Acetate Molecules Research Articles

In silico neuroprotective properties of volatile constituents of grape (Vitis vinifera L.) seed extract against Parkinson's disease

Aggregation of α-synuclein is one of the significant factors in the pathogenesis of Parkinson's disease. Many natural extracts demonstrate neuroprotective activity against PD by inhibiting α-synuclein aggregation. In India, the grape extract is traditionally used as a brain tonic to boost memory power. Hence in this study, the neuroprotective activity of grape seed extract against Parkinson's disease under in silico conditions was investigated. Molecular docking studies indicated that volatile constituents of ethanolic extract of grape seed could bind to both C-terminal and N-terminal regions of α-synuclein with more preference towards the formation of hydrogen bonds than hydrophobic interactions. Also, the compounds most commonly interacted with the residues Val40, Lys43 and Lys45 of N-terminal to form both hydrogen bonds and hydrophobic interactions. Among the compounds studied, Dasycarpidan-1-methanol, acetate (ester) molecule showed superior binding affinity, Blood-Brain Barrier penetration, drug-likeness and lead-likeness properties.

Insight into amoxicillin sodium heterosolvates and non-solvated form: crystal structures, phase transformation behaviors, and desolvation mechanism

Methanol and methyl acetate molecules played different roles in the formation of SM–M amoxicillin sodium heterosolvate. A two-step desolvation mechanism of novel heterosolvates was proposed.

The non-covalent interaction studies of o-nitrophenol and methyl acetate in benzene: By ultrasonics, FTIR and DFT methods

The velocity of ultrasonic waves (U), density (ρ) and viscosity (η) of o-nitrophenol (o-NP) with methyl acetate (MA) in benzene was measured at 303 K in seven different weight fractions. The other related acoustic and thermodynamic parameters like adiabatic compressibility (β), free length (Lf), free volume (Vf), internal pressure (πi), and Gibb’s free energy (ΔG) were acquired. The obtained parameters are played a significant role in studying the basis of the molecular interactions. The FTIR analysis was carried out to identify the functional groups of the mixture o-NP + MA. The optimized geometry of the mixture o-NP + MA is analyzed extensively by the DFT method. In addition, non-covalent interactions were confirmed by the Multiwave function and VMD software packages. The possibilities of H-bonding formation between o-nitrophenol and methyl acetate molecules were identified and their corresponding hydrogen bond wavelengths were calculated using Gaussian software. The FTIR spectra of pure o-NP, pure MA and a mixture of o-NP + MA were recorded, which confirms the existence of non-covalent interactions (NCI’s) within the solute species. The frequency deviations in the functional groups of the mixture are analyzed with characteristic regions. The identified NCI’s are validated by ultrasonic and DFT analysis.

Study on the deactivation process of dimethyl ether carbonylation reaction over Mordenite catalyst

The deactivation of Mordenite (MOR) catalyst in dimethyl ether (DME) carbonylation reaction was systematically studied. The influence of coke deposition on the structure, morphology and acid sites were characterized and the transformation of coke deposition was investigated. Characterization results revealed that coke deposition had little effect on the structure and morphology of the catalyst. Soft and hard coke could be identified on the catalysts throughout the reaction process. The acid sites decreased more rapidly in the induction period of carbonylation reaction due to the formation of reaction intermediates and soft coke while the hard coke mainly accumulated in the deactivation period. C2H4 generated in the desorption process of DME and methyl acetate (MA) molecules were speculated as an important source of coke deposition. The soft coke was mostly formed via degradation of DME molecules at first half of reaction period, which gradually transformed into hard coke by releasing CH4 and H2. The hard coke mainly derived from MA molecules and transformation of soft coke.

Study of the Surface Acetate-Cellulose Layer in the Compositional Membranes by the Vibrational Spectroscopy Method

