference drugs. The complex 2 showed more cytotoxic activity than complex 1. The complex 2 was 4.2, 3.7, and 1.7 fold more active than cisplatin against HT‐29, MDA‐MB‐231, MCF‐7 cancer cell lines, respectively. The inhibition of thioredoxin reductase of complexes 1 and 2 including cytosolic (TrxR1) and mitochondrial (TrxR2) thioredoxin reductase and also the inhibition of glutathione reductase (GR) were studied in detail. Moreover, the cellular uptake and reactive oxygen species (ROS) generation of compounds were investigated. Based on the DFT calculations a relationship between the σ‐donor ability of the isolated ligands and cytotoxicity is suggested.

The water-solubilisation of the metalloligand [Pt2(μ2-S)2(PPh3)4] using 1,3,5-triaza-7-phospha-adamantane (PTA)

The synthesis of the platinum(II) μ2-sulfide complex [Pt2(μ2-S)2(PTA)4] (PTA = phosphatriazaadamantane), as a water-soluble analogue of the well-known triphenylphosphine complex [Pt2(μ2-S)2(PPh3)4], has been explored through a range of synthetic routes. A direct synthesis, from cis-[PtCl2(PTA)2] and Na2S·9H2O in benzene was found to be the most effective, while attempted ligand substitution of the PPh3 ligands of [Pt2(μ2-S)2(PPh3)4] with PTA resulted in rearrangement of the {Pt2S2} core, and formation of a series of PTA-substituted trinuclear species of the general composition [Pt3(μ3-S)2(PPh3)x(PTA)6-x]2+. The fully-substituted complex [Pt3(μ3-S)2(PTA)6]2+ was also obtained when cis-[PtCl2(PTA)2] was reacted with a sulfide ion-exchange resin. Reaction of [PtCl2(cod)] (cod = 1,5-cyclooctadiene) with Na2S·9H2O in benzene gave a red solid identified as crude [Pt2(μ2-S)2(cod)2]. Reaction of this labile {Pt2S2} precursor with PTA resulted in the formation of [Pt2(μ2-S)2(PTA)4] along with PTA -oxide and -sulfide. ESI mass spectrometry was widely employed as a convenient tool for exploring this chemistry, in conjunction with 31P{1H} NMR spectroscopy. These PTA-Pt-sulfide species, especially those containing {Pt2S2} cores, have a tendency to decompose in solution. Additional confirmation of the formation of [Pt2(μ2-S)2(PTA)4] was provided by its reaction with [Rh2(μ2-Cl)2(cod)2], resulting in the formation of the adduct [Pt2(μ3-S)2(PTA)4Rh(cod)]+, identified using ESI MS.

Quantum chemical investigation of the oxidative addition reaction of allyl carboxylates to Ni(0) and Pd(0) complexes

Objectives. The first allylpalladium complex was synthesized and characterized 60 years ago at the Department of Physical Chemistry of M.V. Lomonosov Moscow State University of Fine Chemical Technology (MITHT). This discovery was an important stage in the development of a new direction in chemistry - metal complex catalysis, which subsequently led to understanding the strategy for studying the mechanisms of catalysts action, and gave a powerful impetus to the study of intermediates of catalytic reactions. The key sta.ge in many catalytic processes involving transition metal complexes is the oxidative addition stage. The study’s aim was the quantum chemical modeling of the oxidative addition stage of allylic carboxylates to the Ni(0) and Pd(0) complexes. Methods. Quantum chemical calculations were carried out under the Kohn-Sham method for the density Junctional theory using the PBE exchange-correlation Junctional and all-electron L11 basis set. Results. As a result of theoretical study, we showed that the oxidative addition of allyl acetate to the triisopropylphosphite complex of nickel(0) and allyl formate to the triphenylphosphine complex of palladium(O) can proceed along two routes. In the first of them, in the coordinated breaking of the С - О bond and the formation of the metal-O bond, the same oxygen atom is involved, thus forming a three-center transition state. In the second route, the restructuring of relations is carried out in a five-center transition state. The chelating effect in the five-centered transition state of the second route reduces the reaction’s activation barrier by 12.7 kcal/mol for allyl acetate and the nickel(0) triisopropylphosphite complex Ni(P(QPr) 3 ) 2 and by 9.9 kcal/mol for allyl formate and the palladium(O) triphenylphosphine complex Pd(PPh 3 ). The presence of the second triphenylphosphine ligand in Pd(PPh 3 ) 2 reduces the activation barrier by only 2.6 kcal/mol. Conclusions. The quantum chemical modeling performed allowed us to determine the preference for the oxidative addition of allyl carboxylates to the Ni(0) and Pd(0) complexes through a five-center transition state. The reaction’s activation barriers through the “classical” three-center interaction are 9.9-12.7 kcal/mol higher, and the chelating effect is more noticeable for the Ni complex The presence in the coordination sphere of several bulky ligands, such as triphenylphosphine, practically eliminates the chelating effect in the oxidative addition of allyl carboxylates.

New square-planar nickel(II)-triphenylphosphine complexes containing ONS donor ligands: Synthesis, characterization, electrochemical and antioxidant properties

Five new mixed ligand nickel(II) complexes with the general formula [Ni(L)(PPh3)], [C1–C5], were prepared from the reaction of triphenylphosphine (PPh3) with ONS donor ligands (L) [where R = Η (L1); 4-OCH3 (L2); 4-OCH2(CH2)6CH3 (L3); 4-OCH3, 4′-CH3 (L4) and 4-OCH2CHCH2 (L5)] derived from 2-hydroxybenzophenones and thiocarbohydrazide. The structures of the complexes were characterized by elemental analysis, IR, 1H and 31P NMR spectroscopy, conductivity measurements. The crystal structures of ligand (L2) and complex (C2) were determined by single crystal X-ray diffraction method. The ligand is coordinated to the nickel core through the phenolate oxygen, azomethine nitrogen and sulfur atoms, while the fourth coordination site is occupied by the P atom of a triphenylphosphine ligand. X-ray analysis indicated distorted square-planar structure for the complex C2. Electrochemical behaviors of thiocarbohydrazone ligands (L1-L5) and their nickel(II) complexes (C1–C5) were studied and effects of the type of substituents were compared. All ligands illustrated two irreversible reductions and one irreversible oxidation. Complexing of the ligands with Ni(III) ion considerably influenced their redox behaviors. Electron transfer process of the complexes get easier and became more reversible when compared with those of the corresponding ligands. Moreover, Ni(II) complexes illustrated NiII/NiI and NiII/NiIII processes in addition to the ligand-based electron transfer reactions. In-situ spectroelectrochemical responses of the ligands considerably changed after formation of Ni(II) complexes. Total antioxidant capacity and free radical scavenging activity of the compounds have been tested using CUPRAC and DPPH methods, respectively. The results of Ni(II) complexes were compared with a standard antioxidant compound.