Kinetic Study of the Isotope Exchange Reactions of Malonic Acid and Malonate Ion Using 1H NMR Spectroscopy. Inhibition of Acid and Base

The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D₂O solutions, respectively, using ¹H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO₃ (0–3 M) and DSO₄^? ion (0–0.1 M), whereas it is catalyzed by the presence of DSO₄^? ion (> 0.2 M), D₃PO₄, D₂PO₄^? ion or DPO₄^2– ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D₂O is DPO₄^2– > D₂PO₄^? > D₃PO₄ > DSO₄^? > DNO₃. The rate of the isotope exchange reaction of malonate ion in D₂O decreases to a minimum and then increases with increased [NaOD]₀. The mechanism of the isotope exchange reaction of malonic acid in acidic D₂O is different from the general acid-catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic acids. The bimalonate ion plays an important role in the isotope exchange reactions of this system.     

Study on carbon-hydrogen activation of ketones by Gold(III) complexes and the synthesis and characterization of two ketonylgold(III) complexes

The acetonylgold(III) compound [Au(ppy)(CH₂COCH₃)Cl] (1) (ppy = 2-phenylpyridine) was unexpectedly obtained during the crystallization process of Au(III) lactate complex [Au(ppy)(CH₃CHOHCOO⁻)Cl]. This new structure prompted us to further study the role of Au(III) complexes on the carbon-hydrogen activation of ketones. Complex [Au(ppy)(CH₂COCH₃)NO₃] (2) was synthesized by reacting [Au(ppy)(NO₃)₂] with acetone while the ketonyl Au(III) complex [Au(apd)Cl₂] (3) (Hapd = 2-acetylpyridine) was obtained through carbon-hydrogen bond activation of the acetyl group. The crystal structures of 1 and 2 have common features: a square-planar Au(III) centre coordinated by one five-membered chelate ring, one acetonyl ligand and one anion (chloride or nitrate). Both structures show that carbon-hydrogen activation of acetone by 2-phenylpyridine-Au(III) complexes leads to the formation of acetonyl-Au(III) complexes. The Au-CH₂ bond lengths (2.067(7) Å, 1 and 2.059(5) Å, 2) are similar to each other but longer than the Au-C (phenyl) bond lengths. The two softest ligands (carbanion) are also cis to each other in the thermodynamically most stable isomer. In complex 3, the σ-bonded acetyl group is confirmed by ¹³C DEPT NMR spectroscopy.     

Gold(I) ‐Nickel(II)‐4,4′‐bpy‐Phosphine Complexes: Synthesis and Multinuclear NMR Study

Silver triflate [AgOTf] assisted de‐bromination gives [Ni(dppm/dppe/(PPh₃)₂) (OTf)₂], which on reaction with 4,4′‐bpy and gold(I) phosphines in dichloromethane medium by the self assemble technique leads to [{(L)Ni}{(4,4‐bpy)Au(PPh₃)}₂](OTf)₄, ( 1,2,3 ) [{(L)Ni(4,4‐bpy)}₄](OTf)₈, ( 4,5,6 ) [L = dppm/dppe/(PPh₃)₂ = diphenyl phosphino‐methane, ‐ethane, bis‐triphenylphosphine, OSO₂CF₃ is the triflate anion]. The maximum molecular peak of the corresponding molecule is observed in the ESI mass spectrum. Ir spectra of the complexes show ‐C=C‐, ‐C=N‐, as well as phosphine stretching. The ¹H NMR spectra as well as ³¹P (¹H)NMR suggest solution stereochemistry, proton movement, and phosphorus proton interaction. Considering all the moieties, there are a lot of carbon atoms in the molecule reflected by the ¹³C NMR spectrum. In the ¹H‐¹H COSY spectrum of the present complexes and contour peaks in the ¹H^?13C HMQC spectrum, we assign the solution structure and stereoretentive transformation in each step.     

