Crabtree concept

Dehydrogenative silylation of alkynes also may become a predominant route under the optimum conditions [1-5, 102, 120]. According to the Crabtree concept, in the presence of (for example) the cationic iridium complex, [IrH-(H20)(bq)L2]SbF6 (L = PPh3, bq = [7, 8]benzoquinolinato), the above process... 

Crabtree and coworkers used the disappearance of color to monitor the activity of 12 potential catalysts for hydrosilation reactions [6], The group used alkenes and imines with ferrocenyl and pyrimidyl substituents at either end as colored reactants. On hydrosilation the color is bleached, because conjugation between the electron donor and acceptor groups is reduced. The bleaching is easily observed by eye and can be recorded quantitatively by means of a digital camera (Figure 5.4.1). By use of this method, the known Wilkinson catalyst was identified in a proof-of-concept experiment. A palladacycle, [ Pd (o-tolylfi PQ H4 OAc 2, usually used in Heck reactions, was also found to be catalytically active. 

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