Lewis acids perfluoroaryl boranes

Nonetheless, several attempts to quantify Lewis acidity have been made and a few methods are useful in the context of perfluoroaryl borane chemistry. The Childs method9 involves measurement of the perturbation of the 1H NMR signal for the (3-proton... 

Jakle and co-workers have recently incorporated the PhB(C6Fs)2 framework into a polymeric matrix, giving the first perfluoroaryl borane functionalized polymers (Scheme 13).86 The Lewis acid centers in this polymer were judged to have a Childs acidity of 0.60, a comparable value to that obtained for monomeric PhB(C6F5)2. Of note in this work is that the reagent [Cu(C6F5)]4 87 was used to institute the pentafluorophenyl... 

In addition to the familiar and extensive role perfluoroaryl boranes and borates fill as co-catalysts for the coordination polymerization of ethylene and a-olefins, these compounds can act as initiators for other polymerization reactions due to their high Lewis acidity. 

E. Perfluoroaryl Boranes in Organic Synthesis 1. Use of B(C6F5)3 as a Conventional Lewis Acid... 

An overview of recent work from the Takats laboratory deals with divalent Ln(Tp Bu Me) complexes and preparation, molecular structure, NMR characteristics and reactivity of [Yb( x-H)(TptBu,Me)]2. Reactions of this compound with Lewis bases and Lewis acids, such as the perfluoroaryl boranes, a-bond metathesis reactions generally involving acidic H-X bonds, but also an example of C-Si bond cleavage, and insertion chemistry, primarily involving alkynes have been described. The molecular structures of representative complexes have been determined by X-ray crystallography.110... 

Dendrimers are well-defined hyperbranched macromolecules and have been applied to the preparation of the dendrimeric catalysts [37]. Activities of the den-drimeric catalysts are generally comparable to those of the parent low-molecular-weight catalyst. In some cases even higher activities can be observed with the dendrimeric catalyst by means of so called dendritic effects [38]. Piers et al. developed (perfluoroaryl)borane-functionalized carbosilane dendrimers (66), which were used as Lewis acid catalysts for the hydrosilation of acetophenone [39]. In the presence of (66) as a catalyst, the hydrosilylation of acetophenone cleanly proceeded to essentially 100% conversion over the course of several minutes at 5% catalyst loadings at room temperature as shown in Scheme 19.16. 

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