Thermodynamics and kinetics of the formation of the supramolecular complexes bisacetato(5,10,15,20-tetraphenylporphinate)zirconium(IV) with pyridine and imidazole

The equilibria and rates of step reactions for the formation of the supramolecular complexes of bisacetato(5,10,15,20-tetraphenylporphinate)zirconium(IV) (AcO)₂ZrTPP and bioactive bases pyridine (Py) and imidazole (Im) in toluene were studied using UV-Vis and IR spectroscopy. The step stoichiometric mechanism, including the reversible coordination of two Py molecules (K ₁ = 1.8 × 10⁸ l²/mol²), the equilibrium of the displacement of two AcO⁻ into the second coordination sphere by increasing the concentration of the solvent polar component (K ₂ = 2.4), and the coordination of the third and fourth Py molecules in a one step with the formation of [(Py)₄ZrTPP]²⁺ · 2(AcO)⁻ (K ₃ = 2.8 × 10⁴ l²/mol²), was verified. It was established that the spectrophotometric titration is sensible for the two-stage π-π-complexation of [(Py)₄ZrTPP]²⁺ · 2(AcO)⁻ with Py molecules (K ₄ = 29 l/mol and K ₅ = 1.8 l/mol). It was shown that the stronger base Im reacts irreversibly with (AcO)₂ZrTPP. The thermodynamic and optical characteristics of (AcO)₂ZrTPP required for using the complex in the detection of bioactive bases were studied.     

Synthesis and stability of bis(acetato)(5,10,15,20-tetraphenylporphyrinato)zirconium(IV)

The results of studying a unique synthesis method, the kinetics and mechanism of dissociation in acid media, and the stability of a new octacoordinated zirconium complex with two bidentate acetate ligands and one 5,10,15,20-tetraphenylporphine ligand, (AcO)₂ZrTPP, are presented. The method of synthesis is distinguished by the use of stable ZrOCl₂ in the complex formation reaction, instead of readily hydrolyzed zirconium tetrachloride, in boiling phenol, which exhibits the reduction properties. The UV, visible, IR, and ¹H NMR spectral parameters and the values of chromatographic mobility and stability of the complex are obtained. A protolytic dissociation scheme, which is universal for mixed porphyrin-containing zirconium complexes, is substantiated using data on the dissociation rates of an (Cl)₂ZrTPP analogue, depending on the temperature and acidity of the medium. The scheme includes a trimolecular rate-determining step (the complex ionized at one or both noncyclic ligands and two nonionized sulfuric acid molecules) and kinetically significant equilibria of dissociation of the noncyclic acido ligands and sulfuric acid.     

Kinetic and mechanistic studies of the interaction of 2-mercapto pyridine with dichloro[1-alkyl-2-(arylazo)imidazole]palladium(II) complexes

Nucleophilic substitution of Pd(RaaiR′)Cl₂ [(RaaiR′ = 1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-N=N-C₃H₂NN-1-R′; where R = H(a)/ Me(b)/ Cl(c) and R′ = Et(1)/Bz(2)] with 2-Mercaptopyridine (2-SH-Py) in acetonitrile (MeCN) at 298 K, to form [Pd₂(2-S-Py)₄], has been studied spectrophotometrically under pseudo-first-order conditions and the analyses support the nucleophilic association path. The reaction follows the rate law, Rate = {k ₀ + k [2-SH-Py] ₀ ² }[Pd(RaaiR′)Cl₂]: first order in Pd(RaaiR′)Cl₂ and second order in 2-SH-Py. The rate of the reaction follows the order: Pd(RaaiEt)Cl₂ (1) < Pd(RaaiBz)Cl₂ (2) and Pd(MeaaiR′)Cl₂ (b) < Pd(HaaiR′)Cl₂ (a) < Pd(ClaaiR′)Cl₂ (c). External addition of Cl⁻ (LiCl) and HCl suppresses the rate (Rate ∝ 1/[Cl⁻]₀ & ∝1/[HCl]₀). The reactions have been studied at different temperatures (293–308 K) and activation parameters (Δ^‡ H° and Δ ^‡ S°) of the reactions were calculated from the Eyring plot and support the proposed mechanism.     

