Carbonylation studies of Pd-methyl complexes modified with 1,4-Cs-symmetrical diphosphine ligands

Neutral palladium methyl chloride 2a-d [PdCH₃(PˆP′)Cl] and cationic palladium methyl acetonitrile mono-triflate 3a-d [PdCH₃(PˆP′)(CH₃CN)](CF₃SO₃) complexes were synthesized and fully characterized (PˆP′ = 1a-d). All the neutral and cationic complexes containing a C_s-symmetric diphosphine exist in solution as a mixture of geometric isomers. The carbonylation at atmospheric pressure of the neutral and cationic complexes revealed that migratory insertion of carbon monoxide is not stereospecific in these systems. The neutral and cationic acyl complexes were formed in situ as mixtures of stereoisomers, which were characterized by means of NMR spectroscopy.The crystal structures of [Pd(1a)Cl]₂(OTf)₂ and 2d are described.     

Olefin insertion in Pd-acyl complexes modified with 1,4-Cs-symmetrical diphosphine ligands

The insertion of ethene and propene was investigated in palladium(II) acyl complexes of the type [PdC(O)CH₃(P^∧P′)(CH₃CN)](OTf) modified with the C_s-symmetric diphosphines 2-4 and the parent ligand 1, described by C_2v-symmetry and taken as a reference.Ethene insertion was investigated for acyl complexes containing the ligands 2 and 3. Two insertion products formed in a ratio of approximately 1:1 for both systems, irrespective of the electronic properties of the ligands.Propene as an α-olefin can insert according to a 1,2- or 2,1-insertion mode into a palladium acyl bond, arising regioselectivity issues. Moreover, due to the C_s-symmetry of the ligands, two stereoisomers can result upon insertion, as the alkyl group of the formed five-membered metallacycle can be cis or trans to each non-equivalent moiety. Propene insertion was indeed neither stereo- nor regioselective in the cases of 3 and 4, in which the products arising from both 1,2- and 2,1-insertion were observed. 2 displayed total control of stereo- and regioselectivity, with the formation of one primary insertion product. Similar regioselectivity was observed for the reference ligand 1. The regioisomeric distribution was different from equimolar for propene insertion, where the ratio of the products might be controlled by a combination of steric and electronic factors.     

NMR approach for the identification of dinuclear and mononuclear complexes: The first detection of [Pd(SPh)2(PPh3)2] and [Pd2(SPh)4(PPh3)2] - The intermediate complexes in the catalytic carbon-sulfur bond formation reaction

In the present study we have analyzed the nature of palladium complexes in the catalytic system for selective carbon-sulfur bond formation via the addition of S-S and S-H bonds to alkynes. For the first time the mononuclear and dinuclear palladium complexes were clearly detected by DOSY NMR under the catalytic conditions. It was demonstrated that the concentration of these palladium complexes strongly depends on the amount of phosphine ligand available under reaction conditions.     

NMR spectra of paramagnetic complexes of 1-vinylimidazole with iron group metals

The high-resolution ¹H and ¹³C NMR spectra of 1-vinylimidazole complexes with iron group metals were recorded. The contact coupling in these systems was established in the ¹H and ¹³C NMR spectra. The applicability of the NMR spectra transformed by long-range hyperfine coupling for elucidating the molecular structure of the ligand was shown. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1430–1433, June, 2005.     

Inclusion complexes of cryptophane-E with dichloromethane and chloroform: A thermodynamic and kinetic study using the 1D-EXSY NMR method

Complexation equilibria and kinetics of exchange of chloroform and dichloromethane molecules between the cavity of cryptophane-E and bulk solution were investigated using NMR methods. Using one-dimensional magnetization transfer (1D-EXSY type sequence), chemical exchange rates were measured in different temperature ranges, limited by the equilibrium constant values of the complexes and the boiling points of the guest substances. From the kinetic data, activation energies were calculated using the Arrhenius equation. From the temperature-dependence of the association constant data, the enthalpy and entropy of complexation were estimated and compared with values for similar complexes of other cryptophanes.     

