The addition of protic acids to [Mn2(CO)5(Ph2PCH2PPh2)2] to give bridging hydrido-compounds

Abstract

Addition of protic acids with weakly co-ordinating anions (HBF₄ or HSO₃F) to dichloromethane solutions of [Mn₂(CO)₅(dppm)₂](dppm = Ph₂PCH₂PPh₂) containing a µ-σ,η²-CO ligand leads to the cationic complexes [Mn₂H(CO)₆(dppm)₂][Y](Y = BF₄ or SO₃F·nH₂O). The extra CO must have come from destruction of a manganese carbonyl intermediate compound, but under an atmosphere of CO one molecule of CO is absorbed and better yields are obtained. Addition of HCl to [Mn₂(CO)₅(dppm)₂] gives the neutral adduct [Mn₂H(Cl)(CO)₅(dppm)₂]. Trifluoroacetic acid shows both types of behaviour normally giving [Mn₂H(CO)₆(dppm)₂][(CF₃CO₂)₂H], but if the reaction solution is flushed with N₂ or is kept under reduced pressure then an analogue of the chloro-compound, [Mn₂H(CF₃CO₂)(CO)₅(dppm)₂], with monodentate trifluoroacetate is obtained. All protonated compounds give ¹H n.m.r. quintets at high field consistent with bridging hydride ligands. The products were further characterised by their ³¹P-{¹H} n.m.r. spectra.