ARM-OFF REACTIONS OF THE TRIPODAL POLYPHOSPHANE MEC(CH2PPH2)(3) IN OCTAHEDRAL RHODIUM(III) COMPLEXES OF HETEROCYCLIC THIOAMIDES

Arm-off kappa(3)P-->kappa(2)P processes of the tripodal polyphosphane MeC(CH2PPh2)(3) have been studied for reactions of [RhCl3(triphos)] (1 a) and [Rh(MeCN)(3)(triphos)](CF3SO3)(3) (1b) with chelating bi- and t ridentate anionic ligands. Treatment of 1a with the heterocyclic thioa mides Hmpym (2-mercaptopyrimidine) or Hmtz (2-mercapto-1-methylimidazo le) affords the complexes [RhCl(mpym)(triphos)]Cl (2) and [RhCl(mtz)(t riphos)]Cl (3), which are stereochemically rigid in CDCl3 solution at room temperature. In contrast, the presence of two broad unstructured resonances at 10.6 and 13.5 ppm in the P-31 NMR spectrum of [Rh(mpym)( MeCN)(triphos)](CF3SO3)(2) (4) in CD3CN solution at 25 degrees C indic ates a rapid exchange of the phosphorus environments, for which either an acetonitrile or a triphos arm-off dissociation can be postulated. Such a kappa(3)P-->kappa(2)P mechanism is required for the formation o f [Rh(mpym)(2)(triphos)](CF3SO3) (5), [Rh(mbt)(2)(triphosO)](CF3SO3) ( 6), [Rh(mmim)(2)(triphosO)](CF3SO3) (7) and [RhH(HBpz(3))(triphosO)](C F3SO3) (8) on treatment of 1b with the required ligand (Hmbt = 2-merca ptobenzothiazole; Hmmim = 2-mercapto-1-methylimidazole) at a stoichiom etric ratio. Rapid oxidation of the liberated dangling triphos arm to the phosphane oxide O=P(Ph-2)CH2C(CH3)(CH2PPh2)(2) (triphosO) is typic al for kappa(2)P coordinated Rh(III) complexes. (C) 1998 Elsevier Scie nce S.A.