Arenesulfonyl bromides: The second universal class of functional initiators for the metal‐catalyzed living radical polymerization of methacrylates,acrylates, and styrenes

The metal‐catalyzed living radical polymerization of methyl methacrylate, n‐butyl acrylate, and styrene, initiated with p‐toluenesulfonyl bromide and phenoxybenzene‐4,4′‐disulfonyl bromide and catalyzed with CuBr/2,2′‐bipyridine (bpy) and various self‐regulated Cu‐based catalytic systems such as Cu₂O/bpy, Cu₂S/bpy, Cu₂Se/bpy, and Cu₂Te/bpy, is reported. Similarities and differences between the arenesulfonyl chloride and arenesulfonyl bromide initiators are discussed. The arenesulfonyl bromide initiators require reduced reaction times to produce polymers in high conversions under milder reaction conditions than the corresponding arenesulfonyl chloride initiators. At the same time, they exhibit 100% initiator efficiency and generate polymers with narrow molecular weight distributions and functional chain ends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 319–330, 2005     

Determination of propagation‐rate constant of vinylidene chloride by emulsion polymerization

The propagation‐rate constant of vinylidene chloride (VDC) was determined at 40 and 50 °C, respectively, by applying the so‐called Ugelstad plot to the polymerization‐rate data of the seeded and unseeded emulsion polymerizations of VDC. The values of the propagation‐rate constant k_p thus determined are k_p = 64 dm³/mol · s at 50 °C and k_p = 52 dm³/mol · s at 40 °C, respectively. From these k_p values, the activation energy for propagation reaction was determined to be E_p = 4.2 kcal/mol, which is close to that of vinyl chloride (3.7 kcal/mol). © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1005–1015, 2001     

Kinetics and mechanism of the cationic polymerization of trioxane. II. Consideration of hydride transfer

The occurrence of hydride-transfer reactions during the cationic polymerization of trioxane was demonstrated, and rate constants were obtained. The donor of hydride ions in the transfer reactions was the monomer. The hydride-transfer reaction was a first-order reaction with respect to the concentration of the monomer, and it was governed, just as polymerization and depolymerization were (Shieh, Y. T.; Chen. S. A. J. Polym. Sci. Part A: Polym. Chem. 1999, 37, 483–492) by morphological changes. The hydride-transfer rate constants were 5 orders of magnitude smaller than those for polymerizations and depolymerizations. The rate constants for the reactions, including the polymerizations, depolymerizations, and hydride transfers, were smaller for the active centers on the solid surface than for those in solution, that is, k^′_p was less than k_p, k^′_d was less than k_d, and k^′_ht was less than k_ht. As a reaction medium, benzene had special effects on the kinetics of the cationic polymerization of trioxane. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4198–4204, 1999     

Effect of fullerene on radical polymerization of vinyl acetate

The effect of fullerene (C₆₀) on the radical polymerization of vinyl acetate (VAc) with dimethyl 2,2′‐azobisisobutyrate (MAIB) in benzene was investigated kinetically and by means of ESR. C₆₀ was found to act as an effective inhibitor in the present polymerization. All C₆₀ molecules used were incorporated into poly(VAc) during polymerization. The relationship of induction period and initiation rate reveals that a C₆₀ molecule can trap 15 radicals formed in the polymerization system. The polymerization rate (R_p) after the induction period is given by R_p = k [MAIB]^0.6 [VAc]^2.0 (60 °C), which is similar to that observed in the absence of C₆₀. Stable fullerene radical (C) was observed in the polymerization system by ESR. The C concentration increased with time and was then saturated. The saturation time well corresponds to the induction period observed in the polymerization. About 20% of C₆₀ molecules added could survive as stable C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2572–2578, 2000     

Kinetic and ESR studies on the radical polymerization of α‐n‐(α′‐methylbenzyl) β‐ethyl itaconamates derived from racemic and (s)‐α‐methylbenzylamines