The thermodynamic characteristics of step complex formation in the (5,10,15,20-tetraphenylporphyrinato)(chloro)indium(III)-pyridine-toluene system

The thermodynamic characteristics, step mechanism, and spectral manifestations of step reactions between (5,10,15,20-tetraphenylporphyrinato)(chloro)indium(III) ((Cl)InTPP) and organic base pyridine (Py) in inert toluene were studied using spectrophotometric titration and physicochemical analysis of intermediate forms. The coordination of Py molecule (K ₁ = 9.45 × 10² l/mol at 298 K) with the formation of (Cl)(Py)InTPP, the substitution of Cl^? in (Cl)(Py)InTPP with the second Py molecule (K ₂ = 2.3 × 10² l/mol), and the coordination of the third Py molecule to produce [(Py)₃ InTPP]⁺ · Cl^? (K ₃ = 8.7 l/mol) were observed at the first, second, and third steps, respectively. The fourth reaction stage most likely corresponds to π?π complex formation equilibrium between the aromatic complex and pyridine with a 1: 2 stoichiometry. The thermodynamic parameters of step reactions ΔH ^° and ΔS ^° well correspond to the stoichiometric mechanism of the reaction. Prospects for the use of the metalloporphyrin as a receptor of organic N-bases are considered.     

Quantum chemical study of C—H bond activation in methane molecule by AuIII aqua chloride complexes

The mechanism of the reactions of methane with the gold(III) complexes [AuCl_x(H₂O)_{4− x} ]^3−x (x = 2, 3, or 4) was studied by the DFT/PBE method with the SBK basis set. High activation barriers obtained for the reactions of [AuCl₄]⁻ and [Au(H₂O)Cl₃] with methane suggest these reactions cannot proceed under mild conditions. The reaction of the [Au(H₂O)₂Cl₂]⁺ complex with methane has a rather low energy barrier and proceeds through the formation of an intermediate complex. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 191–201, February, 2006.     

Standard molar enthalpies of formation of [RE(Gly)<Subscript>4</Subscript>(Im)(H<Subscript>2</Subscript>O)](ClO<Subscript>4</Subscript>)<Subscript>3</Subscript> (<Emphasis Type="Italic">RE</Emphasis>=Eu,Sm)

The two complexes, [RE(Gly)₄(Im)(H₂O)](ClO₄)₃(s)(RE = Eu, Sm), have been synthesized and characterized. The standard molar enthalpies of reaction for the following reactions, RECl₃·6H₂O(s)+4Gly(s)+Im(s)+3NaClO₄(s) = =[RE(Gly)₄(Im)(H₂O)](ClO₄)₃(s)+3NaCl(s)+5H₂O(l), were determined by solution-reaction colorimetry. The standard molar enthalpies of formation of the two complexes at T = 298.15 K were derived as Δ_f H _m^Θ {Eu(Gly)₄(Im)(H₂O)}(ClO₄)₃(s)} = = −(3396.6±2.3) kJ mol⁻¹ and Δ_f H _m^Θ {Sm(Gly)₄(Im)(H₂O)}(ClO₄)₃(s)} = −(3472.7±2.3) kJ mol⁻¹, respectively.     

