{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,17]],"date-time":"2025-12-17T08:36:17Z","timestamp":1765960577689,"version":"build-2065373602"},"reference-count":62,"publisher":"Wiley","issue":"8","license":[{"start":{"date-parts":[[2006,2,21]],"date-time":"2006-02-21T00:00:00Z","timestamp":1140480000000},"content-version":"vor","delay-in-days":3491,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Chemistry A European J"],"published-print":{"date-parts":[[1996,8]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>The rates and mechanism of the reactions of a series of aryl\u2010ligated, anionic palladium(0) complexes Ar\u2010Pd<jats:sup>0<\/jats:sup>\u2010(PPh<jats:sub>3<\/jats:sub>)<jats:sup>\u2010<\/jats:sup><jats:sub>2<\/jats:sub> with <jats:italic>para<\/jats:italic>\u2010substituted iodobenzenes were investigated by means of transient electrochemistry. The reaction was found to be first order in each reactant and to proceed similarly to oxidative addition of aryl halides to the halide\u2010ligated species X\u2010Pd<jats:sup>0<\/jats:sup>(PPh<jats:sub>3<\/jats:sub>)<jats:sup>\u2010<\/jats:sup><jats:sub>2<\/jats:sub>, although much faster and less sensitive to electronic factors. Owing to the short lifetime (<jats:italic>t<\/jats:italic><jats:sub>1\/2<\/jats:sub> \u2248\ufe01 1 \u2013 5 ms) of the product of this reaction, it could not be characterized in detail. However, based on kinetic results, this transient species is thought to be an anionic pentacoordinated bisarylpalladium(II) complex, which undergoes rapid loss of halide ligand to yield, most probably, a bisarylpalladium(II) neutral species. Based on the study of this reaction and on previously reported results, we propose a mechanism for the palladium\u2010catalyzed homocoupling of aryl halides consisting of a catalytic cycle initiated by oxidative addition of an aryl halide to a zerovalent tris\u2010ligated palladium center. Two\u2010electron reduction of the pentacoordinated arylpalladium(II) anionic species thus formed gives a tris\u2010ligated anionic arylpalladium(0) center, which undergoes oxidative addition with a second aryl halide molecule to eventually lead to a bisaryl\u2010palladium(II) neutral species. Reductive elimination of a bisaryl molecule from this center closes the catalytic cycle by regenerating the initial zerovalent palladium complex. The application of this sequence to the catalytic heterocoupling of aryl halides is discussed, and it is concluded, on the basis of Hammett correlations, that statistical yields should be observed, in agreement with the results obtained for preparative reactions in DMF.<\/jats:p>","DOI":"10.1002\/chem.19960020810","type":"journal-article","created":{"date-parts":[[2007,9,19]],"date-time":"2007-09-19T12:06:00Z","timestamp":1190203560000},"page":"957-966","source":"Crossref","is-referenced-by-count":78,"title":["Oxidative Addition of Aryl Halides to Transient Anionic \u00e0\u2010Aryl\u2013Palladium(0) Intermediates\u2014Application to Palladium\u2010Catalyzed Reductive Coupling of Aryl Halides"],"prefix":"10.1002","volume":"2","author":[{"given":"Christian","family":"Amatore","sequence":"first","affiliation":[]},{"given":"Emmanuelle","family":"Carr\u00e9","sequence":"additional","affiliation":[]},{"given":"Anny","family":"Jutand","sequence":"additional","affiliation":[]},{"given":"Hideo","family":"Tanaka","sequence":"additional","affiliation":[]},{"given":"Qinghua","family":"Ren","sequence":"additional","affiliation":[]},{"given":"Sigeru","family":"Torii","sequence":"additional","affiliation":[]}],"member":"311","published-online":{"date-parts":[[2006,2,21]]},"reference":[{"key":"e_1_2_1_1_2","unstructured":"For earliest works see: a)J. F.Fauvarque A.Jutand Bull. Soc. Chim. Fr.1976 765."