Why Does the Intramolecular Trimethylene‐Bridged Frustrated Lewis Pair Mes2PCH2CH2CH2B(C6F5)2 Not Activate Dihydrogen?

The methyl labelled C₃‐bridged frustrated phosphane borane Lewis pair (P/B FLP) 2 b was prepared by treatment of Mes₂PCl with a methallyl Grignard reagent followed by anti‐Markovnikov hydroboration with Piers’ borane [HB(C₆F₅)₂)]. The FLP 2 b is inactive toward dihydrogen under typical ambient conditions, in contrast to the C₂‐ and C₄‐bridged FLP analogues. Dynamic NMR spectroscopy showed that this was not due to kinetically hindered P???B dissociation of 2 b . DFT calculations showed that the hydrogen‐splitting reaction of the parent compound 2 a is markedly endergonic. The PH⁺/BH^? H₂‐splitting product of 2 b was indirectly synthesized by a sequence of H⁺/H^? addition. It lost H₂ at ambient conditions and confirmed the result of the DFT analysis.     

A Frustrated and Confused Lewis Pair

We report a new class of frustrated Lewis pairs (FLPs) by the hydroboration of bulky isocyanates ^iPr2ArNCO (^iPr2Ar=2,6‐iPr₂C₆H₃) and ^Ph2tBuArNCO (^Ph2tBuAr=2,6‐Ph₂‐4‐tBuC₆H₂) with Piers’ borane (HB(C₆F₅)₂). While hydroboration of smaller isocyanates such as ^iPr2ArNCO leads to isocyanate—N/B FLP adducts, hydroboration of the bulkier ^Ph2tBuArNCO allows isolation of the substrate‐free aminoborane with a short, covalent N?B bond. This confused FLP reversibly binds unsaturated substrates such as isocyanates and isocyanides, suggesting the intermediacy of a “normal” FLP along the reaction pathway, supported by high‐level DFT studies and variable‐temperature NMR spectroscopy. These results underscore the possibility of FLP behavior in systems that possess no obvious frustrated Lewis acid–base interaction.     

Kinetic isotope effects and rate constants for the gas‐phase reactions of three deuterated toluenes with OH from 298 to 353 K

The rate constants for the gas‐phase reactions of three deuterated toluenes with hydroxyl radicals were measured using the relative rate technique over the temperature range 298–353 K at about 1 atm total pressure. The OH radicals were generated by photolysis of H₂O₂, and helium was used as the diluent gas. The disappearance of reactants was followed by online mass spectrometry, which resulted in high time resolution, allowing for a large amount of data to be collected and used in the determination of the Arrhenius parameters. The following Arrhenius expressions have been determined for these reactions (in units of cm³ molecule^?1 s^?1): k=(6.42_?0.99^+1.17)×10^?13exp [(661±54)/T] for toluene‐d₃, k=(2.11_?0.69^+1.03)×10^?12exp [(287±128)/T]for toluene‐d₅, and k=(1.40^+0.44_?0.33)×10^?12exp [(404±88)/T]for toluene‐d₈. The kinetic isotope effects (KIEs, k_H/k_D) of these reactions were 1.003 ± 0.042 for all three compounds at 298 K. The KIE for toluene‐d₃ was temperature dependent; at 350 K, its KIE was 1.122^+0.048_?0.046. The KIE of toluene‐d₅ and toluene‐d₈ did not vary significantly with temperature. These KIE results suggest that methyl H‐atom abstraction is more important than aromatic OH addition at higher temperatures. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 821–827, 2012     

Kinetics of thermal gas‐phase decomposition of 2‐bromopropene using static system

The gas phase elimination kinetics of 2‐bromopropene was studied over the temperature range of 571–654 K and pressure range of 12–46 Torr using the seasoned static reaction system. Propyne was the only olefinic product formed and accounted for >98% of the reaction. This product was formed by homogeneous, unimolecular pathways with high‐pressure first‐order rate constant k_∞ given by the equation k_∞ = 10^{13.47 ± 0.6} exp^{?208.2 ± 6.7} (kJ mol^?1)/RT. The error limits are 95% certainty limits. The observed Arrhenius parameters are consistent with the four centered activated complex. The presence of methyl group on α‐carbon lowers the activation energy by 41 kJ mol^?1. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 1–5, 2007     

