Comparative Analysis of Nickel-Phosphine Complexes with Cumulated Double Bond Ligands: Structural Insights and Electronic Interactions via ETS-NOCV and QTAIM Approaches.

This study presents a comprehensive analysis of nickel-phosphine complexes, specifically Ni(PH3)2(OCCH2), Ni(PH3)2(H2CCO), Ni(PH3)2(H2CCCH2), Ni(PH3)2(NNCH2), and Ni(PH3)2(η1-H2CNN). Utilizing ETS-NOCV analysis, we explored orbital energy decomposition and the Hirshfeld charges of the ligands, providing insights into the electronic structures and donor-acceptor interactions within these complexes. The interactions in the ketene and allene complexes exhibit similar deformation densities and NOCV orbital shapes to those calculated for Ni(PH3)2(NNCH2), indicating consistent interaction characteristics across these complexes. The total interaction energy for all η2 complexes is observed to be over 60 kcal/mol, slightly exceeding that of the analogous carbon dioxide complex reported earlier. Furthermore, the study highlights the stronger back-donation as compared to donor interactions across all η2 complexes. This is further corroborated by Hirshfeld analysis, revealing the charge distribution dynamics within the ligand fragments. The research offers new perspectives on the electron distribution and interaction energies in nickel-phosphine complexes, contributing to a deeper understanding of their catalytic and reactive behaviors.

27 Years of Catalytic Carbonylative Coupling Reactions in Hungary (1994-2021).

Palladium-catalyzed carbonylation reactions, in the presence of nucleophiles, serve as very potent tools for the conversion of aryl and alkenyl halides or halide equivalents to carboxylic acid derivatives or to other carbonyl compounds. There are a vast number of applications for the synthesis of simple building blocks as well as for the functionalization of biologically important skeletons. This review covers the history of carbonylative coupling reactions in Hungary between the years 1994 and 2021.

Stereoisomeric Tris-BINOL-Menthol Bulky Monophosphites: Synthesis, Characterisation and Application in Rhodium-Catalysed Hydroformylation.

Four stereoisomeric monoether derivatives, based on axially chiral (R)- or (S)-BINOL bearing a chiral (+)- or (-)-neomenthyloxy group were synthesised and fully characterised by NMR spectroscopy and X-ray crystallography. The respective tris-monophosphites were thereof prepared and fully characterised. The coordination ability of the new bulky phosphites with Rh(CO)2(acac), was attested by 31P NMR, which presented a doublet in the range of δ = 120 ppm, with a 1J(103Rh-31P) coupling constant of 290 Hz. The new tris-binaphthyl phosphite ligands were further characterised by DFT computational methods, which allowed us to calculate an electronic (CEP) parameter of 2083.2 cm-1 and an extremely large cone angle of 345°, decreasing to 265° upon coordination with a metal atom. Furthermore, the monophosphites were applied as ligands in rhodium-catalysed hydroformylation of styrene, leading to complete conversions in 4 h, 100% chemoselectivity for aldehydes and up to 98% iso-regioselectivity. The Rh(I)/phosphite catalytic system was also highly active and selective in the hydroformylation of disubstituted olefins, including (E)-prop-1-en-1-ylbenzene and prop-1-en-2-ylbenzene.

DFT Study on the Mechanism of Iron-Catalyzed Diazocarbonylation.

The mechanism of the carbonylation of diazomethane in the presence of iron-carbonyl-phosphine catalysts has been investigated by means of DFT calculations at the M06/def-TZVP//B97D3/def2-TZVP level of theory, in combination with the SMD solvation method. The reaction rate is determined by the formation of the coordinatively unsaturated doublet-state Fe(CO)3(P) precursor followed by the diazoalkane coordination and the N2 extrusion. The free energy of activation is predicted to be 18.5 and 28.2 kcal/mol for the PF3 and PPh3 containing systems, respectively. Thus, in the presence of less basic P-donor ligands with stronger π-acceptor properties, a significant increase in the reaction rate can be expected. According to energy decomposition analysis combined with natural orbitals of chemical valence (EDA-NOCV) calculations, diazomethane in the Fe(CO)3(phosphine)(η1-CH2N2) adduct reveals a π-donor-π-acceptor type of coordination.