Chemistry of azopyrimidines. Part IV. Aromatic hydroxylation in palladium(II)-arylazopyrimidines

2-(Arylazo)pyrimidines (aapm) are N,N′-chelating ligands and synthesise orange-red complexes of composition [Pd(aapm)Cl₂],1, with Pd(MeCN)₂Cl₂ in MeCN. The complex hascis-PdCl₂ configuration [v(Pd-Cl): 340, 360 cm⁻¹]. The treatment of Tollen’s reagent (‘AgOH’) leads to chelatative hydroxylation in the pendant aryl ring, affording a green phenolato complex, Pd(aapmO)Cl,5 (aapmO is deprotonated 2-((8-hydroxo)arylazo)pyrimidine). The reaction is also carried out by controlled addition of dilute sodium hydroxide in air or by the addition of PhIO/m-chloroperbenzoic acid to a MeCN suspension of the complex. A single Pd-Cl stretch at 360 cm⁻¹ supports the composition of phenolato complex. Unlike Pd(aapm)Cl₂ the hydroxylated product, Pd(aapmO)Cl, has a structured intense absorption in the visible region near 670 nm. The Pd-Cl bond in Pd(aapmO)Cl is highly sensitive to nucleophilic substitution and slowly hydrolyses in aqueous medium. For Parts I and II, see references 16 and 17; for Part III,Synth. React. Inorg. Met.- Org. Chem. (in press)     

A new unsymmetrical vic-dioxime bearing salicylaldehyde 4-aminobenzoylhydrazone and its homo-and heterotrinuclear complexes with copper(II) and nickel(II) ions

A new vic-dioxime, N-{4-[[(2-hydroxyphenyl)methylene]hydrazinecarbonyl]phenyl}aminoglyoxime (H₃L), was prepared by the reaction of anti-chloroglyoxime with salicylaldehyde 4-aminobenzoylhydrazone. The reaction of H₃L with Cu(II) salts and an appropriate simple ligand gave only homotrinuclear complexes [Cu₃(HL)₂X₂], whereas the reaction of H₃L with Ni(II) salts gave mono-and homotrinuclear complexes [Ni(H₂L)₂ and Ni₃(HL)₂X₂]. Also, heterotrinuclear complexes of H₃L were prepared by the reaction of Ni(H₂L)₂ with Cu(II) salt and an appropriate simple ligand, [NiCu₂(HL)₂X₂], X = Cl⁻, NO ₃ ⁻ , SCN⁻, CN⁻, and N ₃ ⁻ . The new vic-dioxime and its complexes were identified by elemental analyses, IR, ¹H NMR, UV-VIS, magnetic susceptibility, and mass spectral data. The elemental analyses and spectral data indicated that the hydrazone side of H₃L acted as monobasic tridentate and the fourth position was occupied by simple ligands, such as Cl⁻, NO ₃ ⁻ , SCN⁻, CN⁻, and N ₃ ⁻ . The text was submitted by the author in English.     

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

The kinetics of the reactions between Fe(phen) ₃ ²⁺ [phen = tris–(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm⁻³ (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H⁺] = 0.01 mol dm⁻³) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm³ mol⁻¹ s⁻¹. Ion-pair constants K _ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 10⁴, 3.00 × 10² and 4.02 × 10⁴ mol⁻¹ dm⁻³ for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K⁻¹ mol⁻¹) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K⁻¹) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E _a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm³ mol⁻¹ s⁻¹) = (7.079 ± 0.035) × 10¹⁶, (1.413 ± 0.011) × 10¹⁷, and (9.772 ± 0.027) × 10²⁰ for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions.     

Complexes of Co(II), Ni(II), and Cu(II) chlorides and bromides with tetrazol-1-yl-tris(hydroxymethyl)methane: Synthesis and structure

The reactions of Co(II), Ni(II), and Cu(II) chlorides and bromides and their metallic powders with tetrazol-1-yl-tris(hydroxymethyl)methane (L) afforded new complexes ML₂Hal₂ · mH₂O(M = Co(II) or Ni(II), Hal = Cl⁻; M = Cu(II), Hal = Cl⁻ or Br⁻, m = 0; and M = Co(II) or Ni(II), Hal = Br⁻, m = 2), MLnCl₂ (M = Co(II) or Ni(II), n = 2 or 4; M = Cu(II), n = 2), and MLnBr₂ · mH₂O (M = Ni(II), n = 2, m = 2; M = Cu(II), n = 2, m = 0). The compositions and structures of the synthesized complexes were determined by elemental analysis, IR spectroscopy (50–4000 cm⁻¹), and X-ray diffraction analysis. The introduction of a bulky substituent into position 1 of the tetrazole cycle was shown to exert almost no effect on the coordination mode but affected the composition and structure of the complexes.     

Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)₂(H₂O)₂]³⁺ in CF₃SO₃H solution ([Co^III] = (2–6) × 10⁻³ m, [ptz] = 2.5 × 10⁻⁴ m, [H⁺] = 0.02 − 0.05 m, I = 0.1 m (H⁺, K⁺, CF₃SO ₃ ⁻ ), T = 288–308 K) and [Co(edta)]⁻ in aqueous HCl ([Co^III] = (1 − 4) × 10⁻³ m, [ptz] = 1 × 10⁻⁴ m, [H⁺] = 0.1 − 0.5 m, I = 1.0 m (H⁺, Na⁺, Cl⁻), T = 313 − 333 K) were studied under the condition of excess Co^III using u.v.–vis. spectroscopy. The reactions produce a Co^II species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k _obs) on [Co^III] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)₂(H₂O)₂]³⁺ ion was found to be independent of [H⁺]. In the case of the [Co(edta)]⁻ ion, the k _obs dependence on [H⁺] was linear and the increasing [H⁺] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows: ΔH ^≠ = 105 ± 4 kJ mol⁻¹, ΔS ^≠ = 93 ± 11 J K⁻¹mol⁻¹ for [Co(en)₂(H₂O)₂]³⁺; ΔH ^≠ = 67 ± 9 kJ mol⁻¹, ΔS ^≠ = − 54 ± 28 J K⁻¹mol⁻¹ for [Co(edta)]⁻.     

Catecholase biomimetic catalytic activity of copper(II) complexes with 2-methyl-3-amino-(3H)-quinazolin-4-one

The oxidation of catechol by molecular oxygen in the presence of a catalytic amount of copper(II) complex with 2-methyl-3-amino-(3H)quinazoline-4-one (MAQ) and various anions (Cl⁻, Br⁻, ClO ₄ ⁻ , SCN⁻, NO ₃ ⁻ and SO ₄ ^– ) was studied. The catecholase biomimetic catalytic activity of the copper(II) complexes has been determined spectrophotometrically by monitoring the oxidative transformation of catechol to the corresponding light absorbing o-quinone (Q). The rate of the catalytic oxidation reaction was investigated and correlated with the catalyst structure, time, concentration of catalyst and substrate and finally solvent effects. Addition of pyridine or Et₃N showed a dramatic effect on the rate of oxidation reaction. Kinetic investigations demonstrate that the rate of oxidation reaction has a first order dependence with respect to the catalyst and catechol concentration and obeying Michaelis–Menten Kinetics. It was shown that the catalytic activity depends on the coordination environment of the catalyst created by the nature of counter anions bound to copper(II) ion in the complex molecule and follows the order: Cl⁻ > NO ₃ ⁻ > Br⁻ > SO ₄ ^– > SCN⁻ > ClO ₄ ⁻ . To further elucidate the catalytic activity of the complexes, their electrochemical properties were investigated and the catecholase mimetic activity has been correlated with the redox potential of the Cu²⁺/Cu⁺ couple in the complexes.     

A study of ion exchange equilibrium for some uni-univalent and uni-divalent reaction systems using strongly basic anion exchange resin Indion-830 (Type 1)

A study of the thermodynamics of ion exchange equilibrium for uni-univalent Cl⁻/I⁻, Cl⁻/Br⁻ and uni-divalent Cl⁻/SO ₄ ²⁻ , Cl⁻/C₂O ₄ ²⁻ reaction systems was carried out using ion exchange resin Indion-830 (Type 1). The equilibrium constant K was calculated by taking into account the activity coefficients of ions both in solution and in the resin phase. For uni-univalent ion exchange reaction systems, the equilibrium constants K′ were also calculated from the mole fraction of ions in the resin phase. The K values calculated for uni-univalent and uni-divalent anion exchange reaction systems increased as the temperature grew, indicating the endothermic character of the exchange reactions with enthalpies of 38.2, 32.3, 7.6, and 11.4 kJ/mol, respectively. The article is published in the original.     