Coordination modes of 1,2,3,4-tetrahydro-1,4-diphenyl-1,4-benzodiphosphinine (bedip) to Pt and Pd metal ions: Synthesis and structural characterization of mono- and bi-nuclear complexes

Within this study, coordination properties of the cyclic diphosphine 1,2,3,4-tetrahydro-1,4-diphenyl-1,4-benzodiphosphinine (bedip) are investigated, through the preparation of neutral and cationic Pt(II), Pt(IV) and Pd(II) complexes. The diphosphine acts as bridging ligand in the neutral Pt(II) and Pd(II) complexes, affording [MX(CH₃)(μ-bedip)]₂ (X = Cl, Br, I, CH₃) species. Chelation is observed in all the remaining complexes. The molecular structures of [PtX(CH₃)(μ-bedip)]₂ (X = Br, I) and [PtI(CH₃)₃(bedip)] are also determined.     

Preparation and cis-to-trans transformation study of square-planar [Pt(Ln)2Cl2] complexes bearing cytokinins derived from 6-benzylaminopurine (Ln) by view of NMR spectroscopy and X-ray crystallography

Mononuclear, square-planar platinum(II) complexes involving derivatives of aromatic cytokinins as the ligands, and having the general formula cis-[Pt(L_n)₂Cl₂] (1–3) and trans-[Pt(L_n)₂Cl₂] (4–6), where n = 1–3, L₁ = 2-chloro-6-(benzylamino)-9-isopropylpurine, L₂ = 2-chloro-6-[(4-methoxybenzyl)amino]-9-isopropylpurine and L₃ = 2-chloro-6-[(2-methoxybenzyl)-amino]-9-isopropylpurine, have been synthesized and characterized by elemental analysis, MALDI-TOF mass, FT IR, ¹H, ¹³C, ¹⁵N and ¹⁹⁵Pt NMR spectral measurements. Dynamic cis-to-trans isomerization process of complex 1 in N,N′-dimethylformamide (DMF) has been investigated by means of multinuclear NMR spectroscopy. The solid-state structures of 1, 4 · (DMF)₂, and 5 have been determined by single crystal X-ray analysis. X-ray structures revealed that the heterocyclic ligands are coordinated to platinum via nitrogen atom N(7) in all the complexes studied. In vitro cytotoxicity of the prepared complexes against MCF7, G361, K562, and HOS has been evaluated. Owing to low solubility of the complexes in water, the cytotoxicity has been only tested up to 5 μM concentration. Unfortunately, all complexes have been found to be non-cytotoxic in the accessible concentration range.     

Synthesis and reactivity of new methylallylpalladium(II) complexes with bidentate 2-(methylthio-N-benzylidene)anilines

This work describes the synthesis, characterisation and reactivity of new methylallyl Pd(II) complexes that contain bidentate 2-(methylthio-N-benzylidene)anilines as ligands. The reaction of the binuclear complex [(η³-Me-allyl)Pd(μ-Cl)₂] with AgBF₄ causes the total abstraction of the chloride bridges, with the subsequent formation of an intermediary fragment of Pd(II). This fragment in turn reacts with neutral bidentate 2-(methylthio-N-benzylidene)anilines to give cationic complexes of Pd(II) of general formula [(η³-Me-allyl)Pd(η²-S,N-MeSC₆H₄NCHC₆H₄(X)Y)]BF₄ [X=H, Y=H (1); X=F, Y=H (2); X=Me, Y=H (3); X=H, Y=Cl (4); X=H, Y=Me₂N (5); X=H, Y=NO₂ (6)]. The new complexes were characterised by means of elemental analysis, IR, NMR [¹H, ¹⁹F{¹H}, ¹³C{¹H}, ³¹P{¹H}, Dept, ¹H-¹H-COSY, HSQC, HMBC] and mass spectroscopies. The reaction of the Pd(II) complexes with nucleophiles such as NaI, (EtO)₂PS₂K, KCN, KSCN or NaH lead to the deco-ordination of the bidentate ligands to give dimeric or polymeric complexes of Pd(II). The reactivity pattern observed is discussed by a theoretical analysis based on Fukui functions.     