Kinetic Study of the Ce(III)‐, Mn(II)‐, or Ferroin‐Catalyzed Belousov‐Zhabotinsky Reaction with Allylmalonic Acid

In a stirred batch experiment and under aerobic conditions, ferroin (Fe(phen)₃²⁺) behaves differently from Ce(III) or Mn(II) ion as a catalyst for the Belousov‐Zhabotinsky (BZ) reaction with allylmalonic acid (AMA). The effects of bromate ion, AMA, metal‐ion catalyst, and sulfuric acid on the oscillating pattern were investigated. The kinetics of the reaction of AMA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was studied under aerobic or anaerobic conditions. The order of reactivity of metal ions toward reaction with AMA is Fe(phen)₃³⁺ > Mn(III) > Ce(IV) under aerobic conditions whereas it is Mn(III) > Ce(IV) > Fe(phen)₃³⁺ under anaerobic conditions. Under aerobic or anaerobic conditions, the order of reactivity of RCH(CO₂H)₂ (R = H (MA), Me (MeMA), Et (EtMA), allyl (AMA), n‐Bu (BuMA), Ph (PhMA), and Br (BrMA)) is PhMA > MA > BrMA > AMA > MeMA > EtMA > BuMA toward reaction with Ce(IV) ion and it is MA > PhMA > BrMA > MeMA > AMA > EtMA > BuMA toward reaction with Mn(III) ion. Under aerobic conditions, the order of reactivity of RCH(CO₂H)₂ toward reaction with Fe(phen)₃³⁺ ion is PhMA > BrMA > (MeMA, AMA) > (BuMA, EtMA) > MA. The experiment results are rationalized.     

Synthesis of Phosphanes Bearing 2‐Imino‐1,3‐thiazolidine Ligands – X‐Ray Analyses and NMR Spectroscopy

Pseudo‐ephedrine derived 2‐imino‐1,3‐thiazolidine 1 reacts with tris(diethylamino)phosphane by stepwise replacement of the diethylamino group to give the mono‐, bis‐ and tris(imino)phosphanes 2 , 3 and 4 , respectively, of which 4 could be isolated in pure state. The analogous reaction with diethylamino‐diphenylphosphane affords the imino‐diphenylphosphane 5 . The iminophosphanes react with sulfur or selenium to give the corresponding phosphorus(V) compounds. In contrast, the reaction of the iminophosphanes with oxygen is very slow; anhydrous trimethylamine N‐oxide reacts in the melt with the phosphanes to give the oxides 4(O) and 5(O) . The molecular structures of 4(O) (in mixture with 4 ), 4(Se) , 5(S) and 5(Se) were determined by X‐ray analysis. In all cases the ring‐sulfur and the phosphorus atoms are in cis‐positions at the C=N bonds. The analogous solution structures were determined by ¹H, ¹³C, ¹⁵N, ³¹P and ⁷⁷Se NMR spectroscopy. In the case of the compounds 5 , 5(O) , 5(S) and 5(Se) the isotope‐induced chemical shifts ¹δ^14/15N(³¹P) were determined, using INEPT‐HEED experiments.     

Kinetics and Mechanism of Oxidation of Chromium(III)‐guanosine 5‐Monophosphate Complex by Periodate

The kinetics of oxidation of the chromium(III)‐guanosine 5‐monophosphate complex, [Cr^III(L)(H₂O)₄]³⁺(L = guanosine 5‐monophosphate) by periodate in aqueous solution to Cr^VI have been studied spectrophotometrically over the 25–45 °C range. The reaction is first order with respect to both [IO₄^?] and [Cr^III], and increases with pH over the 2.38–3.68 range. Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner‐sphere mechanism via coordination of IO₄^? to chromium(III).     

