GROUP AND SITE-SELECTIVE SIGMA-BOND METATHESIS REACTIONS OF H3SCCH2CH3-D-2]PROPANE,[1,1,1,4,4,4-D-6]-N-BUTANE, [2-D]ISOBUTANE, AND N-PENTANE( WITH [2,2)

Fourier transform ion cyclotron resonance mass spectrometry has been u sed to examine the reactions of CH3ScCH2CH3+ with [D-4]methane, ethane , [2,2-D-2]propane, [1,1,1,4,4,4-D-6]-n-butane, [2-D]isobutane, n-pent ane, and [D-12]-n-pentane, CH3ScCH2CH3+ is not observed to react with methane or ethane, but for propane, n-butane, isobutane, and n-pentane sigma-bond metathesis with ethane elimination is the initial and domi nant reaction observed, with further dehydrogenation of the resulting products occurring as additional reaction channels. For propane, n-but ane, and isobutane, no methane elimination is observed. For n-pentane, methane elimination is a minor reaction channel. For propane, n-butan e, and isobutane, the initial sigma-bond metathesis involves predomina ntly the primary C-H bonds of the hydrocarbon. These processes are fac ile at room temperature and occur with little or no activation energy. Measured total bimolecular rate constants with [2,2-D-2]propane, [1,1 ,1,4,4,4-D-6]-n-butane, [2-D]isobutane, and n-pentane are 0.87 x 10(-1 0), 0.98 x 10(-10), 1.7 x 10(-10) and 6.4 x 10(-10) cm(3) s(-1) molecu le(-1), respectively. With the butanes and pentane a second intramolec ular metathesis reaction follows the initial addition to yield a metal lacycle product. In accordance with earlier theoretical predictions th ese metathesis reactions appear to proceed via an allowed four-center mechanism similar to that of a 2(sigma) + 2(sigma) cycloaddition. The higher reactivity of the metal-ethyl bond compared to the metal-methyl bond and the observed C-H bond specificity are also in agreement with theoretical predictions.