The polymerization of α‐N‐(α′‐methylbenzyl) β‐ethyl itaconamate derived from racemic α‐methylbenzylamine (RS‐MBEI) by initiation with dimethyl 2,2′‐azobisisobutyrate (MAIB) was studied in methanol kinetically and with ESR spectroscopy. The overall activation energy of polymerization was calculated to be 47 kJ/mol, a very low value. The polymerization rate (R_p ) at 60 °C was expressed by R_p = k[MAIB]^0.5±0.05[RS‐MBEI]^2.9±0.1. The rate constants of propagation (k_p ) and termination (k_t ) were determined by ESR. k_p was very low, ranging from 0.3 to 0.8 L/mol s, and increased with the monomer concentration, whereas k_t (4–17 × l0⁴ L/mol s) decreased with the monomer concentration. Such behaviors of k_p and k_t were responsible for the high dependence of R_p on the monomer concentration. R_p depended considerably on the solvent used. S‐MBEI, derived from (S)‐α‐methylbenzylamine, showed somewhat lower homopolymerizability than RS‐MBEI. The k_p value of RS‐MBEI at 60 °C in benzene was 1.5 times that of S‐MBEI. This was explicable in terms of the different molecular associations of RS‐MBEI and S‐MBEI, as analyzed by ¹H NMR. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4137–4146, 2000     

Studying Cu2–xSe phase transformation through DSC examination

The thermal effect accompanying the transition of Cu_2–xSe into a superionic conduction state was studied by non-isothermal measurements, at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C min^–1). During heating the peak temperature (T_p) remains almost stable for all values of β, (136.8±0.4°C for Cu₂Se and 133.0±0.3°C for Cu_1.99Se). A gradual shift of the initiation of the transformation towards lower temperatures is observed, as the heating rate increases. During cooling there is a significant shift in the position of the peak maximum (T_p) towards lower temperatures with the increase of the cooling rate. A small hysteresis is observed, which increases with the increase of the cooling rate, β. The mean value of transformation enthalpy was found to be 30.3±0.8 J g^–1 for Cu₂Se and 28.9±0.9 J g^–1 for Cu_1.99Se. The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)^n(1+kcatX), with activation energy E=175 kJ mol^–1, exponent value n equal to 0.2, logA=20 and log(k_cat)= 0.5.     

Photoinitiated polymerization of methacrylic monomers in a polystyrene matrix: Kinetic,mechanistic, and structural aspects

The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6‐hexanediol dimethacrylate (HDDMA) and 2‐ethylhexyl methacrylate (EHMA)] in a polystyrene (PS) matrix were studied. The aggregation state, vitreous or rubbery, of the monomer/matrix system and the intermolecular strength of attraction in the monomer/matrix and growing macroradical/matrix systems are the principal factors influencing the kinetics and mechanism. For the PS/HDDMA system, where a relatively high intermolecular force of attraction between monomer and matrix and between growing macroradical and matrix occurs, a reaction‐diffusion mechanism takes place at low monomer concentrations (<30–40%) from the beginning of the polymerization. For the PS/EHMA system, which presents low intermolecular attraction between monomer and matrix and between growing macroradical and matrix, the reaction‐diffusion termination is not clear, and a combination of reaction‐diffusion and diffusion‐controlled mechanisms explains better the polymerization for monomer concentrations below 30–40%. For both systems, for which a change from a vitreous state to a rubbery state occurs when the monomer concentration changes from 10 to 20%, the intrinsic reactivity and k_p/k_t^1/2 ratio (where k_p is the propagation kinetic constant and k_t is the termination kinetic constant) increase as a result of a greater mobility of the monomer in the matrix (a greater k_p value). The PS matrix participates in the polymerization process through the formation of benzylic radical, which is bonded to some extent by radical–radical coupling with the growing methacrylic radica, producing grafting on the PS matrix. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2049–2057, 2001     

Influence of the stereochemical configuration on the radical polymerization of methacrylic monomers: cis‐ and trans‐(2‐cyclohexyl‐1,3‐dioxan‐5‐yl) methacrylate