Kinetics and Mechanism of the Concurrent Reactions of Hexathionate with S(IV) and Thiosulfate in a Slightly Acidic Medium.

Reactions of hexathionate with thiosulfate and sulfite have been investigated by high-performance liquid chromatography via monitoring the concentration-time series of tetrathionate, pentathionate, hexathionate, and thiosulfate simultaneously within the pH range of 4.0-5.0. In both reactions, elementary sulfur forms; more significant sulfur precipitation may be observed in the case of the hexathionate-thiosulfate reaction, but slight turbidity in the other system means that elementary sulfur also appears in a detectable amount in the hexathionate-sulfite reaction. Initial rate studies have revealed that the formal kinetic orders of both reactants in both systems are clearly unity but pH-dependence can only be observed in the case of the hexathionate-sulfite reaction. The proposed kinetic model appears to suggest that nucleophilic attack of sulfite and thiosulfate may also occur on the ß- or γ-sulfur of the polythionate chain and breakages of the α-ß, ß-γ, and γ-γ' bonds are all conceivable possibilities to drive the reactions. Consequently, the generally accepted sulfur-chain elongating effect of thiosulfate on longer polythionates is also proven to be accompanied by sulfur-chain shortening pathways, eventually leading to the formation of elementary sulfur.

Computational Characterization of Bidentate P-Donor Ligands: Direct Comparison to Tolman's Electronic Parameters.

The applicability of two types of transition-metal carbonyl complexes as appropriate candidates for computationally derived Tolman's ligand electronic parameters were examined with density functional theory (DFT) calculations employing the B97D3 functional. Both Pd(0)L2(CO) and HRh(I)L2(CO) complexes correlated well with the experimental Tolman Electronic Parameter scale. For direct comparison of the electronic effects of diphosphines with those of monophosphines, the palladium-containing system is recommended. The t r a n s influence of various phosphines did not show a major difference, but the decrease of the H-Rh-P angle from linear can cause a significant change.

Theoretical insights into the nature of PtSn bond: Reevaluating the bonding/back-bonding properties of trichlorostannate with comparison to the cyano ligand.

The coordinating properties of the trichlorostannate ligand in hydrido platinum trichlorostannato and platinum bis-trichlorostannato complexes, containing various phosphine ligands, have been elucidated by means of charge decomposition analysis, the Ziegler-Rauk Energy Decomposition with the Natural Orbitals for Chemical Valence, Domain-Averaged Fermi Hole, and natural bond orbital methods. Trichlorostannate has been found to be a strong σ-donor and a weak π-acceptor ligand with coordination properties not far from those of the cyano ligand. For back-bonding, the tin-chlorine σ∗ orbitals are mostly responsible. In contrast to previous assumptions, the 5d orbitals of tin play no role at all in the interaction with the platinum center. QTAIM calculations suggest, that the platinum-tin interaction should be interpreted as donor-acceptor, rather than covalent type. Trichlorostannate has been found to have weaker trans influence in comparison to the cyano ligand. © 2017 Wiley Periodicals, Inc.

Thermal Ring Contraction Reactions of 9-Aryl-5H,7H-[1,2,5]thiadiazolo[3,4-h][2,3,4]benzothiadiazepine 6,6-Dioxides. Experimental and Computational Studies for Understanding the Course of the Transformations.

When refluxing with sodium hydrogen carbonate in acetonitrile, 7-chloro-5-(4-fluorophenyl)-1,3-dihydro-2,3,4-benzothiadiazepine 2,2-dioxide afforded, after loss of dinitrogen and subsequent ring contraction, the corresponding sulfone in 83% yield. Similar treatment of the related thiadiazolo-fused tricycles, i.e. 9-aryl-5H,7H-[1,2,5]thiadiazolo[3,4-h][2,3,4]benzothiadiazepine 6,6-dioxides, resulted in a substantially different product mixture: formation of sultines and benzocyclobutenes was observed, while only small amounts of the sulfones were formed, if any. Density functional theory calculations support the mechanism proposed for the transformations involving a zwitterionic intermediate formed by the tautomerization of the thiadiazepine ring followed by dinitrogen extrusion. When starting from 7-chloro-substituted 2,3,4-benzothiadiazepine 2,2-dioxide, the formation of sulfone via o-quinodimethane is the preferred pathway from the zwitterion. However, in the case of thiadiazolobenzothiadiazepine 6,6-dioxides it has been found that the ring closure of the zwitterion leading to the formation of sultines was kinetically preferred over the loss of sulfur dioxide leading to o-quinodimethane, which is the key intermediate to benzocyclobutene-type products. The calculations explain the differences observed between the product distributions of the chloro-substituted and the thiadiazolo-fused derivatives.

