213135-41-2Relevant academic research and scientific papers
Strong metallophilic interactions in the palladium arylation by gold aryls
Perez-Temprano, Monica H.,Casares, Juan A.,De Lera, Angel R.,Alvarez, Rosana,Espinet, Pablo
, p. 4917 - 4920 (2012)
It's the second step that counts: Arylation of Pd by Au takes place through transition states and intermediates featuring strong Au/Pd metallophilic interactions (see picture). However, the aryl transfer from [AuArL] to [PdArClL2] is thermodyna
Mechanism of the Stille reaction. 1. The transmetalation step. Coupling of R1I and R2SnBu3 catalyzed by trans-[PdR1IL2] (R1 = C6Cl2F3; R2 = vinyl, 4-methoxyphenyl; L = AsPh3)
Casado, Arturo L.,Espinet, Pablo
, p. 8978 - 8985 (2007/10/03)
The so far accepted mechanism of the Stille reaction (palladium- catalyzed cross-coupling of organotin reagents with organic electrophiles) is criticized. Based on kinetic studies on catalytic reactions, and on reactions with isolated intermediates, a corrected mechanism is proposed. The couplings between R1I (1) (R1 = C6-Cl2F3 = 3,5-dichlorotrifluorophenyl) and R2SnBu3 (R2 = CH=CH2, 2a; C6H4-4-OCH3, 2b), catalyzed by trans- [PdR1I(AsPh3)2] (3a), give R1-R2 and obey a first-order law, r(obs) = a[3a][2a]/(b + [AsPh3]), with a = (2.31 ± 0.09) x 10-5 s-1 and b = (6.9 ± 0.3) x 10-4 mol L-1, for [1] = [2a] = 0-0.2 mol L-1, [3a] = 0-0.02 mol L-1, and [AsPh3] = 0-0.07 mol L-1, at 322.6 K in THF. The only organopalladium(II) intermediate detected under catalytic conditions is 3a. The apparent activation parameters found for the coupling of 1 with 2a support an associative transmetalation step (ΔH((±))(obs) = 50 ± 2 kJ mol-1, ΔS((±))(obs) = -155 ± 7 J K-1 mol-1 in THF; and ΔH((±))(obs) = 70.0 ± 1.7 kJ mol-1, ΔS((±))(obs) = -104 ± 6 J K-1 mol-1 in chlorobenzene, with [1]0 = [2]0 = 0.2 mol L-1, [3a] = 0.01 mol L-1). The reactions of 2a with isolated trans-[PdR1X(AsPh3)2 (X = halide) show rates Cl > Br > I. From these observations, the following mechanism is proposed: Oxidative addition of R1X to PdL(n) gives cis- [PdR1XL2], which isomerizes rapidly to trans[PdR1XL2]. This trans complex reacts with the organotin compound following a S(E)2 (cyclic) mechanism, with release of AsPh3 (which explains the retarding effect of the addition of L), to give a bridge intermediate [PdR1L(μ-X)(μ-R2)SnBu3]. In other words, an L-for-R2 substitution on the palladium leads R2 and R1 to mutually cis positions. From there the elimination of XXnBu3 yields a three- coordinate species cis-[PdR1R2L], which readily gives the coupling product R1-R2.