Acenaphthylene-1,2-diamine radical cation. Molecular structure of the [(dpp-BIAN)H2]·+[X]− complex ((dpp-BIAN)H2 is N,N′-bis(2,6-diisopropylphenyl)-acenaphthylene-1,2-diamine; X = Cl or I)

Oxidation of N,N′-bis(2,6-diisopropylphenyl)acenaphthylene-1,2-diamine (dpp-BIAN)H₂ with silicon tetrachloride or mercury(II) chloride affords the [(dpp-BIAN)H₂]·⁺[Cl]⁻ compound. The corresponding iodine derivative, [(dpp-BIAN)H₂]·⁺[I]⁻, was prepared by hydrolysis of the reaction products of the magnesium complex (dpp-BIAN)Mg(THF)₃ with tetraiodosilane. X-ray diffraction study demonstrated that the [(dpp-BIAN)H₂]^·+ radical cation in these compounds chelates the corresponding halide anion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 436–440, March, 2006.     

Protonation of Chloro-, Bromo- and Iodo-pentacyanocobaltate(III) Complexes

The reactions between Fe(Phen)₃²⁺[phen = tris-(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been studied in aqueous acidic solutions at 25 °C and ionic strength in the range I = 0.001–0.02 mol dm⁻³ (NaCl/HCl). Plots of k₂ versus √I, applying Debye–Huckel Theory, gave the values −1.79 ± 0.18, −1.65 ± 0.18 and 1.81 ± 0.10 as the product of charges (Z_AZ_B) for the reactions of Fe(Phen)₃²⁺ with the chloro-, bromo- and iodo- complexes respectively. Z_AZ_B of ≈ −2 suggests that the charge on these Co^III complexes cannot be −3 but is −1. This suggests the possibility of protonation of these Co^III complexes. Protonation was investigated over the range [H⁺] = 0.0001 −0.06 mol dm⁻³ and the protonation constants K_a obtained are 1.22 × 10³, 7.31 × 10³ and 9.90 × 10² dm⁶ mol⁻³ for X = Cl, Br and I, respectively.     

Studies on the magnetic properties of two cobalt(II) complexes bearing 1,4-phenylenediacetate ligands

One reported compound [Co(PDA)(4,4′-bipy)]_n·nH₂O and one new compound [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O were prepared by the reactions of Co(NO₃)₂·6H₂O or Co(OH)₂ with 1,4-phenylenediacetic acid (H₂PDA) in the presence of the ancillary ligands 4,4′-bipyridine (4,4′-bipy) or imidazole (Im), and their magnetic properties were investigated. The presence of 4,4′-bipy in [Co(PDA)(4,4′-bipy)]_n·nH₂O results in a μ ₃-bridging mode of the PDA²⁻ ligand with one μ ₂-carboxylato group and one chelating carboxylato group and the construction of a 2D framework as reported in the literature. The introduction of Im ligand in [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O helps to construct a one dimensional chain with the two carboxylato groups of PDA²⁻ ligand in monodentate coordination modes. The magnetic studies reveal the presence of dominant antiferromagnetic interaction in [Co(PDA)(4,4′-bipy)]_n·nH₂O with a field-induced magnetic transition due to spin-flop. Magnetically, [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O presents a mononuclear structure. This work reveals that the introduction of ancillary ligands in the Co(II)-PDA system adjusts the linking modes of PDA²⁻ and therefore the resulting frameworks and their magnetic properties.     