The synthesis of two new isomeric monomers, cis‐(2‐cyclohexyl‐1,3‐dioxan‐5‐yl) methacrylate (CCDM) and trans‐(2‐cyclohexyl‐1,3‐dioxan‐5‐yl) methacrylate (TCDM), starting from the reaction of glycerol and cyclohexanecarbaldehyde, is reported. The process involved the preparation of different alcohol acetals and esterification with methacryloyl chloride of the corresponding cis and trans 5‐hydroxy compounds of 2‐cyclohexyl‐1,3‐dioxane. The radical polymerization reactions of both monomers, under the same conditions of temperature, solvent, monomer, and initiator concentrations, were studied to investigate the influence of the monomer configuration on the values of the propagation and termination rate constants (k_p and k_t ).The values of the ratio k_p /k_t ^1/2 were determined by UV spectroscopy by the measurement of the changes of absorbance with time at several wavelengths in the range 275–285 nm, where an appropriate change in absorbance was observed. Reliable values of the kinetics constants were determined by UV spectroscopy, showing a very good reproducibility of the kinetic experiments. The values of k_p /k_t ^1/2, in the temperature interval 45–65 °C, lay in the range 0.40–0.50 L^1/2/mol^1/2s^1/2 and 0.20–0.30 L^1/2/mol^1/2s^1/2 for CCDM and TCDM, respectively. Measurements of both the radical concentrations and the absolute rate constants k_p and k_t were also carried out with electron paramagnetic resonance techniques. The values of k_p at 60 °C were nearly identical for both the trans and cis monomers, but the termination rate constant of the trans monomer was about three times that of the cis monomer at the same temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3883–3891, 2000     

Radical polymerization of benzyl N-(2,6-dimethylphenyl)itaconamate

The polymerization of benzyl N-(2,6-dimethylphenyl)itaconamate (BDMPI) with benzoyl peroxide (BPO) in N,N-dimethylformamide (DMF) was studied kinetically by ESR. The polymerization rate (R_p) at 70°C was given by R_p = k[BPO]^0.78[BDMPI]^1.1. The overall activation energy of polymerization was determined to be 83.7 kJ/mol. The number-average molecular weight of poly(BDMPI) was in the range of 1500–2000 by gel permeation chromatography. From the ESR study, the polymerization system was found to involve ESR-observable propagating radicals of BDMPI under practical polymerization conditions. Using the polymer radical concentration by ESR, the rate constants of propagation (k_p) and termination (k_t) were determined in the temperature range of 50–70°C. The k_p value seemed dependent on the chain-length of propagating radical. The analysis of polymers by the MALDI-TOF mass spectrometry suggested that most of the resulting polymers contain the dimethylamino terminal group. The copolymerization of BDMPI (M₁) and styrene (M₂) at 50°C in DMF gave the following copolymerization parameters; r₁ = 0.49, r₂ = 0.26, Q₁ = 1.2, and e₁ = +0.63. The thermal behavior of poly(BDMPI) was examined by dynamic thermogravimetry and differential scanning calorimetry. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1891–1900, 1997     

Effects of hydration and hydrophilicity on Na‐Clay‐supported aqueous‐phase catalysis for atom transfer radical polymerization

Hydrated sodium montmorillonite (Na‐clay) has been used as a catalyst support for the heterogeneous atom transfer radical polymerization of benzyl methacrylate in the presence of various concentrations of water, reducing agent, and CuBr₂ in anisole at ambient temperature. The polymerization was promoted via reduction of Cu^II to Cu^I through the addition of sodium ascorbate (NaAsc) as a reducing agent in aqueous solution. The polymerizaton proceeded in a controlled manner and produced poly(benzyl methacylate) with moderately narrow molecular weight distribution (MWD) when performed under optimum conditions of hydration (10 wt % ≤ H₂O/Na‐clay ≤ 21 wt %) and reducing agent (0.15 ≤ [NaAsc]/[I] ≤ 0.23). The polymerization was uncontrolled if hydration and NaAsc exceed above their optimum range of concentrations. Apparent rate of the polymerization (k_app) increased in the presence of decane–anisole (1/3, v/v) mixture solvent. Selective adsorption of decane at the interfaces of the hydrated clay was attributed for the rate enhancement due to increased polymer and hydrophobic interface interaction. The polymerization progressed in a controlled manner as confirmed by the first‐order time‐conversion plot, linear increase in molecular weights, and moderately narrow MWDs over conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Organocopper‐catalyzed living radical polymerization initiated with aromatic sulfonyl chlorides