Selectively Measuring π Back‐Donation in Gold(I) Complexes by NMR Spectroscopy

Even though the Dewar–Chatt–Duncanson model has been successfully used by chemists since the 1950s, no experimental methodology is yet known to unambiguously estimate the constituents (donation and back‐donation) of a metal–ligand interaction. It is demonstrated here that one of these components, the metal‐to‐ligand π back‐donation, can be effectively probed by NMR measurements aimed at determining the rotational barrier of a C?N bond (ΔH_r^≠) of a nitrogen acyclic carbene ligand. A large series of gold(I) complexes have been synthesized and analyzed, and it was found that the above experimental observables show an accurate correlation with back‐donation, as defined theoretically by the appropriate charge displacement originated upon bond formation. The proposed method is potentially of wide applicability for analyzing the ligand effect in metal catalysts and guiding their design.     

Aqueous Solution Chemistry of Scandium(III) Studied by Raman Spectroscopy and ab initio Molecular Orbital Calculations

Aqueous solutions of Sc(ClO₄)₃,ScCl₃, and Sc₂(SO₄)₃ were studied by Ramanspectroscopy over a wide concentration range. In aqueous perchlorate solutionSc(III) occurs as an hexaaqua cation. The weak, polarized Raman band assignedto the ₁(a _1g) ScO₆ mode of the hexaaqua-Sc (III) ion has been studied as afunction of concentration and temperature. The ₁(a _1g) ScO₆ mode at 442 cm^–1of the hexaaqua—Sc(III) shifts only 3 cm^–1 to lower frequency and broadensabout 20 cm^–1 for a 60°C temperature increase. The Raman spectroscopic datasuggest that the hexaaqua-Sc (III) ion is stable in perchlorate solution within theconcentration and temperature range measured. Besides the polarized componentat 442 cm^–1, two weak depolarized modes at 295 and 410 cm^–1 were measuredin the Raman effect. These two modes of the ScO₆ unit were assigned to ₃(f _2g)and ₂(e ), respectively. The infrared active mode ₃(f _1u) was measured at 460cm^–1. The frequency data confirm the centrosymmetry of the Sc(III) aquacomplex, contrary to earlier Raman results. The powder spectrum of crystallineSc(ClO₄) ₃ · 6H₂O shows the above described Raman modes as well. Thesefindings are in contrast to Sc₂(SO₄)₃ solutions, where sulfate replaces water inthe first hydration sphere and forms thermodynamically strong sulfato complexes.In ScCl₃ solutions thermodynamically weak chloro complexes could be detected.Ab initio molecular orbital calculations were performed at the HF and MP2 levelsof theory using different basis sets up to 6–31 + G(d). Gas-phase structures,binding energies, and enthalpies are reported for the Sc³⁺(OH₂)₆ and Sc³⁺(OH₂)₇cluster. The Sc—O bond length for the Sc³⁺(OH₂)₆ cluster reproduces theexperimentally determined bond length of 2.18 Å (recent EXAFS data) almost exactly.The theoretical binding energy for the hexaaqua Sc(III) ion was calculated andaccounts for ca. 54–59% of the experimental hydration enthalpy of Sc(III). Thethermodynamic stability of the Sc³⁺(OH₂)₆(OH₂) cluster was compared to thatof the Sc³⁺(OH₂)₇ cluster, demonstrating that hexacoordination is inherently morestable than heptacoordination in the scandium (III) system. The calculated ₁ScO₆frequency of the Sc⁺(OH²)⁶ cluster is ca. 12% lower than the experimentalfrequency. Adding an explicit second hydration sphere to give Sc³⁺ (OH²)¹⁸,denoted Sc[6 + 12], is shown to correct for the discrepancy. The frequencycalculation and the thermodynamic parameters for the Sc[6 + 12] cluster aregiven and the importance of the second hydration sphere is stressed. Calculatedfrequencies of the ScO₆ subunit in the Sc[6 + 12] cluster agree very well withthe experimental values (for example, the calculated ₁ScO₆ frequency was foundto be 447 cm^–1, in excellent agreement with the above-reported experimentalvalue). The binding enthalpy for the Sc[6 + 12]cluster predicts the single ionhydration enthalpy to about 89%.     

