Arm-off reactions of the tripodal polyphosphane MeC(CH 2PPh 2) 3 in octahedral rhodium(III) complexes of heterocyclic thioamides

Abstract

Arm-off κ t P → κ 2 P processes of the tripodal polyphosphane MeC(CH 2PPh 2) 3 have been studied for reactions of [RhCl 3(triphos)] ( 1a) and [Rh(MeCN) 3(triphos)](CF 3SO 3) 3 ( 1b) with chelating bi- and tridentate anionic ligands. Treatment of 1a with the heterocyclic thioamides Hmpym (2-mercaptopyrimidine) or Hmtz (2-mercapto-1-methylimidazole) affords the complexes [RhCl(mpym)(triphos)]Cl ( 2) and [RhCl(mtz)(triphos)Cl ( 3), which are stereochemically rigid in CDCl 3 solution at room temperature. In contrast, the presence of two broad unstructured resonances at 10.6 and 13.5 ppm in the 31P NMR spectrum of [Ohi(mpym)(MeCN)(triphos)](CF 3SO 30 2 ( 4) in CD 3CN solution at 25°C indicates a rapid exchange of the phosphorus environments, for which either an acetonitrile or a triphos arm-off dissociation can be postulated. Such a κ 3 P → κ 2 P mechanism is required for the formation of [Rh(mpym) 2(triphos)] (CF 3SO 3) ( 5). [Rh(mbt) 2(triphosO)](CF 3SO 3) ( 6). [Rh(mmim) 2(triphosO)](CF 3SO 3) ( 7) and [RhH(HBpz 3)(triphosO)](CF 3SO 3) ( 8) on treatment of 1b with the required ligand (Hmbt = 2-mercaptobenzothiazole: Hmmin = 2mercapto-1-methylimidazole) at a stoichiometric ratio. Rapid oxidation of the liberated dangling triphos arm to the phosphane oxide OP(Ph 2)CH 2C(CH 3(CH 2PPh 2) 2(triphosO) is typical for κ 2 P coordianted Rh(III) complexes.