The paper presents the structural organization of the surface (selective) layer. The amorphous phase of the cellulose acetate composite membrane is formed at a certain stage of the technological cycle of producing the cellulose acetate membrane. It presents a mass of broken, entangled, and twisted macromolecular chains connected by a network of hydrogen bonds of various strengths. Analysis of the IR spectra, where the shapes of the absorption bands of the valence vibrations of hydroxyl groups at ν = 3339.14–3366.2 cm–1 with the asymmetry coefficient varying from ~1 for a dry sample to 0.79 for a wet sample, suggests that the bulk supramolecular structure of the cellulose acetate layer of the air-dry sample is formed by two types of hydrogen bonds and the dipole–dipole interactions of the carbonyl groups. The interactions of macromolecules in the equatorial plane are formed by a network of hydrogen bonds of the OH…O type with the participation of a single hydroxyl group of the pyranose ring in cellulose acetate. In the axial direction, the supramolecular structure is organized through the hydrogen bonds of the CH…O=C type between the methane and carbonyl groups, as well as possibly the dipole–dipole interactions between the coplanar ordered dipoles of the C=O groups. The coefficient of asymmetry of the absorption bands of hydroxyl groups is reduced to 0.81–0.79 and the intensity of the absorption band of methyl groups is reduced by factors of 2.56, 3.3, and 3.8 in water-saturated samples due to the destruction of the supramolecular structure and the reorganization of the hydrogen bonds between the active groups of cellulose acetate and water molecules. The absence of an absorption band of ν = 873.53–851.9 cm–1 in the water-saturated samples indicates a conformational rearrangement of the macromolecules into a linear form with the formation of narrow mesopores of cellulose acetate between the macromolecules.

FTIR spectroscopic studies and DFT calculations on the binary solution of methyl acetate with m-xylene

FTIR spectra have been recorded for pure methyl acetate, pure m-xylene and their equimolar binary solution. Shifts have been observed in all the vibrational modes of methyl acetate, m-xylene in the solution indicating the possibilities for molecular interactions. To get more precise information on the molecular interactions, DFT calculations have been performed. From these calculations it is found that methyl acetate dimers of four different geometries are possible. The most stable among these dimers is the one with C − H⋯O = C interactions stronger than the C − H⋯O − C. If the scenario is opposite in a dimer, the stability becomes the least. These four dimers dissociate in the investigated binary solution and 1:2 (m-xylene:methyl acetate) complexes of five different geometries are formed. In one of the complexes, the homointeractions C − H⋯O = C among the methyl acetate molecules are more stronger than any other interactions and the stability of the complex is the least. In all the other complexes the interactions (methyl acetate)C − H⋯π (m − xylene) are the strongest. In complexes where the hydrogens attached to ring carbons of m-xylene do not involve in hydrogen bonds with methyl acetate, the stability of the complexes is more. If these hydrogen bonds are formed, the stabilities of those complexes are reduced.

Insight into the deactivation mechanism of water on active Cu species for ester hydrogenation: Experimental and theoretical study

Water is inevitably existed in the industrial production and counted as a critical issue; however, the effect of water on Cu/SiO2 catalysts was often ignored and the relation between of water and deactivation mechanism in the hydrogenation reaction is rarely studied. In this work, the effect of water on ester hydrogenation was investigated experimentally and theoretically. The hydrogenation of ethyl acetate was chosen as probe reaction and the reagent containing water was used to simulate industrial feedstock. The obtained experimental results of the hydrogenation and the in-situ DRIFT and DFT calculation have demonstrated that the presence of water is hardly affected ethanol selectivity but decreased the catalytic activity. The main reason for the showed catalyst deactivation is the competitive adsorption (reversible) mechanism of water and ethyl acetate molecules. More precisely, the active species of Cu+ surface is preferred the adsorption of H2O over ethyl acetate molecule consequently leads to a rapidly decreasing in the conversion ratio of ethyl acetate. Although the adsorption of water molecule is only occupied the Cu+ sites in the catalyst and could also release at reaction temperature, the conversion was partially recovered due to the growth, leaching and oxidation of copper species caused by water when water was removed.

Effect of Distortions on the Geometric and Electronic Structures of One-Electron Oxidized Vanadium(IV), Copper(II), and Cobalt(II)/(III) Salen Complexes.