General pathway of sulfur-chain breakage of polythionates by iodine confirmed by the kinetics and mechanism of the pentathionate-iodine reaction.

The pentathionate-iodine reaction has been studied spectrophotometrically at T = 25.0 ± 0.1 °C and at an ionic strength of 0.5 M in both the absence and presence of an initially added iodide ion at the pH range of 3.95-5.15. It was found that the pH does not affect the rate of the reaction; however, the iodide ion produced by the reaction strongly inhibits the oxidation. Therefore, it acts as an autoinhibitor. The kinetic curves also support the fact that iodide inhibition cannot be explained by the formation of the unreactive triiodide ion, and S(5)O(6)I(-) along with the iodide ion has to be involved in the initiating rapid equilibrium being shifted far to the left. Further reactions of S(5)O(6)I(-), including its hydrolysis and reaction with the iodide ion, lead to the overall stoichiometry represented by the following equation: S(5)O(6)(2-) + 10I(2) + 14H(2)O → 5SO(4)(2-) + 20I(-) + 28H(+). A nine-step kinetic model with two fitted parameters is proposed and discussed, from which a rate equation has also been derived. A brief discussion about the general pathway of sulfur-chain breakage of polythionates supported by theoretical calculations has also been included.

Theoretical insights into the nature of nickel-carbon dioxide interactions in Ni(PH3)2(η2-CO2).

DFT calculations were carried out for the Ni(0) complex Ni(PH(3))(2)(η(2)-CO(2)), which is a model compound for the well-known Ni(0) carbon dioxide complexes containing various tertiary phosphane ligands. The electronic structure of the complex was elucidated using domain-averaged Fermi hole (DAFH), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), charge decomposition analysis (CDA), and natural bond orbital (NBO) methods. The carbon dioxide ligand in the complex reveals an unexpected coordination behavior. Apart from the expected π-donation interaction, the C-O σ bond takes also part in the electron donation. Moreover, the back-donation is slightly influenced by the phosphorus atom adjacent to the noncoordinated O of carbon dioxide as it transfers electron density directly to carbon. This unconventional way of back-donation may also explain the bent character of the Ni-C bond path. Due to excess kinetic energy density, no bond critical point was found between the coordinating oxygen and the nickel center. A strong relationship has been found between the DAFH and the NBO methods, which can provide additional information for the interpretation of DAFH eigenvectors.

Palladium-Catalyzed Synthesis of Amidines via tert-Butyl isocyanide Insertion.

Para-substituted iodobenzenes were reacted with tert-butyl isocyanide and piperidine as nucleophiles in the presence of palladium-diphosphine catalysts. Both single and double insertion of the isocyanide was observed and the corresponding amidines and ketimine-amidines were obtained in yields of practical interest. With the increase of the tert-butyl isocyanide/iodobenzene ratio, 100% chemoselectivity toward the ketimine-amidine was achieved. The formation of the products was rationalized on the basis of a catalytic cycle analogous to that of the aminocarbonylation reactions. Clear connection was found between the activity and the electronic structure of the proposed catalyst Pd(diphosphine) by computational studies, as the more negative partial charge on palladium resulted in higher conversion. Among five isocyanide substrates, only tert-butyl isocyanide was proved to be active.

Viable pathways for the oxidative addition of iodobenzene to palladium(0)-triphenylphosphine-carbonyl complexes: a theoretical study.