The living radical polymerization of methyl methacrylate initiated from aromatic sulfonyl chlorides and catalyzed by the new catalytic systems CuSBu/bpy CuSPh/bpy and CuCCPh/bpy (bpy = 2,2′‐bipyridine) is described. For a target degree of polymerization of 200, lowering the ratio of catalyst to sulfonyl chloride group from 1/1 to 0.25/1 mol/mol decreases the values of the experimental rate constant of polymerization from 5.12 × 10⁻², 2.4 × 10⁻², and 1.87 × 10⁻² min⁻¹ to 1.8 × 10⁻³, 4.9 × 10⁻³, and 4.2 × 10⁻³ min⁻¹ for CuSBu, CuSPh, and CuCCPh, respectively, whereas the corresponding initiator efficiency increases from 62 to 99%. The external orders of reaction in the catalyst are 0.79 for CuSPh, 0.88 for CuCCPh, and 1.64 for CuSBu. A mechanistic interpretation that involves the in situ generation of, most likely, the real catalyst CuCl, starting from combinations of CuSBu, CuSPh, and CuCCPh and sulfonyl chloride or alkyl halide growing species, is suggested. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4353–4361, 2000     

Kinetic study on the radical polymerization of 2‐methacryloyloxyethyl phosphorylcholine

Polymerization of 2‐methacryloyloxyethyl phosphorylcholine (MPC) was kinetically investigated in ethanol using dimethyl 2,2′‐azobisisobutyrate (MAIB) as initiator. The overall activation energy of the homogeneous polymerization was calculated to be 71 kJ/mol. The polymerization rate (R_p) was expressed by R_p = k[MAIB]^0.54±0.05 [MPC]^1.8±0.1. The higher dependence of R_p on the monomer concentration comes from acceleration of propagation due to monomer aggregation and also from retardation of termination due to viscosity effect of the MPC monomer. Rate constants of propagation (k_p) and termination (k_t) of MPC were estimated by means of ESR to be k_p = 180 L/mol · s and k_t = 2.8 × 10⁴ L/mol · s at 60 °C, respectively. Because of much slower termination, R_p of MPC in ethanol was found at 60 °C to be 8 times that of methyl methacrylate (MMA) in benzene, though the different solvents were used for MPC and MMA. Polymerization of MPC with MAIB in ethanol was accelerated by the presence of water and retarded by the presence of benzene or acetonitrile. Poly(MPC) showed a peculiar solubility behavior; although poly(MPC) was highly soluble in ethanol and in water, it was insoluble in aqueous ethanol of water content of 7.4–39.8 vol %. The radical copolymerization of MPC (M₁) and styrene (St) (M₂) in ethanol at 50 °C gave the following copolymerization parameters similar to those of the copolymerization of MMA and St; r₁ = 0.39, r₂ = 0.46, Q₁ = 0.76, and e₁ = +0.51. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 509–515, 2000     

载体H+含量对CuY甲醇氧化羰基化反应性能影响

通过过量浸渍Cu(NO_3)_2溶液于Y分子筛载体上,制备出Cu负载量为6.4%的CuY催化剂,考察了甲醇氧化羰基化反应的催化性能,并采用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、透射电子显微镜(TEM)和NH3程序升温脱附(NH3-TPD)等手段对催化剂表面微观结构进行了表征。研究表明,随Y分子筛载体H+含量的增加,可使更多Cu物种落位于分子筛微孔笼结构中,且高度分散,而笼内未交换的Na+能进一步促进铜物种更多落位于载体超笼结构中,形成更多甲醇氧化羰基化反应的Cu+活性中心。同时随铜物种引入,催化剂中产生了明显的中强酸,酸量随落位于载体笼结构中的Cu物种的增加而增加,催化剂总酸量随之增加,导致甲醇氧化羰基化产物分布发生改变,碳酸二甲酯(DMC)选择性明显降低。对比等体积浸渍法制备的92.3%的高DMC选择性CuY催化剂,以不含H+的NaY分子筛为载体,过量浸渍法制备的CuY催化剂酸量少、Cu物种活性中心多,在保持82.4%的高DMC选择性时,其DMC的时空收率(STY)也高达109.1mg·g~(-1)·h-1。     

