FORMATION AND REACTIVITY OF METAL-CARBONYL ANIONS IN THE GAS-PHASE

The reactions of metal carbonyl anions (M(CO)n-; M = Cr, Mn and Fe; n = 1-3) with n-heptane, water and methanol were studied with use of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with an external ion source. The M(CO)n- ions were formed in the FT-ICR cell by collision-induced dissociation of the most abundant primary ion generated by electron impact of the appropriate metal carbonyl compound present in the external ion source. The M(CO)n- ions were allowed subsequently to undergo nonreactive collisions with argon in order to remove possible excess internal/translational energy prior to the ion/molecule reaction. Only the Cr(CO)3-, Mn(CO)3- and Fe(CO)2- ions react with n-heptane. This reaction proceeds by loss of H-2 from the collision complex and the Cr(CO)3- and Fe(CO)2- ions react about three times more efficiently than the Mn(CO)3- ion. With water, Mn(CO)- and Fe(CO)3- are unreactive, whereas the other ions react by loss of one or two CO molecules from the collision complex. The rate of the reaction with water decreases in the order Cr(CO)3-, Fe(CO)2-, Cr(CO)2-, Fe(CO)-, Mn(CO)3- and Mn(CO)2-. With methanol, the Cr(CO)2- ion reacts by loss of two CO molecules from the collision complex, whereas loss of one CO molecule and elimination of CO + H-2 occur in the reaction with Cr(CO)3-. CoMpeting loss of CO and one or two H-2 molecules occurs in the reactions of Mn(CO)3- and Fe(CO)2- With Methanol. The rate of the reaction with methanol decreases in the order Cr(CO)3-, Fe(CO)2-, Cr(CO)2- and Mn(CO)3-.