MoP-03


A FT/ICR-MS STUDY OF LASER ABLATED FIRST ROW TRANSITION METAL CATION REACTIONS WITH BENZENE

Adriana Dinca, Keith J. Fisher, Derek R. Smith, Gary D. Willett

School of Chemistry, University of New South Wales, Sydney 2052


First row transition metal cations were formed by laser ablation of the metal or the metal oxide inside the ICR cell of a Fourier Transform mass spectrometer using the fundamental frequency of a Nd:YAG laser (1064 nm) in the Q-switch mode, and in the presence of a background of benzene at a typical pressure of 10-7 mbar (uncorrected). After a cooling period in the presence of the reactant benzene and argon the metal ions were isolated by use of an ejection pulse. The intensities of the metal ion and of the product ions were monitored as a function of time. From suitable hypothetical reaction schemes matching reaction profiles were obtained. Using the data processing application IGOR® the fitting of predicted curves to the experimental data was refined, and the corresponding second order rate constants obtained. From this we are able to postulate mechanistic pathways, such as for example:

Mn+ + C6H6 --> MnC6H6+ + C6H6 --> Mn(C6H6)2+

For some metals the experimental data indicates that more than one reaction channel is open, as for example the scandium cations for which the first product is primarily the complex Sc(benzyne)+ formed by dehydrogenation of the benzene. Subsequently the above complex reacts further with benzene:

Sc(C6H4)+ + C6H6 --> Sc(C6H4)C6H6+

Sc(C6H4)C6H6+ + C6H6 --> Sc(C6H4)(C6H6 )2+


Figure


Reaction profile of the vanadium cation with benzene.