Kinetic study of azidopentaammine cobalt(III) complex as photoinitiator and termination agent of N‐vinylpyrrolidone radical polymerization

N‐Vinylpyrrolidone polymerization photoinitiated at 365 and 546 nm by azidopentaammine cobalt(III) {[Co(NH₃)₅N₃]²⁺} was investigated at room temperature in an argon atmosphere. By excitation into the ligand to metal charge transfer (LMCT), the cobalt complex showed an efficient photoredox process leading to the formation of a cobalt(II) and an azide radical (N, Φ_photoredox = 0.24). The same process was found to occur by excitation into the ligand field band with a low but not negligible quantum yield (Φ_photoredox = 0.016). Two different domains were clearly present when the plot of the rate of polymerization as a function of the cobalt(III) complex was studied; for [Co(III)] < 2.0 × 10⁻⁴ M, the termination step mainly involved a mutual annihilation of growing radicals whereas an oxidative termination was present in the range of 2.0 × 10⁻⁴ M < [Co(III)] < 1.0 × 10⁻³ M. Within the former domain the rate of polymerization (R_p ) varied with the first power of the monomer concentration and with the square root of the absorbed light intensity while for the latter domain the R_p was proportional to the monomer concentration and absorbed light intensity. Further investigations using the viscosity‐average molecular weight data allowed us to corroborate the proposed polymerization mechanism. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3997–4005, 2000     

Kinetic and ESR studies on radical polymerization behavior of N‐(2‐phenylethoxycarbonyl)methacrylamide

Polymerization of N‐(2‐phenylethoxycarbonyl)methacrylamide (PECMA) with dimethyl 2,2′‐azobisisobutyrate (MAIB) was investigated in tetrahydrofuran (THF) kinetically and by means of electron spin resonance (ESR). The overall activation energy of the polymerization was calculated to be 58 kJ/mol. The initial polymerization rate (R_p) is expressed by R_p = k[MAIB]^0.3[PECMA]^2.3 at 60 °C. Such unusual kinetics may be ascribable to primary radical termination and to acceleration of propagation due to monomer association. Propagating poly(PECMA) radical was observed as a 13‐line spectrum by ESR under practical polymerization conditions. ESR‐determined rate constants of propagation (k_p, 4.7–10.5 L/mol s) and termination (k_t, 4.6 × 10⁴ L/ml s) at 60 °C are much lower than those of methacrylamide and methacrylate esters. The Arrhenius plots of k_p and k_t gave activation energies of propagation (24 kJ/mol) and termination (25 kJ/mol). The copolymerizations of PECMA with styrene (St) and acrylonitrile were examined at 60 °C in THF. Copolymerization parameters obtained for the PECMA (M₁) − St(M₂) system are as follows: r₁ = 0.58, r₂ = 0.60, Q₁ = 0.73, and e₁ = +0.22. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4264–4271, 2000     

Kinetic analysis of styrene atom transfer radical polymerization: Extraction of radical‐radical termination rate coefficients

Kinetic studies of the atom transfer radical polymerization (ATRP) of styrene are reported, with the particular aim of determining radical‐radical termination rate coefficients (<k_t>). The reactions are analyzed using the persistent radical effect (PRE) model. Using this model, average radical‐radical termination rate coefficients are evaluated. Under appropriate ATRP catalyst concentrations, <k_t> values of approximately 2 × 10⁸ L mol^?1 s^?1 at 110 °C in 50 vol % anisole were determined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5548–5558, 2004     

Synthesis and kinetics of polymerization of acrylic and methacrylic monomers containing 1,3-dioxane groups in their structure