氢过碘酸）合银（III）配离子氧化L-脯氨酸的反应动力学及机理

L-脯氨酸独有的亚胺基使其在生物医药领域具有许多独特的功能,并广泛用作不对称有机化合物合成的有效催化剂。本文在碱性介质中研究了二（氢过碘酸）合银（III）配离子氧化 L-脯氨酸的反应。经质谱鉴定,脯氨酸氧化后的产物为脯氨酸脱羧生成的 γ-氨基丁酸盐;氧化反应对脯氨酸及Ag(III) 均为一级;二级速率常数 k′ 随 [IO₄^-] 浓度增加而减小,而与 [OHˉ] 的浓度几乎无关;推测反应机理应包括 [Ag(HIO₆)₂]^5-与 [Ag(HIO₆)(H₂O)(OH)]^2-之间的前期平衡,两种Ag（III）配离子均作为反应的活性组分,在速控步被完全去质子化的脯氨酸平行地还原,两速控步对应的活化参数为： k₁ (25 ^oC)＝1.87±0.04（mol·L^-1)^-1s^-1,∆ H₁^≠＝45±4 kJ · mol^-1, ∆ S₁^≠＝-90±13 J· K^-1·mol^-1 and k₂ (25 ^oC) ＝3.2±0.5（mol·L^-1)^-1s^-1, ∆ H₂^≠＝34±2 kJ · mol^-1, ∆ S₂^≠＝-122 ±10 J· K^-1·mol^-1。本文第一次发现 [Ag(HIO₆)₂]^5-配离子也具有氧化反应活性。     

Kinetics and mechanisms in carbocationic polymerization: The quest for true rate constants

This article is a critical analysis of kinetic dataavailable on carbocationic polymerizations. A survey of published propagation rate constant (k_p) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6‐trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, k_p = 1.35 × 10⁴ L mol^?1 s^?1 was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded k_p = 1.01 × 10⁷ L mol^?1 s^?1, close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2‐ chloro‐2,4, 4‐ trimethylpentane (TMPCl)/TiCl₄ from various laboratories yielded of ΔH ～?25 and ?34.5 kJ/mol for high and low TMPCl/TiCl₄ ratios, respectively. Aromatic (cumyl‐type) initiators show ΔH ～ ?40 kJ/mol, whereas H₂O/TiCl₄ in the presence of the strong electron‐ pair donor dimethylacetamide gave ΔH = ?12 kJ/mol. The significant differences indicate different underlying mechanisms with complex elementary reactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5394–5413, 2005     

Kinetics and Mechanisms for the Reactions of Phenyl Radical with Ketene and its Deuterated Isotopomer: An Experimental and Theoretical Study

Kinetics and mechanism for the reaction of phenyl radical (C₆H₅) with ketene (H₂C_β?C_α?O) were studied by the cavity ring‐down spectrometric (CRDS) technique and hybrid DFT and ab initio molecular orbital calculations. The C₆H₅ transition at 504.8 nm was used to detect the consumption of the phenyl radical in the reaction. The absolute overall rate constants measured, including those for the reaction with CD₂CO, can be expressed by the Arrhenius equation k=(5.9±1.8)×10¹¹ exp[?(1160±100)/T] cm³ mol^?1 s^?1 over a temperature range of 301–474 K. The absence of a kinetic isotope effect suggests that direct hydrogen abstraction forming benzene and ketenyl radical is kinetically less favorable, in good agreement with the results of quantum chemical calculations at the G2MS//B3LYP6‐31G(d) level of theory for all accessible product channels, including the above abstraction and additions to the C_α, C_β, and O sites. For application to combustion, the rate constants were extrapolated over the temperature range of 298–2500 K under atmospheric pressure by using the predicted transition‐state parameters and the adjusted entrance reaction barriers E_α=E_β=1.2 kcal mol^?1; they can be represented by the following expression in units of cm³ mol^?1 s^?1: k_α=6.2×10¹⁹ T^?2.3 exp[?7590/T] and k_β=3.2×10⁴ T^2.4 exp[?246/T].     