3‐Mercapto‐2,6‐Pyridinedicarboxylic Acid: A Small Lanthanide‐Binding Tag for Protein Studies by NMR Spectroscopy

Paramagnetic effects from lanthanide ions present powerful tools for protein studies by nuclear magnetic resonance (NMR) spectroscopy provided that the lanthanide can be site‐specifically and rigidly attached to the protein. A new, particularly small and rigid lanthanide‐binding tag, 3‐mercapto‐2,6‐pyridinedicarboxylic acid (3MDPA), was synthesized and attached to two different proteins via a disulfide bond. The complexes of the N‐terminal domain of the E. coli arginine repressor (ArgN) with seven different paramagnetic lanthanide ions and Co²⁺ were analyzed in detail by NMR spectroscopy. The magnetic susceptibility anisotropy (Δχ) tensors and metal position were determined from pseudocontact shifts. The 3MDPA tag generated very different Δχ tensor orientations compared to the previously studied 4‐mercaptomethyl‐DPA tag, making it a highly complementary and useful tool for protein NMR studies.     

Base‐Induced Decarboxylation of Polyunsaturated α‐Cyano Acids Derived from Malonic Acid: Synthesis of Sesquiterpene Nitriles and Aldehydes with β‐, φ‐, and ψ‐End Groups

Catalytic base‐induced decarboxylation of polyunsaturated α‐cyano‐β‐methyl acids derived from malonic acid led to the corresponding nitriles 3 (Schemes 2 and 3), 6 (Scheme 5), and 9 (Scheme 6). This decarboxylation occurred with previous deconjugation of the α,β‐alkene moiety of the α‐cyano‐β‐methyl acid, leading to an α‐cyano‐β‐methylene propanoic acid which was easily decarboxylated (see Scheme 2). β‐Methylene intermediates, in some cases, could be isolated; mechanistic pathways are proposed. The nitriles 3, 6 , and 9 were reduced to the sesquiterpene aldehydes 4 (β‐end group), 7 (φ‐end group), and 10 (ψ‐end group), respectively.     

1,2‐, 1,7‐ and 1,12‐Dicarba‐closo‐dodecaborane(12) Derivatives Revisited by 13C NMR Spectroscopy and DFT Calculations. First Observation of Isotope‐Induced Chemical Shifts 1Δ10/11B(13C), and the Signs and Magnitudes of Coupling Constants 1J(13C,13C) and 1J(13C,11B)

The origin of broadening of ¹³C(carborane) NMR signals of 1,2‐, 1,7‐ and 1,12‐dicarba‐closo‐dodecaboranes(12) and several diphenylsilyl derivatives has been examined in detail and could be traced only partially to unresolved ¹³C–¹¹B spin‐spin coupling. Other contributions to the line widths arise from ¹³C–¹H dipole‐dipole interactions and, in particular, from isotope‐induced chemical shifts ¹Δ^10/11B(¹³C), observed here for carboranes for the first time. In the case of 1‐diphenylsilyl‐1,2‐dicarba‐closo‐dodecaborane(12), the coupling constant ¹J(¹³C,¹³C) = 9.3 Hz was measured in natural abundance of ¹³C. The small value of this coupling constant and its negative sign is predicted by calculations based on optimised structures [B3LYP/6‐311+G(d,p) level of theory] of the parent carboranes and 1‐silyl‐1,2‐dicarba‐closo‐dodecaborane(12) as a model compound [calcd. ¹J(¹³C,¹³C) = –10.5 Hz]. Calculated coupling constants ¹J(¹³C,¹¹B) are small (<7 Hz), in contrast to published assumptions, and of either sign, whereas ¹J(¹¹B,¹¹B) are all positive and range up to 15 Hz.     

