Palladium catalysis palladacycles

The intramolecular arylation of sp3 C-H bonds is observed in the reaction of l-/ r/-butyl-2-iodobenzene under palladium catalysis (Equation (71)) 94 94a 94b The oxidative addition of Arl to Pd(0) gives an ArPdl species, which undergoes the electrophilic substitution at the tert-butyl group to afford the palladacycle. To this palladacycle, another molecule of Arl oxidatively adds, giving the Pd(iv) complex. 

A variety of palladium(II) and palladium(O) complexes serve as effective precatalysts or precursors to the active palladium(O) catalyst. The most commonly used precatalysts in Heck chemistry are Pd(OAc)2, Pd2(dba)3, and PdCl2(PPh3)2. Typical catalyst loading is in the range of 5-10mol-%. The discovery of the unique catalytic activity of a dimeric palladacycle (Pd2(P(o-Tol)3)( Li-OAc)2) by Herrmann and Belle/ has set a milestone in palladium catalysis as it allows the use of even unreactive chloroaryl substrates intransformations. 

The Suzuki-Miyaura synthesis is one of the most commonly used methods for the formation of carbon-to-carbon bonds [7]. As a palladium catalyst typically tetrakis(triphenylphosphine)palladium(0) has been used, giving yields of44—78%. Recently, Suzuki coupling between aryl halides and phenylboronic acid with efficient catalysis by palladacycles was reported to give yields of 83%. 

Cyclometallated iridium complexes, for OLEDs, 12, 145 Cyclometallated palladium(II) complexes from amines and pyridines, 8, 280 with C,C-chelating ligands, 8, 291 enantioselective synthesis, 8, 296 ferrocene-based palladacycles, 8, 292 four-membered palladacycles, 8, 297 imine- and oxime-based complexes, 8, 285 with N-N and N=N bonds, 8, 288 palladacycle catalysis, 8, 297... 

---