Kinetics of phenyl radical reactions with propane,n‐butane,n‐hexane,and n‐octane: Reactivity of C6H5 toward the secondary C?H bond of alkanes

The kinetics of C₆H₅ reactions with n‐C_nH_2n+2 (n = 3, 4, 6, 8) have been studied by the pulsed laser photolysis/mass spectrometric method using C₆H₅COCH₃ as the phenyl precursor at temperatures between 494 and 1051 K. The rate constants were determined by kinetic modeling of the absolute yields of C₆H₆ at each temperature. Another major product C₆H₅CH₃ formed by the recombination of C₆H₅ and CH₃ could also be quantitatively modeled using the known rate constant for the reaction. A weighted least‐squares analysis of the four sets of data gave k (C₃H₈) = (1.96 ± 0.15) × 10¹¹ exp[?(1938 ± 56)/T], and k (n‐C₄H₁₀) = (2.65 ± 0.23) × 10¹¹ exp[?(1950 ± 55)/T] k (n‐C₆H₁₄) = (4.56 ± 0.21) × 10¹¹ exp[?(1735 ± 55)/T], and k (n?C₈H₁₈) = (4.31 ± 0.39) × 10¹¹ exp[?(1415 ± 65)T] cm³ mol^?1 s^?1 for the temperature range studied. For the butane and hexane reactions, we have also applied the CRDS technique to extend our temperature range down to 297 K; the results obtained by the decay of C₆H₅ with CRDS agree fully with those determined by absolute product yield measurements with PLP/MS. Weighted least‐squares analyses of these two sets of data gave rise to k (n?C₄H₁₀) = (2.70 ± 0.15) × 10¹¹ exp[?(1880 ± 127)/T] and k (n?C₆H₁₄) = (4.81 ± 0.30) × 10¹¹ exp[?(1780 ± 133)/T] cm³ mol^?1 s^?1 for the temperature range 297‐‐1046 K. From the absolute rate constants for the two larger molecular reactions (C₆H₅ + n‐C₆H₁₄ and n‐C₈H₁₈), we derived the rate constant for H‐abstraction from a secondary C? H bond, k_s?CH = (4.19 ± 0.24) × 10¹⁰ exp[?(1770 ± 48)/T] cm³ mol^?1 s^?1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 49–56, 2004     

ArticleMicrocalorimetric Investigation on the Kinetics of the Oxidation of Ascorbic Acid with Hydrogen Peroxide

Introduction Ascorbic acid is still attractive due to its wide-rang-ing role in biological processes and chemical fields. Consequently the knowledge of the kinetics of ascorbate reduction is highly desirable. In previous papers,1-11 spectroscopy and electronics methods were generally used to study the oxidation of ascorbic acid, and only a first-order reaction rate constant was obtained by these methods. Since the reaction is a complicated process involving several reactive species, the previo…     

Autoinduced Catalysis and Inverse Equilibrium Isotope Effect in the Frustrated Lewis Pair Catalyzed Hydrogenation of Imines

The frustrated Lewis pair (FLP)‐catalyzed hydrogenation and deuteration of N‐benzylidene‐tert‐butylamine ( 2 ) was kinetically investigated by using the three boranes B(C₆F₅)₃ ( 1 ), B(2,4,6‐F₃‐C₆H₂)₃ ( 4 ), and B(2,6‐F₂‐C₆H₃)₃ ( 5 ) and the free activation energies for the H₂ activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol^?1) for the H₂ activation by the imine compared to the amine. Surprisingly, the imine reduction using D₂ proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect.     

Structure–Reactivity Relationship in the Frustrated Lewis Pair (FLP)‐Catalyzed Hydrogenation of Imines

The autoinduced, frustrated Lewis pair (FLP)‐catalyzed hydrogenation of 16‐benzene‐ring substituted N‐benzylidene‐tert‐butylamines with B(2,6‐F₂C₆H₃)₃ and molecular hydrogen was investigated by kinetic analysis. The pK_a values for imines and for the corresponding amines were determined by quantum‐mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k₁ (simple catalytic cycle) and k₂ (autoinduced catalytic cycle) with pK_a difference between imine and amine pairs (ΔpK_a) or Hammett's σ parameter served as useful parameters to establish a structure–reactivity relationship for the FLP‐catalyzed hydrogenation of imines.     