},{"key":"e_1_2_1_1_3","doi-asserted-by":"publisher","DOI":"10.1016\/S0022-328X(00)93215-7"},{"key":"e_1_2_1_2_2","doi-asserted-by":"publisher","DOI":"10.1021\/ar50136a006"},{"key":"e_1_2_1_2_3","doi-asserted-by":"publisher","DOI":"10.1351\/pac198052030669"},{"key":"e_1_2_1_2_4","doi-asserted-by":"publisher","DOI":"10.1021\/ar00083a001"},{"key":"e_1_2_1_2_5","doi-asserted-by":"publisher","DOI":"10.1002\/0471264180.or027.02"},{"key":"e_1_2_1_2_6","unstructured":"(e)R. F.Heck Palladium in Organic Synthesis; Academic Press New York 1985."},{"key":"e_1_2_1_2_7","doi-asserted-by":"publisher","DOI":"10.1002\/anie.198605081"},{"key":"e_1_2_1_3_2","doi-asserted-by":"publisher","DOI":"10.1021\/jo00430a041"},{"key":"e_1_2_1_3_3","doi-asserted-by":"crossref","unstructured":"(b)A.Minato K.Tamao T.Hayashi K.Suzuki M.Kumada Tetrahedron Lett.1980 845;","DOI":"10.1016\/S0040-4039(00)71521-8"},{"key":"e_1_2_1_3_4","unstructured":"Ibid1981 5319."},{"key":"e_1_2_1_3_5","doi-asserted-by":"crossref","unstructured":"(c)D. A.Widdowson Y. Z.Zhang Ibid1986 2111.","DOI":"10.1016\/S0040-4020(01)87628-6"},{"key":"e_1_2_1_3_6","first-page":"67","volume":"66","author":"Negishi E. I.","year":"1987","journal-title":"Organic Synthesis"},{"key":"e_1_2_1_3_7","doi-asserted-by":"publisher","DOI":"10.1016\/0022-328X(90)85107-A"},{"key":"e_1_2_1_4_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00751a062"},{"key":"e_1_2_1_4_3","doi-asserted-by":"publisher","DOI":"10.1021\/ja00846a084"},{"key":"e_1_2_1_4_4","doi-asserted-by":"publisher","DOI":"10.1021\/ja00411a034"},{"key":"e_1_2_1_5_2","doi-asserted-by":"crossref","unstructured":"(a)M.Zembayashi K.Tamao J.Yoshida M.Kumada Tetrahedron Lett.1977 4089.","DOI":"10.1016\/S0040-4039(01)83434-1"},{"key":"e_1_2_1_5_3","doi-asserted-by":"publisher","DOI":"10.1021\/jo00364a002"},{"key":"e_1_2_1_6_2","doi-asserted-by":"publisher","DOI":"10.1021\/om00100a019"},{"key":"e_1_2_1_6_3","doi-asserted-by":"publisher","DOI":"10.3891\/acta.chem.scand.44-0755"},{"key":"e_1_2_1_7_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00044a018"},{"key":"e_1_2_1_7_3","unstructured":"(b) In (a) where Ar is apara\u2010substituted phenyl ligand two distinct oxidation peaks were observed for Ar\u2010Pd0L\u20102(O2) and Pd0L2(O3) but no peak (O*) could be observed for the phenyl anions (compare wave O*in Figs. 1a\u2010c when Ar is a 2\u2010thienyl ligand) owing to the fast follow\u2010up reactions of this species [Eq. (7)]. The observation of distinct peaks for Ar\u2010Pd0L2and Pd0L2may appear kinetically incompatible with the existence of an equilibrium [Eq. (6)] between these species since a fast equilibrium is expected to lead to the observation of a single oxidation peak (featuring a CE mechanism) [8] in the potential range where the first oxidation wave (i.e. O2) is detected. This would be true in the absence of reaction (7) which consumes the aryl anion within the time required to span the potential between the peak of wave R1and the potential range where waves O2 O3 and possibly O*are found (compare the small size of this wave in Fig. 1 a). Thus even when the equilibrium in Equation (6) is totally established at all scan rates considered one expects to observe a wave O2corresponding to the concentration of Ar\u2010Pd0L\u20102with a minor CE contribution due to the small amount of surviving aryl anions followed by a wave O3corresponding to the reoxidation of Pd0L2 which cannot afford Ar\u2010Pd0L\u20102[by the reverse reaction in