The ligands N,N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,2-ethanediamine and N,N'-bis(3-tert-butyl-5-methoxysalicylidene)-1,3-propanediamine were chelated to V(IV)═O (1, 2), Cu(II) (3, 4), Co(II) (5), and Co(III) (6). The X-ray crystal structures of 1-6 were solved. The vanadium center in 1-2 resides in square pyramidal geometry, with an axially bound oxo ligand, whereas the metal ion displays a tetrahedrally distorted square planar geometry in 3-5. The extent of distortion is correlated to the length of the diamine spacer: The longer the linker, the larger the tetrahedral distortions. Complex 6 is octahedral with a bidentate acetate molecule that completes the coordination sphere. All the complexes were characterized by UV-vis and EPR spectroscopies, as well as DFT calculations and electrochemistry. Complexes 1-6 exhibit a reversible one-electron oxidation wave in the range -0.11-0.26 V vs Fc+/Fc. The cations 1+ and 2+ were structurally characterized, showing an octahedral V(V) ion with one oxo and one water molecule coordinated in axial positions. Their vis-NIR spectra are dominated by a band at 727 and 815 nm, respectively, which is assigned to a phenolate-to-vanadium(V) charge transfer (CT) transition. The crystal structures of 3+ and 4+ are congruent with Cu(II)-radical species, wherein the metal center remains four-coordinated. Both feature a Class II (Robin-Day classification scale) IVCT transition at around 1200 nm (ε > 1 mM cm-1), indicative of partial localization of the radical. The structure of 5+ displays a square pyramidal cobalt ion, where the fifth (axial) coordination is occupied by a water molecule. It displays a NIR feature at 1244 nm and is described as intermediate between high spin Co(III) and Co(II) radical. In the presence of acetate the dimer [(5)2(μ-OAc)]+ forms, which was structurally characterized and shows a blue shift and lowering in intensity of the NIR absorption band in comparison to 5+. Complex 6+ is a genuine Co(III) radical complex, wherein the phenoxyl moiety is localized on one side of the molecule.

A Study of the Structural Organization of the Surface Layer and the State of Water in Composite Ultrafiltration Membranes

The structural organization of the surface (active) layer and the state of water in composite ultrafiltration membranes have been investigated by means of the methods of vibrational IR spectroscopy and differential scanning calorimetry (DSC). Analysis of the shape of the absorption band of stretching vibrations of hydroxyl groups at ν = 3366.2 cm–1 with an asymmetry coefficient of ~1 and the activity of vibrations of methyl groups with ν = 2884.02 and 2942.35 cm—1 has demonstrated that the bulk supramolecular structure of a cellulose acetate layer of a dry sample is formed by two types of hydrogen bonds and dipole–dipole interactions of carbonyl groups. The interaction of macromolecules in the equatorial plane is formed by a lattice of hydrogen bonds of the (OH…O) type with participation of the only hydroxyl group of a pyranose ring in cellulose acetates. In the axial direction, the supramolecular structure is organized by hydrogen bonds between methine and carbonyl groups of the (CH…O=C) type and dipole interactions of coplanar ordered dipoles of (C=O) groups. The decrease in the intensity and the coefficient of asymmetry down to 0.81 of the absorption band of hydroxyl groups and the absorption band of methyl groups with frequencies ν = 2884.02–2942.35 cm–1 by 2.56 and 3.3 times in water-saturated samples occurs due to the destruction of the supramolecular structure and the reorganization of hydrogen bonds of active groups of cellulose acetate and water molecules blocking intermolecular interactions of the macromolecules. The manifestation of hydroxyl groups with frequencies of 3302.7 and 33 105 sh cm–1 and ν = 3600.6 and ν = 3598.8 sh cm–1 on the absorption band indicates the interaction of associated water molecules of the bound and capillary forms. The absence of the absorption band with ν = 873.53 cm–1 in the water-saturated sample is explained as an empirical indicator of the conformational transition of macromolecules into a linear form. Deconvolution of the endothermic peak on the DSC curve in the temperature range from 50 to 110°C into five Gaussians has demonstrated the multilevel structural organization of water molecules sorbed in pores and between macromolecules of the amorphous phase.

Stationary and transient acoustically induced birefringence of methyl acetate molecules dissolved in ethanol

A detailed study of the acoustically induced birefringence has been performed in methyl acetate molecules in solutions with ethanol to evaluate the relative variations of the acoustic intensity. Static and dynamic birefringence signals are ascribed to the orientation of the molecules along the direction of the applied ultrasonic field. The birefringence in dilute and concentrated solutions was investigated as a function of frequency, ultrasonic intensity and concentration. The transient behavior of the birefringence is indicative of a single exponential function implying a single relaxation mechanism. Systematic analysis of the experimental results is performed in the context of the presence of two distinct types of MA molecules in the solutions, namely the molecules that are similar to those existing in bulk material and the “solution”-type molecules that are distorted after the interaction with the ethanol/solvent molecules. The estimated relatively slow relaxation times, obtained from the transient birefringence measurements, imply that the acoustically induced birefringence is affected by the collective motion over the short-to-medium range order. Relaxation times exhibit a characteristic change below and above ~ 0.6 volume fraction of MA, which is related to the presence of the two discrete types of methyl acetate molecules in the solutions.