Ab initio reaction path for cisplatin interaction with L‐cysteine and L‐methionine

Ab initio calculations are used to track the reaction pathway of interaction between cisplatin and the sulfur‐containing amino acids cysteine (Cys) and methionine (Met). Structures of all reactive species as well as thermodynamic and kinetic properties were calculated and discussed based on the role played by the level of theory. Twenty‐three different levels of theory were examined including HF, DFT, and perturbation theory at MP2 and MP4(SDQ) orders. The rate constant for a second‐order associative ligand exchange mechanism (k₂) was calculated by means of transition state theory. This quantity is quite sensitive to small fluctuation of activation free energy, therefore is a good benchmark to assess the performance of different methods of calculations. The k₂ values predicted by DFT methods were in best agreement with experiment, found equal to (10²k₂ in M^?1 s^?1) 3.42 for Met (PBE1PBE) and 1.90 for Cys (B3P86). The experimental values are 3.6 and 2.2 for Met and Cys, respectively. The solvent effect plays a primary role to the kinetic properties, accounting for ～30% of the activation Gibbs free energy. The outcomes from the present study promptly show the adequacy of distinct theoretical approaches to describe the reactivity of cisplatin, thus might be useful for further studies involving other Pt(II) complexes. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Kinetics of the gas‐phase reactions of cyclo‐CF2CFXCHXCHX – (X = H,F, Cl) with OH radicals at 253–328 K

Rate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo‐CF₂CF₂CHFCH₂? (k₁), trans‐cyclo‐CF₂CF₂CHClCHF? (k₂), cyclo‐CF₂CFClCH₂CH₂? (k₃), trans‐cyclo‐CF₂CFClCHClCH₂? (k₄), and cis‐cyclo‐CF₂CFClCHClCH₂? (k₅) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H₂O? O₃? O₂? He gas mixture in an 11.5‐dm³ temperature‐controlled reaction chamber. Rate constants of k₁ = (5.52 ± 1.32) × 10^?13 exp[–(1050 ± 70)/T], k₂ = (3.37 ± 0.88) × 10^?13 exp[–(850 ± 80)/T], k₃ = (9.54 ± 4.34) × 10^?13 exp[–(1000 ± 140)/T], k₄ = (5.47 ± 0.90) × 10^?13 exp[–(720 ± 50)/T], and k₅ = (5.21 ± 0.88) × 10^?13 exp[–(630 ± 50)/T] cm³ molecule^?1 s^?1 were obtained at 253–328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%–15% uncertainty to the uncertainty of k₁–k₅. The reactivity trends of these OH radical reactions were analyzed by using a collision theory–based kinetic equation. The rate constants k₁–k₅ as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their C? H bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo‐CF₂CF₂CHFCH₂? , trans‐cyclo‐CF₂CF₂CHClCHF? , cyclo‐CF₂CFClCH₂CH₂? , trans‐cyclo‐CF₂CFClCHClCH₂? , and cis‐cyclo‐CF₂CFClCHClCH₂? , respectively, by scaling from the lifetime of CH₃CCl₃. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532–542, 2009     

Kinetic study of the reactions of atomic chlorine with several volatile organic compounds at 240–340 K

The rate constant for the reactions of atomic chlorine with 1,4‐dioxane (k₁), cyclohexane (k₂), cyclohexane‐d₁₂(k₃), and n‐octane (k₄) has been determined at 240–340 K using the relative rate/discharge fast flow/mass spectrometer (RR/DF/MS) technique developed in our laboratory. Essentially, no temperature dependence for these reactions was observed over this temperature range, with an average of k₁ = (1.91 ± 0.20) × 10^?10 cm³ molecule^?1 s^?1, k₂ = (2.91 ± 0.31) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.73 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1, and k₄ = (3.22 ± 0.36) × 10^?10 cm³ molecule^?1 s^?1, respectively. The kinetic isotope effect of the reaction of cyclohexane with atomic chlorine has also been determined to be 1.14 by directly monitoring the decay of both cyclohexane and cyclohexane‐d₁₂ in the presence of chlorine atoms, which is consistent with the literature value of 1.20. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 386–398, 2006     