Eq. (6)] because of partial or complete consumption of Ar\u2010. So under such circumstances (Ar = phenyl) a CE mechanism cannot take place at the electrode surface despite the reversibility of reaction (6) [7a]. c) In the case of Figure 1 despite the greater stability of the 2\u2010thienyl anion the situation is very similar as evidenced by the small magnitude of the wave O*. Yet the fact that this wave is present shows that the backward reaction of Equation (6) is much slower than in the case of the phenyl ligands because otherwise this wave should be absent all thienyl anions being consumed at the level of wave O2in a CE mechanism [12]."},{"key":"e_1_2_1_8_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00022a026"},{"key":"e_1_2_1_8_3","first-page":"443","volume-title":"Electrochemical Methods","author":"Bard A. J.","year":"1980"},{"key":"e_1_2_1_8_4","unstructured":"(c) Note that reaction of Pd0L3with aryl halides is still possible [8a] yet it requires timescales that are much longer than those considered here (t\u2264 100 ms) because it must proceed via a transient Pd0L2intermediate formed by the energetically unfavorable dissociation of Pd0L3[reverse of Eq. (11)] [14]. d) Note that in agreement with our previous observations [8a] the oxidation of Pd0(PPh3)3formed in Equation (11) is observed in the same potential range where the oxidation of Pd0(PPh3)2occurs (wave O3). The reason for the almost equal oxidation potentials is not yet clear. However this does not in any way affect the oxidative process at wave O2(which occurs at less positive potentials) or the homogeneous steps. For this reason and for sake of simplicity in the following we use the same label for the two waves."},{"key":"e_1_2_1_9_2","doi-asserted-by":"crossref","unstructured":"S.Torii H.Tanaka K.Morisaki Tetrahedron Lett.1985 1655.","DOI":"10.1016\/S0040-4039(00)98576-9"},{"key":"e_1_2_1_10_2","unstructured":"(a) In addition to wave O2 which is the main wave at high scan rates two other oxidation waves are also observed. One of these (labeled O3) corresponds to the two\u2010election oxidation of the zerovalent palladium moiety formed in Equation (6) [7a b]. The second labeled O*(cf. Fig. 1 a and Table 2) is observed only when the decomposition in Equation (6) affords s\u0300\u2010aryl anions with rather long lifetimes (i.e. larger than a few milliseconds as for the 2\u2010thienyl s\u0300\u2010anion in this study but not for the substituted phenyl ones) and corresponds to the oxidation of the s\u0300\u2010aryl anion. b) In the presence of added aryl halide ArI a fourth oxidation wave O4 is also observed corresponding to the oxidation of iodide ions (peak potential at 0.40 V vs. SCE for 0.2 Vs\u22121). In the absence of added aryl halide wave O4is not observed because iodide ions are quantitatively consumed during the oxidations of palladium(0)\u2010based complexes (2 equiv of halide ligands are formally required per palladium center oxidized in order to generate a stable PdIIXYL2species at waves O2and O3) and are therefore scavenged from the electrode vicinity (for a discussion of this effect see ref. [24]). This is no longer true when an excess of iodide ions is present in the diffusion layer with respect to the overall amount of oxidizable palladium species. In other words the observation of wave O4under our present experimental conditions is a proof that a significant fraction of palladium species generated at wave R1is present in the diffusion layer in a non\u2010oxidizable form [Eq. (24)]."