Gamma radiation-initiated polymerization of styrene at high pressure. I. Kinetic parameters with intermittent irradiation

By adapting the rotating sector technique to provide an intermittent source of cobalt-60 radiation the activation volumes for all reaction steps of the bulk polymerization of styrene have been shown to be independent of pressure up to 208 MPa. The activation volumes determined for polymerization, initiation, propagation and termination were, respectively, ΔV^≠_pol = ?20.5 ± 0.22, ΔV^≠_i = +2.0 ± 0.18, ΔV^≠_p = ?18.6 ± 0.44, and ΔV^≠_t = +5.8 ± 0.55 cm³ mol^?. The values for the effect of pressure on the degree of polymerization ΔDP and the radical lifetime Δτ were, respectively, ?22.6 ± 0.16 and ?3.9 ± 0.29. The average radical lifetime increased from 4.5 s at atmospheric pressure to 6.3 s at 208 MPa. Because ΔV^≠_t is less than ΔV^≠_t and both are positive, the molecular weight increased with pressure at a faster rate than the polymerization rate. Although fewer radical chains were initiated per second under pressure the macroradical concentration increased with pressure because of the longer average lifetime of the radicals.     

A study of radical polymerization of N-vinylpyrrolidone in the presence of poly(methacrylic acid) templates by DSC

The template polymerization of N-vinylpyrrolidone (NVP) along syndiotactic poly(methacrylic acid) (s1-PMAA) templates has been studied by differential scanning calorimetry (DSC) using the scanning as well as the isothermal technique. The resulting Arrhenius plot covers a temperature range between 65 and 120°C and two parts can be distinguished. Below 80°C the overall activation energy, E_a, and entropy ΔS^≠, are 76 kJ · mol^?1 and ?79 J · mol^?1 · K^?1 respectively, in excellent agreement with previous dilatometric results. These values differ slightly from those of the blank polymerization leading to rate enhancement by a factor of only two. The small difference in activation parameters is explained by the occurrence of desolvation of st-PMAA chains during propagation of the polyvinylpyrrolidone (PVP) radicals along the template. Above 80°C, the decreasing tendency to form complexes between PVP and st-PMAA results in a decreasing template effect and a gradual change of apparent E_a and ΔS^≠ values towards those of the blank polymerization. Similar results were obtained with atactic and isotactic PMAA templates, but smaller rate enhancements were observed due to weaker complex formation.     

Radical polymerization of methyl methacrylate in the presence of isotactic poly(methyl methacrylate). VIII. Influence of template concentration

The influence of template concentration on the radical polymerization of methyl methacrylate along isotactic poly(methyl methacrylate) template was studied. The polymerizations were carried out on three template polymers with different molar masses in dimethylformamide at ?5°C. The initial polymerization rate increased linearly with template concentration until the distribution of template chain segments became homogeneous. At that critical concentration a strong increase in the polymerization rate was observed, whereas still higher template concentrations had only a slight effect on the polymerization rate. The polymerizations were stopped when the weight ratio of formed polymer and template was equal to one. The viscometrically determined molar mass of the formed polymers showed a remarkable behavior in the low template concentration region. It was obviously related to the molar mass of the template polymer and was lower than the molar mass found for blank polymerization. This decrease in molar mass was most pronounced in the case of the lowest template molar mass. It is suggested that nondegradative chain transfer occurring near a template chain end is responsible for this decrease. An increase in the molar mass occurred at the critical concentration, similarly to the change of polymerization rate. However, at still higher template concentrations, where template coils started to overlap each other, the molar mass of the formed polymers increased further. The growing chains could leap from one template chain to another and attain a greater chain length than the blank polymerizate.     