Synthesis of Molecular Wires of Linear and Branched Bis(terpyridine)‐Complex Oligomers and Electrochemical Observation of Through‐Bond Redox Conduction

Films of linear and branched oligomer wires of Fe(tpy)₂ (tpy=2,2′:6′,2′′‐terpyridine) were constructed on a gold‐electrode surface by the interfacial stepwise coordination method, in which a surface‐anchoring ligand, (tpy? C₆H₄N?NC₆H₄? S)₂ ( 1 ), two bridging ligands, 1,4‐(tpy)₂C₆H₄ ( 3 ) and 1,3,5‐(C?C? tpy)₃C₆H₃ ( 4 ), and metal ions were used. The quantitative complexation of the ligands and Fe^II ions was monitored by electrochemical measurements in up to eight complexation cycles for linear oligomers of 3 and in up to four cycles for branched oligomers of 4 . STM observation of branched oligomers at low surface coverage showed an even distribution of nanodots of uniform size and shape, which suggests the quantitative formation of dendritic structures. The electron‐transport mechanism and kinetics for the redox reaction of the films of linear and branched oligomer wires were analyzed by potential‐step chronoamperometry (PSCA). The unique current‐versus‐time behavior observed under all conditions indicates that electron conduction occurs not by diffusional motion but by successive electron hopping between neighboring redox sites within a molecular wire. Redox conduction in a single molecular wire in a redox‐polymer film has not been reported previously. The analysis provided the rate constant for electron transfer between the electrode and the nearest redox‐complex moiety, k₁ (s^?1), as well as that for intrawire electron transfer between neighboring redox‐complex moieties, k₂ (cm² mol^?1 s^?1). The strong effect of the electrolyte concentration on both k₁ and k₂ indicates that the counterion motion limits the electron‐hopping rate at lower electrolyte concentrations. Analysis of the dependence of k₁ and k₂ on the potential gave intrinsic kinetic parameters without overpotential effects: k₁⁰=110 s^?1, k₂⁰=2.6×10¹² cm² mol^?1 s^?1 for [n Fe 3 ], and k₁⁰=100 s^?1, k₂⁰=4.1×10¹¹ cm² mol^?1 s^?1 for [n Fe 4 ] (n=number of complexation cycles).     

1，1－二氨基2，2－二硝基乙烯（DADE）的热化学性质、热行为和热分解机理

The constant-volume combustion energy, △cU （DADE, s, 298.15 K）, the thermal behavior, and kinetics and mechanism of the exothermic decomposition reaction of 1,1-diamino-2,2-dinitroethylene （DADE） have been investigated by a precise rotating bomb calorimeter, TG-DTG, DSC, rapid-scan fourier transform infrared （RSFT-IR） spectroscopy and T-jump/FTIR, respectively. The value of △cHm （DADE, s, 298.15 K） was determined as （-8518.09±4.59） j·g^-1. Its standard enthalpy of combustion, △cU （DADE, s, 298.15 K）, and standard enthalpy of formation, △fHm （DADE, s, 298.15 K） were calculated to be （-1254.00±0.68） and （- 103.98±0.73） kJ·mol^-1, respectively The kinetic parameters （the apparent activation energy Ea and pre-exponential factor A） of the first exothermic decomposition reaction in a temperature-programmed mode obtained by Kissinger＇s method and Ozawa＇s method, were Ek=344.35 kJ·mol^-1, AR= 1034.50 S^-1 and Eo=335.32 kJ·mol^-1, respectively. The critical temperatures of thermal explosion of DADE were 206.98 and 207.08 ℃ by different methods. Information was obtained on its thermolysis detected by RSFT-IR and T-jump/FTIR.     