Excited state proton transfer processes of pyranine studied by femtosecond stimulated Raman spectroscopy

As one of the most fundamental processes, proton transfer reaction plays an important role in chemical and biological process, and to reveal the choreography of the proton motion intra- and intermolecularly, a spectroscopic technique capable of capturing molecular structural dynamics of excited-state proton transfer motions on an intrinsic time scale is needed. In this study, We utilize wavelength-tunable femtosecond stimulated Raman spectroscopy with a time resolution of ~100 fs, spectral resolution of 15 cm<sup>–1</sup> and spectral range of 400 cm<sup>–1</sup>—1800 cm<sup>–1</sup>, combined with traditional transient absorption spectroscopywith a time window between 0 and 600 ps to simultaneously achieve reaction dynamics for transient reactant and product of the photoacid pyranine (8-hydroxypyrene1, 3, 6-trisulfonic acid, HPTS) molecules undergoing excited-state proton transfer reaction in complex with water and acetate molecules. Marker bands attributed to the deprotonated form of HPTS in a frequency range from 400 cm<sup>–1</sup> to 1700 cm<sup>–1</sup> are obtained under the excitation of 400 nm laser pulses. The marker band at 1516 cm<sup>–1</sup>, which is assigned to phenolic ring carbon carbon double band stretching accompanied with carbon hydrogen in-plane rocking motions, exhibits complex rise and decay dynamics. The simultaneously observed excited-state Raman mode at 920 cm<sup>–1</sup> which is assigned to the excited carbon-carbon single bond stretch mode in the protonated acetic acid root molecule, helps us to clearly resolve the reaction rates of excited-state proton transfer. Based on the multi-exponential fitting results, the dynamics of excited-state Raman mode at 920 cm<sup>–1</sup> exhibits bi-exponential processes with time constants of ~470 fs and ~3 ps. The ultrafast time component indicates that the excited-state proton transfer originates from an HPTS-acetate complex, indicating that part of the ground-state HPTS molecules are in the “tight” hydrogen bonding configuration that can quickly shift the excited-state proton charge toward the acetate acceptor molecule through a direct hydrogen bond. The second slower time component implies a significant subpopulation of HPTS in the ground state, i.e. hydrogen bonds to an acetate ion via an intervening water molecule, and upon photo excitation, the proton transfers to the water solvent before proton is picked up by the acetate ion.

Structural, spectroscopic and theoretical studies of sodium (2-carbamoylphenoxy) acetate salt

Sodium (2-carbamoylphenoxy) acetate salt crystal belongs to the P-1 space group of triclinic system, Z = 2. The asymmetric part of the unit cell consists of four (2-carbamoylphenoxy) acetate (CBA) molecules. Three Na+ ions are surrounded by six O atoms and one Na+ ion is surrounded by five O atoms. The mean Na1+ … O and Na2+ … O distance is 2.47 Å while Na3+ … O is 2.43 Å and Na4+ … O is 2.49 Å. The supramolecular self-assembly of the four (2-carbamoylphenoxy) acetate molecules is realized by hydrogen bonds, and a variety of intermolecular interactions. The interactions within the bulk of the crystal structure were highlighted with Hirshfeld surfaces. FT-IR and Raman spectra of the studied compound are reported for the first time. Assignments of the normal modes was done with the aid of density functional theory frequency calculations on the monomer and two dimers, at B3LYP/6-311 + G(2d,p) level of theory.

An Unexpected Trinuclear Cobalt(II) Complex Based on a Half-Salamo-Like Ligand: Synthesis, Crystal Structure, Hirshfeld Surface Analysis, Antimicrobial and Fluorescent Properties

An unexpected trinuclear Co(II) complex, [Co3(L2)2(μ-OAc)2(CH3OH)2]·2CH3OH (H2L2 = 4,4′-dibromo-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) constructed from a half-Salamo-based ligand (HL1 = 2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Co(OAc)2·4H2O, has been synthesized and characterized by elemental analyses, infrared spectra (IR), UV-Vis spectra, X-ray crystallography and Hirshfeld surface analysis. The Co(II) complex contains three Co(II) atoms, two completely deprotonated (L2)2− units, two bridged acetate molecules, two coordinated methanol molecules and two crystalline methanol molecules, and finally, a three-dimensional supramolecular structure with infinite extension was formed. Interestingly, during the formation of the Co(II) complex, the ligand changed from half-Salamo-like to a symmetrical single Salamo-like ligand due to the bonding interactions of the molecules. In addition, the antimicrobial activities of HL1 and its Co(II) complex were also investigated.

