CC versus CH Activation and versus Agostic CC Interaction Controlled by Electron Density at the Metal Center

Based on the PCN ligand 2 , a remarkable degree of control over CC versus CH bond activation and versus formation of an agostic CC complex was demonstrated by choice of cationic [Rh(CO) n (C 2 H 4 ) 2− n ] ( n =0, 1, 2) precursors. Whereas reaction of 2 with [Rh(C 2 H 4 ) 2 (solv) n ]BF 4 results in exclusive CC bond activation to yield product 5 , reaction with the dicarbonyl precursor [Rh(CO) 2 (solv) n ]BF 4 leads to formation of the CH activated complex 9 . The latter process is promoted by intramolecular deprotonation of the CH bond by the hemilabile amine arm of the PCN ligand. The mixed monocarbonyl monoethylene Rh species [Rh(CO)(C 2 H 4 )]BF 4 reacts with the PCN ligand 2 to give an agostic complex 7 . The CC activated complex 5 is easily converted to the CH activated one ( 9 ) by reaction with CO; the reaction proceeds by a unique sequence of 1,2‐metal‐to‐carbon methyl shift, agostic interaction, and CH activation processes. Similarly, the CC agostic complex 7 is converted to the same CH activated product 9 by treatment with CO.