(5-Ethyl-1,3-dioxane-5-yl) methyl acrylate (HEDA) and (5-ethyl-1,3-dioxane-5-yl)methyl methacrylate (HEDMA) were synthesized by reaction between acryloyl and methacryloyl chloride with 5-ethyl, 5-hydroxymethyl, 1,3-dioxane. The kinetics of the polymerization of both are studied at different temperatures in benzene solution. Dilatometric techniques and nonlinear least-squares methods were used to obtain the kinetic data and to determine the kinetic constants, respectively. The values of k_p/k^1/2_t for the acrylic and methacrylic monomers are higher than those corresponding to methyl acrylate and methyl methacrylate, respectively. Important changes in k_p/k^1/2_t with temperature occur in the polymerization of HEDA, and the corresponding Arrhenius plot gives an activation energy of 5.6 kcal mol⁻¹. On the contrary, only slight changes with temperature are observed in this ratio for HEDMA and the activation energy associated with the polymerization reaction is ca. 1.7 kcal mol⁻¹. The stereo-structure of both polymers was determined by ¹³C-NMR spectroscopy and the molar fractions of tactic dyads, triads (and in the case of the methacrylic polymer also pentads) were determined from different resonance signals. Finally, the glass transition temperatures of both PHEDA and PHEDMA are 33 and 123°C, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1125–1132, 1997     

Living cationic polymerization of isobutylene coinitiated by FeCl3 in the presence of isopropanol

A simple but effective FeCl₃‐based initiating system has been developed to achieve living cationic polymerization of isobutylene (IB) using di(2‐chloro‐2‐propyl) benzene (DCC) or 1‐chlorine‐2,4,4‐trimethylpentane (TMPCl) as initiators in the presence of isopropanol (iPrOH) at ?80 °C for the first time. The polymerization with near 100% of initiation efficiency proceeded rapidly and completed quantitatively within 10 min. Polyisobutylenes (PIBs) with designed number‐average molecular weights (M_n) from 3500 to 21,000 g mol^?1, narrow molecular weight distributions (MWD, M_w/M_n ≤ 1.2) and near 100% of tert‐Cl terminal groups could be obtained at appropriate concentrations of iPrOH. Livingness of cationic polymerization of IB was further confirmed by all monomer in technique and incremental monomer addition technique. The kinetic investigation on living cationic polymerization was conducted by real‐time attenuated total reflectance Fourier transform infrared spectroscopy. The apparent constant of rate for propagation (k_p^A) increased with increasing polymerization temperature and the apparent activation energy (ΔE_a) for propagation was determined to be 14.4 kJ mol^?1. Furthermore, the triblock copolymers of PS‐b‐PIB‐b‐PS with different chain length of polystyrene (PS) segments could be successfully synthesized via living cationic polymerization with DCC/FeCl₃/iPrOH initiating system by sequential monomer addition of IB and styrene at ?80 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

In Situ Generation of ArCu from CuF2 Makes Coupling of Bulky Aryl Silanes Feasible and Highly Efficient

A bimetallic system of Pd/CuF₂, catalytic in Pd and stoichiometric in Cu, is very efficient and selective for the coupling of fairly hindered aryl silanes with aryl, anisyl, phenylaldehyde, p‐cyanophenyl, p‐nitrophenyl, or pyridyl iodides of conventional size. The reaction involves the activation of the silane by Cu^II, followed by disproportionation and transmetalation from the Cu^I(aryl) to Pd^II, upon which coupling takes place. Cu^III formed during disproportionation is reduced to Cu^I(aryl) by excess aryl silane, so that the CuF₂ system is fully converted into Cu^I(aryl) and used in the coupling. Moreover, no extra source of fluoride is needed. Interesting size selectivity towards coupling is found in competitive reactions of hindered aryl silanes. Easily accessible [PdCl₂(IDM)(AsPh₃)] (IDM = 1,3‐dimethylimidazol‐2‐ylidene) is by far the best catalyst, and the isolated products are essentially free from As or Pd (<1 ppm). The mechanistic aspects of the process have been experimentally examined and discussed.