NUCLEOPHILIC-ADDITION TO ETA-6-ARENETRICARBONYLMANGANESE CATIONS - THE ROLE OF INTERMEDIATES IN THE REACTIONS WITH PHOSPHINES

The structures of adducts of phosphines (e.g. PEt3) with the eta-6-arenetricarbonylmanganese cations [(eta-6-XYC6H4)Mn(CO)3]+ (Ia, X = Y = H; Ib, X = Me, Y = H; Ic, X = Cl, Y = H; Id, X = Cl, Y = p-Me) in acetone have been determined by low-temperature H-1 and C-13 NMR spectroscopy. In all cases regiospecific exo addition occurs at the arene ring with formation of eta-5-cyclohexadienylphosphoniumtricarbonylmanganese cations [(eta-5-XYC6H4PEt3)Mn(CO)3]+ with Ib giving meta addition only (IIb) and Ic and Id forming both meta and ortho adducts (IIc, IIIc and IId, IIId, respectively). Increase in temperature reverses the equilibria for IIa and IIb with formation of [(arene)Mn(CO)2(PEt3)]+ whereas IIc, IIIc and IId, IIId form fac-Mn(CO)3(PEt3)2Cl involving direct attack by the PEt3 at the chlorine-bearing ring carbon atom rather than through a metal-hydride intermediate.