C-H Bond Activation by a Ruthenium(II) β-Diketonate Complex: A Mechanistic Study

Ruthenium(II)-catalysed C-H bond activation of arenes containing a functional directing group depends on the ligand coordinated to ruthenium(II). In this study, 2-phenylpyridine C-H activation catalysed by a "piano-stool" ruthenium(II) complex containing a fluorinated beta-diketonate ligand was examined by ESI-MS in combination with CID experiments. [Ru(beta-diketonate)((PhPy)-Ph-CT)Cl](+) was identified as an active intermediate, and its collisional activation leads to C-H activation. CID analysis indicates proton transfer from the phenylpyridine to the chlorine anion, showing HCl elimination, while the beta-diketonate ligand is retained in the complex together with the activated phenylpyridine. Furthermore, DFT calculations were performed for the neutral analogue [Ru(beta-diketonate)(PhPy)Cl] to identify all ruthenium intermediates along the C-H activation reaction pathway. The results suggest that the most stable structure of [Ru(beta-diketonate)(PhPy)Cl] has pre-activated 2-phenylpyridine with a partly developed Ru-H bond. Further, we show that K2CO3 is not directly involved in the C-H activation step and it serves in the reaction as a base.