Some aspects on the polymerization of N-vinylpyrrolidone in the presence of poly(methacrylic acid) templates

N-Vinylpyrrolidone (NVP) was polymerized in dimethylformamide (DMF) at 60°C in the presence of poly(methacrylic acids) (PMAA) of different tacticities and molecular weights. The rate enhancement, which was ascribed to chain growth of the poly(vinylpyrrolidone) (PVP) radical along the polyacid template, became more pronounced with increasing chain length and syndiotacticity of the PMAA template. The results can be expressed by v_R = aP _vⁿ, where v_R is the polymerization rate relative to that of the blank experiment, P _v is the viscosity-average degree of polymerization of PMAA, and a and n are constants depending on the reaction conditions and tacticity of PMAA. In the presence of excess monomer the rate enhancement decreased when the quantity of PVP produced corresponded to a stoichiometric ratio of 1:1 with the available PMAA. It is proposed that the template effect is caused mainly by delay of the bimolecular termination step of growing PVP radicals associated with PMAA. Diffusion of polymer radicals, and consequently termination, will be more impaired if the attached PMAA has a greater length (size) and if the binding forces between PVP radical and PMAA template are stronger. The latter implies that PVP forms the strongest complexes with syndiotactic PMAA. This is supported by experiments concerning complex stability.     

Mechanistic Aspects of Ligand Substitution on the Hydroxopentaaquarhodium(III) Ion in Aqueous Solution by Sulfur‐Containing Bioactive Ligands

The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k₁ ～10^?3 s^?1 and k₂ ～10^?5 s^?1) and activation parameters (for thioglycolic acid: ΔH₁^≠ = 22.4 ± 3.0 kJ mol^?1, ΔS₁^≠ = ?220 ± 11 J K^?1 mol^?1, ΔH₂^≠ = 38.5 ± 1.3 kJ mol^?1, ΔS₂^≠ = ?204 ± 4 J K^?1 mol^?1; for 2‐thiouracil: ΔH₁^≠ = 42.2 ± 2.0 kJ mol^?1, ΔS₁^≠ = ?169 ± 6 J K^?1 mol^?1, ΔH₂^≠ = 66.1 ± 0.5 kJ mol^?1, ΔS₂^≠ = ?124 ± 2 J K^?1 mol^?1; for glutathione: ΔH₁^≠ = 47.2 ± 1.7 kJ mol^?1, ΔS₁^≠ = ?155 ± 5 J K^?1mol^?1, ΔH₂^≠ = 73.5 ± 1.1 kJ mol^?1, ΔS₂^≠ = ?105 ± 3 J K^?1 mol^?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as      

Activation of the aromatic system by the SO2CF3 group: Kinetics study and structure–reactivity relationships

The rate constants for the reaction of 2,6‐bis(trifluoromethanesulfonyl)‐4‐nitroanisole with some substituted anilines have been measured by spectrophotometric methods in methanol at various temperatures. The data are consistent with the S_NAr mechanism. The effect of substituents on the rate of reaction has been examined. Good linear relationships were obtained from the plots of log k₁ against Hammett σ_para constants values at all temperature with negative ρ values (?1.68 to ?1.11). Activation parameters Δ^≠H varied from 41.6 to 54.3 kJ mol^?1 and Δ^≠S from ?142.7 to ?114.6 J mol^?1 K^?1. The δΔ^≠H and δΔ^≠S reaction constants were determined from the dependence of Δ^≠H and Δ^≠S activation parameters on the σ substituent constants, by analogy with the Hammett equation. A plot of Δ^≠H versus Δ^≠S for the reaction gave good straight line with 177°C isokinetic temperature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 203–210, 2010     

Kinetics of Oxygen Exchange in the System BrO - H2O (D2O)

The kinetics of oxygen exchange between water (H₂O, D₂O) and ¹⁸O-labelled bromate ion has been investigated over the range of 1.7 ≤ pH ≤ 14.3 and 20 ≤ °C ≤ 95. At 60° and ionic strength I ? 1.0M (NaNO₃), the experimental results were consistent with the rate laws (R in moll^?1 s^?1): From the temperature dependence of the rate constants the activation parameters ΔH^≠, ΔS^≠ and ΔC^≠ were derived. In the acid-catalysed region the form of the rate law and the direction of the solvent isotope effect were the same as previously found, but the numerical values of ΔH^≠ and k_2H/k_2D differ considerably. For the spontaneous and the OH^?-catalysed exchange reactions bimolecular displacement mechanisms are proposed.     

