Agostic species

It should be noted that the silylhydrides 106 109 were the only products of the reaction shown in Eq. (30). The isomeric agostic species, related to the niobium species 64 and 65 were not identified, and all attempts to convert 106-109 into these or other rearranged species at elevated temperatures resulted in decomposition. 

It has also been suggested that the experimental barrier of activation for propagation in olefin polymerisation is due to rearrangement of y-agostic species into those with a-agostic interactions in order to free the coordination site for the insertion of the next monomer molecule, rather than the actual insertion (Figure 3.19) [358],... 

Agostic C-H- -M interactions bear considerable similarity to alkane complexes, and Hoff and Kubas show that the agostic species W(CO)3(PCy3)2 is an intermediate in the ligand displacement reaction in Eq. (7.42).1 A normal KIE effect of 12 is... 

OA of the agostic C-H bond is very common and referred to as cyclometallation Eq. (12.2)].37,38 Cyclometallated species are important in organic synthesis, catalysis, asymmetric synthesis, and photochemistry. Although the agostic species is normally an unobserved transient in Eq. (12.2), equilibrium between agostic and... 

Resonance form 9b is preferred, as expected for this Fischer carbene. At -80 °C, an intermediate agostic species (10) is seen, leading to the mechanistic proposal shown in Fig. 4. The cis-hydride is proposed to have the role of promoting departure of H, an observed (NMR) product of the reaction. 

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