Mechanistic and Spectral Studies of the Ruthenium(III) Catalysed Oxidation of Sulfanilic Acid by Alkaline Hexacyanoferrate(III)

Summary. The kinetics of ruthenium(III) catalysed oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium at a constant ionic strength of 2.5mol·dm^–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 2:8 stoichiometry (SNA:HCF(III)). The reaction showed first order kinetics in [hexacyanoferrate(III)] and [ruthenium(III)] and apparent less than unit order in both sulfanilic acid and alkali concentrations. The reaction rate increases with increasing ionic strength but the relative permittivity (_T) of the medium has a negligible effect on the rate of the reaction. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of a complex between sulfanilic acid and hydroxylated species of ruthenium(III) has been proposed. The active species of HCF(III) and ruthenium(III) are understood as [Fe(CN)₆^3–] and [Ru(H₂O)₅OH]²⁺, respectively. The main products were identified by IR, NMR, and mass spectral studies. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.     

The Stereochemistry of 1,2,3‐Triols Revealed by 1H NMR Spectroscopy: Principles and Applications

The conformational compositions of the tris(α‐methoxy‐α‐phenylacetic acid) ester derivatives of 1,2,3‐prim,sec,sec‐triols are presented. These conformations have been determined by theoretical and experimental data (i.e., energy‐ and chemical‐shift calculations, circular dichroism (CD) experiments, coupling‐constant analysis, enantioselective deuteration experiments, and low‐temperature NMR spectroscopic studies). A detailed analysis of the anisotropic effects due to the most significant conformers in the ¹H NMR spectra supported the correlation between the ¹H NMR spectra (Δδ^RS value of H(3′) and |Δ(Δδ^RS)| parameters) and the absolute configuration of the substrate. The study also allows the identification of the pro‐R and pro‐S methylene protons from their vicinal coupling constants and relative chemical shifts.     

Complexes of oxamic acid with Au(III) and Rh(III)

The preparation and some properties of the deprotonated complexes of oxamic acid with Au(III) and Rh(III) are reported. On the basis of analytical results, conductometric measurements, magnetic moments and spectral data (IR and UV-visible), a square planar structure is proposed for K[AuL(OH)₂] and octahedral for K₃[RhL ₃] 3H₂O (whereLH₂=oxamic acid).L ^2– acts as a bidentate, non-bridging ligand.

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Komplexe der Oxamidsäure mit Au(III) und Rh(III)

Zusammenfassung Es wird über die Darstellung und einige Eigenschaften von deprotonierten Komplexen der Oxamidsäure mit Au(III) und Rh(III) berichtet. Auf der Grundlage von analytischen Ergebnissen, Leitfähigkeitsmessungen, magnetischen Momenten und IR- und UV(vis)-spektroskopischen Daten wird für K[AuL(OH)₂] eine quadratisch planare und für K₃[RhL ₃] 3 H₂O eine oktaedrische Struktur vorgeschlagen (LH₂=Oxamidsäure).L ^2– reagiert als zweizähniger, nicht überbrückender Ligand.

     

Oxidative Addition to Gold(I) by Photoredox Catalysis: Straightforward Access to Diverse (C,N)‐Cyclometalated Gold(III) Complexes

Herein, we report the oxidative addition of aryldiazonium salts to ligand‐supported gold(I) complexes under visible light photoredox conditions. This method provides experimental evidence for the involvement of such a process in dual gold/photoredox‐catalyzed reactions and delivers well‐defined (C,N)‐cyclometalated gold(III) species. The remarkably mild reaction conditions and the ability to widely vary the ancillary ligand make this method a potentially powerful synthetic tool to access diverse gold(III) complexes for systematic studies into their properties and reactivity. Initial studies show that these species can undergo chloride abstraction to afford Lewis acidic dicationic gold(III) species.     

