Rigid bidentate nitrogen ligands in organometallic chemistry and homogeneous catalysis. 7. Stabilization of high oxidation states by rigid bidentate nitrogen ligands: synthesis and characterization of diorgano- and triorganopalladium(IV) and cationic triorganoplatinum(IV) complexes

Abstract

Dimethylpalladium(I1) and (di)methylplatinum(II) complexes containing the rigid bidentate nitrogen ligands his@-toly1imino)acenaphthene @Tol-BIAN) and bis(pheny1imino)camphane (Ph-BIC) readily undergo oxidative addition of a variety of (organic) halides, to give the corresponding octahedral diorgano-and triorganopalladium(1V) and -platinum(IV) complexes.The palladium complexes PdMeZ(R)X(NN) (RX = MeI, PhCHZBr; NN = pTol-BIAN, Ph-BIC) were synthesized and isolated a t 20 "C and were fully characterized.Reductive elimination from these complexes in chloroform obeyed first order kinetics and was slower than for other reported triorganopalladium(1V) complexes.The new diorganopalladium(1V) complexes PdMe212(NN), synthesized via oxidative addition of diiodine to PdMeANN) are much less stable than the triorganopalladium(1V) complexes studied.PtMez(R)X@Tol-BIAN) (RX = MeI, PhCHZBr, EtI, PhCH(Me)Br, MeC(O)Cl, 12) and Pt(Me)I(R)X(pTol-BIAN) (RX = MeI, PhCHZBr, 12) were obtained via oxidative addition to PtMez WTol-BIAN) and Pt(Me)I@Tol-BIAN), respectively.Reaction of PtMez(R)X(pTol-BIAN) with AgS03CF3 led to the formation of remarkably stable five-coordinate [PtMe2(R)pTol-BIAN)1SO3CF3 complexes (R = Me, CHz-Ph, C(O)Me), which were fully characterized and can be isolated and kept at 20 "C.The complexes are very stable toward reductive elimination, e.g. in CDCl3 and CD3CN [PtMedCHZ-Ph)(pTol-BIAN)]SO&F3 was stable for at least 7 days a t 20 "C or 40 h at 50 "C.The analogous complex [PtMe&HzPh)(phen)IS03CF3 was also stable a t 50 "C in CD3CN for a t least 40 h, whereas [PtMez(CHZPh) @Tol-DAB)] SO3CF3 gave 30-35 % reductive elimination under these conditions.From the observed order of reductive elimination from Pd(1V) and Pt(1V) complexes the rigidity of thepTol-BIAN and Ph-BIC ligands appears to be the major factor in determining the stability of these complexes.