},{"key":"e_1_2_1_11_2","unstructured":"The mechanism of the two\u2010electron reduction of arylpalladium(II) complexes [7 a] taking place at wave R1has never been described in detail. However since a two\u2010electron direct reduction can be discounted this reduction certainly proceeds through an EE\u2010 or ECE\u2010based mechanism [12] i.e. through the production of a short\u2010lived arylpalladium(I) intermediate."},{"volume-title":"Electrochemical Methods","year":"1980","author":"Bard A. J.","key":"e_1_2_1_12_2"},{"key":"e_1_2_1_13_2","unstructured":"(a)C.Amatore E.Carr\u00e9 A.Jutand unpublished results (1995)."},{"key":"e_1_2_1_13_3","unstructured":"(b) It was noted by one referee that the smaller size of wave O2in DMF relative toTHF is consistent with the existence of equilibrium (9) in DMF. Indeed both equilibria (i.e. Eqs. (6) or (9)) are expected to be displaced toward their right\u2010hand side in DMF relative to THF owing to a stronger stabilization of low\u2010coordinate palladium(0) moieties in DMF."},{"key":"e_1_2_1_14_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0022-328X(00)86726-1"},{"key":"e_1_2_1_14_3","doi-asserted-by":"publisher","DOI":"10.1021\/om00158a026"},{"key":"e_1_2_1_15_2","unstructured":"This should be compared to the increased basicity of electrogenerated bases (i.e. B\u2010NR+4) relative to their usual analogues (i.e. [B\u2010M+] M = Li Na K etc.)."},{"key":"e_1_2_1_15_3","first-page":"1265","volume-title":"Organic Electrochemistry","author":"Baizer M.","year":"1991"},{"key":"e_1_2_1_16_2","first-page":"331","volume-title":"Organic Electrochemistry","author":"Peters D. G.","year":"1991"},{"key":"e_1_2_1_17_2","unstructured":"The fact that two\u2010electron waves are observed for the reduction of aryl halides (i.e. ThI or PhI here) establishes that the s\u0300\u2010aryl anion does not react with its precursor. Indeed such a father\u2010son process would correspond to a one\u2010electron overall stoichiometry [18]."},{"key":"e_1_2_1_18_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00293a003"},{"key":"e_1_2_1_19_2","unstructured":"As established by comparison with the independent cyclic voltammetry (Ep= \u2010 2.60 V vs. SCE at 0.5 Vs\u22121) of an authentic sample of 2\u2010phenylthiophene prepared according to ref. [3e]."},{"key":"e_1_2_1_20_2","unstructured":"One could also conceive that Ar\u2013Pd0L\u20102or the s\u0300\u2010aryl anion formed in Equation (6) act as a nucleophile in the reaction with the Ar\u2013Pd11XL2starting material [Eqs. (1 2)] [1 2]. However this would lead to an overall one\u2010electron consumption during the reduction of Ar\u2013Pd11XL2because of this father\u2013son mechanism [18] in contradiction with the experimental two\u2010electron stoichiometry [7 a]. We believe that the expected facile reaction of s\u0300\u2010phenyl anions with Ar\u2013Pd11XL2is prevented by their rapid protonation. However this reaction can be observed when Ar\u2010is a 2\u2010thienyl anion and Ar\u2013Pd11XL2a phenyl derivative. Thus by generating Th\u2010by electrochemical reduction of 2\u2010iodothiophene [Eqs. (13\u201315)] in the presence of the less readily reduced Ph\u2010Pd11XL2 one observes a significant formation of 2\u2010phenylthiophene [19] in cyclic voltammetry at small scan rates (ca. 50% yield at 0.2 Vs\u22121; i.e. t1\/2\u2248 1.5s for the formation of 2\u2010phenylthiophene). The formation of 2\u2010phenylthiophene proceeds along a two\u2010step sequence at least since the reaction of Th\u2010is faster (t1\/2\u2248 0.5 s) than the production of 2\u2010phenylthiophene. Yet even in this favorable case the nucleophilic substitution of Ph\u2013Pd11XL2is too slow to compete efficiently with the oxidative addition