Kinetics and mechanism of decomposition of intermediate complex during oxidation of pectate polysaccharide by potassium permanganate in alkaline solutions

The kinetics of decomposition of an [Pect·Mn^VIO₄^2?] intermediate complex have been investigated spectrophotometrically at various temperatures of 15–30°C and a constant ionic strength of 0.1 mol dm^?3. The decomposition reaction was found to be first‐order in the intermediate concentration. The results showed that the rate of reaction was base‐catalyzed. The kinetic parameters have been evaluated and found to be ΔS^≠ = ? 190.06 ± 9.84 J mol^?1 K^?1, ΔH^≠ = 19.75 ± 0.57 kJ mol^?1, and ΔG^≠ = 76.39 ± 3.50 kJ mol^?1, respectively. A reaction mechanism consistent with the results is discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 67–72, 2003     

Quantitative Line-Shape Analysis of Temperature- and Concentration-Dependent 13C-NMR Spectra of 6Li- and 13C-Labelled Organolithium Compounds. Kinetic and Thermodynamic Data for Exchange Processes in Dibromomethyllithium, (Phenylthio)methyllithium,and Butyllithium

Using the ‘permutation of indices’ method proposed by Kaplan and Fraenkel, we could formulate the density-matrix equations required to fit the temperature-dependent ¹³C-NMR spectra observed with the title compounds. For ⁶Li¹³CHBr₂ ( 1 ) and ⁶Li¹³CH₂SC₆H₅ ( 2 ) an exchange mechanism is proposed by which monomers interchange C- and Li-atoms via a non-observed dimeric intermediate; the activation parameters of these intermolecular dynamic processes have been found to be ΔH^≠ = 10.2 kcal/mol, ΔS^≠ = 13.7 cal/mol·K for 1 and ΔH^≠ = 11.1 kcal/mol, ΔS^≠ = 20.6 cal/mol·K for 2 ((D₈)THF as solvent). In the case of (⁶Li)butyllithium ( 3 ), the observed low-temperature spectra indicate that dimeric ( 3b ) and tetrameric ( 3a ) species are in dynamic equilibrium interchanging the C₃HCH₂ groups (and THF molecules) bonded to the ⁶Li-atoms. The relative concentrations of the dimer and of the tetramer have been determined by peak integration or by line-shape fitting; the ‘pseudo’- equilibrium constant, defined by K′_eq = [ 3b ]²/[ 3a ], was found to be 2.6·10^?2 mol/1 (at ?88°) and corresponds to ΔG_R (?88°) = 2 ΔG°_f( 3b ) – ΔG°_f( 3a ) = 1.34 kcal/mol. The activation parameters of the dynamic process responsible for the exchange were estimated as ΔH^≠ = 3.78 kcal/mol and ΔS^≠ = ?31.3 cal/mol·K. Tentative interpretation of the thermodynamic and kinetic parameters is given.     

Protonenresonanzuntersuchungen an Aminoboranen—II: Einflüsse von para-Phenylsubstituenten auf die Rotationsbarriere um die N?B-Bindung

The electronic influence of substituents on the free enthalpy of rotation around the N? B bond in aminoboranes was investigated in two series of compounds: (a) (CH₃)₂N?BCl (phenyl-p-X), containing the para-phenyl substituent at the boron atom, and (b) (p-X-phenyl)CH₃N?B(CH₃)₂, containing the para-phenyl substituent at the nitrogen atom of the N? B linkage (X = ? NR₂, ? OCH₃, ? C(CH₃)₃, ? Si(CH₃)₃, ? H, ? F, ? Cl, ? Br, ? I, ? CF₃ and ? NO₂). By comparing the rotational barriers in corresponding compounds of both series, a reverse effect of the substituents could be observed. Electron-withdrawing substituents in the para position of the phenyl ring increase the ΔG_c^≠ if the phenyl group is attached to the boron atom; on the other hand, a lower ΔG_c^≠ is observed if the phenyl ring is bonded to the nitrogen atom of the N? B system. Substitution of the phenyl ring with electron-donating substituents in the paraposition exerts the opposite effect. Within each series of compounds, the differences of ΔG_c^≠ values [δ(ΔG_c^≠) = ΔG_c^≠ (X) ? ΔG_c^≠ (X = H)] between substituted and unsubstituted compounds can be explained in terms of inductive and mesomeric effects of the ring substituents and can be correlated with the Hammett σ constant of each substituent. A comparison of the slopes of the plotted lines shows that the influence of the ring substituents is more pronounced in compounds with N-phenyl-p-X than in those with B-phenyl-p-X.     

