Abstract
The coupling reaction of silyl hydrides with alkoxysilanes to produce siloxanes and hydrocarbons catalyzed by tris(pentafluorophenyl)borane was studied by gas chromatography and UV spectroscopy using model reagent systems: Ph2MeSiH + Ph2MeSiOn-Oct (I) and Ph2MeSiH + Me3SiOn-Oct (II). Detailed kinetic studies performed for system I showed that the reaction is first order in both substrates and the rate is proportional to the catalyst concentration. A highly negative apparent entropy of activation points to a crowded transition state structure, leading to a significant dependence of the rate on steric effects. Studies of system II demonstrated that the exchange of the Si−H and Si−OR functionality accompanies the coupling process and in many cases is the dominating reaction in this system. Ultraviolet spectra recorded during the reaction show a distinct strong absorption band with λmax = 303−306 nm, which is due to an allowed electronic transition in the uncomplexed B(C6F5)3 molecule. This absorption also g...
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