SIGMA-BOND METATHESIS REACTIONS OF SC(CH3)(2)(-H BONDS - REACTIVITY WITH CYCLOHEXANE AND CYCLOPENTANE() WITH SECONDARY C)

Fourier transform ion cyclotron resonance mass spectrometry has been u sed to examine the sigma-bond metathesis reactions of Sc(CH3)(2)(+) wi th the secondary C-H bonds of cyclohexane and cyclopentane. Methane el imination, accompanied by further dehydrogenation, is the initial and dominant reaction observed. These processes are facile at room tempera ture and involve little or no activation energy. Measured total bimole cular rate constants for the reaction of Sc(CH3)(2+) With cyclohexane and cyclopentane are 6.2 x 10(-10) and 5.1 x 10(-10) cm(3) s(-1) molec ule(-1), respectively. The total bimolecular rate constant for the rea ction of Sc(CD3)(2)(+) with cyclohexane is measured to be 6.6 x 10(-10 ) cm(3) s(-1) molecule(-1). In accordance with earlier theoretical pre dictions these metathesis reactions appear to proceed via an allowed f our-center mechanism similar to that of a 2(sigma) + 2(sigma) cycloadd ition. The observed gas phase reactivity is also compared to the liqui d phase reactivity of similar complexes and the implications are discu ssed.