Zweikernige Palladiumkomplexe – Vorstufen oder Katalysatoren?

Abstract

Berechnungen helfen: Ein neuerer Beitrag der Gruppe um Schoenebeck hat die meisten Zweifel daran ausgeräumt, dass die in der Kupplungschemie häufig verwendeten dimeren LPdIBr‐Katalysatoren über eine vorherige formale Reduktion zu LPd0‐Spezies reagieren. Umgekehrt können L2Pd0‐Katalysatoren durch eine Oxidation aktiviert werden. In anderen Fällen kann eine zweikernige Spezies auch während des Katalysezyklus fortbestehen.

Highly Efficient CSeCF3 Coupling of Aryl Iodides Enabled by an Air‐Stable Dinuclear PdI Catalyst

“…[4] In contrast our group recently established that more robust dinuclear Pd I complexes that are less prone to the release of Pd (0) may function directly as catalysts in cross-coupling of aryl halides by alternative coupling cycles. [5,6] In this context we recently succeeded in the catalytic I/Br halogen exchange [5a,b] and the trifluoromethylthiolation of aryl halides, [5c] employing the iodine-bridged Pd I -dimer 1.N otable practical advantages of this concept are the air-stability of 1 and the straightforward recoverability of the dinuclear entity after reaction completion, avoiding the handling of sensitive Pd (0) complexes or ligands.B uilding on this work, we herein report the first catalytic method to synthesize ArSeCF 3 compounds.…”

Trifluoromethylthiolation of Aryl Iodides and Bromides Enabled by a Bench‐Stable and Easy‐To‐Recover Dinuclear Palladium(I) Catalyst

“…[6] Little is understood about the reactivities at such dinuclear palladium(I) sites,a nd the role of such dimers in catalysis has generally been ascribed to being off-cycle precursors to the actual catalytically active palladium(0) species. [7] Indeed, the Pd I dimer 1 [8] has found use as efficient pre-catalyst in cross-coupling reactions (Figure 1). [9] By contrast, the iodinated analogue 2 does not act as an efficient reservoir for Pd 0 .…”

“…To gain additional support we undertook kinetic investigations of the 4-mediated trifluoromethylthiolation of 9iodoanthracene (7). Under pseudo-first-order conditions (7 was employed in considerable excess), we determined afirstorder kinetic dependence in 4 and an overall activation barrier of DG°= 28.0 AE 3.9 kcal mol À1 for the ArI!ArSCF 3 exchange process.…”

Site‐Selective C−S Bond Formation at C−Br over C−OTf and C−Cl Enabled by an Air‐Stable, Easily Recoverable, and Recyclable Palladium(I) Catalyst

“…In this context, the emerging concept of dinuclear Pd I catalysis has shown promise in displaying features of air stability,r obustness,a nd recoverability in applications employing the iodine-bridged dinuclear Pd I complex 1 (Figure 1). [3,4] In our previous work, we developed Pd I dimer catalyzed C sp 2 ÀC sp 2 ,C sp 2 ÀC sp 3 ,C ÀSeCF 3 ,a nd CÀSCF 3 bond formations and provided mechanistic data in support of dinuclear catalysis being operative. [3,5] Aside from the mentioned specialized fluorinated examples,t od ate, carbon-heteroatom bond formation is clearly underdeveloped in the Pd I arena, but would benefit from widening of the repertoire.T hiolation reactions (to make aryl or alkyl sulfides) are of importance in the pharmaceutical and agrochemical industry as the C À Sb ond is widely encountered in bioactive molecules.…”