Reversible CH Bond Activation Reactions of the N‐Heterocyclic Carbene Ligands in Ru(Ph2PCH2CH2CH2PPh2)(IMes)(CO)H2 and Ru(Ph2AsCH2CH2PPh2)(IMes)(CO)H2 (IMes=1,3‐Dimesityl‐1,3‐dihydro‐2H‐imidazol‐2‐ylidene)

Thermolysis of Ru(IMes)(dppp)(CO)H2 (1, IMes=1,3‐dimesityl‐1,3‐dihydro‐2H‐imidazol‐2‐ylidene; dppp=Ph2PCH2CH2CH2PPh2) in the presence of trimethylvinylsilane yields Ru(IMes')(dppp)(CO)H (2) resulting from intramolecular ArCH2–H CH bond activation of the N‐heterocyclic carbene ligand. The structures of 1 and 2 have been established by X‐ray crystallography. Treatment of Ru(IMes)(arphos)(CO)H2 (3, arphos=Ph2AsCH2CH2PPh2) with CH2CHSiMe3 at 85 °C produces a mixture of three CH activated products 4a–c. The CH activated complexes 2 and 4a–c reform their dihydride precursors upon heating under hydrogen.