Search of structure and ligands exchange for palladium(II) complexes with N-allylimidazole; X-ray and solid-state/solution NMR studies

Two coordination compounds of palladium(II) with N-allylimidazole (l) of the general formula [PdL₄]Cl₂ · 3H₂O (1) and trans-[PdL₂Cl₂] (2) have been synthesized. The crystal and molecular structure of complexes 1 and 2 was established by single-crystal X-ray diffraction analysis. The X-ray structural data were supplemented by solid-state ¹³C NMR measurements (CP MAS and PASS 2D). The 1D and 2D NMR studies in solution reveal that complex 1 is unstable at room temperature and undergoes reversible decomposition to 2. The method for how to preserve a complex with four allyl-imidazole ligands in solution is shown.     

Solid-state 31P and 109Ag CP/MAS NMR as a powerful tool for studying of silver(I) complexes with N-thiophosphorylated thiourea and thioamide ligands

A family of three- and four-coordinated silver(I) complexes of formulas [Ag(PPh₃)₂L], [Ag(PPh₃)L], and [AgL]_n with N-thiophosphorylated thiourea and thioamide ligands of general formula RC(S)NHP(S)(OPri)₂ [R = Ph, PhNH, iPrNH, tBuNH, NH₂] have been studied by solid-state ¹⁰⁹Ag and ³¹P CPMAS NMR spectroscopy. ¹⁰⁹Ag NMR spectra have provided valuable structural information about Ag coordination, which is in good accordance with the available crystal structure data. The data presented in this work represent a significant addition to the available ¹⁰⁹Ag chemical shifts and chemical shifts anisotropies. The silver chemical shift ranges for different P,S-environments and coordination state were discussed in detail. The ¹J(³¹P–^107/109Ag) and ²J(³¹P–³¹P) values were determined and analyzed.     

Organometallic complexes in supported ionic-liquid phase (SILP) catalysts: a PHIP NMR spectroscopy study

para-Hydrogen induced polarization (PHIP) NMR spectroscopy emerges as an efficient and robust method for on-line monitoring of gas-phase hydrogenation reactions. Here we report detailed investigations of supported ionic liquid phase (SILP) catalysts in a continuous gas-phase hydrogenation of propene with PHIP NMR spectroscopy. A relocation of the rhodium complex in the thin layer of ionic liquid in the SILP catalyst at the initial stage of the propene hydrogenation is demonstrated. PHIP NMR spectroscopy can provide profound insight into the evolution of SILP catalysts during hydrogenation reactions.     

Genistein complexes with amines. Part II: ab initio study of the complexes with piperazine and triethylamine

The piperazine and triethylamine complexes of genistein, exhibiting high immunosuppressant activity, were ab initio modeled at RHF/6-31G^** level and results were compared with those obtained for genistein–morpholine complexes by X-ray, NMR, and theoretical methods. The most stable genistein–piperazine complex is formed due to hydrogen bonding of genistein's OH group at position C7 to piperazine's nitrogen atom. In the most stable genistein–triethylamine complex genistein's OH group at position C4′ (position para to phenyl substituent) and trimethylamine nitrogen atom are engaged in hydrogen bond formation. The calculations confirmed our previous NMR conclusion that piperazine is more strongly complexed by genistein than is morpholine or triethylamine. The theoretical ¹³C NMR spectra correlate fairly well with the experimental spectra.     