Carbon-13 NMR spectra of a series of para-substituted phenyl isothiocyanates. Linear free energy relationships for carbon-13 substituent chemical shifts

Carbon-13 chemical shifts are reported for 16 para-substituted phenyl isothiocyanates measured at 1 and 10 mol % in chloroform-d solution. Data for the ? N?C?S group were not obtained at 1 mol %, but concentration effects for the other resonances were negligible. Hammett, dual substituent parameter (DSP) and DSP-nonlinear resonance (DSP-NLR) analyses were used to evaluate substituent effects on the substituent chemical shifts (SCS) for the ipso-carbon (C-1), C-2, and the ? N?C?S carbon atoms. A good Hammett correlation was observed for C-1 (ν_p⁺ = 8.1 ppm, r = 0.98 at 1 mol %) but was improved for the higher order correlations with the following results, DSP:ρ _I = 5.4, ρ_R° = 22.2, r = 0.998; DSP-NLR: ρ_I = 5.6, ρ_R° = 20.5, ? = ?0.22, r = 0.999. The 10 mol % data were very similar except the value of ? was ?0.26 and confirms the phenyl-bonded ? N?C?S moiety as a mild electron acceptor substituent. Hammett correlations were unsuccessful for the C-2 data, but fairly good results were obtained from the higher order analyses. For the 1 mol % data, DSP: ν_I = 1.6, ν_R° = ?2.0, r = 0.976; DSP-NLR: ν_I = 1.8, ν_R° = ?2.6, ? = 1.1, r = 0.982. Excellent correlations were obtained for the 10 mol % ? N?C?S carbon data. Hammett: ν_p° = 6.2, r = 0.997; DSP: ν_I = 5.9, ν_R° = 7.0, r = 0.997; DSP-NLR: ν_I = 5.8, ν_R° = 7.6, ? = 0.25, r = 0.997. The positive ν values in these three correlations contrast the negative values usually observed for carbonyl and thiocarbonyl carbons, and more closely parallel results previously reported for the β-carbon of styrenes and benzylidene anilines with para-substituents in the aniline ring.     

铀(Ⅵ)与不对称希夫碱配合物的合成和热分解反应动力学

邻苯二胺与5－氯－2－羟基二苯酮、邻香草醛作用合成了一种不对称希夫碱配体C₂₇H₂₁N₂O₃Cl（H₂L）。在正丁醇和甲醇体系中硝酸铀酰与该配体反应合成了一种固体希夫碱配合物[UO₂(HL)(NO₃)(H₂O)]·H₂O。通过元素分析、IR、UV、¹H NMR、TG-DTG及摩尔电导率分析等手段对合成的配合物进行了表征,用非等温热重法研究了铀(Ⅵ)配合物的热分解反应动力学,推断出第三步热分解的动力学方程为：d α /d t = A · e^{- E/RT} ·3/2[(1- α )^-1/3-1]^-1,得到了动力学参数E和A。并计算出了活化熵△S^¹和活化吉布斯自由能△G^¹。     

Cobaltchelate als Hydrierkatalysatoren. III. Die Hydridbildung des [Co(dpnH)]+-Komplexes in Gegenwart von Pyridin als axialer Base

Cobalt Chelates as Hydrogenation Catalysts. III. Hydride Formation of the [Co(dpnH)]⁺ Catalyst in the Presence of Pyridine as Axial Base The rate of the hydrogen uptake for [Co(dpnH)]⁺ is 2^nd order with respect to the complex concentration and depends on the amount of added pyridine, in accord with the assumption of a more active mono- and an inactive bis-pyridine adduct. The rate law, formulated on this basis agrees very well with the measured data. The ΔH^≠ - and Δ_RH°-values, calculated from the temperature dependence of the rate constants and equilibrium constants are in agreement with the suggested model, whereas the ΔS^≠ and Δ_RS° values do not correspond completely with these expectations.     