of Ar'X and Ar\u2013Pd0L\u20102 which occurs much more rapidly as has been shown in the present study. Indeed from the values reported in Table 3 t1\/2for the the reaction between Ar\u2013Pd0L\u20102and aryl halides lies in the range between 7\/nand 15\/nmilliseconds wherenis the number of equivalents of added aryl halide. So even in the least favorable case (n= 1) this reaction is at least thirty times faster than the nucleophilic substitution of the parent Ar\u2013Pd11XL2by aryl anions. This latter reaction should nevertheless become the major route for homo\u2010 or cross\u2010coupling whenever the aryl halide is more easily reducible than Ar\u2013Pd11XL2."},{"key":"e_1_2_1_21_2","unstructured":"In the presence of triphenylphosphine the sequence in Equations (6 + 7 + 11) is kinetically equivalent to a first\u2010order decomposition of the arylpalladium(0) anionic species; the rate determining step is the forward reaction in Equation (6) (rate constantk0). Indeed under these conditions the rapid interception of the Pd0L2moiety by the triphenylphosphine ligand [Eq. (11)] [8] opposes the facile backward recombination in Equation (6) [7a]. For this reason the sequence of reactions (6 + 7 + 11) can be represented in Scheme 2 by its kinetically equivalent first\u2010order process with a rate constantk0."},{"key":"e_1_2_1_22_2","unstructured":"Equation (16) and its integrated forms [Eqs. (17\u201319)] assume that the reactions between the aryl halide and the arylpalladium(0) anionic complexes are first\u2010order in each reactant. The validity of this hypothesis is provided by the experimental observation of linear relationships when In(i0\/i) is plotted as a function of [Ar'X]\/n\u0308 (compare Eq. (19) and Fig. 4a) since \u0394Eis constant for the series of measurements."},{"key":"e_1_2_1_23_2","unstructured":"This is required to ensure the constancy of the function \ud835\udc9c in Equations (17) and (18) (see Experimental Section)."},{"key":"e_1_2_1_24_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00074a018"},{"key":"e_1_2_1_25_2","unstructured":"(a)trans\u2010Bisarylpalladium(II) complexes are not supposed to undergo direct reductive elimination yet since this step was not investigated kinetically in this work we preferred to formulate it as a global reaction."},{"key":"e_1_2_1_25_3","doi-asserted-by":"publisher","DOI":"10.1021\/ja00815a009"},{"key":"e_1_2_1_25_4","doi-asserted-by":"publisher","DOI":"10.1016\/0022-328X(87)80048-7"},{"key":"e_1_2_1_25_5","unstructured":"(b) Such intermediates are expected to be reducible. However in this study examination of the reductive side of the voltammograms was hampered because of the excess of iodobenzene orpara\u2010substituted iodobenzene under our experimental conditions. c) Since we have no structural information on the bisarylpalladium(II) intermediate we postulate that this is a classicaltranscomplex only to remain in agreement with previous authors (see [25 a]). This species may however be for example aciscomplex or a solvent\u2010coordinated neutral pentacoordinate species [24]. Note that our conclusion must remain true because of stoichiome\u2010try even when the final product of Scheme 4 is not a classical bisarylpalladium(II) complex."},{"key":"e_1_2_1_26_2","unstructured":"This was ascribed to a facile CE electrochemical process: indeed the fast but up\u2010hill dissociation of one halide ion ligand from Ar\u2013Pd11XX'L\u20102affords Ar\u2013Pd11YL2(Y = X or X') which is reducible at this potential [24]."