Solid state NMR study of intercalate complexes of poly(ethylene oxide) and small molecules

From solid state NMR spectra, a lower shielding of poly(ethylene oxide) (PEO) protons, in contrast to higher shielding of PEO carbons, has been found for PEO/hydroxybenzene and PEO/LiCF₃SO₃ complexes in comparison with neat PEO. The same PEO chemical shifts were found both for crystalline and amorphous phase of PEO/LiCF₃SO₃ polymer electrolyte, confirming the same interaction in both phases. Measurements of 2D ¹H CRAMPS exchange NMR spectra have been used to characterize proton distances in complexes of PEO and benzene derivatives. A close contact (∼ 0.3 nm) between aromatic and PEO protons was detected in some cases. From the measurements of the cross polarization ¹H → ¹³C, using Lee-Goldburg irradiation of ¹H nuclei, the distance between LiCF₃SO₃ carbon and the nearest PEO protons in the PEO/LiCF₃SO₃ complex was determined.     

Synthesis, mechanism and NMR spectra of lanthanide complexes with a novel unsymmetrical Schiff base

Owing to its two unsymmetrical-NH_2 groups sited on different terminals, 2, 6-diaminocaproic acid (lysine) was used as a reactant for synthesizing a novel unsymmetrical Schiff base with salicylaldehyde on one side and ovanillin on the other for the first time. It is a new way to synthesize such a special unsymmetrical Schiff base. It is named "hetero bis-Schiff base" for distinguishing it from others. The synthesis method, formation mechanism as well as twelve new lanthanide complexes with the above ligand are reported and discussed herein. They were characterized by elementary analysis, molar conductivity, IR-spectra and especially by ~1H and ~(13)C NMR spectra. The results obtained may provide a new promising method for synthesizing similar unsymmetrical Schiff bases and their complexes.     

Lithium-7, sodium-23, and cesium-133 NMR and far infrared study of alkali complexes with C222-dilactam in various solvents

Nuclear magnetic resonances of alkali nuclei,⁷Li,²³Na, and¹³³Cs, as well as far infrared measurements are used to study alkali complexes of a bicyclic diazapolyoxa ligand—the dilactam of cryptand C222. Measurements were carried out in pyridine, tetrahydrofuran, acetonitrile, nitromethane, dimethylformamide, and aqueous solutions. The complexing ability of the dilactam is similar to, but weaker than, that of the cryptand C222. The limiting chemical shifts of the complexed cations were solvent-dependent, indicating incomplete enclosure of the cation by the ligand. Formation constants of Li⁺ and Cs⁺ complexes were calculated from the chemical-shift dependence on the ligand/metal ion mole ratio.     

Steric and electronic effects in stabilizing allyl-palladium complexes of “P-N-P” ligands, X2PN(Me)PX2 (X = OC6H5 or OC6H3Me2-2,6)

The chemistry of η³-allyl palladium complexes of the diphosphazane ligands, X₂PN(Me)PX₂ [X = OC₆H₅ (1) or OC₆H₃Me₂-2,6 (2)] has been investigated.The reactions of the phenoxy derivative, (PhO)₂PN(Me)P(OPh)₂ with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = H or Me; R′ = H, R″ = Me) give exclusively the palladium dimer, [Pd₂{μ-(PhO)₂PN(Me)P(OPh)₂}₂Cl₂] (3); however, the analogous reaction with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = Ph) gives the palladium dimer and the allyl palladium complex [Pd(η³-1,3-R′,R″-C₃H₃)(1)](PF₆) (R′ = R″ = Ph) (4). On the other hand, the 2,6-dimethylphenoxy substituted derivative 2 reacts with (allyl) palladium chloro dimers to give stable allyl palladium complexes, [Pd(η³-1,3-R′,R″-C₃H₃)(2)](PF₆) [R′ = R″ = H (5), Me (7) or Ph (8); R′ = H, R″ = Me (6)].Detailed NMR studies reveal that the complexes 6 and 7 exist as a mixture of isomers in solution; the relatively less favourable isomer, anti-[Pd(η³-1-Me-C₃H₄)(2)](PF₆) (6b) and syn/anti-[Pd(η³-1,3-Me₂-C₃H₃)(2)](PF₆) (7b) are present to the extent of 25% and 40%, respectively. This result can be explained on the basis of the steric congestion around the donor phosphorus atoms in 2. The structures of four complexes (4, 5, 7a and 8) have been determined by X-ray crystallography; only one isomer is observed in the solid state in each case.     