Synthesis and Diels-Alder Reactivity of 2,3,5,6-Tetramethylidenenorbornane

Pd-catalyzed double carbomethoxylation of the Diels-Alder adduct of cyclo-pentadiene and maleic anhydride yielded the methyl norbornane-2,3-endo-5, 6-exo-tetracarboxylate ( 4 ) which was transformed in three steps into 2,3,5,6-tetramethyl-idenenorbornane ( 1 ). The cycloaddition of tetracyanoethylene (TCNE) to 1 giving the corresponding monoadduct 7 was 364 times faster (toluene, 25°) than the addition of TCNE to 7 yielding the bis-adduct 9 . Similar reactivity trends were observed for the additions of TCNE to the less reactive 2,3,5,6-tetramethylidene-7-oxanorbornane ( 2 ). The following second order rate constants (toluene, 25°) and activation parameters were obtained for: 1 + TCNE → 7 : k₁ = (255 + 5) 10^?4 mol^?1 · s^?1, ΔH≠ = (12.2 ± 0.5) kcal/mol, ΔS≠ = (?24.8 ± 1.6) eu.; 7 + TCNE → 9 , k₂ = (0.7 ± 0.02) 10^?4 mol^?1 · s^?1, ΔH≠ = (14.1 ± 1.0) kcal/mol, ΔS≠ = ( ?30 ± 3.5) eu.; 2 + TCNE → 8 : k₁ = (1.5 ± 0.03) 10^?4 mol^?1 · s^?1, ΔH≠ = (14.8 ± 0.7) kcal/mol, ΔS≠ = (?26.4 ± 2.3) eu.; 8 + TCNE → 10 ; k₂ = (0.004 ± 0.0002) 10^?4 mol^?1 · s^?1, ΔH≠ = (17 ± 1.5) kcal/mol, ΔS≠ = (?30 ± 4) eu. The possible origins of the relatively large rate ratios k₁/k₂ are discussed briefly.     

Homolytic substitution in trialkyltin iodides by photochemically generated iodine atoms. I. Kinetics

The kinetics of the homolytic substitution of several trialkyltin iodides by iodine atoms are presented. Rate constants have been determined at three different temperatures and the following activation parameters calculated: A, E_a, and ΔS°^≠. The observation that the activation energy, ΔG^≠, is related to the driving force of the ion-pair formation, leads to the conclusion that the charge-transfer model is a valid approach for substitution in the reaction between R₃SnI compounds and iodine atoms.     

Hindered rotation around the aryl-to-nitrogen bond of n-acetyl,n-ethoxycarbonylmethyl-2-amino, 5-nitrothiophen

Two stereoisomers of the title compound are observed by H NMR at 10°. Their spectra coalesce at higher temperature (10°-90°). The equilibrium and rate constants K and k, strongly dependent on the solvent used (1,4-dioxane, tetrahydrofuran, acetone, chloroform); typical values for these parameters and the related thermodynamic functions are: K(25°)= 0.170; k(25°)=23.2s^?1; ΔH_R and ΔH^≠=4.94 and 17.9 kcal.mol.^?1; ΔS_R and ΔS^≠ =13.1 and 7.7 e.u, in a 0.2 molar solution in 1,4-dioxane. The two isomers are shown to result from a hindered rotation around the aryl-to-nitrogen bond, presumably due to a direct resonance effect between the amide and nitro groups. The more abundant isomer was assigned a planar molecular structure in which the O atom of the amide group is close to the S atom of the thiophen ring, presumably on account of an electrostatic interaction between these two atoms which bear partial electrical charges of opposite sign.     

Micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate

The kinetics of micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate in the presence of different surfactants has been studied at 303?K. The rate of reaction has been found to be first order with respect to both [substrate] and [HCl]. The cationic micelles of cetylpyridinium chloride (CPC), anionic micelles of di-octyl sodium sulphosuccinate (AOT), and non-ionic micelles of polyoxyethylene sorbitan monooleate (Tween 80) enhanced the rate of reaction to a maximum value and after that the increase in concentration of surfactant decreased the reaction rate. The applicability of different kinetic models has been tested to explain the observed micellar effects. The various thermodynamic activation parameters (E_a, ΔH^≠, ΔS^≠, ΔG^≠) have been evaluated. The added salts viz. KCl, KNO₃, K₂SO₄ enhanced the rate of reaction in the presence of CPC, AOT, and Tween 80 micelles. The kinetic parameters were determined from the rate (surfactant) profile and a suitable mechanism consistent with the experimental finding has been proposed.     

