STABILIZATION OF HIGH OXIDATION-STATES BY RIGID BIDENTATE NITROGEN LIGANDS - SYNTHESIS AND CHARACTERIZATION OF DIORGANOPALLADIUM AND TRIORGANOPALLADIUM(IV) AND CATIONIC TRIORGANOPLATINUM(IV) COMPLEXES

Dimethylpalladium(II) and (di)methylplatinum(II) complexes containing the rigid bidentate nitrogen ligands bis(p-tolylimino)acenaphthene (pTol-BIAN) and bis(phenylimino)camphane (Ph-BIC) readily undergo oxidative addition of a variety of (organic) halides, to give the corresponding octahedral diorgano- and triorganopalladium(IV) and -platinum(IV) complexes. The palladium complexes PdMe2(R)X(NN) (RX = MeI, PhCH2Br; NN = pTol-BIAN, Ph-BIC) were synthesized and isolated at 20-degrees-C and were fully characterized. Reductive elimination from these complexes in chloroform obeyed first order kinetics and was slower than for other reported triorganopalladium(IV) complexes. The new diorganopalladium(IV) complexes PdMe2I2(NN), synthesized via oxidative addition of diiodine to PdMe2(NN) are much less stable than the triorganopalladium(IV) complexes studied. PtMe2(R)X(pTol-BIAN) (RX = MeI, PhCH2Br, EtI, PhCH(Me)Br, MeC(O)Cl, I2) and Pt(Me)I(R)X(pTol-BIAN) (RX = MeI, PhCH2Br, I2) were obtained via oxidative addition to PtMe2(pTol-BIAN) and Pt(Me)I(pTol-BIAN), respectively. Reaction of PtMe2(R)X(pTol-BIAN) with AgSO3CF3 led to the formation of remarkably stable five-coordinate [PtMe2(R)pTol-BIAN)]SO3CF3 complexes (R = Me, CH2-Ph, C(O)Me), which were fully characterized and can be isolated and kept at 20-degrees-C. The complexes are very stable toward reductive elimination, e.g. in CDCl3 and CD3CN [PtMe2(CH2-Ph)(pTol-BIAN)]SO3CF3 was stable for at least 7 days at 20-degrees-C or 40 h at 50-degrees-C. The analogous complex [PtMe2(CH2Ph)(phen)]SO3CF3 was also stable at 50-degrees-C in CD3CN for at least 40 h, whereas [PtMe2(CH2Ph)(pTol-DAB)]SO3CF3 gave 30-35% reductive elimination under these conditions. From the observed order of reductive elimination from Pd(IV) and Pt(IV) complexes the rigidity of the pTol-BIAN and Ph-BIC ligands appears to be the major factor in determining the stability of these complexes.