Phenyliodine(III) Triflate Mediated Synthesis of 5‐Benzoyldihydro‐2(3H)‐furanones

A direct and efficient method for the preparation of 5‐benzoyldihydro‐2(3H)‐furanones was realized by cyclization of 4‐benzoylbutyric acids in the presence of phenyliodine(III) triflate.     

Linear-dichroic infrared and NMR spectroscopic analysis of an Au(III) complex of glycylmethioninylglycine

A solid state, linear dichroic IR analysis of a mononuclear Au(III) complex of the tripeptide glycylmethioninylglycine (GlyMetGly) oriented in a nematic liquid crystal has been carried out. Structural results are compared with ¹H and ¹³C NMR data. The ligand coordinates to Au(III) as a tridentate in [Au(C₉H₁₇N₃O₄S)Cl]Cl₂, binding through S, and the N- and O-atoms of neighbouring CONH– and COO^? groups. The fourth position is occupied by a terminal Cl^? ligand.     

Organometallic Gold（Ⅲ） Derivatives with Anionic Oxygen Ligands-mononuclear Hydroxo,Alkoxo, and Acetato Complexes： Synthesis and Spectral Study

A variety of gold（Ⅲ） adducts having a-ligated oxygen-donor ligands have been prepared from [Au（ppy）Cl2]（ppy.phenylpyridine）（1） either by partial or total replacement of the chloride ions. The new species comprise hydroxo-[Au（ppy）（OH）Cl]（2）, and [Au（ppy）（OH）2]（3）, oxo-[Au2（ppy）2（μ-O）2]（4）, acetate-[Au（ppy）（O2CMe2）] （5）, and alkoxo complexes-[Au（ppy）（OR）Cl]（6, 7） and [Au（ppy）（OR）2]（8--10）（R=Me, 6 and 8; Et, 7 and 9; Pr, 10）. The dihydroxo and the oxo complexes can be interconverted by refluxing the former in anhydrous THF and the latter in water. The hydroxides 2 and 3 and the acetato complex 5 undergo σ-ligand metathesis in ROH solution（R=Me, Et or Pr） to give the corresponding alkoxides.     

Syntheses,Characterization and x-ray Structures of Gold(III) Complexes Obtained by Addition of Bases to Gold(III)(2-Pyridinecarboxaldehyde)

Reaction of potassium tetrachloroaurate(III), KAuCl₄, with 2-pyridinecarboxaldehyde (2CHO-py) have been examined in protic HX (X=OH, OMe, OEt, OCH₂CH₂CH₂, OCH₂CH₂CH₂CH₃, OCH₂CF₃) solvents. Compounds in which the pyridine ligand is N or N-O coordinated in a newly carbonyl hydrated or in semi- and acetal-forms, derived by addition of one or two hydroxylic molecules, have been isolated; these include dichloro[pyridine-2(α-hydroxymethanolato)]gold(III) (1), dichloro[pyridine-2(α-ethoxymethanolato)] gold(III) (2), dichloro[pyridine-2[α-(2,2,2-trifluoroethoxymethanolato)]gold(III) (3), trichloro(2-pyridinecarboxaldehyde dimethyl acetal)gold(III) (4), trichloro(2-pyridinecarboxaldehyde diethyl acetal)gold(III) (5), trichloro(2-pyridinecarboxaldehyde di-1-propyl acetal)gold(III) (6) and trichloro(2-pyridinecarboxaldehyde di-1-butyl acetal)gold(III) (7). The crystal and molecular structures of (2), (5) and (7) have been determined by X-ray methods. Compound (2) crystallizes in space group Pna2₁ with Z=4, a=7.8914(4), b=17.3660(4) and c=8.3873(5)Å; (5) crystallizes in space group P&1macr; with Z=2, a=7.7779(3), b=8.2878(2) and c=13.3202(6)Å, α=96.975(2), β=95.096(2), γ=115.027(2)°; (7) crystallizes in space group P2₁/a with Z=4, a=14.5438(12), b=8.9865(7) and c=15.0362(11)Å.