Metal carbonyl anions as model metal-centered nucleophiles in aromatic and vinylic substitution reactions

Abstract

The mechanism of reactions of metal carbonyl anions, [CpFe(CO) 2 ] -, [Re(CO) 5 ] -and [Mn(CO) 5 ], with various polyfluorinated (Hal= Cl, Br, I) and non-fluorinated (Hal=Br, I) aryl and alkenyl halides has been examined with the help of anion trapping experiments. Reactions discussed in this communication are shown to proceed via the initial attack of metal carbonyl anion on halogen. The halogen-metal exchange mechanism is demonstrated by the trapping of the intermediate aryl (alkenyl) carbanion and by the formation of halo(acyl)metallate anions cis-[R(CO)M(CO) 4 Hal] -instead of RM(CO) 5 complexes (M=Re, Mn) in the reactions with [Re(CO) 5 ] -and [Mn(CO) 5 ] -. The yield of nucleophilic substitution products varies widely from trace in certain reactions with [CpFe(CO) 2 ] -, which give the [CpFe(CO) 2 ] 2 dimer, to quantitative in reactions with [Re(CO) 5 ] -.