ZnO Nanoparticles, Nanorods, Hexagonal Plates and Nanosheets Produced by Polyol Route and the Effect of Surface Passivation by Acetate Molecules on Optical Properties

We carried out synthesis of shape-controlled ZnO nanoparticles following a polyol route using either ethylene glycol (EG) or polyethylene glycol (PEG) as solvent, which exhibited wurtzite structures as identified by XRD patterns. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses of the synthesized structures showed that the size and the shape are strongly dependent on the reaction medium, resulting in nanospheres, rods, hexagonal plates or sheets, which were characterized by different spectroscopy techniques such as: Raman scattering, x-ray photoelectron spectroscopy (XPS), UV–Vis and photoluminescence (PL). The Raman analysis showed that the resulting surface is passivated with acetate molecules and also monitored the presence of superficial defects, whose spectroscopic patterns (Raman spectroscopy) indicated that the passivation with acetate molecules reduces the number of defects, such as oxygen vacancies. This result was confirmed by XPS analyses that identified chemisorbed oxygen species onto the oxide surface and an oxygen-deficient component in the sample prepared as reference, without a passivation with EG or PEG. Photoluminescence results showed that the passivation, size and shape of the particles influenced the optical features, mainly at the emission at the green region of spectrum that has been related with surface defects. This green emission is favoured at the ZnO sample prepared without passivation and with large amount of defects. Current–voltage characteristic (J–V) of an inverted organic solar cell showed the potential application of these ZnO nanostructures as electron transport material in organic photovoltaic devices.

Problem in the molecular area of polar probe molecules used in inverse gas chromatography

Although the inverse gas chromatography technique has been used to measure the surface acid-base properties for almost 50 years, several basic problems still hinder its further development and application. One of the problems is that for the polar probe molecules of dichloromethane, acetone, ethyl acetate, tetrahydrofuran, and ethanol, the molecular area of each probe has different values in literature. In this paper, we point out the incorrect molecular area values presented in the literature by comparing these values with those indicated in Smallwood's Handbook of Organic Solvent Properties. The correct molecular area values of 11 polar probes are determined by plotting the molecular areas of the polar probes versus the van der Waals surface areas reported in the handbook. The correct molecular areas for six common polar probes, namely, dichloromethane, trichloromethane, acetone, ethyl acetate, diethyl ether, and tetrahydrofuran, are 38.0, 44.0, 42.5, 48.0, 47.0, and 45.0 Å2, respectively. Benzene is a specific molecule with a conjugated π-bond structure, and its molecular area is estimated to be larger than that of other molecules. Therefore, benzene is unsuitable for use as a probe molecule.

A New Half-Salamo-Based Homo-Trinuclear Nickel(II) Complex: Crystal Structure, Hirshfeld Surface Analysis, and Fluorescence Properties

A new homo-trinuclear Ni(II) half-salamo-based complex [Ni3(L)2(μ-OAc)2(OAc)2(CH3OH)2]·2CH3OH was synthesized via the reaction of a tridentate ligand HL (2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Ni(OAc)2·4H2O, and characterized using elemental analyses, IR spectra, UV-Vis absorption spectra, X-ray crystallography, and Hirshfeld analysis. Interestingly, single-crystal X-ray analysis showed that the two acetate molecules were bonded simultaneously with the Ni(II) atoms by mono-dentate chelating and bidentate bridging coordination modes, respectively, and the resulting hexa-coordinate geometries were ultimately formed. Furthermore, the Hirshfeld analysis of the complex was studied. Compared with HL, the complex fluorescence intensity was significantly lowered, indicating that the Ni(II) ions have fluorescence quenching characteristics.

Dynamics and vibrational coupling of methyl acetate dissolved in ethanol

The structure and vibrational dynamics of methyl acetate (MA) molecules solvated in ethanol have been investigated by means of Raman and IR spectroscopies. Two distinct vibrational bands have been resolved and assigned to two different types of MA molecules, namely the “free” molecules that exist in bulk material and the “solution” molecules which interact with ethanol molecules. All the measured physical properties exhibit a characteristic change near a specific volume fraction (∼0.6) of MA. This behavior is associated to the existence of the two kinds of methyl acetate groups coexisting in the solutions. The micro-viscosity model provides reasonable agreement with the experimental vibrational relaxation times up to a characteristic volume fraction ∼0.6, but fails for higher values since it takes into account solvent instead of solute characteristics. Finally, the so-called non-coincidence effect (NCE) has been observed due to repulsive interactions and is of key importance for the vibrational relaxation process.