Thermodynamics of mixed-ligand complexation of mercury(II) ethylenediaminetetraacetate with histidine and lysine in aqueous solution

The formation of mixed-ligand complexes HgEdtaIm²⁻, HgEdtaL³⁻, HgEdtaHL²⁻, and (HgEdta)₂L⁵⁻ (L is histidine, lysine; Im is imidazole) was studied by calorimetry, pH-metry, and NMR spectroscopy. The thermodynamic parameters (logK, ΔrG ⁰, ΔrH, Δr _S) for the reactions of complex formation at 298.15 K and ion strength of 0.5 (KNO₃) were determined. The most likely coordination mode for the complexone and amino acid in the mixed complexes was identified.     

Kinetic studies on the dehydration of trans-dichlorotetrammine-cobalt (III) iodate dihydrate

Summary The dehydration of trans-[Co(NH₃)₄Cl₂)IO₃·2H₂O was studied isothermally by t.g.a. In the 0.1 < α < 0.8 range, where α is the fraction of the reaction complete, most of the runs gave the best fit to a second order rate law. Early stages of the reaction appear to follow a rate law based on reaction order while later stages (0.3 < α < 0.5) appear to be controlled by diffusion of H₂O. The reaction in the 0.1 < α < 0.3 range gave a best fit to a third order rate law, while the 0.3 < α < 0.5 range gave the best fit to a three dimensional control rate law. The activation energy for the overall reaction was ca. 103 kJ mol⁻¹. For α < 0.3 the activation energy was ca. 79.9 kJ mol⁻¹, but for 0.3 < α < 0.5 it was ca. 110 kJ mol⁻¹.     

Theoretical study of the structure and stability of the Na2Cl+, NaCl 2? , Na3Cl 2+ , and Na2Cl 3? ions

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na₂Cl⁺, NaCl ₂ ⁻ , Na₃Cl ₂ ⁺ , and Na₂Cl ₃ ⁻ ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na₂Cl⁺ and NaCl ₂ ⁻ triatomic ions have a linear equilibrium D _∞h configuration. The pentaatomic ions can exist in the form of the D _∞h linear isomer, C _2v planar cyclic isomer, or D _3h bipyramidal isomer. At ∼1000 K the Na₃Cl ₂ ⁺ and Na₂Cl ₃ ⁻ ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions Δ_f H ⁰(0 K) was determined: 230 ± 2 kJ/mol (Na₂Cl⁺), −96 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ), −616 ± 2 kJ/mol (NaCl ₂ ⁻ ), and −935 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ). Original Russian Text Copyright ? 2007 by T. P. Pogrebnaya, A. M. Pogrebnoi, and L. S. Kudin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 6, pp. 1053–1061, November–December, 2007.     

Kinetics and Mechanism of the Reactions of Picolinic Acid with Dichloro-{1-alkyl-2-(arylazo)imidazole}palladium(II) Complexes

The reaction between Pd(N,N′)Cl₂ [N,N′ ≡ 1-alkyl-2-(arylazo)imidazole (N,N′) and picolinic acid (picH) have been studied spectrophotometrically at λ = 463 nm in MeCN at 298 K. The product is [Pd(pic)₂] which has been verified by the synthesis of the pure compound from Na₂[PdCl₄] and picH. The kinetics of the nucleophilic substitution reaction have been studied under pseudo-first-order conditions. The reaction proceeds in a two-step-consecutive manner (A → B → C); each step follows first order kinetics with respect to each complex and picH where the rate equations are: Rate 1 = {k′₀ + k′₂[picH]₀} × [Pd(N,N′)Cl₂] and Rate 2 = {k′′₀ + k′′₂[picH]₀}[Pd(N,O)(monodentate N,N′)Cl₂] such that the first step second order rate constant (k′₂) is greater than the second step second order rate constant (k′′₂). External addition of Cl⁻ (as LiCl) suppresses the rate. Increase in π-acidity of the N,N′ ligand, increases the rate. The reaction has been studied at different temperatures and the activation parameters (Δ^‡H° and Δ^‡S°) were calculated from the Eyring plot.