Agostic Interactions as Precursors to H-Transfer Reactions

Recently it has been shown [45] that C-H bonds of (terminal) methyl groups in alkyl or aryl ligands can be oxidatively added to coordinatively unsaturated, com-plexed metal ions, as in 

The initial approach angle (C-H-M) of about 130° was rationalized in terms of a proposed interaction between the C - H o bond and an empty metal d orbital, and back-donation from a filled d orbital to a a orbital of the C-H system, but this angle may also result from geometrical factors. The role of steric and conformational effects in the balance between cyclometallation and attack on an external substrate (such as an alkane), was discussed in the context of the above reaction path. The conclusion was that sterically uncongested metal systems are more likely to activate alkanes, than to undergo cyclometallation. 

---