Metal‐Free Addition/Head‐to‐Tail Polymerization of Transient Phosphinoboranes,RPH‐BH2: A Route to Poly(alkylphosphinoboranes)

Mild thermolysis of Lewis base stabilized phosphinoborane monomers R¹R²P? BH₂?NMe₃ (R¹,R²=H, Ph, or tBu/H) at room temperature to 100 °C provides a convenient new route to oligo‐ and polyphosphinoboranes [R¹R²P‐BH₂]_n. The polymerization appears to proceed via the addition/head‐to‐tail polymerization of short‐lived free phosphinoborane monomers, R¹R²P‐BH₂. This method offers access to high molar mass materials, as exemplified by poly(tert‐butylphosphinoborane), that are currently inaccessible using other routes (e.g. catalytic dehydrocoupling).     

ATRP-template dispersion polymerization of methacrylic Acid/PVP

ATRP-template dispersion polymerization of methacrylic acid （MAA） on the template of polyvinyl pyrrolidone （PVP K-30） was carried out in the aqueous solution by using methyl 2-bromopropionate （MBP）/CuC1/2,2＇-bipyridine （bpy） as the initiation system. The scanning electron microscopy （SEM）, dynamic light scattering （DLS） and gel permeation chromatography （GPC） were employed for evaluating the results of polymerization. As a result, the minimonomer droplets formed due to the H-bond interaction of PVP-MAA. The stability of droplets was dependent on pH and the concentrations of both PVP and MAA. When pH 〈 2, the coagulum of PVP-MAA formed, whereas when pH 〉 4.5, the droplets were not observable by DLS. In order to prepare the stable latex, the concentration of PVP should be lower than 9 wt%, whilst the concentration of MAA should be lower than 5.5 wt%. The optimum condition was pH 2.4, PVP 4.76 wt% and MAA 5 wt%, by which the stable latex of ca. 50 nm nanoparticles of PMAA/PVP was prepared by ATRP polymerization and simultaneously the molar mass of PVP was duplicated by PMAA according to GPC diagrams. In contrast, by using AIBN, KPS and KPS-Na2SO3 redox initiation system, the coagulum accompanying with the larger molar mass of PMAA was obtained, irrespective of pH and concentrations of PVP and MAA.     

Heterolysis of H2 Across a Classical Lewis Pair, 2,6‐Lutidine⋅BCl3: Synthesis,Characterization, and Mechanism

We report that 2,6‐lutidine?trichloroborane (Lut?BCl₃) reacts with H₂ in toluene, bromobenzene, dichloromethane, and Lut solvents producing the neutral hydride, Lut?BHCl₂. The mechanism was modeled with density functional theory, and energies of stationary states were calculated at the G3(MP2)B3 level of theory. Lut?BCl₃ was calculated to react with H₂ and form the ion pair, [LutH⁺][HBCl₃^?], with a barrier of ΔH^≠=24.7 kcal mol^?1 (ΔG^≠=29.8 kcal mol^?1). Metathesis with a second molecule of Lut?BCl₃ produced Lut?BHCl₂ and [LutH⁺][BCl₄^?]. The overall reaction is exothermic by 6.0 kcal mol^?1 (Δ_rG°=?1.1). Alternate pathways were explored involving the borenium cation (LutBCl₂⁺) and the four‐membered boracycle [(CH₂{NC₅H₃Me})BCl₂]. Barriers for addition of H₂ across the Lut/LutBCl₂⁺ pair and the boracycle B?C bond are substantially higher (ΔG^≠=42.1 and 49.4 kcal mol^?1, respectively), such that these pathways are excluded. The barrier for addition of H₂ to the boracycle B?N bond is comparable (ΔH^≠=28.5 and ΔG^≠=32 kcal mol^?1). Conversion of the intermediate 2‐(BHCl₂CH₂)‐6‐Me(C₅H₃NH) to Lut?BHCl₂ may occur by intermolecular steps involving proton/hydride transfers to Lut/BCl₃. Intramolecular protodeboronation, which could form Lut?BHCl₂ directly, is prohibited by a high barrier (ΔH^≠=52, ΔG^≠=51 kcal mol^?1).