AN ARYL EXCHANGE-REACTION WITH FULL RETENTION OF CONFIGURATION OF THECOMPLEXES - MECHANISM OF THE ARYL EXCHANGE BETWEEN [PDR2L2] COMPLEXESIN CHLOROFORM (R = PENTAHALOPHENYL, L = THIOETHER)

The complexes [Pd(3,5-C6Cl2F3)(2)L-2] and [Pd(C6F5)(2)L-2] (L = SC4H8 (tht), or SMe2) react in CCl3D to give a mixture also containing the h eteroaryl products [Pd(3,5-C6Cl2F3)(C6F5)L-2], whereas for L = PPh3, A sPh3, 2-picoline, 4-picoline, or 1/2COD, this exchange is not observed . The F-19 NMR kinetic study supports that the scrambling of the aryl groups takes place with retention of configuration at both Pd centers via a triply-bridged binuclear activated complex F3)Pd(mu-C6Cl2F3)(mu- C6F5)(mu-L)Pd(C6F5)L].(double dagger) The aryl double bridge is suppor ted by a bridging S-donor ligand facilitating an otherwise difficult e xchange (not observed for other weak L ligands, such as picolines, lac king a second lone pair). This constitutes the first reported example of reversible migration of sigma-C-bonded groups between bis-organo Pd (II) complexes proceeding without cis-trans isomerization. The isomeri zation process is also observed, occurring at a much slower rate.