Prussian Blue‐Modified Titanate Nanotubes: A Novel Nanostructured Catalyst for Electrochemical Reduction of Hydrogen Peroxide

Prussian blue (PB) modified titanate nanotubes (PB‐TiNT) have been synthesized by the reaction of Fe²⁺‐modified TiNT with hexacyanoferrate(III) ions. The rate constant for heterogeneous catalytic reaction between PB‐TiNT and H₂O₂ was found to be k=2×10⁴ dm³ mol^?1 s^?1, which is an order of magnitude higher than the values of k reported for conventionally prepared, electrochemically deposited PB films. On the PB‐TiNT modified electrode with subnanomolar surface concentration of PB (Γ(PB)=2.8×10^?11 mol/cm²), a stable, reproducible and linear response towards H₂O₂ was obtained in the concentration range 0.02–4 mM, with the sensitivity of 0.10 AM^?1 cm^?2 at ?150 mV.     

σ‐Insertive Mechanism versus Concerted Non‐insertive Mechanism in the Intramolecular Hydroamination of Aminoalkenes Catalyzed by Phenoxyamine Magnesium Complexes: A Synthetic and Computational Study

The phenoxyamine magnesium complexes [{ONN}MgCH₂Ph] ( 4 a : {ONN}=2,4‐tBu₂‐6‐(CH₂NMeCH₂CH₂NMe₂)C₆H₂O^?; 4 b : {ONN}=4‐tBu‐2‐(CH₂NMeCH₂CH₂NMe₂)‐6‐(SiPh₃)C₆H₂O^?) have been prepared and investigated with respect to their catalytic activity in the intramolecular hydroamination of aminoalkenes. The sterically more shielded triphenylsilyl‐substituted complex 4 b exhibits better thermal stability and higher catalytic activity. Kinetic investigations using complex 4 b in the cyclisation of 1‐allylcyclohexyl)methylamine ( 5 b ), respectively, 2,2‐dimethylpent‐4‐en‐1‐amine ( 5 c ), reveal a first‐order rate dependence on substrate and catalyst concentration. A significant primary kinetic isotope effect of 3.9±0.2 in the cyclisation of 5 b suggests significant N?H bond disruption in the rate‐determining transition state. The stoichiometric reaction of 4 b with 5 c revealed that at least two substrate molecules are required per magnesium centre to facilitate cyclisation. The reaction mechanism was further scrutinized computationally by examination of two rivalling mechanistic pathways. One scenario involves a coordinated amine molecule assisting in a concerted non‐insertive N?C ring closure with concurrent amino proton transfer from the amine onto the olefin, effectively combining the insertion and protonolysis step to a single step. The alternative mechanistic scenario involves a reversible olefin insertion step followed by rate‐determining protonolysis. DFT reveals that a proton‐assisted concerted N?C/C?H bond‐forming pathway is energetically prohibitive in comparison to the kinetically less demanding σ‐insertive pathway (ΔΔG^≠=5.6 kcal mol^?1). Thus, the σ‐insertive pathway is likely traversed exclusively. The DFT predicted total barrier of 23.1 kcal mol^?1 (relative to the {ONN}Mg pyrrolide catalyst resting state) for magnesium?alkyl bond aminolysis matches the experimentally determined Eyring parameter (ΔG^≠=24.1(±0.6) kcal mol^?1 (298 K)) gratifyingly well.     

Kinetics and mechanism of the reaction of allyl chloride with trichlorosilane catalyzed by carbon‐supported platinum

The kinetics of substrate conversions in the commercially important hydrosilylation of allyl chloride with trichlorosilane, catalyzed by active carbon‐supported platinum, as well as the yields of the main product (3‐chloropropyltrichlorosilane) and by‐products (tetrachlorosilane, propyltrichlorosilane) have been studied. On the basis of the measurements performed, the pseudo first‐order rate constants (k_obs, k₁ and k₂ from the model of competitive reactions) and activation energy (E_a = 11 kcal mol^?1 (46.2 kJ mol^?1)) were determined. The data obtained point to a non‐linear dependence of k_obs on the catalyst amount. From the kinetic relationships, the kinetic equation was deduced. All the results of kinetic, IR spectroscopic and thermogravimetric measurements, as well as the derived kinetic equation, have confirmed the general model of consecutive–competitive reaction involving the formation of a surface complex C₁ which can decompose in two directions according to the Chalk–Harrod mechanism. Copyright © 2003 John Wiley & Sons, Ltd.