Structural correlations for 1H, 13C and 15N NMR coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with lutidines and collidine

¹H, ¹³C and ¹⁵N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with dimethylpyridines (lutidines: 2,3‐lutidine, 2,3lut; 2,4‐lutidine, 2,4lut; 3,5‐lutidine, 3,5lut; 2,6‐lutidine, 2,6lut) and 2,4,6‐trimethylpyridine (2,4,6‐collidine, 2,4,6col) having general formulae [AuLCl₃], trans‐[PdL₂Cl₂] and trans‐/cis‐[PtL₂Cl₂] were performed and the respective chemical shifts (δ^1H, δ^13C, δ^15N) reported. The deshielding of protons and carbons, as well as the shielding of nitrogens was observed. The ¹H, ¹³C and ¹⁵N NMR coordination shifts (Δ^1H_coord, Δ^13C_coord, Δ^15N_coord; Δ_coord = δ_complex ? δ_ligand) were discussed in relation to some structural features of the title complexes, such as the type of the central atom [Au(III), Pd(II), Pt(II)], geometry (trans‐ or cis‐), metal‐nitrogen bond lengths and the position of both methyl groups in the pyridine ring system. Copyright © 2010 John Wiley & Sons, Ltd.     

Solid state and solution NMR studies of some new complexes of mercury selenocyanate with imidazolidine-2-thione and its derivatives

Reactions of imidazolidine-2-thione (Imt), 1,3-diazinane-2-thione (Diaz) and 1,3-diazipane-2-thione (Diap) with mercury(II) selenocyanate in acetonitrile resulted in formation of 2?:?1 complexes. Both solid state and solution NMR, confirm the exocyclic sulfur atom to be the donor in all cases. ¹⁹⁹Hg shielding tensors and anisotropies were calculated from the solid-state NMR spectra. Based on the solid NMR data a distorted tetrahedral disposition of ligands around mercury is proposed.     

Anisotropic effect of the nitrate anion—manifestation of diamagnetic proton chemical shifts in the H NMR spectra of NO3 coordinated complexes

The anisotropic effect of the planar nitrate anion NO₃⁻ has been ab initio calculated employing the Nucleus-Independent Chemical Shift (NICS) concept of von Ragué Schleyer and visualized as Iso-Chemical-Shielding Surfaces (ICSSs) of various (de)shieldings. Complexation-induced shifts in the ¹H NMR spectra of nitrate/metal complexes or nitrate/receptor supramolecules can be separated now into anisotropic influences of the suitably coordinated nitrate anions and effects originating from differential sources.     

Stereochemically non-rigid transition metal complexes of 2,6-bis[(1-phenylimino) ethyl]pyridine (BIP) part 1. Dynamic NMR studies of [M(C6F5) 2(BIP)] (M = Pd or Pt)

The complexes [M(C₆F₅)₂(BIP)] (M = Pd^II or Pt^II, BIP = 2,6-bis[(1-phenylimino)ethyl]pyridine) have been synthesised and characterised as involving BIP as a bidentate chelate ligand. In solution they undergo 1,4 metallotropic shifts of the M(C₆ F₅)₂ moiety, E,Z isomerisation of the pendant imine bond, and restricted C-C rotation of the pendant portion of the BIP ligand. ¹H and ¹⁹F dynamic NMR studies yielded activation energies for these three types of fluxion. ΔG^≠ (298 K) values for the three processes were 89.6, 86.6 and 47.4kJmol⁻¹ respectively for the Pt^II complex. Values for the Pd^II complex were significantly lower in magnitude, namely 71.6, 70.4 and 41.8 kJ mol⁻¹ respectively.