The oxidative addition of 4-substituted iodobenzenes on Pd(0) catalysts under CO atmosphere was investigated by means of density functional calculations employing the M06//B97-D3 level of theory. The 18-electron triphenylphosphine-tricarbonyl complex was found to be the global minimum. Several coordinatively unsaturated species are predicted to be present both in N,N-dimethylformamide and toluene solution. In terms of activating iodobenzene, bis(triphenylphosphine)palladium(0) was proved to be the most active. However, due to its lower thermodynamic stability, it is slightly inferior to the Pd-triphenylphosphine-carbonyl complex, which is predicted to react with a free energy of activation of 23.2 kcal mol-1 with respect to the initial resting state tetrakis(triphenylphosphine)palladium(0). The effect of 4-substituents of iodobenzene on reaction energetics is also discussed. The activity of the Pd(0) catalyst was found to be governed by the donor-acceptor strength of the ancillary ligands: the barrier decreases with increasing basicity and decreasing back-donating capability.

Synthesis of ferrocene-labeled steroids via copper-catalyzed azide-alkyne cycloaddition. Reactivity difference between 2ß-, 6ß- and 16ß-azido-androstanes.

Copper-catalyzed cycloaddition of steroidal azides and ferrocenyl-alkynes were found to be an efficient methodology for the synthesis of ferrocene-labeled steroids. At the same time, a great difference between the reactivity of 2ß- or 16ß-azido-androstanes and a sterically hindered 6ß-azido steroid toward both ferrocenyl-alkynes and simple alkynes, such as phenylacetylene, 1-octyne, propargyl acetate and methyl propiolate, was observed.

Spectroscopic detection and theoretical confirmation of the role of Cr2(CO)5(C5R5)2 and .Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by .Cr(CO)3(C5R5) (R = H, CH3).

Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes .Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr[triple bond]Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)]2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, .Cr(CO)2(ketene)(C5R5) and Cr2(CO)5(C5R5)2 have been detected spectroscopically. The complex .Cr(13CO)2(O=13C=CHSiMe3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)2(C5H5)]2 and CO addition to 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show DeltaH approximately equal 23 kcal mol(-1) for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr[triple bond]Cr bond strength in [Cr(CO)2(C5H5)]2 as 72 kcal mol(-1). The complex [Cr(CO)2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50 degrees C implying that 3Cr2(CO)5(C5H5)2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.

Preparation and structural characterization of ionic five-coordinate palladium(II) and platinum(II) complexes of the ligand tris[2-(diphenylphosphino)ethyl]phosphine. Insertion of SnCl(2) into M-Cl bonds (M = Pd, Pt) and hydroformylation activity of the Pt-SnCl(3) systems.

The five-coordinate palladium(II) and platinum(II) complexes [M(PP(3))Cl]Cl [M = Pd (1), Pt (2)] (PP(3) = tris[2-(diphenylphosphino)ethyl]phosphine) were prepared by interaction of aqueous solutions of MCl(4)(2-) salts with PP(3) in CHCl(3). Complexes 1 and 2 undergo facile chloro substitution reactions with KCN in 1:1 and 1:2 ratios to afford complexes [M(PP(3))(CN)]Cl [M = Pt (3)] and [M(PP(3))(CN)](CN) [M = Pd (4), Pt (5)] possessing M-C bonds, both in solution and in the solid state. The reaction of 1 and 2 with SnCl(2) in CDCl(3) occurs with insertion of SnCl(2) into M-Cl bonds leading to the formation of [M(PP(3))(SnCl(3))](SnCl(3)) [M = Pd (6), M = Pt (7)]. The isolation as solids of complexes 6 and 7 by addition of SnCl(2) to the precursors requires the presence of PPh(3) which activates the cleavage of M-Cl bonds, favors the SnCl(2) insertion, and does not coordinate to M in any observable extent. Solutions of 6 in CDCl(3) undergo tin dichloride elimination in higher proportion than solutions of 7. The reaction of complexes 1 and 2 with SnPh(2)Cl(2) leads to [M(PP(3))Cl](2)[SnPh(2)Cl(4)] [M = Pd (8)]. Complexes 2, 5, 7, and 8 were shown by X-ray diffraction to contain distorted trigonal bipyramidal monocations [M(PP(3))X](+) [M = Pt, X = Cl(-) (2), X = CN(-) (5), X = SnCl(3)(-) (7); M = Pd, X = Cl(-) (8)], the central P atom of PP(3) being trans to X in axial position and the terminal P donors in the equatorial plane of the bipyramids. The "preformed" catalyst 7 showed a relatively high aldehyde selectivity compared to most of the platinum catalysts.