Carbon−Oxygen Bond Formation at Organopalladium Centers: The Reactions of PdMeR(L 2 ) (R = Me, 4-tolyl; L 2 = tmeda, bpy) with Diaroyl Peroxides and the Involvement of Organopalladium(IV) Species

The group 16 oxidants dibenzoyl- and bis(4-trifluoromethylbenzoyl)-peroxide react with dimethylpalladium(II) and methyl(4-tolyl)palladium(II) complexes of the bidentate nitrogen donor ligands 2,2‘-bipyridine and N, N, N ‘, N ‘ -tetramethylethylenediamine in discrete stepwise processes as the temperature is raised from −70 °C. Carbon−oxygen bonds are formed during this reaction sequence but not from those Pd(IV) complexes detected spectroscopically. The initial reaction gives undetected “Pd IV (O 2 CAr) 2 MeR(L 2 )” (Ar = Ph, Ar F; R = Me, Tol; L 2 = bpy, tmeda), which immediately undergo methyl aroate exchange with Pd II MeR(L 2 ) to give Pd II (O 2 CAr)R(L 2 ) and Pd IV (O 2 CAr)Me 2 R(L 2 ), where all products except for Pd IV (O 2 CAr)Me 2 Tol(tmeda) were detected by 1 H NMR spectroscopy. On raising the temperature, the Pd IV Me 3 complexes reductively eliminate Me−Me, and the Pd IV Me 2 Tol complexes eliminate Me−Me and Tol−Me. The resultant Pd(II) complexes Pd II (O 2 CAr)R(L 2 ) react with (ArCO 2 ) 2 at higher temperatures to form Pd II (O 2 CAr) 2 (L 2 ) and R-O 2 CAr (R = Me, Tol), except for Pd II (O 2 CAr)Tol(tmeda), which forms Pd II (O 2 CAr) 2 (tmeda) and 4,4‘-bitolyl. Each reaction step has been confirmed by the independent synthesis of intermediates Pd II (O 2 CAr) 2 (L 2 ) and Pd II (O 2 CAr)R(L 2 ) (Ar = Ph, Ar F; R = Me, Tol; L 2 = bpy, tmeda) and Pd IV (O 2 CR)Me 2 R(L 2 ) (R = Ph, Ar F; R = Me, Tol; L 2 = bpy) by metathesis reactions of halogeno complexes with Ag[O 2 CAr], followed by temperature-dependent studies of both the decomposition of Pd(IV) complexes and reactions of Pd(II) complexes with (ArCO 2 ) 2 . Attempts to prepare “Pd IV (O 2 CAr) 2 MeR(bpy)” in a similar manner (and thus in the absence of PdMeR(bpy) with which they undergo exchange reactions) were unsuccessful, but the complexes Pd IV I 2 MeR(bpy) (R = Me, Tol) that formed on reaction of diiodine with PdMeR(L 2 ) were detected and found to reductively eliminate iodomethane. X-ray structural studies are reported for the square-planar palladium(II) complexes Pd(O 2 CPh) 2 (bpy), Pd(O 2 CAr) 2 (tmeda) (Ar = Ph, Ar F ), and Pd(O 2 CPh)(Tol)(bpy)·CH 2 Cl 2 .