Duet of Acetate and Water at the Defects of Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are porous crystalline materials with promising applications in molecular adsorption, separation, and catalysis. It has been discovered recently that structural defects introduced unintentionally or by design could have a significant impact on their properties. However, the exact chemical composition and structural evolution under different conditions at the defects are still under debate. In this study, we performed multidimensional solid-state nuclear magnetic resonance (SSNMR) coupled with computer simulations to elucidate an important scenario of MOF defects, uncovering the dynamic interplay between residual acetate and water. Acetate, as a defect modulator, and water, as a byproduct, are prevalent defect-associated species, which are among the key factors determining the reactivity and stability of defects. We discovered that acetate molecules coordinate to a single metal site monodentately and pair with water at the neighboring position. The acetates are highly flexible, which undergo fast libration as well as a slow kinetic exchange with water through dynamic hydrogen bonds. The dynamic processes under variable temperatures and different hydration levels have been quantitatively analyzed across a broad time scale from microseconds to seconds. The integration of SSNMR and computer simulations allows a precision probe into defective MOF structures with intrinsic dynamics and disorder.

Time-controlled synthesis of the 3D coordination polymer U(1,2,3-Hbtc)2 followed by the formation of molecular poly-oxo cluster {U14} containing hemimellitate uranium(iv).

Two coordination compounds bearing tetravalent uranium were synthesized in the presence of tritopic hemimellitic acid in acetonitrile with a controlled amount of water (H2O/U ≈ 8) and structurally characterized. Compound 1, [U(1,2,3-Hbtc)2]·0.5CH3CN is constructed around an eight-fold coordinated uranium cationic unit [UO8] linked by the poly-carboxylate ligands to form dimeric subunits, which are further connected to form infinite corrugated ribbons and a three-dimensional framework. Compound 2, [U14O8(OH)4Cl8(H2O)16(1,2,3-Hbtc)8(ox)4(ac)4] ({U14}) exhibits an unprecedented polynuclear {U14} poly-oxo uranium cluster surrounded by O-donor and chloride ligands. It is based on a central core of [U6O8] type surrounded by four dinuclear uranium-subunits {U2}. Compound 1 was synthesized by a direct reaction of hemimellitic acid with uranium tetrachloride in acetonitrile (+H2O), while the molecular species ({U14} (2)) crystallized from the supernatant solution after one month. The slow hydrolysis reaction together with the partial decomposition of the starting organic reactants into oxalate and acetate molecules induces the generation of such a large poly-oxo cluster with fourteen uranium centers. Structural comparisons with other closely related uranium-containing clusters, such as the {U12} cluster based on the association of inner core [U6O8] with three dinuclear sub-units {U2}, were performed.

Palladium-catalyzed microwave-assisted Hirao reaction utilizing the excess of the diarylphosphine oxide reagent as the P-ligand; a study on the activity and formation of the “PdP2” catalyst

Abstract The microwave-assisted Hirao reaction of bromobenzene and diarylphosphine oxides was performed at 120 °C using triethylamine as the base, and 5% of palladium acetate as the catalyst in ethanol. 5% Excess of the >P(O)H reagent served as the reducing agent, while another 10% as the preligand (in the >POH tautomeric form). It was found that the P–C coupling reaction was significantly faster with (2-MeC6H4)2P(O)H (A) and (3,5-diMeC6H3)2P(O)H (B), than with Ph2P(O)H (C) and (4-MeC6H4)2P(O)H (D). Moreover, species A and B could be applied as selective P-ligands in the reaction of bromobenzene with C or D. Dependence of the effectiveness of “PdP2” catalysts with diarylphosphine oxide preligands on the methyl substituents followed a reversed order as the reactivity of the diarylphosphine oxide species in the P–C coupling itself. Formation of the “PdP2” catalyst from palladium acetate and diarylphosphine oxide has never been studied, but now it was evaluated by us at the B3LYP level of theory applying 6-31G(d,p) for C,H,P,O and SDD/MW28 for Pd including the explicit-implicit solvent model. The novel mechanism requiring three equivalents of the >P(O)H species for each of the palladium acetate molecule was in agreement with the preparative experiments. The ligation of palladium(0) with different P(III) species comprising the >POH form of the >P(O)H reagent was also studied, and the critical role of the steric hindrance on the ligation, and hence on the activity of the “PdP2” catalyst was substantiated. Last but not least, the influence of the Me substituents in the aromatic ring of the P-reagents on the energetics of the elemental steps of the Hirao reaction itself was also evaluated.