},{"key":"e_1_2_1_27_2","unstructured":"The yields of homo\u2010 or heterocoupling products were less than 10% and a few percent of products resulting from coupling with the phenyls borne by the phosphine ligands were also produced. Moreover most of the aryl halides reactants underwent reduction. This indicates that the palladium catalyst is rapidly decomposed when the reaction is performed on a preparative scale in THF. The same occurs when the reaction is performed in a batch procedure in THF (compare Table 1 last row in DMF)."},{"key":"e_1_2_1_28_2","unstructured":"(a) For the reaction of Ar2Pd11L2complexes with strong nucleophilic bases see e.g."},{"key":"e_1_2_1_28_3","doi-asserted-by":"publisher","DOI":"10.1021\/om00074a007"},{"key":"e_1_2_1_28_4","doi-asserted-by":"publisher","DOI":"10.1021\/jo00106a006"},{"key":"e_1_2_1_28_5","doi-asserted-by":"publisher","DOI":"10.1021\/ja00016a082"},{"key":"e_1_2_1_29_2","doi-asserted-by":"crossref","unstructured":"D. T.Rosevear F. G.Stone J. Chem. Soc. A1968 164.","DOI":"10.1039\/j19680000164"},{"key":"e_1_2_1_30_2","doi-asserted-by":"crossref","unstructured":"(a)P.Fitton M. P.Johnson J. E.Mc Keon J. Chem. Soc. Chem. Commun.1968 6.","DOI":"10.1039\/c19680000006"},{"key":"e_1_2_1_30_3","doi-asserted-by":"crossref","unstructured":"(b)D. R.Coulson Ibid1968 1530.","DOI":"10.1039\/c19680001530"},{"key":"e_1_2_1_30_4","doi-asserted-by":"publisher","DOI":"10.1016\/S0022-328X(00)84578-7"},{"key":"e_1_2_1_31_2","doi-asserted-by":"publisher","DOI":"10.1016\/0022-0728(90)80024-Z"},{"key":"e_1_2_1_32_2","unstructured":"\u03b4 values depend on the duration \u0394E\/n\u0308 of the overall electrochemical experiment: \u03b4\u221d(D\u0394E\/n\u0308)1\/2[12]. Yet for a given experiment \u03b4 is a constant term since D \u0394E and n\u0308 are constant. This allows straight divisions by \u03b4 to be performed under derivative and integral operators."},{"key":"e_1_2_1_33_2","unstructured":"\u03b2 an adjustable parameter whose value is close to unity is introduced to account for the finite widths of the waves. Indeed because of these finite widths the electrogeneration of Ar\u2013Pd0L\u20102is not instantaneous. It starts before the peak of wave R1is reached and carries on after this peak has been scanned; similarly its detection begins before that of wave O2is reached and is not complete after this peak is scanned. The real reaction time to be considered is therefore not \u0394E\/n\u0308 but \u03b2\u0394E\/n\u0308. An average value \u03b2 = 0.97 has been evaluated empirically by using simulations based on an ECEC mechanism with average \u0394Eand half\u2010peak widths values comparable to those found in this study (cf. Fig. 1)."}],"container-title":["Chemistry \u2013 A European Journal"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/api.wiley.com\/onlinelibrary\/tdm\/v1\/articles\/10.1002%2Fchem.19960020810","content-type":"unspecified","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/chemistry-europe.onlinelibrary.wiley.com\/doi\/pdf\/10.1002\/chem.19960020810","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T13:01:41Z","timestamp":1760274101000},"score":1,"resource":{"primary":{"URL":"https:\/\/chemistry-europe.onlinelibrary.wiley.com\/doi\/10.1002\/chem.19960020810"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1996,8]]},"references-count":62,"journal-issue":{"issue":"8","published-print":{"date-parts":[[1996,8]]}},"alternative-id":["10.1002\/chem.19960020810"],"URL":"https:\/\/doi.org\/10.1002\/chem.19960020810","archive":["Portico"],"relation":{},"ISSN":["0947-6539","1521-3765"],"issn-type":[{"type":"print","value":"0947-6539"},{"type":"electronic","value":"1521-3765"}],"subject":[],"published":{"date-parts":[[1996,8]]}}}