Agostic interactions deprotonation

The silanol complex 57 exhibits a Si H M agostic interaction characterized by a /(Si-H) of 41 Hz and a Si-H distance of 1.70(7) It would be incautious to interpret such a low value of the Si-H coupling in terms of a significant Si-H bond activation, because the Si-H bond forms rather acute angles with the Si-C and Si-Si bonds (about 82 and 101°, respectively) and thus must have a considerable p character on silicon, which should contribute to the decrease of /(Si-H). The silanol ligand is -coordinate to ruthenium and the Ru-Si bond of 2.441(3) A is not exceptional, but the Si(SiMe3)3 deviates from the silanol plane by 19.0°, probably as a result of the Si-H interaction. Deprotonation of 57 by strong bases affords a neutral ruthenocene-like product. 

Figure 1.4 (a) Pd-catalyzed formation of cyclobutarenes and (b) transition state for C(sp )-H activation via deprotonation of a C-H bond that is geminal to an agostic interaction key distances in A [14]. 

Route I (oxidative addition) involves a concerted oxidative addition process with the formation of metal-hydride species A. Alternatively, an electrophilic attack by the metal center on the aryl ip o-carbon may afford a metal arenium (Wheland) complex B followed by proton loss. In the agostic C-H bond activation route, the six-membered transition state C including a hydrogen-metal interaction has been found to initiate the C-H activation process, leading to an agostic intermediate D and acting simultaneously as an intramolecular base for deprotonation. 

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